Development of Nanofree, Silane-Free, and Fluorine-Free Cardanol-Based Multifunctional, Superhydrophobic Wood Coating

Abstract

A superhydrophobic approach free from toxic nanoparticles and silane- and fluorine-based compounds is the need of the hour in order to develop ecofriendly and sustainable materials for multifunctional applications. The extremely hygroscopic nature of the wood reduces its service life, which can be addressed with a renewable sourced polymeric coating to explore the wide use and enhanced durability. The current work describes the catalyst-free modification of CNSL (cashew nut shell liquid)-sourced cardanol diol with saturated fatty acids of varying carbon number (C16–C18). The esterification was carried out using palmitic acid and stearic acid in different stoichiometries to form prepolymers and characterized through FTIR, 1H NMR, and 13C NMR. In addition, curing behavior, thermal degradation profile, lap shear strength, and hydrophobicity of both samples were studied and subsequently optimized for further studies. Stearic acid-modified cardanol prepolymer (Sa-Cd) coating showed higher superhydrophobicity on soft wood and hard wood substrates with water contact angles of 153–156° and hysteresis 3–7°. SEM, OSP, and SPM analyses were carried out to understand the superhydrophobic feature attributed to the synergistic effect of inherent roughness of wood and chemical functionality of polymers. The coated substrates displayed excellent self-cleaning properties along with anti-icing and oil in water removal. Also, the coated substrates retained superhydrophobicity against water, corrosive chemicals, heat, and abrasion (100 cycles). The developed green materials offer a superhydrophobic functional coating for wood in order to widen its applications.