Thermo-Chemical Devulcanization of Sulfur-Vulcanized SBR Assisted by De-Vulcanization Aids and Oxidation Stabilizers

Ground tire rubber (GTR) from whole passenger car tires is composed of several types of rubbers and fillers, making devulcanization of this material rather complicated. The most critical component in this material is SBR, as it tends to degrade and re-combine during the commonly used reclaiming processes. 

In a thermo-chemical devulcanization process with diphenyldisulfide (DPDS) as devulcanization aid, a reduction of crosslink density is observed up to a temperature of 220°C. Beyond this temperature threshold, the crosslink density rises again. This is due to intra-molecular rearrangements of chain fragments of butadiene moieties from uncontrolled degradation and oxidation effects. By the addition of oxidation stabilizers, degradation is suppressed and the oxidation cycles are interrupted. By choosing an appropriate stabilizer for SBR, a further decrease in crosslink density can be achieved at temperatures higher than 220°C. 

This combination of DPDS as de-vulcanization aid and oxidation stabilizers significantly enhances the devulcanization efficiency of SBR versus DPDS alone. The results are interpreted in terms of mechanisms of main chain and sulfur bridge scission and the degradative cycles triggered by the presence of oxygen.