Water-resistant degradable foam and method of making the same

Details Water-resistant degradable foam and method of making the same Water-resistant degradable foam and method of making the same

1999-05-06

2001-02-06

Foelak, Morton (Department: 1711)

Synthetic resins or natural rubbers -- part of the class 520 ser

Synthetic resins

Cellular products or processes of preparing a cellular...

C521S138000, C521S916000, C521S082000

Reexamination Certificate

active

06184261

ABSTRACT:

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° 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° 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, 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

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