1. There is an eruption phenomenon when the freeze-dried product is evacuated: this is because the vacuum is evacuated before the product is frozen, and the pre-freezing temperature has not been lower than the eutectic point temperature, or has been lower than the eutectic point temperature, but the time is not enough , the freezing of the product has not been completed.
The solution is to lower the pre-freezing temperature and prolong the pre-freezing time.
2. Freeze-dried products have shrinkage and bubbling phenomenon: this is due to partial melting during the sublimation drying process, which evaporates from liquid to vapor, resulting in volume reduction, or the dried product dissolves into liquid, resulting in volume reduction. Seriously. Melting can cause bubbling due to high heating or poor partial vacuum that causes the product temperature to exceed the eutectic or disintegration point temperature.
The solution is to reduce the heating temperature and increase the vacuum degree of the freeze-drying box. The product temperature should be controlled so that it is 5°C lower than the eutectic point or disintegration point temperature.
3. No fixed shape: This is because the dry matter in the freeze-dried product is too small, the product concentration is too low, and no skeleton is formed, and even the dried product is brought out of the container by the sublimation vapor flow.
The solution is to increase the product concentration or add excipients.
4. Freeze-dried products are not finished: freeze-drying is completed when there is still frozen ice in the product, and the frozen part is melted into liquid after being out of the box, and a small amount of liquid is sucked away by the dried product, forming a "vacancy".
All the product dissolves into the liquid and becomes a concentrated liquid. When this product is out of the box, if you touch the bottom of the container, it will feel cold. Even if the product looks good, the residual water content will not be qualified.
The solution is to increase the heat supply, increase the temperature of the board layer or use vacuum adjustment, or it may be that the drying time is not enough, and the time for sublimation drying or desorption drying needs to be extended.
5. Uneven color of freeze-dried product: The product has a crystalline pattern, which is caused by the slow freezing rate.
The solution is to increase the freezing rate and not stay at temperatures around 0°C, so that the product freezes into smaller crystals. Sometimes a circle of darker layered lines can be seen in the product, which is often caused by poor vacuum in a short period of time during sublimation, and this phenomenon will occur after a short power outage.
6. The upper layer of the freeze-dried product is good, but the lower layer is not good: the sublimation stage has not yet ended, and the desorption stage is entered in advance, which is equivalent to increasing the temperature of the plate layer in advance, and as a result, the lower layer product is overheated and melted.
The solution is to extend the time of the sublimation stage; some products have too much loading thickness, or the resistance of the drying product is too large, when the product is dried to the lower layer, the sublimation resistance increases, and the partial vacuum deterioration will also cause the melting of the lower layer product. The solution is to lower the plate temperature and increase the vacuum in the freeze-drying box.
7. The upper layer of freeze-dried products is not good, and the lower layer is good: the surface of the product forms an airtight glass-like structure during freezing, but no reheat treatment is performed. Sublimation can proceed normally.
The solution is to do heat treatment when pre-freezing
8. The moisture content of the freeze-dried product is unqualified: the time in the desorption stage is not enough, or the vacuum adjustment is not used during the desorption drying, or the vacuum adjustment is used, but the high vacuum is not restored after the product reaches the maximum allowable temperature.
The solution is to extend the desorption drying time, use vacuum conditioning and restore high vacuum after the product reaches high temperature.
9. Poor solubility of freeze-dried products: Evaporation occurs during the drying process of the product, and the product is partially concentrated. For example, there is a hard block inside the product, which is melted during sublimation, resulting in evaporative drying and product concentration.
The solution is to appropriately lower the plate temperature, increase the vacuum degree of the freeze-drying box, or prolong the sublimation drying time.
10. Freeze-dried products lose vacuum: when the vacuum is corked, the vacuum in the bottle is good, but the vacuum is lost soon after storage. It may be that the cork is not matched or the aluminum cap is pressed too loosely, and the vacuum is lost due to air leakage. The solution is to replace the cork Or adjust the tightness of the pressed aluminum cap; it may also be that the water content of the product is too high, and the vacuum is lost due to the water vapor pressure.
The solution is to extend the time of the desorption phase. In addition, there is a quality problem that is not related to the freeze-drying curve and affects the product, due to leakage of silicone oil or hydraulic oil in the freeze-drying box.
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