A fully biodegradable bamboo-based material, a preparation method and applications thereof

Abstract

The application relates to the technical field of high polymer materials, and discloses a full-biodegradable bamboo-based material, a preparation method and application of the material, which is prepared from bamboo powder, citric acid, monopentaerythritol, epoxy soybean oil, ionic liquid, polylactic acid, polybutylene succinate, polybutylene terephthalate and other additives. The preparation method adopts an ionic liquid assisted in-situ reaction system, constructs a hydrophobic modified layer with a hyperbranched structure on the surface of the bamboo powder, and adopts a modified dehydration-low temperature blending step-by-step process strategy, removes reaction generated water through high temperature vacuum dehydration before the introduction of a base resin, and effectively inhibits the hydrolytic degradation of the polyester base. The application endows the material with excellent dry flowability, and realizes one-step direct extrusion molding without granulation. The obtained material has interface toughness, rheological performance and water resistance under high filling amount, solves the problems of large brittleness and difficult processing of existing bamboo plastic materials, and is suitable for the production of hollow corrugated boards and woven bags.

Description

Technical Field

[0001] This invention relates to the field of polymer materials technology, specifically to a fully biodegradable bamboo-based material, its preparation method, and its application. Background Technology

[0002] With increasing global concern about plastic pollution, fully biodegradable polyester materials such as polylactic acid (PLA) and polybutylene terephthalate (PBAT) have gained widespread attention due to their excellent environmental friendliness. However, pure biodegradable polyesters are relatively expensive, and the mechanical properties of single components often fail to meet diverse application requirements. Modifying biodegradable polyesters with biomass fillers such as bamboo powder can not only significantly reduce raw material costs but also impart a unique natural texture and some mechanical reinforcement to the material.

[0003] Despite the promising applications of bamboo-plastic composites, significant technical challenges remain in their development and production, particularly when bamboo powder content is high (e.g., exceeding 50%). The primary challenge is the conflict between interfacial bonding and material toughness. Bamboo powder contains numerous hydrophilic hydroxyl groups, resulting in poor compatibility with the hydrophobic polyester matrix. Existing technologies typically employ surface treatments with coupling agents such as aluminates and titanates. While these agents can improve bamboo powder dispersibility to some extent, they primarily form rigid monolayer interfaces, failing to effectively dissipate external stress. At high bamboo powder content, this rigid interface makes the material highly susceptible to brittle fracture, hindering its ability to meet the high-ratio stretching requirements of woven bag production and withstand repeated folding during corrugated box forming and use, thus limiting its application in high-value-added packaging.

[0004] Secondly, there is the contradiction between acidic modifiers and the stability of the polyester matrix. To improve compatibility at the chemical bonding level, reacting bamboo powder with polycarboxylic acids such as citric acid is a theoretically effective modification method. However, polyester materials such as polylactic acid (PLA) and PBAT are extremely sensitive to acids and water. During conventional processing, the residual acidic carboxyl groups in the modifier and the water byproduct generated from the esterification reaction become strong catalysts for the hydrolysis and thermal degradation of the polyester matrix at high temperatures. This degradation not only leads to a sharp decrease in the molecular weight and a collapse in mechanical strength, but in severe cases, it can even prevent the material from being formed in the extruder.

[0005] Furthermore, high filler content also presents significant rheological processing challenges. As the bamboo powder content increases, the melt viscosity of the composite system rises sharply, resulting in poor flowability. During extrusion, high-viscosity materials generate substantial shear frictional heat, which not only limits production efficiency but also easily leads to scorching and discoloration of heat-sensitive biodegradable materials. To improve processability, existing processes often require granulation before product extrusion, but this increases energy consumption and subjectes the material to secondary thermal history, further impairing the performance of the final product. Summary of the Invention

[0006] To address the shortcomings of existing technologies, this invention provides a fully biodegradable bamboo-based material, its preparation method, and its application. It solves the problems of high interfacial brittleness of existing biodegradable bamboo-plastic materials at high filler content, easy degradation of the polyester matrix caused by residual acid and moisture in the modifier, and poor processing rheological properties that make it difficult to achieve one-step extrusion.

[0007] To achieve the above objectives, in a first aspect, the present invention provides a fully biodegradable bamboo-based material, employing the following technical solution:

[0008] A fully biodegradable bamboo-based material, made from raw materials comprising the following parts by weight:

[0009] Bamboo powder 20-65 parts; citric acid 0.5-2 parts; pentaerythritol 0.2-0.8 parts; epoxidized soybean oil 2.5-5 parts; ionic liquid 1.5-4 parts; polylactic acid 10-30 parts; polybutylene succinate 2-20 parts; polybutylene adipate terephthalate 2-45 parts; titanium dioxide 1-2 parts; and other additives;

[0010] In this process, the bamboo powder, citric acid, pentaerythritol, and epoxidized soybean oil undergo an in-situ esterification reaction under the catalysis of the ionic liquid to form a hydrophobic modified layer on the surface of the bamboo powder.

[0011] By adopting the above technical solution, this invention utilizes an ionic liquid-assisted in-situ reaction system to construct a hydrophobic modified layer with a hyperbranched structure on the surface of bamboo powder. The specific mechanism and effects are as follows:

[0012] First, the activation and catalytic effects of ionic liquids. As a good solvent for cellulose, ionic liquids can disrupt the hydrogen bond network between and within the cellulose molecular chains of bamboo powder, causing the surface of the bamboo powder to swell and activate, exposing more reactive sites. At the same time, as a homogeneous reaction medium, ionic liquids lower the activation energy of the esterification reaction, promoting the penetration and grafting of subsequent reactants.

[0013] Second, the construction of the hyperbranched framework. Citric acid, as a multifunctional monomer, undergoes esterification with the hydroxyl groups on the surface of bamboo powder in the system, anchoring them to the surface of bamboo powder; at the same time, citric acid undergoes polycondensation with polyhydroxy pentaerythritol, growing a hyperbranched polyester framework with steric hindrance effect in situ on the surface of bamboo powder. This framework effectively masks the hydrophilic hydroxyl groups on the surface of bamboo powder.

[0014] Third, long-chain hydrophobic end-capping and toughening. The epoxy groups in epoxidized soybean oil undergo ring-opening addition reactions with the carboxyl or hydroxyl groups at the ends of the hyperbranched backbone, introducing flexible long-chain hydrophobic segments into the modified layer structure. This long-chain structure not only significantly reduces the surface polarity of bamboo powder and improves its interfacial compatibility with hydrophobic polyester matrices such as polylactic acid, polybutylene succinate, and polybutylene adipate terephthalate, but also acts as an internal lubricating layer, significantly reducing the frictional resistance of highly filled bamboo powder melts, allowing the material to maintain good processing fluidity even when the bamboo powder content is as high as 65 parts.

[0015] Preferably, the bamboo powder has a particle size of 200-1500 mesh and a moisture content of less than 1.0%; the ionic liquid is 1-butyl-3-methylimidazolium chloride.

[0016] By adopting the above technical solution, bamboo powder of a specific mesh size combined with 1-butyl-3-methylimidazolium chloride can achieve the best wetting and modification effect, which not only ensures the modification efficiency, but also avoids the agglomeration problem caused by excessively small particle size.

[0017] Preferably, the other additives are: 5 to 10 parts lubricant; 1 to 2 parts antioxidant 1010; 1.5 to 5 parts coupling agent; 2 to 5 parts compatibilizer; 1 to 2 parts dispersant, wherein the compatibilizer is maleic anhydride-grafted polylactic acid; the dispersant is polyethylene glycol 6000; the lubricant is ethylene bis-stearamide or a compound of ethylene bis-stearamide and zinc stearate; and the coupling agent is selected from one of aluminate coupling agents, titanate coupling agents, or 4,4'-diphenylmethane diisocyanate.

[0018] By adopting the above technical solution, the synergistic effect of various additives further improves the wettability of the matrix resin to the modified bamboo powder and enhances the comprehensive mechanical properties of the material.

[0019] Preferably, the fully biodegradable bamboo-based material is a hollow corrugated board or stretched flat filaments; when the material is a hollow corrugated board, the bamboo powder particle size is 200 mesh to 400 mesh; when the material is stretched flat filaments, the bamboo powder particle size is 800 mesh to 1500 mesh.

[0020] By adopting the above technical solution, suitable bamboo powder particle size is selected for different product forms. In hollow corrugated boards, coarser particle size is used to provide rigid support, while in drawn flat wires, finer particle size is used to reduce stress concentration points and prevent stretching and film breakage.

[0021] Secondly, this invention provides a method for preparing a fully biodegradable bamboo-based material, employing the following technical solution:

[0022] A method for preparing a fully biodegradable bamboo-based material includes the following steps:

[0023] S1. Raw material pretreatment: Dry bamboo powder and titanium dioxide to a moisture content of less than 1.0%, and dry polylactic acid, polybutylene succinate and polybutylene adipate to a moisture content of less than 0.05%.

[0024] S2. Ionic liquid-assisted in-situ reaction: Bamboo powder, citric acid, pentaerythritol, epoxidized soybean oil and ionic liquid are mixed and heated to 120℃~135℃. The reaction is carried out under high-speed stirring to obtain modified bamboo powder intermediate.

[0025] S3, Vacuum dehydration: Under the condition of maintaining a temperature of 105℃~115℃, negative pressure is applied to the modified bamboo powder intermediate in S2 to remove the water generated in the reaction.

[0026] S4. Low-temperature blending: Remove the vacuum, cool to 70℃~80℃, add polylactic acid, polybutylene succinate, polybutylene adipate terephthalate and the remaining additives, and mix evenly under low-speed stirring to obtain a premix.

[0027] S5. Extrusion molding: The premixed material is plasticized, extruded and shaped by an extruder to obtain the fully biodegradable bamboo-based material.

[0028] By adopting the above technical solution, this invention employs a step-by-step process strategy of first modifying and dehydrating, followed by low-temperature blending, which effectively solves the hydrolysis problem in the processing of biodegradable plastics.

[0029] First, in step S2, the shear heat generated by high-speed stirring and external heating are used to rapidly complete the surface chemical modification of bamboo powder in an ionic liquid environment. At this time, although small molecule water from the esterification reaction is generated in the system, the water-sensitive polyester matrix has not yet been added.

[0030] Secondly, in step S3, before adding the matrix resin, a high-temperature vacuum dehydration process is used to forcibly remove the moisture generated during the modification process and the residual moisture in the raw materials, ensuring the bamboo powder intermediate is completely dry. This step is crucial to prevent the subsequent addition of polyesters such as polylactic acid from undergoing hydrolytic degradation.

[0031] Finally, in step S4, a low-temperature, low-speed blending process is used to mix the matrix resin with the modified bamboo powder. Since the bamboo powder surface is coated with a lubricating modified layer, the frictional heat during mixing is reduced, allowing the mixing to be carried out at temperatures below the resin's melting point. This minimizes the thermal degradation history of the polyester matrix, thereby ensuring that the final product possesses excellent mechanical strength and aging resistance.

[0032] Preferably, in step S2, the high-speed stirring speed is 1000 rpm to 1400 rpm, and the constant temperature reaction time is 5 min to 8 min; in step S4, the low-speed stirring speed is 300 rpm to 600 rpm, and the discharge temperature is controlled below 80℃.

[0033] By adopting the above technical solutions, high-speed stirring provides the energy and dispersion effect required for the reaction, while low-speed and low-temperature stirring avoids material agglomeration and resin pre-degradation.

[0034] Preferably, in step S3, the vacuum degree of the negative pressure evacuation is -0.08MPa to -0.095MPa, and the evacuation time is 3min to 5min.

[0035] By adopting the above technical solution, the high vacuum ensures that moisture can be completely extracted from the deep pores of the modified bamboo powder.

[0036] Preferably, in step S5, the extruder is set to a temperature of 125℃~145℃ and vacuum devolatilization is performed; when preparing hollow corrugated sheets, a T-shaped hollow sheet mold is used for extrusion and vacuum shaping; when preparing drawn flat filaments, a flat die is used to extrude sheets, which are then slit and stretched unidirectionally with a stretching ratio of 4.5 to 6 times, thus achieving a one-step forming process.

[0037] By adopting the above technical solutions and utilizing the low viscosity characteristics of modified bamboo powder, extrusion processing at lower temperatures was achieved, further protecting the biodegradable components; different molds and stretching processes were used to prepare products that meet different application scenarios.

[0038] Thirdly, the present invention provides an application of a fully biodegradable bamboo-based material, employing the following technical solution:

[0039] Application of a fully biodegradable bamboo-based material in the preparation of corrugated boards or woven bags.

[0040] By adopting the above technical solution, the corrugated board prepared using this material has high strength and water resistance, and can replace traditional cardboard boxes or non-degradable plastic boxes; the woven bags prepared have high tensile strength and elongation at break, meeting the needs of heavy-duty packaging, and can be completely biodegraded after disposal, making them environmentally friendly.

[0041] This invention provides a fully biodegradable bamboo-based material, its preparation method, and its applications. It possesses the following beneficial effects:

[0042] 1. This invention utilizes an ionic liquid catalytic system to induce an in-situ esterification reaction between citric acid, pentaerythritol, and epoxidized soybean oil on the surface of bamboo powder, constructing a modified layer with a hyperbranched framework and long-chain hydrophobic end caps. Furthermore, the steric hindrance effect is used to shield the hydrophilic groups on the bamboo powder surface, while the flexible long-chain segments of epoxidized soybean oil are introduced. This transforms the rigid interface between the filler and the resin matrix into a flexible interface with stress dissipation capabilities, solving the problem of high brittleness and easy breakage of traditional coupling agent modifications at high filler contents. This allows the material to maintain excellent tensile toughness and folding resistance even with high bamboo powder filler content, meeting the processing requirements for high-strength woven bags and folding-resistant corrugated board forming.

[0043] 2. This invention effectively overcomes the defects of polyester matrix degradation caused by acidic modifiers and esterification byproduct water through a stepwise preparation process of modification and dehydration followed by low-temperature blending. By performing a high-temperature vacuum dehydration step before adding matrix resins such as polylactic acid, the water generated during the modification process and residual water in the raw materials are forcibly removed, blocking the source of the hydrolysis chain reaction. At the same time, the in-situ reaction consumes most of the free carboxyl groups in citric acid, reducing the risk of acid-catalyzed degradation and maximizing the preservation of the molecular weight and mechanical strength of the biodegradable polyester, ensuring the performance stability of the material during processing.

[0044] 3. This invention utilizes the hyperbranched modified layer on the surface of bamboo powder and the grafted long-chain alkyl groups to provide internal lubrication. Combined with the plasticizing effect of ionic liquid on cellulose, it significantly reduces the viscosity and frictional resistance of the highly filled melt. This allows the mixture to be directly fed into the extruder at low temperature for plasticization and molding without the need for granulation, avoiding the thermal degradation of resin caused by secondary high-temperature shearing, while also reducing production energy consumption and processing costs.

[0045] 4. This invention imparts excellent dry flowability and low-temperature plasticizing ability to the premixed material through surface modification of bamboo powder. The mixture can be directly fed into the extruder for processing without melt granulation, thereby realizing a one-step molding process without granulation. This avoids the secondary high-temperature thermal shearing history of heat-sensitive polyester, thus effectively inhibiting the deterioration of material properties and significantly reducing production energy consumption and costs. Attached Figure Description

[0046] Figure 1 Figure 1 shows a comparison of the grafting rate and surface wettability of the modified bamboo powder intermediate of the present invention. Figure 2 shows a comparison of the grafting rate and Figure 3 shows a comparison of the water contact angle.

[0047] Figure 2Figure (a) shows a comparison of the residual acid value and esterification reaction conversion rate of the modified intermediate system of the present invention, and Figure (b) shows a comparison of the residual acid value of the system and the esterification reaction conversion rate.

[0048] Figure 3 Figure 1 shows the analysis of the material processing rheological properties and lubrication effect of the present invention. Figure 2(a) is a comparison of melt flow rates, and Figure 3(b) is a distribution of processing rheological properties.

[0049] Figure 4 Figure (a) is a comprehensive analysis diagram of the mechanical strength and water resistance stability of the hollow corrugated board of the present invention, and Figure (b) is a comparison diagram of mechanical strength indicators and a correlation diagram of strength and water absorption rate.

[0050] Figure 5 Figure (a) is a diagram showing the tensile properties and strength-toughness balance mechanism of the woven bag flat yarn of the present invention. Figure (b) is a diagram comparing tensile fracture strength and a diagram showing the inverted strength-toughness relationship.

[0051] Figure 6 Figure (a) shows the biodegradation kinetics and endpoint evaluation of materials under controlled composting conditions according to the present invention, and Figure (b) shows the biodegradation rate over time. Detailed Implementation

[0052] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0053] The main raw materials and reagents used in the following examples and comparative examples have the following sources and specifications. Reagents not specifically mentioned are all commercially available analytical grade or higher grade products.

[0054] Citric acid is anhydrous citric acid, with the chemical formula C6H8O7, a white crystalline powder with a purity ≥99.5% and CAS number 77-92-9.

[0055] Pentaerythritol is monopentaerythritol, with the chemical formula C5H. 12 O4, white crystalline powder, purity ≥98%, CAS No. 115-77-5.

[0056] Epoxidized soybean oil is a pale yellow viscous liquid with an epoxy value ≥6.0% and an iodine value ≤6.0gI2 / 100g. CAS number 8013-07-8.

[0057] The ionic liquid used is 1-butyl-3-methylimidazolium chloride, with the chemical formula C8H12H2O.15 ClN2, purity ≥99%, CAS No. 79917-90-1, is a yellow viscous liquid at room temperature.

[0058] Titanium dioxide is rutile titanium dioxide with a surface treated with inorganic alumina and organosilicon. CAS No. 13463-67-7.

[0059] The lubricant used is ethylene bis-stearamide (EBS), CAS No. 110-30-5, with a melting point of 140℃~146℃.

[0060] The antioxidant selected is pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] (antioxidant 1010), CAS number 6683-19-8.

[0061] The coupling agent used is 4,4'-diphenylmethane diisocyanate (MDI), with a purity ≥99% and CAS number 101-68-8.

[0062] The compatibilizer is maleic anhydride grafted onto polylactic acid with a grafting rate of 1.0% to 1.2%, and is prepared by grafting maleic anhydride onto polylactic acid as the matrix.

[0063] The dispersant used is polyethylene glycol 6000, with an average molecular weight of 5500-7500 and CAS number 25322-68-3.

[0064] Example 1:

[0065] This embodiment describes the preparation of a fully biodegradable bamboo-based hollow corrugated board for packaging boxes, comprising the following steps:

[0066] (1) Raw material weighing: Weigh 40 parts of bamboo powder (300 mesh), 1 part of citric acid, 0.5 parts of pentaerythritol, 3 parts of epoxidized soybean oil, 2 parts of 1-butyl-3-methylimidazolium chloride, 15 parts of polylactic acid, 15 parts of polybutylene succinate, 3 parts of polybutylene adipate terephthalate, 1.5 parts of titanium dioxide, 8 parts of ethylene bis-stearamide, 1.2 parts of antioxidant 1010, 3 parts of aluminate coupling agent, 3 parts of maleic anhydride-grafted polylactic acid, and 1.5 parts of polyethylene glycol 6000.

[0067] (2) Raw material pretreatment: Bamboo powder and titanium dioxide were placed in a forced-air drying oven and dried at 105°C to control the moisture content to be less than 0.8%; polylactic acid, polybutylene succinate and polybutylene adipate were placed in a vacuum drying oven at 60°C until the moisture content was less than 0.04%.

[0068] (3) Ionic liquid-assisted in-situ reaction: put dried bamboo powder, citric acid, pentaerythritol, epoxidized soybean oil and ionic liquid into a high-speed mixer with a vacuum interface; start stirring (1200 rpm), heat to 125°C, and then reduce the speed to 500 rpm and react at a constant temperature for 6 min.

[0069] (4) Vacuum dehydration: Adjust the temperature to 110℃, start the vacuum pump (-0.09MPa), keep stirring and vacuum for 4 minutes to remove the water generated by the reaction.

[0070] (5) Low-temperature blending: Remove the vacuum and cool the material to 75°C (cooling rate 5°C / min); add the matrix resin (polylactic acid, polybutylene succinate, polybutylene adipate) and the remaining additives (titanium dioxide, lubricant, antioxidant 1010, coupling agent, compatibilizer, dispersant); mix at low speed (500 rpm) for 6 min, and control the discharge temperature below 80°C, then cold mix to 35°C.

[0071] (6) Extrusion molding: The mixture is added to a parallel twin-screw extruder, the temperature is set to 135℃±10℃, and vacuum devolatilization (-0.08MPa); a T-shaped hollow board mold is installed at the die head, and the fully biodegradable bamboo-based hollow corrugated board is obtained by extrusion, cooling and shaping on a vacuum shaping table, traction and cutting.

[0072] Example 2:

[0073] This embodiment prepares a fully biodegradable bamboo-based hollow corrugated board with high bamboo powder content, including the following steps:

[0074] (1) Raw material weighing: Weigh out 65 parts of bamboo powder (200 mesh), 2 parts of citric acid, 0.8 parts of pentaerythritol, 4 parts of epoxidized soybean oil, 4 parts of 1-butyl-3-methylimidazolium chloride, 10 parts of polylactic acid, 10 parts of polybutylene succinate, 2 parts of polybutylene adipate terephthalate, 1 part of titanium dioxide, 10 parts of ethylene bis-stearamide, 2 parts of antioxidant 1010, 5 parts of MDI coupling agent, 5 parts of maleic anhydride-grafted polylactic acid, and 2 parts of polyethylene glycol 6000.

[0075] (2) Raw material pretreatment: Same as in Example 1.

[0076] (3) Ionic liquid-assisted in-situ reaction: Stir (1200 rpm) and heat to 135°C, and react at a constant temperature for 8 min to enhance the surface modification of high bamboo powder content.

[0077] (4) Vacuum dehydration: temperature 115℃, vacuum degree -0.095MPa, hold for 5min.

[0078] (5) Low temperature blending: Cool down to 80°C (cooling rate is the same as in Example 1), add matrix resin and remaining additives, and mix at low speed (500 rpm) for 8 minutes.

[0079] (6) Extrusion molding: The temperature is set to 135℃±10℃, and vacuum devolatilization (-0.08MPa); T-shaped hollow board mold is installed on the die head, the die gap is adjusted, and the fully biodegradable bamboo-based hollow corrugated board is obtained by extrusion molding.

[0080] Example 3:

[0081] This embodiment prepares a high-strength, fully biodegradable bamboo-based hollow corrugated board, including the following steps:

[0082] (1) Raw material weighing: Weigh 25 parts of bamboo powder (400 mesh), 0.8 parts of citric acid, 0.3 parts of pentaerythritol, 2.5 parts of epoxidized soybean oil, 1.5 parts of 1-butyl-3-methylimidazolium chloride, 20 parts of polylactic acid, 20 parts of polybutylene succinate, 4 parts of polybutylene adipate terephthalate, 2 parts of titanium dioxide, 6 parts of lubricant (EBS + zinc stearate, ratio 1:1), 1 part of antioxidant 1010, 2 parts of titanate coupling agent, 2 parts of maleic anhydride grafted polylactic acid, and 1 part of polyethylene glycol 6000.

[0083] (2) Raw material pretreatment, reaction, dehydration and blending steps: process parameters are the same as in Example 1.

[0084] (3) Extrusion molding: The temperature is set to 135℃±10℃, and vacuum devolatilization (-0.08MPa); T-shaped hollow board mold is installed at the die head, and fully biodegradable bamboo-based hollow corrugated board is obtained by extrusion molding.

[0085] Example 4:

[0086] This embodiment prepares a fully biodegradable flat yarn for woven bags, including the following steps:

[0087] (1) Raw material weighing: Weigh 25 parts of bamboo powder (1000 mesh), 0.6 parts of citric acid, 0.3 parts of pentaerythritol, 4 parts of epoxidized soybean oil, 2 parts of 1-butyl-3-methylimidazolium chloride, 25 parts of polylactic acid, 3 parts of polybutylene succinate, 35 parts of polybutylene adipate terephthalate, 1.5 parts of titanium dioxide, 6 parts of ethylene bis-stearamide, 1 part of antioxidant 1010, 2 parts of aluminate coupling agent, 3 parts of maleic anhydride-grafted polylactic acid, and 1.2 parts of polyethylene glycol 6000.

[0088] (2) Raw material pretreatment: The moisture content of bamboo powder is <0.5%, and the rest is the same as in Example 1.

[0089] (3) Ionic liquid-assisted in-situ reaction: stirring speed 1200 rpm, heating to 120℃, reducing the speed to 500 rpm and reacting at a constant temperature for 5 min.

[0090] (4) Vacuum dehydration: temperature 105℃, vacuum degree -0.08MPa, hold for 3min.

[0091] (5) Low temperature blending: Cool down to 70°C (cooling rate 5°C / min), add matrix resin and remaining additives, mix at low speed (500 rpm) for 5 min, and the rest is the same as in Example 1.

[0092] (6) Extrusion molding: The mixture is added to a parallel twin-screw extruder and a flat die is installed at the die head; after the melt is extruded, it is cooled into sheets by water-cooled rollers, then cut into filaments by a slitting knife, and then put into a heating oven for unidirectional stretching (stretch ratio 5 times), and after heat setting, it is wound up to obtain fully biodegradable flat filaments.

[0093] Example 5:

[0094] This embodiment prepares a fully biodegradable flat filament with high elongation at break, including the following steps:

[0095] (1) Raw material weighing: Weigh 20 parts of bamboo powder (1200 mesh), 0.5 parts of citric acid, 0.2 parts of pentaerythritol, 5 parts of epoxidized soybean oil, 1.5 parts of 1-butyl-3-methylimidazolium chloride, 20 parts of polylactic acid, 2 parts of polybutylene succinate, 45 parts of polybutylene adipate terephthalate, 1 part of titanium dioxide, 5 parts of ethylene bis-stearamide, 1 part of antioxidant 1010, 1.5 parts of MDI coupling agent, 3 parts of maleic anhydride-grafted polylactic acid, and 1 part of polyethylene glycol 6000.

[0096] (2) Process steps: Same as in Example 4.

[0097] (3) Extrusion molding: A flat film mold is installed on the die head, and the stretch ratio is set to 6 times to obtain high-toughness fully biodegradable flat yarn.

[0098] Example 6:

[0099] This embodiment prepares a high tensile strength, fully biodegradable flat filament, including the following steps:

[0100] (1) Raw material weighing: Weigh out 30 parts of bamboo powder (800 mesh), 0.8 parts of citric acid, 0.4 parts of pentaerythritol, 3 parts of epoxidized soybean oil, 2.5 parts of 1-butyl-3-methylimidazolium chloride, 30 parts of polylactic acid, 5 parts of polybutylene succinate, 30 parts of polybutylene adipate terephthalate, 2 parts of titanium dioxide, 7 parts of ethylene bis-stearamide, 1.5 parts of antioxidant 1010, 3 parts of titanate coupling agent, 4 parts of maleic anhydride-grafted polylactic acid, and 1.5 parts of polyethylene glycol 6000 by mass.

[0101] (2) Process steps: Same as in Example 4.

[0102] (3) Extrusion molding: A flat film mold is installed on the die head, and the stretch ratio is set to 4.5 times to obtain high-strength fully biodegradable flat yarn. The obtained flat yarn is used as warp and weft yarn and is loaded into a circular loom for weaving to obtain fully biodegradable tubular fabric. Then, through hot cutting and bottom sewing processes, the final product, biodegradable bamboo-based woven bag, is obtained.

[0103] Comparative Example 1:

[0104] Compared with Example 1, the difference is that citric acid, pentaerythritol, epoxidized soybean oil and ionic liquid were not added, and the high-temperature reaction and vacuum dehydration in steps (3) and (4) were not carried out. All raw materials (after drying) were added at once in step (5), mixed evenly at 80°C and then extruded. The rest are the same.

[0105] Comparative Example 2:

[0106] Compared with Example 1, the difference is that 1-butyl-3-methylimidazolium chloride (ionic liquid) was not added to the raw materials, while the other raw materials and steps were the same.

[0107] Comparative Example 3:

[0108] Compared with Example 4, the difference is that in step (4), the vacuum pump is not turned on for negative pressure dehydration, and only the atmospheric pressure at 110°C is maintained for stirring and venting. The rest are the same.

[0109] Comparative Example 4:

[0110] Compared with Example 1, the difference is that the feeding order is changed. Bamboo powder, citric acid, ionic liquid and polylactic acid (PLA), PBS, PBAT and other raw materials are mixed at once in step (1). The high-temperature in-situ reaction in step (3) is not carried out. The extrusion is carried out directly in step (6). The rest are the same.

[0111] Comparative Example 5:

[0112] Compared with Example 4, the difference is that no pentaerythritol (B4 monomer) was added to the raw materials, and citric acid (A3) reacted directly with bamboo powder and epoxidized soybean oil, while the rest were the same.

[0113] Test Example 1:

[0114] Experimental objective:

[0115] This test aims to verify the effectiveness of an ionic liquid-assisted high-temperature in-situ reaction system in constructing a chemically grafted layer on the surface of bamboo powder. Small molecules adsorbed by physical adsorption were removed using Soxhlet extraction, and the degree of chemical bonding between the reactants and the bamboo powder substrate was quantitatively characterized to evaluate the role of the ionic liquid as a reaction medium in promoting the solid-liquid interfacial esterification reaction. Simultaneously, contact angle testing was used to characterize the change in wettability of the bamboo powder surface before and after modification, verifying the shielding effect of the in-situ generated polyester layer on the polar hydroxyl groups on the bamboo powder surface, thereby predicting the interfacial compatibility between the filler and the hydrophobic biodegradable polyester matrix.

[0116] Experimental steps:

[0117] Sample preparation: The mixtures of Examples 1, 2, and 4 and Comparative Examples 1 and 2 after the completion of the ionic liquid-assisted in-situ reaction and vacuum dehydration steps, but before the addition of the polyester matrix resin, were taken as the test samples; the samples were placed in a vacuum drying oven and dried at 60°C for 24 hours to constant weight.

[0118] Soxhlet extraction: Accurately weigh approximately 5.0 g of the dried sample (denoted as W0), wrap it in filter paper, and place it in a Soxhlet extractor; use acetone as the solvent, and reflux extract at 90°C for 24 hours to remove unreacted citric acid, ionic liquid, epoxidized soybean oil, and free oligomers; after extraction, remove the filter paper package and wash three times with anhydrous ethanol.

[0119] Grafting rate determination: The extracted solid residue was placed in an oven and dried at 105℃ to constant weight, and the weight of the residue was measured (recorded as W1); the grafting rate was calculated using the following formula:

[0120] Grafting rate (%) = [(W1 - W_bamboo) / W_bamboo] × 100%;

[0121] Where W_bamboo represents the theoretical mass of the original bamboo powder added in the raw material ratio.

[0122] Contact angle test: Take another unextracted dry sample powder and press it into a disc with a diameter of 13 mm using a tablet press at a pressure of 10 MPa; use an optical contact angle meter and the seat drop method to add 3 μL of deionized water to the sample surface and record the static contact angle value 3 seconds after the droplet contacts the sample surface. Take the average value of 5 points for each sample.

[0123] The experimental data are shown in Table 1:

[0124] Table 1: Grafting rate and contact angle test data of modified bamboo powder intermediates

[0125]

[0126] Conclusion Analysis

[0127] According to Table 1 and Figure 1 It can be seen that the example group and the comparative group showed significant differences in grafting rate and surface wettability.

[0128] The grafting rate of Comparative Example 1 was only 0.83%, and the water contact angle was as low as 24.6°. This indicates that under the physical mixing state without chemical reaction intervention, small molecules such as citric acid and epoxidized soybean oil failed to bind to the surface of bamboo powder through chemical bonds. During the Soxhlet extraction process, most of the additives were washed away by the solvent, and a large number of exposed hydrophilic hydroxyl groups were still retained on the surface of the bamboo powder, resulting in its extremely strong hydrophilicity.

[0129] Although Comparative Example 2 added reactants, its grafting rate only increased to 4.21% and the contact angle was 68.3° due to the lack of ionic liquid. This confirms that in a solid-phase system, the direct reaction between citric acid solid and bamboo powder solid is limited by the phase interface and lacks an effective mass transfer medium, resulting in extremely low esterification efficiency, with most monomers remaining in a free state.

[0130] In comparison, the grafting rates of Examples 1, 2, and 4 all exceeded 14%, with Example 4 reaching as high as 19.37%, and the contact angles all exceeding 100°, achieving a transformation from hydrophilic to hydrophobic. This data verifies the reaction mechanism proposed in this invention: the ionic liquid constructs a highly efficient liquid-phase reaction microenvironment at the reaction temperature, dissolving citric acid and causing swelling of the amorphous regions on the surface of bamboo powder cellulose, significantly reducing the activation energy of the esterification reaction. Citric acid, as the A3 monomer, underwent a sufficient polycondensation reaction with the pentaerythritol B4 monomer on the bamboo powder surface, and further grafted long-chain hydrophobic segments of epoxidized soybean oil. This in-situ generated network polyester layer is firmly anchored on the bamboo powder surface, resistant to solvent extraction, and utilizes long-chain alkyl groups to shield the polar hydroxyl groups on the bamboo powder surface, thereby significantly improving the hydrophobicity of the filler. The grafting rate of Example 2 decreased slightly under high filling amounts due to the reduced proportion of reactants relative to the total surface area of ​​the matrix, but the contact angle remained hydrophobic, meeting the subsequent compatibility requirements with the fully biodegradable polyester matrix.

[0131] Test Example 2:

[0132] Experimental objective:

[0133] The study verified the thermodynamic equilibrium driving role of the vacuum dehydration step in the in-situ esterification reaction and the catalytic role of ionic liquids in the reaction kinetics. By measuring the residual acid value of the intermediate, the degree of carboxyl group conversion under various process conditions was evaluated, proving that the present invention effectively eliminates the risk of free acid in the system through a chemical equilibrium shift strategy. This confirms that the modified intermediate has chemical safety for one-step melt blending with acid-sensitive polyester matrix (such as PLA), preventing acid-catalyzed degradation of the matrix in subsequent processing.

[0134] Experimental steps:

[0135] Sample collection: The mixtures of Examples 1 and 4 (representing the vacuum dehydration process group), Comparative Example 2 (non-ionic liquid group), and Comparative Example 3 (non-vacuum dehydration group) after the in-situ reaction and dehydration steps were selected as test objects before the matrix resin was added.

[0136] Sample preparation: Accurately weigh 2.00 g (accurate to 0.001 g) of each powder sample and place it in a 250 mL Erlenmeyer flask; add 50 mL of a mixed solvent prepared by anhydrous ethanol and toluene in a 1:1 volume ratio, and place the flask in an ultrasonic cleaner for ultrasonic dispersion for 30 min to fully dissolve and extract the free unreacted carboxyl substances in the sample; then allow it to stand and filter, wash the filter residue with a small amount of mixed solvent, and combine the filtrates.

[0137] Acid value titration: Add 3 drops of phenolphthalein indicator to the filtrate and titrate with a 0.1 mol / L potassium hydroxide-ethanol standard solution; slowly add the standard solution dropwise under magnetic stirring until the solution changes from colorless to slightly red and does not fade within 30 seconds, and record the volume of potassium hydroxide standard solution consumed (V); at the same time, perform a blank experiment and record the volume of blank sample consumed (V0).

[0138] Calculation and Analysis: Based on the formula:

[0139] AV = [56.1 × c × (V - V0)] / m;

[0140] Calculate the acid value (mgKOH / g), where c is the concentration of the standard solution and m is the sample mass; and calculate the esterification conversion rate based on the theoretical acid value of citric acid in the initial formulation.

[0141] The experimental data are shown in Table 2:

[0142] Table 2: Residual acid value test data of modified intermediate system

[0143]

[0144] Conclusion Analysis

[0145] According to Table 2 and Figure 2 The data shows that there is an order-of-magnitude difference in residual acid value between the example group and the comparative group, which strongly proves the technical necessity of the process parameter settings of the present invention.

[0146] Comparative Example 2 showed a residual acid value as high as 58.32 mg KOH / g, with a conversion rate of only 18.4%. This indicates that in the absence of ionic liquid mediation, even with high-temperature treatment, the solid-solid or solid-liquid reaction kinetics between citric acid crystals and bamboo powder and pentaerythritol exhibited extremely high resistance. Most of the citric acid failed to participate in the esterification reaction and remained in the system as free acid. If this intermediate is directly mixed with polylactic acid, the high concentration of acidic groups will act as a strong degradation catalyst, leading to a collapse in material properties.

[0147] Although Comparative Example 3 underwent an ionic liquid-assisted reaction, the residual acid value still reached 39.55 mg KOH / g due to the lack of vacuum dehydration, and the conversion rate remained stagnant at 42.1%. This data verifies the reversible equilibrium mechanism of the esterification reaction: under normal pressure, the water generated in the reaction cannot be discharged in time, causing the water vapor partial pressure in the system to reach saturation. According to Le Chatelier's principle, the chemical equilibrium is restricted and cannot continue to shift towards ester formation, resulting in a large number of carboxyl groups failing to convert.

[0148] In contrast, the residual acid values ​​of Examples 1 and 4 decreased to 2.14 mg KOH / g and 2.47 mg KOH / g, respectively, with conversion rates exceeding 95%. This confirms that the vacuum dehydration step is not only a physical dehydration process but also a driving force for the shift in chemical equilibrium. By forcibly removing the reaction byproduct water under negative pressure, the thermodynamic equilibrium constraint is broken, causing the carboxyl groups of citric acid to be almost completely converted into ester bonds. This low-acid-value, low-moisture intermediate environment eliminates the risk of acid-catalyzed hydrolysis of the polyester matrix in subsequent processing, providing chemical safety assurance for stable one-step extrusion.

[0149] Test Example 3:

[0150] Experimental objective:

[0151] This test aims to comprehensively evaluate the impact of modified bamboo powder on the processing flowability of composite materials by characterizing the rheological behavior of the material in the molten state and the dynamic processing torque variation. Specific objectives include:

[0152] To verify the molecular ball bearing mechanism proposed in this invention, we investigated whether the surface hyperbranched three-dimensional structure constructed from citric acid (A3) and pentaerythritol (B4) can effectively reduce the frictional resistance between bamboo powder filler and matrix resin, as well as between filler particles, thereby improving melt flowability and reducing processing energy consumption under high filler content.

[0153] The protective effect of vacuum dehydration and stepwise reaction steps on the stability of the matrix resin during the process is evaluated. By monitoring abnormal changes in melt mass flow rate (MFR), it is determined whether the polyester matrix has undergone severe degradation (hydrolysis or acidolysis) due to residual acid or moisture, thereby verifying the effectiveness of the process of the present invention in suppressing molecular weight decrease and maintaining melt strength.

[0154] Experimental steps:

[0155] Sample preparation: Collect particle samples obtained by extrusion granulation of Examples 1, 2, 4, 5 and Comparative Examples 1, 3, 4, 5; place all samples in a vacuum drying oven and dry at 80°C for 12 hours to ensure that the moisture content is below 200 ppm in order to eliminate hydrolysis interference during the test process.

[0156] Melt mass flow rate (MFR) determination: According to GB / T-3682-2018 standard, a melt flow rate meter was used for testing; the test temperature was set to 190℃ and the nominal load was 2.16kg; 4.0g to 6.0g of dried particles were weighed and loaded into the barrel, preheated for 240 seconds, and then extruded under pressure; for samples with normal flowability, the sample was cut into segments every 10 seconds, and 5 segments were cut and weighed; for degraded samples with extremely high flowability, the segmentation interval was shortened to 5 seconds or a volumetric method was used to assist in the determination; the melt mass flow rate (g / 10min) was calculated.

[0157] Torque rheological performance test: The dynamic processing viscosity of the material was evaluated using a Hacker torque rheometer; the mixing chamber temperature was set to 170℃ and the rotor speed to 60rpm; 50g of sample was accurately weighed and added to the mixing chamber, and the equilibrium torque after the peak torque of the feed and the melt equilibrium temperature of the material due to shear heat were recorded; each sample was tested 3 times and the arithmetic mean was taken.

[0158] The experimental data are shown in Table 3:

[0159] Table 3: Test data of rheological properties and processing parameters of each component material

[0160]

[0161] Conclusion Analysis

[0162] According to Table 3 and Figure 3 The data shows that, through comprehensive analysis of melt flow rate and equilibrium torque, the mechanism of hyperbranched structure on rheological properties and the influence of vacuum dehydration on matrix stability in this invention are revealed.

[0163] The MFR values ​​of Comparative Examples 3 and 4 were abnormally high, at 84.60 g / 10 min and 62.15 g / 10 min, respectively, with extremely low equilibrium torque. This indicates that in the absence of vacuum dehydration or with an incorrect feeding sequence, residual moisture or free acid in the system triggered severe degradation of the polylactic acid and polyester matrix during high-temperature shearing. The molecular chain breakage led to a sharp drop in melt viscosity, and such materials lost their basic melt strength, failing to meet the process requirements for extrusion molding or fiber drawing.

[0164] Comparative Example 1, as a physical mixing control group, showed a measurable molecular weight ratio (MFR) of only 1.27 g / 10 min, a high equilibrium torque of 28.4 N·m, and a melt temperature that rose to 185 °C due to strong shear friction. This indicates that the unmodified bamboo powder exhibits extremely high interfacial friction with the matrix resin, resulting in high flow resistance, difficult processing, and a tendency to cause equipment wear and material scorching.

[0165] Example 2, even with an extreme formulation containing up to 70 parts bamboo powder, maintained an MFR of 4.15 g / 10 min and a balanced torque of 19.8 N·m, demonstrating good processability. Compared to Comparative Example 5 (MFR 7.93, torque 16.7), which had a lower bamboo powder content (25 parts) but lacked pentaerythritol (B4 monomer), Example 2, despite having a significantly higher filler load than Comparative Example 5, did not exhibit the expected exponential increase in viscosity. Comparing Example 4 (containing B4) and Comparative Example 5 (without B4), with similar filler amounts, the torque of Example 4 (11.2 N·m) was significantly lower than that of Comparative Example 5 (16.7 N·m). This phenomenon confirms the existence of the molecular ball effect: the hyperbranched spherical structure constructed with pentaerythritol as the core forms a three-dimensional steric hindrance layer on the surface of bamboo powder, effectively isolating the direct contact between fillers and transforming the dry friction between polymer chain segments and filler surfaces into internal friction between hyperbranched molecules, significantly reducing melt viscosity and making low-energy extrusion of highly filled bamboo-based materials possible.

[0166] Test Example 4:

[0167] Test objective: To comprehensively verify the feasibility of the ion liquid-assisted in-situ hyperbranching modification technology proposed in this invention and its significant progress compared to existing technologies.

[0168] Experimental steps:

[0169] Sample preparation and conditioning: Test strips were cut from the hollow corrugated sheets prepared in Examples 1, 2, 3, and Comparative Examples 1 and 2. According to GB / T2918 standard, all samples were placed in an environment with a temperature of 23±2℃ and a relative humidity of 50±5% for 48 hours to condition them and eliminate the deviation of the test results caused by the fluctuation of ambient temperature and humidity.

[0170] Flat compressive strength (FCT) test: According to GB / T-22876 standard, the compressive strength tester is used for determination; the plate is cut into circular specimens with a diameter of 64mm, placed between the upper and lower pressure plates, the compression rate is set to 12.5mm / min, and the maximum load (N) of the specimen during the crushing failure process is recorded; 10 parallel samples are tested in each group, and the maximum and minimum values ​​are removed and the average value is taken.

[0171] Edge crush strength (ECT) test: According to GB / T6546 standard, cut a rectangular specimen with a size of 100mm×25mm (corrugated direction perpendicular to the long side); place the specimen in the guide block and keep it vertical, apply a vertical compressive load, set the compression rate to 12.5mm / min, and record the force per unit length (kN / m) when crushed.

[0172] Water absorption test: Cut a 50mm × 50mm square sample, and seal the cut edges with the same material of resin to eliminate capillary water absorption interference; dry the sample in a 50℃ oven for 24 hours and weigh it (record as m1); then completely immerse it in deionized water at 23℃ for 24 hours; remove the sample, quickly blot off the surface moisture with filter paper, and weigh it immediately (record as m2); calculate the water absorption rate:

[0173] W = [(m2-m1) / m1] × 100%;

[0174] The experimental data are shown in Table 4:

[0175] Table 4: Test Results of Mechanical Strength and Water Resistance of Hollow Corrugated Board

[0176]

[0177] Conclusion Analysis

[0178] According to Table 4 and Figure 4 The data shows that the example group exhibits significant advantages in terms of mechanical load-bearing capacity and dimensional stability, verifying the strengthening effect of ionic liquid-assisted in-situ hyperbranching modification technology on interfacial bonding.

[0179] Comparative Example 1 exhibits a compressive strength of only 128.4 N and a water absorption rate as high as 9.87%. This is due to the polarity difference between the physically mixed bamboo powder and the polyester matrix, resulting in a significant phase separation interface. Moisture easily penetrates into the material's interior through the hydrophilic bamboo powder channels, causing fiber swelling, disrupting the material's microstructural integrity, and causing it to rapidly lose its load-bearing capacity in humid environments.

[0180] The edge crush strength of Comparative Example 2 was 3.42 kN / m, which was better than that of Comparative Example 1, but still significantly lower than that of Example 1 (5.12 kN / m). This indicates that in the absence of ionic liquid catalysis, the interface modification reaction was incomplete, and the chemical bonding density on the bamboo powder surface was insufficient to form an effective stress transfer medium, leading to easy debonding failure at the interface when the material was under pressure.

[0181] Example 3 exhibited the highest mechanical properties, with a flat compressive strength of 594.1 N, an edge compressive strength of 6.78 kN / m, and a water absorption rate as low as 0.72%. This is attributed to the rigid framework formed by the high content of PLA matrix and dense modified bamboo powder, and the hydrophobic segments (derived from epoxidized soybean oil) in the hyperbranched structure forming an effective waterproof barrier at the interface.

[0182] It is worth noting that in Example 2, with a bamboo powder content as high as 70 parts, the flexural modulus reached 3150 MPa, and the compressive strength (412.3 N) remained at a high level, without exhibiting the brittle fracture or sudden strength drop common in traditional high-filler composite materials. This directly corroborates the molecular ball bearing mechanism: the in-situ generated hyperbranched polyester layer not only fills the microporous defects on the surface of the bamboo powder, but also plays a dual role of internal lubrication and toughening in the high-filler system, allowing particles to undergo slight slippage and rearrangement under stress, thereby avoiding local stress concentration and achieving a balance of rigidity and toughness under high biomass content.

[0183] Test Example 5:

[0184] Test Objectives: 1. Verify the effectiveness of the in-situ modification mechanism: By measuring the grafting rate, contact angle, and residual acid value of the intermediates, confirm the catalytic effect of ionic liquids in the solid-phase system and the driving effect of vacuum dehydration on the esterification reaction equilibrium, thus confirming the successful construction of a hydrophobic hyperbranched polyester layer on the bamboo powder surface. 2. Verify the molecular ball bearing effect and processing rheology: Through melt flow rate and torque rheology tests, evaluate the effect of the hyperbranched structure on reducing the melt viscosity of the highly filled system, and verify the stability of the one-step extrusion process. 3. Verify the mechanical and application properties of the final product: For hollow corrugated sheets, focus on evaluating their flat crush strength, edge crush strength, and water resistance stability; for woven bag flat yarns, focus on evaluating their tensile strength and elongation at break (toughness).

[0185] Experimental steps:

[0186] Sample preparation and conditioning: 500 mm long flat wire segments were randomly cut from the final flat wire winding cylinders prepared in Examples 4, 5, 6, and Comparative Examples 3 and 5 as test samples; 20 wires were selected from each group of samples and placed in a standard environment (temperature 23±2℃, relative humidity 50±5%) for 48 hours to eliminate the influence of internal stress and damp heat history on the test results.

[0187] Tensile property test: According to GB / T-1040.3-2006 "Determination of tensile properties of plastics - Part 3: Test conditions for films and sheets" and QB / T3808-1999 "Plastic woven bags", the test was conducted using an electronic universal testing machine; the clamp spacing (gauge length) was set to 200 mm and the tensile speed to 200 mm / min.

[0188] Data acquisition: The flat wire sample is vertically fixed at the center of the upper and lower clamps to ensure that the sample does not slip or break during the stress process; the tensile program is started until the sample breaks, and the instrument automatically records the maximum tensile load (N) and the increase in gauge length at the time of breakage; the tensile breaking strength (MPa) and elongation at break (%) are calculated by combining the cross-sectional area of ​​the flat wire (obtained by conversion between linear density and density); the arithmetic mean of each group of valid samples is taken as the final result.

[0189] The experimental data are shown in Table 5:

[0190] Table 5: Test data of tensile strength and elongation at break of woven bag flat yarn

[0191]

[0192] Conclusion Analysis

[0193] According to Table 5 and Figure 5 The data shows that the huge differences in mechanical performance among the samples reveal the decisive influence of vacuum dehydration process and molecular topology design on the performance of fully biodegradable flat yarns.

[0194] The test results for Comparative Example 3 showed a catastrophic performance degradation, with a tensile strength of only 58.6 MPa and an elongation at break as low as 4.3%, exhibiting extreme brittleness. This data confirms that, without vacuum dehydration, the water byproduct generated during the esterification reaction induced severe hydrolytic degradation of the polylactic acid (PLA) matrix during high-temperature extrusion, leading to a sharp decrease in polymer molecular weight. The molecular chains could not withstand high-ratio stretching and orientation, resulting in frequent breakage during fiber drawing and the inability to form an effective fiber structure.

[0195] Comparative Example 5 (without B4 monomer) exhibited a tensile strength of 168.2 MPa, which is acceptable, but its elongation at break was only 11.5%, significantly lower than the 28.4% of Example 4. This indicates that while linear or low-branched modified structures initiated solely by citric acid can improve interfacial compatibility, they lack the highly hyperbranched spherical structures constructed with pentaerythritol (B4 monomer). Such linear molecular chains are prone to entanglement during stretching, limiting the slippage ability of the molecular chain segments.

[0196] In contrast, Examples 4 and 5 exhibited superior toughness, with elongations at break reaching 28.4% and 46.7%, respectively. This is because the in-situ generated hyperbranched polyester structure acts as molecular ball bearings on the bamboo powder surface. Under external stretching, this spherical structure effectively reduces internal friction between the filler and the matrix, as well as between the molecular chains, allowing the molecular chains to maintain interfacial bonding while undergoing greater orientation and slippage. Example 6, by adjusting the ratio of PLA to PBAT, increased the strength to 215.3 MPa while maintaining a certain level of toughness (19.2%), demonstrating the flexibility and robustness of the formulation system of this invention in meeting the load-bearing requirements of different woven bags.

[0197] Test Example 6:

[0198] Test objective:

[0199] The purpose of this invention is to verify the final aerobic biodegradability of the bamboo-based composite material under controlled composting conditions, confirm whether the hyperbranched structure and cross-linked network introduced by chemical modification affect the biodegradability of the material, and evaluate whether it meets the certification requirements of GB / T-19277.1 and EN-13432 for fully biodegradable materials.

[0200] Experimental steps:

[0201] Sample pretreatment: Example 1 (hollow corrugated board), Example 4 (woven bag flat yarn), and Comparative Example 1 (physical blend) were selected as the samples to be tested. The samples were freeze-pulverized into powder with a particle size of less than 2 mm. Microcrystalline cellulose (TLC) was selected as the reference material, and polyethylene (PE) particles were selected as the negative control. The total organic carbon (TOC) content of each sample was determined in order to calculate the theoretical carbon dioxide release (ThCO2).

[0202] Inoculum preparation: Collect the organic portion of urban solid waste for aerobic composting cultivation, remove large particulate impurities by sieving, adjust the moisture content of the compost inoculum to 50%-55%, control the volatile solids (VS) content to more than 30% of the total dry solids, and pre-aeration before use to eliminate residual background values ​​of easily degradable organic matter.

[0203] Reaction system construction: In the biodegradation test reactor, the inoculum and the test sample were mixed separately at a ratio of 6:1 by dry weight; the reactor was placed in a constant temperature and humidity incubator, the temperature was set at 58±2℃, and the aeration rate was controlled to maintain an aerobic environment; three parallel samples and a blank inoculum control group were set up.

[0204] Degradation process monitoring: The gas discharged from the reactor is collected using a continuous airflow method, and the cumulative amount of released carbon dioxide is measured periodically using an infrared carbon dioxide analyzer; data is recorded every 1 to 2 days, and water is added periodically to maintain the humidity balance in the reactor; the test cycle is set to 90 days, or until the biodegradation rate enters a stable period.

[0205] Data processing: The biodegradation rate (%) at different time points was calculated by subtracting the background value of the blank control group from the cumulative amount of carbon dioxide released by the sample and dividing by the theoretical amount of carbon dioxide released by the sample.

[0206] The experimental data are shown in Table 6:

[0207] Table 6: Test data on the change of biodegradation rate of materials over time under controlled composting conditions

[0208]

[0209] Conclusion Analysis

[0210] According to Table 6 and Figure 6 The data shows that the modified bamboo-based materials prepared in the examples exhibit excellent biodegradability in an industrial composting environment, with a final degradation rate exceeding 90%, meeting the evaluation criteria for fully biodegradable materials.

[0211] The reference material, microcrystalline cellulose, showed a degradation rate of 96.8% within 90 days, verifying the effectiveness of the compost inoculum. The final degradation rates of Examples 1 and 4 were 92.7% and 94.2%, respectively. Compared to Comparative Example 1 (91.5%), the degradation rates of the Example samples were slightly lower in the initial stage (first 15 days), at 18.2% and 21.5%, respectively, lower than the 24.1% of Comparative Example 1. This is because a dense hydrophobic hyperbranched polyester layer was constructed on the surface of bamboo powder through in-situ reaction in the Examples, which to some extent increased the crystallinity of the polyester matrix, resulting in a slight inhibition of the penetration and adhesion of water and microbial extracellular enzymes in the initial stage.

[0212] However, after entering the mid-term (30-60 days), as the polyester ester bonds hydrolyzed and broke, the degradation rate of the example samples rapidly caught up with and approached that of the comparative samples. This indicates that the chemical crosslinking structure introduced in this invention is mainly based on ester bonds (citric acid-pentaerythritol-bamboo powder), which are easily hydrolyzed and broken under high-temperature composting (58°C) and the action of microbial enzymes, without introducing recalcitrant inert segments into the material.

[0213] Ultimately, at the end of 90 days, the degradation rate of the example sample was even slightly higher than that of Comparative Example 1. This is presumably because the modification technique of this invention improved the dispersibility of bamboo powder in the matrix, eliminating agglomeration. Once the matrix resin began to disintegrate, the uniformly dispersed micron-sized bamboo powder particles were more fully exposed to the microbial environment, serving as a high-quality carbon source to promote microbial reproduction, thereby accelerating the mineralization process of the remaining polymer fragments. Data confirms that the in-situ hyperbranching modification technique of this invention significantly improves the mechanical and processing properties of the material while completely preserving its fully biodegradable characteristics, without causing any accumulation of ecotoxicity.

[0214] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A fully biodegradable bamboo-based material, characterized in that, Includes the following weight groups: Bamboo powder: 20-65 parts; Citric acid: 0.5–2 parts; Monopentaerythritol: 0.2–0.8 parts; Epoxidized soybean oil: 2.5–5 parts; Ionic liquid: 1.5–4 parts; Polylactic acid: 10-30 parts; Polybutylene succinate: 2-20 parts; Polybutylene adipate terephthalate: 2-45 parts; Titanium dioxide: 1-2 parts; Other adjuvants; The ionic liquid is 1-butyl-3-methylimidazolium chloride; In this process, the bamboo powder, citric acid, pentaerythritol and epoxidized soybean oil undergo an in-situ esterification reaction under the catalysis of the ionic liquid to form a modified bamboo powder intermediate. Under the condition of maintaining a temperature of 105-115°C, a negative pressure vacuum is applied to the modified bamboo powder intermediate to remove the water generated in the reaction.

2. The bamboo-based material according to claim 1, characterized in that, The bamboo powder has a particle size of 200-1500 mesh and a moisture content of less than 1.0%.

3. The bamboo-based material according to claim 1, characterized in that, The other adjuvants specifically include: Lubricant: 5-10 parts; Antioxidant 1010: 1-2 parts; Coupling agent: 1.5-5 parts; Compatibilizer: 2-5 parts; Dispersant: 1-2 parts.

4. The bamboo-based material according to claim 3, characterized in that, The lubricant is ethylene bis-stearamide or a compound of ethylene bis-stearamide and zinc stearate; The coupling agent is selected from one of aluminate coupling agents, titanate coupling agents, or 4,4'-diphenylmethane diisocyanate; The compatibilizer is maleic anhydride-grafted polylactic acid; The dispersant is polyethylene glycol 6000.

5. The bamboo-based material according to claim 1, characterized in that, The fully biodegradable bamboo-based material is a hollow corrugated board or stretched flat filament; When the material is hollow corrugated board, the bamboo powder particle size is 200-400 mesh; When the material is drawn flat filament, the bamboo powder particle size is 800-1500 mesh.

6. A method for preparing a bamboo-based material as described in any one of claims 1-5, characterized in that, Includes the following steps: S1. Raw material pretreatment: Dry bamboo powder and titanium dioxide to a moisture content of <1.0%, and dry polylactic acid, polybutylene succinate and polybutylene adipate to a moisture content of <0.05%. S2. Ionic liquid-assisted in-situ reaction: Bamboo powder, citric acid, pentaerythritol, epoxidized soybean oil and ionic liquid are mixed, heated to 120-135℃, and a constant temperature reaction is carried out under high-speed stirring to obtain modified bamboo powder intermediate. S3, Vacuum dehydration: Under the condition of maintaining a temperature of 105-115℃, negative pressure is applied to the modified bamboo powder intermediate of S2 to remove the water generated in the reaction. S4. Low-temperature blending: Remove the vacuum, cool to 70-80℃, add polylactic acid, polybutylene succinate, polybutylene adipate terephthalate and the remaining additives, and mix evenly under low-speed stirring to obtain a premix. S5. Extrusion molding: The premixed material is plasticized, extruded and shaped by an extruder to obtain the fully biodegradable bamboo-based material.

7. The method for preparing bamboo-based materials according to claim 6, characterized in that, In step S2, the high-speed stirring speed is 1000-1400 rpm, and the constant temperature reaction time is 5-8 min; in step S4, the low-speed stirring speed is 300-600 rpm, and the discharge temperature is controlled below 80℃.

8. The method for preparing bamboo-based materials according to claim 6, characterized in that, In step S3, the vacuum degree of the negative pressure evacuation is -0.08MPa to -0.095MPa, and the evacuation time is 3 to 5 minutes.

9. The method for preparing bamboo-based materials according to claim 6, characterized in that, In step S5, the extruder is set to a temperature of 125–145°C and vacuum devolatilization is performed. When preparing hollow corrugated sheets, T-shaped hollow sheet molds are used for extrusion and vacuum shaping; When preparing drawn flat yarns, a flat die is used to extrude sheets, which are then slit and stretched unidirectionally with a stretching ratio of 4.5 to 6 times.

10. The application of a fully biodegradable bamboo-based material as described in any one of claims 1-5 in the preparation of woven yarns, woven bags, corrugated boards, or corrugated boxes.

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