Diluent Segregation in Crystalline/Amorphous Poly(vinylidene fluoride)/Poly(vinyl acetate) Blends. Segregation Distance Dominated by the Crystal Growth Kinetics

Abstract

We systematically studied the effects of composition and crystallization temperature (Tc) on the morphological patterns of poly(vinylidene fluoride) (PVDF)/poly(vinyl acetate) (PVAc) blends by means of small angle X-Ray scattering (SAXS). The absolute intensity was measured so that the morphological structures can be resolved from the intensity perturbation. The scattering intensity associated with the PVDF lamellar stacks was strongly enhanced upon blending with PVAc. This was due to the presence of amorphous PVAc in the interlamellar regions that enhanced the electron density contrast between the crystalline and amorphous layers. Except for an intermediate Tc of 110°C where the systems attained the maximum crystal growth rate, partial extralamellar segregation of PVAc became prevalent when the PVAc composition exceeded 20 or 30 wt%. Even crystallization at as low as 20°C (where the diluent mobility was expected to be sluggish) produced a large extent of extralamellar segregation due to slow crystal growth. The results suggested that the crystal growth kinetics has dominated over the diluent mobility in controlling the average distance of diluent segregation in PVDF/PVAc with the prescribed molecular weight combination.