| Firefighting is of great significance for ensuring the safety of people’s life and property.As one of the important equipment for ensuring the personal safety of firefighters,fire-fighting suit has always been a focus in research of thermal protection.Good firefighter uniforms should not only have a good barrier to the external heat,but also have certain heat and moisture transfer capability.Therefore the research on the influence of the heat and humidity transport of moistened flame retardant fabrics on the thermal protective performance in radiant heat exposure is of great significance.Firstly,the moisture migration process of aramid ⅢA,aramid 1313 / viscose,aramid 1414 / modal and the flame retardant cotton under wet state are analyzed from microcosmic point of view by using LF-NMR technology in this paper.The experimental results show that there are at most three different forms of absorbed moisture in the wet flame retardant fabrics: bound water,capillary water and free water.In the process of desorption,free water is first stripped.And the three forms of absorbed moisture bond more closely with the fabric in the process of desorption,the motility of the moisture is reduced.Then,the experimental platform is set up to explore the surface temperature variations of aramid 1313 / viscose and 2 kinds of flame retardant cotton fabrics in dehydration process exposed to radiant heat.Results from the moisture loss and temperature change data indicate that the drying process of fabric could be divided into three stages:(1)the first stage in which drying velocity and the temperature increase rapidly and the moisture content decrease slowly;(2)the second stage in which the drying velocity kept stable and the temperature increased slowly,while the moisture content decreased rapidly;(3)the third stage in which the drying velocity slowed down and the moisture content decreased tardily.When the moisture content decreasing to 20%,the surface temperature rise rapidly.Afterwards,the application of three different mathematical models to simulate the drying kinetics of the porous fabrics has been evaluated by fitting the experimental data: Page,Newton and Henderson model.The results reveal that the dynamic drying process of single-layer fabric in low-level radiant heat exposures could be described mathematically by Page equation.Secondly,the effects of moisture on thermophysical characteristic and optical property of flame-retardant fabrics are studied in this paper.The transient planar heat source technique is used to test the transient thermal conductivity of aramid ⅢA,aramid 1313 / viscose,aramid 1414 / modal and the flame retardant cotton containing different amount of water,and take thermal conductivity as dependent variable,the moisture content as regression independent variables to set up one-dimensional linear regression equation.The results indicate that the moisture content and the thermal conductivity present a significant positive correlation.The change of the radioresistance properties such as reflectance and transmittance of aramid ⅢA,aramid 1313 / viscose,aramid 1414 / modal,the flame retardant cotton and PDSTA within the scope of near-infrared radiation of 800~2500nm are analyzed by using Aligent Cary5000 UV/VIS/NIR spectrophotometer.Results show that the infrared reflectivity of the flame-retardant fabrics decrease with the increase of the moisture content.In the near-infrared radiation of 800~1400nm,the infrared transmittance of the five kinds of fabrics increase with the increase of moisture content.In the near-infrared radiation of 1400 ~ 2500 nm,the infrared transmittance of aramid ⅢA and PDSTA decrease with the increase of moisture content;with the increase of moisture content,the infrared transmittance of aramid 1313 / viscose,aramid 1414 / modal and the flame retardant cotton decrease first,and rebound shortly in the clause boundary of the capillary water and bound water,then continue to decline.Finally,a RPP tester is used to analyze the temperature variations for the facecloth side of aramid,knitting aramid,flame-retardant cotton and knitting flame-retardant cotton under different moisture content and different intensity of radiation heat from microcosmic point of view in this paper.Experimental results show that the addition of moisture had a positive influence on the thermal protective performance during the constant temperature period when heat radiation time was more than 60 s.As the heat radiation time increased beyond 500 s,the thermal protective performance of moistened fabrics became worse than that of dried fabrics.Then,aramid 1313,aramid 1313 / viscose,two kinds of flame-retardant cotton fabrics,PTFE membrane and aramid fiber mat are selected to combine into four-layer fire-retardant fabric combinations.The comfort layer is moistened to simulate the situation that the fabric absorbed perspiration from a sweating firefighter,and the outer flame-retardant fabric is moistened to simulate the condition that the fabric is wetted by fire water.A TPP tester is employed to measure the thermal protective performance of the four-layer fire-retardant fabric combinations.The data show that low-level moisturizing of fire-retardant multilayer fabric combinations(moisture regain under 32%)has a negative impact on its thermal protective performance.And when its moisture regain is up to 26%,the thermal protective performance reaches the minimum. |
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