Influence of heat treatment conditions on the structure of hollow carbon fibers prepared from solid PVA fibers using iodine pretreatment

The influence of heating conditions on the structure of hollow carbon fibers (H-CFs) during their fabrication from solid poly(vinyl alcohol) (PVA) fibers is reported. The hollow structure of PVA-derived carbon was formed by selective iodination and subsequent stabilization of precursor PVA fiber close to the fiber surface followed by carbonization. The broadening of X-ray diffraction peaks due to disorder and the small size effects of the (002) plane were strongly reduced by increasing the heat treatment temperature (HTT) from 800 to 3000 °C, but the asymmetric shape of (10) and (110) reflections suggests turbostratic layer stacking. The increase of HTT to 3000 °C increased the degree of graphitization evident from the decrease of interplanar spacing from 0.360 to 0.338 nm and the intensity ratio of D to G bands in Raman spectra from 0.93 to 0.58. The crystallite size, orientation and electrical conductivity of the resultant H-CFs were also improved with higher HTT. Besides, the size of the hollow core was also influenced by the HTT and both wall thickness and carbon yield decreased with higher HTT. The core of the H-CFs could be easily filled with polymer by bulk polymerization of monomer.