Flame retardancy of an intumescent epoxy resin containing cyclotriphosphazene: experimental, computational and statistical studies

The current study is directed towards the evaluation of thermal stability and flame retardancy of the epoxy resin hexaglycidyl cyclotriphosphazene (HGCP) cured with 4,4′-methylene dianiline (MDA) and its polymer composite reinforced with bisphenol-A diglycidyl ether (DGEBA) by means of experimental, computational, and statistical approaches. The thermal properties of the polymer materials DGEBA-MDA (M1), HGCP-MDA (M2), and their mixture DGEBA-20%HGCP-MDA (M3) were evaluated using differential scanning calorimetry (DSC) and thermogravimetry–infrared spectroscopy (TG-FTIR) coupled analysis. The morphology was studied by scanning electron microscopy–energy dispersive X-ray analysis (SEM–EDX). The vertical flammability test was done used for the evaluation of the flame retardancy. The temperatures of exothermic peak (To) of the polymer materials M1, M2 and M3 were 95 °C, 77 °C and 93 °C, respectively. The results revealed that the addition of 20% of HGCP enhances the thermal stability compared to DGEBA and provides a DGEBA UL-94 V0 rating. SEM–EDX analysis showed that HGCP promotes the foaming and expansion of the coal as well as improved the gullies on the coal surface. Heteroskedasticity and autocorrelation consistent (HAC) covariance were performed to combine the results of the thermal degradation of the examined epoxy resins as a function of EHOMO and ELUMO, which were obtained from the optimized structure of the epoxy resins using the density functional theory. Consequently, the HAC model was validated by comparing the predicted theoretical results with experimental thermal degradation of the serial of compounds studied.