Compostable or biobased foams

Abstract

The present invention describes compostable or biobased foams that are useful for fabricating foamed articles and methods for producing the same. The foams are produced using a compound comprising a compostable or biobased polyester and a blowing agent. Additives including plasticizers and chain extenders are optionally included in the compostable or biobased composition. These foams can be produced using conventional melt processing techniques, such as single and twin-screw extrusion processes. In one embodiment, foamed strand profiles are cooled and cut using conventional strand pelletizing equipment. In another embodiment, foamed beads are produced by cutting the foamed strand at the face of the extrusion die and the foamed bead or strand is subsequently cooled. The resulting compostable or biobased foamed bead has a density less than 0.15 g/cm3 and the foam is compostable, as determined by ASTM D6400.

What is claimed is: 
     
         1 . A method of making a molded article, comprising:
 forming biobased polymer foam beads;   pressurizing the biobased polymer foam beads in a sealed vessel;   depressurizing the sealed vessel;   feeding the biobased polymer foam beads into a mold; and   molding the biobased polymer foam beads to form a molded article,   wherein the biobased polymer foam beads undergo a secondary expansion during molding, and   wherein the molded article has a density of less than or about 0.03 g/cm 3 .   
     
     
         2 . The method of  claim 1 , wherein the step of forming the biobased polymer foam beads comprises:
 mixing a feed composition and a blowing agent in an extruder to form a biobased polymer melt,   wherein the extruder has a temperature that is above a melting point of the feed composition.   
     
     
         3 . The method of  claim 2 , wherein the feed composition comprises:
 a nucleating agent in an amount from about 0.5% to about 5% by weight;   a chain extender in an amount from about 0.1% to about 10% by weight; and   polylactic acid in an amount of at least 40% by weight.   
     
     
         4 . The method of  claim 2 , wherein the step of forming the biobased polymer foam beads further comprises:
 extruding the biobased polymer melt by forcing the melt through an extrusion die opening to form an extrudate,   wherein a temperature of an exit of the extrusion die is lower than a melting temperature of the biobased polymer melt, and   wherein the blowing agent expands within the extrudate upon exiting the extrusion die opening.   
     
     
         5 . The method of  claim 4 , wherein the step of forming the biobased polymer foam beads further comprises:
 cutting the extrudate at a face of the extrusion die to produce the biobased polymer foam beads.   
     
     
         6 . The method of  claim 4 , wherein extruding the biobased polymer melt induces crystallization without the use of an annealing step. 
     
     
         7 . The method of  claim 5 , wherein the biobased polymer foam beads have a density of less than about 0.045 g/cm 3 . 
     
     
         8 . The method of  claim 1 , wherein the step of pressurizing the biobased polymer foam beads in a sealed vessel comprises pressurizing the biobased polymer foam beads at about 0.45 MPa for less than 30 minutes. 
     
     
         9 . The method of  claim 1 , wherein the step of depressurizing the sealed vessel comprises a rapid depressurization. 
     
     
         10 . The method of  claim 1 , wherein the step of depressurizing the sealed vessel produces biobased polymer foam beads having an internal pressure exceeding atmospheric pressure. 
     
     
         11 . The method of  claim 1 , wherein the step of feeding the biobased polymer foam beads into a mold is performed within 1 minute of removal from the sealed vessel. 
     
     
         12 . The method of  claim 1 , wherein the step of feeding the biobased polymer foam beads comprises heating the mold to an initial temperature of 25° C. 
     
     
         13 . The method of  claim 1 , wherein the step of feeding the biobased polymer foam beads comprises vacuum feeding. 
     
     
         14 . The method of  claim 1 , wherein the step of molding the biobased polymer foam beads comprises purging the mold for 1 second at 0.55 bar steam pressure. 
     
     
         15 . The method of  claim 14 , wherein the step of molding the biobased polymer foam beads further comprises subjecting the mold to a cross steam process for 20 seconds at 0.55 bar steam pressure. 
     
     
         16 . The method of  claim 15 , wherein the step of molding the biobased polymer foam beads further comprises subjecting the mold to a second cross steam process in which a direction of steam flow is reversed for 20 seconds at 0.65 bar. 
     
     
         17 . The method of  claim 16 , wherein the step of molding the biobased polymer foam beads further comprises applying cooling water for 15 seconds, followed by applying cooling air for 30 seconds at 4 bar. 
     
     
         18 . The method of  claim 17 , wherein the step of molding the biobased polymer foam beads further comprises subjecting the mold to vacuum for 5 seconds. 
     
     
         19 . The method of  claim 1 , wherein the step of molding the biobased polymer foam beads comprises subjecting the mold to a cross steam process. 
     
     
         20 . The method of  claim 1 , wherein the step of molding the biobased polymer foam beads comprises applying a cooling water followed by applying a cooling air.