Crystallization Rates for Amorphous Sucrose and Lactose Powders from Spray Drying: A Comparison

Abstract

Sorption tests have been used to assess the effects of temperature, relative humidity, and molecular structure on the crystallization process within spray-dried lactose and sucrose at both room temperature and 40°C. Increasing the temperature by 10°C more than doubled the crystallization rate, up to three times for the case of lactose. Below a threshold value of the relative humidity, little to no crystallization was found, with this threshold being 51% for sucrose, at room temperature, which was lowered to 32% at 40°C. These results are consistent with the picture of the process as an activated rate one. Lactose and sucrose, which have the same molecular weight of 342 g/mol but different molecular structures and thus glass transition temperatures, showed similar overall crystallization rates for the same material temperatures, in contrast with the overall predictions of the Williams-Landel-Ferry (WLF) equation. The WLF equation suggests that the crystallization rate is a function of the difference between the material and the glass transition temperatures, but it is still possible that this equation may predict the effect of changing material temperature and relative humidity for a particular material.