Cellulose dissolution in aqueous NaOH–ZnO : effect of pulp pretreatment at macro and molecular levels

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Journal Title
Journal ISSN
Volume Title
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
Date
2021-05
Major/Subject
Mcode
Degree programme
Language
en
Pages
12
4385-4396
Series
Cellulose, Volume 28, issue 7
Abstract
This paper discusses the effect of hydrolytic pretreatments on pulp dissolution in the aqueous NaOH–ZnO solvent system. Eight samples were studied. They consisted of a never-dried softwood kraft pulp that was hydrolyzed under seven different conditions as well as the pulp without hydrolysis as a reference. The dissolution of the pulps was evaluated both at the macro level as well as at the molecular level based on their reactivity with 4-acetamido-2,2,6,6-tetramethylpiperidine-1-oxo-piperidium (4-AcNH-TEMPO+). The fiber properties (i.e. the extent of fibrillation, amount of fines and fiber width, coarseness, and length) as well as the chemical composition (hemicellulose and cellulose contents) and the viscosity of the pulps was investigated. The results show that hydrolysis at medium consistency (10%) was successful in increasing the solubility of cellulose. Hydrolysis at high consistency (50%), on the other hand, increased the solubility only to some extent. With extended treatment time the fibers formed aggregates and their dissolution became poor. This phenomenon could be overcome by mechanically refining the fibers after the hydrolysis. Moreover, comparison of the viscosity of the pulp over the degree of oxidation revealed that the viscosity needed to decrease below ca. 400 ml/g in order for the outer layers of the fibers to dissolve. Finally, when pulps with similar viscosities where compared against each other, the ones with the higher glucomannan contents formed gels over time. This was true also for the pulp with the lowest viscosity and the highest solubility of the studied samples.
Description
Funding Information: This work was done in collaboration between UPM-Kymmene Corporation and Aalto University. The research team is thanked for the fruitful discussions at the project meetings. In addition, we are grateful for the support from Business Finland, Walter Ahlström foundation and the FinnCERES Materials Bioeconomy Ecosystem. Finally, M.Sc. Rubina Ajdary is highly thanked for her work in optimizing the dissolution system and Mrs. Rita Hatakka for her assistance with the HPAEC measurements. Funding Information: Open access funding provided by Aalto University. This work was a part of a joint research project between UPM-Kymmene Oyj and Aalto University. In addition, the authors would like to acknowledge the financial support from Business Finland, Walter Ahlström foundation and the FinnCERES Materials Bioeconomy Ecosystem. Publisher Copyright: © 2021, The Author(s). Copyright: Copyright 2021 Elsevier B.V., All rights reserved.
Keywords
Cellulose, Dissolution, Hydrolysis, Reactivity, TEMPO-oxidation
Other note
Citation
Väisänen , S , Kosonen , H , Ristolainen , M & Vuorinen , T 2021 , ' Cellulose dissolution in aqueous NaOH–ZnO : effect of pulp pretreatment at macro and molecular levels ' , Cellulose , vol. 28 , no. 7 , pp. 4385-4396 . https://doi.org/10.1007/s10570-021-03779-w