Batch foaming of chain extended PLA with supercritical CO2: Influence of the rheological properties and the process parameters on the cellular structure

This study has been dedicated to the foaming of modified poly (lactic acid) with supercritical CO₂. The first part of this work consisted in a rheological modification of neat PLA through chain extension. Improvement of the melt viscosity and elasticity has been achieved by the use of an epoxy additive during a reactive extrusion process. Rheological characterizations confirmed an increase of the melt strength due to this chain extension process. Foaming was then performed on the neat and modified PLAs using a batch process with supercritical CO₂ as blowing agent. The investigation of the foaming temperature revealed an enlarged processing window for modified PLAs compared to neat PLA. Depending on the foaming parameters, foams with a cellular structure ranging from macro scale to micro scale have been obtained. A concomitant effect of the CO₂-plasticization and the crystallisation on the melt rheology could explain this wide range of cellular morphologies.