The Outer Shell of the jacket and pants of the firefighter s protective clothing is constructed of a fabric that is commonly a blend of polyaramid, polybenzimidazole, and/or poly(melamine-formaldehyde) fibers. The Outer Shell contributes to the thermal and moisture protection of the garment, but its primary purpose is to provide protection from other physical hazards, such as sharps objects and abrasive surfaces. The research discussed in this manuscript indicates the mechanical performance, which is critical to the Outer Shell providing protection against these physical hazards, of polyaramid and polybenzimidazole based Outer Shells will rapidly deteriorate when exposed to ultraviolet light at 50 degreeC and 50% relative humidity. For example, as high as an 80% reduction in the tear and tensile strength was measured after 13 d of exposure to these conditions. The mechanical performance deterioration resulted from photo-induced decomposition of the polymer backbone, as measured by infrared spectroscopy. Polymer and fiber decomposition was also visually observed using confocal microscopy. These microscopy images showed the exposure conditions caused pitting on the surface of the fibers, fiber shape deformation, and/or a switch from ductile to brittle failure. Even though the exposure conditions caused catastrophic mechanical failure, the amount of ultraviolet light transmitted through these fabrics is insufficient to photolytic degrade the undergarments of the protective clothing.
Citation: Technical Note (NIST TN) - 1657
NIST Pub Series: Technical Note (NIST TN)
Pub Type: NIST Pubs
Firefighter protective clothing, turnout gear, polyaramid, polybenzimidazole, polymer fiber, NIST SPHERE, tear strength, tensile strength, laser scanning confocal microscopy, ultraviolet transmittance, fourier transform infrared (FTIR) spectroscopy, textiles, service life, polymer aging.