Preparation of a novel mono-component intumescent flame retardant for enhancing the flame retardancy and smoke suppression properties of epoxy resin
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A novel mono-component intumescent flame retardant named pentaerythritol phosphate melamine salt (PPMS)-functionalized expandable graphite (PPMS-EG) was synthesized and carefully characterized by Fourier transform infrared spectroscopy, 1H nuclear magnetic resonance spectroscopy, scanning electron microscopy (SEM)–energy-dispersive X-ray spectrometry, and thermo-gravimetric (TG) analyses. Then, PPMS-EG was incorporated into epoxy resin (EP) to enhance fire safety. The flammability properties of EP composites were investigated by limiting oxygen index (LOI), UL94 vertical burning test, and cone calorimeter test. As expected, PPMS-EG imparts good flame retardancy to epoxy resin, and EP matrix with 20 mass% PPMS-EG passes the UL94 V-0 rating and the LOI value reaches 27.3%. Cone calorimeter test shows that the incorporation of PPMS-EG dramatically reduces the heat release and smoke production of EP, and the peak heat release rate and peak smoke production rate of EP composite with 15 mass% PPMS-EG are reduced by 68.7% and 46.3%, respectively, compared to those of EP. By comparison with either PPMS or expandable graphite, the same addition of PPMS-EG produces higher flame-retardant and smoke suppression efficiencies in EP matrix due to the formation of a more compact and intumescent char layer, as determined from digital photographs and SEM images. TG results show that PPMS-EG significantly enhances the thermal stability and char-forming ability of EP composites. Char residue analysis reveals that PPMS-EG positively contributes to the formation of more phosphorus-rich cross-linking char and aromatic char in the condensed phase, thus exhibiting a more thermally stable char against the release of heat and smoke. Overall, PPMS-EG can be used as a highly efficient mono-component intumescent flame retardant for preparing super flame-retarded EP composites.
KeywordsExpandable graphite Mono-component intumescent flame retardant Epoxy resin Flammability Thermal behavior
This work was supported by the National Natural Science Foundation of China (No. 51676210), the Hunan Provincial Natural Science Foundation of China (No. 2018JJ3668), the Postdoctoral Science Foundation of Central South University, and the Project funded by China Postdoctoral Science Foundation (No. 2017M612587).
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