Effects of Refining and Fiber Type on the Electrical Properties of Environmentally Friendly Conductive Cellulose Paper

Economic growth and the expanding demands of modern technologies have traditionally relied on processes and materials that harm the environment. For this reason, renewable biopolymers such as cellulose and its derivatives, together with carbon-based conductive fillers like carbon nanotubes, graphite, graphene, and carbon black, are at the forefront of the transition from toxic materials to sustainable alternatives. Building on previous work that developed a conductive substrate with fully water-based carbon black coating using sodium-carboxymethyl cellulose (CMC) as a non-toxic binder and dispersant, this study investigates how papermaking variables, such as fiber refining levels and fiber type, influence the electrical performance of conductive cellulose paper. Handsheets were prepared from 100% hardwood (HW), 100% softwood (SW), and hardwood–softwood blends at different refining levels. They were first characterized by surface roughness and other physical properties, and then coated on their rough and smooth sides with the carbon black/CMC formulation. After coating, the coat weight and sheet resistance were assessed. The results showed that fiber type, refining, and blend ratio significantly affect coating retention and conductivity. Unrefined 100% hardwood substrates provided the most favorable and predictable performance: the rough side with a single coating layer reached 4.55 kΩ/sq, and multilayer coatings reduced the estimated sheet resistance to 0.009 kΩ/sq while preserving flexibility and mechanical integrity. These outcomes appear to be closely related to the variations in coating weight observed for those samples. Certain blends were found to be comparable, as the rough side of an unrefined sheet containing 65% hardwood (35% softwood) achieved 4.77 kΩ/sq with a single coating layer, closely matching the 100% hardwood reference under the same conditions.