Influence of the ethylene-(methacrylic acid)-Zn2+ ionomer on the thermal and mechanical properties of blends of poly(propylene) (PP)/ethylene-(vinyl alcohol) copolymer (EVOH)

The thermal and mechanical properties and the morphologies of blends of poly(propylene) (PP) and an ethylene-(vinyl alcohol) copolymer (EVOH) and of blends of PP/EVOH/ethylene-(methacrylic acid)-Zn2+ ionomer were studied to establish the influence of the ionomer addition on the compatibilization of PP/EVOH blends and on their properties. The oxygen transmission rate (O2TR) values of the blends were measured as well. PP and EVOH are initially incompatible as was determined by tensile tests and scanning electronic microscopy. Addition of the ionomer Zn2+ led to good compatibility and mechanical behaviour was improved in all blends. The mechanical properties on extruded films were studied for 90/10 and 80/20 w/w PP/EVOH blends compatibilized with 10% of ionomer Zn2+. These experiments have shown that the tensile properties are better than in the injection-moulded samples. The stretching during the extrusion improved the compatibility of the blends, diminishing the size of EVOH domains and enhancing their distribution in the PP matrix. As was to be expected, the EVOH improved the oxygen permeation of the films, even in compatibilized blends. (C) 2004 Society of Chemical Industry.