Electrospinning and melt blowing are the most commonly used processes for producing microfibrous nonwoven materials. A whipping motion during electrospinning has been observed by several researchers. However, much less work has been done on the fiber whipping dynamics in the melt blowing process. In this study, a hot-wire anemometer was used to measure the turbulent air flow field below a single-orifice melt-blowing slot die. The characteristics of the mean velocity, mean temperature, and fluctuating velocity were obtained. Then, a high-speed camera was used to record the motion of a fiber below the die. The fiber whipping path was observed, and the amplitude and frequency of the whipping were obtained. It was found that the turbulent fluctuations are related to the fiber motion in the melt-blowing process. This work examines the physics of turbulent melt-blowing jets and the fiber whipping occurring during melt blowing using an experimental approach.

Melt blowing is a major process for producing nanofibrous nonwovens. Compared to studies on the air flow field and the fiber diameter measurement, much less has been done on the observations of whipping in the melt-blowing process. In this study, a high-speed camera was used to capture the fiber path below a single-orifice melt-blowing slot die. The behavior of loops resulted from whipping was revealed. The characteristics of the whipping amplitude, whipping frequency, and fiber velocity were obtained. Fiber attenuation contributed by whipping was calculated by measuring the perimeter of the loops. The study shows the laws of fiber whipping in a slot-die melt-blowing process and indicates that whipping plays a role in fiber attenuation.

Electrospinning and melt blowing are the most commonly used processes for producing microfibrous nonwovens. In this paper, we study mass production of electrospinning with a multineedle system. To achieve uniform fibers at a high production rate, an auxiliary plate electrode has been used to be connected to a three-needle system to obtain a more uniform electric field. The spinnerets with two kinds of needle array, linear three-needle and triangular three-needle, are studied. The results of electrospinning experiments and electric field simulation demonstrate that the multineedle spinneret with an auxiliary plate can produce finer and more uniform nanofibers. And the fibers can be collected in a more concentrated area with the auxiliary plate. We also focus on the effect of the needle length protruded outside the plate. This study shows a possibility that by designing the electric field distribution, we can produce thinner fibers and more concentrated collection mats at a high production rate.

A three-dimensional computational model is established to simulate the air flow patterns in the rotor spinning unit of a rotor spinning machine. The effects of rotor speed, rotor diameter and rotor slide wall angle on air flow characteristics and hence yarn properties are investigated. The airstream accelerates from the transfer channel inlet to the outlet. There are velocity differences in both the cross-section and along the transfer channel, causing hooked fibers to straighten. The airstream swirls around the rotor at a high speed. However, vortices that can cause fiber curving and buckling are formed inside the rotor. The effect of rotor speed is significant. There are more vortices near the wall at a lower rotor speed, while too large a rotor speed can lead to an excessive centrifugal force, thus increasing yarn breakages. The rotor diameter affects the flow characteristics in a way similar to that of rotor speed. As a smaller slide wall angle generates higher velocities in the transfer channel and more stable velocities in the rotor groove, a small angle is preferable. Computational modeling has provided a useful insight into the rotor spinning flow pattern, thus it can be used to optimize the rotor design to produce better rotor spun yarn.

Melt blowing is an industrially important process in producing microfibrous nonwovens. Over the past decades, there has been a considerable amount of fundamental research on this technique, driven by the development of advanced materials in the areas of filtration, absorption, and isolation. This work presents a comprehensive overview of the research on the air flow field and fiber formation process. Specific attention is concentrated on experimental and numerical studies that have been applied. The measuring methods and devices, results of the air flow field characteristics, and the fibers motion patterns under different types of dies are summarized. It is concluded that the properties of resultant nonwovens are influenced by the air flow field and fiber formation process. These fundamental researches are significant for the melt blowing technique in controlling the manufacturing process, reducing energy consuming, and improving the product performance.

Melt blowing involves applying a jet of hot air to an extruding polymer melt and drawing the polymer stream into microfibers. This study deals with the dynamic modeling of the instabilities and related processes during melt blowing. A bead-viscoelastic element model for fiber formation simulation in the melt blowing process was proposed. Mixed Euler-Lagrange approach was adopted to derive the governing equations for modeling the fiber motion as it is being formed below a melt-blowing die. The three-dimensional paths of the fiber whipping in the melt blowing process were calculated. Predicted parameters include fiber diameter, fiber temperature, fiber stress, fiber velocity, and the amplitude of fiber whipping. The mathematical model provides a clear understanding on the mechanism of the formation of microfibers during melt blowing.

This article proposes a new needleless electrospinning apparatus applying the method of splashing polymer solution onto the surface of a metal roller spinneret. When a high voltage is applied, many spinning jets form on the free surface of polymer solutions. Multiple electrified jets undergo strong stretching and bending instability, solvent evaporates, and solidified nanofibers deposit on the collector, as in an ordinary single‐needle electrospinning process. The production of nanofibers is enhanced by 24–45 times comparing with a single‐needle system. And the productivity is easy to scale up. The effects of processing parameters, including solution concentration, applied voltage, distance between spinneret to collector, and rotational speed of the roller spinneret on the morphology of nanofibers are investigated in this article. POLYM. ENG. SCI., 2010. © 2010 Society of Plastics Engineers

A CFD (computational fluid dynamics) model is developed to simulate the air flow patterns inside the nozzle of an air-jet spinning machine. The design parameters of the nozzle are related to the flow characteristics, so they affect yarn properties. Three parameters are discussed: The effect of nozzle pressure is significant. With increasing nozzle pressure, both the axial and tangential velocity in the nozzle increase, thus increasing the tensile properties of the yarn. However, it is not sensible to increase nozzle pressure to a very high level. The jet orifice angle affects flow characteristics in a complex way. It dramatically affects the axial velocity and the negative pressure at the jet inlet. The selection of a jet orifice angle is a compromise of several factors. Even though the influence of the jet orifice position on the flow structure is insignificant, its design must be optimized. This work demonstrates that CFD can be used to optimize the nozzle design to produce air-jet spun yarns with better properties.Because air-jet spinning is advantageous for production rates, costs, and adaptability to processing control, this system is becoming an important spinning technique. The key to this technology is the design of the nozzle. Several researchers have used experimental methods to study the influence of design parameters such as nozzle pressure ( 1-6], jet orifice angle [ 1,5], and the diameter and surface friction of the twisting chamber [5] on air-jet spun yarn properties. Those parameters are closely related to the flow characteristics, so it is important to study air flow in the nozzle to attain optimized yam properties. Earlier researchers [7] used laser Doppler anemometry to measure air velocities in the nozzle and to study the influence of the design parameters on the flow characteristics. In this paper, we simulate the air flow in the nozzle using a numerical method, and we compare the computational results with earlier experimental data.