LAP SHEAR ADHESION OF STYRENIC TRIBLOCK COPOLYMERS TO POLYPROPYLENE AND POLYSTYRENE

Shear mode adhesive strength of several styrenic triblock copolymers t o Polypropylene (PP) and Polystyrene (PS) was examined as a function o f midblock structure, styrene content, and molecular weight. A modifie d lap shear test was designed to allow adhesive strength measurement i n strongly adhering adhesive joints where, in the conventional lap she ar test, tensile failure in one of the adherends occurred before the a dhesive strength was attained. To both substrates, the adhesive streng th was highest for poly(ethylenebutylene) midblock (S-EB-S), followed by polyisobutylene midblock (S-IB-S), polybutadiene midblock (S-B-S), and finally polyisoprene midblock (S-I-S). For the S-IB-S copolymers, as the styrene content and molecular weight increased the adhesive str ength increased to the PS substrate but remained nearly constant to th e PP substrate. Lap shear adhesive strength was related to the nanosca le block copolymer morphology. Adhesive strength increased as the adhe ring phase of the triblock, styrene when bonding to PS and the rubber midblock when bonding to PP, became more continuous.