A promising degumming method to prepare kenaf fibers by using recyclable deep eutectic solvents

Traditional degumming methods of bast fibers are largely limited due to long procedures, high energy consumption, serious environmental pollution, or low efficiency. In this study, deep eutectic solvents (DESs) synthesized with hydrogen bond acceptor (HBA) and three representative hydrogen bond donors (HBDs) were applied to kenaf bast degumming. The morphologies, chemical compositions, crystallinities, polymerization degrees and physical properties of the kenaf fibers were determined. The effects and mechanisms of different DESs on dispersing kenaf bast were discussed. The results showed that alkalinity amide DES (ChCl-urea, CU) showed the best degumming effect. The optimal processing temperature is 160 °C and the processing time is 2 h. Due to competition from chloride ions, DES first weakens the hydrogen bond interaction in kenaf fibers. Then, the alkalinity amide DES removed lignin by deprotonation of phenolic hydroxyl groups and breakage of β-O-4 bonds for different lignin units. Finally, the solvent can be reused at least 3 times. The results showed that CU degumming treatment could effectively remove the gummy components in kenaf bast and had the potential to prepare refined dry kenaf fibers. This study provided a simple and green degumming method for kenaf bast.