Four specimens were prepared from one continuous Carbon Fiber Reinforced Thermoplastic Polymer (CFRP) tape and nondestructively tested using 2D X-ray micrographs and 3D X-ray Computed Tomography (CT). They were each polished on one front side and imaged by optical microscopy using a Keyence VK-X1000 confocal scanning microscope. These two-dimensional micrographs provided high-resolution reference data of the polished tape surfaces. CT was performed on the same specimens with a Zeiss Xradia 520 Versa at voxel sizes of 0.8, 2.0, and 3.5 µm each. The field of view was adjusted to include the polished front side, and the rotation axis was kept constant in between scans of one specimen. This configuration enabled the CT datasets to be registered into a common coordinate system. The registered stacks were subsequently cropped to the tape volume to optimize memory usage. The 3D CT datasets were segmented using structure tensor analysis and Trainable Weka Segmentation to extract fiber, matrix and pore regions in the CFRP tapes’ microstructure. The 2D microscopy images were used as complementary benchmarks to evaluate the required spatial resolution. The overall aim was to determine whether reliable microstructural characterization demands full fiber-level resolution, or whether coarser CT scans provide sufficient information.

The stochastic microstructure of recycled carbon fibre-reinforced composites poses significant challenges for process optimization and performance prediction, due to the disparity in scales between fibre diameter and fibre agglomerates size. This study establishes a comprehensive quantitative characterization framework to evaluate the microstructural evolution of recycled carbon fibre thermoplastic tapes processed under two distinct melt-compounding regimes with contrasting processing conditions. Utilizing a deep learning-based EfficientNet-B4 model and computer vision for robust fibre segmentation, we analysed the interplay between fibre morphology, orientation, and dispersion on large-field high-resolution micrographs. A novel quantitative approach revealed microstructural notions, hard to detect otherwise, and uncovered a critical trade-off governed by shear mixing history: while a shorter processing scenario preserved fibre length (>600μm), it resulted in a planar-random orientation state driven by the tumbling of large aggregates. Conversely, the longer processing scenario induced significant fibre fragmentation but facilitated a transition towards uniaxial alignment. To identify these changes in microstructure, novel homogenization factors (Cluster Prevalence Indicator (CPI) μ and Intra-Cluster Density Indicator (IDI) κ) and a Collective Similarity Index (CSI) were introduced. These metrics demonstrated that extended mixing transitions the material from a state dominated by volumetrically large, internally dense super-clusters to a locally dispersed microstructure, without altering the invariant global spatial periodicity (d^∗≈260μm). Furthermore, a comparative evaluation of statistical descriptors highlighted that while conventional topological metrics (e.g., Voronoi statistics) proved insensitive to processing variations, the proposed cluster-based metrics and eigenvalue-based orientation tensors successfully captured the structural nuances. This framework provides essential methods for tailoring the processing-structure relationships in recycled discontinuous fibre composites.

The drawback of biobased polymer matrix composites (PMCs) is their limited temperature stability, resulting from degradation, which restricts their processability in established composite manufacturing processes requiring elevated temperatures. These key issues not only affect the mechanical properties but ultimately limit the utilization of flax fibers as fiber reinforcement in PMCs. In this study, kinetic models for the thermal degradation of flax fibers and PA11 are derived and combined with a model for thermo-chemical fiber degradation. Selective degradation of the fibers and mechanical testing establishes a link between degradation and the accompanying deterioration of the mechanical performance. The deterioration of flax fiber mechanical properties under concurrent thermal and thermo-chemical degradation is primarily governed by the thermos-chemical contribution (chain scission) up to 3% thermal degradation, beyond which the influence of thermal degradation becomes evident. Even 1% thermal degradation of flax fibers results in a pronounced reduction in their mechanical performance. In contrast, equal degradation values enhance the PMCs' strength, which may be attributed to improved fiber-matrix interactions. Compiling results into processing maps establishes a framework for designing tailored processing of temperature-sensitive materials, offering transfer opportunities to individual processing conditions and heat treatments, enabling broader research on bio-based PMCs.

With initiatives such as the European Green Deal establishing more stringent environmental requirements, there is an increasing need to develop aircraft technologies and sustainable aviation practices with reduced climate impacts. Additionally, conventional environmental Life Cycle Assessments (LCAs) often struggle to capture the dynamic and complex nature of aircraft operations; in particular, non-CO₂ in-flight impacts, which contribute significantly to climate change, are often overlooked. In this study, we improve a discrete-event LCA approach with a climate impact evaluation model and apply it to scenario analyses comparing different aircraft designs, fuel types, and flight schedules. Our findings reveal that, contrary to previous LCA studies, the climate impact per kilometre flown increases with longer flight distances and that an efficiently planned flight schedule can reduce the overall environmental impact. The study highlights the necessity of incorporating non-CO₂ effects and operational scenarios into LCA to achieve a more accurate understanding of aviation's environmental impact.

Our aim with this work was to evaluate how the thermoplastic resin used in the composite adherends and on the energy director affected the static ultrasonic welding process in both parallel and misaligned configurations. Polyetheretherketone (PEEK) and low-melt polyaryletherketone (LMPAEK) were the resins used and their thermomechanical properties were characterized via dynamic-mechanical analysis and modulated differential scanning calorimetry. With parallel adherends, neither the welding time nor the through-thickness heating in the adherends vary significantly. This similarity was attributed to a larger heat capacity of the PEEK energy director counterbalancing its higher viscoelastic heating rate. With misaligned adherends, the welding time was larger for PEEK welds than for LMPAEK welds and LMPAEK adherends presented a larger though-thickness heating. These effects were attributed to the larger bulk viscoelastic heating rate of carbon fibre reinforced/LMPAEK adherends adding up to the lower heat capacity of LMPAEK.

Sustainable polymers are essential to reducing the environmental impact of conventional plastics. While the use of renewable feedstocks plays a significant role, the adoption of green processes, including sustainable solvent selection and efficient polymer purification, is equally essential. This study presents a green synthesis route for polymers based on two renewable vinyl lactone monomers: α-methylene-γ-valerolactone (MeGVL) and α-methylene-γ-butyrolactone (MeGBL). Polymerization was performed in renewable solvents as Cyrene®, γ-valerolactone, and 2-methyltetrahydrofuran via solution and in biobased alcohols through precipitation methods. While solution polymerization requires additional purification step through polymer precipitation, precipitation polymerization enables efficient polymer recovery and solvent reuse. The resulting polymers made via precipitation polymerization exhibit properties with glass transition temperatures of 99 °C (polyMeGVL) and 94 °C (polyMeGBL), and visible light transmittance over 96% between 450-700 nm of both polymer films of thickness around 100 μm. Water contact angles of the films were 62° for polyMeGVL and 51° for polyMeGBL showing difference despite having a similar chemical composition. These results highlight a scalable, low-impact pathway for producing commodity polymers entirely from renewable resources.

In developing Type V hydrogen tanks for energy storage in commercial airliners, the key design criterion is maintaining leak-tightness under cryogenic conditions. A concern is that anomalies in the laminate could cause microcracks, potentially compromising leak-tightness. This study investigates how resin flow, caused by mandrel expansion during curing, creates a gradient in the local fiber volume fraction (FVF) along the laminate thickness. An experimental study was performed comparing two resin systems, Hexcel 6376 and Teijin Q183. Cylindrical specimens were manufactured incorporating piezoresistive sensors to measure contact pressure at the mandrel-laminate interface during the autoclave cycle, serving as an indicator of resin flow and FVF variation. Micrographs of the specimen were taken, and a machine learning-based segmentation model was used to detect fibers and resin in the images, enabling calculation of the local FVF. The results show distinct through-the-thickness gradients in FVF for both laminates with a spread of 11.6 %pt. for Hexcel 6376 and 4.5 %pt. for Teijin Q183. These observations could be correlated to the processing characteristics of the two systems and therefore provide valuable insights for developing strategies to minimize FVF gradients in the design of carbon fiber-reinforced polymer (CFRP) tanks for liquid hydrogen.

The development of epoxy resin formulations from renewable feedstocks has been thoroughly explored in the chemical literature. A simple one-pot chemical reaction involving sustainable phenolic molecules and epichlorohydrin results in the production of renewable epoxy monomers. These monomers can be cured with amines or anhydrides to yield cross-linked thermosetting resins. Although a wide variety of recipes exist, there is a notable gap in the application of these sustainable resin formulations to engineering contexts. This gap is primarily due to the lack of comprehensive, standardized analyses of these resin recipes, which impede their potential use in advanced composite applications. In this study, we reveal a high-performance resin formulation utilizing epoxidized phloroglucinol derived from brown algae in combination with an aerospace-grade amine hardener. The resin processing and thermomechanical properties are investigated using ASTM standard tests including tensile strength, flexural strength, fracture toughness, and interlaminar shear strength. Given the detailed comparative analysis, the partially renewable resin recipe outperforms petroleum derived analogues.

As the aviation industry strives to minimise its environmental footprint, understanding the full life cycle impacts, including maintenance, becomes essential for sustainable development. This paper addresses the critical research gap in the environmental assessment of aircraft maintenance by conducting a comprehensive life cycle assessment based on an Airbus A320 aircraft. By combining a top-down check-level analysis and a detailed examination of the aircraft manufacturer's maintenance planning document, this study provides significant insights into the environmental implications of maintenance activities. The check-level analysis provides a general overview, while the analysis of the maintenance planning document delves into individual tasks, enabling the identification of components with the highest ecological impacts. This research emphasises the importance of including aircraft maintenance activities in life cycle assessment studies and provides valuable guidance for researchers, industry practitioners, and policy makers in prioritising sustainability measures and enhancing the environmental performance of aircraft throughout their life cycle.