Barrier properties of polypropylene/polyamide blends produced by microlayer coextrusion

The gas barrier properties of injection molded structures prepared from polymer microlayers were investigated. Polypropylene and polyamide-66 were combined as microlayers with tens to thousands of layers. A thin tie layer of compatibilizer coextruded between the layers provided adhesion. Injection molding the microlayered materials at a temperature intermediate between the melting points of the constituents resulted in a high volume fraction of high aspect ratio polyamide-66 microplatelets dispersed in a polypropylene matrix. The resulting material had significantly reduced permeability to oxygen and carbon dioxide compared to the conventional melt blend. Structural models for permeability indicated that enhanced barrier arose primarily from increased tortuosity of the diffusion pathway provided by the oriented, flat platelets of high aspect ratio in the skin region of the complex injected molded structure.