Evidence of silane coupling in torrefied agro-industrial residue-filled poly(styrene-co-butadiene) rubber compounds

Authors: Torres, Lennard; McCaffrey, Zachariah - Zach; Williams, Tina; Wood, Delilah - De; Orts, William; McMahan, Colleen

Submitted to: Journal of Applied Polymer Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/7/2023
Publication Date: 1/21/2023
Citation: Torres, L.F., McCaffrey, Z., Williams, T.G., Wood, D.F., Orts, W.J., McMahan, C.M. 2023. Evidence of silane coupling in torrefied agro-industrial residue-filled poly(styrene-co-butadiene) rubber compounds. Journal of Applied Polymer Science. 140(12). Article e53646. https://doi.org/10.1002/app.53646.
DOI: https://doi.org/10.1002/app.53646

Interpretive Summary: The agricultural industry produces significant quantities of biomass residues including rice hulls as part of food production. Alternative, value-added uses of agricultural residues are needed to supplement farmer income, lower disposal costs, and reduce landfill space. Biomass could be used as fillers and as replacements for petroleum-derived products thereby reducing greenhouse gas emissions. In this study, we heat-treated rice hulls (to produce torrefied rice hulls, or TRH) and evaluated the heat-treated biomass as full or partial replacements for silica filler in rubber compounds. At partial replacement levels comparable physical properties were found. Remarkably, chemical couplers designed for use with silica also reacted with the TRH fillers, suggesting SBR tire tread compounds made with TRH filler plus coupler would not compromise tire performance. Overall, results show the potential for the use of agricultural residues as a sustainable and renewable resource for the production of engineered high-performance materials.

Technical Abstract: Heat-treated rice hull residues were evaluated as fillers in poly (styrene-co-butadiene) rubber (SBR) compounds. The currently used precipitated silica filler was replaced with torrefied filler in concentrations varying from 0 to 100'wt. %, and the influence of coupler concentration varying from 0% to 3% (7 phr total) on the filler-rubber interaction was investigated. The curing process, dynamic properties, and mechanical properties of the SBR compounds was examined for silica-filled and torrefied rice hull (TRH) filled materials with and without the coupling agent. Partial or full replacement of silica with TRH resulted in a systematic decrease in compound viscosity. Longer scorch (ts2) and shorter cure times (t90) were also observed. Incorporation of TRH increased compound modulus (M100 and Young’s modulus) but decreased tensile strength and elongation. The presence of coupler brought about improved dynamic and mechanical properties and 30% lower than delta at the 3 phr level. Results provided the first evidence that, when used as a filler in an SBR compound, torrefied rice hulls can be chemically coupled to the SBR polymer, resulting in increased polymer-filler interactions analogous to the conventional silica-coupler-polymer system.