Elucidation of smear wear layer structure and ageing mechanisms of filled tyre tread compounds

This paper explores the microstructure of smear wear particles generated during the abrasion of tyre tread compounds made from different polymers. The compounds tested were synthetic polyisoprene rubber (IR) and styrene-butadiene rubber (SBR) reinforced with either carbon black or silica. This study used a range of different experimental techniques including Gel Permeation Chromatography (GPC), Dynamic Mechanical Analysis (DMA Rheology), Thermal Gravimetric Analysis (TGA) and Scanning Electron Microscopy (SEM) on both fresh and aged smear wear particles to understand their structure and ageing mechanisms. This research reveals that there is significant difference between the molecular weights of the initial uncured rubber and smear wear particles. Significant differences are also observed in the filler volume fraction and the nature of polymer filler interaction between the cured rubber and smear wear particles generated from abrasion. The results also reveal a second relaxation process in smear wear particles, which is attributed to decrosslinked polymer content. After comparing the ageing effect of 1 day and 1 month to smear wear particle properties it was also discovered that the ageing mechanisms are dominated by the recovery of the filler network in the short term and by oxidation-driven crosslinking in the polymer over the longer time frame. The microstructure of the smear wear particles proposed from these results is confirmed by a detailed investigation using SEM techniques.