The circular economy (CE) has recently emerged as a key strategy for promoting sustainability and reducing waste in various industrial sectors. This paper provides an overview of the definition, assessment and enhancement of circularity in general and in five key industries, including aerospace, wind energy, transportation, automotive and sports goods, by using data and information from the literature and for the section of the definitions of the CE also using information from the EC funded project “RECREATE”. The survey reviews in detail the different definitions, assessment methods and metrics used to explore and evaluate circularity, including assessment frameworks such as Life Cycle Assessment (LCA) and assessment indicators. Furthermore, it explores the challenges, possibilities and available tools for enhancing circularity, focusing on digital tools. The survey highlights the importance of a holistic and systemic approach to circularity concerning all stakeholders along the value chain. Overall, this study aims to contribute to a better understanding of the circular economy's definition, assessment, and enhancement and provides insights for future research.

The recycling of carbon-fiber reinforced polymers (CFRPs) presents significant challenges due to their thermosetting matrix, which complicates end-of-life management and often results in energy-intensive disposal or significant waste accumulation. Despite advancements in recycling methods, knowledge gaps remain regarding their sustainability and economic viability. This study undertakes a comprehensive Life Cycle Assessment and Environmental Life Cycle Costing analysis of four key recycling techniques: mechanical recycling, pyrolysis, solvolysis, and high-voltage fragmentation (HVF). By using the SimaPro software, this study identifies mechanical recycling and HVF as the most sustainable options, with the lowest cumulative energy demand (CED) of 5.82 MJ/kg and 4.97 MJ/kg and global warming potential (GWP) of 0.218 kg CO₂eq and 0.0796 kg CO₂eq, respectively. In contrast, pyrolysis imposes the highest environmental burdens, requiring 66.3 MJ/kg and emitting 2.84 kg CO₂eq. Subcritical solvolysis shows more balanced environmental impacts compared to its supercritical counterpart. Cost analysis reveals that for mechanical recycling and pyrolysis, material costs are negligible or zero. In contrast, solvolysis and HVF incur material costs primarily due to the need for deionized water. Regarding energy costs, pyrolysis stands out as the most expensive method due to its high energy demands, followed closely by solvolysis with supercritical water.

Circular economy has recently emerged as a key strategy for promoting sustainability and reducing waste in various industrial sectors. This paper provides an overview of circularity in aerospace, wind energy, transportation, automotive and sports goods using data and information from the literature and the EC funded project "RECREATE". The survey reviews the different definitions, assessment methods and metrics used to explore and evaluate circularity, including assessment frameworks such as Life Cycle Assessment (LCA) and assessment indicators. Furthermore, explores the challenges, possibilities and the available tools for enhancing circularity, such as digital tools. The survey highlights the importance of a holistic and systemic technique to circularity, concerning all stakeholders along the value chain. Overall, this study aims to contribute to a better understanding of circular economy and provides insights for future research.

Composites, and especially carbon-fiber-reinforced plastics (CFRPs), are increasingly used in the automotive, aerospace, and aviation industries, and as a result, CFRP production has increased dramatically, leading to a corresponding increase in waste. Landfills and the incineration of waste are likely to be restricted as a result of legislation, thus highlighting the need for efficient recycling methods for CFRPs. However, the recycling of CFRPs is very challenging, mainly due to the difficulty of removing their thermosetting matrix. This study reports a pre-screening of the solvolysis recycling process for CFRPs based on the mechanical properties of the recovered fibers. To this end, solvolysis tests were conducted on unidirectional CFRP samples under supercritical and subcritical conditions using acetone and water. The solvolysis tests were conducted for various conditions of temperature, pressure, and reaction time, without the use of any catalyst. Also, the loading rate (volume of solvent/volume of reactor) was constant. The efficiency of the recycling processes has been evaluated through a morphological and a mechanical characterization of the recovered fibers. In most cases, the decomposition efficiency of the epoxy resin, measured in terms of mass, ranged between 90 and 100%. Moreover, the scanning electron microscopy images of the recovered fibers showed negligible traces of resin residues and no detectable signs of physical damage or any changes in morphology with regard to diameter. Finally, the single-fiber tension tests revealed that that the recovered fibers retained more than 61% of their initial Young’s modulus and 70% of their tensile strength.

Composites, and especially carbon fiber reinforced plastics (CFRPs), are increasingly used in the automotive, aerospace, and aviation industries, and as a result, CFRP production has increased dramatically, leading to a corresponding increase of waste. Landfill and incineration of waste are likely to be restricted as a result of the legislation, thus highlighting the need for efficient recycling methods for CFRPs. However, the recycling of CFRP is very challenging, mainly due to the difficulty of removing the thermosetting matrix. This study reports a pre-screening of the solvolysis recycling process for CFRPs based on the mechanical properties of the recovered fibers. To this end, solvolysis tests were conducted on unidirectional CFRP samples under supercritical and subcritical conditions using acetone and water. The solvolysis tests were conducted for various conditions of temperature, pressure, and reaction time. The efficiency of the recycling processes has been evaluated through a morphological and a mechanical characterization of the recovered fibers. In most cases, the decomposition efficiency of the epoxy resin, measured in terms of mass, ranged between 90 and 100%. Moreover, the scanning electron microscopy images of the recovered fibers showed negligible traces of resin residues and no detectable signs of physical damage or any changes in morphology with regard to diameter. Finally, the single-fiber tension tests revealed that that the recovered fibers retained more than 61% of their initial Young's modulus and 70% of their tensile strength.

Recycling carbon fiber reinforced polymers (CFRPs) is essential to address the growing waste generated by their increased use in industries such as aerospace, automotive, and wind energy. This study compares two recycling methods, pyrolysis (with and without oxidation) and solvolysis, for the recovery of carbon fibers from a 3D woven CFRP. Pyrolysis experiments were conducted at 500°C for 2 and 6 h, followed by oxidation at different durations. A mass balance approach was employed to monitor material transformations, quantifying outputs including syngas, char, hydrocarbons, and recovered carbon fibers. Solvolysis experiments were carried out using supercritical water under different conditions of temperature, pressure, and reaction time. The efficiency of resin decomposition was assessed, while the morphological characteristics and mechanical properties of the recycled fibers were characterized for both processes using scanning electron microscopy (SEM) and single fiber tensile testing. Scanning electron microscopy (SEM) and mechanical tests were conducted for both processes to characterize the purity and performance of the recycled fibers. The results showed that pyrolysis followed by oxidation achieved high resin removal efficiency, with the optimal balance for fiber degradation, process control, and industrial costs being achieved with 2 h of pyrolysis followed by 30 min of oxidation. Under these conditions, the mechanical degradation of recycled fibers was limited to approximately 10% of the virgin fiber tensile strength. Solvolysis performed at 390°C, 265 bar, for 60 min also demonstrated effective resin removal while maintaining satisfactory mechanical properties of the recovered fibers.