Influence of nonuniform network on mechanical properties of nano-silica reinforced silicone rubber

Abstract

Nonuniform networks were introduced into the nano-silica reinforced silicone rubbers, by co-cross-linking of silicone gum containing 0.05 mol% vinyl (G_L) and gum containing 3 mol% vinyl (G_H), so as to improve the mechanical properties. Their network characteristics were investigated by nuclear magnetic resonance measurement, swelling experiment, dynamic mechanical analysis, and rubber process analysis. Nonuniform networks displayed high tear strengths up to 41 kN m⁻¹ and improved tensile strengths and elongations at break. Nonuniform networks with 7–10 phr of G_H had optimal mechanical properties, since densely cross-linked domains scattered in base network and imparted maximum heterogeneity. In this structure, dense domains favored high modulus, while dominated long chains contributed to large extensibility. Hence, such structure could display large elongation before fracture while showing twice modulus upturns and stick-slip tearing characteristics, which were demonstrated by Mooney–Rivlin curves, tearing curves, and scanning electron microscopic images.