Preparation method and application of degradable triazine alkane oligoester epoxy resin modifier

Abstract

The application discloses a preparation method and application of a degradable triazine alkane oligoester epoxy resin modifier. The method uses 4-amino-1-butanol and a formaldehyde solution as starting reactants to prepare tri-branching triazine alkane butanol. The tri-branching triazine alkane butanol contains hydroxyl groups, can react with different structures of dicarboxylic acids to generate carboxyl-terminated oligoesters, and then react with a diglycidyl ether to prepare an epoxy group-terminated oligoester modifier. The preparation process of the obtained modifier is a green synthesis method under catalyst-free and solvent-free conditions, and the modifier has a branched structure. The epoxy resin toughness is increased, and the mechanical properties and thermal stability of the cold-cured epoxy polymer can be maintained or improved. The modified epoxy resin can be recycled under acidic conditions, can be applied to the recycling of high-end products such as carbon fiber reinforced composites, and has wide industrial application prospects in the fields of wind power, new energy, low-altitude aircraft and the like.

Description

Technical Field

[0001] This invention belongs to the field of biodegradable and recyclable epoxy resin technology, and relates to an epoxy resin modifier, specifically to a method for preparing a biodegradable triazine alkyl low-polyester epoxy resin modifier and its application in the field of resin-based composite materials. Background Technology

[0002] Epoxy resins are widely used in aerospace, rail transportation, wind turbine blades, electronic packaging, coatings, and adhesives due to their excellent adhesion, corrosion resistance, electrical insulation, and mechanical strength. However, after curing, epoxy resins form a three-dimensional cross-linked network with high cross-linking density and restricted molecular chain movement, resulting in brittleness and poor impact resistance, making it difficult to meet the application requirements of high-toughness structural components. Furthermore, cross-linked epoxy resins are insoluble and infusible, making them extremely difficult to recycle after disposal, resulting in a significant waste of polymer resources and a substantial environmental burden.

[0003] In recent years, to improve the toughness of epoxy resins, methods such as toughening with rubber elastomers, thermoplastics, core-shell nanoparticles, and hyperbranched polymers have been mainly used. However, these methods suffer from drawbacks such as "the performance of epoxy resins fluctuates, catalyst residues, and environmentally unfriendly processes." There is an urgent need to develop a highly efficient, balanced, green, and cold-curing epoxy resin modification scheme. A branched low-polyester modifier with epoxy-terminated ends can chemically react with the amine curing agent of epoxy resin at room temperature and permanently connect to a three-dimensional cross-linked network through chemical bonds. During curing, this reaction-induced microphase separation forms an ideal "island structure"—the rigid epoxy resin is the continuous phase (sea), while the flexible polyester segments self-assemble to form nano / micro-sized spherical particles as the dispersed phase (islands). By "weaving" itself into the epoxy network, an excellent balance between efficient toughening and heat resistance / stiffness is achieved, solving the problem of traditional rubber toughening agents sacrificing key performance characteristics.

[0004] Triazine ring derivatives are nitrogen-containing six-membered saturated heterocycles that can undergo degradation reactions under specific acidic or high-temperature conditions, reverting to a small molecule state. This allows the resin matrix to dissolve and separate from fiber-reinforced composites, enabling the green recycling of high-value fillers such as carbon fibers and solving the problem of difficult recycling of thermosetting resins. Branched low-polyesters containing triazine structures are intelligent toughening agents that not only physically solve the toughening problem of epoxy resins but also endow thermosetting resins with "thermoplastic-like" behavior—repairable, reprocessable, and recyclable—by introducing dynamic covalent bonds. Summary of the Invention

[0005] The purpose of this invention is to provide a method for preparing a biodegradable triazine alkyl polyester epoxy resin modifier and its application. This method uses 4-amino-1-butanol and formaldehyde solution as starting reactants to prepare tribranched triazine alkyl butanol. Since the tribranched triazine alkyl butanol contains hydroxyl groups, it can react with dicarboxylic acids of different structures to generate carboxyl-terminated polyesters. These polyesters are then reacted with diglycidyl ether to prepare epoxy-terminated polyester modifiers. The resulting modifier is prepared using a green synthesis method under catalyst-free and solvent-free conditions and possesses a branched structure. While increasing the toughness of epoxy resin, it can maintain or improve the mechanical properties and thermal stability of cold-cured epoxy polymers. Furthermore, the modified epoxy resin is biodegradable and recyclable under acidic conditions, making it suitable for recycling high-end products such as carbon fiber reinforced composites. It has broad industrial application prospects in fields such as wind power, new energy, and low-altitude aircraft.

[0006] The objective of this invention is achieved through the following technical solution:

[0007] A method for preparing a biodegradable triazine alkyl oligoester epoxy resin modifier includes: first, reacting 4-amino-1-butanol with formaldehyde solution to prepare a tribranched triazine tributanol with a defined structure; then reacting it with dicarboxylic acids of different structures to generate carboxyl-terminated branched oligoesters; and finally reacting it with diglycidyl ether to obtain epoxy-terminated branched oligoesters. The method specifically includes the following steps:

[0008] Step 1: Preparation of hexahydro-1,3,5-triazine-1,3,5-tributanol:

[0009] Step 1-1: Dissolve 4-amino-1-butanol in an organic solvent, and add 37% formaldehyde aqueous solution dropwise while stirring in an ice bath, wherein the molar ratio of 4-amino-1-butanol to formaldehyde is 1:(1~1.2); the organic solvent is one of water, methanol, ethanol, ethanol-water, tetrahydrofuran, and acetonitrile;

[0010] Steps 1-2: After the addition is complete, under the protection of an inert gas (such as nitrogen or argon), heat to 60-80℃ and stir for 6-10 hours.

[0011] Steps 1-3: After the reaction is complete, cool to room temperature and remove the organic solvent by rotary evaporation to obtain the target product, hexahydro-1,3,5-triazine-1,3,5-tributanol (I), which is a yellow, transparent, oily liquid.

[0012] The chemical reaction equation is as follows:

[0013]

[0014] Step 2: Preparation of carboxyl-terminated low-polyester:

[0015] Step 2-1: Mix the target product (I) with a dicarboxylic acid at a carboxyl:hydroxyl molar ratio of (1.3~1.6):1, ensuring excess carboxyl groups to avoid the risk of gelation. Perform a polycondensation reaction under an inert atmosphere for 8~9 hours, wherein the polycondensation reaction temperature is 135~150℃; the dicarboxylic acid is selected from any one or more of the following mixtures: aliphatic C4~C 12 Straight-chain dicarboxylic acids, including but not limited to succinic acid, adipic acid, and sebacic acid; alicyclic dicarboxylic acids, including but not limited to 1,4-cyclohexanedicarboxylic acid; aromatic dicarboxylic acids, including but not limited to terephthalic acid and isophthalic acid;

[0016] Step 2-2: No catalyst is required during the reaction. Acid value can be measured to track the reaction progress. When the acid value drops to 135~160mgKOH / g, it is considered the reaction endpoint, and carboxyl-terminated low polyester (II) is obtained.

[0017] The chemical reaction process is as follows:

[0018]

[0019] Step 3: Preparation of terminal epoxy group low-polyester:

[0020] Step 3-1: Mix carboxyl-terminated low polyester (II) with diglycidyl ether at a molar ratio of epoxy group to carboxyl group of (2.1~2.2):1, ensuring a slight excess of epoxy group to ensure complete conversion of terminal epoxy and compensate for minor losses. Under an inert atmosphere, stir and heat the system to 130~140℃ and react at this temperature for 5~7 hours. The diglycidyl ether includes, but is not limited to, one of ethylene glycol diglycidyl ether, diethylene glycol diglycidyl ether, 1,4-butanediol diglycidyl ether, neopentyl glycol diglycidyl ether, and trimethylolpropane triglycidyl ether. Multifunctional glycidyl ethers can introduce branching points and increase the crosslinking density of the final product.

[0021] Step 3-2: Take samples at regular intervals to determine the acid value and epoxy value of the system. The reaction endpoint is reached when the acid value drops to ≤2mgKOH / g and the epoxy value reaches 6~9mol / 100g (determined by the hydrochloric acid-acetone method), thus obtaining the epoxy-terminated low polyester modifier (III).

[0022] The chemical reaction process is as follows:

[0023]

[0024] A method for preparing a modified epoxy resin includes the following steps:

[0025] The epoxy-terminated low-polyester modifier (III) prepared by the above method is mixed with epoxy resin, and an amine curing agent is added. The mixture is then cured at room temperature for 24-28 hours in a mold. The resulting cured product has excellent mechanical properties and thermal stability, and can be degraded under acidic conditions. The degradation products can be recycled and reused. The mass ratio of modifier to epoxy resin is 3-20:97-80, and the amount of curing agent is 28-32% of the mass of epoxy resin. The epoxy resin is one of E-51 epoxy resin, bisphenol A liquid epoxy resin, or bisphenol F type epoxy resin. The amine curing agent includes, but is not limited to, polyetheramine curing agents, aliphatic polyamines, and alicyclic polyamines. Polyetheramine D-230 is preferred. The curing agent reaches usable strength after 24 hours of curing at room temperature, has good compatibility with the modifier, and does not cause triazine ring-opening side reactions due to severe exothermic reactions.

[0026] A method for degrading modified epoxy resin includes the following steps:

[0027] The modified epoxy resin prepared by the above method is pulverized and then soaked in a strong acid solution with pH < 3. Stirred at 50-60°C, obvious swelling can be observed after 4-8 hours. After 24 hours, it is basically completely degraded into low molecular weight products. The strong acid solution includes, but is not limited to, hydrochloric acid, sulfuric acid, and p-toluenesulfonic acid.

[0028] Compared with the prior art, the present invention has the following advantages:

[0029] 1. This invention uses hexahydro-1,3,5-triazine-1,3,5-tributanol as the starting reactant to prepare an epoxy-terminated tribranched low-polyester modifier. After mixing the modifier with epoxy resin, it is cured at room temperature using an amine curing agent. The resulting cured product has excellent mechanical properties and thermal stability, and can be degraded under acidic conditions. The degradation products can be recycled and reused.

[0030] 2. The epoxy groups at the end of the modifier can react with amine curing agents to introduce the epoxy crosslinking network through chemical bonding, effectively preventing phase separation; its long-chain aliphatic structure and diethylene glycol ether bonds can undergo chain segment extension and rearrangement under stress, thereby dissipating impact energy; the triazine branched core can reduce the crosslinking density of the epoxy network, increase the spacing between crosslinking points, and enhance the molecular chain mobility, achieving precise control over the crosslinking density and network topology.

[0031] 3. The process of preparing the modifier in this invention does not require catalysts or solvents, significantly reducing energy consumption compared to traditional processes and reducing waste treatment costs accordingly, thus possessing green and environmentally friendly advantages. In addition, as a nitrogen-containing six-membered saturated heterocycle, the CN single bond of the triazine ring is easily broken under specific conditions such as acid catalysis and high-temperature heating, initiating a ring-opening reaction and promoting material degradation, thereby enabling the recycling and reuse of resin materials. Detailed Implementation

[0032] The technical solution of the present invention will be further described below with reference to the embodiments, but it is not limited thereto. Any modifications or equivalent substitutions to the technical solution of the present invention without departing from the spirit and scope of the technical solution of the present invention should be covered within the protection scope of the present invention.

[0033] Example 1: Preparation of hexahydro-1,3,5-triazine-1,3,5-tributanol:

[0034] Accurately weigh 56 mmol (5 g) of 4-amino-1-butanol into a 250 mL three-necked flask, add 50 mL of ethanol as solvent, and dropwise add 67 mmol (5.46 g) of 37% formaldehyde aqueous solution under N2 atmosphere and stirring in an ice bath. After the addition is complete, stir, raise the temperature to 80 °C, and react for 8 hours. After the reaction is complete, cool to room temperature, remove the organic solvent by rotary evaporation, and obtain the target product (I) as a yellow transparent oily liquid.

[0035] Example 2: Preparation of carboxyl-terminated low-polyester:

[0036] Accurately weigh 31.94 g (0.1 mol) of the target product (I) and 58.46 g (0.4 mol) of adipic acid into a 250 mL four-necked flask, purge with nitrogen and stir (flow rate 20 mL / min), and slowly heat the system to 135 °C. o C±3 o C. React for 8 hours, and take samples every 2 hours to measure the acid value. When the acid value of the system stabilizes between 150 and 160 mg KOH / g, the reaction is considered to be over. Cool to 60°C and transfer to a vacuum drying oven (80°C, 0.09 MPa) to dry for 2 hours to obtain carboxyl-terminated low polyester (II).

[0037] Example 3: Preparation of terminal epoxy group low-polyester:

[0038] Accurately weigh 0.086 mol of carboxyl-terminated low-polyester (II) and 0.095 mol of diethylene glycol diglycidyl ether into a 500 mL four-necked reaction flask, and heat to 132 °C ± 3 °C under nitrogen protection. o C reaction for 7 hours; samples were taken every 2 hours to measure the acid value. When the acid value dropped to 2 mgKOH / g, the epoxy value no longer changed, and the reaction was stopped; cooled to room temperature and vacuum dried (80℃, 0.09MPa) for 2 hours to obtain terminal epoxy low polyester (III).

[0039] Example 4: Preparation and properties of modified epoxy resin:

[0040] Mix an appropriate amount of modifier (III) with E-51 epoxy resin, add polyetheramine-D230 curing agent, and cure at room temperature for 4 hours in a mold. The mass ratio of modifier to epoxy resin is 3~20:97~80, and the amount of curing agent is 28~32% of the mass of epoxy resin.

[0041] Modified epoxy resins were prepared according to the proportions in Table 1. The mechanical properties of the epoxy resins were tested and compared with those of epoxy resins without modifiers. The results are shown in Table 1.

[0042] Table 1 Properties of Modified Epoxy Resins

[0043]

[0044] Example 5: Degradation of modified epoxy resin:

[0045] The cured resin sample prepared according to Example 4 was pulverized to 20-40 mesh. 10.0 g of resin powder and 100 mL of 1 M HCl aqueous solution were added to a 250 mL round-bottom flask equipped with a reflux condenser. The mixture was stirred in a water bath at 60 ± 1 °C for 12 hours. After the reaction was complete, the mixture was cooled to room temperature. The mixture was filtered, and the filtrate was collected. The solid phase was washed with deionized water until neutral, dried, and weighed. The filtrate was extracted three times with dichloromethane (DCM) (30 mL each time). The organic phases were combined, dried over anhydrous sodium sulfate, and concentrated by rotary evaporation to remove the solvent, yielding a viscous degradation product with a degradation yield >90%.

[0046] Example 6

[0047] The difference between this embodiment and Embodiment 2 is that the dicarboxylic acid is succinic acid, sebacic acid, 1,4-cyclohexanedicarboxylic acid, terephthalic acid, or isophthalic acid.

[0048] Example 7:

[0049] The difference between this embodiment and Embodiment 3 is that the diglycidyl ether is ethylene glycol diglycidyl ether, 1,4-butanediol diglycidyl ether, neopentyl glycol diglycidyl ether, or trimethylolpropane triglycidyl ether.

[0050] Example 8:

[0051] The difference between this embodiment and Embodiment 4 is that the amine curing agent is an aliphatic polyamine or an alicyclic polyamine.

[0052] Example 9:

[0053] The difference between this embodiment and embodiments 1-8 is that the epoxy resin is a bisphenol A type liquid epoxy resin and a bisphenol F type epoxy resin.

Claims

1. A method for preparing a biodegradable triazine-based low-polyester epoxy resin modifier, characterized in that... The method includes the following steps: Step 1: Preparation of hexahydro-1,3,5-triazine-1,3,5-tributanol: Step 1-1: Dissolve 4-amino-1-butanol in an organic solvent, and add 37% formaldehyde aqueous solution dropwise while stirring in an ice bath, controlling the molar ratio of 4-amino-1-butanol to formaldehyde to be 1:(1~1.2). Steps 1-2: After the addition is complete, under the protection of inert gas, heat to 60-80℃ and stir for 6-10 hours. Steps 1-3: After the reaction is complete, cool to room temperature and remove the organic solvent by rotary evaporation to obtain hexahydro-1,3,5-triazine-1,3,5-tributanol; Step 2: Preparation of carboxyl-terminated low-polyester: Step 2-1: Mix hexahydro-1,3,5-triazine-1,3,5-tributanol and dicarboxylic acid at a molar ratio of carboxyl group to hydroxyl group of (1.3~1.6):1, and carry out polycondensation reaction for 8~9 hours under an inert atmosphere, controlling the temperature of polycondensation reaction at 135~150℃. Step 2-2: When the acid value drops to 135~160 mgKOH / g, it is considered the reaction endpoint, and carboxyl-terminated low polyester is obtained; Step 3: Preparation of terminal epoxy group low-polyester: Step 3-1: Mix the carboxyl-terminated low polyester with diglycidyl ether at a molar ratio of epoxy group to carboxyl group of 2.1~2.2:

1. Under an inert atmosphere, stir and heat the system to 130~140℃ and react at this temperature for 5~7 hours. Step 3-2: The reaction endpoint is reached when the acid value drops to ≤2mgKOH / g and the epoxy value reaches 6~9mol / 100g, yielding an epoxy-terminated low-polyester modifier.

2. The preparation method of the biodegradable triazine-based low-polyester epoxy resin modifier according to claim 1, characterized in that... The organic solvent is one of water, methanol, ethanol, ethanol-water, tetrahydrofuran, or acetonitrile.

3. The preparation method of the biodegradable triazine-based low-polyester epoxy resin modifier according to claim 1, characterized in that... The dicarboxylic acid is an aliphatic C4~C6 group. 12 One or more of the following: straight-chain dicarboxylic acids, alicyclic dicarboxylic acids, and aromatic dicarboxylic acids.

4. The preparation method of the biodegradable triazine-based low-polyester epoxy resin modifier according to claim 1, characterized in that... The diglycidyl ether is one of ethylene glycol diglycidyl ether, diethylene glycol diglycidyl ether, 1,4-butanediol diglycidyl ether, neopentyl glycol diglycidyl ether, and trimethylolpropane triglycidyl ether.

5. An epoxy-terminated low-polyester modifier prepared by the method of any one of claims 1-4.

6. A method for preparing a modified epoxy resin, characterized in that... The method includes the following steps: The epoxy-terminated low-polyester modifier prepared by the method according to any one of claims 1-4 is mixed with epoxy resin, an amine curing agent is added, and the mixture is cured at room temperature in a mold for 24-28 hours, wherein the mass ratio of the modifier to the epoxy resin is 3-20:97-80, and the amount of curing agent is 28-32% of the mass of the epoxy resin.

7. The method for preparing the modified epoxy resin according to claim 6, characterized in that... The epoxy resin is E-51 epoxy resin; the amine curing agent is one of polyether amine curing agents, aliphatic polyamines, or alicyclic polyamines.

8. The method for preparing the modified epoxy resin according to claim 7, characterized in that... The amine curing agent is polyetheramine D-230.

9. A method for degrading modified epoxy resin, characterized in that... The method includes the following steps: The modified epoxy resin prepared by the method according to any one of claims 7-8 is pulverized and then soaked in a strongly acidic solution with pH < 3 and degraded by stirring at 50~60°C.

10. The method for degrading the modified epoxy resin according to claim 9, characterized in that... The strong acid solution is one of hydrochloric acid, sulfuric acid, or p-toluenesulfonic acid.

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