Composite Nanofibers Produced by Electrospinning Technique

Transcription

1 Composite Nanofibers Produced by Electrospinning Technique Nuray UCAR, Onur AYAZ, Mustafa OKSUZ, Aysen ONEN, Elif BAHAR, Mehmet UCAR, Ali DEMĐR, Youjiang WANG Abstract Developing new composite materials and hence applications of such materials have been an active field of research in recent years. Composite nano fibers are submicronsized fibers that contain nano-sized reinforcements. Comparing with composite materials containing micron or larger sized reinforcing materials, nano-sized reinforcements provide better properties and thus less material is needed for a given application and lower cost is possible. In addition to the plastics industry, composite nano fiber materials can be used in different areas such as technical textiles in aerospace, automotive, building, defense, bioengineering (wound dressing, drug delivery systems, artificial organs) etc. In most application, nano fiber materials have much better properties, hence wider application areas than nano particles because of higher specific surface area (area to volume ratio), higher aspect ratio (length to diameter ratio) and higher molecular orientation. It is also possible to produce a three dimensional nano fiber web that offers better filtration performance than most other filtration media. In this study, composite nano fiber consisted of cellulose nano whiskers filler (CNW) and elastomeric polymer matrix (EPM) has been produced by electrospinning technique. During electrospinning, sometimes the tip of needle was clogged because of rapidly evaporation of solvent. The diameter of both composite nanofiber with CNW and reference nanofiber without CNW change between nano level and micro level. It has been seen that the diameter and CV value (coefficient of variation) of composite nano fiber is higher than those of reference nanofiber, because of the cavities and protrusions resulted from agglomeration of CNW and also interaction of slow evaporation of water and quick evaporation of Acetone. Some of electrospun fiber was spread out because of slow evaporation resulted from high boiling point of Dimethylformaid and water. Index Terms Composite nanofiber, electrospinning, elastomeric polymer, cellulose nanowhiskers Manuscript received December, 25, This work was supported by TUBITAK under Grant 109M267. Nuray UÇAR is with the Textile Engineering Department, Gumussuyu, Istanbul Technical University, Istanbul, TURKEY (corresponding author, phone: (2712 line); fax: ; ucarnu@itu.edu.tr or ucarnuray@gmail.com ). Onur AYAZ(Master Science student) is with the Textile Engineering Department, Gumussuyu, Istanbul Technical University, Istanbul, TURKEY ( onur.ayaz@yahoo.com ). D I. INTRODUCTION eveloping new composite materials and hence applications of such materials have been an active field of research in recent years. Composite nanofibers are submicron-sized fibers that contain nano-sized reinforcements. Comparing with composite materials containing micron or larger sized reinforcing materials, nano-sized reinforcements provide better properties and thus less material is needed for a given application and lower cost is possible. In addition to the plastics industry, composite nanofiber materials can be used in different areas such as technical textiles in aerospace, automotive, building, defense, bioengineering (wound dressing, drug delivery systems, artificial organs) etc. In most application, nanofiber materials have much better properties, hence wider application areas than nano particles because of higher specific surface area (area to volume ratio), higher aspect ratio (length to diameter ratio) and higher molecular orientation. It is also possible to produce a three dimensional nanofiber web that offers better filtration performance than most other filtration media. Electrospinning is very convenient technique to produce nanofiber. Generally, polymer solution or melted polymer fed by a syringe pump is forced by high voltage. The jet at the tip of needle is pulled, stretched, elongated and bent by this electrical force. Mustafa OKSUZ is with the Polymer Engineering Department of Yalova University, Yalova, TURKEY and also Metal&Material Education Department of Marmara University, Istanbul, TURKEY ( moksuz@marmara.edu.tr or muoksuz@gmail.com ). Ayşen ÖNEN is with the Chemistry Department, Maslak, Istanbul Technical University, Istanbul, TURKEY ( onen@itu.edu.tr). Elif BAHAR(Master Science student) is with the Chemistry Department, Maslak, Istanbul Technical University, Istanbul, TURKEY ( elifrafiye@gmail.com ). Mehmet UÇAR is with the Mechanical Education Department of Kocaeli University, Izmit, TURKEY ( ucarm@kocaeli.edu.tr ) Ali DEMIR is with the Textile Engineering Department, Istanbul technical University, Gumussuyu, Istanbul, TURKEY and OSYM ( ademir@itu.edu.tr ) Youjiang WANG is with School of Material Scieng&Engineeering, Georgia Institute of Technology, Atlanta, GA, USA ( youjiang.wang@ptfe.gatech.edu )

2 Proceeding of the 8th Saudi Engineering Conference (SEC8), Buraydah, Saudi Arabia, Nov , By the way, during travel of solution from the tip of needle to the collector, solvent evaporates rapidly and nano fiber occurs (Figure 1). Production of nano sized fiber by electrosppining technique has been extensively studied in the last two decades. For example, Baumgaten, was among the first groups of researchers who studied on the effects of process factors (e.g. applied potential, solution feed rate, etc.) and some solutions properties (e.g., concentration, viscosity, etc.) on structural properties of the electrospun polyacrylonitril (PAN) fibers. He pointed out that an increase of viscosity leads to an increase of the diameter of PAN nano fiber, while an increase in the solution feed rate did not affect much the diameter of the fibers [1],[2]. Jarusuwannapoom, et.al. [3] studied the effect of solvents on electrospinnability of Polystyrene. They pointed out that electrospinnability of PS improves when dipole moment and conductivity of both solvent and solution increases. Manee-in, et.al.[3], produced nanofiber from Polystyrene (PS) and pointed out that LiCl and KCl (1 % w/v) increases both the conductivity of the PS solution and the size of the fibers. They pointed out that an increase of applied potential or decrease of distance between collector and needle result to a decrease of beads. Increase of electrostatic field strength and the concentration of the solution results to an increase of fiber diameter. Kim, et.al, [4], produced nano fiber from PS by electrospinning system. They also concluded that the higher concentration of solution results the thicker fibers with fewer beads. Evaporation of the solvents affects a splitting and splaying of the fibers during production. Fig 1. Schematic illustration of electrosppining system There are several studies related with composite nano fiber consisted of cellulose based material and other polymer material. For example, Junkasem, et.al.[5], produced composite nanofibers with polyvinyl alcohol (PVA) and α- chitin whiskers by electrospinning method. Lu, et.al.[6] produced nanocomposite fibrous membranes by electrospinning cellulose nanocrystal (CNC)-loaded poly(acrylic acid) (PAA) ethanol mixtures. They pointed out that an increase of CNC loading (in the range of 0-20 %) leads to decrease of nanocomposite fibers (nano fibers) diameters and an increase of fiber uniformity. Peresin, et.al. [7] used Polyvinyl Alcohol (PVA) and Cellulose Nanocrystals (CNs) to produce composite nanofiber. They pointed out that neither the surface tension nor the viscosity of the solution was significantly affected by CNs. Increase of the amount of CNs in the solution leads to an increase of conductivity of solution and a decrease of fiber s diameter. Rojas, et.al. [8], used Polystyrene (PS) and Cellulose Nano whiskers (CNW) to produce composite nanofiber. They have pointed out that tendency of bead formation increases with an increase of CNW because of poor dispersion or compatibility of CNW with PS. An increase of CNW results to decrease of fiber s diameter. Presence of CNW causes a twist along the nanofiber. A. Materials II. MATERIALS AND METHODS Elastomeric polymer matrix (Polystyrene-block-poly(ethyleneran-butylene)-block-polystyrene-graft-maleic anhydride) (EPM) were purchased from Sigma Aldrich. Cyclohexane (Merck, boiling point 81 o C, dielectric constant 2,02 ) was used to solve EPM. Dimethylformaid (DMF, Merck, boiling point 153 o C, dielectric constant 38), Tetrahydrofuran (THF, Merck, boiling point 66 o C, dielectric constant 7,5), Acetone (Merck, boiling point 56 o C, dielectric constant 21) were used to improve the electrospinnability. As a filler material, cellulose nanowhiskers (CNW) have been used. B. Production of CNW CNW was produced at the laboratory by acid hydrolysis method, which is similar method applied by Marcovich, et.al [9]. Microcrystalline cellulose powder (Avicel Type GP1030) (MCC) which is supplied from FMC was used to produce CNW. The MCC was treated by sulfuric acid solution (95-98 %,Merck) at 45 o C for 139 min. The excess of sulfuric acid was removed by repeated cycles of centrifuge at 8000 for 30 minutes (between 9 and 11 cycle) (Nüve NF 800 R). The supernatant was removed from the sediment and was replaced by deionized water. The centrifugation continued until the supernatant became turbid. After first several cycle, materials was washed with NaOH, until the PH value became 9 or 10. C. Production of Solution Two different composite solutions with CNW were prepared. In one application, EPM was solved in Cyclohexane, THF, Acetone (Solution 1). THF were used to improve the electrospinnibility, Acetone was used to accelerate the

3 Proceeding of the 8th Saudi Engineering Conference (SEC8), Buraydah, Saudi Arabia, Nov , evaporation. Concentration of EPM is 15 % w/w. Percentage of each compound is % w/w for Cyclohexane, THF, Acetone, respectively. This mixture contained EPM was kept waiting in laboratory condition for 4-5 days. CNW in dionized water (10 % w/w) was treated with ultrasonic sonification (Bandelin Sonopuls) for 30 minute at three intervals each lasting for 10 minutes. Ice bath was used to cool the suspension. This suspension with CNW was added into solution with EPM. Thus, the percentage of CNW in EPM is around 1%, then, all mixture was mixed by homogenizator (WiseTis Homogenizer) at 9000 rpm for 15 min. This solution which contains CNW and also the solution without CNW were processed by electrospining system. At the other application, EPM was solved in Cyclohexane, DMF, THF (Solution 2). DMF and THF were used to improve the electrospinnibility. Concentration of EPM is 10 % w/w. Percentage of each compound is % w/w for Cyclohexane, DMF, THF, respectively. This mixture contained EPM was kept waiting in laboratory condition for 4-5 days. CNW in dionized water (10 % w/w) was treated with ultrasonic sonification (Bandelin Sonopuls) for 30 minute at three intervals each lasting for 10 minutes. Ice bath was used to cool the suspension. This suspension with CNW was added into solution with EPM. Thus, the percentage of CNW in EPM is around 15 %, then, all mixture was mixed by homogenizator (WiseTis Homogenizer) at 9000 rpm for 15 min. This solution which contains CNW and also solution without CNW were processed by electrospinning system. D. Electrospinning The electrospinning was carried out by the conventional system shown in Figure 1. The high power was supplied by Matsusada high power supply. The solution was fed by syringe pump (Sıno mdt, sn-50c6/c6t). The needle gauge was 0.80 x38mm. Electrospinning settings for solution 1 are 20 kv, 1.5 ml/h, 15 cm for voltage, feed rate and distance between needle tip and aluminum collector, respectively. Electrospinning settings for solution 2 are 25 kv, 1 ml/h, 15 cm for voltage, feed rate and distance between needle tip and aluminum collector, respectively. E. Scanning Electron Microscopy Scanning Electron Microscopy (SEM, JEOL, Model JSM- 5910LV ) was used to obtain microphotographs of the composite nano fiber with CNW and reference nano fiber without CNW. SEM was operated with an accelerating voltage 20 kv. The sample was sputtered with an approximately 5nm layer of gold/palladium (Au/Pd-80-20%). The size and morphology of nanofibers were examined. III. EXPERIMENTAL RESULTS AND DISCUSSIONS Figure 2 and Figure 3 show composite nanofiber with CNW and reference nanofiber without CNW obtained from solution 1 (Cyclohexane, THF, Acetone), respectively. Figure 4 and Figure 5 show composite nanofiber with CNW and reference nanofiber without CNW obtained from solution 2 (Cyclohexane, DMF, THF), respectively. For solution 1, average values of diameters which are taken from 50 measurements and also maximum, minimum diameter have been shown in Figure 6. For solution 2, diameter of composite electrospun fiber could not be measured since electrospun fiber does not have certain configuration and also spread out. Following observation and results have been obtained: 1- As seen from Figure 2 and Figure 3, there is clear difference on the appearance of composite nanofiber with CNW (Figure 2) and reference nanofiber without CNW (Figure 3). 2-As seen from Figure 2, there is some cavities and protrusions on the surface of the composite nanofiber, compared to reference nanofiber (Figure 3). It may be due to the fact that of agglomeration of CNW and also interaction of slow evaporation of water and quick evaporation of Acetone (low boiling point 56 o C). However, for solution 2, it could not be possible to observe certain configuration for the electrospun composite fiber (Figure 4), although reference electrospun fiber with certain configuration could be obtained (Figure 5). Electrospun composite fiber which is obtained from solution 2 was spread out because of slow evaporation resulted from high boiling point of water and DMF (boiling point of water is 100 o C and boiling point of DMF is 153 o C) 2- During electrospinning of solution 1, occasionally, the tip of needle was clogged because of rapidly evaporation of solvent (low boiling point of Acetone, 56 o C). However, during electrospinning of solution 2, clogging of needle s tip was very seldom, because of high boiling point of DMF, 153 o C. 3-The diameter of both composite nanofiber with CNW and reference nanofiber without CNW change between nano level and micro level. 4- As seen from Figure 4, for solution 1, average diameter of composite fiber is 1.98 micron (coefficient of variation, CV%: 65 %, maximum diameter: 4.88 micron, minimum diameter: 0.55 micron (550 nanometer)), while average diameter of reference fiber is 1.4 micron (coefficient of variation, CV%: 43 %, maximum diameter: 2.5 micron, minimum diameter: 0.33 micron (330 nanometer)). Average diameter of reference electrospun fiber obtained from solution 2 is 1.13 micron (coefficient of variation, CV%: 49 %, maximum diameter: 3,18 micron, minimum diameter: 0,45 micron (450 nanometer)). 5- Diameter and CV value of composite nanofiber is higher than those of reference nanofiber, because of the cavities and protrusions resulted from agglomeration of CNW and also interaction of slow evaporation of water and quick evaporation of Acetone

4 Proceeding of the 8th Saudi Engineering Conference (SEC8), Buraydah, Saudi Arabia, Nov , Fig 2.Composite nanofiber with CNW obtained from solution 1 (Cyclohexane, THF, Acetone) Fig 5. Nanofiber without CNW obtained from solution 2(Cyclohexane, DMF, THF) Fig 3. Nanofiber without CNW obtained from solution 1 (Cyclohexane, THF, Acetone) Fig 6. Diameter of nanofibers obtained from solution 1 (Cyclohexane, THF, Acetone) (maximum, minimum and average diameters) IV. CONCLUSIONS It could be possible to produce composite nanofiber composed of elastomeric polymer and cellulose nano whiskers by electrospinning process. It has been seen that both solvent type and water content are very important parameters for the morphology of the composite electrospun fiber with CNW. In the future studies, the effect of some other production parameters and solution properties on composite nanofiber structure and mechanical and thermal properties of composite nano fiber web will be studied. Fig 4. Nanofiber without CNW obtained from solution 2 (Cyclohexane, DMF, THF) REFERENCES [1] P.K. Baumgarten, Electrostatic spinning of acrylic microfibers, Journal of Colloid and Interface Science, 36, 71-79, 1971 [2] J. Manee-im, M. Nithitanakul, P. Supaphol, Effects of Solvents Properties, Solvent System, Electrostatic Field Strenght and Inotgani Salt Addition on Electrospun Polystyrene Fibers, Iranian Polymer Journal, 15,4, , 2006 [3] T. Jarusuwannapoom, W. Hongrojjanawiwat, S. Jitjaicham, L. Wannatong, M. Nithitanakul, C. Pattamaprom, P. Koombhongse, R.

5 Proceeding of the 8th Saudi Engineering Conference (SEC8), Buraydah, Saudi Arabia, Nov , Rangkupan, P. Supaphol, Effect of Solvents on Electro-spinnability of polystyrene solutions and morphological appearance of resulting electrospun polystyrene fibers, European Polymer Journal, 41, , 2005 [4] G.T. Kim, Y.J. Hwang, Y.C. Ahn, H.S. Shin, J.K. Lee, C.M. Sung, The Morphology of Electrospun Polystyrene Fibers, Korean Journal of Chemical Engineering, 22, 1, , 2005 [5] J. Junkasem, R. Rujiranavit, P. Supaphol, Fabrication of α-chitin whiskers-reinforced poly(vinyl alcohol) nanocomposite nanofibers by electrospinning, Nanotechnology, 17, , 2006 [6] P. Lu, Y.L. Hsieh, Cellulose Nanocrystal-filled poly(acrylic acid) nanocomposite fibrous membranes, Nanotechnology, 20, 1-9, 2009 [7] M.S. Peresin, Y., Habibi, J.O. Zoppe, J.J., Rojas, O.J. Pawlak, Nanofiber Composites of Polyvintl Alcohol and Cellulose Nanocrystals: Manufacture and Characterization, Biomacromolecules, 11, , 2010 [8] O.J. Rojas, G.A. Montero, Y. Habibi, Electrospun Nanocomposites from Polystyrene Loaded with Cellulose Nanowhiskers, Journal of Applied Polymer Science, 113, , 2009 [9] N.E. Marcovich, M.L. Auad, N.E. Bellesi, S.R. Nutt, M.I. Aranguren, Cellulose Micro/Nanocrystals Reinforced Polyurethane, J.Mater. Res. 21, 4, , 2006 Youjiang Wang;.BcS(1982), MSc (1985), PhD (1989) Textile Engineering of Donghua University, mechanical Engineering of Massachusetts Institute of TechnologySchool. He works at the Material Science and Engineering of Georgia Institute of Technologyas a Professor. Current research topics are mechanics of composite, nanofiber spinning, synthetic filament production Nuray Uçar ; born in Istanbul,Turkey,1968. BcS (1989), Ms (1992), PhD (1996) Textile Eng. Istanbul Technical University. She works at the Textile Engineering department of Istanbul Technical University as a Professor. Current researches on Textile, Nano fiber, Nano polymer composite, Smart textile. She has also many of paper and several book related with nano fiber, nano polymer composite, smart textile, image processing&analyses, artificial intelligient, mechanics of textile material, knitting technology. Dr. Ucar has a several award from TUBITAK and ITU. She has a two patent and one patent application. Onur Ayaz; Turkey BcS (2010) Textile Eng. Istanbul Technical University. He is Ms student at Nano Science and Tech. Istanbul Technical University. Current researches are Nanofibers, Nano polymer composites. Mustafa Öksüz; Turkey,1969. BcS (1992), Ms (1995), PhD (1999) Dept. of Metal Education Marmara University. He works at the Metal Education department of Marmara University and Yalova University Polymer Eng. Dept., Associated Professor. Current researches on polymer composites, polymer processing Ayşen Önen; Turkey, 1962.BcS(1983), MSc (1986), PhD (1990) Inst. Of Science and Technology Chemistry Dept. Istanbul Technical University. She works at the Faculty of Sciences&Technology, Department of Chemistry as a Professor. Current researches on polymeric materials, synthesis& applications, polymer coatings, polymeric nano composites Elif Rafiye Bahar; Turkey BcS (2009) Chemical Eng. Yildiz Technical University. She is Ms student at Polymer Science and Tech. Istanbul Technical University. Current researches are Nanofibers, Nano polymer composites. Mehmet Ucar ; Tukey,1968. BcS (1990) Mech. Edu. Marmara Univ., MsC (1992) Mech. Eng. Marmara Univ. and PhD(1995) Mech. Eng. Marmara Univ. Istanbul-Turkey. Machine design and Manufacturing, Vehicle Design and Power Transmission Systems. He works on Kocaeli Univ. Current researches on the machine design, shape optimization, fatigue and failure analysis and vehicle design. Ali Demir;1959, BSc (1982) in Mechanical Eng., MSc (1984) in Design Eng., PhD(1987) in Textile Eng, at Loughborough University of Tech., England. He works as a professor at Textile Engineering Department of Istanbul Technical University. Current research topics are filament yarn production and texturing, technical textiles, nanofibre spinning and development, photovoltaic fibers.