Lignin carbon fiber: advancement from precursor chemistry to manufacturing

Lignin, as a renewable biopolymer from plant cell walls and also a byproduct stream from biorefining and paper industry, has displayed its great potential for producing sustainable and cost-effective carbon fiber. Nevertheless, its commercialization is still largely hindered by the poor mechanical performance, since the underlying science for processing-structure-properties relationship from lignin precursor chemistry to manufacturing technologies is still under well-understood. In this review, we thus comprehensively reviewed the advancements in lignin chemistry and the technologies to tailor it for superior carbon fiber, especially focusing on the molecular structural features of lignin and its derived precursor fiber, carbon fiber, and graphited carbon fiber. In addition, we also systematically reviewed the fundamental chemistry for the synthesis of lignin-based carbon fiber, such as spinning, thermostabilization, carbonization, and graphitization, as well as the fundamentals and technologies of surface processing of as-prepared carbon fibers, including oxidation, coating, and plasma treatment. Revisiting these fundamentals could inspire innovations in lignin-based carbon fibers to enhance their performance and advance toward industrialization.