3 | Product description
Büchi Labortechnik AG
14/100
Operation Manual Lyovapor™ L-200/L-200 Pro
If using a drying chamber with heatable shelves, heat transfer takes place by direct
contact. The temperature of the heatable shelves is controllable. Control of the
thermal energy transferred is then possible.
Controlling the heat transfer prevents the following critical temperatures for
amorphous and crystalline materials to be reached:
the glass transition temperature T
g
' of the frozen preparation
the collapse temperature T
c
.
the eutectic temperature T
eu
.
Above the glass transition temperature and the collapse temperature, the viscosity
of the frozen preparation increases. The increased viscosity leads to the collapse of
the preparation's matrix structure.
Above the eutectic temperature, the preparation melts.
During the main drying phase, the product temperature must remain below the
collapse temperature for amorphous materials in the preparation.
Sublimation of the ice crystals progresses downwards from the surface of the
product. Above the sublimation boundary, the product is dry ("freeze-dried cake"),
while further inside the product is still frozen.
The end of the main drying phase is reached when all ice crystals have been
removed from the preparation.
After the main drying phase, the remaining fluid content in the preparation can still
be between 5 to 10%.
3.1.3
Secondary-drying phase
In the secondary drying phase, the unfrozen water is removed from the sample by
desorption. The secondary drying function is performed by the heatable shelves in
the drying chamber of the Lyovapor™.
In the secondary drying phase, the temperature of the heatable shelves is raised and
held for several hours.
The end of the secondary drying phase is reached when the residual moisture in the
sample is between 1% and 5% or the end point determination is succeeded.
