Influence of process variables on chemical devulcanization of sulfur-cured natural rubber

Chemical devulcanization of sulfur cured natural rubber (NR) was investigated using benzoyl peroxide (BPO) as a devulcanizing agent. The influence of important reclaiming parameters such as reaction time, reaction temperature and concentration of the devulcanizing agent on the devulcanization process and mechanical properties of the resulting products were studied. At devulcanization reaction time of 2 h (instead of 4 h) and lower concentrations of the devulcanizing agent selective scission of sulfur crosslinks were observed, however, both longer of the reaction time and higher concentrations of the devulcanizing agent process resulted non-selective chain scission. Mechanical properties of the devulcanized and revulcanized samples using 6 phr of BPO, with different reaction times and temperatures were also investigated. Longer reaction time led to lower crosslink density which in turn caused tensile strength and elongation at break to decrease significantly. Likewise, higher reaction temperature accelerated scission of network crosslinks and resulted lower tensile properties. Blending of 40 wt% of the virgin rubber with the devulcanized one in the compound had no adverse effect on the scorch and optimum cure time and also does not extremely deteriorate the mechanical properties of the virgin rubber. This provided an effective route for chemical devulcanization of NR. (C) 2015 Elsevier Ltd. All rights reserved.