Blendas de polietilenos de fonte renovável: comportamento reológico e instabilidades de fluxo.

Abstract

The polyethylene presents a high degree of diversity in relation to the molecular structure, being able to present long and short branches and varied molecular weight distribution, which affects its rheological behavior. The study of the rheological properties, such as apparent viscosity, shear stress and extrudate swelling of HDPE/LLDPE blends is extremely important in order to determine ideal processing conditions and obtain control over the flow instabilities present in polymers at shear rates employed during processing. This work aims to study the rheological behavior and flow instabilities of polyethylene blends from renewable sources (HDPE/LLDPE) at low and high strain rates. The effects of LLDPE concentration and strain rate on extrudate swelling and flow instability were investigated. In all the analyzed compositions there was an increase of the extrudate swelling with the increase of the deformation rate. For pure PELBD and higher PELBD blends, swelling was attenuated by the emergence of sharkskin type flow instabilities, stick-slip and gross melt fracture. Extrudate swelling corroborated the damping coefficient (tan ) where LLDPE, which exhibits more elastic behavior, exhibits greater extrudate swelling.