ADHESION AND HYSTERETIC FRICTION OF TIRE TREAD RUBBERS HAVING PROCESS OILS WITH DIFFERENT AROMATIC CONTENT

The extent of modification of wet grip of tire tread rubber by safe aromatic process oils has been the subject of controversy, as this property has conventionally been judged by indirect methods such as the loss factor at 0 °C. The present work aims to directly measure the dry and wet frictional behavior of rubbers containing various loadings of distillate aromatic extract (DAE) or treated distillate aromatic extract (TDAE) and to elucidate the contributions resulting from the adhesion and the hysteretic terms of friction. Physico-mechanical tests including rubber hardness, rubber–substrate work of adhesion, rubber–oil compatibility, hysteretic properties, and the rubber glass transition temperature were evaluated to disclose the underlying friction mechanisms. Interestingly, TDAE-containing rubbers presented a comparable or even better hysteretic friction not only at low oil loadings but also at high oil levels. As the loss factor properties of DAE and TDAE are very close to each other and there is the possibility of a crossover point within the frictional zone, care must be exercised not to merely rely on the values of tanδ at 0 °C in judging the preference of DAE or TDAE with regard to the wet grip performance.