Study on the phase structures and toughening mechanism in PP/EPDM/SiO_2 ternary composites

摘要

In this paper,EPDM rubber and nano-SiO_2 particles were employed to modify PP simultaneously.Our goal was to control the distribution and dispersion of EPDM and nano-SiO_2 particles in PP matrix by using an appropriate processing method and adjusting the wettability of nano-SiO_2 particles toward PP and EPDM,so as to achieve a simultaneous enhancement of toughness and modulus of PP.With regard to this,two kinds of nano-SiO_2 particles (with hydrophilic or hydrophobic) as well as two processing methods (one-step or two-step) were employed to prepare PP/EPDM/SiO_2 ternary composites.A unique structure with the majority of EPDM particles surrounded by SiO_2 particles was first observed by using hydrophilic SiO_2 and two-step processing method,resulting in a dramatically increase of Izod impact strength as the rubber content in the range of brittle-ductile transition (15-20 wt%).The observation that poor adhesion and poor compatibility between particles and PP matrix could result in a significant increase in Izod impact strength was unusual and needed further investigation.This could be tentatively understood as a consequence of the overlap of the 'stress volume' between EPDM and SiO_2 particles due to the formation of the unique structure.Our work provided a deep understanding of the toughening mechanism and a new way for the preparation of high performance polymer composites.