Morphology prediction and the effect of core‐shell structure on the rheological behavior of PP/EPDM/HDPE ternary blends

In this work, the morphologies of polypropylene (PP)/ethylene‐propylene‐diene (EPDM) rubber/high density polyethylene (HDPE) 70/20/10 blends were studied and compared with the predictions of the spreading coefficient and minimum free energy models. The interfacial tension of PP/HDPE, PP/EPDM, and HDPE/EPDM blends were obtained by fitting the experimental dynamic storage modulus data to Palierne's theory. The prediction results showed core‐shell morphology (core of HDPE and shell of EPDM) in PP matrix. The PP/EPDM/HDPE blends were respectively prepared by direct extrusion and lateral injection method. Core‐shell morphology (core of HDPE and shell of EPDM) could be obtained with direct extrusion corresponding to the predicted morphology. The morphology of PP/EPDM/HDPE blends could be effectively controlled by lateral injection method. For PP/EPDM/HDPE blend prepared by lateral injection method, HDPE and EPDM phase were dispersed independently in PP matrix. It was found that the different morphology of PP/EPDM/HDPE blends prepared by two methods showed different rheological behavior. When the core‐shell morphology (core of HDPE and shell of EPDM) appeared, the EPDM shell could confine the deformation of HDPE core significantly, so the interfacial energy contribution of dispersed phase on the storage modulus of blends would be weaken in the low frequency region. POLYM. ENG. SCI., 2011. © 2011 Society of Plastics Engineers