Fibrillar Structure and its Relevance to Diffusion, Shrinkage, and Relaxation Processes in Nylon Fibers

Quantitative prediction of the properties in fibers of semicrystalline polymers requires a detailed description of the fibrillar structure. Use of small-angle x-ray and neutron scattering (saxs and sans) and wide-angle x-ray diffraction (waxd) to obtain such information is illustrated with data from drawn and annealed nylon 6 fibers. The length, diameter, and orientation of the fibrils and the lamellae, and the spacing between the fibrils and the lamellae, are determined using saxs. Diffusion characteristics of the interlamellar and the interfibrillar regions are studied by following the diffusion of solvent molecules (D₂O) using sans. Changes in the amorphous orientation are studied by analytically separating the amorphous scattering in waxd patterns into isotropic and anisotropic components. Our data suggest that the glass transition temperature is due to the superposition of relaxations of unoriented and oriented amorphous components. Diffusion is interpreted as occurring through a network of interconnected interfibrillar (voids and mostly oriented amorphous or noncrystalline chain segments) and interlamellar (primarily unoriented amorphous or noncrystalline chain segments) channels. These channels respond differently to drawing and heat setting. The influence of the crystallization of oriented components of the amorphous phase on shrinkage behavior is discussed.