Extrusion Foaming of Poly(Lactic acid) Blown with CO ₂ : Toward 100% Green Material

This paper presents a thorough investigation of the continuous extrusion foaming of amorphous poly(lactic acid) (PLA) using carbon dioxide (CO 2 ) as the blowing agent. Detailed results describing the plasticization induced by CO 2 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: CO 2 content lower than ca. 7 wt% did not lead to significant foam expansion while foams blown at CO 2 contents larger than 8.3 wt% showed severe shrinkage upon ageing.