Thermal properties of tristearin by adiabatic and differential scanning calorimetry

The thermal behavior of tristearin was studied by adiabatic calorimetry and differential scanning calorimetry (DSC). Specific heat capacities of two polymorphic forms were measured in the adiabatic calorimeter, where the beta-form was measured from 10 K to 370 K and the a-form was measured from 175 K to 370 K. The start of the measurement of the stable beta-form from 10 K allowed the calculation of its entropy, so we report the derived values of absolute entropy for the two forms of tristearin at 298.15 K. The enthalpies of fusion and melting temperatures for each polymorph were calculated from both the adiabatic and the DSC experimental data and are compared to the literature values. The values for the enthalpies of fusion of the stable beta-form are in excellent agreement, being (221.6 +/- 1) J center dot g(-1) and (219.6 +/- 2) J center dot g(-1) according to the adiabatic and DSC measurements, respectively. The data for the a-form are not in so good agreement, which we attribute to the difficulty to crystallize this phase in its pure form. Moreover, we examined the fleeting existence of the beta'-form and its transformation to the beta-phase under isothermal conditions.