Dual role of PDMS on improving supercritical CO2 foaming of polypropylene: CO2-philic additive and crystallization nucleating agent

•PDMS increases CO2 solubility and diffusion coefficient in PP/PDMS blends.•PDMS decreases CO2 desorption rate in PP/PDMS blends.•PDMS with Mw of 4000 g/mol to 9000 g/mol enhances crystallization of PP.•PDMS with Mw of 4000 g/mol to 9000 g/mol optimizes cellular structure of PP foam.