Effect of moisture exposure on scratch resistance of polymers
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Copyright (2014) by the Society of Plastics Engineers. Effects of moisture exposure on scratch performance of polymethylmathacrylate (PMMA) and polypropylene (PP) were investigated. Three different grades of PMMA and PP with varying levels of polarity and molecular weight were chosen and their scratch resistance compared in both dry and moist conditions. Linear increasing load scratch tests were performed according to ASTM D7027/ISO 19252 standards. Results indicate a drop in scratch resistance with initial exposure to moisture in all three PMMA systems. In the two highly polar PMMA systems, the scratch resistance recovers to that of the dry condition after exposure to moisture while PP scratch resistance remains unchanged. It is proposed that the moisture absorbed initially acts as a plasticizer causing weakening of the surface for PMMA. In the case of more polar systems this moisture absorption continues until saturation where water molecules cluster and impart a degree of lubrication and consequently improve scratch resistance.