Co-continuity and thermal expansion of injection-molded EPDM/PP blends with heterogeneous dispersion of nanoparticles

The effects of heterogeneous distribution of organoclay and silica nanoparticles on the co-continuity and thermal expansion of the injection-molded ethylene–propylene–diene terpolymer (EPDM)/isotactic polypropylene (PP) blends were investigated. The organoclay was selectively located in the EPDM domains regardless of the blending sequences, which significantly induced a fine but co-continuous microlayer structure. The silica nanoparticles were preferentially dispersed in the PP domains, and the addition of silica showed negative effects on the formation of the co-continuous structure. The coefficient of linear thermal expansion of the injection-molded EPDM/PP composites exhibited a sharp decrease with the addition of organoclay, whereas the silica-filled composites decreased linearly with the increasing amount of silica. This discrepancy in the thermal expansion behavior was further discussed based on considerations of various factors including PP crystallinity, the ratio of Young's modulus between EPDM and PP, aspect ratio of the PP microlayers, as well as their co-continuities. The co-continuity of the microlayer structure was shown to play a vital role in reducing the thermal expansion coefficient.