Low-density high-performance full-biodegradable composite material and green preparation method thereof

Abstract

The invention relates to the technical field of biodegradable materials, and discloses a low-density high-performance full-biodegradable composite material and a green preparation method thereof. Comprising PBAT resin, low-melting-point modified PGA resin, PPC resin, PLA resin, modified PFM plant fibers, activated hydroxyapatite, a reactive epoxy compatibilizer, a bio-based composite plasticizer, a nano composite nucleating agent and a natural antioxidant system. The preparation method comprises the following steps: treating the PFM plant fibers and the hydroxyapatite; mixing and spraying a liquid bio-based composite plasticizer; and injecting a supercritical fluid, and carrying out underwater pelletizing and drying. The low-melting-point modified PGA resin and the modified PFM plant fiber are introduced, and the reaction type epoxy compatibilizer reacts at the multi-phase matrix interface of the PBAT resin, the PPC resin and the PLA resin to enhance the interface bonding force, so that the high-performance composite material with low density, high strength, high toughness and excellent thermal stability is obtained.

Description

Technical Field

[0001] This invention relates to the field of biodegradable materials technology, specifically to low-density, high-performance, fully biodegradable composite materials and their green preparation methods. Background Technology

[0002] With the increasing application of fully biodegradable materials in packaging, agriculture, and daily consumer goods, matrix resins such as polybutylene adipate / terephthalate (PBAT), polypropylene carbonate (PPC), and polylactic acid (PLA) have become research hotspots. However, single-component biodegradable resins often struggle to simultaneously meet the demands for high performance and lightweight applications. For example, while PBAT resin exhibits good toughness, it falls short in terms of strength and barrier properties, while PLA resin, despite its high hardness, suffers from brittleness. To improve mechanical properties, existing technologies often employ the addition of inorganic fillers. However, this typically leads to an increase in the density of the composite material, making it difficult to meet the requirements for low-density and lightweight construction. Furthermore, simple blending often results in brittle fracture under stress due to insufficient interfacial bonding.

[0003] In the pursuit of high-performance biodegradable materials, polyglycolic acid (PGA) has been introduced as a reinforcing component due to its excellent mechanical strength and barrier properties. However, conventional PGA resins have high melting points, typically above 220°C, while resins such as PBAT and PPC have relatively low thermal stability and are prone to thermal decomposition or chain scission at high temperatures. This mismatch in processing temperature windows creates a dilemma in the preparation of multi-component composites: while ensuring sufficient melting and plasticization of PGA, other heat-sensitive matrix resins degrade, leading to a decrease in molecular weight and yellowing of the composite material, thus affecting its overall performance. Furthermore, the polarity differences between different types of polyester resins result in poor compatibility and weak interfacial bonding in the blend system, limiting further improvements in material performance.

[0004] Furthermore, using natural plant fibers to reinforce biodegradable polyesters is an effective means of reducing costs and improving degradation performance. However, the surface of natural plant fibers contains a large number of hydrophilic hydroxyl groups, which have a natural compatibility difference with the hydrophobic polyester matrix. This leads to the fibers easily agglomerating in the matrix, making it difficult to disperse evenly and thus failing to exert effective reinforcement and toughening effects. At the same time, traditional inorganic fillers such as hydroxyapatite also have the problem of difficult dispersion in the polymer matrix, easily forming stress concentration points. Therefore, how to achieve a good interfacial bond between the multiphase matrix and inorganic and organic fillers while ensuring the processing stability of each component, thereby preparing a fully biodegradable composite material with both low density and high mechanical properties, is a technical problem that needs to be solved in this field. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides a low-density, high-performance, fully biodegradable composite material and its green preparation method. This solves the problems of existing fully biodegradable materials having high density and difficulty in balancing mechanical strength and toughness, multi-component systems being prone to thermal degradation due to mismatched processing temperature windows, and poor interfacial compatibility between natural plant fibers and polyester matrix.

[0006] To address the above problems, the present invention provides the following technical solution:

[0007] This invention provides a low-density, high-performance, fully biodegradable composite material, employing the following technical solution:

[0008] Low-density, high-performance, fully biodegradable composite material, made from raw materials comprising the following parts by weight:

[0009] 25-30 parts of PBAT resin;

[0010] 20-25 parts of low-melting-point modified PGA resin;

[0011] 15-25 parts of PPC resin;

[0012] 5-8 parts of PLA resin;

[0013] 10-18 parts of modified PFM plant fiber;

[0014] 3-6 parts of activated hydroxyapatite;

[0015] 4-6 parts of reactive epoxy compatibilizer;

[0016] 5-8 parts of bio-based composite plasticizer;

[0017] 1.0-1.8 parts of nanocomposite nucleating agent;

[0018] 0.5-1.0 parts of natural antioxidant system.

[0019] By adopting the above technical solution, PBAT resin is used as the continuous phase matrix to provide toughness, PPC resin provides toughening and degradation control of the amorphous phase, and PLA resin provides rigid support. The PBAT resin, PPC resin, and PLA resin construct a multiphase polymer matrix. The low-melting-point modified PGA resin is introduced to compensate for the defects of PBAT resin by utilizing its high barrier and high strength properties. The epoxy groups of the reactive epoxy compatibilizer react in situ with the carboxyl or hydroxyl groups at the polyester end, and the resulting graft copolymer is distributed at the phase interface, reducing the interphase interfacial tension and making the dispersed phase particles smaller and more uniformly distributed. The modified PFM plant fiber and the activated hydroxyapatite work synergistically to construct a rigid skeleton, which promotes crystallization under the induction of the nanocomposite nucleating agent, thereby obtaining the low-density, high-performance, fully biodegradable composite material with low density, high strength, excellent toughness, and good barrier properties.

[0020] The low-melting-point modified PGA resin is obtained by ring-opening copolymerization of glycolide and comonomer in the presence of stannous octoate catalyst and lauryl alcohol initiator;

[0021] Wherein, the comonomer is L-lactide or ε-caprolactone, and the molar ratio of lactide to the comonomer is (80-90):(10-20).

[0022] The amount of catalyst stannous octoate added is 0.01%-0.03% of the total mass of glycolide and the comonomer, and the amount of initiator lauryl alcohol added is 0.1%-0.2% of the total molar mass of glycolide and the comonomer; the melting point of the low-melting-point modified PGA resin is 151℃-164℃.

[0023] By employing the above-mentioned technical solutions, the melting point of ordinary PGA resin is typically higher than 220℃, which is higher than the thermal decomposition initiation temperature of PBAT resin, making it impossible for the two to be processed within the same temperature range. This invention introduces L-lactide or ε-caprolactone as comonomers, disrupting the molecular chain regularity of the glycolide homopolymer, thereby reducing the crystal perfection and melting point, and adjusting the melting point of the low-melting-point modified PGA resin to 151℃-164℃. This temperature range matches the processing temperature of PBAT resin, achieving melt blending of the two under mild conditions, avoiding thermal degradation of the matrix resin, and preserving the mechanical properties of the material.

[0024] The reactive epoxy compatibilizer is copolymerized from styrene, butyl acrylate and glycidyl methacrylate in the presence of azobisisobutyronitrile (AIBN).

[0025] The mass ratio of the styrene, the butyl acrylate, and the glycidyl methacrylate is (30-40):30:(30-40).

[0026] By employing the above technical solution, the glycidyl methacrylate in the reactive epoxy compatibilizer provides highly reactive epoxy groups, capable of undergoing chain extension reactions with the polyester molecular chain ends; the styrene segments provide rigidity and are compatible with PLA resin, while the butyl acrylate segments provide flexibility and are compatible with PBAT resin. This multi-block structure connects incompatible polymers, improves interfacial adhesion, repairs molecular weight loss during processing, and enhances the mechanical strength of the low-density, high-performance, fully biodegradable composite material.

[0027] The modified PFM plant fiber is prepared by the following steps:

[0028] PFM plant fibers were dispersed in phosphate buffer and pretreated with cellulase and xylanase. Then, the PFM plant fibers that had undergone the pretreatment were dispersed in a saturated calcium hydroxide solution, carbon dioxide was introduced and diammonium hydrogen phosphate was added dropwise for in-situ mineralization treatment, forming an inorganic layer on the surface of the PFM plant fibers, thus obtaining the modified PFM plant fibers.

[0029] The amount of cellulase used is 20-25 U / g of the PFM plant fiber, and the amount of xylanase used is 15-20 U / g of the PFM plant fiber; the amount of inorganic layer deposited is 5%-8% of the mass of the PFM plant fiber.

[0030] By employing the aforementioned technical solutions, directly adding natural plant fibers often leads to agglomeration with the hydrophobic polyester matrix due to their strong hydrophilicity. This invention first utilizes cellulase and xylanase to moderately etch the surface of PFM plant fibers, exposing more active hydroxyl sites and increasing surface roughness. Subsequently, in-situ mineralization technology is used to deposit an inorganic layer of calcium carbonate or calcium phosphate on the fiber surface. This inorganic layer enhances the bond between the fiber and the matrix through physical bonding and also acts as a transition layer between the organic fibers and the inorganic filler, namely the activated hydroxyapatite, improving dispersibility and enabling the modified PFM plant fibers to exert a reinforcing effect.

[0031] In step S1, the specific conditions for the bio-enzymatic pretreatment are as follows:

[0032] The PFM plant fibers were dispersed in a phosphate buffer solution with a pH of 5.0-6.0 and stirred at 50-60°C for 2-4 hours.

[0033] The specific conditions for the in-situ mineralization treatment are: reacting at a temperature of 30-40℃ for 1-2 hours.

[0034] By adopting the above technical solution, the pH value and temperature of the enzymatic hydrolysis are controlled, ensuring the activity of the enzyme and avoiding excessive hydrolysis that leads to a decrease in fiber strength or insufficient hydrolysis that leads to insufficient surface active sites. The control of in-situ mineralization conditions ensures that the inorganic layer is densely crystallized and firmly bonded.

[0035] The activated hydroxyapatite is prepared by dispersing hydroxyapatite in an activation solution and treating it with constant temperature oscillation at 45-55℃ for 12-24 hours.

[0036] By adopting the above technical solution, hydroxyapatite is activated to remove surface impurities and adsorbed water, and active functional groups are introduced, enabling it to be better dispersed in the polymer matrix and to act as nucleation sites to induce polymer crystallization, thereby improving the heat distortion temperature and modulus of the material.

[0037] This invention also provides a green preparation method for low-density, high-performance, fully biodegradable composite materials, employing the following technical solution:

[0038] A green preparation method for low-density, high-performance, fully biodegradable composite materials includes the following steps:

[0039] S1. PFM plant fibers are pretreated by bio-enzymatic hydrolysis, followed by in-situ mineralization treatment, and dried to obtain modified PFM plant fibers.

[0040] S2. Hydroxyapatite is activated and dried to obtain activated hydroxyapatite.

[0041] S3. Weigh the PBAT resin, low-melting-point modified PGA resin, PPC resin, PLA resin, reactive epoxy compatibilizer, nanocomposite nucleating agent, natural antioxidant system, modified PFM plant fiber, and activated hydroxyapatite into a high-speed mixer for mixing. During the mixing process, liquid bio-based composite plasticizer is sprayed in. After mixing, vacuum drying is performed to obtain a dry mixture.

[0042] S4. The dried mixture is added to a twin-screw extruder for melt extrusion to obtain an extruded melt;

[0043] S5. Inject supercritical fluid into the front section of the die head of the twin-screw extruder. The extruded melt is pelletized by an underwater pelletizing system and dried to obtain the low-density, high-performance, fully biodegradable composite material.

[0044] By employing the above-mentioned technical solution, this method utilizes supercritical fluid-assisted extrusion processing. On one hand, the supercritical fluid acts as a physical foaming agent, instantly depressurizing and nucleating at the extruder head to form a microporous structure within the composite material, thereby reducing the material density without sacrificing excessive mechanical properties. On the other hand, the supercritical fluid acts as a plasticizer and viscosity reducer in the melt, allowing processing to be carried out at lower temperatures and protecting the heat-sensitive biodegradable polymer molecular chains from damage. Furthermore, the underwater pelletizing system ensures uniform particle appearance and rapid cooling, preventing the collapse of the microporous structure.

[0045] In step S2, the mixing conditions are: mixing for 5-8 minutes at a temperature of 40-50℃ and a rotation speed of 800-1000rpm.

[0046] The vacuum drying conditions are: drying at 60-80℃ for 6-8 hours.

[0047] By adopting the above technical solution, high-speed mixing ensures that all components, especially the reactive epoxy compatibilizer and the bio-based composite plasticizer, are uniformly coated on the surface of the resin particles; vacuum drying controls the moisture content and prevents the polyester from undergoing hydrolytic degradation during subsequent extrusion processing.

[0048] In step S3, the processing temperature of the twin-screw extruder is set to 140℃-170℃, the screw speed is 180-220 rpm, and the vacuum degree is controlled to be -0.085MPa to -0.095MPa. The temperature settings for the 18 temperature zones of the twin-screw extruder are as follows:

[0049] Zones 1-6 are the melting and plasticizing zones, with a temperature gradient set at 140℃-168℃;

[0050] Zones 7-12 are the reactive extrusion zones, with a temperature gradient set at 158℃-170℃.

[0051] Zones 13-18 are slow cooling and shaping zones, with a temperature gradient set at 140℃-162℃.

[0052] The head temperature is set to 140℃-145℃.

[0053] By employing the above technical solution, setting a temperature gradient is a characteristic of the process of this invention. The lower temperature gradient in zones 1-6 ensures gradual softening of the resin, avoiding bridging at the feed inlet; the slightly higher temperature in zones 7-12 promotes the grafting reaction of the reactive epoxy compatibilizer; the gradually decreasing temperature in zones 13-18, combined with the low-temperature setting at the die head, is to establish sufficient melt strength to meet the subsequent injection of supercritical fluid and foaming nucleation requirements. If the temperature is too high, the melt strength will be insufficient, and the bubbles will burst and merge, failing to form a microporous structure.

[0054] In step S4, the supercritical fluid is supercritical carbon dioxide, the injection pressure is 8-12 MPa, and the injection amount is 0.5%-1.5% of the total flow rate of the extruded melt.

[0055] The underwater pelletizing system controls the pelletizing water temperature at 35-45℃ and the cutter speed at 2000-3000 rpm. The pellets are then centrifuged and dehydrated before being dried by airflow at 40-50℃.

[0056] By adopting the above technical solution, controlling the injection pressure and injection amount of supercritical carbon dioxide can adjust the density and growth rate of bubble nuclei, thereby controlling the density and cell morphology of the final material; suitable pelleting water temperature and rotation speed prevent particle adhesion and deformation, ensuring the appearance quality and dimensional uniformity of the product.

[0057] This invention provides a low-density, high-performance, fully biodegradable composite material and its green preparation method. It possesses the following beneficial effects:

[0058] 1. This invention introduces low-melting-point modified PGA resin, modified PFM plant fiber, and activated hydroxyapatite, and utilizes reactive epoxy compatibilizers to conduct chemical reactions at the interface of the multiphase matrix composed of PBAT resin, PPC resin, and PLA resin to enhance interfacial bonding. Combined with the microporous structure generated during the extrusion process of supercritical fluid, a low-density, high-performance, fully biodegradable composite material with low density characteristics, high tensile strength, high impact strength, and excellent thermal stability is obtained.

[0059] 2. This invention achieves mild processing of composite materials at lower temperatures by adjusting the melting point of low-melting-point modified PGA resin to a range that matches the processing temperature of PBAT resin, and by combining the multi-temperature gradient setting of the twin-screw extruder with the plasticizing and viscosity-reducing effect of supercritical fluid. This effectively avoids the thermal degradation of heat-sensitive components such as PBAT resin and PPC resin during processing, ensuring the integrity of the material's molecular structure and the mechanical properties of the final product.

[0060] 3. This invention improves the dispersibility and interfacial compatibility of modified PFM plant fibers in a hydrophobic polyester matrix by performing bio-enzymatic pretreatment and in-situ mineralization treatment on the fiber surface to construct an inorganic layer. Furthermore, by utilizing the synergistic reinforcing effect of modified PFM plant fibers and activated hydroxyapatite, as well as the inherent characteristics of fully biodegradable raw materials, the resulting low-density, high-performance, fully biodegradable composite material can achieve biodegradation in the natural environment while possessing excellent physical properties. Detailed Implementation

[0061] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the preparation examples, examples, comparative examples, and test examples. 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.

[0062] Preparation Examples 1-9:

[0063] Preparation Example 1:

[0064] This preparation example provides a low-melting-point modified PGA resin, comprising the following steps:

[0065] Glycolide and L-lactide were mixed uniformly at a molar ratio of 80:20 to serve as polymerization monomers. The mixed monomers were added to a reactor, evacuated to remove water, and heated to 100°C under nitrogen protection to completely melt them. Subsequently, stannous octoate (Sn(Oct)₂) catalyst (0.03% of the total monomer mass) and lauryl alcohol initiator (0.2% of the total monomer molar mass) were added.

[0066] The reaction system was heated to 170℃ and reacted at a constant temperature for 8 hours with mechanical stirring at 60 rpm. After the reaction, the product was pulverized and subjected to Soxhlet extraction with ethyl acetate at 60℃ for 20 hours to remove unreacted monomers. Finally, it was dried in a vacuum drying oven at 75℃ for 10 hours. The obtained modified PGA resin had a melting point of 151℃, an intrinsic viscosity of 1.10 dL / g, and a terminal carboxyl group content of 22 mmol / kg.

[0067] Preparation Example 2:

[0068] This preparation example provides a low-melting-point modified PGA resin, comprising the following steps:

[0069] Ethyl glycol and L-lactide were mixed uniformly at a molar ratio of 85:15 to serve as the polymerization monomers. The mixed monomers were added to a reactor, evacuated to remove water, and heated to 105°C under nitrogen protection to completely melt them. Subsequently, stannous octoate catalyst (0.02% of the total monomer mass) and lauryl alcohol initiator (0.15% of the total monomer molar mass) were added.

[0070] The reaction system was heated to 175℃ and reacted at a constant temperature for 7 hours with mechanical stirring at 80 rpm. After the reaction, the product was pulverized and extracted with ethyl acetate at 65℃ using a Soxhlet extractor for 24 hours to remove unreacted monomers. Finally, it was dried in a vacuum drying oven at 80℃ for 12 hours. The obtained modified PGA resin had a melting point of 158℃, an intrinsic viscosity of 1.25 dL / g, and a terminal carboxyl group content of 25 mmol / kg.

[0071] Preparation Example 3:

[0072] This preparation example provides a low-melting-point modified PGA resin, comprising the following steps:

[0073] Ethyl glycolide and ε-caprolactone were mixed uniformly at a molar ratio of 90:10 to serve as the polymerization monomers. The mixed monomers were added to a reactor, evacuated to remove water, and heated to 110°C under nitrogen protection to completely melt them. Subsequently, stannous octoate catalyst (0.01% of the total monomer mass) and lauryl alcohol initiator (0.1% of the total monomer molar mass) were added.

[0074] The reaction system was heated to 180℃ and reacted at a constant temperature for 6 hours with mechanical stirring at 100 rpm. After the reaction, the product was pulverized and extracted with ethyl acetate at 70℃ using a Soxhlet extractor for 28 hours to remove unreacted monomers. Finally, it was dried in a vacuum drying oven at 85℃ for 14 hours. The obtained modified PGA resin had a melting point of 164℃, an intrinsic viscosity of 1.38 dL / g, and a terminal carboxyl group content of 28 mmol / kg.

[0075] Preparation Example 4:

[0076] This preparation example provides a reactive epoxy compatibilizer, including the following steps:

[0077] A monomer mixture was prepared in a mass ratio of styrene, butyl acrylate, and glycidyl methacrylate of 30:30:40. Toluene was used as the solvent, and the solid content of the solution was controlled at 40%. Azobisisobutyronitrile (AIBN) was added as an initiator at a rate of 1.0% of the total monomer mass.

[0078] Under nitrogen protection, the solvent in the reactor was heated to 80°C, and the above-mentioned mixed monomer solution was added dropwise to the reactor at a uniform rate over 2 hours. After the addition was complete, the reaction was continued at 80°C for 4 hours. After the reaction was completed, the solvent and unreacted monomers were removed by vacuum distillation at 90°C and -0.085 MPa to obtain a solid product. The compatibilizer has a number-average molecular weight of 5,500 g / mol and an epoxy equivalent of 210 g / eq.

[0079] Preparation Example 5:

[0080] This preparation example provides a reactive epoxy compatibilizer, including the following steps:

[0081] A monomer mixture was prepared in a mass ratio of styrene, butyl acrylate, and glycidyl methacrylate of 35:30:35. Toluene was used as the solvent, and the solid content of the solution was controlled at 45%. Azobisisobutyronitrile (AIBN) was added as an initiator at 0.75% of the total monomer mass.

[0082] Under nitrogen protection, the solvent in the reactor was heated to 75°C, and the above-mentioned mixed monomer solution was added dropwise to the reactor at a uniform rate over 2.5 hours. After the addition was complete, the reaction was continued at 75°C for 5 hours. After the reaction was completed, the solvent and unreacted monomers were removed by vacuum distillation at 95°C and -0.090 MPa to obtain a solid product. The compatibilizer has a number-average molecular weight of 9,800 g / mol and an epoxy equivalent of 320 g / eq.

[0083] Preparation Example 6:

[0084] This preparation example provides a reactive epoxy compatibilizer, including the following steps:

[0085] A monomer mixture was prepared in a mass ratio of styrene, butyl acrylate, and glycidyl methacrylate of 40:30:30. Toluene was used as the solvent, and the solid content of the solution was controlled to be 50%. Azobisisobutyronitrile (AIBN) was added as an initiator at a rate of 0.5% of the total monomer mass.

[0086] Under nitrogen protection, the solvent in the reactor was heated to 70°C, and the above-mentioned mixed monomer solution was added dropwise to the reactor at a uniform rate over 3 hours. After the addition was complete, the reaction was continued at 70°C for 6 hours. After the reaction was completed, the solvent and unreacted monomers were removed by vacuum distillation at 100°C and -0.095 MPa to obtain a solid product. The compatibilizer has a number-average molecular weight of 14,500 g / mol and an epoxy equivalent of 440 g / eq.

[0087] Preparation Example 7:

[0088] This preparation example provides a modified PFM plant fiber, comprising the following steps:

[0089] PFM plant fibers were dispersed in a phosphate buffer solution with a pH of 5.0, and cellulase (20 U / g fiber) and xylanase (15 U / g fiber) were added. The mixture was stirred at 50°C for 2 hours. Subsequently, the wet fibers were dispersed in a saturated calcium hydroxide solution, CO2 was introduced and diammonium hydrogen phosphate was added dropwise, and the mixture was reacted at 30°C for 1 hour to deposit an inorganic layer of 5% of the fiber mass. The mixture was then dried for later use.

[0090] Preparation Example 8:

[0091] This preparation example provides a modified PFM plant fiber, comprising the following steps:

[0092] PFM plant fibers were dispersed in a phosphate buffer solution with a pH of 5.5, and cellulase (22.5 U / g fiber) and xylanase (17.5 U / g fiber) were added. The mixture was stirred at 55°C for 3 hours. Subsequently, the wet fibers were dispersed in a saturated calcium hydroxide solution, CO2 was introduced and diammonium hydrogen phosphate was added dropwise, and the mixture was reacted at 35°C for 1.5 hours to deposit an inorganic layer of 6.5% of the fiber mass. The mixture was then dried for later use.

[0093] Preparation Example 9:

[0094] This preparation example provides a modified PFM plant fiber, comprising the following steps:

[0095] PFM plant fibers were dispersed in a phosphate buffer solution with a pH of 6.0, and cellulase (25 U / g fiber) and xylanase (20 U / g fiber) were added. The mixture was stirred at 60°C for 4 hours. Subsequently, the wet fibers were dispersed in a saturated calcium hydroxide solution, CO2 was introduced and diammonium hydrogen phosphate was added dropwise, and the mixture was reacted at 40°C for 2 hours to deposit an inorganic layer of 8% of the fiber mass. The mixture was then dried for later use.

[0096] Examples 1-3:

[0097] Example 1:

[0098] This embodiment provides a green preparation method for low-density, high-performance, fully biodegradable composite materials, including the following steps:

[0099] S1. Disperse hydroxyapatite in the activation solution, and treat it with constant temperature shaking at 45°C for 12 hours. Filter and dry for later use.

[0100] S2. Weigh 25 parts of PBAT resin, 20 parts of low-melting-point modified PGA resin prepared in Preparation Example 1, 15 parts of PPC resin, 5 parts of PLA resin, 10 parts of modified PFM plant fiber prepared in Preparation Example 7, 3 parts of activated hydroxyapatite prepared in step S1, 4 parts of reactive epoxy compatibilizer prepared in Preparation Example 4, 5 parts of bio-based composite plasticizer, 1.0 part of nano-composite nucleating agent, and 0.5 parts of natural antioxidant system; put all the above raw materials into a high-speed mixer and mix for 5 minutes at 40°C and 800 rpm. During the mixing process, spray in liquid bio-based composite plasticizer. Dry the mixture in a vacuum drying oven at 60°C for 8 hours.

[0101] S3. Add the dried mixture to a twin-screw extruder with a length-to-diameter ratio of 64:1. Set the screw speed to 180 rpm, the main motor torque to 60%, and the vacuum to -0.085 MPa. Set the temperatures of the 18 zones of the extruder as follows: Zones 1-6 (melting and plasticizing zones) are 140℃, 145℃, 150℃, 155℃, 160℃, and 162℃ respectively; Zones 7-12 (reactive extrusion zones) are 162℃, 164℃, 164℃, 162℃, 160℃, and 158℃ respectively; Zones 13-18 (slow cooling and shaping zones) are 158℃, 155℃, 152℃, 150℃, 145℃, and 140℃ respectively; and the die head temperature is 140℃.

[0102] S4. Inject supercritical CO2 fluid into the front section of the extruder head at a pressure of 8 MPa and an injection rate of 0.5% of the total melt flow. The melt is pelletized by an underwater pelletizing system with a pelletizing water temperature of 35°C and a cutter speed of 2000 rpm. The pellets are then centrifuged and dehydrated before being dried in an airflow at 40°C.

[0103] Example 2:

[0104] This embodiment provides a green preparation method for low-density, high-performance, fully biodegradable composite materials, including the following steps:

[0105] S1. Disperse hydroxyapatite in the activation solution, and treat it with constant temperature shaking at 50°C for 18 hours. Filter and dry for later use.

[0106] S2. Weigh 28 parts of PBAT resin, 22 parts of low-melting-point modified PGA resin obtained in Preparation Example 2, 20 parts of PPC resin, 6.5 parts of PLA resin, 14 parts of modified PFM plant fiber obtained in Preparation Example 8, 4.5 parts of activated hydroxyapatite obtained in step S1, 5 parts of reactive epoxy compatibilizer obtained in Preparation Example 5, 6.5 parts of bio-based composite plasticizer, 1.4 parts of nanocomposite nucleating agent, and 0.75 parts of natural antioxidant system; put all the above raw materials into a high-speed mixer and mix for 6.5 minutes at 45°C and 900 rpm. During the mixing process, spray in liquid bio-based composite plasticizer. Dry the mixture in a vacuum drying oven at 70°C for 7 hours.

[0107] S3. Add the dried mixture to a twin-screw extruder with a length-to-diameter ratio of 64:1. Set the screw speed to 200 rpm, the main motor torque to 70%, and the vacuum to -0.090 MPa. Set the temperatures of the 18 zones of the extruder as follows: Zones 1-6 (melting and plasticizing zones) are 140℃, 145℃, 152℃, 158℃, 162℃, and 165℃ respectively; Zones 7-12 (reactive extrusion zones) are 165℃, 168℃, 168℃, 166℃, 164℃, and 162℃ respectively; Zones 13-18 (slow cooling and shaping zones) are 160℃, 158℃, 155℃, 150℃, 145℃, and 140℃ respectively; and the die head temperature is 142℃.

[0108] S4. Inject supercritical CO2 fluid into the front section of the extruder head at a pressure of 10 MPa and an injection rate of 1.0% of the total melt flow. The melt is pelletized by an underwater pelletizing system with a pelletizing water temperature of 40°C and a cutter speed of 2500 rpm. The pellets are then centrifuged and dehydrated before being dried in an airflow at 45°C.

[0109] Example 3:

[0110] This embodiment provides a green preparation method for low-density, high-performance, fully biodegradable composite materials, including the following steps:

[0111] S1. Disperse hydroxyapatite in the activation solution, and treat it with constant temperature shaking at 55℃ for 24 hours. Filter and dry for later use.

[0112] S2. Weigh 30 parts of PBAT resin, 25 parts of low-melting-point modified PGA resin obtained in Preparation Example 3, 25 parts of PPC resin, 8 parts of PLA resin, 18 parts of modified PFM plant fiber obtained in Preparation Example 9, 6 parts of activated hydroxyapatite obtained in step S1, 6 parts of reactive epoxy compatibilizer obtained in Preparation Example 6, 8 parts of bio-based composite plasticizer, 1.8 parts of nanocomposite nucleating agent, and 1.0 part of natural antioxidant system; put all the above raw materials into a high-speed mixer and mix for 8 minutes at 50°C and 1000 rpm. During the mixing process, spray in liquid bio-based composite plasticizer. Dry the mixture in a vacuum drying oven at 80°C for 6 hours.

[0113] S3. Add the dried mixture to a twin-screw extruder with a length-to-diameter ratio of 64:1. Set the screw speed to 220 rpm, the main motor torque to 80%, and the vacuum to -0.095 MPa. Set the temperatures of the 18 zones of the extruder as follows: Zones 1-6 (melting and plasticizing zones) are 140℃, 148℃, 155℃, 160℃, 165℃, and 168℃ respectively; Zones 7-12 (reactive extrusion zones) are 168℃, 170℃, 170℃, 168℃, 166℃, and 164℃ respectively; Zones 13-18 (slow cooling and shaping zones) are 162℃, 160℃, 158℃, 155℃, 150℃, and 145℃ respectively; and the die head temperature is 145℃.

[0114] S4. Inject supercritical CO2 fluid into the front section of the extruder head at a pressure of 12 MPa and an injection rate of 1.5% of the total melt flow. The melt is pelletized by an underwater pelletizing system with a pelletizing water temperature of 45°C and a cutter speed of 3000 rpm. The pellets are then centrifuged and dehydrated before being dried in an airflow at 50°C.

[0115] Comparative Examples 1-4:

[0116] Comparative Example 1:

[0117] Compared with Example 2, the difference is that a commercially available ordinary PGA resin with a melting point of 220°C was used instead of the low-melting-point modified PGA resin prepared in Example 2, the processing temperature remained unchanged, and the other parameters and steps were the same.

[0118] Comparative Example 2:

[0119] Compared with Example 2, the difference is that a commercially available ordinary PGA resin with a melting point of 220°C was used instead of the low-melting-point modified PGA resin prepared in Example 2, and the temperature setting of zones 7-12 (reaction extrusion zone) of the twin-screw extruder in step S3 was uniformly adjusted to 230°C. All other parameters and steps are the same.

[0120] Comparative Example 3:

[0121] Compared with Example 2, the difference is that the reactive epoxy compatibilizer prepared in Example 5 was not added, while the other parameters and steps are the same.

[0122] Comparative Example 4:

[0123] The modified PFM plant fiber prepared in Example 8 was replaced with raw PFM plant fiber that had been simply physically dried at 60°C, and step S1 was omitted. Raw hydroxyapatite that had been simply physically dried at 60°C was used directly to replace the activated hydroxyapatite prepared in step S1. All other parameters and steps were the same.

[0124] Test Examples 1-4:

[0125] Test Example 1: Mechanical Property Test

[0126] Experimental description:

[0127] This test case aims to evaluate the macroscopic mechanical properties of low-density, high-performance, fully biodegradable composite materials prepared in different groups. Through three key indicators—tensile strength, elongation at break, and notched cantilever beam impact strength—it verifies the effects of raw material pretreatment, the introduction of reactive compatibilizers, and low-temperature gradient processing on the material structure and final properties. The experimental procedures were conducted in accordance with national standards to ensure the accuracy and comparability of the data.

[0128] Experimental steps:

[0129] First, the composite material granules prepared in Examples 1 to 3 and Comparative Examples 1 to 4 were placed in a vacuum drying oven and dried at 60°C for 6 hours to remove moisture. The dried granules were then injection molded using a precision injection molding machine to prepare Type 1A multipurpose specimens conforming to GB / T1040.1 and rectangular specimens conforming to GB / T1843.

[0130] The injection molding process parameters were set as follows: barrel temperature range 140℃ to 165℃, mold temperature 35℃, injection pressure 60MPa, holding time 10 seconds, and cooling time 20 seconds. After all samples were prepared, they were placed in a standard environment at 23±2℃ and 50±5% relative humidity for 48 hours to adjust their condition.

[0131] After conditioning, tensile properties were tested using a universal testing machine equipped with a high-precision extensometer. The tensile speed was set to 50 mm / min. The maximum load and gauge length elongation at the time of specimen fracture were recorded, and the tensile strength and elongation at break were calculated.

[0132] The notched impact strength of cantilever beams was tested using a pendulum impact testing machine. The notch type was A, and the notch was fabricated by a notch preparation machine. The pendulum energy was 2.7 J. The energy absorbed per unit cross-sectional area when the specimen fractured was recorded. Five valid specimens were selected for testing in each group of experiments. After removing data with obvious defects or excessive dispersion, the arithmetic mean was taken as the final result.

[0133] Experimental data:

[0134] Table 1. Test data of mechanical properties of composite materials in different experimental groups

[0135]

[0136] Experimental conclusion:

[0137] Based on the test data in Table 1 and the technical principle analysis of this solution, it can be seen that the composite materials of Examples 1 to 3 all exhibit good mechanical properties. Among them, Example 2 has the best overall performance, with a tensile strength of 38.7 MPa, an elongation at break of 753.2%, and an impact strength of 32.6 kJ / m. 2 .

[0138] The PFM plant fiber surface, after undergoing bio-enzymatic hydrolysis and in-situ mineralization treatment, exposes a large number of active hydroxyl groups and deposits a nanoscale inorganic layer. This improves the fiber's dispersibility in the matrix and enhances the interfacial bonding between the fiber and the resin matrix through chemical bonding, thus achieving effective stress transfer.

[0139] Low-melting-point modified PGA resin can completely melt within a low-temperature processing range and react chemically with the prepared reactive epoxy compatibilizer. The epoxy groups on the compatibilizer molecular chain undergo in-situ grafting reactions with the terminal carboxyl groups of PBAT and PGA, as well as the hydroxyl groups on the fiber surface, forming a stable chemical cross-linking network. This network structure effectively suppresses phase separation and improves the toughness and strength of the material.

[0140] Comparing the data from each comparative example shows that the mechanical properties of the material decrease to varying degrees when the above-mentioned modification methods or processing techniques are lacking. This, in turn, proves the effectiveness of the green modification of raw materials, the design of reactive compatibilizers, and the low-temperature process in this scheme, and successfully constructs a high-performance fully biodegradable composite material with tight interfacial bonding and stable structure.

[0141] Test Example 2: Multi-environmental degradation performance test

[0142] Experimental description:

[0143] This test case aims to evaluate the biodegradation behavior of composite materials under different waste disposal environments, focusing on the mass loss under three typical scenarios: industrial composting, household composting, and natural soil landfill. By comparing the degradation rates of each group of materials, the test verifies the regulatory effects of the introduction of low-melting-point modified PGA resin, the pretreatment method of biomass fibers, and the structure of the composite material on the degradation process, confirming whether the material possesses the ability to degrade in multiple scenarios.

[0144] Experimental steps:

[0145] Composite material granules prepared in Examples 1 to 3 and Comparative Examples 1 to 4 were selected and hot-pressed at 150°C and 10MPa using a flat vulcanizing machine to prepare film samples with a thickness of 0.2 mm. The films were then cut into square pieces with a size of 50 mm × 50 mm. After all the samples were placed in a desiccator and conditioned for 48 hours, their initial mass was measured and recorded as M0.

[0146] The samples were then placed in three different degradation environments for testing.

[0147] The first group was an industrial composting environment. According to the ISO14855 standard, the samples were buried in a matrix composed of mature composting inoculum, sawdust and kitchen waste. The ambient temperature was controlled at 58±2℃ and the moisture content was 55%.

[0148] The second group is a home composting environment, simulating normal temperature aerobic composting conditions, with the temperature controlled between 25℃ and 30℃, and the substrate mainly consisting of garden waste.

[0149] The third group is the natural soil environment. According to the ISO17556 standard, the outer surface humus soil was collected, sieved, and then buried 10cm underground. The soil water holding capacity was maintained at 60% of the maximum water holding capacity, and the ambient temperature fluctuated with the room temperature.

[0150] On day 90 of the test, samples from each group were removed, and the surface of any adhering soil and microbial film was carefully washed with deionized water. The samples were then dried in a vacuum oven at 45°C until constant weight, and the final mass was recorded as M1. The mass loss rate was calculated using the formula. Three parallel samples were set up for each experiment, and the arithmetic mean of the results was taken.

[0151] Experimental data:

[0152] Table 2. Test data on the degradation mass loss rate of composite materials under different environmental conditions after 90 days

[0153]

[0154] Experimental conclusion:

[0155] Analysis of the data in Table 2 and the material design mechanism of this scheme shows that the composite materials of Examples 1 to 3 all exhibited good degradation performance in the three test environments. Among them, Example 2 demonstrated a relatively ideal and controllable degradation rate while ensuring the mechanical integrity of the material. This performance stems from the synergistic degradation mechanism of multiple components within the system.

[0156] First, low-melting-point modified PGA resin preferentially undergoes hydrolysis in a humid environment. The resulting glycolic acid lowers the local pH value of the system, thereby exerting an acid catalytic effect on the PBAT and PPC matrix and accelerating the breaking of ester bonds.

[0157] Secondly, the PFM plant fibers, after enzymatic hydrolysis and in-situ mineralization, form hydrophilic channels in the matrix, which facilitates the penetration of water and microorganisms into the material, allowing the degradation process to proceed evenly from the surface to the interior, which is the so-called flow guiding effect.

[0158] These two mechanisms ensure that the material maintains a certain level of degradation activity even in non-high-temperature environments such as home composting or natural soil. In contrast, data from the comparative examples show that without low-crystallinity modified PGA or without hydrophilic channels constructed from modified fibers, the degradation rate of the material under mild conditions is significantly limited; while forced processing at high temperatures, although resulting in a high mass loss rate, is mostly due to physical disintegration caused by thermal degradation rather than biodegradation. In summary, Example 2 successfully achieved effective biodegradation of the material under mild conditions by controlling the crystallization behavior of the components and constructing hydrophilic channels.

[0159] Test Example 3: Test on the ecological impact of degradation products on soil

[0160] Experimental description:

[0161] This test case aims to assess the long-term impact of composite material degradation products on the soil environment from a microecological perspective, focusing on changes in soil physicochemical properties after material degradation and potential toxicity or promoting effects on plant growth. The experiment quantitatively analyzed changes in soil organic matter and available phosphorus content, and combined this with a plant seed germination index experiment to verify whether the unique fiber surface mineralization modification and hydroxyapatite activation technology in this scheme endow the degraded material with soil-improving functions, thus confirming the ecological safety of the material during its natural return process.

[0162] Experimental steps:

[0163] Approximately 500g of soil samples from Example 2 and Comparative Example 4 were collected after 180 days of degradation in the natural soil environment of Test Example 2. Simultaneously, uncontaminated background soil was collected as a blank control group. All three soil samples were air-dried, and obvious undegraded large particles and stones were removed. The samples were then ground through a 2mm sieve for later use.

[0164] According to NY / T1121.6 standard, the organic matter content of each soil group was determined by the potassium dichromate oxidative dilution heat method. The organic carbon content was calculated by titrating the amount of ferrous sulfate consumed and then converted into organic matter content. According to NY / T1121.7 standard, the available phosphorus content of the soil was determined by the sodium bicarbonate extraction molybdenum antimony colorimetric method.

[0165] Phytotoxicity testing was conducted using the wheat seed germination method. Soil extracts for each group were prepared at a soil-to-water ratio of 1:10, and filtered after shaking extraction. Plump, uniformly sized wheat seeds were selected, surface-sterilized with 3% hydrogen peroxide solution, and 20 seeds were evenly placed in a petri dish lined with filter paper. 5 mL of soil extract from each group was added to each dish. The petri dishes were then incubated in a constant temperature incubator at 25±1℃ in the dark for 72 hours.

[0166] After cultivation, record the number of germinated seeds and measure the root length. Calculate the seed germination index using the formula.

[0167] Experimental data:

[0168] Table 3. Test data of soil physicochemical properties and plant germination index after material degradation

[0169]

[0170] Experimental conclusion:

[0171] Analysis of the test data in Table 3, combined with the material preparation mechanism, shows that the soil sample corresponding to Example 2 exhibits significant advantages in both physicochemical indicators and plant growth promotion. Compared with the blank control group, the soil organic matter content in Example 2 increased to 19.8 g / kg, the available phosphorus content increased to 29.7 mg / kg, and the seed germination index reached 127.6%. This result confirms the ecological benefit mechanism of the green preparation process in this scheme.

[0172] After pretreatment with cellulase and xylanase, PFM plant fibers partially depolymerize their dense cell wall structure, making them more easily converted into humus by soil microorganisms during degradation, thereby effectively improving the soil organic matter level.

[0173] The inorganic layer deposited in situ on the fiber surface, along with the added activated hydroxyapatite, undergoes an acid-induced phosphorus release effect under the influence of glycolic acid produced by the hydrolysis of PGA, a product of acidic degradation. This slowly releases phosphate and calcium ions. This mechanism not only buffers the local acidity that may occur during degradation but also replenishes the soil with phosphorus, an essential element for plant growth.

[0174] The GI value of Example 2 group was significantly greater than 100%, indicating that the degradation products promoted plant growth, and the material produced an effect similar to slow-release fertilizer after degradation. In contrast, the data in the comparative group showed smaller changes, suggesting that components without specific biochemical modification were unlikely to produce the same soil improvement effect after degradation. In summary, the composite material prepared by this scheme achieves full biodegradation while improving soil fertility through unique component design, demonstrating good environmental friendliness.

[0175] Test Example 4: Life Cycle Energy Consumption and Carbon Emission Assessment

[0176] Experimental description:

[0177] This test case, based on the door-to-door principle of life cycle assessment, quantitatively evaluates the energy consumption and carbon emission levels in the production process of low-density, high-performance, fully biodegradable composite materials. The assessment boundary is set as the entire preparation process from before the raw materials enter the mixer (including the activation of auxiliary raw materials) to the final pelleting and packaging. The focus is on monitoring the electricity consumption and direct carbon emissions per unit mass of product in the raw material activation pretreatment, mixing melt extrusion, and pelleting and drying stages.

[0178] To establish an effective comparative benchmark, in addition to Example 2 and Comparative Example 2, a reference group was introduced that produced general-purpose PBAT and PLA composite materials using conventional processes. The experiment involved installing high-precision industrial power meters at the power input terminals of the high-speed mixer, twin-screw extruder, and auxiliary equipment such as the temperature control system and pelletizer to record the total power consumption in real time for producing 1000 kg of qualified pellets.

[0179] Based on the energy conversion factor published by the National Bureau of Statistics, electricity consumption was converted to standard coal equivalent, with a conversion factor of 0.1229 kgce / kWh. Indirect carbon emissions were calculated based on the regional power grid average emission factor, with an emission factor of 0.5810 kgCO2 / kWh. Simultaneously, the average melt pressure and main unit load rate during the production process were recorded to assess the impact of processing efficiency on unit energy consumption.

[0180] Experimental data:

[0181] Table 4. Energy consumption and carbon emission assessment data for the production process.

[0182]

[0183] Experimental conclusion:

[0184] Analysis of the monitoring data in Table 4 shows that Example 2 demonstrates significant advantages in energy consumption control and carbon emission reduction. Compared with the reference process group and Comparative Example 2, the carbon emissions per unit product of Example 2 were reduced by 17.6% and 28.9%, respectively.

[0185] The low-temperature rheological properties of the raw material system reduce the thermal energy requirement. The low-melting-point modified PGA resin used in this solution reduces the melt processing window of the compound system from the traditional above 220°C to about 160°C, which directly reduces the power consumption of the extruder barrel heating zone.

[0186] Supercritical fluid-assisted processing technology improves efficiency. Example 2 introduces supercritical carbon dioxide fluid into the extrusion process, utilizing its swelling and plasticizing effects in the polymer melt to effectively reduce intermolecular friction in high-viscosity melts. Data shows that the average load rate of the main machine in Example 2 decreased to 68.5%, meaning that the motor output torque is lower and mechanical energy consumption is lower at the same speed. Simultaneously, the viscosity-reducing effect of supercritical fluid improves melt flowability, increasing production efficiency to 102.4 kg / h. The increased output per unit time further reduces fixed energy consumption, thereby achieving a reduction in overall energy consumption and carbon emissions per unit product.

[0187] In summary, this solution, through the deep integration of material design and process innovation, has successfully constructed a low-energy-consumption and high-efficiency green manufacturing path.

Claims

1. A low-density, high-performance, fully biodegradable composite material, characterized in that, Made from the following ingredients in parts by weight: 25-30 parts of PBAT resin; 20-25 parts of low-melting-point modified PGA resin; 15-25 parts of PPC resin; 5-8 parts of PLA resin; 10-18 parts of modified PFM plant fiber; 3-6 parts of activated hydroxyapatite; 4-6 parts of reactive epoxy compatibilizer; 5-8 parts of bio-based composite plasticizer; 1.0-1.8 parts of nanocomposite nucleating agent; 0.5-1.0 parts of natural antioxidant system.

2. The low-density, high-performance, fully biodegradable composite material according to claim 1, characterized in that, The low-melting-point modified PGA resin is obtained by ring-opening copolymerization of glycolide and comonomer in the presence of stannous octoate catalyst and lauryl alcohol initiator; Wherein, the comonomer is L-lactide or ε-caprolactone, and the molar ratio of lactide to the comonomer is (80-90):(10-20). The amount of catalyst stannous octoate added is 0.01%-0.03% of the total mass of glycolide and the comonomer, and the amount of initiator lauryl alcohol added is 0.1%-0.2% of the total molar mass of glycolide and the comonomer; the melting point of the low-melting-point modified PGA resin is 151℃-164℃.

3. The low-density, high-performance, fully biodegradable composite material according to claim 1, characterized in that, The reactive epoxy compatibilizer is copolymerized from styrene, butyl acrylate and glycidyl methacrylate in the presence of azobisisobutyronitrile (AIBN). The mass ratio of the styrene, the butyl acrylate, and the glycidyl methacrylate is (30-40):30:(30-40).

4. The low-density, high-performance, fully biodegradable composite material according to claim 1, characterized in that, The modified PFM plant fiber is prepared by the following steps: PFM plant fibers were dispersed in phosphate buffer and pretreated with cellulase and xylanase. Then, the PFM plant fibers that had undergone the pretreatment were dispersed in a saturated calcium hydroxide solution, carbon dioxide was introduced and diammonium hydrogen phosphate was added dropwise for in-situ mineralization treatment, forming an inorganic layer on the surface of the PFM plant fibers, thus obtaining the modified PFM plant fibers. The amount of cellulase used is 20-25 U / g of the PFM plant fiber, and the amount of xylanase used is 15-20 U / g of the PFM plant fiber; the amount of inorganic layer deposited is 5%-8% of the mass of the PFM plant fiber.

5. The low-density, high-performance, fully biodegradable composite material according to claim 4, characterized in that, The specific conditions for the bio-enzymatic hydrolysis pretreatment are as follows: The PFM plant fibers were dispersed in a phosphate buffer solution with a pH of 5.0-6.0 and stirred at 50-60°C for 2-4 hours. The specific conditions for the in-situ mineralization treatment are: reacting at a temperature of 30-40℃ for 1-2 hours.

6. The low-density, high-performance, fully biodegradable composite material according to claim 1, characterized in that, The activated hydroxyapatite is prepared by dispersing hydroxyapatite in an activation solution and treating it with constant temperature oscillation at 45-55℃ for 12-24 hours.

7. A green preparation method for low-density, high-performance, fully biodegradable composite materials, characterized in that, The preparation of the low-density, high-performance, fully biodegradable composite material as described in any one of claims 1-6 includes the following steps: S1. Hydroxyapatite is activated and dried to obtain activated hydroxyapatite. S2. Weighed PBAT resin, low-melting-point modified PGA resin, PPC resin, PLA resin, reactive epoxy compatibilizer, nanocomposite nucleating agent, natural antioxidant system, modified PFM plant fiber, and activated hydroxyapatite are put into a high-speed mixer for mixing. Liquid bio-based composite plasticizer is sprayed in during the mixing process. After mixing, the mixture is vacuum dried to obtain a dry mixture. S3. The dried mixture is added to a twin-screw extruder for melt extrusion to obtain an extruded melt; S4. Inject supercritical fluid into the front section of the die head of the twin-screw extruder. The extruded melt is pelletized by an underwater pelletizing system and dried to obtain the low-density, high-performance, fully biodegradable composite material.

8. The green preparation method according to claim 7, characterized in that, In step S2, the mixing conditions are: mixing for 5-8 minutes at a temperature of 40-50℃ and a rotation speed of 800-1000 rpm. The vacuum drying conditions are: drying at 60-80℃ for 6-8 hours.

9. The green preparation method according to claim 7, characterized in that, In step S3, the processing temperature of the twin-screw extruder is set to 140℃-170℃, the screw speed is 180-220 rpm, and the vacuum degree is controlled to be -0.085MPa to -0.095MPa. The temperature settings for the 18 temperature zones of the twin-screw extruder are as follows: Zones 1-6 are the melting and plasticizing zones, with a temperature gradient set at 140℃-168℃; Zones 7-12 are the reactive extrusion zones, with a temperature gradient set at 158℃-170℃. Zones 13-18 are slow cooling and shaping zones, with a temperature gradient set at 140℃-162℃. The head temperature is set to 140℃-145℃.

10. The green preparation method according to claim 7, characterized in that, In step S4, the supercritical fluid is supercritical carbon dioxide, the injection pressure is 8-12 MPa, and the injection amount is 0.5%-1.5% of the total flow rate of the extruded melt. The underwater pelletizing system controls the pelletizing water temperature at 35-45℃ and the cutter speed at 2000-3000 rpm. The pellets are then centrifuged and dehydrated before being dried by airflow at 40-50℃.

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