Correlation between thermal properties and conformational changes in poly(ethylene terephthalate)/poly(ether imide) blends

Miscibility, crystallisation and melting behaviour in blends of virgin and recycled poly(ethylene terephthalate) (PET) with poly(ether imide) (PEI) ha ve been examined using DSC. The blends exhibit single, composition-dependen t Tg's over the entire composition range and a negative value of the Flory interaction parameter, indicating miscibility of the amorphous polymers. Th e crystallisation of the PET/PEI blends was dramatically slowed by PEI cont ents higher than 20%. A linear correlation between a structure-dependent pa rameter RT (from FTIR measurements) and the enthalpy of fusion (from DSC me asurements) for both types of PET samples used in the blends, make the dete rmination of the degree of crystallinity of the PET in any PET/PEI blend po ssible. In agreement with the melting behaviour of the PET/PEI blends, the average values of the activation energy for trans- conformer formation conf irm the negative effect of the PEI on the crystallisation of the PET. (C) 2 001 Elsevier Science Ltd. All rights reserved.