A P/N/S-containing high-efficiency flame retardant endowing epoxy resin with excellent flame retardance, mechanical properties and heat resistance

In order to improve the flame retardancy while maintaining the excellent mechanical properties and heat resistance of epoxy resin, a novel P/N/S-containing high efficiency flame retardant named TAP was designed and synthesized by a simple one-pot reaction among 2-thenaldehyde, 2-aminobenzothiazole (ABZ) and 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO). The chemical structure of TAP was characterized by Fourier transform infrared (FTIR) spectroscopy, 1H and 31P nuclear magnetic resonance (NMR) spectroscopy. Compared to pure EP, the introduction of TAP can reduce the thermal decomposition rate of epoxy resin and increase the char residue. Meantime, when the phosphorus content was only 0.48%, EP/7.5%TAP passed the vertical burning V-0 rating, obtaining a high flame-retardant efficiency. With the addition of 10 wt% TAP, the limiting oxygen index (LOI) value increased from 22.8% of pure EP to 31.5%, while the peak heat release rate (PHRR), total heat release (THR) and total smoke production (TSP) values decreased by 41.26%, 35.70% and 24.03%, respectively. In addition, the glass transition temperature (Tg) of the epoxy resin decreased from 185 °C to 177 °C, while the storage modulus at 30 °C increased. Subsequently, the flexural tests of the samples revealed that the mechanical properties were well maintained. All these results demonstrated that the TAP was a novel high efficiency flame retardant for EP, which enabled the cured EP to maintain excellent heat resistance and mechanical properties.