High-efficiency and recyclable ramie cellulose fiber degumming enabled by deep eutectic solvent

Gummy components in raw ramie are required to be removed to extract cellulose fibers. However, current common degumming techniques are largely limited because of long procedures, heavy environmental pollution, high energy consumption, and insufficient efficiency. Here, deep eutectic solvent (DES) was explored to ramie cellulose fiber degumming without combining any further treatment. Three DESs, namely, choline chloride-urea (CU), choline chloride-imidazole (CI), and ethylamine hydrochloride-ethylene glycol (EE), were demonstrated to be capable of removing non-cellulose impurities in 2 h in one-step boiling process without damaging cellulose structure. The purified fibers were systematically characterized in terms of mechanical properties and chemical constitutions. Results showed that the DES can effectively remove most non-cellulosic materials from raw ramie. The CU treated fibers exhibited a higher tenacity (6.51 cN/dtex) and lower residual gum content (3.76 %), which was nearly in the same level of traditional alkaline (TAL) treated fibers. The fibers degummed with CI showed the highest break elongation (3.30 %) and relatively good tenacity (5.50 cN/dtex). Comparatively, the EE treated fibers exhibited the poorest tenacity (3.05 cN/dtex) despite of the lowest residual gum content (3.15 %). Besides, the DES was reusable and recyclable, which can be repeatedly used for many times. The cellulose fibers achieved high tenacity and low residual gum content after the fifth cycles' treatment with DES, which still met the requirement of downstream applications. Finally, the lignin in degumming waste solution was further fractionated, and the purity of the extracted lignin was proved to be 9.54 %. Featured with high efficiency, short process, less chemical and energy usage, high quality fibers as well as easy reutilization of solvent, this approach is of great potential for cellulose fiber isolation.