ADHESION ENHANCEMENT IN IMMISCIBLE POLYMER BILAYER USING ORIENTED MACROSCOPIC ROUGHNESS

The use of oriented macroscopic roughness to enhance the effective adh esion between two immiscible polymers was demonstrated. Bilayer specim ens of polycarbonate and poly(styrene-co-acrylonitrile) (SAN) were pro duced with rough interfaces by scribing grooves of varying depths and spacings into the polycarbonate (PC) before joining the layers. The SA N, having a significantly lower glass transition temperature than poly carbonate, flows into the grooves during annealing at temperatures jus t over the PC glass transition, creating a mechanically interlocking i nterface. Subsequent measurements of bilayer interfacial fracture toug hness showed up to a twenty-fold increase from that of a smooth interf ace when grooves were oriented perpendicular to the direction of inter facial crack propagation. The increase in toughness was shown to be gr eater as grooves were spaced closer together, and as groove depths wer e increased. Propagation of interface cracks followed a stick-slip mec hanism, slowing considerably at each groove. Analysis of fracture surf aces indicates the increase in toughness to be mainly due to cohesive failure and deformation of the polymers at the grooves. Interface toug hness was also enhanced with grooves scribed parallel to the propagati on direction, but to a lesser degree than with perpendicular orientati on. Copyright (C) 1996 Elsevier Science Ltd.