WO1997031979A1

WO1997031979A1 - Biodegradable polyester compositions with natural polymers and articles thereof

Info

Publication number: WO1997031979A1
Application number: PCT/US1997/003310
Authority: WO
Inventors: Julious L. Willett; William N. Doane; Wayne Xu
Original assignee: Biotechnology Research And Development Corporation; The United States Of America As Represented By The Secretary Of Agriculture
Priority date: 1996-02-28
Filing date: 1997-02-26
Publication date: 1997-09-04
Also published as: AU2064597A

Abstract

Compositions of the invention include a hydroxy-functional polyester and a natural polymer. Articles can be made from such a composition so as to have sufficiently strong tensile strengths as to form disposable utensils or to have sufficient elasticity so as to form thin wrap films. Because the inventive compositions include a significant amount of natural polymer like starch, the resulting articles are more biodegradable and thus more environmentally friendly than commodity plastics such as polyethylene or polystyrene. Particular preferred natural polymers are granular starches derived from any combination of grains, roots, and legumes.

Description

BIODEGRADABLE POLYESTER COMPOSITIONS WITH NATURAL POLYMERS AND ARTICLES THEREOF

Field of the Invention

The present invention generally relates to compositions useful for forming articles by means such as thermoplastic processing (e.g., molding, extrusion and casting), and more particularly relates to hydroxy- functional polyester containing compositions. Articles with good mechanical properties, such as tensile strength and/or tensile elongation, can be made with such polyesters in combination with natural polymers. Such articles are biodegradable and have a reduced cost of manufacture due to the inclusion of a low cost natural polymer, such as starch.

This invention was made with government support under Grant Agreement No. 59-3K95-3-126 awarded by the United States Department of Agriculture. The government has certain rights in this invention.

Background of the Invention Starches and modified starches have been the focus of considerable research interest in attempts to use these as fillers in order to decrease polymer costs and to use polymers that are biodegradable. As several recent examples, U.S. Patent 5,384,187, issued January 24, 1995, inventors Uemura et al., U.S. Patent 5,391,423, issued February 21, 1995, inventors Wnuk et al., and U.S. Patent 5,412,005, issued May 2, 1995, inventors Bastioli et al., all represent domestic and foreign based attempts to achieve biodegradable polymer compositions in which natural polymers such as starches have been added to synthetic polymers. Unfortunately, while the inclusion of starches can reduce costs, the mechanical properties of the synthetic polymer can be so adversely affected by inclusion of starch as to vitiate the cost advantages.

Among examples of physical strength loss when starch is blended with various synthetic polymers are those described in several recent articles. Thus, for example, Koenig and Huang, TMSE, 67 , pp. 290-291 (1992) used three different types of synthetic polymers in combination with starch and starch derivatives and reported their properties. When polycaprolactone ("PCL") was filled with 25 wt.% starch or a starch derivative the yield strength and the tensile strength were reduced by half.

Ramsay et al.. Applied and Environmental Microbiology, 59 , pp. 1242-1246 (1993) studied poly-β- hydroxyalkanoates with starch. The biodegradable polymer [P(HB-co-HV) ] was said to hold biodegradable promise, but the polymer is significantly higher in price than a commodity plastic such as polyethylene or polystyrene. The inclusion of 25 wt.% granular starch was reported to result in a composition with a tensile strength of about 60% the original (16 MPa by contrast to 27 MPa). The authors acknowledged that the use of unmodified granular starch as a particulate filler in the (P(HB-co-HV) ] polymer reduced the tensile strength and did not offer any appreciable reinforcement in the mechanical rigidity, presumably due to poor adhesion of the polymer granule interface. The authors concluded it would be necessary to develop formulations with improved adhesion.

Accordingly, attempts continue to find synthetic polymer based compositions that can be formed into articles, such as for example disposable plastic utensils or stretchable thin films for food packaging purposes, that are reasonably competitive in price with commodity plastics such as polyethylene or polystyrene, but which are more environmentally friendly.

Summary of the Invention

The present invention has several embodiments that solve the problems discussed above.

In one aspect of the present invention, a formed article comprises a continuous synthetic polymer phase and a discontinuous natural polymer phase. The synthetic polymer phase includes a hydroxy-functional polyester that is surprisingly compatible with the natural polymer phase. Articles of this embodiment can be formulated so as to have a tensile strength above about 20 MPa (sufficiently strong for example, so as to form disposable utensils) or to have a tensile elongation above about 200% (sufficient stretchability, for example, so as to form thin wrapping films). With one particularly preferred embodiment, a composition is provided with 45 wt.% starch granules (derived from corn) having an elongation of about 500%, while another is a composition composed of about 50 wt.% starch granules (derived from corn) which has a tensile strength of about 50 MPa.

The hydroxy-functional polyesters with which inventive compositions and articles may be formed by inclusion of natural polymer granules show a remarkable compatibility with natural polymers. This is illustrated by tests showing that inclusion of small amounts of granular starch into several hydroxy- functional polyesters actually increases the tensile strength of the hydroxy-functional polyester. Another example of the remarkable compatibility of the hydroxy- functional polyesters and granular starch is shown in instances where inclusion of plasticizer actually leads to moderately improved tensile strength although presence of plasticizer in other polymer compositions typically softens such compositions.

Compositions of the invention are useful for formed articles, particularly by thermoforming techniques such as molding, extrusion and casting, and preferably comprise a hydroxy-functional polyester, such as a poly(hydroxyester) or a poly(hydroxyester ether), admixed with starch or modified starch granules derived from a grain, a root, a legume, or mixtures thereof. By "modified" is meant that the starch can be derivatized or modified by typical processes known in the art (e.g. esterification, etherification, oxidation, acid hydrolysis, cross-linking and enzyme conversion). Thus, for example, a modified starch may be a starch ester, a starch ether, or a crosslinked starch. Conventional modifications of starch are described in publications such as Starch : Chemistry and Technology, 2d edition, editor Whistler et al., and Starch Derivatives : Production and Uses , Rutenberg et al.. Academic Press, Inc., 1984. The granules preferably have less than about

15 wt.% water and preferably have a particle size of less than about 50 μm.

In addition to the two essential components of hydroxy-functional polyester and natural polymer, compositions of the invention can optionally include various additional materials, such as for example plasticizers, processing aids, and filler materials, such as for example cellulose, vegetable fibers, calcium carbonate, talc, etc. Other advantages and aspects of the present invention will become apparent upon reading the specification and the appended claims.

Brief Description of the Drawings

Figure 1 is a scanning electron micrograph of one inventive embodiment at a magnification of 1000;

Figure 2 is another scanning electron microgram of another inventive embodiment, but again at a magnification of 1000, and was made following an elongation test; Figures 3A and 3B are electron micrographs of a composition at two different stages of mixing: Figure 3A is a micrograph of an inventive composition (designated 53) after it has been compounded once and thus only partially mixed; and Figure 3B is a micrograph of this inventive composition (now designated 53') after it has been compounded twice and is an example of a thoroughly mixed composition;

Figure 4 is an electron micrograph of an inventive composition designated 77"; and, Figure 5 is an electron micrograph of an inventive composition designated 78".

Detailed Description of the Preferred Embodiments

In one aspect of the present invention, compositions made from a mixture of synthetic and natural polymers are disclosed. Broadly, the inventive compositions comprise essentially two critical components: the first component is an hydroxy- functional polyester, and the second component is a natural polymer. Forming a continuous polymer matrix (sometimes also described as a continuous polymer phase), the hydroxy-functional polyester provides much of the structural framework of the resulting composition. In the inventive compositions, these granules are dispersed throughout the continuous polymer matrix formed by the hydroxy-functional polyester. These natural polymer granules remain discrete units within the polyester polymer matrix, and thus the natural polymer granules are sometimes referred to as being in a discontinuous phase.

The natural polymer is preferably in the form of granules derived from starch or a derivatized (modified) starch, but can also be granules of other natural polymers (e.g. guar gum, cellulose, and the like). Granules should have a particle size of less than about 100 μm, and preferably have a particle size of up to 50 μm and a water content of less than about 15 wt.%, more preferably less than about 10 or 11 wt.%. These two essential components are admixed in varying amounts. The natural polymer may be present in a trace amount or may comprise up to 75% of the resulting composition by weight. Preferred compositions contain between about 15% to about 75 % natural polymer by weight. Particularly preferred compositions contain between about 40% to about 75% natural polymer by weight. Generally, because of decreased costs and increased biodegradability associated with the inclusion of natural polymers, higher amounts of natural polymer are preferred. However, as one uses higher amounts of natural polymer, more energy is normally required to disperse adequately the granules throughout the continuous polymer matrix. In order to facilitate thorough dispersal, particularly when higher amounts of natural polymers are used, compositions of the present invention might be multiply compounded, or compounded using a more efficient processing apparatus (e.g. a twin screw extruder as is known to the art) . In addition, other strategies for more efficient mixing as known to the art may be used such as the addition of dispersal agents.

For example, multiple compoundings have been found effective in significantly improving properties of the resulting compositions by thoroughly dispersing the granules so as each substantially to be in contact with (surrounded by) the polymer matrix. With multiple compoundings, compositions have been made containing between about 45% and about 75% by weight of the natural polymer and having tensile strengths above about 20 MPa and generally above about 30 MPa. In one particularly preferred embodiment, a composition containing 50% starch by weight had a tensile strength of about 50 MPa.

To better illustrate the present invention, each of the components suitable for preparing compo- sitions of the invention will now be more fully described.

Suitable Hydroxy-Functional Polyesters

Useful hydroxy-functional polyesters for this invention may be prepared from base-catalyzed nucleo- philic addition of suitable acids to epoxies, which reaction generates both an ester linkage and a pendent hydroxyl group. Transesterification and cross linking reactions are eliminated through use of quaternary ammonium halide salts as initiators for the reaction of diacids with diglycidyl ethers, providing convenient preparation of high molecular weight, thermoplastic, hydroxy-functional polyesters in ether solvents at temperatures from 80°C-160°C. The preparation and structures for such hydroxy-functional polyesters suit- able in practicing this invention may be as described by U.S. Patent 5,171,820, inventors Mang and White, issued December 15, 1992, which is hereby incorporated in its entirety by reference. Data provided by the Dow Chemical Company (manufacturer of hydroxy-functional polyesters such as described by U.S. Patent 5,171,820) indicates the biodegradable nature of these polymers through the ability of various soil bacteria (such as Pseudomonas putida ) to use the synthetic polymers as a substrate for cell culture growth.

Representative structures for suitable hydroxy-functional polyesters in practicing this invention are preferably represented by Formula A (where n provides a sufficient molecular weight, such as for example a m.w. of about 50,000-100,000). Higher molecular weights are preferred due to higher strength.

FORMULA A

In Formula A each of R¹ and R² is individually a divalent organic moiety which is predominately hydrocarbon, each R³ is individually hydrogen or lower alkyl, y is a fraction from 0 to 0.5 and x is a fraction from about 0.05 to about 0.4. Typically Y is hydrogen or glycidyl and Y' is glycidyl arylene ether, glycidyl alkyene ester, glycidyl alkylene ether or glycidyl arylene ester.

Thus, suitable polyesters have repeating units represented by Formula B (where each of R¹, R², R³, x, and y are as defined above). FORMULA B

Particularly preferred such polyesters are prepared from diglycidyl esters of an aliphatic diacid such as adipic due to the ready availability and reasonable price for adipic acid as a source of reactant. Other particularly preferred polyesters may be prepared from dihydric phenols, such as hydroquinone.

Four particularly preferred hydroxy-functional polyesters, used extensively to illustrate (but not to limit) the present invention, are sometimes hereinafter designated "BIS CHD," "BIS Adipic," "HQ DDCA" and "BIS DDCA." Repeating unit structures for these four illustrative hydroxy-functional polyesters are illustrated by Formulas C-F and several of their properties of interest for the invention are summarized in Table A.

FORMULA C

FORMULA D

FORMULA E

FORMULA F

O

JT jo α -

OH O

In the Formulas C-F, "n" preferably is as earlier described.

With reference to the data of Table A, one sees that two of the hydroxy-functional polyesters used to illustrate this invention have a quite high percentage elongation property (HQ DDCA and BIS DDCA). When one wished to formulate an embodiment of the invention that had high percent elongation, one of these could be chosen, or one could include plasticizer to increase the elongation property. Similarly, if one wished to formulate an inventive embodiment with outstanding tensile strength, a hydroxy-functional polyester such as BIS CHD could be chosen; however, due to the remarkable compatibility of natural polymers with the hydroxy-functional polyesters, even a polyester with a relatively modest tensile strength, such as BIS adipic, can be formulated to have substantially improved tensile strength. This will be demonstrated hereinafter by Table 3 of Example 4.

Natural Polymers

Among the natural polymers suitable and preferred for practicing this invention is starch. Starch is a low-cost and abundant natural polymer composed of amylose and amylopectin. Amylose is essentially a linear polymer having a molecular weight in the range of 100,000-500,000, whereas amylopectin is a highly branched polymer having a molecular weight of up to several million. Unmodified, natural starches are obtained in granular form and may be derived from cereals or grains (such as corn, wheat, rice and sorghum), roots (such as cassava), legumes (such as peas). Such starch granules typically have a particle size less than about 50 μm, which is the preferred particle size. While less preferred, flours whose contents are predominately starch, and which may also contain protein, oil and fiber, are operative in the invention. Where such other natural polymers are used, they should be processed so as to be in granular form and preferably will have a relatively uniform particle size of about 50 μm or less. Starch granules for use in this invention will normally have a water content of less than about 15 wt.%, more preferably less than about 10-11 wt.%. As will be exemplified, granules may be pre-dried to less than about 1% moisture before compounding. Although preferred, pre-drying is not believed necessary.

Derivatized (modified) starches are also suitable for use in this invention. By "derivatized starches" is meant to include starches which have been chemically treated so as to form starch esters, starch ethers, and crosslinked starches. By "modified" is meant that the starch can be derivatized or modified by typical processes known in the art (e.g. esterification, etherification, oxidation, acid hydrolysis, cross- linking and enzyme conversion). Typically, modified starches include esters, such as the acetate ester of dicarboxylic acids/anhydrides. Particularly useful are the alkenyl-succinic acids, and hydrides, ethers (such as the hydroxyethyl and hydroxypropyl starches), starches oxidized with hypochlorite, starches reacted with cross-linking agents such as phosphorus oxychloride, epichlorhydrin, hydrophobic cationic epoxides, and phosphate derivatives prepared by reaction with sodium or potassium orthophosphate or tripolyphosphate and combinations thereof. These and other conventional modifications of starch are described in publications such as Starch : Chemistry and Technology, 2d edition, editor Whistler et al., and Starch Derivatives : Production and Uses , Rutenberg et al.. Academic Press, Inc., 1984. For example, starch esters may be prepared using a wide variety of anhydrides, organic acids, acid chlorides, or other esterification reagents. Examples of anhydrides are acetic, propionic, butyric, and so forth. Further, the degree of esterification can vary as desired, such as from one to three per glucosidic unit of the starch, or as appropriate given the number of hydroxyl groups in the monomeric unit of the natural polymer, if selected to be other than starch. Similar or different esterified natural polymers, with varying degrees of esterification, can be blended together for practicing the invention. Although esterified starches are stable to attack by amylases, in the environment the esterified starches are attached by microorganisms secreting esterases which hydrolyze the ester linkage.

Starch esters tend to be hydrophobic in contrast to starch raw materials (that is, derived by usual techniques from natural sources such as corn) .

Thus, depending upon the particular application, one may prefer to choose an hydrophobic starch ester rather than a hydrophilic starch in formulating compositions of the invention.

Starches are preferred for use as the natural polymers, particularly due to ready availability and low cost, but other suitable natural polymers (in or prepared to be in granular form of a suitable particle size) are hydroxyl containing polymers such as cellulose, hemicellulose, chitin, guar gum, locust bean gum, pectin, xanthan, algin, agar, and dextran. Some of these can play the role of filler, also. Excellent results have been obtained with both granulated guar gum and cellulose powder, as will be exemplified hereinafter. Optional Components

Processing aids such as plasticizers can be added to inventive compositions to achieve greater material processability and product flexibility, although plasticizers typically soften the compositions in which they are included. This is not always true, however, of compositions of the invention, as will be discussed hereinafter. Molded articles and films prepared from blends including plasticizers preferably use plasticizers that are biodegradable. Examples of biodegradable plasticizers include various esters, such as phthalate esters, and various other biodegradable esters known in the chemical arts.

Inorganic and organic fillers can be added, such as talc, calcium carbonate, diatomaceous earth, and so forth. Biodegradable organic fillers, such as cellulose and other fibers and the like are well known.

Compositions of the invention, as earlier noted, can be processed by various methods such as extrusion, injection molding, and film forming methods. For example, extrusion casting can give translucent, flexible films.

EXPERIMENTAL

Aspects of the invention will now be illustrated, without intending any limitation, by the following examples.

EXAMPLE 1

Inventive embodiments were prepared from premixed batches of starch or derivatized starch and polyester and optionally containing plasticizer or other additives. The starches were pre-dried to less than 1% moisture before compounding. Compounding was then accomplished on a Brabender PL2000 torque rheometer using a mixing screw with a fluted dispersive mixing section and a notched distributive section. Strands from the die were air cooled and pelletized.

The compounded pellets were then injection molded into tensile bars (ASTM D638 Type V) either with a Cincinnati Millicron Model ACT-75B or a Rabit Hy-4 ram-type machine with a single cavity mold. For some compositions tensile bars were compression molded in a Carver Press or were stamped from compression molded blanks formed in a Carver Press. Tensile bars were conditioned at 50% RH and 23°C for one day before testing in order to provide equivalent conditions in comparing one run to another. Selected compositions were also tested after immersion in water for one day. Tensile tests were performed on an Instron Model 4201 testing system.

As illustrated by the Tables 1-5 and Table 6 data, inventive compositions may be made as formed articles. Compositions of the invention are suitable for thermoplastic processing, such as molding, extrusion and casting, in applications where solid articles are desired as well as where thin, stretchable films are desired. Normally, processability places an upper limit on the starch content (e.g. about 70 wt.% or 80 wt.%).

EXAMPLE 2

Embodiments of the invention were prepared as described by Example 1. Four were selected or having a tensile strength above about 20 MPa, as is set out by the data of Table 1. The natural polymer used for all four compositions was corn derived starch granules.

The inventive composition 1 is remarkable in its tensile strength property when one considers that the tensile strength of 100% BIS CHD polymer is 60-61 MPa. This means the inventive composition with 15 wt.% starch has a tensile strength that is increased with respect to the polyester itself. This is another illustration of the remarkable compatibility between natural polymers, such as the granular starch component, and the hydroxy-functional polyester for compositions of the invention.

Returning to the data of Table 1, although inventive compositions 3 and 4 had only about Vb the tensile strength in comparison to a composition with all polyester, nevertheless even the highly starch filled composition had a tensile strength adequate for forming a number of useful articles, such as for example disposable utensils.

EXAMPLE 3

Further embodiments of the invention were prepared as described by Example 1. Nine were selected for having a tensile strength at about 20 MPa or greater. These are set out by the data of Table 2. The granules used as natural polymers for the Table 2 compositions were corn derived starch.

TABLE 2

^a The hydroxy-functional polyester was BIS CHD. Compositions 11-14 included ESTAFLEX plasticizer (acetyltributylcitrate), compositions 15-16 included PARAPLEX plasticizer (epoxidized soybean oil), compositions 7-9 included either PEG 3350 or PEGC 20M plasticizer (polyethylene glycols).

The data of Table 2 illustrate the uses of various optional components, such as different plasticizers, in compositions of the invention. A comparison of inventive composition 3 from Table 1 with inventive composition 15 of Table 2 illustrates that the use of particular plasticizers can even moderately improve tensile strengths. This is another example of the remarkable compatibility of the two essential components of the invention because plasticizer is normally used to improve processing, but normally softens the composition. Inventive compositions 16 and 7-9 of Table 2 and inventive compositions 3 and 4 of Table 1 have tensile strength values in the range of about 18-23 MPa. That is, these inventive compositions have better tensile strength than the biodegradable compositions reported by Ramsey, supra , but by contrast to the Ramsey compositions the inventive compositions included between about 45-60 wt.% starch granules (whereas the Ramsey compositions included only about 25 wt.% granular starch) .

EXAMPLE 4

Yet more embodiments of the invention were prepared as described by Example 1, and four were selected for having a tensile strength above about 20 MPa, the data for which are set out by Table 3.

TABLE 3

The data of Table 3 illustrate inventive compositions with yet another hydroxy-functional polyester. While inventive composition 28 (with 15 wt.% starch) has good tensile strength, it is considerably less than that found with inventive composition 1 where the hydroxy-functional ester was BIS CHD. However, with increased amounts of starch granules (in the range of 30 wt.% to 45 wt.% starch) the tensile strength improved. Fig. 1 illustrates inventive composition 31. As illustrated, the discontinuous starch granules are well adhered in the continuous polyester phase. By contrast, non-inventive compositions of starch and with various polyesters were found readily to fall apart and when viewed with analogously magnified micrographs to have visible holes where the non-adhered starch granules had fallen out.

EXAMPLE 5

Further embodiments prepared with a particularly preferred hydroxy-functional polyester, BIS DDCA, were prepared and selected for the property of elongation.

TABLE 4

Inventive compositions 23-25 gave outstanding elongation properties. For comparison, for example, the elongation to break (percent) for 100% high density polyethylene is 759. Thus, inventive compositions 23-25 compare quite favorably in elongation to 100% high density polyethylene, yet include up to 45 wt.% in starch granules. EXAMPLE 6

The data of Table 5 illustrate use of yet another hydroxy-functional polyester for compositions of the invention, where the two inventive compositions have excellent elongation properties.

TABLE 5

Fig. 2 illustrates inventive composition 19.

One again sees the remarkable adherency of the granules in the hydroxy-functional polyester. This Fig. 2 micrograph was made after the elongation test had been performed.

EXAMPLE 7

Unlike the preparations of Example 1, embodiments of the invention were prepared where the starch granules were not pre-dried. Instead, starch granules (containing about 10-11 wt.% water) were prepared in a manner analogous to that reported in Example 1 but with no pre-drying step. From reviewing tests performed with these embodiments, we conclude that the pre-drying step, while preferred, does not appear necessary. Alternatively, if desired to remove some moisture from the granules, such could be done during an extrusion step rather than as a separate, pre-drying step. EXAMPLE 8

The previously described examples 1-6 were compositions that were formed into tensile bars. We turned to using compositions in another form. Thus, thin films having less than about 0.1 mm thickness were prepared with a torque rheometer fitted with a one inch blown film die. The films obtained were conditioned at 23°C and 50% relative humidity before testing. The data from Table 6 illustrate properties of two different inventive compositions so formed into films.

44 30 70 17.4

^a The hydroxy-functional polyester was BIS Adipic. ^b Plasticizer was a modified polyethylene glycol.

EXAMPLE 9

Compositions were prepared with other starches or derivatized starches. Thus, diepoxide corn (a reaction product of bisphenol A diglycidyl ether (10%) and corn starch), hydroxyethyl corn, and corn flour were each formulated with BIS Adipic polyesters in amounts of about 40%-50% flour or derivatized starch. However, the Table 3 compositions (using BIS adipic) have to date been found to be preferred to all the flours and derivatized starches tested.

EXAMPLE 10

Another set of tensile bar formed compositions were prepared, but instead of starch, flour or derivatized starch, the natural polymers used were either guar gum or cellulose. Both were in granule form with particle sizes well below 100 μm. The method of preparation for the compositions was the same as described in Example 1. Table 7 summarizes the results.

TABLE 7

Inventive Composition Tensile Strength fMPai

30 wt.% guar gum and 70 wt.% Bis Adipic 33

30 wt.% cellulose powder and 70 wt.% Bis Adipic 37

EXAMPLE 11

Multiple compoundings have been found useful in dispersing compositions with large amounts of natural polymer. In order to readily differentiate these multiply compounded compositions from once compounded compositions, the numbers of the multiply compounded compositions are followed by a prime (i.e. inventive composition 46 ' ) . With the exception of performing the compounding step multiple times, the compositions are prepared using the steps previously outlined in Example 1. The starches were pre-dried to less than 1% moisture and then compounded with a Brabender PL2000 torque rheometer using a mixing screw with a fluted dispersive mixing section and a notched distributive section. Strands from the die were air cooled and pelletized. The compounded pellets were passed a second time through the Brabender PL2000 torque rheometer and the extruded strands were again air cooled and pelletized.

At this point, if it were desirable to perform the compounding step again, the pellets would then be passed through the Brabender PL2000. The resulting strands would then be air cooled and pelletized. This may be repeated until the compounding step no longer substantially improves the properties (such as tensile strength or tensile elongation) of the resulting compositions.

All the embodiments described in Tables 8-10 (except inventive composition 52) have been compounded twice. Strength data for the twice compounded compositions are shown in Table 8. Starch derived from corn was used as the natural polymer and the ESTAFLEX (acetyltributyl-citrate) was used as the plasticizer.

TABLE 8

^■ The starch was derived from corn ^b ESTAFLEX (acetyltributylcitrate) was used as the plasticizer.

Figs. 3A and 3B dramatically illustrate the difference in electron micrographs when the composition is thoroughly mixed. Fig. 3A is a scanning electron micrograph of inventive composition 53 after a single compounding step. Because this composition was processed in essentially the same way as previous inventive compositions 1-44, not surprising, Fig. 3A is similar to the micrographs illustrated by Figs. 1 and 2. It has been discovered that if the scanning electron micrograph displays granules that are substantially uncovered by the continuous polymer matrix like those shown by Figs. 1-3A, then the resulting composition is only partially mixed.

Fig. 3B is a scanning electron micrograph of composition 53 after the mixture has been compounded twice. In this micrograph, discrete granules are not readily visible. Although the granules remain discrete units within the admixture, the composition is so thoroughly mixed that the granules are each substantially surrounded by the continuous polymer matrix. Without being bound by theory, it is believed that the resulting strength of the composition increases as the granules become better mixed within the continuous polymer matrix. As a result, using electron micrographs or other means known to the art for monitoring (or to have made empirical, prior determinations of preferred processing factors), compositions are preferably mixed until each granule is substantially surrounded by the continuous polymer matrix. Table 9 illustrates twice compounded embodiments with starch from various sources.

EXAMPLE 12

Embodiments of the invention were essentially prepared as described by Example 11. However, in this example, the moisture content of the starch was adjusted to various levels before the first compounding. The starch was derived from corn. Results are shown in Table 10.

TABLE 10

EXAMPLE 13

Premixed batches of cornstarch (pre-dried to less than 1% moisture) and BIS Adipic polyester and optionally calcium carbonate were compounded once as described in Example 1. Extruded strands were pelletized and the pellets were injection molded in a Cincinnati Millicron ACT 75B injection molder fitted with a three-cavity mold with cavities for a spoon, knife and fork. Flexural tests were performed on the knife on an Instron Model 4201 testing system. The results are shown in Table 11.

Although compounded only once, these compositions were subjected to a second "mixing" step by being processed through an injection molder. As the strength data in Table 11 demonstrates, it is the thoroughness of mixing, and not necessarily a particular process for mixing, that improves the strength characteristics of the inventive compositions. EXAMPLE 14

An alternative to multiple compoundings is to use a more efficient processing apparatus. In this example, starch and polyester resin and optionally calcium carbonate and plasticizer were compounded once using Werner Pfleiderer ZSK 30 mm co-rotating twin screw extruder having 14 barrel zones. Polyester resin was fed into the first barrel section and starch premixed with other optional ingredients was fed into the ninth barrel section. The last barrel section was equipped with a die head assembly which was fitted with two 3 mm rod dies. Extruded strands were chopped into pellets which were compression molded into tensile bars using a Carver press. After conditioning the bars for 24 hours at 50% relative humidity and at 23°C, they were tested on an Instron Model 4201 testing system. Results are shown in Table 12. In order to distinguish these well mixed compositions from the multiply compounded ones, the composition numbers are followed by a double prime (e.g. inventive composition 77").

Figs. 4 and 5 are scanning electron micrographs of inventive compositions 77" and 78". Despite having been compounded only once, because a more efficient processing apparatus was used, the resulting compositions are still thoroughly mixed.

EXAMPLE 15

Pellets of inventive compositions 77" and 78" were processed on a Brabender PL2000 torque rheometer fitted with a 4 inch adjustable ribbon die which was adjusted to an opening of 0.015 inches. The resulting extruded ribbons of the inventive compositions were air cooled and cut into lengths of about 12 inches. Two sections of each inventive composition, each measuring about 3-4 inches by 12 inches were thermoformed into trays measuring about 5 inches by 9 inches. For a tray this size, two sections which overlapped at the center of the mold were required. The thermoforming process was at 50°C and 75°C for inventive compositions 77" and 78" respectively. Thermoformed trays from each inventive composition were functional and sturdy.

It is to be understood that while the invention has been described above in conjunction with preferred specific embodiments, the description and examples are intended to illustrate and not limit the scope of the invention, which is defined by the scope of the appended claims.

Claims

It is Claimed:

1. A composition, useful for formed articles, comprising:

a hydroxy-functional polyester; and,

granules of a natural polymer admixed with the polyester.

2. The composition as in claim 1 wherein the natural polymer granules are starch, a modified starch, cellulose, or guar gum.

3. The composition as in claim 1 wherein the natural polymer granules are derived from a modified starch, the modified starch being a starch ester, a starch ether, or a crosslinked starch.

4. The composition as in claim 2 wherein the granules have less than about 15% water by weight.

5. The composition as in claim 3 wherein the granules have a particle size of less than about 50 μm, the natural polymer granules when from a starch or modified starch being from a grain, a root, a legume, or mixtures thereof.

6. The composition as in claim 1 wherein the polyester is a poly(hydroxy ester) or a poly(hydroxy ester ether).

7. The composition as in claim 2 wherein the natural polymer constitutes between about 15% and about 75% of the composition by weight.

8. The composition as in claim 2 wherein the natural polymer constitutes between about 40% and 75% of the composition by weight.

9. The composition as in claim 1 further including one or more of a processing and a plasticizer and a filler.

10. The composition as in claim 2 wherein the hydroxy-functional polyester has repeating units represented by Formula B:

wherein each of R¹ and R² is individually a divalent organic moiety which is predominately hydrocarbon, each R³ is individually hydrogen or lower alkyl, y is a fraction from 0 to 0.5 and x is a fraction from about 0.05 to about 0.4.

11. The composition as in claim 10 wherein the natural polymer constitutes between about 15% and about 75% of the composition by weight and granules have a water content of less than about 11% by weight.

12. The composition as in claim 10 wherein the natural polymer constitutes between about 40% to about 75% of the composition by weight and granules have a water content of less than about 11% by weight.

13. The composition as in claim 1 wherein the natural polymer is a corn starch and the corn starch constitutes between about 15% to about 75% of the composition by weight.

14. The composition as in claim 1 wherein the natural polymer is a corn starch and the corn starch constitutes between about 40% to about 75% of the composition by weight.

15. The composition as in claim 1 or 4 wherein the natural polymer granules are substantially evenly dispersed throughout a matrix formed by the polyester.

16. The composition as in claim 13 or 14 wherein the polyester is BIS CHD, whose repeating structure is shown by Formula C and where "n" is sufficient to provide a desired molecular weight:

17. The composition as in claim 13 or 14 wherein the polyester is BIS adipic, whose repeating structure is shown by Formula D and where "n" is sufficient to provide a desired molecular weight:

18. The composition as in claim 13 or 14 wherein the polyester is HQ DDCA, whose repeating structure is shown by Formulas E and where "n" is sufficient to provide a desired molecular weight:

19. The composition as in claim 13 or 14 wherein the polyester is BIS DDCA, whose repeating structure is shown by Formula F and where "n" is sufficient to provide a desired molecular weight

20. A formed article comprising:

a continuous synthetic polymer matrix formed by a hydroxy-functional polyester and

discrete natural polymer granules, wherein the granules are substantially evenly dispersed throughout the synthetic polymer matrix.

21. The formed article as in claim 20 wherein the article has a tensile strength above about 20 MPa or a tensile elongation above about 200 percent and the granules are starch derived from a grain, a root, a legume, or mixtures thereof.

22. The formed article as in claim 21 wherein the natural polymer granules are substantially surrounded by the continuous synthetic polymer matrix.

23. The formed article as in claim 20 wherein the hydroxy-functional polyester has repeating units represented by Formula B:

24. The formed article as in claim 23 wherein the natural polymer granules constitute between about 15% to about 75% of the article by weight.

25. The formed article as in claim 23 wherein the natural polymer granules constitute between about 40% to about 75% of the article by weight.

26. A method for making a composition useful for forming articles, comprising:

preparing a mixture comprising granules of a natural polymer and a hydroxy-functional polyester; and dispersing the granules throughout the polyester.

27. The method as in claim 26 wherein the natural polymer is starch or a modified starch being from a grain, a root, a legume, or mixtures thereof.

28. The method as in 26 wherein the hydroxy- functional polyester is BIS CHD, BIS Adipic, HQ DDCA, or BIS DDCA.

29. The method as in claim 27 or 28 wherein the natural polymer constitutes between about 15% and about 75% of the mixture by weight.

30. The method as in claim 27 or 28 wherein the natural polymer constitutes between about 40% to about 75% of the mixture by weight.