Influences of molecular weight and crystalline structure on fracture behavior of controlled-rheology-polypropylene prepared by reactive extrusion

Abstract

The molecular weight of ethylene- block- co-polypropylene (co-PP) was adjusted by reactive extrusion with the incorporation of dicumyl peroxide (DCP), and the effect of molecular weight on the crystallization behavior, crystal morphology, and fracture behavior was investigated. It was found that, with increasing DCP content, the molecular weight (MW) decreased and the polydispersity ( M w/ M n) slightly decreased. After modification, the number of spherulites with obscure boundaries increased, and the size of the spherulites was more even due to increasing amount of grafting and micro-cross-linking structures, generated in co-PP degradation, which were acting as nucleating agents. Evaluated by essential work of fracture method, the specific essential work of fracture, w e, was found to be strongly dependent on the molecular weight, especially, on the number average molecular weight ( M n) linearly, while the specific non-essential work of fracture, βw p, was enhanced with decreasing z-average molecular weight ( M z), probably owing to the reduction of ultra-high molecular weight component in degraded co-PP.