Kinetic process of enthalpy relaxation of glassy starch and effect of physical aging upon its water vapor permeability property

The enthalpy relaxation during aging below Tg of an amorphous starch was examined via the Kohlrausch–Williams–Watts (KWW) relation in order to describe its kinetic process quantitatively. The experimental data were fitted satisfactorily by the KWW equation of stretched exponential form. Comparison to the results reported in previous studies reveals that both the values of the mean relaxation time τ and the relaxation time distribution β(0.23–0.34) obtained through the fitting process were reasonable. Furthermore, the effect of physical aging below Tg on the water vapor permeability (WVP) of starch film was investigated. The WVP was reduced by aging below Tg, which agreed with the results reported previously for several synthetic polymer systems. Consequently, in the present study, the reduction of moisture transfer during aging can also be interpreted as a result of decreasing free volume, which occurs simultaneously with enthalpy relaxation.