| As one of the main types of building structures,steel structure is prone to collapse due to its poor heat resistance and deformation in fire.Therefore,effective fire protection measures need to be taken.At present,the method of spraying water-based fire retardant coating is mostly used.In order to solve the problems of poor fire resistance and water resistance of waterborne fire retardant coatings,the compound of melamine polyphosphate(MPP)and triazine charring agent(CFA)is used as flame retardant in steel structure fire retardant coatings.The fire resistance of coatings is studied by experimental methods,and its fire resistance mechanism is preliminarily revealed.The specific research contents are as follows:First,four kinds of lotion,acrylic acid,styrene acrylic,silicon acrylic and acrylic acrylic emulsion were selected as the film forming material of steel structure fire retardant coating.The effects of film forming substances on the fire resistance and thermal stability of the coating were studied by simulating plate combustion,cone calorimeter and thermogravimetric(TG).The results show that the minimum back temperature of steel plate of acrylic fire retardant coating is 268℃,the peak heat release rate(phrr)and total heat release(THR)are the smallest,and the thermal stability of acrylic emulsion film is the highest.It shows that acrylic fire retardant coating has the best fire resistance and the best matching degree with MPP/CFA intumescent flame retardant system.Acrylic acid was used as the film-forming material of steel structure fire retardant coating.The effects of the ratio of MPP and CFA and the content of flame retardant on the fire resistance of the coating were studied by simulated large plate combustion method and cone calorimetry.The orthogonal test scheme was designed to optimize the formula of fire retardant coating,and the fire resistance and water resistance were compared with the traditional ammonium polyphosphate/pentaerythritol/melamine(P-C-N)fire retardant coating.The results show that when MPP:CFA=1:3 and the content of flame retardant MPP/CFA is 35%,the maximum back temperature,phrr and thr of the steel plate are the lowest.Compared with P-C-N fire retardant coating,the water absorption of MPP/CFA coating is reduced by 71.5%,THR is reduced by 20.4%,and the total smoke production is reduced by 31.4%.MPP/CFA fire retardant coating shows better water resistance,fire resistance and smoke suppression.Finally,through TG,SEM,FTIR,XRD and other tests,the experimental parameters such as pyrolysis behavior,material change and residual carbon morphology of the fire retardant coating are obtained,the change law in the combustion and pyrolysis process of the fire retardant coating is analyzed,and its charring mechanism is comprehensively analyzed.The results show that the thermal decomposition process of MPP/CFA fire retardant coating is mainly divided into four stages.After combustion,a relatively continuous and dense carbon layer is formed.The phosphorus carbon layer with cross-linked structure formed by the polyphosphoric acid produced by MPP thermal decomposition and the triazine ring produced by CFA plays the main role of heat insulation and oxygen isolation,and also has the role of gasphase flame retardant,which improves the fire resistance of the fire retardant coating. |
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