Interlayer composite material based on melamine foamed plastic and preparation method thereof

Abstract

The invention relates to the field of sound-absorbing materials, in particular to an interlayer composite material based on melamine foamed plastic and a preparation method of the interlayer composite material. Comprising the following steps: coordination of Co and nano bacterial cellulose; the preparation method comprises the following steps: preparing Co-BC-melamine foam; and compounding the porous diatomite adhesive and the Co-BC-melamine foam. According to the invention, the nano bacterial cellulose provides good porosity through a high specific surface area and a microfiber structure, after the nano bacterial cellulose is matched with the cobalt acetylacetonate, cobalt ions are coordinated with surface hydroxyl groups of the nano bacterial cellulose to form a stable composite structure, and the composite not only enhances the mechanical properties of the material, but also improves the porosity of the material; in addition, due to the natural characteristics of the nano bacterial cellulose, the nano bacterial cellulose serves as an excellent sound wave absorption medium in the composite material, and therefore the sound absorption capacity of the interlayer material can be effectively improved.

Description

Technical Field

[0001] The present invention relates to the field of sound-absorbing materials, and particularly to a sandwich composite material based on melamine foam and a preparation method thereof. Background Art

[0002] With the rapid development of modern industry and technology, the problem of noise pollution from various equipment and transportation means has become increasingly serious. Noise has become the third largest pollution problem globally after water pollution and air pollution. Moreover, long-term exposure to a noisy environment has many adverse effects on human health, such as tinnitus, insomnia, fatigue, and even cardiovascular diseases. In addition, noise not only harms human health but also affects the service life of instrument equipment and building structures.

[0003] Currently, solving the problem of noise pollution has become a topic with global influence. The current noise control methods mainly include three types: reducing the generation of noise sources, reducing noise by dissipating sound energy during the propagation of sound waves, and reducing the impact of noise through sound wave blocking measures. In particular, dissipating sound energy through sound-absorbing materials is an important means to effectively reduce noise hazards and improve human health protection at present. Sound-absorbing materials are widely used in noise control, especially in environments where noise sources such as household appliances, transportation means, and factory equipment are generated, and have a significant noise reduction effect.

[0004] Common sound-absorbing materials include resonance sound-absorbing materials and porous sound-absorbing materials. Resonance sound-absorbing materials have a narrow absorption frequency band and can effectively absorb sound waves of certain specific frequencies. They have good sound-absorbing performance in the low-frequency range. However, due to their narrow sound-absorbing frequency band, this limits their wide application. At the same time, the structure of resonance sound-absorbing materials is usually relatively complex, and the manufacturing and processing are difficult. Porous materials include natural fibers, melamine foam, polyurethane foam, aluminum foam, etc. They perform well in the sound-absorbing frequency range and stability, and the material selection is wide, and the manufacturing process is relatively simple. Therefore, they are widely used in industrial, architectural, and transportation noise control. However, porous sound-absorbing materials usually have poor sound-absorbing performance in the low-frequency range (100 - 800 Hz), and in order to ensure a satisfactory sound-absorbing coefficient, it is often necessary to increase their thickness and mass. Therefore, designing an efficient sound-absorbing material that can solve the low-frequency sound-absorbing problem, is light in weight, and has a thin thickness is extremely challenging. Summary of the Invention

[0005] In order to solve the above technical defects, the present invention has developed a preparation method of a sandwich composite material based on melamine foam. By preparing a porous diatomite binder to bond Co - BC - melamine foam, the obtained sandwich composite material has good sound-absorbing performance in the high, medium, and low-frequency ranges.

[0006] A preparation method of a sandwich composite material based on melamine foam, comprising the following steps:

[0007] S1: Coordination of Co with nanocellulose

[0008] The nanocellulose is oxidized with hydrogen peroxide and then dispersed in an ethanol solution to obtain a nanocellulose dispersion. Cobalt acetylacetonate and acetic acid are added to the nanocellulose dispersion, and after magnetic stirring, a Co-nanocellulose complex dispersion is obtained;

[0009] S2: Preparation of Co-BC-melamine foam

[0010] The melamine foam is heat-treated at a high temperature in an air atmosphere and then immersed in a 3-mercaptopropyltrimethoxysilane solution prepared from 3-mercaptopropyltrimethoxysilane and an ethanol solution. After washing and drying, a silane-modified melamine foam is obtained. The silane-modified melamine foam is immersed in the Co-nanocellulose complex dispersion for ultrasonic treatment, and after cyclic freezing and lyophilization, Co-BC-melamine foam is obtained;

[0011] S3: Composite of porous diatomite adhesive and Co-BC-melamine foam

[0012] The diatomite is heat-treated and purified to obtain purified diatomite. The purified diatomite and sodium dodecylbenzenesulfonate are added to an aqueous polyurethane solution for high-speed mixing to obtain a porous diatomite adhesive. The porous diatomite adhesive is coated on the upper surface of the Co-BC-melamine foam, and then laminated and hot-pressed with another piece to obtain a melamine foam sandwich composite material.

[0013] Further, the coordination of Co with nanocellulose in step S1 includes the following steps:

[0014] S1.1: The nanocellulose is dispersed and soaked in a hydrogen peroxide solution with a concentration of 4-6%, and then left to stand at 50-70 °C for 1-2 hours, filtered and rinsed 3-4 times with deionized water to obtain oxidized nanocellulose. 2-3 parts by weight of the oxidized nanocellulose, 0.3-0.4 parts by weight of polyvinyl alcohol and 80-100 parts by weight of an ethanol solution are mixed and placed in an ultrasonic disperser, and ultrasonic treatment is carried out at an ultrasonic power of 300-350 W for 10-30 minutes to obtain a nanocellulose dispersion;

[0015] S1.2: Add 1 - 1.5 parts by weight of cobalt acetylacetonate to the nano - bacterial cellulose dispersion obtained in step S1.1, then add 0.1 - 0.5 wt% of acetic acid, and perform magnetic stirring at a rotation speed of 150 - 200 rpm at 50 - 60 °C for 2 - 3 hours to obtain a Co - nano - bacterial cellulose complex dispersion.

[0016] Further, the preparation of Co - BC - melamine foam in step S2 includes the following steps:

[0017] S2.1: Immerse the melamine foam in absolute ethanol, then place it in an ultrasonic cleaner for ultrasonic cleaning at an ultrasonic frequency of 25 - 30 kHz for 15 - 20 minutes, then immerse it in deionized water for ultrasonic cleaning at an ultrasonic frequency of 25 - 30 kHz for 15 - 20 minutes, and then place it in a muffle furnace. Under an air atmosphere, heat it at a heating rate of 5 - 10 °C / min to 180 - 200 °C, keep it warm for 2 - 2.5 hours, and then naturally cool to room temperature to obtain pre - oxidized melamine foam;

[0018] S2.2: Mix 3 - mercaptopropyltrimethoxysilane and ethanol solution in a volume ratio of 1:(40 - 60) and place it in a container, stir until 3 - mercaptopropyltrimethoxysilane is completely dissolved, and let it stand for 1 - 2 hours to obtain a 3 - mercaptopropyltrimethoxysilane solution. Immerse the pre - oxidized melamine foam in the 3 - mercaptopropyltrimethoxysilane solution for 1.5 - 2 hours, clamp the pre - oxidized melamine foam every 20 - 30 minutes to stir it in the 3 - mercaptopropyltrimethoxysilane solution for 1 - 2 minutes, then take it out and rinse the surface with deionized water 2 - 3 times, and then place it in an oven at 60 - 80 °C and heat it for 8 - 10 hours to obtain silane - modified melamine foam;

[0019] S2.3: Completely immerse the silane - modified melamine foam in the Co - nano - bacterial cellulose complex dispersion prepared in step S1.2, then place it in an ultrasonic water bath, ultrasonicate it at an ultrasonic frequency of 35 - 40 kHz at a temperature of 45 - 50 °C for 30 - 40 minutes, freeze it at - 25 - - 20 °C for 6 - 8 hours, then place it at room temperature for 10 - 12 hours, repeat the cycle 3 - 4 times, then freeze it in liquid nitrogen, and finally transfer it to a freeze - dryer for freeze - drying to obtain Co - BC - melamine foam.

[0020] Further, the compounding of the porous diatomite binder and Co - BC - melamine foam in step S3 includes the following steps:

[0021] S3.1: Place 2 - 4 parts by weight of diatomaceous earth in a container, then put it into a constant-temperature drying oven and heat it at 105 - 110 °C until the mass of the diatomaceous earth no longer changes, obtaining heat-treated diatomaceous earth. Mix the heat-treated diatomaceous earth evenly with 8 - 12 parts by weight of a hydrochloric acid solution with a concentration of 6 - 8%, place it in a microwave oven and irradiate it at a power of 700 - 750 W for 4 - 6 minutes, wash it with distilled water until the pH of the washed distilled water is neutral, then perform vacuum filtration and dry it at 105 - 110 °C for 10 - 12 hours to obtain purified diatomaceous earth;

[0022] S3.2: Add the purified diatomaceous earth prepared in step S3.1 and 0.03 - 0.04 parts by weight of sodium dodecylbenzenesulfonate to 60 - 65 parts by weight of an aqueous polyurethane solution, then place it in a high-speed stirrer and stir at a speed of 1200 - 1500 rpm for 50 - 60 minutes, add 0.1 - 0.5% of an anti-settling agent, and then stir at a stirring speed of 1800 - 2000 rpm for 25 - 30 minutes to obtain a porous diatomaceous earth adhesive;

[0023] S3.3: Apply the porous diatomaceous earth adhesive to the upper surface of Co-BC-melamine foam with a sizing amount of 600 - 800 g / m 2 evenly, after the sizing is completed, let it stand for 6 - 8 minutes to obtain sized Co-BC-melamine foam. Then take another piece of Co-BC-melamine foam and stack it on the upper surface of the sized Co-BC-melamine foam, and hot press it at 100 - 120 °C under a pressure of 0.1 - 0.2 MPa for 8 - 10 minutes, and cool it to obtain a melamine foam sandwich composite material.

[0024] Further, the concentration of the ethanol solution in step S1.1 is 10 - 15%.

[0025] Further, in step S2.1, the diameter of the melamine foam is 10 cm and the thickness is 2 cm.

[0026] Further, the concentration of the ethanol solution mixed with 3-mercaptopropyltrimethoxysilane in step S2.2 is 96 - 98%.

[0027] Further, the solid content of the aqueous polyurethane solution in step S3.2 is 40 - 45%.

[0028] Further, the anti-settling agent in step S3.2 is an aqueous anti-settling agent 2521.

[0029] A sandwich composite material based on melamine foam, which is prepared by the preparation method of the above-mentioned sandwich composite material based on melamine foam.

[0030] The beneficial effects are as follows: 1. In the present invention, nano-bacterial cellulose provides good porosity through its high specific surface area and microfiber structure, which helps to enhance the sound absorption performance of the composite material. After being combined with cobalt acetylacetonate, cobalt ions coordinate with the surface hydroxyl groups of nano-bacterial cellulose to form a stable composite structure. This composite not only enhances the mechanical properties of the material but also improves its porosity, further enhancing the sound absorption effect. The introduction of cobalt ions also helps to enhance the thermal stability and antibacterial properties of the composite material, and these characteristics can ensure that the material maintains good sound absorption performance during long-term use, avoiding performance degradation caused by bacterial growth or environmental changes. In addition, the natural properties of nano-bacterial cellulose enable it to act as an excellent sound wave absorption medium in the composite material, thus effectively improving the sound absorption capacity of the sandwich material.

[0031] 2. In the present invention, porous diatomite has an extremely high specific surface area and a rich microporous structure, which can significantly improve the sound absorption performance of the composite material. Diatomite is mixed with an aqueous polyurethane solution to form an adhesive with strong bonding performance and form a uniform coating on the surface of the composite material. The microporous structure and high specific surface area of diatomite not only provide more sound wave absorption points but also help to reduce the reflection and propagation of sound waves, improving the overall acoustic performance of the material. The aqueous polyurethane solution, as an adhesive, not only provides good adhesion to ensure the uniform distribution of diatomite particles in the composite material but also has good low-frequency sound wave absorption ability. Combining the characteristics of diatomite and aqueous polyurethane, the pore structure of this composite material helps to improve the sound wave absorption efficiency, making it exhibit excellent sound absorption ability in a wide frequency band. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 It is a flowchart of the preparation method of the sandwich composite material based on melamine foam adopted in the embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0033] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0034] Example 1

[0035] A sandwich composite material based on melamine foam and its preparation method, as Figure 1 shown, includes the following steps:

[0036] S1: Coordination of Co with nano-bacterial cellulose

[0037] S1.1: Immerse nano-bacterial cellulose in a 4% hydrogen peroxide solution, then let it stand at 50 °C for 1 hour, filter and rinse with deionized water 3 times to obtain oxidized nano-bacterial cellulose. Mix 2 parts by weight of oxidized nano-bacterial cellulose, 0.3 parts by weight of polyvinyl alcohol and 80 parts by weight of a 10% ethanol solution in an ultrasonic disperser and ultrasonically treat it at an ultrasonic power of 300 W for 10 minutes to obtain a nano-bacterial cellulose dispersion;

[0038] S1.2: Add 1 part by weight of cobalt acetylacetonate to the nano-bacterial cellulose dispersion prepared in step S1.1, then add 0.1 wt% acetic acid and magnetically stir at a speed of 150 rpm at 50 °C for 2 hours to obtain a Co-nano-bacterial cellulose complex dispersion.

[0039] S2: Preparation of Co-BC-melamine foam

[0040] S2.1: Immerse a melamine foam with a diameter of 10 cm and a thickness of 2 cm in absolute ethanol, then place it in an ultrasonic cleaner and ultrasonically clean it at an ultrasonic frequency of 25 kHz for 15 minutes, then immerse it in deionized water and ultrasonically clean it at an ultrasonic frequency of 25 kHz for 15 minutes, and then place it in a muffle furnace. Heat it to 180 °C at a heating rate of 5 °C / min in an air atmosphere, keep it warm for 2 hours and then naturally cool to room temperature to obtain a pre-oxidized melamine foam;

[0041] S2.2: Mix 3-mercaptopropyltrimethoxysilane and a 96% ethanol solution in a volume ratio of 1:40 in a container, stir until 3-mercaptopropyltrimethoxysilane is completely dissolved, let it stand for 1 hour to obtain a 3-mercaptopropyltrimethoxysilane solution. Immerse the pre-oxidized melamine foam in the 3-mercaptopropyltrimethoxysilane solution for 1.5 hours, clamp the pre-oxidized melamine foam every 20 minutes to stir it in the 3-mercaptopropyltrimethoxysilane solution for 1 minute, then take it out and rinse the surface with deionized water 2 times, and then place it in an oven at 60 °C and heat it for 8 hours to obtain a silane-modified melamine foam;

[0042] S2.3: Immerse the silane-modified melamine foam completely in the Co-nano-bacterial cellulose complex dispersion prepared in step S1.2, then place it in an ultrasonic water bath, ultrasonically treat it at an ultrasonic frequency of 35 kHz at a temperature of 45 °C for 30 minutes, freeze it at -25 °C for 6 hours and then let it stand at room temperature for 10 hours, repeat the cycle 3 times and then freeze it in liquid nitrogen, and finally transfer it to a freeze dryer for freeze-drying to obtain Co-BC-melamine foam.

[0043] S3: Composite of porous diatomite adhesive and Co-BC-melamine foam

[0044] S3.1: Place 2 parts by weight of diatomaceous earth in a container, then put it into a constant-temperature drying oven and heat it at 105 °C until the mass of the diatomaceous earth no longer changes, obtaining heat-treated diatomaceous earth. Mix the heat-treated diatomaceous earth evenly with 8 parts by weight of a hydrochloric acid solution with a concentration of 6%, place it in a microwave oven and irradiate it at a power of 700 W for 4 minutes, wash it with distilled water until the pH of the washed distilled water is neutral, then carry out vacuum filtration and dry it at 105 °C for 10 hours to obtain purified diatomaceous earth;

[0045] S3.2: Add the purified diatomaceous earth prepared in step S3.1 and 0.03 parts by weight of sodium dodecylbenzenesulfonate to 60 parts by weight of an aqueous polyurethane solution with a solid content of 40%, then place it in a high-speed stirrer and stir at a speed of 1200 rpm for 50 minutes. Then add 0.1% of aqueous anti-settling agent 2521, and then stir at a speed of 1800 rpm for 25 minutes to obtain a porous diatomaceous earth binder;

[0046] S3.3: Apply the porous diatomaceous earth binder to the upper surface of Co-BC-melamine foam with a sizing amount of 600 g / m 2 evenly, and after the sizing is completed, let it stand for 6 minutes to obtain sized Co-BC-melamine foam. Then take another piece of Co-BC-melamine foam and stack it on the upper surface of the sized Co-BC-melamine foam, and hot-press it at 100 °C under a pressure of 0.1 MPa for 8 minutes, and cool it to obtain a melamine foam sandwich composite material.

[0047] Example 2

[0048] A sandwich composite material based on melamine foam and its preparation method, as Figure 1 shown, includes the following steps:

[0049] S1: Coordination of Co with nanocellulose

[0050] S1.1: Disperse and soak nanocellulose in a hydrogen peroxide solution with a concentration of 4%, then let it stand at 50 °C for 1 hour, filter and rinse it 3 times with deionized water to obtain oxidized nanocellulose. Mix 3 parts by weight of oxidized nanocellulose, 0.4 parts by weight of polyvinyl alcohol and 100 parts by weight of an ethanol solution with a concentration of 10% and place it in an ultrasonic disperser, and ultrasonically treat it at an ultrasonic power of 300 W for 10 minutes to obtain a nanocellulose dispersion;

[0051] S1.2: Add 1.5 parts by weight of cobalt acetylacetonate to the nanocellulose dispersion prepared in step S1.1, then add 0.1 wt% of acetic acid, and carry out magnetic stirring at 50 °C at a speed of 150 rpm for 2 hours to obtain a Co-nanocellulose complex dispersion.

[0052] S2: Preparation of Co-BC-Melamine Foam

[0053] S2.1: Immerse the melamine foam with a diameter of 10 cm and a thickness of 2 cm in absolute ethanol, then place it in an ultrasonic cleaner and perform ultrasonic cleaning for 15 minutes at an ultrasonic frequency of 25 kHz. Then immerse it in deionized water and perform ultrasonic cleaning for 15 minutes at an ultrasonic frequency of 25 kHz. Then place it in a muffle furnace and heat it to 180 °C at a heating rate of 5 °C / min in an air atmosphere, keep it warm for 2 hours, and then naturally cool it to room temperature to obtain pre-oxidized melamine foam;

[0054] S2.2: Mix 3-mercaptopropyltrimethoxysilane and an ethanol solution with a concentration of 96% in a volume ratio of 1:60 and place them in a container. Stir until 3-mercaptopropyltrimethoxysilane is completely dissolved, and let it stand for 1 hour to obtain a 3-mercaptopropyltrimethoxysilane solution. Immerse the pre-oxidized melamine foam in the 3-mercaptopropyltrimethoxysilane solution for 1.5 hours. Clamp the pre-oxidized melamine foam every 20 minutes and stir it in the 3-mercaptopropyltrimethoxysilane solution for 1 minute. Then take it out and rinse the surface with deionized water 2 times, and then place it in an oven at 60 °C and heat it for 8 hours to obtain silane-modified melamine foam;

[0055] S2.3: Completely immerse the silane-modified melamine foam in the Co-nanobacterial cellulose complex dispersion prepared in step S1.2, then place it in an ultrasonic water bath and ultrasonicate it for 30 minutes at a temperature of 45 °C and an ultrasonic frequency of 35 kHz. Freeze it at -25 °C for 6 hours and then let it stand at room temperature for 10 hours. Repeat the cycle 3 times, then freeze it in liquid nitrogen, and finally transfer it to a freeze dryer for freeze-drying to obtain Co-BC-melamine foam.

[0056] S3: Composite of Porous Diatomite Adhesive and Co-BC-Melamine Foam

[0057] S3.1: Place 4 parts by weight of diatomite in a container, then put it in a constant temperature drying oven and heat it at 105 °C until the mass of the diatomite no longer changes to obtain heat-treated diatomite. Mix the heat-treated diatomite and 12 parts by weight of a 6% hydrochloric acid solution evenly, place it in a microwave oven and irradiate it at a power of 700 W for 4 minutes, wash it with distilled water until the pH of the washed distilled water is neutral, then perform vacuum filtration and dry it at 105 °C for 10 hours to obtain purified diatomite;

[0058] S3.2: Add the purified diatomite obtained in step S3.1 and 0.04 parts by weight of sodium dodecylbenzenesulfonate into 65 parts by weight of an aqueous polyurethane solution with a solid content of 40%, then place it in a high-speed mixer and stir at a speed of 1200 rpm for 50 minutes. Then add 0.5% of the aqueous anti-settling agent 2521, and then stir at a speed of 1800 rpm for 25 minutes to obtain a porous diatomite adhesive.

[0059] S3.3: Apply the porous diatomite adhesive to the upper surface of the Co-BC-melamine foam evenly at a sizing amount of 800 g / m 2 . After the sizing is completed, let it stand for 6 minutes to obtain the sized Co-BC-melamine foam. Then take another piece of Co-BC-melamine foam and stack it on the upper surface of the sized Co-BC-melamine foam, and hot-press it at 100 °C under a pressure of 0.1 MPa for 8 minutes. After cooling, a melamine foam sandwich composite material is obtained.

[0060] Example 3

[0061] A sandwich composite material based on melamine foam and its preparation method, as Figure 1 shown, includes the following steps:

[0062] S1: Coordination of Co with nanofibrillated bacterial cellulose

[0063] S1.1: Disperse and soak the nanofibrillated bacterial cellulose in a hydrogen peroxide solution with a concentration of 6%, then let it stand at 70 °C for 2 hours, filter and rinse it 4 times with deionized water to obtain oxidized nanofibrillated bacterial cellulose. Mix 2 parts by weight of the oxidized nanofibrillated bacterial cellulose, 0.3 parts by weight of polyvinyl alcohol and 80 parts by weight of an ethanol solution with a concentration of 15% and place it in an ultrasonic disperser, and ultrasonically treat it at an ultrasonic power of 350 W for 30 minutes to obtain a nanofibrillated bacterial cellulose dispersion;

[0064] S1.2: Add 1 part by weight of cobalt acetylacetonate to the nanofibrillated bacterial cellulose dispersion obtained in step S1.1, then add 0.5 wt% of acetic acid, and carry out magnetic stirring at 60 °C at a speed of 200 rpm for 3 hours to obtain a Co-nanofibrillated bacterial cellulose complex dispersion.

[0065] S2: Preparation of Co-BC-melamine foam

[0066] S2.1: Immerse the melamine foam with a diameter of 10 cm and a thickness of 2 cm in absolute ethanol, then place it in an ultrasonic cleaner and perform ultrasonic cleaning for 20 minutes at an ultrasonic frequency of 30 kHz. Then immerse it in deionized water and perform ultrasonic cleaning for 20 minutes at an ultrasonic frequency of 30 kHz. Then place it in a muffle furnace and heat it to 200 °C at a heating rate of 10 °C / min in an air atmosphere, keep it warm for 2.5 hours, and then naturally cool it to room temperature to obtain pre-oxidized melamine foam;

[0067] S2.2: Mix 3-mercaptopropyltrimethoxysilane and an ethanol solution with a concentration of 98% in a volume ratio of 1:40 and place them in a container. Stir until 3-mercaptopropyltrimethoxysilane is completely dissolved, and let it stand for 2 hours to obtain a 3-mercaptopropyltrimethoxysilane solution. Immerse the pre-oxidized melamine foam in the 3-mercaptopropyltrimethoxysilane solution for 2 hours, clamp the pre-oxidized melamine foam every 30 minutes and stir it in the 3-mercaptopropyltrimethoxysilane solution for 2 minutes, then take it out and rinse the surface 3 times with deionized water, and then place it in an oven at 80 °C and heat it for 10 hours to obtain silane-modified melamine foam;

[0068] S2.3: Immerse the silane-modified melamine foam completely in the Co-nanobacterial cellulose complex dispersion prepared in step S1.2, then place it in an ultrasonic water bath and ultrasonicate it at a temperature of 50 °C and an ultrasonic frequency of 40 kHz for 40 minutes. Freeze it at -20 °C for 8 hours and then let it stand at room temperature for 12 hours. Repeat this cycle 4 times, then freeze it in liquid nitrogen, and finally transfer it to a freeze dryer for freeze-drying to obtain Co-BC-melamine foam.

[0069] S3: Composite of porous diatomite adhesive and Co-BC-melamine foam

[0070] S3.1: Place 2 parts by weight of diatomite in a container, then put it in a constant temperature drying oven and heat it at 110 °C until the mass of the diatomite no longer changes to obtain heat-treated diatomite. Mix the heat-treated diatomite and 10 parts by weight of a hydrochloric acid solution with a concentration of 8% evenly, place it in a microwave oven and irradiate it at a power of 750 W for 6 minutes, wash it with distilled water until the pH of the washed distilled water is neutral, then perform vacuum filtration and dry it at 110 °C for 12 hours to obtain purified diatomite;

[0071] S3.2: Add the purified diatomite prepared in step S3.1 and 0.03 parts by weight of sodium dodecylbenzenesulfonate to 60 parts by weight of an aqueous polyurethane solution with a solid content of 45%, then place it in a high-speed stirrer and stir it at a speed of 1500 rpm for 60 minutes. Then add 0.1% of an aqueous anti-settling agent 2521, and then stir it at a stirring speed of 2000 rpm for 30 minutes to obtain a porous diatomite adhesive;

[0072] S3.3: Apply the porous diatomite binder evenly on the upper surface of the Co-BC-melamine foam at an application rate of 600 g / m 2 After the coating is completed, let it stand for 8 minutes to obtain the coated Co-BC-melamine foam. Then, take another piece of Co-BC-melamine foam and stack it on the upper surface of the coated Co-BC-melamine foam. Hot press it at 120 °C under a pressure of 0.2 MPa for 10 minutes, and after cooling, obtain the melamine foam sandwich composite material.

[0073] Comparative Example 1: Compared with Example 1, the difference in Comparative Example 1 is that in Comparative Example 1, step S1.2 is removed, and the subsequent Co-nanobacterial cellulose complex dispersion is replaced with an equal mass of nanobacterial cellulose dispersion. The remaining steps are the same as those in Example 1. The prepared melamine foam sandwich composite material is denoted as Comparative Example 1.

[0074] Comparative Example 2: Compared with Example 1, the difference in Comparative Example 2 is that in Comparative Example 2, step S3.1 is removed, purified diatomite is not added in step S3.2, and the prepared waterborne polyurethane binder is used to replace the subsequent porous diatomite binder with an equal mass. The remaining steps are the same as those in Example 1. The prepared melamine foam sandwich composite material is denoted as Comparative Example 2.

[0075] Sound absorption performance test: Take the melamine foam sandwich composite materials prepared in Examples 1-3 and Comparative Examples 1-2, and use the Danish BK4206 dual impedance tube to test the sound absorption coefficient NRC value of the melamine foam sandwich composite material by the standing wave method. The larger the NRC value, the better the sound absorption effect. The test frequencies are 500 Hz, 1 kHz, 2 kHz, 3 kHz, 5 kHz, and 6 kHz. Each material is tested three times, and the average value is taken. The test results are recorded in Table 1 as follows.

[0076] Table 1: Sound absorption performance of the melamine foam sandwich composite material

[0077] NRC value 500 Hz 1 kHz 2 kHz 3 kHz 4 kHz 5 kHz 6 kHz Example 1 0.22 0.41 0.82 0.96 0.92 0.91 0.88 Example 2 0.24 0.43 0.85 0.97 0.93 0.92 0.9 Example 3 0.21 0.39 0.79 0.94 0.9 0.89 0.86 Comparative Example 1 0.16 0.33 0.71 0.83 0.84 0.81 0.75 Comparative Example 2 0.14 0.29 0.68 0.79 0.81 0.78 0.73

[0078] It can be seen from the data of Examples 1-3 and Comparative Example 1 in Table 1 that when cobalt acetylacetonate is not added to the nanobacterial cellulose dispersion, the sound absorption coefficient NRC value of the melamine foam sandwich composite material decreases, which can prove that cobalt acetylacetonate can coordinate with nanobacterial cellulose, improve the porosity, and enhance the sound absorption effect of the material;

[0079] It can be seen from the data of Examples 1-3 and Comparative Example 2 in Table 1 that when purified diatomaceous earth is not added to the waterborne polyurethane adhesive, the NRC value of the sound absorption coefficient of the melamine foam sandwich composite material decreases. It can be proved that diatomaceous earth is mixed with the waterborne polyurethane solution to form an adhesive with strong bonding performance and form a uniform coating on the surface of the composite material. The microporous structure and high specific surface area of diatomaceous earth not only provide more sound wave absorption points, but also help reduce the reflection and propagation of sound waves, improving the overall acoustic performance of the material.

[0080] The above embodiments are only illustrative of the principles and effects of the present invention, and are not intended to limit the present invention. Any person familiar with this technology can modify or change the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or changes completed by those with ordinary knowledge in the technical field without departing from the spirit and technical idea disclosed by the present invention should still be covered by the claims of the present invention.

Claims

1. A method for preparing a sandwich composite material based on melamine foam, characterized in that: The following steps are involved: S1: Coordination of Co with nanobacterial cellulose The nano bacterial cellulose is oxidized by hydrogen peroxide, and then dispersed in an ethanol solution to obtain a nano bacterial cellulose dispersion liquid, cobalt acetylacetonate and acetic acid are added to the nano bacterial cellulose dispersion liquid, and a Co-nano bacterial cellulose complex dispersion liquid is obtained after magnetic stirring; S2: Preparation of Co-BC-melamine foam The melamine foam is subjected to high temperature treatment in an air atmosphere, and then immersed in a 3-mercaptopropyltrimethoxysilane solution prepared from 3-mercaptopropyltrimethoxysilane and an ethanol solution, washed and dried to obtain a silane-modified melamine foam, and the silane-modified melamine foam is immersed in a Co-nanobacterial cellulose complex dispersion for ultrasonic treatment, and after cyclic freezing and freeze-drying, a Co-BC-melamine foam is obtained; S3: Composite of porous diatomaceous earth adhesive and Co-BC-melamine foam The diatomaceous earth is heat-treated and purified to obtain purified diatomaceous earth, the purified diatomaceous earth and sodium dodecylbenzene sulfonate are added into an aqueous polyurethane solution and mixed at a high speed to obtain a porous diatomaceous earth adhesive, the porous diatomaceous earth adhesive is coated on the upper surface of the Co-BC-melamine foam, and then another piece is used for overlapping and hot pressing to obtain a melamine foam sandwich composite material.

2. A method for preparing a sandwich composite material based on melamine foam according to claim 1, It is characterized in that Step S1: The coordination of Co and nano bacterial cellulose comprises the following steps: S1.1: Disperse and soak the nano bacterial cellulose in a hydrogen peroxide solution with a concentration of 4-6%, then stand at 50-70°C for 1-2 hours, filter and rinse with deionized water 3-4 times to obtain oxidized nano bacterial cellulose, mix 2-3 parts by weight of oxidized nano bacterial cellulose, 0.3-0.4 parts by weight of polyvinyl alcohol and 80-100 parts by weight of ethanol solution in an ultrasonic disperser, and ultrasonically treat at an ultrasonic power of 300-350W for 10-30 minutes to obtain a nano bacterial cellulose dispersion; S1.2: Add 1-1.5 parts by weight of cobalt acetylacetonate to the nano bacterial cellulose dispersion prepared in step S1.1, then add 0.1-0.5wt% of acetic acid, and stir magnetically at 50-60°C at a speed of 150-200rpm for 2-3 hours to obtain a Co-nano bacterial cellulose complex dispersion.

3. A method for preparing a sandwich composite material based on melamine foam according to claim 2, It is characterized in that Step S2 Preparation of Co-BC-melamine foam, The following steps are involved: S2.1: soaking the melamine foam in anhydrous ethanol, then placing it in an ultrasonic cleaning machine for 15-20 minutes at an ultrasonic frequency of 25-30kHz, then soaking it in deionized water for 15-20 minutes at an ultrasonic frequency of 25-30kHz, and then placing it in a muffle furnace, heating it to 180-200°C at a heating rate of 5-10°C / min in an air atmosphere, keeping it warm for 2-2.5 hours, and then naturally cooling it to room temperature to obtain pre-oxidized melamine foam; S2.2: 3-mercaptopropyltrimethoxysilane and ethanol solution are mixed in a container at a volume ratio of 1:(40-60), stirred until 3-mercaptopropyltrimethoxysilane is completely dissolved, and allowed to stand for 1-2 hours to obtain a 3-mercaptopropyltrimethoxysilane solution, and the pre-oxidized melamine foam is immersed in the 3-mercaptopropyltrimethoxysilane solution for 1.5-2 hours, and the pre-oxidized melamine foam is clamped every 20-30 minutes to stir it in the 3-mercaptopropyltrimethoxysilane solution for 1-2 minutes, and then taken out and rinsed with deionized water 2-3 times, and then placed in an oven at 60-80° C. and heated for 8-10 hours to obtain a silane-modified melamine foam; S2.3: Completely immerse the silane-modified melamine foam in the Co-nano bacterial cellulose complex dispersion prepared in step S1.2, then place it in an ultrasonic water bath, ultrasonicate it at a temperature of 45-50°C and an ultrasonic frequency of 35-40kHz for 30-40 minutes, freeze it at -25--20°C for 6-8 hours, then place it at room temperature for 10-12 hours, cycle it 3-4 times, then freeze it in liquid nitrogen, and finally transfer it to a freeze dryer for freeze-drying to obtain Co-BC-melamine foam.

4. The method for preparing a sandwich composite material based on melamine foam according to claim 3, characterized in that: Step S3: Compounding the porous diatomaceous earth adhesive and the Co-BC-melamine foam, comprising the following steps: S3.1: 2-4 parts by weight of diatomaceous earth are placed in a container, and then placed in a constant temperature drying oven and heated at 105-110°C until the mass of the diatomaceous earth no longer changes, thereby obtaining heat-treated diatomaceous earth; the heat-treated diatomaceous earth and 8-12 parts by weight of a 6-8% hydrogen chloride solution are mixed evenly, and then placed in a microwave oven and irradiated at a power of 700-750W for 4-6 minutes, and washed with distilled water until the pH of the washed distilled water is neutral, and then vacuum filtered and dried at 105-110°C for 10-12 hours to obtain purified diatomaceous earth; S3.2: adding the purified diatomaceous earth obtained in step S3.1 and 0.03-0.04 parts by weight of sodium dodecylbenzene sulfonate to 60-65 parts by weight of an aqueous polyurethane solution, and then placing the mixture in a high-speed stirrer at a speed of 1200-1500 rpm for 50-60 minutes, and then adding 0.1-0.5% of an anti-settling agent, and then stirring the mixture at a stirring speed of 1800-2000 rpm for 25-30 minutes to obtain a porous diatomaceous earth adhesive; S3.3: Apply porous diatomaceous earth adhesive at 600-800g / m 2 The upper surface of the Co-BC-melamine foam is evenly coated with glue with a coating amount of glue, and the glue is allowed to stand for 6-8 minutes after the coating is completed to obtain the glue-coated Co-BC-melamine foam, and then a piece of Co-BC-melamine foam is overlapped on the upper surface of the glue-coated Co-BC-melamine foam, and hot-pressed at 100-120° C. and a pressure of 0.1-0.2 MPa for 8-10 minutes, and a melamine foam sandwich composite material is obtained after cooling.

5. The method for preparing a sandwich composite material based on melamine foam according to claim 2, characterized in that: The concentration of the ethanol solution in step S1.1 is 10-15%.

6. The method for preparing a sandwich composite material based on melamine foam according to claim 2, characterized in that: The diameter of the melamine foam in step S2.1 is 10 cm and the thickness is 2 cm.

7. The method for preparing a sandwich composite material based on melamine foam according to claim 5, characterized in that: The concentration of the ethanol solution mixed with 3-mercaptopropyltrimethoxysilane in step S2.2 is 96-98%.

8. The method for preparing a sandwich composite material based on melamine foam according to claim 5, characterized in that: The solid content of the aqueous polyurethane solution in step S3.2 is 40-45%.

9. The method for preparing a sandwich composite material based on melamine foam according to claim 5, characterized in that: The anti-settling agent in step S3.2 is a water-based anti-settling agent 2521.

10. A sandwich composite material based on melamine foam, characterized in that: The composite material is prepared by the method for preparing a melamine foam-based sandwich composite material as described in any one of claims 1 to 8.

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