Design of a bio-based flame-retardant epoxy/amine cross-linked coatings

Epoxy cross-linked coatings are widely used to protect and beautify many surfaces all around us. However, these coatings possess a dense carbonaceous structure, rendering them susceptible to ignition, spread, and propagation of flames. Therefore, flame-retardant (FR) materials are added into these coatings as additives to improve flame resistance properties. Many of the commercially available FR additives are halogenated, metal oxide, and alkyl phosphate-based compounds, often originating from nonrenewable resources. Some of these compounds produce undesirable toxic fumes and byproducts upon combustion. To overcome these challenges, we tested bio-based phytic acid (PA) as an FR additive in epoxy resin, cross-linked with bio-based phenalkamine (NX)—a material derived from cashew oil nutshell. Our findings demonstrate that the incorporation of PA into an NX-cross-linked epoxy coating system significantly enhances the FR properties of the coatings while preserving their physico-mechanical characteristics such as solvent resistance and hardness. Additionally, the inclusion of PA markedly enhances the FR performance of the coatings by reducing flame spread rate, minimizing dripping, and suppressing ignition temperature. Moreover, upon addition of 10% w/w PA increases the ignition time, decreases peak heat release rate (PHRR) by more than 25%, reduces total heat release (THR) by the similar amount, and suppresses total smoke production by >40% compared to the coatings containing FR- agents based on metal oxides and alkyl phosphates. Our work clearly demonstrates the feasibility of using PA as the FR additive for producing eco-friendly and low-flammable epoxy cross-linked coatings.