Thermal Relaxation of Gelatin and Date Flesh Measured by Isothermal Condition in Differential Scanning Calorimetry (DSC) and its Relation to the Structural and Mechanical Glass Transition

Abstract

A new innovative method was developed to measure the thermal-relaxation by maintaining isothermal condition in a Differential Scanning Calorimetry (DSC). The DSC thermal-relaxation characteristics of gelatin and date flesh were found to be related with the structural- and mechanical-glass transition measured by conventional DSC linear-heating and thermal-mechanical analysis (i.e, Differential Thermal Mechanical Analysis, DMTA). Initial slope of the thermal relaxation curve (i.e., heat flow versus relaxation time) was determined and it was plotted as a function of relaxation temperature (i.e., isothermal condition). The initial slope-temperature graph showed three thermal relaxation characteristics: limited mobile, freely mobile and restricted mobile regions. The region 1 showed limited molecular mobility with increasing temperature, while region 2 showed free mobility with increasing temperature sensitivity. The intersection of the regions 1 and 2 was related to the structural-glass transition measured by conventional linear-heating in a DSC. The region 3 showed restricted mobility due to enhanced interactions of the phases at higher temperature. This region 3 was related to the entangled flow region measured by thermal-mechanical analysis in a DMTA.