MXPA98009702A - Biodegradable compositions of polyester and natural polymer and expanded items of the mis - Google Patents

Abstract

Expanded items that have a compressible, resilient body that includes two biodegradable components. The component is preferably starch or a modified starch. Another component is a synthetic polymer insoluble in water, preferably a polyester with hydroxy functional groups. The article can be thermoformed, it has some exterior surfaces with substantial resistance to the humed

Description

BIODEGRADABLE POLYESTER AND NATURAL POLYMER COMPOSITIONS AND EXPANDED ARTICLES THEREOF Field of the invention The present invention relates generally to expanded articles, and in particular, refers to biodegradable blends of polyester with hydroxy functional groups and natural polymers that can be expanded as low density, compressible, resilient articles, which are resistant against moisture, and are useful for applications such as packaging or packaging.This invention is made with governmental support under the Concession Agreement No. 59-3K95-3-l6 granted by the North American Department of the Agricultural Research Service. The American Government has certain rights in this invention.

Background of the Invention U.S. Patent No. 4,863,655, to the inventors Lacourse et al., Issued September 5, 1989, describes the problems of REF .: -28865 disposal associated with most of the packaging or packaging materials currently used, formed from synthetic polymers. For example, although expanded polystyrene is a packed, protective, resilient, compressible, low-density filling material approximately 0.25 pounds / ft3) and performs its protective function well (eg, as oblique "peanuts"), it does not It is biodegradable. Thus, U.S. Patent No. 4,863,655 also discloses a biodegradable packaging material as an alternative to expanded polystyrene comprising an expanded amylose-starch product. Although it is biodegradable, the special component of high amylose content used is highly expensive. Also, another difficulty with the solution described by US Pat. No. 4,863,655, is that the expanded amylose-expanded starch material is not, by itself, suitable for preparing containers where moisture resistance is a necessary property (eg. several fast food containers, to go). The behavior of starch during extrusion and injection molding has been the focus of considerable studies. The state of starch in These various physical changes have been described under names such as molten starch, molecularly dispersed or divided starch, destroyed starch, and so on. A historical review of the transformation of starch when extruded is described by Shogren et al, "Development of Starch-Based Plastics - A Reexamination of Selected Polymer Systems in Historical Perspective," Sarchy / S tarke, 45, pp. 722-948. 276-280 (1993). U.S. Patent No. 5,095,054, from the inventors Lay et al., Issued March 10, 1992, discloses mixtures of destructurized starch and one or more polymers. Although these mixtures and articles made thereof are said to exhibit improved dimensional stability in moist air when compared to unstructured, non-mixed starch, however, the articles are said to retain a high degree of disintegration in contact with liquid water. . Although this disintegration can assist in the disposal of such articles in landfills and the like, the high degree of disintegration in contact with liquid water is disadvantageous for many applications where substantial moisture is present.

U.S. Patent No. 5,272,181, by the inventors Boehmer et al., Issued December 21, 1993, discusses starch graft copolymers as another alternative to packaging or packaging material, materials that are also said to disintegrate easily. or wet conditions. Although this disintegration can assist in the disintegration of materials on earth, the materials described are not entirely biodegradable due to the presence of synthetic resins (such as polyacrylates). Furthermore, as already mentioned, this property of wettability is disadvantageous for applications where moisture will be present. U.S. Patent No. 5, 185,382, "from the inventors Neuman et al., Issued on February 9, 1993, describe biodegradable packaging or packages formed from starch and a polyalkylene glycol or derivative thereof A preferred polyalkylene glycol is polyethylene glycol, however, the use of these Water-soluble component means that the expanded products have little resistance to moisture.In addition, the apparent bulk density property of many of the formulations tends to be rather high.

Accordingly, attempts are still made to find expanded compositions that are biodegradable, reasonably competitive in price with convenience plastics such as polyethylene or polystyrene, but are more environmentally friendly and have adequate moisture resistance properties.

BRIEF DESCRIPTION OF THE INVENTION In one aspect of the present invention, a composition comprises a synthetic polymer and a natural polymer. The synthetic polymer includes a polyester with hydroxy functional groups, biodegradable, insoluble in water. The natural polymer is preferably starch or a modified starch in gelatinized form. -This composition is usefully subjected to a process of expansion, whereby an expansion agent (eg, water) and a nucleating agent that causes bubbles to form, or cells, which results in articles -expanded, desired . The composition in this manner is usually required as a "precursor" composition. In this way, the compositions of the precursor of this invention are mixtures of two essential components: polyester with hydroxy functional groups and natural polymer, such as starch, preferably in the form of gelatinized starch. Polyesters with hydroxy functional groups with which precursor, inventive, and expanded articles can be formed show marked compatibility with natural polymers, such as starch and modified starch, and the expanded articles thereof are resistant to Water. For example, inventive foamed articles have not shown substantial disintegration when immersed in water at ambient conditions for at least about 30 minutes. One embodiment of the invention is where the composition of the precursor is a molten mixture which, in the presence of an expanding agent and a nucleating agent, can be extruded as a matrix of substantially closed, low density, compressible cells, resilient From this compressible, resilient matrix can be the final, desired, desired article (eg, packaging "peanuts" or can be further processed to form desired articles, particularly by a thermoforming technique such as molding. The molded articles have exterior surfaces with sufficient moisture resistance to be suitable as packaging materials or packaging with a liquid component, such as hot fast food (which emits moisture). In this way, another aspect of the invention is an article comprising a compressible and resilient body. The body includes two biodegradable components. The first component is preferably starch or a modified starch. The second component is a synthetic polymer, insoluble in water, preferably a polyester with hydroxy functional groups, such as a pol i (hydroxyester) or a poly (hydroxyester ether). The body has an outer surface where the synthetic polymer predominates and transmits resistance to water. The interior has the starch component that predominates. Representative chemical structures for suitable polyesters with hydroxy functional groups in the practice of this invention are preferably represented by Formula A (where n provides a sufficient molecular weight, such as, for example, a p.m. of approximately 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 that is predominantly hydrocarbon, each R3 is individually hydrogen or lower alkyl, and 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 alkylester ester, glycidyl alkylene ether or glycidyl aryl ester. Suitable polyesters have repeat units represented by Formula B (where each of R1, R2, R3, x, and y are as defined above).

FORMULA B As described above, the body has the synthetic polymer that predominates on an outer surface, while the starch component dominates the interior. This article is particularly useful as a packaging or packaging material where moisture resistance is desirable. The preferred starch component is derived from a gelatinized starch or modified, gelatinized starch. By "modified" it 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 enzymatic 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, 2nd edition, editor histler and collaborators, and Starch Dervatives: Production and Uses, Rutenberg et al., Academic Press, Inc. 1984. The precursor composition, of a preferred embodiment, has 10% by weight of a polyester containing hydroxy, 89% by weight of gelatinized starch and water (approximately 17% by weight of the total composition is water), and 1% by weight of the nucleating agent, which is expanded in twin screw extruder, to scale pilot. This results in expanded articles with an apparent bulk density of approximately 0.64 pounds / feet3 (2.5 x 10 ~ 2 g / cm3), a resilience of approximately 64% and a compressibility of approximately 0.10 MPa. These expanded articles were tested for moisture resistance. Even after being immersed in water at room temperature and stirred with a magnetic stir bar, at 200 rpm for 30 minutes, the water remained clear, indicating that no substantial disintegration of the articles had occurred.

Other advantages and aspects of the present invention will become apparent in reading the specification and appended claims.

Brief Description of the Drawings Figure 1 is an exploratory electron micrograph of an inventive mode at an increase of 250.

Detailed Description of the Preferred Modalities In a broad manner, the compositions of the precursor of the present invention include two essential components: the first component is a biodegradable, water-soluble, synthetic polymer, preferably a polyester with hydroxy functional groups; and, the second component is a natural polymer, preferably a modified starch or starch in gelatinized form. These two essential components may be present in varying amounts, although the natural polymer in the total precursor composition, and in the resulting expanded articles, after extrusion will be present as much as 50% of the total, preferably more than about 70% by weight of the total, and preferably up to about 97% of the total. The synthetic polymer will be present in minor amounts, such as from a few percent by weight to about 30% by weight of the total. Particularly preferred ranges of the synthetic polymer in the foamed articles will be about 5-10% by weight. Each of the components suitable for preparing the compositions of the invention will now be described more fully.

Suitable Polyesters with Functional Hydroxy Groups Synthetic, water-insoluble, biodegradable, useful polymers for use in the inventive compositions and expanded articles include polyesters with hydroxy-functional groups, which can be prepared from acid-catalyzed nucleophilic addition of suitable acids to epoxies. This reaction generates both an ester bond and a pending hydroxyl group. Transesterification and cross-linking reactions are eliminated through the use of halide salts of quaternary ammonium as initiators for the reaction of diacids with diglycidyl ethers, which provides the convenient preparation of polyesters with hydroxy, thermoplastic, high molecular weight functional groups, in ether solvents at temperatures from 80 ° C-160 ° C. The preparation and structures for polyesters with hydroxy functional groups suitable in the practice of this invention can be as those described in US Patent No. 5,171,820, of the inventors Mang and White, issued December 15, 199, which is incorporated by reference in its entirety. incorporated in this way in its entirety by reference. The data provided by the Dow Chemical Company (manufacturer of polyesters with hydroxy functional groups such as described by US Pat. No. 5,171,820) indicates the biodegradable nature of these polymers through the ability of several soil bacteria (such as Pseudomonas putida) to use synthetic polymers as a substrate for cell culture development. Representative structures for polyesters with suitable hydroxy functional groups, in the practice of this invention are preferably represented by Formula A (where n provides a sufficient molecular weight, such as, for example, a p.m. 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 that is predominantly hydrocarbon, each R3 is individually hydrogen or lower alkyl, and 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-irylene-ether, glycidyl-alkylene-ester, glycidyl-alkylene-ether or glycidyl-arylene-ester. In this manner, suitable polyesters have repeating units represented by Formula B (where each of R 1, R 2, R 3, x and y are as defined above).

FORMULA B Particularly preferred these polyesters are prepared from diglycidyl esters of such an aliphatic acid. as adipic acid due to the easy availability and reasonable price of adipic acid as a source of reagent. Other particularly preferred polyesters can be prepared from dihydric phenols, such as hydroquinone. Four polyesters with hydroxy functional groups, particularly preferred, used extensively to illustrate (but not to limit) the present invention, are sometimes referred to subsequently as "BIS CHD", "Adipic BIS", "HQ DDCA" and "BIS DDCA". The structures with repeating units for these four hydroxy functional polyesters, illustrated, 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 In Formulas C-F, "n" preferably is as described above.

TABLE A Polyester components with hydroxy-Tg functional groups (° C) BIS CHD 66 BIS Adipic "45 HQ DDCA 10 BIS DDCA 20 Natural Polymers Among the suitable and preferred natural polymers for practicing this invention is starch. Starch is a low cost and abundant natural polymer composed of amylose and amylopectm. Amylose is essentially a linear polymer having a molecular weight in the range of 100,000-500,000, while amylopectin is a highly branched polymer having a molecular weight of up to several million.

Natural, unmodified starches are obtained in granular form and can be derived from cereals or grains (such as starch, wheat, rice, and sip), roots (such as cassava), legumes (such as peas) and tubers such as potato and sugar cane. While they are less preferred, flours whose contents are predominantly starch, and which may also contain protein, oil and fiber are operative in the invention. When the starch is said to be "gelatinized" it has melted and loses its crystalline state. The starch molecules have taken a disordered, random-configuration, the starch chains have become entangled. In this way, when the gelatinized starch is mixed with the synthetic polymer under extrusion conditions, so that the entire mixture melts, the first two melts (natural polymer and synthetic polymer) will be expected to disperse homogeneously throughout the length of the body of the extruded product in the respective proportions of each component; however, this does not "occur for the practice of the invention, In contrast, the synthetic polymer has been found to be divided so as to predominate along the outer surfaces of the extruded body and remains as a predominant component throughout the exterior surfaces of the processed, additional items - (for example, thermoformed). This is a desirable property because the synthetic polymer is insoluble to water and thus imparts water resistance to the articles ultimately formed from the inventive precursor compositions. Derivatized (modified) starches are also suitable for the use of this invention. By "derivatized starches" is meant that they include starches that have been chemically treated to form starch esters, starch ethers, and articulated starches. By "modified" it 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, the modified starches include esters, such as acetate ester and dicarboxylic acids / anhydrides. Particularly useful are alkenyl succinic acids, and anhydrides, ethers (such as hydroxyethyl and hydroxypropyl starches), starches oxidized with hypochlorite, starches made with crosslinking agents such as phosphorus oxychloride, epichlorohydrin, hydrophobic cationic epoxides, and phosphate derivatives prepared by the reaction with sodium orthophosphate or potassium and tripolyphosphate and combination thereof. These and other conventional modifications and combinations of starch are described in publications such as Siarch: Chemistry and Technology, 2nd edition, editor Whistler et al., And Starch Derivatives: Prodution and Uses, Rutenberg et al., Academic Press, Inc. 1984. For example , the starch esters can be prepared using a variety of anhydrides, organic acids, acid chlorides, and other esterification reagents. Examples of anhydrides are acetic, propionic, butyric, and so on. In addition, the degree of esterification can vary as desired, such as from one to three per glucidic unit of the starch, or as appropriate given the number of hydroxyl groups in the monomer unit of the natural polymer, if it is selected to be another starch. The natural polymers esterified, similar, or different, with varying degrees of esterification, can be mixed together to practice the invention. Although the esterified starches are stable to the attack of the amylases, in the environment the esterified starches are attacked by microorganisms that secrete esterases that hydrolyze the ester bond.

The starch esters tend to be hydrophobic in contrast to the starch raw materials (ie, derived by usual techniques from natural sources such as corn). Thus, depending on the particular application, a hydrophobic starch ester may be preferred and chosen in place of a hydrophilic ester in the formulation of compositions of the invention. Starches are preferred for use as natural polymers, particularly because of easy availability and low cost.

Other components The extruded products of the inventive precursor compositions have substantially closed cell substructures, with good resilience and compressibility. The expansion, or foaming, of the precursor compositions in the molten form is achieved. The precursor compositions of the invention will typically be processed with a suitable apparatus, such as an individual screw extruder, or a twin screw extruder as is well known in the field of food science. The food extruders can be consider as short-time, high-temperature reactors, in which the granular starch having a unit content of about 10-25% is first compressed into a dense compact solid, and then converted into a soft, melted mass, by mechanical cutting forces, heat and high pressure, found during the procedure. The extruded products of starch that tend to expand at the exit of the extruder nozzle. As noted above, - Shogren et al., Supra, describes the extrusion of starch and cites a number of reviews regarding the food process. Twin screw extruders tend to be more expensive, but allow the addition of water as a people of expansion during the procedure. These means that the precursor composition fed into a twin screw extruder need not have the starch in the gelatinized form, since the gelatinization of the starch can occur during the extrusion process itself as the water is added. In this way, water can serve as both a gelatinization agent for the natural polymer as well as the blowing agent for the composition of the precursor.When an individual screw extruder is used, then usually the composition of the precursor will already have gelatinized the starch. A precursor composition in which the starch component is to be gelatinized will typically have water present in a range of about 25% by weight to 30% by weight with respect to the total composition. Of course, water is the liquid in which the starch is gelatinized, and its role in gelatinization can be seen as a plasticizer. While water is preferred, other gelatinization agents, or plasticizers, for example, such as urea or glycerol can be used. When water is also used as an expanding agent, then it is normally present in a precursor composition in a range. from about 15% by weight to 20% by weight, most preferably about 17-18% by weight of the total composition of the precursor. Expansion agents other than water are known, however, in the art. For example, U.S. Patent No. 5,252,271, of the inventor Jeffs, issued October 12, 1993, discloses compositions for forming expansive products that include mild acid and a carbonate source so that the derived carbon dioxide serves as an expanding agent. Nitrogen or other appropriate agents for expansion can also be used. In addition to the inclusion of an expanding agent, the precursor compositions of the invention may include several different components known in the art. For example, among the components known for the compositions to be expanded are the nucleating agents, which can improve the uniformity of the cells formed during the expansion and which have the smallest cells. Suitable nucleating agents are well known in the art, include, for example, plastic, silicon dioxide, soft silicates, spray-dried silica, calcium carbonate, and the like. Another optional, suitable material is a plasticizer (in addition to the gelatinization agent as already discussed). A plasticizer may be added to the inventive compositions to achieve greater material processability and product flexibility, although plastifiants typically soften the compositions in which it is included. However, this is not always true, of the compositions of the invention. When incorporated in the composition of the invention, the plasticizers are preferably biodegradable. Examples of biodegradable plasticizers include various esters, such as phthalate esters, and various other biodegradable esters known in the art. the chemical technique EXPERIMENTAL PART Now aspects of the invention will be illustrated, without any limitation being proposed, with the following examples. Three important indications for the expanded products useful in. Packing applications in packaging are apparent bulk density, resilience, and compressibility. The volumetric density values should be in the order of less than about 2 pounds / ft3 (less than about 0.032 g / cm :). The method used to determine the apparent bulk density in the following experiments was the volume replacement method described by Hwang et al., Journal of Food Science, 45, p. 140D-1707 (1980). Resilience refers to the ability of a material to recover its original shape after it has been deformed by a force. The expanded products preferably have a resilience of at least about 50%, most preferably 60%. Resilience was determined in the following described methods using a Stevens LFRA texture analyzer employing a cylindrical probe (TA-6, 0.25 inches in diameter) running at a probe speed of 0.5 mm / sec. and a probe distance of 0.3 mm. Compressibility describes the force required to deform a material. The desired compressibility for extruded products is in a range from about 50 to 1000 g / cm2 (0.05 MPa to 1 MPa). Compressibility in the following experiments was determined using the apparatus and conditions as described already in the resilience measurement. These three properties, particularly the apparent bulk density, are influenced not only by the precursor compositions fed in an extrusion apparatus, but also by the size of the extrusion apparatus. The pressures that can be adjusted during extrusion processes can be significantly larger in twin screw extruders, commercial size. In this way, in larger extruders can usually be practiced at low temperatures and achieve lower volumetric density. Most of the examples that follow were prepared in a twin screw extruder, laboratory type, or a single screw extruder. While the properties of apparent bulk density, resilience, and compressibility due to the expressions for the invention were accepted, when the precursor compositions of the invention were processed. invention in a larger machine (Wenger PX 52 twin screw extruder), dramatic decreases in apparent bulk density values are seen. Thus, as is known to those skilled in the art, the process is preferred with a twin screw extruder or single screw, commercial size, since bulk densities can be optimized.

EXAMPLE 1 The precursor compositions of the invention were prepared in two steps. The first step was where the starch granules, polyester agglomerates containing hydroxy, and a small amount of talc (as a nucleating agent) were mixed, with water. This mixture was stirred, heated and the starch was gelatinized ("combined"). This combination was performed on a Brabender PL 2000 force torque rheometer using a mixing screw. The water content was 18-21% by weight before the combination. The temperatures during the combination ranged from about 90 ° C to about 135 ° C. The compositions of the resulting precursor in which the inhibitor was present in gelatinized form were in the initial form of strands, which were then cooled with air and pelleted. The agglomerates were adjusted to 17% by weight of moisture and then processed in the second expansion step. This second step was an individual screw expansion in which the temperatures used in different barrels were in the range of 70 ° C to about 210 ° C. (By example, the inventive composition 6_ was expanded to 150 rpm with a nozzle temperature of 15.0 ° C and barrels 1, 2, and 3, which are, respectively, at 70 ° C, 20 ° C, and 200 ° C). The use, like the present one, of an individual screw extruder tends to leave a high volumetric density - especially for the extruded product. Also, the lower capacity of the apparatus generally requires higher temperatures in order to avoid pressure build-up during extrusion. However, as shown by the data summarized in Table 1, generally acceptable properties were obtained for the extruded, inventive, processed products as well.

TABLE 1 Density Volume Composition Inventive Compressibility (pound / foot- ') Resilience (%) (MPa) (94% by weight of corn starch 1.35 5% by weight of 55.2 0.1562 Bis-adipic 1% by weight of talc) 2 ss (89% by weight of corn starch 1.15 10% by weight of 57.7 0.1403 BIS-adipic 1% in talc pee) (94% by weight of corn starch 1.70 58.6 5% by weight of 0.1684 BIS CHD 1% by weight of talc) (89% by weight of corn starch 1.85 10% by weight of 55.4 0.1531 BIS DDCA 1% by weight of talc EXAMPLE 2 The same formulation summarized in Table 1 as "2 ss" (indicating "single screw" processing) was again prepared as described in the first step of Example 1, but the strands (newly sedimented or agglomerated and adjusted to approximately 17 % moisture) then it is. processed in a Wenger TX-52 twin screw extruder. The extruder is a pilot scale machine, and although it is not as large as the preferred commercial size extruders, however, it provides a dramatically decreased bulk density (and modestly improved resilience and compressibility) for products expanded by the same formulation, such as it is shown by the data in Table 2. The extrusion conditions were 285"rpm, a nozzle temperature of 102 ° C, and temperatures in barrels 1, 2, and 3, respectively, of 76 ° C, 140 ° C, and 135 ° C.

TABLE 2 Density Volumetric Composition Compressive Resilience (pound / pJ) (%) lity (MPa) 2 ts (89% by weight of corn starch 0.64 63.9 0.1085 % by weight Bis-adipic 1 i by weight of talc) EXAMPLE 3 Three inventive formulations were processed in a twin screw extruder in a manner analogous to those runs supported in Table 2 of Example 2, but the extruder used was smaller (a twin screw extruder Werner £ Pfleíderer ZSK 30) operated at temperatures in zones 1, 2, and 3 of barrel of 49 ° C, 93 ° C, and 140 ° C. The data is summarized in Table 3.

TABLE 3 Density Volumetric Composition Resilience Inventive Compressibility [pound / pT (MPa) 12 (91.75% by weight of corn starch 0.9 63 0.2011 7. 5% by weight of Bis-adipic 0.75% by weight of talc) 13 (94.25% by weight of corn starch 1.19 63.3 0.1895 5 <by weight of BIS-adipic 0.75% by weight of talc) 14 (97 5% by weight corn starch weight 1.77 62.7 0.3029 2 by weight of BIS-adipic 0.5% by weight of talc) The comparison of the apparent bulk density values summarized in Table 1 (where the volumetric density decreased with less resin) to the volumetric density values summarized in Table 3 (where the bulk density was increased with less resin) indicate that the type and The size of the machine that is used for the procedure and the process conditions (particularly pressures, temperature and moisture content) are important factors that influence the apparent bulk density. In this way, the optimizations of these factors and of the resin content will normally be after empirical determinations from the particular process machine that is used.

EXAMPLE 4 Two inventive precursor compositions were formulated, and then extruded in a manner analogous to that described in Example 3, but the starches were derived from wheat and potato, respectively.

TABLE 4 Composition Density Resilience Inventive Compressibility Volumetric (%). (MPa) (lJbra / pJ) ~ 15 (94.5% by weight of wheat starch 1.35 60.1 0.2635 by weight of Bis-adipic 0.5% by weight of talc). 16 (94.5% by weight of potato 5 - by weight of 1.40 60.2 0.3214 BIS-adipic 0.5% by weight of talc) EXAMPLE 5 The formulations of corn starch (85-95%), Bis-adipic polyester (5-15%) and talc (0.5-1%) were prepared and the humidity adjusted to approximately 17%. These compositions were processed in a Wenger TX-52 twin screw extruder equipped with a 0.3 mm x 6 mm aperture nozzle. The extruded products of the various compositions were expanded tapes of approximately 25-30 mm and 10-12 mm thick. The sections of the tapes of approximately 25 cm in length were placed through a mold cavity configured for produce a suitcase with a width of 130 mm, a length of 215 mm, a depth of 20 mm and a thickness of approximately 3 mm. The tapes extended beyond the width and length of the mold cavity. The mold was heated to 100 ° C and the mold closed for approximately 10 seconds. At the opening of the mold, the foam tapes became compressed and became rigid and assumed the shape of the mold cavity. - The rigidity of the thermoformed tapes increased with the increase of the polyester content. This example illustrates the practice of the invention for producing thermoformed articles.

EXAMPLE 6 The articles prepared from the extrusion of the precursor compositions of the invention were tested to determine the wettability (or moisture resistance) these inventive articles were compared to three commercially available packaging materials (in the form of "peanut"). "). A first comparative material was "Eco-Foam" by National starch and -Chemicals (mani comparative 1). A second comparative product was "Clean-Green" of Clean Green (peanut comparative 2) a third comparative product was "Enpak" of DuPont (peanut comparative 3). The inventive peanut was prepared as described by Example 2. Each of the three comparative peanuts and the inventive peanut were placed in a 200 ml flask of water at room temperature and then stirred with a magnetic stir bar 200 rpm. The comparative peanut 1 started to disintegrate after 1 minute. The comparative peanut 2 started to disintegrate after 2 minutes 20 seconds. The comparative peanut 3 began to disintegrate after 2 minutes. Nevertheless, the inventive peanut showed no sign of disintegration after 30 minutes and the water in which it dispersed remained transparent. In this way, the inventive peanut was resistant to gua. As illustrated by Figure 1, a "peanut" of the invention is illustrated in a S.E.M. to an increase of 250. Most of the cells in the matrix are closed. The sizes of the cells have a diameter from about 100 μm to about 150 μm.

The foamed articles, or bodies, of the invention have a thin layer of synthetic polymer, which predominates on the outer surface, which gives the water resistance to them. articles. This outer layer is observable. at a macroscopic level since it gives a rather fixed surface to the former terjLor. It is to be understood that while the invention has been described above in conjunction with specific, preferred embodiments, the description and examples are intended to illustrate and not to limit the scope of the invention, which is defined by the scope of the appended claims. .

It is noted that in relation to this date, the best method known by the applicant to carry out the present invention, is the conventional one for the manufacture of the objects to which it refers.

Having described the invention as above, the content of the following is claimed as property:

Claims (5)

1. CLAIMS. 1. A composition, useful in the formation of biodegradable articles, resistant to moisture, characterized in that it comprises: a mixture, the mixture having as the main component a gelatinized starch or a modified, gelatinized starch, having as a minor component, a polyester "with hydroxy functional groups, wherein the polyester with hydroxy-functional groups has repeating units represented by Formula B: wherein each of R1 and R2 is individually a divalent organic portion which is predominantly hydrocarbon, each R3 is individually hydrogen or lower alkyl, and is a fraction from 0 to 0.5, and x is "a fraction from about 0.05 to about 0.4.
2. 2. The composition according to claim 1, characterized in that the mixture is melted.
3. 3. The composition according to claim 1, characterized in that the modified starch is a starch ester, a starch ether, or a cross-linked starch.
4. 4. The composition according to claim 1, characterized in that it also includes an extrusion agent.
5. 5. The composition according to claim 1, characterized in that the polyester is BIS CHD, and the repeat structure is shown by Formula C, and where "n" is sufficient to provide a desired molecular weight: 6. The composition according to claim 1, characterized in that the polyester is BIS-a.dico, whose repeating structure is shown by Formula D and where "n" is sufficient to provide the desired molecular weight: 7. The composition according to claim 1, characterized in that the polyester is HQ DDCA, whose repeat structure is shown by Formula E and where "n" is sufficient to provide a desired molecular weight: 8. The composition according to claim 1, characterized in that the polyester is BIS DDCA, whose repeating structure will be shown by Formula F and where "n" is sufficient to provide a desired molecular weight: 9. The composition according to claim 4, characterized in that the extruding agent includes water. 10. The composition according to claim 4, characterized in that it includes a nucleating agent. 11. The composition of. according to claim 10, characterized in that the polyester with hydroxy functional groups is in an amount of less than about 30% by weight of the mixture. 12. The composition according to claim 10, characterized in that the polyester with hydroxy functional groups is in an amount from about 2% by weight to less than about 30% by weight. 13. An expanded article, characterized in that it comprises: a resilient, compressible body, a body including two biodegradable bodies, the first component being starch or a modified starch, the second component being a synthetic polymer insoluble in water, the body having an outer surface and a lower cellular structure, the synthetic polymer that predominates on the outer surface, the starch component that predominates in the inner cellular structure, and wherein the synthetic synthetic polymer is a polyester with hydroxy functional groups having the units of repetition represented by the Formula B: wherein each of R1 and R2 is individually a divalent organic portion that is predominantly hydrocarbon, each R3 is individually hydrogen or lower alkyl, and is a fraction from 0 to 0.5, and x is a fraction from about 0.05 to about 0.4. 14. The expanded article according to claim 13, characterized in that the modified starch is an ester of starch, a starch ether, or a crosslinked starch. 16. The expanded article according to claim 13, characterized in that the body is substantially resistant to dissolution in water at room temperature for at least about 30 minutes. 17. The expanded article according to claim 16, characterized in that the functional polyester is an average amount with respect to the body from about 2% by weight to less than about 30% by weight.