Orientation and structure development in polyamide 6 fibers upon drawing

Drawn polyamide 6 (PA6) fibers were characterized with X‐ray diffraction, Fourier transform infrared (FTIR) spectroscopy, density measurement, and optical microscopy. The α and amorphous orientation functions were determined by polarized FTIR spectroscopy. It was demonstrated for the first time that the infrared band at 1124 cm −1 could be used to determine the amorphous orientation functions of drawn PA6 fibers and films. α, γ, and amorphous orientation functions increased rapidly at lower draw ratios and increased slowly at higher draw ratios. The amorphous orientation functions measured by polarized FTIR spectroscopy did not agree with those determined by a combination of wide‐angle X‐ray diffraction (WAXD) and optical birefringence measurements, attributed to possible error in the estimated birefringence. The α and γ crystallinity of undrawn fiber (DR = 1) were ∼24 and 6%, respectively, which increased to ∼13 and 39% at a draw ratio of 4 (DR = 4). The WAXD data suggested that γ crystal grew in the hydrogen‐bonding direction as well as the van der Waals direction during deformation. The decrease in γ crystallinity and increase in γ crystallite size with the draw ratio were attributed to the disappearance of small crystallites and an increase in the average γ crystallite size population during the deformation process. The increase in density with the draw ratio was attributed to crystal‐to‐crystal transformation as well as strain‐induced crystallization.