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Polymers
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Carbon Fiber Reinforced Polymer Composites: Advancements in Recycling and Sustainability
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Carbon Fiber Reinforced Polymer Composites: Advancements in Recycling and Sustainability

A special issue of Polymers (ISSN 2073-4360). This special issue belongs to the section "Polymer Composites and Nanocomposites".

Deadline for manuscript submissions: closed (30 April 2026) | Viewed by 8611

Editors

Prof. Dr. Christian Brauner

E-Mail Website
Guest Editor
Institute for Polymer Engineering, Lightweight Design & Composite Technologies, FHNW University of Applied Sciences and Arts Northwestern Switzerland, 5210 Windisch, Switzerland
Interests: composite; simulation; lightweight design; advanced manufacturing
Special Issues, Collections and Topics in MDPI journals
Dr. Julian Kupski

E-Mail Website
Guest Editor
Institute of Polymer Engineering, FHNW University of Applied Sciences and Arts Northwestern Switzerland, Klosterzelgstrasse 2, 5210 Windisch, Switzerland
Interests: carbon fibre composites and structural mechanics; recycling of carbon fibre composites; secondary bonding and repair of composites; design, repair and re-use of alpine skies

Special Issue Information

Dear Colleagues,

"Carbon Fiber Reinforced Polymer Composites: Advancements in Recycling and Sustainability" is a Special Issue that delves into the intricate realm of recycling carbon fiber-reinforced polymer composites (CFRPs).

As the demand for lightweight, high-strength materials surges across industries like aerospace, automotive, and renewable energy, the consequential rise in CFRP production underscores the urgent need for sustainable disposal and recycling solutions.

This Special Issue will serve as a crucible for research, offering a platform for scholars, engineers, and industry experts to disseminate their findings, innovations, and challenges related to CFRP recycling. Through a blend of theoretical insights, experimental studies, and industrial perspectives, contributors explore diverse aspects of CFRP recycling, including technological advancements, economic viability, environmental impacts, and regulatory frameworks. By facilitating knowledge exchange and fostering dialogue, this Special Issue will propel the CFRP recycling discourse forward, driving transformative change towards a more sustainable and circular economy. Ultimately, this Special Issue will provide an indispensable resource, illuminating pathways towards greener, more efficient, and socially responsible practices in CFRP utilization and recycling.

Prof. Dr. Christian Brauner
Dr. Julian Kupski
Guest Editors

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All submissions that pass pre-check are peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 250 words) can be sent to the Editorial Office for assessment.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Polymers is an international peer-reviewed open access semimonthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2700 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

  • discontinuous fiber topology
  • chemolysis
  • pyrolysis
  • sorting
  • staple fibers
  • LCA

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Published Papers (4 papers)

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Research

26 pages, 6517 KB  
Article
Hydrothermal Treatment with Different Solvents for Composite Recycling and Valorization Under Subcritical and Supercritical Conditions
by José M. Vázquez-Fernández, Belén García-Jarana, Milagrosa Ramírez-del Solar, Lucio Cardozo-Filho, Juan R. Portela-Miguélez and José M. Abelleira-Pereira
Polymers 2026, 18(1), 89; https://doi.org/10.3390/polym18010089 - 28 Dec 2025
Cited by 1 | Viewed by 862
Abstract
Worldwide, carbon fiber (CF) demand has been rising over the last decade, which contrasts with the fact that up to 30–50% of composite materials in aircraft production are scrapped. This situation highlights the increasing need for recycling methods to reduce fabrication costs and [...] Read more.
Worldwide, carbon fiber (CF) demand has been rising over the last decade, which contrasts with the fact that up to 30–50% of composite materials in aircraft production are scrapped. This situation highlights the increasing need for recycling methods to reduce fabrication costs and global warming potential. Emerging technologies focus on recovering long CFs, as they represent the most valuable form but are also the most difficult to reclaim using conventional recycling methods. Hydrothermal treatments offer a promising alternative to valorize this waste by decomposing the polymer matrix under subcritical and supercritical conditions without significantly damaging the fibers. Water, isopropanol, and mixtures of water/isopropanol or water/acetone were tested as solvents, with and without the addition of zinc chloride (ZnCl2) as a homogeneous catalyst. The influence of temperature, pressure, and solvent composition on resin degradation was evaluated. In this work, degradation rates of up to 92% were achieved at 415 °C, 233 bar, 120 min, 5 wt.% IPA, and ZnCl2 0.1 M. It should be noted that ZnCl2 caused reactor corrosion. Furthermore, the recovered fibers retained their morphology, including the sizing layer, and showed mechanical properties similar to the original material, while a small H2-rich gaseous fraction was generated as a byproduct of the hydrothermal degradation. Using water–isopropanol solutions resulted in the reactor being significantly cleaner than when using water alone, which can be advantageous for future scale-up and for reducing maintenance requirements. These results confirm the potential of hydrothermal processing as an efficient and selective method for the recycling and valorization of carbon-fiber-reinforced composites from the aeronautical industry. Full article
(This article belongs to the Special Issue Carbon Fiber Reinforced Polymer Composites: Advancements in Recycling and Sustainability)
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17 pages, 1798 KB  
Article
Mild Two-Step Thermochemical Recovery of Clean Glass Fibers from Wind-Blade GFRP
by AbdulAziz AlGhamdi, Imtiaz Ali and Salman Raza Naqvi
Polymers 2025, 17(24), 3344; https://doi.org/10.3390/polym17243344 - 18 Dec 2025
Cited by 4 | Viewed by 1016
Abstract
End-of-life wind turbine blade accumulation is a growing global materials management problem and current industrial recycling routes for glass fiber-reinforced polymer composites remain limited in material recovery value. There is limited understanding on how to recover clean glass fibers while keeping thermal exposure [...] Read more.
End-of-life wind turbine blade accumulation is a growing global materials management problem and current industrial recycling routes for glass fiber-reinforced polymer composites remain limited in material recovery value. There is limited understanding on how to recover clean glass fibers while keeping thermal exposure and energy input low, and existing studies have not quantified whether very short isothermal thermal residence can still result in complete matrix removal. The hypothesis of this study is that a mild two-step thermochemical sequence can recover clean glass fibers at lower temperature and near zero isothermal dwell if pyrolysis and oxidation are separated. We used wind-blade epoxy-based GFRP in a step-batch reactor and combined TGA-based thermodynamic mapping, short pyrolysis at 425 °C, and mild oxidation at 475 °C with controlled dwell from zero to thirty minutes. We applied model-free kinetics and machine learning methods to quantify activation energy trends as a function of conversion. The thermal treatment of 425 °C for zero minutes in nitrogen, followed by 475 °C for fifteen minutes in air, resulted in mechanically sound, visually clean white fibers. These fibers retained 76% of the original tensile strength and 88% of the Young’s modulus, which indicates the potential for energy-efficient GFRP recycling. The activation energy was found to be approximately 120 to 180 kJ mol−1. These findings demonstrate energy lean recycling potential for GFRP and can inform future industrial scale thermochemical designs. Full article
(This article belongs to the Special Issue Carbon Fiber Reinforced Polymer Composites: Advancements in Recycling and Sustainability)
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26 pages, 8150 KB  
Article
Coefficients of Thermal Expansion in Aligned Carbon Staple Fiber-Reinforced Polymers: Experimental Characterization with Numerical Investigation
by Julian Kupski, Lucian Zweifel, Miriam Preinfalck, Stephan Baz, Mohammad Hajikazemi and Christian Brauner
Polymers 2025, 17(8), 1088; https://doi.org/10.3390/polym17081088 - 17 Apr 2025
Cited by 5 | Viewed by 2603
Abstract
Carbon staple fiber composites are materials reinforced with discrete-length carbon fibers processed using traditional textile technologies, offering moderate mechanical properties and flexibility in manufacturing. These composites can be produced from recycled carbon staple fibers, aligned into yarn and tape-like structures, providing a more [...] Read more.
Carbon staple fiber composites are materials reinforced with discrete-length carbon fibers processed using traditional textile technologies, offering moderate mechanical properties and flexibility in manufacturing. These composites can be produced from recycled carbon staple fibers, aligned into yarn and tape-like structures, providing a more sustainable alternative while balancing performance, cost-effectiveness, and environmental impact. Aligning staple fibers into tape-like structures enables similar applications to those of continuous-fiber-based products, while allowing control over fiber orientation distribution, fiber volume fraction, and length distribution, which are all critical factors influencing both mechanical and thermo-mechanical properties. This study focuses on the experimental characterization and numerical investigation of Coefficients of Thermal Expansion (CTEs) in aligned carbon staple fiber composites. The effects of fiber orientation and volume fraction on coefficients of thermal expansion under different fiber alignment parameters are analyzed, revealing distinct thermal expansion behavior compared to typical aligned unidirectional continuous carbon fiber composite laminates. Unlike continuous unidirectional laminates, which typically exhibit transversely isotropic behavior without tensile–shear coupling, staple fiber composites demonstrate different in-plane axial, transverse, and out-of-plane CTE characteristics. To explain these deviations, a modeling approach is introduced, incorporating detailed experimental information on fiber distributions and microstructural features rather than averaged fiber orientation values. This involves a multi-scale analysis based on a laminate analogy through which all composite thermo-elastic properties can be predicted, accounting for variations in fiber orientations, volume fractions, and tape thicknesses. It is shown that while the local variation of fiber volume fraction has a small effect on the homogenized value of the coefficients of thermal expansion, fiber misalignment, tape thickness, and asymmetry in fiber orientation distribution will significantly affect the measurements of CTEs. For the case of carbon staple fiber composites, the asymmetry in fiber orientation distribution significantly influences the measurements of axial CTE. Fiber orientation asymmetry causes tensile–shear coupling under mechanical and thermal loading, leading to an unbalanced laminate with in-plane shear–tensile deformation. This coupling disrupts uniform displacement, complicating strain measurements and the determination of composite properties. Full article
(This article belongs to the Special Issue Carbon Fiber Reinforced Polymer Composites: Advancements in Recycling and Sustainability)
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25 pages, 7197 KB  
Article
Performance Restoration of Chemically Recycled Carbon Fibres Through Surface Modification with Sizing
by Dionisis Semitekolos, Sofia Terzopoulou, Silvia Zecchi, Dimitrios Marinis, Ergina Farsari, Eleftherios Amanatides, Marcin Sajdak, Szymon Sobek, Weronika Smok, Tomasz Tański, Sebastian Werle, Alberto Tagliaferro and Costas Charitidis
Polymers 2025, 17(1), 33; https://doi.org/10.3390/polym17010033 - 26 Dec 2024
Cited by 14 | Viewed by 2970
Abstract
The recycling of Carbon Fibre-Reinforced Polymers (CFRPs) is becoming increasingly crucial due to the growing demand for sustainability in high-performance industries such as automotive and aerospace. This study investigates the impact of two chemical recycling techniques, chemically assisted solvolysis and plasma-enhanced solvolysis, on [...] Read more.
The recycling of Carbon Fibre-Reinforced Polymers (CFRPs) is becoming increasingly crucial due to the growing demand for sustainability in high-performance industries such as automotive and aerospace. This study investigates the impact of two chemical recycling techniques, chemically assisted solvolysis and plasma-enhanced solvolysis, on the morphology and properties of carbon fibres (CFs) recovered from end-of-life automotive parts. In addition, the effects of fibre sizing are explored to enhance the performance of the recycled carbon fibres (rCFs). The surface morphology of the fibres was characterised using Scanning Electron Microscopy (SEM), and their structural integrity was assessed through Thermogravimetric Analysis (TGA) and Raman spectroscopy. An automatic analysis method based on optical microscopy images was also developed to quantify filament loss during the recycling process. Mechanical testing of single fibres and yarns showed that although rCFs from both recycling methods exhibited a ~20% reduction in tensile strength compared to reference fibres, the application of sizing significantly mitigated these effects (~10% reduction). X-ray Photoelectron Spectroscopy (XPS) further confirmed the introduction of functional oxygen-containing groups on the fibre surface, which improved fibre-matrix adhesion. Overall, the results demonstrate that plasma-enhanced solvolysis was more effective at fully decomposing the resin, while the subsequent application of sizing enhanced the mechanical performance of rCFs, restoring their properties closer to those of virgin fibres. Full article
(This article belongs to the Special Issue Carbon Fiber Reinforced Polymer Composites: Advancements in Recycling and Sustainability)
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