Isoconversional Kinetics of Glass Aging

Differential scanning calorimetry (DSC) has been applied to study the enthalpy relaxation in maltitol glass at 39-42 degrees C. Isoconversional kinetic analysis of the data has revealed that the effective activation energy of the process increases significantly upon the conversion from the glassy to supercooled liquid state. For the early stages of aging, the activation energy is found to be similar to 117 kJ mol(-1), which is considerably smaller than the activation energy of the alpha-relaxation (413 kJ mol(-1)). The latter value is reached at the later stages of aging. The temperature dependence of the initial aging rates estimated at 10-30 degrees C yields activation energies in the range 60-80 kJ mol(-1). The obtained results suggest that the effective activation energy for the early stages of aging tends to approach the value characteristic of the beta-relaxation.