Description of morphological changes of particles along spray drying

A description of morphological changes of particles along spray drying was carried out by means of scanning electron and light microscopy. Samples of atomized material (40% maltodextrin solution) were withdrawn during drying from a laboratory spray drier at various vertical distances from the atomizing nozzle, photographs of these materials were taken and images analyzed for detecting processes such as crust formation, inflation and shrinking. Final product was analyzed by SEM, mean size of particles determined and fractal dimension of projected perimeter was evaluated by means of the box counting method. This parameter of particles allowed for distinguishing between irregular and smooth contours of final powders. It was possible to explore qualitative relations of morphology and moisture content of particles with air drying temperatures along the actual drying operation, especially those related to breakage and inflation (intermediate and high drying temperatures) and with collapse (low-temperature drying). (C) 2004 Elsevier Ltd. All rights reserved.