Extrusion foaming of poly(lactic acid) blown with Co2:: Toward 100% green material

This paper presents a thorough investigation of the continuous extrusion foaming of amorphous poly(lactic acid) (PLA) using carbon dioxide (CO2) as the blowing agent. Detailed results describing the plasticization induced by CO2 dissolution as measured from two different methods, on-line rheometry and in-line ultrasonic technique, are given. Characteristics of the foams obtained from extrusion performed under various processing conditions are also reported. Extrusion of PLA foams in the 20-25 kg/m(3) density range was achieved. However, the associated processing window was very narrow: CO2 content lower than ca. 7 wt% did not lead to significant foam expansion while foams blown at CO2 contents larger than 8.3 wt% showed severe shrinkage upon ageing.