ANALYTICAL MODELLING OF DRY-JET WET SPINNING

Transcription

1 THERMA SCIENCE, Year 017, Vol. 1, No. 4, pp ANAYTICA MODEING OF DRY-JET WET SPINNING by Hong-Yan IU a,b,c*, Zhi-M I d, Yan-Ju YAO b, c and Frank K. KO a National Engeerg aboratory for Modern Silk, College of Textile and Clothg Engeerg, Soochow University, Suzhou, Cha b School of Fashion Technology, Zhongyuan University of Technology, Zhengzhou, Cha c Department of Materials Engeerg, University of British Columbia, Vancouver, B. C., Canada d Rieter Textile Instrument Co., Shanghai, Cha Origal scientific paper This paper troduces an analytical method for the analysis and design of a dry-jet wet spng system. The 1-D mass conservation equation is used, and velocity distribution is assumed to derive a simple relationship among various spng parameters. The effect of spneret mass flow rate, solution density, spneret structure cludg velocity and air-gap length, and drawg velocity on the dry-jet wet spng was simulated usg the proposed analytical model. Theoretical prediction of fiber diameter is obtaed, which depends upon spng conditions, solution properties, and spneret structure. The theoretical results were verified by comparg experimental data with the numerical solution. It was found obviously that the theoretical prediction has comparable accuracy as that by numerical computation. The analytical model can be useful for prelimary design of a spng process for fabrication of fibers with controllable diameter by adjustg parameters spng conditions. Key words: analytical solution, dry-jet wet spng, fiber diameter Introduction Wet spng is a widely used technology polymer science and textile engeerg [1-7]. Dry-jet wet spng technology, a modification of wet spng, combes both the advantages of melt spng and wet spng, which can be used to fabricate high-performance fibers [8-1]. For the dry-jet wet spng process, the process is usually considered to be composed of two separate parts: the elongational flow the air-gap region, and the double diffusion the coagulation bath. The dynamics the coagulation bath can be regarded as the dynamics of wet spng, whereas the elongational flow the air-gap region is usually referred to as a model of the dynamics of melt spng or dry spng. Some of the benefits of dry-jet wet spng are: (a) high speed of spng, (b) high concentration of dope, (c) high degrees of jet-stretch ratios, and (d) control of coagulation ketics by monitorg coagulation bath parameters. Among these benefits, (a) to (c) are derived because of the use of dry-jet and the air-gap, while (d) is derived from the use of wet coagulation. * Correspondg authors, phdliuhongyan@yahoo.com

2 1808 THERMA SCIENCE, Year 017, Vol. 1, No. 4, pp In this method the polymer is dissolved an appropriate solvent to make the fiber solution. This solution is then extruded under heat and pressure to an air-gap before it enters a coagulation bath. The produced fiber is then washed and dried before it is heat treated and drawn. This is an alternative method to wet spng and is required as spng directg to the bath, for some fibers, creates micro-voids that negatively affect the fiber properties, this is due to the solvent beg drawn out of the liquid too quickly. An ert atmosphere may be required to prevent oxidization some polymers, if so fibers are extruded to a nitrogen atmosphere. This method is often required for high performance fibers with a liquid crystal structure. Due to their structural properties their melt temperature is either the same as, or dangerously close to their decomposition temperature, therefore they must be dissolved an appropriate solvent and extruded this manner. Several research works give valuable sight to dry-jet wet spng. Hauru et al. [1] explored spng stability and discussed the effects of extrusion velocity, draw ratio, spneret aspect ratio, and bath temperature on mechanical properties and orientation of cellulose filaments from Ionic liquid solution usg dry-jet wet spng method. Qian et al. [13] studied the mechanism and characteristics of dry-jet wet spng of acrylic fibers. Tan et al. [14] vestigated the spnability the dry-jet wet spng of polyacrylonitrile (PAN) precursor fiber. Yang et al. [15] produced ultra-fe fibers usg dry-jet wet spng. The effects of the polymer composition, coagulation bath temperature, and draw ratio on the cross-sectional morphology, structure, and tensile properties were reported by Bajaj et al. [16]. From the previous discussion, it is seen that a mathematical model for the spng process is useful for understandg the relationship between the spng conditions and fiber properties [17, 18]. Recently Xia et al. [, 4] suggested a full 3-D model to predict numerically the fiber diameter along the spng le, and important formation was revealed. The numerical results can be used for optimal design of the spng process, however, numerical simulation can not pick out an explicit relationship among spng conditions, spneret structure, and fiber properties. Therefore, an analytical model is very much needed for practical applications. We adopt the mass conservation equation the dry-jet wet spng process and obta a simple analytical equation for the model. The analytical prediction is compared with the experimental data and numerical results by Xia et al. [] to show the validity of our method. Figure 1. Schematic illustration of the dry-jet wet spng process One-dimensional model A 1-D model is widely used the morphology control fiber fabrication process cludg the bubble electrospng [19] and the bubbfil spng [0]. As shown fig. 1 the dry-jet wet spng process is described [4]. The spng solution enters the spneret. A polymer filament is extruded from a spneret to an air-gap region at a mass flow rate, Q. The filament is then elongated by a take-up device with a take-up speed, u out. The filament cools as it passes through the air-gap region with a specific length,, and orientation begs to occur at a certa take-up force. The gap between the

3 THERMA SCIENCE, Year 017, Vol. 1, No. 4, pp spneret and the coagulation bath surface, called air-gap, varies with the type of polymer and technology beg used. In acrylic spng, this gap may be as small as a few millimeters, while lyocell spng, it may be up to several centimeters. The jet, as illustrated fig. 1 durg the spng process can be approximately considered as a steady 1-D compressible flow. The mass conservation equation is shown [19, 1]: 1 π 4 D ρ u = Q (1) where D is the jet diameter, ρ the fluid density, u the jet velocity, and Q the flow rate. The jet velocity can be solved by the momentum equation and the energy equation. It is a complex solution process, but it can be solved numerically []. A simple assumption is made this paper to have a quick look to the relationship between spng conditions and fiber diameter. We assume that the jet velocity changes learly along the spng le: uout u uz ( ) = u + z () where u is the velocity of the spng le at the spneret exit, u out the drawg velocity as illustrated fig. 1, and the distance between the spneret exit and the roller. From eq. (1) we can obta: D Q = (3) u 4 Substitute eq. () to eq. (3) we acquire: D ( z) = u After a simple calculation, we have: u + out u z (4) Dz ( ) = u u + Equation (5) is an analytical model for predictg the fiber diameter without any complex numerical simulation or computation. This equation gives an explicit relationship among the spng condition (the flow rate, Q), solution property (density, ρ), spneret structure, u, and drawg velocity, u out. We use the experimental data [] to verify the prediction of eq. (5) by assumg that the density of the spng le remas constant durg spng process. The values of parameters volved eq. (5) are: Q = g/m = kg/s, ρ = kg/m 3, u out = 0. m/s, and 18 cm. The diameter of the spneret orifice is D 0 = 0. mm, accordg to eq. (1), we have: out u z (5) u 3 D0 ρ = = = 0.06 m/s π π(0. 10 ) (6)

4 1810 THERMA SCIENCE, Year 017, Vol. 1, No. 4, pp Submittg all the previous parameters to eq. (5), we can predict the fal fiber diameter: D(18 cm) = = uout u u + z = = m π (7) which is very closed to the experimental observation, 100 μm [], fig.. Results discussion By substitutg eq. (6) to eq. (5), we can re-write eq. (5) the form: Figure. Comparison of the theoretical prediction with experimental data and numerical solution by Xia et al. [] 1 Dz ( ) = = = D0 uout u 1 u + z uout πd πd 4 0 ρ + z Q 1 πd0 ρ 1+ 0 ρuout where D 0 is the diameter of the spneret orifice. Equation (8) reveals that the fiber size depends learly upon the size of spneret orifice. When D 0 is the range of hundreds of micrometers, nanofibers can be prepared as discussed by iu et al. [], where the spneret nozzle has a diameter of about 78 μm. Substitute z = to eq. (8), the fal fiber diameter can be written the form: z (8) Q D ( ) = (9) 1 π ρuout 4 This equation shows that a higher drawg velocity or a lower flow rate results a smaller fiber diameter. Similar phenomena were also observed the bubble electrospng [19], the bubbfil spng [0], and electrospng [, 3] Conclusions This paper suggests a simple analytical model for predictg the fiber diameter the dry-jet wet spng process. Neither complex numerical simulation nor complex derivation is volved, only simple mass conservation, eq. (1), is volved. The prediction equation, eq. (5), reveals the relationship among let conditions (flow rate), solution property (density), spneret structure (put velocity), spng length, and drawg velocity. Although the analytical model only provides an approximated solution, the calculated results of prediction has almost the same accuracy as numerical one as illustrated fig., this simple analytical model pro-

5 THERMA SCIENCE, Year 017, Vol. 1, No. 4, pp vides a helpful guide for prelimary design of a broad range of spng processes for fabrication of fibers with controllable diameter by adjustg parameters volved eq. (5). Acknowledgment The work is supported by Priority Academic Program Development of Jiangsu Higher Education Institutions (PAPD), National Natural Science Foundation of Cha under Grant No , Jiangsu Planned Projects for Postdoctoral Research Funds under Grant No B, Cha Postdoctoral Science Foundation under Grant Nos. 015M and 016T90495, Cha National Textile and Apparel Council Project under Grant No , Key Scientific Research Projects of Henan Provce under Grant No. 16A540001, and program by Cha Scholarship Council. The support provided by the NSERC Discovery Grant is also appreciated. References [1] Hauru,. K., et al., Dry Jet-Wet Spng of Strong Cellulose Filaments from Ionic iquid Solution, Cellulose, 1 (014), 6, pp [] Xia, X., et al., Dynamic Modelg of Dry-Jet Wet Spng of Cellulose/[Bmim] Cl Solution: Complete Deformation the Air-Gap Region, Cellulose, (015), 3, pp [3] Zhang, W., et al., Effect of Epichlorohydr on the Wet Spng of Carrageenan Fibers under Optimal Parameter Conditions, Carbohydrate Polymers, 150 (016), Oct., pp [4] Xia, X., et al., Numerical Investigation of Spneret Geometric Effect on Spng Dynamics of Dry Jet Wet Spng of Cellulose/[Bmim] Cl Solution, Journal of Applied Polymer Science, 133, (016), 38, pp [5] Park, S. K., Farris, R. J., Dry-Jet Wet Spng of Aromatic Polyamic Acid Fiber Usg Chemical Imidization, Polymer, 4 (001), 6, pp [6] Xia, X., et al., Rheological Behaviors of Cellulose/[Bmim] Cl Solutions Varied with the Dissolvg Process, Journal of Polymer Research, 1 (014), 7, pp. 1-7 [7] Xia, X., et al., Simulation on Contraction Flow of Concentrated Cellulose/1-Butyl-3-Methylimidazolium Chloride Solution through Spneret Orifice, Materials Research Innovations, 18 (014), Supp., pp. S-874-S [8] Chae, D. W., et al., Physical Properties of yocell Fibers Spun from Isotropic Cellulose Dope Nmmo Monohydrate, Textile Research Journal, 7 (00), 4, pp [9] Choe, E. W., Kim, S. N., Synthesis, Spng, and Fiber Mechanical-Properties of Poly(Para- Phenylenebenzobisoxazole, Macromolecules, 14 (1981), 4, pp [10] Fk, H. P., et al., Structure Formation of Regenerated Cellulose Materials from Nmmo-Solutions, Progress Polymer Science, 6 (001), 9, pp [11] Kim, D. B., et al., Dry Jet-Wet Spng of Cellulose/N-Methylmorphole N-Oxide Hydrate Solutions and Physical Properties of yocell Fibers, Textile Research Journal, 75 (005), 4, pp [1] Wan, S. X., et al., Acrylic Fibers Processg with Ionic iquid as Solvent, Polymers for Advanced Technologies, 0 (009), 11, pp [13] Qian, B., et al., The Mechanism and Characterstics of Dry Jet Wet Spng of Acrylic Fibers, Advances Polymer Technology, 6 (1986), 4, pp [14] Tan,., et al., Investigatg the Spnability the Dry Jet Wet Spng of Pan Precursor Fiber, Journal of Applied Polymer Science, 110 (008), 4, pp [15] Yang, W., et al., Poly (M Phenylene Isophthalamide) Ultrafe Fibers from an Ionic iquid Solution by Dry Jet Wet Electrospng, Journal of Macromolecular Science, Part B, 45 (006), 4, pp [16] Bajaj, P., et al., Structure Development Durg Dry-Jet-Wet Spng of Acrylonitrile/Vyl Acids and Acrylonitrile/Methyl Acrylate Copolymers, Journal of Applied Polymer Science, 86 (00), 3, pp [17] Gupta, B., et al., Preparation of Poly (actic Acid) Fiber by Dry Jet Wet Spng. I. Influence of Draw Ratio on Fiber Properties, Journal of Applied Polymer Science, 100 (006),, pp [18] Gupta, B., et al., Preparation of Poly (actic Acid) Fiber by Dry-Jet-Wet Spng. Ii. Effect of Process Parameters on Fiber Properties, Journal of Applied Polymer Science, 101 (006), 6, pp

6 181 THERMA SCIENCE, Year 017, Vol. 1, No. 4, pp [19] iu, H. Y.,Wang, P., A Short Remark on Wan Model for Electrospng and Bubble Electrospng and Its Development, International Journal of Nonlear Sciences and Numerical Simulation, 16 (015), 1, pp. 1- [0] He, C.-H., et al., Bubbfil Spng for Fabrication of Pva Nanofibers, Thermal Science, 19 (015),, pp [1] Dou, H., et al., A Mathematical Model for the Blown Bubble-Spng and Stab-Proof of Nanofibrous Yarn, Thermal Science, 0 (016), 3, pp [] iu, Z., et al., Active Generation of Multiple Jets for Producg Nanofibers with High Quality and High Throughput, Materials & Design, 94 (016), Mar., pp [3] iu, Z., et al., Tunable Surface Morphology of Electrospun Pmma Fiber Usg Bary Solvent, Applied Surface Science, 364 (016), Feb., pp Paper submitted: January 10, 016 Paper revised: May 5, 016 Paper accepted: October 1, Society of Thermal Engeers of Serbia. Published by the Vča Institute of Nuclear Sciences, Belgrade, Serbia. This is an open access article distributed under the CC BY-NC-ND 4.0 terms and conditions.