Abstract
Soybean oil (SBO) is a renewable material used as an alternative to conventional petroleum-derived oils in the processing of rubber composites. Upon chemical modifications, such as epoxidation, its performance in the processing of rubber can be significantly improved, as indicated by a considerable reduction of the mixing energy. Although it has been hypothesized that hydrogen bonding between functional groups (e.g., epoxy) of SBOs and silanols present on the silica surface plays a key role, there is still a lack of direct evidence supporting this hypothesis. In this work, it is demonstrated that there is an overall correlation between the epoxy concentration of SBOs and the mixing energy, consistent with the long-held hypothesis. In particular, a correlation between the SBO-silica adsorption affinity and the degree of epoxidation is revealed by a set of surface-selective solid-state nuclear magnetic resonance (ssNMR) experiments. In addition, the surface-selective ssNMR technique demonstrated in this work could also be used to evaluate the adsorption affinity of other oils and/or additives more broadly.
Highlights
It has recently been shown that vegetable oils such as soybean oil (SBO) are promising alternatives to conventional rubber processing aids such as treated distillate aromatic extracts (TDAEs).[5−17] Chemically modified SBOs can be synthesized through the controlled epoxidation of SBO.[18−22] The use of vegetable oils provides many benefits
In order to establish structure-to-property relationships describing the behavior of process oils in the context of silica-filled rubber processing, we proposed to semiquantitatively measure the adsorption affinities of a series of SBOs using a solid-state nuclear magnetic resonance (ssNMR) technique called {1H−29Si−}1H MCP inverse detection (MCPi)
The results showed that the mixing energies of model silica-filled rubber compounds correlate very well with the adsorption affinities of the SBOs, which confirmed a long-held hypothesis: the vegetable oil−silica interaction is responsible for aiding the rubber processing
Summary
With climate change increasingly tangible, the sustainability of industrial production is emphasized more than ever.[1,2] For example, silica, a reinforcing filler frequently used in the manufacturing of tires, is partially produced from rice husks.[3,4] it has recently been shown that vegetable oils such as soybean oil (SBO) are promising alternatives to conventional rubber processing aids such as treated distillate aromatic extracts (TDAEs).[5−17] Chemically modified SBOs can be synthesized through the controlled epoxidation of SBO.[18−22] The use of vegetable oils provides many benefits. Vegetable oils are generally recognized for their attractive safety profile related to humans, animals, and the environment[14,23−25] and for reducing our dependence on petroleum. Most importantly, these benefits can be realized with no performance penalty. Numerous reports have shown that modified vegetable oils can significantly improve the processability of silica-filled elastomer composites.[9−12,26,27]
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