- Email: [email protected]
An example of industrialization of melt electrospinning: Polymer melt differential electrospinning
Advanced Industrial and Engineering Polymer Research 2 (2019) 110e115
Contents lists available at ScienceDirect
Advanced Industrial and Engineering Polymer Research journal homepage: http://www.keaipublishing.com/aiepr
An example of industrialization of melt electrospinning: Polymer melt differential electrospinning Chen Mingjun a, Zhang Youchen a, Li Haoyi a, Li Xiangnan a, Ding Yumei a, Mahmoud M. Bubakir b, Yang Weimin a, * a b
College of Mechanical and Electrical Engineering, Beijing University of Chemical Technology, Beijing, 100029, China Gharyan Engineering College Mechanical and Industrial Engineering, Department Gharyan University, Gharyan, Libya
a r t i c l e i n f o
a b s t r a c t
Article history: Received 8 May 2019 Received in revised form 4 June 2019 Accepted 16 June 2019
In recent years, researchers are paying more attention to high efficiency, high process stability and ecofriendly nanofiber fabrication techniques. Among all of the nanofiber fabrication methods, electrospinning including solution electrospinning and melt electrospinning is the most promising method for nanofiber mass production. Compared to solution electrospinning, melt electrospinning could be applied in many areas such as tissue engineering and wound dressings due to the absence of any toxic solvent involvement. Capillary melt electrospinning generates only one jet with low efficiency. Hence, we have proposed polymer melt differential electrospinning (PMDES) method, which could produce multiple jets with smallest interjet distance of 1.1 mm from an umbrella shape spinneret, thus improving the production efficiency significantly. Many techniques such as material modification, suction wind, and multistage electric field were proposed to refine the fibers and nanofibers with average diameter of about 300 nm were obtained. Scale up production line of PMDES with capacity of 300e600 g/h was established by arraying umbrella shape spinnerets. PMDES is a promising technology to meet the requirements of nanofiber production in commercialization. © 2019 Kingfa SCI. & TECH. CO., LTD. Production and Hosting by Elsevier B.V. on behalf of KeAi Communications Co., Ltd. This is an open access article under the CC BY-NC-ND license (http:// creativecommons.org/licenses/by-nc-nd/4.0/).
Keywords: Nanofiber Electrospinning Melt electrospinning Polymer melt differential electrospinning (PMDES)
1. Introduction The unique properties of nanofibers and their applications in many areas such as high efficiency filtration [1], biomedical [2], tissue engineering [3] and battery separators [4] were largely demonstrated in the past 20 years. The global market for nanofiber products may grow from $927 million in 2018 to $4.3 billion by 2023 at a compound annual growth rate of 36.2% [5]. Therefore, eco-friendly nanofiber fabrication methods with high efficiency and high process stability are attracting more and more attention. In order to fulfill the above mentioned requirement, researchers have improved and invented many fiber-spinning processes such as melt-blown [6], bi-component spinning [7], and force-spinning [8]. However, the widely used nanofiber fabrication process is electrospinning because of its simple operation to change nanofiber diameter and porosity [9], its versatility in spinning a wide variety
* Corresponding author. Fax: þ0086 010 64434734. E-mail address: [email protected] (Y. Weimin).
of materials from polymer to ceramic [2], and its ability to produce continuous fiber that can reach kilometers long [2e4]. Therefore, electrospinning that includes both solution electrospinning and melt electrospinning is considered as the most promising method for mass production of nanofibers in commercialization. A typical solution electrospinning equipment, which consisted of a capillary or needle with small diameter, a high electric supplier and a metal collector, is widely used in many laboratories. The yield of the typical solution electrospinning was around 0.01 g/min [10], which is far from meeting the requirements of commercialization. Multi-needle electrospinning is one way to improve the nanofiber outputs, but the mechanical design was complex and the interferential electric field would lower the nanofiber quality [11]. In recent years, electrospinning from free surface have developed fast with the aim of improving nanofiber output significantly. Some novel spinnerets such as rotating disk [12], plucked string [13], plate edge [14] and multiple ring [15] have been developed to increase the nanofiber preparation efficiency. Realizing the huge business opportunities of nanofibers, many companies such as Elmarco (www.elmarco.com), E-Spin Nanotech
https://doi.org/10.1016/j.aiepr.2019.06.002 2542-5048/© 2019 Kingfa SCI. & TECH. CO., LTD. Production and Hosting by Elsevier B.V. on behalf of KeAi Communications Co., Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).
C. Mingjun et al. / Advanced Industrial and Engineering Polymer Research 2 (2019) 110e115
(www.espinnanotech.com), and HiNanofiber (www.hinanofiber. com) developed commercial solution electrospinning set-ups based on research and development results. However, due to the widely and mass use of toxic solvents, solution electrospinning with industrial scale production developed very slowly. The toxic solvent, which constitutes more than 90% of the solution being electro-spun, could cause potential environmental pollution and health damage to workers; the residual toxic solvent has limited the application of electrospun fibers in many fields such as biomedical and tissue engineering. In addition, solution electrospinning is not suitable for non-soluble polymers such as Polypropylene (PP), Polyethylene (PE) and Polyphenylene sulfide (PPS), which are used in large quantities in wide fields. In contrast to solution electrospinning, melt electrospinning is a solvent free, efficient, green nanofiber manufacturing technology. In recent years, more and more researchers are paying attention to melt electrospinning, and the technique has achieved great progress. Melt electros-pun fibers within nanoscale were prepared by mixing melt polymer with salt [16], or adding assisted wind [17] to strengthen the driving force, or adding plasticizers [18] to decrease the viscosity of polymer melt. Nanofiber preparation efficiency have increased by proposing novel spinneret such as rotating disk [19], umbrella cone [20], liner polymer sheet [21] and liner slot [22]. Some pilot production lines of melt electrospinning were established to fabricate nanofiber in industrial scale [23,39]. We have proposed drastically new polymer melt differential electrospinning (PMDES) methods, which can produce multiple jets with smallest interjet distance of 1.1 mm from one umbrella shape spinneret [24]. The average diameter of the fiber fabricated by PMDES method could be as small as about 300 nm [25]. Scale up production line of PMDES with capacity of 300e600 g/h was established by arraying spinnerets [26]. This article will review in detail the PMDES method from principle, equipment, process parameters to scale up equipment. 2. Principle of PMDES Although researchers proposed different types of melt electrospinning spinnerets [19e22], most of which were kept in laboratory due to the low efficiency and uneven molten polymer distribution. We have proposed a novel umbrella-shaped nozzle, which could distribute molten polymer uniformly and strengthen electrical intensity where the Taylor cone is located. Based on the umbrella-like nozzle, we investigated the effects of process parameters on fiber properties and the number of jets. Multiple jets with interjet distance about 1.1 mm were obtained from the umbrella-like nozzle.
111
nozzle, the molten polymer film will attenuate further, which could reduce the Taylor cone and thus the resulted fibers. Once the molten polymer film reaches the bottom of the umbrella nozzle, it will be selforganized into multiple jets under high electrical field [27]. The resulted fibers produced from the umbrella-like nozzle have the same properties because of the uniform polymer melt distribution and identical electrical strength intensity which the polymer melt jets subjected to. The electric field where the jets produced in PMDES was stronger than that of capillary electrospinning, and the fibers obtained would be smaller than that obtained by capillary electrospinning under the same conditions [30]. In addition, the umbrella-like spinneret could avoid fluid plugging and high cost maintenance caused by simple combination of multiple needles. Fig. 1(b) is a schematic diagram of PMDES. There were four main highlights in equipment of PMDES. First, the umbrella-like nozzles could produce multiple jets at the same time (Fig. 1(c)). Second, the hollow electrode plate could provide a channel for fibers to pass through, thus laying the foundation of multi-stage electric field for stretching fiber. Third, by applying high voltage to collector, the interface between high voltage and heating system was avoided. And finally, auxiliary air-flow could strengthen the driving force to produce and thin the nanofibers.
2.2. Optimization of PMDES process parameters Because of the unique structure of umbrella-like spinneret, process parameter values, which were suitable for PMDES, could be different from other melt electrospinning equipments. The effects of process parameters such as collection distance, electrical field intensity and temperature on fiber diameter were investigated. In PMDES, the average fiber diameter continuously decreased when applied voltage increased at a fixed collection distance. When applied voltage was fixed, the average fiber diameter decreased first then increased with increasing collection distance. These results suggested that at too short collection distance, the melt jet did not have sufficient time to elongate [31]. The appropriate electrical field intensity is 4 kv/cm, the appropriate spinning distance is 15 cm, and the appropriate spinning temperature of PP [24], PE [31] and polylactic acid (PLA) [32] in PMDES were 250 C, 355 C and 210 C respectively. Orthogonal experiment result in PMDES showed that influence of the three factors on the average fiber diameters could be listed in the following order: voltage > distance > temperature, and with regard to the standard deviation of the diameter, the list changed to temperature > distance > voltage [31].
2.1. Equipment of PMDES 2.3. Interjet distance of PMDES In melt electrospinning, the jet formation of molten polymer is based on the balance of electric force and surface tension. When the electrical force at the tip of spinning dope is greater than the surface tension, a jet comes from the spinning dope and travels to the collector [28]. In addition, electro-fluid free surface will self-assembly to multiple jets under high electric field according to the theory of electrohydrodynamics [29]. Based on that electrohydrodynamic theory, umbrella-like spinneret that could produce multiple jets from molten polymer film under high electric field was proposed. As shown in Fig. 1(a), polymer melt supplied by a micro extruder flows through the melt inlet into the ring-like melt distributor. In the melt distributor, polymer melt was distributed uniformly around the circumference due to the flow resistance, and thus was distributed on the top circumference of the umbrella-like nozzle uniformly. When melt polymer flows from the top to the bottom of the umbrella-like
Interjet distance was defined as the distance between adjacent Taylor cones. Investigation of the mechanism, which could control interjet distance, is helpful to predict and adjust nanofiber membrane density. Based on the geometric model of umbrella-like spinneret as shown in Fig. 2, we demonstrated the applicability of the relationship between interjet distance and electrical field intensity, surface tension of molten polymer, and relative permittivity of the surrounding gas, as shown in equation (1), which was widely accepted in free surface solution electrospinning [29].
,"
l0 ¼ 12pg
2εE02
rffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi # 2 2εE02 12grg þ
(1)
112
C. Mingjun et al. / Advanced Industrial and Engineering Polymer Research 2 (2019) 110e115
Fig. 1. Melt polymer differential electrospinning (a) schematic diagram of umbrella-like spinneret (b) schematic diagram of melt polymer differential electrospinning equipment (c) picture of PMDES (modified from reference [25,27]).
l0 interjet distance; g surface tension; ε relative permittivity of the surrounding gas; E0 electric field intensity; r density of molten polymer; g gravitational acceleration. Two main factors that affect interjet distance are electric field intensity and temperature. The interjet distance decreased with increasing the electric field intensity [27]. When the electric field intensity surpass a certain value, the air will be broken down and the spinning process could not carry on. Therefore, we have proposed air suction to decrease the air density between nozzle and collector, thus to increase the electrical field intensity in spinning zone [33]. Experimental results showed that the number of Taylor cones could reach as many as 115 when the velocity of airflow was 25 m/s [25]. As for temperature, the interjet distance first decreased with increasing it; however, when the process temperature surpass a certain value, the interjet distance would not increase with increasing temperature [27]. The smallest interjet distance we obtained was 1.1 mm, which was much smaller than 10 mm and 6.3 mm obtained by multineedle electrospinning [23] and cleft electrospinning [21], respectively. Experiment result also showed that at the same feed rate of polymer melt, the smaller the interjet distance was, the thinner the fiber obtained.
3. Key techniques to refine nanofibers Due to the high viscosity and low electrical conductivity of molten polymer, it is harder to refine fiber into nanoscale by melt electrospinning than by solution electrospinning [34]. Although fibers would be thinner by optimizing process parameter, the diameter of fibers was still in micrometer scale [24]. Techniques such as material modification, multistage electric field and airsuction assisted were proposed to refine the fiber. PLA nanofiber
Fig. 2. Definition of inter-jet distance.
with average diameter of 236 nm [25] and PP nanofiber with average diameter of 440 nm [35] were obtained. 3.1. Tug of war effect in melt electrospinning In traditional fiber spinning process, drag force was loaded on the end of the jet as shown in Fig. 3(a). Every cross-section along the jet subjects to the same stretch force. However, the stretch force in melt electrospinning is different from that of traditional fiber spinning. In order to uncover the mechanism of fiber stretching in melt electrospinning process, we adapted microscopic simulation method of dissipative particle dynamics (Fig. 3(d)) [36] and tracer technology (Fig. 3(e)) [37] to investigate the process of fiber dropping. We observed that there were three main stages in dropping process: the first was straight jet stage with a distance of about 3 cm; the second was three-dimensional whipping stage; and the last was solidification stage. The stretching of polymer jet was fastest at the first stage and then gradually slows down to zero at the third stage [36,37]. We attributed this phenomenon to drag forces in melt electrospinning, which came from repelling forces of the adjacent charges and attracting force of charges in electrical field (Fig. 3(b)). The polymer molten close to the beginning of jet bears larger stretching force than that of the end, just like those of string in tug of war game (Fig. 3(c)) [36]. The mechanism in fiber thinning of melt electrospinning lighted the road to propose suitable technology for thinning fibers. 3.2. Modification of materials PP, a massively and widely used polymer, and PLA, a biodegradable and green polymer, were two main materials extensively adopted by melt electrospinning. However, as mentioned above, due to the high viscosity and low electrical conductivity, the diameter of pure PP fiber and pure PLA fiber prepared by PMDES were 4.57 mm [24] and 7.85 mm respectively [32]. In order to prepare PP nanofiber efficiently, we attempted to decrease the viscosity of PP by mixing it with different additives such as hyper-branched [38], molecular weight regulator [39], supercritical CO2 [40] and stearic acid [35]. The thinnest PP fiber with average diameter of 420 nm was successfully produced with 4% weight of stearic acid at an airflow velocity of 29 m/s [35]. As for PLA, the thermal degradation is the biggest obstacle in PMDES. In order to minimize degradation of PLA, technologies such as mixing with antioxidant, setting spinning temperature separately, increase applied voltage were necessary [32]. The smallest average diameter of the PLA fiber is about 256 nm, which was
C. Mingjun et al. / Advanced Industrial and Engineering Polymer Research 2 (2019) 110e115
113
Fig. 3. Schematic process of (a) industrial melt spinning, (b) melt electrospinning, (c) Tug of war, (d) DPD simulation model of melt electrospinning and (e) photo of melt electrospinning (modified from reference [36]).
obtained at the condition of 6% weight of polylactic acid and the airflow velocity of 25 m/s [25]. 3.3. Multistage electrical field for stretching fibers Electrical force was the main stretching force compared to gravity, charge repulsion in melt electrospinning. However, the electrical force is limited by the critical electrical intensity when the air breaks down, and voltage that high electrical power can supply. In order to strengthen the drawing effect on fiber by electrical fore, we proposed hollow disc electrode and gas-assisted method into PMDES (Fig. 4(a)) [41,42]. A lower voltage (e.g. 20 kV) was applied to the hollow disc electrode to form a first stage electric field between the umbrella
Fig. 4. Multistage electrical field for stretching fiber (a) schematic diagram of multistage electrical field (b) simulation of multistage electrical field.
spinneret and hollow disc electrode. A higher voltage (e.g. 45 kV) was applied to the collector electrode to form a second stage electric field between hollow disc electrode and collector electrode (Fig. 4(b)) [43]. Multiple jets were firstly stretched under first stage electric field, and passed through the hollow disc electrode under inducing airflow, then were further stretched under second stage electric field. Fiber would be thinner by drawing with two stages electrical force than by only one stage electrical force. 3.4. Air-suction to refine fibers Stretching fibers by wind was widely used in traditional fiber spinning process such as melt blown [6], jet spinning [44], and spun-bonding [45]. In melt electrospinning process, the diameter of nanofibers prepared by assisted hot gas flow is nearly 20 times smaller than that of fibers without airflow-assisted refining [17]. We proposed air-suction ejector into PMDES to refine fibers [38]. The air-suction ejector (air-flow auxiliary) was installed at the hollow electrode plate (Fig. 1(a)) and the schematic diagram of airsuction ejector was shown in Fig. 5(a). When the compressed air inlet was connected to compressed air, the air between air suction ejector and the spinneret would flow into the air suction ejector. Melt polymer jet would be thinned by the driving force produced not only by electrical field but also by the flowing air. With increasing the velocity of compressed air, the velocity of induced air would increase and the produced fibers would be thinner [25,35,38]. In addition, the flowing of induced air could decrease the density of air between the spinneret and electrode plate, which could increase the critical electrical intensity when the air breaks down. This made it possible to apply a higher electrical intensity between the spinneret and electrode plate (Fig. 5(b)), which could increase
Fig. 5. Influence of air suction on melt electrospinning. (a) Schematic diagram of air-suction, (b) Taylor cone number and critical voltage changed with airflow velocity (modified from reference [25]).
114
C. Mingjun et al. / Advanced Industrial and Engineering Polymer Research 2 (2019) 110e115
Fig. 6. Technology of periodically changing electric field (a) fiber islands produced by 32 spinnerets, (b) simulation of electrical intensity caused by louver-type electrode (c) membrane with uniform density.
Fig. 7. Scale up production line of nanofiber by MEPS, (a) scale up equipment of MEPS (b) spinnerets arrayed and hollow disc electrode (c) the nanofiber membrane.
the number of Taylor cones and driving forces (Fig. 5(b)). The average fiber diameter was as small as 256 nm when the compressed air velocity was 28 m/s [ 25].
4. Scale-up fabrication equipment of PMDES In order to increase nanofiber fabrication throughout, scale-up fabrication equipment was established by arraying 32 umbrellalike spinnerets. However, due to the repulsion caused by identical charge of adjacent spinnerets, the nanofibers from the spinnerets deposited to form 32 islands independently just like in Fig. 6(a). Application of fibers collected in this form were largely limited. In our experiments, we observed that the fiber would deposit at the place where the biggest electrical intensity was. Based on the phenomenon observed, we have proposed louver-type electrode that could periodically change the position of the strongest electric field density (Fig. 6(b)). The periodically dynamically changing electric field would induce periodical changes in deposit position of the fiber, thus forming uniform membrane (Fig. 6(c)). The main parameters of the scale up production line (Fig. 7) are as follows: fiber diameter 200e800 nm, diameter variance 0.19, basis weight 5e130 g/m2, membrane width 1.6 m, laying speed 1e10 m/min, production capacity 300e600 g/h which can be expanded to 6 kg/h by adding more spinnerets [39].
5. Conclusion and prospect PMDES is a highly efficient and green technology for nanofiber preparation and manufacturing. The production efficiency was 500e1000 times comparing to that of capillary solution electrospinning, and was 80 times of the capillary melt electrospinning. The average diameter of fiber prepared by melt polymer differential electrospinning was as small as about 300 nm, equal to solution electrospinning. The output could increase easily just by adding more spinnerets. PMDES could decrease nanofiber fabrication cost dramatically and light the road to the industrialization and commercialization of nanofibers.
PMDES laid a foundation for widespread usage of nanofibers. The application of melt nanofiber in biomedical, clean energy, biochemical protection and other fields may be investigated in more depth. The raw materials in melt polymer differential electrospinning were mainly PP and PLA, and it is necessary to further investigate the spinning process and material modification methods of other thermoplastic polymers to expand the range of raw materials for PMDES. As for fineness, there is still a big gap between the nanofibers in strict definition (below 100 nm) and the fiber obtained so far. It is still necessary to find a new method to further reduce the fiber diameter. Conflict of interest We declare that we have no financial and personal relationships with other people or organizations that can inappropriately influence our work. There is no professional or other personal interest of any nature or kind in any product, service and/or company that could be construed as influencing the position presented in, or the review of, the manuscript entitled, “An example of industrialization of melt electrospinning: polymer melt differential electrospinning”. Acknowledgements The National Key Research and Development Program of China (2016YFB0302000) and the National Natural Science Foundation of China (51603009) supported this work. References [1] R. Gopal, S. Kaur, Z. Ma, et al., Electrospun nanofibrous filtration membrane, J. Membr. Sci. 281 (1) (2006) 581e586. [2] R. Jayakumar, M. Prabaharan, S.V. Nair, et al., Novel chitin and chitosan nanofibers in biomedical applications, Biotechnol. Adv. 28 (1) (2010) 142e150. [3] Q.P. Pham, U. Sharma, A.G. Mikos, Electrospinning of polymeric nanofibers for tissue engineering applications: a review, Tissue Eng. 12 (5) (2006) 1197e1211. [4] K.K. Fu, Y. Gong, J. Dai, et al., Flexible, solid-state, ion-conducting membrane with 3d garnet nanofiber networks for lithium batteries, Proc. Natl. Acad. Sci. U. S. A. 113 (26) (2016) 7094e7099. [5] BCC research, Global Markets and Technologies for Nanofibers. Report Code: NAN043E, 2019.
C. Mingjun et al. / Advanced Industrial and Engineering Polymer Research 2 (2019) 110e115 [6] C.J. Ellison, A. Phatak, D.W. Giles, et al., Melt blown nanofibers: fiber diameter distributions and onset of fiber breakup, Polymer 48 (11) (2007) 3306e3316. [7] N.H.A. Tran, H. Br Nig, C. Hin Ber, et al., Melt spinning of biodegradable nanofibrillary structures from poly(lactic acid) and poly(vinyl alcohol) blends, Macromol. Mater. Eng. 299 (2) (2014) 219e227. [8] K. Shanmuganathan, Y. Fang, D.Y. Chou, et al., Solventless high throughput manufacturing of poly(butylene terephthalate) nanofibers, ACS Macro Lett. 1 (8) (2012) 960e964. [9] Z.-M. Huang, Y.-Z. Zhang, M. Kotaki, et al., A review on polymer nanofibers by electrospinning and their applications in nanocomposites, Compos. Sci. Technol. 63 (15) (2003) 2223e2253. [10] A. Haider, S. Haider, I.-K. Kang, A comprehensive review summarizing the effect of electrospinning parameters and potential applications of nanofibers in biomedical and biotechnology, Arab. J. Chem. 11 (8) (2018) 1165e1188. [11] R. Nayak, R. Padhye, I.L. Kyratzis, et al., Recent advances in nanofibre fabrication techniques, Textil. Res. J. 82 (2) (2012) 129e147. [12] H. Niu, T. Lin, X. Wang, Needleless electrospinning. I. A comparison of cylinder and disk nozzles, J. Appl. Polym. Sci. 114 (6) (2009) 3524e3530. [13] X. Chen, Y. Zhang, X. He, et al., Electrospinning on a plucked string, J. Mater. Sci. 54 (1) (2019) 901e910. [14] N.M. Thoppey, J.R. Bochinski, L.I. Clarke, et al., Unconfined fluid electrospun into high quality nanofibers from a plate edge, Polymer 51 (21) (2010) 4928e4936. [15] X. Wang, T. Lin, X. Wang, Scaling up the production rate of nanofibers by needleless electrospinning from multiple ring, Fibers Polym. 15 (5) (2014) 961e965. [16] R. Nayak, I.L. Kyratzis, Y.B. Truong, et al., Fabrication and characterisation of nanofibres by meltblowing and melt electrospinning[C]//Advanced Materials Research, Trans. Tech. Publ. 472 (2012) 1294e1299. [17] E. Zhmayev, D. Cho, Y.L. Joo, Nanofibers from gas-assisted polymer melt electrospinning, Polymer 51 (18) (2010) 4140e4144. [18] N. Detta, T.D. Brown, F.K. Edin, et al., Melt electrospinning of polycaprolactone and its blends with poly(ethylene glycol), Polym. Int. 59 (11) (2010) 1558e1562. [19] J. Fang, L. Zhang, D. Sutton, et al., Needleless melt-electrospinning of polypropylene nanofibres, J. Nanomater. 2012 (2012) 16. [20] R. Deng, Y. Liu, Y. Ding, et al., Melt electrospinning of low-density polyethylene having a low-melt flow index, J. Appl. Polym. Sci. 114 (1) (2010) 166e175. [21] N. Shimada, H. Tsutsumi, K. Nankne, et al., Poly(ethylene-co-vinyl alcohol) and nylon 6/12 nanofibers produced by melt electrospinning system equipped with a line-like laser beam melting device, J. Appl. Polym. Sci. 116 (5) (2010) 2998e3004. [22] M. Komarek, L. Martinova, Design and evaluation of melt-electrospinning electrodes, in: Proceedings of the 2nd Nanocon International Conference, 2010, pp. 72e77. [23] D.W. Hutmacher, P.D. Dalton, Melt electrospinning, Chem. Asian J. 6 (1) (2011) 44e56. [24] Y. Liu, R.J. Deng, M.F. Hao, et al., Orthogonal design study on factors effecting on fibers diameter of melt electrospinning, Polym. Eng. Sci. 50 (10) (2010) 2074e2078. [25] Y. Qin, L. Cheng, Y. Zhang, et al., Efficient preparation of poly (lactic acid) nanofibers by melt differential electrospinning with addition of acetyl tributyl citrate, J. Appl. Polym. Sci. 135 (31) (2018) 46554.
115
[26] W.M. Yang, H.Y. Li, Principle and equipment of polymer melt differential electrospinning preparing ultrafine fiber, in: IOP Conf. Ser. Mater. Sci. Eng., 64, 2014, p. 012013. [27] H. Li, H. Chen, X. Zhong, et al., Interjet distance in needleless melt differential electrospinning with umbellate nozzles, J. Appl. Polym. Sci. 131 (15) (2014). [28] T.D. Brown, P.D. Dalton, D.W. Hutmacher, Melt electrospinning today: an opportune time for an emerging polymer process, Prog. Polym. Sci. 56 (2016) 116e166. [29] D. Lukas, A. Sarkar, P. Pokorny, Self-organization of jets in electrospinning from free liquid surface: a generalized approach, J. Appl. Phys. 103 (8) (2008) 084309. [30] K. Morikawa, A. Vashisth, C.J. Grimme, et al., Wire melt electrospinning of thin polymeric fibers via strong electrostatic field gradients, Macromol. Mater. Eng. 304 (1) (2019) 1800417. [31] R. Deng, Y. Liu, Y. Ding, et al., Melt electrospinning of low-density polyethylene having a low-melt flow index, J. Appl. Polym. Sci. 114 (1) (2009) 166e175. [32] F. Zhao, Y. Liu, H. Yuan, et al., Orthogonal design study on factors affecting the degradation of polylactic acid fibers of melt electrospinning, J. Appl. Polym. Sci. 125 (4) (2012) 2652e2658. [33] H.Y. Li, M.M. Bubakir, T. Xia, et al., Mass production of ultra-fine fibre by melt electrospinning method using umbellate spinneret, Mater. Res. Innov. 18 (Suppl. 4) (2014) S4-S921eS4-S925. [34] R. Nayak, I.L. Kyratzis, Y.B. Truong, et al., Melt-electrospinning of polypropylene with conductive additives, J. Mater. Sci. 47 (17) (2012) 6387e6396. [35] X. Ma, L. Zhang, J. Tan, et al., Continuous manufacturing of nanofiber yarn with the assistance of suction wind and rotating collection via needleless melt electrospinning, J. Appl. Polym. Sci. 134 (20) (2017). [36] Z. Liu, Y. Liu, Y. Ding, et al., Tug of war effect in melt electrospinning, J. NonNewtonian Fluid Mech. 202 (2013) 131e136. [37] Y. Liu, Z.X. Liu, L. Deng, et al., Experimental study on falling process of melt electrospinning fiber[C]//Key Engineering Materials, Trans. Tech. Publ. 561 (2013) 36e40. [38] L.T. Xia, Y. Liu, Y.M. Ding, et al., Application of hyper-branched polymer in melt electrospinning, Plastics 41 (6) (2012) 1e3 (in Chinese). [39] H.Y. LI, Princlple, Method, and Equipment of Melt Differential Electrospinning, Beijing University of Chemical Technology, Beijing, 2014 (in Chinese). [40] M.Z. Chen, W.M. Yang, H.Y. Li, et al., Properties of PP fiber prepared by melt differential electrospinning with supercritical CO2, Chinese Plastics 30 (6) (2016) 70e73 (in Chinese). [41] H.B. Chen, H.Y. Li, X.L. Ma, et al., Large scaled fabrication of microfibers by airsuction assisted needleless melt electrospinning, Fibers Polym. 17 (4) (2016) 576e581. [42] Z. Liu, H. Li, W. Wu, et al., Effect of electric field on gas-assisted melt differential electrospinning with hollow disc electrode, J. Polym. Eng. 35 (1) (2015) 61e70. [43] H.Y. Li, W.F. Wu, M.M. Bubakir, et al., Polypropylene fibers fabricated via a needleless melt-electrospinning device for marine oil-spill cleanup, J. Appl. Polym. Sci. 131 (7) (2014) 9. [44] E.S. Medeiros, G.M. Glenn, A.P. Klamczynski, et al., Solution blow spinning: a new method to produce micro- and nanofibers from polymer solutions, J. Appl. Polym. Sci. 113 (4) (2009) 2322e2330. [45] Ofosu S K, Kobylivker P M, DeLucia M L, et al. High Strength Spunbond Fabric From High Melt Flow Rate Polymers: U.S. Patent 5,681,646[P]. 1997-10-28.
Contents lists available at ScienceDirect
Advanced Industrial and Engineering Polymer Research journal homepage: http://www.keaipublishing.com/aiepr
An example of industrialization of melt electrospinning: Polymer melt differential electrospinning Chen Mingjun a, Zhang Youchen a, Li Haoyi a, Li Xiangnan a, Ding Yumei a, Mahmoud M. Bubakir b, Yang Weimin a, * a b
College of Mechanical and Electrical Engineering, Beijing University of Chemical Technology, Beijing, 100029, China Gharyan Engineering College Mechanical and Industrial Engineering, Department Gharyan University, Gharyan, Libya
a r t i c l e i n f o
a b s t r a c t
Article history: Received 8 May 2019 Received in revised form 4 June 2019 Accepted 16 June 2019
In recent years, researchers are paying more attention to high efficiency, high process stability and ecofriendly nanofiber fabrication techniques. Among all of the nanofiber fabrication methods, electrospinning including solution electrospinning and melt electrospinning is the most promising method for nanofiber mass production. Compared to solution electrospinning, melt electrospinning could be applied in many areas such as tissue engineering and wound dressings due to the absence of any toxic solvent involvement. Capillary melt electrospinning generates only one jet with low efficiency. Hence, we have proposed polymer melt differential electrospinning (PMDES) method, which could produce multiple jets with smallest interjet distance of 1.1 mm from an umbrella shape spinneret, thus improving the production efficiency significantly. Many techniques such as material modification, suction wind, and multistage electric field were proposed to refine the fibers and nanofibers with average diameter of about 300 nm were obtained. Scale up production line of PMDES with capacity of 300e600 g/h was established by arraying umbrella shape spinnerets. PMDES is a promising technology to meet the requirements of nanofiber production in commercialization. © 2019 Kingfa SCI. & TECH. CO., LTD. Production and Hosting by Elsevier B.V. on behalf of KeAi Communications Co., Ltd. This is an open access article under the CC BY-NC-ND license (http:// creativecommons.org/licenses/by-nc-nd/4.0/).
Keywords: Nanofiber Electrospinning Melt electrospinning Polymer melt differential electrospinning (PMDES)
1. Introduction The unique properties of nanofibers and their applications in many areas such as high efficiency filtration [1], biomedical [2], tissue engineering [3] and battery separators [4] were largely demonstrated in the past 20 years. The global market for nanofiber products may grow from $927 million in 2018 to $4.3 billion by 2023 at a compound annual growth rate of 36.2% [5]. Therefore, eco-friendly nanofiber fabrication methods with high efficiency and high process stability are attracting more and more attention. In order to fulfill the above mentioned requirement, researchers have improved and invented many fiber-spinning processes such as melt-blown [6], bi-component spinning [7], and force-spinning [8]. However, the widely used nanofiber fabrication process is electrospinning because of its simple operation to change nanofiber diameter and porosity [9], its versatility in spinning a wide variety
* Corresponding author. Fax: þ0086 010 64434734. E-mail address: [email protected] (Y. Weimin).
of materials from polymer to ceramic [2], and its ability to produce continuous fiber that can reach kilometers long [2e4]. Therefore, electrospinning that includes both solution electrospinning and melt electrospinning is considered as the most promising method for mass production of nanofibers in commercialization. A typical solution electrospinning equipment, which consisted of a capillary or needle with small diameter, a high electric supplier and a metal collector, is widely used in many laboratories. The yield of the typical solution electrospinning was around 0.01 g/min [10], which is far from meeting the requirements of commercialization. Multi-needle electrospinning is one way to improve the nanofiber outputs, but the mechanical design was complex and the interferential electric field would lower the nanofiber quality [11]. In recent years, electrospinning from free surface have developed fast with the aim of improving nanofiber output significantly. Some novel spinnerets such as rotating disk [12], plucked string [13], plate edge [14] and multiple ring [15] have been developed to increase the nanofiber preparation efficiency. Realizing the huge business opportunities of nanofibers, many companies such as Elmarco (www.elmarco.com), E-Spin Nanotech
https://doi.org/10.1016/j.aiepr.2019.06.002 2542-5048/© 2019 Kingfa SCI. & TECH. CO., LTD. Production and Hosting by Elsevier B.V. on behalf of KeAi Communications Co., Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).
C. Mingjun et al. / Advanced Industrial and Engineering Polymer Research 2 (2019) 110e115
(www.espinnanotech.com), and HiNanofiber (www.hinanofiber. com) developed commercial solution electrospinning set-ups based on research and development results. However, due to the widely and mass use of toxic solvents, solution electrospinning with industrial scale production developed very slowly. The toxic solvent, which constitutes more than 90% of the solution being electro-spun, could cause potential environmental pollution and health damage to workers; the residual toxic solvent has limited the application of electrospun fibers in many fields such as biomedical and tissue engineering. In addition, solution electrospinning is not suitable for non-soluble polymers such as Polypropylene (PP), Polyethylene (PE) and Polyphenylene sulfide (PPS), which are used in large quantities in wide fields. In contrast to solution electrospinning, melt electrospinning is a solvent free, efficient, green nanofiber manufacturing technology. In recent years, more and more researchers are paying attention to melt electrospinning, and the technique has achieved great progress. Melt electros-pun fibers within nanoscale were prepared by mixing melt polymer with salt [16], or adding assisted wind [17] to strengthen the driving force, or adding plasticizers [18] to decrease the viscosity of polymer melt. Nanofiber preparation efficiency have increased by proposing novel spinneret such as rotating disk [19], umbrella cone [20], liner polymer sheet [21] and liner slot [22]. Some pilot production lines of melt electrospinning were established to fabricate nanofiber in industrial scale [23,39]. We have proposed drastically new polymer melt differential electrospinning (PMDES) methods, which can produce multiple jets with smallest interjet distance of 1.1 mm from one umbrella shape spinneret [24]. The average diameter of the fiber fabricated by PMDES method could be as small as about 300 nm [25]. Scale up production line of PMDES with capacity of 300e600 g/h was established by arraying spinnerets [26]. This article will review in detail the PMDES method from principle, equipment, process parameters to scale up equipment. 2. Principle of PMDES Although researchers proposed different types of melt electrospinning spinnerets [19e22], most of which were kept in laboratory due to the low efficiency and uneven molten polymer distribution. We have proposed a novel umbrella-shaped nozzle, which could distribute molten polymer uniformly and strengthen electrical intensity where the Taylor cone is located. Based on the umbrella-like nozzle, we investigated the effects of process parameters on fiber properties and the number of jets. Multiple jets with interjet distance about 1.1 mm were obtained from the umbrella-like nozzle.
111
nozzle, the molten polymer film will attenuate further, which could reduce the Taylor cone and thus the resulted fibers. Once the molten polymer film reaches the bottom of the umbrella nozzle, it will be selforganized into multiple jets under high electrical field [27]. The resulted fibers produced from the umbrella-like nozzle have the same properties because of the uniform polymer melt distribution and identical electrical strength intensity which the polymer melt jets subjected to. The electric field where the jets produced in PMDES was stronger than that of capillary electrospinning, and the fibers obtained would be smaller than that obtained by capillary electrospinning under the same conditions [30]. In addition, the umbrella-like spinneret could avoid fluid plugging and high cost maintenance caused by simple combination of multiple needles. Fig. 1(b) is a schematic diagram of PMDES. There were four main highlights in equipment of PMDES. First, the umbrella-like nozzles could produce multiple jets at the same time (Fig. 1(c)). Second, the hollow electrode plate could provide a channel for fibers to pass through, thus laying the foundation of multi-stage electric field for stretching fiber. Third, by applying high voltage to collector, the interface between high voltage and heating system was avoided. And finally, auxiliary air-flow could strengthen the driving force to produce and thin the nanofibers.
2.2. Optimization of PMDES process parameters Because of the unique structure of umbrella-like spinneret, process parameter values, which were suitable for PMDES, could be different from other melt electrospinning equipments. The effects of process parameters such as collection distance, electrical field intensity and temperature on fiber diameter were investigated. In PMDES, the average fiber diameter continuously decreased when applied voltage increased at a fixed collection distance. When applied voltage was fixed, the average fiber diameter decreased first then increased with increasing collection distance. These results suggested that at too short collection distance, the melt jet did not have sufficient time to elongate [31]. The appropriate electrical field intensity is 4 kv/cm, the appropriate spinning distance is 15 cm, and the appropriate spinning temperature of PP [24], PE [31] and polylactic acid (PLA) [32] in PMDES were 250 C, 355 C and 210 C respectively. Orthogonal experiment result in PMDES showed that influence of the three factors on the average fiber diameters could be listed in the following order: voltage > distance > temperature, and with regard to the standard deviation of the diameter, the list changed to temperature > distance > voltage [31].
2.1. Equipment of PMDES 2.3. Interjet distance of PMDES In melt electrospinning, the jet formation of molten polymer is based on the balance of electric force and surface tension. When the electrical force at the tip of spinning dope is greater than the surface tension, a jet comes from the spinning dope and travels to the collector [28]. In addition, electro-fluid free surface will self-assembly to multiple jets under high electric field according to the theory of electrohydrodynamics [29]. Based on that electrohydrodynamic theory, umbrella-like spinneret that could produce multiple jets from molten polymer film under high electric field was proposed. As shown in Fig. 1(a), polymer melt supplied by a micro extruder flows through the melt inlet into the ring-like melt distributor. In the melt distributor, polymer melt was distributed uniformly around the circumference due to the flow resistance, and thus was distributed on the top circumference of the umbrella-like nozzle uniformly. When melt polymer flows from the top to the bottom of the umbrella-like
Interjet distance was defined as the distance between adjacent Taylor cones. Investigation of the mechanism, which could control interjet distance, is helpful to predict and adjust nanofiber membrane density. Based on the geometric model of umbrella-like spinneret as shown in Fig. 2, we demonstrated the applicability of the relationship between interjet distance and electrical field intensity, surface tension of molten polymer, and relative permittivity of the surrounding gas, as shown in equation (1), which was widely accepted in free surface solution electrospinning [29].
,"
l0 ¼ 12pg
2εE02
rffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi # 2 2εE02 12grg þ
(1)
112
C. Mingjun et al. / Advanced Industrial and Engineering Polymer Research 2 (2019) 110e115
Fig. 1. Melt polymer differential electrospinning (a) schematic diagram of umbrella-like spinneret (b) schematic diagram of melt polymer differential electrospinning equipment (c) picture of PMDES (modified from reference [25,27]).
l0 interjet distance; g surface tension; ε relative permittivity of the surrounding gas; E0 electric field intensity; r density of molten polymer; g gravitational acceleration. Two main factors that affect interjet distance are electric field intensity and temperature. The interjet distance decreased with increasing the electric field intensity [27]. When the electric field intensity surpass a certain value, the air will be broken down and the spinning process could not carry on. Therefore, we have proposed air suction to decrease the air density between nozzle and collector, thus to increase the electrical field intensity in spinning zone [33]. Experimental results showed that the number of Taylor cones could reach as many as 115 when the velocity of airflow was 25 m/s [25]. As for temperature, the interjet distance first decreased with increasing it; however, when the process temperature surpass a certain value, the interjet distance would not increase with increasing temperature [27]. The smallest interjet distance we obtained was 1.1 mm, which was much smaller than 10 mm and 6.3 mm obtained by multineedle electrospinning [23] and cleft electrospinning [21], respectively. Experiment result also showed that at the same feed rate of polymer melt, the smaller the interjet distance was, the thinner the fiber obtained.
3. Key techniques to refine nanofibers Due to the high viscosity and low electrical conductivity of molten polymer, it is harder to refine fiber into nanoscale by melt electrospinning than by solution electrospinning [34]. Although fibers would be thinner by optimizing process parameter, the diameter of fibers was still in micrometer scale [24]. Techniques such as material modification, multistage electric field and airsuction assisted were proposed to refine the fiber. PLA nanofiber
Fig. 2. Definition of inter-jet distance.
with average diameter of 236 nm [25] and PP nanofiber with average diameter of 440 nm [35] were obtained. 3.1. Tug of war effect in melt electrospinning In traditional fiber spinning process, drag force was loaded on the end of the jet as shown in Fig. 3(a). Every cross-section along the jet subjects to the same stretch force. However, the stretch force in melt electrospinning is different from that of traditional fiber spinning. In order to uncover the mechanism of fiber stretching in melt electrospinning process, we adapted microscopic simulation method of dissipative particle dynamics (Fig. 3(d)) [36] and tracer technology (Fig. 3(e)) [37] to investigate the process of fiber dropping. We observed that there were three main stages in dropping process: the first was straight jet stage with a distance of about 3 cm; the second was three-dimensional whipping stage; and the last was solidification stage. The stretching of polymer jet was fastest at the first stage and then gradually slows down to zero at the third stage [36,37]. We attributed this phenomenon to drag forces in melt electrospinning, which came from repelling forces of the adjacent charges and attracting force of charges in electrical field (Fig. 3(b)). The polymer molten close to the beginning of jet bears larger stretching force than that of the end, just like those of string in tug of war game (Fig. 3(c)) [36]. The mechanism in fiber thinning of melt electrospinning lighted the road to propose suitable technology for thinning fibers. 3.2. Modification of materials PP, a massively and widely used polymer, and PLA, a biodegradable and green polymer, were two main materials extensively adopted by melt electrospinning. However, as mentioned above, due to the high viscosity and low electrical conductivity, the diameter of pure PP fiber and pure PLA fiber prepared by PMDES were 4.57 mm [24] and 7.85 mm respectively [32]. In order to prepare PP nanofiber efficiently, we attempted to decrease the viscosity of PP by mixing it with different additives such as hyper-branched [38], molecular weight regulator [39], supercritical CO2 [40] and stearic acid [35]. The thinnest PP fiber with average diameter of 420 nm was successfully produced with 4% weight of stearic acid at an airflow velocity of 29 m/s [35]. As for PLA, the thermal degradation is the biggest obstacle in PMDES. In order to minimize degradation of PLA, technologies such as mixing with antioxidant, setting spinning temperature separately, increase applied voltage were necessary [32]. The smallest average diameter of the PLA fiber is about 256 nm, which was
C. Mingjun et al. / Advanced Industrial and Engineering Polymer Research 2 (2019) 110e115
113
Fig. 3. Schematic process of (a) industrial melt spinning, (b) melt electrospinning, (c) Tug of war, (d) DPD simulation model of melt electrospinning and (e) photo of melt electrospinning (modified from reference [36]).
obtained at the condition of 6% weight of polylactic acid and the airflow velocity of 25 m/s [25]. 3.3. Multistage electrical field for stretching fibers Electrical force was the main stretching force compared to gravity, charge repulsion in melt electrospinning. However, the electrical force is limited by the critical electrical intensity when the air breaks down, and voltage that high electrical power can supply. In order to strengthen the drawing effect on fiber by electrical fore, we proposed hollow disc electrode and gas-assisted method into PMDES (Fig. 4(a)) [41,42]. A lower voltage (e.g. 20 kV) was applied to the hollow disc electrode to form a first stage electric field between the umbrella
Fig. 4. Multistage electrical field for stretching fiber (a) schematic diagram of multistage electrical field (b) simulation of multistage electrical field.
spinneret and hollow disc electrode. A higher voltage (e.g. 45 kV) was applied to the collector electrode to form a second stage electric field between hollow disc electrode and collector electrode (Fig. 4(b)) [43]. Multiple jets were firstly stretched under first stage electric field, and passed through the hollow disc electrode under inducing airflow, then were further stretched under second stage electric field. Fiber would be thinner by drawing with two stages electrical force than by only one stage electrical force. 3.4. Air-suction to refine fibers Stretching fibers by wind was widely used in traditional fiber spinning process such as melt blown [6], jet spinning [44], and spun-bonding [45]. In melt electrospinning process, the diameter of nanofibers prepared by assisted hot gas flow is nearly 20 times smaller than that of fibers without airflow-assisted refining [17]. We proposed air-suction ejector into PMDES to refine fibers [38]. The air-suction ejector (air-flow auxiliary) was installed at the hollow electrode plate (Fig. 1(a)) and the schematic diagram of airsuction ejector was shown in Fig. 5(a). When the compressed air inlet was connected to compressed air, the air between air suction ejector and the spinneret would flow into the air suction ejector. Melt polymer jet would be thinned by the driving force produced not only by electrical field but also by the flowing air. With increasing the velocity of compressed air, the velocity of induced air would increase and the produced fibers would be thinner [25,35,38]. In addition, the flowing of induced air could decrease the density of air between the spinneret and electrode plate, which could increase the critical electrical intensity when the air breaks down. This made it possible to apply a higher electrical intensity between the spinneret and electrode plate (Fig. 5(b)), which could increase
Fig. 5. Influence of air suction on melt electrospinning. (a) Schematic diagram of air-suction, (b) Taylor cone number and critical voltage changed with airflow velocity (modified from reference [25]).
114
C. Mingjun et al. / Advanced Industrial and Engineering Polymer Research 2 (2019) 110e115
Fig. 6. Technology of periodically changing electric field (a) fiber islands produced by 32 spinnerets, (b) simulation of electrical intensity caused by louver-type electrode (c) membrane with uniform density.
Fig. 7. Scale up production line of nanofiber by MEPS, (a) scale up equipment of MEPS (b) spinnerets arrayed and hollow disc electrode (c) the nanofiber membrane.
the number of Taylor cones and driving forces (Fig. 5(b)). The average fiber diameter was as small as 256 nm when the compressed air velocity was 28 m/s [ 25].
4. Scale-up fabrication equipment of PMDES In order to increase nanofiber fabrication throughout, scale-up fabrication equipment was established by arraying 32 umbrellalike spinnerets. However, due to the repulsion caused by identical charge of adjacent spinnerets, the nanofibers from the spinnerets deposited to form 32 islands independently just like in Fig. 6(a). Application of fibers collected in this form were largely limited. In our experiments, we observed that the fiber would deposit at the place where the biggest electrical intensity was. Based on the phenomenon observed, we have proposed louver-type electrode that could periodically change the position of the strongest electric field density (Fig. 6(b)). The periodically dynamically changing electric field would induce periodical changes in deposit position of the fiber, thus forming uniform membrane (Fig. 6(c)). The main parameters of the scale up production line (Fig. 7) are as follows: fiber diameter 200e800 nm, diameter variance 0.19, basis weight 5e130 g/m2, membrane width 1.6 m, laying speed 1e10 m/min, production capacity 300e600 g/h which can be expanded to 6 kg/h by adding more spinnerets [39].
5. Conclusion and prospect PMDES is a highly efficient and green technology for nanofiber preparation and manufacturing. The production efficiency was 500e1000 times comparing to that of capillary solution electrospinning, and was 80 times of the capillary melt electrospinning. The average diameter of fiber prepared by melt polymer differential electrospinning was as small as about 300 nm, equal to solution electrospinning. The output could increase easily just by adding more spinnerets. PMDES could decrease nanofiber fabrication cost dramatically and light the road to the industrialization and commercialization of nanofibers.
PMDES laid a foundation for widespread usage of nanofibers. The application of melt nanofiber in biomedical, clean energy, biochemical protection and other fields may be investigated in more depth. The raw materials in melt polymer differential electrospinning were mainly PP and PLA, and it is necessary to further investigate the spinning process and material modification methods of other thermoplastic polymers to expand the range of raw materials for PMDES. As for fineness, there is still a big gap between the nanofibers in strict definition (below 100 nm) and the fiber obtained so far. It is still necessary to find a new method to further reduce the fiber diameter. Conflict of interest We declare that we have no financial and personal relationships with other people or organizations that can inappropriately influence our work. There is no professional or other personal interest of any nature or kind in any product, service and/or company that could be construed as influencing the position presented in, or the review of, the manuscript entitled, “An example of industrialization of melt electrospinning: polymer melt differential electrospinning”. Acknowledgements The National Key Research and Development Program of China (2016YFB0302000) and the National Natural Science Foundation of China (51603009) supported this work. References [1] R. Gopal, S. Kaur, Z. Ma, et al., Electrospun nanofibrous filtration membrane, J. Membr. Sci. 281 (1) (2006) 581e586. [2] R. Jayakumar, M. Prabaharan, S.V. Nair, et al., Novel chitin and chitosan nanofibers in biomedical applications, Biotechnol. Adv. 28 (1) (2010) 142e150. [3] Q.P. Pham, U. Sharma, A.G. Mikos, Electrospinning of polymeric nanofibers for tissue engineering applications: a review, Tissue Eng. 12 (5) (2006) 1197e1211. [4] K.K. Fu, Y. Gong, J. Dai, et al., Flexible, solid-state, ion-conducting membrane with 3d garnet nanofiber networks for lithium batteries, Proc. Natl. Acad. Sci. U. S. A. 113 (26) (2016) 7094e7099. [5] BCC research, Global Markets and Technologies for Nanofibers. Report Code: NAN043E, 2019.
C. Mingjun et al. / Advanced Industrial and Engineering Polymer Research 2 (2019) 110e115 [6] C.J. Ellison, A. Phatak, D.W. Giles, et al., Melt blown nanofibers: fiber diameter distributions and onset of fiber breakup, Polymer 48 (11) (2007) 3306e3316. [7] N.H.A. Tran, H. Br Nig, C. Hin Ber, et al., Melt spinning of biodegradable nanofibrillary structures from poly(lactic acid) and poly(vinyl alcohol) blends, Macromol. Mater. Eng. 299 (2) (2014) 219e227. [8] K. Shanmuganathan, Y. Fang, D.Y. Chou, et al., Solventless high throughput manufacturing of poly(butylene terephthalate) nanofibers, ACS Macro Lett. 1 (8) (2012) 960e964. [9] Z.-M. Huang, Y.-Z. Zhang, M. Kotaki, et al., A review on polymer nanofibers by electrospinning and their applications in nanocomposites, Compos. Sci. Technol. 63 (15) (2003) 2223e2253. [10] A. Haider, S. Haider, I.-K. Kang, A comprehensive review summarizing the effect of electrospinning parameters and potential applications of nanofibers in biomedical and biotechnology, Arab. J. Chem. 11 (8) (2018) 1165e1188. [11] R. Nayak, R. Padhye, I.L. Kyratzis, et al., Recent advances in nanofibre fabrication techniques, Textil. Res. J. 82 (2) (2012) 129e147. [12] H. Niu, T. Lin, X. Wang, Needleless electrospinning. I. A comparison of cylinder and disk nozzles, J. Appl. Polym. Sci. 114 (6) (2009) 3524e3530. [13] X. Chen, Y. Zhang, X. He, et al., Electrospinning on a plucked string, J. Mater. Sci. 54 (1) (2019) 901e910. [14] N.M. Thoppey, J.R. Bochinski, L.I. Clarke, et al., Unconfined fluid electrospun into high quality nanofibers from a plate edge, Polymer 51 (21) (2010) 4928e4936. [15] X. Wang, T. Lin, X. Wang, Scaling up the production rate of nanofibers by needleless electrospinning from multiple ring, Fibers Polym. 15 (5) (2014) 961e965. [16] R. Nayak, I.L. Kyratzis, Y.B. Truong, et al., Fabrication and characterisation of nanofibres by meltblowing and melt electrospinning[C]//Advanced Materials Research, Trans. Tech. Publ. 472 (2012) 1294e1299. [17] E. Zhmayev, D. Cho, Y.L. Joo, Nanofibers from gas-assisted polymer melt electrospinning, Polymer 51 (18) (2010) 4140e4144. [18] N. Detta, T.D. Brown, F.K. Edin, et al., Melt electrospinning of polycaprolactone and its blends with poly(ethylene glycol), Polym. Int. 59 (11) (2010) 1558e1562. [19] J. Fang, L. Zhang, D. Sutton, et al., Needleless melt-electrospinning of polypropylene nanofibres, J. Nanomater. 2012 (2012) 16. [20] R. Deng, Y. Liu, Y. Ding, et al., Melt electrospinning of low-density polyethylene having a low-melt flow index, J. Appl. Polym. Sci. 114 (1) (2010) 166e175. [21] N. Shimada, H. Tsutsumi, K. Nankne, et al., Poly(ethylene-co-vinyl alcohol) and nylon 6/12 nanofibers produced by melt electrospinning system equipped with a line-like laser beam melting device, J. Appl. Polym. Sci. 116 (5) (2010) 2998e3004. [22] M. Komarek, L. Martinova, Design and evaluation of melt-electrospinning electrodes, in: Proceedings of the 2nd Nanocon International Conference, 2010, pp. 72e77. [23] D.W. Hutmacher, P.D. Dalton, Melt electrospinning, Chem. Asian J. 6 (1) (2011) 44e56. [24] Y. Liu, R.J. Deng, M.F. Hao, et al., Orthogonal design study on factors effecting on fibers diameter of melt electrospinning, Polym. Eng. Sci. 50 (10) (2010) 2074e2078. [25] Y. Qin, L. Cheng, Y. Zhang, et al., Efficient preparation of poly (lactic acid) nanofibers by melt differential electrospinning with addition of acetyl tributyl citrate, J. Appl. Polym. Sci. 135 (31) (2018) 46554.
115
[26] W.M. Yang, H.Y. Li, Principle and equipment of polymer melt differential electrospinning preparing ultrafine fiber, in: IOP Conf. Ser. Mater. Sci. Eng., 64, 2014, p. 012013. [27] H. Li, H. Chen, X. Zhong, et al., Interjet distance in needleless melt differential electrospinning with umbellate nozzles, J. Appl. Polym. Sci. 131 (15) (2014). [28] T.D. Brown, P.D. Dalton, D.W. Hutmacher, Melt electrospinning today: an opportune time for an emerging polymer process, Prog. Polym. Sci. 56 (2016) 116e166. [29] D. Lukas, A. Sarkar, P. Pokorny, Self-organization of jets in electrospinning from free liquid surface: a generalized approach, J. Appl. Phys. 103 (8) (2008) 084309. [30] K. Morikawa, A. Vashisth, C.J. Grimme, et al., Wire melt electrospinning of thin polymeric fibers via strong electrostatic field gradients, Macromol. Mater. Eng. 304 (1) (2019) 1800417. [31] R. Deng, Y. Liu, Y. Ding, et al., Melt electrospinning of low-density polyethylene having a low-melt flow index, J. Appl. Polym. Sci. 114 (1) (2009) 166e175. [32] F. Zhao, Y. Liu, H. Yuan, et al., Orthogonal design study on factors affecting the degradation of polylactic acid fibers of melt electrospinning, J. Appl. Polym. Sci. 125 (4) (2012) 2652e2658. [33] H.Y. Li, M.M. Bubakir, T. Xia, et al., Mass production of ultra-fine fibre by melt electrospinning method using umbellate spinneret, Mater. Res. Innov. 18 (Suppl. 4) (2014) S4-S921eS4-S925. [34] R. Nayak, I.L. Kyratzis, Y.B. Truong, et al., Melt-electrospinning of polypropylene with conductive additives, J. Mater. Sci. 47 (17) (2012) 6387e6396. [35] X. Ma, L. Zhang, J. Tan, et al., Continuous manufacturing of nanofiber yarn with the assistance of suction wind and rotating collection via needleless melt electrospinning, J. Appl. Polym. Sci. 134 (20) (2017). [36] Z. Liu, Y. Liu, Y. Ding, et al., Tug of war effect in melt electrospinning, J. NonNewtonian Fluid Mech. 202 (2013) 131e136. [37] Y. Liu, Z.X. Liu, L. Deng, et al., Experimental study on falling process of melt electrospinning fiber[C]//Key Engineering Materials, Trans. Tech. Publ. 561 (2013) 36e40. [38] L.T. Xia, Y. Liu, Y.M. Ding, et al., Application of hyper-branched polymer in melt electrospinning, Plastics 41 (6) (2012) 1e3 (in Chinese). [39] H.Y. LI, Princlple, Method, and Equipment of Melt Differential Electrospinning, Beijing University of Chemical Technology, Beijing, 2014 (in Chinese). [40] M.Z. Chen, W.M. Yang, H.Y. Li, et al., Properties of PP fiber prepared by melt differential electrospinning with supercritical CO2, Chinese Plastics 30 (6) (2016) 70e73 (in Chinese). [41] H.B. Chen, H.Y. Li, X.L. Ma, et al., Large scaled fabrication of microfibers by airsuction assisted needleless melt electrospinning, Fibers Polym. 17 (4) (2016) 576e581. [42] Z. Liu, H. Li, W. Wu, et al., Effect of electric field on gas-assisted melt differential electrospinning with hollow disc electrode, J. Polym. Eng. 35 (1) (2015) 61e70. [43] H.Y. Li, W.F. Wu, M.M. Bubakir, et al., Polypropylene fibers fabricated via a needleless melt-electrospinning device for marine oil-spill cleanup, J. Appl. Polym. Sci. 131 (7) (2014) 9. [44] E.S. Medeiros, G.M. Glenn, A.P. Klamczynski, et al., Solution blow spinning: a new method to produce micro- and nanofibers from polymer solutions, J. Appl. Polym. Sci. 113 (4) (2009) 2322e2330. [45] Ofosu S K, Kobylivker P M, DeLucia M L, et al. High Strength Spunbond Fabric From High Melt Flow Rate Polymers: U.S. Patent 5,681,646[P]. 1997-10-28.