I. Devotta et al., UNUSUAL RETARDATION AND ENHANCEMENT IN POLYMER DISSOLUTION - ROLE OF DISENGAGEMENT DYNAMICS, Chemical Engineering Science, 50(16), 1995, pp. 2557-2569
This work addresses the issue of resolution of some unusual observatio
ns in the swelling-dissolving problem in polymers. There are observati
ons showing several fold increase in the rate of dissolution when the
residual solvent content is increased only marginally. Additionally, b
y using an in situ NMR technique to study dissolution, we have found t
he existence of an intermediate plateau in the dissolution curve indic
ating an unusual retardation in the rate of dissolution under certain
conditions. Interestingly, this plateau disappears on either increasin
g the molecular weight of the polymer or on doing dissolution under sh
earing rather than under stagnant conditions. An improved model is pro
posed to explain these results, which cannot be explained by the exist
ing models. The new feature is the incorporation of a kinetic model to
relate the disengagement rate to the swelling rate, through the chang
ing mobility of the disengaging macromolecule at the gel-liquid interf
ace. The present study thus enables a clearer elucidation of the role
of disengagement dynamics in the dissolution process.