Solvent-free intumescent fire protection epoxy coatings with excellent smoke suppression, toxicity reduction, and durability enabled by a micro/nano-structured P/N/Si-containing flame retardant

The development of solvent-free intumescent fire protection epoxy (EP) coatings with excellent durability is an extremely important issue for the protection of storage tanks and structural steels in the coating industry. In this work, a micro/nano-structured phosphorus/nitrogen/silicon-containing flame retardant (APP@Si) was synthesized by silica nanoparticles-modified ammonium polyphosphate, which was utilized to prepare high-performance intumescent fire protection epoxy resin (EP) coatings via a solvent-free method. APP@Si enhanced fire protection, smoke suppression, toxicity reduction, mechanical properties, and durability of solvent-free EP coatings. APP@Si with a 10 wt% loading level endowed solvent-free EP coating (EP/10APP@Si) with a limiting oxygen index value of 32.4 % and a UL-94 V-0 rating. Meanwhile, APP@Si declined the peak heat release rate, smoke factor, and peak CO production rate values of EP/10APP@Si by 77.5 %, 92.6 %, and 56.4 %, respectively, compared with those of pure EP. Moreover, the maximum back temperature of EP/10APP@Si was as low as 126.4 °C under heating for 1200 s in the back temperature test, which was 221.5 °C lower than that of pure EP. The increase in fire protection of EP/APP@Si coating was mainly attributed to forming an intumescent and dense char layer with strong strength and high expansion degree during combustion. In addition, APP@Si enhanced the flexural strength and impact strength of EP/10APP@Si by 12.0 % and 24.6 % compared with those of EP/10APP. Moreover, APP@Si also increased the water contact angles of EP/APP@Si coatings from 87.9° for pure EP to 93.3° for EP/10APP@Si. And the weight change rate of EP/10APP@Si was the lowest among all coatings after immersing in the deionized water for 20 days. Therefore, this work presented a feasible strategy for fabricating multifunctional solvent-free intumescent fire protection epoxy coatings, which was expected to be applied in the coating industry.