Classifications

• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08L—COMPOSITIONS OF MACROMOLECULAR COMPOUNDS
  • C08L3/00—Compositions of starch, amylose or amylopectin or of their derivatives or degradation products
  • C08L3/12—Amylose; Amylopectin; Degradation products thereof
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08L—COMPOSITIONS OF MACROMOLECULAR COMPOUNDS
  • C08L29/00—Compositions of homopolymers or copolymers of compounds having one or more unsaturated aliphatic radicals, each having only one carbon-to-carbon double bond, and at least one being terminated by an alcohol, ether, aldehydo, ketonic, acetal or ketal radical; Compositions of hydrolysed polymers of esters of unsaturated alcohols with saturated carboxylic acids; Compositions of derivatives of such polymers
  • C08L29/02—Homopolymers or copolymers of unsaturated alcohols
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08L—COMPOSITIONS OF MACROMOLECULAR COMPOUNDS
  • C08L29/00—Compositions of homopolymers or copolymers of compounds having one or more unsaturated aliphatic radicals, each having only one carbon-to-carbon double bond, and at least one being terminated by an alcohol, ether, aldehydo, ketonic, acetal or ketal radical; Compositions of hydrolysed polymers of esters of unsaturated alcohols with saturated carboxylic acids; Compositions of derivatives of such polymers
  • C08L29/02—Homopolymers or copolymers of unsaturated alcohols
  • C08L29/04—Polyvinyl alcohol; Partially hydrolysed homopolymers or copolymers of esters of unsaturated alcohols with saturated carboxylic acids
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08L—COMPOSITIONS OF MACROMOLECULAR COMPOUNDS
  • C08L3/00—Compositions of starch, amylose or amylopectin or of their derivatives or degradation products
  • C08L3/02—Starch; Degradation products thereof, e.g. dextrin
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08L—COMPOSITIONS OF MACROMOLECULAR COMPOUNDS
  • C08L3/00—Compositions of starch, amylose or amylopectin or of their derivatives or degradation products
  • C08L3/04—Starch derivatives, e.g. crosslinked derivatives
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08L—COMPOSITIONS OF MACROMOLECULAR COMPOUNDS
  • C08L2201/00—Properties
  • C08L2201/06—Biodegradable

Definitions

• 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.
• 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.
• 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.
• 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.
• One method 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.
• 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.
• the present invention provides, inter alia, such an alternative.
• Ind. Eng. Chem. Prod. Res. Dev. (194; 23, page 594-595) describes the extrusion of starch extended water-soluble polyvinyl alcohol.
• 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 t ⁇ e 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.
• thermoplastics 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.
• 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.
• 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.
• plasticizer includes solvent plasticisers, non-solvent plasticisers and internal plasticisers.
• 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.
• 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 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.
• 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.
• 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
• 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.
• 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.
• compositions 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.
• 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;
• 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 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.
• 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).
• 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.
• 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.
• 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.
• 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.
• 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.
• 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.
• 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.
• ethylene/vinyl alcohol polymers EVOH
• 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.
• the lower limit for the amylose content of the starch preferably is about 10 to about 15%, likewise by weight.
• 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.
• 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.
• 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.
• the polymer or copolymer for example the polyvinyl alcohol
• 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 polymer or copolymer for example polyvinyl alcohol
• 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.
• 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.
• 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.
• 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
• 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.
• water-soluble synthetic polymers such as: poly(acrylic acids) and their salts and essentially water soluble « poly(
• 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 -
• 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 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.
• 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.
• 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;
• 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%.
• composition may further comprise flame retardants- which, for example, comprise phosphorous, sulphur and halogens, or mixtures thereof.
• 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.
• 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 decab
• 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 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 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.
• 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.
• thermoplastic melts on heating under conditions of controlled temperature and pressure.
• the present invention also refers to such processes when used to shape the composition or melt of the present invention.
• 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.
• 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 starch 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.
• 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
• 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
• 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 process for forming the composition of the present invention into foams comprises:
• 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.
• composition may be molded subsequent to its extrusion using known thermoforming processes.
• 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.
• a twin screw extruder Leistritz model LSM 34
• 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 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.
• the extrudate 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.
• Example 1 is repeated, but with different quantities of 3polyvinyl alcohol.
• 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 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.
• 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.
• 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:
• 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 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.
• This Example describes the injection molding of candle cups from an extruded blend of polyvinyl alcohol and starch.
• 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.
• 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:

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• 1992
  • 1992-03-13 BR BR9205783A patent/BR9205783A/pt not_active Application Discontinuation
  • 1992-03-13 AU AU17595/92A patent/AU656586B2/en not_active Ceased
  • 1992-03-13 EP EP92910383A patent/EP0578759A1/en not_active Withdrawn
  • 1992-03-13 CA CA002105479A patent/CA2105479A1/en not_active Abandoned
  • 1992-03-13 HU HU9302633A patent/HUT66562A/hu unknown
  • 1992-03-13 WO PCT/US1992/002004 patent/WO1992016584A1/en not_active Application Discontinuation
  • 1992-03-13 JP JP4510594A patent/JPH06508866A/ja active Pending
  • 1992-03-13 BR BR9205781A patent/BR9205781A/pt not_active Application Discontinuation
  • 1992-03-13 CA CA002105480A patent/CA2105480A1/en not_active Abandoned
  • 1992-03-13 JP JP4509064A patent/JPH06507193A/ja active Pending
  • 1992-03-13 HU HU9302632A patent/HUT66717A/hu unknown
  • 1992-03-13 AU AU16845/92A patent/AU1684592A/en not_active Abandoned
  • 1992-03-13 EP EP92909925A patent/EP0581843A1/en not_active Withdrawn
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  • 1992-03-18 IL IL101282A patent/IL101282A0/xx unknown
  • 1992-03-18 IL IL101283A patent/IL101283A0/xx unknown
  • 1992-03-18 IE IE085492A patent/IE920854A1/en unknown
  • 1992-03-18 IE IE085592A patent/IE920855A1/en unknown
  • 1992-03-19 CN CN92102949.7A patent/CN1067253A/zh active Pending
  • 1992-03-19 CN CN92103117.3A patent/CN1066077A/zh active Pending
  • 1992-03-19 PT PT100266A patent/PT100266A/pt not_active Application Discontinuation
  • 1992-03-19 PT PT100265A patent/PT100265A/pt not_active Application Discontinuation
  • 1992-03-19 MX MX9201222A patent/MX9201222A/es unknown
• 1993
  • 1993-09-17 FI FI934094A patent/FI934094A/fi not_active Application Discontinuation
  • 1993-09-17 FI FI934095A patent/FI934095A0/fi not_active Application Discontinuation

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