Revisiting the dissolution of cellulose in H3PO4(aq) through cryo-TEM, PTssNMR and DWS

Luís Alves; Bruno Medronho; Alexandra Filipe; Anabela Romano; Maria G Rasteiro; Björn Lindman; Daniel Topgaard; Irina Davidovich; Yeshayahu Talmon

doi:10.1016/j.carbpol.2020.117122

Revisiting the dissolution of cellulose in H₃PO₄(aq) through cryo-TEM, PTssNMR and DWS

Carbohydr Polym. 2021 Jan 15:252:117122. doi: 10.1016/j.carbpol.2020.117122. Epub 2020 Sep 29.

Authors

Luís Alves¹, Bruno Medronho², Alexandra Filipe³, Anabela Romano⁴, Maria G Rasteiro³, Björn Lindman⁵, Daniel Topgaard⁶, Irina Davidovich⁷, Yeshayahu Talmon⁷

Affiliations

¹ CIEPQPF, Department of Chemical Engineering, University of Coimbra, Pólo II - R. Silvio Lima, 3030-790 Coimbra, Portugal. Electronic address: luisalves@ci.uc.pt.
² MED - Mediterranean Institute for Agriculture, Environment and Development, University of Algarve, Faculty of Sciences and Technology, Campus de Gambelas, Ed. 8, 8005-139 Faro, Portugal; FSCN, Surface and Colloid Engineering, Mid Sweden University, SE-851 70 Sundsvall, Sweden.
³ CIEPQPF, Department of Chemical Engineering, University of Coimbra, Pólo II - R. Silvio Lima, 3030-790 Coimbra, Portugal.
⁴ MED - Mediterranean Institute for Agriculture, Environment and Development, University of Algarve, Faculty of Sciences and Technology, Campus de Gambelas, Ed. 8, 8005-139 Faro, Portugal.
⁵ FSCN, Surface and Colloid Engineering, Mid Sweden University, SE-851 70 Sundsvall, Sweden; Division of Physical Chemistry, Department of Chemistry, Center for Chemistry and Chemical Engineering, Lund University, SE-221 00 Lund, Sweden.
⁶ Division of Physical Chemistry, Department of Chemistry, Center for Chemistry and Chemical Engineering, Lund University, SE-221 00 Lund, Sweden.
⁷ Chemical Engineering, Technion-Israel Institute of Technology, Haifa 3200003, Israel.

PMID: 33183588
DOI: 10.1016/j.carbpol.2020.117122

Abstract

Cellulose can be dissolved in concentrated acidic aqueous solvents forming extremely viscous solutions, and, in some cases, liquid crystalline phases. In this work, the concentrated phosphoric acid aqueous solvent is revisited implementing a set of advanced techniques, such as cryo-transmission electronic microscopy (cryo-TEM), polarization transfer solid-state nuclear magnetic resonance (PTssNMR), and diffusing wave spectroscopy (DWS). Cryo-TEM images confirm that this solvent system is capable to efficiently dissolve cellulose. No cellulose particles, fibrils, or aggregates are visible. Conversely, PTssNMR revealed a dominant CP signal at 25 °C, characteristic of C-H bond reorientation with correlation time longer than 100 ns and/or order parameter above 0.5, which was ascribed to a transient gel-like network or an anisotropic liquid crystalline phase. Increasing the temperature leads to a gradual transition from CP to INEPT-dominant signal and a loss of birefringence in optical microscopy, suggesting an anisotropic-to-isotropic phase transition. Finally, an excellent agreement between optical microrheology and conventional mechanical rheometry was also obtained.

Keywords: Anisotropy; Cellulose dissolution; DWS; Liquid crystalline phase; PTssNMR; Phosphoric acid; cryo-TEM.