Classifications

• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08G—MACROMOLECULAR COMPOUNDS OBTAINED OTHERWISE THAN BY REACTIONS ONLY INVOLVING UNSATURATED CARBON-TO-CARBON BONDS
  • C08G65/00—Macromolecular compounds obtained by reactions forming an ether link in the main chain of the macromolecule
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08G—MACROMOLECULAR COMPOUNDS OBTAINED OTHERWISE THAN BY REACTIONS ONLY INVOLVING UNSATURATED CARBON-TO-CARBON BONDS
  • C08G75/00—Macromolecular compounds obtained by reactions forming a linkage containing sulfur with or without nitrogen, oxygen, or carbon in the main chain of the macromolecule
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08L—COMPOSITIONS OF MACROMOLECULAR COMPOUNDS
  • C08L71/00—Compositions of polyethers obtained by reactions forming an ether link in the main chain; Compositions of derivatives of such polymers
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08L—COMPOSITIONS OF MACROMOLECULAR COMPOUNDS
  • C08L81/00—Compositions of macromolecular compounds obtained by reactions forming in the main chain of the macromolecule a linkage containing sulfur with or without nitrogen, oxygen or carbon only; Compositions of polysulfones; Compositions of derivatives of such polymers

Definitions

• the present invention relates to epoxy compositions, which may be disassembled by immersion in an appropriate solvent.
• the present invention relates to the addition of amine- and disulfide-containing compounds, such as L- cystine, to commercially relevant epoxy-based compositions to prepare
• one major goal concerning sustainability is to optimize the use of the world's resources by keeping materials as high value resources for as long as possible creating value far beyond end-of-life of the product.
• the disassembly ensures the re-entry of the material in a production cycle either as raw material for new products or in other composite structures.
• Current state-of-the-art composites typically used in e.g. wind turbine blades are based on layers of carbon-fibre/glass-fibre joined together with an epoxy matrix, as depicted in figure 1A.
• This conventional approach uses thermosets, i.e. a polymer that cures irreversible, as the polymeric matrix.
• thermoset-based composites As depicted in figure IB.
• thermosets due to its abilities as a material with great strength, chemical resistance and low heat sensitivity.
• epoxy-based composite materials are also utilized in the aviation, automotive and ship industries and any advances achieved within the development of new recyclable epoxy-based composite materials may therefore be extrapolated to a variety of industries.
• Cleavable crosslinking systems for polymer matrices have been derived.
• One reported approach is the disulfide-based system, which can be reversible cleaved using external stimuli.
• the disulfide moiety may be utilized by swelling (e.g. in CHC , THF, MeOH, DMF) and addition of a reductant, e.g. thiols, or electrochemical reduction.
• the disulfide-based system has found its application in other materials, such as gels and films, and has the benefit of being resistant to many environmental aspects, including heat, salt concentration, UV, shear and pH due to the nature of some disulfides.
• a disulfide-based epoxy composition has recently been proposed in what was described as a dynamic thermoset (de Luzuriaga et a/., Materials Horizons, 2016). It was demonstrated that disulfide bridges could be incorporated in an epoxy matrix and the dynamics of the thiol-disulfide exchange was utilized to dismantle the matrix. Further, it was shown that a grinded matrix could be reassembled by heating and high pressure.
• the disulfide compound 4-aminophenyl disulfide (AFD)
• AFD 4-aminophenyl disulfide
• an improved epoxy-based composite material that may be disassembled under mild conditions would be advantageous.
• an additive for epoxy compositions that may be directly utilized in conjunction with typical commercial epoxy-based composites and facilitate disassembly of otherwise non-recyclable material using green chemistry would be advantageous.
• amine and disulfide-moeities are introduced into the epoxy matrix by addition of a disulfide-additive containing polyamine cross- linkers.
• This approach will incorporate a cleavable cross-link in the epoxy composition, facilitating fragmentation of epoxy-based polymer composites.
• a swelling-assisted methodology is utilized. This process will leave the structural units (e.g. glass- or carbon-fibre) separated from the polymer matrix and they may subsequently be collected and recycled.
• an object of the present invention relates to the provision of an improved epoxy-based polymer composite that may be disassembled under mild conditions while retaining or improving the advantageous mechanical properties of state of the art epoxy compositions and composites thereof.
• one aspect of the invention relates to an epoxy composition
• an epoxy composition comprising the reaction product of a set of reactants comprising :
• R 1 , R 2 , and R 3 are independently selected from the group consisting of H, and an optionally substituted C1-C5 alkyl group,
• R 4 is selected from the group consisting of -H, -OH, -SH, -CN, -OCN, and -COOR, wherein
• R is selected from the group consisting of H and an optionally substituted C1-C5 alkyl group
• n is an integer from 1-10.
• Another aspect of the present invention is a method of manufacturing an epoxy composition comprising the steps of:
• R 1 , R 2 , and R 3 are independently selected from the group consisting of H, and an optionally substituted C1-C5 alkyl group,
• R 4 is selected from the group consisting of -H, -OH, -SH, -CN, -OCN, and COOR, wherein
• R is selected from the group consisting of H and an optionally substituted C1-C5 alkyl group
• n is an integer from 1-10
• R 1 , R 2 , and R 3 are independently selected from the group consisting of H, and an optionally substituted C1-C5 alkyl group,
• R 4 is selected from the group consisting of -H, -OH, -SH, -CN, -OCN, and COOR, wherein R is selected from the group consisting of H and an optionally substituted C1-C5 alkyl group, and
• n is an integer from 1-10
• Figure 1 shows the state-of-the-art method of producing polymer composites comprising epoxy matrix as well as the inclusion of cleavable cross-linkers proposed in the present invention.
• the incorporation of cleavable cross-linkers enables the introduction of a disassembly strategy in which the structural units/fibres of the polymer composite may be recycled.
• Figure 2 shows the typical formation of an epoxy matrix.
• the amine hardener reacts with the least hindered spot on the epoxy in order to open the ring and form an amine and an alcohol (1), which subsequently reacts with another epoxy unit (2).
• the created macromolecules can now be used to cross-link the rest of the matrix (3). This curing continues until a network is formed with low to none mobility.
• the epoxide unit (4) which is the essential moiety of all epoxy resins.
• Figure 3 shows (A) the mixture before curing, (B) the amine reacting with epoxies, (C) the curing at elevated temperature, and (D) the epoxy matrix from a macro perspective.
• Figure 4 shows the standard epoxy (left) and an epoxy composition comprising 20 mol% L-cystine (right) in acetic acid at 70°C. It is shown as (A) initial, (B) 265 minutes, and (C) 530 minutes immersion in the solvent. While nothing noteworthy happens to the standard epoxy, the epoxy composition comprising 20 mol% L-cystine is gradually swollen and eventually dismantled.
• Figure 5 shows a series of epoxy compositions comprising various mol% of L- cystine immersed in acetic acid.
• the samples were tested in duplicates with samples A and B corresponding to 5 mol% L-cystine, C and D corresponding to 10 mol% L-cystine, and E and F corresponding to 20 mol% L-cystine.
• the effect of acetic acid on the epoxy compositions comprising a varying quantity of L-cystine is shown before (A) and after (B-C) immersion in the solvent. In all cases, the epoxy composition is dismantled.
• Figure 6 shows (A) ATR-FTIR spectrum of the standard cured epoxy matrix (1), applied hardener (2) and epoxy resin (3), and (B) ATR-FTIR spectrum of the standard, Cys20mol%, Hyd20mol% and Phy20mol% epoxy matrices from top to bottom, respectively. (C) Normalized spectra of Cys20mol% (top), Hyd20mol% (middle), and Phy20mol% (bottom) versus STD.
• Figure 7 shows (A) liquid state NMR of epoxy resin (dot line), hardener (solid line) and solid state NMR of the cured standard epoxy matrix (broad peaks, solid line). The insert from 180-100 ppm shows the aromatic area. The septet at 39.52 ppm corresponds to the DMSO solvent peak. (B) Solid state NMR spectra of the standard, Cys20mol%, Hyd20mol% and Phy20mol% epoxy matrices from top to bottom, respectively. Figure 8 shows the volumetric swelling as a function of time for the STD
• Figure 10 shows a series of compositions comprising glass fibres infused with standard epoxy, Cys5mol% modified epoxy or Cysl0mol% modified epoxy immersed in acetic acid.
• xxxxyymol% where xxxx may be either of cys (L-cystine), hyd (2-hydroxyethyl disulfide), or phen (4-aminophenyl disulfide), and yymol% may be either of 5mol%, 10mol%, 15mol% or 20mol% corresponding to "the percentage of active mole sites of the standard hardener, which have been exchanged with the new additive. "STD" is used for the standard epoxy made without any additives.
• mol% is the mol% of substituted active sites.
• substituting 5% with an additive that has two active sites doubles the amount of additive.
• substituting with an additive containing eight active sites will result in an addition of half the amount of additive, thereby ensuring one to one active site substitution between hardener and additive.
• epoxy resin refers to a low molecular weight epoxy monomer, pre-polymer or higher molecular weight polymer, which normally contain at least two epoxide groups.
• the epoxy resin compound may be, but are not limited to, saturated or unsaturated aliphatic, cycloaliphatic, aromatic or heterocyclic compounds, which possesses at least one epoxy group.
• epoxy resins of the present invention may also include monoepoxides, diepoxides, polyepoxides or mixtures thereof.
• Figure 2, compound 4 illustrates a generic structure of an epoxide monomer.
• Such compounds may be substituted with one or more non-interfering compounds
• epoxy resins include, but are not limited to, bisphenol A epoxy resins, bisphenol F epoxy resins, novolac epoxy resins, aliphatic epoxy resins, glycidylamine epoxy resins and combinations thereof.
• epoxy resins suitable for the present invention may include, but are not limited to, the glycidyl polyethers of polyhydric phenols and polyhydric alcohols.
• epoxy resins of the present invention include the diglycidyl ethers of resorcinol, catechol, hydroquinone, bisphenol, bisphenol A, bisphenol AP (1,1- bis(4-hydroxylphenyl)-l-phenyl ethane), bisphenol F, bisphenol K,
• tetrabromobisphenol A phenol-formaldehyde novolac resins, alkyl substituted phenol-formaldehyde resins, phenol-hydroxybenzaldehyde resins, cresol- hydroxybenzaldehyde resins, dicyclopentadiene-phenol resins, dicyclopentadiene- substituted phenol resins tetramethylbiphenol, tetramethyl-tetrabromobiphenol, tetramethyltribromobiphenol, tetrachlorobisphenol A; and any combination thereof.
• hardener refers to compound that reacts with an uncured epoxy resin to produce a cross-linked epoxy matrix.
• hardener and “curing agent” are used interchangeably.
• thermoset structure with improved mechanical, chemical and heat resistance properties.
• Hardeners may be chosen from, but are not limited to, polyfunctional amines, acids (and acid anhydrides), phenols, alcohols, thiols, ketones, aldehydes, isocyanate, and cyanide.
• Amine hardeners may be primary, secondary, or tertiary amines of aliphatic, cycloaliphatic, or aromatic types, preferably primary amines.
• the hardener may also be a compound comprising an amine group and an alcohol group such as, but not limited to, monoethanolamine; 2-amino-2-hydroxymethyl- 1,3-propanediol; 2-amino-2-methyl-l,3-propanediol; diethanolamine and mixtures thereof.
• additive refers to a compound that is partly substituting and/or added to an epoxy composition comprising an epoxy resin and a hardener, such as commercially available epoxy composition. It is important to note that the additive in the present invention is not used to entirely replace any components of standard epoxy compositions. The additive is substituting a fraction of hardener present in the epoxy composition, thereby creating a three- component epoxy composition. Consequently, the epoxy compositions of the present invention may be utilized in conjunction with already available epoxy compositions. Additives of the present invention are defined by the presence of an amine group and a disulfide bridge. The additive may also encompass other functionalities such as carboxylic acids, ethers, halogens or other functional moieties. It is preferred that the additive comprise carboxylic acids. Reaction product
• reaction product refers to the reaction product of the reaction between an epoxy resin, a hardener and an additive. This reaction product forms an epoxy matrix.
• the size of the reaction product may vary depending on the choice of epoxy resin, hardener and additive. Furthermore, the size of the reaction product will vary depending on the material ratio between epoxy resin, hardener and additive used in the formation of the reaction product.
• structural fibre refers to a component that is mixed with an epoxy composition to form a polymer composite material.
• structural fibre and “structural unit” is used interchangeably herein.
• structural fibres including sizing may be chosen from, but are not limited to, glass, carbon, cellulose, ceramics, natural fibres, pre-pregs, continuous fibres, platelet materials and graphene. Swelling
• swelling refers to a state of an epoxy composition sample, in which it maintained its appearance, just scaled in three dimensions, upon immersion into a solvent. Thus, a swollen sample is not dismantled or mechanically broken, but still constitutes a single piece of material.
• the term "mechanically broken” refers to a state of an epoxy composition sample, in which it is physically separated in a few (e.g. 2-5) large otherwise non-affected pieces upon immersion into a solvent.
• dismantle refers to a state of an epoxy composition sample, in which it is separated into a plethora of very small bits of material upon immersion into a solvent.
• the terms “dismantle”, “disassemble” and “fractionated” is used interchangeably herein. It is also known as chemical dismantling.
• curing refers to the process, in which the epoxy resin and hardener reacts to form a thermoset structure. In the present curing may also be performed subsequent to addition of the additive to the epoxy composition.
• curing is performed at elevated temperatures. It is particularly preferred that the curing temperature is performed at or above the glass transition temperature. The temperature may be increased step-wise to control the rate of curing and ensure that heat is not accumulated from the exothermic reaction. However, in some incarnations of the present invention, curing may also be performed at ambient temperature.
• the glass transition temperature, T g is defined as a transition from a glassy more brittle state, to a rubbery or more flexible state.
• ASTM E1356 - 08(2014) is used as the standard test method for assignment of the T g by differential scanning calorimetry (DSC).
• Elastic modulus (Emoduius), ultimate tensile strength (UTS), elongation at break (%EL at break) and toughness
• Emoduius, UTS and %EL at break is calculated according to ISO 527 1- 5 : 2012. Toughness is given as the integral from start until rupture, and is described as
• e is the strain
• e B is the strain at break
• ⁇ is the stress
• the simplest type of reaction to form an epoxy matrix is a two-component mixture of an epoxy resin and a hardener.
• the hardener is typically, but not limited to, a primary amine due to the reactivity and the number of reactive sites.
• Alcohols, thiols or isocyanates can also react with epoxies.
• the epoxide unit is the essential moiety of all epoxy resins.
• An epoxide is a cyclic ether with a three-atom ring. This ring approximates an equilateral triangle, which makes it strained, and hence highly reactive, more so than other ethers.
• the present invention is not limited to any specific types of epoxy resins and the specific experiments shown herein is only an example of a commercially available epoxy composition.
• the epoxide unit (see figure 2, item 4) may be associated/combined with any suitable group.
• Epoxy composition comprising an amine- and disulfide-containinq additive
• additives are added to the epoxy matrix in order to obtain epoxy compositions with new features.
• Such epoxy compositions can be used in the preparation of sustainable epoxy-based polymer composites that may be fragmented into recyclable parts due to the introduction of the cleavable cross- linkers.
• the inventors have found that additives with both amine- and disulfide-moieties were suitable for preparing additives enabling the disassembly of epoxy
• a first aspect of the present invention relates to an epoxy composition
• an epoxy composition comprising the reaction product of a set of reactants comprising :
• R 1 , R 2 , and R 3 are independently selected from the group consisting of H, and an optionally substituted C1-C5 alkyl group,
• R 4 is selected from the group consisting of -H, -OH, -SH, -CN, -OCN, and -COOR, wherein
• R is selected from the group consisting of H and an optionally substituted C1-C5 alkyl group
• n is an integer from 1-10.
• Another aspect of the present invention relates to an epoxy composition comprising :
• R 1 , R 2 , and R 3 are independently selected from the group consisting of H, and an optionally substituted C1-C5 alkyl group,
• R 4 is selected from the group consisting of -H, -OH, -SH, -CN, -OCN, and COOR, wherein
• R is selected from the group consisting of H and an optionally substituted C1-C5 alkyl group
• n is an integer from 1-10.
• the epoxy resin and hardener may be encompassed in a single molecule. As an example, this may be the case if an aromatic amine is incorporated into an epoxy resin. It is to be understood within the present context that such "pseudo" one-component epoxy compositions are considered to be equivalent to the two-component epoxy compositions recited herein, as they comprise both an epoxy resin element and a hardener element. Therefore, addition of an additive to an epoxy composition according to the present invention is not limited by the number of other components in the epoxy, but is applicable to epoxy compositions comprising one, two or more components besides the additive.
• the additive of the epoxy composition can take several forms and may thus be described by a selection of embodiments.
• An embodiment of the present invention relates to an epoxy composition as described herein, wherein the optionally substituted C1-C5 alkyl groups comprises one or more substituents selected from the group consisting of a C1-C5 alkyl, halogen, cycloalkyls, heterocycloalkyls, aromatic and heteroaromatic groups.
• Another embodiment of the present invention relates to an epoxy composition as described herein, wherein R 4 is -COOH.
• Yet another embodiment of the present invention relates to an epoxy composition as described herein, wherein n is 1.
• a further embodiment of the present invention relates to an epoxy composition as described herein, wherein R 1 is H.
• An even further embodiment of the present invention relates to an epoxy composition as described herein, wherein R 2 is H.
• Still another embodiment of the present invention relates to an epoxy composition as described herein, wherein R 3 is H.
• L-cystine is interesting for the investigation of a sustainable epoxy system as an additive, since it contains both a disulfide bridge together with primary amines and carboxylic acids. If the disulfide bridge of L-cystine is broken by e.g. a thiol- disulfide exchange it yields the thiol counterpart known as the amino acid cysteine.
• L-cystine The main issue, when working with L-cystine is its solubility.
• the powerful internal hydrogen bonding interactions makes the compound hard to dissolve.
• a way to break the bonds is to change the pH.
• the pKa of L-cystine is 1.50 and 8.80 for the carboxylic acid and amine, respectively.
• Methanol and concentrated hydrochloric acid can be used as media to lower the pH and break the hydrogen bonds, hereby causing the L-cystine to swell.
• L-cystine is easily available from natural sources and the use of L-cystine as additive is therefore perfectly aligned with object of providing new sustainable materials.
• a preferred embodiment of the present invention is related to an epoxy composition as described herein, wherein the additive is cystine, preferably L- cystine.
• the additive according to the present invention may in principal be added to any epoxy compositions.
• the use of the additive is not limited to addition to any particular epoxy composition.
• an aspect of the present invention relates to the use of a compound represented by formula (I)
• R 1 , R 2 , and R 3 are independently selected from the group consisting of H, and an optionally substituted C1-C5 alkyl group,
• R 4 is selected from the group consisting of -H, -OH, -SH, -CN, -OCN, and COOR, wherein
• R is selected from the group consisting of H and an optionally substituted C1-C5 alkyl group
• n is an integer from 1-10, as an additive in an epoxy composition further comprising :
• the present invention is readily applicable to already commercially available epoxy compositions and may as such immediately be used to introduce new features to known epoxy-based polymer composites.
• Many different types of epoxy compositions i.e. mixtures of epoxy resins and hardeners) is currently applied in industries relying on epoxy-based polymer composites, all of which may be mixed with the additive of the present invention.
• an embodiment of the present invention relates to an epoxy composition as described herein, wherein the at least one epoxy resin is selected from the group consisting of bisphenol A epoxy resins, bisphenol F epoxy resins, novolac epoxy resins, aliphatic epoxy resins, glycidylamine epoxy resins and combinations thereof.
• Another embodiment of the present invention relates to an epoxy composition as described herein, wherein the at least one epoxy resin is selected from the group consisting of bisphenol A diglycidyl ether, bisphenol F diglycidyl ether,
• a further embodiment of the present invention relates to an epoxy composition as described herein, wherein the at least one hardener is selected from the group consisting of amine hardeners, anhydride hardeners, phenol hardeners, thiol hardeners and combinations thereof.
• composition as described herein, wherein the at least one hardener is selected from one or more of the group consisting of poly(oxypropylen)diamine, 3- aminomethyl-3,5,5-trimethylcyclohexylamine,
• Epoxy compositions may comprise one or more epoxy resins and one or more hardeners. Many available epoxy compositions obtain their enhanced thermal and mechanical features from the interplay between several epoxy resins and several hardeners.
• the additive of the present invention is not limited to epoxy
• compositions comprising a single epoxy resin and a single hardener, but may be applied to any epoxy composition comprising any number of epoxy resins and hardeners.
• An example of a commercially available epoxy resin comprising two individual epoxy resins is a resin A containing 2,2-bis[p-(2,3- epoxypropoxy)phenyl and l,4-Bis(2,3-epoxypropyloxy)butane.
• An example of a commercially available hardener comprising two individual hardeners is a hardener B containing poly(oxypropylene) diamine and 3-aminomethyl-3,5,5- trimethyl-cyclohexylamine.
• the mixture of resin A and hardener B is one example of a typical epoxy composition used in epoxy-based polymer composites.
• an embodiment of the present invention relates to an epoxy composition as described herein, wherein the at least one epoxy resin comprises 2,2-bis[p-(2,3- epoxypropoxy)phenyl and l,4-Bis(2,3-epoxypropyloxy)butane, and the at least one hardener comprises poly(oxypropylene) diamine and 3-aminomethyl-3,5,5- trimethyl-cyclohexylamine.
• the present invention relates to epoxy compositions that comprise at least three different components; epoxy resin, hardener and additive.
• epoxy resin e.g., epoxy resin, hardener and additive.
• most currently available epoxy composition comprise only two components; epoxy resin and hardener.
• Introduction of a third component in an epoxy composition may potentially alter thermal or mechanical properties of the original epoxy
• an embodiment of the present invention relates to an epoxy composition as described herein, wherein the additive constitutes less than 25 mol%.
• Another preferred embodiment of the present invention relates to an epoxy composition as described herein, wherein the additive constitutes 0.01-25 mol%, such as 0.05-20 mol%, such as 0.1-15 mol%, such as 0.5-10 mol%, such as 1-5 mol%.
• the preparation of the epoxy composition may extend beyond simple mixing of each component.
• the incorporation of the additive in the epoxy matrix, and ultimately the thermal and mechanical properties of the resulting epoxy may extend beyond simple mixing of each component.
• composition may be influenced by the method of preparation. Therefore, the method of manufacture of the epoxy composition may be optimized by introducing process steps to enhance the incorporation of additive in the epoxy matrix.
• a second aspect of the present invention relates to a method of manufacturing an epoxy composition comprising the steps of:
• R 1 , R 2 , and R 3 are independently selected from the group consisting of H, and an optionally substituted C1-C5 alkyl group,
• R 4 is selected from the group consisting of -H, -OH, -SH, -CN, -OCN, and COOR, wherein
• R is selected from the group consisting of H and an optionally substituted C1-C5 alkyl group
• n is an integer from 1-10
• the epoxy composition may be further improved by thermal treatment of the epoxy composition.
• an embodiment of the present composition relates to a method as described herein, wherein the epoxy composition is cured subsequent to step c) by applying a predetermined specific temperature profile.
• the method of manufacture may be further enhanced by selection of suitable solvent for swelling the additive prior to pre-treatment with the epoxy resin.
• a preferred embodiment of the present invention relates to a method as described herein, wherein the swelling of the additive is performed by mixing of the additive in an alcohol followed by titration with an acid.
• Another embodiment of the present invention relates to the method as described herein, wherein the alcohol is selected from the group consisting of methanol, ethanol, propanol, butanol and combinations thereof.
• a further embodiment of the present invention relates to the method as described herein, wherein the acid is selected from the group consisting of hydrochloric acid, sulfuric acid, acetic acid, citric acid, lactic acid, malic acid and combinations thereof.
• an embodiment of the present invention relates to the method as described herein, wherein the swelling of the additive is performed by mixing of the additive in an alcohol followed by titration with a base, such as NaOH.
• One preferred use of the additive or epoxy composition of the present invention is as a component in epoxy-based polymer composite materials.
• Such materials typically comprise structural unit, such as fibres, and an epoxy composition.
• an aspect of the present invention relates to a polymer composite material comprising :
• a preferred embodiment of the present invention relates to the composite material as described herein, wherein the structural fibres are of a material selected from the group consisting of glass, carbon, cellulose, ceramics, natural fibres, pre-pregs, continuous fibres, platelet materials and graphene.
• the three-component epoxy composition comprising structural fibres as described herein may be used for the preparation of epoxy-based polymer composites within a wide range of industries such as the aviation, automotive, ship and wind industries.
• an aspect of the present invention relates to a wind turbine blade
• the resin matrix comprising the epoxy composition as described herein.
• Another aspect of the present invention relates to a wind turbine blade comprising the polymer composite material as described herein.
• cleavable cross-linkers are efficiently introduced into an epoxy composition of choice. These cross-linkers may be cleaved by use of an appropriate solvent thereby resulting in the disassembly of the epoxy matrix.
• the epoxy matrix is the component that binds the structural units of epoxy-based polymer composite materials together, such a disassembly of the epoxy matrix also results in the fractionation of the composite into structural units.
• an embodiment of the present invention relates to the composite material as described herein, wherein the composite material can be fractionated by immersion into a dismantling solvent.
• the efficiency with which the dismantling solvent works is erratic and it is not readily predictable which groups of solvents will disassemble the epoxy matrix and not simply swell, mechanically brake or have no effect on the epoxy matrix.
• the effect of the dismantling solvent cannot be predicted by characteristics such as chemical structure, polarity or acidity of the solvent.
• the inventors have surprisingly found that a few selected solvent are particularly suitable for the dismantling of epoxy matrices comprising an additive according to the present invention.
• a preferred embodiment of the present invention relates to the composite material as described herein, wherein the dismantling solvent comprises a compound selected from the group consisting of acetic acid, chloroform and N- methyl-2-pyrrolidone or a mixture thereof.
• the dismantling solvent may comprise compounds with similar reactivity to the additive of the present invention, and may include compounds selected from the group consisting of amines such as aliphatic amines and/or aromatic amines and reducing agents, such as disulfides. Disulfides may include dithiothreitol. Dismantling solvents may comprise the compounds in concentrated form, i.e. as the sole component or in dilute form, including e.g. aqueous compositions.
• a particularly preferred embodiment of the present invention relates to the composite material as described herein, wherein the dismantling solvent comprises acetic acid. Furthermore, an aspect of the present invention relates to a method of
• An embodiment of the present invention relates to the method as described herein, wherein the dismantling solvent comprises a compound selected from the group consisting of acetic acid, chloroform and N-methyl-2-pyrrolidone.
• the dismantling solvent comprises a compound selected from the group consisting of acetic acid, chloroform and N-methyl-2-pyrrolidone.
• Example 1 Materials and methods
• L-cystine 10.00 g L-cystine is added to 100 mL MeOH. 12 mL HCI is added dropwise under stirring until L-cystine swells. The swollen mixture is poured into a petri dish and left in the oven at 80°C overnight.
• the commercial epoxy resin is pre-treated with the swollen L-cystine, before it is mixed with the commercial hardener. The pre-treatment is done in an ultrasound bath at 55°C for 30 hours. L-cystine is expected to have six active sites, neglecting any reaction kinetics, whereas the commercial hardener have four reaction sites.
• the overall procedure is the same as for the standard epoxy mixture.
• the number of moles is corrected depending on the number of reactions available on the molecule.
• the terminal alcohols can attack one epoxy each, where the
• Test epoxy matrix elements were prepared in pieces of roughly the dimension 10x20x4 mm 3 , with an approximate weight of 0.5-1.0 g (referred to as test coupons). Glass transition temperature
• the glass transition temperature of the cured epoxy is measured with a
• thermogram of the epoxy is used to determine the glass transition temperature (T g ).
• T g glass transition temperature
• the sample is heated from 0°C to 200°C with a scan rate of lOK/min.
• Analysis is performed on the second up-scan as first scan is thermal homogenization.
• test coupons used for testing follows the ISO 527-2 standards type 1A
• test specimens are put in a 20 mL glass vial with snap cap, where approx. 12- 15 mL solvent is added (in excess to cover the sample).
• Example 2 Incorporation of additives in the epoxy matrix and glass transition temperature of epoxy compositions
• the formation of the epoxy compositions (e.g. curing and incorporation of additives) was investigated and compared to a standard epoxy with known characteristics.
• the epoxy matrices were characterized by FTIR to investigate the curing process.
• FTIR spectra of the cured standard epoxy matrix can be found in Figure 6A together with spectra of the epoxy resin and hardener.
• the cured STD epoxy matrix ( Figure 6A, curve 1) shows a broad O-H band at 3403 cm -1 , and there are no bands from either oxirane, or primary or secondary amines, indicating a fully cured material.
• Hyd20mol% (middle), and Phy20mol% (bottom) versus STD are given in figure 6C and show the differences between the modified matrices and the standard matrix.
• the peaks originating from the additives recur in the normalized spectra, thus supporting the indication that the additives have been incorporated in the matrices.
• the epoxy compositions were also chararcterized by solution-state NMR and solid-state NMR.
• Solution-state NMR spectra of the epoxy resin and the hardener is provided in Figure 7A, together with solid-state NMR spectra of the cured epoxy matrix (STD). Comparing the cured STD epoxy matrix to the epoxy resin, it can be seen that the peak at 44 ppm is absent, whereas the oxirane peak at 51 ppm cannot be identified, indicating a fully cured epoxy matrix.
• Figure 7B shows the solid-state spectra of the standard and modified epoxy matrices.
• the peak at 18 ppm (-CH3) has reduced intensities owing to mass reduction of the commercial hardener, and no peaks from the oxirane or carbons neighbouring the primary amine groups (44-51 ppm) can be identified, indicating full curing.
• the mixtures with same compositions have T g values, which indicates the process is very reproducible.
• the trend is that the 2-hydroxyethyl disulphide lowers the T g as larger amounts are introduced.
• the 4-Aminophenyl disulfide increases the T g when high concentrations are added. Whereas the amount of L-cystine is similar at all ratios compared to the standard epoxy system.
• Epoxy compositions comprising no additive (STD), L-cystine, 2-hydroxyethyl disulfide or 4-aminophenyl disulfide was tested for swelling in a variety of solvents as described herein.
• the solvents used were diethyl ether (1), chloroform (2), methanol (3), 1,1,1- tricholoroethane (4), ethyl acetate (5), hydrochloric acid cone. (6), sulfuric acid cone. (7), acetonitrile (8), demineralized water (9), 1,4-dioxane (10), acetic acid (11), 2-ethoxyethanol(12), xylene (13), cyclohexanone (14), and N-methyl-2- pyrrolidone (15).
• composition comprising L-cystine mechanically broke when immersed into e.g. 1,4-dioxane and cyclohexanone, it were instead surprisingly rapidly dismantled when immersed into acetic acid, chloroform and N-methyl-2-pyrrolidone.
• acetic acid and N-methyl-2-pyrrolidone mechanical broke the standard epoxy.
• the epoxy composition comprising 2-hydroxyethyl disulfide was also mechanically broken by N-methyl-2-pyrrolidone.
• Table 4 is given the rates of the volumetric swelling after 10 days at 70 °C (unless otherwise stated) of the standard, Cys20mol%, and Hyd20mol% epoxy matrices in a variety of solvents.
• Table 4 shows that the modified epoxy matrices tend to swell, break, or fractionate more than the STD epoxy matrix. It is important to distinguish between the terms mechanically broken and fractionated.
• the fractionated matrices are reduced to very small pieces (see also example 6), whereas the mechanically broken matrices form larger pieces during swelling in the vials.
• the similarity of densities compared to STD indicates that no significant changes in density occur upon modification.
• the data shows that the modified epoxy matrices have the same resistance to water as the standard epoxy matrix, while displaying increased solvability in other solvents, such as N-methyl-2-pyrrolidone, acetic acid and chloroform. Furthermore, the densities of the modified epoxy matrices are comparable to the standard epoxy matrix, thereby permitting a strong, yet lightweight material.
• Example 5 Disassembly of epoxy compositions in acetic acid
• the photographs illustrates that the 20 mol% L-cystine epoxy starts to swell and slowly dismantles over time, whereas little happens to the standard epoxy.
• the 20 mol% L-cystine epoxy behaved similar in chloroform and N-methyl-2- pyrrolidone.
• Example 6 Disassembly of epoxy compositions comprising different mol% L- cystine in acetic acid, chloroform and N-methyl-2-pyrrolidone
• compositions comprising a varying quantity of L-cystine (5 mol%, 10 mol%, and 20 mol%) in acetic acid, chloroform and N-methyl-2-pyrrolidone.
• the glass vials were left in a water bath at 70°C.
• Photographs (figure 5A-C) document the influence of acetic acid on immersion of epoxy compositions comprising a varying quantity of L-cystine before (A) and after (B-C) immersion in the solvent.
• samples A and B corresponding to 5 mol% L-cystine
• C and D corresponding to 10 mol% L-cystine
• E and F corresponding to 20 mol% L-cystine.
• the experiment showed no lower boundary of additive concentration for dismantling the epoxy composition comprising L-cystine in acetic acid, chloroform and N-methyl-2-pyrrolidone.
• Example 7 Polymer composite material comprising glass fibres and epoxy composition with additive
• Polymer composite materials comprising glass fibres mixed with two different modified epoxy compositions (Cys5mol% or Cysl0mol%) were tested for their tensile properties and benchmarked against two polymer composite materials based on the most utilized commercially available epoxy compositions
• the 762H/766H epoxy compositions is a standard composition, which is known to cure fast.
• Representative tensile tests of the polymer composite materials comprising glass fibres mixed with standard (STD) epoxy composition and Cys5mol% are depicted in figures 9A and 9B, respectively. The quantified results of the tensile testing is given in table 5.
• Table 5 Table 5
• chloroform, acetic acid and N-methyl-2-pyrrolidone showed to be able to dismantle the L-cystine epoxies without further additives added .
• the standard epoxy and epoxy made with 2-hydroxyethyl or 4-aminophenyl disulfide did not show the same dismantling tendencies.
• the 4-aminophenyl disulfide compound is an interesting component for enhanced mechanical properties and a higher Tg, but not as a recyclable epoxy as was the same case for the 2-hydroxyethyl disulfide compound.
• the L-cystine matrix was the only compound showing the promising dismantling properties.
• the solvents facilitating the dismantling of the epoxy composition comprising L-cystine are very different in chemical structure. They are not limited to only being depending on the polarity or acidity of the solvent, e.g. acetic acid worked whereas concentrated hydrochloric acid did not.
• modified epoxy compositions comprising additives were fully cured with the additives intrinsically incorporated into the epoxy matrix, yielding epoxy compositions with comparable water resistance and mechanical properties as the standard epoxy composition.

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