Alumina fiber surface modification method

Abstract

The invention belongs to the technical field of alumina fiber surface modification, and relates to an alumina fiber surface modification method. And cleaning the continuous alumina fiber, and drying in a drying oven. Mixing the following substances in parts by weight: 60-75 parts of deionized water, 23-39 parts of ceramic powder, 0.1-0.5 part of an organic dispersant and 0.5-1.5 parts of organic gel to obtain a modifier, immersing fibers in the modifier to obtain pre-impregnated fibers, and curing the pre-impregnated fibers in an air dry oven; and calcining to obtain the granular villus-shaped alumina fiber. The surface of the alumina fiber prepared by the method provided by the invention is uniformly covered with fluffy particles, so that the roughness of the fiber is effectively increased, the interface bonding force between the fiber and a resin matrix is improved, and the mechanical property of an alumina fiber reinforced resin matrix composite material is improved. The process provided by the invention is simple and controllable in preparation process, high in yield and suitable for large-scale industrial application and popularization.

Description

Technical Field

[0001] The present invention belongs to the technical field of alumina fiber surface modification and relates to a method for modifying the surface of alumina fibers. Background Art

[0002] Continuous alumina fibers have excellent properties such as high strength, high modulus, high temperature resistance, and corrosion resistance, and have broad application prospects in the fields of aerospace, rail transit, high-temperature filtration, composite materials, etc. However, continuous alumina fibers have a smooth surface and high inertness, resulting in poor interfacial bonding force with the resin matrix, which limits their application in composite materials. Therefore, surface modification of continuous alumina fibers to improve their interfacial bonding force with the resin matrix is the key to expanding their application fields. At present, the commonly used methods for surface modification of continuous alumina fibers mainly include: Surface coating method: Coating a layer of coupling agent or polymer on the fiber surface to improve the compatibility between the fiber and the resin. However, the coating is prone to peeling off, affecting the durability of the modification effect. Chemical vapor deposition method: Depositing a layer of active substance on the fiber surface to improve the surface activity of the fiber. However, this method requires expensive equipment and complex processes, and it is difficult to achieve continuous production. Plasma treatment method: Using plasma to etch and activate the fiber surface to increase the surface roughness and activity of the fiber. However, plasma treatment is likely to damage the fiber and affect its mechanical properties. In summary, the current alumina fiber surface modification processes generally have technical problems such as poor uniformity and stability, and limited increase in roughness, resulting in low interfacial bonding force between the fiber and the resin matrix, thus affecting the mechanical properties of alumina fiber reinforced resin matrix composites. The existing processes are difficult to realize the industrial production of continuous alumina fiber reinforced resin matrix composites. Summary of the Invention

[0003] The present invention proposes a new method for modifying the surface of alumina fibers in view of the problems existing in the traditional alumina fiber modification process.

[0004] In order to achieve the above object, the present invention is implemented by adopting the following technical solutions: A method for modifying the surface of alumina fibers, comprising the following steps: (1) Sequentially adding continuous alumina fibers into acetone, ethanol, and deionized water and cleaning them for 10 - 60 s respectively to remove surface oil stains and impurities.

[0005] (2) Placing the cleaned fibers in an oven and drying to remove the surface solvent.

[0006] (3) Mix the following substances in parts by weight to obtain a modifier: 60 - 75 parts of deionized water, 23 - 39 parts of ceramic powder, 0.1 - 0.5 part of an organic dispersant, and 0.5 - 1.5 parts of an organic gel; the organic gel is a mixture of polyvinyl alcohol and glycerol, and the organic dispersant is an ammonium salt dispersant, preferably the colorless 4075 type ammonium salt dispersant, with a solid content of 40%, a pH value of 6 - 7, a specific gravity of 1.0 - 1.15, and a viscosity (at 20 °C) of 100 - 300 mPa·s; the ceramic powder is high-purity nano-aluminum oxide powder, and the average particle size D50 of the ceramic powder is 150 nm. The pH value of the modifier is 4 - 5, and the components in the modifier are mixed and stirred at a speed of 300 - 1000 rmp for 1 - 3 h.

[0007] (4) Immerse the fibers obtained in step (2) in the modifier to obtain pre-impregnated fibers.

[0008] (5) Place the pre-impregnated fibers in a blast drying oven for curing; to obtain coated fibers. A layer of PVA-αAl 2 O 3 modified film is formed on the fiber surface, and the film thickness is 150 - 300 nm.

[0009] (6) Calcinate the coated fibers in an atmosphere of a mixture of air and nitrogen to obtain granular and villous alumina fibers.

[0010] Preferably, in step (3), the mass ratio of polyvinyl alcohol to glycerol is (1.2 - 3):1.

[0011] Preferably, in step (4), the immersion temperature of the fibers is 10 - 30 °C, and the immersion time is 30 - 60 s. The pre-impregnation is mainly to coat a layer of modified slurry on the fiber surface to facilitate subsequent curing. If the pre-impregnation time is too short, the coverage rate of dendritic particles on the subsequent fiber surface will be insufficient, and if the time is too long, the size of the dendritic particles may be too large.

[0012] Preferably, in step (5), the curing temperature is 100 - 200 °C, and the time is 100 - 1000 s.

[0013] Preferably, in step (6), the volume ratio of air to nitrogen is 1:1, nitrogen and air are simultaneously introduced separately at a rate of 10 - 30 L / min, the calcination temperature is 800 - 1000 °C, and the calcination time is 10 - 60 min. Too low a temperature will result in insufficient decomposition of the precursor, and too high a temperature may cause fiber damage. Dendritic particles of metal oxides are deposited on the fiber surface by reaction, and after natural cooling, modified continuous alumina fibers are obtained. The diameter of the dendritic particles of metal oxides is 150 - 300 nm, and the length is 100 - 500 nm. The dendritic particles of metal oxides are evenly distributed on the fiber surface, and the coverage rate is greater than 90%.

[0014] Principle: At the temperature and humidity provided by the present invention, by utilizing the hydrophobic segments of the organic modifier, high-activity oxide particles are attached to the surface of continuous alumina fibers with the assistance of van der Waals forces. Further, through the hydroxyl groups (Al-OH) rich on the surface of the continuous alumina fibers and the active groups in the modifier (such as PVA-αAl-OH) through a condensation reaction (Al-OH + Al-OH → PVA-αAl-O-Al + H 2 O), a stable bonding structure is formed, thereby forming a uniform PVA-αAl 2 O 3 modified film on the fiber surface. The film thickness is controlled by controlling the impregnation time, and the organic matter on the fiber surface is removed by high-temperature cracking in an atmosphere of equal ratio mixture of air and nitrogen. Finally, a villous particle with its root bonded to the fiber through Al-O-Al bonds is formed, and it can be uniformly attached to the fiber surface.

[0015] Compared with the prior art, the advantages and positive effects of the present invention are as follows: 1. The surface of the alumina fibers prepared by the method proposed in the present invention is uniformly covered with villous particles, effectively increasing the roughness of the fibers, improving the interfacial bonding force between the fibers and the resin matrix, and enhancing the mechanical properties of the alumina fiber reinforced resin matrix composite.

[0016] 2. The preparation process of the process proposed in the present invention is simple and controllable, with a high yield, and is suitable for large-scale industrial application and promotion. Description of the Drawings

[0017] Figure 1 It is the SEM image of the unmodified unidirectional bundle continuous alumina fiber filaments.

[0018] Figure 2 It is the SEM image of the modified unidirectional continuous alumina fibers prepared in Example 1.

[0019] Figure 3 It is the SEM image of the unidirectional bundle continuous alumina fiber filaments obtained in Comparative Example 3.

[0020] Figure 4 It is the SEM image of the unidirectional bundle continuous alumina fiber filaments obtained in Comparative Example 4. Detailed Embodiments

[0021] In order to more clearly understand the above objects, features, and advantages of the present invention, the present invention will be further described below in conjunction with specific embodiments. It should be noted that, without conflict, the embodiments of the present application and the features in the embodiments can be combined with each other.

[0022] In the following description, many specific details are set forth in order to provide a thorough understanding of the present invention. However, the present invention may be practiced in other ways different from those described herein. Therefore, the present invention is not limited by the limitations of the specific embodiments disclosed in the following specification.

[0023] The following are some of the manufacturers or material specifications in the following examples: Continuous alumina fiber: Molun (Zhuhai) New Materials Technology Co., Ltd., model: Morlion 857-1K, fiber diameter 9-12μm.

[0024] Plain weave cloth of continuous alumina fiber: Molun (Zhuhai) New Materials Technology Co., Ltd., model: Morlion 857-1K, fiber diameter 9-12μm, areal density 430g / m 2 , thickness 0.35mm, width 10cm.

[0025] High-purity nano-alumina powder: Guozhuang New Materials Technology (Jiangsu) Co., Ltd., crystal phase is α-phase, purity ≥99.99%, average particle size D50 is 150nm, BET is 10.2m 2 / g.

[0026] 4075-type ammonium salt dispersant: Guangzhou Yongxi New Materials Co., Ltd., solid content 40%, pH value 6-7, specific gravity 1.0-1.15, viscosity (20°C) 100-300mpa.s.

[0027] Polyvinyl alcohol: degree of polymerization 800-2000, Aladdin Reagent (Shanghai) Co., Ltd.

[0028] Epoxy resin: general bisphenol A type epoxy resin (E51), Guangzhou Yingrun Chemical Co., Ltd.

[0029] For the rest of the substances not specifically stated, alumina fiber or conventional commercially available reagents in the chemical industry are used.

[0030] Example 1 Mix 1.2kg of deionized water, 774g of high-purity nano-alumina powder, 10g of 4075-type ammonium salt dispersant, 5.45g of polyvinyl alcohol (degree of polymerization 800), and 4.55g of glycerol, and then stir at 800rpm for 2h to obtain a fiber modifier.

[0031] Take 10 m of unidirectional continuous alumina fiber filaments, continuously draw and immerse them successively into containers filled with acetone, ethanol, and deionized water, and keep staying in each container for 30 s to remove surface oil stains and impurities. Then continue to draw the fibers into the first tubular air drying oven for drying. The temperature of the air drying oven is maintained at 125 °C, and the residence time of the fibers in the air drying oven is 50 s. Then continue to draw the fibers into the modifier for pre-impregnation treatment. The pre-impregnation temperature is 10 °C, and the pre-impregnation residence time is 30 s. Then draw the pre-impregnated fibers to the second tubular air drying oven for curing. The temperature of the second tubular air drying oven is 200 °C, and the curing residence time is 200 s, so that a layer of PVA-αAl 2 O 3 modified film is formed. After testing, the thickness of the obtained film is 150 nm. Place the cured continuous alumina fibers in the third tubular atmosphere high-temperature furnace, and simultaneously introduce nitrogen and air as circulating reaction gases. The inlet rates of the two gases are 15 L / min. After 2 min of ventilation, heat up the tubular furnace to 900 °C at a heating rate of 60 °C / min, and calcine at 900 °C for 30 minutes to react and deposit dendritic particulate fluff of metal oxides on the fiber surface. After natural cooling, the modified unidirectional continuous alumina fibers are obtained.

[0032] Take electron microscope pictures of the unidirectional continuous alumina fiber filaments before modification and the modified unidirectional continuous alumina fibers prepared in this example. The results are respectively as Figure 1 and Figure 2 . It can be seen from the figure that the dendritic particulate fluff of metal oxides is evenly distributed on the fiber surface, and the coverage rate reaches 95%.

[0033] The modified unidirectional bundle continuous alumina fiber filaments prepared above were cut into 20-cm specifications using ceramic scissors, and then a sample plate was prepared using a 20×10×2-cm stainless steel mold. The fibers were filled into bisphenol A epoxy resin (E51), and the fiber filling volume fraction was 55%. The mold was set with a curing temperature of 180°C, a total time of 4 h, and a heating rate of 1°C / min. After curing, it was naturally cooled to room temperature and demolded to obtain a unidirectional continuous alumina fiber-reinforced resin matrix composite sample plate. According to the standards: GB / T 1447-2005 Test methods for tensile properties of fiber-reinforced plastics, GB / T 1449-2005 Test methods for flexural properties of fiber-reinforced plastics, and GB / T 1450.1-2005 Test methods for interlaminar shear strength of fiber-reinforced plastics, the unidirectional continuous alumina fiber-reinforced epoxy resin matrix composite sample plate was processed and its mechanical properties were tested respectively. The room-temperature tensile strength of the test sample plate was 1250 MPa, the flexural strength was 1850 MPa, and the interlaminar shear strength was 85 MPa. According to the ASTM D7334 standard, using the Wilhelmy dynamic contact angle method, the modified continuous alumina fiber monofilaments were vertically immersed in epoxy resin (E-51), and the contact angle between the fiber and the resin was measured to be 30° using a German Krüss K100 type contact angle meter.

[0034] Example 2 3.0 kg of deionized water, 1935 g of high-purity nano-alumina powder, 25 g of 4075-type ammonium salt dispersant, 13.6 g of polyvinyl alcohol (degree of polymerization 1000), and 11.4 g of glycerol were mixed, and then stirred at 800 rpm for 2 h to obtain a fiber modifier.

[0035] Take 10 m of continuous alumina fiber plain weave cloth, continuously traction it and immerse it successively in containers filled with acetone, ethanol, and deionized water, and keep the residence time in each container for 60 s to remove surface oil stains and impurities. Then the fiber was continuously tractioned into the first tubular air-blowing drying oven for drying, and the temperature of the air-blowing drying oven was maintained at 125°C, and the residence time of the fiber in the air-blowing drying oven was 100 s. Then the fiber was continuously tractioned into the modifier for pre-impregnation treatment, the pre-impregnation temperature was 20°C, and the pre-impregnation residence time was 60 s. Then the pre-impregnated fiber was tractioned to the second tubular air-blowing drying oven for curing, the temperature of the second tubular air-blowing drying oven was 180°C, and the curing residence time was 500 s to form a layer of PVA-αAl on the surface of the alumina fiber. 2 O 3The modified film, after testing, has a film thickness of 150 nm. The cured continuous alumina fibers are placed in a third tubular atmosphere high-temperature furnace, and nitrogen and air are respectively and simultaneously introduced as circulating reaction gases. The inlet rates of the two gases are 30 L / min. After 2 minutes of gas injection, the tubular furnace is heated to 900 °C at a heating rate of 60 °C / min and calcined at 900 °C for 45 minutes. Dendritic particulate fluff of metal oxides is deposited on the fiber surface by reaction, and the modified unidirectional continuous alumina fibers are obtained after natural cooling. It is detected that the dendritic particulate fluff of metal oxides is evenly distributed on the fiber surface, and the coverage rate reaches 93%.

[0036] Use ceramic scissors to cut the above-mentioned modified continuous alumina fiber plain cloth. The size of a single piece of fiber cloth is 20 cm * 10 cm * 0.35 mm. Use a 20 * 10 * 2 cm stainless steel mold to prepare a sample. The epoxy resin is a general bisphenol A type epoxy resin (E51). The filling ratio of the fiber cloth in the sample is 50%, and the other molding process conditions are the same as those in Example 1. A 2D continuous alumina fiber-reinforced epoxy resin matrix composite is prepared. And it is detected by the same method as in Example 1. The room-temperature tensile strength of the test specimen is 1180 MPa, the flexural strength is 1750 MPa, and the interlaminar shear strength is 80 MPa. Immerse the modified continuous alumina fiber monofilament vertically into the epoxy resin (E-51), and use a German Krüss K100 type contact angle meter to measure that the contact angle between the fiber and the resin is 45°.

[0037] Comparative Example 1 The difference between this comparative example and Example 1 is that the fiber filaments are not modified, but unidirectional bundle continuous alumina fiber filaments are directly cut, and then a sample of alumina fiber-reinforced epoxy resin matrix composite is prepared for detection. The room-temperature tensile strength of the test sample is 950 MPa, the flexural strength is 1450 MPa, and the interlaminar shear strength is 65 MPa. Use a German Krüss K100 type contact angle meter to measure that the contact angle between the fiber and the resin is 70°.

[0038] Comparative Example 2 The difference between this comparative example and Example 2 is that the continuous alumina fiber plain cloth is not modified, but directly cut and then a fiber-reinforced epoxy resin matrix composite is prepared for detection. The room-temperature tensile strength of the test sample is 800 MPa, the flexural strength is 1200 MPa, and the interlaminar shear strength is 50 MPa. Use a German Krüss K100 type contact angle meter to measure that the contact angle between the fiber cloth and the resin is 85°.

[0039] Comparative Example 3 The difference between this comparative example and Example 1 is that after the surface of the unidirectional continuous alumina fiber is cleaned and dried, the pre-impregnation temperature remains unchanged at 10 °C, and only the impregnation time is shortened to 10 s, while the subsequent curing and sintering processes remain unchanged, resulting in modified continuous alumina fibers. As Figure 3 shown, it can be seen that the dendritic particle fluff on the fiber surface is sparse, the particles are small and uneven, and the modification effect is poor.

[0040] Comparative Example 4 The difference between this comparative example and Example 1 is that after the surface of the unidirectional continuous alumina fiber is cleaned and dried, the pre-impregnation temperature remains unchanged at 10 °C, and only the impregnation time is increased to 100 s, while the subsequent curing and sintering processes remain unchanged, resulting in modified continuous alumina fibers. As Figure 4 shown, it can be seen that the dendritic particle fluff on the fiber surface accumulates and agglomerates, the thickness is relatively thick and uneven, and the modification effect is poor.

[0041] Comparative Example 5 The difference between this comparative example and Example 1 is that the addition amount of high-purity nano-alumina powder is 4.5 kg, and the subsequent curing and sintering processes remain unchanged. As a result, the modifier cannot be well dispersed, the impregnation effect is poor, and the obtained modified continuous alumina fiber film is unevenly distributed.

[0042] Comparative Example 6 The difference between this comparative example and Example 1 is that the addition amount of high-purity nano-alumina powder is 200 g, and the subsequent curing and sintering processes remain unchanged. As a result, the dendritic particle fluff on the fiber surface is sparse, the particles are small, and the distribution is uneven.

[0043] The above are only the preferred embodiments of the present invention, and are not intended to limit the present invention in other forms. Any person skilled in the art may use the disclosed technical content to make changes or modifications into equivalent embodiments with equivalent changes and apply them to other fields. However, as long as it does not depart from the technical solution content of the present invention, any simple modification, equivalent change and modification made to the above embodiments based on the technical essence of the present invention still fall within the protection scope of the technical solution of the present invention.

Claims

1. A method for surface modification of alumina fiber, characterized in that: Here are the steps: (1) Washing alumina fibers in acetone, ethanol and deionized water in sequence; (2) The cleaned fibers are placed in an oven for drying; (3) Mixing the following materials in parts by weight to obtain a modifier: 60-75 parts of deionized water, 23-39 parts of ceramic powder, 0.1-0.5 parts of an organic dispersant, and 0.5-1.5 parts of an organic gel; the organic gel is a mixture of polyvinyl alcohol and glycerol, and the organic dispersant is an ammonium salt dispersant; (4) immersing the fiber obtained in step (2) in a modifier to obtain a pre-impregnated fiber; (5) placing the pre-impregnated fiber in a forced air drying oven for curing; obtaining coated fibers; (6) The coated fiber is calcined in a mixed gas atmosphere of air and nitrogen to obtain granular fluffy alumina fibers.

2. The method for surface modification of alumina fiber according to claim 1, characterized in that: In step (3), the mass ratio of polyvinyl alcohol to propylene glycol is (1.2-3):

1. The ceramic powder is a high-purity nano-alumina powder, and the average particle size D50 of the ceramic powder is 150 nm; the pH value of the modifier is 4-5, and the components in the modifier are mixed and stirred at a speed of 300-1000 rpm for 1-3 hours.

3. The method for surface modification of alumina fiber according to claim 1, characterized in that: In step (4), the fiber immersion temperature is 10-30°C and the immersion time is 30-60s.

4. The method for surface modification of alumina fiber according to claim 1, characterized in that: In step (5), the curing temperature is 100-200°C and the curing time is 100-1000s.

5. The method for surface modification of alumina fiber according to claim 1, characterized in that: In step (6), the volume ratio of air to nitrogen is 1:1, nitrogen and air are introduced simultaneously at a rate of 10-30 L / min, the calcination temperature is 800-1000° C., and the calcination time is 10-60 min.

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