Enhancing silicone rubber performance through surface grafting of γ-MPS onto nano-SiO2 particles

Abstract

The reinforcing of silicone rubber using nano-SiO₂ is currently constrained by the weak interfacial interactions dominated by hydrogen bonding and van der Waals forces between particles and the matrix. This limitation hinders the development of silicone rubbers with high-strength and high-transparency. In this study, a novel organic modification approach involving “hydrolysis mixing, spray drying, and thermal treatment” was developed to graft γ-(methacryloxypropyl)trimethoxysilane (γ-MPS), containing double-bonds, onto the surface of precipitated SiO₂ particles. During curing, these surface-grafted double-bonds react with the double-bonds on the silicone rubber side chains, forming an interfacial cross-linking network between inorganic particles and the organic matrix. Experimental results show that composites incorporating SiO₂ particles modified with 2 wt% γ-MPS adding exhibit the highest tensile strength of 9.47 MPa, attributed to the optimal particle dispersion and formation of interfacial cross-linked network. Particle dispersion which is quantified by a dispersion index reached the lowest values at 2 % γ-MPS, indicating the uniform dispersion. Consistently, curing rheology showed the maximum effective torque reaching 3.16 dN m at 2 %, reflecting the highest double bond interfacial cross-link density. Silicone rubber composites with 0.5 %–2 % γ-MPS modified particles exhibit optimal tensile strength and transparency. However, the increasing amount of γ-MPS leads to intensified condensation of hydrolyzed silane species, resulting in particle agglomeration and multilayer grafting on the particle surfaces, which adversely affects mechanical performance and transparency. To prepare high-strength and high-transparency silicone rubber, effective suppression of the condensation of silane coupling agent hydrolysis products and achievement of monolayer grafting on particle surfaces are necessary.