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

Abstract

The invention provides a low-frequency sound-absorbing nanofiber composite material and a preparation method thereof, and belongs to the technical field of sound-absorbing nanofiber composite materials, and the nanofiber composite sound-absorbing material is formed by compounding liquid spraying nanofibers and kapok pulp. According to the preparation method, the nanofibers are prepared in batches through a liquid jet spinning process, the kapok pulp fibers are blown into the nanofibers through high-speed airflow when the nanofibers are drafted, online compounding of the kapok pulp is achieved through a designed spraying device, and the efficient nanofiber sound-absorbing composite material is prepared. According to the composite sound absorption material, the specific surface area and porosity of the material can be improved, more sound energy absorption paths and more effective sound wave energy loss are provided, so that the sound absorption performance of the sound absorption material is improved, the mass of the material is reduced, and the composite sound absorption material has the characteristics that the low-frequency sound absorption effect is good, the frequency band is wide, and the preparation method is simple and convenient to operate.

Description

Technical Field

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

[0002] With the continuous development of urbanization and industrialization, noise seems to be an inevitable part of life and has become an important factor affecting people's normal learning and life. Low-decibel noise can make people irritable and difficult to fall asleep, while high-decibel noise can make people unbearable and even cause death. It poses a serious threat to human physical and mental health. In addition, noise may also damage the ecological environment and cause economic losses. There are two main ways to solve the noise problem. One is to control the sound source; the other is to use sound-absorbing materials. The use of sound-absorbing materials is an effective passive sound absorption method and the most effective noise control method in practical applications. According to the different structures of sound-absorbing materials, sound-absorbing materials can be divided into three categories: porous, resonant, and special structures.

[0003] At present, porous sound-absorbing materials are the most widely used, mainly including four categories: inorganic fibers, inorganic foams, foam plastics and organic fibers. Inorganic fiber sound-absorbing materials have good sound absorption performance and are light and non-flammable. They have the characteristics of flame retardancy, high temperature resistance and high strength. However, they are inconvenient to install, pollute the environment, and affect people's health. At the same time, they are expensive and have complex processes. Inorganic foam sound-absorbing materials have the advantages of light weight, non-corrosiveness, non-flammability, odorlessness, and convenient construction, but the process is difficult to control and the cost is high. Foam plastic sound-absorbing materials refer to a lightweight, sound-absorbing, heat-insulating, flame-retardant, corrosion-resistant and shock-proof material made of various resins as the base material, with a small amount of auxiliary materials such as foaming agents, catalysts, stabilizers, etc., and heated and foamed. At present, polyurethane foam sound-absorbing materials are widely used, but they have low strength and are inconvenient to use. In the early days, organic fiber sound-absorbing materials mainly referred to natural plant fibers, which had good sound absorption performance in the medium and high frequency ranges, but poor fire resistance, corrosion resistance, moisture resistance and other properties. At present, organic fiber sound-absorbing materials at home and abroad have good sound absorption effects in the medium and high frequency ranges, but the low-frequency sound absorption effect is not ideal.

[0004] Nonwoven materials are porous, soft and elastic. When sound waves are incident on the surface of the material, part of them penetrate into the material and propagate left and right in the micropores. Due to the viscosity and heat conduction effects, part of the sound energy will be consumed. The nonwoven material itself is a porous medium material with a three-dimensional random distribution. There are a large number of interconnected micropores between the fibers. The large specific surface area, porosity and fluffy structure give the nonwoven material good sound absorption performance. Existing nonwoven sound-absorbing materials are usually composited with multiple layers of needle-punched nonwoven fabrics with different structures, that is, needle-punched nonwoven fabrics with different needle-punching densities, different thicknesses and different materials are formed by chemical bonding and thermal bonding.

[0005] CN106739226A discloses a sound-absorbing and sound-insulating needle-punched nonwoven fabric for automobile interior and a preparation method thereof. The invention has a simple structure, is easy to use, and has the advantages of high strength, light weight, good sound absorption effect, and good sound insulation effect. In the invention disclosure patent of CN106739226A, a sound-absorbing and sound-insulating needle-punched nonwoven fabric for automobile interior and a preparation method thereof are disclosed, which composites the surface fabric and the base fabric of different surface densities and different materials through an adhesive layer. This nonwoven fabric formed by the needle-punching process has defects in sound absorption. Due to the increase in the needle-punching frequency and the needle-punching density, its internal structure is more compact, and the resonance effect of the sound wave is deteriorated. In addition, the process of the method is cumbersome, the bonding process control requirements are high, and the preparation process is complicated.

[0006] At present, the common nanofiber preparation processes include electrospinning, centrifugal spinning, sol-gel method, etc., but the scale of nanofibers produced by these processes is still at the laboratory level and cannot meet the production requirements of enterprises. At the same time, the spinning parameters of these spinning processes are numerous and strict, which has certain safety hazards.

[0007] The fiber diameters of common sound-absorbing materials are around millimeters and micrometers. Nanofibers have extremely high specific surface areas, which can provide more surfaces to capture and convert sound wave energy. At the same time, the porous structure of nanofibers helps the sound waves to be scattered and absorbed multiple times when propagating inside the material.

[0008] In order to ensure good sound absorption effect, the common sound absorption materials are relatively heavy. Nanofiber sound absorption materials can be made into ultra-thin structures. Compared with other traditional sound absorption materials, they can achieve the effect of weight reduction without sacrificing sound absorption performance.

[0009] At present, the common low-frequency sound-absorbing materials generally adopt the method of increasing the thickness of the sound-absorbing materials. Although this can improve the low-frequency sound-absorbing performance of the materials, the effect is not obvious, and the use is also limited by space, material volume and cost. In addition, there are also sound-absorbing materials designed into various geometric shapes, such as spheres, cones, cylinders, hexahedrons, tetrahedrons, etc. Although this expands the effective area of ​​sound absorption and can obtain better sound absorption effects, the manufacturing process is more complicated and will be limited by the use space, so it cannot be widely used. Summary of the invention

[0010] One object of the present invention is to provide a low-frequency sound-absorbing nanofiber composite material, which utilizes the special structure of nanofibers and kapok hollow fibers to design a composite structure of natural fibers and nanofibers to improve sound absorption performance, that is, by utilizing the high-density porous material of nanofibers and the hollow structure of kapok pulp and their random arrangement in the composite material, the sound is alternately emitted and attenuated in the kapok hollow space, thereby increasing the sound absorption effect of the composite material and the energy loss of sound waves.

[0011] Another object of the present invention is to provide a method for preparing a low-frequency sound-absorbing nanofiber composite material, which is directly composited online with another kapok short fiber material without the need for chemical adhesives or thermal bonding processes. The online composite is coordinated by the spinning airflow and the spraying device airflow, thereby reducing the composite process steps and cutting costs.

[0012] To solve the above technical problems, the purpose of the present invention is achieved as follows:

[0013] The low-frequency sound-absorbing nanofiber composite material of the present invention comprises kapok pulp fibers, wherein the kapok pulp fibers are three-dimensionally distributed in PAN nanofibers; and part of the PAN nanofibers enter the cavity of the kapok pulp fibers.

[0014] A method for preparing a low-frequency sound-absorbing nanofiber composite material according to the present invention comprises the following steps:

[0015] S1. Preparation of kapok pulp fiber: chopping kapok fiber into short fibers of 1-2 cm in length, beating the fibers with running water in a pulping machine, collecting the fibers, and drying the fibers to obtain kapok pulp fiber;

[0016] S2. Preparation of nanofiber composite material: first prepare a precursor solution, and then use a liquid jet spinning device to prepare nanofibers; the precursor solution is composed of polyacrylonitrile and N,N-dimethylformamide;

[0017] The liquid jet spinning device comprises 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 fibers are injected into a spraying device and sprayed onto a receiving device;

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

[0020] The spinning assembly comprises a high-pressure airflow channel, a guide wall and a nozzle assembly, wherein the nozzle assembly is used to place a polymer solution, the high-pressure airflow channel is used to transport a high-pressure and high-speed airflow, and the guide wall is used to control the direction of the high-pressure and 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 draw the polymer solution in the nozzle assembly into nanofibers through the high-pressure and high-speed airflow;

[0021] The spraying assembly includes a transparent shell, a transport roller, a needle, a stripping plate, a conveyor belt, a hopper and a motor; the transparent shell is used to observe whether the material is transported smoothly, the transport roller is used to transport fibers, the needle is used to pierce and obtain fibers, the stripping plate is used to strip the fibers carried by the needle on the transport roller, the conveyor belt is used to transport the fibers stripped by the stripping plate, and the hopper is used to place materials.

[0022] On the basis of the above scheme and as a preferred scheme of the above scheme: the angle of the spray assembly can be adjusted from 30° to 60° horizontally.

[0023] On the basis of the above scheme and as a preferred scheme of the above scheme: it is characterized in that the hopper has an openable and closable sealing structure.

[0024] On the basis of the above scheme and as a preferred scheme of the above scheme: the precursor solution includes PAN with a mass fraction of 8%-16% and the balance DMF.

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

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

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

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

[0029] The nanofibers in the present invention are obtained by a liquid-jet spinning process, which has significant advantages in safety compared to the traditional electrostatic spinning process. The liquid-jet spinning process uses a high-speed airflow to stretch the polymer solution, and does not require the use of high voltage, thereby greatly reducing the risk of electric shock and fire, making the entire spinning process safer. In addition, the liquid-jet spinning equipment is simple to operate and has low cost, which also helps to improve the safety of the process.

[0030] In the present invention, during the process of preparing nanofibers, kapok pulp fibers are directly brought onto the nanofiber membrane through the high-speed airflow during spinning, thereby achieving online compounding of materials, reducing process steps, and reducing costs.

[0031] In the present 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 high porosity, more sound energy absorption paths and more effective sound wave energy loss are provided, thereby improving the sound absorption performance of the sound-absorbing cloth and reducing the weight of the material.

[0032] In the present invention, kapok pulp fibers are added to the inner core layer material mainly composed of nanofibers, and the unique large hollow structure of kapok pulp fibers is utilized to enable the material to effectively absorb sound wave energy and reduce sound wave reflection, thereby improving the sound absorption effect. BRIEF DESCRIPTION OF THE DRAWINGS

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

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

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

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

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

[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 of kapok pulp nanofiber composites and nanofibers with different mass fractions. DETAILED DESCRIPTION

[0041] The present invention is further described below in conjunction with the accompanying drawings and specific embodiments.

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

[0043] S1. Preparation of kapok pulp fiber: The kapok fiber was cut into short fibers with a length of 1 mm by mechanical cutting. The SEM image of the kapok fiber was as follows: Figure 4After being beaten with running water in a pulping machine for 2-3 hours, the pulp was collected and dried in an oven at 50°C for 3-4 hours. After the water was evaporated, the kapok pulp fibers were collected. The SEM image of the kapok pulp is shown in Figure 5 shown.

[0044] S2, preparation of nanofiber composite material: The preparation method of low-frequency sound-absorbing nanofiber composite material used in the present invention is liquid jet spinning, which mainly produces nanofibers in batches by high-speed airflow drafting. The 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, the pressure regulating valve and the rotary nozzle are connected by a leather hose to transport high-pressure air. The syringe and the spinneret in the rotary nozzle are connected by a thin conduit to transport the polymer spinning solution.

[0045] A precursor solution is prepared first, and then a liquid jet spinning device is used to prepare a nanofiber composite material; the precursor solution consists of polyacrylonitrile (PAN, C3H3N) and N,N-dimethylformamide (DMF, C3H7NO).

[0046] The precursor solution can be obtained from PAN with a mass fraction of 8%-16% and the corresponding DMF. In this embodiment, a spinning solution with a PAN content of 14% and a DMF content of 86% is used. The precursor solution is formed by stirring at 60-75°C for 3-5 hours. In this embodiment, the precursor solution 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; during the production of the product, the polymer solution extrusion rate is 0.09 ml / min, the air pressure is 0.025 MPa, the inner diameter of the needle is 0.39 mm, and the receiving distance is 50 cm.

[0048] First, connect the conduit of the air compressor and the pressure regulating valve to the air inlet in the rotary nozzle, turn on the air compressor, and set the air pressure to 0.025Mpa through the pressure regulating valve. Secondly, turn on the receiving device and start it to rotate to evenly receive the nanofibers. Inject the configured PAN / DMF spinning precursor solution with a mass fraction of 14% into the syringe. Connect it to the spinneret in the rotary nozzle through the conduit, and slowly squeeze the spinning solution into the conduit and fill the conduit. Set the extrusion speed to 0.09ml / min on the micro-injection pump. Add 0.48g of kapok pulp fiber to the hopper 26 of the spray assembly 20, seal it, adjust the speed of the motor 27, set the extrusion amount to 0.025g / min, and adjust the assembly angle to a horizontal 45°. At this point, preparation is complete, start the micro-injection pump, and start the spray assembly.

[0049] The precursor solution is squeezed out of the rotating nozzle by the ejector pump and then sucked in by the high-speed airflow generated by the air compressor. The air flow rate is adjusted by the air compressor regulating valve to generate different air pressures to suck in the polymer jet to obtain nanofibers.

[0050] The kapok pulp fibers are injected into the spraying device and sprayed onto the receiving device; the kapok pulp fibers are sprayed online through the spraying device between the nozzle and the receiving device, and are controlled by setting the mass pushed out 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, wherein the nozzle assembly 13 is used to place a polymer solution, the high-pressure airflow channel 11 is used to transport a 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, and the high-pressure airflow channel 11 and the guide wall 12 draw the polymer solution in the nozzle assembly 13 into nanofibers through the high-pressure and high-speed airflow;

[0053] The spray assembly 20 includes a transparent housing 21, a transport roller 22, a needle 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 transported smoothly, the transport roller 22 is used to transport fibers, the needle 23 is used to pierce and obtain fibers, the stripping plate 24 is used to strip the fibers carried by the needle 23 on the transport roller 22, the conveyor belt 25 is used to transport the fibers stripped by the stripping plate 24, and the hopper 26 is used to place materials. The angle of the spray assembly 20 can be adjusted from 30° to 60° horizontally to meet the needs of different requirements.

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

[0055] A low-frequency sound-absorbing nanofiber composite material is prepared, including kapok pulp fibers 1, wherein the kapok pulp fibers 1 are three-dimensionally distributed in PAN nanofibers 2; and part of the PAN nanofibers 2 will enter the cavity of the kapok pulp fibers 1. After the sound waves come into contact with the prepared low-frequency sound-absorbing nanofiber composite material, three situations will occur: part of the sound waves are rebounded, part of the sound waves are absorbed by the material, and the remaining part continues to propagate through the material. After the sound waves enter the nanofibers and kapok pulp fibers, the porosity and high porosity of the materials provide more sound energy absorption paths and more effective sound wave energy loss, thereby achieving sound wave absorption.

[0056] The precursor solution is squeezed from the syringe into the nozzle assembly 13 by a micro-injection pump. As the micro-injection pump is continuously squeezed, the polymer solution is squeezed out of the nozzle assembly 13, and the high-pressure and high-speed airflow in the high-pressure airflow channel 11 will stretch the polymer solution. At the same time, the motor 27 drives the transport roller 22 to start rotating, and the kapok pulp fibers are adsorbed on the roller through the extraction effect of the needles 23 on the transport roller 22. Through the stripping effect of the stripping plate 24, the kapok pulp fibers are stripped onto the conveyor belt 25, and then enter the liquid jet spinning for online compounding. 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 as follows. Figure 6 , Figure 7 shown.

[0057] The produced nanofiber sound-absorbing composite material was subjected to the impedance tube method sound absorption test. Figure 8 .Depend on Figure 8 The low-frequency sound absorption comparison diagram of kapok pulp nanofiber composite materials with different mass fractions and pure nanofiber sound-absorbing materials is shown. It can be seen from the figure that the addition of kapok pulp greatly improves the sound absorption coefficient within 450-1200Hz, which plays a role in effectively absorbing low-frequency noise.

[0058] The preferred specific embodiments of the present invention are described in detail above. It should be understood that a person skilled in the art can make many modifications and changes based on the concept of the present invention without creative work. Therefore, any technical solution that can be obtained by a person skilled in the art through logical analysis, reasoning or limited experiments based on the concept of the present invention on the basis of the prior art should be within the scope of protection determined by the claims.

Claims

1. A low-frequency sound-absorbing nanofiber composite material, characterized in that: It comprises kapok pulp fibers (1), wherein the kapok pulp fibers (1) are three-dimensionally distributed in PAN nanofibers (2); and part of the PAN nanofibers (2) enter the cavity of the kapok pulp fibers (1).

2. A method for preparing a low-frequency sound-absorbing nanofiber composite material, characterized in that: The steps include: S1. Preparation of kapok pulp fiber: Cut wood pulp fiber into pieces with a length of 1-2 cm, beat them with running water in a pulping machine, collect them, and dry them to obtain kapok pulp fiber; S2. Preparation of nanofiber composite materials: first preparing a precursor solution, and then using a liquid jet spinning device to prepare nanofibers; The precursor solution consists of polyacrylonitrile and N,N-dimethylformamide; The liquid jet spinning device comprises 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 fibers are injected into a spraying device and sprayed onto a receiving device; The spraying device comprises a spinning assembly (10) and a spraying assembly (20); The spinning assembly (10) comprises a high-pressure airflow channel (11), a guide wall (12) and a nozzle assembly (13); the nozzle assembly (13) is used to place a polymer solution; the high-pressure airflow channel (11) is used to transport a 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) draw the polymer solution in the nozzle assembly (13) into nanofibers through the high-pressure and high-speed airflow; The spraying assembly (20) comprises a transparent shell (21), a transport roller (22), a needle (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 transported smoothly, the transport roller (22) is used to transport fibers, the needle (23) is used to pierce and obtain fibers, the stripping plate (24) is used to strip the fibers carried by the needle (23) on the transport roller (22), the conveyor belt (25) is used to transport the fibers stripped by the stripping plate (24), and the hopper (26) is used to place materials.

3. The method for preparing a low-frequency sound-absorbing nanofiber composite material according to claim 2, characterized in that: The angle of the spray assembly (20) can be adjusted from 30° to 60° horizontally.

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

5. The method for preparing a low-frequency sound-absorbing nanofiber composite material according to claim 2, characterized in that: The precursor solution comprises PAN with a mass fraction of 8%-16% and the balance of DMF.

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

7. The method for preparing a low-frequency sound-absorbing nanofiber composite material according to claim 2, characterized in that: The extrusion rate of the precursor solution is 0.09 ml / min, the air pressure is 0.025 MPa, the inner diameter of the needle is 0.39 mm, and the receiving distance is 50 cm.

8. The method for preparing a low-frequency sound-absorbing nanofiber composite material according to claim 2, characterized in that: The spraying speed of the kapok pulp fiber is 0.025 g / min.

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