Method of Producing Compostable or Biobased Foams

Abstract

The present invention describes compostable or biobased foams that are useful for fabricating foamed articles. 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 specific gravity less than 0.15 g/cm 3 and the foam is compostable, as determined by ASTM D6400.

1 . A method comprising:
 blending a melt processable composition comprising a compostable or biobased polymer with a blowing agent;   processing the composition in an extruder to form an extrudate; and   pelletizing the extrudate to form a bead of a substantially closed cell structure.   
     
     
         2 . The method of  claim 1 , said melt processable composition further comprising a nucleating agent. 
     
     
         3 . The method of  claim 1 , further comprising:
 extruding the extrudate through a nozzle die attached to an end of the extruder.   
     
     
         4 . The method of  claim 3 , the wherein the pelletizing occurs at the face of the die of the extruder. 
     
     
         5 . The method of  claim 3 , further comprising:
 cutting the extrudate with a rotary blade in contact with the front end surface of the nozzle die while allowing the extrudate to foam to produce foamed beads.   
     
     
         6 . The method of  claim 5 , wherein pelletization of the extrudate at the face of the extrusion die occurs prior to complete expansion of the extrudate foam. 
     
     
         7 . The method of  claim 5 , wherein said foamed beads have a density less than 0.3 g/cm 3 . 
     
     
         8 . The method of  claim 1 , wherein said blowing agent comprises a physical blowing agent. 
     
     
         9 . The method of  claim 1 , wherein said blowing agent comprises super critical CO 2 . 
     
     
         10 . The method of  claim 1 , said compostable polymer comprising a polymer of polylactic acid. 
     
     
         11 . The method of  claim 1 , further comprising:
 pressurizing the bead with a liquid or gaseous blowing agent.   
     
     
         12 . The method of  claim 11 , wherein said gas is selected from the group consisting of:
 air;   CO 2 ;   N 2 ; and   hydrocarbon.   
     
     
         13 . The method of  claim 5 , wherein foaming of the bead occurs after pelletization of the extrudate mixture of polymer and blowing agent. 
     
     
         14 . The method of  claim 1 , further comprising:
 moving the beads into a mold; and further expanding and fusing the beads in the mold by application of heat.   
     
     
         15 . The method of  claim 1 , wherein the bead is capable of holding an internal pressure inside the closed cell structure providing volumetric expansion of the foamed bead during heating. 
     
     
         16 . A method for producing a foamed molded product, comprising the steps of:
 creating foamed beads according to the method of  claim 5 ;   bringing the foamed beads under temperature and pressure conditions so that a foamed molded product is obtained.   
     
     
         17 . The method of  claim 16 , wherein the method uses heated gas to promote fusion of the foamed beads. 
     
     
         18 . The method of  claim 17 , wherein the method uses steam. 
     
     
         19 . The method of  claim 17 , wherein the method uses air or a mixture of air and steam.