Tuning hydroxyl groups for quality carbon fiber of lignin

Lignin-based carbon fiber is struggling to apply into industry, due to its low mechanical performance. Our concept is that lignin chemical features impact its interactions with guest molecules and crystallite formation in carbonization, and thus carbon fiber mechanical performance. We recently demonstrated that fractionating lignin polymers according to their molecular weight enhanced the elastic modulus, but the process used costly enzyme and dialysis tubes and difficult to scale up. Here we present a simple one-pot lignin processing technology that only precipitates lignin into aqueous acid. Our approach is based on manipulating lignin hydroxyl groups, which improves multiple hydrogen bonding and linear chemical linkages to enhance molecular interactions and thereby carbon fiber crystallite structures. Carbon fiber out of the presented technique has elastic modulus comparable with that derived from the costly enzymatic and dialysis fractionation methods, and even the traditional PAN-based carbon fibers. The presented technology offered a route to make quality lignin-based biorenewable carbon fiber by regulating fiber precursor at the molecular level, which has a broad application in upgrading industrial lignin waste of paper-making industry and lignocellulosic biorefinery.