Miscibility and Crystallization Behavior of Poly(ethylene terephthalate)/Poly(vinylidene fluoride) Blends

Abstract

Poly(ethylene terephthalate) (PET) and poly(vinylidene fluoride) (PVF2) are miscible in the melt-state for the whole composition range. The glass transition temperature (Tg) of the solvent cast film decreases with the decrease in WPET (weight fraction of PET) in the blend, however, the Tg for the repeated melt quenched blends remains invariant with WPET. The melting point (Tm) and crystallization temperature (Tc) of PET decrease significantly with decrease in WPET in the blend, but the Tm and Tc of PVF2 decrease slightly with increase in WPET. The crystallinity of both PET and PVF2 decreases with increasing concentration of the other component in the blend, however, the decrease is larger for the former. The equilibrium melting points (Tm0's) of PET in the blends are determined by the extrapolation procedures using (i) Tm–Tc method for 5% crystallinity and (ii) Tm–Ta method, where Tm, Tc and Ta are melting, crystallization and annealing temperatures, respectively. The data of both the methods indicate a large depression of Tm0 of PET with increase in PVF2 concentration. The χ12 values determined from both the data are essentially the same, –0.14. This negative value of χ12 indicates that the two polymers are miscible in the melt-state, however, they are not miscible in the crystalline state. The onset of degradation of PET increases with increase in PVF2 concentration in the blend.