Recycled Carbon Fiber Research Articles

Tensile Properties of Different Yarn Structures Based on Recycled Carbon Fibre for Sustainable Thermoset Composites

The development of different hybrid yarn structures from recycled carbon fibre (rCF) (rCF content approx. 50% by weight) and thermoplastic fibres for thermoplastic composites has been reported earlier. However, manufacturing of yarns with high rCF content (>90%) required for thermoset composites is still not realizable due to high shortening (≥ 70%) in fibre length of rCF, which occurs during different processing steps of spinning. The reason lies in low shear strength, smooth fibre surface, small diameter and high brittleness of rCF. In addition to this, lack of crimp in rCF leads to drafting error during drawing and spinning process. Therefore, there is a high demand on rCF yarns for thermoset composites, as around 70% of composites are produced based on thermoset matrix. In this paper, yarns consisting of staple rCF with high rCF content (>90 weight%) are developed on DREF-friction spinning and wrap spinning technologies. For the production of yarns, slivers with different rCF content are produced using carding and drawing machine. The effect of different spinning parameters suction air pressure for DREF friction spun yarns and yarn twist for wrap spun yarns is investigated and their effect on tensile properties of yarn is analysed. The results show that the tensile properties of yarns can be adjusted to a wide range varying the yarn structure and spinning parameters.

Toward a circular economy: zero-waste manufacturing of carbon fiber-reinforced thermoplastic composites

Fiber-reinforced composites are becoming ubiquitous as a way of lightweighting in the wind, aerospace, and automotive industries, but current recycling technologies fall short of a circular economy. In this work, fiber-reinforced composites made of recycled carbon fiber and polyphenylene sulfide were recycled and remanufactured using common processing technologies such as compression and injection molding. An industrially viable size-exclusive sieving technique was used to retain fiber length and reduce variability in the mechanical properties of the remanufactured composites. Fiber length reduction alone could not explain the strength reductions apparent in the composites, which we propose are due to microstructural inhomogeneity as defined by poor dispersion of the fibers. Future recycling efforts must focus on fiber length retention and good dispersion to make composite remanufacturing a viable path toward a circular economy.

Continuous carbon fiber recycling technology using the electrolytic sulfuric acid method

Our objective is to achieve the societal implementation of the Circular Economy Program for Automobile Carbon Fibers. This involves recycling carbon fibers sourced from carbon fiber reinforced plastics/carbon fiber reinforced thermoplastics (CFRP/CFRTP) discarded from automobiles and reintegrating them into the manufacturing processes of automobiles. Although, the existing carbon fiber recycling technology recycles the carbon fiber into a finely chopped state; it is not the original continuous carbon fiber product. A novel recycling technology is elucidated herein, referred to as the electrolytic sulfuric acid method (ESAM). The ESAM recycles carbon fibers by decomposing only the resin component of CFRP/CFRTP into CO2 and water using oxidative active species generated by electrolytic sulfuric acid. This method can (1) be applied to all resins, (2) maintains strength of the recycled carbon fibers, and (3) regenerates continuous carbon fibers. Moreover, it is the only technology applicable to CFRP pressure tanks. The successful recycling of continuous carbon fiber from pressure tanks has been achieved, enabling the production of new tanks and unidirectional CFRTP tape. This technology recycles the original continuous carbon fiber product, thus enabling a “close” resource circulation cycle. We have not yet confirmed the number of times recycling can be performed. However, according to the method described in this paper, the recycling process can yield continuous carbon fibers without a decrease in physical properties. Therefore, theoretically, it becomes possible to recycle indefinitely and revert the fibers to their original state, provided that the strength reduction during product use is not a significant consideration.

Rapid stress relaxation and degradable aromatic disulfide vitrimer for recyclable carbon fiber reinforced composite

Rapid stress relaxation and degradable aromatic disulfide vitrimer for recyclable carbon fiber reinforced composite

Optimization of prepreg compression molding process for production of structures with recycled carbon fibers

Carbon fibers are widely used in a growing number of industrial sectors. Their high strength to weight ratio makes carbon fibers suitable for high-value-added applications. However, significant environmental and economic problems are related to composite waste disposal and consumption of non-renewable resources for their production. European legislation has imposed more controls on composite materials waste management. Consequently, development of processes for the recovery of the added value of wastes, instead of its simple disposal, is crucial to promoting the application of EU requirements and the realization of a circular economy model. Currently, thermal processes represent the most promising technology in this direction. Thermal processes include pyrolysis, fluidized bed pyrolysis, and microwave-assisted pyrolysis, but only pyrolysis is implemented on an industrial scale in Europe because of its economic viability and technical feasibility. Although the recovery of carbon fibers has reduced cost, compared to virgin fibers, length, orientation, and sizing of the fibers are lost. In this context the challenge is to realize composites reinforced with reclaimed fibers that can compete economically and in terms of mechanical performance with composite with virgin fibers. In this work, prepreg compression molding technique was used to produce a window frame with non-woven fabrics of recycled carbon fibers impregnated with a fast-curing resin. The fibers were coated with a sizing developed by CETMA and compatible with fast-curing epoxy resin.

Characterization and prediction of tensile properties of carbon fiber-reinforced thermoplastics composed of hybrid short carbon fiber/PA6 fiber nonwoven mats

Hybrid carbon fiber/resin fiber nonwoven mats are considered as a highly promising application of recycled carbon fibers due to their low cost and simple synthesis process. However, the mechanical properties of hybrid nonwoven mats are subject to uncertainties due to nonuniformity of fiber orientations during production procedures, which restricts their use in structural components. This study investigates the characteristics of various types of hybrid nonwoven mats with different volume fractions and fiber orientation distributions. Notably, the investigation yields noteworthy tensile properties, exemplified by a tensile strength of 367.20 MPa and a stiffness of 32.85 GPa, when the volume fraction is 28.9%. Tensile properties of the hybrid nonwoven mats and their fluctuations are then analyzed through statistical analyses. A three-dimensional microstructure-based fiber network model is established using the Monte Carlo method to represent the statistical and stochastic properties of the material. Furthermore, a prediction method of tensile properties based on microstructural properties in the model is proposed, which shows good agreement with all experimental results for adjustments of the volume fraction of carbon fibers, distribution of fiber lengths, and anisotropy of the materials, significantly reducing the experimental burden for optimization research. The tensile characteristics of composites are reliably anticipated with a nominal error margin below 10%. Additionally, this prediction method enables the prediction of scatter and stable standard deviation, making it possible to apply hybrid nonwoven mats in recycling and industrial processes.

Pretreating Recycled Carbon Fiber Nonwoven with a Sizing Formulation to Improve the Performance of Thermoplastic Recycled Fiber-Reinforced Composites.

Pyrolysis is already an established recycling method to recover the carbon fibers of end-of-life composites. However, the pyrolysis process removes the fiber sizing. Fiber sizing is a critical step in composite material production, influencing adhesion, protection and overall performance. In this study, recycled carbon nonwoven reinforcements made from pyrolyzed carbon fibers were pretreated to improve the mechanical properties of polyamide and polypropylene composites. The pretreatment involved applying specific coatings (sizings) on the nonwoven by spraying. Pretreated and non-pretreated composites were prepared by compression molding to investigate the impact of the fiber pretreatment on the tensile properties and interlaminar shear strength. The tests were performed in the 0° and 90° directions of the composite plate. The results revealed that pretreatment had little effect on the polyamide composites. However, significant improvements were obtained for the polypropylene composites, as an increase of more than 50% in tensile strength was achieved in the 0° direction and more than 35% in the 90° direction. In addition, the interlaminar shear strength increased from 11.9 MPa to 14.3 MPa in the 0° direction and from 14.9 MPa to 17.8 MPa in the 90° direction.

Comparative study on the mechanical behaviors of compression molded, additively manufactured, and injection molded recycled carbon fiber reinforced rHDPE composites

Adding fibers into recycled plastics and converting them into composites have drawn significant attention because of improved strength and modulus for the recycled plastic. This work focuses on developing recycled carbon fiber (rCF) reinforced recycled high-density polyethylene (rHDPE) composites using three common processing methods and comparably studying their mechanical behaviors. Compression molding (CM), additive manufacturing (AM), and injection molding (IM) were used to produce rCF/rHDPE composite samples with different fiber contents (10 wt% and 20 wt%) for tensile testing and thermal characterization. The mechanical performance varied significantly among composite samples from different processes. Tensile strength and modulus increased with higher rCF content in all samples. Adding 10% rCF led to tensile strength increases of 11.2%, 15.2%, and 72.1% for CM, AM, and IM samples, respectively, compared to neat samples. Doubling the fiber content to 20% rCF resulted in further enhancements of 29.3%, 58.2%, and 91.4%. Fiber alignment notably influenced tensile modulus, while void content had a greater impact on tensile strength. A combination of ductile and brittle fracture modes were found in both CM and IM samples. These findings emphasize the critical role of manufacturing processes and material composition in determining composite performance.

A Critical Review on the Application of Recycled Carbon Fiber to Concrete and Cement Composites

Carbon fiber (CF) exhibit extraordinary properties, such as high specific and tensile strength, high elastic modulus, light weight, and weather resistance, which has led to a rapid increase in the use of CF in sectors such as aerospace, sports equipment, energy storage, automotive, construction, and wind energy applications. However, the increase in CF applications has led to a massive production of CF waste. As CF is non-biodegradable, it results in CF accumulation in landfills. CF waste is a rapidly growing ecological hazard because of its high energy consumption and expensive production methods. The properties of carbon fibers can be preserved even after recycling given the development of recycling technology; therefore, multiple studies have been conducted to demonstrate the effect of recycled carbon fiber (RCF) in different composites such as cement-based composites. This review presents the results of studies conducted on the application of RCF to cement composites and analyzes those results to investigate the effect of RCF on the properties of cement composites such as mechanical properties (compressive strength, flexural strength, and tensile strength), fracture characteristics (fracture toughness and fracture energy), electrical properties, and workability. Overall, the studies demonstrated a positive trend in the application of RCF to cement composites.

Manufacturing of automotive mat using recycled carbon fiber: Obtaining strong physical properties through isotropic fiber orientation and improved adhesion of epoxy resin

Manufacturing of automotive mat using recycled carbon fiber: Obtaining strong physical properties through isotropic fiber orientation and improved adhesion of epoxy resin

Bio-inspired polydopamine modification of recycled carbon fibers for improving the performance of recycled carbon fiber reinforced mortars

The hydrophobicity nature of the waste carbon fiber felt (WCF) surface results in the formation of a weak interface with the paste during the curing process of WCF concrete, which seriously affects the performance of WCF concrete and the reuse of WCF. To address this problem, this paper utilized polydopamine (PDA) for the functionalization of WCF to enhance bonding between WCF and paste. The wettability, Ca2+ complexation, and functional groups of PDA coating on WCF were analyzed by contact angle, ICP-OES, and XPS, respectively. Additionally, the effects of incorporating PDA-functionalized WCF on the flowability, compressive strength, hydration kinetics, pore structure, water absorption capillary, and SEM of mortars were tested. Experimental results showed that the PDA coating improved the wettability of WCF and enhanced the flowability of WCF mortar. What's more, the PDA coating could chelate Ca2+ and promote the formation and deposition of hydration products on the WCF surface, resulting in a denser interfacial transition zone (ITZ). Compared with ordinary WCF mortar, the compressive strength of the PDA-modified WCF mortar was increased by 18% at 28d. Furthermore, the capillary water absorption of the modified group mortar was also decreased by up to 13%, significantly enhancing the durability of mortars. This paper presents a green and simple bio-inspired method to strengthen the ITZ between WCF and paste, which is fundamentally different from the traditional modification methods, and also offers a theoretical basis and technical foundation for the sustainable utilization of WCF.

Mechanical Strength and Surface Analysis of a Composite Made from Recycled Carbon Fibre Obtained via the Pyrolysis Process for Reuse in the Manufacture of New Composites.

This work aims to obtain recycled carbon fibre and develop an application for this new material. The carbon fibres were obtained by recycling aerospace prepreg waste via the pyrolysis process. The recycled fibres were combined with an Araldite LH5052/Aradur LY5053 epoxy resin/hardener system using manual lay-up and vacuum bagging processes. For comparison, the same resin/hardener system was used to produce a composite using commercial carbon fibre. The recycled and commercial composites were subjected to flexural, tensile and Mode I testing. Fracture aspects were analysed via scanning electron microscopy (SEM). The pyrolysis process did not affect the fibre surface as no degradation was observed. The fracture aspect showed a mixture of failure in the recycled composite laminate and interlaminar/translaminar failure near the surface of the commercial composite caused by flexural stress. Flexural and tensile tests showed a loss of mechanical strength due to the recycling process, but the tensile values were twice as high. The sand ladder platform was the project chosen for the development of a product made with recycled carbon fibres. The product was manufactured using the same manufacturing process as the specimens and tested with a 1243 kg car. The method chosen to design, manufacture and test the prototype sand ladder platform made of recycled carbon fibre was appropriate and gave satisfactory results in terms of high mechanical strength to bending and ease of use.

Tensile properties of unidirectional thermosetting composites reinforced with ring-spun hybrid yarns including recycled carbon fiber

The study of composites reinforced with aligned recycled carbon fiber (CF) is gaining increasing attention, particularly in light of the circular economy. Hybrid yarns, among other oriented reinforcements, have gained interest from researchers who have already utilized them to produce unidirectional thermoplastic composites. Nevertheless, the evaluation of unidirectional thermosetting composites reinforced with hybrid yarns is still lacking. This article presents their production, leveraging a recently developed process, and mechanical characterization. The results show that the amount of recycled CF and the number of draw frame doublings within the hybrid yarns affect the tensile properties of the composite, while the thermoplastic fiber has no influence, as also suggested by the main effect plots. Two-way interactions exhibit different behaviors depending on the tensile property considered. Overall, the composite material with the best tensile properties was that reinforced with a ring-spun hybrid yarn consisting of 70% recycled CF, 30% polyamide, and five draw frame doublings.

A novel strategy for the design of cooperatively reinforced, shape-memory, recyclable ESO-based carbon fiber composites

To improve the poor performance of epoxidized soybean oil (ESO) thermosetting materials in preparing high-performance carbon fiber composites, we synthesized novel bio-based epoxy monomers using naringin (EN) as an epoxy monomer. EN's hydrogen bonding and benzopyrenone structure enhanced the crosslinking density, rigidity, bond shear strength, glass transition temperature (Tg), tensile and lap shear strength, and shape memory ability of ESO/MeHHPA/EN. The resulting carbon fiber composites had high tensile strength (349 MPa) and could be fully recovered using ethanolamine, with the recovered fibers maintaining almost 100% of the mechanical properties of the original sample. This study provides a new approach for fabricating multifunctional, high-performance, and recyclable ESO-based carbon fiber reinforced composites.

Influence of Carbon-Based Fillers on the Electromagnetic Shielding Properties of a Silicone-Potting Compound.

The effect of carbon-based additives on adhesives and potting compounds with regard to electrical conductivity and electromagnetic interference (EMI) shielding properties is of great interest. The increasing power of wireless systems and the ever-higher frequency bands place new demands on shielding technology. This publication gives an overview of the effect of carbon-based fillers on electrical conductivity, electromagnetic shielding properties, and the influence of different fillers and filler amounts on rheological behavior. This work focuses on carbon black (CB), recycled carbon fibers (rCF), carbon nanotubes (CNTs), and complex nanomaterials. Therefore, silicon samples with different fillers and filler amounts were prepared using a dual asymmetric centrifuge and a three-roll mill. It has been found that even with small filler amounts, the electromagnetic shielding properties were drastically raised. The filler content as well as the dispersion technique have a significant influence on most of the fillers. It has also been found that the complex viscosity is strongly influenced by the dispersion technique as well as by the choice and amount of filler. In the experiments carried out, shielding values of over 20 dB were achieved with several fillers, whereby even 43 dB were reached with complex, pre-crosslinked fillers. This signal reduction of up to 99.99% enables almost complete shielding of the related frequency.

Chemical Recycling of CFRP in an Environmentally Friendly Approach.

A novel and environmentally friendly recycling approach for carbon-fiber-reinforced plastics (CFRP) was studied using not only nitric acid (HNO3) but also our chosen alkaline, sodium hydrogen carbonate (NaHCO3). The CFRP specimen was first immersed into 8 M HNO3 at 80 °C for 8 h, and then into 0.1 M NaHCO3 at 80 °C for 15 min to obtain resin-free recycled carbon fiber (rCFs). Using this new recycling method, it was shown that the recycling time was reduced to 8.3 h, whereas it originally took 24 h, as reported previously. It was shown that immersing the CFRP specimen into NaHCO3 caused a transesterification reaction with the remaining resin residue on the CF surface, which led to dissolving the resin into the NaHCO3 aqueous solution all at once. Additionally, NaHCO3 produced carbon dioxide gas while reacting with the resin residue; the CO2 gas physically helped removing the resin from the CF's surface. Moreover, evaluating the physical properties of the rCFs demonstrated an improvement in fiber strength and adhesiveness to resin. Therefore, this recycling method was shown to be effective in recovering high-quality rCFs in a relatively short recycling period.

Assessing sustainability and green chemistry in synthesis of a Vanillin-based vitrimer at scale: Enabling sustainable manufacturing of recyclable carbon fiber composites

Sustainable manufacturing of carbon fibre (CFs) reinforced polymer (CFRP) composites featured technically by low-cost and rapid manufacturing techniques, use of renewable materials, and non-destructive recycling process. By developing an inherently recyclable thermoset, this research bridges between these three components of sustainable manufacturing by focusing on a fast cured vanillin-based Schiff base polyimide network in all-solid state. In this study, a multifunctional vanillin-based monomer was synthesised at scale in water which can be cured using a diamine without requiring any organic solvent. A CFRP was fabricated using this newly developed Schiff base polymer using compression moulding technique, and its mechanical and thermal/fire performance were compared to a CFRP made of a commercially available automotive grade epoxy resin. The resulting Schiff base CFRP composite demonstrated exceptional fire retardancy, complemented by remarkable tensile strength and modulus values of 427 MPa and 45 GPa, respectively. These characteristics meet the criteria for a broad spectrum of high-performance applications. In contrast to conventional CF reclaiming processes, a novel and efficient chemical recycling approach was introduced, enabling the delamination of CF layers containing the Schiff base network without requiring the separation and purification of the polymer matrix. This approach facilitates the low-cost remanufacturing of new CFRP composites with mechanical performance comparable to the original composite. Finally, green chemistry matrices as well as simplified life cycle assessment (LCA)-like approaches, including the EcoScale and GREEN MOTION rates, were employed to evaluate the efficiency and environmental impact of the CFRP manufacturing process.

High biomass content, anti-flammable and degradable epoxy thermosets by curing a tyramine-derived epoxy monomer with a furan-derived diamine for non-destructively recyclable carbon fiber composite application

High biomass content, anti-flammable and degradable epoxy thermosets were prepared by curing a tyramine-derived epoxy monomer (TVEP) with a furan-derived diamine (DFDA) for non-destructively recyclable carbon fiber composite application.

Investigation of Tensile Properties of FDM-Printed Reclaimed Carbon Fiber Reinforced Reclaimed Polyamide-6 Composites (rCF/rPA) via Various Densities of Infill Patterns

This work determined the effect of different infill patterns with various infill densities on the tensile properties of FDM-printed reclaimed carbon fiber reinforced reclaimed polyamide-6 (rCF/rPA) composites. The rCFs were derived from recycled carbon fiber composite wastes by pyrolysis, while the rPA recyclates were obtained by mechanical recovery of end-of-life (EoL) nylon fishnets. The comparison between honeycomb and triangular infill patterns within rCF/rPA coupons via the FDM recycling was performed under the various relative densities of 10%, 30%, 50%, 70%, and 90%. The best performance of rCF/rPA coupons occurred in honeycomb infill patterns with 90% relative infill densities. The tensile strength and modulus of those specimens were 76.5 GPa ± 3.5 MPa and 4.8 GPa ± 0.1 GPa, respectively.

Reliability assessment of carbon fiber mortar: Combined pulse velocity, point load, and compressive strength tests

Cement mortar is used as an adhesive and plaster for brick walls, drainage channels or irrigation with river stones or mountain stones, and in the manufacturing of short revetments. The performance of cement mortar requires continuous improvement by construction materials researchers, scientists, and building contractors. Recently, carbon fiber sheet has gained popularity for use in retrofitting and improvement to the performance of building elements. This study aims to recycle small sheets of unused carbon fiber by cutting them into short carbon fiber (SCF) with a uniform length of 12 mm, which is used as an internal reinforcement in the cement mortar. All plain and fibrous mortar were prepared with a 50 mm cube mold. In addition, tests were conducted to provide reliable data regarding the application of recycled carbon fiber sheets as discrete fiber reinforcement in the improvement of cement mortar; these include ultrasonic pulse velocity (UPV), compressive strength, and point load strength index (PLSI) (known for performance rock testing in geotechnical and geological environments) tests. The test results for UPV, PLSI, and compressive strength showed that the addition of carbon fiber improves the performance of the mortar when compared to plain mortar. Furthermore, two simplified relationships are made: the first correlation was for PLSI with compressive strength, and the second correlation was for UPV with compressive strength. Finally, these correlations were compared with those of experimental tests obtained from published literature, thus demonstrating the correctness of the PLSI, compressive strength, and UPV values obtained in this study.