High-temperature-resistant water-based sizing agent, preparation method and application thereof

Abstract

The application discloses a high-temperature-resistant water-based sizing agent and a preparation method and application thereof. The preparation method comprises the following steps: mixing and reacting dianhydride, polyamine and a salt forming agent in deionized water to obtain a prepolymer; and adding polyether amine into the prepolymer to continue the reaction to prepare a polyimide-polyether amine copolymer water-based sizing agent. The preparation process is free of organic solvent, is green and environment-friendly; the obtained sizing agent is a uniform aqueous solution, has good storage stability, and has no change after standing for 30 days; the thermal decomposition temperature of the sizing agent can reach above 538 DEG C, the high-temperature-resistant performance is excellent, and the high-temperature processing requirement of thermoplastic resin is met; especially, the flexibility of carbon fiber after sizing is significantly improved by introducing polyether amine copolymerization, fiber damage is avoided, and the interface bonding between the fiber and the resin matrix is enhanced. The sizing agent can be widely applied to the interface treatment of carbon fiber reinforced resin matrix composite materials, and is especially suitable for high-temperature forming resin systems such as polyether ether ketone and epoxy.

Description

Technical Field

[0001] This invention belongs to the field of sizing agent preparation technology, specifically relating to a high-temperature resistant water-based sizing agent, its preparation method, and its application. Background Technology

[0002] Carbon fiber reinforced polymer composites have wide applications in aerospace, automotive, and high-temperature processing. Under high-temperature processing conditions, carbon fiber sizing agents are prone to thermal decomposition. The resulting carbonization and pyrolysis residues or escaped small molecules can cause localized defects in the material's interface layer, affecting the overall performance of the composite material. Therefore, it is necessary to develop a high-temperature resistant carbon fiber sizing agent.

[0003] Most commercially available sizing agents are epoxy-based and not heat-resistant. Existing research shows that heat-resistant sizing agents are mainly polyetheretherketone (PEEK) and polyimide-based sizing agents. For example, patent application CN201510912048.4 discloses a water-based epoxy emulsion-type carbon fiber sizing agent, but its main component is epoxy resin, which is prone to decomposition under high-temperature molding and processing conditions, causing interface defects. Patent application CN202411844812.4 discloses a fiber sizing liquid, including polyaryletherketone (PAEK) containing imide side groups, but this sizing agent uses a large amount of organic solvents, resulting in high cost and environmental unfriendliness. Patent application CN118029161A uses polyamic acid as the main component of the sizing agent, combined with an emulsifier to prepare an emulsion-type sizing agent, but the emulsion stability is greatly affected by temperature, prone to phase separation, and emulsifier residue may corrode equipment. Patent application CN118185556A discloses a water-soluble polyimide adhesive that can be used as a sizing agent for carbon fibers. However, this patent application does not add a salting agent, and the synthesized polyamic acid is easily hydrolyzed in water, so the sizing agent cannot be stored for a long time.

[0004] Recently, patent application CN119505317A disclosed a high-performance waterborne polyimide / carbon nanotube composite electromagnetic shielding film and its preparation method. The method involves reacting diamine, dianhydride, and a salt-forming agent in an aqueous phase to obtain a waterborne polyamic acid salt, which is then mixed with polyvinylpyrrolidone-modified carbon nanotubes and subjected to thermal imidization treatment to obtain the film. However, the waterborne polyimide salt molecules prepared in this patent application have a rigid structure. If used to prepare a sizing agent for carbon fibers, it will result in insufficient fiber flexibility, high stiffness, and easy fiber damage during subsequent processing. Therefore, it cannot be directly used as a sizing agent resin.

[0005] Therefore, it is of great significance to develop a water-based carbon fiber sizing agent that is free of organic solvents, stable in storage, resistant to high temperatures, and has good fiber flexibility after treatment. Summary of the Invention

[0006] The technical problem to be solved by the present invention is to overcome the problems of existing carbon fiber sizing agents containing organic solvents, poor storage stability, poor high temperature resistance, and poor fiber flexibility after treatment with existing water-based polyimide sizing agents, and to provide a high temperature resistant water-based carbon fiber sizing agent and its preparation method.

[0007] To solve the above-mentioned technical problems, the present invention adopts the following technical solution:

[0008] A method for preparing a high-temperature resistant water-based carbon fiber sizing agent includes the following steps: mixing and reacting dianhydride, polyamine and salt-forming agent in deionized water to obtain a prepolymer; adding polyetheramine to the prepolymer and continuing the reaction to obtain a polyimide-polyetheramine copolymer water-based sizing agent.

[0009] Furthermore, the salt-forming agent is an imidazole salt-forming agent.

[0010] Furthermore, the salt-forming agent is 1,2-dimethylimidazole.

[0011] Furthermore, the dianhydride is 3,3',4,4'-biphenyltetracarboxylic acid dianhydride.

[0012] Further, the polyamine is selected from at least one of 1,4-cyclohexanediamine, 3,5-diaminobenzoic acid, 4,4'-diaminodiphenyl ether, 4,4'-diaminodiphenylmethane, and p-phenylenediamine.

[0013] Further, the molar ratio of the dianhydride to the polyamine is 1:(0.95-1.1), the molar ratio of the dianhydride to the salt-forming agent is 1:(2-5), and the amount of polyetheramine added is twice the molar amount of the dianhydride.

[0014] Furthermore, it also includes the step of adding an auxiliary agent to the reaction system, wherein the auxiliary agent is selected from at least one of antistatic agents, leveling agents, and lubricants.

[0015] Furthermore, the temperature of the mixing reaction is 60–80°C, and the time is 8–20 h; the reaction time after adding polyetheramine is 2–4 h.

[0016] The present invention also provides a high-temperature resistant water-based carbon fiber sizing agent, which is prepared by the preparation method described above, wherein the sizing agent is an aqueous solution of polyimide-polyetheramine copolymer.

[0017] The present invention also provides the application of the high-temperature resistant water-based carbon fiber sizing agent as described above in the surface treatment of carbon fiber. The sizing agent is diluted to a solid content of 1-3%, and the carbon fiber is sized and then dried at 150-200°C to form a film.

[0018] Beneficial effects

[0019] Compared with the prior art, the present invention has the following beneficial effects:

[0020] 1. Green and environmentally friendly, with simplified process

[0021] This invention employs a one-step aqueous phase synthesis method for polyimide-polyetheramine copolymer sizing agents. The entire process requires no addition of organic solvents, eliminating environmental pollution and safety hazards caused by organic solvent volatilization at the source. Compared to the traditional two-step method of "organic solvent synthesis-separation-resolution," this invention simplifies the process to a continuous reaction in the aqueous phase. The product can be directly diluted and used without separation and purification, significantly reducing energy consumption and production costs, aligning with the development concept of green manufacturing.

[0022] 2. Completely water-soluble and stable during storage.

[0023] This invention utilizes a salt-forming agent (1,2-dimethylimidazole) to form an ionic polyamic acid salt, and further introduces a polyetheramine to enhance hydrophilicity, resulting in a final copolymer product with excellent water solubility, capable of directly forming a homogeneous, transparent, and stable aqueous solution. Experiments have demonstrated that the sizing agent of this invention exhibits no precipitation, stratification, or discoloration after standing at room temperature for 30 days, demonstrating significantly superior storage stability compared to existing water-based polyimide sizing agents, facilitating industrial storage and transportation.

[0024] 3. Excellent high-temperature resistance, suitable for high-temperature molding processes.

[0025] The sizing agent of this invention is mainly composed of rigid polyimide segments, with a thermal decomposition temperature reaching 538.42℃, far exceeding the 264.51℃ of commercial epoxy sizing agents. Under high-temperature processing and molding conditions of carbon fiber reinforced resin matrix composites (such as hot pressing of PEEK composites at 380℃), this sizing agent is not prone to thermal decomposition, effectively avoiding interface defects caused by the escape of small molecules or residual carbonized layers due to carbonization and decomposition of the sizing agent, thus ensuring the interface integrity and overall mechanical properties of the composite material under high-temperature environments.

[0026] 4. Improves fiber softness and prevents processing damage.

[0027] To address the shortcomings of existing water-based polyimide sizing agents, which result in excessive fiber stiffness and susceptibility to damage, this invention introduces polyetheramine copolymerization with polyimide, significantly reducing the rigidity of the sizing resin while maintaining high-temperature resistance. Carbon fibers treated with this sizing agent exhibit good bundle cohesion, moderate stiffness, and a soft feel. They are less prone to fuzzing and fiber breakage during subsequent weaving, lay-up, and winding processes, effectively reducing fiber damage rates and improving the molding quality and production efficiency of composite materials.

[0028] 5. Enhance interfacial bonding and improve composite material performance.

[0029] The sizing agent of this invention forms a uniform polyimide-polyetheramine copolymer film on the surface of carbon fibers. This film serves as a modulus transition layer between the carbon fibers and the resin matrix: the polyimide segments exhibit good compatibility with the fiber surface and high-temperature resistant resins (such as PEEK), while the polyetheramine segments have affinity for resins such as epoxy. This "amphiphilic" structure effectively improves the interfacial wettability and chemical compatibility between the fibers and resins, and enhances the interfacial bonding strength, while satisfying the functions of fiber bundling and protection. Experimental data show that the interlaminar shear strength of CF / PEEK composite materials treated with the sizing agent of this invention can reach 98.5 MPa, significantly higher than that of unsized or control samples using pure polyimide sizing agents.

[0030] 6. Functional additives are adjustable and highly adaptable.

[0031] This invention allows for the flexible addition of functional additives such as antistatic agents, leveling agents, and lubricants (0-1%) according to specific application requirements, thereby imparting antistatic properties to the sizing agent, improving film uniformity, and reducing friction and wear between fibers and equipment. This modular design enables the sizing agent of this invention to adapt to the diverse needs of different resin systems (thermoplastic / thermosetting) and different molding processes (hot pressing, winding, pultrusion, etc.).

[0032] 7. Overall performance is superior to existing technologies.

[0033] Compared with the many patents cited in the background art, this invention solves multiple technical problems such as organic solvent pollution, poor storage stability, poor high temperature resistance, and poor fiber flexibility. It achieves synergistic effects of green synthesis, stable storage, high temperature resistance, fiber friendliness, and interface enhancement, and has significant technological progress and broad application prospects in the field of carbon fiber sizing agents. Attached Figure Description

[0034] Figure 1 Thermogravimetric curves comparing the polyimide sizing agent prepared in Example 1 of this invention with those of a commercial epoxy sizing agent.

[0035] Figure 2 This is a photograph of the polyimide sizing agent prepared in Example 1 of the present invention after standing for 30 days. Detailed Implementation

[0036] The present invention will be further described below with reference to the accompanying drawings and specific embodiments. The described examples are merely some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0037] I. Reaction Mechanism

[0038] The synthesis reaction of the high-temperature resistant water-based carbon fiber sizing agent of this invention follows an integrated mechanism of "aqueous phase salt formation - polycondensation - introduction of flexible segments". The specific process is as follows:

[0039] Step 1: Activation and Salt Formation of Amines

[0040] Polyamines (diamines) are mixed with a salt-forming agent (1,2-dimethylimidazole) in deionized water. The salt-forming agent, as a weak organic base, undergoes proton transfer or forms hydrogen-bonded complexes with the amino group in the diamine molecule, which significantly improves the solubility of the diamine in water. At the same time, it regulates the pH value of the reaction system, providing an alkaline environment for subsequent polycondensation.

[0041] Step 2: Dihydride ring-opening polycondensation to form a prepolymer

[0042] Upon addition of dianhydride (3,3',4,4'-biphenyltetracarboxylic acid dianhydride), the anhydride group of the dianhydride undergoes a nucleophilic ring-opening reaction with the amino group of the diamine in an alkaline aqueous solution, generating a polyamic acid intermediate. Due to the presence of an excess salt-forming agent in the system, the carboxyl groups on the polyamic acid molecular chain are rapidly neutralized by the salt-forming agent, forming a polyamic acid salt (PAAS). This salt has an ionic structure, is stably soluble in water, effectively suppresses the reversible hydrolysis side reaction of polyamic acid, and ensures molecular weight growth.

[0043] Step 3: Introducing flexible segments through polyetheramine copolymerization

[0044] Adding polyetheramine to the prepolymer allows the terminal amino groups of the polyetheramine to react with the carboxyl or anhydride groups at the ends of the polyamic acid salt chain, forming a polyimide-polyetheramine block copolymer. The flexible segments of the polyetheramine effectively reduce the rigidity of the entire molecule, while its ether bond structure further improves the water solubility of the product.

[0045] Step 4: Adding optional additives

[0046] Add antistatic agents, leveling agents, lubricants and other additives as needed, and stir evenly to obtain the finished sizing agent.

[0047] Key reaction diagram:

[0048] Diamine + dianhydride + salt-forming agent → (H2O, 60-80℃, N2) → polyamic acid salt prepolymer

[0049] Polyamate prepolymer + polyetheramine — (react for another 3 hours) — → polyimide-polyetheramine copolymer + H2O

[0050] II. Implementation Examples

[0051] Example 1

[0052] 1 mol of p-phenylenediamine and 3 mol of 1,2-dimethylimidazole were added to deionized water and stirred at 25°C for 30 min until completely dissolved, at a speed of 200–300 r / min. An equimolar amount of 3,3',4,4'-biphenyltetracarboxylic acid dianhydride was added, and the mixture was heated and stirred at 60–80°C for 10 h under a nitrogen atmosphere, at a speed of 200–300 r / min, to obtain a prepolymer. Two molar amounts of polyetheramine were added to the prepolymer, and the reaction was continued for 3 h to prepare a sizing agent solution. The solution was diluted with deionized water to a solid content of 3%, and finally, 1% antistatic agent was added.

[0053] T300 was sized with 3% sizing agent and then dried at 200℃ for 2 minutes to form a film on the fiber surface. The sized carbon fibers and PEEK films were alternately laminated in 13 layers, and the CF / PEEK composite material was prepared by gradient heating from 200℃ to 380℃ under a pressure of 10MPa.

[0054] Characterization and testing:

[0055] Thermogravimetric analysis (TGA) Figure 1 )

[0056] Figure 1 The thermogravimetric curves (TGA) of the polyimide sizing agent prepared in Example 1 of this invention and the commercial epoxy sizing agent are shown. The results show that the commercial epoxy sizing agent decomposes significantly at around 264.51℃, indicating insufficient heat resistance; while the polyimide sizing agent prepared in this invention decomposes significantly at around 538.42℃, demonstrating significantly improved heat resistance and meeting the requirements for high-temperature processing.

[0057] Storage stability ( Figure 2 )

[0058] Figure 2 This is a photograph of the polyimide sizing agent prepared in Example 1 of the present invention after standing for 30 days. As can be seen from the figure, the sizing agent synthesized in this invention is a completely homogeneous and transparent solution with good water properties. After standing for 30 days, there is no obvious precipitation, layering, or discoloration, indicating good stability.

[0059] Fiber softness

[0060] The carbon fiber bundles treated with the sizing agent in Example 1 are soft to the touch, have moderate stiffness, and are not brittle. They can pass smoothly through subsequent weaving and layup processes without significant fiber damage.

[0061] Example 2

[0062] 1 mol of 4,4'-diaminodiphenyl ether and 4.5 mol of 1,2-dimethylimidazole were added to deionized water and stirred at 30°C for 25 min until completely dissolved, at a speed of 200–300 rpm. An equimolar ratio of 3,3',4,4'-biphenyltetracarboxylic acid dianhydride was added, and the mixture was heated and stirred at 60–80°C for 15 h under a nitrogen atmosphere, at a speed of 200–300 rpm, to obtain a prepolymer. Two molar amounts of polyetheramine were added to the prepolymer, and the reaction was continued for 3 h to prepare a sizing agent solution. The solution was diluted with deionized water to a solid content of 1%, and finally, 0.8% leveling agent was added.

[0063] T300 was sized with 1% sizing agent and then dried at 200℃ for 2 minutes to form a film of sizing agent on the fiber surface. The sized carbon fibers were then alternately laminated with epoxy resin in 16 layers, and the CF / EP composite material was prepared by gradient heating from 80℃ to 130℃ under a pressure of 5MPa.

[0064] Example 3

[0065] 0.7 mol of p-phenylenediamine, 0.3 mol of 1,4-cyclohexanediamine, and 3 mol of 1,2-dimethylimidazole were added to deionized water and stirred at 25°C for 30 min until completely dissolved, at a speed of 200–300 rpm. 1 mol of 3,3',4,4'-biphenyltetracarboxylic acid dianhydride was added, and the mixture was heated and stirred at 60–80°C for 18 h under a nitrogen atmosphere, at a speed of 200–300 rpm, to obtain a prepolymer. Two molar amounts of polyetheramine were added to the prepolymer, and the reaction was continued for 3 h to prepare a sizing agent solution. The solution was diluted with deionized water to a solid content of 3%, and finally, 1% antistatic agent was added.

[0066] T300 was sized with 3% polyimide sizing agent and then dried at 200℃ for 2 minutes to form a film of sizing agent on the fiber surface. The sized carbon fibers and PEEK films were alternately laminated in 12 layers, and the CF / PEEK composite material was prepared by gradient heating from 200℃ to 380℃ under a pressure of 10MPa.

[0067] Comparative Example 1 (without salt-forming agent)

[0068] The formulation and process were the same as in Example 1, but 1,2-dimethylimidazole was not added. A white precipitate appeared immediately upon the addition of dianhydride, making it impossible to obtain a uniform and stable sizing agent. This comparative example illustrates that the salting agent is crucial for inhibiting the hydrolysis of polyamic acid and forming a water-soluble system.

[0069] Comparative Example 2 (Copolymer without Polyetheramine)

[0070] The formulation and process were the same as in Example 1, but the step of adding polyetheramine was omitted. The resulting sizing agent was a pure polyimide aqueous solution. After sizing T300 carbon fiber with it, the fiber stiffness was high, and it felt brittle and hard. During the subsequent layup process, obvious fuzzing and fiber breakage occurred, and the fiber was severely damaged.

[0071] III. Performance Test Summary

[0072] The sizing agents and their application performance in each embodiment and comparative example were tested, and the results are shown in the table below.

[0073]

[0074] The results show that by introducing polyetheramine copolymerization, the present invention significantly improves the softness of the sized fiber while maintaining the excellent high-temperature resistance of polyimide, and also has good storage stability. Its overall performance is superior to that of the prior art.

[0075] The above embodiments are merely preferred embodiments of the present invention, used to illustrate the technical solutions of the present invention, and are not intended to limit the scope of protection of the present invention. Any modifications, improvements, or equivalent substitutions made to the present invention by those skilled in the art without departing from the technical concept and solutions of the present invention should fall within the scope of protection of the present invention.

Claims

1. A method for preparing a high-temperature resistant water-based carbon fiber sizing agent, characterized in that, Includes the following steps: The dianhydride, polyamine, and salt-forming agent are mixed and reacted in deionized water to obtain the prepolymer; Polyetheramine was added to the prepolymer and the reaction continued to obtain an aqueous sizing agent of polyimide-polyetheramine copolymer.

2. The preparation method according to claim 1, characterized in that, The salt-forming agent is an imidazole salt-forming agent.

3. The preparation method according to claim 2, characterized in that, The salt-forming agent is 1,2-dimethylimidazole.

4. The preparation method according to claim 1, characterized in that, The dianhydride is 3,3',4,4'-biphenyltetracarboxylic acid dianhydride.

5. The preparation method according to claim 1, characterized in that, The polyamine is selected from at least one of 1,4-cyclohexanediamine, 3,5-diaminobenzoic acid, 4,4'-diaminodiphenyl ether, 4,4'-diaminodiphenylmethane, and p-phenylenediamine.

6. The preparation method according to claim 1, characterized in that, The molar ratio of the dianhydride to the polyamine is 1:(0.95-1.1), the molar ratio of the dianhydride to the salt-forming agent is 1:(2-5), and the amount of polyetheramine added is twice the molar amount of the dianhydride.

7. The preparation method according to claim 1, characterized in that, It also includes the step of adding an auxiliary agent to the reaction system, wherein the auxiliary agent is selected from at least one of antistatic agents, leveling agents, and lubricants.

8. The preparation method according to claim 1, characterized in that, The mixing reaction is carried out at a temperature of 60–80°C for 8–20 hours; the reaction continues for 2–4 hours after the addition of polyetheramine.

9. A high-temperature resistant water-based carbon fiber sizing agent, characterized in that, The sizing agent is prepared by any one of the preparation methods described in claims 1 to 8, wherein the sizing agent is an aqueous solution of polyimide-polyetheramine copolymer.

10. The application of the high-temperature resistant water-based carbon fiber sizing agent as described in claim 9 in carbon fiber surface treatment, characterized in that, The sizing agent is diluted to a solid content of 1-3% and used to sizing carbon fibers, which are then dried at 150-200°C to form a film.

Images