Impact fracture morphology of copolyester toughened with a maleited core-shell impact modifier

A maleited impact modifier (TPEg) with polyethylene-octene rubber shell and semi-crystalline polymer core was used to toughen non-crystalline copolyester (PETG) resin. TPEg has a significant toughening effect on PETG. A sharp transition from brittle to super-tough states for PETG/TPEg blends occurred when the TPEg content was up to 10%. Although the maleited polyethylene-octene rubber (POEg) also results in a brittletough transition, this transition takes place at a higher POEg content indicating that the loss of thensile strength and modulus of PETG blends in more serious. The effects of TPEg on impact toughness of PETG blends are well reflected from their evolution processes of topography and morphology formed during the impact fracture testing. The impact fractured surface of PETG blend with 5 wt% TPEg exhibits a very small area of its slow crack growth region and feather-like markings in its fast crack growth region under low magnification, indicating a brittle appearance. Whereas the impact fractured surface of PETG blend with 10wt% TPEg exhibits a very large area of its slow crack growth region and some parabola-like markings in its fast crack growth region under low magnification. Moreover, an extensive shear yielding of matrix can be seen both in the slow and the fast crack growth regions of the PETG/TPEg(90/10) blend under high magnification. It may dissipate a significant amount of impact energy,thereby responsible for the super toughness.