Closing the loop for silica-filled passenger car tire rubber

Discarding tires after their service life causes significant societal and environmental challenges. Recycling and reuse offer the best solution to address this issue. Devulcanization, a controlled process that breaks crosslinks while preserving the polymer backbones, is the most sustainable recycling method. This study aims to create a sustainable closed-loop system for passenger car tires by producing high-quality devulcanizate.
A thermo-mechanical-chemical devulcanization process using an alkenyl silane was developed for silica-filled passenger car tire rubber. Parameters such as time, temperature, shear force, devulcanization aid concentration were optimized. The effectiveness of the process was evaluated based on the degree of network breakdown, miscibility of the devulcanized material with a virgin compound, and mechanical properties of the de- and revulcanized material. Besides, a correlation was established between number and size of undevulcanized particles and tensile strength of the revulcanizate. The best devulcanizate showed a network breakdown of 70%-75%, tensile strength of 8.6MPa, and 150% elongation at break.
This devulcanizate was blended with a virgin silica-based model tire tread compound at a concentration of 20% without a significant reduction in tensile strength. Blending 50% devulcanizate with the virgin model compound resulted in a 30% decrease in tensile strength and a 50% reduction in elongation at break. In addition to its efficiency, this devulcanization aid is more environmentally sustainable than conventional ones and meets environmental regulations. The resulting devulcanizate can be used in high-performance products such as tires, to create a closed, sustainable passenger car tire loop.