Spinning Nozzle Research Articles

Centrifugal force spinning of PA6 nanofibers – processability and morphology of solution-spun fibers

Forcespinning™ is a newly developed process that employs centrifugal force to spin nanofibers from polymer solutions or melts. Nanofibers and nanofibrous structures have remarkable properties due to their small diameter and high surface area to volume ratio. The ability to control the average value and dispersion of fiber diameter is critical for applications such as filtration and tissue engineering scaffolds, where the performance of the nanofiber membranes depends on fiber diameter. This research investigates the interactions among polymer fluid viscosity and Forcespinning parameters, and their impact on fiber morphology and diameter using PA6 as a spinning material. The results indicate a positive relationship between spinning solution viscosity and fiber diameter. Increasing the solution viscosity both shifts the diameter distribution and increases its spread toward higher values, which results in the alteration of its shape. In addition to fiber diameter, viscosity appeared to also play a major role in determining the spinnability of the solution. Other spinning parameters, i.e. spinneret speed and spinning nozzle gage, played a minor role relative to the polymer solution viscosity, in determining both processability and fiber diameter distribution.

Parameter Optimization by Taguchi Method for Thermoplastic Polymer Using a Melt Spinning Machine

Fused spinning method is the most commonly used method to manufacture man-made fiber and the most important physical property of as-spun fiber is tenacity, which is affected by process parameters including spinning nozzle temperature, cooling temperature, cooling wind speed and winding speed. First, we selected the appropriate orthogonal array for the experimental plan to conduct experiments. Coupled with signal-to-noise (SN) ratio and main effect analysis, we understood the impact of process parameters on quality and confirmed the reproducibility of the experiment, and furthermore obtained the optimal combination of process parameters.

나노섬유 방사노즐 설계를 위한 거미 실크 방적장치의 생체모사 분석

고강성 나노섬유 생산이 가능한 전기방사장치 방사노즐의 설계를 위해 자연을 모방하는 공학적 방법론을 도입하여, 무당거미(Nephila clavata L.Koch) 대병상선의 토사관과 그 생체방적 시스템이 지닌 미세구조적 특성을 고해상도의 전자현미경 관찰을 통해 분석하였다. 자연계에서 가장 강도가 높은 드래그라인을 생성, 분비하는 대병상선의 토사관은 bullet type spigot을 통해 전방적돌기 표면에 개구되어 있었으며, 신축성 구조를 지닌 토사관 말단마디의 노즐을 통해 고체상의 실크가 생성되었다. 분비낭과 토사관 사이를 연결한 분비관은 루프를 형성한 후 방적돌기에 수납되었고, 분비관 내강의 직경은 점진적으로 축소되어 노즐을 통해 방사되는 실크의 직경은 펀넬 부위의 1/10 이하인 것으로 관찰되었다. 한편, 실크 중합과정에서 수분을 제거하기 위한 큐티클의 특수구조가 관찰되었는데, 분비낭의 펀넬 부위에서는 해면상 큐티클 구조가 그리고 분비관의 말단부에서는 비후된 subcuticle 구조와 함께 잘 발달된 상피의 미세융모 층이 확인되었다. 또한 분비관의 내강부 큐티클 표면에서 확인된 나선형 강선구조는 실크 전구물질의 신속한 유동을 촉진하는 장치일 것으로 해석되었다. The biomimetic approach on the cuticular spinning nozzles of the major ampullate silk glands in the golden-web spider Nephila calvata has been attempted using various visualizing techniques of light and electron microscopes to improve the design of spinning nozzle for producing synthetic nanofibers spun from electrospinning apparatus. The major ampullate spigot which has the most effective nozzle system to produce nanofibers for dragline silk with high strength and elasticity is connected via the bullet type spigot on anterior spinneret with flexible terminal segment. The excretory duct which transports the liquid silk feedstock from ampulla to spigot is divided into 3 limbs by loops back on itself to form an S-shape morphology that is bundled in connective tissue. Final diameter of the nanofibers at nozzle was dramatically reduced by gradual narrowing of duct cuticle less than 10 times comparing to its original size of funnel region. Moreover, the funnel has a characteristic cuticular organization with porous microstructure which seems to be related to water removal from feedstock of silk precursors. High magnification electron micrographs also reveal the presence of the spiral grooves on the surface of the cuticular intima near the valve which presumed to reduce friction during rapid flow of liquid silk.

Investigation on the motion of different types of fibers in the vortex spinning nozzle

AbstractA numerical model is presented to simulate the fiber motion in the airflow inside the vortex spinning nozzle (VSN). The coupling between the fiber and airflow together with the fiber‐wall contact is solved. Based on the numerical model, the motional characteristics of four types of fibers—cotton, viscose rayon, lyocell, and polyester fibers—in the airflow inside the vortex spinning nozzle are simulated and analyzed. The vortex yarn structure is viewed under the scanning electron microscope and the fiber strength utilization factors of the vortex yarns spun from different types of fibers are compared to verify the wrapping effects of different types of fibers in the vortex yarns obtained by the numerical simulation. The agreement between the numerical and experimental results shows that the numerical modeling methodology proposed in this research provides a reliable way of investigating the fiber dynamics in airflow and an efficient solution to the mechanical problems in polymer/textile manufacturing processes involving fluid–solid coupling. POLYM. ENG. SCI., 2011. © 2011 Society of Plastics Engineers

Prediction of the vortex yarn tenacity from some process and nozzle parameters based on numerical simulation and artificial neural network

In this study, two methods, the numerical simulation and the artificial neural network, are adopted to predict the vortex yarn tenacity from some process and nozzle parameters. The fiber-airflow interaction and the motional characteristics of the fiber inside the vortex spinning nozzle are analyzed through the numerical simulation method to predict the yarn tenacity from the parameters of the jet orifice diameter and the yarn delivery speed. The back-propagation multilayer perceptron (MLP) neural network is adopted to predict the tenacity of vortex yarn spun from modal fibers. The following parameters are used as inputs: nozzle pressure, jet orifice angle, distance between the guiding needle and the spindle, and spindle cone angle. The predicted and measured tenacities show low relative errors and a high correlation coefficient, indicating the artificial neural network method provides accurate prediction results. In addition, the effects of these parameters on the yarn tenacity are also analyzed.

Simulating the motion of a flexible fiber in 3D tangentially injected swirling airflow in a straight pipe—Effects of some parameters

A numerical model for particle-level simulation of fiber suspensions has been used to simulate fiber dynamics in three-dimensional tangentially injected swirling airflow in air-jet spinning nozzles. The fiber is modeled as chains of beads connected through massless rods, and its flexibility is defined by the bending and twisting displacements. The effects of some parameters, such as fiber initial position, the injection angle and the injector diameter on fiber motion and yarn properties are discussed. The springy, snake-like and week helical regimes of fiber motion are observed under the most cases. The far from the tube center the fiber release position, the smaller the fiber flexibility is. For a smaller injection angle, the self-entanglement regimes of fiber motion are observed in the downstream of the injectors. The model also predicted the complex helical configuration in the nozzle with a small injector diameter. The predictions of yarn properties coincide with the experimental results reported by several researchers.

Investigation on the Dynamic Behavior of the Fiber in the Vortex Spinning Nozzle and Effects of Some Nozzle Structure Parameters

Vortex spinning, which adopts high speed airflow to insert twist into the yarn, is one of the most promising technological innovations in the textile industry. In vortex spinning, the dynamic behavior of the fiber inside the nozzle, which involves fiber-airflow interaction and fiber-wall contact, plays an important role in the twist insertion process. This paper investigates the airflow characteristics and the fiber dynamic behavior inside the vortex spinning nozzle via a two-dimensional numerical model with the fiber-airflow interaction and fiber-wall contact included. The fiber is assumed to be isotropic, elastic material. The airflow inside the nozzle is assumed to be turbulent, viscous and incompressible. The numerical results show that two vortices with momentarily changed sizes are created upstream of the jet orifice outlets. The imbalance of the pressure around the fiber causes the fiber to move and deform. The trailing end of the fiber rotates with wave shape within the nozzle chamber for several periods to insert twist into the yarn. Based on the model, the effects of three nozzle structure parameters – the jet orifice angle, jet orifice diameter, distance between the nozzle inlet and the hollow spindle, on the dynamic behavior of the fiber, and in turn, the yarn structure and tensile property are investigated. The results show that the appropriate jet orifice angle for obtaining the best yarn tenacity is 70°. The optimal jet orifice diameter is 0.4 mm. The spun yarn has the highest tenacity when the distance between the nozzle inlet and the hollow spindle is 14 mm.

NUMERICAL ANALYSIS OF COSSERAT ROD AND STRING MODELS FOR VISCOUS JETS IN ROTATIONAL SPINNING PROCESSES

This work deals with the curling behavior of slender viscous jets in rotational spinning processes. In terms of slender-body theory, an instationary incompressible viscous Cosserat rod model is formulated which differs from the approach of Ribe et al.,18 in the incompressibility approximation and reduces to the string model of Marheineke and Wegener13 for a vanishing slenderness parameter. Focusing exclusively on viscous and rotational effects on the jet in the exit plane near the spinning nozzle, the stationary two-dimensional scenario is described by a two-point boundary value problem of a system of first-order ordinary differential equations for jet's center-line, tangent, curvature, velocity, inner shear and traction force and couple. The numerical analysis shows that the rod model covers the string model in an inertia-dominated jet regime. Beyond that it overcomes the limitations of the string model studied by Götz et al.10 and enables even the handling of the viscous-inertial jet regime. Thus, the rod model shows its applicability for the simulation of industrially relevant parameter ranges and enlarges the domain of validity with respect to the string approach.

3D tangentially injected swirling recirculating flow in a nozzle with a slotted‐tube—Effects of groove parameters

AbstractA numerical prediction for 3D swirling recirculating flow in an air‐jet spinning nozzle with a slotted‐tube is carried out with the realizable k–ε turbulence model. The effects of the groove parameters on the flow and yarn properties are investigated. The simulation results show that some factors, such as reverse flow upstream of the injector, vortex breakdown downstream of the injector, corner recirculation zone (CRZ) behind the step and vortex ring in the groove caused by the groove geometric variation, are significantly related to fluid flow, and consequently to yarn properties. With increasing groove height, the length of the CRZ increases, while the initial vortex ring in the groove decreases and a same direction rotating vortex forms in the bottom of the groove. Similarly, as the groove width increases, the extent of both vortex breakdown in downstream of the injectors and the vortex ring in the groove increases slightly, whereas the CRZ lengths in stream‐wise direction decrease. Some factors, such as the negative tangential velocities, the size of the vortex rings in the grooves and the CRZ, are constant for nozzles with different groove lengths. Copyright © 2009 John Wiley & Sons, Ltd.

Measuring tensile strength of nanofibers using conductive substrates and dynamic mechanical analyzer

Though the tensile strength of nanofibers is essential to determine their application fields, few studies have been conducted on this topic, due to the difficulties involved in the preparation of single nanofiber tensile specimens, the manipulation of the clamping device, and the sensing of the nano- force and strain. A bundle testing method was employed in this work to measure the tensile strength of nanofibers. For this purpose, a conductive substrate was designed to hold several thousand nanofibers extruded from a spinning nozzle and align them uniaxially during the electrospinning process. This substrate was designed for a dynamic mechanical analyzer (DMA), because most DMAs are equipped with fine sensors sensitive enough to measure a very small force and strain. Nylon 6 nanofibers were electrospun and collected on the substrate. Then, they were elongated simultaneously in the DMA until they were fractured, showing that the aligned nanofibers have superior tensile strength and modulus compared to their counterpart microfibers and thus suggesting that polymeric nanofibers have the potential to be used as reinforcement fibers for composite materials.

Highly oriented electrospun polycaprolactone micro/nanofibers prepared by a field-controllable electrode and rotating collector

Highly aligned electrospun nanofibers were fabricated using a field-controllable electrospinning process. The technique involved a cylindrical electrode connected to a spinning nozzle to stabilize the initial jet, and a field-controllable electrode generating an alternating current (AC) electric field fixed with a rotating collector. Aligned polycaprolactone (PCL) micro/nanofibers were prepared successfully using this process. Due to two electrostatic forces, the Coulombic force and the field-induced torque due to dipole-dipole interaction, the PCL micro/nanofibers were highly stretched in the direction of the electric field; the alignment depended on the applied frequency of the electrode. Wide-angle X-ray diffraction measurement was used to observe the crystallinity and molecular orientation of the electrospun fiber mats. As using the field-controllable rotating collector, the molecular orientation of PCL was improved relative to that of the normal electrospinning process. The oriented electrospun PCL fibers exhibited an increased storage modulus compared to conventionally fabricated electrospun fibers. In addition, the average fiber diameter was reduced and the distribution was narrower compared to those fabricated by the conventional electrospinning process.

Effect of Nozzle Diameter on Mechanical Properties of Poly(ethylene terephthalate) Fibers Prepared in Melt Spinning Process

Melt spinning of poly(ethylene terephthalate) with intrinsic viscosity of 1.0 dl/g was carried out to investigate the effect of the spinning nozzle diameter on characteristics of as-spun fibers. In general, tensile strength increased and elongation at break decreased with an increase in the take-up velocity. With the decrease of the nozzle diameter, such correlation in the elongation versus strength plot shifted to the upper-right direction. This result indicated the improvement of toughness. Network draw ratio of as-spun fibers prepared at different take-up velocities was analyzed through the matching of the true-stress versus true-strain curves by shifting the curves along the true-strain axis to create a master curve. The starting point of the strain hardening in the master curve shifted to lower strain with the decrease of nozzle diameter. From the linear relation between the obtained network draw ratio and thermal shrinkage stress, entanglement density was estimated based on the rubber-elasticity theory. The entanglement density was found to increase significantly with a decrease in the nozzle diameter. Numerical simulation of the melt spinning process suggested the decreases of the maximum tensile strain rate and the Deborah number in the spinning line with the decrease of nozzle diameter. There is a significant decrease of the draw-down ratio as well. It was speculated that these factors play a dominant role for the variation of the state of entanglement and network draw ratio in the as-spun fibers. Continuous two-step drawing of the as-spun fibers revealed that the improvement of toughness in the as-spun fibers prepared using a small-diameter nozzle can be maintained in the drawn fibers.

Micro-Hole Drilling on Silicon Nitride Ceramics in Ethanol

Micro-hole drilling of engineering ceramics has potential for application to fuel injection nozzles and fiber spinning nozzles, etc. To date among engineering ceramics, less study has been reported on the micro-hole drilling of silicon nitride. We therefore conducted micro-hole drilling of hot-pressed silicon nitride using a chemical vapor deposition (CVD) diamond-coated tool with ethanol as the cutting fluid. As a result, the successful drilling of silicon nitride was achieved with a smooth drilled surface and sufficient accuracy of the hole size. Wear damage of the CVD coated diamond tool and drilling debris of silicon nitride were investigated using scanning electron microscopy (SEM) with energy-dispersive X-ray spectroscopy (EDX). As a result, it is suggested that tribochemical reaction of silicon nitride effectively contributed to the micro-hole drilling characteristics; that is, smoother hole surface was obtained due to the polishing action of wear debris and tribochemical reaction products. The hole inlet size, varied during successive drilling process, could be explained in relation to the wear damage of the diamond-coated drill tip.

Thermal Transport During Liquid Jet Impingement from a Confined Spinning Nozzle

Liquid jet impingement heat transfer from a uniformly heated solid disk of finite thickness and radius is considered in this investigation. The jet nozzle is fitted with a confinement disk that spins with a constant angular velocity about the axis of the nozzle. This arrangement is suitable for microgravity applications in which centrifugal force due to disk rotation can be used to force the fluid over the heated surface. The model covers the entire fluid region (impinging jet and flow spreading out under the confined spinning surface) and solid disk as a conjugate problem. The aim of this paper is to examine how the heat transfer is affected by adding a secondary rotational flow over the jet impingement region. Calculations were done for a range of jet Reynolds numbers (500-1500), rotational rates of 0-750 rpm or Ekman numbers (7.08 x 10 -5 - ∞), nozzle-to-target spacings (β = 0.25-5.0), and disk-thicknesses-to-nozzle-diameter ratios (b/d n = 0.25-1.67). Calculations were done for ammonia (NH 3 ), water (H 2 O), flouroinert (FC-77), and oil (MIL-7808), which were used as working fluids, and copper, silver, constantan, and silicon, which were used as solid disk materials. This provided a Prandtl number range of 1.29-124.44 and a solid-to-fluid thermal conductivity ratio of 36.91-2222. Plate materials with higher thermal conductivity maintained a more uniform and lower interface temperature distribution. A higher Reynolds number increased the local heat transfer coefficient over the entire interface. The rotational rate increased the local heat transfer coefficient under most conditions.

Numerical study of an air-jet spinning nozzle with a slotting-tube

Slotting-tube is a critical component of a nozzle of an air-jet spinning machine. It affects flow characteristics in the nozzle, and the fibres motion and yarn properties as well. A realizable k-εturbulence model is adopted to simulate the airflow field inside the nozzle with the slotting-tube.

Fabrication of a biocomposite reinforced with hydrophilic eggshell proteins

Soluble eggshell proteins were used as a reinforcing material of electrospun micro/nanofibers for tissue engineering. A biocomposite composed of poly(ε-caprolactone) (PCL) micro/nanofibers and soluble eggshell protein was fabricated with a two-step fabrication method, which is an electrospinning process followed by an air-spraying process. To achieve a stable electrospinning process, we used an auxiliary cylindrical electrode connected with a spinning nozzle. PCL biocomposite was characterized in water contact angle and mechanical properties as well as cell proliferation for its application as a tissue engineering material. It showed an improved hydrophilic characteristic compared with that of a micro/nanofiber web generated from a pure PCL solution using a typical electrospinning process. Moreover, the fabricated biocomposite had good mechanical properties compared to a typical electrospun micro/nanofiber mat. The fabricated biocomposite made human dermal fibroblasts grow better than pure PCL. From the results, the reinforced polymeric micro/nanofiber scaffold can be easily achieved with these modified processes.

Electrospinning process using field‐controllable electrodes

AbstractFor the production of uniaxially oriented nanofibers and a three‐dimensional, biodegradable scaffold consisting of nanosized fibers, an electrospinning process was modified with a cylindrical auxiliary electrode that was connected to a spinning nozzle to stabilize the initially spun solution and a parallel‐plate electrode as a collector generating an alternating‐current electric field for collecting spun jets. With the complex electric field in the electrospinning process, biodegradable poly(ε‐caprolactone) nanofibers were stacked on a thin, dielectric substrate covering the electrode according to a predetermined design. The degree of orientation of spun nanofibers to the field direction of a target electrode was highly dependent on the applied frequency and field strength of the target electrode. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 1426–1433, 2006

Cooperative Charging Effects of Fibers from Electrospinning of Electrically Dissimilar Polymers

Electrical charging and residual charge decay of electro-spun nonwoven webs comprised of two electrically dissimilar polymers were studied in an effort to investigate their filtration properties. Polystyrene (PS) and polyacrylonitrile (PAN) were electrospun separately, in a layer-by-layer configuration and simultaneously in a side-by-side bi-component apparatus into thin webs on a polypropylene spunbond substrate. During electrospinning of the PS and PAN polymer solutions, the fibers became positively charged when positive voltage was applied to the solution-filled spinning nozzle and became negatively charged when negative voltage was applied. This study was undertaken to examine the effect of cooperative charging from electrospinning of the two polymers, the effect of the three types of web constructions on charge retention, and filtration properties of the fibers. It was found that single, multilayered, and bi-component webs retained surface charges in the thousands of volts that diminished very little over a 20-hour period, but eventually bled off while resting for three months. Filtration properties were found to be exceptionally high for some, but not all, electrospun samples; filtration was found to have a weak dependence on both surface charge and web geometrical factors, particularly the fiber diameter, that influence pressure drop of the aerosol test.

Deformability of WC–Co sinters and 17-4 PH steel brazed joints

Tests of the vacuum brazing joints of WC–Co sinters and age-hardened steels of the 17-4 PH using the Cu solder were carried out. Stresses and strains of the joints have been analysed. The joints have been used in large dimension spinning nozzles of a die for polyethylene granulation, in that considerable strength and ductility of the joints are required. Shearing tests of the joints have been executed on specimens done in the spinning nozzle brazed joint model. The results of mechanical properties of the joint tests were a base for the fooling them numerical investigations. Numerical calculation of tensions and deformations of the joints have been made by means of the finite element method of the ADINA system. Influence of the geometrical parameters of the joints like the connection thickness as well as a fixed load on stresses and displacements of the joints have been analysed. Results of the experimental test were the base for identification and verification of the theoretical model parameters. The thickness of the joints has an essential influence on the values of the local stress and the significant influence on the joint rigidity. In a case of the considered joints the values of the local stress differences have been considerable (a few hundred percent) in dependence of a fixed load manner.

Electrospinning P(LLA‐CL) Nanofiber: A Tubular Scaffold Fabrication with Circumferential Alignment

AbstractIn this paper a synthetic Poly(L‐lactic‐co‐ϵ‐caprolactone) [P(LLA‐CL)] (75:25) copolymer has been fabricated into a nanofibrous structure by electrospinning. The polymer crystal structure has been investigated by DSC and x‐ray diffraction method. During electrospinning at room temperature, a crystallization of LLA sequence in the P(LLA‐CL) copolymer could not form, while a relatively regular arrangement of CL sequence was observed. In order to obtain a tubular scaffold, a rotating mandrel was designed to collect the fiber, so that the tubular scaffold can be retrieved from the mandrel with an inner diameter same as that of the outer diameter of the mandrel. An auxiliary electrode with a sharp edge and a negative charge was set under the mandrel to guide the fiber deposition on the mandrel. When the sharp edge bar was vertical to the rotating axle of the mandrel and just beneath the spinning nozzle, nanofibers with circumferential alignment were obtained. With this method it is possible to obtain a tubular scaffold with suitable fiber alignment for blood vessel tissue engineering.