Domain structure of nylon 6 fibers

Stained and unstained sections of nylon 6 fibers are examined by means of transmission electron microscopy. Data are presented regarding dimensions and shape of macrofibrils, microfibrils, amorphous, and crystalline domains of the microfibril and the spacing between the microfibrils. The new results support the conclusions of a previous SAXS and diffusion study carried out with the same fibers.     

Creep failure in highly oriented nylon 6 fibers

Creep failure in oriented nylon 6 fibers has been studied. The results suggest that the variations in the lifetime under various loading histories are inherent, but statistical, characteristics of the material itself. The treatment of experimental data by a stochastic theory shows that the creep failure can be regarded as a nucleation process. An interpretative analysis of the structural changes during creep indicates that the nucleation is brought about by bond rupture in the amorphous regions of the fiber structures.     

The fatigue process in highly oriented nylon 6 fibers

The micromechanism of the fatigue process in highly oriented nylon 6 fibers is discussed on the basis of changes in mechanical and structural properties during fatiguing. Experimental results show that the fatigue process can be divided into two stages. The characteristic features in the initial period are increases in breaking strength, long period, and molecular orientation, and a reduction in dye penetration. In the second period, after about 500 cycles, breaking strength and orientation decrease slightly, and the long period, permanent strain, and dye penetration increase with duration of fatiguing. It is demonstrated that the structural changes mainly occur in the amorphous regions of the fiber structure. The structural and mechanical changes in the initial period lead to the conclusion that the initial cyclic strain causes strain hardening caused by extended tie chains which do not rupture. A combination of load bearing by tie chains and sliding motion of the fibrillar elements can explain the progressive degradation of the fiber during the second stage of fatiguing.     

Drawing of nylon 6 fibers (bristles)

By means of electron microscopy of surface replicas and both small-angle and wide-angle x-ray scattering, nylon 6 fibers were investigated in the as-spun state, after drawing at 180°C to a draw ratio up to 4.95, and after subsequent annealing. As spun, the fiber exhibits a small fraction of row-nucleated cylindrites and a great many spherulites (with an average diameter of a few microns) side by side. Drawing deforms the spherulites into spindle-shaped structures (λ = 2) and subsequently produces well-aligned microfibrils. Small-angle x-ray scattering yields a two-point diagram at small λ and a fourpoint diagram at high λ. The long period seems to decrease slightly with draw ratio. Annealing at temperatures above the temperature of drawing increases the long period to a greater extent with samples of lower λ. The crystal lattice orientation is nearly complete at λ = 4.95.     

Conformational behavior of nylon 6 in mixed solvents

The intrinsic viscosity [η], Huggins constant (K_H), laser light scattering, UV and IR measurements of Nylon 6 are made in m‐cresol and its mixture with 1,4‐dioxane at 20–60 °C. The intrinsic viscosity, R_g, A₂, (<S>²)^1/2 (calculated from viscosity data), R_H, and UV absorbance initially increase and then decrease with the rise in 1,4‐dioxane contents. The K_H and the transmittance of ? OH group in IR spectra show an opposite trend to that of [η]. The dielectric constant calculated from the refractive index of the solvent (m‐cresol with 1,4‐dioxane) and polymer solution shows a continuous decrease with the amount of 1,4‐dioxane. Activation energy shows a minimum while linear expansion coefficient (α³) maximum with the addition of 1,4‐dioxane. Change in [η], K_H, and other characteristics of the polymer solutions with alterations in solvent composition and temperature are the result of variation in the thermodynamic quality of the solvent, its selective adsorption, hydrogen bonding, and conformational transitions. It has been concluded that the addition of 1,4‐dioxane first enhances the quality of the solvent, encourages hydrogen bonding, and specific adsorption, and then deteriorates, bringing conformational transitions in the polymer molecules. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 534–541, 2005     

Melting behavior of nylon 6 fiber in textiles

The melting process of constrained nylon 6 fibers has been studied to estimate the true melting point of its original crystals. The melting peak became simpler in shape and shifted to higher temperature with increasing fiber-axis restricting force. When heating rate, β, was increased, the temperature where the melting curve initially departs from its baseline, Tsm, decreased steeply in the range of 45 to 60°C min^-1, and increased linearly with increasing β above 60°C min^-1. By linear extrapolation of Tsm to 0°C min^-1, the temperature of ca 190°C was obtained for the melting temperature of the original nylon 6 crystals. This seems to correspond to the zero-entropy-production melting of the most imperfect crystallites of the nylon 6 fabric. This revised version was published online in July 2006 with corrections to the Cover Date.     

Melting behavior and morphology of drawn nylon 6

Thermal analysis has been carried out on drawn nylon 6 filaments annealed at various temperatures between 150 and 210°C and then methoxymethylated to various degrees. It is shown that the melting point inherent to the morphology of drawn nylon 6 can be obtained from samples in which the reorganization of defect crystallites in the course of thermal analysis is prevented by a proper degree of methoxymethylation of amorphous regions. The melting point thus obtained is in linear relation with the reciprocal crystallite size in the direction of fiber axis which has been obtained from small-angle x-ray data and crystallinity. The extrapolation and the slope of this linear relation give the equilibrium melting point of nylon 6 as 245°C and an end-surface free energy of 42 erg/cm². The results seem to provide strong support for the presence of chain-fold surfaces in the drawn and annealed polymers.     

Production and properties of fibers spun from nylon 6/lithium chloride mixtures

The possibility of producing high-modulus nylon 6 fibers by incorporation of lithium chloride (LiCl) in the polymer prior to spinning and drawing has been examined. Samples containing 2% and 4% LiCl (w/w) together with an unsalted control were studied. Particular attention was given to optimizing the spinning process by varying the melt temperature and the draw-down. The spun fibers were subsequently drawn in a tensile testing machine at 135°C, preliminary studies having established that this was desirable for the production of high-modulus material. The influence of annealing after drawing was also examined. Drawn fiber moduli in the range 8–9 GPa were obtained, compared with ca. 5–6 GPa for unsalted material. Limited structural studies (birefringence and wide-angle x-ray diffraction) suggest that the enhancement of modulus is due to an increase in the stiffening effect of extended molecules in the noncrystalline regions. Dynamic mechanical measurements show that there is reduced chain mobility in the disordered regions of the polymer, suggesting strong polymer-ion interactions. The salt can be readily removed by washing the fibers in boiling water, with significant reduction in moduli. This militates against commercial application of the salted fibers.     

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.     

Annealing experiments on drawn nylon 66 fibers

Drawn, nylon 66 yarns have been annealed in oil under relaxed conditions. Shrinkage and tensile modulus were measured and the yarns were examined by wide- and small- angle x-ray diffraction. The results are similar to those obtained by Dismore and Statton, but there are significant differences. The data indicate a model for a drawn nylon 66 fiber in which substantial amounts of folds remain.     

Effect of processing consitions on the development of morphology in clay nanoparticle filled nylon 6 fibers

The effect of melt temperature on the phase behavior and preferential orientation development in Nylon 6/montmorillonite nanocomposites were investigated at melt spinning temperatures ranging from 230° to 250°C. The fibers were found to exhibit mostly γ crystalline form that is typical of Nylon 6 filled with montmorillonite nanoparticles. At higher take-up speeds α-crystals begin to appear in the crystalline phase. The presence of nanoparticles was found to impart substantial chain orientation levels even at low to moderate take up speeds reaching a plateau at moderate take up speeds. This was attributed to the increased spin line stress in the presence of nanoparticles that increase the overall viscosity due to their large contact areas with the polymer chains. This increased spinline tension was found to cause fiber breakup at moderate speeds. Increasing melt temperature from 230° to 250°C alleviated this problem.     

Effect of water absorption on the plastic deformation behavior of nylon 6

The tensile behavior of nylon 6 films has been investigated in relation to water content. Modification of chain mobility in the amorphous phase via water plasticization appears to have a determining impact on the stress-strain response. More specifically, both yield stress value and hardening behavior over a large strain domain are strikingly equivalent for samples drawn at same ΔT between draw temperature T_d and main amorphous relaxation temperature T_α. This apparent lack of thermal activation of crystal plasticity in the fibrillar transformation suggests that crystal block fragmentation proceeds via H-bond unzipping through water penetration at defective crystal interfaces.     

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     

Analysis of small-angle X-ray scattering from fibers: Structural changes in nylon 6 upon drawing and annealing

The changes in the fibrillar and the lamellar structure in nylon 6 fibers resulting from drawing and annealing were studied by a detailed analysis of their two-dimensional small-angle scattering patterns. The scattering object that gives to rise the diffuse equatorial scattering in the angular range of Q = 0.02 to 0.3 Å⁻¹ is assumed to be a fibril. There are two distinct regimes in the equatorial diffuse scattering. The scattering at Q < 0.1 Å⁻¹ is dominated by scattering due to the longitudinal dimension of the fibril, and that at Q > 0.1 Å⁻¹ to the lateral dimensions/organization of the fibril. The interfibrillar regions, unlike the interlamellar regions that are essentially made of amorphous chain segments, may have microvoids in addition to amorphous chain segments. The intensity distribution within the lamellar reflections was used to obtain the lamellar spacings and the dimension of the lamellar stacks. The length of the fibrils is between 1000 and 3000 Å, the higher values being more prevalent at lower draw ratios. The fibril length is larger than the length of the lamellar stack, and approaches the latter at higher draw ratios. Annealing does not change the lengths of the fibrils, but the length of the lamellar stack increases. The fibrils form crystalline aggregates with a coherence length of ∼200 Å at higher draw ratios. The diameter of the fibrils (50–100 Å) determined from the lamellar reflection using both the Scherrer equation and the Guinier law are consistent with the lateral size of the crystallites derived from wide-angle x-ray diffraction. The longitudinal correlation of the lamellae between the neighboring fibrils improves upon drawing and decreases upon annealing. The degree of fibrillar and lamellar orientation is about the same as the crystalline orientation. Lamellar spacing increases upon drawing (from ∼60 to 95 Å) and annealing (from ∼85 to 100 Å). This is accompanied by an increase in the width of the amorphous domains from 30 to 50 Å in drawn fibers, and from 45 to 55 Å in annealed fibers. The diameter of the fibrils decreases slightly upon drawing and increases considerably upon annealing. © 1996 John Wiley & Sons, Inc.     

Electron paramagnetic resonance study of mechanically degraded poly(ethylene terephthalate) and nylon 6 fibers

Peroxide radical concentrations were measured from both PET and nylon 6 fibers mechanically stretched in air at room temperature and quickly quenched into liquid nitrogen. The radical concentrations depend on degree of stretching as well as conditions under which the fibers were made, i.e., morphology. Drawn fibers of PET and nylon 6 produced peroxide radical concentrations of the same order of magnitude at the breaking points. These results indicate that chain scissions occur both in PET and nylon 6 under mechanical stretching.     

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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With 6 figures 2 tables     

Solution crystallization of nylon 6

Electron microscopy and x-ray diffraction data have been obtained on nylon 6 which has been crystallized from solutions in 1,6-hexanediol and 1,2,6-hexanetriol. Lamellar single crystals and spherulites of the γ form are obtained by crystallization from 1,2,6-hexanetriol. The morphology of the single crystals is different from that obtained from glycerine solutions. The spherulites of the γ form are composed of larger lamellae. Sheaflike crystals of the α form are obtained from both solvents. α-form and γ-form crystals both grow from 1,2,6-hexanetriol at appropriate crystallization temperatures. α-form crystals alone are obtained from 1,6-hexanediol solution at every crystallization temperature. The long periods measured by small-angle x-ray diffraction for the solution-grown crystals are in the range 56 to 66 Å. The melting behavior of the solution-grown crystals is examined and discussed. Effects of solvent on growth of the two crystalline forms from solution are investigated.     

多尺度结构Ag/PA6纳米纤维膜的制备及其催化性能

随着工业的进步,废水处理特别是印染废水的处理成为亟待解决的问题.银纳米粒子因其特殊的物理化学性能而表现出催化活性,但银纳米粒子的团聚限制了其使用,所以出现了一系列新的载体材料,如微球、薄膜和纤维等.其中电纺纳米纤维由于具有高比表面积,作为载体材料具有非常大的优势,而将常规电纺纳米纤维作为载体也已有报道.但是,将具有更高比表面积的电纺纳米纤维作为载体,特别是一种类似于树枝状结构的多尺度纳米纤维作为载体还鲜有报道.本文制备了一种多尺度结构的PA6纳米纤维膜,该纳米纤维膜由直径为50?120 nm的主纤维和10?50 nm的分支纤维构成;由于分支纤维的出现,多尺度结构纳米纤维膜的比表面积得到了提高,可以为银纳米粒子的负载提供更多附着位点.制备的多尺度结构纳米纤维膜通过银胶溶液浸渍成功地负载银纳米粒子,对制备的纳米纤维膜的形态、化学结构以及对亚甲基蓝的催化性能进行了探讨.SEM,EDS和TEM结果表明,银纳米粒子成功地负载在多尺度结构纳米纤维的表面,并且银纳米粒子的粒径以及负载量可以通过变换银胶溶液的浓度合理调控.此外,与常规PA6纳米纤维膜相比,多尺度结构纳米纤维膜更有利于银纳米粒子的分散,同样通过银胶溶液A浸渍,负载在多尺度结构纳米纤维上银纳米粒子粒径为8.6 nm,而负载在普通PA6纳米纤维上银纳米粒子粒径为11.2 nm.XPS分析表明,银纳米粒子成功地负载到多尺度结构纳米纤维上,并且经不同银胶溶液处理,纳米纤维膜的载银量不同.通过O的高能XPS分析发现,银纳米粒子与PA6分子间形成了配位键,这在一定程度上有利于Ag纳米粒子的固定,阻止了Ag纳米粒子的团聚.Ag/PA6纳米纤维膜以及多尺度结构Ag/PA6纳米纤维膜催化降解实验表明,多尺度结构Ag/PA6纳米纤维膜具有较高的催化活性,反应2 h后对10 mg/L亚甲基蓝的降解率达到98.13%,并且降解过程符合伪一级动力学.不同浸渍液浓度处理纳米纤维膜催化实验表明,Ag纳米粒子的大小以及含量都会影响纳米纤维的催化活性,纳米粒子粒径越小,其催化活性越高;不同NaBH4加入量催化体系催化实验表明,随着NaBH4加入量的增大,催化体系的降解率增高,其对催化体系的催化性能起着至关重要的作用;其他条件一定,随着染料初始浓度的增大,催化体系的催化性能下降;循环实验表明,经5次循环之后,其降解率仍高达83.5%,该纳米纤维膜具有一定的循环使用性能.     

Annealing of melt-crystallized nylon 6

Effect of annealing on thermal behaviour and crystalline structure of meltcrystallized nylon 6 has been investigated.The annealing process is found to be characterized by an incubation period followed by a more or less doubling of the SAXS long spacing and of the crystallinity.The extrapolated heat of melting of the crystalline phase of nylon 6 in the-modification is 188 Jg^–1 and its extrapolated equilibrium melting temperature is 260 °C.Presented in part at 28th IUPAC Symposium on Macromolecules, Strasbourg, July, 1981.