The effects of an epoxide-based chain-extender (CE) on the properties of poly(lactic acid) (PLA) foams obtained by chemical foaming extrusion using 4 wt.% of chemical foaming agent (CFA) were studied. PLA/CE blends with different weight ratios of CE were initially processed using a co-rotating twin-screw extruder. PLA/CE foams were then produced using a single-screw extruder. Various PLA/CE foams characterizations, including solution viscosity, thermal properties (DSC, TGA), cellular structure (void fraction, cell size, open cell content), mechanical and dynamic rheological behaviors, were investigated. Results show that the addition of CE enhances the viscosimetric average molecular weight and rheological properties (viscosity and storage modulus) of PLA, but it has no significant effects on the thermal properties of PLA, except the occurring of a cold crystallization. The CE incorporation also led to a decrease in the void fraction of cellular PLA, in the cell size and in the open cell content and to an increase in the cell density. Furthermore, the tensile mechanical properties such as yield stress and elongation at break of cellular materials increased with the addition of CE.

The present study aims at assessing the extrusion foaming characteristics of two commercial grades of poly(lactic acid) (PLA) using a chemical foaming agent (CFA). For each PLA the process was optimized based on a maximal void fraction criterion. The extruder die temperature significantly affects the void content (maximal for about 195 C). An increase in the barrel temperature profile was also correlated with an increase in the void fraction. Moreover an increase in CFA concentration increased the PLA void fraction, and in some cases induced a decrease in cell density and an increase in cell size. Finally, an optimal value of 47% void fraction was obtained. Finally, optimally processed PLAs with varying CFA contents were tensile tested. The results pointed out that it was possible to observe significant decrease in the density and increase in some specific mechanical properties by controlling the extrusion foaming process.