Effects Of Thermal Radiation On Thermal Protective Performance And Durability Of Firefighter Protective Clothing

Two outer shell fabrics used for firefighter protective clothing were exposed to different radiant intensity environments (6.5kw/m2,9.7kw/m2and17.2kw/m2). Radiant heat flux was provided by quartz tube radiometer while fabric surface temperature was recorded by NI virtual apparatus. The radiant time was set as5、10、20and30minutes. Then the parameters used to characterize the mechanical performance and thermal protective performance were tested. The results show that the surface temperature of domestic aramid fabric is higher than that of Nomex ⅢA fabric in the different thermal radiation conditions. That shows the thermal insulation of NomexⅢA fabric is much better than that of domestic aramid fabric. In the intensity of6.5kw/m2thermal radiant environment, the surface temperature of two kinds of fabric is under the glass transition temperature (270℃). At this time, fabric can maintain its68.9%-84.6%of tear strength in half an hour. And it causes an improvement in thermal protective performance following low-level thermal radiation. In the intensity of6.5kw/m2thermal radiant environment, the surface temperature of two kinds of fabric is up to300℃above. This moment the tensile strength and tear strength decrease significantly with radiation time increasing, especially the warp tearing strength of aramid fabric drops60.5%while the weft tearing strength of it drops58.8%. However, the increasing TPP value shows the improvement in thermal protective performance.For a further study on the variation of aggregated structure and chemical structure during heat ageing process of fabric, the polymer before and after thermal radiation was tested and analyzed by the scanning electron microscope, X-Ray Diffraction and Fourier transform infrared-Raman spectrometer. The results show that as thermal radiation strength increases, the calculated crystallinity of polymer decreases. In the thermal radiation intensity of9.7kw/m2, the crystallinity of NomexⅢA fabric drops27%and crystallization size decreases at the same time, which means the degree of crystalline perfection reduces. The observed decrease of crystallinity after thermal treatments is in good agreement with the results of the deterioration in the mechanical performance. So that’s the main reason why the tensile strength and tear strength decrease. In the thermal radiation intensity of17.2kw/m2, the surface temperature of fabric is up to380℃. And the crystallinity of fabric decreases44.5%～52.7%while the fiber cracks in the surface. Fourier transform infrared-Raman spectroscopy analyses validate the crystallinity results, and implies the thermal degradation of fabric and the degree of domestic aramid fabric degradation is much greater.Finally, a forecasting model is developed to predict values of the tensile strength and tear strength after thermal radiation treatments from color change based on Matlab. The purpose of the model is to evaluate life cycle of outer shell fabrics used for firefighter protective clothing.