Method for making articles from polymer blends

Abstract

Polymer blends comprising a continuous matrix phase of thermoplastic polymer with a discontinuous phase of thermoplastic polymer distributed through it are produced by extruding a blend of immiscible thermoplastic polymers through an annular extrusion die which subjects the polymer blend to transverse shear forces prior to passing through the die lips. The application of the shear forces to the polymer blends produces improved uniformity of distribution of the continuous phase within the matrix, producing better properties in the finished article which may be a blown film or a blow molded product. The continuous matrix phase is suitably a polyolefin such as polyethylene and the discontinuous phase may be selected to provide the desired properties in the extruded article, for example, vapor barrier properties, strength, stiffness, and tear resistance. Typical polymers for the discontinuous phase are polyamides, EVA copolymers, polyacrylonitrile, polystyrene and various copolymers. The annular extrusion die which is used has an annular flow passage between two relatively moving walls in which the resin blend is subjected to the shear forces which promote the distribution of the continuous phase in the matrix.