The quest for sustainable materials has stimulated extensive research into biobased carbon fibers, with lignin–cellulose composite fibers emerging as promising candidates. However, challenges persist, for example, the leaching of lignin during fiber spinning, which limits the process efficiency and carbon fiber yield. Thus, this work aims to understand the causes and the impact of lignin leaching. The lignin was varied in terms of source, extraction technique, and molecular weight, and the lignin yield, fiber morphology, and mechanical performance of cellulose–lignin composite fibers were elucidated. The results demonstrated that the lignin’s functional groups significantly influence lignin yield in spun fibers, and a high molecular weight is beneficial. An expressive decrease in lignin yield was observed for lignin with a higher content of polar functional groups such as carboxylic acid groups and a lower content of condensed lignin moieties. Furthermore, leaching of lignin was also associated with the observed defects and deteriorated mechanical properties of the precursor fiber. Addressing these challenges is thus critical for maximizing the potential of biobased carbon fibers, emphasizing the need to mitigate lignin leaching and optimize fiber processing parameters for enhanced fiber quality and performance.
Bengtsson et al. (Wed,) studied this question.