| United States Patent |
6,184,261 |
|
Biby
, et al.
|
February 6, 2001
|
Water-resistant degradable foam and method of making the same
Abstract
A foam that is the extrudate of a mixture of a biodegradable polymer,
starch, talc, and a blowing agent is provided. This foam is made by
extruding a mixture of the above-listed components. This foam is
water-resistant and in some variations waterproof making it an effective
packing material. Still further, this foam is biodegradable, and thus, it
can be disposed without creating environmental waste. In addition, the
foam may be extruded into sheets and then thermoformed to form various
articles.
| Inventors: |
Biby; Gerald (Omaha, NE), Hanna; Milford (Lincoln, NE), Fang; Qi (Lincoln, NE) |
| Assignee: |
Board of Regents of University of Nebraska
(Lincoln,
NE)
|
| Appl. No.:
|
09/305,937 |
| Filed:
|
May 6, 1999 |
| Current U.S. Class: |
521/84.1 ; 521/138; 521/82; 521/916 |
| Current International Class: |
C08J 9/14 (20060101); C08J 9/00 (20060101); C08J 009/00 () |
| Field of Search: |
521/84.1,138,916,82
|
References Cited
U.S. Patent Documents
| | |
|
5272181 |
December 1993 |
Boehmer et al. |
|
5308879 |
May 1994 |
Akamatu et al. |
|
5589518 |
December 1996 |
Bastioli et al. |
|
5665786 |
September 1997 |
Xu et al. |
|
5705536 |
January 1998 |
Tomka |
|
5736586 |
April 1998 |
Bastioli et al. |
|
5801207 |
September 1998 |
Bastioli et al. |
|
5854345 |
December 1998 |
Xu et al. |
|
|
Primary Examiner: Foelak; Morton
Attorney, Agent or Firm:Shook, Hardy & Bacon LLP
Parent Case Text
CROSS REFERENCE TO RELATED APPLICATIONS
This application claims priority benefits under Title 35, United States
Code .sctn. 119(e) of U.S. Provisional Application No. 60/084,090, filed
May 7, 1998.
Claims
We claim:
1. A foam that is the extrudate of a mixture comprising:
a biodegradable polymer that is selected from the group
consisting of poly(tetramethylene adipate-co-terephthalate) and a resin
comprised of 10-50% by weight ethylene acrylic acid copolymer, 20-70%
by weight destructured starch, 2-40% by weight
plasticizer, 0-10% by weight urea, 1-5% by weight water, and 0.002-0.4%
by weight boron compounds; starch having at least 25% amylopectin; talc; and a blowing agent.
2. The foam of claim 1, wherein said starch is extracted from a
plant selected from the group consisting of corn, wheat, sorghum,
potato, rice, rye, oats, and tapioca.
3. The foam of claim 2, wherein said blowing agent is selected from the group consisting of water, carbon dioxide, and pentane.
4. The foam of claim 1, wherein said foam is biodegradable and water-resistant.
5. The foam of claim 4, wherein said foam is waterproof.
6. The foam of claim 1, wherein said foam has a density between about 0.5 and 0.8 pounds per square foot.
7. The foam of claim 1, wherein said foam is used as a packing material.
8. The foam of claim 1, wherein said mixture is comprised of
about 10-50% biodegradable polymer, about 2-10% talc, and up to about
88% starch.
9. A process for making a foam, comprising:
contacting a mixture of water, starch having at least 25%
amylopectin, talc, and a biodegradable polymer selected from the group
consisting of poly(tetramethylene adipate-co-terephthalate and a resin
comprised of 10-50% by weight ethylene acrylic
acid copolymer, 20-70% by weight destructured starch, 2-40% by weight
plasticizer, 0-10% by weight urea, 1-5% by weight water and 0.002-0.04%
by weight boron compounds, under conditions sufficient to form a foam.
10. The process of claim 9, wherein said water, said starch,
and said talc are mixed together before said polymer is added to said
mixture.
11. The process of claim 9, wherein said mixture is extruded through an extruder.
12. The process of claim 11, wherein said mixture is extruded
through a heated extruder that is heated to between about 140 and
190.degree. C.
13. The process of claim 11, wherein said extruder is a twin screw extruder.
14. The process of claim 9, further comprising:
thermoforming said foam.
15. The process of claim 14, wherein said mixture is extruded
into sheets and said sheets are thermoformed into various articles.
Description
STATEMENT REGARDING FEDERALLY-SPONSORED RESEARCH OR
DEVELOPMENT
Not applicable.
BACKGROUND OF THE INVENTION
The present invention relates generally to foam. More
specifically, the present invention relates to water-resistant,
biodegradable foam that can be used as a packing material or as other
foam articles.
Foam is used as a loose-fill packing material to ship various
industrial and household products. Conventionally, loose-fill packing
materials are manufactured from petroleum plastics. Expanded
polystyrene foam, which is made from petroleum
plastics, is the most commonly used packing material because it has
desirable functionable properties such as a low density, high
resiliency, and good water resistance. However, petroleum plastics take
an extremely long period of time to degrade after
their disposal thus creating environmental pollution.
Degradable foam has been created. However, such foam is not
water-resistant, and thus, it does not remain resilient in a high
moisture environment. As a result, it is not suitable for use as a
packing material.
In order to overcome the disadvantages of currently available
packing materials, a foam that is made from renewable resources and
which is also biodegradable is provided. Still further, this foam is
water-resistant and in some variations is
waterproof.
SUMMARY OF THE INVENTION
It is a primary object of the present invention to provide a
foam that is biodegradable so that it can be disposed without creating
environmental waste but which is also water-resistant so that it can be
used as a packing material.
According to the present invention, the foregoing and other
objects are achieved by a foam that is the extrudate of a mixture that
includes a biodegradable polymer, starch, talc, and a blowing agent.
This foam is biodegradable and
water-resistant. Another aspect of this invention is a process for
making this foam by extruding a mixture of a biodegradable polymer,
starch, talc, and a blowing agent through a heated extruder and
allowing a foam to form as the mixture exits the
extruder.
Additional objects, advantages and novel features of the
invention will be set forth in part in the description which follows,
and in part will become apparent to those skilled in the art upon
examination of the following, or may be learned from
practice of the invention. The objects and advantages of the invention
may be realized and attained by means of the instrumentalities and
combinations particularly pointed out in the appended claims.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
The foam of the present invention is the extrudate of a mixture
that includes a biodegradable polymer, starch, talc, and a blowing
agent.
The biodegradable polymer can be any biodegradable polymer
including, but not limited to, polylactic acid (PLA),
poly(tetramethylene adipate-co-terephthalate), or a resin of a
thermoplastic polymer, destructured starch and a plasticizer. If the
biodegradable polymer is polylactic acid, both amorphous and
semi-crystalline forms of polylactic acid resins are usable.
Preferably, the polylactic acid used has a number average molecular
weight from about 40,000 to about 180,000. Most preferably,
the polylactic acid has a number average molecular weight from about
55,000 to about 87,000. The polylactic acid should have a D-lactide
content of between about 0 and 50%. The PLA resin should be dried at
40.degree. C. for 24 hours before it is used. Polylactic acid is water
insoluble. It adds ductility and resilience to the foam improving its
physical and mechanical properties. It is also fully biodegradable.
If the biodegradable polymer is poly(tetramethylene
adipate-co-terephthalate), it may be obtained under the tradename
Eastar Bio from Eastman Chemical Company, Kingsport, Tenn. 37662.
Poly(tetramethylene adipate-co-terephthalate) is made by
condensing 1,4-benzendicarboxylic acid with 1,4,-butandiol and
hexanedioic acid.
If a resin of a thermoplastic polymer, destructured starch,
and a plasticizer is used as the biodegradable polymer, the starch
component of the resin may be any starch of natural or plant origin
which is composed essentially of amylose and/or
amylopectin. It can be extracted from various plants, such as potatoes,
rice, tapioca, maize, as well as cereals, such as rye, oats, wheat and
the like. Maize starch is preferred. Preferably, the starch component
has an amylopectin content of more
than 70% by weight. Chemically-modified starches and starches of
different genotypes can also be used. Still further, ethoxy derivatives
of starch, starch acetates, cationic starches, oxidized starches,
cross-linked starches and the like may be used.
Starch is provided as part of the resin without processing,
such as drying, and without the addition of any water (the intrinsic
bound water content of the commercial products is approximately 10-13%
by weight). The starch is then destructured
at temperatures above 90.degree. C. and preferably above 120.degree. C.
The term "destructured starch" means a starch which has been
heat-treated above the glass transition temperatures and melting points
of its components, so that the components are
subjected to endothermic transitions to thereby produce a consequent
disorder in the molecular structure of the starch granules. In other
words, the crystallinity of the starch is destroyed.
The plasticizer used in the resin is preferably a polyol,
polyol derivative, polyol reaction product, polyol oxidation product or
a mixture thereof. Preferably, the plasticizer has a boiling point of
at least 150.degree. C. Examples of
plasticizers that can be used include, but are not limited to,
glycerine, polyglycerol, glycerol, polyethylene glycol, ethylene
glycol, propylene glycol, sorbitol, mannitol, and their acetate,
ethoxylate, or propoxylate derivatives, and mixtures thereof. Specific
plasticizers that can be used include, but are not limited to, ethylene
or propylene diglycol, ethylene or propylene triglycol, polyethylene or
polypropylene glycol, 1,2-propandiol, 1,3-propandiol, 1,2-, 1,3-,
1,4-butandiol, 1,5-pentandiol,
1,6-, 1,5-hexandiol, 1,2,6-, 1,3,5-hexantriol, neopentylglycol
trimethylolpropane, pentaerythritol, sorbitol acetate, sorbitol
diacetate, sorbitol monoethoxylate, sorbitol dipropoxylate, sorbitol
diethoxylate, sorbitol hexaethoxylate, aminosorbitol,
trihydroxymethylaminomethane, glucose/PEG, the product of reaction of
ethylene oxide with glucose, trimethylolpropane, monoethoxylate,
mannitol monoacetate, mannitol monoethoxylate, butyl glucoside, glucose
monoethoxylate, alpha-methyl glucoside, the
sodium salt of carboxymethylsorbitol, polyglycerol monoethoxylate and
mixtures thereof. The amount of plasticizer in the resin is
approximately 0.05-100% of the weight of the starch, and preferably
about 20-100% of the weight of the starch.
The thermoplastic polymer in the resin is a synthetic
polymeric component which includes a polymer or copolymer of at least
one ethylenically unsaturated monomer, the polymer or copolymer having
repeating units provided with at least a polar
group such as hydroxy, alkoxy, carboxy, carboxyalkyl, alkyl carboxy or
acetal group. Preferred polymeric components included in the resin are
polyethylene, polyvinyl alcohol, polyacrylonitrile, ethylene-vinyl
alcohol copolymer, ethylene-acrylic acid
copolymer and other copolymers of an olefin selected from ethylene,
propylene, isobutene and styrene with acrylic acid, vinyl alcohol,
and/or vinyl acetate and mixtures thereof. Most preferably, one of the
polymers in the resin is an ethylene-acrylic
acid copolymer with ethlylene contents of from about 10 to 44% by
weight. The resin also may contain relatively low amounts,
approximately 5% or less by weight of the overall composition, of
hydrophobic polymers, such as polyethylene, polypropylene and
polystyrene. Still further, other polymers such as polyamide,
polyacrylic, polyester, and polyether may be in the resin. The polymer
and starch of the resin may be combined in a 1:19 to 19:1 ratio by
weight.
Other components such as destructuring agents, cross-linking
agents and neutralizing agents may, optionally, be added to the resin
but are not essential components. Preferably, a destructuring agent is
added while making the resin. The
destructuring agent may be urea, alkaline and alkaline-earth
hydroxides, and mixtures thereof. Examples of alkaline and
alkaline-earth hydroxides include but are not limited to sodium,
potassium and calcium hydroxides. Most preferably, urea is added as
the destructuring agent. Urea improves the gelling of the starch with
small amounts of water, and hence enables the production of a uniform
film. Preferably, the amount by weight of destructuring agent added to
the resin is 2-20% of the weight of the
starch. However, if a destructuring agent is not added, it is still
possible to destructure the starch through heat or pressure.
The resin also may contain cross-linking agents such as
aldehydes like formaldehyde, paraformaldehyde, and paraldehyde;
keytones and glyoxals; epoxides like epichlorohydrin; process
coadjuvants and release agents; and lubricants which are
normally incorporated in compositions for molding or extrusion such as
fatty acids, esters of fatty acids, higher alcohols, polythene waxes,
and low density polyethylene (LDPE).
The resin further may contain a neutralizing agent, such as
ammonia or any amine, sufficient to neutralize some or all of the acid
groups of the polymer if an acidic polymer such as ethylene-acrylic
acid copolymer is used. Ammonia may be added
to the resin in quantities up to about 7% of the weight of the dry
starch. However, most of the ammonia should be removed before or during
extrusion. Preferably, about 0.5% or less by weight of the ammonia
remains in the final resin formulation. Urea,
in addition to functioning as a destructuring agent, also may function
as a neutralizing agent.
Although optional, the use of boron containing compounds
results in substantially better interpenetration between the
hydrophilic starchy phase and the hydrophobic polymeric phase, with a
resultant substantial improvement in mechanical
properties, particularly tear strength and transparency of sheets and
films obtained from various formulations of the resin. Boron, boric
acid, borax, metaboric acid, or other boron derivatives may be used in
the resin. Preferably, the boron containing
compound, expressed as the boron content, is between about 0.002 and
0.4% and preferably between about 0.01 and 0.3% of the total weight of
the resin.
Other additives also may be mixed into the resin. For example,
polyvinyl alcohol may be added to change the behavior of molded
articles with water; UV stabilizers, such as, carbon black, may be
added to improve the resistance of the articles to
sunlight; and flame-proofing agents may be added if desired. The
addition of inorganic salts of alkali or alkaline-earth metals,
particularly lithium chloride and sodium chloride at concentrations
between about 0.1 and 5% by weight of the resin,
preferably between about 0.5 and 3% by weight, also was found
advantageous. Other additives which may be in the resin include the
conventional additives generally incorporated in starch-based molding
compositions, such as fungicides, herbicides,
antioxidants, fertilizers, opacifiers, stabilizers and plasticizers.
All these additives may be used in conventional quantities as known to
experts in the field or as easily determined by routine tests, and
these additives may constitute up to about 20%
by weight of the final composition.
The resin is made by mixing the essential components, namely,
the starch, plasticizer and thermoplastic polymer, and any other
optionally included components, in a conventional device, such as a
heated extruder, which ensures conditions of
temperature and shearing stress suitable to render the starch and the
polymer compatible from a rheological point of view. The starch's
structure is interpenetrated or at least partially interpenetrated by
the thermoplastic polymer so as to obtain a
thermoplastic melt. The starch may be destructured before it is
combined with the polymer, or as it is combined. A destructuring agent
may be mixed with the starch and the plasticizer in a heated extruder
to destructure it. Preferably, the mixture is
extruded to form the resin at a temperature between about 100.degree.
C. and 220.degree. C.
Preferably, the resin is a film-grade material comprised of
about 10-90% by weight polymer or copolymer, about 10-90% by weight
destructured starch, about 2-40% by weight plasticizer, about 0-20% by
weight destructuring agent, and about 0-6% by
weight water. More preferably, the resin is comprised of about 20-70%
by weight destructured starch, about 10-50% by weight polymer or
copolymer, about 2-40% by weight plasticizer, about 0-10% by weight
destructuring agent, about 1-5% by weight water,
and about 0.002-0.4% by weight boron compounds. One of the most
preferred formulations of the resin is 41% by weight ethylene-acrylic
acid copolymer with 20% by weight acrylic acid, 12% by weight urea, 41%
by weight destructured starch, 20% by weight
plasticizer, and 6% by weight water.
Most preferably, the resin which is used as the biodegradable
polymer in making the foam of this invention is resin sold by Novamont,
S.p.A., via G. Fauser, 8-28100 Novara, Italy, under the trademark Mater
Bi.TM..
The starch used in making the foam of the present invention
may be any starch of natural or plant origin, which is composed of at
least 25% amylopectin. Examples of plants it may be extracted from
include, but are not limited to, corn, wheat,
sorghum, potato, rice, rye, oats, or tapioca. If corn starch is used,
it should have an amylose content between about 0 and 75%. It should
have a moisture content between about 16 and 24% on a dry basis (d.b.).
Preferably, it has a moisture content
between about 18 and 20%. If waxy corn starch (100% amylopectin) is
used, a foam with better resilience and a smoother surface is created.
Preferably, the starch is granulated into particles of a diameter of
about 1 to 5 millimeters before it is mixed
with the other components to form the foam of the present invention.
Starch is used in making this foam because it has an inherent expansion
characteristic when you extrude it. It gives a foam-type structure, and
in addition, it is inexpensive and
readily available. The starch gives the foam a fairly rigid structure.
So, although starch is used for its foaming ability, it should not be
used alone but instead should be with a biodegradable polymer. The
biodegradable polymer then provides the
resilient properties of the foam. Still further, starch is somewhat
soluble in water, however, when it is combined with a biodegradable
polymer, a foam is obtained that is water-resistant. Still further, the
starch is biodegradable and is obtained from
a renewable resource.
The talc used in forming the foam of the present invention is
magnesium silicate. It functions as a nucleating agent. It further
functions to improve the texture of the foam by providing foam with a
smoother surface.
Any commercial blowing agent or method to cause expansion of
the material can be used in forming the foam of the present invention.
Examples of blowing agents may be used include, but are not limited to,
water, carbon dioxide, and pentane. Preferably, distilled water is used
as the blowing agent. The blowing agent functions to expand the product
and turn it into a foam.
Optionally, a colorant may be added to the mixture that forms the foam of the present invention.
The foam may include about 10 to 50% biodegradable polymer,
about 2 to 10% talc, and up to about 88% starch. Preferably, it
includes about 4 to 5% talc. The blowing agent should be about 16 to
26% of the weight of the starch. Preferably, the
blowing agent is about 22 to 23% of the weight of the starch. If more
biodegradable polymer is used, the foam will have better resilience and
water resistance.
The foam of the present invention is made by mixing starch,
talc, and a blowing agent together and then adding a biodegradable
polymer to the mixture. The starch, talc, and blowing agent are mixed
for about 3 to 8 minutes at ambient temperature
and then the biodegradable polymer is added and mixed with the mixture
for about 2 to 5 minutes. Preferably, a double ribbon mixer is used.
The resulting mixture is then processed through an extruder to form a
biodegradable, water-resistant foam. More
specifically, the starch and talc are mixed in a mixture for about 5
minutes. Distilled water is used to adjust the moisture content of the
starch to the desired level. The biodegradable polymer is added and
mixed with the other ingredients. An
additional blowing agent besides the distilled water is optional. The
mixture should be stored in a sealed container to prevent it from
losing more moisture. The feed is fed into an extruder by means of a
screw feeder. The feed rate can be adjusted
accordingly. The operating parameters of the extruder can be controlled
by a computer. The screw speed of the extruder should be between about
100 and 300 revolutions per minute. Usually, the mixture stays in the
extruder for between about 30 seconds
and 11/2 minutes. Preferably, a twin screw extruder is used so that all
the ingredients are more thoroughly mixed providing a foam with a more
uniform structure. Still further, preferably, this twin screw extruder
has conical mixing screws and a
compression ration of about 3:1. Alternatively, the starch, talc,
blowing agent and biodegradable polymer can all be added directly to
the extruder at the same time without mixing these components together
beforehand.
The temperature profile of the extruder barrel varies
depending on the various zones of the extruder. Preferably, the first
zone, the feeding zone, has a temperature between about 15 and
90.degree. C. Preferably, the second, third, and die
section zones have temperatures between about 140 and 190.degree. C.
Most preferably, the first zone has a temperature between about 20 and
40.degree. C. Most preferably, the second zone, the third zone, and the
die section have a temperature between
about 160 and 185.degree. C. The extruder pressurizes the mixture to
between about 1000 and 5000 psi. Once the mixture exits the extruder
into a room at ambient temperature and pressure, it expands forming
foam. The foam should then be allowed to
cool. The foam can be cut into shapes such as rods.
The foam of the present invention is biodegradable and
water-resistant. Some variations of this foam are even waterproof. For
example, formulations where PLA is used as the biodegradable polymer
are waterproof. The density of the foam of the
present invention is between about 0.5 and 0.8 pounds per cubic foot.
The foam has improved abrasion resistance over typical starch-based
foam.
The foam of the present invention may be used as a loose-fill
packing material. Still further, it may be extruded into sheets which
are then thermoformed into plates, bowls, and fast food packaging
containers (clam shells).
The following are examples of various biodegradable foams in
methods of making the same which are within the scope of this
invention. These examples are not meant in any way to limit the scope
of this invention.
In each of the following examples, a C.W. Brabender twin screw
extruder (Model CTSE-V, C.W. Brabender, Inc., S. Hackensack, N.J.) was
used to run the extrusion. This was a non-mixing mixing co-rotating,
twin screw extruder. The screw was
conical shaped and had a diameter of 43 millimeters at the feeding end
decreasing to 28 millimeters at the die end. The screw length was 365
millimeters. The screws were rotated at a speed between about 40 and
200 revolutions per minute. Preferably,
the screws rotated at between about 80 and 120 revolutions per minute.
The size of the nozzle opening from the extruder varied in the
different examples. Preferably, the nozzle opening is cylindrical and
is between about 2 to 8 millimeters. Most
preferably, it is between about 3 and 5 millimeters.
EXAMPLE 1
30% by weight of polylactic acid having a molecular weight of
85,000, 4% by weight of talc (magnesium silicate) and 66% by weight of
waxy corn starch having a moisture content of 20% (d.b.) were premixed
and then fed to a C.W. Brabender CTSE-V
co-rotating twin screw extruder. The conical screws had variable
diameters decreasing from 43 to 28 mm along their length from the
feeding end toward the exiting end. The screws had a length to diameter
ratio of 20:1. On the screws there was a mixing
zone consisting of incomplete flights. The barrel of the extruder was
divided into three heating zones. The die section that was connected to
the barrel had a nozzle opening of 3 mm in diameter. Barrel and die
temperatures were maintained by
electrical heaters.
The temperature at the feeding section of the barrel was held
at room temperature while the other two sections and the die were
maintained at 150.degree. C. The screws rotated at 150 rpm. The
expanded extrudate having a diameter of 12 to 20 mm
was cut into cylindrical shapes of one inch long using a rotating
cutter mounted in front of the extruder nozzle.
EXAMPLE 2
25% of weight of Eastar Bio Copolyester 14766 from Eastman
Chemical Co. (Kingsport, Tenn.), 5% by weight of talc (magnesium
silicate) and 71% by weight of 25% amylose corn starch having a
moisture content of 22% (d.b.) were premixed and then fed
to a C.W. Brabender CTSE-V co-rotating twin screw extruder. The conical
screws had variable diameters decreasing from 43 to 28 mm along their
length from the feeding end toward the exiting end. The screws had a
length to diameter ratio of 20:1. On
the screws there was a mixing zone consisting of incomplete flights.
The barrel of the extruder was divided into three heating zones. The
die section that was connected to the barrel had a nozzle opening of 3
mm in diameter. Barrel and die
temperatures were maintained by electrical heaters.
The temperature at the feeding section of the barrel was held
at room temperature while the other two sections and the die were
maintained at 150.degree. C. The screws rotated at 160 rpm. The
expanded extrudate having a diameter of 12 to 18 mm
was cut into cylindrical shapes of one inch long using a rotating
cutter mounted in front of the extruder nozzle.
EXAMPLE 3
20% by weight of Mater-Bi ZF03U/A from Novamont S.p.A. (Milan,
Italy), 5% by weight of talc (magnesium silicate) and 71% by weight of
25% amylose corn starch having a moisture content of 18% (d.b.) were
premixed and then fed to a C.W. Brabender
CTSE-V co-rotating twin screw extruder. The conical screws had variable
diameters decreasing from 43 to 28 mm along their length from the
feeding end toward the exiting end. The screws had a length to diameter
ratio of 20:1. On the screws there was a
mixing zone consisting of incomplete flights. The barrel of the
extruder was divided into three heating zones. The die section that was
connected to the barrel had a nozzle opening of 3 mm in diameter.
Barrel and die temperatures were maintained by
electrical heaters.
The temperature at the feeding section of the barrel was held
at room temperature while the other two sections and the die were
maintained at 150.degree. C. The screws rotated at 180 rpm. The
expanded extrudate having a diameter of 10 to 16 mm
was cut into cylindrical shapes of one inch long using a rotating
cutter mounted in front of the extruder nozzle.
EXAMPLE 4
40% by weight of polylactic acid having a molecular weight of
150,000, 4% by weight of talc (magnesium silicate) and 56% by weight of
waxy corn starch having a moisture content of 24% (d.b.) were premixed
and then fed to a C.W. Brabender CTSE-V
co-rotating twin screw extruder. The conical screws had variable
diameters decreasing from 43 to 28 mm along their length from the
feeding end toward the exiting end. The screws had a length to diameter
ratio of 20:1. On the screws there was a mixing
zone consisting of incomplete flights. The barrel of the extruder was
divided into three heating zones. The die section that was connected to
the barrel had a nozzle opening of 3 mm in diameter. Barrel and die
temperatures were maintained by
electrical heaters.
The temperature at the feeding section of the barrel was held
at room temperature while the other two sections and the die were
maintained at 150.degree. C. The screws rotated at 200 rpm. The
expanded extrudate having a diameter of 14 to 25 mm
was cut into cylindrical shapes of one inch long using a rotating
cutter mounted in front of the extruder nozzle.
EXAMPLE 5
30% by weight of Eastar Bio Copolyester 14766 from Eastman
Chemical Co. (Kingsport, Tenn.), 5% by weight of talc (magnesium
silicate) and 65% by weight of waxy corn starch having a moisture
content of 22% (d.b.) were premixed and then fed to a
C.W. Brabender CTSE-V co-rotating twin screw extruder. The conical
screws had variable diameters decreasing from 43 to 28 mm along their
length from the feeding end toward the exiting end. The screws had a
length to diameter ratio of 20:1. On the
screws there was a mixing zone consisting of incomplete flights. The
barrel of the extruder was divided into three heating zones. The die
section that was connected to barrel had a rectangular nozzle opening
of 30.times.2 mm. Barrel and die
temperatures were maintained by electrical heaters.
The temperature at the feeding section of the barrel was held
at room temperature while the other two sections and the die were
maintained at 150.degree. C. The screws rotated at 160 rpm. The
expanded extrudate having a rectangular dimension of
30.times.8 mm was cut into one inch long pieces using a rotating cutter
mounted in front of the extruder nozzle.
EXAMPLE 6
40% by weight of polylactic acid having a molecular weight of
100,000, 6% by weight of talc (magnesium silicate) and 54% by weight of
waxy corn starch having a moisture content of 24% (d.b.) were premixed
and then fed to a C.W. Brabender 2003
GR-8 single screw extruder. The screw had a diameter of 19 mm. The
screw had a length to diameter ratio of 20:1, and a compression ratio
of 3:1. On the screw there was a mixing zone consisting of incomplete
flights. The barrel of the extruder was
divided into two heating zones. The die section connecting to the
barrel had a nozzle opening of 3 mm in diameter. Barrel and die
temperatures were maintained by electrical heaters.
The temperature at the feeding section of the barrel was held
at room temperature while the other two sections and the die were
maintained at 150.degree. C. The screw rotated at 150 rpm. The expanded
extrudate having a diameter of 10 to 24 mm
was cut into cylindrical shapes of one inch long using a rotating
cutter mounted in front of the extruder nozzle.
From the foregoing, it will be seen that this invention is one
well adapted to attain all the ends and objects hereinabove set forth
together with other advantages which are obvious and inherent to the
structure. It will be understood that
certain features and subcombinations are of utility and may be employed
without reference to other features and subcombinations. This is
contemplated by and is within the scope of the claims. Since many
possible embodiments may be made of the invention
without departing from the scope thereof, it is to be understood that
all matter herein set forth is to be interpreted as illustrative and
not in a limiting sense.
