Cashew nutshell liquid derivatives as a sustainable route to alkyd-free surface coatings

Abstract

Feedstocks derived from waste materials are advantageous for valorisation due to their low cost and role in addressing waste disposal issues. Cashew nutshell liquid (CNSL), derived from inedible cashew nut shells, has emerged as a notable precursor in the coating industry, replacing petroleum and other detrimental chemicals. CNSL resins are cost-effective, eco-friendly, high-temperature stable, and offer strong adhesion and flexibility. The present work demonstrates an eco-friendly technique for producing and characterising coatings devoid of alkyds, utilising CNSL, a bio-derived precursor, and boric acid crosslinking. CNSL, aliphatic alcohols, and sulphamic acid (catalyst) were employed in the development of sustainable polymeric films for bio-based coatings. Using the same synthetic route, CNSL-based resins were successfully synthesised by substituting boric acid for aliphatic alcohols, with sulphamic acid serving as a catalyst. Bio-based coatings were synthesised by amalgamating the resins with CNSL-based polymers, eliminating the necessity for alkyds. The films and coatings produced were evaluated for their physical and functional properties using FTIR, 1HNMR, SEM-EDS, zeta potential analysis, particle size measurement, viscosity assessment, and mechanical performance testing. The boric acid-modified coatings exhibited a promising combination of stability, hardness, and favourable mechanical properties relative to a commercial coating, indicating their potential application in the coatings industry. Future studies on corrosion resistance and long-term environmental stability would enhance the evaluation of the coatings’ industrial applicability. The study, which advocates greener industrial coatings, indicates that the sustainable CNSL-based coatings performed comparably to commercial coating systems, which is promising for their durability.