Effects of absorbed moisture on high-performance organic fibers.

摘要

The problem addressed in this thesis is that of absorbed moisture in high-performance fibers. The goal is to determine what physical form absorbed moisture exists in as a function of environmental conditions and to obtain a better understanding of the physical state of absorbed moisture as a function of fiber chemical and physical structure. A number of different fiber systems were examined and include: three Kevlar fibers (Kevlar 29, 49, and 149), two aramid copolymer fibers (X-500 and Technora), two polybenzimidazole fibers (unmodified and sulfonated), and six poly(vinyl alcohol) fibers.; Thermogravimetric analysis studies provided information about: (1) the amount of absorbed moisture as a function of %RH, (2) the maximum rate moisture loss temperature, and (3) the weight fraction of an initial, quick moisture loss process. Nuclear magnetic resonance experiments as a function of %RH and temperature assessed chemical environment and/or mobility state differences among various fibers.; TGA measurements show that fiber chemical and physical structures have a significant effect on the amount of absorbed moisture associated with a given fiber. S-shaped moisture absorption profiles versus %RH are observed in all cases. Strong upturns in fiber moisture absorption at high %RH may be accounted for on the basis of transverse fiber swelling. NMR results suggest that water is present in an amorphous form. Mobility cessation temperatures are observed which correspond to the solidification of water into a glasslike state, but there is no evidence for ice formation in any of the fibers examined.; Factors controlling the physical structure of water in fibers are based on the potential for hydrogen bond interactions. These are directly related to fiber chemical structure and moisture accessibility to those sites. The most important parameter is accessibility to potential sites, which is controlled by fiber physical structure. Chemically related factors are evident at secondary levels.; Experimental results and model calculations suggest that water may exist in three potential states among the high-performance fibers evaluated. These include: (1) polymer-water hydrogen bond interactions, (2) water-water bridge structures between oriented, adjacent intermolecular sites or microfibrillar crystallite domains, and (3) water of hydration associated with ionic impurities.