Many materials in the food, chemical and pharmaceutical industries, from raw materials, additives and intermediates through to manufactured products, are supplied as relatively free-flowing powders suitable for the manufacturing process or final application. These materials are often stored for extended periods, during which time some powders will gain strength due to particle/particle interactions. This is generally referred to as ‘caking’ and can significantly limit the ability of a powder to pass through the process train without interruption and can detrimentally impact product quality.
Many pharma packaging machinery manufacturers and companies have been working on the packing and storing on medicine. Let's see how this problem has been solved.
Caking occurs through one or more mechanisms – typically, mechanical, chemical and thermal – with the migration and absorption of water often the most influential. Limiting caking can be achieved by managing environmental conditions to keep materials in an optimal state; by adjusting the operational parameters (typically limiting the time the material is stationary) or by modifying the product formulation.
Through testing and understanding the behaviour of each material, it becomes possible to assess and minimize the risk of caking at different points in the process, to maximize and maintain product quality. Powder testing results can inform, for example, decisions about how often the material needs to be tumbled or agitated to keep it in a fit state for subsequent processing, and whether it can maintain its quality if packed in bags, kegs, bulk containers or tankers.
Regardless of the mechanism, however, determining the precise conditions which minimise the potential for caking requires a comprehensive understanding of the changes in flow properties that occur as a consequence.
The FT4 Powder Rheometer® is a universal powder tester that provides automated, reliable and comprehensive measurement of bulk material characteristics. This information can be correlated with process experience to improve processing efficiency and aid quality control. Specialising in the measurement of dynamic flow properties, the FT4 also incorporates a shear cell, and the ability to measure bulk properties such as density, compressibility and permeability.
In this study, the dynamic method was used to measure the flow energy of powder samples before and after caking to quantify changes in flowability. Flow energy is determined by means of a patented measurement principle that evaluates the resistance to the motion of a specially shaped blade moving along a prescribed path through a precise volume of powder. The resulting torque and force measurements are converted into a flow energy[1].
Samples are prepared by filling a test vessel with powder, and using the bespoke Conditioning cycle to generate a uniform packing structure. The vessel is then split to ensure a fixed sample volume which is then stored under the desired conditions.
Most of the powders experience an increase in their resistance to flow through the creation of stronger inter-particulate bonds. In some instances, these changes are reversible, but in many cases the powder has undergone surface changes that result in permanent bonds being created.
Humidity-Enhanced Caking
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