A porous sound-absorbing material based on a controllable pore size and orientation structure, and a preparation method and application thereof

Abstract

The present invention belongs to the field of acoustic absorption materials, and provides a porous acoustic absorption material based on controllable pore size and oriented structure, and a preparation method and application thereof. The preparation method uses multi-components such as modified polyurethane dispersion liquid, modified chitosan-polyacrylate copolymer, polyethylene glycol-polycaprolactone block copolymer, and methacryloyloxyethyl imidazole functionalized polymer. Through chemical modification and molecular structure design, enhanced functionality and compatibility are imparted to each component. During the material forming process, the mixed solution forms an ice crystal template under freezing conditions. The growth of ice crystals is comprehensively affected by the solution viscosity, intermolecular interaction of components, and freezing rate. By regulating the solid content of aqueous polyurethane and the material thickness, the size and distribution of ice crystals can be changed, thereby affecting the pore size and porosity, and providing a porous acoustic absorption material with excellent acoustic absorption effect and adjustable pore structure.

Description

Technical Field

[0001] The present invention belongs to the field of acoustic absorption materials, and relates to a porous acoustic absorption material based on controllable pore size and orientation structure, a preparation method thereof and an application thereof. Background Art

[0002] Currently, the porous acoustic absorption materials on the market can effectively absorb high-frequency sounds. However, due to their relatively wide acoustic absorption frequency range, which often covers the main frequency bands of human voices (300 Hz to 3400 Hz), it results in voice distortion or unclearness. Therefore, it is of great significance to develop an acoustic absorption material that can selectively absorb high-frequency noise without affecting the clarity of human voices. The Chinese patent with the authorization announcement number CN115710102B discloses a porous acoustic absorption / super-elastic vibration reduction coupled noise reduction type polyurethane mixture, which realizes the noise reduction effect by mixing mineral materials, rubber particles and a moisture-curing one-component polyurethane adhesive. Its advantages lie in adopting a high porosity and rubber particles, which can reduce the tire-road noise by 10 - 13 dB. However, this technology has problems of complex preparation processes and material selection, is mainly applied to road engineering, and has not been specifically optimized for the effective acoustic absorption of higher-frequency noises in buildings and equipment and the retention of human voices. The Chinese patent application with the publication number CN118126403A discloses a centripetal porous aerogel, which uses bacterial cellulose to react with polycarboxylic acids to form a porous matrix framework, having good mechanical resilience performance and acoustic absorption performance. Its acoustic absorption ability covers the high, medium and low frequency ranges and is applicable to various fields. However, the acoustic absorption effect of this technology in the frequency band above 4000 Hz has not been fully optimized, and at the same time, due to the limitations of material properties, it is unable to effectively avoid excessive absorption of the human voice frequency band. Therefore, developing an acoustic absorption material that can selectively absorb high-frequency noises above 4000 Hz while retaining the clarity of the main frequency bands of human voices has become an urgent problem to be solved. Summary of the Invention

[0003] Aiming at the deficiencies of the existing technology, the purpose of the present invention is to provide a porous acoustic absorption material based on controllable pore size and orientation structure, a preparation method thereof and an application thereof. React an aqueous polyurethane dispersion with acrylic monomers (such as methyl acrylate, butyl acrylate, etc.) and an initiator to modify the polyurethane, making it have better structural controllability, providing a basis for the subsequent porous structure. Through the copolymerization reaction of chitosan and acrylic monomers, a copolymer with a uniform pore structure is formed, further enhancing the acoustic absorption characteristics and adjustability of the material. By means of chemical polymerization, cross-linking reaction and freeze-drying, etc., the pore size, pore distribution and orientation structure of the pores of the material are precisely controlled, so as to meet the needs of actual production.

[0004] To achieve this purpose, the present invention adopts the following technical solutions:

[0005] In a first aspect, the present invention provides a method for preparing a porous sound-absorbing material based on a controllable pore size and orientation structure, the preparation method comprising:

[0006] Step A1: Heat the aqueous polyurethane dispersion to a first temperature, add mixed monomer A and stir evenly, then add an initiator, heat to a second temperature and react fully. After the reaction is completed, cool to a third temperature, add tetrabutylammonium bromide and an aqueous solution of epichlorohydrin, heat to the second temperature and react fully. After the reaction is completed, cool to room temperature to obtain a modified polyurethane dispersion;

[0007] Step A2: Add chitosan to an acetic acid aqueous solution and stir to dissolve, adjust the pH to 5.0 to obtain a chitosan solution. Under a nitrogen atmosphere, disperse mixed monomer B, sodium dodecyl sulfate and azobisisobutyronitrile in deionized water and stir to form a monomer emulsion. Heat to the second temperature, and drop the monomer emulsion and ammonium persulfate solution into the chitosan solution, keep stirring and react fully. After the reaction is completed, cool to room temperature, adjust the pH to 7.0 with a sodium hydroxide solution, and filter to obtain a modified chitosan-polyacrylate copolymer;

[0008] Step S1: Under a nitrogen atmosphere, heat polyethylene glycol to a third temperature, add ε-caprolactone, adjust the temperature to a fourth temperature, add stannous octoate and triethylamine and react fully. After the reaction is completed, cool to room temperature, add dichloromethane to dissolve the product, add the dissolved product to ice methanol for precipitation, filter and collect the precipitate, and vacuum dry at the first temperature to obtain a polyethylene glycol-polycaprolactone block copolymer;

[0009] Step S2: Dissolve imidazole in N,N-dimethylformamide, add anhydrous potassium carbonate, stir evenly and then add 2-chloroethanol, heat to a fifth temperature and react fully. Cool to room temperature, and perform vacuum distillation to obtain 2-imidazole ethanol. Dissolve 2-imidazole ethanol in toluene, add methacrylic acid and hydroquinone and react fully. After the reaction is completed, cool to room temperature and dry with anhydrous magnesium sulfate to obtain a monomer. Dissolve the monomer in tetrahydrofuran, under a nitrogen atmosphere, add azobisisobutyronitrile, and react fully at the second temperature. After the reaction is completed, add it to anhydrous ether for precipitation, filter and collect the precipitate, and vacuum dry at the first temperature to obtain a methacryloyloxyethylimidazole functionalized polymer;

[0010] Step S3: Disperse the polyethylene glycol - polycaprolactone block copolymer in tetrahydrofuran, disperse the modified chitosan - polyacrylate copolymer in deionized water, disperse the methacryloyloxyethyl imidazole functionalized polymer in deionized water, dissolve PNIPAM in its deionized water, and mix the polyethylene glycol - polycaprolactone block copolymer dispersion, the modified chitosan - polyacrylate copolymer dispersion and the methacryloyloxyethyl imidazole functionalized polymer dispersion to form a mixed solution. Then, sequentially add the modified polyurethane dispersion and the PNIPAM solution into the mixed solution, stir evenly and then perform ultrasonic dispersion treatment. Freeze the treated mixed solution, and freeze - dry the frozen sample under vacuum to obtain a porous sound - absorbing material with a controllable pore size and oriented structure.

[0011] Polyurethane particles are composed of polyurethane macromolecules. The polyurethane molecules contain polar groups that can form hydrogen bonds or other weak interactions with water molecules, making them partially hydrophilic. The hydrophobic part of the polyurethane molecules tends to stay away from the water phase, driving the hydrophobic self - assembly of the particles. When polyurethane is dispersed in the water phase, the action of the hydrophobic groups promotes self - assembly between the particles, while the polar group part interacts with the water phase to stabilize the dispersed state of the particles. The hydrophobicity causes the polyurethane particles to approach each other, forming a certain aggregation state or template, resulting in a stable preliminary template with uniform particle distribution and a highly uniform pore template, forming regularly distributed pores. This pore structure can improve the sound - absorbing and other properties of the material. To further improve the dispersion stability of the particles, epichlorohydrin is introduced as a modifier. The epoxy group in the epichlorohydrin molecule undergoes a ring - opening reaction with the active groups (hydroxyl or amino groups) on the surface of the polyurethane particles, generating hydroxyl - modified polyurethane particles. The hydroxyl groups introduced by this reaction increase the hydrophilicity of the particle surface, thus significantly enhancing the dispersion stability of the particles in the water phase. The epoxy ring - opening reaction also introduces flexible ether bonds on the particle surface, and these flexible chain segments can reduce the interaction force between the particles, further inhibiting the agglomeration phenomenon of the particles. The particles modified by epichlorohydrin have higher hydrophilicity and dispersibility, which not only ensure the uniformity of the particle template but also provide a more stable reaction matrix for the subsequent construction of the cross - linked network.

[0012] On the surface of polyurethane particles, a crosslinked network is formed through the free radical polymerization reaction of methyl acrylate, butyl acrylate, and acrylic acid, thereby further regulating the pore size and distribution. Under the action of the initiator ammonium persulfate, the double bonds of methyl acrylate, butyl acrylate, and acrylic acid undergo a free radical polymerization reaction to generate a crosslinked polymer network. This chain growth reaction occurs on the surface of polyurethane particles, connecting the particles through crosslinking points to form a stable pore framework. The carboxyl group of acrylic acid provides crosslinking points, which can increase the crosslinking density. A high concentration of acrylic acid will result in a denser network, thereby forming fine pores. The methyl acrylate molecule has strong rigidity, and its introduction makes the crosslinked network more compact, increasing the rigidity of the pore wall and simultaneously reducing the pore size. A high proportion of methyl acrylate is suitable for high-frequency sound absorption designs that require fine pores; the butyl acrylate molecule has a flexible long-chain alkyl side chain, increasing the flexibility of the network and is suitable for the pore structure of low-frequency sound absorption.

[0013] Chitosan is first added to an aqueous acetic acid solution, and the acidic environment of the aqueous acetic acid solution helps the dissolution of chitosan. The amino groups in chitosan are partially protonated under acidic conditions, enhancing its solubility. The amino groups in chitosan molecules serve as active sites and can undergo an addition reaction with the double bonds of monomers such as acrylic acid, butyl acrylate, and methyl methacrylate under the action of the initiator azobisisobutyronitrile. In the aqueous phase, sodium dodecyl sulfate is used as a dispersant to help the monomers disperse evenly to form an emulsion. Emulsion polymerization helps the monomers disperse evenly and prevents the over-aggregation of polymer chains. Azobisisobutyronitrile releases free radicals under the action of temperature, promoting the polymerization reaction of the monomers. At the same time, the aqueous phase environment in the emulsion also provides a stable system for this reaction. There may be hydrogen bonding or covalent crosslinking between the amino groups in chitosan and the carboxyl groups in the polyacrylate chains. Especially at high temperatures, chemical reactions may occur between the amino groups in chitosan and the double bonds or carboxyl groups in acrylate monomers to form a stable crosslinked structure. During the emulsion polymerization process, the tiny polymer particles formed by the monomers and the initiator will form a small capsule-like dispersion in the system. As the reaction progresses, the polymer chains grow inside the particles, and due to the removal of the aqueous phase solvent, pores will form between the particles. During the subsequent freeze-drying process, the gaps between these small particles will expand to form a microporous structure.

[0014] Polyethylene glycol is a hydrophilic molecule. Its molecular structure contains a large number of polar ether oxygen and hydroxyl groups, which can have strong affinity with water or other polar molecules through hydrogen bonding or dipole-dipole interactions. The hydrophilicity of the polyethylene glycol segment makes it tend to be distributed at the solvent / nonsolvent interface or pore surface; polycaprolactone is a hydrophobic molecule, mainly composed of nonpolar methylene segments and ester groups in its molecular structure, with weak polarity within the molecule and unable to effectively interact with polar molecules. The hydrophobicity of the polycaprolactone segment makes it tend to aggregate into pore walls, away from the hydrophilic region. The formation of hydrophilic and hydrophobic regions is achieved through microphase separation of the polyethylene glycol and polycaprolactone segments, and the microphase separation drives the orderly formation of pores. During the freezing and drying processes, the polycaprolactone segments form crystalline regions, and the crystalline regions provide high-strength physical cross-linking points through the regular packing of molecular chains. The crystallinity of the polycaprolactone segments can significantly enhance the rigidity and strength of the pore walls, avoiding pore collapse or deformation.

[0015] The chain of the modified chitosan-polyacrylate copolymer contains a large number of amino and hydroxyl groups, and these groups can interact with the polyethylene glycol-polycaprolactone block copolymer through hydrogen bonding, electrostatic interaction, and van der Waals forces. The modified chitosan-polyacrylate copolymer introduces hydrophobic segments, and this structure makes chitosan both hydrophilic and has a certain degree of hydrophobicity, thus being able to exhibit interfacial activity in a multiphase system. In the polyethylene glycol-polycaprolactone block copolymer, the polyethylene glycol part is hydrophilic, while the polycaprolactone part is hydrophobic. This block structure is prone to microphase separation in a water or tetrahydrofuran system, forming a hydrophilic-hydrophobic interface. The hydroxyl groups on the polyethylene glycol chain can combine with the amino or hydroxyl groups of chitosan by forming hydrogen bonds, constituting a stable intermolecular network. In the mixed solution, the amino groups of chitosan and the hydroxyl groups of polyethylene glycol repeatedly form hydrogen bonds and cross-link to form a molecular network. During the freeze-drying process, the formation of ice crystals will expel solvent molecules (such as water and tetrahydrofuran), and the hydrogen bond network between chitosan and the polyethylene glycol-polycaprolactone block copolymer becomes tighter. Although the chitosan molecular chain has a certain degree of rigidity, due to its large molecular weight and flexible main chain structure, it is easy to orient along the surface of the ice crystals. The amino and hydroxyl groups on the chitosan molecular chain can interact with the surface of the ice crystals through hydrogen bonding or van der Waals forces, further inducing the molecular chain to align along the direction of ice crystal growth. During the growth of ice crystals, the chitosan molecules will tend to the surface of the ice crystals due to their hydrophilicity, and this adsorption behavior causes the chitosan segments to form a directional arrangement at the interface of the ice crystals.

[0016] The imidazole group contains two key functional sites. The pyridine-type nitrogen has a lone pair of electrons and can act as a hydrogen bond acceptor to form hydrogen bonds with water molecules on the ice crystal surface. The pyrrole-type nitrogen has a proton available for hydrogen bonding and can act as a hydrogen bond donor to bind to the unsaturated hydrogen bonds on the ice crystal surface. The ice crystal surface is a regular water molecule network, which exhibits polar characteristics due to the incomplete saturation of hydrogen bonds. This surface property enables the imidazole group to be firmly adsorbed on the ice crystal surface through hydrogen bonding or electrostatic interactions. During the freezing process, water molecules in the solution gradually crystallize to form ice crystals. When the ice crystals grow along a direction, the imidazole group, due to its strong adsorption to the ice crystal surface, tends to align along the growth direction of the ice crystal, thus forming a regular orientation distribution at the microscopic level. This interfacial adsorption effect not only enhances the directional growth of ice crystals but also causes the imidazole group and its connected molecular chains (such as chitosan and PNIPAM) to align along the growth direction of the ice crystal.

[0017] During freeze-drying, the growth of ice crystals determines the final pore size, and the size of ice crystals is directly significantly affected by the solution concentration. As the solid content of the modified waterborne polyurethane increases, the content of non-ice components in the solution increases, resulting in more restrictions on the growth of ice crystals during the growth process. This is because when the solid content of the waterborne polyurethane increases, the number of polyurethane molecular chains or dispersed particles in the solution increases, leading to enhanced intermolecular and interparticle interactions, thereby increasing the viscosity of the solution. At the same time, the polar groups on the polyurethane molecular chains are prone to form weak molecular network structures through hydrogen bonding or other intermolecular interactions. Under high solid content conditions, the density of this network increases, thereby increasing the viscosity and inhibiting the diffusion of water molecules to the ice crystal interface, thus restricting the growth of ice crystals. As a result, smaller ice crystals are formed, leaving smaller pore sizes after freeze-drying, and the porosity will also decrease accordingly; at low concentrations, the viscosity of the solution is low, and water molecules can migrate to the ice crystal interface more freely, allowing ice crystals to grow more rapidly and over a larger range. As a result, larger ice crystals are formed, leaving larger pore sizes after freeze-drying.

[0018] As a preferred technical solution of the present invention, in step A1, the first temperature is 40 - 50 °C. For example, it can be 40.0 °C, 41.0 °C, 42.0 °C, 43.0 °C, 44.0 °C, 45.0 °C, 46.0 °C, 47.0 °C, 48.0 °C, 49.0% or 50.0 °C, but is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0019] In some alternative examples, the mass ratio of the mixed monomer A to the aqueous polyurethane dispersion is 1:(3 - 4), for example, it can be 1:3, 1:3.1, 1:3.2, 1:3.3, 1:3.4, 1:3.5, 1:3.6, 1:3.7, 1:3.8, 1:3.9 or 1:4, but is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0020] In some alternative examples, the components of the mixed monomer A are methyl acrylate, butyl acrylate, and acrylic acid, and the mass ratio is 3:2:1.

[0021] In some alternative examples, the initiator is ammonium persulfate, and its mass is 0.3 - 0.5% of the mass of the aqueous polyurethane dispersion. For example, it can be 0.3%, 0.32%, 0.34%, 0.36%, 0.38%, 0.4%, 0.42%, 0.44%, 0.46%, 0.48% or 0.5%, but is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0022] In some alternative examples, the second temperature is 70 - 80 °C. For example, it can be 70.0 °C, 71.0 °C, 72.0 °C, 73.0 °C, 74.0 °C, 75.0 °C, 76.0 °C, 77.0 °C, 78.0 °C, 79.0% or 80.0 °C, but is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0023] In some alternative examples, the reaction time for adding the initiator is 4 - 5 h. For example, it can be 4.0 h, 4.1 h, 4.2 h, 4.3 h, 4.4 h, 4.5 h, 4.6 h, 4.7 h, 4.8 h, 4.9 h or 5.0 h, but is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0024] In some alternative examples, the third temperature is 30 - 40 °C. For example, it can be 30.0 °C, 31.0 °C, 32.0 °C, 33.0 °C, 34.0 °C, 35.0 °C, 36.0 °C, 37.0 °C, 38.0 °C, 39.0% or 40.0 °C, but is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0025] In some alternative examples, the mass of the tetrabutylammonium bromide is 0.2 - 0.3% of the mass of the aqueous polyurethane dispersion. For example, it can be 0.2%, 0.21%, 0.22%, 0.23%, 0.24%, 0.25%, 0.26%, 0.27%, 0.28%, 0.29% or 0.3%, but is not limited to the listed values. Other unlisted values within this numerical range are equally applicable.

[0026] In some alternative examples, the mass of the epichlorohydrin aqueous solution is 18 - 20% of the mass of the aqueous polyurethane dispersion. For example, it can be 18.0%, 18.2%, 18.4%, 18.6%, 18.8%, 19.0%, 19.2%, 19.4%, 19.6%, 19.8% or 20.0%, but is not limited to the listed values. Other unlisted values within this numerical range are equally applicable.

[0027] In some alternative examples, the mass fraction of the epichlorohydrin aqueous solution is 40 - 50 wt.%. For example, it can be 40.0 wt.%, 41.0 wt.%, 42.0 wt.%, 43.0 wt.%, 44.0 wt.%, 45.0 wt.%, 46.0 wt.%, 47.0 wt.%, 48.0 wt.%, 49.0 wt.% or 50.0 wt.%, but is not limited to the listed values. Other unlisted values within this numerical range are equally applicable.

[0028] In some alternative examples, the reaction time for adding the epichlorohydrin aqueous solution is 3 - 4 h. For example, it can be 3.0 h, 3.1 h, 3.2 h, 3.3 h, 3.4 h, 3.5 h, 3.6 h, 3.7 h, 3.8 h, 3.9 h or 4.0 h, but is not limited to the listed values. Other unlisted values within this numerical range are equally applicable

[0029] As a preferred technical solution of the present invention, in step A2, the mass ratio of the chitosan to the acetic acid aqueous solution is 1:(7 - 8). For example, it can be 1:7, 1:7.1, 1:7.2, 1:7.3, 1:7.4, 1:7.5, 1:7.6, 1:7.7, 1:7.8, 1:7.9 or 1:8, but is not limited to the listed values. Other unlisted values within this numerical range are equally applicable.

[0030] In some alternative examples, the mass fraction of the acetic acid aqueous solution is 1 wt.%.

[0031] In some alternative examples, the mass ratio of the chitosan to the mixed monomer B is 1:3.

[0032] In some alternative examples, the components of the mixed monomer B are acrylic acid, butyl acrylate, and methyl methacrylate, and the mass ratio is 4:5:3.

[0033] In some alternative examples, the mass of sodium dodecyl sulfate is 5-6% of the mass of chitosan. For example, it can be 5.0%, 5.1%, 5.2%, 5.3%, 5.4%, 5.5%, 5.6%, 5.7%, 5.8%, 5.9%, or 6.0%, but is not limited to the listed values. Other unlisted values within this range are equally applicable.

[0034] In some alternative examples, the mass of azobisisobutyronitrile is 1-2% of the mass of chitosan. For example, it can be 1.0%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, or 2.0%, but is not limited to the listed values. Other unlisted values within this range are equally applicable.

[0035] In some alternative examples, the mass ratio of deionized water to chitosan is (2-3):1. For example, it can be 2:1, 2.1:1, 2.2:1, 2.3:1, 2.4:1, 2.5:1, 2.6:1, 2.7:1, 2.8:1, 2.9:1, or 3:1, but is not limited to the listed values. Other unlisted values within this range are equally applicable.

[0036] In some alternative examples, the mass of the ammonium persulfate solution is 50-60% of the mass of chitosan. For example, it can be 50.0%, 51.0%, 52.0%, 53.0%, 54.0%, 55.0%, 56.0%, 57.0%, 58.0%, 59.0%, or 60.0%, but is not limited to the listed values. Other unlisted values within this range are equally applicable.

[0037] In some alternative examples, the mass fraction of the ammonium persulfate solution is 9-10 wt.%. For example, it can be 9.0 wt.%, 9.1 wt.%, 9.2 wt.%, 9.3 wt.%, 9.4 wt.%, 9.5 wt.%, 9.6 wt.%, 9.7 wt.%, 9.8 wt.%, 9.9 wt.%, or 10.0 wt.%, but is not limited to the listed values. Other unlisted values within this range are equally applicable.

[0038] In some alternative examples, the reaction time for adding the ammonium persulfate solution is 4 - 5 h. For example, it can be 4.0 h, 4.1 h, 4.2 h, 4.3 h, 4.4 h, 4.5 h, 4.6 h, 4.7 h, 4.8 h, 4.9 h or 5.0 h. However, it is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0039] In some alternative examples, the concentration of the sodium hydroxide solution is 1 M.

[0040] As a preferred technical solution of the present invention, in step S1, the polyethylene glycol is polyethylene glycol - 2000.

[0041] In some alternative examples, the third temperature is 110 - 120 °C. For example, it can be 110.0 °C, 111.0 °C, 112.0 °C, 113.0 °C, 114.0 °C, 115.0 °C, 116.0 °C, 117.0 °C, 118.0 °C, 119.0% or 120.0 °C. However, it is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0042] In some alternative examples, the mass ratio of ε - caprolactone to polyethylene glycol is 2:1.

[0043] In some alternative examples, the fourth temperature is 140 - 150 °C. For example, it can be 140.0 °C, 141.0 °C, 142.0 °C, 143.0 °C, 144.0 °C, 145.0 °C, 146.0 °C, 147.0 °C, 148.0 °C, 149.0% or 150.0 °C. However, it is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0044] In some alternative examples, the mass of stannous octoate is 0.5 - 1.0% of the mass of polyethylene glycol. For example, it can be 0.5%, 0.6%, 0.7%, 0.8%, 0.9% or 1.0%. However, it is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0045] In some alternative examples, the mass of triethylamine is 2 - 3% of the mass of polyethylene glycol. For example, it can be 2.0%, 2.1%, 2.2%, 2.3%, 2.4%, 2.5%, 2.6%, 2.7%, 2.8%, 2.9% or 3.0%. However, it is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0046] In some alternative examples, the reaction time for adding triethylamine is 8 - 9 h. For example, it can be 8.0 h, 8.1 h, 8.2 h, 8.3 h, 8.4 h, 8.5 h, 8.6 h, 8.7 h, 8.8 h, 8.9 h or 9.0 h. However, it is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0047] In some alternative examples, the temperature of the ice methanol is 0 - 5 °C. For example, it can be 0.0 °C, 1.0 °C, 2.0 °C, 3.0 °C, 4.0 °C or 5.0 °C. However, it is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0048] In some alternative examples, the time for vacuum drying is 20 - 30 h. For example, it can be 20.0 h, 21.0 h, 22.0 h, 23.0 h, 24.0 h, 25.0 h, 26.0 h, 27.0 h, 28.0 h, 29.0 h or 30.0 h. However, it is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0049] As a preferred technical solution of the present invention, in step S2, the mass ratio of imidazole to N,N - dimethylformamide is 1:(7 - 8). For example, it can be 1:7, 1:7.1, 1:7.2, 1:7.3, 1:7.4, 1:7.5, 1:7.6, 1:7.7, 1:7.8, 1:7.9 or 1:8. However, it is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0050] In some alternative examples, the mass ratio of anhydrous potassium carbonate to imidazole is 3:5.

[0051] In some alternative examples, the mass ratio of 2 - chloroethanol to imidazole is 1:1.

[0052] In some alternative examples, the fifth temperature is 80 - 90 °C. For example, it can be 80.0 °C, 81.0 °C, 82.0 °C, 83.0 °C, 84.0 °C, 85.0 °C, 86.0 °C, 87.0 °C, 88.0 °C, 89.0% or 90.0 °C. However, it is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0053] In some alternative examples, the reaction time for adding 2 - chloroethanol is 6 - 7 h. For example, it can be 6.0 h, 6.1 h, 6.2 h, 6.3 h, 6.4 h, 6.5 h, 6.6 h, 6.7 h, 6.8 h, 6.9 h or 7.0 h. However, it is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0054] In some alternative examples, the mass ratio of toluene to imidazole is 1:10.

[0055] In some alternative examples, the mass ratio of methacrylic acid to imidazole is (1 - 1.4):1. For example, it can be 1:1, 1.1:1, 1.2:1, 1.3:1, or 1.4:1, but is not limited to the listed values. Other unlisted values within this numerical range are equally applicable.

[0056] In some alternative examples, the mass of hydroquinone is 0.5 - 1% of the mass of imidazole. For example, it can be 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, or 1.0%, but is not limited to the listed values. Other unlisted values within this numerical range are equally applicable.

[0057] In some alternative examples, the reaction time for adding hydroquinone is 6 - 7 h. For example, it can be 6.0 h, 6.1 h, 6.2 h, 6.3 h, 6.4 h, 6.5 h, 6.6 h, 6.7 h, 6.8 h, 6.9 h, or 7.0 h, but is not limited to the listed values. Other unlisted values within this numerical range are equally applicable.

[0058] In some alternative examples, the mass of azobisisobutyronitrile is 1 - 1.5% of the mass of imidazole. For example, it can be 1.0%, 1.1%, 1.2%, 1.3%, 1.4%, or 1.5%, but is not limited to the listed values. Other unlisted values within this numerical range are equally applicable.

[0059] In some alternative examples, the reaction time for adding azobisisobutyronitrile is 6 - 7 h. For example, it can be 6.0 h, 6.1 h, 6.2 h, 6.3 h, 6.4 h, 6.5 h, 6.6 h, 6.7 h, 6.8 h, 6.9 h, or 7.0 h, but is not limited to the listed values. Other unlisted values within this numerical range are equally applicable.

[0060] In some alternative examples, the time for vacuum drying is 20 - 30 h. For example, it can be 20.0 h, 21.0 h, 22.0 h, 23.0 h, 24.0 h, 25.0 h, 26.0 h, 27.0 h, 28.0 h, 29.0 h, or 30.0 h, but is not limited to the listed values. Other unlisted values within this numerical range are equally applicable.

[0061] As a preferred technical solution of the present invention, in step S3, the mass ratio of the polyethylene glycol - polycaprolactone block copolymer to tetrahydrofuran is 1:4.

[0062] In some optional examples, the mass ratio of the modified chitosan-polyacrylate copolymer to deionized water is 1:10.

[0063] In some optional examples, the mass ratio of the methacryloyloxyethyl imidazole-functionalized polymer to deionized water is 1:8.

[0064] In some optional examples, the mass ratio of the PNIPAM to deionized water is 1:3.

[0065] In some optional examples, the solid content of the modified polyurethane dispersion is 10 - 20%, for example, it can be 10.0%, 11.0%, 12.0%, 13.0%, 14.0%, 15.0%, 16.0%, 17.0%, 18.0%, 19.0% or 20.0%, but is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0066] In some optional examples, the mass ratio of the polyethylene glycol-polycaprolactone block copolymer, modified chitosan-polyacrylate copolymer, methacryloyloxyethyl imidazole-functionalized polymer, PNIPAM to the modified polyurethane dispersion is 6:3:2:1.5:14;

[0067] In some optional examples, the time for ultrasonic dispersion is 20 - 30 min, for example, it can be 20 min, 21 min, 22 min, 23 min, 24 min, 25 min, 26 min, 27 min, 28 min, 29 min or 30 min, but is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0068] In some optional examples, the freezing temperature is -30 °C, the cooling rate is 2 °C / min, and the freezing time is 4 - 6 h, for example, it can be 4.0 h, 4.1 h, 4.2 h, 4.3 h, 4.4 h, 4.5 h, 4.6 h, 4.7 h, 4.8 h, 4.9 h, 5.0 h, 5.1 h, 5.2 h, 5.3 h, 5.4 h, 5.5 h, 5.6 h, 5.7 h, 5.8 h, 5.9 h or 6.0 h, but is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0069] In some optional examples, the drying time is 40 - 50 h, for example, it can be 40.0 h, 41.0 h, 42.0 h, 43.0 h, 44.0 h, 45.0 h, 46.0 h, 47.0 h, 48.0 h, 49.0 h or 50.0 h, but is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0070] In a second aspect, the present invention provides a porous sound-absorbing material based on a controllable pore size and orientation structure obtained by the preparation method described in the first aspect.

[0071] In a third aspect, the present invention provides the application of the porous sound-absorbing material based on a controllable pore size and orientation structure prepared by the said preparation method in the preparation of audio equipment and industrial noise reduction equipment.

[0072] Compared with the prior art, the beneficial effects of the present invention are as follows: (1) The present invention uses waterborne polyurethane as the base material, and through the introduction of functional monomers such as methyl acrylate, butyl acrylate, and acrylic acid for free radical copolymerization reaction, significantly improves the functionality and bonding performance of the waterborne polyurethane dispersion. By initiating the formation of polymer chain segments with ammonium persulfate and further cross-linking with epichlorohydrin, higher mechanical strength and chemical stability are imparted to the polyurethane dispersion; (2) The imidazole group can be firmly adsorbed on the surface of ice crystals through hydrogen bonding or electrostatic interaction. During the freezing process, when ice crystals grow along a direction, due to its strong adsorption effect on the surface of ice crystals, the imidazole group tends to align along the growth direction of the ice crystals, thus forming a regular orientation distribution at the microscopic level. This interfacial adsorption effect not only strengthens the directional growth of ice crystals but also causes the imidazole group and its connected molecular chains (such as chitosan, PNIPAM) to orient along the growth direction of the ice crystals; (3) During the freezing and drying processes, the polycaprolactone chain segments will form crystalline regions, and the crystalline regions provide high-strength physical cross-linking points through the regular packing of molecular chains. The crystallinity of the polycaprolactone chain segments can significantly enhance the rigidity and strength of the pore walls, avoiding pore collapse or deformation. Description of the Drawings

[0073] Figure 1 SEM image of the porous sound-absorbing material prepared in Example 1 of the present invention (scale bar is 50 μm);

[0074] Figure 2 SEM image of the porous sound-absorbing material prepared in Example 1 of the present invention (scale bar is 500 μm). Detailed Embodiments

[0075] The technical solution of the present invention will be described in detail below in conjunction with specific embodiments and their accompanying drawings. The embodiments recorded herein are specific specific embodiments of the present invention and are used to illustrate the concept of the present invention; these descriptions are all explanatory and exemplary and should not be construed as limiting the embodiments of the present invention and the protection scope of the present invention. Except for the embodiments recorded herein, those skilled in the art can also adopt other obvious technical solutions based on the content disclosed in the claims and the specification of the present application, and these technical solutions include technical solutions that make any obvious substitutions and modifications to the embodiments recorded herein.

[0076] The chemical reagents used in the examples and comparative examples of the present invention are all commercially available products and have not been further purified.

[0077] Example 1

[0078] This example provides a preparation method of a porous sound-absorbing material based on a controllable pore size and orientation structure. The preparation method specifically includes the following steps:

[0079] Step A1: Heat the aqueous polyurethane dispersion with a solid content of 30% to 46°C, add the mixed monomer A composed of methyl acrylate, butyl acrylate and acrylic acid and stir evenly. The mass ratio of methyl acrylate, butyl acrylate and acrylic acid is 3:2:1, and the mass ratio of the mixed monomer A to the aqueous polyurethane dispersion is 1:3.6. Then add ammonium persulfate accounting for 0.39% of the mass of the aqueous polyurethane dispersion, heat up to 76°C and react fully for 4.6 h. After the reaction is completed, cool down to 38°C, add tetrabutylammonium bromide accounting for 0.26% of the mass of the aqueous polyurethane dispersion and an aqueous solution of epichlorohydrin with a mass fraction of 46 wt.% accounting for 18.9% of the mass of the aqueous polyurethane dispersion, heat up to 77°C and react fully for 3.6 h. After the reaction is completed, cool to room temperature to obtain a modified polyurethane dispersion.

[0080] Step A2: Add chitosan to a 1 wt.% acetic acid aqueous solution and stir to dissolve it. The mass ratio of chitosan to the acetic acid aqueous solution is 1:7.6, and adjust the pH to 5.0 to obtain a chitosan solution. Under a nitrogen atmosphere, disperse the mixed monomer B composed of acrylic acid, butyl acrylate and methyl methacrylate, sodium dodecyl sulfate accounting for 5.3% of the mass of chitosan and azobisisobutyronitrile accounting for 1.6% of the mass of chitosan in deionized water and stir to form a monomer emulsion. The mass ratio of acrylic acid, butyl acrylate and methyl methacrylate is 4:5:3, the mass ratio of chitosan to the mixed monomer B is 1:3, and the mass ratio of deionized water to chitosan is 2.6:1. Heat up to 77°C, and drop the monomer emulsion and an ammonium persulfate solution with a mass fraction of 9.5 wt.% accounting for 53% of the mass of chitosan into the chitosan solution, keep stirring and react fully for 4.3 h. After the reaction is completed, cool to room temperature, adjust the pH to 7.0 with 1M sodium hydroxide solution, and filter to obtain a modified chitosan-polyacrylate copolymer.

[0081] Step S1: Under a nitrogen atmosphere, heat polyethylene glycol-2000 to 116°C, add ε-caprolactone with a mass ratio to polyethylene glycol of 2:1, adjust the temperature to 147°C, add stannous octoate accounting for 0.64% of the mass of polyethylene glycol-2000 and triethylamine accounting for 2.6% of the mass of polyethylene glycol-2000 and react fully for 8.6 h. After the reaction is completed, cool to room temperature, add dichloromethane to dissolve the product, add the dissolved product to ice methanol at 2°C to precipitate, filter and collect the precipitate, and vacuum dry at 46°C for 24 h to obtain a polyethylene glycol-polycaprolactone block copolymer.

[0082] Step S2: Dissolve imidazole in N,N-dimethylformamide with a mass ratio of imidazole to N,N-dimethylformamide of 1:7.3. Add potassium carbonate with a mass ratio to imidazole of 3:5. After stirring evenly, add 2-chloroethanol with a mass ratio to imidazole of 1:1. Heat to 86 °C and react fully for 6.5 h. Cool to room temperature and perform vacuum distillation to obtain 2-imidazole ethanol. Dissolve 2-imidazole ethanol in toluene with a mass ratio to imidazole of 1:10. Add methacrylic acid with a mass ratio to imidazole of 1.2:1 and hydroquinone accounting for 0.64% of the mass of imidazole and react fully for 6.3 h. After the reaction, cool to room temperature and dry with anhydrous magnesium sulfate to obtain the monomer. Dissolve the monomer in tetrahydrofuran. Under a nitrogen atmosphere, add azobisisobutyronitrile accounting for 1.3% of the mass of imidazole, heat to 73 °C and react fully for 6.1 h. After the reaction, add it to anhydrous ether for precipitation, filter and collect the precipitate, and dry it under vacuum at 43 °C for 24 h to obtain the methacryloyloxyethyl imidazole-functionalized polymer;

[0083] Step S3: Disperse the polyethylene glycol-polycaprolactone block copolymer in tetrahydrofuran with a mass ratio of the polyethylene glycol-polycaprolactone block copolymer to tetrahydrofuran of 1:4. Disperse the modified chitosan-polyacrylate copolymer in deionized water with a mass ratio of the modified chitosan-polyacrylate copolymer to deionized water of 1:10. Disperse the methacryloyloxyethyl imidazole-functionalized polymer in deionized water with a mass ratio of the methacryloyloxyethyl imidazole-functionalized polymer to deionized water of 1:8. Dissolve PNIPAM in deionized water with a mass ratio of PNIPAM to deionized water of 1:3. Mix the dispersion of the polyethylene glycol-polycaprolactone block copolymer, the dispersion of the modified chitosan-polyacrylate copolymer, and the dispersion of the methacryloyloxyethyl imidazole-functionalized polymer to form a mixed solution. Add the modified polyurethane dispersion with a solid content of 13% and the PNIPAM solution to the mixed solution in sequence. The mass ratio of the polyethylene glycol-polycaprolactone block copolymer, the modified chitosan-polyacrylate copolymer, the methacryloyloxyethyl imidazole-functionalized polymer, PNIPAM to the modified polyurethane dispersion is 6:3:2:1.5:14. After stirring evenly, perform ultrasonic dispersion treatment for 23 min. Freeze the treated mixed solution at -30 °C for 4.6 h, and freeze-dry the frozen sample under vacuum at -80 °C for 44 h to obtain the porous sound-absorbing material with controllable pore size and orientation structure.

[0084] Figure 1 、 Figure 2 Figure shows the SEM image of the porous sound-absorbing material prepared in this example. It can be seen that the surface of the material has a relatively rough structure, forming rich micro-textures, which helps to increase the surface area, thereby increasing the contact area between the sound wave and the material and enhancing the sound-absorbing performance.

[0085] Example 2

[0086] This embodiment provides a preparation method of a porous sound-absorbing material based on a controllable pore size and orientation structure. The preparation method specifically includes the following steps:

[0087] Step A1: Heat the aqueous polyurethane dispersion with a solid content of 30% to 43°C, add the mixed monomer A composed of methyl acrylate, butyl acrylate, and acrylic acid and stir evenly. The mass ratio of methyl acrylate, butyl acrylate, and acrylic acid is 3:2:1, and the mass ratio of the mixed monomer A to the aqueous polyurethane dispersion is 1:4.0. Then add ammonium persulfate accounting for 0.50% of the mass of the aqueous polyurethane dispersion, heat to 80°C and react fully for 5.0 h. After the reaction is completed, cool to 34°C, add tetrabutylammonium bromide accounting for 0.20% of the mass of the aqueous polyurethane dispersion and an aqueous solution of epichlorohydrin with a mass fraction of 40 wt.% accounting for 20.0% of the mass of the aqueous polyurethane dispersion, heat to 70°C and react fully for 4.0 h. After the reaction is completed, cool to room temperature to obtain a modified polyurethane dispersion.

[0088] Step A2: Add chitosan to a 1 wt.% acetic acid aqueous solution and stir to dissolve it. The mass ratio of chitosan to the acetic acid aqueous solution is 1:7.0, adjust the pH to 5.0 to obtain a chitosan solution. Under a nitrogen atmosphere, disperse the mixed monomer B composed of acrylic acid, butyl acrylate, and methyl methacrylate, sodium dodecyl sulfate accounting for 5.3%, 5.0%, 6.0%, and 5.7% of the mass of chitosan, and azobisisobutyronitrile accounting for 1.0% of the mass of chitosan in deionized water and stir to form a monomer emulsion. The mass ratio of acrylic acid, butyl acrylate, and methyl methacrylate is 4:5:3, the mass ratio of chitosan to the mixed monomer B is 1:3, and the mass ratio of deionized water to chitosan is 3.0:1. Heat to 80°C, and drop the monomer emulsion and an ammonium persulfate solution with a mass fraction of 9.0 wt.% accounting for 50% of the mass of chitosan into the chitosan solution, keep stirring and react fully for 4.0 h. After the reaction is completed, cool to room temperature, adjust the pH to 7.0 with a 1M sodium hydroxide solution, and filter to obtain a modified chitosan-polyacrylate copolymer.

[0089] Step S1: Under a nitrogen atmosphere, heat polyethylene glycol-2000 to 110°C, add ε-caprolactone with a mass ratio to polyethylene glycol of 2:1, adjust the temperature to 150°C, add stannous octanoate accounting for 0.50% of the mass of polyethylene glycol-2000 and triethylamine accounting for 2.0% of the mass of polyethylene glycol-2000 and react fully for 8.0 h. After the reaction is completed, cool to room temperature, add dichloromethane to dissolve the product, add the dissolved product to ice methanol at 3°C for precipitation, filter to collect the precipitate, and vacuum dry at 40°C for 20 h to obtain a polyethylene glycol-polycaprolactone block copolymer.

[0090] Step S2: Dissolve imidazole in N,N-dimethylformamide with a mass ratio of imidazole to N,N-dimethylformamide of 1:7.0. Add potassium carbonate with a mass ratio to imidazole of 3:5. After stirring evenly, add 2-chloroethanol with a mass ratio to imidazole of 1:1. Heat up to 80 °C and react fully for 6.0 h. Cool to room temperature and perform vacuum distillation to obtain 2-imidazole ethanol. Dissolve 2-imidazole ethanol in toluene with a mass ratio to imidazole of 1:10. Add methacrylic acid with a mass ratio to imidazole of 1.0:1 and hydroquinone at 0.50% of the mass of imidazole and react fully for 6.0 h. After the reaction ends, cool to room temperature and dry with anhydrous magnesium sulfate to obtain the monomer. Dissolve the monomer in tetrahydrofuran. Under a nitrogen atmosphere, add azobisisobutyronitrile at 1.0% of the mass of imidazole and react fully at 70 °C for 6.0 h. After the reaction ends, add it to anhydrous ether for precipitation, filter and collect the precipitate, and vacuum dry at 40 °C for 20 h to obtain the methacryloyloxyethyl imidazole-functionalized polymer;

[0091] Step S3: Disperse the polyethylene glycol-polycaprolactone block copolymer in tetrahydrofuran with a mass ratio of the polyethylene glycol-polycaprolactone block copolymer to tetrahydrofuran of 1:4. Disperse the modified chitosan-polyacrylate copolymer in deionized water with a mass ratio of the modified chitosan-polyacrylate copolymer to deionized water of 1:10. Disperse the methacryloyloxyethyl imidazole-functionalized polymer in deionized water with a mass ratio of the methacryloyloxyethyl imidazole-functionalized polymer to deionized water of 1:8. Dissolve PNIPAM in deionized water with a mass ratio of PNIPAM to deionized water of 1:3. Mix the dispersion of the polyethylene glycol-polycaprolactone block copolymer, the dispersion of the modified chitosan-polyacrylate copolymer and the dispersion of the methacryloyloxyethyl imidazole-functionalized polymer to form a mixed solution. Add the modified polyurethane dispersion with a solid content of 10% and the PNIPAM solution to the mixed solution in sequence. The mass ratio of the polyethylene glycol-polycaprolactone block copolymer, the modified chitosan-polyacrylate copolymer, the methacryloyloxyethyl imidazole-functionalized polymer, PNIPAM to the modified polyurethane dispersion is 6:3:2:1.5:14. After stirring evenly, perform ultrasonic dispersion treatment for 20 min. Freeze the treated mixed solution at -30 °C for 4.0 h. Freeze-dry the frozen sample at -80 °C under vacuum for 48 h to obtain the porous sound-absorbing material with controllable pore size and orientation structure.

[0092] Example 3

[0093] This example provides a preparation method of a porous sound-absorbing material with controllable pore size and orientation structure. The preparation method specifically includes the following steps:

[0094] Step A1: Heat the aqueous polyurethane dispersion with a solid content of 30% to 50°C, add mixed monomer A composed of methyl acrylate, butyl acrylate, and acrylic acid and stir evenly. The mass ratio of methyl acrylate, butyl acrylate, and acrylic acid is 3:2:1, and the mass ratio of mixed monomer A to the aqueous polyurethane dispersion is 1:3.9. Then add ammonium persulfate accounting for 0.44% of the mass of the aqueous polyurethane dispersion, heat up to 73°C and react fully for 4.3 h. After the reaction ends, cool down to 30°C, add tetrabutylammonium bromide accounting for 0.24% of the mass of the aqueous polyurethane dispersion and an aqueous solution of epichlorohydrin with a mass fraction of 43 wt.% accounting for 19.6% of the mass of the aqueous polyurethane dispersion, heat up to 74°C and react fully for 3.4 h. After the reaction ends, cool down to room temperature to obtain a modified polyurethane dispersion;

[0095] Step A2: Add chitosan to an aqueous acetic acid solution with a concentration of 1 wt.% and stir to dissolve. The mass ratio of chitosan to the aqueous acetic acid solution is 1:7.4, adjust the pH to 5.0 to obtain a chitosan solution. Under a nitrogen atmosphere, disperse mixed monomer B composed of acrylic acid, butyl acrylate, and methyl methacrylate, sodium dodecyl sulfate accounting for 6.0% of the mass of chitosan, and azobisisobutyronitrile accounting for 1.8% of the mass of chitosan in deionized water and stir to form a monomer emulsion. The mass ratio of acrylic acid, butyl acrylate, and methyl methacrylate is 4:5:3, the mass ratio of chitosan to mixed monomer B is 1:3, and the mass ratio of deionized water to chitosan is 2.4:1. Heat up to 70°C, and drop the monomer emulsion and an ammonium persulfate solution with a mass fraction of 10.0 wt.% accounting for 58% of the mass of chitosan into the chitosan solution, keep stirring and react fully for 4.7 h. After the reaction ends, cool down to room temperature, adjust the pH to 7.0 with 1M sodium hydroxide solution, and filter to obtain a modified chitosan-polyacrylate copolymer;

[0096] Step S1: Under a nitrogen atmosphere, heat polyethylene glycol-2000 to 113°C, add ε-caprolactone with a mass ratio to polyethylene glycol of 2:1, adjust the temperature to 140°C, add stannous octoate accounting for 0.82% of the mass of polyethylene glycol-2000 and triethylamine accounting for 2.4% of the mass of polyethylene glycol-2000, and react fully for 9.0 h. After the reaction ends, cool down to room temperature, add dichloromethane to dissolve the product, add the dissolved product to ice methanol at 0°C for precipitation, filter to collect the precipitate, and vacuum dry at 42°C for 26 h to obtain a polyethylene glycol-polycaprolactone block copolymer;

[0097] Step S2: Dissolve imidazole in N,N-dimethylformamide with a mass ratio of imidazole to N,N-dimethylformamide of 1:8.0. Add anhydrous potassium carbonate with a mass ratio to imidazole of 3:5. After stirring evenly, add 2-chloroethanol with a mass ratio to imidazole of 1:1. Heat to 83 °C and react fully for 6.7 h. Cool to room temperature and perform vacuum distillation to obtain 2-imidazole ethanol. Dissolve 2-imidazole ethanol in toluene with a mass ratio to imidazole of 1:10. Add methacrylic acid with a mass ratio to imidazole of 1.4:1 and hydroquinone accounting for 0.84% of the mass of imidazole and react fully for 6.8 h. After the reaction, cool to room temperature and dry with anhydrous magnesium sulfate to obtain the monomer. Dissolve the monomer in tetrahydrofuran. Under a nitrogen atmosphere, add azobisisobutyronitrile accounting for 1.5% of the mass of imidazole and react fully at 76 °C for 6.6 h. After the reaction, add it to anhydrous ether for precipitation, filter and collect the precipitate, and vacuum dry at 48 °C for 28 h to obtain methacryloyloxyethylimidazole-functionalized polymer;

[0098] Step S3: Disperse poly(ethylene glycol)-poly(caprolactone) block copolymer in tetrahydrofuran with a mass ratio of poly(ethylene glycol)-poly(caprolactone) block copolymer to tetrahydrofuran of 1:4. Disperse modified chitosan-polyacrylate copolymer in deionized water with a mass ratio of modified chitosan-polyacrylate copolymer to deionized water of 1:10. Disperse methacryloyloxyethylimidazole-functionalized polymer in deionized water with a mass ratio of methacryloyloxyethylimidazole-functionalized polymer to deionized water of 1:8. Dissolve PNIPAM in deionized water with a mass ratio of PNIPAM to deionized water of 1:3. Mix the poly(ethylene glycol)-poly(caprolactone) block copolymer dispersion, modified chitosan-polyacrylate copolymer dispersion and methacryloyloxyethylimidazole-functionalized polymer dispersion to form a mixed solution. Add a modified polyurethane dispersion with a solid content of 16% and a PNIPAM solution to the mixed solution in sequence. The mass ratio of poly(ethylene glycol)-poly(caprolactone) block copolymer, modified chitosan-polyacrylate copolymer, methacryloyloxyethylimidazole-functionalized polymer, PNIPAM to the modified polyurethane dispersion is 6:3:2:1.5:14. After stirring evenly, perform ultrasonic dispersion treatment for 26 min. Freeze the treated mixed solution at -30 °C for 5.2 h. Freeze-dry the frozen sample at -80 °C under vacuum for 40 h to obtain a porous sound-absorbing material with controllable pore size and orientation structure.

[0099] Example 4

[0100] This example provides a preparation method of a porous sound-absorbing material with controllable pore size and orientation structure. The preparation method specifically includes the following steps:

[0101] Step A1: Heat the aqueous polyurethane dispersion with a solid content of 30% to 40°C, add mixed monomer A composed of methyl acrylate, butyl acrylate and acrylic acid and stir evenly. The mass ratio of methyl acrylate, butyl acrylate and acrylic acid is 3:2:1, and the mass ratio of mixed monomer A to the aqueous polyurethane dispersion is 1:3.0. Then add ammonium persulfate accounting for 0.30% of the mass of the aqueous polyurethane dispersion, heat up to 70°C and react fully for 4.0 h. After the reaction is completed, cool down to 40°C, add tetrabutylammonium bromide accounting for 0.30% of the mass of the aqueous polyurethane dispersion and an aqueous solution of epichlorohydrin with a mass fraction of 50 wt.% accounting for 18.0% of the mass of the aqueous polyurethane dispersion, heat up to 80°C and react fully for 3.0 h. After the reaction is completed, cool down to room temperature to obtain a modified polyurethane dispersion;

[0102] Step A2: Add chitosan to 1 wt.% acetic acid aqueous solution and stir to dissolve. The mass ratio of chitosan to acetic acid aqueous solution is 1:8.0, adjust the pH to 5.0 to obtain a chitosan solution. Under a nitrogen atmosphere, disperse mixed monomer B composed of acrylic acid, butyl acrylate and methyl methacrylate, sodium dodecyl sulfate accounting for 5.7% of the mass of chitosan and azobisisobutyronitrile accounting for 2.0% of the mass of chitosan in deionized water and stir to form a monomer emulsion. The mass ratio of acrylic acid, butyl acrylate and methyl methacrylate is 4:5:3, the mass ratio of chitosan to mixed monomer B is 1:3, and the mass ratio of deionized water to chitosan is 2.0:1. Heat up to 75°C, and drop the monomer emulsion and an ammonium persulfate solution with a mass fraction of 9.3 wt.% accounting for 60% of the mass of chitosan into the chitosan solution, keep stirring and react fully for 5.0 h. After the reaction is completed, cool down to room temperature, adjust the pH to 7.0 with 1 M sodium hydroxide solution, and filter to obtain a modified chitosan-polyacrylate copolymer;

[0103] Step S1: Under a nitrogen atmosphere, heat polyethylene glycol-2000 to 120°C, add ε-caprolactone with a mass ratio to polyethylene glycol of 2:1, adjust the temperature to 143°C, add stannous octanoate accounting for 1.0% of the mass of polyethylene glycol-2000 and triethylamine accounting for 3.0% of the mass of polyethylene glycol-2000 and react fully for 8.4 h. After the reaction is completed, cool down to room temperature, add dichloromethane to dissolve the product, add the dissolved product to ice methanol at 5°C for precipitation, filter and collect the precipitate, and vacuum dry at 50°C for 30 h to obtain a polyethylene glycol-polycaprolactone block copolymer;

[0104] Step S2: Dissolve imidazole in N,N-dimethylformamide with a mass ratio of imidazole to N,N-dimethylformamide of 1:7.6. Add potassium carbonate with a mass ratio to imidazole of 3:5. After stirring evenly, add 2-chloroethanol with a mass ratio to imidazole of 1:1. Heat to 90 °C and react fully for 7.0 h. Cool to room temperature and perform vacuum distillation to obtain 2-imidazole ethanol. Dissolve 2-imidazole ethanol in toluene with a mass ratio to imidazole of 1:10. Add methacrylic acid with a mass ratio to imidazole of 1.1:1 and hydroquinone at 1.0% of the mass of imidazole and react fully for 7.0 h. After the reaction, cool to room temperature and dry with anhydrous magnesium sulfate to obtain the monomer. Dissolve the monomer in tetrahydrofuran. Under a nitrogen atmosphere, add azobisisobutyronitrile at 1.2% of the mass of imidazole, and react fully at 80 °C for 7.0 h. After the reaction, add it to anhydrous ether for precipitation, filter and collect the precipitate, and dry it under vacuum at 50 °C for 30 h to obtain methacryloyloxyethyl imidazole functionalized polymer;

[0105] Step S3: Disperse poly(ethylene glycol)-poly(ε-caprolactone) block copolymer in tetrahydrofuran with a mass ratio of poly(ethylene glycol)-poly(ε-caprolactone) block copolymer to tetrahydrofuran of 1:4. Disperse the modified chitosan-polyacrylate copolymer in deionized water with a mass ratio of modified chitosan-polyacrylate copolymer to deionized water of 1:10. Disperse the methacryloyloxyethyl imidazole functionalized polymer in deionized water with a mass ratio of methacryloyloxyethyl imidazole functionalized polymer to deionized water of 1:8. Dissolve PNIPAM in deionized water with a mass ratio of PNIPAM to deionized water of 1:3. Mix the poly(ethylene glycol)-poly(ε-caprolactone) block copolymer dispersion, the modified chitosan-polyacrylate copolymer dispersion and the methacryloyloxyethyl imidazole functionalized polymer dispersion to form a mixed solution. Add the modified polyurethane dispersion with a solid content of 20% and the PNIPAM solution to the mixed solution in sequence. The mass ratio of poly(ethylene glycol)-poly(ε-caprolactone) block copolymer, modified chitosan-polyacrylate copolymer, methacryloyloxyethyl imidazole functionalized polymer, PNIPAM to the modified polyurethane dispersion is 6:3:2:1.5:14. After stirring evenly, perform ultrasonic dispersion treatment for 30 min. Freeze the treated mixed solution at -30 °C for 6.0 h, and freeze-dry the frozen sample under vacuum at -80 °C for 50 h to obtain a porous sound-absorbing material with controllable pore size and orientation structure.

[0106] Comparative Example 1

[0107] This comparative example provides a preparation method of a porous sound-absorbing material with controllable pore size and orientation structure. The difference from Example 1 is that in step S2, the mass ratio of chitosan to mixed monomer B is 1:4. Compared with Example 1, the mass ratio of mixed monomer B increases by 1, and other process parameters and operating conditions are exactly the same as those in Example 1.

[0108] Comparative Example 2

[0109] This comparative example provides a preparation method of a porous sound-absorbing material based on a controllable pore size and orientation structure. The difference from Example 1 is that in step S2, the mass ratio of chitosan to mixed monomer B is 1:2. Compared with Example 1, the mass ratio of mixed monomer B is reduced by 1, and other process parameters and operating conditions are exactly the same as those in Example 1.

[0110] Comparative Example 3

[0111] This comparative example provides a preparation method of a porous sound-absorbing material based on a controllable pore size and orientation structure. The difference from Example 1 is that in step S5, the solid content of the modified polyurethane dispersion is 26%. Compared with Example 1, the solid content is increased by 13%, and other process parameters and operating conditions are exactly the same as those in Example 1.

[0112] Comparative Example 4

[0113] This comparative example provides a preparation method of a porous sound-absorbing material based on a controllable pore size and orientation structure. The difference from Example 1 is that in step S5, the solid content of the modified polyurethane dispersion is 3%. Compared with Example 1, the solid content is reduced by 10%, and other process parameters and operating conditions are exactly the same as those in Example 1.

[0114] In the present invention, the test standard for the sound absorption coefficient of the prepared material is GB / T 18696.1-2004, and the test results are shown in Table 1.

[0115] Table 1 Test results of porous sound-absorbing materials based on controllable pore size and orientation structure prepared in Examples 1-4 and Comparative Examples 1-4

[0116]

[0117] As can be seen from the data in the table, compared with Example 1, the sound absorption coefficient of Comparative Example 1 increases in the range of 300 - 5000 Hz; compared with Example 1, the sound absorption coefficient of Comparative Example 2 increases in the range of 300 - 4000 Hz and decreases in the range of 4000 - 5000 Hz. This is because in Comparative Example 1, the proportion of mixed monomer B increases, the polyacrylate chains increase in the copolymer, and the flexibility of the pore walls increases. However, too many flexible segments may result in insufficient strength of the pore walls, leading to pore collapse. At the same time, too high a proportion may increase the viscosity of the system, hinder the free growth of the ice crystal template, and form uneven small pore diameters. In the medium and low frequency range (300 - 4000 Hz), the retention depends on larger pores. The increased flexibility of the pore walls may cause the pore walls to vibrate and dissipate part of the energy of medium and low frequency sound waves, thus weakening the retention ability of medium and low frequency sounds; in the high frequency range (4000 - 5000 Hz), the wavelength of sound waves is shorter, and it depends more on multiple scattering and reflection absorption of the pore walls. Increasing the proportion of monomer B may make the pore walls softer and the porosity increase, which is beneficial to the absorption of high frequency sound waves, and the sound absorption effect in the high frequency band increases. In Comparative Example 2, the proportion of mixed monomer B decreases, resulting in chitosan dominating in the copolymer, the overall rigidity of the material increases, the flexibility of the pore walls decreases, the pore diameter may increase and the distribution becomes more uniform. In the medium and low frequency range, the larger pore diameter is beneficial to the penetration of medium and low frequency sound waves, thus achieving the retention of medium and low frequency sounds; in the high frequency range, sound waves rely more on the scattering and reflection effects of the pore walls. Reducing the proportion of monomer B leads to an increase in the rigidity of the pore walls, and this rigid structure may reduce the dissipation ability of high frequency sound waves, resulting in a decrease in the high frequency sound absorption effect.

[0118] As can be seen from the data in the table, compared with Example 1, the sound absorption coefficient of Comparative Example 3 increases in the range of 300 - 5000 Hz; compared with Example 1, the sound absorption coefficient of Comparative Example 4 increases in the range of 300 - 5000 Hz and decreases in the range of 4000 - 5000 Hz. In Comparative Example 3, the solid content of the modified polyurethane dispersion is too high, resulting in a significant increase in the solution viscosity. It is difficult for ice crystals to grow freely during the freezing process, forming smaller ice crystal templates. After freeze-drying, the remaining pore size is small and the porosity decreases, leading to a decrease in the retention ability of medium and low frequency sounds; the high frequency sound absorption performance depends more on the scattering and reflection of the pore walls. The smaller pore diameter can effectively capture high frequency sound waves and increase the high frequency sound absorption coefficient. When the pore walls are too thick and the hardness increases, some sound waves may be reflected rather than absorbed, resulting in a limited increase in the high frequency sound absorption performance. In Comparative Example 4, the solid content of the modified polyurethane dispersion is too low, resulting in a significant decrease in the solution viscosity. Ice crystals can grow freely during the freezing process, forming larger ice crystal templates. After freeze-drying, the remaining pore size is small and the porosity increases, thus achieving the retention of medium and low frequency sounds; high frequency sound waves require small pore diameters and thick pore walls to enhance scattering and absorption, so the high frequency sound absorption performance decreases.

[0119] The above are only specific embodiments of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily thought of by those skilled in the art within the technical scope disclosed by the present invention fall within the protection scope and the disclosure scope of the present invention.

Claims

1. A preparation method of a porous sound-absorbing material based on a controllable pore size and an oriented structure, characterized in that, The preparation method includes: Step S1, under a nitrogen atmosphere, heat up polyethylene glycol and add ε-caprolactone, then add stannous octoate and triethylamine and react to obtain a polyethylene glycol-polycaprolactone block copolymer; Step S2, disperse imidazole in N,N-dimethylformamide, add anhydrous potassium carbonate and 2-chloroethanol, react to obtain 2-imidazole ethanol, then add methacrylic acid and hydroquinone and react to obtain a monomer. Under a nitrogen atmosphere, add azobisisobutyronitrile and react fully at a second temperature to obtain a methacryloyloxyethylimidazole-functionalized polymer; Step S3, disperse the polyethylene glycol-polycaprolactone block copolymer in tetrahydrofuran, disperse the modified chitosan-polyacrylate copolymer in deionized water, disperse the methacryloyloxyethylimidazole-functionalized polymer in deionized water, dissolve PNIPAM in deionized water, and mix the polyethylene glycol-polycaprolactone block copolymer dispersion, the modified chitosan-polyacrylate copolymer dispersion and the methacryloyloxyethylimidazole-functionalized polymer dispersion to form a mixed solution. Add the modified polyurethane dispersion and the PNIPAM solution to the mixed solution in sequence, and freeze-dry to obtain a porous sound-absorbing material with controllable pore size and orientation structure; Step A2, add chitosan to an acetic acid aqueous solution to adjust the pH to 5.0 to obtain a chitosan solution. Under a nitrogen atmosphere, disperse the mixed monomer B, sodium dodecyl sulfate and azobisisobutyronitrile in deionized water to form a monomer emulsion, and drop the monomer emulsion and the ammonium persulfate solution into the chitosan solution. After the reaction, adjust the pH to 7.0 and filter to obtain a modified chitosan-polyacrylate copolymer; The solid content of the modified polyurethane dispersion is 10-20%; The mass ratio of the polyethylene glycol-polycaprolactone block copolymer, the modified chitosan-polyacrylate copolymer, the methacryloyloxyethylimidazole-functionalized polymer, PNIPAM and the modified polyurethane dispersion is 6:3:2:1.5:14; The mass ratio of chitosan to the mixed monomer B is 1:

3.

2. The preparation method of a porous sound-absorbing material based on a controllable pore size and orientation structure according to claim 1, wherein, The preparation method of the modified polyurethane dispersion is: Step A1, add the mixed monomer A and an initiator to an aqueous polyurethane dispersion, heat up and react, then add tetrabutylammonium bromide and an aqueous solution of epichlorohydrin, and react to obtain a modified polyurethane dispersion.

3. The preparation method of a porous sound-absorbing material based on a controllable pore size and orientation structure according to claim 1, characterized in that, In step S1, The mass ratio of ε-caprolactone to polyethylene glycol is 2:1; The mass of stannous octoate is 0.5-1.0% of the mass of polyethylene glycol; The mass of triethylamine is 2-3% of the mass of polyethylene glycol.

4. The preparation method of a porous sound-absorbing material based on a controllable pore size and orientation structure according to claim 1, characterized in that, In step S2, The mass ratio of imidazole to N,N-dimethylformamide is 1:(7-8); The mass ratio of 2-chloroethanol to imidazole is 1:1; The mass ratio of methacrylic acid to imidazole is (1-1.4):1; The mass of hydroquinone is 0.5-1% of the mass of imidazole.

5. The preparation method of a porous sound-absorbing material based on a controllable pore size and orientation structure according to claim 2, characterized in that, In step A1, The mass ratio of the mixed monomer A to the aqueous polyurethane dispersion is 1:(3-4); The components of the mixed monomer A are methyl acrylate, butyl acrylate and acrylic acid, and the mass ratio is 3:2:1; The mass of the tetrabutylammonium bromide is 0.2 - 0.3% of the mass of the aqueous polyurethane dispersion; The mass of the epichlorohydrin aqueous solution is 18 - 20% of the mass of the aqueous polyurethane dispersion.

6. The preparation method of a porous sound-absorbing material based on a controllable pore size and orientation structure according to claim 1, wherein, In step A2, The components of the mixed monomer B are acrylic acid, butyl acrylate and methyl methacrylate, and the mass ratio is 4:5:3; The mass of the sodium dodecyl sulfate is 5 - 6% of the mass of the chitosan; The mass of the ammonium persulfate solution is 50 - 60% of the mass of the chitosan.

7. A porous sound-absorbing material based on a controllable pore size and orientation structure obtained by the preparation method according to any one of claims 1 - 6.

8. Use of a porous sound-absorbing material based on a controllable pore size and orientation structure obtained by the preparation method according to any one of claims 1 - 6 in the preparation of audio equipment and industrial noise reduction equipment.

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