Effect of Temperature on Foaming Behaviors of Homo- and Co-polymer Polypropylene/Polydimethylsiloxane Blends with CO2

Poly(dimethylsiloxane) (PDMS) was blended with two different types of polypropylene (PP). The blends were subsequently batch-foamed with supercritical CO 2 at a series of temperatures that varied by a narrow increment of 2°C to investigate the effect of the foaming temperature on foaming. In the case of the random copolymer PP, it was found that the cell density of the blends containing PDMS increased significantly and good cell structures could be obtained across a wide temperature spectrum. PDMS typically generated high CO 2 concentration and low surface tension, which positively impacted the cell nucleation. In the case of linear homopolymer PP, the addition of PDMS did not result in any pronounced improvement to cell morphology; however, at very low temperatures, much lower than the melting point, a few very small cells appeared. In both experiments, the addition of maleic anhydride grafted PP (PP-g-MAH) as a compatibilizer promoted the dispersion of PDMS and yielded a better cell morphology within a specific temperature range. Moreover, the presence of a compatibilizer enhanced the melt strength, which in turn served to broaden the processing window.