酸源与气源配比对膨胀阻燃剂炭层形成和阻燃性能的影响

[Objective]This study aims to investigate the correlation between the acid and gas source ratio and the flame retardant effect of intumescent flame retardants(IFR),and analyze their impact on the combustion characteristics of flame-retardant-treated poplar wood(FW).[Method]Phytic acid and urea were selected as acid source and gas source,respectively.IFRs with different ratios(1:3,1:6,1:10,and 1:12)were prepared and labeled as PAN-3,PAN-6,PAN-10,and PAN-12.The ratio of nitrogen and phosphorus elements in the four IFRs were verified and analyzed with a fully automatic elemental analyzer.FW samples were obtained through vacuum impregnation,and their thermal degradation and combustion characteristics were analyzed by thermogravimetric analysis(TGA)and cone calorimetry(CONE).Scanning electron microscopy(SEM),laser Raman microscopy,and X-ray diffraction(XRD)were used to investigate the microscopic morphology and degree of graphitization of wood char residues.[Result]As gas source content increased(gas source:acid source≥3),the expanded structure of the flame-retardant poplar wood promoted the higher temperature shift of the maximum degradation temperature on the TGA curve and formed a more thermally stable char layer.Additionally,the thickness of the cell wall of the char residue showed an initial increase and then a decrease.It was found that the inhibitory effect of the expanded char structure on heat release and mass loss was greater with the addition of gas source,which was reflected in the continuous increase of the degree of graphitization of the char residue.When the gas source ratio increased to certain degree(gas source:acid source≥10),an excess of gas source resulted in the rupture of the expanded structure,and a decrease in the thermal insulation and oxygen insulation properties. CONE results showed that the total heat release(THR)and the peak of heat release rate(PHRR)of the FW samples decreased compared with that of the untreated group,wherein the reduction of the PAN-6 group reached 63.97%and 64.1%.Ammonia was produced by the gas source decomposition at 103℃-193℃,and the acid source was transformed into pyrophosphate,catalyzing wood dehydration into char at 193℃-291℃.A high stability and integrity char layer was formed based on the synergistic effect of gas and acid source,which had a inhibitory effect on the heat release,as well ad smoke and carbon monoxide release.The PAN-6 group showed a decrease of 63.97%and 64.1%for THR and PHRR,respectively.However,when the integrity of the expanded char layer was destroyed,the PAN-12 group showed an increase of 17.58%and 2.53%for smoke release and heat release,respectively.[Conclusion]The addition of gas source could produce a char layer with high integrity and stability,improving the flame retardancy and smoke suppression properties of the IFRs.However,when the gas and acid source ratio is higher than 10,the destruction of the char layer's integrity increased in heat release and smoke release of the FW.