Effect of three structurally different epoxy resins on fire resistance, optical transparency, and physicomechanical properties of intumescent fire-retardant transparent coatings

Abstract

Transparent intumescent fire-retardant (IFR) coatings are the newest passive fireproofing materials which maintain structural integrity without losing aesthetic appearance of the substrate. In this present paper, effects of three IFR coatings with structurally different epoxy resins, namely aliphatic, cycloaliphatic, and aromatic, on the fire resistance, transparency, and physicomechanical properties were investigated. Different phosphate resin acids (PRA) were prepared by reacting synthesized phosphate ester acid (PEA) with aliphatic, cycloaliphatic, and aromatic epoxy resins. The chemical structures of the above PEA and PRAs were confirmed by Fourier transform infrared spectroscopy (FTIR), 1H-nuclear magnetic resonance spectroscopy (1H-NMR), and 31P-nuclear magnetic resonance spectroscopy (31P-NMR). Subsequently, transparent IFR coatings were prepared by mixing these PRAs with hexamethoxy methyl melamine resin. Transparency of the coatings was confirmed by UV–Vis–NIR spectrophotometeric studies. Fire protection property and char compressive strength were done to investigate the fire protection ability of the coatings, and the quality of the char formed was analyzed by field emission scanning electron microscope. The decomposition process of prepared fire-retardant coatings was studied by thermogravimetric analysis. Results showed that aliphatic epoxy-based transparent coating produced tough and compact char, but the char height was negligible, and aromatic epoxy-based transparent coating produced soft and fluffy char having excellent char height; however, the fluffy char reduced protection for longer duration. Cycloaliphatic epoxy-based transparent coating produced tough and compact char with good char height, thereby reducing heat transfer during combustion, and also showed superior scratch, abrasion, impact, and water resistance compared to other compositions.