Effects of Nano-sized Boron Nitride on Thermal Decomposition Behaviour of Epoxy-based Intumescent Coating

Intumescent fire retardant coating (IFRC) is one of the easiest ways of fire protection system and the problems within current market are its toxicity, failure due to humidity, low thermal performance and high filler loading requirement. The aim of the current study is to investigate thermal decomposition behaviour of IFRC formulated with nano-sized boron nitride with respect to toxicity and thermal performance before and after exposure to humidity. Boron nitride is superior in term of humidity resistance with high temperature stability. In addition, nano-sized filler could mitigate the high filler loading requirement. In present research work, IFRC formulations were developed using ammonium polyphosphate (APP), expandable graphite (EG), melamine (MEL), boric acid (BA) and Bisphenol A with polyamide amine H-2310 as curing agent. Nano-sized boron nitride (BN) and nano-sized alumina (Al2O3) were added as inorganic fillers. The coated steel substrates were subjected to furnace fire test at 500°C for 2h and fire protection test for 1h. The coatings were characterized by thermogravimetric analysis (TGA) and gas chromatography mass spectrometry (GCMS) to determine the toxicity level, while the char from fire test were characterized by field emission scanning electron microscopy (FESEM), X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR). The steel substrates were then characterized by optical microscope and Rockwell hardness test.
Furnace fire test showed that IFRC reinforced with 4wt.% of nano-sized BN expanded more than 54.84% compared to control formulation and with addition of 0.1wt.% of nano-sized alumina, the char expansion increased up to 83.78%. Fire protection test performed for 1h showed minimum substrate temperature of 140°C with 4wt.% of BN which proved that it can successfully protect steel substrates within its critical temperature. A maximum of 44.49wt.% residual weight was also recorded for the same coating. XRD analysis revealed that the remaining char contained boron phosphate, boron nitride and phosphoric nitride which are stable at high temperature thus assisted in reducing heat flow to the substrate. The presence of these compounds was also confirmed by functional group analysis using FTIR.