Foaming polypropylene prepared by a novel one-step silane-grafting and crosslinking method

Abstract

High-melt-strength polypropylene (HMSPP) used for foaming was prepared by a novel one-step of silane grafting and crosslinking of a normal isotactic polypropylene (IPP) in a twin-screw extruder. The HMSPP has been achieved using vinyl unsaturated silane with long chain as a grafting monomer, benzoyl peroxide (BPO) as an initiator, styrene as a coagent, trace amounts of water as a catalyst for crosslinking. The function of each agent in the formulation for the IPP modification was investigated. The results indicate that all of the agents are effective and necessary, and the proportions of the components, especially BPO, highly influenced the melt flow rate (MFR) of the HMSPP. Due to the presence of traced water in the system, the crosslinking of IPP is accompanied by the grafting of silane, which leads to a one-step production of crosslinked IPP. A high-qualified foam with uniform, closed and independent cells were fabricated from the HMSPP with appropriate MFR. With the decrement of the MFR of the HMSPP, the average size of the cells and the number of the unclosed cells decrease while the density of the cells increases.