Phenolic Resin-Based Carbon Thin Fibers Prepared by Electrospinning: Additive Effects of Poly(vinyl butyral) and Electrolytes

Abstract

Phenolic resin-based carbon nanofibers with a diameter of about 110 nm, the highest electrical conductivity of 5.29 S/cm and highest BET specific surface area of 792.7 m 2 /g were prepared by electrospinning, followed by successive carbonization. The addition of a high-molecular-weight polymer, poly(vinyl butyral) (M w ¼ 340;000), and electrolytes, pyridine and sodium carbonate, to the phenolic resin/MeOH solution can effectively form a thinner smooth fiber by electrospinning, and then the as-spun fabrics were successfully carbonized at 900 C for 2 h. Thus the prepared carbonized fabrics are very flexible and showed a thinner diameter, a higher conductivity and a higher specific surface area as already described.KEY WORDS: Electrospinning / Carbon Nanofiber / Phenolic Resin / Flexibility / Recently, carbon nanofibers with a high conductivity, chemical stability, and mechanical strength have attracted much attention in many fields including electrodes, capacitors, emitters, catalyst supports, sorbents, filter media, and reinforcements.1,2 It has been pointed out that a smaller diameter gives rise to the higher electrical conductivity of the single carbon fiber and higher specific surface areas of carbon fabrics.3 In addition, a two-or three-dimensional carbon nanofiber network with a high conductivity is a promising material for flexible electronic and optical devices.4 Therefore, carbon nanofibers or nanofibrous fabrics with thinner diameters are required.Electrospinning is a straightforward method based on an electrohydrodynamic process for forming continuous thin fibers. [5][6][7] The advantages of electrospinning are (i) forming nano-microscaled fibers and (ii) the one-step forming of the two-or three-dimensional nanofiber network structure. On the other hand, the internal structures are irregular due to rapid solidification during electrospinning.8 Therefore, the reported mechanical properties of the carbonized fibers by electrospinning have not been very good. To overcome this disadvantage, we have reported the preparation of novolac phenolic resin-based carbon fabrics composed of microscaled fibers by electrospinning. 9 The major advantage of the phenolic resin as the precursor of the carbon fibers is thermal stability leading to a dimensional stability after carbonization (curing of the as-spun fibers also improves the thermal stability). Another advantage is the high microporosity of the carbonized fibers (phenolic resin is well-known as a material for activated carbon). Therefore, the phenolic resin-based carbon fabrics were dimensionally stable, flexible, and highly porous. However, since the molecular weight of the phenolic resin is not very high, the spinnability is low and the formation of a fiber thinner than a micron has been difficult to date. 9For electrospinning, the fiber diameter depends on the solution properties (e.g., viscosity, conductivity, surface tension, permittivity, and boiling point) and/or operating conditions (e.g., applied voltage, nozzle-to-target distance, and flow rate). Part...

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