Influence of the material properties of blowing agent loaded melts on the formation and structure of polymer foams

塑料发泡在塑料工业中扮演着重要的角色，因为它可以用来生产低密度以及良好的隔热和隔音性能的部件。泡沫组分性能曲线的决定因素是泡沫结构，它随工艺参数和所用材料的不同而变化很大。到目前为止，对含有溶解发泡剂的塑料熔体所产生的泡沫结构的预测是通过单独考虑发泡过程的各个步骤来实现的。对于气泡的成核和气泡的生长都存在各种模型，但由于它们仍然不能令人满意地预测发泡结果，这些模型直到今天仍被频繁地修改。一个主要原因是缺乏准确的发泡剂塑料熔体在与工艺相关的状态下的性能数据。目前应用的简化假设，如牛顿粘度行为和加载熔体的恒定状态无关扩散系数，与发泡过程的复杂性相矛盾。后者的特点是工作材料的性质、状态和工艺步骤本身的相互依赖性。本研究的目的是基于系统选择的模型系统，更好地了解含有溶解发泡剂的塑料熔体均匀混合物的溶解度、扩散系数和粘度对聚合物泡沫形成过程的影响。在未来，这应该能够根据温度、压力和混合物组成等可测量和可控制的状态特性来预测泡沫塑料特性。为此，我们将研究各种性能与泡沫结构之间的联系。与熔体相关的材料属性将被表示为状态属性的函数，并且进一步彼此关联。为了分析从填充发泡剂的熔体到得到的塑料泡沫的整个过程链，将使用并部分发展动态光散射、拉曼光谱、流变学、泡沫挤出和计算机层析等实验方法。分子动力学(MD)模拟将被用来深入了解流体结构并得出相应的结构-性质关系。此外，还应测试MD方法，以确定相关熔体的足够准确的热物理性质。确定的结构-性质关系用于解释宏观性质以及进一步发展描述发泡过程中气泡形成和增长的模型。

The foaming of plastics plays an important role in the plastics industry, as it can be used to produce components with low density as well as with excellent thermal and sound insulation properties. The decisive factor for the obtained profile of properties of the foamed components is the foam structure, which varies severely depending on the process parameters and the materials used. The prediction of the foam structure resulting from the plastic melt loaded with dissolved blowing agent has so far been realized by considering the individual steps of the foaming process separately. Various models exist for both the nucleation of gas bubbles as well as bubble growth, which have been frequently modified until today because they still cannot predict the foaming result satisfactorily. One major reason for that is the lack of accurate property data for blowing agent loaded plastic melts at process-relevant states. Currently applied simplifying assumptions, such as a Newtonian viscosity behavior and a constant state-independent diffusion coefficient of the loaded melt, are in contradiction with the complexity of the foaming process. The latter is characterized by interdependencies of the properties of the working materials, their states and the process steps themselves.The aim of this research project is to better understand the influences of especially solubility, diffusion coefficients and viscosities of homogeneous mixtures of plastic melts containing dissolved blowing agents on the formation process of polymer foams based on systematically selected model systems. In the future, this should enable the prediction of foam properties as a function of the measurable and controllable state properties such as temperature, pressure and mixture composition. For that purpose, the connections between the individual properties and the foam structure will be examined. The melt-related material properties will be represented as a function of the state properties and further related with each other. For the analysis of the complete process chain from the melt loaded with blowing agent up to the obtained plastic foam, experimental methods such as dynamic light scattering, Raman spectroscopy, rheometry, foam extrusion and computer tomography will be used and partly further developed. Molecular dynamics (MD) simulations will be utilized to gain insight into the fluid structure and to derive corresponding structure-property relationships. Furthermore, the MD-method should also be tested regarding the determination of sufficiently accurate thermophysical properties of the relevant melts. The identified structure-property relationships serve for the interpretation of the macroscopic properties as well as for the further development of models describing bubble formation and growth in the foaming process.