Low-frequency sound-absorbing nanofiber composite material and preparation method thereof

Abstract

The application provides a low-frequency sound-absorbing nanofiber composite material and a preparation method thereof, and belongs to the technical field of sound-absorbing fiber composite materials. The nanofiber composite sound-absorbing material is composed of liquid spraying nanofiber and kapok pulp. The nanofiber is prepared in batches through a liquid spraying spinning process, and kapok pulp fiber is blown in by using high-speed airflow when the nanofiber is drawn. The online compounding of the kapok pulp is realized through a designed spraying device, and the high-efficiency nanofiber sound-absorbing composite material is prepared. The composite sound-absorbing material can improve the specific surface area and porosity of the material, provide more sound energy absorption paths and more effective sound wave energy loss, thereby improving the sound absorption performance of the sound-absorbing material and reducing the mass of the material. The composite material has the characteristics of good low-frequency sound-absorbing effect, wide frequency band and simple and convenient preparation method.

Description

Technical Field

[0001] This invention relates to a low-frequency sound-absorbing nanofiber composite material and its preparation method, belonging to the technical field of sound-absorbing fiber composite materials. Background Technology

[0002] With the continuous development of urbanization and industrialization, noise seems to be an unavoidable part of life, becoming a significant factor affecting people's normal study and life. Low-decibel noise can cause irritability and difficulty falling asleep, while high-decibel noise can be unbearable, and in severe cases, may even lead to death, posing a serious threat to human physical and mental health. Furthermore, noise can damage the ecological environment and cause economic losses. There are two main ways to solve the noise problem: controlling the sound source and using sound-absorbing materials. Using sound-absorbing materials is an effective passive sound absorption method and also the most effective noise control method in practical applications. Based on their structure, sound-absorbing materials can be divided into three categories: porous, resonant, and special structure.

[0003] Currently, porous sound-absorbing materials are the most widely used, mainly including four categories: inorganic fibers, inorganic foams, foamed plastics, and organic fibers. Inorganic fiber sound-absorbing materials have good sound absorption performance, are lightweight, non-flammable, and possess characteristics such as flame retardancy, high temperature resistance, and high strength. However, they are inconvenient to install, pollute the environment, and can affect human health. They are also relatively expensive and have complex manufacturing processes. Inorganic foam sound-absorbing materials have advantages such as being lightweight, non-corrosive, non-flammable, odorless, and easy to construct, but their manufacturing process is difficult to control and their cost is high. Foamed plastic sound-absorbing materials refer to lightweight, sound-absorbing, heat-insulating, flame-retardant, corrosion-resistant, and shock-absorbing materials made by heating and foaming various resins as a base material with the addition of small amounts of foaming agents, catalysts, stabilizers, and other auxiliary materials. Currently, polyurethane foam sound-absorbing materials are widely used, but their strength is low and their use is inconvenient. Early organic fiber sound-absorbing materials mainly referred to natural plant fibers, which have good sound absorption performance in the mid and high frequency range, but poor fire resistance, corrosion resistance, and moisture resistance. At present, organic fiber sound-absorbing materials at home and abroad have good sound absorption effect in the mid and high frequency range, but their low frequency sound absorption effect is not ideal.

[0004] Nonwoven materials possess porosity, softness, and elasticity. When sound waves strike the material surface, some penetrate into the interior, propagating laterally within the micropores. Due to viscosity and thermal conductivity, some sound energy is dissipated. Nonwoven materials themselves are porous media with a three-dimensional, randomly distributed structure, containing numerous interconnected micropores between fibers. Their large specific surface area, porosity, and loose structure endow them with excellent sound absorption properties. Existing nonwoven sound-absorbing materials are typically composed of multiple layers of needle-punched nonwoven fabrics with different structures, formed through chemical and thermal bonding using needle-punched nonwoven fabrics of varying needle densities, thicknesses, and materials.

[0005] CN106739226A discloses a sound-absorbing and sound-insulating needle-punched nonwoven fabric for automotive interiors and its preparation method. This invention has a simple structure, is easy to use, and possesses advantages such as high strength, light weight, excellent sound absorption, and good sound insulation. The invention disclosed in CN106739226A involves bonding a surface fabric and a base fabric of different surface densities and materials using an adhesive layer. However, this type of nonwoven fabric formed through a needle-punching process has defects in sound absorption. Due to the increased needle-punching frequency and density, its internal structure becomes denser, resulting in a poorer resonance effect for sound waves. Furthermore, this method involves a cumbersome composite process, requires high control of the bonding process, and has a complex preparation process.

[0006] Currently, common nanofiber preparation processes include electrospinning, centrifugal spinning, and the sol-gel method. However, the nanofibers produced by these processes are still at the laboratory level and cannot meet the production requirements of enterprises. Furthermore, these spinning processes involve numerous and stringent spinning parameters, posing certain safety risks.

[0007] Currently, common sound-absorbing materials use fibers with diameters in the millimeter or micrometer range. Nanofibers, on the other hand, have extremely high specific surface areas, providing more surface area to capture and convert sound wave energy. Furthermore, the porous structure of nanofibers facilitates multiple scattering and absorption of sound waves as they propagate within the material.

[0008] Currently, common sound-absorbing materials are relatively heavy to ensure good sound absorption. Nanofiber sound-absorbing materials can be made into ultra-thin structures, achieving weight reduction without sacrificing sound absorption performance compared to other traditional sound-absorbing materials.

[0009] Currently, common low-frequency sound-absorbing materials generally improve their low-frequency sound absorption performance by increasing the material's thickness. While this can enhance the material's low-frequency sound absorption, the effect is not significant, and its application is limited by space constraints, material volume, and cost. Alternatively, sound-absorbing materials can be designed into various geometric shapes, such as spheres, cones, cylinders, hexahedrons, and tetrahedrons. While this increases the effective sound-absorbing area and can achieve better sound absorption, the manufacturing process is more complex, and its application is limited by space constraints, preventing its widespread use. Summary of the Invention

[0010] One objective of this invention is to provide a low-frequency sound-absorbing nanofiber composite material. By utilizing the special structures of nanofibers and hollow kapok fibers, a composite structure of natural fibers and nanofibers is designed to improve sound absorption performance. Specifically, by utilizing the high-density porous material of nanofibers and the hollow structure of kapok pulp, as well as their random arrangement in the composite material, sound is alternately emitted and attenuated in the hollow space of the kapok, thereby increasing the sound absorption effect and energy loss of the sound waves of the composite material.

[0011] Another objective of this invention is to provide a method for preparing low-frequency sound-absorbing nanofiber composite materials, which directly composites with another type of kapok short fiber material online without the need for chemical adhesives or thermal bonding processes. The online composite is achieved through the coordinated online composite process of spinning airflow and spraying device airflow, reducing the number of composite process steps and lowering costs.

[0012] To solve the above-mentioned technical problems, the objective of this invention is achieved as follows:

[0013] The present invention relates to a low-frequency sound-absorbing nanofiber composite material, comprising kapok pulp fibers, wherein the kapok pulp fibers are three-dimensionally distributed within PAN nanofibers; and some of the PAN nanofibers enter the cavity of the kapok pulp fibers.

[0014] The present invention relates to a method for preparing a low-frequency sound-absorbing nanofiber composite material, comprising the following steps:

[0015] S1. Preparation of Kapok Pulp Fiber: Kapok fiber is cut into short fibers of 1-2cm in length, collected after being beaten by a pulping machine, and dried to obtain Kapok pulp fiber.

[0016] S2. Preparation of nanofiber composite material: First, a precursor solution is prepared, and then nanofibers are prepared using a liquid-jet spinning device; the precursor solution is composed of polyacrylonitrile and N,N-dimethylformamide;

[0017] The liquid jet spinning device includes an air compressor, a pressure regulating valve, a syringe, a micro-injection pump, a nozzle, a spraying assembly, a heating device, and a receiving device;

[0018] The kapok pulp fiber is injected into the spraying device and sprayed onto the receiving device;

[0019] The spraying device includes a spinning assembly and a spraying assembly;

[0020] The spinning assembly includes a high-pressure airflow channel, a guide wall, and a nozzle assembly. The nozzle assembly is used to hold the polymer solution, the high-pressure airflow channel is used to transport high-pressure, high-speed airflow, and the guide wall is used to control the direction of the high-pressure, high-speed airflow. The nozzle assembly is located in the middle of the guide wall, and the high-pressure airflow channel and the guide wall use the high-pressure, high-speed airflow to stretch the polymer solution in the nozzle assembly into nanofibers.

[0021] The spraying assembly includes a transparent housing, a transport roller, needles, a stripping plate, a conveyor belt, a hopper, and a motor. The transparent housing is used to observe whether the material is being transported smoothly. The transport roller is used to transport fibers. The needles are used to pierce and obtain fibers. The stripping plate is used to strip the fibers attached to the needles on the transport roller. The conveyor belt is used to transport the fibers stripped off by the stripping plate. The hopper is used to hold the material.

[0022] Based on the above scheme and as a preferred embodiment of the above scheme: the angle of the spraying component can be adjusted from 30° to 60° horizontally.

[0023] Based on the above scheme and as a preferred embodiment of the above scheme, the hopper is characterized by having an openable and closable sealing structure.

[0024] Based on the above scheme and as a preferred embodiment of the above scheme: the precursor solution comprises 8%-16% PAN by mass and the balance being DMF.

[0025] Based on the above scheme and as a preferred embodiment of the above scheme: the precursor solution is formed by stirring PAN and DMF at 60-75°C for 3-5 hours.

[0026] Based on the above scheme and as a preferred embodiment of the above scheme: the precursor solution extrusion rate is 0.09 ml / min, the air pressure is 0.025 MPa, the needle inner diameter is 0.39 mm, and the receiving distance is 50 cm.

[0027] Based on the above scheme and as a preferred embodiment of the above scheme: the spraying speed of the kapok pulp fiber is 0.025 g / min.

[0028] Compared with the prior art, the present invention has the following beneficial effects:

[0029] In this invention, nanofibers are obtained through a liquid-jet spinning process, which offers significant safety advantages compared to traditional electrospinning. Liquid-jet spinning uses a high-speed airflow to stretch the polymer solution, eliminating the need for high voltage and thus greatly reducing the risk of electric shock and fire, making the entire spinning process safer. Furthermore, the simple operation and low cost of liquid-jet spinning equipment also contribute to improved process safety.

[0030] In this invention, during the nanofiber preparation process, kapok pulp fibers are directly introduced onto the nanofiber membrane via a high-speed airflow during spinning, achieving online material composite, reducing process steps, and reducing costs.

[0031] In this invention, nanofibers are used as the main material of the composite sound-absorbing material. By reducing the diameter of the fiber material, increasing the specific surface area and porosity, more sound energy absorption paths are provided and sound wave energy loss is more effective, thereby improving the sound absorption performance of the sound-absorbing cloth and reducing the mass of the material.

[0032] In this invention, kapok pulp fibers are added to the inner core material, which is mainly composed of nanofibers. By utilizing the unique large hollow structure of kapok pulp fibers, the material can effectively absorb sound wave energy, reduce sound wave reflection, and thus improve the sound absorption effect. Attached Figure Description

[0033] Figure 1 This is a schematic diagram of the structure of a low-frequency sound-absorbing nanofiber composite material;

[0034] Figure 2 It is a technical route for low-frequency sound-absorbing nanofiber composite materials;

[0035] Figure 3 This is a schematic diagram of the spraying device;

[0036] Figure 4 This is a scanning electron microscope image of kapok fibers;

[0037] Figure 5 This is a scanning electron microscope image of kapok pulp fibers;

[0038] Figure 6 This is a scanning electron microscope image of a low-frequency sound-absorbing nanofiber composite material with a scale of 100 μm.

[0039] Figure 7 This is a scanning electron microscope image of a low-frequency sound-absorbing nanofiber composite material with a scale of 40 μm.

[0040] Figure 8 This is a comparison chart of low-frequency sound absorption between kapok pulp nanofiber composites with different mass fractions and nanofibers. Detailed Implementation

[0041] The present invention will be further described below with reference to the accompanying drawings and specific embodiments.

[0042] Combination Figures 1 to 8 The present invention will be described in detail below. A method for preparing a low-frequency sound-absorbing nanofiber composite material according to the present invention includes the following steps:

[0043] S1. Preparation of Kapok Pulp Fiber: Kapok fiber was mechanically cut into short fibers with a length of 1 mm. The SEM image of the obtained kapok fiber is shown below. Figure 4As shown in the image. The pulp was subjected to continuous beating in a pulping machine for 2-3 hours, then collected and dried in an oven at 50℃ for 3-4 hours. After the moisture was evaporated, the kapok pulp fiber was collected. The SEM image of the obtained kapok pulp is shown in the image. Figure 5 As shown.

[0044] S2. Preparation of Nanofiber Composite Materials: The low-frequency sound-absorbing nanofiber composite material prepared in this invention is prepared by liquid-jet spinning, which mainly uses high-speed airflow to draw nanofibers in batches. This process mainly consists of an air compressor, a pressure regulating valve, a rotary nozzle, a micro-injection pump, a syringe, a heating device, and a receiving device. The air compressor, pressure regulating valve, and rotary nozzle are connected by tubing to deliver high-pressure air. The syringe and the spinneret inside the rotary nozzle are connected by a thin conduit to transport the polymer spinning solution.

[0045] A precursor solution was first prepared, and then a nanofiber composite material was prepared using a liquid-jet spinning device. The precursor solution was composed of polyacrylonitrile (PAN, C3H3N) and N,N-dimethylformamide (DMF, C3H7NO).

[0046] The precursor solution can be obtained from PAN and the corresponding DMF at a mass fraction of 8%-16%. In this example, a spinning solution with a PAN content of 14% and a DMF content of 86% is used. The solution is formed after stirring at 60-75°C for 3-5 hours. In this example, it is obtained by heating and stirring at 70°C for 3 hours.

[0047] The liquid-jet spinning device includes an air compressor, a pressure regulating valve, a syringe, a micro-injection pump, a nozzle, a spraying assembly, a heating device, and a receiving device; the polymer solution extrusion rate during product production is 0.09 ml / min, the air pressure is 0.025 MPa, the needle inner diameter is 0.39 mm, and the receiving distance is 50 cm.

[0048] First, connect the air compressor and pressure regulating valve conduits to the air inlet of the rotary nozzle, turn on the air compressor, and set the air pressure to 0.025 MPa using the pressure regulating valve. Next, turn on the receiving device to start its rotation and uniformly receive the nanofibers. Inject the prepared 14% (w / w) PAN / DMF spinning precursor solution into the syringe. Connect it to the spinneret inside the rotary nozzle through the conduit, and slowly squeeze the spinning solution into the conduit until it is full. Set the extrusion speed on the micro-injection pump to 0.09 ml / min. Add 0.48 g of kapok pulp fiber to the hopper 26 of the spray assembly 20, seal it, adjust the motor 27 speed, set the extrusion rate to 0.025 g / min, and adjust the assembly angle to 45° horizontally. At this point, preparation is complete; start the micro-injection pump and activate the spray assembly.

[0049] The precursor solution is extruded from a rotating nozzle by an ejector pump and then drawn in by a high-speed airflow generated by an air compressor. The airflow rate is adjusted by a regulating valve in the air compressor to generate different air pressures, which draw in the polymer jet, thereby obtaining nanofibers.

[0050] The kapok pulp fiber is injected into the spraying device and sprayed onto the receiving device; the kapok pulp fiber is sprayed online through the spraying device between the nozzle and the receiving device, and the spraying speed is controlled by setting the output quality per minute.

[0051] The spraying device includes a spinning assembly 10 and a spraying assembly 20;

[0052] The spinning assembly 10 includes a high-pressure airflow channel 11, a guide wall 12, and a nozzle assembly 13. The nozzle assembly 13 is used to hold a polymer solution, the high-pressure airflow channel 11 is used to transport high-pressure, high-speed airflow, and the guide wall 12 is used to control the direction of the high-pressure, high-speed airflow. The nozzle assembly 13 is placed in the middle of the guide wall 12. The high-pressure airflow channel 11 and the guide wall 12 use the high-pressure, high-speed airflow to stretch the polymer solution in the nozzle assembly 13 into nanofibers.

[0053] The spraying assembly 20 includes a transparent housing 21, a transport roller 22, needles 23, a stripping plate 24, a conveyor belt 25, a hopper 26, and a motor 27. The transparent housing 21 is used to observe whether the material is being transported smoothly. The transport roller 22 is used to transport fibers. The needles 23 are used to pierce and obtain fibers. The stripping plate 24 is used to strip the fibers attached to the needles 23 on the transport roller 22. The conveyor belt 25 is used to transport the fibers stripped by the stripping plate 24. The hopper 26 is used to hold the material. The angle of the spraying assembly 20 can be adjusted from 30° to 60° horizontally to meet different needs.

[0054] Furthermore, the hopper 26 has an openable and closable sealing structure. The transport roller 22 is powered by a motor 27, which has the ability to control the power level and can quantitatively transport fibers for compounding by controlling the rotation speed.

[0055] A low-frequency sound-absorbing nanofiber composite material was prepared, comprising kapok pulp fibers 1, which are three-dimensionally distributed within PAN nanofibers 2; and some of the PAN nanofibers 2 enter the cavity of the kapok pulp fibers 1. When sound waves come into contact with the prepared low-frequency sound-absorbing nanofiber composite material, three scenarios occur: some sound waves are reflected, some are absorbed by the material, and the remaining portion continues to propagate through the material. After entering the nanofibers and kapok pulp fibers, the porosity and high porosity of the material provide more sound energy absorption paths and more effective sound energy loss, thus achieving sound wave absorption.

[0056] The precursor solution is injected into the nozzle assembly 13 by a micro-injection pump through a syringe. As the micro-injection pump continues to squeeze, the polymer solution is extruded from the nozzle assembly 13. The high-pressure, high-speed airflow in the high-pressure airflow channel 11 stretches the polymer solution. Simultaneously, the motor 27 drives the transport roller 22 to rotate. Kapok pulp fibers are adsorbed onto the roller by the extraction action of the needles 23 on the transport roller 22. Through the peeling action of the peeling plate 24, the kapok pulp fibers are peeled onto the conveyor belt 25, thus entering the liquid-jet spinning process for online composite formation. Finally, the composite sound-absorbing material of kapok pulp fibers and nanofibers is collected after drying. The SEM image of the prepared nanofiber sound-absorbing composite material is shown below. Figure 6 , Figure 7 As shown.

[0057] The produced nanofiber sound-absorbing composite material was subjected to impedance tube sound absorption testing, see [link to relevant documentation]. Figure 8 .Depend on Figure 8 The image shows a comparison of low-frequency sound absorption between composite materials made from kapok pulp nanofibers with different mass fractions and pure nanofiber sound-absorbing materials. As can be seen from the image, the addition of kapok pulp significantly increases the sound absorption coefficient within the 450-1200Hz range, effectively absorbing low-frequency noise.

[0058] The preferred embodiments of the present invention have been described in detail above. It should be understood that those skilled in the art can make numerous modifications and variations based on the concept of the present invention without creative effort. Therefore, all technical solutions that can be obtained by those skilled in the art based on the concept of the present invention through logical analysis, reasoning, or limited experimentation on the basis of existing technology should be within the scope of protection defined by the claims.

Claims

1. A method for preparing a low-frequency sound-absorbing nanofiber composite material, characterized in that, The low-frequency sound-absorbing nanofiber composite material includes kapok pulp fiber (1), which is three-dimensionally distributed in PAN nanofiber (2); and some of the PAN nanofiber (2) enters the cavity of the kapok pulp fiber (1); The preparation method includes the following steps: S1. Preparation of Kapok Pulp Fiber: Kapok fiber is cut into 1-2cm lengths, then collected after being beaten by a pulping machine for 2-3 hours, and dried in an oven at 50℃ for 3-4 hours to evaporate the moisture and obtain kapok pulp fiber. S2. Preparation of nanofiber composite material: First, a precursor solution is prepared, and then nanofibers are prepared using a liquid-jet spinning device; the precursor solution is composed of polyacrylonitrile and N,N-dimethylformamide; The liquid jet spinning device includes an air compressor, a pressure regulating valve, a syringe, a micro-injection pump, a nozzle, a spraying assembly, a heating device, and a receiving device; The kapok pulp fiber is injected into the spraying device and sprayed onto the receiving device; The spraying device includes a spinning assembly (10) and a spraying assembly (20); the spraying assembly (20) is arranged adjacent to each other on both sides of the spinning assembly (10); the angle between the spraying assembly (20) and the horizontal direction is 30° to 60°. The spinning assembly (10) includes a high-pressure airflow channel (11), a guide wall (12), and a nozzle assembly (13). The nozzle assembly (13) is used to hold the polymer solution, the high-pressure airflow channel (11) is used to transport high-pressure and high-speed airflow, and the guide wall (12) is used to control the direction of the high-pressure and high-speed airflow. The nozzle assembly (13) is placed in the middle of the guide wall (12). The high-pressure airflow channel (11) and the guide wall (12) use the high-pressure and high-speed airflow to stretch the polymer solution in the nozzle assembly (13) into nanofibers. The spraying assembly (20) includes a transparent shell (21), a transport roller (22), needles (23), a stripping plate (24), a conveyor belt (25), a hopper (26), and a motor (27); the transparent shell (21) is used to observe whether the material is being transported smoothly, the transport roller (22) is used to transport fibers, the needles (23) are used to pierce and obtain fibers, the stripping plate (24) is used to strip the fibers carried by the needles (23) on the transport roller (22), the conveyor belt (25) is used to transport the fibers stripped off by the stripping plate (24), and the hopper (26) is used to hold the material.

2. The method for preparing a low-frequency sound-absorbing nanofiber composite material according to claim 1, characterized in that, The hopper (26) has an openable and closable sealing structure.

3. The method for preparing a low-frequency sound-absorbing nanofiber composite material according to claim 1, characterized in that, The precursor solution comprises 8%-16% PAN by mass and the balance being DMF.

4. The method for preparing a low-frequency sound-absorbing nanofiber composite material according to claim 3, characterized in that, The precursor solution is formed by stirring PAN and DMF at 60-75°C for 3-5 hours.

5. The method for preparing a low-frequency sound-absorbing nanofiber composite material according to claim 1, characterized in that, The precursor solution was extruded at a rate of 0.09 ml / min, with an air pressure of 0.025 MPa, a needle inner diameter of 0.39 mm, and a receiving distance of 50 cm.

6. The method for preparing a low-frequency sound-absorbing nanofiber composite material according to claim 1, characterized in that, The spraying rate of the kapok pulp fiber is 0.025 g / min.

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