V. Tanrattanakul et al., FRACTURE MECHANISMS OF POLY(ETHYLENE-TEREPHTHALATE) AND BLENDS WITH STYRENE-BUTADIENE-STYRENE ELASTOMERS, Journal of Materials Science, 32(18), 1997, pp. 4749-4758
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.