A time-domain NMR study of the state of water in wet granules with different fillers and its contribution to the wet granulation process and to the characteristics of granules

The different states of water incorporated in wet granules were studied by a low-field benchtop ¹H-NMR time-domain NMR (TD-NMR) instrument. Wet granules consisting different fillers [cornstarch (CS), microcrystalline cellulose (MCC), and D-mannitol (MAN)] with different water contents were prepared using a high-speed granulator, and then their spin–spin relaxation time (T₂) was measured using the NMR relaxation technique. The experimental T₂ relaxation curves were analyzed by the two-component curve fitting, and then the individual T₂ relaxation behaviors of solid and water in wet granules were identified. According to the observed T₂ values, it was confirmed that the molecular mobility of water in CS and MCC granules was more restricted than that in the MAN granule. The state of water appeared to be associated with the drying efficiency and moisture absorption capacity of wet granules. Thus, it was confirmed that the state of water significantly affected the wet granulation process and the characteristics of the resultant granules. In the final phase of this study, the effects of binders on the molecular mobility of water in granulation fluids and wet granules were examined. The state of water in granulation fluids was substantially changed by changing the binders. The difference was still detected in wet granules prepared by addition of these fluids to the fillers. In conclusion, TD-NMR can offer valuable knowledge on wet granulation from the viewpoint of molecular mobility of water.