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 sp ontaneously from solution in the form of a tetrahydrate, the eutectic, liquidus and solidus curves of which can be measured up to a sugar co ncentration of 86% w/w. Thereafter, crystallisation becomes too slow t o be observable in real time. The eutectic conditions for the binary s ystem tetrahydrate-anhydrous trehalose or the melting temperature of t he anhydrous sugar cannot therefore be established. The path of crysta llisation was found to be complex, and complete crystallisation of wat er and sugar could not be achieved, despite the application of various annealing procedures. A glass-transition profile could be fitted to t he experimental data for the amorphous mixtures by means of the Gordon -Taylor equation. Evidence is presented for the possibility of a polym orphic transition of the tetrahydrate at 272 K.