Abstract
Structural changes of polypropylene fibers during a direct draw melt spinning process were analyzed by comparing fibers which have gone through the direct draw melt spinning process with those for which the drawing step was omitted. The relative contribution of the drawing step was evaluated so that the information on the stages of development of the structure can be applied as a basis for future research on functional or high performance fibers. Four different molecular weights and take-up speeds were applied to study the effect of these variables on the development of the structure. When the effect of differences in molecular weight was compared with that of differences in take-up speed on the physical properties, the variation width of the properties for the former appeared about 2~4.5 times higher than for the latter. When the properties of the drawn filaments were taken as reference and the degree of structure formation in the undrawn filaments was described by the percentage thereof, 85 and 95% of crystallinity and crystalline orientation had already been developed prior to the drawing step, respectively. On the other hand, the overall orientation was found to be more dependent on the drawing process, with about 64-73% of the orientation being developed in the drawing step and 26.8-36.1% being developed prior to the drawing step. The amorphous orientation of the undrawn fibers exhibited a negative value suggesting that the rotation of lamella to the final structure occurs in the drawing step.