An interfacial intergrowth charring method is designed and employed in glass fabric-reinforced epoxy resin composites.

A novel flame-retardant (FR) epoxy (EP) composite based on melamine cyanurate (MCA) and aluminum diethylphosphinate (AlPi) was successfully prepared and its flame retardancy was systematically investigated. Firstly, the facile surface modification was adopted to effectively solve the aggregation of FRs in EP matrix during the curing process. The influence of modified MCA/AlPi on the fire behavior and thermal degradation of EP were studied by using limiting oxygen index (LOI), vertical burning (UL94) tests, thermogravimetric analysis and pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS). The experimental results showed that EP/MCA/AlPi composite achieved UL-94V0 rating and LOI value of 33.0% at the optimum mass fraction of MCA/AlPi of 2/1. The chemical composition and structure of residue were characterized by X-ray photoelectron spectroscopy, Fourier transform infrared spectrometry and scanning electron microscopy. MCA mainly acted in gaseous phase during the initial combustion stage, and therefore to provide enough time for the formation of carbon layer in condenses phase. As a result, the synergistic effect of MCA and AlPi can effectively promote the formation of the char layer and the FR efficiency.

In this research, a new synergistic mechanism based on an acid-buffer action for cyclotriphosphazene (CPZ)/melamine cyanurate (MCA) flame retardant epoxy resin (EP) was proposed. This mechanism broke through the conventional well-recognized phosphorus-nitrogen interaction one. It revealed that CPZ had not only acid-catalytic charring but also acid-catalytic degrading effect on EP. The former that occurs in higher temperature range to improve the flame resistance in the condensed phase is a mechanism generally accepted for the phosphorus flame retardant, but the later that occurs in lower temperature range to deteriorate the flame retardance is usually ignored by the people. For CPZ/MCA flame retardant EP, the produced organic base from decomposed MCA can neutralize the acids from CPZ. Decline of the acidity effectively weakened the acid-catalytic effect, and reduced the volatiles release rate of the degraded resin in the initial stage, thus slowing down the combustion in the gaseous phase. With increasing temperature, the neutralized products were converted to the phosphoruscontaining acids again to promote the formation of the chars. A series of characterizations such as vertical burning test, X-ray photoelectron spectra, micro-scale combustion calorimetry, thermogravimetric, and differential thermogravimetric analysis of the flame retardant materials and the pH value detection of the corresponding carbonation products were performed to investigate the acid-buffer mechanism. The experimental results including no NAP forms in the condensed phase obviously improved flame retardance and increased degradation temperature of CPZ/MCA/EP compared with CPZ/EP, as well as the enhanced pH value of the former carbonation residue confirmed the above mechanism. POLYM. ENG.