Agglomeration of pharmaceutical, detergent, chemical and food powders — Similarities and differences of materials and processes

Product developers tend to make a distinction between different types of agglomerated powders depending on whether they are produced by the pharmaceutical, detergent, chemical or food industry. This is perfectly valid for the hygiene, quality, safety or economical aspects of processes and products. However, from a process engineering point of view a different classification is needed in order to identify similarities between product categories and to facilitate an effective cross-fertilisation between different industries. The current contribution shows that a classification of the different materials according to their molecular polarity and their supra-molecular structure enables to understand the behaviour of the powder particles in different agglomeration processes. Basically one can distinguish between hydrophilic/hydrophobic amorphous and hydrophilic/hydrophobic crystalline materials. Depending on their polarity, particles made of amorphous materials can be plasticized using either polar or apolar liquids. They have a viscoelastic behaviour and their mechanical properties are strongly dependant on plasticiser content, temperature and deformation speed. Conversely, the mechanical properties of crystalline materials are hardly affected by the vapour pressure of plasticising liquids until they dissolve at a substance-specific vapour pressure value. The mechanical properties of crystals are also less sensitive to temperature changes. As a consequence, particles made of these four material classes have to be agglomerated differently which means different binder solutions and different process conditions are required. Moreover, the agglomeration processes applied by different industries are discussed while considering the mentioned product classes. Similarities between agglomeration technologies are elaborated and the reasons why certain processes are preferred by some industries are explained.