Recycled Carbon Fiber Research Articles

Use of fibres in improving the mechanical properties of a multifunctional cement for structural repair purposes

Calcium phosphate cement (CPC) is a multifunctional cement whose potential application depends on the reactants used to synthesise it. Just like many inorganic cements, the pure CPCs synthesised in all cases are very brittle and have low toughness values under loading. In this research, the CPC material is formed from the exothermic reaction between phosphoric acid and calcium silicate at controlled room temperature. Three fibre types, namely; macro polypropylene fibres, amorphous metallic fibres and recycled carbon fibres were chosen due to their corrosion resistance in acid to enhance the mechanical performance of this cement as a repair material. 1.5% by volume of each of these fibres were added to the CPC material and autogenously cured for 14 days at room temperature. Mechanical destructive and non-destructive tests were carried out on the resulting composites. The experimental results revealed that each type of fibre contributes to increase flexural strength, compressive strength, fracture energy and dynamic elastic modulus of CPC material. However, for this purpose the recycled carbon fibres have proven to be more efficient.

Manufacturing of long recycled carbon fibre composites by injection

Due to the rapid growth in the use of composite materials, environmental concerns have become an increasingly influential topic, making recyclability of composite materials a key issue. Furthermore, several related European laws have been passed to minimize the environmental impact of composites (EU 2000/53/CE [1], 2000/76/EC [2], 2004/35/EC [3]). Caused by the high energetic requirements and the huge amount of composite materials used in the manufacturing process, recycling supposes a reduction of a 70% in the costs and 98% in the energy demanded [4]. Once the fibers are obtained through pyrolysis, with a high retention of mechanical properties, the next step is the manufacturing process by injection using a thermoplastic polymeric matrix of polypropylene, a polymer widely used in the composite industry. For that purpose, a study of the compatibility of the fiber with the maleic anhydride polypropylene at different relations -10, 20 and 30%- has been carried out. In order to enhance the mechanical properties, a combination of homopolymer polypropylene, maleic anhydride polypropylene and recycled carbon fibers is studied through the production of a masterbach composed of maleic anhydride polypropylene and carbon fibers, followed by the addition of the homopolymer polypropylene. Once the pellets are obtained, they are injected. The samples injected are analyzed in terms of fiber distribution by scanning electron microscopy and tomography, thus the mechanical properties are evaluated through tensile, impact and bending tests, to determine the optimum fiber/resin ratio.

Reducing down-cycling of carbon fibre by fibre architecture preservation: Multi-layer fibre surface quality investigation

Carbon fibre has a high mechanical reinforcement capability associated with fibre architectures. However, it is significantly down-cycled in the current recycling practice as a result of a loss of fibre architecture. Without the use of chopping/shredding process, the architecture of carbon fibre can be preserved, but the surface cleanliness of recycled carbon fibre (rCF) is not clear. In this study, an investigation is carried out on the surface quality of architecture-preserved rCF obtained from multiple layers of a carbon fibre reinforced polymer (CFRP). Carbon fibre woven fabrics are manufactured into CFRP, recycled using a pyrolysis technique, and inspected using visual and microscopic techniques. The results indicate a good preservation of fibre architecture in all five layers of CFRP. Nonetheless, the residue from the pyrolysis of resin is increased in the internal layers (4th and 5th) of rCF in comparison to the external layers (1st to 3rd). The results suggest that fibre architecture preservation has a potential to reduce the down-cycling of carbon fibre, but the impact is limited in internal fibre layers due to reduced fibre surface cleanliness. The insights from this study provide a further understanding on the approach to reduce the down-cycling of carbon fibre and move the carbon fibre industry towards circular economy.

コンクリート材料としてのリサイクル炭素繊維の可能性と展望

コンクリート材料としてのリサイクル炭素繊維の可能性と展望

Recovering recycled carbon fiber by pyrolysis of cured prepregs

Due to the rapid growth of the composite market, several European laws have emerged to minimize their environmental impact (EU 2000/53 / EC, End of life vehicles), as well as to make rational use of landfills (EU 1999/31 / EC). For example, in the aeronautical sector, composites can reach 50% by weight of the aircraft. Consequently, recyclability is a key issue. The objective of this work is the study of the recycling techniques of carbon fiber composites with thermoset polymer matrix in order to obtain fibers with similar properties to the original ones. In this way, the fibers could be reused in new composites by themselves or together with flass fibers in the manufacture of new hybrid composite materials. By this hybridization, materials with properties far superior to the GFRP would be obtained, but at much lower cost than the original CFRP. Therefore, this recycling and reprocesing strategies provides great economical attractiveness.  The main objective of the project is to study and optimize the recyclability of cured carbon fiber / epoxy prepregs for use in hybrid materials. Starting from a pyrolysis in a controlled atmosphere reactor, followed by a oxidation, carbon fibers with properties similar to virgin fibers are obtained, with a loss less than 20% of the tensile strength. An evaluation of the different parameters of the recycling process has been carried out in order to optimize the procedure. The characterization of the fibers includes tensile tests, scanning electron microscopy and Raman spectroscopy.

Lightweight, Flexible, and Highly Conductive Recycled Carbon Fiber Felt for Electromagnetic Interference Shielding

Lightweight, Flexible, and Highly Conductive Recycled Carbon Fiber Felt for Electromagnetic Interference Shielding

Mechanical and Physical Properties of Recycled-Carbon-Fiber-Reinforced Polylactide Fused Deposition Modelling Filament.

Carbon-fiber-reinforced plastic materials have attracted several applications, including the fused deposition modelling (FDM) process. As a cheaper and more environmentally friendly alternative to its virgin counterpart, the use of milled recycled carbon fiber (rCF) has received much attention. The quality of the feed filament is important to avoid filament breakage and clogged nozzles during the FDM printing process. However, information about the effect of material parameters on the mechanical and physical properties of short rCF-reinforced FDM filament is still limited. This paper presents the effect of fiber loading (10 wt%, 20 wt%, and 30 wt%) and fiber size (63 µm, 75 µm, and 150 µm) on the filament’s tensile properties, surface roughness, microstructure, porosity level, density, and water absorptivity. The results show that the addition of 63 µm fibers at 10 wt% loading can enhance filament tensile properties with minimal surface roughness and porosity level. The addition of rCF increased the density and reduced the material’s water intake. This study also indicates a clear trade-off between the optimized properties. Hence, it is recommended that the optimization of rCF should consider the final application of the product. The findings of this study provide a new manufacturing strategy in utilizing milled rCF in potential 3D printing-based applications.

Degradable benzyl cyclic acetal epoxy monomers with low viscosity: Synthesis, structure-property relationships, application in recyclable carbon fiber composite

Degradable thermosets can address the recycle issue of conventional thermosets and downstream materials like carbon fiber composites. Significant advances have been achieved on their recyclability even on high performance, but their processability was neglected. Herein, for the first time, from the processing point of view, degradable epoxy monomers with low viscosity were designed. Ethyl or methyl group was incorporated into the benzyl cyclic acetal structure to obtain three acetal epoxy monomers by the acetalization between p-hydroxybenzaldehyde analogues and triols to achieve diols, followed by reacting with epichlorohydrin. Two benzyl cyclic acetal epoxy monomers with ethyl group are liquid. The viscosity and structure-property relationship of epoxy monomers were systematically investigated from experiments to simulate computation. The cured epoxies possessed favorable thermal properties, mechanical properties and controllable degradability. Furthermore, the epoxy monomer with suitable viscosity was used to prepare carbon fiber composites with excellent performance via vacuum assisted resin transfer molding (VARTM) process. Meanwhile, the non-destructive recovery of carbon fiber was realized by taking advantage of the degradability of the acetal epoxy matrix.

Using taguchi approach for investigating mechanical properties of recycled carbon fibre reinforced thermoplastics for injection moulding applications

Demand for carbon fibre reinforced plastic (CFRP) increases due to its popular demand in sectors such as automotive and aerospace. This leads to high volume of manufacturing and end of life CFRP waste. The challenge is to recycle the heterogenous waste and utilise the recycled carbon fibre (rCF) in potential applications, including the injection moulding process. However, the effect of processing parameters such as type of new thermoplastics, filler weight loading and particle size on product mechanical properties is not well understood. This study carried out experimental trials based on L4 Taguchi orthogonal design. It is found that the mechanical and physical properties significantly depend on the selected parameters. Optimisation of the parameters should depend on final application of the product. This study highlights potential use of rCF in reinforcing pure thermoplastics, as well as an alternative material to virgin carbon fibre (CF).

The effect of waterborne polyurethane coating on the mechanical properties of epoxy-based composite containing recycled carbon fibres

The current study focuses on the influence of waterborne polyurethane surface-modified recycled carbon fibre (rCF) on tensile, flexural, and low-velocity impact properties of the epoxy-based composite. The recycled carbon fibres were coated by five different concentrations of waterborne polyurethane (WBPU) bonded with 3-aminopropyltriethoxysilane. The chemical bonding between the fibres and the coating and their morphological structures are demonstrated by Fourier-transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM), respectively. Furthermore, the single fibre tensile tests showed the enhancement of tensile strength and Young's modulus results after the coating. The thermal stability of the coated fibres was changed significantly compared to the uncoated fibres and the contact angle of their surface was reduced dramatically. The measured contact angles between the single fibres and the resin decreased from 70° to 40°. The epoxy-based composites were manufactured by the vacuum infusion method at room temperature. Significant improvements were attained in the tensile and flexural properties of the composites reinforced by coated fibres. The tensile and flexural strength of the mentioned composites were enhanced by up to 107% and 68%, respectively. Fractography confirmed the strong adhesion between the coated fibres and the matrix. Eventually, the impact resistivity of the fabricated composites was improved by approximately 49%.

Effect of the Fibre Orientation Distribution on the Mechanical and Preforming Behaviour of Nonwoven Preform Made of Recycled Carbon Fibres

Recycling carbon-fibre-reinforced plastic (CFRP) and recovering high-cost carbon fibre (CF) is a preoccupation of scientific and industrial committees due to the environmental and economic concerns. A commercialised nonwoven mat, made of recycled carbon fibre and manufactured using carding and needle-punching technology, can promote second-life opportunities for carbon fibre. This paper aims to evaluate the mechanical and preforming behaviour of this nonwoven material. We focus on the influence that the fibre orientation distribution in the nonwoven material has on its mechanical and preforming behaviour at the preform scale, as well as the tensile properties at composite scale. The anisotropy index induced by fibre orientation is evaluated by analysing SEM micrographs using the fast Fourier transform (FFT) method. Then, the anisotropy in the tensile, bending, and preforming behaviour of the preform is inspected, as well as in the tensile behaviour of the composite. Additionally, we evaluate the impact of the stacking order of multi-layers of the nonwoven material, associated with its preferred fibre orientation (nonwoven anisotropy), on its compaction behaviour. The nonwoven anisotropy, in terms of fibre orientation, induces a strong effect on the preform mechanical and preforming behaviour, as well as the tensile behaviour of the composite. The tensile behaviour of the nonwoven material is governed by the inter-fibre cohesion, which depends on the fibre orientation. The low inter-fibre cohesion, which characterises this nonwoven material, leads to poor resistance to tearing. This type of defect rapidly occurs during preforming, even at too-low membrane tension. Otherwise, the increase in nonwoven layer numbers leads to a decrease in the impact of the nonwoven anisotropy behaviour under compaction load.

Fully recyclable carbon fiber reinforced vanillin-based epoxy vitrimers

Fabrication of recyclable and reprocessable epoxy vitrimers is opening more application opportunities for carbon fiber (CF) recycling. Despite the extensive study of epoxy thermosets from lignin-based monomer of vanillin, however, few works have been focused on its vitrimers, let alone their mechanical, interfacial, solvent resistance and fully recyclable properties of vanillin-based epoxy vitrimers /CF composite. Here the effect of four types of curing agents on the above properties has been carefully studied. Two-layer CF reinforced vanillin-based epoxy vitrimers composites that was cured with Isophoronediamine shows higher tensile strength at break and Young’s Modulus than those of Bisphenyl A epoxy (E51)/CF and other epoxy vitrimers/CF composites, which reaches 571 MPa and 11.7 GPa, respectively. All vanillin-based epoxy vitrimers are easily degradable at room temperature in acid solution except for that cured with 4,4′-Diaminodiphenylmethane. The surface morphology and chemical structure of CF are not altered after degradation. Importantly, completely recyclable vanillin-based epoxy vitrimers are achieved by imine exchange reaction; however, the mechanical and thermal properties of it are slightly inferior to the origins. This work demonstrates that the mildly degradable, fully recyclable vanillin-based epoxy vitrimers and readily recycling of CF are desirable for the development of lignin based functional materials.

Recyclable separation and recovery of carbon fibers from CFRP composites: Optimization and mechanism

• Carbon fibers are recovered from CFRP via chemical swelling and electrochemical oxidation. • Solvent DMSO is recyclable in this separation and recovery method. • Recovered carbon fibers exhibit good surface morphology and mechanical properties. Chemical swelling and electrochemical oxidation are combined to realize the separation and recovery of carbon fibers from carbon fiber-reinforced plastic (CFRP) in dimethyl sulfoxide (DMSO) at normal temperature and pressure. The results showed that the depolymerization rate of epoxy resin in CFRP increased with increasing ammonium acetate concentration and current density, and the influence of the current density was more significant than that of the concentration. Microscopic analysis showed that the recycled carbon fibers had few residual resin on their surfaces and mild electrochemical oxidation etching, and recycled carbon fiber monofilament achieved a tensile strength and an interfacial shear strength that were 93.55% and 118.76% those of the original fibers.

Grinding, Melting and Reshaping of EoL Thermoplastic Polymers Reinforced with Recycled Carbon Fibers

This article assesses the technical feasibility of a recycling process based on grinding, melting and re-shaping of carbon fibers (CFs) reinforced thermoplastic polymers, in order to obtain new products that can be introduced in different markets, depending on mechanical properties retained. The idea at the basis of our study is that this kind of recycling process lies at the edge of the stages of recycling and re-use of materials, considering that the latter is preferable when considering the waste management hierarchy. Lower cost and similar mechanical strength of virgin CFs allowed the spread of recycled CFs in the automotive sector in the form of composite materials. Taking into account the Directive 2000/53/EC that sets out measures to prevent and limit waste from end-of-life (EoL) vehicles and their components, and ensures that where possible this is reused, recycled or recovered, we considered worth to investigate the recyclability of composite materials made with recycled CFs when they will reach the state of EoL materials. Considering this premise, an additional scope of this paper is therefore to provide some useful information about the possibility to perform a multiple closed loop recycling of rCF thermoplastic composites. Experiments carried out demonstrated that re-shaping of composites is technically feasible. Some square plates were produced without any setback. The mass balance of the recycling process demonstrated that about 88% of the EoL material can be recovered. Calculation of energy consumption showed that approximately 16 MJ are necessary in the treatment of 1 kg of EoL composites.

Fully recyclable, flame-retardant and high-performance carbon fiber composites based on vanillin-terminated cyclophosphazene polyimine thermosets

Carbon fiber reinforced polymer composites (CFRPs) have been widely applied in various high-tech fields because of their superior performance. However, with the increasing consumptions of CFRPs, the nondestructive recycling of expensive carbon fibers (CFs) and the reduction of fire-hazards are highly desirable for the sustainable and safe utilization of CFRPs. Herein, a fully recyclable CFRPs with high flame retardance was newly designed by incorporating the vanillin-terminated phosphazene monomer (HVP) into the polyimine binder material. The six-functional HVP monomer makes the polyimine thermosets have a high crosslinking density and high P/N content, thereby ensuring the excellent flame retardancy and mechanical performances of the resulted composites. And the preparation of this kind of composites just need simple hot-pressing at lower temperature and shorter time, which is more energy-saving and efficient. Owing to the degradable imine bonds, the nondestructive closed-loop recycling of CFs and HVP monomers from the composites are achieved under mild conditions, which is extremely vital to preserve the structure of virgin CFs and HVP functional monomer. The regenerated CFRPs displayed same performance with that of fresh ones, and it also could be reprocessed and repaired within few minutes at elevated temperatures. More importantly, due to the rational combination of cyclophosphazene and imine bond, the excellent synergistic effect of gas phase and condensed phase during combustion endows the composites with superior flame retardancy. This work prepared bio-based recyclable, flame-retardant CFRPs, offering a green, sustainable and fire-safe strategy for designing eco-friendly high-performance composites. ● A vanillin terminated cyclophosphazene (HVP) was synthesized through a facile one-step reaction ● Dynamic polyimine resin for CFRP was prepared by HVP and D230 without catalyst. ● High recyclability and flame retardance are simultaneously attained in this CFRP. ● The comprehensive properties of recycled CFs are same with that of virgin ones. ● Near total flame-retardant monomer HVP could be retrieved.

Comparison of the Mechanical Behavior of Concrete Containing Recycled CFRP Fibers and Polypropylene Fibers

The incorporation of natural or recycled fibers in concrete represents a field for improvement in this structural material and a step towards sustainability. The objective of this research is to determine whether the addition of recycled carbon fibers (CFRP), which have been hardened using epoxy resin, improves the behavior of concrete and whether its performance is comparable to that achieved by adding polypropylene fibers, which would result in a viable recycling alternative for this type of fiber. In order to explore this objective, 120 specimens were produced, on which compression, flexural, and impact tests were performed, and into which recycled CFRP fibers or polypropylene fibers were incorporated. By comparing the results obtained, it may be concluded that the addition of fibers substantially improves the ductility of the concrete and reduces the spalling effect when compared to concretes without added fibers. The concretes containing recycled CFRP fibers in quantities of 3 kg/m3 and 6 kg/m3 obtain better flexural and impact behaviors than concretes featuring the same amounts of polypropylene fibers, making this recycling alternative viable for CFRP fibers as well as reducing the amount of energy and raw materials that would be used to manufacture the fibers.

Room-Temperature Self-Healable and Mechanically Robust Thermoset Polymers for Healing Delamination and Recycling Carbon Fibers.

The advocacy of carbon neutrality and circular economy encourages people to pursue self-healing and recycling of glassy thermoset polymers in a more realistic and energy-saving manner, the best being intrinsic healing under room temperature. However, the high mechanical robustness and healing ability are mutually exclusive because of their completely opposite requirements for the mobility of the polymer networks. Here, we report a dual-cross-linked network by slightly coupling the low-molecular-weight branched polyethylenimine with an ester-containing epoxy monomer in a nonstoichiometric proportion. The highly mobile and dense noncovalent hydrogen bonds at the chain branches and ends can not only complement the mechanical robustness (tensile strength of 61.6 MPa, elastic modulus of 1.6 GPa, and toughness of 19.2 MJ/m3) but also endow the glassy thermoset polymer (Tg > 40 °C) with intrinsic self-healing ability (healing efficiency > 84%) at 20 °C. Moreover, the resultant covalent adaptive network makes the thermoset polymer stable to high temperatures and solvents, yet it is readily dissolved in ethylene glycol through internal catalyzed transesterification. The application to room temperature delamination healing and carbon fiber recycling was demonstrated as a proof-of-concept.

Recent Progress in Carbon Fiber Reinforced Polymers Recycling: A Review of Recycling Methods and Reuse of Carbon Fibers.

The rapid increase in the application of carbon fiber reinforced polymer (CFRP) composite materials represents a challenge to waste recycling. The circular economy approach coupled with the possibility of recovering carbon fibers from CFRP waste with similar properties to virgin carbon fibers at a much lower cost and with lower energy consumption motivate the study of CFRP recycling. Mechanical recycling methods allow the obtention of chopped composite materials, while both thermal and chemical recycling methods aim towards recovering carbon fibers. This review examines the three main recycling methods, their processes, and particularities, as well as the reuse of recycled carbon fibers in the manufacture of new composite materials.

A Review of Recent Developments in Composites Made of Recycled Carbon Fiber Textiles

Carbon fiber recycling has garnered significant attention in recent years due to the large volume of manufacturing waste and upcoming end-of-life products that will enter the waste stream as the current generation of aircraft is retired from service. Recycled carbon fibers have been shown to retain most of their virgin mechanical properties, but their length is generally reduced such that continuous fiber laminates cannot be remade. As such, these fibers are typically used in low-performance applications including injection molding, extrusion/compression molding, and 3D printing that further degrade the fiber length and resulting composite properties. However, recent advances in the processing of long discontinuous fiber textiles have led to medium- to high-performance composites using recycled carbon fibers. This review paper describes the recent advances in recycled carbon fiber textile processing that have made these improvements possible. The techniques used to manufacture high-value polymer composites reinforced with discontinuous recycled carbon fiber are described. The resulting mechanical and multifunctional properties are also discussed to illustrate the advantages of these new textile-based recycled fiber composites over the prior art.

CFRP Laminates with Recycled Carbon Fiber: Resin Infusion and Mechanical Characterisation

The possibility to produce new components using reclaimed non-woven carbon fabric has been investigated. Being composite waste production increased, different strategies and technologies for recycling are developing to face criticalities and economic aspects related to their disposal. In this scenario, CFRP laminates with recycled carbon fiber and epoxy vinyl ester resin have been fabricated by Resin Infusion under Flexible Tooling (RIFT) and mechanical characterization has been performed to investigate their behavior under tensile, flexural and macro-indentation loads.