"Fiber Sage" - Development of a generalized material model for high performance fibers with incorporated nanoparticles

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Modern functional high performance fibers feature high mechanical properties on the one hand and outstanding functions like electrical conductivity on the other hand. The functionalization of the fibers can be achieved by a coating or directly by the incorporation of nanoparticles in the spinning process. For the second possibility, the specific adjustment of properties can only be reached if the mutual influence of polymer structure and incorporated nanoparticles is known. Unfortunately, there has been only small progress in this field although numerous studies were carried out. Above all, no model exists, which describes filament properties as a function of spinning parameters as well as type, geometric form, size and distribution of nanoparticles.In this research project, such a material model shall be developed, which is capable of predicting the main properties of nanomodified polymeric fibers. In the first part of the project, representative model systems (polyester and polyamide modified with carbon nanotubes (CNT)) were examined regarding the position and orientation of the nanoparticles, since these polymers represent the most important fiber materials and spinning parameters have a large influence on CNT orientation. For the exact determination of position and orientation, electron tomography was used to determine a three dimensional model of the nanostructure. The most important spinning parameters having an influence on the nanostructure and therefore on the mechanical properties are the spinning speed, the melt draw ratio and the solid state draw ratio. By comparing the nanostructure to the polymer structure determined by diffraction experiments, it was possible to show for the very first time, that the mechanical properties are not determined by the nanoparticles themselves, but by the changes in polymer structure caused by the orientation of the particles.In the following project phase, the material model shall therefore be extended to the component of polymer structure. The effect of nanoparticles on the polymer structure will be examined in detail by a parameter variation in the melt spinning process. Beside further parameter variations with CNT, layered silicates will be used as a model system for sheet like nanostructures, which have other effects on the fiber properties. The analysis of nanostructure is complemented by x-ray diffraction and scattering as well as electron nano diffraction to show the interaction between nanoparticles and polymer structure. By researching the relations between process, structure, nanoparticles and filament properties, an abstract model in the form of a neural network can be omitted and analytical equations can be used to describe the interaction. In the future, such a model could also be used to model further functionalities like electrical conductivity.