In food and pharmaceutical industries powders are very common intermediate or end products, and the understanding of their performance in their application is vital. The interactions of the powder with moisture and water have a strong influence on the functional properties of the powder. Water interactions play a vital role in the drying processes, such as spray- and freeze drying, and in formation of the structure of the particles. Milling is also a process where moisture can play an important role for the material properties of the produced powder, and its behaviour in subsequent processes. The formation of the particle surface in a drying process is strongly influenced by the adsorption of different components to the air-water interface in spray-drying, or ice-liquid interface in freeze-drying. This will be discussed for spray-dried and freeze-dried powders. Single droplet drying can be used for more detailed investigations, although the differences in time scale and length scale become important. Exposure of the powder to high relative humidity usually influences the structure and behaviour of the powder. when considering powders containing (poly)saccharides and/or proteins, the powder is typically at least partly amorphous and hygroscopic. The interactions with moisture can severely influence the powder structure, behaviour and stability. In particular, amorphous saccharides may undergo crystallization, leading to distortion of the powder structure, as will be illustrated in the presentation for both spray-dried and milled powders. Many powders will in their applications be dispersed or dissolved in water-based media. The wetting, dispersion and dissolution processes is complex, with these three processes occurring in parallel. Not only the surface properties and initial wetting are important, but also the overall composition of the powder. The physical structure of the powder needs also to be considered. These aspect will be discussed in the presentation.

Powder structure and the influence of water from drying to dissolution

255th National Meeting (2018)

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