Note: Descriptions are shown in the official language in which they were submitted.
WO92/165~ PCT/US92/020~
2 1 ~
--1--
Biodearadable comPositions comprisina starch
The present invention relates to biodegradable polymer
compositions capable of being formed by heat and pressure
into articles having substantial dimensional stability.
The invention relates particularly to biodegradable
compositions comprising starch and at least one member
selected rom al~enol homopolymers and/or alkenol
copolymers. Such compositions are suitable for use,
inter alia, in injection molding, in film formation, and
in the formation of foamed packaging materials.
BACKGROUND TO THE INVENTION
It is known that natural starch which is found in
vegetable products can be treated at elevated
2~ temperatures to form a melt.
Such a melt may preferably be formed by heating the
starch material above the glass transition and melting
temperatures of its components so that such undergo
2S endothermic rearrangement. Preferably the starch
material contains a defined amount of a plasticizer,
which preferably is water, and melt formation is carried
out at an elevated temperature in a closed volume, and
hence at an elevated pressure.
It is po~sible to melt starch substantially in the
absence of water, but in the presence of another suitable
plasticizer, for example a liquid having a boiling point
higher than the starch glass transition and melting
3~ temperature.
Different degrees of uniformity in melt formation, which
can be measured by various methods, are possible. One
method, for example, is to microscopically determine the
amount of granular structure remaining in a starch melt.
It is preferred that the starch is destructurisea, viz,
w092/t6~ O PCT/US92/020
-- 2
that the melt is substantially uniform in character, that
light microscopy at a magnification of about 500 X,
indicates a substantial lack of, or reduction in,
granular structure, that the starch so melted exhibits
little or no birefringence and that x-ray studies
indicate a substantial reduction in, or lack of, starch
crystallinity in the melt.
~0
~t is an advantage of the present invention that
compositions may be formed from starch which has a
relatively low degree of destructurisation.
EP-A-0 375 831 and EP-A-0 376 201 in the name of National
Starch and Chemical Corporation discuss the problems
associated with the environmental handling of plastics
waste materials. Such discussion is incorporated herein
by reference.
Both of the publications disclose low density, closed
cell, starch productc suitable for use, inter alia, as
packaging materials, in which the starch has an amylose
content of at least 45%, and preferably of at least 65%.
2~ Additionally EP-A 0 376 201 discloses that the addition
of salt to the starch material, in concentrations of from
2% with respect to the weight of said material, leads to
an expanded closed cell product having an improved
uniform cell structure.
The above mentioned prior starch compositions, in so far
as they have been applied to the manufacture of
biodegradable packaging materials, have, for one reason
or another, generally not provided a tenable alternative
3~ to the synthetic materials that it is desired that they
should replace.
The present invention provides, inter alia, such an
alternative.
W092tl65~ PCT/US92/02~
210~
-- 3
Moreover, Ind. Eng. Chem. Prod. Res. ~ev. (194; 23, page
594-595) describes the extrusion of starch extended
water-soluble polyvinyl alcohol. According to this
disclosure, the melt flow index of such an extrudate
decreases with increasing starch concentrations qo that a
composition comprising a 1:1 ratio of a low molecular
weight (20,000) polyvinyl alcohol and a low molecular
weight (30,000) corn starch possesses a melt flow index
of 0.53. A compo~ition comprising such a low melt flow
~ndex is not suitable for the injection molding of
articles therefrom, wherein a melt flow index of about 7
or higher is typically required. Accordingly, it is
1~ surprising that the present inventive compositions, which
comprise relatively high concentrations of starch, can
easily be injection molded.
The melt flow index of the composition is defined as the
20 amount (in grams) of a thermoplastic material which can
be forced in 10 minutes through a 2.0665mm orifice when
subjected to a force of 0.2160 grams.
It is implicit in the art of forming thermoplastics that
2~ the major components thereof should be of high molecular
weight, and preferably that the molecular weights of such
major components should be of similar magnitudes.
It is surprising that articles having excellent physical
30 properties and dimensional stability can be formed from
the present inventive compositions, wherein the polyvinyl
alcohol, which has a low molecular weight in comparison
with that of the starch component of the composition, is
present in high concentrations relative thereto.
3~
SUMMARY OF THE INVENTION
According to the present invention, there is provided a
biodegradable composition as obtained from a melt
comprising starch, a plasticize~ and at least one member
selected from alkenol homopolymers and/or alkenol
W092/16~84 PCT/US92/02~W
2 ~ 8 ~
-- 4 --
copolymers which are combined under conditions sufficient
to ensure uniform melt formation, characterized in that
the at least one member is present in the composition at
a concentration of from 10 to 120 parts per 100 parts of
dry starch.
By plasticizer is meant a substance which can be
incorporated into a material to increase its flexibility,
workability or distensibility or reduce the melt
viscosity, lower the temperature of a second order
transition, or lower the elastic modulus of the product.
The term plasticizer includes solvent plasticisers,
1~ non-solvent plasticisers and internal plasticisers.
The preferred plasticizer is water.
The invention also includes the melt which is obtained
20 from said composition as well as shaped articles,
particularly foams, films, laminates and injection molded
articles made from said melt.
Such a uniform melt is generally thermoplastic, and it is
2~ particularly preferred that it is thermoplastic.
In one embodiment of the composition, the starch is a
high amylose variety and has an amylose content by weight
of up to about 95%, and preferably of between 70 and 95%.
Said starch, however, does not have to be a high amylose
variety, and may have an amylose content of up to about
6S%, up to about 45%, and up to about 35%. It is
possible that the amylose content of the starch is
35 between 25 and 35%. The lower limit for the amylose
content of the starch preferably is about 10 to about
15%, likewise by weight.
The composition according to this invention may
preferably comprise from about iO to about 100 parts of
said polymer and / or copolymer per 100 parts by weight
W092/165~ PCT/US92/02~W
210~8'~
-- 5 --
of dry starch, and in a more preferred embodiment, the
composition comprises from about 10 to about 85 parts of
said polymer or copolymer per 100 parts of starch.
The composition may also comprise a polymer or copolymer
content of from 10 to 65 parts, and particularly from 20
to 40 parts with respect to 100 parts of starch.
The alkenol homopolymer is preferably a polyvinyl alcohol
which may be pre-plasticised with a polyhydric alcohol
such as glycerol. The polyvinyl alcohol preferably is
hydrolysed to an extent of from about 45 and about 100%
1~ and preferably has a number average molecular weight of
about 15,000 to about 250,000, and more preferably has a
number average molecular weight of from 15,000 to
150, 000.
20 It is particularly preferred that the composition
contains pre-treated polyvinyl alcohol in the form of a
melt, obtained previously by adding sufficient energy to
polyvinyl alcohol to melt it and substantially eliminate
crystallinity in the melt. It is particularly preferred
2~ that the such crystallinity is substantially completely
eliminated. Such pre-treatment of polyvinyl alcohol is
disclosed in EP-A 0 415 357.
Alkenol copolymers as mentioned above are preferably
30 synthetic copolymers containing vinyl alcohol units as
well as aliphatic units as are obtained by
copolymerization of vinyl esters, preferably vinyl
acetate with monomers preferably ethylene, propylene,
isobutylene and/or styrene with subsequent hydrolysis of
35 the vinyl ester group.
Such copolymers are known and are described in
"Encyclopedia of Polymer Science and Technology,
Interscience Publ. Vol. 14, 1971"
WO92/165~ PCT/US92/02
2~0~ll8 0 ~ - 6 -
The composition may further include compounds selected
from the group consisting of nucleating agents, fillers,
~tabilisers, coloring agents and flame retardants and
~boron containing compounds. Said composition may further
include known processing aids, such as lubricants, mould
release agents and plasticisers.
It will be appreciated that the concentration of the
~ components in the composition can be derived according to
a Master-batching process, if desired.
The starch may be modified to contain ether or ester
l~ groups.
The invention also provides a method for producing the
composition, comprising:
20 a) providing a starting composition comprising starch,
plasticizer and at least one member selected from alkenol
homopolymers and/or alkenol copolymers which are present
in the composition at a concentration of from lO to 120
parts per lO0 parts of said starch;
2~
b) adjusting the plasticizer content of the composition
to between about 0.5 and about 40% by weight of the total
composition during processing or plastification;
30 c) heating the thereby adjusted composition to a
temperature of between lO0 and 220C and for a time at
least sufficient to form a uniform melt of the
composition;
3S d) removing any excess moisture before the extruder die
to obtain a moisture content of between about 5% and
about 20%; and-
e) e~truding the thereby heated composition.
The present invention further includes a melt as obtainedaccording to the method.
WO92/165~ PCT/US92/02~4
~71Q348~)
The pre~ent invention further refers to a method of
working ~aid composition under controlled plasticizer
content, temperature and pressure conditions as a
~thermoplastic melt wherein said proce~s is any known
process, such as for example, foaming, filming,
compression molding, injection molding, blow molding,
vacuum forming, thermoforming, extrusion, coextrusion,
and combinations thereof.
The invention will be further apparent from the following
de~cription, in conjunction with the following examples
and the appended claims.
SPECIFIC DESCRIPTION
The present invention is defined in the appended claims.
20 In particular, the invention refers to a biodegradable
composition as obtained from a melt comprising starch, a
plasticizer and at least one member selected from alkenol
homopolymers and/or alkenol copolymers which are combined
under conditions sufficient to ensure uniform melt
2~ formation, in which the at least one member is present
in the composition at a concentration of from 10 to 120
parts per 100 parts of dry starch. Such a uniform melt
is thermoplastic ïn character.
30 The alkenol homopolymer is preferably polyvinyl alcohol
(PVA) having a number average molecular weight of at
least about lS,000 (which corresponds to a degree of
polymerization of at least 340). It is more preferred
that the PVA has a number average molecular weight of
3~ between about 50,000 and 250,000, and most preferred that
it has a number average molecular weiqht of about 80,000
to 120,000. Where the composition is foamed it is
preferred that the number average molecular weight of the
polyvinyl alcohol is between about 160,000 and 250,000
and more preferably between 160,000 and 200,000.
W092/165~ PCT/US92/02~
21~80 - 8 -
Polyvinyl alcohol (PVA) i8 generally made from
hydrolysis, or alcoholysis of polyvinyl acetate. The
degree of hydrolysis to provide a polyvinyl alcohol for
~use in the present invention preferably is from about 75
to about 99.9 mole %, and more preferably is from about
80 to 99.9 mol %. It is most preferred that the degree
of hydrolysis i8 from about 87 to 99.9 mol%.
~ Such polyvinyl alcohols are known and are sold, by Air
Products And Chemicals Inc, of~7201 Hamilton Boulevard,
Allentown, USA, under the name of Airvol 540S (degree of
hydrolysis 87-89%, molecular weight about 106 -110, 000);
Airvol 205S (degree of hydrolysis 87-89%, molecular
weight about 110 - 31,000), Elvanol 90-50 (degree of
hydrolysis 99.0 to 99.8%, molecular weight about 35 to
about 80,000) and Airvol 107 (degree of hydrolysis 98.0
to 98.8%, molecular weight 11,000 to 31,000).
EP-A 0 415 357 in the name of Air Products and Chemicals
Inc, describes extrudable polyvinyl alcohol compositions,
and methods for their preparation. The method according
to EP-A 0 415 357 comprises adding sufficient energy to
2S the polyvinyl alcohol to both melt it and e~sentially
eliminate the crystallinity in the melt whilst
simultaneously removing energy from the melt at a rate
sufficient to avoid decomposition of the polyvinyl
alcohol.
Accordingly, the present invention contemplates the use
in the present inventive compositions of polyvinyl
alcohol pre-treated according to the disclosure of EP-A 0
415 357. Thus the present inventive composition contains
3~ pre-treated polyvinyl alcohol in the form of a melt which
has been obtained previously by adding sufficient energy
to polyvinyl alcohol io both melt it and substantially
eliminate crystallinity in the melt, whilst
simultaneously removing energy from the polyvinyl alcohol
melt at a rate sufficient to avoid its decomposition.
W~92/165~ 2 ~ PCT/US92/02
The pre-treated polyvinyl alcohol may be plasticised by
the addition thereto of a polyhydric alcohol plasticizer
in an amount of from 2 to 30% by weight of the polyvinyl
i alcohol. It i~ preferred that the pre-treated polyvinyl
alcohol i8 plasticised by the addition thereto of a
polyhydric alcohol plasticizer in an amount of from 2 to
20X by weight of the polyvinyl alcohol. The
pre-treated polyvinyl alcohol may further comprise sodium
~ acetate and phosphoric acid in a molar ratio of about 2
to l. The sodium acetate is present in the polyvinyl
alcohol as a by product of its method of production and
under the conditions of melt formation æuch sodium
acetate acts as a catalyst for decomposition of the
polyvinyl alcohol. Accordingly, pho~phoric acid may be
added to the polyvinyl alcohol composition from which the.
pre-treated polyvinyl alcohol melt is made, in the ratio
of l mole of acid per 2 moles of acetate, in order to
20 neutralize said sodium acetate. Low ash polyvinyl
alcohol, which is essentially free of sodium acetate,
does not require the addition of such phosphoric acid.
The pre-treated melt of polyvinyl alcohol has a maximum
2~ melt temperature, as determined by differential scanning
calorimetry, which is at least about 5C lower than that
of the corresponding untreated polyvinyl alcohol,
preferably at least about 10C lower than that of the
untreated polyvinyl alcohol, and particularly preferably
30 at least about 15C lower than that of the untreated
polyvinyl alcohol.
The formation of such a pre-treated melt of polyvinyl
alcohol requires the input of at least about 0.27kWh/kg
of specific energy to the polyvinyl alcohol, and
typically requires from about 0.3 to about 0.6kWh/kg of
such energy.
The upper practical limit of energy input would be about
0.6kWh/kg because any energy beyond that necessary to
melt the polyvinyl alcohol and eliminate crystallinity
W092/16S~ PCT/US92/02004
O - 10-
mu~t be removed as "waste energy" reducing the efficiency
of the formation of the pre-treated polyvinyl alcohol.
Optimally the polyvinyl alcohol requires an input of
about O.35 to about O.45kWh/kg both to melt it and
substantially eliminate crystallinity in the melt.
The compo~ition preferably comprises from about lO to
about lO0 parts of said PVA per lOO parts of starch, and
in a particularly preferred embodiment, the composition
comprises from about lO to about 85 parts of said PVA per
lOO parts of starch.
A likewise polymer or copolymer content of from lO to 65
parts, and particularly from 20 to 40 parts with respect
to lOO parts of starch is also highly suitable.
~0 Preferred alkenol copolymers are those containing vinyl
alcohol units and aliphatic chain units as obtained by
co-polymerization of vinyl acetate with ethylene and/or
propylene, preferably with ethylene and subsequent
hydrolysis of the vinyl acetate group. Such copolymers
2~ may have differing degrees of hydrolysis.
Preferred are ethylene/vinyl alcohol polymers ~EVOH) and
propylene/vinyl alcohol polymers. Most preferred are the
ethylene/vinyl alcohol polymers. The molar ratio of vinyl
30 alcohol units to alkylene units is preferably from about
40 : 60 to about 9O : lO and preferably from about 45 :
55 to about 70 : 30. The most preferred EVOH has ar.
ethylene content of 44%.
3~ The starch which is pre~ent in the composition of the
present invention is at least one member selected from
the group consi stinq of native starches of vegetable
origin, which starches are derived from potatoes, rice,
tapioca, corn, pea, rye, oats, wheat, including
physically modified starch, irradiated starch, starch in
which mono or divalent ions associated with phosphate
W092/l65~ PCT/US92/02~
2i3^~Q
groups therein have been removed, either partly or
wholly, and optionally replaced, either partly or wholly,
by different divalent ions or with mono or polyvalent
ions; pre-extruded starches and starches which have been
so heated as to undergo the specific endothermic
transition characteristically preceding oxidative and
thermal degradation.
For certain applications it is preferred that the starch
is a high amylose starch having an amylose content of
between about 70% and about 95%, preferably between about
75% and about 85%, the percentages being by weight with
1~ re~pect to that of the starch.
The lower limit for the amylose content of the starch
preferably is about lO to about 15%, likewise by weight.
20 The starch component of the composition according to the
invention includes starch melted in the absence of added
water, but in the presence of another plasticizer - such
as glycerol.
2~ The preferred plasticizer is, however, water.
Preferably the starch is formed into a melt in the
presence of water which may be present in the starting
composition, from which the composition of the present
invention is made, at between about 0.5 and about 40% by
weight, based on the total weight of the starting
composition.
The composition according to the invention has a water
3S content of between about 10 and about 20~o by weight, and
preferably of between about 14 and about 18% by weight,
and particularly of about 17% by weight, based on the
weight of the composition as explained herein.
Starch may be mixed with the polymer or copolymer and
optionally other additives as mentioned hereinbelow in
W092~165~ 2 1 0 ~ ~ ~ Q PCT/US92/02~
- 12 -
any desired sequence. For example, the starch may be
mixed with all of the intended additives, including
polymer or copolymer to form a blend, which blend may
then be heated to form a uniform melt which will, in
general, be thermoplastic.
The starch may, however, be mixed with optional
additives, the starch melted and granulated before
addition of the polymer or copolymer, for example the
polyvinyl alcohol, which mix may then be further
processed.
Preferably, however, the starch is mixed with additives
together with the polymer or copolymer, for example
polyvinyl alcohol, to form a free flowing powder, which
i8 useful for continuous processing, and melted and
either granulated or extruded directly into the
solidified composition of the present invention.
The composition may optionally consist at least of the
combination of starch and one member selected from
alkenol homopolymers and copolymers which have been
2~ pre-processed. Such pre-processing may involve the
provision of granulates or pellets which have been
manufactured under conditions sufficient to have obtained
uniform melt formation of the components.
Alternatively, and or additionally, the alkenol
homopolymers and copolymers may have been pre-plasticised
with, for example, a polyhydric alcohol such as glycerol.
The starch present in the composition may have been
3~ pre-melted in the presence of from 15 to 40% moisture, by
weight thereof, and at a temperature and pressure within
the ranges as given above.
Optionally the composition comprises at least one member
selected from the group consisting of extenders, fillers,
W092/165~ 2 ~ U PCT/US92/02
- 13 -
lubricants, mould release agents, pla~ticisers,
stabilisers, coloring agents, and flame retardants.
~The extenders include water-soluble an/or water-swellable
polymers including known thermoplastic polymers such as
gelatin, vegetable gelatins, acrylated proteins;
water-soluble polysaccharides such as: alkylcelluloses,
hydroxyalkylcelluloses and hydroxyalkylalkylcelluloses,
such as: methylcellulose, hydroxymethylcellulose,
hydroxyethylcellulose, ~ hydroxypropylcellulose,
hydroxyethylmethylcellulose,
hydroxypropylmethylcellulo~e,
hydroxybutylmethylcellulose, cellulo~e esters and
hydroxyalkylcellulose esters such as: cellulose
acetylphtalate (CAP), Hydroxypropylmethyl-cellulose
(HPMCP); carboxyalkylcelluloses,
carboxyalkyl-alkylcelluloses, carboxyalkylcellulose
20 esters such as: carboxymethylcellulo~e and their
alkali-metal salts; the analogous derivatives of starch
as named for all the cellulose derivatives above;
water-soluble ~ynthetic polymers such as: poly(acrylic
acids) and their salts and essentially water soluble
2~ poly(acrylic acid) esters, poly(methacrylic acids) and
their salts and essentially water-soluble
poly(methacrylic acid) esters, essentially water soluble
poly(vinyl acetates), poly(vinyl acetate phthalates~
(PVAP), poly(vinyl pyrrolidone), poly(crotonic acids);
30 cationically modified acrylates and methacrylates
possessing, for example, a tertiary or quaternary amino
group, such as ~he diethylaminoethyl group, which may be
quaternized if desired; and mixtures of such polymers.
3~ By the term "water-soluble or water-swellable polymer" is
meant a polymer which absorbs or adsorbs at least 30% of
water by weight with respect to that.of the dry polymer
when such is immersed in liquid water at room
temperature.
W092~16~ PCT~USg2/OZ~
~ 1 O~ll8 0 - 14 -
Suitable fillers include, for example, wood-derived
materials, and oxides of magnesium, aluminum, silicon,
and titanium. The fillers are present in the composition
at a concentration of up to about 20% by weight, and
preferably between about 3.0 and about 10%, by weight,
based on the total weight of the composition.
The lubricants include stearates of aluminum, calcium,
magnesium, and tin, as well as the free acid and
magnesium silicate, silicones and substances such
lecithin, and mono and diglycerides, which - for the
purpose of the present invention -
function in like-manner. Suitable lubricants further
include unsaturated fatty acid amides, preferably amides
of C 18 - C 24 unsaturated fatty acids, such as the amide
of cis-l3-docosenoic acid (erucamide) and amides of C l~
- C 24 carboxylic acids, such as the amide of docosanoic
20 acid (behenamide). The particularly preferred lubricant
is stearic acid, which is present in the composition in
an amount of up to lO parts per lO0 parts of starch,
preferably in an amount of from l to 3 parts per lO0
parts of starch, and most preferably is present in the
2~ composition in an amount of l part per lO0 parts of
starch.
The composition of the present invention may also
comprise a nucleating agent, - particularly so where the
30 composition is in foamed form - having a particle s~ze of
from O.Ol to 5 microns, selected from the group
consisting of silica, titania, alumina, barium oxide,
magnesium oxide, sodium chloride, potassium bromide,
magnesium phosphate, barium sulphate, aluminum sulphate,
3~ boron nitrate and magnesium silicate, or mixtures
thereof. It is preferred that said nucleating agent is
selected from amo~g~t silica, titania, alumina, barium
oxide, magnesium oxide, sodium chloride, and magnesium
silicate, or mixtures thereof.
W092/165~ PCT/US92/02~
2~{35'1~J
- 15 -
The particularly preferred nucleating agent is magnesium
silicate (micro talcum), which is present in the
composition in an amount of up to 10 parts of agent per
100 parts of starch. Preferably the agent is present in
the composition in an amount of from 1 to 3 parts per 100
parts of starch, and most preferably in an amount of 2
parts per 100 parts of starch.
Plastici~ers include urea and low molecular weight
poly(alkylene oxides), such as, for example,
poly(ethylene glycols), poly(propylene glycols)
poly(ethylene-propylene glycols), organic plasticisers of
low molecular mass, such as, for example, glycerol;
pentaerythritol; glycerol monoacetate, diacetate, or
triacetate; propylene glycol; sorbitol; sodium
diethylsulfosuccinate; triethyl citrate and tributyl
citrate and other substances which function in like
20 manner.
Such plasticisers are preferably present in the
composition at a concentration of between about 0.5% and
about 40% by weight, and more preferably between about
2~ 0-5% and about 5% by weight, based on the weight of all
of the components, including the water therein.
Preferably the sum of the plasticizer (including water
where such is present as a plasticizer) content of the
composition does not exceed about 25% by weight, and most
preferably does not exceed about 20% by weight, based on
the total weight of the composition.
Stabilisers include anti-oxidants such as thiobisphenols,
3~ alkylidenbisphenols, secondary aromatic amines;
stabilisers against photo-decomposition, such as, for
example, uv absorbers and quenchers; hydroperoxide
decomposers; free radical scavengers, and anti-microbial
agents.
WO ~2/16584 PCr/US92/02004
21 Q ~ Q - 16 -
Coloring agents include known azo dyes, organic or
inorganic pigments, or coloring agents of natural origin.
Inorganic piglTents are preferred, such as the oxides of
iron or titanium, these oxides being present in the
composition at a concentration of between about 0.01 and
about 10% by weiqht, and preferably present at a
concentration of between about 0.05 and about 3% by
weight, based on the total weight of the composition.
Most pref~rably the coloring agents are present in the
composition in an amount of about 0.03 to about 0.07% by
weight with respect to the total composition. Iron oxide
in an amount of 0.05% by weight with respect to that of
1~ the 0.05%.
The composition may further comprise flame retardants-
which, for example, comprise phosphorous, sulphur and
halogens, or mixtures thereof.
Suitable phosphorous-containing flame retardants include
diethyl-N,N-bis(2-hydroxyethyl) aminomethyl pho~phonate;
dimethyl methylphosphonate; phosphonic acid, methyl-,
dimethylester, polymer with oxirane and phosphorous
2~ oxide; aliphatic phosphate/phosphonate oligomers;
tributyl phosphate; triphenyl phosphate; tricresyl
phosphate; 2-ethylhexyl diphenyl phosphate; and
tributoxyethyl phosphate. These retardants are available
from Akzo Chemicals Inc. of 300 South Riverside Plaza,
30 Chicago, Illinois, USA.
Further suitable phosphorous-containing retardants
include: bis (hydroxypropyl) sec.butyl phosphine oxide
which can be obtained from the Chemical Products ~roup of
FMC Corporation, 2000 Market Street, Philadelphia,
Pennsylvania 19103, USA; and the following compounds
obtainable from Albright and Wilson, Americas Inc, of
P.o. Box 26229, Richmond, Virginia, 23260, USA:
polypropoxylated dibutyl pyrophosphoric acid; a mixture
of phosphonic acid,
methyl-,(5-ethyl-2-methyl-1,3,2-dioxaphosphorinan-5-yl)m-
WO 92/16~84 2 1 0 ~ 1 8 1~ PCI`/US92/02004
-- 17 --
ethyl ethyl ester, P-oxide and phosphonic acid, methyl-,
bis [(5-ethyl-
2-methyl-1,3,2-dioxapho~phorinan-5-yl)methyl] ester,
P,P`-dioxide as sold under the trade name Amgard V19;
ammonium polyphosphate; ethylendiamine polypho phate;
melamine phosphate; dimelamine phosphate; and
microencapsulated red phosphorous.
Where ammonium polyphosphate and ethylendiamine
polyphosphate are u~ed as flame retardants, it is
preferred that they are buffered with disodium
orthophosphate so that they are thereby less corrosive to
the equipment used for processing the composition
comprising them.
A still further ~uitable phosphorous containing flame
retardant is guanidinium phosphate which can be obtained
20 from Chemie Linz GmbH of St Peter Strasse 25, A-4021,
I,inz, Au~tria.
Suitable halogen-containing flame retardants include
chlorinated paraffin, which is obtainable from Occidental
25 Chemical Corporation, of 360 Rainbow Boulevard South, Box
728, Niagra Falls, New York 14302; tetrabromo phthalic
anhydride, and penta-, octa- and decabromo diphenyl
oxide, which are obtainable from Great Lakes Chemical
Corporation, of P.O. Box 2200, West Lafayette, Indiana,
30 47906, USA; and bromochlorinated paraffin, brominated
epoxy resin, brominated polystyrene, tris (2-
chloropropyl) phosphate and tetrakis hydroxymethyl
phosphonium chloride which may be obtained from Albright
and Wil~on at the address given above.
3~
Further suitable halogen-containing compounds include
dibromo neopentyl glycol and tribromo neopentyl alcohol
which are obtainable from AmeriBrom Inc of 1250 Broadway
New York, New York 10001, USA.
W092/165~ PCT~US92/02~4
21~5~8~ - 18 -
Suitable sulphur containing-retardants include ammonium
sulfate; ammonium sulfamate; and tetrakis (hydroxymethyl)
phosphonium sulfate; all of which may be obtained from
the American Cyanomid Company, of One Cyanamid Plaza,
Wayne, New Jersey, 07470, USA. Guanidinium sulfate,
obtainable from Chemie Linz at the address given above,
may also be used as a flame retardant.
The above mentioned flame retardants are present in the
starch-containing ~omposition in an amount of from 0.1 to
10%, preferably from 1 to 6%, and most preferably from 2
to 4%, all percentages being by weight with respect to
that of the starch component of the composition.
1~
Other suitable flame retardants which may be present in
the composition of the present invention include aluminum
trihydrate; aluminum acetylacetonate; aluminum acetate;
sodium aluminum hydroxy carbonate; magnesium aluminum
20 hydroxy carbonate; antimony oxide; molybdic oxide;
ammonium octamolybdate; zinc molybdate; magnesium
hydroxide; zinc borate; ammonium pentaborate; boric acid;
and sodium tetraborate. These flame retardants are
generally available, and the Borax compounds in
2~ particular may be obtained from the United States Borax
and Chemical Corporation, of 3075 Wilshire Boulevard, Los
Angeles, California 90010, USA.
These latter flame retardants may be present in the
composition in an amount of from 1 to 90% by weight with
respect to the starch component of the composition, and
preferably are present in the composition in an amount of
from 20 to 80% ~nd most preferably from 40 to 75%.
3~ The particularly preferred flame retardants are
guanidinium phosphate, ammonium polyphosphate and/or
ethylenediamine polyphosphate (in the presence or absence
of disodium orthophosphate), and guanidinium sulphate or
ammonium sulphate.
WO92/16S~ PCT/US92/02~M
2 ~ Q ~
-- 19 --
Still further substances which may be added to the
composition include animal or vegetable fats, preferably
in their hydrogenated forms, especially those which are
solid at room temperature. Such fats preferably have a
melting point of at least 50C and include triglyceride~
of C12-, C14-, C16-and C18- fatty acids.
10 The fats are added to the material comprising the
thermoplastic melt alone without extenders or
plasticisers, or to the melt together with mono- or di-
glycerides or phosphatides, of which lecithin is
preferred. Said mono- and diglycerides are preferably
derived from said animal or vegetable fats.
The total concentration of said fats, mono-, di-
glycerides and phosphatides may be up to 5% by weight,
ba~ed on the total weight of the composition.
Still further compounds which may be added to, or present
in the composition include boron-containing compounds,
particularly so when the composition is formed into
films, sheets or fibers. The presence of such compounds
2~ in the composition yields articles which have improved
transparency, Young's modulus and tear strength. The
preferred boron-containing compounds are boric acid,
metaboric acid, alkali and alkaline earth metal salts,
borax and derivatives thereof. Said compounds may be
30 present in the composition in an amount of between 0.002
and 0.4%, by weight with respect to that of the
composition, and preferably are present at a
concentration of between about 0.01 and 0.3%, likewise by
weight.
Inorganic salts of alkali or alkaline earth metals,
particularly LiCl and ~aCl may be additionally present in
the composition in an amount of between 0.1 and 5% by
weight with respect to that of the total composition.
The presence of such salts in the composition still
WO92~16584 PCT/US92/020~
~ `80 20 -
further improves the Young's modulus, transparency and
tear strength of articles made from the composition.
It will be appreciated that the concentration of the
components, particularly the coloring agents and borax
containing compounds, in the composition can be derived
according to a Master-batching process, if desired.
The compositions described herein above form
thermoplastic melts on heating under conditions of
controlled temperature and pressure. Insofar as such
melts may be proce~ed by any conventional shaping
process the present invention also refers to such
processes when u~ed to shape the composition or melt of
the present invention. Thus such melts can be processed
in the manner used for conventional thermoplastic
materials, such as injection molding, blow molding,
extrusion, coextrusion, compression molding, vacuum
forming, and thermoforming to produce shaped articles.
Whilst ~uch articles include containers, cartons, trays,
CUp8 (particularly for candles where the composition
compris0s a flame retardant), dishes, sheets, and
packaging materials, including the loose fill variety,
2S the shaped articles also include pellets and granulates
which may be ground to make powders for use in the
manufacture of shaped articles. Particularly preferred
articles are in foamed form, in injection molded form or
are in extruded form.
The range of pressures and temperatures suitable for
injection molding, filming, foaming and extrusion molding
are as disclosed hereinbelow.
35 Iniection moldina of the com~osition
In order to melt the starch accordincJ to the invention,
it is heated at a sufficient temperature for a time
sufficient to enable uniform melt formation.
W092/165~ PCT/US92/020W
2 1U~
- 21 -
The composition is preferably heated in a closed volume,
such as a closed vessel, or in the finite volume created
by the sealing action of unmolten feed material, which
action is apparent in the screw and barrel of an extruder
or injection molding equipment.
Thus ~aid screw and barrel is to be understood as a
closed volume. Pressures created in such a volume
correspond to the vapor pressure of the plasticizer
(usually water) at the used temperature. It will be
appreciated that pressures may be applied or generated,
as is known to be possible in the use of said screw and
1~ barrel.
The preferred applied and/or generated pressures are in
the rànge of pres~ures which occur in injection molding
or extrusion are known per ~-e, being up to about 150 x
20 105N/m2 , preferably ~p to about 75 x 105N/m2 and most
preferably up to about 50 x 105 N/m2.
The temperature u~ed in injection molding of the
composition is preferably within the range of 100C to
2~ 220C, more preferably within the range of from 160 to
200C, and most preferably within the range of 160 to
180C, the precise temperature being dependent up on the
type and nature of the starch used. In terms of ease of
processing it is preferred that potato or corn starch is
30 used.
The thus obtained melted starch composition is granulated
and is ready to be mixed with further components
according to a chosen mixing and processing procedure to
3~ obtain a granular mixture of melted starch starting
material to be fed to the screw barrel.
Filmina of the comPoSi tion
The composition is plasticised as above, except tha'
preferably it is heated to a temperature typically about
WO92/16~ PCTtUS92/02~
2~
- 22 -
lO to about 20C higher than those routinely used during
injection molding and extrusion of the composition.
Foamina of the ComPosition
The process for forming the composition of the present
invention into foams comprises:
10 a) providing a starting composition comprising starch,
plastici~er and at least one member selected from alkenol
homopolymers and/or alkenol copolymers which are present
in the composition at a concentration of from lO to 120
1~ parts per lO0 parts of said starch;
b) adjusting the plasticizer content of the composition
to between about 15 and about 40% by weight of the total
composition during processing or plastification;
c) heating the thereby adjusted composition at a
temperature of between lO0 and 220C and for a time at
least sufficient to form a uniform melt of the
composition;
2~ .
d) removing any excess moisture before the extruder die
to obtain a moisture content of between about 10% and
about 20%; and -
e) extruding the thereby heated composition under
30 conditions whereby the extrudate assumes a cross section
greater than that of the exit orifice of the extruder
die.
It is preferred that the plasticizer is water and that,
3~ prior to extrusion, the moisture content of the
composition is adjusted to between 14 and 20%, more
preferably between 16 and 18% and most preferably to 17%
by weight of the total composition, and that the
. composition is heated at a temperature of from about
160C to about 200C and most preferably from about 180C
W092/165~ 2 1 ~) 5 ~ ~ ~ PCT/US92/02~
- 23 -
to about 200C, and at a pressure corresponding at least
to the moisture vapor pressure at said temperature for a
time of at least 30 seconds.
The composition may be molded subsequent to its extrusion
using known thermoforming processes.
The invention will be further apparent from a
consideration of the following Examples.
ExamDle
lOkg of potato starch, 2.8 kg of polyvinyl alcohol having
a number average molecular weight of about 106,000 to
110,000 and degree of hydrolysis of between 87 and 89%,
(Airvoll 540S), 200g of magnesium silicate and lOOg of
stearic acid are combined. The moisture content of the
combined components is then adjusted to about 28% by
20 weight of the moistened starch mix. The moisture content
of the combined components may be adjusted to from about
to 30% by weight with similar results to those
obtained below.
25 The thus adjusted starch is fed into the entry port of a
twin screw extruder (Leistritz model LSM 34) having
screws co-rotating in a horizontal cylindrical barrel and
an outlet die mounted at the discharge end of the
extruder, opposite its entry port.
The starch composition is then heated to a temperature of
155C for about 70 seconds at a suitable pressure
necessary to avoid the formation of water vapor at said
temperature.
~5
The thus melted starch is extruded from the outlet die of
the extruder, and the extrudate cooled and pelletized.
The pelletized melted starch mix is conditioned to a
moisture content of about 17%, and then fed into the
WO92/165~ PCT/US92/02004
~ 24 -
entry port of a single screw extruder having a screw
length to diameter ratio of in the range of 25.
Extruders having a ratio of from 10 to 30 are also
useable in the process according to the present
invention.
The thus formed mix is heated to 190C for from 20-60
seconds and then extruded. Upon emerging from the exit
~ orifice of the extruder die, the extrudate assumes a
cross section greater than that of the said orifice to
form a foam material suitable for use as a packaging
material. Open and closed cell foams are thus produced
which have excellent properties with respect to density,
resilience and compressibility.
The extrudate is allowed to cool whereupon its bulk
density is determined in accord with the method described
20 by ~wang and Hayakawa in J. ~ood Sci., Vol. 45, pp 1400
to 1407, which description is incorporated herein by
reference. The resiliency and compressibility of the
extrudates are determined using a Texture Analyzer, known
to those skilled in the art, according to the procedure
2~ disclosed in European Patent Application No. 89111295.5
~Publication No. 0 375 831), which disclosure likewise is
incorporated by reference into the present application.
The bulk density, resilience and compressibility of the
30 foams are given in Table 1.
ExamDles 2 - 5
Example 1 is repeated, but with different quantities of
3~ polyvinyl alcohol. Thus the compositions of Examples 2 -
- 5 contain polyvinyl alcohol contents of 20, 25, 30, and
35% by weight with respect to the dry weight of the
starch component. The bulk densities, resilience and
compressibilities of the compositions thus formed are
listed in Table 1.
WO92/165~ 2 1 ~ ~ ~ 8 0 PCT/US92/020~
- 25 -
Examples 6-9
Example 1 is repeated except that potato starch is
replaced by maize starch, and the concentration of
polyvinyl alcohol is 10%, 20%, 25% or 30% by weight with
respect to that of the dry starch.
The resilience, compressibilities and bulk densities of
10 the foams thus produced are similar to those for potato
starch as given above in Table 1, with the
characteristics of the foam comprising 20% polyvinyl
alcohol being particularly good.
a~
WO 92/16584 26 PCI/US92/02004
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WO92/165~ PCT/US92/02
- 27 -
ExamPle 10
lOkg of starch, 4.5 kg of polyvinyl alcohol having a
number average molecular weight of about 106 to about
110, 000 and a degree of hydrolysis of between 87 and 89%
(Airvoll 540S), 200g of magnesium silicate and lOOg of
stearic acid are combined. The moisture content of the
combined components is then adjusted to 22% by weight of
10 the moistened starch mix. The thus adjusted starch is
fed into ~,he entry port of a twin screw extruder having a
screw rotating in a horizontal cylindrical barrel and an
outlet die mounted at the discharge end of the extruder,
opposite its entry port. The starch composition is then
heated to a temperature of 155C for about l minute at
the minimum pressure necessary to avoid the formation of
water vapor at said temperature.
The thus melted starch is extruded from the outlet die of
the extruder, and the extrudate cooled and pelletized.
The pelletized starch mix is conditioned to a moisture
content of about 17%, and then fed into the entry port of
2~ a single screw extruder having a screw length to diameter
ratio of 25.
The starch mix is then heated to from 180 to 200C for
from 0.3 to 1 minute and then extruded in the form of a
sheet which is subsequently thermo-formed according to
known techniques into articles such as trays, cups, and
dishes .
ExamPle 11
3~
This example describes the injection molding of tensile
test pieces from an extruded blend of polyvinyl alcohol,
pre-treated so as to be in the form of a pelletized melt,
~nd starch.
W092/165~ PCT/US92/02~M
`' 1 n .r~ ~ 8 0
- 28 -
Fifty part~ of high molecular weight, partially
hydrolysed (87-89 mole%) polyvinyl alcohol (Airvol 540)
having a degree of polymerization of about 2,200 and
~having an ash content of about 0.19% are introduced into
a high intensity Littleford 180L mixer and the mixer
started at 900 RPM.
When the temperature of the polyvinyl alcohol reaches
10 65C, 12.5 part~ of glycerol are added to the blender at
a ~low steady rate. After the addition of the glycerol,
0.17 parts of 85% phosphoric acid and 0.25 parts of
glycerol mono-oleate are added to the mixture as a
1~ processing aid.
Cooling water is added to the mixer jacket and controlled.
to maintain the product temperature below 100C at all
times. After the mono-oleate addition is complete,
20 mixing is continued at low speed until a free flowing
polyvinyl alcohol mixture is obtained. The mixture is
then discharged into a Littleford 400L cooling mixer and
the product temperature lowered to 40C. The mixture so
produced is free flowing and ~ree of clumps or degraded
2~ material.
The thus formed polyvinyl alcohol material is loaded into
a volumetric feeder and fed into a 46 mm reciprocating,
rotating extruder of the kind known to those skilled in
30 the art. The screw is designed to achieve a high degree
of mechanical energy input without product degradation.
The extruder is a devolatilizing extruder, and a vacuum
of 254 torr (lOin Hg) is applied at the vent port located
at 7 diameters to remove any residual moisture in the
polymer and acetic acid formed from the conversion of
sodium acetate to disodium monohydrogen phosphate. The
melt temperature of the polymer in tne working zone of
the extruder is maintained at the upper end of the
polymer melting curve as indicated by a Differential
Scanning Calorimeter (DSC~.
WO92/16~ PCT/US92/02~
2 ~ l 8 0
- 29 -
Melt temperatures are measured at 183C, 197C, and
199C. Typical operating conditions are:
Screw Speed 300 RPM
Screw Temperature 140C
Barrel Temperatures
1st zone 150C
2nd zone 150C
Production Rate 21.7 kg/hr
Max. Melt Temp. 201C
Screw Power 6.5 KW
Specific Energy Input 0.30 KW/hr
The product exits the extruder and is immediately cooled
below its glass transition temperature to prevent product
degradation and cry~tallization of the polymer that would
lead to gel formation during subsequent thermal shaping
operations. The strandæ are cut in a conventional manner
20 into pellets and collected.
The pellets produced are substantially free of
crystallinity and are gel-free, smooth and have a straw
color.
(a) 9500g of potato starch containing 15.1% water are
placed in a high speed mixer and 2875g (30% with respect
to the weight of the starch component) of the polyvinyl
alcohol pellets as produced above, 80.75g of hydrogenated
30 fat (lubricant release agent) sold as Boeson VP by
Boehringer Ingelheim, 40.37g of a melt flow accelerator
(lecithin~ sold as Metarin P by Lucas Meyer are added
under stirring. The water content of the final mixture
is 14.43%.
3g
(b) lO.OOOg of the mixture prepared under (a) is fed
through a hopper into a Werner & Pf~eiderer co-rotating
twin screw extruder (model Continua 37).
The temperature profile of the four sections of the
barrel is respectively 20~C/180C/180C/80C. Extrusion
WO92/16~84 PCT/US92/02~M
2 l- 3 ~ n - 30 _
of the blend is carried out with a mixture output of 8
kg/hr (screw speed 200 rpm). Water is added at the
inlet with a flow rate of 2 kgs/hr to bring the water
content of the material during extrusion to 31.5%. In the
last ~ection of the extruder 80 mbar reduced pressure is
applied to remove part of the water as water vapor.
The water content of the granulates is 17.5%, measured
after they had equilibrated at room temperature.
(c) The granulates of the pre-blended mixture as
obtained under (b) (H20 content: 17.5%) are fed through a
1~ hopper to an injection molding machine (Arburg
329-210-750) for the production of tensile test pieces.
The temperature profile of the barrel is:
90C/165C/165C.
20 The shot weight i8 8g, the re~idence time 450 sec., the
injection pressure 2082 bar, the back pressure 80 bar,
and the screw speed 180 rpm.
The tensile test pieces, which are of ~tandard design
2~ (DIN No. 53455), thus produced are conditioned in a
climatic cabinet at 50% R.H. for five days as an
arbitrary standard condition.
(d) The conditioned tensile test piece are then tested
30 for their stress/strain behavior on a Zwick tensile test
apparatus.
The samples are measured at room temperature using an
extension rate of 10 mm per minute. The test pieces thus
3~ obtained exhibit improved dimensional stability and
physical properties when compared with like test pieces
made from polyvinyl alcohol which is not pre-treated.
exam~le 12
(a) 8000g of potato starch containing 15% water are
WO92/165~ PCT/US92/020
210r3d~0
- 31 -
placed in a high speed mixer and 3200g (40% by weight
with respect to the starch component) of pre-treated
polyvinyl alcohol pellets; 68g of hydrogenated fat
(lubricant release agent~ sold as Boeson VP by Boehringer
Ingelheim, 34g of a melt flow accelerator (lecithin) sold
as Metarin P by Lucas Meyer are added under stirring.
The water content of the final mixture was 15.6%.
~0
(b) lO.OOOg of the mixture prepared under (a) are fed
into the hopper of a Werner & Pfleiderer co-rotating twin
screw extruder (model Continua 37).
1~ The temperature profile of the four sections of the
barrel was respectively 20C/50C/100C/50C. Extrusion
was carried out with a mixture output of 8 kg/hr (screw
speed 200 rpm). Water is added at the inlet with a flow
rate of 1 kg/hr to bring the water content of the
20 material during extrusion to 25%. In the last ~ection
of the extruder, 22 mbar reduced pressure was applied to
remove part of the water as water vapor.
The water content of the granulates thus produced is
2~ 14.8% as measured after they had equilibrated at room
temperature. The water content of the granulates is
adjusted to 17% by spraying water under stirring in a
conventional mixer.
30 (c) The granulates of the pre-blended mixture as
obtained under (b) (H20 content: 17%) are fed through a
hopper to an injection molding machine Arburg 329-210-750
for the production of tensile test pieces. The
temperature profile of the barrel is:
3~ 90C/185C/185/185C.
The shot weight is 7.9g, the residence time 450 sec., the
injection pressure 2200 bar, the back pressure 80 bar,
the screw speed 180 rpm.
W092/16S~ PCT/US92/02
~ - 32 -
The tensile test pieces (DIN No. 53455~ thus produced are
conditioned in a climatic cabinet at 50% R.H. for five
days as an arbitrary standard condition to equilibrate
them to a water content of about 14%.
(d) The conditioned tensile test pieces are then tested
for their stress/strain behavior on a Zwick tensile test
10 apparatus as described in Example 7. The test pieces
thus obtained exhibit improved dimensional stability and
physical properties when compared with like test pieces
made from polyvinyl alcohol which is not pre-treated.
1~ Exam~le 13
This Example describes the injection molding of candle
cups from an extruded blend of polyvinyl alcohol and
~tarch.
2~
A mixture of maize starch or high amylose starch (Hylon
VII obtainable from National Starch and Chemical
Corporation of Finderne Avenue PØ Box 6500 Bridgewater,
New Jersey 08807 USA), Boeson VP (as sold by Boehringer
2S Ingelheim), and lecithin (as sold as Metarin P by Lucas
Meyer) present in the ratio of 100: 2: 1 respectively is
prepared.
13.6 kg of this mixture is fed into the entry port of a
30 twin screw extruder (Leistritz model LSM 34) having
screw~ co-rotating in a horizontal cylindrical barrel and
an outlet die mounted at the discharge end of the
extruder, opposite its entry port.
3~ To this mixture is added 440 grams of glycerol, S.2 kg
of pre-plasticised polyvinyl alcohol having a number
average molecular weight of about 15,000 to 45,000 and a
degree of hydrolysis of 88 to 99%, and sufficient water
to ena~le the combined mixture to be compounded
appropriately. The amount of water added is dictated to
wog2/16~ 2 1 ~ PCT/US92/02~
- 33 -
a large extent by the nature of the starch and is easily
determined by the skilled man.
The starch composition is then heated to a temperature of
about 175C for about 30 to 120 seconds at a suitable
pressure necessary to avoid the formation of water vapor
at said temperature.
Ammonium sulphate is dissolved in water and added to the
heated and pressurized starch composition prior to
extrusion of the composition rom the outlet die of the
extruder.
1~
The ammonium ~ulphate is added in such an amount that its
f~nal concentration in the cooled extrudate is 3.5% by
weight with respect to that of the starch component
thereof.
Tho thus melted starch is extruded from the outlet die of
the extruder, and the extrudate cooled and pelletized.
The pellets of the pre-blended miY~ture as obtained above
2~ (H20 content preferably a~out 11%) are fed through a
hopper to an injection molding machine (Arburg 320)
fitted with a moul.d suitable for the production o~ candle
C~lpS .
30 In the case of maize starch, the melt temperature is
165C, the shot weight is 9g, the residence time is 240
sec., the injection pressure 110~ bar, the screw speed
190 rpm, and the mou}d temperatu_e 17~C.
~5 The candle CUp9 SO produced ha~s excellent physical
properties, substantial dimension~a' stability and are
made from a composition ~hich is sufficiently flame
re'arded to meet the DI~ /5200 flame retardancy
standards.
WO92/165~ PCT/US92/02004
- 34 -
ExamPles 14-16
Example 13 is repeated except that the composition from
which the candle cups are made is altered. Suitable
further compositions are given in Table 2 below. The
injection molding pressure, residence time etc. are
essentially as for Example 13 except for a slight
increase (to about 1200 bar) in the injection molding
~ pressure in the case where the polyvinyl alcohol is not
pre-plasticised.
Exam~le 17
Example 13 is repeated except that the flame retardant
used is ethylenediamine polyphosphate, present in the
composition in an amount of 4% by weight with respect to
that of the starch component thereof.
In Examples 13 to 17, the flame retardant is added at a
late stage in the compounding of the composition prior
to its injection molding, and the residence of the
composition (now comprising the flame retardant) in the
2~ extruder is kept to a minimum.
In addition, that part of the extruder which contacts the
flame retarded starch composition may be especially
adapted to reduce the corrosive effects of the retardant
3~ on the extruder.
The candle cups produced according to Examples 13 to 17
have excellent physical properties, substantial
dimensional stability and are made from a composition
3~ which is sufficiently flame retarded to meet the DIN
75200 flame retardancy standards.
WO 92/16584 2 ~ o PCI/US92/02004
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W092/165~ PCT/US92/02
- 36 -
Example 18
A composition comprising polyvinyl alcohol, glycerin,
maize starch, Boeson, lecithin, and water present in the
ratio of 96:24:100:1:0.5:12 is prepared. The polyvinyl
alcohol has a number average molecular weight of about
106,000 to 110,000 and degree of hydrolysis of about 88%
(Airvoll 540S).
The composition is fed into the entry port of a twin
screw extruder ~Leistritz model LSM 34) having screws
co-rotating in a horizontal cylindrical barrel and an
outlet die mounted at the discharge end of the extruder,
opposite its entry port.
The starch composition is then heated to a temperature of
between 171 and 185C for about 60 to 120 seconds, with
20 mec~anical energy being provided by a strong screw
configuration (as i8 known to those skilled in the art)
at a suitable pressure necessary to avoid the formation
of water vapor at said temperature.
2~ The composition is plasticised in the extruder until
uniform melt formation is achieved, thereafter the
moisture content of the composition is reduced to about
10% before exit of the composition from the extruder
barrel.
The melt is formed into films of varying thickness
between 0.2 and 0.5 mm using conventional down stream
equipment. The obtained films, whilst suitable for use
per se, in packaging applications for example, can be
3~ used in the preparation of laminates comprising said film
and a metal (preferably aluminum) foil. A film
thickness of 0.4mm is particularly preferred.
ExamPle 19
Pellets are made according to the above examples from
W092/165~ ~ 0 PCT/US92/02
- 37 -
compositions comprising maize starch, 1% by weight with
respect to that of the starch of stearic acid; 2%
likewise by weight of Chematalc 5M and optionally 0.05%
likewise by weight of iron oxide. The compositions
further contain 20% by weight with respect to that of the
starch of the following polyvinyl alcohols:
a) Airvol S40 having a degree of hydrolysis of 87-89%;
~ b) Mowiol 56-98 having a degree of hydrolysis of 98.4%;
c) Mowiol 66-100 having a degree of hydrolysis of
99-7%; and
d) Airvol 16S having a degree of hydrolysis of 99.3%.
The pellets containing the various polyvinyl alcohols are
each stirred in demineralized water at 30C for 72 hours,
the samples then filtered and the weight loss as a
consequence o dissolution of the pellet determined.
Table 3 below indicates that the starch compositions
comprising high degree of hydrolysis polyvinyl alcohols
are substantially resistant to dissolution, whereas those
samples comprising relatively reduced degree of
2~ hydrolysis polyvinyl alcohol are considerably more
soluble. The compositions according to Example 19 which
are relatively water resistant are, for example, highly
suitable for use in the preparation of sustained release
fertilizer systems.
TABLE 3
SampleWeight loss of observations
sample (%~
a 27.1 strong dissolution
b 0.9 no change
c 1.3 no change
d 2.2 no change
WO92~165~ PCT/US92/02~
2-.a~33 - 38 - `
It will be appreciated that it is not intended to limit
the invention to the above examples only, many variations
thereto and modifications thereof being possible to one
skilled in the art without departing from its scope,
which i8 defined by the appended claims.
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