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Atomic force microscopy (AFM) in tapping mode has been used to characterise surface damage on deformed polypropylenes induced during a scratch test. Atomic force micrographs revealed differences in microstructures that could be used to predict the deformation resistance of two different types of polypropylene. The undeformed surface of the two types of polypropylene (identi® ed as polypropylene-L and polypropylene-R) was characterised by differences in arrangement (regular or irregular) of ® brils depending on their melt¯ow conditions. Polypropylene-L is a polymer with longer chains and with restricted¯ow, whereas polypropylene-R has shorter chains obtained by controlled rheology. The micro® brils in undeformed polypropylene-L bend, forming raised surface features of height in the region of 10 ± 50 nm. In comparison to polypropylene-L, the micro® brils in undeformed polypropylene-R exhibited surface features of relatively lower height (10 ± 20 nm). 30630 nm scan AFM images provided details of micro® brils containing chains of molecules of~0 . 5 nm wide. Surface deformation induced by the scratch resulted in the formation of scratch tracks characterised by regions of quasi-periodic (consecutive) cracking. This type of deformation is attributed to higher applied loads or to higher contact strains. This is particularly important in semicrystalline polymers, where there is partial reorganisation of microstructure on the application of surface stresses because of their viscoelastic properties. Atomic force micrographs of mechanically deformed polypropylene-L and polypropylene-R at a scan size of 161 l m indicated a lesser amount of reorganisation of microstructure in polypropylene-L as compared with polypropylene-R. Surface pro® les and section analysis of the AFM micrographs suggested that polypropylene-R is more scratch resistant in comparison to polypropylene-L under identical scratch test conditions, consistent with Raman spectroscopy observations of tensile deformed polypropylene.MST/5253

The surface damage induced during tensile deformation of polyethylene at different strain rates was studied by atomic force microscopy (AFM) operated in tapping mode, before and subsequent to uniaxial tensile plastic deformation. Atomic force microscopy revealed striking differences in the deformed microstructures up to the nanoscale range. The surface of undeformed polyethylene was characterised by ribbonlike ® brils of width 0 . 25 m m and surface features of height about 20 ± 60 nm. Fibrils were considered to consist of micro® brils of width 0 . 03 ± 0 . 04 m m. Small scan (30630 nm) AFM images provided details of micro® brils containing chains of molecules of ~0. 5 nm wide. Tensile deformation in the plastic region involved stretching of ® brils and micro® brils resulting in the formation of surface openings. The ability of the ribbonlike surface ® brils and micro® brils to stretch, merge, and acquire an oriented and ¯at structure increased with increase in strain rate in the uniaxial tensile test. Also, with increase in strain rate the chains of molecules unfold and align to produce an oriented and elongated structure. The impact of deformation on amorphous regions could only be observed at high strain rates.MST/5140

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