Bulk properties of synthetic polymer‐inorganic salt systems. V. Mechanical properties of oriented poly(caproamide)

Single filaments of nylon‐6 and of its mixtures with KCl, LiCl, and LiBr (salt content up to 5% w/w) were prepared by extrusion at 265°C. As‐spun filaments with a varying degree of orientation were obtained by altering the take‐up velocity a t constant outflow velocity. These as‐spun filaments were further subjected to controlled thermal and mechanical treatments. Determinations of the elastic modulus, of birefringence, of wide‐angle x‐ray scattering, and of shrinkage were carried out for the as‐spun and for the treated filaments. While KCl caused no detectable alteration of the properties of nylon‐6, lithium halides caused a considerable increase of the elastic modulus of the polymer. Under the conditions adopted, moduli up to 14 GPa were obtained. The birefringence of as‐spun fibers was, however, lower when lithium salt was present. Greater shrinkage a t 170°C was exhibited by the salted than by the pure polymer. The body of results has been interpreted in terms of a more efficient orientation of the extruded polymer when lithium salt is present. The latter effect is associated with the role of these salts in reducing the crystallization rate and in increasing the melt viscosity of the polyamide as characterized in preceding papers of this series. Lithium salts also favor the α → γ transformation between the two crystalline forms of nylon‐6. The transformation was, however, reversed under sufficiently high applied stress.