Longitudinal swelling kinetics of cellulose acetate films sorbing acetone vapor at 30 degrees C were studied under various conditions and correlated with the corresponding sorption kinetic measurements reported in Part I. The results were analyzed in the light of (1) previous theoretical studies of simple viscoelastic polymer-penetrant model systems and (2) mechanical stress-strain data on the cellulose acetate-acetone system, which are also reported here. The conclusions drawn from this analysis confirm and/or amplify (particularly as regards the effect of longitudinal differential swelling stresses) our previous interpretations based on sorption kinetic analysis, concerning the physical nature and causes of various features of the non-Fickian kinetic behavior of cellulosic polymer-micromolecular penetrant systems. History-dependent long-term aging effects were also observed and investigated.