Please use this identifier to cite or link to this item: https://hdl.handle.net/10316/107659
Title: New Insights on the Role of Urea on the Dissolution and Thermally-Induced Gelation of Cellulose in Aqueous Alkali
Authors: Alves, Luís 
Medronho, Bruno 
Filipe, Alexandra 
Antunes, Filipe E. 
Lindman, Björn Olof 
Topgaard, Daniel 
Davidovich, Irina
Talmon, Yeshayahu
Keywords: cellulose; gelation; urea; NaOH; microrheology; cryo-transmission electronic microscopy; polarization transfer solid-state NMR; hydrophobic interactions
Issue Date: 11-Dec-2018
Publisher: MDPI
Project: This work was financially supported by Portuguese Foundation for Science and Technology (FCT, project PTDC/AGR-TEC/4814/2014 and researcher grant IF/01005/2014). The authors also acknowledge ESMI (European Soft Matter Infrastructure) for the financial support (Proposal E160700746). The Coimbra Chemistry Centre, CQC, supported by FCT, through the project PEstOE/QUI/UI0313/2013, is also acknowledged. The cryo-TEM work was performed in the Technion Center for Electron Microscopy of Soft Matter, supported by the Technion Russell Berrie Nanotechnology Institute (RBNI). 
Serial title, monograph or event: Gels
Volume: 4
Issue: 4
Abstract: 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.
URI: https://hdl.handle.net/10316/107659
ISSN: 2310-2861
DOI: 10.3390/gels4040087
Rights: openAccess
Appears in Collections:I&D CQC - Artigos em Revistas Internacionais

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