Nowadays, polymer-metal hybrids are covering a broad range of advanced applications, especially in the automotive or aerospace industries where high performance and lightweight components are highly demanded. Hybrid parts may offer additional functionality regarding strength, durability, impact and wear resistance without sacrificing size or weight of the full component. However, there are still challenges regarding improving the adhesion between dissimilar materials such as metals to polymers and its composites. There is a lack of research about the influence of a post heat treatment on adhesion and durability in polymer-metal hybrids manufactured through an overmolding processing chain. There is also a need for using adhesive promoters that may offer simultaneous corrosion protection to metallic substrates in order to extend the lifecycle of the part when subjected to diverse harsh environments.
In this work, two organic coatings used as adhesive promoters on steel substrates were investigated: the first one is a polyester-based powder-coat adhesive developed in the Leibniz-Institute in Dresden. The second one is a high performance anti-corrosive electrophoretic paint that has never been reported in the literature as an intermediate adhesive layer in a thermoplastic-polyurethane (TPU) overmolding processing chain. A TPU was overmolded on both pre-coated steel substrates, and the adhesion of the polymer to the metal substrate was investigated after a heat treatment (annealing), and a subsequent hygrothermal aging at different temperature-humidity conditions. The influence of the annealing process on the adhesion and durability of the multilayered specimen was investigated in depth; similarly, failure modes and lifetimes were evaluated after the hygrothermal aging. Lifetime predictions calculated from kinetic parameters for solid decomposition -obtained from thermogravimetric analysis- were validated experimentally with polyurethane-steel hybrids commonly used as district heat pipes.
Adhesion of TPU on the steel substrate using both organic coatings as adhesive promoters was successful due to the contribution of new physical-chemical and mechanical interactions at the polymer-coating interface, especially after annealing at 100 °C for 20 h. Additionally, heat treated hybrids exhibited a much better performance because of the apparent increased in the anchoring density at the polymer-metal interfaces. It is conclusive that progressive failure of the multilayered specimen is strongly dependent on water diffusion rather than thermolysis of any of the components, as it was detected by FTIR, and observed in the micrographs on the artificially-aged hybrid surfaces.
Finally, accelerated aging was used to correlate lifetime predictions throughout the analysis of the kinetics of degradation using TGA experiments and mechanical tests. The calculated values of the activation energy evidence that durability of the polyurethane-based polymers is affected by temperature and humidity at the conditions described in this work. Lifecycle is directly related to kinetic parameters, and especially to the activation energy, EA. This kinetic parameter for pre-aged specimens, and particularly for those subjected to higher temperature conditions, were lower when compared to the fresh polymer; as it was demonstrated that TGA analysis is a primary tool to predict lifetime for thermoplastic and thermosetting polyurethanes.
| Identifer | oai:union.ndltd.org:DRESDEN/oai:qucosa:de:qucosa:23538 |
| Date | 07 August 2018 |
| Creators | Puentes-Parodi, Jaime Alejandro |
| Contributors | Gehde, Michael, Gehde, Michael, Wagenknecht, Udo, Technische Universität Chemnitz, Leibniz Institut für Polymerforschung |
| Source Sets | Hochschulschriftenserver (HSSS) der SLUB Dresden |
| Language | English |
| Detected Language | English |
| Type | info:eu-repo/semantics/acceptedVersion, doc-type:doctoralThesis, info:eu-repo/semantics/doctoralThesis, doc-type:Text |
| Rights | info:eu-repo/semantics/openAccess |
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