Influence of Shearing Histories on the Rheological Properties and Processability of Branched Polymers

Abstract

Several papers^1–3 on anomalous viscoelastic behaviour of branched polymers have been published for the last several years. In these articles the term “anomalous viscoelastic behavior” means the following two notable phenomena: Firstly, when the branched polymers are sheared continuously, appreciable changes appear in their viscoelastic properties (e.g., an increase in melt flow rate, decrease in extrusion swelling, and reduction of surface roughness of extrudates), though no variation takes place in their primary molecular parameters such as molecular weight, molecular weight distribution, and the long-chain branching frequency during the shearing process. Secondly, the increased melt flow rate or the decreased extrusion swelling returns to its original value before the shearing by holding the shear-worked material in a molten state for several hours or by dissolving it in hot xylene and subsequently sucking the solvent with a vacuum pump.