Utilization of deep eutectic solvent as a degumming protocol for Apocynum venetum bast

Deep eutectic solvent (DES) pretreatment coupled with alkaline degumming on Apocynum venetum bast was studied for developing an eco-friendly and effective degumming method. A 1:2 mixture of choline chloride and urea was used in a microwave-assisted DES pretreatment optimized to 60 min and 110 °C. The impact of the deep eutectic solvent pretreatment on the properties of produced semi-degummed and refined dry fibers were assessed by examining the fiber chemical composition, surface microstructure, cellulose crystallinity, degree of polymerization, and fiber thermal properties. The combined DES and alkaline degumming treatment effectively removed the gummy matter including hemicellulose and lignin from the A. venetum bast, providing a smooth and clean fiber surface. This combined DES and alkaline degumming treatment also shows the ability to extract amorphous cellulose, leading to an increase of fiber crystallinity and a decrease of the average cellulose molecular weight. The thermal stability of the fibers was improved significantly after the degumming treatment. The refined dry fibers produced by this combined DES-alkaline treatment exhibited comparable chemical and physical properties (e.g. residual gum content, fiber length, fiber fineness, breaking tenacity) compared with traditionally alkali degumming method. These results revealed that DES is a practical and feasible pretreatment protocol for A. venetum bast degumming.