The International Istanbul Textile Congress 2013 May 30th to June 1th 2013, Istanbul, Turkey

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ELECTROSPINNING CELLULOSE AND OTHER POLYMER FIBRE PRECURSORS FOR CARBON FIBER PRODUCTION

S.J. EICHHORN1, L. DENG2, R.J. YOUNG2, I.A. KINLOCH2, A. LEWANDOWSKA1

1College of Engineering, Maths & Physical Sciences, University of Exeter, Devon, UK 2 School of Materials, University of Manchester, Manchester, UK.

s.j.eichhorn@exeter.ac.uk

Abstract: This talk will discuss some work carried out to electrospin cellulose and other polymer (PAN) precursors for the production of carbon fibres. Cellulose acetate is first electrospun and the fibres are aligned using a mandrel to collect the filaments. Carbon nanotubes to nucleate the growth of graphite crystals are also included. Deacetylation of the cellulose acetate nanofibres is carried out to produce pure cellulose fibres. These fibres are then carbonised at a range of temperatures to induce both stabilisation and then subsequently graphitisation. The use of catalyst materials is discussed inducing interesting carbon forms such as polygonal graphite crystals on the surface of the fibres. It is also shown how the fibres can be deposited in non-woven, woven and oriented geometries, opening up the potential for textile reinforced materials. Keywords: Carbon, Fibers, Cellulose, Electrospun 1. Introduction Carbon fibres are amongst the lightest inorganic materials on earth, being comprised entirely of one element, carbon. Their development can be traced back to the production of light-bulb filaments by Edison, who originally used cotton and bamboo. The history of carbon fibre production from cellulose dates back to the middle part of last century when Union Carbide ran a programme of production from cellulose fibres [1,2]. This work led to a very successful programme of research and the development of products including a woven textile rocket nozzle cone from a cellulose precursor. Subsequent to this polyacrylonitrile and pitch-based fibres were first developed in Japan [3,4] and then took over most production in the 1970s and onwards. However, in recent times there has been renewed interest in the use of cellulose (and lignin) for the production of carbon fibres. This renewed interest stems from the fact that there is a general trend towards less reliance on oil-based feed-stocks in general for the production of materials, and from the fact that the PAN produces some toxic waste gases that are becoming harder to justify in an environmentally conscious world. The present paper focusses on the developments [5] at the groups based in Manchester and Exeter on the production of carbon fibres from cellulose and PAN produced using an electrospinning process. 2. Materials and Methods Cellulose acetate (CA, Avg. Mol. Wt. = 100,000 g mol-1), acetone, N, N-dimethylacetamide (DMAc) and poly(acrylonitrile) (PAN, Avg. Mol. Wt. = 78,000-80,000 g mol-1) were purchased from Sigma-Aldrich and ethanol, NaOH and potassium hydroxide (KOH) were purchased from Fisher Scientific. Multi-walled nanotubes (MWNTs) were purchased from Nanocyl (Belgium) Ltd. Solutions of nanotubes and dissolved cellulose or PAN were prepared and ultrasonicated in a sonic bath for 12h. In the both polymers the MWNTs content was 1wt% relative to the polymers. Electrospinning was carried out using a customised rig with spinning voltages ranging between 10 and 16 kV. A range of flow rates and needle to collector distances were used to collect the fibres. The fibres were both collected in a mat and also using a stationary plate. In the case of the CA fibres they were deacetylated prior to carbonisation to regenerate to cellulose. Carbonisation of the fibres proceeded by first stabilising them at a temperature in the range 200-300 °C in air, followed by a 60 minute isotherm at the final maximum temperature. The fibres were then carbonized by heating at a rate of 10°C min-1 for, followed by a 150 minute isotherm at 1000 °C in an argon atmosphere. Heat treatments of the fibres were carried out using a Carbolite CTF16/75 furnace. The mats of fibres were

The International Istanbul Textile Congress 2013 May 30th to June 1th 2013, Istanbul, Turkey

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then activated in a steam/argon (30% vol.) atmosphere at 800 °C for 1 hour to impart a porous structure and a large surface area to the fibres. Raman spectra of the fibres were then recorded using a Renishaw system 1000 microscope system to reveal the carbonised structures. 3. Results Typical SEM micrographs of the fibres are shown in Figure 1, showing fibres both containing MWNTs and those without any inclusions. It is clear that a uniform fibre can be produced using this method. Typical Raman spectra of the fibres, both before and after the inclusion of MWNTs are shown in Figure 2. The existence of Raman bands consistent with the presence of the MWNTs are noted. Post carbonisation it was found that the fibres exhibited some graphitization (from TEM and Raman analysis) suggesting that the nanotubes act as a nucleation of graphitic zones. (a)

(b)

Figure 1. SEM images of (a) neat cellulose and (b) cellulose/MWNT nanofibres.

500 1000 1500 2000 2500 3000

Inte

nsity

Raman shift (cm-1)

Cell/MWNT Cell

Figure 2. Typical Raman spectra of neat electrospun cellulose and cellulose/MWNT nanofibres.

4. Conclusions It has been shown that both cellulose and PAN can be electrospun in the presence of multiwalled carbon nanotubes. The presence of the nanotubes alters the Raman spectra of the fibres. Their presence appears to nucleate graphitic zones upon heat treatment.

Acknowledgements The authors wish to thank the EPSRC for funding and one of the authors (SJE) for COST Action MP1206 for travel funding.

The International Istanbul Textile Congress 2013 May 30th to June 1th 2013, Istanbul, Turkey

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References [1] Tang, M.M., Bacon. R. Carbonization of Cellulose Fibers. 1. Low Temperature Pyrolysis, Carbon, 2

(1964) No.3, pp. 211-220. [2] Bacon, R., Tang, M.M. Carbonization of Cellulose Fibers. 2. Physical Property Study, Carbon, 2 (1964)

No. 3, pp. 221-225. [3] Shindo, A. Studies on Graphite Fibre, Report 317 (1961), Government Industries Research Institute,

Osaka. [4] Otani, S., Yamada, K., Koitabas, T., Yokoyama, A. On Raw Materials of MP Carbon Fiber, Carbon, 4

(1965), pp. 425-432. [5] Deng, L., Young, R.J., Kinloch, I.A., Zhu, Y., Eichhorn, S.J. Carbon Nanofibres Produced from

Electrospun Cellulose Nanofibres, Carbon, 58 (2013), pp. 66-75.