Influence of Surface Modification on Tribological Properties of Elastomer Composites

Friction of elastomer materials, apart their volume composition and structure, should be also considered from a point of view of their surface layer. Similarly, to the migration of low molecular weight components in rubber mixes, the surface segregation also takes place in polymer blends. The produced surface layer can either be of an amorphous or a crystalline character, lubricating the tribological contact or making it stiffer adequately, in the both cases acting to reduce friction. The surface hardness gradient of rubber vulcanizates is the result of the surface profile of their crosslink density and structure. It can be modified either by some changes to the composition of a curing system or by the application of an appropriate post-treatment, realized by various chemical and physical modifications (halogenation, plasma, laser or ion beam), very often accompanied by the changes to the surface microroughness and energy. Studies on the surface composition, structure and morphology and the related changes to hardness, microroughness and the surface energy of elastomer composites revealed a great potential to modify and/or to control their friction, what was discussed on some examples. The research methodology included an equilibrium swelling and a thiol-amine analysis, infra-red-, Raman-, X-rays photoelectron-, secondary ion mass- and Rutherford Back Scattering spectroscopies, atomic force-, scanning electron- and optical microscopies, a micro indentation, the surface profilometry and the contact angle determinations. The experimental results were correlated to the friction of various elastomer composites determined with a block-on-ring tribometer. The relations observed can be used for a knowledge-based designing of elastomer materials, their processing, modification and exploitation, enabling for tailoring friction of these materials.