Bamboo-based degradable masterbatch material and preparation method thereof

Abstract

This invention discloses a bamboo-based biodegradable masterbatch material and its preparation method, belonging to the field of bio-based fully degradable polymer composite materials. The masterbatch material is composed of bamboo-based fibers, a biodegradable resin system, carbon nanotubes, mineral fillers, and functional additives. The bamboo-based fibers adopt a dual particle size distribution system, and the carbon nanotubes are anchored to the fiber surface through a heat-preserving and stirring reaction to form a nano-bridging network. The preparation method includes fiber pretreatment, mineral composite, nano-modification, resin blending, and total mixing and molding processing. No pre-drying treatment of bamboo powder is required throughout the process. The resulting masterbatch has a tensile strength of not less than 15 MPa, an elongation at break of not less than 100%, and a degradation rate of not less than 95%.

Description

Technical Field

[0001] This invention belongs to the field of bio-based fully degradable polymer composite materials technology, specifically relating to a bamboo-based biodegradable masterbatch material and its preparation method. Background Technology

[0002] With the increasingly severe global plastic pollution problem, biodegradable resins, represented by polylactic acid (PLA), polybutylene adipate-co-butylene terephthalate (PBAT), and polybutylene succinate (PBS), have become an important direction for replacing petroleum-based plastics. In 2020, my country issued the "Opinions on Further Strengthening the Governance of Plastic Pollution," explicitly requiring the promotion of alternative products such as biodegradable shopping bags and packaging films. In 2023, the National Forestry and Grassland Administration and other departments jointly released the "Three-Year Action Plan for Accelerating the Innovative Development of Bamboo-Based Plastic Substitution," further promoting the industrial application of bamboo-based biodegradable materials. However, the aforementioned biodegradable resins generally suffer from high production costs (PBAT approximately RMB 15,000-20,000 / ton, PLA approximately RMB 18,000-25,000 / ton, far exceeding the traditional polyethylene cost of RMB 7,000-9,000 / ton) and unstable processing performance, which limit their large-scale application in major consumer sectors such as packaging and agricultural films. It has become an industry consensus to reduce overall costs by adding low-cost natural plant fiber fillers to biodegradable resins, but how to maintain excellent mechanical and processing properties with high filler content remains a core technical challenge for the industry.

[0003] Bamboo, as a fast-growing and renewable natural resource, is widely distributed in my country, with an annual production of approximately 30 million tons. It possesses natural advantages such as high yield, short growth cycle (mature in 3-5 years), high fiber strength, and excellent biodegradability. Introducing bamboo powder as a filler into biodegradable resin matrices has become an effective way to reduce material costs and increase bio-based content. Currently, publicly available bamboo powder / biodegradable resin composite material technologies mainly suffer from the following shortcomings: First, the interfacial compatibility between bamboo powder and biodegradable resin is poor. Because bamboo fiber contains a large number of polar groups such as hydroxyl groups on its surface, there is a serious interfacial incompatibility problem with hydrophobic polyester resin, resulting in uneven dispersion of bamboo powder in the resin matrix and severely affecting the mechanical properties of the composite material. Existing technologies typically use silane coupling agents (such as KH-550) or aluminate coupling agents to modify the surface of bamboo powder to improve compatibility. However, these chemical modification treatments increase process complexity and cost, and coupling agent residues may affect the biodegradability of the material. For example, CN202110423560.0 discloses a method of emulsifying and coating bamboo powder with a PBAT / chloroform solution to improve interfacial bonding, but this method uses the organic solvent chloroform, posing environmental toxicity risks and high solvent recovery costs.

[0004] Second, the amount of bamboo powder added is limited. Due to interfacial compatibility constraints, the proportion of bamboo powder added in existing technologies is generally below 30% (mass fraction). When the bamboo powder content exceeds this threshold, the tensile strength and elongation at break of the composite material drop sharply, typically with tensile strength falling below 10 MPa and elongation at break falling below 50%, failing to meet the actual processing requirements of blown film and injection molding. This directly limits the advantages of bamboo-based composite materials in cost control and carbon emission reduction, and also hinders the realization of the strategic goal of replacing plastics with bamboo.

[0005] Third, the process is cumbersome and energy-intensive. Bamboo powder typically has a moisture content of 8% to 15%, and it must undergo thorough pre-drying (usually at 80 to 120°C for 4 to 8 hours) before being melt-blended with thermoplastic resin. Otherwise, the moisture will cause the resin to hydrolyze and degrade, resulting in product defects such as air bubbles, at the processing temperature. This pre-drying step significantly prolongs the production cycle, increases energy consumption, and is not conducive to continuous industrial production.

[0006] Fourth, the use of a single resin system leads to insufficient overall performance. Existing bamboo powder composites mostly use PBAT or PLA as a single resin matrix, making it difficult to balance the material's toughness, rigidity, and processing fluidity. While PBAT has good flexibility and elongation at break, its tensile strength and rigidity are insufficient; PLA has high rigidity and transparency, but it is brittle and has poor toughness. A single resin system cannot meet the comprehensive performance requirements of various molding processes (blown film, injection molding, vacuum forming).

[0007] Fifth, there is a lack of nano-reinforcement methods. There are few reports on introducing nanoscale reinforcing phases into existing bamboo powder / biodegradable resin composites to simultaneously improve interfacial bonding and mechanical properties, resulting in limited room for improvement in the overall performance of the materials, especially making it difficult to achieve significant breakthroughs in mechanical properties while maintaining a high bamboo powder content.

[0008] Therefore, there is an urgent need to develop a bamboo-based biodegradable masterbatch material and its preparation method that can achieve high bamboo powder addition, no drying process, multi-process adaptability, high mechanical properties, and full biodegradability. While research on bamboo-based biodegradable composite materials has made some progress both domestically and internationally, nano-reinforcement modification methods are still in their infancy. Most existing literature and patent disclosures focus on traditional methods such as chemical coupling modification of bamboo powder (silane coupling agents, aluminate coupling agents) or thermoplastic starch compatibilization. There are no reports of technical solutions that introduce carbon nanotubes into bamboo fiber / biodegradable resin composite systems and achieve interface reinforcement through in-situ nano-modification under thermal insulation conditions. Furthermore, existing technologies lack technical solutions for improving fiber bulk density and dispersion uniformity through dual-particle-size graded bamboo fiber design. In addition, technical solutions for ternary blending of PBAT, PLA, and PBS—three biodegradable resins with complementary properties—are rarely reported in the field of bamboo-based masterbatches; most existing technologies are limited to PBAT / PLA two-component systems or single resin systems. These technological gaps provide a clear direction and creative space for this invention. Summary of the Invention

[0009] In view of the technical problems in the prior art, such as poor compatibility between bamboo powder and biodegradable resin, limited bamboo powder addition amount, complicated process and insufficient mechanical properties, the purpose of this invention is to provide a bamboo-based biodegradable masterbatch material and its preparation method.

[0010] To achieve the above objectives, this invention provides a bamboo-based biodegradable masterbatch material, comprising, by mass percentage: 10%–60% bamboo-based fiber, 26%–80% biodegradable resin system, 0.5%–5% carbon nanotubes, 2%–6% mineral filler, and 2%–6% functional additives. The bamboo-based fiber is a dual-particle-size gradation system composed of bamboo-based fiber powder with a particle size of 5–10 μm and ultrafine bamboo fiber powder with a particle size of 500–1000 nm. The biodegradable resin system is a ternary blend system composed of PBAT, PLA, and PBS. The carbon nanotubes are anchored to the surface of the bamboo-based fiber through a heat-insulated stirring reaction to form a nano-bridging network structure.

[0011] The present invention also provides a method for preparing the above-mentioned bamboo-based biodegradable masterbatch material, which includes six steps in sequence: fiber pretreatment, mineral composite, nano-modification, resin blending, and total mixing and molding. In the nano-modification step, the water content of the bamboo fiber itself is used to promote the penetration and anchoring of carbon nanotubes on the fiber surface under the heat preservation condition of 50~70°C, and no pre-drying treatment of bamboo powder is required throughout the process.

[0012] This invention constructs a bamboo-based fiber system with dual particle size distribution, employs in-situ carbon nanotube nanomodification technology and a synergistic formulation of PBAT / PLA / PBS ternary biodegradable resins, and combines a drying-free stepwise mixing process with integrated stirring, mixing, and extrusion molding technology to achieve high dispersibility and high interfacial bonding strength with a wide range of flexible addition of bamboo powder from 10% to 60%. In the dual particle size distribution system, coarse fibers form the load-bearing skeleton, while ultrafine fibers fill the gaps and increase the anchoring area of ​​carbon nanotubes. The carbon nanotubes construct a nano-bridging network at the fiber / resin interface to achieve efficient stress transfer. The resulting masterbatch material exhibits excellent mechanical properties, including a tensile strength of not less than 15 MPa, an elongation at break of not less than 100%, a flexural modulus of not less than 1.0 GPa, and a biodegradability of not less than 95%. It is suitable for various molding and processing technologies such as blown film, injection molding, and vacuum forming, while reducing production energy consumption by more than 30% through the drying-free process.

[0013] The beneficial effects of this invention include: (1) The dual-particle-size graded bamboo-based fiber system breaks through the technical bottleneck of bamboo powder addition through the synergistic filling of coarse and fine fibers and the bridging effect of carbon nanotubes, achieving a wide range of adjustable 10%~60%, significantly reducing material costs by 20%~30%; (2) In-situ nano-modification of carbon nanotubes forms a nanoscale conductive network and physical anchoring points on the surface of bamboo fibers, greatly improving the interfacial bonding force and stress transmission efficiency, so that the tensile strength can still reach more than 18 MPa under 50% bamboo powder content; (3) The PBAT / PLA / PBS ternary resin system achieves a synergistic balance of toughness-rigidity-processability, adapting to various molding processes such as blown film, injection molding, vacuum forming, and casting, with a flexural modulus of more than 1.0 GPa; (4) The step-by-step mixing process without drying innovatively utilizes the moisture content of bamboo fibers to promote the interfacial anchoring of carbon nanotubes, eliminating the bamboo powder pre-drying step, shortening the production process by more than 40%, reducing energy consumption by more than 30%, and significantly reducing production costs and carbon emissions; (5) All components are biodegradable, 180 Under composting conditions, the degradation rate reaches over 95%, with no microplastic residue. Bamboo can regenerate and fix carbon, achieving the dual goals of carbon reduction and fixation, which is in line with the national strategy of replacing plastics with bamboo and the policy orientation of carbon neutrality. Detailed Implementation

[0014] The present invention will be further described in detail below with reference to specific embodiments. These embodiments are for illustrative purposes only and do not constitute a limitation on the scope of protection of the present invention.

[0015] Example 1 This embodiment provides a bamboo-based biodegradable masterbatch material. Based on 10 kg of finished product, the components and their amounts are as follows: 4.5 kg of bamboo-based fiber powder with a particle size of 5-10 μm, 0.5 kg of ultrafine bamboo fiber powder with a particle size of 800 nm, with bamboo powder accounting for 50% of the total mass; 2.4 kg of PBAT, 0.8 kg of PLA, 0.3 kg of PBS, with ternary resin accounting for 35% of the total mass; 0.2 kg of chain extender, 0.1 kg of antioxidant, 0.08 kg of dispersant, 0.05 kg of lubricant, 0.03 kg of glycerin, with functional additives accounting for 4.6% of the total mass; 0.2 kg of calcium carbonate with a particle size of 5 μm, 0.3 kg of talc powder with a particle size of 10 μm, with mineral fillers accounting for 5% of the total mass; and 0.3 kg of multi-walled carbon nanotubes, accounting for 3% of the total mass. The chain extender is an ADR-4468 type epoxy functional group chain extender, the antioxidant is a 1:1 mass ratio compound of hindered phenolic antioxidant 1010 and phosphite antioxidant 168, the dispersant is ethylene bis-stearamide (EBS), the lubricant is calcium stearate, and the carbon nanotubes are multi-walled carbon nanotubes with an outer diameter of 10~20 nm and a length of 5~15 μm.

[0016] The preparation method of the above-mentioned bamboo-based biodegradable masterbatch material includes the following steps: Fiber pretreatment: 4.5 kg of bamboo-based fiber powder with a particle size of 5-10 μm and 0.5 kg of ultrafine bamboo fiber powder with a particle size of 800 nm are added to a high-speed mixer and stirred for 15 min at a stirring speed of 1200 r / min to ensure thorough and uniform mixing of the two particle sizes, resulting in a dual-particle-size graded bamboo-based fiber mixed powder. The bamboo-based fiber powder is made from moso bamboo, obtained through steam explosion, mechanical grinding, and air classification. It has a cellulose content of not less than 65%, a lignin content of 8%-15%, a hemicellulose content of 10%-18%, and a moisture content of 8%-12%. The ultrafine bamboo fiber powder is further refined from the above bamboo-based fiber powder using a high-energy ball milling method, with a specific surface area of ​​not less than 15 m². 2 / g. During this mixing process, 800 nm ultrafine fibers fill the gaps between 5~10 μm coarse fibers, forming a dense fiber gradation and packing structure, effectively reducing fiber agglomeration. A high-speed mixer, model SHR-50A, was selected. The mixing blades employ a three-layer dispersion disc structure, with the bottom blade having a linear velocity of approximately 18.8 m / s. The resulting shear force is sufficient to break up the initial agglomerates of bamboo fibers without causing excessive shearing and breakage. After mixing, samples were taken for laser particle size analysis, confirming a bimodal particle size distribution (peaks located near 7 μm and 800 nm, respectively). The peak area ratio was consistent with the feed mass ratio, indicating that the mixing was uniform and met the standards.

[0017] Mineral composite: 0.2 kg of calcium carbonate with a particle size of 5 μm and 0.3 kg of talc powder with a particle size of 10 μm are added to a low-speed mixer and stirred for 10 min at a stirring speed of 600 r / min to ensure thorough and uniform mixing of the two mineral fillers, resulting in a mineral composite powder. The calcium carbonate is stearic acid-treated activated heavy calcium carbonate with a whiteness of not less than 95%, an oil absorption value of 18~22 mL / 100 g, and an activation degree of not less than 95%. The talc powder is hydrated magnesium silicate with a lamellar structure, a whiteness of not less than 92%, and an aspect ratio of not less than 15:1. Calcium carbonate, as a rigid particle, provides heterogeneous nucleation sites and enhances the rigidity of the material. After surface treatment with stearic acid, its compatibility with polyester resin is significantly improved, and it does not cause filler agglomeration or surface roughness of the product during processing. The layered structure of talc helps improve processing fluidity and material dimensional stability. Its layered silicate crystal structure is oriented along the melt flow direction, forming a micro-reinforcing structure similar to overlapping fish scales, effectively improving the flexural modulus and heat distortion temperature of the material. The particle size difference between the two mineral fillers (5 μm and 10 μm) creates a complementary gradation effect. Fine calcium carbonate particles fill the gaps between the talc layers, further improving the packing density of the mineral fillers and their dispersion uniformity in the resin matrix.

[0018] Nano-modification: The above-mentioned dual-particle-size graded bamboo-based fiber mixed powder was added to a reaction vessel along with 0.3 kg of multi-walled carbon nanotubes. The mixture was stirred continuously for 2 h at a stirring speed of 800 r / min and a temperature of 60°C, allowing the carbon nanotubes to be uniformly adsorbed and entangled on the surface of the bamboo fibers, forming a bamboo-based fiber nanocomposite powder. The multi-walled carbon nanotubes had an outer diameter of 10–20 nm, a length of 5–15 μm, a purity of not less than 95% (mass fraction), and a specific surface area of ​​250–350 m². 2 / g, ash content less than 3%. The reactor is a stainless steel reactor with jacketed heating and stirring functions, with an effective volume of 50 L. The stirring blade is an anchor-type stirring blade, which can achieve a uniform temperature and shear field distribution at 60°C. Under the 60°C heat preservation condition, the residual moisture (moisture content 8%~12%) on the surface of bamboo fiber moderately softens the non-crystalline region on the surface of cellulose microfibrils, allowing hemicellulose and lignin molecular chain segments to obtain a certain degree of thermal freedom. The opening of micropores and grooves (pore diameter 50~500 nm) on the fiber surface increases, which is conducive to the firm anchoring of carbon nanotubes to the fiber surface through van der Waals forces and mechanical interlocking, constructing a nanoscale bridging network. Specifically, the π-π interaction between the π electron cloud of the carbon nanotube wall and the π electron of the pyran ring in the bamboo cellulose molecule, combined with the hydrogen bonding between the carboxyl groups at the defect sites of the carbon nanotube end and the hydroxyl groups on the cellulose surface, multiple non-covalent interactions synergistically constitute a stable interfacial anchoring system. Samples were taken every 30 minutes during the reaction, and the coverage and uniformity of carbon nanotubes on the fiber surface were observed under a microscope. After the reaction, the nanocomposite powder was taken out for X-ray photoelectron spectroscopy (XPS) characterization to confirm the presence and binding state of carbon nanotubes on the fiber surface. This step utilizes the moisture content of bamboo powder itself to promote the interfacial bonding between carbon nanotubes and fibers under mild heating conditions, fundamentally eliminating the bamboo powder pre-drying step in the traditional process, while achieving an interfacial bonding effect superior to that of chemical coupling agent treatment.

[0019] Resin blending: 2.4 kg PBAT, 0.8 kg PLA, 0.3 kg PBS, 0.2 kg chain extender, 0.1 kg antioxidant, 0.08 kg dispersant, and 0.03 kg glycerol were sequentially added to a dedicated mixer and stirred at 1000 r / min for 20 min until the materials were completely and uniformly blended, yielding a ternary resin blend. The PBAT had a melt index of 3~6 g / 10 min (190°C, 2.16 kg) and a density of 1.20~1.26 g / cm³. 3The PLA is poly(L-lactic acid) (PLLA) with a molecular weight of 150,000 - 200,000, a D-isomer content of less than 2%, and a glass transition temperature of 55 - 60 °C. The melt index of the PBS is 4 - 8 g / 10min (190 °C, 2.16 kg), and the crystallinity is 30% - 40%. In this process, the chain extender ADR-4468 undergoes ring-opening addition reactions with the terminal carboxyl and hydroxyl groups of PLA and PBAT through its multi-epoxy functional groups (epoxy equivalent of 285 g / eq, containing about 9 epoxy groups per molecule) respectively, generating a block or branched structure connected by covalent bonds, significantly improving the compatibility and melt strength of the ternary resin system. This chain extension reaction can be slowly initiated at room temperature under stirring and shearing conditions,预埋ing reactive sites for the subsequent high-temperature rapid reaction in the extrusion processing stage. As a bio-based plasticizer (with a molecular weight of 92.09), glycerol penetrates between the PLA molecular chains凭借 its trihydroxy structure, weakening the intermolecular forces between the PLA segments through hydrogen bonding, reducing the glass transition temperature of the system by about 8 - 12 °C, and improving the low-temperature toughness and processing fluidity. The antioxidant 1010 / 168 compound system effectively captures free radicals and decomposes peroxides at the processing temperature, preventing the ternary resin from undergoing thermal-oxidative degradation and molecular weight reduction during high-temperature shearing, ensuring the long-term thermal stability and mechanical property retention rate of the material. The bisamide structure of the dispersant EBS forms a lamellar slip structure in the resin melt, reducing the interfacial tension and promoting the uniform dispersion of bamboo fibers in the subsequent overall mixing stage.

[0020] Overall mixing process: The above-mentioned bamboo-based fiber nanocomposite powder, mineral mixture powder, and ternary resin blend are combined and fed into a blender. Stir for 25 min at a stirring speed of 800 r / min to make the three fully mixed evenly, obtaining a raw material mixture. The feeding order is to first feed the ternary resin blend. After stirring for 3 min to form an adhesion layer on the inner wall of the blender, then feed the bamboo-based fiber nanocomposite powder in three batches successively (with an interval of 5 min between each batch), and finally feed the mineral mixture powder and continue stirring until the specified time. This batchwise feeding strategy can effectively prevent dust flying and local high-concentration agglomeration phenomena caused by一次性投入大量纤维粉. In this step, the surface hydrophobicity of the bamboo fibers modified by carbon nanotubes is enhanced (the water contact angle increases from 35° before modification to 78°), significantly improving the wettability with the resin matrix. At the same time, the one-dimensional nanostructure of the carbon nanotubes constructs a bridging channel between the fibers and the resin, promoting stress transfer and effectively solving the technical problem of interfacial debonding under a high bamboo powder content. During the stirring process, the mixing state of the material is monitored in real time through the observation window and sampling port of the blender. When the material呈现均匀的浅棕色且手捏成团、松手即散, it is determined that the overall mixing is qualified. The loose bulk density of the raw material mixture after overall mixing is 0.45 - 0.55 g / cm 3The moisture content is reduced to 4%~6% (about 50% lower than the original moisture content of bamboo fiber, which is 8%~12%), with some moisture evaporating naturally during the nano-modification at 60°C and stirring for 25 minutes.

[0021] Molding and processing: The above raw material mixture, along with 0.05 kg of lubricant, is fed into an integrated mixing and internal mixing extruder. The feed section temperature is set to 170°C, the melting section temperature to 175°C, and the extrusion section temperature to 180°C. Under continuous process conditions of simultaneous mixing, internal mixing, and extrusion, the material undergoes thorough shearing, mixing, and plasticizing homogenization. It is then extruded into coarse filaments through a special shaped die, and subsequently rapidly cooled to room temperature by a series of cold air streams (wind speed 3~5 m / s). The filaments are then automatically pelletized into uniform particles with a particle size of 2~4 mm by an automatic pelletizer, and vacuum-sealed to obtain bamboo-based biodegradable masterbatch material. The integrated mixing and internal mixing extruder is a specialized device that integrates mixing, internal mixing, and extrusion functions. It has a screw length-to-diameter ratio of 28~36:1, a screw speed of 40~80 r / min, and a mixing element inside the barrel to achieve dispersion and distribution mixing of the material. The extrusion temperature gradient design follows the principle of low-temperature feeding - medium-temperature melting - high-temperature homogeneous extrusion. The 170°C feeding section temperature is lower than the complete melting temperature of PBAT (approximately 175°C), allowing the material to be conveyed and initially compacted by the screw in a semi-molten state, preventing premature complete melting of the resin and subsequent sedimentation, stratification, or localized carbonization of the bamboo powder in the low-viscosity melt. The 175°C melting section ensures that the ternary resin is fully plasticized and forms a continuous melt coating layer with the bamboo fiber nanocomposite powder. The chain extender completes its main chain extension reaction at this stage. The 180°C extrusion section ensures that the material flowability meets the requirements of the shaped die. The exit section of the shaped die is clover-shaped or cross-shaped, which is beneficial to increasing the specific surface area of ​​the masterbatch particles and the melting rate during subsequent secondary processing. The tandem cold air cooling device consists of 8-12 sets of industrial fans arranged side by side, with the air temperature at room temperature (15-30°C). The cooling section is 2-3 m long, and the residence time of the coarse filaments in the cold air section is 10-20 s. Rapid cold air cooling inhibits excessive PLA segment crystallization (controlling PLA crystallinity between 25% and 30%), maintaining the material's toughness and secondary molding properties, while avoiding the problems of surface residual moisture and excessive PLA crystallinity associated with water cooling. The automatic pelletizer's cutter speed is dynamically adjusted according to the extrusion rate to ensure uniform particle size (particle size variation coefficient less than 10%) and prevent sticking and tailing. The final product, after being inspected by a metal detector, is vacuum-packed in aluminum foil composite bags, 25 kg per bag, and stored in a cool, dry place with a shelf life of no less than 12 months.

[0022] The performance of the bamboo-based biodegradable masterbatch material prepared in this embodiment was tested. Mechanical properties were tested according to GB / T 1040.2-2006 standard. Samples were injection molded at 185°C using an injection molding machine, with an injection pressure of 80-100 MPa, a holding time of 15 s, and a cooling time of 30 s. Biodegradability was tested under composting conditions according to GB / T 19277.1-2011 standard. The results showed that the masterbatch material prepared in this embodiment had a tensile strength of 18.6 MPa, an elongation at break of 135%, a flexural modulus of 1.28 GPa, a flexural strength of 22.5 MPa, and a notched impact strength of 8.3 kJ / m². 2 The Vicat softening temperature is 85°C, the composting degradation rate after 180 days is 97.2%, and the melt index (190°C, 2.16 kg) is 5.8 g / 10 min. Blown film processing performance tests show that the film bubble is stable under extrusion temperatures of 175–185°C and a blow-up ratio of 2.5:1. The film has a uniform and transparent appearance, a thickness uniformity deviation of less than 5%, a tensile strength (longitudinal) of 12.3 MPa, and an elongation at break (longitudinal) of 180%, meeting the requirements for applications such as shopping bags and agricultural films. SEM cross-sectional observation shows that the bamboo fiber is uniformly dispersed in the resin matrix, with a fiber dispersion coefficient (CV) of 11.2%. Carbon nanotubes are distributed in a network at the fiber / resin interface, and obvious carbon nanotube bridging remnants can be observed on the fiber pull-out cross-section, indicating good interfacial bonding. DSC analysis showed that the PLA component had a crystallinity of 28.6%, the PBAT component had a melting peak at 125.3°C, and the PBS component had a melting peak at 113.8°C. The thermal behaviors of the three components were independent, but the covalent cross-linking formed by the chain extender stabilized the interfacial bonding between the phases. TGA analysis showed the initial decomposition temperature (T0) of the material. 5% The maximum decomposition rate temperature (T) is 268°C. max The temperature is 362°C, and it has sufficient thermal stability margin within the processing temperature range of 170~185°C.

[0023] Example 2 This embodiment provides a bamboo-based biodegradable masterbatch material. Based on 10 kg of finished product, the components and their amounts are as follows: 5.0 kg of bamboo-based fiber powder with a particle size of 5-10 μm, 1.0 kg of ultrafine bamboo fiber powder with a particle size of 800 nm, with bamboo powder accounting for 60% of the total mass; 1.8 kg of PBAT, 0.6 kg of PLA, 0.2 kg of PBS, with ternary resin accounting for 26% of the total mass; 0.15 kg of chain extender, 0.08 kg of antioxidant, 0.06 kg of dispersant, 0.04 kg of lubricant, and 0.02 kg of glycerol; 0.15 kg of calcium carbonate with a particle size of 5 μm, and 0.25 kg of talc powder with a particle size of 10 μm; and 0.45 kg of multi-walled carbon nanotubes, accounting for 4.5% of the total mass. The preparation method in this embodiment is the same as that in Example 1, wherein the stirring speed in the fiber pretreatment step is 1500 r / min and the stirring time is 20 min; the temperature in the nano-modification step is 65°C and the reaction time is 2.5 h; and the extrusion temperature gradient in the molding process is 168°C (feeding section), 173°C (melting section), and 178°C (extrusion section).

[0024] In this embodiment, the bamboo powder content is increased to 60%, representing the highest addition amount. To compensate for the impact of high fiber content on processing flowability, the carbon nanotube dosage is simultaneously increased to 4.5% to enhance fiber dispersibility and interfacial bonding. The stirring speed is increased to 1500 r / min to strengthen the mixing effect, and the dosage of ultrafine bamboo fiber powder is also simultaneously increased to 1.0 kg (coarse to fine mass ratio 5:1) to increase fiber gap filling efficiency and carbon nanotube anchoring density. The nano-modification temperature is increased to 65°C, and the reaction time is extended to 2.5 h to ensure that a higher content of carbon nanotubes is uniformly anchored on a larger area of ​​fiber surface. The extrusion temperature gradient is appropriately reduced by 2°C to reduce the carbonization risk of the high bamboo powder content system. Test results show that the masterbatch material prepared in this embodiment has a tensile strength of 15.3 MPa, an elongation at break of 102%, a flexural modulus of 1.56 GPa, a 180-day compost degradation rate of 98.5%, and a melt flow index of 4.2 g / 10 min. Compared with Example 1, due to the significantly increased bamboo powder content, the rigidity of the material is enhanced (flexural modulus increased by 21.9%), but the toughness is slightly reduced. It still meets the requirements of injection molding, the cost is reduced by about 30% compared with pure biodegradable resin, and the bio-based content is increased to more than 65%.

[0025] Example 3 This embodiment provides a low-bamboo-powder-content bamboo-based biodegradable masterbatch material. Based on 10 kg of finished product, the components and their amounts are as follows: 0.8 kg of bamboo-based fiber powder with a particle size of 5-10 μm, 0.2 kg of ultrafine bamboo fiber powder with a particle size of 800 nm, totaling 10% of the total bamboo powder. 4.5 kg of PBAT, 2.0 kg of PLA, 1.5 kg of PBS, totaling 80% of the total ternary resin. 0.25 kg of chain extender, 0.12 kg of antioxidant, 0.1 kg of dispersant, 0.06 kg of lubricant, 0.04 kg of glycerol, 0.1 kg of calcium carbonate with a particle size of 5 μm, 0.15 kg of talc with a particle size of 10 μm, and 0.08 kg of multi-walled carbon nanotubes. The preparation method in this embodiment is the same as in Example 1, wherein the temperature of the nano-modification step is 55°C and the reaction time is 1.5 h; the extrusion temperature gradient of the molding process is 172°C (feeding section), 178°C (melting section), and 183°C (extrusion section).

[0026] In this embodiment, the bamboo powder content is 10%, representing the minimum addition threshold scheme, suitable for film products requiring high transparency and surface gloss. Test results show that the masterbatch material prepared in this embodiment has a tensile strength of 22.4 MPa, an elongation at break of 285%, a 180-day compost degradation rate of 95.8%, and a melt flow index of 8.5 g / 10 min, which meets the processing requirements of blown film and cast film, and the film surface is smooth with no obvious particle feel.

[0027] Example 4 This embodiment provides a bamboo-based biodegradable masterbatch material using an alternative resin system. Based on 10 kg of finished product, the components and their amounts are as follows: 3.5 kg of bamboo-based fiber powder with a particle size of 5-10 μm, 0.5 kg of ultrafine bamboo fiber powder with a particle size of 800 nm, with bamboo powder accounting for 40% of the total mass; 2.0 kg of polyhydroxyalkanoates (PHA), 1.5 kg of polypropylene carbonate (PPC), 1.0 kg of PLA, with the alternative resin accounting for 45% of the total mass; 0.2 kg of chain extender, 0.1 kg of antioxidant, 0.08 kg of dispersant, 0.05 kg of lubricant, and 0.03 kg of glycerol; 0.25 kg of talc powder with a particle size of 10 μm, and 0.2 kg of kaolin with a particle size of 5 μm; and 0.35 kg of multi-walled carbon nanotubes. The preparation method of this embodiment is the same as in Example 1, except that kaolin replaces calcium carbonate in the mineral composite step, and PHA and PPC replace PBAT and PBS in the resin blending step.

[0028] This embodiment verifies the substitutability of the resin system and mineral filler. The introduction of PHA further improves the biodegradation rate of the material, while PPC, as a CO2 copolymer, provides good barrier properties and flexibility. Test results show that the masterbatch material prepared in this embodiment has a tensile strength of 16.8 MPa, an elongation at break of 118%, a 180-day composting degradation rate of 98.1%, and a melt flow index of 5.1 g / 10 min.

[0029] Example 5 This embodiment provides a biodegradable masterbatch material using alternative plant fibers. Based on 10 kg of finished product, the components and their amounts are as follows: 3.5 kg of sugarcane bagasse fiber powder (5-10 μm particle size), 0.5 kg of ultrafine straw fiber powder (800 nm particle size), with plant fibers accounting for 40% of the total mass; 2.8 kg of PBAT, 1.0 kg of PLA, 0.5 kg of PBS; 0.2 kg of chain extender, 0.1 kg of antioxidant, 0.08 kg of dispersant, 0.05 kg of lubricant, and 0.03 kg of glycerol; 0.15 kg of calcium carbonate (5 μm particle size), 0.25 kg of talc (10 μm particle size); and 0.3 kg of multi-walled carbon nanotubes. The preparation method of this embodiment is the same as in Example 1, except that sugarcane bagasse fiber and straw fiber replace bamboo-based fibers.

[0030] This embodiment verifies the wide applicability of plant fiber raw materials. Test results show that the masterbatch material prepared in this embodiment has a tensile strength of 15.9 MPa, an elongation at break of 108%, and a compost degradation rate of 96.3% after 180 days. Compared with the bamboo-based fiber solution, the mechanical properties are slightly lower, mainly because the cellulose content and crystallinity of bagasse fiber are lower than those of bamboo fiber.

[0031] Comparative Example 1 The difference between this comparative example and Example 1 is that carbon nanotubes were not added; all other components and processing conditions were the same as in Example 1. The 0.3 kg mass of carbon nanotubes was replaced with PBAT. Test results showed that the masterbatch material had a tensile strength of 11.2 MPa, an elongation at break of 68%, a flexural modulus of 0.95 GPa, and a notched impact strength of 4.1 kJ / m. 2Compared to Example 1, the tensile strength decreased by 39.8%, the elongation at break decreased by 49.6%, the flexural modulus decreased by 25.8%, and the notched impact strength decreased by 50.6%. SEM cross-sectional observation showed a significant debonding gap (approximately 0.5–2 μm wide) at the fiber / resin interface, and the fiber pull-out surface was smooth with no resin residue, indicating extremely weak interfacial bonding. This suggests that the introduction of carbon nanotubes plays a crucial role in improving the interfacial bonding and mechanical properties of bamboo fiber / resin. In the system without carbon nanotubes, the bamboo fiber and resin are bonded only by physical entanglement and van der Waals forces, resulting in low interfacial shear strength (estimated at approximately 2–3 MPa). Under tensile stress, interfacial debonding and fiber pull-out are prone to occur, and cracks propagate rapidly along the fiber / resin interface, leading to early material fracture and a significant decrease in mechanical properties.

[0032] Comparative Example 2 The difference between this comparative example and Example 1 is that only 5.0 kg of bamboo-based fiber powder with a single particle size of 5-10 μm was used, omitting 800 nm ultrafine bamboo fiber powder. All other components and process conditions remained the same as in Example 1. Test results showed that the masterbatch material had a tensile strength of 14.1 MPa, an elongation at break of 86%, and a fiber dispersion coefficient (CV) of 23.5%. Compared to Example 1 (CV=11.2%), the tensile strength decreased by 24.2%, the elongation at break decreased by 36.3%, and the fiber dispersion uniformity significantly deteriorated. SEM observation revealed numerous fiber agglomeration regions (agglomerate size 50-200 μm) in the single coarse-particle-size fiber system. Insufficient resin penetration within these agglomeration regions created weak points for stress concentration and crack initiation. This indicates that the dual-particle-size gradation design significantly contributes to the improvement of the material's mechanical properties. The ultrafine fibers fill the gaps between the coarse fibers to form a dense packing structure, eliminating large voids between the coarse fibers, improving the fiber volume filling efficiency and the contact area with the resin, while the ultrafine fibers have a high specific surface area (not less than 15 μm²). 2 / g (approximately 10 times that of coarse fibers) enhances the adsorption and anchoring density of carbon nanotubes, increasing the coverage of carbon nanotubes around each coarse fiber from approximately 40% in a single-size system to approximately 75% in a dual-size system, further improving the interfacial bonding effect.

[0033] Comparative Example 3 The difference between this comparative example and Example 1 is that only 3.5 kg of PBAT was used as the single resin matrix, without PLA and PBS. All other components and process conditions were the same as in Example 1. Test results showed that the masterbatch material had a tensile strength of 12.8 MPa and an elongation at break of 178%, but a flexural modulus of only 0.52 GPa and a Vicat softening temperature of only 62°C (compared to 85°C in Example 1). During blown film production, the bubble stability was poor, with the bubble oscillation exceeding 20% ​​of the tube diameter, and the film thickness deviation exceeding 15%. The resulting product surface was soft, sticky, and lacked stiffness. Compared to Example 1 (flexural modulus 1.28 GPa, thickness deviation less than 5%), the rigidity was severely insufficient. This indicates that the synergistic design of the ternary resins—PLA providing a rigid framework (PLA's flexural modulus is approximately 3.5 GPa, seven times that of PBAT) and PBS providing processing fluidity and heat resistance (PBS has a fast crystallization rate and high crystallinity, allowing for rapid curing and shaping during the cooling stage)—is crucial for achieving multi-process adaptability. In the ternary system, PLA's semi-crystalline structure provides dimensional stability and surface hardness, PBS improves processing window width and low-temperature toughness, and PBAT provides flexibility and tear resistance. The synergistic effect of the three achieves a comprehensive performance balance that cannot be achieved by a single resin.

[0034] Comparative Example 4 The difference between this comparative example and Example 1 is that the bamboo powder underwent a pre-drying treatment at 110°C for 4 hours before use, omitting the 60°C heat treatment process in the nano-modification step (replacing it with simple stirring and mixing of carbon nanotubes at room temperature for 30 minutes). All other components and process conditions remained the same as in Example 1. Test results showed that the masterbatch material had a tensile strength of 16.5 MPa and an elongation at break of 120%. Compared to Example 1 (tensile strength 18.6 MPa, elongation at break 135%), the mechanical properties were slightly reduced. More importantly, the pre-drying step consumed an additional 8.5 kW·h / batch of energy, extended the production cycle by approximately 5 hours, and increased the energy consumption per unit product by approximately 32%. This indicates that the drying-free stepwise mixing process of this invention not only simplifies the production process and reduces energy consumption, but also achieves superior mechanical properties by retaining the moisture content of the bamboo fiber under gentle heating conditions to promote interfacial anchoring of carbon nanotubes.

[0035] Comparative Example 5 The difference between this comparative example and Example 1 is that the extrusion temperature was uniformly set at 180°C (without gradient), and the cooling method was changed to water cooling (water temperature 20°C). All other components and process conditions remained the same as in Example 1. Test results showed that the masterbatch material had a tensile strength of 15.8 MPa and an elongation at break of 92%. Slight charring and discoloration appeared on the particle surface, and the particles adhered after pelleting. Compared to Example 1, uniform high-temperature extrusion caused localized carbonization of the bamboo fiber in the feed section, producing a burnt odor. Water cooling resulted in excessively high PLA crystallinity (DSC test showed 42.3% crystallinity, compared to 28.6% in Example 1), leading to increased material brittleness and a significant decrease in elongation at break. Additionally, residual moisture on the surface of the water-cooled particles increased the risk of mold growth after packaging.

[0036] Performance testing methods: Mechanical property testing: Tensile strength and elongation at break were tested according to GB / T 1040.2-2006 standard using a universal testing machine (model CMT4104), with a tensile rate of 50 mm / min. The specimen size was a standard type 1A dumbbell-shaped strip, and at least 5 parallel specimens were tested in each group, with the average value taken. Flexural modulus testing was conducted according to GB / T 9341-2008 standard, with a span of 64 mm and a loading rate of 2 mm / min.

[0037] Melt flow index test: conducted according to GB / T 3682-2000 standard, test temperature 190°C, load 2.16 kg, using melt flow indexer (model XNR-400A), sample taken and weighed after preheating for 4 min.

[0038] Biodegradation performance test: Biodegradation test was conducted in accordance with GB / T 19277.1-2011 / ISO 14855-1:2012 standard under composting conditions of 58°C±2°C for 180 days. The degradation rate was calculated by measuring the CO2 release.

[0039] Mixing uniformity test: The microstructure of the masterbatch cross-section was observed using a scanning electron microscope (SEM, model Zeiss Sigma 300), and the elemental surface area analysis (EDS) was used to evaluate the dispersion state of bamboo fibers and the distribution of carbon nanotubes. Mixing uniformity was characterized by the fiber dispersion coefficient. The coefficient of variation (CV) was calculated by statistically analyzing the fiber area ratio of at least 20 equal-area regions in the SEM image. A CV less than 15% was considered as uniform mixing.

[0040] Thermal performance testing: Differential scanning calorimetry (DSC, model TA Q2000) was used for thermal analysis under a nitrogen atmosphere, with a heating rate of 10°C / min and a test range of -60°C to 250°C. Thermal stability testing was performed using a thermogravimetric analyzer (TGA, model Netzsch STA 449F5), under a nitrogen atmosphere, with a heating rate of 10°C / min and a test range of 30°C to 600°C.

[0041] Film blowing performance test: A single-screw blown film machine (model SJ-45, screw diameter 45 mm) was used for blown film test. The extrusion temperature was set to 170~185°C, the blow-up ratio was 2.5:1, and the traction ratio was 4:1. The stability of the film bubble, the appearance of the film and the uniformity of the thickness were recorded.

[0042] The core performance test data of the above embodiments and comparative examples are summarized in Tables 1 and 2.

[0043] Table 1 Performance test data of bamboo-based biodegradable masterbatch materials in each embodiment

[0044] Table 2 Performance comparison data of each comparative example and Example 1

[0045] Table 3 Performance change rate of each comparative example relative to Example 1

[0046] As shown in Table 1, Examples 1-5 achieved the performance targets of tensile strength not less than 15 MPa, elongation at break not less than 100%, and compost degradation rate not less than 95% within a wide range of bamboo powder content from 10% to 60%. As the bamboo powder content increased from 10% (Example 3) to 60% (Example 2), the tensile strength decreased from 22.4 MPa to 15.3 MPa, a decrease of 31.7%, but the flexural modulus increased from 0.85 GPa to 1.56 GPa, an increase of 83.5%, indicating that increasing the bamboo fiber content is beneficial to improving the material's rigidity. Simultaneously, the degradation rate increased from 95.8% to 98.5%, indicating that high bamboo powder content helps accelerate the material's biodegradation. The performance data of Example 4 (PHA / PPC / PLA alternative resin system) and Example 5 (bagasse / straw alternative fiber) demonstrate the wide applicability and substitutability of the formulation system of this invention.

[0047] Comparative analysis of Tables 2 and 3 allows for the quantitative determination of the independent contribution of each technical feature to material properties. Carbon nanotube nanomodification is the primary factor in improving mechanical properties; its absence (Comparative Example 1) leads to a 39.8% decrease in tensile strength, a 50.6% decrease in notched impact strength, and a 66.1% deterioration in fiber dispersion coefficient. This is because the nano-bridging network constructed by carbon nanotubes on the bamboo fiber surface is the core structural basis for achieving efficient stress transfer and uniform fiber dispersion. Without carbon nanotubes, the interfacial shear strength is significantly reduced, and fiber pull-out becomes the main failure mode. The absence of the dual-particle-size gradation design (Comparative Example 2) leads to a 109.8% deterioration in fiber dispersion coefficient (from 11.2% to 23.5%), indicating that the filling effect of ultrafine fibers on the gaps between coarse fibers is key to achieving uniform dispersion. The deterioration in dispersion coefficient directly results in a 24.2% decrease in tensile strength and a 36.3% decrease in elongation at break, respectively. The lack of ternary resin synergy (Comparative Example 3) resulted in a 59.4% decrease in flexural modulus, a drop in Vicat softening temperature to 62°C, and a film thickness deviation exceeding 15%. This is one of the most irreplaceable technical features of this invention. The rigidity contribution of PLA and the crystallization rate control of PBS are crucial for precision molding processes such as blown film. The comparison of the pre-drying process (Comparative Example 4) is particularly noteworthy: the pre-drying scheme not only increased energy consumption by 32% (from 25.3 kW·h to 33.8 kW·h per batch), but also resulted in inferior mechanical properties compared to the pre-drying scheme (tensile strength decreased by 11.3%), fully verifying the innovative mechanism of this invention that utilizes the moisture content of bamboo fiber to promote the micropore interlocking of carbon nanotubes. Temperature gradient extrusion combined with combined cold air cooling (Comparative Example 5) effectively avoided bamboo fiber carbonization (appearance charring and discoloration) caused by uniform high temperature and excessive PLA crystallization (crystallinity increased from 28.6% to 42.3%) caused by water cooling. Excessive PLA crystallinity is the direct cause of the sharp drop in elongation at break from 135% to 92%.

[0048] Analysis of the data in Tables 1-3 leads to the conclusion that the five core technical features of this invention (dual-particle-size graded bamboo fiber, carbon nanotube nano-modification, ternary resin synergy, drying-free stepwise mixing, and gradient temperature extrusion + cold air cooling) are not simply a combination of technologies, but rather constitute a mutually supportive and synergistic technical system. The effectiveness of carbon nanotube modification relies on the high specific surface area provided by the dual-particle-size gradation; the feasibility of the drying-free process is based on the microporous interlocking mechanism of carbon nanotubes; and the compatibility of the ternary resin requires the chain extender to fully react under gradient temperature conditions. The absence of any single technical feature would lead to a significant decrease in material properties (tensile strength reduction of 11.3%~39.8%). The synergistic effect of the five features enables this invention to achieve comprehensive performance of 18.6 MPa tensile strength, 135% elongation at break, and 1.28 GPa with 50% bamboo powder content, far exceeding the level of existing technologies.

[0049] The superior comprehensive performance of the bamboo-based biodegradable masterbatch material of this invention stems from the systematic construction of a multi-level synergistic enhancement mechanism.

[0050] At the fiber gradation level, the dual-size bamboo-based fiber system follows the particle gradation packing theory. 5–10 μm coarse fibers form the skeletal network, undertaking the main load transfer function, while 800 nm ultrafine fibers fill the gaps between the coarse fibers, improving volumetric filling efficiency and increasing the fiber-resin interface contact area. According to the Andreasen continuous gradation model, the particle size ratio of coarse to fine fibers is approximately 6–12, close to the theoretical optimal gradation range (5–15). Therefore, the dual-size system can achieve a fiber packing density and dispersion uniformity far exceeding those of a single-size system.

[0051] At the level of nanoscale modification, carbon nanotubes possess high aspect ratios (approximately 500–1500) and ultra-large specific surface areas (200–400 m²). 2 A dense nano-entangled network is formed on the surface of bamboo fiber using carbon nanotubes ( / g). Physical adsorption between carbon nanotubes and bamboo cellulose molecular chains is achieved through van der Waals forces and hydrogen bonds. Simultaneously, the defect sites on the carbon nanotube walls can form weak chemical bonds with the hydroxyl groups on the cellulose surface. More importantly, one end of the carbon nanotube is anchored to the bamboo fiber surface, while the other end extends into the resin matrix, creating a nano-pinning effect and constructing an efficient stress transfer bridge at the fiber / resin interface. When external forces are applied to the composite material, the stress is uniformly transferred from the resin matrix to the bamboo fiber skeleton through the carbon nanotube bridging network, avoiding stress concentration and interfacial debonding. This results in a significant improvement in mechanical properties while maintaining a high bamboo powder content.

[0052] At the resin synergy level, the PBAT / PLA / PBS ternary system achieves a three-dimensional balance of toughness, rigidity, and processability. PBAT, as the main resin (accounting for approximately 69% of the total resin), provides flexibility and high elongation at break; its aliphatic-aromatic copolymer structure endows the material with excellent toughness and tear resistance. PLA (accounting for approximately 23% of the total resin), as the rigid component, provides tensile strength and flexural modulus; its semi-crystalline structure enhances the material's dimensional stability and surface hardness. PBS (accounting for approximately 8% of the total resin), as the processability modifier, improves the processing window width of the ternary system with its excellent melt flowability and low-temperature toughness. The chain extender ADR-4468 forms a covalent crosslinking network through the reaction of polyepoxy functional groups with the end groups of the three polyesters, effectively improving the compatibility and melt strength of the ternary system, resulting in stable film bubbles and uniform film thickness during blown film production.

[0053] At the level of the no-drying mechanism, this invention innovatively transforms the inherent moisture content of bamboo fiber (approximately 8%–12%) from a defective factor in traditional processes into a promoting factor for carbon nanotube interface modification. During the 60°C heat-preservation nano-modification process, the adsorbed and bound water on the surface of the bamboo fiber moderately softens the non-crystalline regions of the cellulose microfiber surface, giving the cellulose molecular chain segments a certain degree of freedom of movement, which is conducive to the penetration and embedding of carbon nanotubes into the micropores and grooves on the fiber surface. Specifically, the cell wall micropores (pore size 50–500 nm) on the surface of bamboo fiber open moderately in the hydrated state due to the swelling effect of water molecules, increasing their pore size by approximately 20%–40%, which precisely matches the outer diameter of the carbon nanotubes (10–20 nm), allowing the carbon nanotubes to be partially embedded in the micropores to form a "mortise and tenon" mechanical interlocking structure. When the moisture evaporates and the micropores shrink in subsequent processing stages, the carbon nanotubes are "clamped" in the micropores, forming a more robust anchoring effect, a unique advantage that cannot be achieved with dried bamboo fiber. Simultaneously, water molecules act as "molecular lubricants" between the carbon nanotube walls and the cellulose surface, lowering the energy barrier for carbon nanotube rearrangement on the fiber surface and promoting the transition of carbon nanotubes from random distribution to oriented alignment along the fiber's long axis, further enhancing the isotropic nature of the nano-bridging effect. Furthermore, under mild heating conditions of 60°C, the hemicellulose component in bamboo fiber undergoes partial hydrolysis, releasing small-molecule sugars such as xylooligosaccharides and arabinose. These sugar molecules can form a thin coating on the carbon nanotube walls, simultaneously forming chemical bridges with the carbon nanotube walls (π-π interactions) and the cellulose surface (hydrogen bonding) through the polyhydroxy structure of the sugar molecules, further strengthening the bonding strength at the carbon nanotube-fiber interface. In the subsequent total blending and extrusion processing stage (170~180°C), residual moisture escapes as vapor, preventing defects such as bubbles or hydrolysis in the final product, as the carbon nanotubes have already formed a stable physical anchoring structure on the fiber surface, unaffected by moisture escape. The steam pressure at the processing temperature actually helps to generate a slight expansion effect inside the material, promoting the penetration and wetting of the resin melt into the fiber gaps, and further improving the integrity of the interfacial bonding.

[0054] The aforementioned multi-level synergistic mechanism enables the bamboo-based biodegradable masterbatch material of this invention to achieve excellent mechanical properties such as tensile strength of 18.6 MPa and elongation at break of 135% even with a bamboo powder content of 50%. This far exceeds the technical bottleneck in existing technologies where performance declines sharply when the bamboo powder content exceeds 30%. Simultaneously, the 180-day composting degradation rate reaches 97.2%, meeting the requirements for full biodegradation. From the perspective of degradation mechanism, the biodegradation process of the material of this invention follows a three-stage degradation model of "surface erosion - bulk hydrolysis - microbial digestion." First, the hydrophilicity and porous structure of bamboo fiber provide channels for microorganisms and water molecules to enter the material's interior, allowing degradation to rapidly advance from the surface to the bulk phase. Second, the aliphatic ester bonds of PBAT and PBS undergo enzymatic hydrolysis catalyzed by lipases and esterases produced by microorganisms, while PLA undergoes non-enzymatic hydrolysis at composting temperature (58°C) to produce lactic acid monomers, which are subsequently metabolized by microorganisms into CO2 and H2O. Carbon nanotubes, due to their low dosage (3%~5%) and dispersed state at the fiber / resin interface, do not affect the enzymatic degradation process of the polyester matrix by microorganisms. Bamboo cellulose is gradually degraded into glucose units by cellulase, and ultimately completely converted into CO2 and H2O, achieving complete biodegradation with no microplastic residue. The mineral fillers (calcium carbonate and talc) are natural minerals that return to the soil as inorganic powder during degradation, causing no secondary pollution to the environment.

[0055] The above description is merely 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 scope of the claims of the present invention.

Claims

1. A bamboo-based biodegradable masterbatch material, characterized in that, The masterbatch material comprises the following components by mass percentage: 10%~60% bamboo-based fiber, 26%~80% biodegradable resin system, 0.5%~5% carbon nanotubes, 2%~6% mineral filler, and 2%~6% functional additives; the bamboo-based fiber is a dual-particle-size gradation system composed of bamboo-based fiber powder with a particle size of 5~10 μm and ultrafine bamboo fiber powder with a particle size of 500~1000 nm in a mass ratio of (7~10):(1~3); the biodegradable resin system is a ternary blend system composed of polybutylene adipate-co-butylene terephthalate, polylactic acid, and polybutylene succinate in a mass ratio of (5~8):(1.5~3):(0.5~2); the carbon nanotubes are multi-walled carbon nanotubes with an outer diameter of 5~30 nm and a length of 1~20 μm, which are adsorbed and anchored on the surface of bamboo-based fiber through a heat-insulating stirring reaction to form a nano-bridging network structure.

2. The bamboo-based biodegradable masterbatch material according to claim 1, characterized in that, The functional additives include chain extenders, antioxidants, dispersants, lubricants, and glycerin. The chain extenders are acrylate chain extenders containing polyepoxy functional groups, and the antioxidants are a compound of hindered phenolic antioxidants and phosphite antioxidants.

3. The bamboo-based biodegradable masterbatch material according to claim 1, characterized in that, The mineral filler includes calcium carbonate with a particle size of 3-8 μm and talc with a particle size of 8-15 μm, wherein the mass ratio of calcium carbonate to talc is (1-3):(2-5).

4. The bamboo-based biodegradable masterbatch material according to claim 1, characterized in that, The polybutylene adipate-co-butylene terephthalate in the biodegradable resin system can be replaced by polyhydroxyalkanoates, and the polybutylene succinate can be replaced by polypropylene carbonate; the bamboo-based fiber can be replaced by bagasse fiber, straw fiber or coconut shell fiber.

5. The bamboo-based biodegradable masterbatch material according to claim 1, characterized in that, The masterbatch material has a tensile strength of not less than 15 MPa, an elongation at break of not less than 100%, a biodegradability of not less than 95% under 180-day composting conditions, and a melt flow index of 3~10 g / 10 min.

6. A method for preparing bamboo-based biodegradable masterbatch material as described in any one of claims 1 to 5, characterized in that, The process includes the following steps: fiber pretreatment, in which bamboo-based fiber powder with a particle size of 5-10 μm and ultrafine bamboo fiber powder with a particle size of 500-1000 nm are put into a high-speed mixer and stirred for 10-25 min at a stirring speed of 1000-1800 r / min to obtain a bamboo-based fiber mixed powder with dual particle size distribution. Mineral composite: Calcium carbonate and talc powder are stirred at a stirring speed of 400~800 r / min for 8~15 min to obtain mineral mixed powder; Nano-modification: A mixture of bamboo-based fiber powder with dual particle size distribution and carbon nanotubes is added to a reactor and stirred at a stirring speed of 600-1000 r / min and a temperature of 50-70°C for 1-3 h to obtain bamboo-based fiber nanocomposite powder; Resin blending: Polybutylene adipate-co-butylene terephthalate, polylactic acid, polybutylene succinate, chain extender, antioxidant, dispersant and glycerol are stirred at a stirring speed of 800-1200 r / min for 15-25 min to obtain a ternary resin blend; The overall mixing process involves mixing bamboo-based fiber nanocomposite powder, mineral mixed powder, and ternary resin blends at a stirring speed of 600~1000 r / min for 20~30 min to obtain a raw material mixture. The molding process involves feeding the raw material mixture and lubricant into an integrated mixing and mixing extruder, followed by gradient temperature extrusion, cold air cooling, and pelletizing to obtain bamboo-based biodegradable masterbatch material.

7. The preparation method according to claim 6, characterized in that, In the nano-modification step, the natural moisture content of bamboo-based fibers (8%~15%) is utilized to soften the non-crystalline region on the surface of cellulose microfibers under a heat preservation condition of 50~70°C. This promotes the penetration and embedding of carbon nanotubes into the micropores and grooves on the fiber surface to form physical anchoring. No pre-drying treatment of bamboo-based fibers is required throughout the process.

8. The preparation method according to claim 6, characterized in that, In the molding process, the gradient temperature is set to 165~172°C for the feeding section, 170~178°C for the melting section, and 175~185°C for the extrusion section. The cold air cooling adopts a row-type cold air device with a wind speed of 3~6 m / s, which quickly cools the extruded coarse filaments to room temperature and then cuts them into particles with a particle size of 2~5 mm by an automatic pelletizer.

9. The preparation method according to claim 6, characterized in that, The stirring speed in the fiber pretreatment step is 1200~1500 r / min, and the stirring time is 15~20 min; the stirring speed in the nano-modification step is 800 r / min, the temperature is 60~65°C, and the reaction time is 2~2.5 h.

10. The preparation method according to claim 6, characterized in that, In the resin blending step, the amount of chain extender added is 2% to 8% of the total mass of the biodegradable resin system. The chain extender forms a covalent cross-linked network by undergoing ring-opening addition reactions with the terminal carboxyl groups and terminal hydroxyl groups of polylactic acid and polybutylene adipate-co-butylene terephthalate through polyepoxy functional groups.

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