BIODEGRADABLE COMPOSITIONS COMPRISING STARCH

Abstract: There is provided a biodegradable composition as obtained from a melt comprising starch, a plasticizer and at least one member selected from alkenol homopolymers and/or alkenol copolymers which are combined under conditions sufficient to ensure uniform melt formation, characterized in that the at least one member is present in the composition at a concentration of from 10 to 120 parts per 100 parts of dry starch. The invention further relates to methods of making the composition, and to articles made from said composition.

Description: Biodeqradable compositions comprising starch The present invention relates to biodegradable polymer compositions capable of being formed by heat and pressure into articles having substantial dimensional stability. The invention relates particularly to biodegradable compositions comprising starch and at least one member selected from alkenol homopolymers and/or alkenol copolymers. Such compositions are suitable for use, inter alia, in injection molding, in film formation, and in the formation of foamed packaging materials. BACKGROUND TO THE INVENTION It is known that natural starch which is found in vegetable products can be treated at elevated temperatures to form a melt. Such a melt may preferably be formed by heating the starch material above the glass transition and melting temperatures of its components so that such undergo endothermic rearrangement. Preferably the starch material contains a defined amount of a plasticizer, which preferably is water, and melt formation is carried out at an elevated temperature in a closed volume, and hence at an elevated pressure. It is possible to melt starch substantially in the absence of water, but in the presence of another suitable plasticizer, for example a liquid having a boiling point higher than the starch glass transition and melting temperature. Different degrees of uniformity in melt formation, which can be measured by various methods, are possible. One method, for example, is to microscopically determine the amount of granular structure remaining in a starch melt. It is preferred that the starch is destructurised, viz, that the melt is substantially uniform in character, that light microscopy at a magnification of about 500 X, indicates a substantial lack of, or reduction in, granular structure, that the starch so melted exhibits little or no birefringence and that x-ray studies indicate a substantial reduction in, or lack of, starch crystallinity in the melt. It is an advantage of the present invention that compositions may be formed from starch which has a relatively low degree of destructurisation. EP-A-0375 831 and EP-A-0 376201 in the name of National Starch and Chemical Corporation discuss the problems associated with the environmental handling of plastics waste materials. Such discussion is incorporated herein by reference. Both of the publications disclose low density, closed cell, starch products suitable for use, inter alia, as packaging materials, in which the starch has an amylose content of at least 45%, and preferably of at least 65%. Additionally EP-A 0 376 201 discloses that the addition of salt to the starch material, in concentrations of from 2% with respect to the weight of said material, leads to an expanded closed cell product having an improved uniform cell structure. The above mentioned prior starch compositions, in so far as they have been applied to the manufacture of biodegradable packaging materials, have, for one reason or another, generally not provided a tenable alternative to the synthetic materials that it is desired that they should replace. The present invention provides, inter alia, such an alternative. Moreover, Ind. Eng. Chem. Prod. Res. Dev. (194; 23, page 594-595) describes the extrusion of starch extended water-soluble polyvinyl alcohol. According to this disclosure, the melt flow index of such an extrudate decreases with increasing starch concentrations so that a composition comprising a 1:1 ratio of a low molecular weight (20,000) polyvinyl alcohol and a low molecular weight (30,000) corn starch possesses a melt flow index of 0.53. A composition comprising such a low melt flow index is not suitable for tήe injection molding of articles therefrom, wherein a melt flow index of about 7 or higher is typically required. Accordingly, it is surprising that the present inventive compositions, which comprise relatively high concentrations of starch, can easily be injection molded. The melt flow index of the composition is defined as the amount (in grams) of a thermoplastic material which can be forced in 10 minutes through a 2.0665mm orifice when subjected to a force of 0.2160 grams. It is implicit in the art of forming thermoplastics that the major components thereof should be of high molecular weight, and preferably that the molecular weights of such major components should be of similar magnitudes. It is surprising that articles having excellent physical properties and dimensional stability can be formed from the present inventive compositions, wherein the polyvinyl alcohol, which has a low molecular weight in comparison with that of the starch component of the composition, is present in high concentrations relative thereto. SUMMARY OF THE INVENTION According to the present invention, there is provided a biodegradable composition as obtained from a melt comprising starch, a plasticizer and at least one member selected from alkenol homopolymers and/or alkenol copolymers which are combined under conditions sufficient to ensure uniform melt formation, characterized in that the at least one member is present in the composition at a concentration of from 10 to 120 parts per 100 parts of dry starch. By plasticizer is meant a substance which can be incorporated into a material to increase its flexibility, 10 workability or extensibility or reduce the melt viscosity, lower the temperature of a second order transition, or lower the elastic modulus of the product. The term plasticizer includes solvent plasticisers, non-solvent plasticisers and internal plasticisers. S The preferred plasticizer is water. The invention also includes the melt which is obtained from said composition as well as shaped articles, 0 particularly foams, films, laminates and injection molded articles made from said melt. Such a uniform melt is generally thermoplastic, and it is $ particularly preferred that it is thermoplastic. In one embodiment of the composition, the starch is a high amylose variety and has an amylose content by weight of up to about 95%, and preferably of between 70 and 95%. 0 Said starch, however, does not have to be a high amylose variety, and may have an amylose content of up to about 65%, up to about 45%, and up to about 35%. It is possible that the amylose content of the starch is between 25 and 35%. The lower limit for the amylose content of the starch preferably is about 10 to about 15%, likewise by weight. The composition according to this invention may preferably comprise from about 10 to about 100 parts of said polymer and / or copolymer per 100 parts by weight of dry starch, and in a more preferred embodiment, the composition comprises from about 10 to about 85 parts of said polymer or copolymer per 100 parts of starch. 5 The composition may also comprise a polymer or copolymer content of from 10 to 65 parts, and particularly from 20 to 40 parts with respect to 100 parts of starch. 10 The alkenol homopolymer is preferably a polyvinyl alcohol which may be pre-plasticised with a polyhydric alcohol such as glycerol. The polyvinyl alcohol preferably is hydrolysed to an extent of from about 45 and about 100% and preferably has a number average molecular weight of about 15,000 to about 250,000, and more preferably has a number average molecular weight of from 15,000 to 150,000. - j . It is particularly preferred that the composition contains pre-treated polyvinyl alcohol in the form of a melt, obtained previously by adding sufficient energy to polyvinyl alcohol to melt it and substantially eliminate crystallinity in the melt. It is particularly preferred 3 that the such crystallinity is substantially completely eliminated. Such pre-treatment of polyvinyl alcohol is disclosed in EP-A 0415 357. Alkenol copolymers as mentioned above are preferably 0 synthetic copolymers containing vinyl alcohol units as well as aliphatic units as are obtained by copolymerization of vinyl esters, preferably vinyl acetate with monomers preferably ethylene, propylene, isobutylene and/or styrene with subsequent hydrolysis of 5 the vinyl ester group. Such copolymers are known and are described in "Encyclopedia of Polymer Science and Technology, Interscience Publ. Vol. 14, 1971" The composition may further include compounds selected from the group consisting of nucleating agents, fillers, stabilisers, coloring agents and flame retardants and boron containing compounds. Said composition may further include known processing aids, such as lubricants, mould release agents and plasticisers. It will be appreciated that the concentration of the components in the composition can be derived according to a Master-batching process, if desired. The starch may be modified to contain ether or ester groups. The invention also provides a method for producing the composition, comprising: a) providing a starting composition comprising starch, plasticizer and at least one member selected from alkenol homopolymers and/or alkenol copolymers which are present in the composition at a concentration of from 10 to 120 parts per 100 parts of said starch; b) adjusting the plasticizer content of the composition to between about 0.5 and about 40% by weight of the total composition during processing or plastification; c) heating the thereby adjusted composition to a temperature of between 100 and 220°C and for a time at least sufficient to form a uniform melt of the composition; d) removing any excess moisture before the extruder die to obtain a moisture content of between about 5% and about 20%; and- e) extruding the thereby heated composition. The present invention further includes a melt as obtained according to the method. The present invention further refers to a method of working said composition under controlled plasticizer content, temperature and pressure conditions as a thermoplastic melt wherein said process is any known process, such as for example, foaming, filming, compression molding, injection molding, blow molding, vacuum forming, thermoforming, extrusion, coextrusion, and combinations thereof. The invention will be further apparent from the following description, in conjunction with the following examples and the appended claims. SPECIFIC DESCRIPTION The present invention is defined in the appended claims. In particular, the invention refers to a biodegradable composition as obtained from a melt comprising starch, a plasticizer and at least one member selected from alkenol homopolymers and/or alkenol copolymers which are combined under conditions sufficient . to ensure uniform melt formation, in which the at least one member is present in the composition at a concentration of from 10 to 120 parts per 100 parts of dry starch. Such a uniform melt is thermoplastic in character. The alkenol homopolymer is preferably polyvinyl alcohol (PVA) having a number average molecular weight of at least about 15,000 (which corresponds to a degree of polymerization of at least 340). It is more preferred that the PVA has a number average molecular weight of between about 50,000 and 250,000, and most preferred that it has a number average molecular weight of about 80,000 to 120,000. Where the composition is foamed it is preferred that the number average molecular weight of the polyvinyl alcohol is between about 160,000 and 250,000 and more preferably between 160,000 and 200,000. Polyvinyl alcohol (PVA) is generally made from hydrolysis, or alcoholysis of polyvinyl acetate. The degree of hydrolysis to provide a polyvinyl alcohol for use in the present invention preferably is from about 75 to about 99.9 mole %, and more preferably is from about 80 to 99.9 ol %. It is most preferred that the degree of hydrolysis is from about 87 to 99.9 mol%. Such polyvinyl alcohols are known and are sold, by Air Products And Chemicals Inc, of7201 Hamilton Boulevard, Allentown, USA, under the name of Airvol 540S (degree of hydrolysis 87-89%, molecular weight about 106 -110, 000); Airvol 205S (degree of hydrolysis 87-89%, molecular weight about 110 - 31,000), Elvanol 90-50 (degree of hydrolysis 99.0 to 99.8%, molecular weight about 35 to about 80,000) and Airvol 107 (degree of hydrolysis 98.0 to 98.8%, molecular weight 11,000 to 31,000). EP-A 0 415 357 in the name of Air Products and Chemicals Inc, describes extrudable polyvinyl alcohol compositions, and methods for their preparation. The method according to EP-A 0 415 357 comprises adding sufficient energy to the polyvinyl alcohol to both melt it and essentially eliminate the crystallinity in the melt whilst simultaneously removing energy from the melt at a rate sufficient to avoid decomposition of the polyvinyl alcohol. Accordingly, the present invention contemplates the use in the present inventive compositions of polyvinyl alcohol pre-treated according to the disclosure of EP-A 0 415357. Thus the present inventive composition contains pre-treated polyvinyl alcohol in the form of a melt which has been obtained previously by adding sufficient energy ' to polyvinyl alcohol to both melt it and substantially eliminate crystallinity in the melt, whilst simultaneously removing energy from the polyvinyl alcohol melt at a rate sufficient to avoid its decomposition. The pre-treated polyvinyl alcohol may be plasticised by the addition thereto of a polyhydric alcohol plasticizer in an amount of from 2 to 30% by weight of the polyvinyl alcohol. It is preferred that the pre-treated polyvinyl alcohol is plasticised by the addition thereto of a polyhydric alcohol plasticizer in an amount of from 2 to 20% by weight of the polyvinyl alcohol. The pre-treated polyvinyl alcohol may further comprise sodium acetate and phosphoric acid in a molar ratio of about 2 to 1. The sodium acetate is present in the polyvinyl alcohol as a by product of its method of production and under the conditions of melt formation such sodium acetate acts as a catalyst for decomposition of the S polyvinyl alcohol. Accordingly, phosphoric acid may be added to the polyvinyl alcohol composition from which the- pre-treated polyvinyl alcohol melt is made, in the ratio of 1 mole of acid per 2 moles of acetate, in order to neutralize said sodium acetate. Low ash polyvinyl 0 alcohol, which is essentially free of sodium acetate, does not require the addition of such phosphoric acid. The pre-treated melt of polyvinyl alcohol has a maximum . melt temperature, as determined by differential scanning calorimetry, which is at least about 5°C lower than that of the corresponding untreated polyvinyl alcohol, preferably at least about 10°C lower than that of the untreated polyvinyl alcohol, and particularly preferably Q at least about 15°C lower than that of the untreated polyvinyl alcohol. The formation of such a pre-treated melt of polyvinyl alcohol requires the input of at least about 0.27kWh/kg 5 of specific energy to the polyvinyl alcohol, and typically requires from about 0.3 to about 0.6kWh/kg of such energy. The upper practical limit of energy input would be about 0.6kWh/kg because any energy beyond that necessary to melt the polyvinyl alcohol and eliminate crystallinity must be removed as "waste energy" reducing the efficiency of the formation of the pre-treated polyvinyl alcohol. Optimally the polyvinyl alcohol requires an input of about 0.35 to about 0.45kWh/kg both to melt it and substantially eliminate crystallinity in the melt. The composition preferably comprises from about 10 to about 100 parts of said PVA per 100 parts of starch, and in a particularly preferred embodiment, the composition comprises from about 10 to about 85 parts of said PVA per 100 parts of starch. A likewise polymer or copolymer content of from 10 to 65 parts, and particularly from 20 to 40 parts with respect- to 100 parts of starch is also highly suitable. Preferred alkenol copolymers are those containing vinyl alcohol units and aliphatic chain units as obtained by co-polymerization of vinyl acetate with ethylene and/or propylene, preferably with ethylene and subsequent hydrolysis of the vinyl acetate group. Such copolymers may have differing degrees of hydrolysis. Preferred are ethylene/vinyl alcohol polymers (EVOH) and propylene/vinyl alcohol polymers. Most preferred are the ethylene/vinyl alcohol polymers. The molar ratio of vinyl alcohol units to alkylene units is preferably from about 40 : 60 to about 90 : 10 and preferably from about 45 : 55 to about 70 : 30. The most preferred EVOH has an ethylene content of 44%. The starch which is present in the composition of the present invention is at least one member selected from the group consisting of native starches of vegetable origin, which starches are derived from potatoes, rice, tapioca, corn, pea, rye, oats, wheat, including physically modified starch, irradiated starch, starch in which mono or divalent ions associated with phosphate groups therein have been removed, either partly or wholly, and optionally replaced, either partly or wholly, by different divalent ions or with mono or polyvalent ions; pre-extruded starches and starches which have been so heated as to undergo the specific endothermic transition characteristically preceding oxidative and thermal degradation. 0 For certain applications it is preferred that the starch is a high amylose starch having an amylose content of between about 70% and about 95%, preferably between about 75% and about 85%, the percentages being by weight with - respect to that of the starch. The lower limit for the amylose content of the starch preferably is about 10 to about 15%, likewise by weight. Q The starch component of the composition according to the invention includes starch melted in the absence of added water, but in the presence of another plasticizer - such as glycerol. The preferred plasticizer is, however, water. Preferably the starch is formed into a melt in the presence of water which may be present in the starting composition, from which the composition of the present invention is made, at between about 0.5 and about 40% by weight, based on the total weight of the starting composition. The composition according to the invention has a water content of between about 10 and about 20% by weight, and preferably of between about 14 and about 18% by weight, and particularly of about 17% by weight, based on the weight of the composition as explained herein. Starch may be mixed with the polymer or copolymer and optionally other additives as mentioned hereinbelow in any desired sequence. For example, the starch may be mixed with all of the intended additives, including polymer or copolymer to form a blend, which blend may then be heated to form a uniform melt which will, in general, be thermoplastic. The starch may, however, be mixed with optional additives, the starch melted and granulated before addition of the polymer or copolymer, for example the polyvinyl alcohol, which mix may then be further processed. Preferably, however, the starch is mixed with additives together with the polymer or copolymer, for example polyvinyl alcohol, to form a free flowing powder, which is useful for continuous processing, and melted and either granulated or extruded directly into the solidified composition of the present invention. The composition may optionally consist at least of the combination of starch and one member selected from alkenol homopolymers and copolymers which have been pre-processed. Such pre-processing may involve the provision of granulates or pellets which have been manufactured under conditions sufficient to have obtained uniform melt formation of the components. Alternatively, and or additionally, the alkenol homopolymers and copolymers may have been pre-plasticised with, for example, a polyhydric alcohol such as glycerol. The starch present in the composition may have been pre-melted in the presence of from 15 to 40% moisture, by weight thereof, and at a temperature and pressure within the ranges as given above. Optionally the composition comprises at least one member selected from the group consisting of extenders, fillers. lubricants, mould release agents, plasticisers, stabilisers, coloring agents, and flame retardants. The extenders include water-soluble an/or water-swellable polymers including known thermoplastic polymers such as gelatin, vegetable gelatins, acrylated proteins; water-soluble polysaccharides such as: alkylcelluloses, hydroxyalkylcelluloses and hydroxyalkylalkylcelluloses, 0 such as: methylcellulose, hydroxymethylcellulose, hydroxyethylcellulose, " hydroxypropylcellulose, hydroxyethylmethylcellulose, hydroxypropylmethylcellulose, hydroxybutylmethylcellulose, cellulose esters and hydroxyalkylcellulose esters such as: cellulose acetylphtalate (CAP), Hydroxypropylmethyl-cellulose (HPMCP); carboxyalkylcelluloses, carboxyalkyl-alkylcelluloses, carboxyalkylcellulose - esters such as: carboxymethylcellulose and their alkali-metal salts; the analogous derivatives of starch as named for all the cellulose derivatives above; water-soluble synthetic polymers such as: poly(acrylic acids) and their salts and essentially water soluble « poly(acrylic acid) esters, poly(methacrylic acids) and their salts and essentially water-soluble poly(methacrylic acid) esters, essentially water soluble poly(vinyl acetates), poly(vinyl acetate phthalates) (PVAP), poly(vinyl pyrrolidone), poly(crotonic acids); 0 cationically modified acrylates and methacrylates possessing, for example, a tertiary or quaternary amino group, such as the diethylaminoethyl group, which may be quaternized if desired; and mixtures of such polymers. By the term "water-soluble or water-swellable polymer" is meant a polymer which absorbs or adsorbs at least 30% of water by weight with respect to that. of the dry polymer when such is immersed in liquid water at room temperature. Suitable fillers include, for example, wood-derived materials, and oxides of magnesium, aluminum, silicon, and titanium. The fillers are present in the composition at a concentration of up to about 20% by weight, and preferably between about 3.0 and about 10%, by weight, based on the total weight of the composition. The lubricants include stearates of aluminum, calcium, magnesium, and tin, as well as the free acid and magnesium silicate, silicones and substances such lecithin, and mono and diglycerides, which - for the purpose of the present invention - .- function in like-manner. Suitable lubricants further include unsaturated fatty acid amides, preferably amides of C 18 - C 24 unsaturated fatty acids, such as the amide of cis-13-docosenoic acid (erucamide) and amides of C 12 - C 24 carboxylic acids, such as the amide of docosanoic - fl acid (behenamide) . The particularly preferred lubricant is stearic acid, which is present in the composition in an amount of up to 10 parts per 100 parts of starch, preferably in an amount of from 1 to 3 parts per 100 parts of starch, and most preferably is present in the 3 composition in an amount of 1 part per 100 parts of starch. The composition of the present invention may also comprise a nucleating agent, - particularly so where the 0 composition is in foamed form - having a particle size of from 0.01 to 5 microns, selected from the group consisting of silica, titania, alumina, barium oxide, magnesium oxide, sodium chloride, potassium bromide, magnesium phosphate, barium sulphate, aluminum sulphate, 5 boron nitrate and magnesium silicate, or mixtures thereof. It is preferred that said nucleating agent is selected from amongst silica, titania, alumina, barium oxide, magnesium oxide, sodium chloride, and magnesium silicate, or mixtures thereof. The particularly preferred nucleating agent is magnesium silicate (micro talcum), which is present in the composition in an amount of up to 10 parts of agent per 100 parts of starch. Preferably the agent is present in the composition in an amount of from 1 to 3 parts per 100 parts of starch, and most preferably in an amount of 2 parts per 100 parts of starch. 10 Plasticisers include urea and low molecular weight poly(alkylene oxides), such as, for example, poly(ethylene glycols), poly(propylene glycols) poly(ethylene-propylene glycols), organic plasticisers of low molecular mass, such as, for example, glycerol; IS pentaerythritol; glycerol monoacetate, diacetate, or triacetate; propylene glycol; sorbitol; sodium diethylsulfosuccinate; triethyl citrate and tributyl citrate and other substances which function in like _,_ manner. 20 Such plasticisers are preferably present in the composition at a concentration of between about 0.5% and about 40% by weight, and more preferably between about 3 0.5% and about 5% by weight, based on the weight of all of the components, including the water therein. Preferably the sum of the plasticizer (including water where such is present as a plasticizer) content of the 30 composition does not exceed about 25% by weight, and most preferably does not exceed about 20% by weight, based on the total weight of the composition. Stabilisers include anti-oxidants such as thiobisphenols, 35 alkylidenbisphenols, secondary aromatic amines; stabilisers against photo-decomposition, such as, for example, uv absorbers and quenchers; hydroperoxide decomposers; free radical scavengers, and anti-microbial agents. Coloring agents include known azo dyes, organic or inorganic pigments, or coloring agents of natural origin. Inorganic pigments are preferred, such as the oxides of iron or titanium, these oxides being present in the composition at a concentration of between about 0.01 and about 10% by weight, and preferably present at a concentration of between about 0.05 and about 3% by weight, based on the total weight of the composition. Most preferably the coloring agents are present in the composition in an amount of about 0.03 to about 0.07% by weight with respect to the total composition. Iron oxide in an amount of 0.05% by weight with respect to that of the 0.05%. The composition may further comprise flame retardants- which, for example, comprise phosphorous, sulphur and halogens, or mixtures thereof. Suitable phosphorous-containing flame retardants include diethyl-N,N-bis(2-hydroxyethyl) aminomethyl phosphonate; dimethyl methylphosphonate; phosphonic acid, methyl-, dimethylester, polymer with oxirane and phosphorous oxide; aliphatic phosphate/phosphonate oligomers; tributyl phosphate; triphenyl phosphate; tricresyl phosphate; 2-ethylhexyl diphenyl phosphate; and tributoxyethyl phosphate. These retardants are available from Akzo Chemicals Inc. of 300 South Riverside Plaza, Chicago, Illinois, USA. Further suitable phosphorous-containing retardants include: bis (hydroxypropyl) sec.butyl phosphine oxide which can be obtained from the Chemical Products Group of FMC Corporation, 2000 Market Street, Philadelphia, Pennsylvania 19103, USA; and the following compounds obtainable from Albright and Wilson, Americas Inc, of P.O. Box 26229, Richmond, Virginia, 23260, USA: polypropoxylated dibutyl pyrophosphoric acid; a mixture of phosphonic acid, methyl-, (5-ethyl-2-methyl-1,3,2-dioxaphosphorinan-5-yl)m- ethyl ethyl ester, P-oxide and phosphonic acid, methyl-, bis [(5-ethyl- 2-methyl-l,3,2-dioxaphosphorinan-5-yl)methyl] ester, P,P * -dioxide as sold under the trade name Amgard V19; ammonium polyphosphate; ethylendiamine polyphosphate; melamine phosphate; dimelamine phosphate; and microencapsulated red phosphorous. Where ammonium polyphosphate and ethylendiamine polyphosphate are used as flame retardants, it is preferred that they are buffered with disodium orthophosphate so that they are thereby less corrosive to the equipment used for processing the composition comprising them. A still further suitable phosphorous containing flame retardant is guanidinium phosphate which can be obtained from Chemie Linz GmbH of St Peter Strasse 25, A-4021, Linz, Austria. Suitable halogen-containing flame retardants include chlorinated paraffin, which is obtainable from Occidental Chemical Corporation, of 360 Rainbow Boulevard South, Box 728, Niagra Falls, New York 14302; tetrabromo phthalic anhydride, and penta-, octa- and decabromo diphenyl oxide, which are obtainable from Great Lakes Chemical Corporation, of P.O. Box 2200, West Lafayette, Indiana, 47906, USA; and bromochlorinated paraffin, brominated epoxy resin, brominated polystyrene, tris (2- chloropropyl) phosphate and tetrakis hydroxymethyl phosphonium chloride which may be obtained from Albright and Wilson at the address given above. Further suitable halogen-containing compounds include dibromo neopentyl glycol and tribromo neopentyl alcohol which are obtainable from AmeriBrom Inc of 1250 Broadway New York, New York 10001, USA. Suitable sulphur containing-retardants include ammonium sulfate; ammonium sulfamate; and tetrakis (hydroxymethyl) phosphonium sulfate; all of which may be obtained from the American Cyanomid Company, of One Cyanamid Plaza, Wayne, New Jersey, 07470, USA. Guanidinium sulfate, obtainable from Chemie Linz at the address given above, may also be used as a flame retardant. The above mentioned flame retardants are present in the 10 starch-containing composition in an amount of from 0.1 to 10%, preferably from 1 to 6%, and most preferably from 2 to 4%, all percentages being by weight with respect to that of the starch component of the composition. S Other suitable flame retardants which may be present in the composition of the present invention include aluminum trihydrate; aluminum acetylacetonate; aluminum acetate; sodium aluminum hydroxy carbonate; magnesium aluminum Q hydroxy carbonate; antimony oxide; molybdic oxide; ammonium octamolybdate; zinc molybdate; magnesium hydroxide; zinc borate; ammonium pentaborate; boric acid; and sodium tetraborate. These flame retardants are generally available, and the Borax compounds in particular may be obtained from the United States Borax and Chemical Corporation, of 3075 Wilshire Boulevard, Los Angeles, California 90010, USA. These latter flame retardants may be present in the composition in an amount of from 1 to 90% by weight with respect to the starch component of the composition, and preferably are present in the composition in an amount of from 20 to 80% and most preferably from 40 to 75%. The particularly preferred flame retardants are guanidinium phosphate, ammonium polyphosphate and/of ethylenediamine polyphosphate (in the presence or absence of disodium orthophosphate), and guanidinium sulphate or ammonium sulphate. Still further substances which may be added to the composition include animal or vegetable fats, preferably in their hydrogenated forms, especially those which are solid at room temperature. Such fats preferably have a melting point of at least 50°C and include triglycerides of C12-, C14-, C16-and C18- fatty acids. The fats are added to the material comprising the thermoplastic melt alone without extenders or plasticisers, or to the melt together with mono- or di- glycerides or phosphatides, of which lecithin is preferred. Said mono- and diglycerides are preferably derived from said animal or vegetable fats. The total concentration of said fats, mono-, di¬ glycerides and phosphatides may be up to 5% by weight, based on the total weight of the composition. Still further compounds which may be added to, or present in the composition include boron-containing compounds, particularly so when the composition is formed into films, sheets or fibers. The presence of such compounds in the composition yields articles which have improved transparency, Young's modulus and tear strength. The preferred boron-containing compounds are boric acid, metaboric acid, alkali and alkaline earth metal salts, borax and derivatives thereof. Said compounds may be present in the composition in an amount of between 0.002 and 0.4%, by weight with respect to that of the composition, and preferably are present at a concentration of between about 0.01 and 0.3%, likewise by weight. Inorganic salts of alkali or alkaline earth metals, particularly LiCl and NaCl may be additionally present in the composition in an amount of between 0.1 and 5% by weight with respect to that of the total composition. The presence of such salts in the composition still further improves the Young's modulus, transparency and tear strength of articles made from the composition. It will be appreciated that the concentration of the components, particularly the coloring agents and borax containing compounds, in the composition can be derived according to a Master-batching process, if desired. The compositions described herein above form thermoplastic melts on heating under conditions of controlled temperature and pressure. Insofar as such melts may be processed by any conventional shaping process the present invention also refers to such processes when used to shape the composition or melt of the present invention. Thus such melts can be processed in the manner used for conventional thermoplastic materials, such as injection molding, blow molding, extrusion, coextrusion, compression molding, vacuum forming, and thermoforming to produce shaped articles. Whilst such articles include containers, cartons, trays, cups (particularly for candles where the composition comprises a flame retardant), dishes, sheets, and packaging materials, including the loose fill variety, the shaped articles also include pellets and granulates which may be ground to make powders for use in the manufacture of shaped articles. Particularly preferred articles are in foamed form, in injection molded form or are in extruded form. The range of pressures and temperatures suitable for injection molding, filming, foaming and extrusion molding are as disclosed hereinbelow. Injection molding of the composition In order to melt the starch according to the invention, it is heated at a sufficient temperature for a time sufficient to enable uniform melt formation. The composition is preferably heated in a closed volume, such as a closed vessel, or in the finite volume created by the sealing action of unmolten feed material, which action is apparent in the screw and barrel of an extruder or injection molding equipment. Thus said screw and barrel is to be understood as a closed volume. Pressures created in such a volume correspond to the vapor pressure of the plasticizer (usually water) at the used temperature. It will be appreciated that pressures may be applied or generated, as is known to be possible in the use of said screw and barrel. The preferred applied and/or generated pressures are in. the range of pressures which occur in injection molding or extrusion are known per se, being up to about 150 x 10 5N/m2 , preferably up to about 75 x 105N/m2 and most preferably up to about 50 x 10 5 N/m2. The temperature used in injection molding of the composition is preferably within the range of 100°C to 220°C, more preferably within the range of from 160 to 200°C, and most preferably within the range of 160 to 180°C, the precise temperature being dependent up on the type and nature of the starch used. In terms of ease of processing it is preferred that potato or corn starch is used. The thus obtained melted starch composition is granulated and is ready to be mixed with further components according to a chosen mixing and processing procedure to obtain a granular mixture of melted starch starting material to be fed to the screw barrel. Filming of the composition The composition is plasticised as above, except that preferably it is heated to a temperature typically about 10 to about 20°C higher than those routinely used during injection molding and extrusion of the composition. 5 Foaming of the Composition The process for forming the composition of the present invention into foams comprises: 0 a) providing a starting composition comprising starch, plasticizer and at least one member selected from alkenol homopolymers and/or alkenol copolymers which are present in the composition at a concentration of from 10 to 120 parts per 100 parts of said starch; S b) adjusting the plasticizer content of the composition to between about 15 and about 40% by weight of the total composition during processing or plastification; c) heating the thereby adjusted composition at a temperature of between 100 and 220°C and for a time at least sufficient to form a uniform melt of the composition; d) removing any excess moisture before the extruder die to obtain a moisture content of between about 10% and about 20%; and - e) extruding the thereby heated composition under conditions whereby the extrudate assumes a cross section greater than that of the exit orifice of the extruder die. It is preferred that the plasticizer is water and that, prior to extrusion, the moisture content of the composition is adjusted to between 14 and 20%, more preferably between 16 and 18% and most preferably to 17% by weight of the total composition, and that the composition is heated at a temperature of from about 160°C to about 200°C and most preferably from about 180°C to about 200°C, and at a pressure corresponding at least to the moisture vapor pressure at said temperature for a time of at least 30 seconds. The composition may be molded subsequent to its extrusion using known thermoforming processes. The invention will be further apparent from consideration of the following Examples. Example 1 10kg of potato starch, 2.8 kg of polyvinyl alcohol having a number average molecular weight of about 106,000 to 110,000 and degree of hydrolysis of between 87 and 89%, (Airvoll 540S), 200g of magnesium silicate and lOOg of" stearic acid are combined. The moisture content of the combined components is then adjusted to about 28% by weight of the moistened starch mix. The moisture content of the combined components may be adjusted to from about 25 to 30% by weight with similar results to those obtained below. The thus adjusted starch is fed into the entry port of a twin screw extruder (Leistritz model LSM 34) having screws co-rotating in a horizontal cylindrical barrel and an outlet die mounted at the discharge end of the extruder, opposite its entry port. The starch composition is then heated to a temperature of 155°C for about 70 seconds at a suitable pressure necessary to avoid the formation of water vapor at said temperature. The thus melted starch is extruded from the outlet die of the extruder, and the extrudate cooled and pelletized. The pelletized melted starch mix is conditioned to a moisture content of about 17%, and then fed into the entry port of a single screw extruder having a screw length to diameter ratio of in the range of 25. Extruders having a ratio of from 10 to 30 are also * useable in the process according to the present invention. The thus formed mix is heated to 190°C for from 20-60 seconds and then extruded. Upon emerging from the exit 0 orifice of the extruder die, the extrudate assumes a cross section greater than that of the said orifice to form a foam material suitable for use as a packaging material. Open and closed cell foams are thus produced which have excellent properties with respect to density, S resilience and compressibility. The extrudate is allowed to cool whereupon its bulk density is determined in accord with the method described by Hwang and Hayakawa in J. Food Sci., Vol. 45, pp 1400 0 to 1407, which description is incorporated herein by reference. The resiliency and compressibility of the extrudates are determined using a Texture Analyzer, known to those skilled in the art, according to the procedure disclosed in European Patent Application No. 89111295.5 (Publication No. 0 375 831), which disclosure likewise is incorporated by reference into the present application. The bulk density, resilience and compressibility of the foams are given in Table 1. Examples 2 - 5 Example 1 is repeated, but with different quantities of 3polyvinyl alcohol. Thus the compositions of Examples 2 - 5 contain polyvinyl alcohol contents of 20, 25, 30, and 35% by weight with respect to the dry weight of the starch component. The bulk densities, resilience and compressibilities of the compositions thus formed are listed in Table 1. Examples 6-9 Example 1 is repeated except that potato starch is replaced by maize starch, and the concentration of polyvinyl alcohol is 10%, 20%, 25% or 30% by weight with respect to that of the dry starch. The resilience, compressibilities and bulk densities of the foams thus produced are similar to those for potato starch as given above in Table 1, with the characteristics of the foam comprising 20% polyvinyl alcohol being particularly good. TABLE 1 3 3 Example 10 10kg of starch, 4.5 kg of polyvinyl alcohol having a number average molecular weight of about 106 to about 110, 000 and a degree of hydrolysis of between 87 and 89% (Airvoll 540S), 200g of magnesium silicate and lOOg of stearic acid are combined. The moisture content of the combined components is then adjusted to 22% by weight of the moistened starch mix. The thus adjusted starch is fed into the entry port of a twin screw extruder having a screw rotating in a horizontal cylindrical barrel and an outlet die mounted at the discharge end of the extruder, opposite its entry port. The starch composition is then heated to a temperature of 155°C for about 1 minute at the minimum pressure necessary to avoid the formation of water vapor at said temperature. The thus melted starch is extruded from the outlet die of the extruder, and the extrudate cooled and pelletized. The pelletized starch mix is conditioned to a moisture content of about 17%, and then fed into the entry port of a single screw extruder having a screw length to diameter ratio of 25. The starch mix is then heated to from 180 to 200°C for from 0.3 to 1 minute and then extruded in the form of a sheet which is subsequently thermo-formed according to known techniques into articles such as trays, cups, and dishes. Example 11 This example describes the injection molding of tensile test pieces from an extruded blend of polyvinyl alcohol, pre-treated so as to be in the form of a pelletized melt, and starch. Fifty parts of high molecular weight, partially hydrolysed (87-89 mole%) polyvinyl alcohol (Airvol 540) having a degree of polymerization of about 2,200 and having an ash content of about 0.19% are introduced into a high intensity Littleford 180L mixer and the mixer started at 900 RPM. When the temperature of the polyvinyl alcohol reaches 106 -5 FΛ °C, 12.5 parts of glycerol are added to the blender at a slow steady rate. After the addition of the glycerol, 0.17 parts of 85% phosphoric acid and 0.25 parts of glycerol mono-oleate are added to the mixture as a processing aid. S Cooling water is added to the mixer jacket and controlled, to maintain the product temperature below 100°C at all times. After the mono-oleate addition is complete, mixing is continued at low speed until a free flowing 0 polyvinyl alcohol mixture is obtained. The mixture is then discharged into a Littleford 400L cooling mixer and the product temperature lowered to 40°C. The mixture so produced is free flowing and free of clumps or degraded 5 material. The thus formed polyvinyl alcohol material is loaded into a volumetric feeder and fed into a 46 mm reciprocating, rotating extruder of the kind known to those skilled in the art. The screw is designed to achieve a high degree of mechanical energy input without product degradation. The extruder is a devolatilizing extruder, and a vacuum of 254 torr (lOin Hg) is applied at the vent port located at 7 diameters to remove any residual moisture in the polymer and acetic acid formed from the conversion of sodium acetate to disodium monohydrogen phosphate. The melt temperature of the polymer in the working zone of the extruder is maintained at the upper end of the polymer melting curve as indicated by a Differential Scanning Calorimeter (DSC) . Melt temperatures are measured at 183°C, 197°C, and 199°C. Typical operating conditions are: Screw Speed Screw Temperature Barrel Temperatures 1st zone 2nd zone Production Rate Max. Melt Temp. Screw Power Specific Energy Input The product exits the extruder and is immediately cooled below its glass transition temperature to prevent product degradation and crystallization of the polymer that would lead to gel formation during subsequent thermal shaping operations. The strands are cut in a conventional manner into pellets and collected. The pellets produced are substantially free of crystallinity and are gel-free, smooth and have a straw color. (a) 9500g of potato starch containing 15.1% water are placed in a high speed mixer and 2875g (30% with respect to the weight of the starch component) of the polyvinyl alcohol pellets as produced above, 80.75g of hydrogenated fat (lubricant release agent) sold as Boeson VP by Boehringer Ingelheim, 40.37g of a melt flow accelerator (lecithin) sold as Metarin P by Lucas Meyer are added under stirring. The water content of the final mixture is 14.43%. (b) lO.OOOg of the mixture prepared under (a) is fed through a hopper into a Werner & Pfleiderer co-rotating twin screw extruder (model Continua 37). The temperature profile of the four sections of the barrel is respectively 20 o C/180°C/180 o C/80°C. Extrusion of the blend is carried out with a mixture output of 8 kg/hr (screw speed 200 rpm) . Water is added at the inlet with a flow rate of 2 kgs/hr to bring the water content of the material during extrusion to 31.5%. In the last section of the extruder 80 mbar reduced pressure is applied to remove part of the water as water vapor. The water content of the granulates is 17.5%, measured 0 after they had equilibrated at room temperature. (c) The granulates of the pre-blended mixture as obtained under (b) (H 2 0 content: 17.5%) are fed through a - hopper to an injection molding machine (Arburg 329-210-750) for the production of tensile test pieces. The temperature profile of the barrel is: 90°C/165°C/165°C. Q The shot weight is 8g, the residence time 450 sec, the injection pressure 2082 bar, the back pressure 80 bar, and the screw speed 180 rpm. The tensile test pieces, which are of standard design (DIN No. 53455), thus produced are conditioned in a climatic cabinet at 50% R.H. for five days as an arbitrary standard condition. (d) The conditioned tensile test piece are then tested for their stress/strain behavior on a Zwick tensile test apparatus. The samples are measured at room temperature using an extension rate of 10 mm per minute. The test pieces thus obtained exhibit improved dimensional stability and physical properties when compared with like test pieces made from polyvinyl alcohol which is not pre-treated. example 12 (a) 8000g of potato starch containing 15% water are placed in a high speed mixer and 3200g (40% by weight with respect to the starch component) of pre-treated polyvinyl alcohol pellets; 68g of hydrogenated fat (lubricant release agent) sold as Boeson VP by Boehringer Ingelheim, 34g of a melt flow accelerator (lecithin) sold as Metarin P by Lucas Meyer are added under stirring. The water content of the final mixture was 15.6%. (b) lO.OOOg of the mixture prepared under (a) are fed into the hopper of a Werner & Pfleiderer co-rotating twin screw extruder (model Continua 37). The temperature profile of the four sections of the barrel was respectively 20 o C/50°C/100 o C/50°C. Extrusion was carried out with a mixture output of 8 kg/hr (screw speed 200 rpm). Water is added at the inlet with a flow rate of 1 kg/hr to bring the water content of the material during extrusion to 25%. In the last section of the extruder, 22 mbar reduced pressure was applied to remove part of the water as water vapor. The water content of the granulates thus produced is 14.8% as measured after they had equilibrated at room temperature. The water content of the granulates is adjusted to 17% by spraying water under stirring in a conventional mixer. (c) The granulates of the pre-blended mixture as obtained under (b) (H 2 0 content: 17%) are fed through a hopper to an injection molding machine Arburg 329-210-750 for the production of tensile test pieces. The temperature profile of the barrel is: 90 o C/185°C/185 o /185°C. The shot weight is 7.9g, the residence time 450 sec, the injection pressure 2200 bar, the back pressure 80 bar, the screw speed 180 rpm. The tensile test pieces (DIN No. 53455) thus produced are conditioned in a climatic cabinet at 50% R.H. for five days as an arbitrary standard condition to equilibrate them to a water content of about 14%. (d) The conditioned tensile test pieces are then tested for their stress/strain behavior on a Zwick tensile test apparatus as described in Example 7. The test pieces thus obtained exhibit improved dimensional stability and physical properties when compared with like test pieces made from polyvinyl alcohol which is not pre-treated. Example 13 This Example describes the injection molding of candle cups from an extruded blend of polyvinyl alcohol and starch. A mixture of maize starch or high amylose starch (Hylon VII obtainable from National Starch and Chemical Corporation of Finderne Avenue P.O. Box 6500 Bridgewater, New Jersey 08807 USA), Boeson VP (as sold by Boehringer Ingelheim), and lecithin (as sold as Metarin P by Lucas Meyer) present in the ratio of 100: 2: 1 respectively is prepared. 13.6 kg of this mixture is fed into the entry port of a twin screw extruder (Leistritz model LSM 34) having screws co-rotating in a horizontal cylindrical barrel and an outlet die mounted at the discharge end of the extruder, opposite its entry port. To this mixture is added 440 grams of glycerol, 5.2 kg of pre-plasticised polyvinyl alcohol having a number average molecular weight of about 15,000 to 45,000 and a degree of hydrolysis of 88 to 99%, and sufficient water to enable the combined mixture to be compounded appropriately. The amount of water added is dictated to a large extent by the nature of the starch and is easily determined by the skilled man. The starch composition is then heated to a temperature of about 175°C for about 30 to 120 seconds at a suitable pressure necessary to avoid the formation of water vapor at said temperature. Ammonium sulphate is dissolved in water and added to the heated and pressurized starch composition prior to extrusion of the composition from the outlet die of the extrude . The ammonium sulphate is added in such an amount that its final concentration in the cooled extrudate is 3.5% by weight with respect to that of the starch component thereof. The thus melted starch is extruded from the outlet die of the extruder, and the extrudate cooled and pelletized. The pellets of the pre-blended mixture as obtained above (H_0 content preferably about 11%) are fed through a hopper to an injection molding machine (Arburg 320) fitted with a mould suitable for the production of candle cups. In the case of maize starch, the melt temperature is 165°C, the shot weight is 9g, the residence time is 240 sec, the injection pressure 1100 bar, the screw speed 190 rpm, and the mould temperature 17°C. The candle cups so produced have excellent physical properties, substantial dimensional stability and are made from a composition which Is • sufficiently flame retarded to meet the DIM 75200 flame retardancy standards. Examples 14-16 Example 13 is repeated except that the composition from which the candle cups are made is altered. Suitable further compositions are given in Table 2 below. The injection molding pressure, residence time etc. are essentially as for Example 13 except for a slight increase (to about 1200 bar) in the injection molding pressure in the case where the polyvinyl alcohol is not pre-plasticised. Example 17 Example 13 is repeated except that the flame retardant used is ethylenediamine polyphosphate, present in the composition in an amount of 4% by weight with respect to that of the starch component thereof. In Examples 13 to 17, the flame retardant is added at a late stage in the compounding of the composition prior to its injection molding, and the residence of the composition (now comprising the flame retardant) in the extruder is kept to a minimum. In addition, that part of the extruder which contacts the flame retarded starch composition may be especially adapted to reduce the corrosive effects of the retardant on the extruder. The candle cups produced according to Examples 13 to 17 have excellent physical properties, substantial dimensional stability and are made from a composition which is sufficiently flame retarded to meet the DIN 75200 flame retardancy standards. Example 18 A composition comprising polyvinyl alcohol, glycerin, maize starch, Boeson, lecithin, and water present in the ratio of 96:24:100:1:0.5:12 is prepared. The polyvinyl alcohol has a number average molecular weight of about 106,000 to 110,000 and degree of hydrolysis of about 88% (Airvoll 540S). The composition is fed into the entry port of a twin screw extruder (Leistritz model LSM 34) having screws co-rotating in a horizontal cylindrical barrel and an outlet die mounted at the discharge end of the extruder, opposite its entry port. The starch composition is then heated to a temperature of between 171 and 185°C for about 60 to 120 seconds, with mechanical energy being provided by a strong screw configuration (as is known to those skilled in the art) at a suitable pressure necessary to avoid the formation of water vapor at said temperature. The composition is plasticised in the extruder until uniform melt formation is achieved, thereafter the moisture content of the composition is reduced to about 10% before exit of the composition from the extruder barrel. The melt is formed into films of varying thickness between 0.2 and 0.5 mm using conventional down stream equipment. The obtained films, whilst suitable for use per se, in packaging applications for example, can be used in the preparation of laminates comprising said film and a metal (preferably aluminum) foil. A film thickness of 0.4mm is particularly preferred. Example 19 Pellets are made according to the above examples from compositions comprising maize starch, 1% by weight with respect to that of the starch of stearic acid; 2% likewise by weight of Chematalc 5M and optionally 0.05% likewise by weight of iron oxide. The compositions further contain 20% by weight with respect to that of the starch of the following polyvinyl alcohols: a) Airvol 540 having a degree of hydrolysis of 87-89%; b) Mowiol 56-98 having a degree of hydrolysis of 98.4%; c) Mowiol 66-100 having a degree of hydrolysis of 99-7%; and d) Airvol 165 having a degree of hydrolysis of 99.3%. The pellets containing the various polyvinyl alcohols are each stirred in demineralized water at 30°C for 72 hours, the samples then filtered and the weight loss as a consequence of dissolution of the pellet determined. Table 3 below indicates that the starch compositions comprising high degree of hydrolysis polyvinyl alcohols are substantially resistant to dissolution, whereas those samples comprising relatively reduced degree of hydrolysis polyvinyl alcohol are considerably more soluble. The compositions according to Example 19 which are relatively water resistant are, for example, highly suitable for use in the preparation of sustained release fertilizer systems. TABLE 3 It will be appreciated that it is not intended to limit the invention to the above examples only, many variations thereto and modifications thereof being possible to one skilled in the art without departing from its scope, which is defined by the appended claims.

Claims: WHAT WE CLAIM IS: 1. A biodegradable composition as obtained from a melt comprising starch, a plasticizer, and at least one member selected from alkenol homopolymers and/or alkenol copolymers which are combined under conditions sufficient to ensure uniform melt formation, characterized in that the at least one member is present in the composition at a concentration of from 10 to 120 parts per 100 parts of dry starch. 2. A composition according to claim 1, wherein the starch has an amylose content of up to about 95%. 3. A composition according to the previous claim, wherein the starch has an amylose content of between about 70 and about 95%. 4. A composition according to claim 1, wherein the starch has an amylose content of up to about 65%. 5. A composition according to the previous claim, wherein the starch has an amylose content of up to about 45%. 6. A composition according to claim 4, wherein the starch has an amylose content of up to about 35%. 7. A composition according to claim 4, wherein the starch has an amylose content of at least about 15 to about 25%. 8. A composition according to claim 1, in which the composition comprises from about 10 to about 100 parts of said polymer per 100 parts of starch.. 9. A composition according to claim 1, in which the composition comprises from about 10 to about 85 parts of said polymer per 100 parts of starch. 10. A composition according to claim 1, in which the composition comprises from about 20 to about 40 parts of said polymer per 100 parts of starch. S 11. A composition according to claim 1, in which the alkenol homopolymer is polyvinyl alcohol. 12. A composition according to claim 11, in which the polyvinyl alcohol is substantially completely hydrolysed. 13. A composition according to claim 11, in which the polyvinyl alcohol is hydrolysed to an extent of from about 75 to about 100%. 14. A composition according to claim 11, in which the. polyvinyl alcohol is hydrolysed to an extent of from about 85 to about 99%. 15. A composition according to claim 11, in which the polyvinyl alcohol is hydrolysed to an extent of from about 87 to about 99.9%. 16. A composition according to claim 11, in which the polyvinyl alcohol has a number average molecular weight of from 15,000 to 250,000. 17. A composition according to claim 16, in which the polyvinyl alcohol has a number average molecular weight of from 15,000 to 150,000. 18. A composition according to claim 16, in which the polyvinyl alcohol has a number average molecular weight of from 160,000 to 250,000. 19. A composition according to claim 1, in which the polyvinyl alcohol has a degree of hydrolysis of at least about 97% and has a number average molecular weight of from about 15,000 to about 150,000. 20. A composition according to claim 19, in which the polyvinyl alcohol has a degree of hydrolysis of at least about 97% and has a number average molecular weight of from about 50,000 to about 150,000. 21. A composition according to claim 19, in which the polyvinyl alcohol has a degree of hydrolysis of at least about 97% and has a number average molecular weight of from about 70,000 to about 150,000. 22. A composition according to claim 19, in which the polyvinyl alcohol has a degree of hydrolysis of at least about 97% and has a number average molecular weight of from about 100,000 to about 150,000. 23. A composition according to claim 1, in which the alkenol homopolymer or copolymer is a pre-treated polyvinyl alcohol which has been obtained from a melt of polyvinyl alcohol which has been formed by adding sufficient energy to the polyvinyl alcohol to both melt it and substantially eliminate crystallinity in the melt, whilst simultaneously removing energy from the polyvinyl alcohol melt at a rate sufficient to avoid its decomposition. 24. A composition according to claim 1, further comprising an alkenol copolymer containing vinyl alcohol units and aliphatic chain units as obtained by co-polymerization of vinyl acetate with ethylene and/or propylene with subsequent hydrolysis of the vinyl acetate groups. 25. A composition according to the preceding claim, in which the copolymer comprises ethylene/vinyl alcohol. 26. A composition according to claim 24, in which the molar ratio of vinyl alcohol units to alkylene units is from about 40:60 to about 90:10. 27. A composition according to the preceding claim, in said molar ratio is from about 45:55 to about 70:30. 28. A composition according to claim 27, in which the ethylene vinyl alcohol has an ethylene content of 44%. 29. A composition according to claim 23, in which the pre-treated polyvinyl alcohol has a maximum melt 10 temperature, as determined by differential scanning calorimetry, which is at least about 5°C lower than that of the corresponding untreated polyvinyl alcohol. 30. A composition according to claim 29, in which the S maximum melt temperature is at least about 10°C lower than that of the untreated polyvinyl alcohol. 31. A composition according to claim 1, in which the composition further includes at least one member selected 0 from the group consisting of extenders, fillers, lubricants, mould release agents, plasticisers, stabilisers, coloring agents flame retardants, alkali or alkaline earth metal salts, and boron-containing * compounds. 32. A composition according to claim 31, in which said fillers are present in said composition at a concentration of between about 0.02% and about 20% by 0 weight, based on the weight of the composition. 33. A composition according to claim 32, in which said fillers are present in said composition at a concentration of between about 3 and about 10% by weight, based on the weight of the composition. 34. A composition according to claim 31, in which said plasticisers are present in said composition at a concentration of between about 0.5% and about 15% by weight, based on the weight of the composition. 35. A composition according to claim 34, in which said plasticisers are present in said composition at a concentration of between about 0.5% and about 5% by weight, based on the weight of the composition. 36. A composition according to claim 35, in which the sum of the plasticizer and water content of said composition does not exceed about 25% by weight, based on the weight of the composition. 37. A composition according to the preceding claim, in which the sum of the plasticizer and water content of said composition does not exceed about 20% by weight, based on the weight of the composition. 38. A composition according to claim 31, in which said coloring agents are present in said composition at a concentration of between about 0.01 and about 10% by weight, based on the weight of the composition. 39. A composition according to claim 31, in which said lubricants are selected from the group consisting of mono or diglycerides, lecithin and stearic acid. 40. A composition according to claim 39, in which the lubricant is stearic acid. 41. A composition according to the previous claim, in which the lubricant is present in the composition at a concentration of up to 10 parts per 100 parts of starch. 42. A composition according to the previous claim, in which the lubricant is present at a concentration of between 1 and 3 parts per 100 parts of starch. 43. A composition according to claim 39, in which the lubricant is present in the composition at a concentration of 1 part per 100 parts of starch. 44. A composition according to claim 1, in which the composition comprises a nucleating agent, having a particle size of from about 0.01 to about 5 microns, selected from the group consisting of silica, titania, alumina, barium oxide, magnesium oxide, sodium chloride, potassium bromide, magnesium phosphate, barium sulphate, aluminum sulphate, boron nitrate and magnesium silicate, or mixtures thereof. 45. A composition according to the previous claim, in which the nucleating agent is magnesium silicate (micro talcum). 46. A composition according to claim 44, in which the composition comprises up to 10 parts of agent per 100 parts of starch. 47. A composition according to claim 46, in which the composition comprises from 1 to 3 parts of said agent per 100 parts of starch. 48. A composition according to claim 47, in which the composition comprises 2 parts of said agent per 100 parts of starch. 49. A composition according to claim 39, in which the flame retardant is selected from the group consisting of guanidinium phosphate: diethyl-N,N-bis(2-hydroxyethyl) aminomethyl phosphonate; dimethyl methylphosphonate; phosphonic acid, methyl-, dimethylester, polymer with oxirane and phosphorous oxide; aliphatic phosphate/phosphonate oligomers; tributyl phosphate; triphenyl phosphate; tricresyl phosphate; 2-ethylhexyl diphenyl phosphate; and tributoxyethyl phosphate; bis (hydroxypropyl) sek.butyl phosphine oxide; polypropoxylated dibutyl pyrophosphoric acid; a mixture of phosphonic acid, methyl-, (5-ethyl-2-methyl-l,3,2-dioxaphosphorinan-5-yl)m- ethyl ethyl ester, P-oxide and phosphonic acid, methyl-, bis [ (5-ethyl-2-methyl-l,3,2-dioxaphosphorinan-5-yl)methyl] ester, P,P * -dioxide as sold under the trade name Amgard V19; ammonium polyphosphate; ethylendiamine polyphosphate; melamine phosphate; dimelamine phosphate; and microencapsulated red phosphorous. 50. A composition according to claim 49, wherein the »fl- retardant 1. a^oniuπ, polyphosphate or ethylendiamine polyphosphate or a mixture thereof. 51. A composition according to claim 50, wherein the ammonium polyphosphate or ethylenediamine polyphosphate IS are buffered with disodium orthophosphate. 52. A composition according to claim 39, wherein the flame retardant is selected from the group consisting of guanidinium sulfate; ammonium sulfate; ammonium 20 sulfamate; and tetrakis (hydroxymethyl) phosphonium sulfate. 53. A composition according to any claim 39, wherein the 23 flame retardant is present in the composition in an amount of from about 0.1 to about 10%, by weight with respect to that of the starch component of the composition. 30 54. A composition according to claim 52, wherein the flame retardant is present in the composition in an amount of from about 1 to about 6%, by weight with respect to that of the starch component of the composition. 35 55. A composition according to claim 54, wherein the flame retardant is present in the • composition in an amount of from about 2 to about 4% by weight with respect to that of the starch component of the composition. 56. A composition according to claim 31, in which the boron containing compounds are selected from the group consisting of boric acid, metaboric acid, alkali and alkaline earth metal salts, borax and derivatives thereof. 57. A composition according to claim 56, in which said compounds are present in the composition in an amount of between 0.002 and 0.4%, by weight with respect to that of the composition. 58. A composition according to claim 57, in which said compounds are present in the composition in an amount of between 0.01 and 0.3%, by weight with respect to that of the composition. 59. A composition according to claim 31, in which the inorganic salts of alkali or alkaline earth metals are present in an amount of from 0.1 to 5% by weight with respect to that of the composition, and are selected from the group consisting of LiCl and NaCl. 60. A composition according to claim 1, in which the starch is at least one member selected from the group consisting of native starches of vegetable origin, which starches are derived from potatoes, rice, tapioca, corn, pea, rye, oats, wheat, including physically modified starch, irradiated starch, starch in which mono-valent and di-valent ions associated with phosphate groups therein have been removed, either partly or wholly, and optionally replaced, either partly or wholly, by different divalent ions or with mono or polyvalent ions; pre-extruded starches and starches which have been so heated as to undergo the specific endothermic transition characteristically preceding oxidative and thermal degradation. 61. A composition according to any preceding claim which is in the form of a member selected from the group consisting of a melt, foam, film, granulate, pellet, and powder. 62. A composition according to claim 61, which is in the form of a foam. 10 63. A composition according to claim 62, in which the bulk density of the composition is in the range of about 3 8.5 to about 30kg/m . 64. A composition according to claim 62, in which the S resiliency of the composition is in the range of about 46 to 63%. 65. A composition according to claim 62, in which the compressibility of the composition is in the range of 0 about 6 to 15%. 66. A composition according to claim 61, in the form of a melt. 5 67. A composition according to claim 61, when used in the manufacture of shaped articles including bottles, films, pipes, rods, laminated films, sacks, bags, granules, powders, pellets, foams, containers, cartons, trays, cups, dishes, sheets, packaging materials, and foamed packaging materials -including loose fill. 68. A composition according to claim 1, when shaped by a process selected from the group consisting of foaming, 5 filming, compression molding, injection molding, blow molding, vacuum forming, thermoforming, extrusion, coextrusion, and combinations thereof. 69. A composition according to claim 1, when shaped by a foaming process. 70. A composition according to claim 1, when shaped by a filming process. 71. A composition according to claim 1, when injection molded. 72. A composition according to claim 1, when extruded or co-extruded. 10 73. A composition according to ' claim 1, when shaped by a process selected from the group consisting of compression molding, blow molding, vacuum forming, thermoforming, and combinations thereof. S 74. A method for producing the composition of claim 1, characterized by: a) providing a starting composition comprising starch, 0 a plasticizer and at least one member selected from alkenol homopolymers and/or alkenol copolymers which are present in the composition at a concentration of from 10 to 120 parts per 100 parts of said starch; 5 b) adjusting the plasticizer content of the composition to between about 0.5 and about 40% by weight of the total composition during processing or plastification; Q c) heating the thereby adjusted composition in a closed volume at a temperature of between 100 and 220°C and at a pressure corresponding at least to the moisture vapor pressure at said temperature for a time at least sufficient to form a melt of the composition; 5 d) removing any excess moisture before the extruder die to obtain a moisture content of between about 5% and about 20%; and - e) extruding the thereby heated composition. 75. The method of the preceding claim, in which the plasticizer is water. 76. The method of the preceding claim, wherein the plasticizer content in step b) is adjusted to between about 15 and about 40% by weight of the total composition, in which the obtained moisture content in step d) is between about 10% and about 20%, and in which 0 the heated composition optionally is extruded under conditions whereby the extrudate assumes a cross section greater than that of the exit orifice of the extruder die. S 77. The method of claim 82, in which the said at least one member comprises polyvinyl alcohol. 78. The method of the preceding claim, in which the Q alkenol homopolymer and/or copolymer is a pre-treated polyvinyl alcohol which has been obtained from a melt which has been formed by adding sufficient energy to the polyvinyl alcohol to both melt it and substantially eliminate crystallinity in the melt, whilst 3 simultaneously removing energy from the polyvinyl alcohol melt at a rate sufficient to avoid its decomposition. 79. The method of the preceding claim, in which the composition further comprises sodium acetate and 0 phosphoric acid in the molar ratio of about 1 to 2. 80. The method of claim 78, in which the pre-treated polyvinyl alcohol has a maximum melt temperature, as determined by differential scanning calorimetry, which is 5 at least about 5°C lower than that of the corresponding untreated polyvinyl alcohol. 81. The method of claim 78, in which at least about 0.27kWh/kg of specific energy is added to the polyvinyl alcohol during pre-treatment both to melt it and substantially eliminate crystallinity in the melt. 82. The method according to the preceding claim, in which the amount of specific energy is about 0.3 to 0.6kWh/kg. 83. The method of claim 75, in which, prior to extrusion, the moisture content of the composition is adjusted to from 10 to 20% by weight of the total composition and in which the composition is heated at a 10 temperature of from 100 to 200°C, and at a pressure corresponding at least to the moisture vapor pressure at said temperature for a time of from 0.5 to 2 minutes. 84. The method of claim 75, in which, prior to IS extrusion, the moisture content of the composition is adjusted to from 15 to 18% by weight of the total composition and in which the composition is heated at a temperature of from 150 to 200°C and at a pressure 2 Q corresponding at least to the moisture vapor pressure at said temperature for a time of from 0.5 to 1 minute. 85. The method of claim 76, in which, prior to extrusion, the moisture content of the composition is 23 adjusted to 17% by weight of the total composition and in which the composition is heated at a temperature of from 180 to 200°C and at a pressure corresponding at least. to the moisture vapor pressure at said temperature for a time of from 0.5 to 1 minute. 30 86. The method according to claim 82, in which the composition is heated to a temperature above the melting and glass transition temperature of the starch material. 35 87. The method of claim 75, wherein the starting composition optionally consists at least of the combination of starch and one member selected from alkenol homopolymers and copolymers which have been pre-combined under conditions sufficient to have formed a melt. 88. The method of the preceding claim, wherein the starting composition has been melted in the presence of from 15 to 40% moisture, by weight of the composition. 5 89. The method according to the preceding claim, wherein the starting composition has been melted at a temperature of from 100 to 200°C. 10 90. A method of shaping the composition of claim 1, selected from the group consisting of foaming, filming, compression molding, injection molding, blow molding, vacuum forming, thermoforming, extrusion, coextrusion, and combinations thereof. S 91. A method of shaping the composition of claim 66, selected from the group consisting of foaming, filming, compression molding, injection molding, blow molding, 0 vacuum forming, thermoforming, extrusion, coextrusion, and combinations thereof. 5 0 5

Inventors: BORCHERS GERD, DAKE INGO, DREIBLATT ADAM, RATHMER PETER, ZDRAHALA RICHARD, BORCHERS, GERD, DAKE, INGO, DREIBLATT, ADAM, RATHMER, PETER, ZDRAHALA, RICHARD
Applicants: PARKE DAVIS & CO, PARKE, DAVIS & COMPANY
Application year: 1992
Main classification: C08L3
IPC codes: C08J5, C08J9, C08L3, C08L29, C08L101