Note: Descriptions are shown in the official language in which they were submitted.
- WO 94/17121 215 2 6 7 7 PCTIGB93/00164
- POLY[(R)-3-HYDROXYBUTYRATE] BASED POLYESTER
THIS ~ 0N relates to polyester and shaped polyester
articles in particular to polyester and such articles restored
to their original non-aged pro~e.Lies after ageing has taken
place and a process of de-ageing ~uch polyester and article~.
Whereas the polyester poly[(R)-3-h~ x~LuLyLate] (PHB)
when freshly moulded ~how8 ductile behaviour, sub~e~u2nL ageing
seriously embrittles it and h ,~`~ its applieability. Within
several weeks of storage at room temperature, the tensile
modulu~ doubles, and the elongation at break drops below 10%.
A mild de-ageing treatment by the employment of heat up to 70C
result~ in a ~light and trn,- ary i v~ --t in ~~~hanical
p~ope.Lies.
It has now been found that such ageing can be .e~- sed by
lS a defined heat treatment and the so-treated polyester and
articles are less subject to suL~e~enL ageing.
According to the p~8LAt invention there i8 provided a
polyester consisting essentially of polyt(R)-3 h~dY~yLuLy~ate]
units in which ageing has oc-~--ed, characterised in that (i)
the polyester is restored to its original non ag~d properties
by a heat treatment, and (ii) ~u~se~r~L ageing of the
polyester is retarded as ; nA; rated by substantial stability of
at least one measurement indicative of ageing.
According to a further aspect of the invention there is
provided a shaped article at least partly made of polyester
consisting essentially of poly[(R)-3 h~d,oAybuL~rate] units in
which ageing has occu..ed, characterised in that (i) the shaped
article is restored to its original non-aged p ~pe.~ies by
heating, and (ii) 8Ub3E~nt ageing of the shaped article is
retarded as indicated by substantial ~tability of at least one
measurement indicative of ageing.
~At least partly made~ means having structural ~ : ~ Ls
made of PHB to such an extent that ageing of the PHB c~ - ~g
ages the whole article. Thus for example, PHB may be
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- W0 94117121 PCT/GB93/00164
h ~r - _sly mixed with other biode~radable polymers such as
polylactide~. In such mixtures the i ni amount of P~B is at
least 30% ~/w. Also articles having PHB __ - L8 linked to
other r ,~ ~ L8 such as razors and toothbrushe~, and articles
made of a matri~ of ~ome other biodegradable ~e.g. starch~ or
non-biodegradeable polymer (e.g. polypropylene) with PHB
inclu~ions, are within the invention. In such mixture~ the
in; amount of PHB i~ at least 30% ~/w. Articles made of
PHB alone, nucleated or otherwise, benefit most from the
invention.
PHB ~consisting essentially of~ (R)-3 o~LuLyrate units
includes PHB homopolymer, and PHB copolymer~ contai ni ng up to 1
mol percent of other oxy~l~Anoate units whether introduced
deliberately or not.
lS ~Substantial stability" means that the polyester or
article is for practical puL~ose~ not defective for brittleness
for at least one month after the de-ageing trer ~ L. For
eY le, using the el~ng~ti~n to break measurement, this means
a value of not less than 50% of the original non ~ge~ value at
one month after the de-ageing treatment when stored at ambient
t~ ~ ~ture.
Aged polyester or ~haped article in the p.~BEn~ context
mean~ that it has the ~ ni r~l p~G~e~ Lies equivalent to the
polye~ter or article having been ~tored for 24 hour~ or more at
20C. Non-aged polyester or ~haped article in the pre~ent
context mean~ that it has the --'-ni C~ Lies eguivalent
to the polyester or shaped article having been freshly
processed, i.e --h~nical p o~e~Lie3 equivalent to storage for
up to 24 hour~ at 20C, preferably storage for up to and
including 1 hour at 20C of having been proc~sed.
The P~B is capable of a relatively high level of
crystallinity, for example over 30%, especially 50-90%, in the
- W0 94/17121 21 S 2 6 7 7 PCT/GB93/00164
ab~ence of plastici~er. It con~i~t~ of repetitive units of
formula I:
~ ~ Cm Hn ~ CO -
J where m i~ 3 or 4 and n i~ 2m or 2m-2. Typically Cm Hn
S contains 2 carbon atoms in the polymer chain and a C1 or C2
cide chain on the carbon next to oxygen in the chain.
- Particular polyester6 contain at lea~t 99 mol~ of m=3 unit~,
the ~. -; ndor being m = 4 unite or fractional percentage~ of
units having higher values of m. The molecular weight Mw of
the PHB i9 for example from 50000 to 2 x 106, e~pecially over
100000 .
The PHB can be a product of fermentation, especially of a
microbiological process in which a microorgani~m lay~ down PHB
during growth or is caused to do ~o by cultivation in
starvation of one or more nutrient~ noces~a~y for cell
multiplication. The miC~oo-~ni r ~ may be wild or mutated or
may have the noce~c~ry genetic material int.~duced into it.
Alternatively the noceesAry genetic material may be harboured
by an eukaryote, to effect the microbioiogical process.
Examples of ~uitable microbiological proco~se~ are the
following:
for F~ 1 A I material with m = 3 or m = partly 3, partly 4 :
EP-A-69497 lAlcalioene~ eutroDhus~
for F~_ 1 A I materials with m = 3
US 410533 (A. eutro~hue)
EP-A-144017 (A. latuc);
The PHB can be extracted from the fermentation product
cells by mean~ of an organic ~olvent, or the cellular protein
material may be de~ _esd leaving microscopic granule~ of PHB.
Alternately, the PHB can be a product of cynthetic
chemistry (Bl~_ ~_ y_n, S. and Holden, D. A., Macromolecule~.
1989, 22, pl656-1663).
The ~o~e-~ie8 of the polyester or article of the present
invention can be anse~sed u~ing the following mea~u,~ c :
_ WO 94/17121 2 1 S 2 6 7 7 PCT/GB93/00164
stre3~-strain curve including calculations of elongation to
break, Youngs modulus, and tensile strength; impact testing,
for example IZOD; and dynamic --hani cal thermal analysis
(DMTA). These are all ~tandard methods for testing ~chani
properties.
The invention also provides a process of de-aging an aged
polyester consisting essentially of poly~(R)-3-hydLo~butyrate]
units which comprises heating at a temperature wl.eLeby ~i) the
polyester i~ restored to its original non-aged p 0~2L Lies, and
(ii) subsequent ageing of the polyester is retarded as
indicated by substantial stability of at least one measurement
indicative of ageing.
The invention also extend~ to shaped articles of the
polyester subjected to the above process.
Any one or more of the abu~L ~ tioned characterising
~.~pe.Lies can be used to monitor the p,oy,ass of the heat
treatment. In practice it is often sufficient to test the
polyester or article by taking a sample from a batch, cooli ng
it to room temperature and subjecting it to manual flexing. In
e~tablished manufacturing it is often possible to fix the
heating temperature and then adopt a t me that is fully
adequate and affords a small margin to cover accidental
variation~.
The heating t~ ~ aLure i~ preferably in the range from
90C to 150C, especially in the range from 100C to 140C
The heating time is typically at least a few sec~n~,
preferably from 5 eeonn~ to 20 hours, especially 0.5 min to 14
hours, after the article has reached the intended t- - aLu~e.
The heating time required for optimal effect iB d~p~n~nt on
the heating temperature, i.e. the higher the t -lature the
less time that i8 required to achieve optLmal effect. Also the
t~ - ature can be chogen to 8uit the characteristics of the
processing plant and ec~r ic requirements.
Heating can be effected in air or Gaygen depleted or
SBI 37404 21 S2 6 7 7
inert gas or in vacuo, or in water or a fluid which does not
interfere with the integrity of the polyester, or in a mould.
Heat transfer can be by conduction, radiation, convection or
resitive heating.
s In the accompanying drawings:
Figure 1 shows stress-strain curves at ambient conditions
for specimens (a~ aged by storage for 150 days, (b) treated as
in (a) and subsequently heated for 10 h at 100C, (c) treated
as in (b) and stored for another 120 days.
Example 1
Comparison of stress strain behaviour of aged samples and
samples de-aged according to the pres-nt invQntiOn PHB
homopolymer powder ("BIOPOL" from ICI) having Mw 539000, Mw/Mn
3.5 was mixed with 1.0% of boron nitride nucleating agent in a
lS Hobart (RTM) mixer for about 10 min. The mixture was fed to a
Betol 2520 (RTM) 25 mm screw extruder operated at m-x;~lm 180C
temperature with a screw speed of 100 rpm. The 4 mm strand so
produced was crystallised at 60C in a water bath and
granulated. The granules were dried at 40C for 20 h and
injection-moulded into specimen 2 x S x 12 mm using a Boy lSS
(RTM) machine at a -x;mllm barrel temperature 180C, injection
time lS sec, screw speed 220 rpm, injection pressure SMPa,
mould temperature 60C, cooling time lS sec. The specimens
were allowed to age for 150 days at ambient temperature. Then
the specimens were subjected to the following treatments :
(a) no further treatment
(b) heated for 10 h at 100C
(c) treated as in (b) and stored for a further 120 days at
ambient temperature.
The three specimens were ~x~m;ned for stress-strain
behaviour using an Instron (RTM) 1122 tensile testing machine
fitted with a Nene data analysis system. A clamp separation of
50 mm and a crosshead speed of 20 mm.min~l were used. The
injection moulded specimens were dumbbell-shaped according to
AMENDED S~ET
W0 94/17121 21 ~ 2 6 7 7 pcTlGB93lool64
ISO ~ 537/2, their prismatic part meanuring 40 x 5 x 2 mm.
The variation of percen~age exten~ion with applied ~tre~s
(MPa) ic chown in Figure l. It i9 evident that, wherea~
specimen (a) fractured at a ctre~s producing le~s than 10%
~train, ~pecimen (b) demonstrate~ deaging hac taken place ac
exemplified by the large i~ ~a ~-~ in the stre~-strain
relation~hip. Specimen (c) retained the i ~o~ed ageing
perf-_ -nce for the 120 days further ctorage. Thus the heat
treatment ha~ not only rectored the original non-aged
proprrLiec of the material but ha~ pre~ented, or at lea~t
retarded subcequent ageing.
