Modelization of flow electrification in a polymer melt

Flow electrification of polymer melts is an important side effect of polymer processing. The studies dealing with this phenomenon are seldom and most of the scientific work has been focused on flow electrification of aqueous and insulating Newtonian liquids. From that prior art it is well established that the flow electrification in Newtonian liquids is a consequence of the formation of an ionic double layer. Convection of this layer induces the electrification of the liquid at the outlet of the pipe. In those models, the key parameters governing the flow electrification are thus the intrinsic electrical properties of the polymer and the flow characteristics. In this work, we reconsider the assumptions made previously and we propose a new approach to modelise the flow electrification in the particular case of non-Newtonian polymer materials in laminar flow conditions. We establish that, a key parameter for the electrification quantification in the polymer melt is the shape of the velocity profile. Additionally, in some cases, we show that a slip velocity at the polymer/die wall interface must be considered to describe accurately the electrification. As a consequence, we deduce that the slip velocity at the interface can be calculated by measuring the electrification: this work gives an alternative manner to measure the slip velocity during polymer flow

Linear viscoelasticity of incompatible polymer blends in the melt in relation with interfacial properties

A quite general characteristic of the rheology of incompatible polymer blends in the melt is their highly elastic behaviour at low fiequencies, corresponding to long-time relaxation processes. For emulsions of Newtonian liquids, this property can be readily connected to interfacial tension α : in a macroscopic flow, suspended droplets of radius R are subjected on the one hand to a viscous drag related to the viscosity µm of the matrix liquid and tending to deform their shape, and on the other hand to an elastic force of the order of α/R opposing the deformation. From a rheological point of view, the emulsion shows viscoelastic behaviour with characteristic relaxation times of the order of µmR/α. Blends of incompatible uncrosslinked polymers in the molten state can also be considered as emulsions, but the behaviour of the phases becomes viscoelastic by itself. A recent model, which accounts for the viscoelasticity of the phases, the polydispersity in size of the droplets and their hydrodynamic interactions, allowed us to explain the linear viscoelasticity of some selected polymer blends