Recycled Carbon Fiber Research Articles

Influence of the Thermoplastic Fiber Ratio on the Mechanical Properties of Recycled Carbon Fibers During the Carding Process

This study investigates the impact of carding and blending recycled carbon fibers (rCF) with crimped thermoplastic polypropylene (PP) fibers on the mechanical properties of rCF, using a Weibull statistical approach. Tensile properties of rCF were evaluated before and after carding with varying rCF/PP blend ratios (100/0%, 85/15%, 70/30%, and 50/50%). A comparison between the two-parameter and three-parameter Weibull models showed that the two-parameter model provided a better fit for rCF properties before carding. The results show that adding crimped PP fibers during carding helps to decrease the stress-at-break disparity and move their distribution to higher values. Furthermore, a slight increase in tensile modulus was observed in carded rCF, with higher PP ratios associated with smaller scatter modulus distributions. Elongation at break remained consistent, with the Weibull modulus increasing slightly with carding and the inclusion of PP fibers, indicating improved consistency. Overall, carding rCF with PP fibers helped in the mechanical property uniformity of the resulting carded webs without compromising tensile performance. This work shows the potential of the carding process with or without thermoplastic fibers to efficiently realign and give continuity to discontinuous recycled carbon fibers.

Recovery of Carbon Fibres From Aged Epoxy Matrix Composites Using H2O2 as an Oxidant: A Thermodynamic and Technoeconomic Analysis

There is an effort to use hydrogen peroxide for recycling carbon fibre from epoxy matrix composites because it is an ecofriendly material, and the related technology is feasible. However, there is little information on the technoeconomic impact of this method, thus whether it is economically better than current techniques. Therefore, in this paper, we discuss the technoeconomic analysis of recycling using hydrogen peroxide. The analysis also includes a thermodynamic model to calculate the amount of energy required to decompose the epoxy matrix. Various financial indicators, including the payback period, net present value (NPV), internal rate of return (IRR) and profitability index (PI), were used. The technoeconomic assessment revealed favourable outcomes across all key financial indicators, demonstrating the viability and potential benefits of the process. A capital investment of $17.34M over 10 years was required. The NPV of $15.56M with a 15% minimum discounted rate of return (WACC) was computed. The project is more likely to succeed with an annual production cost of $176.5 million for 50,000 tons in the first year, with this amount subject to annual inflation. A sensitivity analysis was also performed to assess the effect of input variables. In the sensitivity analysis, we calculated between 25,000 and 100,000 tons. The price of hydrogen peroxide and recovered carbon fibre are essential variables that have a high effect on the model.

Electromagnetic shielding enhancement in cement composites: a comparative study of mechanically and thermally recycled carbon fibers

Abstract The recycling of carbon fibers that have reached the end of their service life and their reintegration into new applications hold significant importance from an environmental and sustainable perspective. In this study, the aim is to enhance the electromagnetic wave shielding properties of cement-based composites by incorporating mechanically and thermally recycled and ball-milled carbon fibers at volumetric ratios of 1%, 2%, and 3%. Electromagnetic tests are conducted in the X-band frequency range (8-12.5 GHz), commonly preferred for microwave applications. The obtained results demonstrate an improvement in the SEA (absorption loss )and SET (total power loss) values of the composite with the use of recycled fibers. This improvement is particularly more pronounced in composites containing thermally recycled fibers. The enhanced performance is attributed to the electrical conductivity imparted by carbon fibers. At a frequency of 11.9 GHz, the SET value increased from 8.5 dB for the control sample to 9.2 dB for composites with 3% mechanically recycled fibers and up to 19 dB for composites with 3% thermally recycled fibers. These findings indicate that using recycled carbon fibers enhances the electromagnetic wave shielding properties, with thermal recycling contributing more significantly to this enhancement.

Performance Restoration of Chemically Recycled Carbon Fibres Through Surface Modification with Sizing.

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.

Inhibition of interlaminar damage in CFRP laminates by inserting non-woven carbon fiber interlaminar reinforced tissue

Carbon fiber-reinforced plastics (CFRPs) are known for their high strength and stiffness, essential in high-performance applications. However, in complex structures with fiber discontinuities, such as tapered sections and bolt holes, CFRP laminates are prone to interlaminar damage due to low interlaminar toughness. This study aimed to enhance CFRP interlaminar fracture toughness by inserting non-woven carbon-fiber-reinforced layers. Two non-woven tissues were used: resin-impregnated conventional carbon fiber and resin-free recycled carbon fiber. Evaluations of modes I and II interlaminar fracture toughness revealed that laminates with non-woven inserts had fracture toughness values two to three times higher than pristine CFRP. Non-woven tissues of varying lengths were embedded at ply discontinuities, and tensile tests were conducted to assess their effectiveness. Results confirmed that both non-woven tissues significantly improved interlaminar toughness and effectively suppressed delamination, attributed to high fiber content and complex crack paths, enhancing energy absorption and mechanical performance in CFRP laminates.

Reinforcing Bus Living Space with Recycled Carbon Fibers from Expired Prepreg in the Aircraft Industry.

Due to increasing mobility and energy conservation needs, improving bus and coach safety without adding weight is essential. Many crashes with fatal outcomes for vehicle occupants are associated with the rollover of the vehicle, revealing the structural weakness of the steel pillars between windows, which must resist high levels of bending during rollovers. This study aims to reinforce these pillars with expired carbon fiber prepreg from the aircraft industry, improving safety and reducing environmental waste. To manufacture the pillars, shot-blasted hollow S275 steel tubes with a side length of 25 mm and a thickness of 1.5 mm were used. Bidirectional GG600T woven carbon fiber, CF, and aircraft-grade recycled carbon fiber-reinforced plastic, rCFRP, prepreg M21EV/IMA/3 were used as composite reinforcements. The first composite was made from a CF weave using the rigid epoxy resin Sicomin® 8500/Sicomin® SD8601. The rCFRP composite was frayed, and a new composite was made with the same rigid epoxy resin. Both composites were joined to the steel tube using a tough structural adhesive (SikaPower® 1277). A third composite was obtained using the frayed rCFRP and the structural adhesive as a polymer matrix. All composites were treated with an APPT (atmospheric-pressure plasma torch) before being joined to the steel pillar with the structural adhesive. The comparison of the three reinforcements showed that the steel reinforced with the recycled prepreg composite manufactured with the rigid adhesive performed best, with a 50% increase in specific bending strength and only a 32% increase in weight. It also absorbed 71% more energy, which shows that this novel option for upcycling can noticeably increase the crashworthiness of structures.

Recycled Carbon Fibers from Wind Turbine Blades: Advancing the Mechanical Performance of Concrete

Abstract Recycled carbon fibers from wind turbine blades offer a sustainable approach to enhancing concrete’s mechanical properties. This study investigates the preliminary performance of concrete reinforced with fibers recovered via pyrolysis. Experimental results demonstrate improvements in flexural strength (up to 30%) and fracture mechanics parameters (e.g., KIc and CTODc). Planned research will focus on optimizing mix designs and exploring deformation criteria for quasi-brittle materials, paving the way for environmentally friendly construction solutions.

Machinability investigation on CNC milling of recycled short carbon fiber reinforced magnesium matrix composites

Abstract This study investigates the machinability of magnesium matrix composites reinforced with short carbon fibers, which represent novel materials in the field. AZ91 alloy and its composites containing 2.5 and 5 wt% recycled carbon fiber (rCF) reinforcements were used as workpieces. Face milling was conducted using uncoated carbide cutting tools under dry cutting conditions with varied cutting speeds (480–560–640 m min−1) and feed rates (0.65–0.8–0.95 mm min−1). The experimental design was based on the Taguchi L9 (33) orthogonal array. Analysis included cutting forces, surface roughness, wear on cutting inserts, and chip morphology to assess machinability. Taguchi, analysis of variance, and regression methods were employed to analyze cutting force and surface roughness results. Findings indicated satisfactory machinability for AZ91 alloy and comparatively poorer performance for the 5 wt% rCF reinforced composite, with increased reinforcement content correlating with higher cutting force and surface roughness. SEM and EDX analyses revealed significant built-up layer formation on cutting inserts, with predominantly spiral-shaped continuous chips observed in the experiments. Overall, the study affirmed the machinability of the composites and identified suitable cutting parameters for further investigations.

Material extrusion additive manufacturing of recycled discontinuous carbon fibre reinforced thermoplastic composites with high fibre efficiency

The study proposes a novel method, named angled feeding extrusion (AFE), for material extrusion additive manufacturing (MEX AM) of discontinuous recycled carbon fibre (rCF) reinforced thermoplastic composites with high fibre efficiency. The AFE system is also integrated with a 5-axis printer to enable the fabrication of complex structures. Characterisation of fibre morphology and structure is conducted using X-ray computed microtomography (μCT), and the mechanical properties of the AFE-manufactured rCF composites are investigated through mechanical testing. The results show that AFE demonstrates effectiveness in reducing the fabrication difficulty of rCF composites with high fibre efficiency, fibre efficiency encompasses factors such as fibre fraction, length, and orientation. Moreover, rCF composites additively manufactured by the AFE system achieve rCF lengths of up to 3.8mm and a fibre volume fraction of 30.3%. The tensile strength and modulus are 178MPa and 9.9GPa respectively. It exhibits a significant improvement of 90% and 254% in tensile strength and modulus compared to short fibre reinforced composites. Similarly, compressive tests of AFE-manufactured composite rings show an increase of 80% in ultimate compressive load.

Dual-composite additive manufacturing of glass fibre and recycled carbon fibre reinforced thermoplastic composites with customised fibre layout

Dual-composite additive manufacturing of glass fibre and recycled carbon fibre reinforced thermoplastic composites with customised fibre layout

(Invited) Electrolytic Application of Boron-Doped Diamond Powders

Boron-doped diamond (BDD) electrodes or diamond electrodes are known to be useful for a durable electrode for electrolysis with a high efficiency base on their wide potential window and physical and chemical stabilities. As a result of electrolysis of concentrated sulfuric acid at diamond electrode, reactive oxidizing species, such as peroxodisulfate, peroxomonosulfate, and hydrogen peroxide, can be generated at a high current efficiency. Such electrolyzed sulfuric acid exhibits strong oxidizing power, and is used for mineralization of organic compounds. Carbon fiber reinforced plastics (CFRP) are widely used because it is light in weight and corrosion resistant with high strength and stiffness. Technology for recycling carbon fibers from waste CFRP is desired because it can reduce the amount of carbon fibers disposed of in landfills as waste. When CFRP is treated with electrolyzed sulfuric acid, only the resin is completely decomposed, and nearly intact carbon fibers can be recovered. Therefore, the electrolyzed sulfuric acid method should be a promising candidate for carbon fiber recycling technology. Usually, diamond electrodes are used for the production of electrolyzed sulfuric acid. The diamond electrode consists of a polycrystalline BDD thin film deposited on a conductive substrate by chemical vapor deposition (CVD) method. Therefore, the size of diamond electrode is limited depending on the size and power of the CVD equipment. In this study, we developed a new method to fabricate a large-sized diamond electrode that can be used for electrolyzed sulfuric acid production using BDD powder (BDDP).BDDP was prepared by deposition of a BDD layer on the surface of diamond powder with a particle size of 3-6 μm via microwave plasma-assisted CVD. The BDDP was added to tetraethyl orthosilicate/ethanol solution, followed by addition of ultrapure water and nitric acid and stirring to prepare a BDDP/silica sol solution. The BDDP/silica sol solution was spray-coated on a hydrophilic titanium substrate, and after baking at 150 °C for 1 h, a spray-coated diamond electrode consisted of a BDDP/silica layer formed on the substrate was obtained. Constant-current electrolysis of 50% sulfuric acid was performed in a two-compartment electrochemical cell with the spray-coated diamond electrode as an anode. Concentrations of peroxodisulfate, peroxomonosulfate, and hydrogen peroxide in the sulfuric acid after electrolysis were estimated by titration method, and the current efficiency of the reactive oxidizing species formation was calculated.Scanning electron microscopy observation revealed that the BDDPs were packed densely on the surface of the spray-coated diamond electrode. 10 mL of 50% sulfuric acid was electrolyzed at a constant current density of 20 mA/cm2 for 90 min at a spray-coated diamond electrode (electrode area: 0.5 cm2). During the electrolysis, the electrode potential was stable around +3 V vs. Ag/AgCl, indicating that no deterioration of the electrode occurred even at highly positive potentials in concentrated sulfuric acid. Current efficiency of reactive oxidizing species formation was calculated from the concentration estimated by titration to be 41%. These results confirm that the spray-coated diamond electrode can be used for electrolyzed sulfuric acid production. A large-sized spray-coated diamond electrode was also prepared in the same way using a 20×20 cm2-sized titanium substrate. Electrolysis of 50% sulfuric acid was performed at selected points on the electrode surface (electrode area for electrolysis: 1 cm2), and a constant current density of up to 32 mA/cm2 could be applied for 90 min, with a current efficiency of 67% for reactive oxidizing species formation. Therefore, the spray coating method is expected to be useful for scaling up of a diamond electrode for sulfuric acid electrolysis.

Direct injection molding of polypropylene composites reinforced with recycled carbon fibers

Direct injection molding of polypropylene composites reinforced with recycled carbon fibers

Advancing Circular Economy: Comparative Analysis of Recycled and Virgin Carbon Fiber 3D Printed Composites on Performance and Eco-Efficiency

Carbon fiber-reinforced polymer composites are widely used for their corrosion resistance, high strength, stiffness, and lightweight properties. However, the extensive use of carbon fiber generates significant waste at the end of its lifecycle. Recycling technologies can effectively recover carbon fiber from this waste, making it suitable for reuse in various applications. Recently, there has been a growing trend in using recycled carbon fiber as a reinforcement material in polymer matrices, offering a cost-effective alternative to virgin carbon fiber while maintaining excellent mechanical properties. However, most studies focus on the mechanical strength of parts made from recycled and virgin carbon fibers, with less attention given to the environmental impacts of these materials. The primary objective of this study is the comparative analysis of the specimens manufactured using recycled and virgin carbon fiber-reinforced polyamide-12 material based on the mechanical performance, life cycle cost, and environmental impact. The experimental investigations showed that the mechanical performance of the recycled carbon fiber polyamide-12 (rCFRP12) composites are more efficient than the specimens manufactured using the virgin carbon fiber polyamide-12 (vCFRP12) composites such as three-point bending test results show that parts made from rCFRP12 composites achieved a flexural strength of 56.25 MPa, outperforming those made with vCFRP12 (49.9 MPa). Additionally, the recycled composite specimens also exhibited higher tensile strength than their virgin carbon fiber counterparts. The life cycle analysis revealed that samples made with recycled carbon fiber have a lower environmental impact, reducing global warming, ozone depletion, and carcinogenic effects by 11.98% compared to those made with virgin carbon fiber. Additionally, the production cost of recycled carbon fiber is significantly lower than that of virgin carbon fiber.

Study on recycled carbon fiber obtained by thermal activated oxide semiconductor and mechanical properties of its reinforced polymer composites

Study on recycled carbon fiber obtained by thermal activated oxide semiconductor and mechanical properties of its reinforced polymer composites

Upcycling end-of-life carbon fiber in high-performance CFRP composites by the material extrusion additive manufacturing process

Each year, a significant amount of waste is produced from carbon fiber polymer composites at the end of its lifecycle due to extensive use across various applications. Utilizing regenerative carbon fiber as a feedstock material offers a promising and sustainable approach to additive manufacturing based on materials. This study proposes the additive manufacturing of recycled carbon fiber with a polyamide-12 polymer composite. Filaments of recycled carbon fiber-reinforced polyamide-12 (rCF-PA12) with different recycled carbon fiber contents (0%, 10%, and 15% by weight) in the polyamide-12 matrix are developed. These filaments are utilized for 3D printing of specimens by using various infill density parameters (80% and 100%) on a fused deposition modeling 3D printer. The study examined how the fiber content and infill densities influenced the flexural performance of the printed specimens. Notably, the part containing 15 wt% recycled carbon fiber (rCF) composites showed a significant improvement in flexural performance due to enhanced interface bonding and effective fiber alignment. The results indicated that reinforcing the printed part with 10% and 15 wt% recycled carbon fiber (rCF) improved the flexural properties by 49.86% and 91.75%, respectively, compared to the unreinforced printed part under the same infill density and printing parameters. The investigation demonstrates that the additive manufacturing-based technique presents a potential approach to use carbon fiber-reinforced polymers waste and manufacture high-performance engineering, economic, and environmentally friendly industrial applications with the complicated design using different polymer matrices.

Novel insights into the correlation composition-structure-property of recyclable carbon fiber reinforced thermosetting resin composites

As widely used lightweight and high-strength materials, the sustainable development of thermosetting composites is hampered by their limited recyclability. Developing simple methods for the efficient and upgraded recycling is desirable but challenging. Herein, carbon fiber reinforced degradable thermosetting resin composites were prepared, and the effects of resin degradation process and its derivatives on the sustainable recycling of carbon fiber were studied. Through the tunable departure and re-adsorption of degradation derivatives in cleaning post-treatment, recycled carbon fibers achieved not only non-destructive recovery but also simultaneously improvements in tensile strength from 3.0 GPa to 3.7 GPa and surface energy from 47.2 mN/m to 66.7 mN/m. The adhered derivatives, rich in -NH- and oxygen-containing groups, exhibited good interactions with the fiber surface and epoxy resin. Benefiting from this, the inter laminar shear strength of recycled carbon fibers reinforced epoxy composite effectively improved 24.3 %. In this work, directly reusing resin degradation products for the recycling of reinforced fibers was proposed and the key role of the composition and distribution of degradation products in recycling properties was revealed. The strategy of integrating characteristics of components to enhance material recyclability is expected to have widespread applicability, promoting the sustainable transition for thermosetting composites.

Enhancing flame retardancy in 3D printed polyamide composites using directionally arranged recycled carbon fiber

Combining recycled carbon fiber (rCF) and 3D printing technology has shown great potential for fabricating functional prototypes and production parts used in the aerospace and automotive industries. However, it is still a challenge to design flame-retardant 3D printed parts with high mechanical properties and flame-retardant rating. In the work, a flame-retardant polyamide (PA)-based composite for material extrusion 3D printing was prepared by utilization of rCF, polyhedral oligomeric silsesquioxanes (POSS), and 9,10-Dihydro-9-oxa-10-phosphaphenanthrene (DOPO)-based flame retardant. The 3D-printed composites have high thermal stability, mechanical properties, and excellent flame retardancy with a V-0 rating. With the benefits of material extrusion 3D printing, directionally arranged rCF in 3D printed composites could effectively inhibit the fire spread, extend the time to ignition (TTI), reduce the total heat release (THR) and total smoke release (TSR) of 3D printed composites. The directional flame-retardant mechanism is mainly the thermal conductivity mechanism of the condensed phase and the promotion of stable ordered carbon layer formation. It provides a promising path for designing high-performance flame-retardant materials.

Investigation of pull-out and mechanical performance of fibre reinforced concrete with recycled carbon fibres

This paper presents the pull-out bonding behaviour and mechanical performance of recycled carbon fibre (rCF) reinforced concrete based on the recent investigation of fibre reinforced concrete (FRC) with rCF recovered from pyrolysis. Single fibre pull-out tests have been carried out to identify the apparent interfacial shear strength of different types of rCF and virgin carbon fibre (vCF) to identify the fibre matrix connection. Furthermore, a series of tests have been carried out to identify the workability, compressive strength and tensile strength of FRC. Besides rCF, also vCF and steel fibre were used for fabrication of FRC test specimens. rCF have shown the same adhesion behaviour and strength like vCF. Furthermore, the use of unsized or acrylate-based sized rCF creates an adhesion between fibre and matrix material. During the pull-out tests, the failure does not occur as an adhesive crack between fibre and cement matrix, but as a cohesive crack in the cement matrix. The mechanical performance of FRC with rCF was compared with mortar and FRC with vCF and steel fibres. The results of compressive test conducted for FRC with vCF and rCF indicated that the influence of vCF and rCF on the compressive strength of FRC was insignificant. On the other hand, the results of tensile test conducted for FRC with vCF and rCF indicated that the tensile strength of FRC with rCF was at least 14.9% greater than that of FRC with vCF.

Piezoresistive response and self-sensing properties of UHPC reinforced with recycled carbon fibers

This research explores Ultra-High-Performance Concrete (UHPC) reinforced with recycled carbon fibers to verify its potential application in self-sensing concrete for structural health monitoring. The improved electrical conductivity due to the inclusion of carbon fibers enables the emergence of piezoresistivity, transforming UHPC into a sensitive sensor for detecting mechanical stresses. By incorporating various characterization tests alongside investigations into fiber type (loose versus fibrillated sheets) and content variations, the study aims to establish a correlation between the electrical properties and the resulting piezoresistive response. Resistivity will be measured using impedance scanning, while piezoresistivity will be determined through loading and unloading cycles with a datalogger recording the variations in electrical resistance. The inclusion of carbon fibers suggests an improvement in mechanical performance, up to 42 % in flexural strength and 26 % in compression compared to UHPC without fibers. Resistivity ranges from 1 to 2 Ω⋅m and gauge factor reach 38. These results are comparable to those reported in other studies on UHPC with carbonaceous additions, highlighting the potential of recycled carbon fibers as a sustainable and effective reinforcement strategy.

Machine learning constructs the microstructure and mechanical properties that accelerate the development of CFRP pyrolysis for carbon-fiber recycling

The increasing use of carbon-fiber-reinforced plastic (CFRP) has led to its post-end-of-life recycling becoming a research focus. Herein, we studied the macroscopic and microscopic characteristics of recycled carbon fiber (rCF) during CFRP pyrolysis by innovatively combining typical experiments with machine learning. We first comprehensively studied the effects of treatment time and temperature on the mechanical properties, graphitization degree, lattice parameters, and surface O content of rCF following pyrolysis and oxidation. The surface resin residue was found to largely affect the degradation of the mechanical properties of the rCF, whereas oxidation treatment effectively removes this residue and is the critical recycling condition that determines its mechanical properties. In contrast, pyrolysis affected graphitization in a more-pronounced manner. More importantly, a random forest machine-learning model (RF model) that optimizes using a particle swarm algorithm was developed based on 336 data points and used to determine the mechanical properties and microstructural parameters of rCF when treated under various pyrolysis and oxidation conditions. The constructed model was effectively used to forecast the recovery conditions for various rCF target requirements, with the predictions for different recycling conditions found to be in good agreement with the experimental data.