Several factors affecting the freeze-drying effect of laboratory freeze-drying machines

An experimental freeze-drying machine is a device that first cools a substance containing a large amount of water to below its melting point or glass transition temperature, causing most of the water in the material to freeze into ice, while the remaining hydration and material components form an amorphous state. Then, under vacuum conditions, the frozen material is heated at low temperature to sublimate and dry the ice in the material. Next, the material is heated under vacuum conditions to remove adsorbed water and achieve analytical drying, while the material itself remains in the frozen ice shelf, so that the dried product does not lose its original solid skeleton structure, maintains its original form, and has rehydration properties.

Freeze drying or freeze-drying is one of all drying methods that is beneficial for the product. The sublimation physical phenomenon it relies on means transitioning directly from the solid state to the vapor state, bypassing the liquid aggregation state. Therefore, frozen products are dried under vacuum without thawing.

At present, experimental freeze-drying machines are widely used in the fields of biopharmaceuticals, traditional Chinese medicine health products, blood products, biological products, pharmaceuticals, and active substances, especially in the pharmaceutical industry. What factors will affect the freeze-drying effect during the freeze-drying process, that is to say, what are the factors that determine the success or failure of the experimental freeze-drying machine?

1. Co melting point:

During the drying process of experimental freeze-drying machine products, as the temperature gradually increases, the solidified solutes and solvents begin to melt continuously, and this temperature is also known as the melting point.

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 degree, the formed ice crystals no longer continue to increase, and the residual solution concentration will increase. The solute and remaining water will form a highly viscous glass state, and this temperature is also the glass transition temperature.

3. Eutectic point:

During the pre freezing process of the product, for the crystallization system, as the temperature continuously decreases, ice nuclei form in the system when the product reaches below the freezing point. The ice nuclei gradually grow, and the concentration of solutes in the remaining solution gradually increases. When it reaches supersaturation, crystals will precipitate. The temperature continues to decrease until the remaining solution solidifies into a mixture of ice and solute crystals. At this point, the temperature is also the eutectic point. But there is a situation where the eutectic point of some substances is not a specific temperature value, but a temperature range.

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 originally occupied by the ice crystals will become voids, resulting in a porous honeycomb like sponge structure in the drying layer. When the solid matrix temperature of the strange nest like structure is high, its rigidity continuously decreases. When the temperature reaches a certain critical value, the rigidity of the solid matrix is not sufficient to maintain the honeycomb structure, and the solid matrix wall of the cavity will collapse. The original channel for steam diffusion will be closed, preventing sublimation and resulting in a high moisture content in the finished product. This critical temperature is also the collapse temperature.