Simultaneously improving the thermal stability, mechanical properties and flame retardancy of epoxy resin by a phosphorus/nitrogen/sulfur-containing reactive flame retardant

Abstract

In order to broaden the application field of epoxy resin (EP), it is significant to heighten the fire safety without deteriorating the comprehensive performance. A high-efficiency reactive phosphorus/nitrogen/sulfur flame retardant (SAD) derived from 2-Thenaldehyde, 9,10-dihydro-9-oxa-10-phosphaphenanthrene10-oxide (DOPO) and 3-amino-1H-1,2,4-triazole (ATA) was designed, acting as the co-curing agent for DGEBA/DDM system. Fourier transform infrared (FTIR) spectra and nuclear magnetic resonance (NMR) were used to confirmed the chemical structure of SAD. Besides, the glass transition temperature (Tg) was gradually increased from 150.4 ℃ for EP to 156.9 ℃ for EP-7.5 and the maximum thermal decomposition rate was decreased after the introduction of SAD. The samples exhibited excellent thermal stability. Meanwhile, SAD promoted cross-linking reaction during curing process. Compared with EP, EP-5 (phosphorus content was 0.39 wt%) reached V-0 rating in vertical burning (UL-94) test and acquired a remarkable enhancement from 25.7% to 34.7% in the limited oxygen index (LOI) value, an obvious blowing out effect occurred when the samples burned. Furthermore, from the data of cone calorimeter (CC) tests, there was a reduction of 19.1% and 16.6% for EP-7.5′s the total heat release (THR) and the peak heat release rate (PHRR) compared with EP. And the analysis of char residue and incomplete combustion products indicated that SAD displayed bi-phase flame-retardant effect. It is very meaningful that the mechanical properties of materials were slightly enhanced after the introduction of SAD. The results showed that SAD has a broad prospect in practical application.