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

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 parts per hundred rubber or phr total) on the filler-rubber interaction was investigated. The curing process, dynamic properties, and mechanical properties of the SBR compounds were 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 (t(s2)) and shorter cure times (t(90)) were also observed. Incorporation of TRH increased compound modulus (stress at 100% elongation or 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 tan delta at 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.

Automated summary

Heat-treated rice hull residues were used as fillers in poly(styrene-co-butadiene) rubber (SBR) compounds instead of precipitated silica filler. The influence of coupler concentration on the filler-rubber interaction was investigated. Results showed that the replacement of silica with torrefied rice hulls resulted in a decrease in compound viscosity, longer scorch and shorter cure times. Incorporation of torrefied rice hulls increased compound modulus but decreased tensile strength and elongation. The presence of coupler improved dynamic and mechanical properties and reduced tan delta.