Splitting characteristics of polyethylene films

Abstract

Ripping of thin polyethylene films (thickness less than 30μm) during packing processes in the packaging industry is often encountered. This type of failure is characterised by the slitting of the film with well defined sharp edges to the failure. This work investigated if, in addition to the intrinsic resin properties, the blow-up-ratio had an influential effect on this particular physical film characteristics, keeping other important processing conditions constant. Different types of polyethylene blends were chosen for this study. They differed from each other in their important physical properties such as melt index, and degree of side-chain branches of the molecules. A 45 mm diameter single-screw blown-film extruder was employed for making the films. The screw had a 25 L/D ratio and was incorporated with a Maddock mixing device located at its metering section. A 100 mm diameter die with a gap of 1.5 mm was used. The film thickness was kept at 20μm. It was found that films blown with a small blow-up-ratio have a higher tendency to be rippen open (i.e. split) than those blown with a high blow-up-ratio. On the mechanical properties of the films, the Elmendorf tear resistance and the dart drop impact resistance of the films were particularly examined. It was found that the splitting characteristic of the polyethylene films was best reflected by the dart drop impact resistance.