Novel insight into cellulose supramolecular structure through 13C CP-MAS NMR spectroscopy and paramagnetic relaxation enhancement

13C CP-MAS NMR and paramagnetic relaxation enhancement provide novel insight into the supramolecular structure of solid cellulose I and II. Separable NMR signals associated with crystalline interiors, solvent accessible and inaccessible surfaces, as well as non-crystalline material are assigned and confirmed. For the first time solvent accessibility is evidenced and monitored through 13C T1 NMR relaxation enhancement in paramagnetic medium. Established NMR signal assignments for cellulose I have been confirmed. Existing cellulose II resonance attributions have been modified and extended. Novel spectral fitting routines for cellulose II allow for the reproducible quantification of separable signal contributions. Results from NMR line shape analyses are straightforwardly introduced into a model for cellulose II supramolecular structure.