Effective thermomechanical devulcanization of ground tire rubber with a co-rotating twin-screw extruder

Abstract We thermomechanically devulcanized ground tire rubber (GTR) in a co-rotating twin-screw extruder at different barrel temperatures and screw speeds. We measured the soluble content and the cross-link density of the samples and then evaluated them by Horikx's analysis. The results showed that at lower temperatures, selective cross-link scission is dominant, and screw speed has no effect. At higher temperatures and screw speeds, the degradation of the polymer chains becomes more and more severe. With the appropriate parameters, cross-link scission can be maximized without severe degradation of the main chains. Two devulcanized ground tire rubber (dGTR) samples were chosen for further study. Natural rubber (NR) based rubber mixtures were produced with conventional and two-step mixing. Tensile and tear strength decreased significantly with dGTR content. These results are in agreement with Horikx's analysis, i.e. the greater the degradation of dGTR, the more mechanical properties were impaired. However, elongation at break did not follow such a trend. With two-step mixing, mechanical properties improved, especially tear strength. Additional experiments were also conducted with Horikx's analysis. The aim was to reveal the accuracy and usability of the analysis, and it showed the theoretical maximum of devulcanization.