Melt flow index on high molecular weight polyethylene: A comparative study of experiments and simulation

The flow that takes place in a melt flow index (MFI) experiment has been simulated for two grades of high molecular weight polyethylene. Both materials present very similar rheological behaviour in the characteristic times involved in the MFI measure so an exhaustive experimental work has been necessary in order to reveal slight but important molecular differences. The materials have been characterized through an integral viscoelastic model K-BKZ. It has been adopted an isothermal assumption and the shape of the free jet downstream is included in the calculations. Further considerations about flow morphology, i.e. die swell and vortex enhancement, are discussed. Rheological experimental results have pointed out a molecular difference that is directly reflected in the flow extrusion behaviour of the materials studied.