Unveiling the importance of process parameters on droplet shrinkage and crystallization behaviors of easily crystalline material during spray drying

This study investigated droplet shrinkage and crystallization behaviors of easily crystalline mannitol model material. Different sized droplets were generated from feeds of different solid contents and dried into uniform microparticles via a microfluidic jet spray dryer. The droplet shrinkage behavior was characterized by comparing the size of dried microparticles and initially atomized droplets. Morphology and polymorphs of the microparticles were analyzed via SEM and XRD. Droplet shrinkage and crystallization behaviors were shown to be closing related to size, morphology, and polymorph of the spray dried microparticles. Droplets with small size or low solid content followed perfect shrinkage behavior, while droplets with larger sizes or higher solid contents demonstrated less shrinkage due to the earlier precipitation of a crust. Dense, partially hollow, or hollow spherical particles with different polymorphs (mixture of alpha- and beta-mannitol or fully beta-mannitol) were obtained depending on the process parameters, indicating the occurrence of different crystallization behaviors.