The essential role of porous structure modification in enhancing cellulose swelling and dissolution efficiency in NMMO solution

The method of N-methyl-morpholine-N-oxide (NMMO) as a green and efficient solvent for dissolving fibers to prepare lyocell fibers is well known. Although we all know that the chemical composition, morphology, and pore structure of fibers determine the dissolution time of NMMO solution, it is difficult to evaluate the greatest impact factor on dissolution efficiency among the comprehensive factors. Herein, the relationship among the pore structure (specific surface area), swelling performance (maximum NMMO-retention value), and dissolution performance (dissolution time) of cellulose fibers in aqueous NMMO solution was quantitatively investigated. The novelty of this work is the quantitative evaluation of the impact of a single influencing factor (porous characteristics) on the swelling and dissolution properties. The porous characteristics of cellulose were effectively regulated without changing significant chemical structure using freeze-drying and hot-dried at 80 ℃ and 105 ℃ methods. Compared to hot-dried treatment, the freeze-dried cellulose fibers exhibited the high specific surface area (11.12 m 2 /g), highest NMMO-retention value (612%), the shortest dissolution time (40 min), which was shortened by 20 min. Higher specific surface area corresponded to the higher swell extent and dissolution efficiency by facilitating the diffusion of NMMO solution in cellulose fibers. Improving the porous characteristics of cellulose fibers not only effectively increased the NMMO retention value and swell extent but also shortened dissolution time without affecting the rheological properties of cellulose-NMMO solutions. Graphical abstract