H-1 and H-2 NMR mobility in cellulose

Mobility of water in cellulose was studied by solid-state H-1 and high-reso lution H-2 NMR as a function of moisture content within the unfreezable moi sture range (0-19% dry basis). Measurements of relative mobilities were bas ed on relative intensities, transverse and longitudinal relaxation times an d lineshape analysis. At 2-16% moisture content (dry basis), water molecule s reoriented anisotropically, suggesting an interaction with cellulose fibe rs. 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 s harp increase in liquid or mobile H-1 intensity (accompanied by a decreased LW) and increases in H-2 NMR T-1 and T-2 relaxation times were observed as moisture increased above 9% (dry basis). At this moisture content the mole cular mobility approached the fast exchange regime. The data confirmed earl ier reports that unfreezable water could be highly mobile and not in a rigi d state. No glass transition was observed by DSC. However, NMR showed a significant mobility transition as the material transformed from a slow exchange (retar ded mobility) to a fast exchange regime. (C) 2001 Elsevier Science Ltd. All rights reserved.