Interaction of cellulose and water upon drying and swelling by 13C CP/MAS NMR

Abstract

Associated water plays a significant role in the morphology of cellulose and the molecular interactions between polymer chains. It also affects the material properties and influences the interpretation of analysis results. In the present study the interaction of cellulose and water in well-defined cellulose samples, hydrogel beads prepared by regeneration of microcrystalline cellulose from organic electrolyte solution, are investigated by solid state ¹³C CP/MAS NMR. Drying of the hydrogel beads under ambient conditions gave condensed cellulose xerogel beads, which could be partly reswollen in water. The analysis of beads of different moisture content and under repeated drying and swelling afforded a better understanding of the hierarchical organization and crystallinity of cellulose II, which is broadly divisible into crystalline and surface residues in CP/MAS, and the nature of cellulose hornification. The changes in the ¹³C CP/MAS spectra of water- and D₂O-swollen beads also provide new information on the role of immobilized bound water in intermolecular polarization transfer from water to cellulose during the cross-polarization pulse sequence, and evidence of the cellulose II reducing-end-group, which is more prominently observable in CP/MAS under dry conditions.

Graphical abstract