EFFECT OF ELASTOMER FUNCTIONALITY ON TOUGHENED PET

Poly(ethylene terephthalate) (PET) was blended with up to 5% of an SEB S elastomer. The elastomer was functionalized with 0 to 4.5wt% maleic anhydride grafted onto the ethylene-butylene midblock. Graft copolymer formed by reaction of PET hydroxyl end groups with the anhydride in s itu was thought to act as an emulsifier to decrease interfacial tensio n and promote adhesion. All the elastomers increased the melt viscosit y of PET, however the amount and functionality of the elastomer did no t have a large effect on blend theology. In contrast, particle size wa s strongly dependent on the elastomer functionality: the higher the fu nctionality, the smaller the particle size and the narrower the partic le sine distribution. Furthermore, elastomer content had less effect o n the particle size as the functionality increased, and the tendency t oward increasing particle size with increasing elastomer content dimin ished. These trends were attributed to an increase in the degree of gr afting on the in situ graft copolymer. Particles of functionalized SEB S were primarily spherical in injection moulded blends in contrast to the highly elongated particles of unfunctionalized SEBS. In un-notched tensile tests, blending PET with any SEBS elastomer enhanced the stab ility of the propagating neck. Notched tensile tests differentiated am ong the blends in terms of their toughness. The least effective elasto mer was the unfunctionalized SEBS. The most effective was the SEBS wit h only 1% anhydride. The decrease in toughness with increasing functio nality was attributed to decreasing particle size. (C) 1997 Elsevier S cience Ltd.