WO1999011699A1

WO1999011699A1 - Biodegradable plastic articles having a reduced rate of moisture-induced degradation

Info

Publication number: WO1999011699A1
Application number: PCT/US1998/018332
Authority: WO
Inventors: Milford Hanna; Anantha Kollengode; Gerald Biby
Original assignee: The Board Of Regents Of The University Of Nebraska
Priority date: 1997-09-05
Filing date: 1998-09-04
Publication date: 1999-03-11
Also published as: AU9219098A

Abstract

The present invention comprises methods of extruding a substantially biodegradable plastic by combining initial ingredients comprising a biodegradable fiber, a stiffener, and a biodegradable polymer and extruding the resulting material. The invention also comprises extrudable fiber-based compositions comprising a natural fiber, a stiffener, and a biodegradable polymer such that said compositions can be extruded under heat to produce a substantially biodegradable extrudate. The invention further comprises coated plastic articles and composites produced according to these methods.

Description

BIODEGRADABLE PLASTIC ARTICLES HAVING A REDUCED RATE OF MOISTURE-INDUCED DEGRADATION

FIELD OF THE INVENTION

The present invention relates to the formulation of a range of biodegradable plastic materials, articles, and composites as well as the process for mixing different materials to fabricate biodegradable plastics. The compositions have varying levels of water solubility, greater physical elasticity, less physical stickiness or "tackiness," and an improved color over pre-existing biodegradable materials.

BACKGROUND OF THE INVENTION

Many different formulations are currently used for the production of biodegradable materials. Several such materials are composed solely of sugar and cellulosic fibers. These sugar-fiber bioplastics are designed to be quite readily water soluble and degradable, any contact with moisture will initiate the rapid degradation of the material. This makes these materials ideal for certain uses, especially those of relatively short duration where the high level of water solubility does not affect their performance. However, in other applications that require more lengthy exposure to moisture, the use of these materials is not practical.

Because these sugar-fiber bioplastics are made from a combination of sugars and cellulosic fibers, once they are processed they become extremely rigid and brittle and lack physical flexibility. This limits their use in applications that require flexible materials.

In addition, the sugar content of these sugar-fiber bioplastics causes their surface to become sticky or "tacky" when exposed to limited moisture, such as humidity, condensation, or sweat, which further limits their usefulness in many applications. Finally, the color of these sugar-fiber bioplastics is a dark brown due to the caramelization of the sugar in the material. This color obviously hinders the ability to print on or color the sugar-fiber bioplastic, and limits its application to areas where color is not of importance.

For these and other reasons, such bioplastics are widely perceived to be impracticable for extrusion processing of a great variety of plastic articles. The handles of disposable razors, for example, are generally made from non-biodegradable materials. To minimize the environmental impact of this, many such handles are injection-molded to form a hollow barrel, minimizing the amount of materials used and the weight of the resulting non- biodegradable product. Although such materials are sometimes recyclable in theory, the great majority of such razors are not recycled due to the burden of sorting. As a result, materials like disposable razors comprise a significant volume of non-biodegradable materials now entering sanitary landfills and will continue to do so for the foreseeable future.

Therefore, it is a desirable improvement to formulate a biodegradable plastic which has a reduced, preferably controllable rate of degradation when exposed to moisture, and which has the desirable physical characteristics of flexibility and non-tackiness, which has an improved color which can be printed upon, and which is useable in extrusion processing so as to generate the formation of free radicals, to graft the sugar other ingredients, and increase the manufacturing methods for which it is usable.

U.S. Patent 5,317,037 discloses several materials which can be used to create a suitable non-sticky, moisture-resistant coatings on molded articles. Numerous hydrophobic polymers known in the art are suitable for this purpose, such as polyethylene, polypropylene, and polystyrene. Lacquers, varnishes, enamels, urethane, epoxy, acrylic, and flaky pigments such as mica and talc and numerous other materials can also be used for this purpose.

U.S. Patent 5,710,190 teaches the use of many foaming agents, proteins, fillers, bleaching agents, colorants, preservatives, lubricants, and modified starches which can be used with the present invention. Many such ingredients are compatible with extrusion processes under certain conditions, as discussed therein.

U.S. Patent 5,582,670 teaches the use of hydraulically settable composites in extruded and rolled materials, and also of a water-dispersible organic polymer binder, extruded and rolled to form "highly inorganically filled" organic polymer sheets.

None of these references disclose extruding a substantially biodegradable plastic comprising a fiber, a stiffener, and an open-chain polymer as described and claimed in the present application.

SUMMARY OF THE INVENTION

It is an object of the present invention to disclose substantially biodegradable plastic articles with the following characteristics: various, controllable levels of water solubility and speed of biodegradation; increased physical flexibility compared to previous biodegradable materials; improved color compared to other biodegradable materials; and less tackiness than other biodegradable materials. One of these biodegradable plastics comprises cellulosic fibers, simple sugars, and natural biodegradable polymers. A second biodegradable plastic disclosed herein which satisfies these criteria is a biodegradable plastic comprising: starch, cellulosic fiber, plasticizer, protein, and initiators. This composition could also further comprise natural biodegradable polymers.

It is still a further object of the present invention to disclose a process for making a biodegradable plastic for which the above characteristics can readily be modified.

Materials of the present invention can optionally be characterized as extrudable materials, extrudates, extruded articles, and composites made from extruded articles. 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.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a graph of the water absorption data for three mixtures incorporating sisal as the cellulosic fiber with MB = 20% ZF03U/A natural biodegradable polymer. NM = non- mixing twin screw extruder, TM = twin mixing extruder, 60/40 60% high fructose corn syrup 40% sucrose, HFCS = 100 % high fructose corn syrup.

FIG. 2 is a graph of the water absorption data for three mixtures incorporating ponderosa fluff as the cellulosic fiber with MB = 20% ZF03U/A natural biodegradable polymer. NM = non-mixing twin screw extruder, TM = twin mixing extruder, 60/40 = 60% high fructose corn syrup 40% sucrose, HFCS = 100 % high fructose corn syrup.

FIG. 3 is a graph of the unit density of six different mixtures. NM = non-mixing twin screw extruder, TM = twin mixing extruder, 60/40 = 60% high fructose corn syrup 40% sucrose, HFCS = 100 % high fructose corn syrup.

FIG. 4 is a graph of the flexural strength of six different mixtures. NM = non-mixing twin screw extruder, TM = twin mixing extruder, 60/40 = 60% high fructose corn syrup 40% sucrose, HFCS = 100 % high fructose corn syrup.

FIG. 5 is a graph of the decomposition of sisal and fluff based mixtures compared to a control mixture as measured in cumulative CO₂ production vs. time.

DETAILED DESCRIPTION OF THE INVENTION

The present invention is embodied in biodegradable plastics which can be formulated with varying levels of water solubility, which have increased physical flexibility, which have less tackiness, and which have improved color over previous sugar-fiber bioplastics and other biodegradable materials.

The present invention can be used to make a disposable razor handle, for example, that is improved over the currently available articles with regard to cost-effectiveness, biodegradability, and perceived quality. Extrusion is generally more efficient than injection molding in terms of tooling, energy, and necessary additives. The present invention can greatly reduce the volume of non-biodegradable materials in the razor handle, even if they include a hydrophobic coating. Moreover, the selection of materials taught herein for slower, controlled degradation (as compared with other sugar-fiber compositions) lend themselves to leaving (or producing) gaps in such an inert coating. Finally, the present invention lends itself to the manufacture of solid items including, but not limited to, disposable razor handles, improving the "feel" of the product over present hollow handles.

The present invention can be used to manufacture a great variety of products. It is particularly adapted to manufacturing articles with limited exposure to moisture and mechanical stress, and those with fairly uniform cross-sections (picture frames, sticks for cotton swabs, and display stands, e.g.). A lower-fiber embodiment can be rolled and severed (preferably by cutting or crushing) into pieces less than 1 cm in cross-section, and then used in an injection-molding process. A higher-fiber embodiment can be shaped in a substantially solid form such as by lathing, milling, carving, drilling, machining, and the like, as is known in the art.

Such articles can be painted to form substantially biodegradable figurines, novelty items, candle holders, or game pieces. Replacing the bulk of petroleum-based items of manufacture with substantially biodegradable ones particularly reduces the social and environmental costs of manufacturing and thus enhances the value of such items to many consumers.

The present invention discloses a biodegradable plastic comprising a cellulosic fiber, a simple sugar, and a natural biodegradable polymer. The following invention also discloses a biodegradable plastic comprising a stiffener, a cellulosic fiber, a plasticizer, a protein, and initiators. This composition can further comprise natural biodegradable polymers.

The term "starch" refers herein to a single starch or combination of starches as known to the art.

The term "cellulosic fiber" refers to a single natural cellulosic fiber or combination of different natural cellulosic fibers as known to the art including but not limited to: sawdust, wood shavings from either hydrolyzed or unhydrolyzed hard or soft woods, cotton fiber, sugar beet fiber, straw from small grains (e.g. wheat, rye, barley, etc.) or commercially available cellulosic fibers such as but not limited to the sisal fiber line available from International Filler Corp., Bridge N. Tonawanda, NY 14120 or Ponderosa Fluff from Ponderosa Fibers of

America, 1100 Circle, Atlanta, GA 30339-3024 or Ponderosa Fibers, 858 W. Leather Ave. Tomahawk, WI 54487.

The term "simple sugars" refers to a single sugar or combination of sugars as known to the art including but not limited to: glucose, sucrose, fructose, maltose, galactose, arabinose, raffinose, and stachyose.

The term "plasticizers" refers to a single plasticizer or combination of plasticizers as known to the art including but not limited to: triethyl citrates, glycerol mono, di- or tri- acetates, or triethlyene glycol diethylhexoate.

The term "proteins" refers to a single protein or combination of proteins to serve as a binder for the starch and cellulosic fiber as known to the art. These include but are not limited to: casein, wheat gluten, corn zein, and soy protein.

As used herein, a property deemed "controllable" and "controlled" refers to the general ability to raise or lower a conventional measure of the property within reasonable bounds, without undue experimentation. One skilled in the art, for example, knows that caramelization can affect the color of a heated sugar, and that the degree of caramelization can be controlled by suitable selection of curing temperature and duration. Color is therefore "controlled" even though this process cannot generate a great variety of colors, and is generally undesirable in the context of the present invention.

The term "initiators" refers to a single initiator or combination of initiators as known to the art including but not limited to: Epon 828, oxirane, and hydantoin.

The term "biodegradable polymers" refers to a group of chemicals including, but not limited to, poly lactic acid, poly gly colic acid, and copolymers of polylactic and polyglycolic acids, or the commercial compounds, LDPE, ZF03/A, ZF03/U, ZI01U, ZF03U/A, ZF03U, or ZI01U/T available from Novamont, S.P.A., P. Le Donegani 4, 05100 Terni (I), Milan, Italy. Some physical properties of these chemicals are provided in Table 1. A practitioner skilled in the art will recognize that the chemicals useful as biodegradable polymers in this invention will share at least some similarity with the chemicals on this table, but that any given property or properties may range plus or minus 100% of any of the values provided and still be within the scope of this invention. The term "Matter Bi" is also used herein to refer to certain propriety chemicals in this group.

The following paragraphs discuss one embodiment of the invention which is a biodegradable plastic comprising: cellulosic fiber, simple sugars, and biodegradable polymers.

A sugar-fiber mixture comprising about 25-75% simple sugars and about 25-75% natural cellulosic fibers by weight, preferably about 50% simple sugars and about 50% natural cellulosic fibers, is combined for sufficient time to ensure the elements have been thoroughly incorporated, preferably in a mixer for a period of not more than one hour. After mixing, the sugar-fiber mixture is then stored in an airtight container for a period of time sufficient to allow moisture in the sugar-fiber mixture to equilibrate between the fiber and the sugar, preferably not less than 12 hours. Then a given amount of biodegradable polymer is added to the mixture preferably to result in about 5% to about 35%, more preferably resulting in about 8%> to about 20%, of the final mixture being biodegradable polymer. As is discussed in further detail hereafter, the amount of biodegradable polymer added to the sugar-fiber mixture is chosen to create a biodegradable plastic with specific characteristics. Once the biodegradable polymer has been added, the resulting final mixture is again mechanically agitated or mixed until all of the elements have been thoroughly incorporated.

Once thoroughly combined, the final mixture goes through a radical generation step to form the compositions of the present invention. A radical generation step may be by any means known to the art for creating radicals essential for grafting (for example, conjugating, adhering, binding, covalently boding or by linking via an intermediate compound) the sugar to the natural fiber and biodegradable polymer including, but no limited to extrusion, chemical initiation, or irradiation. The product produced after the radical generation step and subsequent reaction is the biodegradable plastic.

The preferred method for obtaining the biodegradable plastic of the present invention involves extrusion processing using a twin-screw extruder. It should be noted that a twin non-mixing screw or a twin mixing screw extruder with at least a 1 :1.5 compression ratio could be used. The extruder can be set to any combination of screw speed and temperatures as known to the art that are sufficient to produce an output, but not to burn or damage the final mixture. The preferred settings of the extruder are to set the screw speed between about 90 and about 190 rpm, the temperature between about 140 and about 180 degrees Celsius, and the barrel temperature between about 120 and about 160 degrees Celsius. The die can be chosen depending on the desired shape of the extruded material, as is well known in the art.

The radical generation step creates the grafting between the sugar and the cellulosic fibers. In addition, biodegradable polymers can form cross linkages with the other materials in the mixture. The compositions obtained through this process have improved resistance to moisture, improved flexibility, enhanced color, and a substantial reduction or complete elimination of physical tackiness compared to other biodegradable materials, while still maintaining biodegradability, The present invention has a range of water-absorption from 3 to 100% by weight in 2 hours. This range may be partially controlled by varying selection and ratio of sugar and cellulosic fibers in the formulation and by varying the processing conditions. However, the most effective means for regulating the water-resistance and speed of biodegradability of the present invention is to modify the amount of natural biodegradable polymer incorporated into the final mixture. The more biodegradable polymer added to the final mixture, the more water-resistant the resulting composition will be. Conversely, the less biodegradable polymer added to the mixture, the less water-resistant the resulting compositions will be. The change in water-resistance also leads to a similar relationship with respect to the characteristic of tackiness. The tackiness of the resulting material lessens as more natural biodegradable polymer is incorporated into the mixture.

Physical flexibility is also regulated by the percent of natural polymer in the mixture. Between about 5% and about 35% biodegradable polymer the flexibility increases as the polymer content increases. Above about 35% biodegradable polymer, the level of flexibility of the resulting compositions remained fairly constant. Below about 5% biodegradable polymer, the product is rigid and lacks the desired flexibility.

The compositions synthesized in this manner have a lighter color than the previous materials. The color can be controlled through various methods. By increasing the amount of natural biodegradable polymer added to the mixture, the resulting biodegradable plastic can be lightened. The choice of the cellulosic fiber can also change the color, using lighter colored cellulosic fibers can also result in a lighter color in the compositions. The temperature of the extruder can be lowered to reduce the caramelization of the sugar which further lightens the color of the resulting biodegradable plastic. Finally, the color may also be affected by adding Maillard reaction inhibitors such as sulfites to the final mixture that will prevent the browning of biodegradable plastic as is well known to the art. This allows the compositions to be printed upon with greater success than previous biodegradable materials. Since the compositions comprising the present invention are formed through mixing or agitation and can be used in an extrusion process, they have a greater range of applicability in thermo forming and injection molding applications than previous biodegradable plastics.

The following paragraph discusses a biodegradable plastic comprising: a stiffener, cellulosic fiber, plasticizer, protein, and initiators which could also further comprise natural or synthetic biodegradable polymers.

This biodegradable plastic is fabricated by a method similar to that discussed above. Preferably the elements are used in the following percentages:

Preferred More Preferred

Stiffener 15 to 75% 30-50%

Cellulosic fibers 15 to 75% 30-50%

Plasticizer 5 to 45% 10-30%

Protein 5 to 45% 10-25%

Initiators 2.5 to 30% 5-20%

This combination also can be formulated with varying levels of water solubility, can have increased physical flexibility, can have less physical tackiness, and can have improved color over previous sugar-fiber bioplastics and other biodegradable materials.

Natural or synthetic biodegradable polymer can be further added to the above combination in order to allow further control of the properties of the resultant biodegradable plastic as was discussed previously.

Example 1

Biodegradable plastics were formed of sugars, cellulosic fibers, and the commercially available ZF03U/A natural biodegradable polymer as in the above method. The fibers and sugar were combined in an approximate 1-1 ratio and were mixed in a laboratory Hobart mixer for about 60 minutes. Compositions were allowed to sit overnight for at least 12 hours in an airtight container. The radical generation step was performed using extrusion processing in a twin-screw laboratory extruder (model 2803, Plasticorder, purchased from C. W. Brabender Instruments, Inc. of South Hackensack, New Jersey) utilizing 1 :1.5 compression ratio. The extruder was set at 140 rpm screw speed, three temperature zones were maintained at 150-160-160 degrees Celsius, the barrel temperature was set to at least

140 C, and the biodegradable plastic was extruded using a flat die. The plastics fabricated, as well as various properties computed for them are given in the tables, figures, and examples herein.

Table 1 shows physical properties for polymers used herein. Table 2 shows some of the sample mixtures analyzed. Table 3 details the level of water absorption for the sample mixtures. Table 4 shows differential scanning calorimetry data for the sample mixtures. Table 5 shows flexural strength data obtained on the sample mixtures. These tables clearly show the relationship between the components of the plastic and some of the desired physical characteristics.

The biodegradable fiber of the present invention, desirably comprising 5 to 50% of the total weight of said initial ingredients, preferably comprises natural, cellulosic fibers such as those from cotton, sisal, jute, flax, ramie, silk, hemp, and pine wood. For applications which require a lesser degree of toughness, recycled paper fibers may be preferred. Such applications may also permit the use of less-expensive inorganic fillers such as calcium carbonate, kaolin, or magnesium hydroxide. Many such materials are environmentally superior to paper, plastic, or metal because they consume much less energy to manufacture.

The stiffener of the present invention, desirably biodegradable, substantially crystalline, and comprising up to 40% of the total weight of said ingredients, optionally comprises glucose, fructose, and sucrose. Alternatively, high fructose com syrup (HFCS) can be used as a stiffener in the present invention. Preferably, the selected stiffener is substantially amenable to consumption by bacteria (i.e., having growth-inducing properties comparable to fructose) and tempered by a very low selected concentration of a growth inhibitor (preservative), another means of controlling the rate of bio-degradation. The biodegradable polymer of the present invention is optionally synthetic (i.e., not naturally-occurring), although a natural polymer such as collagen can also be used. It preferably comprises an open-chain structure based on acetylene, olefin, or paraffin hydrocarbons or their derivatives. Exemplary compounds include polylactic acid (PLA), polyglycolic acid (PGA), and copolymers of PLA and PGA. The polymer desirably comprises 5 to 20% of the total weight of the initial ingredients.

The initial ingredients of the present invention optionally include additional ingredients (additives) comprising a foaming agent, a surfactant, a protein, a filler (or "aggregate"), a bleaching agent, a surfactant, a colorant, an initiator, a preservative, and a lubricant.

The mixing of the ingredients of the present invention are optionally carried out at an elevated temperature, such as in a heated chamber of a mixing extruder, heating said stiffener to a temperature high enough substantially to destroy any crystallinity in said stiffener. For a product that does not soften when handled, the stiffener preferably comprises carbohydrate composition that is substantially crystalline at body temperature. Many such stiffeners do not have a single melting temperature per se, but soften and gradually turn into (decreasingly) viscous fluids as their temperature is raised. Excessive heating, or holding at a high temperature for extended periods, however, can cause caramelization. Because this can negatively affect color and certain other properties of some ingredients, the stiffener temperature is preferably maintained to within about 20 degrees (Celsius) above that which produces the desired crystallinity. The stiffener is preferably allowed to cool within about a minute of reaching the desired decrystallization, moreover, to substantially avoid undue caramelization. A person of ordinary skill in the art can recognize the presence of undesired caramelization and can adjust the temperature or timing to eliminate it. An ideal manufacturing process allows the ingredients to be heated for a desired degree of intimate interbonding without inducing undesired darkening or cross-linking due to caramelization.

Preferably, the temperature is kept low enough substantially to minimize or avoid significant temperature-induced caramelization and oxidation among any of said ingredients. To avoid undesired polymer transformation, a polymer with a high melting point such as polyvinylalcohol and certain copolymers of ethylene-vinylalcohol known in the art is preferable. Polymer compositions comprising polylactic acid, polyglycolic acid, their copolymers, and other aliphatic polyesters are examples of biodegradable polymers for the present invention. Note that solvents such as water may also be used to reduce the crystallinity of a stiffener and might thus reduce the temperature necessary for successful extrusion. Also note that typical stiffeners of the present invention inherently comprise up to about 12%) water.

Once extruded, the resulting substantially biodegradable plastic extrudate is preferably into pieces within a predetermined size range. In manufacturing articles to be handled as a part of their intended use (examples would include game pieces, carnival novelties, pencils, tampon applicators, and handles of disposable razors), the predetermined size range would be about 2 to 20 centimeters, or quite commonly 5 to 7 cm. Other sizes and size ranges can be used, depending on the intended use of the extruded items. Articles to be used as a raw material (examples would include posts for standing lamps and picture frames) might necessitate a predetermined size range of 10 to 200 cm, or quite commonly 80 to 100 cm. Where feasible, it is generally preferred that a predetermined size range maximum be about .01% larger than the minimum. A large fraction (preferably about 80 to 99.99%) of the surface of these pieces is desirably coated with a petroleum-based film. This can be accomplished, for example, by applying a moisture-resistant material to a piece (substantially coating it), and then removing a portion of the material.

According to the present invention, a variety of articles conventionally made of wholly non-biodegradable materials (i.e., those that typically require 20 years or more to break down, even in a sunny, humid environment) can be replaced with substantially biodegradable materials (i.e., those consisting of at least 97% biodegradable materials, by weight). The inventive articles, moreover, can generally be made to accomplish this improvement without any significant loss in performance in any measurable criterion significant to their intended use. Articles made according to the present invention will not resist water degradation as well as their wholly non-biodegradable counterparts (at least not when broken), for example, but many applications exist where this is not a significant criterion of performance.

More importantly, articles of the present invention perform well in several significant, measurable aspects. Polymer ingredients and coatings of the present invention, for example, can serve to reduce tackiness (as measured, e.g., by adhesion force between an articles' moistened surface per square centimeter contact area with a given porous, planar surface) to practically any degree desired. A substantially biodegradable article having a surface fully coated with PLA, for example, is essentially non-tacky.

An aspect of the present invention comprises substantially coating said plastic with a moisture-resistant, petroleum-based film. Petroleum-based coatings can have the undesirable effect of retarding, and possibly even preventing, biodegradation. To counteract this, and to allow an additional mechanism by which the present invention controls the rate of moisture- induced degradation, it is preferred that articles of the present invention incorporate one or more small openings in such film coatings. Such openings (or localized reductions in film thickness) can be produced by scratching, drilling, controlled application of a spray solvent, or other similar methods known in the art. Alternatively, if a conventional dipping process is used for application of the coating, the use of a gripping apparatus may be convenient or creating such openings simply by holding the articles in a selected position while the film dries, creating the film and the opening(s) in a single step. The film desirably covers more than 90%> of the surface area of each extruded articles with a uniform thickness of the coating, leaving some area less than 10% of said surface area with a lesser quantity of the coating material. Note that coating the extrudate before severing may be desirable, creating openings for accelerating bio-degradation where the extrudate is severed.

Application of glycerin or a similar polyalcohol can optionally soften a portion of the extrudate of the present invention, where desired. This may be useful, for example, in creating a hinged article from an extruded sheet. The present invention further comprises composite articles and materials that incorporate materials and methods described above. Even applications that have higher performance requirements than can be achieved by wholly biodegradable compositions can benefit from the current invention. The blade of an ice scraper, for example, is typically made of hard plastic or metal, having a portion extending into the handle. The blade must typically be a hardened material to serve its intended purpose, but the handle typically encounters much lesser stress levels. A lacquered slab made according to the present invention could thus easily be made into a substantially biodegradable ice scraper handle by a manufacturer of ordinary skill.

Although the description above contains many specific recitations; these should not be construed as limiting the scope of the invention but merely providing illustrations of some of the presently -preferred embodiments of this invention. The potential uses for the present invention include the development of a range of products with varying levels of degradation by composting or by contact with any type or level of moisture, ultraviolet light, and/or bacteria. The present invention can also be incorporated into a wide range of products in the area of printable plastics.

All patents referenced herein are incorporated by reference insofar as they are consistent with assertions herein.

Table 1. Physical Characteristics of Mater-Bi Films

PROPERTY METHOD UNIT ZF03U/A ZF03U LDPE

Density gr/cm³ 1 12 1 12 0 91 Thickness μm 30 30 30 Haze ASTM D1003 % 85 Gloss 60 ASTM D2457 % 8 5 C O F ASTM D 1894 <0 7 <0 7

Tensile strength at yield ASTM D882(*) MPa MD 8 3 12 8 5 CD 1 1 Tensile elongation at yield ASTM D882(*) MPa MD 25 19 13 CD 27 Tensile breaking strength ASTM D882(*) MPa MD 21 30 16 CD 24 Tensile elongation at break ASTM D882(*) % MD 780 800 870 CD 720 Tensile modulus AST M D882(*) MPa MD 160 296 191 CD 251 Tensile energy at break AS I D882(*) KJΛZ MD 5000 7500 5740 CD 5900

Tear resistance at 23 °C, 55%RH AST M 1938 N/mm MD

72 68 63

P 72 68 63

CD I 69 84

P 69 84

Tear resistance at 23 °C, 20%RH ASTM 1938 N/mm MD

I 72 33

P 72 33

CD I 90 80 P 90 80

Melt flow rate Load=5Kg I =150°C g/10 mm 3 5 T=150 C

Water vapor permeability ASTM E398 g-30μm/m^"-24h 900 450 18 Oxygen permeability 25 °C=0%RH cc-20μm/m²-24h-bar 80 10000

(*) Cross head speed =50 mm/mmute MD=Machιne Dn ection, CD=Cross Direction. I=pπmer load, p=propagatιon

Table 2

TM: Twin screws with mixing elements

MB: Matter Bi HFCS: High fructose com syrup

NM: Non-mixing twin screws 60/40: 60% HFCS and 40% sucrose

Table 3

Water absorption data for fibers

TM: Twin screws with mixing elements

MB: Matter Bi HFCS: High fructose corn syrup

NM: Non-mixing twin screws 60/40: 60% HFCS and 40% sucrose

Table 4

DSC (Differential Scanning Caloriemetry) data for fibers

NA: could not be determined

TM: Twin screws with mixing elements

MB: Matter Bi HFCS: High fructose corn syrup

NM: Non-mixing twin screws 60/40: 60% HFCS and 40% sucrose

Table 5

Flexural strength of fibers

NA: could not be determined

TM: Twin screws with mixing elements

MB: Matter Bi HFCS: High fructose corn syrup

NM: Non-mixing twin screws 60/40: 60% HFCS and 40% sucrose

Claims

We claim:

1. A method of extruding a substantially biodegradable plastic comprising the steps of:

(a) combining ingredients comprising a biodegradable fiber, a stiffener, and a biodegradable, open-chain polymer; and

(b) extruding the material resulting from step (a).

2. The method according to claim 1 wherein said biodegradable fiber is cotton, sisal, jute, flax, ramie, silk, hemp, wood, or recycled paper.

3. The method according to claim 1 wherein said ingredients are deposited into said extruder continuously.

4. The method according to claim 1 wherein said step (a) is carried out in a heated chamber of a mixing extruder.

5. The method according to claim 4, further comprising the step of elevating said stiffener to a temperature high enough substantially to destroy any crystallinity in said stiffener.

6. The method according to claim 1 wherein the temperature of each of said ingredients is kept low enough during and between said steps (a) and (b) to substantially avoid temperature-induced oxidation among said ingredients.

7. The method according to claim 1, further comprising the subsequent step of dividing the extrudate resulting from step (b) into pieces within a desired size range.

8. The method according to claim 1 , further comprising the step of coating a fraction of the surface of the extrudate resulting from step (b) with a petroleum-based film.

9. The method according to claim 8, further comprising the subsequent step of shaping one of the pieces in a substantially solid form into a shape suitable for its intended use.

10. The method according to claim 9, further comprising the subsequent steps of substantially coating at least one of said pieces with a moisture-resistant material and removing a portion of said material.

11. A composite article made from the shaped piece resulting from the method of claim 9.

12. A plastic article made from the substantially biodegradable plastic piece produced according to the method of claim 1.

13. An extrudable composition comprising a natural fiber, a stiffener, and a biodegradable, open-chain polymer such that said composition can be extruded under heat to produce a substantially biodegradable extrudate.

14. The extrudable composition according to claim 13 wherein said stiffener is biodegradable and comprises up to 40%> of the total weight of said ingredients.

15. The extrudable composition according to claim 13 wherein said biodegradable fiber is selected from the group consisting of cotton, sisal, jute, flax, ramie, silk, hemp, wood, or recycled paper; and wherein said biodegradable polymer is selected from the group consisting of polylactic acid (PLA), polyglycolic acid (PGA), and copolymers of PLA and PGA.

16. The extrudable composition according to claim 13, further comprising an additive selected from the group consisting of a foaming agent, a protein, a filler, a bleaching agent, a colorant, an initiator, a preservative, a surfactant, and a lubricant.