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

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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.