Foaming PLA with Thermoplastic Starch by Extrusion Assisted by Supercritical CO 2

The manufacture of biopolymers foams with poly-lactic acid (PLA) and thermoplastic starch (TPS) using the green process of extrusion assisted by supercritical CO 2 is a promising way towards new applications. A parametric study evidenced that the porosity is strongly correlated with the die temperature, CO 2 content and TPS load. To get a high porosity, die temperature has to be diminished to block the gas escape from the extrudate sample. This reduction in temperature was only feasible when it was associated to an increase in CO 2 content to lower melt viscosity in the extruder. Higher TPS content led to foam samples with lower porosity, due to a weaker melt strength which in turn favoured the CO 2 escape instead of forming pores. Finally, for the 80 % PLA-20 % TPS blend, porosity as high as 96 % has been obtained.