Silicon carbide wet-laid nonwoven fibrous mat and method of making

Abstract

This invention discloses a wet-laid silicon carbide nonwoven fiber felt and its preparation method. The method involves subjecting silicon carbide fibers to plasma surface hydrophilic modification treatment, adding a nano-dispersion liquid, followed by dehydration, molding, bonding, and drying curing to obtain the final product. This invention uses chopped silicon carbide fibers as raw materials and employs wet-laid felting technology to prepare silicon carbide fiber felt with uniform mass distribution per unit area, good appearance, and high-temperature resistance. The preparation method is simple, easy to operate, and suitable for mass production.

Description

Technical Field

[0001] This invention belongs to the field of high-temperature resistant materials and relates to a silicon carbide wet-laid nonwoven fiber felt and its preparation method. Technical Background

[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] In existing technologies, silicon carbide fiber felt is prepared using wet-process felting technology, all using polycarbosilane as a precursor. For example, Chinese patent CN105386237A describes a method for preparing silicon carbide fiber felt and a wet deposition apparatus for its preparation. This method uses polycarbosilane-based infusible fibers as a precursor, which are loosened by airflow and mixed into pulp. After wet deposition and drying, the fibers are placed in a high-temperature furnace for sintering to obtain silicon carbide fiber felt. Specifically, the polycarbosilane-based infusible fiber felt is placed in a high-temperature furnace and heated to 1000–1300°C at a rate of 15–240°C / h under high-purity nitrogen protection, and held at this temperature for 1–1.5 hours to obtain silicon carbide fiber felt. Although this method successfully prepared silicon carbide fiber felt, it firstly struggled to ensure the uniformity of the properties of organic fiber felt during the ceramic transformation process. Secondly, the size of the ceramic fiber felt was severely limited by the size of the ceramic transformation equipment, such as the high-temperature sintering furnace. Furthermore, the operation process of this type of wet nonwoven felt technology is still relatively complex. It uses polycarbosilane as a precursor for preparation, followed by sintering 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 also high. Summary of the Invention

[0005] In view of the shortcomings of the prior art, the first objective of the present invention is to provide a silicon carbide wet-laid nonwoven fiber felt with excellent mechanical properties, low moisture content and low thermal conductivity.

[0006] The second objective of this invention is to provide a method for preparing silicon carbide wet-laid nonwoven fiber felt. This method employs wet-laid nonwoven fiber felt technology, has a simple process flow, is easy to operate, and can be mass-produced. Simultaneously, during the preparation process, plasma, in conjunction with a special nano-dispersion, effectively modifies the surface physical and chemical properties of silicon carbide fibers, thereby effectively improving the material's mechanical properties and high-temperature resistance.

[0007] To achieve the above-mentioned technical objectives, the present invention provides a method for preparing a silicon carbide wet-laid nonwoven fiber felt. The method involves subjecting silicon carbide fibers to plasma surface hydrophilic modification treatment, adding a nano-dispersion liquid, and then dehydrating, molding, bonding, and drying to obtain the felt. The nano-dispersion liquid is composed of the following components by weight: 0.5-25 parts surfactant, 0.2-15 parts fumed silica, 0.1-10 parts thickener, 0.1-0.5 parts defoamer, 0.5-10 parts softener, and 39.5-98.6 parts water.

[0008] This invention employs a wet-process felting technique, directly using chopped silicon carbide fibers as raw materials to prepare silicon carbide fiber felt products. This method offers rapid production and avoids the instability of the jet, unsuitable spinning solution viscosity, and fiber damage or even breakage caused by needle punching that occur in electrospinning. The process is simple, easy to operate, and suitable for mass production. However, silicon carbide has numerous silicon-based hydrophobic groups on its surface, making solution modification difficult. This invention addresses this by using low-temperature plasma to treat the chopped fibers, altering only the physical and chemical properties of the material surface. It introduces hydrophilic groups such as carboxyl, hydroxyl, and carbonyl groups onto the silicon carbide fiber surface, improving its wettability and facilitating dispersion in nano-dispersion solutions. Compared to conventional oxidation methods, the surface etching effect is more pronounced, reducing the rigidity of the silicon carbide fibers to some extent, improving fiber flexibility, and mitigating flocculation problems during dispersion. It also increases the contact area between the fibers and resin materials, improving bonding strength and enhancing composite material performance. Furthermore, the amount of hydrophilic groups introduced by plasma treatment is not significantly different.

[0009] This invention also involves mixing and impregnating a nano-dispersion with chopped silicon carbide fibers, which effectively improves the surface properties of silicon carbide. The surfactant in the nano-dispersion improves the viscosity and flowability of the dispersion and promotes wetting and dispersion of the fiber material. It possesses dispersion, wetting, and surface tension reduction properties, forming a thin film between the fiber material and the liquid, thus improving the compatibility between the fiber material and the mixture. Simultaneously added fumed silica provides skeletal support and surface modification, significantly impacting the performance of the thin felt. Firstly, the fumed silica forms a mesh structure during the thin felt forming process, providing a robust support framework to prevent deformation and breakage of the silicon carbide fibers. This skeletal support makes the overall structure of the thin felt more stable, increasing its mechanical strength and tensile properties. Furthermore, this structure helps the thin felt maintain a certain thickness and shape, making it more suitable for various applications. 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 the 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 felt. The added fumed silica and thickener also help to change the viscosity and thixotropic properties of the dispersion, preventing the silicon carbide fibers from settling and thus improving the uniformity of the silicon carbide fiber felt's performance. The softener can improve the antistatic properties and increase the hydrophilicity of the fibers, improving their softness. Further preferably, 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.

[0010] As a preferred embodiment, the length of the silicon carbide fiber is 4–15 mm. Controlling the length of the silicon carbide fiber in this invention is beneficial for subsequent dispersion.

[0011] As a preferred embodiment, the conditions for the plasma surface hydrophilic modification treatment are: time of 5–90 min, power of 600–900 W, and pressure of 0.1–0.2 MPa. Higher power and pressure during the plasma surface hydrophilic treatment result in a more pronounced surface etching effect on the silicon carbide fibers.

[0012] 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, the pH is adjusted to 2-12, and then the mixture is milled and slurried. In this invention, the pH can be adjusted according to the fiber dispersion rate; the faster the dispersion rate, the better, as a suitable pH value can accelerate the dispersion process.

[0013] As a preferred embodiment, the softener is a polyether-modified silicone oil and / or a hydrophilic amino silicone oil.

[0014] 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; and the thickener is at least one selected from carboxymethyl cellulose, hydroxypropyl methyl cellulose, hydroxyethyl cellulose, and polyethylene oxide.

[0015] As a preferred embodiment, the defoamer is at least one selected from butyl phosphate, silicone, alkyl polyether, and polyether siloxane. Examples of butyl phosphate used in this invention include tributyl phosphate, silicone such as Defeng 2854, alkyl polyether such as Xinwancheng S-717, and polyether siloxane such as Tego 902W.

[0016] As a preferred embodiment, the viscosity of the silicon carbide nano-dispersion is 5–400 mPa·s; the air content is 2–20%. The viscosity of the silicon carbide nano-dispersion affects the stability of silicon carbide fibers in the slurry, while the air content affects the unit area weight during fiber mat forming. More preferably, the viscosity is 185–300 mPa·s, and the air content is 2–5%.

[0017] As a preferred embodiment, the sand milling and pulping time is 20–180 min.

[0018] The present invention also provides a silicon carbide wet-laid nonwoven fiber felt, which is resistant to high temperature, has high tensile strength and low moisture content.

[0019] Compared with the prior art, the present invention has the following beneficial effects:

[0020] 1) The wet felting technology used in this invention offers high production speed and avoids issues such as unstable jet flow, unsuitable spinning solution viscosity, and fiber damage or even breakage caused by needle punching, which are common problems in electrospinning. Furthermore, directly using silicon carbide ceramic fibers as raw materials to prepare fiber felt allows full utilization of the high performance of silicon carbide fibers themselves; the size of the fiber felt is essentially unrestricted, the process is simple and easy to operate, and mass production is possible.

[0021] 2) This invention, through the configuration of a unique nano-dispersion liquid, enables the uniform and stable dispersion of silicon carbide fibers, thereby preparing silicon carbide fiber felt with uniform and controllable properties. The prepared silicon carbide fiber felt has a uniform mass distribution, good appearance, and can withstand high temperatures up to 1200℃. It weighs 25–85 g per square meter, with an 85 g / m² specification fiber felt exhibiting a longitudinal tensile breaking force of 523 N, and a 30 g / m² specification fiber felt exhibiting a longitudinal tensile breaking force of 156 N. The moisture content is less than 0.5%, and the thermal conductivity of a 0.3 mm thick fiber felt is as low as 0.021 W / (mK). Attached Figure Description

[0022] Figure 1 This is a photograph of the silicon carbide fiber felt product prepared in Example 1.

[0023] Figure 2 A physical image of the silicon carbide fiber felt product prepared for Comparative Example 1. Detailed Implementation

[0024] 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.

[0025] 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.

[0026] Example 1

[0027] 1) Cut the silicon carbide fiber into 4mm short fibers using a fiber cutter;

[0028] 2) The short-cut fibers obtained in step 1) were surface treated for 30 minutes using a low-temperature plasma surface treatment machine with a power of 800W and a working pressure of 0.101Mpa.

[0029] 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 GTE 902w 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.

[0030] 4) Weigh a certain amount of silicon carbide fiber from step 2) and add it to the nano-dispersion prepared in step 3). Stir and disperse the mixture in a dispersion tank to prepare a uniform silicon carbide nano-dispersion with a viscosity of 185 mPa·s and an air content of 5%.

[0031] 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.

[0032] Example 2

[0033] 1) Cut the silicon carbide fiber into 12mm short fibers using a fiber cutter;

[0034] 2) The short-cut fibers obtained in step 1) were surface treated for 40 minutes using a low-temperature plasma surface treatment machine with a power of 800W and a working pressure of 0.101Mpa.

[0035] 3) Add 69.2g of water to the dispersion tank, then add 15g of sodium hexametaphosphate, 5g of polyvinylpyrrolidone, 1.5g of hydrophilic fumed silica, 4g of carboxypropyl methylcellulose, 0.3g of tributyl phosphate and 5g of polyether silicone modified silicone oil in sequence. Adjust the pH value to 10-12, and after sand milling for 1.5h, the nano-dispersion is ready.

[0036] 4) Weigh a certain amount of silicon carbide fiber from step 2) and add it to the nano-dispersion prepared in step 3). Stir and disperse the mixture in a dispersion tank to prepare a uniform silicon carbide nano-dispersion with a viscosity of 200 mPa·s and an air content of 5%.

[0037] 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.

[0038] Comparative Example 1

[0039] The only difference between this comparative example and Example 1 is that plasma surface treatment was not performed; all other conditions and steps were the same. The prepared silicon carbide fiber suspension was transported to a grid for dehydration and molding, followed by the addition of an adhesive and drying and curing in a forced-air oven. The resulting fiber felt product had a surface like... Figure 1 The fiber agglomeration shown indicates that the product quality is substandard.

[0040] Comparative Example 2

[0041] The only difference between this comparative example and Example 1 is that hydrophilic fumed silica and polyether silicone-modified silicone oil were not added to the nano-dispersion. All other conditions and steps were the same, resulting in silicon carbide fiber felt.

[0042] Comparative Example 3

[0043] The only difference between this comparative example and Example 2 is that hydrophilic fumed silica and polyether silicone-modified silicone oil were not added to the nano-dispersion. All other steps and conditions were the same, resulting in silicon carbide fiber felt.

[0044] The silicon carbide fiber felts obtained in Examples 1-2 and Comparative Examples 2-3 were subjected to performance tests, and the results are shown in Table 1.

[0045] Table 1

[0046] Example 1 30 1200 156 0.45％ 0.021 Example 2 85 1200 523 0.48％ 0.023 Comparative Example 2 30 1190 132 0.45％ 0.029 Comparative Example 3 85 1180 480 0.48％ 0.026

Claims

1. A method of making a silicon carbide wet-laid nonwoven fibrous mat, characterized by: Silicon carbide fibers are subjected to plasma surface hydrophilic modification treatment, then a nano-dispersion is added, followed by dehydration, molding, bonding, and drying curing to obtain the final product. The nano-dispersion is composed of the following components by weight: 0.5-25 parts surfactant, 0.2-15 parts fumed silica, 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 hydrophilic modification treatment are: time 5~90min, power 600~900W, and pressure 0.1~0.2Mpa; 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 to make a slurry.

2. A method of making a silicon carbide wet-laid nonwoven fibrous felt according to claim 1, characterized in that: The length of the silicon carbide fiber is 4~15mm.

3. The method of claim 1, wherein the method further comprises: The softener is a polyether-modified silicone oil and / or a hydrophilic amino silicone oil.

4. The method for preparing a silicon carbide wet-laid nonwoven fiber felt according to claim 3, characterized in that: 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; The defoamer is at least one of butyl phosphate, organosilicon, alkyl polyether, and polyether siloxane.

5. The method for preparing a silicon carbide wet-laid nonwoven fiber felt according to claim 1, characterized in that: The viscosity of the nano-dispersion is 5~400 mPa·s, and the air content is 2~20%.

6. The method for preparing a silicon carbide wet-laid nonwoven fiber felt according to claim 5, characterized in that: The time for sand milling and pulping is 20~180 minutes.

7. A silicon carbide wet-laid nonwoven fiber felt, characterized in that: It is obtained by the preparation method according to any one of claims 1 to 6.

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