Drying optimum residual moisture

WHO Criteria "the moisture content of the material shall be determined in order to verify that drying is adequate . If the formulation has been freeze-dried previously, the conditions required and achievable residual moisture level will be known. However, for formulations not previously freeze-dried, a series of laboratory tests and pilot studies are performed (see Section III) on the formulation. Results of these tests and trials are used to determine the most suitable freeze-drying conditions, in order to achieve the desired product including optimum residual moisture level. 

During the storage of a freeze-dried product, its qualities can change under the influence of at least three conditions residual moisture content, storage temperature and gas mix in the packing, assuming that the freeze-drying itself has been carried out under optimum conditions and the product had the intended qualities at the end... 

The vaccine against canine distemper also has an optimal residual moisture level at which an optimal freeze-drying efficiency can be obtained this optimum is located at approximately 2% (Figure 4). Stability during storage appears to be improved by a residual moisture of approximately the same order (1.8% Figure 5). 

Most engineering resins are hygroscopic and therefore must be properly dried before processing. Moisture has a generally adverse effect on the melt viscosity, surface, and physical properties of the product. To avoid these problems, resins must be dried, usually to a residual moisture content of < 0.02 percent, by weight. The optimum drying heat and time are given in the manufacturer s data sheet (see Chapter 9). 

The dryer (Miele 6559 TR) has a drum diameter of 110 cm, with a 550 litre volume. The drying air flows through the load horizontally - parallel to the drum axle - from the rear towards the door, thus achieving optimum evaporation level with a short drying time. The necessary temperature progression and precise residual moisture is ensured with precision electronics. 

In many products, the residual moisture in the product after completing primary drying is still too high for optimum storage. 

Moistened filter paper (Whatman No 541) was found to be optimum for collecting the residues from floor surfaces. The filter paper squares containing the powder residues were dried at 50° to remove moisture prior to reactor irradiation. Ba and Sb standards were also prepd to match the geometry of the test samples, and were irradiated under identical conditions... 

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