ENTHALPY RELAXATION AND GLASS-TRANSITION BEHAVIOR OF SUCROSE BY STATIC AND DYNAMIC DSC

The relaxation process of the sucrose in the glassy state and its glas s transition are studied by differential scanning calorimetry in both the conventional and the dynamic mode. The data on the kinetics of gla ssy relaxation are experimentally evaluated by measuring the enthalpy relaxation peaks as a function of the ageing times at three different ageing temperatures, namely 45, 55 and 60 degrees C. It is shown that the ageing process is a complex phenomenon with a rather large distrib ution of relaxation times. The value of the breath of the distribution of relaxation processes, beta, is 0.32 and it is in the lower range o f the distributions commonly observed. The dynamic components of the h eat capacity (C-p' and C-p '') have been obtained from the experiments carried out at different frequency of temperature modulation (nu=8.3- 83 mHz). These components are unaffected by the ageing process and the refore are more reliable for the correct T-g determination. The activa tion energies for the relaxation process and for the glass transition process are also evaluated. (C) 1997 Elsevier Science B.V.