THE INFLUENCE OF HEATING DRYING ON THE CRYSTALLIZATION OF AMORPHOUS LACTOSE AFTER STRUCTURAL COLLAPSE/

This study was designed to investigate the influence of collapse of am orphous lactose on its subsequent behaviour during drying, or other pr ocesses which cause increases in the temperature of the material. Amor phous lactose was prepared by spray drying from aqueous solution. The solid was dried and then exposed to 50% RH for various times in order to induce different amounts of collapse in the amorphous structure. Al l the samples remained amorphous for the range of exposure times used. During heating in a differential scanning calorimeter, the non-collap sed material crystallised at ca. 180 degrees C to give mostly alpha-la ctose, with some beta-lactose present. The collapsed lactose crystalli sed at ca. 70 degrees C and yielded mostly beta-lactose, with some alp ha-lactose monohydrate present. It can be concluded that the collapsed structure will crystallise on drying at lower temperatures than the n on-collapsed lactose. The non-collapsed material rapidly loses its sor bed water (this would occur during the early stages of drying), whilst the collapsed lactose loses its water suddenly during crystallisation . Thermogravimetric analysis revealed (generally) three distinct water loss peaks for the collapsed structure, two of which were believed to be due to crystallisation occurring and the final one being the loss of water of crystallisation. The sudden loss of water from the collaps ed material will make a substantial contribution to the free water con tent of a formulation and as such could cause confusion during drying processes. Material which was partially collapsed behaved in an interm ediate manner between non-collapsed and totally collapsed samples. (C) 1997 Elsevier Science B.V.