Micro- and nanoscale evaluation of scratch damage in poly(propylene)s

The technique of atomic force microscopy (AFM) has been used to obtain comparative evaluation of scratch damage in polymeric materials (low- and high-crystallinity poly(propylene)s and ethylene-propylene diblock copolymers) and examine the surface deformation process. A comparative assessment of scratch damage is made in terms of average surface height of the plastically deformed region, and the depth thickness, and density of the scratch tracks. The resistance to scratch deformation under identical conditions of scratch test follows the sequence: high-crystallinity poly(propylene)s > low-crystallinity poly (propylene)s > ethylene-propylene diblock copolymers. Additionally, short-chain polymers are characterized by a greater resistance to mechanical deformation than their respective long-chain polymers. The scratch tracks in low and high-crystallinity poly(propylene)s are zig-zag in shape, while in ethylene-propylene diblock copolymers they are parabolic with localized plastic flow involving voids. The AFM observations suggest that higher tensile modulus and higher yield stress are key factors responsible for superior resistance to mechanically induced deformation in high-crystallinity poly)propylene)s.