Cure characteristic and mechanical properties of natural rubber vulcanizates with digested rice husk ash (RHA)

Rice husk (RH) is a hard shell that protects the rice grain and can be found in abundance in all rice producing countries. Burning RH as fuel to generate energy would result in a waste product, rice husk ash (RHA). RHA contains approximately 90 – 98% of silica (SiO2), after undergoing a complete combustion process, which is the highest among other agricultural wastes. Silica is one of the commonly used fillers in natural rubber (NR). A chemical treatment for the RHA was developed to collect the silica, via a simple method consisting of alkaline extraction and acid precipitation. This method can produce finer and visually whiter RHA powder. The effects of the chemical treatment on the particle size and surface area of the silica particles were measured. The precipitated silica was then incorporated into NR, using a laboratory-size two-roll mill. For comparison, commercial silica was used as a control. The cure characteristics and mechanical properties of the vulcanizates were evaluated. It was found that the chemical treatment (digestion and precipitation) on RHA has resulted in a significant decrease in its particle size and increase in its specific surface area. However, the mechanical properties of the vulcanizates produced from the treated RHA were lower than that of the commercial silica.