Chain folding in oriented nylon 66 fibers

TL;DR: In this paper, a combination of structural and physical properties measurements: wide and small angle x-ray diffraction, broad and narrow line nuclear magnetic resonance, sonic modulus, density, shrinkage, and tensile properties.

Abstract: When heated to high temperatures under zero tension, some of the molecules in oriented nylon 66 filters change from the elongated to the folded conformation, with no change in crystal orientation. This transformation is shown by a combination of structural and physical property measurements: wide and small angle x-ray diffraction, broad and narrow line nuclear magnetic resonance, sonic modulus, density, shrinkage, and tensile properties. A fortyfold increase of the intensity of the discrete small angle x-ray diffraction is obtained for treatments between 160-and 255°C. as well as an increase of the length of the long period and a change from a smeared four-point to a sharp two-point diagram. Wide angle x-ray measurements show little change in crystallite orientation for treatments up to 250°C. even though much shrinkage occurs. Disruption of some type is observed by sonic measurements, as would be expected if new folds occurred. An increase of density and x-ray crystallinity confirms that heating causes much additional crystallization. The high temperature NMR spectra for these more crystalline yarns show a much larger proportion of fluidlike segments. Shrinkage of the yarns during the heating appears to be governed by the number of folds which are introduced. Tensile strength is reduced by this introduction of folded chains.