A study on the fracture characteristics of rubber toughened poly(ethylene terephthalate) blends

The fracture behaviour of poly(ethylene terephthalate) (PET) modified by a maleic anhydride grafted styrene/ethylene/butadiene/styrene rubber (MA-g-SEBS) was investigated under both quasi-static and impact rates of loading. Under quasi-static loading rate, linear elastic fracture mechanics (LEFM) and the essential work of fracture (EWF) analyses were used to determine the fracture toughness for PET and the MA-g-SEBS/PET blends, respectively. At this loading rate, it was observed that the incorporation of 10 wt% of rubber into PET changed the fracture mode from brittle to ductile. At 20 wt% of rubber addition, fracture toughness (expressed as the specific essential fracture work we) of the blend saturated and further increase of rubber content to 30 wt% did not improve the fracture toughness. The impact fracture toughness was determined from a conventional Charpy impact test. Contrary to results from the quasi-static loading rate fracture test, the blend containing up to 10 wt% of rubber still fractured in a brittle manner under impact. When the rubber content was up to 20 wt%, the blend became highly ductile. Both blends containing 20 and 30 wt% of rubber could not be completely broken during Charpy impact tests, and a prominent outer plastic zone had developed for these two blends. Under both quasi-static and impact tests, the toughening mechanisms in the blends are debonding between the rubber particles and PET and the subsequent cavitation of the PET around the debonding zone. However, the extent of PET cavitation was observed to be more severe under quasi-static loading than under impact testing.