Investigation of the Aging of High-Performance Fabrics used in the Outer Shell of Firefighters’ Protective Clothing
Creators: Hoque, Md Saiful
Publisher: name: University of Alberta Library
Year: 2024

<p>This study has investigated the accelerated hydrothermal, thermal, and photochemical aging behavior of outer shell fabrics made from different blends of high-performance fibres: meta-aramid, para-aramid, aramid copolymer (Technora), polybenzimidazole (PBI), polybenzoxazole (PBO), and liquid crystal polyester (LCP). The objective was to further understand the mechanisms and kinetics of aging of these fabrics used in firefighters’ protective clothing for which studies have shown severe loss in mechanical and barrier performance after service use. In addition, researchers have reported the lack of visible signs of degradation of firefighter outer shell fabrics after heat exposure even though the fabrics had suffered large loss in strength. <br>
The accelerated aging conditions for the study were chosen based on the conditions that firefighters may encounter in the line of duty. The thermal aging of the fabric specimens was carried out in an air-circulating oven at temperatures between 90 and 320 °C for up to 1200 hours. The photochemical aging involved subjecting fabric specimens to UV irradiances between 0.35 and 1.35 W/m2 at temperatures between 40 and 80 °C for up to 600 hours. For the hydrothermal aging, the fabric specimens were immersed in reverse osmosis (RO) and acidic water at temperatures ranging between 21 and 95 °C for up to 1200 hours. The residual performance of the fabrics was assessed in terms of breaking force and apparent water contact angle. Complementary measurements of the physical, chemical, and physicochemical condition after aging were also performed.<br>
Different behaviors were observed in the fabrics depending on the type of aging program and fibre blend. Hydrothermal aging severely affected the para-aramid/PBI blended fabrics. It was attributed to the high amount of residual sulfur measured in the PBI fibres that made the aging water become acidic and resulted in the hydrolysis of fibres such as para-aramid. On the other hand, the meta-aramid and Technora fibres showed good resistance to hydrothermal aging, even in acidic water. All of the fabrics except one with a high percentage of meta-aramid fibre (93%) showed a synergetic effect of water and temperature in the hydrothermal aging process. While some fabrics experienced a decrease in their crystallinity index due to hydrothermal aging, no morphological or chemical changes were observed. The analysis of the hydrothermal aging water identified 276 unique compounds; some of these compounds pointed towards the degradation of fibres, dyes and pigments, or the fabric’s surface finish.<br>
In terms of photochemical aging, the para-aramid/PBI blended fabric offered the best resistance, possibly due to the robust aromatic structure of PBI. Moreover, the pigments responsible for the black color of the para-aramid/PBI blended fabric studied may have acted as a UV absorber and protected the underlying fibres from UV radiation. On the other hand, the Technora/PBO and para-aramid/meta-aramid blended fabrics experienced a large loss in their force at the break after photochemical aging. Although all three fabrics experienced surface finish deterioration and fibre morphology damage, no significant chemical and physicochemical changes were detected. The synergetic effect of UV radiation and temperature was evidenced in all three fabrics studied.<br>
A premature thermal degradation was observed in the para-aramid/PBI blended fabrics at a low temperature. The fabrics lost around 10% of their force at break after 1200 hours of thermal aging at 90 °C. This was ascribed to a possible deterioration of the PBI fibres as no drop in the breaking force was observed in other fabrics with identical para-aramid content. In the most severe thermal aging conditions tested, all three fabrics experienced a major loss in their force at break. This decrease was associated with fibre breakage along with chemical and physicochemical changes. The Technora/PBO blended fabric showed a comparatively higher thermal aging resistance, which was attributed to PBO high thermal stability.<br>
The findings of this study deepen the understanding of the long-term performance of fire-protective fabrics. They will contribute to the development of better protective gear, particularly for firefighters and other individuals exposed to heat and flame, and will directly benefit various stakeholders, from high-performance fibre manufacturers to the end-users of protective clothing. </p>