Biodegradable packaging foam and method of preparation

Claim 1

A method for producing a foamed packing material of biodegradable composition, comprising the steps of: a) selecting a dry, powdered, starch material having no greater than 30% (w) water content; b) admixing to the starch material a mild acid in dry, powdered form selected from the group consisting of malic acid, tartaric acid, citric acid, maleic acid and succinic acid, said acid being at a composition percentage of 0.2 to 7% (w) of the total starch composition; c) admixing to the starch material a dry, powdered carbonate composition capable of reacting with acid to generate CO2 gas, said carbonate composition being at a composition percentage of 0.1 to 2% (w) of the total starch composition; d) introducing the admixed dry materials of steps a), b) and c) within an initial stage of a screw impeller within an extrusion means; e) adding sufficient water to the dry materials of step d) at the initial stage of the impeller to convert the dry materials to a gelatinous state when subjected to elevated temperatures and pressures within the extrusion means; f) mixing and advancing the product of step e) within an extrusion barrel of the extrusion means to generate elevated heat and pressure for converting the material to the gelatinous state; g) concurrently reacting the acid within the extrusion barrel (i) with the starch material for decreasing molecular weight of the starch material while disrupting the uniformity of hydrogen bonding within and between starch chains, and (ii) with the carbonate material to produce CO2 for expanding the starch at reduced molecular weight and increased structural randomness of the starch chains; and h) discharging the product of step g) through a die opening to generate expansion of the CO2 to form a closed cellular structure having a density less than 0.032 grams per cubic centimeter and with resilient properties which enable substantial return of the compressed structure to its original, expanded shape with structural integrity.

Claim 2

A method for producing a foamed packing material of biodegradable composition, comprising the steps of: a) selecting a dry, powdered, starch material having no greater than 30% (w) water content; b) admixing to the starch material a mild acid in dry, powdered form selected from the group consisting of malic acid, tartaric acid, citric acid, maleic acid and succinic acid, said acid being at a composition percentage of 0.2 to 7% (w) of the total starch composition; c) admixing to the starch material a dry, powdered carbonate composition capable of reacting with acid to generate CO2 gas, said carbonate composition being at a composition percentage of 0.1 to 2% (w) of the total starch composition; d) introducing the admixed dry materials of steps a), b) and c) within an initial stage of a screw impeller within an extrusion means; e) adding sufficient water to the dry materials of step d) at the initial stage of the impeller to convert the dry materials to a gelatinous state when subjected to elevated temperatures and pressures within the extrusion means; f) mixing and advancing the product of step e) within an extrusion barrel of the extrusion means to generate elevated heat and pressure for converting the material to the gelatinous state; g) concurrently reacting the acid within the extrusion barrel (i) with the starch material for decreasing molecular weight of the starch material while disrupting the uniformity of hydrogen bonding within and between starch chains, and (ii) with the carbonate material to produce CO2 for expanding the starch at reduced molecular weight and increased structural randomness of the starch chains; and h) discharging the product of step g) through a die opening to generate expansion of the CO2 to form a closed cellular structure having a density less than 0.032 grams per cubic centimeter and with resilient properties which enable substantial return of the compressed structure to its original, expanded shape with structural integrity.