The polymer blend technique has been used widely in the polymer materials field to improve properties of polymers [1], [2] and [3]. We successfully applied the technique to the design of fine carbon materials. The development process from porous carbon fiber to carbon nanotubes (CNTs) is initially described, since their developments are closely related to one another and the process may suggest the direction of subsequent development in the future.
The idea originated from research work on the development of a novel preparation method for porous carbon fibers (activated carbon fibers, ACF). Commercially available ACFs are prepared by oxidizing carbon fibers under steam or CO2 gas at a high temperature around 900 °C [4]. However, since more than half the carbon fiber is consumed to develop the porous structure, the price of ACF is high. We investigated the polymer blend technique to develop a new economical preparation method instead of the conventional techniques [5], [6] and [7].
The method of ACF preparation is shown in Fig. 1. Two kinds of polymers are used as starting materials, viz. polymers with and without carbon residue after heating under an inert atmosphere, and are referred to as a carbon precursor polymer (CPP) and a thermally decomposable polymer (TDP) in this text, respectively. Fine TDP particles are dispersed throughout a CPP matrix. The blend texture is elongated extensively during a spinning process, in which the polymer blend is pulled out through a small hole of less than 1 mm in diameter. Therefore thin and long pores aligned parallel to the fiber axis are left after removing the TDP during the carbonization process.