WO1998040434A1

WO1998040434A1 - Degradable composite polymer and method of making such composite polymer

Info

Publication number: WO1998040434A1
Application number: PCT/US1998/005281
Authority: WO
Inventors: Milford Hanna; Gerald Biby; Qi Fang
Original assignee: Board Of Regents Of University Of Nebraska
Priority date: 1997-03-14
Filing date: 1998-03-13
Publication date: 1998-09-17
Also published as: EP0966502A4; CA2285458A1; AU6564198A; EP0966502A1

Abstract

A novel degradable composite polymer is comprised of a polymer comprised of lactic acid monomers, and a resin comprised of a thermoplastic polymer, destructured starch and a plasticizer. This composite polymer is made by first combining the lactic acid polymer and the resin and subsequently extruding the combination through a heated extruder. These substances may be combined in various proportions to obtain materials of various flexibilities and hardnesses. This degradable composite polymer can be used in many applications, including use as a printable plastic material due to its unique ability to retain ink and as a plastic media blast material as it can be created in a variety of hardness levels.

Description

DEGRADABLE COMPOSITE POLYMERAND METHOD OF MAKING SUCH COMPOSITE POLYMER

Statement Regarding Federally-Sponsored Research or Development

Not applicable.

Cross Reference To Related Applications

This application claims priority from U.S. Provisional Application No.

60/040,779, filed March 14, 1997.

Background of the Invention

The present invention relates to composite polymers and methods for

making such composite polymers. More specifically, the composite polymers of the

present invention are degradable. Still further, the present invention includes applications

for using composite polymers as printable plastic material or as plastic media blast

material.

Plastic materials are any synthetic materials comprised of polymers which

can be shaped or molded. Printable plastic materials are plastic materials which are able

to receive and retain ink. There are a number of disadvantages with currently available

printable plastic materials. Many plastic materials used by the printing industry have a

plasticizer incorporated into their formula which creates a residue on the surface of the

finished plastic products. This residue prevents ink from sticking to the surface during

printing, and surface treatment prior to printing often does not remove all of the

plasticizer residue. Furthermore, many plastic materials currently used by the printing

industry are not degradable.

Polylactic acid resin, a degradable material, offers a quality printing

surface since the biopolymer-based plasticizers used in the manufacture of this resin tend to stay within the material. However, polylactic acid resin does not thermoform well.

Still further, because polylactic acid is extremely hard, it is very abrasive on cutting tools.

Furthermore, when polylactic acid is extruded into sheets, it tends to curl and become

quite brittle. For instance, if a polylactic acid resin is rolled, it tends to stay rolled

forever. Also, because polylactic acid is a brittle material, it fractures, especially at

corners, when cut, and when it is extruded into thicker sheets, it fractures even more.

Other degradable plastics, such as the multipolymer resins sold by

Novamont S.p.A., via G. Fauser, 8-28100 Novara, Italy, under the trademark Mater Bi™,

have a great deal of flexibility, but are too ineffective to use in many sheet extrusion

applications. These resins, which are comprised of a thermoplastic polymer, destructured

starch, and a plasticizer, are very soft and rubbery, and ink cannot be printed on such

resins. It is thus desirable to find a sheet extruded material with high elasticity and an

exceptional ability to retain ink during printing.

There are a number of disadvantages with current methods for removing

coatings from various substrate materials. Commonly used methods for removing

powder coatings include dipping the substrate material to be stripped into a pot of molten

salt so as to turn the powder coating to ash and vapor. Another method involves putting

the substrate material in a high temperature oven, approximately 600-900° F, to turn the

coating to ash. The problem with these methods is that many substrates that are coated

with powdered paint cannot survive the coating removal process, or if they do, their

structural properties are significantly damaged due to the extreme heat used to remove

the coating. Still another method involves using small glass beads in an abrasive process

to remove the coatings. However, when used on relatively soft substrates, the impacting

beads provide an unsatisfactory result by causing surface stress and possibly also changing the texture of the substrate. Thus, many coated materials must be scrapped

since they cannot withstand the conditions of these conventional removal processes.

Another conventional method for removing coatings involves using plastic

media blast material. Plastic media blast is an effective way to surface clean various

materials without damaging the surface of the material being blasted. Currently, certain

petroleum-based plastics which are not too hard or too coarse are used as plastic media

blast material. However, degradable plastics have been found to be too brittle or too

weak to perform adequately as plastic media blast.

In order to overcome the deficiencies found with conventional degradable

polymers, a degradable composite polymer and a method for making such a composite

polymer are needed for a variety of applications including those in which enhanced

strength and flexibility are needed. Still further, such a degradable composite polymer

should have improved printability characteristics for use as a printable plastic material

and should be able to be produced in a variety of hardnesses for use as plastic media blast

material.

Summary of the Invention

It is an object of the present invention to provide a degradable composite

polymer and a method for producing the same wherein the composite polymer can be

used as a plastic.

A further object of this invention is to provide degradable composite

polymers and methods of producing the same wherein the composite polymer can be

produced in various textures and ranges of flexibilities.

It is a further object of the present invention to provide a degradable

composite polymer and a method for producing the same wherein the composite polymer is produced in a range of hardnesses so that it can be used as a plastic media blast

material for a variety of surfaces.

Still another object of this invention is to provide a degradable composite

polymer and a method for producing the same wherein the composite polymer has the

ability to retain ink during printing so that it can be used as a printable plastic material.

It is a further object of this invention to provide a degradable composite

polymer and a method for producing the same wherein the composite polymer is able to

be cut easily without fracturing so that it may be cut into small plastic sheets.

Another object of this invention is to provide a degradable composite

polymer and a method of producing the same wherein the composite polymer has a high

elasticity so that it is able to be extruded into sheets without curling or becoming brittle

and is able to be injection or compression molded.

Still another object of this invention is to provide a method for

manufacturing a degradable composite polymer without the use of any corrosive or

caustic chemicals in order to eliminate the hazards associated with using and disposing

of such chemicals.

Still another object of this invention is to provide a process for producing

a degradable composite polymer which creates little waste.

According to the present invention, the foregoing and other objects are

achieved by a degradable composite polymer comprised of a polymer comprised of lactic

acid monomers and a resin comprised of a thermoplastic polymer, destructured starch and

a plasticizer. This composite polymer is first created by combining the polymer and the

resin, and subsequently, extruding them through a heated extruder. This degradable composite polymer may be used, among other things, as plastic media blast material or

as a printable plastic material.

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 novel degradable composite polymers of the present invention are

comprised of a polymer and a resin. The polymer is comprised of lactic acid monomers,

and the resin is comprised of a thermoplastic polymer, destructured starch, and a

plasticizer. If the polymer comprised of lactic acid monomers is a copolymer, in addition

to the lactic acid monomers, the other monomers in this polymer should be degradable

monomers. Preferably, the polymer is polylactic acid (PL A).

One method of producing PLA includes catalyzing crude lactic acid,

which may contain impurities such as carbohydrates, proteins, amino acids, salts, metal

ions and other organic acids, with 0.05-0.15 weight percent tin oxide (SnO). Other

methods for making PLA also are conventionally available.

Preferably, the polymer comprised of lactic acid monomers has a

molecular weight of between 5,000 and 200,000, depending on the physical properties

of the composite polymer which are desired in a specific application. For example,

polymers having molecular weights at the higher end of this range produce composite

polymers which are relatively stronger and harder. The lactic acid monomers in the polymer may be comprised of between about 0 and 90% D-lactide by weight. Preferably,

between approximately 0 and 25% by weight of the lactic acid in the polymer is D-lactide.

Most preferably, the lactic acid in the polymer is comprised of about 1% or less D-lactide

by weight.

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 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°C and preferably above 120°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°C. Examples of plasticizers that can be used

include, but are not limited to, glycerine, polyglycerol, glycerol, polyethylene glycol, ethylene glycol, propylene glycol, sorbitol, marmitol, 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

poly ether may be in the resin. The polymer and starch may be combined in a 1 : 19 to 19: 1

ratio by weight. Preferably, the polymer component of the resin has a higher molecular

weight than the polymer comprised of lactic acid monomers, the other component used

in forming the composite polymer of the present invention.

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 mixture

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

destr icturing 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, poly vinyl

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°C and 220 °C.

Preferably, according to one formulation of the present invention, 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 in making the degradable

composite polymers of this invention is resin sold by Novamont, S.p.A., via G. Fauser,

8-28100 Novara, Italy, under the trademark Mater Bi™.

The lactic acid polymer, which is preferably PLA, and the resin, which is

preferably Mater Bi™, may be combined to form the degradable composite polymers of

the present invention in a range of proportions depending upon the resultant hardness,

flexibility, and texture which is desired. The addition of the resin to the lactic acid

polymer reduces its brittleness and improves its flow and process ability. Composite

polymers of this invention which contain more resin are softer and more flexible.

Anywhere between about 10 and 90% by weight of the degradable composite polymer

may be a lactic acid polymer and the remaining 10-90%) by weight of the composite

polymer is the resin.

This degradable composite polymer is made by first combining the

polymer and the resin, and by subsequently extruding the combination through a heated

extruder. The polymer and the resin may be combined in a container and then fed into

the extruder, or the polymer and the resin may be combined in the extruder. Any

conventional extruder capable of melting the mixture may be used. The extruder may

have any of a variety of screw configurations, including single, twin, or mixing screws.

A colorant also may optionally be added to the mixture. Preferably, the particles of resin

and polymer added to the extruder are relatively close in size.

The extruder should be sufficiently heated so that the composite polymer

may form at any temperature between about 140 and 230°C. Preferably, it forms at a

temperature of about 160-190°C if used as a printable plastic material, and at a

temperature of about 140-230°C if used as plastic media blast material. If the mixture is heated above 230°C, volatile compounds in the resin begin to evaporate. The

temperature at which the composite polymer forms affects its resultant hardness.

Therefore, the extruder should be at higher temperatures to form harder composite

polymers. Furthermore, the temperature chosen for the process should be influenced by

the melting point of the polymer used. For instance, if a lactic acid polymer having a

relatively higher melting point is used, the composite polymer should be formed at a

higher temperature within the acceptable temperature range. Also, if the lactic acid

polymer has a relatively higher molecular weight, then, preferably, the composite

polymer is formed at higher temperatures within the disclosed temperature range.

The degradable composite polymer forms in the heated extruder after the

polymer and the resin are extruded for about 30-240 seconds. Preferably, the composite

polymer forms after the polymer and the resin are extruded for about 50-90 seconds.

When the mixture comes out of the extruder, it is a very soft, molten material. Because

the crystallinity of the mixture is changed when it is extruded, the product cannot be

reprocessed without re-annealing the mixture.

Preferably, the resulting degradable composite polymer is cut with a

specially hardened die so as not to dull the die. This is especially preferable for those

formulations containing high percentages of a lactic acid polymer. Preferably, for cutting

purposes, the polymer and the resin are combined in approximately a 1 : 1 ratio by weight

so as to cause the least amount of die abrasion.

The degradable composite polymer of the present invention has enhanced

elongation viscosity, improved strength and flexibility, and improved printability

characteristics when compared to other degradable plastics. It also is resistant to tearing and perforation, and it is a good oxygen and carbon dioxide barrier. Still further, it has

a high melting point and the ability to thermoform.

The degradable composite polymer of the present invention is an

environmentally-friendly product because it is made from renewable resources and

degrades in two years or less when composted. Degrades, in this context, means it is

chemically decomposed. Certain formulations of the present invention that contain high

percentages of the resin are even biodegradable, which means they are capable of being

decomposed by naturally biological processes.

The novel degradable composite polymer of the present invention is useful

for a variety of applications. It may be used as a plastic substitute for a wide range of

applications such as those currently reserved for petroleum-based plastics. Articles may

be formed with this composite polymer by injection molding, thermoforming or blowing.

Two specific applications particularly suited for this novel degradable composite polymer

include use as a printable plastic material or as a plastic media blast material.

If used as a printable plastic material, the composition should be

comprised of approximately 10-90%) by weight of a polymer comprised of lactic acid

monomers, and approximately 10-90% by weight of a resin comprised of a thermoplastic

polymer, destructured starch, and a plasticizer. Preferably, for cutting purposes, it is

comprised of approximately 30-70%) by weight of the polymer, and approximately 30-

70% by weight of the resin. Most preferably, for cutting purposes, it is comprised of

approximately 50%> by weight of the polymer, and approximately 50% by weight of the

resin.

This printable plastic material is made by first combining a polymer and

a resin and then extruding this mixture as discussed above . The extruded mixture can be formed into sheets by any method known to those skilled in the art. One method

involves feeding the extruded mixture, which is a soft, hot, molten resin into a sheet die

and forming the composite polymer into a continuous sheet. The composite polymer is

fed through a series of cylindrical rollers, for example, three vertically-arranged rollers,

which are evenly spaced apart so as to shape the composite polymer into a sheet having

a uniform thickness. The spacing of the rollers determines the thickness of the sheets

formed. Conventionally, steam is pumped into the rollers when forming sheets, but with

the present invention, the rollers should be cooler than the temperature of the mixture

leaving the extruder. Preferably, water having a temperature of about 10-50°C is pumped

through the rollers. As the continuous sheet leaves the last roller, it is tensioned to keep

it flat until it cools and hardens enough to be moved. Once the sheets are formed, they

may be cut into large sheets or rolled for storage. It is preferable to store those composite

polymer formulations containing relatively large percentages of lactic acid polymer in

sheets rather than in rolls because if rolled they tend to remain curled.

The stored plastic sheets are subsequently processed. They may be cut

into smaller sheets so as to be used as plastic cards, such as phone cards or credit cards.

If used as credit cards or phone cards, consumers prefer the feel of a material that is 10%

by weight resin and 90% by weight polymer comprised of lactic acid monomers. This

preference must be weighed against the desirability of a 50/50 mixture for cutting

purposes.

Ink is then printed onto the sheets, and this novel degradable composite

polymer is able to act as a substrate and retain the ink. The degradable composite

polymer of the present invention may be printed with conventional or ultraviolet (UV)

inks. Preferably, for printing purposes, the polymer and resin are in about a 50/50 combination by weight so that the printing dies are not worn. If printed with

conventional inks, the ink sets up at ambient temperature when exposed to light. If the

material is printed with UV ink, then UV light must be used to cure or dry the ink.

Preferably, if UV light is used, the UV light is flashed in intervals which last for a

fraction of a second so as to reduce heat build-up on the composite polymer. Still further,

preferably, one does not print on the same print line of both sides of the composite

polymer substrate at the same time because this brings too much heat to the material.

Instead of being extruded into sheets, the degradable composite polymer

of the present invention may be injection or compression molded into shapes and forms

while retaining its ability to be printed upon. This degradable composite polymer can be

molded into stiff and thin wall articles. Preferably, the composite polymer, which is later

molded, is formed at a temperature of about 160-190°C, if used as a printable plastic

material.

Conventional injection molding equipment, such as that used in the

plastics industry, may be used. However, processing conditions should be adjusted to

allow for the fact that the degradable composite polymer of the present invention has a

slower cooling time than typical plastics. Subject to the size and complexity of the

mold's shape, the mold release time, as compared to typical plastics, can be increased

negligibly up to approximately 200%). The usual time increase appears to be about 30%.

However, use of an air cooled or liquid cooled mold will allow cycle times which are

comparable to those of conventional plastics.

If the degradable composite polymer is injection molded, the injection

temperature, preferably, is about 180 to 200 °C. The injection speed can be varied

depending upon the size and shape of the mold and the number of cavities in the mold. Preferably, the nozzle pressure is about 1300 to 1400 bar. Preferably, the mold

temperature is between approximately 10 and 65 °C. Either cold or hot runners may be

used in the injection system, and the minimum gate size is about 1 mm full round.

Preferably, the mold is made of an acid-resistant material such as an acid-resistant metal.

The flowability of this degradable composite polymer into the mold

cavities is enhanced when the molds are specially designed for a degradable material.

One preferable design incorporates the use of rounded corners inside the mold, as

opposed to 90 degree corners, because the degradable composite polymer does not like

to flow into "sharp dead-ends." Most preferably, the mold design should take into

account the following parameters or properties: 1) The rheological and other physical

properties of the resin; 2) if cold runners systems are used, the sprue length should be as

short as possible to avoid the composite polymer breaking inside the mold; 3) flow

channels should have reduced cross-sectional area, free of stagnation points; and 4) gates

should be fully rounded. Molded articles can be colored in numerous ways. The coloring of the

degradable composite polymer can either be accomplished by compounding the PLA

with the desired colorant or by substitution waxes as the matrix for the colorant.

Still further, the materials used in making the degradable composite

polymers of the present invention should be dried before being processed. Also, during

the start-up and shutdown of the extrusion process, to reduce the material costs, the start¬

up can be performed using low density polyethylene (LDPE). Once the operating

temperatures have been achieved, the components comprising the degradable composite

polymer of the present invention can be substituted for the LDPE. At the end of the run,

LDPE can be used to cleanse the equipment of the degradable composite polymer. A plastic media blast process is a process for the rapid, economic, and safe

removal of coating from almost any product. It resembles sandblasting but does not use

a hard abrasive, such as silica sand. A plastic media blast process is a dry stripping

method by which small angular plastic particles are propelled against a covered surface

lifting the covering off and leaving a clean, unmarred substrate. The process employs

specially designed equipment which propels and recovers the sharp-edged non-toxic

plastic granules. It is especially useful on surfaces which cannot tolerate damaging

mechanical sanding or wet chemical stripping. The degradable composite polymer of the

present invention is particularly useful as plastic media blast material. The plastic

particles are pneumatically applied at pressures of about 10-40 psi.

Plastic media blast material is made by first combining a polymer and a

resin and subsequently extruding this mixture as discussed above. The extruded mixture

can be formed into particles by any method known to those skilled in the art. One

method involves feeding the extruded mixture, which is a soft, hot, molten resin, into a

rod die and forming the composite polymer into a continuous rod. Preferably, the rod is

cooled as it exits the rod die. This may be accomplished with a water bath, a fan or

moving the rod through static air. Once the rod has cooled and hardened, it may be cut

into pellets. The pellets are then further reduced in size by grinding so as to form

composite polymer particles of a prescribed fineness. A hammer mill or any type of

conventional grinder may be used to form the particulates. The hardness of the resulting

composite polymer should affect the particular choice of grinders. For degradable

composite polymers of this invention containing a large percentage of lactic acid

polymer, an especially durable grinder must be used. Conventional steel blades may be

destroyed through the grinding of the invented substance. Still further, the plastic media blast material of the present invention may

consist entirely of a polymer comprised of lactic acid monomers. Polymers or

copolymers made from lactic acid monomers make an effective plastic media blast which

is relatively very hard. This is a novel use for such polymers or copolymers. However,

plastic media blast material made entirely from lactic acid polymers cannot be made in

a full range of hardnesses. Thus, in order to make softer plastic media blast material, the

lactic acid polymer must be combined with a resin comprised of a thermoplastic polymer,

destructured starch and a plasticizer.

The grit size of the plastic media blast particles can be varied. However,

particles which are too large or too hard can damage the surface of a substrate.

Preferably, the degradable composite polymer of the present invention is ground to a very

fine powder so that it will not plug up the nozzles of the device which sprays the plastic

media blast material. Preferably, the plastic media blast particles have equivalent

diameters between about 0.2 and 2.5 mm. Most preferably, the plastic media blast

particles have equivalent diameters of between about 0.4 and 1.2 mm. The plastic media

blast material may be created in a variety of hardnesses to remove different substances

from different surfaces. Specifically, it may be created so as to have a hardness between

about 10 and 70 on the Rockwell scale.

The plastic media blast material of the present invention can be used in

a variety of processes including coating removal, substrate abrasion, industrial cleaning,

particle removal, surface finishing, and deflashing molded items. Types of coatings that

can be removed include paint, powder, primers, top coats, residues, contaminants, burrs,

polymer coatings, and epoxy coatings. It may be used on any surface including flexible

surfaces and sensitive substrates such as plastic, honeycomb-shaped structures, fiberglass, polymers, composite materials, metals, and woods, without harming these substrates.

Applications where plastic media blast material can be used include, but are not limited

to, the dry stripping or cleaning of an endless range of consumer household products,

industrial machinery and equipment, vehicles, aerospace components, weapons systems

and marine vessel hulls.

The plastic media blast process is environmentally sound and is an

effective replacement for wet chemical strippers, such as methylene chloride based

chemical strippers which cause adverse environmental impacts. Using the degradable

composite polymer of the present invention as a plastic media blast material avoids the

use of methylene chloride, phenol, corrosives and caustics, methanol, toluene and

acetone.

Using proper techniques, the combination of low operating pressures, soft

plastic particles and high flow rate permits rapid removal without warping panels or

damaging surfaces. Furthermore, clad, anodized, galvanized and phosphate coatings may

be left in tact. And, in many cases, paint can be removed layer by layer down to the base

substrate or to the primer coating.

The following are examples of various degradable composite polymers

which are within the scope of this invention. These examples are not meant in any way

to limit the scope of this invention.

Example 1

A composition containing the following components was prepared:

47.5% by weight of semicrystalline polylactic acid (PLA) containing a trace amount of

D-lactide with a molecular weight of 150,000, 47.5% by weight of ZF03U/A class Mater

Bi™, and 5% by weight of titanium oxide as white colorant. All the components were pre-dried at 40 °C for 23 hours and premixed.

The premixed components were then fed into an extruder attached with a flexible lip

sheet die having an opening width of 724 mm (28.5 in). The screw diameter was 63.5

mm (2.5 in.), with a screw length/diameter ratio of 24: 1. The extruder barrel was divided

into 4 zones. The temperatures employed were 180, 180, 190 and 190°C, respectively,

for the first, second, third and fourth zones.

The operating conditions were as follows: The rotating speed of the screw

was 75 rev/min. The feed flow rate was 85.4 kg/hr (188 lb/hr). The sheeting rolls

consisted of three vertically arranged cylindrical rolls measuring 305 x 1016 mm. The

temperatures for the three rolls were 48, 60, and 43 °C, respectively for the top, middle

and bottom rolls.

The extruded sheets were cooled and cut into 610 mm by 610 mm (24 in

by 24 in) squares and packed.

Example 2

A composition containing the following components was prepared:

90% by weight of amorphous polylactic acid (PLA) containing 18%> D-lactide by weight

with a molecular weight of 80,000, and 10% by weight of ZF03U/A class Mater Bi™.

All the components were pre-dried at 40 °C for 24 hours and premixed.

The premixed components were then fed into a twin screw extruder. The screw diameter

was 20 mm, and the screw length/diameter ratio was 40. The diameter of the nozzle

opening was 3 mm. The extruder barrel was divided into 5 zones. The temperatures

employed were 90, 150, 150, 145, and 145°C, respectively for the first, second, third,

fourth and fifth zones. The operating conditions were as follows: The rotating speed of the screw

as lOO rev/min.

The extrudates were air cooled and then granulated using a C.W.

Brabender laboratory pelletizer. The obtained resins were then ground to particle sizes

having equivalent diameters of about 1.5 mm using a C.W. Brabender Granu-grinder

rotating at 3500 rev/min.

Example 3

A composition containing the following components was prepared:

70% by weight of semicrystalline polylactic acid (PLA) containing a trace amount of D-

lactide with a molecular weight of 150,000, and 30% by weight of ZF03U/A class Mater

Bi™. All the components were then fed into a twin screw extruder. The screw diameter

was 20 mm, and screw length diameter ratio was 40. The diameter of the nozzle opening

was 3 mm. The extruder barrel was divided into 5 zones. The temperatures employed

were 140, 190, 190, 185, and 185°C, respectively for the first, second, third, fourth and

fifth zones.

The operating conditions were as follows: The rotating speed of the screw

as 100 rev/min.

The extrudates were air cooled and then granulated using a C.W.

having equivalent diameters of about 1.0 mm using a C.W. Brabender Granu-grinder

rotating at 3500 rev/min.

Example 4

A composition containing the following components was prepared: 47.5%o by weight of amorphous polylactic acid (PLA) containing 18% D-lactide by

weight with a molecular weight of 80,000, 47.5% by weight of ZF03U/A class Mater

Bi™, and 5% by weight of titanium oxide as a white colorant.

All the components were pre-dried at 40°C for 24 hours and premixed.

mm (2.5 in.), and screw length/diameter ratio was 24: 1. The extruder barrel was divided

into 4 zones. The temperatures employed were 152, 149, 160 and 160°C, respectively

for the first, second, third and fourth zones.

The operating conditions were as follows: The rotating speed of the screw

consisted of three cylindrical rolls arranged vertically. The temperatures for the three

rolls were 48, 60, and 43 °C, respectively for the top, middle and bottom rolls.

The extruded sheets were cooled and cut into 610 mm by 610 mm (24 in

by 24 in) squares and packed.

Example 5

A composition containing the following components was prepared:

67.5%) by weight of semicrystalline polylactic acid (PLA) containing less than 3% D-

lactide by weight with a molecular weight of 80,000, 27.5% by weight of ZF03U/A class

Mater Bi™, and 5% by weight of titanium oxide as white colorant.

All the components were pre-dried at 40°C for 24 hours and premixed.

mm (2.5 in.), and screw length/diameter ratio was 24: 1. The extruder barrel was divided into 4 zones. The temperatures employed were 152, 149, 160 and 160°C, respectively

for the first, second, third and fourth zones.

The operating conditions were as follows; The rotating speed of the screw

rolls were 48, 60 and 43 °C, respectively for the top, middle and bottom rolls.

The extruded sheets were cooled and cut into 610 mm by 610 mm (24 in

by 24 in) squares and packed.

The degradable composite polymers of the present invention can be used

as a plastic. It can be produced in various textures and ranges of flexibilities. It also can

be produced in a range of hardnesses so that it can be used as a plastic media blast

material for a variety of surfaces. The composite polymer also has the ability to retain

ink during printing so that it can be used as a printable plastic material. The composite

polymer is able to be cut easily without fracturing so that it may be cut into small plastic

sheets. It also has a high elasticity so that it is able to be extruded into sheets without

curling and becoming brittle. Still further, it degrades by composting in two years or less

and is made from renewable resources, thus making it an environmentally-friendly

product.

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 or

shown in the accompanying drawings is to be interpreted as illustrative and not in a

limiting sense.

Claims

We claim:

1. A degradable composite polymer, comprised of the following: a

first polymer comprised of lactic acid monomers; and a resin comprised of a

thermoplastic polymer, destructured starch and plasticizer.

2. A composite polymer as in claim 1 wherein said first polymer has

a molecular weight between approximately 5,000 and 200,000.

3. A composite polymer as in claim 1 wherein said first polymer is

polylactic acid.

4. A composite polymer as in claim 1 wherein said lactic acid

monomers are comprised of about 1% or less D-lactide by weight.

5. A composite polymer as in claim 1 wherein said resin is Mater

BiΓäó resin.

6. A composite polymer as in claim 1 wherein said resin is comprised

of about 10-90% by weight polymer or copolymer, about 10-90% by weight destructured

starch, about 0-20% by weight destructuring agent, and about 0-6%> by weight water.

7. A composite polymer as in claim 1 wherein said resin is comprised

of about 20-70%> by weight destructured starch, about 10-50% by weight ethylene-acrylic

acid copolymer, about 2-40%> by weight plasticizer, about 0-10% by weight urea, about

1-5% by weight water and about 0.002-0.4%) by weight boron compounds.

8. A composite polymer as in claim 1, comprised of the

following:approximately 10-90%) by weight of said first polymer; and approximately 10-

90% by weight of said resin.

9. A plastic media blast material, comprising: particulates having

equivalent diameters between about 0.2 and 2.5 mm formed from a mixture of approximately 10-100% by weight of a first polymer comprised of lactic acid monomers,

and approximately 0-90%o by weight of a resin comprised of a thermoplastic polymer,

destructured starch and a plasticizer.

10. A plastic media blast material as in claim 9 wherein said

particulates are formed from a mixture of approximately 30-70% by weight of said first

polymer, and approximately 30-70%) by weight of said resin.

11. A plastic media blast material as in claim 9 wherein said

particulates are formed from a mixture of approximately 50%> by weight of said first

polymer, and approximately 50%> by weight of said resin.

12. A printable plastic material, comprising: a sheet formed from

approximately 10-90% by weight of a first polymer comprised of lactic acid monomers,

and approximately 10-90% by weight of a resin comprised of a thermoplastic polymer,

destructured starch, and a plasticizer.

13. A printable plastic material as in claim 12 wherein said sheet is

formed from approximately 30-70%> by weight of said first polymer, and approximately

30-70% by weight of said resin.

14. A printable plastic material as in claim 12, wherein said sheet is

formed from approximately 50% by weight of said first polymer, and approximately 50%

by weight of said resin.

15. A printable plastic material, comprising: a molded article formed

from approximately 10-90%) by weight of a first polymer comprised of lactic acid

monomers, and approximately 10-90%> by weight of a resin comprised of a thermoplastic

polymer, destructured starch, and a plasticizer.

16. A method for making a degradable composite polymer, comprising

the following steps: combining a first polymer comprised of lactic acid monomers with

a resin comprised of a thermoplastic polymer, destructured starch and a plasticizer; and

extruding said first polymer and said resin through a heated extruder.

17. A method as in claim 16 wherein said composite polymer forms

at a temperature between about 140┬░C and 230┬░C.

18. A method for making printable plastic material, comprising the

following steps: combining a first polymer comprised of lactic acid monomers with a

resin comprised of a thermoplastic polymer, destructured starch and a plasticizer; and

extruding said first polymer and said resin through a heated extruder into a sheet die to

form a sheet of printable plastic material.

19. A method as in claim 18, further comprising: cutting said sheet of

printable plastic material into pieces of a desired size.

20. A method as in claim 18, further comprising: printing ink on said

sheet of printable plastic material.

21. A method for making printable plastic material, comprising the

resin comprised of a thermoplastic polymer, destructured starch and a plasticizer;

extruding said first polymer and said resin mixture through a heated extruder to form a

printable plastic material; and molding said printable plastic material into shaped articles.

22. A method as in claim 21 wherein said printable plastic material is

molded by injection molding or compression molding.

23. A method for making plastic media blast material, comprising the

following steps: combining a first polymer comprised of lactic acid monomers with a resin comprised of a thermoplastic polymer, destructured starch and a plasticizer; and

extruding said first polymer and said resin through a heating extruder into a rod die to

form rods which are then processed into plastic media blast material.

24. A method as in claim 23, further comprising: cooling said rods

which exit from said rod die.

25. A method as in claim 24, wherein said extruded rods are cooled

in a water bath.

26. A method as in claim 23, further comprising: cutting said rods

which exit from said rod die into pellets.

27. A method as in claim 26, further comprising: grinding said pellets

into particles having a prescribed fineness.

28. A method as in claim 23 wherein said rods are ground into

particles having equivalent diameters between 0.2 and 2.5 mm.

29. A method as in claim 23 wherein said plastic media blast material

has a hardness between approximately 10 and 70 on the Rockwell scale.

30. A method for removing material from a substrate, comprising:

projecting particulates formed from a mixture of approximately 10-100% by weight of

a first polymer comprised of lactic acid monomers, and approximately 0-90% by weight

of a resin comprised of a thermoplastic polymer, destructured starch and a plasticizer

against a substrate; and dislodging material from said substrate.