Scratch Hardness of Polypropylenes: Effect of Applied Normal Force

Abstract

A set of model polypropylene (PP) and talc-filled PP with various lubricants were prepared to study the effects of normal force on the scratch hardness of polymers. The effects of additives and annealing treatment on the scratch behavior of neat and talc-filled PP systems were investigated using a multiple-finger scratch test with focus on the influence of applied normal force on the scratch hardness. A way to revise the scratch hardness test method based on ASTM G171-03 (standard test method for scratch hardness of materials using a diamond stylus; ASTM International; West Conshohocken, PA) and ASTM D7027-05 (standard test method for evaluation of scratch resistance of polymeric coatings and plastics using an instrumented scratch machine; ASTM International; West Conshohocken, PA) is given. Differential scanning calorimetry and optical microscopy were used to characterize crystallinity, morphology, and scratch deformation mechanisms in the PP systems. It was found that the scratch hardness is related to the applied normal loads, the friction coefficient, and the fracture features generated during the scratch process. The talc-filled impact copolymer polypropylene (ICPP) exhibited higher scratch hardness than the neat ICPP. Homo-PP exhibited superior scratch resistance and less susceptibility to scratch deformation than ICPP. The addition of lubricant and annealing treatment improved the scratch resistance of both neat and the talc-filled PP systems.