Effects of m-Aramid/p-Aramid Blend Ratio on Tensile Strength due to UV Degradation for Firefighter Clothing Fabrics and Development of Predictive Equation for Tensile Strength

Abstract

This study focused on the m-Aramid/p-Aramid blend ratio of the fabrics, clarified the quantitative relationship between UV exposure and strength retention, and developed a mathematical model to calculate tensile strength from an arbitrary amount of UV exposure energy. The results of tensile strength tests before and after UV exposure showed that the decrease in tensile strength due to UV degradation depended on the combination of p-Aramid and m-Aramid blend percentages. Tensile strength for all blend ratios decreased exponentially with UV exposure energy and was within the range of results for fabrics with p-Aramid 100% and m-Aramid 100%. The retention fraction of tensile strength, which represents the tensile strength after UV exposure relative to the initial tensile strength, decreased exponentially with increasing the fraction of UV exposure energy for all fabrics used in this study. Fitting the retention fraction of tensile strength to the fraction of UV exposure energy, two groups of fabrics were classified based on m-Aramid blends of 40% or more and 60% or less. This model can predict the tensile strength of firefighter clothing fabrics that retain high mechanical strength when exposed to UV light and design the strength of firefighter clothing with consideration of degradation over time.

Quantitative Assessment of Tensile Strength and Degradation Coefficient of m-Aramid/p-Aramid Blended Yarns Used for Outer Layers of Firefighter Clothing under Ultraviolet Light and Correlation with Fabrics Data

“…Since the UV exposure conditions shall be the same as those of the three-layer fabric of firefighter clothing, the yarn specimens were layered in the order of yarn specimen, moisture barrier, and thermal liner from the top, as shown in Figure 2 . Specimen preparation is consistent with the one for fabrics [ 9 ].…”

“…The spun yarns for UV exposure were two-ply spun yarns in warp direction sampled from fabrics used in the tensile test of firefighter clothing outer layers [ 9 ]. Table 1 shows the specification of yarn samples for tests.…”

“…Wakatsuki et al [ 9 ] found a quantitative relationship between UV exposure and strength retention for nine fabrics blended with m-Aramid and p-Aramid. This study also developed an equation to calculate tensile strength from arbitrary UV exposure energy and validated the replacement condition of firefighter clothing in NFPA 1851 [ 10 ] with a case study.…”

“…Previous studies [ 4 , 5 , 6 , 9 ] evaluated the decrease in the tensile strength of fibers and fabrics after UV exposure. However, a correlation between the reduction of tensile strength of a fiber, a spun yarn, and a fabric as woven fiber assemblies after UV exposure was not investigated when the same fibers were used.…”

“…Next, this study makes the curve-fitting formula for the retention fraction of tensile strength after UV exposure. Finally, a comparison was made with the model equations for tensile strength of yarns to woven fabrics made of m-Aramid/p-Aramid blended yarns of the exact specifications [ 9 ].…”