Abstract
Moisture sorption properties and their relation both to noncrystallinity and to crystallite size were investigated for as-polymerized poly (p-phenylene terephthalamide) (PPTA) paricles. Degree of crystallinity in the PPTA particles after heat-treatment estimated from a wide-angle X-ray diffraction measurements was at most 64%, which was lower than that in regular Kevlar. Crystallite size for the PPTA particles was also smaller than that for regular Kevlar. However, crystal lattice struture was almost the same between the particle specimens and Kevlar fibers. The plot of moisture regain vs. heat of wetting showed linear relation, indicating nearly the same magnitude of interaction of water to the amide groups both for the PPTA particles and for Kevlar fibers.The ralation between the heat of wetting (or moisture regain) and degree of noncrystallinity linearly changed among the four kinds of fibers. However, the heat of wetting (or moisture regain) for the PPTA particles showed higher values than estimated from the linear relation in the plot obtained for the fibers. This suggested the difference in the three dimensional noncrystalline stucture between PPTA particles and fibers. Higher amount of free amide groups and easier accessibility of water to the amide groups due to the random orientation of the molecular chains enabled the higher moisture sorption in the as-polymerized PPTA particles.
