Process optimization and comprehensive utilization of recyclable deep eutectic solvent for the production of ramie cellulose fibers

Deep eutectic solvents (DESs) are emerging green chemical reagents, most of which are nontoxic, biodegradable, environmentally friendly, and easy to access. DESs constituted of choline chloride and urea has been proved to be an innovative method for ramie cellulose fibers extraction. However, the costly DESs reagent and inefficient solvent recovery are still challenging for wide application. Here, the optimal extraction conditions and the possibility of DESs solvent recovery were investigated. Specifically, the effect of incremental reuse times of degumming solution on surface morphology, chemical composition, cellulose crystallinity (65.69 ~ 70.11%), thermal stability (thermal decomposition temperature 353 ~ 356℃), degree of polymerization (1679 ~ 2445), and mechanical tenacity of degummed fibers were systematically evaluated. The results showed that reusable degumming solution could still remove the majority of non-cellulosic components from raw ramie, even after four times repeating degumming. The treated fibers achieved the cellulose content of above 90.21%, fiber yield of 74.16 ~ 78.55%, density of 6.30 ~ 7.87 dtex, tenacity of 5.21 ~ 6.72 cN/dtex, respectively. All these mechanical properties fulfilled the requirement of spinning process. Moreover, the insoluble lignin and polysaccharides were successfully separated from degumming solution and the DESs solvent was recycled with ease, beneficially realizing recycle economy and sustainable development for natural fiber extraction.