Applied Mechanics and Materials Vols. 29-32 (2010) pp 1943-1947 Online available since 2010/Aug/13 at www.scientific.net © (2010) Trans Tech Publications, Switzerland doi:10.4028/www.scientific.net/AMM.29-32.1943
Using orthogonal design in optimizing parameters for bubble electrospinning of polyvinyl alcohol (PVA) nanofibers Liang Dong1, 2, a, Wan Shou1, 2 , Yong Liu1, 2, b, Rui Wang1, 2 and Ru-dong Chen3 1
Tianjin and Ministry of Education Key Laboratory of Advanced Textile Composite Materials, Tianjin Polytechnic University, Tianjin 300160, China 2
School of Textiles, Tianjin Polytechnic University, 63 Chenglin Road, Hedong District, Tianjin, 300160, China
3
School of Science, Tianjin Polytechnic University, 63 Chenglin Road, Hedong District, Tianjin, 300160, China a
[email protected], b
[email protected]
Keywords: bubble electrospinning, nanofibers, orthogonal design, morphology
Abstract. The present work was aimed at studying the effects of process parameters on morphologies of Polyvinyl alcohol (PVA) nanofibers in a novel electrospinning technique, bubble electrospinning. The process was optimized by constructing L 9(34) orthogonal experimental array design. Three factors were investigated and nine tests were run under lower, medium and higher levels of these factors. The results showed that PVA solution concentration plays an important role in affecting the morphologies of PVA nanofibers in bubble electrospinning process. With the increase of the concentration of PVA solution, the morphologies of fibers were changed from beaded fibers to uniform cylinder fibers and the average nanofiber diameter also increased. The optimization process was 12w% for PVA solution, 30kV for applied voltage and 10cm for spinning distance. Introduction Bubble electrospinning is a novel and effective process to produce sub-micro and nano- fibers[1-3]. The process is easy to implement and provides the mass production of polymer nanofibers which are as thin in diameter as several tens nanometers (nm) to several microns. The new process has the potential specifically to greatly improve the yield of nanofibers. The mechanism of this process was deceptively simple and primarily based on the produced bubbles on a liquid surface to fabricate a large number of nanofibers in a short time[4, 5]. It is well known that a wide range of parameters, such as applied voltage, spinning distance and solution concentration, affect the morphologies and properties of bubble-electrospun nanofibers. Recently, we have made considerable efforts[6-9] to understand and deepen our knowledge of this process. However, the effect of process parameters on the diameter and morphology of the nanofibers has not been addressed in bubble electrospinning process. In this work, the orthogonal test design was used to arrange sequent experiments to test the effect of the three main factors including applied voltage, spinning distance, solution concentration on the morphologies of nanofibers in bubble electrospinning process. Materials and Methods Materials. PVA samples with degree of polymerization of 550-650 and DH values of 86-89 were supplied by Chang Chun Petrochemistry Co, Ltd., Taiwan. Distilled water and absolute ethyl alcohol (with mass ratio 1:1 in this case) were used as the solvent. Absolute ethyl alcohol was obtained from Hongyan Chemical Reagent Co, Ltd., Tianjin. Distilled water was produced by Tianjin Polytechnic University. All the chemicals were used directly without further purification. The PVA solution concentrations were adjusted to 10, 12, 14 wt%, respectively.
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Bubble electrospinning process. As shown in Figure 1, the bubble electrospinning setup consisted of vertical solution reservoir connecting a gas pump (aco-318, Haili Company, Guangdong) via a gas tube, in which a thin metal electrode fixed along the centerline of tube and a grounded collector over the reservoir. The DC high voltage (DW-P503-lACCC, Dongwen High Voltage Co, Ltd., Tianjin) was applied to the PVA solution via an alligator clip attached to the metal electrode. The polymer bubbles, as Taylor cones in classic electrospinning process, were produced on the liquid surface by releasing the compressed gas in polymer solution. When the voltage reaches the threshold voltage, multiple jets are ejected from the bubbles to the collector. collector
jets
bubble
Solution reservoir
DC high voltage supply
Gas pump
Fig. 1 Schematic drawing of bubble electrospinning setup Characterization. The morphologies of electrospun PVA nanofibers were observed with a Hitachi desktop scanning electron microscope (TM-1000, Hitachi Co. Ltd., Japan). The fiber diameters were determined by an open-source software, ImageJ 1.43u. Orthogonal experimental array. An orthogonal experiment consists of L9(34) orthogonal array was used in this study . Based on previous knowledge of bubble electrospinning, applied voltage, solution concentration, spinning distance between the liquid surface and the collector were chosen as individual parameters. The exact levels were selected using the levels obtained from the light of preliminary tests, which are given in Table 1. The experimental plan is given in Table 2. Table 1 Quantitative value of coded parameter levels Coded Levels Parameters factors 1 2 A Solution concentration (%) 10 12 B Applied voltage (kV) 20 25 C Distance (cm) 6 10
3 14 30 12
Results and discussion In order to examine the effect of different parameters on the morphologies of nanofibers in bubble electrospinning, nine independent experiments were carried out according to Tables 1 and 2. SEM micrographs and fiber diameter distribution of bubble electrospun PVA nanofibers in these experiments are shown in Figure 2. The figure number is displayed in accordance with the experiment number of orthogonal experimental array. It is easy to find that there are many micro-balls and beads in the bubble electrospun nanofibers when the solution concentrations are low, e.g., 10wt% in this case, which is very similar to that in classic electrospinning process[10]. With the increase of PVA solution concentration, the number of micro-balls and beads decreases. Very few balls and beads are found in SEM photograph of 14w% PVA solution nanofiber mat (see Figure 2). On the other hand, the average diameter of nanofibers increases with the increase of solution concentration. When the
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applied voltage increased from 20KV to 30KV, the average nanofiber diameter obviously decreased. The reason might be that the increasing applied voltage caused thicker jets were ejected from the bubble in this process. The smallest average fiber diameter and the narrowest distribution of fiber diameters were obtained at medium level of spinning distance between the liquid surface and the collector. The reason might be that too short spinning distance restrains the stretching of the fluid jet and too long distance reduces the role of applied electric field. According to the experimental results, solution concentration has the most significant effect on the morphology of nanofibers, next are the applied voltage and spinning distance. The optimization criterion was defined as the narrowest distribution of nanofibers diameters and smallest average nanofiber diameter. In our experiments, the optimal process was 12wt% for PVA solution, 30kV for applied voltage and 10cm for spinning distance. Table 2 Orthogonal experiment results Experiment Number
Parameters and their level
Results d /（ m ）
A
B
C
Error
1
1
1
1
1
0.179
0.0411
2
1
2
2
2
0.133
0.0313
3
1
3
3
3
0.143
0.0477
4
2
1
2
3
0.140
0.0345
5
2
2
3
1
0.137
0.0359
6
2
3
1
2
0.131
0.0348
7
3
1
3
2
0.212
0.0761
8
3
2
1
3
0.171
0.0351
9
3
3
2
1
0.162
0.0344
d1
0.152
0.177
0.16
0.159
d2
0.136
0.147
0.145
0.159
d3
0.182
0.145
0.164
0.151
Range R1
0.116
0.111
0.114
0.091
1
0.04
0.051
0.037
0.037
2 3
0.035 0.049 0.014
0.034 0.039 0.017
0.033 0.053 0.02
0.047 0.039 0.01
Range R2
The average diameter and standard deviation are indicated as d and . d i and i (i=1,2,3) denote average diameter and standard deviation at each level. R1, R2 are the ranges of d and respectively.
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Fig. 2 SEM photographs of PVA bubble electrospun nanofibers and their diameter distribution.
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Conclusion In this presentation, PVA nanofibers were prepared via bubble electrospinning. The experimental results show that PVA solution concentration plays an important role in affecting the morphologies of PVA nanofibers in bubble electrospinning process. With the increase of the concentration of PVA solution, the morphologies of fibers were changed from beaded fibers to uniform cylinder fibers and the average nanofiber diameter also increased. There was a decrease in average fiber diameter with increasing applied voltage. There was a very uniform diameter distribution, and the average diameter is the minimum at medium level of spinning distance (10cm). The optimization process was 12w% for PVA solution, 30KV for applied voltage and 10cm for spinning distance. Acknowledgements The present work is supported by National Science Foundation of Tianjin No.10JCYBJC02200, Key Project of Chinese Ministry of Education No.210006, Tianjin Universities Science and Technology Development Fund Project No.20080322. References [1] J.-H. He, Y. Liu, L.-F. Mo, Y.-Q. Wan and L. Xu: Electrospun Nanofibres and Their Applications. (Smithers rapra updates, UK, 2008). [2] Y. Liu and J.-H. He, Int J Nonlinear Sci Numl: Vol. 8 (2007), p.393. [3] Y. Liu, J.-H. He and J.-Y. Yu, Journal of Physics: Conference Series: Vol. 96 (2008), p.012001. [4] Y. Liu, J.-H. He, L. Xu and J.-Y. Yu, J Polym Eng: Vol. 28 (2008), p.55. [5] Y. Liu, J.-H. He, R. Wang, L. Xu and J.-Y. Yu, In: Proceedings of The Fiber Society 2009 Spring Conference, China Textile & Apparel Press, Shanghai, China, Vol. 1, (2009) pp.411-413. [6] R. Yang, J. He, L. Xu and J. Yu, Polymer: Vol. 50 (2009), p.5846. [7] L. Dong, Y. Liu, J. Fan, W.-M. Kang, R. Wang, B.-W. Cheng and L. Xu, Nonl Sci Lett D: Vol. 1 (2010), p.129. [8] L. Dong, Y. Liu, R. Wang, W.-M. Kang and B.-W. Cheng, In: TBIS 2010 International Symposium, Shanghai, China, Vol. (2010) pp.1141-1144. [9] Y. Liu, L. Dong, J. Fan, W.-M. Kang, R. Wang, L. Xu, B.-W. Cheng and J.-Y. Yu, Nonl Sci Lett A: Vol. 1 (2010), p.239. [10] Y. Liu, J.-H. He, J.-Y. Yu and H.-M. Zeng, Polym. Int.: Vol. 57 (2008), p.632.
Applied Mechanics And Mechanical Engineering doi:10.4028/www.scientific.net/AMM.29-32 Using Orthogonal Design in Optimizing Parameters for Bubble Electrospinning of Polyvinyl Alcohol (PVA) Nanofibers doi:10.4028/www.scientific.net/AMM.29-32.1943
