Class-transition and melting behavior of poly(ethylene terephthalate)/poly(ethylene 2,6-naphthalate) blends

The glass-transition temperatures and melting behaviors of poly(ethylene te rephthalate)/poly(ethylene 2,6-naphthalate) (PET/PEN) blends were studied. Two blend systems were used for this work, with PET and PEN of different gr ades. It was found that T-g increases almost linearly with blend compositio n. Both the Gibbs-DiMarzio equation and the Fox equation fit experimental d ata very well, indicating copolymer-like behavior of the blend systems. Mul tiple melting peaks were observed for all blend samples as well as for PET and PEN. The equilibrium melting point was obtained using the Hoffman-Weeks method. The melting points of PET and PEN were depressed as a result of th e formation of miscible blends and copolymers, The Flory-Huggins theory was used to study the melting-point depression for the blend system, and the N ishi-Wang equation was used to calculate the interaction parameter (chi (12 )). The calculated chi (12) is a small negative number, indicating the form ation of thermodynamically stable, miscible blends. (C) 2001 John Wiley & S ons, Inc.