In preceding investigations the overall rate and apparent activation energy for the vulcanization process were calculated for natural rubber compounds, assuming that vulcanization follows first-order kinetics. It was observed that the addition of white rice husk ash (WRHA) increased the rate of crosslinking and lowered the apparent activation energy more profoundly than commercial fillers, precipitated silica (Zeosil-175) and carbon black (N762), with a conventional vulcanization system. In this work, a specific model for the vulcanization process accelerated by N-cyclo-hexylbenzothiazole sulfenamide was used to investigate the real role of WRHA in crosslink formation. Cure studies were carried out at 150degreesC, and the kinetics constants were evaluated. In relation to the other fillers, WRHA seems to develop catalytic activity, resulting in a positive effect on the specific rate of crosslink formation. (C) 2003 Wiley Periodicals, Inc.