3-Amino-4,5-dimethoxybenzylamine as a novel bio-based hardener for epoxy resins, method for its synthesis, its use as a hardener component and epoxy resin with the new hardener

Abstract

The invention relates to a bio-based hardener for epoxy resins, a process for its synthesis, its use as a hardener component together with a resin component for the production of an epoxy resin, and an epoxy resin with the hardener component according to the invention. The object of the present invention is to produce plastics, in particular fiber-reinforced plastics (FRP), based on renewable resources, especially for cabin construction in the aerospace industry, which can replace plastics made from non-renewable or fossil sources in the future, and to improve known bio-based epoxy resins with regard to their thermo-mechanical and mechanical properties to such an extent that they can also meet the high demands of the aerospace industry in an economical manner.This problem is solved according to the invention with a new bio-based hardener according to claim 1, a method for its synthesis according to claim 2, its use as a hardener component for the production of an epoxy resin according to claim 20 and an epoxy resin according to claim 22.

Description

[0001] The invention relates to a new bio-based hardener for epoxy resins, a method for its synthesis, its use as a hardener component together with a resin component for the production of an epoxy resin, and an epoxy resin with the hardener component according to the invention.

[0002] Synthetic resins, such as epoxy or phenolic resins, are reactive resins that react with a hardener to form a thermosetting plastic. Synthetic resins are often reinforced with fibers, thus forming fiber-reinforced plastics (FRP). Fiber-reinforced plastics (FRP) are the synergistic combination of their individual components: the load-bearing fibers and a plastic matrix that protects against environmental influences and provides shape. Due to their outstanding properties and diverse manufacturing technologies, FRPs are used in the electronics, sports and leisure industries, in boatbuilding, plant and wind turbine construction, in the automotive sector, and especially in aviation. Examples include cabin components made of phenolic resin-based FRP or the load-bearing structure of the Airbus A350, which has an FRP content of over 50% by mass. 1, 2, 3, 4, 5, 6, 7

[0003] The use of fiber-reinforced composites (FRCs) is primarily due to their excellent mechanical properties. FRCs exhibit comparable stiffness and strength to conventional materials, such as metals, despite significantly lower density. The resulting weight reduction enables, among other things, energy savings in the form of reduced fuel consumption in automobiles and aircraft. 8, 9, 10

[0004] Although fiber-reinforced composites (FRCs) offer many advantages, they also have some disadvantages: compared to metals, they typically exhibit lower thermal stability and / or flame resistance, and thermoplastic-based systems tend to creep under load, often making them unsuitable for components subjected to continuous, high stress. Some of these disadvantages can be mitigated by using cross-linked plastics, so-called thermosets, and by carefully selecting the underlying type.

[0005] Depending on the class used, thermosets exhibit high heat resistance, are intrinsically flame-resistant, and generally show very little creep. The thermosets used for flame-resistant applications and in aircraft cabin construction are mostly phenol-formaldehyde resins. 11,12,13,14

[0006] Although phenolic resins exhibit the highest fire resistance of all plastics, they crosslink via polycondensation. Due to the condensation products formed in this type of reaction, a poor surface finish is achieved. This results in complex, costly, and time-consuming (manual) post-processing of cabin components manufactured from phenolic resins.

[0007] Therefore, the use of epoxy resins in cabin construction is a goal of the aviation industry. This class of thermosets reacts via a polyaddition reaction to form thermosets. As a result, epoxy resins exhibit a significantly higher surface quality after curing.

[0008] Conventional epoxy resin formulations are typically based on fossil raw materials. However, a looming shortage of fossil resources is a major concern in the materials industry. Consequently, the pressure to reduce petroleum use and emissions will increase further in the future.

[0009] To meet the challenges of a modern and sustainable society, new concepts must be adopted. One possibility is the development of bio-based fiber-reinforced composites (FRCs) from renewable resources. Combined with an epoxy resin matrix, this not only meets the ever-increasing demands for sustainability but also avoids the high costs associated with post-processing.

[0010] A wide variety of organic raw materials can be obtained from renewable resources, which can also be further processed into technically relevant materials. Vanillin is an interesting example of this.

[0011] Vanillin (4-hydroxy-3-methoxybenzaldehyde) is a bio-based aromatic molecule and the main component of vanilla extract. It can be extracted from vanilla beans. However, due to high cultivation and harvesting costs, vanilla beans are not an attractive raw material source. A promising resource of natural origin for aromatic compounds is lignin, a biopolymer and the matrix component of wood. Various aromatic compounds, including vanillin, can be isolated by depolymerizing lignin. Within the framework of the European Union's Liberate project, a process was developed for the resource-efficient production of bio-based vanillin from "kraft lignin," a waste product of paper manufacturing. Since 2021, up to 7.5 tons of vanillin have been produced annually using this method. 15, 16, 17, 18 STATE OF THE ART

[0012] A number of process steps for the further processing of vanillin or structurally related substances, as well as application possibilities for corresponding bio-based materials, are already known from the literature.

[0013] Kiss et al. described a method for the nitration of vanillin to 5-nitrovanillin using 60% nitric acid and acetic acid. The publication also outlined the synthesis of 3,4-dimethoxy-5-nitrovanillin and 3,4-dimethoxy-5-nitrovanillin oxime. 19

[0014] A process for the alkylation of 5-nitrovanillin to 3,4-dimethoxy-5-nitrovanillin with dimethyl sulfate has been described by Bailey and Tan. The article also presents a synthetic route for the preparation of 5-nitrovanillin. 20

[0015] Kiss et al. and Albarrän-Velo et al. have described methods for the introduction of oxime, with Kiss et al. using hydroxylamine hydrochloride to prepare 3,4-dimethoxy-5-nitrovanillin oxime and Albarrän-Velo et al. using hydroxylamine sulfate for the synthesis of 3-hydroxy-4-methoxybenzaldehyde oxime. 19, 21

[0016] In a publication by Rosen and Green, the conversion of 2-indanone oxime to 2-aminoindane by hydrogenation with Raney nickel was described, which was demonstrated in the presence of sodium hydroxide. 22

[0017] The synthesis of the diamine 4-(aminomethyl)-2,6-dimethoxyaniline and its use as a hardener for epoxy resins is known from publications. Wiegand and Osburg described the synthesis, starting from bio-based syringaldehyde, via a Smiles rearrangement and the introduction and reduction of an oxime. Curing was carried out on a mg scale with the diglycidyl ether of bisphenol A (DGEBA) using differential scanning calorimetry (DSC). The glass transition temperature of this system, determined from the DSC curve, was 160°C. However, the overall yield (hardener) across all synthesis steps is very low at 2 wt%. The 3-amino-4,5-dimethoxybenzylamine (ADBA) presented in this invention could be synthesized in a significantly higher overall yield of 51 wt%. Therefore, the glass transition temperature of a cured plastic plate could be determined using Dynamic Mechanical Analysis (DMA) and was 135°C. 23

[0018] In addition to diamine 4-(aminomethyl)-2,6-dimethoxyaniline, Osburg and Wiegand also described the synthesis of diamine 4-(aminomethyl)-2-methoxyaniline in their article and used it as a hardener for epoxy resins. This diamine is vanillin-based and was also synthesized via a Smiles rearrangement and the introduction and reduction of an oxime. A glass transition temperature of 68°C was determined using DGEBA by DSC. According to the authors, this low glass transition temperature could be attributed to an inhomogeneous resin mixture. This is because the hardener is a solid and only moderately soluble in DGEBA. In contrast, a higher glass transition temperature of 135°C can be achieved with the hardener ADBA (3-amino-4,5-dimethoxybenzylamine) and DGEBA (diglycidyl ether of bisphenol A). Furthermore, the overall yield across all three synthesis steps was very low at 5 wt%, while ADBA could be synthesized with an overall yield of 51 wt%.

[0019] 1,3-Bis(aminomethyl)-4,5-dimethoxybenzene (1,3-BAMB, IUPAC: (4,5-dimethoxy-1,3-phenylene)dimethanamine) is a vanillin-based diamine, which is already known for use as a hardener for epoxy resins from WO2023 / 072786A1. 24 The synthesis of 1,3-BAMB proceeds by introducing an additional formyl group into the vanillin, alkylating the phenolic hydroxyl group, and undergoing a double reductive amination at a hydrogen pressure of 80 bar. The overall yield of the reaction is 61 wt% (total yield of ADBA 51 wt%). After curing with DGEBA, the glass transition temperature is 88°C, as determined by DMA. Compared to ADBA, the synthesis of 1,3-BAMB requires significantly higher hydrogen pressures. Furthermore, ADBA with DGEBA leads to higher glass transition temperatures (135°C) than 1,3-BAMB with DGEBA (88°C).

[0020] The object of the present invention is to produce plastics, in particular fiber-reinforced plastics (FRP), based on renewable resources, especially for cabin construction in aviation, which can replace plastics made from non-renewable or fossil sources in the future, and to improve known bio-based epoxy resins with regard to their thermo-mechanical and mechanical properties to such an extent that they can also meet the high requirements of the aviation industry in an economical way.

[0021] This problem is solved according to the invention with a new bio-based hardener according to claim 1, a method for its synthesis according to claim 2, its use as a hardener component for the production of an epoxy resin according to claim 20, and an epoxy resin according to claim 22. Further developments of the invention, in particular specific features and process parameters, are described in the dependent claims.

[0022] The hardener ADBA according to the invention, when combined with DGEBA, resulted in a high glass transition temperature of 135°C.

[0023] The invention further comprises the synthesis pathway for converting vanillin into the promising diamine 3-amino-4,5-dimethoxybenzylamine (ADBA) with a high bio-content of 74%, and its use as a hardener for epoxy resins. Neither the diamine mentioned here, nor its synthesis, nor the use of this compound as a hardener have been described in the literature to date.

[0024] The new process for the synthesis of 3-amino-4,5-dimethoxybenzylamine ADBA from a provided bio-based vanillin comprises four process steps: a) First stage: Synthesis of 5-nitrovanillin (4-hydroxy-3-methoxy-5-nitrobenzaldehyde, VA1) by nitration of vanillin, e.g.: b) Second stage: Synthesis of 3,4-dimethoxy-5-nitrobenzaldehyde (VA2) by methylation of the phenolic hydroxyl group, e.g.: c) Third stage: Synthesis of 3,4-dimethoxy-5-nitrobenzaldehyde oxime (N-[(Z)-(3,4-dimethoxy-5-nitrophenyl)methylidene]hydroxylamine, VA3) by oxime formation with hydroxylamine hydrochloride, e.g.: d) Fourth step: Synthesis of 3-amino-4,5-dimethoxybenzylamine (ADBA) by hydrogenation with Raney nickel, e.g.:

[0025] ADBA was synthesized with overall yields of 51 wt% across all four process steps. This resulted in significantly better yields than previously known methods, and no complex purification of the product was necessary.

[0026] For the nitration reaction, the vanillin is dissolved in a polar solvent, in particular acetic acid. A nitric acid, preferably a 60% to 100% nitric acid, and especially a 60% nitric acid, is used as the nitrating reagent.

[0027] Other reagents used are / are acids, preferably acetic acid or sulfuric acid, in particular acetic acid.

[0028] For the reaction, in the first stage, the mixture is stirred at a temperature of 0°C to 50°C, preferably 5°C to 30°C, particularly 25°C, for 0.25 h to 6 h, preferably 0.5 h to 2 h, particularly 1 h, and 5-nitrovanillin (4-hydroxy-3-methoxy-5-nitrobenzaldehyde, VA1) is obtained.

[0029] In the methylation stage, VA1 is dissolved in a two-phase reaction system of polar and non-polar solvents or polar solvents, preferably water and dichloromethane or acetone, in particular water and dichloromethane, and methylated with dimethyl sulfate, iodomethane, trimethyloxonium tetrafluoroborate (sea wine salt), diazomethane or formic acid, preferably dimethyl sulfate, iodomethane or formic acid, in particular dimethyl sulfate.

[0030] Further reagent(s) used in the methylation process include Brønsted bases, preferably sodium hydroxide or potassium hydroxide, in particular sodium hydroxide.

[0031] For the reaction, the mixture of the second stage is stirred at a temperature of 5°C to 40°C, preferably 5°C to 25°C, particularly 25°C, for 12 h to 48 h, preferably 22 h to 30 h, particularly 26 h. At the end of the second reaction stage, 3,4-dimethoxy-5-nitrobenzaldehyde, VA2, is obtained.

[0032] For the oxime formation, VA2 is dissolved in a polar solvent, preferably ethanol and water, water, methanol or ethanol, in particular ethanol and water, and hydroxylamine hydrochloride or hydroxylamine sulfate, in particular hydroxylamine hydrochloride, is used as a reagent.

[0033] In the third stage, the following reagent(s) are used: sodium acetate, anhydrous, trihydrate or disodium hydrogen phosphate, preferably sodium acetate anhydrous or trihydrate, in particular sodium acetate anhydrous.

[0034] The reaction mixture is stirred at a temperature of 25°C to 100°C, preferably 40°C to 80°C, particularly 78°C, for 1 h to 6 h, preferably 1 h to 4 h, particularly 1 h. At the end of the third reaction step, 3,4-dimethoxy-5-nitrobenzaldehyde oxime (N-[(Z)-(3,4-dimethoxy-5-nitrophenyl)methylidene]hydroxylamine, VA3, is obtained.

[0035] For the hydrogenation, VA3 is dissolved in polar solvents, acetic acid, ethanol, methanol or ethyl acetate, preferably methanol or ethanol, in particular methanol, in the last process step, and Raney nickel, platinum or palladium, in particular Raney nickel, is used as a catalyst.

[0036] In the fourth stage, a Brønsted base or acid, or no reagent, preferably sodium hydroxide, potassium hydroxide, ammonia, or no reagent, in particular sodium hydroxide, is used as a reagent, and a hydrogen pressure of 1 bar to 15 bar, preferably 3.5 bar to 12 bar, in particular 3.5 bar, is set.

[0037] Finally, the reaction mixture is stirred at a temperature of 25°C to 80°C, preferably 25°C to 70°C, particularly 55°C, for 1 h to 15 h, preferably 1 h to 5 h, particularly 1 h. At the end of the fourth stage, 3-Amino-4,5-dimethoxybenzylamine (ADBA) is obtained.

[0038] The problem is further solved by using a hardener containing at least one amine of formula (I) for crosslinking amine-reactive compounds, wherein the amine-reactive compound is preferably an epoxy resin.

[0039] Another solution to the problem involves an epoxy resin composition containing: - a resin component comprising at least one epoxy resin and - a hardener component comprising at least the hardener according to the invention.

[0040] Finally, the problem is also solved by a cured epoxy resin composition, which is obtained from the epoxy resin composition according to claim 22 after mixing the resin component and the hardener component.

[0041] The synthesis process according to the invention is described below again using a specific embodiment carried out in the laboratory.

[0042] The synthesis of ADBA underlying the invention requires four synthesis steps:

[0043] First stage: Synthesis of 5-nitrovanillin (4-hydroxy-3-methoxy-5-nitrobenzaldehyde, VA1) by nitration of vanillin.

[0044] Vanillin was nitrated in a two-necked flask equipped with a magnetic stem, internal thermometer, and a pressure-equalizing dropping funnel. A solution of vanillin (20 g, 0.132 mol, 1.0 eq) in acetic acid (200 ml) was pre-treated with 60% nitric acid (14.1 g, 0.134 mol, 1.0 eq) added dropwise over 5 minutes via the dropping funnel. To maintain the reaction mixture at room temperature, the addition was performed under cooling. The resulting reddish-brown suspension was then stirred at room temperature for one hour before being transferred to ice water (1000 ml) and stirred for another hour. The product was then isolated using a Büchner funnel, with the filter cake being washed twice with 100 ml of water each time. After drying in a vacuum drying oven (45°C, 25 mbar) until mass constant, 20.9 g (80.3 wt% of the theoretical yield) of a yellow solid remained.

[0045] Second stage: Synthesis of 3,4-dimethoxy-5-nitrobenzaldehyde (VA2) by methylation of the phenolic hydroxyl group.

[0046] VA1 was methylated with dimethyl sulfate and sodium hydroxide in a two-necked flask equipped with a magnetic stirrer, a stopcock and olive-shaped nozzle, and a balloon serving as a nitrogen reservoir. For this purpose, VA1 (7.0 g, 0.003 mol, 0.08 eq) was placed in a round-bottom flask in water (95 ml) and dichloromethane (95 ml). The reaction mixture was then stirred under a nitrogen atmosphere for a total of 26 h. After the addition of all reaction components, a suspension was initially present. After 8 h of reaction time, two clear, transparent phases were observed in which the components were completely dissolved. Therefore, sodium hydroxide (0.72 g, 0.018 mol, 0.5 eq) was added after 8 h and again after a further 24 h of reaction time to achieve the most complete conversion possible. After the 26 h reaction time, two dissolved phases were again present, which were separated using a separatory funnel.The organic phase was collected and the aqueous phase was washed twice with 30 ml of dichloromethane.

[0047] After combining the organic phases, the dichloromethane was completely separated using a rotary evaporator (T Heizbad = 60°C, p Ende = 920 mbar). A residual yellow solid was dissolved in diethyl ether (90 ml) and the resulting solution was diluted twice with 40 ml of water and twice with 40 ml of ammonia solution (c = 2 mol· 1¯). 1 ) and twice with 40 ml of sodium hydroxide solution each time (c = 2 mol · 1¯ 1 The organic phase was washed with 30 ml of a saturated sodium chloride solution. The aqueous phase was discarded in each case.

[0048] After drying the diethyl ether phase over sodium sulfate, the diethyl ether was separated using a rotary evaporator (T HeizbadThe solution was heated to 60°C (without reduced pressure) to obtain 6.8 g (90 wt% of the theoretical yield) of the crude product. The crude product was then recrystallized from water (10 ml) and acetone (32 ml). After drying in a vacuum oven (45°C, 25 mbar) to constant mass, 5.8 g of a cream-colored solid remained, corresponding to an overall yield of 76.4 wt%.

[0049] Third stage: Synthesis of 3,4-dimethoxy-5-nitrobenzaldehyde oxime (N-[(Z)-3,4-dimethoxy-5-nitrophenyl)methylidene]hydroxylamine, VA3) by oxime formation with hydroxylamine hydrochloride.

[0050] The conversion of the aldehyde from VA2 to the oxime VA3 was carried out with hydroxylamine hydrochloride in a three-necked flask equipped with a magnetic stirrer, internal thermometer, intensive condenser, and pressure-equalizing dropping funnel. For the reaction, 3,4-dimethoxy-5-nitrobenzaldehyde (14.0 g, 0.066 mol, 1.0 eq), hydroxylamine hydrochloride (5.5 g, 0.079 mol, 1.2 eq), and sodium acetate (6.0 g, 0.073 mol, 1.1 eq) were placed in ethanol (210 mL) and water (70 mL) and heated to reflux. After 1 h of stirring under reflux, the mixture was cooled to room temperature, whereupon water (500 mL) was added dropwise over 20 min to precipitate the product. After the complete addition of water, the suspension was stirred at room temperature for 20 min, followed by isolation of the product via a Büchner funnel and washing of the filter cake twice with water (100 ml each time).

[0051] After drying in a vacuum drying oven (45°C, 25 mbar) until mass constant, 14.2 g (95.0 wt% of the theoretical yield) of a light cream-colored product remained.

[0052] Fourth stage: Synthesis of 3-amino-4,5-dimethoxybenzylamine (ADBA) by hydrogenation with Raney nickel.

[0053] The hydrogenation of VA3 to ADBA was carried out in a Monel autoclave equipped with an internal thermometer, stirrer, gas inlet tube, and heating jacket. For the hydrogenation, VA3 (3.4 g, 0.015 mol, 1.0 eq), sodium hydroxide (0.7 g, 0.018 mol, 1.2 eq), activated Raney nickel (1.7 g, 50 wt% based on VA3), and methanol (100 ml) were placed in the reactor, and the reactor was sealed.

[0054] While stirring, the hydrogen pressure was adjusted to 3.5 bar and the mixture was then heated to 55°C. At this temperature, a pressure of 4.5 bar was reached. This pressure and temperature of 55°C were maintained for 1 hour. After this time, no further hydrogen uptake was observed, and the reactor was cooled to room temperature followed by venting.

[0055] The catalyst was separated via a folded filter, washed three times with 30 ml of methanol each time, and the filtrate was completely concentrated on a rotary evaporator (T Heizbad = 60°C, p Ende = 100 mbar). The residue, a greenish-brown solid, was suspended and filtered four times in 40 ml of ethyl acetate each time. The filtrates were concentrated and filtered on a rotary evaporator (T Heizbad = 60°C, p End . = 80 mbar) completely constricted, resulting in a yellowish oil.

[0056] The oil was then dried to constant mass in a vacuum drying oven (50°C, 20 mbar). The described synthesis yielded 2.4 g of ADBA, corresponding to a yield of 87.5 wt% of the theoretical yield.

[0057] The proof for ADBA and its properties is illustrated in the figures. They show: Fig. 1 1 H-NMR (nuclear magnetic resonance) of ADBA (3-amino-4,5-dimethoxybenzylamine) in DMSO-d6 (dimethyl sulfoxide), Fig. 2 13 C-NMR of ADBA in DMSO-d6, Fig. 3 a chromatogram (left) and a mass spectrum (right) of the MS (mass spectrometry) measurement of ADBA, Fig. 4 a cured, transparent epoxy resin sheet (ADBA + DGEBA (diglycidyl ether of bisphenol A)) Fig.5 a manufactured test specimen for DMA measurements (Dynamic Mechanical Analysis) to determine the glass transition temperature of the epoxy resin system made of ADBA and DGEBA, Fig. 6. A measurement curve of the resin mixture of ADBA and DGEBA to determine the curing temperature. Fig. 7 a DMA measurement of the epoxy resin system from ADBA and DGEBA, Fig. 8 a comparison of glass transition temperatures of different epoxy resin systems based on DGEBA and Fig. 9. A comparison of the TGA (thermogravimetric analysis) measurement curves of three different epoxy resin systems: the system made of ADBA and DGEBA shows a higher percentage of residual mass than the systems made of IPDA or DDS and DGEBA.

[0058] Fig. 1 and Fig.Figure 2 shows the results of NMR (nuclear magnetic resonance) and GC-MS (gas chromatography-mass spectrometry) measurements of ADBA. NMR spectra reveal the chemical shift of resonance lines relative to a standard. This chemical shift is characteristic of substituents or functional groups that replace a hydrogen atom in a molecule. From this, conclusions can be drawn about the structure of the resulting compound. In addition to the 1 H-NMR spectrum from Fig. 1 is also a 13 C-NMR spectrum, as seen in Fig. Figure 2 is helpful in clarifying the structure of the resulting compound. The two NMR spectra confirm that 3-amino-4,5-dimethoxybenzylamine (ADBA) was synthesized via the described route.

[0059] Since the synthesized ADBA is of particular interest as a hardener for epoxides, the content of basic nitrogen (X) was determined. T The analysis was conducted in accordance with the standard DIN EN ISO 9702, which determines the nitrogen content by titration. The determination was based on the total basicity of the diamine, which is determined by the two amino groups. Because the diamine contains nitrogen only in the amino groups, the nitrogen content can be inferred from the total basicity. The determined nitrogen content was 14.4 wt%. This value is very close to the theoretical value of 15.4 wt%.

[0060] The following describes the curing of an epoxy resin with ADBA and the characterization of the produced sample plate.

[0061] The newly synthesized hardener ADBA was combined with the diglycidyl ether of bisphenol A (DGEBA) with an epoxide equivalent of 175 g·mol -1The procedure was implemented to obtain a hardened sample plate. The hardened plate was then used to determine the glass transition temperature using dynamic mechanical analysis (DMA).

[0062] For curing, 1.2 g of ADBA was mixed with 4.4 g of DGEBA in a rectangular silicone mold, followed by degassing under vacuum. The mixture was then heated in an oven using a temperature program up to 220°C (step-by-step temperature increase from 25°C to 220°C within 290 minutes, with holding times of 20 minutes each at 60°C, 80°C, 100°C, 120°C, 140°C, 160°C, and 180°C). The resulting transparent and solid plastic sheet ( Fig. 4) Test specimens (L x W x H: 40 mm x 4.4 mm x 2.3 mm) were cut out using a precision saw ( Fig. 5), which were measured using DMA and a dual cantilever attachment to determine the glass transition temperature. Fig.Figure 6 shows a measurement curve of the resin mixture of ADBA and DGEBA to determine the curing temperature.

[0063] A DMA measurement curve of the system consisting of ADBA and DGEBA is in Fig. Figure 7 shows the glass transition temperature that could be achieved with the synthesized ADBA and DGEBA after hardening was 135°C.

[0064] The glass transition temperature determined with the newly synthesized hardener and DGEBA was compared with the glass transition temperatures of other hardeners with DGEBA-based epoxy resins ( Fig. 8) The comparison was made with the common hardeners isophorone diamine (IPDA) and 4,4'-diaminodiphenyl sulfone (DDS), as well as the bio-based hardener 1,3-bis(aminomethyl)-4,5-dimethoxybenzene (1,3-BAMB), which is also based on vanillin and is claimed by SIKA Technology AG (Baar, Switzerland) (WO2023 / 072786A1).

[0065] The hardener ADBA exhibits a lower glass transition temperature compared to the commercial hardeners IPDA and DDS ( Fig. 8) In contrast to 1,3-BAMB, DGEBA achieves a significantly higher glass transition temperature. Additionally, the synthesized hardener ADBA has a higher bio-based content of 74% compared to 1,3-BAMB at 69%. Harder Organic share T g with DGEBA 1.3 - BAMB 69 % 88°C ADBA 74 % 135°C IPDA (VESTAMIN® IPD eCo, Evonik Industries AG, Essen, Germany) 73 % 164°C DDS 0% 238°C

[0066] IPDA can also be obtained in a bio-based form with a bio-content of 73% (VESTAMIN®, EPD eCo, Evonik Industries AG, Essen, Germany). While an epoxy resin system made of IPDA and DGEBA results in a higher glass transition temperature than an epoxy resin system made of ADBA and DGEBA, the aromatic structure of ADBA suggests a higher fire resistance. This assumption can be confirmed by thermogravimetric analysis (TGA) measurements of the respective systems. Fig.Figure 9 shows that a system of ADBA and DGEBA results in more residue than a system of IPDA and DGEBA. Therefore, greater charring and consequently higher fire resistance can be assumed. Additionally, the resin mixture with ADBA exhibits a longer processing time (curing begins at approximately 45°C, see Figure 9). Fig. 3) than the resin mixture with IPDA, which already hardens at room temperature. 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HTTPS: / / DOI.ORG / 10.1016 / J.FUPROC.2019.04.007. 16) FACHE, M.; BOUTEVIN, B.; CAILLOL, S.: VANILLIN, A KEY-INTERMEDIATE OF BI-OBASED POLYMERS, EUROPEAN POLYMER JOURNAL 2015, 68, 488-50. HTTPS: / / DOI.ORG / 10.1016 / J.EURPOLYMJ.2015.03.050. 17) M. ZIRBES, T. GRAßL, R. NEUBER, S. R. WALDVOGEL, PEROXODICARBONATE AS A GREEN OXIDIZER FOR THE SELECTIVE DEGRADATION OF KRAFT LIGNIN INTO VANILLIN. ANGEW. CHEM. INT. ED. 2023, 62 (14). HTTPS: / / DOI.ORG / 10.1002 / ANIE.202219217. 18) T. RÜCKER, ET AL.: PILOT SCALE ELECTROCHEMICAL PLANT AT TILLER, NORWAY. HTTPS: / / LIBERATE-PROJECT.EU / PILOT-SCALE-ELECTROCHEMICAL-PLANT-AT-TILLER-NORWAY / . ABRUFDATUM: 17.05.2024 UM 14:20 UHR. 19) L. KISS; H. FERREIRA, ET AL.: DISCOVERY OF A LONG-ACTING, PERIPHERALLY SELECTIVE INHIBITOR OF CATECHOL-O-METHYLTRANSFERASE. J. MED. CHEM. 2010, 53 (8), S. 3396-3411 20) K. BAILEY, E. TAN: SYNTHESIS AND EVALUATION OF BIFUNCTIONAL NITROCATECHOL INHIBITORS OF PIG LIVER CATECHOL-O-METHYLTRANSFERASE. BIOORG. MED. CHEM. 2005, 13 (20), S. 5740-5749. 21) J. ALBARRÁN-VELO, M. LOPEZ-IGLESIAS ET AL.: SYNTHESIS OF NITROGENATED LIGNIN-DERIVED COMPOUNDS AND REACTIVITY WITH LACCASES. STUDY OF THEIR APPLICATION IN MILD CHEMOENZYMATIC OXIDATIVE PROCESSES. RSC ADV. 2017, 7 (80), S. 50459-50471. 22) W. ROSEN, M. GREEN: THE REDUCTION OF 2-INDANONE OXIME TO 2-AMINOINDANE. METHODS AND MECHANISMS. J. ORG. CHEM. 1963, 28 (10), S. 2797-2804. 23) T. Wiegand; A. Osburg: Synthesis, Curing and Thermal Behavior of Amine Hardeners from Potentially Renewable Sources. Polymers 2023, 15 (4). 24) M. Huber, E. Kasemi, F. Häfliger: Biobasierte Aminhärter für härtbare Zusammensetzungen (WO2023 / 072786A1) ZITATE ENTHALTEN IN DER BESCHREIBUNG

[0000] This list of documents cited by the applicant was automatically generated and is included solely for the reader's convenience. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions. Cited patent literature

[0000] WO 2023 / 072786A1 [0019, 0064, 0066] Cited non-patent literature

[0000] Kiss et al. and Albarrän-Velo et al. have described methods for introducing oxime, with Kiss et al. using hydroxylamine hydrochloride

[0015] DIN EN ISO 9702

[0059] SCHLOTT, S.: BMW plant Landshut starts carbon production, ATZproduktion, 5 (No. 2), 2012, pp. 84-87

[0066] DIRSCHMID, F.: The CFRP body of the BMW i8 and its design, In: Tecklenburg, G.: Karosseriebautage Hamburg - 13th ATZ Conference, Springer Fachmedien, Wiesbaden, 2014, pp. 217-231

[0066] COMPOSITES EUROPE: BMW i3 boosts composite materials industry, 2014, http: / / www.composites-europe.com / Pressemitteilung / BMW-i3-befl%C3%BCgelt-Verbundwerkstoff-Industrie / n60 / , accessed on 12.02.2015

[0066] MARSH, G.: Wing worker for the world, Reinforced Plastics, 54 (No. 3), 2010, pp. 24-28

[0066] WITTEN, E.; KRAUS, T.; KÜHNEL, M.: Composites Market Report 2014. Market developments, trends, outlook and challenges, 2014, http: / / www.avk-tv.de / files / 20141023_20141008_marktbericht_gfkcfk.pdf, accessed on 12.05.2021

[0066] HENNING, F.; MOELLER, E.: Handbook of Lightweight Construction - Methods, Materials, Manufacturing, Carl Hanser Verlag, Munich, Vienna, 2011, pp. 309-336; pp. 341-392

[0066] MICHAELI, W.; WEGENER, M.: Introduction to the technology of fiber-reinforced plastics, Carl Hanser Verlag, Munich, Vienna, 1989, pp. 1-2

[0066] LÄSSIG, R.; EISENHUT, M.; MATHIAS, A. ; SCHULTE, RT ; PETERS, F.; KÜH-MANN, T. ; WALDMANN, T. ; BEGEMANN, W.: Series production of high-strength fiber composite components: Perspectives for the German mechanical and plant engineering industry, 2012, http: / / www.rolandberger.de / expertise / branchenexpertise / grundstoffe / 2012-09-26-rbsc-pub-Serienproduktion_hochfester_Faserverbundbauteile.html, accessed on 01.10.2014

[0066] ROMMEL, S.; GEIGER, R.; SCHNEIDER, R.; BERGOLD, D. ; SCHNEIDER, M.; GROß-MANN, M.; KOPP, G.; SCHMITT, A.: Lightweight construction in mobility and manufacturing - opportunities for Baden-Württemberg, 2012, http: / / www.ipa.fraunhofer.de / fileadmin / www.ipa.fhg.de / Publikationen / Leichtbaustudie.pdf, accessed on 16.01.2015

[0066] DOMININGHAUS, H: In: EYERER, P.; HIRTH, T. ; ELSNER, P. (eds.): Plastics. Properties and Applications, Springer Verlag, Berlin, Heidelberg, 2008, pp. 7-8; pp. 27-29; pp. 52-60; pp. 1200-1230

[0066] SCHÜRMANN, H: Designing with Fiber-Reinforced Plastics, Springer-Verlag, Berlin, Heidelberg, 2007, pp. 1-12; pp. 21-81; pp. 125-126; pp. 129-132

[0066] WITTEN, E.; JAHN, B.: Composites Market Report 2011: Market developments, trends, challenges and opportunities, 2011, http: / / www.avk-tv.de / files / 20110929 marktbericht_2011_englisch.pdf, accessed on 13.05.2021

[0066] EICKENBUSCH, H.; KRAUSS, O.: Material innovations for sustainable MOBILITY AND ENERGY SUPPLY, ASSOCIATION OF GERMAN ENGINEERS, DÜSSELDORF, 2014, p. 66. C

[0066] LIU, S. WU, H. ZHANG, R. XIAO, CATALYTIC OXIDATION OF LIGNIN TO VALUABLE BIOMASS-BASED PLATFORM CHEMICALS: A REVIEW. FUEL PROCESS. TECHNOL. 2019, 191, pp. 181-201. HTTPS: / / DOI.ORG / 10.1016 / J.FUPROC.2019.04.007

[0066] FACHE, M.; BOUTEVIN, B.; CAILLOL, S.: VANILLIN, A KEY-INTERMEDIATE OF BI-OBASED POLYMERS, EUROPEAN POLYMER JOURNAL 2015, 68, 488-50. HTTPS: / / DOI.ORG / 10.1016 / J.EURPOLYMJ.2015.03.050

[0066] M. ZIRBES, T. GRAßL, R. NEUBER, S. R. WALDVOGEL, PEROXODICARBONATE AS A GREEN OXIDIZER FOR THE SELECTIVE DEGRADATION OF KRAFT LIGNIN INTO VANILLIN. ANGEW. CHEM. INT. ED. 2023, 62 (14). HTTPS: / / DOI.ORG / 10.1002 / ANIE.202219217.

[0066] T. RÜCKER, ET AL.: PILOT SCALE ELECTROCHEMICAL PLANT AT TILLER, NORWAY. HTTPS: / / LIBERATE-PROJECT.EU / PILOT-SCALE-ELECTROCHEMICAL-PLANT-AT-TILLER-NORWAY / . ABRUFDATUM: 17.05.2024 UM 14:20 UHR

[0066] L. KISS; H. FERREIRA, ET AL.: DISCOVERY OF A LONG-ACTING, PERIPHERALLY SELECTIVE INHIBITOR OF CATECHOL-O-METHYLTRANSFERASE. J. MED. CHEM. 2010, 53 (8), S. 3396-3411

[0066] K. BAILEY, E. TAN: SYNTHESIS AND EVALUATION OF BIFUNCTIONAL NITROCATECHOL INHIBITORS OF PIG LIVER CATECHOL-O-METHYLTRANSFERASE. BIOORG. MED. CHEM. 2005, 13 (20), S. 5740-5749

[0066] J. ALBARRÁN-VELO, M. LOPEZ-IGLESIAS ET AL.: SYNTHESIS OF NITROGENATED LIGNIN-DERIVED COMPOUNDS AND REACTIVITY WITH LACCASES. STUDY OF THEIR APPLICATION IN MILD CHEMOENZYMATIC OXIDATIVE PROCESSES. RSC ADV. 2017, 7 (80), S. 50459-50471

[0066] W. ROSEN, M. GREEN: THE REDUCTION OF 2-INDANONE OXIME TO 2-AMINOINDANE. METHODS AND MECHANISMS. J. ORG. CHEM. 1963, 28 (10), S. 2797-2804

[0066] T. Wiegand; A. Osburg: Synthesis, Curing and Thermal Behavior of Amine Hardeners from Potentially Renewable Sources. Polymers 2023, 15 (4)

[0066] M. Huber, E. Kasemi, F. Häfliger: Biobasierte Aminhärter für härtbare Zusammensetzungen

[0066]

Claims

Bio-based hardener for epoxy resins with the designation 3-Amino-4,5-dimethoxybenzylamine (ADBA) and the structural formula: Method for the synthesis of 3-amino-4,5-dimethoxybenzylamine (ADBA) from a provided bio-based vanillin with the following process steps: a) first step: synthesis of 5-nitrovanillin (4-hydroxy-3-methoxy-5-nitrobenzaldehyde, VA1) by nitration of vanillin, e.g.: b) Second stage: Synthesis of 3,4-dimethoxy-5-nitrobenzaldehyde (VA2) by methylation of the phenolic hydroxyl group, e.g.: c) Third stage: Synthesis of 3,4-dimethoxy-5-nitrobenzaldehyde oxime (N-[(Z)-(3,4-dimethoxy-5-nitrophenyl)methylidene]hydroxylamine, VA3) by oxime formation with hydroxylamine hydrochloride, e.g.: d) Fourth step: Synthesis of 3-amino-4,5-dimethoxybenzylamine (ADBA) by hydrogenation with Raney nickel, e.g.: The method according to claim 2, characterized in that polar solvents, in particular acetic acid, are used as solvents in the first stage. Method according to claim 2 or 3, characterized in that in the first stage nitric acid, preferably 60% to 100% nitric acid, in particular 60% nitric acid, is used as the nitrating reagent. Method according to claim 2, 3 or 4, characterized in that in the first stage acids, preferably acetic acid or sulfuric acid, in particular acetic acid, are used as reagent(s). Method according to claim 2, 3, 4 or 5, characterized in that in the first stage stirring takes place at a temperature of 0°C to 50°C, preferably 5°C to 30°C, in particular 25°C, for 0.25 h to 6 h, preferably 0.5 h to 2 h, in particular 1 h. Method according to one of claims 2 to 6, characterized in that in the second stage a two-phase reaction system of polar and non-polar solvents or polar solvents, preferably water and dichloromethane or acetone, in particular water and dichloromethane, is used as a solvent. Method according to one of claims 2 to 7, characterized in that in the second stage Brønsted bases, preferably sodium hydroxide or potassium hydroxide, in particular sodium hydroxide, are used as reagent(s). A method according to any one of claims 2 to 8, characterized in that in the second stage dimethyl sulfate, iodomethane, trimethyloxonium tetrafluoroborate (sea wine salt), diazomethane or formic acid, preferably dimethyl sulfate, iodomethane or formic acid, in particular dimethyl sulfate, is used as a methylating reagent. Method according to one of claims 2 to 9, characterized in that in the second stage stirring takes place at a temperature of 5°C to 40°C, preferably 5°C to 25°C, in particular 25°C, for 12 h to 48 h, preferably 22 h to 30 h, in particular 26 h. Method according to one of claims 2 to 10, characterized in that in the third stage polar solvents, preferably ethanol and water, water, methanol or ethanol, in particular a mixture of ethanol and water, are used as solvents. Method according to any one of claims 2 to 11, characterized in that in the third stage sodium acetate anhydrous, trihydrate or disodium hydrogen phosphate, preferably sodium acetate anhydrous or trihydrate, in particular sodium acetate anhydrous, is used as reagent(s). Method according to one of claims 2 to 12, characterized in that in the third stage hydroxylamine hydrochloride or hydroxylamine sulfate, in particular hydroxylamine hydrochloride, is used as a reagent for oxime formation. Method according to one of claims 2 to 13, characterized in that in the third stage, stirring takes place at a temperature of 25°C to 100°C, preferably 40°C to 80°C, in particular 78°C, for 1 h to 6 h, preferably 1 h to 4 h, in particular 1 h. Method according to one of claims 2 to 14, characterized in that in the fourth stage polar solvents, acetic acid, ethanol, methanol or ethyl acetate, preferably methanol or ethanol, in particular methanol, are used as solvents. A method according to any one of claims 2 to 15, characterized in that in the fourth stage a Brønsted base or acid or no reagent, preferably sodium hydroxide, potassium hydroxide, ammonia or no reagent, in particular sodium hydroxide, is used as a reagent. Method according to one of claims 2 to 16, characterized in that in the fourth stage Raney nickel, platinum or palladium, in particular Raney nickel, is used as a catalyst. Method according to one of claims 2 to 17, characterized in that in the fourth stage a hydrogen pressure of 1 bar to 15 bar, preferably 3.5 bar to 12 bar, in particular 3.5 bar, is set. Method according to one of claims 2 to 18, characterized in that in the fourth stage, stirring takes place at a temperature of 25°C to 80°C, preferably from 25°C to 70°C, in particular from 55°C, for 1 h to 15 h, preferably from 1 h to 5 h, in particular for 1 h. Use of a hardener according to claim 1, comprising at least one amine of formula (I) for crosslinking amine-reactive compounds: Use according to claim 20, characterized in that the amine-reactive compound is an epoxy resin. Epoxy resin composition comprising: - a resin component comprising at least one epoxy resin and - a hardener component comprising at least the hardener according to claim 1. Cured epoxy resin composition obtained from the epoxy resin composition according to claim 22 after mixing the resin component and the hardener component and crosslinking, particularly at elevated temperatures.

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