Natural fiber reinforced degradable automotive interior nonwoven fabric and preparation method thereof

Abstract

The application discloses a kind of natural fiber reinforced degradable automotive interior nonwoven fabric and preparation method thereof, belong to the technical field of automotive interior composite material, with tannic acid / iron ion metal polyphenol network coating modification natural plant fiber as reinforcing phase, with PLA / PHBV sheath-core bicomponent fiber as degradable matrix, by coffee acid molecular bridging and EGCG functionalized nanocellulose whisker nano bridging three-level hierarchical interface is constructed, by gradient density needle punching and hot-pressing forming preparation, tensile strength 50-80 MPa, flexural modulus 3.5-6.0 GPa, 180 days compost degradation rate is greater than 90%, compared with GMT weight loss 25-35%.

Description

Technical Field

[0001] This invention belongs to the field of automotive interior composite materials technology, specifically relating to a natural fiber reinforced biodegradable automotive interior nonwoven fabric with a three-phase gradient interface constructed using natural plant fibers as the reinforcing phase, biodegradable polymer fibers as the matrix, and epoxidized soybean oil as a reactive compatibilizer, and its preparation method. Background Technology

[0002] Lightweighting and green sustainable development are dual strategic requirements facing the automotive industry today. Traditional automotive interior structural components, such as door panel substrates, trunk lids, and spare tire covers, widely utilize glass fiber reinforced thermoplastic (GMT) or natural fiber reinforced polypropylene (NF-PP) composites. While GMT material boasts excellent mechanical properties, its density is as high as 1.6-1.8 g / cm³. 3 This is detrimental to overall vehicle weight reduction, and glass fiber is difficult to recycle; the dust and debris generated from incineration pose a threat to the environment and human health. NF-PP material uses polypropylene as its matrix. Although natural fibers are introduced, polypropylene is a petroleum-based non-degradable plastic, and the entire material cannot be biodegraded after its service life, still facing serious end-of-life disposal problems.

[0003] Polylactic acid (PLA) is currently the most commercially promising fully biodegradable thermoplastic polyester. Its raw materials are derived from renewable resources such as corn starch, and its final degradation products are CO2 and water, resulting in a carbon footprint far lower than that of petroleum-based plastics. However, PLA has several inherent drawbacks: its glass transition temperature is only about 58°C, and its heat distortion temperature is between 55-65°C, far below the 100°C or higher typically required for automotive interior materials; PLA's elongation at break is only 3-6%, and its impact toughness is approximately 2.5 kJ / m². 2 PLA exhibits significant brittleness; its crystallization rate is extremely slow, with a crystallinity of only 20-30% under conventional processing conditions, making it difficult to improve heat resistance through crystallization. Poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) is another type of fully biodegradable polyester synthesized by microbial fermentation. Its elongation at break can reach 15-25%, and its melting point can be flexibly controlled to the range of 130-160°C by adjusting the content of 3-hydroxyvalerate units, forming a good toughening complement to PLA.

[0004] CN103306051A discloses a thin jute fiber nonwoven fabric for packaging and its production method, which is prepared by enzymatic degumming, carding, needle punching pre-entanglement and hot rolling processes using 65-75% jute fiber and 25-35% PLA fiber. However, this solution is geared towards the packaging field and does not address the high mechanical properties and thermal stability requirements of automotive interiors. Furthermore, the simple hot rolling method cannot achieve sheet-level composite molding. CN102173141A discloses a nonwoven composite material for automotive interiors and its preparation method, which uses jute fiber combined with polypropylene fiber and polyester fiber through needle punching and molding. However, its matrix materials are all non-degradable plastics. CN109563661B discloses a nonwoven fabric containing polylactic acid, which improves the surface properties of PLA fibers by blending with secondary alkyl sulfonates. However, no natural fiber reinforcement is introduced, and the tensile strength is only 25-35 MPa, which is insufficient to meet the load-bearing requirements of automotive interior structural components.

[0005] In terms of interface modification, existing technologies mainly employ chemical modification methods such as silane coupling agents, alkali treatment, or maleic anhydride grafting. The hydrolysis and condensation products of silane coupling agents are non-biodegradable, reducing the overall degradation rate of the composite material upon introduction; excessive alkali treatment damages the fiber structure; maleic anhydride grafting requires high temperatures and free radical initiators, making the process demanding and posing a risk of small molecule residue migration. More importantly, these methods are all single-level interface modification strategies, forming only a single chemical bond or physical adsorption at the fiber-matrix interface, resulting in limited interface reinforcement efficiency. The fundamental problem with the natural fiber-biodegradable polyester interface lies in the thermodynamic incompatibility between the strongly polar hydroxyl network on the cellulose surface and the hydrophobic ester chain segments of PLA, making it difficult to construct an efficient stress transfer interface using a single modification method. In recent years, inspired by the adhesion mechanism of byssal proteins in marine mussels, researchers have developed biomimetic surface coating technologies, represented by the self-polymerization of dopamine (catechol-amine structure). However, dopamine coating requires a long reaction time (12-24 h) under alkaline conditions, making it difficult to precisely control the coating thickness. Furthermore, dopamine is expensive, limiting its industrialization costs. Tannic acid / metal ion coordination self-assembly offers another more efficient biomimetic surface modification pathway. Tannic acid, as the most abundant plant polyphenol in nature, is widely available and inexpensive. Combined with Fe... 3+ Coordination self-assembly can form a uniform nano-coating on almost any material surface in just minutes, with a deposition rate approximately 50-100 times higher than that of dopamine. However, there is currently no technical solution that combines metal polyphenol network coating technology with natural fiber-reinforced biodegradable composites. Therefore, it is urgent to redesign the multi-level, multi-mechanism synergistic interface architecture at the molecular level to achieve efficient interface reinforcement while maintaining biodegradability. Summary of the Invention

[0006] The purpose of this invention is to address the shortcomings of existing technologies in biodegradable composite materials reinforced with natural fibers, such as limited interfacial modification levels, high matrix brittleness, and a lack of molecular-level interfacial design. This invention provides a biodegradable automotive interior composite nonwoven fabric reinforced with natural fibers based on a three-level hierarchical interfacial molecular architecture, and its preparation method. The core molecular design innovation of this invention lies in constructing a three-level hierarchical interface from the fiber surface to the matrix using three natural phenolic compounds—tannic acid, caffeic acid, and epigallocatechin gallate. Each level utilizes different molecular recognition and chemical bonding mechanisms to achieve specific interfacial functions.

[0007] The technical solution adopted in this invention is: a natural fiber-reinforced biodegradable automotive interior composite nonwoven fabric, comprising natural plant fibers and biodegradable matrix fibers that have undergone three-level hierarchical interface modification treatment. The first-level interface is tannic acid / Fe 3+ Metal polyphenol network (MPN) nanocoating, through the interaction of 25 phenolic hydroxyl groups in tannic acid molecules with Fe 3+ The coordination self-assembly of the polymer forms a conformal coating with a thickness of 10-50 nm on the fiber surface, which is strongly bonded to the cellulose surface through hydrogen bonds and coordination bonds. The secondary interface is a caffeic acid molecular bridging layer. Caffeic acid has a unique catechol-vinylcarboxylic acid bifunctional structure, and its catechol end connects with Fe in the MPN coating. 3+ The coordination bonds are anchored to the fiber side, and the vinyl carboxylic acid end undergoes esterification with the terminal hydroxyl and carboxyl groups of the PLA / PHBV matrix during hot pressing to form a covalent bridge. The third-level interface is an EGCG-functionalized cellulose nanofiber (CNC) nanobridge network. EGCG molecules are adsorbed onto the CNC surface at multiple points through eight phenolic hydroxyl groups. The three aromatic rings of EGCG form pi-pi stacking interactions with the caffeic acid molecule bridging layer, constructing a three-dimensional nano-reinforcement network in the fiber-matrix interface transition region. The biodegradable matrix fiber is a PLA / PHBV core-sheath bicomponent fiber. The mass ratio of natural plant fiber to biodegradable matrix fiber is 35-45:55-65, and it is prepared by gradient density needle punching and hot pressing.

[0008] The beneficial effects of this invention are as follows. First, the three-level hierarchical interface architecture constructs a multi-level interfacial adhesion system at the molecular scale, synergistically employing four bonding mechanisms: covalent bonds, coordination bonds, hydrogen bonds, and pi-pi stacking. The interfacial shear strength is increased by 65-90% compared to the unmodified system and by 30-45% compared to the traditional single silane coupling agent modified system. Second, tannic acid / Fe 3+The deposition process of the metal polyphenol network coating is completed in an aqueous solution at room temperature, with a reaction time of only 10-30 minutes. It requires no organic solvents or high-temperature treatment, making it the mildest and most efficient nano-coating technology for fiber surfaces currently available. Third, caffeic acid possesses excellent free radical scavenging activity (hydroxyl radical IC50 = 0.5 μM), endowing the composite material with inherent antioxidant and light-stabilizing properties. After 500 hours of UV aging, the mechanical properties retain more than 85%, an unexpected additional effect not found in traditional interface modifiers. Fourth, the PLA / PHBV core-sheath bicomponent fiber utilizes the synergistic effect of PHBV's low-melting-point preferential melt coating and PLA's high-modulus oriented skeleton, resulting in an 80-120% increase in impact toughness compared to a pure PLA matrix, while maintaining a heat distortion temperature above 125°C. Fifth, all components are bio-based or naturally derived, with a biodegradability rate of over 90% within 180 days under composting conditions, resulting in a carbon footprint that is 35-45% of traditional GMT materials. The surface density of the composite nonwoven fabric is 1.0-1.8 kg / m³. 2 It has a tensile strength of 50-80 MPa and is 25-35% lighter than GMT material. Attached Figure Description

[0009] Figure 1 This is a scanning electron microscope (SEM) image of the surface of unmodified flax fibers.

[0010] Figure 2 For tannic acid / Fe 3+ SEM microstructure of flax fiber surface after metal polyphenol network coating deposition.

[0011] Figure 3 A transmission electron microscope (TEM) cross-sectional image of flax fibers modified with a metal polyphenol network coating.

[0012] Figure 4 TEM image of EGCG-functionalized cellulose nanofiber whiskers.

[0013] Figure 5 The image shows the cross-sectional SEM morphology of the gradient density needle-punched precast felt.

[0014] Figure 6 This is a SEM image of the tensile fracture surface of the composite nonwoven fabric in Example 1.

[0015] Figure 7 This is a SEM image of the tensile fracture surface of the composite nonwoven fabric in Comparative Example 1. Detailed Implementation

[0016] The present invention will be further described in detail below through specific embodiments. The tannic acid (galactotannic acid, molecular weight 1701.21) used in the embodiments of the present invention was purchased from Sigma-Aldrich; ferric chloride (FeCl3) was analytical grade; tris(hydroxymethyl)aminomethane hydrochloride (Tris-HCl) was purchased from Sinopharm Group; caffeic acid was analytical grade; epigallocatechin gallate (EGCG) was purchased from Shanghai Yuanye Biotechnology Co., Ltd., with a purity greater than 98%; polylactic acid resin was NatureWorks 4032D, with a number average molecular weight of approximately 120,000; the 3-hydroxyvalerate molar content in the poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) resin was 12 mol%; and nanocellulose whiskers (CNC) were prepared by sulfuric acid hydrolysis of microcrystalline cellulose.

[0017] Example 1

[0018] This embodiment provides a natural fiber reinforced biodegradable automotive interior composite nonwoven fabric with flax fiber as the reinforcing phase. The specific preparation process is as follows.

[0019] First-level interface: Tannic acid / Fe 3+ Metal polyphenol network nanocoating deposition. Degummed flax short fibers with a length of 60-80 mm and a linear density of approximately 4 dtex were selected. Figure 1 As shown, the surface of unmodified flax fibers exhibits the longitudinal orientation texture of natural cellulose microfibrils and is relatively smooth. 1000 mL of a 50 mM Tris-HCl buffer solution with a pH of 8.0 was prepared, and 4 mg / mL of tannic acid was added. Flax fibers were immersed in the solution at a bath ratio of 1:20, stirred thoroughly, and then FeCl3 solution was added to achieve a concentration of 0.8 mg / mL (tannic acid:FeCl3 mass ratio = 5:1). The reaction was allowed to proceed statically at 25°C for 20 min. The catechol / pyrogallol groups in the tannic acid molecules reacted with FeCl3... 3+ Rapid coordination self-assembly occurs, forming a uniform metal-polyphenol network nanocoating on the fiber surface. The molecular mechanism of coating formation is as follows: the 10 galloyl groups in the tannic acid molecule provide coordination sites for pyrogallol, and each group of 3 pyrogallol groups interacts with 1 Fe group. 3+ A tris-coordinate complex is formed, and under alkaline conditions (pH=8.0), a thermodynamically stable tris-complex structure is preferentially formed, with multiple tannic acid molecules sharing Fe. 3+Coordination centers form a cross-linked network. The coating is anchored to the fiber surface through multiple hydrogen bonds between the hydroxyl groups at C-2, C-3, and C-6 positions of the cellulose chain and the phenolic hydroxyl groups of tannic acid. After the first deposition cycle, the fiber is removed and washed twice with deionized water. The deposition process is repeated for one more cycle (a total of two cycles) to ensure the uniformity and integrity of the coating. Finally, it is dried in a 75°C forced-air oven until the moisture content is below 4%. Figure 2 As shown, after MPN coating deposition, the fiber surface exhibits a uniform nanoparticle morphology, and the original smooth cellulose texture is completely covered by the dense coating; as Figure 3 As shown, TEM cross-sectional observation revealed that the MPN coating thickness was approximately 25 nm, with a tight interface between the coating and the cellulose substrate, exhibiting no obvious gaps or delamination. XPS analysis showed the presence of Fe 2p peaks (711.2 eV) and N 1s peaks (400.1 eV, originating from amino groups in the Tris buffer), confirming the successful deposition of the metal polyphenol network. The fiber surface contact angle increased from 38° in the unmodified state to 82°, and the surface energy increased from 42.3 mJ / m². 2 Increased to 58.6 mJ / m 2 .

[0020] Preparation of EGCG-functionalized cellulose nanofibers. 10 g of microcrystalline cellulose was hydrolyzed in 500 mL of 64 wt% sulfuric acid at 48°C for 45 min. After dilution to terminate the reaction, the nanofibers were purified by dialysis (molecular weight cutoff 12000-14000) to pH 5-6, and then ultrasonically dispersed (400 W, 30 min) to obtain a CNC suspension (2% solids content). The obtained CNCs had a diameter of 8-15 nm, a length of 150-300 nm, and a crystallinity of 85%. 100 mL of the CNC suspension was mixed with an aqueous solution of EGCG (C22H18O11, MW=458.38, 8 phenolic hydroxyl groups) to achieve a mass ratio of EGCG to CNC of 0.5:1. Adsorption was performed at 40°C with magnetic stirring for 4 h. EGCG molecules adsorbed through multi-point hydrogen bonds formed by their eight phenolic hydroxyl groups with the hydroxyl groups on the CNC surface. Simultaneously, the three aromatic rings of EGCG formed additional non-covalent interactions with the pyranose rings on the CNC surface through pi-pi stacking. After adsorption, the mixture was centrifuged at 10000 r / min for 15 min, the supernatant was discarded, and the mixture was resuspended in deionized water and washed twice to remove free EGCG. Finally, the EGCG-CNC suspension (solid content 1.5%) was obtained by resuspending in deionized water. Figure 4 As shown, EGCG-CNC exhibits a typical needle-like nanocrystal morphology, with a slightly rougher surface compared to unfunctionalized CNC. The whisker diameter is approximately 10-18 nm, and the length is approximately 150-350 nm. The EGCG content in the supernatant was detected by UV-Vis spectroscopy, and the adsorption rate was calculated to be 72%, meaning that 0.36 g of EGCG is adsorbed per gram of CNC.

[0021] Preparation of core-sheath bicomponent fibers: PLA resin and PHBV resin were dried separately in a vacuum drying oven at 80°C for 12 h until the moisture content was below 200 ppm. A bicomponent composite spinning unit was used. PLA was melt-plasticized at 195°C via a core-layer screw extruder, and PHBV was melt-plasticized at 165°C via a sheath-layer screw extruder. The two melts were combined in a core-sheath composite spinneret, extruded through the spinneret orifice, cooled and cured by side blowing, and then oiled and wound. The winding speed was 800 m / min. After two-stage drawing (draw ratio of 3.0 times, drawing temperature of 70°C) and steam crimping (cracking temperature of 95°C, crimp count of 12-15 / 25 mm), the fibers were cut into short fibers with a length of 64 mm. The linear density of the resulting core-sheath bicomponent fiber is 6 dtex, the core-sheath mass ratio is 35:65, the melting point of the PHBV sheath is about 152°C, and the melting point of the PLA core is about 168°C.

[0022] Fiber opening, blending, carding, and web laying. MPN-coated flax fibers and bicomponent chopped fibers (core and sheath) are weighed and blended at a mass ratio of 40:60. The two fibers are thoroughly mixed and opened using a multi-bin blending machine, followed by further opening and impurity removal using a coarse opener and a fine opener. The blended fibers are then evenly fed into a double-cylinder, double-doffer carding machine with a cylinder to doffer speed ratio of 1.8:1 and a carding speed controlled at 25 m / min. The carded fiber web is then laid in 8 layers using a cross-laying machine at an angle of ±60° to ensure a balanced fiber orientation in both the longitudinal and transverse directions. The final fiber web density is controlled at 1000 g / m². 2 .

[0023] Gradient density needle punching reinforcement. The fiber web after laying undergoes three gradient density needle punching processes: the first pre-needling uses No. 36 triangular cross-section needles, with a needle punching density of 40 needles / cm. 2 The needle insertion depth was 14 mm, and the needle plate frequency was 600 times / min; the second main needle insertion used a No. 40 star-shaped cross-section needle, and the needle insertion density was 100 needles / cm². 2 The needle depth was 10 mm, and the needle frequency was 800 times / min; the third finishing needle was applied using a No. 42 forked cross-section needle, with a needle density of 180 needles / cm². 2 The needle insertion depth was 4 mm, and the needle plate frequency was 1000 times / min. For example... Figure 5 As shown, the three needle punches create a gradient density structure with a dense surface and a loose core. Cross-sectional SEM clearly shows that the surface fibers are tightly packed with low porosity, while the core fibers are three-dimensionally intertwined with high porosity. This gradient structure prefabricated felt has a thickness of approximately 6 mm and a surface density of 1000 g / m³. 2 .

[0024] Secondary and Tertiary Interfaces: Preparation and Impregnation of Reactive Immersion Solution. Caffeic acid was dissolved at 3 wt% in a 60% (v / v) aqueous ethanol solution and stirred until completely dissolved. EGCG-CNC suspension was added to achieve a final concentration of 1.0 wt% for the functionalized CNC, and the mixture was ultrasonically dispersed for 15 min to ensure uniform distribution. The pre-fabricated felt was completely immersed in the above reactive immersion solution and impregnated at room temperature for 20 min to allow the immersion solution to fully penetrate the felt. During impregnation, the catechol ends of the caffeic acid molecules interact with the Fe in the MPN coating on the fiber surface. 3+ Coordination exchange or supplementary coordination occurs, forming a secondary molecular bridging layer; EGCG-CNC particles are uniformly distributed in the interfiber gaps and fiber-matrix interface regions, and the aromatic ring structure of EGCG and caffeic acid molecules form an ordered molecular recognition network through pi-pi stacking. After removal, pre-dry in a 55°C forced-air oven for 15 min until semi-dry, with the residual ethanol content controlled at 8-12%.

[0025] Hot-press composite molding. The pre-baked pre-formed felt is placed in a flatbed hot press mold preheated to 165°C. Preheating is first applied at 0.5 MPa for 3 min to soften the PHBV skin, followed by a molding pressure of 3.5 MPa for 5 min. During the holding pressure process, the PHBV skin completely melts, flowing to coat the natural fibers and fill the gaps. The PLA core layer only partially softens but retains its fiber morphology, recrystallizing upon cooling to form an oriented microcrystalline framework. At 165°C, the vinyl carboxylic acid terminus of the caffeic acid molecule undergoes esterification and Michael addition reactions with the terminal hydroxyl groups of PLA and the terminal carboxyl groups of PHBV, forming a covalent chemical bridge that covalently connects the first-stage MPN coating to the matrix via caffeic acid molecules. EGCG-CNC nanoparticles form a three-dimensional bridging network in the interfacial transition region. The polyphenolic hydroxyl groups of EGCG form hydrogen bonds with the ester bonds in the matrix, while the high crystallinity and high aspect ratio of CNC provide microscopic reinforcement. After the holding pressure is completed, the material is cooled under pressure to 55°C for demolding. The resulting composite board has a thickness of approximately 2.5 mm and an areal density of 1.35 kg / m³. 2 FTIR spectroscopy analysis showed that the ester bond absorption peak intensity of the composite plate at 1735 cm⁻¹ was significantly enhanced compared to the control sample without caffeic acid. A new absorption peak appeared at 1630 cm⁻¹ after the disappearance of the carbon-carbon double bond, confirming that the vinyl group of caffeic acid did indeed participate in the chemical reaction during the hot pressing process. DSC temperature scanning showed that the cold crystallization peak temperature of PLA decreased from 128°C in the pure PLA system to 112°C, and the cold crystallization enthalpy increased from 18.5 J / g to 28.3 J / g. This indicates that the MPN coating and EGCG-CNC acted as heterogeneous nucleating agents during the cooling process, significantly accelerating the crystallization of PLA. This is the key reason why the heat distortion temperature increased significantly from 65°C in the pure PLA system to 132°C.

[0026] Example 2

[0027] This embodiment uses jute fiber as the reinforcing phase. The differences from Example 1 are as follows: First-stage interface deposition: Jute fiber length 50-70 mm, linear density approximately 6 dtex, tannic acid concentration increased to 6 mg / mL, FeCl3 concentration increased to 1.2 mg / mL, deposition for 3 cycles to accommodate the higher lignin content and larger surface roughness of jute fiber. The lignin content of jute fiber (12-15%) is higher than that of flax (2-5%). There is a pi-pi stacking affinity between the methoxyphenylpropane structure in lignin and the galloyl group of tannic acid, which is beneficial for the anchoring of the MPN coating in the lignin-rich region. TEM observation shows that the coating thickness increased to 35 nm, the coating surface exhibits a granular nano-morphology, and the root mean square roughness (Rq) measured by AFM is 3.2 nm. XPS analysis shows that the Fe 2p3 / 2 peak in the Fe 2p region is located at 711.5 eV, corresponding to Fe... 3+ The tris-catecholato coordination state and Fe content of 2.8 at%, higher than 1.9 at%, in Example 1, indicate that three deposition cycles effectively improved the coverage density of the MPN coating. Core-sheath bicomponent fiber: The molar content of 3-hydroxyvalerate in PHBV was increased to 15 mol% to lower the sheath melting point to 145°C; the core-sheath ratio was adjusted to 40:60; the fiber linear density was 4 dtex; and the cut length was 51 mm. Fiber ratio: The mass ratio of jute fiber to bicomponent fiber was 45:55; 10 layers were laid; and the areal density was 1100 g / m². 2 The cross-laying angle is set to ±45° to enhance longitudinal bending stiffness. During carding, the cylinder to doffer speed ratio is controlled at 2.0:1 to accommodate the high rigidity of jute fibers. Reactive impregnation solution: 5 wt% caffeic acid, 1.5 wt% EGCG-CNC, impregnation for 25 min. Increasing the amount of caffeic acid can compensate for the effect of jute lignin on Fe... 3+ Competition for coordination sites. Hot-pressing temperature 160°C, pressure 4.0 MPa, holding time 6 min. The resulting composite plate has a thickness of 2.8 mm and an areal density of 1.50 kg / m³. 2 The bending modulus of this embodiment reaches 5.2 GPa, which is the highest among the three embodiments, making it suitable for automotive door panel substrates with strict stiffness requirements.

[0028] Example 3

[0029] This embodiment uses a hybrid reinforcement of flax and sisal fibers, leveraging the complementary reinforcement of the high tensile strength (approximately 800 MPa) of flax fibers and the high elongation at break (3-7%) of sisal fibers. MPN coatings were deposited on degummed flax fibers (65 mm in length) and sisal fibers (70 mm in length, linear density approximately 8 dtex), with a tannin concentration of 5 mg / mL and a FeCl3 concentration of 1.0 mg / mL, for two cycles. The tracheid structure of sisal fibers provides a larger specific surface area, resulting in a higher MPN coating coverage than flax fibers. XPS analysis showed that the Fe content of sisal fibers (2.3 at%) was higher than that of flax fibers (1.9 at%). The core-sheath bicomponent fiber parameters were the same as in Example 1. Fiber ratio: flax fiber accounted for 60% of the total natural fiber, and sisal fiber accounted for 40%, with a natural fiber to bicomponent fiber mass ratio of 38:62. Nine layers were laid, with an areal density of 950 g / m². 2 Reactive impregnation solution: caffeic acid 2 wt%, EGCG-CNC 0.8 wt%. Hot pressing temperature 165°C, pressure 3.0 MPa, holding time 5 min. The resulting composite board thickness is 2.2 mm, and the areal density is 1.15 kg / m³. 2 The flax / sisal hybrid design offers superior overall tensile and impact strength compared to a single-fiber system: flax fibers, with a high cellulose content of 70-75%, provide high tensile stiffness, while sisal fibers, with their larger microfibril angles (approximately 20-25°), absorb more energy under impact loads through fiber deformation and progressive pull-out. The differences in length and linear density between the two fibers also contribute to a more uniform fiber distribution during the carding process. This embodiment exhibits the lowest areal density, making it suitable for interior components with stringent weight reduction requirements, such as spare tire covers and coat racks. SEM fracture morphology shows an interleaved distribution of the two fibers at the fracture surface, with some sisal fibers exhibiting clear progressive pull-out marks, confirming the effective operation of the hybrid-enhanced energy dissipation mechanism.

[0030] Comparative Example 1

[0031] This comparative example uses flax fibers without any interface modification treatment, and all other conditions are exactly the same as in Example 1. The flax fibers are directly mixed with the core-sheath bicomponent fibers after only washing and drying, without MPN coating deposition or the use of reactive wetting solutions. This comparative example aims to verify the contribution of the three-level hierarchical interface architecture to the interfacial properties and overall mechanical properties of the composite material.

[0032] Comparative Example 2

[0033] This comparative example only performed the first-stage MPN coating deposition (conditions same as in Example 1), but did not use the reactive wetting solution containing caffeic acid and EGCG-CNC; the remaining conditions were the same as in Example 1. The pre-fabricated felt was directly hot-pressed after needle punching. This comparative example aims to verify the incremental contribution of the second-stage caffeic acid molecular bridging and the third-stage EGCG-CNC nano-bridging to the mechanical properties.

[0034] Comparative Example 3

[0035] This comparative example uses a conventional silane coupling agent (gamma-aminopropyltriethoxysilane, KH-550) instead of the three-level hierarchical interface modification. Flax fibers were immersed in a 2 wt% KH-550 ethanol-water solution (ethanol:water = 80:20) and treated at 70°C for 2 h. After washing and drying, they were mixed with the core-sheath bicomponent fibers. No reactive wetting solution was used, and the remaining conditions were the same as in Example 1. This comparative example represents a typical chemical coupling agent interface modification scheme in the prior art.

[0036] Comparative Example 4

[0037] This comparative example uses pure PLA single-component chopped fibers instead of PLA / PHBV core-sheath bicomponent fibers, with all other conditions identical to Example 1, including tertiary interface modification. The PLA fiber linear density is 6 dtex, and the cut length is 64 mm. This comparative example aims to verify the contribution of the core-sheath bicomponent fiber design to toughness and molding uniformity.

[0038] Comparative Example 5

[0039] This comparative example uses the traditional NF-PP system as a control. Unmodified flax fiber and polypropylene fiber were mixed at a mass ratio of 40:60, and then carded, laid into a web, and needle-punched at a uniform density (100 needles / cm). 2 The flax fibers were prepared by hot pressing (200°C, 3 MPa, 5 min). The linear density of the polypropylene fibers was 6 dtex, and the melt index was 25 g / 10 min (230°C, 2.16 kg). The high processing temperature of 200°C caused thermal degradation of the hemicellulose portion in the flax fibers, resulting in a darker fiber color and a burnt odor. TGA analysis showed that the 5% mass loss temperature of the fibers after hot pressing at 200°C decreased from 318°C to 286°C, confirming that high-temperature processing caused irreversible thermal damage to the fibers. This comparative example represents a typical natural fiber-reinforced polypropylene automotive interior material in the prior art and serves as a benchmark for the biodegradable system of this invention in terms of mechanical properties, weight, degradation performance, VOC release, and weather resistance.

[0040] Detection methods

[0041] Mechanical property testing: Tensile properties were tested according to GB / T 1040.4-2006 standard, with a specimen size of 250 mm x 25 mm and a tensile speed of 5 mm / min; Bending properties were tested according to GB / T 9341-2008 standard, with a specimen size of 80 mm x 10 mm, a span of 64 mm, and a loading speed of 2 mm / min; Impact strength was tested according to GB / T 1043.1-2008 standard for simply supported beam unnotched impact testing.

[0042] Thermal performance testing: Heat distortion temperature was tested according to GB / T 1634.2-2004 standard, with a loading stress of 0.45 MPa; DSC analysis was performed using TA Instruments Q200, with a heating rate of 10°C / min and a nitrogen atmosphere; TGA analysis was performed using TA Instruments Q500, with a heating rate of 10°C / min and a nitrogen atmosphere.

[0043] Interfacial performance testing: Interfacial shear strength (IFSS) was determined using the single-fiber pull-out method. Fiber embedment depth was 200-400 μm, pull-out speed was 0.5 mm / min, and the average value was taken from at least 20 fibers per group. Microstructure was characterized using SEM (ZEISS Sigma 300, accelerating voltage 5 kV) and TEM (JEM-2100, 200 kV). Fiber cross-sectional coating thickness was measured using TEM. XPS analysis was performed using a Thermo Scientific K-Alpha instrument with an Al Ka ​​X-ray source to determine the elemental composition of the fiber surface and the coordination state of Fe. FTIR analysis was performed using a Nicolet iS50 instrument in ATR mode, with a scanning range of 4000-400 cm⁻¹, a resolution of 4 cm⁻¹, and 32 scans to verify the esterification reaction of caffeic acid and the chemical reactions involving vinyl groups.

[0044] Degradation performance testing: Biodegradation tests were conducted under controlled composting conditions according to GB / T 19277.1-2011 standard. The composting temperature was 58±2°C, the relative humidity was 60%, and the cycle was 180 days, with microcrystalline cellulose as a positive reference. Accelerated damp heat aging tests were also conducted, with samples placed in a constant temperature and humidity chamber at 70°C and 90% relative humidity for 7, 14, 28, and 56 days, respectively, to determine the mass loss rate and residual mechanical property retention rate. Water absorption testing was conducted according to GB / T 1034-2008 standard, with samples immersed in deionized water at 23°C for 14 days. Flame retardancy testing was conducted according to GB 8410-2006 standard to determine the horizontal burning rate. Ultraviolet aging testing was conducted according to GB / T 16422.3-2014 standard, with fluorescent ultraviolet lamp aging for 500 h, and the mechanical property retention rate before and after aging was tested. VOC testing was conducted according to the PV3925 standard at 65°C to determine TVOC and formaldehyde, while the odor level was evaluated according to the GB / T 27630-2011 standard.

[0045] The performance test results of each embodiment and comparative example are as follows. Example 1 showed a tensile strength of 68.5 MPa, a flexural strength of 89.3 MPa, a flexural modulus of 4.6 GPa, and an unnotched impact strength of 30.2 kJ / m. 2 The heat distortion temperature is 132°C, the IFSS is 22.4 MPa, and the areal density is 1.35 kg / m³. 2 The composting degradation rate after 180 days was 93%, and the TVOC release was 38 ug / m³. 3 After 500 hours of UV aging, the tensile strength retention rate was 88%. Example 2 showed a tensile strength of 63.8 MPa, a flexural strength of 95.6 MPa, a flexural modulus of 5.2 GPa, and an unnotched impact strength of 26.5 kJ / m. 2 The heat distortion temperature is 128°C, the IFSS is 20.8 MPa, and the surface density is 1.50 kg / m³. 2 The degradation rate was 91%, and the TVOC was 34 ug / m³. 3 The UV aging retention rate was 86%. Example 3 showed a tensile strength of 61.2 MPa, a flexural strength of 82.1 MPa, a flexural modulus of 4.1 GPa, and an unnotched impact strength of 35.6 kJ / m. 2 The heat distortion temperature is 130°C, the IFSS is 21.2 MPa, and the areal density is 1.15 kg / m³. 2 The degradation rate is 95%, and the TVOC is 42ug / m³. 3 The UV aging retention rate is 87%.

[0046] The tensile strength of Comparative Example 1 (without interface modification) was 38.5 MPa, and the IFSS was 10.2 MPa, representing decreases of 43.8% and 54.5%, respectively, compared to Example 1. Figure 7 As shown, the SEM morphology of the fracture surface in Comparative Example 1 reveals a large number of smooth fibers with long pull-out lengths, and obvious gaps and debonding marks between the fibers and the matrix; in stark contrast, as shown in the figure... Figure 6 As shown, in Example 1, a large number of matrix fragments remained on the fiber surface at the fracture point, and the fiber pull-out length was extremely short, with most fibers breaking rather than being pulled out, indicating that the adhesive strength of the three-level hierarchical interface exceeded the fiber bulk strength. Comparative Example 2 (MPN coating only) had a tensile strength of 52.3 MPa and an IFSS of 15.8 MPa, representing decreases of 23.6% and 29.5% respectively compared to Example 1. This indicates that the first-level MPN coating contributed approximately 60% of the interface reinforcement effect, while the second-level caffeic acid bridging and the third-level EGCG-CNC nano-bridging jointly contributed the remaining 40% of the increase. DSC analysis showed that the crystallinity of the PLA core layer in Example 1 reached 40.2%, far higher than the 23.8% in Comparative Example 1, indicating that the heterogeneous nucleation effect of the MPN coating and EGCG-CNC significantly promoted PLA crystallization. Comparative Example 3 (silane coupling agent KH-550) exhibited a tensile strength of 54.8 MPa and an IFSS of 16.5 MPa, which are lower than the 68.5 MPa and 22.4 MPa of Example 1, respectively. This indicates that the interface reinforcement efficiency of the three-level hierarchical interface architecture is significantly superior to the single-layer chemical bonding of traditional silane coupling agents. Furthermore, the 180-day composting degradation rate of Comparative Example 3 was only 78%, suggesting that the non-degradability of the silane coupling layer reduced the overall degradation performance. Comparative Example 4 (pure PLA fiber) had an impact strength of only 16.8 kJ / m². 2 Compared to Example 1, the tensile strength decreased by 44.4%, the heat distortion temperature dropped to 118°C, and the uniformity of the sheet surface after hot pressing was poor, confirming the necessity of the core-sheath bicomponent fiber design. Comparative Example 5 (NF-PP system) had a tensile strength of 55.2 MPa and a areal density of 1.62 kg / m³. 2 The degradation rate after 180 days is only 2.8%, and the TVOC is 125 ug / m³. 3 .

[0047] The UV aging test results showed that Example 1 retained 88% of its tensile strength after 500 h of fluorescent UV aging, while Comparative Example 1 retained 62% and Comparative Example 3 retained 71%. This unexpected anti-aging effect stems from the intrinsic antioxidant activity of caffeic acid molecules—ChEMBL bioactivity data showed that caffeic acid's IC50 for scavenging hydroxyl radicals was only 0.5 μM (pChEMBL=6.30), and the free radical chain termination function provided by the polyphenolic structure of EGCG. Under UV irradiation, caffeic acid and EGCG preferentially capture free radicals as sacrificial antioxidants, protecting the PLA and PHBV backbone from photo-oxidative degradation, thereby endowing the composite material with weather resistance and aging resistance far exceeding those of traditional interface modification systems. TGA analysis showed that the initial thermal decomposition temperature (T5%) of Example 1 was 292°C, higher than 265°C of Comparative Example 1 and 278°C of Comparative Example 3, and the tannic acid / Fe 3+ The thermal stability contribution of the coordination network and EGCG polyphenol structure is an important reason for the increase in thermal decomposition temperature. Water absorption test results show that the water absorption rate of Example 1 after soaking in deionized water at 23°C for 14 days was 8.2%, compared to 15.6% for Comparative Example 1 and 10.8% for Comparative Example 3. The hydrophobic aromatic ring structure of the MPN coating and the covalent cross-linked network of the caffeic acid bridging layer effectively block the penetration path of water molecules to the fiber-matrix interface. The reduction in water absorption rate is beneficial for the composite material to maintain dimensional stability and mechanical properties under humid and hot environments. Flame retardant test results show that the horizontal burning rate of Example 1 was 68 mm / min, Example 2 was 62 mm / min, and Example 3 was 72 mm / min, all meeting the requirements of GB 8410-2006 standard (not greater than 100 mm / min). 3+ The catalytic char formation effect and the polyphenolic structure of tannic acid help to form a dense char layer during combustion to suppress flame spread.

[0048] This invention achieves superior comprehensive performance of natural fiber-reinforced biodegradable automotive interior composite nonwoven fabric through the synergistic effect of a three-level hierarchical interface molecular design, PLA / PHBV core-sheath bicomponent fibers, and gradient density needle-punched structures. The molecular design logic of the three-level interface is as follows: the first level addresses fiber surface energy regulation and primary adhesion; the second level addresses coating-matrix chemical bonding; and the third level addresses nano-reinforcement of the interface transition region. Spatially, the three levels progress sequentially from the fiber surface (0-50 nm) to the matrix interior (50 nm-10 μm). In terms of chemical bonding mechanisms, they transition sequentially from coordination bonds (first level) to covalent bonds (second level) and then to hydrogen bonds and pi-pi stacking (third level), forming a complete interface gradient transition region.

[0049] Primary tannins / Fe 3+Metal polyphenol network (MPN) coatings address the issues of fiber surface energy modulation and primary adhesion. Tannic acid is the largest molecular weight water-soluble polyphenol found in nature, and its 10 galloyl groups provide at least 25 phenolic hydroxyl groups as coordination and hydrogen bonding sites. Under pH 8.0 conditions, the pyrogallol groups react with Fe... 3+ A tris-catecholato complex is formed, with a coordination bond energy of approximately 260 kJ / mol, far exceeding that of hydrogen bonds (10-40 kJ / mol), ensuring the structural stability of the coating under humid and hot conditions and during hot pressing. The MPN coating transforms the fiber surface from hydrophilic cellulose to an amphiphilic surface with both polar coordination sites and hydrophobic aromatic ring structures, increasing the surface energy from 42.3 mJ / mol to 58.6 mJ / mol. 2 Surface energy of PLA / PHBV matrix (40-45 mJ / m 2 It is a better match and reduces the interfacial wetting barrier from a thermodynamic perspective.

[0050] The second-level caffeic acid molecular bridging layer addresses the chemical bonding issue between the fiber surface coating and the polymer matrix. Caffeic acid possesses a unique catechol-trans-vinylcarboxylic acid bifunctional molecular structure. The catechol end (3,4-dihydroxyphenyl) binds to Fe in the MPN coating... 3+ Coordination exchange anchors to the fiber surface - in the existing tannic acid-Fe 3+ In a three-coordinate structure, the catechol of caffeic acid can substitute for a galloyl group coordination site or occupy a Fe group. 3+ The vacant coordination sites form mixed ligand complexes. The reactivity of the vinyl carboxylic acid terminus (-CH=CH-COOH) originates from the alpha, beta-unsaturated carboxylic acid structure: at a hot-pressing temperature of 165°C, the carboxyl group undergoes a Fischer esterification reaction with the terminal hydroxyl group of PLA, while the carbon-carbon double bond can undergo Michael addition with the terminal free radical of PHBV. Both reaction pathways covalently bridge the MPN coating on the fiber side and the polyester segment on the matrix side through caffeic acid molecules.

[0051] The third-level EGCG-functionalized cellulose nanofiber whiskers (EGCG-CNC) address the issues of nanoscale reinforcement and energy dissipation in the interfacial transition region. The eight phenolic hydroxyl groups of EGCG enable multi-point hydrogen bond adsorption with the CNC surface (adsorption energy approximately 120-160 kJ / mol / molecule), forming a stable surface functionalized layer. The three aromatic rings of EGCG (A, B, and D rings) form face-to-face or edge-to-face pi-pi stacks with the benzene rings in the second-level caffeic acid bridging layer, with a stacking distance of approximately 0.35-0.40 nm. This intermolecular recognition mechanism macroscopically manifests as the ordering and densification of the interfacial transition region. The high crystallinity (85%) and high longitudinal modulus (approximately 130 GPa) of CNC allow it to act as a nanoscale short fiber reinforcement in the matrix, dissipating impact energy through crack deflection, crack bridging, and fiber pull-out.

[0052] At the degradation level, all components of this invention are biodegradable under composting conditions. Tannic acid and Fe... 3+ The formed MPN coating is hydrolyzed by extracellular enzymes of microorganisms, and the released tannins are broken down by microbial tanninases; the ester bonds and vinyl structures of caffeic acid can be degraded by microorganisms; EGCG, as a natural tea polyphenol, can be metabolized by microorganisms; the cellulose structure of CNC is hydrolyzed by cellulase; PLA is first non-enzymatically hydrolyzed and then mineralized by microorganisms in a humid and hot environment; PHBV is directly degraded by PHB depolymerase. The degradation rates of each component show a gradient distribution—natural fibers and PHBV are the fastest, followed by PLA, and the MPN coating is the slowest—this temporal difference allows the composite material to maintain interfacial integrity during its service life, and under composting conditions, it can achieve a biodegradation rate of more than 90% within 180 days.

[0053] In summary, the three-level hierarchical interface molecular design of this invention fundamentally solves the thermodynamic incompatibility problem of the natural fiber-biodegradable polyester interface. Four bonding mechanisms (coordinate bonds, covalent ester bonds, hydrogen bonds, and pi-pi stacking) work synergistically at different spatial scales, forming a continuously gradual interface transition zone from the fiber surface to the matrix interior. This eliminates the stress concentration effect of traditional binary interfaces and forms the microstructural basis for achieving an interface reinforcement efficiency 30-45% higher than traditional silane coupling agent modified systems. Furthermore, the intrinsic antioxidant activity of caffeic acid and EGCG (caffeic acid hydroxyl radical IC50 = 0.5 μM, EGCG's superoxide radical scavenging efficiency reaches over 95%) provides the composite material with photo-oxidative aging protection functions completely absent in traditional interface modification systems. This unexpected technical effect, resulting from the selection of specific natural phenolic compounds as interface building blocks based on molecular design thinking, constitutes the key creative contribution that distinguishes this invention from existing technologies. From an application perspective, the composite nonwoven fabric prepared by this invention can fully match or even surpass the traditional NF-PP system in terms of mechanical properties, heat resistance, and areal density. At the same time, it has significant environmental advantages of being fully biodegradable and having ultra-low VOC release, fully meeting the performance requirements of interior structural parts such as automotive door panel substrates, trunk lids, and spare tire covers, and has broad prospects for industrial application.

[0054] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A natural fiber-reinforced biodegradable automotive interior composite nonwoven fabric, characterized in that, The composite nonwoven fabric comprises natural plant fibers and biodegradable matrix fibers that have undergone a three-stage hierarchical interface modification treatment. The natural plant fibers are one or more of flax, jute, or sisal fibers. The three-stage hierarchical interface modification treatment includes: a first stage, forming a metal polyphenol network nanocoating on the surface of the natural plant fibers through coordination self-assembly of tannic acid and ferric ions; a second stage, anchoring the catechol end of caffeic acid molecules to the surface of the metal polyphenol network coating via coordination bonds, so that the vinyl carboxylic acid end of the caffeic acid molecules faces the matrix side; and a third stage, dispersing epigallocatechin gallate-functionalized nanocellulose whiskers on... A nano-bridging network is formed at the fiber-matrix interface; the biodegradable matrix fiber is a bicomponent short-cut fiber with a core-sheath structure prepared by blending polylactic acid and poly(3-hydroxybutyrate-co-3-hydroxyvalerate), wherein poly(3-hydroxybutyrate-co-3-hydroxyvalerate) is the sheath layer and polylactic acid is the core layer; the mass ratio of the natural plant fiber to the biodegradable matrix fiber is 35-45:55-65; the composite nonwoven fabric is prepared as a pre-fabricated felt by opening and mixing, carding into a web, cross-laying, and then reinforced by gradient density needle punching, and then hot-pressed after being treated with a reactive impregnation solution containing caffeic acid and epigallocatechin gallate functionalized nanocellulose whiskers.

2. The natural fiber-reinforced biodegradable automotive interior composite nonwoven fabric according to claim 1, characterized in that, The preparation method of the first-level metal polyphenol network nanocoating is as follows: natural plant fibers are immersed in a tris(hydroxymethyl)aminomethane hydrochloride buffer solution containing tannic acid, and ferric chloride solution is added to allow tannic acid and ferric ions to coordinate and self-assemble. The concentration of tannic acid is 2-8 mg / mL, the concentration of ferric chloride is 0.4-1.6 mg / mL, the mass ratio of tannic acid to ferric chloride is 5:1, the pH value of the buffer solution is 7.8-8.2, the reaction temperature is 20-30°C, the reaction time is 10-30 min, the deposition cycle is 1-3 cycles, and the material is washed with water after each cycle.

3. The natural fiber-reinforced biodegradable automotive interior composite nonwoven fabric according to claim 1, characterized in that, The preparation method of the epigallocatechin gallate functionalized nanocellulose whiskers is as follows: the nanocellulose whisker suspension is mixed with the epigallocatechin gallate solution, and the mixture is stirred and adsorbed at 30-50°C for 2-6 h. The mass ratio of epigallocatechin gallate to nanocellulose whiskers is 0.3-1.0:

1. After adsorption, the free epigallocatechin gallate is removed by centrifugation and washing, and the mixture is resuspended and dispersed for later use.

4. The natural fiber-reinforced biodegradable automotive interior composite nonwoven fabric according to claim 1, characterized in that, The number-average molecular weight of polylactic acid in the core-sheath structure bicomponent short-cut fiber is 80,000-150,000, the molar content of 3-hydroxyvalerate in poly-3-hydroxybutyrate-co-3-hydroxyvalerate is 8-15 mol%, the core-sheath mass ratio is 30-40:60-70, the fiber linear density is 3-8 dtex, and the cut length is 51-76 mm.

5. The natural fiber-reinforced biodegradable automotive interior composite nonwoven fabric according to claim 1, characterized in that, The gradient density acupuncture reinforcement includes three acupuncture processes: the first pre-acupuncture has a needle density of 30-50 needles / cm. 2 The needle insertion depth is 12-15 mm, and the needle density of the second main needle insertion is 80-120 needles / cm. 2 The needle insertion depth is 8-12 mm, and the needle density of the third finishing needle insertion is 150-200 needles / cm². 2 The needle insertion depth is 3-6 mm.

6. The natural fiber-reinforced biodegradable automotive interior composite nonwoven fabric according to claim 1, characterized in that, The reactive wetting solution comprises caffeic acid, epigallocatechin gallate functionalized nanocellulose whiskers, and an aqueous ethanol solution. The mass fraction of caffeic acid is 1-5%, the mass fraction of functionalized nanocellulose whiskers is 0.5-2.0%, and the volume concentration of the aqueous ethanol solution is 50-70%.

7. The natural fiber-reinforced biodegradable automotive interior composite nonwoven fabric according to claim 1, characterized in that, The hot pressing temperature is 155-175°C, the pressure is 2-5 MPa, the holding time is 3-8 min, and the cooling method is to demold under pressure until the temperature drops below 60°C.

8. A method for preparing a natural fiber-reinforced biodegradable automotive interior composite nonwoven fabric according to any one of claims 1 to 7, characterized in that, Includes the following steps: Step 1: Immerse natural plant fibers in a buffer solution containing tannic acid and ferric chloride (tris(hydroxymethyl)aminomethane) hydrochloride for metal polyphenol network coating deposition at a reaction temperature of 20-30°C for 1-3 cycles. After washing, dry at below 80°C until the moisture content is less than 5%. Step 2: Weigh and mix the metal polyphenol network-coated natural plant fibers with core-sheath bicomponent chopped fibers at a mass ratio of 35-45:55-65, and sequentially open, card, and cross-lay the mixture. Step 3: Reinforce the laid fiber web with three gradient density needle punching processes: pre-needling, main needle punching, and finishing needle punching, to achieve an areal density of 800-1200 g / m². 2 Step 4: Prepare a reactive impregnation solution containing caffeic acid and epigallocatechin gallate functionalized nanocellulose whiskers, immerse the pre-made felt in the solution for 10-30 min, remove it and pre-dry it at 50-60°C until semi-dry; Step 5: Place the pre-dried pre-made felt in a hot press mold, hold it under pressure at 155-175°C and 2-5 MPa for 3-8 min, and then cool it under pressure to below 60°C to demold it.

9. The preparation method according to claim 8, characterized in that, The tannic acid mentioned in step one is gallotannic acid; the caffeic acid mentioned in step four has a catechol structure and a trans-vinylcarboxylic acid structure; the epigallocatechin gallate ester mentioned in step four has 8 phenolic hydroxyl groups and 3 aromatic rings.

10. The preparation method according to claim 8, characterized in that, The composite nonwoven fabric has a tensile strength of 50-80 MPa, a flexural strength of 65-100 MPa, a flexural modulus of 3.5-6.0 GPa, and a areal density of 1.0-1.8 kg / m³. 2 The heat distortion temperature at 180°C is greater than 125°C, the biodegradability rate under composting conditions is greater than 90% within 180 days, the composite material has antioxidant and light-stabilizing functions conferred by the caffeic acid catechol structure, and the mechanical property retention rate is greater than 85% after 500 h of UV aging.

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