Determining the influence of material structure and sizing on the comminution behaviour of carbon fibres

Mit der stetig wachsenden Nachfrage nach Carbonfasern (CF) und carbonfaserverstärkten Kunststoffen (CFK) steigt die Menge der CFK-Abfälle, die am Ende ihrer Lebensdauer verwertet werden müssen. Die Kenntnis der Abhängigkeiten des Zerkleinerungsverhaltens von CF von ihren mechanischen Eigenschaften, unter Berücksichtigung der möglichen Erzeugung und Freisetzung von lungengängigen Faserfragmenten (WHO-Fasern) während der Zerkleinerung, ist essentiell für alle optionalen Verwertungsverfahren. Zu diesem Zweck wurde eine Auswertungsroutine entwickelt, die aus einer Probenvorbereitung der gemahlenen CF, der Bilderzeugung durch optische Digitalmikroskopie, der automatischen Bildanalyse und der Datennachbearbeitung besteht. In dieser Studie wurden drei verschiedene CF auf Basis von Polyacrylnitril und eine auf Basis von Mesophasenpech in einer Planetenkugelmühle bei ausgewählten spezifischen Energieeinträgen unter Variation der Drehzahl und der Mahldauer zerkleinert und das Zerkleinerungsverhalten mit den mechanischen Fasereigenschaften (Zugfestigkeit, Elastizitätsmodul) verglichen. In einer weiteren Versuchsreihe wurden dieselben CF vor der mechanischen Zerkleinerung pyrolysiert, um den Einfluss der Schlichte auf das Zerkleinerungsverhalten der CF zu bestimmen. Die Versuche zeigten, dass der Einfluss der Schlichte auf das Zerkleinerungsverhalten von CF deutlich größer ist als der der Zugfestigkeit und des Elastizitätsmoduls. Zu erwähnen ist, dass bei allen Zerkleinerungsversuchen lungengängige Faserfragmente entstanden sind, was im Hinblick auf die Gesundheitsgefährdung bei der mechanischen Behandlung von CF zu berücksichtigen ist

Structured modeling and analysis of stochastic epidemics with immigration and demographic effects

Stochastic epidemics with open populations of variable population sizes are considered where due to immigration and demographic effects the epidemic does not eventually die out forever. The underlying stochastic processes are ergodic multi-dimensional continuous-time Markov chains that possess unique equilibrium probability distributions. Modeling these epidemics as level-dependent quasi-birth-and-death processes enables efficient computations of the equilibrium distributions by matrix-analytic methods. Numerical examples for specific parameter sets are provided, which demonstrates that this approach is particularly well-suited for studying the impact of varying rates for immigration, births, deaths, infection, recovery from infection, and loss of immunity

The nature and persistence of the effects of posthypnotic suggestions on food preferences: The final report of an online study

The persistence of food preferences, which are crucial for diet-related decisions, is a significant obstacle to changing unhealthy eating behavior. To overcome this obstacle, the current study investigates whether posthypnotic suggestions (PHSs) can enhance food-related decisions by measuring food choices and subjective ratings. After assessing hypnotic susceptibility in Session 1, at the beginning of Session 2, a PHS was delivered aiming to increase the desirability of healthy food items (e.g., vegetables and fruit). After the termination of hypnosis, a set of two tasks was administrated twice, once when the PHS was activated and once deactivated in counterbalanced order. The task set consisted of rating 170 pictures of food items, followed by an online supermarket where participants were instructed to select enough food from the same item pool for a fictitious week of quarantine. After 1 week, Session 3 mimicked Session 2 without renewed hypnosis induction to assess the persistence of the PHS effects. The Bayesian hierarchical modeling results indicate that the PHS increased preferences and choices of healthy food items without altering the influence of preferences in choices. In contrast, for unhealthy food items, not only both preferences and choices were decreased due to the PHS, but also their relationship was modified. That is, although choices became negatively biased against unhealthy items, preferences played a more dominant role in unhealthy choices when the PHS was activated. Importantly, all effects persisted over 1 week, qualitatively and quantitatively. Our results indicate that although the PHS affected healthy choices through resolve, i.e., preferred more and chosen more, unhealthy items were probably chosen less impulsively through effortful suppression. Together, besides the translational importance of the current results for helping the obesity epidemic in modern societies, our results contribute theoretically to the understanding of hypnosis and food choices.Peer Reviewe

Thermal Stability and Material Balance of Nanomaterials in Waste Incineration

Nanostructured materials are widely used to improve the properties of consumer products such as tires, cosmetics, light weight equipment etc. Due to their complex composition these products are hardly recycled and thermal treatment is preferred. In this study we investigated the thermal stability and material balance of nanostructured metal oxides in flames and in an industrial waste incinerator. We studied the size distribution of nanostructured metal oxides (CeO₂, TiO₂, SiO₂) in a flame reactor and in a heated reaction tube. In the premixed ethylene/air flame, nano-structured CeO₂ partly evaporates forming a new particle mode. This is probably due to chemical reactions in the flame. In addition sintering of agglomerates takes place in the flame. In the electrically heated reaction tube however only sintering of the agglomerated nanomaterials is observed. Ceria has a low background in waste incinerators and is therefore a suitable tracer for investigating the fate of nanostructured materials. Low concentrations of Ceria were introduced by a two-phase nozzle into the post-combustion zone of a waste incinerator. By the incineration of coal dust in a burning chamber the Ceria nanoparticles are mainly found in the size range of the fly ash (1 – 10 µm) because of agglomeration. With gas as a fuel less agglomeration was observed and the Ceria nanoparticles were in the particle size range below 1 µm

Thermal treatment of carbon-fibre-reinforced polymers (Part 2: Energy recovery and feedstock recycling)

The use of carbon fibre (CF)-reinforced plastics has grown significantly in recent years, and new areas of application have been and are being developed. As a result, the amount of non-recyclable waste containing CF is also rising. There are currently no treatment methods for this type of waste. Within this project different approaches for the treatment of waste containing CF were investigated. Main subject of the research project were large-scale investigations on treatment possibilities and limits of waste containing CF in high temperature processes, with focus on the investigation of process-specific residues and possible fibre emission. The results showed that the two conventional thermal waste treatment concepts with grate and rotary kiln firing systems are not suitable for a complete oxidation of CFs due to the insufficient process conditions (temperature and dwell time). The CFs were mainly discharged via the bottom ash/slag. Due to the partial decomposition during thermal treatment, World Health Organization (WHO) fibres occurred in low concentrations. The tests run in the cement kiln plant have shown the necessity of comminution for waste containing CF. With respect to the short testing times and moderate quantities of inserted CF, a final evaluation of the suitability of this disposal path was not possible. The use of specially processed waste containing CF (carbon-fibre-reinforced plastic (CFRP) pellets) as a carbon substitute in calcium carbide production led to high carbon conversion rates. In the unburned furnace dust, which is marketed as a by-product of the process, CFs in relevant quantities could be detected

Prospective Sustainability Screening of Sodium-Ion Battery Cathode Materials

Sodium-ion batteries (SIB) are considered as a promising alternative to overcome existing sustainability challenges related to Lithium-ion batteries (LIB), such as the use of critical and expensive materials with high environmental impacts. In contrast to established LIBs, SIBs are an emerging technology in an early stage of development where a challenge is to identify the most promising and sustainable cathode active materials (CAM) for further research and potential commercialization. Thus, a comprehensive and flexible CAM screening method is developed, providing a fast and comprehensive overview of potential sustainability hotspots for supporting cathode material selection. 42 different SIB cathodes are screened and benchmarked against eight state-of-the-art LIB-cathodes. Potential impacts are quantified for the following categories: i) Cost as ten-year average; ii) Criticality, based on existing raw material criticality indicators, and iii) the life cycle carbon footprint. The results reveal that energy density is one of the most important factors in all three categories, determining the overall material demand. Most SIB CAM shows a very promising performance, obtaining better results than the LIB benchmark. Especially the Prussian Blue derivatives and the manganese-based layered oxides seem to be interesting candidates under the given prospective screening framework

Prospective Sustainability Screening of Sodium-Ion Battery Cathode Materials

Sodium-ion batteries (SIB) are considered as a promising alternative to overcome existing sustainability challenges related to Lithium-ion batteries (LIB), such as the use of critical and expensive materials with high environmental impacts. In contrast to established LIBs, SIBs are an emerging technology in an early stage of development where a challenge is to identify the most promising and sustainable cathode active materials (CAM) for further research and potential commercialization. Thus, a comprehensive and flexible CAM screening method is developed, providing a fast and comprehensive overview of potential sustainability hotspots for supporting cathode material selection. 42 different SIB cathodes are screened and benchmarked against eight state-of-the-art LIB-cathodes. Potential impacts are quantified for the following categories: i) Cost as ten-year average; ii) Criticality, based on existing raw material criticality indicators, and iii) the life cycle carbon footprint. The results reveal that energy density is one of the most important factors in all three categories, determining the overall material demand. Most SIB CAM shows a very promising performance, obtaining better results than the LIB benchmark. Especially the Prussian Blue derivatives and the manganese-based layered oxides seem to be interesting candidates under the given prospective screening framework