Morphological, thermal, barrier and mechanical properties of LDPE/EVOH blends in extruded blown films

We have investigated the morphological, thermal, barrier, and mechanical properties of low-density polyethylene/ethylenevinyl alcohol blend (LDPE/EVOH; 85/15 wt%) in highly and biaxially oriented blown films. Maleic anhydride-grafted linear low-density polyethylene (LDPE-g-MAH) in various concentrations (from 0 to 10 phr) was used as the compatibilizer for the immiscible system. Thermal analysis of the blend films shows that their melting temperatures, crystallization temperatures, and heats of fusion stay almost constant upon varying the amount of compatibilizer. The addition of the compatibilizer did not adversely affect the inherent properties of the blends, especially their barrier properties, through constraint effects of the grafted EVOH (EVOH-g-LD). The heat of fusion of EVOH obtained during the first heating is much higher than that of the second as a result of stress-induced crystallization during the blown film process. Oxygen permeation measurements show that the oxygen barrier properties of both highly and biaxially oriented blown films decrease upon increasing the amount of compatibilizer. although morphological analysis showed that the blends exhibit better laminar dispersion of the EVOH phase in the LDPE matrix when LDPE-g-MAH is added. The increase in oxygen permeability results from the presence of microvoids at the interface between the two phases during the process. Mechanical measurements showed that there exists an optimal amount of LDPE-g-MAH for maximizing both the tensile and tear properties in both the machine and transverse directions.