Title of Invention

A METHOD FOR PREPARING HETEROPHASIC COMPOSITIONS

Abstract

ABSTRACT A method for preparing Heterophasic compositions (IN/PCT/2001/00078/CHE) The present invention relates to a method for preparing heterophasic compositions comprising starch, a thermoplastic polymer which is incompatible with starch and which is capable of forming complexes with starch, and a plasticizer, in which the starch constitutes the dispersed phase and the thermoplastic polymer the continuous phase, said compositions being characterized in that they have impact-traction energy greater than 30 KJ/m2 (measured on blown film having a thickness of 30 urn at lO'C and RH less than 5% and using a double-edge notched specimen), and in that the X-ray diffraction-spectrum of the compositions presents a peak at an angle 2 9 in the range of 13-14° with intensity in relation to that of the peak of amorphous starch, which appears at about an angle 2 0 of 20.5°, less than 2 and greater than 0.02, the method comprising the step of extruding a melt comprising starch, the thermoplastic incompatible polymer, a plasticizer liquid at room temperature used in amount from 2 to 8% on the weight of the starch and the thermoplastic polymer and water in amount less than 5 % measured at the exit of the extruder before conditioning.

Full Text

The present invention relates to method for preparing heterophasic polymeric compositions having a high resistance to ageing, even under conditions of low temperature and humidity, comprising thermoplastic starch and a thermoplastic polymer incompatible with starch, in which the starch constitutes the dispersed phase and the polymer the continuous phase. The invention relates particularly to manufactured products which maintain high impact strength and tear strength in low humidity conditions. It is known that products (in particular films) manufactured from compositions containing thermoplastic starch and a thermoplastic polymer incompatible with starch, in which the starch constitutes the dispersed phase, show a significant deterioration in their mechanical properties, in particular, their impact strength and tear strength, due to the fact that the starch gives up or absorbs water until it reaches equilibrium with the ambient humidity at its interface. In relatively low humidity conditions, the material tends to become brittle, as the dispersed phase becomes insufficiently plasticised due to the loss of water which takes the glass transition temperature above ambient temperature. This phenomenon can damage the interface with the matrix when the interface is not sufficiently bonded. Under these conditions, when the starch particles constituting the dispersed phase are subjected to stress, they are unable to deform and absorb the stress, but instead remain rigid, thus initiating a tear. Italian patent application No. TO96AOOO890 filed by the Applicant describes compositions comprising thermoplastic starch and a thermoplastic polymer incompatible with the starch, having improved characteristics of resj-stance to ageing under conditions of relatively low Jiumidity, obtained by iiitEo^u^mg_^n_a5e^^Jxaving an interfacing action during the mixing of the components. This compatibility-inducing action improves the adhesion between the matrix and the dispersed particles. Reducing the interface tension also enables the dimensions^ of the particles to be ^reduced to submicronic values, whereby the materials have the characteristics of a polymeric alloy. Compositions comprising^taxch^j^a^tjiermoplastj.^poj^er and a plasticiser are widely described in patent literature. However, the concentrations of these plasticisers at which the ^mechanical properties of jthe compositions. ..__are._gre_a£gst are never taught, nor suggested, in the prior art. EP-A-0 327 505 describes compositions in which the plasticiser is used in a quantity of from 0.5 to 15%, preferably between 0.5 and 5% by weight, together with such quantities of water that the sum of the plasticiser and the water does not exceed 25% by weight of jthe compositions (the quantitative minimum of water in these compositions is 10% by weight). WO92/19680" describes compositions comprising starch, a polyester of a hydroxyacid or the corresponding lactone such as, for example, polycaprolactone, and a plasticiser usable in a quantity of from 1 to 50% by weight, preferably 1-40%, and more preferably 5-25% by weight of the composition. The compositions preferably have a final water content of between 1.5 and 5% by weight (measured on leaving the extrusion press, before conditioning) . In the aforementioned document, there is no use of nor any indication of the existence of a possible critical range of the concentration of the plasticiser corresponding to that for obtaining very high mechanical properties, nor is there any indication of which plasticisers are suitable for this purpose. The quantity of plasticiser used in the examples is always greater than 10% by weight of the composition. US-5 334 634 describes compositions comprising starch, an ethylene-vinyl alcohol^ cqpolymer _and_"_a plasticiser usable in a quantity of from 0.5 to 100% by weight of the starch . In this case also, the quantity of plasticiser effectively used is always greater than 10% by weight of the composition. It is known that starch, in particular, its amylose fraction, fojcms.. n-V"-type complexes with synthetic polymers such as polyethylene vinyl alcohol or polyethylene-acid acrylate (C.Bastioli and others in "Biodegradable Plastics and Polymers", pages 200-213/ 1994, Elsevier Science). In such multiphase systems in which the synthetic polymer comprises the continuous phase and the starch the dispersed phase, the complex acts as a compatibility-inducer or phasing agent. Similar complexes can form between starch and aliphatic polyesters or aliphatic/aromatic copolyesters. However, if, in the preparation of the compositions 'comprising starch and the aforementioned polyesters, relatively high quantities of the starch plasticisers are used to ensure the plasticity of the material under the conditions of use of the manufactured product and low specific energy for destructurization and complexation is used, the quality of the interface is insufficient to ensure the toughness of the material at low temperatures and humidity in the presence of the plasticiser itself. Furthermore, if Plagt Reisers which are solid at room temperature are used in relatively high concentrations, at which the complex between __starch and incompatible polymer can form in a quantity, sufficient to ensure an effective compatibility-inducing action,, these plasticisers cause, in conditions changing from high to low relative humidity, brittleness in the material. It has unexpectedly been found that it is possible to prepare heterophasic compositions comprising starch and a thermoplastic polymer incompatible with starch, in which the starch constitutes the dispersed phase and the thermoplastic polymer the continuous matrix, which compositions have characteristics of high impact "strength even when passing from conditions of high to low relative humidity if they are prepared using a quantity of plasticiser that iS(liquicT^at room, temperature comprised within a critical range wherein -the concentration of the complex between starch and the incompatible polymer reaches a maximum, and a specific energy of destructurization of starch higher than a certain value. The critical quantity of plasticiser, which is preferably glycerin, is generally from_2^ to 8% and preferably from JL_to_ 7% by weight of the starch and the thermoplastic polymer. Quantities outside this range are, however, possible, depending on the type of plasticiser and its efficacy. The specific energy for the destructurization o.£ the starch and its complexation are comprised from 0,1 to 0.5 Kw.h/Kg, preferably from 0£15 to 0jJ_ Kw..h/_Kg and most preferably from _0_,2 to 0,35 Kw.h/Kg. For specific energy for the destructurization and complexation of the starch it is to meant the energy supplied by an extruder the screw or screws of which are capable of developing .a specific energy of at least 0,1 Kw.h/Kg at the extrusion temperature of 120 - 210 °c. The specific energy is determined according to the formula: A xBxC/DxExF wherein A = engine power B= RPM C= energy absorption D= RPM max E28 energy absorption max F== flow rate Until now, critical values as indicated above had never been used nor suggested in prior art compositions. It has been discovered, and this constitutes a characterising aspect of the invention, that the complex of starch and ip.compatible polymer reaches maximum concentration values within the aforesaid critical range. The presence of the complexes of starch ..and incompatible polymer can be demonstrated by the presence in the second derivative FTIR spectra of a band at a wavelength of 947 cm-1 (specific to the complex) and in the X-ray diffraction spectra of a peak in the range of 13-14° on the 2 theta scale (with Cu Kaifa radiation of 1.5418 A°). In both cases, the position of the J^and or the peak of the complex remains unchanged, , even on changing the nature of the complexed polymer. Figures 1 and 2 show the X-ray and second derivative FTIR spectra, and are typical of the formulations based' on starch and aliphatic polyesters (PCL in particular) . It , has been found that in the X-ray spectra of the compositions of the invention, the Hc/Ha ratio between the height of the peak (He) in the range of 13 - 14° of the complex and the height of the peak (Ha) of the amorphous starch which appears at about 20.5° (the profile of the peak in the amorphous phase having been reconstructed) is less than 2 and greater than 0.02. In the spectrum of Figure 1, the heights He and Ha, are indicated for the peaks of the complex and the amorphous starch respectively. In case of crystalline polymers with a crystallinity content higher than 30% the lower limit of the ratio Hc/Ha is 0.2; in case of amorphous polymers or polymers with a cristallinity content less than 30% the lower limit of the ratio Hc/Ha is lower than 0.2. The heterophasic compositions of the invention therefore comprise starch, a thermoplastic polymer incompatible with the starch, a starch plasticiser or a mixture of starch plasticisers, in which the starch constitutes the discontinuous phase, and the thermoplastic polymer the continuous phase., and are characterised in that they form films having characteristics of high impact strength higher than, 30 Kj/m2, preferably higher than 45 Kj/m2 and most preferably higher than 60 Kj/m2 (measured on blown film 30 micron thick at 10°C and less than 5% relative humidity) and have an X-ray spectrum having a peak at angle 2 theta in the range from 13 to 14° with an intensity related to that of the peak of the amorphous starch which appears at an angle 2 theta of 20.5° less than 2 and greater than 0.02. The compositions are obtainable by extrusion of a melt comprising starch, the thermoplastic polymer, the plasticiser in a quantity within the critical range, and water ina quantity^ less than 5% by__wejjght (measured on leaving the extrusion press, before conditioning) and supplying a s^ecific...^nergy of at least 0,1 Kw.h/Kg and lower than 0,5 Kw.n/Kg. The preparation of the compositions by extrusion is carried out according to known temperature conditions, operating, for example, at temperatures of between 120 and 210°C, preferably from 13_0_ to.. 190 ,°C. Suitable usable extruders are those provided with screws having a "reverse" profile for more than 30% of the length of the screw (a reverse profile causes the material to advance with a piston effect). The water content in the extrusion stage can be high in the phase of destructurization of starch and can be regulated at the end of the estrusion at the desired values of less__than 5% by weight by degassing or by using a starting starch with a low water content (the water content is measured at the exit of the extruder, prior conditioning). If the compositions or the manufactured products obtainable therefrom are washed with water, the plasticiser contained therein is extracted but the compositions and the manufactured product maintain mechanical properties, in particular impact strength, comparable.. to the properties of the film before washing. These compositions and manufactured products also form part of the invention. The starch-incompatible thermoplastic polymers are preferably chosen from the aliphatic (co)polyesters obtained from hydroxyacids haying_ 2 __or more carbon^ atoms, and from the corresponding lactones or lactides, or from aliphatic bicarboxylic acids having 2-22 carbon atoms, and from diols having 2-22 carbon atoms, polyester-amides, polyester-urea and aliphatic-aromatic copolyesters and mixtures thereof. These thermoplastic polymers, or mixtures thereof, have a meJLting point 'lower than 130°C and preferably lower than Representative examples of the polymers mentioned above are: - poly-epsylon-caprolactone, polyethylene- and polybutylene-succinate, polyhydroxybutyrate-hydroxyvalerate, polylactic acid, polyalkyleneadipate, polyalkyleneadipate-succinate, polyalkyleneadipate-caprolactame, polyalkyleneadipate-epsylon -caprolactone, polyadipate of diphenol diglycidylether, poly-epsylon-caprolactone/epsylon-caprolactame, polybutylene adi-pate-co-terephthalate, polyalkylenesebacate, polyalkylene-azelate and copolymers thereof or mixtures thereof. These polymers can also be "chain-extended" with diisocyanates, polyepoxides and similar multifunctional compositions. Poly-epsylon-caprolactone and the aliphatic-^aromatic copolyesters are preferred^. Other polymers which can be used are the esters and ethers of cellulose and of starch. The st arch-incompatible polymer is present in a quantity sufficient to form the continuous phase of the heterophasic composition. In general, this quantity is between approximately 30 and 90%_by weight of the starch. The -. polymers can be used in mixtures having smaller proportions of polymers of the ethylene/vinyl alcohol, ejthylene/acrylic acid type and polyvinylalchol. The usable starch is native starch such as, for example, com, potato, rice, tapioca starch, or is a physically or chemically modified starch such as, for example, ethoxylated starch, starch acetate and hydroxypropylated starch, cross-linked starch or oxidated starch, dextrinized starch, dextrins and mixtures thereof. The starch plasticisers which can be used are polyhydric alcohols having from 2__to 22 carbon atoms, in particular, polyhydric alcohols having from 1 to 20 hydroxylated units containing from 2 to 6 carbon atoms, the ethers, thioethers and the organic and inorganic esters of these polyhydric alcohols. Examples of plasticisers that can be used are: glycejcijie^ ethoxylated. pclyglycerol, ethylene glycol, polyethylene glycol/ 1,2-propandiol, 1,3-propandiol, 1, 4-butandiol, neopentylglycol, sorbitol monoacetate, sorbitol diacetate, sorbitol monoethoxylate, sorbitol diethoxylate and mixtures thereof. The compositions can also include interfacia^L agents of the kind described in Italian patent application T096A000890, chosen from: a) esters of polyhydric alcohols with mono- or polycarboxylic acid having a dissociation constant pK less than 4.5 (with reference to the pK of the first carboxylic group in the case of the polycarboxylic acids), and a hydrophilic/lipophilic index (HLB) greater than 8; b) esters of polyhydric alcohols with mono- or polycarboxylic acid having fewer than 12 carbon atoms, pK values greater than 4.5, and HLB indexes of from 5.5 to 8; c) esters of polyhydric alcohols with C12-C22 fatty acids, having an HLB. index of less than 5.5; d) non-ionic, water soluble surfactants, and e) products of the reaction between aliphatic or aromatic diisocyanates and polymers containing terminal groups that react with the diisocyanates. The compositions of the invention can also contain additives such as urea in a quantity of up to 2JD% Joy_ weight, compounds of boron, particularly „boric acid, proteins such as casein, gluten and^abietinic acid or rosinic acid, natural rubbers, flame retardant agents, antioxidants, fungicides, herbicides, fertilisers, opacifiers, compositions having a repellent effect on rodents, waxes, antislipping agents (such as erucamide, calcium stearate, zinc stearate) . They can also contain organic and inorganic fillers from 0.5 to 70% by weight and natural fibers. The compositions of the invention find particular application in the preparation of films, sheets,^ in thermoforming and, in general, in all applications in which good mechanical properties of the manufactured product are required, together with high resistance to ageing, even under conditions of low temperature and humidity. Examples of products which can be manufactured using the compositions of the invention include, in addition to those mentioned above, bags, laminates, moulded and blown articles, expanded sheets, expanded materials, biofillers for tyres, backsheets for diapers, wrapping films, mulching films, multilayer films, sacks for mowing grass, shoppers, nonwoven fabric, toys, pet toys, dog collars, products with controlled release for use in the agricultural field, threads. Accordingly the present invention provides a method for preparing heterophasic compositions comprising starch, a thermoplastic polymer which is incompatible with starch and which is capable of forming complexes with starch, and a plasticizer, in which the starch constitutes the dispersed phase and the thermoplastic polymer the continuous phase, said compositions being characterized in that they have impact-traction energy greater than 30 KJ/m2 (measured on blown film having a thickness of 30 um at 10°C and RH less than 5% and using a double-edge notched specimen), and in that the X-ray diffraction-spectrum of the compositions presents a peak at an angle 2 B in the range of 13-14° with intensity in relation to that of the peak of amorphous starch, which appears at about an angle 2 0 of 20.5°, less than 2 and greater than 0.02, the method comprising the step of extruding a melt comprising starch, the thermoplastic incompatible polymer, a plasticizer liquid at room temperature used in amount from 2 to 8% on the weight of the starch and the thermoplastic polymer and water in amount less than 5 % measured at the exit of the extruder before conditioning. Accordingly the present invention also provides a method for preparing the compositions of any of Claims from 1 to 10, in which a melt comprising the starch, the starch-incompatible thermoplastic polymer, the plasticizer and water with a final content adjusted to less than 5 % by weight, is extruded in an extruder provided with screws having a reverse profile for more than 30 % of the length of the screw. The following examples are given to illustrate and not to limit the scope of the invention. Example 1 A mixture formed from (parts by weight): Globe 03401-Cerestar natural starch* 27 Tone-787 PCL 65 glycerine 4.5 water 3.5 100.0 * water content 12% wt was supplied to a two screw OMC extruder of 60mm diameter, L/D = 36, RPM=180. The temperature profile was as follows: 60/145/175/180x4/155x2°C. It was operated with free degassing. The specific energy supplied was 0,4 Kw.h/Kg. The extruded material was pelletised. The water content was 1.3% by weight. The pellets were used to manufacture films using Ghioldi apparatus provided with Maillefer-type screws of 60mm diameter and L/D = 30. The thermal profile was as follows: 90/120/140/150x3/147x2°C. The film head had a diameter of 180mm. The film produced, approximately 30 u thick, was tested as such for its mechanical properties. A sample of the same film was on the other hand immersed in water for 24 hours to remove the starch plasticisers; after this, the samples taken from the washed film were left to condition for 72 hours in an environment with a temperature and humidity equal to those used for detecting the mechanical properties. Example 2 A mixture of (parts by weight) : Globe 03401 corn starch 33.4 Tone-787 PCL 54.3 glycerine 5.8 water 6.5 . 100.0 was supplied to a two screw APV-2030 extruder; L/D = 35 + 5XLT; RPM »,170; thermal profile: 60/100/170xl4°C, The extruder was operated with free degassing. The specific energy supplied was 0,17 Kw.h/Kg. The extruded material was pelletised. The water content was 1.5% in weight. The pellets were used to produce a sheet via cast-extrusion, using a modified AEMME extruder "provided with 1:3 constant taper screws;, diameter 30mm; L/D = 25; RPM = 35. The extruder had a flat head 150mm wide with a lip aperture of 0.8mm. The sheet obtained was 0.6mm thick. A quantity of pellets was separately made into a film as described in example 1 to obtain samples to test for their mechanical properties (samples of the film as produced and washed in water). Example 3 The test of example 2 was repeated using a composition (parts by weight) of 33.4 parts starch of the type used in example 2, 54.3 parts of Tone-787 PCL, 4.8 parts of glycerine and 7.5 parts of water. The film thus obtained was tested for its mechanical properties (film as produced and washed in water). Comparison Example 1 A mixture formed from (parts by weight): Globe 03401 corn starch 33.4 Tome-787 PCL 54.3 glycerine 9.7 water 5.5 100.0 was mixed in an extruder and made into a film as in example 1. The specific energy supplied was 0,22 Kw.h/Kg. The film obtained was tested for its mechanical properties (film as produced and washed in water as in example 1) . Comparison Example 2 A composition comprising 65 parts potato starch at 6% humidity and 35 parts of a mixture of glycerine: sorbitol 1:1 by weight (sorbitol is solid at ambient temperature) was supplied to the two screw APV-2030 extruder, as used in example 1, . operating with the following thermal profile: 60/100/190x14°c. Compounding was done with active degassing to obtain an extrudate having a water content of less than 0.5%. Then, 35 parts of dried pellets and 65 parts of Tone-787 PCL were mixed in an APV-2030 extruder; the extruded material was made into pellets and finally made into a film of approximately 30 u thickness, exactly as in example 1. Example 4 The test of example 3 was repeated with the only difference being that 3.8 parts glycerine and 8.5 parts water were used. The film thus obtained was tested for its mechanical properties (film as produced and washed in water as in example 1). Example 5 A mixture formed from (parts by weight): Globe 03401-Cerestar natural starch 26.4 Ecoflex® 63.8 glycerine 5.5 water 4.3 Erucamide 0«3 100.0 was supplied to a two screw OMC extruder of 60mm diameter, L/D = 36, RfM = 180. Ecoflex is a registered trade mark of BASF and refers to a polybutylene adipate-co-terephthalate copolymer. The temperature profile was as follows: 60/140/175/180x4°C. It was operated with free degassing. The specific energy supplied was 0,36 Kw.h/Kg. The extruded material was pelletised. The water content was 1.7% by weight. The pellets were used to manufacture films using Ghioldi apparatus provided with Maillefer-type screws of 60mm diameter and L/D - 30. The thermal profile was as follows: 120/135/145x5/140°C. The film head had a diameter of 100mm. The film produced, approximately 30 u thick, was tested as such for its mechanical properties. A sample of the same film was on the other hand immersed in water for 24 hours to remove the starch plasticisers; after this, the samples taken from the washed film were left to condition for 72 hours in an environment with a temperature and humidity equal to those used for detecting the mechanical properties. TABLE 1 PROPERTIES OF BLOWN FILM AT 23°C & 50% RH ( ASTM Standard d 882) Breaking Breaking Modulus of Breaking Hc/Ha Load elongation elasticity energy Examples Mpa % Mpa KJ/m2 1 as produced 37.1 880 503 8600 0.44 1 washed 31.6 747 501 7750 1 cf. as 28.3 810 310 5640 0.07 produced • 1 cf. Washed 20.0 120 603 327 2 as produced 31.2 880 520 8230 0.33 2 washed 25.8 637 631 6630 3 as produced 29.2 756 541 6194 0.29 3 washed 21.1 539 598 4930 4 as produced 24.5 662 632 5980 0.27 4 washed 20.2 521 606 4760 5 as produced 23.1 489 136 4155 0.07 Table 2 shows the characteristics of roughness of the sheets of examples 2-4, and comparison examples 1-2. A high level of roughness, although spoiling the aesthetic appearance, is critical for the printability of the sheet with printing inks. TABLE 2 SURFACE ROUGHNESS EXAMPLE 2 3 4 1 2 cf. cf. ROUGHNESS (micron) 0.20 0.20 0.24 0.14 1.17 Tables 3 and 4 show test data for tear and impact traction, TABLE 3 TEAR TESTS AT 23oC & 50% RH(*) Examples Start tearing N/mm 1 as produced 116.5 2 as produced 85.6 1 cf. as produced 64 Propagation N/mm 116.5 85.7 63.8 (*) ASTM standard d-1938 . TABLE 5 PROPERTIES OF SHEET FORMED VIA CAST-EXTRUSION Examples Load Elongation Modulus Mpa % " Mpa 2 as produced 37.3 892 271 2 washed 30.1 630 464 3 as produced 35.0 846 379 3 washed 26.2 595 550 4 as produced 32.5 745 351 4 washed 21.0 531 495 Figures 1 and 2 show respectively the second derivative FTIR and X-ray spectra of the composition of example 1. WE CLAIM: 1. A method for preparing heterophasic compositions comprising starch, a thermoplastic polymer which is incompatible with starch and which is capable of forming complexes with starch, and a plasticizer, in which the starch constitutes the dispersed phase and the thermoplastic polymer the continuous phase, said compositions being characterized in that they have impact-traction energy greater than 30 KJ/m2 (measured on blown film having a thickness of 30 urn at 10°C and RH less than 5% and using a double-edge notched specimen), and in that the X-ray diffraction-spectrum of the compositions presents a peak at an angle 2 0 in the range of 13-14° with intensity in relation to that of the peak of amorphous starch, which appears at about an angle 2 0 of 20.5°, less than 2 and greater than 0.02, the method comprising the step of extruding a melt comprising starch, the thermoplastic incompatible polymer, a plasticizer liquid at room temperature used in amount from 2 to 8 % on the weight of the starch and the thermoplastic polymer and water in amount less than 5 % measured at the exit of the extruder before conditioning. 2. The method according to claim 1 wherein said melt is extruded by applying an extrusion energy of 0.2 to 0.5 Kw.h/Kg. 3. The method according to Claim 1, in which the quantity of plasticizer or mixture of plastic izers is between 3 and 7% by weight of the total of the starch and the thermoplastic polymer and the specific extrusion energy is from 0.2 to 0.5 Kw.h/Kg. 4. The method according to any of Claims 1 to 3 in which the starch-incompatible thermoplastic polymer is chosen from the group comprising the aliphatic polyesters obtainable from aliphatic hydroxyacids having 2 or more carbon atoms, or from the corresponding lactones or lactides, or from aliphatic bicarboxylic acids having 2 or more carbon atoms, and from diols having 2 or more carbon atoms, from aliphatic- aromatic copolyesters, polyester-amides, polyester-ether-amides, polyester-urethanes, polyester-urea and mixtures therof. 5. The method according to Claim 4, in which the polyester is poly-epsylon- caprolactone, polyethylene or polybutylene-succinate, polyalkyleneadipate, diphenol diglycidylether polyadipate, polyalkyleneadipate-succinate, polyalkyleneadipate- epsylon-caprolactone,poly-epsylon-caprolactone/epsylon-caprolactame, polybuty leneadipate-co-tereph-thalate, poly alky lenesebaca-te, poly alky lenezelate. 6. The method according to any of Claims 1 to 5, in which the plasticizer is a polyhydric alcohol having from 2 to 22 carbon atoms. 7. The method according to Claim 6, in which the plasticizer is chosen from the group comprising glycerine, polyglycerol, glycerol ethoxylate, sorbitol acetate, sorbitol diacetate, sorbitol mono- and diethoxylate and mixtures thereof. 8. The method according to claim 7 wherein the plasticizer is glycerine. 9. The method according to any of Claims 1 to 8, including an interfacing agent chosen from the following classes of compounds: a) esters of polyhydric alcohols with mono- or polycarboxylic acid with a dissociation constant pK less than 4.5 (compared to the pK of the first carboxylic group in the case of polycarboxylic acids), and a hydrophilic/lipophilic index (HLB) greater than 8; b) esters of polyhydric alcohols with mono- or polycarboxylic acid having fewer than 12 carbon atoms, pK values of less than 4.5 and an HLB index of from 5.5 to 8; c) esters of polyhydric alcohols with C12-C22 fatty acids having an HLB index less than 5.5; d) non-ionic, water soluble surfactants; and e) reaction products of aliphatic or aromatic diisocyanates with polymers containing terminal groups reactive with the diisocyanates. 10. The method according to any of Claims 1 to 9, wherein the compositions present a band at 947cm"1 in the second derivative FTIR spectrum thereof. 11. The method for preparing the compositions of any of Claims 1 to 10, in which a melt comprising the starch, the starch-incompatible thermoplastic polymer, the plasticizer and water with a final content adjusted to less than 5% by weight, is extruded in an extruder provided with screws having a reverse profile for more than 30% of the length of the screw. 12. A method for preparing the compositions substantially as hereinbefore described and exemplified with reference to the accompanying drawings.

Documents:

in-pct-2001-0078-che abstract.pdf

in-pct-2001-0078-che claims duplicate.pdf

in-pct-2001-0078-che claims.pdf

in-pct-2001-0078-che correspondence-others.pdf

in-pct-2001-0078-che correspondence-po.pdf

in-pct-2001-0078-che description (complete) duplicate.pdf

in-pct-2001-0078-che description (complete).pdf

in-pct-2001-0078-che drawings.pdf

in-pct-2001-0078-che form-1.pdf

in-pct-2001-0078-che form-19.pdf

in-pct-2001-0078-che form-26.pdf

in-pct-2001-0078-che form-3.pdf

in-pct-2001-0078-che form-5.pdf

in-pct-2001-0078-che pct search report.pdf

in-pct-2001-0078-che pct.pdf

in-pct-2001-0078-che petition.pdf