Microwave devulcanization of ground tire rubber and applicability in SBR compounds

Rubber recycling is a major environmental challenge, as their covalently crosslinked structure makes it impossible to reprocess via conventional polymer processing technologies. Devulcanization of rubber waste, whereby crosslinks are selectively broken, may provide a solution, as it allows it to be remolded into new shapes. We used two types of ground tire rubbers (GTRs) for this study; mechanically ground and waterjet-milled GTRs with different particle sizes. First, we revealed the effects of GTR particle size on the devulcanization process. We examined the sol content of the samples before and after devulcanization with two different microwave ovens, a power-controlled conventional one, and a temperature-controlled laboratory oven. In the latter one, heating rate and maximum temperature were controlled. We studied the effects of temperature, atmosphere in which the rubber was treated, heating rate, and holding time at maximum temperature. We prepared styrene-butadiene rubber-based rubber compounds containing GTR and optimally devulcanized GTR (dGTR_WJ). The physical and mechanical properties of the samples were assessed. The results indicate that both GTR_WJ and dGTR_WJ have an accelerating and a mildly softening effect on curing and dGTR_WJ has a less significant negative effect on mechanical properties: 15 phr GTR_WJ has the same effect as 45 phr dGTR_WJ. © 2019 The Authors. Journal of Applied Polymer Science published by Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020, 137, 48351.