Interfacial rheology testing of molten polymer systems: Effect of molecular weight and temperature on the interfacial properties

Abstract

The development of new interfacial rheological setup (IRS) for characterizing the interfacial viscoelastic properties of polymer systems is a subject of growing interest and constitutes a well-known challenge of high scientific and industrial application value. Recently, biconical and double-wall Ring (DWR) devices that can easily be attached to standard rheometers have been marketed for this purpose, but measurements must be made below 70 °C to ensure a stable homogeneous temperature at the interface. Meanwhile each device has its own limitation: the bicone has high inertia and a relatively low Boussinesq number, giving it a low signal-to-noise ratio, while the DWR is too fragile to probe the interfaces of high viscous systems in the molten state. Currently, to predict the dynamic interfacial properties of molten polymer systems, the interfacial rheology characterization is based mainly on indirect methods such as numerical modeling. In this study, a novel high temperature resistant interfacial rheology cell has been developed. This new setup allows direct interfacial rheology measurements up to 200 °C with temperature gradients of 1 °C at the polymer-polymer interface. To validate this new IRS device, the surface/interfacial properties of different model fluids having different well-known structure and viscoelastic characteristics have been investigated. To enable a more sensitive measurement of interfacial rheological properties, lightweight titanium based biconical geometry was newly designed. The effect of the molecular weight and the temperature was highlighted. Finally, the interfacial rheology testing of molten semicrystalline polymer systems has been achieved for the first time. The measured apparent interfacial shear properties in both oscillatory and steady flow modes were carefully corrected, considering the contribution of the bulk-subphases during processing of the numerical data.