FRACTURE MECHANISMS OF POLY(ETHYLENE-TEREPHTHALATE) AND BLENDS WITH STYRENE-BUTADIENE-STYRENE ELASTOMERS

Poly(ethylene terephthalate) (PET) was blended with 5 wt % of an elast omeric block copolymer. The hydrogenated styrene-butadiene-styrene (SE ES) elastomers were functionalized with 0-4.5 wt % maleic anhydride gr afted on the midblock. Notched tensile tests in the temperature range -40-55 degrees C differentiated among the blends in terms of their tou ghness. The least effective elastomer was the unfunctionalized SEES; a ll the functionalized SEES elastomers effectively increased the toughn ess of PET. Fractographic analysis indicated that PET and the blend wi th unfunctionalized SEES fractured through a pre-existing craze. Altho ugh adhesion of the unfunctionalized SEES to the matrix was poor, the elastomer strengthened the craze somewhat, as indicated by an increase in length of the pre-existing craze when final separation occurred. A functionalized SEES caused the fracture mechanism to change from craz ing to ductile yielding. Graft copolymer formed by reaction of PET hyd roxyl end groups with the anhydride in situ was thought to act as an e mulsifier to decrease particle size and improve adhesion. These factor s promoted cavitation, which relieved the triaxiality at the notch roo t and permitted the matrix to shear yield.