AbstractNylon 6 yarns were wound at speeds varying from 700 to 5500 mpm. The effect of the winding speed on both α‐ and γ‐type crystals in these undrawn yarns was studied. Also the effects of dry heat, tension, and heating in saturated steam were included in this investigation, since they provide useful information for drawing and heat‐setting processes. The emphasis was put on the characterization of the crystalline part of the yarns. By applying recently developed techniques, relative amounts of the two crystalline components, as well as their orientation factors, could be determined. Concerning the undrawn, conditioned yarns, it was found that the amount of γ type increases with the winding speed. The γ crystals are much better oriented than the α crystals, and the crystal dimensions of the γ structure largely depend on the winding speed in contrast to those of the α crystals. Indications were found that γ crystals are mainly generated from orientation‐induced nuclei at speeds higher than 2500 mpm and that α crystals grow slowly at relatively low temperatures after moisture pickup during conditioning. Drawing at high ratios causes a transition from γ to α, while the thermal stability of the γ crystals appears to be slightly below that of the α crystals, resulting in γ crystal to α crystal transitions at extremely high temperatures or under usual
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