Reactive extrusion foaming of poly(lactic acid): tailoring foam properties through controlling in-process chemical reactions

A continuous extrusion foaming process was performed on poly(lactic acid) (PLA) in the presence of different chemical foaming agents (CFAs) and a chain extender additive using different extruder barrel and die temperature profiles. Chemical reactions, which are involved in the extrusion foaming process of PLA, are intensely investigated to control the reactive extrusion process and tailor the foam final properties. A set of experiments was designed using the response surface methodology to evaluate the effects of material and processing parameters and optimize the PLA foam property. The results showed that the maximum void fraction, i.e. 0.55, was obtained by exothermic CFA at higher extruder temperatures. In contrast to the exothermic CFA, the addition of endothermic CFAs did not result in lightweight biodegradable foams. The void fractions of these extruded foams were less than 0.05. The presence of water molecules as a by-product of the decomposition reaction and also relatively lower decomposition temperatures of the endothermic CFAs have been considered as the main reasons. Among the variables studied, the CFA type had the strongest impact on the foam properties. In the second step, the barrel and die temperatures were adjusted accordingly.