Mechanical, chemical, and curing characteristics of cardanol–furfural-based novolac resin for application in green coatings

The present research work focuses on the mechanical, chemical, and curing characteristics of novolac resin based on renewable resource materials such as cardanol and furfural. Cardanol, a metasubstituted phenol, is a renewable organic resource obtained as a byproduct of the cashew industry. Furfural, an aromatic aldehyde, is also a renewable resource obtained as an agricultural waste product. Novolac resin has been synthesized by the condensation of cardanol with furfural in the presence of an oxalic acid catalyst and using varied molar proportions of the reacting monomers. The reaction was performed at 120°C. The progress of the reaction was monitored by determining the free formaldehyde and free phenol content. The prepared cardanol–furfural-based novolac resins were further characterized by various techniques such as infrared and nuclear magnetic resonance spectroscopic analysis. The resins were cured using the most suitable agent, hexamethylenetetramine. The differential scanning calorimetric technique was used to investigate the curing behavior of the prepared samples. The cured film samples were used for the determination of mechanical properties such as adhesion, flexibility, scratch hardness, gloss, and impact resistance; these cured film samples were also used to observe the effect of various chemicals and solvents (chemical resistance properties) such as sulfuric acid, acetic acid, sodium hydroxide, sodium carbonate and methanol, methyl ethyl ketone, xylene, and deionized water, respectively, on the surface of the film. The resulting coatings based on prepared cardanol–furfural resin were found to have excellent mechanical and chemical resistance properties.