Closed-loop recycled bio-based high-toughness epoxy resin and composite material thereof, preparation method and application thereof
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- TIANJIN UNIV
- Filing Date
- 2026-04-30
- Publication Date
- 2026-07-24
AI Technical Summary
Existing recyclable epoxy resins have high viscosity, making it difficult to meet the low viscosity and high flowability requirements of vacuum infusion processes. Furthermore, they cannot achieve high strength, high heat resistance, long-term stability, and fully closed-loop recycling of composite materials. The recycling process is complex and the depolymerization products have low purity.
An epoxy prepolymer containing dynamic hydrogen bonds and active hydroxyl groups was constructed by reacting biomass polyphenolic epoxy monomers with bio-based multi-functional hydrogen bond donors. This prepolymer was then mixed with a bio-based acid anhydride curing agent to form a dynamic ester bond and hydrogen bond crosslinking network. This process was used to prepare a closed-loop recycled bio-based high-strength and tough epoxy resin, which utilizes the synergistic effect of hydrogen bond nanostructure domains and dynamic ester bonds to achieve enhancement, toughening, and self-healing.
Low-viscosity, high-strength, and heat-resistant epoxy resins and their composites were prepared. They can achieve full closed-loop recycling under mild conditions, with high depolymerization rate. The components of the composites can be easily separated and purified, with polymer recovery rate ≥90% and filler recovery rate ≥95%. They are suitable for vacuum casting molding and significantly improve properties such as thermal conductivity.
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Abstract
Description
Technical Field
[0001] This disclosure relates to the field of bio-based polymer composite materials technology, specifically to a closed-loop recycled bio-based high-strength and tough epoxy resin and its composite materials, preparation method, and application. Background Technology
[0002] Currently, recyclable epoxy resins mainly achieve topological rearrangement and depolymerization of the resin network by introducing dynamic covalent bonds (such as dynamic ester bonds, imine bonds, disulfide bonds, etc.), and are mostly made from castor oil, furfural, etc. They have defects such as low heat resistance (Tg < 100℃) and insufficient strength (tensile strength < 80 MPa), and the system viscosity is high (room temperature > 1000 mPa·s), which cannot meet the molding requirements of vacuum infusion process for low viscosity, high fluidity, and full fiber impregnation. At the same time, due to the high viscosity, the amount of filler added to the composite system is limited, which further affects the thermal conductivity and other related properties of the composite material, restricting its application range.
[0003] Furthermore, the recovery of recyclable epoxy resins used in vacuum infusion often employs strong acid and alkali methods or incineration. This process is complex, results in low purity depolymerization products, and makes it difficult to recover the raw materials, thus failing to achieve closed-loop recycling. Modification also easily leads to a decline in the resin's mechanical properties, failing to meet the high strength, toughness, heat resistance, and long-term stability requirements of high-end applications. More importantly, the aforementioned recyclability only achieves simple depolymerization of the resin phase; the separation of multi-component fillers requires complex chemical reagents or high-temperature processes, resulting in low filler recovery rates and poor purity. This prevents the realization of closed-loop recycling of epoxy resin composite materials and hinders the high-value utilization of resources.
[0004] Therefore, developing an epoxy resin and its composite materials that are bio-based, have low viscosity and are easy to inject, have high strength, toughness and heat resistance after curing, and can be efficiently recycled in a closed loop after service has become a key research focus and challenge in the field of bio-based recyclable composite materials. Summary of the Invention
[0005] In view of this, this disclosure provides a closed-loop recyclable bio-based high-strength and high-toughness epoxy resin and its composite material, preparation method, and application, which solves the problems of high viscosity, difficulty in closed-loop recycling, and difficulty in balancing high strength and toughness with recyclability of existing recyclable epoxy resins and epoxy injection adhesive composite materials.
[0006] To achieve the above-mentioned objectives, the method for preparing closed-loop recycled bio-based high-strength and tough epoxy resin disclosed herein includes: Preparation of biomass polyphenol-based epoxy monomers based on biomass polyphenols; An epoxy prepolymer containing dynamic hydrogen bonds and active hydroxyl groups was obtained by reacting biomass polyphenolic epoxy monomers with bio-based multi-functional hydrogen bond donors. The epoxy prepolymer is mixed with a bio-based anhydride curing agent to obtain an epoxy curing precursor; the epoxy curing precursor is cured and molded to construct a crosslinked network containing dynamic ester bonds and dynamic hydrogen bonds, thereby obtaining the closed-loop recycled bio-based high-strength and tough epoxy resin.
[0007] Preferably, the biomass polyphenols are natural polyphenols, selected from one or more of grape pomace polyphenols, olive leaf polyphenols, tea polyphenols, lignin polyphenols, eugenol, guaiacol, and rosinol; The biomass polyphenols have a purity ≥98% and a number average molecular weight of ≥98%. M n 200–500 g / mol, molecular weight distribution coefficient M w / M n : 1.0~1.35.
[0008] Preferably, the biomass polyphenols are natural polyphenols obtained by compound extraction of grape pomace and olive leaves. The extraction method includes: extracting the mixture of grape pomace and olive leaves by PEF-microwave co-extraction at a mass ratio of 3:2. The PEF-microwave synergistic extraction parameters are as follows: solid-liquid ratio 1:10-20 g / mL, pulse electric field 15-20 kV / cm, pulse width 20 μs, pulse electric field duration 10-15 min; microwave power 300 W, extraction temperature 45℃, and microwave synergistic extraction 20-25 min.
[0009] Preferably, the method for preparing biomass polyphenol-based epoxy monomers based on biomass polyphenols includes: The biomass polyphenol and glycidyl trimethylammonium chloride are subjected to an epoxy ring-opening addition reaction in a molar ratio of 1:1.8 to 3.6 to obtain the biomass polyphenol-based epoxy monomer.
[0010] Preferably, the method for obtaining an epoxy prepolymer containing dynamic hydrogen bonds and active hydroxyl groups by reacting a biomass polyphenolic epoxy monomer with a bio-based multi-functional hydrogen bond donor includes: Based on a molar ratio of 1:0.2~0.5 between biomass polyphenolic epoxy monomer and bio-based multifunctional hydrogen bond donor, the biomass polyphenolic epoxy monomer and the bio-based multifunctional hydrogen bond donor are stirred at 40~60℃ for 30~50 min to obtain an epoxy prepolymer containing dynamic hydrogen bonds and active hydroxyl groups with a room temperature viscosity ≤ 160 mPa・s.
[0011] Preferably, the bio-based multifunctional hydrogen bond donor is selected from at least one of lignin-based multifunctional hydrogen bond donors, citric acid-based multifunctional hydrogen bond donors, castor oil-based multifunctional hydrogen bond donors, tannin-based multifunctional hydrogen bond donors, chitosan-based multifunctional hydrogen bond donors, sorbitol-based multifunctional hydrogen bond donors, and itaconic acid-based multifunctional hydrogen bond donors; its hydroxyl functionality is ≥3, and its primary hydroxyl content is ≥60%; and / or, The bio-based anhydride curing agent is selected from one or more of the following: methyl hexahydrophthalic anhydride, hexahydrophthalic anhydride, and nadic anhydride, which are derived from bio-based maleic anhydride.
[0012] Preferably, based on the total molar amount of hydroxyl groups in the system, a bio-based acid anhydride curing agent with a functional group molar amount of 0.8 to 1.0 times the total molar amount of hydroxyl groups is added, and mixed with the epoxy prepolymer, and stirred at 25 to 40°C for 60 to 90 minutes to obtain the epoxy curing precursor; and / or, The method for curing the epoxy curing precursor is to first pre-cur it at 80-100℃ for 1-2 hours, and then raise the temperature to 120-150℃ and keep it at a constant temperature for 3-5 hours for complete curing.
[0013] Secondly, the closed-loop recycled bio-based high-strength and tough epoxy resin described in this disclosure is prepared by any of the methods described in the first aspect.
[0014] Thirdly, the closed-loop recycled bio-based high-strength and high-toughness epoxy composite material disclosed herein comprises the closed-loop recycled bio-based high-strength and high-toughness epoxy resin described in the second aspect.
[0015] Fourthly, the application of the closed-loop recycled bio-based high-strength and tough epoxy composite material described in the third aspect as a vacuum infusion material.
[0016] The present invention has the following beneficial effects: This invention synthesizes a low-viscosity epoxy monomer from all biomass raw materials. By combining raw material selection and proportioning with component physicochemical control, a bio-based high-strength and tough epoxy resin and its composite materials capable of closed-loop recycling are prepared, achieving a synergistic performance of low-viscosity molding, high strength and heat resistance, efficient self-healing, and fully closed-loop recycling. Specifically, the prepolymer of this epoxy resin exhibits excellent processing performance at room temperature (composite viscosity < 380 cp). After molding, the resin benefits from the structural rigidity and reversibility of the epoxy-anhydride covalent crosslinking network, as well as the nanostructure reinforcement domains formed by the self-aggregation of multi-functional hydrogen bonds. The resin possesses mechanical and thermal properties comparable to or even higher than traditional commercial thermosetting resins, with a maximum tensile strength of 126 MPa and an elongation at break of up to 12%. Furthermore, through the synergistic network structure design of hydrogen-bonded nanostructure domains and dynamic chemical crosslinking, the resin not only exhibits high strength characteristics during service but also achieves complete green closed-loop recycling under relatively mild conditions after its service life. This composite material achieves high-value closed-loop recycling of resin under mild conditions through dynamic ester bonds, exhibiting a high depolymerization rate and reusable recycled products. Furthermore, it utilizes the physicochemical differences of its components to achieve full closed-loop recycling of the composite material via simple room-temperature deposition. In addition, the low-viscosity epoxy monomer effectively overcomes the bottleneck of limited filler addition. Its prepolymer, as a bio-based recyclable epoxy potting compound, allows for the addition of more fillers, significantly improving its various properties, including thermal conductivity.
[0017] The epoxy resin and its composite material preparation and recycling process of this invention is simple, adaptable to a variety of closed-mold molding processes, and easy to industrialize and promote. It fills the gap in the full recycling of bio-based recyclable epoxy injection adhesive composite materials, has broad application prospects in many high-end fields, and is of great significance to promoting the green and low-carbon development of the composite material industry. Attached Figure Description
[0018] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with this disclosure and, together with the specification, serve to illustrate the technical solutions of this disclosure.
[0019] Figure 1 Viscorography of the epoxy resin prepolymer of Example 1; (a) Prepolymer viscosity as a function of temperature; Prepolymer viscosity as a function of (b) shear rate and (c) time at room temperature; Figure 2 This is a negatively stained transmission electron microscope image of the nanoscale hydrogen bond domain structure in Example 1; Figure 3 The three-point bending stress-strain curve (a), statistical bar chart (b), and physical image (c) of the closed-loop recycled bio-based high-strength and tough epoxy resin of Example 1 are shown. Figure 4 The degradation kinetics curve and physical image of the resin obtained in Example 1 at 80°C are shown. Detailed Implementation
[0020] Various exemplary embodiments, features, and aspects of this disclosure will now be described in detail with reference to the accompanying drawings. Although various aspects of embodiments are shown in the drawings, they are not necessarily drawn to scale unless specifically indicated otherwise. The term “exemplary” as used herein means “serving as an example, embodiment, or illustration.” Any embodiment illustrated herein as “exemplary” is not necessarily to be construed as superior to or better than other embodiments.
[0021] To address the technical problems mentioned in the background, the core technology for preparing the closed-loop recycled bio-based high-strength and tough epoxy resin disclosed in this invention lies in: Biomass polyphenol-based epoxy monomers are prepared based on biomass polyphenols; an epoxy prepolymer containing dynamic hydrogen bonds and active hydroxyl groups is obtained by reacting the biomass polyphenol-based epoxy monomer with a bio-based multi-functional hydrogen bond donor; the epoxy prepolymer is mixed with a bio-based acid anhydride curing agent to obtain an epoxy curing precursor; the epoxy curing precursor is cured and molded to construct a crosslinked network containing dynamic ester bonds and dynamic hydrogen bonds, thereby obtaining the closed-loop recycled bio-based high-strength and tough epoxy resin.
[0022] The mechanism by which the epoxy resin and its composite materials prepared by the above method possess properties such as closed-loop recycling, high strength and toughness, and high thermal conductivity is as follows: In a bio-based anhydride / epoxy system, a reversible, multi-functional hydrogen bond donor is introduced to construct a reversible, multi-strength structure. This guides the directional interaction between the hydrogen bond donor and the epoxy curing product, spontaneously forming unique, uniformly sized, and evenly dispersed nano-hydrogen bond domains in situ. Energy dissipation through deformation and fracture enhances the resin's strength and toughness. Simultaneously, the introduction of dynamic ester bonds reveals a novel mechanism for autocatalytic exchange through intramolecular hydrogen bond proton transfer, innovatively endowing the resin with powerful comprehensive properties and self-healing, reprocessing, and closed-loop recycling capabilities. The synergistic effect of the aforementioned hydrogen bond nano-domains and dynamic ester bonds achieves enhanced toughness, efficient self-healing, and mild closed-loop recycling of the resin. The resulting epoxy resin exhibits a room temperature viscosity ≤380 mPa·s and a tensile strength ≥120 MPa, combining low viscosity, high strength and toughness, and high heat resistance. Furthermore, based on the epoxy resin composite material, the differences in the physicochemical properties of each component of the composite material are utilized to achieve simple separation and purification of epoxy resin and filler, achieving full recovery of the composite material with a polymer recovery rate of ≥90% and a filler recovery rate of ≥95%, making it suitable for vacuum injection molding. Moreover, the low viscosity of the epoxy resin increases the amount of filler added, thereby improving the thermal conductivity of the composite material.
[0023] Based on the aforementioned core technologies and mechanisms, and through precise molecular structure and network design, the epoxy resin and materials disclosed herein can achieve four core synergistic functions: ① Using hydrogen bonds as non-covalent sacrificial bonds, they aggregate in the resin network to form nano-hydrogen bond domains, which preferentially dissociate under stress to dissipate energy and achieve reinforcement and toughening; ② Using dynamic ester bonds as reversibly dissociatable covalent bonds, they undergo directional dissociation under thermal stimulation and specific depolymerization systems, achieving closed-loop recycling of the polymer; ③ Intramolecular hydrogen bonds have proton transfer characteristics, which can internally catalyze ester bond exchange, and synergize with dynamic ester bonds to achieve efficient self-repair of the resin; ④ Utilizing the differences in physicochemical properties of the polymer and filler in terms of shape, size, and density after depolymerization, the two are separated and purified through simple and slow deposition, achieving full closed-loop recycling of the composite material (polymer recycling is the starting monomer, and the mixed filler is completely recycled and separated).
[0024] Meanwhile, the bio-based epoxy monomer disclosed herein has low viscosity characteristics, which can effectively overcome the bottleneck of high viscosity and limited filler addition in current thermally conductive composite materials. It can add more fillers, thereby significantly improving the composite material’s performance in many aspects, including thermal conductivity.
[0025] Therefore, this invention can solve the technical problems of low self-healing efficiency of existing recyclable epoxy resins, complex recycling processes of composite materials, and inability to recycle them as starting materials. Due to its complete biological origin, good processing performance and excellent mechanical properties, the prepared composite material can be used in aerospace, wind power sheets, electronic packaging and other fields, thereby realizing the green and sustainable development of the entire life cycle of composite materials with high efficiency, intelligent self-healing and full closed-loop recycling.
[0026] In a specific embodiment, the biomass polyphenol-based epoxy monomer is an epoxy group-containing compound obtained by modifying biomass polyphenol derivatives, and is selected from one or more of eugenol-based epoxy compounds, resorcinol-based epoxy compounds, guaiacol-based epoxy compounds, and rosinol-based epoxy monomers.
[0027] The method for preparing biomass polyphenol-based epoxy monomers based on biomass polyphenols is as follows: the biomass polyphenols and glycidyl trimethylammonium chloride are subjected to an epoxy ring-opening addition reaction based on a molar ratio of 1:1.8~3.6 to obtain the biomass polyphenol-based epoxy monomers.
[0028] In a specific embodiment, the biomass polyphenols are natural polyphenols extracted from agricultural and forestry waste and natural plants, including one or more of grape pomace polyphenols, olive leaf polyphenols, tea polyphenols, lignin polyphenols, eugenol, guaiacol, and rosinol. Preferably, the biomass polyphenols are natural polyphenols extracted from a combination of grape pomace and olive leaves, and the purity of the biomass polyphenols is ≥98%, with a number average molecular weight of ≥98%. M n200–500 g / mol, molecular weight distribution coefficient M w / M n The concentration of the biomass polyphenols is 1.0–1.35. The extraction method for the biomass polyphenols is as follows: The mixture of grape pomace and olive leaves is extracted using a PEF-microwave co-extraction method at a mass ratio of 3:2. The PEF-microwave co-extraction parameters are: solid-liquid ratio 1:15 g / mL, pulsed electric field 15–20 kV / cm, pulse width 20 μs, pulsed electric field duration 10–15 min; microwave power 300 W, extraction temperature 45℃, and microwave co-extraction time 20–25 min.
[0029] In a specific embodiment, the method for obtaining an epoxy prepolymer containing dynamic hydrogen bonds and active hydroxyl groups by reacting a biomass polyphenolic epoxy monomer with a bio-based multi-functional hydrogen bond donor includes: stirring the biomass polyphenolic epoxy monomer and the bio-based multi-functional hydrogen bond donor at 40-60°C for 30-50 min, based on a molar ratio of 1:0.2-0.5, to obtain an epoxy prepolymer containing dynamic hydrogen bonds and active hydroxyl groups with a room temperature viscosity ≤ 160 mPa·s. This epoxy prepolymer lays the foundation for a homogeneous reaction for the subsequent in-situ formation of hydrogen-bonded nanostructure domains.
[0030] The bio-based multifunctional hydrogen bond donor has a hydroxyl functionality ≥3 and a primary hydroxyl content ≥60%; it is selected from at least one of lignin-based multifunctional hydrogen bond donors, citric acid-based multifunctional hydrogen bond donors, malic acid-based multifunctional hydrogen bond donors, castor oil-based multifunctional hydrogen bond donors, tannin-based multifunctional hydrogen bond donors, chitosan-based multifunctional hydrogen bond donors, xylitol-based multifunctional hydrogen bond donors, sorbitol-based multifunctional hydrogen bond donors, and itaconic acid-based multifunctional hydrogen bond donors.
[0031] In a specific embodiment, the method for mixing the epoxy prepolymer with a bio-based anhydride curing agent to obtain the epoxy curing precursor is as follows: based on the total molar amount of hydroxyl groups in the system, a bio-based anhydride curing agent with a functional group molar amount of 0.8 to 1.0 times the total molar amount of hydroxyl groups is added and mixed with the epoxy prepolymer. The mixture is stirred at 25 to 40°C for 60 to 90 minutes to obtain the epoxy curing precursor. The bio-based anhydride curing agent is selected from one or more of bio-based maleic anhydride-derived methylhexahydrophthalic anhydride, hexahydrophthalic anhydride, and nadic anhydride.
[0032] In a specific embodiment, the method for curing the epoxy curing precursor is to first pre-cur it at 80–100°C for 1–2 h, and then raise the temperature to 120–150°C for complete curing at a constant temperature for 3–5 h. By controlling the temperature gradient during the curing process, the bio-based multifunctional hydrogen bond donors in the system interact directionally with the epoxy curing product, spontaneously forming uniformly sized and evenly dispersed nano-hydrogen bond domains in situ. This in-situ domain formation method does not require additional templates or subsequent modifications, which is a unique innovation that distinguishes it from traditional preparation processes. It allows hydrogen bonding to act precisely at the molecular level, ultimately yielding a fully recyclable bio-based high-strength and tough epoxy resin.
[0033] In a specific embodiment, the preparation of a closed-loop recyclable bio-based high-strength and tough epoxy resin composite material involves taking 60-85 parts by weight of epoxy resin prepolymer, adding 13.4-40 parts by weight of mixed filler, dispersing at high speed at 45 °C for 5-45 min, and degassing at -0.098 MPa for 5-25 min to obtain a vacuum-injection adhesive. This vacuum-injection adhesive is then used to impregnate a substrate using a vacuum injection process, followed by curing according to the aforementioned epoxy resin curing method to obtain a fully recyclable bio-based high-strength and tough epoxy composite material. The mixed filler is selected from one or more of nano-silica, nano-boron nitride, micron-sized boron nitride, and diamond powder.
[0034] In a specific embodiment, the method for closed-loop recycling of bio-based high-strength and tough epoxy resin is as follows: the cured epoxy resin is placed in an alcohol / weak base composite depolymerization system, and the dynamic ester bonds are dissociated and the hydrogen bonds are depolymerized under thermal stimulation at 70~90 °C. The depolymerization product is then preliminarily filtered, extracted, separated, and purified to obtain the starting material (including anhydride curing agent). The alcohol is selected from one or more of methanol, ethanol, glycerol, and ricinoleic acid, and the weak base is selected from one or more of metal carbonates. The resin depolymerization rate of this disclosure is ≥95% and it is recyclable. After molding, the vacuum-injected adhesive prepared by the recycling of this disclosure retains ≥95% of the thermal conductivity and ≥90% of the mechanical properties of the composite material.
[0035] The following are preferred embodiments of this disclosure.
[0036] In the following embodiments, viscosity was tested according to GB / T 2794-2013 standard, and tensile and elongation at break properties were tested according to GB / T 2567-2021 standard. The material damage healing status was monitored using a combination of optical microscopy and digital camera. The degradation rate was evaluated using a combination of high-performance liquid chromatography-mass spectrometry (HPLC-MS), infrared spectroscopy (IR), and gel permeation chromatography (GPC). The specific evaluation method is as follows: the degradation experiment was conducted at a constant temperature of 80℃. The cured polymer sample was placed in an alcohol / weak base composite depolymerization system and stirred at a constant temperature. Samples were taken at different degradation time points. HPLC-MS was used to detect the composition and purity of the degradation products (mobile phase: methanol-water = 7:3, flow rate 1.0 mL / min). IR analysis was used to analyze the changes in characteristic functional groups during the degradation process (scanning range 4000~400 cm⁻¹). -1 The molecular weight and molecular weight distribution of the polymer before and after degradation were determined by GPC (mobile phase: tetrahydrofuran, flow rate: 1.0 mL / min, column temperature: 35℃); the polymer and packing recovery rates were calculated as the ratio of the mass of the recovered product to the mass of the initial feed; the thermal conductivity was tested according to GB / T 22588-2008 standard.
[0037] In each embodiment, the bio-based maleic anhydride-derived methylhexahydrophthalic anhydride, hexahydrophthalic anhydride, and nadic anhydride were purchased from Beijing Innocare Reagent Co., Ltd.; hydroxypropylated alkali lignin (hydroxyl value 320~380 mg KOH / g), citric acid, and castor oil (hydroxyl value 155~165 mg KOH / g, average functionality f≈3, state as a pale yellow transparent oily bio-based polyol at room temperature) were purchased from Tianjin Xiens Biochemical Technology Co., Ltd. Example 1
[0038] Closed-loop recycling of bio-based high-strength and tough epoxy resin Preparation of closed-loop recycled bio-based high-strength and tough epoxy resin ① Preparation of biomass polyphenols Using grape pomace and olive leaves at a mass ratio of 3:2 as raw materials, after pretreatment, PEF-microwave synergistic extraction and purification were performed to obtain a purity ≥98% and a number average molecular weight of [missing information]. M n ≈ 350 g / mol, molecular weight distribution coefficient M w / M n ≈1.08 biomass polyphenols.
[0039] The PEF-microwave synergistic extraction parameters are: solid-liquid ratio 1:15 g / mL, pulsed electric field 15–20 kV / cm, pulse width 20 μs, pulsed electric field duration 10–15 min; microwave power 300 W, extraction temperature 45℃, and microwave synergistic extraction 20–25 min.
[0040] ② Preparation of biomass polyphenolic epoxy monomers The above-mentioned biomass polyphenols were mixed with glycidyltrimethylammonium chloride at a molar ratio of 1:1.8 in an isopropanol / water mixture (mass ratio 3:1) to carry out an epoxy ring-opening addition reaction. The dropping rate was controlled at 1 drop / 3 s, and the reaction was carried out at 80℃ with stirring for 4 h. After purification, the reaction product was used to obtain a biomass polyphenol-based epoxy monomer with an epoxy value of 0.57 eq / 100g and a viscosity (25℃) of ~600 mPa∙s.
[0041] ③ Preparation of epoxy prepolymer containing dynamic hydrogen bonds and active hydroxyl groups: 60 mol of biomass polyphenolic epoxy monomer and 10 mol of citric acid were added to a nitrogen-protected reactor and stirred at 50°C for 40 min to obtain an epoxy prepolymer containing dynamic hydrogen bonds and active hydroxyl groups, with a room temperature viscosity of 110 mPa·s. Figure 1 ); ④ Preparation of epoxy curing precursor: 70 mol of bio-based anhydride curing agent (bio-based maleic anhydride-derived methylhexahydrophthalic anhydride: bio-based maleic anhydride-derived nadic anhydride = 9:1, molar ratio) was added to the epoxy prepolymer and stirred at 30℃ for 7 min to obtain the epoxy curing precursor, at which time the viscosity at room temperature was 360 mPa∙s; Figure 1 Rheological tests (a, b, c) show that the epoxy-cured precursor exhibits typical Newtonian fluid behavior, a wide processing window, and excellent flowability.
[0042] ⑤ Curing and molding of epoxy curing precursor: The epoxy curing precursor was pre-cured at 110℃ for 2 h, and then fully cured at 150℃ for 4 h to obtain the closed-loop recycled bio-based high-strength and tough epoxy resin of Example 1.
[0043] (2) Performance testing of closed-loop recycled bio-based high-strength and tough epoxy resin ① The step-curing regime of pre-curing at 110℃ for 2 hours and then curing at 150℃ for 4 hours can fully react the epoxy groups and achieve a crosslinking conversion rate of over 95%, while avoiding phase separation and structural disorder caused by high-temperature rapid heating. Figure 2TEM images directly confirmed that under these curing conditions, uniformly distributed nanoscale hydrogen bond domains were formed in situ within the resin. These nanoscale domains were uniform in size and dispersion, with no obvious agglomeration. These nanoscale hydrogen bond domains can preferentially dissociate and dissipate energy under external force, thus bringing significant reinforcement and toughening effects to the material.
[0044] ② Mechanical tests show that the closed-loop recycled bio-based high-strength and high-toughness epoxy resin has a tensile strength of up to 126 MPa and an elongation at break of 12.6%, exhibiting excellent synergistic properties of high strength and high toughness; Figure 3 Bending tests on samples a and 3b showed that its bending strength reached up to 160 MPa, with a deflection greater than 10%. Figure 3 c. The physical image confirms its high ductility; ③ Self-healing: The sample prepared by closed-loop recycled bio-based high-strength and tough epoxy resin was scratched with a blade with a depth of 0.2 mm and a length of 2 cm, and placed on a hot table at 160℃ for 2 h. The self-healing rate of the scratch was 95%.
[0045] ④ Polymer closed-loop recovery: 100g of closed-loop recovered bio-based high-strength and tough epoxy resin was placed in 500g of an alcohol / weak base composite depolymerization system (methanol:potassium carbonate = 15:1, mass ratio), and stirred at 80℃ for 5 days. The resin depolymerization rate was 98%. Figure 4 a\b); The depolymerization product was filtered to obtain crude polymer, which was then purified by extraction and rotary evaporation to obtain 92 g of high-purity bio-based epoxy prepolymer and polyol mixture. The mixture was confirmed as the starting material by liquid chromatography-mass spectrometry.
[0046] 2. Closed-loop recycling of bio-based vacuum infusion composite materials (1) Preparation of closed-loop recycled bio-based vacuum infusion composite material Take 60 parts by mass of the above epoxy prepolymer containing dynamic hydrogen bonds and active hydroxyl groups, add 40 parts by mass of mixed filler (micron boron nitride: diamond powder = 3:1, mass ratio), disperse at high speed at 45℃ for 5 min, and degas at -0.098 MPa for 5 min to obtain vacuum potting adhesive, which has a viscosity of 19.0 Pa∙s at 100℃ and a pot life of 1.5 h at 110℃.
[0047] The aforementioned potting adhesive was impregnated onto the circuit board using a vacuum potting process, followed by a curing process of 110℃ / 2h + 150℃ / 4h, resulting in a high thermal conductivity closed-loop recycled bio-based vacuum potting composite material of Example 1, with a porosity of 0.3% and a thermal conductivity of 2.7 W / m². -1 ·K -1 .
[0048] (2) Performance testing of closed-loop recycled bio-based vacuum infusion composite materials ①Recycling performance Depolymerization of composite materials: 100 g of the above high thermal conductivity bio-based epoxy composite material was placed in 500 g of alcohol / weak base composite depolymerization system (ethanol: sodium carbonate = 15:1, mass ratio) and stirred at 80°C for 5 days. The composite material was dispersed into a suspension system of liquid polymer crude product and solid mixed filler.
[0049] Slow sedimentation separation: The above suspension system is allowed to stand at room temperature of 25°C for 40 minutes. The mixed filler naturally settles at the bottom of the container, while the liquid polymer floats on the upper layer, thus achieving initial separation between the two.
[0050] Polymer purification: The upper liquid polymer was extracted with ethyl acetate, rotary evaporated, and dried under vacuum at 60°C to obtain 92g of high-purity polymer recovery product with a polymer recovery rate of 92%.
[0051] Packing material separation and graded recovery: The bottom solid mixed packing material was washed with deionized water and dried at 80°C. Nano-silica and nano-boron nitride were then recovered by sedimentation and sieving. The recovery rate of each packing material was 89%.
[0052] Fully closed-loop reuse: The purified polymer and the graded recycled filler are used to prepare vacuum casting adhesive again according to the method of this embodiment. The prepared casting adhesive has a room temperature viscosity of 21 Pa∙s and the thermal conductivity retention rate of the molded composite material is 95%.
[0053] ②The results of the thermal conductivity test are shown in Table 1. Example 2
[0054] 1. Closed-loop recycling of bio-based high-strength and tough epoxy resin (1) Preparation of closed-loop recycled bio-based high-strength and tough epoxy resin ① The synthesis of biomass polyphenolic epoxy monomers is the same as in Example 1.
[0055] ② Preparation of epoxy prepolymers containing dynamic hydrogen bonds and active hydroxyl groups 100 mol of biomass polyphenolic epoxy monomer and 10 mol of hydroxypropylated alkali lignin (hydroxyl value 320~380 mg KOH / g) were added to a nitrogen-protected reactor and stirred at 50°C for 40 min to generate a bio-based epoxy prepolymer with a room temperature viscosity of 130 mPa∙s.
[0056] ③ Preparation of epoxy curing precursor Add 95 mol of bio-based anhydride curing agent (bio-based maleic anhydride-derived methylhexahydrophthalic anhydride: bio-based maleic anhydride-derived nadic anhydride = 8:2, molar ratio) to the above epoxy prepolymer and stir at 30°C for 7 min to obtain an epoxy curing precursor with a room temperature viscosity of 240 mPa∙s.
[0057] ④ Curing and molding of epoxy curing precursors The epoxy curing precursor was pre-cured at 90°C for 1.5 h, and then cured at 130°C for another 4 h to obtain the closed-loop recycled bio-based high-strength and tough epoxy resin of Example 2.
[0058] (2) Performance testing of closed-loop recycled bio-based high-strength and tough epoxy resin ① Self-healing: The sample prepared by the above-mentioned closed-loop recycled bio-based high-strength and tough epoxy resin was scratched with a blade with a depth of 0.2 mm and a length of 2 cm, and placed on a hot table at 160℃ for 2 h. The self-healing rate of the scratch was 92%.
[0059] ②Recycling performance: 100g of closed-loop recycled bio-based high-strength and tough epoxy resin was placed in 500g of alcohol / weak base composite depolymerization system (ethanol: sodium carbonate = 15:1, mass ratio) and stirred at 80℃ for 3h. The resin depolymerization rate was 98%. The depolymerization product was filtered to obtain crude polymer, which was purified by extraction and rotary evaporation to obtain 92g of high-purity bio-based epoxy prepolymer and polyol mixture.
[0060] ③The tensile strength and elongation at break properties of the resin are shown in Table 1.
[0061] 2. Closed-loop recycling of bio-based vacuum infusion composite materials (1) Preparation of closed-loop recycled bio-based vacuum infusion composite material By weight, 60 parts of the above epoxy resin prepolymer were taken, and 40 parts of mixed filler (nano silica: nano boron nitride = 1:1, mass ratio) were added. The mixture was dispersed at high speed at 45°C for 45 min, and then degassed at -0.098 MPa for 25 min to obtain a vacuum-filled adhesive with a viscosity of 19.6 Pa∙s at 90°C and a pot life of 1 h at 90°C. The above-mentioned adhesive was used to impregnate a circuit board using a vacuum infusion process. The curing process was 90°C / 1.5 h + 130°C / 4 h, resulting in a high thermal conductivity closed-loop recyclable bio-based vacuum-filled composite material as described in Example 2. The material had a porosity of 0.3% and a thermal conductivity of 2.2 W / m². -1 ·K -1 .
[0062] (2) Recycling performance test of closed-loop recycled bio-based vacuum infusion composite material Depolymerization of composite materials: 100 g of the above high thermal conductivity bio-based epoxy composite material was placed in 500 g of alcohol / weak base composite depolymerization system (ethanol: sodium carbonate = 15:1, mass ratio) and stirred at 80°C for 5 days. The composite material was dispersed into a suspension system of liquid polymer crude product and solid mixed filler.
[0063] Slow sedimentation separation: The above suspension system is allowed to stand at room temperature of 25°C for 40 minutes. The mixed filler naturally settles at the bottom of the container, while the liquid polymer floats on the upper layer, thus achieving initial separation between the two.
[0064] Polymer purification: The upper liquid polymer was extracted with ethyl acetate, rotary evaporated, and dried under vacuum at 60°C to obtain 55 g of high-purity polymer recovery product with a polymer recovery rate of 91.7%.
[0065] Packing material separation and graded recovery: The bottom solid mixed packing material was washed with deionized water and dried at 80℃. The nano-silica and nano-boron nitride were recovered by sedimentation and sieving. The recovery rate of each packing material was 96%.
[0066] Fully closed-loop reuse: The purified polymer and the graded recycled filler are used to prepare vacuum casting adhesive again according to the method of this embodiment. The prepared casting adhesive has a room temperature viscosity of 21 Pa∙s and the thermal conductivity retention rate of the molded composite material is 95%. Example 3
[0067] 1. Closed-loop recycling of bio-based high-strength and tough epoxy resin (1) Preparation of closed-loop recycled bio-based high-strength and tough epoxy resin ① Synthesis of biomass polyphenolic epoxy monomers: Same as in Example 1.
[0068] ② Preparation of epoxy prepolymer containing dynamic hydrogen bonds and active hydroxyl groups: 60 mol of biomass polyphenolic epoxy monomer and 8 mol of castor oil were added to a nitrogen-protected reactor and stirred at 50°C for 40 min to produce the epoxy prepolymer containing dynamic hydrogen bonds and active hydroxyl groups of Example 3, with a room temperature viscosity of 150 mPa∙s. ③ Preparation of epoxy curing precursor: 70 mol of bio-based maleic anhydride-derived methylhexahydrophthalic anhydride was added to 68 mol of epoxy prepolymer containing dynamic hydrogen bonds and active hydroxyl groups, and stirred at 30℃ for 7 min to obtain epoxy curing precursor with a room temperature viscosity of 330 mPa∙s. ④ Curing and molding of epoxy curing precursor: The above epoxy curing precursor was pre-cured at 110°C for 2 h and then cured at 150°C for 4 h to obtain the closed-loop recycled bio-based high-strength and tough epoxy resin of Example 3.
[0069] (2) Performance testing of closed-loop recycled bio-based high-strength and tough epoxy resin ① Self-healing: The sample prepared by closed-loop recycled bio-based high-strength and tough epoxy resin was scratched with a blade with a depth of 0.2 mm and a length of 2 cm, and placed on a hot table at 160℃ for 2 h. The self-healing rate of the scratch was 96%.
[0070] ②Recycling performance: 100g of closed-loop recycled bio-based high-strength and tough epoxy resin was placed in 500g of alcohol / weak base composite depolymerization system (methanol: potassium carbonate = 15:1, mass ratio) and stirred at 80℃ for 5 days. The resin depolymerization rate was 98%. The depolymerization product was filtered to obtain crude polymer, which was purified by extraction and rotary evaporation to obtain 87g of high-purity bio-based epoxy prepolymer and polyol mixture.
[0071] ③The tensile strength and elongation at break properties of the resin are shown in Table 1.
[0072] 2. Preparation of closed-loop recycled bio-based vacuum infusion composite materials Take 60 parts by weight of the above epoxy resin prepolymer, add 40 parts by weight of mixed filler (micron boron nitride: diamond powder = 3:1, mass ratio), disperse at high speed at 45℃ for 5 min, and finally degas at -0.098MPa for 5 min to obtain vacuum potting adhesive with a viscosity of 18.2 Pa·s at 100℃.
[0073] The aforementioned potting adhesive was impregnated onto the circuit board using a vacuum potting process, followed by a curing process of 110℃ / 2h + 150℃ / 4h, resulting in the high thermal conductivity closed-loop recyclable bio-based vacuum potting composite material of Example 3. This composite material has a porosity of 0.4% and a thermal conductivity of 2.6 W / m². -1 ·K -1 .
[0074] Comparative Example 1 This comparative example provides a conventional petrochemical-based non-recyclable low-viscosity vacuum injection adhesive, which is prepared by means of 60 g of bisphenol A epoxy resin E-51, 40 g of AGE active crosslinking agent, 120 g of methylhexahydrophthalic anhydride, 1.2 g of benzyl dimethylamine accelerator, 12 g of nano silica + 37 g of micron calcium carbonate mixed filler, and has a processing viscosity of 18.3 Pa·s.
[0075] Curing and molding: The prepolymer is pre-cured at 110℃ for 2 h and then cured at 150℃ for 4 h to obtain the vacuum-infused composite material.
[0076] Comparative Example 2 This comparative example provides a commercially available bio-based recyclable epoxy resin vacuum thermal conductive adhesive (filler content of 40%), purchased from Henson Specialty Chemicals, Inc., USA. It only introduces dynamic ester bonds and does not have hydrogen bond synergistic modification. The processing viscosity is 49 Pa·s (equivalent to the epoxy prepolymer containing dynamic hydrogen bonds and active hydroxyl groups in Example 1, whose viscosity is only 19 Pa·s).
[0077] Curing and molding: The prepolymer is pre-cured at 110℃ for 2 hours, and then cured at 150℃ for 4 hours to obtain the vacuum-infused composite material. Curing and recycling are performed according to the manufacturer's recommended process. Composite material recycling requires a high-temperature acid washing process to separate the polymer and filler, but the starting polymer raw material cannot be recovered.
[0078] Self-healing test: The epoxy resin sample was scratched with a blade with a depth of 0.2 mm and a length of 2 cm, and placed on a 160℃ hot table for 2 h. The self-healing rate of the scratch was 12%.
[0079] Comparative Example 3 Compared with Example 1, this comparative example is identical in all aspects except that the curing process is changed to "curing at 120 ℃ for 6 h" and the composite material curing process is changed to "120 ℃ / 6 h".
[0080] The performance test results of the above-described embodiments and comparative examples of the closed-loop recyclable bio-based high-strength and high-toughness epoxy resin and the corresponding high thermal conductivity vacuum-infused composite material are shown in Table 1 below: Table 1. Performance test results of resins and composite materials in Examples 1-3 and Comparative Examples 1-3
[0081] The performance test results in Table 1 show that: ① The closed-loop recyclable bio-based high-strength and high-toughness epoxy resin and high thermal conductivity composite material prepared in Examples 1-3 of this disclosure exhibit excellent performance in terms of raw material greening, moldability, mechanical and heat resistance, self-healing, and depolymerization properties. The epoxy resin prepolymer possesses a hydrogen-bonded aggregated nanostructure domain and a dynamic ester bond dual-synergistic reversible multi-strength structure. This prepolymer exhibits good processing performance at room temperature (composite viscosity < 380 cp) and excellent mechanical properties after molding. Performance indicators meet the following requirements: glass transition temperature... T g ≥ 80 ℃, tensile strength ≥ 120 MPa, tensile modulus ≥ 1.4 GPa, flexural strength ≥ 110 MPa, resin depolymerization rate ≥ 95%, and polymer recycling product reuse performance retention rate ≥ 90%. The porosity of the high thermal conductivity composite material is ≤ 0.8%, and the thermal conductivity is ≥ 2.2 W / m². -1 ・K -1The viscosity of the injection adhesive at 90~110 ℃ is ≤ 19.6 Pa・s, and the pot life is ≥ 1 h. After the vacuum injection adhesive is recycled and re-prepared, the thermal conductivity of the composite material is retained by ≥ 95%, and the mechanical properties are retained by ≥ 90%.
[0082] ② Compared with Comparative Examples 1 and 2, Examples 1-3 achieved a high filler loading of 40% under low viscosity conditions of 18.2~19.6 Pa·s, breaking through the bottleneck of "high viscosity and limited filler addition" in traditional thermally conductive resin systems. At the same time, due to the inherent dynamic ester bond and hydrogen bond interaction, Examples 1-3 have excellent self-healing properties.
[0083] ③ Compared with Comparative Example 3, which did not use temperature gradient controlled curing (single temperature curing), the resin of Example 1 has a maximum tensile strength of 126 MPa and an elongation at break of 12.6%. Compared with Comparative Example 3, it has achieved significant improvements in the mechanical properties of the resin, the thermal conductivity of the composite material, and recyclability. This confirms that the in-situ construction of nano-hydrogen bond domains by temperature gradient controlled curing improves the resin's various properties, such as mechanical properties and thermal conductivity.
[0084] ④ Compared to Comparative Examples 1 and 2, the resins and their composites in Examples 1-3 can be recycled in a closed loop as starting materials. However, although Comparative Example 2 is recyclable, only the filler can be recycled, and it cannot be recycled as an initial raw material.
[0085] In summary, this disclosure synthesizes a low-viscosity epoxy monomer from all biomass raw materials and uses it to construct epoxy resins and high thermal conductivity composites with closed-loop recyclability and superior toughness. Through a dual-synergistic structural design of a dynamic ester bond covalent reversible network and hydrogen bond nanostructure domains, combined with precise control of the physicochemical properties of the components, it achieves for the first time the synergistic unity of four major functions: nano-hydrogen bond reinforcement and toughening, efficient self-repair through hydrogen bond internal catalysis, dynamic ester bond mild closed-loop recycling, and physicochemical difference-driven full closed-loop recycling of composite materials. The core innovation lies in utilizing hydrogen bond aggregation to form nanoscale hydrogen bond domains and internally catalyze ester bond exchange, and achieving simple and efficient full-component recycling through the control of filler physicochemical properties. This material combines the advantages of green raw materials, low viscosity for easy injection, high strength, toughness, and high heat resistance, solving many pain points of existing technologies and filling the gap in the full recycling of bio-based recyclable epoxy injection adhesive composites. It has significant industrial application value in high-end composite material fields such as wind power and aerospace, and is of great significance for promoting the green and low-carbon development and high-value utilization of resources in the composite material industry.
[0086] The various embodiments of this disclosure have been described above. These descriptions are exemplary and not exhaustive, nor are they limited to the disclosed embodiments. Many modifications and variations will be apparent to those skilled in the art without departing from the scope and spirit of the described embodiments. The terminology used herein is chosen to best explain the principles, practical application, or technical improvements to the embodiments in the market, or to enable others skilled in the art to understand the embodiments disclosed herein.
Claims
1. A method for preparing a closed-loop recycled bio-based high-strength and tough epoxy resin, characterized in that, include: Preparation of biomass polyphenol-based epoxy monomers based on biomass polyphenols; An epoxy prepolymer containing dynamic hydrogen bonds and active hydroxyl groups was obtained by reacting biomass polyphenolic epoxy monomers with bio-based multi-functional hydrogen bond donors. The epoxy prepolymer is mixed with a bio-based anhydride curing agent to obtain an epoxy curing precursor; the epoxy curing precursor is cured and molded to construct a crosslinked network containing dynamic ester bonds and dynamic hydrogen bonds, thereby obtaining the closed-loop recycled bio-based high-strength and tough epoxy resin.
2. The method for preparing closed-loop recycled bio-based high-strength and tough epoxy resin according to claim 1, characterized in that: The biomass polyphenols are natural polyphenols, selected from one or more of grape pomace polyphenols, olive leaf polyphenols, tea polyphenols, lignin polyphenols, eugenol, guaiacol, and rosinol; The biomass polyphenols have a purity ≥98% and a number average molecular weight of ≥98%. M n 200–500 g / mol, molecular weight distribution coefficient M w / M n : 1.0~1.
35.
3. The method for preparing closed-loop recycled bio-based high-strength and tough epoxy resin according to claim 2, characterized in that: The biomass polyphenols are natural polyphenols obtained by compound extraction of grape pomace and olive leaves. The extraction method includes: extracting the mixture of grape pomace and olive leaves by PEF-microwave co-extraction at a mass ratio of 3:
2. The PEF-microwave synergistic extraction parameters are as follows: solid-liquid ratio 1:10-20 g / mL, pulse electric field 15-20 kV / cm, pulse width 20 μs, pulse electric field duration 10-15 min; microwave power 300 W, extraction temperature 45℃, and microwave synergistic extraction 20-25 min.
4. The method for preparing closed-loop recycled bio-based high-strength and tough epoxy resin according to any one of claims 1-3, characterized in that, The method for preparing biomass polyphenol-based epoxy monomers based on biomass polyphenols includes: The biomass polyphenol and glycidyl trimethylammonium chloride are subjected to an epoxy ring-opening addition reaction in a molar ratio of 1:1.8 to 3.6 to obtain the biomass polyphenol-based epoxy monomer.
5. The method for preparing closed-loop recycled bio-based high-strength and tough epoxy resin according to any one of claims 1-3, characterized in that, The method for obtaining an epoxy prepolymer containing dynamic hydrogen bonds and active hydroxyl groups by reacting a biomass polyphenolic epoxy monomer with a bio-based multi-functional hydrogen bond donor includes: Based on a molar ratio of 1:0.2~0.5 between biomass polyphenolic epoxy monomer and bio-based multifunctional hydrogen bond donor, the biomass polyphenolic epoxy monomer and the bio-based multifunctional hydrogen bond donor are stirred at 40~60℃ for 30~50 min to obtain an epoxy prepolymer containing dynamic hydrogen bonds and active hydroxyl groups with a room temperature viscosity ≤ 160 mPa・s.
6. The method for preparing closed-loop recycled bio-based high-strength and tough epoxy resin according to claim 5, characterized in that: The bio-based multifunctional hydrogen bond donor is selected from at least one of lignin-based, citrate-based, castor oil-based, tannin-based, chitosan-based, sorbitol-based, and itaconic acid-based hydrogen bond donors; its hydroxyl functionality is ≥3, and its primary hydroxyl content is ≥60%; and / or, The bio-based anhydride curing agent is selected from one or more of the following: methyl hexahydrophthalic anhydride, hexahydrophthalic anhydride, and nadic anhydride, which are derived from bio-based maleic anhydride.
7. The method for preparing closed-loop recycled bio-based high-strength and tough epoxy resin according to any one of claims 1-3, characterized in that: Based on the total molar amount of hydroxyl groups in the system, a bio-based anhydride curing agent with a functional group molar amount of 0.8 to 1.0 times the total molar amount of hydroxyl groups is added and mixed with the epoxy prepolymer. The mixture is stirred at 25 to 40°C for 60 to 90 minutes to obtain the epoxy curing precursor; and / or, The method for curing the epoxy curing precursor is to first pre-cur it at 80-100℃ for 1-2 hours, and then raise the temperature to 120-150℃ and keep it at a constant temperature for 3-5 hours for complete curing.
8. A closed-loop recycled bio-based high-strength and tough epoxy resin, characterized in that: Prepared by the method described in any one of claims 1-7.
9. A closed-loop recycled bio-based high-strength and tough epoxy composite material, characterized in that, Its components include: The closed-loop recycled bio-based high-strength and tough epoxy resin of claim 8.
10. The application of the closed-loop recycled bio-based high-strength and tough epoxy composite material of claim 9 as a vacuum infusion material.