Abstract
Rubber used in tire is usually strengthened by nanofiller, and the most popular nanofiller for tire tread rubber is nano silica, which can not only strengthen rubber but also lower the tire rolling resistance to reduce fuel consumption. However, silica particles are difficult to disperse in the rubber matrix because of the abundant silicon hydroxyl on their surface. Silane coupling agents are always used to modify silica and improve their dispersion, but a large number of volatile organic compounds (VOCs) are emitted during the manufacturing of the nanosilica/rubber composites because of the condensation reaction between silane coupling agents and silicon hydroxyl on the surface of silica. Those VOCs will do great harm to the environment and the workers’ health. In this work, epoxidized solution polymerized styrene-butadiene rubbers (ESSBR) with different epoxy degrees were prepared and used as macromolecular coupling agents aimed at fully eliminating VOCs. Fourier transform infrared (FTIR) spectroscopy and nuclear magnetic resonance (NMR) analyses verified that the different ESSBRs were successfully synthesized from solution polymerized styrene-butadiene rubbers (SSBR). With the help of the reaction between epoxy groups and silicon hydroxyl without any VOC emission, nanosilica can be well dispersed in the rubber matrix when SSBR partially replaced by ESSBR which was proved by Payne effect and TEM analysis. Dynamic and static mechanical testing demonstrated that silica/ESSBR/SSBR/BR nanocomposites have better performance and no VOC emission compared with Bis-(γ-triethoxysilylpropyl)-disulfide (TESPD) modified silica/rubber nanocomposites. ESSBR is very hopeful to replace traditional coupling agent TESPD to get high properties silica/rubber nanocomposites with no VOCs emission.
Highlights
In recent years, with the stricter requirements for tire performance, shortage of petroleum resources, and people’s attention to environmental protection, better wet-skid resistance property as well as lower rolling resistance are demanded when rubber is applied to tire tread [1,2,3]
The new peaks at 1260 and 801 cm−1, which refer to the symmetrical stretching deformation absorption peak of C–O–C and the asymmetric extension deformation vibration absorption peak of C–O–C, respectively, can be observed from the epoxidized solution polymerized styrene-butadiene rubbers (ESSBR) curve, indicating that the epoxy groups have been introduced into the molecular chain of the solution polymerized styrene-butadiene rubbers (SSBR)
ESSBR with the epoxy degree from 7% to 25% were prepared and got ready to use as macromolecule coupling agents, because the epoxy groups can react with the silicon hydroxyl on silica surface, and ESSBR has good compatibility with the SSBR/BR matrix, the residual double bonds on ESSBR can crosslink with SSBR/BR matrix by vulcanizing agent
Summary
With the stricter requirements for tire performance, shortage of petroleum resources, and people’s attention to environmental protection, better wet-skid resistance property as well as lower rolling resistance are demanded when rubber is applied to tire tread [1,2,3]. To improve the performance of silica/rubber nanocomposites and lower the VOCs emission, as opposed to modifying the silica surface, the compatibility of silica and rubber can be improved by the functionalization of the rubber molecular chain, e.g., introducing functional groups like carboxyl groups [24,25], hydroxyl groups [26,27,28,29,30], alkoxysilane groups, and epoxy groups [3,20,28] onto rubber chains during post-polymerization process. The performance of silica/ESSBR/SSBR/BR composites were examined by transmission electron microscopy (TEM), rubber process analyzer (RPA), tension tester, and dynamic mechanical thermal analysis (DMTA)
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