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技术热塑性塑料进行改性是一种经济高效且常用的性能调整方法。因此，将不同的聚合物与填料共混是开发现代塑料加工中新塑料的关键一步。改性的目的始终是物理性质的改变。活性填料能够提高力学性能，而弹性填料能够提高拉伸行为。聚合物中所有改性剂的高度均匀度对于实现所需的性能是必不可少的。根据本领域的现状，不同几何形状、数量和类型的添加剂在低剪切速率下表现出相同的屈服现象。从一定浓度和低剪切速率的阈值来看，似乎建立了一种颗粒结构，即所谓的颗粒网络结构，它抵消了流动，显著增加了机器的压力要求。预计这种流动抑制作用也会在伸展应变下发生。然而，它很可能处于与剪应力作用下不同的浓度。在较高的变形速率下，网络在拉伸应变下的破坏是预期的。本建议的目的是通过实验验证上述假设，并在一般模型中描述剪切和拉伸流动的差异。还需要研究添加剂对应变硬化的影响，例如对长链支化聚丙烯的影响。一方面，高填充聚合物的剪切流动和拉伸流动的差异可以归结为颗粒浓度、颗粒形状和变形速率的不同。另一方面，剪切和拉伸流动的差异可以用粘性函数的时间和应变率的函数来描述。由于添加剂的影响，所选择的模型必须扩展到屈服和粘度变化。除了上面的建模，还需要开发一种分析方法(如Cogswell)，利用这种方法可以直接根据毛细管流变仪测量来确定拉伸粘度。这提供了从毛细管流变仪测量未填充和填充塑料的伸长率数据的便捷途径。在成功的项目之后，所建立的模型旨在总体上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需求，并更准确地总体预测加工行为。

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.