An efficient flame retardant (1,4‐methylenephenylphosphinic acid) piperazine (MPPAP) is successfully synthesized. The application of MPPAP in epoxy (EP) thermosets increases limited oxygen index values of composites to 30.2% and 6 wt% or more loading makes the materials get through UL94 V‐0 rating. The investigation of the combustion process indicates that MPPAP clearly changes the combustion behavior of EP composites, forms a char layer on the surface of the composites, and presents an effective flame inhibition effect, consequently resulting in clear reduction of the flammability and smoke production. The thermal degradation process of MPPAP/EP indicates that MPPAP promotes the matrix to decompose earlier and increases the char‐forming ability of composites. The morphology and structure of the final char shows MPPAP can promote the formation of cross‐linking structures and increase the graphitization degree of char residues acting as an excellent barrier. Furthermore, the flame‐retardant mechanism illuminates that MPPAP can reduce the generation of volatile fuels, and the pyrolysis products of MPPAP contain PO and PO2, which exert free radical quenching effect in the gas phase. Therefore, MPPAP is a terrific flame retardant for epoxy thermosets which manifests a flame retarding action in the gas phase and condensed phase.
The flame retardancy and thermal degradation behavior of intumescent flame retardant EP (EP-IFR) composites based on ammonium polyphosphate (APP) and a hyperbranched triazine carbon forming agent (HTCFA) were investigated by the means of limited oxygen index (LOI), vertical combustion test (UL-94), thermogravimetric analysis (TGA) and cone calorimeter test (CONE). The results exhibited that the combination of APP and HTCFA obviously imparted better flame retardancy to EP than them applied alone. EP composites containing 10 wt% APP/HTCFA (4/1) passed UL-94V-0 rating with a LOI value of 32%, while there was no rating for EP-APP or EP-HTCFA. In addition, the combination of APP and HTCFA influenced the fire behavior of composites with more efficient heat/smoke release suppression. The carbonaceous residues after cone presented expanded structures with compact and continuous surfaces. TGA results presented that there was an obvious synergistic effect between them, significantly enhancing the thermal stability and promoting the formation of char residues. The flame retardant mechanism was also involved based on the residue analysis by scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectrometry (FTIR) and laser Raman spectrometer (LRS). Results illustrated high-quality foamed cellular char layers with highly graphitic degree contributed to better flame retardant and smoke suppression properties of EP-APP/HTCFA composite.
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