Highly conductive and porous lignin-derived carbon fibers.

Bio-based carbon fibers derived from lignin have gained significant attention due to their diverse and renewable sources, ease of extraction, and low cost. However, the current limitations of low specific surface area and insufficient electrical conductivity hinder the widespread application of lignin-derived carbon fibers (LCFs). In this work, highly conductive and porous LCFs are developed through melt-blowing, pretreatment, and carbonization processes. The effects of the carbonization temperature and heating rate on the structures and properties of the LCFs are systematically investigated. The resultant LCFs exhibit high electrical conductivity (71 400 S m-1) and a large specific surface area (923 m2 g-1). The assembled lithium-ion battery based on the LCF anodes demonstrates a long cycle life of >800 cycles and a high specific capacity of 466 mA h g-1. The findings of this study hold practical significance for promoting the utilization of lignin in the fields of energy storage, adsorption, and beyond.

Lignin-based carbon fibers: Insight into structural evolution from lignin pretreatment, fiber forming, to pre-oxidation and carbonization.

Lignin remains the second abundant source of renewable carbon with an aromatic structure. However, most of the lignin is burnt directly for power generation, with an effective utilization rate of <2 %, making value addition on lignin an urgent requirement. From this perspective, preparation of lignin-based carbon fibers has been widely studied as an effective way to increase value addition on lignin. However, lignin species are diverse and complex in structure, and the pathway that enables changes in lignin structure during pretreatment, fiber formation, stabilization, and carbonization is still uncertain. In this review, we condense the common structural evolution route from the previous studies, which can serve as a guide towards engineered lignin carbon fibers with high performance properties.

Piezoresistive Fibers with Large Working Factors for Strain Sensing Applications.

Piezoresistive fibers with large working factors remain of great interest for strain sensing applications involving large strains, yet difficult to achieve. Here, we produced strain-sensitive fibers with large working factors by dip-coating nanocomposite piezoresistive inks on surface-modified polyether block amide (PEBA) fibers. Surface modification of neat PEBA fibers was carried out with polydopamine (PDA) while nanocomposite conductive inks consisted of styrene-ethylene-butylene-styrene (SEBS) elastomer and carbon black (CB). As such, the deposition of piezoresistive coatings was enabled through nonconventional hydrogen-bonding interactions. The resultant fibers demonstrated well-defined piezoresistive linear relationships, which increased with CB filler loading in SEBS. In addition, gauge factors decreased with increasing CB mass fractions from ∼15 to ∼7. Furthermore, we used the fatigue theory to predict the endurance limit (Ce) of our fibers toward resistance signal stability. Such a piezoresistive performance allowed us to explore the application of our fibers as strain sensors for monitoring the movement of finger joints.

Effect of pre-oxidation temperature and heating rate on the microstructure of lignin carbon fibers.

Lignin is a biopolymer with high carbon content, making lignin-based carbon fiber an important research direction. In the process of carbonization to prepare carbon fibers, lignin fibers are easily softened and fused, which destroys the microstructure of fibers, thereby reducing the quality of lignin-based carbon fibers. Therefore, it is non-negligible to pre-oxidize lignin fibers before carbonization to prevent fiber fusion and maintain fiber structure. Therefore, the effects of pre-oxidation temperature and heating rate on the structure of pre-oxidation lignin fibers with controllable diameter and thickness prepared by melt-blowing were studied in detail. During pre-oxidation, crosslinking and aromatization of lignin fibers occurred, and alkyl and benzene rings were mainly oxidized to form carbonyl groups. The aromatization degree of the pre-oxidized product was recorded at 280 °C and 0.25 °C/min, and the oxygen content reached 15 %-20 %, making it suitable for the preparation of bio-based carbon fibers. On this basis, carbon fibers with porous morphology can be prepared with a graphitization of 0.54 and a resistivity of 0.02 Ω cm-1. These materials are expected to be applicable in sensors, catalytic materials and other fields.