Modulated temperature differential scanning calorimetry for examination oftristearin polymorphism: I. Effect of operational parameters

The transformations of tristearin were examined by modulated temperature di fferential scanning calorimetry (MTDSC) in order to study the effect of ope rational parameters on the nature of information obtained from this techniq ue. Tristearin has been used as a model polymorphic system showing metastab le phases and complicated transformation routes occurring at relatively slo w rates. The parameters examined were underlying heating/cooling rates and the amplitude of modulation. The first conclusion is that MTDSC enables ove rlapping alpha-melting and beta-crystallization events to be separated, thu s increasing the information obtained compared to normal thermal analysis. Other general conclusions are that observation of reversible processes is s trongly influenced by the underlying heating rate; low to moderate heating rates are recommended. Amplitude of modulation has a complicated effect on the phenomenon being studied; when studying systems that exhibit metastable or polymorphic transitions, it is recommended that a range of amplitudes b e tested to enable confirmation of whether an observed "recrystallization" effect is a new phase or the same phase as the one melting. Cooling with mo dulation disturbs the crystallization process, possibly leading to smaller or imperfect crystals; however, the phases obtained are not different compa red to normal DSC. The usefulness of MTDSC in analyzing these types of comp licated systems is primarily qualitative at the moment. Some recommendation s have been made as to the combinations of parameters for studying such sys tems.