A method for high-concentration and stable dispersion of carbon fiber

Abstract

The invention discloses a carbon fiber high-concentration stable dispersion method, comprising the following steps: step 1, configuring an alkaline solution with a concentration of 0.5-1.5 mol / L, adding alkali lignin to the alkaline solution to form a mixed solution; wherein the concentration of the alkali lignin in the mixed solution is 1-2 wt%; step 2, heating the mixed solution to 60-70 ° C, then adding urea with a concentration of 0.3-0.8 wt% to the mixed solution to obtain a dispersion; step 3, heating to 80-100 ° C, adding carbon fiber to a cellulose suspension and stirring, ultrasonic stirring treatment for 1-3 minutes to complete the dispersion of carbon fiber. The present invention can achieve efficient dispersion of carbon fiber and has the characteristics of simplicity and convenience.

Description

Technical Field

[0001] The present invention relates to the technical field of carbon fiber applications, and in particular to a method for high-concentration and stable dispersion of carbon fibers. Background Art

[0002] As part of a proton exchange membrane fuel cell (PEMFC), the gas diffusion layer (GDL) supports the catalyst layer and collects current. Currently, carbon fiber paper is the preferred material for GDLs. Carbon fiber is a superfiber material composed of over 90% carbon. It offers advantages such as high conductivity, high modulus, high strength, and corrosion resistance. Carbon fiber paper is typically made from any of polypropylene, asphalt, or cellulose-based materials, with a fiber diameter of 5-20 μm and a length of 4-20 mm. The surface of carbon fiber exhibits a chaotic graphite structure with grooves and distinct fissures. This rough surface results in high interfiber friction and difficulty separating individual fibers. Carbon fibers are connected by non-polar covalent bonds, resulting in a low number of surface active groups, making them less wettable by water, prone to flocculation in water, and poor dispersion. Furthermore, unlike plant fibers, carbon fibers lack hydrogen bonding, resulting in a lack of interfiber bonding strength, making them difficult to shape and form into paper. Therefore, improving interfiber bonding strength is crucial for wet-process carbon fiber papermaking. However, due to the low surface activity of carbon fiber, it is insoluble in water, difficult to combine, and difficult to paper into shape. Therefore, the key to papermaking carbon fiber paper is to uniformly disperse the carbon fiber in the water phase and improve the bonding strength between the fibers. Summary of the Invention

[0003] The purpose of the present invention is to provide a method for dispersing carbon fibers at a high concentration and in a stable manner. The present invention can achieve efficient dispersion of carbon fibers and is simple and convenient.

[0004] The technical solution of the present invention is a method for high-concentration and stable dispersion of carbon fibers, comprising the following steps:

[0005] Step 1: preparing an alkaline solution with a concentration of 0.5-1.5 mol / L, and adding alkali lignin to the alkaline solution to form a mixed solution; wherein the concentration of the alkali lignin in the mixed solution is 1-2 wt%;

[0006] Step 2: heating the mixed solution to 60-70° C., and then adding urea with a concentration of 0.3-0.8 wt % to the mixed solution to obtain a dispersion;

[0007] Step 3: Raise the temperature to 80-100° C., add the carbon fibers into the cellulose suspension and stir, and perform ultrasonic stirring for 1-3 minutes to disperse the carbon fibers.

[0008] In the above-mentioned high-concentration stable dispersion method of carbon fibers, in step 1, the alkaline solution is a sodium hydroxide solution with a concentration of 1 mol / L.

[0009] In the aforementioned high-concentration stable dispersion method for carbon fibers, the concentration of the alkali lignin is 1.5 wt%.

[0010] In the aforementioned high-concentration stable dispersion method for carbon fibers, in step 2, the temperature at which the mixed solution is heated is 65°C.

[0011] In the aforementioned high-concentration stable dispersion method for carbon fibers, in step 2, the concentration of urea is 0.5 wt %.

[0012] In the aforementioned high-concentration stable dispersion method for carbon fibers, in step 3, the temperature of the ultrasonic stirring is 90°C.

[0013] In the aforementioned high-concentration stable dispersion method for carbon fibers, in step 3, the ultrasonic stirring time is 2 minutes.

[0014] In the aforementioned high-concentration stable dispersion method for carbon fibers, in step 3, the power of the ultrasonic stirring is 500W.

[0015] In the aforementioned high-concentration and stable dispersion method for carbon fibers, the length of the carbon fibers is 4-8 mm.

[0016] Compared with the prior art, the present invention first configures an alkaline solution of alkali lignin, then heats it and adds urea to form an alkali lignin-urea alkaline solution system. Under this system, the active groups of the alkali lignin are used to modify the carbon fibers, thereby increasing the surface hydrophilic groups and the surface roughness structure. At the same time, under the action of heating and ultrasonic stirring, the viscosity of the alkali lignin-urea alkaline solution system decreases with increasing temperature, thereby increasing the dispersion speed of the carbon fibers, reducing the interaction force between the carbon fibers, and reducing the internal friction between the carbon fibers, thereby achieving rapid dispersion of the carbon fibers under the influence of multiple factors. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 is a dispersion diagram of carbon fibers in the embodiment;

[0018] Figure 2 Statistical graph of the uniformity of dispersed carbon fiber papermaking in Examples 3-6 and Comparative Example 2;

[0019] Figure 3 Schematic diagram of the dispersed carbon fiber stability index of Examples 3-6 and Comparative Example 2. DETAILED DESCRIPTION

[0020] The present invention will be further described below with reference to the accompanying drawings and examples, but they are not intended to limit the present invention.

[0021] Example 1: A method for high-concentration and stable dispersion of carbon fibers, comprising the following steps:

[0022] Step 1: preparing an alkaline solution with a concentration of 0.5 mol / L, and adding alkali lignin to the alkaline solution to form a mixed solution; wherein the concentration of the alkali lignin in the mixed solution is 1 wt%;

[0023] Step 2: heating the mixed solution to 60° C., and then adding 0.3 wt % urea to the mixed solution to obtain a dispersion;

[0024] Step 3: Heat to 80°C, add carbon fibers to the cellulose suspension, and stir. Ultrasonic stirring is performed for 3 minutes to disperse the carbon fibers. In this step, the carbon fibers are 4 mm long and the ultrasonic stirring power is 500W.

[0025] Example 2: A method for high-concentration and stable dispersion of carbon fibers, comprising the following steps:

[0026] Step 1: preparing an alkaline solution with a concentration of 0.75 mol / L, and adding alkali lignin to the alkaline solution to form a mixed solution; wherein the concentration of the alkali lignin in the mixed solution is 1.5 wt%;

[0027] Step 2: heating the mixed solution to 65° C., and then adding 0.3 wt % urea to the mixed solution to obtain a dispersion;

[0028] Step 3: Heat to 80°C, add carbon fibers to the cellulose suspension, and stir. Ultrasonic stirring is performed for 2 minutes to disperse the carbon fibers. In this step, the carbon fibers are 6 mm long and the ultrasonic stirring power is 500W.

[0029] Example 3: A method for high-concentration and stable dispersion of carbon fibers, comprising the following steps:

[0030] Step 1: preparing an alkaline solution with a concentration of 1 mol / L, and adding alkali lignin to the alkaline solution to form a mixed solution; wherein the concentration of the alkali lignin in the mixed solution is 2 wt%;

[0031] Step 2: heating the mixed solution to 70° C., and then adding 0.5 wt % urea to the mixed solution to obtain a dispersion;

[0032] Step 3: Heat to 85°C, add carbon fibers to the cellulose suspension, stir, and perform ultrasonic stirring for 2 minutes to disperse the carbon fibers. In this step, the carbon fibers are 8 mm long and the ultrasonic stirring power is 500W.

[0033] Example 4: A method for high-concentration and stable dispersion of carbon fibers, comprising the following steps:

[0034] Step 1: preparing an alkaline solution with a concentration of 0.75 mol / L, and adding alkali lignin to the alkaline solution to form a mixed solution; wherein the concentration of the alkali lignin in the mixed solution is 2 wt%;

[0035] Step 2: heating the mixed solution to 60° C., and then adding 0.5 wt % urea to the mixed solution to obtain a dispersion;

[0036] Step 3: Heat to 100°C, add carbon fibers to the cellulose suspension, stir, and perform ultrasonic stirring for 1 minute to disperse the carbon fibers. In this step, the carbon fibers are 6 mm long and the ultrasonic stirring power is 500W.

[0037] Example 5: A method for high-concentration and stable dispersion of carbon fibers, comprising the following steps:

[0038] Step 1: preparing an alkaline solution with a concentration of 1 mol / L, and adding alkali lignin to the alkaline solution to form a mixed solution; wherein the concentration of the alkali lignin in the mixed solution is 1.5 wt%;

[0039] Step 2: heating the mixed solution to 65° C., and then adding urea with a concentration of 1.5 wt % to the mixed solution to obtain a dispersion;

[0040] Step 3: Heat to 100°C, add carbon fibers to the cellulose suspension, stir, and perform ultrasonic stirring for 1 minute to disperse the carbon fibers. In this step, the carbon fibers are 6 mm long and the ultrasonic stirring power is 500W.

[0041] Example 6: A method for high-concentration and stable dispersion of carbon fibers, comprising the following steps:

[0042] Step 1: preparing an alkaline solution with a concentration of 1 mol / L, and adding alkali lignin to the alkaline solution to form a mixed solution; wherein the concentration of the alkali lignin in the mixed solution is 1.5 wt%;

[0043] Step 2: heating the mixed solution to 65° C., and then adding 0.5 wt % urea to the mixed solution to obtain a dispersion;

[0044] Step 3: Heat to 90°C, add carbon fibers to the cellulose suspension, stir, and perform ultrasonic stirring for 2 minutes to disperse the carbon fibers. In this step, the carbon fibers are 6 mm long and the ultrasonic stirring power is 500W.

[0045] Comparative Example 1: Dispersion of untreated carbon fibers in water.

[0046] Comparative Example 2: Prepare 1 mol / L sodium hydroxide solution, add carbon fiber and stir for 30 minutes.

[0047] Comparative Example 3: 1 mol / L sodium hydroxide solution was prepared, carbon fiber was added and ultrasonic stirring was performed for 15 minutes at a power of 500W.

[0048] The applicant has demonstrated the dispersed carbon fibers in Examples 1-8 and Comparative Examples 1 and 2. Figure 1 As shown. Figure 1 It can be seen that the undispersed carbon fibers in Comparative Example 1 show agglomeration in the aqueous phase. Comparative Example 1 uses conventional alkali solution treatment, and there is still obvious agglomeration, and the dispersion is not uniform. Comparative Example 2 uses alkali solution and ultrasonic treatment. Although the dispersibility is greatly improved compared with Comparative Example 2, the ultrasonic time is long, the noise is large, and re-agglomeration is easy to occur after ultrasonic treatment. The carbon fiber dispersion shown in Examples 1-6 of the present invention is greatly improved compared with Comparative Examples 1-3, and the carbon fibers are evenly dispersed. Among them, the preferred parameters of Example 6 achieve the best dispersion effect.

[0049] Furthermore, papermaking was carried out using the dispersed carbon fibers in Examples 3-6 and Comparative Example 2. The preparation of the wet paper web is to filter the carbon fibers in each group of suspensions, disperse them evenly into two parts, add 1g of APAM to each of the two parts, add 800mL of 80°C hot water and 600mL of cold water to each part to help disperse the carbon fibers, and then put the two parts into a deflaking machine at the same time for deflaking. After deflaking for 15 minutes, 0.7g of PVA fiber and 600mL of 80°C hot water were evenly added to the two suspensions, and the deflaking was continued for 5 minutes before being taken out. The two groups were poured into a paper sheet forming machine at the same time for papermaking. Drying after papermaking: First, use filter paper to absorb the moisture on the surface of the carbon fiber paper, then remove the wet paper web and put it into a wire mesh, place it in a flat dryer to dry for 15 minutes, then take it out, and place it in a flat vulcanizer for hot pressing for 10 minutes to obtain the carbon fiber paper with the measured data. The uniformity of each group of papermaking is then statistically analyzed, and the structure is as follows: Figure 2 As shown. Figure 2 It can be found that the uniformity of the paper prepared in Examples 3-6 increases steadily. This is because the carbon fiber pretreatment of the present application can increase the surface hydrophilic groups and surface roughness structure, improve its hydrophilicity, and make the carbon fiber more evenly dispersed in the suspension, thereby increasing the uniformity of the papermade carbon fiber paper.

[0050] Furthermore, the stability index test of the dispersed carbon fibers in Examples 3-6 and Comparative Example 2 was conducted, and their stability was measured by a multiple light scattering instrument. During the test, about 20 mL of the dispersed sample was slowly added to a transparent quartz sample bottle, and the prepared sample pool was gently picked up vertically, adjusted in the direction, and placed in a turbiscan room at a temperature of 30°C. The Turbisoft shortcut was double-clicked, and the sample was tested according to the TurbiscanLab stability analyzer SOP operating procedures. The results are as follows: Figure 3 As shown. Figure 3 It can be seen that the methods of Examples 3-6 have a significant promoting effect on reducing the suspension stability index, and the promoting effect is best in Example 6.

[0051] In summary, the present invention first configures an alkaline solution of alkali lignin, then heats it and adds urea to form an alkali lignin-urea alkaline solution system, thereby using the active groups of alkali lignin to modify the carbon fibers in this system, thereby increasing the surface hydrophilic groups and the surface roughness structure, and at the same time, under the action of heating and ultrasonic stirring, the viscosity of the alkali lignin-urea alkaline solution system decreases with increasing temperature, thereby increasing the dispersion speed of the carbon fibers, reducing the interaction force between the carbon fibers, and reducing the internal friction between the carbon fibers, thereby achieving rapid dispersion of the carbon fibers under the influence of multiple factors.

Claims

1. A method for high-concentration and stable dispersion of carbon fibers, characterized by: The steps include: Step 1: preparing an alkaline solution with a concentration of 0.5-1.5 mol / L, and adding alkali lignin to the alkaline solution to form a mixed solution; wherein the concentration of the alkali lignin in the mixed solution is 1-2 wt%; Step 2: heating the mixed solution to 60-70° C., and then adding urea with a concentration of 0.3-0.8 wt % to the mixed solution to obtain a dispersion; Step 3: Raise the temperature to 80-100° C., add the carbon fibers into the dispersion and stir, and perform ultrasonic stirring for 1-3 minutes to complete the dispersion of the carbon fibers.

2. The method for high-concentration and stable dispersion of carbon fibers according to claim 1, characterized in that: In step 1, the alkaline solution is a sodium hydroxide solution with a concentration of 1 mol / L.

3. The method for high-concentration and stable dispersion of carbon fibers according to claim 1, wherein: The concentration of the alkali lignin is 1.5 Wt%.

4. The method for high-concentration and stable dispersion of carbon fibers according to claim 1, wherein: In step 2, the mixed solution is heated to 65°C.

5. The method for high-concentration and stable dispersion of carbon fibers according to claim 1, wherein: In step 2, the concentration of urea is 0.5 wt%.

6. The method for high-concentration and stable dispersion of carbon fibers according to claim 1, characterized in that: In step 3, the temperature of the ultrasonic stirring is 90°C.

7. The method for high-concentration and stable dispersion of carbon fibers according to claim 1, characterized in that: In step 3, the ultrasonic stirring time is 2 minutes.

8. The method for high-concentration and stable dispersion of carbon fibers according to claim 1, characterized in that: In step 3, the power of the ultrasonic stirring is 500W.

9. The method for high-concentration and stable dispersion of carbon fibers according to claim 1, characterized in that: The length of the carbon fiber is 4-8 mm.

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