Novel Cashew Nutshell Liquid-based Waterborne Curing Agents Designed for High-Performance and Low-VOC Protective Epoxy Coatings

By Hong Xu, Joe Mauck, Fernanda Tavares, Anbu Natesh, Jing Li

A series of zero-volatile organic compound (VOC) waterborne epoxy curing agents based on cardanol, a non-food chain and renewable biomaterial, has been developed to meet stricter regulation, as well as high-performance requirements. This article presents the latest performance studies of applying those new Cashew Nutshell Liquid-based waterborne curing agents in typical formulations for heavy duty, industrial, and transportation coatings applications.

Test results revealed that the novel waterborne curing agents enable the formulations of low-VOC (< 75 g/L) direct-to-metal primer systems with excellent performance, such as balanced fast cure and long pot life, superior adhesion, and long-term corrosion protection of numerous metal substrates. Furthermore, the influence of various solid epoxy dispersions, different cure processes, and cosolvents upon film formation, adhesion, and anti-corrosion performance are reviewed, and the challenges of improving long-term corrosion protection of waterborne primer systems over galvanized steel substrates are discussed.

Cashew Nutshell Liquid (CNSL) is a sustainable and non-food chain biomaterial that can be obtained as a byproduct of the cashew industry.¹ CNSL is contained in the honeycomb structure of the cashew nutshell (Figure 1), and it is primarily composed of 60% to 70% anacardic acid, 10% to 20% cardols, 3% to 10% cardanols, and 2% to 5% 2-methylcardols.²