Effect of polymer content and molecular weight on the morphology and heat- and moisture-induced transformations of spray-dried composite particles of amorphous lactose and poly(vinylpyrrolidone)

Purpose. The aim was to investigate the influence of polymer content and molecular weight on the morphology and heat- and moisture-induced transformations, as indicators of stability, of spray-dried composite particles of amorphous lactose and poly( vinylpyrrolidone) (PVP). Methods. Amorphous lactose and composite particles of amorphous lactose with different contents and molecular weights of PVP were prepared by spray drying. The nanostructure of the particles was analyzed by x-ray powder diffractometry, the morphology by light microscopy and SEM, the glass transition temperatures (T-g), crystallization temperatures (T-c), heats of crystallization and melting temperatures by differential scanning calorimetry, and moisture-induced crystallizations gravimetrically and by microcalorimetry. Results. All the types of particles prepared were amorphous. The T-g was unchanged or only marginally increased as a result of the inclusion of PVP. However, crystallization temperature, time to moisture-induced crystallization, and particle morphology were affected by both content and molecular weight of PVP. Conclusions. Increased content and molecular weight of PVP may have the potential to increase the physical stability of amorphous lactose. However, T-g seems not to be a relevant indicator for the stability of this type of amorphous composite materials.