Polymorphism and orientation development in melt spinning, drawing, and annealing of nylon‐6 filaments

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Abstract
A new method has been developed for determining the total crystallinity and relative amounts of α‐ and γ‐phases in nylon‐6 samples. The procedure is based on a combination of X‐ray and density data and does not require complicated analytical procedures to separate overlapping reflections. The technique has been applied to study the structural changes accompanying the melt spinning, annealing, and drawing of nylon‐6 filaments. Higher spin draw ratios result in higher crystallinity, greater relative amounts of γ‐phase, and higher orientation. Annealing up to 2 h in boiling water or a 20% aqueous formic acid solution decreases the γ‐phase content, increases the α‐phase content and total crystallinity, but does not eliminate all of the γ‐phase in samples spun with high spin draw ratios. Annealing in vacuum also increases the α‐phase content when annealing is carried out at temperatures above 120°C, but there is little effect below this temperature. Drawing of as‐spun and conditioned filaments at 90°C also increases the α‐phase content and decreases the γ‐phase content. The total crystalline content increases with draw ratio for samples with low spin draw ratios, but drawing has little effect on the total crystalline content of samples spun with higher spin draw ratios. Drawing also results in substantial increases in orientation, especially for samples spun with low spin draw ratios. The effects of these changes in structure on the mechanical properties are also described.