Quantitative and qualitative use of thermal analysis for the investigation of the properties of granules during fluid bed melt granulation

This study describes a novel approach for the use of thermal analysis to study the aftermath of the fluid bed melt granulation process and to depict the growth mechanism of the granules by quantifying the enthalpies of the granules at every physicochemical change using DSC and their mass loss through TG coupled to MS for a qualitative determination of the composition and amount of the evolved gases for the corresponding fragment ion. The experiments were made in situ with lactose monohydrate and two viscosity grades of PEG (2000 and 6000) as meltable binders with different contents and size fractions. DSC showed the presence of a beta lactose endotherm peak after the melting of alpha lactose and a proportional increase in its intensity with the increase in the particle size and the content of the binder, which suggested a relation with the agglomeration growth. Interestingly, TG and MS showed a larger reduction in the water content from lactose with the increase in the binder particle size, making it possible to evaluate the dehydration during the melt granulation. Indeed, during the distribution mechanism the low binder particle size and viscosity exposed lactose to a high heat transfer from the fluidizing air. However, a high binder particle size results in lactose immersed in the PEG particles, causing water to be trapped inside the granules and hence a larger reduction in water mass loss indicating the immersion mechanism. Therefore, thermal analysis is a promising tool for granulation growth control.