The CO2 pressure and temperature were then increased to the final saturation temperature, Tsat, and saturation pressure, psat, which were maintained for a certain time, t, according to previous studies on PLA foaming.25,26 In the present case, psat was set to 200 bar for all the tests, and Tsat to 155C, 165C( t¼10 min) or 190C( t¼20 min) for the chain-extended materials. Cell nucleation and growth (foam expansion) were initiated by the thermodynamic instability created by depressurization.