Rheology and phase structure of PP/EPDM/SiO2 ternary composites

In this article, the rheological properties of polypropylene (PP)/ethylene–propylene–diene terpolymer (EPDM)/silicon dioxide (SiO2) ternary composites were systematically investigated. Two kinds of nano-SiO2 particles (with hydrophobic (denoted as A-SiO2) or hydrophilic (denoted as B-SiO2)) as well as two processing methods (one-step or two-step) were first employed to prepare PP/EPDM/SiO2 ternary composites. Then the deep mixing and morphology evolution of polymer composite with mixing time were assessed by rheological method, on the focus of formation of filler-network, and compared with scanning electron microscopy (SEM) observations. Linear viscoelastic behavior was observed for PP/EPDM and PP/SiO2 binary system, showing no evidence of the formation of filler-network structure. However, a solid-like rheological behavior, which was attributed to the formation of the filler-network structure as confirmed by SEM observation, could be observed in some PP/EPDM/SiO2 ternary systems, depending on the SiO2 surface property, processing method and EPDM content. It seemed that SiO2 with hydrophilic surface was necessary for the formation of filler-network in PP/EPDM/SiO2 ternary system. Besides, two-step processing method made the solid-like behavior occurred at an earlier stage compared with that of a one-step processing method, also, the higher elastomer content facilitated the formation of the filler-network structure. The results were in good agreement with those reported in our previous publications [Yang H, Zhang Q, Guo M, Wang C, Du R, Fu Q. Polymer 2006;47:2106] [Yang H, Zhang X, Qu C, Li B, Zhang L, Zhang Q, et al. Polymer 2007;48:860].