Maleic anhydride functionalized graphene oxide modified bismaleimide resin and preparation method thereof

Abstract

The invention relates to functionalized graphene oxide modified bismaleimide resin and a preparation method thereof, and belongs to the technical field of thermosetting resin. The preparation method provided by the invention comprises the following steps: carrying out functional modification on graphene oxide by using maleic anhydride; carrying out dilute solution blending and ball milling dispersion on the functionalized graphene oxide and diphenyl bismaleimide; removing the solvent by adopting methods of solvent replacement, suction filtration and the like; the modified diphenyl bismaleimide and diallyl bisphenol A are subjected to heating prepolymerization, blending and vacuum curing. The functional modification of the graphene oxide is beneficial to improving the interface bonding capacity of the graphene oxide and the resin; according to the preparation method, a ball-milling-assisted dilute solution blending mode is beneficial to overcoming the agglomeration problem, and effective dispersion of graphene oxide in resin is realized; according to the method disclosed by the invention, a solvent replacement extraction mode is adopted to remove the solvent, so that the difficulty in removing the solvent in a high-boiling-point solvent system is overcome, and massive and rapid extraction of the resin is realized.

Description

Technical Field

[0001] The invention relates to a maleic anhydride functionalized graphene oxide modified bismaleimide resin and a preparation method thereof, and belongs to the technical field of toughening and modification of thermosetting resins. Background Art

[0002] Bismaleimide resin (BMI) is a high-performance resin system derived from a polyimide resin system. It is based on a bifunctional compound with maleimide (MI) as the active end group. BMI resin exhibits a variety of excellent physical and chemical properties due to its unique molecular structure, which contains rigid groups such as benzene rings and imide heterocycles. The operating temperature of BMI resin is higher than that of traditional epoxy resins, and the processing difficulty is lower than that of polyimide resins. It is an extremely important thermosetting resin in the aerospace field. However, BMI has a high cross-linking density, strong molecular chain rigidity, and poor toughness, which seriously hinders the further development and application of BMI resin. Traditional toughening methods such as adding rubber containing active groups, diamine chain extension, and forming an interpenetrating network structure can usually reduce the cross-linking density of BMI resin and increase the toughness of the resin. These methods will also have a certain impact on the rigidity of BMI resin, and will also lead to a decrease in the glass transition temperature of the resin, affecting the heat resistance of the resin. Graphene oxide (GO) has certain oxygen-containing functional groups on its surface and has excellent mechanical properties. When added to BMI resin, it can, on the one hand, increase the steric hindrance of the polymer chain, hinder the movement of the molecular chain, increase the "thawing" potential of its chain segment, and increase the glass transition temperature of the resin; on the other hand, GO can effectively enhance the modulus of the resin in the BMI matrix and increase the rigidity of the resin; in addition, when the BMI load-bearing capacity is damaged, the GO nanoscale can deflect the cracks and improve the toughness of the resin, that is, it can simultaneously achieve the effects of toughening, increasing rigidity, and improving the temperature resistance of the BMI resin.

[0003] Although GO can effectively modify the resin matrix, its large specific surface area and high surface activation energy associated with the nanoscale make it very easy to agglomerate, especially after functionalization, the surface functional groups change, and the dispersibility often decreases further. In order to further mix it with other substances, it is often necessary to heat and dry the functionalized GO, freeze-dry it, etc. to obtain powder, which is cumbersome and resource-consuming, and is not conducive to large-scale preparation. In addition, BMI resin has extremely high viscosity or solid at room temperature and has extremely poor fluidity, so it is very difficult to mix and disperse GO in BMI resin. The common mixing method is high-temperature melting or using solvents (N,N-dimethylformamide, DMF) to improve the fluidity of the resin, and then disperse the GO powder more evenly in it by mechanical stirring or ultrasonic dispersion, but the effect is not ideal, and it is difficult to avoid GO agglomeration. In addition, the commonly used good solvent for BMI resin is DMF, which has a high boiling point and is close to the gel point of bismaleimide resin. The common method of removing the solvent by heating and evaporation is difficult to completely remove the DMF solvent. The residual DMF will form defects in the resin, seriously affecting the mechanical properties of the resin. The aforementioned heating to melt the resin and heating to evaporate the solvent also easily leads to premature gelation of the resin. Therefore, it is urgent to develop a convenient, rapid, and batch-production potential preparation method for nanoparticle-modified resins. Summary of the invention

[0004] The purpose of the present invention is to provide a maleic anhydride (MAH) functionalized GO modified BMI resin and a preparation method thereof, wherein the prepared maleic anhydride functionalized graphene oxide (MAH-GO) has good interface bonding with the BMI resin, and the modified BMI resin has excellent mechanical properties and thermal properties.

[0005] In order to achieve the above-mentioned object of the invention, the present invention provides the following technical solutions:

[0006] The present invention provides a method for preparing a maleic anhydride (MAH) functionalized GO modified BMI resin, comprising the following steps:

[0007] (1) Graphene oxide (GO) was surface modified with maleic anhydride (MAH), and then washed with N,N-dimethylformamide (DMF) and centrifuged to remove unreacted MAH. A certain amount of DMF was added to prepare a functionalized graphene oxide (MAH-GO) modification solution.

[0008] (2) MAH-GO and diphenylbismaleimide were solution blended.

[0009] (3) The DMF is removed from the mixed solution obtained in (2) by solvent replacement, filtration and drying.

[0010] (4) The resin powder obtained in (3) is prepolymerized with diallyl bisphenol A by heating to obtain a resin glue solution with good fluidity, (4) and poured into a mold, vacuumed, and cured according to a curing system.

[0011] Preferably, the concentration of the GO solution and the MAH-GO solution in step (1) is 1 to 10 mg / g. The mass ratio of the added MAH to GO is between 10:1 and 50:1, and the reaction conditions are 70 to 100°C for 1 to 5 hours. The obtained product does not require any common drying treatments and can be stored in the form of a solution for subsequent use, which is convenient and easy to scale up.

[0012] Preferably, the method of blending MAH-GO with diphenyl bismaleimide in step (2) comprises the following steps: firstly, diphenyl bismaleimide is dispersed in DMF at a certain concentration to obtain a resin solution, and the concentration of the resin solution is 0.02-0.2 g / mL. Then, according to the mass ratio, the mass ratio of the added diphenyl bismaleimide to MAH-GO is 1:0.0001-1:0.01, and the MAH-GO solution is added to the resin solution and stirred thoroughly, and stirred at a speed of 1000-8000 r / min for 1-2 hours to obtain a premixed solution. Then, the premixed solution is poured into the tank of a ball mill and mixed at a speed of 200-800 r / min for 2-8 hours. Different from the common method of directly mixing nano dopants with resin monomers or modifiers and using mechanical stirring and ultrasonic dispersion, this method first uses a dilute resin monomer solution of the same solvent system to blend with the MAH-GO solution, maintaining the dispersion state of the MAH-GO solution to the greatest extent; then, the resin monomer and MAH-GO are effectively and strongly dispersed by ball milling to make them uniformly mixed, and the resin molecules and MAH-GO are fully in contact, so that a small amount of sparse monomer molecules are grafted and wrapped on the surface of the MAH-GO layer to form a spherical shell structure. This structure can effectively reduce the mutual contact between MAH-GO and avoid the agglomeration of MAH-GO at high concentrations when treated in step (3), which is beneficial to the performance of its mechanical properties.

[0013] Preferably, the solution used for the solvent replacement in step (3) includes but is not limited to low-boiling poor solvents of diphenylbismaleimide such as deionized water, anhydrous ethanol, and acetone. The amount of solvent added is 5 to 10 times the amount of solvent used in the resulting mixed solution. Since the boiling point of DMF solvent is high and close to the gel point of bismaleimide resin, the common method of heating and evaporating to remove the solvent cannot completely remove the DMF solvent. The residual DMF will form defects in the resin, seriously affecting the mechanical properties of the resin, and heating DMF is likely to cause the resin to gel prematurely. The process of step (3) can effectively reduce the heating temperature and time for solvent removal, without the need for long-term, high-temperature heating, and can achieve large-scale, rapid, and efficient extraction of MAH-GO modified resin monomers.

[0014] Preferably, in step (4), the molar ratio of diphenyl bismaleimide to the added diallyl bisphenol A is 1:0.5 to 1:1.5. The prepolymerization is carried out at 110 to 140°C with a mechanical stirring rate of 1000 to 3000 r / min and a prepolymerization time of 0.5 to 2 h.

[0015] The present invention uses MAH to functionally modify GO, so that the active double bonds that can react with diphenyl bismaleimide are grafted on the surface of GO, which improves the interface performance between GO and BMI resin and improves the interface bonding force. The present invention adopts a solution blending method, does not require the common drying and powdering process, and is easy to operate. The resin and MAH-GO are dispersed in a good solvent of the two at the same time, and the distribution of MAH-GO in the resin is further improved by mechanical stirring and ball milling, and a spherical shell structure of the resin coated on the surface of MAH-GO is formed, which can weaken the agglomeration of MAH-GO. The present invention adopts a solvent replacement extraction method to remove the solvent, which is simple and fast to operate, has little pollution, does not require long-term, high-temperature heating, has high efficiency and high quality in extracting resin, and has the potential for large-scale production. The flexural strength of the MAH-GO modified BMI resin prepared by the present invention can be increased by 20%, the flexural modulus can be increased by 10%, and the heat resistance (glass transition temperature) can be increased by about 10°C. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 The stress-strain curve (left) and dynamic mechanical curve (right) of MAH-GO modified BMI resin. DETAILED DESCRIPTION

[0016] The technical solution of the present invention is further described below in conjunction with specific implementation methods.

[0017] Example 1

[0018] The preparation method of the MAH-GO modified BMI resin of this embodiment comprises the following steps:

[0019] (1) 60 g GO slurry, 90 g DMF, and 20 g MAH were added to a three-necked flask, reacted at 60 °C for 3 h, washed with DMF and centrifuged to remove unreacted MAH, and finally 600 mL DMF was added to obtain a DMF dispersion of MAH-GO.

[0020] (2) Add 10 parts by mass of diphenyl bismaleimide and 30 parts of DMF solution to a flask, ultrasonicate until the resin is dissolved, and add MAH-GO with a mass ratio of 0.0001 to 0.01 at 30°C. Stir at 2000 r / min for 1 hour. Then add the remaining 90 parts of bismaleimide resin and stir at 2000 r / min for 1 hour for premixing.

[0021] (3) Pour the premixed solution obtained in (2) into the tank of a ball mill and mix at a rotation speed of 300 r / min for 8 h.

[0022] (4) The uniformly mixed solution obtained in (3) was poured into 300 parts of deionized water to precipitate the resin, and the mixture was washed with deionized water and filtered several times to obtain a uniformly mixed resin powder, which was then dried at 100°C.

[0023] (5) Add diallyl bisphenol A in a molar ratio of 1:0.5 to diphenyl bismaleimide to the above resin powder at 120° C. Prepolymerize with mechanical stirring at a speed of 1500 r / min for 1.5 h.

[0024] (6) After degassing in a vacuum oven at 140°C, step curing is performed in an oven.

[0025] Example 2

[0026] The preparation method of the MAH-GO modified BMI resin of this embodiment comprises the following steps:

[0027] (1) 60 g GO slurry, 90 g DMF, and 20 g MAH were added to a three-necked flask, reacted at 80 °C for 1.5 h, washed with DMF and centrifuged to remove unreacted MAH, and finally 300 mL DMF was added to obtain a DMF dispersion of MAH-GO.

[0028] (2) Add 10 parts of diphenyl bismaleimide and 50 parts of DMF solution into a flask, ultrasonicate until the resin is dissolved, and add MAH-GO with a mass ratio of 0.0001 to 0.01 at 30°C. Stir at 2000 r / min for 1 hour. Then add the remaining 90 parts of bismaleimide resin and stir at 2000 r / min for 1 hour for premixing.

[0029] (3) Pour the premixed solution obtained in (2) into the tank of a ball mill and mix at a rotation speed of 500 r / min for 5 h.

[0030] (4) Pour the uniform mixture obtained in (3) into 500 parts of deionized water to precipitate the resin. Repeat the deionized water treatment several times.

[0031] The uniformly mixed resin powder was obtained by washing and filtering, and then dried at 100°C.

[0032] (5) Add diallyl bisphenol A in a molar ratio of 1:1 to diphenyl bismaleimide to the above resin powder at 130° C. Prepolymerize with mechanical stirring at a speed of 1800 r / min for 1 hour.

[0033] (6) After degassing in a vacuum oven at 130°C, step curing is performed in an oven.

[0034] Test experiment example

[0035] The mechanical properties and thermal properties of the MAH-GO modified BMI resin prepared in Example 2 were tested.

[0036] The bending mechanical properties test uses an INSTRON 5966 electronic universal material testing machine to test the resin casting. The test method is: GB / T 2567-2021. The thermal properties test uses DMA 242E dynamic mechanical analysis to characterize the change in the glass transition temperature of the modified resin. The test method is: ASTMD7028-07 (2015), three-point bending mode. The test results (stress-strain curve and dynamic mechanical curve) are shown in Figure 1 The results confirm that the addition of a certain amount of MAH-GO can significantly improve the flexural strength, flexural modulus and glass transition temperature of the resin.

[0037] It can be seen from the above embodiments that the present invention provides a MAH-GO toughened and stiffened BMI resin and a preparation method thereof. By utilizing MAH functionalized GO, a mixing and dispersion method that is quick, convenient, has better dispersibility, and is suitable for large-scale production is proposed, thereby successfully improving the mechanical properties and thermal properties of the BMI resin.

[0038] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as protection of the present invention.

Claims

1. A method for preparing graphene oxide by functional modification to improve the toughness, rigidity and heat resistance of bismaleimide resin, characterized in that: The following steps are involved: (1) Graphene oxide (GO) was surface modified with maleic anhydride (MAH), and then washed with N,N-dimethylformamide (DMF) and centrifuged to remove unreacted MAH. A certain amount of DMF was added to prepare a functionalized graphene oxide (MAH-GO) modification solution. (2) MAH-GO and diphenylbismaleimide were solution blended. (3) The DMF is removed from the mixed solution obtained in (2) by solvent replacement, filtration and drying. (4) Prepolymerizing the resin powder obtained in (3) with diallyl bisphenol A by heating to obtain a resin glue solution with good fluidity, and then pouring it into a mold, evacuating the mold, and curing it according to a curing system.

2. The preparation method according to claim 1, characterized in that: The concentration of the GO solution and the MAH-GO solution in step (1) is 1-10 mg / g. The mass ratio of the added MAH to GO is between 10:1 and 50:1, and the reaction conditions are 70-100° C. for 1-5 hours.

3. The preparation method according to claim 2, characterized in that: The obtained product does not require any common drying treatments and can be stored in the form of a solution for subsequent use, which is convenient and easy to mass produce.

4. The preparation method according to claim 1, characterized in that: The method of blending MAH-GO with diphenyl bismaleimide in step (2) comprises the following steps: firstly dispersing diphenyl bismaleimide in DMF at a certain concentration to obtain a resin solution, wherein the concentration of the resin solution is 0.02 to 0.2 g / mL. Then, according to the mass ratio, the mass ratio of the added diphenyl bismaleimide to MAH-GO is 1:0.0001 to 1:0.01, and the MAH-GO solution is added to the resin solution and stirred thoroughly, and stirred at a speed of 1000 to 8000 r / min for 1 to 2 hours to obtain a premixed solution. Then, the premixed solution is poured into the tank of a ball mill and mixed at a speed of 200 to 800 r / min for 2 to 8 hours.

5. The preparation method according to claim 4, characterized in that: This method firstly uses a dilute resin monomer solution of the same solvent system to blend with a MAH-GO solution, thereby maintaining the dispersed state of the MAH-GO solution to the greatest extent; then, ball milling is used to effectively and vigorously disperse the resin monomer and MAH-GO so that the resin molecules are in full contact with MAH-GO, so that a small amount of sparse monomer molecules are grafted and wrapped on the surface of the MAH-GO layer to form a spherical shell structure.

6. According to the spherical shell structure of claim 5, this structure can effectively reduce the mutual contact between MAH-GO, avoid the agglomeration of MAH-GO at high concentration during the treatment in step (3), and is beneficial to the performance of its mechanical properties.

7. The preparation method according to claim 1, characterized in that: The solution used for the solvent replacement in step (3) includes, but is not limited to, deionized water, anhydrous ethanol, acetone and other low-boiling poor solvents for diphenylbismaleimide. The amount of solvent added is 5 to 10 times the amount of solvent used in the resulting mixed solution.

8. The preparation method according to claim 7, characterized in that: This process can effectively reduce the heating temperature and time of solvent removal, avoid resin gelation, and eliminate the need for long-term, high-temperature heating. It can achieve large-scale, rapid, and efficient extraction of MAH-GO modified resin monomers.

9. The preparation method according to claim 1, characterized in that: In the step (4), the molar ratio of diphenyl bismaleimide to the added diallyl bisphenol A is 1:0.5 to 1:1.

5. The prepolymerization is carried out under mechanical stirring at 110 to 140°C, with a stirring rate of 1000 to 3000 r / min and a prepolymerization time of 0.5 to 2 hours.

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