In this research, natural rubber was reinforced with cardanol-formaldehyde resins prepared from cashew nut shell liquid. Cardanol-formaldehyde resins both resole and novolak were synthesized from cardanol which extracted from cashew nut shell. These were done via a condensation polymerization of cardanol and formaldehyde in the presence of base and. acid catalysts. Cardanol-formaldehyde resin, resole type : CF-resole, with highest yield of 75.37% was prepared by using a molar ratio of formaldehyde/cardanol at pH 8.0 and 90°c for 8 hours. Cardanol-formaldehyde resin, novolak type : CF-novolak, with highest yield of 79.68% was prepared by using a molar ratio of 0.8 formaldehyde/cardanol at pH 2.2 with. 100°c for 7 hours. Spectroscopic techniques, FT-IR and ¹³C NMR were employed to characterize the chemical structure of the obtained cardanol-formaldehyde resins. The resins were found to be compatible with natural rubber in various formulations. The cured behaviors of natural rubber blended with either the CF-resole or CF-novolak was investigated. It was found that the cured behaviors of CF-resole and CF-novolak samples were quite different, reflecting differences in chemical reactivities. Furthermore, the incorporation of cardanol-formaldehyde resins into natural rubber gave significant improvements in mechanical properties such as hardness, tensile strength, modulus at 100% and 300% elongation and abrasion resistance. However, elongation at break and compression set of the blends were decreased as expected.
