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Flugreisen und Luftverkehr sind brennende Themen, wenn es um den ökologischen Fußabdruck geht. Damit beschäftigt sich das Forschungsteam um Prof. Dr. Gerd Wehnert und Prof. Dr.-Ing. Dominik Söthje von der Fakultät Angewandte Chemie. In ihrem Projekt bio-Lufa entwickelt es Faserverbundwerkstoffe auf Grundlage von nachwachsenden Rohstoffen für die Luftfahrt.
In diesem Vorhaben wurden verschiedene Bindemittel für die Herstellung von Hochleistungskeramiken analysiert. Ziel war es, biobasierte Binder zu identifizieren, die konventionelle auf fossilen Ressourcen basierende Systeme in Zukunft ersetzen können. Es wurden drei erdölbasierte Referenz-Bindersysteme und sieben biobasierte Alternativen bezüglich ihrer thermischen Stabilität unter Sauerstoffatmosphäre, der Viskosität ihrer wässrigen Lösungen oder Dispersionen sowie daraus hergestellter Schlicker und ihrer Haftung auf Aluminiumoxid-basierter Keramik untersucht. Im Rahmen des Vorhabens konnte ein biobasiertes Bindersystem mit Eigenschaften, vergleichbar zum besten Referenzmaterial gefunden werden. Unter Einsatz des biobasierten Binders sowie zweier ausgewählter Referenz-Bindersysteme
wurden Grünkörper hergestellt und deren Festigkeit ermittelt. Die Grünkörperfestigkeit ist in der keramischen Industrie ein entscheidender Faktor und stark vom gewählten Bindersystem abhängig. Die
erhaltenen Resultate deuten darauf hin, dass der Bio-Binder auch hinsichtlich der Festigkeitswerte den konventionellen Referenz-Bindersystemen als gleichwertig anzusehen ist. Die in diesem Vorlauf-
forschungsprojekt gewonnenen Erkenntnisse können als Ausgangslage für die Beantragung weiterer Fördermittel und die Akquise direkter Drittmittel aus der Industrie dienen.
Epoxy resins (EPs) are crucial for high-performance applications like lightweight materials, due to their excellent properties. However, the commonly used diglycidyl ether of bisphenol A (DGEBA) has two major disadvantages: it is synthesized mainly from petrochemicals and includes the health concerning bisphenol A. Eugenol is a bio-based aromatic compound that can be modified into di- or triglycidyl ether. Through investigations four monomers are obtained based on eugenol and crosslinked with two curing agents isophorone diamine and 4,4′-diaminodiphenyl sulfone to compare the properties of the resulting EPs with references containing DGEBA. Using new synthesis routes, the bio-content of the monomers can be increased up to 94 wt%. Intramolecular cyclization occurs if a hydroxy group is in ortho-position to the glycidyl ether group. The crosslinking conditions of the bio-based monomers are comparable to or lower than those of DGEBA. The eugenol-based triglycidyl monomers exhibit very high glass transition temperatures of up to 271 °C, almost 50 °C above the reference value, which can enable their use for lightweight construction such as matrices for fiber-reinforced plastics. The char content of all bio-based EPs after pyrolysis is significantly higher in comparison to the references, which may have a favorable effect on fire resistance.
AbstractThe increased use of carbon fiber reinforced thermosets generates more waste and end‐of‐life products. However, an efficient recycling method for the expensive carbon fibers has not yet been developed. The selective decomposition of amine‐cured epoxy resin under mild conditions is presented. A two‐step method was investigated to decompose the epoxy resin. The optimum parameters were initially determined using a model compound. By analysis of the reaction products, a cleavage of the C–N bond according to the Cope elimination could be proven. Therefore, the Cope elimination is suggested as the main step of the decomposition of amine‐cured epoxy resins in presence of hydrogen peroxide. By dissolving the resin, it is possible to recover resin‐free fibers with unimpaired mechanical properties.
The use of recycled carbon fibers (rCFs) in cement composites is beneficial regarding strength improvements and environmental aspects. In this paper, we present the addition of carbon fibers recovered from reinforced epoxides using hydrogen peroxide (H2O2) to cement-based composites. Two degrees of depolymerization were investigated regarding the physiochemical properties of the fibers and the interfacial interactions. Although regained CFs exhibited a smaller amount of oxygen-containing groups on the surface than virgin CF (vCF), they exhibit better adhesion and pullout resistance, as proved in single-fiber pullout tests from a cementitious matrix. The subsequent incorporation of recovered CFs into cement-based composites resulted in a pronounced increase in flexural and compressive strengths compared with the plain matrices and the cement reinforced with virgin CFs. Furthermore, the rCFs with a higher degree of depolymer-ization showed a better interfacial interaction toward cement matrices and hence also a better reinforcing effect.
Carbonfasern zurückgewinnen
(2023)
Faserverbundkunststoffe mit Duromermatrix lassen sich bisher nur unzureichend recyceln. Die starke Vernetzung der Duromere steht dem im Wege. Durch eine spezielle organisch-chemische Spaltungsreaktion können Carbonfasern nun jedoch aus Epoxidharz-basierten Faserverbundkunststoffen zurückgewonnen werden.
Abstract In initial experiments the effects of aromatic model substances on carbon nanotube (CNT) dispersions in dimethylformamide (DMF) were investigated. Electron‐deficient aromatics interact strongly with CNTs, causing increased agglomeration and sedimentation. Conversely, electron‐donating aromatics stabilize CNT dispersions in DMF. Polymers with electron‐deficient aromatics, such as polyd initrostyrene (PDNS), exhibit a concentration‐dependent effect: low concentrations lead to stabilization of dispersions, while higher concentrations lead to sedimentation. This suggests that such polymers can enhance attraction between the matrix of CNT‐reinforced polymers as well as stabilize the dispersed CNTs. Polycarbonate, modified with polydinitrocarbonate (PDNC) and reinforced with CNTs showed improved mechanical properties. The addition of 6 wt.% CNTs and 6 wt.% PDNC resulted in a notable improvement with a 22% increase in tensile strength, a 29% increase in flexural strength, a 39% increase in Young's modulus and a 47% increase in flexural modulus. This enhancement resulted in an overall mechanical performance comparable to the high‐performance polymer polyetherimide. However, there must be noted, that the addition of PDNC increases the CNT particle size, which can negatively affect mechanical properties. The results highlight the additive's dual role in enhancing adhesive interactions while potentially increasing CNT agglomerate sizes.Highlights
Interactions of CNTs dispersed in DMF and various aromatics were investigated.
Polydinitrocarbonate (PDNC) was synthesized as a new additive for CNT‐composites.
Polycarbonate/CNT‐composites were obtained using extrusion.
Test specimens with CNT contents up to 6 wt.% were obtained.
Mechanical properties of polycarbonate reached the level of polyetherimide.
It is known that ethylene plays an important role in the quality characteristics of fruits, especially in storage. To avoid the deterioration of fruits caused by ethylene, titanium dioxide (TiO2) has been used due to its photocatalytic capacity. The aim of this study was to develop films based on two types of biopolymers, Mater-Bi (MB) and poly-lactic acid (PLA), with nanoparticles of TiO2 and to determine their ethylene removal capacity and its application in bananas. First, the films were fabricated through an extrusion process with two different concentrations of TiO2 (5 and 10% w/w). Then, the films were characterized by their structural (FTIR), morphological (SEM), thermal (DSC and TGA), dynamic (DMA), barrier, and mechanical properties. The ethylene removal capacities of the samples were determined via gas chromatography and an in vivo study was also conducted with bananas for 10 days of storage. Regarding the characterization of the films, it was possible to determine that there was a higher interaction between PLA with nano-TiO2 than MB; moreover, TiO2 does not agglomerate and has a larger contact surface in PLA films. Because of this, a higher ethylene removal was also shown by PLA, especially with 5% TiO2. The in vivo study also showed that the 5% TiO2 films maintained their quality characteristics during the days in storage. For these reasons, it is possible to conclude that the films have the capacity to remove ethylene. Therefore, the development of TiO2 films is an excellent alternative for the preservation of fresh fruits.