The eect of multifunctional additive in white rice husk ash ®lled natural rubber compounds Hana® Ismail *, M.N. Nasaruddin, H.D. Rozman School of Industrial Technology, Universiti Sains Malaysia, 11800 Minden, Penang, Malaysia Received 27 May 1998; accepted 24 August 1998 Abstract This paper reports the potential of white rice husk ash (WRHA) as a ®ller for natural rubber compounds. The optimum loading of WRHA to obtain maximum physical properties was achieved at 10 phr after which there was deterioration in properties. The incorporation of multifunctional additive (MFA) improves the curing characteristics and physical properties of WRHA ®lled natural rubber compounds. At 10 phr optimum loading, 3 phr of MFA is found to give maximum physical properties. Scanning electron microscopy studies indicate that the incorporation of MFA improves ®ller dispersion. # 1999 Elsevier Science Ltd. All rights reserved. 1. Introduction Rice husk ash (RHA) when burnt in the open air outside the rice mill yields two types of ®llers, white rice husk ash (WRHA) and black rice hush ash (BRHA). The upper layer of the RHA mound is sub- jected to open burning in air and yields BRHA in the form of a carbonized layer. However, the inner layer of the mound, being subjected to higher temperature, yields WRHA. WRHA has been analysed to have about 96% silica content, while the BRHA has a lower silica content, typically about 54% and a substantial carbon content, about 44%. It has been shown that with WRHA [1], apart from exhibiting better physical properties than BRHA, approaches the properties of commercial carbon blacks. It was reported that n-fallow-1-3-propane diamine salt of a carboxylic acid having the general formula [RNH + 2 (CH 2 ) 3 NH + 3 ] [R 0 COO  ] 2 enhances the mechan- ical properties of carbon black-®lled natural and syn- thetic rubbers [2, 3]. This surfactant was called a multifunctional additive (MFA) since it was observed that it can function as a processing aid, a ®ller dispersant, a cure accelerator, and a mould release agent. In our pre- vious works [4±9] we have reported the eect of MFA on the processing and mechanical properties of silica and carbon black-®lled natural rubber compounds. In this study white rice husk ash (WRHA) was used as a ®ller in the natural rubber compounds and the semi-ecient sulphur vulcanization (semi-EV) system was used. The work was carried out to achieve the fol- lowing objectives: (a) To determine the optimum loading of WRHA for natural rubber compounds (without multifunc- tional additive). (b) To study the eect of multifunctional additive in natural rubber compound at optimum loading of WRHA. 2. Experimental 2.1. Compounding ingredient and formulations SMR-L grade natural rubber was obtained from Rubber Research Institute of Malaysia (RRIM), while European Polymer Journal 35 (1999) 1429±1437 0014-3057/99/$ - see front matter # 1999 Elsevier Science Ltd. All rights reserved. PII: S0014-3057(98)00223-7 PERGAMON * Corresponding author. Tel.: +4-6577888 (ext. 2214); fax: +4-6573678.