Sorption of Water by Aromatic Polyamides

Isotherms of water-vapor sorption by aramid fibers and films of various nature were determined by static sorption methods. Structural and morphological characteristics of aramid fibers were investigated by the methods of transmission and scanning electron microscopy, X-ray structural analysis. It is shown that the studied industrial aramids are X-ray amorphous mesophases. The diffusion coefficients of water in aramids of various thermal prehistories have been determined. Greater interest is presented by the region of high humidity, where a rather sharp increase in the diffusion coefficients is observed for fibers and membrane films, which is associated with an increase in the segmental mobility of aramids and the onset of the process of devitrification of sorbents. The factor of complication of the transport paths during the transition from copolyamide membranes to fibers has been calculated. The sorption capacity of industrial aramid fibers in the entire range of water-vapor activity is significantly lower than the sorption capacity of films, membranes, and model sorbents. It is shown that paracrystalline mesophases act as “impermeable particles” in aramids. It is shown that absorbed water in polymers can exist in a nonassociated state or in the form of clusters. The number of water molecules included in the clusters has been determined.