Influence of surface roughness and contact load on friction coefficient and scratch behavior of thermoplastic olefins
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To study the effects of surface roughness and contact load on the friction behavior and scratch resistance of polymers, a set of model thermoplastic olefins (TPO) systems with various surface roughness (R a ) levels were prepared and evaluated. It is found that a higher R a corresponds to a lower surface friction coefficient ( s ). At each level of R a , s gets larger as contact load increases, with a greater increase in s as R a level increases. It is also observed that with increasing contact load and increasing R a , the s tend to level off. In evaluating TPO scratch resistance, a lower s would delay the onset of ductile drawing-induced fish-scale surface deformation feature, thereby raising the load required to cause scratch visibility. However, as the contact load is further increased, the s evolves to become scratch coefficient of friction (SCOF) as significant sub-surface deformation and tip penetration occur and material displacement begins, i.e., ploughing. No dependence of R a and s on the critical load for the onset of ploughing is observed. In this work, the distinction between s and SCOF will be illustrated. Approaches for improving scratch resistance of polymers via control of R a are also discussed. 2008 Elsevier B.V. All rights reserved.
