An evaluation of the use of modulated temperature DSC as a means of assessing the relaxation behaviour of amorphous lactose

Purpose. To evaluate the use of Modulated Temperature DSC (MTDSC) as a mean s of assessing the relaxation behaviour of amorphous lactose via measuremen t of the heat capacity, glass transition (Tg) and relaxation endotherm. Methods. Samples of amorphous lactose were prepared by freeze drying. MTDSC was conducted using a TA Instruments 2920 MDSC using a heating rate of 2 d egrees C/minute, a modulation amplitude of +/-0.3 degrees C and a period of 60 seconds. Samples were cycled by heating to 140 degrees C and cooling to a range of annealing temperatures between 80 degrees C and 100 degrees C, followed by reheating through the Tg region. Systems were then recooled to allow for correction of the Tg shift effect. Results. MTDSC enabled separation of the glass transition from the relaxati on endotherm, thereby facilitating calculation of the relaxation time as a function of temperature. The relative merits of using MTDSC for the assessm ent of relaxation processes are discussed. In addition, the use of the fict ive temperature rather than the experimentally derived Tg is outlined. Conclusions. MTDSC allows assessment of the glass transition temperature, t he magnitude of the relaxation endotherm and the value of the heat capacity , thus facilitating calculation of relaxation times. Limitations identified with the approach include the slow scanning speed, the need for careful ch oice of experimental parameters and the Tg shift effect.