The novel epoxy/PEPA phosphate flame retardants: Synthesis, characterization and application in transparent intumescent fire resistant coatings

Abstract

Abstract A series of novel epoxy/PEPA phosphate (EPP) flame retardants were synthesized by 1-oxo-4-hydroxymethyl-2,6,7-trioxa-l-phosphabicyclo[2.2.2]octane (PEPA), polyphosphoric acid (PPA), and epoxies of bisphenol A epoxy resin E51 (EP) and 1,4-butanediol diglycidyl ether (BDE) with different proportions. The structure of EPP was characterized by 1H nuclear magnetic resonance (1H NMR) and Fourier transform infrared spectroscopy (FTIR). Then EPPs as flame retardants were blended with amino resin to prepare the transparent intumescent fire resistant coatings. The fire protection test showed that the best fire protection was obtained when the ratio of EP/BDE was 1/2. The char layers of coatings were investigated by intumescence ratio and scanning electron microscopy (SEM). The intumescence ratio result illustrated that the intumescence ratio of char layers decreased with the increase of EP/BDE ratio. The SEM images demonstrated that incorporation of EP could significantly improve the foam structure of char layers when the ratio of EP/BDE was no more than 1/2. Next, the thermal decomposition behaviors of the coatings were studied by thermogravimetric analysis (TGA) under nitrogen and air. The results demonstrated that incorporation of EP could enhance the thermal stability and residual weight of fire resistant coating as well as the thermo-oxidation resistance of the char layers. Finally, the real-time FTIR proved that the decomposition process of fire resistant coatings included three stages bellow 550 °C, which was consistent with the result in TGA.