Method for extracting thermosetting resin part for decomposition and reuse

Abstract

A method of extracting a thermoset epoxy material portion from a composite structure comprising a matrix of thermoset epoxy material having a network structure and embedded solid element (s) is described. The method includes providing a swelling fluid and immersing the composite structure with the swelling fluid, including swelling the thermoset epoxy material matrix, the swelling fluid entering the network structure of the thermoset epoxy material matrix for a sufficient time to mechanically disrupt the network structure, and immersing the composite structure with the swelling fluid. To form a large number of thermoset epoxy material fractions that are decoupled from the solid element. At least a portion of the thermoset epoxy material portion is separated from the solid element to obtain a swelling fluid slurry comprising the portion of the thermoset epoxy material portion in a swelling fluid. The swelling fluid comprises at least 1 mol / L formic acid.

Description

Technical Field

[0001] The present invention relates to a method for extracting a thermosetting resin fraction from a composite material for decomposition and reuse. Background Art

[0002] The use of thermosetting polymer materials, especially in the form of complex composite structures, is generally increasing. In particular, in the production of raised panels or, for example, wind turbine blades, the use of epoxy materials comprises complex compositions of elements, such as metal layers and / or fiber layers, for example, glass fiber layers, embedded in epoxy resin.

[0003] Many attempts have been made to reuse such thermosetting resin materials.

[0004] US10,968,329 describes a method for recovering decomposition products of a thermosetting resin cured product, the method comprising the steps of bringing an object to be treated containing the thermosetting resin cured product into contact with a treatment liquid containing an alkali metal compound and an alcohol solvent to decompose and dissolve the thermosetting resin cured product; mixing the treatment liquid in which the decomposition products of the thermosetting resin cured product are dissolved with an acidic aqueous solution to separate the mixture into an aqueous layer and an organic layer containing the decomposition products; and recovering the organic layer.

[0005] WO2017 / 175100 discloses a method for separating a reinforcing material from a polymer matrix composite material comprising a reinforcing material within a thermosetting polymer matrix. The method comprises: (i) contacting the polymer matrix composite material with a recycling composition comprising a phenolic compound and an acidic or basic catalyst. Upon contact with the recycling composition, the thermosetting polymer matrix degrades through chain scission and becomes soluble in the recycling composition, releasing the reinforcing material into the recycling composition.

[0006] CN113603929 describes a method for recycling epoxy resin composite materials, the resulting glass fibers, and applications of the glass fibers, and relates to the field of organic solid material recovery. The preparation method specifically comprises the following steps: S1, mixing the epoxy resin composite material with a composite solvent, placing the mixture in a pressure vessel, controlling the reaction temperature to 120-150 degrees Celsius, and reacting for 3-7 hours to produce a solid-liquid mixture; and S2, filtering the solid-liquid mixture to obtain a decomposition filtrate and a solid-phase product, wherein the solid-phase product is glass fiber, which is used in the fields of waterproof substrates, energy-saving auxiliary reinforcement materials, reinforced cementing materials, and architectural decorative materials. The composite solvent is used to degrade epoxy resin composite materials, with a simple experimental process, mild reaction conditions, and excellent product performance. The composite solvent is also environmentally friendly and economically beneficial.

[0007] Generally speaking, these prior art methods are suitable for small epoxy components or prepreg components. However, these methods require large reactors for heating or pressing, and / or require the epoxy products to be relatively small, or require cutting or grinding the epoxy. Consequently, these methods are not ideal or suitable for applications involving recycling thermosetting polymer materials, such as epoxy resins from large panels or, for example, wind turbine blades, which contain complex components embedded in cured epoxy resin.

[0008] New epoxy resin compositions that are easier to disassemble have been proposed, for example as described in WO18050189, but there is still no documented evidence that such new epoxy resins are fully comparable to conventional epoxy resins in terms of mechanical properties and / or cost.

[0009] Therefore, there remains a need for new and efficient methods for extracting thermoset resin parts from large composite structures. Summary of the Invention

[0010] The object of the present invention is to provide a relatively fast and cost-effective method for extracting thermosetting polymer parts from large composite structures, such as wind turbine blades or other relatively large structures comprising a complex composition of elements embedded in epoxy material, such as metal layers, fiber layers and / or other elements.

[0011] In one embodiment, it is an object to provide a method for extracting a thermosetting epoxy portion from a relatively large composite structure comprising a thermosetting epoxy matrix, such as a wind turbine blade, wherein the extracted thermosetting epoxy portion is in the form of particles suitable for chemical decomposition and, optionally, reuse in the production of fresh epoxy resin.

[0012] In one embodiment, it is an object to provide a method for extracting thermosetting epoxy material portions from large composite structures that is economical and efficient and that can be performed relatively quickly even when the composite structures are very large.

[0013] These and other objects have been achieved by the present invention or embodiments thereof as defined in the claims and / or described herein below.

[0014] It has been discovered that the present invention or embodiments thereof have numerous additional advantages which will become apparent to those skilled in the art from the following description.

[0015] The inventors of the present invention have discovered that, as defined in the claims, a surprisingly effective method for breaking down epoxy materials into relatively small epoxy components, even in large and complex composite structures, can be provided by using a swelling fluid comprising formic acid. This method is not only extremely effective but also requires very little manpower, making it economically attractive. Furthermore, it has been discovered that the swelling fluid can be reused in this method, thereby also achieving a very low cost for the swelling fluid.

[0016] Since even very large composite structures can be used without cutting into smaller pieces, this method is highly attractive for extracting thermosetting resin parts from building elements of composite materials or building elements containing composite materials, as will be described further below.

[0017] As used herein, the phrase "composite structure" refers to any structure comprising a thermosetting epoxy matrix and at least one embedded solid element of a non-thermosetting epoxy material. Typically, there are several embedded solid elements, for example, arranged in layers. Examples of embedded solid elements include reinforcing elements such as fibers and / or metal elements, polymer elements, filler elements, glue, fasteners, and the like. Composite structures may also include non-embedded or partially embedded solid elements or portions thereof, such as coatings, for example, paint and / or UV / weatherproof coatings.

[0018] The term "embedded" is understood herein to mean that the embedded element is at least partially embedded in the matrix, preferably such that at least 50% by volume of the element is below the surface of the matrix. Advantageously, the embedded element is completely embedded in the matrix, i.e., the embedded element is surrounded by the matrix.

[0019] The term "solid element" is understood herein to mean any solid element that is at least partially embedded in an epoxy matrix before or in a swollen state.

[0020] Thus, the solid element or elements include all elements other than the thermosetting epoxy matrix and parts thereof.

[0021] The term "network structure" is understood herein to refer to the cross-linked structure of the thermosetting epoxy matrix, which is established when the epoxy resin is cured to form the thermosetting epoxy matrix.

[0022] The term "thermosetting epoxy matrix" is understood herein to mean a matrix comprising a cured epoxy resin, also known as a polyepoxide. Curing is generally carried out by mixing with a hardener.

[0023] The terms "hardener" and "curing agent" are used interchangeably to refer to the component responsible for reacting with the epoxy groups of the epoxy resin to produce a thermosetting epoxy matrix.

[0024] The term "soaking" is understood herein to mean that the composite structure is thoroughly wetted, preferably such that a major area of ​​the surface of the composite structure is wetted. Advantageously, the phrase "soaking the composite structure" means that the composite structure is completely wetted by the swelling fluid.

[0025] The term "spraying" is understood herein to mean soaking the composite material structure by spraying so that the main area of ​​the composite material structure surface is completely wetted. Spraying can be continuous or discontinuous, with spraying periods and non-spraying periods, and the non-spraying periods are advantageously short enough to dry the wetted surface of the composite material structure. Preferably, the non-spraying period is less than 10 minutes, such as less than 5 minutes, such as less than 1 minute. Advantageously, the spraying period is longer than the non-spraying period.

[0026] The term "spray" includes splashing and spraying.

[0027] The terms "cleaning" and "cleaning process" are understood herein to mean cleaning a previously embedded solid element with a cleaning fluid to obtain a cleaning fluid slurry comprising at least a portion of the thermosetting resin portion in the cleaning fluid.

[0028] When flushing with a fluid (flushing fluid) is used for cleaning, the cleaning and cleaning process are referred to as "flushing" and "flushing process", respectively.

[0029] The term "swelling fluid" as used herein is understood to mean a fluid comprising formic acid and capable of swelling the thermosetting epoxy matrix. Advantageously, the swelling fluid is at least partially liquid under the swelling conditions. Conveniently, the swelling fluid can be a mixture of gas and liquid under the swelling conditions. In one embodiment, the swelling fluid is liquid under the swelling conditions.

[0030] The term "cleaning fluid" is understood herein to mean a liquid containing fluid under cleaning conditions (temperature and pressure), preferably comprising or consisting of water. Conveniently, the cleaning fluid comprises surfactant(s), for example in the form of a detergent, preferably a low-foaming detergent.

[0031] The term "flushing fluid" is understood herein to mean a sag, a liquid or a mixture thereof under flushing conditions (temperature and pressure). Conveniently, the flushing fluid may comprise water or steam or compressed air.

[0032] The term "thermosetting epoxy portion" is understood herein to mean a portion of the thermosetting epoxy matrix that is free of embedded or previously embedded solid elements. Advantageously, the thermosetting epoxy portion is a relatively small portion having an irregular surface.

[0033] The term "rigid" is understood herein to mean that the rigid body is hard during normal and intended use of the rigid body in question.

[0034] The term "epoxy resin" is understood herein to mean polyepoxides including reactive prepolymers and / or polymers containing epoxy groups.

[0035] The phrases "cured epoxy matrix" and "thermoset epoxy matrix" are used interchangeably and are understood herein to include any cross-linked reaction product comprising an epoxy resin.

[0036] The terms "swelling" and "swell" are understood herein to mean the incorporation of a fluid (swelling fluid) into a material, such as a thermosetting epoxy matrix, resulting in an increase in size and / or mass.

[0037] The term "slurry" is understood herein to mean a flowable mixture of a fluid and a thermosetting epoxy portion. When the fluid consists of a gas, the thermosetting epoxy portion can be separated from the fluid, whereby the slurry consists of the thermosetting epoxy portion and optionally the remaining fluid.

[0038] The term "maximum dimension" is understood herein to refer to the maximum geometric dimension of the composite structure, determined as the distance from outside to outside across the composite structure, such as from turbine blade root to turbine blade tip.

[0039] The term "vibration" is understood herein to mean exposure to mechanical stress, such as shock experienced when shaken or repeatedly subjected to collisions with rigid elements.

[0040] The term "step" herein refers to a process comprising one or more actions. Each step of a method may include any number of sub-steps, which may also be referred to as steps.

[0041] It should be emphasized that the term "comprises" / comprising" when used in this document should be interpreted as an open term, that is, it should be understood to specify the presence of specifically stated (multiple) features, such as (multiple) elements, (multiple) units, (multiple) integers, (multiple) steps, (multiple) components and (multiple) combinations thereof, but does not exclude the presence or addition of one or more other features.

[0042] Throughout the specification and claims, the singular encompasses the plural and the plural encompasses the singular unless the context dictates or requires otherwise.

[0043] "Embodiment" should be interpreted as including examples of the invention that incorporate the feature(s) of the referenced embodiment(s).

[0044] The term "substantially" should be understood herein to include normal product differences and tolerances. All features of the invention and embodiments of the invention described herein, including ranges and preferred ranges, can be combined in various ways within the scope of the invention, unless there is a specific reason not to combine such features.

[0045] Unless otherwise stated, any properties, ranges of properties and / or measurements and / or analysis conditions (swelling conditions) are given, measured or performed at 1 atmosphere (1.01325 bar) and 25°C.

[0046] All features of the invention and embodiments of the invention described herein, including ranges and preferred ranges, may be combined in various ways within the scope of the invention, unless such features are incombinable or appear to be incombinable.

[0047] The method of the present invention comprises extracting a thermosetting epoxy portion from a composite structure, wherein the composite structure comprises a thermosetting epoxy matrix and one or more embedded solid elements. As explained above, the composite structure can be relatively large and can comprise several embedded solid elements of different structures or materials, as further described below.

[0048] The thermosetting epoxy matrix has a network structure in which the embedded solid elements are partially or fully embedded.

[0049] The method comprises:

[0050] • Provide swelling fluid,

[0051] • immersing the composite structure in a swelling fluid and causing the thermosetting epoxy matrix to swell, with the swelling fluid entering the network structure of the thermosetting epoxy matrix for a sufficient time to mechanically disrupt the network structure to form a plurality of thermosetting epoxy portions separated from the solid component(s), and

[0052] • separating at least a portion of the thermosetting epoxy material portion from at least one of the solid element(s) to obtain a swelling fluid slurry comprising said portion of the thermosetting epoxy material portion in a swelling fluid.

[0053] The swelling fluid contains at least 1 mol / L formic acid.

[0054] Formic acid, also known as Methanoic acid, is a liquid at 20°C and 1 atmosphere pressure.

[0055] The desired concentration of formic acid in the swelling fluid may depend on the composition and / or crosslink density of the thermosetting epoxy matrix.

[0056] Advantageously, the swelling fluid comprises at least 3 mol / L formic acid, such as at least 5 mol / L, such as at least 10 mol / L, such as at least 18 mol / L, such as at least 20 mol / L, such as at least 22 mol / L, such as at least 24 mol / L, such as at least 26 mol / L formic acid.

[0057] Providing the swelling fluid may include any number of steps, including purchasing a ready-to-use swelling fluid, such as an aqueous solution of formic acid.

[0058] Advantageously, the swelling fluid is an aqueous solution comprising formic acid.

[0059] In one embodiment, the method comprises providing a swelling fluid comprising the other components. The step of providing the swelling fluid may comprise mixing formic acid with one or more other components and optionally allowing a reactive component to form.

[0060] The additional component(s) may include added other component(s) and / or reaction product(s) formed by adding one or more such added other component(s).

[0061] In one embodiment, the step of providing a swelling fluid comprises mixing formic acid with one or more additional components, optionally applying the formic acid in the form of an aqueous solution.

[0062] The further component(s) of the swelling fluid may in principle be any component that is compatible with formic acid.

[0063] Examples of further component(s) include at least one further organic acid, such as acetic acid, trifluoroacetic acid, trichloroacetic acid, propionic acid, methanesulfonic acid, trifluoromethanesulfonic acid, performic acid, lactic acid, oxalic acid or anhydrides of any of these acids.

[0064] In one embodiment, the one or more additional components include at least one inorganic acid, such as hydrochloric acid, nitric acid, sulfuric acid, phosphoric acid, boric acid, and / or hydrobromic acid.

[0065] Other examples of additional component(s) include at least one alcohol, such as methanol, ethanol, propanol, isopropanol, butanol, tert-butanol and / or pentanol.

[0066] In principle, any alcohol, such as any liquid alcohol or any alcohol soluble in the swelling fluid, can be used as the additional component, including primary, secondary and tertiary alcohols. When using an alcohol as the additional component, advantageously, the potential esterification of formic acid should be taken into account to ensure that the concentration of formic acid is at the desired level.

[0067] Other examples of additional component(s) include at least one additional solvent such as tetrahydrofuran (THF), dimethylformamide (DMF), N-methyl-2-pyrrolidone (NMP), dimethyl sulfoxide (DMSO), dichloromethane, chloroform, acetone, acetonitrile, chlorobenzene, diethyl ether, dioxane, ethylene glycol, polyethylene glycol (PEG), glycerol, hexamethylphosphoramide (HMPA), nitromethane, pyridine, trimethylamine, toluene, xylene, benzene, dimethylacetamide (DMAc), dimethoxyethane (DME), diglyme and / or dichloroethane.

[0068] The one or more additional components may also include at least one dissolved salt, such as NaCl, KCl, CsCl, NaHCO3, KHCO3, CsHCO3, Na2CO3, K2CO3, Cs2CO3, any salt containing a quaternary ammonium cation and / or any salt containing a tetrafluoroborate anion or a hexafluorophosphate anion.

[0069] Adding salt to the swelling fluid can have the effect of altering the solubility of certain materials in the swelling fluid. For example, when the swelling fluid is aqueous, the addition of salt can alter the hydrophobic effect of the swelling fluid. In one embodiment, the addition of salt to the swelling fluid can function to reduce the risk of decomposition of the embedded solid element(s), thereby ensuring that the embedded solid element(s) do not decompose into small pieces that are difficult to separate from the thermosetting epoxy material portion.

[0070] In one embodiment, the further component or components comprise at least one surfactant, preferably selected from anionic and / or nonionic surfactants such as sulfates, sulfonates, gluconates, cocamide, ethoxylates and / or alkoxylates.

[0071] Adding a surfactant may be particularly desirable when the swelling fluid is an aqueous swelling fluid and the composite structure is fully or partially covered with a hydrophobic coating material or includes internal layer(s) of a hydrophobic coating material.

[0072] In one embodiment, the type and amount of the at least one additional component can be selected based on the embedded solid element, for example, to ensure that immersion of the composite structure in the swelling fluid does not result in any significant dissolution or decomposition of the embedded solid element. Thus, the resulting thermosetting epoxy material portion can be substantially free of or completely free of embedded solid elements or portions thereof.

[0073] In one embodiment, the pH of the swelling fluid is 2 or greater, such as between 2.5 and 4. The pH may be selected to ensure low risk of decomposition or corrosion of the embedded solid elements while ensuring efficient and relatively rapid swelling of the thermosetting epoxy matrix.

[0074] In principle, the thermosetting epoxy matrix can be of any type, such as the epoxy composite materials described in Introduction to Epoxy Composites: Fabrication, Characterization and Applications. Pages 1-21, First Edition, published by WILEY-VCH GmbH, 2021.

[0075] The method of the present invention has been found to be particularly beneficial when applied to a thermosetting epoxy matrix that is highly crosslinked, i.e., has a high crosslink density (the number of effective crosslinks per unit volume). Generally, the higher the degree of crosslinking, the greater the structural strength of the thermosetting epoxy matrix. Consequently, composite structures derived from large structural elements such as wind turbine blades, aircraft, ships, automobiles, bridge decks, boats, and aircraft are most commonly made from composite materials containing a thermosetting epoxy matrix with a high crosslink density. Surprisingly, the swelling fluid used in the method of the present invention is able to effectively swell into the network structure of a thermosetting epoxy matrix with a relatively high crosslink density and mechanically disrupt the network structure, thereby forming a large number of thermosetting epoxy parts.

[0076] The size of the thermosetting epoxy portion depends primarily on the type of epoxy and its crosslink density. The higher the degree of crosslinking, i.e., the greater the number of crosslinks per unit volume of the thermosetting epoxy matrix, the smaller the size of the thermosetting epoxy portion will be. Advantageously, the average size (maximum dimension) of the thermosetting epoxy portion can be 2 cm or less, such as 1 cm or less, such as 5 mm or less, or even 2 mm or less.

[0077] Advantageously, the average size of the thermosetting epoxy material portion is sufficiently small to ensure that at least 50 wt. %, preferably at least 90 wt. %, of the thermosetting epoxy material portion passes through a sieve having a nominal aperture of 20 mm or more, such as 14 mm or more, according to ISO 3310-12016. Advantageously, the average size of the thermosetting epoxy material portion is sufficiently large to ensure that at least 50 wt. %, preferably at least 90 wt. %, of the thermosetting epoxy material portion does not pass through a sieve having a nominal aperture of 20 mm or less, such as 10 mm or less, such as 5 mm or less, such as 2 mm or less, according to ISO 3310-12016.

[0078] The thermosetting epoxy matrix of the composite structure comprises an epoxy based on at least one reactant comprising at least one epoxy resin, wherein the epoxy resin has been cured.

[0079] Curing can be carried out by any means, such as by radiation (e.g., ionization, infrared radiation, electron beam, etc.) and / or by the action of at least one hardener, such as one or more anhydride curing agents, one or more thiol curing agents, and / or one or more amine curing agents. Such curing agents are well known in the art.

[0080] Curing can be carried out with or without external heating. In addition, curing can be carried out under reduced pressure to reduce the size of bubbles that may be trapped. In one embodiment, curing includes a step of vacuum degassing to remove these bubbles that may be trapped before completing the curing process.

[0081] The at least one reactant may include two, three or more reactants, as is well known in the art.

[0082] At least one reactant includes at least one epoxy resin, such as a liquid or solid bisphenol A epoxy resin, bisphenol F epoxy resin, epoxy novolac resin, cycloaliphatic epoxy resin, or water-based epoxy resin. Additional reactants may include a reactive diluent and a curing agent. For example, Aditya Birla Chemicals offers curing agents such as those containing optionally modified phenalkamines, polyamides, aliphatic amines, cycloaliphatic amines, and water-based curing agents. Reactive diluents may include, for example, BDDGE (1,4-butanediol diglycidyl ether), HDDGE (1,6-hexanediol diglycidyl ether), and / or acrylates.

[0083] Other additives may include flow agents, accelerators, plasticizers, and rheological additives.

[0084] Examples of epoxy materials forming the matrix of the thermosetting epoxy material include networks comprising at least one component selected from the group consisting of glycidyl ethers derived from bisphenols or polyphenols, such as bisphenol A, bisphenol F, bisphenol S, bisphenol T, phenol or cresol; phenolic resins; cycloaliphatic, aliphatic, aromatic mono- or polyols, such as C12 and C16 fatty alcohols, 1,4-butanediol, 1,6-hexanediol, 1,4-cyclohexanedimethanol, trimethylolpropane, glycerol, polyglycerol, pentaerythritol, sorbitol and o-cresol; glycidyl compounds derived from aromatic amines, such as p-aminophenol, aniline and methylenedianiline.

[0085] Conveniently, the thermosetting epoxy matrix is ​​cured by chemical reaction using a curing agent as described above under various pressure and temperature conditions depending on the chemical nature of the curing agent(s). Advantageously, the curing agent comprises at least one reactive moiety selected from the group consisting of: a carboxylic anhydride, such as phthalic anhydride or a derivative of partially hydrogenated phthalic anhydride; an aromatic, aliphatic, cycloaliphatic, araliphatic monoamine or polyamine, such as methylenedianiline, polyalkyleneoxymonoamine or polyamine, polyalkylenepolyamine, isophoronediamine and xylenediamine; a diphenol or polyphenol, such as the extension product of DGBPA (bisphenol A diglycidyl ether) and BPA (bisphenol A) or a phenolic cyanamide, such as DiCy (dicyandiamide); and a substituted urea, such as monuron or diuron.

[0086] Recently, recyclable epoxy materials have been developed that contain disulfide bridges within a thermosetting epoxy matrix, such as those described in WO18050189. Such epoxy materials are relatively easy to decompose by cleaving the disulfide bridges using suitable solvents. However, such disulfide-bridged epoxies are rarely used in today's large composite structures. In one embodiment, the thermosetting epoxy matrix does not contain disulfide bridges.

[0087] The method of the present invention has been shown to be particularly effective when the thermosetting epoxy matrix is ​​fully or partially cured by a hardener or hardener composition comprising at least one amine-based hardener, such as an aliphatic amine-based hardener, an aromatic amine-based hardener and / or a polyfunctional amine hardener, such as the hardeners described in US Pat. No. 8,865,917 B2.

[0088] Suitable aliphatic amine based hardeners include polyetheramines, ethyleneamines such as DETA, TETA, etc. and cycloaliphatic amines such as PACM-H12MDI. Exemplary aromatic amines include DETDA, MBOEA and other substituted methylenedianiline derivatives.

[0089] The embedded solid element may comprise any type of solid element and may be used for different purposes. In one embodiment, the embedded solid element comprises at least one of: i) one or more reinforcing elements; ii) one or more supporting elements.

[0090] The supporting elements may comprise any element which does not actually have a reinforcing function, such as fillers, forming aids, electrical components, lightning protection elements, coatings such as lacquer, glue and / or core elements such as foam and / or wood.

[0091] In one embodiment, the embedded plurality of solid elements comprises at least one reinforcement layer, such as two or more reinforcement layers, such as layers comprising one or more of fiber, metal, polymer, wood, ceramic, silicate and / or lacquer, optionally bonded together by a thermosetting epoxy matrix.

[0092] In one embodiment, the embedded plurality of solid elements comprises fibers selected from one or more of synthetic fibers, semi-synthetic fibers, regenerated fibers, plant fibers, carbon fibers, basalt fibers, glass fibers and / or metal fibers, and the fibers may preferably be in the form of at least one sheet comprising fibers, for example at least one sheet comprising fibers embedded in a polymer different from a thermosetting epoxy matrix.

[0093] Advantageously, the fibers may form one or more reinforcing elements or form a portion of one or more reinforcing elements. Synthetic fibers may include at least one of nylon, polyester, acrylic, polyvinyl chloride, polyurethane, vinylon, or aramid fibers. Semisynthetic fibers may include at least one of acetate, triacetate, or promix fibers. Regenerated fibers may include at least one of rayon, cupro, or polynosic fibers. Plant fibers may include at least one of cotton or hemp fibers. Carbon fibers may include at least one of pure carbon or pitch carbon. Metal fibers may include at least one of silver or steel fibers.

[0094] In one embodiment, fiber comprises glass fiber, synthetic fiber, carbon fiber, vegetable fiber and / or metal fiber.Advantageously, fiber can exist with the form of weaving or nonwoven mat, or comprise the line or the fiber that is cut into shortened length.Advantageously, fiber can exist with the form of one or more layers, and described layer is bonded together by thermosetting matrix, and described thermosetting matrix can be thermosetting epoxy material matrix or non-epoxy material type thermosetting matrix.In one embodiment, fiber can be coated with for example priming paint.Such priming paint is commonly referred to as sizing agent.

[0095] In one embodiment, the fibers include glass fibers, such as E-glass fibers, which are aluminoborosilicate glass with a low content of alkali metal oxides. Conveniently, the glass fibers may be coated, for example, with a resin coating and / or a silane coupling agent to increase the interfacial strength between the glass fibers and the thermosetting epoxy matrix. Examples of silane coupling agents include epoxy-functionalized organosilanes or 3-glycidoxypropyltrimethoxysilane (GPTMS).

[0096] Advantageously, the fibers may be in the form of woven or non-woven mats and / or in the form of bundles and / or rovings. In one embodiment, the thermosetting epoxy matrix comprises multiple layers of fiber mats bonded together mechanically or chemically, for example by a glue such as a thermosetting matrix, which may be a thermosetting epoxy matrix or a thermosetting non-epoxy matrix.

[0097] In one embodiment, the embedded solid element(s) comprise chopped glass fibers and / or hollow glass beads.

[0098] In one embodiment, the embedded solid element(s) comprise wood, such as balsa wood.

[0099] Balsa wood is a biomaterial that is well-suited for forming the core of sandwich composite structures. It has an extremely high strength-to-stiffness-to-weight ratio and bonds excellently with all types of resins and adhesives. For more information on balsa wood and its applications, see "Review of balsa core sandwich composite structures" by Joel Galos et al., Materials & Design, Volume 221 (September 2022), 111013. Elsevier Ltd. https: / / doi.org / 10.1016 / j.matdes.2022.111013.

[0100] In one embodiment, the embedded solid element(s) comprise a foamed plastic, such as a foamed plastic comprising at least one of polystyrene (PS), polyurethane (PU), polyvinyl chloride (PVC), polyethylene terephthalate (PET), polyolefins (polyethylene (PE) and polypropylene (PP)) and ABS foam, preferably the foamed plastic is rigid.

[0101] Advantageously, the foamed plastic is a closed-cell foam.

[0102] Advantageously, expanded plastics offer high fire resistance and ensure lightweight composite structures, which is desirable in some applications. PVC, in particular, has a high stiffness and strength-to-weight ratio. Conveniently, PVC can be cross-linked. Other polymers, such as PET and PU foams, also offer excellent mechanical properties.

[0103] In one embodiment, the reinforcing element comprises a metal such as steel, aluminum, titanium, chromium, cobalt, nickel, copper, zinc, tin, lead, and any alloy comprising at least one of the foregoing, preferably in the form of (a plurality of) metal wires and / or a metal mesh. In one embodiment, the reinforcing element comprises metal fibers and / or metal beams.

[0104] In one embodiment, the embedded plurality of solid elements comprises at least one additional thermoset matrix comprising a cross-linked polyester, a polyurethane, a vulcanized rubber, a cross-linked polyvinyl ester, a cross-linked polyimide, a cross-linked phenolic, a cross-linked polybenzoxazine, a cured amino resin, a cured furan resin, a cured maleimide resin, or a cured silicone, or any combination comprising at least one of the foregoing.

[0105] The term "additional thermosetting matrix" refers to a thermosetting polymer matrix other than the thermosetting epoxy matrix of the composite structure. Conveniently, the additional thermosetting matrix may be a non-epoxy thermosetting polymer matrix, ie a thermosetting polymer matrix that does not contain epoxide-based crosslinks.

[0106] The step of soaking the composite structure with the swelling fluid can be performed at any temperature. Preferably, the step of soaking the composite structure is performed with liquid formic acid. Preferably, for a 90% weight / weight aqueous solution of formic acid (23.9 mol / L), at 1 atmosphere, the temperature is below the boiling point of formic acid and above its freezing point, which is below 105°C and above -5°C.

[0107] In one embodiment, the step of soaking the composite structure with the swelling fluid is performed at a swelling fluid temperature of up to 100°C, such as 8°C to 75°C, such as 10°C to 50°C, such as 20°C to 35°C, such as 22°C to 27°C.

[0108] Advantageously, the step of soaking the composite structure with the swelling fluid is carried out at room temperature or a slightly elevated temperature, such as 20-25°C. This allows costs to be kept low, as heating of the swelling fluid may not be necessary. It has been found that the method of the present invention is highly effective even at relatively low temperatures, however, when the temperature is room temperature or higher, the swelling rate may increase with increasing temperature.

[0109] Conveniently, the step of soaking the composite structure with the swelling fluid may be carried out at atmospheric pressure. Thus, the apparatus used need not be completely airtight.

[0110] In one embodiment, the step of soaking the composite structure with the swelling fluid is at least partially performed at elevated pressure, such as a pressure of up to 3 bar, such as a pressure of up to 2 bar, such as a pressure of up to 1.5 bar.

[0111] Elevated pressure may conveniently be achieved by carrying out the steps of soaking the composite structure in a closed processing vessel and then increasing the temperature until the desired temperature and pressure are achieved.

[0112] During the step of soaking the composite structure with the swelling fluid, contact between the composite structure and the swelling fluid may be performed by any method.

[0113] In one embodiment, the step of soaking the composite structure with the swelling fluid comprises contacting the composite structure with the swelling fluid in a processing vessel. In one embodiment, the processing vessel can be an open container, such as a container with an opening for supplying or removing the composite structure or components thereof. Advantageously, if the processing vessel is opened during processing, the processing vessel or the area immediately surrounding the processing vessel can include suitable protective features to protect potential operators or process observers. Advantageously, the container can be a closed or closable container.

[0114] In one embodiment, the step of soaking the composite structure with the swelling fluid comprises placing the composite structure in a volume of swelling fluid in a processing vessel and / or spraying the composite structure with the swelling fluid in the processing vessel. The processing vessel may be as described above.

[0115] In one embodiment, the step of soaking the composite structure with a swelling fluid comprises gradually or continuously conveying the composite structure through a treatment station, wherein the composite structure is treated with the swelling fluid at the treatment station, for example, by spraying the composite structure with the swelling fluid at the treatment station. The method may, for example, comprise arranging the composite structure on a conveyor belt and conveying the composite structure through a treatment vessel, wherein the composite structure is treated with the swelling fluid in the treatment vessel, for example, by spraying the composite structure with the swelling fluid. Using spraying for the soaking step can be advantageous because the amount of swelling fluid used is relatively low and the swelling fluid can be repeatedly recycled.

[0116] Conveniently, the step of soaking the composite structure with the swelling fluid may comprise contacting the composite structure with the swelling fluid for a period of up to 144 hours, such as 1 to 130 hours, such as 10 to 100 hours, such as 24 to 96 hours, for example up to 72 hours, such as up to 48 hours (soaking time). The desired soaking time depends on several factors, such as the type of thermosetting epoxy matrix of the composite structure, the degree of cross-linking of the thermosetting epoxy matrix, the size of the composite structure, the shape of the composite structure, the temperature and pressure during the soaking step, the composition of the swelling fluid, and the effectiveness of the soaking step.

[0117] Therefore, it has been found that the desired soaking time can be reduced by subjecting the composite structure to mechanical influences during at least a portion of the soaking step.

[0118] In one embodiment, the step of soaking the composite structure with the swelling fluid comprises subjecting the composite structure and / or the swelling fluid to a mechanical influence, including vibration, for example using ultrasound, and / or subjecting the swelling fluid to motion, for example using stirring / shaking and / or blowing gas into and through the swelling fluid.

[0119] The step of separating the thermoset portion may be performed in any suitable manner.

[0120] In one embodiment, the step of separating the thermosetting epoxy material portion from the solid element comprises separating the solid element and the swelling fluid by removing the swelling fluid from the solid element to obtain a swelling fluid slurry or by removing the solid element from the swelling fluid to obtain a swelling fluid slurry. For example, the swelling fluid can be removed from the solid element by pumping out the swelling fluid or by filtering the thermosetting epoxy material portion and the swelling fluid through a filter with a large pore size, thereby obtaining a slurry containing at least a portion of the thermosetting epoxy material portion, while retaining the solid element.

[0121] In one embodiment, the step of separating the thermosetting epoxy portion from the solid element comprises agitating, such as mechanically vibrating, the solid element to release the thermosetting epoxy portion.

[0122] In one embodiment, the step of separating the thermosetting epoxy portion from the solid element comprises subjecting the solid element to at least one cleaning process. Conveniently, the cleaning process may comprise cleaning the previously embedded solid element with a cleaning fluid to obtain a cleaning fluid slurry comprising at least a portion of the thermosetting resin portion in the cleaning fluid. In one embodiment, the cleaning fluid may be water, such as tap water. Advantageously, the cleaning fluid comprises a surfactant, wherein the surfactant preferably comprises an anionic surfactant and / or an amphiphilic surfactant, such as a quaternary ammonium surfactant.

[0123] The role of the surfactant is to reduce the surface tension of the solid component, thereby increasing its wetting properties to separate the thermosetting epoxy material portion from the solid component.

[0124] In one embodiment, the step of separating the thermosetting epoxy material portion from the solid element comprises subjecting the solid element to at least one flushing process. Advantageously, the flushing process may be a high-pressure flushing process using a flushing fluid selected from a flushing gas, a flushing liquid, or a mixture thereof. Thus, a flushing fluid slurry containing at least a portion of the thermosetting resin portion in the flushing fluid may be obtained.

[0125] When the flushing fluid consists of a flushing gas, the thermosetting resin portion can be detached from the flushing fluid immediately after separation from the solid element. Thus, the flushing fluid slurry is provided by the detached thermosetting epoxy portion.

[0126] Advantageously, the flushing fluid is water or water containing a surfactant, such as an anionic surfactant and / or an amphoteric surfactant, such as a quaternary ammonium surfactant.

[0127] When the solid element is subjected to a cleaning process and a rinsing process, the obtained cleaning fluid slurry and the obtained rinsing fluid slurry may be mixed into a combined slurry, eg for further processing as described below.

[0128] In one embodiment, the step of separating the thermosetting epoxy material portion from the solid element comprises mechanically deforming the solid element, such as crushing the solid element and / or vibrating the solid element.

[0129] Conveniently, the step of mechanically deforming the solid element may be performed before the cleaning process and / or before the rinsing process. Alternatively, the additional cleaning process and / or additional rinsing process may be performed after or simultaneously with the mechanically deforming of the solid element. Conveniently, the resulting cleaning fluid slurry and / or the resulting rinsing fluid slurry may be added to form part of the combined slurry.

[0130] In one embodiment, the step of separating the thermosetting epoxy portion from the solid element further comprises mechanically removing the thermosetting epoxy portion from the solid element, such as by scraping and / or combing to remove the thermosetting epoxy portion from the solid element.

[0131] Conveniently, such a step of mechanically removing the portion of the thermosetting epoxy material from the solid component may be performed before the cleaning process and / or before the rinsing process. Alternatively, an additional cleaning process and / or an additional rinsing process may be performed after or simultaneously with the mechanical removal of the portion of the thermosetting epoxy material from the solid component. Conveniently, the resulting cleaning fluid slurry and / or the resulting rinsing fluid slurry may be added to form part of the combined slurry.

[0132] The step of separating the thermosetting epoxy material portion from the solid element may further comprise filtering, such as filtering the cleaning fluid slurry, the rinsing fluid slurry and / or the combined slurry, thereby obtaining at least a portion of the thermosetting epoxy material portion from the cleaning fluid slurry and / or the rinsing fluid slurry and / or the combined slurry.

[0133] In one embodiment, the method further comprises filtering the swelling fluid slurry to collect at least a portion of the thermosetting epoxy material portion from the swelling fluid slurry, wherein the method preferably further comprises recycling the swelling fluid, such as for use in a method for extracting the thermosetting epoxy material portion from the composite structure as described above.

[0134] Advantageously, when the swelling fluid is recirculated, the concentration of formic acid can be adjusted because formic acid is hygroscopic and tends to absorb moisture from the air, which can cause the formic acid concentration to decrease. In addition, over time, formic acid decomposes into carbon monoxide and water, which can also affect the formic acid concentration.

[0135] In one embodiment, the method comprises subjecting the thermosetting epoxy portion(s) of the collected portion to a further step of washing the thermosetting epoxy portion(s) of the collected portion and / or drying the thermosetting epoxy portion(s) of the collected portion.

[0136] Such a further washing step can, for example, have the function of removing some solid elements, such as small portions of varnish or fibers.

[0137] The resulting thermosetting epoxy portion can be stored for later use, such as for depolymerization.

[0138] In one embodiment, the method further comprises subjecting the thermosetting epoxy material to a partial depolymerization step, for example using a good solvent NMP (N-methyl-2-pyrrolidone), an organic catalyst triazabicyclodecene (TBD), and the alcohol ethylene glycol (EG).

[0139] Depolymerization can be carried out by any method, such as methods known in the art, for example, the method described by Xiao Kuang et al. in "Recycling of Epoxy Thermoset and Composites via Good Solvent Assisted and Small Molecules Participated Exchange Reactions", ACS Sustainable Chem., Page 1-27. Eng DOI: 10.1021 / acssuschemeng.8b01538 - Publication Date (Web): 29 May 2018. https: / / pubs.acs.org / doi / 10.1021 / acssuschemeng.8b01538.

[0140] By using the thermosetting epoxy material portion as the starting point for depolymerization, the depolymerization becomes very rapid and efficient, and the resulting depolymerized component containing epoxy oligomers can be obtained in a desirably high purity.

[0141] The method of the present invention can be implemented even with relatively large composite structures. Advantageously, the maximum dimension of the composite structure is at least 0.1 m, such as at least 1 m, such as at least 5 m, such as at least 10 m, such as 15 to 200 m, such as 20 to 100 m.

[0142] Examples of composite structures from which extraction of thermoset epoxy portions may be performed may include all or portions of wind turbine blades, airplanes, boats, automobiles, bridge decks, boats, aircraft, and / or circuit boards.

[0143] In one embodiment, the composite structure is obtained from a wind turbine blade including a spar cap as described in WO 2022 / 188934.

[0144] The limiting dimensions of the composite structure are in principle the dimensions of the process vessel.

[0145] Thus, in one embodiment, the composite structure is an entire wind turbine blade. In one embodiment, the composite structure is half of a wind turbine blade. In one embodiment, the composite structure is one-tenth or more of a wind turbine blade.

[0146] Brief description of implementation scheme and examples

[0147] The present invention will be further described below by way of a description of several illustrative and non-limiting embodiments and examples of the present invention with reference to the accompanying drawings.

[0148] The accompanying drawings are schematic, not drawn to scale, and may be simplified for clarity. Throughout the text, the same or corresponding parts are marked with the same reference numerals.

[0149] Figure 1a is a schematic diagram of a composite structure in the form of a wind turbine blade.

[0150] Figure 1b yes Figure 1a Cross-sectional view of a wind turbine blade along the cross-sectional line AA'.

[0151] Figure 1c is Figure 1b Close-up view of portion B of the cross-sectional view as seen in FIG.

[0152] Figures 2 to 5 are flow charts of different examples of processes for implementing the methods of the present invention.

[0153] Figure 7 and Figure 8 This is an image related to Example 3.

[0154] Figure 9 、 10 1 and 11 are images and diagrams related to Example 4, respectively.

[0155] Figure 12 This is a chart related to Example 5.

[0156] Figure 13 and14 They are respectively diagrams and images related to Example 6.

[0157] Figure 15 and 16 (ad) are graphs and images related to Example 7, respectively.

[0158] Figures 17a-17c This is a diagram illustrating the 20th embodiment.

[0159] Figure 1a The composite structure shown is an example of a wind turbine blade obtained from a wind turbine. Most prior art wind turbines include a rotor with three wind turbine blades. It should be understood that the composite structure can be any type of wind turbine blade that includes a composite material in whole or in part.

[0160] The shape of a wind turbine blade is generally referred to as an airfoil and comprises a root portion 2a, a curved mid-span portion 2b and a tip portion 2c.

[0161] The wind turbine blade has an edge 1 at which it is cut or separated from the rest of the wind turbine. At the edge 1 a number of reinforcing beams 1a can be seen which ensure a strong connection of the neck 2a to the rest of the wind turbine.

[0162] Figure 1b The cross-sectional view taken along the line AA' in the middle span portion 2b of the wind turbine blade is shown in FIG. Figure 1a In the example shown, the wind turbine blade has a shell structure 3, a structural unit 4 and a first hollow space 5a and a second hollow space 5b.

[0163] The first hollow space 5a and the second hollow space 5b may coincide at the tip portion 2c of the wind turbine blade.The first hollow space 5a and / or the second hollow space 5b may contain further structural elements not shown, such as a foamed polymer and optionally a portion of a thermosetting epoxy matrix.

[0164] Figure 1c is Figure 1bA close-up view of section B of the cross-sectional view visible in FIG. In the illustrated example, the shell structure 3 includes, from the outside inward, a paint layer 6a, optionally covered with a repelling layer (not shown) and / or an anti-corrosion layer, for protecting the wind turbine blade. Beneath the paint layer 6a, the shell structure 3 includes a first composite material structure 6b comprising one or more fiberglass layers embedded in a thermosetting epoxy matrix. A lightning protection net 6c is embedded in the first composite material structure 6b. Beneath the first composite material structure 6b, the shell structure 3 includes a core material 6d, such as balsa wood or a closed-cell polymer foam such as PVC, or a combination thereof. Beneath the core material 6d, the shell structure 3 includes a second composite material structure 6e comprising one or more fiberglass layers embedded in a thermosetting epoxy matrix. The core material 6d may be embedded in the thermosetting epoxy matrix between the first composite material structure 6b and the second composite material structure 6e.

[0165] Structural element 4 includes at least one composite material layer 7a, which comprises one or more fiberglass layers embedded in a thermosetting epoxy matrix. The at least one composite material layer 7a at least partially surrounds a core 7b of structural element 4. Core 7b can be made of any material. In this embodiment, core 7b is made of a core material such as balsa wood or a closed-cell polymer foam, such as PVC, or a combination thereof. It should be understood that the structural elements of the illustrated wind turbine blade and the other embedded solid elements are examples and may differ for other wind turbine blades.

[0166] In the embodiment shown, the structural unit 4 is bonded to the shell structure 3 by an excess of glue 8. The glue may be an epoxy material, whereby the glue forms part of the thermosetting epoxy matrix.

[0167] Figure 2 A first embodiment of a method for implementing the present invention is shown. In step 1a, a composite material structure is provided. The composite material structure can be as described above. In step 1b, the composite material structure is immersed in a swelling fluid containing formic acid as described above, wherein the swelling fluid is at room temperature or an elevated temperature, for example, at an elevated temperature as described above, such as at a swelling fluid temperature of about 25°C, such as about 35°C, such as about 50°C, such as about 80°C, or such as about 95°C. The swelling fluid can be maintained at this temperature throughout the immersion process, or can be gradually cooled. The swelling fluid can be stirred or agitated during the immersion process.

[0168] In step 1c, the swelling fluid is separated from the solid elements, for example as described above and preferably by filtration to obtain a swelling fluid slurry comprising a slurry of thermosetting epoxy material portions in the swelling fluid.

[0169] In step 1d, the swelling fluid slurry is filtered to obtain a first portion of the thermosetting epoxy material. Thereafter, in step 1e, each solid element is rinsed with a cleaning fluid to obtain a cleaning fluid slurry. Conveniently, each solid element can be rinsed with a respective portion of the cleaning fluid, and then the respective portions of the cleaning fluid are combined to obtain a cleaning fluid slurry.

[0170] In step 1f, the cleaning fluid slurry is filtered and a second portion of the thermosetting epoxy material is collected.

[0171] Conveniently, the first and second parts of the thermosetting epoxy material may be partially mixed and subjected to further processing, such as depolymerization as described above.

[0172] Figure 3 A second embodiment of the method for carrying out the present invention is shown.

[0173] In step 2a, a composite material structure is provided in the form of a composite material structure cut from a wind turbine blade. The wind turbine blade may be, for example, Figure 1a -1c.

[0174] In step 2b, the composite structure is sprayed with a swelling fluid, such as the swelling fluids described above. The swelling fluid is maintained at a temperature above 20°C, such as about 50°C, such as about 80°C, or such as about 95°C. After contact with the swelling fluid for an appropriate swelling time, such as the swelling time described above, in step 2c, the swelling fluid is separated from the solid element, for example, as described above, preferably by filtration, to obtain a swelling fluid slurry comprising a slurry of the thermosetting epoxy material portion in the swelling fluid.

[0175] In step 2d, the swelling fluid slurry is filtered to obtain a first portion of the thermosetting epoxy material. Thereafter, in step 2e, each solid component is high-pressure rinsed with a rinse fluid to obtain a rinse fluid slurry. Conveniently, each solid component can be rinsed with its own portion of the rinse fluid, which can then be combined to obtain a rinse fluid slurry.

[0176] In step 2f, the rinse fluid slurry is filtered and a second portion of the thermosetting epoxy material is collected.

[0177] Conveniently, the first thermosetting epoxy part and the second thermosetting epoxy part may be mixed and subjected to further processing, such as depolymerization as described above.

[0178] Figure 4 A third embodiment of the method for carrying out the present invention is shown.

[0179] In step 3a, a composite structure is provided in the form of a composite structure cut from an aircraft wing.

[0180] In step 3b, the composite structure is immersed in a swelling fluid vapor. The swelling fluid can be in a vaporized state, as described above. Conveniently, the swelling fluid vapor can be at a reduced pressure and / or elevated temperature, such as about 80°C, about 90°C, or about 100°C. After a suitable swelling time in contact with the swelling fluid, such as the swelling time described above, in step 3c, the swelling fluid is removed from the solid element, preferably by removing / pumping the swelling fluid vapor from the processing vessel. Thus, the solid element and the thermosetting epoxy material portion remain in the processing vessel.

[0181] In step 3d, the solid element is washed using a first washing fluid to obtain a first washing fluid slurry. Conveniently, the washing may be performed while the solid element remains in the processing vessel.

[0182] In step 3e, the first cleaning fluid slurry is filtered and a first portion of the thermosetting epoxy material portion is collected.

[0183] In step 3f, the individual solid elements are removed from the processing container and each of the individual solid elements is subjected to a deformation process, such as described above, to release other thermosetting epoxy material portions.

[0184] In step 3g, each deformed solid element is washed with the second washing fluid to obtain a second washing fluid slurry. Conveniently, each deformed solid element may be washed with a respective portion of the second washing fluid and then the portions combined to obtain the second washing fluid slurry.

[0185] In step 3h, the second cleaning fluid slurry is filtered and a second portion of the thermosetting epoxy material portion is collected.

[0186] The thermosetting epoxy portions of the sections may be combined as described above.

[0187] Figure 5 A fourth embodiment of the method for carrying out the present invention is shown.

[0188] In step 4a, a composite material structure in the form of a wind turbine blade is provided. The wind turbine blade may be, for example, Figure 1a -1c.

[0189] In step 4b, the composite structure is immersed in a swelling fluid comprising formic acid as described above, wherein the swelling fluid is at room temperature or elevated temperature and is subjected to vibration, for example, provided by ultrasound. Conveniently, the temperature of the swelling fluid may be as described above, such as at a swelling fluid temperature of about 50°C, such as about 80°C, or such as about 95°C. The swelling fluid may be maintained at this temperature, for example, throughout the immersion process, or may be allowed to cool gradually.

[0190] After a suitable swelling time in contact with the swelling fluid, such as the swelling time described above, the swelling fluid is separated from the solid element in step 4c, such as described above, and preferably the swelling fluid is separated from the solid element by filtration to obtain a swelling fluid slurry comprising a portion of the thermosetting epoxy material in the swelling fluid.

[0191] In step 4d, the swelling fluid slurry is filtered to obtain a first portion of the thermosetting epoxy material. Thereafter, in step 4e, the solid component is dried.

[0192] In step 4f, each solid element is subjected to a deformation process, for example as described above, to release other thermosetting epoxy portions.

[0193] In step 4g, each of the deformed solid elements is washed with a washing fluid to obtain a washing fluid slurry. Conveniently, each deformed solid element may be washed with a respective portion of the washing fluid and then the portions combined to obtain the washing fluid slurry.

[0194] In step 4h, the cleaning fluid slurry is filtered and a second portion of the thermosetting epoxy material portion is collected.

[0195] The portions of thermosetting epoxy material may be combined as described above.

[0196] Figure 6 A fifth embodiment of the method for carrying out the present invention is shown.

[0197] In step 5a, the composite material structure is obtained, for example as described above, and cut into a processable size. As described above, the maximum processable size depends on the size of the processing container.

[0198] In step 5b, the composite structure is immersed in a swelling fluid comprising formic acid as described above, wherein the swelling fluid is at an elevated temperature, and the composite structure is subjected to an ultrasonic field.

[0199] Conveniently, the temperature of the swelling fluid may be as described above, such as at a swelling fluid temperature of about 50° C., such as about 80° C., or such as about 95° C. The swelling fluid may be maintained at this temperature, for example, throughout the soaking process, or may be allowed to cool gradually.

[0200] After a suitable swelling time in contact with the swelling fluid, such as the swelling time described above, the swelling fluid is separated from the solid element in step 5c, such as described above, and preferably the swelling fluid is separated from the solid element by filtration to obtain a swelling fluid slurry comprising a slurry of the thermosetting epoxy material portion in the swelling fluid.

[0201] In step 5d, the swelling fluid slurry is filtered to obtain a first portion of the thermosetting epoxy material portion.

[0202] Subsequently, in step 5e, the solid element is flushed using a high-pressure flushing fluid to obtain a flushing fluid slurry.

[0203] The solid elements may be subjected to flushing in the treatment vessel, and / or individual solid elements may be flushed using respective portions of the flushing fluid, which may then be combined to obtain a flushing fluid slurry.

[0204] In step 5f, the flushing fluid slurry is filtered and a second portion of the thermosetting epoxy material portion is collected.

[0205] In step 5g, the solid elements are dried and then in step 5h, each solid element is deformed, for example as described above, to release the other thermosetting epoxy portions.

[0206] In step 5i, each deformed solid element is cleaned using a cleaning fluid to obtain a cleaning fluid slurry.

[0207] Conveniently, each deformed solid element may be cleaned using a respective portion of the cleaning fluid, and the portions may then be combined to obtain a cleaning fluid slurry.

[0208] In step 5j, the wash fluid slurry is filtered and a third portion of the thermosetting epoxy material portion is collected.

[0209] The thermosetting epoxy material portions of the portions are then combined in step 5k to obtain a combined thermosetting epoxy material portion of the portions.

[0210] In step 51, the thermosetting epoxy material portion of the combined portion is cleaned and dried. The dried thermosetting epoxy material portion of the combined portion can be stored for subsequent use or further processed as described above. Example

[0211] Some illustrative and non-limiting examples of the present invention are provided below

[0212] Example 1: Preparation of a standard epoxy clear cast dog bone.

[0213] 100.00 g of epoxy resin (commercially available) was manually mixed with 30.00 g of curing agent (commercially available) in an aluminum foil tray. The mixture was then degassed in a desiccator under vacuum for at least 20 minutes, until no more bubbles were observed. The mixture was poured into a silicone mold and cured at 50°C for 1 hour, followed by a post-cure at 80°C for 3 hours.

[0214] Example 2: Experiments with Clear Cast Epoxy Dog Bones in a Beaker

[0215] The clear cast epoxy dog-bone prepared in Example 1 was added to a 250 mL beaker. Formic acid (100% by volume (v / v%)) was added to the beaker. The dog-bone was observed to begin to decompose with a noise from the crushing material, resulting in settling into the glass, which appeared as an accumulation of decomposed epoxy material in the form of a slurry that settled to the bottom of the beaker.

[0216] Example 3: Decomposition rate measurement

[0217] The fractionation rate was measured using standard epoxy clear cast dog bones prepared in Example 1. Each dog bone was placed in a 100 mL graduated cylinder with volume markings per mL on the glassware. At time = 0 minutes, the swelling fluid (78 v / v %) was poured onto the dog bone. A time-lapse camera was set up to record the progress of the decomposition. During the decomposition process, the cured epoxy resin particles fell off the sample and settled as a slurry at the bottom of the measuring cup. Starting from the time the liquid solvent was poured onto the dog bone, the decomposition progress (measured in %) at each time period of the experiment was defined as the volume of powder obtained over the time period divided by the final volume reached by each sample, which was determined to be a plateau after sufficient time had passed, i.e., the decomposition progress reached a maximum.

[0218] Figure 7 Shown are images taken mid-experiment as an example of the experimental setup when measuring decomposition rates, in this case of 12 different formulations of clear cast epoxy in a swelling fluid in the form of aqueous formic acid (78 v / v %).

[0219] Figure 8 Photograph of a thermoset epoxy section after filtering from a swelling fluid and vacuum drying for 24 hours. The thermoset epoxy section is a sample from a test run to measure the decomposition rates of different clear cast epoxy formulations.

[0220] Example 4: Decomposition rate measurement using other acids

[0221] Decomposition rates were measured using standard epoxy clear cast dogbones prepared as described in Example 1. Each dogbone was placed in a 100 mL graduated cylinder with volume markings per mL on the glassware. At time = 0 minutes, liquid solvent was poured onto the dogbone. A time-lapse camera was set up to record the decomposition process. If decomposition occurred, cured epoxy resin particles would fall off the sample and settle as a slurry at the bottom of the measuring cup. Starting from the time the liquid solvent was poured onto the dogbone, at each elapsed time point in the experiment, the decomposition progress (measured in %) was defined as the powder volume reached after a certain period of time divided by the final volume reached by each sample. The final volume was determined as the plateau after sufficient time, indicating that the decomposition progress reached its maximum. The solutions studied included swelling fluids consisting of formic acid (75 v / v% in water), acetic acid (75 v / v% in water), propionic acid (75 v / v% in water), lactic acid (75 v / v% in water), hydrochloric acid (37 v / v% in water), and sulfuric acid (50 v / v% in water).

[0222] This experiment provides an approximate estimate of the degradation rate of such samples in this medium, showing that using a swelling fluid containing formic acid results in an approximately 11-fold acceleration of swelling-induced decomposition compared to using a solvent containing acetic acid. This acceleration is even greater than using solvents containing other acids, such as propionic acid and lactic acid, which also induce decomposition, but at significantly lower rates than the swelling fluid containing formic acid. For example, after 300 hours, the decomposition rate is almost zero when using a solvent containing lactic acid.

[0223] Figure 9 Shown are examples of timed experiments in which a clear cast epoxy dog-bone was exposed to (left) a swelling fluid containing formic acid and (right) the corresponding acetic acid solution.

[0224] Figure 10 Comparison of the extent of decomposition achieved by transparent cast epoxy dogbones in aqueous solutions containing 75% v / v of acid over experimental times measured in hours. The acids studied were: formic, acetic, propionic, and lactic. These results show that formic acid decomposes significantly faster than all other acids.

[0225] Figure 11 This image was taken midway through an experiment to screen the decomposition rates of formic, acetic, propionic, and lactic acids.

[0226] Example 5: Measurement of decomposition rate at different formic acid concentrations

[0227] The decomposition rate was measured using standard epoxy clear cast dog bones prepared as in Example 1. Each dog bone was placed in a 100 mL graduated cylinder with volume markings per mL on the glassware. At time = 0 minutes, the swelling fluid was poured onto the dog bone. A time-lapse camera was set up to record the progress of the decomposition. During the decomposition process, thermosetting epoxy resin particles fell off the sample and settled as a slurry at the bottom of the measuring cup. Starting from the time the liquid solvent was poured onto the dog bone, the decomposition progress (measured in %) was defined as the powder volume reached after a period of time divided by the final volume reached for each sample at each elapsed time of the experiment, which was determined as a plateau after sufficient time had passed, i.e., the decomposition progress reached a maximum. The solutions studied included swelling fluids containing formic acid in water, with the volume percentages of formic acid in water being 20 v / v% (5 mol / L), 40 v / v% (10 mol / L), 60 v / v% (16 mol / L), 80 v / v% (21 mol / L), and 100 v / v% (26 mol / L).

[0228] This experiment provides an approximate estimate of the degradation rates of such samples in these solutions, indicating that even when diluted with water to 20% aqueous volume, the swelling fluid containing formic acid leads to swelling-induced decomposition, and based on extrapolation of the data points, this is likely true even at lower concentrations. Furthermore, the experiments show that decomposition occurs faster at higher formic acid concentrations.

[0229] Figure 12 The following chart compares the extent of decomposition of transparent cast epoxy dogbones after experimental times measured in hours in swelling fluids containing 20 vol / vol% (5 mol / L), 40 vol / vol% (10 mol / L), 60 vol / vol% (16 mol / L), 80 vol / vol% (21 mol / L), and 100 vol / vol% (26 mol / L) formic acid in water. These results indicate that the more diluted the formic acid, the slower the decomposition rate.

[0230] Example 6: Measurement of Swelling Rate of Glass Fiber Pultrusion Samples

[0231] Swelling rates were measured using samples of five different unidirectional pultruded products containing glass fibers embedded in five different cured thermosetting epoxy resin formulations. Samples were cut into 20 cm x 1 cm x 0.2 cm sections, with the fiber direction along the longest (20 cm) dimension. All five samples were immersed in a swelling fluid containing formic acid (78 vol / vol% in water) for an extended period of time. Every hour, a camera imaged the samples from a fixed distance. Swelling was observed perpendicular to the fiber direction. Swelling along that axis was reported as a percentage of elongation relative to the original dimension of 1 cm on each camera image.

[0232] Figure 13 is a graph showing the swelling of five different epoxy pultrusions composed of five different cured thermosetting epoxy resin and glass fiber formulations over an elapsed time of 900 minutes. The graph reveals that for each type of cured thermosetting epoxy resin, all five samples elongated by more than 25% along the axis perpendicular to the fiber direction due to swelling after at least 200 minutes and up to 850 minutes of exposure to the solution.

[0233] Figure 14 This is a photograph of a pultruded sample after 900 minutes of exposure to a swelling fluid containing 78% v / v formic acid in water. At this point, loosened glass fiber strands were exposed, and tiny thermoset epoxy sections that had detached from the thermoset epoxy matrix were observed on the underlying plastic sheet.

[0234] Example 7: Disassembly of epoxy-fiberglass laminate

[0235] A glass fiber reinforced composite laminate consisting of 12 layers of commercial glass fiber mat and a thermosetting epoxy matrix obtained from commercial epoxy and hardener resin was vacuum infused into the glass fiber layers, cut into smaller squares of approximately 10 cm x 10 cm. Figure 15 As shown in the figure, a hole (12) was drilled in one corner and an incision 11 was made below the hole from the outside to the middle layer. The sample 10 was suspended by a rope 13 passing through the drilled hole 12 and placed in a 1-liter beaker containing a swelling fluid consisting of a 78 volume / volume % formic acid aqueous solution. The entire process was filmed with a video camera for 12 hours. After about 2 hours, the outermost layer of the fiber / epoxy composite material detached from the sample and fell to the bottom of the beaker. Continuously over the next 10 hours, the outermost layers detached from the structure layer by layer and deposited on the bottom, leaving only the two innermost layers hanging on the rope. During the process, a slurry of white epoxy material was observed, and larger pieces of decomposed epoxy material were also noted on the glass fiber layer and on the bottom of the beaker.

[0236] Figure 15A simple schematic diagram of the experiment is shown, wherein a string 13 is passed through a drilled hole 12 in a sample 10 of a laminated structure. Below the hole 12, a cut 11 is made on each side from the outside into the innermost layer, ensuring that the sample 10 can be suspended from the string 13 as long as the surrounding thermosetting epoxy matrix holds the layers together, but after the thermosetting epoxy matrix decomposes, the layers are lost.

[0237] Figure 16 (a)-16(d) show the disassembly of an epoxy-glass laminate suspended from a string 13 from the top of a 1000 mL beaker filled with 78 v / v % formic acid in water after 27 minutes (a), 101 minutes (b), 6 hours 56 minutes (c), and 8 hours 54 minutes (d). Continuous separation of the glass laminate and partial detachment of the thermosetting epoxy were observed.

[0238] Example 8: Disassembly of a complex sample from a scrapped wind turbine blade

[0239] A sample cut into a 25 cm x 25 cm rectangle was prepared from a scrapped wind turbine blade, which, in addition to the structural elements, consisted of at least some thermosetting epoxy matrix and glass fiber composite material, as well as a layer of cured epoxy-based glue. This sample was immersed in a swelling fluid containing 78% v / v formic acid in water and left under cover at room temperature for 40 hours. Afterwards, the entire structure was manually separated into its components, including:

[0240] • Fiberglass layer

[0241] •Lightning protection net

[0242] • A pile of decomposed epoxy

[0243] •paint

[0244] •Carbon reinforced composite materials

[0245] • Core element

[0246] Place each solid component on the above list in a fume hood to dry for at least 24 hours, or until the odor of formic acid disappears.

[0247] The remaining swelling fluid, consisting of a slurry of decomposed epoxy fragments in the swelling fluid, was filtered to obtain a clarified swelling fluid and even more of the thermosetting epoxy portion. The filtered swelling fluid was then used in a similar experiment using a sample cut from another composite structure similar to the one described above. The reused swelling fluid performed similarly to new, highlighting the potential for reusing swelling fluids.

[0248] Example 9: Disassembly using other organic acids

[0249] Samples of composite structures from scrapped wind turbine blades, consisting of structural units and fibers embedded in an epoxy thermoset matrix, were cut into approximately 25 cm x 25 cm squares. These samples were immersed in a swelling fluid containing two parts formic acid and one part at least one other organic acid, such as acetic acid, trifluoroacetic acid, trichloroacetic acid, propionic acid, methanesulfonic acid, trifluoromethanesulfonic acid, performic acid, or an anhydride of any of these organic acids. The composite structures were placed under a lid for 40 hours. The swelling fluid was then drained through an outlet into a waste container. The solid elements were rinsed three times with water and dried in a ventilated atmosphere. Upon drying, each solid element was manually separated and collected, and the released thermoset epoxy portion was collected.

[0250] Example 10: Disassembly using alcohol

[0251] Samples of composite structures from scrapped wind turbine blades, consisting of structural units and fibers embedded in an epoxy thermoset matrix, were cut into approximately 25 cm x 25 cm squares. These samples were immersed in a swelling fluid containing two parts formic acid and one part at least one alcohol, such as methanol, ethanol, propanol, isopropanol, butanol, tert-butanol, or amyl alcohol. The composite structures were placed under a lid for 40 hours. The swelling fluid was then drained through an outlet into a waste container. The solid elements were rinsed three times with water and dried in a ventilated atmosphere. Once dry, each solid element was manually separated and collected.

[0252] Example 11: Disassembly using solvent

[0253] Samples of composite structures from scrapped wind turbine blades, consisting of structural units and fibers embedded in an epoxy thermoset matrix, were cut into approximately 25 cm x 25 cm squares. These samples were immersed in a swelling fluid consisting of two parts formic acid and one part another solvent, such as tetrahydrofuran (THF), dimethylformamide (DMF), N-methyl-2-pyrrolidone (NMP), dimethyl sulfoxide (DMSO), dichloromethane, chloroform, acetone, acetonitrile, chlorobenzene, diethyl ether, dioxane, ethylene glycol, polyethylene glycol (PEG), glycerol, hexamethylphosphoramide (HMPA), nitromethane, pyridine, trimethylamine, toluene, xylene, benzene, dimethylacetamide (DMAc), dimethoxyethane (DME), diglyme, or dichloroethane. The composite structures were placed under a lid for 40 hours. Afterwards, the swelling fluid was discharged through an outlet into a waste container. The solid components were washed three times with water and dried in a ventilated atmosphere. When dry, each solid component was manually separated and collected by hand, and the released thermosetting epoxy material portion was collected.

[0254] Example 12: Disassembly using salt

[0255] Samples of composite structures from scrapped wind turbine blades, consisting of structural units and fibers embedded in an epoxy thermoset matrix, were cut into approximately 25 cm x 25 cm squares. These samples were immersed in a swelling fluid comprising a saturated aqueous solution of two parts formic acid and at least one dissolved salt, such as NaCl, KCl, CsCl, NaHCO₃, KHCO₃, CsHCO₃, Na₂CO₃, K₂CO₃, and Cs₂CO₃. The composite structures were placed under a cover for 40 hours. The swelling fluid was then drained through an outlet into a waste container. The solid elements were rinsed three times with water and dried in a ventilated atmosphere. Upon drying, each solid element was manually separated and collected, and the released thermoset epoxy material was collected.

[0256] Example 13: Disassembly using surfactants

[0257] Samples of composite structures from scrapped wind turbine blades, consisting of structural units and fibers embedded in an epoxy thermoset matrix, were cut into approximately 25 cm x 25 cm squares. These samples were immersed in a swelling fluid consisting of two parts formic acid and an aqueous solution containing a surfactant. The composite structures were placed under a cover for 40 hours. The swelling fluid was then drained through an outlet into a waste container. The solid elements were rinsed three times with water and dried in a ventilated atmosphere. Upon drying, each solid element was manually separated and collected, and the released thermoset epoxy material was collected.

[0258] Example 14: Disassembly of a Wind Turbine Blade

[0259] A 1000-liter (L) IBC tank was modified with a removable, impermeable lid and two tubes connected to an external heater with a circulation pump. Wind turbine blades were cut into suitable composite sheets that fit into the 1000-liter IBC tank. The composite sheets were stacked as high as possible without disturbing the lid. A swelling fluid containing formic acid was added to the top of the composite sheets and sealed with the lid. Heating was initiated and the swelling fluid was allowed to stand for an appropriate amount of time to completely disassemble the composite sheets. At the end of the experiment, the swelling fluid was pumped through a filter and into a separate 1000-liter tank. The lid was removed and the empty tank was allowed to evaporate any remaining swelling fluid. The thermosetting epoxy material was collected from the filter and stored. Once the formic acid odor had dissipated upon drying, each solid element, including the fiber material, was moved to a separate tank where it was rinsed with a high-pressure water jet (flushing fluid) to remove any adhering thermosetting epoxy material. The water slurry from the rinsed thermosetting epoxy material portion is filtered and the thermosetting epoxy material portion from the filter is stored with other collected thermosetting epoxy material portions and allowed to dry. The cleaned solid components are dried and divided into appropriate recycling bins.

[0260] Example 15: Disassembly of an entire wind turbine blade.

[0261] The composite structure, in the form of a complete wind turbine blade, is removed from the wind turbine nacelle and transported to the facility. There, it is tied down with chains connected to a crane. The wind turbine blade is slowly lowered into a pool of swelling fluid containing formic acid. The pool is sealed with a suitable impermeable plate, heated throughout, and agitated using a recirculating jet. After an appropriate disassembly time, the plate covering the pool is removed. The pool is emptied, and the swelling fluid is transferred to a separate container and filtered to collect the thermosetting epoxy material. The solid components remain in the previously empty pool. The pool is given time to evaporate most of the formic acid and is then fed into a condenser, which is responsible for recovering most of the formic acid for recycling. Once fully dried, the chain is reattached to the crane to gently remove the largest solid components, such as large fiberglass fabrics, core elements such as foam, lightning protection elements, wires, etc. The thermosetting epoxy material is recovered from the bottom of the pool area. The fiber pieces and other solid components to which the thermosetting epoxy portion adheres are rinsed using a high-pressure water jet. The slurry of water and the thermosetting epoxy portion from this rinse is filtered to separate even more of the thermosetting epoxy portion. The remaining solid components, including the fibers, are dried. All solid components are then sorted into appropriate recycling bins based on their material.

[0262] Example 16: Disassembly of wind turbine blade sections by rinsing

[0263] Sprinklers are installed on the top and side walls of the sealed container. A drain pipe with a fine screen is installed at the bottom of the container for filtration. The filtered swelling fluid is circulated to a tank, from which the sprayers extract the swelling fluid, which in this case contains formic acid. A fan is installed at the top of the container and connected to a pipe mounted on a condensing unit. The fan ensures that formic acid vapor from the container is drawn into the condenser, where it condenses and drips into the tank, from which the sprayers extract the liquid.

[0264] Place suitable composite structural sheets cut from wind turbine blades into the container. After closing the door, turn on the external shower and fan. After rinsing the wind turbine blade composite structural sheets with the swelling fluid for an appropriate amount of time, turn off the shower and set the fan to high speed to remove any remaining formic acid from the sheets.

[0265] Once secured, the door is opened and each solid element is separated. Each solid element containing fibrous material is moved to a separate tank, where it is rinsed with a high-pressure water jet to remove any adhering thermosetting epoxy material. The aqueous slurry from the rinsed thermosetting epoxy material is filtered, and the thermosetting epoxy material from the filter is collected and stored together with the thermosetting epoxy material captured by the screen located at the bottom of the container. The cleaned solid elements are dried and divided into appropriate recycling bins.

[0266] Example 17: Decomposition Rate Measurement of Transparent Castings of Different Epoxy Materials

[0267] Decomposition rates of 11 cured dog-bone samples I-XI made from the epoxy resins and hardeners listed in Table 1. Each epoxy resin and hardener was obtained from Olin Corporation (olinepoxy.com). Each dog-bone sample was prepared using the same method as described in Example 1.

[0268] All samples were mixed according to the proportions recommended by the supplier.

[0269] Each dog bone was placed in a 100 mL graduated cylinder and analyzed using a swelling fluid in the form of an aqueous formic acid solution (78 v / v %) according to the experimental procedure described in Example 3. The results obtained from the analysis of each of the 11 dog bone samples revealed that the applied swelling fluid decomposed the various epoxy material formulations.

[0270] Decomposition rates were categorized into four groups. Each group was defined by comparing the decomposition rate of the standard epoxy clear cast dog bone described in Example 3. Group 1) Decomposed at a faster rate than the reference in Example 3. Group 2) Decomposed at a rate corresponding to the decomposition rate of the reference in Example 3. Group 3) Decomposed at a slower rate than the decomposition rate of the reference in Example 3. Group 4) Decomposed at a much slower rate (>50% slower) than the decomposition rate of the reference in Example 3.

[0271] Table 1

[0272]

[0273] TETA = triethylenetetramine

[0274] IPDA = Isophorone diamine

[0275] MXDA = meta-xylenediamine

[0276] As described above, the decomposition rate of each thermosetting epoxy composition can be optimized, for example, by adjusting the composition of the swelling fluid or by soaking at elevated temperature and / or pressure.

[0277] Example 18: Measurement of decomposition rate at different temperatures

[0278] Decomposition rates were measured using transparent cast dog bones prepared as in Example 1. Four dog bones were each placed in a 100 mL graduated cylinder, which was immersed in a 500 mL beaker filled with demineralized water and a magnetic stir bar, placed on top of a temperature-controlled magnetic stirrer. Each beaker was set to a temperature of 20, 40, 60, or 80°C. At time = 0 minutes, a swelling fluid in the form of an aqueous formic acid solution (78 vol / vol%) was poured over each dog bone. The swelling fluid was at a temperature of 25°C at the time of pouring. A time-lapse camera was set to record the decomposition process. Decomposition was analyzed according to the experimental procedure in Example 3. From this experiment, degradation rates at different temperatures were derived. It was found that the degradation rate increased approximately 2-fold for every 20°C increase in temperature. Therefore, it can be concluded that increasing the temperature leads to even faster decomposition rates.

[0279] Example 19: Decomposition rate measurement in saline fluids

[0280] Preparation of saline solution

[0281] Several days in advance, prepare a saturated stock solution of salt in water. Prepare the stock solution by dissolving 40 g of salt (see table) in 100 mL of demineralized water in a beaker. If the salt is completely dissolved, add another 20 g. Continue this process, adding 20 g of salt until residual salt is observed as an undissolved precipitate. After the solutions have been allowed to stand for five days, all solutions will have a visible precipitate of undissolved salt at the bottom of the beaker.

[0282] Prepare 15 stock solutions using one of the following salts: ZnCl2, NaOAc, NaI, KCl, NaSO4, NaCl, KOAc, CuCl2, NaBr, CaCl2, LiBr, AlCl3, NaNO3, KNO3, NH4NO3.

[0283] Decomposition rates were measured using transparent cast dog bones prepared as in Example 1. Each dog bone was placed in a 100 mL graduated cylinder with volume markings per mL on the glassware. At time 0 minutes, a swelling fluid consisting of formic acid (99 v / v%, 75 mL) and a saturated salt stock solution (25 mL) was poured over the dog bone. A time-lapse camera was set up to record the decomposition process. The decomposition rate and degradation effect of each swelling fluid were analyzed according to the experimental procedures in Example 3.

[0284] From this experiment, the approximate disintegration rates of individual dog bones degraded with various swelling fluids containing different dissolved salts were derived, allowing an assessment of the effect of using swelling fluids containing dissolved salts from various 15 stock solutions on the disintegration rate of the dog bones.

[0285] All recorded decomposition rates were significantly slower compared to the reference experiment using the same process with formic acid (99 v / v%, 75 mL) and demineralized water (25 mL) as fluid media.

[0286] For the experiments using NaSO4 and KNO3 salt solutions, the decomposition rate was slightly higher than that of the reference experiment by 50%. For the experiments using other salt solutions, the decomposition rate was slower than that of the reference experiment by more than 50%.

[0287] Example 20 Loss of Mechanical Strength of Epoxy-Fiberglass Laminate

[0288] A glass fiber-reinforced composite laminate, consisting of four layers of commercial glass fiber mat and a thermosetting epoxy matrix vacuum-infused with a commercial epoxy and hardener resin, was cut into smaller rectangular panels approximately 2 cm x 15 cm. The panels were immersed in a 2-liter crystallization beaker and secured horizontally in the center with a clamp. At time 0, a swelling fluid in the form of an aqueous formic acid solution (78 vol / vol%) was poured over the panels to completely bury them. A time-lapse camera was set up to record the changes over time.

[0289] Figure 17a The plate is shown at time = 0. As can be seen, the plate is completely intact and oriented horizontally.

[0290] Figure 17b Shown is the plate at time = 3 hours. As can be seen, the plate maintains its horizontal orientation, but slight signs of degradation are visible on the lower surface of the plate.

[0291] Figure 17c Shown is the board at time = 6 hours. The board is no longer horizontally oriented and shows obvious signs of degradation including separation of the fiberglass mat layers.

[0292] This experiment demonstrated the loss of mechanical strength of the epoxy-fiberglass laminate over time. This phenomenon was observed when the board began to delaminate into separate pieces of fiberglass mat, which then bowed toward the bottom of the beaker due to the pull of gravity.

Claims

1. A method for extracting a thermosetting epoxy material part from a composite material structure, the composite material structure comprising a thermosetting epoxy material matrix and embedded solid element(s), wherein the thermosetting epoxy material matrix has a network structure, the method comprising: • Provide swelling fluid, • immersing the composite structure in a swelling fluid and causing the thermosetting epoxy matrix to swell, with the swelling fluid entering the network structure of the thermosetting epoxy matrix for a sufficient time to mechanically disrupt the network structure to form a plurality of thermosetting epoxy portions separated from the solid component(s), and • separating at least a portion of said thermosetting epoxy material portion from the solid element(s) to obtain a swelling fluid slurry comprising said portion of said thermosetting epoxy material portion in said swelling fluid, wherein the swelling fluid comprises at least 1 mol / L formic acid, such as at least 3 mol / L, such as at least 5 mol / L, such as at least 10 mol / L, such as at least 18 mol / L, such as at least 20 mol / L, such as at least 22 mol / L, such as at least 24 mol / L, such as at least 26 mol / L formic acid.

2. The method of claim 1 , wherein the step of providing a swelling fluid comprises providing a swelling fluid comprising an additional component, optionally wherein the step of providing a swelling fluid comprises mixing formic acid with one or more of the other components and optionally the formed reaction components.

3. The method of claim 1 or claim 2, wherein the swelling fluid is an aqueous solution comprising the formic acid.

4. A process as claimed in claim 2 or claim 3, wherein the further components comprise at least one further organic acid, such as acetic acid, trifluoroacetic acid, trichloroacetic acid, propionic acid, methanesulfonic acid, trifluoromethanesulfonic acid, performic acid or an anhydride of any of these organic acids and / or at least one inorganic acid, such as hydrochloric acid.

5. The method of any one of the preceding claims 2-4, wherein the further component comprises at least one alcohol, such as methanol, ethanol, propanol, isopropanol, butanol, tert-butanol, pentanol.

6. The method of any one of claims 2 to 5, wherein the additional components include additional solvents such as tetrahydrofuran (THF), dimethylformamide (DMF), N-methyl-2-pyrrolidone (NMP), dimethyl sulfoxide (DMSO), dichloromethane, chloroform, acetone, acetonitrile, chlorobenzene, diethyl ether, dioxane, ethylene glycol, polyethylene glycol (PEG), glycerol, hexamethylphosphoramide (HMPA), nitromethane, pyridine, trimethylamine, toluene, xylene, benzene, dimethylacetamide (DMAc), dimethoxyethane (DME), diglyme and / or dichloroethane.

7. The method of any of claims 2 to 6, wherein the additional component comprises at least one dissolved salt, such as NaCl, KCl, CsCl, NaHCO 3 , KHCO 3 , CsHCO 3 , Na 2 CO 3 , K 2 CO 3 , Cs 2 CO 3 , any salt comprising a quaternary ammonium cation, and any salt comprising a tetrafluoroborate anion or a hexafluorophosphate anion.

8. The method of any one of the preceding claims 2 to 7, wherein the further components comprise at least one surfactant, preferably selected from anionic and / or nonionic surfactants such as sulfates, sulfonates, gluconates, cocamide, ethoxylates and / or alkoxylates.

9. The method of any of the preceding claims 2 to 8, wherein the type and amount of the at least one further component is selected depending on the embedded solid elements, preferably to ensure that immersion of the composite structure in the swelling fluid does not cause any significant dissolution or decomposition of the embedded solid elements.

10. A method according to any preceding claim, wherein the swelling fluid has a pH of 2 or greater, such as between 2.5 and 4.

11. The method of any of the preceding claims, wherein the thermosetting epoxy matrix of the composite structure comprises an epoxy material based on at least one reactant, the at least one reactant comprising at least one epoxy resin, wherein the epoxy resin has been cured by radiation (e.g., ionizing, infrared radiation, electron beam, etc.) and / or by passage through at least one hardener, such as one or more anhydride curing agents, one or more thiol curing agents, and / or one or more amine curing agents.

12. The method of any of the preceding claims, wherein the thermosetting epoxy matrix of the composite structure comprises an epoxy material based on at least one epoxy resin, wherein the epoxy resin has been cured by at least one hardener, the at least one hardener comprising an amine-based hardener, such as an aliphatic amine-based hardener, an aromatic amine-based hardener and / or a multifunctional amine hardener.

13. The method of any one of the preceding claims, wherein the thermosetting epoxy matrix does not include disulfide bridge moieties.

14. The method of claim 2, wherein the reactants do not include a disulfide bridge moiety.

15. The method of any of the preceding claims, wherein the embedded solid element(s) comprise at least one of a reinforcing element(s) and a supporting element, wherein the supporting element comprises any element having no reinforcing function, such as fillers, molding aids, electrical components, lightning protection elements, coatings, glue and / or core elements such as foam and / or wood.

16. A method as claimed in any preceding claim, wherein the embedded solid element(s) comprise at least one reinforcement layer, such as two or more reinforcement layers, such as layers comprising one or more of fibres, metals, polymers, wood, ceramics, silicates and / or paint, bonded together by a thermosetting epoxy matrix.

17. The method according to any of the preceding claims, wherein the embedded solid element(s) comprise fibers selected from one or more of synthetic fibers, semi-synthetic fibers, regenerated fibers, plant fibers, carbon fibers, basalt fibers, glass fibers and / or metal fibers, the fibers preferably being in the form of at least one sheet comprising fibers, for example at least one sheet comprising fibers embedded in a polymer different from a thermosetting epoxy matrix.

18. The method of any of the preceding claims, wherein the embedded solid element(s) comprise wood, such as balsa wood and / or foamed plastic, such as foamed plastic comprising at least one of polystyrene (PS), polyurethane (PU), polyvinyl chloride (PVC), polyethylene terephthalate (PET), polyolefins (polyethylene (PE) and polypropylene (PP)) and ABS foam, preferably the foamed plastic being rigid.

19. The method of any of the preceding claims, wherein the solid element(s) comprise reinforcing elements comprising at least one metal such as steel, aluminum, titanium, chromium, cobalt, nickel, copper, zinc, tin, lead and any alloy comprising at least one of the foregoing, preferably the metal comprises a mesh, wire and / or beam.

20. The method of any of the preceding claims, wherein the embedded solid element(s) comprise at least one further thermosetting matrix comprising a cross-linked polyester, a polyurethane, a vulcanized rubber, a cross-linked polyvinyl ester, a cross-linked polyimide, a cross-linked phenolic, a cross-linked polybenzoxazine, a cured amino resin, a cured furan resin, a cured maleimide resin or a cured silicone or any combination comprising at least one of the foregoing.

21. The method of any one of the preceding claims, wherein the step of soaking the composite structure with a swelling fluid is performed at a swelling fluid temperature of up to 100°C, such as 8°C to 75°C, such as 10°C to 50°C, such as 20°C to 35°C, such as 22°C to 27°C.

22. The method of any one of the preceding claims, wherein the step of soaking the composite structure with the swelling fluid is performed at atmospheric pressure or elevated pressure, such as a pressure of up to 3 bar, such as a pressure of up to 2 bar, such as a pressure of up to 1.5 bar.

23. The method of any one of the preceding claims, wherein the step of soaking the composite structure with the swelling fluid comprises contacting the composite structure with the swelling fluid in a treatment vessel, wherein the vessel is preferably a closed or closable vessel.

24. The method of any of the preceding claims, wherein the step of soaking the composite structure with the swelling fluid comprises placing the composite structure in a volume of swelling fluid in a processing vessel and / or spraying the composite structure with the swelling fluid in the processing vessel.

25. The method of any of the preceding claims, wherein the step of soaking the composite structure with a swelling fluid comprises conveying the composite structure stepwise or continuously through a treatment location, wherein the composite structure is treated with the swelling fluid at the treatment location, preferably, the step of soaking the composite structure with the swelling fluid comprises arranging the composite structure on a conveyor belt and conveying the composite structure through a treatment container, wherein the composite structure is treated with the swelling fluid, for example by spraying it with the swelling fluid.

26. The method of any of the preceding claims, wherein the step of soaking the composite structure with the swelling fluid comprises contacting the composite structure with the swelling fluid for a period of up to 144 hours, such as 1 to 130 hours, such as 10 to 100 hours, such as 24 to 96 hours, for example up to 72 hours, such as up to 48 hours.

27. The method of any of the preceding claims, wherein the step of soaking the composite structure with the swelling fluid comprises subjecting the composite structure and / or the swelling fluid to vibrations, for example using ultrasound, and / or subjecting the swelling fluid to motion, for example using stirring, shaking and / or blowing gas into and through the swelling fluid.

28. The method of any preceding claim, wherein the step of separating the thermosetting epoxy material portion from the solid element comprises: The solid element and the swelling fluid are separated by removing the swelling fluid from the solid element to obtain said swelling fluid slurry or by removing the solid element from the swelling fluid to obtain said swelling fluid slurry.

29. The method of any one of the preceding claims, wherein the step of separating the thermosetting epoxy material portion from the solid element comprises subjecting the solid element to at least one cleaning process, preferably comprising cleaning the solid element with a cleaning fluid to obtain a cleaning fluid slurry of at least a portion of the thermosetting resin portion in the cleaning fluid, wherein the cleaning fluid preferably comprises a surfactant, wherein the surfactant preferably comprises an anionic surfactant and / or an amphiphilic surfactant, such as a quaternary ammonium surfactant.

30. The method of any of the preceding claims, wherein the step of separating the thermosetting epoxy material portion from the solid element comprises subjecting the solid element to at least one flushing process, such as high pressure flushing, using a flushing fluid selected from a flushing gas, a flushing liquid or a mixture thereof, thereby obtaining a flushing fluid slurry of at least a portion of the thermosetting resin portion in the flushing fluid.

31. A method as claimed in any preceding claim, wherein the step of separating the thermosetting epoxy material portion from the solid element comprises mechanically deforming the solid element, such as crushing the solid element and / or vibrating the solid element.

32. A method as claimed in any preceding claim, wherein the step of separating the thermosetting epoxy material portion from the solid element comprises mechanically removing the thermosetting epoxy material portion from the solid element, for example by scraping and / or combing the thermosetting epoxy material portion from the solid element.

33. The method of any preceding claim, wherein the step of separating the thermosetting epoxy material portion from the solid element comprises subjecting the solid element to vibration and / or shaking, such as applying an ultrasonic field to the solid element and / or moving the solid element back and forth.

34. The method of any preceding claim, wherein the step of separating the thermosetting epoxy material portion from the solid element comprises filtering.

35. The method of any of the preceding claims, wherein the method further comprises filtering the swelling fluid slurry to collect at least a portion of the thermosetting epoxy material portion from the swelling fluid slurry, wherein the method preferably further comprises recycling the swelling fluid, such as for use in a method according to any of the preceding claims.

36. The method of any of the preceding claims 29-35, wherein the method further comprises filtering the cleaning fluid slurry and / or the flushing fluid slurry to collect at least a portion of the thermosetting epoxy material portion from the cleaning fluid slurry and / or the flushing fluid slurry.

37. The method of claim 35 or claim 36, wherein the method comprises subjecting the collected portion(s) of thermosetting epoxy material to a further washing step and / or drying the portion(s) of thermosetting epoxy material.

38. The method of any of the preceding claims, wherein the method further comprises subjecting the thermosetting epoxy material portion to a depolymerization step, such as a depolymerization step using a good solvent NMP (N-methyl-2-pyrrolidone), an organic catalyst triazabicyclodecene (TBD), and the alcohol ethylene glycol (EG).

39. A method as claimed in any preceding claim, wherein the composite structure has a maximum dimension of at least 0.1 m, such as at least 1 m, such as at least 5 m, such as at least 10 m, such as 15 to 200 m, such as 20 to 100 m.

40. A method as claimed in any preceding claim, wherein the composite structure is the whole or part of a wind turbine blade, an aircraft, a boat, an automobile, a bridge deck, a boat, an aircraft and / or a circuit board.

Images