Effects of accelerated aging on the performance of moisture barriers used in firefighters’ protective clothing
Creators: Munevar-Ortiz, Laura K.
Publisher: name: University of Alberta Library
Year: 2024

<p>The moisture barrier is a critical layer in firefighters protective clothing as it prevents liquid penetration inside the garment while allowing perspiration to exit. The moisture barrier is a laminate fabric structure consisting of a base fabric, an adhesive, and a membrane. This study examined the effect of accelerated thermal, hydrothermal, and ultraviolet (UV) aging on the tear force retention, water vapour transmission rate (WVTR), and apparent contact angle of three moisture barriers commonly used in firefighters’ protective clothing in North America. Thermal aging was conducted at temperatures between 95 and 240°C. Hydrothermal aging was conducted by immersing the specimens in water at five temperatures (20, 60, 80, 90, and 95°C). For UV aging, four irradiance levels (0.35, 0.68, 1.00, and 1.35 W/m2 measured at 340 nm) and four temperatures (40, 50, 70, and 80°C) were used. Complementary high-speed imaging, Field Emission Scanning Electron Microscope (FESEM) and Fourier-transform infrared (FTIR) analysis were also conducted. Differences in tear force retention, WVTR, and apparent contact angle were noted after the different accelerated aging treatments. These changes were impacted by factors including the base fabric structure; fibre content; adhesive configuration; water-repellent finish; and the presence of an extra flame-resistant polyurethane (FR PU) coating on the expanded polytetrafluoroethylene (ePTFE) membrane. </p>

<p>Utilizing high-speed imaging, the tearing process of moisture barriers revealed distinct tearing behaviours influenced by factors such as: the base fabric structure; presence of an extra FR PU coating; and adhesive configuration. The effect of thermal aging included delamination between the membrane and base fabric, increased WVTR due to crack formation in the membrane, and hydrophobic to superhydrophilic transition on the base fabric side. For hydrothermal aging, slight tear force decreases were attributed to PU adhesive hardening and aramid fibre degradation. Synergistic effects between water and heat were observed on the WVTR and apparent contact angle. After UV aging, all moisture barriers exhibited an initial sharp decrease in tear force retention associated with photo-oxidation of aramid fibres. Reduced water vapour transmission occurred due to membrane pore closure and a transition to a superhydrophilic behaviour was observed on the fabric side in one instance. UV aging emerged as the most influential factor on performance losses of the moisture barriers. </p>

<p>The analysis of the results shed light on the base fabric&#39;s structure and fibre content, adhesive configuration, and presence of an extra FR PU coating on the membrane. The fibre content had a large effect on the tear force retention of the thermally and UV aged specimens. The structure of the base fabric – woven vs. nonwoven – also affected the tear force retention of the moisture barriers to thermal and hydrothermal aging. If the adhesive configuration did not affect the performance of the aged moisture barriers by itself, it played a role in their residual performance via the interaction between the adhesive layer configuration and the base fabric structure. Finally, the extra FR PU coating influenced the tear force retention after thermal aging and impacted the WVTR after thermal and hydrothermal aging. </p>

<p>These insights inform not only the current understanding of moisture barrier dynamics but also serve as a foundation for future research and product development in the field, ultimately contributing to advancements in firefighter safety.</p>