Phytic acid based novel optically transparent intumescent fire-retardant coating for protection of combustible substrates with retention of aesthetic appearance

Phosphorus source in transparent intumescent fire-retardant (IFR) coatings plays a crucial role in determining its performance against protecting structures from fire. In the present work, naturally occurring environmentally benign phosphorus-rich phytic acid (PA) was used as a phosphorus source. Phosphate ester resin (PER) was synthesized using PA and hyperbranched polyol (HBP), which was then used as a precursor for preparing optically transparent IFR coatings. The prepared PER was further modified with hydrogenated bisphenol-A (DGEHBA)-based epoxy resin in different wt% (25–100) to get PER-1, PER-2, PER-3, and PER-4, respectively. The formation of the PER resins was confirmed by Fourier transform infrared spectroscopy (FTIR), ¹³C-nuclear magnetic resonance, ³¹P-nuclear magnetic resonance spectroscopy (³¹P-NMR), and acid value analysis. The transparent IFR coatings were prepared by suitably mixing PER with hexamethoxy methyl melamine (HMMM) resin, and their performance was studied by measuring mechanical properties, optical transparency, thermal stability, fire retardancy, and smoke emission characteristics using various analytical instruments. The combination of PA and hyperbranched polyol improved the physicomechanical properties of PER-based transparent IFR coatings. The char formed after burning was also analyzed using FESEM and UTM. Results revealed that phytic acid and HBP combination increased the height as well as strength of the char. Among the prepared transparent IFR coatings, PER-0 and PER-1 have shown higher char height and strength.