De- and rehydration behavior of α,α-trehalose dihydrate under humidity-controlled atmospheres Original Research Article

Effects of humidity were investigated on de- and rehydration behavior of α,α-trehalose dihydrate (Th) throughout simultaneous measurements of differential scanning calorimetry and X-ray diffractometry (DSC–XRD) and simultaneous thermogravimetry and differential thermal analysis (TG–DTA). When Th was heated from room temperature under dry nitrogen atmosphere, a metastable anhydrous crystal (Tα) was formed at 105 °C after dehydration of Th. The resulting Tα melted at 125 °C and became amorphous, followed by cold crystallization from 150 °C giving rise to a stable anhydrous crystal Tβ. Under a highly humid atmosphere, on the other hand, Tβ was formed at 90 °C directly as a result of Th dehydration. Tα was readily rehydrated and turned back to Th when nitrogen gas with low water vapor pressure of 2.1 kPa was admitted, whereas high water vapor pressure up to 7.4 kPa was required for rehydration of Tβ into Th. This study provided a picture of pathways that link various solid forms of trehalose, taking into account the effects of a humid environment.