WO1998036018A1

WO1998036018A1 - Biodegradable polymers

Info

Publication number: WO1998036018A1
Application number: PCT/US1998/002681
Authority: WO
Inventors: Kent Blizard; Robert Kovar; Leslie Rubin; Justyna Teverovsky
Original assignee: Foster-Miller, Inc.
Priority date: 1997-02-14
Filing date: 1998-02-13
Publication date: 1998-08-20
Also published as: EP0966500A4; EP0966500A1

Abstract

The present invention provides biodegradable polymer compositions comprising at least one thermally processable (e.g., thermoplastic) biodegradable polymer material and at least one organic filler material. The amount of filler material added to the biodegradable polymer material results in the altering and therefore, tailoring of properties of the biodegradable polymer material and the resulting biodegradable polymer composition.

Description

BIODEGRADABLE POLYMERS

STATEMENT OF GOVERNMENT INTEREST

This invention was made with U.S. Government support under contract no. N62269-95-C-0111 awarded by the U.S. Navy. The U.S. Government has certain rights in the invention claimed herein.

FIELD OF THE INVENTION

This invention relates to a biodegradable composition comprising at least one biodegradable polymer material and at least one organic filler, and having certain improved properties, such as increased tensile strength, over the biodegradable polymer material.

BACKGROUND OF THE INVENTION

The disposal of plastic products is a well-known waste-management problem. More and more consumer products are manufactured from plastic and more and more of these products are intended to be thrown away after use.

The use of biodegradable polymers to manufacture these products has become widespread and has prompted research into the development of new polymers and new uses for old polymers. A biodegradable polymer is one which undergoes a change in its chemical structure as a function of naturally occurring microorganisms such as bacteria, fungi and algae. The change in structure results in a loss of properties that can be measured by standard test methods appropriate for the polymer and the application.

Useful biodegradable polymers withstand the processing conditions necessary to create products that will perform their intended function. Useful biodegradable polymers also maintain their mechanical integrity, are adaptable for use in existing polymer processing equipment and are cost-effective for production. Many presently available biodegradable polymers cannot be used to make products meeting the standards for high performance thermoplastics which are used in a wide variety of applications from food storage to instrumentation because properties such as high tensile strength, certain thermal properties, and so forth are not adequate. Furthermore, many uses of thermoplastics require what is known in the art as "engineering thermoplastics" which combine lightness and corrosion resistance with a balance of stiffness and toughness which is maintained over a wide range of temperatures. Presently known biodegradable polymers do not have the necessary qualities to qualify as engineering thermoplastics.

It would be useful to be able to tailor the properties of presently known biodegradable thermoplastic polymers to improve the properties for use as engineering thermoplastics in order to produce a quality product that is biodegradable. The thermoplastic should maintain its properties during the lifetime of the product, yet be manufactured in such a way so that its components biodegrade at the end of the useful lifetime of the product.

Certain products are manufactured for intentional release into the environment. For example, devices such as sonobuoys, ocean sensors, bathythermograms and drift cards are used at sea. The U.S. Navy releases between approximately 50,000 to 100,000 expendable sonobuoys into the oceans each year. The Naval Oceanographic Office (N00) uses bathythermograms to measure circulation patterns of the oceans thermally, hydrodynamically and bathymetrically. The NOO also releases drift cards to study surface ocean currents. The drift cards are plastic cards which have a preprinted address and phone number and instructions for the person finding the card to call or write. These cards have a low rate of retrieval. Oceanographic research facilities also use a variety of sensors and measuring devices which are designed to be retrieved and reused. Retrievable ocean sensors are also used at operations like deep-sea ocean wells. However, accidental losses in the ocean as the result of cable malfunction, severe weather or other factors are relatively common. Thus, it would be environmentally advantageous if these products or some or all of their components were made out of a biodegradable material. Additionally, approximately 200 radiosondes (weather balloons) are released each day throughout the world. In theory the radiosondes are retrievable; a parachute deploys when the balloon breaks and a label on the radiosonde provides instructions to return the sensor. However, in practice, the radiosondes are rarely recovered. This low recovery rate is primarily attributed to a high percentage of ocean landings, rather than landfalls. Currently radiosondes use polystyrene foam in their construction. A biodegradable foam could reduce the environmental impact of the sensors.

Other commercial applications/markets for a low- cost, multi-function, expendable, environmentally friendly, sensor probe include the following examples. An expendable environmental probe can be used in acoustical oceanography for taking surveys, making oceanographic database updates, and for making global weather predictions associated with current flow, wave height spectrums and temperature. The Coast Guard can use these probes for ice patrol, rescue operations and as marker buoys for localization. The probes can be used in the construction industry for short and long term monitoring of wind and wave stresses to future on and off-shore structures, and for current scouring in the construction of bridges and piers. Geographic surveys can be conducted using the probes to determine bottom type. Environmental uses include monitoring under hazardous conditions, determining bottom type and long term effects of waves, determining local climate (wind, waves, temperature, currents) , studying effluent discharge impact on littoral environment, thermal, turbidity, conductivity, etc. , oil spill management response, and HAZMAT remote monitoring (requires special sensor, could sense chemical spills) .

The products described above are designed to be released into the environment and, due the nature of their use, a high percentage are bound to be lost into the environment. Thus, it makes sense environmentally to manufacture these products from biodegradable materials. However, biodegradable materials are not limited to such applications. Most disposable products end up in landfills, i.e., they are returned to the environment. Manufacture of many disposable products from biodegradable polymers would also lessen their impact on the environment.

Currently known biodegradable polymers include starch, cellulose acetate, polyhydoxylalkanoates, poly(vinyl alcohol), polycaprolactone and poly(lactic acid) . Starch is an especially preferred biodegradable thermoplastic polymer because it is very inexpensive and easily obtainable. Thermoplastic starch can be processed from corn, potato, wheat and rice. One such commercially available starch is a product named NOVONTM available from Novon International, Inc. However, starch and the other above mentioned polymers do not have the properties necessary to impart to these products the high performance required. For example, NOVONTM is a rubbery material that has 100% elongation at breaking strength. Also, many of these polymers lack the thermal properties to withstand the injection molding techniques used to manufacture these high performance products. Many such polymers also lack the mechanical properties, e.g., they are too soft or brittle, to impart strength to the products necessary for proper functioning of the product. Furthermore, many of these polymers degrade too quickly under certain environmental conditions, e.g. in water, to maintain the required useful lifetime of the product. Methods used in the past to alter the properties of biodegradable polymers have included blending the polymer with other polymers or particulate matter. For example, starch is thermally processable but when extruded it produces a brittle foam. It can be blended with more hydrophobic polymers when used for injection molding and blown film. Mayer, J.M and Kaplan, D.L., TRIP, Vol.2 No. 7, Sept. 1994, p.227-235. However, such blends lack the tensile strength necessary to be useful for some applications and also tend to be sensitive to water.

It would be useful to tailor the properties of existing biodegradable polymers, e.g., starch, to create biodegradable compositions having the properties desired for specific applications. For example, products which are intentionally released into the ocean desirably withstand salt water exposure during their useful lifetime, but then degrade within a reasonable time to prevent pollution of the ocean. Similarly, these biodegradable products should have sufficient strength to withstand the forces of the ocean, such as waves, rocks and floating debris.

A need therefore exists for improved biodegradable compositions that have the qualities of engineering thermoplastics, and are used to manufacture products that perform their intended function and are biodegradable.

SUMMARY OF THE INVENTION

In accordance with the above, the present invention provides biodegradable polymer compositions comprising at least one thermally processable (e.g., thermoplastic) biodegradable polymer material and at least one organic filler material. The amount of filler material added to the biodegradable polymer material results in the altering and therefore, tailoring of properties of the biodegradable polymer material and the resulting biodegradable polymer composition.

In particularly preferred embodiments of biodegradable compositions of the present invention, the polymer is selected from starch-based thermoplastic polymers. Preferred starch based polymers are based on wheat starch, potato starch, rice starch, or corn starch and are available commercially from a number of vendors. A particularly preferred starch based thermally processable biopolymer for use in the present invention is the corn starch based polymer NOVONTM thermoplastic starch, available from Novon International, Inc. (Tonawanda, New York) a division of Ecostar in a number of grades. In an especially preferred embodiment, the biodegradable polymer is NOVONTM grade M1801, thermoplastic starch. Alternatively, the thermoplastic starch can be made using known methods by one of skill in the art.

In other preferred biodegradable compositions of the present invention, the biodegradable polymer comprises one or more copoly ers. Examples of copolymers useful in the practice of the present invention include starch based polymers blended with any biodegradable hydrolyzable polymer including polycaprolactone, polyvinyl alcohol, polylactic acid, polyhydroxybutyrate or polyhydroxyvalerate. Preferably, the copolymer comprises at least about 20% starch-based thermoplastic polymer.

The filler material selected for use in the present invention may be any one of a number of organic materials which are capable of environmental remediation. Preferred organic filler materials include nutshell flours, grain flours, starches and cellulose based particulate material. Although any particle size of the filler material is useful, the particle size is preferably equal to or smaller than about 100 Tyler mesh. Nutshell flours are generally useful as a filler in the present invention. Preferred nutshell flours include walnut shell flour and pecan nut shell flour. Examples of grain flours for use in the present invention comprise buckwheat flour, high gluten wheat flour (bread flour) , corn flour or corn meal, and soy flour. Natural starches for use as fillers in the present invention comprise potato starch, corn starch, rice starch, soy starch and wheat starch. Examples of cellulose based materials which are useful as fillers in the present invention comprise wood flours and other ground organic matter, e.g. corn cob grit. Any type of wood flour is useful as filler in the present invention, e.g. flour made from hard or soft woods.

The biodegradable polymer compositions of the present invention comprise organic filler material (s) in an amount that improves the desired property of the biodegradable polymer composition. Such properties include, but are not limited to, tensile strength. Young's modulus, elongation, impact strength, biodegradability, water susceptibility (rate of absorption/dissolution) , flow properties/rheology, hardness, stiffness of material as function of temperature, conductivity/resistivity, density, flexural properties, shrinkage (coefficient of thermal expansion) , and permeability to oxygen and water vapor.

By altering the weight percent of filler in the composition, i.e, the loading of filler in the biodegradable polymer, the property of interest can be tailored to the specific application. In preferred embodiments of the present invention, the mechanical properties of the composition to be tailored include tensile strength, modulus and elongation at peak loading. In these embodiments, the organic filler is added to the biodegradable polymer in an amount to obtain, e.g., the tensile strength desired. The appropriate amount of filler material (s) to achieve a desired property can readily be determined by adding varying amounts to the polymer composition under study and testing for change in the desired property. In preferred embodiments, the biodegradable compositions of the present invention comprise from about 1 to about 40 weight percent (wt %) filler. More preferably, the compositions comprise from about 10 to 25 wt % filler. In especially preferred embodiments, thermoplastic starch is loaded with from about 10 to 25 wt % walnut shell flour.

Preferred biodegradable polymer compositions of the present invention have a tensile strength which is from about 5 to about 150% greater than the pure biopolymer. More preferably, the resulting compositions have a tensile strength of from about 35% to about 150% greater than the pure biopolymer. The biodegradable compositions of the present invention preferably have an elongation at break which is similar to the elongation at break of the pure biopolymer. Preferred compositions have a range of increase in Young's modulus of about 5% to about 100% over the pure biopolymer. More preferably, the range is about 5% to about 65% increase in Young's modulus. With this combination of increased tensile strength and slight change of elongation at break, a higher strength biodegradable engineering thermoplastic is produced.

In other embodiments of the present invention, the property to be tailored is water susceptibility. In these embodiments, the organic filler is added in an amount to the polymer to prolong the lifetime of the final product in water as desired. In preferred embodiments, the filler is added to thermoplastic starch in a range of from about 1 to about 40 weight percent. More preferably, the filler is added in a range of from about

10 wt% to about 25 wt%. Preferred embodiments are less sensitive to water immersion than the pure, unfilled polymer. In preferred compositions of the present invention, the filter is walnut shell flour and the polymer is thermoplastic starch, and the resulting composition is more resistant to degradation in water than pure thermoplastic.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 depicts the peak load of NOVOΠTM thermoplastic starch grade M1801 compounds blended with walnut shell flour, and a non-degradable control ABS.

Figure 2 depicts the peak load of Novon™ thermoplastic starch grade M1801 compounds blended with walnut shell flour.

Figure 3 depicts elongation at peak load of Novon™ thermoplastic starch grade M1801 compounds blended with walnut shell flour. Figure 4 depicts the elastic moduli of Novon™ thermoplastic starch grade M1801 compounds blended with walnut shell flour.

Figure 5 depicts the percent weight gain of Novon™ thermoplastic starch grade M1801/walnut shell flour compounds as a function of composition.

Figure 6 depicts the percent weight gain of Novon™ thermoplastic starch grade M1801/walnut shell flour compounds as a function of immersion time.

Figure 7 is a graph showing a summary of tensile strengths of injection molded samples of a pure NOVON™ thermoplastic starch grade M1801 control and NOVONTM thermoplastic starch grade M1801 blended with different filler materials.

Figure 8 is a graph which shows the effect of the addition of different amounts of walnut shell flour on the tensile strength of NOVON™ starch based thermoplastic M1801 .

Figure 9 is a graph showing a summary of moduli testing of the same samples as in Figure 7. Figure 10 is a graph showing a summary of elongation at breaking strength of the same samples as in Figures 7 and 9.

DETAILED DESCRIPTION OF THE INVENTION It has been unexpectedly found that the addition of organic filler(s) to thermally processable biodegradable polymer compositions, such as thermoplastic starch, provides a biodegradable composition which has improved properties over the neat biodegradable polymer composition. Although it is traditionally known in the art that the addition of particulate matter to a polymer will make the resulting composition more brittle, the inventors have found that properties of certain biodegradable polymers can be enhanced by blending those polymers with an organic filler as described herein. The improved properties of the biodegradable compositions of the present invention enable the manufacture of high performance products, and components for use in high performance products, which are biodegradable.

The biodegradable compositions of the present invention comprise at least one thermally processable (e.g., thermoplastic) biodegradable polymer material and at least one organic filler material. The amount and type of filler material added to the biodegradable polymer material alters the properties of the biodegradable polymer material and the resulting biodegradable composition.

The mechanical properties of the biodegradable polymers can be altered by blending or compounding with an organic filler to obtain the biodegradable compositions of the present invention which has enhanced properties over the neat biodegradable polymers composition. For example, by altering the amount of filler, by weight percent, added to thermoplastic starch, one can adjust the tensile strength and elongation or modulus of the resulting biodegradable composition, and therefore, the tensile strength and elongation or modulus of the end product. Other characteristics of the biodegradable polymers can be adjusted, such as, but not limited to, water susceptibility, impact strength, hardness, stiffness, stiffness of the material as a function of temperature, flow properties (rheology) , conductivity/resistivity, density, flexural properties, shrinkage and permeability to oxygen and water vapor. For example, in one preferred embodiment of the present invention, the amount of filler is adjusted to alter the tensile strength of the resulting biodegradable composition, and therefore, the final product made from that composition. In formulating the overall composition of the biodegradable composition of the present invention, a number of variables including the properties of the biodegradable polymer material, the properties of the filler material and the properties of the resulting product which will be manufactured from the composition are taken into consideration. Using these variables, the composition is tailored and optimized in accordance with the present teachings to provide a biodegradable composition to meet a particular end use specification (e.g., high tensile strength, decreased water susceptibility, or certain thermal properties) .

The biodegradable polymer compositions of the present invention can be used to manufacture any end product that requires thermally processable polymers. The biodegradable compositions of the present invention are cost effective because they can by used in any method used to process thermoplastics, e.g., injection molding or compression molding techniques or extrusion methods. The biodegradable compositions of the present invention are especially useful for making articles of manufacture that withstand exposure to sea water and fresh water during the operating lifetime of the product without any adverse effect on the performance of the product, and that will biodegrade after the useful lifetime of the product. The biodegradable polymers useful in the practice of the present invention may be referred to as ••biopolymers" and are defined as polymers that can undergo microbially-induced chain scission leading to mineralization. Suitable thermally processable biopolymers for use in the present invention include, but are not limited to, starch-based thermoplastic polymers and copolymers. Preferred starch-based polymers are based on wheat starch, rice starch, potato starch, or corn starch and can be manufactured by one of skill in the art. A preferred commercially available starched-based polymer comprises corn starch based polymer NOVON™, available from Novon

International, Inc. (Tonawanda, New York) a division of

Ecostar. NOVON™ is described in U.S. Patent No. 5,095,054, which is incorporated herein by reference. U.S. Patent No. 5,095,054 describes a thermoplastic polymer composition comprising: (a) a destructurized starch, and either (b) an effective amount of at least one compound selected from the following: (1) a polymer which contains at least two different types of functional groups, one of said types of these groups being hydroxyl groups; (2) at least one polymer which does not contain hydroxyl groups and is selected from the group consisting of polymers which contain at least two types of functional groups bound to the same molecule one type of these groups being carboxylate groups; (3) at least one polymer selected from the group consisting of polymers which contain tertiary amino groups and/or salts thereof and/or quaternary ammonium groups; (4) at least one polymer selected from the group of polysaccharides which have been chemically modified to contain added hydroxyalkyl groups and/or contain alkyl ether groups, and/or contain ester groups; (5) at least one compound selected from the group consisting of copolymers of vinyl pyrrolidone; (6) at least one compound selected from the group consisting of cationically modified polysaccharides; (7) at least one compound selected from the group consisting of anionically modified polysaccharides; (8) at least one polymer selected from the group of copolymers containing vinyl alcohol units together with aliphatic chain units as are obtained by copolymerization of vinyl esters, preferably vinyl acetate, with unsaturated monomers containing no functional group with subsequent hydrolysis of the vinyl ester group; (9) at least one compound selected from the group consisting of polysaccharide graft copolymers and graft copolymers of polysaccharide derivatives; (10) at least one compound selected from the group consisting of polyalkyleneimine polymers and polyalkyleneimine copolymers; (11) at least one compound selected from the group consisting of styrene sulfonic acid polymers, styrene sulfonic acid copolymers, and salts thereof; and (12) at least one compound selected from the group consisting of polymers and copolymers which contain carboxylic groups which partially or wholly are present in the form of their salts and wherein said polymers or copolymers do not contain further functional groups; or (c) at least one substantially water-insoluble thermoplastic polymer combinations of (a) , (b) and (c) . Preferably, the starch is selected from NOVONTM thermoplastic starch grades M1801, M0121 and M0282, more preferably, NOVON™ thermoplastic starch grade M1801. Pure, unprocessed NOVONTM thermoplastic starch grade M1801 has the following properties:

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Tests conducted after conditioning at 50% RH, 73°F. * Spiral Flow conducted at 365°F Melt Temperature, 73°F Mold Temperature and 17,000 psi Injection Pressure.

Preferred copolymers for use in the present invention include blends of thermoplastic starch with other biodegradable polymers such as, but not limited to, polylactic acid, polyvinyl alcohol, polyhydroxybutyrate and polyhydroxyvalerate, polycaprolactone. Preferably the copolymers useful in the present invention comprise at least 20% starch based thermoplastic polymer.

The filler material selected for use in the present invention may be any one of a number of organic materials which are capable of environmental remediation. Preferred organic filler materials include nutshell flours, grain flours, starches and cellulose based particulate materials. Although a wide variety of particle sizes of the filler material are useful in the practice of the present invention, the particle size is preferably equal to or smaller than about 100 Tyler mesh. Nutshell flours are generally useful as a filler in the present invention. Examples of preferred nutshell flours include walnut shell flour and pecan nut shell flour. Nutshell flours are commercially available, e.g., from Composition Materials, East Fairfield, CT, and are readily made by known methods. Examples of grain flours for use in the present invention comprise buckwheat flour, high gluten wheat flour (bread flour) , corn flour or corn meal, and soy flour. These grain flours can be obtained at grocery stores and health food/organic food stores. Natural starches for use as fillers in the present invention comprise potato starch, corn starch, rice starch, soy starch and wheat starch. Examples of cellulose based materials which are useful as fillers in the present invention comprise wood flours and other ground organic matter, such as corn cob grit. Any type of wood flour is useful as filler in the present invention, e.g. flour made from hard or soft woods. The amount of filler materials for use in the present invention is selected based upon the qualities desired in the finished product. Preferably, the biodegradable compositions of the present invention contain a weight percent of filler to polymer of at least about 1%, but less than about 40%. More preferably, the compositions have about 10% to about 25 weight % filler. In the methods of the present invention, at least one biodegradable organic filler is compounded with at least one thermally processable biopolymer to achieve the desired results and processed by methods known in the art for processing thermoplastic compounds. In one preferred method, the filler is compounded with a thermally processable biopolymer in sequential extrusion and cooling.

Methods useful to provide filled biodegradable polymer materials having improved properties in accordance with the present invention include:

(a) feeding at least one thermally processable biodegradable polymer and at least one biodegradable organic filler material into an extruder; (b) heating the polymer (s) and filler(s) of step

(a) under appropriate conditions in an extruder to form a melt;

(c) exposing the melt of step (b) to a cooling means to form a solid product; and

(d) forming the solid product of step (c) into a useful size and shape, such as pellets, tubes, rods or films. The melting steps of the methods are accomplished through the use of conventional compounding and extrusions methods as described herein. To assist in the determination of appropriate extrusion conditions for a particular biopolymer composition, the biopolymer composition may be characterized using differential scanning calorimetry (DSC) and torque rheometry.

During the extrusion process, up to about 99% weight percent of at least one thermally processable biopolymer and up to about 40 weight percent of at least one biodegradable organic filler material is fed into an extruder where the mixture is heated to form a melt. Because the most expensive component (and one of the softer components) of the present invention is typically the biopolymer, it is preferable to keep the polymer content of the melt as low as possible while maintaining the objectives of the present invention.

Preferably, the biopolymer and the filler material are fed simultaneously in a metered fashion into the extruder, but those skilled in the art will recognize that the filler material may also be fed into the extruder downstream, after the biopolymer has melted. However, downstream addition may not be appropriate in cases where steam losses are important to the final product.

Conventional extruders are useful in practicing the present invention. Preferably, a single screw or twin screw extruder is used during the extrusion process. Additional conveying and low compression screw elements may be used to minimize shear and heat during the extrusion process to reduce biopolymer degradation and to provide more uniform extrudate. After the biopolymer and filler material have been heated to form a melt, the melt is carried through a die slot. Upon exiting the extruder, the melt is cooled and dried by a cooling means.

Optional components may be added to the melt of the present invention, provided there is no interference with formation or with the desired final properties of the ultimate biodegradable composition. Such components or additives may include but are not limited to anti-static agents, such as zirconates and titinates, coupling agents, hydrophobic wetting agents, silanes, dispersants, pigments and so forth, and are well-known to those of ordinary skill in the art of polymer processing. Preferably, any optional components will be wholly or partially biodegradable. Specific processing considerations are important when extruding the biopolymer to better control water content of the resulting extruded product, particularly with starch-based polymers. In many instances, it is desirable that some or all of the vents of the extruders used in the present invention be plugged during the extrusion to prevent loss of water as steam during processing. More preferably, a non-vented extruder is used in the present invention where control of water content is important. In some embodiments, water is added downstream of the vents. Another preferred method of controlling the water content of the resulting biodegradable composition is to use air cooling as the cooling means since the filled biopolymer, as a melt, can take up water from the liquid cooling means traditionally used during extrusion. Liquid nitrogen may also be used to avoid such water uptake. Particularly preferred for air cooling is a tube containing small air holes which direct streams of cool, dry air onto the extrudate. Another preferred embodiment employs a dry ice trough of solid CO₂ as the cooling means.

The cooled biodegradable composition is formed into a shape and size which is useful for shipping, storage and/or processing the polymer into the end product. The biodegradable composition can be formed into pellets, sheets, roads or tubes. In preferred embodiments, the solid is pelletized. Pelletizing can be accomplished by methods known in the art, for example, by using a Randcastle pelletizer. The pellets can then be further processed by methods known in the art of thermoplastic processing to produce the desired end product, such as injection molding, extrusion, compression molding and blow molding. The effect of filler on the desired properties can be determined by forming the pellets into shaped samples, e.g., by injection molding, and subjecting these samples of the biodegradable polymers to standard tests known in the art. For example, in compositions where the addition of filler material increases the mechanical strength of the resulting biodegradable polymer composition, standard tests include those for testing peak load, percent elongation and modulus. In a preferred embodiment of the present invention, the tensile strength of the NOVON™ starch based thermoplastic M1801 is increased by the addition of organic filler material. The amount of increase is variable depending upon the amount and type of a filler added. Preferably, the resulting biodegradable compositions of the present invention have a tensile strength which is from about 5 to about 150% greater than the neat biopolymer. More preferably, the resulting compositions have a tensile strength of from about 35% to about 150% greater than the pure biopolymer. The biodegradable compositions of the present invention preferably have an elongation rate which is similar to the elongation rate of the neat biopolymer. Preferably, the compositions of the present invention have an increase in Young's modulus of within about 5% to about 100%. More preferably, the compositions of the present invention have an about 5% to about 65% increase in Young's modulus.

With this combination of increased tensile strength and slight change of elongation at break, a higher strength biodegradable engineering thermoplastic is produced.

To illustrate the tailoring of properties of the biodegradable composition(s) in accordance with the present invention, various biodegradable compositions were prepared as taught herein. The ratios of filler and polymer in the total composition were adjusted to obtain biodegradable compositions having the desired properties as is shown in the following examples.

EXAMPLE I The properties of NOVON™ thermoplastic starch grade M1801 were tailored and tested in accordance with the teachings of the present invention. Walnut shell flour (Composition Materials, East Fairfield, CT) was compounded into the biopolymer. The compounding was performed using a Wayne 5/8 inch extruder with a throughput of 1-1/2 lb/hr. The extruded material was air cooled then pelletized using a Randcastle pelletizer.

Approximately 2 lb of compound were produced. The compounds are described in Table 1, along with the processing conditions used in compounding. Cycolac L ABS (GE Plastics) , and Lexan 141-111 polycarbonate (GE Plastics) were also extruded to use as controls.

The compounded material and the controls were formed into plaques using a Tetrahedron vacuum press. The temperature of the press was set to the processing temperature of the compound. A minimum vacuum of 15 in. of mercury was attained before the press cycle was initiated. The plaques were then machined into test specimens. All samples underwent tensile testing and sea water stability testing as described below.

Table 1. Processing conditions for biopolymer compounds

A) Mechanical Testing

Tensile testing was performed on bars compression molded from the biodegradable composition and having dimensions of 0.5 x 0.21 x 5 inch. The length tested was 2 inch. Five samples of each material were tested using a Universal mechanical testing apparatus. An extensometer was used to measure the elongation of the samples. Table 2 summarizes the data obtained in mechanical testing.

This page is intentionally left blank. Table 2. Tensile properties of biodegradable compounds

As can be seen in Table 2, the addition of filler (i.e., walnut flour) to the biodegradable thermoplastic starch raised the values of the peak load, elongation and modulus from the values for the neat biopolymer. The mechanical properties of the composition of biopolymer (NOVON™ thermoplastic starch grade M1801) and filler (walnut flour) are much greater than the pure biopolymer (NOVONTM thermoplastic starch grade M1801) . The mechanical properties of the controls (ABS and polycarbonate) are comparable to that of the biopolymer composition. Figures 1, 2, 3, and 4 show the impact of fillers on thermoplastic starch such as Novon™ grade M1801.

The Novon™ 1801 compounded well with walnut shell flour, and was easy to process. The resulting material had a higher peak load capacity and elongation than the neat thermoplastic starch, and was somewhat stiffer than the neat Novon™ thermoplastic starch grade M1801. Figures 2 and 3 indicate that an optimum walnut shell flour loading exists at which the strength and elongation are maximized.

B) Sea Water Susceptibility

Specimens of each compound, including the ABS and polycarbonate controls, were immersed in a 2.5 weight percent solution of sodium chloride in water at room temperature. The specimens were bars approximately 1.25 inches long, 0.6 inches wide, and 0.2 inches thick. The exact dimensions and weight of each specimen (three per material) were measured and recorded, and the specimens were immersed. Measurements of the weight and thickness were taken at 1, 3, 8, and 24 hours of immersion.

Articles manufactured from these biodegradable polymers must function properly during their required lifetime. For example, a sonobuoy must perform for up to 8 hours in sea water without failure. The biodegradable polymers of the present invention withstand the operating life of the sonobuoy in sea water without adversely affecting the performance of the sonobuoy. The data is summarized in Table 3. The effect of sea water immersion on the thickness of the specimens was minimal, with small detectable changes first being seen at 24 hours.

As was expected, the control materials were not affected by immersion in sea water.

Table 3. The effect of sea water immersion on biopolymer blends and compounds and the control materials

The addition of fillers to the biodegradable polymers changed the susceptibility of the biopolymers to sea water. Figures 5 and 6 show the effect of walnut shell flour on the sea water susceptibility of NOVONTM thermoplastic starch grade 1801. Figure 5 shows the percent weight gain of compounds as a function of composition at various times, and Figure 6 show the percent weight gain as a function of time for various compositions. These figures indicate that the sensitivity of NOVONTM thermoplastic starch grade 1801 to sea water can be drastically reduced by even low loadings of walnut shell flour, making this a cost- effective way to lengthen the aquatic lifetime of NOVON™ thermoplastic starch grade 1801 for other uses.

EXAMPLE II: A) Extrusion: The compounding of the materials was performed in a Berstoff 25 mm twin screw extruder. The screw configuration consisted of a feed zone, a metering/mixing zone, and a compression zone. The extruder has eight heating zones: three in the feed zone, three in the metering/mixing zone, and two in the compression zone. For the compounding, a break plate was used. Due to the particulate nature of the filler, a screen pack was not used.

Novon™ thermoplastic starch grade M1801 was fed into the extruder using a Novatec pellet feeder with a variable speed digital controller. The fillers were fed by a K-Tron (Pitman, NJ) powder feeder with a variable speed digital controller. The extruders were "starve fed", meaning that no material was allowed to build up in the throat of the extruder, in order to ensure that the filler loading was as desired.

The temperature profile used was based on the thermal characteristics of the thermoplastic starch. The following temperatures were used: 240-300°F in the feed zone, 240-300°F in the metering/mixing zone, and 260-340°F in the compression zone. A particularly preferred profile was 240°F Zone 1, 300°F Zone 2, 300°F Zone 3, 260°F Zone 4, 260°F Zone 5, 260°F Zone 6, 260°F Zone 6, 260°F Zone 7, and 337°F Zone 8. Under this temperature profile, the temperature experienced by the melt in the extruder barrel was between 330 and 340°F. The head pressure ranged between 500 and 800 psi. The extrudate passed through a basic two-strand rod die. Immediately upon exiting the extruder, the hot strands were passed through a C.W. Brabender two- roll film mill to compress the material. The strands were then cooled by traveling through chilled forced air troughs for a minimum of ten feet of travel. The cooled rods were then pelletized in a basic Berlyn (Worcester, MA) pelletizer.

B) Injection Molding:

The pellets of filled material were injection molded using standard equipment and methods. The injection molder has a 25-ton clamping force capability. The molding temperature was 350°F, but a range from about 350 to 390°F is acceptable. A medium injection pressure was used. The mold used was an ASTM D 638 dog bone tensile specimen mold. The mold temperature was 100°F, but a range from about 90 to 120°F is acceptable.

C) Tensile Testing:

The dog bone tensile specimens were tested in and Instron Model 5582 equipped with a Merlin Instron data collection system. The test was a standard static tensile properties test, performed with a crosshead speed of 0.20 inches/minute. A 50 kN load cell was used. The tested length on the sample was 5.25 inches for all specimens. The ambient temperature and humidity was monitored, and varied within the ranges of 70 to 73°F and 30 to 37 percent relative humidity. The results are summarized in Table 4.

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Table 4. Mechanical Properties of NOVON™ thermoplastic starch mixed with different fillers.

Table 4 and Figure 7, summarizing the tensile strengths, show that the addition of organic fillers into starch based thermoplastic polymers, e.g., NOVONTM thermoplastic starch grade M1801, enhances the tensile strength. Typical increases in tensile strength range from about 5% to about 110% over the neat thermoplastic starch used as the control material. These strength increases do not strongly affect the elongation of the material at break, as is shown in Figure 10. In most cases, the elongation at break is not statistically different from the neat, unfilled NOVON™ thermoplastic starch grade M1801 control. Preferred compositions of the present invention has a range of elongation which is statistically insignificant, e.g., for the data shown in Table 4, a decrease or increase of 13% in the percent elongation at break.

With the significant increase in strength, and the relatively insignificant effect on the elongation at break, the filled materials exhibit an increase in Young' s modulus as shown in Figure 9. The broadest range of increase is about 5% to about 100%. Preferably, the compositions of the present invention have a about 5% to about 65% increase in Young's modulus. With this combination of increased tensile strength and slight change of elongation at break, a higher strength biodegradable engineering thermoplastic is produced.

EXAMPLE III: A) Thermoplastic starch:

Potato starch granules are mixed in an unvented twin-screw extruder with water and glycerin under heat and pressure. This mixing causes gelatinization of the starch, i.e. the starch granules swell and break apart. The temperature of gelatinization is between 110 and 180°C The pressure is the natural pressure built up in the extruder by the superheated water. A plasticizing biodegradable polymer such as polycaprolactone is added downstream once gelatinization is achieved. The thermoplastic starch produced by this method is comprised of about 5 to about 25% water, about 1 to about 20% glycerin, about 5 to about 15% polycaprolactone, and about 40 to about 89% destructured potato starch. The thermoplastic starch is extruded and cooled.

B) Extrusion:

To improve the mechanical properties of the thermoplastic starch, it is compounded with a filler such as walnut shell flour in loading levels between about 1 and about 40%. The thermoplastic potato starch and the walnut shell flour are starve fed into a twin screw extruder and pass through a feeding zone, a mixing/metering zone, and a compression zone as described in Example II. The filled thermoplastic starch passes through a rod die, is cooled in chilled forced air tubes and is pelletized. The pellets are then formed into the end product via injection molding, compression molding, blow molding, or any other thermoplastic processing method. Samples are tested, e.g. as described in Example II C) above. The inventions has been described in detail with particular reference to the preferred embodiments thereof. However, it will be appreciated that modifications and improvements within the spirit and teachings of this inventions may be made by those in the art upon considering the present disclosure.

Claims

What is claimed is:

1. A biodegradable composition comprising at least one thermally processable biodegradable polymer and at least one organic filler.

2. The composition according to claim 1, wherein at least one of the biodegradable polymers is a starch based thermoplastic polymer.

3. The composition according to claim l, wherein at least one of the biodegradable polymers is a starch based thermoplastic polymer, wherein the starch comprises corn starch, wheat starch, rice starch or potato starch.

4. The composition according to claim l, wherein the organic filler comprises a nutshell flour.

5. The composition according to claim 4, wherein the nutshell flour is selected from walnut shell flour or pecan nut shell flour.

6. The composition according to claim l, wherein the organic filler comprises a grain flour.

7. The composition according to claim 6, wherein the grain flour comprises buckwheat flour, whole wheat flour, high gluten whole wheat flour, soy flour, corn flour or corn meal.

8. The composition according to claim 1, wherein the organic filler comprises a cellulose based particulate material.

9. The composition according to claim 9, wherein the cellulose based material comprises wood flour or corncob grit.

10. The composition according to claim 1, wherein the organic filler comprises natural starch.

11. The composition according to claim 10, wherein the natural starch comprises potato starch, corn starch, rice starch, wheat starch, and soy starch.

12. The composition according to claim 1, wherein the thermally processable biodegradable polymer comprises a copolymer of at least about 20% starch based thermoplastic polymer.

13. The composition according to claim 12, further comprising a polymer selected from polylactone, polyvinyl alcohol, polycaprolactone, polyhydroxybutyrate and polyhydroxyvalerate.

14. The composition according to claim 1, wherein the filler comprises from about l to about 40 weight percent of the composition.

15. The composition according to claim 1, wherein the filler comprises from about 10 to about 25 weight percent of the composition.

16. The composition according to claim 1, wherein the organic filler is present in such an amount to increase the tensile strength of the thermally processable biodegradable polymer.

17. The composition according to claim 1, wherein the organic filler is present in such an amount to decrease the water susceptibility of the thermally processable biodegradable polymer.

18. A method of altering a mechanical property of a thermally processable biodegradable polymer composition comprising adding from about 1 to about 40 weight percent of at least one organic filler.

19. The method according to claim 18, wherein the mechanical property is tensile strength.

20. The method according to claim 18, wherein the polymer is thermoplastic starch.

21. The method according to claim 18, wherein the organic filler is a nutshell flour.

22. The method according to claim 21, wherein the nutshell flour is walnut shell flour.

23. A method of producing a biodegradable composition have one or more predetermined properties and comprising at least one thermally processable biodegradable polymer and at least one organic filler wherein the method comprises

(a) feeding at least one thermally processable biodegradable polymer and at least one biodegradable organic filler material into an extruder;

(b) heating the polymer (s) and filler (s) of step (a) under appropriate conditions in an extruder to form a melt;

(c) exposing the melt of step (b) to a cooling means to form a solid product.

24. The method of claim 23, further comprising forming the solid product of step (c) into a useful size and shape, such as pellets, tubes, rods or films.

25. An article of manufacture comprising a biodegradable composition according to claim 1.