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

Abstract

The present invention belongs to the technical field of sizing agents, and discloses a preparation method for an epoxy resin water-soluble carbon fiber sizing agent. One end of a sizing agent in the present invention is a hydrolysable group which can be bonded with -OH on the surfaces of carbon fibers, and the other end thereof is a non-hydrolysable group which can react with resin, such that introducing functional groups in a slurry into the surfaces of the carbon fibers improves the surface activity of the carbon fibers, thus improving the chemical bonding effect of the carbon fibers and a resin matrix. In addition, the sizing agent has a good self-emulsifying function, thus overcoming the problem of stability of emulsion type sizing agents. The self-emulsifying epoxy resin sizing agent has high safety, is environment-friendly and convenient to use, and can select the use time according to processing requirements, so as to be emulsified for use.

Description

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

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

[0002] Carbon fiber composites have been widely recognized for their excellent properties, but their widespread use is limited by the quality, price, and performance stability of carbon fiber composites. This is mainly because carbon fiber will experience friction and wear during subsequent processing, resulting in lint. This not only affects the smooth progress of subsequent processes but also reduces the overall performance of the carbon fiber. Therefore, sizing treatment is required for carbon fiber.

[0003] Sizing agents are a layer of chemical slurry applied to the fiber surface. Sizing is an essential step in carbon fiber production. The primary functionalities of sizing agents include: first, protecting the carbon fiber surface from damage during winding, packaging, and transportation; and shielding the carbon fiber from air, preventing dust and moisture from adsorbing onto the surface. Second, sizing agents effectively enhance the carbon fiber's bundling properties, acting like a binder to hold the fibers together, improving processability and facilitating processing. Furthermore, sizing agents, like coupling agents, can compensate for surface defects, improve the chemical bond between the carbon fiber and the resin, enhance the mechanical properties of the composite, reduce composite preparation time, and improve product quality. Therefore, developing high-performance carbon fiber sizing agents is crucial for improving both carbon fiber quality and composite material performance. However, simple emulsion-based sizing agents, which often combine two immiscible liquids with the addition of surfactants, suffer from poor stability, delamination after prolonged standing, and demulsification during transportation. Furthermore, existing sizing agents suffer from poor interfacial adhesion, resulting in limited improvement in the mechanical properties of carbon fiber materials.

[0004] Therefore, how to provide a sizing agent with good stability, improved interfacial bonding with carbon fibers, and increased carbon fiber strength is a problem that needs to be urgently solved by those skilled in the art.

[0005] Summary of the Invention

[0006] To overcome the shortcomings and deficiencies of the prior art, the present invention provides a method for preparing a water-soluble epoxy resin carbon fiber sizing agent, which has good self-emulsification properties and overcomes the stability issues of emulsion-type sizing agents. Polyethylene glycol modified with phthalic anhydride is used as a modifier and grafted with a compounded epoxy resin to form a modified polyethylene glycol with a hydrophobic epoxy end at one end and a hydrophilic end at the other end, thereby improving the interfacial bonding between the carbon fiber and the epoxy resin.

[0007] In order to achieve the above object, the present invention adopts the following technical solutions:

[0008] A method for preparing an epoxy resin water-soluble carbon fiber sizing agent comprises the following steps:

[0009] (1) distilling polyethylene glycol under reduced pressure in a rotary evaporator to remove water molecules;

[0010] (2) adding polyethylene glycol and phthalic anhydride from which water molecules have been removed into a reaction kettle, performing modification and grafting of polyethylene glycol in an acidic environment, performing condensation and reflux while stirring, and introducing nitrogen protection to obtain phthalic anhydride-modified polyethylene glycol;

[0011] (3) compounding two different epoxy resins to obtain a compounded epoxy resin;

[0012] (4) Phthalic anhydride-modified polyethylene glycol and compounded epoxy resin are subjected to a grafting reaction under the action of a catalyst to obtain an epoxy resin water-soluble carbon fiber sizing agent with self-emulsifying properties.

[0013] Preferably, the molecular weight of the polyethylene glycol in step (1) is 1000-4000.

[0014] Preferably, the molar ratio of phthalic anhydride to polyethylene glycol in step (2) is 1:1.6-2.4.

[0015] Preferably, the pH of the acidic environment in step (2) is 3-5; and the stirring rate is 180-300 r / min.

[0016] The beneficial effects of the above technical solution are: too high a stirring speed is not conducive to polymerization, while too low a stirring speed will result in poor dispersion and incomplete polymerization.

[0017] Preferably, the reaction temperature of the modified grafting in step (2) is 105-140° C., and the reaction time is 2-4 h.

[0018] Preferably, the epoxy resin in step (3) includes E51, E44, 6004, and F44.

[0019] Preferably, the epoxy equivalent of the compounded epoxy resin in step (3) is 180-210.

[0020] The flexibility and heat resistance of a single epoxy resin cannot meet the requirements for preparing subsequent composite materials. The present invention selects different epoxy resins for compounding to impart suitable flexibility and adhesion to the sizing agent. The epoxy equivalent weight of the compounded epoxy resin is calculated based on the epoxy equivalent weights of the selected different epoxy resins and their ratios, and then the molar ratio of the compounded epoxy resin to the phthalic anhydride-modified polyethylene glycol is calculated.

[0021] 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.

[0022] Preferably, the catalyst in step (4) is selected from potassium persulfate and ammonium persulfate.

[0023] Preferably, the reaction temperature of the grafting reaction in step (4) is 110-140° C., and the reaction time is 2-5 h.

[0024] In the present invention, the equation for the reaction of phthalic anhydride-modified polyethylene glycol is as follows:

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

[0026] It can be seen from the above technical solution that, compared with the prior art, the present invention provides a method for preparing an epoxy resin water-soluble carbon fiber sizing agent, which has the following beneficial effects:

[0027] (1) The aqueous sizing agent of the present invention has good self-emulsification function, which overcomes the stability problem of emulsion-type sizing agents. The epoxy resin is compounded to meet the requirements of the sizing agent having good adhesion and flexibility. At the same time, one end of the sizing agent of the present invention is a hydrolyzable group that can combine with the -OH on the carbon fiber surface, and the other end is a non-hydrolyzable group that can react with the resin, introducing the functional groups in the slurry into the carbon fiber surface, increasing the activity of the carbon fiber surface, and then increasing the chemical bonding between the carbon fiber and the resin matrix.

[0028] (2) The present invention utilizes polyethylene glycol modified with phthalic anhydride as a modifier for grafting with epoxy resin. Because the molecular structure of phthalic anhydride has a large steric hindrance, it can ensure that during the reaction with epoxy resin, most of the reactions are mainly one-end grafting reactions, which is beneficial for improving the preparation of a self-emulsifying epoxy resin water-soluble carbon fiber sizing agent with one hydrophobic end and one hydrophilic end. This self-emulsifying epoxy resin sizing agent is highly safe, environmentally friendly, and easy to use. The time of use can be selected according to processing needs and emulsified. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are merely embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the provided drawings without paying any creative work.

[0030] FIG1 is an infrared spectrum of each substance in Example 2; wherein: a-polyethylene glycol 2000, b-compounded epoxy resin, c-epoxy resin water-soluble carbon fiber sizing agent.

[0031] FIG2 is a SEM photograph of the epoxy resin water-soluble carbon fiber sizing agent of Example 4.

[0032] FIG3 is a SEM photograph of the carbon fiber surface after sizing with the epoxy resin water-soluble carbon fiber sizing agent of Example 1. DETAILED DESCRIPTION

[0033] The following is a clear and complete description of the technical solutions in the embodiments of the present invention. Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making any creative efforts are within the scope of protection of the present invention.

[0034] Example 1

[0035] Weigh 1000 polyethylene glycol and distill it under reduced pressure on a rotary evaporator to completely remove the water molecules in the polyethylene glycol. Weigh phthalic anhydride and polyethylene glycol at a molar ratio of 1:1.6. This mixture, at a pH of 4.0, is added to a four-necked glass reactor equipped with a thermometer, a stirrer, reflux, and nitrogen protection for polyethylene glycol modification and grafting. The reaction temperature is 115°C and the reaction time is 2.5 hours.

[0036] Epoxy resins E51 and E44 were compounded at a mass ratio of E51:E44 of 2:1. Based on the epoxy equivalent weights of E51 being 190 and E44 being 220, the epoxy equivalent weight of the compounded epoxy resin was calculated to be 200. The phthalic anhydride-modified polyethylene glycol prepared above was added to the compounded epoxy resin in a molar ratio of 1:1. 0.1 g of potassium persulfate was added and the mixture was reacted at 125°C under nitrogen for 4 hours to obtain an epoxy resin water-soluble carbon fiber sizing agent.

[0037] Example 2

[0038] Weigh polyethylene glycol 2000 and distill it under reduced pressure in a rotary evaporator to completely remove the water molecules in the polyethylene glycol. Weigh phthalic anhydride and polyethylene glycol at a molar ratio of 1:2. This mixture, at a pH of 3.5, is added to a four-necked glass reactor equipped with a thermometer, a stirrer, reflux, and nitrogen protection for polyethylene glycol modification and grafting. The reaction temperature is 125°C and the reaction time is 3 hours.

[0039] Epoxy resins E51 and 6004 were compounded at a mass ratio of 1:1. Based on the epoxy equivalent weights of E51 (190) and 6004 (185), the epoxy equivalent weight of the compounded epoxy resin was calculated to be 187. The phthalic anhydride-modified polyethylene glycol prepared above was added to the compounded epoxy resin in a molar ratio of 1:0.8. 0.1 g of potassium persulfate was added to the mixture at 110°C and the mixture was reacted under nitrogen for 5 hours to obtain an epoxy resin water-soluble carbon fiber sizing agent.

[0040] Example 3

[0041] Weigh polyethylene glycol 4000 and distill it under reduced pressure on a rotary evaporator to completely remove the water molecules in the polyethylene glycol. Weigh phthalic anhydride and polyethylene glycol at a molar ratio of 1:1.8. This mixture, at a pH of 3.0, is added to a four-port glass reactor equipped with a thermometer, a stirrer, reflux, and nitrogen protection for polyethylene glycol modification and grafting. The reaction temperature is 140°C and the reaction time is 2 hours.

[0042] Epoxy resins E51 and E44 were compounded at a mass ratio of E51:E44 of 1:2. Based on the epoxy equivalent weights of E51 being 190 and E44 being 175, the epoxy equivalent weight of the compounded epoxy resin was calculated to be 180. The phthalic anhydride-modified polyethylene glycol prepared above was added to the compounded epoxy resin in a molar ratio of 1:0.6. 0.1 g of potassium persulfate was added and the mixture was reacted at 140°C under nitrogen for 4 hours to obtain an epoxy resin water-soluble carbon fiber sizing agent.

[0043] Example 4

[0044] Weigh 1000 polyethylene glycol and distill it under reduced pressure on a rotary evaporator to completely remove the water molecules in the polyethylene glycol. Weigh phthalic anhydride and polyethylene glycol at a molar ratio of 1:2.4. This mixture, at a pH of 4.5, is added to a four-necked glass reactor equipped with a thermometer, a stirrer, reflux, and nitrogen protection for the polyethylene glycol modification grafting. The reaction temperature is 105°C and the reaction time is 4 hours.

[0045] Epoxy resins E51 and E414 were compounded at a mass ratio of E51:E414 of 1:2. Based on the epoxy equivalent weights of E51 being 190 and E414 being 220, the epoxy equivalent weight of the compounded epoxy resin was calculated to be 210. The phthalic anhydride-modified polyethylene glycol prepared above was added to the compounded epoxy resin in a molar ratio of 1:1.4. 0.1 g of potassium persulfate was added to the mixture at 130°C and the mixture was reacted under nitrogen for 3 hours to obtain an epoxy resin water-soluble carbon fiber sizing agent.

[0046] Example 5

[0047] Weigh polyethylene glycol 2000 and distill it under reduced pressure on a rotary evaporator to completely remove the water molecules in the polyethylene glycol. Weigh phthalic anhydride and polyethylene glycol at a molar ratio of 1:2.2. This mixture, at a pH of 5.0, is added to a four-necked glass reactor equipped with a thermometer, stirrer, reflux, and nitrogen protection for polyethylene glycol modification and grafting. The reaction temperature is 110°C and the reaction time is 4 hours.

[0048] Epoxy resin 6004 and E414 were compounded at a mass ratio of 6004:E414 of 3:1. Based on the epoxy equivalent weight of 6004 being 185 and the epoxy equivalent weight of E414 being 220, the epoxy equivalent weight of the compounded epoxy resin was calculated to be 194. The phthalic anhydride-modified polyethylene glycol prepared above was added to the compounded epoxy resin in a molar ratio of 1:1.2. 0.1 g of potassium persulfate was added and the mixture was reacted at 120°C under nitrogen for 3.5 hours to obtain an epoxy resin water-soluble carbon fiber sizing agent.

[0049] Test method:

[0050] This test used a NanoBrook 90plus PALS laser particle size analyzer from Brookhaven Instruments (USA) to measure the particle size and zeta potential of the test samples. In terms of emulsion stability, emulsions with a particle size range of 70-180 nm are highly stable, exhibiting no sedimentation after 3-6 months. However, for particles larger than 200 nm, the chance of particle collisions increases, leading to decreased stability and some sedimentation after 3 months. Therefore, the optimal emulsion particle size is considered to be less than 180 nm. Zeta potential measurements show that all emulsions have a negative charge, ranging from -40 to -10. Zeta potential values ​​with large absolute values ​​indicate a high level of negative surface charge. Because all particles are negatively charged, a high surface charge creates a greater repulsion between particles, which improves the stability of the emulsion system. Conversely, a low absolute zeta potential value reduces stability.

[0051] The mechanical stability of the epoxy resin water-soluble carbon fiber sizing agent was tested using a high-speed desktop centrifuge (TGL-16B, Shanghai Anting Scientific Instrument Factory) at 3000 r / min for 10 minutes without any stratification when the particle size was below 180 nm. No obvious stratification was observed when the particle size was below 180 nm. No obvious stratification was observed when the particle size was below 180 nm after 3000 r / min or 3 hours after 1000 r / min.

[0052] Field emission freeze-drying scanning electron microscopy (JSM-7610FPlus, JEOL); an epoxy resin water-soluble carbon fiber sizing agent emulsion from the example was freeze-dried in liquid nitrogen, cut with a knife, and subjected to a gold-plated treatment to analyze the particles of the sizing agent emulsion. The resulting emulsion particles exhibited uniform morphology, with a size close to that measured by a laser particle size analyzer, indicating uniform spherical shape.

[0053] Table 1 Particle size and Zeta potential of the examples

[0054] Table 2 Mechanical stability test results (1000r / min)

[0055] Table 3 Application performance test of epoxy resin water-soluble carbon fiber sizing agent

[0056] According to Table 3, the sizing and unsizing of the carbon fiber tows in the above examples show that the width of the carbon fiber tows is significantly improved after sizing. This performance index can significantly improve the dispersion ability of the carbon fiber tows in the resin. Because of the improved dispersion performance, the carbon fiber filaments are better combined with the resin, and the tensile strength of the composite material is also significantly increased. The tensile strength of the resulting composite material is significantly improved, higher than the 3.52GPa of the unsizing tow.

[0057] In Figure 1, line a is the infrared spectrum of polyethylene glycol 2000, line b is the infrared spectrum of the epoxy resin compounded in Experimental Example 2, and line c 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 line a at 3371 cm -1 The strong absorption broad peak is the stretching vibration peak of -OH in polyethylene glycol, at line b at 3478 cm -1 The strong absorption broad peak at 2865cm is the stretching vibration peak of -OH in epoxy resin, but the peak position in line c obviously disappears, indicating that the sample reacts at this position and -OH is consumed; at line a at 2865cm -1 and line b 2965cm -1 The absorption shoulder peak is the stretching vibration absorption peak of -CH3, at c line 2858cm -1 A weak absorption peak is shown at 2358cm -1 and line b 2088cm -1 ~1885cm -1 The strong absorption peak at 1112cm is the bending vibration of -CH2, which disappears obviously at the c line, indicating that the sample-CH2 bond is well combined; -1 The strong absorption peak at 1092 cm is attributed to the stretching vibration of COC. -1There is a weak absorption peak at 1032cm -1 The strong absorption peak is caused by the absorption of the end epoxy group, at the c line 1092cm -1 The above characteristic peaks indicate that the sample contains the reactants of polyethylene glycol and epoxy resin, that is, it still has hydrophilic alcohol hydroxyl groups and hydrophobic epoxy groups after the reaction.

[0058] Figure 3 is an SEM photograph of the carbon fiber surface after sizing with the sizing agent of Example 1. As can be seen, at a magnification of 2500x, the carbon fiber surface has a few grooves, which are not very deep and are relatively evenly distributed, indicating a clear layer of sizing agent and uniform sizing. After sizing with the sizing agent of Example 1, the carbon fiber filaments are well dispersed and free of fuzz.

[0059] Comparative Example 1

[0060] Weigh polyethylene glycol 2000 and distill it under reduced pressure on a rotary evaporator to completely remove the water molecules in the polyethylene glycol. Weigh phthalic anhydride and polyethylene glycol at a molar ratio of 1:2.8. This mixture, at a pH of 5.0, is added to a four-necked glass reactor equipped with a thermometer, a stirrer, reflux, and nitrogen protection for polyethylene glycol modification and grafting. The reaction temperature is 110°C and the reaction time is 4 hours.

[0061] Epoxy resins 6004 and E414 were compounded at a mass ratio of 6004:E414 of 3:1. Based on the epoxy equivalent weights of 6004 being 185 and E414 being 220, the epoxy equivalent weight of the compounded epoxy resin was calculated to be 194. The phthalic anhydride-modified polyethylene glycol prepared above was added to the compounded epoxy resin in a molar ratio of 1:1.2. 0.1 g of potassium persulfate was added and the mixture was reacted at 120°C under nitrogen for 3.5 hours to obtain a sizing agent.

[0062] After emulsification, the obtained sizing agent had a particle size of 273 nm and a zeta potential of -13.25. After being placed for 45 days, it had obvious sedimentation. Compared with Example 5, the main reason is that when preparing the phthalic anhydride-modified polyethylene glycol, the proportion of polyethylene glycol is relatively high, so there will be excessive unmodified polyethylene glycol to react with the epoxy resin, resulting in a relatively large number of double-sided epoxy groups reacting with the polyethylene glycol, reducing the segments with self-emulsification function, and also resulting in larger segment particle size after polymerization, resulting in reduced stability.

[0063] Comparative Example 2

[0064] Weigh polyethylene glycol 4000 and distill it under reduced pressure on a rotary evaporator to completely remove the water molecules in the polyethylene glycol. Weigh phthalic anhydride and polyethylene glycol at a molar ratio of 1:1.5. This mixture, at a pH of 3.0, is added to a four-necked glass reactor equipped with a thermometer, a stirrer, reflux, and nitrogen protection for polyethylene glycol modification and grafting. The reaction temperature is 140°C and the reaction time is 2 hours.

[0065] Epoxy resins E51 and E44 were compounded at a mass ratio of 1:2. Based on the epoxy equivalent weights of E51 (190) and E44 (175), the epoxy equivalent weight of the compounded epoxy resin was calculated to be 180. The phthalic anhydride-modified polyethylene glycol prepared above and the compounded epoxy resin were added in a molar ratio of 1:0.6, and 0.1 g of potassium persulfate was added at 140°C. The mixture was reacted under nitrogen for 4 hours to obtain a sizing agent.

[0066] After emulsification, the resulting sizing agent had a particle size of 170 nm and a Zeta potential of -5.24. After 45 days of storage, significant sedimentation occurred. Compared with Example 3, the main problem is that the proportion of polyethylene glycol in the preparation of phthalic anhydride-modified polyethylene glycol is relatively low. After reacting with the epoxy resin, the amount of modified polyethylene glycol is significantly small, and the epoxy group cannot fully react with the polyethylene glycol, resulting in a reduction in the number of self-emulsifying chain segments. The resulting epoxy resin water-soluble carbon fiber sizing agent has a low charge, which reduces its stability.

[0067] The various embodiments in this specification are described in a progressive manner, with each embodiment focusing on the differences from other embodiments. Reference can be made to the common and similar parts between the various embodiments. 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 method section.

[0068] The above description of the disclosed embodiments is intended to enable one skilled in the art to implement or use the present invention. Various modifications to these embodiments will be readily apparent to one 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. Therefore, the present invention is not limited to the embodiments shown herein but is intended to conform to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for preparing an epoxy resin water-soluble carbon fiber sizing agent, characterized in that: The following steps are involved: (1) distilling polyethylene glycol under reduced pressure in a rotary evaporator to remove water molecules; (2) adding polyethylene glycol and phthalic anhydride from which water molecules have been removed into a reaction kettle, performing modification and grafting of polyethylene glycol in an acidic environment, performing condensation and reflux while stirring, and introducing nitrogen protection to obtain phthalic anhydride-modified polyethylene glycol; (3) compounding two different epoxy resins, calculating the epoxy equivalent, and obtaining a compounded epoxy resin; (4) The phthalic anhydride-modified polyethylene glycol and the compounded epoxy resin are subjected to a grafting reaction under the action of a catalyst to obtain an epoxy resin water-soluble carbon fiber sizing agent with self-emulsifying properties.

2. The method for preparing a water-soluble epoxy resin carbon fiber sizing agent according to claim 1, characterized in that: The molecular weight of the polyethylene glycol in step (1) is 1000-4000.

3. The method for preparing a water-soluble epoxy resin carbon fiber sizing agent according to claim 1, characterized in that: The molar ratio of phthalic anhydride to polyethylene glycol in step (2) is 1:1.6-2.

4.

4. The method for preparing a water-soluble epoxy resin carbon fiber sizing agent according to claim 1, characterized in that: The pH of the acidic environment in step (2) is 3-5; the stirring rate is 180-300 r / min.

5. The method for preparing a water-soluble epoxy resin carbon fiber sizing agent according to claim 1, characterized in that: The reaction temperature of the modified grafting in step (2) is 105-140° C., and the reaction time is 2-4 hours.

6. The method for preparing a water-soluble epoxy resin carbon fiber sizing agent according to claim 1, characterized in that: The epoxy resin in step (3) includes E51, E44, 6004, and F44.

7. The method for preparing a water-soluble epoxy resin carbon fiber sizing agent according to claim 1, characterized in that: The epoxy equivalent of the compounded epoxy resin in step (3) is 180-210.

8. The method for preparing a water-soluble epoxy resin carbon fiber sizing agent according to claim 1, characterized in that: The molar ratio of the phthalic anhydride modified polyethylene glycol to the compounded epoxy resin in step (4) is 1:0.6-1.

4.

9. The method for preparing a water-soluble epoxy resin carbon fiber sizing agent according to claim 1, characterized in that: The catalyst in step (4) is selected from potassium persulfate and ammonium persulfate.

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

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