Biodegradable pellets foamed by irradiation

Abstract

This invention relates to biodegradable starch-based pellets which foamable by irradiation, which are particularly suitable for the manufacture of foam articles, characterised in that they have a porous structure with a low porous external skin. This invention also relates to foam articles obtained from these.

1 . Biodegradable low density, self-sealing pellets foamable by irradiation particularly suitable for the production of foamed articles, said pellets comprising starch essentially free of native crystallinity which does not have endothermic gelatinisation peaks associated with a ΔH of more than 0.4 J/g of dry starch when analysed by differential scanning calorimetry in a hermetic capsule with a water/dry starch ratio of 4, said pellets being characterised by:
 a porous internal structure having void area greater than 15% with respect to the area of the cross-section of the pellet; 
 a mean equivalent diameter of pores less than 100 microns and 
 an external skin with pores in number less than 80% with respect to the internal structure having a mean equivalent diameter lower or equal to the mean equivalent diameter of the pores of the internal structure. 
 
     
     
         2 . Biodegradable pellets according to  claim 1 , wherein the fact of comprising at least a further polymer of synthetic or natural origin. 
     
     
         3 . Biodegradable pellets according to  claim 2 , wherein the fact of comprising:
 10-99.5% by weight of starch essentially devoid of native crystallinity,   0.5-90% by weight of at least a further polymer of synthetic or natural origin,   0.1-60% by weight of water,   with respect to the total weight of the dry pellet.   
     
     
         4 . Biodegradable pellets according to  claim 2 , wherein said further polymer of natural origin is selected from cellulose, lignin, proteins, phospholipids, casein, polysaccharides, natural gums, rosinic acid, dextrins, their mixtures and derivatives thereof. 
     
     
         5 . Biodegradable pellets according to  claim 2 , wherein said further polymer of synthetic origin is selected from:
 thermoplastic polymers comprising homopolymers and copolymers of linear or branched aliphatic hydroxyacid having C2-C24 main chain, their lactons and lactides as well as their copolymers with aliphatic polyesters of the diacid/diol type;   vinyl polymers comprising polyvinyl alcohol with various degrees of hydrolysis, possibly modified with acrylates or methacrylates, polyvinyl alcohol-co-vinylacetate block and random copolymers with degree of hydrolysis >70%, preferably higher than 80 and even preferably higher than 85 mol %, polyvinyl alcohol plasticized or modified for the purpose of lowering its melting point, polyvinylacetate, copolymers of vinylacetate at various degrees of hydrolysis with vinylpyrrolidone and/or styrene, polyethyloxazoline or polyvinylpiridine;   polycarbonates;   ethylene-vinyl alcohol copolymers, preferably with up to 50% by weight of ethylenic units, copolymers of ethylene with vinyl acetate or unsaturated acids, polyamides 6, 6-6, 6-9, 6-10, 9, 9-9, 10, 10-10, 11,11-11, 12, 12-12 and their mixtures, aliphatic polyurethanes, random and block copolymers polyurethane-polyamide, polyurethane-polyether, polyurethane-polyesters, polyamide-polyether, polyamide-polyester, polyester-polyether and epoxy resins;   random and block aliphatic and aliphatic-aromatic polyesters and copolyesters of the diacid/diol type;   synthetic rubbers;   non biodegradable polymers such as polyolefins, aromatic polyesters, polyvinylchloride, polystyrene, acrylonitrile-butadiene-styrene copolymers;   polyoxyalkylenes with molecular weight >50000.   
     
     
         6 . Biodegradable pellets according to  claims 5 , wherein said further polymer of synthetic origin is a polyvinyl alcohol-co-vinylacetate copolymer with degree of hydrolysis >70 mol %. 
     
     
         7 . Biodegradable pellets according to  claim 1 , wherein said pores are characterized by a mean equivalent diameter of less than 50 μm, 
     
     
         8 . Biodegradable pellets according to  claim 1 , wherein the fact of showing, when conditioned to a water content of 22±2% by weight with respect to the total weight of the dry composition, a density <1.1 g/cm3 and higher than 0.5 g/cm3. 
     
     
         9 . Biodegradable pellets according to  claim 1 , wherein said starch shows an intrinsic viscosity higher than 1.5 dl/g and lower than 3 dl/g. 
     
     
         10 . Process for the preparation of biodegradable low density, self-sealing pellets foamable by irradiation wherein:
 a porous internal structure having void area greater than 15% with respect to the area of the cross-section of the pellet;   a mean equivalent diameter of pores less than 100 microns and   an external skin with void area lower than 15%, with respect to the area of the external skin of the pellet.   said process being characterized by the fact of comprising the steps of:   (a) feeding a composition comprising starch and water to an extruder,   (b) extruding said composition to form a melt and at an extrusion rate, residence time and shear rate at the outlet suitable to destroy the native crystallinity of the starch and to produce a swelling followed by collapsing of the extrudate on leaving the nozzle,   (c) cutting the collapsed extrudate into the form of pellets soon after the exit from the die in such a way that the extrudate is cut when it is not yet completely solidified to seal possible open pores and reconstitute a skin at the cut surface,   (d) conditioning said pellets in order to adjust the moisture content at level between 10 and 45%, with respect to the total dry weight of a pellet by exposure to air at room temperature or higher.   
     
     
         11 . Foamed articles obtained by irradiation of the biodegradable pellets according to  claim 1 , wherein the fact of showing an intrinsic viscosity in the range 1.9-3 dl/g. 
     
     
         12 . Foamed articles according to  claim 11 , wherein the fact of showing density of less than 80 kg/m 3 . 
     
     
         13 . Use of the foamed articles according to  claim 11 , for producing protective packaging for home appliances, products for the electronic industry, furnitures, food packaging, agricultural packaging. 
     
     
         14 . Biodegradable pellets according to  claim 3 , wherein said further polymer of natural origin is selected from cellulose, lignin, proteins, phospholipids, casein, polysaccharides, natural gums, rosinic acid, dextrins, their mixtures and derivatives thereof. 
     
     
         15 . Biodegradable pellets according to  claim 3 , wherein said further polymer of synthetic origin is selected from:
 thermoplastic polymers comprising homopolymers and copolymers of linear or branched aliphatic hydroxyacid having C2-C24 main chain, their lactons and lactides as well as their copolymers with aliphatic polyesters of the diacid/diol type;   vinyl polymers comprising polyvinyl alcohol with various degrees of hydrolysis, possibly modified with acrylates or methacrylates, polyvinyl alcohol-co-vinylacetate block and random copolymers with degree of hydrolysis >70%, preferably higher than 80 and even preferably higher than 85 mol %, polyvinyl alcohol plasticized or modified for the purpose of lowering its melting point, polyvinylacetate, copolymers of vinylacetate at various degrees of hydrolysis with vinylpyrrolidone and/or styrene, polyethyloxazoline or polyvinylpiridine;   polycarbonates;   ethylene-vinyl alcohol copolymers, preferably with up to 50% by weight of ethylenic units, copolymers of ethylene with vinyl acetate or unsaturated acids, polyamides 6, 6-6, 6-9, 6-10, 9, 9-9, 10, 10-10, 11,11-11, 12, 12-12 and their mixtures, aliphatic polyurethanes, random and block copolymers polyurethane-polyamide, polyurethane-polyether, polyurethane-polyesters, polyamide-polyether, polyamide-polyester, polyester-polyether and epoxy resins;   random and block aliphatic and aliphatic-aromatic polyesters and copolyesters of the diacid/diol type;   synthetic rubbers;   non biodegradable polymers such as polyolefins, aromatic polyesters, polyvinylchloride, polystyrene, acrylonitrile-butadiene-styrene copolymers;   polyoxyalkylenes with molecular weight >50000.   
     
     
         16 . Biodegradable pellets according to  claim 4 , wherein said further polymer of synthetic origin is selected from:
 thermoplastic polymers comprising homopolymers and copolymers of linear or branched aliphatic hydroxyacid having C2-C24 main chain, their lactons and lactides as well as their copolymers with aliphatic polyesters of the diacid/diol type;   vinyl polymers comprising polyvinyl alcohol with various degrees of hydrolysis, possibly modified with acrylates or methacrylates, polyvinyl alcohol-co-vinylacetate block and random copolymers with degree of hydrolysis >70%, preferably higher than 80 and even preferably higher than 85 mol %, polyvinyl alcohol plasticized or modified for the purpose of lowering its melting point, polyvinylacetate, copolymers of vinylacetate at various degrees of hydrolysis with vinylpyrrolidone and/or styrene, polyethyloxazoline or polyvinylpiridine;   polycarbonates;   ethylene-vinyl alcohol copolymers, preferably with up to 50% by weight of ethylenic units, copolymers of ethylene with vinyl acetate or unsaturated acids, polyamides 6, 6-6, 6-9, 6-10, 9, 9-9, 10, 10-10, 11,11-11, 12, 12-12 and their mixtures, aliphatic polyurethanes, random and block copolymers polyurethane-polyamide, polyurethane-polyether, polyurethane-polyesters, polyamide-polyether, polyamide-polyester, polyester-polyether and epoxy resins;   random and block aliphatic and aliphatic-aromatic polyesters and copolyesters of the diacid/diol type;   synthetic rubbers;   non biodegradable polymers such as polyolefins, aromatic polyesters, polyvinylchloride, polystyrene, acrylonitrile-butadiene-styrene copolymers;   polyoxyalkylenes with molecular weight >50000.   
     
     
         17 . Biodegradable pellets according to  claim 2 , wherein said pores are characterized by a mean equivalent diameter of less than 50 μm, 
     
     
         18 . Biodegradable pellets according to  claim 3 , wherein said pores are characterized by a mean equivalent diameter of less than 50 μm, 
     
     
         19 . Biodegradable pellets according to  claim 4 , wherein said pores are characterized by a mean equivalent diameter of less than 50 μm, 
     
     
         20 . Biodegradable pellets according to  claim 5 , wherein said pores are characterized by a mean equivalent diameter of less than 50 μm,