Spin-lattice relaxation behaviour of water in cellulose materials in relation to the tablet forming ability of microcrystalline cellulose particles

Medical tablet forming ability of microcrystalline cellulose (MCC) was investigated in relation to the mobility of water molecules in MCC particles, For this purpose, the spin-lattice relaxation time T-1 of water in the system was measured by H-1-NMR. Over a wide range of water contents (0.02 less than or equal to H2O/cellulose (g/g) less than or equal to 1.79), two different T-1 (T-1,T-l and T-1,T-s) values were observed for water in each MCC sample, Below the equilibrium water content, water having these two different T-1 values exchange with each other in an MCC particle reaching an equilibrium state within a given time scale (equilibrium constant K). The T-1,T-l, T-1,T-s and K values for water in MCC, estimated at the equilibrium water content, showed fairly good correlations with the hardness of the tablets made by the MCC samples, Sample with a shorter T-1, or larger K tended to have a stronger tablet forming ability, In the spin-spin relaxation time T-2 measurements for protons in an MCC/D2O system, two T-2 components originating from the glassy cellulose solid (T-2,T-G) and the swelling region (T-2,T-J) were observed. It was found that the mole fraction x(L) of protons with T-2,T-L in the system exhibits a clear linear correlation with K, From these results, a structural model for the distribution of water in MCC particles was propoed by taking the surface of each microfibril and the disordered region within the microfibril into consideration.