STUDIES OF STRUCTURE AND MORPHOLOGY DEVELOPMENT DURING THE HEAT-DRAW PROCESS OF NYLON-66 FIBER BY SYNCHROTRON X-RAY-DIFFRACTION AND SCATTERING TECHNIQUES

Online studies of structure and morphology development during continuo us drawing of a nylon 66 fiber at different temperatures were carried out using synchrotron wide-angle X-ray diffraction (WAXD) and small-an gle X-ray scattering (SAXS) techniques. From the two-dimensional (2D) WAXD measurement, unit-cell parameters were determined. The results co nfirm that the triclinic cell structure persists above the Brill trans ition temperature (about 443 K). With increasing temperature, the unit -cell dimension a (dominated by hydrogen bonding) remains almost uncha nged, while b increases and c decreases (both show a step-change at 40 3 K, prior to the Brill transition). The constant value of a agrees wi th the argument that the hydrogen bonding is relatively immobile at hi gh temperatures prior to melting. The step-changes in b and c suggest that a premelting process of small (or defective) crystals precedes th e Brill transition. As a result, the anisotropic thermal expansion of the surviving larger crystals results in a step-change behavior. This hypothesis is consistent with the crystal density data as well as the morphology evaluation by SAXS. Several dimensions were extracted from the 2D SAXS data: lamellar crystal and amorphous thicknesses (along th e fiber) determined by the correlation function method and crystal fib ril width (perpendicular to the fiber) determined by the Pored analysi s, These results also indicate that drawing annihilates small crystals , but the strain effect is much less than the temperature effect.