Simultaneous enhancements of toughness and tensile strength for thermoplastic/elastomer blends through interfacial photocrosslinking with UV radiation

Hongjun Xu, Yaqiong Zhang, Jingjing Yang, Lei Ye, Qianghua Wu, Baojun Qu, Qiao Wang and Zhigang Wang*

Polym. Chem., 2013, 4, 3028-3038

An easy procedure to introduce a photocrosslinked interface for polypropylene (PP)/maleic anhydride grafted styrene-b-(ethylene-co-butylene)-b-styrene triblock copolymer (mSEBS) thermoplastic/elastomer blends by UV radiation is reported. This procedure involves free-radical crosslinking at the interface between the mSEBS domain phase and the PP matrix phase and in the mSEBS phase domains with benzophenone (BP) as the photoinitiator and triallyl isocyanurate (TAIC) as the crosslinking agent. Compared with the absence of photocrosslinking, the structured PP/mSEBS blends with photocrosslinked interfaces confirmed by rheological measurements demonstrate simultaneous enhancements of toughness and tensile strength because of the enhanced interfacial adhesion and the more rigid mSEBS particle-like phase domains due to photocrosslinking. The tensile strength for the PP/mSEBS thermoplastic/elastomer blends with photocrosslinking increases with increasing mSEBS contents even at high mSEBS contents, and eventually approaches that for neat PP. Furthermore, the ultimate elongation at break increases with increasing crosshead speed, opposite to the general observation in that polymers tend to become brittle with increasing crosshead speed, indicating an enhanced tensile resistance for the UV radiation treated PP/mSEBS thermoplastic/elastomer blends. The procedure reported here is promising for preparing high-performance polymer blends used in high impact fields. For the purpose of comparison, PP/ethylene-propylene-diene rubber (PP/EPDM) blends were subjected to the same studies, however, the above observed simultaneous enhancements of toughness and tensile strength for the PP/mSEBS blends are completely absent for the PP/EPDM blends, simply because the UV radiation-induced interfacial crosslinking between the dispersed EPDM phase domains and the PP matrix phase does not occur.