Use of naturally small molecule as an intelligent interfacial modifier for strengthening and toughening silica-filled rubber composite

The incorporation of interfacial modifiers into silica-filled rubber composite is necessary to optimize the composite properties because abundant silanol groups on silica surface make it essentially incompatible with non-polar rubbers. The modification of silica-filled composites with the commonly used silanes generally causes many constraints such as excessive silane dosage, high temperature compounding, volatile organic compound emission, and loss of toughness of the composite. In this contribution, we reported the use of naturally small molecule thioctic acid (TA) as an intelligent interfacial modifier for silica-filled styrene-butadiene rubber (SBR) composite. The carboxyl group of TA can interact with silica through hydrogen bonds, meanwhile the disulfide bond of TA can be cleaved to generate sulfur radicals and then couple with SBR macroradicals during compounding and curing, making TA a bridge between silica and SBR matrix. In the TA-modified composite, silica dispersion is greatly improved and hydrogen bond-mediated interface is constructed. When comparing with the most widely used bis-(γ-triethoxysilylpropyl)-tetrasulfide, TA-modified composites exhibit simultaneously improved strength, modulus, toughness and tear strength, which is on account of the reversible energy-dissipating mechanism of the hydrogen bond-mediated interfaces. • Thioctic acid as an interfacial bridge constructs hydrogen bond-mediated interface in silica-filled rubber composites. • Silica dispersion is improved and interfacial adhesion is strengthened in the composites upon modifying with thioctic acid. • The modified composites exhibit simultaneously improved tensile strength, modulus, toughness and tear strength. • Breaking-reformation of hydrogen bonds facilitates energy-dissipating and chain orientation for reinforcing and toughening.