Toughening Effect of Ethylene Propylene DieneTerpolymer-Graft-Styrene-Acrylonitrile Copolymer (EPDM-g-SAN) on SAN Resin

The reaction product EPDM-g-SAN, synthesized by suspension graft copolymerization of styrene (St) and acrylonitrile (AN) in the presence of ethylene-propylene-diene terpolymer (EPDM), was blended with a commercial styrene-acrylonitrile copolymer (SAN resin) to prepare AES blends with high impact strength. The effects of AN mass percentage in the St-AN comonomer mixture (f (AN)), EPDM mass percentage in the feed of EPDM and St-AN (f (EPDM)) and reaction time on monomer conversion ratio (CR), grafting ratio (GR), and AES notched Izod impact strength were characterized. The notched Izod impact strength of AES containing 15wt% EPDM reached its maximum with f (AN) of 40wt% and f (EPDM) of 45wt%; this was attributed to the polarity of the SAN copolymer obtained being appropriate with that of the SAN resin matrix. The dependences of GR and the notched Izod impact strength of AES containing 25wt% EPDM on the reaction time were in rough agreement. The effect of EPDM content on the AES notched Izod impact strength indicated that the brittle-ductile transition of AES occurred for an EPDM content from 12.5 to 15wt%. TEM and SEM analysis showed that the phase structure of AES exhibited a "salami" like structure, and the toughening mechanism of AES was shear yielding of the SAN resin matrix, which endowed AES with excellent toughness.