Soybean oil derived-process oil prepared via recyclable organocatalysis for eco-friendly styrene–butadiene rubber composites

Abstract

Process oil, one of the primary chemicals used in the compounding of tire tread, is an important ingredient because it makes up the largest portion of the tire tread and can be modified to change the tire's characteristics. We designed a new process oil by controlling the number of functional groups in the oil molecules, resulting in the incorporation of multiple coordination sites followed by the enhanced dispersion of silica filler particles which are commonly used in tire tread. Through the introduction of a new recyclable organocatalyst, specifically 4-(N,N-dimethylamino)pyridine benzyl bromide salt (DMAP-BB), we have developed a selective ring opening system that can be used to synthesize various types of acid-esterified soybean oils (ASOs) (99% conversion and up to 93% selectivity), which have multiple ester groups with diverse molecular structures. Furthermore, excellent efficiency of DMAP-BB was observed under the optimized conditions with an average 96% recovery of the catalyst in five cycles without loss of conversion or selectivity. Finally, these newly developed bio-based processing oils are revealed to be highly efficient in the manufacturing process of a styrene–butadiene rubber (SBR) composite, i.e., tire tread. A silica-filled SBR composite prepared with a mixture that included palmitic acid-esterified soybean oil with 99% selectivity (PASO99) exhibited a remarkable Payne effect in an un-vulcanized batch, suggesting excellent dispersibility of the silica filler during compounding. This can be observed through the change in the storage modulus (G′), which decreased from 1315 kPa for SBR/ESO to 1008 kPa for SBR/PASO99 (23% improvement). We also found that excellent viscoelastic and mechanical properties could be achieved in the vulcanized batch of SBR/PASO99, which includes outstanding rolling resistance (tan δ at 60 °C = 0.158 for SBR/ESO to tan δ at 60 °C = 0.116 for SBR/PASO99, 27% improvement) and abrasion resistance (DIN abrasion loss = 180 mm³ for SBR/ESO to DIN abrasion loss = 140 mm³ for SBR/PASO99, 22% improvement). We believe that the implementation of these novel fully bio-based process oils can offer significant opportunities for reducing the environmental footprint of rubber goods and promoting the development of sustainable, high-performance tire.