Enhancing Properties of Deproteinized Natural Rubber with Rice Husk Ash Silica for Use as a Dental Material

Abstract

Rice husk is an agricultural residue from a rice-mill known as a rich source of silica. In this study, the rice husk was extracted for the contained silica by pretreatment with hydrochloric and calcination at 700 °C, and the white rice husk ash (WRA) mainly consisting of the silica was finally obtained. WRA was then investigated for its composition and structure with X-ray fluorescence (XRF) and X-ray diffractometer (XRD). The results showed that WRA contained a large amount of silica (90%) with amorphous structure. After that, WRA was used as filler for the preparation of natural rubber products. Two kinds of the natural rubber products were prepared here: 1) the pure natural rubber (PNR) product and 2) the deproteinized natural rubber (DNR) product. DNR was a protein removal natural rubber which is suitable for use as a dental material with the low allergenic properties caused from the proteins. Additionally, DNR used in this study could be provided by removing proteins from the natural rubber latex with 0.1 % urea in the presence of surfactant at room temperature. It was found that the nitrogen content (main element of proteins) of DNR was lower than PNR under the test condition. For the preparation of natural rubber products, WRA was mixed into the PNR and DNR latexes comparing with the commercial silica (Hisil-233). All finished latexes were compounded to obtain the natural rubber products. The viscoelastic properties and the cure characteristics of the entire products were investigated. It can be observed that WRA can be comparable with the commercial silica for use as filler for the natural rubber products. This is an attractive option to produce dental materials from the agricultural residues, which will reduce the cost of the production and also add value to the agricultural residues.