Uncovering the Structural Defect Effect on Thermal Transport in Carbon Fiber Mat by Thermal Reffusivity Dependence on Temperature

Low-cost carbon fiber based on eco-friendly precursors is very sought. Although much work focuses on the manufacturing process and mechanical properties improvement of lignin-based carbon fiber, the thermal and electrical properties are seldom investigated. This work reports on systematic investigation about the thermal and electrical properties of lignin/PAN-based carbon fiber mat (CFM). The carbon fiber mat is produced by an industrially available hydrolytic lignin. At room temperature, the thermal conductivity of CFM is determined to be 0.10–0.32 W·m −1 ·K, indicating that the CFM is a promising candidate for thermal insulation. Furthermore, the structural defect effect on thermal and electrical properties is intensively studied. It is found that the electrical properties of five samples are parallel to each other as temperature is higher than 140 K, which directly indicates the defect effect on electrical transport. For the thermal transport, a new parameter: thermal reffusivity (inverse to thermal diffusivity), is defined which is analogously to the electrical resistivity. The thermal reffusivity theory analyzes the structural defect level quantitatively. The thermal reffusivity theory will guide to tailor the grain size and thermal properties of fabricated materials in the future.