New epoxy resin compositions for use as structural adhesives.

Abstract

The present invention relates to a method for preparing a curable composition based on pulverized composite material obtained from recycling discarded composite components, such as old pipes or rotor blades from wind power plants. The pulverized composite material can replace virgin short glass fibers and fumed silica that are typically used in such compositions used as structural adhesives, essentially without any adverse effect on performance.

Description

[Technical field]

[0001] The present invention relates to a method for preparing a curable composition, particularly useful for adhesive applications, characterized in that it contains ground composite material made from discarded composite elements, such as old pipes or rotor blades from wind power plants, and its epoxy resin and hardener components. The present invention also relates to the corresponding curable compositions and their components, to the curing of such compositions and the corresponding cured epoxy resins, and to their use as structural adhesives. In such curable compositions, the recycled ground composite material can replace virgin short glass fibers and fumed silica conventionally used in curable compositions used as structural adhesives, essentially without any adverse effect on performance. [Background technology]

[0002] Epoxy resins are well known and are used as adhesives, as materials for surface coatings, and as materials for molding and laminating, and for making fiber-reinforced composites, due to their toughness, flexibility, adhesion and chemical resistance.

[0003] Typical curing agents for epoxy resins are polyamines which cause a polyaddition reaction (chain extension). Highly reactive polyamines are generally added to the epoxy resin only shortly before the desired cure. These systems are therefore so-called two-component (2K) systems. These two-component systems are widely used for the production of fiber-reinforced composites with embedded or impregnated reinforcing fibers, for example by injection or injection processes such as vacuum-assisted resin transfer molding (VARTM) or resin transfer molding (RTM), pultrusion or filament winding processes, or by curing prepregs, sheet molding compounds (SMC), bulk molding compounds (BMC) or structural adhesives. A commonly used reinforcing fiber is glass fiber.

[0004] The use of structural adhesives for bonding components requiring high mechanical strength, for example in the assembly of large composite materials such as large wind turbine blades or structural parts of car bodies, is becoming increasingly important.

[0005] Structural adhesives for such applications usually contain a large amount of short glass fibers to reduce exothermic reactions, as well as to improve mechanical stability and fatigue properties and minimize shrinkage of the bond (Hexion Technical Information for Adhesive EPIKOTE™ Resin MGS® BPR 135G3, publ. 2006). In addition, such structural adhesives usually need to have thixotropic behavior (Henningsen & Ruckdaeschel, “Chemie im Rotorblatt”, Chemie in unserer Zeit, Vol. 55, p. 406-421; section “Verkleben”). The two components (epoxy resin component and hardener component) and the mixed curable composition need to be a high viscosity paste that provides good storage stability without separation of its component elements (e.g. glass fibers and epoxy resin) and allows good application in thick layers or even on vertical surfaces. On the other hand, a low viscosity is required to efficiently mix the components and allow good handling. Such thixotropic behavior is typically achieved by adding fumed silica to the composition, which is a relatively expensive additive. Summary of the Invention [Problem to be solved by the invention]

[0006] Against this background, there is therefore a need, in particular for use as a structural adhesive, for further epoxy resin-based curable compositions in which the normally used short glass fibres, and also eventually partially fumed silica, are replaced by materials obtained from sustainable resources, such as recycled materials, which exhibit at least similar mechanical and adhesive performances, and at least similar or improved thixotropic properties, compared to conventional structural adhesives.

[0007] In the context of the present invention, new epoxy resin-based curable compositions with ground composites are identified that exhibit at least similar or improved mechanical and adhesive performance and thixotropic properties compared to known epoxy resin-based adhesive pastes that use virgin short glass fibers instead. The addition of such ground composites even makes it possible to reduce the amount of expensive fumed silica added, without compromising the thixotropic properties. [Means for solving the problem]

[0008] The present invention therefore relates to a method for preparing a curable composition starting from providing an epoxy resin component comprising at least one epoxy resin and a hardener component comprising at least one amino hardener, the process comprising: (a) providing at least one pulverized composite material prepared by pulverizing a composite material comprising a polymer matrix and glass fibers; (b) combining and mixing at least one ground composite material of step (a) with an epoxy resin component or a hardener component or both; (c) combining and mixing the epoxy resin component resulting from step (b) and the hardener component, at least one of which contains at least one pulverized composite material, preferably by means of an asymmetric centrifugal mixer, a planetary mixer, a high intensity mixer (such as an "Eirich-Mixer"), or a paste metering system equipped with a positive displacement pump for dispensing high viscosity components.

[0009] Also provided is a method for preparing an epoxy resin component comprising at least one ground composite material by combining and mixing at least one ground composite material prepared by grinding a composite material comprising a polymer matrix and glass fibers with an epoxy resin component comprising at least one epoxy resin.

[0010] Also provided is a method for preparing a hardener component comprising at least one ground composite material by combining and mixing at least one ground composite material prepared by grinding a composite material comprising a polymer matrix and glass fibers with a hardener component comprising at least one amino hardener.

[0011] Mixing of the at least one ground composite material with the epoxy resin component, and mixing of the at least one ground composite material with the hardener component, is preferably carried out using an asymmetric centrifugal mixer, a planetary mixer, or an intensive mixer (e.g., an "Eirich mixer"). DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] A further aspect of the present invention is a curable composition obtainable or obtainable by the inventive process for preparing a curable composition.

[0013] Thus, there is provided a curable composition comprising an epoxy resin component comprising at least one epoxy resin and a hardener component comprising at least one amino hardener, characterized in that the epoxy resin component, the hardener component, or both components further comprise at least one ground composite material prepared by grinding a composite material comprising a polymer matrix and glass fibers.

[0014] The present invention further relates to an epoxy resin component comprising at least one epoxy resin, characterized in that the epoxy resin component further comprises at least one ground composite material prepared by grinding a composite material comprising a polymer matrix and glass fibers. Such an epoxy resin component, when combined with a hardener component comprising at least one amino hardener, is particularly suitable for the preparation of a curable composition for use as a structural adhesive. Similarly, the present invention further relates to a hardener component comprising at least one amino hardener, characterized in that the hardener component further comprises at least one ground composite material prepared by grinding a composite material comprising a polymer matrix and glass fibers. Such a hardener component, when combined with an epoxy resin component comprising at least one epoxy resin, is particularly suitable for the preparation of a curable composition for use as a structural adhesive.

[0015] The epoxy resin component according to the present invention optionally comprises one or more further components, preferably selected from the group consisting of reactive diluents, virgin short glass fibers, other reinforcing fibers, fumed silica, and additives. In a particular embodiment, the epoxy resin component according to the present invention comprises at least one epoxy resin, optionally one or more ground composite materials, and optionally one or more further components, selected from the group consisting of reactive diluents, virgin short glass fibers, other reinforcing fibers, fumed silica, and additives. The hardener component according to the present invention optionally comprises one or more further components, preferably selected from the group consisting of anhydride hardeners, virgin short glass fibers, other reinforcing fibers, fumed silica, and additives. In a particular embodiment, the hardener component according to the present invention comprises at least one amino hardener, optionally one or more ground composite materials, and optionally one or more further components, selected from the group consisting of anhydride hardeners, virgin short glass fibers, other reinforcing fibers, fumed silica, and additives. In a particular embodiment, the curable composition according to the present invention comprises an epoxy resin component and a hardener component.

[0016] Preferably, the polymer matrix of the composite material used to make at least one comminuted composite material is a cured epoxy resin or a cured unsaturated polyester resin. Thus, in a preferred embodiment of the present invention, the polymer matrix of at least one comminuted composite material comprises a cured epoxy resin or a cured unsaturated polyester resin, preferably a cured epoxy resin. More preferably, the cured epoxy resin and the cured unsaturated polyester resin make up at least 50% by weight of the total amount of the polymer matrix, in particular the cured epoxy resin and the cured unsaturated polyester resin make up at least 90% by weight of the total amount of the polymer matrix, and more particularly the polymer matrix of at least one comminuted composite material consists of a cured epoxy resin or a cured unsaturated polyester resin or a mixture thereof. In a particular embodiment, the cured epoxy resin makes up at least 50% by weight of the total amount of the polymer matrix, in particular the cured epoxy resin makes up at least 90% by weight of the total amount of the polymer matrix, and more particularly the polymer matrix of at least one comminuted composite material consists of a cured epoxy resin. Typically, the composite members used to make the comminuted composite material are discarded pipes, silo members, or rotor blades of wind power plants, or similar members. Typically, these components are disassembled, cut, shredded, and optionally granulated prior to grinding. This pretreatment typically removes most of the other components, such as wood, metal, and foam. Grinding can be performed, for example, using a pin mill. For finer ground fractions, a fine impact mill can be used.

[0017] The particle size of the ground composite material can be determined by sieving according to standard DIN 66165 (2016). Preferably, the coarse fraction with a particle size of more than 300 μm, as determined by sieving (woven wire mesh sieve with opening size of 300 μm, equivalent to US mesh 50), is removed by sieving from the ground composite material used for the components of the curable composition. Preferably, the amount of very fine fraction of ground composite material with a particle size of less than 32 μm, as determined by sieving (woven wire mesh sieve with opening size of 32 μm, equivalent to US mesh 450), is less than 40% by weight, most preferably less than 25% by weight, based on the total amount of ground composite material. Thus, in a preferred embodiment of the present invention, the particle size of at least 75% by weight of all ground composite material is in the range of 32 to 300 μm, as determined by sieving using woven wire mesh sieves with opening sizes of 32 μm and 300 μm, respectively. Preferably, at least 20% by weight of all ground composite materials has a particle size in the range of 32 to 71 μm as determined by sieving using woven wire mesh sieves having opening sizes of 32 μm and 71 μm, respectively, as specified by standard DIN ISO 3310-1 (2001).

[0018] The glass fibers of at least one of the ground composites (used in the curable composition or the corresponding epoxy resin or hardener component), after removal of fiber-bound and free matrix polymer residues by a baking step, e.g. at a temperature of 650° C. for 2 hours, followed by slow cooling to room temperature, e.g. over a period of 2 hours, preferably have a length-weighted average fiber length in the range of 0.1-1.0 mm, in particular in the range of 0.2-0.9 mm, more in particular in the range of 0.4-0.7 mm, as determined by optical measurements and image analysis, and preferably a fiber diameter in the range of 5-100 μm, in particular in the range of 10-20 μm (as an average of all ground composites used in the curable composition or the corresponding epoxy resin or hardener component).

[0019] Preferably, all ground composites (used in the curable composition or the corresponding epoxy resin or hardener component) have a total inorganic material content in the range of 40-90% by weight, more preferably 50-80% by weight, in particular 55-75% by weight. The amount of inorganic material is determined by thermogravimetric analysis according to the standard DIN EN ISO 1172 (1998). The inorganic material is the sum of glass fibers and any other inorganic materials such as inorganic fillers (such as calcium carbonate powder) that are part of the ground composite. The composite material used for grinding contains, in addition to the amount of glass fibers based on the total amount of inorganic materials, less than 20% by weight, more preferably less than 10% by weight, in particular less than 5%, more in particular less than 1% of such other inorganic materials.

[0020] The ground composite material can be used to replace a proportion of virgin short glass fibers typically contained in the structural adhesive in whole or in part. In certain embodiments of the curable composition, the epoxy resin component and the hardener component contain less than 5 wt. %, more particularly less than 2 wt. %, more particularly less than 1 wt. %, and especially no such virgin glass fibers.

[0021] Preferably, the (total) content of at least one ground composite in the curable composition of the invention is in the range of 5-35% by weight, more preferably in the range of 15-30% by weight, based on the sum of the epoxy resin component and the hardener component. Preferably, the ground composite is evenly distributed between the two components of the curable composition, such that each component (epoxy resin component and hardener component) contains in the range of 5-35% by weight, preferably in the range of 15-30% by weight, of ground composite. In a particular embodiment of the invention, when the ground composite is used to only partially replace a fraction of virgin glass fibers, it is preferred that the total of the ground composite and virgin glass fibers in the curable composition of the invention is in the range of 5-35% by weight, more preferably in the range of 15-30% by weight, based on the sum of the epoxy resin component and the hardener component. It is preferred that the total of the ground composite and virgin glass fibers is in the range of 5-35% by weight, more preferably in the range of 15-30% by weight, based on the sum of the epoxy resin component and the hardener component, based on the sum of the epoxy resin component and the hardener component. It is preferred that the total of the ground composite and virgin glass fibers is in the range of 5-35% by weight, more preferably in the range of 15-30% by weight, based on each component (epoxy resin component and hardener component).

[0022] If virgin glass fibres are used in the curable composition in addition to the ground composite material, these glass fibres are preferably short fibres, preferably with a maximum length in the range of 0.5 to 5.0 mm, in particular in the range of 0.7 to 1.7 mm, and preferably with a length-weighted average fibre length in the range of 0.1 to 1.0 mm, in particular in the range of 0.2 to 0.9 mm, more in particular in the range of 0.3 to 0.7 mm. The diameter of such virgin glass fibres, determined by optical measurements and image analysis, is preferably in the range of 5 to 100 μm, in particular in the range of 10 to 20 μm. The virgin glass fibres used are typically fibres of E-glass, but also fibres of R-glass, S-glass and T-glass.

[0023] Epoxy resin and hardener pastes of structural adhesives usually contain fumed silica as a thixotropic agent. Such fumed silica can be unmodified or modified, for example hydrophobically modified. The presence of such fumed silica increases the consistency of the paste so that the viscosity is high enough to avoid separation of the components of these pastes (e.g. glass fiber or filler and epoxy resin or hardener), which increases the shelf stability of the paste. Such an increase in viscosity is also important in many applications of structural adhesives that need to be applied in thick layers on vertical surfaces and still adhere. At the same time, such thixotropic fumed silica reduces the viscosity under shear, which allows for effective mixing.

[0024] In certain embodiments, the epoxy resin component or the hardener component of the present invention or both also contain fumed silica. Preferably, the content of fumed silica in the corresponding component is in the range of 3-15 wt%, more preferably in the range of 5-10 wt%, based on the sum of the corresponding components. Preferably, the fumed silica is evenly distributed between the two components of the hardenable composition such that each component (epoxy resin component and hardener component) contains fumed silica in the range of 3-15 wt%, preferably in the range of 5-10 wt%.

[0025] Surprisingly, the ground composite is not only a good replacement for virgin short glass fibers in structural adhesives, but also exhibits thixotropic properties, and therefore can partially replace the addition of fumed silica, especially when used in higher amounts. Thus, in certain embodiments, the curable composition of the present invention also comprises, based on the total curable composition, 2-13 wt. % of fumed silica and 8-55 wt. % of ground composite, respectively, more preferably 2.5-11 wt. % of fumed silica and 15-45 wt. % of ground composite, in particular 3.5-9 wt. % of fumed silica and 20-40 wt. % of ground composite. Preferably, the fumed silica and the ground composite are evenly distributed between the two components of the hardenable composition such that each component (epoxy resin component and hardener component) contains, respectively, based on the sum of the corresponding components, in the range of 2 to 13 wt. % fumed silica and in the range of 8 to 55 wt. % ground composite, more preferably in the range of 2.5 to 11 wt. % fumed silica and in the range of 15 to 45 wt. % ground composite, especially in the range of 3.5 to 9 wt. % fumed silica and in the range of 20 to 40 wt. % ground composite.

[0026] When used as an adhesive paste, the yield point of the curing agent component measured at room temperature (25° C.) is preferably in the range of 500 to 1500 Pa. If the yield point is low, the paste components are more likely to separate, shortening the storage period, whereas if the yield point is high, the workability (mixing, portioning, and application) of the paste is reduced.

[0027] When used as an adhesive paste, the maximum viscosity of the hardener component is preferably in the range of 0.5 to 3.5 MPa·s measured at room temperature (25°C). If the maximum viscosity is low, the paste components are more likely to separate, shortening the storage period, while if the maximum viscosity is high, the workability of the paste (mixing, portioning, and application) decreases.

[0028] When used as an adhesive paste, the viscosity of the epoxy resin component, measured according to DIN ISO 3219 (1993) at a shear rate of 50 Hz and room temperature (25°C), is preferably in the range of 20 to 100 Pa·s, in particular in the range of 30 to 80 Pa·s. If the viscosity is low, the paste components will be more likely to separate, shortening the shelf life, while if the viscosity is high at a shear rate of 50 Hz, the workability of the paste (mixing, portioning, and application) will be reduced.

[0029] The epoxy resin according to the invention typically has 2 to 10, preferably 2 to 6, even more preferably 2 to 4, in particular 2 epoxy groups. The epoxy groups are in particular glycidyl ether groups formed by reaction of an alcohol group with epichlorohydrin. The epoxy resin generally has an average molecular weight (M n) or higher molecular weight compounds (polymers). Such polymeric epoxy resins preferably have a degree of oligomerization of 2 to 25 units, more preferably 2 to 10 units. The resins may be aliphatic or cycloaliphatic compounds or compounds with aromatic groups. In particular, epoxy resins are compounds with two aromatic or aliphatic 6-membered rings or oligomers thereof. Industrially important epoxy resins are those which can be obtained by reaction of epichlorohydrin with compounds having at least two reactive hydrogen atoms, in particular with polyols. Of particular importance are epoxy resins which can be obtained by reaction of epichlorohydrin with compounds containing at least two, preferably two hydroxyl groups and two aromatic or aliphatic 6-membered rings. Such compounds include in particular bisphenol A and bisphenol F, and also hydrogenated bisphenol A and bisphenol F, the corresponding epoxy resins being the diglycidyl ethers of bisphenol A or bisphenol F, or of hydrogenated bisphenol A or bisphenol F. The epoxy resin used according to the invention is typically bisphenol A diglycidyl ether (DGEBA). Suitable epoxy resins according to the invention also include tetraglycidylmethylenedianiline (TGMDA) and triglycidylaminophenol or mixtures thereof. Also suitable are reaction products of epichlorohydrin with other phenols, for example cresol or phenol-formaldehyde adducts, especially phenol-aldehyde resins such as novolaks. Epoxy resins not derived from epichlorohydrin are also suitable. Examples of useful resins include epoxy resins containing epoxy groups by reaction with glycidyl (meth)acrylate. According to the invention, it is preferred to use epoxy resins or mixtures thereof that are liquid at room temperature (25° C.). The epoxy equivalent weight (EEW) indicates the average mass of epoxy resin in g per mole of epoxy group.

[0030] In certain embodiments, the epoxy resin component of the present invention may further comprise a reactive diluent. A reactive diluent in the context of the present invention is a compound that reduces the viscosity of the epoxy resin component and the corresponding curable composition and forms chemical bonds with the developing network of the epoxy resin and the curing agent during the curing of the curable composition. In the context of the present invention, the preferred reactive diluent is a low molecular weight organic compound, preferably an aliphatic compound, that contains one or more epoxy groups.

[0031] The reactive diluent of the present invention is preferably selected from the group consisting of butane-1,4-diol diglycidyl ether, hexane-1,6-diol diglycidyl ether (HDDE), glycidyl neodecanoate, glycidyl versatate, 2-ethylhexyl glycidyl ether, neopentyl glycol diglycidyl ether, p-tert-butyl glycidyl ether, butyl glycidyl ether, C8-C10-alkyl glycidyl ethers, C12-C14-alkyl glycidyl ethers, nonylphenyl glycidyl ether, p-tert-butylphenyl glycidyl ether, phenyl glycidyl ether, o-cresyl glycidyl ether, polyoxypropylene glycol diglycidyl ether, trimethylolpropane triglycidyl ether (TMP), glycerol triglycidyl ether, triglycidyl paraaminophenol (TGPAP), divinylbenzyl dioxide and dicyclopentadiene diepoxide. They are more preferably selected from the group consisting of butane-1,4-diol diglycidyl ether, hexane-1,6-diol diglycidyl ether (HDDE), 2-ethylhexyl glycidyl ether, C8-C10-alkyl glycidyl ethers, C12-C14-alkyl glycidyl ethers, neopentyl glycol diglycidyl ether, p-tert-butyl glycidyl ether, butyl glycidyl ether, nonylphenyl glycidyl ether, p-tert-butylphenyl glycidyl ether, phenyl glycidyl ether, o-cresyl glycidyl ether, trimethylolpropane triglycidyl ether (TMP), glycerol triglycidyl ether, divinylbenzyl dioxide and dicyclopentadiene dipoxide. They are in particular selected from the group consisting of butane-1,4-diol diglycidyl ether, C8-C10-alkyl monoglycidyl ethers, C12-C14-alkyl monoglycidyl ethers, hexane-1,6-diol diglycidyl ether (HDDE), neopentyl glycol diglycidyl ether, trimethylolpropane triglycidyl ether (TMP), glycerol triglycidyl ether and dicyclopentadiene dipoxide.

[0032] The reactive diluent according to the invention preferably accounts for a proportion of up to 30% by weight, more preferably up to 25% by weight, in particular from 1% to 20% by weight, based on the amount of epoxy resin.

[0033] In the context of the present invention, amino hardeners are understood to mean amines having an NH functionality of ≧2 (thus, for example, a primary monoamine has an NH functionality of 2, a primary diamine has an NH functionality of 4, an amine with 3 secondary amino groups has an NH functionality of 3).

[0034] The amino curing agent used in the hardener component of the present invention can be any aliphatic, cycloaliphatic and aromatic polyamine. Examples of suitable amino curing agents include: Aliphatic amines, such as diethylenetriamine (DETA), triethylenetetramine (TETA), tetraethylenepentamine (TEPA), 1,12-diaminodecane, 1,10-diaminodecane, 1,5-diaminopentane (cadaverine), propane-1,2-diamine, propane-1,3-diamine, Cycloaliphatic amines, such as dimethicone, dimethyldimethicone (DMDC), isophoronediamine (IPDA), 1,3-bis(aminomethyl)cyclohexane (1,3-BAC), bis(p-aminocyclohexyl)methane (PACM), 4-methylcyclohexane-1,3-diamine, 2-methylcyclohexane-1,3-diamine, mixtures of 4-methylcyclohexane-1,3-diamine and 2-methylcyclohexane-1,3-diamine (MCDA), 1,2-diaminocyclohexane (DACH), menthane diamine, Aromatic amines, for example methylenedianiline (e.g. 4,4'-methylenedianiline), diaminodiphenylmethane (DDM), diaminodiphenylsulfone (DDS), toluene-2,4-diamine, toluene-2,6-diamine, 2,4-diamino-3,5-diethyltoluene, 2,6-diamino-3,5-diethyltoluene (DETDA), 1,2-diaminobenzene, 1,3-diaminobenzene, 1,4-diaminobenzene, diaminodiphenyl oxide, 3,3',5,5'-tetramethyl-4,4'-diaminodiphenyl, 3,3'-dimethyl-4,4'-diaminodiphenyl, Polyetheramines, such as, for example, D230 polyetheramine, D400 polyetheramine, D2000 polyetheramine or T403 polyetheramine, 4,9-dioxadodecane-1,12-diamine (DODA), 4,7,10-trioxatridecane-1,13-diamine (TTD), ether amines, e.g. 2,2'-oxydi(ethylamine), polyaminoamides, such as Versamid® 140 or Epilox® H15-40, Amidoamines, and Arylamines, such as metaxylylenediamine (MXDA), Resin adducts produced by reacting excess amounts of the aforementioned amines with epoxy resins, Ketimines, which are reaction products of the above-mentioned primary amines and ketones, Mannich base adducts which are reaction products of the aforementioned amines with formaldehyde and phenol or phenol derivatives.

[0035] Preferably, the at least one amino hardener in the context of the present invention is one or more amines selected from the group consisting of polyaminoamides, their resin adducts, polyetheramines, their resin adducts, cycloaliphatic amines, their resin adducts, and Mannich base adducts.The hardener component of the present invention may also contain anhydride hardeners, but is preferably free or substantially free of anhydride hardeners.In the context of the present invention, anhydride hardeners are understood to mean intramolecular carboxylic acid anhydrides, such as 4-methyltetrahydrophthalic anhydride.

[0036] In the curable composition of the present invention, the epoxy compound (epoxy resin with optional reactive diluent having epoxy groups) of the epoxy resin component and the amino curing agent of the curing agent component are preferably used in an approximately stoichiometric ratio based on the epoxy group and NH functionality. A particularly suitable ratio of epoxy group to NH functionality is, for example, 1:0.8 to 1:1.2. Alternatively, in a specific embodiment of the present invention, the epoxy compound (epoxy resin with optional reactive diluent having epoxy groups) and the amino curing agent are preferably used in an approximately equivalent ratio in the epoxy resin composition of the present invention, preferably in a ratio ranging from 1:0.8 to 1:1.2, based on the EEW of the epoxy compound and the AHEW of the amino curing agent.

[0037] The curable composition of the present invention (its epoxy resin component and / or its hardener component) may also contain additional reinforcing fibers, such as carbon fibers or virgin long glass fibers, in addition to the glass fibers or additional virgin short glass fibers that are part of the ground composite material. In certain embodiments, the curable composition does not contain such additional reinforcing fibers.

[0038] The curable composition of the present invention (its epoxy resin component and / or its hardener component) may also comprise further additives, such as inert diluents, curing accelerators, curing catalysts, pigments, colorants, fillers, mold release agents, reinforcing agents, flow agents, defoamers, flame retardants or thickeners. Such additives are typically added in functional amounts, i.e., for example, pigments are typically added in an amount that provides the composition with the desired color. The composition of the present invention typically comprises 0% to 50% by weight, preferably 0% to 20% by weight, for example 2% to 20% by weight, based on the entire curable composition, relative to the total of all additives. In the context of the present invention, additives is understood to mean all additives to the curable composition (or its epoxy resin component or hardener component), which are neither epoxy compounds (epoxy resins or reactive diluents with epoxy groups), nor hardeners (amino hardeners and / or anhydride hardeners), nor ground composites, nor fumed silica, nor virgin short glass fibers, nor other reinforcing fibers. In the context of the present invention, the additives are preferably selected from the group consisting of inert diluents, curing accelerators, curing catalysts, pigments, colorants, fillers, mold release agents, reinforcing agents, flow agents, defoamers, flame retardants and thickeners.

[0039] The present invention further provides a method for preparing a cured epoxy resin by curing the curable composition of the present invention. To this end, a curable composition is provided by combining and mixing its components (epoxy resin component and hardener component) and then cured at a temperature viable for use. Curing is preferably carried out at a temperature of at least 50°C, more preferably at least 60°C. Curing can be carried out at a temperature below 120°C, especially below 100°C, especially at a temperature in the range of 50-120°C, most preferably at a temperature in the range of 60-120°C. Curing can preferably be carried out under standard pressure. The process for producing the cured material includes wet compression methods such as bulk moulding compression or sheet moulding compression.

[0040] In certain embodiments, the present invention provides a method of bonding at least two substrates, the method comprising: (i) applying the curable composition of the present invention to at least one substrate to obtain a substrate at least partially coated with the curable composition; (ii) contacting at least two substrates, at least one of which is coated with a curable composition; (iii) curing the curable composition.

[0041] Preferred substrates for the bonding method are one or more materials selected from the group consisting of metal, glass, concrete, and plastics, such as polyethylene, polypropylene, polyurethane, polyester, polyamide, or polyepoxide, including any composites thereof. Preferably, the curable composition is provided by mixing the epoxy resin component, the hardener component, and optionally further components such as additives, before applying it to at least one substrate, by means of an asymmetric centrifugal mixer, a planetary mixer, a high-intensity mixer (e.g., an "Eirich mixer"), or a paste metering system equipped with a positive displacement pump for dispensing high viscosity components. Preferably, the curable composition is provided at a temperature in the range of -10 to 40°C, in particular at room temperature, and applied to at least one substrate. Preferably, the curable composition is applied to at least one substrate with a thickness in the range of 1 to 50 mm, in particular in the range of 3 to 30 mm. Preferably, the curing in step (iii) is carried out by exposing the curable composition to a temperature in the range of 50 to 120°C, preferably for 0.5 to 24 hours, more preferably for 1 to 15 hours, in particular for 2 to 10 hours.

[0042] The present invention further provides a cured epoxy resin comprised of the curable composition of the present invention. More specifically, the present invention provides a cured epoxy resin obtainable or obtainable by curing the curable composition of the present invention. More specifically, the present invention provides a cured epoxy resin obtainable or obtainable by the process of the present invention for preparing a cured epoxy resin.

[0043] The cured epoxy resin essentially represents the length distribution of the short fibers used in the underlying curable composition in the form of virgin short fiber material or in the form of ground composite. Thus, the glass fibers of the cured epoxy resin of the present invention, after removal of fiber-bound and free matrix polymer residues, for example by baking at a temperature of 650° C. for 2 hours followed by slow cooling to room temperature over a period of, for example, 2 hours, preferably have a length-weighted average fiber length in the range of 0.05 to 1.0 mm, in particular in the range of 0.1 to 0.8 mm, more particularly in the range of 0.3 to 0.7 mm, and a fiber diameter in the range of 5 to 100 μm, in particular in the range of 10 to 20 μm, determined by optical measurement and image analysis.

[0044] In the curable compositions of the present invention, virgin short glass fibers and fumed silica are replaced with ground composite material made from discarded composite components such as wind farm pipes and rotor blades with essentially no adverse or even beneficial impact on their performance as structural adhesives, allowing for sustainable use of these composite components through such recycling.

[0045] The present invention further provides the use of the curable composition of the present invention as a structural adhesive.

[0046] The particle size of the ground composite material or virgin short glass fiber material can be determined by sieving according to standard DIN 66165 (2016) using a vibrating sieve shaker (e.g. AS300 from Retsch) equipped with standardized sieves (e.g. woven wire mesh sieves according to standard DIN ISO 3310-1 (2001) from Retsch) with specific mesh or opening sizes (e.g. a stack consisting of a lid, a 500 μm sieve, a 300 μm sieve, a 125 μm sieve, a 71 μm sieve, a 32 μm sieve and a bottom). It should be noted that in this method, fibers that deviate significantly from a spherical shape are assigned a smaller particle size, even though they may be much longer.

[0047] The fiber size (length and diameter distribution) of virgin short glass fibers and of fiber pieces in crushed composites can be determined by optical measurements and image analysis. To analyze fiber size in crushed composites or in cured epoxy resins, fiber-bound and free matrix polymer residues must first be removed from the fiber pieces by baking at a temperature of preferably 650 °C for 2 h, followed by slow cooling to room temperature, for example over 2 h. Slow cooling minimizes thermal tensions that can cause fiber breakage. To determine the fiber length distribution of cured resin samples, samples of at least 4 × 10 × 10 mm are required to avoid underestimating the upper limit of reasonable fiber lengths. 3 A piece of size 0.01 mm should be used. Digital images with sufficient resolution for fiber length analysis are obtained by optical microscopy or by high-resolution scans (at least 2400 dpi) acquired with a flatbed scanner. The length of each individual fiber can be recorded and classified manually using common image analysis software such as ImageJ, or using dedicated software for automated fiber length distribution analysis such as FiVer (Sueddeutsches Kunststoffzentrum Wuerzburg). The following parameters are suitable to describe the fiber length distribution: arithmetic mean fiber length (Ln), length-weighted mean fiber length (Lw), and arithmetic and weighted percentile values ​​(dn25, dn50, dn75, dn95, and dw25, dw50, dw75, dw95). The length-weighted mean fiber length is calculated by dividing the sum of the squares of the individual fiber lengths by the sum of the individual fiber lengths. In the context of the present invention, the term maximum length is understood as the dw95 value (the 95% percentile length-weighted fiber length, meaning that 95% of the total fiber weight measured is comprised of fibers shorter than this value). A statistically valid distribution is obtained when at least 1,000, preferably at least 10,000 fibers are analyzed per sample.

[0048] The viscosity of the epoxy resin component or the hardener component can be determined according to the standard DIN ISO 3219 (1993). The viscosity is measured using a shear stress controlled rheometer (e.g. MCR301 from Anton Paar) with a plate-plate configuration (e.g. sandblasted plate with a diameter of 25 mm and a gap width of 1 mm (e.g. PP25-S configuration from Anton Paar). The measurement temperature and the shear rate are important factors in these measurements, since they have a large effect on the viscosity. Therefore, to be comparable, the viscosity needs to be determined at a specific temperature, such as room temperature (25° C.), and at a specific shear rate, such as 50 Hz. For best reproducibility, the rheological measurements are carried out 24 hours after mixing the paste (epoxy resin component or hardener component).

[0049] The maximum viscosity of the hardener component can be determined using a shear stress controlled rheometer (e.g. MCR301 from Anton Paar) with a plate-plate configuration (e.g. PP25-S configuration with sandblasted plates of 25 mm diameter and 1 mm gap width) to measure the viscosity, e.g., for a period of 1,500 seconds, as a function of shear stress in the range of e.g. 1-3,000 Pa, at room temperature (25° C.). The maximum viscosity is defined as the average of all measured viscosity values ​​above a value of 100,000 Pa·s.

[0050] The yield point is a measure of the stress at which an elastic material ceases to behave elastically under increasing stress. Under conditions of tensile strength, the elongation is no longer proportional to the increase in stress. The yield point of the hardener component can be determined, for example, by measuring the viscosity as a function of shear stress in the range of, for example, 1 to 3,000 Pa, for a period of, for example, 1,500 seconds, at room temperature (25°C), using a shear stress controlled rheometer (for example, MCR301 from Anton Paar) with a plate-plate arrangement (for example, PP25-S arrangement of sandblasted plates with a diameter of 25 mm and a gap width of 1 mm). The yield point is defined as the shear stress at which the viscosity falls below a value of 10,000 Pa·s.

[0051] Amine hydrogen equivalent weight (AHEW) can be determined theoretically or experimentally as described by B. Burton et al (Huntsman, “Epoxy Formulations using Jeffamine Polyetheramines”, Apr. 27, 2005, p. 8-11). The theoretically calculated amine hydrogen equivalent weight is defined as the molecular weight of the amine divided by the number of available amine hydrogens (e.g., 2 per primary amino group plus 1 per secondary amino group). For example, for IPDA with a molecular weight of 170.3 g / mol and 2 primary amino groups, i.e., 4 available amine hydrogens, the theoretically calculated amine hydrogen equivalent weight is 170.3 / 4 g / eq = 42.6 g / eq. Experimental determination of amine hydrogen equivalent weight can be used to determine the maximum heat distortion resistance (heat distortion temperature (HDT)) or maximum glass transition temperature (T g Therefore, to experimentally confirm the amine hydrogen equivalent, a mixture of a fixed amount of epoxy resin and various amounts of amino hardener is cured as completely as possible and its HDT or T is obtained. g is determined and the properties thus ascertained are plotted against the ratio of starting materials. The experimental amine hydrogen equivalent is particularly important when the theoretically calculated amine hydrogen equivalent cannot be obtained, for example in the case of mixtures of polymerizable amines. In the context of the present invention, the AHEW is calculated by dividing the theoretical hydrogen equivalent, if available, by the maximum T g (measured by DSC according to standard ASTM D3418-15(2015))

[0052] The adhesive strength of an adhesive paste, such as the curable composition of the present invention, on a particular surface material can be determined as follows: the freshly mixed adhesive paste is applied as a layer of a defined thickness (e.g. 3 mm) to a test surface (e.g. a plate of cured epoxy resin material) to fix a dolly (e.g. aluminum with a diameter of 20 mm). The adhesive paste is then cured (e.g. 12 hours at 80°C). The adhesive strength is then determined by applying an increasing tensile strength at a defined increasing rate (e.g. an increasing rate of 0.2 MPa / s) to measure the adhesive strength to peel of the glued dolly according to standard ISO4624 (2016). Test runs in which the dolly peels off from the cured adhesive are considered invalid and are not counted, since such peeling is not related to the adhesive strength between the adhesive paste and the test surface.

[0053] The mechanical properties (e.g., tensile modulus (Et), tensile stress at break (σ-B), tensile elongation, flexural modulus, flexural strength, and flexural elongation) of test specimens constructed of cured epoxy resin materials can be determined at room temperature (25°C) according to standard ISO 527-2:1996, combining ISO 527-1 (2012) and ISO 178 (2006).

[0054] The glass transition temperature (T g ) can be determined using a differential scanning calorimeter (DSC), for example according to standard ASTM D3418 (2015). This involves heating a very small amount of sample (e.g., about 10 mg) in an aluminum crucible (e.g., at 5 °C / min) and measuring the heat flow to a reference crucible. The T of the heat flow curve g The process evaluation can be determined via the inflection point according to the half-width or midpoint temperature method. EXAMPLES

[0055] Example 1 Preparation of milled composite materials The ground composites (samples A, B, C, and D) were prepared from glass fiber reinforced composites based on cured epoxy resin (EP) or unsaturated polyester resin (UP) as matrix material in a pin mill (PM) for coarse powders or in a fine impact mill (FIM). Coarse particles with particle size above 300 μm were removed by sieving (US mesh 50).

[0056] The particle size distribution was determined by sieving according to standard DIN 66165 (2016) using a vibrating sieve shaker (AS300, from Retsch) (the natural resonance frequency of this device is determined by the setup and loading of the stack). The stack consisted of the following sieves (woven wire mesh sieves according to standard ISO 3310-1, from Retsch): lid, 500 μm sieve, 300 μm sieve, 125 μm sieve, 71 μm sieve, 32 μm sieve, bottom. Classification was achieved by sieving 100 g of material for 5 min with an amplitude of 1.55 mm. The particle size distribution of virgin short glass fibres (E glass, type F2F, from Profill) used for the comparative example (GF) was determined in the same way.

[0057] The proportion of inorganic material was determined by thermogravimetric analysis according to standard DIN EN ISO 1172 (1998). These results are summarized in Table 1. The starting material used for grinding contained essentially no other inorganic material (such as inorganic fillers) in addition to short glass fibres, as evidenced by electron microscopy of the resulting ground composite material.

[0058] The length distribution of glass fiber fragments and virgin short glass fibers in these ground composites was also determined by image analysis of high-resolution (2,400 dpi) flatbed scanner images. Residues of matrix polymer in the ground composite samples were removed prior to imaging by calcining approximately 1 g of ground composite at 650 °C for 2 h, followed by slow cooling to room temperature over 2 h. A spatula tip of the calcined fiber was added to a 250 mL bottle filled with water and dispersed by shaking. Before the fibers settled, an aliquot of the dispersion was transferred to a clear Petri dish placed on the scanner bed. After the bottom of the Petri dish was completely covered with liquid, the fibers were allowed to stand for at least 1 min before scanning the still-wet sample. Virgin short glass fiber material was analyzed in the same way. Digital images of the samples were analyzed using an automated algorithm in the fiber length analysis software (FiVer, Sueddeutsches Kunststoffzentrum Wuerzburg) that counted at least 10,000 particles per sample, and the arithmetic mean fiber length (Ln), length-weighted mean fiber length (Lw), arithmetic percentile values ​​(dn25, dn50, dn75, dn95), and weighted percentile values ​​(dw25, dw50, dw75, dw95) are summarized in Table 1.

[0059] [Table 1]

[0060] Example 2 Preparation and rheological analysis of resin paste (epoxy resin component) 69 wt. % bisphenol A diglycidyl ether epoxy resin (EEW:187), 7.7 wt. % 1,6-hexanediol diglycidyl ether reactive diluent (EEW:150), 7.3 wt. % fumed silica, and 16 wt. % ground composite of Example 1 (A, B, C, or D) were vigorously mixed for 5 min at 2,100 rpm at 20 mbar using a double asymmetric centrifugal mixer (SpeedMixer®, from Hauschild, SM) or for 10 min at 300 rpm (blade stirrer tool) and 3,000 rpm (dispersing disc tool) using a planetary mixer (Labotop with dispersing disc and blade stirrer tool, from PC Laborsystems, LT) at 10 mbar.

[0061] In further tests, epoxy resin component B was modified to replace a higher proportion of ground composite (26.3 wt%) and a reduced portion of the fumed silica to 6.0 wt% (combined with 61.0 wt% bisphenol A diglycidyl ether epoxy resin and 6.7 wt% 1,6-hexanediol diglycidyl ether reactive diluent, B') or 5.3 wt% (combined with 61.5 wt% bisphenol A diglycidyl ether epoxy resin and 6.9 wt% 1,6-hexanediol diglycidyl ether reactive diluent, B''). These tests were mixed accordingly.

[0062] For comparison, samples with 16 wt. % virgin short glass fibre (E glass, type F2F, from Profill) instead of the ground composite (GF) or with neither ground composite nor virgin short glass fibre (with increasing amounts of other components) (NF) were prepared accordingly.

[0063] The viscosity of the resulting resin paste at a shear rate of 50 Hz (η R-50Hz) was measured at room temperature (25 °C) using a shear stress controlled rheometer (MCR301 from Anton Paar) with a plate-plate configuration (PP25-S, plate diameter 25 mm, sandblasted plates, gap width: 1 mm) according to standard DIN ISO 3219 (1993). The viscosity as a function of shear rate was measured in the range 0.0001 to 100 Hz using a logarithmic ramp over a total measurement period of 19.425 s. The viscosity at 50 Hz (η R-50Hz ) was read from the linear interpolation curve. Tests were performed with at least five replicates, and the mean and SEM of all replicates were calculated. The results are summarized in Table 2.

[0064] [Table 2]

[0065] All pastes containing ground composites (A, B, C, D, B', B'') had significantly higher η than the paste containing virgin glass fibers (GF) prepared in the same way. R-50Hz Even higher values ​​were obtained for samples with a reduced fumed silica content of 20% (B') or 30% (B''), allowing the preparation of stable pastes with suitable rheological profiles at low cost. All samples showed pronounced thixotropy. Pastes containing ground composites had viscosities of at least 50 kPa·s in the low shear rate range below 0.001 Hz, exceeding those of the corresponding prepared reference samples that did not contain ground material or contained only virgin short glass fibers. Thus, the samples containing ground composites show comparable shear thinning behavior and similarly good workability, while promising at least a comparable shelf life to the reference.

[0066] Example 3 Preparation of hardener paste (hardener component) and rheological analysis 76 wt.% of a commercial amino hardener blend containing polyaminoamides, polyetheramines, and cycloaliphatic diamines (overall AHEW of 80), 7 wt.% fumed silica, and 17 wt.% of the ground composite material of Example 1 (A, B, C, or D) were vigorously mixed using a double asymmetric centrifugal mixer (SpeedMixer®, from Hauschild, SM) or a planetary mixer (Labotop, from PC Laborsystems, LT) as described for mixing the epoxy components in Example 2.

[0067] In further tests, hardener component B was modified to replace a higher proportion of ground composite (27.9 wt%) with a reduced portion of the fumed silica, either 5.7 wt% (combined with 66.4 wt% amino hardener mixture, B') or 5.0 wt% (combined with 67.1 wt% amino hardener mixture, B''). These components were mixed accordingly.

[0068] For comparison, samples with 17% virgin short glass fibre (E-glass, type F2F, from Profill) instead of the ground composite (GF) or with neither ground composite nor virgin short glass fibre (with increasing amounts of other components) (NF) were prepared accordingly.

[0069] The yield point (yp) and maximum viscosity (η 最大 ) was measured at room temperature (25 °C) using a shear stress controlled rheometer (MCR301 from Anton Paar) with a plate-plate configuration (PP25-S, plate diameter 25 mm, sandblasted plates, gap width: 1 mm). The viscosity was measured as a function of shear stress from 1 Pa to 3,000 Pa for a period of, for example, 1,500 seconds (corresponding to 2 seconds per data point or an increase in shear stress of 2 Pa / s). The maximum viscosity is given as the average of all measured viscosity values ​​above a value of 100,000 Pa·s, and the yield point is given as the shear stress at which the viscosity falls below a value of 10,000 Pa·s. The tests were performed in at least five replicates and the average and SEM of all replicates were calculated. The results are summarized in Table 3.

[0070] [Table 3]

[0071] The pastes containing ground composites (A, B, C, D, B', B'') have yp and η values ​​equal to or exceeding those of the paste containing virgin glass fibers (GF) prepared in the same manner. 最大 When prepared in the Labotop mixer, the samples containing the milled composites showed significantly higher yp and η values ​​than the corresponding pastes containing virgin short glass fibres. 最大 Even samples with a fumed silica content reduced by 20% (B') or 30% (B'') showed higher values, allowing the preparation of stable pastes with suitable rheological profiles at low cost. All samples showed thixotropic behavior with pronounced shear thinning. All pastes containing milled composites showed yield points above 500 Pa, guaranteeing a shelf life and good workability at least comparable to the GF criteria.

[0072] Example 4 curing speed Epoxy resin pastes (B, D, and Comparative GF) and hardener pastes (B, D, and Comparative GF) were prepared using a double asymmetric centrifugal mixer (SpeedMixer®, from Hauschild) (SM) or a planetary mixer (Labotop, from PC Laborsystems) (LT) as described in Examples 2 and 3. The corresponding epoxy resin pastes (100 g) and hardener pastes (45 g each) were vigorously mixed using a double asymmetric centrifugal mixer (SpeedMixer®, from Hauschild). Samples (10-20 mg each) of the resulting two-component compositions were weighed directly into the sample pans, then closed with a perforated lid and cured in an oven at 70° C. for the samples mixed with LT or 80° C. for the samples mixed with SM for various times (2 h, 4 h, 6 h, 8 h, or 15 h). The glass transition temperatures (Tg ) was measured immediately after these various cure times by modulated differential scanning calorimetry (PS Gill, et al. Journal of Thermal Analysis (1993), vol. 40, pages 931-939) using the following temperature profile: 10°C → 5K / min, up to 100°C, modulating by 1K every 60 seconds. g The values ​​of were obtained from the reversing heat flow curves. The results are summarized in Table 5.

[0073] [Table 4]

[0074] The replacement of virgin glass fibers (GF) with ground composites (B, D) results in a slight decrease in the cure rate during the initial cure period. For both types of ground composites (UP and EP systems), the glass transition temperatures are comparable to those obtained with virgin glass fibers.

[0075] Example 5 Peel test using structural adhesives The epoxy resin paste and the hardener paste were prepared using a double asymmetric centrifugal mixer (SpeedMixer®, from Hauschild) or a planetary mixer (Labotop, from PC Laborsystems) as described in examples 2 and 3. The corresponding epoxy resin paste (100 g) and hardener paste (45 g) were mixed vigorously using a double asymmetric centrifugal mixer (SpeedMixer®) accordingly. The obtained two-component adhesive paste was applied as a layer of 3 mm thickness to a surface (a plate of glass fiber reinforced (unidirectional mat) composite material made by the VARTM process using amine-cured epoxy resin as matrix polymer) and a dolly (aluminium, 20 mm in diameter) was fixed. The adhesive paste was cured at 80° C. for 12 hours. The adhesive strength was determined by applying an increasing tensile strength (0.2 MPa / s) to measure the adhesive strength against peeling of the glued dolly (PosiTest AT, from DeFelsko) according to standard ISO 4624 (2016). Tests in which the dolly peeled off the cured adhesive were considered invalid and were not counted. Tests were performed with at least three valid replicates in order to calculate the mean and SEM of all replicates. The results are summarized in Table 5.

[0076] [Table 5]

[0077] Comparable values ​​of adhesion strength were obtained for all samples. Since the substrate used can be considered as a model system of wind blade halves, the results suggest that virgin short glass fibres can be completely replaced by the milled composite used without adversely affecting the adhesion strength.

[0078] Example 6 Mechanical properties of cured structural adhesives. Epoxy resin pastes and hardener pastes were prepared using a double asymmetric centrifugal mixer (SpeedMixer®, from Hauschild) (SM) or a planetary mixer (Labotop, from PC Laborsystems) (LT) as described in Examples 2 and 3. The corresponding epoxy resin pastes (100 g) and hardener pastes (45 g each) were vigorously mixed using a double asymmetric centrifugal mixer (SpeedMixer®, from Hauschild). The resulting two-component compositions were molded into plates with a thickness of 4 mm using a hydraulic vacuum press. The compositions were cured in the vacuum press at 100° C. for 2 hours, followed by 80° C. for 12 hours.

[0079] After curing, dog-bone specimens of geometry type 1B according to ISO 527-2 (1996) were produced from the plates using a CNC milling machine. The mechanical properties of the cured resins (tensile modulus (Et) and tensile stress at break (σ-B)) were determined at room temperature according to standard ISO 527-2 (1996). Tests were performed with at least four valid replicates in order to calculate the mean and SEM of all replicates.

[0080] In addition, the glass transition temperature (T g ) was determined by differential scanning calorimetry according to standard ASTM D3418 (2015) using the following temperature profile: 0 ° C → 5 K / min up to 150 ° C. The results are summarized in Table 6.

[0081] [Table 6]

[0082] The samples containing milled composites prepared in the SpeedMixer (SM-A, -B, -C, -D) showed slightly lower values ​​of Et than the corresponding samples prepared in the SpeedMixer with virgin short glass fibers (SM-GF), despite having at least 29% less glass content. Increasing the amount of milled composite to match the inorganic content with that of the GF samples (LT-B', -B'' resin and hardener components) further improved the measured Et values ​​compared to the formulations containing only virgin short glass fibers. All samples containing milled composites showed values ​​of σ-B comparable to or exceeding those of the corresponding prepared samples based on virgin short glass fibers. The best values ​​were obtained for the samples containing milled composites B and D, which showed the longest average fiber length in the optical analysis (see Tables 1 and 7).

[0083] Example 7 Length distribution of glass fibre fragments in cured structural adhesives. Cured structural adhesive samples using various ground composites (A, B, C, and D, corresponding to Example 1) were prepared as described in Example 5. Approximately 1 g of material was cut from the cured samples (i.e., plates prepared using a hydraulic vacuum press as described in Example 6) and baked at 650° C. for 2 hours, followed by slow cooling to room temperature over 2 hours to remove the matrix polymer and liberate the fibers. The length distribution of the fibers without the matrix polymer was determined as described in Example 1. The results are summarized in Table 7.

[0084] [Table 7]

[0085] Processing the ground composites into an adhesive paste and subsequent curing had little effect on the fiber length distribution of finely ground composites A and C. A slight decrease in fiber length was observed in samples B and D, which contain, on average, longer fibers.

Claims

1. 1. A method for preparing a curable composition beginning with providing an epoxy resin component comprising at least one epoxy resin and a hardener component comprising at least one amino curing agent, the process comprising: (a) providing at least one pulverized composite material prepared by pulverizing a composite material comprising a polymer matrix and glass fibers; (b) combining and mixing the at least one pulverized composite material of step (a) with the epoxy resin component or the hardener component or both; (c) mixing the epoxy resin component resulting from step (b) with the hardener component, at least one of which includes the at least one pulverized composite material.

2. 2. The method of claim 1, wherein the polymer matrix of the at least one pulverized composite material comprises a cured epoxy resin or a cured unsaturated polyester resin, preferably wherein the polymer matrix of the at least one pulverized composite material comprises a cured epoxy resin.

3. 10. The method of claim 1, wherein the glass fibers of the at least one pulverized composite material have a weight average length in the range of 0.3 to 1.0 mm, as determined by optical measurement and image analysis, after removing fiber-bound and free matrix polymer residues by a calcination step at a temperature of 650°C for 2 hours.

4. 2. The method of claim 1, wherein the amount of very fine fraction of the at least one ground composite material having a particle size of less than 32 μm, determined by sieving according to standard DIN 66165 (2016) using a woven wire sieve with an opening size of 32 μm, is less than 40% by weight, based on the total amount of ground composite material.

5. 2. The method according to claim 1, wherein the content of total inorganic materials of all the ground composite materials, determined by thermogravimetric analysis according to standard DIN EN ISO 1172 (1998), is in the range of 40 to 90% by weight.

6. 10. The method of claim 1, wherein the content of the at least one ground composite material in the curable composition is in the range of 5 to 35 wt %, based on the total of the epoxy resin component and the hardener component.

7. 10. The method of claim 1, wherein the epoxy resin component or the hardener component or both also contain fumed silica in the range of 2 to 13 wt. % based on the corresponding component, and the content of the at least one ground composite material is in the range of 8 to 55 wt. % based on the corresponding component.

8. 10. The method of claim 1, wherein the at least one amino curing agent is one or more amines selected from the group consisting of polyaminoamides, resin adducts thereof, polyetheramines, resin adducts thereof, cycloaliphatic amines, resin adducts thereof, and Mannich base adducts.

9. 10. The method of claim 1, wherein the mixing in step (b) is carried out using an asymmetric centrifugal mixer, a planetary mixer, or an intensive mixer.

10. A method for preparing an epoxy resin component comprising at least one pulverized composite material by combining and mixing at least one pulverized composite material prepared by pulverizing a composite material comprising a polymer matrix and glass fibers with an epoxy resin component comprising at least one epoxy resin.

11. A method for preparing a curing agent component comprising at least one pulverized composite material by combining and mixing at least one pulverized composite material prepared by pulverizing a composite material comprising a polymer matrix and glass fibers with a curing agent component comprising at least one amino curing agent.

12. A curable composition obtainable by the method of claim 1.

13. an epoxy resin component comprising at least one epoxy resin; a curing agent component comprising at least one amino curing agent; A curable composition comprising:

1. A curable composition, wherein the epoxy resin component, the hardener component, or both components further comprise at least one pulverized composite prepared by pulverizing a composite comprising a polymer matrix and glass fibers.

14. 14. The curable composition of claim 13, wherein the glass fibers of the at least one pulverized composite material have a weight average length in the range of 0.3 to 1.0 mm, determined by optical measurement and image analysis, after removing fiber-bound and free matrix polymer residues by a calcination step at a temperature of 650°C for 2 hours.

15. 14. The curable composition of claim 13, wherein the at least one amino curing agent is one or more amines selected from the group consisting of polyaminoamides, resin adducts thereof, polyetheramines, resin adducts thereof, cycloaliphatic amines, resin adducts thereof, and Mannich base adducts.

16. 1. An epoxy resin component comprising at least one epoxy resin, the epoxy resin component further comprising at least one pulverized composite material produced by pulverizing a composite material comprising a polymer matrix and glass fibers.

17. 17. The epoxy resin component of claim 16, wherein the glass fibers of the at least one pulverized composite material have a weight average length in the range of 0.3 to 1.0 mm, as determined by optical measurement and image analysis, after removing fiber-bound and free matrix polymer residues by a baking process at a temperature of 650°C for 2 hours.

18. 1. A hardener component comprising at least one amino curing agent, the hardener component further comprising at least one pulverized composite material produced by pulverizing a composite material comprising a polymer matrix and glass fibers.

19. 19. The hardener component of claim 18, wherein the glass fibers of the at least one pulverized composite material have a weight average length in the range of 0.3 to 1.0 mm, determined by optical measurement and image analysis, after removing fiber-bound and free matrix polymer residues by a calcination process at a temperature of 650°C for 2 hours.

20. A method for preparing a cured epoxy resin by curing the curable composition of claim 12.

21. 1. A method for bonding at least two substrates, comprising: (i) applying the curable composition of claim 12 to at least one of the substrates to obtain a substrate at least partially coated with the curable composition; (ii) contacting the at least two substrates, at least one of which is coated with the curable composition; (iii) curing the curable composition; A method comprising:

22. A cured epoxy resin obtainable by the method of claim 20.

23. 23. The cured epoxy resin of claim 22, wherein the glass fibers of the cured epoxy resin have a weight average length in the range of 0.3 to 1.0 mm, as determined by optical measurement and image analysis, after removing fiber-bound and free matrix polymer residues by a baking process at a temperature of 650°C for 2 hours.

24. 13. Use of the curable composition of claim 12 as a structural adhesive.