Laminar morphology development and oxygen permeability of LDPE/EVOH blends

Morphology and oxygen barrier properties of LDPE/EVOH blends have been studied. Laminar dispersion of ethylene-vinyl alcohol copolymer (EVOH) with high oxygen barrier properties was obtained in the matrix of low density polyethylene (LDPE) when extruded through an annular blown film die. Various laminar morphologies were observed and the main factors determining the morphology of the blends were viscosity ratio of the components, processing conditions, and compatibilizer level. Oxygen permeation tests have shown that thinner and longer EVOH layers in larger numbers were more effective in reducing the oxygen permeability. The oxygen permeability of the compatibilized blend having 6 phr of LLD-g-MAH was reduced by a factor of 740. The correlation between morphology and oxygen permeability was explained as a function of the EVOH layer size (L x R) and the number of EVOH layers (N), which were closely related to the predeformed domain size (L(o) x R(o)). The high Weber number (resulted from large L(o) x R(o) and low interfacial tension) and low viscosity ratio yielded large L x R. However, small L(o) x R(o) produced high N. Experimental results of oxygen permeability were well correlated with (L x R) x N.