BINARY INTERACTIONS IN DIMETHYL TEREPHTHALATE BIS(2-ETHYLHEXYL)ADIPATE POLY(VINYL CHLORIDE) BLENDS STUDIED BY MELTING-POINT DEPRESSION METHOD

A novel approach is developed to estimate the interaction energy densi ty, B, of polymer solutions by the melting point depression method usi ng a crystallizable molecule as the probe. It rests on the classical F lory-Huggins lattice model of polymer solutions, and considers the pol ymer-solvent interaction parameter to be concentration dependent. The ternary system dimethyl terephthalate (DMT)/bis(2-ethylhexyl)adipate ( DOA)/poly(vinyl chloride) (PVC) is chosen for the present study. The d ata of B for the three possible binary interactions are reported as th e functions of composition at elevated temperatures. For a plasticized PVC resin containing 20 vol % DOA, the B is estimated to be 6 MJ m(-3 ), which is approximately 2 MJ m(-3) higher than the B value cited in the literature for the PVC mixed with almost 100% DOA. The thermodynam ic stability of the ternary system is discussed. (C) 1996 John Wiley & Sons, Inc.