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New Insights on the Role of Urea on the Dissolution and Thermally-Induced Gelation of Cellulose in Aqueous Alkali

The gelation of cellulose in alkali solutions is quite relevant, but still a poorly understood process. Moreover, the role of certain additives, such as urea, is not consensual among the community. Therefore, in this work, an unusual set of characterization methods for cellulose solutions, such as c...

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Autores principales: Alves, Luis, Medronho, Bruno, Filipe, Alexandra, E. Antunes, Filipe, Lindman, Björn, Topgaard, Daniel, Davidovich, Irina, Talmon, Yeshayahu
Formato: Online Artículo Texto
Lenguaje:English
Publicado: MDPI 2018
Materias:
Acceso en línea:https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6318579/
https://www.ncbi.nlm.nih.gov/pubmed/30674863
http://dx.doi.org/10.3390/gels4040087
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author Alves, Luis
Medronho, Bruno
Filipe, Alexandra
E. Antunes, Filipe
Lindman, Björn
Topgaard, Daniel
Davidovich, Irina
Talmon, Yeshayahu
author_facet Alves, Luis
Medronho, Bruno
Filipe, Alexandra
E. Antunes, Filipe
Lindman, Björn
Topgaard, Daniel
Davidovich, Irina
Talmon, Yeshayahu
author_sort Alves, Luis
collection PubMed
description The gelation of cellulose in alkali solutions is quite relevant, but still a poorly understood process. Moreover, the role of certain additives, such as urea, is not consensual among the community. Therefore, in this work, an unusual set of characterization methods for cellulose solutions, such as cryo-transmission electronic microscopy (cryo-TEM), polarization transfer solid-state nuclear magnetic resonance (PTssNMR) and diffusion wave spectroscopy (DWS) were employed to study the role of urea on the dissolution and gelation processes of cellulose in aqueous alkali. Cryo-TEM reveals that the addition of urea generally reduces the presence of undissolved cellulose fibrils in solution. These results are consistent with PTssNMR data, which show the reduction and in some cases the absence of crystalline portions of cellulose in solution, suggesting a pronounced positive effect of the urea on the dissolution efficiency of cellulose. Both conventional mechanical macrorheology and microrheology (DWS) indicate a significant delay of gelation induced by urea, being absent until ca. 60 °C for a system containing 5 wt % cellulose, while a system without urea gels at a lower temperature. For higher cellulose concentrations, the samples containing urea form gels even at room temperature. It is argued that since urea facilitates cellulose dissolution, the high entanglement of the cellulose chains in solution (above the critical concentration, C*) results in a strong three-dimensional network.
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spelling pubmed-63185792019-01-17 New Insights on the Role of Urea on the Dissolution and Thermally-Induced Gelation of Cellulose in Aqueous Alkali Alves, Luis Medronho, Bruno Filipe, Alexandra E. Antunes, Filipe Lindman, Björn Topgaard, Daniel Davidovich, Irina Talmon, Yeshayahu Gels Article The gelation of cellulose in alkali solutions is quite relevant, but still a poorly understood process. Moreover, the role of certain additives, such as urea, is not consensual among the community. Therefore, in this work, an unusual set of characterization methods for cellulose solutions, such as cryo-transmission electronic microscopy (cryo-TEM), polarization transfer solid-state nuclear magnetic resonance (PTssNMR) and diffusion wave spectroscopy (DWS) were employed to study the role of urea on the dissolution and gelation processes of cellulose in aqueous alkali. Cryo-TEM reveals that the addition of urea generally reduces the presence of undissolved cellulose fibrils in solution. These results are consistent with PTssNMR data, which show the reduction and in some cases the absence of crystalline portions of cellulose in solution, suggesting a pronounced positive effect of the urea on the dissolution efficiency of cellulose. Both conventional mechanical macrorheology and microrheology (DWS) indicate a significant delay of gelation induced by urea, being absent until ca. 60 °C for a system containing 5 wt % cellulose, while a system without urea gels at a lower temperature. For higher cellulose concentrations, the samples containing urea form gels even at room temperature. It is argued that since urea facilitates cellulose dissolution, the high entanglement of the cellulose chains in solution (above the critical concentration, C*) results in a strong three-dimensional network. MDPI 2018-12-11 /pmc/articles/PMC6318579/ /pubmed/30674863 http://dx.doi.org/10.3390/gels4040087 Text en © 2018 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/).
spellingShingle Article
Alves, Luis
Medronho, Bruno
Filipe, Alexandra
E. Antunes, Filipe
Lindman, Björn
Topgaard, Daniel
Davidovich, Irina
Talmon, Yeshayahu
New Insights on the Role of Urea on the Dissolution and Thermally-Induced Gelation of Cellulose in Aqueous Alkali
title New Insights on the Role of Urea on the Dissolution and Thermally-Induced Gelation of Cellulose in Aqueous Alkali
title_full New Insights on the Role of Urea on the Dissolution and Thermally-Induced Gelation of Cellulose in Aqueous Alkali
title_fullStr New Insights on the Role of Urea on the Dissolution and Thermally-Induced Gelation of Cellulose in Aqueous Alkali
title_full_unstemmed New Insights on the Role of Urea on the Dissolution and Thermally-Induced Gelation of Cellulose in Aqueous Alkali
title_short New Insights on the Role of Urea on the Dissolution and Thermally-Induced Gelation of Cellulose in Aqueous Alkali
title_sort new insights on the role of urea on the dissolution and thermally-induced gelation of cellulose in aqueous alkali
topic Article
url https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6318579/
https://www.ncbi.nlm.nih.gov/pubmed/30674863
http://dx.doi.org/10.3390/gels4040087
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