Silicon carbide fiber composite mat and method of making

Abstract

The application discloses a silicon carbide fiber composite felt and a preparation method thereof. Short-cut silicon carbide fibers are subjected to plasma surface treatment, then one of short-cut glass fibers, short-cut carbon fibers and the short-cut silicon carbide fibers are added into a nano-dispersion liquid to obtain a fiber suspension, and the fiber suspension is subjected to dewatering forming, drying and solidification to obtain the silicon carbide fiber composite felt. The application introduces hydrophilic groups such as carboxyl, hydroxyl and carbonyl on the surface of the short-cut fibers through low-temperature plasma, improves the wettability of the surface of the silicon carbide fibers, disperses different fibers through specific nano-dispersants, and finally obtains the silicon carbide fiber composite felt which can adjust and control the electromagnetic wave absorption rate of different electromagnetic wave bands and has excellent toughness and softness.

Description

Technical Field

[0001] This invention relates to a method for preparing a silicon carbide fiber composite felt, and particularly to a silicon carbide fiber composite felt and its preparation method. Background Technology

[0002] Wet-laid nonwoven fabric technology uses water as a medium to uniformly suspend short fibers. The water flow then causes the fibers to deposit onto a permeable curtain or porous roller, forming a wet web. The International Nonwovens Association defines it as: "A paper-like nonwoven fabric produced by the deposition of fibers suspended in a water tank, followed by a series of processing steps including web fixing." In other words, wet-laid nonwoven fabric is a nonwoven fabric obtained by dehydrating a fiber web of water, fibers, and chemical auxiliaries in a specialized forming device, followed by web fixing using physical and chemical methods.

[0003] Currently, the main methods for preparing silicon carbide fiber felt are electrospinning and needle punching. Electrospinning is extremely slow and has low yield; needle punching is difficult due to the high modulus and low cohesion of silicon carbide fibers, and the fibers are also brittle, causing significant damage during the needle punching process. Compared to these two methods, wet nonwoven technology is quite superior for fiber materials with high fiber density, poor flexibility, high rigidity, and poor interfiber cohesion. The primary issue in wet nonwoven technology is whether the fiber raw material can be successfully dispersed in the slurry; therefore, preparing a slurry with excellent dispersion properties for silicon carbide fibers is a key condition for the preparation of wet-laid silicon carbide fiber felt.

[0004] However, due to the inert surface of silicon carbide fibers, the lack of oxygen-containing functional groups, and the large fiber modulus, it is difficult to prepare uniform aqueous dispersion slurry and form a uniform surface. Therefore, patent CN 105386237 A uses polycarbosilane infusible fibers as a precursor. After being loosened by airflow, the precursor is mixed into the pulp, wet-deposited and dried, and then sintered in a high-temperature furnace to obtain silicon carbide fiber felt. The polycarbosilane infusible fiber felt is placed in a high-temperature furnace and heated to 1000-1300℃ at a rate of 15-240℃ / h under the protection of high-purity nitrogen, and held at that temperature for 1-1.5h to obtain silicon carbide fiber felt.

[0005] The existing silicon carbide fiber felt preparation technology is relatively complex. It uses polycarbosilane as a precursor for preparation, and then sintersects after molding. The preparation time is long, the equipment requirements are high, the single preparation volume is small, the output is low, the basis weight of the fiber felt cannot be accurately controlled, continuous production is difficult, high temperature and high purity nitrogen protection are required, and the energy consumption is high. Summary of the Invention

[0006] To address the shortcomings of existing technologies, the first objective of this invention is to provide a method for preparing silicon carbide fiber composite felt. The preparation method provided by this invention has a simple preparation process, low production cost, continuous production capability, and freely controllable product specifications. It can also adjust the electromagnetic wave absorption rate of silicon carbide fiber composite felt in different electromagnetic bands.

[0007] A second objective of this invention is to provide a silicon carbide fiber composite felt prepared by the above-described method. This silicon carbide fiber composite felt can control the electromagnetic wave absorption rate of different electromagnetic bands and possesses excellent toughness and softness.

[0008] To achieve the above objectives, the present invention adopts the following technical solution:

[0009] This invention discloses a method for preparing silicon carbide fiber composite felt. The method involves plasma surface treatment of chopped silicon carbide fibers, followed by adding one of chopped glass fibers or chopped carbon fibers along with the chopped silicon carbide fibers to a nano-dispersion liquid to obtain a fiber suspension. The fiber suspension is then dehydrated, shaped, dried, and cured to obtain the final product. The nano-dispersion liquid comprises the following components by weight: 0.5–25 parts surfactant, 0.2–15 parts fumed silica powder, 0.1–10 parts thickener, 0.1–0.5 parts defoamer, 0.5–10 parts softener, and 39.5–98.6 parts water.

[0010] The preparation method of this invention first involves surface treatment of short-cut fibers using low-temperature plasma. This only alters the physical and chemical properties of the material surface, introducing hydrophilic groups such as carboxyl, hydroxyl, and carbonyl groups onto the surface of silicon carbide fibers. This improves the wettability of the silicon carbide fiber surface, which is beneficial for fiber dispersion in nano-dispersion liquid. Compared with conventional oxidation methods, the surface etching effect is more significant, which can reduce the rigidity of silicon carbide fibers to a certain extent, improve fiber flexibility, and reduce flocculation problems during dispersion to a certain extent. It also helps to increase the contact area between the fiber and the resin material, improve the bonding strength, and enhance the performance of the composite material. In addition, the amount of hydrophilic groups introduced by plasma treatment is not significantly different.

[0011] Then, one of the short-cut glass fibers and short-cut carbon fibers is placed together with short-cut silicon carbide fibers in a nano-dispersion liquid for dispersion. The present invention can simultaneously adapt to short-cut glass fibers, short-cut carbon fibers, and surface-modified short-cut silicon carbide fibers, enabling them to be uniformly dispersed in the nano-dispersion liquid. The present invention incorporates fumed silica powder into the dispersion liquid, which can further play a role in surface modification, promote the dispersibility of silicon carbide in water, and also play a role in skeletal support. First, fumed silica forms a mesh structure during the composite felt forming process. This structure provides a strong support framework, which can prevent the composite fibers from deforming and breaking during the forming process. This skeletal support makes the overall structure of the composite felt more stable, increases its mechanical strength and tensile properties. In addition, this structure also helps the thin felt maintain a certain thickness and shape, making it more suitable for various application scenarios. Secondly, fumed silica can form a silica coating layer on the surface of silicon carbide fibers, thereby modifying the fiber surface. This surface modification can improve the chemical stability and antioxidant properties of silicon carbide fibers, extending their service life. Simultaneously, this coating layer can reduce friction between fibers, improving their flexibility and wear resistance. Furthermore, the surface modification of silica can also affect the bonding performance between the fibers and the matrix, enhancing the overall stability of the fiber composite felt. Meanwhile, the surfactants in the nano-dispersion can improve the viscosity and flowability of the dispersion, promoting the wetting and dispersion of the fiber material. They possess dispersing, wetting, and surface tension reduction properties, forming a thin film between the fiber material and the liquid, improving the compatibility of the fiber material with the mixture. Thickeners also help to change the viscosity and thixotropic properties of the dispersion, preventing fiber dispersion and sedimentation. Softeners can improve the antistatic properties and increase the hydrophilicity of the fibers, improving their softness. More importantly, this makes the softness of silicon carbide fibers more compatible with other fibers, resulting in a uniformly dispersed composite felt.

[0012] As a preferred embodiment, the composition includes 15-20 parts surfactant, 1-5 parts fumed silica, 4-10 parts thickener, 0.1-0.5 parts defoamer, 5-10 parts softener, and 39.5-98.6 parts water.

[0013] As a preferred embodiment, the lengths of the chopped silicon carbide fibers, chopped glass fibers, and chopped carbon fibers are all 4–15 mm. Controlling the fiber length to 4–15 mm in this invention facilitates subsequent dispersion and compounding, while simultaneously ensuring the mechanical properties of the composite felt.

[0014] As a preferred embodiment, the plasma surface treatment conditions are: time 5–90 min, power 600–900 W, and pressure 0.1–0.2 MPa. The inventors have found that controlling the plasma surface treatment conditions within this range yields the best results. If the power or pressure is too high, the etching may be too pronounced, potentially reducing the mechanical properties of the silicon carbide fiber; conversely, if the power or pressure is too low, the improvement is limited.

[0015] As a preferred embodiment, the mass ratio of the chopped silicon carbide fiber to the chopped glass fiber is 0.1–10:90–99.

[0016] Composite glass fiber mats made by combining chopped silicon carbide fibers and chopped glass fibers are low in cost. Under less demanding conditions, adding appropriate silicon carbide fibers with specific resistivity can be used to regulate the absorption capacity of specific wavebands.

[0017] As a preferred embodiment, the mass ratio of chopped silicon carbide fibers to chopped carbon fibers is 60-90:10-40. In this invention, by controlling the mass ratio of chopped silicon carbide fibers to chopped carbon fibers within the above range, a silicon carbide fiber composite felt with excellent high-temperature performance, electrical conductivity, and wave absorption properties can be obtained. However, if excessive carbon fibers are required, it will affect the high-temperature resistance of the silicon carbide fiber felt and will also be detrimental to obtaining products for specific wavelengths.

[0018] As a preferred embodiment, the preparation process of the nano-dispersion is as follows: surfactant, fumed silica, thickener, defoamer, and softener are added to water, and the pH is adjusted to 2-12, preferably 3-6, followed by sand milling to form a pulp. The inventors have discovered that a suitable pH can promote the dispersion of the two fibers; when the pH is between 3 and 6, the dispersion process can be accelerated, and the dispersion can be made more uniform.

[0019] As a preferred embodiment, the softener is at least one of polyether silicone-modified silicone oil and hydrophilic amino silicone oil.

[0020] As a preferred embodiment, the surfactant is at least one selected from sodium hexametaphosphate, fatty alcohol polyoxyethylene ether, fatty amine polyoxyethylene ether, alkyl ammonium salt, fatty alcohol and ethylene oxide condensate, polyethylene glycol, polyoxyethylene sorbitan monostearate, polyvinylpyrrolidone, and cetearyl alcohol polyoxyethylene ether; the thickener is at least one selected from carboxymethyl cellulose, hydroxypropyl methyl cellulose, hydroxyethyl cellulose, and polyethylene oxide; and the defoamer is at least one selected from amides, phosphate esters, silicones, polyethers, and polyether siloxane copolymers.

[0021] The butyl phosphates used in this invention include tributyl phosphate, organosilicon compounds such as Defeng 2854, alkyl polyethers such as Xinwancheng S-717, and polyether siloxanes such as Tego 902W.

[0022] As a preferred embodiment, the sand milling and pulping time is 20–180 min.

[0023] As a preferred embodiment, the viscosity of the fiber suspension is 5–400 mPa·s; and the gas content is 2–20%.

[0024] In actual operation, the fiber suspension will be sent to a grid for dehydration and molding.

[0025] As a preferred embodiment, the felt obtained after dehydration and molding is mixed with an adhesive and then dried and cured. The amount of adhesive added is 5-15% of the mass of the felt.

[0026] As a further preferred embodiment, the adhesive is selected from one of acrylic resin, polyurethane, silicone resin, phenolic resin, and epoxy resin. The adhesive is added by dip coating.

[0027] The present invention also provides a silicon carbide fiber composite felt prepared by the above preparation method.

[0028] Principles and advantages

[0029] The preparation method of this invention first involves surface treatment of chopped fibers using low-temperature plasma, which only alters the physical and chemical properties of the material surface. Hydrophilic groups such as carboxyl, hydroxyl, and carbonyl groups are introduced onto the surface of silicon carbide fibers, improving the wettability of the silicon carbide fiber surface and facilitating the dispersion of the fibers in the nano-dispersion liquid. Then, one of chopped glass fibers or chopped carbon fibers is placed together with the chopped silicon carbide fibers in the nano-dispersion liquid for dispersion. The method provided by this invention can simultaneously adapt to chopped glass fibers, chopped carbon fibers, and surface-modified chopped silicon carbide fibers, enabling them to be uniformly dispersed in the nano-dispersion liquid. Finally, the composite felt is obtained through dehydration, molding, drying, and curing.

[0030] By adopting the above technical solution, the present invention has at least the following advantages:

[0031] ① This invention can be formed in one step without secondary processing: silicon carbide fiber is directly used as raw material to obtain silicon carbide fiber composite glass fiber felt and silicon carbide fiber composite carbon fiber felt products in one step.

[0032] ②Because it can be molded in one step, it can be continuously mass-produced.

[0033] ③ The process is simple, the production efficiency is high, and there is no fiber damage: there is no slow production efficiency of electrospinning process, and no fiber damage or breakage caused by needle punching.

[0034] ④ Low production cost and no high-energy-consuming processes: All raw materials used in production can be reused, and the preparation process has no high-temperature processes and low energy consumption.

[0035] ⑤ Production specifications are free and controllable, and the quality of molded products is stable: Wet nonwoven felting technology is used to directly control the thickness of fiber felt and the mass per unit area, as well as the weight ratio and mass per unit area of ​​glass fiber to silicon carbide fiber and carbon fiber to silicon carbide fiber, resulting in stable and reliable products.

[0036] ⑥ The weight ratio of silicon carbide fiber to glass fiber and silicon carbide fiber to carbon fiber can be freely controlled. At the same time, silicon carbide fiber has adjustable electrical properties, which can be used to prepare silicon carbide fiber composite glass fiber mat products with good absorption effect on electromagnetic waves of different bands. By combining silicon carbide fiber / carbon fiber, the two fibers are evenly distributed, which improves the flexibility of silicon carbide fiber mat and enhances its physical properties. Detailed Implementation

[0037] The present invention will be further described below with reference to specific embodiments, but the scope of protection of the present invention is not limited to the following specific embodiments. Obviously, the embodiments described below are only a part of the embodiments, and all other embodiments obtained by those skilled in the art without creative effort are still within the scope of protection of the present invention.

[0038] Unless otherwise specified, all raw materials, reagents, instruments and equipment used in this invention can be purchased from the market or prepared by existing methods.

[0039] Example 1

[0040] This invention provides a method for preparing silicon carbide fiber felt, comprising the following steps:

[0041] 1. Use a fiber cutting machine to cut silicon carbide fibers into 5mm pieces and glass fibers into 12mm short fibers;

[0042] 2. The short-cut silicon carbide fibers obtained in step (1) are surface treated for 30 minutes using a low-temperature plasma surface treatment machine with a power of 800W and a working pressure of one atmosphere.

[0043] 3. Add 74.9g of water to the dispersion tank, then add 10g of sodium hexametaphosphate, 5g of polyethylene glycol, 1g of hydrophilic fumed silica, 4g of carboxymethyl cellulose, 0.1g of polydimethylsiloxane and 5g of polyether silicone modified silicone oil in sequence. Adjust the pH value to 3-6, and after sand milling for 1 hour, the nano-dispersion is ready.

[0044] 4. Weigh a certain amount of silicon carbide fiber from step (2) and glass fiber from step (1), add them to the nano-dispersion prepared in step (3), and stir and disperse them in a dispersion tank to prepare a uniform silicon carbide / glass fiber suspension.

[0045] The silicon carbide fiber accounts for 5% by weight, and the glass fiber accounts for 95% by weight.

[0046] 5. The silicon carbide fiber suspension prepared in step (4) is transported to a grid for dehydration and molding. Then, an adhesive is added and the product is dried, cured, and cut in a forced-air oven to obtain the silicon carbide fiber felt product.

[0047] Example 2

[0048] This invention provides a method for preparing silicon carbide fiber felt, comprising the following steps:

[0049] 1. Use a fiber cutting machine to cut silicon carbide fibers into 10mm pieces and carbon fibers into 5mm pieces;

[0050] 2. The short-cut silicon carbide fibers obtained in step (1) are surface treated for 30 minutes using a low-temperature plasma surface treatment machine with a power of 800W and a working pressure of one atmosphere.

[0051] 3. Add 69.2g of water to the dispersion tank, then add 15g of sodium hexametaphosphate, 5g of polyethylene glycol, 1.5g of hydrophilic fumed silica, 4g of carboxymethyl cellulose, 0.3g of polydimethylsiloxane and 5g of polyether silicone modified silicone oil in sequence. Adjust the pH value to 10-12, and after sand milling for 1 hour, the nano-dispersion is ready.

[0052] 4. Weigh a certain amount of silicon carbide fiber from step (2) and carbon fiber from step (1), add them to the nano-dispersion prepared in step (3), and stir and disperse them in a dispersion tank to prepare a uniform silicon carbide fiber / carbon fiber suspension.

[0053] The silicon carbide fiber accounts for 90% by weight, and the carbon fiber accounts for 10% by weight.

[0054] 5. The silicon carbide fiber suspension prepared in step (4) is transported to a grid for dehydration and molding. Then, an adhesive is added and the product is dried, cured, and cut in a forced-air oven to obtain the silicon carbide fiber felt product.

[0055] Comparative Example 1

[0056] This invention provides a method for preparing silicon carbide fiber felt, comprising the following steps:

[0057] 1. Use a fiber cutting machine to cut silicon carbide fibers into 10mm pieces and carbon fibers into 5mm pieces;

[0058] 2. Add 69.2g of water to a dispersion tank, then add 15g of sodium hexametaphosphate, 5g of polyethylene glycol, 1.5g of hydrophilic fumed silica, 4g of carboxymethyl cellulose, 0.3g of polydimethylsiloxane and 5g of polyether silicone modified silicone oil in sequence. Adjust the pH value to 10-12, and after sand milling for 1 hour, the nano-dispersion is ready.

[0059] 3. Weigh a certain amount of silicon carbide fiber and carbon fiber from step (1), add them to the nano-dispersion prepared in step (2), stir and disperse them in a dispersion tank to prepare a uniform silicon carbide fiber / carbon fiber suspension.

[0060] The silicon carbide fiber accounts for 90% by weight, and the carbon fiber accounts for 10% by weight.

[0061] The silicon carbide fiber suspension prepared in step (3) is transported to a grid for dehydration and molding. Then, an adhesive is added and the product is dried and cured in a blower oven. The resulting product has fiber agglomeration on its surface, which is a defective product.

[0062] Comparative Example 2

[0063] Other conditions were the same as in Example 1, except that the silicon carbide fibers were not subjected to low-temperature plasma treatment. Instead, the obtained short-cut silicon carbide fibers were added to a mixed aqueous solution of hydrofluoric acid and phosphoric acid in a ratio of 5:2, heated to 120°C, kept at that temperature for 2 hours, removed, washed with alcohol 4 times, and then dried in a 60°C oven for 3 hours before being added to the nano-dispersion.

[0064] During the cleaning and drying process, the acid-treated modified silicon carbide fibers tend to clump together, increasing the difficulty of fiber dispersion and manufacturing costs. The resulting felt still exhibits uneven agglomeration on the surface.

[0065] Comparative Example 3

[0066] The only difference between this comparative example and Example 1 is that hydrophilic fumed silica was not added to the nano-dispersion, resulting in the tendency for the nano-dispersion to form bundles.

[0067] The silicon carbide composite felts obtained in the examples and comparative examples were subjected to performance tests, and the results are shown in Table 1.

[0068] Table 1

[0069]

Claims

1. A method for preparing a silicon carbide fiber composite felt, characterized in that: Short-cut silicon carbide fibers are subjected to plasma surface treatment. Then, one of short-cut glass fibers or short-cut carbon fibers is added to a nano-dispersion liquid along with the short-cut silicon carbide fibers to obtain a fiber suspension. The fiber suspension is then dehydrated, shaped, dried, and solidified to obtain the final product. The nano-dispersion liquid is composed of the following components by weight: 0.5-25 parts surfactant, 0.2-15 parts fumed silica powder, 0.1-10 parts thickener, 0.1-0.5 parts defoamer, 0.5-10 parts softener, and 39.5-98.6 parts water. The conditions for plasma surface treatment are: time of 5-90 min, power of 600-900 W, and pressure of 0.1-0.2 MPa. The mass ratio of the chopped silicon carbide fiber to the chopped glass fiber is 0.1~10:90~99; The mass ratio of the chopped silicon carbide fiber to the chopped carbon fiber is 60-90:10-40; The preparation process of the nano-dispersion is as follows: after adding surfactant, fumed silica, thickener, defoamer and softener to water, the pH is adjusted to 2-12 and then sand milling is performed; the sand milling time is 20-180 min.

2. The method for preparing a silicon carbide fiber composite felt according to claim 1, characterized in that: 15-20 parts surfactant, 1-5 parts fumed silica, 4-10 parts thickener, 0.1-0.5 parts defoamer, 5-10 parts softener, and 39.5-98.6 parts water.

3. The method for preparing a silicon carbide fiber composite felt according to claim 1, characterized in that: The lengths of the chopped silicon carbide fibers, chopped glass fibers, and chopped carbon fibers are all 4 to 15 mm.

4. The method for preparing a silicon carbide fiber composite felt according to claim 1, characterized in that: The viscosity of the fiber suspension is 5~400 mPa·s; The gas content is 2-20%.

5. The method for preparing a silicon carbide fiber composite felt according to claim 1, characterized in that: The softener is at least one of polyether silicone modified silicone oil and hydrophilic amino silicone oil; The surfactant is at least one of sodium hexametaphosphate, fatty alcohol polyoxyethylene ether, fatty amine polyoxyethylene ether, alkyl ammonium salt, fatty alcohol and ethylene oxide condensate, polyethylene glycol, polyoxyethylene sorbitan monostearate, polyvinylpyrrolidone, and cetearyl alcohol polyoxyethylene ether; the thickener is at least one of carboxymethyl cellulose, hydroxypropyl methyl cellulose, hydroxyethyl cellulose, and polyethylene oxide; and the defoamer is at least one of amides, phosphate esters, silicones, and polyethers.

6. The method for preparing a silicon carbide fiber composite felt according to claim 1, characterized in that: The felt obtained after dehydration and molding is then mixed with an adhesive and dried and cured. The amount of adhesive added is 5-15% of the mass of the felt. The adhesive is selected from one of acrylic resin, polyurethane, silicone resin, phenolic resin, and epoxy resin.

7. The silicon carbide fiber composite felt prepared by the preparation method according to any one of claims 1-6.

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