Phase Composition and Molecular Mobility in Nylon 6 Fibers as Studied by Proton NMR Transverse Magnetization Relaxation

Abstract

Summary: The phase composition and molecular mobility of Nylon 6 fibers has been studied using 1H solid‐state NMR transverse magnetization relaxation (T2 relaxation) spectroscopy. One of the objectives of this work is to determine the usefulness of the NMR relaxation method to accurately determine the crystallinity of Nylon 6 fibers. The NMR relaxation results have been interpreted using a three‐phase model, which is proposed on the basis of distinct differences in chain mobility in the crystalline phase, the semi‐rigid crystal‐amorphous interface, and the soft amorphous phase. In order to obtain accurate data on the phase composition, the effects of absorbed water and annealing of fibers at elevated temperatures were studied in detail. It was shown that water mainly plasticizes the soft fraction of the amorphous phase. Changes in the phase composition and molecular mobility caused by fiber annealing at elevated temperatures were studied with real‐time NMR T2 relaxation experiments. The most pronounced annealing effects (changes in the phase composition) were observed for undrawn fibers with low molecular orientation. Annealing slows down for fibers produced at larger winding speed and especially those with a high draw ratio. Fiber processing conditions, i.e., winding speed and draw ratio, are found to affect the phase composition and molecular mobility in different phases. It was shown that the present NMR relaxation method provides a fast and accurate technique to analyze the phase composition of Nylon 6 fibers. The amount of rigid phase determined from NMR is in good agreement with the crystallinity of the fiber obtained using the traditional method for Nylon 6 fibers, which involves a combination of density measurement, wide‐angle X‐ray diffraction and 13C NMR spectroscopy. Hence, the present NMR relaxation method greatly simplifies measurement of crystallinity in Nylon 6 fibers.The effect of draw ratio on the phase composition in Nylon 6 fibers as studied by NMR and the traditional method.magnified imageThe effect of draw ratio on the phase composition in Nylon 6 fibers as studied by NMR and the traditional method.

Quantitative Water Uptake Study in Thin Nylon-6 Films with NMR Imaging

“…40 The amorphous phase is composed of a soft amorphous region and a rigid noncrystalline interfacial region. They stated that the rigid fraction is not affected by water and has a signal decay much shorter than 100 μs.…”

“…The relaxation time starts to increase at moisture content of 2.5%. The first fraction of water (θ ≤ 2.5%) will be strongly bound to the polymer matrix 40 and therefore exhibits a fast signal decay. As NMR is more sensitive to local mobility changes the NMR relaxation time increases before the glass transition temperature reaches room temperature.…”

Complex Morphology of Melt‐Spun Nylon‐6 Fibres Investigated by1H Double‐Quantum‐Filtered NMR Spin‐Diffusion Experiments

“…The component with an intermediate Dn 1/2 was attributed to the less-mobile amorphous regions, while the component with the highest Dn 1/2 was related to the crystalline regions and to a small fraction of the amorphous phase that is rigid at room temperature. [35] An increase in the winding speed or draw ratio leads to an increase in the crystalline content. This increase is due to the fact that a part of the amorphous regions transforms into crystalline form.…”

Hydrogen bonding, mobility, and structural transitions in aliphatic polyamides

“…5(a)]. Spin-lattice relaxation time (T 1q ) measurements have been used to identify three phases with different relaxation times: immobile crystalline phase, immobile (intermediate or rigid) amorphous phase, and mobile amorphous regions with T 1q values of 0.003, 0.013, and 0.005 s, respectively, at a temperature of 300 K. 66,67 The increase in T 1q of the amorphous chain segments with the spinning speed or orientational stress that is seen in the figure even after the crystalline phase has saturated is consistent with the XRD results. XRD data show that the crystalline regions reach their final orientation fairly rapidly and the amorphous phase rather slowly [ Fig.…”