The Effect of Different Atomizing Gases and Drying Media on the Crystallization Behavior of Spray-Dried Powders

Abstract

The use of different atomizing gases (N₂ and CO₂) was found not to alter the calorimetric behavior of the spray-dried powders significantly compared with air-atomized spray-dried powders in a Buchi B-290 (Postfach, Switzerland) mini spray dryer. However, the drying medium (N₂ and CO₂) was found to influence other powder properties, as seen from the alteration of morphology for the powders. An inert loop was attached to the dryer to recirculate the drying medium (N₂ and CO₂ gases) and to provide better control over the humidity of the drying medium by condensing the evaporated solvent. The degree of crystallinity of the spray-dried powder was measured using moisture-induced crystallization (a moisture sorption test) and modulated differential scanning calorimetry (MDSC). The sorption peak height was found to be lowest in the case of N₂ gas (5 ± 1%, mean ± standard deviation, indicating more crystalline powder) and highest for CO₂ gas (9.3 ± 0.1%, indicating more amorphous powder) compared with air (7.4 ± 0.3%). However, the MDSC analysis found that the thermal behavior did not vary significantly. It is suggested that the gases’ physical properties seem to be the main cause for some of these alterations in the product behavior. Different atomizing gases and gas media used during the spray-drying process can potentially be used to achieve different product behaviors.

Keywords:

• Atomizing gas
• Crystallinity
• Drying medium
• Inert gas
• Morphology
• Sorption
• Spray-dried powder
• Spray drying

Notes

Data from Aftel et al.^{[ 11 ]}

*Standard temperature and pressure (STP).