Synchrotron X-ray Scattering and Precise Structural Analyses of Poly(ethylene terephthalate) Fibers Prepared by High Speed Melt Spinning

Abstract

Precise structural analyses of high speed melt spinning fibers provide useful information of appropriate nano-structures for imparting ultra-high strength to general fibers. For quantitative and precise analyses by X-ray scattering measurements, strong X-ray source is required. In this paper, we demonstrate significance of the synchrotron X-ray scattering and precise structural analyses of poly(ethylene terephthalate) fibers prepared by high speed melt spinning, with the take-up velocity ranging 1∼9 km/min. Systematic changes in the 2d-SAXS (two-dimensional small-angle X-ray scattering) patterns were clearly observed as a function of the take-up velocity. For 3 km/min, only streaks on the equator were distinct. For 4∼6 km/min, characteristic X-shaped cross-streaks appeared with the streaks on the equator. Then, at 7∼9 km/min, a pair of broad streaked peaks parallel to the equator appeared instead of the cross-streaks, while the equatorial streaks still coexist. We ascribed the X-shaped cross-streaks to a zig-zag fibril structure, and the equatorial streaks with the broad streaked peaks to a shish-kebab structure. Then, based on the 2d-SAXS results, change in the fiber structures with an increase of the take-up velocity is considered. For 4∼6 km/min, the zig-zag fibril is dominant. However, a trivial amount of shish seems to coexist. The shape of fibril changed from zig-zag to straight with an increase of the take-up velocity, while the shish-kebab fraction was considered to increase. It is noted here that the zig-zag fibril consists of somewhat different from an ordinary fibril, but rather thicker-and-looser agglomerates of crystallites. At 9 km/min, fibril is no more the zig-zag, but a straight shish, with a well-developed kebab structure.