Automobile plant fiber sound insulation pad and preparation method thereof

Abstract

The present application relates to the technical field of automobile interior sound insulation materials, and discloses a kind of automobile plant fiber sound insulation pad and preparation method thereof.The sound insulation pad includes surface fiber protection layer, plant fiber sound absorption layer, limited permeation isolation interface layer and damping sound insulation layer which are sequentially stacked.The plant fiber sound absorption layer includes jute fiber, bamboo fiber and first low-melting-point polyester fiber.The limited permeation isolation interface layer includes interface support framework formed by interweaving second low-melting-point polyester fiber and polylactic acid staple fiber, and thermoplastic starch, flaky inorganic micropowder and plasticizing humidity regulator distributed therein.The melting point of the first low-melting-point polyester fiber is 115-130℃, and the melting point of the second low-melting-point polyester fiber is 105-120℃.The sound insulation pad is conducive to improving the interlayer bonding stability and maintaining the pore sound absorption effect of the plant fiber sound absorption layer.

Description

Technical Field

[0001] This invention relates to the technical field of automotive interior sound insulation materials, and in particular to an automotive plant fiber sound insulation pad and its preparation method. Background Technology

[0002] Automotive sound insulation pads are typically installed in the passenger compartment, trunk, engine compartment, or on the inner side of the vehicle's sheet metal. Their main function is to reduce the transmission of noise generated by tires, road surface, engine, wind noise, and vehicle body structure vibrations into the vehicle interior during driving. With increasing demands for lightweight, low-odor, and environmentally friendly vehicles, fiber-based sound insulation materials are gradually replacing some traditional heavy-duty sound insulation materials and are being used in noise reduction components in automotive interiors.

[0003] Existing automotive sound insulation pads typically employ composites of polyester fibers, recycled fibers, low-melting-point fibers, flame-retardant fibers, or adhesive layers. For example, CN103303214B discloses an automotive sound insulation pad and its manufacturing process, which involves stacking low-melting-point PET fiber layers, mixed fiber felt, and low-melting-point PET fiber layers, followed by needle punching and steam molding to improve the sound absorption performance of the automotive sound insulation pad and reduce odor and volatile organic compound release. As another example, CN105252852A discloses a recycled polyester fiber laminate sheet for automotive interior damping, vibration reduction, and sound insulation. This sheet has a density structure that decreases along its thickness, and an adhesive layer is laminated onto the surface of the tightly packed layer to balance sound absorption, sound insulation, and vibration reduction requirements.

[0004] The aforementioned materials can meet certain automotive sound insulation requirements. However, in composite structures containing porous fiber sound-absorbing layers and damping sound-insulating layers, the material flow at the interface and the interlayer compaction state are difficult to control stably during hot-pressing. If the interface bonding is insufficient, the stability and durability of the interlayer composite are prone to decrease; if the interface is compacted or too much resin phase enters the fiber pores, the effective pore volume of the porous fiber layer is easily reduced, affecting its sound absorption effect.

[0005] Therefore, existing automotive fiber sound insulation pads still need to address the problem of achieving both stable bonding and porosity maintenance during the hot-pressing process of combining porous fiber sound-absorbing layers and damping sound-insulating layers. Summary of the Invention

[0006] The purpose of this invention is to overcome the problem in the prior art that it is difficult to achieve stable bonding and porosity maintenance at the interface during the hot-pressing composite process of porous fiber sound-absorbing layer and damping sound-insulating layer in automotive fiber sound insulation pads, and to provide an automotive plant fiber sound insulation pad and its preparation method.

[0007] To achieve the above objectives, the first aspect of the present invention provides an automotive plant fiber sound insulation pad, comprising a surface fiber protective layer, a plant fiber sound absorption layer, a permeation-limiting isolation interface layer, and a damping sound insulation layer stacked sequentially. The plant fiber sound-absorbing layer includes jute fiber, bamboo fiber, and a first low-melting-point polyester fiber; The permeation-limiting isolation interface layer is located between the plant fiber sound-absorbing layer and the damping sound insulation layer. The permeation-limiting isolation interface layer includes an interface support skeleton formed by interwoven second low-melting-point polyester fibers and polylactic acid short fibers, as well as thermoplastic starch, flake inorganic powder and plasticizer and moisture conditioner distributed in the interface support skeleton. The melting point of the first low-melting-point polyester fiber is 115-130°C. The melting point of the second low-melting-point polyester fiber is 105–120°C; The length of the second low-melting-point polyester fiber is greater than the length of the polylactic acid short fiber; The D50 particle size of the flaky inorganic micro powder is 5-15 μm, and the average aspect ratio is 8-20. The thermoplastic starch, the flaky inorganic powder, and the plasticizer and moisture conditioner together form a composite dispersed phase, which accounts for 25% to 42% of the total mass of the permeation-limiting and isolating interface layer. The damping sound insulation layer is hot-pressed together with the plant fiber sound absorption layer through the permeability-limiting isolation interface layer.

[0008] By adopting the above technical solution, the sound insulation pad forms an intermediate interface between the plant fiber sound-absorbing layer and the damping sound insulation layer, which has the functions of fiber support, thermal bonding, and filling adjustment. The first low-melting-point polyester fiber is located in the plant fiber sound-absorbing layer. Its melting point is relatively high. During hot pressing, it mainly undertakes the bonding between fibers and shape maintenance within the plant fiber layer, making the porous skeleton composed of jute and bamboo fibers less prone to over-compactment. The second low-melting-point polyester fiber is located in the permeation-limiting isolation interface layer. Its melting point is relatively low. During hot pressing, it is easier to soften and bond first, thereby forming thermal bonding points and a support network at the interface. After this treatment, hot pressing is not simply pressing the damping sound insulation layer onto the plant fiber sound-absorbing layer, but rather forming an interface layer between the two that can support, bond, and buffer the flow of the resin phase.

[0009] Secondly, the length of the second low-melting-point polyester fiber is greater than that of the polylactic acid short fiber, giving the interfacial support skeleton an intralayer structure in which both long and short fibers participate. The longer second low-melting-point polyester fiber is more likely to form bridging thermal bonding pathways within the interfacial layer, while the shorter polylactic acid short fibers are distributed between these pathways, playing a supporting, gap-filling, and restricting local flow functions. This long-short fiber combination makes the composite dispersed phase less likely to migrate and concentrate during hot pressing, and also makes the interfacial pressure state between the damping sound insulation layer and the plant fiber sound absorption layer more uniform.

[0010] The D50 particle size and average diameter-to-thickness ratio of the flake-like inorganic micropowder are limited to the above range, which allows the flake particles to form a relatively stable dispersion state within the interfacial support framework. If the particle size is too small, it is not conducive to forming sufficient flake-like barrier paths, while if the particle size is too large, it is easy to generate agglomeration or local hard spots in the interfacial layer. When the average diameter-to-thickness ratio is controlled between 8 and 20, the flake-like inorganic micropowder has a certain flake-layer overlap ability and can be coated or wetted by thermoplastic starch and plasticizers, thereby forming a relatively soft filling barrier effect within the interfacial layer.

[0011] Thermoplastic starch, flake-shaped inorganic powder, and plasticizer / humidifier together form a composite dispersed phase, with its proportion limited to 25%–42%. This ensures that the dispersed phase provides sufficient interfacial filling and flow restriction without causing the interfacial layer to become an excessively dense, hard layer. Thermoplastic starch exhibits a certain softening ability under humid and hot conditions, while the flake-shaped inorganic powder provides flake-like pathways and interfacial stability. The plasticizer / humidifier regulates the degree of softening and moisture response of the thermoplastic starch during humid and hot processes. The combined effect of these three components allows the permeation-limiting and isolating interfacial layer to form a relatively stable interfacial bond during hot pressing and humid and hot setting, achieving a good balance between maintaining the porosity of the plant fiber sound-absorbing layer, the interlayer bonding of the damping sound insulation layer, and the overall composite stability of the sound insulation pad.

[0012] Preferably, the plant fiber sound-absorbing layer comprises, by weight: 35-55 parts jute fiber, 15-35 parts bamboo fiber, 12-24 parts first low-melting-point polyester fiber, 3-10 parts polylactic acid fiber, and 2-8 parts flame-retardant polyester fiber.

[0013] Through the aforementioned plant fiber sound-absorbing layer formulation, jute fiber provides a coarser fiber skeleton and higher structural support; bamboo fiber improves the micropore distribution within the fiber layer and reduces surface frictional energy dissipation; the first low-melting-point polyester fiber forms inter-fiber bonding points during hot pressing; polylactic acid fiber enhances the compatibility and intralayer toughness of the plant-based fiber system; and flame-retardant polyester fiber provides a flame-retardant foundation for automotive interior applications. This formulation does not simply increase the plant fiber content, but rather allows coarse and fine fibers, thermally bonded fibers, and functional fibers to jointly constitute a sound-absorbing layer that combines open-pore sound absorption, structural retention, and hot-pressing stability.

[0014] Preferably, the jute fiber has a length of 35-75 mm, the bamboo fiber has a length of 25-55 mm, and the porosity of the plant fiber sound-absorbing layer is 68%-88%.

[0015] Using jute and bamboo fibers in different length ranges facilitates the formation of a more stable fiber overlap structure during web laying and needle punching. Longer jute fibers improve the overall cohesion and tear resistance of the plant fiber sound-absorbing layer, while shorter bamboo fibers more easily fill and distribute between the jute fiber skeleton, creating multi-scale pores within the fiber layer. When the porosity is controlled between 68% and 88%, sound waves entering the fiber layer can generate air viscosity loss and fiber surface frictional energy dissipation within the pores, while the fiber layer still maintains necessary compressibility resilience and thermo-pressing composite stability.

[0016] Preferably, the permeation-limiting isolation interface layer comprises, by weight: 42-54 parts of second low-melting-point polyester fiber, 14-22 parts of thermoplastic starch, 12-20 parts of polylactic acid short fiber, 7-13 parts of flake inorganic powder, and 2-5 parts of plasticizer and moisture conditioner, wherein the areal density of the permeation-limiting isolation interface layer is 35-95 g / m³. 2 .

[0017] Through the above-mentioned proportions of the permeation-limiting isolation interface layer, the second low-melting-point polyester fiber occupies a relatively high proportion in the interface layer, ensuring the formation of a sufficient thermal bonding network during hot pressing. Polylactic acid short fibers provide incompletely melted short fiber support, preventing the interface layer from completely collapsing into a film under pressure. Thermoplastic starch and flake-like inorganic micropowder together provide filling and flow-limiting effects, while the plasticizer and moisture conditioner regulate the humid and heat softening state of the thermoplastic starch. The areal density is controlled between 35 and 95 g / m², giving the interface layer a material load that can be stably laid and hot-pressed, effectively covering the interface between the plant fiber sound-absorbing layer and the damping sound-insulating layer without significantly increasing the overall heaviness of the sound insulation pad.

[0018] Preferably, the length of the second low-melting-point polyester fiber in the permeation-limiting isolation interface layer is 4-12 mm, the length of the polylactic acid short fiber is 2-8 mm, and the length ratio of the second low-melting-point polyester fiber to the polylactic acid short fiber is 1.5-4:1.

[0019] The length relationship between the second low-melting-point polyester fiber and the polylactic acid short fiber further clarifies the formation mechanism of the interfacial support skeleton. When the length of the second low-melting-point polyester fiber is 4–12 mm, it can form bridging and entanglement in a relatively thin interfacial layer; when the length of the polylactic acid short fiber is 2–8 mm, it is easier to disperse between the second low-melting-point polyester fiber. Controlling the length ratio to 1.5–4:1 allows the interfacial layer to simultaneously have continuous support from long fibers and localized gap filling from short fibers. This difference in fiber size within the layer is beneficial for confining the composite dispersed phase within the interfacial layer and improving the uniformity of interfacial bonding after hot pressing.

[0020] Preferably, the thermoplastic starch is glycerol-plasticized corn starch or glycerol-plasticized cassava starch; the plasticizer and moisture conditioner is one or more of glycerol, sorbitol, or triethyl citrate; and the mass ratio of the thermoplastic starch to the plasticizer and moisture conditioner is 4 to 10:1.

[0021] Glyceryl-plasticized corn starch and glyceryl-plasticized cassava starch exhibit good softening and film-forming tendencies under humid heat conditions, enabling them to flexibly bond with the fibrous skeleton within the interfacial layer. Glyceryl, sorbitol, or triethyl citrate can regulate the moisture response and softening degree of thermoplastic starches, ensuring they achieve the necessary binding properties during humid heat setting without excessive flow. When the mass ratio of thermoplastic starch to plasticizer is 4–10:1, the thermoplastic starch maintains its bulk filling function, while the plasticizer acts as a softening regulator to stabilize the interfacial state. This results in a softer interfacial layer that is less prone to forming a brittle interface.

[0022] Preferably, the flaky inorganic powder is one or more of flaky talc powder, sericite powder, or flaky calcium carbonate; the mass ratio of the thermoplastic starch to the flaky inorganic powder is 1.2 to 3.0:1.

[0023] Flaky talc, sericite powder, or flaky calcium carbonate all possess a flaky structure and high surface area, enabling them to form tortuous filling paths within the interfacial support framework. When the mass ratio of thermoplastic starch to flaky inorganic powder is 1.2–3.0:1, the thermoplastic starch can coat, adhere to, and disperse the flaky inorganic powder, while the flaky inorganic powder enhances the morphology retention of the composite dispersed phase in the interfacial layer. When combined, the interfacial layer is less prone to single resinous flow under thermo-pressing pressure, instead forming a filled state with a certain degree of particle support and flexible bonding.

[0024] Preferably, the damping sound insulation layer comprises, by weight: 45-65 parts of ethylene-vinyl acetate copolymer, 10-25 parts of polyolefin elastomer, 20-40 parts of heavy calcium carbonate, 2-6 parts of maleic anhydride-grafted polyolefin, 0.5-2 parts of zinc stearate, and 0.2-1 parts of antioxidant.

[0025] Ethylene-vinyl acetate copolymer provides the basic flexibility and hot-press adhesion of the damping sound insulation layer. Polyolefin elastomer improves the layer's elastic recovery and low-temperature flexibility. Heavy calcium carbonate increases the layer's surface density and enhances its mass barrier effect during sound wave propagation. Maleic anhydride-grafted polyolefin helps improve the compatibility between the inorganic filler and the polymer matrix. Zinc stearate improves processing flow and demolding properties, while antioxidants enhance stability during hot working and long-term use. When combined with a permeation-limiting interface layer, this damping sound insulation layer achieves stable adhesion during hot pressing and provides damping energy dissipation and sound insulation support during use.

[0026] A second aspect of the present invention provides a method for preparing an automotive plant fiber sound insulation pad as described above, comprising the following steps: S1: Mix jute fiber, bamboo fiber, first low melting point polyester fiber, polylactic acid fiber and flame retardant polyester fiber, lay them into a web and needle punch them to obtain a plant fiber sound-absorbing layer; S2: Mix the second low-melting-point polyester fiber and polylactic acid short fiber and lay them into an interface fiber network. Mix thermoplastic starch, flake inorganic powder and plasticizer moisture conditioner to form a composite dispersed phase and distribute the composite dispersed phase in the interface fiber network to obtain a permeation-limiting isolation interface layer preform. S3: The preformed impermeable isolation interface layer is laid on one side of the plant fiber sound-absorbing layer; S4: The damping sound insulation layer is attached to the side of the preformed permeability-limiting isolation interface layer away from the plant fiber sound absorption layer, and then hot-pressed composite is performed. S5: Perform wet heat setting on the hot-pressed composite material to soften and bond the thermoplastic starch within the permeation-limiting isolation interface layer; S6: Cool and cut the material after wet heat setting to obtain automotive plant fiber sound insulation pad.

[0027] Through the above preparation method, the plant fiber sound-absorbing layer, the permeation-limiting isolation interface layer, and the damping sound insulation layer are not pressed all at once in the same mixed system. Instead, a porous sound-absorbing base layer and an interface layer preform are first formed separately, and then the interlayer bonding is completed through hot pressing and hygrothermal setting. In S1, the mixing and needle punching first form a stable porous fiber network in the plant fiber sound-absorbing layer; in S2, the second low-melting-point polyester fiber, polylactic acid short fiber, and composite dispersed phase are organized into a preform, so that the interface material already has a certain layered distribution before entering the hot pressing; the hot pressing in S4 causes the second low-melting-point polyester fiber to soften and bond preferentially; and the hygrothermal setting in S5 further softens and bonds the thermoplastic starch within the interface layer. In this way, the formation of the interface layer is not completed by pressure compaction alone, but is completed continuously through fiber pre-forming, hot bonding, and hygrothermal softening, resulting in a more stable interlayer structure.

[0028] Preferably, in step S2, thermoplastic starch, flake inorganic powder, and plasticizer / humidifier are stirred at 60–80°C for 5–15 min to obtain a composite dispersed phase. The composite dispersed phase accounts for 25%–42% of the total mass of the preformed permeability-limiting interface layer, and the areal density of the preformed permeability-limiting interface layer is 35–95 g / m³. 2 ; In step S4, the hot-pressing temperature is 125-150°C, and the hot-pressing temperature is 5-35°C higher than the melting point of the second low-melting-point polyester fiber; the pressure is 0.4-1.0 MPa; and the time is 45-100 s. In step S5, the temperature for wet heat setting is 70–88℃, the relative humidity is 70%–88%, and the processing time is 1–3 hours.

[0029] In step S2, the thermoplastic starch, flake inorganic powder, and plasticizer / humidifier are stirred at 60–80°C for 5–15 minutes. This allows the thermoplastic starch to be in a more easily dispersed and wetted state, and enables the flake inorganic powder and plasticizer / humidifier to enter the same composite dispersion system more uniformly. The composite dispersed phase accounts for 25%–42% of the total mass of the preformed permeation-limiting isolation interface layer, and is formulated with 35–95 g / m³ of... 2 The preformed surface density allows the interface layer to have stable material load and layup integrity before hot pressing.

[0030] In step S4, the hot-pressing composite temperature is 5–35°C higher than the melting point of the second low-melting-point polyester fiber, allowing the second low-melting-point polyester fiber to obtain sufficient softening space in the interface layer, while preventing all fibers and dispersed phases in the interface layer from losing their support state. A pressure of 0.4–1.0 MPa and a time of 45–100 seconds provide the necessary contact pressure and thermal action time for interlayer bonding, ensuring a stable bond between the damping sound insulation layer, the permeation-limiting isolation interface layer, and the plant fiber sound-absorbing layer.

[0031] In step S5, the humid heat setting conditions of 70–88℃, 70%–88% relative humidity, and 1–3 hours allow the thermoplastic starch to continue softening and interfacial bonding in the presence of the plasticizer and moisture conditioner, further stabilizing the bonding state of the interfacial layer after hot pressing. This humid heat treatment process helps release localized stress after hot pressing and makes the bonding between the composite dispersed phase and the interfacial support skeleton more uniform, thereby improving the interlayer stability and acoustic performance retention of the sound insulation pad during subsequent use.

[0032] The present invention, by adopting the above technical solution, has the following beneficial effects: 1. This invention establishes a permeation-limiting isolation interface layer between the plant fiber sound-absorbing layer and the damping sound-insulating layer. This prevents the plant fiber sound-absorbing layer and the damping sound-insulating layer from directly contacting and pressing together during the hot-pressing process. Instead, they are connected through an intermediate layer that provides support and adjustment. This permeation-limiting isolation interface layer improves the pressure state and material distribution during the interlayer bonding process, enhancing the interlayer bonding stability of the sound insulation pad and reducing the concentrated intrusion of the damping sound-insulating layer into the pores of the plant fiber sound-absorbing layer under hot pressing.

[0033] 2. This invention incorporates a first low-melting-point polyester fiber within a plant fiber sound-absorbing layer and a second low-melting-point polyester fiber within a permeation-limiting isolation interface layer, allowing the low-melting-point polyester fibers in different layers to undertake different hot-pressing effects. The relatively high melting point of the first low-melting-point polyester fiber helps the plant fiber sound-absorbing layer maintain its porous fiber skeleton during hot pressing; the relatively low melting point of the second low-melting-point polyester fiber facilitates the preferential formation of a thermally bonded structure at the interface, thus balancing the preservation of the sound-absorbing layer's porosity and the stability of the interface layer's connection.

[0034] 3. This invention utilizes a second low-melting-point polyester fiber and polylactic acid short fiber interwoven to form an interfacial support skeleton, with the length of the second low-melting-point polyester fiber being greater than the length of the polylactic acid short fiber. This results in a permeation-limiting and isolating interfacial layer with a synergistic support structure of long and short fibers. The longer second low-melting-point polyester fiber facilitates the formation of a cross-bonding network within the interfacial layer, while the shorter polylactic acid short fiber helps fill the gaps between fibers and provide local support, thereby improving the distribution stability of the composite dispersed phase in the interfacial layer and the interface uniformity after hot pressing.

[0035] 4. This invention forms a composite dispersed phase using thermoplastic starch, flake-shaped inorganic powder, and a plasticizer / humidifier, and controls the mass ratio of this composite dispersed phase in the permeation-limiting isolation interface layer. This allows the interface layer to simultaneously possess flexible bonding, flake-like filling, and moisture-temperature regulation functions. Thermoplastic starch can undergo moderate softening under moist-heat conditions, the flake-shaped inorganic powder can form flake-like filling paths within the interface layer, and the plasticizer / humidifier can regulate the moist-heat response state of the thermoplastic starch. This helps to reduce concentrated flow of interface materials during hot pressing and maintains the flexibility and stability of the interface layer.

[0036] 5. This invention utilizes a continuous process of hot-pressing lamination and moist heat setting to achieve thermal bonding of the second low-melting-point polyester fiber in the permeation-limiting isolation interface layer during the hot-pressing stage, while the thermoplastic starch undergoes further softening and bonding during the moist heat setting stage. This process ensures that the bonding of the interface layer does not solely rely on pressure compaction, but rather achieves a stable composite state through the combined thermal bonding of fibers and moist heat softening. This is beneficial for improving the composite stability, sound absorption retention, and durability of automotive plant fiber sound insulation pads. Detailed Implementation

[0037] The following provides a detailed description of specific embodiments of the present invention. It should be understood that the specific embodiments described herein are for illustrative and explanatory purposes only and are not intended to limit the scope of the invention.

[0038] Unless otherwise defined, all scientific and technical terms used in this invention have the same meaning as commonly understood by one of ordinary skill in the art.

[0039] 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.

[0040] Unless otherwise specified, all materials and reagents used in the following examples are commercially available.

[0041] The present invention will now be described in detail with reference to specific embodiments, which are intended to understand rather than limit the invention.

[0042] Unless otherwise specified, in this invention, the porosity of the plant fiber sound-absorbing layer is determined using the apparent density calculation method. The plant fiber sound-absorbing layer is cut into 100mm × 100mm samples, equilibrated at 23℃ and 50% relative humidity for 24 hours, and then the sample thickness and mass are measured to calculate the apparent density. The theoretical true density is calculated based on the mass fraction of each fiber component in the plant fiber sound-absorbing layer and the corresponding material true density. Porosity according to calculate. Example 1

[0043] This embodiment discloses an automotive plant fiber sound insulation pad, comprising a surface fiber protective layer, a plant fiber sound-absorbing layer, a permeation-limiting isolation interface layer, and a damping sound insulation layer stacked sequentially.

[0044] The surface fiber protective layer is a polyester nonwoven fabric layer with an areal density of 45 g / m². 2 .

[0045] The plant fiber sound-absorbing layer comprises 45 parts jute fiber, 25 parts bamboo fiber, 18 parts low-melting-point polyester fiber, 6 parts polylactic acid fiber, and 5 parts flame-retardant polyester fiber. The jute fiber is 55 mm long, and the bamboo fiber is 40 mm long. The low-melting-point polyester fiber is a core-sheath type, with a sheath melting point of 125°C and a core of polyethylene terephthalate, each 50 mm long. The polylactic acid fiber is 45 mm long. The flame-retardant polyester fiber is a phosphorus-based copolymer flame-retardant polyester fiber, also 45 mm long. The plant fiber sound-absorbing layer has a thickness of 12.3 mm and a surface density of 846 g / m³. 2 The porosity is 78.4%.

[0046] The permeation-limiting isolation interface layer comprises 48 parts of a second low-melting-point polyester fiber, 18 parts of thermoplastic starch, 16 parts of polylactic acid short fibers, 10 parts of flake inorganic micropowder, and 3 parts of a plasticizer and moisture conditioner. The second low-melting-point polyester fiber is a core-sheath type low-melting-point polyester fiber, with a sheath melting point of 112℃ and a core layer of polyethylene terephthalate with a length of 8 mm. The polylactic acid short fibers have a length of 4 mm. The thermoplastic starch is glycerol-plasticized corn starch with a glycerol content of 18%. The flake inorganic micropowder is flake talc with a D50 particle size of 10 μm, an average aspect ratio of 12, and a moisture content of 0.3%. The plasticizer and moisture conditioner is sorbitol. The thermoplastic starch, flake inorganic micropowder, and plasticizer and moisture conditioner together form a composite dispersed phase, accounting for 32.6% of the total mass of the permeation-limiting isolation interface layer. The surface density of the permeation-limiting isolation interface layer is 64.8 g / m³. 2 .

[0047] The damping sound insulation layer comprises 55 parts ethylene-vinyl acetate copolymer, 18 parts polyolefin elastomer, 30 parts heavy calcium carbonate, 4 parts maleic anhydride-grafted polyolefin, 1 part zinc stearate, and 0.5 parts antioxidant. The ethylene-vinyl acetate copolymer is Sipchem EVA 3522 CO, with a vinyl acetate content of 22% and a melt index of 3.5 g / 10 min. The polyolefin elastomer is Dow Engage. TM 8200 polyolefin elastomer is an ethylene-octene copolymer. The heavy calcium carbonate D50 particle size is 8 μm. The maleic anhydride-grafted polyolefin is from SI Group Polybond. TM 3009 is maleic anhydride-modified high-density polyethylene with a maleic anhydride content of 0.8%–1.2%. The antioxidant used is BASF IRGANOX® 1010 hindered phenolic antioxidant. The damping sound insulation layer has a thickness of 1.02 mm and a surface density of 856 g / m³. 2 .

[0048] The damping sound insulation layer is prepared as follows: ethylene-vinyl acetate copolymer, polyolefin elastomer, maleic anhydride-grafted polyolefin, zinc stearate, and antioxidant are added to a mixer and mixed at 115°C for 6 minutes; heavy calcium carbonate is added and mixing continues for 8 minutes to obtain a damping compound; the damping compound is then calendered into sheets using a two-roll calender at 105°C to obtain a sheet with a thickness of 1.0 mm and a surface density of 850 g / m³. 2 The damping sound insulation layer.

[0049] The automotive plant fiber sound insulation pad of this embodiment is prepared according to the following steps.

[0050] S1. Jute fiber, bamboo fiber, first low-melting-point polyester fiber, polylactic acid fiber, and flame-retardant polyester fiber are respectively fed into an opening machine for pre-opening. After opening, the maximum size of the incompletely loosened fiber bundles in the fiber clump is controlled to be less than 20mm. The opened fibers are dried at 75℃ for 2 hours to achieve a fiber moisture content of 8%. Then, 45 parts of jute fiber, 25 parts of bamboo fiber, 18 parts of first low-melting-point polyester fiber, 6 parts of polylactic acid fiber, and 5 parts of flame-retardant polyester fiber are weighed and sequentially fed into a blending machine for 8 minutes. The mixture is then air-laid to form a plant fiber web. The plant fiber web is then needle-punched to a density of 130 needles / cm². 2 The needle penetration depth is 9mm, and after needle penetration, the material is pre-shaped with hot air at 120℃ for 90s to obtain a plant fiber sound-absorbing layer.

[0051] S2. 48 parts of the second low-melting-point polyester fiber and 16 parts of polylactic acid short fiber are added to a short fiber mixing device and mixed for 5 minutes. Then, an interfacial fiber web is formed by air-jet laying. Separately, 18 parts of thermoplastic starch, 10 parts of flake inorganic powder, and 3 parts of plasticizer / humidifier are added to a mixing container equipped with a paddle agitator and stirred at 70°C for 10 minutes at a stirring speed of 300 r / min to obtain a composite dispersed phase. The composite dispersed phase is distributed in the interfacial fiber web using a vibratory spreading method. After spreading, it is lightly pressed and fixed at a pressure of 0.05 MPa for 15 seconds. By controlling the amount of interfacial fiber web laid and the amount of composite dispersed phase spread, the surface density of the preformed permeability-limiting isolation interfacial layer is made to be 65 g / m³. 2 .

[0052] S3. Lay the surface fiber protective layer flat on one side of the plant fiber sound-absorbing layer, and lay the fiber interface adjustment layer preform flat on the other side of the plant fiber sound-absorbing layer, so that the fiber interface adjustment layer preform covers the surface of the plant fiber sound-absorbing layer facing the damping sound insulation layer. During the laying process, keep each layer free of obvious wrinkles and local accumulation.

[0053] S4. The damping sound insulation layer is bonded to the side of the preformed permeation-limiting isolation interface layer away from the plant fiber sound-absorbing layer, so that the surface fiber protective layer, plant fiber sound-absorbing layer, permeation-limiting isolation interface layer preform, and damping sound insulation layer are stacked in sequence, and then fed into a flat plate hot press for hot pressing composite. The hot pressing composite temperature is 135℃, which is 23℃ higher than the melting point of the second low melting point polyester fiber; the hot pressing pressure is 0.7MPa, and the hot pressing time is 70s.

[0054] S5. Place the hot-pressed composite material into a constant temperature and humidity chamber for wet heat setting. The wet heat setting temperature is 80℃, the relative humidity is 80%, and the processing time is 2 hours, so that the thermoplastic starch softens and bonds in the permeation-limiting isolation interface layer.

[0055] S6. Take out the material after heat setting and cool it flat at 25°C for 8 minutes. Then cut it according to the target size of the car interior sound insulation pad to obtain the car plant fiber sound insulation pad. Example 2

[0056] This embodiment discloses an automotive plant fiber sound insulation pad, which differs from Embodiment 1 in the following aspects.

[0057] The plant fiber sound-absorbing layer comprises 38 parts jute fiber, 32 parts bamboo fiber, 14 parts low-melting-point polyester fiber, 4 parts polylactic acid fiber, and 3 parts flame-retardant polyester fiber. The jute fiber is 40 mm long, and the bamboo fiber is 50 mm long. The first low-melting-point polyester fiber sheath has a melting point of 118℃ and a length of 45 mm. The plant fiber sound-absorbing layer is 8.2 mm thick and has a surface density of 604 g / m³. 2 The porosity is 83.6%.

[0058] The permeation-limiting isolation interface layer comprises 54 parts of a second low-melting-point polyester fiber, 14 parts of thermoplastic starch, 20 parts of polylactic acid short fibers, 8 parts of flake inorganic micropowder, and 3 parts of plasticizer and moisture conditioner. The second low-melting-point polyester fiber sheath has a melting point of 106℃ and a length of 6 mm. The polylactic acid short fibers have a length of 3 mm. The thermoplastic starch is glycerol-plasticized corn starch with a glycerol content of 16%. The flake inorganic micropowder is flake calcium carbonate with a D50 particle size of 6 μm, an average aspect ratio of 9, and a moisture content of 0.4%. The plasticizer and moisture conditioner is glycerol. The composite dispersed phase accounts for 25.3% of the total mass of the permeation-limiting isolation interface layer. The surface density of the permeation-limiting isolation interface layer is 39.7 g / m³. 2 .

[0059] The damping sound insulation layer comprises 50 parts ethylene-vinyl acetate copolymer, 22 parts polyolefin elastomer, 24 parts heavy calcium carbonate, 3 parts maleic anhydride-grafted polyolefin, 0.8 parts zinc stearate, and 0.3 parts antioxidant. The damping sound insulation layer has a thickness of 0.62 mm and a surface density of 458 g / m³. 2 The preparation sequence and mixing and calendering method of the damping sound insulation layer are carried out in accordance with Example 1. Each component is weighed according to the damping sound insulation layer formula of this example, and the corresponding thickness and areal density are obtained by adjusting the calendering gap.

[0060] During the preparation process, the needle density in S1 is 100 needles / cm². 2 The needle-punching depth is 7 mm; in S2, the thermoplastic starch, flake inorganic powder, and plasticizer / humidifier are stirred at 62°C for 8 min; in S4, the hot-pressing composite temperature is 128°C, which is higher than the melting point of the second low-melting-point polyester fiber by 22°C, the hot-pressing pressure is 0.5 MPa, and the hot-pressing time is 55 s; in S5, the wet heat setting temperature is 72°C, the relative humidity is 72%, and the processing time is 1.5 h. The remaining steps are performed in accordance with the method of Example 1. Example 3

[0061] This embodiment discloses an automotive plant fiber sound insulation pad, which differs from Embodiment 1 in the following aspects.

[0062] The plant fiber sound-absorbing layer comprises 53 parts jute fiber, 18 parts bamboo fiber, 23 parts low-melting-point polyester fiber, 9 parts polylactic acid fiber, and 7 parts flame-retardant polyester fiber. The jute fiber is 70 mm long, and the bamboo fiber is 30 mm long. The first low-melting-point polyester fiber sheath has a melting point of 129°C and a length of 60 mm. The plant fiber sound-absorbing layer is 16.4 mm thick and has a surface density of 1192 g / m³. 2 The porosity is 70.8%.

[0063] The permeation-limiting interface layer comprises 43 parts of a second low-melting-point polyester fiber, 22 parts of thermoplastic starch, 13 parts of polylactic acid short fibers, 13 parts of flake-like inorganic micropowder, and 5 parts of a plasticizer and moisture conditioner. The second low-melting-point polyester fiber sheath has a melting point of 118℃ and a length of 12 mm. The polylactic acid short fibers have a length of 5 mm. The thermoplastic starch is glycerol-plasticized cassava starch with a glycerol content of 20%. The flake-like inorganic micropowder is sericite powder with a D50 particle size of 14 μm, an average aspect ratio of 18, and a moisture content of 0.2%. The plasticizer and moisture conditioner is triethyl citrate. The composite dispersed phase accounts for 41.7% of the total mass of the permeation-limiting interface layer. The surface density of the permeation-limiting interface layer is 89.6 g / m³. 2 .

[0064] The damping sound insulation layer comprises 62 parts ethylene-vinyl acetate copolymer, 12 parts polyolefin elastomer, 38 parts heavy calcium carbonate, 5 parts maleic anhydride-grafted polyolefin, 1.5 parts zinc stearate, and 0.8 parts antioxidant. The damping sound insulation layer has a thickness of 1.83 mm and a surface density of 1346 g / m³. 2 The preparation sequence and mixing and calendering method of the damping sound insulation layer are carried out in accordance with Example 1. Each component is weighed according to the damping sound insulation layer formula of this example, and the corresponding thickness and areal density are obtained by adjusting the calendering gap.

[0065] During the preparation process, the needle density in S1 was 165 needles / cm³. 2 The needle-punching depth was 11 mm; in S2, the thermoplastic starch, flake inorganic powder, and plasticizer / humidifier were stirred at 78°C for 14 min; in S4, the hot-pressing composite temperature was 148°C, which is 30°C higher than the melting point of the second low-melting-point polyester fiber, the hot-pressing pressure was 0.9 MPa, and the hot-pressing time was 95 s; in S5, the wet heat setting temperature was 86°C, the relative humidity was 86%, and the processing time was 2.8 h. The remaining steps were performed in accordance with the method of Example 1. Example 4

[0066] This embodiment discloses an automotive plant fiber sound insulation pad, which differs from Embodiment 1 in the following aspects.

[0067] The first low-melting-point polyester fiber sheath has a melting point of 130℃ and a length of 50mm. The second low-melting-point polyester fiber sheath has a melting point of 108℃ and a length of 8mm. The permeation-limiting isolation interface layer comprises 48 parts of the second low-melting-point polyester fiber, 18 parts of thermoplastic starch, 16 parts of polylactic acid short fibers, 10 parts of flake inorganic micropowder, and 3 parts of plasticizer and moisture conditioner. The composite dispersed phase accounts for 32.6% of the total mass of the permeation-limiting isolation interface layer.

[0068] In S4, the hot-pressing temperature is 136°C, which is higher than the melting point of the second low-melting-point polyester fiber (28°C); the hot-pressing pressure is 0.7 MPa, and the hot-pressing time is 70 s. The remaining raw materials, layer structure, and preparation steps are performed in accordance with the method of Example 1. Example 5

[0069] This embodiment discloses an automotive plant fiber sound insulation pad, which differs from Embodiment 1 in the following aspects.

[0070] The second low-melting-point polyester fiber has a length of 10 mm, and the polylactic acid (PLA) short fiber has a length of 3 mm, with a length ratio of 3.3:1. The melting point of the second low-melting-point polyester fiber sheath is 112℃. The permeation-limiting isolation interface layer comprises 48 parts of the second low-melting-point polyester fiber, 18 parts of thermoplastic starch, 16 parts of PLA short fiber, 10 parts of flake-like inorganic micropowder, and 3 parts of plasticizer and moisture conditioner. The surface density of the permeation-limiting isolation interface layer is 65 g / m³. 2 The remaining raw materials, layer structure, and preparation steps were performed in accordance with the method described in Example 1.

[0071] The following comparative examples illustrate the impact of different variables on the structure and performance of automotive plant fiber sound insulation pads.

[0072] Comparative Example 1 Comparative Example 1 provides an automotive plant fiber sound insulation pad, which differs from Example 1 in that it does not include a permeation-limiting isolation interface layer. During preparation, S1 prepares the plant fiber sound-absorbing layer according to Example 1; S2 and S3 are omitted; in S4, the damping sound insulation layer is directly bonded to one side of the plant fiber sound-absorbing layer and hot-pressed at 135°C and 0.7 MPa for 70 seconds; in S5, it is treated at 80°C and 80% relative humidity for 2 hours to maintain the same post-treatment conditions as Example 1; in S6, it is cooled and cut. The raw materials and parameters of the surface fiber protective layer, the plant fiber sound-absorbing layer, and the damping sound insulation layer are all performed according to the method of Example 1.

[0073] Comparative Example 2 Comparative Example 2 provides an automotive plant fiber sound insulation pad, which differs from Example 1 in that the second low-melting-point polyester fiber is a core-sheath type low-melting-point polyester fiber with a sheath melting point of 125°C, making the sheath melting points of the first and second low-melting-point polyester fibers the same. The first low-melting-point polyester fiber is 50 mm long, and the second low-melting-point polyester fiber is 8 mm long. The hot-pressing composite temperature in S4 is 135°C, which is 10°C higher than the melting point of the second low-melting-point polyester fiber. The remaining raw materials, layer structure, and preparation steps are performed in accordance with the method of Example 1.

[0074] Comparative Example 3 Comparative Example 3 provides an automotive plant fiber sound insulation pad, which differs from Example 1 in that the length of the second low-melting-point polyester fiber is 3 mm, and the length of the polylactic acid short fiber is 6 mm. The length of the second low-melting-point polyester fiber is shorter than that of the polylactic acid short fiber. The melting point of the second low-melting-point polyester fiber sheath is 112°C, and the material of the polylactic acid short fiber remains unchanged. The remaining raw materials, layer structure, and preparation steps are performed in accordance with the method of Example 1.

[0075] Comparative Example 4 Comparative Example 4 provides an automotive plant fiber sound insulation pad, which differs from Example 1 in that thermoplastic starch is not added to the permeation-limiting interfacial layer, and the amount of the second low-melting-point polyester fiber is adjusted to 66 parts, while the amounts of polylactic acid short fibers (16 parts), flake inorganic powder (10 parts), and plasticizer / humidifier (3 parts) remain unchanged. Since thermoplastic starch is not added, the flake inorganic powder and plasticizer / humidifier serve as interfacial filler components, accounting for 13.7% of the total mass of the permeation-limiting interfacial layer. In step S2, the flake inorganic powder and plasticizer / humidifier are stirred at 70°C for 10 minutes and then distributed in the interfacial fiber web. The remaining raw materials, layer structure, and preparation steps are performed as in Example 1.

[0076] Comparative Example 5 Comparative Example 5 provides an automotive plant fiber sound insulation pad, which differs from Example 1 in that no flake inorganic powder is added to the permeation-limiting interfacial layer, and the amount of thermoplastic starch is adjusted to 28 parts, while the amounts of second low-melting-point polyester fiber (48 parts), polylactic acid short fiber (16 parts), and plasticizer (3 parts) remain unchanged. The thermoplastic starch and plasticizer are used as interfacial filler components, and their combined mass accounts for 32.6% of the total mass of the permeation-limiting interfacial layer. In step S2, the thermoplastic starch and plasticizer are stirred at 70°C for 10 minutes and then distributed in the interfacial fiber web. The remaining raw materials, layer structure, and preparation steps are performed in accordance with the method of Example 1.

[0077] Comparative Example 6 Comparative Example 6 provides an automotive plant fiber sound insulation pad, which differs from Example 1 in that no plasticizer or moisture conditioner is added to the permeation-limiting interfacial layer, and the amount of thermoplastic starch is adjusted to 21 parts, while the amounts of the second low-melting-point polyester fiber (48 parts), polylactic acid short fiber (16 parts), and flake inorganic powder (10 parts) remain unchanged. The thermoplastic starch and flake inorganic powder are used as interfacial filler components, and their combined mass accounts for 32.6% of the total mass of the permeation-limiting interfacial layer. In step S2, the thermoplastic starch and flake inorganic powder are stirred at 70°C for 10 minutes and then distributed in the interfacial fiber network. The remaining raw materials, layer structure, and preparation steps are performed in accordance with the method of Example 1.

[0078] Comparative Example 7 Comparative Example 7 provides an automotive plant fiber sound insulation pad, which differs from Example 1 in that the impermeable barrier interface layer comprises 56 parts of a second low-melting-point polyester fiber, 8 parts of thermoplastic starch, 22 parts of polylactic acid short fibers, 6 parts of flake inorganic powder, and 2 parts of a plasticizer and moisture conditioner. The composite dispersed phase formed by the thermoplastic starch, flake inorganic powder, and plasticizer and moisture conditioner accounts for 17.0% of the total mass of the impermeable barrier interface layer. The second low-melting-point polyester fiber skin has a melting point of 112°C and a length of 8 mm; the polylactic acid short fibers have a length of 4 mm. The surface density of the impermeable barrier interface layer is 65 g / m³. 2 The remaining raw materials, layer structure, and preparation steps were performed in accordance with the method described in Example 1.

[0079] Comparative Example 8 Comparative Example 8 provides an automotive plant fiber sound insulation pad, which differs from Example 1 in that the impermeable isolation interface layer comprises 34 parts of a second low-melting-point polyester fiber, 28 parts of thermoplastic starch, 10 parts of polylactic acid short fibers, 16 parts of flake inorganic powder, and 5 parts of a plasticizer and moisture conditioner. The composite dispersed phase formed by the thermoplastic starch, flake inorganic powder, and plasticizer and moisture conditioner accounts for 52.7% of the total mass of the impermeable isolation interface layer. The second low-melting-point polyester fiber skin has a melting point of 112°C and a length of 8 mm; the polylactic acid short fibers have a length of 4 mm. The surface density of the impermeable isolation interface layer is 65 g / m³. 2 The remaining raw materials, layer structure, and preparation steps were performed in accordance with the method described in Example 1.

[0080] Comparative Example 9 Comparative Example 9 provides an automotive plant fiber sound insulation pad, which differs from Example 1 in that it does not undergo heat-setting during preparation. Steps S1 to S4 are performed as in Example 1; after hot-pressing, the heat-setting process in Step S5 of Example 1 is not performed. Instead, the hot-pressed material is directly laid flat and cooled at 25°C for 8 minutes before being cut into automotive plant fiber sound insulation pads. The remaining raw materials, layer structure, and hot-pressing parameters are performed as in Example 1.

[0081] Comparative Example 10 Comparative Example 10 provides a conventional fiber composite sound insulation mat, comprising a surface fiber protective layer, a plant fiber sound-absorbing layer, and a damping sound insulation layer, without a fiber interface conditioning layer. The plant fiber sound-absorbing layer comprises 45 parts jute fiber, 25 parts bamboo fiber, 18 parts first low-melting-point polyester fiber, 6 parts polylactic acid fiber, and 5 parts flame-retardant polyester fiber. The first low-melting-point polyester fiber sheath has a melting point of 125°C and a length of 50 mm. The composition of the surface fiber protective layer and the damping sound insulation layer is as described in Example 1. During preparation, the surface fiber protective layer, the plant fiber sound-absorbing layer, and the damping sound insulation layer are sequentially stacked, hot-pressed at 135°C and 0.7 MPa for 70 s, then laid flat to cool for 8 min at 25°C and cut to obtain the conventional fiber composite sound insulation mat.

[0082] The automotive plant fiber sound insulation pads prepared in Examples 1-5 and Comparative Examples 1-9 were subjected to performance testing. Before testing, all samples were placed in an environment with a temperature of 23°C and a relative humidity of 50% for 24 hours to equilibrate. Three samples were taken from each group for testing, and the data in the table are the average values ​​of the three samples.

[0083] 1. Interlayer peel strength test The automotive plant fiber sound insulation pads prepared in the various embodiments and comparative examples were cut into strips 25 mm wide and 200 mm long. Approximately 50 mm of the strips were pre-peeled between the plant fiber sound-absorbing layer and the damping sound insulation layer to serve as a clamping end. A 180° peel test was performed using an electronic universal testing machine at a tensile speed of 100 mm / min. The average peel force during the stable peeling stage was recorded, and the interlayer peel strength was expressed as N / 25 mm. This test was used to evaluate the composite stability between the plant fiber sound-absorbing layer, the permeation-limiting isolation interface layer, and the damping sound insulation layer.

[0084] 2. Airflow resistance detection The automotive plant fiber sound insulation pads prepared in each embodiment and comparative example were cut into circular samples with a diameter of 100 mm and tested using an airflow resistance tester. During the test, air was passed perpendicularly through the thickness direction of the sample, and the test pressure difference was controlled at 100 Pa. The airflow resistance per unit area was recorded, and the results were expressed in Pa·s / m. This test is used to evaluate the overall airflow obstruction state of the sound insulation pad. Too low airflow resistance indicates insufficient interfacial barrier and interlayer adjustment, while too high airflow resistance indicates that the airflow path of the porous fiber sound-absorbing layer is significantly affected.

[0085] 3. Sound absorption coefficient test The automotive plant fiber sound insulation pads prepared in each embodiment and comparative example were cut into circular samples matching the impedance tubes. The normal incident sound absorption coefficient of the samples at different frequencies was tested using the standing wave tube method. The test frequencies were 500Hz, 1000Hz, 2000Hz, and 3150Hz, and the average sound absorption coefficient in the 1000–3150Hz frequency band was calculated. This test was used to evaluate the absorption capacity of the plant fiber sound-absorbing layer for mid-to-high frequency noise after being composited into a sound insulation pad.

[0086] 4. Insertion loss detection The automotive plant fiber sound insulation pads prepared in each embodiment and comparative example were cut into 300mm × 300mm plate-shaped samples and placed between the sound source side and the receiving side of a small acoustic test chamber, keeping the sample edges sealed. The sound pressure level on the receiving side was recorded in both the no-sample and sample-installed states. Test frequencies of 500Hz, 1000Hz, and 2000Hz were selected. Insertion loss was calculated based on the difference in sound pressure level between the no-sample and sample-installed states, and the average insertion loss in the 500–2000Hz frequency band was also calculated. This test is used to evaluate the attenuation capability of damping sound insulation layers and composite interfaces on the propagation of mid-to-low frequency noise.

[0087] 5. Performance retention rate test after damp heat treatment The automotive plant fiber sound insulation pads prepared in each embodiment and comparative example were placed in a constant temperature and humidity chamber and treated for 72 hours at 85°C and 85% relative humidity. After removal, they were equilibrated for 4 hours in an environment with 23°C and 50% relative humidity. Subsequently, the interlaminar peel strength and the average sound absorption coefficient from 1000 to 3150 Hz were tested after damp heat treatment according to the above-mentioned interlaminar peel strength test method and sound absorption coefficient test method, and the interlaminar peel strength retention rate and sound absorption coefficient retention rate after damp heat treatment were calculated.

[0088] The test results are shown in Table 1 below.

[0089] Table 1 Example 1 3.42 1820 0.66 15.2 92.4 94.1 Example 2 2.86 1465 0.64 13.8 89.7 92.6 Example 3 3.88 2260 0.61 16.4 91.5 90.8 Example 4 3.56 1768 0.67 15.5 93.2 94.5 Example 5 3.61 1715 0.68 15.4 93.8 95.0 Comparative Example 1 1.74 2840 0.49 12.6 71.3 78.4 Comparative Example 2 2.45 2315 0.55 13.4 82.6 84.2 Comparative Example 3 2.18 2048 0.56 13.1 79.8 85.7 Comparative Example 4 2.36 1388 0.57 12.9 76.5 82.1 Comparative Example 5 2.68 1265 0.58 12.7 84.0 86.5 Comparative Example 6 2.74 1942 0.6 13.5 75.8 83.6 Comparative Example 7 2.41 1216 0.59 12.4 81.7 87.2 Comparative Example 8 3.12 3185 0.47 14.1 86.4 76.9 Comparative Example 9 2.97 1805 0.62 14.6 74.9 84.8 Comparative Example 10 1.96 2658 0.51 12.9 73.8 80.6 As shown in Table 1, the interlayer peel strength of Examples 1-5 is all higher than 2.80 N / 25 mm, the average sound absorption coefficient of 1000-3150 Hz is not lower than 0.61, and the average insertion loss of 500-2000 Hz is not lower than 13.8 dB. This indicates that after using the permeability-limiting isolation interface layer, a relatively stable composite interface can be formed between the plant fiber sound-absorbing layer and the damping sound insulation layer, while maintaining good sound absorption and sound insulation effects. The airflow resistance of Examples 1-5 is between 1465 and 2260 Pa·s / m, indicating that the sound insulation pad as a whole has a moderate airflow resistance state, without showing insufficient interface adjustment or excessive closure of the porous fiber layer.

[0090] In Comparative Example 1, without a permeation-limiting isolation interface layer, the interlayer peel strength decreased to 1.74 N / 25 mm, and the average sound absorption coefficient from 1000 to 3150 Hz decreased to 0.49. This indicates that when the damping sound insulation layer is directly hot-pressed with the plant fiber sound-absorbing layer, both the interlayer bonding stability and sound absorption retention effect are affected. In Comparative Example 2, the first and second low-melting-point polyester fibers have the same melting point, but the interlayer peel strength, sound absorption coefficient, and performance retention rate after humid heat are all lower than in Example 1. This indicates that using low-melting-point polyester fibers with different melting points for the plant fiber sound-absorbing layer and the permeation-limiting isolation interface layer is more conducive to forming a layered thermally bonded state. In Comparative Example 3, the length of the second low-melting-point polyester fiber is shorter than that of the polylactic acid short fiber, resulting in a decrease in interlayer peel strength and the retention rate of peel strength after humid heat. This indicates that a longer second low-melting-point polyester fiber is more conducive to forming a bridging bond and support structure in the interface layer.

[0091] Comparative Example 4 did not contain thermoplastic starch, Comparative Example 5 did not contain flake inorganic powder, and Comparative Example 6 did not contain plasticizer or moisture conditioner. The overall performance of all three was lower than that of Example 1. Among them, Comparative Example 4 showed a significant decrease in interlayer peel strength and insertion loss, indicating that thermoplastic starch plays an important role in interfacial flexible bonding and filling stability. Comparative Example 5 showed lower airflow resistance and insertion loss, indicating that flake inorganic powder contributes to the interfacial filling path and sound barrier effect. Comparative Example 6 showed a lower peel strength retention rate after humid heat, indicating that plasticizer and moisture conditioner help regulate the softened bonding state of thermoplastic starch under humid heat conditions and improve interfacial stability after humid heat.

[0092] In Comparative Example 7, the proportion of the composite dispersed phase was below the specified range, resulting in lower airflow resistance and insertion loss. This indicates that insufficient composite dispersed phase leads to inadequate filling adjustment and interfacial barrier effects of the permeability-limiting isolation interface layer. In Comparative Example 8, the proportion of the composite dispersed phase was too high. Although the interlayer peel strength remained at a certain level, the airflow resistance increased to 3185 Pa·s / m, and the average sound absorption coefficient from 1000 to 3150 Hz decreased to 0.47. This suggests that excessive composite dispersed phase can cause the interface layer to become too dense, affecting the effective airflow and sound absorption of the plant fiber sound-absorbing layer. In Comparative Example 9, after the removal of hygrothermal setting, the peel strength retention rate and sound absorption coefficient retention rate after hygrothermal setting were significantly lower than in Example 1. This indicates that hygrothermal setting helps the thermoplastic starch to further soften and bond within the permeability-limiting isolation interface layer, and improves the performance retention of the sound insulation pad under hygrothermal conditions.

[0093] The above description is merely a preferred embodiment of the present invention. The scope of protection of the present invention is not limited to the above embodiments. All technical solutions falling within the scope of the present invention's concept are within the scope of protection of the present invention. It should be noted that for those skilled in the art, any improvements and modifications made without departing from the principles of the present invention should also be considered within the scope of protection of the present invention.

Claims

1. A car plant fiber sound insulation pad, characterized in that, It includes a surface fiber protective layer, a plant fiber sound-absorbing layer, a permeation-limiting isolation interface layer, and a damping sound insulation layer, which are stacked in sequence. The surface fiber protective layer is a polyester nonwoven fabric layer, a polylactic acid nonwoven fabric layer, or a polyester / polylactic acid composite nonwoven fabric layer, and the areal density of the surface fiber protective layer is 25-80 g / m². 2 And it is hot-pressed and composited on the side of the plant fiber sound-absorbing layer away from the permeation-limiting isolation interface layer; The plant fiber sound-absorbing layer includes jute fiber, bamboo fiber, and a first low-melting-point polyester fiber; The permeation-limiting isolation interface layer is located between the plant fiber sound-absorbing layer and the damping sound insulation layer. The permeation-limiting isolation interface layer includes an interface support skeleton formed by interwoven second low-melting-point polyester fibers and polylactic acid short fibers, as well as thermoplastic starch, flake inorganic powder and plasticizer and moisture conditioner distributed in the interface support skeleton. The first low-melting-point polyester fiber has a melting point of 115-130°C, and the second low-melting-point polyester fiber has a melting point of 105-120°C; and the melting point of the first low-melting-point polyester fiber is 5-25°C higher than the melting point of the second low-melting-point polyester fiber. The length of the second low-melting-point polyester fiber is greater than the length of the polylactic acid short fiber; The D50 particle size of the flaky inorganic micro powder is 5-15 μm, and the average aspect ratio is 8-20. The thermoplastic starch, the flaky inorganic powder, and the plasticizer and moisture conditioner together form a composite dispersed phase, which accounts for 25% to 42% of the total mass of the permeation-limiting and isolating interface layer. The damping sound insulation layer is hot-pressed together with the plant fiber sound absorption layer through the permeability-limiting isolation interface layer.

2. The automotive plant fiber sound insulation pad according to claim 1, characterized in that, The plant fiber sound-absorbing layer comprises, by weight: 35-55 parts jute fiber, 15-35 parts bamboo fiber, 12-24 parts first low-melting-point polyester fiber, 3-10 parts polylactic acid fiber, and 2-8 parts flame-retardant polyester fiber.

3. The automotive plant fiber sound insulation pad according to claim 2, characterized in that, The jute fiber has a length of 35–75 mm, the bamboo fiber has a length of 25–55 mm, and the porosity of the plant fiber sound-absorbing layer is 68%–88%.

4. The automotive plant fiber sound insulation pad according to claim 1, characterized in that, The permeation-limiting isolation interface layer comprises, by weight: 42-54 parts of second low-melting-point polyester fiber, 14-22 parts of thermoplastic starch, 12-20 parts of polylactic acid short fiber, 7-13 parts of flake inorganic powder, and 2-5 parts of plasticizer and moisture-regulating agent. The areal density of the permeation-limiting isolation interface layer is 35-95 g / m³. 2 .

5. The automotive plant fiber sound insulation pad according to claim 1, characterized in that, The second low-melting-point polyester fiber in the permeation-limiting isolation interface layer has a length of 4-12 mm, the polylactic acid short fiber has a length of 2-8 mm, and the length ratio of the second low-melting-point polyester fiber to the polylactic acid short fiber is 1.5-4:

1.

6. The automotive plant fiber sound insulation pad according to claim 1, characterized in that, The thermoplastic starch is glycerol-plasticized corn starch or glycerol-plasticized cassava starch; the plasticizer and moisture conditioner is one or more of glycerol, sorbitol, or triethyl citrate; the mass ratio of the thermoplastic starch to the plasticizer and moisture conditioner is 4 to 10:

1.

7. The automotive plant fiber sound insulation pad according to claim 1, characterized in that, The flaky inorganic powder is one or more of flaky talc powder, sericite powder, or flaky calcium carbonate; the mass ratio of the thermoplastic starch to the flaky inorganic powder is 1.2 to 3.0:

1.

8. The automotive plant fiber sound insulation pad according to claim 1, characterized in that, The damping sound insulation layer comprises, by weight: 45-65 parts of ethylene-vinyl acetate copolymer, 10-25 parts of polyolefin elastomer, 20-40 parts of heavy calcium carbonate, 2-6 parts of maleic anhydride-grafted polyolefin, 0.5-2 parts of zinc stearate, and 0.2-1 parts of antioxidant.

9. A method for preparing an automotive plant fiber sound insulation pad according to any one of claims 1 to 8, characterized in that, Includes the following steps: S1: Mix jute fiber, bamboo fiber, first low melting point polyester fiber, polylactic acid fiber and flame retardant polyester fiber, lay them into a web and needle punch them to obtain a plant fiber sound-absorbing layer; S2: Mix the second low-melting-point polyester fiber and polylactic acid short fiber and lay them into an interface fiber network. Mix thermoplastic starch, flake inorganic powder and plasticizer moisture conditioner to form a composite dispersed phase and distribute the composite dispersed phase in the interface fiber network to obtain a permeation-limiting isolation interface layer preform. S3: Lay the surface fiber protective layer on one side of the plant fiber sound-absorbing layer, and lay the fiber interface conditioning layer preform on the other side of the plant fiber sound-absorbing layer. S4: The damping sound insulation layer is attached to the side of the fiber interface conditioning layer preform away from the plant fiber sound absorption layer, so that the surface fiber protective layer, the plant fiber sound absorption layer, the fiber interface conditioning layer preform and the damping sound insulation layer are stacked in sequence and then hot-pressed together. S5: Perform wet heat setting on the hot-pressed composite material to soften and bond the thermoplastic starch within the permeation-limiting isolation interface layer; S6: Cool and cut the material after wet heat setting to obtain automotive plant fiber sound insulation pad.

10. The preparation method according to claim 9, characterized in that, In step S2, thermoplastic starch, flake inorganic powder, and plasticizer / humidifier are stirred at 60–80°C for 5–15 min to obtain a composite dispersed phase. The composite dispersed phase accounts for 25%–42% of the total mass of the preformed permeability-limiting and insulating interface layer, and the areal density of the preformed permeability-limiting and insulating interface layer is 35–95 g / m³. 2 ; In step S4, the hot-pressing temperature is 125-150°C, and the hot-pressing temperature is 5-35°C higher than the melting point of the second low-melting-point polyester fiber; the pressure is 0.4-1.0 MPa; and the time is 45-100 s. In step S5, the temperature for wet heat setting is 70–88℃, the relative humidity is 70%–88%, and the processing time is 1–3 hours.