Surface and wear behavior of bis-(4-hydroxyphenyl) cyclohexane (bis-Z) polycarbonate/polycarbonate-polydimethylsiloxane block copolymer alloys

The utilization of block copolymers containing siloxane segments is well known to be of great interest for surface modifications. This paper focuses on the use of segmented bis-(4-hydroxyphenyl) cyclohexane (bis-Z) polycarbonate-polydimethylsiloxane copolymers as an additive to improve surface and wear properties of this non-crystallizable polycarbonate. The effects of chemical composition, block size, and casting solvent on surface and wear properties of the modified polycarbonate were elucidated by using angle-dependent X-ray photoclectron spectroscopy (XPS), tapping mode atomic force microscopy, and mechanical testing. XPS results showed that the siloxane segments were enriched on the surface even at bulk composition as low as 1 wt% siloxane, depending on siloxane block size and casting solvent. The friction coefficient was strongly dependent not only on the surface enrichment of siloxane but also on the molecular weight of siloxane block segment. The initial friction coefficient had a little influence on the overall wear resistance due to the rapid wear process of the uppermost surface. Instead, stress-strain behavior of the samples played a key role in the observed wear resistance. The latter first increased and then deteriorated with siloxane concentration. A modified Ratner model was successfully employed to interpret the results. (C) 2002 Published by Elsevier Science Ltd.