Polyurethane with coupled sound absorption layer and buffer layer and application of polyurethane in noise reduction earmuffs

Abstract

The invention discloses polyurethane with a sound absorption layer coupled with a buffer layer and application of the polyurethane in noise reduction earmuffs, and belongs to the technical field of polyurethane. The sound absorption layer comprises an isocyanate prepolymer, polysilsesquioxane / polyacrylate hybrid core-shell structure polyol emulsion, a chain extender, a silicone oil foam stabilizer, a delayed catalyst, an organic tin catalyst and a foaming agent; the buffer layer is prepared from an isocyanate prepolymer, a magnolol-(3-mercapto-1, 2-propylene glycol) adduct, a chain extender, hydroxyl-terminated polydimethylsiloxane, methoxypolyethylene glycol, a cross-linking agent, a silicone oil foam stabilizer, a catalyst and a foaming agent. According to the invention, polysilsesquioxane / polyacrylate hybrid core-shell structure polyol and magnolol-(3-sulfydryl-1, 2-propylene glycol) adduct are added into different layers of polyurethane, and interface coupling is carried out in combination with an NCO index, so that triple functions of sound absorption, buffering and antibiosis of the double-layer coupled polyurethane are realized.

Description

Technical Field

[0001] This invention relates to the field of polyurethane technology, specifically to a polyurethane with a sound-absorbing layer and a buffer layer coupled together, and its application in noise-canceling earmuffs. Background Technology

[0002] With rapid industrialization and urbanization, noise pollution has become a significant environmental problem affecting human health. Long-term exposure to high-intensity noise can lead to serious consequences such as hearing loss, sleep disorders, cardiovascular disease, and decreased work efficiency. Statistics show that approximately 430 million people worldwide suffer hearing loss due to noise exposure, and occupational noise-induced hearing loss has become one of the most common occupational diseases in my country. Noise-canceling earmuffs, as an important component of personal hearing protection equipment, are widely used in high-risk noise environments such as industrial production, military training, aviation ground support, and rail transportation. In recent years, with the development of the consumer electronics market, both active and passive noise-canceling headphones have placed higher demands on acoustic materials, requiring not only excellent sound insulation performance but also wearing comfort, antibacterial hygiene, and long-term durability.

[0003] Polyurethane is a porous polymer with multiple -NHCOO- structural units embedded in its molecular backbone. It is typically synthesized through a series of chemical reactions between binary or polyisocyanates and polyols. It boasts advantages such as high design flexibility, convenient molding and construction, high porosity, lightweight, high specific strength, and excellent energy absorption capacity, making its applications extremely wide-ranging. Traditional noise-canceling earmuffs mostly use a single-formulation polyurethane soft foam as the sound-absorbing material. While it has a certain sound absorption coefficient, it suffers from the following significant drawbacks: narrow sound absorption bandwidth, poor absorption of mid-to-low frequency noise (<1000 Hz); simple pore structure, lack of impedance gradient design, resulting in severe sound wave reflection on the material surface; unadjustable mechanical properties, failing to simultaneously meet the dual requirements of acoustic performance and wearing comfort; and significant permanent compression deformation after long-term use, leading to a significant decrease in sound insulation performance. Some high-end products employ a physical stacking method using multiple layers of foam with varying densities, bonded together with adhesives or physically pressed. This results in clear interlayer interfaces and significant abrupt changes in acoustic impedance, causing sound waves to reflect at these interfaces and reducing overall sound absorption efficiency. Furthermore, the adhesive layer itself becomes an acoustic weakness, prone to aging and failure, with a high risk of delamination after long-term use. Other research has attempted to fill polyurethane matrices with inorganic nanoparticles (such as silica, calcium carbonate, and activated carbon) to improve sound absorption. However, physically mixed or filled inorganic particles exhibit poor compatibility with the organic matrix, leading to agglomeration, uneven dispersion, weak interfacial bonding, low stress transfer efficiency, and increased material brittleness. Moreover, the lack of precise control over particle spatial distribution makes it difficult to form an effective sound scattering network. Additionally, the long-term contact of polyurethane foam with the ear and face can easily breed bacteria and fungi, and repeated compression and rebound can cause fatigue damage, issues that remain to be addressed. Summary of the Invention

[0004] To address the shortcomings of existing technologies, this application provides a polyurethane with a coupled sound-absorbing layer and a buffer layer, and its application in noise-canceling earmuffs. By adding polysilsesquioxane / polyacrylate hybrid core-shell polyol and magnolol-(3-mercapto-1,2-propanediol) adduct to polyurethane in different layers, and combining the NCO index for interfacial coupling, the triple functions of sound absorption, buffering, and antibacterial properties of the double-layer coupled polyurethane are achieved.

[0005] This invention is achieved through the following technical solution: A polyurethane with a sound-absorbing layer coupled to a buffer layer, wherein the raw materials of the sound-absorbing layer include the following components by weight: 100 parts of isocyanate prepolymer, 10-20 parts of polysilsesquioxane / polyacrylate hybrid core-shell polyol emulsion, 4-8 parts of chain extender, 1.5-2.5 parts of silicone oil foam stabilizer, 0.15-0.2 parts of delayed catalyst, 0.01-0.05 parts of organotin catalyst, and 1-2 parts of foaming agent.

[0006] The raw materials of the buffer layer, calculated by weight, include the following components: 100 parts isocyanate prepolymer, 2-4 parts magnolol-(3-mercapto-1,2-propanediol) adduct, 5-10 parts chain extender, 2-5 parts hydroxyl-terminated polydimethylsiloxane, 0.5-1 parts polyethylene glycol monomethyl ether, 0.5-2 parts crosslinking agent, 1-2 parts silicone oil foam stabilizer, 0.2-1 parts catalyst, and 0.5-2 parts foaming agent.

[0007] In one specific embodiment, the NCO index of the raw material of the sound-absorbing layer is controlled at 1.05~1.15, and the NCO index of the raw material of the buffer layer is controlled at 0.85~0.95.

[0008] In one specific embodiment, the preparation method of the polysilsesquioxane / polyacrylate hybrid core-shell structured polyol emulsion is as follows: S1. Methacryloxypropyltrimethoxysilane and dimethyldimethoxysilane are mixed in a molar ratio of (2-4):1 and subjected to hydrolysis-condensation reaction in the presence of an alkaline catalyst, a surfactant and water to obtain a polysilsesquioxane core emulsion with polymerizable carbon-carbon double bonds enriched on the surface. S2. Acrylate monomer, terminal hydroxyl monomer and initiator are added dropwise at a uniform rate to polysilsesquioxane core emulsion, and emulsion polymerization is carried out at 75-85℃ to obtain polysilsesquioxane / polyacrylate hybrid core-shell polyol emulsion, which is then purified and dehydrated to a solid content of 50-60%.

[0009] In one specific embodiment, the acrylate monomer is composed of butyl acrylate and methyl methacrylate in a mass ratio of (75-85):(15-25); the terminal hydroxyl monomer is composed of polyethylene glycol acrylate and hydroxyethyl methacrylate in a mass ratio of (40-60):(40-60); the initiator is potassium persulfate; the alkaline catalyst is sodium hydroxide or potassium hydroxide; the surfactant includes at least one of ionic surfactants and nonionic surfactants, wherein the ionic surfactant is selected from one or more of sodium dodecyl sulfate and sodium dodecylbenzene sulfonate; and the nonionic surfactant is selected from one or more of octylphenol polyoxyethylene ether and fatty alcohol polyoxyethylene ether.

[0010] In one specific embodiment, the honokiol-(3-mercapto-1,2-propanediol) adduct comprises one or more of Formula 1 or Formula 2: Formula 1; Equation 2.

[0011] In one specific embodiment, the method for preparing the honokiol-(3-mercapto-1,2-propanediol) adduct includes the following steps: Magnolol and 3-mercapto-1,2-propanediol were dissolved in anhydrous ethanol at a molar ratio of 1:(1.0-2.0). A photoinitiator was added, and the reaction was carried out under nitrogen protection at room temperature to 40-50°C and irradiated with 365 nm ultraviolet light for 4-8 hours. After the reaction was completed, the magnolol-(3-mercapto-1,2-propanediol) adduct was obtained by column chromatography.

[0012] It should be noted that during the foaming process of the polyurethane buffer layer, although the aliphatic hydroxyl groups on the honokiol-(3-mercapto-1,2-propanediol) adduct will preferentially react with -NCO, a small amount of phenolic hydroxyl groups may still participate in the reaction. However, this has no significant impact on the antibacterial properties of the polyurethane buffer layer.

[0013] In one specific embodiment, the foaming agent is deionized water.

[0014] In one specific embodiment, the catalyst is an organic amine catalyst and an organotin catalyst, wherein the mass ratio of the organic amine catalyst to the organotin catalyst is 2:1; the chain extender is one or more of ethylene glycol, 1,4-butanediol, and 1,6-hexanediol; the crosslinking agent is at least one of trimethylolpropane, glycerol, triethanolamine, pentaerythritol, and sorbitol; the delayed catalyst is selected from at least one of temperature-activated tertiary amine catalysts, chemically blocked tertiary amine catalysts, or slow-release microcapsule catalysts, preferably any one of Dabco 8154, Dabco BL-17, Jeffcat ZF-20, or Dabco 2040.

[0015] In one specific embodiment, the viscosity of the hydroxyl-terminated polydimethylsiloxane is 55~75 cSt, and the molecular weight of the polyethylene glycol monomethyl ether is 500~2000 g / mol.

[0016] Another object of the present invention is to provide a method for preparing polyurethane that protects the coupling of the sound-absorbing layer and the buffer layer, comprising the following steps: (1) The polysilsesquioxane / polyacrylate hybrid core-shell structured polyol emulsion is premixed and stirred with a chain extender for a period of time, then transferred to a reaction vessel with a distillation receiver, heated to 40~60℃, vacuum dehydration is turned on until the moisture content is <0.1wt%, then mixed with isocyanate prepolymer, silicone oil foam stabilizer, delayed catalyst, organotin catalyst and foaming agent, injected into a mold for foaming, and the reaction temperature is controlled at 50-60℃. The reaction is carried out until a semi-gel state is reached to obtain a sound-absorbing layer semi-finished product; (2) Mix isocyanate prepolymer, hydroxyl-terminated polydimethylsiloxane, honokiol-(3-mercapto-1,2-propanediol) adduct, polyethylene glycol monomethyl ether, chain extender, crosslinking agent, silicone oil foam stabilizer, catalyst and foaming agent to obtain buffer layer mixture; (3) Within a time window of 2 to 5 minutes after the semi-finished sound-absorbing layer reaches a semi-gel state, the buffer layer mixture is poured onto the surface of the sound-absorbing layer, and the residual isocyanate groups on the surface of the sound-absorbing layer react with the active hydrogen compounds of the buffer layer to form chemical bonds. (4) The double-layer structure is cured together at a temperature of 80~90℃ for 20~40 minutes and cooled to room temperature to obtain a polyurethane with a sound-absorbing layer and a buffer layer coupled together.

[0017] Another object of the present invention is to protect the use of the polyurethane coupled with the sound-absorbing layer and the buffer layer in noise-canceling earmuffs or passive noise-canceling headphones.

[0018] Beneficial effects

[0019] This application provides a polyurethane with a sound-absorbing layer and a buffer layer coupled together, and its application in noise-canceling earmuffs. Compared with the prior art, it has the following significant advantages: 1. In the sound-absorbing layer design, the introduction of polysilsesquioxane / polyacrylate hybrid core-shell structured polyols constructs a unique acoustic functional network. These core-shell particles, with a rigid siloxane cross-linked network as the core and a flexible polyacrylate shell, exhibit a gradient mismatch in acoustic impedance with the polyurethane matrix. Incident sound waves undergo multiple scatterings at the particle-matrix interface, significantly extending the sound propagation path. Simultaneously, the particles act as heterogeneous nucleating agents, regulating cell nucleation and growth, forming a multi-level porous structure with micropores, mesopores, and macropores. Micropores enhance the thermal conductivity loss of mid-to-high frequency sound waves, while macropores provide mass-spring resonance dissipation for mid-to-low frequency sound waves, thereby broadening the effective sound absorption frequency band. More importantly, the reactive hydroxyl groups enriched on the surface of the core-shell particles form chemical bonds with the isocyanate, preventing particle migration and aggregation, and ensuring the long-term stability of the acoustic function.

[0020] 2. The performance optimization of the buffer layer stems from the synergy between the reactive molecular design of magnolol derivatives and the soft-segment thermosensitive structure. The magnolol-(3-mercapto-1,2-propanediol) adduct is synthesized via a thiol-ene click reaction. Its aliphatic hydroxyl groups react with isocyanates to achieve molecular anchoring, while most phenolic hydroxyl groups remain in a free state, endowing the material with long-lasting antibacterial activity. The introduction of hydroxyl-terminated polydimethylsiloxane utilizes its surface migration properties to reduce the coefficient of friction, while the hydrophilic hanging chains of polyethylene glycol monomethyl ether construct perspiration channels. These two elements synergistically optimize surface comfort performance.

[0021] 3. The interfacial coupling between the sound-absorbing layer and the buffer layer is based on a dual mechanism of chemical reaction and physical interpenetration. Through the differentiated design of the NCO index of the two layers with precise control, the excess isocyanate groups retained on the surface of the sound-absorbing layer react with the active hydrogen of the polyol in the buffer layer at the interface to form urethane bonds and urea bonds, constructing a covalent bond. At the same time, the prepolymer of the buffer layer is cast in the semi-gel state of the sound-absorbing layer, and the prepolymer that penetrates into the open-pore structure forms a mechanical interlock with the sound-absorbing layer after curing. This chemical-physical synergistic interface design eliminates the clear interface of traditional multilayer structures, avoids reflection loss caused by abrupt changes in acoustic impedance, and ensures the long-term stability of the interlayer bonding. Attached Figure Description

[0022] Figure 1 The synthetic route for magnolol-(3-mercapto-1,2-propanediol) adducts.

[0023] Figure 2 The 1H NMR spectrum is of the magnolol-(3-mercapto-1,2-propanediol) adduct.

[0024] Figure 3 Infrared spectra of polysilsesquioxane core and polysilsesquioxane / polyacrylate hybrid core-shell polyols. Detailed Implementation

[0025] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0026] Unless otherwise specified, the experimental methods used in the embodiments are conventional methods, and the materials and reagents used are commercially available unless otherwise specified.

[0027] The raw materials used in the examples and comparative examples are described below: Isocyanate prepolymer: Lupranate 5230, NCO content 14.1%, viscosity 1450@25℃ (cps), purchased from BASF; Chain extender: 1,4-Butanediol: analytical grade, purchased from Shanghai Adamas Reagent Co., Ltd.; Catalysts: The organotin catalyst was dibutyltin dilaurate, 95%, catalog number D806313, purchased from Shanghai Maclean Biochemical Technology Co., Ltd.; the organic amine catalyst was triethylenediamine, industrial grade, purchased from American Gas Company; the mass ratio of organic amine catalyst to organotin catalyst was 2:1. Delayed catalyst: Dabco 8154, Evonik; Organotin catalyst: Dibutyltin dilaurate, 95%, product number D806313, purchased from Shanghai Maclean Biochemical Technology Co., Ltd. Hydroxyl-terminated polydimethylsiloxane: 65 cst, purchased from Sigma-Aldrich, USA; Polyethylene glycol monomethyl ether: average molecular weight 750 g / mol, Shanghai Maclean Biochemical Technology Co., Ltd. Crosslinking agent: Trimethylolpropane, 98%, commercially available; Silicone oil foam stabilizer: AK8805, 40cst, purchased from Guangdong Yunxing Biotechnology Co., Ltd. Foaming agent: Deionized water; Ionic surfactant: Sodium dodecyl sulfate, analytical grade, commercially available; Nonionic surfactant: Triton X-100, commercially available; Polysilsesquioxane / polyacrylate hybrid core-shell polyol emulsion: self-made, preparation method as follows: S1. Dissolve 0.12 g of sodium hydroxide, 0.8 g of the ionic surfactant sodium dodecyl sulfate, and 0.4 g of the nonionic surfactant Triton X-100 in 120 g of deionized water to prepare aqueous solutions. Transfer the solutions to a four-necked flask equipped with a paddle stirrer, reflux condenser, thermometer, and nitrogen inlet tube. Stir at 250 r / min for 30 min at room temperature under nitrogen protection. Then, use a precision syringe pump to inject the solution at 0.015 cm⁻¹. 3 0.12 mol of methacryloxypropyltrimethoxysilane and 0.04 mol of dimethyldimethoxysilane were simultaneously added dropwise to a flask at a dropping rate of / min. After the addition was complete, the reaction mixture was stirred in two stages: the first stage was carried out at room temperature for 24 hours; the second stage was heated to 50°C and stirred for another 24 hours. After the reaction was completed, the temperature was lowered to 35°C, and 0.1 mol / L dilute hydrochloric acid was added dropwise while stirring to adjust the pH to 7. Then the temperature was set to 45°C, and the vacuum distillation was carried out at -0.095 MPa for 3 hours. The resulting emulsion was passed through a dialysis bag with a molecular weight cutoff of 10 kDa and replaced with deionized water four times to obtain a polysilsesquioxane core emulsion with polymerizable carbon-carbon double bonds on the surface, with a solid content of 20%.

[0028] S2. Add 50g of polysilsesquioxane core emulsion and 180g of deionized water to a four-necked flask equipped with a paddle stirrer, a reflux condenser, a thermometer, and a nitrogen inlet tube. Stir at 250r / min for 30min under a nitrogen atmosphere to uniformly disperse the polysilsesquioxane core emulsion. Heat the system to 80℃, and then add the following simultaneously at a dropping rate of 0.083cm³ / min: (1) 20ml of potassium persulfate aqueous solution, wherein the concentration of potassium persulfate is 0.1wt%; (2) 16g of acrylic monomer mixture, wherein the acrylic monomer mixture consists of 80wt% butyl acrylate and 20wt% methyl methacrylate; (3) 4g of terminal hydroxyl monomer mixture, wherein the terminal hydroxyl monomer mixture consists of 80wt% butyl acrylate and 20wt% methyl methacrylate. The mixture consisted of 50 wt% polyethylene glycol acrylate (molecular weight 280 g / mol) and 50 wt% hydroxyethyl methacrylate. After the addition was complete, the mixture was reacted at 80 °C for 4.5 hours, cooled to room temperature, and discharged to obtain a polysilsesquioxane / polyacrylate hybrid core-shell polyol emulsion. The core-shell emulsion was then subjected to vacuum distillation at 45 °C and a vacuum of -0.095 MPa for 4 hours to remove volatile monomers butyl acrylate, methyl methacrylate, and dimethyl dimethoxysilane. The resulting emulsion was then passed through a dialysis bag with a molecular weight cutoff of 50 kDa and replaced four times with deionized water to remove water-soluble residues such as potassium persulfate and hydrolysate of methacryloyloxypropyltrimethoxysilane. The resulting emulsion was then dehydrated under reduced pressure to a solid content of 55% to obtain a purified core-shell nano-polyol emulsion. The hydroxyl content was determined to be 185 mg KOH / g by chemical titration, and the weight-average molecular weight was determined to be 125,000 g / mol by GPC.

[0029] Polysilsesquioxane / polyacrylate hybrid core-shell emulsion: Compared with the preparation method of polysilsesquioxane / polyacrylate hybrid core-shell polyol emulsion, the difference is that in step S2, (3) 4g of terminal hydroxyl monomer mixture is not added dropwise.

[0030] Polysilsesquioxane / polyacrylate core-shell structured polyol emulsion: Compared with the preparation method of polysilsesquioxane / polyacrylate hybrid core-shell structured polyol emulsion, the difference is that 0.12 mol of methacryloyloxypropyltrimethoxysilane and 0.04 mol of dimethyldimethoxysilane are replaced with 0.16 mol of methacryloyloxypropyltrimethoxysilane.

[0031] Honokiol-(3-mercapto-1,2-propanediol) adduct: prepared in-house, as follows: Honokiol and 3-mercapto-1,2-propanediol were dissolved in anhydrous ethanol at a molar ratio of 1:1.2 to prepare a 1.0 mol / L solution. Irgacure 2959 photoinitiator was added at 1.5% of the molar amount of honokiol, and the mixture was bubbled under nitrogen for 30 minutes to remove oxygen. The reaction was carried out at room temperature under 365 nm UV irradiation for 8 hours, and the reaction progress was monitored by TLC. The solvent was removed by rotary evaporation, and the product was purified by silica gel column chromatography (elution with a gradient of petroleum ether / ethyl acetate = 1:1 to 1:2). The honokiol-(3-mercapto-1,2-propanediol) adduct fraction was collected and dried under vacuum to obtain a pale yellow viscous liquid product with a yield of 75%.

[0032] Unless otherwise specified, all components and raw materials used in the embodiments and comparative examples of this invention are commercially available, and the same type of components and raw materials are used in each parallel experiment.

[0033] Examples and Comparative Examples A polyurethane with a coupled sound-absorbing layer and a buffer layer is prepared by the following method, and the specific raw materials and formulations are shown in Table 1: (1) The polysilsesquioxane / polyacrylate hybrid core-shell structured polyol emulsion is premixed and stirred with a chain extender for a period of time, then transferred to a reaction vessel with a distillation receiver, heated to 40~60℃, vacuum dehydration is turned on until the moisture content is <0.1wt%, then mixed with isocyanate prepolymer, silicone oil foam stabilizer, delayed catalyst, organotin catalyst and foaming agent, injected into a mold for foaming, and the reaction temperature is controlled at 50-60℃. The reaction is carried out until a semi-gel state is reached to obtain a sound-absorbing layer semi-finished product; (2) The isocyanate prepolymer, hydroxyl-terminated polydimethylsiloxane, magnolol-(3-mercapto-1,2-propanediol) adduct, polyethylene glycol monomethyl ether, chain extender, crosslinking agent, silicone oil foam stabilizer, catalyst and foaming agent are mixed in sequence to obtain the buffer layer mixture; (3) Within a time window of 2 to 5 minutes after the semi-finished sound-absorbing layer reaches a semi-gel state, the buffer layer mixture is poured onto the surface of the sound-absorbing layer, and the residual isocyanate groups on the surface of the sound-absorbing layer react with the active hydrogen compounds of the buffer layer to form chemical bonds. (4) The double-layer structure is cured together at a temperature of 80~90℃ for 20~40 minutes and cooled to room temperature to obtain a polyurethane with a sound-absorbing layer and a buffer layer coupled together.

[0034] Table 1. Raw materials and their weight parts of polyurethane used in the coupling of sound-absorbing and buffering layers.

[0035] It should be noted that the NCO index of the raw materials for the sound-absorbing layer in Table 1 is controlled at around 1.1, and the NCO index of the raw materials for the buffer layer is controlled at around 0.9.

[0036] The polyurethanes prepared in the examples and comparative examples were subjected to the following performance tests, and the results are shown in the attached figures and Table 2, respectively.

[0037] 1. 1H NMR spectroscopy: The magnolol-(3-mercapto-1,2-propanediol) adduct was dissolved in deuterated chloroform to prepare a 1.0 wt% solution. The NMR spectrum of the sample was measured using a 1H NMR spectrometer at 400 MHz. The results are as follows: Figure 2 As shown.

[0038] 2. Infrared Spectroscopy: Polysilsesquioxane cores and polysilsesquioxane / polyacrylate hybrid core-shell polyols were vacuum-dried and then mixed with potassium bromide at a ratio of 1:50 to prepare tablets. An Avatar 380 spectrometer was used for this test. Before testing, a blank background scan was performed, followed by the placement of the tableted samples for analysis. The scanning range was 500-4000 cm⁻¹. -1 The result is as follows Figure 3 As shown.

[0039] 3. Aperture ratio determination: Based on scanning electron microscope images, the aperture ratio is calculated using statistical methods, with no less than 15 representative regions for each sample.

[0040] 4. Interface coupling strength: The peel strength between the two layers is determined by a 180° peel test or an overlap shear test.

[0041] 5. Sound Absorption Coefficient Measurement: The sound absorption coefficient at perpendicular incidence was determined using the impedance tube method (dual-microphone transfer function method), with the testing standard referring to ISO 10534-2. Specifically, a cylindrical sample (100 mm diameter for low-frequency testing, 30 mm diameter for high-frequency testing, and 20-50 mm thickness) was placed on an impedance tube sample holder. Two 1 / 4-inch microphones were used to measure the sound pressure within the frequency range of 800-6300 Hz, and the sound absorption coefficient was calculated using the transfer function. Each sample was measured at least three times, and the average value was taken.

[0042] 6. Compressive stress: Tested using a universal testing machine (UTM) according to ASTM D3574-17. A sample with dimensions of 50mm × 50mm × 25mm was uniaxially compressed at a compression rate of 50mm / min, and the stress-strain curve was recorded. The compressive stress at 50% compressive strain was determined.

[0043] 7. Compression set: Refer to standard ISO 1856:2018. Test the original height by installing the sample in the fixture and compressing it to 50%. The test conditions are a temperature of 70 ℃. After holding the sample for 22 hours, remove the sample and loosen the fixture. Let it stand at room temperature for one hour and then measure and record the measurement data.

[0044] 8. Damping characteristics: The loss factor (tan δ) was measured in compression mode using a dynamic mechanical analyzer. Test conditions: frequency 1 Hz, amplitude 40 μm, temperature range -80℃ to 20℃, heating rate 5℃ / min, to evaluate the damping characteristics of the material.

[0045] 9. Antibacterial performance: Cut off a piece of polyurethane buffer layer and place it in a dry petri dish. Expose it to a dark and humid environment for one month and observe whether bacterial spots or mold grow on the sample surface to test the antibacterial performance.

[0046] Table 2 Performance test results of polyurethane

[0047] from Figure 2 It can be seen that the honokiol-(3-mercapto-1,2-propanediol) adduct is mainly the honokiol-(3-mercapto-1,2-propanediol) monoadduct (i.e., the structure of formula 1), while also containing a small amount of honokiol-(3-mercapto-1,2-propanediol) diadduct (i.e., the structure of formula 2).

[0048] from Figure 3 It can be seen that in the FTIR spectrum of polysilsesquioxane, the peaks appear at 1640 and 1720 cm⁻¹. -1 The peaks at 1260 cm⁻¹ correspond to stretching vibrations at C=C and C=O, respectively. -1 The characteristic peak of Si-CH3 symmetric deformation appears at 1080 cm⁻¹. -3 A shoulder peak of the Si-O-Si stretching vibration of dimethyldimethoxysilane appears at 1034 cm⁻¹. -1 The methacryloyloxypropyltrimethoxysilane exhibits a bimodal structure with a Si-O-Si peak at 2960 cm⁻¹. -1 and 2870 cm -1 The enhanced CH3 stretching vibration peak indicates the successful synthesis of the polysilsesquioxane core. In the FTIR spectra of polysilsesquioxane / polyacrylate hybrid core-shell polyols, the vinyl C=C peak disappears, and the peak value is observed in the range of 3100 to 2800 cm⁻¹. -1 The broad absorption bands observed within the range are attributed to the stretching vibrations of the CH bonds contained in the CH2 and CH3 groups of the acrylate monomers, at 1455 cm⁻¹. -1 Symmetric stretching of the COC group attributable to polyethylene glycol acrylate was detected, indicating the successful synthesis of polysilsesquioxane / polyacrylate hybrid core-shell polyol.

[0049] As shown in Table 2, Example 2 exhibits the best overall performance. This is because the core-shell particles, acting as heterogeneous nucleating agents, form a three-tiered pore structure of "micropore-mesopore-macropore" at a dosage of 15 parts. The micropores originate from the interior of the core-shell, the mesopores from inter-particle stacking, and the macropores from foaming. At this point, the acoustic impedance gradient is most abundant, and the sound absorption coefficient reaches 0.85. In Example 3, excessive particles lead to local agglomeration, which reduces the open porosity to 65% and slightly decreases the sound absorption coefficient to 0.82. In Comparative Example 1, the absence of terminal hydroxyl monomers in step S2 results in a lack of reactive hydroxyl groups on the core-shell surface, leading to poor compatibility with the polyurethane matrix. Particle agglomeration forms "defect sites," causing pore wall rupture, an abnormally high open porosity, but a reduction in effective sound absorption structures (closed / semi-closed pores), and a significant decrease in sound scattering efficiency due to interfacial debonding. In Comparative Example 2, no D-type dimethyldimethoxysilane was added to the polysilsesquioxane core. Due to excessive cross-linking, the pure polysilsesquioxane core was rigid, had a high nucleation density, small pores but many closed pores, and few airflow channels, resulting in insufficient mid-to-high frequency sound absorption.

[0050] Meanwhile, in the embodiments, the active hydrogen (hydroxyl groups of magnolol adduct and silicone oil hydroxyl groups) of the sound-absorbing layer and the buffer layer form urea / urethane covalent bonds at the interface. Simultaneously, the buffer layer, cast in a semi-gel state, forms a mechanical interlock, thereby improving the interfacial coupling strength. Regarding resilience, in Example 3, 20 parts of core-shell emulsion provide a reinforcing effect with a rigid siloxane core, while 4 parts of magnolol introduce a rigid biphenyl structure, synergistically enhancing load-bearing capacity. Compared to Comparative Example 3, which lacks magnolol adduct, the buffer layer lacks rigid aromatic ring support, and the crosslinking density is reduced due to the presence of monofunctional PEG, resulting in a soft and weak polyurethane foam material. Comparative Example 4, without hydroxyl-terminated polydimethylsiloxane, has an overly rigid buffer layer, losing effective buffering against impact energy, while the compression set increases to 7.5%, reducing resilience. Comparative Example 5, without polyethylene glycol monomethyl ether, allows moisture to easily accumulate at the interface, leading to stuffiness and the risk of bacterial growth. In the embodiments of this application, the core-shell structure (soft shell-hard core) of polyurethane and magnolol (rigid ring-flexible thioether bond) form a multiple energy dissipation mechanism, with a tanδ peak value of 0.42; thereby improving the sound absorption performance, and magnolol also brings antibacterial effect, meeting the needs of long-term use.

[0051] The preferred embodiments of the present invention disclosed above are merely illustrative of the invention. These preferred embodiments do not exhaustively describe all details, nor do they limit the invention to the specific implementations described. Clearly, many modifications and variations can be made based on the content of this specification. This specification selects and specifically describes these embodiments to better explain the principles and practical applications of the invention, thereby enabling those skilled in the art to better understand and utilize the invention. The invention is limited only by the claims and their full scope and equivalents.

Claims

1. A polyurethane system in which a sound-absorbing layer and a buffer layer are coupled, characterized in that, The raw materials of the sound-absorbing layer, calculated by weight, include the following components: 100 parts isocyanate prepolymer, 10-20 parts polysilsesquioxane / polyacrylate hybrid core-shell polyol emulsion, 4-8 parts chain extender, 1-2 parts silicone oil foam stabilizer, 0.15-0.2 parts delayed catalyst, 0.01-0.05 parts organotin catalyst, and 1-2 parts foaming agent; The raw materials of the buffer layer, calculated by weight, include the following components: 100 parts isocyanate prepolymer, 2-4 parts magnolol-(3-mercapto-1,2-propanediol) adduct, 5-10 parts chain extender, 2-5 parts hydroxyl-terminated polydimethylsiloxane, 0.5-1 parts polyethylene glycol monomethyl ether, 0.5-2 parts crosslinking agent, 1-2 parts silicone oil foam stabilizer, 0.2-1 parts catalyst, and 0.5-2 parts foaming agent.

2. The polyurethane with a coupled sound-absorbing layer and a buffer layer as described in claim 1, characterized in that, The NCO index of the raw material of the sound-absorbing layer is controlled at 1.05~1.15, and the NCO index of the raw material of the buffer layer is controlled at 0.85~0.

95.

3. The polyurethane with a coupled sound-absorbing layer and a buffer layer as described in claim 1, characterized in that, The preparation method of polysilsesquioxane / polyacrylate hybrid core-shell structured polyol emulsion is as follows: S1. Methacryloxypropyltrimethoxysilane and dimethyldimethoxysilane are mixed in a molar ratio of (2-4):1 and subjected to hydrolysis-condensation reaction in the presence of an alkaline catalyst, a surfactant and water to obtain a polysilsesquioxane core emulsion with polymerizable carbon-carbon double bonds enriched on the surface. S2. Acrylate monomer, terminal hydroxyl monomer and initiator are added dropwise at a uniform rate to polysilsesquioxane core emulsion, and emulsion polymerization is carried out at 75-85℃ to obtain polysilsesquioxane / polyacrylate hybrid core-shell polyol emulsion, which is then purified and dehydrated to a solid content of 50-60%.

4. The polyurethane with a coupled sound-absorbing layer and a buffer layer as described in claim 3, characterized in that, The acrylate monomer is composed of butyl acrylate and methyl methacrylate in a mass ratio of (75-85):(15-25); the terminal hydroxyl monomer is composed of polyethylene glycol acrylate and hydroxyethyl methacrylate in a mass ratio of (40-60):(40-60); the initiator is potassium persulfate; the alkaline catalyst is sodium hydroxide or potassium hydroxide; the surfactant includes at least one of ionic surfactant and nonionic surfactant, wherein the ionic surfactant is selected from one or more of sodium dodecyl sulfate and sodium dodecylbenzene sulfonate; and the nonionic surfactant is selected from one or more of octylphenol polyoxyethylene ether and fatty alcohol polyoxyethylene ether.

5. The polyurethane with a coupled sound-absorbing layer and a buffer layer as described in claim 1, characterized in that, The magnolol-(3-mercapto-1,2-propanediol) adduct comprises one or more of Formula 1 or Formula 2: Formula 1; Formula 2.

6. The polyurethane with a coupled sound-absorbing layer and a buffer layer as described in claim 1, characterized in that, The foaming agent is deionized water.

7. The polyurethane with a coupled sound-absorbing layer and a buffer layer as described in claim 1, characterized in that, The catalyst is an organic amine catalyst and an organotin catalyst, wherein the mass ratio of the organic amine catalyst to the organotin catalyst is 2:1; the chain extender is one or more of ethylene glycol, 1,4-butanediol, and 1,6-hexanediol; the crosslinking agent is at least one of trimethylolpropane, glycerol, triethanolamine, pentaerythritol, and sorbitol; the delayed catalyst is selected from at least one of temperature-activated tertiary amine catalysts, chemically blocked tertiary amine catalysts, or slow-release microcapsule catalysts.

8. The polyurethane with a coupled sound-absorbing layer and a buffer layer as described in claim 1, characterized in that, The viscosity of the hydroxyl-terminated polydimethylsiloxane is 55~75 cSt, and the molecular weight of the polyethylene glycol monomethyl ether is 500~2000 g / mol.

9. A method for preparing polyurethane with a coupled sound-absorbing layer and a buffer layer as described in any one of claims 1 to 8, characterized in that, Includes the following steps: (1) The polysilsesquioxane / polyacrylate hybrid core-shell structured polyol emulsion is premixed and stirred with a chain extender for a period of time, then transferred to a reaction vessel with a distillation receiver, heated to 40~60℃, vacuum dehydration is turned on until the moisture content is <0.1wt%, then mixed with isocyanate prepolymer, silicone oil foam stabilizer, delayed catalyst, organotin catalyst and foaming agent, injected into a mold for foaming, and the reaction temperature is controlled at 50-60℃. The reaction is carried out until a semi-gel state is reached to obtain a sound-absorbing layer semi-finished product; (2) Mix isocyanate prepolymer, hydroxyl-terminated polydimethylsiloxane, honokiol-(3-mercapto-1,2-propanediol) adduct, polyethylene glycol monomethyl ether, chain extender, crosslinking agent, silicone oil foam stabilizer, catalyst and foaming agent to obtain buffer layer mixture; (3) Within a time window of 2 to 5 minutes after the semi-finished sound-absorbing layer reaches a semi-gel state, the buffer layer mixture is poured onto the surface of the sound-absorbing layer, and the residual isocyanate groups on the surface of the sound-absorbing layer react with the active hydrogen compounds of the buffer layer to form chemical bonds. (4) The double-layer structure is cured together at a temperature of 80~90℃ for 20~40 minutes and cooled to room temperature to obtain a polyurethane with a sound-absorbing layer and a buffer layer coupled together.

10. The application of polyurethane with a sound-absorbing layer coupled to a buffer layer as described in any one of claims 1 to 8 in noise-canceling earmuffs or passive noise-canceling headphones.

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