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- ItemStrong Wet and Dry Adhesion by Cupped Microstructures(Washington, DC : American Chemical Society, 2019) Wang, Y.; Kang, V.; Arzt, E.; Federle, W.; Hensel, R.Recent advances in bio-inspired microfibrillar adhesives have resulted in technologies that allow reliable attachment to a variety of surfaces. Because capillary and van der Waals forces are considerably weakened underwater, fibrillar adhesives are however far less effective in wet environments. Although various strategies have been proposed to achieve strong reversible underwater adhesion, strong adhesives that work both in air and underwater without additional surface treatments have yet to be developed. In this study, we report a novel design - cupped microstructures (CM) - that generates strong controllable adhesion in air and underwater. We measured the adhesive performance of cupped polyurethane microstructures with three different cup angles (15, 30, and 45°) and the same cup diameter of 100 μm in dry and wet conditions in comparison to standard mushroom-shaped microstructures (MSMs) of the same dimensions. In air, 15°CM performed comparably to the flat MSM of the same size with an adhesion strength (force per real contact area) of up to 1.3 MPa, but underwater, 15°CM achieved 20 times stronger adhesion than MSM (∼1 MPa versus ∼0.05 MPa). Furthermore, the cupped microstructures exhibit self-sealing properties, whereby stronger pulls lead to longer stable attachment and much higher adhesion through the formation of a better seal. © 2019 American Chemical Society.
- ItemInfluence of the Reaction Injection Moulding Process on the Thermomechanical Behaviour of Fast Curing Polyurethane(Basel : MDPI, 2022) Lehmenkühler, Peter; Stommel, MarkusIn this contribution, the influence of the reaction injection moulding process on the thermomechanical material behaviour of aliphatic hexamethylene diisocyanate (HDI) based fast curing polyurethane is demonstrated. Uniaxial tensile tests, temperature-frequency dependent dynamic mechanical thermal analysis (DMTA) and Differential Scanning Calorimetry (DSC) are used to show the differences in properties for ten different sets of process parameters. The mould and resin components temperature, the mass flow during the filling process and the residence time during the reaction process of the polyurethane are varied in several stages. Further experiments to determine the molar mass of the molecular chain between two crosslinking points of the polyurethane are used to explain the process influences on the thermomechanical properties. Thus, a direct correlation between manufacturing and material properties is shown. In addition, the mutual effect of the different parameters and their overall influence on the material behaviour is presented.
- ItemMetal Plastic Hybrids: Optimisation in model experiments [Metall-Kunststoff-Verbunde: Modellversuche zur Optimierung](Weinheim : Wiley-VCH, 2019) Bräuer, M.; Edelmann, M.; Lehmann, D.; Tuschla, M.Metal plastic hybrids will become more important as components for lightweight constructions. It is reported about optimisation of making three layer hybrids consisted of a steel plate, an adhesion layer based of uretdione powder coating material and a flexible component polyurethane in model experiments. Hybrid formation is performed in a compression moulding process. The adhesion layer and the polyurethane are modified to increase the hybrid bond strength. Peel test are conducted to quantitatively characterize the bond strength and an apparent energy release rate is calculated based on the peel force. For hybrids with widths of 2 mm polyurethane stripes it is possible to increase the apparent energy release rate for about 30 % to 16 N/mm in comparison with a hybrid with unmodified components. These hybrids have the same high bond strength level as the strongest hybrids reported in literature. Concluding the optimisation results are discussed related to their relevancy for the interpretation of the adhesion mechanisms in the interface between adhesion layer and polyurethane. © 2019 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA.
- ItemAbschlussbericht zum Verbundvorhaben "Neuartige Polymere auf Basis von Triglyceriden" : Darstellung der erzielten Ergebnisse für die Teilvorhaben mit den Partnern ; Teilvorhaben 1: Entwicklung von Katalysatoren und Herstellung neuer Monomere, Leibniz-Institut für Katalyse e.V. an der Universität Rostock (LITKAT) ; Teilvorhaben 2: Herstellung der Polyamide und Polyurethane, Fraunhofer-Institut für Chemische Technologie (ICT) ; Teilvorhaben 3: Entwicklung von Verfahren zur Herstellung von Monomeren für Kunststoffe aus plfanzlichen Ölsäuren, Evonik Oxeno GmbH (Oxeno) ; Teilvorhaben 4: Herstellung der Polyamide sowie Bewertung, Evonik Degussa GmbH (High Performance Polymers [HPP]) ; Teilvorhaben 5: Herstellung der Polyurethane sowie Bewertung und Dokumentation, Rampf Ecosystems GmbH & Co KG ; Laufzeit des Vorhabens/Berichtszeitraum: 01.10.2008 bis 31.12.2011(Hannover : Technische Informationsbibliothek (TIB), 2012) Kugler, Michael; Baumann, Franz-Erich; Fehrenbacher, Ulrich; Fridag, Dirk; Köckritz, Angela; Petrat, Frank-Martin; Tübke, Beatrice; Walter, Guido[no abstract available]