Intumescent, Epoxy-Based Flame-Retardant Coatings Based on Poly(acrylic acid) Compositions

Intumescent coatings expand upon exposure to a flame to create a protective char layer between the flame and underlying substrate. Widely used commercially, these coatings are applied notably to steel load-bearing beams, significantly extending their time to failure. Boric acid has proved to be a particularly effective additive in the formulation in these coatings, although regulatory concerns are driving an urgent need for more environmentally friendly additives. We report here the characterization of poly(acrylic acid) (PAA) for its use as a novel material in flame-retardant and intumescent coatings. Thermogravimetric analysis (TGA) and microscale combustion calorimetry (MCC) were performed on the novel flame-retardant additives to evaluate individual degradation mechanisms and heat release rates. Promising compositions were immobilized in an epoxy binder and formulated with other intumescent additives such as ammonium polyphosphate (APP) and melamine (MEL) to evaluate performance in a coating system. These formulations were then evaluated via quantitative cone calorimetry. Particular PAA-containing formulations show peak heat release rates (PHRR) and total heat release (THR) of 283 kW/m² and 50.5 MJ/m², respectively, which compare favorably to data for BA-containing systems, specifically PHRR = 229 kW/m² and THR = 43.1 MJ/m². Results showed promise and need for further investigation into PAA as a multifunctional additive for use in flame-retardant and intumescent coatings.