The normal appearance of freeze-dried products is uniform color, dense pores, basically unchanged volume and shape before freeze-drying, forming sponge mass structure. If there are hard shell, collapse, cavity, ash dispersion and fragmentation, they are all abnormal shapes and unqualified products. The incomplete drying of lyophilizer products may be caused by the following reasons:
A. The drying time is too short or the temperature is too low, or both. If the thermometer and vacuum gauge are normal and several consecutive batches of drying are not complete, the drying time shall be extended and the sublimation temperature shall be increased if possible. If the previous product quality is normal, the drying time shall also be appropriately extended if it may be caused by sub packaging error, freezing rate error and vacuum degree error, The actual sublimation temperature is lower than the set sublimation temperature
B. The freezing rate is too fast. The grain is too fine, which slows down the sublimation rate. Due to the reduction of loading, or the long cooling time of empty box, the temperature is too low, the freezing rate will accelerate, the grain will become fine, and the escape of water vapor will be hindered. Therefore, it is necessary to extend the drying time or reduce the freezing rate
C. Incomplete freezing causes a gap or air resistance between the frozen product and the container wall, reducing the heat transfer effect. Due to incomplete freezing, evaporation freezing occurs during vacuum sublimation, reducing the volume of the product, forming a gap between the product and the container wall, and heat cannot be transmitted to the product. With the progress of Shenghua, the ice around the frozen block sublimates first, forming an insulating dry layer to surround the frozen block, It makes it more difficult to transfer heat to the frozen matter, so the drying time is prolonged
D. Some products are not completely dried. It may be caused by too large temperature difference between shelves, too severe distortion of trays or shelves, uneven or uneven bottom surface of bottles containing products, or uneven sub packaging of products. For lyophilizers with inferior quality, only extend the freeze-drying time to make the moisture content of most products meet the requirements
