COMPARISON BETWEEN RICE HUSK SILICA-FILLED EPOXIDIZED NR CROSS-LINKED WITH FUMARIC ACID AND VULCANIZED WITH SULFUR

Abstract

ABSTRACT A wide variety of fillers are used in the rubber industry to modify the properties of rubber compounds and reduce the cost of products in different applications. Silica produced from rice husk could be an alternative filler to commercial precipitated silica widely used in sulfur-vulcanized rubber formulations. High purity amorphous silica (>99% SiO2) was produced after pretreatment of rice husk with dilute sulfuric acid before combustion at 600 °C. Epoxidized NR (ENR) with 50 mol% epoxide groups (ENR50) containing various silica loadings was cured with fumaric acid via reactions of the epoxide group with –COOH, whereas sulfur vulcanization used the carbon–carbon double bonds, as confirmed by Fourier transform infrared spectroscopy (FTIR) analysis. Increasing silica loading in both of types of samples led to an increase in rheometer torque and a decrease in percentage of solvent swelling due to the stiffening effect of silica, with no change in glass-transition temperature, which presumably was due to no chemical reaction between silica and ENR. The tensile strength of fumaric acid–cured ENR50 slightly increased with increasing silica loading and remained unchanged upon aging. The sulfur-vulcanized ENR50 containing 30 phr silica exhibited higher tensile strength, but further increase of silica weakened these properties. After aging, the tensile strength reduced by 5–7 MPa. Fumaric acid–cured rubbers have shown superior aging properties.