Comparing the crystallization of sucrose and lactose in spray dryers

The relative extent of crystallization for lactose and sucrose within spray dryers allows the WLF equation to be tested for this type of in-process crystallization, since this equation suggests that the crystallization rate is related to the difference between the material temperature and the glass-transition temperature of that particular material. In this study, the amount of sucrose crystallization during drying was studied using a bench-top spray dryer (Buchi B290) over a practical range of inlet gas temperatures (95–220 °C). It has been found that very large changes in the degree of crystallinity for the final spray-dried product can be achieved for sucrose by using different inlet gas temperatures, compared with much smaller changes in the crystallinity of lactose for a similar range of inlet temperatures. This result supports the suggestion that the crystallization rate is related to the difference between the material temperature and the glass-transition temperature, since sucrose has a much lower glass-transition temperature than lactose. The results have the potential to be implemented to achieve specified degrees of crystallinity in many powder materials produced from spray-drying processes.