Rheological and Film-Casting Properties of Well-Characterised Polyethylenes with Different Branching Structure

We investigated the influence of branching structure on cast-film properties, i.e. the neck-in profile and final cast-film dimensions, for a series of metallocene catalysed PE as well as tubular reactor PE with various branching levels. For this study a lab extruder has been employed due to the small sample quantities available. The materials and flow conditions have been chosen specifically in order to match for various polyethylenes with different molecular structures at the die exit. Non-linear visco-elastic properties in shear and uniaxial elongation have been determined from constant strain-rate tests and fitted with a multi-mode Pom-Pom model, the parameters of which are discussed with respect to the molecular analysis of the branching structure. The experimental results for the film-casting behaviour as a function of long-chain branching content and draw ratio will be further compared to model predictions using recent theoretical approaches together with the Pom-Pom constitutive equation.