Study On Combustion Behaviors And Potential Fire Hazards Evaluation Of Flame Retardant Flexible Polyurethane Foam

Flexible polyurethane foam(FPUF)has found extensive applications in various fields such as construction,transportation,and household due to its high resilience,thermal insulation properties,chemical stability,and sound absorption characteristics.However,this material is highly flammable,with rapid flame propagation,high smoke generation,and high toxicity.In response to these issues,this study synthesized additive,reactive,and surface-coating flame retardants,in conjunction with typical commercial flame retardants,to prepare flame-retardant and non-flame-retardant FPUFs.The thermal degradation,combustion,and smoke release behaviors of FPUFs were investigated under the combined effects of flame retardants and environmental factors.Additionally,a comprehensive evaluation of the fire hazard of the materials was conducted.The specific research contents are outlined as follows:In this study,surface functionalization of black phosphorus was achieved using a metal-organic framework material to synthesize BP@MIL-53.The layer-by-layer selfassembled surface coating(BP@MIL-53-CNT)for flexible polyurethane foam(FPUF)was prepared by combining BP@MIL-53 with multi-walled carbon nanotubes(MWCNTs).Phosphorus-containing reactive flame retardant(PCP)was synthesized by using diphenylphosphoryl chloride and ethylene glycol.A phosphorus-containing additive flame retardant(DOPO-DICY)was synthesized using 9,10-dihydro-9-oxa-10phosphophenanthrene-10-oxide and melamine(MEL).Additionally,three commercial flame retardants were selected:dimethyl methylphosphonate(DMMP),expandable graphite(EG),and ammonium polyphosphate(APP).In total,17 flame-retardant FPUF samples were prepared,including BP@MIL-53-CNT,which resulted in an increased Limiting Oxygen Index(LOI)of FPUFs up to 25%.Following international airworthiness standards,five FPUFs and one untreated control sample were selected for subsequent research.To investigate the influence of flame retardants on the thermal decomposition behavior of the foam,thermogravimetric analysis was conducted to measure the weight loss process of each sample under a nitrogen atmosphere.The results showed that:(1)All samples exhibited two main weight loss stages,and the flame retardants affected the thermal decomposition process of these stages,thereby altering the thermal stability and char yield;(2)The F WO method and the DAEM were used to study the relationship between activation energy and conversion rate.To investigate the combined effects of ventilation conditions and flame retardants on the combustion smoke toxicity of FPUF,steady-state tube furnace experiments were conducted under oxygen-deficient,oxygenrich,and stoichiometric conditions.The results showed that:(1)The use of various flame retardants increased the smoke production during material combustion,but some flame retardants suppressed the release of carbon monoxide(CO),reducing smoke toxicity;(2)Under oxygen-rich conditions,carbon(C)elements in FPUF tended to convert into carbon dioxide(CO2),whereas under oxygen-deficient conditions,it predominantly converted into CO.To investigate the influence of radiant heat power on the combustion heat and smoke hazards of FPUF,cone calorimeter tests were conducted on samples at four different power levels:15,25,35,and 45 kW/m2.The study revealed the following findings:(1)The heat radiation power can alter the process and total amount of heat release during material combustion,but for smoke emissions,it only affects the process and not the total release amount;(2)All flame retardants were able to suppress the heat release and CO2 emission of FPUF,except for PCP,which led to an increase in the average smoke and CO release;(3)Under the influence of 9 wt%BP@MIL-53-CN,PHRR is reduced by an impressive 77.68%;however,it simultaneously promotes smoke emissions.Furthermore,the addition of 15 wt%PCP leads to a substantial decrease in THR by 45.01%.The flame retardant mechanisms of the five flame retardants were investigated by analyzing the thermal decomposition gas products and char residue of the samples.In response to the limitations of traditional evaluation methods,an optimization a pproach was employed,combining Pearson correlation coefficient analysis,CRITIC m ethod,and rank-sum ratio method.This approach aimed to enhance the selection of ev aluation indicators,calculation of weights,and assignment of scores to samples.The r esulting evaluation model exhibits more objective weights,is less sensitive to outliers,and can mitigate the influence of small-range data fluctuations on evaluation outcome s.Finally,a comprehensive evaluation ranked the fire hazard of six polyurethane foam materials from high to low as follows:FPUF,FPUF/9%BP@MIL-53-CNT,FPUF/10%DOPO-DICY,FPUF/10%DMMP,FPUF/10%DMMP-MEL,and FPUF/15%PCP.