04 Fakultät Energie-, Verfahrens- und Biotechnik

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Author: search.filters.author.Ratka, Marcel

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    Experimental and simulative analysis of the pressure development in a closed injection pultrusion process with multiple chamber geometries
    (2023) Strauss, Sebastian; Wilhelm, Frederik; Senz, Andreas; Engelen, Herbert; Boysen, Simon; Rilli, Niko; Celik, Alptekin; Ratka, Marcel; Bonten, Christian
    The use of innovative higher-performance highly reactive resin systems requires an enhancement of the established method of fiber impregnation (open bath) towards closed resin-injection pultrusion (CIP), due to the short pot life of the resin systems. The result is that the open bath is developed into a closed injection and impregnation chamber (“ii-chamber”). In this study, three parameters - resin viscosity, opening angle and opening factor at the injection point on the ii-chamber - are varied, each in three stages. For each set of parameters, a pultrusion trial is conducted and the process pressures in the ii-chamber and pultrusion die measured. This enables direct feedback via the process conditions of the as yet uncured composite. The data obtained are used to validate a newly developed simulation model. The model is based on Darcy’s law, which has been extended to take fiber movement into account and thus represent the resulting pressure increase in the die. The flexible ii-chamber and die concept enhance our understanding of the processes taking place in the die system. The sensitivity of the process pressures can be shown for the three influencing variables. The experiment shows that of the three influencing variables investigated, viscosity has the greatest sensitivity to pressure development. In general, it can be said that over the length of the pultrusion die system, the pressure level increases across the three measuring points.
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    Mutual and thermal diffusivities in binary mixtures of polystyrene with dissolved N2 or CO2 by dynamic light scattering
    (2024) Schmidt, Patrick S.; Jander, Julius H.; Alhadi, Fatima; Ratka, Marcel; Bonten, Christian; Klein, Tobias; Fröba, Andreas P.
    In physical foaming processes of thermoplastics, a liquid mixture consisting of a molten polymer with a dissolved blowing agent is extruded through a die or injected into a mold. The morphology of the foam matrix strongly depends on the mutual diffusion coefficient D11 of the liquid polymer-blowing agent mixture. For a better understanding of the underlying physical mechanisms during the foaming process and the development of corresponding models, accurate knowledge of D11 is needed. This work reports on the simultaneous measurement of D11 and the thermal diffusivity a of liquid mixtures consisting of polystyrene melts with dissolved nitrogen (N2) or carbon dioxide (CO2) at mass fractions wsolute up to 0.003 or 0.02 and temperatures T between (433 and 533) K using dynamic light scattering (DLS). The determined D11 range is between (1 and 4) × 109 m2⋅s-1 and are slightly larger for the mixtures containing N2 at a given T and wsolute. D11 could be determined with an average expanded relative uncertainty of 18%. Considering all investigated state points and the achieved experimental uncertainties, both D11 and a are independent on the amount of dissolved gas, despite relatively large mole fractions of the dissolved blowing agents xsolute of 0.997 and 0.93.