Influence of molecular weight of PEG on thermal and fire protection properties of PEPA-containing polyether flame retardants with high water solubility

Abstract

Abstract A series of novel PEPA-containing polyether (PAPEG) flame retardants with high water solubility were synthesized by pentaerythritol phosphate (PEPA), phosphorus oxychloride (POCl3) and polyethylene glycol (PEG) with different molecular weight. Their chemical structures were confirmed by 1H nuclear magnetic resonance spectroscopy (1H NMR) and Fourier transform infrared spectroscopy (FTIR). The influence of molecular weight of PEG on the thermal property of PAPEGs was investigated by thermogravimetric analysis (TGA) and a possible thermal degradation mechanism was speculated to illustrate the char-forming ability of PEG. Afterwards, the influence of molecular weight of PEG on the fire protection of the transparent fire resistant coatings (FRC) was investigated in detail by fire protection test, intumescence ratio, scanning electron microscopy (SEM) and TGA. The fire protection test found that the coatings with low molecular weight PEG presented good fire retardancy, supplying effective fire protection for the plywood boards. The intumescence ratio and SEM results well demonstrated that the fire protection of coatings and foam structure of char layers were significantly improved when the molecular weight of PEG was low. TGA result showed that the residual weights of the fire resistant coatings presented the order of FRC200 > FRC150 > FRC400 > FRC600. It indicated that low molecular weight PEG could enhance the char-forming ability of the coatings. TGA and real-time FTIR results proved that blowing agent and carbon source degraded in the same temperature range, which resulted in the formation of intumescent char layer.