Depolymerization of nylon 6 waste fibers

The depolymerization of nylon 6 was carried out with various solvents, such as formic acid, hydrochloric acid, and sulfuric acid, followed by heating under reflux for different times. From the polymer dissolved and refluxed in formic acid, degradation products with different ranges of molecular weights were collected by fractional precipitation, with small lots of distilled water added as a nonsolvent. The characterization of different fractions was carried out by the measurement of the viscosity‐average molecular weight, the number‐average molecular weight, and the number of amino end groups. The presence of the monomer, aminocaproic acid, was confirmed by thin‐layer chromatography in the case of hydrochloric acid treated nylon 6. With a strongly acidic ion‐exchange resin, the monomer was separated in its purest form, and the melting point was noted. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 186–190, 2006     

Tensile deformation of nylon 6 fibers

Nylon 6 fibers which had been relaxed to different extents by annealing were examined at fixed strains by small angle and wide angle X-ray techniques. It was found that the strain of the long period of the semicrystalline microfibrils is identical to the macroscopic fiber strain. Approximately 1/3 of the tensile deformation results from molecular shear of imperfectly oriented crystalline chains. Virtually no evidence for intercrystalline slip is found; the orientation of the intercrystalline amorphous regions results in a low compliance for the shear of crystals past one another. The majority of the microfibril deformation occurs by stretching these intercrystalline amorphous regions, accompanied by the flow of extrafibrillar amorphous material to maintain constant volume. In highly annealed fibers this “filling” mechanism is less efficient, as the amount of extrafibrillar material has been reduced during shrinkage. This effect leads to a decrease in Poisson's ratio after increasingly severe annealing. A related result of annealing is the dehomogenization of the microstructure, leading to the presence of more stress-induced “microcracks” during the stretching of annealed fibers.     

Thermal properties of photo-oxidized nylon 6 fibers

Nylon 6 fiber begins to increase in weight at about 180°C when heated in oxygen. The increase is attributed to an uptake of oxygen resulting from thermal oxidation. A similar weight increase is not found in photo-oxidized nylon 6 on heating in oxygen. It appears that nylon 6 tends to form volatile compounds more easily on heating after photodegradation. Changes detected by differential thermal analysis and also by thermomechanical analysis after nylon 6 has been exposed to sunlight are discussed primarily in terms of the supramolecular structure of the fiber.     

Drawing and ultimate tensile properties of nylon 6/nylon 6 clay composite fibers

This study systematically investigated the drawing and ultimate tenacity properties of the Nylon 6 (NY6)/nylon 6 clay (NYC) composite fiber specimens prepared at varying NYC contents and drawing temperatures. The achievable draw ratio (D_ra) values of NY6_x(NYC)_y as‐spun fiber specimens initially increase in conjunction with NYC content, and then approach a maximum value, as their NYC contents and drawing temperature approach the 0.5 wt% and 120°C, respectively. The percentage crystallinity (X_c) values of NY6_x(NYC)_y as‐spun fiber specimens increased significantly, as their NYC contents increased from 0 to 2 wt%. As revealed by high power wide angle X‐ray diffraction analysis, α form NY6 crystals grew at the expense of γ form NY6 crystals originally present in NY6_x(NYC)_y as‐spun fiber specimens as their draw ratios increased. The ultimate modulus, tenacity, and orientation factor values of NY6_x(NYC)_y fiber specimens approach a maximum value, as their NYC contents and drawing temperatures approach the 0.5 wt% and 120°C optimum values, respectively. The thermal and melt shear viscosity experiments were performed on NY6_x(NYC)_y resins and/or fiber specimens to determine the optimum NYC content and possible deformation mechanisms accounting for the interesting drawing, orientation, and ultimate tenacity properties found above. POLYM. ENG. SCI., 2012. © 2012 Society of Plastics Engineers     

Tie chains and modulus of nylon 6 fibers

A large number of nylon 6 fiber samples with varying internal structure were obtained by changing draw ratios, drawing temperature, and quenching immediately after drawing. Modulus of these samples is analyzed by Takayanagi model and fraction of tie chains is obtained. It is observed that the modulus of these samples is directly proportional to the fraction of tie chains.     

Biconstituent fibers from segmented polyurethanes and nylon 6

The characteristics of Monvelle, a new biconstituent fiber from nylon 6 and a segmented polyurethane, are reviewed briefly, and some of the technical problems inherent in producing such a fiber are discussed. The characterization of two series of polyurethanes which can be melt spun is given in detail. The chemical composition of the hard segment was maintained constant, being derived from 4,4′-diphenylmethane diisocyanate (MDI) and 1,4-butanediol, in all polymers. In one series using poly(butylene adipate) of MW 2000 as the soft segment, the average hard segment content was varied from 33% to 54%. In the other series, the hard segment content was held at 43%, and three additional soft segments, each at MW 2000, were used: poly(ethylene adipate), polycaprolactone and poly-1,4-oxybutylene glycol (PBG). Characterizations include molecular weight distributions, thermal analysis, rheological studies, and selected small-angle and wide-angle x-ray diffraction and polarized light microscopy. Crystallinity, melt viscosity, and activation energy of flow increased with increasing hardsegment content. Changes in the polyester soft segments had little effect on the properties studied, but with PBG the crystalline melting point of the polymer, without annealing, was higher and the melt viscosity was slightly higher than corresponding polyester-based samples, in agreement with previous reports of sharper phase separation in polyether urethanes, compared to polyester urethanes.     

Reinforcement of natural rubber with nylon 6 short fibers

The properties of natural rubber vulcanizates reinforced with nylon 6 short fibers were studied. It was found that the stress of vulcanizates decreased with initial fiber loading, followed by an increase with increasing the amount of fiber. The effect of reinforcing carbon black HAF on the physicomechanical properties was studied in the presence and absence of hydrated silica.     

Characterization of nylon 6 fibers grafted by acrylic monomers

Samples of nylon 6 fibers grafted with the acrylic monomers methyl methacrylate (MMA), ethyl methacrylate (EMA), and n-butyl methacrylate (n-BMA) with various graft levels were investigated by infrared, X-ray and scanning electron microscopic studies and the changes due to grafting with respect to the parent nylon 6 fibers were studied. The IR spectra of grafted nylon 6 samples show that there is a little change in the peak heights by grafting of nylon 6 with various monomers. The characteristic peaks of parent nylon are, more or less, maintained in the case of grafted samples. A peak at 1730 cm^?1 of the ester group was noted which confirms that the polymer has been grafted with the monomer. X-ray diffraction data on the grafted samples show some remarkable variations with the degree of grafting, depending upon the nature of the graft monomer. The percentage of crystallinity varies with the degree of grafting. In the initial stages of grafting it shows a decrease in the case of PMMA graft and an increase in the case of PEMA and Pn-BMA graft. At higher degrees of grafting (above 50% graft add-on) the percentage of crystallinity decreases in all the three cases. Orientation index has been found to increase in the initial stages of grafting in the case of EMA and n-BMA grafted nylon 6 and it decreases later on, whereas in the case of MMA graft it decreases continuously even at low graft level. The studies of surface characteristics for the parent and grafted samples show that spectacular changes on the surface of the various samples have taken place. With the increase in the graft level the diameter of the fiber increases and also the voids and cracks appear on the surface.     

Interpretive nonlinear viscoelasticity: Dynamic properties of nylon 6, nylon 66, and nylon 12 fibers

Nonlinear response of nylon 6, nylon 66, and nylon 12 fibers to sinusoidal straining under relatively large strain amplitude is analyzed in terms of the changes in properties during the straining, i.e., the change in modulus, change in internal friction and change in structure which involves energy release or absorption in straining. Modulus generally increases with strain but it decreases with increase of strain amplitude, the effect of strain amplitude being largest with nylon 6 and smallest with nylon 66. Mechanical loss increase with the increase of strain amplitudes in nonlinear manner, and the magnitude of change is largest with nylon 66 and smallest with nylon 6. During the extension phase, structural change occurring in nylon 6 is predominantly an increase in order or orientation while that with nylon 66 is crack opening or cavitation. Various aspects of the experiments and analysis of the data are described in detail.     

Morphology and crystallization behavior of nylon 6‐clay/neat nylon 6 bicomponent nanocomposite fibers

Nylon 6‐clay hybrid/neat nylon 6, sheath/core bicomponent nanocomposite fibers containing 4 wt % of clay in sheath section, were melt spun at different take‐up speeds. Their molecular orientation and crystalline structure were compared to those of neat nylon 6 fibers. Moreover, the morphology of the bicomponent fibers and dispersion of clay within the fibers were analyzed using scanning electron microscopy and transmission electron microscopy (TEM), respectively. Birefringence measurements showed that the orientation development in sheath part was reasonably high while core part showed negligibly low birefringence. Results of differential scanning calorimetry showed that crystallinity of bicomponent fibers was lower than that of neat nylon 6 fibers. The peaks of γ‐crystalline form were observed in the wide‐angle X‐ray diffraction of bicomponent and neat nylon 6 fibers in the whole take‐up speed, while α‐crystalline form started to appear at high speeds in bicomponent fibers. TEM micrographs revealed that the clay platelets were individually and evenly dispersed in the nylon 6 matrix. The neat nylon 6 fibers had a smooth surface while striped pattern was observed on the surface of bicomponent fibers containing clay. This was speculated to be due to thermal shrinkage of the core part after solidification of the sheath part in the spin‐line. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2014 , 131, 39996.     

Structure development in the melt spinning of nylon 66 fibers and comparison to nylon 6

The development of crystallinity and orientation during the melt spinning of nylon 66 was investigated. Nylon 66 was found to crystallize in the spinline to form the Bunn-Garner α-triclinic structure. This behavior differs from that of nylon 6. Nylon 66 was found to develop lower crystalline orientation than nylon 6 under comparable spinning conditions.     

Photoinduced graft copolymerization of nylon 6 fibers with acrylamide. II. Characterization and evaluation of properties

Nylon 6-g-polyacrylamide graft copolymer prepared by photoinduced initiation was characterized and some of its properties were evaluated. Intrinsic viscosity of the graft copolymer increased continously with percent grafting. Thermal stability decreased corresponding to the increase in add-on %. The moisture regain, diameter, and density showed an increase with percent grafting. The acid dyeability of the graft copolymer decreased with increase in graft level, whereas the disperse dye uptake increased initially up to a graft add-on of 28.9% and then showed a decrease.     

Crosslinking and scission in thermooxidative degradation of PVC

Summary Crosslinking and chain scission in thermooxidative PVC degradation have been studied. Gel formation was found to give linear Charlesby-Pinner plots, consistent with the constant rate of crosslinking and scission. Similarly to thermal degradation, partial reversibility of crosslinking was observed also in oxygen.     

Crystallization of cyclic oligomers on the surface of nylon 6 fibers

When scoured nylon 6 filament was exposed to either water vapor or n-alcohol vapor, a portion of the cyclic [NH(CH₂)₅CO]_x, with x = 2 through 7, and the ?-caprolactam present migrated to the filament surface and crystallized. A variety of crystal forms were observed. The variations depended partly on the vapor to which the sample had been exposed. During water vapor exposures, the cyclic dimer migrated more easily to the filament surface than the cyclic monomer and the cyclic tetramer migrated more easily than the cyclic trimer. It is postulated that the secondary valence forces acting between the dimer and the nylon 6 polymer are weaker than that between the ?-caprolactam and the polymer since the dimer forms intramolecular hydrogen bonds. Consequently, the dimer migrates more easily than the monomer, which can form hydrogen bonds with the polymer. Also the cyclic trimer can form hydrogen bonds with the nylon 6 polymer and thus migrates less easily than the cyclic tetramer, which can form intramolecular hydrogen bonds. In alcohol vapor exposures, the n-alcohol used influenced the concentration of cyclic monomer and oligomer, which migrated to the surface of the nylon 6 filament. The variation of the monomer and oligomer concentration on the fiber surface with the alcohol used in the exposure is discussed.     

Transcrystalline morphology of nylon 6 on the surface of aramid fibers

In this paper, the isothermal crystallization of nylon 6 in the presence of Kevlar 129 fiber was investigated by polarized optical microscopy (POM). The formation of a transcrystalline domain was found to be mainly controlled by crystallization conditions, such as the temperature of the isothermal crystallization, residual time at melting temperature and the cooling rate of the melt. The nucleation rate of nylon 6 on the fibers was mainly affected by the crystallization temperature. The interfacial transcrystallinity of nylon 6 occurred on the surface of Kevlar 129 fiber in the temperature range 130–190 °C. The reason for the formation of interfacial transcrystalline morphology is discussed from the molecular level, based on the understanding of the packing mode of nylon 6 chains around fibers and the interaction between matrix and fibers. It was found that the lattice matching and hydrogen‐bonding between nylon 6 and poly(p‐phenylene terephthalamide) (PPTA) crystals play an important role in the epitaxial crystallization. Copyright © 2004 Society of Chemical Industry     

Development of macrostructural effects of cold drawing on nylon 6 fibers

This work reports measurement of the molecular orientation by two techniques for nylon 6 fibers drawn at room temperature. The changes in the strain and optical parameters are used to obtain some macrostructural parameters to evaluate the cold‐drawing process values of the mechanical orientation functions, [P₂(cos θ)], [P₄(cos θ)], amorphous and crystalline orientation functions (F_c and F_a), and the molar number of chain segments per unit volume (N_e). Also the crosslink density (N₀), the chain entanglement density (N_s), the average optical orientation F_av, the dielectric constant (ε), the dielectric susceptibility (η), the shrinkage stress (k_s), and other parameters were calculated. Relationships between the calculated parameters are given. The present study demonstrates changes in the molecular reorientation factors and the obtained new physical properties resulting from cold‐drawing process. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 94: 287–295, 2004     

Mechanical properties of nylon 6 fibers gel-spun from benzyl alcohol solution

The drawing behavior and mechanical properties of gel-spun nylon 6 fibers were investigated in relation to the growth rate and morphology of gels. The sol-gel transition temperature of a nylon 6/benzyl alcohol solution increased with polymer concentration and, at higher concentration, appeared with gel melting. From the measurements of gelation time, the growth rate of gels was estimated assuming an Arrhenius type of gelation rate. It was found that gel growth of nylon 6 in benzyl alcohol was nearly three-dimensional, evidenced by the presence of spherical gels observed in the scanning electron microscope. A draw of asspun fibers was performed at one-stage or two-stage hot drawing. Modulus and tenacity increased with increase of the draw ratio and were nearly independent of the draw temperature. A two-stage draw was more effective to obtain a higher modulus than that of the one-stage draw and it was ascribed to the difference in the molecular orientation mechanism. However, it was difficult to obtain a higher modulus than 6.2 GPa by the gel-spinning of nylon 6 in this study and it was regarded as a result of the presence of spherical gels which hindered the sample to elongate to a higher draw ratio. © 1996 John Wiley & Sons, Inc.