Search Results (115)

The recycling of carbon fiber-reinforced polymers (CFRPs), particularly carbon fiber-reinforced epoxy polymers (CFREPs), is a challenging problem because of their broad application spectrum, the amount of laminates produced per year, and the cost per kg of the carbon fiber fabric. Recently, several papers were published on the recycling of CFREPs through solvothermal methods that allow the recovery of the carbon fiber fabrics with a relatively low environmental impact. In the present paper, for the first time, the effect of the presence of flame retardants is discussed. A carbon fiber-reinforced epoxy polymer (CFREP) charged with P-, Zn-, B- and Al-based flame retardants, supplied by the aerospace industry, was subjected to a double-step solvothermal treatment. The epoxy matrix was successfully dissolved in monoethanolammine after a preswelling step in acetic acid. The experimental results show that the proposed process allows the full recovery of the carbon fabric with its original sizing layer without injury to the fiber. As confirmation, CFREP laminates produced with the recycled carbon fiber fabrics exhibited mechanical properties close to that of laminates obtained from the virgin epoxy/carbon prepreg. Contrary to what is reported in the literature, the present paper also shows that, in the studied case, whilst acetic acid treatment promotes swelling, it also causes the formation of a degraded surface layer that would impede complete removal of the polymeric matrix and full recovery of the carbon fabric if only acetic acid was used. On the basis of the known mechanism of flame retardancy of phosphates and borates, the degraded layer formation is attributed to the acidic character of the acetic acid. It is worth pointing out that the paper suggests, therefore, that the presence of flame retardants may strongly affect the solvothermal processes. Full article

The growing volume of fiber-reinforced polymer composite waste creates an urgent need for efficient recycling technologies. While solvolysis effectively breaks down thermoset matrices for fiber reinforcement recovery, the process generates hydrocarbon-rich liquid by-products that require further management. This study validates the use of these liquid recycling streams—derived from the solvolysis of unsaturated polyester and epoxy resins—as sustainable carbon precursors for the growth of carbon nanomaterials. Synthesis was performed via catalytic chemical vapor deposition (CVD) at 850 °C using iron nanoparticles impregnated on a zeolite substrate. Morphological analysis confirmed the production of one-dimensional nanostructures (carbon nanotubes/nanofibers), with average diameters below 100 nm. Raman spectroscopy revealed a high degree of graphitization, with I_D/I_G ratios ranging from 0.25 to 0.58, which is comparable to structures synthesized from conventional precursors. Thermogravimetric analysis (TGA) demonstrated high thermal stability and carbon purity reaching up to 90.3%. These findings demonstrate a viable upcycling pathway that enhances the economic attractiveness of composite recycling by transforming waste into advanced nanomaterials. Full article

Fiber-reinforced polymer composites (FRPCs) are increasingly used in construction due to their high performance and low environmental footprint. However, their widespread adoption has raised concerns over end-of-life management, particularly under European regulations mandating high recycling rates for construction and demolition waste (CDW). This study evaluates different systems for the chemical recycling of FRPCs through microwave (MW)-assisted solvolysis using green solvents, including deep eutectic solvents (DESs) and biobased acetic acid. The process targets thermoset resin depolymerization while preserving fiber integrity, operating at reduced temperatures (≤230 °C) and lower energy demand than conventional techniques, such as pyrolysis. A systematic experimental design was applied to CDW-derived polyester composites and extended to industrial epoxy and vinyl ester composites. Among the tested solvents, glacial acetic acid + ZnCl₂ (5 wt.%), achieved the highest degradation efficiency, exceeding 94% in small-scale trials and maintaining over 78% upon upscaling. Recovered fibers showed moderate property retention, with tensile strength and elongation losses of ~30% and ~45% for infusion-based epoxy composites, while those from pultrusion-based epoxy composites exhibited 16–19% and retained similar properties to the virgin material, respectively. The method facilitates fiber recovery with limited degradation and aligns with circular economy principles through solvent reuse and minimizing environmental impact. Full article

Unlike typical fiber-reinforced polymers, aerospace composites consist of 90% carbon and 10% glass fabrics impregnated with thermosetting resin. Due to the strong bonding between fibers and the thermoset nature of the matrix, recycling these materials is particularly challenging. This study evaluates mechanical recycling of aircraft composite waste via industrial grinding and chemical recycling through a solvolysis process. Recovered fibrous fractions were integrated into an epoxy matrix at 50 wt% loading using hot-pressing and into polyamide 12 at 15 wt% via a twin-screw extrusion process. The mechanical results showed that chemically recycled fibers in epoxy reached a flexural modulus of 9.9 GPa and strength of 112 MPa, significantly outperforming mechanically recycled fillers (6.1 GPa and 98.0 MPa) compared to virgin carbon fibers (11.3 GPa and 132 MPa). In PA12, the addition of chemically recycled fibers yielded a 2.14 GPa modulus and a 67.7 MPa strength. Furthermore, life cycle assessment confirmed that both recycling routes drastically reduce global warming potential and aquatic ecotoxicity compared to landfilling. These findings indicate that while mechanical recycling is simpler, chemical solvolysis provides a superior pathway for the high-value circular reuse of complex aerospace waste in new thermoplastic and thermoset applications. Full article

The increasing urgency to mitigate plastic pollution has accelerated the shift from linear manufacturing toward circular systems. This review synthesizes current advances in mechanical, chemical, biological, and upcycling pathways, emphasizing how artificial intelligence (AI) is reshaping decision-making, performance prediction, and system-level optimization. Intelligent sensing technologies—such as FTIR, Raman spectroscopy, hyperspectral imaging, and LIBS—combined with Machine Learning (ML) classifiers have improved material identification, reduced reject rates, and enhanced sorting precision. AI-assisted kinetic modeling, catalyst performance prediction, and enzyme design tools have improved process intensification for pyrolysis, solvolysis, depolymerization, and biocatalysis. Life Cycle Assessment (LCA)-integrated datasets reveal that environmental benefits depend strongly on functional-unit selection, energy decarbonization, and substitution factors rather than mass-based comparisons alone. Case studies across Europe, Latin America, and Asia show that digital traceability, Extended Producer Responsibility (EPR), and full-system costing are pivotal to robust circular outcomes. Upcycling strategies increasingly generate high-value materials and composites, supported by digital twins and surrogate models. Collectively, evidence indicates that AI moves from supportive instrumentation to a structural enabler of transparency, performance assurance, and predictive environmental planning. The convergence of AI-based design, standardized LCA frameworks, and inclusive governance emerges as a necessary foundation for scaling circular plastic systems sustainably. Full article

The mechanical behavior of carbon-fiber-reinforced polymer (CFRP) laminates manufactured using plasma-assisted solvolysis recycled fibers was evaluated experimentally through a comprehensive mechanical testing campaign. The plasma-assisted solvolysis parameters were selected based on an earlier sensitivity analysis. Prepregs made from both virgin and recycled carbon fibers were fabricated via a hand lay-up process and manually stacked to produce unidirectional laminates. Longitudinal tension tests, longitudinal compression tests, and interlaminar shear strength (ILSS) tests were performed to assess the fundamental mechanical response of the recycled laminates and quantify the retention of mechanical properties relative to the virgin-reference material. Prior to mechanical testing, all laminates underwent ultrasonic C-scan inspection to assess manufacturing quality. While both laminate types exhibited generally satisfactory quality, the recycled-fiber laminates showed a higher density of defects. The recycled laminates preserved around 80% of their original tensile strength and maintained an essentially unchanged elastic modulus. Compressive strength was more susceptible to imperfections introduced during remanufacturing, with the recycled laminates exhibiting roughly a 14% decrease compared with the virgin material. On the contrary, the compressive modulus was largely retained. The most substantial reduction occurred in ILSS, which dropped by 58%. Overall, the results demonstrate that plasma-assisted solvolysis enables the recovery of carbon fibers suitable for remanufacturing CFRP laminates, while the observed reduction in mechanical properties of recycled CFRPs is mainly attributed to defects in manufacturing quality rather than to intrinsic degradation of the recycled carbon fibers. Full article

Considering the high demand for efficient chemical recycling and reusability of polyurethane foams (PUFs), combined microwave-assisted solvolysis routes have been applied to a widely used commercial PUF for pipe pre-insulation, and the reusability of as-received recycled products in the original formulation was studied. The influence of the type and amount of recyclate on the main foaming parameters, shrinkage behavior, density, compression properties, morphology, thermal stability, and humidity uptake was determined. Based on shrinkage as the main exclusion criterion, recycling products of two routes have been evaluated as suitable for reuse in the original formulation without any purification or fractionation. However, a maximum of 5 wt.% of the original polyol compound could be replaced by these recycled products to fulfill the requirement of ≤5% shrinkage, which also resulted in foam performance that is well acceptable for use in pre-insulated pipes. The most beneficial property profiles were achieved by replacing 3 wt.% of the original polyol component. Full article

Wind turbine blades (WTBs) have always been considered one of the greatest engineering achievements. They primarily use glass fiber-reinforced polymers (GFRPs) because of their lightweight nature, impressive strength-to-weight ratio, and durability. Until now, typical disposal methods of End-of-Life (EoL) WTBs are landfill or incineration. However, such practices are neither environmentally sustainable nor compliant with current regulations. This study investigates a low-temperature solvolysis process using a poly(ethylene glycol)/NaOH system under ambient pressure for efficient decomposition of the polyester matrix, promoting the potential of chemical recycling as an alternative to landfilling and incineration by offering a viable method for recovering glass fibers from WTB waste. A parametric study evaluated the influence of reaction time (4–5.5 h) and catalyst-to-resin ratio (0.1–2.0 g NaOH per g resin) on solvolysis efficiency. Optimal conditions (200 g PEG200, 12.5 g NaOH, 10 g GFRP, 5.5 h) achieved an ~80% decomposition efficiency and fibers exhibiting minimal surface degradation. SEM and EDX analyses confirmed limited morphological damage, while excessive NaOH (>15 g) caused notable etching of the glass fibers. ICP-OES of liquid residues detected high Na (780 mg/L) and Si (139 mg/L) concentrations, verifying partial dissolution of the fiber structure under strongly alkaline conditions. After applying a commercial sizing agent (Hydrosize HP2-06), TGA confirmed ~1.2% sizing mass, and nanoindentation analysis showed the interfacial modulus and hardness of re-sized fibers improved by over 70% compared to unsized recycled fibers, approaching the performance of virgin fibers. Full article

The rapid expansion of carbon-fiber-reinforced polymer (CFRP) applications in aerospace, automotive, and energy sectors has intensified concerns over end-of-life waste and the absence of efficient recycling solutions. Plasma-assisted solvolysis has emerged as a promising hybrid approach, combining oxidative chemical treatment with plasma activation to accelerate matrix degradation. In this study, CFRP cylinders (6.4 cm height, 5.5 cm internal, and 6.0 cm external diameter) were processed in a closed-loop plasma solvolysis system under varied operational parameters, including plasma power, plasma gas composition, and nitric acid concentration. The mechanical performance of the recovered carbon fibers was assessed through single-fiber tensile and microbond tests, evaluating both tensile and interfacial properties. In most cases, the recycled fibers retained—or even exceeded—the tensile strength of their virgin counterparts, reaching up to 1.49 times that of the virgin fibers. Young’s modulus, though more variable, ranged from 0.48 to 1.67 times the reference value depending on treatment conditions. Elongation at break generally increased, particularly in the 24K (24,000-filaments) fiber sets, suggesting improved surface ductility. Weibull statistical analysis indicated higher consistency in 3K (3000-filaments) fiber batches compared to 24K, whereas interfacial shear strength was moderately retained across conditions. Overall, balanced plasma and acid conditions enabled efficient fiber recovery with high strength and interfacial performance, validating plasma-assisted solvolysis as a viable route for recovering high-performance fibers suitable for structural reuse, in alignment with circular economy principles. Full article

The current study investigates plasma-assisted chemical recycling as an innovative approach to recover valuable carbon fibers from composite waste while minimizing environmental impact. Nitrogen and argon plasma-in-bubbles are employed in a concentrated nitric acid solution, thus enhancing conventional nitric acid solvolysis with plasma chemistry. A systematic process framework is presented, revealing key operational stages, including composite pretreatment, composite solvolysis, carbon fiber recovery/characterization, NO_x recovery, nitric acid circulation, and byproduct management, demonstrating their role in the overall process efficiency and environmental impact. Moreover, the research examined different processing conditions, including plasma power, acid concentration, and reactor design, while comparing open-air systems to systems equipped with single-stage or two-stage wet scrubbers for NO_x recovery. Remarkably, recycled fibers from plasma-assisted solvolysis demonstrated preserved or even slightly enhanced mechanical properties compared to those of the virgin fibers. Recycled carbon fibers originating from the operation at 1200 W and 12 M HNO₃ demonstrated the best mechanical properties with 3138.92 MPa tensile strength and 307.02 GPa Young’s modulus. However, the parametric analysis revealed that operating the plasma reactor at 1200 W and 14 M, equipped with a two-stage scrubber, achieved optimal environmental performance. Full article

Recycling multilayer films (MLFs) presents significant challenges to achieving circularity. Mechanical recycling, solvolysis (chemical recycling), and dissolution (physical recycling) have been introduced in the past with their strengths and weaknesses. This study uses a series of advanced, pilot-scale processes to improve the quality of recyclates. These include Near Infrared/Digital Watermarking (NIR/DW), super-critical CO₂ decontamination, dissolution, and innovative mechanical recycling techniques (METEOR and multi-nano layering, MNL). Findings from TRL 5–8 pilots show that recycling different MLF compositions with two routes (dissolution-based and METEOR/MNL-based) can improve the overall quality but this comes with a trade-off. Using 10% recycled content from PET/PE and metalized PP films in 2050 could even increase greenhouse gas (GHG) emissions by 21% and 85%, respectively, compared to landfill incineration. However, PE/PA and PE/EVOH films showed GHG reductions of 0.5% and 4%, respectively. Raising recycled content from 0% to 50% can cut GHG emissions by 36%. These results challenge the current 10% recycled content target, advocating for a more ambitious goal of exceeding 25% by 2050 to enhance sustainability. Full article

Wind turbines are reaching end-of-life in increasing volumes, presenting a growing sustainability challenge. In the United States, prevailing waste management practices, primarily landfilling, undermine circular economy objectives by discarding recoverable materials and energy. This study applies life cycle assessment (LCA) to quantify 16 midpoint environmental impacts across three end-of-life pathways—landfilling, recycling, and repurposing—of major turbine components (steel, concrete, and composite blades). An avoided burden approach is used to quantify environmental credits from substituting recovered materials for virgin equivalents. Results show that nearly all recycling and repurposing pathways outperform landfilling across most impact categories. Mechanical recycling of both glass and carbon fiber blades performed better than landfilling in all 16 categories, while pyrolysis and solvolysis improved outcomes in 14–15 of 16 categories (CO₂ eq emissions were higher for pyrolysis and solvolysis than for the landfilling option). Repurposing blades likewise showed broad advantages (15 of 16 categories; ozone depletion was slightly higher), extending material lifetimes before waste treatment. For conventional materials, steel and concrete recycling reduced impacts in most categories, with concrete outperforming landfilling in 15 of 16 categories (marine eutrophication was nearly equal to the landfilling option). The only mixed pathway was cement co-processing of GFRP, which split evenly between benefits and burdens. Sensitivity analysis underscores that improving the quality of recovered materials is critical to maximizing environmental benefits. Overall, both recycling and repurposing offer substantial environmental advantages over landfilling, reinforcing the importance of circular end-of-life strategies in sustaining wind energy across its full life cycle. Full article

Wind power is integral to the transformation of energy systems towards sustainability. However, the increasing number of wind turbines approaching the end of their service life presents significant challenges in terms of waste management and environmental sustainability. Rotor blades, typically composed of thermoset polymer composites reinforced with glass or carbon fibres, are particularly problematic due to their low recyclability and complex material structure. The aim of this article is to provide a system-level review of current end-of-life strategies for wind turbine components, with particular emphasis on blade recycling and decision-oriented comparison, and its integration into circular economy frameworks. The paper explores three main pathways: operational life extension through predictive maintenance and design optimisation; upcycling and second-life applications; and advanced recycling techniques, including mechanical, thermal, and chemical methods, and reports qualitative/quantitative indicators together with an indicative Technology Readiness Level (TRL). Recent innovations, such as solvolysis, microwave-assisted pyrolysis, and supercritical fluid treatment, offer promising recovery rates but face technological and economic as well as environmental compliance limitations. In parallel, the review considers deployment maturity and economics, including an indicative mapping of cost and deployment status to support decision-making. Simultaneously, reuse applications in the construction and infrastructure sectors—such as concrete additives or repurposed structural elements—demonstrate viable low-energy alternatives to full material recovery, although regulatory barriers remain. The study also highlights the importance of systemic approaches, including Extended Producer Responsibility (EPR), Digital Product Passports and EU-aligned policy/finance instruments, and cross-sectoral collaboration. These instruments are essential for enhancing material traceability and fostering industrial symbiosis. In conclusion, there is no universal solution for wind turbine blade recycling. Effective integration of circular principles will require tailored strategies, interdisciplinary research, and bankable policy support. Addressing these challenges is crucial for minimising the environmental footprint of the wind energy sector. Full article

The dissolution kinetics in conventional nitric acid and plasma-enhanced nitric acid solvolysis of composites were investigated. Unidirectional carbon fiber epoxy laminates originating from the scar of wind turbine blades were used for the study. The carbon fiber retrieval rate was experimentally determined as a function of dissolution time and composite mass. A kinetic model, which included disintegration of the polymer matrix and the mass transport of polymer fragments to the liquid phase, was implemented to investigate the main parameters that affect the dissolution rate. The plasma enhancement and the increase of the composite mass favor the carbon fiber retrieval rate, while process time slows down the matrix dissolution rate. The composite surface in contact with the liquid, solid-to-liquid volume ratio, solubility of the polymer matrix, and disintegration and mass transport rate coefficients have a significant effect on the dissolution rate, and the rate-limiting factors were revealed and analyzed. Full article

Aromatic compounds are vital in both natural and synthetic chemistry, and they are traditionally sourced from non-renewable petrochemicals. However, plant biomass, particularly lignin, offers a renewable alternative source of aromatic compounds. Lignin, a complex polymer found in plant cell walls, is the largest renewable source of aromatic compounds, though its degradation remains challenging. Lignin can be chemically degraded through oxidation, acid hydrolysis or solvolysis. As an alternative, microorganisms, including fungi, could offer a sustainable alternative for breaking down lignin. The aromatic compounds released from lignin, by either microbial, chemical or enzymatic degradation, can be used by microorganisms to produce valuable compounds. Fungi possess unique enzymes capable of converting aromatic compounds derived from lignin or other sources into chemical building blocks that can be used in several industries. However, their aromatic metabolic pathways are poorly studied compared to bacterial systems. In the past, only a handful of genes and enzymes involved in the aromatic metabolic pathways had been identified. Recent advances in genomics, proteomics, and metabolic engineering are helping to reveal these metabolic pathways and identify the involved genes. This review highlights recent progress in understanding fungal aromatic metabolism, focusing on how Aspergillus niger converts plant-derived aromatic compounds into potentially useful products and the versatility of aromatic metabolism within the Aspergillus genus. Addressing the current knowledge gaps in terms of fungal pathways could unlock their potential for use in sustainable technologies, promoting eco-friendly production of chemical building blocks from renewable resources or bioremediation. Full article