1H and 2H NMR mobility in cellulose
2001
Vittadini, E. | Dickinson, L.C. | Chinachoti, P.
Mobility of water in cellulose was studied by solid-state (1)H and high-resolution (2)H NMR as a function of moisture content within the unfreezable moisture range (0-19% dry basis). Measurements of relative mobilities were based on relative intensities, transverse and longitudinal relaxation times and lineshape analysis. At 2-16% moisture content (dry basis), water molecules reoriented anisotropically, suggesting an interaction with cellulose fibers. At moisture content below the monolayer value (2.8%, dry basis), 90% of the protons were immobile and no liquid deuterium signal was detected. A sharp increase in liquid or mobile (1)H intensity (accompanied by a decreased LW) and increases in (2)H NMR T1 and T2 relaxation times were observed as moisture increased above 9% (dry basis). At this moisture content the molecular mobility approached the fast exchange regime. The data confirmed earlier reports that unfreezable water could be highly mobile and not in a rigid state. No glass transition was observed by DSC. However, NMR showed a significant mobility transition as the material transformed from a slow exchange (retarded mobility) to a fast exchange regime.
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