Study of thermal properties of flame retardant epoxy resin treated with hexakis[p-(hydroxymethyl)phenoxy]cyclotriphosphazene

Hexakis[p-(hydroxymethyl)phenoxy]cyclotriphosphazene (HHPCP) is prepared and characterized by FTIR, ¹H-NMR, and ³¹P-NMR spectroscopy. Then an investigation of the flame retardancy, thermal decomposition behavior of epoxy resin (EP) containing HHPCP is carried out using limiting oxygen (LOI) test, horizontal flame test, smoke density rate (SDR) test, thermogravimetric analysis (TG), and thermal gravimetric analyzer-mass spectrometry (TG-MS). The decomposition process of HHPCP is studied by TG-MS and FTIR. The result shows that the LOI value of EP increase from 20.5 to 26.5 %, when 7.5 mass% HHPCP is added into EP. The addition of 1 mass% nano-montmorillonite (nMMT) into EP–7.5 mass% HHPCP sample as synergist can increase the LOI value of EP–7.5 mass% HHPCP–1 mass% nMMT sample from 26.5 to 27.5 %. The SDR test indicates that smoke suppression of HHPCP on EP is not significant. TG analysis reflects that the EP–7.5 mass% HHPCP sample and EP–7.5 mass% HHPCP–1 mass% nMMT show higher thermal stability properties with an increasing T _onset and T _max comparing with neat-EP. TG-MS result indicates that the main pyrolysis product of EP is H₂O, CO, CO₂, C₆H₆, C₆H₅OH, HOC₆H₄CH₃, and flammable hydrocarbon fragments C_xH_y. Compared with neat-EP sample, nonflammable water vapor of EP–7.5 mass% HHPCP sample increased, whereas CO₂ and the flammable hydrocarbon fragments C_xH_y and flammable gas CO decreased. TG-MS and FTIR result suggests that HHPCP decomposed first by inter-molecular dehydration, then P–N hexatomic ring of HHPCP decomposed during 470 and 560 °C, and a little no-flame gas containing nitrogen element volatilized into the gaseous phase.