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.
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.
This study covers the synthesis and characterization of two new bio-based epoxy monomers, diglycidyl-4-allylphenol (DG-4A) and triglycidyl-diallylphenol (TG-DA). Both are derived from estragole, a naturally occurring allylbenzene and a major component of the essential oils in basil. The resulting epoxy monomers, with high bio-contents of 92% (DG-4A), respectively 72% (TG-DA), were cured using two different amine hardeners: isophorone diamine (IPDA) and 4,4´-diaminodiphenyl sulfone (DDS). The curing agents were selected for their distinct properties: IPDA for its bio-based availability, and DDS for its ability to impart high thermal stability and rigidity. Dynamic mechanical analysis (DMA) showed that DG-4A/DDS had a high glass transition temperature (Tg) of 236°C, which can compete with the petrochemical-based reference system DGEBA/DDS (Tg = 238°C). For the TG-DA networks, the resulting Tgs were 235°C (IPDA) and 300°C (DDS), both were higher than those of the DGEBA reference systems, due to higher crosslinking density. The dynamic viscosities of DG-4A and TG-DA were 80 and 15 times lower than those of the reference DGEBA at room temperature. These results suggest that DG-4A and TG-DA are sustainable alternatives to DGEBA, as they offer comparable or higher glass transition temperatures while maintaining lower viscosities, making them promising candidates for applications requiring high thermal performance, such as in the aerospace and automotive sectors.
Carbonfasern zurückgewinnen
(2023)
Das Vorhaben bioFEDA hatte die Unterstützung der Erforschung und Entwicklung von Faserverbundkunststoffen mit biobasierter Harzmatrix zum Ziel. Im Besonderen sollte ein Verständnis des temperaturabhängigen dynamisch-mechanischen Verhaltens gewonnen werden. Das Projekt schließt hinsichtlich der weiterführenden frequenzabhängigen Charakterisierung biobasierter Epoxidharze direkt an die Ziele des derzeit am Lehr- und Forschungsgebiet Makromolekulare Chemie und Kunststofftechnik laufenden Projektes bio-Lufa an. Eine studentische Hilfskraft hatte durch die aktive Mitgestaltung Kontakt mit dem in den Leitthemen der Hochschule verankerten Bereich der Nachhaltigkeit. Die im Projekt erhaltenen Erkenntnisse finden direkten Einsatz in den Lehrveranstaltungen des Lehr- und Forschungsgebietes.