Preparation method and application of self-emulsifying cationic waterborne polyurethane emulsion sizing agent

Abstract

The invention relates to the technical field of carbon fiber sizing agents, in particular to a preparation method and application of a self-emulsifying cationic waterborne polyurethane emulsion sizing agent. The preparation method comprises the following steps: firstly, preparing the cationic waterborne polyurethane emulsion by adopting a self-emulsifying method, then mixing the cationic waterborne polyurethane emulsion with the lubricant, the surfactant and the coupling agent, adding distilled water, and stirring and diluting to prepare the sizing agent. According to the cationic waterborne polyurethane emulsion prepared by the method disclosed by the invention, the performance of the emulsion is improved, and the cationic waterborne polyurethane emulsion can be prepared by changing different synthesis raw materials, the ratio of the raw materials and the content of a solid intermediate and introducing a nano SiO2 structure. The emulsion has different hydrophilicity and lipophilicity, different particle sizes and different heat resistance degrees, is applied to fiber production with different requirements, and has the properties of improving the chemical bonding property and wettability of a resin and fiber interface, improving the tensile strength of fibers, enhancing the interlaminar shear strength of composite materials and the like.

Description

Technical Field

[0001] The present invention relates to the technical field of sizing agents for carbon fibers, and particularly to a preparation method and application of a self-emulsifying cationic aqueous polyurethane emulsion sizing agent. Background Art

[0002] In recent years, green chemistry has attracted much attention. Early-developed solvent-based chemical products have gradually withdrawn from the market, and have been replaced by green and environmentally friendly aqueous chemical products. Aqueous resin products are a general term for a class of polymers using water as a medium. It has the advantages of environmental friendliness, low cost, etc. In particular, it reduces the harm and pollution of solvent volatilization to the human body and the environment, and reduces the hidden danger of fire, so its application range has also become wider.

[0003] Aqueous polyurethane (WPU) is one of the currently widely used green and environmentally friendly aqueous materials. During its preparation and application processes, water evaporates or there is no organic solvent volatilization, the process is simple and safe, and its special structure can endow unique physical and chemical properties, such as adjustable film hardness and softness, good wear resistance, good weather resistance and other characteristics. Therefore, WPU materials have attracted attention and are widely used in the synthesis of composite materials. Aqueous polyurethane uses water as a medium and needs to introduce hydrophilic groups such as carboxyl groups and hydroxyl groups into its molecular structure to make its water resistance better than that of traditional solvent-based chemicals. While aqueous polyurethane has many advantages, it also has disadvantages. In particular, its mechanical properties and moisture resistance still need to be optimized, and water vapor in the air and microorganisms in the environment can damage its coating, not only making the substrate lose its protective effect, but also causing harm to the human body. In order to improve the performance of carbon fibers and broaden their application fields, introducing aqueous polyurethane into hydrophobic and silicone and other chain segment structures for modification has become a key research direction. Currently, people improve the physical and chemical properties of aqueous polyurethane by changing the molecular structure and composition of polyurethane itself, or introducing structures such as acrylate, epoxy resin and silicone, and by introducing functionalized functional groups and other methods.

[0004] The synthesis methods of aqueous polyurethane generally include external emulsification method and self-emulsification method. The external emulsification method includes direct emulsification method and phase inversion emulsification method. The emulsion particles obtained by the direct emulsification method are unstable, with relatively large particle sizes, and the size is uneven and uncontrollable. The type of emulsifier also has a great influence on the preparation of the emulsion. Moreover, the emulsifier has poor compatibility and matching with the resin, which easily causes disadvantages such as unstable emulsion system and uneven particle size. The phase inversion emulsification method, also known as the phase inversion method, is a relatively effective means for preparing polymer resin-based systems. At present, the production of aqueous polyurethane emulsion mostly adopts the phase inversion method. The phase inversion method is simple to operate, and the emulsion particle size is small and the distribution is relatively narrow. Preparing film-forming agents by the phase inversion method has many advantages, but external emulsifiers are still required. The presence of emulsifiers will affect the polymer interface and other properties, such as strength, water resistance, etc. Therefore, adding less or no emulsifier is the main development direction of sizing agents.

[0005] The self-emulsification method is also known as the chemical modification method. By using the active functional groups and hydrophilic groups or segments carried by the resin itself, hydrophilic groups are introduced into the resin structure, making it form an amphiphilic polymer that is both hydrophilic and lipophilic. It can be self-emulsified and dispersed into an emulsion in water without adding external emulsifiers, with small particle sizes, narrow particle size distribution, and high stability.

[0006] Taking polyurethane as an example, according to the active groups on the molecular chain structure of aqueous polyurethane, aqueous polyurethane can be divided into cationic type, anionic type and non-ionic type. (1) Anionic aqueous polyurethane is made by introducing sulfonic acid groups and carboxylic acid groups, but most of them use side chains containing ionic groups. (2) Cationic aqueous polyurethane (ACPU) is usually prepared by introducing tertiary amine functional groups or segments into the macromolecules of polyurethane. Generally, a diol containing a tertiary amine group is used as a chain extender, and quaternization is carried out with an alkylating agent or an appropriate acid to obtain cationic groups. (3) Non-ionic aqueous polyurethane, that is, aqueous polyurethane whose molecules are composed of non-ionic groups.

[0007] Two common methods for preparing aqueous polyurethane by the self-emulsification method: prepolymer dispersion method and acetone method. The acetone method is also a solution method. It is a method of reducing the viscosity of the prepolymer or dissolving the prepolymer with an organic solvent and then emulsifying. Acetone is usually used as the solvent, so it is called the acetone method. The prepolymer method usually has a relatively high viscosity, resulting in a relatively high molecular weight, which affects the properties of aqueous polyurethane, such as relatively large particle sizes and poor storage stability; if the molecular weight is small, there are more urea bond groups after emulsification, and the polyurethane film is harder and has poor flexibility. Summary of the Invention

[0008] The technical problem to be solved by the present invention is to provide a preparation method of a self-emulsifying cationic aqueous polyurethane emulsion sizing agent, so as to improve the surface defects of fibers, enhance the bundling property, short-cutting property, wettability, penetration property, etc. of fibers, enhance the wettability and chemical bonding property of the fiber-resin interface, and greatly improve the mechanical and application properties of the composite material.

[0009] The technical solution adopted by the present invention is as follows:

[0010] A preparation method of a self-emulsifying cationic aqueous polyurethane emulsion sizing agent, comprising the following steps:

[0011] (1) Octadecyl acrylate and diethanolamine are put into a reaction vessel for reaction. After the heating reaction is completed, it is washed to remove the excess diethanolamine, and a solid intermediate is obtained after cooling.

[0012] (2) The prepared solid intermediate, dihydroxy polymer, diol and N-methylpyrrolidone are added to a reactor, heated to remove moisture, and then diisocyanate is added, and the reaction is carried out by heating.

[0013] (3) After the reaction is completed, the temperature is lowered, and an equal volume of acetone is added and stirred to reduce the viscosity of the reaction system. Then, a cationic hydrophilic chain extender is used to carry out a chain extension reaction under the action of a catalyst.

[0014] (4) After the chain extension reaction is completed, glacial acetic acid is added for neutralization reaction, and finally distilled water is added, and emulsification is carried out under stirring to obtain a cationic aqueous polyurethane emulsion.

[0015] (5) The cationic aqueous polyurethane emulsion, lubricant, surfactant and coupling agent are mixed, and then distilled water is added and stirred for dilution to prepare a sizing agent.

[0016] Preferably, in the step (1), the molar ratio of octadecyl acrylate to diethanolamine is 1:1.5. First, the reaction is carried out at 30-50 °C for 2-3 h, and then the temperature is gradually raised to 60-80 °C and the reaction is carried out for 4-5 h.

[0017] Preferably, in the step (1), heated distilled water is used for washing to remove the excess diethanolamine until the organic phase becomes a transparent liquid on the upper layer of the distilled water. After cooling, the lower-layer distilled water is poured out, and the organic phase becomes a white transparent solid intermediate.

[0018] Preferably, in the step (2), under the protection of nitrogen, it is stirred and heated to 120 °C for 3 h to remove moisture; after removing moisture, the temperature is lowered to 35-40 °C, then diisocyanate is added, and then the temperature is slowly raised to 70-80 °C and the reaction is carried out for 3-4 h.

[0019] Preferably, in the step (2), the dihydroxy polymer is polypropylene glycol 1000 or polytetrahydrofuran; the diol is 1,4-butanediol; the cationic hydrophilic chain extender is N-methyldiethanolamine, and the diisocyanate is 2,4-toluene diisocyanate or isophorone diisocyanate.

[0020] Preferably, in the step (3), the temperature is lowered to 40°C, the cationic hydrophilic chain extender is N-methyldiethanolamine, a catalyst dibutyltin dilaurate is added during the reaction, and the reaction is carried out at a temperature of 45 - 50°C for 2 h.

[0021] Preferably, in the neutralization reaction of the step (4), the dosage of glacial acetic acid is adapted to the chain extender.

[0022] Preferably, in the step (5), in the sizing agent prepared, by mass fraction, the cationic aqueous polyurethane emulsion is 1% - 3%; the lubricant is 0.1% modified mineral oil 6440 and 0.3% polyethylene glycol monooleate, the surfactant is 0.05% FC - 4430, the coupling agent is 0.3% - 0.5% KH560 or KH570, and the balance is distilled water, thus obtaining the cationic aqueous polyurethane emulsion sizing agent (cationic aqueous polyurethane film-forming agent).

[0023] Preferably, in the preparation, by weight parts, the dihydroxy polymer is 41 - 46 parts, the diol is 8 - 14 parts, the solid intermediate is 20 - 25 parts, N-methylpyrrolidone is 0.5 part; the diisocyanate is 28 - 34 parts, the cationic hydrophilic chain extender is 2 - 5 parts, and the catalyst dibutyltin dilaurate is 0.001 - 0.004 part.

[0024] Application of a sizing agent prepared by a preparation method of a self-emulsifying cationic aqueous polyurethane emulsion sizing agent in carbon fibers.

[0025] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0026] The present invention uses a self-emulsification method to obtain a cationic aqueous polyurethane emulsion. Self-emulsification does not require an external emulsifier. It not only improves the performance of the emulsion itself, but also by changing different synthetic raw materials and introducing a nano-SiO₂ structure, the emulsion can have different hydrophilic-lipophilic properties, different particle sizes, different heat resistance levels, so that it can be applied to fiber production with different requirements. At the same time, it can improve the interfacial chemical adhesion and wettability between the resin and the fiber, increase the tensile strength of the fiber, and enhance the interlaminar shear strength of the composite material. The interlaminar shear strength of the composite material made of carbon fiber reaches 132.4 Mpa. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 It is a flow chart of the preparation method of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0028] The accompanying drawings are only for illustrative purposes; the following detailed description only represents some embodiments and aims to provide further explanation of the present invention. Unless otherwise specified, all technical and scientific terms used in the present invention have the same meaning as commonly understood by those of ordinary skill in the technical field to which the present invention belongs.

[0029] Embodiment 1:

[0030] As Figure 1 shown, a preparation method of a self-emulsifying cationic aqueous polyurethane emulsion sizing agent. Pretreatment: The N-methyldiethanolamine used is dried under vacuum at 120 °C for 2 h with a vacuum pump; acetone is dried in advance in a molecular sieve activated at high temperature for more than 6 h. The preparation method includes the following steps:

[0031] Step 1: The molar ratio of octadecyl acrylate to diethanolamine is 1:1.5. First, react at a low temperature of 50 °C for 3 h, then gradually raise the temperature to 70 °C and react for about 4 h. Finally, wash away the excess diethanolamine with heated distilled water until the organic phase becomes a transparent liquid on the upper layer of the distilled water. After cooling, pour out the lower layer of water, and the organic phase becomes a slightly transparent white solid intermediate. Then place it in a vacuum oven at 110 °C for drying for 2 h and store it in a desiccator for standby.

[0032] The infrared data of the solid intermediate is as follows: absorption peak near 3400 cm -1 : -OH; absorption peak near 2850 cm -1 : -CH2; absorption peak near 1715 cm -1 : -C=O; absorption peak near 1330 cm -1 : C-N bond; absorption peak near 1630 cm -1 Absorption peak disappearance: C=C bond disappearance.

[0033] Step 2: Add polypropylene glycol 1000, 1,4-butanediol, the intermediate, and N-methylpyrrolidone to the reactor. Under nitrogen protection, stir and heat to 120 °C for 3 h to remove moisture. After removing moisture, cool down. After reaching 40 °C, add 2,4-toluene diisocyanate and slowly raise the temperature to 70 °C and react for 3 h until the remaining amount of isocyanate is less, and then proceed to the next reaction.

[0034] Step 3: Cool down to below 40 °C, add acetone to reduce its viscosity, and then use the cationic hydrophilic chain extender N-methyldiethanolamine for chain extension reaction. After adding the catalyst dibutyltin dilaurate, react at a temperature of 45 °C for 2 h, and then proceed to the next reaction.

[0035] Step 4: Add glacial acetic acid for neutralization and salt formation reaction according to the amount of the cationic hydrophilic chain extender added. Finally, add distilled water and carry out emulsification under stirring to obtain a cationic aqueous polyurethane emulsion.

[0036] The infrared data of the cationic aqueous polyurethane emulsion are as follows: the vibration absorption peak near 2270 cm -1 disappears: the N=C=O group disappears and the -NCO group in the isocyanate reacts; the absorption peak near 1223 cm -1 : the C-O bond in the -COO structure; the absorption peak near 1541 cm -1 : the characteristic peak of the quaternary ammonium salt; the absorption peak near 1647 cm -1 : the C=O bond in the urethane -NHCOO structure; the absorption peak near 2970 cm -1 : the asymmetric saturated alkyl group -CH2; the absorption peak near 3327 cm -1 : the N-H bond forms a hydrogen bond with water.

[0037] Step 5: The sizing agent is compounded from 2% cationic aqueous polyurethane emulsion, lubricants (0.1% modified mineral oil 6440, 0.3% polyethylene glycol monooleate), 0.05% fluorosurfactant (FC-4430) and 0.3% coupling agent (KH560, KH570), and is prepared by adding distilled water and stirring for dilution.

[0038] Example 2:

[0039] A preparation method of a self-emulsifying cationic aqueous polyurethane emulsion sizing agent, comprising the following steps:

[0040] The difference from Example 1 is that after the reaction of octadecyl acrylate and diethanolamine, the temperature is gradually raised to 80 °C.

[0041] The dihydroxy polymer used is polytetrahydrofuran; after adding the diisocyanate and reacting, the temperature is lowered to below 35 °C for the next reaction.

[0042] Other parts not mentioned are the same as in Example 1.

[0043] Example 3:

[0044] A preparation method of a self-emulsifying cationic aqueous polyurethane emulsion sizing agent, comprising the following steps:

[0045] The difference from Example 1 is that after the reaction of octadecyl acrylate and diethanolamine, the temperature is gradually raised to 80 °C.

[0046] The dihydroxy polymer used is polypropylene glycol 1000; after adding the diisocyanate and reacting, the temperature is lowered to below 35 °C for the next reaction.

[0047] Other places not mentioned are the same as those in Example 1.

[0048] Example 4:

[0049] A preparation method of a self-emulsifying cationic aqueous polyurethane emulsion sizing agent, comprising the following steps:

[0050] The difference from Example 1 is that the dihydroxy polymer used is polytetrahydrofuran; after adding the diisocyanate and reacting, the next reaction is cooled to below 40 °C.

[0051] Comparative Example 1:

[0052] Zhongfu Shenying carbon fiber without sizing agent.

[0053] The physical properties of the sizing agents prepared in Examples 1-4 of the present invention, the carbon fibers after sizing treatment, and the unsized Comparative Example 1 were measured respectively. The test methods are as follows:

[0054] (1) Particle size distribution test: Using a NanoBrook Omni type laser particle size analyzer from Brookhaven Corporation, USA, a 3% mass fraction sizing agent sample was diluted with distilled water, 2 μl was taken and added to the sample cell. After ultrasonic treatment for 30 min, the test was carried out, and the average value was taken after 3 tests.

[0055] (2) Storage stability: The emulsion was prepared into a 5% solid content and placed in a 25 ml graduated colorimetric tube. It was left standing at room temperature, and the time of precipitation, stratification, and demulsification was observed.

[0056] (3) Thermal stability test: A small amount of the emulsion sample was placed in an oven, and vacuum was pumped with a circulating water vacuum pump at 120 °C for more than 8 h. The sample after drying the moisture and solvent was tested for heat resistance performance using a thermogravimetric analyzer (NETZSCH TG209F1) at a heating rate of 10 °C / min from 30 to 500 °C, and finally a heat-resistant decomposition temperature curve was obtained.

[0057] (4) Surface tension test: The sample was prepared into a 3% mass fraction solution, and the density was measured using a density bottle. Using the measured density, the surface tension was measured using a surface tension meter (Kruss GmbH K100SF) by the ring method. After multiple tests, the average value was taken.

[0058] (5) Interlaminar shear strength test method: The interlaminar shear test was carried out according to the method specified in GB / T 30969-2014. The thickness of the specimen was 2 mm, the width was 6 mm, the loading rate was 2 mm / min, and the fiber volume content of the specimen was 50%-55%.

[0059] (6) Tensile strength test: The terms and definitions as well as the test standards defined in the national standard GB / T 3362-2017 are adopted for the tensile strength test method. The tensile property test is carried out according to the method specified in GB / T 3362-2017.

[0060] (7) Linear density test: Straighten the carbon fiber multifilament, cut three 1m-long multifilaments, and the allowable error of the measured length is ±1mm. Weigh the sample with an electronic balance, accurate to 0.1mg. Take the arithmetic mean of the measurement results of three carbon fiber multifilament samples as the linear density of the carbon fiber multifilament. The results are shown in Table 1.

[0061] Table 1 Comparison of Test Performance Results of Examples 1-4 and Comparative Example 1

[0062]

[0063] The maximum tensile strength of the carbon fiber sized with the sizing agent compounded with the cationic aqueous polyurethane emulsion prepared in Examples 1-4 is 4.93 GPa, the maximum tensile modulus is 235 GPa, the elongation at break is 2.1-2.5%, the linear density is 803.2-815.5 g / Km, and the bulk density is 1.7-1.9 g / cm 3 , and the interlaminar shear strength of the composite material made of the carbon fiber sized with Example 3 reaches 132.4 MPa. It shows that the sizing agent prepared from the cationic aqueous polyurethane emulsion synthesized in the present invention has good wettability with the carbon fiber, improves the adhesion between the carbon fiber and the resin, enhances the mechanical properties of the composite material, and provides an excellent optional sizing agent for carbon fiber production.

[0064] The Chinese names of the English abbreviations used in the present invention are as follows:

[0065] FC-4430: Fluoroaliphatic polymer resin;

[0066] KH560: γ-Glycidoxypropyltrimethoxysilane;

[0067] KH570: γ-(Methacryloyloxy)propyltrimethoxysilane.

[0068] Of course, the above description is not a limitation of the present invention, and the present invention is not limited to the above examples. Changes, modifications, additions or substitutions made by those skilled in the art within the essence of the present invention should also fall within the protection scope of the present invention.

Claims

1. A preparation method of a self-emulsifying cationic aqueous polyurethane emulsion sizing agent, characterized in that, It includes the following steps: (1) Octadecyl acrylate and diethanolamine are put into a reaction vessel for reaction. After the heating reaction ends, it is washed to remove the excess diethanolamine, and a solid intermediate is obtained after cooling; (2) The prepared solid intermediate, dihydroxy polymer, diol and N-methylpyrrolidone are added to a reactor to heat and remove moisture, then diisocyanate is added, and the reaction is heated; (3) After the reaction ends, the temperature is lowered, and an equal volume of acetone is added and stirred to reduce the viscosity of the reaction system. Then, a cationic hydrophilic chain extender is used to carry out a chain extension reaction under the action of a catalyst; (4) After the chain extension reaction ends, glacial acetic acid is added for neutralization reaction, and finally distilled water is added, and emulsification is carried out under stirring to obtain a cationic aqueous polyurethane emulsion; (5) After mixing the cationic aqueous polyurethane emulsion, lubricant, surfactant and coupling agent, distilled water is added and stirred for dilution to prepare a sizing agent.

2. The preparation method of a self-emulsifying cationic aqueous polyurethane emulsion sizing agent according to claim 1, characterized in that In the step (1), the molar ratio of octadecyl acrylate to diethanolamine is 1:1.

5. First, the reaction is carried out at 30-50 °C for 2-3 h, and then the temperature is gradually raised to 60-80 °C and the reaction is carried out for 4-5 h.

3. The preparation method of a self-emulsifying cationic aqueous polyurethane emulsion sizing agent according to claim 1, characterized in that, In the step (1), heated distilled water is used for washing to remove the excess diethanolamine until the organic phase becomes a transparent liquid on the upper layer of the distilled water. After cooling, the lower-layer distilled water is poured out, and the organic phase becomes a white transparent solid intermediate.

4. The preparation method of a self-emulsifying cationic aqueous polyurethane emulsion sizing agent according to claim 1, wherein, In the step (2), under nitrogen protection, it is stirred and heated to 120 °C to remove moisture for 3 h; after removing moisture, the temperature is lowered to 35-40 °C, then diisocyanate is added, and then the temperature is slowly raised to 70-80 °C and the reaction is carried out for 3-4 h.

5. The preparation method of a self-emulsifying cationic aqueous polyurethane emulsion sizing agent according to claim 1, characterized in that, In the step (2), the dihydroxy polymer is polypropylene glycol 1000 or polytetrahydrofuran; the diol is 1,4-butanediol; the cationic hydrophilic chain extender is N-methyldiethanolamine, and the diisocyanate is 2,4-toluene diisocyanate or isophorone diisocyanate.

6. The preparation method of a self-emulsifying cationic aqueous polyurethane emulsion sizing agent according to claim 1, characterized in that, In the step (3), the temperature is lowered to 40 °C, the cationic hydrophilic chain extender is N-methyldiethanolamine, and the catalyst dibutyltin dilaurate is added to the reaction. The reaction is carried out at a temperature of 45-50 °C for 2 h.

7. The preparation method of a self-emulsifying cationic aqueous polyurethane emulsion sizing agent according to claim 1, characterized in that, In the neutralization reaction of the step (4), the dosage of glacial acetic acid is adapted to the chain extender.

8. The preparation method of a self-emulsifying cationic aqueous polyurethane emulsion sizing agent according to claim 1, characterized in that, In the step (5), in the prepared sizing agent by mass fraction, the cationic aqueous polyurethane emulsion is 1%-3%, the lubricant is 0.1% modified mineral oil 6440 and 0.3% polyethylene glycol monooleate, the surfactant is 0.05% fluorinated aliphatic polymer resin FC-4430, the coupling agent is 0.3%-0.5% KH560 or KH570, and the rest is distilled water.

9. The preparation method of a self-emulsifying cationic aqueous polyurethane emulsion sizing agent according to claim 1, wherein, When preparing, the raw materials are in parts by weight, 41-46 parts of dihydroxy polymer, 8-14 parts of diol, 20-25 parts of solid intermediate, 0.5 part of N-methylpyrrolidone; 28-34 parts of diisocyanate, 2-5 parts of cationic hydrophilic chain extender, 0.001-0.004 part of catalyst dibutyltin dilaurate.

10. Application of the sizing agent prepared by the preparation method of a self-emulsifying cationic aqueous polyurethane emulsion sizing agent according to any one of claims 1-9 in carbon fiber.

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