Tc, Teu and Tg´
The system collapse temperature (Tc) is the point at which softening progresses to structural collapse of the dried cake. This can visually be observed by use of a Freeze Drying Microscopy (FDM).
For a crystalline system, collapse occurs if the lowest eutectic melting temperature (Teu) is exceeded. The collapse temperature for an amorphous system is determined by the glass transition temperature of the freeze-concentrated phase (Tg’). Teu and Tg’ can be determined using differential scanning calorimetry (DSC). The upper primary drying temperature is usually set 2-5 °C below Tc, Teu and Tg’.