Stability adjusting method for epoxy resin sizing agent for carbon fibers

Abstract

Disclosed in the present invention is a stability adjusting method for an epoxy resin sizing agent for carbon fibers, specifically comprising the following steps: adding a nonionic surfactant to an epoxy resin sizing agent for carbon fibers until the HLB value of the system is 9.67-13.30, and carrying out ultrasonic dispersion to obtain a highly dispersed and stable epoxy resin sizing agent for carbon fibers. The method of the present invention remarkably improves the stability of epoxy resin sizing agents for carbon fibers, reduces formation of small latex particle precipitates during transportation and storage, and reduces surface defects on carbon fibers undergoing sizing, thus improving the application performance of carbon fiber-reinforced epoxy resin-based composites.

Description

A method for adjusting the stability of carbon fiber epoxy resin sizing agent Technical Field

[0001] The present invention relates to the technical field of polymer materials, and more particularly to a method for adjusting the stability of a carbon fiber epoxy resin sizing agent. Background Art

[0002] Carbon fiber refers to a high-strength, high-modulus inorganic fiber material made from acrylic and viscose fibers through high-temperature oxidation and carbonization, with a carbon content of over 90%. It ranks first among all chemical fibers in terms of high-temperature resistance and is an excellent material for manufacturing high-tech equipment such as aerospace. However, due to its inherent brittleness, a large number of fuzz and surface grooves are generated during production, transportation, and subsequent processing. These factors not only reduce the strength of the carbon fiber itself but also affect the overall mechanical properties of the carbon fiber-reinforced composite material.

[0003] Carbon fiber reinforced thermosetting resin composites have excellent properties such as high specific strength, high specific modulus, corrosion resistance, and lightweight, making them widely used in various fields such as aerospace, sports and leisure. The most commonly used thermosetting resin for carbon fiber reinforced resin is epoxy resin. The mechanical properties of carbon fiber reinforced epoxy resin-based composites are mainly determined by the mechanical properties of the reinforcing carbon fiber and the epoxy resin matrix itself, as well as the interfacial bonding properties between the carbon fiber and the epoxy resin matrix. Therefore, the fiber needs to be sizing treated to improve the poor interfacial bonding between the carbon fiber and the epoxy resin matrix.

[0004] The sizing process is the best surface modification method to improve the interfacial properties of carbon fibers. Carbon fiber epoxy resin sizing agents can fill the many grooves on the carbon fiber surface, improve the strength of the carbon fiber itself, and increase the carbon fiber's bundling and wettability, thereby improving the interface between the carbon fiber and the epoxy resin matrix, and enhancing the interlaminar shear strength and interfacial shear strength of the composite material.

[0005] At present, carbon fiber epoxy resin sizing agent is mainly based on emulsion sizing agent, which is a water-soluble sizing agent formed by adding surfactants and other additives to the main polymer and using water as dispersant. It has the advantages of less pollution, low cost and low residue.

[0006] The stability of carbon fiber epoxy resin sizing agent is an important performance indicator. There is a van der Waals force (attraction) between latex particles, and the van der Waals force causes the liquid particles to attract each other and spontaneously aggregate. Generally speaking, the smaller the emulsion particle size, the better the emulsion stability and the better the sizing uniformity; if the emulsion particle size is too large, it will not only affect the stability of the emulsion, but also affect the sizing uniformity because the large particles are not easy to penetrate between the filaments. In addition, the higher the Zeta potential, the more similar the charge carried by the emulsion particles, and the greater the mutual repulsion between each other; when the repulsive force between the two is greater than the van der Waals force, the liquid droplets are not easy to contact, so the possibility of aggregation is reduced, thereby improving the stability of the emulsion.

[0007] Therefore, how to improve the stability of carbon fiber epoxy resin sizing agent is a problem that needs to be solved urgently by those skilled in the art.

[0008] Summary of the Invention

[0009] In view of this, an object of the present invention is to provide a method for adjusting the stability of a carbon fiber epoxy resin sizing agent to address the deficiencies in the prior art.

[0010] In order to achieve the above object, the present invention adopts the following technical solutions:

[0011] A method for adjusting the stability of a carbon fiber epoxy resin sizing agent specifically comprises the following steps: adding a nonionic surfactant to the carbon fiber epoxy resin sizing agent until the HLB value of the system is 9.67-13.30, and ultrasonically dispersing the mixture to obtain a highly dispersed and stable carbon fiber epoxy resin sizing agent.

[0012] Furthermore, the nonionic surfactant is at least one of Span 40, Tween 40, Tween 80 and Tween 85.

[0013] Furthermore, the above-mentioned nonionic surfactant is Tween 80 and Tween 85 in a mass ratio of 1:2; or, Tween 40 and Tween 85 in a mass ratio of 1:1; or, Span 40 and Tween 40 in a mass ratio of 2:1; or, Span 40 and Tween 80 in a mass ratio of 2:3; or, Span 40 and Tween 85 in a mass ratio of 1:4.

[0014] Furthermore, the amount of the nonionic surfactant is 1% by weight of the carbon fiber epoxy resin sizing agent.

[0015] Furthermore, the ultrasonic dispersion time is 0.5-3 min, preferably 2 min.

[0016] Furthermore, the carbon fiber epoxy resin sizing agent comprises the following raw materials: polyethylene glycol, phthalic anhydride and epoxy resin, with a molar ratio of 1:1:1.

[0017] Furthermore, the above polyethylene glycol is polyethylene glycol 1000.

[0018] The beneficial effect of adopting the above further technical solution is that polyethylene glycol 1000 (PEG1000) is a mixture formed by the condensation of ethylene oxide and water, and its molecular formula is HO(CH2CH2O) n H, wherein n represents the average number of oxyethylene groups.

[0019] Furthermore, the epoxy resin includes epoxy resin E51 and epoxy resin E44.

[0020] The beneficial effect of adopting the above-mentioned further technical solution is that epoxy resin E51 is a thermosetting polymer synthetic material with excellent bonding, corrosion resistance, insulation, and high strength properties. The product has a high epoxy value, low viscosity, and light color. Epoxy resin E44 is a bisphenol A-type liquid epoxy resin, a basic epoxy resin, and a low-toxic, colorless or light yellow viscous liquid.

[0021] Furthermore, the mass ratio of the epoxy resin E51 to the epoxy resin E44 is 2:1.

[0022] The beneficial effect of adopting the above further technical solution is that, according to the epoxy equivalent of epoxy resin E51 being 190 and the epoxy equivalent of epoxy resin E44 being 220, the epoxy equivalent of the compounded epoxy resin is calculated to be 200.

[0023] Furthermore, the preparation method of the above carbon fiber epoxy resin sizing agent specifically includes the following steps:

[0024] (1) Weighing the raw materials according to the molar ratio of the carbon fiber epoxy resin sizing agent;

[0025] (2) subjecting the polyethylene glycol to reduced pressure distillation to obtain anhydrous polyethylene glycol;

[0026] (3) mixing anhydrous polyethylene glycol and phthalic anhydride, adding catalyst A to react, and obtaining phthalic anhydride-modified polyethylene glycol;

[0027] (4) Phthalic anhydride-modified polyethylene glycol and epoxy resin are mixed, and catalyst B is added to react to obtain a carbon fiber epoxy resin sizing agent.

[0028] Furthermore, in the above step (3), catalyst A is toluenesulfonic acid; the reaction is carried out under nitrogen protection at a temperature of 120°C for 2.5 hours; in the above step (4), catalyst B is potassium persulfate; the reaction is carried out under nitrogen protection at a temperature of 125°C for 4 hours.

[0029] The beneficial effect of adopting the above-mentioned further technical solution is that the present invention uses polyethylene glycol modified with phthalic anhydride as a modifier for grafting with epoxy resin. Because the steric hindrance of the molecular structure of phthalic anhydride is large, it can ensure that most of the reactions during the reaction with epoxy resin are mainly one-end grafting reactions, which is conducive to the preparation of a water-soluble carbon fiber epoxy resin sizing agent with one end hydrophobic, one end hydrophilic and self-emulsifying properties.

[0030] It can be seen from the above technical solution that compared with the prior art, the beneficial effects of the present invention are as follows:

[0031] 1. For the application needs of the stability of carbon fiber epoxy resin sizing agent, it is necessary to ensure that the carbon fiber epoxy resin sizing agent prepared has a relatively small emulsion particle size. At the same time, the Zeta potential of the carbon fiber epoxy resin sizing agent is also increased, so that the repulsion between the emulsion particles is increased, and the possibility of emulsion particles gathering and merging is reduced. For this reason, the present invention is used to improve the Zeta potential of the carbon fiber epoxy resin sizing agent emulsion by adding a commonly used surfactant, one or two of which are compounded surfactants. Because the stability of the carbon fiber epoxy resin sizing agent is improved, it is possible to reduce the formation of small latex particle precipitation during transportation and storage time, reduce carbon fiber surface defects after sizing, thereby improving the application performance of carbon fiber reinforced epoxy resin-based composite materials.

[0032] 2. The present invention improves the stability of the carbon fiber epoxy resin sizing agent by increasing its Zeta potential. At the same time, in order to adapt to the application range of the stability of various carbon fiber epoxy resin sizing agents, the present invention selects different surfactants for compounding to meet the needs of carbon fiber epoxy resin sizing agents with different particle sizes.

[0033] 3. The present invention utilizes a surfactant compounding method to adjust the HLB value (hydrophile-lipophile balance) of the system so that the prepared carbon fiber epoxy resin sizing agent has good stability, dispersibility and storage time. In addition, the present invention studies the influence of the HLB value calculated by the compounded surfactant (i.e., the "compound emulsifier" in Figure 1) at different mixing ratios on the stability, interfacial binding, particle size, etc. of the carbon fiber epoxy resin sizing agent on the surface modification of the carbon fiber, and analyzes the effect of the carbon fiber epoxy resin sizing agent on the formation of effective chemical bonds on the carbon fiber surface by analyzing performance tests such as particle size, Zeta potential, SEM and mechanical stability, aiming to establish a stable impregnation system, modify the surface of inert carbon fiber, thereby improving the bundling and dispersibility of the carbon fiber tow. The research work of this part is shown in Figure 1.

[0034] 4. The present invention first adds a compound surfactant to the carbon fiber epoxy resin sizing agent, and then uses ultrasonic dispersion in an aqueous solution system for 0.5-3min to obtain a highly dispersed and stable carbon fiber epoxy resin sizing agent (i.e., the "sizing agent" in Figure 2), and then impregnates the surface treated carbon fiber for sizing, and performs surface gold treatment on the sized carbon fiber. Finally, a field emission scanning electron microscope is used to observe the effect of the carbon fiber surface modification, and the particle size and Zeta potential of the carbon fiber epoxy resin sizing agent are tested to investigate the effect of the HLB value of the compound surfactant on the stability of the carbon fiber epoxy resin sizing agent. The research work of this part is shown in Figure 2. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] FIG1 is a diagram illustrating the emulsification and stabilization process of the carbon fiber epoxy resin sizing agent;

[0036] FIG2 is a diagram illustrating the surface impregnation and modification process of carbon fiber;

[0037] FIG3 is a surface SEM image of a carbon fiber tow after surface treatment, sizing with the carbon fiber epoxy resin sizing agent of Example 2-3, and surface gold addition treatment;

[0038] FIG4 is a physical picture of the carbon fiber epoxy resin sizing agent of Examples 2-6 after storage for 30 days, 60 days, 180 days and 300 days respectively. DETAILED DESCRIPTION

[0039] The following is a clear and complete description of the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the 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.

[0040] Example 1

[0041] A carbon fiber epoxy resin sizing agent comprises the following raw materials: polyethylene glycol 1000, phthalic anhydride and epoxy resin in a molar ratio of 1:1:1; wherein the epoxy resin is obtained by compounding epoxy resin E51 and epoxy resin E44 in a mass ratio of 2:1;

[0042] The preparation method of the above-mentioned carbon fiber epoxy resin sizing agent specifically comprises the following steps:

[0043] (1) Weighing the raw materials according to the molar ratio of the carbon fiber epoxy resin sizing agent;

[0044] (2) placing polyethylene glycol 1000 in a rotary evaporator and performing reduced pressure distillation to completely remove the water molecules therein to obtain anhydrous polyethylene glycol 1000;

[0045] (3) Anhydrous polyethylene glycol 1000 and phthalic anhydride were mixed and placed in a four-mouth separated glass reactor equipped with a thermometer, a stirrer, a condenser reflux and nitrogen protection. Toluenesulfonic acid was added for catalysis and the mixture was heated to 120°C for 2.5 hours to obtain phthalic anhydride modified polyethylene glycol;

[0046] (4) Phthalic anhydride-modified polyethylene glycol and epoxy resin were mixed and placed in a four-mouth separated glass reactor equipped with a thermometer, a stirrer, condensation reflux and nitrogen protection, potassium persulfate was added for catalysis, and the mixture was heated to 125°C for reaction for 4 hours to obtain a carbon fiber epoxy resin sizing agent.

[0047] Example 2

[0048] The stability adjustment method of the carbon fiber epoxy resin sizing agent specifically comprises the following steps: adding 1 wt% of a nonionic surfactant obtained by compounding Tween 80 and Tween 85 in a mass ratio of 1:2 to the carbon fiber epoxy resin sizing agent prepared in Example 1 until the HLB value of the system is 12.30, and ultrasonically dispersing for 1 minute to obtain a highly dispersed and stable carbon fiber epoxy resin sizing agent.

[0049] Example 3

[0050] The stability adjustment method of the carbon fiber epoxy resin sizing agent specifically comprises the following steps: adding 1 wt% of a nonionic surfactant obtained by compounding Tween 40 and Tween 85 in a mass ratio of 1:1 to the carbon fiber epoxy resin sizing agent prepared in Example 1 until the HLB value of the system is 13.30, and ultrasonically dispersing for 2 minutes to obtain a highly dispersed and stable carbon fiber epoxy resin sizing agent.

[0051] Example 4

[0052] The stability adjustment method of the carbon fiber epoxy resin sizing agent specifically comprises the following steps: adding 1 wt% of a nonionic surfactant obtained by compounding Span 40 and Tween 40 in a mass ratio of 2:1 to the carbon fiber epoxy resin sizing agent prepared in Example 1 until the HLB value of the system reaches 9.67, and ultrasonically dispersing for 3 minutes to obtain a highly dispersed and stable carbon fiber epoxy resin sizing agent.

[0053] Example 5

[0054] The stability adjustment method of the carbon fiber epoxy resin sizing agent specifically comprises the following steps: adding 1 wt% of a nonionic surfactant obtained by compounding Span 40 and Tween 80 in a mass ratio of 2:3 to the carbon fiber epoxy resin sizing agent prepared in Example 1 until the HLB value of the system is 11.68, and ultrasonically dispersing for 1.5 minutes to obtain a highly dispersed and stable carbon fiber epoxy resin sizing agent.

[0055] Example 6

[0056] The stability adjustment method of the carbon fiber epoxy resin sizing agent specifically comprises the following steps: adding 1 wt% of a nonionic surfactant obtained by compounding Span 40 and Tween 85 in a mass ratio of 1:4 to the carbon fiber epoxy resin sizing agent prepared in Example 1 until the HLB value of the system is 10.14, and ultrasonically dispersing for 0.5 min to obtain a highly dispersed and stable carbon fiber epoxy resin sizing agent.

[0057] Performance Testing

[0058] 1. Particle size and Zeta potential measurement test

[0059] The carbon fiber epoxy resin sizing agent prepared in Example 1 and the highly dispersed and stable carbon fiber epoxy resin sizing agents prepared in Examples 2-6 were each diluted in distilled water to 50-100 kcps (Kilo Count Per Second). The particle size and zeta potential were then measured using a laser particle size analyzer (NanoBrook 90plus PALS, Brookhaven Instruments, USA). The changes in particle size and zeta potential before and after the addition of the compounded surfactant were compared. The results are shown in Table 1.

[0060] Table 1 Particle size and Zeta potential of carbon fiber epoxy resin sizing agent of Examples 1-6

[0061] As shown in Table 1, compared with Example 1, after adding the compounded surfactant, the zeta potential values ​​of the highly dispersed and stable carbon fiber epoxy resin sizing agents of Examples 2-6 are as high as 35 or above. In addition, in terms of the overall trend, the larger the HLB value, the better the hydrophilicity, and thus the smaller the obtained emulsion particle size, which is more conducive to improving the stability of the carbon fiber epoxy resin sizing agent.

[0062] 2. Mechanical stability test

[0063] The highly dispersed and stable carbon fiber epoxy resin sizing agents prepared in Examples 2-6 were centrifuged at 3000 rpm for 30 minutes using a high-speed desktop centrifuge (TGL-16B, Scientific Instrument Factory, Anting, Shanghai). The delamination was observed at 5, 10, 15, 20, 25, and 30 minutes. The results are shown in Table 2.

[0064] Table 2 Mechanical stability of carbon fiber epoxy resin sizing agent of Examples 2-6

[0065] As shown in Table 2, after the compound surfactant was added, the stability of the carbon fiber epoxy resin sizing agent of Example 2-6 was significantly improved, and no stratification was observed after high-speed centrifugation at 3000 r / min for 30 minutes.

[0066] 3. Sizing effect test

[0067] The highly dispersed and stable carbon fiber epoxy resin sizing agents prepared in Examples 2 and 3 were uniformly applied to surface-treated T300 carbon fiber tows. The sized carbon fiber tows were then subjected to a surface gold-adding treatment. The application effect of the carbon fiber epoxy resin sizing agents was tested using a field emission scanning electron microscope (JSM-7610F Plus, JEOL). The results are shown in Figure 3.

[0068] In Figure 3, Figure 3(a) is a surface SEM image of the carbon fiber tow after surface treatment, sizing with the carbon fiber epoxy resin sizing agent of Example 2 and surface gold addition treatment, and Figure 3(b) is a surface SEM image of the carbon fiber tow after surface treatment, sizing with the carbon fiber epoxy resin sizing agent of Example 3 and surface gold addition treatment.

[0069] As shown in FIG3 , the highly dispersed and stable carbon fiber epoxy resin sizing agents of Example 2 and Example 3 can form a complete coating on the carbon fiber surface, and the dispersion effect on the carbon fiber surface is improved.

[0070] 4. Storage stability test

[0071] The highly dispersed and stable carbon fiber epoxy resin sizing agents prepared in Examples 2-6 were stored for 300 days. The bottom of the sizing agents was observed for sedimentation at 30, 60, 180, and 300 days. The results are shown in FIG4 .

[0072] In FIG4 , “one”, “two”, “three”, “four” and “five” correspond to the highly dispersed and stable carbon fiber epoxy resin sizing agents of Examples 2-6 respectively.

[0073] As shown in FIG4 , within 300 days, there were no sedimented particles at the bottom of the highly dispersed and stable carbon fiber epoxy resin sizing agent of Examples 2-6.

[0074] 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 adjusting the stability of a carbon fiber epoxy resin sizing agent, characterized in that: The specific steps include: A nonionic surfactant is added to the carbon fiber epoxy resin sizing agent until the HLB value of the system is 9.67-13.30, and ultrasonic dispersion is performed to obtain a highly dispersed and stable carbon fiber epoxy resin sizing agent.

2. The method for adjusting the stability of a carbon fiber epoxy resin sizing agent according to claim 1, characterized in that: The nonionic surfactant is at least one of Span 40, Tween 40, Tween 80 and Tween 85.

3. The method for adjusting the stability of a carbon fiber epoxy resin sizing agent according to claim 2, characterized in that: The nonionic surfactant is Tween 80 and Tween 85 in a mass ratio of 1:2; or Tween 40 and Tween 85 in a mass ratio of 1:1; or Span 40 and Tween 40 in a mass ratio of 2:1; or Span 40 and Tween 80 in a mass ratio of 2:3; or Span 40 and Tween 85 in a mass ratio of 1:

4.

4. A method for adjusting the stability of a carbon fiber epoxy resin sizing agent according to any one of claims 1 to 3, characterized in that: The nonionic surfactant is used in an amount of 1% by weight of the carbon fiber epoxy resin sizing agent.

5. The method for adjusting the stability of a carbon fiber epoxy resin sizing agent according to claim 1, characterized in that: The ultrasonic dispersion time is 0.5-3 min.

6. The method for adjusting the stability of a carbon fiber epoxy resin sizing agent according to claim 1, characterized in that: The carbon fiber epoxy resin sizing agent comprises the following raw materials: polyethylene glycol, phthalic anhydride and epoxy resin, with a molar ratio of 1:1:

1.

7. The method for adjusting the stability of a carbon fiber epoxy resin sizing agent according to claim 6, characterized in that: The polyethylene glycol is polyethylene glycol 1000.

8. The method for adjusting the stability of a carbon fiber epoxy resin sizing agent according to claim 6, characterized in that: The epoxy resin includes epoxy resin E51 and epoxy resin E44, with a mass ratio of 2:

1.

9. A method for adjusting the stability of a carbon fiber epoxy resin sizing agent according to any one of claims 6 to 8, characterized in that: The preparation method of the carbon fiber epoxy resin sizing agent specifically comprises the following steps: (1) weighing the raw materials according to the molar ratio of the carbon fiber epoxy resin sizing agent according to any one of claims 6 to 8; (2) subjecting the polyethylene glycol to reduced pressure distillation to obtain anhydrous polyethylene glycol; (3) mixing anhydrous polyethylene glycol and phthalic anhydride, adding catalyst A to react, and obtaining phthalic anhydride-modified polyethylene glycol; (4) The phthalic anhydride-modified polyethylene glycol and the epoxy resin are mixed, and a catalyst B is added to react to obtain the carbon fiber epoxy resin sizing agent.

10. The method for adjusting the stability of a carbon fiber epoxy resin sizing agent according to claim 8, characterized in that: In step (3), the catalyst A is toluenesulfonic acid; the reaction is carried out under nitrogen protection at a temperature of 120° C. for 2.5 hours; in step (4), the catalyst B is potassium persulfate; the reaction is carried out under nitrogen protection at a temperature of 125° C. for 4 hours.

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