Crystalline and amorphous phases in the binary system water-beta,beta-trehalose

The solid-liquid equilibrium phase relationships-and glass transitions, softening points and devitrification behaviour of binary water-beta,beta-trehalose have been studied by differential scanning calorimetry (DSC) over the accessible composition range. The sugar crystallises spontaneously from solution in the form of a tetrahydrate, the eutectic, liquidus and solidus curves of which can be measured up to a sugar concentration of 86% w/w. Thereafter, crystallisation becomes too slow to be observable in real time. The eutectic conditions for the binary system tetrahydrate-anhydrous trehalose or the melting temperature of the anhydrous sugar cannot therefore be established. The path of crystallisation was found to be complex, and complete crystallisation of water and sugar could not be achieved, despite the application of various annealing procedures. A glass-transition profile could be fitted to the experimental data for the amorphous mixtures by means of the Gordon-Taylor equation. Evidence is presented for the possibility of a polymorphic transition of the tetrahydrate at 272 K.