Aqueous Dispersion of Carbon Fibers and Expanded Graphite Stabilized from the Addition of Cellulose Nanocrystals to Produce Highly Conductive Cellulose Composites

Conductive cellulose composites have received much attention as emerging materials due to their unique properties, such as biodegradability and flexibility. However, the achievable levels of conductivity of these cellulose composites are generally low due to the intrinsically nonconductive properties of cellulose. In this study, cellulose nanocrystals (CNC) were applied for preparation of a carbon fibers/expanded graphite (CF/EG) dispersion which was coated on cellulose paper to prepare highly conductive cellulose composites. Such composite materials were characterized based on transmission electron microscopy (TEM) and field emission scanning electron microscopy (FE-SEM) observation, FT-IR, XPS, and XRD and by determining the zeta potential, particle size, contact angle, and rheological behavior. It was found that the addition of CNC resulted in a significant improvement in the stability of the CF/EG dispersion. These results were explained by the following facts: (1) CNC improved the surface charge of the CF and EG due to the presence of negatively charged groups on the CNC surface, and (2) CNC increased the wettability of the CF and EG due to large availability of hydroxyl groups from CNC. The as-prepared CF/EG/CNC dispersion was then applied by coating cellulose paper surfaces, and the obtained papers presented superior conductivity and high flexibility.