Thermal stability and thermal degradation kinetics of bio-based epoxy resins derived from cardanol by thermogravimetric analysis

Cardanol is a naturally occurring chemical compound consisting of meta substituted alkyl phenol. Two types of epoxy resins have been synthesized from cardanol. The synthesized epoxy resins have been characterized by FTIR and NMR spectroscopic analyses. The thermal stabilities and kinetics of the thermal degradation of cardanol-based resins were studied by thermogravimetric analysis under a nitrogen atmosphere with heating rates of 5, 10, 15 and 20 °C min⁻¹. The molecular weights of the prepared novolac and epoxidized novolac resins were determined by gel permeation chromatography analysis. There is intense interest in understanding the degradation behavior and properties of cardanol-based epoxy resins. Three model-free methods, Kissinger, Kissinger–Akahira–Sunose (KAS) and Flynn–Wall–Ozawa (FWO), and the model-fitting Coats–Redfern method were employed to identify the kinetic triplet including activation energy, pre-exponential factor and reaction model. It was established that the Coats–Redfern model-fitting method is suitable for determining the kinetic reaction mechanism, but the most probable reaction functions R3 and D3 can be evaluated on the basis of the activation energy value which is nearest to the value of activation energy obtained by the FWO and KAS methods. A kinetic compensation effect was also observed for the above-mentioned bio-based epoxy resins.