To characterize an activity of silica toward elastomers usually the parameters of the filler structure and a possibility of its interactions with macromolecules of a matrix are taken into consideration [1,2,3]. As a rule, low molecular weight substances of different polarity are dissolved in a rubber mix (e.g. accelerators, activators, crosslinking substances, etc). They undergo adsorption on the surface of active fillers what exerts an effect on a structure of a network formed and influences mechanical properties of vulcanizates at the same time.
Surface migration of the carboxylic acids (C 10 H 21 COOH, C 11 H 23 COOH, C 12 H 25 COOH, C 15 H 31 COOH, C 16 H 33 COOH, and C 17 H 35 COOH) in styrene-butadiene rubber (SBR) matrix was investigated together with its influence on tribological properties of the vulcanisates. Macro-and microtribological properties were correlated with properties that come from carboxylic acid addition to the samples. A plastifying effect was characterized by a decrease of the rubber glass transition temperature measured by the DSC method. Thickness of an acid bloom was directly determined from an indentation experiment and estimated from the DSC curve as well as from FTIR reflection spectra. Morphology of the bloom was studied using an AFM technique to characterize topography as well as microroughness of the bloom surface. Macrofriction was studied using block-on-ring tribometer. Microfriction was examined with a Nano Test apparatus, applying ball-on-plate contact. Despite correlation found between plastification, morphology, and bloom thickness on the one hand, and tribologic properties of the rubber on the other hand, influence of the chain length of carboxylic acids on properties of the samples still needs further qualitative investigation. Tribological properties of SBR modified with carboxylic acids are the result of balance of two opposite effects: plastification of rubber-leading to an increase of friction and lubrication-which causes a decrease of friction of the rubber. Apart from plastifying and lubrication effects microroughness also plays an important role in friction.
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