Biaxially oriented polypropylene (BOPP) films with high oxygen barrier and high clarity were produced through the layer-multiplying, forced assembly process technique. 15-mil thick sheets with 33 alternating polypropylene (PP) / poly(ethylene oxide) (PEO) layers were coextruded and subsequently biaxial oriented at 135-150 °C. The biaxial orientation resulted in a layer thickness reduction from the microscale to the nanoscale. Crystallization of PEO was confined in the nano-layers where lamellae could only grow within a two dimensional plane. Highly in-plane oriented PEO lamellae improved the oxygen barrier by an order of magnitude. On the other hand, the films retained the high clarity.
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