Modified soybean oil-extended SBR compounds and vulcanizates filled with carbon black

Abstract

Soybean oil (SO) was modified through the reaction with dicyclopentadiene (DCPD) to convert carbon double bonds in the soybean oil molecules into norbornyl groups of different ratios. Styrene-butadiene rubber (SBR) compounds with carbon black (CB) containing different extender oils including SO, modified SO (MSO) and naphthenic oil (NO) were prepared for comparison. The gel fraction, crosslink density, bound rubber fraction, curing behavior, thermal, mechanical and dynamic properties and reactions between the SO, MSO and curatives were investigated. It was found that with an increase of the modification level, the gel fraction of the SBR/MSO vulcanizates slightly increased while the crosslink density and bound rubber fraction decreased. The SBR/SO and SBR/MSO compounds and vulcanizates showed a lower glass transition temperature (Tg) and better thermal stability than those of the SBR/NO compounds and vulcanizate. The SBR/MSO compounds exhibited faster curing. Their vulcanizates showed lower modulus and higher elongation at break and tensile strength in comparison with the SBR/NO vulcanizates. The dynamic mechanical analysis of SBR/MSO vulcanizates indicated that use of this rubber in tire tread is expected to improve traction but increase rolling resistance compared to the SBR/NO vulcanizates. After adjusting the curative recipe, the modulus and tensile strength and abrasion resistance of the SBR/MSO vulcanizates with low level of modification were tremendously improved with the tensile strength and elongation at break being significantly higher than that of SBR/NO vulcanizate. The use of this recipe is expected to achieve similar traction and lower rolling resistance compared to the SBR/NO recipe. The addition of MSO to SBR has a promising possibility to replace petroleum oils in the rubber along with improvement of safety in tire production.