Effect of supercritical carbon dioxide treatment on structure and mechanical properties of β-nucleated polypropylene processed at different temperatures

Polypropylene (PP) was compounded with beta-nucleating agent and injection-molded at 180 degrees C or 220 degrees C. The samples were subsequently treated by supercritical carbon dioxide (scCO(2)) at different temperatures. Results show that processing temperature and scCO(2) treatment could strongly influence the tensile and impact properties of beta-nucleated PP. In particular, the sample processed at 220 degrees C and treated at 120 degrees C exhibit much enhanced impact strength (4.8 times that of its untreated counterpart). RIR, WAXD, SEM and DMA were performed to explore the effects of processing temperature and scCO(2) treatment on structure of the samples. Deformation-induced plastic flow and micro-voids were also evaluated to construct structure-property relations. It was found that the influence of processing temperature on mechanical properties is mainly associated with the beta-form content and beta-crystalline morphology, while the structural changes in the crystalline lamellar scale may be responsible for the toughening effect of scCO(2) treatment. (C) 2017 Elsevier Ltd. All rights reserved.