Preparation of novel CNSL‐based urethane polyol via nonisocyanate route: Curing with melamine‐formaldehyde resin and structure–property relationship

In this study, we report preparation of a novel cashew nut shell liquid (CNSL)‐based polyol bearing urethane groups. The urethane group in the polyol was induced via isocyanate free route from the reaction of cyclic carbonate with primary amine. The polyol was characterized by determination of hydroxyl number, Fourier transform infrared spectroscopy, nuclear magnetic resonance spectroscopy, and so forth. The polyol was then used as coating component and cured with hexamethoxy methylene melamine (HMMM). Another CNSL‐based polyol without urethane moiety from our earlier reported work was used for preparation of coating for comparative study to determine the effect of urethane group on the coating properties. The coating formulations based on these two polyols were cured with variable amounts of HMMM hardener to optimize coating properties. All the coatings were evaluated for mechanical properties such as adhesion, flexibility, pencil and scratch hardness, impact resistance, pull‐off, and adhesion. The optimized coatings were also evaluated for chemical and thermal properties. It was observed that the urethane containing polyol resulted in better adhesion to the metal substrate at higher quantity of HMMM hardener compared to the other polyol providing significant improvement in various coating properties. The final coating properties were also compared with the acrylic polyurethane coatings.