Morphology and oxygen barrier properties of LDPE/EVOH blends

The morphology of the dispersed phase in immiscible polymer blends can have a significant effect on the final may be omitted physical properties. Laminar dispersion of an 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. A large range of morphology was observed and indicated that the main factors determining the morphology of the blends were the composition, the viscosity ratio of the components, the processing conditions, and the elongational fields at the exit of the die. Increasing amount of EVOH (front 5 to 20 vol %) resulted in increasing number of stacked layers. Highly elongated laminar structure was formed when the viscosity ratio (η_d(EVOH)/η_m(LDPE)) was close to one and slightly lower. Large predeformed domains in the extruder outlet (before drawing and blowing) with short residence time under high screw rpm and lower viscosity ratio in the die temperature favored the formation of well-developed laminar structure. Oxygen permeation tests have shown high barrier effects due to the formation of the laminar dispersion which acted as barriers to the permeant molecules by providing a long tortuous path.