Eco-friendly phosphonic acid piperazine salt toward high-efficiency smoke suppression and flame retardancy for epoxy resins

In the field of electronic and electrical applications, it has always been a challenge to synchronously improve the flame-retardant and smoke-suppression properties for epoxy resins. In this research, a novel flame-retardant phosphonic acid piperazine salt (PTPAP) was successfully synthesized in an environmentally friendly manner and used to fabricate flame-retardant EP thermosets. The fire safety and flame-retardant mechanisms of EP/PTPAP thermosets were detailedly studied. When merely 6 wt% PTPAP was introduced into EP substrate, the EP/PTPAP thermosets gained UL-94V-0 grade and their LOI value improved from 21.3% of pure EP to 28.3% with the increase of 32.9%. The introduction of PTPAP promoted the premature degradation and charring of EP matrix, and the intumescent, compact, and sealed char layer was produced on the surface of EP/PTPAP thermosets during combustion. Besides, PTPAP decomposed and produced the PO. and inert gases, which efficaciously exerted the free radical trapping and dilution effect in vapor phase. Therefore, the emission of smoke and heat was distinctly constrained and the EP/PTPAP thermosets was endowed with the superior fire safety. This flame-retardant EP/PTPAP thermosets showed broad application prospects under the environment of sustainable development because of the eco-friendly and simplicity of the synthesis of PTPAP.