Thermal characterization of cardanol-formaldehyde resins and cardanol-formaldehyde/poly(methyl methacrylate) semi-interpenetrating polymer networks

Abstract

Thermal characteristics of cardanol-formaldehyde (CF) (both novolac and resol) polymers and cardanol-formaldehyde/poly(methyl methacrylate) (PMMA) resin interpenetrating network (IPN) polymers have been investigated. Cardanol-formaldehyde resins were synthesized, and thermal degradation data are compared with those of phenolics. Cardanol-formaldehyde products decompose at a faster rate and hence have lower thermal stability. Between cardanol-formaldehyde (resol) and cardanol-formaldehyde (novolac) products, the former decomposes at a faster rate. The TG of semi-IPNs indicates that thermal degradation of PMMA is slowed down by formation of IPNs. PMMA is known to degrade to show 50% weight loss at 350 ° C, whereas cardanol-formaldehyde (resol) based semi-IPNs show only 15% weight loss at this temperature. The PMMA stabilization is greater in the case of novolac resin based semi-IPN systems. Coats-Redfem plots are drawn for both homopolymers and semi-IPNs, and good fits are obtained for the reaction parameter n = 1. Two distinct stages of decomposition are indicated in both cases, and activation energies are deduced from the slopes of the plots. The activation energies for the first stage of decomposition for the CF(resol)/PMMA semi-IPNs range from 40–55 kJ mol −1, whereas the corresponding values for semi-IPNs based on the novolac system are between 44 and 65 kJ mol −1. The second stage of decomposition, which is between 400 ° C and 500 ° C, has an activation energy between 90 and 110 kJ mol −1 for the semi-IPNs, whereas it is 139 kJ mol −1 for the CF resin. The differences in the values are interpreted on the basis of the structure of the polymer.