Method for improving wear resistance of carbon fibers sized with polyimide

Abstract

A method for improving the wear resistance of carbon fibers sized with polyimide, the method relating to the field of materials. The method for improving the wear resistance of carbon fibers in the present invention comprises the following steps: using an impregnation method to attach a water-based sizing agent to carbon fibers for surface sizing, and drying same at 140-260℃. The wear resistance of the carbon fibers is improved by changing the drying temperature in the carbon fiber sizing process. The sized carbon fibers have the advantages of good wear resistance and minimal fuzzing, thus being capable of withstanding further weaving and processing.

Description

A method for improving the wear resistance of polyimide-sized carbon fiber Technical Field

[0001] The present invention relates to the field of materials, and in particular to a method for improving the wear resistance of polyimide-sized carbon fibers. Background Art

[0002] Carbon fiber is made by high-temperature sintering of chemical fiber precursors such as viscose, acrylic, aramid, and asphalt. As an inorganic polymer specialty fiber, it is an ideal reinforcement for composite materials, characterized by high specific strength and modulus. Carbon fiber also has electrical and thermal conductivity, high-temperature resistance, and corrosion resistance. Carbon fiber-reinforced composites have important applications in aerospace, transportation, energy, medical care, and sporting goods.

[0003] In the carbon fiber production process, surface sizing is a very important process step. Carbon fiber is a brittle material. During the subsequent weaving and processing process, it is easy to produce fuzz and single filament breakage due to mechanical friction. The fiber strength is reduced, which also leads to a decrease and stagnation in production and processing efficiency. In the process of preparing carbon fiber prepreg, the presence of fuzz also makes it difficult for the matrix resin to fully impregnate the carbon fiber, resulting in a large porosity in the prepared composite material, which affects the performance of the composite material. Surface sizing can form a protective film on the surface of the carbon fiber, improve the bundling and wear resistance of the carbon fiber tow, and reduce the amount of fiber fuzzing. At the same time, the sizing can form the interface layer of the composite material, increase the interfacial bonding effect of the composite material, and improve the performance of the composite material.

[0004] Traditional carbon fiber sizing agents use epoxy resins and polyurethanes as sizing agents. These sized carbon fibers are primarily used in epoxy resin composites for low-temperature applications. However, when applied to high-temperature resistant composites such as polyimide and polyetheretherketone, these sizing agents are susceptible to degradation at high processing temperatures (>300°C) and high operating temperatures, affecting the composite's interfacial bonding and thus reducing its mechanical properties at high temperatures. In recent years, researchers have begun to focus on the development of sizing agents suitable for high-temperature resistant carbon fiber composites. JP2014125688 formulated a high-temperature resistant solvent-based sizing agent by mixing a polyimide with hydroxyl or carboxyl groups with epoxy resins such as bisphenol A glycidyl ether and phenolic glycidyl ether. US20140343218(A1), CN103614923(A), CN103174026(A), and CN109265998A report water-based polyimide sizing agents formulated with water-soluble polyamic acid salts synthesized from aromatic dianhydrides and aromatic diamines. The aromatic main chain structure of the polyimide sizing agent has high thermal stability and a high degree of matching with the high-temperature resistant resin matrix, which can effectively improve the temperature resistance and mechanical properties of carbon fiber reinforced composites in high-temperature environments.

[0005] However, the molecular main chain structure of polyimide high temperature resistant sizing agent is rigid, and the stiffness of carbon fiber after sizing is large. At the same time, polyimide sizing agent is difficult to be evenly distributed on the carbon fiber surface, and easily forms local agglomeration. In the subsequent processing steps of carbon fiber, the rigid carbon fiber and the rough surface of carbon fiber lead to relatively intense friction between carbon fiber monofilaments and carbon fiber tows, thereby causing fuzzing and broken wires of carbon fiber, affecting the quality of the final composite material. Therefore, the wear resistance of carbon fiber sizing with high temperature resistant sizing agents such as polyimide is in urgent need of improvement. SUMMARY OF THE INVENTION

[0006] The present invention improves the wear resistance of carbon fibers by changing the drying temperature in the carbon fiber sizing process.

[0007] The method for improving the wear resistance of carbon fiber provided by the present invention comprises the following steps: adhering an aqueous sizing agent to the carbon fiber by an impregnation method for surface sizing, and drying; the drying temperature is 140-260°C, preferably 180-240°C. Technical issues

[0008] The purpose of the present invention is to improve the wear resistance of carbon fiber. Technical Solutions

[0009] The present invention first provides a method for improving the wear resistance of carbon fiber, comprising the following steps: adhering an aqueous sizing agent to the carbon fiber by an impregnation method to perform surface sizing, and drying.

[0010] In the above method, the drying temperature is 140-260°C, preferably 180-240°C.

[0011] The drying time is 100-150s, specifically 140s.

[0012] In the above method, the main agent in the aqueous sizing agent is polyamic acid.

[0013] In the above method, the aqueous sizing agent comprises polyamic acid, a cosolvent and water;

[0014] The solid content of the aqueous sizing agent is 0.5wt% to 2wt%; if the solid content of the sizing agent is less than 0.5wt%, the sizing effect is poor and the carbon fiber is prone to produce fuzz; if the solid content of the sizing agent exceeds 2wt%, the carbon fiber is too hard, affecting the processing performance.

[0015] The solid content in the aqueous sizing agent refers to the percentage of the mass of the polyamic acid to the total mass of the aqueous sizing agent solution.

[0016] In the above method, the co-solvent may be triethylamine, which is used to help dissolve the main slurry; the mass ratio of water to triethylamine is 20-25:1, specifically 23:1.

[0017] In the above method, the polyamic acid is prepared by a method comprising the following steps: dissolving an aromatic diamine in a protic non-polar solvent under inert gas protection, slowly adding dianhydride, and performing a condensation reaction to obtain a polyamic acid solution; and using a precipitant to precipitate a polyamic acid solid to obtain the polyamic acid.

[0018] In the above method, the dianhydride is added to the aromatic diamine solution at 0-35°C; specifically, it can be added at room temperature;

[0019] Under stirring, slowly adding the dianhydride to the solution of the aromatic diamine;

[0020] The polycondensation reaction is carried out under inert gas protection and ice bath conditions; the polycondensation reaction time is 10 to 18 hours;

[0021] The precipitant is acetone;

[0022] The preparation method of polyamic acid further comprises a step of drying the polyamic acid solid; specifically, the drying temperature is 30-80°C; specifically, it can be 30°C;

[0023] The aromatic diamine is at least one of 4,4'-diaminodiphenyl ether, 3,4'-diaminodiphenyl ether, 2,2'-bis[4-(4-aminophenoxyphenyl)]propane, 2,2'-bis[3-(3-aminobenzoyl)-4-hydroxyphenyl]hexafluoroisopropyl and 2,2-bis(3-amino-4-hydroxyphenyl)hexafluoropropane;

[0024] The protic non-polar solvent is at least one of N,N-dimethylformamide, N,N-dimethylacetamide, N-methylpyrrolidone and dimethyl sulfoxide;

[0025] The dianhydride is at least one of 3,3',4,4'-benzophenonetetracarboxylic dianhydride, 3,3',4,4'-diphenyl ether tetracarboxylic dianhydride, 2,3,3',4'-diphenyl ether tetracarboxylic dianhydride, 1,2,4,5-cyclohexanetetracarboxylic dianhydride and 4,4'-(4,4'-isopropyldiphenoxy)bis(phthalic anhydride);

[0026] The molar ratio of the aromatic diamine to the dianhydride is 1:1;

[0027] The total mass of the aromatic diamine and dianhydride accounts for 20% to 30% of the total mass of the aromatic diamine, protic non-polar solvent and dianhydride, and can be specifically 30%.

[0028] The inert atmosphere may specifically be a nitrogen atmosphere.

[0029] The room temperature mentioned in the present invention is well known to those skilled in the art, and is generally 15-35°C, and specifically 25-30°C.

[0030] In the above method, the carbon fiber is immersed in the aqueous sizing agent for 10 to 30 seconds, specifically 10 seconds.

[0031] Furthermore, the present invention also provides carbon fibers prepared by the above method. Beneficial effects

[0032] The sized carbon fibers, produced using the method of the present invention, exhibit excellent heat resistance. The polyimide coating on the carbon fibers protects the fibers, enabling them to withstand processing temperatures exceeding 300°C (300°C) for high-temperature-resistant resins such as polyimide and polyetheretherketone. Furthermore, the sized carbon fibers exhibit excellent wear resistance and are less prone to fuzzing, making them durable for further weaving and processing. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 is a schematic diagram of the sizing and drying process of carbon fiber.

[0034] Figure 2 is a schematic diagram of a method for determining the drape value of a carbon fiber bundle; in the figure, 1 is a fixing belt; 2 is a carbon fiber bundle; 3 is a 100g weight; 4 is a base; 5 is a carbon fiber bundle; 6 is a fixing belt; L is the horizontal distance between the end of the carbon fiber bundle and the base.

[0035] Figure 3 is a schematic diagram of the carbon fiber fuzzing test; in the figure, 1 unwinding device; 2 guide ring; 3 guide rod; 4 guide and yarn spreading device; 5 height difference; 6 fuzz collecting material; 7 loading block; 8 height adjustment device; 9 winding device.

[0036] Figure 4 is a surface morphology picture of the sized carbon fibers prepared in Comparative Example 1 and Examples 1 to 4, with a magnification of 20k; wherein, (a) in Figure 4 is Comparative Example 1; (b) is Example 1; (c) is Example 2; (d) is Example 3; and (e) is Example 4.

[0037] FIG5 is a surface morphology picture of the sized carbon fiber prepared in Example 4, with a magnification of 2.5k. Modes for Carrying Out the Invention

[0038] The present invention is described in further detail below in conjunction with specific embodiments. The examples provided are only for illustrating the present invention, not for limiting the scope of the invention. The experimental methods in the following examples are conventional methods unless otherwise specified. The materials, reagents, instruments, etc. used in the following examples are all commercially available unless otherwise specified. The quantitative tests in the following examples were performed in triplicate, and the results were averaged.

[0039] In the following examples, the carbon fiber used is the unsized CCF800H-6K carbon fiber produced by Weihai Tuozhan Fiber Co., Ltd.

[0040] In the following examples, the method for sizing the carbon fibers and testing their performance after treatment is as follows:

[0041] 1. Glass transition temperature of sizing agent (T g ) and 5% thermal weight loss temperature (T d5 )

[0042] 5 g of the 1.3 wt% sizing agent was taken and dried under blast drying at 130°C to remove moisture. The polyamic acid was then vacuum dried at 350°C for 1 hour to completely imidize the polyamic acid. The resulting solid was tested by differential scanning calorimetry and thermogravimetric analysis to obtain the glass transition temperature (T g ) and the 5% thermal weight loss temperature in air atmosphere (T d5 ).

[0043] 2. Method for sizing carbon fiber

[0044] The sizing and drying process of carbon fiber is shown in Figure 1. After the bare carbon fiber yarn is unwound, it is fully impregnated with the sizing agent in a glue tank for 10 seconds. It is then heated and dried in a hot oven at 130°C to 240°C for 140 seconds, and finally rolled to obtain the sized carbon fiber.

[0045] 3. Sizing amount

[0046] The evaluation method of sizing rate is to take 1.0~1.5g of carbon fiber material and accurately weigh its weight (W i ), then Soxhlet extraction of carbon fiber was performed with 400~450mL of N-methylpyrrolidone for 4 hours, and then rinsed and soaked with acetone. The sample was placed in an oven at 110℃ for drying, and the weight of the dried carbon fiber (W f ). The sizing amount is calculated according to the following formula:

[0047]

[0048] 4. Overhang value

[0049] Cut a carbon fiber bundle with an effective length of 40 cm, fix one end vertically as shown in Figure 2 (a), and hang a 100g weight from the other end to correct the bending and twisting of the carbon fiber bundle. Let it stand for 30 minutes. Then remove the weight and fix the carbon fiber bundle on a horizontal rectangular base as shown in Figure 2 (b) and fix it with a fixing belt so that the length of the carbon fiber bundle is 25 cm. At this time, the support body (not shown in the figure) keeps the carbon fiber bundle level with the base. After removing the support body, the carbon fiber bundle bends downward due to its own weight. Let it stand for 2 minutes, measure the horizontal distance L, measure it three times, and take the average value to obtain the drape value of the sized carbon fiber.

[0050] 5. Amount of fuzz

[0051] The carbon fiber fuzz test method is based on GB / T41956-2022. As shown in Figure 3, the carbon fiber was passed through four guide rods at a rate of 15 m / min, then through two sheets of polyurethane foam with a 100g weight placed above the foam. The run length was set at 50 m. The mass of the fuzz collected on the polyurethane foam was weighed. The test was repeated three times for each sample, and the average value was calculated.

[0052] Comparative Example 1

[0053] (1) Preparation of polyamic acid

[0054] Under nitrogen, 361.25 g (0.88 mol) of 2,2'-bis[4-(4-aminophenoxyphenyl)]propane was dissolved in 500 g of N,N-dimethylacetamide. 197.27 g (0.88 mol) of 1,2,4,5-cyclohexanetetracarboxylic dianhydride and 803.21 g of N,N-dimethylacetamide were slowly added at room temperature (25-30°C) with stirring. The polycondensation reaction was then stirred for 18 hours under nitrogen in an ice bath to produce a homogeneous, transparent polyamic acid solution. The polyamic acid was then precipitated with sufficient acetone. The solid was then air-dried at 30°C for 6 hours.

[0055] (2) Preparation of sizing agent

[0056] While stirring and heating at 40°C, 78g of polyamic acid solid was dissolved in 5675.25g of deionized water. 246.75g of triethylamine was added to dissolve the polyamic acid. After stirring for 3-4 hours, a homogeneous polyamic acid solution with a solids content of 1.3wt% was obtained, which was the polyimide sizing agent.

[0057] The sizing agent in this example was used to sizing the carbon fibers on the carbon fiber sizing production line shown in FIG1 , and the drying temperature was set at 130° C.

[0058] The thermal properties of the sizing agent and the processability of the sized fiber were evaluated, as shown in Table 1. The 5% thermal weight loss temperature of the sizing agent was 449°C; the carbon fiber sizing percentage was 0.77%, the carbon fiber drape value was 186 mm, and the fuzz was 25.9 mg / 50 m.

[0059]

[0060] Example 1

[0061] The carbon fibers were sized using the 1.3 wt % polyimide sizing agent prepared in Comparative Example 1 according to the carbon fiber sizing process shown in FIG1 , and the drying temperature was set to 180° C.

[0062] The processability of the sizing fibers was evaluated, as shown in Table 2. The carbon fiber sizing percentage was 0.75%, the carbon fiber drape value was 124 mm, and the fuzz was 12.9 mg / 50 m.

[0063]

[0064] Example 2

[0065] The carbon fibers were sized using the 1.3 wt % polyimide sizing agent prepared in Comparative Example 1 according to the carbon fiber sizing process shown in FIG1 , and the drying temperature was set at 200° C.

[0066] The processability of the sizing fibers was evaluated, as shown in Table 3. The carbon fiber sizing percentage was 0.51%, the carbon fiber drape value was 114 mm, and the fuzz was 9.2 mg / 50 m.

[0067]

[0068] Example 3

[0069] The carbon fibers were sized using the 1.3 wt % polyimide sizing agent prepared in Comparative Example 1 according to the carbon fiber sizing process shown in FIG1 , and the drying temperature was set to 220° C.

[0070] The processability of the sizing fibers was evaluated, as shown in Table 4. The carbon fiber tape sizing percentage was 0.60%, the carbon fiber drape value was 132 mm, and the fuzz was 7.0 mg / 50 m.

[0071]

[0072] Example 4

[0073] The carbon fibers were sized using the 1.3 wt % polyimide sizing agent prepared in Comparative Example 1 according to the carbon fiber sizing process shown in FIG1 , and the drying temperature was set at 240° C.

[0074] The processability of the sizing fibers was evaluated, as shown in Table 5. The carbon fiber sizing percentage was 0.70%, the carbon fiber drape value was 156 mm, and the fuzz was 1.4 mg / 50 m.

[0075]

[0076] The above embodiments and carbon fiber test results show that increasing the drying temperature during the carbon fiber sizing process can reduce the amount of carbon fiber fuzzing and improve the wear resistance of carbon fiber. The fuzzing amount of carbon fiber dried at 130°C is 25.9 mg / 50m. When the drying temperature is increased to 180°C, the fuzzing amount is reduced to 12.9 mg / 50m; when the drying temperature is 240°C, the fuzzing amount is 1.4 mg / 50m. Figure 4 shows the micromorphology of carbon fibers prepared at different drying temperatures. The increase in drying temperature leads to an increase in the smoothness of the sized carbon fiber surface, thereby inhibiting the friction between the carbon fibers, and thus improving the wear resistance of the carbon fiber, which is consistent with the results of the fuzzing test. Figure 5 is a surface morphology picture of the sized carbon fiber prepared in Example 4, with a magnification of 2.5k. Industrial Applicability

[0077] The sized carbon fiber of the present invention has the advantages of good wear resistance and low fuzzing, and can withstand further weaving and processing.

Claims

1. A method for improving the wear resistance of carbon fiber, comprising the following steps: adhering an aqueous sizing agent to the carbon fiber by an impregnation method to perform surface sizing, and drying.

2. The method according to claim 1, wherein: The drying temperature is 140-260°C.

3. The method according to claim 2, wherein: The drying temperature is 180-240°C.

4. The method according to any one of claims 1 to 3, wherein: The main agent in the water-based sizing agent is polyamic acid.

5. The method according to claim 4, wherein: The aqueous sizing agent comprises polyamic acid, a cosolvent and water; and the solid content of the aqueous sizing agent is 0.5 wt % to 2 wt %.

6. The method according to claim 5, wherein: The cosolvent is triethylamine; the mass ratio of water to triethylamine is 20-25:

1.

7. The method according to claim 4, wherein: The polyamic acid is prepared by a method comprising the following steps: dissolving an aromatic diamine in a protic non-polar solvent under inert gas protection, slowly adding dianhydride, and performing polycondensation to obtain a polyamic acid solution; and using a precipitant to precipitate a polyamic acid solid to obtain the polyamic acid.

8. The method according to claim 7, wherein: The aromatic diamine is at least one of 4,4'-diaminodiphenyl ether, 3,4'-diaminodiphenyl ether, 2,2'-bis[4-(4-aminophenoxyphenyl)]propane, 2,2'-bis[3-(3-aminobenzoyl)-4-hydroxyphenyl]hexafluoroisopropyl and 2,2-bis(3-amino-4-hydroxyphenyl)hexafluoropropane; The protic non-polar solvent is at least one of N,N-dimethylformamide, N,N-dimethylacetamide, N-methylpyrrolidone and dimethyl sulfoxide; The dianhydride is at least one of 3,3',4,4'-benzophenonetetracarboxylic dianhydride, 3,3',4,4'-diphenyl ether tetracarboxylic dianhydride, 2,3,3',4'-diphenyl ether tetracarboxylic dianhydride, 1,2,4,5-cyclohexanetetracarboxylic dianhydride and 4,4'-(4,4'-isopropyldiphenoxy)bis(phthalic anhydride); The dianhydride is added to a solution of aromatic diamine at 0-35°C; The polycondensation reaction is carried out under inert gas protection and ice bath conditions; specifically, the polycondensation reaction time is 10 to 18 hours; The precipitant is acetone; The molar ratio of the aromatic diamine to the dianhydride is 1:1; The total mass of the aromatic diamine and the dianhydride accounts for 20% to 30% of the total mass of the aromatic diamine, the protic non-polar solvent and the dianhydride.

9. The method according to any one of claims 1 to 8, wherein: The carbon fiber is immersed in the aqueous sizing agent for 10 to 30 seconds.

10. Carbon fiber prepared by the method according to any one of claims 1 to 9.

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