Preparation method of water-soluble sizing agent for epoxy resin carbon fiber

Abstract

The present invention belongs to the technical field of sizing agents, and discloses a preparation method of a water-soluble sizing agent for epoxy resin carbon fiber. One end of the sizing agent of the present invention is a hydrolyzable group, which can combine with -OH on the surface of carbon fiber, and the other end is a non-hydrolyzable group, which can react with resin to introduce functional groups in the slurry onto the surface of carbon fiber, increasing the activity of the carbon fiber surface, and further increasing the chemical bonding effect between the carbon fiber and the resin matrix. At the same time, it has good self-emulsifying function, overcoming the problem of the stability of emulsion-type sizing agents. This self-emulsifying epoxy resin sizing agent has high safety, is environmentally friendly, and is easy to use. It can select the use time according to processing needs for emulsification use.

Description

Technical Field

[0001] The present invention belongs to the technical field of sizing agents, and more specifically relates to a preparation method of an epoxy resin water-soluble carbon fiber sizing agent. Background Art

[0002] Carbon fiber composites have been widely recognized for their various excellent properties. However, their popularization and application are mainly limited by the quality and price of carbon fibers and the performance stability of their carbon fiber composites. This is mainly because carbon fibers will experience friction, wear, and generate fuzz during subsequent processing, which not only affects the smooth progress of subsequent processes but also reduces the overall performance of carbon fibers. Therefore, it is necessary to perform sizing treatment on carbon fibers.

[0003] A sizing agent is a layer of chemical slurry coated on the fiber surface, and the sizing process is an essential process in the production of carbon fibers. The functionality of the sizing agent is mainly manifested in: First, it protects the carbon fiber surface from damage during winding, packaging, and transportation; it isolates air and prevents the CF surface from adsorbing dust and moisture in the air. Second, the sizing agent can effectively improve the bundling property of carbon fibers, making the fibers aggregate together like an adhesive, improving the processability and facilitating processing. Moreover, the sizing agent is similar to a coupling agent, which can make up for the defects on the carbon fiber surface, improve the chemical bonding between carbon fibers and resins, enhance the mechanical properties of the composite material, reduce the preparation time of the composite material, and improve the product quality. Therefore, researching and developing carbon fiber sizing agents with excellent performance has positive significance in improving the quality of carbon fibers and the performance of composite materials. However, a simple emulsion-type sizing agent is mostly composed of two immiscible liquids, and with the addition of other surfactants, the fusion of the two is achieved, but its stability is poor. Stratification will occur after standing for too long, and demulsification will also occur during transportation. At the same time, the interfacial adhesion of the existing sizing agent is poor, and the improvement effect on the mechanical properties of carbon fiber materials is not good.

[0004] Therefore, how to provide a sizing agent with good stability, improved interfacial bonding with carbon fibers, and enhanced carbon fiber strength is an urgent problem to be solved by those skilled in the art. Summary of the Invention

[0005] In order to overcome the shortcomings and deficiencies of the prior art, the present invention provides a preparation method of an epoxy resin water-soluble carbon fiber sizing agent, which has a good self-emulsifying function and overcomes the stability problem of emulsion-type sizing agents. Polyethylene glycol modified with phthalic anhydride is used as a modifier to carry out graft polymerization with a compounded epoxy resin to form an epoxy resin water-soluble carbon fiber sizing agent with a hydrophobic epoxy end at one end, a hydrophilic modified polyethylene glycol at the other end, and capable of self-emulsification, thereby improving the interfacial bonding between carbon fibers and epoxy resins.

[0006] In order to achieve the above object, the present invention adopts the following technical solutions:

[0007] A preparation method of a water-soluble sizing agent for epoxy resin carbon fiber, comprising the following steps:

[0008] (1) Carry out vacuum distillation on polyethylene glycol in a rotary evaporator to remove water molecules;

[0009] (2) Add the polyethylene glycol from which water molecules have been removed and phthalic anhydride into a reaction kettle, carry out modification grafting of polyethylene glycol in an acidic environment, carry out condensation reflux while stirring, and introduce nitrogen for protection to obtain phthalic anhydride-modified polyethylene glycol;

[0010] (3) Compound two different epoxy resins to obtain a compounded epoxy resin;

[0011] (4) Carry out a grafting reaction on the phthalic anhydride-modified polyethylene glycol and the compounded epoxy resin under the action of a catalyst to obtain a water-soluble sizing agent for epoxy resin carbon fiber with self-emulsifying properties.

[0012] Preferably, the molecular weight of the polyethylene glycol in step (1) is 1000-4000.

[0013] Preferably, the molar ratio of phthalic anhydride to polyethylene glycol in step (2) is 1:1.6-2.4.

[0014] Preferably, the pH of the acidic environment in step (2) is 3-5; the stirring rate is 180-300 r / min.

[0015] The beneficial effect of the above technical solution is that too high a stirring speed is not conducive to polymerization, and too low a speed will not disperse evenly and the polymerization will be incomplete.

[0016] Preferably, the reaction temperature of the modification grafting in step (2) is 105-140 °C, and the reaction time is 2-4 h.

[0017] Preferably, the epoxy resins in step (3) include E51, E44, 6004, and F44.

[0018] Preferably, the epoxy equivalent of the compounded epoxy resin in step (3) is 180-210.

[0019] The flexibility and heat resistance of a single epoxy resin cannot meet the requirements for the preparation of subsequent composite materials. The present invention selects different epoxy resins for compounding to endow the sizing agent with suitable softness and adhesiveness. Calculate the epoxy equivalent of the compounded epoxy resin according to the epoxy equivalent and its proportion of the selected different epoxy resins, and then calculate the molar ratio of the compounded epoxy resin to the phthalic anhydride-modified polyethylene glycol.

[0020] Preferably, the molar ratio of the phthalic anhydride-modified polyethylene glycol to the compounded epoxy resin in step (4) is 1:0.6 - 1.4.

[0021] Preferably, the catalyst described in step (4) is selected from one of potassium persulfate and ammonium persulfate.

[0022] Preferably, the reaction temperature of the grafting reaction in step (4) is 110 - 140 °C, and the reaction time is 2 - 5 h.

[0023] In the present invention, the reaction equation of the phthalic anhydride-modified polyethylene glycol is as follows:

[0024]

[0025] In the present invention, the reaction equation of the phthalic anhydride-modified polyethylene glycol and the compounded epoxy resin is as follows:

[0026]

[0027] Through the above technical solutions, compared with the prior art, the present invention provides a preparation method of an epoxy resin water-soluble carbon fiber sizing agent, having the following beneficial effects:

[0028] (1) The aqueous sizing agent of the present invention has a good self-emulsifying function, overcoming the stability problem of the emulsion-type sizing agent. The compounding of epoxy resins is carried out to meet the good adhesiveness and flexibility of the sizing agent. At the same time, one end of the sizing agent of the present invention is a hydrolyzable group, which can combine with -OH on the carbon fiber surface, and the other end is a non-hydrolyzable group, which can react with the resin, introducing functional groups in the sizing agent onto the carbon fiber surface, increasing the activity of the carbon fiber surface, and further increasing the chemical bonding effect between the carbon fiber and the resin matrix.

[0029] (2) The present invention uses phthalic anhydride-modified polyethylene glycol as a modifier for grafting with epoxy resin. Because the spatial hindrance of the molecular structure of phthalic anhydride is relatively large, it can ensure that during the reaction with epoxy resin, most of the reactions are mainly one-end grafting reactions, which is beneficial to the preparation of an epoxy resin water-soluble carbon fiber sizing agent with self-emulsifying properties that is hydrophobic at one end and hydrophilic at the other end. Such a self-emulsifying epoxy resin sizing agent has high safety, is environmentally friendly, and is convenient to use. It can be emulsified and used at a selected time according to processing needs. Description of the Drawings

[0030] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the accompanying drawings required in the description of the embodiments or the prior art. Obviously, the accompanying drawings in the following description are only the embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other accompanying drawings can also be obtained based on the provided drawings.

[0031] Figure 1 It is the infrared spectrum diagram of each substance in Example 2; wherein: a - polyethylene glycol 2000, b - compounded epoxy resin, c - water-soluble carbon fiber sizing agent for epoxy resin.

[0032] Figure 2 It is the SEM photograph of the water-soluble carbon fiber sizing agent for epoxy resin in Example 4.

[0033] Figure 3 It is the SEM photograph of the surface of carbon fiber after sizing with the water-soluble carbon fiber sizing agent for epoxy resin in Example 1. Specific Embodiments

[0034] The following will clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of them. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts belong to the scope of protection of the present invention.

[0035] Example 1

[0036] Weigh polyethylene glycol 1000, and carry out reduced-pressure distillation on it in a rotary evaporator to completely remove the water molecules in the polyethylene glycol. Weigh phthalic anhydride and polyethylene glycol according to a molar ratio of 1:1.6, and add this mixture to a four-necked split glass reaction kettle equipped with a thermometer, a stirrer, a condenser reflux, and nitrogen protection at pH = 4.0 to carry out the modification grafting of polyethylene glycol. The reaction temperature is 115°C, and the reaction time is 2.5 h.

[0037] Compound epoxy resins E51 and E44, where the mass ratio of E51:E44 is 2:1. According to the epoxy equivalent of E51 being 190 and the epoxy equivalent of E44 being 220, calculate the epoxy equivalent of the compounded epoxy resin to be 200. Add 0.1 g of potassium persulfate to the phthalic anhydride-modified polyethylene glycol prepared above and the compounded epoxy resin at a molar ratio of 1:1 at 125°C, and react for 4 h under nitrogen protection to obtain a water-soluble carbon fiber sizing agent for epoxy resin.

[0038] Example 2

[0039] Weigh polyethylene glycol 2000 and carry out vacuum distillation on it in a rotary evaporator to completely remove the water molecules in the polyethylene glycol. Weigh phthalic anhydride and polyethylene glycol in a molar ratio of 1:2, and add this mixture to a four-necked separable glass reaction kettle equipped with a thermometer, a stirrer, a condensing reflux device and nitrogen protection at pH = 3.5 to carry out the modification grafting of polyethylene glycol. The reaction temperature is 125 °C and the reaction time is 3 h.

[0040] Compound epoxy resins E51 and 6004, where the mass ratio of E51:6004 is 1:1. According to the epoxy equivalent of E51 being 190 and the epoxy equivalent of 6004 being 185, calculate that the epoxy equivalent of the compounded epoxy resin is 187. Take the molar ratio of the above-prepared phthalic anhydride-modified polyethylene glycol to the compounded epoxy resin as 1:0.8, add 0.1 g of potassium persulfate at 110 °C, and react for 5 h under nitrogen protection to obtain an epoxy resin water-soluble carbon fiber sizing agent.

[0041] Example 3

[0042] Weigh polyethylene glycol 4000 and carry out vacuum distillation on it in a rotary evaporator to completely remove the water molecules in the polyethylene glycol. Weigh phthalic anhydride and polyethylene glycol in a molar ratio of 1:1.8, and add this mixture to a four-necked separable glass reaction kettle equipped with a thermometer, a stirrer, a condensing reflux device and nitrogen protection at pH = 3.0 to carry out the modification grafting of polyethylene glycol. The reaction temperature is 140 °C and the reaction time is 2 h.

[0043] Compound epoxy resins E51 and E44, where the mass ratio of E51:E44 is 1:2. According to the epoxy equivalent of E51 being 190 and the epoxy equivalent of E44 being 175, calculate that the epoxy equivalent of the compounded epoxy resin is 180. Take the molar ratio of the above-prepared phthalic anhydride-modified polyethylene glycol to the compounded epoxy resin as 1:0.6, add 0.1 g of potassium persulfate at 140 °C, and react for 4 h under nitrogen protection to obtain an epoxy resin water-soluble carbon fiber sizing agent.

[0044] Example 4

[0045] Weigh polyethylene glycol 1000 and carry out vacuum distillation on it in a rotary evaporator to completely remove the water molecules in the polyethylene glycol. Weigh phthalic anhydride and polyethylene glycol in a molar ratio of 1:2.4, and add this mixture to a four-necked separable glass reaction kettle equipped with a thermometer, a stirrer, a condensing reflux device and nitrogen protection at pH = 4.5 to carry out the modification grafting of polyethylene glycol. The reaction temperature is 105 °C and the reaction time is 4 h.

[0046] Epoxy resins E51 and E414 were compounded, with the mass ratio of E51:E414 being 1:2. According to the epoxy equivalent of E51 being 190 and that of E414 being 220, the epoxy equivalent of the compounded epoxy resin was calculated to be 210. The molar ratio of the above-prepared phthalic anhydride-modified polyethylene glycol to the compounded epoxy resin was 1:1.4. At 130 °C, 0.1 g of potassium persulfate was added, and the reaction was carried out for 3 h under nitrogen protection to obtain a water-soluble sizing agent for carbon fiber made of epoxy resin.

[0047] Example 5

[0048] Weigh 2000 of polyethylene glycol and carry out vacuum distillation on it in a rotary evaporator to completely remove the water molecules in the polyethylene glycol. Weigh phthalic anhydride and polyethylene glycol in a molar ratio of 1:2.2, and add this mixture to a four-necked separable glass reaction kettle equipped with a thermometer, a stirrer, a condensing reflux device and nitrogen protection at pH = 5.0 to carry out the modification grafting of polyethylene glycol. The reaction temperature was 110 °C and the reaction time was 4 h.

[0049] Epoxy resins 6004 and E414 were compounded, with the mass ratio of 6004:E414 being 3:1. According to the epoxy equivalent of 6004 being 185 and that of E414 being 220, the epoxy equivalent of the compounded epoxy resin was calculated to be 194. The molar ratio of the above-prepared phthalic anhydride-modified polyethylene glycol to the compounded epoxy resin was 1:1.2. At 120 °C, 0.1 g of potassium persulfate was added, and the reaction was carried out for 3.5 h under nitrogen protection to obtain a water-soluble sizing agent for carbon fiber made of epoxy resin.

[0050] Test method:

[0051] In this test, a NanoBrook 90plus PALS laser particle size analyzer from Brookhaven Instruments Corporation of the United States was used to measure the particle size and Zeta potential of the test samples. Considering the emulsion stability, emulsions with particle sizes in the range of 70 - 180 nm have relatively high stability and will not show sedimentation phenomena after being placed for 3 - 6 months. For particle sizes > 200 nm, the chance of mutual collision between particles increases and the stability will decrease, and there will be partial sedimentation phenomena after 3 months. Therefore, the optimal emulsion particle size is considered to be less than 180 nm. All the emulsions obtained from the Zeta potential test are negatively charged, and the potential range is within -40 to -10. Among them, the larger the absolute value of the Zeta potential, the more negative charges the surface carries. Because the particles are all negatively charged, when the surface charge is large, the mutual repulsion force between particles is also large, which will improve the stability of the emulsion system. On the contrary, the stability of emulsions with a small absolute value of the Zeta potential will decrease.

[0052] The mechanical stability of the water-soluble sizing agent for epoxy resin carbon fiber was tested with a high-speed bench centrifuge (model TGL-16B, Shanghai Anting Scientific Instrument Factory). When the particle size was below 180 nm and the speed was 3000 r / min, no delamination was observed after centrifugation at high speed for 10 minutes. When the speed was 1000 r / min and centrifugation was carried out at low speed for 3 h, no obvious delamination was observed either.

[0053] Field emission freeze-dried scanning electron microscope (model JSM-7610F Plus, JEOL, Japan); The emulsion of the water-soluble sizing agent for epoxy resin carbon fiber in the examples was freeze-dried in liquid nitrogen, the cross-section was cut with a cutter, and the cross-section was treated with gold plating to test the particles of the sizing agent emulsion. It can be seen that the obtained emulsion particles have a uniform morphology, and the particle size is similar to the value measured by the laser particle size analyzer, and they are uniform spheres.

[0054] Table 1 Particle size and Zeta potential of the examples

[0055]

[0056] Table 2 Test results of mechanical stability (1000 r / min)

[0057]

[0058]

[0059] Table 3 Test on the application performance of the water-soluble sizing agent for epoxy resin carbon fiber

[0060]

[0061] According to Table 3, comparing the sized carbon fiber tow with the unsized one in the above examples, it was found that the spreading width of the sized carbon fiber tow was significantly improved. This performance index can significantly improve the dispersion ability of the carbon fiber tow in the resin. Also, due to the improved dispersion performance, the carbon fiber and the resin are better combined. Therefore, the tensile strength of the composite material will also increase significantly. The tensile strength of the obtained composite materials has all increased significantly, higher than 3.52 GPa of the unsized tow.

[0062] In Figure 1 , the a line is the infrared spectrum of polyethylene glycol 2000, the b line is the infrared spectrum of the compounded epoxy resin in Experimental Example 2, and the c line is the infrared spectrum of the modified epoxy resin sizing film-forming agent emulsion sample obtained in Experimental Example 2. As can be seen from the figure, at 3371 cm -1 of the a line, the strong absorption broad peak is the stretching vibration peak of -OH in polyethylene glycol. At 3478 cm -1 of the b line, the strong absorption broad peak is the stretching vibration peak of -OH in epoxy resin. However, the peak position has significantly disappeared in the c line, indicating that a reaction has occurred at this point and -OH has been consumed; at 2865 cm -1 of the a lineand the absorption shoulder at 2965 cm of line b -1 The absorption peak at this position is the stretching vibration absorption peak of -CH3. There is a weak absorption peak at 2858 cm of line c -1 with a weak absorption peak; at 2358 cm of line a -1 and at 2088 cm of line b -1 ~1885 cm -1 The strong absorption peak at this position is the bending vibration of -CH2, which disappears significantly at line c, indicating that the -CH2 bond in the sample is well combined; at 1112 cm of line a -1 The strong absorption peak belongs to the stretching vibration of C-O-C. There is a weak absorption peak at 1092 cm of line c -1 with a change in peak position; at 1032 cm of line b -1 The strong absorption peak at this position is generated by the absorption of terminal epoxy groups. There is a weak absorption peak at 1092 cm of line c -1 The above characteristic peaks indicate that there are reactants of polyethylene glycol and epoxy resin in the sample, that is, there are still hydrophilic alcohol hydroxyl groups and hydrophobic epoxy groups after the reaction.

[0063] Figure 3 Figure is the SEM photograph of the surface of carbon fiber after sizing with the sizing agent of Example 1. It can be seen that when the magnification is 2500 times, there are a few grooves on the surface of the carbon fiber. The grooves are not very deep and are distributed relatively evenly. There is obviously a layer of sizing agent attached and the sizing is uniform. After sizing with the sizing agent of Example 1, it can be seen that the carbon fiber filaments can be better dispersed and there are no fuzzes.

[0064] Comparative Example 1

[0065] Weigh 2000 of polyethylene glycol and carry out vacuum distillation on it in a rotary evaporator to completely remove the water molecules in the polyethylene glycol. Weigh phthalic anhydride and polyethylene glycol according to a molar ratio of 1:2.8, and add this mixture to a four-necked split glass reaction kettle equipped with a thermometer, a stirrer, a condenser reflux and nitrogen protection under the condition of pH = 5.0 to carry out the modification grafting of polyethylene glycol. The reaction temperature is 110 °C and the reaction time is 4 h.

[0066] Compound epoxy resins 6004 and E414, where the mass ratio of 6004:E414 is 3:1. According to the epoxy equivalent of 6004 being 185 and the epoxy equivalent of E414 being 220, calculate the epoxy equivalent of the compound epoxy resin to be 194. Add 0.1 g of potassium persulfate to the phthalic anhydride-modified polyethylene glycol prepared above and the compound epoxy resin at a molar ratio of 1:1.2 at 120 °C and react for 3.5 h under nitrogen protection to obtain the sizing agent.

[0067] After emulsification, the size of the obtained sizing agent is 273 nm, the Zeta potential is -13.25, and there is obvious sedimentation after 45 days of placement. Compared with Example 5, mainly when preparing phthalic anhydride-modified polyethylene glycol, the proportion of polyethylene glycol is relatively high, so there will be an excessive amount of unmodified polyethylene glycol reacting with epoxy resin, resulting in more bilateral epoxy groups reacting with polyethylene glycol, reducing the self-emulsifying functional segments. At the same time, it also leads to a larger particle size of the polymerized segments, resulting in a decrease in its stability.

[0068] Comparative Example 2

[0069] Weigh 4000 of polyethylene glycol, carry out reduced-pressure distillation on it in a rotary evaporator to completely remove the water molecules in the polyethylene glycol. Weigh phthalic anhydride and polyethylene glycol in a molar ratio of 1:1.5, and add this mixture to a four-necked separable glass reaction kettle equipped with a thermometer, a stirrer, a condensing reflux, and nitrogen protection at pH = 3.0 to carry out the modification grafting of polyethylene glycol. The reaction temperature is 140 °C and the reaction time is 2 h.

[0070] Compound epoxy resins E51 and E44, where the mass ratio of E51:E44 is 1:2. According to the epoxy equivalent of E51 being 190 and the epoxy equivalent of E44 being 175, calculate the epoxy equivalent of the compounded epoxy resin to be 180. Add 0.1 g of potassium persulfate to the phthalic anhydride-modified polyethylene glycol prepared above and the compounded epoxy resin at a molar ratio of 1:0.6 at 140 °C, and react for 4 h under nitrogen protection to obtain the sizing agent.

[0071] After emulsification, the size of the obtained sizing agent is 170 nm, the Zeta potential is -5.24, and there is obvious sedimentation after 45 days of placement. Compared with Example 3, mainly when preparing phthalic anhydride-modified polyethylene glycol, the proportion of polyethylene glycol is relatively low. After reacting with epoxy resin, the amount of modified polyethylene glycol is significantly less, and the epoxy groups and polyethylene glycol cannot react sufficiently, reducing the self-emulsifying functional segments. The charge carried by the obtained water-soluble carbon fiber sizing agent of epoxy resin is relatively low, resulting in a decrease in its stability.

[0072] The various embodiments in this specification are described in a progressive manner. Each embodiment focuses on the differences from other embodiments. The same or similar parts among the various embodiments can be referred to each other. For the solutions disclosed in the embodiments, since they correspond to the methods disclosed in the embodiments, the description is relatively simple, and the relevant parts can be referred to the description in the method section.

[0073] The foregoing description of the disclosed embodiments enables those skilled in the art to practice or use the present invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Thus, the present invention is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A preparation method of a water-soluble sizing agent for epoxy resin carbon fiber, characterized in that, It includes the following steps: (1) Carry out vacuum distillation on polyethylene glycol in a rotary evaporator to remove water molecules; (2) Add the polyethylene glycol from which water molecules have been removed and phthalic anhydride into a reaction kettle, carry out the modification grafting of polyethylene glycol in an acidic environment, carry out condensation reflux while stirring, and introduce nitrogen for protection to obtain phthalic anhydride-modified polyethylene glycol; (3) Compound two different epoxy resins, calculate the epoxy equivalent to obtain a compounded epoxy resin; (4) Carry out a grafting reaction on the phthalic anhydride-modified polyethylene glycol and the compounded epoxy resin under the action of a catalyst to obtain a water-soluble sizing agent for carbon fiber with self-emulsifying properties for epoxy resin; In step (2), the molar ratio of phthalic anhydride to polyethylene glycol is 1:1.6 - 2.4; In step (3), the epoxy resins are any two of E51, E44, 6004, and F44; In step (3), the epoxy equivalent of the compounded epoxy resin is 180 - 210; In step (1), the molecular weight of the polyethylene glycol is 1000 - 4000; In step (4), the molar ratio of the phthalic anhydride-modified polyethylene glycol to the compounded epoxy resin is 1:0.6 - 1.

4.

2. The preparation method of a water-soluble sizing agent for epoxy resin on carbon fiber according to claim 1, wherein, In step (2), the pH of the acidic environment is 3 - 5; the stirring rate is 180 - 300 r / min.

3. The preparation method of a water-soluble sizing agent for epoxy resin-coated carbon fiber according to claim 1, characterized in that, In step (2), the reaction temperature for the modification grafting is 105 - 140 °C, and the reaction time is 2 - 4 h.

4. The preparation method of a water-soluble sizing agent for epoxy resin-coated carbon fiber according to claim 1, characterized in that, In step (4), the catalyst is selected from one of potassium persulfate and ammonium persulfate.

5. The preparation method of a water-soluble sizing agent for epoxy resin on carbon fiber according to claim 1, characterized in that, In step (4), the reaction temperature for the grafting reaction is 110 - 140 °C, and the reaction time is 2 - 5 h.

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