The use of freeze-drying technology is becoming more and more extensive. This technology can maintain the original physical and chemical properties and biological properties of the dried product, and make the drug easier to dissolve and store for a long time.
In the freeze-drying technology, a vacuum freeze dryer is used. In the process of freeze-drying, what factors will affect the freeze-drying effect, that is to say, what are the factors that determine the success or failure of freeze-drying in a vacuum freeze-drying machine?
1. Eutectic point
During the pre-freezing process of the product, for the crystallization system, as the temperature continues to decrease, when the product reaches below the freezing point, ice nuclei are formed in the system, the ice nuclei are gradually growing, and the concentration of solutes in the rest of the solution will gradually increase.
When supersaturation is reached, crystals will precipitate, and the temperature will continue to decrease until the remaining solution completely solidifies into a crystalline mixture of ice and solute. The temperature at this time is also the eutectic point.
But there is such a situation, the eutectic point of some substances is not a specific temperature value, but a temperature range.
2. Glass transition temperature
During the pre-freezing process of the product, for the amorphous system, when the temperature of the product drops to a certain level, the formed ice crystals will not continue to increase, the residual solution will be concentrated, and the solute and the remaining water will form a very viscous liquid. Glassy state, the temperature at this time is also the glass transition temperature.
3. Eutectic point
During the drying process of vacuum freeze dryer products, as the temperature gradually increases, the completely solidified solute and solvent begin to melt continuously, and the temperature at this time is also the eutectic point.
4. Collapse temperature
During the drying process of the product, when the temperature of the drying layer rises to a certain value, the ice crystals in the material will gradually disappear, and the space occupied by the ice crystals becomes a cavity, so the drying layer has a porous honeycomb sponge structure.
When the temperature of the solid matrix of the honeycomb structure is higher, its rigidity decreases continuously.
When the temperature reaches a certain critical value, the rigidity of the solid matrix is not enough to maintain the honeycomb structure, the solid matrix wall of the cavity will collapse,
and the original steam diffusion channel will be closed, preventing the sublimation from proceeding, resulting in a high moisture content of the finished product. high.
This critical temperature is the collapse temperature.