A Review on the Studies of Air Flow Field and Fiber Formation

Review Cite This: Ind. Eng. Chem. Res. 2019, 58, 11624−11637

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A Review on the Studies of Air Flow Field and Fiber Formation Process during Melt Blowing Xibo Hao† and Yongchun Zeng*,† †

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College of Textiles, Donghua University, Shanghai 201620, China ABSTRACT: 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.

1. INTRODUCTION Melt blowing is a common method used in industry for producing microfibrous nonwovens. As depicted in Figure 1,

Generally speaking, synthetic polymers, mostly polyolefins, are the raw materials of melt blown products.6 Due to the fact that polypropylene produces the best web among the low cost resins, it has become the most commonly used polymer for melt blown nonwoven products.7 However, there are also literatures reporting that natural polymers,8,9 such as starch and cellulose, have been processed into nonwoven products by melt blowing technology. There are several techniques applied to prepare micro/ nanofibers, among which melt blowing is of particular interest. Melt blowing does not require solvents, which translates into a more economical and environmental benign process with a relatively high production rate. Moreover, this method is compatible with broad types of polymers.10 The melt blown fibers are collected as nonwoven webs, where significant bonding strength through fiber entanglement can be observed. The entanglement of the microfibers provides microscale voids, resulting in high porosity, high surface area per unit weight, excellent barrier properties, and good insulation effect of the melt blown nonwovens. These properties make them suitable for making high quality filters,11,12 absorbent mediums, and protective apparel.6 Recently, their applications extended to wound dressing, tissue scaffolding,13 and drug delivery.14 Since the excellent properties of the melt blown nonwovens are based on their microscale fineness of the fiber, extending the diameter of melt blown fibers to nanoscale will not only boost the product performance but also broaden its application fields. Apart from this, controlling the manufacturing process

Figure 1. Schematic of melt blowing process of (a) the single-orifice die and (b) the multiorifice die. (b) Reprinted with permission from ref 5. Copyright 2016 Elsevier.

during melt blowing, the extruded molten polymer through small orifices is stretched by hot and high speed air jets to create fibers with average diameter of 1−2 μm.1 The stretched fibers are solidified and captured upon a collector placed some distance away from the die. Since the melt blowing process was developed by Van Wente in 1950s at the American Naval Research Laboratory to monitor the radiation after nuclear tests,2 it has experienced tremendous development. The researchers at oil company Exxon extended Van Wente’s design by modifying sheet die technology and first demonstrated the commercial-scale production of melt blown microfibers. Since then, various commercial nonwoven products were produced by companies such as Vose, 3M, Kimberlye Clark, Cummins, and Johns Manville.3,4 © 2019 American Chemical Society

Received: Revised: Accepted: Published: 11624

March 27, 2019 June 5, 2019 June 7, 2019 June 7, 2019 DOI: 10.1021/acs.iecr.9b01694 Ind. Eng. Chem. Res. 2019, 58, 11624−11637

Review

Industrial & Engineering Chemistry Research

Figure 2. Schematics of the melt blowing die structures. (a) Cross-section view of a slot die. (b) Cut away view of a commercial slot melt blowing die. (c) Cross-section view of the annular die. (d) Bottom view of a multiorifice annular melt blowing die. (e) Cross-section view of a swirl die. (f) Bottom view of a swirl die. (b) Reprinted with permission from ref 32. Copyright 1988 American Chemical Society. (d) Reprinted with permission from ref 33. Copyright 1993 American Chemical Society. (e, f) Reprinted with permission from ref 19. Copyright 2006 American Chemical Society.

Table 1. Summary of Experimental Studies on Air Flow Field Author Uyttendaele and Shambaugh, 198949 Majumda and Shambaugh, 199117 Mohammed and Shambaugh, 1993,33 Mohammed and Shambaugh, 199451 Harpham and Shambaugh, 199618 Harpham and Shambaugh, 199734 Tate and Shambaugh, 1998,22 Tate and Shambaugh, 200436 Moore et al., 200442 Xie and Zeng, 201243 Xie et al., 201844 Xie et al., 201945 Tan et al., 201227

Measurement instrument

Condition

Pitot tube Pitot tube and thermocouple Pitot tube and thermocouple Pitot tube Pitot tube and thermocouple Pitot tube and thermocouple Pitot tube and thermocouple Hot-wire anemometer Hot-wire anemometer Hot-wire anemometer Schlieren visualization

and reducing the energy consuming are also of great interest for the industry. To achieve these goals, the exploration of the underlying mechanism behind the melt blowing process is necessary. The air flow field and fiber formation process are the two key factors in determining the efficiency of the melt blowing process. A massive effort has been devoted to fundamentally understanding and improving the air flow field and fiber formation process. The objective of this work is to detail the scientific and technological advances in the study of the melt blowing process in the last 30 years and help the related researchers to develop an in depth and overall understanding of it. It is worth noting that with the multiorifice die used in industry, it is difficult to study the single filament and air flow field under the die. In addition, the modification of a multiorifice die configuration is time and cost consuming. Therefore, most of the investigations on the air flow field and fiber formation process were conducted on a laboratory-scale

Measurement content

Isothermal Nonisothermal

Velocity under an annular die Velocity and temperature under an annular die

Nonisothermal

Velocity and temperature under a multiorifice annular die

Isothermal Nonisothermal

Velocity under a slot die Velocity and temperature under a slot die

Nonisothermal Nonisothermal

Effects of geometry parameters of slot dies on the air velocity and temperature Air velocity and temperature under a multiorifice slot die

Nonisothermal Nonisothermal Nonisothermal Nonisothermal

Turbulence fluctuation Turbulence fluctuation Turbulence fluctuation Air density oscillation

single-orifice melt blowing apparatus. In the rest part of this article, unless otherwise stated, the melt blowing machine used in the studies reviewed is a laboratory-scale single-orifice device.

2. AIR FLOW FIELD It is known that the air jets used in the melt blowing process not only provide an attenuation force but also have a function of delaying polymer solidification.15 Knowledge of the velocity and temperature distribution of the air flow field is of vital importance for predicting the performance of the die and understanding the melt blowing process and modeling of the fiber formation process.16−18 Given constant processing conditions, the melt blowing air flow field is determined by die configurations. There are various die configurations existing, among which slot (Figure 2a, b) and annular (Figure 2c, d) dies are the most common designs. A slot die is the type where the air is emitted from a pair of slots, with the plane of 11625

DOI: 10.1021/acs.iecr.9b01694 Ind. Eng. Chem. Res. 2019, 58, 11624−11637

Review


inset, and outset sharp dies shown in Figure 3) and developed correlations to predict the velocity fields below these dies. Several years later, they measured the temperature fields below the three slot dies with different geometries with a thermocouple.36 Chen and Huang37 developed a theoretical approach to predict the velocity distribution along the centerline of the air flow field by describing the two plane jet flows as a vortex pair. The reliability of this approach was confirmed by Harpham’s and Shambaugh’s18 experimental data. Benefitting from the development of computer science, the CFD technique was becoming more and more widely used in the early 21st century. To the best of our knowledge, the first try using the CFD technique to examine the melt blowing air flow field was carried out by Krutka et al.38 In their research, the air flow field under slot dies with different geometries were studied, and Figure 4a presents one of them. Because the slot length of the actual die might be 1 m or more, in which case the end effect could be neglected, the die can be modeled as a 2-D jet. For the convenience of comparison with experimental data, the computational domains were based on the experimental setup of Harpham and Shambaugh18 and Tate and Shambaugh.22 The presence of the polymer was neglected as was the case in the study of Harpham and Shambaugh and Tate and Shambaugh. For the reduction of computational intensity, the axial symmetry boundary was taken into consideration to reduce the computation domain. Because of the rectangular shape of the computational domain, it was convenient to use a structured grid with quadrilateral cells. The grid resolution was increased in the area of greatest interest, where the convergence of the two air streams occurs. The model parameters were calibrated by using the experimental data of Harpham and Shambaugh and Tate and Shambaugh. With the calibrated model, the effects of slot angles of blunt and sharp dies on the air flow field were examined. In the next year, Krutka et al.23 continued to examine the effects of the sharp die nosepiece position (inset and outset) on the air flow field condition with the CFD technique. Comparison between different dies gave the message that the more that the nosepiece is recessed the larger the mean velocity is under the die, but at the same time, the turbulence becomes stronger. Then, the nonisothermal condition was introduced into their simulation study, in which the velocity and temperature distributions under the blunt die and sharp die were discussed.39 The studies of Krutka et al. have proved the feasibility of the CFD technique in the investigation of the melt blowing air flow field and provided valuable experience for the subsequent CFD studies of the melt blowing process. Using the CFD technique, Chen et al.40 performed nonisothermal simulation of the air flow field under the slot dies and discussed the effects of die geometry parameters (slot angle, slot width, and nosepiece width) on the velocity and temperature distributions. Xin and Wang24 investigated the velocity and temperature distributions under dies with different slot angles numerically and found the optimal angle for producing the finest fibers. To optimize the air flow field under a slot die during melt blowing, Sun et al.15,25 improved the geometry parameters of the slot die by combining the CFD technique and genetic algorithm. The simulation studies mentioned above were performed with the assumption that the effect of the fiber on the air flow field was negligible. Krutka et al.41 tested this assumption by including the fiber as a boundary in the computational domain.

each slot being at a certain angle relative to the die face. An annular die is the type with each polymer orifice surrounded by an annular air outlet. Apart from the slot and the annular dies, there are some other die designs reported in literatures such as the swirl die (Figure 2e, f)19,20 and the parallel plate die.21 Researches on die designs are divided into two categories. The first type is a modification of the die itself.22−25 The other type involves using add-on devices to the existing die.26−31 Researches of the melt blowing air field comprise the experimental study and CFD (Computational Fluid Dynamics) study. The experimental measurement is the most basic way to gain insight into the melt blowing air flow field, during which various instruments were applied as depicted in Table 1. However, through experimental investigations, it is difficult to obtain velocity, pressure, and temperature data in several circumstances, e.g., in the region very close to the die and under the processing conditions of extremely high speed and high temperature of the air. Such restrictions can be overcome using the numerical simulation method. In addition, the numerical investigation has time and cost savings compared with the experimental method. Therefore, CFD has been the method predominantly used in the studies of melt blowing air flow fields in recent years. 2.1. Air Flow Field under Slot Die. According to the shape of nosepiece, the slot dies can be divided into a blunt die, where the nosepiece has a flat area which runs along its length (Figure 3a), and sharp die, where the nosepiece is sharp

Figure 3. Schematics of the slot die configurations: (a) blunt die with a flush nosepiece, (b) sharp die with a flush nosepiece, (c) sharp die with an inset nosepiece, and (d) sharp die with an outset nosepiece.

(Figure 3b−d). On the basis of nosepiece location, the slot dies can also be classified into an inset die, where the nosepiece tip is withdrawn a distance into the body of the die (Figure 3c), a flush die, where the nosepiece is flush with the die face (Figure 3a, b), and an outset die, where the nosepiece extends below the die face (Figure 3d).22,23 The investigation of the air flow field of slot dies started from the air velocity measurement of the isothermal condition, which was carried out by Harpham and Shambaugh18 below a blunt die with a Pitot tube. A correlation that could predict the velocity at any position below the die was also developed. In the next year, they extended their work to a nonisothermal air jet, in which the velocity and temperature fields were measured using a Pitot tube and thermocouple.34 Their measurements demonstrated the similarity between the temperature and velocity profiles. Hence, analogous correlations were developed to describe both the velocity and temperature fields. The empirical equations developed by Harpham and Shambaugh18 were improved by Wang and Ke35 through introducing the influence of the ratio of die width to air slot width. Using a Pitot tube, Tate and Shambaugh22 tested velocity fields of several slot dies with different geometries (i.e., blunt, flush, 11626


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Figure 4. Air flow field simulation under different dies: (a) slot die, (b) slot die equipped with a diverging tube, (c) slot die with air constrictor, (d) annular die, (e) annular die with a stabilizing piece, and (f) swirl die. (a) Reprinted with permission from ref 38. Copyright 2002 American Chemical Society. (b) Reprinted with permission from ref 27. Copyright 2012 Elsevier. (c) Reprinted with permission from ref 29. Copyright 2016 American Chemical Society. (d, e) Reprinted with permission from ref 31. Copyright 2013 American Chemical Society. (f) Reprinted with permission from ref 20. Copyright 2014 Springer.

the Laval nozzle configuration modified the air flow field by increasing the maximum air centerline velocity and eliminating the compression waves at a certain inlet pressures (Figure 4b). At the same time, the Schlieren visualization technique was used to capture the density oscillations in the supersonic flow field exiting the Laval nozzle. Hassan et al.29 combined a computer simulation with experiments to investigate new die configurations installed with vertical or inclined air constrictors (Figure 4c). Their work demonstrated that the constrictor would maintain a centerline air velocity at high values and would keep the polymer temperature around the melting point near the die face, resulting in a higher polymer attenuation. To alleviate the localized overthickening of the nonwoven mat, Chelikani and Sparrow made use of the Coanda effects, which was realized by introducing a plane wall into the air flow field, to control the fiber motion trajectories.28 Their research is another try by means of numerical simulation without the cost of the experiment. Besides modifications of the die configurations, there are other efforts made to improve the air flow field of the slot die for producing finer fibers. Milligan et al.47 introduced an additional cross flow into the air flow field, which resulted in finer and more uniform fibers. Based on the principle of resonance of a mechanical system, Tyagi and Shambaugh48 used oscillating air jets to attenuate a polymer jet during melt blowing, and finer fibers were produced than the traditional continuous air jet. 2.2. Air Flow Field under Annular Die. Similar to the slot dies, the investigation of the air flow field of annular dies started from the air velocity measurement of the isothermal condition. Uyttendaele and Shambaugh49 first carried out the work to examine the velocity distribution of air flow fields under an annular die with a Pitot tube. They divided the velocity field into three distinct regions. In the first flow region, the jet velocity profile gradually transforms from a bimodal, blunt-peaked curve into a single bell-shaped curve, which develops into a final form in the second region. The third

The presence of the fiber was found to have an important impact on the air flow. However, the assumption that the fiber on the air flow field was negligible is still widely used by researchers in the investigations of the melt blowing air flow field. The air flow field of a practical multiorifice slot die was examined by Moore et al.42 experimentally, in which a Pitot tube and a thermocouple were applied once more. They proved that the mean air velocity and temperature decayed in a manner similar to that observed in the single-orifice slot die. At the same time, they found that the air temperature will influence the air velocity due to the fluctuations of air density. It is known that the air flow under the melt blowing die is turbulent. However, the experimental examinations of turbulent characteristics are rarely reported. The Pitot tube and thermocouple, which were used in previous measurements, can only obtain the mean velocity and mean temperature. To acquire the turbulence information, Xie et al.43−45 used a hotwire anemometer to measure the fluctuation in the air flow field below a slot die. It was proved that the turbulent fluctuations of the air flow field have great relationship with the fiber motion as well as fiber diameter evenness of melt blown products. This was the first time that the turbulent fluctuation of the melt blowing air field had been reported. Through adding additional device to the die to improve air flow field has been studied by several researchers. Shambaugh et al.46 introduced a “plateau” into the air flow field, which is able to increase the attenuation of a fiber for a given air flow rate. In a mathematical concept, the plateau is a vertical range over which the air velocity and temperature are constant. To experimentally achieve the plateaus discussed in the modeling work described above, Shambaugh et al.26 installed a pair of louvers under a slot die, creating a higher centerline air velocity value compared with the air flow field without louvers. Inspired by the laval nozzle theory, Tan et al.27 installed an add-on device with a divergent function under the slot die and constructed a laval nozzle. Their simulation results showed that 11627


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Industrial & Engineering Chemistry Research region is of fully developed flow, where all data points fall on the same dimensionless curve. Two years later, Majumda and Shambaugh17 expanded Uyttendaele and Shambaugh’s work to a nonisothermal condition. A Pitot tube and a thermocouple were used to investigate the velocity and temperature fields under annular dies, respectively. The patterns of velocity and temperature distributions are found independent of the Reynolds number, length-to-diameter ratio, operating temperature, and annulus diameter. Moore et al.50 used the CFD technique to simulate the air flow discharged from an annular die, and the model was calibrated by the experimental results available. Based on the computational and experimental results, a correlation was proposed to predict the centerline velocity profiles in both the near- and far-field regions. There are also some works focusing on the air flow field of multiple jets under the multiorifice annualar die. Mohammed and Shambaugh33,51 measured the velocity and temperature fields under a Schwarz die (a commercial multiorifice slot die) and developed a correlation which can be applied to predict the temperature value at any position below the nozzle array. Using CFD technique, Krutka et al.52,53 performed a simulation study on the air flow field of the Schwarz die in isothermal and nonisothermal conditions. However, their work was performed without the presence of the fiber under the assumption that the effect of the fiber on the air flow field is negligible. To fill the gap, Krutka et al.54 examined the effect of the fiber on the air flow field from an annular die numerically. Their work indicated that the fiber shows a dampening effect on the turbulence. Also, the presence of the fiber increases the rate of jet spreading. To obtain finer fibers with less energy consuming, Wang and Wang31 designed a new annular die with an inner stabilizing piece and predicted the die performance using the CFD approach. The results demonstrated that the new design could improve the velocity and temperature distributions of the air flow field (Figure 4d, e). 2.3. Air Flow Field under Other Dies. Swirl nozzles are widely used in the manufacturing industry for the deposition of adhesives in controlled patterns.55 For the swirl nozzle used in melt blowing, Moore56 conducted an experimental and computational study to investigate the air flow field. The experimental investigation indicated that the air jets under the swirl die has a higher decay constant than either circular or annular jets, which might be due to the higher levels of turbulence generated by the multiple interacting jets. Based on the experimental data, the k-ε model was found to perform much better than the RSM model for the swirl die simulations. It was found that by varying the twist angle the behavior of the air jets exiting from the swirl nozzle transits from merging to diverging. Xie and Zeng20 also conducted CFD simulations of the air flow field of the swirl die (Figure 4f) and made a comparison with that of the slot die. Kwok57 provided a novel die design in the form of a parallel plates assembly that consists of orifices for the polymer melt to flow through and another set of orifices surrounding the polymer orifices for air to flow through. The parallel plates die not only shows simplicity in design but also economization in energy cost. Hassan et al.21 assessed the performance of the parallel plates die from the melt blown fibers. Unfortunately, they did not carry out any experimental or numerical study on the air flow field under the parallel plates die.

3. FIBER FORMATION PROCESS The fiber formation process, which is influenced by the air flow field, processing conditions, and polymer properties, is crucial to the efficiency of the melt blowing process. To better understand and control the melt blowing process, researchers have been making efforts to study the fiber formation process experimentally and theoretically. It is worth noting that a fiber in motion is usually referred to as a polymer jet.58−60 In this review, we prefer to use “fiber” to represent the fibers in the melt blowing process and resultant nonwovens. 3.1. Experimental Study. In this section, we focus on four important aspects (i.e., fiber motion, fiber diameter, fiber temperature, and fiber morphology) involved in the fiber formation process during melt blowing. The measuring methods applied in the experiments are summarized in Table 2. 3.1.1. Fiber Motion. Characterization of the fiber motion in a typical melt blowing process has always been a technical challenge. The experimental research of fiber motion involves measurements of fiber velocity, trajectory, and whipping. Using the photography technique, Uyttendaele and Shambaugh16 conducted the first work to acquire fiber velocity during melt blowing. In their method, the fiber velocity was derived indirectly, based on the assumption of continuity and the fiber diameter measured by the photographing technique. Wu and Shambaugh61 used another fluid measuring technique, laser doppler velocimetry (LDV), to measure the fiber velocities under an annular die. However, photography has always been the dominating approach in the measurement of melt blown fiber motion. During melt blowing, the fiber is moving at such a high speed that the motion pattern cannot be discerned by sight and a normal camera with regular exposure time. Bresee and his co-workers62,63 did a series work in measuring fiber velocity. They took photographs of the fibers in a 600-orifice melt blowing line, using a rapid framing rate camera (1000 frames/s) with pulsed laser illumination. Different from the method adopted by Uyttendaele and Shambaugh,16 the velocity and acceleration were derived based on the laser pulse separation time and fiber moving distance during the interval time. To determine the fiber velocity in the melt blowing process, Xie and Zeng64 employed a camera with higher speed (5000 frames/s) to capture the fiber motion. In their method, the fiber velocity was calculated by monitoring a marker point on the fiber. Based on the previous experimental studies, it is concluded that fiber velocity accelerates to a maximum value only a few centimeters from the die, and this is also the area where most of the attenuation occurs. Then, it decreases over the majority of the distance between the die and collector. High speed photography is the main method for studying melt blown fiber trajectory, especially the whipping of fibers. The fiber whipping in the melt blowing process, which was previously called fiber vibration, was first recorded by Rao and Shambaugh65 and Chhabra and Shambaugh80 using multiple exposure strobe photographing method under the single-orifice annular die (Figure 5a) and slot die (Figure 5b), respectively. They showed that the fiber motion seemed to be splaying, and the view appeared to be a “bundle of jets” with each jet leading toward a single fiber. This observation was similar to that from the naked eye. The apparent splaying obtained by naked eye and by low speed photography is an optical illusion formed by a very fast whipping motion of the fiber. A similar image of a 11628


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Although the photography technique has been adopted to investigate the melt blown fiber motion for several years, the trajectory of a single fiber has never been captured until Beard et al.67 used a high speed camera to record the motion of fibers below a melt blowing slot die (Figure 5d) and a swirl die (Figure 5e), respectively. Xie and co-workers64,68 employed a high speed camera working at 5000 frames/s to capture the fiber trajectories. Unlike the images of fiber whipping recorded by Beard et al.,67 the successive images of fiber trajectory in a wider field of view were exhibited (Figure 5f−i, j−l). Specifically, the gradually expanding process of the whipping amplitude was clearly presented. The online study of fiber motion is difficult due to the very high speed of air jets exiting from the die. To date, the measurements of melt blown fiber motion are still under the air velocity that is far below the commercial condition (i.e., above 250 m/s). Based on the images of fiber motion, the whipping amplitude and frequency were studied. According to the images recorded from multiple exposure strobe photographs, Rao and Shambaugh65 defined a “cone” to describe the “bundle of fiber jets” appearing under an annular die. They characterized the whipping amplitude by the maximum lateral displacement in a certain position, and the whipping frequency was determined by counting the number of times that the fiber element crosses the centerline of the fiber attenuation area. They found that the amplitude increases progressively as the distance from the die increases, and the frequency is nearly constant over the entire threadline. Chhabra and Shambaugh66 measured the “cone” diameter under a slot die, which represented the fiber whipping amplitude, with both multiple-image flash photography and laser doppler velocimetry (LDV) under a slot die. Their study gave the message that the cross section of the “fiber cone” is slightly elliptical, with different amplitudes in two directions perpendicular to the threadline. The “cone” becomes more circular as the distance from the die increases. Meanwhile, the whipping frequency of the fiber was measured with LDV. The measurements showed that the whipping frequency is roughly constant along the threadline. Beard et al.67 and Xie and Zeng20,64 investigated the effects of processing condition parameters on the frequency and amplitude of fiber vibration under a slot die and a swirl die through high speed photography. For both the slot die and swirl die, the whipping frequency decreases as the polymer flow rate increases, as the air flow rate decreases, and as the polymer temperature increases. The frequency of fiber whipping is not dependent on air temperature. For the slot die, the amplitude increases when the air flow rate increases and does not appear to change if either air temperature or polymer temperature are changed. For the swirl die, there appears to be no major change in fiber amplitude as the polymer flow rate changes and as the distance from the die increases. The amplitude then decreases with increasing polymer temperature. The air temperature and air flow rate both have effects on the whipping amplitude of the swirl die. Using the multiple exposure photographing method, Moore et al.42 investigated the effects of processing condition parameters on the whipping amplitude of the fiber operating under a practical melt blowing slot die. It was found that there is a strong correlation between whipping amplitude and die temperature. The mean vibration amplitude increases with increasing air flow rate.

Table 2. Summary of Experimental Studies on Fiber Formation Process Authors

Measuring content

Uyttendaele and Shambaugh, 199016 Wu and Shambaugh, 199261 Rao and Shambaugh, 199365 Chhabra and Shambaugh, 199666 Yin et al., 2002,62 200069 Moore et al., 200442 Bresee and Qureshi, 200470 Beard et al., 200767 Xie and Zeng, 2012,43 201364

Fiber motion

Uyttendaele and Shambaugh, 199016 Yin et al., 200262

Fiber diameter development (online)

Measuring instruments speed camera Laser Doppler velocimetry

High speed camera Ensemble laser diffraction

Bansal and Shambaugh, 199871 Yin et al., 200069 Moore et al., 200472 Marla et al., 200973 Xie et al., 201468 Shambaugh, 198832 Bresee and Ko, 200363

Fiber diameter and its distribution (offline)

Moore et al., 200442

Optical microscopy Scanning electron microscopy

Bresee and Qureshi, 200674 Ellison et al., 20074 Tan et al., 201010 Balogh et al., 201514 Bansal and Shambaugh, 199875 Yin et al., 200069 Bresse and Ko, 200363 Marla et al., 200776 Marla et al., 200973

Fiber temperature

Infrared camera infrared thermometer

Majumdar and Shambaugh, 199077 Ju and Shambaugh, 199478

Air drag on fiber

Electronic balance

Yin et al., 200069

Fiber morphology

Atomic force microscope Differential scanning calorimeter Polarized optical microscopy Wide-angle X-ray diffraction Small-angle X-ray scattering

Bressee and Ko, 200363 De Rovere et al., 200079

melt blown fiber under a swirl die (Figure 5c) was photographed by Marla et al.19 11629


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Figure 5. (a−c) Multiple-image photograph of fiber exiting from the annular die, slot die, and swirl die, respectively. (d, e) Single frame image of fiber exiting from the slot die and swirl die, respectively. (f−i) Fiber whipping development under a slot die. (j−l) Fiber whipping development under a swirl die. (a) Reprinted with permission from ref 65. Copyright 1993 American Chemical Society. (b) Reprinted with permission from ref 66. Copyright 1996 American Chemical Society. (c) Reprinted with permission from ref 19. Copyright 2006 American Chemical Society. (d, e) Reprinted with permission from ref 67. Copyright 2007 American Chemical Society. (f−i) Reprinted with permission from ref 64. Copyright 2013 American Chemical Society. (j−l) Reprinted with permission from ref 68. Copyright 2014 American Chemical Society.

Figure 6. (a) Experimental apparatus used to measure drag force for the case with filaments parallel with the air stream. (b) Experimental apparatus used to measure drag force for the case with filaments oblique to the air stream. (c) Experiment setup of Yarin et al. (a) Reprinted with permission from ref 77. Copyright 1990 American Institute of Physics. (b) Reprinted with permission from ref 78. Copyright 1994 Wiley. (c) Reprinted with permission from ref 58. Copyright 2010 American Institute of Physics.

In the melt blowing process, a polymer jet is drawn by the air to become microfibers. Fiber motion is determined by the

air drag force directly. Earlier researchers used an experimental method to measure the air drag force exerted on polymer jets 11630


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an increasing effect on the average fiber diameter and almost no effect on the coefficient of variance (CV), while increasing the elasticity appeared to decrease CV and increase average fiber diameter. Producing nanoscale melt blown fibers has always been the target in both scientific and industrial communities. In recent years, several strategies were put forward by researchers to obtain fibers with lower diameters. Using a pilot-scale multiorifice die with an orifice diameter of 0.127 mm, Hassan et al.11 got melt blown nonwoven fibers with average diameters of 300 nm. By melt blowing immiscible polymer blends and selectively removing the majority phase with a solvent, Zuo et al.85 isolated melt blown nonwoven fibers with average diameters as small as 70 nm. This method provides a potentially inexpensive, high throughput, one-step route to scalable quantities of polymeric nanofibers. Deng et al.86 achieved multiscale micro/nanomelt blown nonwoven fibers by utilizing the incompatibility of the two types of polymers, which made the viscosity of the blended melt fluctuate continuously, and the obtained nonwovens possessed both enhanced filtration efficiency and reduced pressure drop. The attenuation process of fibers during melt blowing is of importance for understanding the fiber structure evolution. For the measurement of fiber attenuation, the online method is more accurate than obtaining it by offline methods like optical microscopy or scanning electron microscopy (SEM). However, online studies have always been challenging due to the high speed motion of fibers. The photographing technique is the mainstream method for the online investigation of fiber diameter. In earlier researches, Uyttendaele and Shambaugh,16 Bansal and Shambaugh,71 and Yin et al.62 used a photographing technique to conduct online investigations of fiber diameter during melt blowing. In their research, the fiber diameter was measured from the photography images directly. Based on the fiber velocity and fiber path which were obtained from the high speed photographs, Xie et al.68 developed a model to calculate the fiber diameter. One drawback of the photographing method is that it cannot offer real-time diameter information. Moore et al.72 used an ensemble laser diffraction (ELD) technique to record the fiber diameter distribution under a multiorifice slot die. The ELD technique could measure the fiber diameter at normal operation conditions and provide fiber diameters in near real time. The results of all the aforementioned online measurements demonstrated that most of the fiber attenuation occurred within several centimeters of the die exit, and the attenuation does not stop until it reaches the collector. Yin et al.,62 through observing the fiber attenuation under the multiorifice die, discovered that apart from the aerodynamic force fiber−fiber interaction may also contribute to the fiber attenuation. Bresee and Qureshi74 indicated that fiber diameters also may increase through at least two ways, fiber contact/fusion and fiber shrinkage, which probably results in broader fiber diameter distributions. 3.1.3. Fiber Temperature. Fiber temperature development, which determines fiber attenuation and solidification, is a critical factor in the melt blowing process. Compared with fiber diameter, less work was conducted on fiber temperature development in the melt blowing process. Bansal and Shambaugh71 investigated the fiber temperature under a single-orifice slot die via an infrared camera. A similar method was adopted by Yin et al.69 and Bresee and Ko63 to examine the fiber temperature online. However, for an infrared camera,

during melt blowing. Majumdar and Shambaugh77 studied the air drag on the polymer stream in the melt blowing process (Figure 6a). A wide range of fiber diameters, fiber velocities, and fiber Reynolds numbers were used. The data are fit well by the theoretical relation Cf = 0.78(ReD)−0.61 for the turbulent boundary layer developed by Matsui.81 Majumdar and Shambaugh’s research was based on the assumption that the fiber is parallel with the air flow. However, due to the turbulence of the air jet in the melt blowing process, the nature of the force acting on the polymer is more complicated than drag force simply acting in the axial direction along a taut fiber. This is true even for the air stream that is parallel in the die. Therefore, in melt blowing, the fiber axis has a nonzero angle relative with the gas velocity. Ju and Shambaugh78 extended Majumdar and Shambaugh’s work to the measurements for air drag on a polymer stream whose axes are oriented at oblique or normal angles to the air velocity (Figure 6b). It is known that melt blowing is an aerodynamically driven process, in which polymer streams are accelerated and attenuated by high speed gas jets.58 Benefiting from the progress of high speed photography technique, the fiber motion in the melt blowing process has already been captured clearly. However, the basic physical mechanisms responsible for fiber whipping are relatively unexplored. The turbulence of air flow has always been assumed to be associated with fiber whipping in melt blowing. To evaluate the role of turbulent pulsations in the melt blowing process, Yarin et al.58 conducted an experiment on a situation model where solid flexible sewing threadlines were subjected to parallel high speed isothermal gas jets (Figure 6C). Based on the experimental measurements, they developed a comprehensive theory of fiber whipping during melt blowing. 3.1.2. Fiber Diameter. The studies on fiber diameter in the melt blowing process could be divided into two categories: the diameter of the final product and the diameter development in the attenuation process. Fiber diameter is a significant factor that determines the property of a melt blown product and provides valuable clues for exploration about the physics mechanism of the process.4 The investigation of fiber diameter of the resultant nonwoven fiber is mainly through optical microscopy and scanning electron microscopy offline.10,14,63,82 Kayser and Shambaugh83 investigated the effects of processing parameters (die dimension, die temperature, polymer resin type, air and polymer flow rates) on the diameter of resultant products, and a correlation equation was developed to relate these parameters with the diameter of the final product. Bresee et al.84 compared the quantitative experimental measurements of the influence of several processing parameters on the fiber diameter and concluded that fiber diameter is influenced most substantially by die temperature, moderately by primary air flow rate, moderately by resin throughput rate, only slightly by die to collector distance (DCD), and insignificantly by collector speed. Studies devoted to exploring the basic mechanism behind the diameter control during melt blowing have also been reported. Analysis of fiber diameter distribution by Ellison et al.4 revealed that they are in a conformity of a log-normal distribution function regardless of average fiber diameter, indicating that the underlying mechanisms of fiber attenuation were retained even when producing nanofibers. Through bending polystyrene materials with different molecular weights, Tan et al.10 discovered that increasing the melt viscosity of a polymer had 11631


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Figure 7. Simulations of fiber motion in the melt blowing process with different models. (a) Fiber whipping of the bead-viscoelastic model simulated by Zeng et al. (b) Distributed forces acting on perturbed melt blowing fiber subjected to high speed gas flow described by Yarin et al. (c) Fiber whipping simulated by Hübsch et al. (d) Whipping motions of fibers in three-dimensions predicted by Chung and Kumar. (e) Simulation of air−polymer coupled flow field with level-set method by Hao et al. (a) Reprinted with permission from ref 87. Copyright 2011 Wiley. (b) Reprinted with permission from ref 58. Copyright 2010 American Institute of Physics. (c) Reprinted with permission from ref 88. Copyright 2013 Springer. (d) Reprinted with permission from ref 60. Copyright 2013 Elsevier. (e) Reprinted with permission from ref 89. Copyright 2019 SAGE.

blowing fibers have less molecular orientation than fibers produced by conventional melt spinning. Bresee and Ko63 employed polarized optical microscopy, wide-angle X-ray diffraction (WAXD), and small-angle X-ray scattering (SAXS) to acquire the information about fiber structure development. The results of all the characterization methods consistently indicated that PP crystallization did not occur during melt blowing until fibers reached the collector. As to fiber surface morphologies, De Rovere et al.79 used an atomic force microscope (AFM) to analyze the morphology of melt blown fibers. They revealed that all the melt blown fibers consist of edge-to-edge spherulites and contain a very small amount of amorphous material between spherulites. In addition, the surface roughness of the melt blown fibers decreases with decreasing fiber diameters. 3.2. Modeling Study. Mathematical modeling aided by a computer offers an alternative method to costly or unapproachable experimental investigations and has proved to be a promising tool to provide valuable information on the process mechanisms and role of individual processing parameters. In the last three decades, massive efforts have been devoted to modeling of the melt blown fiber formation process. Modeling of the melt blowing process is particularly challenging due to the complex interplay between the polymer jet (i.e., fiber) and the high speed turbulent air jets with high temperature. However, researches devoted to the modeling of the melt blowing process have never ceased. 3.2.1. Polymer Jet Motion in Air. The initial modeling works on melt blown fibers concentrated on the simplest model of a single straight jet with the assumption that fiber

reading errors could occur when the target dimensions are of the same order of magnitude as that of each element of the thermal sensor. Also, the temperature reading is also affected by the diameter of the small fibers.76 To overcome these problems, Marla et al.76 developed a procedure to improve the accuracy of polymer fiber temperature measurements by an infrared camera. Their measurements indicated that most of the fiber temperature decrease happens within several centimeters near the die. This is the same area where most of the fiber attenuation occurs, owing to the fact that higher fiber temperature results in a lower polymer viscosity that in turn leads to higher attenuation of the fiber. Experimental measurements also confirmed that fine fibers are cooling faster than coarse fibers, which was verified by experimental measurements of fiber molecular orientation development (optical birefringence) during melt blowing. 3.1.4. Fiber Morphology. Fiber morphology, which has an important influence on the final polymer products, is a reflection of the particular process and processing conditions used to shape and modify the fiber.79 With a commercial multiorifice machine, Bresee and co-workers69,63 did a series of work on microscopic morphologies of melt blown fibers. Yin et al.69 investigated the fiber birefringence offline with a polarized optical microscopy, and the samples were taken at various locations between the die and collector. They also conducted offline differential scanning calorimetry (DSC) measurements of webs collected to predict the temperatures of solidification and crystallization during melt blowing. It was discovered that both fiber crystallization and fiber molecular orientation occur after most fiber attenuation is achieved. In general, melt 11632


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Figure 8. (a) Snapshot of simulation configurations of 62 nonisothermal polymer jets melt blown onto a moving screen. (b, c) Predicted distribution of polymer mass over the moving collector screen with screen velocity of 0.1 and 10 m/s, respectively. (d, e) Three-dimensional structure of lay-down over the moving collector screen with the screen velocity of 0.1 and 10 m/s, respectively. (f, g) Comparison of fiber diameter distribution between numerical prediction and experimental investigation. (h) Comparison of angular distribution between numerical prediction and experimental investigation. (i) Predicted melt blowing web structure formed under multiorifice die by Sun et al. Weight distribution of melt blowing web formed under multiorifice die: (j) predicted result and (k) experimental result by Sun et al. (a) Reprinted with permission from ref 100. Copyright 2013 Elsevier. (b−e) Reprinted with permission from ref 5. Copyright 2016 Elsevier. (f−h) Reprinted with permission from ref 5. Copyright 2016 Elsevier. (i−k) Reprinted with permission from ref 101. Copyright 2016 American Chemical Society.

frequency of fiber whipping were conducted. Marla and Shambaugh90 expanded the model into 3D space. Shambaugh and co-workers applied their 1D, 2D, and 3D models to the case of an annular die. The modeling results showed reasonable agreement with the experimental values. However, the models underpredicted the fiber whipping amplitude, which could be explained by the fact that the models did not include turbulence effects. By modifying the equations in the previous models,16,90 Marla et al.91 developed 1D and 3D models to predict hollow fiber production. Their simulation results indicated that hollow fibers have higher fiber amplitude and higher frequency than solid filaments, which could increase the quality of fiber laydown in terms of web uniformity. Chen and co-workers92,93 created a 1D model which considered the effects of polymer temperature on the density and specific heat capacity of the polymer. Based on the model they developed, the effects of processing and die design parameters on fiber diameter were discussed. The models described above treated the polymer jet as an elongational fluid and did not include the fiber solidification in

motion is one-dimensional in space. Considering that melt blowing has many similarities with conventional melt spinning, some of the methods and formulas of melt spinning can be borrowed in modeling of the melt blowing process. The modeling work of the melt blown fiber formation process started in 1990. With the assumption that the fiber motion is parallel with the air flow, Uyttendaele and Shambaugh16 developed a comprehensive one-dimensional (1D) model. The model comprises the momentum, energy, and continuity equations of the fiber spin line. For relatively low spinning speeds, their model works well in predicting the fiber profile in the region of high fiber attenuation. Nevertheless, the predictions of the final fiber diameters are higher than the experimental results, which might be due to the neglect of fiber whipping in the model. To make the model closer to the practical process, Rao and Shambaugh65 expanded the 1D model into a 2D one in which fiber whipping (fiber vibration in their work) was considered. Based on Rao and Shambaugh’s model, more predictions including the fiber diameter, fiber temperature, amplitude, and 11633


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Industrial & Engineering Chemistry Research the melt blowing process. Jarecki and co-workers94,95 proposed a single-filament 1D model for the melt blowing process, which for the first time comprised the effects of polymer crystallization.96 Inspired by the work of Jarecki and coworkers, and Shambaugh et al.96 continued their research on modeling by introducing fiber crystallization into a 1D model for the melt blowing process. There is excellent concordance in the results of Jarecki’s and Shambaugh’s models. Zeng et al.87 develop a bead-viscoelastic element fiber model, and their mixed Euler−Lagrange approach was adopted to simulate the three-dimensional fiber motion, especially the whipping motion in the process of melt blowing (Figure 7a). The Maxwell model was adopted to describe rheological behavior of the melt blowing fiber. Han and Wang97 compared the effects of the different constitutive equations of polymer rheological behaviors on the model of the fiber formation process. It is found that the standard linear solid model was a better option to predict the polymer’s response under the same air flow field conditions. Turbulence of the air flow field was first considered in the modeling for the melt blowing process by Yarin et al.58,59 They outlined the basic theory of melt blowing, which revealed the role turbulence played in fiber whipping. The initial perturbations of the polymer jets are imposed by large turbulent eddies of the surrounding air flow. The aerodynamic lift force distributed along the polymer jets helps to amplify the bending perturbations; meanwhile, the stretching force by air imposes restrictions on large amplitude bending (Figure 7b). Under industrial conditions, Hübsch et al.88 established a simple isothermal model for the polymer jet dynamics with consideration of the impact of the turbulent velocity fluctuations on the jets dynamic, and the numerical results of their model showed a qualitatively appropriate jet thinning in magnitude (Figure 7c). The model of Yarin et al. was used by Chung and Kumar60 to undertake a systematic study aiming at elucidating the factors that determine the onset of whipping during melt blowing (Figure 7d). Through comparison of results from several different constitutive models, they came to the conclusion that melt inertia rather than melt rheology is the more dominant factor in controlling fiber shapes. In the latest work of our group,89 a two-dimensional model considered the air−polymer coupling effect by introducing a level-set method. Through comparison with the experiment results, the model has shown superiority in predicting fiber velocity and diameter during melt blowing (Figure 7e). To investigate the influence of viscosity and elasticity on the diameter and diameter distribution of the melt blowing fibers, Tan et al.10 built an 1D slender melt blown jet model which assumed constant shear stress acting on the fiber surface and neglected heat transfer effects. This model shows a variation in the melt blown fiber diameter that depends on polymer viscoelasticity and proved to be in qualitative agreement with the experimental data. Their research gave an important message that tailoring the viscoelasticity of polymers used in melt blowing can be an additional method to control the fiber diameter and diameter distribution. Zhou et al.98 improved the model of Tan et al.10 by considering more constitutive models, the effects of a nonuniform shear stress along the fiber length, and the effects of heat transfer. Simulation results show that viscoelasticity reduces the magnitude of disturbance amplification, suggesting a mechanism for the narrower fiber diameter distribution observed in the experiments of Tan et al.10

3.2.2. Multiple Jets Lay-Down onto the Collector. The modeling work mentioned above concentrated on the single jet motion from one orifice in the space between the die and collector. In industry, nonwovens are formed from multiple polymer jets exiting from multiple orifices. Therefore, without accounting for the presence of the multiple jets and their deposition onto a collector, the practically important questions related with nonwoven web structure cannot be addressed. Recently, models predicting the lay-down process of multiple jets were reported. With the model previously developed,58,59 Yarin and co-workers5,99,100 have done a great deal of work in the modeling of melt blown nonwovens lay-down formed by multiple jets. As shown in Figure 8a, 62 jets were present in their simulation, and several important laydown properties were predicted, which included mass distribution (Figure 8b, c), three-dimensional structure (Figure 8d, e), fiber diameter distribution (Figure 8f, g), and angular distribution (Figure 8h). The influences of processing conditions, especially the collector screen speed, on these properties were discussed in detail. The predicted values were compared with several sets of experimental values acquired from the literatures. It was demonstrated that the models developed by Yarin et al. are proved to be capable of predicting the lay-down properties in a reasonable agreement with the experimental values. Sun et al.101 carried out a modeling study on nonwoven web formation. The model predicted that a variation coefficient of basis weight in the cross direction is larger than that in the machine direction of the nonwoven web (Figure 8i, j), which is similar to the pattern shown by experiments (Figure 8k).

4. CONCLUSIONS As a common method for producing microfibrous nonwovens, the melt blowing technique has experienced great progress in the last few decades. 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. In this work, we have reviewed the studies on the air flow field and fiber formation process during melt blowing. The velocity and temperature distribution of air flow fields under different dies have been investigated experimentally and computationally. To enhance the velocity and temperature of the air flow field, several types of auxiliary devices were introduced into the die. The experimental observation of the fiber formation process included the fiber motion, diameter, temperature, and morphology. Numerous studies have concentrated on the modeling of the fiber formation process, which involves the process of single jet motion in the space between the die and collector and the multiple jets lay-down onto the collector. With the deepening of research, the discrepancies between the predicted values and experimental values are decreasing. The models are expected to be promising tools to address the problems encountered in the melt blowing industry.

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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. ORCID

Yongchun Zeng: 0000-0003-4640-5524 Notes

The authors declare no competing financial interest. 11634


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(23) Krutka, H. M.; Shambaugh, R. L.; Papavassiliou, D. V. Effects of Die Geometry on the Flow Field of the Melt-Blowing Process. Ind. Eng. Chem. Res. 2003, 42, 5541. (24) Sanfa, X.; Xinhou, W. Investigation into the effect of the angle of dual slots on an air flow field in melt blowing via numerical simulation. e-Polymers 2016, 16, 337. (25) Sun, Y.; Wang, X. Optimization of Air Flow Field of the Melt Blowing Slot Die via Numerical Simulation and Genetic Algorithm. J. Appl. Polym. Sci. 2010, 115, 1540. (26) Shambaugh, R. L.; Krutty, J. D.; Singleton, S. M. Melt Blowing Dies with Louvers. Ind. Eng. Chem. Res. 2015, 54, 12999. (27) Tan, D. H.; Herman, P. K.; Janakiraman, A.; Bates, F. S.; Kumar, S.; Macosko, C. W. Influence of Laval nozzles on the air flow field in melt blowing apparatus. Chem. Eng. Sci. 2012, 80, 342. (28) Chelikani, S.; Sparrow, E. M. Numerical simulations of planewall coanda effects for control of fiber trajectories in the melt-blown process. Ind. Eng. Chem. Res. 2013, 52, 11639. (29) Hassan, M. A.; Anantharamaiah, N.; Khan, S. A.; Pourdeyhimi, B. Computational Fluid Dynamics Simulations and Experiments of Meltblown Fibrous Media: New Die Designs to Enhance Fiber Attenuation and Filtration Quality. Ind. Eng. Chem. Res. 2016, 55, 2049. (30) Wang, Y.; Wang, X. Numerical Analysis of New Modified MeltBlowing Dies for Dual Rectangular Jets. Polym. Eng. Sci. 2014, 54, 110. (31) Wang, Y.; Wang, X. Investigation on a New Annular MeltBlowing Die Using Numerical Simulation. Ind. Eng. Chem. Res. 2013, 52, 4597. (32) Shambaugh, R. L. A macroscopic view of ther melt-blowing process for producing microfibers. Ind. Eng. Chem. Res. 1988, 27, 2363. (33) Mohammed, A.; Shambaugh, R. L. Three-Dimensional Flow Field of Rectangular Array of Practical Air. Ind. Eng. Chem. Res. 1993, 32, 976. (34) Harpham, A. S.; Shambaugh, R. L. Velocity and Temperature Fields of Dual Rectangular Jets. Ind. Eng. Chem. Res. 1997, 36, 3937. (35) Wang, X.; Ke, Q. Empirical formulas for distributions of air velocity/temperature along the spinline of a dual slot die. Polym. Eng. Sci. 2005, 45, 1092. (36) Tate, B. D.; Shambaugh, R. L. Temperature Fields below MeltBlowing Dies of Various Geometries. Ind. Eng. Chem. Res. 2004, 43, 5405. (37) Chen, T.; Huang, X. Study on the flow field of the air jet from dual slot die in the melt blowing process. Polym. Eng. Sci. 2001, 41, 971. (38) Krutka, H. M.; Shambaugh, R. L.; Papavassiliou, D. V. Analysis of a Melt-Blowing Die: Comparison of CFD and Experiments. Ind. Eng. Chem. Res. 2002, 41, 5125. (39) Krutka, H. M.; Shambaugh, R. L.; Papavassiliou, D. V. Effects of temperature and geometry on the flow field of the melt blowing process. Ind. Eng. Chem. Res. 2004, 43, 4199. (40) Chen, T.; Wang, X.; Huang, X. Modeling the Air-Jet Flow Field of a Dual Slot Die in the Melt Blowing Nonwoven Process. Text. Res. J. 2004, 74, 1018. (41) Krutka, H. M.; Shambaugh, R. L.; Papavassiliou, D. V. Effects of the polymer fiber on the flow field from a slot melt blowing die. Ind. Eng. Chem. Res. 2008, 47, 935. (42) Moore, E. M.; Papavassiliou, D. V.; Shambaugh, R. L. Air Velocity, Air Temperature, Fiber Vibration and Fiber Diameter Measurements on a Practical Melt Blowing Die. Int. Nonwovens J. 2004, os-13, 43. (43) Xie, S.; Zeng, Y. Turbulent air flow field and fiber whipping motion in the melt blowing process: Experimental study. Ind. Eng. Chem. Res. 2012, 51, 5346. (44) Xie, S.; Han, W.; Jiang, G.; Chen, C. Turbulent air flow field in slot-die melt blowing for manufacturing microfibrous nonwoven materials. J. Mater. Sci. 2018, 53, 6991. (45) Xie, S.; Han, W.; Xu, X.; Jiang, G.; Shentu, B. Lateral Diffusion of a Free Air Jet in Slot-Die Melt Blowing for Microfiber Whipping. Polymers 2019, 11, 788.

ACKNOWLEDGMENTS This research was supported by the National Natural Science Foundation of China (No. 11672073), Fundamental Research Funds for the Central Universities, and Graduate Student Innovation Fund of Donghua University (No. CUSF-DH-D2019030).

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REFERENCES

(1) Uppal, R.; Bhat, G.; Eash, C.; Akato, K. Meltblown nanofiber media for enhanced quality factor. Fibers Polym. 2013, 14, 660. (2) Van Wente, A. Superfine Thermoplastic Fibers. Ind. Eng. Chem. 1956, 48, 1342. (3) McCulloch, J. G. The History of the Development of Melt Blowing Technology. Int. Nonwovens J. 1999, os-8, 139. (4) Ellison, C. J.; Phatak, A.; Giles, D. W.; Macosko, C. W.; Bates, F. S. Melt blown nanofibers: Fiber diameter distributions and onset of fiber breakup. Polymer 2007, 48, 3306. (5) Ghosal, A.; Sinha-Ray, S.; Yarin, A. L.; Pourdeyhimi, B. Numerical prediction of the effect of uptake velocity on threedimensional structure, porosity and permeability of meltblown nonwoven laydown. Polymer 2016, 85, 19. (6) Dutton, K. C. Overview and analysis of the meltblown process and parameters. J. Text Apparel, Technol. Manag. 2008, 6, 25. (7) Choi, K. J.; Spruiell, J. E.; Fellers, J. F.; Wadsworth, L. C. Strength properties of melt blown nonwoven webs. Polym. Eng. Sci. 1988, 28, 81. (8) Luo, M.; Roscelli, V. A.; Camarena, S.; Neogi, A. N.; Yanncy, M. J. Process for melt blowing continuous lyocell fibers. U.S. Patent US6306334B1, 2001. (9) Mackey, L. N.; James, M. D.; Gordon, G. C.; Michael, J. G.; Trokhan, P. D.; Bailey, V. A. Melt processable starch composition. U.S. Patent US7041369B1, 2006. (10) Tan, D. H.; Zhou, C.; Ellison, C. J.; Kumar, S.; Macosko, C. W.; Bates, F. S. Meltblown fibers: Influence of viscosity and elasticity on diameter distribution. J. Non-Newtonian Fluid Mech. 2010, 165, 892. (11) Khan, S. A.; Wilkie, A.; Yeom, B. Y.; Pourdeyhimi, B.; Hassan, M. A. Fabrication of nanofiber meltblown membranes and their filtration properties. J. Membr. Sci. 2013, 427, 336. (12) Hassan, M. A.; Khan, S. A.; Pourdeyhimi, B. Fabrication of micro-meltblown filtration media using parallel plate die design. J. Appl. Polym. Sci. 2016, 133, 42998. (13) Lukas, D.; Sanetrnik, F.; Chvojka, J.; et al. The combination of meltblown and electrospinning for bone tissue engineering. Mater. Lett. 2015, 143, 172. (14) Balogh, A.; Farkas, B.; Faragó, K.; et al. Melt-blown and electrospun drug-loaded polymer fiber mats for dissolution enhancement: A comparative study. J. Pharm. Sci. 2015, 104, 1767. (15) Sun, Y. F.; Liu, B. W.; Wang, X. H.; Zeng, Y. C. Air-Flow Field of the Melt-Blowing Slot Die via Numerical Simulation and Multiobjective Genetic Algorithms Y. J. Appl. Polym. Sci. 2011, 122, 3520. (16) Uyttendaele, M. A. J.; Shambaugh, R. L. Melt blowing: General equation development and experimental verification. AIChE J. 1990, 36, 175. (17) Majumdar, B.; Shambaugh, R. Velocity and temperature fields of annular jets. Ind. Eng. Chem. Res. 1991, 30, 1300. (18) Harpham, A. S.; Shambaugh, R. L. Flow Field of Practical Dual Rectangular Jets. Ind. Eng. Chem. Res. 1996, 35, 3776. (19) Marla, V. T.; Shambaugh, R. L.; Papavassiliou, D. V. Using Swirl Dies To Spin Solid and Hollow Fibers. Ind. Eng. Chem. Res. 2006, 45, 2331. (20) Xie, S.; Zeng, Y. Fiber Spiral Motion in a Swirl Die MeltBlowing Process. Fibers Polym. 2014, 15, 553. (21) Hassan, M. A.; Khan, S. A.; Pourdeyhimi, B. Fabrication of micro-meltblown filtration media using parallel plate die design. J. Appl. Polym. Sci. 2016, 133, 1. (22) Tate, B. D.; Shambaugh, R. L. Modified Dual Rectangular Jets for Fiber Production. Ind. Eng. Chem. Res. 1998, 37, 3772. 11635


Review

Industrial & Engineering Chemistry Research (46) Shambaugh, B. R.; Papavassiliou, D. V.; Shambaugh, R. L. Modifying air fields to improve melt blowing. Ind. Eng. Chem. Res. 2012, 51, 3472. (47) Milligan, M. W.; Lu, F.; Buntin, R. R.; Wadsworth, L. C. Use of crossflow to improve nonwoven melt-blown fibers. J. Appl. Polym. Sci. 1992, 44, 279. (48) Tyagi, M. K.; Shambaugh, R. L. Use of Oscillating Gas Jets in Fiber Processing. Ind. Eng. Chem. Res. 1995, 34, 656. (49) Uyttendaele, M. A. J.; Shambaugh, R. L. The flow field of annular jets at moderate Reynolds numbers. Ind. Eng. Chem. Res. 1989, 28, 1735. (50) Moore, E. M.; Shambaugh, R. L.; Papavassiliou, D. V. Analysis of isothermal annular jets: Comparison of computational fluid dynamics and experimental data. J. Appl. Polym. Sci. 2004, 94, 909. (51) Mohammed, A.; Shambaugh, R. L. Three-dimensional temperature field of a rectangular array of practical air jets. Ind. Eng. Chem. Res. 1994, 33, 730. (52) Krutka, H. M.; Shambaugh, R. L.; Papavassiliou, D. V. Analysis of Multiple Jets in the Schwarz Melt-Blowing Die Using Computational Fluid Dynamics. Ind. Eng. Chem. Res. 2005, 44, 8922. (53) Krutka, H. M.; Shambaugh, R. L.; Papavassiliou, D. V. Analysis of the temperature field from multiple jets in the Schwarz melt blowing die using computational fluid dynamics. Ind. Eng. Chem. Res. 2006, 45, 5098. (54) Krutka, H. M.; Shambaugh, R. L.; Papavassiliou, D. V. Effects of the Polymer Fiber on the Flow Field from an Annular Melt-Blowing Die. Ind. Eng. Chem. Res. 2007, 46, 655. (55) Gun, A.; Boger, B. J.; Dwayne, N. Adhesive spray gun and nozzle attachment. U.S. Patent 4785996, 1988. (56) Moore, E. M. Experimental and Computational Analysis of The Aerodynamics of Meltblowing Dies. Ph.D. Thesis, University of Oklahoma, 2004. (57) Kwok, K.-C. Meltblowing method and apparatus. U.S. Patent US005902540A, 1999. (58) Sinha-Ray, S.; Yarin, A. L.; Pourdeyhimi, B. Meltblowing: Ibasic physical mechanisms and threadline model. J. Appl. Phys. 2010, 108, 034912. (59) Yarin, A. L.; Sinha-Ray, S.; Pourdeyhimi, B. Meltblowing: IIlinear and nonlinear waves on viscoelastic polymer jets. J. Appl. Phys. 2010, 108, 034913. (60) Chung, C.; Kumar, S. Onset of whipping in the melt blowing process. J. Non-Newtonian Fluid Mech. 2013, 192, 37. (61) Wu, T. T.; Shambaugh, R. L. Characterization of the melt blowing process with laser Doppler velocimetry. Ind. Eng. Chem. Res. 1992, 31, 379. (62) Yin, B. H.; Yan, Z.; Bresee, R. R. Experimental Study of the Meltblowing Process. Int. Nonwovens J. 2002, os-8, 60. (63) Bresee, R. R.; Ko, W.-C. Fiber Formation during Melt Blowing. Int. Nonwovens J. 2003, os-12, 21. (64) Xie, S.; Zeng, Y. Online measurement of fiber whipping in the melt-blowing process. Ind. Eng. Chem. Res. 2013, 52, 2116. (65) Rao, R. S.; Shambaugh, R. L. Vibration and Stability in the Melt Blowing Process. Ind. Eng. Chem. Res. 1993, 32, 3100. (66) Chhabra, R.; Shambaugh, R. L. Experimental Measurements of Fiber Threadline Vibrations in the Melt-Blowing Process. Ind. Eng. Chem. Res. 1996, 35, 4366. (67) Beard, J. H.; Shambaugh, R. L.; Shambaugh, B. R.; Schmidtke, D. W. On-line Measurement of Fiber Motion During Melt Blowing. Ind. Eng. Chem. Res. 2007, 46, 7340. (68) Xie, S.; Zheng, Y.; Zeng, Y. Influence of Die Geometry on Fiber Motion and Fiber Attenuation in the Melt-Blowing Process. Ind. Eng. Chem. Res. 2014, 53, 12866. (69) Yin, H.; Yan, Z.; Ko, W.-C.; Bresee, R. R. Fundamental Description of the melt blowing process. Int. Nonwovens J. 2000, os-9, 25. (70) Bresee, R. R.; Qureshi, U. A. Influence of processing conditions on melt blown web structure, Part 1: DCD. Int. Nonwovens J. 2004, os13, 49.

(71) Bansal, V.; Shambaugh, R. L. On-line Determination of Diameter and Temperature during Melt Blowing of Polypropylene. Ind. Eng. Chem. Res. 1998, 37, 1799. (72) Moore, B. E. M.; Shambaugh, R. L.; Papavassiliou, D. V. Ensemble Laser Diffraction for Online Measurement of Fiber Diameter Distribution During the Melt Blowing Process. Int. Nonwovens J. 2004, os-13, 42. (73) Marla, V. T.; Shambaugh, R. L.; Papavassiliou, D. V. Online measurement of fiber diameter and temperature in the melt-spinning and melt-blowing processes. Ind. Eng. Chem. Res. 2009, 48, 8736. (74) Bresee, R. R.; Qureshi, U. A. Influence of process conditions on melt blown web structure, Part IV: fiber diameter. J. Eng. Fiber Fabr. 2006, 1, 32. (75) Bansal, V.; Shambaugh, R. L. On-line Determination of Diameter and Temperature during Melt Blowing of Polypropylene. Ind. Eng. Chem. Res. 1998, 37, 1799. (76) Marla, V. T.; Shambaugh, R. L.; Papavassiliou, D. V. Use of an Infrared Camera for Accurate Determination of the Temperature of Polymer Filaments. Ind. Eng. Chem. Res. 2007, 46, 336. (77) Majumdar, B.; Shambaugh, R. L. Air drag on filaments in the melt blowing process. J. Rheol. 1990, 34, 591. (78) Ju, Y. D.; Shambaugh, R. L. Air Drag on Fine Filaments at Oblique and Normal Angles to the Air Stream. Polym. Eng. Sci. 1994, 34, 958. (79) De Rovere, A.; Shambaugh, R. L.; O'rear, E. A. Investigation of Gravity-Spun, Melt-Spun, and Melt-Blown Polypropylene Fibers Using Atomic Force Microscopy. J. Appl. Phys. 2000, 77, 1921. (80) Chhabra, R.; Shambaugh, R. L. Experimental Measurements of Fiber Threadline Vibrations in the Melt-Blowing Process. Ind. Eng. Chem. Res. 1996, 35, 4366. (81) Matsui, M. Air Drag on a Continuous Filament in Melt Spinning. Trans Soc. Rheol. 1976, 20, 465. (82) Lee, Y.; Wadsworth, L. C. Effects of melt-blowing process conditions on morphological and mechanical properties of polypropylene webs. Polymer 1992, 33, 1200. (83) Kayser, J. C.; Shambaugh, R. L. The manufacture of continuous polymeric filaments by the melt-blowing process. Polym. Eng. Sci. 1990, 30, 1237. (84) Bresee, R. R.; Qureshi, U. A. Influence of process Conditions on Melt Blown Web Structure. Part IV - Fiber Diameter. J. Eng. Fiber Fabr. 2006, 1, 32. (85) Zuo, F.; Tan, D. H.; Wang, Z.; Jeung, S.; MacOsko, C. W.; Bates, F. S. Nanofibers from melt blown fiber-in-fiber polymer blends. ACS Macro Lett. 2013, 2, 301. (86) Deng, N.; Cheng, B.; Ben Ticha, E.; et al. One-step meltblowing of multi-scale micro/nano fabric membrane for advanced airfiltration. Polymer 2019, 165, 174. (87) Zeng, Y. C.; Sun, Y. F.; Wang, X. H. Numerical approach to modeling fiber motion during melt blowing. J. Appl. Polym. Sci. 2011, 119, 2112. (88) Hübsch, F.; Marheineke, N.; Ritter, K.; Wegener, R. Random Field Sampling for a Simplified Model of Melt-Blowing Considering Turbulent Velocity Fluctuations. J. Stat. Phys. 2013, 150, 1115. (89) Hao, X.; Huang, H.; Zeng, Y. Simulation of jet velocity in the melt-blowing process using the coupled air − polymer model. Text. Res. J. 2018, 004051751880904. (90) Marla, V. T.; Shambaugh, R. L. Three-Dimensional Model of the Melt-Blowing Process. Ind. Eng. Chem. Res. 2003, 42, 6993. (91) Marla, V. T.; Shambaugh, R. L.; Papavassiliou, D. V. Modeling the melt blowing of hollow fibers. Ind. Eng. Chem. Res. 2006, 45, 407. (92) Chen, T.; Huang, X. Modeling Polymer Air Drawing in the Melt Blowing Nonwoven Process. Text. Res. J. 2003, 73, 651. (93) Chen, T.; Wang, X.; Huang, X. Effects of Processing Parameters on the Fiber Diameter of Melt Blown Nonwoven Fanbrics. Text. Res. J. 2005, 75, 76. (94) Jarecki, L.; Ziabicki, A. Mathematical Modelling of the pneumatic melt spinning of Isotactic polypropylene part II. Dynamic model of melt blowing. Fibres Text. East Eur. 2008, 16, 17. 11636


Review

Industrial & Engineering Chemistry Research (95) Jarecki, L.; Lewandowski, Z. Mathematical modelling of the pneumatic melt spinning of isotactic polypropylene. Part III. Computations of the process dynamics. Fibres Text. East Eur. 2009, 72, 17. (96) Shambaugh, B. R.; Papavassiliou, D. V.; Shambaugh, R. L. Next-generation modeling of melt blowing. Ind. Eng. Chem. Res. 2011, 50, 12233. (97) Han, W.; Wang, X. Modeling melt blowing fiber with different polymer constitutive equations. Fibers Polym. 2016, 17, 74. (98) Zhou, C.; Tan, D. H.; Janakiraman, A. P.; Kumar, S. Modeling the melt blowing of viscoelastic materials. Chem. Eng. Sci. 2011, 66, 4172. (99) Yarin, A. L.; Sinha-Ray, S.; Pourdeyhimi, B. Meltblowing: Multiple polymer jets and fiber-size distribution and lay-down patterns. Polymer 2011, 52, 2929. (100) Sinha-Ray, S.; Yarin, A. L.; Pourdeyhimi, B. Prediction of angular and mass distribution in meltblown polymer lay-down. Polymer 2013, 54, 860. (101) Sun, G.; Yang, J.; Sun, X.; Wang, X. Simulation and Modeling of Microfibrous Web Formation in Melt Blowing. Ind. Eng. Chem. Res. 2016, 55, 5431.

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A Review on the Studies of Air Flow Field and Fiber Formation

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