Manufacture of polylactic acid foams using liquid carbon dioxide

Abstract

Methods of producing CO 2 -impregnated crystallisable polylactic acid resins and expanded polylactic acid foams.

1 . A method of producing CO 2  impregnated crystallisable polylactic acid resin, the method comprising
 providing a crystallisable polylactic acid resin, and   contacting the resin with liquid CO 2  at a temperature of about −57° C. to about 2° C. to impregnate the resin with CO 2 .   
     
     
         2 . A method of  claim 1  wherein the CO 2  concentration of the resin after impregnation is up to about 55% by weight. 
     
     
         3 . A method of producing polylactic acid foam, the method comprising
 providing a crystallisable polylactic acid resin that has been impregnated with liquid CO 2  at a temperature of about −57° C. to about 2° C., and   expanding the impregnated resin to produce a foam.   
     
     
         4 . A method of  claim 3 , wherein the foam has a density of about 5 to about 200 g/L. 
     
     
         5 . A method of  claim 4 , wherein the foam exhibits a volumetric shrinkage of less than about 35% at 70° C. 
     
     
         6 . A method of  claim 5 , further comprising holding the impregnated resin under conditions to prevent a significant increase in crystallinity prior to the expanding step. 
     
     
         7 . A method of  claim 6 , further comprising holding the impregnated resin at a temperature and pressure that prevents the resin from expanding while allowing the level of impregnated CO 2  to reduce to about 5 to 35% by weight prior to the expanding step. 
     
     
         8 . A method of  claim 3 , wherein the CO 2  concentration of the impregnated resin immediately before expansion is up to about 35% by weight. 
     
     
         9 . A method of  claim 3 , wherein the expanding step comprises pre-expansion, pre-expansion then moulding, or moulding without pre-expansion. 
     
     
         10 . A method of  claim 3 , wherein the expanding step comprises heating the impregnated polylactic acid resin at a temperature of about 15° C. to about 140° C. 
     
     
         11 . A method of  claim 1 , wherein the PLA comprises at least about 88% by weight L- or D-lactic acid or is a blend of poly(L-lactic acid) and poly(D-lactic acid) homopolymer, or a blend of PLA block copolymers where each block has an isomer purity of greater than 88% of L-lactic acid or D-lactic acid. 
     
     
         12 . A method of  claim 1 , wherein the resin comprises a PLA copolymer, a PLA block copolymer, a PLA homopolymer or a blend of PLA with one or more other polymers. 
     
     
         13 . A method of  claim 1 , wherein the impregnated resin is in the form of a particle, bead, rod, bar, sheet, film, moulded shape or extruded shape. 
     
     
         14 . A method of  claim 1 , wherein the resin further comprises one or more fillers, additives, nucleating agents, plasticisers or co-blowing agents, or any combination of any two or more thereof. 
     
     
         15 . A method of  claim 6 , wherein impregnation step, the holding step, or the impregnation step and the holding step are conducted at a temperature at or below the glass transition temperature of the resin. 
     
     
         16 . An expanded polylactic acid foam comprising a density of less than about 200 g/L and a volumetric shrinkage of less than about 35% at 70° C. 
     
     
         17 . A foam of  claim 16  comprising at least about 88% by weight L or D lactic acid or a blend of poly-L-lactic acid and poly-D-lactic acid homopolymer, or a blend of PLA block copolymers where each block has an isomer purity of greater than 88% of L-lactic acid or D-lactic acid. 
     
     
         18 . A foam of  claim 16  further comprising one or more fillers, additives, nucleating agents, plasticisers or co-blowing agents, or any combination of any two or more thereof. 
     
     
         19 . A foam of  claim 16 , wherein the foam exhibits linear shrinkage of less than about 5% up to a temperature of about 70° C. when subjected to a compressive force of about 10 kPa. 
     
     
         20 . A foam of  claim 16 , wherein the resin has a crystallinity of less than about 20% by weight. 
     
     
         21 . A foam of  claim 16 , wherein the resin has a crystallinity of less than about 15% by weight. 
     
     
         22 . A foam of  claim 16 , wherein the crystallinity of the expanded resin or foam is at least about 5% by weight. 
     
     
         23 . A method of  claim 3 , wherein the foam exhibits linear shrinkage of less than about 5% up to a temperature of about 70° C. when subjected to a compressive force of about 10 kPa. 
     
     
         24 . A method of  claim 3 , wherein the resin has a crystallinity of less than about 20% by weight. 
     
     
         25 . A method of  claim 3 , wherein the resin has a crystallinity of less than about 15% by weight. 
     
     
         26 . A method of  claim 3 , wherein the crystallinity of the expanded resin or foam is at least about 5% by weight.