Low-viscosity carbon nanotube reinforced epoxy resin system and preparation method thereof

Abstract

The invention provides a low-viscosity carbon nanotube reinforced epoxy resin system and a preparation method thereof, and belongs to the technical field of composite materials. On the basis of performing non-covalent bond modification on the surface of the carbon nano tube, the fluidity of the resin is improved by adjusting the viscosity of the epoxy resin, and the carbon nano tube is dispersed into the curing agent in a stirring and ultrasonic treatment manner, so that the efficient and stable dispersion of the carbon nano tube in an epoxy resin system is realized; the mechanical property of the cured resin is improved, and the application range of the carbon nano tube in a resin system is expanded.

Description

Technical Field

[0001] The invention belongs to the technical field of composite materials and relates to a low-viscosity carbon nanotube reinforced epoxy resin system and a preparation method thereof. Background Art

[0002] Epoxy resins are an important class of thermosetting polymers. Their molecular structure contains at least two epoxy groups, which form a stable three-dimensional network structure after reacting with a curing agent. Low-viscosity epoxy resins easily wet and fill complex molds, and their excellent mechanical properties and chemical stability make them widely used in industries such as aerospace, composites, adhesives, coatings, and civil construction. However, epoxy resins' inherent insulating properties and insufficient fatigue and impact resistance after curing have limited their application, making them difficult to meet the technical requirements of certain projects. Therefore, the modification of epoxy resins has long been a research focus in the materials field. In recent years, researchers have discovered that integrating carbon nanotubes with a large aspect ratio into epoxy resins can significantly enhance the resin's properties. Once bonded to the epoxy resin, they can reduce crack propagation and absorb energy, thereby enhancing the epoxy resin's strength and toughness.

[0003] The performance of carbon nanotube / epoxy composites depends entirely on the dispersion quality of the carbon nanotubes in the epoxy system. Due to the generally high viscosity of current epoxy resin systems, the carbon nanotubes are easily agglomerated due to poor dispersion in the resin system, which reduces the performance of the composite. Summary of the Invention

[0004] In order to solve the above problems, the present invention provides a low-viscosity carbon nanotube-reinforced epoxy resin system and a preparation method thereof.

[0005] The technical solution adopted in the present invention is as follows:

[0006] A low-viscosity carbon nanotube-reinforced epoxy resin system comprises the following components, recorded by mass fraction: 100 parts of epoxy resin, 30-150 parts of curing agent, 0.02-0.2 parts of carbon nanotubes, 0.02-0.4 parts of dispersant and 0.2-2 parts of accelerator.

[0007] Furthermore, the epoxy resin is selected from one or more of bisphenol A epoxy resin, bisphenol F epoxy resin, and alicyclic epoxy resin.

[0008] Furthermore, the curing agent is an anhydride curing agent, specifically one or more of nadic methyl anhydride, hexachloromethylenetetrahydrophthalic anhydride, maleic anhydride, phthalic anhydride, dodecenyl succinic anhydride, and tetrahydrophthalic anhydride.

[0009] Furthermore, the dispersant is selected from one or more of polyvinyl pyrrolidone, oleyl alcohol polyether, sodium dodecylbenzene sulfonate, and polyvinyl alcohol.

[0010] Furthermore, the accelerator is selected from one or more of 2,4,6-tris(dimethylaminomethyl)phenol, methylhydrazine, and imidazole.

[0011] A method for preparing the low-viscosity carbon nanotube-reinforced epoxy resin system comprises the following steps:

[0012] Step 1: Determine the type and amount of epoxy resin to be added: Select one or more suitable epoxy resins based on the requirements for mechanical strength, heat resistance, cost, etc. during actual use. If multiple epoxy resins are required for compounding, the logarithmic mixing ratio calculation is required to preliminarily determine the amount of different epoxy resins to be added, and then the final ratio is determined based on experimental testing. The logarithmic mixing ratio calculation formula is as follows:

[0013]

[0014] Among them, x i represents the volume fraction of group i, μ i Represents the viscosity of the i-th component.

[0015] When selecting epoxy resin, in addition to viscosity, the compatibility between the epoxy resin components must also be considered to avoid poor compatibility between the resins, which may form an island structure and lead to performance degradation.

[0016] Step 2: Determine the type of curing agent: One or more anhydride curing agents are selected and compounded based on the curing system requirements and the desired mechanical properties after curing to further maximize the synergistic effects of the curing agents. Due to their low viscosity and high dosage requirements, anhydride curing agents can also reduce the viscosity of epoxy resin systems. This ensures low viscosity and high temperature resistance while maintaining the mechanical properties of the cured specimen, avoiding the degradation of mechanical properties that can occur when adding solvents or diluents to epoxy resins to reduce viscosity.

[0017] Step 3, carbon nanotube dispersion: add 0.02-0.4 parts of dispersant to 30-150 parts of curing agent, and after mechanical stirring at room temperature, add 0.02-0.2 parts of carbon nanotubes to the mixture of curing agent and dispersant, and continue to use mechanical stirring at room temperature, the stirring speed is: 1000-1500rpm, the stirring time is 15-25min, and then the obtained solution is ultrasonically treated at room temperature for 40-60min. During the treatment process, the dispersant is adsorbed on the surface of the carbon nanotubes through van der Waals force, completing the non-covalent bond modification of the carbon nanotube surface. The specific treatment time can be determined according to the amount of curing agent and viscosity. The higher the viscosity, the longer the treatment time is required, so that the carbon nanotubes form a monodisperse system in the curing agent.

[0018] Step 4, adding epoxy resin: add 100 parts of epoxy resin heated to 50-90°C to the mixture obtained in step 3, mechanically stir at 1000-1500 rpm at room temperature for 15-25 minutes, then ultrasonically treat for 20-40 minutes, and finally add 0.2-2 parts of accelerator and mix to obtain a low-viscosity carbon nanotube-reinforced epoxy resin system.

[0019] Furthermore, when multiple epoxy resins are selected for compounding, the epoxy resins can be premixed and then added to the mixture obtained in step 3; if the viscosity of the epoxy resin is too high (>2000cp), each epoxy resin can be added to the mixture obtained in step 3 in descending order of viscosity, and mechanical stirring and ultrasonic treatment are required after each addition of the epoxy resin to promote sufficient mixing of the curing agent and the epoxy resin.

[0020] The innovation of this invention lies in the fact that the mainstream method for dispersing carbon nanotubes is to modify the surface of the carbon nanotubes using a dispersant, including covalent and non-covalent modifications. This invention, based on surface modification, improves the fluidity of the epoxy resin by adjusting the viscosity of the resin, and disperses the carbon nanotubes into the curing agent through stirring and ultrasonic treatment, thereby achieving efficient and stable dispersion of the carbon nanotubes in the epoxy resin system. During the stirring process, external force can be more easily transmitted to the carbon nanotube aggregates, effectively breaking up the agglomerate structure formed by van der Waals forces and improving dispersion efficiency. When ultrasonically treating low-viscosity resins, the cavitation bubbles generated by the ultrasound are more easily broken, and the released energy is more concentrated, thereby more effectively exfoliating the carbon nanotube aggregates. In addition, low-viscosity resins have lower surface tension, which can better wet the surface of carbon nanotubes and reduce the tendency to agglomerate due to high surface energy. In low-viscosity resin systems, resin molecules or dispersants (if added) can diffuse faster to the surface of carbon nanotubes, forming a stable interface layer to prevent reagglomeration. Therefore, in engineering, by selecting low-viscosity epoxy resins or adjusting their viscosity, the dispersion state of carbon nanotubes can be significantly optimized, thereby improving the performance of composite materials (such as strength, conductivity, and thermal stability). The processing convenience of low-viscosity resins (such as shortening mixing time and reducing energy consumption) also makes them more advantageous in industrial applications. In summary, low-viscosity epoxy resins provide an ideal environment for the efficient dispersion of carbon nanotubes by improving shear force transmission, wettability, ultrasonic efficiency, and dispersion stability, making carbon nanotubes less likely to agglomerate and entangle during the dispersion process. This achieves rapid dispersion of carbon nanotubes in epoxy resin, improves the mechanical properties of the cured resin, and expands the application range of carbon nanotubes in resin systems.

[0021] The beneficial effects of the present invention are:

[0022] (1) Viscosity reduction during operation: Liquid anhydride molecules (such as methyltetrahydrophthalic anhydride and methylhexahydrophthalic anhydride) do not contain strong polar groups. The intermolecular forces (van der Waals forces and hydrogen bonds) are weaker than those of epoxy resin itself, resulting in better fluidity. At room temperature, the viscosity is extremely low (200-500cp), much lower than that of epoxy resin (about 10,000-15,000cp). Acid anhydride is added to high-viscosity epoxy as a low-viscosity fluid, directly diluting the interaction between resin molecules and reducing the overall viscosity.

[0023] (2) The resin system is easy to store after dispersion: Acid anhydride curing agents react very slowly with epoxy groups at room temperature in the absence of accelerators and will not quickly form a cross-linked network. After mixing, the system can still maintain a low viscosity state for several hours to several days (long operating period) until heating triggers the curing reaction. DETAILED DESCRIPTION

[0024] The technical solution of the present invention will be further described below in conjunction with specific embodiments, but the protection scope of the present invention is not limited thereto.

[0025] Example 1

[0026] (1) Determination of epoxy resin curing agent: 4,4'-diaminodiphenylmethane epoxy resin (AG80) and bisphenol F diglycidyl ether (BPF) were selected based on product performance requirements and processing methods. According to the mechanical property test results and comprehensive consideration of the mechanical properties of the resin after curing, the two resins were compounded in a mass ratio of 1:1.

[0027] (2) Selection of curing agent: Due to the requirements of curing time and viscosity, methylnadic anhydride (MNA) is selected as the curing agent.

[0028] (3) An appropriate amount of 0.1 g of polyvinylpyrrolidone (PVP) was added to 117 g of MNA, and after mechanical stirring at a speed of 1500 rpm, 0.1 g of carbon nanotube powder was added to the mixture of MNA and PVP, and stirring was continued at a speed of 1500 rpm for 20 min. The resulting solution was then ultrasonically treated at room temperature for 60 min to achieve non-covalent bond modification and dispersion of the carbon nanotube surface, thereby obtaining a carbon nanotube dispersion.

[0029] (4) 45 g of BPF heated to 90 °C was added to the carbon nanotube dispersion, mechanically stirred at 1500 rpm for 20 min at room temperature, and then ultrasonically treated for 30 min. Then, 45 g of AG80 preheated to 90 °C was added to BPF, mechanically stirred again, and ultrasonicated for 20 min. 1 g of 2,4,6-tris(dimethylaminomethyl)phenol (DMP30) was added and mixed to obtain carbon nanotube-toughened AG-80 / BPF epoxy resin.

[0030] Comparative Example 1

[0031] Taking the epoxy resin not modified with carbon nanotubes as a comparative example, the preparation process is as follows: 50g BPF heated to 90°C is added to 50g AG80 preheated at the same temperature, and then added to 117g MNA. At room temperature, mechanical stirring is carried out at a speed of 1500rpm for 20min, and then ultrasonic treatment is carried out for 30min. Then, 1g DMP30 accelerator is added and mixed to obtain the epoxy resin not modified with carbon nanotubes for use.

[0032] Resin castings were prepared using the epoxy resin systems prepared in Example 1 and Comparative Example 1, respectively. The preparation process was as follows: the epoxy resin system was poured into a casting mold, vacuum degassed at 50°C for 1 hour, and finally cured using a curing cycle of 80°C / 2h + 120°C / 2h + 160°C / 1.5h + 180°C / 1h to produce the resin castings. Mechanical testing of the resin castings revealed the impact strengths of the two materials, as shown in Table 1:

[0033] Table 1 Summary of impact properties of Example 1 and comparative examples

[0034]

[0035] As can be seen from Table 1, after adding carbon nanotubes, the impact strength of the resin casting is increased by 10.12%, which effectively improves the impact toughness of the epoxy resin.

[0036] Example 2

[0037] (1) Determination of epoxy resin curing agent: AG80 and bis(3,4-epoxycyclohexylmethyl) adipate were selected based on product performance requirements and processing methods. According to the mechanical property test results and comprehensive consideration of the mechanical properties of the resin after curing, the two resins were compounded in a mass ratio of 1:1.

[0038] (2) Selection of curing agent: Due to the requirements of curing time and viscosity, maleic anhydride is selected as the curing agent here.

[0039] (3) 0.02 g of oleyl alcohol polyether was added to 150 g of maleic anhydride, and the mixture was mechanically stirred at 1000 rpm until uniform. Then, 0.2 g of carbon nanotube powder was added, and the mixture was stirred at 1500 rpm for 15 min. The obtained solution was then ultrasonically treated for 40 min to obtain a carbon nanotube dispersion.

[0040] (4) 50 g of bis(3,4-epoxycyclohexylmethyl)adipate heated to 50° C. was added to the carbon nanotube dispersion, mechanically stirred at 1000 rpm for 15 min at room temperature, then ultrasonically treated for 40 min, and then 50 g of AG80 preheated to 50° C. was added, ultrasonicated for 20 min, and 0.2 g of methylhydrazine was added and mixed to obtain an epoxy resin system.

[0041] Comparative Example 2

[0042] 50 g of bis(3,4-epoxycyclohexylmethyl)adipate heated to 50° C. was added to 50 g of AG80 preheated to 50° C., and then added to 150 g of maleic anhydride. The mixture was mechanically stirred at 1000 rpm for 15 minutes at room temperature, and then ultrasonically treated for 40 minutes. 0.2 g of methylhydrazine was added and mixed to obtain an epoxy resin that was not modified with carbon nanotubes for use.

[0043] The epoxy resin systems prepared in Example 2 and Comparative Example 2 were used to prepare NOL rings, respectively. The preparation process was as follows:

[0044] (a) Apply the release agent evenly on the surface of the winding tooling and then assemble them one by one.

[0045] (b) Debug the winding machine and set the specified winding program.

[0046] (c) The epoxy resin systems prepared in Example 2 and the comparative example were respectively introduced into a dipping tank, heated to 55° C., and then subjected to a winding process. During the winding process, the tension was kept constant.

[0047] (d) The wound mold is placed in an oven for curing according to a curing schedule of 80°C / 2 h + 120°C / 2 h + 160°C / 1.5 h + 180°C / 1 h. After curing, the mold is polished and cut to obtain a NOL ring of a specified size.

[0048] As required, the NOL ring cut samples were tested for interlaminar shear performance. The test results are shown in Table 2:

[0049] Table 2 Summary of interlaminar shear properties of carbon fiber composites before and after modification

[0050]

[0051] From the results in Table 2, it can be seen that the addition of carbon nanotubes significantly improves the interlaminar shear strength of carbon fiber composites from 40.22 MPa to 60 MPa.

[0052] Example 3

[0053] (1) Determination of epoxy resin curing agent: AG80 and BPF were selected based on product performance requirements and processing methods. According to the mechanical property test results and comprehensive consideration of the mechanical properties of the resin after curing, the two resins were compounded in a mass ratio of 2:3.

[0054] (2) Selection of curing agent: Due to the requirements of curing time and viscosity, dodecenyl succinic anhydride was selected as the curing agent.

[0055] (3) 0.4 g of sodium dodecylbenzenesulfonate was added to 30 g of dodecenyl succinic anhydride, and the mixture was mechanically stirred at 1200 rpm until uniform. Then, 0.02 g of carbon nanotube powder was added, and the mixture was stirred at 1200 rpm for 25 min. The mixture was then ultrasonically treated for 50 min to obtain a carbon nanotube dispersion.

[0056] (4) 40 g of BPF heated to 80°C was added to the carbon nanotube dispersion, mechanically stirred at 1200 rpm for 25 min, and then ultrasonically treated for 20 min. 60 g of AG80 preheated to 80°C was added, and ultrasonication was continued for 20 min. 2 g of imidazole was added and mixed to obtain an epoxy resin system.

[0057] Comparative Example 3

[0058] 60 g of BPF heated to 80° C. was added to 40 g of AG80 preheated to 80° C., and then added to 30 g of dodecenyl succinic anhydride. The mixture was mechanically stirred at 1200 rpm for 25 min, and then ultrasonically treated for 20 min. 2 g of imidazole was added and mixed to obtain an epoxy resin not modified with carbon nanotubes for use.

[0059] Composite laminates were prepared using the epoxy resin systems prepared in Example 3 and Comparative Example 3, respectively. The process was as follows: a certain amount of the prepared epoxy resin system was applied between layers of T700 carbon fiber unidirectional woven cloth, and the composite laminates were prepared by a wet compression molding process. The curing process was 80°C / 2h+120°C / 2h+160°C / 1.5h+180°C / 1h.

[0060] As required, specimens were cut from the prepared composite laminates for bending performance testing. The test results are shown in Table 3:

[0061] Table 3 Summary of bending properties of carbon fiber composites before and after modification

[0062]

[0063] From the results in Table 3, it can be seen that the addition of carbon nanotubes increases the flexural strength of carbon fiber composite materials from 1023 MPa to 1205 MPa, with an increase of 17.8%.

[0064] The above examples show that the carbon nanotubes after mechanical stirring and ultrasonic dispersion have good dispersion in the resin, and have a significant enhancement effect on the mechanical properties of epoxy resin and carbon fiber composites after curing. After modification, they have higher stability, and the impact strength, interlaminar shear strength and bending strength are greatly improved.

[0065] The above-described embodiments merely express the implementation methods of the present invention, but should not be understood as limiting the scope of the patent of the present invention. It should be pointed out that for those skilled in the art, several variations and improvements can be made without departing from the concept of the present invention, and these all fall within the scope of protection of the present invention.

Claims

1. A low-viscosity carbon nanotube-reinforced epoxy resin system, characterized in that: The invention comprises the following components recorded by mass fraction: 100 parts of epoxy resin, 30-150 parts of curing agent, 0.02-0.2 parts of carbon nanotubes, 0.02-0.4 parts of dispersant and 0.2-2 parts of accelerator.

2. The low-viscosity carbon nanotube-reinforced epoxy resin system according to claim 1, characterized in that: The epoxy resin is selected from one or more of bisphenol A epoxy resin, bisphenol F epoxy resin, and alicyclic epoxy resin.

3. The low-viscosity carbon nanotube-reinforced epoxy resin system according to claim 1, characterized in that: The curing agent is an anhydride curing agent.

4. The low-viscosity carbon nanotube-reinforced epoxy resin system according to claim 3, characterized in that: The curing agent is specifically selected from one or more of methylnadic anhydride, hexachloromethylenetetrahydrophthalic anhydride, maleic anhydride, phthalic anhydride, dodecenyl substituted succinic anhydride, and tetrahydrophthalic anhydride.

5. The low-viscosity carbon nanotube-reinforced epoxy resin system according to claim 1, characterized in that: The dispersant is selected from one or more of polyvinyl pyrrolidone, oleyl alcohol polyether, sodium dodecylbenzene sulfonate and polyvinyl alcohol.

6. The low-viscosity carbon nanotube-reinforced epoxy resin system according to claim 1, characterized in that: The accelerator is selected from one or more of 2,4,6-tris(dimethylaminomethyl)phenol, methylhydrazine and imidazole.

7. A method for preparing a low-viscosity carbon nanotube-reinforced epoxy resin system according to any one of claims 1 to 6, characterized in that: The steps include: Step 1: Determine the type and amount of epoxy resin to be added: Select one or more suitable epoxy resins based on the requirements for mechanical strength, heat resistance, and cost; Step 2: Determine the type of curing agent: Select one or more anhydride curing agents for compounding based on the curing system requirements and mechanical properties after curing; Step 3, dispersing carbon nanotubes: add 0.02-0.4 parts of dispersant to 30-150 parts of curing agent, and mechanically stir at room temperature until uniform. Then, add 0.02-0.2 parts of carbon nanotubes to the mixture of curing agent and dispersant, and continue mechanically stirring at room temperature at a speed of 1000-1500 rpm for 15-25 minutes. Then, ultrasonically treat at room temperature for 40-60 minutes. Step 4, adding epoxy resin: add 100 parts of epoxy resin heated to 50-90°C to the mixture obtained in step 3, mechanically stir at 1000-1500 rpm at room temperature for 15-25 minutes, then ultrasonically treat for 20-40 minutes, and finally add 0.2-2 parts of accelerator and mix to obtain a low-viscosity carbon nanotube-reinforced epoxy resin system.

8. The method for preparing the low-viscosity carbon nanotube-reinforced epoxy resin system according to claim 7, characterized in that: In step 1, if multiple epoxy resins are required for compounding, the amount of each epoxy resin to be added must be preliminarily determined using the logarithmic mixing law shown below, and then the final ratio can be determined based on experimental testing: Among them, x i represents the volume fraction of group i, μ i Represents the viscosity of the i-th component.

9. The method for preparing the low-viscosity carbon nanotube-reinforced epoxy resin system according to claim 7, wherein: In step 4, when multiple epoxy resins are selected for compounding, the epoxy resins are premixed and then added to the mixture obtained in step 3.

10. The method for preparing the low-viscosity carbon nanotube-reinforced epoxy resin system according to claim 7, characterized in that: When multiple epoxy resins are selected for compounding, if the viscosity of the epoxy resin is too high, each epoxy resin is added to the mixture obtained in step 3 in descending order of viscosity. After each addition of epoxy resin, mechanical stirring and ultrasonic treatment are required to promote sufficient mixing of the curing agent and the epoxy resin.

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