Recycling Of Carbon Fiber Reinforced Plastics Research Articles

A pre-screening of the solvolysis recycling process for CFRPs based on the mechanical properties of the recovered fibers.

Over the past few decades, composite materials, and specifically carbon fiber reinforced plastics (CFRPs), are finding increasing use in the automotive, aerospace, and aeronautics industries. As a result, the production of CFRPs has been significantly increased, thus leading to a corresponding increase in waste production. In the near future, landfill and incineration disposal of waste will likely be prevented due to legislation, thereby bringing forward the need to develop efficient recycling processes for CFRPs. However, recycling of CFRPs is very challenging, mainly due to the difficulty in removing the thermosetting matrix. This paper reports a pre-screening of the solvolysis recycling process for CFRPs on the basis of the mechanical properties of the recovered fibers. To this end, solvolysis tests were conducted on unidirectional CFRP samples under supercritical and subcritical conditions using acetone and water. The solvolysis tests were conducted for various conditions of temperature, pressure, and reaction time. The efficiency of the recycling processes has been evaluated by means of single-fiber tension tests on the recovered fibers, which were conducted according to the ASTM C 1557-14 standard. In most cases, the decomposition efficiency of the epoxy resin in the CFRP, measured in terms of mass, ranged between 90 and 100%. Moreover, the mechanical tests showed that the recovered fibers retained more than 58% of their initial Young’s modulus and tensile strength.

A Preliminary Investigation on a Water- and Acetone-Based Solvolysis Recycling Process for CFRPs.

Composites, and especially carbon-fiber-reinforced plastics (CFRPs), are increasingly used in the automotive, aerospace, and aviation industries, and as a result, CFRP production has increased dramatically, leading to a corresponding increase in waste. Landfills and the incineration of waste are likely to be restricted as a result of legislation, thus highlighting the need for efficient recycling methods for CFRPs. However, the recycling of CFRPs is very challenging, mainly due to the difficulty of removing their thermosetting matrix. This study reports a pre-screening of the solvolysis recycling process for CFRPs based on the mechanical properties of the recovered fibers. To this end, solvolysis tests were conducted on unidirectional CFRP samples under supercritical and subcritical conditions using acetone and water. The solvolysis tests were conducted for various conditions of temperature, pressure, and reaction time, without the use of any catalyst. Also, the loading rate (volume of solvent/volume of reactor) was constant. The efficiency of the recycling processes has been evaluated through a morphological and a mechanical characterization of the recovered fibers. In most cases, the decomposition efficiency of the epoxy resin, measured in terms of mass, ranged between 90 and 100%. Moreover, the scanning electron microscopy images of the recovered fibers showed negligible traces of resin residues and no detectable signs of physical damage or any changes in morphology with regard to diameter. Finally, the single-fiber tension tests revealed that that the recovered fibers retained more than 61% of their initial Young's modulus and 70% of their tensile strength.

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.

Advanced oxidative chemical recycling of carbon-fiber reinforced plastic using hydroxyl radicals and accelerated by radical initiators

We herein report a method for the chemical depolymerization of the epoxy resin present in a carbon composite through an advanced oxidation reaction using hydroxyl radicals. It was found that decomposition of the epoxy resin by the hydroxyl radicals generated from NaOCl was complete within 2 h at 100 °C and ambient pressure in an aqueous solution. The effects of different radical initiators (i.e., potassium persulfate (KPS) and 4,4′-azobis(4-cyanovaleric acid) (ACVA)) on the acceleration of hydroxyl radical generation from NaOCl were also evaluated. More specifically, the rate of hydroxyl radical formation in the presence and absence of a radical initiator was determined using the 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical method, and it was confirmed that the radical generation rate was increased by up to 3 times when the KPS radical initiator was employed (c.f., in the absence of an initiator). Interestingly, it was confirmed that the reaction rate constant (k) increased by up to 5.3 times when the combination of NaOCl and radical initiator KPS was applied to the recycling of carbon fiber-reinforced plastic (CFRP). In addition, X-ray photoelectron spectroscopy, Raman spectroscopy, and Field-emission scanning electron microscopy observations of the reclaimed carbon fiber demonstrated that no significant damage occurred during the reaction. This result is expected to lead to novel methods for enhancing the rate of CFRP chemical recycling processes.

Fast chemical recycling of carbon fiber reinforced plastic at ambient pressure using an aqueous solvent accelerated by a surfactant

The properties of infusibility and insolubility in organic solvent of cured epoxy resin makes it difficult to recycle carbon fiber reinforced plastics (CFRP). We have reported the recycling of CFRPs using the oxidizing power of hydroxyl radicals generated from NaOCl solution. In our study, we used benzyltrimethylammonium bromide (BTAB) and sodium dodecyl sulfate (SDS) for the interfacial separation between the epoxy resin and carbon fibers (CF). The surfactant system maximized recycling efficiency in both pretreatment and the main reaction of the CFRP recycling process. In the second step, the reaction time to successfully reclaim the CFs was much shorter, only one hour, compared with the two-hour reaction time for the non-SDS process previously reported by us. Scanning electron microscope images and Raman analyses showed that the surface of the reclaimed CF (r-CFs) was clean and smooth without any defects, and there was no significant structural change compared to virgin CF (v-CFs). The tensile strength of r-CF was 3.42 GPa which is 96.9% of the v-CF. Thus, the CFRP recycling process using SDS not only results in r-CF with good mechanical and physical properties, but also increases recycling efficiency by reducing the time.

Recycling fiber-reinforced plastic using supercritical acetone

Carbon-fiber-reinforced plastic (CFRP) can be difficult to recycle owing to the presence of thermosetting plastics such as epoxy resin. Therefore, it is important to develop more efficient methods for recycling CFRP. Herein, we investigated the chemical recycling of CFRP containing an epoxy matrix resin via a process involving superheated and supercritical acetone. The decomposition efficiency of the epoxy resin in the CFRP at 2–14 MPa and 350 °C increased with increasing reaction time over the first 60 min, but then decreased over longer reaction times because the decomposition products carbonized. Furthermore, the decomposition efficiency increased with increasing reaction pressure and acetone density, to a maximum of 95.6% at 350 °C, 60 min, and a density of 4.35 mol/L (14 MPa). The decomposition rate of the epoxy resin in CFRP using superheated and supercritical acetone is rationalized by a surface-reaction and shrinking-core model, with large negative activation volumes.

Thermo-Catalytic Treatment of Vapors in the Recycling Process of Carbon Fiber-Poly (Benzoxazine) Composite Waste by Pyrolysis

Recycling carbon fiber from residual carbon fiber reinforced plastics (CFRP) is one of the key aspects of the future in the field of waste management. This work presents the possibility of recovering chemical compounds through the thermo-catalytic treatment of the gases and vapors produced from the decomposition of the polymeric resin that takes place in the recycling of CFRP by pyrolysis. A lab-scale installation consisting of two reactors placed in series has been used for the experiments. In the first reactor, pyrolysis of poly(benzoxazine)-based composite waste has been carried out at 500 °C. In the second reactor, the thermo-catalytic treatment of gases and vapors has been performed at 900 °C in the presence of a commercial and a lab-prepared reforming catalyst. The thermal treatment of gases and vapors leads to a significant reduction in the collected liquids and a H2-rich gas fraction. When reforming catalysts are used, the organic fraction of the liquids is virtually eliminated and gas fractions containing more than 50% H2 in volume are generated. The results obtained show that it is possible to valorize the material content of the polymer resin, which represents an important advance in the recycling of CFRP by pyrolysis.

Recycling of carbon fiber-reinforced plastic using supercritical and subcritical fluids

The recycling of waste plastics is important for the prevention of the exhaustion of fossil resources. In this paper, recycling techniques of carbon fiber-reinforced plastic (CFRP) using supercritical and subcritical fluids were reviewed. The matrix resin of CFRP such as epoxy resin or resol resin was decomposed by supercritical and subcritical fluids, and the carbon fiber without thermal damage was recovered from CFRP. Mainly, water or alcohol was used as decomposition medium.