THE EFFECT OF CHAIN-LENGTH AND SOLVENT INTERACTIONS ON THE DISSOLUTION OF THE B-TYPE CRYSTALLINE POLYMORPH OF AMYLOSE IN WATER

To characterize the effectiveness of water as a diluent in depressing the melting temperature of amylose crystals, maltooligomer/water inter actions were probed, as a function of composition, by calorimetry and vapour sorption measurements. These studies, in part analysed using th e Flory-Huggins theory of polymer solutions, showed that although ther e is a strong energetic interaction between water and the oligomeric c hain, this is balanced by an opposing, first neighbour entropic contri bution. At room temperature, water was characterized as a poor solvent for the amylose chain. The dissolution in water of the B-type crystal line polymorph of amylose, crystallized from fractions of limited poly dispersity, ranging in chain length from 12 to 55 residues, was examin ed by scanning calorimetry. With increasing chain length in this range , the dissolution temperature, at a volume fraction of water of 0.8, i ncreased from 57 to 119 degrees C. The extrapolated dissolution temper ature for the high molecular weight polymer at this water content was 147 degrees C. (C) 1997 Elsevier Science Ltd.