(461b) Novel Approach for the Characterization of Powder Caking

Storage and transport conditions such as temperature and humidity can have a wide range of effects on the physical properties of powders such as loss of pharmaceutical potency, food spoilage and powder caking. Powder caking is the undesirable process of a powder forming agglomerates, referred to as “cakes”. Industrial methods of determining caking conditions are often time-consuming, require large sample volumes and provide little scientific insight. However, current analytical techniques rarely represent “real-world conditions” and may provide inaccurate data when compared to the storage and transport lifetime of the powder sample.

We have developed a novel characterization method for assessing the role of humidity in caking, allowing for in-situ measurements of powder flow while exposed to a tunable environment of humidities. It is faster than current industry standards and correlates to common methods used. The technique uses commercially available equipment such as the FT4 Powder Rheometer, correlates to common experimental methods used in solids handling industries and is easily reproducible due to its modular design. Among other parameters, the instrumental setup measures flowability energy, as a function of relative humidity. Powder flow energy is a measure for a powder’s resistance to flow. Parameters that influence powder flow energy include particle size, shape, cohesivity, density, elasticity and electrostatic charge.

To further understand the interaction of relative humidity with the studied powders and the mechanism of caking, supporting DVS (Dynamic Vapor Sorption) experiments were performed. DVS is a gravimetrical analysis tool that measures a materials uptake of water vapour and potentially a variety of other gases while allowing tight control over the temperature in ranges typical for industrial storage and transport (10-50°C), (0-95% RH). We were especially interested in equilibrium sorption capacities and the kinetics of the water uptake. DVS can be combined with Raman and near IR spectroscopy to provide insight in phase transitions, swelling behaviour and deliquescence of materials.

Our measurement protocol is designed to assess caking conditions, but the flexibility of the setup has the potential to be utilized more broadly for determining the moisture-induced changes in powder rheology for example in wet granulation, drying and mixing processes. This way of characterization can be used for a wide range of powders differing in crystallinity, morphology, particle size and chemical structure.