Quantitative evaluation of cellulose swelling and dissolution behavior by monitoring the retention of NMMO solvent in cellulose fiber structure

The swelling performance of the biological macromolecules of cellulose in aqueous N -methyl-morpholine-N-oxide (NMMO) solution is a critical factor in improving cellulose dissolution efficiency during lyocell process. We focused on the diffusion behavior of NMMO solvent during cellulose swelling and dissolution process using a novel centrifugation method, clarifying the relationship between NMMO retention value, fiber structural properties, and dissolution efficiency. An effective quantitative index for evaluating the swelling performances of cellulose is NMMO-retention, which was defined by investigating the removal of aqueous NMMO solution from swollen cellulose fibers using centrifugal method. Based on the variation of NMMO-retention and centrifugal force at 500 and 3000  g , the removal process was divided into three stages: rapid removal stage (0–500 g), slow removal stage (500–3000 g), and residual removal stage (3000–5000 g). In addition, the relationship between fiber structural properties (fiber length, width, fine content, and specific surface area) and swelling-dissolution performance was established. The results indicate that the NMMO-retention of cellulose is a comprehensive reflection of the fiber structural characteristics, and it shows an obvious negative correlation with the dissolution time of cellulose. The cellulose that shows the highest NMMO-retention (729.5 %) after swelling has the shortest dissolution time (20 min) during subsequent dissolution.