Rubber content effect on scratch behavior in acrylonitrile-styrene-acrylate copolymers

The scratch behavior of butyl-acrylate rubber-modified styrene-acrylonitrile thermoplastics is investigated following the ASTM D7027 linearly increasing normal load test methodology. The critical normal loads at the onset of the major transitions along the scratch path, such as groove formation, scratch visibility, microcrack formation, and plowing, are reported and quantitatively analyzed. It is found that the scratch resistance generally deteriorates with increasing butyl-acrylate rubber content, and is strongly related to the tensile and compressive yield stresses of the blends. Microscopy investigation indicates that a rubber content of up to 30 wt % in a styrene-acrylonitrile copolymer (SAN) does not alter the scratch-induced damage mechanisms, but only reduces the critical onset loads for the observed damage transitions. The present finding suggests that addition of rubber causes reductions in modulus, tensile, and compressive yield stresses, thus leading to deterioration in scratch resistance. It appears that the improvement in ductility for SAN after the rubber toughening does not benefit scratch resistance. Implication of rubber toughening on scratch behavior of polymers is discussed. (c) 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012