On the Role of Hydrophobic Interactions in Cellulose Dissolution and Regeneration: Colloidal Aggregates and Molecular Solutions

Bruno Medronho ¹ Luís Alves ² Björn Lindman ^3,4

¹Faculty of Sciences and Technology, University of Algarve, Faro, Portugal
²Department of Chemistry, University of Coimbra, Coimbra, Portugal
³Division of Physical Chemistry, Department of Chemistry, Lund University, Lund, Sweden
⁴Materials Science and Engineering, Nanyang Technological University, Singapore, Singapore

The development of state of the art dissolution/regeneration strategies for cellulose constitutes an increasingly active research field. These are fundamental aspects of many production processes and applications. A wide variety of suitable solvents for cellulose are already available, however, these are of highly different nature giving great challenges in the understanding of the subtle balance between the different interactions. Insolubility is often attributed to strong intermolecular hydrogen bonding between cellulose molecules. However, our recent work rather emphasizes the role of hydrophobic interactions. Here, we report the effect of two different solvents on the dissolution of cellulose on multiple length scales and its consequences on the characteristics of the regenerated material. While an aqueous tetraalkylammonium hydroxide solution gives rise to what appears to be dissolution down to the molecular level, the cold alkali solvent (NaOH based) does not dissolve cellulose molecularly but rather leaves aggregates of high crystallinity stable in the cellulose dope. It is suggested that such striking difference in the solubility pattern resides in the hydrophobicity of the tetraalkylammnium cation (contrasting to the polar inorganic cation of the alkali system) which is capable of weaken the hydrophobic interactions in cellulose solubilizing the biopolymer molecularly.

bfmedronho@ualg.pt