Pharmaceutical Amorphous Organic Materials Characterization by Using the Differential Scanning Calorimetry and Dynamic Mechanical Analysis

This research has been carried out in order to demonstrate the use of differential scanning calorimetry (DSC) in detecting and measuring αand β-relaxation processes in amorphous pharmaceutical systems. DSC has been employed to study amorphous samples of poly (vinylpyrrolidone) (PVP), indomethacin (InM), and ursodeoxycholic acid (UDA) that are annealed at temperature (Ta) around 0.8 of their glass transition temperature (Tg). Dynamic mechanical analysis (DMA) is used to measure βrelaxation in PVP. Yet, the DSC has been used to study the glassy indomethacin aged at 0 and -10 oC for periods of time up to 109 and 210 days respectively. The results demonstrate the emergence of a small melting peak of the α-polymorph after aging for 69 days at 0°C and for 147 days at -10°C (i.e., ~55°C below the glass transition temperature) that provides evidence of nucleation occurring in the temperature region of the β-relaxation. The evolution of an endothermic recovery peak temperature features a plateau at longer annealing times, suggesting that the glass has made a signifi cant progress toward reaching the supercooled liquid state. It has been found that the melting peaks become detectable after the recovery peak reaches the plateau. The results highlight the importance of studying physical aging in the temperature region of the β – relaxation as a means of evaluating the physical stability of amorphous pharmaceutical materials.