Structural and thermal properties of deep eutectic solvent-extracted lignin from oil palm biomass for carbon fiber applications

This study explores the extraction of lignin from oil palm biomass using deep eutectic solvents (DESs), specifically choline chloride (ChCl) and glycerol, to develop a sustainable precursor for carbon fiber applications. Oil palm fronds (OPF) and empty fruit bunches (EFB) were treated with ChCl:Glycerol at various molar ratios (1:3-1:5), reaction times (3-6 h), and temperatures (130-170 degrees C) to extract lignin (DES-L). The DES-L was characterized to determine its phenolic hydroxyl group (PhOH) content, functional group distribution, purity, glass transition temperature (Tg), and average molecular weight (Mw). The findings revealed that OPF-derived lignin exhibited higher phenolic hydroxyl group content (0.738-1.426 mmol/g), indicating superior structural disintegration compared to EFB-derived lignin (0.625-0.639 mmol/g). FTIR analysis revealed the presence of lignin-specific functional groups in DES-L, with peak intensities varying with ChCl:Glycerol molar ratio. The lignin purity ranged from 74.64% to 97.31% and increased with the temperature and reaction time. The Tg (99.96 - 144.15 degrees C) and average Mw (2851 - 3835 g/mol) of DES-L demonstrated good thermal stability, which is suitable for carbon fiber precursors. This study demonstrates the potential of lignin extracted from oil palm biomass using DES as a viable and sustainable precursor for carbon fiber production. Additionally, it contributes to the enhanced utilization and value creation of agricultural waste. Optimizing the extraction parameters has uncovered a pathway for developing high-performance, eco-friendly carbon fibers. This approach addresses both economic and environmental challenges associated with current carbon fiber production methods.