How do morphological changes of caffeine hydrate influence caking

Morphological changes in hydrates during the drying process can cause various potential problems. The crystal properties of caffeine, such as morphology and particle size distribution (PSD), vary with drying temperatures. We studied the mechanism of morphological changes in caffeine hydrate and their effect on caking behavior. During the drying process, caffeine crystals maintained their original needle-like morphology at lower temperatures (≤338 K), whereas numerous burrs were formed on the surface at higher temperatures. The morphological changes at different temperatures can be explained by the correlation between isothermal dehydration data and various kinetic models. A lot of burrs peeled away from the crystal surface and the products had wider PSDs and poorer morphology at higher temperatures because the removal of water in the crystal lattices is accelerated and there is not enough time to rearrange the crystal structure. The accelerated caking test indicated that products after agitated drying at higher temperatures exhibited a higher caking tendency.