Extrusion-foaming in the presence of carbon dioxide of branched polylactide: relationship composition - rheological behavior - crystallization

This work investigates the effect of macromolecular chain-branching on polylactide (PLA) rheology, crystallization, and foamability. An amorphous and a semicrystalline PLA were branched using a multifunctional styrene-acrylic-epoxy copolymer. The branching of PLA and its foaming were achieved in one-step extrusion process. Carbon dioxide, CO2, with concentration up to 9%, was used as expansion agent to obtain foams from the two PLA branched using chain-extender contents up to 2%. The foamed materials were investigated with respect to their shear and elongational behavior, crystallinity, morphology, and density. The addition of the chain-extender led to an increase in complex viscosity, elasticity, elongational viscosity, and in the manifestation of the strain-hardening phenomena. Low-density foams were obtained starting from 5% CO2 for semicrystalline PLA and only at 9% CO2 in the case of the amorphous PLA. The differences observed between the foaming behaviours and foam microstructures of the two PLA grades were due to their different crystallization behaviours.Peer reviewed: YesNRC publication: Ye