Recycling NR/SBR waste using probe sonication as a new devulcanizing method; study on influencing parameters.

In this work, a vulcanized blend of natural rubber (NR) and styrene butadiene rubber (SBR) ( i.e. at weight ratio of 50 : 50) as a model for tire rubber was devulcanized using probe sonication. The effect of processing parameters such as sonication media, power, temperature and time on sol/gel contents and devulcanization percent of rubbery samples was investigated. Moreover, the influence of pre-immersion of vulcanized NR/SBR samples in different liquids ( i.e. water, oil and toluene) was assessed for different sonication times ( i.e. 10 to 60 min) and powers ( i.e. 30 to 60 W). It was found that pre-immersion of rubber particles in oil significantly increased the devulcanization percent. The optimum conditions for devulcanization of the NR/SBR blend via probe sonication were found to be 60 Watts, 20 min, oil and 24 h for sonication power, sonication time, pre-immersion/sonication media and pre-immersion time, respectively. The highest obtained devulcanization percent in this step was about 40%. The effects of two devulcanizing chemical agents ( i.e. diphenyl disulfide and VitaX) on devulcanization performances of the samples were also studied. Results showed that higher devulcanization percent ( i.e. about 52%) was obtained by using VitaX. It was also observed that VitaX significantly improved re-vulcanization speed ( i.e. cure rate index) and decreased scorch time. It was also found that lower content of VitaX ( i.e. 0.6 phr) caused better curing properties but lower mechanical properties compared to the higher content ( i.e. 1.2 phr).