Skipping Oxidative Thermal Stabilization for Lignin-Based Carbon Nanofibers

Abstract

Oxidative thermal stabilization is considered a critical process before carbonization to prevent fusion of fibers, while aiding in the formation of homogeneous fiber cross sections during carbon fiber manufacturing. In this study, we investigated the impact of nanocrystalline cellulose (NCC) on the thermal, electrical, and mechanical properties of electrospun lignin-derived carbon nanofibers when the oxidative thermal stabilization step was skipped. Results showed that by adding small amounts of NCC (up to 5 wt %), uniform lignin-based carbon nanofibers were prepared with direct carbonization processes without oxidative thermal stabilization. SEM images revealed that NCC filled lignin carbon nanofibers retained their fibrous morphology after the heat treatment, dependent upon the carbonization rate. Further, carbonization conditions were exploited to form a unique interconnected structure, which increased the electrical conductivity of carbon nanofiber mats from 5 to 35 S/cm. Dynamic thermomechanical analysis of NCC/lignin nanofiber mats showed a reduction of the tan δ peak during the glass transition indicating NCC restricted the molecular mobility of lignin’s chains. Through thermal rheological evidence, this study revealed significant interaction of NCC and lignin blends that prevented the fusion of nanofibers during heat treatment. This study is unique that it provides a method to reduce processing time and energy cost associated with carbon fiber production, while controlling fiber mat structure.