Morphology and Mechanical Properties of Poly(vinyl Chloride)/Ethylene-Vinyl Alcohol Copolymer Blends

The effects of mixing conditions on the morphology and the mechanical properties of poly(vinyl chloride) (PVC)/ethylene-vinyl alcohol copolymer (EVOH) blends were studied. Four kinds of EVOH having various ethylene contents in the range from 29 to 44 mol% were mixed with PVC, using a mixing roll at from 170 to 200°C and two procedures: one-step and two-step additions. The yield stress of the blend was affected not only by the EVOH contents but also by the mixing conditions. When the blends were mixed at 190°C by two-step addition, PVC first then EVOH, little decrease in the PVC yield stress was observed by the blending with the EVOH in the range from 10 to 40 parts by weight for all EVOH used. The heterogeneous structure in which the EVOH domains were dispersed in the PVC matrix was observed by means of a scanning electron microscopic observation of the polished surfaces of the blends. The domain size of the blend prepared by the above procedure was smaller than that of those mixed by the other methods. The viscoelastic properties showed that the blend was an incompatible system. In general, the yield stress of the incompatible blend was lower than that of its components. It was confirmed that the good dispersibility of incompatible domains mitigated the decrease in the mechanical properties.