Note: Descriptions are shown in the official language in which they were submitted.
W092/16583 PCT/US92/02~3
7 9
Biodearadable comPositions comPrisina starch derivatives
i
The present invention relates to biodegradable polymer
compositions capable of being formed by heat and pressure
into articles having substantial dimensional stability.
10 The invention relates particularly to biodegradable,
compositions comprising a starch derivative, 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
SS formation. 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
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 it8 components so that such undergo
endothermic rearrangement. Preferably the starch
material contains a defined amount of water and melt
formation is carried out at an elevated temperature in a
closed volume, and hence at an elevated pressure.
It is, however, possible to melt starch substantially in
the absence of water, but in the presence of another
suitable plastici2er, for example a liquid having a
boiling point higher than the starch glass transition and
melting temperature.
Different degrees of melt formation, which can be
measured by various methods, are possible. One method,
for example, is to microscopically determine the amount
WO92tl6583 PCT/US92/02~3
9 2 -
of ~ranular struct~re remaining in a starch melt. It is
preferred that the starch is destructurised, viz, 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.
It is an advantage of the present invention that
compositions may be formed from starch which has a
~S relatively low degree of destructurisation.
Ind. Eng. Chem. Prod. ~es. Dev. (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 decrea~es with
increasing starch concentrations so 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
2S composition comprising such a low melt flow index is not
suitable for the injection molding of articles therefrom,
wherein a melt flow index of about 7 or higher is
typically required. It is surprising that the present
inventive compositions, which comprise relatively high
concentrations of starch derivatives, can easily be
injection molded.
The melt flow index of the composition is defined as the
amount (in grams) of a thermoplastic material which can
3S be forced in 10 minutes through a 2.0665mm orifice when
subjected to a force of 0.2160 grams.
Moreover, it is implicit in the art of forming
thermoplastics that the major components thereof should
be of high molecular weight, and preferably that the
WO92/16583 PCT/US92/02003
231~rj~79
molecular weights of such components should be of similar
magnitudes.
; It is surprising that articles having excellent physical
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 derivative component of the
composition, is present in high concentrations relative
thereto.
SUMMARY OF THE INVENTION
lS
According to the present invention, there is provided a
biodegradable composition as obtained from a melt
comprising a plasticizer and at least one member selected
from alkenol homopolymers and/or alkenol copolymers which
20 are combined under conditions sufficient to ensure
un~form melt formation, characterized in that the
composition includes a starch derivative.
By plasticizer is meant a substance which can be
2~ incorporated into a material to increase its flexibility,
workability or distensibility or reduce the melt
viscoaity, ~ower the temperature of a aecond order
transition, or lower the elastic modulus of the product.
The term plasticizer includes solvent plasticizers and
30 internal plasticizers.
The preferred plasticizer is water.
The starch derivative may be selected from the group
~5 consisting of starch esters and starch ethers, and the
degree of substitution of said starch der~vative may be
from about O.l to about 3.O.
It is preferred that the degree of substitution of said
derivative is at least 0.8, and more preferred that the
degree of substitution is from about 0.8 to about 2.l.
WO92/16~B3 PCT/US92/02003
~ l a ~
-- 4 --
In one embodiment of the composition, the starch
derivative has an amylose content of up to about 95% by
weight with respect to that of the starch derivative. It
is preferred that the lower limit of the amylose content
i~ between about 10 and about 15% by weight with respect
to that of the starch derivative.
The starch derivative preferably has an equilibrium
moisture content of less than about 7% at 25C and a
r~lative humidity of about 50%.
The at least one member may be present in the composition
at a concentration of from 10 to 200 parts per 100 parts
of dry starch derivative.
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%
and preferably has a number average molecular weight of
about lS,0~0 to about 250,000, and more preferably has a
number average molecular weight of from 15,000 to
2~ l5O,ooo.
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
30 polyvinyl alcohol to melt it and substantially eliminate
crystallinity in the melt. It is particularly preferred
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
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,
W092/16~83 2 ~ 7 9 PCT/US92/02~3
isobutylene and/or styrene with subsequent hydrolysis of
the vinyl ester group.
; Such copolymers are known and are described in
Encyclopedia of Polymer Science and Technology,
Inter~cience Publ. Vol. 14, 1971"
The composition may further comprise one or more
~ compounds selected from the group of water-soluble and/or
water-swellable polymers and one or more hydrophobic
thermoplastic polymer(s) which is/are substantially
water-insoluble.
~S
The composition may still further comprise at least one
member selected from the group consisting of extenders,-
fillers, lubricants, mold release agents, other
plasticisers, stabilisers, coloring agents, nucleating
20 agents, flame retardants, boron-containing compounds and
alkali and alkaline earth metal salts.
It will be appreciated that the concentration of the
components in the composition, particularly the coloring
2~ agents, can be derived according to a Master-batching
process, if desired.
The present invention further relates to compositions in
the form of a melt comprising a plastic1zer and at least
30 one member selected from alkenol homopolymers and/or
alkenol copolymers which are combined under conditions
sufficient to ensure uniform melt formation,
characterized in that the composition includes a starch
derivative.
The present invention still further relates to shaped
articles, including a granulate or pellet, made from said
composition or melt.
The melted compositions may be further processed into
shaped articles by a process selected from the group
W092/16~83 PCT/US92/02~3
~10~7~
-- 6 --
consisting of: injection molding, compression molding,
filming, blow molding, vacuum forming, thermoforming,
extrusion, co-extrusion, foaming, and combinations
; thereof.
The present invention further relates a method for
producing the composition of the present invention,
characterized by:
~0
a) providing a starting composition comprising a starch
derivative, a plasticizer and at least one member
selected from alkenol homopolymers and/or alkenol
copolymers;
lS
b) adjusting the plasticizer content of the composition
to between about 0.5 and about 40% by weight of the total
composition during proce~sing or plastification;
c) heating the thereby adjusted composition in a
closed volume at a temperature of between 100 and 220C
and at a pressure corresponding at least to the moisture
vapor pressure at said temperature for a time at least
2S sufficient to form a melt of the composition;
d) removing any excess moisture before the extruder die
to obtain a moisture content of between about 5% and
about 20%;
and -
e) extruding the thereby heated composition.
The pre~ent invention further includes a melt as obtained
35 according to the method.
The invention will be further apparent from the following
description, in conjunction with the following examples
and the appended claims.
WO92/16583 2 1 i~ ~ '1 7 9 PCT/US92/02~3
SPECIFIC DESCRIPTION
The present invention is defined by the appended claims.
In particular, the invention provides a biodegradable
compo~ition as obtained from a melt comprising 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
formation, characterized in that the composition
includes a starch derivative.
The melt preferably is thermoplastic in character.
Said derivative is made according to known methods from
at least one member selected from the group consisting of
starches of vegetable origin, which starches are obtained
from potatoes, rice, tapioca, corn, pea, rye, oats and
20 wheat.
The starch derivative may be selected from the group
consisting of starch e~ters and starch ethers, and may
have a degree of substitution of from about O.l to about
25 3 0
It is preferred that the degree of substitution of said
derivative is at least 0.8, and more preferred that the
degree of substitution is from about 0.8 to about 2.l.
The derivative may be a starch ester selected from the
group consisting of acetates, propionates, butyrates and
the starch esters of C5 to Cl2 fatty acids.
3~ Where the derivative is a starch acetate the deqree of
substitution is from about 0.5 to about 1.8, more
preferably the starch is substituted to a degree of from
about 0.7 to about 1.8, and most preferably the degree of
substitution is from about 0.8 to about l.5.
W092/16583 PCT/US92/02~3
2 1 ~ ~ ~ 7 9 - 8
Where the derivative is a starch propionate, the degree
of substitution is from about 0.5 to about 1.6, and more
preferably is from about 0.7 to about 1.4.
The derivative may be selected from the group consisting
of alkyl ethers and hydroxyalkyl ethers,
hydroxyalkylalkylethers and mixtures thereof.
~0
Preferred starch ethers include the methyl ether,
ethylether, propylether, butylether, hydroxymethylether,
hydroxyethylether, hydroxypropylether,
hydroxyethylmethylether and hydroxypropylmethylether and
derivatives thereof.
In one embodiment of the composition, the starch
derivative has an amylose content of up to about 95% by
weight with respect to that of the starch.
In another embodiment of the composition, the derivative
has an amylose content of up to about 85% by weight with
respect to that of the starch.
2~ In a further embodiment of the composition, the
derivative has an amylose content of up to about 75% by
weight with respect to that of the starch.
In a still further embodiment of the composition, the
30 derivative has an amylose content of up to about 65% by
weight with respect to that of the starch.
In a still further embodiment of the composition, the
derivative has an amylose content of up to about 45% by
3S weight with respect to that of the starch.
In a still further embodiment of the composition, the
derivative has an amylose content of between about 30 and
about 35% by weight with respect to that of the starch.
WO92~16583 PCT/US92/02~3
2 ~ Q i~
g
It is preferred that the lower limit of the amylose
content is between about 10 and about 15% by weight with
respect to that of the starch.
The starch derivative may have an equilibrium moisture
content of less than about 7% at 25C and a relative
humidity of about 50%, and more preferably has an
equilibrium moisture content of less than about 5% at
25C and a relative humidity of about 50%.
The at least one member may be present in the compositio~
at a concentration of from 10 to 200 parts per 100 parts
1~ of dry starch.
The composition may comprise from about 10 to about 120
parts of said polymer and / or copolymer per 100 parts by
weight of dry starch derivative, and in a preferred
embodiment, the composition comprises from about 10 to
about 100 parts of said polymer or copolymer per 100
parts of ~tarch derivative.
The composition may also comprïse a polymer or copolymer
2~ content of from 10 to 65 parts, and particularly from 20
to 40 parts with respect to 100 parts of starch
derivative.
The alkenol homopolymer is preferably polyvinyl alcohol
30 (PVA) having a number average molecular weight of at
least about 15,000 (which corresponds to a degree of
polymerization of at least 340). It is more preferred
that the PVA has a number average molesular weight of
between about 50,000 and 250,000, and most preferred that
3S it has a number average molecular weight 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.
WO92/16583 PCT/US92/02003
2io~ 9 - lo-
Polyvinyl alcohol (PVA) is generally made from
hydrolysis, or alcoholysis of polvvinyl 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 is from about 87 to 99.9 mol%.
.0
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 20~S (degree of hydrolysis 87-89%, molecular
weight about 110 - 31,000), Elvanol 90-S0 (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).
~0
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
2~ the polyvinyl alcohol to both melt it and essentially
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 ~57. Thus the present inventive composition contains
pre-treated polyvinyl alcohol in the form of a melt which
has been obtained previously by adding sufficient enerqy
to polyvinyl alcohol to 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 O 92/16583 PC~r/US9~/02003
2~ 79
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
alcohol. It is preferred that the pre-treated polyvinyl
alcohol is plasticised by the addition thereto of a
polyhydric alcohol plasticizer in an amount of from 2 to
20% by weight of the polyvinyl alcohol. The
1~ pre-treated polyvinyl alcohol may further comprise sodium
acetate and phosphoric acid in a molar ratio of about 2
to 1. 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 such sodium
acetate acts as a catalyst for decomposition of the
polyvinyl alcohol. Accordingly, phosphoric acid may be
added to the polyvinyl alcohol composition from which the-
pre-treated polyvinyl alcohol melt is made, in the ratio
of 1 mole of acid per 2 moles of acetate, in order to
20 neutralize said sodium acetate. Low ash polyvinyl
alcohol, which is es~entially 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 10~ lower than that of the
untreated polyvinyl alcohol, and particularly preferably
3q 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
35 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 energv beyond that necessary to
melt the polyvinyl alcohol and eliminate crystallinity
W092/16583 PCT/US92/02003
2~ 79 - 12 -
must be removed as "waste energy" reducing the efficiency
of the formation of the pre-treated polyvinyl alcohol.
Optimally the polyvinyl alcohol reguires an input of
about 0.35 to about 0.45kWh/kg both to melt it and
substantially eliminate crystallinity in the melt.
Said alkenol copolymers may contain vinyl alcohol units
and alipha~ic chain units and may be 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
1~ 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
20 alcohol units to alkylene units is preferably from about
40 : 60 to about 9O : lO and more preferably from about
45 : 55 to about 70 : 30. The most preferred EVOH has an
ethylene content of 44%.
2~ The starch derivative which is present in the composition
is at least one member selected from the group consisting
of chemically modified starches of vegetable origin,
which starches are obtained from potatoes, rice, tapioca,
corn, pea, rye, oats, wheat, including physically
30 modified ~tarch, irradiated starch, starch in which mono
or divalent ions associated with phosphate 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;
3~ pre-extruded starches and starches which have been so
heated ~s to undergo the specific endothermic transition
characteristically preceding oxidative and thermal
degradation.
The starch component of the composition according to the
invention includes starch melted in the absence of added
WO92/16583 PCT/US92/02003
7 9
- 13 -
water, but in the presence of another plasticizer - such
as glycerol.
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
0 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 may-thus have
a water content of between about 10 and about 20% 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.
The starch derivative may be mixed with the polymer or
copolymer and optionally other additives as mentioned
hereinbelow in any desired sequence. For example, the
derivative may be mixed with all of the intended
2~ 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 derivative may, however, be mixed with
30 optional additives, the derivative melted and granulated
before addition of the polymer or copolymer, for example
the polyvinyl alcohol, which mix may then be further
processed.
35 Prefera~ly, however, the derivative is mixed with
additives together with the polymer or copolymer, for
example polyvinyl alcohol, to form a free flowing powder,
which is useful for continuous processing, and melted and
either granulated or extruded directly into the
solidified composition of the present invention.
WOg2~16583 PCT/US92/02~3
2 1~ l r~ 9
- 14 -
The composition may optionally consist at least of the
combination of a starch derivative and one member
selected from alkenol homopolymers and copolymers which
have been 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.
Alte~natively, and or additionally, the alkenol
homopolymers and copolymers may have been pre-plasticised
with, for example, a polyhydric alcohol such as glycerol.
1~ The starch derivative present in the composition may have
been 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.
20 Optionally the composition comprises at least one member
selected from the group consisting of extenders, fillers,
lubricants, mould release agents, plasticisers,
stabilisers, coloring agents, and flame retardants.
2~ The composition may further contain in an amount up to 60
%, preferably in an amount up to 35% and most preferably
in an amount up to 25% by weight of the total
compo~ition, one or more hydrophobic thermoplastic
polymer(s) which is/are substantially water-insoluble.
30 Such a polymer is one that dissolves water at a rate of
less than 25 grams per 100 grams of the dry polymer, and
more preferably at a rate of less than 15 grams per lO0
grams of dry polymer when immersed in water at room
temperature. Examples of hydrophobic thermoplastic
3~polymers are polyolefines, such as polyethylene (PE),
polyisobutylenes, polypropylenes, vinylpolymers such as
poly(vinyl chloride) (PVC), poly~vinyl acetates),
polystyrenes; polyacrylonitriles (PAN);
polyvinylcarbazoles (PVK); substantially water-insoluble
poly(acrylic acid) esters or poly(methacrylic acid)
esters; polyacetals (POM); polycondensates such as
WO92/16583 2 ~ ~ ~ '1 7 ~ PCT/US92/02003
- 15 -
polyamides (PA), thermoplastic polyesters, polycarbon-
ates, polyurethanes, poly~alkylene terephthalates);
polyarylethers; thermoplastic polyimides; but also
poly(hydroxybutyrate) (PHB) and high molar-mass,
substantially water-insoluble poly(alkylene oxides) such
as polymers of ethylene oxide and propylene oxide as well
as their copolymers are included.
Further included are hydrophobic thermoplastic copolymers
of the different kinds known such as ethylene/vinyl
acetate-copolymers (EVA); ethylene/vinyl
alcohol-copolymers (EVOH); ethylene/acrylic
~S acid-copolymers (EAA); ethylene/ethyl acrylate-copolymers
(EEA); ethylene/methyl acrylate-copolymers (EMA); ABS -
copolymers; styrene/acrylonitrile-copolymers (SAN); and
mixtures thereof.
20 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,
2~ such as: methylcellulose, hydroxymethylcellulose,
hydroxyethylcellulose, hydroxypropylcellulose,
hydroxyethylmethylcellulose,
hydroxypropylmethylcellulose,
hydroxybutylmethylcellulose, cellulose esters and
30 hydroxyalkylcellulose esters such as: cellulose
acetylphtalate (CAP), Hydroxypropylmethyl-cellulose
(HPMCP); carboxyalkylcelluloses,
carboxyalkyl-alkylcelluloses, carboxyalkylcellulose
esters such as: carboxymethylcellulose and their
3S alkali-metal salts; the analogous derivatives of starch
as named for all the cellulose derivatives above;
water-soluble synthetic polymers suc~ as: poly(acrylic
acids~ and their salts and essentially water soluble
poly~acrylic acid) esters, poly(methacrylic acids) and
their salts and essentially water-soluble
poly(methacrylic acid) esters, essentially water soluble
W092/16583 PCT/US92/02~3
- 16 -
poly(vinyl acetates), poly(vinyl acetate phthalates)
(PVAP), poly(vinyl pyrrolidone), poly(crotonic acids);
cationically modified acrylates and methacrylates
possessing, for example, a tertiary or quaternary amino
group, such as the diethylaminoethyl group, which may be
~uaternized if desired; and mixtures of such polymers.
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
1~ temperature.
Suitable fillers incl~de, for example, wood-derived
materials, and oxides of magnesium, aluminum, silicon,
and titanium. The fillers are present in the composition
20 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,
2~ 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
30 include unsaturated fatty acid amides, preferably amides
of C 18 - C 24 unsaturated fatty acids, such as the amide
of cis-13-docosenoic acid (erucamide) and amides of C 12
- C 24 carboxylic acids, such as the amide of docosanoic
acid (behenamide). The particularly preferred lubricant
3~ is stearic acid, which is present in the composition in
an amount of up to 10 parts p~r 100 parts of starch
derivatiYe, preferably in an amount of from 1 to 3 parts
per 100 parts of derivative, and most preferably is
present in the composition in an amount of 1 part per 100
parts of derivative.
W O 92tl6583 2 1 ~ 7 9 PC~r~US92/02003
- 17 -
The composition of the present invention may also
comprise a nucleating agent, - particularly so where the
composition is in foamed form - having a particle size 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,
0 boron nitrate an~ magnesium silicate, or mixtures
thereof. It is preferred that said nucleating agent is
selected from amongst silica, titania, alumina, barium
oxide, magnesium oxide, sodium chloride, and magnesium
silicate! or mixtures thereof.
The particularly preferred nucleating agent is magnesium
silicate (micro talcum), which is present in the-
composition in an amount of up to lO parts of agent per
lOO parts of derivative. Preferably the agent is present
20 in the composition in an amount of from 1 to 3 parts per
lOO parts of derivative, and most preferably in an amount
of 2 parts per lOO parts of derivative.
Plasticisers include urea and low molecular weight
25 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
manner.
~5 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
0.5% and about 5% by weight, based on the weight of all
of the components, including the water therein.
WO92J16~83 PCT/US92/02~3
2~ 7 9 ` ` _ 18 -
Preferably the sum of the plasticizer (including water
where ~uch is pre~ent 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,
alkylidenbi~phenols, secondary aromatic amines;
stabilisers against photo-decomposition, such as, for
example, uv absorbers and quenchers; hydroperoxide
decomposers; free radical scavengers, and anti-microbial
agents.
1~
Coloring agents include ~nown azo dyes, organic or
inorganic pigments, or coloring agents of natural origin.-
Inorganic pigments are preferred, such as the oxides of
iron or titanium, theRe oxides being present in the
20 composition at a concentration of between about 0.01 and
about 10% by weight, 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 preferably the coloring agents are present in the
2~ 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
the 0.05%.
~0 The composition may further comprise flame retardants
which, for example, comprise phosphorous, sulphur and
halogens, or mixtures thereof.
Suitable phosphorous-containing flame retardants include
3~ diethyl-N,N-bis(2-hydroxyethyl) aminomethyl phosphonate;
dimethyl methylphosphonate; phosphoni- acid, methyl-,
dimethylester, polymer with oxirane and phosphorous
oxide; aliphatic phosphate/phosphon~te oligomers;
tributyl phosphate; triphenyl phosphate; tricresyl
phosphat~; 2-ethylhexyl diphenyl phosphate; and
tributoxyethyl phosphate. These retardants are available
W O 92/16~83 PC~r/US92/02003
7 ~
from Akzo Chemicals Inc. of 300 South Riverside Plaza,
Chica~o, Illinois, USA.
Further suitable phosphorous-containing retardants
include: bis (hydroxypropyl) sec.butyl phosphine oxide
which can be obtained from the Chemical Products Group 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,
1~ methyl-,(~-ethyl-2-methyl-1,3,2-dioxaphosphorinan-5-yl)m-
ethyl ethyl ester, P-oxide and phosphonic acid, methyl-,
bis 1(5-ethyl-
2-methyl-1,3,2-dioxaphosphorinan-5-yl)methyl] ester,
P,P`-dioxide as sold under the trade name Amgard Vl9;
20 ammonium polyphosphate; ethylendiamine polyphosphate;
melamine phosphate; dimelamine phosphate; and
microencapsulated red phosphorous.
Where ammonium polyphosphate and ethylendiamine
2~ polyphosphate are used as flame retardants, it is
preferred that they are buffered with disodium
orthophosphate so that they are thereby less corr~sive to
the eguipment used for processing the composition
comprising them.
A still further suitable phosphorous containing flame
retardant is guanidinium phosphate which can be obtained
from Chemie Linz GmbH of St Peter Strasse 25, A-4021,
Linz, austria.
3~
Suitable halogen-containing flame retardants include
chlorinated paraffin, which is obtainable from Occidental
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
W O 92/16~83 PC~r/US92/02003
2 1 ~ 9
- 20 -
Corporation, of P.O. Box 2200, West Lafayette, Indiana,
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 Wilson at the address given above.
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.
Suitable sulphur containing-retardants include ammonium
sulfate; ammonium sulfamate; and tetrakis (hydroxymethyl)
phosphonium sulfate; all of which may be obtained from
the American Cyanamid Company, of One Cyanamid Plaza,
Wayne, New Jersey, 07470, USA. Guanidinium sulfate,
~0 obtainable from Chemie Linz at the address given above,
may also be u~ed as a flame retardant.
The above mentioned flame retardants are present in the
starch-containing composition in an amount of from 0.1 to
25 10%, preferably from 1 to 6%, and most preferably from 2
to 4%, all percentages being by weight with respect to
that of the derivative component of the composition.
Other suitable flame retardants which may be present in
30 the composition of the present invention include aluminum
trihydrate; aluminum acetylacetonate; aluminum acetate;
sodium aluminum hydroxy carbonate; magnesium aluminum
hydroxy carbonate; antimony oxide; molybdic oxide;
ammonium octamolybdate; zinc molybdate; magnesium
3~hydroxide; zinc borate; ammonium pentaborate; boric acid;
and sodium tetraborate. These flame retardants are
generally available, and the Borax compounds in
particular may be obtained from the United States Borax
and Chemical Corporation, of 3075 Wilshire Boulevard, Los
Angeles, California 90010, USA.
WO92/16~83 ~ 1 Q 3/~7~ PCT/US92/02003
- 21 -
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 derivative component of the
composition, and preferably are present in the
composition in an amount of from 20 to 80% and most
preferably from 40 to 75%.
The particularly preferred flame retardants are
guanidinium phosphate, ammonium polyphosphate and/or
ethylenedi~mine polyphosphate (in the presence or absence
of disodium orthophosphate), and guanidinium sulphate or
ammonium sulphate.
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
20 melting point of at least 50C and include triglycerides
of C12-, C14-, C16-and C18- fatty acids.
The fats are added to the material comprising the
thermoplastic melt alone without extenders or
25 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.
30 The total concentration of said fats, mono-, di-
glycerides and phosphatides may be up to 5% by weight,
based 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
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,
WO92/16583 PCT/US92/02003
~lU5479 - 22 -
borax and derivatives thereof. Said compounds may be
present in the composition in an amount of between 0.002
and 0.4%, by weight with respect to that of the
composition, an~ preferably are present at a
concentration of between about O.Ol and 0.3%, likewise by
weight.
Inorganic salts of alkali or alkaline earth metals,
lO particularly LiCl and NaCl may be additionally present in
the composition in an amount of between O.l and 5% by
weight with respect to that of the total composition.
The presence of such salts in the composition still
l~ 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
20 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
2~ controlled temperature and pressure. Insofar as such
melts may be processed by any conventional shaping
process the present invention also refers to such
processes when used to shape the composition or melt of
the present invention. Thus such melts can be proces~ed
30 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 such articles include containers, cartons, trays,
3~ cups (particularly for candles where the composition
compri~es a flame retardant), dishes, sheets, and
packaging materials, including the loose fill variety,
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
WO92/16583 PCT/US92/02~3
2~05'1-1~
- 23 -
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.
Iniection moldina of the com~osition
~0
In order to melt the starch according to the invention,
it is heated at a sufficient temperature for a time
sufficient to enable uniform melt formation.
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
20 or injection molding equipment.
Thus said 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
2~ (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
barrel.
30 The preferred applied and/or generated pressures are in
the range of pressures which occur in injection molding
or extrusion are known er se, being up to about 150 x
lO5N/m2 , preferably up to about 75 x 10 N/m2 and most
preferably up to about 50 x 105 N/m2.
3~
The te~perature used in injection molding of the
~omposition is preferably within the range of 100C to
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 derivative used. In terms of
W092/l6~83 PCT/US92/02~3
2 1 ~ ~ 4 1 9 - 24 -
ease of processing it is preferred that potato or corn
starch derivative i 8 used.
The thus obtained melted composition is granulated and is
ready to be mixed with further components according to a
chosen mixing and proce~sing procedure to obtain a
granular mixture of melted starch starting material to be
fed to the screw barrel.
~0
Filmina of the comPosition
The composition is plasticised as above, except that
preferably it i8 heated to a temperature typically about
10 to about 20C higher than those routinely used during
injection molding and extrusion of the composition.
Foamina of the ComDosition
20 The process for forming the composition of the present
invention into foams comprises:
a) providing a starting composition comprising a starch
derivative, plasticizer and at least one member selected
2~ from alXenol homopolymers and/or alkenol copolymers;
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;
3~
d) removing any excess moisture before the extruder die
to obtain a moisture content of bet~een about 10% and
about 20%; and -
e) extruding the thereby heated composition under
conditions whereby the extrudate assumes a cross section
W092/16583 PCT/US92/02003
~ 1 U ~
- 25 -
greater than that of the exit orifice of the extruder
die.
It i~ preferred that the plasticizer is water and that,
prior to extrusion, the moisture content of the
compo~ition i8 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
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.
~0
The invention will be further apparent from a
consideration of the following Examples.
ExamPle 1
2~
This Example describes the injection molding of candle
cup~ from an extruded blend of polyvinyl alcohol and a
starch derivative.
30 A mixture of hydroxy propylated maize starch or hydroxy-
propylated high amlylose starch (Hylon VII and
hydroxypropylated Hylon VII respectively, obtainable from
National Starch and Chemical Corporation of Finderne
Avenue PØ Box 6500 Bridgewater, New Jersey 08807 USA),
~5 Boeson VP (as sold by Boehringer 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
twin screw extruder (Leistritz model LSM 34) having
screws co-rotating in a horizontal cylindrical barrel and
W092/16583 PCT/US92/02~3
.
2105'~9 - 26 -
an outlet die mounted at the discharge end of the
extruder, opposite its entry port.
To this mixture is added 440 grams of glycerol, 5.2 kg
of pre-plasticised polyvinyl alcohol having a number
average molecular weight of about 15,000 to 45,000 and a
degree o hydrolysis of 88 to 99X, and sufficient water
to ena~le the combined mixture to be compounded
appropriately. The amount of water added is dictated to
a large extent by the nature of the derivative and i~
easily determined by the skilled man.
The composition is then heated to a temperat~re of about
175C for about 30 to 120 seconds at a suitable pressure
necessary to avoid the formation of water vapor at said
temperature.
20 Ammonium sulphate i8 di~olved in water and added to the
heated and preP~urized starch composition prior to
extrusion of the composition from the outlet die of the
extruder.
2~ The ammonium sulphate is added in such an amount that its
final concentration in the cooled extrudate is 3.5% by
weight with respect to that of the starch derivative
component thereof.
The thus melted composition is extruded from the outlet
die of the extruder, and the extrudate cooled and
pelletized.
The pellets of the pre-blended mixture as obtained above
(H20 content preferably about 11%) are fed through a
hopper to an injection molding machine (Arburg 320)
fitted with a mould suitable for the p~oduction of candle
cups .
The candle cups so produced have excellent physical
properties, substantial dimensional stability and are
W092/~6583 2 1 ~ 5 ~ PCT/US92/02003
- 27 -
made from a composition which is sufficiently flame
retarded to meet the DIN 75200 flame retardancy
standards.
ExamPle 2
Example 1 is repeated except that the composition from
which the candle cups are made is altered. The altered
composition compri~es hydroxy-propylated 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 Ingelheim),
lS and lecithin tas sold as Metarin P by Lucas Meyer)
present in the ratio of 100: 2: 1 respectively.
10 kg of this mixture is fed into the entry port of a
twin screw extruder (Leistritz model LSM 34) having
20 ~crew~ co-rotating in a horizontal cylindrical barrel and
an outlet die mounted at the discharge end of the
extruder, opposite its entry port.
To thi~ mixture i~ added 440 grams of glycerol, 3 kg of
2~ polyvinyl alcohol having a number average molecular
weight of about 11,000 to 31,000 and a degree of
hydrolysis of 98 to 98.8%, and sufficient water to enable
the combined mixture to be compounded appropriately.
10 The starch composition is then melted at a presRure
(about 1200 bar) necessary to avoid the formation of
water vapor at the temperature at which the composition
is melted.
3~ Ammonium sulphate is dissolved in water and added to the
heated and pressurized composition prior to extrusion of
the composition from the outlet die of the extruder.
The ammonium sulphate is added in such an amount that its
final concentration in the cooled extrudate is 3.5% by
W092/16~83 ~ PCT/US~2/02003
2~ 05~79
- 28 -
weight with respect to that of the starch derivative
component thereof.
The thus melted starch is extruded from the outlet die of
the extruder, and the extrudate cooled and pelletized.
The pellets of the pre-blended mixture as obtained above
(H20 content preferably about 11%) are ~ed through a
hopper to an in~ection molding machine (Arburg 320)
fitted with a mould suitable for the production of candle
cups.
1~ The candle cups 80 produced have excellent physical
properties, substantial dimensional stability and are
made from a composition which is sufficiently flame
retarded to meet the DIN 75200 flame retardancy
~tandards.
E~amDle 3
Example 1 i8 repeated except that the flame retardant
used is ethylenediamine polyphosphate, present in the
2~ composition in an amount of 4% by weight with respect to
that of the starch derivative component thereof.
In Examples 1 to 3, the flame retardant is added at a
late stage in the compounding of the composition prior to
3~ its injection molding, and the residence of the
composition (now comprising the flame retardant) in the
extruder iY kept to a minimum.
In addition, that part of the extruder which contacts the
3~ flame retarded starch composition may be especially
adapted to reduce the corrosive effects of the retardant
on the extruder.
E~ample 4
lOkg of corn starch acetate having a degree of
W092tl6~83 2 1 O- ~7 ~ PCT/VS92/02~3
substitution of about .8, 2kg 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 between 25 to 30%
by weight with respect to the moistened starch mix.
10 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
1~ extruder, opposite its entry port.
The starch composition is then heated to a temperature of
170~C for about 70 seconds at a suitable pressure
necessary to avoid the formation of water vapor at said
20 temperature
The thus melted starch is extruded from the outlet die of
the extruder, and the extrudate cooled and pelletized.
2~ The pelletized melted starch mix is conditioned to a
moisture content of about 17%, and then fed into the
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
30 useable in the process according to the present
invention.
The thus formed mix is heated to 190C for from 20-60
seconds and then e~truded. Upon emerging from the exit
3S orifice of the extruder die, the extrudate assumes a
cro~s 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 ~ave excellent properties with respect to density,
resilience and compressibility.
2 1 ~ ~ ll 7 9 PCT/~S92/02003
- 30 -
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
5 skilled in the art without departing from its scope,
which is defined by the appended claims.
