Synthesis and characterization of sustainable inverse vulcanized copolymers from non-edible oil

Abstract

Inverse vulcanization is a facile solvent-free process, which offers interesting sustainable copolymers from the reaction of sulfur with petro-based monomers or edible vegetable oils. However, sulfur reaction with the former contradicts green chemistry, whereas the latter reduces the viability of the product and can contribute to the food crisis. Herein, we report the preparation of sulfur-based polymer (SBP) by the reaction of rubber seed oil, RSO (a non-edible oil), to produce a sustainable sulfur-based copolymer for the first time. The properties of the new polymer were evaluated using different techniques such as Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy coupled with energy dispersive X-rays (SEM-EDX-mapping), powdered X-ray diffractometer (p-XRD), thermogravimetric analysis (TGA), and differential scanning calorimetry (DSC). The polymer was found to be soluble in tetrahydrofuran, thermally stable to 200 °C, and a low glass transition temperature (−6.41 to −7.85 °C for a polymer with 50 to 70 wt % S). The polymer morphological and DSC analysis demonstrated a uniform surface possessing a small amount of unreacted microscale sulfur particles that is lesser than similar polymers from other oils, which was confirmed by DSC. The P-XRD analysis revealed the amorphous nature of the copolymer caused by a heavily crosslinked structure. The effect of the post-polymerization treatment on the properties of the copolymers was also investigated which revealed that increasing the curing temperature or quenching medium temperature increases the glass transition temperature of the copolymer. The polymer properties were dramatically improved by reducing the amount of the unreacted sulfur by the addition of a small amount of 1,3-diisopropeynyl benzene (crosslinker), leading to 99.75 % sulfur conversion, the highest ever value achieved in such SBPs. It can be concluded that the use of RSO with sulfur enhances the sustainability of SBP and promotes their adding products.