Structure development during melt spinning of linear polyethylene fibers

Apparatus has been developed for studying the development of crystallinity and orientation during the melt spinning of synthetic fibers. Tension in the fiber and temperature, diameter, and x-ray diffraction patterns are measured as a function of distance from the spinneret for a running monofilament. Measurements are presented for linear polyethylene over a range of spinning variables together with other investigations carried out on the final as-spun fibers. These data indicate that the development of crystallinity in polyethylene is controlled by a balance between increased crystallization kinetics caused by the stress in the fiber and a tendency for increased supercooling with change in any spinning variable that increases cooling rates in the fiber. The type of crystalline orientation observed, its development during the spinning process, and the changes observed with changes in spinning conditions suggest a model for the as-spun fiber structure in which varying amounts of row nucleation and twisting of lamellar, folded-chain crystal overgrowths occur depending on the spinning conditions. As-spun fiber birefringence was shown to depend primarily on the crystalline orientation. Mechanical properties correlated well with c-axis crystalline orientation function and spinline stress.     

锦纶66与锦纶6帘线的性能对比

对锦纶66与锦纶6帘线的性能进行对比。与锦纶6帘线相比，锦纶66帘线具有良好的基本耐热性能、尺寸稳定性及耐高温性能，在受热状态下的断裂强力保持率较高；用其生产轮胎时可提高硫化温度，缩短硫化时间，提高生产效率，而轮胎使用寿命长，安全性和耐久性较优。     

Structure development in melt spinning poly(vinylidene fluoride) fibers and tapes

A series of poly(vinylidene fluoride)s of varying molecular weight have been melt spun to form fibers and tapes. These have been characterized with wide angle X-ray diffraction (WAXD), differential scanning calorimetry (DSC), birefringence, and small angle light scattering (SALS). WAXD and DSC have detected both the α and β crystal structures in melt spun fibers with the relative amount of β increasing with drawdown stress. WAXD and birefringence have been used to detect orientation in the fibers. Hermans–Stein orientation factors have been computed for the α-phase as a function of drawdown stress. Superstructure has been investigated using SALS. The mechanical properties of fibers have been determined with a tensile testing machine and correlated with orientation and spinline stress.     

Dynamics and structure development during high-speed melt spinning of nylon 6. II. Mathematical modeling

A mathematical model of the melt spinning process that includes crystallization has been used to compute the velocity, diameter, temperature, and birefringence as a function of distance from the spinneret. An improved inversion procedure is described and is shown to give better results for the computed apparent elongational viscosity and heat-transfer coefficient data. The computed profiles have been compared directly to the experimental profiles determined earlier and reported in Part I of this paper. The results show that the model describes the major features of the melt spinning process. The reasons for the observed differences between experimental profiles and those computed from the model are discussed.     

Effect of molecular weight on high-speed melt spinning of nylon 6

An extensive experimental study of the structure and properties developed in as-spun nylon 6 filaments is reported. Five polymers representing different molecular weights in the range 25,000–73,000 g/mol (viscosity average) were studied. These polymers were melt spun over a range of spinning speeds using an air drag type of drawdown device. Maximum take-up velocities achieved were in the neighborhood of 4000 m/min. The structure and properties of the as-spun filaments were characterized using density, DSC, WAXS, SAXS, birefringence, and tensile tests. The structural characteristics and properties of the filaments are strongly dependent on molecular weight. Generally, higher molecular weight leads to higher modulus and filament tenacity and lower elongation to break in the as-spun filaments. The structural changes with molecular weight are rather complicated; the complications are explained in terms of changes of crystallization rate and attainable crystallinity.     

Vibration welding of nylon 6 to nylon 66

Vibration welding of dissimilar nylons is a promising technique for assembling complex components made of different polymers. The effects of pressure and meltdown on the tensile strength of nylon 6 (PA 6) to nylon 66 (PA 66) vibration welds were determined in this study using an experimental design and three weld geometries. Weld strengths were generally improved by increasing meltdown and decreasing weld pressure. The weld strength was also shown to vary with the position of the lower melting material for T‐welds. Using differential scanning calorimentry and fracture surface analyses, it is concluded that for all geometries, higher weld strengths can be achieved when both materials are melted. Polym. Eng. Sci. 44:760–771, 2004. © 2004 Society of Plastics Engineers.     

Structure development during polymer processing: Studies of the melt spinning of polyethylene and polypropylene fibers

Experimental studies of structure development in melt spinning of polyethylene and polypropylene fibers are described. Emphasis is given to the influence of applied stresses on the rates of crystallization and on the development of crystalline morphology. The relationship of fiber morphology to mechanical properties, especially “hard elastic fibers” is considered. The relevance of such studies to other polymer processing operations such as film extrusion is discussed.     

Structural studies of electrospun nylon 6 fibers from solution and melt

Nylon 6 (N6) fibers have been fabricated via two different electrospinning schemes, from solution of N6 and formic acid at room temperature as well as from N6 melt at elevated temperature. The crystal structures of electrospun N6 fibers from solution and melt, and the annealing effect on the structures were studied by using various techniques. Combined analysis of the differential scanning calorimetry (DSC) at various heating rates, temperature-dependent X-ray diffraction (XRD), and Fourier-transform infrared (FTIR) spectroscopy indicates that N6 fibers from melt predominantly exhibit the meta-stable γ-crystalline forms and low molecular orientation, while solution electrospun fibers from slowly evaporating solvent show both α- and γ-form crystals and higher degree of molecular orientation. At high annealing temperature, the meta-stable γ-crystals in melt electrospun fibers easily transform into thermodynamically stable α-form crystals, while crystals in solution electrospun fibers exhibit higher thermal stability. Nonisothermal modeling and in-situ measurements of jet temperature indicate that rapid quenching due to enhanced heat transfer by electrohydrodynamically driven air flow near the jet is responsible for the less stable γ-crystals and lower degree of molecular orientation in melt electrospun fibers.     

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.     

Melt spinning of nylon 6: Structure development and mechanical properties of as-spun filaments

The structure of melt-spun nylon 6 filaments was studied using on-line x-ray diffraction and birefringence measurements. Measurements were also made on as-spun and treated filaments. On-line wide-angle x-ray scattering measurements indicated that crystallization did not occur on the nylon 6 spinline at spinning rates up to 1000 m/min when spinning was done into either ambient air of 60% relative humidity or into wet saturated air. The filaments did crystalline gradually on the bobbin to a paracrystalline pseudohexagonal (γ) form. The rate of crystallization was dependent on the molecular orientation developed in the spun filaments. Crystalline orientation factors based on hexagonal symmetry were computed as a function of take-up velocity for fibers which were conditioned 24 hr in air at 65% relative humidity. Annealing in air or treatment in water or 20% formic acid solution causes a transformation from the pseudohexagonal form to the α monoclinic form. The tangent modulus of elasticity and tensile strength of spun and conditioned filaments increase with increasing take-up velocity and spinline stress, while elongation to break decreases with these variables.     

熔体直纺高强超低热收缩尼龙66纤维生产工艺探讨

以质量分数52.8％的尼龙66盐液为原料,采用一步法连续聚合熔体直纺工艺生产高强超低热收缩尼龙66纤维,探讨了聚合物相对黏度、纺丝温度、上油率、拉伸倍数、热定型温度、松弛比等工艺参数对生产及产品质量的影响.结果表明:较佳的生产工艺条件为尼龙66聚合物相对黏度77～79、纺丝温度298～302℃ 、上油率(0.80±0....     

Studies on melt spinning of nylon 6. I. Cooling and deformation behavior and orientation of nylon 6 threadline

The melt spinning of nylon 6 filament yarns was studied by measuring the filament tensions at the takeup roll, the filament temperatures θ(x), filament diameters d(x), and birefringence Δn(x) as functions of distance x from the spinneret, and by observing how the molecular orientation was affected by these differences in cooling and thinning. Results were as follows: The thinning of the filament line, d(x), is affected little by the spinning temperature or by the degree of polymerization of the yarns taken up; it however depends heavily on the takeup speed V_Tu and the rate Q of production. Trouton viscosity β(T) as a temperature function derived from these experiments on nylon 6 is expressed consistently by the equation β ? 0.34 exp (3250/T), where T is absolute temperature. Nylon 6 filaments exhibit higher Trouton viscosity values than polyester or polypropylene filaments under the same spinning temperature. Filament temperature θ(x) versus distance x agreed well with theoretical values. The speed of molecular orientation was highest in the temperature range from 120°C to 40°C (the latter being the glass transition temperature of nylon 6). Furthermore, the larger the time rate of polymer deformation and the longer the residence time of polymer in the above temperature range, the higher was the orientation of the filament yarns taken up.     

Dynamics and structure development during high speed melt spinning of nylon 6. I. On-line experimental measurements

On-line experimental measurements of filament diameter, temperature, and birefringence as a function of distance from the spinneret were carried out during melt spinning of two nylon 6 resins of differing molecular weight. Filament tension was also measured. A rapid diameter attenuation or “necking” was observed in the spinline for both resins at take-up velocities above 6000 m/min. Evidence of crystallization in the spinline was also observed at these high spinning speeds. An analytical technique was used to extract apparent elongational viscosity for each resin and heat transfer coefficient for the melt spinning process from the experimental results.     

Polypropylene/nylon 6 blends: Phase distribution morphology,rheological measurements,and structure development in melt spinning

A series of polypropylene (PP)/nylon 6 (N6) blends of composition 75/25, 50/50, and 25/75 have been prepared in a screw extruder combined with a Koch static mixer. The phase morphology was observed with a scanning electron microscope. The influence of heating in the reservoir of a rheometer followed by subsequent extrusion through a capillary on the phase morphology was investigated. Phase size growth as a function of time was observed under quiescent and mild deformation rate conditions. The discrete phase size was observed to decrease with increasing extrusion rate through dies. The shear viscosity and principal normal stress difference of the blends were measured as a function of composition. The crystalline orientation of both polypropylene and nylon 6 in blend melt spun fibers was characterized by wide angle X-ray diffraction and interpreted in terms of Hermans–Stein orientation factors. The orientation increases with drawdown ratio. The orientation factors for the polypropylene phase vary with spinline stress in a manner independent of composition and identical to that for pure polypropylene. Extracting melt spun blend fibers with formic acid has produced small-diameter polypropylene minifilaments with diameters of the order of microns.     

Structure development in the early stages of crystallization during melt spinning

The earliest stage of crystallization during melt spinning was examined for four polymers: HDPE, PVDF, nylon 6 and poly(oxymethylene). The four polymers have very similar melt viscosities. Of particular interest is the dependence of the time for the onset of detectable crystallization on the take-up speed. The results for all four polymers lie on the same onset time versus take-up speed curve, indicating that this condition depends chiefly upon chain orientation and not appreciably on chain chemistry or specific undercooling. The result is consistent with a condition of critical strain level. A similar, but less stringent, result is found for further crystallization in the spinline.     

Comparison of nanocomposites based on nylon 6 and nylon 66

Nylon 6 and nylon 6,6 organoclay nanocomposites were prepared by melt processing using a twin screw extruder. The effects of polyamide type and processing temperature on the mechanical properties and the morphology of the nanocomposites were examined. Mechanical properties, transmission electron microscopy (TEM), wide-angle X-ray diffraction (WAXD), percentage crystallinity and isothermal thermo-gravimetric analysis (TGA) data are reported. A particle analysis was performed to quantitatively characterize the morphology; these results are later employed in modeling the modulus of these materials using composite theory. No significant difference was observed in the mechanical properties and morphology of PA-6 nanocomposites processed at two different temperatures. PA-6 nanocomposites had superior mechanical properties than those made from PA-66. The tensile strength of PA-66 nanocomposites deviated from linearity at high levels of MMT. WAXD and TEM results show that the PA-6 nanocomposites are better exfoliated than the PA-66 nanocomposites, which exhibit a mixture of intercalated and exfoliated structures. Mechanical properties were consistent with the morphology. DSC reveals a higher percentage of crystallinity in the PA-66 samples. Isothermal TGA shows only a 5% difference in the degradation of the organic modifier on the organoclay processed at 240 °C versus 270 °C. Particle analysis shows a higher average particle length and thickness, and a lower average particle density and aspect ratio in nanocomposites based on PA-66 versus PA-6. The Halpin-Tsai and Mori-Tanaka composite theories predict satisfactorily the behavior of the PA-6 nanocomposites, while the PA-66 nanocomposites were predicted acceptably up to a certain volume fraction where the non-linear behavior takes effect. All the results indicate that there is a lower degree of exfoliation in the nanocomposites produced with a PA-66 matrix apparently stemming from the chemical differences between PA-6 and PA-66.     

Radial temperature differences during the melt spinning of fibers

In this investigation, a numerical model was developed to predict the temperature distribution in a fiber during melt spinning. This model uses the implicit Crank–Nicolson method to solve the governing differential equation for the problem. The model was applied to a series of numerical experiments on a liquid crystalline fiber which is melt-spun. These simulations used typical sets of operating conditions to determine the effect of various operating parameters on the predicted radius profile, spinline tension, and temperature distribution. The effects of spinneret capillary diameter, mass flow rate, ambient air temperature, spinning temperature, and elongational viscosity were investigated. The results of the various runs showed that ambient air temperature and mass flow rate had a significant effect on the predicted radius profile, spinline tension, and temperature distribution. The spinning temperature was an important parameter, but its only significant effect was on the spinline tension. Spinneret capillary diameter and elongational viscosity had little effect on the predicted results.     

Structure and tensile properties of Nanoclay–Polypropylene fibers produced by melt spinning

Nanocomposite fibers of polypropylene and montmorillonite‐based organoclay were produced by a melt‐spinning process, and their structures and mechanical properties were studied. The addition of nanoclay in polypropylene increased the rate of crystallization and altered the microstructures of the fibers. Increases in the crystal size and a reduction in the molecular orientation were observed in the nanoclay–polypropylene composite fibers. The tensile properties of nanoclay composite fibers were also studied, and decreases in the fiber modulus and tenacity and increases in the strain at break were observed. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Influence of spinning velocity on mechanical and structural behavior of PET/nylon 6 fibers

Influence of spinning velocities on the mechanical and structural properties of polyethylene terephthalate (PET)/nylon 6 blend fibers have been reported. Fibers of PET/nylon 6 containing a small percentage of nylon (5% by weight) have been melt-spun at 3 different spinning velocities (2,900; 3,200; 3,600 m/min). The fibers have been characterized by thermal, morphological, structrual, and mechanical analysis. Various techniques such as SEM, DSC, X-ray diffraction, hot water shrinkage (HWS), viscosity, and birefringence have been used. SEM analysis revealed that in the blend, nylon 6 is well-dispersed as spheres in the PET matrix. The blend shows a marked decrease in the melt-flow index, which in turn leads to a beneficial effect on the rheological properties of the PET without negatively influencing its mechanical characteristics. This finding results in a saving on energetical requirements of the processing, as both temperature and pressure of spinning can be decreased. © 1995 John Wiley & Sons, Inc.