On the processability of metallocene-catalysed polyethylene: effects of blending with ethylene–vinyl acetate copolymer

The rheological properties of metallocene-catalysed linear polyethylenes and those of blends prepared with ethylene–vinyl acetate copolymers were evaluated. The pure polyethylenes showed characteristic features of linear polymers in the melt state, but poor processability, as would be expected for materials of narrow molecular weight distribution. The characteristic sharkskin and slip-stick regimes appear at around 0.16 and 0.35 MPa, respectively, during extrusion. Blending polyethylene with ethylene/vinyl acetate copolymers gave rise to smooth extrusion for a characteristic blend composition. The linear viscoelastic response of the blends revealed the behaviour of heterogeneous emulsion-like polymer systems. Through the application of several rheological criteria, we were able to locate the phase inversion concentration of the system. This concentration was found to closely correspond to that at which distortion regimes disappear during extrusion.