Study of surface damage of polypropylene under progressive loading

A systematic study of surface damage exerted by a progressive scratching load is performed on model polypropylene (PP) systems. Mar-scratch and stress-whitening transitions can be readily observed, and the corresponding critical loads determined. Distinctive surface damage features are determined before and after the transitions. The progressive load test enables the scratch hardness values to be obtained using the graphical method, thereby allowing scratch resistance to be accurately quantified and ranked among materials. Visibility of the scratched surface is quantified using a gray level analysis via a flatbed scanner and a commercial image analysis tool. It is found that the onset of scratch visibility can be determined accurately and reproducibly using the custom-built scratcher under progressive loading condition. Exposed talc particles on the surface of talc-filled PP are found to be responsible for the increased light scattering, leading to greatly increased visibility. The observed scratch visibility is also found to be related to the corresponding friction force profiles. Approaches for producing scratch resistant PP are discussed.