Atomic force microscopy characterisation of scratch deformation in long and short chain isotactic polypropylenes and ethylene-propylene copolymers

Abstract

Surface damage induced during the scratch process in two different grades of high isotactic (high crystallinity) polypropylenes, long and short chain, has been examined by atomic force microscopy (AFM) and scanning electron microscopy (SEM). Atomic force microscopy enabled qualitative and quantitative prediction of the extent of scratch damage, by analysing AFM images before and after scratch deformation. Surface deformation induced by the scratch test on long and short chain high isotactic polypropylenes involved the formation of zigzag scratch tracks. Scratch tracks were regular in long chain and irregular/nonuniform in short chain high isotactic polypropylenes. The line profile and section analysis of AFM images indicated that short chain high isotactic polypropylene is more resistant to mechanically induced surface damage than long chain high isotactic polypropylene. Furthermore, a comparison of scratch damage behaviours of high isotactic polypropylenes, low isotactic polypropylenes, and ethylene-propylene copolymers indicated that the resistance to scratch deformation follows the sequence: high isotactic (high crystallinity) polypropylenes > low isotactic (low crystallinity) polypropylenes > ethylene-propylene copolymers.