Rapid Dissolution of Cellulose in LiOH/Urea and NaOH/Urea Aqueous Solutions

TLDR

The study systematically investigated rapid dissolution of cellulose in LiOH/urea and NaOH/urea aqueous solutions. The authors evaluated cellulose dissolution by 13 C NMR, optical microscopy, WAXD, FT‑IR, DSC, and viscometry, focusing on urea carbonyl shifts in LiOH and NaOH solutions. Cellulose with Mη of 11.4 × 10⁴ and 37.2 × 10⁴ dissolved in 7 % NaOH/12 % urea and 4.2 % LiOH/12 % urea pre‑cooled to –10 °C within 2 min, but not in KOH/urea, with solvent power ranking LiOH/urea > NaOH/urea ≫ KOH/ure.

Abstract

Abstract Summary: Rapid dissolution of cellulose in LiOH/urea and NaOH/urea aqueous solutions was studied systematically. The dissolution behavior and solubility of cellulose were evaluated by using 13 C NMR, optical microscopy, wide‐angle X‐ray diffraction (WAXD), FT‐IR spectroscopy, DSC, and viscometry. The experiment results revealed that cellulose having viscosity‐average molecular weight ( $\overline M _\eta $ ) of 11.4 × 104 and 37.2 × 104 could be dissolved, respectively, in 7% NaOH/12% urea and 4.2% LiOH/12% urea aqueous solutions pre‐cooled to −10 °C within 2 min, whereas all of them could not be dissolved in KOH/urea aqueous solution. The dissolution power of the solvent systems was in the order of LiOH/urea > NaOH/urea ≫ KOH/urea aqueous solution. The results from DSC and 13 C NMR indicated that LiOH/urea and NaOH/urea aqueous solutions as non‐derivatizing solvents broke the intra‐ and inter‐molecular hydrogen bonding of cellulose and prevented the approach toward each other of the cellulose molecules, leading to the good dispersion of cellulose to form an actual solution. 13 C NMR chemical shifts of carbonyl carbon for urea in LiOH (a) and NaOH (b) of the cellulose solutions. magnified image 13 C NMR chemical shifts of carbonyl carbon for urea in LiOH (a) and NaOH (b) of the cellulose solutions.