RESIDUAL MOISTURE-CONTENT AS RELATED TO COLLAPSE OF FREEZE-DRIED SUGAR MATRICES

Amorphous sugars were prepared by freeze-drying 20% (w/w) aqueous solu tions of lactose, sucrose, trehalose and maltose. The dried samples we re further dehydrated over P2O5 for 1 wk at 25, 35 or 45 degrees C, an d the residual moisture content was determined using oven drying or a thermogravimetric balance. Results indicated a small amount of residua l moisture (usually 1-2%) which was not removed by the desiccation tre atment for 1 wk at 25 degrees C over P2O5. The dried samples, heated a t a temperature near the published ''anhydrous'' glass transition temp eratures (T-g) exhibited different behavior depending on whether they were heated in open or sealed vials. Structural collapse, a sharply vi sible shrinkage of the matrix, was found in all samples in sealed vial s, while those samples in open Vials did not collapse. Thus, removal o f the last amount of residual moisture by heating in uncovered vials i ncreased T-g, preventing or delaying collapse.