A similar effect was also observed for an industrial waterborne automotive basecoat due to added aluminum flakes. A fourfold increase of the elongational relaxation time was observed upon the addition of 3.5 vol.% of glass flakes to such a highly shear-thinning system. Second, a substantial increase in the elongational flow resistance was achieved by adding a small amount of plate-like particles without affecting the shear viscosity of these thickener solutions. First, two acrylic thickener solutions that differ with respect to the fraction of hydrophobic co-monomers and hence with respect to their degree of inter- and intramolecular hydrophobic association were mixed to vary the elongational relaxation time, as determined using capillary breakup elongational rheometry (CaBER), by almost two orders of magnitude without affecting shear viscosity of these solutions in a wide, processing-relevant shear rate range. Here, we present two strategies that allow for varying the elongational flow behavior independent of shear rheology. Fully exploiting the potential of these technologies suffers from a lack of knowledge regarding how elongational flow properties of the processed fluids affect the results of these operations. Finally, the evolution of the morphology of homogeneous polymers, as well as of multiphase polymer-based systems, such as blends and micro- and nano-composites, subjected to the elongational flow is discussed, highlighting the potential and the unique characteristics of the processing operations based on elongation flow, as compared to their shear-dominated counterparts.Ĭomplex flow fields including high elongational deformation occur in numerous industrial processes such as spraying, coating, fiber spinning, and screen or inkjet printing. In particular, after a brief discussion on the theoretical features associated with the elongational flow and the differences with other flow regimes, the attention is focused on the rheological properties in elongation of the most industrially relevant polymers. This paper reviews the main achievements regarding the processing-structure-properties relationships of polymer-based materials processed through different operations with dominating elongational flow. To gain a thorough knowledge of the material-processing behavior, the evaluation of the rheological properties of the polymers experiencing this kind of flow is fundamental. Film blowing, fiber spinning and foaming are some examples in which the polymer melt is subjected to elongational flow during processing. Polymer-processing operations with dominating elongational flow have a great relevance, especially in several relevant industrial applications. The difference between the predicted pressure drops and the relevant experimental data is minimized such that the estimation of extensional viscosity is optimized herein. Under given various values of Trouton’s ratio for extensional viscosity, the GNF-X model is introduced to perform three-dimensional flow simulations of capillary rheometry over a range of apparent shear rates. Recently, the GNF-X (eXtended Generalized Newtonian Fluid) model with a weighted shear/extensional viscosity was proposed to show the typical extension-induced vortex growth in entrance flow simulations. However, using Cogswell´s extensional viscosity has always resulted in over-predictions of pressure drop.

The famous Cogswell method was derived analytically from the pressure drop of entrance flow in commercial capillary rheometers for estimating the extensional viscosity.

It is difficult to directly measure the steady extensional viscosity of thermoplastic composite materials, especially at high extension rates.

Cogswell cogs