The thermodynamics of enhanced dope stability of cellulose solution in NaOH solution by urea

Yu Chen; Yoshiharu Nishiyama; Ang Lu; Yan Fang; Ziqiang Shao; Tao Hu; Dongdong Ye; Haisong Qi; Xiaodong Li; Jakob Wohlert; Pan Chen

doi:10.1016/j.carbpol.2023.120744

The thermodynamics of enhanced dope stability of cellulose solution in NaOH solution by urea

Carbohydr Polym. 2023 Jul 1:311:120744. doi: 10.1016/j.carbpol.2023.120744. Epub 2023 Mar 4.

Authors

Yu Chen¹, Yoshiharu Nishiyama², Ang Lu³, Yan Fang⁴, Ziqiang Shao¹, Tao Hu⁵, Dongdong Ye⁶, Haisong Qi⁷, Xiaodong Li⁸, Jakob Wohlert⁹, Pan Chen¹⁰

Affiliations

¹ Beijing Engineering Research Centre of Cellulose and Its Derivatives, School of Materials Science and Engineering, Beijing Institute of Technology, 100081 Beijing, PR China.
² Univ. Grenoble Alpes, CNRS, CERMAV, 38000 Grenoble, France. Electronic address: yoshi@cermav.cnrs.fr.
³ College of Chemistry and Molecular Sciences, Wuhan University, Wuhan 430072, China.
⁴ Fujian Key Laboratory of Polymer Materials, College of Chemistry and Materials Science, Fujian Normal University, Fujian 350007, PR China.
⁵ School of Materials Science and Engineering, State Key Laboratory of Advanced Special Steels, Shanghai University, Shanghai 200444, China.
⁶ School of Textile Materials and Engineering, Wuyi University, Jiangmen 529020, PR China.
⁷ State Key Laboratory of Pulp and Paper Engineering, South China University of Technology, Guangzhou, 510640, PR China.
⁸ School of Materials Science and Engineering, Beijing Institute of Technology, 100081 Beijing, PR China.
⁹ Wallenberg Wood Science Center, Department of Fiber and Polymer Technology, KTH Royal Institute of Technology, Teknikringen 56-58, SE-10044 Stockholm, Sweden. Electronic address: jacke@kth.se.
¹⁰ Beijing Engineering Research Centre of Cellulose and Its Derivatives, School of Materials Science and Engineering, Beijing Institute of Technology, 100081 Beijing, PR China. Electronic address: panchen@bit.edu.cn.

PMID: 37028854
DOI: 10.1016/j.carbpol.2023.120744

Abstract

The addition of urea in pre-cooled alkali aqueous solution is known to improve the dope stability of cellulose solution. However, its thermodynamic mechanism at a molecular level is not fully understood yet. By using molecular dynamics simulation of an aqueous NaOH/urea/cellulose system using an empirical force field, we found that urea was concentrated in the first solvation shell of the cellulose chain stabilized mainly by dispersion interaction. When adding a glucan chain into the solution, the total solvent entropy reduction is smaller if urea is present. Each urea molecule expelled an average of 2.3 water molecules away from the cellulose surface, releasing water entropy that over-compensates the entropy loss of urea and thus maximizing the total entropy. Scaling the Lennard-Jones parameter and atomistic partial charge of urea revealed that direct urea/cellulose interaction was also driven by dispersion energy. The mixing of urea solution and cellulose solution in the presence or absence of NaOH are both exothermic even after correcting for the contribution from dilution.

Keywords: Dope stability of cellulose solution; Molecular dynamics simulation; Thermodynamics; Urea.