660 Technische Chemie
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Within the scope of the present cumulative doctoral thesis six scientific papers were published which illustrates that modern reaction model-free (=isoconversional) kinetic analysis (ICKA) methods represents a universal and effective tool for the controlled processing of thermosetting materials. In order to demonstrate the universal applicability of ICKA methods, the thermal cure of different thermosetting materials having a very broad range of chemical composition (melamine-formaldehyde resins, epoxy resins, polyester-epoxy resins, and acrylate/epoxy resins) were analyzed and mathematically modelled. Some of the materials were based on renewable resources (an epoxy resin was made from hempseed oil; linseed oil was modified into an acrylate/epoxy resin). With the aid of ICKA methods not only single-step but also complex multi-step reactions were modelled precisely. The analyzed thermosetting materials were combined with wood, wood-based products, paper, and plant fibers which are processed to various final products. Some of the thermosetting materials were applied as coating (in form of impregnated décor papers or powder and wet coatings respectively) on wood substrates and the epoxy resin from hempseed oil was mixed with plant fibers and processed into bio-based composites for lightweight applications. From the final products mechanical, thermal, and surface properties were determined. The activation energy as function of cure conversion derived from ICKA methods was utilized to predict accurately the thermal curing over the course of time for arbitrary cure conditions. Furthermore the cure models were used to establish correlations between the cross-linking during processing into products and the properties of the final products. Therewith it was possible to derive the process time and temperature that guarantee optimal cross-linking as well as optimal product properties
The self-healing effect of melamine-based surfaces, triggered by temperature, was investigated. The temperature triggered reversible healing chemistry, on which the self-healing effect is based, was the Diels-Alder (DA) reaction between furan and malemeide groups. Melamine-furan containing building blocks were connected by multi-functional maleimide crosslinker via a Diels-Alder (DA) reaction to giva a DA adduct. The DA adduct was then reacted with formaldehyde to form a network by conventional condensation reaction of melamine amino groups with formaldehyde. The obtained resin was characterised and used for the impregnation of paper. Impregnated papers and neat resin werde used to perform scratch-healing tests and mechanical analysis of the novel coating system.
We report an investigation into the distribution of copper oxidation states in oxide films formed on the surfaces of technical copper. The oxide films were grown by thermal annealing at ambient conditions and studied using Auger depth profiling and UV–Vis spectroscopy. Both Auger and UV–Vis data were evaluated applying multivariate curve resolution (MCR). Both experimental techniques revealed that the growth of Cu2O dominates the initial ca. 40 nm of oxide films grown at 175 °C, while further oxide growth is dominated by CuO formation. The largely coincident results from both experimental approaches demonstrates the huge benefit of the application of UV–Vis spectroscopy in combination with MCR analysis, which provides access to information on chemical state distributions without the need for destructive sample analysis. Both approaches are discussed in detail.
Es wird ein Verfahren zum Ermitteln von Deskriptoren DI, welche mit Eigenschaften eines Partikelkollektivs korrelieren, beschrieben. Die Deskriptoren Di werden durch Auswerten von Messsignalen, welche mittels einer optischen Reflexions- oder Transmissionsmethode ermittelt wurden, bei der Licht in das Partikelkollektiv eingestrahlt und rückreflektiertes Licht mittels eines Fotodetektors detektiert wird, ermittelt. Das Verfahren weist die folgenden Schritte auf: a) Aufnehmen eines Intensitätssignals I(t) von dem Fotodetektor, wobei das Intensitätssignals I(t) eine zeitabhängige Intensität von durch den Fotodetektor detektiertem Licht angibt; b) Erstellen eines digitalisierten Intensitätssignals It durch Digitalisieren des aufgenommenen Intensitätssignals I(t) mit einer Samplingperiode &Dgr;t innerhalb eines Abtastfensters T vorbestimmter Zeitdauer; c) Erstellen eines Satzes von Koeffizientenwerten ai durch Umwandeln des digitalisierten Intensitätssignals It mithilfe einer mathematischen, vorzugsweise surjektiven Transformation; d) Ableiten der Deskriptoren DI aus den erstellten Koeffizientenwerten. Das Verfahren und eine zu dessen Ausführung vorgesehene Vorrichtung können deutlich einfacher implementiert werden als herkömmliche Verfahren, bei denen Partikelkollektive durch Erstellen einer Sehnenlängenverteilung (CLD) untersucht werden sollen. Die mittels des Verfahrens ermittelten Deskriptoren können bei einer Prozessanalyse verwendet werden, um beispielsweise einfach und schnell erkennen zu können, wenn sich ein Partikelkollektiv anomal verhält.
Melamine Formaldehyde (MF) resins are thermosetting synthetic materials. The present work deals with the evaluation of the impregnation process, modification of resin structure and abrasion resistant applications. During the industrial process paper is impregnated by aqueous oligomers. The drying procedure and the corresponding residual volatile content is a crucial step during production, because of its influence on the later surface quality. Standard measurement routines do not differentiate between physical and chemical origin. Using TGA and DSC methods, the evaporation of water could be characterized as a clear separation of solvent evaporation and the release of water during condensation. The method could be used to upgrade current quality control as well as reaction condition tuning. According to the characteristics of duroplastic material, the formed network is very dense but also brittle. Challenging applications require highly modified resins in order to decrease the network density. Substances from bio renewable resources offer chemical possibilities for covalent crosslinking. Several substance classes have been tested for compatibility via hydroxyl groups or amines. The addition of polyols under appropriate reaction conditions showed chemical incorporation into the MF prepolymer. NMR methods have been used to characterize the resins. The synthesized polymers represent a suitable alternative for the usage in challenging furniture and flooring laminate applications. MF applications for scratch and wear resistant surfaces are commonly reinforced by multiple layer setups with inorganic particles. Fulfilling normative requirements a one sheet setup of decorative paper has been developed and tested. The incorporation of special corundum particles directly on the decorative printed paper combined with a new coating system resulted in surfaces of the requested quality for wear resistance surfaces.
Decorative laminates are the most important class of surface-finished engineered wood products. However, while there are numerous scientific publications published dealing with the technology of wood, wood-based products and also liquid coating systems, there is practically no scientific research work available in the field of paper-based laminates. In view of an ever increasing global competition it is time to systematically apply and pursue scientific approaches in this field. The present work is based on a knowledge-based manufacturing paradigm. The application of scientific methodology (e.g. instrumental analysis, process analytics, design of experiments, chemometrics, process modeling) to the preparation of decorative laminates covering the whole process chain from resin synthesis to paper impregnation and to final laminate should enable a targeted design of material functionality.
Polycaprolactone (PCL) was electrospun with the addition of arginine (Arg), an α-amino acid that accelerates the haeling process. The efficient needleless electrospinning technique was used for the fabrication of the nanofibrous layers. The materials produced consisted mainly of fibers with diameters of between 200 and 400 nm. Moreover, both microfibers and beads were present within the layers. Higher bead sized were observed with the increased addition of arginine.
Woven piezoelectric sensors as part of the textile reinforcement of fiber reinforced plastics
(2019)
Sensor integration in fiber reinforced plastic (FRP) structures enables online process and structural health monitoring (SHM). This paper describes the development and application of woven fabric-based piezoelectric impact and bending sensors for integration into FRP. The work focuses on design and characterization of woven piezoelectric sensors, especially as a part of the reinforcement structure. The reinforcement of the component acts as a sensor in itself and therefore no additional external objects in the form of sensor components or sensor fibers, which could create unwanted weak points within the FRP, are added. The bending test results reveal a direct relationship between the applied load and the sensor signal. Furthermore, the appropriate sensor position in the component cross section was determined and the influence of thermal polarization on the sensor properties was investigated.
In addition to increased safety by detecting possible overload, continuous component monitoring by sensor integration makes the use of fiber reinforced plastics more cost-effective. Since the components are continuously monitored, one can switch from time-based to condition-based maintenance. However, the integration of conventional sensor components causes weak points, as foreign objects are inserted into the reinforcing structure. In this paper, we examine the use of the textile reinforcement as a sensor in itself. We describe how bending sensors can be formed by slightly modifying in the composite’s reinforcement structure. We investigated two different sensor principles. (1) The integration of textile plate capacitors into the structure; (2) The construction of textile piezo elements as part of the reinforcing structure. The bending test results reveal that textile plate capacitors show a load-dependent signal output. The samples with textile piezo elements show a significant increase in signal strength.
Rational strain engineering requires solid testing of phenotypes including productivity and ideally contributes thereby directly to our understanding of the genotype-phenotype relationship. Actually, the test step of the strain engineering cycle becomes the limiting step, as ever advancing tools for generating genetic diversity exist. Here, we briefly define the challenge one faces in quantifiying phenotypes and summarize existing analytical techniques that partially overcome this challenge. We argue that the evolution of volatile metabolites can be used as proxy for cellular metabolism. In the simplest case, the product of interest is a volatile (e.g., from bulk alcohols to special fragrances) that is directly quantified over time. But also nonvolatile products (e.g., from bulk long-chain fatty acids to natural products) require major flux rerouting that result potentially in altered volatile production. While alternative techniques for volatile determination exist, rather few can be envisaged for medium to high-throughput analysis required for phenotype testing. Here, we contribute a detailed protocol for an ion mobility spectrometry (IMS) analysis that allows volatile metabolite quantification down to the ppb range. The sensivity can be exploited for small-scale fermentation monitoring. The insights shared might contribute to a more frequent use of IMS in biotechnology, while the experimented aspects are of general use for researchers interested in volatile monitoring.