Dual Role of PDMS on Improving Supercritical CO2 Foaming of Polypropylene: CO2-philic Additive and Crystallization Nucleating Agent

Abstract A systematic study was done to screen for the polydimethylsiloxane (PDMS) with molecular weight (Mw) from 770 g/mol to 17,000 g/mol to optimize the supercritical CO2 foaming process of semi-crystalline polypropylene (PP). The solubility and diffusion measurements demonstrated that the high solubility and slow desorption rate of CO2 were achieved in PP/PDMS blends via incorporating PDMS. Rheology results showed the viscosity of PP/PDMS blends increased with the increase of Mw of PDMS. The crystallization behaviors of PP and PP/PDMS blends were thoroughly investigated in the presence of CO2. PDMS with Mw from 4000 g/mol to 9000 g/mol enhanced the crystallization of the blend evidently. Since PDMS with medium Mw could work as a CO2-philic additive and crystallization nucleating agent in PP, the resultant foams exhibited a more uniform cellular morphology with smaller cell size (decreased from 23 to 13 μm) and higher cell density compared with that of PP foam.