Structure and Properties of Reactive Extruded Ethylene-block-co-Polypropylene: Influence of Dicumyl Peroxide and Divinylbenzene

The reaction of an ethylene-block-co-polypropylene (co-PP) with a polyfunctional monomer—divinylbenzene (DVB)—in the presence of dicumyl peroxide (DCP) was performed in a single screw extruder. It was found that the chain structure of co-PP was significantly influenced by the DVB concentration when the DCP content was fixed. Without DVB, degradation of co-PP chains, induced by DCP, mainly occurred. But when DVB was incorporated, reactions of crosslinking and branching prevailed in the system. The crystallization temperature of the modified co-PP was enhanced and the number of spherulites was increased, accompanied with a decrease of the spherulite size, due to the branched and crosslinked structure. The essential work of the fracture (EWF) method was adopted to characterize the fracture performance of the modified co-PP. The specific essential work of fracture, w_e, first decreased gradually to a minimum, and then climbed with increasing DVB concentration, which might be attributed to the variations of the length of the DVB segment (LDS) acting as the crosslinking node and the spherulite size of co-PP. The specific, nonessential work of fracture, β w_p, of the modified co-PP was elevated to some extent with an increasing concentration of DVB. It was speculated that the crosslinked and branched structures favored stress transfer among molecular chains and spherulites, which was beneficial to the enlargement of the plastic deformation zone.