Improvement of thermo-mechanical and fatigue crack growth resistance of tire sidewall compound by introducing syndiotactic polybutadiene

Thermoplastic elastomer (TPE) has potential to meet stringent requirements of reduced rolling resistance coefficient (RRc) of tires by lowering the hysteresis of the compound. Syndiotactic polymers could impart their reinforcing nature to the matrix, enhancing compound modulus, hysteresis and fatigue cut growth (FCG) properties with an added advantage of compound weight reduction. In this study, two grades of VCR (Vinyl Cis Rubber) with 12% (VCR412) and 17% (VCR617) of syndiotacticity have been introduced in a 50/50 Natural rubber (NR)/cis-Butadiene rubber (BR) based sidewall compound. 50% and 100% replacement of BR by VCR have been experimented in modified formulations from where 15 phr of carbon black is also withdrawn. This modification led to reduction of 24% and 18% in loss factor (tan delta) at 70 degrees C in VCR412 and VCR617 respectively in comparison with reference compound. Improvement in 12% dynamic stiffness is also found by employing 50 phr of VCR617. Homogeneous dispersion of VCR in rubber matrix is confirmed by Atomic Force Microscopy (AFM) analysis. Fatigue Crack Growth (FCG) rate of sidewall compound with VCR617 reveals lower crack propagation realized by crack path deviation. Complete replacement of BR by VCR617 lead to optimized thermo-mechanical properties related to hysteresis, dynamic stiffness and fatigue resistance.

Automated summary

This study investigates the use of VCR to improve the rolling resistance coefficient (RRc) of tires by reducing the hysteresis of the compound. The results show that the replacement of Syndiotactic polymers in the compound can enhance its modulus, hysteresis, and fatigue crack growth (FCG) properties. AFM analysis confirms the homogeneous dispersion of VCR in the rubber matrix.