Recent advances in the recycling of rubber waste
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the rubber molecules at low temperatures. In the degradation reaction of polyisoprene rubber with the PH–FeCl2 system in air, the phenyl hydrazine is the main reagent and FeCl2 acts as catalyst: the rate of degradation of the rubber is determined by the phenyl hydrazine concentration. Phenyl hydrazine is itself easily degraded by oxygen and it is known that nitrogen gas is liberated in this reaction [21]. The rate of degradation is very high in the presence of a metal salt. The initial oxidative degradation of rubber molecules with the PH–FeCl2 system is outlined below (Fig. 1). If sufficient oxygen is present, the various radicals formed by this reaction degrade the rubber molecules as indicated in Fig. 2 [22]. The hydroperoxide is decomposed in the presence of transition metals as shown in Fig. 3.
Figure 1. Oxidation mechanism for the PH–FeCl2 system [adapted from Ref. 21].
Figure 2. Bolland oxidation mechanism (RH = rubber hydrocarbon) [Reproduced with permission from Ref. 22].