Cardanol-based novolac-type phenolic resins. I. A kinetic approach

Novolac resins having two different mole ratios of cardanol-to-formalclehyde (1:0.6 and 1:0.8) were prepared by using aliphatic tricarboxylic acid as catalyst at four different temperatures ranging between 100 and 130 degrees C with an interval of 10 degrees C. The synthesized novolacs were confirmed by infrared spectroscopic analysis with the appearance of characteristic groups of the novolac resin. The reaction between cardanol (C) and formaldehyde (F) was found to follow second-order rate kinetics as determined by two different approaches. The over all rate constant (k) increased with the increase of CIF molar ratio. Based on the value of k, various other kinetic parameters such as activation energy (E-a), change in enthalpy (Delta H), entropy (Delta S), and free energy (Delta G) of the reaction were also evaluated. The values of E-a and Delta H were found to be decreased with the increase of CIF molar ratio from 1:0.6 to 1:0.8. These values revealed the nature of the condensation reaction between cardanol and formaldehyde in presence of tricarboxylic acid catalysts. (c) 2006 Wiley Periodicals, Inc.