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

Abstract

Poly(ethylene terephthalate) (PET) and poly(vinylidene fluoride) (PVF 2 ) are miscible in the meltstate for the whole composition range. The glass transition temperature (T g ) of the solvent cast film decreases with the decrease in W PET (weight fraction of PET) in the blend, however, the T g for the repeated melt quenched blends remains invariant with W PET . The melting point (T m ) and crystallization temperature (T c ) of PET decrease significantly with decrease in W PET in the blend, but the T m and T c of PVF 2 decrease slightly with increase in W PET . The crystallinity of both PET and PVF 2 decreases with increasing concentration of the other component in the blend, however, the decrease is larger for the former. The equilibrium melting points (T 0 m 's) of PET in the blends are determined by the extrapolation procedures using (i) T m - T c method for 5% crystallinity and (ii) T m -T a method, where T m , T c and T a are melting, crystallization and annealing temperatures, respectively. The data of both the methods indicate a large depression of T 0 m of PET with increase in PVF 2 concentration. The χ 12 values determined from both the data are essentially the same, -0.14. This negative value of χ 12 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 PVF 2 concentration in the blend.