Combined effects of deep eutectic solvent and microwave energy treatments on cellulose fiber extraction from hemp bast

Extracting pure cellulose fibers from hemp fibers for value-added applications like industrial textile requires the removal of non-cellulosic gummy substances. However, traditional degumming methods are largely limited due to their long process time, high energy consumption, and detrimental environmental pollution. Herein, several deep eutectic solvents (DESs) combined with microwave energy (MWE) were explored to degum hemp fibers without any further treatment. The purified hemp cellulose fibers were systematically characterized using advanced analytical techniques. Results revealed that the synergetic effect of combined MWE-DES treatment was capable of removing non-cellulosic components such as lignin, hemicellulose, amorphous cellulose, and impurities from the fiber structure without damaging the cellulose structure. MWE-DES treated fibers had higher thermal stability (maximum degradation temperature of MWE-DES treated fibers reached 356 °C), lower residual lignin content (2.88%), and higher crystallinity (83.27% for choline chloride and urea DES). Moreover, MWE-DES treated fibers showed the inhibition of bacterial growth, comparable with that from untreated raw hemp fibers containing bioactive compounds (flavonoid). Featured with high efficiency, very short process time, less chemical and energy consumption, and high-quality fibers, this treatment method has a great potential for hemp cellulose fiber extraction. Graphical abstract