Selective degradation of nylon 6,6. I. Description of the degradation technique and preliminary morphological characterization

A technique for the selective degradation of amorphous regions in nylon 6,6 is reported. Samples of unoriented film and single-crystal mats have been subjected to selective degradation by refluxing in hydrazine. Weight loss, viscosity-average molecular weight, density, and small-angle x-ray scattering of these samples were monitored as a function of time of degradation. In addition, selected samples have been investigated by gel permeation chromatography (GPC) and transmission electron microscopy. Based on the results of these investigations it is concluded that the reported degradation technique is unique in that the debris is not monodisperse in molecular weight distribution. The Weight loss, density, small-angle x-ray scattering, and microscopy data demonstrate that the unordered or noncrystalline regions of the material are removed upon treatement. However, the relatively high molecular weight and broad molecular weight distribution of the debris indicate that regular folds at lamellar surfaces are intact after degradation treatment.     

High-temperature annealing of drawn nylon 66 fibers

The structure and morphology of highly oriented fibers were modified by thermal treatments at varying tensions. The structural changes were characterized by wide- and small-angle x-ray diffraction, broadline nuclear magnetic resonance, and electron microscopy of surface replicas. Increasing temperatures caused increases in local ordering, number of regular chain folds, mobile fraction or amount of fluidlike mobility, and surface recrystallization in localized areas. Each of these changes was also a function of the amount of tension on the fiber during the annealing; each change was maximized when the fiber was free to shrink but minimized when the fiber was stretched.     

Application of the high-tension multiannealing to nylon 46 fibers

Nylon 46 fibers produced by the high-temperature zone-drawing treatment were treated by repeating high-tension annealing treatments, that is, a high-tension multiannealing (HTMA) treatment to improve their tensile properties. The HTMA treatment was carried out at a repetition time of 10 times and treating temperature of 110°C under high tension (538.2 MPa) close to the tensile strength at break. Although the HTMA treatment was carried out at 110°C, which is much lower than the crystallization temperature of 265°C for nylon 46, the degree of crystallinity increased up to 59%. The orientation factor of crystallites increased dramatically up to 0.949 by the first high-temperature zone-drawing treatment and slightly during the subsequent treatments. This observation indicated that the orientation of crystallites due to slippage among molecular chains did not occur during the HTMA treatment. The treatments shifted the melting peak to slightly higher temperatures, and the HTMA fiber has a melting endotherm peaking at 285°C. The fiber obtained finally had a storage modulus of 12.5 GPa at 25°C. © 1998 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 36: 2737–2743, 1998     

Polymer fibers drawn to the limit

The orientational drawing of polymers is known to be terminated because of sample rupture. The limiting draw ratio λ_lim reached may be different (either large or small) depending on the polymer and the actual drawing conditions. The purpose of the present work is to identify the change of supermolecular structure of polymer fibers which results in the termination of orientational drawing. Small-and wide-angle x-ray diffraction were used to study the variation of geometrical parameters of this structure with increasing draw ratio λ. The geometrical parameters discussed are the dispersions (fluctuation) of long periods and of longitudinal sizes of crystalline as well as amorphous regions. In this study we used fibers of poly(vinyl alcohol), poly(ε-caprolactam), polyoxymethylene, and poly(4,4′-diphenyloxide) pyromellitimide. It is found that the long period dispersion of these polymers, drawn under different conditions, increases to approximately the same value for different samples drawn to the limit, this relative standard deviation δ_L of long periods being 0.30-0.40. It is also found that the crystallite size dispersion does not increase with increasing λ; the increase of λ_L is due to increasing dispersion of the amorphous region lengths. For poly(vinyl alcohol) fibers drawn to the limit under different conditions and which have different λ_lim, the relative standard deviation of the sizes of amorphous regions δ_A turned out to be about the same (ca. 0.60). The latter evidence gives grounds to suggest that the rupture of polymers under drawing is associated with reaching a high degree of amorphous region size dispersion. In those regions which are considerably below the average size there probably will appear local overstress and molecular ruptures because the relative deformation of these regions is much larger than that of the adjacent regions in the cross section of the sample.     

NMR observations of drawn polymers. VIII. Doubly oriented nylon 66

A wide-line NMR study of chain segmental motion in nylon 66 has been made on a rolled sheet having “double orientation.” In this sheet the crystallite c axis, i.e., the molecular chain axis, is oriented preferentially along the roll direction, and the crystallographic (010) plane lies predominantly parallel to the roll plane, or the plane of the sheet. The direction of the applied magnetic field with respect to the sheet is characterized by two angles, the polar angle γ subtended by the roll direction and the magnetic field, and an azimuthal angle ?. NMR spectra were taken at various values of the angles γ and ? and at three temperatures ?196°C, 20°C, and 180°C. The second moments of the absorption spectra taken at 180°C were compared with theoretical predictions of second moments based on two models for the high-temperature segmental motion (called the α_c process) in crystalline regions of nylon 66. One model consists of rotational oscillation with amplitudes δ of segments around their axies. The second model is denoted 60° flip-flop motion and consists of rotational 60°C jumps of the segments around their axes between two equilibrium sites with the possibility that the segments also oscillate with a general amplitudes δ around each site. The experimental results are consistent with fairly large amplitudes δ, in which case both models approach the limiting case of full segment rotation. For this reason the experiments do not allow a distinction between the two models. From the second moments at ?196°C and 20°C the decrease in second moment due to the low temperature segmental motion, the γ process, is obtained. This motion occurs in noncrystalline regions of nylon 66 and is found to cause a decrease in second moment which is strongly dependent on the two angles γ and ?, implying double orientation of the noncrystalline segments. It is suggested that at low temperatures the noncrystalline segments become immobilized in sites dictated by the crystallite orientation through the extensive hydrogen bonding known to exist in nylon 66.     

Bond rupture in highly drawn nylon 6 fibers influence of strain rate on radical concentration and permanent deformation

Summary In high-drawn nylon 6 fibers the radical concentration caused by the rupture of the tie molecules was measured by ESR at different strains and strain rates, viz. 2.5-500% min^–1.The spectral shape of the radical was temperature-dependent. This was tentatively explained from the fact that the -methylene protons of the secondary radical of nylon 6, (-CO-NH-(aHa-CoH2a) stop rotating at liquid nitrogen temperature.Furthermore the radical concentration depends on the strain rate, and consequently on time, which is explained by assuming that the tie molecules have a length distribution. So it follows that the process is of a viscoelastic nature and has little to do with thermally activated bond rupture. The assumption that the tie molecules have a length distribution is also supported by the value of the elastic modulus which, in contrast with what is sometimes assumed (28), is already accounted for by the relatively few taut tie molecules.Permanent deformation which, like chain rupture also an irreversible process, has been measured as a function of strain and strain rate. Roughly, a linear correlation seems to be present between the number of radicals and the magnitude of the permanent deformation.

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Zusammenfassung In hochverstreckten Nylon-6-Fasern wurde die durch das Zerreißen von Molekülketten entstandene Radikalkonzentration mit Hilfe von ESR bei einer unterschiedlichen Dehnung und bei Dehnungsgeschwindigkeiten zwischen 2,5 und 500% min^–1 gemessen. Die Form des Radikalspektrums war temperaturabhängig. Dies ließ sich aus der Tatsache erklären, daß die -Methylenprotonen des sekundären Radikals von Nylon 6, (-CO-NH-CH_ga-CßH₂), bei der Temperatur von flüssigem Stickstoff zu rotieren aufhören.Weiter ist die Radikalkonzentration von der Dehnungsgeschwindigkeit und somit von der Zeit abhängig. Dies konnte aus der Annahme erklärt werden, daß die Tie-Moleküle eine Längenverteilung haben.So folgt, daß der Prozeß viskoelastischer Natur ist und er wenig mit thermisch aktivierter Bindungsspaltung zu tun hat. Das Vorhandensein einer Längenverteilung für die Tie-Moleküle wird auch durch den Wert des elastischen Moduls unterstützt, der anders, als manchmal angenommen wird (28), schon aus den relativ wenig gespannten Verbindungsmolekülen erklärt werden kann.Die bleibende Deformation, ebenso wie die Kettenspaltung ein irreversibler Prozeß, wurde als Funktion von Dehnung und Dehnungsgeschwindigkeit gemessen. Annähernd gibt es eine lineare Korrelation . zwischen der Radikalkonzentration und der Größe der bleibenden Deformation.

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NMR observations of drawn polymers. VII. Nylon 66 fibers

Wide-line NMR spectra have been obtained on an oriented sample of drawn nylon 66 fibers at temperatures between ?196°C and 200°C and at alignment angles between the fiber axis and the magnetic field of 0°, 45°, and 90°. At ?196°C, 20°C, and 180°C, the complete angle dependence of the NMR spectrum has been measured. The second moments of these spectra have been compared to theoretical second moments calculated for various models of chain segmental motion in an attempt to elucidate the mechanisms involved in the low-temperature segmental motion (γ process) and the high-temperature segmental motion (α_c process). In agreement with earlier suggestions, the present results indicate that the γ process consists of segmental motion in noncrystalline regions. The overall decrease in second moment caused by the γ process is consistent with a model in which all noncrystalline segments rotate around axes nearly fixed in space. Furthermore, this decrease shows a pronounced dependence on the alignment angle. It is believed that this is due to tie molecules which become highly oriented along the fiber axis during drawing; their axes of rotation will therefore be nearly parallel to the fiber axis. The segments in noncrystalline entities such as chain folds and chain ends are less well oriented along the fiber axis and make an essentially isotropic contribution to the second moment decrease. The second moment at 180°C indicates the presence of considerable motion in the crystalline regions, and this motion is denoted the α_c process. The second moment S_c of the crystalline regions is strongly dependent on the alignment angle, the predominant feature being a relatively high value of the second moment when the fiber axis is directed parallel to the magnetic field. This is in qualitative, but not quantitative, agreement with the motional model recently advanced by McMahon, which assumes full rotation of the chains around their axes. Excellent quantitative agreement with experiment has been obtained by superimposition of rotational oscillation around the chain axis of amplitude roughtly 50°, and torsion of the chains with neighboring CH₂ groups oscillating around the C? C bond with a relative amplitude of about 40°. A model in which the chains perform rotational jumps of 60° between two equilibrium sites has also been considered (60° flip-flop motion). A distinction between this model and rotational oscillation has not been possible.     

Effect of annealing conditions on the structure of drawn nylon 66 yarns

Differences in structural parameters, shrinkage, and retractive forces have been compared for nylon 66 tire yarns annealed at several temperatures in silicone oil and in air. It is found that significantly different structural changes occur for oil-annealing and air-annealing. Retractive forces measured in hot oil are characterized by a high initial force, followed by a rapid decay and a second, more gradual, increase which is also followed by a decay at sufficiently high temperatures. In heated air, the first, short-term, retractive force is absent. It is postulated that these differences are due to the different rates of heat transfer at gas–solid and at liquid–solid interfaces, and that rapid heat transfer (as in the case of oil-annealing) promotes two mechanisms of molecular change which are characterized by different degrees of structural parameter change, and by different amounts of shrinkage.     

Strain‐rate dependence of the microstructure and mechanical properties for hot‐air‐drawn nylon 6 fibers

A hot‐air (HA) drawing method was applied to nylon 6 fibers to improve their mechanical properties and to study the effect of the strain rate in the HA drawing on their mechanical properties and microstructure. The HA drawing was carried out by the HA, controlled at a constant temperature, being blown against an original nylon 6 fiber connected to a weight. As the HA blew against the fiber at a flow rate of 90 liter/min, the fiber elongated instantaneously at strain rates ranging from 9.1 to 17.4 s⁻¹. The strain rate in the HA drawing increased with increasing drawing temperature and applied tension. When the HA drawing was carried out at a drawing temperature of 240 °C under an applied tension of 34.6 MPa, the strain rate was at its highest value, 17.4 s⁻¹. The draw ratio, birefringence, crystallite orientation factor, and mechanical properties increased as the strain rate increased. The fiber drawn at the highest strain rate had a birefringence of 0.063, a degree of crystallinity of 47%, and a dynamic storage modulus of 20 GPa at 25 °C. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 1137–1145, 2000     

NMR observations of drawn polymers. IX. Chain mobilization and water mobility in nylon 66

Wide-line NMR spectra of nylon 66 fibers have been obtained at different alignment angles between the fiber axis and the magnetic field, at varying water contents (H₂O and D₂O), and at different temperatures. At 28°C the spectrum of the dry fibers consists of a nearly structureless broad line. At water regains of 1.4% by weight (dry basis) and higher a sharp line appears which originates from highly mobile water molecules. The width of this line decreases with increasing water content, implying an increase of water mobility. Moreover, the width is a function of the alignment angle; this shows that the water is not reorienting isotropically owing to specific water-polymer interaction. The amount of mobile water is always smaller than the amount of water absorbed. At water contents close to saturation, a mobile polymer line appears with a width intermediate between the broad line (immobile polymer) and the sharp water line. This line, most clearly observed at an alignment angle of 0°, is due to a shift of the α_a process to lower temperatures in the presence of water. A similar line is observed in the dry fibers at 120°C. It is shown that the α_a process decreases the NMR second moment only slightly. The shift of the high temperature drop in second moment to lower temperatures in the presence of water is therefore interpreted as due to a shift of the α_c process, and not of the α_a process, to lower temperatures.     

Infrared studies of drawn polyethylene. II. Orientation behavior of highly drawn linear and ethyl-branched polyethylene

Infrared dichroism is employed to study the orientation of chain molecules in linear and ethyl-branched polyethylene in the crystalline and noncrystalline regions during drawing and subsequent annealing. A crystalline (1894 cm^?1) and a noncrystalline (1368 cm^?1) band, as well as the bands at 909 cm^?1 and 1375 cm^?1 resulting from vinyl endgroups and methyl endgroups and sidegroups, are studied. For these bands relative orientation functions are derived and compared as a function of draw ratio and annealing temperature. It is shown that the relative orientation functions as derived from the dichroism of the noncrystalline, vinyl and methyl bands follow the same curve while the orientation function for the crystalline bands does not. These results support a two-phase model for partially crystalline polyethylene and additionally favor segregation of the endgroups and sidegroups in the noncrystalline component during crystallization. It is further shown that shrinkage occurs at the temperature at which the noncrystalline chain molecules start to disorient. From the dichroism of the methyl groups in ethyl-branched polyethylene, a value for the mean orientation of the noncrystalline chain molecules is calculated. We obtain for the orientation function of the noncrystalline regions at highest draw ratios (λ = 15–20), f = 0.35–0.57, while the chain molecules in the crystallites are nearly perfectly oriented (f ≈ 1.0). On the assumption that the noncrystalline component consists of folds, tie molecules, and chain ends, the different contributions of these components to the overall orientation are estimated. From these the relative number of CH₂ groups incorporated into folds, tie molecules, and cilia can be derived. Further, on the basis of a simple structural model, the relative number of chains on the crystal surface contributing to the different noncrystalline components and their average length are estimated.     

Application of infrared spectroscopy and thermal analysis to the examination of the degradation of cotton fibers

The potential of infrared spectroscopy and thermal analysis when determining the degree of damage of historical textiles was investigated. Model samples of artificially aged cotton were used. The results obtained by the two instrumental methods were correlated with the mean degree of polymerization of cellulose and with their tensile strength. Neither of the two instrumental methods on its own was found suitable for the determination of the degree of damage of cellulose-based textile materials. They should be combined with other methods serving to determine the extent of damage of cellulose-based textile materials, e.g. via the degree of polymerization of cellulose.     

Investigation into the morphology,crystallization and melting behaviour of nylon 6,6/LCP blends

Journal of Thermal Analysis and Calorimetry - The morphology, isothermal crystallization and melting behaviour of melt-mixed nylon 6,6/Vectra A950 liquid crystalline polymer (LCP) blends were...     

Structure and mechanical behavior of nylon 6 fibers filled with organic and mineral nanoparticles. II. In situ study of deformation mechanisms

This study reports on the in situ characterization of the deformation mechanisms at room temperature of polyamide 6 (PA6) fibers filled with hyperbranched molecules or montmorillonite (MMT) platelets. A small‐angle X‐ray scattering study shows that the stretching and sliding of the microfibrils takes place concomitantly in the first stage of elastic loading of as‐spun and partially drawn fibers. In the second stage of loading, which is basically plastic, sliding turns out to be the main process of deformation, accompanied by a significant reduction in the microfibril radius. Fibers drawn close to their maximum draw ratio only display the deformation process of microfibril stretching. This in situ study also reveals subtle features of the reversible processes of deformation that could not be detected from ex situ experiments reported previously. A thickening of the crystal blocks in the microfibrils takes place under stress and disappears upon unloading, indicating that some reversible strain‐induced molecular ordering occurs in the amorphous layers close to the crystal surface. The tentative mechanical modeling enabled a characterization of the components of the fibers: the stiffness of the microfibrils appears to be insensitive to the presence of the particles that are excluded in the interfibrillar regions. The presence of HB molecules clearly increases the stiffness of the interfibrillar regions owing to a physical crosslinking effect. Moreover, it seems that the stiffness improvement of the drawn MMT‐PA6 fiber lies in a greater capability of chain unfolding in the interfibrillar amorphous region. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 2633–2648, 2004     

Structure-property relationships of copolyamides. II. crystal structure of drawn copolyamide films

The crystal structures of drawn copolyamides 6/6.6, 6/6.T, 6/6.1, 6/PXD.6, 6/MXD.6, and 6/MXD.I were examined by wide-angle x-ray diffraction. Copolyamide 6/6.6, which follows the inclusion model, shows only α-characteristics at all the comonomer compositions examined (0–33.3 mol%). However, the other copolyamides, which follow either the partial-inclusion or complete-exclusion model, show γ-characteristics more predominantly as the comonomer content increases. The interplanar spacing of the (200) planes, which corresponds to the hydrogen bond distance between antiparallel chains, remain constant, whereas the spacing of the (020) planes corresponding to the distance between hydrogen bonded sheets increases monotonically with increasing the comonomer content. It is also observed that both the crystal perfection index and the crystal thickness decrease as the comonomer content increases.     

Supercritical fluid extraction of nylon 6,6 oligomers and their characterization via liquid chromatography coupled with mass spectrometry.

This research extends previous studies regarding the application of supercritical fluid extraction (SFE) for the analysis of oligomers from nylon 6,6 fibers. The effects of CO2 pressure, extraction temperature, CO2-modifier percentage, static extraction time and dynamic extraction time on the SFE efficiency of nylon 6,6 oligomers were examined. Results from the SFE methods for oligomer extractions were compared to results from conventional solvent extraction. The extracted oligomers were identified by high-performance liquid chromatography (HPLC) with coupled on-line atmospheric pressure chemical ionization mass spectrometry and HPLC fractionation coupled with off-line liquid secondary ion mass spectrometry.     

On the dynamic mechanical behaviour of drawn poly(ethylene terephthalate) fibers

The effect of drawing and annealing treatments on the transition in poly(ethylene terephthalate), PET, yarns has been studied using a combination of X-ray and dynamic mechanical techniques. It was found that drawn, crystalline PET yarns exhibit a shift in the position of the transition to lower temperatures for high annealing temperatures; this effect has been observed for unoriented, crystalline PET. The main difference between the results for the drawn and unoriented yarns lies in the position of the transition on the temperature scale; the transition occurs at higher temperatures the higher the draw ratio. The shift in the position of the transition with anealing is interpreted in terms of the number of crystals whilst the change in position of the transition brought about by drawing is explained by orientation in the amorphous regions.

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Zusammenfassung Der Einfluß von Verstreckung und Temperaturbehandlung auf den -Übergang in Poly(äthylenterephthalat), PET, Garn wurde untersucht unter Anwendung von Röntgen- und dynamisch-mechanischen Methoden. Es wurde gefunden, daß für hohe Vergütungstemperaturen verstreckte, kristalline PET-Garne eine Verschiebung des -Überganges zu niedrigeren Temperaturen aufweisen, ähnlich wie für nicht verstrecktes, kristallines PET. Der Hauptunterschied zwischen verstreckten und nicht verstreckten Garnen ist die Lage des -Überganges auf der Temperaturskala; der -Übergang liegt für höhere Verstreckung bei höheren Temperaturen. Die Verlagerung des -Überganges durch Temperaturbehandlung wird auf die Anzahl der Kristallite zurückgeführt, während seine Verschiebung durch Verstreckung erklärt wird durch die Orientierung in den amorphen Bezirken.

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With 4 figures and 1 table