Surface modification of magnesium hydroxide by γ-aminopropyltriethoxysilane

Abstract

Magnesium hydroxide(MH), which is commonly used as a halogen-free flame retardant filler in composite materials, was modified by silanization reaction with γ-aminopropyltriethoxysilane (γ-APS) in aqueous solution at different pH values (pH range from 8.0 to 12.0). The surface properties of grafted γ-APS on MH surface as a function of solution pH value were studied using elemental analysis, Fourier transform infrared spectroscopy and zeta potential measurement. The results show that hydrolysis and condensation of γ-APS are activated in alkaline solution and lead to multilayer adsorption of γ-APS molecules on the surface of MH. The type of adsorption orientation of γ-APS on MH surface is a function of coverage density that is altered by changing solution pH value. At low coverage density (e.g. 55 nm−2), γ-APS molecules are preferentially adsorbed to the surface with the silicon moiety towards the surface, and increasing coverage density (e.g. 90 nm−2) leads to parallel orientation. At an even higher coverage density (e.g. 115 nm−2), γ-APS molecules bond to the surface with the amino moiety towards the surface.