SEM/STM studies on the surface structure of a novel carbon fiber from lyocell

The surface structure and strengths of two types of cellulose-based carbon fibers, rayon-based carbon fiber (RCF) and lyocell-based carbon fiber (LCF), were investigated through scanning electronic microscopy (SEM) and scanning tunneling microscopy (STM). SEM delineated much smoother surface for LCF, while rougher surface with obvious cracks and grooves for RCF. It is believed that the difference of surface structure between these two carbon fibers results in a decrease in tensile strength for RCF. It can be found from the image of STM (500 nm × 500 nm) that the surfaces of LCF are characterized by bulk structure. Furthermore, it is proven that the bulk structure is composed of the smaller slug-like microstructures, each of which has a width of about 25 nm and length of 150 nm aligned with an angle at 45° to fiber axis when the observation scales down to 50 nm × 50 nm. The distance between two adjacent carbon atoms of LCF estimated by section analysis of STM reveals that no hexagonal carbon ring is formed on the surface of LCF examined.