13C Solid-State NMR Study of Differently Processed Poly(ethylene terephthalate) Yarns

Abstract

A series of fibers of polyethylene terephthalate) with different physical structures, varying from amorphous to 36 % crystalline, has been investigated by 13C solid-state NMR measurements. Several relaxation times, i.e., relaxation times in the rotating frame ( / ), Tip(13C)) and -130 cross-polarization transfer times (7ch), have been studied. 13C CP/MAS spectra show that, especially with respect to the ethylene and carbonyl carbons, the chemical shift for carbons in ordered structural surroundings ("NMR crystalline") is higher than that for carbons in unordered surroundings ("NMR amorphous"). Also the width of the distribution of chemical shifts in an ordered structure is smaller than that in a less ordered structure (narrow vs broad resonance line). Analysis of the line-shape changes during the Tip(13C) relaxation process of semicrystalline yarns showed that the NMR amorphous phase relaxes with two time constants. A threeregion model composed of NMR crystalline, rigid NMR amorphous, and mobile NMR amorphous regions is proposed. The sizes of the rigid domains in semicrystalline PET yarns estimated from / ) measurements correspond well with the crystal sizes as determined with X-ray diffraction. In a yarn, which is almost completely amorphous according to X-ray measurements, fast and slow ethylene and aromatic group motions, relative to a correlation time of 5 X 10-6 s, occur. From 1 ) experiments it can be concluded that both mobile and rigid regions in the amorphous yarn have dimensions smaller than 50 A. Tch measurements reveal that ethylene and aromatic groups in the mobile amorphous domains of all yarns undergo large-amplitude motions. The principal elements of the chemical shift tensor of aromatic carbons remain independent of temperature up to at least 327 K, indicating that, in crystalline regions in semicrystalline yarns and in rigid parts of the amorphous yarn, phenyl reorientations have a very small amplitude (not exceeding ~5°).

NMR and IR characterization of the aluminium complexes of norfloxacin and ciprofloxacin fluoroquinolones

“…24 All the spectra were recorded with an MAS rate of 10 kHz. The carbon spin-lock field was performed at ω 1C /2 D 53 kHz.…”

Microstructural investigation of high-speed melt-spun nylon 6 fibers produced with variable spinning speeds

“…Thus, the occurrence of spin diffusion in the interfacial regions interconnected between amorphous and crystalline regions might hamper the exact calculation of the crystallinity. 19 WAXD intensity curves of equatorial and meridional scans are shown in Figure 8. The intensity curves of the equatorial scans were resolved into a ␥ (001) peak and an amorphous peak that was superposed with an ␣ (002/202) peak.…”

Structural Characterization of Drawn and Annealed Poly(trimethylene terephthalate) Fibers

“…On the other hand, the shortest T 1 components (T 1 < 2:8 s), which exist in all the samples, are attributable to the amorphous region. Moreover, the intermediate T 1 component that exists in the FDY sample is considered to arise from the rigid NMR amorphous region, as pointed out by Gabrielse et al 19 The intermediate T 1 values for FDY are close to those for samples A, B, and C, which indicates that two components for the annealed samples A, B, and C correspond to the amorphous and rigid NMR amorphous regions. In other words, no crystallization occurred during annealing, so there is a distinct difference between drawn and annealed PTT fibers.…”