Keywords: Natural rubber; rice husk ash; mechanical properties; curing characteristics; silica

Abstract

Rice husk ash (RHA) is a silica-rich waste product of the rice industry. Chemical treatment of RHA was developed to obtain high purity and reactive silica, via a simple method consisting of alkaline extraction and acid precipitation. The effects of the chemical treatment on the particle size and surface area were measured. 20 parts per hundred rubber (phr) of precipitated silica was then incorporated into natural rubber (NR), using a laboratory-sized two-roll mill. For comparison, commercial silica was used as a control. The cure characteristics and mechanical properties of the vulcanisates were evaluated. The chemical treatment of the RHA resulted in a significant decrease in its particle size and an increase in its specific surface area. The precipitation of RHA with hydrochloric acid (HCl) and nitric acid (HNO3) resulted in smaller particle sizes with reductions of 55% and 49%, respectively from the initial size before precipitation. Both acid precipitation increases the specific surface area by 53%. These changes involved the removal of organic and metal components from RHA, confirmed by Fourier transform infrared (FTIR) spectroscopy and Energy-dispersive X-ray (EDX) analysis. However, the mechanical properties of the vulcanisates produced from the treated RHA were lower than those of the commercial silica. This biomass-derived filler has the potential to be further developed as an alternative to commercial silica sourced from mining.