Properties and morphology of aramid films and fibers obtained fron a liquid crystalline dope

Abstract

In order to analyze the effect of process variables during the ploy(pphenylene terephthalamide) pulp/fiber production process, the reaction kinetics, kinetics of liquid crystal formation, state of the liquid crystalline dope and the structure/morphology of the fiber and film were investigated. To get information for the polymerization reaction, kinetics of polymerization and liquid crystal formation were studied. A second order reaction model was suitable to describe the polymerization reaction. The Avrami equation was used to describe the liquid crystal formation from the isotopic solution and the Avrami value(n) of 2 was obtained. During the reaction, the onset point of transition from isotopic to anisotropic phase could be confirmed by striation bands produced by shearing between crossed polars under polarized microscope. The conversion at the onset point of transition was nearly the same regardless of initial reaction temperature for the same solid content. The conversion at the onset point is lower at high solid content. The role of pyridine as the coagulating agent was confirmed. I.V. of polymer increased up to about of 2 in pyridine system. When films were made from anisotropic state, the degree of crystallinity and orientation increased linearly as increasing the shear rate, but for films made from isotopic state, the structure was not well developed. The tensile strength of the former is 7-10 times higher than that of latter. The calculated unit cell constant and lattice image for the fiber produced from liquid crystalline prpolymer dope were nearly the same as those of Kevlar, which implies that the basic structural units are the same as Kevlar. However, both the regular defect bands with a periodicity of ca. 250-500 nm and the characteristic features of skin-core structure in kevlar were not observe in this fiber. These differences in the structure may be originated from differences in the dope and spinning process.