Degradable polyester composite material of bamboo fiber super-nano micro-powder melt blending

Abstract

This application relates to the field of polymer composite materials technology, and discloses a biodegradable polyester composite material made by melt blending bamboo fiber ultra-nano powder. This biodegradable polyester composite material is made from L-type polylactic acid resin, pre-dispersed interfacial grafted bamboo fiber masterbatch, and a lubricant. The masterbatch is obtained from micro-nano bamboo fiber wet filter cake with a metal ion-tannic acid coordination modification layer, through online vacuum dehydration and in-situ chemical grafting reaction in an extruder. This invention effectively solves the problems of micro-nano fiber agglomeration and poor interfacial compatibility through dual surface modification and wet processing, and utilizes the pH response characteristics of the coordination layer to regulate the material degradation cycle. The resulting composite material exhibits a 50wt%–60wt% degradation rate in a composting environment after 12 weeks, and a flexural modulus of 3.5GPa–4.0GPa, demonstrating both excellent mechanical properties and controllable biodegradability.

Description

Technical Field

[0001] This invention relates to the field of polymer composite materials technology, specifically to a biodegradable polyester composite material made by melt blending bamboo fiber ultra-nano powder. Background Technology

[0002] While biodegradable polyesters such as polylactic acid (PLA) show great potential in replacing petroleum-based plastics, pure resins generally suffer from inherent defects such as high brittleness, slow crystallization rate, and poor thermal stability. Introducing micro / nano plant fibers with high aspect ratios to construct reinforcing networks is an effective way to improve polyester performance, but it faces significant interface and processing challenges in practical applications.

[0003] First, micro- and nano-scale fabrication significantly increases the specific surface area of ​​the fibers. During the drying process, the dense hydroxyl groups on the fiber surface readily form irreversible hard aggregates through hydrogen bonding. These aggregates are difficult to redisperse in the hydrophobic polyester melt, failing to provide reinforcement and instead becoming internal defects. Second, a natural thermodynamic incompatibility exists between hydrophilic plant fibers and the non-polar polyester matrix, resulting in poor interfacial wettability and hindering effective stress transfer. Furthermore, processing stability and degradation control are pressing issues that current technologies need to address. Residual bound water and surface-active functional groups in the fibers attack the ester bonds of the polyester during high-temperature melt blending, leading to severe matrix degradation. Simultaneously, composite materials often struggle to balance water resistance during service life with biodegradability after disposal: unmodified fibers are highly hygroscopic, resulting in poor weather resistance; while conventional hydrophobic modification improves water resistance, it often excessively inhibits water penetration and microbial erosion, preventing the material from degrading within the specified time under composting conditions, lacking an effective mechanism for controlling the degradation cycle. Therefore, this invention proposes a biodegradable polyester composite material made by melt blending bamboo fiber ultra-nano powder to address the shortcomings of existing technologies. Summary of the Invention

[0004] To address the shortcomings of existing technologies, this invention provides a biodegradable polyester composite material made by melt blending bamboo fiber ultra-nano powder. This solves the problems of irreversible agglomeration and poor interfacial compatibility of micro-nano plant fibers in a hydrophobic polyester matrix, as well as the difficulty in balancing and controlling the water resistance stability during use and the biodegradation rate after disposal of the composite material.

[0005] To address the above problems, the present invention provides the following technical solution: Firstly, the present invention provides a biodegradable polyester composite material made by melt blending bamboo fiber ultra-nano powder, employing the following technical solution:

[0006] A biodegradable polyester composite material is disclosed, which is a melt-blended mixture of bamboo fiber ultra-nano powder. The composite material is made from raw materials comprising the following parts by weight: 60 to 90 parts of L-polylactic acid resin, 10 to 40 parts of pre-dispersed interface-grafted bamboo fiber masterbatch, and 0.2 to 0.8 parts of lubricant. The pre-dispersed interface-grafted bamboo fiber masterbatch comprises micronized bamboo fibers with a tannic acid coordination modification layer having metal ions on its surface and a chemically grafted polymer layer. The composite material exhibits a biodegradation mass loss of 50 wt% to 60 wt% in a composting environment over 12 weeks, and a flexural modulus of 3.5 GPa to 4.0 GPa. By employing the above technical solution, this invention utilizes pre-dispersed interface-grafted bamboo fiber masterbatch to introduce micronized bamboo fibers into a polyester matrix. On the surface of the micronized bamboo fibers, metal ions and tannic acid form a dense coordination layer, shielding the hydroxyl groups on the fiber surface, reducing fiber polarity and hygroscopicity, and minimizing the impact of moisture on the molecular weight of the polyester matrix during melt processing. The chemically grafted polymer layer forms a chemical bonding interface between the fiber and the resin matrix, improving stress transfer efficiency and increasing the flexural modulus of the composite material. Furthermore, the metal ion coordination layer provides water-resistant protection throughout the composite material's service life. In acidic composting environments, it dissociates, exposing the hydrophilic surface of the fiber and inducing accelerated hydrolysis of the matrix, thus regulating the biodegradation cycle.

[0007] Preferably, the raw materials are: 80 parts by weight of L-polylactic acid resin, 20 parts of pre-dispersed interface-grafted bamboo fiber masterbatch, and 0.5 parts of lubricant; the lubricant is ethylene bis-stearamide.

[0008] Preferably, the pre-dispersed interfacial grafted bamboo fiber masterbatch is prepared from raw materials comprising the following parts by weight: 89.3 to 100 parts of modified bamboo fiber wet filter cake, 68 to 73 parts of biodegradable polyester carrier resin, 1.8 to 4.0 parts of styrene-acrylic-epoxy functionalized copolymer chain extender, and 0.2 parts of antioxidant; the solid content of the modified bamboo fiber wet filter cake is 28 wt% to 35 wt%. By adopting the above technical solution, using modified bamboo fiber wet filter cake as raw material, and combining the strong shear field of screw extrusion with vacuum dehydration process, the problems of agglomeration and difficulty in dispersion of dried ultrafine fiber powder are solved. Wet feeding maintains the dispersed state of micro-nano bamboo fibers, and the grafting reaction is carried out directly after in-situ dehydration, preserving the aspect ratio of micro-nano fibers and improving the interfacial reaction efficiency.

[0009] Preferably, the modified bamboo fiber wet filter cake is prepared from micronized bamboo fiber through tannic acid adsorption and metal salt precipitation reaction; the amount of tannic acid added is 2.0 wt% to 5.0 wt% of the oven-dry weight of the micronized bamboo fiber; the molar ratio of metal ions to tannic acid molecules in the metal salt is 8:1 to 12:1; the metal ions are selected from aluminum ions, zinc ions, or iron ions. By adopting the above technical solution, the ratio of tannic acid to metal ions is controlled to form a metal polyphenol network structure on the surface of bamboo fiber. This structure acts as a moisture barrier and utilizes the active sites of the polyphenol structure as binding sites for subsequent chemical grafting reactions. Aluminum ions and zinc ions are used to prepare light-colored products, while iron ions are used to impart color and UV resistance to the products.

[0010] Preferably, the biodegradable polyester carrier resin is polycaprolactone resin or polybutylene adipate terephthalate resin; the styrene-acrylate epoxy functionalized copolymer chain extender is a random copolymer of styrene, methyl acrylate, and glycidyl methacrylate. By adopting the above technical solution, polycaprolactone resin or polybutylene adipate terephthalate resin serves as a carrier, impregnating micro / nano fibers at high filler contents. The styrene-acrylate epoxy functionalized copolymer undergoes a coupling reaction with the functional groups on the bamboo fiber surface, the tannic acid phenolic hydroxyl groups, and the polyester resin end groups through epoxy groups, forming an interfacial bonding layer.

[0011] Preferably, the micro-nano bamboo fiber has an average diameter of 100nm to 300nm and is obtained from bamboo pulp fiber through high shear dispersion and high pressure homogenization.

[0012] Secondly, this invention provides a method for preparing a biodegradable polyester composite material by melt blending of bamboo fiber ultra-nano powder, employing the following technical solution: A method for preparing a biodegradable polyester composite material by melt blending of bamboo fiber ultra-nano powder includes the following steps: S1, adjusting the pH value of a micro-nano bamboo fiber suspension and adding tannic acid for adsorption, followed by adding a metal salt aqueous solution for coordination reaction, and after the reaction, obtaining a modified bamboo fiber wet filter cake by pressure filtration; S2, mixing the modified bamboo fiber wet filter cake, biodegradable polyester carrier resin, and antioxidant, and feeding it into a twin-screw extruder, removing moisture in the vacuum exhaust section, and adding a styrene-acrylic-acrylate-epoxy functionalized copolymer chain extender in the side feeding section after the vacuum exhaust section for reactive extrusion and granulation; S3, mixing pre-dispersed interface-grafted bamboo fiber masterbatch, L-type polylactic acid resin, and lubricant evenly, and obtaining the composite material by melt blending extrusion and injection molding. By adopting the above technical solution, this invention employs a process of aqueous phase coordination and melt grafting carried out in steps. Step S1 utilizes the wetting effect of water to achieve uniform coordination and coating on the surface of micro / nano fibers. Step S2 employs a sequence of dehydration followed by the addition of chain extenders to prevent the hydrolysis of epoxy groups and ensure that the chain extenders primarily undergo grafting reactions with fibers and resins in an anhydrous molten environment, thereby improving the dispersibility and interfacial activity of the masterbatch.

[0013] Preferably, in step S1, the micro-nano bamboo fiber suspension is prepared by circulating high-pressure homogenization of bamboo pulp fibers under a pressure of 400 bar to 600 bar; the pH value of the coordination reaction system is 7.8 to 8.2, the reaction temperature is 25°C to 35°C, and the stirring rate is 400 rpm.

[0014] Preferably, in step S2, the vacuum degree of the twin-screw extruder in the vacuum exhaust section is controlled between -0.098MPa and -0.092MPa; the temperature setting range of the extruder from the feed port to the die head is 90°C to 180°C, wherein the temperature of the side feeding section and the reaction metering zone is 170°C to 180°C.

[0015] Preferably, in step S3, the length-to-diameter ratio of the melt blend extrusion is 40:1, the screw speed is 250 rpm to 300 rpm, and the homogenization section temperature is 185°C.

[0016] This invention provides a biodegradable polyester composite material obtained by melt blending bamboo fiber ultra-nano powder. It possesses the following beneficial effects:

[0017] 1. This invention solves the processing challenges of dispersing and agglomerating micro / nano-scale plant fibers in hydrophobic polymer matrices. By directly using modified bamboo fiber wet filter cake containing specific moisture content as raw material, combined with high-vacuum online dehydration and side-feeding reactive grafting processes using twin-screw extrusion, irreversible hydrogen bond agglomeration of micro / nano fibers during the drying process is avoided. This wet processing method maintains the original micro / nano-scale and high aspect ratio morphology of the fibers, enabling the bamboo fibers to achieve microscopically uniform dispersion in the final polyester matrix, thus ensuring the uniformity of the composite material's properties.

[0018] 2. This invention enhances the interfacial bonding and thermal stability of the composite material by constructing a dual interfacial structure of a metal-polyphenol coordination layer and a chemical grafting layer on the surface of bamboo fiber. The dense metal-polyphenol coordination layer effectively covers the polar hydroxyl groups on the fiber surface, preventing moisture adsorption and reducing the risk of hydrolytic degradation of polyester during high-temperature processing. At the same time, the chemical grafting layer establishes covalent bonds between the fiber and the resin matrix, enabling effective stress transfer between the matrix and the reinforcement, resulting in a higher flexural modulus in the composite material.

[0019] 3. This invention achieves a balanced regulation of the water resistance and biodegradation rate of the composite material. Based on the pH-responsive characteristics of the metal-tannic acid coordination bonds, the composite material exhibits good water resistance under normal use conditions; however, under the acidic conditions and microbial action of the composting environment, the coordination structure dissociates, causing the fibers to re-expose and absorb water, inducing accelerated hydrolysis and disintegration within the polyester matrix. This mechanism effectively resolves the contradiction between maintaining performance during storage and rapid biodegradation after disposal, achieving controllable adjustment of the material's degradation cycle. Attached Figure Description

[0020] Figure 1 This is a schematic diagram of the infrared spectrum of the present invention;

[0021] Figure 2 This is a schematic diagram of the thermogravimetric curve of the present invention;

[0022] Figure 3 This is a columnar schematic diagram of the gel content of the present invention;

[0023] Figure 4 This is a schematic diagram showing a comprehensive comparison of the mechanical properties of the present invention;

[0024] Figure 5 This is a schematic diagram illustrating the processing rheological properties and moisture resistance of the present invention;

[0025] Figure 6 This is a schematic diagram of the biodegradability performance curve of the present invention. Detailed Implementation

[0026] The technical solutions in 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 some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0027] The main raw materials and reagents used in the following examples and comparative examples have the following sources and specifications. Reagents not specifically mentioned are all commercially available analytical grade or higher grade products.

[0028] L-type polylactic acid resin, CAS No. 26100-51-6, weight-average molecular weight (Mw) is approximately 150,000 g / mol, melt index is 4-8 g / 10 min (190℃, 2.16 kg). Poly(butylene adipate / terephthalate) resin, CAS No. 55231-08-8, melt index is 3-5 g / 10 min (190℃, 2.16 kg). Polycaprolactone resin, CAS No. 24980-41-4, number-average molecular weight (Mn) is approximately 60,000 g / mol, melt index is 12-20 g / 10 min (190℃, 2.16 kg). Bamboo pulp fiber, commercially available, bleached sulfate bamboo pulp board, α-cellulose content ≥88%. Tannic acid, CAS No. 1401-55-4, molecular weight is approximately 1701.2 Da. Aluminum trichloride hexahydrate, CAS No. 7784-13-6, purity ≥99.0%. Zinc acetate dihydrate, CAS No. 5970-45-6, purity ≥99.5%. Anhydrous ferric chloride, CAS No. 7705-08-0, purity ≥98.0%. Styrene-acrylate epoxy functionalized copolymer chain extender, a random copolymer of styrene, methyl acrylate, and glycidyl methacrylate, with a weight-average molecular weight (Mw) of approximately 6,800 g / mol and an epoxy equivalent (EEW) of 285 g / mol. Antioxidant 1010, CAS No. 6683-19-8. Ethylene bis-stearamide, CAS No. 110-30-5. Tris(hydroxymethyl)aminomethane, CAS No. 77-86-1.

[0029] Preparation Example 1: This preparation example provides a bamboo fiber wet filter cake with surface aluminum-tannic acid coordination modification, including the following steps:

[0030] (1) Bamboo pulp fiber was soaked in deionized water and dispersed by high shear to prepare a fiber suspension with a solid content of 2.0 wt%. The suspension was then circulated 4 times by a high pressure homogenizer at 500 bar to obtain a micro-nano bamboo fiber suspension with an average diameter of about 100-300 nm.

[0031] (2) Add tris(hydroxymethyl)aminomethane buffer to the above suspension to adjust the pH of the system to 8.0. Under the conditions of mechanical stirring at 30°C and 400 rpm, add 3.0 wt% tannic acid relative to the dry bamboo fiber mass and stir for 15 minutes to adsorb.

[0032] (3) With aluminum ions (Al 3+ The molar ratio of aluminum trichloride to tannic acid molecules is 10:1. An aqueous solution of aluminum trichloride hexahydrate is added dropwise (calculated to be approximately 42.5g of aluminum trichloride hexahydrate for every 30g of tannic acid). The mixture is stirred and reacted for 30 minutes. At this point, the suspension is off-white.

[0033] (4) The suspension after reaction is separated into solid and liquid by plate and frame filter press, and the holding time is controlled to obtain modified bamboo fiber wet filter cake A1 with a solid content of 30wt% (i.e., water content of 70%).

[0034] Preparation Example 2: This preparation example provides a bamboo fiber wet filter cake with surface zinc-tannic acid coordination modification, including the following steps:

[0035] (1) Bamboo pulp fiber was dispersed in deionized water to prepare a suspension with a solid content of 1.5 wt%. The suspension was then circulated three times under a pressure of 400 bar using a high-pressure homogenizer to obtain a micro-nano bamboo fiber suspension.

[0036] (2) Adjust the pH of the suspension to 7.8, and add 2.0 wt% tannic acid relative to the dry bamboo fiber mass under stirring at 25°C, and adsorb for 10 minutes;

[0037] (3) With zinc ions (Zn 2+ Add zinc acetate dihydrate aqueous solution to tannic acid molecules at a molar ratio of 8:1 (calculated to be approximately 20.6g of zinc acetate dihydrate for every 20g of tannic acid), react for 20 minutes, and the suspension will turn a very pale yellow.

[0038] (4) The suspension was centrifuged and dehydrated to obtain a modified bamboo fiber wet filter cake A2 with a solid content of 28wt% (i.e., a water content of 72%).

[0039] Preparation Example 3: This preparation example provides a high-loading coordination-modified bamboo fiber wet filter cake, comprising the following steps:

[0040] (1) Prepare a micro-nano bamboo fiber suspension with a solid content of 3.0 wt% (homogenization pressure 600 bar, 5 cycles).

[0041] (2) Adjust the pH value to 8.2, add 5.0 wt% tannic acid relative to the weight of oven-dried bamboo fiber, and stir to adsorb for 20 minutes;

[0042] (3) With aluminum ions (Al 3+ A solution of aluminum trichloride hexahydrate was added at a molar ratio of 12:1 to tannic acid molecules, and the reaction was allowed to proceed for 40 minutes.

[0043] (4) Pressure filtration and dehydration to obtain modified bamboo fiber wet filter cake A3 with a solid content of 35wt% (i.e., moisture content of 65%).

[0044] Preparation Example 4: This preparation example provides an iron-tannic acid coordination modified (colored) bamboo fiber wet filter cake as a color comparison reference.

[0045] Its preparation process is completely consistent with that of Preparation Example 1, the only difference being that the metal salt used in step (3) is anhydrous ferric chloride, and the iron ions (Fe)3+ The molar ratio of tannic acid molecules to tannins is 10:1. After the reaction, the suspension quickly turns purple-black. The black modified bamboo fiber wet filter cake A4 (solid content 30wt%) is obtained by pressure filtration.

[0046] Preparation Example 5: This preparation example provides a pre-dispersed interfacial grafted bamboo fiber masterbatch based on a PCL carrier, comprising the following steps:

[0047] A co-rotating parallel twin-screw extruder with a length-to-diameter ratio (L / D) of 48:1 is used. Its barrel is divided into feeding zone, melting zone, natural venting zone, first conveying zone, vacuum venting zone, side feeding zone and reaction metering zone along the material conveying direction.

[0048] (1) By weight, accurately weigh 100 parts of the modified bamboo fiber wet filter cake A1 obtained in Preparation Example 1 (containing 30 parts of oven-dried modified fiber and 70 parts of water), 68 parts of polycaprolactone resin (PCL) and 0.2 parts of antioxidant 1010.

[0049] (2) After the above wet filter cake A1, PCL resin particles and antioxidant are mixed evenly, they are continuously fed into the extruder from the main feed port.

[0050] (3) Extruder process settings: screw speed 400 rpm; temperature settings from feed port to die head are as follows: 100℃ (feeding), 140℃ (melting), 150℃ (natural exhaust), 160℃ (conveying), 170℃ (vacuum exhaust), 175℃ (side feeding and reaction), 165℃ (die head).

[0051] (4) In the vacuum exhaust zone, turn on the high vacuum system and maintain the vacuum degree ≤ -0.095MPa to force the removal of moisture from the wet filter cake and ensure that the melt moisture content entering the subsequent zone is less than 0.05%.

[0052] (5) In the side feeding zone (located after the vacuum exhaust zone), 2.0 parts of styrene-acrylic epoxy functionalized copolymer chain extender are added quantitatively through the side feeder. At this time, the moisture in the melt has been removed, and the chain extender mainly undergoes a chemical grafting reaction with the fiber surface and resin end groups.

[0053] (6) The material is extruded through a die head, air-cooled and stretched, pelletized, and then vacuum dried at 80°C to obtain off-white cylindrical masterbatch B1. The theoretical fiber content of this masterbatch is about 30%.

[0054] Preparation Example 6: This preparation example provides a pre-dispersed interfacial grafted bamboo fiber masterbatch based on a PBAT carrier, comprising the following steps:

[0055] A co-rotating parallel twin-screw extruder with a length-to-diameter ratio (L / D) of 52:1 was used.

[0056] (1) Weigh 89.3 parts by weight of the modified bamboo fiber wet filter cake A2 obtained in Preparation Example 2 (which contains 25 parts of oven-dried modified fiber and 64.3 parts of water), 73 parts of poly(butylene adipate) / terephthalate resin (PBAT), and 0.2 parts of antioxidant 1010, and add them from the main feed port.

[0057] (2) Extruder process settings: screw speed 350 rpm; temperature settings: 90-110℃ (feeding), 130-140℃ (melting and natural degassing), 150-160℃ (conveying and vacuum degassing), 170-180℃ (side feeding and reaction), 160℃ (die head).

[0058] (3) The vacuum level in the vacuum exhaust zone is controlled between -0.092MPa and -0.098MPa to ensure sufficient dehydration.

[0059] (4) Add 1.8 parts of styrene-acrylic epoxy functionalized copolymer chain extender to the side feeding zone.

[0060] (5) Extrusion granulation to obtain light yellow masterbatch B2.

[0061] Preparation Example 7: This preparation example provides a masterbatch with a different grafting rate to explore parameter boundaries. The formulation and steps are basically the same as those in Preparation Example 5, except that: (1) the amount of styrene-acrylic epoxy functionalized copolymer chain extender added to the raw materials is adjusted to 4.0 parts (i.e., overgrafting); (2) the temperature of the side feed and reaction zone is increased to 180°C to accelerate the reaction rate at high concentrations. A light yellow masterbatch B3 was obtained.

[0062] Preparation Example 8: This preparation example provides a black pre-dispersed interfacial grafted bamboo fiber masterbatch. The formulation and steps are exactly the same as in Preparation Example 5, except that 100 parts of the black modified bamboo fiber wet filter cake A4 obtained in Preparation Example 4 are used instead of filter cake A1. Black masterbatch B4 is obtained.

[0063] Example 1: This example provides a high-performance bamboo fiber reinforced polylactic acid composite material, including the following steps:

[0064] (1) Accurately weigh 80 parts of dried polylactic acid resin (PLLA), 20 parts of pre-dispersed interfacial grafted bamboo fiber masterbatch B1 obtained in Preparation Example 5, and 0.5 parts of ethylene bis-stearamide (EBS) by weight.

[0065] (2) Add the premixed material to a twin-screw extruder for melt blending. The length-to-diameter ratio of the extruder is 40:1, and the screw speed is set to 250 rpm. The temperature of each temperature zone is set as follows: feeding section 165℃, compression section 175℃, homogenization section 185℃, and die head 180℃.

[0066] (3) After the extruded strip is cooled by water, granulated, and vacuum dried at 80°C for 6 hours, it is injection molded into standard test strips.

[0067] Example 2: This example provides a high-toughness bamboo fiber reinforced PBAT composite material to verify its suitability in a fully biodegradable soft matrix, including the following steps:

[0068] (1) Accurately weigh 75 parts of dried poly(butylene adipate) / terephthalate resin (PBAT), 25 parts of pre-dispersed interfacial grafted bamboo fiber masterbatch B2 obtained in Preparation Example 6 (the carrier is also PBAT), and 0.3 parts of ethylene bis-stearamide by weight.

[0069] (2) After the raw materials are mixed evenly, they are added to the twin-screw extruder and the screw speed is set to 220 rpm. Considering the heat sensitivity of PBAT, a mild temperature profile is set: feeding section 130℃, compression section 145℃, homogenization section 155℃, and die head 150℃.

[0070] (3) Extrusion granulation and drying followed by injection molding.

[0071] Example 3: This example provides a polylactic acid / PBAT blend composite material with toughening effect, verifying the modification effect of dissimilar carrier masterbatch, including the following steps:

[0072] (1) Accurately weigh 80 parts of L-polylactic acid resin (PLLA), 20 parts of masterbatch B2 obtained in Preparation Example 6 (Zn-based, with PBAT as the carrier), and 0.5 parts of ethylene bis-stearamide by weight.

[0073] (2) The mixing and extrusion process parameters are basically the same as those in Example 1: screw speed 250 rpm, homogenization section temperature 185℃; at this temperature, the PBAT carrier in the masterbatch melts and is uniformly distributed in the PLLA continuous phase matrix as a dispersed phase;

[0074] (3) Prepare the specimen.

[0075] Example 4: This example provides a high-transparency, low-content bamboo fiber composite material, comprising the following steps:

[0076] (1) Accurately weigh 90 parts of L-polylactic acid resin (PLLA), 110 parts of masterbatch B1 obtained in Preparation Example 5, and 0.2 parts of ethylene bis-stearamide by weight.

[0077] (2) Extrusion and injection molding were performed using the same process as in Example 1;

[0078] Example 5: This example provides a high-filler bamboo fiber / polylactic acid composite material, comprising the following steps:

[0079] (1) Accurately weigh 60 parts of L-polylactic acid resin (PLLA), 40 parts of masterbatch B1 obtained in Preparation Example 5, and 0.8 parts of ethylene bis-stearamide by weight.

[0080] (2) After mixing, the mixture is extruded. Since the PCL content in the masterbatch is high (about 27% of the total system), in order to ensure the shear dispersion effect, the screw speed is increased to 300 rpm and the homogenization section temperature is set to 185℃.

[0081] Example 6: This example provides a composite material with a high interfacial grafting rate, comprising the following steps:

[0082] (1) Accurately weigh 80 parts of L-polylactic acid resin (PLLA), 320 parts of masterbatch B3 obtained in Preparation Example 7 (the masterbatch was prepared with an excess of chain extender and a high grafting rate), and 0.5 parts of ethylene bis-stearamide by weight.

[0083] (2) Processing was performed using the same process conditions as in Example 1;

[0084] Example 7: This example provides a dark-colored UV-resistant composite material to verify the functionality of iron-based coordination, including the following steps:

[0085] (1) Accurately weigh 80 parts of L-polylactic acid resin (PLLA), 20 parts of the black masterbatch B4 obtained in Preparation Example 8, and 0.5 parts of ethylene bis-stearamide by weight.

[0086] (2) Processing was performed using the same process conditions as in Example 1;

[0087] Comparative Example 1: Compared with Example 1, the difference is that the masterbatch used did not contain a styrene-acrylic epoxy functionalized copolymer chain extender during the preparation process (i.e., in step 4 of Preparation Example 5), and only physical blending extrusion was performed. The other raw material ratios and process parameters were the same.

[0088] Comparative Example 2: Compared with Example 1, the difference is that the modified bamboo fiber wet filter cake used in the preparation process (i.e., in the corresponding preparation example 1) omitted steps (2) and (3), that is, the homogenized bamboo fiber suspension did not add tannic acid and aluminum trichloride, and directly pressure filtered to obtain the raw bamboo fiber wet filter cake, which was then used to prepare masterbatch and subsequent composite materials. The rest were the same.

[0089] Comparative Example 3: Compared with Example 1, the difference is that the modified bamboo fiber wet filter cake used was not added to the fiber surface via aluminum trichloride hexahydrate during the preparation process (i.e., in step 3 of Preparation Example 1). It was adsorbed onto the fiber surface by tannic acid through hydrogen bonds. All other aspects were the same.

[0090] Comparative Example 4: Compared with Example 1, the difference is that the masterbatch preparation process is not used. The specific operation is as follows: the modified bamboo fiber wet filter cake obtained in Example 1 is first dried and pulverized to obtain dried fiber powder. Then, the raw materials are weighed according to the actual effective content of each component in Example 1: 6.0 parts of the dried fiber powder, 13.6 parts of PCL resin, 0.04 parts of antioxidant, and 0.4 parts of styrene-acrylic epoxy functionalized copolymer chain extender are accurately weighed and directly mixed and extruded with 80 parts of PLA matrix resin in an extruder in one go. The remaining total proportions and temperature parameters are the same.

[0091] Comparative Example 5: Compared with Example 1, the difference is that the bamboo fiber raw material used was not subjected to high-pressure homogenization. Specifically, commercially available ordinary 80-mesh bamboo powder was used instead of homogenized bamboo fiber suspension to directly carry out the surface modification (steps 2-3) and subsequent masterbatch preparation in Example 1, while the rest were the same.

[0092] Comparative Example 6: Compared with Example 1, the difference is that the modified bamboo fiber used is not modified by metal-polyphenol coordination, but by the general-purpose silane coupling agent KH-550. Specifically, in Preparation Example 1, steps (2) and (3) were replaced by adding 3.0 wt% KH-550 hydrolysate relative to the fiber mass, while the remaining masterbatch preparation and composite material processing were the same.

[0093] Test Example 1: Verification of Surface Chemical Structure and Interfacial Grafting Reaction

[0094] Experimental description: Fourier transform infrared spectroscopy was used to characterize the interface layer of the fiber and composite material before and after modification to confirm the occurrence of metal-polyphenol coordination reaction and interfacial chemical grafting reaction.

[0095] The experimental steps are as follows:

[0096] (1) Sample preparation: Dry, unmodified bamboo fiber powder was selected as sample A; aluminum-tannic acid modified bamboo fiber (not mixed with resin) obtained in step (2) of preparation example 5 was selected as sample B; 5g of composite material particles prepared in example 1 were selected, placed in a Soxhlet extractor, and extracted by reflux for 48 hours with dichloromethane as solvent to remove the physical blend matrix resin and free chain extender that had not undergone chemical reaction. The remaining solid residue was vacuum dried at 60°C to constant weight and was selected as sample C.

[0097] (2) Sample preparation: Weigh the dried sample A, sample B and sample C respectively, mix them with spectrally pure potassium bromide (KBr) at a mass ratio of 1:100, grind them evenly in an agate mortar, and press them into translucent thin sheets under a pressure of 10MPa in a tablet press.

[0098] (3) Test parameter settings: Fourier transform infrared spectrometer was used for transmission scanning, with a scanning wavenumber range of 4000 cm⁻¹. -1 Up to 400cm -1 4cm resolution -1 The scan was performed 32 times, after deducting background air interference.

[0099] The experimental data are shown in Table 1:

[0100] Table 1: Comparison of wavenumbers of characteristic absorption peaks in infrared spectra of samples at different stages (unit: cm⁻¹) -1 )

[0101]

[0102] Note: The data in the table are typical values ​​obtained from multiple measurements. Due to the influence of sample preparation uniformity, the actual peak position may vary by ±2cm. -1 The deviation; "weak" and "strong" are qualitative descriptions of the relative peak intensity.

[0103] Conclusion: According to the appendix Figure 1 The data in Table 1 and the infrared spectral data were analyzed.

[0104] Comparing sample A and sample B, sample A is at 3421.4 cm. -1 The broad peak at [cm] corresponds to the stretching vibration of hydroxyl groups on the cellulose surface. In sample B, this peak shifts to 3368.2 cm. -1 Furthermore, the peak shape broadened, and at 685.2 cm⁻¹... -1 A new absorption peak appears at 3400 cm⁻¹. -1 The wavenumber redshift in the region indicates the formation of coordination bonds between the phenolic hydroxyl groups of tannic acid and aluminum ions, and the presence of hydrogen bonding between tannic acid and the hydroxyl groups of cellulose; 685.2 cm -1 The absorption peak at that point corresponds to the vibration of the Al-O bond, confirming that the surface of the bamboo fiber is covered with a polyphenol layer containing metal ions.

[0105] Comparing samples B and C, sample C underwent Soxhlet extraction with dichloromethane, which removed the physically entangled polymers. Sample C measured 1748.3 cm⁻¹. -1 A strong absorption peak appears at [value missing], corresponding to the stretching vibration of the ester group (C=O) in the polyester molecular chain, and its intensity is higher than the background values ​​of samples A and B. The presence of this characteristic peak indicates that some polymer segments failed to be eluted by the solvent, and these polymers are anchored to the fiber surface by chemical bonds. Furthermore, a strong absorption peak appears at 1162.1 cm⁻¹ in sample C. -1 The COC ether bond absorption peak at this location is enhanced compared to sample A, and no significant 910 cm⁻¹ peak was detected. -1The characteristic peaks of the nearby epoxy groups indicate that the epoxy functional groups in the chain extender open during extrusion, reacting with active groups on the fiber surface or coating to form ether bonds, thus achieving chemical grafting of polymer chains onto the bamboo fiber surface.

[0106] Test Example 2: Thermogravimetric Analysis and Carbon Residue (TGA)

[0107] Experimental Description: Thermogravimetric analysis (TGA) was used to determine the thermal decomposition characteristics of bamboo fiber samples at different treatment stages to evaluate the thermal protection performance of the surface functional layer, and the loading of metal components was inferred from the high-temperature residual mass.

[0108] The experimental steps are as follows:

[0109] (1) Weigh 5-8 mg of each of the dried raw bamboo fiber (referred to as sample FA), the bamboo fiber with only adsorption of tannic acid obtained in step 2 of preparation example 1 (without metal control, referred to as sample FB), the aluminum-tannic acid modified bamboo fiber obtained in step 4 of preparation example 1 (referred to as sample FC), and the iron-tannic acid modified bamboo fiber obtained in preparation example 4 (referred to as sample FD), and place them in a standard alumina crucible.

[0110] (2) Place the crucible containing the sample onto the furnace balance of the thermogravimetric analyzer (model: TA-Instruments-Q500).

[0111] (3) High-purity nitrogen gas is introduced as a protective atmosphere, and the gas flow rate is set to 40 mL / min to maintain an inert environment in the system.

[0112] (4) Start the heating program, set the heating rate to 20℃ / min, and increase the scanning range from 30℃ to 800℃. Record the percentage data of sample mass change with temperature.

[0113] The experimental data are shown in Table 2:

[0114] Table 2: Comparison of thermogravimetric parameters of bamboo fiber and modified fiber

[0115]

[0116] Note: T5% represents the initial decomposition point of the material's thermal stability; the data are measured values ​​from a single experiment, rounded to one decimal place to reflect the actual fluctuations in experimental values.

[0117] Conclusion: According to the appendix Figure 2According to the data in Table 2, the initial decomposition temperature (T5%) of the unmodified sample FA was 224.5℃, and its thermogravimetric loss mainly originated from the thermal decomposition of hemicellulose and the amorphous regions of cellulose. The T5% of the sample FB, treated with tannic acid physical adsorption, was 231.8℃, showing little change compared to the original sample, indicating that the tannic acid layer without complex formation had a limited effect on improving the fiber's thermal stability. After introducing metal ion coordination, the T5% of samples FC and FD increased to 260.4℃ and 256.7℃, respectively, with the maximum thermal decomposition rate temperature (Tmax) lagging behind the original sample by approximately 20℃. The increase in thermal decomposition temperature indicates that the metal-polyphenol network constructed a covering layer on the fiber surface. The coordination cross-linking structure formed by metal ions with tannic acid and hydroxyl groups on the cellulose surface increased the rigidity of the molecular chains, inhibiting chain segment breakage and volatile matter release in the early stages of thermal degradation.

[0118] At 800℃, sample FA almost completely pyrolyzed, with a char residue of 1.25%. Samples FC and FD showed significantly increased char residues, at 13.92% and 15.65%, respectively. After deducting the carbonization residues of biomass and tannic acid itself, the higher levels of non-combustible residues in samples FC and FD were mainly composed of metal oxides. The char residue data confirmed that metal ions were loaded onto the bamboo fiber surface through an impregnation and precipitation process. The iron-based sample FD had a slightly higher char residue, which is related to the larger atomic weight of iron and the catalytic effect of transition metals on the biomass carbonization process. Thermogravimetric analysis results indicate that the modification method of this invention improves the heat resistance of bamboo fiber, meets the temperature requirements for polymer melt processing, and confirms the successful loading of metal components.

[0119] Test Example 3: Gel Content Determination and Interfacial Crosslinking Degree Analysis

[0120] Experimental Description: The insoluble content (gel content) of the composite material in a good solvent was determined by Soxhlet extraction with a good solvent. This test aims to distinguish between simple physical blending and the chemical crosslinking network constructed in this invention, and to quantitatively evaluate the bonding strength and degree of chemical reaction of the interfacial layer.

[0121] The experimental steps are as follows:

[0122] The injection-molded samples prepared in Examples 1, 1, 3 and 6 of this invention were mechanically crushed and passed through a 60-mesh standard sieve. The powder that passed through the sieve was collected as test samples.

[0123] Accurately weigh approximately 1.000 g (denoted as W0) of the dried powder sample, and tightly wrap it with a known mass of quantitative filter paper to prevent powder leakage.

[0124] The wrapped sample was placed in the main reaction tube of the Soxhlet extractor, and sufficient dichloromethane was added to the flask as the extraction solvent.

[0125] The water bath heating temperature was set to 50°C to keep the dichloromethane in a continuous boiling reflux state, and the extraction time was maintained for 24 hours to ensure that the polymer matrix that had not undergone cross-linking reaction was completely dissolved and eluted.

[0126] After extraction, remove the filter paper package and place it in a fume hood to air dry naturally to remove free solvent. Then, transfer it to an 80°C vacuum oven to dry to constant weight.

[0127] Weigh the dried residue (denoted as W1), subtract the mass of the filter paper, and calculate the gel content according to the formula: Gel%=(W1 / W0)×100%.

[0128] The experimental data are shown in Table 3:

[0129] Table 3: Test data on gel content of composite materials in dichloromethane

[0130]

[0131] Note: Interface grafting rate estimation = average gel content - theoretical fiber content;

[0132] Conclusion: According to the appendix Figure 3 According to the data in Table 3, the gel content of Comparative Example 1 (CP1) was 6.32%, which is close to the theoretical addition amount of bamboo fiber in the formulation of 6.0%, indicating that dichloromethane dissolved most of the polymer matrix. Without the addition of chain extenders, the modified fiber and resin matrix are mainly physically bonded, and the interfacial layer cannot resist the dissolving effect of the good solvent.

[0133] The gel content of Comparative Example 3 (CP3) was increased to 14.15%. After deducting the fiber base mass, approximately 8% of the polymer mass remained. This data indicates that the epoxy groups of the chain extender chemically reacted with the fiber surface and resin end groups, anchoring part of the resin chain to the fiber surface through covalent bonds. Compared with the silane coupling agent modified system of Comparative Example 6 (CP6) (gel content 9.88%), the polymer-type chain extender system used in this invention achieved a higher grafting retention rate on the fiber surface.

[0134] Example 1 (E1) showed a gel content of 19.39% and an interfacial grafted polymer content of approximately 13.39%, the highest among the test groups. Compared to Comparative Example 3, the insoluble content increased by approximately 5% after the introduction of aluminum ions. This confirms the synergistic crosslinking effect of metal ions in interfacial construction: aluminum ions, acting as coordination centers, form coordination complexes with tannic acid, chain extender functional groups, and resin segments on the fiber surface. Simultaneously, Lewis acidic metal ions catalyze the epoxy ring-opening reaction during processing, improving the grafting conversion rate. Experimental results indicate that this technique constructs a stable interfacial network structure within the composite material where metal coordination and covalent bonding coexist.

[0135] Test Example 4: Comprehensive Comparison Test of Basic Mechanical Properties

[0136] Experimental Description: This test refers to the national standard (GB / T series) for testing the mechanical properties of plastics. Tensile, bending and impact properties were tested on the injection-molded specimens prepared in each example and comparative example to evaluate the reinforcing and toughening effect of modified bamboo fiber in a fully biodegradable polyester matrix and the efficiency of interfacial stress transfer.

[0137] Experimental subjects: Groups E1-E3: Standard specimens of composite materials prepared in Examples 1, 2, and 3, respectively (to verify stability under different process parameter fine-tuning). Group C1: Corresponds to Example 1 (without chemical chain extender). Group C2: Corresponds to Example 2 (without MPN coating). Group C4: Corresponds to Example 4 (no masterbatch process, direct dry mixing). Group C6: Corresponds to Example 6 (silane coupling agent modification).

[0138] The experimental steps are as follows:

[0139] (1) Place the injection-molded standard specimens (dumbbell shape and long strip shape) in a constant temperature and humidity chamber at 23±2℃ and 50±5% relative humidity for 48 hours to eliminate the internal stress generated during the specimen preparation process and to unify the moisture absorption state.

[0140] (2) Tensile properties were tested using a universal testing machine according to GB / T-1040.2-2006 standard. The tensile rate was set to 10 mm / min and the gauge length to 50 mm. Five to seven specimens were selected for each group for testing. Invalid data with fracture locations outside the gauge length and those with slippage of the clamps were discarded, and the arithmetic mean of the remaining data was taken.

[0141] (3) Using the same testing machine, change the three-point bending fixture and conduct bending performance tests according to GB / T-9341-2008 standard. Set the span to 64mm and the loading rate to 2mm / min, and record the bending strength and bending modulus data.

[0142] (4) The impact performance was tested using a simply supported beam impact testing machine in accordance with the standard GB / T-1043.1-2008. A V-notch with a depth of 2 mm was pre-machined on the specimen. A 2J energy pendulum was used to impact the specimen. The absorbed energy at the time of specimen fracture was recorded and the notch impact strength was calculated.

[0143] The experimental data are shown in Table 4:

[0144] Table 4: Summary of Mechanical Property Tests for Modified Bamboo Fiber / Polyester Composites

[0145]

[0146] Note: The data are the mean of the original measured records, rounded to two decimal places to reflect the true dispersion; the failure mode is based on preliminary visual assessment of the cross-section.

[0147] Conclusion: According to the appendix Figure 4 According to the test data in Table 4, the tensile strength of Example 1 (E1) reached 54.32 MPa, which is significantly improved compared to 36.44 MPa of Comparative Example 1 (C1). In Group C1, no chemical chain extender was added, and the bamboo fiber and polyester matrix were bonded by physical friction. Under stress, the interface was prone to slippage and debonding, leading to premature material failure. In Group E1, the interfacial chemical bonding introduced by the chain extender achieved effective load transfer between the matrix and the fiber. Furthermore, the strength of Group E1 was higher than that of Comparative Example 6 (C6), which was modified with a silane coupling agent, indicating that the composite interfacial bonding force formed by metal-polyphenol coordination and polymeric chain extender is superior to that of traditional small-molecule silane coupling modification.

[0148] Regarding the flexural modulus, group E1 measured 3.84 GPa, which is superior to 3.15 GPa in Comparative Example 2 and 3.22 GPa in Comparative Example 4. Group C2, lacking the steric hindrance of the metal-polyphenol layer, and Group C4, lacking the masterbatch pre-dispersion process, both resulted in fiber agglomeration in the matrix, reducing the effective aspect ratio and the continuity of the rigid skeleton. The high modulus of group E1 confirms that MPN modification combined with the masterbatch dilution process achieved monodispersion of micro / nano fibers in the matrix.

[0149] Impact performance data reflects the differences in toughness among materials. The notched impact strength of group E1 is 8.92 kJ / m. 2 The elongation at break was 24.15%, exhibiting a ductile fracture mode. The C1 group had an elongation at break of only 3.14 kJ / m. 2 The crack exhibits brittle fracture. This difference stems from the flexible interface layer synergistically constructed by the PCL carrier phase and chain extender in group E1. This structure induces matrix shear yielding and dissipates impact energy during crack propagation, preventing the straight-line penetration of destructive cracks. Data indicates that this technical solution solves the material embrittlement problem caused by high biomass fiber filling content.

[0150] Test Example 5: Processing Rheological Properties and Moisture Absorption Resistance Test

[0151] Experimental Description: This test aims to evaluate the processing stability (rheological behavior) of the modified material in the molten state and its structural stability (hygroscopic resistance) in humid environments. These two indicators are crucial for the molding yield and service life of bio-based polyester materials.

[0152] Experimental subjects: Sample E1: Particles prepared in Example 1 (masterbatch method + intact modification). Sample C2: Particles prepared in Comparative Example 2. Sample C4: Particles prepared in Comparative Example 4. Sample C5: Particles prepared in Comparative Example 5 (without high-shear homogenization treatment).

[0153] The experimental steps are as follows:

[0154] (1) The melt mass flow rate of each group of particle samples was determined by a melt flow rate tester in accordance with GB / T-3682 standard. The test temperature was set at 190℃ and the nominal load was 2.16kg. Each group of samples was cut 5 times, the mass of the cut strip was recorded and the arithmetic mean was calculated. At the same time, the continuity of melt discharge and surface condition during the extrusion process were recorded.

[0155] (2) Water absorption rate test was conducted in accordance with GB / T-1034 standard. Select injection-molded plate-shaped sample (size 60mm×60mm×2mm), place it in an 80℃ vacuum oven and dry it for 24 hours until constant weight, and weigh the initial mass m1 after drying.

[0156] (3) The dried sample was completely immersed in distilled water at 25°C and removed after soaking for 24 hours and 72 hours, respectively. The sample was weighed immediately after the water adhering to the surface was absorbed with filter paper, and the mass was recorded as m24h and m72h, respectively. The water absorption rate was calculated based on the percentage increase in mass.

[0157] The experimental data are shown in Table 5:

[0158] Table 5: Summary of Processing Flowability and Water Absorption Test Results

[0159]

[0160] Note: The MFI data for sample C4 has a very large range, making it impossible to calculate an effective mean and standard deviation. The table lists the measured ranges, reflecting the instability of the processing.

[0161] Conclusion: According to the appendix Figure 5 As shown in Table 5, the melt flow rate of sample C4 fluctuated significantly between 4.20 and 11.50 g / 10 min, and melt fracture occurred during the extrusion process. The direct dry-mixing process failed to destroy the hydrogen-bonded aggregates originally present in the bamboo fiber. Large-sized aggregates caused intermittent blockage and pressure surges in the test capillary, leading to unstable rheological behavior. The MFI value of sample E1 remained stable at around 9.42 g / 10 min, and its surface was smooth and continuous, indicating that the masterbatch process combined with the twin-screw shearing action achieved uniform dispersion of micro and nanofibers in the matrix, ensuring the stability of the processing.

[0162] Water absorption tests showed that sample C2 had a water absorption rate of 4.12% after 72 hours of soaking. The unmodified bamboo fiber surface contained a large number of hydrophilic hydroxyl groups, and microscopic voids existed between it and the hydrophobic polyester matrix. Water penetrated into the interface through capillary action and was absorbed by the fiber. Sample E1 had a 72-hour water absorption rate of only 0.45%, approximately 89% lower than sample C2. The metal-polyphenol network covered the hydroxyl groups on the fiber surface, reducing the surface energy; simultaneously, the interfacial chemical grafting reaction induced by the chain extender eliminated the micropores between the fiber and the matrix, blocking the water penetration channels. The data confirm that this modification scheme improved the processing dispersibility and water resistance of the biomass composite material.

[0163] Test Example 6: Biodegradability Test in Composting Environment

[0164] Experimental Description: Through controlled composting and landfill experiments, the mass loss rate of the material in a microbially active environment was monitored to assess the impact of the modified interface on the biodegradation cycle of the polyester matrix and its environmental friendliness.

[0165] Experimental subjects: Sample E1: Modified bamboo fiber / polyester composite sheet prepared in Example 1. Sample Ref (pure PLA): Pure polylactic acid sheet, used as a reference. Sample C2 (unmodified): Physically blended composite sheet prepared in Comparative Example 2 (bamboo fiber without surface coating). Sample C6 (silane modified): Composite sheet prepared in Comparative Example 6.

[0166] The experimental steps are as follows:

[0167] (1) Each group of granules was hot-pressed to prepare square sheets with dimensions of 30mm×30mm×1mm. The samples were dried in a vacuum oven at 50℃ for 48 hours, and the initial mass M0 was recorded.

[0168] (2) Prepare a mixed soil with a mass ratio of humus, sand and activated sludge of 4:1:1, adjust the pH value to 7.0-7.5, and control the soil moisture to 50%-60%.

[0169] (3) Bury the dried samples 10 cm below the soil surface, with each sample spaced 5 cm apart to avoid mutual interference. The experimental environment temperature is controlled at 30 ± 2℃, and distilled water is sprayed on the soil surface every 3 days to maintain humidity.

[0170] (4) Samples were taken out in weeks 2, 4, 8 and 12 respectively, rinsed with deionized water to remove surface soil, cleaned with an ultrasonic cleaner for 2 minutes, and dried in a vacuum oven to constant weight. The residual mass Mt was recorded.

[0171] (5) According to the formula Loss%=(M0) The mass loss rate is calculated as Mt / M0×100%. Three parallel samples are set up for each group, and the arithmetic mean is taken as the test result.

[0172] The experimental data are shown in Table 6:

[0173] Table 6: Composting degradation mass loss rate (%) of composite materials under different cycles

[0174]

[0175] Note: Due to the uneven distribution of soil microorganisms, the actual data exhibits significant dispersion. The data in the table are the arithmetic mean of three parallel measurements.

[0176] Conclusion: According to the appendix Figure 6 According to the data in Table 6, the unmodified sample C2 exhibited the fastest degradation rate, with a weight loss of 82.15% after 12 weeks. Natural bamboo fiber, with its hydrophilicity and porous structure, facilitated the penetration of soil moisture into the material, initiating hydrolysis of the polyester matrix. Simultaneously, cellulose and hemicellulose, acting as carbon sources, promoted the attachment of microorganisms to the material surface and internal pores, accelerating polymer disintegration. The pure PLA sample Ref showed a weight loss of 14.23% within 12 weeks. PLA's high crystallinity and tight molecular arrangement hindered water penetration and lacked microbial attachment sites, resulting in a longer degradation induction period.

[0177] In Example 1, sample E1 experienced a weight loss of 6.12% in the initial degradation phase (0-4 weeks), lower than sample C2. The metal-polyphenol network and chemical grafting layer constructed a hydrophobic structure on the fiber surface, delaying the penetration of water into the deeper layers of the interface. In the later stages of degradation (8-12 weeks), the degradation rate of E1 accelerated, ultimately reaching a weight loss of 58.91%. As the surface polymer hydrolyzed and sloughed off, the modified bamboo fiber was exposed. Under acidic soil conditions or enzymatic action, the metal-polyphenol coordination bonds dissociated. After the interfacial structure was disrupted, the bamboo fiber regained its bioaccessibility, guiding microorganisms to erode deeper into the material.

[0178] In summary, this technical solution regulates the degradation behavior of materials through interfacial chemical design. The modified layer initially improves the material's water resistance and delays performance degradation; even in the later stages, as the interfacial coordination structure is disrupted, the material still possesses good biodegradability. This solves the problem of poor durability caused by rapid water absorption in biomass composite materials, while also meeting environmental disposal requirements after waste disposal.

Claims

1. A biodegradable polyester composite material made by melt blending bamboo fiber ultra-nano powder, characterized in that, The composite material is made from the following parts by weight of raw materials: 60-90 parts of L-polylactic acid resin, 10-40 parts of pre-dispersed interfacial grafted bamboo fiber masterbatch, and 0.2-0.8 parts of lubricant; The pre-dispersed interface-grafted bamboo fiber masterbatch comprises micro-nano bamboo fibers with a tannic acid coordination modification layer on the surface having metal ions and a chemically grafted polymer layer. The composite material exhibits a biodegradation mass loss rate of 50wt%–60wt% in a composting environment over 12 weeks, and a flexural modulus of 3.5GPa–4.0GPa. The pre-dispersed interface-grafted bamboo fiber masterbatch is prepared from the following raw materials in parts by weight: 89.3 to 100 parts of modified bamboo fiber wet filter cake, 68 to 73 parts of biodegradable polyester carrier resin, 1.8 to 4.0 parts of styrene-acrylic-epoxy functionalized copolymer chain extender, and 0.2 parts of antioxidant; the solid content of the modified bamboo fiber wet filter cake is 28 wt% to 35 wt%. The preparation method of the pre-dispersed interfacial grafted bamboo fiber masterbatch includes the following steps: S1, bamboo pulp fibers are dispersed under high shear and homogenized under high pressure to obtain micro-nano bamboo fiber suspension. After adjusting the pH value of the micro-nano bamboo fiber suspension, tannic acid is added for adsorption. Then, a metal salt aqueous solution is added for coordination reaction. After the reaction is completed, modified bamboo fiber wet filter cake is obtained by pressure filtration. S2 involves mixing modified bamboo fiber wet filter cake, biodegradable polyester carrier resin, and antioxidant, then feeding the mixture into a twin-screw extruder. Moisture is removed in the vacuum exhaust section, and a styrene-acrylic-epoxy functionalized copolymer chain extender is added in the side feeding section after the vacuum exhaust section for reactive extrusion and granulation.

2. The biodegradable polyester composite material of bamboo fiber ultra-nano powder melt blend according to claim 1, characterized in that, The raw materials are in the following weight parts: 80 parts of L-polylactic acid resin, 20 parts of pre-dispersed interface-grafted bamboo fiber masterbatch, and 0.5 parts of lubricant; the lubricant is ethylene bis-stearamide.

3. The biodegradable polyester composite material of bamboo fiber ultra-nano powder melt blend according to claim 1, characterized in that, The modified bamboo fiber wet filter cake is prepared by micronized bamboo fiber through tannic acid adsorption and metal salt coordination reaction. The amount of tannic acid added is 2.0 wt% to 5.0 wt% of the oven-dry weight of the micronized bamboo fiber; The molar ratio of metal ions to tannic acid molecules in the metal salt is 8:1 to 12:

1. The metal ions are selected from aluminum ions, zinc ions, or iron ions.

4. The biodegradable polyester composite material of bamboo fiber ultra-nano powder melt blend according to claim 1, characterized in that, The biodegradable polyester carrier resin is polycaprolactone resin or polybutylene adipate terephthalate resin; the styrene-acrylic acid epoxy functionalized copolymer chain extender is a random copolymer of styrene, methyl acrylate and glycidyl methacrylate.

5. The biodegradable polyester composite material of bamboo fiber ultra-nano powder melt blend according to claim 1, characterized in that, The micro-nano bamboo fiber has an average diameter of 100nm to 300nm and is made from bamboo pulp fiber through high shear dispersion and high pressure homogenization.

6. A method for preparing a biodegradable polyester composite material by melt blending bamboo fiber ultra-nano powder according to any one of claims 1-5, characterized in that, Includes the following steps: S1, bamboo pulp fibers are dispersed under high shear and homogenized under high pressure to obtain micro-nano bamboo fiber suspension. After adjusting the pH value of the micro-nano bamboo fiber suspension, tannic acid is added for adsorption. Then, a metal salt aqueous solution is added for coordination reaction. After the reaction is completed, modified bamboo fiber wet filter cake is obtained by pressure filtration. S2, after mixing modified bamboo fiber wet filter cake, biodegradable polyester carrier resin and antioxidant, feeds it into a twin-screw extruder, removes moisture in the vacuum exhaust section, and adds styrene-acrylic-epoxy functionalized copolymer chain extender in the side feeding section after the vacuum exhaust section for reactive extrusion and granulation. S3, the pre-dispersed interface-grafted bamboo fiber masterbatch, L-rotary polylactic acid resin and lubricant are mixed evenly, and the composite material is obtained by melt blending extrusion and injection molding.

7. The method for preparing the biodegradable polyester composite material of bamboo fiber ultra-nano powder melt blend according to claim 6, characterized in that, In step S1, the micro-nano bamboo fiber suspension is prepared by circulating high-pressure homogenization of bamboo pulp fibers under a pressure of 400 bar to 600 bar; the pH value of the coordination reaction system is 7.8 to 8.2, the reaction temperature is 25℃ to 35℃, and the stirring rate is 400 rpm.

8. The method for preparing the biodegradable polyester composite material of bamboo fiber ultra-nano powder melt blend according to claim 6, characterized in that, In step S2, the vacuum degree of the twin-screw extruder in the vacuum exhaust section is controlled between -0.098MPa and -0.092MPa; the temperature setting range of the extruder from the feed port to the die head is 90℃ to 180℃, of which the temperature of the side feeding section and the reaction metering zone is 170℃ to 180℃.

9. The method for preparing the biodegradable polyester composite material of bamboo fiber ultra-nano powder melt blend according to claim 6, characterized in that, In step S3, the length-to-diameter ratio of the melt blend extrusion is 40:1, the screw speed is 250 rpm to 300 rpm, and the homogenization section temperature is 185℃.

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