Biobased composite carpet and method of production thereof

Abstract

The application provides a bio-based composite carpet and a production method thereof. The bio-based composite carpet is made by hot-pressing and compounding at least three layers of fiber webs, the three layers of fiber webs comprising: a first layer of fiber web with an area density of 750 g / m2-850 g / m2, comprising polylactic acid sheath-core fibers and surface-modified hemp fibers; a second layer of fiber web with an area density of 600 g / m2-750 g / m2, comprising hollow fibers, polylactic acid sheath-core fibers and surface-modified hemp fibers; and a third layer of fiber web with an area density of 900 g / m2-1100 g / m2, comprising hollow fibers, polylactic acid sheath-core fibers and surface-modified hemp fibers; the polylactic acid sheath-core fibers comprise a sheath layer and a core layer, the sheath layer comprises a first polylactic acid, and the core layer comprises a second polylactic acid, the melting point of the first polylactic acid is lower than that of the second polylactic acid, and the three layers of fiber webs are bonded together by the melted first polylactic acid. The application reduces the complexity of the process and the processing cost.

Description

Technical Field

[0001] This invention relates to the field of automotive interior technology, and more particularly to bio-based composite carpets and their production methods. Background Technology

[0002] Automotive carpets are carpet products used inside automobiles. Primarily for decorative purposes, they not only provide dust and slip resistance but are also easy to clean and maintain.

[0003] To improve the appearance and texture while taking into account acoustic performance, automotive carpets generally adopt a multi-layer composite structure: the first layer is a polyethylene terephthalate (PET) tufted or needle-punched woolen surface layer, the second layer is an ethylene-vinyl acetate copolymer (EVA) or ethylene propylene diene monomer (EPDM) heavy-duty sound insulation layer, and the third layer is a polyurethane (PU) foamed sound absorption layer.

[0004] However, this structure has the following technical drawbacks: (1) Environmental issues: Multi-layer heterogeneous material composites require the use of adhesives, and at high temperature environments, they are prone to volatilizing organic compounds such as acetaldehyde and acrolein, which is not environmentally friendly; (2) Difficulty in recycling: The composite of heterogeneous materials makes it difficult to separate and recycle the vehicle after it is scrapped; (3) Complex process: It requires multiple molding processes (including surface weaving, heavy layer lamination, foam layer composite, etc.), resulting in high energy consumption and tooling costs; (4) Bottleneck of appearance of bio-based materials: In the existing technology, although there are studies on the preparation of car carpets using bio-based materials such as natural plant fibers and polylactic acid (PLA), natural fibers have uneven color, many surface burrs and rough touch, which makes it difficult to meet the appearance requirements of passenger car interiors.

[0005] (5) The surface layer cannot achieve both density and abrasion resistance: In order to achieve good abrasion resistance, hemp fibers are usually added to the surface layer. However, hemp fibers have many burrs on the surface, making it difficult to adhere tightly and stack the fibers tightly, thus failing to form a dense surface layer, resulting in poor dust and stain resistance of the carpet.

[0006] Furthermore, the sound absorption performance of existing automotive carpets needs further improvement. Summary of the Invention

[0007] This invention provides a bio-based composite carpet and its production method to solve the technical problems of existing automotive carpets, such as being environmentally unfriendly, difficult to recycle, having complex processes, poor appearance of bio-based carpets, and the inability to balance density and wear resistance of the surface layer, and to improve the sound absorption performance of carpets.

[0008] To achieve the above objectives, the technical solution of the present invention is as follows: This invention provides a bio-based composite carpet, which is made by hot-pressing at least three layers of fiber webs, the three layers of fiber webs comprising: First fiber web layer: with a surface density of 750g / m²-850g / m², preferably 780g / m²-850g / m²; the first fiber web layer includes polylactic acid core-sheath fibers and surface-modified hemp fibers, wherein the surface-modified hemp fibers are prepared by modifying hemp fibers with surface gum removed by an epoxy silane coupling agent; The second fiber web layer has a surface density of 600g / m²-750g / m², preferably 650g / m²-750g / m², and is located on the bottom side of the first fiber web layer. The second fiber web layer includes hollow fibers, the polylactic acid core-sheath fibers, and the surface-modified hemp fibers. The third fiber web layer has a surface density of 900 g / m²-1100 g / m², preferably 950 g / m²-1100 g / m², and is located on the bottom side of the second fiber web layer. The third fiber web layer includes the hollow fiber, the polylactic acid core fiber, and the surface-modified hemp fiber. The polylactic acid core-sheath fiber includes a sheath layer and a core layer. The sheath layer includes a first polylactic acid, and the core layer includes a second polylactic acid. The melting point of the first polylactic acid is lower than that of the second polylactic acid. The first fiber web layer, the second fiber web layer, and the third fiber web layer are bonded together by the molten first polylactic acid. In one embodiment of the present invention, the content of hollow fibers in the second fiber web layer is less than the content of hollow fibers in the third fiber web layer, and the content of polylactic acid core-sheath fibers gradually decreases along the direction from the first fiber web layer to the third fiber web layer.

[0009] In one embodiment of the present invention, the mass percentage of polylactic acid core-sheath fibers in the first fiber web layer is 35%-45%, preferably 38%-45%; the mass percentage of polylactic acid core-sheath fibers in the second fiber web layer is 25%-34%, preferably 28%-34%; and the mass percentage of polylactic acid core-sheath fibers in the third fiber web layer is 15%-24%, preferably 18%-22%.

[0010] In one embodiment of the present invention, the mass percentage of hollow fibers in the second fiber web layer is 25%-35%, preferably 28%-35%; the mass percentage of hollow fibers in the third fiber web layer is 55%-65%, preferably 58%-65%.

[0011] In one embodiment of the present invention, the hollow fiber includes at least one of straw fiber, straw-husk composite fiber and palm fiber.

[0012] In one embodiment of the present invention, the hollow fiber is a fiber obtained by opening treatment and bio-enzyme pretreatment, wherein the bio-enzyme includes cellulase and / or xylanase.

[0013] In one embodiment of the present invention, the total thickness of the three-layer fiber web is 12mm-15mm, preferably 13mm-15mm.

[0014] In one embodiment of the present invention, the thickness of the first fiber web layer accounts for 15%-19% of the total thickness of the three fiber web layers, preferably 16%-19%.

[0015] In one embodiment of the present invention, the thickness of the second fiber web layer accounts for 25%-30% of the total thickness of the three fiber web layers, preferably 28%-30%.

[0016] In one embodiment of the present invention, the first fiber web layer further includes colored polylactic acid fibers.

[0017] In one embodiment of the present invention, the bio-based composite carpet further includes a finishing layer, which is located on the top side of the first fiber web layer. The finishing layer includes a bio-based polyurethane film layer or an aqueous bio-based polyurethane coating located on the top surface of the first fiber web layer.

[0018] In one embodiment of the present invention, the bottom surface of the third fiber web layer is covered with first needle-punched micropores.

[0019] In one embodiment of the present invention, the depth of the first needle-punched micropore is 4mm-6mm, preferably 4.5mm-6mm.

[0020] In one embodiment of the present invention, the distribution density of the first needle-punched micropores is 100-150 per cm², preferably 120-150 per cm².

[0021] In one embodiment of the present invention, the three-layer fiber mesh is covered with second needle-punched micropores penetrating the first fiber mesh layer, the second fiber mesh layer and the third fiber mesh layer.

[0022] This invention also provides a method for producing a bio-based composite carpet as described above, the method comprising the following steps: S1. The polylactic acid core fiber and surface-modified hemp fiber are made into a fiber web with an areal density of 750g / m²-850g / m² to obtain the first fiber web; S2. The hollow fiber, polylactic acid core fiber and surface-modified hemp fiber are made into a fiber web with an areal density of 600g / m²-750g / m² to obtain a second fiber web; S3. The hollow fibers, polylactic acid core fibers and surface-modified hemp fibers are made into a fiber web with an areal density of 900g / m²-1100g / m² to obtain a third fiber web; S4. Stack the first fiber web, the second fiber web and the third fiber web in sequence, needle punch, preheat, hot press composite, cool, and obtain the bio-based composite carpet; The temperature of the hot-pressed composite is higher than the melting point of the first polylactic acid and lower than the melting point of the second polylactic acid.

[0023] In one embodiment of the present invention, in step S4, the temperature is preheated to 100°C-120°C, preferably 110°C-120°C.

[0024] In one embodiment of the present invention, in step S4, the temperature of the hot pressing composite is 155℃-163℃, preferably 158℃-163℃; the duration of the hot pressing composite is 60s-75s, preferably 65s-75s.

[0025] In one embodiment of the present invention, in step S4, the temperature is cooled to 25°C-60°C, preferably 25°C-35°C.

[0026] The beneficial effects of this invention are: In this application, the first, second, and third fiber web layers all contain polylactic acid (PLA) core-sheath fibers. During the subsequent hot-pressing process, the hot-pressing temperature is higher than the melting point of the first PLA fiber (serving as the sheath layer) but lower than the melting point of the second PLA fiber (serving as the core layer). Therefore, the first PLA fiber, with its lower melting point, melts during the subsequent hot-pressing process, while the second PLA fiber, serving as the core layer, is retained, thus preserving the fiber skeleton. The molten first PLA fiber acts as an adhesive, bonding the first, second, and third fiber web layers together. This achieves good bonding strength and preserves the fiber skeleton without the addition of external adhesives, thus achieving "effective bonding" while retaining the fiber skeleton. This method enhances the mechanical strength and toughness of the carpet through an in-situ self-reinforcing mechanism. Furthermore, this application allows for integrated molding, reducing process complexity and processing costs. Secondly, this application eliminates the need for external adhesives, avoiding the environmental problems associated with adding synthetic adhesives. Furthermore, the hollow fiber, polylactic acid core fiber, and surface-modified hemp fiber used in this application are all bio-based materials, which are green, environmentally friendly, and easy to recycle.

[0027] In this application, the content of hollow fibers in the second fiber web layer is less than that in the third fiber web layer. In other words, from the first fiber web layer to the third fiber web layer, this application constructs a porous sound energy dissipation path with a gradually increasing hollow fiber content, i.e., a "pore gradient" structure with increasing pore density. This porous sound energy dissipation path, combined with the first needle-punched micropore structure on the surface of the third fiber web layer, enables mid-to-low frequency sound energy to be gradually dissipated through the pore structure along the direction of the needle-punched micropores from the first fiber web layer to the third fiber web layer, enhancing the dissipation capability of mid-to-low frequency sound energy and thus improving the sound absorption performance of the carpet. Simultaneously, the content of polylactic acid core-sheath fibers gradually decreases along the direction of the first fiber web layer to the third fiber web layer. In other words, from the third fiber web layer to the first fiber web layer, this application constructs a sound energy impedance path with a gradually increasing polylactic acid core-sheath fiber content. The third fiber layer has the lowest polylactic acid (PLA) core-sheath fiber content and the lowest density of the cured adhesive formed by the molten first PLA. Noise from the carpet underside (such as tire noise and chassis vibration noise) can enter the carpet interior with minimal reflection loss. The second fiber layer has a slightly higher PLA core-sheath fiber content and relatively higher density of the cured adhesive formed by the molten first PLA. It can form a "gradually increasing impedance dissipation channel" with the third and first fiber layers, where sound waves experience continuous and smooth viscous friction as they propagate, gradually converting sound energy into heat energy for dissipation. The first fiber layer has the highest PLA core-sheath fiber content and high density of the cured adhesive formed by the molten first PLA, exhibiting the highest sound impedance. This constitutes a "high-impedance acoustic reflection," reflecting most of the residual sound energy penetrating the first fiber layer back into the carpet interior. This energy is then dissipated again via the second and third fiber layers on the return path, further enhancing the carpet's sound absorption performance. In summary, the gradient changes in polylactic acid core fiber content and hollow fiber gradients together construct a dual gradient structure of "impedance gradient" and "pore gradient". The two work synergistically to give the carpet excellent broadband sound absorption performance. Attached Figure Description

[0028] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with this application and, together with the description, serve to explain the principles of this application. It is obvious that the drawings described below are merely some embodiments of this application, and those skilled in the art can obtain other drawings based on these drawings without any inventive effort.

[0029] In the attached diagram: Figure 1 This is a schematic diagram of the structure of a bio-based composite carpet provided in one embodiment of the present invention; Figure 2 A schematic diagram of the structure of a bio-based composite carpet provided in another embodiment of the present invention; Figure 3 A process flow diagram of a method for producing a bio-based composite carpet according to an embodiment of the present invention.

[0030] The attached figures are labeled as follows: First fiber mesh layer 1, second fiber mesh layer 2, third fiber mesh layer 3, finishing layer 4. Detailed Implementation

[0031] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the 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.

[0032] It should be noted that all directional indicators (such as top, bottom, etc.) in the embodiments of the present invention are only used to explain the relative positional relationship and movement of each component in a certain specific posture (as shown in the figure). If the specific posture changes, the directional indicator will also change accordingly.

[0033] To improve the appearance and texture while taking into account acoustic performance, automotive carpets generally adopt a multi-layer composite structure: the first layer is a polyethylene terephthalate (PET) tufted or needle-punched woolen surface layer, the second layer is an ethylene-vinyl acetate copolymer (EVA) or ethylene propylene diene monomer (EPDM) heavy-duty sound insulation layer, and the third layer is a polyurethane (PU) foamed sound absorption layer.

[0034] After analyzing the relevant technologies, the inventors discovered the following technical defects in the carpet with the above-mentioned structure: (1) Environmental issues: Multi-layer heterogeneous material composites require the use of adhesives, and at high temperature environments, they are prone to volatilizing organic compounds such as acetaldehyde and acrolein, which is not environmentally friendly; (2) Difficulty in recycling: The composite of heterogeneous materials makes it difficult to separate and recycle the vehicle after it is scrapped; (3) Complex process: It requires multiple molding processes (including surface weaving, heavy layer lamination, foam layer composite, etc.), resulting in high energy consumption and tooling costs; (4) Bottleneck of appearance of bio-based materials: In the existing technology, although there are studies on the preparation of car carpets using bio-based materials such as natural plant fibers and polylactic acid (PLA), natural fibers have uneven color, many surface burrs and rough touch, which makes it difficult to meet the appearance requirements of passenger car interiors.

[0035] (5) The surface layer cannot achieve both density and abrasion resistance: In order to achieve good abrasion resistance, hemp fibers are usually added to the surface layer. However, natural hemp fibers have many burrs on the surface, making it difficult to adhere tightly and stack the fibers tightly, thus failing to form a dense surface layer and resulting in poor dust and stain resistance of the carpet.

[0036] Furthermore, the sound absorption performance of existing automotive carpets needs further improvement.

[0037] To solve the above technical problems, such as Figure 1 As shown, one embodiment of this application provides a bio-based composite carpet, which is made by hot-pressing at least three layers of fiber webs. The three layers of fiber webs include: First fiber web layer 1: As a dense and wear-resistant surface layer, its areal density is 750 g / m²-850 g / m², preferably 780 g / m²-850 g / m². First fiber web layer 1 includes polylactic acid core-sheath fibers and surface-modified hemp fibers. The surface-modified hemp fibers are prepared by modifying hemp fibers with removed surface pectin using an epoxy silane coupling agent. Examples of hemp fibers include ramie, flax, jute, and sisal fibers. Hemp fibers with removed surface pectin refer to fibers with pectinase removed from their surface, which can be done by enzymatic hydrolysis. The preparation process of surface-modified hemp fibers includes the following steps: pre-treating the hemp fibers with an enzyme treatment bath containing pectinase, washing with water, and drying. Subsequently, spraying the hemp fibers with a modification solution containing an epoxy silane coupling agent and drying. In the enzyme treatment bath, the mass percentage of pectinase is 1%-3%, preferably 2%-3%. The enzyme treatment bath temperature is 50℃-55℃, preferably 52℃-55℃; the pH of the enzyme treatment bath is 4.5-5.5. The pretreatment time is 55min-65min. Washing with water is performed until the pH reaches 6.5-7.0. The drying temperature is 55℃-65℃, preferably 58℃-65℃. The mass percentage of epoxy silane coupling agent in the modified solution is 1%-2%, preferably 1.2%-2%; the temperature of the modified solution is 50℃-55℃, preferably 52℃-55℃. The spray treatment time is 8min-18min, preferably 10min-18min. The drying temperature is 75℃-85℃, preferably 78℃-85℃, and the drying time is 1.5h-2.5h, preferably 1.8h-2.5h.

[0038] Second fiber mesh layer 2: As a sound wave transition zone, it realizes impedance gradient, with a surface density of 600g / m²-750g / m², preferably 650g / m²-750g / m²; Located on the bottom side of the first fiber mesh layer 1, the second fiber mesh layer 2 includes hollow fibers, polylactic acid core-sheath fibers and surface-modified hemp fibers. The third fiber mesh layer 3 has a porous structure and mainly functions as a sound absorber. Its surface density is 900 g / m²-1100 g / m², preferably 950 g / m²-1100 g / m². Located on the bottom side of the second fiber mesh layer 2, the third fiber mesh layer 3 includes hollow fibers, polylactic acid core fibers, and surface-modified hemp fibers. The bottom surface is covered with first needle-punched micropores (not shown). The depth of the first needle-punched micropores is 4 mm-6 mm, preferably 4.5 mm-6 mm. The distribution density of the first needle-punched micropores is 100-150 per cm², preferably 120-150 per cm². For example, low-pressure needles can be used for needle punching. The first needle-punched micropores formed by needle punching can form a micro-loop structure on the bottom surface of the third fiber mesh layer 3, increasing the specific surface area and improving the sound absorption performance. Polylactic acid (PLA) core-sheath fiber comprises a sheath layer and a core layer. The sheath layer comprises a first PLA, and the core layer comprises a second PLA. The melting point of the first PLA is lower than that of the second PLA. The first fiber web layer 1, the second fiber web layer 2, and the third fiber web layer 3 are bonded together by molten first PLA. In other words, the three fiber webs are bonded together by molten first PLA. PLA core-sheath fiber is a commercially available product. For example, a commercially available PLA core-sheath fiber has a PLA melting point of 130°C for the sheath layer and 170°C for the core layer. Further details are omitted here. The three-layer fiber web is covered with second needle-punched micropores penetrating the first fiber web layer 1, the second fiber web layer 2, and the third fiber web layer 3. The distribution density of the second needle-punched micropores is 200-250 per cm², preferably 220-250 per cm². The second needle-punched micropores penetrating the first fiber web layer 1, the second fiber web layer 2, and the third fiber web layer 3 enable the three layers of fibers to be initially entangled together, achieving preliminary composite formation. At the same time, the second needle-punched micropores serve as channels for the flow of molten first polylactic acid, facilitating the bonding of the three layers of fiber web together by the molten first polylactic acid. Hollow fibers include at least one of straw fiber, straw-husk composite fiber, and palm fiber. The hollow fibers are obtained through opening treatment and pretreatment with bio-enzymes, including cellulase and / or xylanase. Straw-husk composite fiber is made from a mixture of crushed straw and husks, with a mass ratio of crushed straw to husks of 55-65:45-35, preferably 58-65:42-35. The length of the crushed straw is 10mm-20mm. Opening treatment can be performed using steam explosion. Straw fiber has abundant hollow pores, which is beneficial for sound energy dissipation. Rice husk and other husk fibers have a high silicon content and high rigidity, which can form a supporting skeleton. The combination of the two can form a unique microporous-rigid skeleton structure, improving sound absorption performance. The mass ratio of cellulase to xylanase is 0.8-1.5:0.3-0.6, preferably 0.9-1.2:0.4-0.6. The cellulase activity is greater than or equal to 1000 IU / g, and the xylanase activity is greater than or equal to 5000 IU / g. These enzymes enable rapid and efficient etching and activation of fiber surfaces. Under conditions lower than conventional burst pressure (1.0-2.0 MPa), they achieve microscopic roughening and activation of the fiber surface, with lower energy consumption, less fiber damage, and avoidance of the use of high-concentration chemical reagents. Enzyme activity is defined as the amount of enzyme required to degrade the corresponding substrates (sodium carboxymethyl cellulose and xylan, respectively) and release 1 μmol of reducing sugar (based on glucose or xylose equivalents) in 1 minute under the following conditions: temperature 50℃-55℃ and pH 5.0. One international unit (IU) of enzyme activity is defined as the amount of enzyme required to degrade the corresponding substrates (sodium carboxymethyl cellulose and xylan, respectively) in 1 minute. During the steam explosion process, the steam pressure is 0.6MPa-0.8MPa, preferably 0.65MPa-0.8MPa; the steam temperature is 160℃-170℃, preferably 165℃-170℃; and the steam explosion duration is 2min-3min, preferably 2.5min-3min. The bio-enzyme pretreatment includes: spraying the steam-exploded material with a bio-enzyme-containing treatment solution, utilizing the residual heat of the fiber to maintain the temperature required for enzyme activity, followed by treatment at 50℃-60℃ for 30min-45min, and then drying. The bio-enzyme content in the treatment solution is 1%-1.5% by mass, preferably 1.2%-1.5%, and the pH of the treatment solution is 4.5-5.5, preferably 4.8-5.5. The drying temperature is 55℃-65℃, preferably 58℃-65℃, until the moisture content (i.e., the mass percentage of moisture) is less than 5%. Examples of straw include wheat straw, cotton straw, and corn straw. Examples of grain husks include rice husks.

[0039] The content of hollow fibers in the second fiber web layer 2 is less than that in the third fiber web layer 3. The mass percentage of hollow fibers in the second fiber web layer 2 is 25%-35%, preferably 28%-35%, and the mass percentage of hollow fibers in the third fiber web layer 3 is 55%-65%, preferably 58%-65%. The content of polylactic acid core-sheath fibers gradually decreases along the direction from the first fiber web layer 1 to the third fiber web layer 3. The mass percentage of polylactic acid core-sheath fibers in the first fiber web layer 1 is 35%-45%, preferably 38%-45%. The mass percentage of polylactic acid core-sheath fibers in the second fiber web layer 2 is 25%-34%, preferably 28%-34%. The mass percentage of polylactic acid core-sheath fibers in the third fiber web layer 3 is 15%-24%, preferably 18%-22%.

[0040] In this application, the first fiber mesh layer has the highest content of polylactic acid (PLA) core-sheath fibers. During the hot-pressing composite process, the first PLA, with its lower melting point, melts and flows, and is fully compacted, resulting in the highest density and largest compression ratio. Although its areal density reaches 800 g / m², its densification degree is high, and its thickness percentage is the smallest. The second fiber mesh layer has a moderate content of both PLA core-sheath fibers and hollow fibers. Its overall structure is dense, but its compactness is not as high as that of the first fiber mesh layer, serving as a good transition of acoustic impedance from the first to the third fiber mesh layer. The third fiber mesh layer has the lowest content of PLA core-sheath fibers, insufficient to fill all the pores; and the hollow fibers have good rigidity and compression resistance, better supporting and preserving the structural cavities during the hot-pressing composite process. Therefore, this layer has the lowest density and the largest thickness percentage, making it the main sound-absorbing functional layer.

[0041] In this application, by removing the surface sizing of hemp fibers, the roughness of the hemp fibers can be reduced, their density improved, and the appearance and texture of the carpet enhanced. Modification of the hemp fibers using an epoxy-silane coupling agent introduces epoxy groups into the fibers (siloxy groups hydrolyze in aqueous solution to generate silanol groups, which can react with the hydroxyl groups in the hemp fibers to form Si-OC covalent bonds, thus introducing the epoxy groups into the hemp fibers via chemical bonding). The introduced epoxy groups have high reactivity and can undergo ring-opening reactions with hydroxyl groups and other groups in the molten first polylactic acid during subsequent hot-pressing lamination, achieving chemical bonding between the hemp fibers and the polylactic acid matrix. This improves the interfacial bonding force between the hemp fibers and polylactic acid, avoiding the problem of interfacial defects caused by the large difference in polarity affecting density. Simultaneously, removing the surface sizing of the hemp fibers and the epoxy-silane coupling agent modification treatment also solve the problem in existing technologies where the surface layer cannot simultaneously achieve both density and abrasion resistance.

[0042] In this application, the hollow structure of the hollow fiber is beneficial for sound energy dissipation, giving the carpet sound absorption properties.

[0043] In this application, the first, second, and third fiber web layers all contain polylactic acid (PLA) core-sheath fibers. During the subsequent hot-pressing process, the hot-pressing temperature is higher than the melting point of the first PLA fiber (serving as the sheath layer) but lower than the melting point of the second PLA fiber (serving as the core layer). Therefore, the first PLA fiber, with its lower melting point, melts during the hot-pressing process, while the second PLA fiber, serving as the core layer, is retained, thus preserving the fiber skeleton. The molten first PLA fiber acts as an adhesive, bonding the first, second, and third fiber web layers together. This achieves good bonding strength and preserves the fiber skeleton without the addition of external adhesives, thus achieving "effective bonding" while retaining the fiber skeleton. This method enhances the mechanical strength and toughness of the carpet through an in-situ self-reinforcing mechanism. Furthermore, this application allows for integrated molding, reducing process complexity and processing costs. Secondly, this application eliminates the need for external adhesives, avoiding the environmental problems associated with adding synthetic adhesives. Furthermore, the hollow fiber, polylactic acid core fiber, and surface-modified hemp fiber used in this application are all bio-based materials, which are green, environmentally friendly, and easy to recycle.

[0044] In one embodiment of this application, the steam explosion treatment generates an "explosion" effect through the instantaneous release of steam, destroying the fiber structure of raw materials such as straw, rice husks, and palm fibers, leading to fiber bundle dissociation, cell wall rupture, and the formation of a porous and rough surface morphology. Cellulase can remove hemicellulose from the surface of raw materials such as straw, rice husks, and palm fibers through enzymatic hydrolysis, while xylanase can remove lignin from the surface of fibers such as straw fibers, straw-rice husk composite fibers, and palm fibers through enzymatic hydrolysis, thereby increasing the surface roughness of the fibers, making them rough and porous, opening the microscopic channels on the fiber surface, increasing the specific surface area and internal cavity volume of the fibers, and increasing the porous structure. When there are microscopic grooves on the surface of the hollow fiber, the molten first polylactic acid flows in and forms "point-like adhesion" at the fiber intersections, which plays a physical and mechanical interlocking role after cooling, effectively improving the interfacial bonding effect between the hollow fiber and the polylactic acid matrix. Unlike traditional single chemical treatments that are prone to interface defects, the interface layer constructed by the physical-chemical synergy in this application is more complete and stable, fundamentally solving the common technical problem of weak interfacial bonding in bio-based composite materials.

[0045] In this application, the content of hollow fibers in the second fiber web layer is less than that in the third fiber web layer. In other words, from the first fiber web layer to the third fiber web layer, this application constructs a porous sound energy dissipation path with a gradually increasing hollow fiber content, i.e., a "pore gradient" structure with increasing pore density. This porous sound energy dissipation path, combined with the first needle-punched micropore structure on the surface of the third fiber web layer, enables mid-to-low frequency sound energy to be gradually dissipated through the pore structure along the direction of the needle-punched micropores from the first fiber web layer to the third fiber web layer, enhancing the dissipation capability of mid-to-low frequency sound energy and thus improving the sound absorption performance of the carpet. Simultaneously, the content of polylactic acid core-sheath fibers gradually decreases along the direction of the first fiber web layer to the third fiber web layer. In other words, from the third fiber web layer to the first fiber web layer, this application constructs a sound energy impedance path with a gradually increasing polylactic acid core-sheath fiber content. The third fiber layer has the lowest polylactic acid (PLA) core-sheath fiber content and the lowest density of the cured adhesive formed by the molten first PLA. Noise from the carpet underside (such as tire noise and chassis vibration noise) can enter the carpet interior with minimal reflection loss. The second fiber layer has a slightly higher PLA core-sheath fiber content and relatively higher density of the cured adhesive formed by the molten first PLA. It can form a "gradually increasing impedance dissipation channel" with the third and first fiber layers, where sound waves experience continuous and smooth viscous friction as they propagate, gradually converting sound energy into heat energy for dissipation. The first fiber layer has the highest PLA core-sheath fiber content and high density of the cured adhesive formed by the molten first PLA, exhibiting the highest sound impedance. This constitutes a "high-impedance acoustic reflection," reflecting most of the residual sound energy penetrating the first fiber layer back into the carpet interior. This energy is then dissipated again via the second and third fiber layers on the return path, further enhancing the carpet's sound absorption performance. In summary, the gradient changes in polylactic acid (PLA) core-sheath fiber content and hollow fiber content together construct a dual gradient structure of "gradual impedance change" and "gradual porosity change." These two gradients work synergistically to endow the carpet with excellent broadband sound absorption performance. In short, this application achieves a gradual change in the acoustic impedance within the material through a three-layer asymmetric structure consisting of a dense first fiber mesh layer, a transitional second fiber mesh layer, and a porous third fiber mesh layer. Combined with the microporous structure formed by the needle-punching treatment of the bottom layer and the hollow cavities retained by the straw fibers, the dissipation capability for mid-to-low frequency sound energy is significantly enhanced. This structure overcomes the deficiency of traditional single-layer porous materials in low-frequency sound absorption performance and can meet the complex broadband sound absorption requirements of passenger vehicles.

[0046] This application uses low-pressure saturated steam (0.6MPa-0.8MPa) instead of traditional high-pressure steam explosion (typically >1MPa), significantly reducing the pressure resistance requirements of the boiler equipment. Simultaneously, combined with subsequent bio-enzyme treatment under normal pressure and mild conditions, it achieves more gentle and safer operating conditions while obtaining ideal fiber opening and activation effects. This process uses water as the medium throughout, combining physical explosion with biological treatment, avoiding the use of high-concentration chemical reagents such as strong acids and alkalis, thus reducing the burden of wastewater treatment at the source. It is an energy-saving and environmentally friendly clean production process. In other words, in this application, the steam pressure during the steam explosion treatment is below 1.0MPa (i.e., low-pressure steam explosion treatment). Compared to traditional high-pressure explosion treatment, this application significantly reduces energy consumption. Furthermore, low-pressure steam explosion treatment allows more moisture to be retained in the raw materials, generating no wastewater, making it safe and environmentally friendly.

[0047] In one embodiment of this application, the total thickness of the three fiber webs is 12mm-15mm, preferably 13mm-15mm. The thickness of the first fiber web layer 1 accounts for 15%-19% of the total thickness of the three fiber webs, preferably 16%-19%. The thickness of the second fiber web layer 2 accounts for 25%-30% of the total thickness of the three fiber webs, preferably 28%-30%.

[0048] In one embodiment of this application, to impart color to the carpet and improve its aesthetics, the first fiber web layer 1 further includes colored polylactic acid (PLA) fibers. The mass percentage of colored PLA fibers in the first fiber web layer 1 is 10%-20%, preferably 13%-20%. Colored PLA fibers refer to PLA fibers containing coloring masterbatches. Examples of colors used include dark gray, beige, and brown, which are commonly used in passenger car interiors. The overall coloring of the first fiber web layer is achieved through the color of the colored PLA fibers themselves.

[0049] In one embodiment of this application, as Figure 2As shown, the bio-based composite carpet also includes a finishing layer 4, which is located on the top side of the first fiber web layer 1. The finishing layer 4 includes a bio-based polyurethane film layer (i.e., a bio-based TPU film layer, where TPU refers to polyurethane) or an aqueous bio-based polyurethane coating (i.e., an aqueous bio-based TPU coating) located on the top surface of the first fiber web layer 1. The thickness of the bio-based polyurethane film layer is 0.1 mm to 0.3 mm, preferably 0.2 mm to 0.3 mm. The thickness of the aqueous bio-based polyurethane coating is 20 μm to 50 μm, preferably 30 μm to 50 μm. Exemplarily, to improve the aesthetics of the carpet, the bio-based polyurethane film layer can be tightly bonded to the cooled felt body using a mold cavity with a pre-etched leather texture (e.g., lychee texture or fabric texture) through a hot-pressing composite method. The aqueous bio-based polyurethane coating is preferably a polyurethane coating with a bio-based content greater than or equal to 60%. Bio-based polyurethane films refer to layered polyurethane films made by copolymerizing or blending biodegradable matrix or components as soft segments and using chain extenders and other components as hardness components. Bio-based polyurethane coatings refer to coatings made by copolymerizing or blending biodegradable matrix or components as soft segments and using chain extenders and other components as hardness components. Bio-based polyurethane films can be tightly bonded to a cooled felt body through hot-pressing to form a smooth, dense, and stain-resistant finish. Furthermore, bio-based polyurethane films are biodegradable, have a soft touch, and can improve the feel of carpets. Bio-based polyurethane films can also increase the scratch resistance of carpets, thereby improving their durability.

[0050] Not limited to this, a bio-based polyurethane film layer can also be added to the top side of the first fiber web layer 1 while adding colored polylactic acid fibers. This not only gives the carpet an aesthetic appeal but also avoids the risk of the film layer showing through after being scratched. In addition, the film layer can give the carpet a good feel and texture.

[0051] In terms of visual quality, the carpet of this application has a uniform color and no pattern differences, and can present various textures such as leather and fabric textures. The appearance effect reaches or exceeds the level of existing mainstream passenger car needle-punched wool carpets. In terms of tactile quality, the carpet of this application has a soft and delicate surface, without the itching sensation of natural fibers, and is scratch-resistant and stain-resistant. It can be cleaned by wiping with a damp cloth. Furthermore, the color and texture of the carpet of this application can be customized according to requirements, and the finished product can be obtained in one molding process. In terms of process, the carpet of this application can obtain a finished product with a complex three-dimensional shape in one molding process, reducing the number of processes by 3-4 compared with the traditional multi-layer composite process, which can significantly reduce manufacturing costs.

[0052] like Figure 3 As shown, another embodiment of this application also provides a method for producing the bio-based composite carpet as described above, comprising the following steps: S1. Polylactic acid core-sheath fibers and surface-modified hemp fibers are used to make a fiber web with an areal density of 750 g / m²-850 g / m² to obtain the first fiber web; S2. Hollow fibers, polylactic acid core-sheath fibers, and surface-modified hemp fibers are made into a fiber web with an areal density of 600 g / m²-750 g / m² to obtain a second fiber web; S3. Hollow fibers, polylactic acid core-sheath fibers and surface-modified hemp fibers are made into a fiber web with an areal density of 900 g / m²-1100 g / m² to obtain a third fiber web; S4. Stack the first fiber web, the second fiber web and the third fiber web in sequence, needle punch, preheat, hot press composite, cool, and obtain a bio-based composite carpet. The hot-pressing temperature is higher than the melting point of the first polylactic acid but lower than the melting point of the second polylactic acid.

[0053] In one embodiment of this application, in step S4, the temperature is preheated to 100℃-120℃, preferably 110℃-120℃. The hot-pressing temperature is 155℃-163℃, preferably 158℃-163℃; the hot-pressing time is 60s-75s, preferably 65s-75s. In step S4, the temperature is cooled to 25℃-60℃, preferably 25℃-35℃.

[0054] For example, in step S4, after needle punching and before preheating, the needle-punched felt formed by needle punching is subjected to hot rolling and calendering treatment. During the hot rolling process, the temperature is 80℃-100℃, preferably 90℃-100℃, and the linear pressure is 50N / mm-100N / mm, preferably 60N / mm-100N / mm. The temperature of the hot rolling treatment is higher than the glass transition temperature of polyurethane (about -50℃), which can soften and spread the polyurethane and seal the fuzz of natural fibers, forming a smooth, clean, and uniformly colored matte or semi-gloss surface, improving the carpet's stain resistance and ease of cleaning.

[0055] For example, if the carpet also includes a bio-based polyurethane film layer, in step S4, after needle punching, the carpet production method further includes the following steps: S4.1 Molding and Surface Treatment (1) Material preparation: Cut the needle-punched felt into pieces, unfold the area according to the target specifications, and reserve 50mm allowance in both the length and width directions. Cut it in advance according to the mold surface.

[0056] (2) Mold preparation: The mold is equipped with an independent rapid heating system (oil heating) and a rapid cooling system (water cooling). The upper and lower mold temperature control systems can be adjusted independently. The mold is installed on the hot press.

[0057] (3) Film Laying and Pre-adsorption: The lower mold is kept at a constant temperature of 80℃-100℃ using an independent temperature control system. Take the bio-based polyurethane film and lay it flat on the lower mold surface. Start the vacuum adsorption system. Since 80℃-100℃ is much higher than the glass transition temperature of bio-based polyurethane (about -50℃), the film softens rapidly and adheres tightly to the mold surface under vacuum negative pressure. At this temperature, the bio-based polyurethane film is still in a highly elastic state with sufficient flexibility, which can perfectly fit the complex three-dimensional curved surface of the mold.

[0058] (4) Laying: Lay the needle-punched felt pieces flat on top of the bio-based polyurethane film that has been coated.

[0059] (5) Mold closing and hot pressing (rapid thermal cycling process) are divided into the following stages: Phase 1: Rapid heating on both sides (melt wetting) The upper mold is pressed down and closed. Simultaneously, the heating systems for both molds are activated, rapidly raising their temperatures to 155℃-163℃ (heating rate ≥3℃ / s), while maintaining the mold closing pressure at 4MPa-6MPa. During this process, the sheath layer of the polylactic acid core-sheath fiber (melting point 130℃) melts uniformly, fully impregnating the surface-modified hemp fiber and hollow fiber, forming a strong interfacial bond. The core layer of polylactic acid (melting point 170℃) maintains a fibrous skeleton, ensuring the structural strength of the product; The upper surface of the bio-based polyurethane film (the side in contact with the felt) softens and partially melts when heated, forming a chemical bond with the molten polylactic acid matrix. Due to the rapid heating and limited holding time, the film does not undergo macroscopic flow, and its shape is still constrained by the mold surface.

[0060] Phase Two: Rapid Cooling of the Lower Mold (Texture Setting) When the pressure is held for 50 seconds (total holding time 60-75 seconds), confirm that the felt is completely compacted and the polylactic acid is fully melted. Immediately switch the lower mold temperature control system, stop heating, and introduce cooling water at 15℃-25℃ to rapidly reduce the lower mold temperature to ≤90℃. The upper mold can continue to maintain its temperature or cool simultaneously as needed to ensure the product is flat.

[0061] (6) Overall cooling and demolding: After the pressure holding is completed, cooling water at 15℃-25℃ is simultaneously introduced into the upper and lower molds to rapidly cool the molds to below 60℃ (cooling time is about 60s). Open the mold and remove the product. At this time, the texture of the bio-based polyurethane film on the surface of the product is clear, and the polylactic acid fiber skeleton is intact.

[0062] (7) Precision cutting: Place the product on the waterjet cutting workbench and cut the outer contour, mounting holes and wire harness slots according to the 3D digital model trajectory.

[0063] (8) Post-processing: Clean the cut product, remove the cutting burrs, and package it after inspection.

[0064] Furthermore, in this invention, descriptions involving "first," "second," "third," etc., are for descriptive purposes only and should not be construed as indicating or implying their relative importance or implicitly specifying the number of technical features indicated. Therefore, a feature defined with "first," "second," or "third" may explicitly or implicitly include at least one of those features. Additionally, the term "and / or" in this application merely describes the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, or B existing alone. Furthermore, the technical solutions of various embodiments can be combined with each other, but this must be based on the ability of those skilled in the art to implement them. When the combination of technical solutions is contradictory or impossible to implement, it should be considered that such a combination of technical solutions does not exist and is not within the scope of protection claimed by this invention.

[0065] Example 1 according to Figure 3 The process shown involves the following steps for producing bio-based composite carpets: S0. Preparation of surface-modified ramie fiber: Ramie fiber was placed in an enzyme treatment bath at 52℃ (the enzyme treatment bath was prepared by adding pectinase to deionized water to a mass percentage of 2%, and adding acetic acid to adjust the pH to 5.0) for 60 min. Then, the ramie fiber was washed with water until the pH reached 7.0, and then dried at 60℃. Subsequently, the ramie fiber was uniformly sprayed with an ethanol solution containing 1.5% KH560 silane coupling agent (the ethanol solution was prepared by adding KH560 silane coupling agent to anhydrous ethanol to a mass percentage of 1.5%) for 15 min. Then, it was dried at 80℃ for 2 h to obtain surface-modified ramie fiber. Preparation of corn stalk-rice husk composite fiber: Corn stalks were crushed and sieved, and corn stalks with a length of 10mm-20mm were taken. The corn stalks and rice husks were mixed evenly at a mass ratio of 60:40 to obtain a mixture. The mixture was subjected to steam explosion treatment at a pressure of 0.7MPa and a temperature of 165℃ for 3 minutes. Subsequently, the mixture after steam explosion treatment was sprayed with a treatment solution containing biological enzymes at pH 5.0 (the treatment solution was prepared by adding biological enzymes to an acetate buffer solution at pH 5.0 and stirring evenly to obtain a treatment solution with a biological enzyme mass percentage of 1%. The biological enzymes consisted of cellulase and xylanase at a mass ratio of 1:0.5, with cellulase activity of 1000 IU / g and xylanase activity of 5000 IU / g). The mixture was then treated at 50℃ for 30 minutes and then dried at 60℃ until the moisture content was less than 5% to obtain corn stalk-rice husk composite fiber. S1. Preparation of the first fiber web: Using a carding machine, surface-modified ramie fiber and commercially available polylactic acid core-sheath fiber (fineness of 8D, cutting degree of 50mm, the polylactic acid core-sheath fiber includes a core layer and a sheath layer, the core layer is polylactic acid with a melting point of 130℃, the sheath layer is polylactic acid with a melting point of 170℃, the same below) are made into a fiber web with a thickness of about 23mm (about 2.2mm after molding) and an areal density of 800g / m² using a mass ratio of 60:40, thus obtaining the first fiber web; S2. Preparation of the second fiber web: Using a combing machine, surface-modified ramie fiber, corn straw-rice husk composite fiber and commercially available polylactic acid core-sheath fiber are mixed in a mass ratio of 40:30:30 to form a fiber web with a thickness of about 17 mm (about 3.5 mm after molding) and a surface density of 600 g / m², thus obtaining the second fiber web; S3. Preparation of the third fiber web: Using a combing machine, surface-modified ramie fiber, corn stalk-rice husk composite fiber and commercially available polylactic acid core-sheath fiber are mixed in a mass ratio of 20:60:20 to form a fiber web with a thickness of about 29 mm (about 6.3 mm after molding) and a surface density of 1000 g / m², thus obtaining the third fiber web; S4. Preparation of bio-based composite carpet: The first fiber web, the second fiber web, and the third fiber web are stacked in order from top to bottom and needle-punched. The needle punching penetrates all three layers of fiber web, and the needle punching density is 200 needles / cm². The felt body is then turned over, and the third fiber web is placed upward (i.e., the third fiber web is on the top layer) in the center of the circular needle punching machine. A fork needle is used to needle the third fiber web, with a needle punching depth of 5mm, a needle punching frequency of 150 times / min, and a needle punching density of 120 needles / cm², to obtain a pre-punched felt. Prepare the above needle-punched felt cut pieces, with the size calculated based on the unfolded area of ​​the product plus a 50mm allowance. Cut them in advance according to the mold surface to obtain the felt body cut pieces.

[0066] Prepare a bio-based TPU film (i.e., a bio-based polyurethane film) with a thickness of 0.1 mm.

[0067] Film Lamination and Pre-Adsorption: The lower mold is kept at a constant temperature of 80°C using an independent temperature control system. The aforementioned bio-based TPU film is taken and laid flat on the lower mold surface. The vacuum adsorption system is activated. Because 80°C is much higher than the glass transition temperature of polyurethane (TPU) (approximately -50°C), the film quickly softens and adheres tightly to the mold surface under vacuum. At this temperature, the TPU remains in a highly elastic state, exhibiting sufficient flexibility to perfectly conform to the complex three-dimensional curved surface of the mold.

[0068] Preheat the felt pieces in an oven to 100°C. Subsequently, the preheated felt sheet is transferred to a molding machine and laid flat on top of the pre-laminated TPU film. The distance between the lower and upper molds (i.e., the gap between the upper and lower molds) is 12mm. The mold is heated to 160℃ and held at 160℃ for 60s. During this process, the polylactic acid in the polylactic acid core-sheath fiber, which serves as the sheath layer, melts and flows, while the polylactic acid in the polylactic acid core-sheath fiber, which serves as the core layer, is retained, i.e., the fiber skeleton is preserved, thus obtaining the felt. Next, the mold is cooled to 60°C and demolded to obtain a bio-based composite carpet.

[0069] Example 2 The difference between this embodiment and Comparative Example 1 is that the distance between the lower mold and the upper mold is 13.5mm.

[0070] Example 3 The difference between this embodiment and Comparative Example 1 is that the distance between the lower mold and the upper mold is 15mm.

[0071] Comparative Example 1 The difference between this comparative example and Example 2 is that the three-layer fiber web is made of surface-modified ramie fiber, corn stalk-rice husk composite fiber and polylactic acid core fiber in a mass ratio of 40:30:30. The areal density and thickness of each layer are the same as in Example 2, that is, the content of corn stalk-rice husk composite fiber and polylactic acid core fiber is not gradient set.

[0072] Comparative Example 2 The difference between this comparative example and Example 2 is that: the first fiber web is made of surface-modified ramie fiber, corn stalk-rice husk composite fiber and polylactic acid core fiber in a mass ratio of 40:30:30; the second fiber web is made of surface-modified ramie fiber, corn stalk-rice husk composite fiber and polylactic acid core fiber in a mass ratio of 30:30:40; and the third fiber web is made of surface-modified ramie fiber, corn stalk-rice husk composite fiber and polylactic acid core fiber in a mass ratio of 50:30:20. The areal density and thickness of each layer are the same as in Example 2, that is, only the content of polylactic acid core fiber is set in a gradient, while the content of corn stalk-rice husk composite fiber is not set in a gradient.

[0073] Comparative Example 3 The difference between this comparative example and Example 2 is that the mold is heated to 120°C and then kept at 120°C for the same duration as in Example 2. In other words, the difference between this comparative example and Example 2 is that the hot-pressing temperature is less than 160°C.

[0074] Comparative Example 4 The difference between this comparative example and Example 2 is that the mold is heated to 180°C and then kept at that temperature for the same duration as in Example 2. In other words, the difference between this comparative example and Example 2 is that the hot-pressing temperature is greater than 160°C.

[0075] test The sound absorption coefficients of carpets prepared in Examples 1-3 and Comparative Examples 1-2 for 500Hz, 1000Hz and 2000Hz sound waves were tested according to GB / T 18696.2-2002 Measurement of sound absorption coefficient and acoustic impedance in acoustic impedance tubes - Part 2: Transfer function method. The results are shown in Table 1. The tensile strength of the carpets prepared in Example 2 and Comparative Examples 3-4 was tested according to GB / T1040.4-2006 Determination of tensile properties of plastics Part 4: Test conditions for isotropic and orthotropic fiber-reinforced plastic composites. The results are shown in Table 1. The peel strength of the carpets prepared in Example 2 and Comparative Examples 3-4 was tested according to GB / T2791-1995 Adhesives T Peel Strength Test Method Flexible Materials to Flexible Materials. The results are shown in Table 1. The benzene, toluene, ethylbenzene, xylene, styrene, formaldehyde, acetaldehyde, and acrolein content of the carpets prepared in Examples 1-3 were tested according to the "Sampling and Determination Method of Volatile Organic Compounds and Aldehydes and Ketones in Vehicle Interiors" (HJ / T400-2007). The results are shown in Table 2.

[0076] Table 1. Test results of sound absorption coefficient, tensile strength, and peel strength

[0077] Note: -- indicates not detected.

[0078] Table 2 Results of Volatile Organic Compound Tests

[0079] Note: < indicates the detection limit is below 5 μg / m³. 3 .

[0080] As shown in Table 1, compared to Example 2, the carpets prepared in Comparative Example 1 and Comparative Example 2 showed a significant decrease in sound absorption coefficients for both 500Hz and 1000Hz sound waves. This result indicates that, in this application, the gradient increase in hollow fiber content from top to bottom and the gradient decrease in polylactic acid core fiber content work synergistically to achieve the sound absorption performance; neither can be omitted. The dual gradients of "impedance gradient" and "pore size gradient" jointly constructed by these two factors are key to achieving excellent broadband sound absorption performance.

[0081] As shown in Table 1, compared with Example 2, the tensile strength and peel strength of the carpets prepared in Comparative Examples 3 and 4 were significantly reduced. This result indicates that precisely controlling the hot-pressing temperature between the melting points of the first polylactic acid (PLA) in the PLA sheath layer and the second PLA (PLA) in the core layer within the PLA sheath-core fibers is key to simultaneously achieving the in-situ self-reinforcing mechanism of "effective bonding" and "skeleton retention," which helps improve the mechanical strength and toughness of the carpet.

[0082] As shown in Table 2, the content of various volatile organic compounds in Examples 1-3 is relatively low. This result indicates that the carpet of this application is safe and environmentally friendly.

[0083] The above embodiments are merely illustrative of the principles and effects of the present invention and are not intended to limit the invention. Any person skilled in the art can modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or alterations made by those skilled in the art without departing from the spirit and technical concept disclosed in the present invention should still be covered by the claims of the present invention.

Claims

1. A bio-based composite carpet, characterized in that, The bio-based composite carpet is made by hot-pressing at least three layers of fiber web, the at least three layers of fiber web comprising: First fiber web layer: with a surface density of 750g / m²-850g / m², the first fiber web layer includes polylactic acid core fiber and surface modified hemp fiber, the surface modified hemp fiber is made by modifying hemp fiber with surface gum removed by epoxy silane coupling agent; The second fiber web layer has an areal density of 600g / m²-750g / m² and is located on the bottom side of the first fiber web layer. The second fiber web layer includes hollow fibers, the polylactic acid core-sheath fibers, and the surface-modified hemp fibers. The third fiber web layer has an areal density of 900g / m²-1100g / m² and is located on the bottom side of the second fiber web layer. The third fiber web layer includes the hollow fiber, the polylactic acid core fiber and the surface-modified hemp fiber. The polylactic acid core-sheath fiber includes a sheath layer and a core layer. The sheath layer includes a first polylactic acid, and the core layer includes a second polylactic acid. The melting point of the first polylactic acid is lower than that of the second polylactic acid. The first fiber web layer, the second fiber web layer, and the third fiber web layer are bonded together by the molten first polylactic acid.

2. The bio-based composite carpet as described in claim 1, characterized in that, The content of hollow fibers in the second fiber web layer is less than the content of hollow fibers in the third fiber web layer, and the content of polylactic acid core-sheath fibers gradually decreases along the direction from the first fiber web layer to the third fiber web layer.

3. The bio-based composite carpet as described in claim 2, characterized in that, The first fiber web has a polylactic acid core-sheath fiber content of 35%-45% by mass, the second fiber web has a polylactic acid core-sheath fiber content of 25%-34% by mass, and the third fiber web has a polylactic acid core-sheath fiber content of 15%-24% by mass. And / or, the hollow fiber content in the second fiber web is 25%-35% by mass, and the hollow fiber content in the third fiber web is 55%-65% by mass.

4. The bio-based composite carpet as described in claim 1, characterized in that, The hollow fiber includes at least one of straw fiber, straw-husk composite fiber and palm fiber.

5. The bio-based composite carpet as described in claim 1, characterized in that, The hollow fiber is obtained by opening treatment and bio-enzyme pretreatment, and the bio-enzyme includes cellulase and / or xylanase.

6. The bio-based composite carpet as described in claim 1, characterized in that, The total thickness of the three-layer fiber web is 12mm-15mm.

7. The bio-based composite carpet as described in claim 6, characterized in that, The thickness of the first fiber web layer accounts for 15%-19% of the total thickness of the three fiber web layers; And / or, the thickness of the second fiber web layer accounts for 25%-30% of the total thickness of the three fiber web layers.

8. The bio-based composite carpet as described in claim 1, characterized in that, The first fiber web layer also includes colored polylactic acid fibers; And / or, the bio-based composite carpet further includes a finishing layer located on top of the first fiber web layer, the finishing layer comprising a bio-based polyurethane film layer or an aqueous bio-based polyurethane coating located on top of the first fiber web layer.

9. The bio-based composite carpet as described in claim 1, characterized in that, The bottom surface of the third fiber mesh layer is covered with first needle-punched micropores.

10. The bio-based composite carpet as described in claim 9, characterized in that, The depth of the first needle-punched micropore is 4mm-6mm; And / or, the distribution density of the first needle-punched micropores is 100-150 per cm².

11. The bio-based composite carpet as described in claim 1, characterized in that, The three-layer fiber mesh is covered with second needle-punched micropores that penetrate the first, second, and third fiber mesh layers.

12. The method for producing a bio-based composite carpet as described in any one of claims 1-11, characterized in that, The method for producing the bio-based composite carpet includes the following steps: S1. The polylactic acid core fiber and surface-modified hemp fiber are made into a fiber web with an areal density of 750g / m²-850g / m² to obtain the first fiber web; S2. The hollow fiber, polylactic acid core fiber and surface-modified hemp fiber are made into a fiber web with an areal density of 600g / m²-750g / m² to obtain a second fiber web; S3. The hollow fibers, polylactic acid core fibers and surface-modified hemp fibers are made into a fiber web with an areal density of 900g / m²-1100g / m² to obtain a third fiber web; S4. Stack the first fiber web, the second fiber web and the third fiber web in sequence, needle punch, preheat, hot press composite, cool, and obtain the bio-based composite carpet; The temperature of the hot-pressed composite is higher than the melting point of the first polylactic acid and lower than the melting point of the second polylactic acid.

13. The method for producing bio-based composite carpet as described in claim 12, characterized in that, In step S4, preheat to 100℃-120℃; And / or, in step S4, the temperature of the hot-pressing composite is 155℃-163℃, and the duration of the hot-pressing composite is 60s-75s; And / or, in step S4, cool to 25°C-60°C.

Images