AbstractThe effect of heating nylon 6 threadline in a spinning tube upon its orientation and crystallization behavior was studied by measuring the filament birefringence ΔnHat the outlet of the spinning tube, the conditioned filament birefringence Δn∞after take‐up, the filament densities and crystallinities of the γ‐form, and by calculating the relative crystallinity of the threadline. Results were as follows: When the filament mean temperaturedocumentclass{article}pagestyle{empty}begin{document}$overline{theta _s left(x right)}$end{document}in the spinning tube was about 80°C, the birefringence ΔnHshowed a peculiar behavior in that, at this temperature, the ΔnHvalue decreased due to partial melting of the semistable molecular structure of the threadline that had been formed before the inlet of the spinning tube. And, when the temperature was over about 80°C, the ΔnHvalue increased due to the setting in of crystallization. The relative crystallinity χ of the threadline was calculated using the kinetic theory of nonisothermal crystallization neglecting the entropy effect of molecular orientation. Assuming that the crystal growth was spherulitic rather than fibroid, the calculated χ values approximately agreed with the exper
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