Optimization of synthesis of inverse vulcanized copolymers from rubber seed oil using response surface methodology

Abstract

Optimization of inverse vulcanization reaction conditions was carried out using response surface methodology (RSM) and a quadratic model was proposed to predict the sulfur conversion, to limit the amount of the unreacted sulfur left in the final copolymer of sulfur and rubber seed oil (non-edible vegetable oil) for the very first time. ANOVA analysis revealed the significance of the selected conditions and of all, the initial sulfur content was the most influential parameter. Although process optimization substantially increased the sulfur conversion, but there was still 5.8% unreacted sulfur present as revealed by DSC (differential scanning calorimetry) analysis. Filtration using tetrahydrofuran as solvent was carried out to further remove the sulfur particles from the copolymer, this strategy yields a copolymer with only 0.25% unreacted sulfur. The sulfur conversion was further improved using another strategy involving the addition of 5–10 wt% of 1,3-diisopropenyl benzene (DIB) or 2,4,6-Triallyloxy-1,3,5- triazine (TAC) crosslinker to the reaction mixture. The field emission scanning electron microscopy (FESEM) confirmed the presence of smooth surfaces in the copolymers whereas their amorphous nature was evident from powdered X-ray diffraction (p-XRD) results. The terpolymers were observed to be more thermally stable than the copolymer.