On compatibilization and toughening of a copolyester with a maleated thermoplastic elastomer

Abstract

A maleated thermoplastic elastomer (TPEg) was prepared from maleic anhydride, grafting a mixture of polyethylene–octene elastomer and semi-crystalline polyolefin plastic (60/40 by weight) in a twin screw extruder. The non-grafted version (TPE) of the mixture was also prepared under the same processing conditions. The TPEg was employed to compatibilize and toughen amorphous copolyester PETG/TPE blends. The addition of the TPEg improves the compatibility between PETG and the TPE and results in fine dispersion of the TPE in the PETG matrix. At a fixed dispersed phase content of 15 wt%, a sharp brittle–ductile transition takes place, when the TPEg content in the dispersed phase increases from 20 to 30 wt%, namely, the TPEg content in the blends increases just from 3 to 4.5 wt%. After the brittle–ductile transition, the blends are maintained at super-tough level with notched impact strength more than twenty-fold higher than that of pure PETG plastic. The influence of the TPEg content on fractography of the PETG/TPE blends was also investigated. When the TPEg content in dispersed phase is below 20 wt%, the impact fracture surface shows a small area of slow crack growth region and numerous feather-like markings in fast crack growth region, indicating a brittle failure mode. While the TPEg content in the dispersed phase is above 30 wt%, the impact fracture surface exhibits drastically enlarged slow crack growth region and some parabolic markings in the fast crack growth region. Massive cavitation and extensive matrix shear yielding are predominant mechanisms of the impact energy dissipation upon impact testing.