Polybutadiene micro/macro structure effect on fatigue life and crack growth resistance in NR/high-cis polybutadiene sidewall compounds has been evaluated. Three high-cis polybutadienes having different 1,4 cis units content have been considered. Fatigue life has been studied performing
fatigue-to-failure tests both in air and in ozone atmosphere and statistical analysis of experimental data has been applied to describe the phenomenon in terms of cumulative distribution functions. Fatigue was further investigated performing crack growth tests according to fracture mechanics principles. Tests parameters (temperature, frequency, strains) have been selected to simulate the sidewall deformation under service conditions and Crack Growth rate vs Tearing Energy plots have been obtained. Dynamic mechanical tests were performed to assess compound hysteresis which may affect crack growth and fatigue resistance reducing the energy available for
tip propagation. The analysis of overall data confirms the correlation between polybutadiene microstructure and fracture resistance which improves increasing 1,4 cis content as previously found for pure polybutadiene compounds. This phenomenon is due to the ability of high-cis polybutadiene to undergo strain-induced crystallization which, acting as reinforcing mechanism, enhances fatigue resistance of sidewall compounds.