A facile methodology to effectively improve the melt strength and microcellular foamability of isotactic polypropylene

摘要

Melt strength is crucial in foam-processing of polymer materials, especially for linear molecular structured isotactic polypropylene (iPP), which has comparatively weak melt strength to hinder its foaming. In this study, a commercial high melt strength polypropylene (HMSPP) was added into the iPP matrix, cooperated with a thermal treatment, aiming to enhance the melt strength and microcellular foamability of iPP under supercritical CO2. Melt strength enhancement effect was proved by rheological and microcellular foaming results. The crystallization and batch foaming behaviors of iPP and its HMSPP added blends at different foaming conditions were investigated. It was observed that the addition of HMSPP could refine the crystals of the blends, and the crystal nucleation sites could be increased apparently. Cooperated with the suitable thermal control schedule during the batch foaming process, the introduced crystals could correspondingly improve the melt strength and cell nucleating ability of HMSPP added iPP. At a given HMSPP content of 20 wt.%, quite fine microcellular foams with the average cell size of 0.8 mu m, and cell density up to 10(12) cells/cm(3) were fabricated.