Cardanol, a by-product of the cashew industry, has been recently proven to be a multifunctional additive (NIFA) in rubbers. It is expected that grafting of cardanol onto natural rubber (NR) would impart inherent MFA characteristics to the rubber. Grafting has been carried out in solution using toluene as the solvent and a peroxide initiator. Optimized conditions of grafting reaction could be arrived at using a statistical tool namely orthogonal array testing strategy, keeping the maximum percentage of grafting as the selection criteria. Further studies were conducted to study the influence of monomer concentration and initiator concentrations. The effect of the reaction temperature and reaction time were also investigated. Characterization of grafted rubber was carried out with the help of infrared spectroscopy, nuclear magnetic resonance spectroscopy and thermal analysis. IR spectrum of cardanol exhibited the characteristic peak of cardanol at 3356 cm(-1). Percent grafting (PG) of cardanol onto NR was determined by residual weight method. PG increased with increasing cardanol quantity reached an optimum and then decreased. The increase in reaction time and reaction temperature also caused increasing levels of the grafted cardanol. However, PG continuously increased with increasing initiator concentrations. Differential scanning calorimetry studies of the grafted NR showed a lower glass transition temperature than that of the raw NR, which is indicative of the plasticization effect of cardanol. The thermogravimetric analysis showed a higher thermo oxidative stability for cardanol-grafted NR. (c) 2007 Wiley Periodicals, Inc.