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THE MORPHOLOGY OF SPRAY-DRIED PARTICLES A QUALITATIVE VIEW

ABSTRACT Industrial and pilot plant spray-dried materials were obtained from various manufacturers and qualitatively examined in order to identify structural and morphological features. Three distinct categories of particle morphology were identified. Namely, crystalline, skin forming and agglomerate. A number of unusual morphological phenomena were also noted Selected properties such as powder flowability. particle size and particle friability, were found to be directly related to morphological structure. Single particles were also produced in a convective drying process analogous to spray drying, in which, different solids or mixtures of solids were dried from solutions, slurries or pastes as single suspended droplets. The localised chemical and physical structures were analysed, and the results related to experimental conditions viz. drying air temperature and initial solids concentration. There was a strong similarity between the industrial spray-dried material and those dried experimentally. The morphologies of multicomponent mixtures were found to be complex, with the respective migration rates of the solids being dependent on drying temperature. The results are of relevance to dryer optimisation and to the optimisation of product characteristics, They also go some way to validating the single droplet drying technique as a useful analytical tool in spray drying research, and possibly other particulate processing industries.