University of Oulu

Phys. Chem. Chem. Phys., 2022,24, 28609-28620

Insights into the role of molar ratio and added water in the properties of choline chloride and urea-based eutectic mixtures and their cellulose swelling capacity

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Author: Sirviö, Juho Antti1; Haataja, Riikka1; Kantola, Anu M.2;
Organizations: 1Fibre and Particle Engineering Research Unit, University of Oulu, P.O. Box 4300, 90014 Oulu, Finland
2NMR Research Unit, University of Oulu, P.O. Box 3000, Oulu, Finland
Format: article
Version: published version
Access: open
Online Access: PDF Full Text (PDF, 1.2 MB)
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Language: English
Published: Royal Society of Chemistry, 2022
Publish Date: 2023-05-25


Eutectic mixtures and deep eutectic solvents (DESs) are promising green media for the pre-treatment of lignocellulose materials. They can be harnessed for the swelling of cellulose and further facilitate cellulose hydrolysis, derivatization, and production of cellulose-based (nano) materials. Several studies indicated that water can take part in the formation of the nanostructure of DES; however, it is still unclear how additional water influences many important properties and functioning of DES, especially when the molar ratio of compounds differs from the eutectic point composition. Here, viscosity, pH, conductivity, solvatochromic and solvatomagnetic solvent parameters, and fiber swelling capacity of choline chloride and urea mixtures demonstrating different molar ratios were investigated in the presence and absence of added water. The participation of water in the formation of molecular clusters with choline chloride and urea was indicated by viscosity, pH, and conductivity measurements. Hydrogen bond acceptor values of aqueous mixtures increased as a function of water content, and the results obtained using both methods were in line, indicating their suitability for the determination of hydrogen bond acidity of aqueous choline chloride–urea mixtures. However, hydrogen bond basicity determined by solvatochromic and magnetic methods exhibited almost opposite trends. The close investigation of the chemical shift of solvatomagnetic probes indicated that the chemical environment of the choline chloride–urea (1 : 2) mixture remained constant until the water content of 30 wt% was in line with previous molecular simulations. When cellulose fibers were treated with mixtures under mixing, the non-ideality of the choline chloride–urea mixture and the absence of water were found to be advantageous; however, aqueous mixtures efficiently increased the diameters of cellulose fibers in the absence of mixing, and water-containing mixtures appeared to be appealing systems for cellulose pretreatments.

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Series: PCCP. Physical chemistry chemical physics
ISSN: 1463-9076
ISSN-E: 1463-9084
ISSN-L: 1463-9076
Volume: 24
Issue: 46
Pages: 28609 - 28620
DOI: 10.1039/d2cp04119g
Type of Publication: A1 Journal article – refereed
Field of Science: 216 Materials engineering
Funding: The research was conducted as a part of the Value for Cellulosics (ValCel) project (No. 42679/31/2020) funded by the ExpandFibre program of Business Finland. Part of the work was carried out with the support of the Centre for Materials Analysis, University of Oulu.
Copyright information: © the Owner Societies 2022. This article is licensed under a Creative Commons Attribution 3.0 Unported Licence.