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

Abstract

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