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Improving foam ability of polypropylene by crosslinking



In this study, silane crosslinked polypropylene (PP) was prepared by grafting of silane onto the backbone of PP in a melt process using a twin-screw extruder and then crosslinking in warm water; an attempt was made to improve the melt strength of PP. In the present work, benzoyl peroxide was used as initiator, silane as a monomer, styrene as assisted crosslinking agent. PP foam board with well-distributed and fine blowing hole was prepared by compression molding technology, employing azodicarbamide as blowing agent, talcum powder as nucleation agent. The effects of silane and peroxide concentration on the silane crosslinked PP were investigated. The surface morphology of the foam was accomplished by scanning electron microscopy (SEM). The thermal behavior of the silane crosslinked PP was studied by differential scanning calorimetry (DSC) and the elastic response was investigated by dynamic mechanical analysis (DMA). The melt strength of the silane crosslinked PP was characterized by tension strength at high temperature tests. The results showed that the melt strength of the crosslinked PP was significantly enhanced, whereas melt flow rate, sag resistance, and tension strength at high temperature tests facilitated the foam formation. DSC analysis showed that the crystallization temperature of the silane crosslinked PP was increased compared with pure PP, which leads to high melting temperature and increased crystallinity. The results revealed that high melt strength PP(HMSPP) could be prepared by a method of silane crosslinking. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011