Toughening PET by blending with a functionalized SEBS block copolymer

Toughened poly(ethylene terephthalate) (PET) was obtained by blending with 1-5wt% of a triblock copolymer with styrene end blocks and a functionalized ethylene/butylene midblock. The midblock was grafted with 2wt% maleic anhydride. The blends were characterized for melt viscosity, domain morphology, and tensile stress-strain behaviour at two strain rates. Blending increased the fracture strain of PET by more than a factor of 10. The fracture strain was affected to some extent by both blend composition and processing conditions. However, neither blend composition nor processing conditions strongly influenced the melt viscosity of the blend or the particle size in the blend. These observations are consistent with in situ formation of a graft copolymer by reaction of PET hydroxyl end groups with maleic anhydride. The graft copolymer acted as an emulsifier to decrease the interfacial tension and reduce the tendency of dispersed particles to coalesce, and promoted adhesion between the phases in the blend. Evidence for the presence of a graft copolymer was obtained by i.r. analysis of blend extracts. (C) 1997 Elsevier Science Ltd.