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

用活性填料、功能性填料或非活性填料对现有的工业热塑性塑料进行改性是一种具有成本效益且常用的性能调节方法。因此，不同聚合物与填料的共混是现代塑料加工中开发新塑料的关键步骤。改性的目的总是改变物理性质。活性填料能够增强机械性能，而弹性填料能够增强拉伸行为。聚合物中所有改性剂的高度均匀性对于实现所需性能至关重要。根据现有技术，使用不同几何形状、量和类型的添加剂显示出在低剪切速率下屈服的相同现象。从一定浓度的阈值和低剪切速率来看，似乎建立了颗粒的结构，即所谓的颗粒网络，其抵消了流动并显著增加了机器的压力要求。预期这种流动抑制也在拉伸应变下发生。然而，它可能处于与剪切应力下不同的浓度。拉伸应变下的网络的破坏预计在更高的变形率。本建议的目的是调查上述实验所示的假设，并在一个通用的模型中描述剪切和拉伸流的差异。添加剂对应变硬化的影响，例如对于长链支化聚丙烯，也需要检查。一方面，高度填充的聚合物的剪切和拉伸流动的差异可以根据颗粒浓度、颗粒形状和使用Trouton比的变形速率来概括。另一方面，剪切和拉伸流动的差异可以用粘度函数的时间和应变速率的函数来描述。选定的模型必须扩展有关屈服和粘度的变化，由于添加剂的影响。除了上述建模之外，还需要开发一种分析方法（如Cogswell），通过该方法可以直接从毛细管流变仪测量中确定拉伸粘度。通过毛细管流变仪的测量，可以方便地获得未填充和填充塑料的拉伸数据。在一个成功的项目之后，所建立的模型旨在普遍预测高填充塑料在拉伸流动中的行为，从而改进工具的设计，更好地估计机器的压力要求，并更准确地预测一般的加工行为。

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.