Modelling of material degradation of polypropylene on the co-rotating twin screw extruder

塑料在加工过程中的降解会影响最终产品的性能。在此过程中，由于机械和热应力的作用，聚合物链会被氧化降解而断裂或降解。除其他因素外，最终产品的断裂性能可能会降低。然而，材料的降解只能在复合过程之后才能确定，这需要大量的金钱和时间。本项目的目的是在同向旋转双螺杆挤出机上开发一个描述聚丙烯加工过程中分子量降解的模型。其目的是开发一种尽可能温和的工艺，但仍要考虑到额外的边界条件，如高产量。考虑了剪切速率、停留时间和温度等参数对模型的影响。通过改变螺杆和温度配置以及不同的速度和产量，上述影响参数也会有所不同。在本项目中，聚丙烯将被用作待检验的塑料，因为这是工业上最重要的散装塑料之一。使用了三种不同的PP类型，它们在MFI方面有所不同。要考察的目标值是特性粘度。Mark-Houwink图使用经验确定的表示聚合物线圈和溶剂之间流体动力相互作用的参数，描述了特性粘度和分子量(平均粘度)之间的比例关系。特性粘度的测定应使用乌氏粘度计。通过比较一定浓度的溶剂和溶液的通过时间，描述了相对粘度。通过Billmeyer的方法，现在可以确定Staudinger指数。这种情况下不采用凝胶渗透层析的评价方法，因为经济支出与效益不成比例，而且特性粘度的测定更容易为以后的应用所用。选定的工作点仍用凝胶渗透色谱进行检查，以验证模型。实验研究及其评价为描述双螺杆挤出机加工过程中的材料降解提供了一种新的模型。

The degradation of plastics during the processing process affects the properties of the final product. By mechanical and thermal stress during the process, polymer chains are broken down or degraded by oxidative degradation. Reduced fracture properties of the end product can be the result, among other things. However, the degradation of material can only be determined after the compounding process, which entails a great amount of money and time. The aim of this project is the development of a model for the description of molecular weight degradation in the processing of polypropylene on the co-rotating twin-screw extruder. The aim is to develop a process that is as gentle as possible, but which nevertheless takes into account additional boundary conditions, such as a high throughput. The parameters shear rate, residence time and temperature should be taken into account as influencing parameters for the model. By varying the screw and temperature configuration as well as different speeds and throughputs, the mentioned influencing parameters are to be varied. For the present project, polypropylene is to be used as a plastic to be examined, since this represents one of the industrially most important bulk plastics. Three different PP types are used, which differ in terms of the MFI. The target value to be investigated is the intrinsic viscosity. Using empirically determined parameters representing the hydrodynamic interactions between polymer coil and the solvent, the Mark-Houwink plot describes the proportional relationship between the intrinsic viscosity and the molecular weight (viscosity average). The determination of the intrinsic viscosity should be done by means of an Ubbelohde viscometer. By comparing the transit time of the solvent and the solution with a certain concentration, the relative viscosity is described. By the approach of Billmeyer the Staudinger index can now be determined. The evaluation method of gel permeation chromatography is not used in this case because the economic outlay is disproportionate to the benefit and the measurement of the intrinsic viscosity is easier for the later application. Selected operating points are still examined by gel permeation chromatography to verify the model. The experimental investigations and their evaluation serve to develop a new model for the description of material degradation during processing on twin-screw extruders.