Studyon Thermal Behavior Of Flame Retardant Fabrics In Fire Scene

Flame retardant fabric is one of the modern social life safety and production safety essentials.With the progress of science and technology,the development of new flame retardant textile materials and the advancement of industrialization,the application of flame retardant textiles has broken through the field of national defense and military,expanded to industry,agriculture,communication and transportation and homelife,etc.Expecially,in the field of firefighting,the application of flame retardant fabrics can effectively curb the spread of flames,ensure the safety of firefighters while working,and reduce the harm of thermal disaster to the life,property and environment.Thus,improving the fire safety of flame retardant fabric and expanding the application of flame retardant fabrics are important ways to reduce the fire and avoid fire harms.Flame retardant cotton,polysulfonamide and aramid fabrics are the three kinds of flame retardant fabrics applied in firefighting achieving industrialization production in our country.Studying thermal behavior of these fabrics in fire scene is helpful to enhance the effectiveness of the rescue,and to promote the generalization of "Military-into-civilian" for flame retardant fabrics development technology.The main ways of heat transfer in fire scene include heat conduction,convection and radiation.The thermal behavior of flame retardant fabrics under the action of heat in the fire scene mainly include: the variation of fire safe,such as pyrolysis,fire resistance,heat release,smokiness,and the change of protective performance,including thermal protective performance,thermal radiation parameters and thermal resistance.Flame retardant cotton,polysulfonamide and aramid ?A were studied in this paper by using the two indexes of thermal behavior: fire safety performance and thermal protective performance.Firstly,the fire safety were studied from micro scale and macro scale.The micro aspect,the pyrolysis kinetics and the pyrolysis mechanism of the polysulfonamide fiber were studied by usingTG-FTIR firstly in this paper.The results showed that the thermal degradation process of the polysulfonamide fiber are divided into dry dehydration stage,transition stage,the main pyrolysis stage,and stage of carbonization.The temperature of initial decomposition under nitrogen atmosphere was around 375?,and the residual carbon rate was near 42% at 800?,The thermal stability was excellent.The average activation energy calculated by using Friedman method and FWO method were 215.62 kJ/mol and 194.65 kJ/mol respectively,which is most likely to conform to the S2 cylindrical symmetry diffusion mechanism combining with the results of the pyrolysis process obtained by Coats-Redfern method.And then the states of flame retardant fabrics before and after pyrolysis were characterized by means of TG and laser microscope.The results showed that the pyrolysis of flame retardant cotton exposing to a convective heat flux of 63kW/m2 for 20 s was more complete,while polysulfonamide and aramid ?A fabric just had partial pyrolysis,and they still had a good stability.Macro aspect,the fire safety of flame retardant cotton,polysulfonamide and aramid ?A were analyzed from the aspects of flame retardant performance,burning behavior,smoke generation,etc.By using vertical burning test,limit oxygen index,cone calorimeter,smoke dendity chamber,it was found that the three kinds of flame retardant fabrics all had good flame retardancy,but the quality loss of flame retardant cotton was bigger when it was heated,polysulfonamide shrunk seriously when encountered heat.The fire safety of aramid ?A was greater than the flame retardant cotton and aromatic polysulfonamide when exposed to radiant heat flux of 25 kW/m2 and 50 kW/m2;The pyrolysis of flame retardant fabrics exposed to heat flux of 25 kW/m2 in flameless mode was slow,whose smoke production were higher than that in flame mode.Secondly,the effect of pyrolysis on heat insulation protection performance and thermal radiation property parameters were studied.Primarily,the pyrolysis of fabrics was simulated by the FPT-30 A flame protection evaluation testing machine,the different states of flame retardant fabric before and after pyrolysis were characterized by TG and laser microscope microscopic,and the RPPtest device was constructed to study the pyrolysis effect on the thermal protection properties of flame retardant fabrics.Results showed that the pyrolysis degree of flame retardant cotton was completed,while only parts of the polysulfonamide and aramid ?A decomposed.The thermal protective performance of polysulfonamide and aramid after pyrolysis decreased comparing to that before pyrolysis,and the highest relative difference was 35.7%.With the rise of the radiation heat flux density,the changing trend of backside temperature differences for polysulfonamide and aramid before and after pyrolysis fabric general rise steeply first and then rise gently.Then,the change of fabric composition after pyrolysis,spectral radiation parameters such as reflectivity and transmittance were analyzed by using the Fourier transform attenuated total reflection infraredspectrometry(ATR-FTIR)and ultraviolet visible near infrared spectrophotometer.Results showed that infrared spectrogram characteristic absorption peak of the three kinds of flame retardant fabrics was less obvious after exposing to a convective heat flux of 63 kW/m2 for 20 s.The reflectivity and transmittance of flame retardant fabrics after pyrolysis decreased,while the absorption rate increased comparing to that before the pyrolysis,and the changing difference of transmittance for fabrics before and after pyrolysis was far less than that of reflectivity.Finally,the change law of fabrics for different pyrolysis degree under the low radiant heat flux(5 kW/m2)was analyzed by constructing thermal resistance test device.It was found that under low radiation intensity,the thermal resistance of flame retardant fabric decreased with the increase of pyrolysis degree;And under the same pyrolysis conditions,thermal resistance of the flame retardant cotton was smallest andthat ofaramid ?Awas maximum.