Transformations of crystalline sugars upon milling

In this paper we compare the solid-state transformations upon room temperature milling of four sugars: lactose, trehalose, mannitol and sorbitol. The two disaccharides (lactose and trehalose) are found to undergo a direct transformation from crystal to glass while the two sugar alcohols (mannitol and sorbitol) are found to undergo polymorphic transformations. The origin of these different behaviors is discussed and ascribed to the relative position of the glass transition temperature (T _g) of the amorphous states with respect to the milling temperature. This point was also finely studied through co-milling experiments of lactose and mannitol. These two compounds having their glass transition respectively above and below room temperature the T _g of the mixture can be conveniently tuned on either side of the milling temperature by varying the concentrations.