Devulcanization of natural rubber/styrene-butadiene rubber unfilled blend in supercritical carbon dioxide using Tulbaghia violacea crude extract

A non-toxic and readily available potential devulcanizing agent, viz. Tulbaghia violacea Harv. plant bulbs crude extract, was used for the first time to non-isothermally devulcanize an unfilled natural rubber/styrene butadiene rubber blend in supercritical carbon dioxide medium. Temperature set-point and pressure were kept at 120 °C and 8 MPa, respectively, while the amount of extract and reaction time were optimized. Based on simultaneous optimization of the amount of extract and the initial time of devulcanization, the reactivity of the organo-sulphur compounds in an extract with the vulcanizate is seemingly dependent on the reaction time and temperature. Though organo-sulphur compounds in the plant bulbs crude extract had a significant effect on the vulcanizate, heat alone also caused chemical bonds breakage. Treatment with plant bulbs crude extract decreased the crosslink density while increasing both the sol fraction % and percent devulcanization to 45% and 75%, respectively, when devulcanization was performed for 6–17 min. Organo-sulphur compounds in plant bulbs crude extract had no effect when the reaction time was 18 min or more. Swelling tests, as well as gel permeation chromatography, Fourier-transform infrared spectroscopy and thermogravimetric analyses, on extract-treated and untreated vulcanizate suggested that the Tulbaghia violacea plant bulbs crude extract has the potential of producing improved-quality recovered rubber.