Effects of Acrylonitrile Content and Molecular Weight on the Scratch Behavior of Styrene-Acrylonitrile Random Copolymers

Fundamental understanding of the scratch behavior of styrene-acrylonitrile (SAN) random copolymers with variation in acrylonitrile (AN) content and molecular weight (MW) is pursued using the methodology outlined in ASTM D7027-05/ISO 19252:08. Two sets of SAN model systems are employed: One that varies the AN content with similar MW and another that varies the MW at the same AN content. Key scratch damage mechanisms (scratch groove formation, periodic micro-cracking, and plowing) are identified and correlated with the compressive and tensile properties of the SAN systems. Scratch visibility is analyzed through the use of a commercial software package. A fundamental structure-property relationship of SAN scratch behavior is proposed by the fact that increasing the AN content or the MW can have a positive effect on increasing the scratch resistance of SAN as it improves its tensile strength and ductility. The implication of material properties and their effect on polymer scratch behavior is discussed. POLYM. ENG. SCI., 51:2282-2294, 2011. (C) 2011 Society of Plastics Engineers