Polyimide emulsion sizing agent and preparation method thereof

Abstract

The application relates to the field of composite materials and discloses a polyimide emulsion sizing agent and a preparation method thereof, which specifically comprises the following steps: mixing anhydride and an alcohol reagent to perform esterification to obtain an esterification mixture, then adding diamine to perform polymerization to obtain a polyimide precursor mixture, and finally obtaining the polyimide emulsion sizing agent through a phase inversion emulsification method. The application also comprises the steps of immersing reinforcing fibers into the obtained sizing agent and then heating and drying to complete sizing. The sizing layer of the application can not only retain the inherent high-temperature resistance and good matching with a matrix resin of the polyimide sizing agent, but also can impart good flexibility, bundling and lubricity to the sized fibers at normal temperature, can effectively reduce fiber damage and reduce the amount of fuzz, and meanwhile, the application does not need organic solvents in the whole preparation and use process, and has the characteristics of green environmental protection, safety and high efficiency.

Description

Technical Field

[0001] This invention relates to the field of composite materials, and more particularly to a polyimide emulsion sizing agent, its preparation method, and a method for preparing sizing-reinforcing fibers. Background Technology

[0002] In recent years, with increasingly stringent requirements for material performance, thermoplastic composites, known for their high toughness, fatigue resistance, and rapid molding capabilities, and polyimide composites, possessing excellent heat resistance and applicable at higher service temperatures, have seen rapid development and accelerated adoption in numerous fields. However, these high-performance composites require very high molding temperatures (typically above 350°C). This temperature significantly exceeds the thermal decomposition limit of traditional epoxy resin-based sizing agents (e.g., CN 116837633A, CN 115341392A), easily leading to defects such as porosity and delamination in the composites, thus weakening their performance. Furthermore, the chemical composition of traditional epoxy resin-based sizing agents is incompatible with both thermoplastic and polyimide resins, resulting in weak interfacial bonding and reduced interlayer strength in the composites.

[0003] To address these issues, many researchers have attempted to develop high-temperature sizing agents with polyimide as the main system. CN107022901B discloses an aqueous polyimide sizing agent with a high thermal decomposition temperature, which effectively enhances the interfacial properties of thermoplastic composites. However, thermoplastic polyimide is in a glassy state at room temperature, causing the sized carbon fibers to exhibit poor bundle cohesion, high stiffness, and difficulty in bending at room temperature. CN110747648A discloses a method for preparing a sizing agent using soluble polyimide, an organic solvent, and deionized water. This method is simple to operate, and the sizing agent has high thermal stability, effectively improving interfacial strength. However, this system still relies on thermoplastic polyimide as the sizing layer, lacking flexibility at room temperature, making it difficult to unwind and weave, and failing to achieve a balance between the interfacial properties and processing performance of the carbon fibers.

[0004] In summary, while traditional epoxy resin-based sizing agents effectively protect fibers, reduce wear, and exhibit excellent fiber bundle properties and flexibility, they cannot withstand the molding temperatures of high-performance composites such as thermoplastic composites and polyimide composites. Furthermore, their poor compatibility with high-performance matrix resins easily leads to performance degradation. Existing polyimide sizing agents, although possessing good heat resistance and enhancing the interfacial strength of composites, lack flexibility and tackiness at room temperature, resulting in poor fiber bundle properties, low flexibility, and susceptibility to fuzzing and wear, thus affecting practical applications. Therefore, developing polyimide sizing agents with excellent room-temperature bundle properties and effective fiber protection is of great significance. Summary of the Invention

[0005] (a) Technical problems to be solved

[0006] The technical problem to be solved by the present invention is that traditional sizing agents are unable to simultaneously ensure the softness, bundledness and lubricity of room temperature sized fibers, as well as retain the inherent high temperature resistance and good compatibility with the matrix resin of the sizing agent.

[0007] (II) Technical Solution

[0008] To solve the above-mentioned technical problems, the present invention provides a method for preparing a polyimide emulsion sizing agent, which includes the following steps:

[0009] S1. Mix the acid anhydride with the alcohol reagent and stir to complete the esterification reaction and obtain the esterified mixture;

[0010] S2. Add diamine to the esterification mixture and stir to complete the polymerization reaction and obtain a polyimide precursor mixture;

[0011] S3. Deionized water is added to the polyimide precursor mixture by reverse emulsification to complete emulsification and obtain a polyimide emulsion sizing agent.

[0012] As a preferred embodiment of the present invention, in step S1, the anhydride is selected from one or more of the following: biphenyltetracarboxylic dianhydride, diphenyl ether tetracarboxylic dianhydride, bisphenol A tetracarboxylic dianhydride, benzophenone tetracarboxylic dianhydride, 4,4'-[hexafluoroisopropene] phthalic anhydride, 1,4-difluoropyromellitic dianhydride, pyromellitic dianhydride, and phthalic anhydride.

[0013] In step S1, the alcohol reagent is selected from one or more of polyethylene glycol, polypropylene glycol, alkyl glycosides, cellulose, fatty alcohols, aromatic alcohols, and alicyclic alcohols.

[0014] As a preferred embodiment of the present invention, in step S2, the diamine is selected from one or more of p-phenylenediamine, diaminodiphenyl ether, diaminodiphenylmethane, 2,2'-bis(trifluoromethyl)diaminobiphenyl, 4,4'-diaminooctafluorodiphenyl ether, and 1,4-bis(4-aminophenoxy)benzene.

[0015] In a preferred embodiment of the present invention, in step S1, the molar ratio of the anhydride group to the hydroxyl group of the alcohol reagent is 1:(1~10).

[0016] In a preferred embodiment of the present invention, in step S1, the relative molecular mass of the alcohol reagent is 500~5000 g / mol.

[0017] In a preferred embodiment of the present invention, the mass fraction of the polyimide emulsion sizing agent is 0.5-50%.

[0018] In a second aspect, the present invention provides a polyimide emulsion sizing agent prepared by the above method.

[0019] In a third aspect, the present invention provides a method for preparing sizing-reinforced fibers, characterized by comprising the steps of:

[0020] S1. Immerse the reinforcing fiber in the polyimide emulsion sizing agent to obtain sizing-coated reinforcing fiber;

[0021] S2. The sized reinforcing fibers are heated and dried to obtain sized reinforcing fibers.

[0022] As a preferred embodiment of the present invention, in step S1, the reinforcing fiber is selected from one or more of carbon fiber, glass fiber, quartz fiber, organic fiber, basalt fiber, and ceramic fiber.

[0023] As a preferred embodiment of the present invention, in step S2, the heating temperature for heating and drying is 100~350℃.

[0024] (III) Beneficial Effects

[0025] The above-mentioned technical solution of the present invention has the following advantages:

[0026] 1. This invention introduces hydrophilic linkages into the sizing agent system through esterification, which not only endows the polyimide sizing agent with the ability to emulsify in water, but also utilizes the flexibility and viscosity of the hydrophilic polymer at room temperature to achieve good lubrication and protection of the sized fibers, providing bundled properties and flexibility.

[0027] 2. The sizing agent provided by this invention is very suitable for high-temperature resistant composite material systems (high-performance thermoplastic composites, polyimide composites, etc.). After heating and drying, it can complete imidization, forming a polyimide sizing layer with excellent heat resistance on the surface of the reinforcing fibers, which can meet the molding and use requirements of high-temperature resistant composite materials, and can be well compatible with the matrix resin, exhibiting excellent interfacial compatibility.

[0028] 3. The sizing agent provided by the present invention can maintain good plasticity and adhesion at room temperature, and can give the reinforcing fiber excellent softness, bundledness and lubrication, effectively reducing fiber damage and reducing fuzzing.

[0029] 4. The sizing agent provided by this invention requires no organic solvents during the entire preparation and use process. The preparation process is simple and the operation is convenient. It is green, environmentally friendly, safe and efficient. Detailed Implementation

[0030] The specific embodiments of the present invention will be described in further detail below with reference to the examples. These examples are for illustrative purposes only and are not intended to limit the scope of the invention.

[0031] Unless otherwise specified, the experimental methods used in the following examples are conventional methods; unless otherwise specified, the reagents and materials used in the following examples are commercially available.

[0032] The method for preparing a polyimide emulsion sizing agent provided by the present invention includes the following steps:

[0033] S1. Mix the acid anhydride with the alcohol reagent and stir to complete the esterification reaction and obtain the esterified mixture;

[0034] S2. Add diamine to the esterification mixture and stir to complete the polymerization reaction and obtain a polyimide precursor mixture;

[0035] S3. Deionized water is added to the polyimide precursor mixture by reverse emulsification to complete emulsification and obtain a polyimide emulsion sizing agent.

[0036] In a preferred embodiment of the present invention, in step S1, the acid anhydride is selected from one or more of biphenyltetracarboxylic dianhydride, diphenyl ether tetracarboxylic dianhydride, bisphenol A tetracarboxylic dianhydride, benzophenone tetracarboxylic dianhydride, 4,4'-[hexafluoroisopropene]phthalic anhydride, 1,4-difluoropyromellitic dianhydride, pyromellitic dianhydride, and phthalic anhydride. The acid anhydride is used to synthesize the molecular backbone of the polyimide sizing agent.

[0037] In a preferred embodiment of the present invention, in step S1, the alcohol reagent is selected from one or more of polyethylene glycol, polypropylene glycol, alkyl glycosides, cellulose, fatty alcohols, aromatic alcohols, and alicyclic alcohols. The alcohol reagent is a hydrophilic hydroxyl-containing compound that can impart hydrophilicity to the polyimide molecular chain, enabling it to emulsify in water.

[0038] In a preferred embodiment of the present invention, in step S2, the diamine is selected from one or more of p-phenylenediamine, diaminodiphenyl ether, diaminodiphenylmethane, 2,2'-bis(trifluoromethyl)diaminobiphenyl, 4,4'-diaminooctafluorodiphenyl ether, and 1,4-bis(4-aminophenoxy)benzene. The diamine is used to synthesize the molecular backbone of a polyimide sizing agent.

[0039] In a preferred embodiment of the present invention, in step S1, the molar ratio of the anhydride group to the hydroxyl group of the alcohol reagent is 1:(1~10). An equimolar or excess amount of alcohol reagent ensures that the anhydride is fully esterified, maximizing the hydrophilicity of the polyimide sizing agent. Simultaneously, the additional alcohol reagent also acts as a lubricant, giving the sized reinforcing fibers good flexibility and adhesion, enhancing the fiber bundle's cohesion and abrasion resistance, and overcoming problems such as fiber stiffness and difficulty in bundle formation caused by traditional polyimide sizing agents.

[0040] In a preferred embodiment of the present invention, in step S1, the relative molecular mass of the alcohol reagent is 500~5000 g / mol. If the molecular weight is too small, the alcohol reagent is insufficient to provide enough hydrophilicity for the polyimide sizing agent; if the molecular weight is too large, the decomposition and volatilization temperature of the alcohol reagent is too high, making it difficult to remove.

[0041] In a preferred embodiment of the present invention, the mass fraction of the polyimide emulsion sizing agent is 0.5-50%, and it can be diluted with water according to the specific reinforcing fiber and the required sizing amount.

[0042] The present invention also provides a polyimide emulsion sizing agent, which is prepared by the method provided by the present invention.

[0043] This invention also provides a method for preparing sizing-reinforced fibers, comprising the steps of:

[0044] S1. Immerse the reinforcing fiber in the polyimide emulsion sizing agent to obtain sizing-coated reinforcing fiber;

[0045] S2. The sized reinforcing fibers are heated and dried to obtain sized reinforcing fibers.

[0046] In a preferred embodiment of the present invention, in step S1, the reinforcing fiber is selected from one or more of carbon fiber, glass fiber, quartz fiber, organic fiber, basalt fiber, and ceramic fiber.

[0047] In a preferred embodiment of the present invention, in step S2, the heating temperature for drying is 100~350℃. This removes moisture and, on the other hand, decomposes the ester bonds in the polyimide sizing agent, removes alcohol reagents, and completes imidization.

[0048] In the above-described technical solution of this invention, an acid anhydride and an alcohol reagent are mixed and esterified to obtain an esterified mixture. Then, a diamine is added and polymerized to obtain a polyimide precursor mixture. A polyimide emulsion sizing agent is obtained through a reverse emulsification method. This invention also completes the sizing process by immersing reinforcing fibers in the obtained sizing agent and then heating and drying it. The sizing layer of this invention retains the inherent advantages of polyimide sizing agents, such as high-temperature resistance and good compatibility with the matrix resin, while also imparting good softness, bundled properties, and lubricity to the sized fibers at room temperature. This effectively reduces fiber damage and fuzzing. Furthermore, this invention requires no organic solvents throughout the preparation and use process, making it green, environmentally friendly, safe, and efficient.

[0049] Example 1

[0050] This embodiment provides a method for preparing a polyimide emulsion sizing agent, including the following steps:

[0051] (1) 32.2g benzophenone tetracarboxylic dianhydride (BTDA) and 150.0g polyethylene glycol 500 (PEG-500) (relative molecular mass of 500g / mol) were mixed and stirred at 80℃ at a speed of 100r / min according to the molar ratio of the reaction groups 1:3. After the solid was dissolved, the reaction was continued for 3h to obtain a fully esterified mixture.

[0052] (2) Keep at 80°C, add 10.8g of m-phenylenediamine (m-PDA) to the esterification mixture, and continue stirring for 4h to obtain a polyimide precursor mixture.

[0053] (3) Cool the system temperature to 65°C, increase the stirring speed to 1000 r / min, and then slowly add 300 g of deionized water to the polyimide precursor mixture to complete the reverse inversion and obtain a milky white polyimide emulsion sizing agent with a mass fraction of about 40%.

[0054] This embodiment also provides a method for preparing sizing-reinforced fibers, including the following steps:

[0055] After cooling, the obtained polyimide emulsion sizing agent was diluted with water to a mass fraction of 1.5%. Then, the carbon fiber was immersed in a glue tank containing the diluted polyimide emulsion sizing agent for sizing, and then dried at 120°C to obtain sized carbon fiber with a polyimide sizing agent layer on the surface.

[0056] The sized carbon fiber was tested for fuzz weight (unwinding tension 200g, winding speed 15m / min, friction load 250g, test length 50m) and the fuzz weight was measured to be 4.5mg.

[0057] Example 2

[0058] This embodiment provides a method for preparing a polyimide emulsion sizing agent, including the following steps:

[0059] (1) 31.0g of diphenyl ether tetracarboxylic dianhydride (ODPA) and 400g of polyethylene glycol monomethyl ether 2000 (mPEG-2000) (relative molecular mass of 2000g / mol) were mixed and stirred at 100r / min at 95℃ according to the molar ratio of the reaction groups 1:1. After the solid was dissolved, the reaction was continued for 3h to obtain a fully esterified mixture.

[0060] (2) Cool the system temperature to 65°C, add 20.0g of diaminodiphenyl ether (ODA) to the esterification mixture, and continue stirring for 4h to obtain a polyimide precursor mixture.

[0061] (3) Keep at 65°C, increase the stirring speed to 1500r / min, and then slowly add 1050g of deionized water to the polyimide precursor mixture to complete the reverse inversion and obtain a milky white polyimide emulsion sizing agent with a mass fraction of about 30%.

[0062] This embodiment also provides a method for preparing sizing-reinforced fibers, including the following steps:

[0063] After cooling, the obtained polyimide emulsion sizing agent was diluted with water to a mass fraction of 1.0%. Then, the carbon fiber was immersed in a glue tank containing the diluted polyimide emulsion sizing agent for sizing. It was further treated at 120℃, 200℃ and 300℃ for 5 minutes respectively to dry the moisture, remove mPEG-2000 and complete imidization, so as to obtain sized carbon fiber with a polyimide sizing agent layer on the surface.

[0064] Example 3

[0065] This embodiment provides a method for preparing a polyimide emulsion sizing agent, including the following steps:

[0066] (1) 52.0g of bisphenol A tetracarboxylic dianhydride (BPADA) and 130g of polyoxyethylene dehydrated sorbitan monooleate (T-80) (relative molecular mass of 1300g / mol) were mixed and stirred at 95℃ at a speed of 100r / min according to the molar ratio of the reaction groups 1:1.5. After the solid was dissolved, the reaction was continued for 3h to obtain a fully esterified mixture.

[0067] (2) Cool the system temperature to 65°C, add 20.0g of diaminodiphenyl ether (ODA) to the esterification mixture, and continue stirring for 4h to obtain a polyimide precursor mixture.

[0068] (3) Keep at 65°C, increase the stirring speed to 1500 r / min, and then slowly add 820 g of deionized water to the polyimide precursor mixture to complete the reverse inversion and obtain a milky white polyimide emulsion sizing agent with a mass fraction of about 20%.

[0069] This embodiment also provides a method for preparing sizing-reinforced fibers, including the following steps:

[0070] After cooling, the obtained polyimide emulsion sizing agent was diluted with water to a mass fraction of 2.0%. Then, the glass fiber was immersed in a glue tank containing the polyimide emulsion sizing agent for sizing, and then further dried at 120°C to obtain sized glass fiber with a polyimide sizing agent layer on the surface.

[0071] Comparative Example 1

[0072] Using Example 1 as the control group, Comparative Example 1 used ethanol (relative molecular mass of 46 g / mol), which has a very low molecular weight, as the alcohol reagent. The other ingredients and process parameters remained unchanged, as follows:

[0073] (1) 32.2g of benzophenone tetracarboxylic dianhydride (BTDA) and 27.6g of ethanol (relative molecular mass of 46g / mol) were mixed and stirred at 100r / min at 80℃ according to the molar ratio of the reaction groups 1:3. After the solid was dissolved, the reaction was continued for 3h to obtain a fully esterified mixture.

[0074] (2) Keep at 80°C, add 10.8g of m-phenylenediamine (m-PDA) to the esterification mixture, and continue stirring for 4h to obtain a polyimide precursor mixture.

[0075] (3) Cool the system temperature to 65°C, increase the stirring speed to 1000 r / min, and then slowly add 300 g of deionized water to the polyimide precursor mixture to complete the reverse inversion and obtain a milky white polyimide emulsion sizing agent with a mass fraction of about 40%.

[0076] This comparative example also provides a method for preparing sized fibers, including the following steps:

[0077] The obtained polyimide emulsion sizing agent was cooled and diluted with water to a mass fraction of 1.5%. The carbon fibers were then immersed in a sizing tank containing the diluted polyimide emulsion sizing agent for sizing, and further dried at 120°C to obtain sized carbon fibers with a polyimide sizing agent layer on the surface. The sized carbon fibers were tested for fuzz weight (unwinding tension 200g, winding speed 15m / min, friction load 250g, test length 50m), and the fuzz weight was measured to be 165.1mg.

[0078] The polyimide emulsion sizing agent obtained in Comparative Example 1 exhibited poor stability, showing significant stratification and precipitation after standing at room temperature for one day. This indicates that the small-molecule alcohol reagents were insufficient to enhance the hydrophilicity of the system, making it difficult to support the stable dispersion of polyimide in water. In contrast, the polyimide emulsion sizing agent obtained in Example 1 remained stable at room temperature for 30 days without stratification, demonstrating that hydrophilic alcohol reagents of appropriate molecular weight can effectively improve the stability of polyimide sizing agents in water.

[0079] Comparing the amount of fibrous fibers, it can be seen that the sized carbon fiber in Example 1 has higher abrasion resistance than the sized carbon fiber in Comparative Example 1. This is because the alcohol reagent in Comparative Example 1 has a too small molecular weight, resulting in a too low boiling point. It is removed during drying and fails to protect and lubricate the fibers. In contrast, the alcohol reagent in Example 1 has an appropriate molecular weight, allowing it to remain on the fiber surface and exhibit a soft, waxy appearance, significantly improving the fiber's bundle structure, flexibility, and abrasion resistance. This indicates that the polyimide sizing agent prepared using alcohol reagents with appropriate molecular weights can effectively protect the fibers and facilitate the full development of their mechanical properties.

[0080] In summary, the polyimide emulsion sizing agent, its preparation method, and its application provided by this invention can overcome the problems of poor flexibility and difficulty in bundling at room temperature while leveraging the inherent advantages of polyimide sizing agents, such as high temperature resistance and good compatibility with matrix resins.

[0081] It should be noted that the various embodiments in this specification are described in a progressive manner, and the same or similar parts between the various embodiments can be referred to mutually. Each embodiment focuses on describing the differences from other embodiments. For the embodiments of the method, relevant parts can be referred to the description of the device embodiments (as appropriate). The present invention is not limited to the specific steps described above. Furthermore, for the sake of brevity, detailed descriptions of known methods and techniques are omitted here.

[0082] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the technical principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing a polyimide emulsion sizing agent, characterized in that, Including the following steps: S1. Mix the acid anhydride with the alcohol reagent and stir to complete the esterification reaction and obtain the esterified mixture; S2. Add diamine to the esterification mixture and stir to complete the polymerization reaction and obtain a polyimide precursor mixture; S3. Deionized water is added to the polyimide precursor mixture by reverse emulsification to complete emulsification and obtain a polyimide emulsion sizing agent; In step S1, the acid anhydride is selected from one or more of biphenyltetracarboxylic dianhydride, diphenyl ether tetracarboxylic dianhydride, bisphenol A tetracarboxylic dianhydride, benzophenone tetracarboxylic dianhydride, 4,4'-(hexafluoroisopropene) phthalic anhydride, 1,4-difluoropyromellitic dianhydride, and pyromellitic dianhydride. In step S1, the alcohol reagent is selected from one or two of polyethylene glycol and polypropylene glycol; In step S1, the molar ratio of the anhydride group to the hydroxyl group of the alcohol reagent is 1:(1~10). In step S1, the relative molecular mass of the alcohol reagent is 500~5000 g / mol.

2. The preparation method according to claim 1, characterized in that, In step S2, the diamine is selected from one or more of p-phenylenediamine, diaminodiphenyl ether, diaminodiphenylmethane, 2,2'-bis(trifluoromethyl)diaminobiphenyl, 4,4'-diaminooctafluorodiphenyl ether, and 1,4-bis(4-aminophenoxy)benzene.

3. The preparation method according to claim 1, characterized in that, The mass fraction of the polyimide emulsion sizing agent is 0.5-50%.

4. A polyimide emulsion sizing agent, made by the method described in any one of claims 1-3.

5. A method for preparing sizing-reinforced fibers, characterized in that, Including the following steps: S1. Immerse the reinforcing fiber in the polyimide emulsion sizing agent as described in claim 4 to obtain sizing-coated reinforcing fiber; S2. The sized reinforcing fibers are heated and dried to obtain sized reinforcing fibers.

6. The method for preparing sizing-reinforced fibers according to claim 5, characterized in that, In step S1, the reinforcing fiber is selected from one or more of carbon fiber, glass fiber, quartz fiber, organic fiber, basalt fiber, and ceramic fiber.

7. The method for preparing sizing-reinforced fibers according to claim 5, characterized in that, In step S2, the heating temperature for drying is 100~350℃.