Real-Time X-ray Study of Nylon-6 Fibers during Dehydration: Equatorial Small-Angle Scattering is Due to Surface Refraction

Abstract

The equatorial streak in the small-angle X-ray scattering (SAXS) pattern from nylon-6 fibers, normally assigned to microvoids or to internal fibrillar structure, is due to scattering from the fiber surfaces. This scattering is best thought of as refraction by the cylindrical fibers. The streak intensity increases by 50 times during the early stages of drying a wet bundle of nylon-6 fibers, when superficial water, water between the fibers in the bundle, is lost. Separate X-ray experiments using a nonpenetrating fluid, a large diameter monofilament, and microbeam SAXS confirmed this assignment. There are many fibers where internal voids are known to be the source of a strong equatorial streak in SAXS, but in general, a check for surface scattering is advised before interpreting this feature. Simultaneous small-and wide-angle X-ray diffraction (WAXD) was obtained during drying. Following the initial loss of superficial water, there are changes in both the WAXD reflections and the SAXS lamellar reflection. In the later stages of drying, WAXD shows that the crystals decrease in perfection, in apparent lateral size and in degree of misorientation. Lamellar structure changes are slower to start and include a 1.3% decrease in axial lamellar spacing and a 40% increase in the contrast between the crystalline lamellae and the interlamellar regions. All these changes are explained as effects of the removal of absorbed water from the interlamellar amorphous regions and their reduction in volume and density. Interpretation of these experimental results thus does not require a fibrillar structure in nylon-6.

Morphological Investigation into Starch Bio-Nanocomposites via Synchrotron Radiation and Differential Scanning Calorimetry

“…Similarly, in the lowmoisture-content samples, greater ellipticity of the patterns indicated higher lamella heterogeneity across the samples. Such behavior had been reported by Grubb and Murthy in nylon-6 fibers during dehydration [24].…”

Central small‐angle diffuse scattering from fibers is made of two components

“…In the more general case, we may know that the polymer fiber contains crystalline arrays or other density fluctuations such as voids, but knowledge of the exact structure is lacking, and alternative interpretations are possible. Thus, the equatorial streak arising from a single type of polymer fiber has been attributed variously to voids,2, 3, 9, 28, 30–32 microfibrils,9, 33, 34 to crystal‐amorphous phase boundaries and to the external fiber surfaces 35. It is always possible to hypothesize a particular structure and fit the data with the calculated scattering to obtain size or orientation distributions for the structural elements.…”

Elliptical Small‐Angle X‐Ray Scattering Patterns from Aligned Lamellar Arrays

“…49. A wet fiber was used for this example because the equatorial streak is largely suppressed in this sample, making it easier to fit the lamellar reflection. The upper half of Figure is the data, showing considerable noise and a 4‐point pattern with some overlap on the meridian.…”