Improved Description of Elongational Flow Behavior During the Processing of Highly Filled Plastics

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The modification of existing technical thermoplastics with active fillers, functional fillers or inactive fillers is a cost efficient and commonly used approach for property adjustments. Hereby is blending of different polymers with fillers a crucial step to develop new plastics in modern plastic processing. The aim of the modification is always a change of physical properties. Active fillers are able to enhance the mechanical properties whereas elastic fillers are able to enhance the elongational behavior. A high homogeneity of all modifiers in the polymer is essential to achieve the desired performance. According to the current state of the art, the same phenomenon of yielding at low shear rates is shown with additives of different geometry, quantity and type. From a threshold value of a certain concentration and at low shear rates, it seems that a structure of the particles, a so-called particle network, is set up which counteracts the flow and significantly increases the pressure requirement of a machine. It is expected that this flow inhibition also set under extensional strain. However, it is likely to be at a different concentration than under shear stress. The destruction of the network under extensional strain is expected at higher deformation rates.The aim of this proposal is to investigate the assumptions shown above experimentally and to describe the differences in shear and extensional flow in a general model. The influence of additives on the strain hardening, such as for long-chain branched polypropylenes needs to be examined as well. On the one hand, the differences in shear and extensional flow of highly filled polymers may be summarized in dependence of the particle concentration, particle shape and the deformation rate using the Trouton ratio. On the other hand, the differences in shear as well as in elongational flow can be described by a function of time as well as strain rate of the viscosity function. The selected model has to be extended concerning yielding and viscosity changes due to the influence of additives. In addition to the modeling above, an analytical method (such as Cogswell) needs to be developed with which the extensional viscosity can be determined directly from capillary rheometer measurements. This provides easy access to elongational data for both unfilled and filled plastics from capillary rheometer measurements.After a successful project, the established model is intended to generally predict the behavior of highly filled plastics in elongational flow and thus improve the design of the tools, better estimate the pressure requirements of the machine and to more accurately predict the processing behavior in general.