Molecular mechanism of cellulose dissolution in N-methyl morpholine-N-oxide: A molecular dynamics simulation study

Mostafa Akhlaghi Bagherjeri; Hassan Monhemi; Abu Naser Md Ahsanul Haque; Maryam Naebe

doi:10.1016/j.carbpol.2023.121433

Molecular mechanism of cellulose dissolution in N-methyl morpholine-N-oxide: A molecular dynamics simulation study

Carbohydr Polym. 2024 Jan 1:323:121433. doi: 10.1016/j.carbpol.2023.121433. Epub 2023 Sep 25.

Authors

Mostafa Akhlaghi Bagherjeri¹, Hassan Monhemi², Abu Naser Md Ahsanul Haque¹, Maryam Naebe³

Affiliations

¹ Deakin University, Institute for Frontier Materials, Geelong, Victoria 3216, Australia.
² Department of Chemistry, University of Neyshabur, Neyshabur, Iran.
³ Deakin University, Institute for Frontier Materials, Geelong, Victoria 3216, Australia. Electronic address: maryam.naebe@deakin.edu.au.

PMID: 37940258
DOI: 10.1016/j.carbpol.2023.121433

Abstract

N-methyl morpholine-N-oxide (NMMO) is the only commercialised solvent to dissolve cellulose and produce lyocell. However, the molecular mechanism of NMMO-induced cellulose solubilisation is unknown which limits further process development. In this work, and for the first time the complete dissolution process of a large cellulose bunch was simulated in NMMO monohydrate using long microsecond molecular dynamic simulations. The dissolution process was also simulated in 1-ethyl-3-methylimidazolium acetate (EmimAc) as an efficient ionic liquid in cellulose dissolution and the results were compared with the aqueous conditions. While the cellulose bunch showed a stable and insoluble structure in pure water, it was completely and efficiently dissolved in both NMMO monohydrate and EmimAc. It was shown that the dissolution time of cellulose in NMMO monohydrate is almost twice that in EmimAc, which is in agreement with the experimental observations. Although it is revealed that hydrogen bonding is the main driving force of cellulose dissolution in NMMO monohydrate, one cannot explain the complete molecular mechanism of NMMO-induced cellulose dissolution only by considering hydrogen bonds. A straightforward molecular mechanism was proposed, in which the interactions of NMMO molecules, not with cellulose, but with the other NMMO molecules play a critical role in the dissolution process.

Keywords: Cellulose; Hydrogen bonds; Hydrophobic interaction; Lyocell; Molecular mechanism; NMMO.