Epoxy resin latent curing agent based on negative thermal expansion principle and preparation method thereof

Abstract

The invention belongs to the technical field of functional polymer materials, and particularly relates to an epoxy resin latent curing agent based on a negative thermal expansion principle and a preparation method thereof. The preparation method comprises the following steps: 1) carrying out surface hydrophilization treatment on a porous negative thermal expansion material to obtain a surface-modified porous negative thermal expansion material; and 2) mixing the surface-modified porous negative thermal expansion material with an aliphatic amine curing agent, so that the aliphatic amine curing agent is adsorbed and diffused to the surface and pore channels of the porous negative thermal expansion material. Compared with an existing latent curing agent, the prepared epoxy resin latent curing agent based on the negative thermal expansion principle has the advantages of being long in storage stable period, high in curing efficiency, controllable in curing process and the like, effectively overcomes the defects in the prior art and has high application value.

Description

Technical Field

[0001] This invention belongs to the field of functional polymer materials technology, specifically relating to an epoxy resin latent curing agent based on the principle of negative thermal expansion and its preparation method. Background Technology

[0002] Epoxy resins are widely used in composite materials, electronic packaging, coatings, and aerospace due to their excellent mechanical properties, chemical resistance, and dimensional stability. However, traditional epoxy resin curing systems still suffer from problems such as poor storage stability, low curing efficiency, and difficulty in precisely controlling the curing process.

[0003] Currently, epoxy resin curing agents can be broadly classified into two categories based on their reactivity: room temperature curing agents and heat-curing agents. Room temperature curing agents (such as aliphatic amines and polyether amines) can react rapidly at room temperature, but their workable time is short, and they cannot be stored for long periods after mixing with resin, making them unsuitable for preparing single-component prepregs and other products. Heat-curing agents (such as acid anhydrides and aromatic amines), while having a longer pot life, typically require prolonged heating at temperatures above 100°C to complete curing, resulting in high energy consumption and low efficiency, limiting their application in low-temperature encapsulation or rapid repair scenarios. Therefore, developing a latent curing agent that combines storage stability with controllable rapid curing capability has become an important research direction in the epoxy resin field.

[0004] In recent years, latent curing agent technologies (such as microencapsulation and chemical modification) have provided new solutions to this problem. However, existing latent curing agents still face challenges such as low release efficiency or insufficient storage stability. Meanwhile, negative thermal expansion materials (NTEs), due to their unique behavior of volume contraction upon heating, have shown great potential in the field of intelligent controlled release. Based on this, utilizing the temperature response characteristics of NTE materials to construct a stable, controllable, and efficient epoxy resin latent curing agent carrier system has significant innovative value and application potential. Summary of the Invention

[0005] The purpose of this invention is to provide an epoxy resin latent curing agent based on the principle of negative thermal expansion and its preparation method. Compared with existing latent curing agents, it has advantages such as long storage stability, high curing efficiency, and controllable curing process, effectively overcoming the shortcomings of the prior art and having great application value.

[0006] Specifically, the present invention provides the following technical solutions: A method for preparing a latent curing agent for epoxy resin based on the principle of negative thermal expansion includes the following steps: 1) The porous negative thermal expansion material is subjected to surface hydrophilization treatment to obtain a surface-modified porous negative thermal expansion material; 2) Mix the surface-modified porous negative thermal expansion material with aliphatic amine curing agent, so that the aliphatic amine curing agent is adsorbed and diffused to the surface and pores of the porous negative thermal expansion material, and the desired product is obtained.

[0007] Preferably, in step 1), the method for preparing the porous negative thermal expansion material includes the following steps: Mix zirconium salt, water, organic acid, and polyethylene glycol thoroughly and label this solution A; mix tungstate salt and water thoroughly and label this solution B. Solution B is added dropwise to solution A while stirring continuously until a sol is formed; then the sol is reacted at 180~190℃ for 2~3 hours to obtain a porous precursor. The porous precursor is calcined at 350~360℃ for 2~3 hours, and then heated to 600~620℃ for 3~4 hours to obtain a porous negative thermal expansion material.

[0008] This invention uses zirconium salts and tungstates as raw materials and employs a sol-gel method to prepare the framework structure of a porous negative thermal expansion material. The carboxyl and hydroxyl groups in the organic acid can react with Zr. 4+ and W 6+ A stable complex is formed, inhibiting premature hydrolysis and precipitation of metal ions and promoting uniform dispersion. Polyethylene glycol can form micelles in water, acting as a pore template, allowing the complex to adsorb onto the micelle surface while preventing complex aggregation and inhibiting its excessive growth. Subsequently, under heating conditions, the complex undergoes dehydration condensation to form a gel composed of Zr / WOC, encapsulating the micelles to form a gel-template structure. Finally, calcination at high temperature decomposes the polyethylene glycol and other residual organic matter, yielding a ZrW2O8 framework material with high specific surface area and porous structure. ZrW2O8 is a high-performance porous negative thermal expansion material. Its crystal structure consists of ZrO6 octahedra and WO4 tetrahedra connected by oxygen atoms sharing vertices, exhibiting high elasticity. As the temperature increases, the transverse vibration of oxygen atoms intensifies, causing the ZrO6 and WO4 sharing vertices to couple and rotate, resulting in a decrease in the distance between the unbonded Zr and W atoms, thus continuously shrinking the volume and generating a negative thermal expansion effect.

[0009] More preferably, the zirconium salt is one or more of zirconium sulfate, zirconium oxynitrate, and zirconium oxychloride; And / or, the tungstate is one or more of sodium tungstate, ammonium tungstate, and ammonium paratungstate; And / or, the organic acid is one or more of citric acid and tartaric acid.

[0010] More preferably, in solution A, the molar concentration of zirconium is 0.23~0.24 mol / L, and the mass ratio of water, organic acid and polyethylene glycol is 1:0.04~0.06:0.01~0.02; In solution B, the molar concentration of tungsten is 0.26~0.27 mol / L; The molar ratio of zirconium in solution A to tungsten in solution B is 1:1.8~2.

[0011] Preferably, step 1) specifically involves immersing the porous negative thermal expansion material in an ethanol solution of a hydrophilic silane coupling agent, stirring the reaction at 60-70°C for 6-7 hours, washing with ethanol after the reaction, and drying to obtain the surface-modified porous NTE material.

[0012] The purpose of this invention to hydrophilize the surface of porous negative thermal expansion materials is to enhance the adsorption capacity of aliphatic amines and prevent leakage. Firstly, the hydrophilic surface allows polar liquids such as aliphatic amines to spread more easily and penetrate into the pores. Secondly, the hydrophilic pores exhibit a strong capillary effect on the polar liquids, promoting their rapid filling of the pores. Finally, the strongly polar amino groups in the aliphatic amines can form hydrogen bonds with the hydrophilic surface, increasing surface tension and thus preventing leakage.

[0013] More preferably, the hydrophilic silane coupling agent is one or more of γ-aminopropyltriethoxysilane, γ-glycidoxypropyltrimethoxysilane, and carboxyethyltriethoxysilane.

[0014] Preferably, in step 2), the aliphatic amine curing agent is one or more of ethylenediamine, diethylenetriamine, triethylenetetramine, and tetraethylenepentamine; And / or, the mass ratio of the porous negative thermal expansion material to the aliphatic amine curing agent is 3.5~4:1.

[0015] Preferably, in step 2), ultrasonic vibration is used to allow the fatty amine curing agent to be adsorbed and diffused onto the surface and pores of the porous negative thermal expansion material.

[0016] Preferably, step 2) further includes the following step: removing the aliphatic amine curing agent adsorbed on the surface of the porous negative thermal expansion material by heating at 50~60℃ for 30~40 minutes.

[0017] The present invention also provides an epoxy resin latent curing agent based on the principle of negative thermal expansion, which is prepared by the above preparation method.

[0018] The beneficial effects of this invention are at least as follows: (1) The latent curing agent prepared by the physical adsorption method of the present invention can greatly extend the storage stability period after mixing with resin without reducing the reactivity, compared with the chemical modification method or microencapsulation method. (2) The latent curing agent prepared by the present invention can instantly shrink the volume of the skeleton material above 80°C, which promotes the discharge of the fatty amine curing agent in the channel. It can be cured quickly at medium temperature (80~100°C) without long-term heating. The curing rate is significantly better than that of the existing medium-temperature latent curing agents. (3) The latent curing agent prepared by the present invention has good dispersibility after release because the fatty amines inside are uniformly distributed in the nanopores, thus avoiding uneven curing or bubble defects caused by local agglomeration. (4) The latent curing agent prepared by the present invention, based on the characteristic of negative thermal expansion material (NTE) shrinking in volume when heated, realizes precise control from "static latent" to "dynamic triggering", providing a highly controllable and widely adaptable solution for high-performance epoxy resin systems. Detailed Implementation

[0019] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention are described clearly and completely below. The following embodiments are used to illustrate the present invention, but are not intended to limit the scope of the present invention. Where specific techniques or conditions are not specified in the embodiments, they shall be performed in accordance with the techniques or conditions described in the literature in the art, or in accordance with the product manual.

[0020] Example 1 Example 1 provides an epoxy resin latent curing agent based on the principle of negative thermal expansion. The preparation steps are as follows: (1) Add 258g of zirconium oxychloride to 3L of deionized water and stir until the solution is clear. Then add 150g of citric acid and 50g of polyethylene glycol 2000 and stir thoroughly until completely dissolved. This solution is called solution A. Add 331g of ammonium paratungstate to 5L of deionized water and stir until the solution is clear. This solution is called solution B. (2) Slowly add solution B to solution A while stirring continuously until a uniform sol is formed; then transfer the sol to a reactor at 180°C for 2.5 h of reaction. After the reaction is completed, collect the precipitate to obtain a porous precursor. (3) The porous precursor was transferred to a muffle furnace and calcined at 350°C for 2 hours to remove organic matter. Then the temperature was raised to 600°C and calcined for 3 hours to obtain porous NTE material. (4) Add 1 part (by weight) of silane coupling agent γ-aminopropyltriethoxysilane to 16 parts (by weight) of ethanol to form an ethanol solution of hydrophilic silane coupling agent. Immerse the porous NTE material in the hydrophilic silane coupling agent / ethanol solution and stir at 60°C for 6 hours to perform surface hydrophilization treatment. After the reaction is complete, wash with ethanol and then dry in an oven at 80°C to obtain the surface-modified porous NTE material; (5) The surface-modified porous NTE material and the fatty amine curing agent ethylenediamine were added to the reaction vessel at a mass ratio of 3.8:1 and ultrasonically vibrated at 25°C for 30 min to allow the curing agent to fully diffuse into the pores of the material, thus obtaining the fatty amine-NTE composite material. (6) Place the fatty amine-NTE composite material into a 50°C forced-air drying oven and heat for 30 minutes to remove the residual fatty amine on the surface of the material, thereby obtaining an epoxy resin latent curing agent based on the principle of negative thermal expansion.

[0021] Performance testing: The prepared latent curing agent was mixed with commercially available bisphenol A type epoxy resin E51 at a mass ratio of 100:8, and then tested.

[0022] (1) Storage stability test: Store the material at room temperature and observe whether it has cured every day; (2) Curing time test: The material was placed in a 90℃ oven for heat curing and the curing time was recorded; (3) Mechanical property test: The tensile and bending properties of the cured material were tested in accordance with GB / T 2567-2021 "Test Method for Properties of Resin Castings".

[0023] Comparative Example 1 Compared with Example 1, the only difference is that the porous NTE material was not subjected to surface hydrophilization treatment, i.e., step (4) was omitted.

[0024] Comparative Example 2 Ethylenediamine was directly added to commercially available bisphenol A type epoxy resin E51 and mixed, with the mass ratio of epoxy resin to ethylenediamine being 100:8.

[0025] The performance test results of the above embodiments and comparative examples are shown in Table 1 below: Table 1

[0026] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing a latent curing agent for epoxy resin based on the principle of negative thermal expansion. The method includes the following steps, characterized in that it includes the following steps: 1) The porous negative thermal expansion material is subjected to surface hydrophilization treatment to obtain a surface-modified porous negative thermal expansion material; 2) Mix the surface-modified porous negative thermal expansion material with aliphatic amine curing agent, so that the aliphatic amine curing agent is adsorbed and diffused to the surface and pores of the porous negative thermal expansion material, and the desired product is obtained.

2. The preparation method according to claim 1, characterized in that, In step 1), the preparation method of the porous negative thermal expansion material includes the following steps: Mix zirconium salt, water, organic acid, and polyethylene glycol thoroughly and label this solution A; mix tungstate salt and water thoroughly and label this solution B. Solution B is added dropwise to solution A while stirring continuously until a sol is formed; then the sol is reacted at 180~190℃ for 2~3 hours to obtain a porous precursor. The porous precursor is calcined at 350~360℃ for 2~3 hours, and then heated to 600~620℃ for 3~4 hours to obtain a porous negative thermal expansion material.

3. The preparation method according to claim 2, characterized in that, The zirconium salt is one or more of zirconium sulfate, zirconium oxynitrate, and zirconium oxychloride. And / or, the tungstate is one or more of sodium tungstate, ammonium tungstate, and ammonium paratungstate; And / or, the organic acid is one or more of citric acid and tartaric acid.

4. The preparation method according to claim 2, characterized in that, In solution A, the molar concentration of zirconium is 0.23~0.24 mol / L, and the mass ratio of water, organic acid and polyethylene glycol is 1:0.04~0.06:0.01~0.

02. In solution B, the molar concentration of tungsten is 0.26~0.27 mol / L; The molar ratio of zirconium in solution A to tungsten in solution B is 1:1.8~2.

5. The preparation method according to any one of claims 1-4, characterized in that, Step 1) Specifically, the porous negative thermal expansion material is immersed in an ethanol solution of a hydrophilic silane coupling agent and stirred at 60~70℃ for 6~7h. After the reaction is completed, the material is washed with ethanol and dried to obtain the surface-modified porous NTE material.

6. The preparation method according to claim 5, characterized in that, The hydrophilic silane coupling agent is one or more of γ-aminopropyltriethoxysilane, γ-glycidoxypropyltrimethoxysilane, and carboxyethyltriethoxysilane.

7. The preparation method according to any one of claims 1-4, characterized in that, In step 2), the fatty amine curing agent is one or more of ethylenediamine, diethylenetriamine, triethylenetetramine, and tetraethylenepentamine; And / or, the mass ratio of the porous negative thermal expansion material to the aliphatic amine curing agent is 3.5~4:

1.

8. The preparation method according to any one of claims 1-4, characterized in that, In step 2), ultrasonic vibration causes the aliphatic amine curing agent to be adsorbed and diffused onto the surface and pores of the porous negative thermal expansion material.

9. The preparation method according to any one of claims 1-4, characterized in that, Step 2) also includes the following steps: heating at 50~60℃ for 30~40 minutes to remove the aliphatic amine curing agent adsorbed on the surface of the porous negative thermal expansion material.

10. A latent curing agent for epoxy resin based on the principle of negative thermal expansion, characterized in that, It is prepared by the preparation method according to any one of claims 1-9.

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