Sound-absorbing and sound-insulating integrated composite material and preparation method thereof

Abstract

This invention relates to the field of composite material technology, and more particularly to an integrated sound absorption and insulation composite material and its preparation method. The invention provides an integrated sound absorption and insulation composite material, comprising plant fibers and thermoplastic resin, wherein the thermoplastic resin fills the network voids formed by the plant fibers; structurally, it is divided into a porous layer and a dense layer along the thickness direction; the porous layer consists of at least two layers; the porous layer has a gradient pore structure with pore diameters of 0.8-3 mm; the pore diameter of each porous layer decreases progressively towards the dense layer; the porosity of the integrated sound absorption and insulation composite material is 1-40%. The composite material provided by this invention integrates sound absorption and sound insulation functions, enabling controllable design of the sound absorption frequency band, while also possessing high mechanical strength and being environmentally friendly.

Description

Technical Field

[0001] This invention relates to the field of composite material technology, and in particular to a composite material with integrated sound absorption and insulation functions and its preparation method. Background Technology

[0002] Sound-absorbing and sound-insulating materials are the cornerstone of protecting personal health and privacy, safeguarding people's hearing, sleep, and mental well-being by resisting noise pollution. Simultaneously, they are a vital link in maintaining the efficient operation and harmonious order of society, creating an indispensable quiet environment for work, study, residence, and safety. Traditional sound-absorbing and sound-insulating materials have limited functions, possessing only sound absorption or sound insulation capabilities. Furthermore, traditional sound-absorbing materials rely on open, porous structures such as glass wool to convert mid-to-high frequency sound energy into heat energy, while sound-insulating materials rely on high-density, dense structures such as gypsum board to reflect sound energy through the mass law to form a sound barrier. Both achieve acoustic control through their inherent material and structural characteristics, but both generally suffer from inherent limitations such as fixed sound absorption frequency bands, poor environmental friendliness, and low mechanical strength. Summary of the Invention

[0003] In view of this, the purpose of this invention is to provide a composite material with integrated sound absorption and sound insulation functions and its preparation method. The composite material provided by this invention integrates sound absorption and sound insulation functions, enables controllable design of the sound absorption frequency band, and has high mechanical strength, is healthy and environmentally friendly.

[0004] To achieve the above-mentioned objectives, the present invention provides the following technical solution: This invention provides an integrated sound-absorbing and sound-insulating composite material. In terms of composition, it includes plant fibers and thermoplastic resin, with the thermoplastic resin filling the network voids formed by the plant fibers. Structurally, it is divided into a porous layer and a dense layer along the thickness direction. The porous layer consists of at least two layers. The porous layer has a gradient pore structure with pore diameters of 0.8-3 mm. The pore diameter of each porous layer decreases progressively towards the dense layer. The porosity of the integrated sound-absorbing and sound-insulating composite material is 1-40%.

[0005] Preferably, holes with a diameter ≥ 1.5 mm are considered large holes, and holes with a diameter < 1.5 mm are considered small holes; the gradient holes are divided into large holes and small holes. The ratio of large holes to small holes is as follows: the perforation rate of the large hole area is 0.5-3%, accounting for 60-85% of the total hole area; the perforation rate of the small hole area is 2-6%, accounting for 15-40% of the total hole area. Alternatively, the ratio of large holes to small holes may be as follows: the perforation rate of the large hole area is 8-15%, accounting for 60-80% of the total hole area; the perforation rate of the small hole area is 5-10%, accounting for 20-40% of the total hole area.

[0006] Preferably, the plant fiber content in the integrated sound absorption and insulation composite material is 5-90% by mass.

[0007] Preferably, the plant fiber includes unmodified plant fiber and / or modified plant fiber; the types of plant fiber include one or more of bamboo fiber, hemp fiber, rice husk fiber, coconut shell fiber and reed fiber.

[0008] Preferably, the thermoplastic resin includes one or more of PP, PET, PE, PLA, PBAT, PBS, and PA.

[0009] Preferably, it also includes additives; the additives include one or more of the following: crosslinking agents, antioxidants, mildew inhibitors, plasticizers, stabilizers, fillers, flame retardants, colorants, abrasion resistant agents, and UV resistant additives.

[0010] This invention provides a method for preparing the integrated sound-absorbing and sound-insulating composite material described above, comprising the following steps: A thermoplastic resin film is laid on both sides of the felt material, and then it is hot-pressed. During the hot-pressing process, the pressure of the upper platen is greater than that of the lower platen, and the pressure difference ΔP between the two is 5-50% of the average pressure. During the hot-pressing process, the thermoplastic resin melts and impregnates the felt material. After cooling, a dense layer is formed on the side near the upper platen, and a porous layer is formed on the side away from the upper platen, forming a gradient pore structure, thus obtaining the integrated sound absorption and insulation composite material. The felt material includes at least two layers, and each layer is directly stacked and in contact with the others. The felt material is either plant fiber felt or plant-thermoplastic resin composite fiber felt.

[0011] This invention provides a method for preparing the integrated sound-absorbing and sound-insulating composite material described above, comprising the following steps: Plant fibers, thermoplastic resins, and pore-forming agents are mixed to obtain multiple preforms; the pore-forming agent particles in each preform have different sizes; the pore-forming agent includes sodium chloride. Plant fibers and thermoplastic resins are mixed to obtain a dense layer preform; First, the dense layer preform is laid in the mold. Then, each group of preforms is laid on the dense layer preform in order of increasing pore size. Hot pressing is performed to melt and mold the resin. After demolding, the preform is removed and the pore-forming agent is removed to obtain the sound-absorbing and sound-insulating integrated composite material.

[0012] Preferably, when the integrated sound-absorbing and sound-insulating composite material includes additives, at least one set of preforms also includes additives.

[0013] This invention provides a method for preparing the integrated sound-absorbing and sound-insulating composite material described above, comprising the following steps: Plant fibers and thermoplastic resins are melt-blended and then granulated to obtain granular material; The granular material is foamed with carbon dioxide to obtain foamed beads; the saturation temperature of the foaming is 110-190℃, the saturation pressure is 5-20MPa, and the saturation time is 0.5-3 hours. The foamed beads are graded to obtain foamed beads of different sizes; The foamed beads of different sizes are laid in layers along the thickness direction, with smaller beads laid on the side closer to the dense layer to be formed and larger beads laid away from the side, and then molded to obtain the integrated sound absorption and insulation composite material. Steam is introduced during the molding process, with a temperature of 110-190℃ and a pressure of 0.1-0.5MPa; the heat and pressure holding time is 30-500 seconds.

[0014] This invention provides an integrated sound absorption and insulation composite material. In terms of composition, it includes plant fibers and thermoplastic resin, with the thermoplastic resin filling the network voids formed by the plant fibers. Structurally, it is divided into a porous layer and a dense layer along the thickness direction. The porous layer consists of at least two layers and has a gradient pore structure with pore sizes of 0.8-3 mm. The pore size of each porous layer decreases progressively towards the dense layer. The porosity of the integrated sound absorption and insulation composite material is 1-40%. The composite material provided by this invention includes a porous layer and a dense layer, where the porous layer provides sound absorption and the dense layer provides sound insulation. The gradient pore size in the porous layer allows for the absorption of sound across multiple frequency bands, achieving superior sound absorption and insulation efficiency, especially at the same thickness. Furthermore, by controlling the proportion of pores with different sizes, specific sound absorption frequency bands can be controlled. This invention improves the mechanical strength of the composite material by combining resin and plant fibers. Simultaneously, the numerous interfaces formed between the plant fibers and resin effectively enhance sound wave scattering and frictional dissipation. Therefore, the composite material provided by this invention can integrate sound absorption and sound insulation functions, realize controllable design of sound absorption frequency band, and has high mechanical strength. It can be used to manufacture transportation vehicles, building interior walls, speaker housings and other fields with high requirements for sound absorption and sound insulation performance and mechanical strength.

[0015] Furthermore, compared with the prior art, the present invention has the following advantages: Traditional sound-absorbing and insulating materials suffer from environmental problems throughout their entire life cycle, including non-renewable raw materials, high energy consumption during production, and difficulty in recycling and degrading after disposal. This invention uses renewable plant resources as raw materials, which have significant carbon emission reduction benefits throughout their entire life cycle due to their low energy consumption characteristics. Furthermore, they are biodegradable after disposal, achieving environmental friendliness throughout the entire process from raw materials to the end product.

[0016] Traditional sound-absorbing and insulating materials often produce fiber dust during production and use, which can irritate the human body and pose health and safety hazards. This invention effectively eliminates dust emission by completely encapsulating the fibers with a resin matrix, significantly improving health and safety during use.

[0017] Traditional sound-absorbing and insulating materials suffer from significant deficiencies in low-frequency sound absorption performance, and their absorption frequency bands are fixed, making it difficult to optimize and adjust them for specific noise levels. This invention, by controlling the composite microstructure of plant fibers and resin, enables the controllable design of the material's sound absorption frequency band, thereby optimizing its acoustic performance for specific noise environments.

[0018] Traditional sound-absorbing and insulating materials suffer from moisture-proof defects such as absorbing moisture and becoming moldy, as well as structural instability and poor processing adaptability due to insufficient mechanical strength. The material of this invention, with the coating effect of the resin matrix on the fibers, has excellent moisture resistance, high mechanical strength, and good processing adaptability, and can be directly molded into integrated acoustic components with complex structures. Attached Figure Description

[0019] Figure 1 A schematic diagram of one type of composite material that integrates sound absorption and insulation functions; Figure 2 This is a schematic diagram of another structure of a composite material that integrates sound absorption and insulation functions. Detailed Implementation

[0020] This invention provides an integrated sound-absorbing and sound-insulating composite material. In terms of composition, it includes plant fibers and thermoplastic resin, with the thermoplastic resin filling the network voids formed by the plant fibers. Structurally, it is divided into a porous layer and a dense layer along the thickness direction. The porous layer has a gradient pore structure with pore diameters of 0.8-3 mm. The pore diameter of each porous layer decreases progressively towards the dense layer. The porosity of the integrated sound-absorbing and sound-insulating composite material is 1-40%.

[0021] The composition of the integrated sound absorption and insulation composite material will be explained below.

[0022] In terms of composition, the integrated sound-absorbing and sound-insulating composite material includes plant fibers and thermoplastic resin.

[0023] In this invention, the plant fiber preferably includes unmodified plant fiber and / or modified plant fiber; the type of plant fiber preferably includes one or more of bamboo fiber, hemp fiber, rice husk fiber, coconut shell fiber, and reed fiber. In this invention, the modified plant fiber is preferably a silane coupling agent modified plant fiber, specifically KH550 modified plant fiber in the embodiments of this invention.

[0024] In this invention, the method for preparing the silane coupling agent modified plant fiber preferably includes the following steps: Plant fibers and silane coupling agents are mixed, and the resulting mixture is then allowed to stand, washed, and dried in sequence to obtain silane coupling agent modified plant fibers.

[0025] In this invention, the mass of the silane coupling agent is preferably 1-3% of the mass of the plant fiber. In this invention, the settling time is preferably 6 hours. This invention utilizes the silane coupling agent to modify the plant fiber, aiming to improve the interfacial bonding ability between the plant fiber and the resin matrix.

[0026] In this invention, the length of the plant fiber is preferably 2-250 mm, and the diameter is preferably 0.01-1.20 mm. In specific embodiments, the length of the plant fiber can be 2, 10, 15, 30, 50, 80, 100, 120, 150, 170, 200, 220, or 250 mm; and the diameter of the plant fiber can be 0.01, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1.0, 1.0, or 1.2 mm.

[0027] In this invention, the thermoplastic resin preferably includes one or more of PP, PET, PE, PLA, PBAT, PBS, and PA. In this invention, the thermoplastic resin can serve as a binder, reducing the use of chemical binders and environmental pollution, while also improving the mechanical strength of the composite material.

[0028] In this invention, the mass of the plant fiber is preferably 5-90% of the total mass of the plant fiber and the thermoplastic resin. In specific embodiments, it can be 5%, 10%, 15%, 20%, 30%, 40%, 50%, 60%, 70%, 80% or 90%.

[0029] In this invention, the integrated sound-absorbing and sound-insulating composite material preferably further includes additives; the additives preferably include one or more of the following: crosslinking agent, antioxidant, mildew inhibitor, plasticizer, stabilizer, filler, flame retardant, colorant, abrasion resistant agent, and UV resistant additive. This invention does not specifically limit the types of additives; any of the above-mentioned additives well-known in the art are acceptable. Specifically, the crosslinking agent can be one or more of maleic anhydride-grafted polyolefin and polyvinyl alcohol, preferably used at 0.5-3% of the integrated sound-absorbing and sound-insulating composite material; the maleic anhydride-grafted polyolefin preferably includes maleic anhydride-grafted polypropylene and / or maleic anhydride-grafted polyPOE; the plasticizer can be triethyl acetylacetic acid, preferably used at 5-10% of the integrated sound-absorbing and sound-insulating composite material; the stabilizer can be phosphite or polycarbodiimide, preferably used at 0.3-0.5% of the integrated sound-absorbing and sound-insulating composite material; the filler can be calcium carbonate or aluminum hydroxide, preferably used at 0-5% of the integrated sound-absorbing and sound-insulating composite material; the flame retardant can be ammonium polyphosphate. The preferred dosage of the following components is 5-15% of the integrated sound absorption and insulation composite material: aluminum diethylphosphonate or melamine; the preferred dosage of the antioxidant is KY-1010; the preferred dosage of the antioxidant is 0.2-0.5% of the integrated sound absorption and insulation composite material; the preferred dosage of the antifungal agent is polystyrene caprolactone, polypyridine, titanium phosphate, or silane; the preferred dosage of the antifungal agent is 0.5-2% of the integrated sound absorption and insulation composite material; the preferred dosage of the wear-resistant agent is silicon carbide micro powder and / or polytetrafluoroethylene powder; the preferred dosage of the antiUV additive is nano-titanium dioxide or nano-zinc oxide; the preferred dosage of the antiUV additive is 0.3-1% of the integrated sound absorption and insulation composite material.

[0030] The structure of the integrated sound absorption and insulation composite material is described below.

[0031] Structurally, the integrated sound-absorbing and sound-insulating composite material is divided into a porous layer and a dense layer along the thickness direction.

[0032] In this invention, the total thickness of the porous layer is preferably 3-55 mm, more preferably 6-25 mm; the thickness of a single porous layer is preferably 1.5-30 mm; and the thickness of the dense layer is 0.3-5 mm, more preferably 0.5-2 mm. The total thickness of the integrated sound-absorbing and sound-insulating composite material is preferably 4-60 mm, more preferably 6-30 mm.

[0033] In this invention, the porous layer consists of at least two layers; the porous layer has a gradient pore structure with a pore diameter of 0.8-3 mm; and the pore diameter of each porous layer decreases progressively along the direction close to the dense layer.

[0034] In this invention, holes with a diameter ≥ 1.5 mm are defined as large holes, and holes with a diameter < 1.5 mm are defined as small holes. The gradient holes are divided into large holes and small holes.

[0035] In this invention, the preferred ratio of large holes to small holes is: the perforation rate of the large hole region is 0.5-3%, accounting for 60-85% of the total hole area; the perforation rate of the small hole region is 2-6%, accounting for 15-40% of the total hole area. In this case, the integrated sound-absorbing and sound-insulating composite material is mainly used to absorb mid-to-low frequency sounds.

[0036] Alternatively, the preferred ratio of large holes to small holes is: a perforation rate of 8-15% in the large hole region, accounting for 60-80% of the total hole area; and a perforation rate of 5-10% in the small hole region, accounting for 20-40% of the total hole area. In this case, the integrated sound absorption and insulation composite material is mainly used to absorb mid-to-high frequency sounds.

[0037] In this invention, the term "mid-low frequency" refers to a frequency range of 250Hz-1000Hz; and the term "mid-high frequency" refers to a frequency range of 1000Hz-4000Hz. Different aperture sizes correspond to different sound absorption frequency bands; larger apertures primarily absorb mid-low frequency sounds, while smaller apertures primarily absorb mid-high frequency sounds. In this invention, a sound-absorbing panel designed to absorb low frequencies should primarily use larger apertures, supplemented by a few smaller apertures to absorb mid-high frequencies; a sound-absorbing panel designed to absorb mid-high frequencies should primarily use smaller apertures, supplemented by larger apertures to absorb low frequencies.

[0038] In this invention, the porosity of the integrated sound absorption and insulation composite material is 1-40%, and in specific embodiments it can be 5%, 10%, 15%, 20%, 25%, 30%, 35%, or 40%. Excessive porosity leads to decreased sound absorption efficiency, reduced material mechanical properties, and poorer sound insulation; conversely, insufficient porosity makes it difficult for sound waves to penetrate the material, resulting in decreased sound absorption efficiency.

[0039] In this invention, the integrated sound-absorbing and sound-insulating composite material can be a regular sheet material (such as...). Figure 1 As shown), it can also be a special-shaped material (such as...). Figure 2 (As shown).

[0040] This invention provides a method for preparing the integrated sound-absorbing and sound-insulating composite material described above, comprising the following steps: A thermoplastic resin film is laid on both sides of the felt material, and then hot-pressed. During the hot-pressing process, the pressure of the upper platen is greater than that of the lower platen, and the pressure difference ΔP between the two is 5-50% of the average pressure. During the hot-pressing process, the thermoplastic resin melts and impregnates the felt material. After cooling, a dense layer is formed on the side near the upper platen, and a porous layer is formed on the side away from the upper platen, forming a gradient pore structure, thus obtaining the integrated sound absorption and insulation composite material.

[0041] In this invention, the felt material is either a plant fiber felt or a plant-thermoplastic resin composite fiber felt. This invention does not impose any special requirements on the preparation method of the felt material; any preparation method well-known in the art or commercially available materials may be used. When it is a plant-thermoplastic resin composite fiber felt, the plant fibers and thermoplastic resin fibers can be fed into an opening machine and a mixing chamber. Mechanical force and airflow are used to thoroughly fluff and disperse the fiber clusters, ensuring a macroscopically uniform mixture of the two fibers. Then, through an airflow web-forming step, the mixed fibers are passed through a high-speed airflow to form a fiber web with randomly arranged fibers, uniform basis weight, and high bulk. Finally, the fiber web is fixed using a hot rolling mill to form the plant-thermoplastic resin composite fiber felt.

[0042] In this invention, when the felt material is a plant-thermoplastic resin composite fiber felt, the plant fiber content in the plant-thermoplastic resin composite fiber felt is preferably 50-85% by mass, and the thermoplastic resin fiber content is preferably 15-50% by mass. In an embodiment of this invention, bamboo fiber-polypropylene composite fiber felt is specifically used, wherein the bamboo fiber content is 70% by mass, and the polypropylene content is 30% by mass.

[0043] In this invention, the thickness of the felt material is preferably 1-40 mm, and in specific embodiments it can be 1, 5, 10, 15, 20, 25, 30, 35 or 40 mm. In this invention, the felt material comprises at least two layers and each layer is directly stacked in contact (i.e., no thermoplastic resin film is placed between the felt materials).

[0044] This invention controls the pressure of the upper and lower plates during hot pressing to adjust the thickness of the dense layer and the pore structure of the porous layer of the integrated composite material with sound absorption and insulation functions.

[0045] In this invention, during the hot pressing process, the pressure of the upper pressure plate is greater than that of the lower pressure plate, and the pressure difference ΔP between the two is 5-50% of the average pressure. In specific embodiments, it can be 5%, 10%, 20%, 30%, 40%, or 50% of the average pressure. In this invention, the average pressure is preferably 0.5-8 MPa, and in specific embodiments, it can be 0.5, 2, 4.5, 6, or 8 MPa. In this invention, the average pressure = (upper pressure plate pressure + lower pressure plate pressure) / 2.

[0046] In this invention, a dense layer is formed on the side near the upper pressure plate, and a porous layer is formed on the side away from the upper pressure plate, forming a gradient pore structure. When ΔP increases, the thickness of the dense layer increases and the porosity of the dense layer decreases; when ΔP decreases, the gradient pore structure weakens or even tends to become a uniform pore structure.

[0047] In this invention, the preferred temperature for hot pressing is 110-210℃, and the preferred holding time is 20-60min.

[0048] This invention provides another method for preparing the integrated sound-absorbing and sound-insulating composite material described in the above-mentioned scheme, comprising the following steps: Plant fibers, thermoplastic resins, and pore-forming agents are mixed to obtain multiple preforms; the pore-forming agent particles in each preform have different sizes; the pore-forming agent includes sodium chloride. Plant fibers and thermoplastic resins are mixed to obtain a dense layer preform; First, the dense layer preform is laid in the mold. Then, each group of preforms is laid on the dense layer preform in order of increasing pore size. Hot pressing is performed to melt and mold the resin. After demolding, the preform is removed and the pore-forming agent is removed to obtain the sound-absorbing and sound-insulating integrated composite material.

[0049] In this invention, the particle size of the porogen can be achieved by using porogens of different particle sizes or by adjusting the content of the porogen. In an embodiment of this invention, a porogen of the same particle size is used, and the particle size is adjusted to form particles of different sizes.

[0050] In this invention, the hot-pressing temperature is preferably 150-180℃, the hot-pressing pressure is preferably 1-6MPa, and the hot-pressing time is preferably 5-15 minutes. This invention preferably involves holding the pressure and cooling to below 40℃ before demolding.

[0051] In this invention, the pore-forming agent is preferably removed by immersion in deionized water for 12-48 hours.

[0052] This invention provides another method for preparing the above-mentioned integrated sound absorption and insulation composite material, comprising the following steps: Plant fibers and thermoplastic resins are melt-blended and then granulated to obtain granular material; The granular material is foamed with carbon dioxide to obtain foamed beads; the saturation temperature of the foaming is 110-190℃, the saturation pressure is 5-20MPa, and the saturation time is 0.5-3 hours. The foamed beads are graded to obtain foamed beads of different sizes; The foamed beads of different sizes are laid in layers along the thickness direction, with smaller beads laid on the side closer to the dense layer to be formed and larger beads laid away from the side, and then molded to obtain the integrated sound absorption and insulation composite material. Steam is introduced during the molding process, with a temperature of 110-190℃ and a pressure of 0.1-0.5MPa; the heat and pressure holding time is 30-500 seconds.

[0053] This invention involves melt-blending plant fibers with thermoplastic resin and then granulating the resulting material to obtain granules.

[0054] In this invention, the melt blending is carried out in a twin-screw extruder; the temperature of the twin-screw extruder from the die head to the die tail is 140-180℃, 150-180℃ and 135-180℃ respectively.

[0055] In this invention, the plant fiber can be modified plant fiber or unmodified plant fiber. When the integrated sound-absorbing and sound-insulating composite material also includes additives, it is preferable to add additives during melt blending.

[0056] After obtaining the granules, the present invention foams the granules with carbon dioxide to obtain foamed beads.

[0057] In this invention, the saturation temperature of the foaming process is 110-190℃, the saturation pressure is 5-20MPa, and the saturation time is 0.5-3 hours. The purpose of foaming in this invention is to precisely construct a multi-scale, gradient, and highly damped solid-gas composite microstructure, transforming the material from a passive "sound barrier" into an active "sound energy absorber and converter," thereby achieving a lightweight, broadband, high-efficiency sound-absorbing material with multiple functions such as heat insulation.

[0058] After obtaining the foamed beads, the present invention classifies the foamed beads to obtain foamed beads of different sizes.

[0059] In this invention, the grading is preferably divided into at least two levels, specifically two, three, or four levels, with three levels being the most preferred. In this invention, the particle size ranges of different particle size grades do not overlap or only partially overlap. When divided into three levels, specifically, there are small particle size grades, medium particle size grades, and large particle size grades; the particle size of the small particle size grade is preferably 0.8-1.5 mm; the particle size of the medium particle size grade is preferably 1.5-2.2 mm; and the particle size of the large particle size grade is preferably 2.2-3.0 mm.

[0060] After obtaining foamed beads of different sizes, the present invention lays the foamed beads of different sizes in layers along the thickness direction, with smaller beads laid on the side closer to the dense layer to be formed, and larger beads laid away from the side, and then molding to obtain the sound-absorbing and sound-insulating integrated composite material.

[0061] In this invention, the small-particle-size layer has smaller initial pores and is more likely to be densely packed under hot pressing, eventually forming a gradient pore structure with pore size gradually decreasing towards the dense layer.

[0062] During the molding process, the beads near the mold wall are first heated and softened. Under the constraint and pressure of the mold wall, they melt and weld together and partially collapse and compact, significantly reducing the porosity and thus forming a dense surface layer. Below this, multiple pores are retained and present a pore / pore size gradient, resulting in an integrated structure of "dense layer + gradient pores".

[0063] In this invention, steam is introduced during the molding process, and the temperature of the steam is 110-190℃ and the pressure is 0.1-0.5MPa; the heat and pressure holding time is 30-500 seconds.

[0064] This invention uses steam to rapidly heat the surface of the beads, softening and welding them into shape, while applying pressure to the mold wall to form a dense surface structure.

[0065] The following detailed description of the integrated sound absorption and insulation composite material and its preparation method provided by the present invention, with reference to the embodiments, should not be construed as limiting the scope of protection of the present invention.

[0066] Example 1 A sound-absorbing and insulating material made from bamboo felt and polypropylene composite material is prepared by the following method: KH550 modified bamboo fiber (10-80 μm in diameter) and polypropylene are fed into an opening machine and a mixing chamber at a mass ratio of 70% bamboo fiber and 30% polypropylene. The fiber clumps are thoroughly fluffed and dispersed by mechanical force and airflow, so that the two fibers are uniformly mixed macroscopically. Then, through the airflow web forming step, the mixed fibers are formed into a fiber web with random fiber arrangement, uniform basis weight and high bulkiness by passing through a high-speed airflow. Finally, the fiber web is fixed by a hot rolling mill to form bamboo fiber felt.

[0067] First, select a surface density of 300 g / m³. 2 A bamboo fiber felt with an initial thickness of approximately 5 mm was used as the reinforcement, and a polypropylene film with a thickness of 0.05 mm and a melt flow index of 25 g / 10 min (230℃ / 2.16 kg) was used as the thermoplastic matrix. The specific layup design adopted a "sandwich" structure, with one layer of polypropylene film on the top and bottom, and two layers of bamboo fiber felt sandwiched in between. The bamboo fiber felt accounted for up to 70% of the total mass, aiming to ensure the formation of a fiber-dominated porous structure. Hot pressing was performed with an upper platen pressure of 5.0 MPa, a lower platen pressure of 4.0 MPa, a hot pressing temperature of 190℃, and a hot pressing time of 30 minutes, resulting in a composite material sheet with a thickness precisely controlled at 4.0 mm (tolerance ±0.2 mm).

[0068] Performance tests on the finished product showed that its apparent density was 0.35 g / cm³. 3With a porosity of approximately 35%, it provides ideal conditions for sound wave energy dissipation. The average sound absorption coefficient, measured using the impedance tube method according to ISO 10534-2, reaches 0.7 in the frequency range of 1000Hz to 4000Hz, demonstrating its excellent mid-to-high frequency sound absorption performance. In terms of mechanical properties, its tensile strength is 8.5MPa, indicating that the material possesses a certain degree of structural integrity and self-supporting ability. Furthermore, this material is environmentally friendly and safe, with no added formaldehyde and no dust generation. Its long-term service temperature, determined by the polypropylene matrix, is below 100℃, making it suitable for conventional building indoor environments. This embodiment successfully demonstrates a feasible technical path for preparing high-performance, green, and environmentally friendly sound-absorbing materials using renewable resources.

[0069] Example 2 A flax fiber / polylactic acid composite sound-absorbing and insulating material with a biomimetic gradient pore structure First, three preforms with different proportions were prepared: the top layer (layer A) was made by mixing flax fibers (10–30 μm in diameter), polylactic acid powder, and sodium chloride pore-forming agent in a 40 / 10 / 50 weight ratio to create high porosity; the middle layer (layer B) had a 40 / 30 / 30 ratio; and the bottom layer (layer C) had a 40 / 50 / 10 ratio to provide mechanical support. A dense layer (layer D) preform was also prepared: flax fibers and PLA were mixed in a 40 / 60 mass ratio (without NaCl). A total of 110... The precast material (g) is laid in the mold in the order of layer D → layer C → layer B → layer A, and hot-pressed at 170℃ and 4MPa for 10 minutes to melt and shape the polylactic acid. It is then held under pressure and cooled to below 40℃ before demolding. The resulting board is immersed in deionized water for 24 hours to completely remove sodium chloride particles, and then dried at 70℃ for 6 hours, finally obtaining a gradient structure sound-absorbing and insulating material with a total thickness of 12.0mm.

[0070] Performance tests show that the overall apparent density of this material is 0.38 g / cm³. 3 The porosity of each layer exhibits a continuous gradient distribution from layer A (approximately 85%) to layer C (approximately 55%). In terms of acoustic performance, the sound absorption coefficient curve of the material within a specified frequency range was measured using the impedance tube method according to ISO 10534-2 standard, and its noise reduction coefficient (NRC) was calculated to be 0.78. Simultaneously, the sound absorption spectrum shows that it has higher sound absorption efficiency in the mid-to-low frequency range compared to homogeneous materials of the same thickness. Regarding sound insulation performance, the sound insulation spectrum was measured and the weighted sound insulation was calculated according to GB / T 19889, resulting in a weighted sound insulation of 38 dB, indicating excellent sound insulation performance. Mechanical property tests show that its flexural strength is 8.2 MPa, possessing sufficient self-supporting capacity. This process, through a biomimetic multilayer structure design, successfully achieves high-efficiency sound absorption over a wide frequency range (especially at low frequencies), while all components (flax, PLA) are biodegradable, demonstrating good functionality and environmental friendliness.

[0071] Example 3 Bamboo fiber and polypropylene were melt-blended and granulated in a twin-screw extruder at a mass ratio of 70 / 30 to obtain granules. The granules were then subjected to CO2 saturation foaming in an autoclave at a saturation temperature of 150℃, a saturation pressure of 10 MPa, and a saturation time of 1.5 h to obtain foamed beads. The foamed beads were sieved and graded using a standard sieve to obtain three particle size grades: small (0.8-1.5 mm), medium (1.5-2.2 mm), and large (2.2-3.0 mm). Small-diameter beads were placed near the die wall, medium-diameter beads were placed in the middle layer, and large-diameter beads were placed away from the die wall. After molding, the mixture was steam-pressed at a steam temperature of 160℃ and a steam pressure of 0.3 MPa for 120 s. After cooling and demolding, the composite material was obtained. The resulting material forms a dense surface layer near the die wall, with the pore size gradually increasing along the thickness direction below, forming a "dense layer + gradient pore" structure.

[0072] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A composite material integrating sound absorption and insulation functions, characterized in that, In terms of composition, it includes plant fibers and thermoplastic resin, with the thermoplastic resin filling the network voids formed by the plant fibers; in terms of structure, it is divided into a porous layer and a dense layer along the thickness direction; the porous layer consists of at least two layers; the porous layer has a gradient pore structure with a pore size of 0.8-3 mm; the pore size of each porous layer decreases gradually towards the dense layer; the porosity of the integrated sound absorption and insulation composite material is 1-40%.

2. The integrated sound-absorbing and sound-insulating composite material according to claim 1, characterized in that, The gradient holes are divided into large holes and small holes, with a diameter ≥ 1.5 mm as large holes and a diameter < 1.5 mm as small holes. The ratio of large holes to small holes is as follows: the perforation rate of the large hole area is 0.5-3%, accounting for 60-85% of the total hole area; the perforation rate of the small hole area is 2-6%, accounting for 15-40% of the total hole area. Alternatively, the ratio of large holes to small holes may be as follows: the perforation rate of the large hole area is 8-15%, accounting for 60-80% of the total hole area; the perforation rate of the small hole area is 5-10%, accounting for 20-40% of the total hole area.

3. The integrated sound-absorbing and sound-insulating composite material according to claim 1, characterized in that, The plant fiber content in the integrated sound absorption and insulation composite material is 5-90%.

4. The integrated sound-absorbing and sound-insulating composite material according to claim 1 or 3, characterized in that, The plant fibers include unmodified plant fibers and / or modified plant fibers; the types of plant fibers include one or more of bamboo fiber, hemp fiber, rice husk fiber, coconut shell fiber and reed fiber.

5. The integrated sound-absorbing and sound-insulating composite material according to claim 1, characterized in that, The thermoplastic resin includes one or more of PP, PET, PE, PLA, PBAT, PBS and PA.

6. The integrated sound-absorbing and sound-insulating composite material according to claim 1, characterized in that, It also includes additives; the additives include one or more of the following: crosslinking agents, antioxidants, mildew inhibitors, plasticizers, stabilizers, fillers, flame retardants, colorants, abrasion resistant agents, and UV resistant additives.

7. A method for preparing the integrated sound-absorbing and sound-insulating composite material according to any one of claims 1-6, characterized in that, Includes the following steps: A thermoplastic resin film is laid on both sides of the felt material, and then it is hot-pressed. During the hot-pressing process, the pressure of the upper platen is greater than that of the lower platen, and the pressure difference ΔP between the two is 5-50% of the average pressure. During the hot-pressing process, the thermoplastic resin melts and impregnates the felt material. After cooling, a dense layer is formed on the side near the upper platen, and a porous layer is formed on the side away from the upper platen, forming a gradient pore structure, thus obtaining the integrated sound absorption and insulation composite material. The felt material includes at least two layers, and each layer is directly stacked and in contact with the others. The felt material is either plant fiber felt or plant-thermoplastic resin composite fiber felt.

8. A method for preparing the integrated sound-absorbing and sound-insulating composite material according to any one of claims 1-6, characterized in that, Includes the following steps: Plant fibers, thermoplastic resins, and pore-forming agents are mixed to obtain multiple preforms; the pore-forming agent particles in each preform have different sizes; the pore-forming agent includes sodium chloride. Plant fibers and thermoplastic resins are mixed to obtain a dense layer preform; First, the dense layer preform is laid in the mold. Then, each group of preforms is laid on the dense layer preform in order of increasing pore size. Hot pressing is performed to melt and mold the resin. After demolding, the preform is removed and the pore-forming agent is removed to obtain the sound-absorbing and sound-insulating integrated composite material.

9. The preparation method according to claim 8, characterized in that, When the integrated sound-absorbing and sound-insulating composite material includes additives, at least one set of preforms also includes additives.

10. A method for preparing the integrated sound-absorbing and sound-insulating composite material according to any one of claims 1-6, characterized in that, Includes the following steps: Plant fibers and thermoplastic resins are melt-blended and then granulated to obtain granular material; The granular material is foamed with carbon dioxide to obtain foamed beads; the saturation temperature of the foaming is 110-190℃, the saturation pressure is 5-20MPa, and the saturation time is 0.5-3 hours. The foamed beads are graded to obtain foamed beads of different sizes; The foamed beads of different sizes are laid in layers along the thickness direction, with smaller beads laid on the side closer to the dense layer to be formed and larger beads laid away from the side, and then molded to obtain the integrated sound absorption and insulation composite material. Steam is introduced during the molding process, with a temperature of 110-190℃ and a pressure of 0.1-0.5MPa; the heat and pressure holding time is 30-500 seconds.

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