Development and evaluation of an optimized solvolysis recycling process for CFRPs : fiber performance and environmental-economic impact
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Date
2026-03-03
Authors
Βογιαντζή, Χριστίνα
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Abstract
The widespread adoption of carbon fiber reinforced polymers (CFRPs) in high-performance engineering applications, including aerospace, automotive, wind energy, and sports sectors, has led to a substantial increase in composite waste at the end of product life. CFRPs are favored due to their exceptional specific strength, stiffness, and durability. However, their end-of-life management remains a significant challenge from both technological and environmental perspectives. This challenge is primarily associated with the widespread use of thermosetting polymer matrices, which form irreversible, cross-linked networks that cannot be remelted or reshaped. As a result, conventional recycling and reuse strategies are largely ineffective, leading to landfill or energy recovery practices that do not take advantage of the high embedded value of carbon fibers. At the same time, the production of virgin carbon fibers (VFs) is an extremely energy-intensive process, associated with high cumulative energy demand and significant greenhouse gas emissions. The recovery and reuse of carbon fibers (CFs) from CFRPs therefore represent a critical opportunity to reduce environmental impacts, conserve raw materials, and support the transition toward a circular economy in composite manufacturing. However, achieving this goal requires recycling
technologies that are capable not only of effectively removing the polymer matrix but also of maintaining the mechanical and interfacial performance of the recovered fibers. This thesis addresses this challenge by developing an integrated experimental, analytical, and sustainability-oriented framework for the recycling of epoxy-based CFRPs. The work focuses primarily on chemical recycling via solvolysis using environmentally friendly (“green”) solvents, while also examining thermal recycling through pyrolysis as a benchmark technology. Unlike many existing studies
that evaluate recycling processes solely based on resin removal efficiency, this research adopts a quality-oriented approach, emphasizing not only the mechanical performance of the recovered fibers but also the environmental footprint and economic viability of the recycling processes. The experimental investigation covers both unidirectional (UD) and three-dimensional (3D) CFRP architectures. In addition to conventional UD laminates, 3D woven CFRPs were considered in order to extend the experimental investigation to composites with more complex fiber architectures. This allowed the evaluation of solvolysis performance and recovered fiber characteristics across different reinforcement configurations, without changing the overall methodological framework of the study. Solvolysis experiments were conducted under controlled subcritical and supercritical conditions. For UD CFRPs, both water and water/ethanol solvent systems were examined, allowing the evaluation of temperature, reaction time, and solvent composition on resin decomposition efficiency and on the properties of the recovered carbon fibers. In contrast, the investigation of 3D woven CFRPs was limited to water-based solvolysis, to assess the response of a more complex fiber architecture under a consistent solvent system. In addition, pyrolysis followed by
oxidative post-treatment was applied to the 3D woven CFRP specimens, serving as a reference thermal recycling route for comparison with the corresponding solvolysis results. The recovered carbon fibers were evaluated through morphological, mechanical and interfacial analyses. Surface morphology was examined using scanning electron microscopy (SEM), while mechanical performance was assessed through single-fiber tensile testing to determine tensile strength and Young’s modulus. Interfacial behavior was evaluated using microbond testing to measure interfacial shear strength (IFSS). Based on these experimental results, property retention indices were used to quantify the extent to which the mechanical and interfacial properties of recycled fibers were preserved relative to VFs. The experimental results demonstrate that optimized green solvolysis conditions can achieve near-complete resin removal while maintaining a high retention of the tensile properties of the recovered carbon fibers, typically exceeding 85–90%. In contrast, a more significant reduction was observed in IFSS, indicating a higher sensitivity of fiber–matrix interfacial properties to the recycling process. For UD CFRPs, the use of mixed water/ethanol solvent systems resulted in improved fiber surface condition and comparatively enhanced mechanical behavior relative to solvolysis in pure water. The results further reveal that composite architecture plays a significant role in solvolysis effectiveness, highlighting the need for architecture-sensitive recycling strategies. Alongside the experimental evaluation of recycling performance, this thesis includes a comprehensive sustainability assessment. Life Cycle Assessment (LCA) was utilized to quantify environmental indicators such as global warming potential and cumulative energy demand, accounting for direct process impacts. In parallel,
Life Cycle Costing (LCC) was used to evaluate the economic performance of the recycling routes, considering operational costs. A representative CFRP sports racket case study, developed within the framework of the RECREATE project, was used to illustrate the application of the sustainability assessment framework. To combine technical, environmental, and economic aspects within a unified evaluation framework, a multi-criteria decision-making (MCDM) approach based on the TOPSIS method was implemented. This approach enabled the comparative ranking of recycling routes and operating conditions, highlighting the compromises between fiber quality, environmental performance, and economic considerations. In summary, this thesis combines experimental investigation and sustainability assessment for the recycling of CFRPs. Solvolysis is examined for different reinforcement architectures, and recycling performance is evaluated in terms of fiber
quality and selected environmental and economic indicators. The proposed assessment framework provides a structured basis for comparing recycling routes under defined technical and sustainability criteria.
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Keywords
Solvolysis, Chemical recycling, Life cycle assessment (LCA), Life cycle cost