Synthesis and characterization of multiwalled CNT–PAN based composite carbon nanofibers via electrospinning
© Kaur et al. 2016
Received: 22 December 2015
Accepted: 24 March 2016
Published: 19 April 2016
Electrospun fibrous membranes find place in diverse applications like sensors, filters, fuel cell membranes, scaffolds for tissue engineering, organic electronics etc. The objectives of present work are to electrospun polyacrylonitrile (PAN) nanofibers and PAN–CNT nanocomposite nanofibers and convert into carbon nanofiber and carbon-CNT composite nanofiber. The work was divided into two parts, development of nanofibers and composite nanofiber. The PAN nanofibers were produced from 9 wt% PAN solution by electrospinning technique. In another case PAN–CNT composite nanofibers were developed from different concentrations of MWCNTs (1–3 wt%) in 9 wt% PAN solution by electrospinning. Both types of nanofibers were undergone through oxidation, stabilization, carbonization and graphitization. At each stage of processing of carbon and carbon-CNT composite nanofibers were characterized by SEM, AFM, TGA and XRD. It was observed that diameter of nanofiber varies with processing parameters such as applied voltage tip to collector distance, flow rate of solution and polymer concentrations etc. while in case of PAN–CNT composite nanofiber diameter decreases with increasing concentration of CNT in PAN solution. Also with stabilization, carbonization and graphitization diameter of nanofiber decreases. SEM images shows that the minimum fiber diameter in case of 3 wt% of CNT solution because as viscosity increases it reduces the phase separation of PAN and solvent and as a consequence increases in the fiber diameter. AFM images shows that surface of film is irregular which give idea about mat type orientation of fibers. XRD results show that degree of graphitization increases on increasing CNT concentration because of additional stresses exerting on the nanofiber surface in the immediate vicinity of CNTs. TGA results shows wt loss decreases as CNT concentration increases in fibers.
KeywordsPolyacrylonitrile Nanocyl multiwalled carbon nanotubes
Electrospinning is a most efficient technique to generate fibers with submicron diameters. Electrospun nanofibers mats are more promising because of high surface area and porosity, which have applications in air filtration, tissue engineering, drug delivery, and energy storage materials (Doshi and Reneker 1995; Formhals 1944). Reliable production of porous nanofibers in a simple and inexpensive way has been attempted by number of groups (Xia and Li 2006) showed that, by using a coaxial spinneret with miscible solvents and immiscible polymers, highly porous fibers could be obtained (Xia and Li 2006). Since the beginning of this century, researchers all over the world have been re-looking at a century old process (Cooley and Morton 1902) currently it is known as electrospinning (Hagewood 2004). Probably unknown to most researchers for most of the last century, electrospinning is able to produce continuous fibers from the submicron diameter down to the nanometer diameter. It was not until the mid-1990s with interest in the field of nanoscience and nanotechnology that researchers started to realize the huge potential of the process in nanofiber production (Doshi and Reneker 1995). Nanofibers and nanowires with their huge surface area to volume ratio, about a thousand times higher than that of a human hair, have aspect area.
Carbon fibers are manufactured through heating and stretching treatments (Shenoy et al. 2005). Polyacrylonitrile (PAN) and pitch are the two most common raw products used to produce carbon fibers. PAN is a synthetic fiber that is pre manufactured and wound onto spools, and pitch is a coal-tar petroleum product that is melted, spun, and stretched into fibers. The production of carbon nano fibrils will achieve a unique property (Mechanical, Electrical and Physical) by keeping the same amount of crystallite size from core to skin and increasing the surface area per unit volume which mimic the same structure of MWCNT (Saito et al. 1998).
This paper reports our findings on testing this concept by electrospinning mixtures of Chopped PAN co-polymer micro fibers of diameter 12.5 µm having polyacrylonitrile with a 6 % monomer methyl methacrylate and N,N-dimethylformamide (DMF) of 99 % purity (B. Pt. = 157 °C) and also Functionalized Carbon Nanotubes (CNT) are used as fillers (Haddon and Itkis 2008). Fibers uniformity and diameter (75–1500 nm) have been shown to increase with increasing concentrations of CNT by controlling solution and processing parameters in whole study (Haddon and Itkis 2008).
Chopped PAN co-polymer micro fibers of diameter 12.5 µm having polyacrylonitrile with a 6 % monomer methyl methacrylate was used as source of PAN. Molecular weight of PAN is 53.0626 ± 0.0028 g/mol, C 67.91 %, H 5.7 %, N 26.4 %.
N,N-dimethylformamide (DMF) of 99 % purity (B. Pt. = 157 °C) from Fisher Scientific.
Functionalized Carbon Nanotubes (CNT) from Nanocyl.
Preparation of PAN nanofibers
The 9 wt% PAN copolymer solution was prepared by taking 0.9 g chopped PAN microfibers was socked in 9.1 g of DMF and mix with glass rod. The mix was sonicated in ultrasonicator till it gives a clear solution and stirred continuously on magnetic stirrer for 5 h to mix well the contents.
Preparation of PAN–CNT composite nanofibers
PAN–CNT (1–3 wt%) 9 % solutions were prepared in following steps: at first 0.01 g functionalized CNTs were dispersed in N,N-dimethylformamide. The mixture was kept in sonicator for 5–8 h to break bundles of CNTs and magnetic stirring to disperse well CNTs in DMF. A good dispersion was achieved in 7 h. Calculated quantity of PAN copolymer chopped microfibers were added in dispersion solution and kept on magnetic stirrer for overnight to mix well the polymer in CNT dispersion. Solution was sonicated for 1 h and then electrospun with ESPIN instrument at voltage 15 kV, flow rate 0.2 ml/h, drum speed 2000 rpm, distance 15 cm to produce PAN–CNT composite nanofibers. It was difficult to prepare solution using higher concentration of CNT. The problem faced was that, in high quantity of CNTs polymer not get dispersed well and form a solid mass. So both CNTs and polymer were dispersed in DMF separately. CNTs and DMF mixture was sonicated for 1 h till all bundles breakup and then kept on magnetic stirrer, good dispersion observed in sun light. Polymer was soaked in DMF well and sonicated for 1 h. Then it was kept on magnetic stirrer till a clear solution was obtained. Same procedure was carried out for PAN–CNT concentrations (2–3 wt%).
Both types of nanofibers were undergone through oxidation, stabilization, carbonization and graphitization. At each stage of processing of carbon and carbon-CNT composite nanofibers were characterized by SEM, AFM, XRD and TGA.
Results and discussions
In the present study we have successfully used the electrospinning for the synthesis of PAN–CNT carbon nanofibers. SEM images shows that the fiber diameter varies from 75 to 1500 nm on increasing concentration of CNT. The presence of black color in fiber, it indicates the presence of CNTs in nanofibers. AFM images show that the surface morphology of the composite nanofibers is smooth at lower concentration of MWCNT but rough at high concentration of MWNTs. Since the MWNTs possess a high electron density compared with the PAN polymer matrix, the nanotubes appear as darker tubular structures embedded in the PAN nanofibers. It is also seen that on Stabilization fibers diameter decreases due to shrinkage in fibers. Degree of graphitization for PAN nanofibers is −20 % and for PAN–CNT nanofibers is −41.86. Degree of graphitization increases due to presence of CNT in fibers. TGA results shows that wt loss is small in case of PAN nanofibers because of high surface area of nanofibers while in case of carbonized PAN–MWCNT carbon nanofibers wt loss is small as comparison to PAN–CNT stabilized because of increase in stability in structure, and removal of nitrogen, water and hydrogen. HCN and another gases and also carbon content increases on carbonization.
All authors have equal contribution in carrying out research work as well as in writing work of manuscript. All authors read and approved the final manuscript.
The authors declare that they have no competing interests.
Open AccessThis article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made.
- Baumgarten PK (1971) Electrostatic spinning of acrylic microfibers. J Colloid Interface Sci 36:71–79View ArticleGoogle Scholar
- Ko F, Gogots Y, Ali A, Naguib N, Ye H, Yang GL, Li C, Wills P (2003) Electrospinning of continuous carbon nanotubes-filled nanofibers yarns. Adv. Matter 15(4):1161–1165Google Scholar
- Cooley, Morton WJ (1902) Method of dispensing fluids, US Patent 705,691Google Scholar
- Doshi J, Reneker DH (1995) Electrospinning process and application of electrospun fibers. J Electrost 35:151–160View ArticleGoogle Scholar
- Drozin VG (1955) J Colloid Sci 10:158–164Google Scholar
- Formhals A (1944) US patent, 2,349,950Google Scholar
- Guo T, Nikolaev P, Thess A, Colbert DT, Smalley RE (1995) Catalytic growth of single-walled manotubes by laser vaporization. Chem Phys Lett 243(1):49–54View ArticleGoogle Scholar
- Gupta P, Wilkes GL (2003) Some investigations on the fiber formation by utilizing a side-by-side bicomponent electrospinning approach. Polymer 44:6353–6359View ArticleGoogle Scholar
- Haddon R, Itkis M (2008) Measurement issues in single wall carbon nanotubes. NIST, pp 20Google Scholar
- He JH, Wan YQ, Yuc JY (2004) Application of vibration technology to polymer electrospinning. Int J Nonlinear Sci Numer Simul 5:243–248Google Scholar
- Hagewood J (2004) Production of polymeric nanofibers. Inter Fiber J 19(1):48–50Google Scholar
- Hendricks CD, Carson RS, Hogan JJ, Schneider JM (1964) Photomicrography of electrically sprayed heavy particles. AIAA J 2:733–737View ArticleGoogle Scholar
- Huang Z-M, Zhang Y-Z, Kotaki M, Ramakrishna S (2003) A review on polymer nanofibers by electrospinning and their applications in nanocomposites. Compos Sci Technol 63:2223–2253View ArticleGoogle Scholar
- Khil MS, Bhattarai SR, Kim HY, Kim SZ, Lee KH (2005) Novel fabricated matrix via electrospinning for tissue engineering. J Biomed Mater Res B 72:117–124View ArticleGoogle Scholar
- Kim J-S, Reneker DH (1999) Mechanical properties of composites using ultrafine electrospun fibers. Polym Compos 20:124–131View ArticleGoogle Scholar
- Ramakrishna S, Fujihara K, Teo WE, Lim TC, Ma Z (2005) An introduction to electrospinning and nanofibers. World Scientific Publishing C. Pte. Ltd., 7–15, 279–338Google Scholar
- Saito R, Dresselhaus G, Dresselhaus MS (1998) Physical properties of carbon nanotubes, vol 35. Imperial College Press, London, pp 73–81View ArticleGoogle Scholar
- Samatham R, Kim KJ, Nam J-D, Whisman N, Adams J (2006) Electrospun nanoscale polyacrylonitrile artificial muscle. Smart Mater Struct 15:N152–N156View ArticleGoogle Scholar
- Shenoy SL, Bates WD, Frisch HL, Wnek GE (2005) Role of chain entanglements on fiber formation during electrospinning of polymer solutions: good solvent, non-specific polymer–polymer interaction limit. Polymer 46:3372–3384View ArticleGoogle Scholar
- Taylor GI (1969) Electrically driven jets. Proc R Soc Lond Ser A 313:453–475View ArticleGoogle Scholar
- Teraoka I (2002) Polymer solutions, an introduction to physical properties. Wiley, New YorkGoogle Scholar
- Xia Y, Li D (2006) US20060226580Google Scholar
- Yarin AL, Koombhongse S, Reneker DH (2001) Taylor cone and jetting from liquid droplets in electrospinning of nanofibers. J Appl Phys 90:4836–4846View ArticleGoogle Scholar
- Zhou Z, Liu K (2010) Graphitic carbon nanofibers developed from bundles of aligned electrospun PAN nanofibers containing phosphoric acid. Polymer 51:2360–2367View ArticleGoogle Scholar