An examination of the crystal structures present in nylon‐6 fibers

Abstract

AbstractThe variety of wide‐angle x‐ray scattering (WAXS) patterns exhibited by nylon‐6 fibers with different fabrication histories is rationalized using a model comprising three limiting structures, viz., an α, a γ, and a pleated α structure. The γ and pleated α structures both have a single broad reflection in the range 2θ = 19° −25°, but differ in their annealing behavior. At 205° (in vacuo), the pleated α structure converts to the normal α structure by removal of the pleats, without breaking any hydrogen bonds. The γ structure, however, remains unchanged under this annealing condition since it is necessary to break all the hydrogen bonding in the structure to convert it to the α form. Different fabrication routes produce fibers which resemble the three ideal structures to varying extents. Fibers extruded at low speeds (and hence low spinline tension) resemble a mixed conventional α/pleated α structure with only a small γ component. Increasing the take‐up speed (and hence the spinline tension) of the as‐spun fiber, or in‐line drawing of the low orientation fiber (without prior storage), increases the γ content. If drawing of the low orientation fiber takes place after several hours storage (off‐line drawing), a largely α structure is produced. The intensity of the 020 reflection in the γ structure is shown to be very dependent on the degree of crystalline orientation in the sample.