Kinetics of Release of Particulate Solutes lncorporated in Cellulosic Polymer Matrices as a Function of Solute Solubility and Polymer Swellability.II.Highly Soluble Solute

摘要

The kinetics of release into water of particulate NaCl (used here as an example of a highly water-soluble solute) incorproated in a cellulose acetate (CA)matrix was investigated in correlation with the concurrent variation of the water content of the matrix.To ensure comparability with the kinetic behavior of sparingly soluble solutes reported in part I,a CA of the same composition,and identical filmforming procedures were employed.In contrast to this sparingly soluble solute behavior,deviations from t~(1/2) release kinetics and temporary osmotically induced retention of excess imbibed water were observed.Both these effects became more noticeable with decreasing salt loads.At the same time the observed release rates were far in excess of what could be expected from measurements of the NaCl transport properties of the particle-depleted matrix or what could be predicted on the basis of model calculations assuming homogeneous and instantaneously reversible osmotically induced excess water uptake.Such a marked enhancement of release rate is commonly attributed to the formation of a pore network in the particle-depleted matrix by mechanical rupture of the "walls" separating neighboring particle-containing cavities,due to osmotically induced ingress of water therein. However, it was shown that such a mechanism is unsustainable in the present context.A new,more general mechanism is proposed that can successfully account for all the salient kinetic features of the combined solute release and water absorption-desorption processes noted here.Additionally,slow molecular relaxation processes were also shown to play a significant role in the mechanism of solute release.