Effects of ammonium polyphosphate and boric acid on the thermal degradation of an intumescent fire retardant coating

•The effect of APP and boric acid on thermal performance of intumescent fire retardant coatings have been investigated.•The substrate temperature of IF4 formulation reached 339 °C after 30 min and 385 °C after 60 min fire test.•An increase in boric acid up to 11.55% in IF5 intumescent coating increased the residual weight up to 28.35 wt%.•IF5 showed the carbon contents in char residues increased up to 47.45% and oxygen content was noted 49.70%.•Accelerated weathering test showed that IF5 coating continued its reliability up to 90 days.

An intumescent coating is an insulating system designed to decrease the heat transfer a substrate structure. The intumescent fire retardant (IFR) coating presented here is based on expandable graphite (EG), ammonium polyphosphate (APP), melamine, and boric acid. Bisphenol epoxy resin BE-188 (BPA) was used as a binder with ACR Hardener H-2310 polyamide amine. Different formulations were developed to study the effects of APP and boric acid on char expansion, heat shielding, char morphology and char composition after a fire test. The coating was tested at 950°C for one hour. Char expansion was examined by furnace using a fire test. The results show that the coating is stable on the substrate. The morphology of the char was studied using Field Emission Scanning Electron Microscope (FESEM) of the coating after a fire test. X-ray Diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR) showed the presence of carbon, borophosphate; boron oxide and sassolite in the residual char. Thermogravimetric analysis (TGA) including derivative plots showed that boric acid and APP enhance the residual weight of intumescent fire retardant coating. X-ray photoelectron spectroscopy (XPS) confirmed that IF5 recorded better carbon content up to 47.45 wt%, in the residual char that enhanced the fire resistance performance of the coating. An accelerated weathering test according to ASTM D 6695-03 showed that the IF5 coating continued its reliability up to 90 days in the hastened weathering chamber.