Description:TECHNICAL FIELD
The present disclosure relates to the recycling and upcycling of fiber-reinforced polymer composite. Moreover, the present disclosure relates to developing an eco-friendly and sustainable method for recovering valuable fibers and polymer from fiber-reinforced polymer composite waste.
BACKGROUND
Fiber-reinforced polymer composites are increasingly utilized across various industries, including aerospace, automotive, and construction, due to their high strength-to-weight ratio, durability, and resistance to environmental degradation. However, the widespread use of fibre reinforced polymer composites has led to significant challenges in waste management.
Current methods for recycling fiber-reinforced polymer composite waste include mechanical recycling, thermochemical processes, and chemical recycling. Mechanical recycling involves size reduction through shredding or grinding, but the resulting material is typically of lower quality and limited to applications such as fillers or sheet moulding compounds. Thermochemical and chemical recycling processes often require harsh conditions, such as high temperatures, strong acids, or supercritical fluids, which can compromise the mechanical properties of the recovered fibers and generate secondary pollutants. The discussed drawbacks, along with the high costs and complexity of these methods, hinder their commercial viability.
Therefore, in light of the foregoing discussion, there exists a need to overcome the aforementioned drawbacks.
SUMMARY
The present disclosure provides a method for recycling fiber-reinforced polymer composites. The present disclosure provides a solution to the technical problem of recycling fiber-reinforced polymer composites. An aim of the present disclosure is to provide a solution that overcomes at least partially the problems encountered in the prior art and provide an improved method that not only recycles fiber-reinforced polymer composites that is cost-effective, but the method that may be easily adopted and uses sustainable and environmentally friendly materials. Thus, the method of the present disclosure manifests a technical advancement as well as economic benefits.
One or more objectives of the present disclosure is achieved by the solutions provided in the enclosed independent claims. Advantageous implementations of the present disclosure are further defined in the dependent claims.
In one aspect, the present disclosure provides a method for recycling the fiber-reinforced polymer composites. The method includes preparing an aqueous recycling solution by mixing at least one bio-based acid and at least one salt in water. The method further includes immersing fiber-reinforced polymer composites in the aqueous recycling solution in a hydrothermal reactor. Further, the method includes heating the hydrothermal reactor to a predefined temperature for a predefined duration. The method includes cooling the hydrothermal reactor and separating the aqueous recycling solution from the decomposed fiber-reinforced polymer composites. The method further includes washing the decomposed fiber-reinforced polymer composites with acetone or ethanol to separate recycled CFRE. Furthermore, the method includes drying the recycled fibers and the recycled polymer to obtain final recycled products.
The method utilizes bio-based acids and salts, which are environmentally friendly and biodegradable. The use of environmentally friendly and biodegradable significantly reduces the ecological footprint compared to conventional recycling methods that often rely on strong, hazardous chemicals. The aqueous recycling solution minimizes the release of toxic substances into the environment, making the process more sustainable and compliant with environmental regulations. The controlled hydrothermal conditions of the method allow the decomposition of the polymer matrix without compromising the mechanical properties of the fibers. The preservation ensures that the recycled fibers retain their original tensile strength and modulus, making them suitable for reuse in demanding applications, such as the aerospace and automotive industries. The hydrothermal process is designed to target the polymer matrix selectively, breaking it down into smaller, manageable fragments while leaving the fibers intact. The selective decomposition allows for a high recovery rate of both fibers and the polymer, facilitating the recycling of complex composite structures. The efficiency of the process reduces waste and maximizes the yield of reusable materials. The method operates under relatively mild temperatures and pressures within the hydrothermal reactor. The relatively mild temperatures and pressure conditions are sufficient to achieve the desired decomposition of the polymer matrix without causing thermal or chemical degradation of the fibers. Mild processing conditions also lead to lower energy consumption, contributing to the overall cost-effectiveness of the recycling process. The subsequent washing of decomposed materials with acetone or ethanol effectively ensures that the recycled fibers and polymer are of high purity and free from contaminants that may compromise their performance in future applications. High purity recycled materials are more desirable for manufacturing as they maintain consistent quality and performance. The ability of the method to recover both fibers and polymer maximizes the value extracted from the waste composite material. Recycled fibers and recycled polymer can be reintroduced into the manufacturing cycle, reducing the need for new raw materials. The closed-loop recycling approach not only lowers material costs but also aligns with industry trends toward resource efficiency and waste reduction. By enabling the recovery and reuse of the fibers and the recycled polymer, the method extends the lifecycle of composite materials and reduces the dependency on virgin resources. The reduction of dependency on virgin resources not only conserves natural resources but also mitigates the environmental impact associated with the production and disposal of the fiber-reinforced polymer composites.
It is to be appreciated that all the aforementioned implementation forms can be combined. All steps which are performed by the various entities described in the present application as well as the functionalities described to be performed by the various entities are intended to mean that the respective entity is adapted to or configured to perform the respective steps and functionalities. It will be appreciated that features of the present disclosure are susceptible to being combined in various combinations without departing from the scope of the present disclosure as defined by the appended claims.
Additional aspects, advantages, features, and objects of the present disclosure would be made apparent from the drawings and the detailed description of the illustrative implementations construed in conjunction with the appended claims that follow.
BRIEF DESCRIPTION OF THE DRAWINGS
The summary above, as well as the following detailed description of illustrative embodiments, is better understood when read in conjunction with the appended drawings. For the purpose of illustrating the present disclosure, exemplary constructions of the disclosure are shown in the drawings. However, the present disclosure is not limited to specific methods and instrumentalities disclosed herein. Moreover, those skilled in the art will understand that the drawings are not to scale. Wherever possible, like elements have been indicated by identical numbers.
Embodiments of the present disclosure will now be described, by way of example only, with reference to the following diagrams wherein:
FIG. 1 is a flowchart depicting a method for recycling fiber-reinforced polymer composites, in accordance with an embodiment of the present disclosure;
FIGs. 2A and 2B depict schematic views of various steps for preparing an aqueous recycling solution, in accordance with an embodiment of the present disclosure;
FIGs. 3A, 3B, and 3C depict schematic views of various steps for recycling fiber-reinforced polymer composites (for example, carbon fiber reinforced epoxy) laminates, in accordance with an embodiment of the present disclosure;
FIG. 3D is a diagram illustrating the reaction scheme of cleavage of epoxy using the aqueous recycling solution, in accordance with an embodiment of the present disclosure;
FIG. 4A is a graph depicting a Raman spectrum of the accrued carbon fiber (ACF) and recycled carbon fiber (RCF), in accordance with an embodiment of the present disclosure;
FIG. 4B is a graphical representation illustrating a comparison of the thermostability of the ACF and the RCF, in accordance with an embodiment of the present disclosure;
FIG. 5A is a graphical representation depicting the FTIR spectrum of a recycled epoxy (REPO), in accordance with an embodiment of the present disclosure;
FIG. 5B is a graphical representation illustrating the thermal decomposition of the REPO, in accordance with an embodiment of the present disclosure;
FIG. 5C is a graphical representation illustrating high-resolution mass spectrometry (HRMS) of the REPO, in accordance with an embodiment of the present disclosure;
FIG. 6A is a graphical representation depicting the FTIR spectrum of a conventional epoxy-hardener (C-Epoxy) and an epoxy-REPO (i.e., the REPO used as hardener), in accordance with an embodiment of the present disclosure;
FIG. 6B is a graphical representation illustrating Differential Scanning Calorimetry (DSC) of the C-epoxy and epoxy REPO, in in accordance with an embodiment of the present disclosure;
FIG. 6C is a graphical representation illustrating the tensile strength of the C-epoxy and the epoxy REPO, in accordance with an embodiment of the present disclosure; and
FIG. 6D is a graphical representation illustrating the comparison of the thermostability of the C-epoxy and the epoxy REPO, in accordance with an embodiment of the present disclosure.
In the accompanying drawings, an underlined number is employed to represent an item over which the underlined number is positioned or an item to which the underlined number is adjacent. A non-underlined number relates to an item identified by a line linking the non-underlined number to the item. When a number is non-underlined and accompanied by an associated arrow, the non-underlined number is used to identify a general item at which the arrow is pointing.
DETAILED DESCRIPTION OF EMBODIMENTS
The following detailed description illustrates embodiments of the present disclosure and ways in which they can be implemented. Although some modes of carrying out the present disclosure have been disclosed, those skilled in the art would recognize that other embodiments for carrying out or practicing the present disclosure are also possible.
FIG. 1 is a flowchart depicting a method for recycling fiber-reinforced polymer composites, in accordance with an embodiment of the present disclosure. With reference to FIG. 1, there is shown a flowchart of a method 100. In some implementations, the method 100 is executed by a skilled person. The method 100 may include steps 102 to 112.
At step 102, the method 100 includes preparing an aqueous recycling solution by mixing at least one bio-based acid and at least one salt in water. The "bio-based acid" refers to an acid derived from renewable or bio-based sources, such as plants or microorganisms, rather than from fossil fuels or petrochemicals. The term "salt" refers to a compound formed when an acid reacts with a base, resulting in the formation of a positively charged ion (i.e., cation) and a negatively charged ion (i.e., anion), which are held together by electrostatic forces.
Initially, the selection of a bio-based acid is done, which is known for its effectiveness in breaking down epoxy matrices. In an implementation, the bio-based acid is citric acid. In some other implementations, the bio-based acid may be maleic acid, succinic acid or tartaric acid. Similarly, in some other implementations, the bio-based acid used in the method 100 may include any other bio-based acid, as per application requirements, without limiting the scope of the present disclosure. In an implementation, the 5-10% by volume of at least one bio-based acid.
Further, the selection of the salt is done. The salt should be such that it aids in the decomposition process and enhances the aqueous recycling solution's reactivity. In an implementation, the salt may be sodium chloride, or potassium chloride. In yet another implementation, the salt may be magnesium chloride, calcium chloride, Epsom salt or pink salt. Similarly, in some other implementations, the salt using the method 100 may include any other salt, as per application requirements, without limiting the scope of the present disclosure. In some other implementations, the salt may be a combination of one or more salts.
In some examples, the aqueous recycling solution contains 7-12% by volume of at least one salt. Further, water is taken as a solvent for mixing the bio-based acid and the salt. In an implementation, the aqueous recycling solution for decomposing the fiber-reinforced polymer composites includes 75-85% by volume of water as a solvent. For example, 100 ml of water is poured into a clean mixing container, preferably made of glass or a material resistant to biobased acid. Further, 20 gm of citric acid is added to water while stirring continuously to ensure citric acid dissolves completely. The stirring helps in dispersing the citric acid uniformly throughout the water. Once the citric acid is fully dissolved, 30 gm of sodium chloride is added to the solution of the water and citric acid. Stirring is done until the sodium chloride is completely dissolved. Continuous stirring is performed for a few more minutes after all components are added to ensure that the mixture is homogeneous. The sequence of mixing acid and salt may be interchanged. The aqueous recycling solution should be clear, indicating that all ingredients are fully dissolved.
After mixing, the pH of the aqueous recycling solution is checked using pH paper. In an implementation, the aqueous recycling solution has a pH in the range of 0.5 to 1.0. If the pH is higher than the desired range, a small amount of additional bio-based acid may be added to lower the pH. Once the aqueous recycling solution is homogeneous and the pH is within the desired range, the aqueous recycling solution is ready for use in the recycling process. The aqueous recycling solution is stored in a sealed container to prevent contamination and evaporation.
In some implementations, the aqueous recycling solution is reused multiple times by adjusting its pH to the range of 0.5 to 1.0. Reusing the solution minimizes the need for fresh chemicals, leading to cost savings in the long run. By reusing the solution, less chemical waste is generated, which decreases the environmental footprint of the recycling process. Adjusting the pH ensures that the solution remains effective in decomposing fiber-reinforced polymer composites, maintaining consistent performance across multiple uses.
At step 104, the method 100 further includes immersing fiber-reinforced polymer composites in the aqueous recycling solution in a hydrothermal reactor. The fiber-reinforced polymer composites (also called a waste of fiber-reinforced polymer composites) is a composite material composed of fibers embedded within the polymer matrix. The fiber-reinforced polymer composites are sourced from various sectors, including manufacturing, where offcuts and defects generated during production contribute to significant waste; end-of-life products such as wind turbine blades, vehicles, and aircraft components also add to the waste stream when they are decommissioned. Additionally, construction and demolition waste, particularly from infrastructure and buildings using fiber-reinforced polymer composites materials, is another major source. Consumer goods and electronics, which incorporate composites for lightweight and durable designs, further contribute to fiber-reinforced polymer composites waste.
The fiber-reinforced polymer composites typically consist of multiple layers of fiber sheets (also called plies) that are impregnated with the polymer and stacked in specific orientations. The multiple layers are then cured (hardened) to form a solid, cohesive material. The hydrothermal reactor is a pressure vessel designed to conduct chemical reactions at high temperatures and pressures. The hydrothermal reactor is typically made of materials resistant to corrosion and capable of withstanding the harsh conditions required for the recycling process.
Before immersion, the hydrothermal reactor is thoroughly cleaned and inspected to ensure it is free from any contaminants or residues that could affect the reaction. The fiber-reinforced polymer composites are cut into manageable sizes to fit inside the hydrothermal reactor. Pieces of the fiber-reinforced polymer composites allow for adequate contact with the aqueous recycling solution, ensuring even decomposition. The fiber-reinforced polymer composites are carefully placed inside the hydrothermal reactor, ensuring it is evenly distributed to maximize exposure to the aqueous recycling solution. The prepared aqueous recycling solution is poured into the reactor, fully submerging the fiber-reinforced polymer composites. The volume of the solution should be sufficient to ensure complete immersion, allowing the chemical reaction to occur uniformly. Once the fiber-reinforced polymer composites and the aqueous recycling solution are in place, the hydrothermal reactor is securely sealed to prevent any leakage. The sealed container is critical as the subsequent steps involve high temperatures and pressures. The hydrothermal reactor is then pressurized to a predefined level, depending on the specific requirements of the recycling process. The pressure helps facilitate the hydrothermal decomposition of the polymer.
At step 106, the method 100 further includes heating the hydrothermal reactor to a predefined temperature for a predefined duration. In an implementation, the predefined temperature for heating the hydrothermal reactor is 230-260 degrees Celsius. The temperature is carefully monitored and controlled to ensure the reaction proceeds at the optimal rate. In an implementation, the predefined duration for heating the hydrothermal reactor is 18-24 hours.
In an implementation, the fiber-reinforced polymer composite is a carbon fiber-reinforced epoxy (CFRE) laminate. Specifically, in an example, the CFRE laminate is kept immersed in the solution at a specified temperature for a specified duration of 18-24 hours. During the predefined duration, the heat and pressure work together to break down the epoxy matrix, freeing the carbon fibers.
In an implementation, the decomposition of the CFRE laminate involves selectively cleaving C-N and C-O bonds in any thermoset (amine or acid cured) or vitrimeric epoxy matrices of carbon fiber-reinforced epoxy laminate waste by exposing the thermoset or vitrimeric epoxy matrices to the aqueous recycling solution under hydrothermal conditions. In thermoset epoxy resins, C-N bonds are found in the amine hardeners used to cure the epoxy. Under hydrothermal conditions, the acidic environment facilitates the hydrolysis of C-N bonds, breaking down the polymer network. The C-O bonds are found in the acid curing of epoxy and are also susceptible to hydrolysis in the acidic, high-temperature environment. The cleavage of the C-O bonds further disintegrates the cross-linked structure, leading to the decomposition of the epoxy matrix. As the C-N and C-O bonds are cleaved, the epoxy matrix breaks down into smaller oligomers and monomers. The decomposition reduces the epoxy to a form that can be separated from the carbon fibers. The process results in the separation of the carbon fibers, which retain their structural integrity, and the decomposed epoxy components, which can be washed away and potentially reused or further processed. The selective cleavage of C-N and C-O bonds ensures that the decomposition process is efficient, targeting the vital structural components of the epoxy resin while preserving the integrity of the carbon fibers. By controlling the decomposition process, the method 100 allows for the recovery of high-quality recycled carbon fibers and potentially usable epoxy, reducing waste and supporting sustainable materials management.
At step 108, the method 100 includes cooling the hydrothermal reactor and separating the aqueous recycling solution from the decomposed fibre-reinforced polymer composite. After the reaction is complete, the hydrothermal reactor is slowly cooled down to a safe temperature. Rapid cooling is avoided to prevent thermal shock, which may damage the fibers. Once the hydrothermal reactor has cooled to a safe temperature, the hydrothermal reactor is slowly depressurized and opened. The aqueous recycling solution, which now contains dissolved or partially dissolved polymer, is carefully drained from the hydrothermal reactor. The hydrothermal reactor may have a bottom drain or be tilted to pour out the liquid. If any small solid particles are suspended in the liquid, a filtration step can be employed to ensure the solution is fully separated from the solid fibers. The solid fibers, now free from the polymer matrix, are carefully removed from the hydrothermal reactor. The removal may be done manually or with the help of tools like tongs or a mechanical arm, depending on the design of the hydrothermal reactor.
At step 110, method 100 includes washing the decomposed fibre-reinforced polymer composite with acetone or ethanol to separate recycled fibers and recycled polymer . After separating the aqueous recycling solution from the decomposed fiber-reinforced polymer composite, the solid material, which includes both fibers and polymer residue, is subjected to a washing process using acetone or the ethanol. The acetone or ethanol effectively dissolves the residual polymer, allowing it to be separated from the fibers. The decomposed fiber-reinforced polymer composite is either immersed in a bath of acetone or the ethanol or rinsed thoroughly with the acetone or the ethanol. The acetone or the ethanol interacts with the polymer, breaking it down further and allowing it to dissolve into the solvent. During this process, the fibers, which do not dissolve in acetone or the ethanol, remain intact. Once the polymer has dissolved in the acetone or the ethanol, the mixture typically undergoes a filtration or decantation process. The liquid phase, which now contains the dissolved polymer, is separated from the solid fibers. The acetone or the ethanol-polymer solution is collected in a separate container, while the solid fibers are left behind, free of most polymer residue. The acetone or the ethanol-polymer solution may be further processed to recover the polymer, or the acetone or the ethanol may be evaporated off, leaving behind the recycled polymer.
At step 112, the method 100 further includes drying the recycled fibers and the recycled polymer to obtain the final recycled products. After the separation of fibers from the polymer, both materials are typically still wet with residual water, acetone or the ethanol, or other solvents used during the recycling process. The materials are carefully placed in a drying apparatus, such as an oven, drying chamber, or under a vacuum, depending on the sensitivity of the materials and the desired drying speed. The fibers are dried at a controlled temperature to avoid any thermal degradation. The temperature is usually kept below the degradation threshold of the fibers, typically around 60 degrees Celsius to 80 degrees Celsius. Drying may be conducted under average air circulation to evaporate the solvents or under vacuum conditions to accelerate solvent removal while preventing oxidation or damage to the fibers. The drying duration may vary depending on the amount of moisture and solvent content, ranging from a few hours to a day. The process continues until the fibers reach a stable, dry state with no detectable moisture or solvent residue. The recycled polymer, which may still contain residual solvents like acetone or ethanol, is gently heated to evaporate these solvents without causing the polymer to soften or degrade. The temperature is typically maintained at a lower range, around 40 degrees Celsius to 60 degrees Celsius. Similar to the fibers, the polymer may also be dried under vacuum or similar conditions. The drying facilitates removing solvents more efficiently and ensures that the epoxy may not retain any volatile components that may affect the performance of the polymer in future applications. The polymer is dried until it reaches a solid, stable form, which may be in the form of a powder, flakes, or small chunks, depending on how it may be processed. Once drying is complete, the dried fibers and the polymer are carefully removed from the drying equipment and allowed to cool, if necessary, to room temperature.
In an implementation, the recycled fiber comprises at least one of the carbon fibers, glass fibers, aramid fibers, flax fibers, hemp fibers, sisal fibers, and areca fibers. In an implementation, the recycled fiber may comprise any other fiber that may be present in the fiber-reinforced polymer composite. In an implementation, the recycled polymer comprises at least one epoxy, phenol formaldehyde resin, polyurethane, novolac, and cyanate ester. In some other implementations, the recycled polymer may comprise any other polymer that may be present in fiber-reinforced polymer composite.
The steps 102 to 112 are only illustrative, and other alternatives can also be provided where one or more steps are added, one or more steps are removed, or one or more steps are provided in a different sequence without departing from the scope of the claims herein.
FIGs. 2A and 2B depict schematic views of various steps for preparing the aqueous recycling solution, in accordance with an embodiment of the present disclosure. FIGs. 2A and 2B are described in conjunction with FIG. 1. With reference to FIG. 2A, there is shown a vessel 202A kept on a hot plate 206A. The vessel contains a solution 204A of the water, the salt, and the bio-based acid. For example, 30 gm sodium chloride and 100 ml water are taken in the vessel 202A. Further, 20 gm of citric acid is mixed into the vessel 202A.
FIG.2B depicts a container 202B holding the aqueous recycling solution 204B. The container 202B is seal-proof in order to avoid any contamination and also maintain the pH of the aqueous recycling solution 204B. The container 202B holds a prepared aqueous solution that is prepared by continuous stirring at room temperature of the bio-based acid and a homogeneous solution of the water and the salt.
FIGs. 3A, 3B and 3C depict schematic views of various steps for recycling CFRE laminates, in accordance with an embodiment of the present disclosure. FIGs. 3A to 3C are described in conjunction with FIG. 1 to 2B. With reference to FIG. 3A, there is shown a sample of the fiber-reinforced polymer composites, for example, a CFRE laminate 302A being taken for obtaining carbon fibers. With reference to FIG. 3B, there is shown a hydrothermal reactor 302B containing the aqueous recycling solution. The CFRE laminates 302A are dissolved inside the aqueous recycling solution. For example, 2 grams (g) of amine-cured epoxy matrix containing CFRE laminate is cut into a rectangular shape and charged into the hydrothermal pressure reactor containing the aqueous recycling solution. The hydrothermal reactor 302B is kept inside an oven at 230 ℃ for 18 hours. After that, the hydrothermal reactor 302B cooled down to room temperature, and the aqueous recycled solution is separated from the decomposed CFRE by filtration. The acetone or the ethanol was used to dissolve the decomposed epoxy matrix and recycle the carbon fibers. The resulting solution is kept inside a hot air oven at 80 ℃ for 2 hours to yield recycled epoxy (REPO). The recycled carbon fiber (RCF) is dried in a vacuum oven at 60 ℃ for 10 hours to reach a constant weight.
With reference to FIG. 3C, there is shown an exemplary diagram 300C including recycled carbon fibers (RCF) 302C and REPO 304C. The REPO 304C is obtained in the form of a solid, which is usually pale yellow. In some implementations, the REPO 304C is used as a hardener for fresh epoxy resin. The REPO 304C may enhance the cross-linking density of the epoxy matrix, potentially leading to a more robust and chemically resistant final product. The existing functional groups in the REPO 304C may react effectively with the epoxy resin, creating a tightly bound network. The REPO 304C is inherently compatible with fresh epoxy resins, ensuring that the REPO 304C integrates well into the existing epoxy network without compromising the integrity of the final product. The compatibility facilitates maintaining consistent product quality.
In some other examples, the REPO 304C may adapted as a crosslinker for polyolefin recycling. Crosslinked polyolefins using the REPO 304C exhibit improved resistance to chemicals, oils, and solvents. Crosslinking makes the recycled material more durable and suitable for use in harsh chemical environments, such as in the chemical processing or petrochemical industry. Crosslinking with the REPO 304C may reduce the creep and shrinkage of polyolefins over time, leading to better dimensional stability, which is important for applications where maintaining the shape and size of the material is critical, such as in precision components or long-term installations.
In an implementation, the REPO 304C may be transformed into virgin epoxy by reaction with epichlorohydrin at an acidic medium. The epichlorohydrin is an organochlorine compound having both an epoxide ring and a chlorine atom. The presence of the epoxide ring makes the epichlorohydrin highly reactive, particularly in the presence of acidic or basic conditions, which allows the epichlorohydrin to form new epoxy groups. The REPO 304C contains hydroxyl (-OH) groups, resulting from the breakdown of the original epoxy matrix during the recycling process. The hydroxyl groups are vital to the transformation process, as they react with the epichlorohydrin to reform the epoxy network. The acidic medium (such as hydrochloric acid, HCl) protonates the hydroxyl groups of the recycled epoxy, increasing their nucleophilicity. The protonated hydroxyl groups of the recycled epoxy attack the less substituted carbon of the epoxide ring in the epichlorohydrin, leading to the formation of a new carbon-oxygen (C-O) bond. The attack of the recycled epoxy on the less substituted carbon results in the opening of the epoxide ring, generating a new hydroxyl group and a chlorohydrin intermediate. The chlorohydrin intermediate may undergo an intramolecular cyclization reaction, where the hydroxyl group displaces the chlorine atom, reforming the epoxide ring and regenerating the virgin epoxy group.
FIG. 3D is a flowchart of a series of operation depicting a reaction scheme of cleavage of epoxy using the aqueous recycling solution, in accordance with an embodiment of the present disclosure. FIG. 3D is described in conjunction with elements from FIGs. 1 to 3C. With reference to FIG. 3D, there is shown a flowchart 300D that includes a series of operations from 302D-to-306D.
At operation 302D, an epoxy network (which is part of some bigger molecular chain present inside the CFRE laminates 302A) reacts with the recycling aqueous solution. In an example, when the CFRE laminates 302A are kept inside the hydrothermal reactor 302B, the epoxy chains present inside the CFRE laminates 302A undergo a reaction with the recycling aqueous solution.
At operation 304D, the aqueous recycling solution reacts with the epoxy structure, as shown in a block 308D. The block 308D depicts the cleaving of the N-C bonds by the action of the aqueous recycling solution. The dotted lines 310D, 312D, 314D, and 316D represent the “disintegration points" where the aqueous recycling solution cleaves the bonds.
At operation 306D, after the disintegration of the C-N bonds, a disintegrated epoxy network is obtained.
FIG. 4A is a graphical representation depicting a Raman Spectroscopy of the accrued carbon fiber (ACF) and the RCF, in accordance with an embodiment of the present disclosure. FIG. 4A is described in conjunction with elements from FIGs. 1 to 3D. With reference to FIG. 4A, there is shown a graphical representation 400A depicting exemplary Raman spectra of the accrued carbon fiber (ACF) and the RCF 302C. Specifically, the graphical representation 400A depicts the absorption of infrared light by the ACF and the RCF 302C at different wavelengths, typically measured in wavenumbers. Wavenumber is expressed in reciprocal centimetres (cm-1) in an abscissa axis. Intensity is expressed in arbitrary units in an ordinate axis.
The graphical representation 400A includes a curve 402A and a curve 408A depicting the Raman spectrum that indicates the absorption of infrared light. Each peak or band in the curve 402A and 408A corresponds to the vibration of specific chemical bonds within the chemical structure of the ACF and the RCF 302C, respectively. The curve 402B and the curve 408B includes a section 404A and a section 406A. The section 404A represents a D band depicting a peak at 1372 cm⁻¹, and the section 406A represents a G band depicting a peak at 1593 cm⁻¹.
The D band corresponds to the presence of defects or disorders in the carbon fiber structure. The defects may arise from imperfections, edges, or other disruptions in the otherwise crystalline graphitic carbon. The G band is associated with the graphitic structure of carbon fibers, representing the in-plane stretching of sp² carbon bonds in a graphitic layer. The G band is indicative of the degree of graphitization and the crystalline nature of the carbon fibers. The ratio of the intensity of the D band (DI) to the intensity of the G band (IG) is an essential parameter for evaluating the quality and structural integrity of carbon fibers. The ID and IG ratio for the RCF 302C is 1.04, which is very close to the ratio ID and IG for the ACF (i.e., 1.02). The similarity in the ratio of ID and IG indicates that the recycling process did not significantly introduce defects or disorder in the carbon fibers, thus preserving their structural integrity.
The RCF 302C maintains structural integrity comparable to the ACF. The Raman spectrum depicted by the graphical representation 400A demonstrates that the structural integrity of the RCF 302C is well-maintained and comparable to the original as the ACF. The close similarity in the ratio of ID and IG ratios further supports that the recycling process did not compromise the graphitic structure or introduce significant defects in the carbon fibers, implying that the recycling method is effective in preserving the essential properties of carbon fibers, making them suitable for reuse in high-performance applications. In an implementation, the RCF 302C is used to fabricate new laminates or as a reinforcing filler in polymer composites. Utilizing the RCF 302C promotes recycling and reduces waste. The recycling approach decreases the need for virgin carbon fiber production, which is energy-intensive and has a larger carbon footprint. The RCF 302C retains a significant portion of the strength and stiffness of virgin carbon fibers. When used as a reinforcing filler in polymer composites, it enhances the mechanical properties of the resulting material, making it suitable for high-performance applications. Like virgin carbon fibers, the RCF 302C offers an excellent strength-to-weight ratio, making the RCF 302C ideal for applications where reducing weight is critical, such as in the automotive, aerospace, and sporting goods industries. The RCF 302C maintains good thermal and electrical conductivity. When used in polymer composites, the RCF 302C may improve the thermal management and electrical performance of the material, which is valuable in electronic components and heat-sensitive applications. Similarly, Raman Spectroscopy of recycled glass fibers, aramid fibers, flax fibers, hemp fibers, sisal fibers, and areca fiber with their corresponding accrued counterpart may be obtained.
FIG. 4B is a graphical representation illustrating the comparison of thermostability of the ACF and the RCF, in accordance with the present disclosure. FIG. 4B is described in conjunction with elements from FIGs. 1 to 4A. With reference to FIG.4B, there is shown a graphical representation 400B showing the variation of weight percent of the ACF and the RCF 302C with the temperature. The temperature is expressed in degrees Celsius in an abscissa axis. Weight per cent is expressed in arbitrary units in an ordinate axis.
The graphical representation 400B includes a curve 402B and a curve 404B, showing the relationship between the weight percent of the ACF and the RCF 302C, respectively and the temperature. The curve 402B depicts that the ACF has a weight loss of approximately 4% over the temperature range of 40 degrees Celsius to 800 degrees Celsius. The minor weight loss suggests that the ACF is highly thermally stable, possibly due to the presence of a protective epoxy layer that remains intact during heating. The epoxy layer effectively shields the carbon fibers from thermal degradation, resulting in minimal weight loss. The curve 404B depicts that the RCF 302C shows a significantly higher weight loss of approximately 13 percent over the same temperature range. The increased weight loss in the RCF 302C indicates the presence of residual epoxy that remains even after the recycling process, implying that the recycling procedure may not have completely removed all the epoxy matrix, leaving some of it behind on the carbon fibers, which contributes to the observed weight loss during heating.
In conclusion, the TGA (thermogravimetric analysis) depicted by the graphical representation 400B highlights the difference in thermal stability between the ACF and RCF. The ACF shows minimal weight loss due to a protective epoxy layer, while the RCF 302C exhibits greater weight loss due to the presence of remaining epoxy after the recycling process. The above observation implies that while the recycling process is effective, it may leave behind some epoxy residues, which slightly compromises the thermal stability of the RCF 302C compared to the ACF.
FIG. 5A is a graphical representation depicting the FTIR spectrum of the polymer ( for example, REPO) in accordance with an embodiment of the present disclosure. FIG.5A is described in conjunction with elements from FIGs. 1 to 4B. With reference to FIG. 5A, there is shown a graphical representation 500A depicting exemplary FTIR spectra of the REPO 304C. Specifically, the graphical representation 500A depicts the absorption of infrared light by the REPO 304C at different wavelengths, typically measured in wavenumbers. Wavenumber is expressed in reciprocal centimetres (cm-1) in an abscissa axis. Transmittance is expressed in percentage in an ordinate axis.
The graphical representation 500A includes a curve 502A, which indicates the absorption of infrared light. Each peak or band in the curve 502A corresponds to the vibration of specific chemical bonds within the chemical structure of the REPO 304C, respectively. The curves 502A includes a first peak 504A at 756 cm-1 depicting N-H wagging (i.e., confirmation of amine group), a second peak 506A at 1110 cm-1 depicting strong peak associated with C-O stretching (from ether linkages in the epoxy structure or newly formed ester bonds confirming the presence of amine groups in the REPO 304C). The curve 502A further includes a third peak 508A, at 1181 cm-1, corresponding to C-N stretching (indicating the presence of amine groups), a fourth peak 510A at 1509 cm-1 depicting aromatic C-C stretching, a fifth peak 512A, at 1608 cm-1 depicting C=C stretching, likely from aromatic rings which confirms the presence of aromatic structures in the REPO 304C. The curve 502A further includes a sixth peak 514A, at 1704 cm-1. The sixth peak 514A shows a strong, sharp peak characteristic of C=O (carbonyl) stretching. The carbonyl group may be from newly formed esters. The curve 502A further includes a seventh peak 516A at 2927 cm-1 depicting aliphatic C-H stretching (i.e., the presence of alkyl groups in the REPO 304C), an eighth peak 518A at 3037 cm-1 depicting a sharp peak corresponding to aromatic C-H stretching (indicating the presence of aromatic rings in the REPO 304C, likely from the original epoxy resin).
Finally, the curve 502A includes a ninth peak 520A. The ninth peak 520A is an abroad peak having a range of 3200-3600 cm-1. The ninth peak 520A corresponds to N-H and O-H stretching frequencies. The broadness indicates hydrogen bonding, which is common in amine and hydroxyl groups, confirming the presence of both amine (-NH2, -NH-) and hydroxyl (-OH) groups in the REPO 304C.
The presence of amine peaks, i.e., the first peak 504A, the third peak 508A and the ninth peak 520A, supports the claim that sodium cation (Na+) selectively cleaves C-N bonds in the crosslinked matrix. This results in the formation of new amine functional groups. The sixth peak 514A is a strong carbonyl peak, and the second peak 506A depicts the formation of ester bonds when citric acid reacts with hydroxyl groups to form esters. The eighth peak 518A, the fourth peak 510, and the fifth peak 512 indicate that the aromatic structures from the original epoxy resin are preserved mainly in the REPO 304C. While the FTIR spectrum doesn't directly show molecular weight, the presence of various functional groups (amines, hydroxyls, carbonyls) that the recycling process has effectively broken down the crosslinked structure into smaller, functionalized units. The presence of amine and hydroxyl groups in the REPO 304C makes it suitable for use as a hardener or reactive component in new epoxy formulations, as these functional groups can participate in further crosslinking reactions. The FTIR analysis provides strong evidence for the selective cleavage of C-N bonds and the formation of new functional groups during the recycling process, supporting the effectiveness of the method 100 in breaking down the crosslinked epoxy structure into useful, reactive oligomers. Similarly, the FTIR spectrum analysis of the polymer, such as phenol formaldehyde resin, polyurethane, novolac, and cyanate ester, may be performed.
FIG. 5B is a graphical representation illustrating the thermal decomposition of the REPO, in accordance with an embodiment of present disclosure. FIG. 5B is described in conjunction with elements from FIGs. 1 to 5A. With reference to FIG. 5B, there is shown a graphical representation 500B including a first curve 502B and a second curve 504B. Specifically, the first curve 502B depicts the thermogravimetric Analysis (TGA) for the REPO 304C. The temperature is expressed in degrees Celsius in an abscissa axis. Weight per cent is expressed in arbitrary units in an ordinate axis (left ordinate axis of the graphical representation 500B). The first curve 502B, depicts the weight loss of the sample as temperature increases. Initial weight loss starts around 100 degrees Celsius, and major weight loss occurs between 200 degrees Celsius and 400 degrees Celsius . The sample reaches a stable weight of about 10 percent around 450 degrees Celsius.
Further, the second curve 504B, depicts the Derivative Thermogravimetric (DTG) curve for the REPO 304C. The DTG analysis is a technique that measures the rate of weight change of a material as a function of temperature. The DTG is derived from the TGA and provides more detailed information about the thermal decomposition processes of the REPO. DTG records the first derivative of the weight loss with respect to temperature, i.e., how quickly the REPO’s weight changes at each point in the temperature range. In a DTG curve, peaks represent specific temperature points where the rate of decomposition is at its maximum. Each peak usually corresponds to a distinct decomposition event or phase change in the material. Temperature is expressed in degrees Celsius in an abscissa axis. The rate of weight change is expressed in percentage per degree Celsius on the ordinate axis.
The DTG is particularly useful for identifying the temperatures at which different stages of decomposition occur and for detecting overlapping reactions that might not be as apparent in a simple TGA curve. The DTG enhances the understanding of thermal events in materials by highlighting the specific temperatures where the most significant changes in weight occur, allowing for a more precise analysis of the decomposition process.
The second curve 504B, includes a first peak 506B, a second peak 508B and a third peak 510B, inferring a multi-step decomposition process. The first peak 506B, occurs at around 200 degrees Celsius, implying the breakdown of labile oxygen functional groups. The second peak 508B, occurs at around 300 degrees Celsius, indicating the cleavage of amine bonds. The third peak 510B, occurs at around 380 degrees Celsius, indicating the primary decomposition of the oligomer structure (i.e., the REPO 304C). The residual 10% weight at high temperatures represents inorganic content or highly stable carbonaceous residue.
FIG. 5C is a graphical representation illustrating the high-resolution mass spectrometry (HRMS) of the REPO, in accordance with an embodiment of the present disclosure. FIG. 5C is described in conjunction with elements from FIGs. 1 to 5B. With reference to FIG. 5C, there is shown a graphical representation 500C depicting high-resolution mass spectrometry (HRMS) obtained for the REPO 304C. The HRMS uses mass spectrometers capable of high resolution and high mass accuracy measurement to determine elemental compositions and identify unknowns. The ratio of mass to charge (m/z), hereinafter referred to as m/z ratio, is expressed in arbitrary units in an abscissa axis. Intensity is expressed in percentage in an ordinate axis.
The HRMS depicted by the graphical representation 500C depicts different types of oligomers formed during the disintegration of the epoxy matrix by the cleaving of C–N bonds. The graphical representation 500C includes a first oligomer 502C i.e., 4-(2-(4-(3-amino-2-hydroxypropoxy)phenyl)propan-2-yl)phenol, a second oligomer 504C i.e., 1,1'-((propane-2,2-diylbis(4,1-phenylene))bis(oxy))bis(propan-2-one), a third oligomer 506C i.e., 1-amino-3-(4-(2-(4-(2-hydroxypropoxy)phenyl)propan-2-yl)phenoxy)propan-2- ol, a fourth oligomer 508C i.e., 1-(ethylamino)-3-(4-(2-(4-(2-hydroxypropoxy)phenyl)propan-2-yl)phenoxy)propan-2-one and a fifth oligomer 510C i.e., 1-amino-3-(4-(2-(4-(3-(butylamino)-2-hydroxypropoxy)phenyl)propan-2-yl)phenoxy)propan-2-one.
The first oligomer 502C is produced at m/z ratio of around 300. The first oligomer 502C is an aromatic compound with a hydroxyl group (-OH) and an amine group (-NH2), inferring to presence of amine and hydroxyl-terminated fragments from the epoxy breakdown. The second oligomer 504C has a peak of at m/z ratio of around 320. The second oligomer 504C has a similar structure as that of the first oligomer 502C but with an additional hydroxyl group(-OH). The additional hydroxyl group (-OH) group indicates further hydroxylation of the epoxy fragment. The third oligomer 506C has a peak m/z ratio at around 340. The third oligomer 506C has two aromatic rings connected by an oxygen bridge, with a carboxylic acid (-COOH) group and hydroxyl group (-OH) group, indicating oxidation and cleavage of the epoxy structure.
The fourth oligomer 508C has a peak of m/z ratio at around 380. The fourth oligomer 508C has a larger fragment with two aromatic rings ether linkages, indicating the presence of larger oligomeric fragments with preserved epoxy backbone structure. The fifth oligomer 510C has a peak of m/z ratio at 429.397. The fifth oligomer 510C is one the most significant fragments obtained after HRMS and contains complex structures, including multiple aromatic rings, ether linkages, and various functional groups.
The graphical representation 500C confirms the formation of a range of oligomeric species during the recycling process. The presence of amine (-NH2), hydroxyl (-OH), and carboxylic acid (-COOH) groups in various fragments supports the FTIR analysis (as shown in FIG. 5A), indicating the formation of amine, hydroxyl, and carboxylic acid functionalities. The preservation of aromatic rings and ether linkages in larger oligomers suggests that parts of the original epoxy structure remain intact. The variety of fragment sizes (from m/z ratio of 300 to 440) indicates a distribution of oligomer molecular weights consistent with the REPO 304C as a low molecular weight oligomer. The presence of carbamate (-NH-CO-) linkage in larger oligomers indicates the formation of amide linkages, which could result from the reaction between amine and carboxylic acid groups during the recycling process.
FIG. 6A is a graphical representation depicting the FTIR spectrum of a conventional epoxy-hardener (C-Epoxy) and an epoxy-REPO (i.e., the REPO used as a hardener) in accordance with an embodiment of the present disclosure. FIG. 6A is described in conjunction with FIGs. 1 to 5C. With reference to FIG. 6A, there is shown a graphical representation 600A depicting exemplary FTIR spectra of a conventional epoxy-hardener (C-Epoxy) and an epoxy REPO (i.e., REPO used as hardener).
In an implementation, the REPO 304C may be adapted to be used as a hardener with virgin epoxy resin. In epoxy, the hardener (also known as a curing agent) is required to initiate the chemical reaction that links the epoxy resin molecules together into a rigid, three-dimensional structure. The REPO 304C contains reactive sites that can serve as a hardener by reacting with the epoxy groups in the virgin resin. By using the REPO 304C as a hardener, the epoxy waste is effectively recycled and reintegrated into new products, which maximizes resource utilization and minimizes waste, contributing to a more sustainable production cycle. The use of the REPO 304C with virgin epoxy resin can maintain or even enhance the mechanical properties of the final product. The enhancement of mechanical properties arises because the REPO 304C, derived from cured epoxy, has a similar chemical structure and can effectively contribute to the crosslinking process, resulting in a product with comparable strength, stiffness, and durability.
Specifically, the graphical representation 600A depicts the absorption of infrared light by the C-Epoxy and the epoxy-REPO at different wavelengths, typically measured in wavenumbers. Wavenumber is expressed in reciprocal centimetres (cm-1) in an abscissa axis. Transmittance is expressed in arbitrary units in an ordinate axis. The graphical representation 600A includes a curve 602A and a curve 604A, depicting the FTIR spectrum that indicates the absorption of infrared light. Each peak or band in the curve 602A and 604A corresponds to the vibration of specific chemical bonds within the chemical structure of the C-epoxy and the epoxy REPO, respectively. The curves 602A and 604A include a section 606A, a section 608A, a section 610A, a section 612A and a section 614A. The section 606A has a range of 900-1200 cm-1 and indicates C-O stretching. The section 606A has multiple peaks with a notable peak at 1109 cm-1, indicating the presence of various C-O bonds (ethers, esters) in the epoxy structure (i.e., C-epoxy and epoxy REPO). The section 608A falls in the range of 1600-1650 cm-1 and depicts C=C stretching with a peak at 1608 cm-1. The section 610A falls in the 1700-1750 cm-1 range with a C=O stretching peak at 1733 cm-1. The section 612A falls in 2800-3000 cm-1 range. Multiple peaks are present in the section 612A, corresponding to various C-H stretching modes. The section 614A falls in 3200-3600 cm-1 range. A broad peak for OH-stretching occurs at around 3400 cm-1, indicating the presence of hydroxyl groups in both epoxy systems (C-epoxy and epoxy REPO). However, the absence of an oxirane peak (epoxy peak) in the C-Epoxy and the Epoxy-REPO implies the complete reaction between the epoxy groups of diglyceryl ether of bisphenol A (DGEBA) with conventional hardener and REPO during the curing cycle.
FIG. 6B is a graphical representation illustrating Differential Scanning Calorimetry (DSC) of the C-epoxy and epoxy REPO, in in accordance with an embodiment of the present disclosure. FIG. 6B is described in conjunction with FIGs. 1 to 6A. With reference to FIG. 6B, there is shown a graphical representation 600B depicting Differential Scanning Calorimetry (DSC) which is obtained after doing characterisation of the C-epoxy and the epoxy REPO. The characterization of the C-epoxy and epoxy REPO is done to determine the Glass Transition Temperature (Tg) by using DSC.
The graphical representation 600B shows the relationship between temperature and the heat flow. The temperature is expressed in degrees Celsius in an abscissa axis. Heat flow is expressed in watts per gram in an ordinate. The graphical representation 600B includes a first curve 602B depicting the characterisation of the C-epoxy and a second curve 604B, depicting the characterisation of the epoxy REPO. The first curve 602B, shows a slight step change in heat flow around at Glass transition temperature (Tg) for 108 °C. The second curve 604B, shows a more pronounced step change in heat flow around at Glass transition temperature (Tg) for 106 °C. The graphical representation 600B demonstrates that the Epoxy-REPO has a slightly lower glass transition temperature compared to the C-Epoxy, indicating a higher crosslinked network formed in C-Epoxy, resulting in higher chain restriction and enhancement of the glass transition temperature. Although the difference is not so high (2 degrees Celsius), it implies complete curing.
FIG. 6C is a graphical representation illustrating the tensile strength of the C-epoxy and the epoxy REPO, in accordance with an embodiment of the present disclosure. FIG. 6C is described in conjunction with FIGs. 1 to 6B. With reference to FIG. 6C, there is shown a graphical representation 600C depicting the relationship between stress and strain for the C-epoxy and the epoxy REPO. Strain is expressed in percentage in an abscissa axis. Stress is expressed in kilopascal in an ordinate axis.
The graphical representation 600C includes a curve 602C indicating the behaviour of C-epoxy and a curve 604C indicating the behaviour of epoxy REPO. The tensile strength of C-Epoxy is 73(±2) megapascal (MPa), and the epoxy-REPO is 69(±4) megapascal (MPa). The higher tensile strength of the C-Epoxy is attributed to its more extensively crosslinked network. The crosslinked network forms during the reaction between the conventional hardener (containing aliphatic tetramine) and the epoxy groups of DGEBA. Aliphatic tetramines typically have four primary amine groups (-NH2). Each primary amine can react with two epoxy groups, forming secondary amines and then tertiary amines. As a result, a highly interconnected, three-dimensional network structure is formed. High crosslink density, uniform distribution of crosslinks, fewer chain ends, and dangling chains lead to improved load distribution throughout the material.
The slightly lower tensile strength of Epoxy-REPO is due to its less extensive and potentially less uniform crosslinking network, which is a result of the complex mixture of reactive groups, i.e., primary amines (-NH2), secondary amines (-NH-) and hydroxyl groups (-OH) present in the epoxy (REPO). Primary amines react similarly to those in conventional hardeners, but there are likely fewer of them. Secondary amines can only react with one epoxy group, leading to less cross-linking. Hydroxyl groups can react with epoxy groups, but this reaction is slower and less efficient in creating crosslinks. Lower crosslink density, less uniform distribution of crosslinks, More chain ends, and potentially more dangling chains result in less efficient load distribution, slightly lower resistance to deformation, and marginally reduced overall mechanical strength.
The difference in tensile strength (73 MPa vs 69 MPa) is relatively small, indicating that the epoxy REPO is quite effective. However, the slightly lower value and higher variability (±4 MPa vs ±2 MPa) in epoxy-REPO suggests reduced crosslink density. Fewer connection points between polymer chains, allowing for slightly easier deformation under stress. The varied reactive groups in REPO may lead to regions of higher and lower crosslink density, creating stress concentration points. Unreacted or partially reacted components in REPO might act as internal plasticizers, slightly reducing overall stiffness. If the REPO 304C contains lower molecular weight fragments, this could lead to a higher concentration of chain ends, potentially reducing overall network integrity. The complex structure of REPO might introduce steric hindrances, preventing some reactive sites from participating in cross-linking. Despite these factors, the relatively close tensile strength values indicate that REPO is a viable alternative to conventional hardeners, offering a good balance between recycling benefits and mechanical performance. The slightly lower properties may be acceptable in many applications, especially considering the environmental advantages of using recycled material.
FIG. 6D is a graphical representation illustrating the comparison of the thermostability of the C-epoxy and the epoxy REPO, in accordance with the present disclosure. FIG. 6D is described in conjunction with FIGs. 1 to 6C. With reference to the FIG. 6D, there is shown a graphical representation 600D showing the relationship variation of weight percent of the C-epoxy and the epoxy REPO with the temperature. The temperature is expressed in degrees Celsius in an abscissa axis. Weight per cent is expressed in arbitrary units in an ordinate axis.
The graphical representation 600D includes a curve 602D and a curve 604D showing the relationship between the weight percent of the C-epoxy and the epoxy REPO respectively, and the temperature. Both C-epoxy and the epoxy REPO show high thermal stability up to about 290 °C. C-epoxy maintains a slightly higher weight % in this range, indicating potentially better thermal stability at lower temperatures. For epoxy-REPO, degradation begins at approximately 290 °C, and for C-Epoxy, degradation begins at 298 °C. The 8 degrees Celsius difference is significant, showing C-Epoxy's superior initial thermal stability.
Both the C-Epoxy and the epoxy-REPO undergo rapid weight loss in 290 degrees Celsius to 450 degrees Celsius temperature range. The C-Epoxy shows a slightly steeper degradation curve, possibly indicating a more uniform network structure. The degradation of the epoxy-REPO is more gradual, suggesting a less homogeneous network with varied bond strengths. At 800 °C, both C-Epoxy and epoxy-REPO have similar residual weight (i.e., about 10-15%), suggesting that despite different degradation onset temperatures, both materials have similar char formation. C-Epoxy shows a more abrupt weight loss, while the curve of the epoxy-REPO is slightly more gradual. The C-Epoxy has a more uniform network structure, leading to more simultaneous bond breakage. The C-Epoxy's higher degradation onset temperature indicates better thermal stability, which is attributed to its more extensive and uniform crosslinked network. The TGA results corroborate the tensile data analysis, showing that the structural differences (degree of crosslinking) affect both mechanical and thermal properties. The more gradual degradation of epoxy-REPO suggests a less uniform network, which could explain its slightly lower tensile strength. Despite starting degradation 8 degrees Celsius earlier, epoxy-REPO shows a comparable overall thermal degradation profile to C-Epoxy, indicating that while the REPO results in slightly reduced thermal stability, it still performs reasonably well compared to the C-epoxy.
Example 1
An example illustrating the method 100 through a series of steps:
Step 1: Preparation of the aqueous recycling solution: 30 gm NaCl and 100 ml deionized water were taken in a 200 ml beaker to prepare a homogeneous solution by continuous stirring. 20g of citric acid was mixed into the homogeneous solution, and finally, a clear solution was obtained with a pH of 0.5 to 1.
Step 2: Mild chemical decomposition of CFRE by the aqueous recycling solution: Approximately 2g (w0) of amine-cured epoxy matrix containing CFRE laminate was cut into a rectangular shape (2 cm × 1 cm × 0.2cm) and charged into a 100 ml hydrothermal pressure reactor with 25 mL of the SM-S. The reactor was kept inside an oven at 220 degrees Celsius for 18 hours. After that, the reactor was cooled down to room temperature, and the SM-S solution was separated from the decomposed CFRP by filtration. Acetone or/ethanol was used to dissolve the decomposed epoxy matrix (REPO) and recycle the carbon fibers. The resulting solution was kept inside a hot air oven at 80 degrees Celsius for 2 hours to yield REPO as a pale-yellow solid. Recycled carbon fiber (RCF) was dried in a vacuum oven at 60 degrees Celsius for 10 hours to reach a constant weight (w1). The decomposition degree (DD%) of CFRP was calculated according to the following equation:
DD%=1-(w_1- w_0)/w_0 ×100
where w0 is the weight of CFRP before decomposition, and w1 is the weight of decomposed CFRP after washing with acetone or ethanol and drying in a vacuum. The carbon fiber and matrix weight percentages in the CFRP were 63% and 37% calculated.
By following these steps,
Modifications to embodiments of the present disclosure described in the foregoing are possible without departing from the scope of the present disclosure as defined by the accompanying claims. Expressions such as "including", "comprising", "incorporating", "have", "is" used to describe and claim the present disclosure are intended to be construed in a non-exclusive manner, namely allowing for items, components or elements not explicitly described also to be present. Reference to the singular is also to be construed to relate to the plural. The word "exemplary" is used herein to mean "serving as an example, instance or illustration". Any embodiment described as “exemplary” is not necessarily to be construed as preferred or advantageous over other embodiments and/or to exclude the incorporation of features from other embodiments. The word "optionally" is used herein to mean "is provided in some embodiments and not provided in other embodiments". It is appreciated that certain features of the present disclosure, which are, for clarity, described in the context of separate embodiments, may also be provided in combination in a single embodiment. Conversely, various features of the present disclosure, which are, for brevity, described in the context of a single embodiment, may also be provided separately or in any suitable combination or as suitable in any other described embodiment of the disclosure.
, Claims:CLAIMS
We Claim:
1. A method (100) for recycling fiber-reinforced polymer composites, the method comprising:
preparing an aqueous recycling solution by mixing at least one bio-based acid and at least one salt in water;
immersing fiber-reinforced polymer composites in the aqueous recycling solution in a hydrothermal reactor (302B);
heating the hydrothermal reactor (302B) to a predefined temperature for a predefined duration;
cooling the hydrothermal reactor (302B) and separating the aqueous recycling solution from the decomposed fiber-reinforced polymer composites;
washing the decomposed fiber-reinforced polymer composites with acetone or ethanol to separate recycled fibers and recycled polymer; and
drying the recycled fibers and the recycled polymer to obtain a final recycled products.
2. The method (100) as claimed in claim 1, wherein the recycled polymer comprises at least one of: epoxy, phenol formaldehyde resin, polyurethane, novolac, and cyanate ester.
3. The method (100) as claimed in claim 1, wherein the recycled fibers comprise at least one of: carbon fibers, glass fibers, aramid fibers, flax fibers, hemp fibers, sisal fibers, and areca fibers.
4. The method (100) as claimed in claim 1, wherein the fiber-reinforced polymer composite is a carbon fiber-reinforced epoxy laminate.
5. The method (100) as claimed in claim 1, wherein the aqueous recycling solution has a pH in the range of 0.5 to 1.0.
6. The method (100) as claimed in claim 1, wherein the aqueous recycling solution is reused multiple times by adjusting its pH to the range of 0.5 to 1.0.
7. The method (100) as claimed in claim 1, wherein the predefined temperature for heating the hydrothermal reactor (302B) is 230-260 degrees Celsius.
8. The method (100) as claimed in claim 1, wherein the predefined duration for heating the hydrothermal reactor (302B) is 18-24 hours.
9. The method (100) as claimed in claim 1, wherein the recycled polymer is a recycled epoxy (304C) adapted for use as a hardener for a fresh epoxy resin.
10. The method (100) as claimed in claim 1, wherein the recycled polymer is a recycled epoxy (304C), which is transformed into a virgin epoxy by reaction with epichlorohydrin at an acidic medium.
11. The method (100) as claimed in claim 1, wherein the recycled polymer is a recycled epoxy (304C) adapted as a crosslinker for polyolefin’s recycling.
12. The method (100) as claimed in claim 1, wherein the recycled fibers are recycled carbon fibers (302C) adapted to fabricate new laminates or as a reinforcing filler in polymer composites.
13. The method (100) as claimed in claim 1, wherein the aqueous recycling solution for decomposing fiber-reinforced polymer composites comprising:
75-85% by volume of water as a solvent;
5-10% by volume of at least one bio-based acid; and
7-12% by volume of at least one salt.
14. The method (100) as claimed in claim 1, wherein at least one bio-based acid and at least one salt is required.
15. The method (100) as claimed in claim 1, further comprising selectively cleaving C-N and C-O bonds in any thermoset (amine or acid cured) or vitrimeric epoxy matrices of carbon fiber-reinforced epoxy laminate waste by exposing the thermoset or vitrimeric epoxy matrices to the aqueous recycling solution under hydrothermal conditions.
16. The method (100) as claimed in claim 1, wherein the recycled polymer is a functional oligomer containing amino groups and hydroxyl groups.
17. The method (100) as claimed in claim 1, wherein the recycled fibers are recycled carbon fiber (302C) maintains structural integrity comparable to as accrued carbon fiber (ACF).
18. The method (100) as claimed in claim 1, the recycled polymer is the recycled epoxy (304C) further adapted for use as hardener with virgin epoxy resin.
19. The method (100) as claimed in claim 18, wherein the recycled epoxy is component of a cured epoxy comprising the epoxy resin, the recycled epoxy, and a catalyst in a ratio of 100:24:5 by weight.