Methods and systems for the solvolysis of plastic streams

Abstract

The present disclosure relates to a method that includes contacting a fiber-reinforced composite with a solvent, where the fiber-reinforced composite is constructed from a fiber and a macromolecule, the contacting results in the formation of a mixture that includes a liquid phase of the solvent and the macromolecule solubilized in the solvent and a solid phase of the fiber, and separating the mixture resulting in a first stream of the solid phase and a second stream of the liquid phase.

Description

[0001] METHODSAND SYSTEMS FOR THE SOLVOLYSIS OF PLASTIC STREAMS

[0002] CROSS-REFERENCE TO RELATED APPLICATIONS

[0003] This application claims priority from U.S. Provisional Patent Application No. 63 / 642,917 filed on May 6, 2024 and U.S. Provisional Patent Application No. 63 / 657,341 and its associated appendix filed on June 7, 2024, the contents of which are incorporated herein by reference in their entirety.

[0004] CONTRACTUAL ORIGIN

[0005] This invention was made with government support under Contract No. DE-AC36-08GO28308 awarded by the Department of Energy. The government has certain rights in the invention.

[0006] FIELD OF THE INVENTION

[0007] The present disclosure relates to the depolymerization of epoxy-amine thermosets and illustrates that end-of-life carbon fiber-reinforced polymers can be effectively depolymerized in a solvent, yielding fractionated, high-quality carbon fiber and the building blocks of the epoxy-amine resins for recycling into new materials.

[0008] BACKGROUND

[0009] Demand for high-performance composite materials is increasing, and an efficient method to recover high-value carbon fibers and resin monomers from these materials is urgently needed. The resiliency of highly crosslinked epoxy-amine polymers, in which carbon fibers are embedded, presents major challenges to achieving this goal. Thus, there remains a need for methods that enable the deconstruction of fiber-reinforced composite materials, the subsequent recovery of both the fiber and polymer deconstruction products, and the reuse of the recovered materials to make next generation polymers and / or fiber-reinforced composite materials.

[0010] SUMMARY

[0011] An aspect of the present disclosure is a method that includes contacting a fiber-reinforced composite with a solvent, where the fiber-reinforced composite is constructed from a fiber and a macromolecule, the contacting results in the formation of a mixture that includes a liquid phase of the solvent and the macromolecule solubilized in the solvent and a solid phase of the fiber, and separating the mixture resulting in a first stream of the solid phase and a second stream of the liquid phase. In some embodiments of the present disclosure, the solvent may include a carboxylic acid functional group. In some embodiments of the present disclosure, the solvent may include a dicarboxylic acid. In some embodiments of the present disclosure, the solvent may include at least one of acetic acid, succinic acid, or a combination thereof.

[0012] In some embodiments of the present disclosure, the fiber may include at least one of a carbon fiber, a glass fiber, a ceramic fiber, a metal fiber, a natural-occurring fiber, or a combination thereof. In some embodiments of the present disclosure, the macromolecule may include at least one of a polymer, a resin, or a combination thereof. In some embodiments of the present disclosure, the macromolecule may include at least one of a thermoset, a thermoplastic, or a combination thereof. In some embodiments of the present disclosure, the macromolecule may include an epoxy-amine.

[0013] In some embodiments of the present disclosure, the contacting may be performed at a temperature between 50 °C and 500 °C. In some embodiments of the present disclosure, the contacting may be performed for a period of time between 5 minutes and 12 hours. In some embodiments of the present disclosure, the separating may be performed using at least one of a settling method, filtration, centrifugation, or a combination thereof.

[0014] In some embodiments of the present disclosure, the method may further include washing the solid phase, resulting in fiber that is essentially solvent free, where the washing utilizes at least one of a organic solvent, water, or a combination thereof. In some embodiments of the present disclosure, the method may further include treating the liquid phase, resulting in the solubilized macromolecule deconstructing into at least one of an oligomer, a smaller molecule, or a combination thereof. In some embodiments of the present disclosure, at least a portion of the treating may be performed during the contacting.

[0015] In some embodiments of the present disclosure, the deconstructing results in the forming of at least one of phenol, phenyl acetate (PA), 4-isoproplyphenyl acetate (4-IPPA), bisphenol A (BP A), monoacetylated BPA (MABPA), diacetylated BPA (DABPA), diacetylated isophorone diamine (DAIPDA), isophorone diamine (IPDA), N-ethyl-N-phenylacetamide (EPA), acetanilide (ACE), or a combination thereof. BRIEF DESCRIPTION OF DRAWINGS

[0016] Some embodiments are illustrated in referenced figures of the drawings. It is intended that the embodiments and figures disclosed herein are to be considered illustrative rather than limiting.

[0017] Figure 1 illustrates a method for the deconstruction of fiber-reinforced composites (FRCs) and the recovery of deconstruction products, including the fiber, according to some embodiments of the present disclosure.

[0018] Figure 2A illustrates a reaction scheme showing the deconstruction of an aliphatic thermoset resin via acetolysis yielding various deconstruction products including diacetylated isophorone diamine (DAIPDA), bisphenol-A (BPA), mono- and diacetylated bisphenol-A (MABPA, DABPDA), phenol, phenyl acetate (PA), and 4-isopropylphenyl acetate (4-IPPA), according to some embodiments of the present disclosure.

[0019] Figure 2B illustrates images of the (Panel A) post-reaction mixtures from temperature screening studies of the deconstruction of the aliphatic thermoset resin via acetolysis and (Panel B) of the post-reaction mixtures from the time course performed at 280 °C shown in Panel A, according to some embodiments of the present disclosure.

[0020] Figure 2C illustrates (Panel A) monomer yields for the temperature screening studies of the acetolysis of the aliphatic thermoset resin shown in Figure 2A (Reaction conditions: 20 mL acetic acid, 30 bar N2 for 3 hours) and (Panel B) illustrates monomer yield for the time course of the acetolysis reaction completed at 280 °C (Reactions conditions: 20 mL acetic acid 280 °C, and 30 bar N2) on the aliphatic thermoset resin shown in Figure 2 A, according to some embodiments of the present disclosure.

[0021] Figure 2D illustrates GPC chromatograms from samples obtained from the times series reactions in Figure 2E, according to some embodiments of the present disclosure.

[0022] Figure 3A illustrates a reaction scheme showing the deconstruction of an aromatic thermoset resin via acetolysis yielding various deconstruction products, according to some embodiments of the present disclosure.

[0023] Figure 3B illustrates (Panel A) the monomer yield as a function of temperature for the deconstruction of the aromatic thermoset resin (each experiment was completed with 3 hours of contacting, under 30 bar N2, and 20 mL acetic acid at the respective temperatures) and (Panel B) illustrates the monomer yield as a function time for the deconstruction of the aromatic thermoset resin (with contacting performed at 280 °C, 30 bar N2, and 20 mL acetic acid for each respective time), according to some embodiments of the present disclosure. Figure 3C illustrates a GPC trace of the aromatic thermoset after 2 hours, 4 hours and 6 hours at 280 °C, 30 bar N2 and 20 mL acetic acid, compared to three standards, bisphenol A (BP A), monoacetylated BPA (MABPA), and diacetylated BPA (DABPA), according to some embodiments of the present disclosure.

[0024] Figure 3D illustrates (Panel A) images of the aromatic thermoset after the temperature screening tests illustrated in Panel A of Figure 3B and (Panel B) illustrates images of the aromatic thermoset after the time course reactions illustrated in Panel B of Figure 3B, according to some embodiments of the present disclosure.

[0025] Figures 4A illustrates the deconstruction products resulting from the acetolysis of a model aliphatic polymer FRC via the reaction scheme illustrated in Figure 2A, according to some embodiments of the present disclosure.

[0026] Figure 4B illustrates monomer yields for the time course acetolysis reaction with the aliphatic polymer FRC shown in Figure 2A, according to some embodiments of the present disclosure. Reaction conditions: 20 mL acetic acid, 30 bar lSh, 280 °C.

[0027] Figure 4C illustrates (Panels A-C) SEM images of recovered carbon fibers after 1 hour, 4 hour, and pristine virgin carbon fibers, respectively, and (Panel D) illustrates single-fiber tensile modulus, E, of the recovered carbon fiber after the respective contact times of the aliphatic polymer FRC with acetic acid, according to some embodiments of the present disclosure. Error bars represent the standard deviation between five replicates. / J- values from unpaired t-tests compared to pristine: 1 hour = 0.8781, 2 hours = 0.6638, 4 hours = 0.8867, n = 5.

[0028] Figure 4D illustrates additional deconstruction products resulting from the acetolysis of the model aromatic polymer (see Figure 3A) FRC yielding the previously described BPA products and mono- and diacetylated 4,4’ -diaminodiphenylmethane (MADDM, DADDM), according to some embodiments of the present disclosure.

[0029] Figure 4E illustrates monomer yields for the time course acetolysis reaction with the aromatic polymer FRC shown in Figure 3A, according to some embodiments of the present disclosure. Contacting conditions: 20 mL acetic acid, 30 bar N2, 280 °C.

[0030] Figures 4F illustrates (Panels A-C) SEM images of recovered carbon fibers after 1 hour, 4 hours, and pristine virgin carbon fibers (vCF), respectively, and (Panel D) illustrates singlefiber tensile modulus, E, of the rCF as a function of contacting time, according to some embodiments of the present disclosure. Residual resin on the 1-hour rCF sample precluded tensile testing. Error bars represent the standard deviation between five replicates. -values from unpaired t-tests compared to the pristine fiber were 2 h = 0.4736, 4 h = 0.0326 n = 5.

[0031] Figures 5A-5E illustrate results from acetolysis of various post-consumer materials, according to some embodiments of the present disclosure. Contacting of all materials tested was performed at 280 °C for 2 hours at varied weight loadings, specified in each sub-caption. In the panels illustrated in each figure, from left to right, are shown the fiber-reinforced polymer substrate, a post-reaction SEM image of the recovered fibers (scale bar = 50 micron), and TGA of the starting FRC and post-reaction fibers, respectively. Figure 5A illustrates photos and data for a substrate of aerospace-grade polymer FRC, 2.5 wt% loading. Figure 5B illustrates photos and data for a substrate for a marine application polymer FRC with aluminum honeycomb, 5 wt% loading. Figure 5C illustrates photos and data for a substrate from a mountain bike polymer FRC, 2.5 wt% loading. Figure 5D illustrates photos and data for a substrate from an orthotic medical device polymer FRC, 5 wt% loading. Figure 5E illustrates photos and data for a substrate from a tidal turbine glass fiber reinforced composite, 5 wt% loading.

[0032] Figure 6 illustrates a plot of mass recovery versus time for seven different epoxy-amines due to contacting with acetic acid, with the epoxy-amine compositions tabulated in Table 5, according to some embodiments of the present disclosure.

[0033] REFERENCE NUMERALS

[0034] 100 method

[0035] 105 fiber-reinforced composite (FRC)

[0036] 107 solvent

[0037] 110 contacting

[0038] 112 liquid / solid mixture

[0039] 120 separating

[0040] 122 recovered fiber

[0041] 124 liquid fraction

[0042] 130 treating

[0043] 132 deconstruction products DETAILED DESCRIPTION

[0044] Among other things, the present disclosure relates to methods and systems for the treating of fiber-reinforced composites (FRC) to recover and reuse the fiber and macromolecules used to make the original FRCs. In some embodiments of the present disclosure, a chemical recycling process utilizing acetolysis is implemented to deconstruct and recover both carbon fiber and macromolecule deconstruction products from FRCs originally constructed of carbon fiber- reinforced epoxy materials. However, the method is not limited to the recovery of carbon fibers and other fibers may be recovered depending on the type of FRC. Further, the method of this disclosure has been investigated using both amine-cured epoxy thermoplastics and thermosets and carbon fiber-reinforced composites using these amine-cured epoxies. For these examples, the epoxy resin and carbon fiber-reinforced epoxy composites were subjected to acetolysis in acetic acid to cleave both C-0 and C-N bonds of the amine-cured epoxy polymer resulting in the forming of various epoxy deconstruction products. As shown herein, at least some of these deconstruction products, the resultant monomers (which are acetylated in this example), were soluble and easily separated from the carbon fiber.

[0045] Figure 1 illustrates a method 100 for treating a fiber-reinforced composite (FRC) 105 (e.g., a carbon fiber-reinforced amine-cured epoxy composite), according to some embodiments of the present disclosure. As illustrated, a method 100 for treating an FRC 105 may begin with contacting 110 an FRC 105 with a solvent 107. An FRC 105 may include at least one type of fiber and at least one macromolecule that binds to the fiber to create the FRC 105. Contacting 110 an FRC 105 with a solvent 107 may result in the forming of a liquid / solid mixture 112, with the FRC 105 immersed in the solvent 107. Further, the contacting 110 of an FRC 105 with a solvent 107 may result in at least the partial solubilizing or complete solubilizing of the macromolecule used in the FRC 105 into the solvent 107. Thus, the solubilizing may result in at least the partial removal or complete removal of the macromolecule (e.g., amine-cured epoxy polymer) from the fiber (e.g., carbon fiber). As described herein, a macromolecule used to construct an FRC 105 may include at least one of a polymer and / or a resin, with examples including amine-cured epoxy thermoplastics and / or amine-cured epoxy thermosets.

[0046] Among other things, contacting 110 may result in the swelling of the macromolecule used in the FRC 105 as the solvent 107 gains access to the internal volume of the macromolecule, thereby enabling further penetration by the solvent 107 into the macromolecule, potentially resulting in the deconstruction (i.e., depolymerization) of the macromolecule. In some embodiments of the present disclosure, deconstruction processes resulting from contacting 110 an FRC 105 with a solvent 107 may include the breaking of chemical bonds within the macromolecule, e.g., polyamide bonds, resulting in the deconstruction of at least a portion of the macromolecule into smaller molecular weight components such as, for example, oligomers and / or smaller molecules. Therefore, in some embodiments of the present disclosure, the breaking of chemical bonds (e.g., C-0 and C-N bonds) in amine-cured epoxies may be achieved by solvolysis, or in the case of acetic acid as the solvent 107, specifically acetolysis. In some embodiments of the present disclosure, a solvent 107 may include other carboxylic acids including at least one of a Cl carboxylic acid, a C2 carboxylic acid, a C3 carboxylic acid, a C4 carboxylic acid, as well as C5+ carboxylic acids, including C8, CIO, and C12 carboxylic acids.

[0047] Examples of Cl carboxylic acids that may be suitable as solvents 107 for performing solvolysis in the methods described herein include formic acid and / or carbonic acid. Examples of C2 carboxylic acids that may be suitable as solvents 107 for performing solvolysis in the methods described herein include acetic acid, glycolic acid, glyoxylic acid, and / or oxalic acid. Examples of C3 carboxylic acids that may be suitable as solvents 107 for performing solvolysis in the methods described herein include propionic acid, acrylic acid, propiolic acid, lactic acid, 3- hydroxypropionic acid, glyceric acid, pyruvic acid, 3-oxopropanoic acid, 2,3-dioxopropanoic acid, malonic acid, tartronic acid, 2,2-dihydroxypropanedioic acid, mesoxalic acid, and / or glycidic acid. Examples of C4 carboxylic acids that may be suitable as solvents 107 for performing solvolysis in the methods described herein include butanoic acid and / or 2- methylpropanoic acid. Further, in some embodiments of the present disclosure, a solvent 107 used to deconstruct an FRC 105 may be a dicarboxylic acid such as oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, and / or suberic acid. In some embodiments of the present disclosure, a solvent 107 may include a mixture of carboxylic acids and / or dicarboxylic acids. In some embodiments of the present disclosure, a solvent 107 may further include at least one of water or an alcohol, with examples of alcohols including at least one of methanol, ethanol, propanol, iso-propanol, butanol, and / or any other alcohols having at least five carbon atoms; e.g., C5, C6, C7, C8, etc.

[0048] In some embodiments of the present disclosure, contacting 110 of an FRC 150 with a solvent 107 (e.g., acetic acid) may be performed in a unit operation operated in a continuous fashion, for example in one or more continuous-stirred tank reactors (CSTRs). In some embodiments of the present disclosure, contacting 110 may be performed in one or more packed-bed reactors, where the packing includes or is the FRC 105 itself and / or a mixture of FRC 105 combined with standard, inert packing material. Regardless of the unit operation chosen for the contacting 110 step, an important design feature is that the contacting does not damage and / or degrade, or at least minimizes damage and / or degradation of the fibers because they are the highest value product recovered by the method 100 and / or a system designed to perform the method. Therefore, in the case of selecting a stirred tank reactor, agitation may need to be maintained below some maximum speed to prevent physical damage to the fibers. In some embodiments of the present disclosure, the speed of an agitator used in a stirred tank used for contacting 110 and / or treating 130 may be maintained at an RPM less than or equal to 100 RPM.

[0049] In some embodiments of the present disclosure, contacting 110 an FRC 105 constructed using carbon fiber and an epoxy-amine with acetic acid (solvent 107) may be performed at a temperature between 50 °C and 500 °C or between 180 °C and 320 °C. In some embodiments of the present disclosure, contacting 110 an FRC 105 constructed using carbon fiber and an epoxy-amine with acetic acid (solvent 107) may be performed in a volume that results in a residence time between 5 minutes and 12 hours or between 30 minutes and 3 hours. In some embodiments of the present disclosure, contacting 110 an FRC 105 constructed using carbon fiber and an epoxy-amine with acetic acid (solvent 107) may be performed in a volume that results in a residence time between 5 minutes and 12 hours or between 30 minutes and 3 hours. In some embodiments of the present disclosure, contacting 110 may be performed in an environment that includes at least one of oxygen, nitrogen, and / or air. In some embodiments of the present disclosure, contacting 110 may be performed in an inert environment, for example an atmosphere that includes at least one of helium, argon, and / or xenon. In some embodiments of the present disclosure, contacting 110 may further include agitation.

[0050] Referring again to Figure 1, after contacting 110 an FRC 105 with a solvent 107, a method 100 may continue with a separating 120 of the liquid / solid mixture 112 resulting in the forming of a solid-containing stream, i.e., recovered fiber 122, and a liquid stream containing macromolecule deconstruction products, i.e., liquid fraction 124, which may also include solvent 107. In some embodiments of the present disclosure, separating 120 may be performed after all or substantially all of the macromolecule (e.g., an amine-cured epoxy) originally present in the FRC 105 has been solubilized and / or deconstructed into smaller molecules contained in the solvent 107 present in the liquid fraction 124, thereby enabling the separating 120 of the recovered fiber 122 in a form that is essentially free or completely free of deconstruction products (e.g., macromolecules, oligomers, and / or smaller molecules). Separating 120 may be accomplished, for example, by at least one of filtration, centrifugation, and / or a gravimetric method resulting in the forming of a first stream of recovered fiber 122 and a second stream, a liquid fraction 124, that includes at least one of the macromolecules, oligomers, and / or small molecules derived from the deconstruction of the starting macromolecule, dissolved or in suspension in the solvent 107 used in the contacting 110. In some embodiments of the present disclosure, recovered fiber 122 may be in condition for reuse immediately after the separating 120. Thus, separating 120 may result in recovered fiber 122 that is essentially free of solvent 107, macromolecules, oligomers, and smaller molecules. Further, as shown herein, the physical structure and integrity of recovered fiber 122 may be essentially the same as the virgin fiber used to manufacture the original FRC. Similarly, in some embodiments of the present disclosure, separating 120 may result in a liquid fraction 124 that is essentially free or completely free of the fiber originally present in the FRC 105.

[0051] In some embodiments of the present disclosure, the separating 120 of recovered fiber 122 from a liquid fraction 124 containing deconstruction products and solvent 107 may be achieved at temperatures similar to those used during the contacting 110 step. For example, a separating 120 may be achieved while maintaining a temperature of a liquid / solid mixture 112 at a temperature between 50 °C and 500 °C or between 180 °C and 320 °C during at least a portion of the separating 120. In some embodiments of the present disclosure, a separating 120 may be achieved while maintaining a temperature of a liquid / solid mixture 112 at a temperature that is less than the temperature used during contacting 110; e.g., between 30 °C and 200 °C or between 30 °C and 100 °C. Suitable process conditions may be determined by the allowable operating temperatures of the equipment used to accomplish the separating 120; e.g., temperature tolerance of the filtration media, etc.

[0052] In some embodiments of the present disclosure, any residual solvent 107 and / or residual solid phase (e.g., macromolecule, oligomer, and / or smaller molecules, etc.) may be removed from recovered fiber 122 by subjecting the recovered fiber 122 to a subsequent washing step (not shown). For example, washing may be achieved by at least one of rinsing and / or immersing the recovered fiber 122 with a second solvent (not shown), e.g., acetone, isopropanol, ethyl acetate. In general, a second solvent may have a higher vapor pressure than the solvent 107 used in the contacting 110 step. Thus, a washing step may displace the solvent 107 used in the contacting 110 with the second solvent enabling the subsequent removal of the second solvent using lower temperatures and / or higher pressures during the washing step, resulting in the forming of a solvent-free, pristine, recovered fiber. For example, in the case of using acetic acid as a solvent 107 for the deconstruction of a molecule contained in an FRC in a contacting 110 step, a second solvent of acetone may be used in a washing step, as acetone has a lower boiling point (56.0 °C) than acetic acid (117.9 °C). Since all of the carboxylic acids listed above have boiling points of 111 °C or higher, any solvent having a boiling point less than 111 °C may be suitable for washing the original solvent 107 used during contacting 110. Other examples of polar aprotic solvents that may be used in a washing step, having boiling points less than 111 °C include at least one of acetone, acetonitrile, di chloromethane, ethyl acetate, and / or tetrahydrofuran. In cases where higher boiling solvents 107 are used during contacting 110, higher boiling solvents may be used in a washing step; e.g., dimethylformamide and / or dimethyl sulfoxide.

[0053] In some embodiments of the present disclosure, removal of any residual solvent from recovered fiber 122, solvent 107 used in the contacting and / or a second solvent used in a washing step, may be achieved by drying the recovered fiber 122 (with or without a washing step), using at least one of heat and / or by exposing the recovered fiber 122 to a gas stream (e.g., an inert gas, air, etc.). In some embodiments of the present disclosure, recovered fiber 122 may be dried of solvent by heating the recovered fiber to a temperature between slightly above room temperature and 150 °C or between 30 °C and 100 °C or between 30 °C and 50 °C.

[0054] Referring again to Figure 1, a method 100 may continue with a treating 130 of the liquid fraction 124 (containing the solubilized macromolecule and / or molecules resulting from its deconstruction) resulting from a separating 120 step to yield deconstruction products 132; e.g., oligomers and / or molecules resulting from the deconstruction of the macromolecule contained in the original FRC 105. Among other things, treating 130 may further deconstruct the macromolecules and / or macromolecule decomposition products into more desirable target compounds having, for example, more desirable target molecular weights, target functional groups, desirable physical properties, and / or desirable performance metrics. In some embodiments of the present disclosure, a treating 130 step may provide additional time for the macromolecule and / or macromolecule deconstruction products to remain in contact with the solvent 107 at an elevated temperature. This additional contact time may, among other things, enable the macromolecule originally used in the FRC 105 and / or its deconstruction products to further deconstruct into smaller molecules.

[0055] In some embodiments of the present disclosure, treating 130 may be performed at a temperature between 50 °C and 500 °C or between 180 °C and 320 °C. In some embodiments of the present disclosure, treating 130 may further include agitation. In some embodiments of the present disclosure, treating 130 may be performed for a period of time between 5 minutes and 12 hours or between 30 minutes and 3 hours. In some embodiments of the present disclosure, treating 130 a liquid fraction 124 containing at least one epoxy-amine decomposition product may be performed in a volume that results in a residence time between 5 minutes and 12 hours or between 30 minutes and 3 hours. In some embodiments of the present disclosure, treating 130 may be performed in an environment that includes at least one of oxygen, nitrogen, and / or air. In some embodiments of the present disclosure, treating 130 may be performed in an inert environment, for example an atmosphere that includes at least one of helium, argon, and / or xenon.

[0056] Referring again to Figure 1, in some embodiments of the present disclosure, at least a portion of the deconstruction of an epoxy-amine (i.e., macromolecule) may occur during contacting 110, in addition to the at least the partial solubilizing of the epoxy-amine and / or epoxy-amine deconstruction products. In some embodiments of the present disclosure, substantially all of the solubilizing and deconstruction of an epoxy-amine and / or epoxy-amine deconstruction products may occur during contacting 110, without the need for additional treating 130. In some embodiments of the present disclosure, an initial contacting 110 may result in only the solubilizing of an epoxy-amine, without any significant deconstruction of the epoxy-amine. In general, the percentage of an epoxy-amine that is solubilized and / or deconstructed at a particular position in a process will depend on the specific epoxy-amine being processed and the process conditions selected (e.g., type of unit operation, temperature, residence time, etc.).

[0057] Treating 130 is shown in Figure 1 as being performed separately from the contacting 110 and separating 120 steps. However, since the deconstruction of macromolecules and / or their deconstruction products may occur in each of the contacting 110, separating 120, and treating 130 steps, in some embodiments of the present disclosure, at least two of the contacting 110, separating 120, and treating 130 steps may be combined into a single step. Deconstruction of the macromolecules and / or macromolecule deconstruction products may occur to some extent during each of the contacting 110, the separating 120 of the recovered fiber 122 from the liquid fraction 124, and / or during the treating 130 of any remaining solubilized macromolecule and / or macromolecule decomposition products to yield the deconstruction products 132.

[0058] Therefore, one or more unit operations may be used to achieve the contacting 110, separating 120, and treating 130. For example, a single unit operation may be configured to complete all three steps of contacting, separating, and treating. Alternatively, the three steps may be achieved using two or three separate unit operations positioned in series. For example, a single stirred tank reactor may be utilized to perform the contacting 110 and the treating 130 and, as macromolecule and / or macromolecule deconstruction products are removed from the FRC 105, quantities of the resulting liquid / solid mixture 112 may be removed from the stirred tank reactor to be directed to a filtration unit to perform the separating 120, yielding recovered fiber 122 and a liquid fraction 124 containing macromolecule and / or macromolecule deconstruction products and solvent 107. The liquid fraction 124 may then be recycled to the stirred tank reactor for additional residence time to achieve additional deconstruction and / or may be directed to a second stirred tank reactor to perform a “finishing step”, i.e., treating 130, to achieve maximum conversion of the macromolecule to the final desired decomposition products.

[0059] In addition, in some embodiments of the present disclosure, the order of the steps illustrated in Figure 1 may be different. For example, the steps may be conducted starting with contacting 110, followed by treating 130, and concluding with separating 120. In this example, it may be preferable to let the deconstruction of the macromolecule used in an FRC 105 go to completion before separating the resultant solid / liquid mixture 112 into a recovered fiber 122 stream and a stream containing the deconstruction products 132. This example may be achieved using a single unit operation (e.g., stirred tank reactor) for the contacting 110 and the treating 130, such that once the macromolecule used in the FRC 105 is transferred from the fiber into the solvent 107, the liquid / solid mixture 112 may then be directed to a separating 120 step (e.g., filtration) to yield recovered fiber 122 and deconstruction products 132.

[0060] In some embodiments of the present disclosure, a method 100 may only include contacting 100 and separating 120. This may be the case where the additional residence provided by an additional treating 130 step is not needed to remove the macromolecule of the FRC 105 from the fiber. Like the previous example, this example may be achieved using a single unit operation (e.g., stirred tank reactor) for both contacting 110 and treating 130, such that once the macromolecule used in the FRC 105 is transferred from the fiber into the solvent 107, the liquid / solid mixture 112 may then be directed to a separating 120 step (e.g., filtration) to yield recovered fiber 122 and deconstruction products 132. In some embodiments of the present disclosure, the method 100 illustrated in Figure 1, or variations thereof, may be completed in batch mode, continuous mode, and / or semi -continuous mode.

[0061] In some embodiments of the present disclosure, the deconstruction products 132 resulting from treating 130 may be directed to one or more separation steps (not shown) to separate the deconstruction products 132 into individual chemical compounds and / or types of compounds (as defined by, for example, molecular weights, functional groups, etc.). Such a separating step of the deconstruction products 132 may also result in the recovery of the solvent 107 using in the contacting 110, thereby enabling the recovered solvent to be recycled to the contacting 110 step. Such separations may be achieved by at least one of distillation, evaporation, chromatography, and / or extraction.

[0062] Further, in some embodiments of the present disclosure, a method 100 may include a pretreatment step (not shown) performed on a FRC 105, before the FRC 105 is subjected to contacting 110 and / or treating 130. For example, a method 100 may include a soaking step that immerses the FRC 105 in a solvent to primarily induce swelling of the epoxy-amine, thereby enabling easier penetration of the solvent into the macromolecule and quick solubilization and / or deconstruction of the macromolecule (e.g., an epoxy-amine) in the subsequent contacting 110 and / or treating 130. In some embodiments of the present disclosure, swelling (i.e., pre-swelling) of a macromolecule may be achieved by immersing the FRC 105 in the same solvent used in the contacting 110, e.g., acetic acid. Such a soaking / pre-swelling step (not shown) may be achieved by maintaining the resultant liquid / solid mixture at a temperature that is less than or equal to the temperature utilized in the contacting 110. Thus, in some embodiments of the present disclosure, a soaking / pre-swelling step may be achieved at a temperature between 50 °C and 500 °C or between 120 °C and 320 °C, such that the soaking / pre-swelling is performed at a temperature that is less than the temperature utilized during contacting 110. In some embodiments of the present disclosure, a soaking / pre-swelling step (not shown) may include mechanical agitation.

[0063] Referring again to Figure 1, a fiber used in an FRC 105 may include at least one of a carbon fiber, a glass fiber, a ceramic fiber, a metal fiber, and / or a natural-occurring fiber. The orientation and / or form of a fiber used in an FRC 105 may be any commonly used in industry. For example, a fiber may be present as a plurality of fibers that are at least one of aligned, unaligned (i.e., random), and / or in a woven form. Fibers may be woven in a variety of ways commonly used in fabrics, textiles, and / or FRCs, including at least one of a plain weave, a twill weave, and / or a satin weave.

[0064] A macromolecule used in an FRC 105 may include at least one of a polymer and / or a resin. In some embodiments of the present disclosure, a macromolecule used in an FRC 105 may include at least one of a thermoset and / or a thermoplastic. In some embodiments of the present disclosure, a macromolecule may include an amine-cured epoxy (i.e., an epoxy-amine). The epoxy used to synthesize an epoxy-amine may include at least one of a di-epoxy, a tri-epoxy and / or a tetra-epoxy. Further, an epoxy used to synthesize the macromolecule used in an FRC may include at least one of a linear aliphatic epoxy, a cyclic aliphatic epoxy, and / or an aromatic epoxy.

[0065] Specific examples of epoxies that may be used to synthesize an epoxy-amine used in an FRC 105 are listed below. These are also examples of some of the materials that a method 100 as described herein can recover, either as pure compounds or mixtures of compounds that can be further reacted in a downstream step to produce an original starting epoxy. Thus, examples of epoxies that may be utilized (and eventually recovered) to produce one or more epoxy-amines (i.e., macromolecules) used to synthesize FRCs include at least one of 1,4-butanediol diglycidyl ether (BDODGE), sorbitol polyglycidyl ether (SPGE), polyethylene glycol diglycidyl ether (PEGDGE), bisphenol -A diglycidal ether (BADGE), 1,6-hexanediol bisglycidyl ether (HDODGE), diglycidyl terephthalate (TPADGE), 4,4'-Di(A,A-diglycidyl amino)diphenyl methane (TGMDA). Some of these epoxies are summarized in Table 1 below.

[0066] Table 1. Epoxies for Synthesizing Epoxy-Amines and for Recovery from a Recycled FRC

[0067] The amine used to synthesize an epoxy-amine used to manufacture an FRC 105 may include at least one of a linear aliphatic amine, a cyclic aliphatic amine, and / or an aromatic amine. These are also examples of some of the materials that a method 100 like that described herein can recover, either as pure compounds, and / or as one or more compounds that can be further deconstructed to an original starting amine in a downstream step and / or reacted in a downstream step to produce an original starting amine. Thus, examples of linear aliphatic amines that may be utilized (and eventually recovered) to produce an epoxy-amine used in an FRC 105 include at least one of trimethylhexamethylenediamine (TMD), 1,4-butylenediamine (14DAB), hexamethylenediamine (HMDA), triethylenetetramine (TETA), and / or N,N'- dimethyl- 1,4-butanediamine (DMP). Examples of cyclic aliphatic amines include at least one of isophorene diamine (IPDA), / ?-menthane-l,8-diamine (pMDA), and / or 1,4- cyclohexanediamine (14CHDA). Examples of aromatic amines include / ?-phenylenediamine (pPDA), 4,4-diaminodiphenylmethane (MDA), and 4,4'-diaminobiphenyl sulfone (DDS). These amines are summarized in Table 2 below.

[0068] Table 2. Amines for Synthesizing Epoxy-Amines and for Recovery from a Recycled FRC

[0069] Further, in some embodiments of the present disclosure, an anhydride may be used to synthesize an epoxy thermoset, where at least a portion of the anhydride is incorporated into the macromolecule. Examples of an anhydride that may be used to synthesize an epoxy thermoset used in an FRC 105 include at least one of methylhexa-hydrophthalic anhydride (MHHPA), glutaric anhydride (GA), and / or citraconic anhydride (CA). These are also examples of some of the materials that a method 100 like those described herein can recover, either as pure compounds and / or as one or more compounds that can be further converted to an original starting anhydride in a downstream step and / or reacted in a downstream step to produce an original starting anhydride. These anhydrides are summarized in Table 3 below.

[0070] Table 3. Anhydrides for Synthesizing Epoxy-Amines and for Recovery from a Recycled

[0071] FRC In some embodiments of the present disclosure, the deconstructing of an epoxy-amine (i.e., macromolecule) used in a starting FRC 105 directed to a method 100 like that described herein may result in the forming of at least one of phenol, phenyl acetate (PA), 4-isoproplyphenyl acetate (4-IPPA), bisphenol A (BP A), monoacetylated BPA (MABPA), diacetylated BPA (DABPA), diacetylated isophorone diamine (DAIPDA), isophorone diamine (IPDA), N-ethyl- N-phenylacetamide (EP A), acetanilide (ACE), diacetylated diaminediphenyl methane (DADDM), monoacetylated 4,4’ -diaminodiphenylmethane (MADDM), and / or diacetylated 4,4’-diaminodiphenylmethane (DADDM). These deconstruction products are summarized in Table 4 below.

[0072] Table 4. Polymer / Resin / Macromolecule Deconstruction Products Experimental Results:

[0073] Using the methods, systems, and materials described above, it is shown herein that acetic acid (solvent 107) efficiently depolymerizes epoxy-amine thermoset resins (i.e., macromolecules) prepared with both the aliphatic and aromatic amine hardeners commonly used in industrial FRC manufacturing. As shown herein, acetic acid cleaves both the ether (C-O) and amine (C- N) bonds, producing high yields deconstruction products, including BPA and amine derivatives. Near-quantitative carbon closure was achieved for the resin components, and the recovered fibers maintained their tensile modulus after resin deconstruction. The versatility of this approach is emphasized by the successful depolymerizing of a diverse set of epoxy-amine resins from post-industrial and post-consumer FRCs from the aerospace, marine craft, and sporting goods industries, all of which produced clean, intact, and reusable carbon fibers.

[0074] A successful deconstruction method for epoxy-amine FRCs ideally deconstructs the recalcitrant epoxy-amine material to chemically stable and soluble products that can be separated from intact, undamaged fibers. To develop a strategy that accomplishes both of these goals, reaction conditions were first evaluated using a model thermoset material (i.e., macromolecule), prepared from BPA diglycidyl ether as the epoxy component and isophorone diamine (IPDA) as the amine hardener without fiber reinforcement (see Figure 2A).

[0075] Using this model thermoset material, tests were conducted by contacting a starting mass of the material (in the form of a cube; no fiber) at temperatures between 200 °C and 300 °C in glacial acetic acid under 30 bar N2 for 3 hours. Contacting at temperatures below 240 °C produced no detectable small molecule products, and the thermoset resin cube was still clearly visible after 3 hours at 200 and 220 °C (see Panel A of Figure 2B). At 240 °C, the thermoset resin cubes began to disintegrate with only small pieces remaining after 3 hours (see Panel B of Figure 2B), which was accompanied by the presence of deconstruction products including a 10 mol% yield of BPA and its acetylated analogs, monoacetylated BPA (MABPA) and diacetylated BPA (DABPA), but no detectable diacetylated analog of IPDA (DAIPDA) (see Panel A of Figure 2C). Contacting at 260 °C, 280 °C, and 300 °C resulted in no solid remaining after 3 hours of contacting time (see Panel A of Figure 2B), with yields of BPA derivatives between 40 and 69 mol% (see Panel A of Figure 2C). The measured yields of DAIPDA varied between 50 and 95 mol% (see Panel A of Figure 2C) and demonstrate that acetolysis can simultaneously cleave both C-0 ether and C-N bonds, enabling recovery of the stabilized amine hardener as its corresponding acetamide. Time course experiments where the contacting (thermoset material only; no fiber) was completed at 260 °C and 280 °C (see Panel A of Figure 2B) showed that the aliphatic thermoset resin was fully solubilized between 30 minutes and 1 hour at 280 °C (see Panel B of Figure 2B) Gel permeation chromatography (GPC) analysis of the liquid fractions identified higher molar mass materials present at short reaction times, which gradually decreased over time (see Figure 2D). A decrease in soluble oligomer deconstruction products coincided with increased DAIPDA yields, with quantitative yield achieved after 4 hours. Deconstruction products BPA and acetylated-BPA derivative yields peaked at 3 hours. BPA was not fully stable at these temperatures, and the deconstruction products, phenol, phenyl acetate (PA), and 4-isopropyl phenylacetate (4-IPPA), increased as the temperature was changed from 260 °C to 300 °C (see Panel A of Figure 2C) and at longer reaction times at the optimal temperatures (see Panel B of Figure 2C). This degradation was further investigated in separate stability testing, where both BPA and its acetylated forms were found to undergo equivalent cleavage reactions at 280 °C.

[0076] Acetolysis experiments with an aromatic thermoset epoxy-amine (without fibers) system exhibited similar results. Again, prioritizing the incorporation of industrially relevant monomers, an aromatic thermoset epoxy-amine was synthesized with BPA diglycidyl ether as the epoxy component and 4,4'-diaminodiphenylmethane (DDM) as the amine crosslinker (see Figure 3A). Complete dissolution of the cured thermoset cube was achieved by contacting with acetic acid for a period of time between 1 and 2 hours at 280 °C (see Panels A and B of Figure 3D), suggesting retrieval of embedded fibers from composites with recalcitrant aromatic resin is also possible at these reaction times. The yield of deconstruction products, BPA derivatives was 30 mol% after 3 hours at 280 °C, and 79 mol% of the acetylated amine product was quantified after 5 hours at 280 °C (see Panel B of Figure 3B). A maximal yield of 87 mol% of the diacetylated DDM was achieved after 3 hours at 300 ° (see Panel A of Figure 3B). Figure 3C illustrates a GPC trace of the aromatic thermoset after 2 hours, 4 hours and 6 hours at 280 °C, 30 bar N2 and 20 mL acetic acid, compared to three standards, bisphenol A (BPA), monoacetylated BPA (MABPA), and diacetylated BPA (DABPA), according to some embodiments of the present disclosure.

[0077] Having verified the ability of acetolysis to deconstruct epoxy-amine resins and produce soluble products, model FRCs prepared in-house were studied next. This allowed accurate quantification of resin-derived monomers and, crucially, pre- and post-reaction fiber characterization to evaluate the impact of the process on fiber integrity. Two fiber reinforced composites (FRCs) were synthesized with the same monomers incorporated in the aliphatic- and aromatic-amine resins studied above, a 3k plain weave carbon fiber fabric (experimental single fiber tensile modulus = 254 GPa), with resin contents of 47.7 wt% and 42.7 wt%, respectively. The pristine fibers utilized were pre-sized for epoxy, containing 0.84 wt% sizing as determined by thermogravimetric analysis (TGA).

[0078] Contacting the aliphatic-amine crosslinked FRC with glacial acetic acid at 280 °C and 30 bar N2 for variable reaction times produced excellent yields of BPA and amine-derived products (see Figures 4A and 4B). Examination of the carbon fibers released after one hour of contacting via scanning electron microscopy (SEM) showed that the fibers were free of resin (i.e., macromolecule) and showed no visible pitting or cracking (see Panels A-C of Figure 4C). Complete resin removal was confirmed via TGA with an average of 0.05 wt% resin remaining (99.9% removed) on the fibers after the contacting, with similar results observed after 4 hours of contacting. The absence of a -0.8% mass loss also indicates the stripping of the sizing from the recovered carbon fiber (rCF).

[0079] Treatment of the aromatic amine-cured (see Figure 3A) FRC also produced good results, with BPA and aromatic amine derivatives (see Figure 4D) yields of 96 and 59%, respectively, at 4 hours (see Figure 4E). The reaction time required to achieve complete resin removal was longer for the aromatic-amine FRC, and SEM images of recovered fibers after one hour of contacting clearly showed partial resin deconstruction (see Panels A-C of Figure 4F), but the mass loss percentage from TGA showed that minimal resin was separated from the fibers. However, after 2, 3, and 4 hours, the fibers were fully clean (i.e., free of macromolecule) by both SEM (see Panel B of Figure 4F) and TGA). For both the aliphatic and aromatic-amine materials, the mechanical properties of the post-reaction recovered carbon fibers were examined via single fiber tensile testing (see Panel D of Figures 4C and 4F, respectively. The tensile moduli of pristine virgin carbon fibers (vCF) and all post-reaction rCF samples, except one (aromatic FRC, 4 hour reaction), were statistically equivalent, which indicates that the structural integrity of the fibers remains intact even at extended reaction times.

[0080] With confirmation that acetolysis (i.e., FRC contacting with acetic acid) can deconstruct model epoxy-amine resins into soluble monomers and preserve the mechanical properties of the fibers, next the applicability of acetolysis to real post-consumer and post-industrial waste fiber- reinforced composites using polymers instead of resins was investigated. Five waste substrates were obtained with unknown resin composition, additives, and filler chemistries as shown in Figures 5A-6E, namely: an aerospace-grade FRC (see Figure 5A), representing an offcut from airplane manufacturing, a FRC aluminum honeycomb panel from a racing sailboat (see Figure 5B), a post-consumer FRC from a mountain bike frame (see Figure 5C), a postconsumer FRC orthosis (see Figure 5D), and a glass fiber-reinforced polymer (an FRC using a polymer instead of a resin) from a post-service tidal turbine blade (see Figure 5E). These materials were subjected to no pre-treatment, except downsizing to fit into 75-mL reactors, before contacting with glacial acetic acid at 280 °C and 30 bar N2 for 2 hours. SEM imaging of the rCF was used to visually evaluate resin removal and inspect the fibers for damage, and TGA of the starting material and the rCF for residual resin content determination. Lastly, gas chromatography -mass spectrometry (GC-MS) was used to characterize the composition of the soluble fraction after deconstruction.

[0081] For the aerospace FRC sample, some residual resin was visible on the fibers after reaction for all FRC weight loadings (see Figure 5A). For the 2.5 wt% loading reaction in Figure 5A, 88.8% of the resin was removed (pre-reaction 27.6% resin, post-reaction 3.1% resin) (see Figure 5A), while post-reaction resin contents were slightly higher for the 5 and 10 wt% loadings (both -3.7% residual). The “resin” remaining on post-reaction fibers is likely a polysulfone thermoplastic additive, often incorporated to meet the durability demands of the aerospace industry, as supported by infrared spectroscopy of the post-reaction rCF surface. Additionally, from the SEM images (see Figure 5A), the residual resin was present as “droplets” rather than a uniform coating, indicative of dissolution and subsequent deposition of the thermoplastic on the fibers as the reaction cooled.

[0082] The marine FRC contained two visibly distinct carbon fiber sheets and an aluminum honeycomb core. Prior to acetolysis, the aluminum was mostly cut out but could not be entirely removed, so it presented an opportunity to examine how residual metal affected the optimized acetolysis protocol. Acetolysis was successful on both the front and the back FRC panels, and fibers recovered from both appear clean and undamaged by SEM (see Figure 5B). TGA indicated 95.5% (front panel: pre-reaction 31.4% resin, post-reaction 1.4% resin) and 97.0% (back panel: pre-reaction 33.8% resin post-reaction 1.0% resin) (see Figure 5B) resin removal, clearly showing that any residual aluminum content had no deleterious effect on the reaction.

[0083] The mountain bike and medical device FRC materials were both amenable to resin removal via acetolysis. Indeed, 99.5+% resin removal was achieved for both substrates after some optimization of weight loadings, with residual resin contents of 0.1% and 0.2%, respectively (see Figured 5C and 5D). SEM images of the post-reaction fibers for both substrates also show clean, undamaged fibers (see Figures 5C and 5D). The end-of-life glass fiber-reinforced polymer tidal turbine blade provided an opportunity to investigate the effect of acetolysis on glass fibers. Of all the materials reported herein, this glass fiber-reinforced polymer substrate proved most amenable to acetolysis. In our initial experiments at 5 wt% loading, a resin removal of 99.8% was achieved (see Figure 5E). Since the glass fiber-reinforced polymer material was significantly denser than its carbon fiber counterparts, it was possible to run reactions at much higher weight loadings, up to 15 and 22.5 wt%, both of which resulted in nearly complete resin removal with confirmation from SEM images showing clean, pristine glass fibers (see Figures 5E).

[0084] For all optimized post-consumer deconstruction reactions, GC-MS analysis was performed on the crude mixtures to identify resin components. In all cases, we observed a complex mixture of deconstruction products. While BPA and its degradation products (e.g., phenol, isopropylphenol, and / or their acetates) are present in all samples except the orthotic, other bisphenols such as bisphenol-F and bisphenol-AF (in the aerospace material) were detectable. For the marine application FRC and tidal turbine glass fiber-reinforced polymer, DAIPDA is detectable along with other amine curing agents, but it appears that no DAIPDA is present in the other substrates. Overall, the chemical complexity of these authentic waste streams was clear in the post-reaction mixtures.

[0085] Figure 6 illustrates a plot of mass recovery versus time for seven different epoxy-amines due to contacting with acetic acid, with the epoxy-amine compositions tabulated in Table 5, according to some embodiments of the present disclosure.

[0086] Table 5. Epoxy-amine Compositions and Dissolution Times a residual = 22.7 wt%,bresidual = 3.1 wt%

[0087] Experimental Methods:

[0088] Acetolysis of thermoset models: In a typical reaction, the substrate was added to 20 mL glacial acetic acid in a titanium grade 4 (Ti 99 minimum commercially pure titanium) high-pressure Parr reactor. The reactor was stirred at 650 rpm and pressurized to 30 bar three times before being leak tested at 80 bar. Upon completion of the leak test, the reactor was then pressurized to 30 bar of N2 prior to heating to the desired temperature for the desired reaction time. To quench the reaction, the reactor was removed from heat and placed into an ice bath until cool, and the measured pressure returned to the starting pressure (for ~15 mins), at which point the reactor was depressurized. The resultant liquid sample matrix was filtered over a 10 pm plastic filter and transferred to a 20 mL scintillation vial. No post-reaction workup was conducted. An aliquot of this sample matrix was diluted with a 50 / 50 mixture of HPLC-grade acetone and nano-pure H2O for HPLC analysis.

[0089] Modification to the procedure above for the acetolysis of carbon fiber-reinforced epoxy-amine composites and post-consumer materials: The reactions were not stirred unless otherwise noted. If stirred, the reactions were stirred at 650 rpm. Upon reaction completion, the reactor was cooled and depressurized as above. The reaction sample was filtered over a 10 pm filter to separate the dissolved epoxy-amine monomer products from the carbon fiber. The acetic acid filtrate was collected in a vial. Into a separate flask, the recovered carbon fiber was rinsed first with 15 mL acetic acid, then twice with 10 mL acetone (this wash was discarded). The filter with the carbon fiber was dried in a vacuum oven overnight at 50 °C. One aliquot from the initial reaction mixture and one aliquot from the rinsed acetic acid mixture were diluted in 50 / 50 HPLC grade acetone and nano-pure H2O for HPLC analysis.

[0090] Preparation of epoxy amine thermosets: Model epoxy amine thermosets were prepared according to the procedure previously reported by DiPucchio etal. (ACS Sustainable Chemistry & Engineering 11, 16946-16954 (2023)), which is incorporated herein by reference in its entirety.

[0091] Aliphatic thermoset FRC synthesis: 2 sheets of 3k weave carbon fiber (purchased from Fiberglast, approximate dimensions of 8 in x 12 in) were warmed to 40 °C in an oven. Bisphenol-A diglycidyl ether (BADGE) (11.1461 g, 79.86 wt%) and isophorone diamine (IPDA) (2.8105 g, 20.14 wt%) were added to a plastic beaker with a screw cap and heated to 120 °C. The hot resin components were placed in a spin-mixer for 5 mins to homogenize the mixture. While the resin was mixing, a steel plate covered in a layer of aluminum foil was placed on a separate hot plate at 80 °C. One carbon fiber sheet was removed from the oven and placed atop the warmed steel plate, and approximately one half of the resin mixture was poured onto the CF sheet and evenly spread with a squeegee tool. The second sheet was removed from the oven, placed atop the now resin-impregnated first sheet, and the remaining resin was poured over and spread evenly, and then a second steel sheet covered in a layer of aluminum foil was placed on top. The uncured composite was transferred to a kiln, compressed with an 8 lb weight and subjected to the following cure cycle: 80 °C for 6 hrs, 100 °C for 12 h, then 180 °C for 1 h with a ramp rate of 1.5 °C / min between each step.

[0092] Thermogravimetric analyses (TGA) were performed on a TA Instruments TGA5000 with platinum pans under a constant 10 mL / min flow of N2. NMR spectra were taken on a 400 MHz Bruker Avance III spectrometer equipped with a Prodigy LN2 cry oprobe and referenced to the solvent residuals for chloroform: 7.27 ppm for1H and 77.00 for13C. Fourier-transform infrared (FT-IR) spectra were recorded with a Perkin-Elmer Spectrum 3 FT-IR Spectrometer equipped with a diamond attenuated total reflectance (ATR) attachment. All other equipment details are provided within their respective experimental descriptions.

[0093] Pre-reaction resin content determination: The resin content of the post-consumer materials was determined via thermogravimetric analysis using the following standard procedure. A small (~10 mg) piece of composite was placed on a platinum TGA pan and loaded into the instrument. Beginning at ambient temperature, a 10 °C / min ramp to 600 °C was performed and the sample was held at that temperature for 15 min to confirm complete resin degradation. Three runs for each in-house CFRP and five runs for each post-consumer CFRP sample were performed, and care was taken to select pieces from diverse areas of the materials so that the reported average more accurately represents the reaction substrate. The weight change from 120 to 600 °C was measured.

[0094] Resin content of post-reaction fibers via thermogravimetric analysis: A high-volume aluminum DSC pan was weighed on an analytical balance (0.01 mg precision, -250 mg tare weight per pan) and then the loose, post-reaction fibers were packed tightly into the pan. The pan was sealed, and two small holes were pierced into the lid to enable off-gassing. The pan was transferred to a platinum TGA pan, loaded into the instrument, and the thermogram was collected with the following procedure. First the temperature was rapidly raised to 150 °C (“jump” command on TA instrument’s TGAs) and held steady for 15 min to volatilize residual acetic acid and dry the substrate, then the temperature was raised to 600 °C at a rate of 10 °C / min. A 15-minute isotherm at 600 °C confirmed that all residue had degraded, and the mass loss was calculated accounting for the tare weight of the DSC pan. This process was repeated in triplicate, and the average calculated. Resin removal percentage was calculated using Equation SI. In some cases, it was necessary to apply data smoothing algorithms (native in TA’s Trios software) to the thermogram to account for oscillations in the measured weight due to the gas flow inside the instrument. This manifests as jagged lines in the plots below, and is particularly pronounced on some of the cleaner samples due to the extremely small weight changes observed (which approach the limits of precision for this instrument). All post-reaction figures below and in the main text are plotted accounting for the tare weight of the DSC pan. That is, only the mass of the fibers and residual resin is plotted. In this Supplementary Materials document, the y-axis scales are adjusted to afford maximum visibility of the weight change.

[0095] Resin removal % = 100

[0096] Single fiber tensile testing: Individual pristine and recovered carbon fibers were extracted and mounted on 1” x 1” paper samples with the center cut out in a diamond pattern. Starbond high strength 5-minute epoxy hardener glue was used to adhere the fibers to the paper. The dried, mounted fiber samples were loaded on a TA Instruments dynamic mechanical analyzer (DMA) Q800 in tensile mode. Once mounted, the edges of the paper were cut such that only the fiber was to be in tension. The fiber samples were then stretched at a displacement rate of 2.5 um / min. Displacement and force measurements were recorded after fibers were under 0.001 N of pretension. All fiber samples were assumed to be 3 pm in radius as confirmed with SEM images (fig. S34) when calculating tensile strength. Youngs modulus (E) was calculated as the slope of the stress strain curve from 0 to 0.5% strain.

[0097] Examples:

[0098] Example 1. A method comprising: contacting a fiber-reinforced composite with a solvent, wherein: the fiber-reinforced composite comprises a fiber and a macromolecule, the contacting results in the formation of a mixture comprising a liquid phase comprising the solvent and the macromolecule solubilized in the solvent and a solid phase comprising the fiber, and separating the mixture resulting in a first stream comprising the solid phase and a second stream comprising the liquid phase.

[0099] Example 2. The method of Example 1, wherein the solvent comprises a carboxylic acid functional group.

[0100] Example 3. The method of either Example 1 or Example 2, wherein the solvent comprises a dicarboxylic acid.

[0101] Example 4. The method of any one of Examples 1-3, wherein the solvent comprises at least one of acetic acid, succinic acid, or a combination thereof. Example 5. The method of any one of Examples 1-4, wherein the fiber comprises at least one of a carbon fiber, a glass fiber, a ceramic fiber, a metal fiber, a natural -occurring fiber, or a combination thereof.

[0102] Example 6. The method of any one of Examples 1-5, wherein the fiber is a plurality of fibers that are at least one of aligned, unaligned, woven, or a combination thereof.

[0103] Example 7. The method of any one of Examples 1-6, wherein the plurality of fibers is woven in at least one of a plain weave, a twill weave, a satin weave, or a combination thereof.

[0104] Example 8. The method of any one of Examples 1-7, wherein the macromolecule comprises at least one of a polymer, a resin, or a combination thereof.

[0105] Example 9. The method of any one of Examples 1-8, wherein the macromolecule comprises at least one of a thermoset, a thermoplastic, or a combination thereof.

[0106] Example 10. The method of any one of Examples 1-9, wherein the macromolecule comprises an epoxy-amine.

[0107] Example 11. The method of any one of Examples 1-10, wherein an epoxy used to synthesize the epoxy-amine comprises at least one of a di-epoxy, a tri-epoxy, a tetra-epoxy, or a combination thereof.

[0108] Example 12. The method of any one of Examples 1-11, wherein the epoxy comprises at least one of a linear aliphatic epoxy, a cyclic aliphatic epoxy, an aromatic epoxy, or a combination thereof.

[0109] Example 13. The method of any one of Examples 1-12, wherein the epoxy comprises at least one of 1,4 -butanediol diglycidyl ether (SPGE), 1,4-butanediol diglycidyl ether (BDODGE), polyethylene glycol diglycidyl ether (PEGDGE), bisphenol-A diglycidal ether (BADGE), hexanediol diglycidal ether (HDGE), butanediol diglycidal ether (BDGE), glycol diglycidyl ether (EGDGE), diglycidyl terephthalate (TPADGE), or a combination thereof.

[0110] Example 14. The method of any one of Examples 1-13, wherein an amine used to synthesize the epoxy-amine comprises at least one of a linear aliphatic amine, a cyclic aliphatic amine, an aromatic amine, or a combination thereof.

[0111] Example 15. The method of any one of Examples 1-14, wherein the linear aliphatic amine comprises at least one of trimethylhexamethylenediamine, 1,4-butylenediamine (14DAB), hexamethylenediamine (HMD A), tri ethylenetetramine (TETA), A,A'-dimethyl-l,4- butanediamine (DMP), or a combination thereof. Example 16. The method of any one of Examples 1-15, wherein the cyclic aliphatic amine comprises at least one of isophorene diamine (IPDA), -Menthane- l ,8-diamine (pMDA), 1,4- cyclohexanediamine (14CHDA), / ?-phenylenediamine (pPDA), or a combination thereof.

[0112] Example 17. The method of any one of Examples 1-16, wherein an anhydride is used to synthesize the epoxy-amine.

[0113] Example 18. The method of any one of Examples 1-17, wherein the anhydride comprises at least one of methylhexa-hydrophthalic anhydride (MHHPA), glutaric anhydride (GA), citraconic anhydride (CA), or a combination thereof.

[0114] Example 19. The method of any one of Examples 1-18, wherein the contacting is performed at a temperature between 50 °C and 500 °C or between 180 °C and 320 °C.

[0115] Example 20. The method of any one of Examples 1-19, wherein the contacting is performed for a period of time between 5 minutes and 12 hours or between 30 minutes and 3 hours.

[0116] Example 21. The method of any one of Examples 1-20, wherein the contacting is performed in an environment comprising oxygen and nitrogen or air.

[0117] Example 22. The method of any one of Examples 1-21, wherein the contacting is performed in an inert environment.

[0118] Example 23. The method of any one of Examples 1-22, wherein the inert atmosphere comprises at least one of helium, argon, xenon, or a combination thereof.

[0119] Example 24. The method of any one of Examples 1-23, wherein the contacting is performed in a unit operation operated in a continuous fashion utilizing at least one of a continuous stirred tank reactor (CSTR), a packed bed reactor (i.e., flow-through reactor), or a combination thereof.

[0120] Example 25. The method of any one of Examples 1-24, wherein the separating is performed using at least one of a settling method (i.e., gravity), filtration, centrifugation, or a combination thereof.

[0121] Example 26. The method of any one of Examples 1-25, further comprising washing the solid phase, resulting in fiber that is essentially solvent free, wherein the washing utilizes at least one of a organic solvent, water, or a combination thereof. Example 27. The method of any one of Examples 1-26, further comprising treating the liquid phase, resulting in the solubilized macromolecule deconstructing into at least one of an oligomer, a smaller molecule, or a combination thereof.

[0122] Example 28. The method of any one of Examples 1-27, wherein at least a portion of the treating is performed during the contacting.

[0123] Example 29. The method of any one of Examples 1-28, wherein at least a portion of the treating is performed subsequent to the contacting.

[0124] Example 30. The method of any one of Examples 1-29, wherein the treating comprises containing the liquid phase in a volume for a residence time between 5 minutes and 12 hours or between 30 minutes and 3 hours.

[0125] Example 31. The method of any one of Examples 1-30, wherein the treating is performed at a temperature between 50 °C and 500 °C or between 180 °C and 320 °C.

[0126] Example 32. The method of any one of Examples 1-31, wherein at least one of the contacting, the treating, or a combination thereof further comprises agitating the liquid phase and the solid phase.

[0127] Example 33. The method of any one of Examples 1-32, wherein the agitating comprises at least one of mechanical agitation, bubbling a gas through the liquid phase and the solid phase, or a combination thereof.

[0128] Example 34. The method of any one of Examples 1-33, wherein the deconstructing results in the forming of at least one of phenol, phenyl acetate (PA), 4-isoproplyphenyl acetate (4-IPPA), bisphenol A (BPA), monoacetylated BPA (MABPA), diacetylated BPA (DABPA), diacetylated isophorone diamine (DAIPDA), isophorone diamine (IPDA), N-ethyl-N- phenyl acetamide (EP A), acetanilide (ACE), or a combination thereof.

[0129] Example 35. The method of any one of Examples 1-34, wherein the epoxy-amine has a structure as defined by Structure I: wherein: each of Ri and R2independently comprise at least one an alkyl group, an aryl group, or a combination thereof, R3 comprises and at least one of a hydrogen atom, an alkyl group, an aryl group, or a combination thereof, Xi and X2 independently comprise at least one of a nitrogen atom, an oxygen atom, or a combination thereof, and n is between 2 and 10,000.

[0130] Example 36. The method of any one of Examples 1-35, wherein Xi is defined by Structure II or Structure III: III) wherein: R4 and R5 are independently at least one of an alkyl group, an aryl group, a halogen, or a combination thereof.

[0131] Example 37. The method of any one of Examples 1-36, wherein Xi comprises at least one of Structures IV - VII:

[0132]

[0133] 38. The method of any one of Examples 1-37, wherein the epoxy-amine has a structure as defined by Structure VIII:

[0134] Example 39. The method of any one of Examples 1-38, wherein the epoxy-amine has a structure as defined by at least one of Structures VIII-XI:

[0135]

[0136] Example 40. The method of any one of Examples 1-38, wherein the epoxy-amine deconstructs according to resulting in the formation of glycerol triacetate, an acetate derived from the epoxy component of the epoxy-amine, and an amide derived from the amine component of the epoxy-amine, wherein Ri and R2 independently comprise an alkyl group or an aryl group; R3 comprises a hydrogen atom, an alkyl group, or an aryl group; and Xi and X2 independently comprise a nitrogen or an oxygen atom.

[0137] The embodiments described herein should not necessarily be construed as limited to addressing any of the particular problems or deficiencies discussed herein. Further, when a particular feature, structure, or characteristic is described in connection with an embodiment, it is submitted that it is within the knowledge of one skilled in the art to affect such feature, structure, or characteristic in connection with other embodiments whether or not explicitly described.

[0138] As used herein the term “substantially” is used to indicate that exact values are not necessarily attainable. By way of example, one of ordinary skill in the art will understand that in some chemical reactions 100% conversion of a reactant is possible, yet unlikely. Most of a reactant may be converted to a product and conversion of the reactant may asymptotically approach 100% conversion. So, although from a practical perspective 100% of the reactant is converted, from a technical perspective, a small and sometimes difficult to define amount remains. For this example of a chemical reactant, that amount may be relatively easily defined by the detection limits of the instrument used to test for it. However, in many cases, this amount may not be easily defined, hence the use of the term “substantially”. In some embodiments of the present invention, the term “substantially” is defined as approaching a specific numeric value or target to within 20%, 15%, 10%, 5%, or within 1% of the value or target. In further embodiments of the present invention, the term “substantially” is defined as approaching a specific numeric value or target to within 1%, 0.9%, 0.8%, 0.7%, 0.6%, 0.5%, 0.4%, 0.3%, 0.2%, or 0.1% of the value or target.

[0139] As used herein, the term “about” is used to indicate that exact values are not necessarily attainable. Therefore, the term “about” is used to indicate this uncertainty limit. In some embodiments of the present invention, the term “about” is used to indicate an uncertainty limit of less than or equal to ±20%, ±15%, ±10%, ±5%, or ±1% of a specific numeric value or target. In some embodiments of the present invention, the term “about” is used to indicate an uncertainty limit of less than or equal to ±1%, ±0.9%, ±0.8%, ±0.7%, ±0.6%, ±0.5%, ±0.4%, ±0.3%, ±0.2%, or ±0.1% of a specific numeric value or target.

[0140] The provided discussion and examples have been presented for purposes of illustration and description. The foregoing is not intended to limit the aspects, embodiments, or configurations to the form or forms disclosed herein. In the foregoing Detailed Description for example, various features of the aspects, embodiments, or configurations are grouped together in one or more embodiments, configurations, or aspects for the purpose of streamlining the disclosure. The features of the aspects, embodiments, or configurations, may be combined in alternate aspects, embodiments, or configurations other than those discussed above. This method of disclosure is not to be interpreted as reflecting an intention that the aspects, embodiments, or configurations require more features than are expressly recited in each claim. Rather, as the following claims reflect, inventive aspects lie in less than all features of a single foregoing disclosed embodiment, configuration, or aspect. While certain aspects of conventional technology have been discussed to facilitate disclosure of some embodiments of the present invention, the Applicants in no way disclaim these technical aspects, and it is contemplated that the claimed invention may encompass one or more of the conventional technical aspects discussed herein. Thus, the following claims are hereby incorporated into this Detailed Description, with each claim standing on its own as a separate aspect, embodiment, or configuration.

[0141] The terms and expressions which have been employed herein are used as terms of description and not of limitation, and there is no intention in the use of such terms and expressions of excluding any equivalents of the features shown and described or portions thereof, but it is recognized that various modifications are possible within the scope of the invention claimed. Thus, it should be understood that although the present invention has been specifically disclosed by preferred embodiments, exemplary embodiments and optional features, modification and variation of the concepts herein disclosed may be resorted to by those skilled in the art, and that such modifications and variations are considered to be within the scope of this invention as defined by the appended claims. The specific embodiments provided herein are examples of useful embodiments of the present invention and it will be apparent to one skilled in the art that the present invention may be carried out using a large number of variations of the devices, device components, methods steps set forth in the present description. As will be obvious to one of skill in the art, methods, and devices useful for the present methods can include a large number of optional composition and processing elements and steps.

[0142] All art-known functional equivalents, of any such materials and methods are intended to be included in this invention. The terms and expressions which have been employed are used as terms of description and not of limitation, and there is no intention that in the use of such terms and expressions of excluding any equivalents of the features shown and described or portions thereof, but it is recognized that various modifications are possible within the scope of the invention claimed. Thus, it should be understood that although the present invention has been specifically disclosed by preferred embodiments and optional features, modification and variation of the concepts herein disclosed may be resorted to by those skilled in the art, and that such modifications and variations are considered to be within the scope of this invention as defined by the appended claims.

Claims

CLAIMSWhat is claimed is:

1. A method comprising: contacting a fiber-reinforced composite with a solvent, wherein: the fiber-reinforced composite comprises a fiber and a macromolecule, the contacting results in the formation of a mixture comprising a liquid phase comprising the solvent and the macromolecule solubilized in the solvent and a solid phase comprising the fiber, and separating the mixture resulting in a first stream comprising the solid phase and a second stream comprising the liquid phase.

2. The method of claim 1, wherein the solvent comprises a carboxylic acid functional group.

3. The method of claim 2, wherein the solvent comprises a dicarboxylic acid.

4. The method of claim 2, wherein the solvent comprises at least one of acetic acid, succinic acid, or a combination thereof.

5. The method of claim 1, wherein the fiber comprises at least one of a carbon fiber, a glass fiber, a ceramic fiber, a metal fiber, a natural -occurring fiber, or a combination thereof.

6. The method of claim 1, wherein the macromolecule comprises at least one of a polymer, a resin, or a combination thereof.

7. The method of claim 6, wherein the macromolecule comprises at least one of a thermoset, a thermoplastic, or a combination thereof.

8. The method of claim 6, wherein the macromolecule comprises an epoxy-amine.

9. The method of claim 1, wherein the contacting is performed at a temperature between 50 °C and 500 °C.

10. The method of claim 1, wherein the contacting is performed for a period of time between 5 minutes and 12 hours.

11. The method of claim 1, wherein the separating is performed using at least one of a settling method, filtration, centrifugation, or a combination thereof.

12. The method of claim 1, further comprising washing the solid phase, resulting in fiber that is essentially solvent free, wherein the washing utilizes at least one of a organic solvent, water, or a combination thereof.

13. The method of claim 1, further comprising treating the liquid phase, resulting in the solubilized macromolecule deconstructing into at least one of an oligomer, a smaller molecule, or a combination thereof.

14. The method of claim 13, wherein at least a portion of the treating is performed during the contacting.

15. The method of claim 13, wherein the deconstructing results in the forming of at least one of phenol, phenyl acetate (PA), 4-isoproplyphenyl acetate (4-IPPA), bisphenol A (BPA), monoacetylated BPA (MABPA), diacetylated BPA (DABPA), diacetylated isophorone diamine (DAIPDA), isophorone diamine (IPDA), N-ethyl-N-phenylacetamide (EPA), acetanilide (ACE), or a combination thereof.

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