Note: Descriptions are shown in the official language in which they were submitted.
WC 0~l3 -1- PCT/~:S91/063~
~: .~ v ` ~ .,
PACXAGING T~ERMOPLASTICS FROM L~CTIC ACID
The present application is derived from and
claims priority of the following four U.S~ applications:
the application entitled BIODEGRADA3LE PACKAGING
THERMOPLASTICS FROM POLYLACTIC ACID having Serial No.
07/579,005, filed September 6, 1990; the application
entitiad BIODEGRADABLE REPLACEMENT OF CRYSTs~L POLYSTYRENE
having Serial No~ 07/579,46S, filed September 6, 1990; the
application entitled BLENDS OF POLYLACTIC ACID having
S~rial No. 07/579,000, filQd Septamber 6, 1990; and the
appli~ation entitled DEG2ADABLE INPACT MODIFIED POLYLACTIC
ACID having Serial No. 07/579,460, filed September 6,
1990; all of the above applications having Battelle
Memorial Institute as assignee.
lS FIELD OF THE INVENTION
A first major embodiment of the present invention
relates to plasticized biodegradable polymers of L-
lactide, D-lactide, D,L-lactide and mixtures thereof
suitable for packaging applications conventionally served
by nondegradable plastics (e~g. polyethylene~. This
embodiment further relates to a method for producing
pliable films and other packaging items from such polymers
and to the unique produc' thereoC. The invention has
utility in producing a product that has the physical
characterist~cs of the usual Cilm for~ing ?lastics, yet is
biodegradable.
The second major embodiment of this invention
discloses a material and process of preparing it which is
an offset, t~at is a replacement for crystal polystyrene,
3~ sometimes known as orientable polystyrene or oPS. The
m2terial is an offset '_r c-ystal polystyrene but is
composed of a polyester capable of degrading in the
environment ove~ apr~xim2~ely one ye2-s time. The
material is ~ polyest~ om-~ised c' poly~e ized lact~c
- _ci~, p-ep2~ed C_O~ ei_her ~-'2C~ ,d ^- _-lactic -c~d,
--2--
and D,L~lactic acid. The ratio of the two polymerized
monomer units, the process treatment and in some cases
certain adjuvants, determine the precise physical
properties required for the exacting requirements of a
crystal polystyrene offset. Thus, at approximately a
ratio of 90/10, L-lactic/D,L-lactic acid, the polymerized
lactic acid (PLA) is a well behaved thermoplastic that is
clear, colorlQss~ and very stiff. ~s suc~ it is very
suit~bl~ for preparing films, foams, and other
thermoformed items of disposable or one-way plastic.
Having served its purpose as a pacXaging plastic, the
poly(lactic acid) slowly environmentally biodegrades to
innocuous products when left in the anviron~ent. This
harmless disappearance can help alleviate the mounting
problems of plastic pollution in the environment.
A third major embodiment of the invention relates
to the blending of conventional thermoplastics with
poly(lactic acid). This provides nove`, environmentally
degradable thermoplastics. The environmentally degradable
thermoplastics are useful in a wide variety of
applications.
A fourth major embodiment of the invention
relates to the blending of compatible elastomers with
polylactides. This provides impact-resistant modified
poly(lactic acids) that are us~ful in a wide variety of
applications including those where impact-modified
polystyrene would be used.
BACKGROUND OF T~ INVENTION
The_e is a need fo_ an envi_onmentall~
3~ biodegradable pack2sin~ thermoplastic 25 2n answer to the
tremendous 2~0un.s o~ ~isc2rce~ plastic packasing
m2terials. '~.a. ~las~ic sales in lq~ we_e ~3.7 billio~
pounds ~f w~i_h 2.7 billion pounds were listed 25
plastics in p2c~agins. A significant amount of 'his
12s~_c i5 __s____ei ni ~2co~es ?l~s.ic ?ollu_2n_ _hc,
is 2 ~ _n _ne 12nisc2pe ~n-` ~re_. =o m~rin~
~'C ~ 91iO6~'-
; -3-
Mortality estimates range as high as 1-2 million seabirds
and 100,000 marine mammals per year.
A further problem with the disposal of plastic
packaging is the concern for dwindling landfill space. It
has been estimated that most major cities will have used
up available land~ills for solid waste disposal by the
early 1990'5~ Plastics comprise approximately 3 percent
by weight and 6 percent of the volume of solid waste.
One ot~er disadvantage o~ conventional plastics
is that they are ultimately derived fro~ petroleum, which
leavQs plastics dependent on the uncertainties of foreign
crude oil imports. A better fe~dstock would be one that
derives ~rom renewable, domestic resources.
However, there are good reasons for the use of
packaging plastics. They provide appealing aesthetic
qualities in the form of attractive packages which can be
quickly fabricated and filled with specified units of
products. The packages maintain cleanliness, storage
stability, and desirable qualities suc~ as transparency
for inspection of contents~ These packages are known for
their low cost of production and chemical stability. This
stability, however leads to very lony li e of plastic, so
that when its one time use is completed, discarded
pac~ages remain on, and in, the environment for
2~ incalculably long times.
The polymers and copolymers o~ lactic acid have
been ~nown for some time as unique materials since they
are biodegr~dzble, biocomp2tible and thermoplastic. These
polymers are well behaved thercoplastics, and are 100
3~ percent bioàegradable in an animal body via hydrolysis
over a time pe-iod of sever2i mor.ths to a year. In a wet
envi-onment they begin ~:~ show de~-~d2_ion a~ter several
e!~s ~ isc~~e~ -'s ~-e ~:~e~ leC_ ~
.n t~e soil o- seaw2ter. ~he dêgr2d2'io~ products 2re
_ la_~ic ~c d, c~ 3n dio~i~e a~d ~ate- all o' whic~ -re
h~ 'ess~
)632-
4 ~ :
.. .
It will be appreciated by those skilled in the
art that duplicating the properties of one thermoplastic
with another is not predictable. Thus, with crystal
polystyrene, there are exacting requirements for satisfac-
tory performance of the polystyrene, which has beendeveloped over many years to meet man~facturing and end-
use specifications of crystal polystyrene grades~
In practice, lactic acid is converted to its
cyclic dimer, lactide, which becomes ~he monomer for
polymeri~ation. Lactic acid is potentially available from
inexpensive feedstocks such as cornstarch or corn syrup,
by fermentation, or from petrochemical feedstocks such as
ethylene. Lactide monomer is conveniently converted to
resin by a catalyzed, melt polymerization, a general
t5 process well-known to plastics producers. By performin~
the polymerization from an intermediate monomer,
versatility in the resin composition is permitted.
Molecular weight can be easily controlled. Compositions
can be varied to introduce specific properties.
Homopolymers and copolymers of various cyclic
esters such as glycolide, lactide, and the lactones have
been disclosed in numerous patents and scientific
publications. Early patents disclosed processes for
pol~erizing lactic acid, lactide, or both, but did not
25 achieve high molecular weight polymers with good physical
properties, and the polymer products were frequently
tacky, sticky materials. See, for example, U.S. Patents
1,995,970; 2,362,511; 2,683,136; and 3,565,869. The Lowa
patent, U.S. Patent 2,668,162, teaches the use of pure
30 glycolide and lactide to 2chieve hi~.h molecula- weisht
?olymers a~d copol~e_s of lactide. Copolymeri~ation of
l~c,ide and glycoli~e im?ar_ed _~ hness ?~d im~-o~e~
~ st~ s~ _s ~ e h-~?-!~~
me-s. E~?hasis ~2s ?l2cec cn o~ien~2ble, c~ld-c-a~able
:8 ~i~e_C. ~ilms ^~e cescri~ed ?S self-su??G--i~, or s'iff,
~ -~ C?2~`~C ~e ?~ -s -~-e~e ~
m~ g an-~ s~iff. '-J._`. ~ a~e-;~ ~ _65.^6~ dis_los_s .he
~V~ '(~13 PCT/~S91/063~
typical attitude to the presence of monomer in
polyglycolide-the removal of the monomer from the product.
In U.S. 2,396,994, Filachione et al disclose a process for
producing poly(lactic acids) of low molecular weights from
lactic acid in the presence of a strong mineral acid
cataly6t. In U.S. 2,438,208, Filachione et al disclose a
continuous process for preparing poly(lactic acid) with an
acidic esCeri'iCatiOn cacalysc. In U.S. 4,683,288, Tanaka
~t al disclose the polymeri~ation or copolymeri2ation of
lactic and/or glycolic acid wit~ a catalyst of acid clay,
activated clay~ The average molecular weight of the
polymer is at least S,000 and preferably 5,000-30,000. In
U.S. 4,789,726, Hutchinson discloses a process for
production of polylactides or poly (lactide-co-qlycolide)
of specified low-mediu~ molecular weight, by controlled
hydrolysis of a higher molecular weight polyester.
Similar disclosures in the patent and other
literature developed the processes of polymerization and
copolymerization of lactide to produce very strong,
20 crystalline, orientable, stiff polymers ~hich were
fabricated into fibers and prosthetic devices that were
biodegradable and biocompatible, sometimes called
absorbable. The pol~ers slowly disappeared by
hydrolysis. See, for example, U.S. Patents 2,703,316;
2,75&,987; 3,297,033; 3,463,158; 3,498,957; 3,531,561;
3,620,218; 3,636,956; 3,?36,646; 3,797,499; 3,839,297;
3,982,543; ~,2~3, /75; ~,~3S,253; 4,~56,~46; 4,621,638;
European ~a~e-.~ Appli_at_on Er 014639O, International
~pplica~ion WO 86/00533, 2nd West German
3~ Offenlequn~ssch-irt ~E ^118127 (1971). U.S. pacents
4,5~a,9ol an~ 4,550,44^ __ m~_n- _eaches ~ h molecul~-
~ - r~_e-~`s s~ c, ;~' G ' -
-es;~_~a~' 2 t~.r~ ?12~_`` _ -~-~e~ ~ , __e ~ r~ ~ C
~ c ~ c ~ ^es ^.~ c_- --_~
. _ _ ~_ . . _ . . ^ c ~ _ _ _ _ _ . . . _ _ _ _ _ . . _ _ ~ ~ _ _ _ v _ c ~ _ ~ .
O9'/~ 3 i'CT/~S~
nerve repair. R.G. Sinclair et al in, Preparation and
Evaluation of Glycolic and Lactic Acid-3ased for Implant
Devices Used in Nanagement of Maxillofacial Trauma, I;
AD748410, National Technical Information Service, prepares
and evaluats polymers and copolymers of L-lactide and
glycolide, the polymers were light brown in the casa of
the polyglycolide with increasing color i~ the case of the
polymers incorporating more lactide, i~ a second series of
polymers the homopolymer of lactide was a snow white
crystalline solid.
Other patents teach thc use of t~ese poly~ers as
stiff surgical elements for biomedical fasteners, screws,
nails, pins, and bone plates. See, for example, U.S.
Patents 3,739,773; 4,060,089; and 4,279,249~
lS Controlled releasQ devices, usiny mixtures of
bioactive substances with the polymers and copolymers of
lactide and/or glycolide, have been disclosed~ See, for
example, U~S. Patents 3,773,919; 3,887,699; 4,273,920;
4,419,340; 4,471,077; 4,578,384; in 4,728,721, Yamamoto et
al disclose t~e treatment of biodegradable high molecular
weiyht polymers with water or a mixture of water and water
soluble organic solvents so as to remove unreacted mono~er
or monomers and polymers of low polymerization deyree.
Poly(lactic acid) and copolymers of lactic and glycolic
acid of 2,000 to 50,000 molecular waight are prepared by
direct condensation for use as an excipient for
microcapsules; R.G. Sinclair, in ~nvi-onmental Science &
~echnology, (10), ~5 ~157 )- R.G. Sinclai_,
P_oceedincs. 5t~. Tnternational S~posium on Controlled
Release of Bioactive ~.~terials, ~.12 ~n~i ~.2, University
cf ~~on ~-ess, '9 ~ T~ese _?~li_Ptions of l_c__~e
pol~e-s cn- -^p^l~er_ ~e_~ai-e~ ~0~ -! O~ clssy
p.~ysi_zl --c?e~~ies --- o_viou- use _n ~e~opl~stlc
_ 2 C ~ `. 5 _ _ `_ _ _ 2 _ S ` ~ c ~ C _ i _
?^'~ -C~ 2- ~ e ~?~ ~ -io~e~-cc`~
~O~'/0~l~ PCT~S91/063~-
Util. Conf., p. 211, June 11-12, 1987, discusses some of
the advantases of lactides as homopolymers and as
copolymers with glycolide and caprolactones.
Some mention has been disclosad in the prior art
for use of lactide copolymers for packaging applications.
Thus, in the aforementioned patent to Lowe, clear, self-
supporting films are noted of a copolymer of lactide and
glycolide. In U.S. Patent 2,703,316 lactide polymers are
described as film formers, which are tou~h and orientable.
"Wrapping tissue" was disclosed that was tough, fle~ible,
and strong, or pliable. However, to obtain pliability the
polylactide must bQ wet with volat~le solvent, otherwise,
~ti~f and brittle polymers were o~tai~ed. This is an
example of the prior art which teaches special
modifications of lactide polymers to obtain pliability.
U.S. Patent 2,758,987 discloses homopolymers of either L-
or D,L-lactide which are described as melt-pressable into
clear, strong, orientable films. The properties of the
poly(L-lactide) are given as: tensile strength, 29,000
psi; percent elongation, 23 percent; and tensile modulus,
710,000 psi. The poly(D,L-lactide) properties were:
26,000 psi tensile strength; 48 percent elongation; and a
tensile modulus of 260,000 psi. Copolymers of L- and D,L-
lactide, that is copolymers of L- and D,L-lactic acid, are
disclosed only for a 50/50 ~y weiqht ~ixt~re. Only tack
point properties are given (Example 3). It was claimed
that one anti?odal (optically acti~e, e.s., L-lac~ide)
monomer s~ecies is --e~e--ed ~o- the ca~e'o~men~ c~ his~
s-_encth~ Th~s, i.. ~J~5~ 2 tan~ ',021,309, lac'~des are
~o c~ol~eri7ed wit~ delta ~alerolac~one and ca~rolactone to
`cc~~ ?~ 5 c~ o~ .i'e,
s~~ e~ ~l`dC~ 5~~_~ sol`_ _O?O1~T2- co-~?csi~ c~
.~ ~ _ ~ ~ _ _ _ ~ . ~ _ _ ~ ~ _ ; _ _ ~ . = . ~ _ _ _ _ _ = _ _ ~ _ _ _ _ _ ~ ~; _ _ _ . . _ _ . . _
~, -di-~_h~ e~ -h~d-~:y?~ -c _
_ r.
r . _ _ _ .,
~09,~ 't~i~`à~!J~3'
_, _
~ 3
preparation of elasto~ers and foams. This patent excludes
lactides and uses compositions based on 7- to 9-membered
r`ng lactones, such as epsilon caprolactone, to obtain the
desired intermediates. No tensile strength, modulus, or
percent elongation data are given. U.S. Patent ~,297,033
teachcs the use of glycolide and glycolide-lactide
copolymers to prepare opaque materials, oriQntable into
~ibers suitable for sutures. It is stated that
"plasticizers interfere with crystallinity, but arc useful
for sponge and films"~ Obvious in these disclosures is
that the lactide polymers and copolymers are stiff unless
plasticized. This is true also of U.S. Patent 3,736,646,
where lactide-glycolide copolymers are softened by the use
of solvents such as methylene chloride, xylene, or
toluene. In U.S. Patent 3,797,499 copolymers of ~-lactide
and D,L-lactide are cited as possessing greater flexi-
bility in drawn fibers for absorbable sutures. These
fibers have strengths greater than 50,000 psi with
elongation percentages of approximately ~0 percent. In
column 5, line 1, Schneider teaches against enhanced
properties in the range provided in the present invention.
Plasticizers such as glyceryl triacetate, ethyl benzoate
and diethyl phthalate are used. Moduli are about one
million psi. These are still quite stiff compositions
compared to most flexible pac~aging compositions,
reflecting their use for sutures. U.S. Paten~ 3,844,987
discloses the use of ~raf' and blends OL biodegradable
poly~ers wf-h natu-a_lv occur~ing biodegradable products,
such 2S cellulosic materi21s, so~a bean ~owder, rice
hulls, anc _rewe-'s yaas~ - a~.icles _` ~anufactu=e
SUCh _~ 2 c~n~ai.e- ~o hc~ a me_~u.~ ~o germin_te and ~ro~
~e~ ea~ e _~ 'ea ~c ~ -e _-e ~.-
_ 2~^ ~ '' _ t - ^ . ~ U _ _; _ ~ , ^ r ~ ~
C ` ~ C ` _ ~ r~ r--s _.~ T ~ r ~e ~-c~-
----~ - ~----^ - ~ --! ^ - `' r' ~ ~ ' ~ ~ ` ~ `~ ~ i " ,_ ~- C _ i ~ _ ~ _ r~ ~ r `~ ~ i ~)~ _ S _ nr
~ 0~0~l~ ~'cr/~ 63'7
. ;.J i ~ ~
suture materials. These disclosures teac~ the use of
highly crystalline materials, which are oriented by
drawing and annealing to obtain tensile strengths and
moduli, typically, greater than 50,000 psi and 1,000,000
psi, respectively. Although ~ormability is mentioned into
a variety of s~aped articles, physical propertiQs of
unoriQnted ~xtrudates and moldings are not mentioned. For
Qxampls, U.S. Patent 3,636,956 toaches t~e preparation of
a copolymer ~avin~ 85/15, 90/10, 92.5~7~5, or a 95/5
1~ weig~t ratio o~ L-lactide/D,L-lactide; drawn, oriented
f ibers are cited; other plasti~izers suc~ as glyceryl
tria~etate, and dibutyl pt~alate are taught; however, i~
is preferred in this disclosure to use pure L-lactide
monomer for greater crystallinity and drawn fiber
~5 strength; and finally, the advantages of the present
invention (e~g~, an intimate dispersion of lactic acid-
based plasticizers that provides unique physical
properties) are not obtained~
U.S. Patent 4,620,999 discloses a biodegradable,
disposable bag composition comprised of pol~.~ers of 3-
hydroxybutyrate and 3-hydroxybutyrate/3-hydroxyvalerate
copolymer. Lactic acid, by comparison, is 2-hydroxy
propionic acid. U~S~ Patent 3,982,543 teaches the use of
volatile solvents as plasticizers wit~ lactide copolymers
25 to obtain pliabilitv. U.S. ~atents 4,045,418 and
4,057,537 rely on copolymeri2ation of caprolactone with
lactides, eit~er ~-lactide, or D,~-lactide, to obtain
pli2~ y. '~. S . ~aten~ ~,0~2,9&& teac~es t~.e use cc poly
(p-~iox2none) ~o o~tain i~proved l:nct tving ~nd l~not
30 security for absor~a~le s~t~res. '~.S. ?atents 4,307,763
znd 4,~-6,6g5 ~isclose ~e use cf lac~i~e z~d clvcolide
?~i~2~-s ~ Ers ~.~ ~E ^ --~~
_ ;~
_ _ i
-_r~ atEri-l~ ~.s ~ -e~
= ~ r _ ~ _ _ . --= _ _ ~ . _ C C . ~ _ _ _ i c _ _ _ _ _ _ _ O _ ~_ c i.. e_
~09'/~ 10- PCT/~S91/n63'-
,~S,
lactide polymers only by plasticizers which are fugitive,
volatile solvents, or other comonomer materials.
Copolymers of L-lactide and D,L-lactide are known
from the prior art, but citations note that pliability is
not an intrinsic physical property. The homopolymers of
L-lactide and D,L-lactide, as wQll as the 75/25, 50/50,
and 25/75, weight ratio, of L-/D,~-lactide copolymers are
exa-mpled in U.S~ Patent ~,951,828. The copol-ymers have
softenir.g points of 110-135 C. No other physical property
data are given relating to sti~'rness and ~lexibility. The
95J5, 92.5/7~5, 90/10, and 85/15, wei~ht ratio, of L-
lactide/D,L-lactide copolymers aro cited in U.S. Patents
3,636,956 and 3,797,499~ They are evaluated as filaments
from drawn fibers and have tensile strengths in excess of
50,000 psi, moduli of about one million, and percent
elongations of approximately 20 percent. Plasticizers,
the same as in U.S. Pa~ent 3,636,956, above, were used to
impart pliability. A snow-white, obviously crystalline
polymer, is cited in Offenlegungsschrift 2118127 for a
90/10, L-lactide/D,L-lactide copolymer. No physical
properties were siven for this copolymer. The paten.
teaches the use of surgical elements.
Canadian Patent 808,731 cites the copolymers of
L- and D,L-lactide where a divalent ~etal of Group II is
~5 part of the structure. The 90/10, L-/D,L-lactide
copalymer (Example 2~ and the L-lactide homopolymer were
àescri'~ed as "suitable ~or films and fibers". The 90/10
copol-ymer is des_ribed as 2 sno~-white copoly~er and the
homo?Ql~er of T~-lac-ide c--n ~e ~olded t3 'ransp2rent
~0 _ilms. (~r,e more c-ystal~ine polymer sho~ld be 'he
s~ e, _~ r.i~e ~ .eri~ c~ ~s ~e ~ c
~'he _~e.~ ~is_'oses `'_he ~_-~ th-_ ~.e ~.ove' ~ l_c=ic.s
_ ~ s ~
-he c-tclis~ i-. _'-_ ~c-m __ ~ '~~~_e is belie-~e~ _o be cr
:-e -~.`I__C-`_~ C-S ~hic:~ -~
~O 9_/0~13 PCT/~S91/Ofi3'-
i _
J
met~ods". No physical property data are given on the
strength and flexibility of the films.
Canadian Patent 863,673 discloses compositions of
L-lactide and D,L-lactide copolymers in the ratios of
5 g7/3, 95/5, 92.5/7.5, 90/10, and 85/15 ratios of L-/D,L-
lactide, respectively. These were all characterized as
drawn filaments for surgical applications. Tensile
strength, approximately 100,000 psi, was ~igh, elongation
was approximately 20 percent and plasti~izers were
mentioned to achieve pliability. D,~-lactide compositions
of less than 15 weig~t percent are claimed.
Canadian Patent 923,245 discloses the copolymers
of L- and D,L-lactide (Exa~ple 15). The 90/10 copoly~er
is described as a snow white polylactide. The
1~ polylactides prepared by the methods of the patent are
stated to have utility in the manufacture of fil~s or
fibers prepared by conventional thermoplastic resin
fabricating methods.
U.S. Patent 4,719,246 teaches the use of simple
blending of poly L-and poly (D-lactide), referred to as
poly (S-lactide~ and poly (R-lactide~. The examples are
all physical mixtures. The special properties of the
~interlocking" stem from racemic compound formation (cf.
"Stereochemistry of Carbon Compounds", E. L. Eliel,
2~ ~cGraw-Hill, 19~2, p. ~5). ~acemic com?ounds consist o~
interlocked enantiomers, that is, the D and L forms (or R
and S) a_e bonded to eac~ c~er by ?olar rorces~ This can
cause a lowe~ n~, o_ ~aising, of t~e c-ystalline melting
~oin_s, de?endin on ~`net~e~ -~e D _o D (or L to L) fo-cQs
~0 r~P less, o_ ~~eater, ~h,_.. -~e D to L forces. Requi_ed o~
-e- ~ c ~ ?~ s ~o ~ t~.e e ^ec~
~t--QC. `~ `-. ?_-~ . ~ 2 ~c) ,--_
_ . _ ~ ~ . , _ _ : _ _ ~ ~ ~ _ _ . . _ _ _ _ _ _ _ = _ _ ,, ,
0~]3 -1-- PCT/~`S91/n63~-
art of racemic compounds has a long history that goes back
to classical chemistry.
Okuzumi et al, U.S. 4,137,921, in Example 4,
teaches a 90/10 random copolymer of L-lactide and D,L-
lactide, however, the advantages of the present inventionare not obtained. Hutchinson, U.S. 4,789,?26, teaches a
process for t~e manufacture of polyestQrs~ particularly
polylactides of low ~olecular weigh~, by for~ing high
molecular weight material and t~en degradin~ it to lower
weight products of controlled polydispersity, however,
monomers are removed in the process.
U.S. Patents 3,736,646; 3,~13,919; 3,887,699;
4,~73,920; ~,471,077; and 4,578,384 teach the use of
lactide polymers and copolymers as sustained-drug release
~5 matrices that are biodegradable and biocompatible. Again,
physical properties of the polymers from ordinary
thermoforming methods such as film extrusion or molding
are not mentioned.
Additional related art includes: Low molecular
weight poly D,L-lactide has been recently added to high
molecular weight D,L-lactide along with a drug such as
caffeine, salicylic acid, or quinidine, see R. Bodmeier et
al, International J. of Pharm. 51, pp. 1-8, (1989).
Chabot et al in polymerizing L-lactide and racemic D,L-
lactide for medical applications removed residual monomer~nd ? ower oligomers, see Polymer, Vol. 24, pp. 53-59,
tl983). A.S. C~wl~ and Chang produced four differant
~olecular ~eight 3,L-la~tide poly~ers ~-u_ re~o~ed monomer
f~ o dec~~d~tion s~eies, see B_omct., ~e~ e~
30 Ar~. Q-S-- 13(-`.~, ?~- 13-162, (1985-85). Xleine 2nd
'leine ~o-~ec_ _e~e~_' 'e; -esi~'u~l monc-e-, -o'y(lc~
__ic~ _ -e~e~~ 7~ eY2`~
;`c~. _~, .-. _~-'~, ':'-5~ ' c`~o r~ es
: _ ~ _ _ _ _ _ ,~ ~ ~, _ ,~ _: _ _ ~ _ ~ _ _ ; , _ _ ~_ ~ ~--, ~ _ _ -- ~ _ ~ = ~ _ ~ _ _, _
~ rc~ t~ _c~ ?~ ~ Scl~c_ ;`~`
~0 9_/0~1~ PC~/~:S91/n63'-
~ 5~
molecular weight polylactides with elimin~tion of residual
monomer, see Makromol. Chem., Suppl~ 5, pp~ 30-41, (1981)~
M. Vert, in Macromol~ Chem.,Macromol~ S~p. 6, pp.l09-122,
(1986), discloses similar poly(~-/D,L-lactide)
5 polylactides, see Table 6, p. 118. In E 3~1,065 ~1989)
poly D r L-lactid~ is prepared as an implant material ~or
drug delivery as t~e ~aterial de~rades, the material
contains drugs, low molecular weig~t polylactide, and
other additives; EP 314,245 (1989) teaches 8 polylactide
having a low amount of residual monom~_, thQ polymer is
prepared by polymerization of meso D,L-lactide or other
monomers; West German Offenlegungsschri f t DE 3,820,299
(1988) teaches the polymerization of meso D,L-lactice with
lactides, however, the advantages of the present invention
are not obtained; and West German Offenlesungsschrift DE
3,820,299 (1988) teaches the polymerization of meso D,L-
lactide with lactides; however, the advantages of the
present invention are not obtained.
Of particular interest, U.S. patent 4,719,246
teaches the blending of homopolymers of L-lactide, D-
lactide, polymers or mixtures thereof; and copolymers of
L-lactide or D-lactide with at least one nonlactide
comonomer. The blending is intended to produce
compositions having interacting segments of poly(L-
lactide) and poly(D-lactide)~
U.S. 3,636,956 teaches an interweaving of fibers
th~t is not blenciny or me'~ blending of a composition to
~_ke ~ physic21 mi~tu-e~ J.S. ?a_en_ ~,719,'~6 teaches
the blen_ing f ~.o~o?ol~e_s cf L-lac'ide, ~-lactide,
~olymers 5f mi~._u-es thereo_; an~ co?olyme-s or L-lac~ice
o~ 3-7actide ~ h __ 'e_s~ one non'ac_ide c-monome~. The
_``~?~ , `S `~ '`t- -~ e c~?os~
_ ~ ~ _ _ _ _ _ ~ .... _ ~ ~ _ _ . ~ ~ _ ~ . _ _ ~ _ _ _ _ ~ _ _ ~ _ _ _ _ _ _, _ ~ . _ , _ _, ~ _
1-_ ~_--). c ~ _s-'~e~ -ec
-_~ec.____ ~ ~_,~____ _ _ _~____ _,__ _ _ _~__ ~
`jO~/0~13 PCT/~S9l/063'-
iY--
synthetic replacements of biological tissues and orqans in
reconstructive surgery. PCT publication ~o 8~/00419 to
Barrows reveals a bone spacer comprising a blend or
mixture of a nonabsorbable polymer and a bioabsorbable
S polvmer, polylactic acid is one of th~ preferred
biodegradable polymers but plasticizers are not revealed
therein. PCT publication WO 84/00~03 to Goyolews~i et al
su~3gests blends of polyesters and polyurethanes for
preparing surgical filam~nts. Cohn et al, in
Biodegradable PEO/~LA Block Copolymers, Journal o~ Biomed.
Mater. Res., Vol. 22, p. ~93, 1988, reveals a physical
mixture of poly(ethylene oxide) and poly~lactic acid).
Nowhere in the prior art is it disclosed t~t
lactic acid or lactide polymers can ~e the source of
lS pliable, highly extensible compositions by the use of
lactide monomers, or lactic acid, or oligomers of lactic
acid, or derivatives of oliqomers of lactic acid, or
oligomers of lactide as the plasticizer~ None of the
prior compositions are suitable for well-defined packaging
needs.
8RIEF DESCRI~TION O~ T~E INVENTIO~
A. The general teaching of the portion of the
invention providing for flexible materials is that
poly~lactic acids) derived fro~ lactic acid (homopolymers
or copolymers of L-lactic acid or D-lactic acid) or
lactides (ho~o?oly~e_s o co~olv~ers of L-lac'ide, D-
lac~ide, ~eso D,~-lac~ide, c~ r~ce~ic D,~ c~`da) th~t
e ~e~ e~ S~ 2~ ?'~s_~c~_e- s~-
~~s '_c~ic a^id, l~c_ide, oligo~e-s o~ 12c_i_ acid,
ol~o~^_s ~ -iv2.~ e~`~
~c~ -~o~s ~ ^c _:~er~ .c~-e ~ v ~
`~ r_2.~_`_~ s~ _e-~ le ?-câ _i^-
~ ~ . _ . ~ ; :: _ _ _ _ _ _ _ _ _ _ _ _ _ .. _ _ ~ ~ _ . ~ ~ _ _ . . ~ . _ ~: . _ _ }: c j . ~ .
= _ _ _~ _ . . = _ . _ _ _ _ _ _ _ . _ _ _ _ c _ _ _ _ _ . ~ _ _ _ . . _ ~,. ~ _ = _
-~ O9'/0~13 ~'CT/~S91/n63-'-
-15-
polymer. Since both lactic acid and lactide can achieve
the same repeating unit, the general term poly(lactic
acid) as used herein refers to polymers having the
repeating unit of formula I without any limitation as to
S how the polymer was made (e.g. from lactides, lactic acid,
or oligomers), and without refersnce to the degree of
polymerization or levsl of plasticization.
In general, a first e~bodiment of the invention
for flexible materials provides for an environmentally
biodeqradable composition useful as a replacement ~or
thermoplastic poly~er compositions comprising a
poly~lactic acid) and a plasti~izer selected from the
groups below, wherein the pl~stici~er is intimately
dispers~d within the polymer~ The poly(lactic acid)
lS polymer has the repeating units of the formula,
~3 1l
~ I ~n
wherein n is the number of repeating units and n is an
integer equal to at least about 150. ~referably the
unoriented composition has the physical properties of:
150 < n < 20,000, a tensile strength of about 300 to about
25 20,000 psi, an elongation to failure of about 50 to about
1,000 percent, and a tangent modulus of about 20,000 to
about 250,000 3si. The intimate dispersior. of the
plasticizer c~n yiel~ a substantially transparent
composition, al_b.ou5~ transpare-._y m2y no~ be obtained
~o with cert~in processes, 2S when the composition is fo2med.
_~ c ~ e~a~ _..e ~ -osi~ _c.~
-epl~ce~er.t 'or ?olyethylene when the ur.oriented
c^~a-s 'ion h~s _ensi;C s~~en -h c- ~àou_ ~,:30 -o cbo~_~
_ _~ 3~-_er._. ~., ~ ~_.~ o__ __ ~ ~
~a~ C~ _r`, ~r~ err~.~
_ ~ ~, r ~ r ~ ~=~ r ~
U`09~ ~l3 l'~/L~9l/(~3'~
-16-
;~ ~. v . _ ~, _,
elongation to failure of about 100 to about 600 percent, a
tangent modulus of about 165,000 to about 225,000, and a
melting point of about 150 to about 190 F.
A further embodiment of the invention provides a
process for producing an environmentally biodegradable
composition useful as a replacement for thermoplastic
polymer compositions having thQ staps: (a) polymeri2ing a
lactide monomer selected from the group consisting of D-
lactide, L-lactide, ~eso D,L-lactide, racemic D,L-lactide,
and mixtures thereof, in t~e presence of a suitable
catalys~; (b) controlling the polymer~zation to allow the
reaction to be stopped prior to complete polymeri2ation;
(c) ~onitoring the level of remaining monomer; (d)
stopping the polymeri~ation prior to complete reaction so
that unreactQd monomer in a predetermined amount is
trapped in association with the polymer; and (e) treating
the polymer and unreacted monomer to obtain an intimately
plasticized composition~ The polymerization reaction is
preferably stopped at a monomer level up to about 40
weight percent. If desired additional plasticizer may be
incorporated into the composition prior to, during, or
after the treating step, wherein the plasticizer is
selected from the group of plasticizers discussed below.
The sum of remaining monomer and additional plasticizer is
preferably below about 40 weight percent and is most
prefarably between about 7 0 and about 40 weight percent
for a pliable composition.
.~ vet f~_the~ embo~iment includes a ?_ocoss fo-
_-o~ucin~ ~ plas_i_i-e~ ~ol~e- of ?o~y('~__ic acid) ~ t
~0 com?-ises mi~in~! he~~in~t 2ni mel_in~ one or more lac~i~e
~_~o~e-~ ~nd ~ _a ~~ e~ .e ~ .e
5~~ ?~ ?~ -e~c~i^.~;
. _ _ _ __ _ _ _ _ . _ . _ ~ _ _ ~ ~ _ ~ ~ ~ . . _ _ . .. ~
_ ~ . _ _ . . _ _ _ _ _ -- _ _ _ . . _ _ _ _ _ _ _ _ ~ _ _ ~ _ _ _ . _ _ _ _ ~ _ . _ . .
e~ p~
?^-`~ c~ a cesc~
09'/0~13 PCT~'S91/063',
17-
~ 3 ~ ~
plasticizers may be added to obtain the desired
properties.
A yet further embodiment includes a process for
the preparation of a biodegradable blown film through the
inclusion of the below listed plasticizers in poly(lactic
acid) to achieve desired properties followed by extrusion
o~ the plasticized poly ( lactic acid) as a blown film.
Plasticizers useful with the invention include
lactic acid, lactide, oligo~ers of lactic acid, oligomers
of lactide, and mixtures thereof. The preferred oligomers
of lactic acid, and oligomers of lactide are defined by
the formula:
IH3 ll
HO ~--C - C~~~ m H II
where m is an integer: 2 < m < 75. ~referably m is an
integer: 2 < m < lO.
Further plasticizers useful in the invention
include oligomeric derivatives of lactic acid, selected
from the group defined by the formula:
I H3 11
R'O ~~~C~~~ q R III
where R = H, 21kyl, aryl, alkylaryl or acetyl, and R is
saturated,
33 whe_e R' = H, 2l~ -yl, a'`~;yl:-yl cr a-e_yl, Gn~ R' is
sat~rated,
S ~ < 5; an~ u_es ~he~ecC ~~e_e_ably c is a~
;C ~e~~.._ ?~-~e..~ ?~ e -`~_~ic~ s
___.. s ___c_.~.__s __ _______, ~ ___~ .e _ _ ______ :__
_ ~ ~ _ c _ _ _ ~ c _ _ ~ _ s ~ . . ::
_: . :: _ . .. _ _ . _ : _ .: _ _ _ : _ _ _ _ _ _ ~ _ _ _ . _ . _ _ _ . . .
WO~ PCT/~S~1/063~7
t ~ ~
This composition allows many of the desirable ch~racter-
istics of nonàegradable polymers, e.g. polyethylene, such
as pliability, transparency, and toughness. In addition,
the presence of plasticizer facilitates ~elt processing,
prevents discoloration, and enhances t~e degradation rate
of the compositions in contact with the environment.
The intimately plasticized composition should be
processed into a final product in a manner adapted to
retain the plasticizer as an intimate dispersion in the
poly~7er. The treat~ents to obtain an inti~ate dispersion
includ~ ) quenching the composition at a rate adapted
to retain the plasticizer as an intimate dispersion; (2)
melt processing and quenching the composition at a rate
adapted to retain the plasticizer as an intimate disper-
sion; and (3) processing the composition into a finalproduct in a manner adapted to maintain the plasticizer as
an intimate dispersion.
The composition may comprise from about 2 to
about 60 weight percent plasticizer. When a lactide is
selected, the composition preferably comprises from about
10 to about 40 weight percent lactide plasticizer selected
from the group consisting of lactic acid, D-lactide, L-
lactide, meso D,L-lactide, racemic D,L-lactide, and mix-
tures thereof.
If desired, the plasticizer can ~e selected from
the group of lactides consisting of D-lactide, L-lactide,
~eso D,L-'ec~iCe. racemic 3,L-12ctice and 2ixt~res thereor
so _ha~ ~ le2st 2rt c~ .he lac'id- Dlas.icize is
s~e-coc~emica~ y di__e-on~ C-cm the ~cnome~ a~sed to
pre~are the ol~e~. ~imi'a-l~y the mlas.icizer m~y
comprise ~ e-s o- '^c~i~e~ ^- c'igQmers ^ lactic
, _ _ ~ ~ _ ~ ~ _ ~ _ ^ _ ~ _ _ _ _ _ _ _ _ . ~ _ _ - . ., _ . _ _ ~ ~ . .
_ _ . . _ _ _ . _ .. . _ _ _ . . _ ~ _ _ _ _ _ _ _ _ _ _ _ . . _ _ ., _ _ ~ ~ _ _ _ _ _ _ _ _ ~. ) _
~0g'~lt PCT/~`S91/063~-
19-
sroup consisting of oligomers of lactic acid, oligomers oflactide, and mixtures thereof; and melt blending with the
blend a second plasticizer selected from the group
consisting of lactic acid, L-lactide, D-lacti~e, meso D,L-
lactide, racemic D,L-lactide, and mixtures thereof. If
desired, a first plasticizer defined by the formula III
may be used alone or in a~mixture with an oligomer of
for~ula II. This procedure allows the blending of the
first plasticizer at a first te~perature and the blending
of the second plasticizer at a second temparature lower
than the first temperature.
B. In general, a first embodiment of the invention
for replacement of c~ystal polystyrene provides for an
environmentally decomposable polymeric composition
suitable for use as a substitute for crystal polystyrene.
The composition comprises a poly(lactic acid), where the
repeating unit is an L- or D-enantiomer and there is a
preponderance of either enantiomer, having intimately
dispersed therein a plasticizer, as described below,
wherein the unoriented composition has the ohysical
properties of a tensile strength of at least 5,000 psi, a
tangent modulus of at least 200,000 psi, and is colorless.
The composition can be adjusted to be form stable above
about 70 C.
A further embodiment of the invention provides
~or a substitute for crystal polystyrene comprising a
__pol~er o~ ~h_ -~r~u't T ~herA n ~ an inte~e- between
about ~50 and abou_ lo,o~ here ~e ~_?eating un _ is an
~0 an2ntiomer; end he~in ~n~i~ct~el~ dispe-sei t~erein
2~ a~ G~ t~ - ?e--r~
_ ~ _ _ _ ~ . ~ = ~ ~ _ ~ ~ _ ~ ~ ~ _ _ _ _ ~ _ _ _ ~_ _ ~ . _ _ . ~ _ _
~=_~-_~. ;_ ~_ _e^~ ~ ~5 ~_~ -.- e r~ o_ . ~ ` s 5 _
_ _ ~2r ~ !2
--20--
V . ~ ~
and most preferably between about 2.5/97~5 and 7.5/92.5,
or between about 32.5/7.5 and s~s/2~
A yet further e~bodiment of the invention
provides a composition comprising a physical mixture of:
(a) a first poly(lactic acid) having a preponderance of
either D- or L- enantiomers; (b) a second poly~lactic
acid) selected from the group consisting of poly~D-lactic
acid) or a poly(~-la~tic acid), wherein t~e wei~ht percent
ratio of the first poly(lactic acid~ to the second
poly(lactic acid) is between about 1~99 and 9g/1; and ~c)
greater than about C.l wei~ht parecent of plasticizer as
described below, wherein the plasticizer is intimately
dispersed within the poly(lactic acid); and the unoriented
composition ~as a tensile strength of at least S,000 psi
~S and a tangent modulus of at least 200,000 psi, is form
stable above 70 C, and is substantially colorless.
Preferred ratios of the first and second polylactic acids
are between about 98/2 to about 75/25, and most preferably
between about 85~15 and about 95/5. The first poly(lactic
acid) may be defined by formula I, where n is an integer
between about 450 and about 10,000; and the second
poly(lactic acid) by the ~ormula:
I H3
t--C---C~ p IV
where p is an inte~e- between about 450 and about 10,000;
?nn rhe ur.o=ien.ed co~pcsi__o~ hzs the ph~-sicc~ prope=,ies
~0 of a tensile s~-en~th o^ z~ least 5,000 psi, a tangen~.
co~posi~_cn _^ ~his embo~i~en_ m~ `e crien~e_ n-
~n-e~'~e- ~ s_~ e-
s -- ~ -- -- .. ~ _ - . -
_ _ ~_ ~ . ~ _ _ _ _ ~ ~_ _ ~ _ ~ . _ ~ ~ _ _ ~ _ _ _ _: _ _ . : , _ _ _ : ~
~ . e~ce~s ~ 3 -s~. c __~ n~
_ ~ ~ _ ~ ~ ~ ~ ~ ~ ~ _ ~, -- -- ~ _, _ _ _ = _,, ~ _ ~-- , _ _ ~_ _ _ _: _ _ ~ _ _ _ ::
~;09",'0~l3 -21- rCTi~S91/n~3'-
temperatures above 70 C. The product can be biaxially
oriented.
A yet further embodiment of the invention
provides ~or an oriented and annealed environmentally
decomposable film or sheet product suitable for use as a
substitute for oriented crystal polystyrenQ film or sheet
comprising: a film or sheet of a copolymer of the formula
I: where n is betwaen a~out 450 and about 10,000; where
thn repeating unit is an L- or D-enantiomer, and there is
a pr~ponderance of either enantiomer; the product having
intimately dispersed therein t~e residue of a plasticizer,
as described below; the oriented and annealQd product
having the physical properties of: a `ensile strength in
excess of 7,500, a ~angent modulus in excess of 350,000,
and dimensional heat stability at temperatures above about
,0 C~ The product may be biaxially oriented~ Other
embodiments of the product may contain the other
plasticizers discussed below~
A further embodiment provides for an oriented and
annealed environmentally decomposable film or sheet
product suitable for use as a substitute for oriented
crystal polystyrene film or sheet comprising: a physical
mixture of between about 0~09 and about 99 weight percent
of a poly~lactic acid) of the formula I: where n is an
~`5 integer between about ~50 and abou_ 1~,000 and having a
preponderance of either the D- or the L-enantiomers;
~etweer. ~b~ c~ ~d ~o~~ 0~0~ e~ ._ ?e-~ett.~ of~ ?~
poly~lactic 2ciii~ of ~he ~ormula I~ nere p is 2n
t, ~ r~--'i2~ ~t-t~ ;t;~1, r ~ ?
~ repe2~n~ us~_ is 2 D- o- cn L-e~ t.e-; below 2
~ _St,`_`_r~~ ~ S t~a;.--~ t~}-;`. ~ is?2-~e `
_ _ ~ _ ~ ~ _ r ~_ ~ _ ~- . _ _ _ _ _ _ ~ ~ _ . . _: _ . . _
-- _ ~. _ _ ~: _ ~I S _ O . . _ _ _, ~ . 2 _ ~
. ~ _. _ _ ~: _ _ _ _ . _: _ . ~ _ _ _ _ . . _ _ _ _ _ . _ _ . . _ _ _ .
~O97/~l3 PCT/~S91/~63'-
-~2-
A further embodiment provides for an environmen-
tally decomposable polymeric foam composition comprising a
copolymer of the formula I: where n is an integer between
about 450 and about 10,000, where the repeating unit is an
L-or D-enantiomer and there is a prepondarance of either
enantiomer; having intimately dispersed therein a
plasticizer discussed belaw and wherein thQ composition is
~orc stable above 70 C.
A yet further embodiment o~ the invention
provides for an environmentally decomposable polylactide
product suitable 2S a substituta for crystal polystyrene
comprising: a poly(lactic acid~; and a plastici~er, as
discussed below, intimately dispersed in the poly(lactic
acid), wherein the poly(lactic acid) has a number averaoe
15 molecular weight, M~, between about 50,000 and 400,000, a
tensile strength of at leas~ about 7500 psi and a tangent
modulus of at least 350,000, form stability above 70 C,
and is substantially clear and colorless after processing
into a product.
Plasticizers contemplated for the compositions
and processes in the present invention include: (a)
lactic acid, D-lactide, L-lactide, meso D,L-lactide,
racemic D,L-lactide, oligomers of lactic acid, oligomers
of lactide, and mixtures thereof; where oligomers of
lactic acid and o!igomers o~ l~ctide defined by the
formula II: where m is an integer: 2 ~ m < 75; and
~à) one o. more ce ivatives o n olicome- o- lac-i- acia
defined by the formula III: where R = n, al~yi, aryl,
,0 al~yl, aryl, a'}:yl2-yl c_ ace~yl, and ~' is saturateà;
_ ., ~. 2
--~ e ~21~e~ i3.~
_ -` _--` _ ~ i ~ ~ _ ~ '` _ _ _ _ _ ~ _. ,. 2 5 i t _ _ . . _ ~ S i . .
. ::: _ _ _ _ . ~ _ _ _ _ ~ _ . . _ _~ _ 5 _ _ _ ~ ~ _ ~
~0 9't()~lt 1'Cr/~`S~I/nh3`'-
3 _
. ` ` ~c3
first plasticizer selected from the group consisting of an
oligomer of lactide, or an oligomer of lactic acid; and a
second plasticizer selected from t~e group consisting of
lactic acid, D-lactide, L-lactide, meso D,L-lactide,
racemic D,L-lactide, and ~ixtures th~reo~; and (b) a first
plasticizer selected from the group consisting of one or
more derivatives of an oligomer of lactic acid defined by
the formula III: where R - H, alkyl, aryl, al~ylaryl or
acetyl, and R is saturated; where R' - H, alXyl, aryl,
alkylaryl or acetyl, and R' is saturated; where R and ~'
cannot both be ~; and where q is an integer: 2 ~ q ~ 75;
and a second plasticizer selected from the ~roup
consisting of lactic acid, D-lactide, L-lactide, meso D,L-
lactide, racemic D,L-lactide, and mixtures thereof.
The amount of plasticizer present must be above
about 0.1 weight percent. The upper limit is defined by
the amount of plasticizer that will give the physical
properties for crystal polystyrene as defined herein. A
preferred amount of plasticizer is between about 0.1
weight percent and about 10 weight percent. The
plasticizer may be added for example in an amount (1)
effective to provide substantial transparency, (2)
effective to prevent degradation during processing, and
(3) effective to prevent discoloration during processing.
The plasticizer ~2y be added ~y methods known in the art
for blending (e.g. ~ill blending) to obtain an intimate
dispersion.
u_.he~ e2bo_imen, ~-o~ides fc- ~ ~roc_ss
~ ~e -~ ~n e~ r~c~ c3r~?0s
`3 `-`1~ cr sheet ~orming poly-~eric composiu ~n comprisins~
c_~cl~,~e~~ r~ 2~. ble~ c ~.o~e- s~ , ,hc
_o-_~ -or.s ~ `_2, n,-`-1~
.~ _ _ _ . _, _ _ _ _ _ _ _ _ _ _ _ ~-- _, _ _ _ _ _ _ _~ = ~ _ ~ ~ _ _ .~ . _ _ _ _
, t~ onc~e~s __ 2 ~
c~ " _ _ _ ~ _ _ S ; _ _ ~ . _ _ _ _ ~ _ . _ 2 ~ _ . _ _ C _ _: _ . _ _ _ . . _ J
~ o-~^-; ,~r.-i~c.~ .e ?cl~ -tic~ c~
~0 ~'~0~1~ PC r/~ssl/nfi3~,
~ 3
intimately dispersed plasticizer as discussed herein, the
unoriented composition having a tensile strength of at
least 5,000 psi and a tangent modulus of at least 200,000
psi; and treating the co~position to maintain the
plasticizer as an intimate dispersion within the polymer
whereby a substantially colorless composition is obtained.
If desired additional plasticizer may be added after the
poymerization reaction is ter~inate~ The composition may
also be rendered transparent as described below.
10The process preferably selects the ty~e and
amount o~ monomer to provide a ratio of L-enantiomer to D-
enantiomer of b~tween about 1/99 and 99/1. More
preferably, the monomer is selected to obtain a ratio of
L-enantiomer to D-enantiomer of between about 2.5~97.5 and
157.5/92.5 or between about 92.5/7.5 and 97.5/2.5. The
proce~s most prefera`oly uses ~he selected monomers in the
molten blend comprising between about 85 and 9S weight
percent D-lactide or L-lactide, and between about 5 and 15
weight percent meso D,L-lactide or racemic D,L-lactide.
~0The polymeric composition may advantageously be
extruded into a film or sheet and physically treated by
orientation and~or annealing to provide a polymeric film
or sheet having a tensile strength of at least ~,500 psi
and a tangent modulus of at least 350,000 psi. An
~S additional treatment comprises ~iaxiallv orienting and
heat treating the polymeric co2position.
The _reatment ~2V c~prise adding nucle~ting
agen~s, adding ~-lac~i_e ~_ L-lac~ice h~opo'~er ~
`~i2~ e~ c-. C~ Q_ ~C~ S C_~ ~e
_C exc'u~ed by pe-_o~in~ ,he ?oly~erizatiQn in ~n inert
.~o~phe~e and a_ ~e~c~ion _en?e~a_u~es ~el~ c.
dwesi--~ .e ~~e_.~nt __e- -_-prises ~-.nea~ ~he
`-~ w-~?_ _ ` ~
er~ c .~.cw- ~ _c ~s ~_~ine_.
r_c~ si_~ co.~?-i~ e~s
W09~/0~3 ~ )632
-25-
~_ ;; r~ r ._ i J `J
polymers selected from the group consisting of a
poly(ethylene terephtbalate), a polymer or copolymer o~
styrene, ethylene, propylene, vinyl cbloride, vinyl
acetate, alkyl methacrylate, al~yl acrylate, and physical
mixtures thereof; and one or more plasticizers discussed
below.
The poly(lactic acid) present in the blends may
be represented by the formula I: where n is an integer
between 75 and 10,000~
Plastici2ers use~ul with the invention include D-
lactic acid, L-lac~ic acid, racemic D,L-lactic acid, D-
lactide, L-lactide, meso D,L-lactide, racemic D,L-lactide,
oligomers of lactic acid, oligomers o~ lactide, And
mixtures thereof. The oligomers of lactic acid and
oligomers of lactide are defined by formula II: where m
is an integer: 2 < m ~ 75~ Preferably m is an integer:
2 < m < 10. These limits correspond to number average
molecular weights below about 5,400 and below about 720,
respectively.
Further plasticizers useful in tbe invention
include oligomeric derivatives of lactic acid, selected
from the group defined by formula III: wbere R = H,
alkyl, aryl, alkylaryl or acetyl, and R is saturated;
where R' = H, alkyl, aryl, alkylaryl or acetyl, and R' is
saturated; wbere R and R' cannot both be H, where q is an
integer: 2 ~ q ~ 75; and mixtures tbereo~. Preferably q
is an integer: 2 ~ q ~ 10~
Tbe p`2s ici~e~s may ~e ~re52n- in ~nv a~ount
tba_ -rovides t~.e desi-e~ cbaracteristics. ?o- e~ample,
~" ~brr VriO'IC t~'?eS 0~ las~ici2ers discusse~ be_ein and in
tbe otbe- gene-~i e-~oc me.~ts p-o~i~e c-: (2) mo~-
~
~ e cs.~.?_~ `a~ o~ e'_ ~ ` ca_~?~Qn._C;
. . _ ( C ~ C _ . ~ _ _ _~ 1 _ . . _
~ _ _ ~. _ _ ~ _ _ ._ _~ . -- -- -- . . -- -- --. -- _ _ .
~ ? `-^i~ s=1~ - _s --eser.^ ~-.
~~ ~ c ~ c ~ v~._~. _ ~, ;-~ ~ ` _ - _ _, ~ e _ ~. . c_ c C= ~ ~
~13 PCT~S91/063'-
-2~-
J :J
lower amounts. The compositions allow many o~ the
desirable characteristics of pure nondegradable polymers.
In addition, the presence of plasticizer facilitates melt
processinq, prevents discoloration, and enhances the
degradation rate of the compositions in contact with the
environment. The intimately plasticized composition
should be processed into a final product in a ~anner
adapted to retain the plastici2er as an intimate
dispersion in the polymer for certain properties. These
can include: (1) quenching the co~position at a rate
adaptQd to ret~in the plasticizer as an intimate
dispersion; (2) melt processing and quenching the
composition at a rate adapted to retain the plastici~er as
an intimate dispersion; and (3) processing the compoeition
into a final product in a manner adapted to maintain the
plasticizer as an intimate dispersion. The plastici2ers
are preferably at least intimately dispersed within the
polylactic acid if not in the coblended polymer.
Particularly advantageous is the sequential
incorporation of plas,icizer into poly(lactic acid) and
the other polymer by melt blending wit~ them a first
plasticizer selected rrom the group consisting of
oligomers o~ lactic acid,- oligomers of lactide, and
~ixtures thereof; and melt blending with the blend a
second plasticize~ selec.ed ^~om ~he grou? consis~ing o~
lactic acid, L-lactide, D-lactide, meso D,L-lactide,
acemic D,L-12__ida, and m`~U-QS ~he~e~. Ir desi_~d, a
rirst plasticizer de^ined by ~he ~or~ul2 II- m2y be used
~ ~ ThiS ?rOCadU_ ~11Q~S the blending Q ^` _he -irs~
_ 1 C 5 _ _ C _ _ ~ _ ~ _ _ _ _ _ = = _ ~ .. ~ ~ _ _ ~ ~_ ~ _ _ . . _ _ . ~ _ _ . _ ~ . _ _ . . _ C ~ . . _
5 _ _ . ~ ~ ~ ~ _ _ _ _ _ _ _ _ ~ ~ ~ _ _ _ ~ . ~ _ ~ _ . ~ ~ ~ _ _ ~ _ ~ _ _ _ _ _ _ . .. .. _
. ~
_ _ ~ _ _ _ ~ _ _ _ _ ~. _ _ . _ . . ~. = ~ . _ . . : _ . . . ~; _ _ ~ ~ , _ _
~,09~ 'CT~Sql/n63~-
-27-
~ ~ J ' ~ ~ j
resistance to the blended composition. Such an elastomer
may be, for example, a Hytrel~: a segmented polyester
which is a block copolymer of hard crystalline segments of
poly(butylene terephthalate) and soft long chain segments
of poly(ether glycol). one example is known by the trade
name as Hytrel~ 4056 (DuPont) segmented polyester~
In addition to the above there are disclosed
blends including on~ or more plastici2ers. T~e blends are
useful with the above materials, as well as with others as
further discussed ~erein.
The poly(lactic acid) present in the blends may
be represented by formula I: where n is an integer
between 75 and 10,000.
Plasticizers useful with the invention include D-
lactic acid, L-lactic acid, racemic D,L-lactic acid, D-
lactide, L-lactide, meso D,L-!actide, racemic D,L-lac~ide,
oligomers of lactic acid, oligomers of lactide, and
mixtures thereof. The oligomers of lactic acid and
cligomers o~ lactide are defined by formula II: where m
is an integer: 2 < m < 75. These limits correspond to
number average molecular weights below about 5,400 and
below about 720, respectively.
Further plasticizers useful in the invention
include oligomaric derivatives of lactic acid, selected
rom th~ ou? defined hv r_rmul~ III: where R = H,
alkyl, aryl, alkylaryl or acetyl, and R is saturated;
whe-e R' = ~ a`~ 1, ai~c~'ar~l c- acc~~;~ and R' is
saturateà; ~he_e R an- R' c~nnot b- h be H; ~here is n
~3 The ? astici~ars .~y be ~resan_ i.... any ?~our
_`._- -~_t~ e _ec~ 5-`'-~ _c,
_ _ _ = ; _ _ -- -- _ -- _ ~ ` _ _ _,~; , __ ,, _ _ ~ ,, _~ _ _ _ , _, . _:
~ e c-_~?_~ ic.............. _ =:~e ~ ?~
_ ~ _ _ ~ _ _ _ ~ _ _ _ _ _ _ _ _ _ _ . ~ ~ _ :. . _ _ _ _ _ . . ~ _ _ _ _ _ :~ ~ ~ = -- _
~: _ = _ _ . ._ ~ ~ _ _ ~ _ = ,, _ _ _ , _ ~ -- _ _ _ ' ~ ~ _ , .
~O9~/t~13 PCT/~s9l/o63~-
_~s_
moisture. For pliability, plasticizer is present in
higher amounts while other characteristics are enhanced by
lower amounts. The compositions allow many of the
desirable characteristics of pure nondegradable polymers.
In addition, t~e presence of plastici2er ~acilitates melt
processing, prevents discoloration, and enhances the
degradation rate of the compositions in contact with the
environment. The intimately plasticized composition
should be processed into a ~inal product in a manner
adapted to retain the plasticizer as an intimate
di~persion in ~he pol~lactic aci~ and~or its coblended
polymer for certain properties. These steps can include:
~1) quenching the composition at a rate adapted to retain
the plasticizer as an intimate dispersion; (2) melt
processing and quenching the composition at a rate adapted
to retain the plasticizer as an intimate dispersion; and
(3) processing the composition into a final product in a
manner adapted to maintain the plasticizer as an intimate
d~sperslon.
Particularly advantageous is the sequential
incorporation of plasticizer into poly(lactic acid) and
the other poly~er by melt blending with them, a first
plasticizer selected from the group consisting of
oliqomers o~ lactic acid, oligomers of lactide, and
mi~tures thereo^; and melt blending with the blend a
second plas~ici~er selected r`ro~ the group consisting of
lacti_ acid, L-la~--ide, 3-lactide, meso D,'-lactide,
`-~C2~`_ D.L-la-=ide, and ~i~_u~es the~eo~. T~ desi_ed, a
ci_st plas~ici e- d~ ed by the fo~ ula T~T mav ~e ~sed
alone or in a_mi~:_m-e ~i_n ~n oiigo~er c_ rc~ula ,1.
~his p-ccec~a~e ~ilo~ he ~lendi?.v oî .he firs.
?e-~
~09'/0~13 -23- PCT/~S91/Q63~,
w ~ v
B~IEF DESC~I~TION O~ ~H~ FIGURES
Fiyure 1 is a graph showing the relationship
between percent lactide (abscis~a X) in the composition as
plasticizer and tensile strength measured in PSI (ordinate
Y)~
Figure 2 is a graph showin~ the relationship
between weight percent lactide (abscissa X) in the
composition as plastici2er and elastic ~odulus measured in
1000 PSI tordinate Y)~
Figure 3 is a graph showing the relationship
b~tween percent oligomer (a~scissa X) in the composition
as plasticizer and tensile strength measured in PSI
(ordinate Y) where curve A is ~or a 90/10 copolymer and
curve B is for a 92.5/7.5 copolymer.
Figure 4 is a graph showing the relationship
between percent oligomer (abscissa X) in the composition
as plasticizer and the elastic modulus measured in 1000
PSI (ordinate Y) where curve A is for a 90/10 copolymer
and curve B is for a 92.5/7.5 copolymer.
Figure 5 is a graph showing a DSC plot of a
control composition prepared by the teachings of the
present invention. Temperature is measured in C (abscissa
X); heat flow is measured in m~ (ordinate Y). curve A
represents a first scan of the ~aterial and curve B the
2~ second scan.
FigurP 6 is 2 yraph sho~ing a DSC plot of the
c^m?os_ti~n Oc ~am?le S~ Temperature is ~e2sur2d i~ C
~absciss2 X); hea~ f' 5~' lS ~e~sured in mW ~o_dinate i).
3~ s_ar..
?-si~ ?~ c ~e~
res~ s-_~ e-~l -.^ c~
_ _ _ _ _ _ _ _ _ _ ~ . ~ _ _ _ _ _ _ . ~ _ _ _ _ _, _ _ . . ~ _ . ~
~'0 9'/()~13 ~ 9~ n~
--30--
copoltlmer of Example 5B. Temperature is measured in C
(abscissa X); heat flow is measured in mW ~ordinate Y).
Curve A is unquenched copolymer; curve ~ is quenched
copolymer.
Figure 9 illustrates the DSC plot o~ t',s material
of Example 5B after remaining at 70 C ~ox 100 minutes.
Temperature is ~easured in C' (abscissa X); heat flow is
measured in mW (ordinate Y). Curve A is unquenched
copol~mer; curve B is quenched copolymer~
Figure 10 illust-ates the DSC plot o~ the
~aterial of Exa~ple 5B after anne~ling in 185 F overnight~
Temperature is measured in C (abscissa X); heat flow is
measurQd in m~ (ordinate Y). Curve A is unquenched
copolymer.
Fi~ure 11 illustrates the DSC plot of the
material of Ex2mple SB that has been blended with 5
percent calcium lactate. Temperature is measured in C
tabscissa X); heat flow is measured in mW (ordinate Y).
Curve A is unquenched copol,vmer; curve B is quenched
copoly~er.
Figure 12 co~pares the melt viscosity (poise) in
thousands (ordinate Y) versus shear rate characteristics
(l/sec) in thousands (abscissa X) of polystyrene (curve A)
at C and the lactide polymer prepared as in Example 8B
(curve B) at ~60 C.
Figure 13 illustrates a DSC ?lo~ for ,he
co~ ,~er c~ am?le ~ 'em?er2tu_e ~s me2sured '~ C
(~sciss~ `~3; h ~a_ fl o~i ~s teas.~-ed in m~ (ordin2~e ~
-~t~-~ et ~ s ~: t~ en_~ct~' -G?ol~,~e-~ c~ e ~ ~` s ~uP t~c~ed
~ O c--_~ o l t,~t t
Fi~u-e '` il`us~-ates ~ DS~ or t~e ;-
_-C-~2 `'`~ ^?;'~ `_ `5 ~t-c~ r` C-?~ '- C-
~ _ _ ., _ ~. _ . . _ . . _ _ . . _ ._ _ _ _' _, .~ _ _ . _ _ _ ~ _ _ _ _ _ . ~ ~ . ~. _ ~ . _ _ ~. _ _ _ _ .
5 ~ __s c. tt~t~ .e ~ e~ c
-~-?-- -- ` ~ ~~~ c ~ ?~ ~r-1 -t --
09'/0~ 31- PCT/~S91/Ofi'.'
~ ' .. ~. 3
and a homopoly~er of L-lactide. Temperature is measured
in c (abscissa x)i heat flow is measured in mW (ordinate
Y). Curve A is the unquenched blend of copolymer and
homopolymer; curve B is the quenched blend of copolymer
and homopolymer.
Figure 16 illustrates a plot of the glass
transition temperature of 90/10, L-/D,L-lactide copolymers
versus residual lactide monomer. Abscissa X is lactide
measured in wt.~; ordinate Y is T~ measured in C.
Figure 17 illustrates a DSC plo~ o~ 90j~0,
L-/D,L-lactide copoly~er blended wit~ S weight percent
polystyrene. Te~perature is measured in C (abscissa X);
heat flow is measured in mW (ordinate Y). Curve A is the
first heating; cur~e B is the second heating.
DET~ILED DESC~IPTION OF
THE INVENTION AN3 PREFERRED EMBODIMENTS
A~__First General Embodiment
The environmentally biodegradable compositions
disclosed herein are completely degradable to
environmentally acceptable and compatible materials. The
intermediate products of the degradation: lactic acid and
short chain oligomers of lactide or lactic acid are widely
distributed naturally occurring substances that are easily
~etaboli-2d by 2 ~ide variety o organis2s. ~hei~ natural
end degradation products are carbon dioxide and water.
~c..~_m?12~oc e~u~valen~s o~ _~ese. com?osit~o~s s~ch as
those .hat _c..~ai~ or amounts o_ o_her ma~eri~ls,
^i'l~-s. _~ rs -~ e'~
enviro~.-e~.t_lly ~eg:~a~le ~v ~ro?e- cho c_ c- mal e~izls.
e _-~?cs~ c-.s ~ r.;i~ n~â`~ e~
_ _ _ _ _ ~ _ c ~
~ .~ic-.al .~ _e __c--~e ~ ej _~^_ l _ _ A,
wos~/~t3 PCT/~S9l/n632
_37_
~ J
more slowly degrading residue will remain. T~is residue
will have a higher surface area than the bulk product and
an expected faster degradation rate.
T~e general applic~tion of the invention results
S in the first and general embodi~ent of the invention. T~e
homopolymers of D-lactide, L-lactide, D,L-lactide as well
as copolymers of D-lactide, L-lactide; D-lactide, D,L-
lactide; L-lactide, D,L-lactide; and D-lactide, L-lactide,
and D,L-lactide all produce ~aterials useful in the
invention when plasticized by lactide monomers, lactic
acid, oligomers of lactide, oligomers of lactic acid,
deriYatives of oligomeric lactide and mixtures thereof
that are intimately dispersed in t~e polymer. A plasti-
cizer may be produced by stopping t~e reaction before
polymerization is completed. Optionally additional
plasticizer consisting of lactide monomers (D-lactide, L-
lactide, D,L-lactide, or mixtures thereof), lactic acid,
oligomers lactide or oligomers of lactic acid or its
derivatives including all L-, D-, and DL- configurations,
and mixtures thereof can be added to the formed polymer.
While aspects of the invention can be applied to various
polylactides in general, one preferred polymer is defined
by the formula:
CH3 O
l ll
whe-e n is _~ 2 r` e~_ee o poly~e~i~~ n (number c-
repeatin~ units), pl2sticized with a pl2sticizer derived
~ r.~e~-s ~sc_ __
p_oduce t:~e po'~e~ T~e m~~e l~._im~tely _~e pl2stlc-~er
~`s ~t2~ te~ wi ~ .2 ?~1~.C- ~ b~_e_ c_e ~,c
_ . ~ _ _ _ _ = _ _ _ ~ _ _ _ _ ~ , _ ~ _ = _ = _ ~ . _ _-- = ~ ~ _ .
~ . _ c~ ~e~, c~ n~m_r -~-
_1___~__ ___~=____~_ __~ __ _____ ~_ ~... ._si__c_ ~.~____
_ _ _ _ _ _ _ . _ : _ . _ ~ _ . ~ _ . ~ ; ~: _ _ _ _ . _ _ s _ _ _ _ . : _ = _ _
,~ rcr/~sql/o
-33-
polymerization. The preferred oligomers of lactic acid,
and oligomers of lactide including all L-, D-, D~-
configurations and mixtures thereof, both random and block
confi~urations, useful for a plasticizer are de.ined by
the formula:
l 3 1
H0 ~ r~
H
where ~ is an inte~er: 2 < m < 75~ Preferably m is an
in~eger: 2 c ~ ~ lO~
The oligomers of lactic acid and its derivatives including
all L-, D-, D~- configurations and mixtures thereof, both
random and block configurations, useful for a plasticizer
are defined by the formula III:
CH3 o
R'O _ q R III
H
where R = H, alkyl, aryl, al~ylaryl or acetyl, and R is
saturated,
and where R' = H, alkyl, aryl, alkylaryl or acetyl, and R'
is saturated,
where R and R' cannot both be H,
where q is an integer: 2 < q < 75; and ~ixtures thereof.
?referzDly a is ^-n in~ege~: 2 ~ q < o.
The plasticisers added to the ~olymer
osi.io~ a _0'13~ .s:
(a) They zct as ?las~lcize-s inl~odu-ing
__-posit_or.s no~ _ound i-. ~?~'y~er-5~
;lscosi~y ~ r _~.e ?o~vr.ers a~ e_s _:.e
_ . _ = _ _ _ ~ , . _ _ . _ _ _ _ _ _ _ ~ _ .
WO '~'/0~ 1 ~ I S~ 63',
--3~--
. .L ~J ~t
(c) The plasticizers prevent heat build up and
consequent discoloration and molecular
weight decrease during extrusion forming of
poly(lactic acid).
(d) The plasticizers add impact resistance to
the compositions not found in the polymer
~lone.
In addition, the plasticizers may act as compatibilizers
for melt-blends of polylactides and other de~radable and
nondegradable poly~ers. That is, molten mixtures of two
dif~erent polymers can more intimately associate and mix
into well-dispersed blends in t~e presence of the
plasticizers. The plasticizers may also improve
performance in solution blendinq.
The subscripts n, m, and q above refer to the
average number of mers (the repeating unit) of the polymer
or oligomer. Number average molecular weight M~ as used
herein is related to the mers by multiplying n, m, or q by
the molecular weight of the individual mer, for
poly(lactic acid) this number is 72. The nu~ber o~ ~ers
present in a polymer is also called the degree of
polymerization. The reader is referred to the following
texts where this subject is discussed further ~olymer
C~emistry an Introduction, 2nd Edition, R. Seymour et al,
~5 Marcel DekXe_, Inc., 1988 cnd Tnt-oduction to Polymer
Chemi~trv, R. Seymour, McGraw-Hill, New York, 1971.
The pro?o__~ons ~ lactice, D-lac~ide, and ~rT_
la~_id- in _he pol~o_ C_ e not c_~ al to c~ n~
'-s~i-s; ho~ . t~ io-C ~ D.~-
~ctide may ~-_ry ca_~ai~ pe__~es as ~~r~er discussed
~elo~ c_=e o~ ~-lcc~ -l_c~ cc~ide
~O9'/~13 rCT/~`S91!063'-
-35-
D-lactide is a dilactone, or cyclic dimer, of D-
lactic acid. Similarly, L-lactide is a cyclic dimer of L-
lactic acid. Meso D,L-lactide is a cyclic di~er of D- and
L-lactic acid. Racemic D,L-lactide comprises a mixture of
D-lactide and L-lactide. Nhen used alone herein, the term
"D,L-lactide" is intended ~o include meso D,L-lactide or
racemic D,L-lactide.
one of the methods raported in t~e literature for
preparing a lactide is to de~ydrate lactic acid under high
vacuum. The product is distillQ~ at a hiqh temperature
and low pressure, Lactides and t~ei- preparation are
discussed by W. ~. Carothers, G. L. Dorough and M. J.
Johnson (J. Am. Chem. Soc. 54, 7~t-762 ~1932]); ~. Gay-
~ussac and J. Pelouse (Ann. 7, 43 ~1833~; C. A. ~ischoff
1 and P. Walden (Chem. Ber. 26, 263 ~1903~; Ann. 279, 171
tl984~); and Heinrich Byk (Cer. Pat. 2~7,826 ~1912~);
through Chem. A~str. 8, 554, 2034 ~1914]).
The optically active acids can be prepared by
direct fermentation of almost any nontoxic carbohydrate
product, by-product or waste, utilizing numerous strains
of the bacterial genus ~actobacillus, e.g~ L2ctobacil~s
delbrueckii, L. salivarius, ~. casei, etc. The optically
active acids can also be obtained by the resolution o~ the
racemic mixture through the zinc ammonium salt, or the
~5 sal' witb alX21cids, such ~s mo ?hine~ L-lac'ide is a
white powder having a molecular weight o~ 144. I_ an im-
~r~ e~ ~ y-~2i~b~ p~~ ie e-~?l~ve~ ~
~ccorc2nce with ~ha present invention, it is p_-efa-able ~o
v ~ alli~_t~n ~ r~
~3 i_cbu~yl l~et^n.e. ~he sno~ hi~a c ys-~ls ^~ `-lzctice
r~ at cc-~~ s usa~ ~E-a`` n ~ha s~ol _ dsno~as
~`e-~ C^~ e?'-_~e ~ c- e`
_ ~. c_: _ e__ ~_ _~.,;~____i: = ~ __ ~- e
W(>s7/n~l~ PCT/~S91/063'7
-36-
.,
. ~ i 3 ~
lactonitrile (acetaldehyde cyanohydrin~ or by direct
fermentation of almost any nontoxic carbohydrate product,
by-product or waste, utili2ing numerous strains of the
bacterial genus Lactobacillus. D,L-lactide is a whlte
powder having a molecular weight of 144. If an i~pure,
commercially-available product is employed in accordance
with the present invention, I prefer to purify it by
recrystalli~ation from anhydrous me~yl isobutyl ketone.
One such commercially available product co~prising a mushy
sémisolid melting at 90-130 C was recrystallized from
methyl isobutyl ketone and decolori2ed using charcoal.
After three suc~ recrystallizations, the product was
t~mble-dried in vacuo under a nitrogen bleed ~or 8 t~ 24
hours at room temperature. The snow white crystals thus
obtained comprise a D,L-lactide mixture melting fro~ 115-
128 C.
In preparing the compositions in accordance with
the invention, it is preferred to carry out the reaction
in the liquid phase in a closed, evacuated vessel in the
presence of a tin ester of a carboxylic acid containing up
to 18 carbon atoms. The c~mpositions, however, can also
be prepared at atmospheric p-essure with the
polymerization system blanketed by an inert gas such as,
for example, nitrogen. If polymerization is conducted in
~5 'he oresence of oxygen or 2ir, some discolor2tion occurs
with a resulting decrease in mole~ular weisht and tensile
s,_2ns~h. 'he p~ocess c_n `~e c~rried out 2t ~e~?eratures
~here the ?o'~e_i_ ~ic~ is s`~ssish in i_s la-e_ ~es
~ is_~s ~ ~ _
_0 mel_. ~re er-ed te~?er2~ures ~ his ?ur?cse Fr_
~ene-~lly ~etwee-. _he meltin~ ?ci..-~ 2~ pure ~ c_i~e _~
~ure ~ lac~i__, ~~ ~^~;ee.~ ~ _c `_, ^ ihi' t _-. ?._ ~i~V
~=E5e..~ el~ 3~ ^ ^ r ~~
_ _ _. ~ _ _ .
_ _ __ __ _ .
~ c-~-.. = `__~ c~r ~ t~
UIO9~ 3 PCT/~S91/063~-
-37-
eutectic mixture, which melts t~ a mobile
fluid that is an intimate solution of one,
two, or three monomers.
2. The ~luid melt is polymerized by catalyst
to form an increasingly viscous solution
and eventually unrQact~d ~onomer is trappQd
in association with the polymer as a
solution, rather than as a distinct
heterogeneous phase. The monomer no longer
can react since the reaction is extremely
di~fusion controlled and cannot efficiently
contact the low concentration of active
end-groups of the poly~er.
3. The polymeri2ation ceases or slows
considerably so that at room temperature
the blend of monomer and polymer are a
solid solution that imparts plasticization,
clarity, and flexibility to the
composition.
4. The catalyst deactivates so that subsequent
melt-fabrication does not reinitiate the
polymerization.
5. The plasticized composition is quite stable
since the residual monomer is very high
.a ~oilin5, e.g., l~ctide has a `aoiling point
of 142 C at 8 torr, and is tightly
~sso__~e~ s~ h i.s o?en-ch_in t~ut~ e~-
polylacti~e.
3~ te~pe-et~-P bet~een the ~elting poi..t o. _he T-lactide ~nd
20G C cn_ ~ c~ s ~ 5~ e
n^~ ~r ~ C~C`~ n_-e~cin~
e~ e -~ a5 ' a ~~ c e~.~~
~0~"~l3 ~cr/ls4l/n~3~/
. v ~
are obtained by heating a mixture of L-lactide and D,L-
lactide at a temperature between about 110 C and 160 C.
The catalysts employed in accordance with the
invention are tin salts and esters o~ c~rboxylic acids
containing up to 18 carbon atoms. Examp~es of such acids
are formic, acetic, propionic, butyric, valeric, caproic,
caprylic, pelargonic, capric, lauric, myri~tic, palmitic,
stearic and benzoic acids. G~od results have been
obtained wieh stannous acetate and stannous caprylate.
1~ The catalyst is used in nor~al ca~alytic amounts.
In aenaral, a c~talyst concentration in the ~ange o~ about
0.001 to about 2 percent by weight, based on the total
weight of the L-lactide and D,L-laceide is sui_able. A
catalyst concentration in the range of ~bout 0.01 to about
1 ~ percent by weight is preferred. Good results were
o~ained when the catalyst concentration is in the range
of about 0.02 to about 0.5 percent by weight. The exact
amount of catalyst in any particular case depends to a
large extent upon the catalyst employed and the operating
variables including time and temperature. The exact
conditions can be easily determined by those skilled in
the art.
The reaction time of the polymeri-ation step, per
se, is governed by the other reaction variables including
~5 the rezc~ion te~perature, t~e particular c~talyst, the
amount o~ cat~lyst and whe~her a liquid vehicle is
em?10Yed. ThP ~eactior. ti~e c~n vary ^~om 2 -~atte_ ^_
s ~ e_~od ~ _s, c~ ys, ~'2p~?.~ t~
~2_ ~ a_ ^ C~ r~s .~ e ?'~ .e-
o_ the mi~tu~-e e~ manome-s is cont`nued ur..il he ~esire~
le~el ~ e-~ s ~ ec_e~ e~
~.~xi2at~ e~G_=i-.e- ~ si~ as~
~ _ . . _ _. _ _ _ . .^~ _ _ _ _ _ _ i _ ~. . ~ _ ~ . _ . _ . _ . . . _ _ _ _ _ ~. ~
~i~ec~ -c=- ?~- E c: ~ ~. ` 5 .
_ ~ _ . ~ _ _ . _ _ _ _ _ _ _ _ _ _ . . . ~ ~ _ _ . . _ _ _ ~ . _ _ _ . ~ ~ _ C _ _ _ _ _ . . . _ _
~o s~/n~l rcr!~s4l~0fi3~-
-39-
. ~ ~
,
attained the conversion of monomer to polymer that is
desired to achieve the desired plasticization. In the
preferred embodiment of the invention, approximately 2 to
30 percent lactide is left unreacted, depending on the
degree of plasticization to be achieved.
In general it is preferred to conduct the
polymerization in the absence of impurities which contain
active hydrogen since t~e presence of suc~ i~pu~ities
tends to deact_~ate t~e catalyst and~or increase the
lQ rea~tion time~ It is also preferred to conduct t~e
polymerization under subst~ntially a~ydrous conditions.
The copolymers of the invention can be prepared
by bulk poly~erization, suspension polymeri~ation or
solution polyneri2ation. The poly~eri2ation can be
carried out in the presence of an inert normally-liquid
organic vehicle such as, for exa~.ple, aromatic
hydrocarbons, e.g., benzene, toluene, xylene, ethylbenzene
and the like; oxygenated organic compounds such as
anisole, the dimethyl and diethyl esters of ethylene
qlycol; normally-liquid saturated hydrocarbons including
open chain, cyclic and alkyl-substituted cyclic saturated
hydrocarbons such as hexane, heptane, cyclohexane,
alkylcyclohexanes, decahydronaphthalene and the li~e.
The polymerization process can be conducted in a
_5 ~ __h, semi-c_~.t~nuous, cr con_~.uous manr.e~
preparing the lactide mono~eric reactants and catalyst for
sl~s~ent ~ io~ y ~-r. ~_ 2d~i~ r.
or~er accorGing ~o ~nown ~oly~eri2ation ~echnicues. Thus,
3~ re2c~an~s. ~he_e2_`_e-, t;~e cr-~lys~-con-2inin ,oao~e_
~ 3e ~ c- ~~ e_. _-~ G
_ ~ _~ ~ ~_ _ _ _ ; ~ _ ~_ ~ ~_ ~ ~ _ _ _ ~_ ~ A _ _ _ A = _ _ = _ _ --~ _ _ _, _ ~ _. _ _ ~ .
--r~ ~ _ , _ _ _ _ _ _ _ _ _ ~ _ ~ _ = _ ~ ~ _ _ _ _ _ _ _ _ _ A = _ _~ _ S
~ = ` ^ ' _ " 3 G
~o~Jo~,l3 rcT'~nl/n6~'~
--~o--
;~ `.; .' .1 :,`',
be added to the catalyst, catalyst solution or catalyst
suspension. Still further, the catalyst and the monomeric
reactants can be added to a reaction vessel simultane-
ously. The reaction vessel can be equipped with a
conventional heat exchanger and/or a mixing device. The
reaction vessel can be any equipment normally employed in
the art of making poly~ers. One suitable vessel, for
example, is a st~inless steel vessel.
The environ~entally biodegradable compositions
produced in accordance with the present invention
depQnding upon the L-lactide, D-lactide, meco D,L-lactide
ratios, ~ind utility in articles of manufacture, such as
~ilms, fibers, moldings and laminates, which are prepared
by conventional fabricating methods. These articles of
manufacture are contemplated for nonmedical uses i.e.
outside the body whe~e they can substitute for the common
environmentally nondegradable plastics.
Filaments, for example, are formed by melt-
extruding the copolymer through a spinneret. Films are
formed by casting solutions of the biodegradable
compositions and then -emo~ing the solvent, by pressing
solid biodegradable compositions in a hydraulic press
having heated platens, or by extrusion through a die,
including Blown Film techniques.
a-io~s ~ech~nisues i.._ludi-.g me'_ blenQi~c, slow
cooling, and rapid cooling (quenc~ing) can be employed in
~r2p~r~g ~._3duc-s ~ s -~ ?~ s a~
copolymers or the invention.
'~ tem~e-2tu-e is --o?-e~ -aDi_l ; ~ --ever.t e~:'e~.sive
-~s~ .2 ?ol~.~e_. ~ s=~
~ _ ~ ,_ ~ _ _ ~ -- ; ' _; _ ~ ~, . _ ~ .~ _ _ ~ _ , _,, _ _ .. ~ _ . . _ _
is ~ ~ e =~ ss--~ si=~ ?~
. ~ _ i ~ ~ ~. `` ` ---- -- ` -- ` _ _ _ i C 2 S . . _ _ _ _ _ _ _ _ `_ _ -- -- ;l -- -- ` -- --
~09'/0~13 -41- PCT/~`S91/Ofi3'-
;t' ~'2~
does not have the ti~e required and remains largely
amorphous. The time required to quench depends on the
thickness of the sample, its molecular weight, melt
viscosity, composition, and its Tg, where it is frozen-in
as a glassy state. Note that melt viscosity and Tg axe
lowered by plasticization and favor quenc~inq. Thin ~ilms
obviously cool very quickly bocause of their high sur~ace-
to-volume ratio while ~olded items cool ~ore slowly with
their greater thicknesses and ti~e spent ~n a warm ~nold
ba~ore removal~ Regular structures such as poly ~L-
lactide) order more easily and crystalli~e more quickly
than more random structures such as a copolymer.
With the polylactides the melting points are
approximately 150-190 C depending on the L-lactide content
and, therefore, the regularity of stru~ture. The Tg of
all the polylactides, including various L and D,L
homopolymers and copolymers is 60 C. The Tg decreases
when residual lactide is intimately dispersed with the
polymer. Q~lenching to an amorphous state reqmires that
the polymer or copolymer in an amorphous melt is rapidly
_ooled fro~ its molten state to a te~pe-ature below its
Tg. Failure to do so allows spherulitic crys~allinity to
develop, that is, crystalline domains of submicron to
micron size. The latter scatters lisht and the polymer
s?~ci~e?~s ~co.~ o~ue~ ~ose _-ys_~lli?~-~ Co~s hGve
i~proved stability to heat distor~ion. This spherulitic
c_vst~ll n~=v is o-_~n cal'ed sho-~ _~ or~el-long rance
~isorder since the c ys~alli.es are ser ~-ted by a~o-?ho~s
,0 crosslini~s ~o -.ain~ain di.e..sional s~2~ y abo~e the T
_ _ _ ~ _ _ ~ ~ _ ~ ~ ~ ~ _ ~ _; _ _ _ _ _ _: _ _ _ _ . _ _
t~oi~ . _.e ?~ _e~c~ - lc.:
_ _ _ ~ _ _ . . _ = _ _ _ .~ . _ _ = _ _ ~ _ . . _ _ _ _ . _ _ ~ _ . . _ _ . ~. _ . i _~ _ _ _ . ~ -- -- --
.. ~ ~ ~ _ _ __ _ _ ~ . ~ _ _ , ~ _ _ _ ; _ _ _ _ ~ ~ _ ~ . _ _. . _ _ _ , ~ _ _ _ ~ _ _ _
. _ _ . . . _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ ~ _ _ ~ _ _ _ _ _ _ _ _ _ _ ~ ~ _ _
~'0 9~ .2- r~ '5(~1/()63~-
different order, called long-range order, short range
disorder. Transparency and resistance to heat distortion
are favored.
A detailed discussion can be found in textbooks,
for example, "Structural Polymer Properties", by Robert J.
Samuels, Wiley Publications, NY, NY 197~
Contemplated equivalents of th~ compositions of
the invention aro those that contain minor amounts of
other materials. ~he copol~ers produced in accordance
with the present invention can be modified, if d~sired, by
the addition of a cross~ ~ing agent, other plasticizers,
a coloring agent, a filler and the lika, or minor amounts
of other lac'one monomers such as glycolide or
caprolactone.
Cross-linXiny can be effected by compounding the
compositions with free-radical initiators such as cumene
hydroperoxide and then molding at elevated ~-emperatures.
This can improve heat-and solvent-resistance. Curing can
also be effected by compounding the copolymers with
multifunctional compounds such as polyhydric alcohols and
molding, or thermoforming under heat and vacuum. Graft-
extruder reactions to effect curing of the polyesters is
an obvious method of cross-lin~ing and chain-extending the
copolymers.
In -reparin~ -oldin~s, a ~il'er _an ~e
incorporated in the compositions prior to curing. A
~iller has _~.e ^unc~i_-. o~ rmodifyinv _he --o?er~ies ef a
moldins, in_`udir.~ hardness, s,-en~~h, vempera-ure
? ~ _e ___ _.1~.
.o -o~de-, ?owde_ed calcium c~r~ona~e, si'i-a, ~aolini~e
~ _ s _ _ _ _
~ 'i_ 5~ ~e~ es~~_`_. ~ ?er~j
~ ~ _ _ _ _ _ _, _ _ _ _ _ _ _ ~ S ~ _ . . _ ._ _ _ _ C _ _ _ _ _ . ~ _ ~
~o ~/n~~ s~l/06,~-
-~3-
.~, .; v _ _ v ~
The compositions prepared according to the
present invention can be used in producing reinforced
laminates according to Xnown procedures~ In general,
laminates are made from a fibrous mat or by assembling a
multiplicity of sheets of material to form a matrix which
is consoli~ated into a unitary structure by ~lowing molten
precuxsor or composition through the fibrou material and
curing it while in a mold or hydraulic press to form t~e
polymQr. Fibers which are used in forming the matrix
i~clud~ natural and synthetic fibers s~ch as cal~ulose
darived from woo~, cotton, linen, hemp, an~ the li~e,
glass, nylon, cellulose acetate and tha lika~
The compositions of the first ~eneral embodiment
and their preparation are further illustrated by the
following specific examples.
~xam~le 1
80/20. ~-lactide/race~ic D.L-lactide
160 grams of L-lactide and 40 grams of racemic
D,L-lactide, both of high purity (Purac, Inc., triply
recrystalli~ed~, were charged into a 500 ml, round-bottom
flask and purged with dry nitrogen overnight. 10 ml of
stannous octoate is dissolved in 60 ml of anhydrous
toluene, and 10 ml of the solvent is distilled to a Dean-
s~~ e~ -o ^-'-ec~ c-yness or this cata'vs~ solu-ion ~v
azeotropic distillation. From the 10 ml of stannous
octoate in _~ ml o- _r~ ~oluene a 0~2 ml ~or~ion ic
removad with 2 syringe ~n~ injec~ec i:_o the ic_-iies in
a si~in~e needle conne_ __n ~hat enters ~ eao_io. l~s];
~~ _`-_s~h ~ ~ se-=~ .=s -~__ 2 `~`P-^- ~ _`_~`'~1_
~ _ ~ _ .
_ _ _ ~ . _ _ ~ ~ ~ _ i ,~ ~_ _ _ _ _~ _ _ ~ _ _ r~ ;_ _ ~ _ ~; ~ _ ~ _ _ _ ~
_ _ _ ~ ~ _ _ _ _ _ _ ~_ .. . _ _ _ _ _ _ _ _~ _ _ _ . . _ ~ _ ~ . = ~ _ _~ _ . ~ ~ _ _ ~ . _ _ _ = _ _. .
_ . ~ _ _ _ ~ _ _ .. ... ~ _ _ . ~ _ ~
~ _, a . ~ _ 2 _ _--. ~ ' _ ^ = ` _ 2 5 `-~ _ 1 _ c:. . . _ _ ~ -- .. i ~ G "
_ _ _ _ ~ _ _ _ _ _ ~ ~ _ _ ~ ~ ~ ~ ~ _ _ _ _ _ ~ . _; _ _ . ~ . _ . . _ _ _ _ _ . . ~ . . ~
~0 '~/n~13 rcr/~ssl/ofi3~-
-~4-
the colorless, transparent products are removed from the
heating bath, cooled, the flask broken, and shocked with
liquid nitrogen to remove glass from the product. The
copolymer was molded in a heated hydraulic press.
Compression molding to 5- to 10-mil t~ick films was
possible at 20,000 lb pressure, at 170 C, in a time period
of 2 minutes. The films were evaluated for their tensile
properties on a Instron tester, and ~he results are listed
in Table 1. Samples 1/8-inc~ thic~ were also molded for
impact strencth testing. A ther~ogravimetric analysis of
t~e product was performed, noting the weig~t loss upon
heating the sample to 150 C in ~ minutes and holding the
temperature at 150 C for 60 minutes. The weight loss of
the sample was 19.5 percent and nearly complete in 60
minutes. T~e weight loss is attributed to loss of lactide
~onomer. Results of differential scanning calorimetry
reveal that the composition has an endothèrm beginning
about 110 C, becoming more pronounced as t~e temperature
increases to 200 C. No melting point was observed.
2~ Specimens were annealed at 185 F overnight and reexamined.
They remained transparent, colorless and pliabls. Samples
of the copolymer could be remolded 6 times without any
discoloration or obvious loss of strength. Thin ~ilms
were clear, transparent, colorless, and quite flexible,
_5 de~pite t~e ~e-e2ted ...ol~_ng.
~09_/0~13 PCT/~S~l/063
: -4~-
~ _.
TABLE 1. PROP~RTIES OF COPOLYMERS(a~ OF L-LACTIDE AN~
D,L-LACTIDE WHtEN PLASTICI~ED BY LACTIDE
Example 1 2 3
.. ..
Film thickness, mil 8 8 10
Tensile strength, 1000 psi, ASTM 3.9 1.~ 7.9
D638
~longation, perce~t 280 S06 3.S
100 percQnt ~odulus, 1~00 psi 0~
200 percent ~odulus, 1000 psi 1.~0 -~ --
Tangent modulus, 1000 psi36.6 -- 289
I20d impact strength, ft-lb/0~3 -- C.4
Mw~ 1000's 540 281 341
Mb, lOOO's 270 11897.5
Residual lactide~C), percent19.5 27.~ 2.7
(a) 80/20, weight ratio, of L-/racemic D,L-lactide
tb~ l/8-inch, notched samples
By isothermal thermogravimetric analysis weight loss
at 150 C
Exa~ple 2
In a 3-liter, round-bottom flas~ was charged 1.84
Kg of L-lactide, 0.46 Kg of racemic D,L-lactide and 2.3 ml
of the stannous octoate solution, similar to Example 1.
T~e mi~ture was purged with a-yon ~r 3 hours, t;nen healec
isothe-ma~ in a '25 C o~l b th. ~he -i~t~re melts, was
ed th.~~ou~h~ ~ s-.~i~liny, ^-n_ rc-~s a ho~ogen~ous,
'~ar.s?a_ent, co~c~less ='~ic ~hos~ viscosi_y in--eases
su~stan~ialiy a~`tDr seve_~l ho~rs. A~te_ ~ ~.ours ,he
fi~sl; was remo~ad f-o~ the heating ~at!l, cooled, and the
3C gl2ss r2~c~ed -_m ~he _'ear, t-ans?c-en_, solid produc_.
~ c ~
~ d -o ~ - s._ll__ si~e in ~ g-inde- ~i.h d_v
_ ~. _ ~ . . _ _ _ _ . . _ ~ _ . _ . ~ _ .~ _ _ _ _ _ _ _ _ _ . . ~ c _ . . _ _
'` C~ r ~C~ ce`~e~c~ ~S~ C~U~ -ie~ o~er~icr,t -_
~~__.~_ ___~_~__~_~ ~_.__e___ .~ _2____ __.~
'0 9~/0~13 PCl~S91/Ofi3~-
40--
~ 3
prepared as described in Example 1 and the films were
examined for their tensile properties and weight loss by
thermogravimetric analysis as shown in Table 1.
ExamDle 3
In a 250-ml, round bottom flas~ was plac~d 79.98
g of L-lactide, 20.04 ~ of racemic D,L-lactide~ and 0.20
ml of stannous octoate solu'io~, simil2x to Example 1.
Tho flas~ was swept ~y nit~o~an through inlets and outlets
and heated in a 125 C oil bath. The mixture melted to a
colorless and ~luid liquid ~hat ~was thoroughly mixed by
swirling th~ flask. After 2 hours, the oil ~ath
temperature was increased to 1~7 C, and after 14 ~.ours
total heating time, the te~perature was decreased to 131
C. Total heating time was 18 hours. The product is
transparent, colorless, and glassy. It was evaluated,
similar to the preceding examples and the results are
recorded in Table 1.
Examples 1 to 3 reveal the effect of reaction
temperature on the properties of the copolymers as
occasioned by the resulting csmposition.
Exam~le 4
Films of the copolymers o Examples 1 and 3 were
immersed in wa_er ~- ce~e_al m~nths~ r.~_r 3 weeks, the
copolymer of Example 1 became hazy while that of Example 3
2~ ~emained clear c- a~__~;im~_aly ~ m_n_hs~ a_te~ 3 cr.th~
the ~ilm of Example 3 became no~icaably ha2y a~ the fil~
in cor.t~c~ ~i_h the "- f _~ar.?le 1 tastas acidic ~hiie
that c' ~ m?le 3 is -_S~2l 25~
~ _ 2 _ _. ~ _ S _~ . ~_ . .; _ _ _ ~ ... ~. . _ . _ _.
i-. ;'~e __~ ;~ ,r ~ 5~ ?-~?~ s
_~.e -~?~ 2- 2~r- _~ `` C~`` .~ C~: `lC.~^-f`ll ~
~097/0~13 ~CT/~S9~/063'-
-47-
? ,. ,i ! ~ ~
tangent modulus compare favorably with polyethylene
compositions used, for example, in plastic trash bags,
general film wrap, plastic shopping bags, sandwich wrap,
six pack yo~es and the like. The shape Q f the stress-
strain curves are approximately the same ~or both thecopolymer and that for a linear low density polyethylene
composition co~monly used in trash bag compositions. A
comparison o~ properties are s~own in Ta~e 2~
TABLE ~. COMP~RISON OF POLYET~YLENE TO POLYLACTIC ACID
Property NA 272 LLDPE~ Lac~ide
Tensile strength, 2.18 2.9 ~.9
1000 psi, ASTM
Standard C
Elongation, S 261 500 280
15 Tangent modulus, 5~.9 51.0 36.6
1000 psi
100~ modulus, 1000 1.77 -- 0.74
psi
200% modulus 1.82 -- 1.20
20 HDT~d), 264 psi, F 95 99 122
~ v . ~, ._ _. _ __ . . _ _ .
(a) Linear low-density polyethylene, 5-10 mil, 2-in./min.,
our experiments.
~b~ Lir.e~- lo~-àensity -ol~ce=~ en2, da~- ~~c~ c~p~t_~
file.
(C~ Copolyme~ cf L-lactide/racemic D,L-12ctide, ~x2mple 1
d ) ~.e2~ deL~ec-~ 3n te~?-`-~`~-e-
r~ e_2 ~ c~e~ -_o-~ '~ c~ e~s~ o . ~ c~~~
~ashio.... This is illus~ rx2~m?1es 1 2nd . T.
t i _ ~ 3 . . _ .~ ._ _ _ S ~. _
C~ ~ C _ ` ~i r c C~ '~ 2 _; ~ 2 ~ ^ r~ i f _ ~ _ r~
WO~2/(~13 i~r,~i~31io~
-~8-
~ 3
The compounding can be accomplished by blending
the molten polymer with lactide monomer in conventional
processing equipment such as a mill roll or a twin screw
compounder. The normally stiff, glassy, lactide polymers
are flexibilized by the lactide and remain transparent,
colorless, and very nearly odorless. The lactide i5 not
very fugitive, requiring heating, and a nitrogen sweep,
typically, 170-200 C for 20-60 minutes to remove the
lactide in a gravimetric analysis. Neither is the lactide
visible in films under an optical microsco~e~ The lactide
d~mains are sub~ic~on in size. T~is lexibili~ing of the
poly tlactic acid) suggests its use as a environmentally
biodegradable replacement for polyolefin, disposable,
pac~aging films.
ExamDles 5-16
A series of experiments were performed in which
copolymers of L- and racemic D,L-lactide were prepared,
melt blended with variable amounts of lactide, and the
physical properties of the blends evaluated as a function
of the lactide composition. Monomer lactide content was
assayed by a pre~iously developed isothermal,
thermogravimetric analysis. The lac.ide contents were
measured before and after compounding and molding into
films.
It ~-as observed t~a, open ~all, ? -oll, milling
tended to volatilize the lactide at temperatures required
~or .~.e ver~ hig~, ~olecula- weig~.t lactide copolymers.
~ese 10SSQS COU~ d be ~inimi2ed by masterbatc~ing o- by
using lo~e~ mo_acui_r ~e_g~ ida __~ai}~--s ~_..`e ~
3~ lo~er a~ta~._2.t mixin~ tem~e~~_ures~. ~ bette- ~i~:ir.~ ano
~le.~in~ me~.o_ ~_s 2 -onve~.ri n-~ in s_re~ e~t~ude~,
in T~bie ~.
_ _ _ C i ;~, _ _ 5 ~ ~ _ ~ i c ;~ _ ~ C ~ i ~ c _ ~ ~,
~` ' ` _~&I~ ~S. ` ~ _ C ` ~ ~'e '_S ~ 3 _ _ eJ_~~:
0~13 PCT/~S~I/Ofi3'-
-49-
- v ~ 3
a flexible film, whereby the oligomers or their
derivatives are added first, allowing the lactide to be
mixed in the melt later at lower temperature. By adding
oligomers first the melt viscosity decreases very
significantly, allowing the temperature to be lowered, and
the lactide can then be mixad in at a lower temperature
without significant volatilization. This is demonstrated
in Example 16~.
~m~
A 90/10, LID,~-lactide copolymer prepared by
methods previously described, and analyzed by gel
permeation c~.romatography to have a weight-average
molecular weight of 480,000, a number average molecular
weight o~ 208,000, was banded, that is, melted and ~ixed
on an open 2-ro~l mill preheated to 350 F. The copolymer
will not melt and band well on the mill below 350 F. To
25 grams of this melted copolymer was added 10 grams of
oligomeric lactic acid of a degrse of polymerization of
2.34. After all of the oligomeric lactic acid mixed in,
the temperature was dropped to 300 F, where the mixing was
still quite good. With the roll temperature at 300 F, 10
grams of L-lactide was added slowly and mixed. The mix
was stripped from the roll and pressed into a thin film in
a press at 30~ he ~ ~il thic~ film was colorless,
transparent and very flexible. ~ithout the lactide the
resulting fi'~ ~oul~ have been s iff~ Withou~ firs~
ad~ing the olisomeric l~ctic acid the lac ide could no
voia.ili~atior,~
c~~ c-.~ '~ e -' ca~` ci~e-
sir~ s_ ;~-~
s _ . ~ _
~__-.sparen~. ~r._e ~e~y f~in_ (?le2s~nc~ o_i~ o lGc=ice
_s ~e~c=ab` _n~ is_2_..7C-lG t~s7~e " - ` cC=i~2 ~'CS
`~ 12s ~ r~?~s t;~re
_ _ _ _ _ _ S _ _ _ _ ~ _ _ _ _ _ _ ~ -- -- ~----~-- -- ! --~-- _ _ . . ) _ ~ _ 1 C ~ e_
~`O97,(~i3 ~'CTi~S91/~
-50-
without shattering or tearing. They stiffen somewhat when
placed in a cooler (5 C, 40 F), but remain flexible and
creasible without breaking. These films noticeably soften
in the hand, indicating a glass transition temperature
S below 37 C. When the lactide content is less than 20
percent, the ~ilms will have a rattle typical of a
polyolefin film. At greater lactide contents the films
have the drape and '`warm'` feel o~ a plasticized poly(vinyl
chloride) (P~C). In fact, the co~positions of the
invention are ~lso a replacement fo~ plas~icized P~C in
~any applications.
As shown in Table 3, the elastic moduli (initial
tangent moduli) can be relatively high, similar to a
linear low density polyethylene (LLDPE~. This is an
indication of potential form stability. Lower moduli and
tensile strengths are similar to low density polyethylene
(LDPE). Physical properties, as a function of lactide
content, were plotted as shown in Figures 1 and 2.
Referring to Table 3, at approximately 17-20 percent
lactide content, the tensile proparties are similar to
polyethylenes used in trash bags and shopping bags.
At lower lactide contents, the blends have a
similarity to polypropylene. Some data can be compared in
Table 3. Table 4 defines the conventional plastics used
in the comparisons.
WO ~t/O~tl3 -51- PCr/l~S91/0632~
c~ ~ I
~J tO N It~ N r7 tt)
X ~ ~ I -~
C r~ N ~r N N N ¦ tt~
;~. C'~ I 1~
U '~o el m ~ I X
n I ~
C I E
O Il) ~ oO N ~ ~ N N 1 6 (a
O ~ N ~ rl ~ O ¦ O
IY c o . ~ a~
8 o ~ o ~ N ~I o~ 0 O N ¦ Ei ~
r~ ul 1 à
U~ c~ n r r~1~ 1 a~
I_~ ~ ~ N ~1 ~1~ r~ O
~ ~ l ~C
~ ~, .7 . ~ ~ ¦ 3 E~
~ 3 ~ ,~ ,i N N ¦ 1.0 C
I (~
! ~ I C~ O
.~ ~ ~ 5~ 1 ~
r~ .
~_
1 . ~ ,
I' I 11^
_ . _
~ " ~
C~ `D ~ ~
v~ m ~
~ ~ C o ~ C~ o U~ ~
m ~ O ~
Q C:
U ~ ~
1~ ~ ~ o
0_ '~0 ~ ~0
.U ~U~8 ~ ~ ) ~:
Z ~ . ~ .- ~ C
~ C O
~n ~ ~ I 1. 1 .c-~ O~x
I i; ~
~ h
C ~ ~ A
~ A ._` h
_ _ _ _, _
~0 `~ 'C~i~:S91/0~
~ ~ ,~ ~ O o ~i
~ 0 h D- ~ ~ lt) O
~ O O r~
I `~ ~ ~ ~ O O ~ O
I U~ r~ o o I 1~ o
c~ a~
IG~
I 6 U h ~ O u'~ O
I O ~ ~ ~n u~ In
:: I u E u~u~ o o o
Z ¦ P: ~D ~ N ~ Ul O
I ~ ~
E
I ~ ~ ~ o r
I ~n u ~ ~ I
I c ~ c~
~:: I a 3~ o o o O o
E~ I
l 6
! ~ c~ ~o
l ~ _ I
I ~3 C ~ ~ L~
. ~ ~ ~ ~ ~ ~ X U
I ~, ~` ~~`' ~ ^ o ~
` O ~ ~ ~ ~ I
; E i
o o ~ 3 C
. _ =
~ 4--
~ 3
Table 3 reveals some data for lactide and
polylactide mixtures. The results do not differ
remarkably from similar compositions of Examples 1 and 2,
prepared by other means. However, those s~illed in the
art will recognize that the precise physical properties
will vary somewhat depending on the intimacy of the
mixture, the tensile testing conditions, and the
fabrication tec~nique for preparing the films.
Comparisons from Table 3 reveal that the lactide-poly~er
mi~tures have a ~road rang~ of controllable compositions
t~at mimic many conventional, nondegradabl~ plastic ~ypes.
Example 17
An oli~omeric poly~lactic acid) (OPL~) t"~as
pre~pared for mixing with polylactides as follows. An 88
percent solution of L-lactic acid (956 g~ was charged to a
3-nec~ flas~ ~1 liter) fitted with a mech nical s~irrer
and a pot thermometer. The reaction mixture was
concentrated under a nitrogen purge at 150-190 ~ at 200 mm
~g for 1 hour until the theoretical water of dilution was
removed. No catalyst was used except for lac~ic acid and
its oligomers. This temperature and vacuum were
maintained and distillation continued for 2 hours until 73
percent of the theoretical water of dehydration was
removed.
'~ T~ -es~ e~ ho-~-s. ~ 5
time the reaction was stopped. The water samples and the
?~ oli~
ecid, 26.2 g, W25 found in ~he waler dis~ . The p~t
en ~_cj: _i-__1_5 ;;i_h s~_nd2_d '.. ~S~ e d2_~ c-a
a_~r~ ~l-a ~ e ~ _`_ ?-'~ C -~
,-he~e ~ s ~ Q5 ~ h~ c~ r~:a~
-~5-
TABLE 5. CH~URACTERIZATION OF OPLA OE EXAMPLE 1
.. .. . .. .... . .. ... . . . .
Total
Percent Titratable Titratable Expre~sed Degrea of
Dehydrated, Acid, Ester, as Lactic Polymeri-
Theoretical percent percent Acid zation
_ percent
S8 34.4 ~2~4 116~ 3.4
~m~
T~e procedure of ~ample 17 was repeated except
the distillation was conducted more slowly. After 8 ~ours
o~ heating during whi_~ t~e temperature was slowly
advanced from 63 to 175 C at 200 mm Hg, a sample of the
pot was titrated to reveal 62.2 percent o~ theoretical
water removal. Titration revealed a deg-ee of
polymerization of 4.3. The molecular weight of the
oligomeric polytlactic acid) was further advanced over 2
hours by heating at 179 C and using a vacuum pump. The
oligomeric poly(lactic acid~ was no longer soluble in 0.lN
NaO~, was water whi,e, and would cold f low . This material
is a second example of an oligomeric poly(lactic ~cid)
preparation with somewhat higher degree o` polymerization
as compared to Example 1. It was mixed with polylactide
i.. E~am?les 22 ~nd 2-~ T_ is es_imated '~ ` the dec~ee of
polymerization was about 6-10.
_xam~le ' 5
ol~ '2~ ~.e~ e-~ si-.~ o.
_ ~ ~ _ _ _ _. _ _ _ _ ~_ _ ~ ~ ~ . _. .~ _ _ ~. ~, _ _ _ _ _ ~ _ _ ~ _ _ _ _ _ _ ~ ~ _ ~ _ _ _ _ .. _ _
~!--?;i~ ~cc F-c~c~ .e __?o~ s ~r _= ~ ` e~
? ~
average molecular weight (Mw) of 182,000 and a number-
average molecular weight (Mn) of 83,000. Residual lactide
monomer by thermogravimetric analysis was 1.7 weight
percent. This blend was mixed with the oligomeric
s poly(lactic acid) of Example 17 to provide material for
Example 20. The tensile properties are listed in Table 6.
~.i~Q
The polymer o~ Example 19 was melt blended with
the oli~omeric polytlactic acid) o~ Example 17 on an open,
2-roll, mill fo~ 20 minUtQS at 325 F. The mix was
compression molded into films and tested as shown i~ Table
6~ The gel permeation chromatography molecular weights
were smooth, monomodal distributions (~wi~n = 2. 6) with Y~
= 192,000 and Mn = 73.000.
~'i'C! '/0~ 1 3 _ ~ 'S9 1 /Ofi3'-
a _ _
H C~ C)
U ~ ~ ~ U
o I 1~
~, 1.' x` I E~
I ~ h ~ r~ ~ ~ O O
O I t~ ~ l ~
t~ I ~
,, I I ` " 3 3
2 I ,Y ~ o ~ r O ~ 3 e
:~ I ~ ~ ~ ~ r~ ~ ~1 ~ ~ O
I ~ al` u~ o ~ r~ ~
~ r~ C~C_ _
I ~ ~ OC ~ c u u
¦ ~ _I o-- ~ :` o ~ O O ~ ~ E E
t~N~ E(~
~' I ~\~ `
O I ~ ~ ~ O O O
I U ` ~ O O O o
O I ~
~/1 I ._ E ~ ~1 ~
Z I ~P C~ Co ~
~1 ~ 3 ~ O~ o~O~O~ Uq
~: 3 ~ O G) O
~: ¦ ~ E )~
O I C c) ~ ~ ô ~ I t~ gG~ ! X
`' li ' ~ ~
1! - ~ I ~ E o O O O O
G jl ~ 1 i ,~ ^ _ '~
L~'7
~ (tl -- '~i O _
~ ~ ~J t! r~ r~ C~
~ v ~ _
_ _ _ _ _ _,
.` ?~ T cn t ~n,~
--58--
` 7~
Exam~le 21-25
The copoly~er of ~xample 19 was melt blended with
20 percent of the L-PLA described in Example 19. The
blend is listed as Example 21 in Table 6, where its
analyses and tensile properties are listed. Example 21
was, in turn, melt blended with various a~ounts of the
oligomeric poly(lactic acid) of Exampla 18 and these were
tested as befcre and listed in Table 6, Examples 22 to 2~.
mable 7 lists the gel permeation chromatography molecular
wei~hts of ~hese composition~. The tensile strengths and
~oduli are compared to the weight percentages of
oligomeric poly(lactic acid~ in Fi~ures 3 and ~ ~Lower
Curves).
~'O C'"O~I~ PCT/~S91/063~-
~t~ m~ ~
U~ ~ ~o
~C ~ ~o~ s
~ ~ S~ ~ 3 t.,
~t~ s~ U~
Z~ ~ ~ ~ o 0
j o r' _ _ _
C . c, ~1 0 0 0 0 ~ ~ ~ o
:~ ~ 3 o o _ _ ~ ~ E~ ~ ~ u
--o v O ~ R
_¦ O E ¦ O o o o o ¦ E ~ ~ ~ ,u
I o I- li E C ~ ~ c~ _
U , ~ I S~ 1~ 0 ~ ~
- t~! ~ 3
ri ixi--~ E E ~i
- r~ ` o ~ x ~ ~
C ~ ~ ~: _
--60--
Exam~les 26-30
A second series o~ copolymers was ~lended with
the oligomeric poly(lactic acid). ~ 9~.5/7.5, L-/racemic
D, ~-lactide copolymer was prepared by methods similar to
Examples 19 and 21. This is E~ample 2~ of Tables 8 and 9.
It was melt blended with the oligomeric poly(lactic acid)
of Example 18 on an open, 2-roll mill at 325 F for
approximately 20 minutes. The blends were compression
molded into 3-5 mil thicX films and their tensile
properties and gel permeation c~romatography molecular
weights measured. The properties are recorded in Tables 8
and 9, and plotted in Figures 3 and 4. The second SeriQs
of blends revealed significantly higher values for the
tensile properties although the molecular weights were
lower. This may be due to lower residual lactide monomer
and/or the change in high poly~er composition. All of the
oligomeric poly(lactic acid) polylactide blends could be
easily molded into tac~ free, transparen~ ~ilms~
~ 0 '`' '0~1 ~ ' 1 PCT/~ ~;i9 1 /Ofi3'-
c ~ l S ~
H
~`
0~ ~ ~ .
X ~ ~ ~e
o
C
O C
U~ ~ ~ ~
O ~,~ O Q, ~ E =
oooo.~ ~-~CE
3 _ o ,~, ,, o ~, ~ E
~ ~ '~ ~
O E ~
Q
?r~ 'nf,~
6_
TABLE 9. MOLECULAR WEIGHTS OF 9.25/7.5,
L-/RACEMIC D,L-LACTIDE COPOLYMERS
.. . . _ _ ..
No. OPLA M~
26 0 63124 2281.95
27 2Q 60108 1891.81
2~ 30 4880 1251~66
5~96 1511.65
5692 1~6~
~ Gel permeation chromatography ~GPC)
molocular weights as re~errQd to
monodisp~rse polystyrene standards
Examples 31 and 32
Film specimens with, and without ~l~sticizer were
exposed to seawater at Daytona, Florida from Narch through
May. The pH of the water varied from ?~3 to 7.6 and the
salinity from 33.2 to 38.~ ppt. The water gradually
warmed in the test from 15 to 27 C. The specimens were
cut into strips and tensile tested before, and after,
periodic intervals in the seawater. The results are shown
in Table 10. All of the samples showed whitening and
physical degradation, which became progressive with time.
Without plasticizer the samples showed whitening and
degradation after six weeks in t~e seawater. The
oligomeric poly(lactic acid) polylactide blend degraded
~2st~, -evealing clear eviden-e c_ degradation 2 ~ter ^
~;e_ks. T~e in^~po_~ti~n o~ ~ ?e-ce-._ lactide ?rovo]~ed
immediate whi~ening ~n- o~vious de -ada_i~n ~~~er one ;;ee~;
of e~:Dosl~re.
~'O ~'/0~:1~ PCT~ 91/()fi3'-
--63--
' .l L ~ ~
X r- ,~ O o o o o~ o o o o u7 o o o
,~ ~ N N N ~ ~q ~ N tq _~
C ~
~ ~ I I I I I I 1 1~1 1 1 1 1 1 1
~ ~ llllllll llllll
,C ~ ~ ~q ~ ~ ,~ o m ~ ~ OD
a ~ C I~ q ~ \D ~q ~ o o
O ~ ~ O ~::
P.~ O .r: I I I I I I I I N I I I I I ~ ~1) C
~ U~` ,G~U ~0 C
1-1 U~ N ~1 I` c tq ~ ~1 ~ ln tq ~ ~1 ~ ~q N ~ 1
c~ c~ ~ ~ ~3~ o -~ (q ~ CD G" o o ~ N N
o c ,, ~ ~q ~q ~ ,q ~ N N 1 ~ N ~ ~q ~ ,,
cn ~ l
~ ,~ ~ u~ u~ r t~ u~ q o N ,~
~ t~ ~ O ~ ~I N U~ t~ ~ ~ ~ O O a~ ~ C C C C
~: c ~ _, ~q ~q ~q N ,q N N N ~ ~ ~q N ~q N I ~ ~
O E~ ~ ~ ~ , .CX.C~
~ ~ a) ~ ~ _ _ _ _ _ _ _ _ _ _ _ ~
.~ t~ ~ tD ~ ~ q tD ~, ~ tD rD
;~3 o ~q ~ o ~q ~ a~ N O ~q ~O ~ N _~ I ____
U~ ~ ~ ~ .'~
o c 1 ~ v~ ~v ~
o 3 3 3 3
~ v ~ C ~ ~ ~1 0 :~
._ ~ c;i u~
~ ~ 3 ~i li C U~ r~l Ul tr!
i- U~ I V O :~ O :S ~ r~
! ~C ~ D
I! r_ I` ~'~` 11 r~
~ v a ,_ _ c ~
;`~ j ~ -- _ L'~ ~ I! C la U) U~ U!
i' '` ~ ' 1. ""`,
-- C ~ C ~I r.
n' ~!~ ' ' t - n(~ ;;n t ~n~
--6~ ~
Exam~le 33
Examples 33 to 51 teach the use of incorporating
lactide in conjunction with quenching to obtain pliability
and transparency. Alternatively, the polymers can be
annealed to improve stability ayainst heat distortion.
Poly L-(lactide) was prepared by methods
previously described. Thus 300 g of triply recrystallizad
and thoroughly dried L-lactide was loaded into a clean,
flame-d_ied, argon-cooled, 500 ~1 round-~ottom flas~. The
~las~ was fitted with a ru~ber septum and inle' and outlet
syringe needles that admitted a continuous argon purge.
Stannous octoate solution was prepared by dissolving 20 g
in 110 ml of toluene, previously dried over molecular
sieves, then distilling 10 ml toluene in order to
azeotropically dry the solution. The ~inal concentration
was 0.2 g/ml stannous octoate in toluene. A 0.3 ml
quantity was injected through the septum onto the L-
lactide. The flask and its contents were placed in a 150
C oil bath, and when melted, swirled vigorously to o~tain
a homogeneous mix. The argon purge continued and a
thermocouple was ~itted through the septum into the uelt.
The melt was 143 C. The temperature of the oil bath was
advanced to 200 C and heating and lig~t purge continued
for 20 hours. The temperature O r the melt advances to
170-174 C in the first two hours Or heating. The final
tempe_atu-e ~'25 170 C. ~ter ~0 hou-s o~ he2._in~ the
flask was cooled in air to room temperature and the solid
O- ~s t---s?~
Pol~er ~;~s recover~c by sho_;~ing _he ~las~ ~lth
~;cs _~__~ ,_2vi~ s~
r~le_-~l2_ ~ s ~ g~ ~r~e-~~ 2~ _ 2
~ ` ~ S
,~ -oin` ando~he_ms ~i_h pe^}~s c_ ^?-ro~:im_~el~ ~ c~ ?
~ el ?e~ 2~~ --c~ c.~- :
~o 9'.'~ Pc r/~ssl /n
--65--
h ~ 3 '
Residual monomer by thermogravimetric analysis was 2.3
percent, (Example 33, Table 11.) The experiment ~hows
that L-lactide can be polymeri2ed above, or near, its
melting point and the products remain transparent and more
S amorphous.
~L
By methods similar to Example 33, 104.0 g of L-
lactide was polymerized using 0~10 ml o~ stannous octoate
catalyst solution. However, the reac_ion temperatures
were 155-1~5 C for 72 hours~ The polymer ~No. 3~ of Table
11) slowly crystallizes upon ~orming and is a white opaque
solid at reaction or room temperature. Since the sample
was smaller than the preceding experiment the polymer
cooled more quickly, but it did still not quench to a
transparent solid. In co~parison to Example 33, the lower
reaction temperature per~its the poly(L-lac~ide) to
crystallize and become opaque, thus an intimate dispersion
of plasticizer does not form.
The temperature is slowly advanced in many of
these experiments to accommodate the poly~erization
exotherm. The reaction temperature must reach at least
170-175 degrees before there is substantial monomer-to-
polymer conversion, otherwise the poly(L-lactide)
cr~stallizes and is difficu't to remelt.
In Examples 36-~2 the polymerization of L-lactide
was ~eceated v~_y n- the conc~tions to obtain ?olv(L-
lac~i_es) wi~h ~ -r-.._ resi~ual l_c~ide _a.._e-.ls and
c-~stallini~ .e es~s a~e sho~n ~n ~ble 1' where
i` is seen -h ~ ?l~a~ ,nc touchness ~ere obt~ined
~a only ;;hen ~he -~odu__ ~.as ~een c~len^h.2d .--ar. _he melt, is
t~c.~pcrcn_ _ -~c~ _e~er~ e~
~ ved ~ e ~.c~~?^'i~-- ~~
?c!~..e-i~ed i-. _~e ~e:t, 2-.d _~ .c~e~ .he ~.anc~e~-
e~-e~ -le- ' c~
-e?.~-o~ 2~ c t ~ e~
-66-
.~iJ.~_ ~ _
properties. ~hen t~e poly(L-lactide) crystallizes during
polymerization because the polymeri-ation temperature is
well below the polymer's melting point, the residual
monomer is no longer effective as a plasticizer. I~ the
S polymer crystallizes upon cooling to room temperature, it
also loses its plasticization. Annealing at elevated
temperatures will restore crystallinity to amorphous
samples.
~O 9'/0~13 f'CT/~ S91/Oh32,
TABLE 11. POLYMERIZATION OF L-LACTIDE
... . . .... - ! ~ r
Eo Amount Temp ~ours Appearance Monomer Si~e
33 0.02 156-201(~ 20 clear 2~30 300
150-174P~ transparont,
hard, glassy
34 0.02 155-165~7~ cryutallinQ, -- 104
opaque, hard,
brlttlQ
0~005 120-200~') 2~crystallina, -- 100
111-200~ opaqu~, hard,
brittle
36 0.02 135-145(') 22crystallinQ(~, 1.1 500
1~5-152~b) opaque, hard,
brittlQ
37 0.02 117-lS52~ ~rystalline,1.74 100
120-175~b~) opaquQ, hard,
brlttle
38 0.02 15~-170(~ 3e~ystalline,2.1~ 2,000
opaque, hard,
br~ttle
39 0.02 145(~)15 cry~talline,3.6 25
137-144~) opaque, hard,
brittlu
0.0553 190l~ 0.3 clear, 10.1 25
160-215 pliable,
tough,
transparent
41 0.05S3 198-193~ 0.29olaa:, 22.9 25
147-200P) transparent,
pliable except
~t edge of
polymeri-ate
42 0.02 l4s~l)2~75 crystalline~,52.5 25
150-133P) opaque, hard,
brlt le
Oil bath ~e~perzture
?ol~ a~~_-2
~d~ ^e~, a-~ r~,o~
ran~?-~:ent a~ -ea_tior. te~?e:2:u:e; --ystall:^es e?on ~ooli~
~ ? ~ r _ ?.'' ~. :~ C~ "-- ' C 2 1 ~ -` c: _ I e~ C ~ e~ `` ~ r c t i O
_o?ol~ e_ P2si~ cucn_.~es ~~ c~ ns~c^.~nt soli-. Tne
--68--
easily. The 100 percent L-lactide polymer quenches with
difficulty fro~ thick sections of the polymer to a
transparent material. Some comparisons are shown by
Examples 43-47 of Table 12. Thinner cross sections, i.e.,
films of the L-lactide polymer can be plasticized and
quenched to pliable and transparent materials. The 80~20
copolymer quenches very easily to a transparent solid.
The latter has only a trace of crystallinity as seen by
di~ferential scanning calorimetry.
TAB~E 1~ T~NSPARENC~' OF ~ACTIDE P~LYMERS
~ . . ~A . _
No Ratlo TemD;, _ _vercent
43 95/5 145-160 67 SO385,000 2.64
44 100 135-152 22 O32~,000 1.1
45 90/10 150-157 4S TS21,000 ~.95
46 90/10 150-170 48 T27&,000 1.37
47 80/20 135-175(C~ 23 T -- - -
(~ Melt temperature (polymerization temperature)
(b~ opaqueness/transparency ~O/T) after air-cooling Or
polymerizates; opaque (O); slightly opaque (So);
transparent (T)
(C~ Slow-cooled for 1 hour
All D,L-lactide is racemic.
All of the lactide poly~ers thermororm easily,
_-Dd ~y 2 ~a~ e~te~ ~._il sc~_, t:~en
5~ r. ~ _t~ e~ he
~z~te-~ c~ th~e mcld e_sil~m :-lo;ia~e~ a poly(L-12c_i~e)
~ec~es ,~-ti~ 2n~ . c~e 9-~5,
!' 0, _~.d ~C~ ?-_~.e~ ~le_~ _~,-`
~ ~ _ _ . ~ _ _ _ _ ~ . ~ _ _ . . _ _ _ . . ~ _ _ ~ _ . ~ . _ _ . ~ . ~ _ .
r~la C
~ ?--~ c~ r~?l~ ~3 ~'GS
~^ . -- i, ~ _ ~ . ~_ ~ ~ -` ~ _,, ,--_ -- ' -- ` _ _ _ ,_~ ~ _ ~, = _ ~ _ = _ _ _ _
W09'/0~13 PCT/~S9l/06327
-69-
~ 3
(190 C), then compression molded at 375 C for 2 minutes,
then air-quenched to room temperature in approximately 30
seconds. Both 7-and 20-mil thick films were prepared.
Both were clear and transparent without trace of haze or
opacity. Residual monomer in the film was 0.79 percent.
The films are very stiff.
Exa~m~ 1 e 4 9
The experiment was repeated except th~t the
milling was con~inued for 10 ~inutes instead o~ S ~inutes.
The films were analyzed by thermogravi~etric analysis
again and found to have 0.38 percent lactide. The films
were clear, transparent, and stiff.
Exa~le 50
The ~ill-rolled polymer ~2s also compression
15 molded into a 1/4 x 1/2 x 1 inch plaque. This plaque
required 5-10 minutes to cool in the press by turning on
the cooling water to the press. The plaque was white,
opaque, and crystalline except for the extreme edges,
which were transparent.
The above Examples 48-50 teach the quenching of
films of poly L-lactide to maintain transparency. When
cooled more slowly, they crystallize and lose their
transparency.
As D,L-lactide is introduced as a comonomer,
quenchinq can be reDlaced by ordinary cooling to retain
transparency~ Spher~ c-ystallinity c~n be intr~duced
into these films bv anne21ing and the 100 percent L-
lactide pol~er is the faslest to crystallize. ~here
t.ansparency is not required the higher L-lactide polymers
can be annealed to greatly improve thei~ resistance to
~hermal disto~~ion. Convers21y, whe_e ~_anspa~ency is
re~uired, such as in a polystyrene offset, great care must
be taken ~o avoid _his ~y~e ~f opa~ue crvs'allinity.
~0~7/~ ?l/n(.,7-
-70-
Exam~le S1
The poly(L-lactide) film samples were annealed on
a hot plate at 240 F (115 C). The film turned hazy in
approximately 1 minute and completely cloudy in
approximately 2 minutes. By way of comparison, a 90/10,
L/D,L-lactide copolymer film required 10 minutes to turn
hazy, 15 minutes to become completely cloudy. When
suspended by one end hori~ontally in an oven and advancinq
the temperature slowly, the annealed poly~L-lactide)
sample remained straig~t until a te~perature of 295 F tl46
C) was obtained~ The film then bent over. The annealed
90/10 copolymer bent over at a temperature of 185 F (8~
C). The results show that the amount of crystallinity of
polylactides can increase thei~ form-stabili~y at elevated
temperatures to a temperature that is well above their Tg.
Examp~es 52-5S
The following examples illustrate the beneficial
effects of addinq lactide during compounding. The
examples show that without lactide as modifier, the
lactide polymer degrades during compounding. With the
addition of lactide both discoloration and molecular
weight decrease are prevented or substantially reduced
during compounding.
Thus, in Example 52, a 90/10, L-/D,L-lactide
2S copolymer prepcred as describe~ ~y previous methods using
0.02 pph SnC12 2H20 catalyst was ground and extruded into
pellets Crom a ~in sc 2W co~pounde-, adding 5 weigh_
percent lactide. The melt zone temperatu~e o~ the
e~-uce- rose ~ .S0 s, t~e p~l~e- disc310~e , _n~ _he
.0 weig~t average moiecul2r weigh` (~, by gel permeat_on
c~romatogr2phy) decre2sed b~ ~pproxim~_e!y ~0 ?e-cen~.
T~.e ~esu'.s ir.__~_~e7 -.-__ insu~ ien_ _a_~i_- ~cs -dde~
_or this ~ery his~ pol~ci_. The -es_l_s ~-e sho~n a
q7~ble 13. ~7~e ?ellets f-om ~his com?ounding ~ere
o~.?o_.7.~ c~ 7~ eic:~_ ?~
WO92/0~13 PCT~`S91/0632-
-71-
the results were much better: further discoloration did
not occur, molecular weight decreased sliyhtly, or within
experimental error, and a pliable composition was
obtained.
5 TABLE 13. EFFECT OF LACTIDE AS MODIFIER
DURING COMPOUNDlNG
Ex. Before Compoundin~ Lactide~b~
No. Color ~ ta) weight percent
52 Light yellow 513 2.15 ~.78
1053 Light ~ellow 278 1.80 1.37
Ex. ~fter Compounding Lactide~)
No. Color Mw~ JM (~) weight percent
52 Dark yellow 322 2.05 5.56(C)
53 Yellow 184 1.90 2.26
1554 Dark yellow 307 2.00 14.4(
colorless(Q~ 324 1.99 14.6
ta) GPC x 10
(b) By thermogravimetric analysis, at 200 C
(~) Five weight percent lactide added during compounding.
(d) Further 10 weight percent lactide added during
compound.
(e) Thin film
To ascertain that the ~econd compounding and
extrusion were facilitated due to the lactide modifier and
not the decreased molecular weight, anothe- compounding
(Example 53~ was per~ormed starting with 2 similar-Mw
copolymer of _0/10, L-/D,L-lactide. In this case, no
lactide was added bac~ in during the compounding. The
melt zone temperature was 382 F, the copolymer was
i~ discolored, ~n_ the M~ decreased ~v approxim2tely 6~
percent. In addition, approxim2tely 5 percent more torque
was required o compound the mix of MW 278, 000 2S co~p2red
~o the one of ~ Or 322,000 ~ith added 'ac'iàe.
~o 97/0~l3 PCr/~S91/063',
7 2--
After compounding twice with lactide, Example 54
was analy~ed by thermogravimetric analysis and found to
have a lactide content of 14.4 percent~ The material of
Example 54 was converted to a blown film by means of a
Haake-Brabender extruder in Example 55. Thin films of
this composition are colorless, highly tr~nsparant, and
very pliable and extensible as described balow in Examples
60 - 64. The Mw by gQl parmeation chromatography was
324,000 ~cf. Mw ~ 307,000 before compounding and
extrusion). The Tg of this plasticized material is 42 C
and diffQrQntial scanning cslorimQtry reveals a very small
amount of ~rystallinity melting at approximately 138 C.
~he amount of lactide present is 14.6 percent as estimated
by thermogravimetric analysis.
15 Exam~les 56 and 57
The compounded polylactides, Example 52 and 53,
were mixed together in the twin-screw compounder with
extra lactide to raise the lactide level to approximately
20 percent. The compounding temperature was 347 F 1175
C), much reduced from the previous 375 to 385 F. The
compounding proceeded smoothly without further
discoloration.
The above results clearly show the beneficial
effects of added lactide as modifier. The required torque
to compound the compositions, the discoloration, and the
working temperature are decreased when adding lactide.
Further evidence of plasticization is seen in the lowered
Tg and the pliability of the compositions. In addition,
molecular weisht decreases are avoided and stable
compositions are obtained. It will be obvious to those
skilled in the art that the amount of lactide empioyed
depends on m2ny factors, in^ludin~ .he desi_ed amount of
plastici2ation sousht, the type of compounder tha~ is
used, and the ~olecular weish~ of the polylactides.
W092/~13 PCT/US91/0632
~ 73-
.~`3~
ExamPles 58 and 59
Examples 58 and 59 illustrate blown film
extrusion of polylactides. These pliable films mimic
polyolefins. The plasticized compounds of Examples 56 and
57 were adjusted to approximately 20 percent lactide in
the twin-ccrew extruder. They were converted to blown
films using a HaaXe-Brabender Qxtruder. This consists of
a 3/4-inch extruder with a blown-film die and take-up
device. The blown-film was achie~ed using a 12.7 mm
outside diameter orifice and a pin to establish an
extrusion gap of 0.48~ mm. An extrudate temperature of
187 C was maintained. A stable bubble was blown at this
temperature with the inflation air at ~ oz/in.2 gauge
pressure. Cooling air was blown against the exterior of
lS the bubble at 18 pci. Since the final average film
thickness was 0.158 mm ~6.2 mil), the blow-up ratio was
3:1. When the extruder gap was reduced from 0.483 to
0.254 mm, or the temperature raised, the polymer quenched
readily to a crystalline, cloudy extrudate that would not
expand. The larger orifice die produced an extrudate that
was thicker and more viscous, cooled more slowly, and
expanded in a consistent manner. The extruded film
exhibited some elastic memory when stretched. The film
also was resistant to tear and puncture and was very
difficult to break by stretching. The blown film had an
average elastic modulus of 117,000 psi, an averaqe tensile
strength of ,73S psi, and an average elongation to break
of 370 percent. This modulus is slightly higher than that
of linear low density polyethylene, but the strength and
elongation to break are comparable. The Elmerdorf Tear
Strength (AST~ 1922) was 424 g in the cross machine
direction ar.d 18~ g in the machine direction. The Tg of
the material ~2s ~6 C, ~r~ by gel permeation chromatography
was 229,000, ~he residual lactide by thermogravimetric
analysis ~-as 19.7 percent, znd the differential scanning
calorimetry c~rves showed a we2k endotherm cen~ered at
2pproximately :,_ C.
C~l/nf)
-74-
Exam~les 60-64
These examples illustrate plasticiza'ion with
oligomeric esters of poly(lactic acid). Copolymers of
90/10, L-/D,L-lactide were melt blended with added
lactide, esters of oligomeric/lactic acid, and mixtures
thereof~ They were characterized by tensile and thermal
properties.
In Example 60, a control copolymer of 90/10,
L-/D,L-lactide was assayed by thermogravimetric analysis
to be 6.74 percent lactide. This was mixe~ with 30
percent by weight oliqomeric polymethyllactate ~Mella) in
Example 61, which was prepared by heating 2,500 g of ~S)-
mathyllactate in an autoclave at 210 C for 3 hours, then
collecting the Mella which fractionally distilled at 81 to
85 C/1.25 torr. The mixture was melt blended on an open
2-roll mill at approximately 350 F. The blend was
compression molded in a press at approximately 350 F into
clear, pliable films. The tensile properties, before and
after, adding the Mella are recorded in Table 1~. The
glass transition temperature (Tg) was reduced by the Mella
plasticizer.
For Example 62, the 90/10, L-/D,L-lactide
copolymer was melt blended with added L-lactide in a twin
screw extruder to adjust the L-lactide content to 20
percent by weight. The blend was further mixed with
oligomeric polvethyllac ate (Ella) (Example 63) znd Mella
(Example 64). The properties of the~e blends are also
-~cc_-e~
~O 9_J0~ j'31 /()OJ_ .
J
TABLE 14. CHU~RACT ~ ISTICS OF POLY ~ CTIDESIa~ PII~STICIZED
WITH OLIGOMERIC ESTERS OF L~C~I~ ACID
. . . _ ... .. .... _
Elastlc ~raak Strain
Ex Plastici~er ~oduluD Strength Break, T~ m(
. . . _ . _ _ _
5 60 6.74~(~ L-l~ctlde 370,000 6,903 ~ 51 141
61 6.7~ -lactlde15~,0002,012 100 301~1
~nd 10~ ~clla(')
62 20~ E-lactida101,0002,~3~ 2~S -- --
63 20~ L-la~tidQ and~,31~ ~,S~l ~39 -- --
3~ Ella~n
6~ 20~ ~-lacCidQ and3,620 ~9S 83 -- --
30~ M~lla~')
(^~ 90/10, L-/racemic D,~-lactlde ~opolymer
~las~ ~ransltion temp4raturQ
(') ~Qlting point
t~ Analyzed by thermoqravLmQtri~ ~nalysi~
I') Methyllactate oligomer
(~ Ethyllactaee oligomer
Examples 65-81
Comparative Examples 65 to 81 were selected from
the patent literature that presented conditions most
likely to result in materials of the present invention.
The materials produced in these patents were not
completely characterized, thus experiments were needed to
allow a more complete characterization of the examples and
provide meaningful comparisons th~t WouiQ damonslrate that
the materials of the present invention a-e indeed novel.
With regard to the present invention, co~Dositions were
sought that had residual lactide or lactic acid contents
~~ a~o~ iS-- ?e_c~ _n -^~
~2y have ~he lac~ic- c- lz__ic aciQ inti~2telv dis~ersed
;i_hi~. the ~ ~e-~ ~h2 -2sUl ts ~all i~-o o~vious
~ei5h~s, ~:~,, less _hz-. I3,~03 d_ n-~ have _~.e p~ ici
?-~?e.~i~s _~ e~ e ?-es~ zc_
s '~~ .es2 1~ .?.~s~ c~
~e .,n~`~_ _- =^ 5-~
~v ~'"~ rT~'7!~(~f~-
-76-
v.~
It is known from the teachings herein that lactic
acid, lactide, or oligomers of lactide or lactic acid, or
derivatives of lactic acid must be, present to provide
plasticization and some pliability~ The lactide must be
present in amounts greater than about 10 weight percent
while the oligomers of lactic acid, oligomers of lactide
and the derivatives of lactic acid must generally be
present above about 40 percent to provide obvious
plasticization and pliability to polylactides. ~owever,
any amount of plas'ici~er as tausht herein when added to
the composition will change properties and can be used to
obtain specialty ormulated compositions. Thus, if
~ ide is intimately dispersed and effectively mixed as
plasticizer, the mix of lactide and polylac`ide is
completely transparent. The heterogeneous domain size of
the lactide is small enough, generally less than one
micron, so that it will no longer scatter light, i.e., it
is intimately dispersed. Conversely, white opaque samples
are always hard ~ecause they have crystallized under the
test conditions. Crystallization squee2es the lactide out
of the polymer mass, resulting in hard stiff compositions
that are a gross mixture of monomer and polymer. This is
also obvious from differential scanning calorimetry (DCS).
Monomeric lactide that has segregated reveals itself with
a separate melting point at 95 to 100 C, whereas well-
plas'ici~ed 52. ?les C'7 not show 2 ~is~inct mon3mer meltin~
point.
One ve-; _____~a.._ r7_n_ ~5 ~h-_ _he ci.ed
patents frequently specify L-lactide homopolyme- ("100
i~c~i~e easily c~ys~ es -ecause 3_ i-s hish ~el_ln
?~in A_ `~ c~--ic.. ~c-~?e--~ s~ '~e ~ ?~l~e-
_ _ . ~ ~ _ _ _ ., _ _ . . _ _ ~ _ _ _ _ _ _, ~ _ _ _, _ _ _ , _ ., _, _ , _ .
c~?~ .io~ _~ `7~5 ~ ..e
~5 -eRc~ion ~e~?e~ctu~e- ~~e L-ls__i^e ?oi~e-i~es so
_ _ _ _ . _ ~ = . . _ _ _ _ _ . ~ _ _ _ _ _ _ _ _ _ , _ .
~0~ ~13 ~ 9ll)6
-~7
-t~ ?~ ~,
polymerization with substantial monomer left in the
product.
Inspecting the results listed in Table 15A and
15B reveals that the comparative examples obtain either
products with low residual lactide or else the
polymerizations did not work or worked so poorly that
greater than 40 percent lactide was left at the end of the
specified polymerizations. Thus, Examples 65, 66 (vQry
similar also to the work of Schneider), 67, 69, 73, 74,
and 75 obtain low residual lactide. The Examples ~0, 71,
72, 7~, 77, and 78 examples did not work well as written
in the patent examples. The best known laboratory
techniques were added to the procedures, described in the
footnotes, on these examples, from a historical standpoint
(monomer purity, for example) in an effort to make the
procedures work, with indifferent success. In no exanples
were pliable products found. Either glassy, or hard,
crystalline, opaque products were obtained. It should be
noted that only those examples using tin compounds as
catalysts appear to be acceptable for many oackaging
applications.
It appeared particularly that the Tunc met~ods
would provide the materials of the present invention. To
ascertain this, it was necessary to do the listed
experiments on the teachings o Tunc in laborious detail
as shown in ExAmples 7g oo 81. Figure 5 is a differential
scanning calorimetry of one of the polylactides of the
p-esent invention~ ~here is no detecsable ~elting point
fo- residual 12ctide mono~er in the vicinity of 95 to 100
nly `~e ?~'y~ ce~ c` ;~s
2~se~ .e-~ .e~-~ 2-.' ~ ' 5 ~
S~O'~ 12, ~ _e-~
~ ; ~ . _ _ . . = _ . ~ _ . . _ _ _ _ _ _ . i ~. _: .:
~r~c=~~c _~ s~`s -c~c`~ e~._ _~ c~i
_c~_~e ~-- o~e c~ __e~â ~ _.. ? ~ c~~
_ _ _ _ _ _ ~ . ~ _ _ _ _ _ _ _ . . . ~ _ . . _ _ _ _ _ _ _. _ _ _ _ .. _ . . _ _ ._ _ _ _ _ _ _ _ _
--78--
i. ~, V.
shown in Figure 6, where a very distinct monomer melting
point is seen. This corresponds to segregated lactide
with a melting point within its own heterogeneous domain.
Whereas this polymer is white, opaque, very hard and
S stiff, the composition of the present invention
preparation is clear, transparent, and very pliable.
A similar result was obtained repeating the
teachings of Tunc in Example 81. This analyzed as 32.2
percent lactide and revealed a monomer melting point
(Figure 7)~ The material was very white, crystalline, and
hard. The results are reviewed in Table 15A and 15B.
0 ~7/()~13 i~tT~i'3l/o6
-79-
TABLE 15A. RELATED ART POLYMERIZATION5 OF LACTIDE
CONDITIONS
p Lactide Catalyst Polymeri~ati
Eox. Patent Eaxt. ~onomer -~ ~ ~-
( 8 ~ Type pph TQCP' Hours
2,7S8,987 1 L- PbO 0.30 150 42
66 2,758,987 3 50/50 PbO 3.00 150 89
L-~D,L
67 3,982,543 3 L- PbO 0.30 150 31
68 DD 14548 2 L- SnO(~) 0 009 193 3
69 4,137,921 4 90/10 Sn~Oct~2, 0.055; 180 0.33
L-/0, L GA/ 190 0.33
dioxanQ~) 210 0.33
Ga 755,447 4 D,L 2nO~') 0.02 150 24
71 GB 755,447 2 D,L powdQirt~ 0.02 140 25.5
72 GB 755,447 6 D,L 2n 0.02 140 2
Carbon- 150 3
i~te Hy-
droxide(C)
73 CA 932,382 1 D,L Tetraphe- 0.02 165 20
nyl Tin
74 CA 923,245 1,7 ~ L- Et,Zn 0.167 105- 2
8 110
DE 946,664 2 D,L(" ZnC12 0.25 140 48
76 DE 1 L- Sn 0.00S7 205- 0.5
1,112,293 - Stuarate as Sn 210
77 2,951,828 1 L-;0 SnCl~ 0.30 160 5
sua~en-
8 ion~)
78 3,268,487 2 D,' T_ifi(2- 0.88 80 24
a~vl)a-
~ina~
108,~_5 ?o!y-
~19S~
~,5i3,~
~,53ci,9 :
e;.~
e~ ~,539,981, ?^1~- _- B~.~3_o)~ 3~33`2~ e j~ c
~,55Q,C~ ~t-2-
-~ct~ l -e~_?e ~ cn~ro~ c~ir~ 5~,c ?P~ c c
- ~o -
Included was glycolic acld as chain transfer agent.
(~) In8Oluble
In~oluble after 24 hours plu~ additional 1.5 hou-~ with 700 ~1 88
p~rcent lactic acid and 100 /~1 H20.
~') In toluene; product colorlens and ~ery viscous.
( In minaral spirit~, Stoddard ~ol~ent No. R-66.
Agglomerated
~ In dioxane containing 0.517 pph ~OH; no polymeri:a~ion.
~V092/1)~13 r~ `S91/~)63'-
61-
~ 3
TABLE 15B. RELATED ART POLYMERIZATIONS OF
LACTID~ RESULTS
RQsidualGPC x loJ
Eo MonomQr,M~ ~ M~/N~ App~arance
0 254~54 7171.79 Ll~ht yellow,
cryntalline, opaqu~
66 0 97187 3221.94 L~ght yellow~
transparQnt
67 0.85 95195 3~52.06 Partially opaquc
cry~tallinQ, partlal
tran~parent
68 l7~s~a) 5 7 91.47 Whlta, crystalllnQ,
7.1S 7~77 8 101.25 opaquQ
69 4.6 116218 3561.88 Li~ht yollow,
transpar~nt
0 70 47.7 -- -- -- -- White, crystalline
(mOnOr~Qr~, opaquo
71 65.3 -- -- -- -- White, crystalline
(monomer)~ opaque
72 79.6 -- -- -- -- Whlte, crystalline
(monomQr~ opaque
73 1.4 116214 3401.84 YQ11OW~ transparent
74 1.9 80150 2351.87 OrangQ, crystalline,
opaque
5.4(~ 164377 6572.3 Hard, colorlQss
2.5; 1.9~1307527808 1.72
76 43.3 30 35 411.17 Hard, crystalline,
opaque
77 8.6; 9.6219343S041.57 Hard, crystalline,
opaque
78 100 -- -- -- -- All crystalline
monomer
79 5,0 :~ 2-`~5 :.SS ',;hite, c_vstallir.e,
oDaque
film~ 14 26 351.82 Some tran~pArency rt
edae~
?0 80 ~0.^~;' Greaec- ch~c. 1,w03,COO h'hiee, c-y~_all_.le,
o .~
~ ate~ r~ e, c_~ e,
o_a ~e
Sc.. ~r_c .. c._c_ ~ ir~
~cmovc c_Lvcn~.
~`~ s~ e ~e;:~ c~ . C ~ --u~ r~ -2 re~^~2;~ c~l~ r~._.
r~ n5?- r~r. ~ rr` ~
'~' unc o~ir.~ `-.1 ?~cen_, ~ c~ _u~ 5~
t~C ~
~:J ~ 1 ~ 3
The above examples establish that an all-lactic
acid composition can be a pliable thermo?lastic useful for
flexible, plastic packaging films and containers. By way
of comparison, nonplasticized homopoly (L-lactide) is a
highly crystalline polymer with a tensile strength of
about 7000 psi with an elongation cf l percent and an
initial modulus of 500,000 psi. It is very brittle,
opaque, and crazes easily. It is not a well behaved
thermoplastic, nor is it transparent. Poly tracemic D,L-
lactide) is an amorphous, glassy, poly~er with a glasstransition temperature of approximately 50 C, a tensile
strength of about 6300 psi, an elongation of approximately
12 percent, and an initial modulus of l~,000 psi. It is
also very brittle although transparent. In stark
contrast, a copolyner of L-lactide/race~ic D,L-lactide
that is plasticized with lactide monomer is remarkably
different. For exa~ple, tha plasticized pol~ers can have
a tensile strength of approximately 3900 psi, an
elongation of 431 percent, and an initial modulus of
2056,000 psi. The plasticized polymer is clear and
colorless, and the blend must be heated to above lO0 c to
remove th~ ?lasticizer.
Allhough theory would predict a more amorphous
structure as a result of plasticization, what is
25~rprising is the pliable, transparent, stable com-
positions th2_ car ~-ise! c~n~, sec~ lv, _he nea-ly e~act
Eit of properties needed for certain packaging
applications, such 25 po;ye~hylene. ~his irve.-~i^n C0225
at a time when there is 2 need for such ini~ial properties
sinc2 i_ CO~_ ld ~11 evic~e -lzs~ic -~ . p__~le~-.
~_ wi;l ~e -??~re-._ -o ~ se ski``~d _: =he er_
~ _ . _ _ _ ~ _ _ ~ . _ _ ~ _ . _ ~ _ _ _; _ _; _ _ ~ . .
?~~ _s c_~_ c~ - r----------_--~ ~~~~~~
-_ `c-~ t:-ie ~ i ?~ ?e~~ies ~ G
2r;'i_ o.. r~ __~c-.__ ~;~
~,J0~l3 p~ 91/()6J
-83-
The amount of plasticizer in the polymer depends
on the compositional characteristics desired. If lac~ide
is used as plasticizer the ranye is preferably 10 to 40
weight percent whereas if only oligomers of lactide or
lactic acid are used the range may be from 10 to 60 weight
percent. Surprisingly, oligomer may be added at up to ~0
weiqht percent without substantially affecting the tensile
strength or modulus. See Fi~ures 3 and 4. Addition of 30
to 60 weight percent oligomers produces significant
plastici~ation and attenuation o~ physical propertieC.
This adds grQat economy to the composition since
oligomeric lactic acid is chcaper than the high molecular
weight polylactide. Oligomer may be prepared from lactic
acid or any lactide. It is important to note that the
oligomer of lactic acid normally contains significant
amounts of lactic acid unless removed. This is an
important consideration in tailoriny compositions having
specific properties. Those skilled in the art and knowing
the teachings of this invention will be able to select
reaction conditions to obtain appropriate chain len~ths
for the polymer, and the proportions of polymer and
plasticizer so as to obtain fabricated compositions having
physical properties similar to commonly used packaging
thermoplastics and yet degrade comparatively rapidly. For
~5 example, higher amounts of plasticizer result in polymers
having increased flexi~ility and increasingly tough
physical p~operties, however, an increasing degradation
-a.e will also be obt2ined. F~-th2~, shorte- chai~
lengths ~o- the pol~er will -equire less plastici~e- to
3~ obtain the same p_c?e~~ies as ~ e_ ieng'hs.
?~e-e~-`y ~ n~e~s is -_
~ e _ e 5 5 _ _ ~ , ~" ~ ~ ~. ~ ~ ~ - O C 2 C 5 ' .~ - _ _ _ ~, r
---- -- -- ~ c~
_ ~2~e_c_~_~e ~ ~el2i~~ e ~`~
e -, ~2-~e_~ _~3~e 1~? ~. _-
_iC-~j C~ ~ 1 ~ C~ `~ 2-~ 2d~ er
--84--
polymerization the retention of monomer during processing
is of course not as critical.
The unoriented compositions of the invention
should have a tensile strength of 300 to 20,000 psi, an
5 elongation to failure of 50 to 1,000 percent and a tangent
modulus of 20,000 to 250,000 psi. Preferably for a
polyolsfin replacement the compositions have a tensile
strength of at least 3000 psi, an elongation to failure of
at least 250 percent, and a tangent modulus of at least
50,000 psi.
A composition for the replacement of polyathylene
is adjusted so that the unoriented composition ~as a
tsnsilQ strength of about t ,200 to about 4,000 psi, an
alongation to failure of about 100 to a~out 800 percent,
and a tangent modulus of about 20,000 to about 75,000 psi,
while a composition for the replacement polypropylene, is
adjusted so that the unoriented composition has a tensile
strength of about 4,500 to about 10,000 psi, an elongation
to failure of about 100 to about 600 percent, a tanqent
modulus of about 165,000 to about 225,000, and a melting
point of about 150 to about 190 F.
The homopolymers and copolymers of the present
invention are insoluble in water but upon constant contact
with water are slowly degradable. However, degradation is
fast when compared to polyolefin compositions that are
-eplaced ~y -he inver._io... ~hus, Ih-ow3nay c~e_~s m_~e
from the polymers are environmentallv attractive in that
~hey slowly de~rade ~o na-niess s~s~nces. ~ ojec~s
made from polymers of the invention are incinera~ed, they
. ~
The c_~r-si~ie~.s he-ein _-e ~se__' _~-
_e?i_cene-._ __ ?o'yci~_irl -snp_si_i~..s ane p2--`~ c`^~ y
^~ t~,e ~o;-e li s~, the ~ethod is `_CE~ -C- =e?lace~e.~ -~
~ __ s~ ` ce~c~-, c`i~
~0 Y'/U~13 ~ i91/~)63',
--85--
V ` ~
from mixtures of the monomers in the listed group and
physical mixtures of the polymers and copolymers of the
above group are likewise replaceable. Those skilled in
the art will recognize that minor amounts of lactide and
lactic acid can be replaced by contemplated equivalents
such as glycolide, glycolic acid, and caprolactone.
B. Second General EmbQdiment
The environmentally degradable compositions
disclosed herein are co~pletely degradable to
environmentally acceptable and compatible materials. The
intermediate products of the degradation: lactic acid is
a widely distributed naturally occurring substance that is
easily metabolized by a wide variety of org~nisms. Its
natural end degradation products are carbon dioxide and
water. Contemplated equivalents of these compositions
such as those that contain minor amounts of other
materials, fillers, or extenders can also be completely
environmentally degradable by proper choice of materials.
The compositions herein provide environmentally acceptable
materials because their physical deterioration and
degradation is much more rapid and complete than the
conventional nondegradable plastics that they replace.
Further, since all or a ma~or portion of the composition
will be poly(lactic acid), and/or a lactic acid derived
~5 lactide or oligomer, no residue or only a small portion of
more slowly degrading residue will remain. This residue
will have 2 higher sur~ace are2 than ~he bulk product and
n e~pected faster de~radction rate. Since both !actic
~ n~ c_~ _c~ e s~ o?_
~3 general ter~ ?olytl~ cic~ ~s ~sed herein -efers -
~?31~e-s h_vi-. =he -e~e-~in unit -f f5~1~ 2 T withou~
: . . _ _ _.: _ ~. _ _ ., _ , : : ~ ^ ~ _ ~ -- -- -- . _ _ _ _ _
e~ -l;~~~ r - ~ ~ - ~ - ~ .; - ~ ,, . _
_ _ _ _ _ ~ _ r _ _ _ _ _ _ _ _ _ ~ _ _ _ _ _ _ _ .~ _ _ _ ~ ~ . . _ . _ _ ~ ~ _ ~.
_ _ . ~ . ~ . _ _ _ _ _ ~ . _ _ _ _ _ _ _ _ _ _ ~ ~ _ . ~ ~ _ _ _ _ _ _ _ _ . . _ _ _ _ _ _ _
; l~s_ic~ c~_^.~.
-86-
~ ~:J i ~ 3 ~
The preferred composition of the present
invention comprises polymerized lactic acid units with
for~ula I: wherein n is an integer with a value between
about 450 and about 10,000 and the alpha carbon is a
random mixture of D and L (or R and S) with a
preponderance of one of the pure enantiomers when
plasticized by lactic acid, lactide monomers, oligomers of
lactide, oligomers of lactic acid, derivatives of
oligomeric lactide and various mixtures thereof. A
plasticizer may be produced by stopping the r_action
beforQ polymeri2ation is completed. Optionally additional
plastici2er consisting of lactide monomers (D-lactide, L-
lactide, D,L-lactide, or mixtures thereof), lac~ic acid,
oligomers lactide or oligomers of lactic acid or its
derivatives including all L-, D-, and DL- configurations,
and mixtures thereof can be added to the formed polymer.
The more intimately the plasticizer is inteqrated within
the polymer the better are its characteristics. In fact
very intimate dispersion and integration is needed to
obtain the advantages of the invention as further
discussed below. If desired, additional monomer or
oligomer plasticizer can be added to any residual monomer
or oligomer remaining in the composition after
polymerization. The oligomers of lactic acid and
oligomers of lactide defined by formula II: where m is an
integer: 2 < - _ .5 (i-_luding ,all L-, ~-, 3L-
configurations and mixtures thereof, both random and block
confiaurations, user~l fo- a pias,ici-e-). '~he
derivatives of oligo~eric lactic acid (including all L-,
2nd ~lo~i; c-n~isu-~ ions, useful _o_ 2 ?lcs~`ci_e~) _~e
~2~ e `o~ lI: wh~e ~ = ;-. ,_~!;~`l -~1,
~ ~ "~ ,~
_ _ _ _ _ _ _ ,
~ e~e ~~ --n~ ?~ r.~
W09'/0~l3 PCr/~'~91/063
-87- ;_~ v ~
and where q i5 an integer: 2 < q ~ 75, however, the
preferable rangè is: 2 < m < 10. The plasticizers added
to the polymer compositions have the following functions:
ta) They act as plastici2ers introducing
s pliability and flexibility into the polymer
compositions not found in polymer-only
composition~
~b) Addition of these plastici2ers to the
polytlactic acid) reduces the melt
viscosity of the polymers and lowers the
temperature, pressure, and shear rate
required to melt form the compositions.
(c) The plasticizers prevent heat build up and
consequent discoloration and molecular
weight decrease during extrusion forming of
poly(lactic acid).
(d) The plasticizers add impact resistance to
the compositions not found in the polymer
alone.
In addition, the plasticizers may act as compatibilizers
for melt-blends of polylactides and other degradable and
nondegradable polymers. That is, molten mixtures of two
different polymers can more intimately associate and mix
into well dispersed blends in the presence of the
plasticizers. The plasticizers ma~v also improve
perform~nce in solution blending.
The su~sc~ipts n, m, p, and ~ above refer to the
averase nu~ber o ~e_s ~he -epeating un,_) of _he pol~er
~_ cl~ e ~`e~ ,ei-h_ ~ ~s use~
e~o~ is ~elc~ Q ~e~_ ~t ~ r., ,~ ~, c.
~y _~e ~^le~ v`~ 2~
Ci~ _5 .~_~__ _S . ~ '' n_ ~_ ~ ~__c
?- ~ 2~ c- i~ rer~
~ t~ __ s~ ?^ ~ ?.. ce~ t -
r~ 9l /n~
--8~--
Marcel Dekker, Inc., 1988 and Introduction to PolYmer
Chemistry, R. Seymour, McGraw-Hill, New YorX, 1971.
When n is low, the poly(lactic acid), is easily
processable, but is considerably weaker than when n is
larger. When n is quite large, e~g., ~000 or greater, the
poly(lactic acid) is quite strong but difficult to
injection mold. Preferably n is approxim~tely 500 to 3000
for the best balance of melt-processability and end-use
physical properties. The amount and type of monomer is
selected to obtain L-/D ratios from lactic ~cid or their
cyclic dimer, lactide, as further discussed below. Both
lactic acid and lactide achieve the repeating poly(lactic
acid) unit, shown above, but lactide is pre~erred since it
more easily obtains the higher molecular weights necessary
for good physical properties. Since lactide has two aipha
carbons which are assymetric, there are three types of
lactide, viz., D,D- (or D-); L, L- (cr L-); and meso D,L-
lactide.
D-lactide is a dilactide, or cyclic dimer, of D-
lactic acid. Similarly, L-lactide is a cyclic dimer of L-
lactic acid. Meso D,L-lactide is a cyclic dimer of D- and
L-lactic acid. Racemic D,L-lactide comprises a 50/50
mixture of D-, and L-lactide. When used alone herein, the
term '`D,L-lactide" is intended to include meso D,L-lactide
2S or racemic D,L lactide. The term intimately dispersed as
used he~ein means t`ee mat-rial is homogeneously and
intimately mixed with the polymer.
e -ol~y'~ -_ic 2cid) an~ poiv(~-lacti^ 2c~d!
~ave poor processi~ c~a-2c~Pris~ics, easiiy c-~ze and
~c~ _ ~.^_ -s ~~- c_ ~~ le ~ .e 1~ e
c~ 2e_s ~ n^~ _- 3 -~ ~ c~ -.~c~_.
~ , _ _ r ~ ~
~ _ ~ c ~ ~ ~ _ ~ _ e _ ~ _ _ i ~ r ~ 0 1 ! ~ _ ~ J ~
_ ~ ., _ _; . ~ _ _: ~_ ;~ ~, _ . .~; _ _ _ ~ . _ -- ~-- _ ~ _ _ _ _ ~ . ._ ~ _ ; _
_ .. ~ _ .. _ _ _ .. .. _ ~ _ ~ . ~ _ ~ _ _ .. _ _ .. _ . _ _ .. _ _ _ _ _ .. _ _ _ .
~13 rCT/~`S91/Ofi3'-
-~3-
difficult to thermoform without crazing and easily becomes
opaque at room temperature. Also, at ratios above ss/5
the material becomes bimorphic and difficult to extrude
because of different crystalline forms that affect the
processing conditions. Further, above ratios of 95/5 the
material must be processed too close to its decomposition
point to obtain reasonable viscosities without color
formation. At lower ratios than 85/lS, the lactide
copolymers exhibit lower moduli than the predominantly L
or D copol~mers. Further, at ratios below 8S~15 it is
dif~icult to obtain a required crystallinity in a
reasonable time period. In between these limits the
copolymers are quenched from the melt in typical
manufacturing/processing equipment of plastics technology
to achieve films and moldings which are clear, colorless,
and extremely rigid. Their properties as formed, above,
are closely matched to those properties of a crystal
polystyrene. However, a wider range of
L-/D-enantiomeric ratio may be useful for special
applications.
Another advantage of this invention is that the
all-lactic acid copolymer can utilize inexpensive
feedstocks. Corn syrup via starch and corn can be
fermented to either L- or racemic D,L-lactic acid,
~5 depending on the microo-qanism. Racemic D,L-lactic acid
is cheaply ob~ainable via ethylene whi_h can be oxidized
to acetaldehYde r which is reacted with hydro~en c~vanide to
m lac~onit~-ile, whi_h is hvd.-olized t3 racemi_ 3,~-
'ac=ic ac,_. _actide i~ s_m-`~ ab~ained by dictil~ cn
-~ of la-ti_ ecid~ ~`o ca~n~e --^ _he ste~eocna~strv cf the
~s~c~e~ _à_-. c^^~__s ~ _c_~
~ -`e ~ ^ci~ c~s~~lla~ _en~__i^-. r~ v-s~
i~ _is_~ c- :~-ei.~ e-~ 2
~ e .~ 3_ ;~as__ i~e-` ~ e~ u~ c-~.
~1~'0 O~ ~t t p(-r/11~S91/Ofi3
--~0--
product; the only difference being that it rotates light
in a different direction.
The copolymers of the present invention are
preferably formed by heating the mixture of monomers to
form a homogeneous melt and adding a catalyst to cause the
lactides to undergo a ring-opening polymerization. The
polymerization is preferably carried out in an inert,
anhydrous, atmosphere, such as nitrogen or ar~on, or in a
vacuum. Suitable catalysts include divalent metal oxides
and organo-metallic compounds such as stannous octo~te,
zinc acetate, cadmium acetata, aluminum acetate or
butanoat~, tin chloride, tin benzoate, and antimony oxide.
Stannous octoate is the preferr~d catalyst because of its
high solubility in the monomers, ease of preparation in
~5 anhydrous form, and low toxicity. The amount o~ catalyst
required can vary from approximately 0.02 to 2 percent by
weight, based on ~lonomers and is preferably about 0.2
percent. The molecular weight and melt viscosities of the
copolymers are controllable by the amount of catalyst
and/or chain-transfer agents such as glycolic acid. The
reaction temperature of the polymerization is between
approximately 100 to 200 C. The least color formation
occurs below 140 C and the rate of polymerization is best
above 135 C. Since racemic D,L-lactide melts at 127 C it
is best for conversion of monomer to polymer to polymerize
at a temperat~~e above 127 C.
Where a su~stantially clear and transparent
co~osition is re~uired, as ~ith crystal polvstyrene
~îf se _s, _~e co?o`~e_s of ~.is in~er._ion _re ~ol~eri-e~
-Q C~ ._el~ ints,
~re cene_-21ly in t~e ~5 ~ ~50 c r_n~e. The mol-_~
~c~i~e c^?~ c -~s'~ ~T~ e- ~` ~.
~--c~s c~ c ~ c~ ?~ ~~ S~_e` `~ ~
_ . . _ _ _ _ ~ _ _ ~ . .: _~ _ _ _ _ ~ . _ ., _ _ .: _ ~ _ _ _ _: ~ _ _ ~ _: _ _ . ~ . .
~ ~ I o . o_ ~ __ , cc~
~ _ _ ~ ~ _ ~ _ . _ _ ~ _ . . _ _ _ _ . . _ _ ~ . _ . . . _
~ /U~13 PCT/~S91~1~63_
31 ~ :
cooling the fabricated item. Thereafter, the copolymers
remain transparent unless heated for several hours above
their glass transition temperature, Tg, and below the
melting point, Tm. Slow cooling of thermoformed sheets,
slabs, films, and molded items can induce spherulite
crystallinity in the copolymers which qains improvemant in
the heat stability of the fabricated item, but causes some
loss of transparency. Nucleating agents such as sodium
benzoate, calcium lactate, and the like, can also induce
rapid and qubstantial crystallinity. ~ modest amount of
drawing of the copolymer, between its Tq and Tm, induces
oriQntation of the polymer molecules and can substantially
improve physical properties without loss of transparency.
Blending of different types of lactide polymer or
copolymer can substantially change the physical
properties. As an e~ample, the mel_-blending of the high-
melting L-lactide polymer with a lower melting lactide
copolymer can provide a transparent material which has a
sufficient amount and type of crystallinity to remain
substantially transparent. ~hose skilled in the art will
recognize that transparency in molded films, great
stiffness, elevated heat distortion temperature, thermo-
processability, and environmental biodegradability are a
rare combination of properties. Thus, the polymers can be
~5 ~lended, as well 25 nucleated, oriented, and controlled bv
molecular weight to provide a great deal of latitude in
the processabili~v and final p-oDerties in the final
_ompounce~` ~hc-_crl~s_i_.
ydr^_~-e ~2cl; :0 12c-ic 2c` o ` n _he presence o~ mois.u~e.
~-n the presence cf ____en_ ci_ ~.d humidi~ _..e h~_olvci~
`_ol~ `s ~_^c-=~ r~ s ___e
`e3--.-`i.- _n _h- ^ -~^si i^- -olecul_- ~ eirhts . ' ~ -
n4~1~ PC-r/~'~i91/l)fi377
--32--
the particular, aqueous environment the copolymers are
placed in. Microorganisms can further reduce the lactic
acid to carbon dio~ide and water. ~s an approximate
measure, the copolymers have a shelf life of several
months, but disappear within about a year when thoroughly
WQt.
The followiny examples are merely illustrative of
the present invention. In Example~ lB to 7B, a
co~position series was prepared and evaluated. It was
discovered, in contrast to the prior art, that there are
distinct di~f~rences in the processing be~avior and
physical properties of the L-lactide/D,L-lactide
copolymers.
XamDle lB
In a dry, ~00 ml, round-bottom flask was charged
160 g of ~-la tide (Purac, Inc., "t iple-star" grade) and
40 g of racemic D,L-lactide (Purac, Inc., "triple star"
grade). This mixture was heated for approximately 1 hour
at 123-129 C under a stopper with a continuous nitrogen
purge throug~ a stopper inlet and outlet. The monomers
form a clear melt, which is mixed thoroughly by swirling
the melt. Catalyst solution was prepared and dried by
azeotropic distillation, that is, 10 ml of stannous
octoate (Polysciences, Inc.) was dissolved in 60 ml of
toluene; 10 21 of tol~uene, with trace water, was distilled
to a Dean-Star~ trap that was vented via a drying tube. A
0~20 ~1 auantitv O r the stannous octoate solution was
pipetted in.o ~he mel` ar.d ~2d ~ho_ough'y~. Th- n_tro3en
s~ ? ~-.'ir.~es ~ s ~r.~ sir. ~ 5
^~0 ~e~ the ne~_ 3 ho_~s. .-eati-.3 _on~inues ,_t ' ,-;27 C fo-
-0-24 hou~s. ~:e ~ u-e w,_c _llo~e~ to c~ol _~ -o-
~
_ ~ . ~ _ _ _ ~ ~ _ _ ~ ~ _ _ ~ . ~ _ _ _ _ . ~ . . _ _ _ _ _~ . _ _ _ . . _ _ _ _
. _ _ _ _ ~ . . _ ~ . _ . ~ _ _ _ . _ _ _ _ . ~ _ _ _ _ _ _ . _ ~ _ _ _ _ ~ ~ ~ _ _
~ e~ f~~ ?~l~e- -i' --?~
- -_e-- ~ c~ S~ s e-;--~ Ir=~~ `.- _ sC~ es--
~V04'/n~l~ ~'C~/~S9l~063',
-93-
in a heated hydraulic press for later tensile testing.
Slabs, 1/~ inch thick were molded for impact testing by
notched Izod, ASTM, D256 and heat deflection temperature,
ASTM, D648. Glass transition temperature (Tg) and melting
point (Tm, center of the endotherm) were evaluated by
differential scanning calorimetry (DSC).
~m~les 2~-73
The procedures of Example lB were repeated except
that the ratio of L- and racemic D,L-lactide were changed
as shown in Table lB with the test results. The pure L-
lactide polymer, Example 7B, would not always mold well at
170 - 200 C since it frequently crazed badly on cooling in
the mold. Frequently, on cooling, it opacified. Figures
lS-18 illustrate DSC plots from material of Example 53 as
further discussed below.
--94--
V
u~ o a~ D In ~ 'd I ~ I I I ~
P. c a ~ `O ~,~ ~
~1 O ¢~ ~ N N )
c oa~ '~ C O
t~ ~n ~ ~ I _
I~ ~ C ~ O ~ m c ~
c~ C ~ h
Ln ct~ ~ tO C
m . .
~ c~ u~ ~ In ~ O ~ ~ n I ~
O O tO O J~ ~
E~ o c: o ~ m, a~ I I I m I ~ O h
O R
¦ ~ _ Ei~-~
3~ ~ u _ o
~ C ~ cl
_ u c ~ ~ c
I r~ o _~
X O ~ o r~
_ _ _
09_~0~1~ ~'CT/~S91/~632
_9,_ ~ `
Exam~le 8B
Similar to Examples 4B and 5B, a 90/10 weight
ratio copolymer of L-lactide/racemic D,L-lactide was
prepared. Into a dry, nitrogen-swept, 2-liter flask was
placed 1045~8 g L-lactide and 116.4 g of racemic D,L-
lactide. A 1.O ml quantity of anhydrous stannous octoate
(0.2 ml per ml of toluene) solution was added. The flas~
was swept with nitrogen overnight, t~en heated in a 141 C
oil bath until the monomers are melted and well mixad, and
10 the heating decreased slowly to 125 C and continued for 72
hours. The poly~er slowly whitens on cooling. After
removing the glass, the cloudy, colorless, glassy copoly-
mer was evaluated. Gel permeation chromatography obtains
a weight-average molecular weight (Mw) of 522,000, and a
15 nu~ber-average molecular weight (Mn) of 149,000,
A DSC o r the lactide polymer reveals a strong Tm
at 145 C, see Figure 13. The lactide polymer was melted,
quenched, and examined again by DSC to reveal no crystal-
lization or melting points. However, a Tg appears at
approximately 50-55 C. The results show the polymer can
be crystalline or amorphous, depending on its heat
history.
Examples 9B-12B
The composition series was extended, using the
2S procedures of Example lB except other L- and racemic D,L-
actide ratios were used and heating was 2 hours 125 C, 14
s 125-1~. C, 'hen 2 ~.o~rs 14--'2' c. T~.e ~esul_s arr
-96-
i~ ~.` i ;3
TABLE 2B. TENSILE AND MODULUS PROPERTIES OF L-LACTIDE
AND D,L-LACTIDE COPOLYMERS
,.. ... .. . . .. ~
Composition, Weight
Rat o, L-Lactide/ 70/30 60/40 20/80 0/100
(Racemic)
Example No. 9B 10B llB 12B
Color/Transparency Colorless/
Clear -~ ~~ -~
Film Thickness, Mil ~-9 4-6 4-5 ;-~
Tensile Strength(~),
1000 ~si, ASTN
D63g(i~ 6.9 6.7 S.8 5.6
Elongation, S 3.2 3.0 2.7 2.8
Tangent Modulus,
1000 psi 287 293 275 278
(a) Films were pulled at a ~aw separation of 0.2"/min. and
chart speed of 5"/min.
The results of the above examples reveal that
only certain compositions have the required properties for
a crystal polystyrene offset. The main requirements for a
crystal polystyrene-like material are clarity and celor-
lessness, tensile strength greater than 7000 psi, tangent
modulus (a measure of stiffnèss) ~reater than 400,000 psi
and well-behaved thermoplasticity. Table 3B lists some
side-by-side comparisons of a crystal polystyrene (OPS)
and a ~7.5 weight percent L-lactide and 12.5 weish.
pe-can~ rG~~emic D,B-lac_ide randor~ co?ol~e~
~>C~ 9l/~1637
-97-
~_ , ;, ,_ ~ J _:
TABLE 3B. PHYSICAL PROPERTY COMPARISONS
Property acid),Polystyrene
Impact strength, notched
Izod, ft-lb/in. 0.4 0 4
Ultimate tensile
strength, psi 8300 7400
Elongation, % 6.0 ~.o
Elastic modulus, psi 694,000450,000
Deflection temperature, F
under load, 264 psi (a) 200
Specific gravity 1.25 1.05
Rockwell hardness (b~ M7~
Vicat softening point, F ~c~ 225
Melt flow rate, D1238(G) 1.7 g~l0 min.(e)
40-46(d)1.6 g/10 min. ~f)
(~ Depends on heat history
(b~ Shore D = 97
(C~ DSC, Tm = 125 C (257 F~ at 10 degree/min.
(d) Flow rate decreases at lower temperature
(e~ Listed by manufacturer
(f ~ By our experiment
Exam~le 13B
The copolymer of Example 2B was molded and
remolded several times to determine if color would develop
in the films and .he molecular weights remained hish.
~5 ~is dete~mines ~ the ce201~G- can ~e -ecycled, an
~mpo--2n_ coneide 2tion o- m~nl~_2ctu_in~ cticos. The
_esul_s of ~ab_e ~3 sho~ ~h2~ ~he co?ol~e- _eri~a r.eG
c~?le-el~ .s~ .~ 2~ SS 2^~ e- -~:?e~te~
n~ _e~ e ~ o _~?ol~
~. ~ ~ _ _ ._ ~ _ _ _ _ . ~ _ _ _ _ _ _ _ _ ~ _ _ _ ~ ~ _ _ _ ~ ~. ~ . _
--'~8-- ~ ~.
`t . . ~
TABLE 4B. EFFECT OF MOLDING ON LACTIDE COPOLYMER
No. History Appearance 10MW0~s 1O00~S ~w/Mn
Example Not Completely 928 218 --
5 2B(a~ molded, transparent
directly and
from colorless
poly~eri-
zation
Exa~ le Ex. 2B Completely 301 135 2.22
13Bt ~ after transparent
molding~b~ and
colorless
Exam~lQ Ex. 2B Completely 137 56.7 2.42
13B~ ) after transparent
molding 6 and
times ~b~ colorless
.. . , .. . .... . , . , ~ . . . .
~ 85/15, ~-lacti~ ./racemic D,L-lactide copolymer
(b) Compression molding at 167 C ~333 F) fo. 7 minutes to
5-mil film
Exam~les 14B-18B
The copolymers c~ Examples 2B, 33 and 6B were
compression molded into f ilms of approximately 20 to 30-
mil thickness and were placed in a heated Instron tester
where the films were drawn 5 times their length at 83 C at
a rate of 0.5 inch per minùte. The f ilms were cooled
quickly upon removal from the Instron, and found to be
approximately 5-mil in thic~ness~ T~ey were clear and
c^lorless. Tensile properties were evaluated and are
~is~ed ia T2blQ 53~ Tihen d-=~. S to 10 ~i~es _heir
len~ e fi'ms ~c-~ ev~`dC-co cf -r~s_al fo -.ation b~A~
vir_ue o_ h~ze Gevelop~en- c?~ SO~' les- o_ `__c?S~ ~-es~
~~ T;~e -esu'~s ce-^ns_~__e _~~_ ve-i 'hi?. f '` l~s C_?.
^. -~ _Cn-~ _c.Sc~~
_. _ ~ _ _ _ _ _ ` _ _ ~ _ _ _ _ _ _, ` ` _ _ ---- ` -- -` ` ~ . _ . _ _
_ ~ _ _ _ _ = _ _ _ _ _ _ C~ . . _ _ _ C~ ;~ _ _ _ _ _~ _ _ _ _ _ _ ~ _ ~_ _ _ J _; ~
~ ~ _ .. _ _ _ ~ .
)~l3 ~'CT/~S9l/063
-39-
~ 3
TABLE 5B. PROPERTIES OF L-LACTIDE/RACEMIC D,L-LACTIDE
COPOLYMERS AFTER ORIENTATION~ a )
.... _ _
Composition,
Weight
Ratio, L-Lactide/ 85/1585t-5 85/15 8~5/12.5 95/5
D, L-Lactide
(Racemic~ _
Example Number 14a 15E7 16B 17B 18B
Film thickness,
mil S.S 5~0 6.5 5.0 4.0
T~nsile strength,
1000 psi 14.0 1~.7 lS.O 13.0 1~.0
Elongation, S31.5 15.4 30.0 23.8 37.4
Tangent modulus,
1000 psi -- 564 41g 432 513
_. ___.. _ _ __,~",~., . .. . . ,_,_ --. ~ . ,~_._
(~) 5X oriented at 83 C using a draw down speed of
0.5 in./min. on Ins~.on
Exam~le 19B
Films of the copolymers of lactide of Table lB
were immersed in water for several months interval. The
copolymers remained clear for approximately 2 months;
after 3 months a slight haziness developed. Upon setting
on the shelf in humid air and with frequent handling, the
films remain virtually unchanged for approximately 1 year
~lthouch Ins'_on d~a ~ill sho~ a slo~ decrease in the
strength and elongation after several months. In a
l_n~_il`, _he ~u_i-` i'_s dis~ æ- i- 5 m2..~hs '- 2
years, de~enning on _he moisru-e, 7~ em~2er~_e,
c1~
~ ~ " ,~ _
~he i2c__-e c~ ~.e~ ~ ~am~ie -7 (c~en_~e-,
--n-ress70n-m2i~e-` _` `` ' n ;`'-S e.~ ` -e-` -y ~`- _ns` -_un-'
;;`~ ``' ~i~ i r~.~' ~o~ !n~
--100--
polymer of Example 5B was annealed in a 185 F oven for 16
hours. The sample turned hazy and the DSC of the sample,
see Figure 10 revealed a pronounced increase in the
crystallinity. The sample showed a 264 psi heat
deflection temperature (~DT) of 90 to 95 C. A similar
sample without annealing ex~ibited a he~t deflection
temperature of 50 to 55 C, which corresponds to its Tg.
Exam~le 21~
Calcium lacta~a, 5 weight percent, was blended on
a heat~d mill ~oll wit~ the lactide copolymer of Example
53 at 170 C or app.o~imately 5 minutes. The blend ~s
stripped off the roll as a sheet and examined. It was
stiff, strong, and hazy. Optical microscopy at ~2X
reveals heterogeneous domains in the size range of from a
few microns to 30 microns. DS~ reveals a substantial
increase in crystallinity in the vicini'y of 145 c, see
Fiyure 11, which remain on quenching and reheating. The
results, above, comparing Examples 8B, 20B, and 21B, show
that nucleating agents are more prompt and efficient in
inducing crystallinity in lactide copolymers. Nucleating
agents such as salts of carboxylic acids may ~e used,
salts of lactic acid are preferred.
Exam~le 22B
T~, 2 500~ -r.ec`;, ~o~ancl ~o~;om -las~, equip~ed
~ith a mechanical stirrer and a nitrogen i:._et and outlet,
12ctide (botn Boehrin~er ~nd Ingelheim, _aGe s)~ ~e
er: s~eC? =~ e `_~ -s _-~_ ~o.: ~ ^~
. ~
~ . s ~ _ _ _ _ . . _ ~ _ . ~ _ _:, ; , _ _ . , _ ~ , ~ _ ,= _ =,, _ ;
~ 5 ~ e.~?_-~ s ci~ -se~
_ _ _ ~ . _ ~ _ _ _ _ _ c _ . . _ _ ~ _ _ . _ _ _ _ . . _ _ _ _ _ . .
WO~2/~W13
--101-- . ~
lactides allowed to polymerize at 141 C over 3 days time.
The highly swollen, polystyrene floats to the top after
turning off the stirrer. The lower, polylactide phase was
cooled and examined by DSC. The sample has a low Tg,
approximately ~5 C, and is otherwise lacking in apparent
temperature transitions. Compression-molded films are
clear, colorless, and very pliable. These results
indicate that the polystyrene thoroughly interrupts
crystallinity formation.
10 E~am~le ~3B
ThQ lactide copolymer of Example 8B was mill-roll
blended with 20 weight percent of the homopolymer of L-
lactide produced in Example 7B. A sample of the
homopolymer was analyzed by DSC, see Figure 14. The
lS blended sample was examined by DSC and ~ound to have a Tg
of 59-6~ C and strong Tm's at 150 and 166 C, see Figure
15. Films were clear to slightly hazy, ~epending on their
cooling rate after pressing. Quenched samples easily
crystallize on heating to approximately 80-~0 C. As a
result the heat deflection temperature of the blend is now
quite high. The blend becomes hazy at 80-90 C but does
not deflect with heat as does the unblended 90/10
copolymer. Tensile data as shown in Table 6B were
obtained on unoriented, compression-molded films and
compared to si~ilarly obtained data for polystyrene.
a~ )l
--102--
TABLE 6B. COMPARISON OF BLEND OF POLYLACTIDE OF
~ EXAMPLE 23B WITH CRYSTAL POLYSTYRENE
_ _
Example Crystal
23B a ~ POlyStyrene ( a, b)
Film thickness, mil 8 14
Tensile strength, ASTM 7.7 6.0
S D882, 1000's psi
Elongation, %, to 6.5 ~.2
yield
Tangent modulus, 323 267
1000's psi
(a) Thin ~ilms, unoriented, compre5sion-molded specimens
t~ Melt Index 1.7
This example illustrates that melt blending is an
excellent way to improve the properties of the copolymer
so that advantageous properties similar to polystyrene are
realized. The higher the amount of homopolymer based on
L-lactide (or D-lactide) blended with the polymer the
higher will be the heat deflection temperature, however,
haziness will also increase. Thus addition of homopolymer
may be combined with other methods of increasing
polystyrene like properties while still retaining clari.y.
As a further example, orienting films produced
from the polymer increases the tensile properties. At
eisht to ten times ~he d_aw `he ?hvsic~il p-operties are
still increasing but the material becomes hazy. The
~S eeqree of orien~a~io~ hus neeid to be cor.~rcll^d ~nd
combined with the othe_ prope-ty changing methods ~o
_~2m~i~s 2~
~ _ c
_ ~ _ _ _ _ _ ;. _ _ . . c , . ~ c = _ _ . ~ _ _ c i~
de~.-nst z._~g .h~_ molei~~'ar ~ei-.._s __n ~c _o..=-ollc~
~s.,.~ ~_cn~Ce~ ~_..~s ~ ^ _s '~ esult--
\~ o s~n~ l ~ P(~ S9 1 /063~ î
--103--
relationship exists between the amount of transfer agent
and the reciprocal of the weight average molecular weight.
Preferred chain transfer agents are lactic acid or
glycolic acid.
5 TABLE 7B. MOLECULAR WEIGHT CONTROL
USING CHAIN TRANSFER AGENTS
_ _ _
Example PPH of~tb~Mw~) /M
No~ CTA rl ~w n
-
24B 0.2213,S00107,300 8~0
10 25B 0~4512,80066,700 5.2
~6B 0~90 7,30029,900 4~1
27B 1~80 4,70013,900 2~9
.. .. ... ..
~a) Parts of glycolic acid chain transfer
agent (CTA) pe~ ~undred parts of lactide
15 in polymerization recipe~
(b~ Gel permeation chromatography in
tetrahydrofuran solvent, 23 C, with 106,
105, 104, and 103 anhstrom columns,
number average, Mn. and weight average,
Mw, molecular weights are calculated
compared to monodisperse polystyrene
standards.
Exam~le 28B
A 4~0-mil, compression-molded film of the lactide
copolymer of E~ample ~B was evaluated as a barrier ;-il~ by
ASTM methods~ The results are shown in Table 8B. The
lac~ide copcl~er is 2 much be,ter bar-ie- to c2rbon
dioxide 2nd oxv~en t~ar. is polvst~rene. 3y compa~ison to
s~ o-~_r ~ c-~ -_`-s, ~ ?~ a
~C cn 2de~u~.e 3a~~ie_ _ilr r^c- man~ ?2c~2~ins a??lic~ions.
~O ~n~ r~r/~ sl/~637-
-iO4-
TABLE 8B. EXAMPLE 28B PERMEABILITY TO GASES( a )
...._ . . -- -
Vinylidi~neOLaotidP C~ystal~) Poly(uthylQne Chlor'de-
UnitsExP plQ 2B Polystyrene terepht~al~te) Chlorlde
.
e~/100 ln.2/
24-hr. /atmo8.
Co2 32.1 900 15-25 3~8-~
~ l9~g 3S0 6-8 0~8-6~9
(') AST~ D1434-75, Exampl~ 25 wa~ a 4~3-m~ omprQ~ion-moldtad film~
Valu~ ~rom Modern Pl~tics ncyclop~di~
10 ~sm~2~
SheQts, 1/8-inch thick of the lactide copolymers
o~ Examples lB-6B were immersed overnight in a mixture of
petroleum ether and methylene chloride, At ratios of
70/30 to 60/40, petroleum ether/methylene chloride, the
copolymers would foam when placed in boiling water.
Irregular, but well expanded, foams would form~
Thus, compatible chemical or physical blowing
` agents may advantageously be used with other processing
steps to produce foamed materials. ~hese materials are
useful where foamed styrene is typically used (e.g. eating
utensils, packaging, building materials and the like).
For example, a foaming agent can be added prior to
extrusion or injection molding.
Example 30
^5 ~ c~m?2rison W25 m2àe of the melt visccsities o~
a ,ommerci21, cryst~l ?olvstyrene tT~re 201, U.untsman
~n2 mel. in~e~:, AS~ 23~ t~-!, c~` _he ?ol~styrene ~2s 1. b
c~o rin~ 2. ~33 C usi-.~ ~he S-n~5-;1 -` ~ '2ich ~ he
e~ s~ s ,.~ -e~ 3 ~ v~ e ~s
t~ r~-2 -`e~ e~ ?--~ c-
~iC^cs~~ies W5S `___2' ne~ c~se~~ing ~ne 2e_= ~iscosi_ies
~!0 9'/()~113 PCI`/~S91/063~
~;05--
J i ' 8`3
of the two polymers in an Instron Capillary Viscometer.
The comparative results are shown in Figure 12. The shear
rates normally encountered during extrusion and injection
moldin~ are approximately 100 to 1000 reciprocal seconds.
Inspection of the data of Fiqure 12 shows that the melt
viscosity of the lactide polymer at 160 C is very similar
to that of the polystyrene at 200 C~
The above results illustrate that lactide
polymers can be ~elt-processed, at lower tempera~ures than
polystyrene, by very similar methods.
E~3~æ~ L-~4~.
Small, test polymerizations of purified
(recrystallized and dried) mesolactide ~meso D,L-lactide~
were carried out as the homopolymer and the copolymer.
i5 The molecular weights were evaluated by GPC and compared
to analogues of D,L-lactide. The results are presented in
Table 9B. The polymers were melt pressed into films and
their physical properties evaluated and compared as shown
in Table 10B. Within experimental differences of sheet
thickness and molecular weight, the copolymers are similar
within experimental error. The homopolymer of mesolactide
is somewhat weaker.
TABLE qB. GPC MOLECULAR WEIGHT COMP~RISONS OF MESO-AN~
RAC_~'IC L~CT-~)E POL~`~lE~S ~ COPOL~;~SE~a
Example C~mpoci~ion ~es. G?C x.~0 ~I~/M~
(a) ;~ ._pT !. __ `'7 - ~ 7 3.~c
} ~ S ~ ~ ~ 5 4
~) ?~c~ __r-
;; 9';~ lOi~- ~CT/Us~l/n~
3 ~3
1~ oo~ !
3 s ~ ,, ~
~^t Ic~
a a s
~ ; V ~ ~ ; I
C E ~ U ~ O
C r~ O ~J O ~ O (~ ¦¦ E
0 9 ' / 0 ~ ¦ ~i I C'T / ~ S 9 1 /1) fi 3 _
--107--
V ~
ExamPles 3SB-478
These examples illustrate the pre~erred copolymer
ratio of the L/D,L polylactide copolymer series (racemic
D,L-lactide was used throughout these examples). of
particular interest were the 80/20, 90/10, 95/5, and 100/0
ratios. Each of these copolymers is a material having
different properties. Table llB contains data on the
thermal properties of these unoriented copolymers. The
~lass transition temperature, Tg, varies with the amount
of intimately dispersed residual lactide monomer~ A
t~ical relationship is shown in Figure 16 where the
residual lactide was measured by TGA and the Tg was
estimated by DSC. To a close approximation, the Tg
~ollows this relationship for all o~ the L-/D,L-lactide
copolymer ratios. The 80/20 copolymer typically is an
amorphous material with a glass transition temperature of
56 C. This copolymer has limited commercial use since its
heat distortion temperature will be on the order of 45-50
C, which is considered too low for many packaging
applications which require a rigid polymer used in
applications up to 70 C.
The other copolymers have the same or only
slightly higher glass transition temperatures, but can be
crYstallized to improve their thermal st~bility. The rate
2S o~ crystallization inc-eases as the D,L content decreases
znd the molecular weight decreases. F-om the point o~
view cf ther.mal prope~ties alone the lOo percent pcly(L-
lac~ide) ~ol~e- is ~os, desirable. ~:owever, when othe~
t~__s___s s~ _~s~ ~ 2 ~
~i~, ex~~uded sh~pes, t~e ca?~ v to -`o so 2t lowe-
_cm?eratU~cS `n``~h ess ;is_~si,y _nd _-lcr ~ G- icn,
-ic~ -e~c~~ ~ r~ ~~};e~ t~
_ë ~_~-__``~__ ___~` ` _~ / ~_ ' _ _ _ `_ ~ - _`__'=.i--`:
_is_~ss~
-108-
TABLE llB. SUMMARY OF THERMAL PROPERTIES
OF LACTIDE COPOLYMERS
.
Ex~ Copolymer Transltion Tempe~atgre
No. Ratio C C
3SB 80/20 56 --
36B 90/10 55 lS0
37B 95/5 59 16~
38B 100/0 53 178
The mechanical properties of sheet extruded from
each of these copolymers also differs somewhat, depending
on copolymer ratio~ Table 12B summarizes data that has
been obtained on as-extruded and 3x biaxially oriented
sheet. The biaxially oriented sheet can be either
amorphous or semi-crystalline through crystal growth
during annealing. The annealed sheet has been found to be
thermally stable up to the annealing temperature,
approximately 110 C.
Since the 80/20 copolymer does not crystallize
upon annealing, it will always be subject to thermal
distortion when heated above its glass transition
temperature. Orientation does increase its room
temperature ~ech~ni~-al pro?ar~ies tc ~eri~ hi~h 'e~els,
howevex~
The 90/10 copol~T~er sho~s an increase i~ rost
~5 properties ~rom ~oth annealing and orientation. The
app-c~,:im~tel~ the sare as `hat c~ the ~0~0 c_?ol~e-.
~he ~~ ~`la~le da.a on ~he ~achanic_l ~ro?e_~ies
th~ ~---e ~ c~ ;_0 _~~3'~ J`~--
~ e, c- e.~ ?le, ~:~?12
and 5~ e mechanical pro?er,ies c- .he ~ c_ie-.,e~
~'09'~n~~ S91/063~,
--109--
f ~ j iJ
80l20 copolymer or the 90/10 copolymer. Howevexl they can
be considered acceptable for most applications~ The
reason for the drop in mechanical properties has been
attribut ~ to numerous micro defects found in the oriented
sheet. The cause of those defects has never been
identified; however, the material is known to craze easily
upon crystallizing.
For comparison Boehrin~er Ingelheim poly~L-
la~tide~, Resomer L21~, a pol~er with a Mw ~f 800,000 is
sho~m as Exa~ples 38B and 47B. The tensile stren~th of
this polymer is not very differQnt from that of the
copolymers examined, but its tangent modulus is
considerably higher; however, the values used in the
tables were as published values not from the tests used to
1~ evaluate the other exa~ples~
TABLE 12B. SUMMARY OF MECHANICAL PROPERTIES
OF LACTIDE COPOLYMERS
Tnn~ile Tangent Elonga-
No Copatioer Morphology Process Strength ~odulus tion
39B 80/20 A E7,500 30S,000 5.7
408 80/20 A 0-3x12,200 427,00018.2
41B 90/10 A E8,000 lS0,000 5.0
C23 90/10 C ~8,500 188,000 4.6
43B 90/10 A 0-3x11,700 494,000~1.2
44B 90~10 C 0-3x10.2Q0 401,00020.7
~5~ 95/5 .~ 0-'x9,~Q0 ^t3,0005S~5
~53 _/5 ~ 0-_~i6,S00 2~5,0006P.C
A / ,r~ ` O3; O r ~Y - r OO~i 30 ~ OOO __
ir~lOl~E
_ = C-ts_~lli^~
r " --
, f; _ _ _~ _; _ ~ ,_ _ _ _ ; _ _ `-- -- `` -- _ _ -- ~ j_ _ _ ~ _ _ = `_ _ _ _ _ _ _ = ~_
_~___ c_ ~ r~ -J`-~ eci_~
~; "~ - r~ n~
--110--
h. ~.` <.~ .. 1 ~; j
hiyher melting point than the copolymers, the 100/0
polymer has to be processed at higher temperatures than
the other two materials. With a Mw of approximately
200,000 pure poly(L-lactide) has to be heated to 200 C in
order to have a zero shear melt viscosity below 100,000
poise. By way of contrast, the 95/5 copolymer and 90/10
copolymers having Mw's of 200,000 have ze~o shear
viscosity of 100,000 poise at 175 C and 160 C,
respectively.
~a~es 48B-56B
Processing aids ~plasticizers) are necessary in
prQventing color during extrusion and compounding. The
pure poly(lactic acid~ can be substantially heated by the
work put into it by a high-shear zone of a twin-screw
extruder. An extruder set at 350 F, will work on a high
molecular weight poly(lactic acid), with no processing
aid, to cause its internal temperature to rise to 390 F,
or higher, causing browning of the extrudate. For a high
shear extruder this can be prevented using approximately 5
percent lactide incorporated into the polymer. I~ is
presently believed that the processing aid acts as a
lubricant to prevent discoloration. Other processing aids
such as calcium lactate, sodium stearate, and sodium
benzoate also are effective. ~ome illustrative results
~5 ~-e shown in Table 13~i. To those s~illed in the a_t it
will be obvious that the e~act amount of processing aid
~`11 dapend or. he ~lecu~2~ weish~s _ r ' he poly(l -tlc
acid) and the 2mount of she2r mi~in~ imposed.
he~_-c~r2c~ c~ r ~~.e ~ e
3~.~ 1 ~ ~, ~ 2_~_ _ _~ __o__ssi.._ ___ ~l~s~i_i~ ;,
_ _ _ _ _ _ _ _ ~ ~ _ _ _ _ _ _ _ ; _ _ _ _ i _ _ _ _ . _ . . ~ .~. . i
ss~ c~ lc~ _= _c .~e_
tha~ o~her p-o_essir~ ai_s su_h _s s~-iium ~en~o_te an~
__l^ium l^_~^=e o__^i-. ~~l_~'-r- -a-~c_~=es w:~en use-` i:
~o ~"~ cr; -~91i~)6,~,
,~. i; v ~ `J
TABLE 13B. USE OF PROCESSING AIDS
Co- Processing Aid zOne(b)
Compositlon Type Wt S Temp, Extrudate
483 95/5 Lactide 15~5 391 Colorless
49B 90/10 Lactide 15.0 381 Colorless
50B 90/10 Lactide 12~ 385 Colorless
51B92.5/7.5 Lactide 8.1 3~4 Colorless
52B 90/lC Lactidc ~,5(C) ~81 Colorless
53B 90/10 Lactid~ 4.6 390 Sliqhtly
brown
5~3 90J10 Lactide 3.~ 40~ Brown
55B 90/10 Sodium 2.0 3~8 Colorless
benzoate
56B 90/10 Calcium 2.0 384 Colorless
lactate
(~ Monomer ratio, L-/racemic D,L-lactide
(b) Temperature at high-shear zone in twin-screw extruder
Exam~le 57B
Examples 57B to 753 teach the incorporation of
lactide in conjunction with quenching to obtain pliability
and transparency. Alternatively, the polymers can be
annealed to i-?rove stability against heat distorti3n.
Poly(L-lactide) was prepared by methods
previously des~ ed~ T~u~ ~00 ~ o~ triply recrystallized
and _horoughly d_ied ~-l=c_ide was loaded into a clean,
~ -c-~e~ A, 5~ u~ o_~ h-
f! as~: was r` ~~e_ wi-h _ ~``~` ~~~ sep~ 2-~d inl_t 2n_ c~tle
s _in~e nee_!es ~2- ~dm` _ ~ csntinuous a-_~n ?u~rJe
.. ct~r.~s ~-_^--~e ~ ; 'D C ~ _ e? _-r~ C `
sieves, ~ s~ "_c.~e
__eo--c?ic~ e c~ i.. a~ 3n
? -~ c ` ~ ~ C_=`- ~ ~e ~-?-~-~- _~.-~ ~^~e _-
~l -- v ~
lactide. The flask and its contents were placed in a lS0
C oil bath, and when melted, swirled vigorously to obtain
a homogeneous mix. The argon pur~e continued a~d a
thermocouple was fitted through the septum into the melt.
The melt was 143 C. The temperature of the oil bath was
advanced to 200 C and heating and l~ght purge continued
for 20 hours. The temperature of the melt advances to
170-174 C in the first two hours of heating. The f~nal
tQmperature was 170 C. Afte 20 hours o~ heating the
~las3~ was cooled in 2i- to roo~ temperature and the solid
polymer was transparent~
Poli~er was reco~ered by shoc~ing the flask with
dry ic~ to free it from the glass. The residual monomer
was analyzed by thermogravimetric analysis and the
molecular weights by gel permeation chromatography.
Differential scanning calorimetry reveals a glass
~ransition temperature ~9) at 53 degrees and two melting
point endother~s with peaks at approximately 170 and 190
C. The gel permeation chromatography molecular weights:
20 Mn = 129,000; MW = 26i,000; Mz = 462,000; 3~W/Mn = 2~08.
~esidual monomer by thermogravimetric analysis was 2.3
percent, (Example 57B, Table 14B.) The experiment shows
that L-lactide can be polymerized above, or near, its
melting point and the products remain transparent and more
amorphous.
Example 58B
ay ~_~ s~ E~ " 0~ O ~ _c L-
l~ctide ~as p~l~eri~ed usin~ 0.,0 ~1 o~ stann~us C_to2~e
_ _ _: ~ _ _ _ ~ . . _ _ _ _ _ ~ ~ ~ ~ _ ~ _ _ ~ . _ ~ i . _ ~: . _ ~. _ _ _ ~ _ _ . .: ~ _ _ _ _ _ _ . _ _
c_C 15~ ``~S. -h_ -~ ?1~ 5c- G,
~_~_e ~ 5~~~-` ~~ -c- ~?-~ ~=i.._ G ~ ~ _ S ; "~ ` ~ r
e~ cn~ ?3~ e- c ~led ~ c ~ic3~
= _ _ _ _ _ ~ ~ _ -- --r _ _ _ _ . _ . ~ ?
_~ _ ~ I _ ~ _ _ = _ ~ ~ ~ _ _ -- ^ - ~ ~ ; ~ , _ _ ;_ _ _ _ _ _ _ _, _ _ _ = ., _
--113-- ` :` ~
poly(L-lactide) to crystallize and become opaque, thus an
intimate dispersion of plasticizer does not form.
The temperature is slowly advanced in many of
these experiments to accommodate the polymerization
exotherm. The reaction temperature must reach at least
170-175 degrees prior to a substantial monomer-to-polymer
conversion, otherwise the poly(L-lactide) crystallizes and
is difficult to remelt~
In Examples 60B-66~ the polymeri2ation of L-
lactid~ was repeated varying the conditions to obtainpoly~L-lactides) with di~rerent residual lactide contents
and crystallinities. The results are shown in Table llB,
where it is seen that pliability and toughness were
obtained only when the product has been quenched from the
melt, is transparent at room temperature, and contained
approximately 10 percent or more residual lac'ide. It is
believed that the L-lactide homopolymer must be
pol~erized in t~e melt, and quenched from the monomer-
polymer melt temperatures, to a transparent material as
~o evidence of its homogeneous and intimately plasticized
properties. When the poly(L-lactide) crystallizes during
polymerization because the polymerization temperature is
well below the polymer's melting point, the res`'ual
monomer is no longer effective as a plasticizer. I the
polymer crystallizes upon cooling to room temperature, it
also loses its pl2sticization. Annealing at elevated
.emperatures will -estore crystallini'y to amorphous
s2m?1es~
9'"`''!~ T'(~/l`~C91/()fi~'-
--114--
.
TABLE 14B. POLY~ERIZATION OF L-I~CTIDE
. . . _ . . _ _
No o~h Temp ~i~e Appuaranc~onomer Size
578 0.02156-201(') 20 cl~ar 2.30 300
150-174 transparent,
hard ~ glaB By
58B 0.02155-165~') 72orystalllne, -- 104
opaque, hard,
brlttln
S9B 0.005120-2C0('~ 2~cry~tall~ne, -- 100
111-200 opaquQ, hard,
brittle
60B 0.02135-145~') 22ory~tallin~ 1 S00
135-152~) opaquQ, hard,
brittlQ
61B 0~02117-185(') 24cry~talllne, 1.74 100
120-175~') opaque, hard,
brittle
62B 0.02160-170(l) 8crystallinQ, 2~18 2,000
opaque, hard,
brittle
63B 0.02145(d lScrystalline, 3.6 25
li/-144 opaque, hard,
brittl~
64B 0.0553~90(') 0.3 clQar, 10.1 25
160-215~) pliable,
touqh,
transparent
6SB 0~0553188-193(~) 0.23 clear, 22~9 2S
147-200 transparent,
pliable except
at edqe of
polymari ate
55~ 0~02145(~) 2~7;crystalline(~,52~5 25
150-ii3`~` opaque, ha_ ,
brittle
"' Oil b~th tem~era-ure
io " Polym~r melt t~m~er2tu e
:) -hi~ polymer -ry~talli-ed a- 160-169 a~ the tem?er.~-ure wa~
paren~ ~ e~?~-a_~_es ~:?_r~ n~
~V09~ 3 1~CT/~S91!~)6~'-
-115-
This transparency and intimacy of association
between polymer and monomer is also affected by the ratio
of L/D,L-lactide. At approximately 95/5 ratio the
copolymer easily quenches to a transparent solid. The
90/10 ratio, L/D,L-lactide copolymer quench2s quite
easily. The 100 percent L-lactide polymer quenches with
difficulty from thick sections of the polymer to a
transparent material. Some comparisons are shown by
Examples 67E3-71B o~ Table 15B. T~inner cross sections,
0 i.Q~ I films of the L-lactide polymer can be plasticized
and qu~nched to pliable and t.ansparent materials~ T~e
80/20 copolymer quenches very easily to a transparent
solid~ The latter has only a trace of crystallinity as
seen by differential sranning calorimetry.
TA.3LE 15B. TRANSPARENCY OF LACTIDE POLYMERS
. .
~x L/D,L- c(ai ~Oumrs O/T(b) GPC Mw Monomer,
67B ss/s 145-160 67 SO385,000 2.64
68B 100 135-152 22 O322,000 1.1
69B 90/10 150-157 45 T821,000 4.95
70B 90/10 150-170 48 T278,000 1.37
71B 80~20 '35-175lC) 23 T -- --
a) Melt temperatu~e (polvmeri~ation temper2ture)
b! Cpaquen2ss/~~_..sp_~ency tGJ~` a~te- air~ lin~ ~f
pcly~er~-~tes; o?aq~e ~); sligh~ly opaque ~SO);
tr~ns~arent ~
ed _5`~ c~~ e ~ol~. t~e~ 1_
\~ o ~ n ~ PC r~ /n~3~-
-116-
. . ;~
~ J
90/10, and 80/20 copolymers are quite clear and
transparent throughout their thermoforms.
ExamDle 7~B
The poly(L-lactide) from Example 57B was melted
and mixed on an open 2-roll mill for 5 minutes at 375 F
~190 C), then compression mold~d at 375 C for 2 minutes,
then air~quenched to room temperature in approximately 30
seconds. Both 7-and 20-mil thick films were prepared.
Both were clear ~nd transparent without trace of ha~e or
opacity. Rasidual monomer in the film was 0.79 percent~
The films are very stiff.
Ex~m~le 73~
The experiment was repeated except that the
milling was continued for 10 minutes instead of 5 minutes.
The films were analyzed by thermogravimetric analysis
again and found to have 0.38 percent lactide. The films
were clear, transparent, and stiff.
Exam~le 74B
The mill-rolled polymer was also compression
molded into a 1/4 x 1/2 x 1 inch plaque. This plaque
required 5-10 minutes to cool in the press by turning on
the cooling water to the press. The plaque was white,
op2oue, 2nd crystalline .e~cept for `he extreme edges,
which were transparent.
~5 ~he a~^ve ~æmples 7~B-743 te~ch the quenching Or
~ilms of poiy(~-12~ e~ -o main~ain _ransparenci. ~ihen
er~
~e~ s `~5C_ :~e~~~. in-~c_~~s
`~ --^?~ ?'~ e~ c~:~en~
_: = _ _ _: _ _ _: _ . _ _ . _ _ _ _, . _ . _ ~ _ = _ ~ _ _ _ _ _ _ _ . ~ ~
3 ~ s i s _ s i ~ p ~ o ~ ~- s s ~ ~ c ` ` i _ i ?. ~ ~ _ 5 _ )
' 2C_^-~.,~ ` '`.- . ;`~'`~-~ ='`~i' is r`c~ e e~e-~
\~09~ 3 I'~ 9l/()6~
.
some time to allow the molecules to order themselves into
extensive crystalline lattices. ~his is callad annealing.
When cooled rapidly from an amorphous melt, the polyme-
does not have the time required and remains largely
amorphous. The time required to quench depends on the
thickness of the sample, its molecular weight, melt
viscosity, composition, and its T~, where it is frozen-in
as a glassy state. Note that melt viscosity and Tg are
lowered by plasticization and favor quenchin~. Thin films
~0 obviouslv cool very quic~ly because o~ their high surface-
to-volun ratio while molde~ items cool more slowly with
th~ir greater thic~nesses and time spent in a warm mold
before removal. Regular structures such as poly(L-
lactide) order more easily and crystallize more quickly
than more random structures such as a copolymer.
With the polylacti~es the melting points are
approximately 150-190 C depending on the L-lactide content
and, therefore, the regularity of structure. The Tg of
all the polylactides, including various L and D,L
homopolymers and copolymers is 60 C. The Tg decreases
when residual lactide is intimately dispersed with the
polymer. Quenching to an amorphous state requires that
the polymer or copolymer in an amorphous ~elt is rapidly
cooled from its molten state to a temperature below its
Tg. Failure to do so allows spherulitic crystallinity to
develop, that is, crystalline domains of su~micron tO
micron size. The lat~er scatters liyht and the. polymer
s~eci~ens be~^me o?a~e~ Thcse c.ystalline ~c~2s ha~e
im?rovQd stcbili_v ~ heat distortion. This spherulitic
-~a c_ys~allini~- is _~en ~ sh__= ~an~e _~~e--~^n_
~iso~de- si-.~c _~.e ~ s ~-~ se?~ e~ _v ~
ecicns~ evc_, ~e ^_ys~e''i~_es ect ~s pse~aco
C i _ ~_ _ _ _ _ . . ~ _~ _ i ~ ~ = _ ~ ~: _ _ _ _ . . _ = _ ~ C _ ~ ~ . = _ _ _ _ _ ~ ~
~~ s_~ e -~~,_ci..e~ C~
.~.C~ C`15 ~l~ e~ ~bc~ e _ts T3 b~lt belo~i i's ~l'i~3
er .~o~ec~ -- _è ~=_c__~c~ __ G~
n~ pcr/~ ~9l/nfi
--118--
some long range ordering, then "heat set" to permit the
ordering to complete, that is, given some time to anneal.
The amorphous polymer is thereby crystallized into a
different order, called long-range order, short range
disorder. Transparency and resistance to heat distortion
are favored.
A detailed discussion can be found in textboo~s,
for example, "Structural Polymer Properties", by Robert J.
Samuels, Wiley Publica~ions, NY, NY 1974.
As D,L-lactide is introduced as a comonomer,
auenching can be replaced by ordinary cooling to retain
transparency. Spherulitic crystallinity can be introduced
into these films by annealing and the 100 percent L-
lactide poly~er is the fastest to crystallize. Where
transparency is not required the higher L-lactide polymers
can be annealed to greatly improve their resistance to
thermal distortion. Conversely, where transparency is
required, such as in a crystal polystyrene offset, great
care must be taken to avoid this ty~e of opaque
crystallinity.
Exam~le 75B
The poly(L-lactide) film samples were annealed on
a hot plate at 240 F (115 C). The film turned hazy in
approximately 1 minute and completely cloudy in
ap~ro~im2tely 2 ~inutes~ By way ol co~pe~ison, a 90/10,
L/D,L-lactide copolymer film required 10 minutes to turn
_ , _ .i..u_es A _ _ C ~ C _ O U _ ~. en
suspended by one end hc-i~ontally in an o~en ~n~ ad~-anciny
.0 s~ lD _ema_ne~ s~-~is~.~ u..~ _e-?2~3;u_~ o ~
~\ r'~~ _~_2~.e~ h.en e~ e-. ~ne -~
e _ ., _ _ _. ,,~_ .__, _ __ ._ _ _ _ _ , _
_ ~ . .~ . . _ _ _~ _ _ _ ~ ~ ~ _ ~ _ ~ ~ _ _ _ . _ _ .~ _ ~ ~ _ _ _ _ _ _ _ _~ _ _ _. . ~ _ _ _ _ _
acl y l~c~ i ces c_n i-cre2se l!~.e_r -o-~-s._b_ 1 ity a= e ` ~vc,~^-
? A~ ~ ~ ~ - ~ ~ r--c ~ ~ ~--^ ` h _ = - ~ 2 '~ ` c 3 ~ ~ 2 ~
!'C~ )o3'~
--119--
~ ~ 3
Ex~mples 76B-79B
The ollowing examples illustrate the beneficial
effects of adding lactide during compounding. The
examples show that without lactide as modifier, the
lactide polymer degrades during compounding. With the
addit~ ~ of lactide both discolorat.ion and molecular
weight decrease are prevented or substantially reduced
duriny compounding.
Thus, in Example 76B, a 90/10, L-/D,L-lactide
copolymer prepared as described by previous methods using
0.02 pph SnC12~21i2O catalyst ~a~ ground and axtruded into
pellets from a twin screw compounder, adding ~ weight
percent lactide~ The melt zone temperature of the
extruder rose to 390 F, the polymer discolored, and the
weight average molecular weight (Mw, by gel permeation
chromatography) decreased by approximately 40 percent~
The results indicated that insufficient lactide was added
for this very high Mw copolymer~ The results are shown in
Table 16B~ The pellets from this compounding were
~0 recompounded adding 2 further 10 weight percent lactide
(Example 78B)~ The melt zone temperature was 375 F, and
the results were much better: further discoloration did
not occur, molecular weight decreased slightly, or within
experimental error, and a pliable composition was
obtained~
~T 'T `,~ !/nfi~--
-12G-
. ~ Ji
TABLE 16B. EFFECT OF LACTIDE AS MODIFIER
DURING COMPOUNDING
Ex. Before Compoundinq Lactide~b~
No. Color M~ M~./Mn(a~ weight percent
76B Light yellow 513 2.15 0.78
77B Li~ht vellow 278 1.80 1.37
Ex. After Compoundin~ Lactide (b~
No. Color M~ta) ~ /M ~a) weisht percent
.6B ~ark yellow 322 2.05 5.56(C)
77B Yellow 184 1.90 2.26
78B Dark yellow 307 2.00 14.4t
79B Colorlesst~ 324 1.99 14.6
(a~ GPC x 10 3
(b~ By thermogravimetric analysis, at 200 C
(~ Five weisht percent lactide added during compoundin~.
(d) Further 10 weight percent lactide added during
compound.
(e~ Thin film
To ascertain that the second compounding and
extrusion were facilitated due to the lactide modifier and
not the decreased molecular weight, another compounding
(Example 77B) was performed starting with a similar-Mw
copolymer of 90/10, L-/D,L-lactide. In this case, no
'actide was added bac~ in durinc t~e co~?oundins. The
melt zone temperature W2S 382 F, the copo!ymer was
~is~ 2~ .e ~ e--2~C~e~ tel~ 5~
percent. In ad~ition, ap?ro~:imat21y 5 pe~ccnl mo_e to~~ue
c _ c
. . c _ .
_ ~ _ _ _ ~.. ~ _ ~. _ _ _ ~ . ~ . _ ~. _ _ _ . ~ . _ _ ~. . _ . _ _ . .
WO9~/0~13 PCT/~S91/()632
-121-
very pliable and extensible as described below in Examples
60B-64B. The Mw by gel permeation chromatography was
324,000 (cf. Mw = 307,000 before compounding and
extrusion). The Tg of this plasticized material is 42 C
and differential scanning calorimetry reveals a very small
amount of crystallinity melting at approximately 138 C.
The amount o~ lactide present is 14.6 percent as estimated
by thermogravimetric analysis.
~amles ~OB and 8~
~he compounded polylactides, E~ampla 7~B and 77B,
wer~ mixed together in the twin-screw compounder wit~
extra lactide to raise the lactide level to approximately
20 percent. The compounding temperature was 347 F tl75
~), much reduced from the previous 375 to 385 F. The
compounding proceeded s~oothly without f urther
discoloration.
The above results clearly show the beneficial
effects of added lactide as modifier. The required torque
to compound the compositions, the discoloration, and the
working temperature are decreased when adding lactide.
Further evidence of plasticization is seen in the lowered
Tg and the pliability of the compositions. In addition,
molecular weight decreases are avoided and stable
compositions are obtained. It will be obvious to those
sXilled in the art that the amount of lactide employed
àepends on many factors, includinc the desired amount of
~lsticiza~icn ~ou~h`, _he s~3e cf _-m?ol~nder ~hat is
~~.~ _~,r ~ e~ _ c_ _~.~ ?31~1~cti~es.
` `'?.~ C ~
~ esa e~:-m?le- illus=-_~_ ?l-s_~ atio~ ti--
_: _ _ _ .~ _ _ _ _ _ _ _ _ ~ . _ ~ _ _ ~ _ _ _ _ ~ _ _ _ _ _, . _ _ ~. _: ... _ ~ _ _ :.
-i~Jia, ~-!r~2~ -e ~e _ ^~ `2_ ~_=.; G
____~c2 ! ~ - - ~ _ C C _ _ ~ _ n~
__e_ro r~he!r .~e_n -~aracte-ir~ tensile an~ thermal
,.7;~ 4l /nf.~~
-122-
i~
In Example 82B, a control copolymer of 90/10,
L-/racemic D,L-lactide was assayed by thermogravimetric
analysis to be 6.74 percent lactide. This was mixed with
percent by weight oligomeric poly(methyl lactate)
(Mella) in Example 83B, which was prepared by heating
2,500 g of (S)-methyl lactate in an autoclav~ at 210 C for
3 hours, then collecting the Mella which ~ractionally
distilled at 81 to 85 Cl1.25 torr~ The mixt~re was melt
blended on an open 2-roll mi~l at approximately 7~50 F.
0 T~e blend was co~pression molded in a press a~
ap~roximately 350 F into clear, pliable films~ The
tensilQ properties, before and after, adding the Mella are
recorded ie Table 17B. The glass transition temperature
tTg) was reduced by the Mella plasticizer.
For Example 84B, the 90/10, L-/racemic D,L-
lactide copoly~er was melt blended with added L-lactide in
a twin screw extruder ~o adjus~ the L-lactide content to
20 percent by weight. The blend was further mixed with
oligomeric poly(ethyl la~tate) (Ella~ (Example 85B~ and
Mella (Example 86B). T~e properties of these blends are
also recorded in Table 17B.
PCT/~ S9 1 /ûfi3',
--123--
,
~ ~ J ` l '~
T~BLE 17B. C~ARACTFRISTICS OF POLYLACTIDES(a) PLASTICI2ED
WITH OLIGOMERIC ESTERS OF LACTIC ACID
~la~tlc Brcak Strain
Ex Pla~tici2er ~odulu~ psi Break, T~) T~(C)
_
82B6.7~ L-lactide 370,000 6,903 2 Sl 1~1
83B6~74~ L-lactidQ lS~,000 2,012 100 30 1~1
and 309 ~ella~
8~B20~ L-lactide 101,000 2.637 2~
SSB20~ L-la_t~d~ and 7,~1~ 2,561 ,39 -- --
30~ Ella~
86B20~ ~-lactid~ and 3,620 495 83 -- --
30~ Mella~')
0 (-! 90/lO, L-/racemic D,L-la~tide copolymer
Gla~s transition temperature
(') ~elt~ng point
(~ Ana:i2ed by thermosravimetric analysis
~ Methyllactate oligomer
(n Ethyllactate olisomQr
Exam~les 87B-92B
These examples illustrate the injection molding
of polylactide copolymers and the process for increasing
their heat distortion temperature.
90/lO L-/racemic D,L-lactide copolymer (about 1.3
weight percent residual monomer~ was injection molded on a
New Britain injec'ion molding m3chine having 75 tons of
clamping capacity and a maximum shot si2e of 6 ounces.
Standard ASTM D-638 tensile bars were molded during these
'~ _rials. The ~.oldiny _o..di~ivns we_e væ ied ove~ a ang2
` o~ A ~e~ e-i~e
ieculc~ we`~ ~ e~ , r^~ ~as suc~ess_~ olded to
_s ~e~ o`~se-~ ~he
~olà `_e- iliin~, ~_= _ri~_ 1- e~,e_~icn, ;c ;a~iC_
_ ~ e ~ ~ ; ~ _ _ _ _ _ _ ~ _ . . . ~. _ ~ _ _ _ _ _ ~ -
~;'0 9','~ r~ n~
-124-
Calcium lactate, at a 1 weight percent
concentration, was compounded into the polymer before
injection molding. This was done to provide nucleation
sites to increase the rate of crystallization.
Crystallization in the injection molded parts was
desirable to increase the heat distortion temperature of
the polymer.
For example, molded parts of the nucleated 90/10
copolymer, were annealed bet~sen metal plates at about 110
C for times betwaen about 30 seconds and about 4 minutes.
Aftar exa~ining L-he DSC cu-ves of the annealed parts for
the presence and degree of crystallinity, it was foun~
t~at annealing times between about 1 and 2 minutes were
required to develop full crystallization when the polymer
is in contact with solid walls at 110 C. Mechanical
properties of injection molded samples are shown in Table
l~B. This table shows that annealing does affect the heat
distortion temperature, but does not strongly influence
the strength, modulus, or elongation to break. The heat
distortion temperatures listed in this table were obtained
under a load of 264 psi. If a 66 psi condition had been
used to deter~ine ~eat distortion temperatures, the
increase observed fo. the annealed sample would have been
even greater.
TABLE lSB. MEC.U~NICAL ~O~-RTTES or INJECTION
MOLDED P3LYLACTIDE
.
~xa~ple ~ St-en t~, ~.o~ulu~, ~lon~a~ion, .~T,
.o~s~ ce~ C
S,a :nje~t.--n 5c~0 ::~0,000 c ~6
~ D. " ~ ! C--'` i ^ ~
~nne~le~
_ ~ _
_al-iur~ lac-2~e-nucle-~_i pol~er ;-s ir,~e~
e~ ir.~c~ = c~ cn~ 1 in-
_ _ ~ _ _ _ _ _ ~ _ ~. . _ . ~ _ _ ~ ~ . _ _ _ . . . _ = i ~ . ~ _ _
~oo~0~ 3 PCI/~S91/063~-
--125--
insl~fficient to develop full crystallinity in the sample.
The mold heating system was improved t~ provide in mold
annealing at temperatures higher t~an 8S C, most
preferably between about 110 and about 135 C.
Samples were also injection molded using a melt
blend of the 90/10 L-/racemic D,L-lactide copolymer and
about 5 to about 20 weight percent poly~L-lactide) as
nucleating agent. The results are shown in Table l9B.
The injection molded specimens were well fo~med with
excellent strengt~s, stiffness, and impact resistance.
T~e heat distortion temperatures shown in Table 19~ c~n be
improved by annealinq.
TABLE l~B. PROPERTIES OF INJECTION MOLDED
BIODEGRADABLE POLY~ER
_ _
Formulation() Tengile 1~ Strain XDT I~od
lS 90/ ~ p8l p8~ ~
89B 95 5 8,245 227,440 7 115 0.34
90B 90 10 8,32S 221,750 7 117 0.34
91B 85 15 8,631 230,150 7 116 0.35
20 92B 80 2C 8,615 228,840 6 117 0.35
(~ 90/10 5 90/10~ L-/racemic D,L-lactid~ copolyme~;
L-PLA = 100 percent L-lactide polymer
E~am~les 93B-10~3
~ o~e: Examples c3~ ,o 'Q~ listed i?. Tables 20AB and 20BB
2-o contain info ~ ation i~entical to Examples 65 to 81 in
`~l~s '~5.~ ~n_ __à c~` se;~
~.m~odiment. ~.e ir~o ~ation is re?ea;ed here for
con~enience i?. disc~ssing these e~alr,ples in rela.iGn to
-r?~eC ~ ere sel~c_-_
'-_~.?~ --__~e t~ 2.._e~ _~n~ ^.s .~
~el~ ~o ~es~}_ i-. r~terials c- ne inventio.. ~he
m ~,2_i:~s ^_O~`_~~~` _.. ~hese p__c-.~ ^.o~ c^~^'etel
~`0 9'~ r(~r/~
--126--
characterized, thus experiments were needed to allow a
more complete characterization of the examples and provide
meaningful comparisons that would demonstrate that the
materials of the present invention are indeed novel.
With regard to the present invention,
compositions were sought that had residual lactide or
lactic acid contents of about 0.1 to about 60 weight
percent and in addition may have the lactide or lactic
acid intimately dispersed within the pol~er. The results
fall into obvious categories. Thus, products with num~er-
average molecular weights, Mnl less than 32,000 do not
have the physical properties required in the present
invention. In fact films from these low ~n compositions
ware too brittle to be handled for tensile measurements.
lS It is known from the teachings herein that lactic
acid, lactide or oligomers of lactide or lactic acid, or
derivatives of lactic acid must be present to provide
plasticization and the advantages of tha invention. The
plasticizer must be present in amounts greater than about
0.10 weight percent up to about 10 weight percent. Thus,
if the plasticizer is intimately dispersed and effectively
mixed, the composition is substantially transparent. The
heterogeneous domain size of the lactic acid, lactide,
oligomer, or oligomeric derivative is small enough,
generally less than one micron, so that it will no longer
sca'ter ligh', i.e., it is intimately dispersed.
Conversely, white opaque samples are always hard because
_~ey h~ve c-ys_a'li~es' ~nder the test conditions.
Cryst~llization squee2es the lactide out o. the poiy~e~
-_ss ~ ~u~e Or mon^re- an' ?ol~e . This is 2150
o~ ious `-om ~ e~e~.=i~l sc~nnin~ _~'o~ime~-y (~C)
~5 r, whe-e2s ~e''-?lcs~ici~ed sam?les do no~ sh_~; c _is, nc_
-^~.^me- .eltin- p^i"_
~O (`':0~13 ~'Cr/l~`S91/Ofi3''-
--127--
~ ~. V ' ~ `~
One very important point is t~at the cited
patents frequently specify L-lactide homopolymer ("100
percent L-" in Tables 20AB and 20BB)~ The homopolymer of
L-lactide easily crystallizes because of its high melting
point. At lower reaction temperatures, the ~omopolymer
can retain appreciable quantities of monomer, but the
composition freezes during polymerization~ At higher,
~elt temperatures, t~e L-lactide polymeri~es so quickly
that it is very difficult to stop the polymerization with
s~lbstantial ~onomer left in th~ product~ This is true to
a lessor extent for poly(L-¦ D,L-lactide~ copolymers also.
Inspecting the results listed in Table 20AB and
20BB reveals that th_ comparative examples obtain either
products with low residual lactide, or products with
residual lactide that is not intimately dispersed as seen
by their color, opaqueness, and crystallinities. Thus,
Example 94B (very similar also to the work of Schneider),
obtained no residual lactide while Example 97B had 4.6
weight percent residual lactide, and both were off colored
products. The best known laboratory techniques were added
~o th~ procedures, described in the footnotes, fo- tnese
examples, from a historical standpoint (monomer purity,
for example) in an effort to make the procedures work,
with indifferent success. Either glassy, or hard,
~5 crystalline, o?aque products were obtained. It should be
noted that only those exam~les using tin compounds as
catalysts a?pear to be acceptable for many packaging
applications.
~ e ~ J~S ~- US
_3 -;/~O~cO~ ~n~ 'S ~ "-~ ld ~ 2 ~~e ~.~te-_~'c c~
_es~ ve~ ~
s~ e ~ e~ ?er~` C~ c- =~ e-~ s
-c ~ .2 e::~c~ -c-i~c ~ c_c
c--e~ ra-~ c ~ s_s ~.o ~- c~
~09~ -. rcT~ ss 1 /nfi
-128-
J
detectable residual lactide, the composition of the
present invention is colorless and contains small amounts
of lactide as a processing aid to prevent color formation
during melt fabrication.
A colored product was obtained repeating the
teachings of Example 97B. The residual monomer analyzed
as 4.6 percent lactide. The material was light yellow,
presumably due to the high poly~erization temperature
which produced color bodies with the lactide polymer~ the
dioxane solvent, and ~tannous octoate.
0 9 . 0 ~1 1 3 C 1' / U S 9 1 / O fi 3 _ 7
--129--
TABLE 20AB. REI~TED ART POLY~ERIZATIONS OF LACTIDE
CONDITIONS
Ex, Paeent Pat- Monomer Oataly~t zation
No. Ex~ ~ D ~ TYPQ pph TomP- Hourc
93B 2,758,987 1 L- PbO Q.30 150 42
~4B 2,758,987 3 50~50 PbO 3.00 150 S9
L-/D,~
95B 1,982,543 3 ~- PbO 0~30 150 31
96B DD 14548 ' L- SnO(') o~o09 193 3
97B 4,137~921 4 90/10 Sn(Oct~2, 0.0553 180 0.33
L-/D,L G~ 190 0,33
dioxane~ 210 0.33
98B G8 755,447 4 D,L 2nOO 0.02 150 24
99B GB 755,447 2 D,L 2n 0.02 140 25.5
Powder~
100B GB 755,447 6 D,L 2n 0.02 140 2
Carbon- 150 3
ate Hy-
droxidet~
101B CA 932,382 1 D,L Tetraphe- 0.02 16S 20
nyl Tin
102B CA 923,245 1,7 Ç L- Et,2n 0.167 105- 2
8 110
'03B DE 946,664 2 D,L(~) 2nCl, 0.25 140 48
104B DE 1 L- - Sn 0.0087 205- 0.5
1,112,293 Stearate as Sn 210
1058 2,951,828 1 L-~0 SnCl~ 0~30 160 5
3~ spen-
~ion~
106B 3,268,487 2 D,L T~is(2- 0~38 80 ~ 24
chlo~o-
ethyl~a-
~ine~
'0.3 ~P ~p~ ~. :- 58.IC-_). û~v~ i5 ~_
:~3,S_~ ?_ ~-
(1934~; me_ ~
~., 550, .t.,C,
4,5i9,SE:
4, 7
g-/o~ 3 PCI/~'~91/063~7
--130--
(') No reaction untll recipe w~s changQd by adding 0.75 pph of 88
percent lactic acid. Product was white, opaque, very hard and
brittle- film too brittle to handle.
~ ) Included was glycolic acid as chain transfer agent.
(C~ Insolubls
(~ Insoluble after 2~ hours plus addltional 1.5 hour~ with 700 yl 88
percent lactic acid and 100 ~1 H20.
(') In toluene; product colorless and very ~iscous.
(~ In min~ral spirits, Stoddard ool~snt No. R-66
10 (~ AgglomeratQd
~ ) In dloxanQ containing O.S17 pph ~OH; no poly~eri~ation.
s~n~l~ PCr/~S91/~632,
--131-- `:
~ ~' ~' . _ _ V J
TABLE 20BB. REII~TED ~ T POL ~ ~ IZATIONS OF
L~CTIDE RESInLTS
E Re8idual GPC x 103 ~ ~ Poly~erizate
No Percent ~ M~ ~ Appearance
5 93B 0 254 454 7171~79 ~i~ht yollow,
crystallinu, opaque
94B 0 97 187 3221.94 Llght y~llow,
tran~pa~ant
9~8 0.35 95 195 3252.05 Partially opaque
crystallinQ~ partial
transparent
96B 17.5~a) 5 7 9 1.47 Whita, cry8talline,
7.1; 7.7 7 8 10 1.25 opaque
97B 4.6 116 218 3561.88 Light yQllow,
transparent
1~ 98B 47.7 ~ Nhite, crystalline
(monomer), opaque
99B 65.3 -- -- ---- Nhite, cry8talline
(monomer), opaque
100B 79.6 -- -- ---- White, crystalline
(monomer), opaque
101B 1.4 116 214 3401.84 Yellow, transparent
1023 1.9 80 1;0 2351.87 Orange, cryqtalline,
opaque
15 103B 5.4('~1643776572.3 Hard, colorless
2.5; 1.9U)307527308 1.72
104B 43.3 30 35 411.17 Hard, crystalline,
opaque
105B 8.6; 9.6219 343504 1.57 Hard, cryntalline,
opaque
1063 100 -- -- -- -- ~11 crystalline
monomer
'C,3 '.0 1~ 35 351.38 White, c-ystalline,
o?aGuc
~ilm~ 5 `5l.S~ Some tran~parency a~
e-.-es
~0 1'`-5 ~0. ~' 5_ee:e- :hen ',0'`^,000 White, c-ys:al'ine,
opacue
13-3 _- ~c~, ~-e~t-- -h._-. `,033,C00 t;hite, c-ys~alline,
~?2J e
3 ~
-emove ~ol~en_.
_~ '~' ~-a~sp2rc.. t, ~ . b~
~ nc obta:ns ;~.1 ?ercen_, ve-y hich molec~ r weicht.
-132-
Compositions having n equal to an integer between
450 and 10,000 have a good balance between strength and
melt processability and are preferred. If a monomer is
selected as a plasticizer a unique composition may be
obtained by adding monomer that is stereochemically
different from that used to obtain the polylactide in the
composition. Similarly, addition of oliqomer
stereochemically different from that which may be obtained
during polymerization of the polymer gives a unique
product. As tau~ht herein the products are colorless in
the absence of coloring agents. Colo~ bodies can be
e~cluded by performing the polymeriza~ion in an in~rt
at~osphorQ and at roaction tempSraturQS preferably at 140
C or below and by appropriate choice of plastici2er in the
composition as described above. Durin~ melt processing, a
sufficient amount of plasticizer is intimately mixed to
~revent discoloration and degradation o~ molecular weight.
Various combinations of the above treatments can be
emplo~ed to obtain the optimum characteristics as those
~o skillPd in the art will appreciate, once knowing the
teachings of the invention.
As can be noted in section A. First General
E~bodiment above, a higher amount of plasticizer can have
significant effect. In the present application, lower
amounts of plasticizer are preferred to impart stiffness.
Plasticizer present in an amount of between about 0.1 and
about 10 weight percent is prererred. The plasticizer can
-emo~e molding strainC~ lubriccte, maintain a lower
processing tempera,ure, ~ain~2in a lower ~elt ~iscosi~y,
? '~ 2r~in~ c-.~ ~e~
5ra~a_ion _i_ e ~ ma_ c^-.?2si`ien -^ntains ?'2sti~i~e- in
;_ d~?e~c. _~ ?ol~ c~i.icr~ c- ~-.
__?_ _~ _e__~
_~e..~ r~--s ~he e-'~
~ : _ _ _ .. _ _ _ ~. _ _ _ _ _ _ _ _ _ _, _ _ _ _ _ _ . . _ _ _
~0Y',U~:13
--133--
3 ~)
derivatives of lactic acid, may also be ? 1ded. Unique
compositions may be obtained by addition of monomer
different from those selected for the polymers in the
composition or oligomers different from those o~tained
during t~e polymerization.
Contemplated equivalents of the compositions of
the invention are those that contain minor amounts o~
other materials. The compositions produced in accordance
with the present invention can be modified, if desired, by
the addition of a cross-lin~ing agent, nucleating agent,
~the~ plastici~ers, a coloring a~ent, a filler and the
li~e. Further treatments such as biaxial orientation and
heat treatment provide for a useful film that is a
replacement for polystyrene.
After treatment there is obtained a biaxially
oriented and annealed environmentally decomposable
polylactide film or sheet suitable for use as a substitute
for bia~ially oriented c~ystal polystyrene film or sheet
comprising, a film or sheet of a copolymer of the formula
I, where n is between about 450 and about 10,000 prepared
from about 85 and 95 weiqht percent D-lactide or L-lactide
and between about 5 and about 15 weight percent D,L-
lactide, said film having intimately dispersed therein the
residue of a modifier selected from the group consisting
of lactic acid, D-lactide, L-lactide, D,L-lactide,
oligomers of said acid and said lac~ides, and mixtures
thereol, said o_iented and annealed film having a tensile
streng~h in e~cess of ,.500 a t~ngent modulus in e~cess of
~50,000, a ~ below a~out 60 C and the capacity of ~eing
ens'c~ 2 ~ ~ ~c' ;;r~ ~ C; C ` c- - ~
_ .
~he composi~io.s he~ein c~n __ processed ~y mei_
-?~ c ~_ c.~ cc~ CisDosc _ ' ~ c~ 2 ~ r~ -s,
se - vi..g _-ay5, 5y_ ince_, ~cidic21 .rays, ~ac~aging _i~ms
~~ 2 --i~ ?~ c-_ c-;
) n~./n~ sl/nfi3~-
--13 1--
can have the characteristics of the usual plastics (eg.
polystyrene) and therefore substitute for them yet degrade
in the environment. The amount of plasticizer serves not
only as a processing aid, but also governs the initial
physical properties. In addition, the amount of
plasticizer governs the environmental degradation rate.
The compositions are especially useful for articles having
only a one time use or a short life span in use before
disposal.
Those s~illed in the art ~ill now recogni~e that
there are contemplated equivalents for minor amounts of
the polymeri2ed lactide and ~onomeric lact~de~ These
include glycolide, caprolactone, valerolactone, and other
cyclic esters a~ ~ono~ers, and the sa~e andlor open chain
aliphatic esters as plasticizers~
C. Third General ~mbodiment
The present invention discloses the blending of
poly(lactic acid) (PLA) with polystyrene (Ps),
polyethylene (PE), polyethylene terephthalate (PET), and
polypropylene (PP)~ ~he invention discloses that
poly(lactic acid) is melt compati~le with these
conventional thermoplastics and the effect on their
physical properties~ Since both lactic acid and lactide
can achieve the same repeating unit, the general term
~5 poly(lactic acid) as used herein refers to polvmers having
the repeating unit o~ the fo~mula I ~ thout any limitation
as to how the ?olymer was made (e.g. from lactides, lactic
a~ , or ol~ e~-s), an~ ho~_ re'æ-ence 'o 'he ~e~-ee
t`^.`~ 2~e`~ c~ s~ ic~
en-v-iron~en_a 1~ Ge ~a~iable c-m?osi~i~n,
c~ ose~ e~~ e -_ l~_s_ ~
_~c_.~
_ ~ _,h,~ - ~ C~ _.__ .~ _e _~:. -: - --
~ ?~ c.~ c - ~`en~s ; =~
~V9'i~l~ i'(~il~9]/~)(.3~~
-'35-
i L 1~ ~
small domain sizes the physical deterioration will destroy
the original formed produc'. The compositions herein
provide environmentally acceptable materials because their
physical deterioration and degradation is much more rapid
than conventional nondegradable plastics. Further, since
a significant portion of the composition can be
poly(lactic acid), and/or a lactic acid derived lactide or
oligomer only a small portion of more slowly degrading
ther~oplastic residue will remain (e.g. polystyrene).
This residue will have a high surface area and is e~pect~d
to deco~pose ~as~ur t~an a ~ul~ formed ~roduct.
D-lactide is a dilactone, or cyclic dimer, of D-
lactic acid. Si~ilarly, L-lactide is a cyclic dimer of L-
lactic acid. Meso D,L-lac~ide is a cyclic dimer o~ D- and
L-lactic acid. Racemic D,L-lactide comprises a 50/50
mixture of D-, and L-lactide. When used alone herein, the
term "D,L-lactide" is intended to include meso D,L-lactide
or racemic D,L-lactide. Poly(lactic acid) may be prepared
from one or more of the above.
Exam~le lC
Polystyrene was solvent blended with poly(lactic
acid~ and solvent cast from CH2C12 to determine optimum
compatibility. The solvent cast ~ilms were translucent
and apparently "noncheesy". A sample, appears homogeneous
2~ to the naked eye and resists folding and handling without
shredding apar_. o~tic2l ~icrosco?y at 310X reveals
~eteroaene.ous dc ains o~ 3 ~ic_-ns cnd less. ~he ~'end is
ap~arentlv ve-v com?ati~le. ~t e~hi~its ro chanGe over 2
~0 d~es its p?.vsic~ ?er~ies s~w evi~er.ce o_ de~rad2ticn.
_ _ _ _ _ _
~ct`_~ c ` -?/?T ~ 5~/0 ~ . c~n~
~'O ~ r~
-136-
Examples 3C-5C
Melt blends were prepared of poly(lactic aci~)
with polystyrene. Both a high molecular weight
polystyrene (Piccolastic, E-125, Hercules) and a low
molecular weight polystyrene (Piccolastic, D-100) were
investigated. Also used was a general purpose
polystyrsne, (~untsman polystyrene 208), a crystal
polystyrene. These were mixed in a Brabender at ~25 F at
different ratios with poly(lactic acid).
The polys~yrene/poly(lactic acid~ ratios use~
were lO0~0 for the control, and 9ollO, and 75/25 for the
Huntsman 208, ~eneral purpose polystyrene.
~am~le~ 6C-/C
Two types of polyethylene terephthalate were
used. (Goodyear's "Clearstuff" and Eastman's XodapaX TN-
0148). These were dried overnight at 90 C and melt
blended at 52S F in a Brabender with poly(lactic acid) for
only a few minutes. The poly(lactic acid) reduced the
melt ~iscosity.
Exam31es ~C-16C
The controls and blends for polypropylene,
general purpose polystyrene, and polyetllylene
terephthalate (Eastman's) from Examples 2C-7C were ground
in an Abbey s-inder and compr-ssion molded into
approximately 5 mil films. Polypropylene-poly(lactic
~_~d) _~ l~e ~:e-e ~ e~ ` ~b~ 0~ ;; ?Ol~st~Qr.e-
poly(lactic acid~ ~12s were o~ained 2t 250-~oo .~;
~ ? ~ t-? - - ? ~ .. . ` ~ 2C ~ ..... s ~ `_. - -?
~ _s ~e~ ? ~Q~-__ c ~~e
_ _ _ _ _ ~ _ _ c ~ _ ~
~ . _ c _
`~e2~e~ ;e~-e~ -c~ e-~ lu~` 5~ 'C`` ~
~ _ __............. sh.~ _ _ 5 ~ ~ _ _ ~ _ .. . _ .. 2
_ ~ _ _ _ _ _ _ _ _ _ _ _ ~ ~ _ ~ _ ~ ~ ~ _ ._ _ _ _ _ _ _ _ _ ~ ~ _ . . . _ _ . _ _ _ _ _ _ _ ~
91/063'-
-137-
~ v._ _~iJ
Exam~les 17C-19C
Three samples of 100 percent poly(lactic acid)
using poly (D,L-lactic acid) were prepared as above but
with film thicknesses of 10-15 mil. Tests were performed
as in Examples 20C-27C below except that the second sample
was tested after 82 hours of exposure to 50 percent
relative humidity at 72 F~
E~am~les 20c-27C
High density polyethylene, HDPE, ~'O~g~0 gj~cc) ~as
mel~ blended with poly(lactic acid) in the Brab~nder
Plasticorder at 151 C for 10 minutes. Blend ratios of
hig~h-density polyethylene/poly~lactic acid) of 1~0/0 for
~he ~ontrols, 90~10, 80/20, and 50fS0 were used. Two
samples of eac~ were prepared. The blends were ground in
an Abbey grinder and compression molded into 10-15 mil
films. The films were tested in an Atlas Weather-O-Meter
set for 51 minutes of carbon arc light and 9 minutes of
water spray. Temperature was varied from ambient to 140
F. Tensile strengths, elongation to yield tests and
classification of the tensile failure were performed for
the samples as shown in Table 2c.
Examples 28C-33c
Low density polyethylene, LDPE, (0.917 g/cc) was
melt blended with poly(lactic acià) in the Brabender
Plasticorder at 151 C for 10 2inutes. Blend ratios of low
densi ~ ~ol~eth~lene/pol~(12c~ic acid) o_ lOOfO f~- the
co~.t~ols 90~10 2nd =Ot50 were used. ~o sam?les of each
~ e c2se ~ 2.~?1~ C~ es-~'_s 2-e ~o;n. ~
_ ~ ?~
wl_h a mec!lnic~' s_i--~ - a-.d ..~. ~_o~,~en _nle~ an~.- cu.' e~,
(~ /n ~ '1 ' rc r/~sslt()fi3~-
-13&-
lactide (both Boehringer and Ingelheim, grade S). The
contents of the flask were heated to 110 C under a
nitrogen sweep to melt the lactides and 20.1 g of
polystyrene (Amoco R3, melt index 3.5 gJ10 min.) was
added. The polystyrene swelled highly and partially
dissolved while stirring overnight and advancing the heat
to 185 C. The temperature was decreased to 141 C and 0.2
ml of anhydrouc stannous octoate solution (0.2 mllml of
toluene) was added. The stirrer was turned off and the
lactides allowed to polymeri~e at 141 C over 3 days time.
The highly swollen, polystyrene floated to the top after
turning off the stirrer. The lower, polylactida phase was
cooled and examinQd by differential scanning calorimetry
(D~C). The sample has 2 lo~ Ts, approximately 35 C, and
~5 is otherwise lac~ing in apparent temperature transitions.
Compression-molded films are clear, colorless, and very
pliable. These ~-esults indicate that the polystyrene
thorou~hly interrupts crystallinity formation under these
conditions.
Example 35c
Poly(lactic acid) was mill roll blended with
crystal polystyrene. Th_ blend revealed excellent
compatibility of polystyrene dispers~d in poly(lactic
acid). Thus 5 weight percent of polystyrene was dispersed
in a 90/10 ratio of L-lracemic D,L-lactide copolymer in a
two roll mill at 170 C. The material became hazy and
exhibited considerable crvstallinity by therm~l analysis.
This example demons~r_~es ~he~ under 'hese c~n~ilicns
-e?.~ si`~ r~ e~ 5 _r~ i?. ?~ly ~ t~ ~
~0 --ci~`. A t~e me_ ar.al~ysis ^f the ma~erial, see Ficu~re 17,
_evea's ~ he ~__e~i~Y emains _~ys_ll~ne even ~!he-
~ e~ c~
?~l~t3~ c ~___~ `_e~e-` t~ .,;r~ ~o~m~
n~ e~G~ e ~?'~ C~ n c_~ c~ ~n; ~r~e~
~;V9'/()J~13 I'C~i~j(3l/l)o~~
-139-
in the mixture depending on the mixin~ or blending
technique used.
Brabender melt-blends of all types exhibited
small heterogeneous particle si~es of 10 microns or less.
The tensile strengths were evaluated before, and after,
simulated weathering. After 1248 hours (52 days) in the
Atlas Weather-O-Meter all of the polypropylene samples
were whitened, extremely brittle and were not able to be
tQsted~ The polypropylene samples were retested at
shorter intervals as shown in Table lC~ ~t approximately
3QO hours of weathering in the Atlas Weather-O-Meter, the
samples exhibited significant environmental degradation~
The polystyrene blends with poly(lactic acid)
exhibited environmental degradation that was apparent
after 300 hours of simulated weathering. The polyethylene
terephthalate blends were also visibly environmentally
degraded in approximately 300 hours.
~o ~/n~lt Pc~ ssl/n~3~-
-140-
~ 3
TABLE lC. TENSILE STRENGTH OF FILMS BEFORE, AND AFTER
ACCELE~ATED ~EATHERIN~a~
Tensile Stren~th~b)/% Elongation
and Materlal Before After, Hours
310 ~00
_ _
100/0 PP(C~/PLA 16~S/61~0 585/1~6 4g4/1~7
90/10, PP/PLA 1568/51~0 954/3~2 34~
~5/25, ~P~PL~ 112~ 0~70/l.i 254/1.0
100/0 PS~d~/PLA 3200/2.0 1066Jl.0 --
90/10, PS/PLA 2350/2.0 582Jl.0 --
75/25, PS/P~A 149~484/1~0 --
100/0 PET(e)/PL~ 3036/--3509J3~0 --
90/10, PET/PL~ 2147/--1378~3~0 --
75J25, PET/PL~ 2743/--2041/3~0 --
.
(~ Weather-o-meter, cycle of 102 minutes of sunshine, 18
minutes of rain
(b~ o~ 05 in~/min~, on the Instron
(C) Hercules polypropylene 825
d) Huntsman 208
~e) Tennessee Eastman, ~odapa~ ~ 01~8
The poly(lactic acid), high density polyethylene,
low density polyethylene, and their blends were evaluated
for physical strength, before, and after simulated
weathering and the results are shown in Table 2C.
W~ 9'/04 113 , ~'Cr/l~S91/06327
~ ~` V .
I ~
~ l ~ ~ ~ ~ ~ ~ ~ Q~
I ~ ~ ,~ .~ .,, .,~ ~ ,~
I ~ ~ 5
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I
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~ I ~ ~ ~ r ,~ ~ S
~ X ¦ C o ~ O
I t2
I ~ ~ t, ~ ~D
~) CO O ,~ ~ O O O O O O O ~ ~ In ~ X
` I l .,~ ~rl ~ I` rl U) ~ O 00 ~ CD L'~ Ul rl ~ 0
C ~ 1~ o ~ ,~ Lr~ ~ C
~D L'~ o o ~ O O t~ d
¦u~ E~ C 3 ~ ~
~ I . -p ~
@P I u~ u
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~: I ~ ~ _ ,.7 r~ L'l ~q .C Ll E~ O ~r a~
~ I o C~ ~ r~ O r~ O ~ O r ~ ~
O ~ I I ~1 --o 3 ~ ~ ~ ~ ~ t~ ` O
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C U~ C ~
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~à l ~ o~ ~ Ll 11 L ~5
,3 ~ I ~ O ~ E Cl h E C ~ C
~ ~ ¦ ~ h -- -- ~ N N L'~ Ir) -i C O ~ h -~
_ _ ¦ ~ C --' O O O ~ --~ C~ U~ L'~ ~ tS h C) X ~ X :~
~ I ~ --~ C U h E U O
" a I -~ E
.C l ~ . C ~ U
I ~ _ ~ I ~';C5 u~ ~ O I C
I _ ~ tn C~ I N C
~:: ~ ~i C IC ~ C C~ ~: C ~:: .C C~ ~ C h 1~ ~ ~
._ ~ ~ I ~ ~
i _ ~ -- ~ E ~ C ~ Cl S
~- ~ ~ ~ ~ ~ r; ~ ~ C:~ ~ ~ ~ O -I
O O O O 0 2. ? .'~ ~ O ~ ~I Cl --I O ~1 d
~ o o o o o ~ 2 ~ c~
_ ~ _ = _ ~ ~_~
_ _ _ _ _ _ _
~ , =~
~O r~'~O~I~ 142 rC~ C91/()63'-
i.. ~.` .i .i l ~ ~
O ~ L
-~ 3 ~
O Ul_l ~ ~ ~ Q)
C
a a c~ ~
D~ _ S~ VJ
a c~ o ~ .
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~ ~ ~ U~
^ ~, ~ O
~O ~ O O O 0,~ ~ X
C V~ ~ ~
~ ~ C CJ ~ O s~ C
_-~ O) ~ P ~ ~3
t~ 3 _ ~ 3 _~
~ ~ ~ ~ U~ o
C C u 1~') m u~ D ~.1 C t:~
O ~ O ~ O ~ o ~ ~ C~
O ~ I ~ ,~ ~ o
U~ ~ S~ u~ ~ O ~ 0 3
~ a ~, ~ O ~
.
Z; _ U~ C ~`
~ ~ ~ 0 ~ O O O C o o ~ n C &
--~ ~ ,~ ~ ~ ~ ~ ~
C ~o --~ C O h C ~_~
C~ E
~~ I ~ O ~:
~ U U
_ O '3 Ul h C ~
1:1 I ~s ~ ~ ~ C 7 --I 3 1~ C
C~ C h I 'E ~ ~ ~;
~ lo o ~ ~ o~r r~/
C ~
~,og-/0~l3 PCT/~S9t/0632
-143-
~ 3~
The poly(lactic acid) and its blends were much
more environmentally degradable than the pure low density
or high density polyethylene. The high density
polyethylene samples degraded substantially without weight
loss while the high density polyethylene-poly(lactic acid)
blends exhibited weight loss, particularly where micros-
copy revealed poly(lactic acid) was exposed at the surface
of the films~ The high density polyethylene degraded by
exposure to acti~ic light as shown by microscopy~
With all of the samples, increasing the
percentage of poly(l~ctio aci~) decreased the tensile
strength before, and after, simulated weathering. The
incorporation of poly(lactic acid) introduced a faste-
de~radation in blends of polypropylene, polystyrene,
polyethylene terephthalate, and high and low density
polyethylene. Presumably, the actinic liyht as well as
hydrolysis of the polyesters degrades the polymer. The
small size of the spherical, microhetero~eneous, domains
of the blend are undoubtedly poly(lactic acid), which is
mostly buriec Therefore, poly(lactic acid) hydrolysis is
slow. Faster degradation via hydrolysis can be achieved
by controlling the location of the poly(lactic acid).
This, in turn, is related to the rheology of the blend
during melt blendin~. The small size of the dispersed,
heterogeneous domains indicates good compatibility of the
mixed polymers~
In a simulated landfill, where light is excluded,
the controls and ~he blends show much slower rates of
degradation~ With hydrolysis, alone, the poly(lactic
acid) samples slowly ~hiten, while tne biends are cualit2-
~ively unchan~ed for the ti~e ?eriod tested~
~ onverseiy, additio-. o~ rino- a~oun~s o
nondes__~able =..e~o?_-s=i_s ~ ?ol~ ci_) to ~^--
_o~patible b'ends, usiny, _o- e~2~ple, ?olypropylene,
^'~ ?-lys~yrene, ?oly--thy'ene `2re?h'h~12te a..d hish ~n* lo-~;
d2nsity -o!yethyle-.e ~i'! ~e_~-d ~he deg-2d~tion rate o.-
~13 ~CT'~S~
-144-
the poly(lactic acid). A preferred compositional range is
from 80-99 weight percent poly(lactic acid).
A general description of the environmentally
degradable composition comprises blends of a physical
mixture of poly(lactic acid) (polylactide), and a polymer
selected from the group consisting of a poly(ethylene
terephthalate), a polymer or copolymer of styrene,
ethylene, propylene, vinyl chloride, vinyl acetate, alkyl
methacrylate, al~yl acrylate, and phys~cal mixtures
th~reo~. Other possible compositional ~lends are listed
below in the discussion of process embodiments of the
invention. While the level of plasticizer can vary over
wide ranges depending on the amount of poly(lactic acid~
p.esent and the type of coblended polymer, the prefe~red
lS amount for a stiff material is generally about 0.1 to
about 10 weight per cent.
The blends preferably use a physical mixture of
poly(lactic acid) of the formula I: where n is an inteqer
between 75 and 10,000; and a polymer selected from the
group consisting of polystyrene, polyethylene,
poly(ethylene terephthalate), and polypropylene and other
compositions further discussed below. The composition of
poly(lactic acid) in the composition may vary over wide
limits such as about 1/99 to about 99l1. A preferred
composition is that where the poly(lactic acid) comprises
to 50 weight percent of the composition. Another
preferred composition has a poly(lactic acid) content of
about 10 to 20 weight percent, and 2nother about 80 to oa.
The ratio will depend on desired characteristics.
~0 The ?ol~ers ~n~ copolymers seleczed f_om the
group above, deeme~ z~e Pdded polymer, c2n be used alone
or in com~inazion~ The rou? is not restric_ed tO t~ose
_` ~2- ~0~'2 ~-~`-.^e oze_~ ?~ ~e- ' ?es ~-e nc_e~ 2S
com?atible ~ilh ?01~('2c-ic aclc). These inclune ~he
polymers and copolyme-s ^om?rised from ,he group of
ethylene, p~opylene, _yrene, vir!i ~hl^.ice, ;in~l
_^~z__--~ h~c-~ e~, c~ r~`-_
~0~ 3 PCTI~`S91/063'
-145-
should be understood that the term copolymers as used
herein includes polymers made from mixtures of the
monomers in the listed group. Physical mixtures of the
polymers and copolymers of the above group are likewise
useful in the invention.
A first embodiment of the process for producing
the composition includes providing a poly~lactic acid~;
selecting a polymer from the group consi~ting of a
poly(ethylene terephthalate), a polymer or copolymer of
styrene, ethylene, propylene, vinyl chloride, ~rinyl
acetate, al~yl me~hac~ylate, alXyl acrylate, and physical
mixtures thereof; and blending the polymers. The blending
may be by melt blending on a mill roll or by compounding
in an extruder or by other mechanical means. The
polytlactic acid) provided preferably has the formula I
and contains plasticizers as discussed herein.
A second embodiment of the process for producing
the composition of the invention includes providing a
lactide selected from the group consisting of D-lactide,
L-lactide, meso D,L-lactide, racemic D,L-lactide, and
mixtures thereof; selecting a polymer from the group
consisting of the polymers or copolymers of styrene,
ethylene, ethylene terephthalate, propylene, vinyl
chloride, vinyl acetate, alkyl methacrylate, alkyl
acrylate, and physical mixtures thereof. The selected
lactide and polymer are mixed and heated to melt the
lactide and at leas~ partiall~ dissolve the pol~me
Finally, the lactide, is at least partially polymerized to
obtain a blend of polylactide, unpolymeri-ed lactide
~0 monomer ~nd ~he selec-ed ?ol~me-. The pol~eri-a~ion is
~e e---blv ~on~-olle~ 20nito_in~ the 2moun~ of lGctide
em2i-.in_ _n~ s~p-i-.~ _he ?ol~.eri--li^.. e~ the desired
~ le~i--.. .~d-`i__o._` ~~~_~e- m_..cme- ~- olhe-
: ~ ?~ ~crL-~~ _- :-c~c
~ c._-s -- l~_~i-e. n- mi~:t_~es the_ec-, ~he-e
~ r ~
'~;0 9'/(~;1 ` rc~r~ ;91/()6'.''-
--14 6--
~ v ' 1 ~ 3
an integer: 2 < m < 75, where the oligomers preferably
have a number average molecular weight below about 5,400
and most preferably below about 720; as well as one or
more derivativas of an oligomer of lactic acid defined by
the formula III: where R = H, alkyl, aryl, alkylaryl or
acetyl, and R is saturated,
where R' ~ H, alkyl, aryl, alkylaryl or acetyl, and R' is
saturated,
where R and R' cannot both be H,
and where q is an integer: 2 < q S 75, can be added to
obtain desired characteristics as taught in parts A and B
abov~, Additionally, the various types of plasticizers
discussed herein and in the other general embodiments
provide for: ~a~ more effective compatibili2ation of the
melt blend components; (b) improved processing
characteristics during the blending and processing steps;
and Ic) control and regulate the sensitivity and
degradation of the polymer by moisture.
It will be obvious to those s~illed in the art
that the proportions of poly(lactic acid) and the added
polymer can vary widely depending on their mutual
solubilities. Solubilities, in turn, vary with the
thoroughness of mixing and the mixing temperature. While
placing both the poly(lactic acid) and the added polymer
into a mutual solvent solution will obtain intimacy, the
use of solvent is impractical for many commercial
processes. Physical mixing, such as melt blending on a
~ill--cll c- extruder is rore prac` ic21, but must be
controlled ~o achieve 2n intimate dispersion, that is,
~o h~ h she~- is ~equired to achieve the desired intimacy
rven ~i~h i-._irate ~ ing -`f~eren' ?o~ers ~y not ~e
_or~?2ti~1e, ~ c, ~~e~ may s_il' sep~_ate i~._o
,~Q_~_~,_,~5 _ _,= ` __, ~. ~_ e2:-r~?le ! 10
~ C =` c-_n 5` ~e~ 0_ la~~e~~ ~h is - s~:~ 5 i~ cnee~'
~i~:_ure, cr _ ~l end ~ i _h p^^- prope-~ies. Wha 5
\Vo 9~ ssl/nO~-
-147-
~ ,t, ~ 8~
compatible with a wide variety of other polymers,
including both polar and nonpolar polymers.
The temperature of the melt blending of the
poly(lactic acid) with other polymers may be varied to
adjust the proportions of the poly(lactic acid) with one,
or more, added polymers. At lower temperatures, the
solubilities may not be adequate, while too high a
te~perature will cause decompos~tion of thQ mixture. A
general temperature range is 100-220 C, and the preferred
range is 1~0-180 C. Egually significant is the melt
viscositie~ of the differe~ polymer co~ponents~ With
in~reasing molecular weight, the viscosities increase
sharply. By controllin~ the proportions of the
poly(lactic acid) and the added polymer, or polymers, the
temperature, the mixing type and time, and the molecular
weight, a wide range of mixtures can be obtained. Thus,
for example, the poly(lactic acid) can be dispersed into
the added polymer, or polymers, or vice versa, and the
size and geometry of the dispersed phase varied greatly,
ranging from discrete spheres to strands of different
diameters or lengths. This results in a wide latitude of
physical properties and degradation times in the
environment. The weiqht percent ratio of poly(lactic
acid) to the selected polymer can be between 99:1 to 1:99.
Where the lactide monomer is used to dissolve the
added polymer and the lactide is subsequently polymerized,
the temperature of mixing and polymerizing must be
balanced between t~e mu.ual solubilities and the
re~c~ivity of _he lactide~ her temperatures generally
3~ ~~oduce lower mo'ec~ c- ei:-~ poli-~12c_i_ 2C`C). ~:
~u-~her mbodi~e?.^ ^- ~he i~ ion is ~o mix 2_ one
_e~pe-^tu-e c-.~ ?^~e~i^e ~_ 2no' ~e- te~pe-_tu-c -~
_S C~ S~ SS~ 2~ e~
'. r~ C C `~ â ~ C ~ ~ _ ?~ C ~ S S ê _ '~
'c__-c__ion ir.-^ ~se_~_l -_ic' e5 ^ m n'_ cC ~'~e .~'' n~ -
~'O 9~/() ' I '' rr/~ /nfi3~-
--14 8--
h
eating utensils, trays, plate~, drinking cups, single
serving trays, syringes, medical trays, packaging films
and the like. The compositions are useful in that they
can have the characteristics of the usual plastics and
therefore substitute for them yet degrade in the
environment. The compositions are especially useful for
articles having only a one time use or a short life span
in use before disposal.
Within the scope of the invention is included
thos~ impact modifiers which are elastomaric discrete,
intimately bound and t~e polylactic (or
polylactide)/i~pact ~odifie ~lend is hydrophobic,
nonporous, nonswellable in water, and hydrolyzes at the
same rate or slower than the poly(lactic acid) (or
polylactide) alone; and melt compatible with poly(lactic
acid). By "melt compatible", it is meant all those
polymers which can be intimately mixed with poly(lactic
acid) as discussed in section c~ Third General
Embodiment. The mix would result in a subs~antially
homogeneous blend. All of the examples herein exhibit
these properties. Since both lactic acid and lactide can
achieve the same repeating unit, the general term
poly(lactic acid) as used herein refers to polymers having
the repeating unit of the formula I without any limitation
as to how the polymer was made (e.g. from lactides, lactic
acid, c- oligo~ers), ~rd without reference to the degree
of polymerization or level of plasticization.
~ e en~iron~e-._~ cegr2da~1e CO~?Osilions
_~ ~is_lcse~ herei-. ~re ~~ le_s~ p~ lly deg-~dc?~le~ ~a_
is _~e ?oly' ~-~ic ~^i^`` --~~ion ^f _he ^om?osi=i^~ ;ill
~ _ ~ ~ `~ 3 ~. 5 _ ~ ^ c ?~ _ C ~ `_ ~ ~ _ ~ ` 5 ` _ _ ` ~ ~ ~ ~ r~o-c~i~.
_ ~he '~`~enc~ exc=~ h~
.?~s~_ic-.~ _~e ~ o~r~ - ~ e~,~r
_ ~ ~ _ _ _ ~, _ _ ~ _ _ . . _ _ . _ _ _ . . _ ~ . ~ _ _ _ _ _ _ ~ _ _ _ _ _ _ _ _ _ _ _ _ ~ _ _ , .. _ _. _ _ _
WO9~/0~13 PCT/~;Sgl/n6327
--1~ 9--
`J u
the original formed product. The compositions herein
provide environmentally acceptable materials because their
physical deterioration and degradation is much more rapid
than conventional nondegradable plastics. Further, since
a major portion of the composition will be poly(lactic
acid), and/or a lactic acid derived lactide or oligomer
only a small portion of more slowly degrading elastomer
residue will remain ~e.g. segmented polyester~. This
residue will have a high surface area and is expected to
decompose faster than a bulk formed product~
The exa~ples below ~how the blending of
poly(lactic acid) (PLA) with a Hytrel~, a se~mented
polyester which is a block copolymer of h2rd crystalline
segments of poly~butylene terephthalate) and soft long-
chain segments of poly(ether glycol). It is shown thatpoly(lactic acid) is 3elt compatible with this elastomer
and the effect on its physical properties.
D-lactide is a dilactide, or cyclic dimer, of D-
lactic acid. Similarly, L-lactide is a cyclic dimer of L-
lactic acid. Meso D,L-lactide is a cyclic dimer of D- and
L-lactic acid. Racemic D,L-lactide comprises a 50J50
mixture of D-, and L-lactide. When used alone herein, the
term "D,L-lactide" is intended to include meso D,L-lactide
or racemic L ~-lactide. Poly(lactic acid) may be prepared
from one or more of the above~
Exam~le lD
A poiylactide copolymer ~ithout Hytre_'Y seqmented
~c'veste~ ~'2S ~ e?2re` ~sir.a the ?ro-edure ~~_m E~m?le 1
o~` sec_icn B~ Second Gene-~' ~mbodi~en~ ~nd tes~ed .o_
T ~ ?zc- ~ _e.~ ~s___s __~ c~ r _ _
C~ .e~ c~?~-~s~ ic ~ e C_c~ G~ne-_'
C -;--_c.C _ ' G~ ~_3 u--` ` Z^--iC~ .
~ o 9'~n~1 ~ Pc r/~ ~9 l /n~3~-
--150--
,~. ~ ., ` ' 1 `~
Exam~le 2D
Into a 3-neck, 250 ml, round-bottom flask is
weighed 10.96 g of D,L-lactide, 108.B6 g of L-lactide, and
5.27 g of Hytrel~ 4056 segmented polyester (Du Pont, a
thermoplastic elastomer). Hytrel~ 4056 segmented
polyester is a polyester elastomer with a Shore D
durometer, low flexural modulus, high melt viscosity, a
melt index of 7, a sp~ gr. of 1.17, a m.p. 334 F, a vicat
softeninq temperature of 234 F, and an extrusion
temperature o~ 340-~00 F. The flas~ is fitted with a
mechanical stirrer and a nitrogen inlet and outlet. The
contents are heated by means of an oil bat~. T~e Hytrel~
segmented polyester dissolves in the molten lactides at
170 C~ A catalyst solution is prepared by dissolvinq 10
ml of stannous octoate in 60 ml of toluene and distilling
10 ml into the toluene. A 100 microliter portion of the
catalyst solution is injected into the solution of lactide
and Hytrel~ segmented polyester. The mixture is stirred
under nitrogen at 155 C for approximately 64 hours.
The viscosity increases sharply and the mixture
turns cloudy. The product is tough and opaque. Films of
8-9 mil thic~ness were compression molded at 155 C and the
tensile properties measured, as shown in Table D.
Slabs, 1/8 inch thick, were compression molded
and their Izod impact strength measured using a 2 pound
pendulum. The ~esults are recorded in Table D where the
data are compared to a similar polylactide copolymer of
~x2m~1e lD witho~t ~ytrel~ se~mented pol~ester, and to
data fo- so-c~lled meci~m-impact polvstyrene, Exam?le 7D.
e 'D
EC5.~ ~ c_ E-~2c_i-e ~ cemic 3,L-
~rel~ se~2en-e~ ?olyes.er. '--_ l_c_i_c co~el j~C~ i S
~ ~ c_~ _~. _~ _ _c?__~=e ~ T - - i _ _ _ _ 0 ~
0~l3 ~CT/~`S91/0637,
-151-
catalyst. The polymer ,poly(L-lactic acid~, is white,
crystalline, and crazes easily when strucX.
An electrically-heated, 2-roll mill is heated to
375 F, then 8.4 g of Hytrel~ segmented polyester and 19.2
g of poly(L-lactic acid) are banded on the roll. To this
was added 172.4 of the lactide copoly~er. The mixture
blends easily and is removed from the rolls, ~olded, and
tested as in Example 2D. The data are recorded in Table
D.
E~2~ D
The lactide copolymer of Example 3D~ 80 g, the
poly(L-lactic acid) of E~ample 3D, 10 g, and 10 q of
Hyt.el~ 4056 ses3ented polyeste- are 2-roll, mill-blended
as described previously in Example 3D. The blend was
tested as before and the data are recorded in Table D.
Exam~le 5D
100 g of the blend of Example 3D was further
blended with 20 ~ of Hytrel~ 4056 segmented polyester.
The mixture easily mixed on the roll and was apparently
quite compatible. The physical properties were measured
as described previously and recorded in Table D.
Exam~les 6D and 7D
Typical crystal polystyrene and medium-im?act
polystyrene we-e tested and used for comparative controls.
The above results clearly indicate .hat
polyl2ctides can be impact-modified~ The blends provided
signi__c2n~1y ~` ghe~ 0 ` `--~_- 5__en5=:.s ~r_el _r.e
c-~ l ?~l~s-~~e~.~ co~ l c~- c !_ C ~ - C-
e-~ 21er.t i.~?~ ~~e~ s ---?~-e~ -~ D~ ?-C~
~~ ~ ~ ----~^ _ C=-- ~_~ r--~
moài~ic-
~o 9~ rc r/~s1/n63~-
-152-
Since polylactides have been shown to be blend-
compatible with numerous other compounds and thermoplas-
tics in section C. Third General ~mbodiment, the process
of impact-modifying polylactides is generic to mixtures of
polylactides and elastomers that are blend-compatible.
Also, those skilled in the art will recognize that the
data of Table D will improve as the blends are injection-
molded, as opposed to compression-molded, since the former
often induces orientation of the specimens and,
consequently, a profound improvement in impact strength~
~? "'/()~13 PCI/I~S91/063',
--153--
O ~ _~ _ ~ U~ ,
~7 o Q o o O
~ o
Q
~ ~D~O
~ ~ ~ ~ ~ I~ ~
Q ~ ~ ~:
~ ,o~
a ~ ~ ,, r~ , I , ~ N
O ~ ~'I~ ~I I ~ h
~: ;~ O
X
~S`^
~ ~ ~ O O
~ ~.a
u~ U C-- ~D~L CO I I ~ O ~ ~
O E~ r ~ r~ D h r
u~ u~ ~ o
s: O ~ X
a: _ ~ D. h ~ c
r-l _-- r r ~ h
C h O ~ CO O O E ~ a)
t~ ~I) ._ ~ X ~ O E h
~ _ ~ h E3 Cl
O ~ h h .C U~ ~ ~ C) E O 111 u~
ct: ,~ aJ ~ ~ ~ c ,~ e ~ c :~
P~ ._1 ~ ~ E E ~ ~ O I h O
:1 a) ~_~ ~ o ~ ~ O U C~
~: 3 ~ O o ~ 2 0 t3~ I O
;~ 1~ ~ ~ C~ -- ~ I ~1 ~ I O
E
O~ O I ~ ~ O
.~~ _ I 11 E ~ I r;5 ~ ~ E
C~ ~ _ I O QJ .~
~_ I ~ ~ ~ ~ O t~ C ri I
~ s~ ~ e
o ~ E I 0 o ~ rl
r~ ~v _ _ ~ _ _ ~ ~ E ~ _~ o I r~
r ~ 11 c ._ ~ j ~ ~ ~ _ O i ~I ~ C O ~ q r ~ h C~
-- . ~ ~ o c,~ ~_ r~
~ ~ C~ O r~ ~ r~
~ I` ~ --~ C ~
'~ ~ ~ O O r~ :~ O I ~ _
_ _ ~ r~ I ~ r~ _` ~ 7 ~ ~ _
, ~ ~ ~ ~ ~ ~ c~
\~'0 ~'/(~1~ rc r/~sl/()63~-
--154--
~; . V ~
The compositions are useful thermoplastics t~at
can be melt fabricated by conventional processes suc~ as
extrusion and molding.
The blends preferably use a physical mixture of
S poly(lactic acid) of the formula I: where n is an integer
between 75 and 10,000; and a polymer comprising a
segmented polyester~ The poly(lactic acid) content may
vary over a wide latitude such as betwaen about 1 and
about 99 wei~ht percent. A useful composition is that
where the poly(lactic acid) comprises 50 to 99 weight
percent of the composition. A preferred composition has a
poly(lactic acid) content of ~0 to 80 weight percent,
while other useful compositions include about 5 to about
20 weight percent, depending on the final use of the
composition.
Two embodiments of the general process for
producing the composition include (1) melt blending of
poly(lactic acid) with a blend compatible polymer that
provides improved impact resistance and is discrete and
intimately bound (such as a segmented polyester); and (2)
solution blending during poly(lactic acid) polymerization
as in Example 2D where Hytrel~ segmented polyester is
dissolved in the poly(lactic acid). The poly(lactic acid~
provided preferably has the formula I. If desired,
plasticizer in pliable forming amounts may be added to the
blend that is selected from the group consisting of
lactide monomer, lactic acid oligomer, lactic acid, and
mixtures thereof. The oligomers are defined by the
~ormula 1~: where m is an in~_~e~: ~ ~ m < 75, and is
rererably ~ ~ m ~ 1~. C~he~ ?l-s`ici-er ~ht m~y be ad~ed
.._lude one cr mo~e deri~ati~es c- -n ^ligome_ o` ia_~ic
'-~ t~ c_~l-c~e~
--~e~
, ~ _ _ _ _ _,
o I ~ PCr/-S91/063
--155--
`:. ``
v ~
and where q is an integer: 2 < q < 75, and is preferably.
Preferably q is an integer: 2 < q < 10.
Addition of plasticizer will provide additional unique
physical properties and processing advantages as discussed
in sections A, B, and C above.
The plasticizers may be present in any amount
that provides the desired characteristics. For example,
the various types of plastici~ers discussed herein and in
sections A, B, and C above provide for ~a) more effectiv~
compatibilization o~ the melt blend co~ponents so that
greater intimacy is achieved; (b~ i~prov~d processing
characteristics during the blending and processing steps;
and (c) control and regulate the sensitivity and
degradation of tbe polymer by moisture. For pliability,
plasticizer is present in hiqher amounts while other
characteristics such as stiffness are enhanced by lower
amounts. Tbe compositions allow many of the desirable
cbaracteristics of pure nondegradable polymers. In
addition, the presence of plasticizer facilitates melt
processing, prevents discoloration, and enbances the
degradation rate of `he ccmpositions in contact with the
environment. The intima~ely plasticized composition
sbould be processed into a final product in a manner
adapted to retain the plasticizer as an intimate
dispersion in the polylactic acid and/or its coblended
polymer for ce-tain properties. These steps can include:
(1) quencbing the co~position at a rate adapted to retain
the plastici^e~ as 2n inti~2te dispersion; (2) melt
~ essin~ ~r.^ ~en^hi~ tbe co~?osition at a r~te ~d2pt-:d
_3 t~ retain th ?!zs~ci^e~ zs an in~irm~te cispersion; cn-
~
~2~1n~:~ 2~ 2i~ ^c_ cs c~. i-`.~`..
c
~.ic-cs_o?i~ e~:_min2t~0n o the `P.~-t-el~ seGmentec
PcT/~9l/n~
-156-
dispersed Hytrel~ segmented polyester is present ln small
spherical domains a few microns or less in size. These
domain sizes can be adjusted by the mixing conditions such
as time, speed of mixing, and temperature.
S Therefore, for example, the polymer, or polymers,
added to the poly(lactic acid), should be generally of
small, heterogeneous domain size, less than 10 microns,
and can be submicroscopic, or dissolved, in the
poly(lactic acid)~ In addition, this impact modifier ~ust
be el2stomeric.
While not wishing to be held to any particular
theory, it is believed that the present invention provides
a continuous matrix of poly(lactic acid) containing
intimately mi~ed microscopic domains of ~ytre~ segmented
polyester that act as crack arresters since the latter is
a thermoplastic elastomer compatible with poly(lactic
acid).
For this purpose, the impact modifier must be
elastomeric and intimately bound into the poly(lactic
acid) as a discrete heterogeneous phase. The added
polymer, the impact modifier, can be a thermoplastic
elastomer, or a crosslinXed rubber, to achieve this
elastic behavior. Examples are natural rubber and
styrene-butadiene copolymers.,
Further exa~ples of impact modifiers useful in
the invention include polyisoprene ~gutta percha),
styrene-isoprene-styrene bloc~ copolymers, acrylonitrile-
but~diene-sty~ene block copoly~ers, styrene-ethvlene-
styrene block copolymers, p~opylere-ethylene-propylene
c~ c ~Q?'~D~ s~?-e~e-?-o?~le~e ~lo_!:
c_polyme_s, ~ -es ~her2~ h- lii;e. P21yu~e~h,-re~
~.. ^_ ~_e r~ isr~r-~ ;ell,~~e ~ 2-e-
~ ~ _ _ _ ~ s
_e__ _~_ ,,,_= a -
.s, ~he ~.~te~Gl ~b_`~_le~ ?--~ ~
~:-2s~ _c ;~ Ct~ 2=e~ t~ e- ~ c
_.______. ____3~
U~9'/~13 1'CT/~S91/063'-
~ -157-
~; J,~
It was further apparent that poly(lactic acid) alone
degraded faster than the Hytrel~ se~mented
polyester/poly(lactic acid~ mixture. T~us Hytrel~
segmented polyester can also be used to retard the
degradation rate of polytlactic acid).
A third component can be added which is
compati~le with the other components discussed above to
achieve improved compatibility. ~us, where the
poly(lactic acid) and the impact modifier have poor
co~patibility, a third component c~n be added to improve
the compatibility. This t~.ird componen~ is usually ad~ed
where it is compatible with the other two, individually,
and where the other two, poly(lactic acid) and impact
modifier are not very compatible. This works bv
lS increasing the interfacial bonding between poly(lactic
acid) and elastomeric impact modifier. However, what is
surprising is the wide latitude of compatibility of
poly(lactic acid) with other polymer types, both polar and
nonpolar. This can be referred to in section C. ~hird
General Embodiment above.
If desired, minor amounts of plasticizer such as
glycolide, poly(glycolic acid), caprolactone, and
valerolactone may be added.
The compositions herein can be processed by melt
fabrication into useful articles of manufacture such as
containers, eating utensils, trays, plates, drinking cups,
single serving trays, syringes, medical trays, and the
like. The com?ositions are especially useful for ~_ticles
havin~ oniy a or.e ~ir~e use or a sho~t ll_e sp~n i~ use
3~ ~2fore disrGsal~
~ ~ _ _ _ _ _ _ _
;~h~ r.~e~ s ~2e~ desc~i~
; ~ _: _ _ ~ _ . ~ _ ~ _ _ ~ _ _ _ _: . _ _ _ . ~ ~ _ . .; _ . . _ ~ _ . _ _ . ~ _ _ _. _ _ ~ =
~ cr.. ? ^~ _r~._.. -s _.~
~-r~ S;~- ~ `Cr~ scO?~ C~
~ r.~c-_~
