Polyimide emulsion sizing agent and preparation method thereof

Abstract

The invention relates to the field of composite materials, and discloses a polyimide emulsion sizing agent and a preparation method thereof.The preparation method specifically comprises the following steps that acid anhydride and an alcohol reagent are mixed and esterified to obtain an esterified mixture, then diamine is added for polymerization to obtain a polyimide precursor mixture, and the polyimide emulsion sizing agent is obtained through a phase inversion emulsification method. Reinforcing fibers are soaked in the sizing agent and then heated and dried, and sizing is completed. The sizing layer can keep the inherent advantages of high temperature resistance and good matching with matrix resin of a polyimide sizing agent, can endow sizing fibers with good flexibility, bundling property and lubricity at normal temperature, can effectively reduce fiber damage and reduce the fuzzing amount, does not need an organic solvent in the whole preparation and use process, and is environment-friendly and energy-saving. The method has the characteristics of environmental protection, safety and high efficiency.

Description

Technical Field

[0001] The invention relates to the field of composite materials, and in particular to a polyimide emulsion sizing agent, a preparation method thereof and a preparation method of sizing reinforced fibers. Background Art

[0002] In recent years, as people's requirements for material performance have become higher and higher, thermoplastic composites known for their high toughness, fatigue resistance, and rapid prototyping, and polyimide composites with excellent heat resistance and can be used at higher operating temperatures, have been promoted and developed rapidly in many fields. However, high-performance composite materials represented by the above systems all require very high molding temperatures (usually above 350°C). This temperature has greatly exceeded the thermal decomposition limit of traditional epoxy resin-based sizing agents (such as: CN 116837633A, CN 115341392A, etc.), which can easily lead to defects such as pores and delamination in composite materials, weakening performance. At the same time, the chemical composition of traditional epoxy resin-based sizing agents does not match thermoplastic resins and polyimide resins, resulting in weak interface bonding of composite materials and decreased interlaminar strength.

[0003] For this reason, many researchers have tried to develop high temperature resistant sizing agents with polyimide as the main system to solve the above problems. CN107022901B discloses a water-based polyimide sizing agent, which has a very high thermal decomposition temperature and can effectively enhance the interfacial properties of thermoplastic composite materials, but thermoplastic polyimide is in a glassy state at room temperature, causing the sizing carbon fiber to show poor bundling, high stiffness, and difficult bending at room temperature. CN110747648A discloses a method for preparing a sizing agent using soluble polyimide, an organic solvent and deionized water. The method has simple process operation, and the sizing agent has high thermal stability, which can effectively improve the interfacial strength, but the system still relies on thermoplastic polyimide as a sizing agent layer, still lacks flexibility at room temperature, is difficult to spread yarn, and weave, and cannot achieve a balance between the interfacial properties and process properties of carbon fibers.

[0004] In summary, although traditional epoxy resin-based sizing agents can well protect fibers, reduce wear, and have excellent fiber bundling and flexibility, they cannot withstand the molding temperature of high-performance composite materials such as thermoplastic composites and polyimide composites, and have poor matching with high-performance matrix resins, which can easily lead to performance degradation; and although existing polyimide sizing agents have good heat resistance and can strengthen the interface strength of composite materials, they lack flexibility and viscosity at room temperature, resulting in poor bundling and low flexibility of sized fibers, easy to fuzz and wear, affecting practical applications. Therefore, it is of great significance to develop polyimide sizing agents with excellent room temperature bundling and effective fiber protection. Summary of the invention

[0005] 1. Technical issues to be resolved

[0006] The technical problem to be solved by the present invention is that it is difficult for traditional sizing agents to simultaneously ensure the flexibility, bundling and lubricity of room temperature sized fibers and retain the inherent high temperature resistance of the sizing agent and good matching with the matrix resin.

[0007] (II) Technical solution

[0008] In order to solve the above technical problems, the present invention provides a method for preparing a polyimide emulsion sizing agent, which comprises the steps of:

[0009] S1. Mixing the anhydride and the alcohol reagent and stirring to complete the esterification reaction to obtain an esterified mixture;

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

[0011] S3. Add deionized water to the polyimide precursor mixture through a phase inversion emulsification method to complete emulsification and obtain a polyimide emulsion sizing agent.

[0012] As a preferred embodiment of the present invention, in step S1, the acid anhydride is selected from one or more of biphenyl tetracarboxylic dianhydride, diphenyl ether tetracarboxylic dianhydride, bisphenol A tetracarboxylic dianhydride, benzophenone tetracarboxylic dianhydride, 4,4'-[hexafluoroisopropylene] diphthalic 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 glycoside, cellulose, fatty alcohol, aromatic alcohol, and alicyclic alcohol.

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

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

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

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

[0019] The third aspect of the present invention provides a method for preparing sizing reinforced fibers, characterized in that it comprises the steps of:

[0020] S1. Immersing the reinforcing fiber in the polyimide emulsion sizing agent according to claim 7 to obtain a reinforcing fiber with slurry;

[0021] S2. The sizing-coated reinforcing fibers are heated and dried to obtain sizing-completed 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 of the heating and drying is 100-350°C.

[0024] (III) Beneficial effects

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

[0026] 1. The present invention introduces hydrophilic chain segments into the sizing agent system through esterification reaction, which not only gives the polyimide sizing agent the ability to emulsify in water, but also can achieve good lubrication and protection of the sizing fiber by virtue of the flexibility and viscosity of the hydrophilic polymer at room temperature, and provide bundling and flexibility.

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

[0028] 3. The sizing agent provided by the present invention can maintain good plasticity and adhesion at room temperature, can give the reinforcing fiber excellent flexibility, bundling and lubricity, can effectively reduce fiber damage and reduce the amount of fuzzing.

[0029] 4. The sizing agent provided by the present invention does not require any organic solvent during the preparation and use process, has a simple preparation process, is easy to use and operate, and is green, environmentally friendly, safe and efficient. DETAILED DESCRIPTION

[0030] The following examples are used to illustrate the present invention, but are not intended to limit the scope of the present invention.

[0031] Unless otherwise specified, the experimental methods used in the following examples are all conventional methods; the reagents, materials, etc. used in the following examples, unless otherwise specified, can be obtained from commercial channels.

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

[0033] S1. Mixing the anhydride and the alcohol reagent and stirring to complete the esterification reaction to obtain an esterified mixture;

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

[0035] S3. Add deionized water to the polyimide precursor mixture through a phase inversion emulsification method to complete emulsification and obtain a polyimide emulsion sizing agent.

[0036] As a preferred embodiment of the present invention, in step S1, the acid anhydride is selected from one or more of biphenyl tetracarboxylic dianhydride, diphenyl ether tetracarboxylic dianhydride, bisphenol A tetracarboxylic dianhydride, benzophenone tetracarboxylic dianhydride, 4,4'-[hexafluoroisopropylene] diphthalic 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] As 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 glycoside, cellulose, fatty alcohol, aromatic alcohol, and alicyclic alcohol. The alcohol reagent is a hydrophilic hydroxyl-containing compound that can impart hydrophilicity to the polyimide molecular chain, enabling it to be emulsified in water.

[0038] 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. The diamine is used to synthesize the molecular backbone of the polyimide sizing agent.

[0039] As a preferred embodiment of the present invention, in step S1, the molar ratio of the anhydride group of the acid anhydride to the hydroxyl group of the alcohol reagent is 1: (1 to 10). An equimolar or excess amount of alcohol reagent can ensure that the anhydride is fully esterified, so that the hydrophilicity of the polyimide sizing agent is increased to the maximum. At the same time, the additional alcohol reagent can also act as a lubricant, so that the reinforcing fiber after sizing has good flexibility and viscosity, enhances the bundling and wear resistance of the fiber bundle, and overcomes the problems that traditional polyimide sizing agents easily cause fiber stiffness and difficulty in bundling.

[0040] As a preferred embodiment of the present invention, in step S1, the relative molecular weight of the alcohol reagent is 500-5000 g / mol. If the molecular weight is too small, the alcohol reagent is insufficient to provide sufficient hydrophilicity for the polyimide sizing agent, and 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] As a preferred embodiment of the present invention, the mass fraction of the polyimide emulsion sizing agent is 0.5-50%, and can be diluted with water according to the specific reinforcing fibers and the required sizing amount.

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

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

[0044] S1. Immersing the reinforcing fiber in the polyimide emulsion sizing agent according to claim 7 to obtain a reinforcing fiber with slurry;

[0045] S2. The sizing-coated reinforcing fibers are heated and dried to obtain sizing-completed reinforcing fibers.

[0046] 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.

[0047] As a preferred embodiment of the present invention, in step S2, the heating temperature of the heating and drying is 100-350° C. On the one hand, moisture is removed, and on the other hand, the ester bond in the polyimide sizing agent can be decomposed, the alcohol reagent can be removed, and imidization can be completed.

[0048] In the above technical scheme of the present invention, an acid anhydride and an alcohol reagent are mixed and esterified to obtain an esterified mixture, and then a diamine is added to polymerize to obtain a polyimide precursor mixture, and a polyimide emulsion sizing agent is obtained by a phase inversion emulsification method. The present invention also immerses the reinforcing fiber in the obtained sizing agent and then heats and dries it to complete the sizing. The sizing layer of the present invention can retain the inherent advantages of the polyimide sizing agent of high temperature resistance and good matching with the matrix resin, and can give the sizing fiber good flexibility, bundling and lubricity at room temperature, which can effectively reduce fiber damage and reduce the amount of fuzzing. At the same time, the present invention does not require organic solvents throughout the preparation and use process, and has the characteristics of green environmental protection, safety and high efficiency.

[0049] Example 1

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

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

[0052] (2) Maintaining the temperature at 80° C., 10.8 g of m-phenylenediamine (m-PDA) was added to the esterification mixture and stirred for 4 h to obtain a polyimide precursor mixture.

[0053] (3) The system temperature was cooled to 65° C., the stirring speed was increased to 1000 r / min, and then 300 g of deionized water was slowly added to the polyimide precursor mixture to complete the phase inversion, thereby obtaining 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, comprising the steps of:

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

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

[0057] Example 2

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

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

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

[0061] (3) Maintaining 65° C., the stirring speed was increased to 1500 r / min, and then 1050 g of deionized water was slowly added to the polyimide precursor mixture to complete the phase inversion, thereby obtaining 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, comprising the steps of:

[0063] The obtained polyimide emulsion sizing agent is cooled and diluted with water to a mass fraction of 1.0%. The carbon fiber is then immersed in a glue tank filled with the diluted polyimide emulsion sizing agent for sizing, and further treated at 120°C, 200°C and 300°C for 5 minutes respectively to dry the moisture, remove mPEG-2000 and complete imidization to obtain a 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, comprising the steps of:

[0066] (1) 52.0 g of bisphenol A tetraacid dianhydride (BPADA) and 130 g of polyoxyethylene sorbitan monooleate (T-80) (relative molecular weight of 1300 g / mol) were mixed and stirred at a reaction group molar ratio of 1:1.5 at 95° C. and a speed of 100 r / min. After the solid was dissolved, the reaction was continued for 3 hours to obtain a completely esterified mixture.

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

[0068] (3) Maintaining 65° C., the stirring speed was increased to 1500 r / min, and then 820 g of deionized water was slowly added to the polyimide precursor mixture to complete the phase inversion, thereby obtaining 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, comprising the steps of:

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

[0071] Comparative Example 1

[0072] Example 1 is used as a control group. Comparative Example 1 uses ethanol with a very small relative molecular mass (relative molecular mass is 46 g / mol) as an alcohol reagent, and the other ingredients and process parameters remain unchanged, as follows:

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

[0074] (2) Maintaining the temperature at 80° C., 10.8 g of m-phenylenediamine (m-PDA) was added to the esterification mixture and stirred for 4 h to obtain a polyimide precursor mixture.

[0075] (3) The system temperature was cooled to 65° C., the stirring speed was increased to 1000 r / min, and then 300 g of deionized water was slowly added to the polyimide precursor mixture to complete the phase inversion, thereby obtaining a milky white polyimide emulsion sizing agent with a mass fraction of about 40%.

[0076] This comparative example also provides a method for preparing sizing fibers, comprising the steps of:

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

[0078] The polyimide emulsion sizing agent obtained in Comparative Example 1 has poor stability, and obvious stratification and precipitation occur after standing at room temperature for 1 day, indicating that the small molecule alcohol reagent has insufficient effect on improving the hydrophilicity of the system and is difficult to support the stable dispersion of polyimide in water. In contrast, the polyimide emulsion sizing agent obtained in Example 1 can be stably maintained at room temperature for 30 days without stratification, indicating that hydrophilic alcohol reagents with appropriate molecular weight can effectively improve the stability of polyimide sizing agents in water.

[0079] By comparing the amount of hair, it can be seen that the sized carbon fiber in Example 1 has higher wear resistance than the sized carbon fiber in Comparative Example 1. This is because the molecular weight of the alcohol reagent in Comparative Example 1 is too small, resulting in its boiling point being too low, and it is removed together when the water is dried, which does not play a role in protecting and lubricating the fiber; while the alcohol reagent in Example 1 has an appropriate molecular weight, can be retained on the fiber surface and present a soft waxy state, and significantly improves the fiber's bundling, compliance, and wear resistance. This shows that the polyimide sizing agent prepared by using an alcohol reagent with an appropriate molecular weight can effectively protect the fiber and is conducive to the full play of the fiber's mechanical properties.

[0080] In summary, the polyimide emulsion sizing agent and its preparation method and application provided by the present invention can overcome the problems of poor flexibility and difficulty in bundling at room temperature while giving full play to the inherent advantages of the polyimide sizing agent such as high temperature resistance and good matching with the matrix resin.

[0081] It should be clear 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 each other, and each embodiment focuses on the differences from other embodiments. For the embodiments of the method, the relevant parts can refer to the partial description of the device embodiment (adopted according to the writing situation). The present invention is not limited to the specific steps described above. In addition, for the sake of brevity, the detailed description of the known method technology is omitted here.

[0082] 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 technical principles of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A method for preparing a polyimide emulsion sizing agent, characterized in that: Includes steps: S1. Mixing the anhydride and the alcohol reagent and stirring to complete the esterification reaction to obtain an esterified mixture; S2. Adding diamine to the esterification mixture and stirring to complete the polymerization reaction to obtain a polyimide precursor mixture; S3. Add deionized water to the polyimide precursor mixture through a phase inversion emulsification method to complete emulsification and obtain a polyimide emulsion sizing agent.

2. The preparation method according to claim 1, characterized in that: In step S1, the acid anhydride is selected from one or more of biphenyl tetracarboxylic dianhydride, diphenyl ether tetracarboxylic dianhydride, bisphenol A tetracarboxylic dianhydride, benzophenone tetracarboxylic dianhydride, 4,4'-[hexafluoroisopropylene] diphthalic anhydride, 1,4-difluoropyromellitic dianhydride, pyromellitic dianhydride, and phthalic anhydride; In step S1, the alcohol reagent is selected from one or more of polyethylene glycol, polypropylene glycol, alkyl glycoside, cellulose, fatty alcohol, aromatic alcohol, and alicyclic alcohol.

3. The preparation method according to claim 1 or 2, 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.

4. The preparation method according to claim 1 or 2, characterized in that: In step S1, the molar ratio of the anhydride group of the acid anhydride to the hydroxyl group of the alcohol reagent is 1:(1-10).

5. The preparation method according to claim 1, characterized in that: In step S1, the relative molecular mass of the alcohol reagent is 500-5000 g / mol.

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

7. A polyimide emulsion sizing agent, prepared by the method according to any one of claims 1 to 6.

8. A method for preparing sizing reinforced fiber, characterized in that: Includes steps: S1. Immersing the reinforcing fiber in the polyimide emulsion sizing agent according to claim 7 to obtain a reinforcing fiber with slurry; S2. The sizing-coated reinforcing fibers are heated and dried to obtain sizing-completed reinforcing fibers.

9. The method for preparing sizing reinforced fiber according to claim 8, 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.

10. The method for preparing sizing reinforced fiber according to claim 8, characterized in that: In step S2, the heating temperature of the heating and drying is 100-350°C.