Preparation process of bamboo fiber grafting modified full-biodegradable composite film material

Abstract

This invention relates to the field of polymer material preparation technology and discloses a preparation process for a fully biodegradable composite membrane material modified by bamboo fiber grafting. The process includes: firstly, preparing a bamboo fiber modified premix by hot mixing and cooling dried bamboo fiber powder, anhydrous citric acid, choline chloride, active zinc oxide, and pentaerythritol; subsequently, mixing biodegradable polyester resin with the premix; adding the mixture to an extruder and injecting epoxidized soybean oil into the cylinder through a liquid metering device, followed by melt extrusion granulation under vacuum degassing conditions; and finally, forming a film by blow molding. This invention achieves surface grafting of bamboo fiber, chain extension of the polyester matrix, and interfacial chemical bonding between the two through multi-component synergistic in-situ reactive extrusion, effectively improving interfacial compatibility, inhibiting degradation during material processing, and significantly enhancing the mechanical properties and thermal stability of the composite membrane material. Furthermore, the process is highly efficient, environmentally friendly, and cost-controllable.

Description

Technical Field

[0001] This invention relates to the field of polymer material preparation technology, specifically to the preparation process of bamboo fiber grafted modified fully biodegradable composite membrane material. Background Technology

[0002] With increasing environmental awareness and the implementation of the "plastic ban" policy, fully biodegradable plastics, represented by polybutylene adipate terephthalate (PBAT) and polylactic acid (PLA), have become important alternative materials for controlling white pollution. To reduce raw material costs and impart higher rigidity and heat resistance to materials, incorporating natural plant fibers such as bamboo fiber into biodegradable polyester matrices to prepare fully biodegradable composite materials has become an important technological direction in the industry. Bamboo fiber, as a renewable biomass resource, has advantages such as wide availability, high specific strength, and complete biodegradability, making it an ideal reinforcing filler.

[0003] However, the application of bamboo fiber in the preparation of biodegradable polyester films has consistently faced the technical bottleneck of poor interfacial compatibility between components. Biodegradable polyester matrices are typically hydrophobic, while bamboo fiber surfaces are rich in hydroxyl groups, exhibiting strong hydrophilicity. This fundamental difference in polarity makes it difficult for the two to form a tight interfacial bond during melt blending, easily leading to phase separation. This microstructural defect directly results in a significant decrease in the macroscopic mechanical properties of the composite material, especially during film blow molding, where problems such as film breakage and insufficient strength easily occur, severely limiting its commercial application.

[0004] Furthermore, bamboo fiber has relatively low thermal stability, making it prone to thermal degradation or the release of trace amounts of moisture during high-temperature melt extrusion. This moisture and acidic degradation products accelerate the hydrolysis of the polyester matrix, leading to polyester molecular chain breakage, a decrease in molecular weight, and consequently, reduced melt strength and unstable processing fluidity. Existing modification technologies often employ methods such as alkaline soaking and wet treatment with silane coupling agents to pretreat bamboo fiber. While these traditional methods can improve interfacial bonding to some extent, the processes are cumbersome, involving multiple steps such as soaking, washing, dehydration, and prolonged drying. This not only results in low production efficiency and high energy consumption but also generates large amounts of industrial wastewater, failing to meet the demands of green manufacturing and low-cost industrial production. Therefore, developing a preparation process that can simultaneously and efficiently modify bamboo fiber, enhance interfacial compatibilization, and inhibit polyester matrix degradation is a pressing technical challenge in this field. Summary of the Invention

[0005] The technical problem this invention aims to solve is that in existing biodegradable composite membrane materials, the poor interfacial compatibility between plant fibers (such as bamboo fiber) and the polyester matrix leads to decreased mechanical properties and a narrow processing window. Furthermore, the introduction of plant fibers easily causes degradation during melt processing, affecting the quality of the final product. This invention aims to provide a preparation process that improves interfacial compatibility and enhances the overall performance of the composite membrane material by in-situ grafting modification of bamboo fiber and optimizing the reactive extrusion process of the composite material.

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

[0007] This invention provides a process for preparing bamboo fiber grafted and modified fully biodegradable composite membrane materials, comprising the following steps:

[0008] (1) Preparation of bamboo fiber modified premix: Dry bamboo fiber powder, anhydrous citric acid, choline chloride, active zinc oxide and pentaerythritol are mixed under heating conditions and cooled to obtain bamboo fiber modified premix;

[0009] (2) Mixing: The biodegradable polyester resin and the bamboo fiber modified premix are mixed evenly to obtain a mixture;

[0010] (3) Reactive extrusion: The mixture is added to the extruder, and epoxidized soybean oil is injected into the extruder barrel through a liquid metering device. Melt extrusion granulation is carried out under vacuum exhaust conditions to obtain modified composite material masterbatch.

[0011] (4) Blow molding: The modified composite material masterbatch is blow molded in a blow molding machine to obtain a composite film material.

[0012] By adopting the above technical solution, the present invention achieves significant technical effects:

[0013] This process first involves surface treatment of bamboo fiber using anhydrous citric acid, choline chloride, active zinc oxide, and pentaerythritol during the premix preparation stage. Subsequently, in the reactive extrusion stage, the aforementioned modified system synergistically interacts with epoxidized soybean oil, initiating a series of in-situ reactions within the biodegradable polyester melt. The main reactions occurring during melt extrusion in this process are as follows:

[0014] Grafting of citric acid and introduction of active sites: Under the high temperature and shearing action of the extruder, the carboxyl groups in anhydrous citric acid molecules undergo esterification with the hydroxyl groups on the surface of bamboo fibers, grafting citric acid molecules onto the bamboo fiber surface. This step initially improves the polarity of the bamboo fiber and introduces citric acid molecules with multiple active carboxyl groups into the bamboo fiber, providing active sites for subsequent reactions.

[0015] Interfacial bridging effect of epoxidized soybean oil: Under the catalysis of choline chloride and active zinc oxide, the epoxy groups on the injected epoxidized soybean oil molecules are activated. These activated epoxy groups can simultaneously react with the remaining carboxyl groups of citric acid grafted onto bamboo fibers, as well as the terminal carboxyl groups or terminal hydroxyl groups of biodegradable polyester resins (such as PBAT). In this way, epoxidized soybean oil molecules form chemical bonds between the bamboo fiber and the polyester matrix, constructing a stable "bamboo fiber-epoxidized soybean oil-polyester" interfacial layer, significantly improving the interfacial bonding between the two.

[0016] Synergistic chain extension and network construction of pentaerythritol: As a polyhydroxy compound, pentaerythritol's four hydroxyl groups can undergo esterification with carboxyl groups (derived from citric acid or polyester end groups) present in the system. This reaction consumes small polyester molecules generated by hydrolysis or thermal degradation, effectively increasing melt viscosity, while simultaneously forming a mildly cross-linked network locally. This network structure further enhances the melt strength of the composite material.

[0017] Effective removal of byproducts: Small molecule byproducts such as water generated during the esterification reaction, if remaining in the melt, will accelerate the hydrolysis of polyester. This process incorporates vacuum exhaust in a specific area of ​​the extruder, which can promptly remove these small molecule byproducts, shifting the reaction equilibrium towards a direction favorable to chain extension and grafting, thereby inhibiting the degradation of the polyester matrix.

[0018] In summary, this invention utilizes a multi-component synergistic in-situ reactive extrusion strategy to achieve grafting of bamboo fibers, chain extension of the polyester matrix, and chemical bridging of the interfacial layer in the molten state. This effectively enhances the interfacial bonding between bamboo fibers and the polyester matrix and inhibits thermal degradation of the material during processing. Consequently, the resulting composite membrane material exhibits excellent mechanical properties, thermal stability, and processing fluidity.

[0019] In a preferred embodiment of the present invention, the bamboo fiber modified premix is ​​made from raw materials comprising the following parts by weight:

[0020] 100 parts dried bamboo fiber powder; 2.5-10 parts anhydrous citric acid; 2.5-10 parts choline chloride; 0.5-2.5 parts active zinc oxide; 2.5-10 parts pentaerythritol.

[0021] As another preferred embodiment of the present invention, the specific steps for preparing the bamboo fiber modified premix are as follows:

[0022] S1: Mix dried bamboo fiber powder, anhydrous citric acid and choline chloride, and heat to 85-95℃ for the first stage of mixing treatment.

[0023] S2: Keep the temperature constant, add active zinc oxide, and carry out the second stage of mixing treatment;

[0024] S3: Keep the temperature constant, add pentaerythritol, and carry out the third stage of mixing treatment;

[0025] S4: After mixing, cool to below 40°C and discharge. By adopting the above technical solution and adding each component in stages, the catalytic system and reactants can be more evenly dispersed, avoiding excessively rapid or uneven local reactions, which helps to ensure the quality of the premix and the stability of subsequent reaction extrusion.

[0026] As another preferred embodiment of the present invention, the weight ratio of each component in steps (2) and (3) is as follows: 100 parts of biodegradable polyester resin; 13.25-43.2 parts of bamboo fiber modified premix; and 2.0-5.0 parts of epoxidized soybean oil.

[0027] By adopting the above technical solution, the components can achieve a good synergistic effect within this ratio range, ensuring that the reaction proceeds fully while maintaining good processing performance and cost-effectiveness of the material.

[0028] As another preferred embodiment of the present invention, the biodegradable polyester resin is polybutylene adipate / terephthalate (PBAT), or a mixture of PBAT and polylactic acid (PLA).

[0029] By adopting the above technical solutions, the type of matrix resin can be flexibly adjusted according to the application requirements of the final product to obtain different rigidity-toughness balances and degradation rates.

[0030] As another preferred embodiment of the present invention, the barrel temperature zoning setting and vacuum exhaust position of the extruder have been specifically optimized.

[0031] By adopting the above technical solution, the precisely controlled temperature curve provides suitable reaction conditions for reactions in different regions (such as esterification, ring opening, and chain extension), while the vacuum exhaust at specific locations ensures [the desired reaction conditions].

[0032] This invention provides a process for preparing a fully biodegradable composite membrane material modified by bamboo fiber grafting. It has the following beneficial effects:

[0033] 1. This invention utilizes the synergistic effect of multiple components, including anhydrous citric acid and epoxidized soybean oil, during the extrusion process to construct chemical bonds between bamboo fiber and the polyester matrix. This in-situ generated interfacial layer replaces the weak van der Waals forces in traditional physical blending, enabling stress to be effectively transferred from the polyester matrix to the reinforcing bamboo fiber, thereby resulting in a composite film material with higher tensile strength and elongation at break.

[0034] 2. The process of this invention utilizes pentaerythritol and epoxidized soybean oil to perform in-situ chain extension and repair of polyester molecules that have experienced chain breakage due to heat, shear, or a small amount of moisture, thereby improving melt strength. Simultaneously, the vacuum exhaust port located in a specific area of ​​the extruder can promptly remove small molecule byproducts such as water generated during the esterification reaction, reducing the hydrolytic degradation of the polyester. The combination of these two aspects ensures the stability of the material's performance during processing.

[0035] 3. This invention integrates the grafting modification of bamboo fiber, the chain extension of the polyester matrix, and the composite process of the two into the core step of reactive extrusion. Compared with traditional processes that require independent and complex pretreatment of fibers, this invention eliminates cumbersome steps such as washing and drying after fiber modification, shortens the production cycle, reduces equipment and energy consumption, and makes the entire preparation process more economical and industrially applicable. Detailed Implementation

[0036] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to comparative examples and test cases. 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.

[0037] Preparation Examples 1-3:

[0038] Preparation Example 1: This preparation example provides a bamboo fiber modified premix, including the following steps:

[0039] Add 1000g (i.e. 100 parts by weight) of dried bamboo fiber powder, 50g (i.e. 5 parts by weight) of anhydrous citric acid and 50g (i.e. 5 parts by weight) of choline chloride to a high-speed mixer equipped with a heating jacket, heat to 90°C, and mix at 900 rpm for 10 minutes.

[0040] Then reduce the speed to 500 rpm, keep the temperature at 90°C, add 15g (i.e. 1.5 parts by weight) of active zinc oxide, and continue mixing for 4 minutes;

[0041] Finally, restore the rotation speed to 900 rpm, add 50g (i.e. 5 parts by weight) of pentaerythritol, and continue mixing for 4 minutes;

[0042] After mixing, the material is discharged into a cold mixer and cooled to below 40°C before being discharged to obtain bamboo fiber modified premix A1.

[0043] Preparation Example 2: This preparation example provides a bamboo fiber modified premix, including the following steps:

[0044] Add 1000g (i.e. 100 parts by weight) of dried bamboo fiber powder, 25g (i.e. 2.5 parts by weight) of anhydrous citric acid and 25g (i.e. 2.5 parts by weight) of choline chloride to a high-speed mixer equipped with a heating jacket, heat to 85°C, and mix at 800 rpm for 8 minutes.

[0045] Then reduce the speed to 400 rpm, keep the temperature at 85°C, add 5g (0.5 parts by weight) of active zinc oxide, and continue mixing for 3 minutes;

[0046] Finally, restore the rotation speed to 800 rpm, add 25g (2.5 parts by weight) of pentaerythritol, and continue mixing for 3 minutes;

[0047] After mixing, the material is discharged into a cold mixer and cooled to below 40°C before being discharged to obtain bamboo fiber modified premix A2.

[0048] Preparation Example 3: This preparation example provides a bamboo fiber modified premix, including the following steps:

[0049] 1000g (i.e. 100 parts by weight) of dried bamboo fiber powder, 100g (i.e. 10 parts by weight) of anhydrous citric acid and 100g (i.e. 10 parts by weight) of choline chloride were put into a high-speed mixer equipped with a heating jacket, heated to 95°C, and mixed at 1000rpm for 12 minutes.

[0050] Then reduce the speed to 600 rpm, keep the temperature at 95°C, add 25g (2.5 parts by weight) of active zinc oxide, and continue mixing for 5 minutes;

[0051] Finally, restore the rotation speed to 1000 rpm, add 100g (i.e. 10 parts by weight) of pentaerythritol, and continue mixing for 5 minutes;

[0052] After mixing, the material is discharged into a cold mixer and cooled to below 40°C before being discharged to obtain bamboo fiber modified premix A3.

[0053] Examples 1-4:

[0054] Example 1: This example provides a process for preparing a fully biodegradable composite membrane material modified by bamboo fiber grafting, including the following steps:

[0055] (1) Weigh 100 parts of poly(butylene adipate / terephthalate) resin and 23.3 parts of bamboo fiber modified premix A1 obtained in Preparation Example 1 (corresponding to 20 parts of bamboo fiber, 1 part of anhydrous citric acid, 1 part of choline chloride, 0.3 parts of active zinc oxide, and 1 part of pentaerythritol), mix them evenly, and add them to the main feed hopper of the twin-screw extruder;

[0056] (2) 3.5 parts of epoxidized soybean oil were injected into the first section of the twin-screw extruder using a liquid metering pump;

[0057] (3) The screw speed of the twin-screw extruder is controlled at 300 rpm, and the barrel temperature zones are set as follows:

[0058] Zone 1: 135℃, Zone 2: 150℃, Zone 3: 160℃, Zone 4: 165℃, Zone 5: 165℃, Zone 6 (vacuum exhaust zone, vacuum degree -0.07MPa): 160℃, Zone 7: 155℃, Head unit: 150℃;

[0059] The material is extruded, water-cooled, pelletized and dried to obtain modified composite material masterbatch;

[0060] (4) The obtained masterbatch is added to a single screw blown film machine and blown into a film under the conditions of machine body temperature of 150-165℃, die head temperature of 160℃ and blow ratio of 3.0:1 to obtain a composite film with a thickness of 30μm.

[0061] Example 2: This example provides a process for preparing a fully biodegradable composite membrane material modified by bamboo fiber grafting, including the following steps:

[0062] (1) Weigh 100 parts of PBAT resin and 13.25 parts of bamboo fiber modified premix A3 obtained in Preparation Example 3 (corresponding to 10 parts of bamboo fiber, 1 part of anhydrous citric acid, 1 part of choline chloride, 0.25 parts of active zinc oxide, and 1 part of pentaerythritol), mix them evenly, and add them to the main feed hopper of the twin-screw extruder.

[0063] (2) 2.0 parts of epoxidized soybean oil were injected into the main feed port of the twin-screw extruder using a liquid metering pump;

[0064] (3) The screw speed of the twin-screw extruder is controlled at 250 rpm, and the barrel temperature zones are set as follows:

[0065] Zone 1: 130℃, Zone 2: 145℃, Zone 3: 155℃, Zone 4: 160℃, Zone 5: 160℃, Zone 6 (vacuum exhaust zone, vacuum degree -0.06MPa): 155℃, Zone 7: 150℃, Head unit: 145℃;

[0066] The material is extruded, water-cooled, pelletized and dried to obtain modified composite material masterbatch;

[0067] (4) The obtained masterbatch is added to a single screw blown film machine and blown into a film at a machine body temperature of 145-160℃, a die head temperature of 155℃, and a blow-up ratio of 2.5:1 to obtain a composite film with a thickness of 20μm.

[0068] Example 3: This example provides a process for preparing a fully biodegradable composite membrane material modified by bamboo fiber grafting, including the following steps:

[0069] (1) Weigh 100 parts of PBAT resin and 43.2 parts of bamboo fiber modified premix A2 obtained in Preparation Example 2 (corresponding to 40 parts of bamboo fiber, 1 part of anhydrous citric acid, 1 part of choline chloride, 0.2 parts of active zinc oxide, and 1 part of pentaerythritol), mix them evenly, and add them to the main feed hopper of the twin-screw extruder.

[0070] (2) 5.0 parts of epoxidized soybean oil were injected into the first section of the twin-screw extruder using a liquid metering pump;

[0071] (3) The screw speed of the twin-screw extruder is controlled at 400 rpm, and the barrel temperature zones are set as follows:

[0072] Zone 1: 140℃, Zone 2: 155℃, Zone 3: 165℃, Zone 4: 170℃, Zone 5: 170℃, Zone 6 (vacuum exhaust zone, vacuum degree -0.08MPa): 165℃, Zone 7: 160℃, Head unit: 155℃;

[0073] The material is extruded, water-cooled, pelletized and dried to obtain modified composite material masterbatch;

[0074] (4) The obtained masterbatch is added to a single-screw blown film machine and blown into a film at a machine body temperature of 155-170℃, a die head temperature of 165℃, and a blow ratio of 3.5:1 to obtain a composite film with a thickness of 50μm.

[0075] Example 4: This example provides a process for preparing a fully biodegradable composite membrane material modified by bamboo fiber grafting, including the following steps:

[0076] (1) Weigh 70 parts of PBAT resin, 30 parts of polylactic acid (PLA) resin, and 35.0 parts of bamboo fiber modified premix A1 obtained in Preparation Example 1 (corresponding to 30 parts of bamboo fiber, 1.5 parts of anhydrous citric acid, 1.5 parts of choline chloride, 0.45 parts of active zinc oxide, and 1.5 parts of pentaerythritol), mix them evenly, and add them to the main feed hopper of the twin-screw extruder;

[0077] (2) 4.0 parts of epoxidized soybean oil were injected into the first section of the twin-screw extruder using a liquid metering pump;

[0078] (3) The screw speed of the twin-screw extruder is controlled at 350 rpm, and the barrel temperature zones are set as follows:

[0079] Zone 1: 135℃, Zone 2: 150℃, Zone 3: 160℃, Zone 4: 165℃, Zone 5: 165℃, Zone 6 (vacuum exhaust zone, vacuum degree -0.07MPa): 160℃, Zone 7: 155℃, Head unit: 150℃;

[0080] The material is extruded, water-cooled, pelletized and dried to obtain modified composite material masterbatch;

[0081] (4) The obtained masterbatch is added to a single screw blown film machine and blown into a film under the conditions of machine body temperature of 150-165℃, die head temperature of 160℃ and blow ratio of 3.0:1 to obtain a composite film with a thickness of 35μm.

[0082] Comparative Examples 1-7:

[0083] Comparative Example 1: This comparative example provides a bamboo fiber / PBAT composite material, which differs from Example 1 in that:

[0084] Anhydrous citric acid, choline chloride, active zinc oxide, pentaerythritol, and epoxidized soybean oil were not added. Instead, 100 parts of PBAT resin were mixed with 20 parts of dried bamboo fiber powder and then extruded and blown into film. All other process parameters were the same.

[0085] Comparative Example 2: This comparative example provides a modified composite membrane material, which differs from Example 1 in that:

[0086] In the preparation of bamboo fiber modified premix, pentaerythritol was not added, and the remaining components and their amounts remained unchanged. That is, the premix consisted only of bamboo fiber, anhydrous citric acid, choline chloride and active zinc oxide, and the remaining preparation steps and process parameters were the same.

[0087] Comparative Example 3: This comparative example provides a modified composite membrane material, which differs from Example 1 in that:

[0088] In the preparation of bamboo fiber modified premix, no active zinc oxide was added, and the remaining components and their amounts remained unchanged. That is, the premix consisted only of bamboo fiber, anhydrous citric acid, choline chloride and pentaerythritol, and the other preparation steps and process parameters were the same.

[0089] Comparative Example 4: This comparative example provides a modified composite membrane material, which differs from Example 1 in that:

[0090] In the preparation of bamboo fiber modified premix, anhydrous citric acid and choline chloride were not added, and no heating pretreatment step was performed. Instead, bamboo fiber, active zinc oxide and pentaerythritol were simply physically mixed at room temperature and used directly. All other components and process parameters were the same.

[0091] Comparative Example 5: This comparative example provides a modified composite membrane material, which differs from Example 1 in that:

[0092] The preparation process was changed, and the step-by-step preparation of "bamboo fiber modified premix" in step (1) was not performed. The specific operation was as follows:

[0093] Mix 100 parts PBAT resin, 20 parts bamboo fiber, 1 part anhydrous citric acid, 1 part choline chloride, 0.3 parts active zinc oxide, and 1 part pentaerythritol evenly, and then add the mixture directly to the main feed hopper of the twin-screw extruder. Epoxidized soybean oil is still injected from the first section of the barrel, and the extrusion process parameters are the same.

[0094] Comparative Example 6: This comparative example provides a composite membrane material modified with a conventional silane coupling agent. The difference between this material and Example 1 is that:

[0095] Instead of using the modified system of this invention (citric acid, choline chloride, zinc oxide, pentaerythritol, epoxidized soybean oil), 1.0 part of γ-aminopropyltriethoxysilane (KH-550) was used to perform conventional surface treatment on 20 parts of bamboo fiber, and then melt-extruded with 100 parts of PBAT resin. The remaining extrusion and blown film process parameters were the same.

[0096] Comparative Example 7: This comparative example provides a conventional free radical grafting modified composite membrane material, which differs from Example 1 in that:

[0097] Instead of using citric acid, choline chloride, zinc oxide, and pentaerythritol, 100 parts PBAT, 20 parts bamboo fiber, 3.5 parts epoxidized soybean oil, and 0.1 parts dicumyl peroxide (DCP, initiator) are mixed and extruded, while the remaining process parameters are the same.

[0098] Test Example 1-2:

[0099] Test Example 1: Processing Rheological Stability and Thermal Degradation Characteristics Test

[0100] Experimental method description:

[0101] This test case aims to verify the rheological stability and resistance to thermo-oxidative degradation of the composite materials prepared in the examples and comparative examples during melt processing. The specific test steps are as follows:

[0102] The dried masterbatch sample was placed in a melt flow rate tester and tested according to ASTM D1238 standard. The test temperature was 190℃ and the piston load was 2.16 kg. After preheating for 240 seconds, the sample was cut and taken. The measured value was recorded as follows. (g / 10min). To characterize the stability of the material during long-term hot processing, the same sample was packed into a barrel, compacted, and held at a constant temperature of 190℃ for 15 minutes. It was then extruded, cut, and weighed. The measured value was recorded as follows: (g / 10min). According to the formula Calculate the rate of change of melt flow rate ( In addition, blow-molded film samples were stacked to an opaque state, and the yellowness index (YI) was measured using a spectrophotometer according to ASTM E313 standard to characterize the change in matrix color.

[0103] Results Analysis and Conclusions:

[0104] The test results for each group of samples are summarized in Table 1.

[0105] Table 1: Rheological stability and appearance color test data of the examples and comparative examples

[0106]

[0107] Note: For Comparative Example 7, the melt was almost non-flowing at 5 minutes, making it impossible to obtain a valid value. Furthermore, it was completely cross-linked and cured after 15 minutes, so the rate of change was not recorded.

[0108] Results Analysis and Conclusions:

[0109] Comparing the data from Example 1 and Comparative Example 3, in the Comparative Example 3 system without the addition of active zinc oxide, The concentration reached 18.54 g / 10 min, and the yellowness index was 26.87. This data indicates that, in the absence of zinc oxide, the eutectic solvent formed by citric acid and choline chloride exhibits strong acidity at a processing temperature of 190°C, catalyzing the hydrolysis and alcoholysis of the ester bonds in the polyester matrix, leading to a decrease in molecular weight and a deterioration in color. In Example 1, after adding active zinc oxide, the MFR change rate was controlled within 10%, and the yellowness index was low. This indicates that active zinc oxide reacts with some carboxyl groups to generate zinc citrate, consuming excess protons in the system, acting as an acidity buffer, and inhibiting the degradation of the polyester matrix.

[0110] Comparing the data of Example 1 and Comparative Example 2, Comparative Example 2 did not contain pentaerythritol, and its The value was 4.82 g / 10 min, but after extending the heating time, The concentration increased to 7.65 g / 10 min, with a change rate of 58.71%. The significant increase in MFR indicates that, in the absence of polyhydroxy components as anchoring sites, the catalytic component diffuses into the polyester matrix during thermal processing, leading to unstable degradation of the matrix. Data from Example 1 show that the presence of pentaerythritol limited the migration of catalytically active centers, controlling the reaction primarily at the fiber-resin interface, thereby maintaining the processing stability of the matrix.

[0111] Comparing the data of Example 1 and Comparative Example 7, Comparative Example 7, which used dicumyl peroxide to initiate free radical grafting, had a measured MFR of only 0.12 g / 10 min, indicating that the system underwent macroscopic crosslinking, resulting in loss of flowability and failing to meet the requirements for blown film processing. The MFR values ​​of Examples 1 to 4 ranged from 2.0 to 3.5 g / 10 min, and the fluctuation rate after prolonged heating was low. This demonstrates that the ring-opening esterification reaction mechanism of the present invention achieves modification without forming an infinite network crosslinked structure, thus preserving the thermoplastic processing properties of the material.

[0112] Test Example 2: Mechanical Properties and Interface Bonding Effect Test

[0113] Experimental methods:

[0114] The blown film samples prepared in each embodiment and comparative example were conditioned for 48 hours at a temperature of 23±2℃ and a relative humidity of 50±5%. Following ASTM D882, the films were cut into strips 15mm wide and subjected to tensile property testing using a universal testing machine with a clamp spacing of 100mm and a tensile speed of 500mm / min. The tensile strength and elongation at break of the samples were recorded. The right-angle tear strength of the samples was tested using the Elmendorf tear test according to ASTM D1922. Five parallel samples were tested for each group, and the average value was taken as the final test result.

[0115] Experimental data:

[0116] The mechanical property test results of each group of samples are summarized in Table 2.

[0117] Table 2: Test data of thin film mechanical properties of the examples and comparative examples

[0118]

[0119] Results Analysis and Conclusions:

[0120] Based on the test data in Table 2, the interfacial bonding mechanism between bamboo fiber and polyester matrix and its impact on the process are analyzed as follows:

[0121] Comparing the data of Example 1 with Comparative Examples 1 and 4, Comparative Example 1, an unmodified physical blend system, had a tensile strength of 14.3 MPa and an elongation at break of less than 100%. Comparative Example 4, which added modifying agents but did not undergo thermal activation treatment with a eutectic solvent, showed little difference in mechanical properties compared to Comparative Example 1. The data indicate that the hydrogen bond network on the surface of the bamboo fiber, without solvation treatment, was not destroyed, resulting in insufficient exposure of active sites and hindering subsequent chemical reactions, thus only serving a physical filling function. Example 1, after in-situ activation and grafting, achieved a tensile strength of 28.4 MPa and an elongation at break exceeding 400%, indicating that the modified bamboo fiber formed chemical bonds with the matrix, improving interfacial compatibility.

[0122] Comparing the data of Example 1 and Comparative Example 5, Comparative Example 5 omitted the stepwise preparation process of the premix and mixed and extruded all materials at once. Its tensile strength was 19.5 MPa and its elongation at break was 212%, which was lower than that of Example 1. This result indicates that the lack of a pre-wetting and anchoring step leads to the dilution of polar auxiliaries by the polyester matrix, preventing the formation of a high-concentration reaction zone on the fiber surface, resulting in a reduced interfacial bonding layer density. The stepwise process used in Example 1 allows the reaction to occur preferentially on the fiber surface, establishing an effective interfacial layer.

[0123] Comparing the data of Example 1 and Comparative Example 6, Comparative Example 6, modified with silane coupling agent KH-550, has a strength of 21.8 MPa, which is lower than that of the embodiments of the present invention. Silane coupling agents typically provide single-point chemical bond connections. The present invention utilizes pentaerythritol and epoxidized soybean oil to construct a branched molecular structure on the fiber surface. This structure, in addition to providing chemical bonding, also increases interfacial friction through the physical entanglement of molecular chains, enabling the material to dissipate more energy under stress, thus exhibiting higher values ​​in terms of strength and toughness.

[0124] Example 4 introduced polylactic acid into the PBAT matrix, achieving a tensile strength of 32.1 MPa, indicating that the addition of the PLA phase improved the material's rigidity. The elongation at break remained at 348%, demonstrating that this interface modification system is suitable for PBAT / PLA blends.

Claims

1. A process for preparing bamboo fiber grafted and modified fully biodegradable composite membrane material, characterized in that, Includes the following steps: (1) Preparation of bamboo fiber modified premix: Dry bamboo fiber powder, anhydrous citric acid, choline chloride, active zinc oxide and pentaerythritol are mixed under heating conditions and cooled to obtain bamboo fiber modified premix; The specific steps for preparing the bamboo fiber modified premix in step (1) are as follows: S1: Mix dried bamboo fiber powder, anhydrous citric acid and choline chloride, and heat to 85-95℃ for the first stage of mixing treatment. S2: Keep the temperature constant, add active zinc oxide, and carry out the second stage of mixing treatment; S3: Keep the temperature constant, add pentaerythritol, and carry out the third stage of mixing treatment; S4: After mixing, cool to below 40℃ and then discharge; (2) Mixing: The biodegradable polyester resin and the bamboo fiber modified premix are mixed evenly to obtain a mixture; (3) Reactive extrusion: The mixture is added to the extruder, and epoxidized soybean oil is injected into the extruder barrel through a liquid metering device. Melt extrusion granulation is carried out under vacuum exhaust conditions to obtain modified composite material masterbatch. (4) Blow molding: The modified composite material masterbatch is blow molded in a blow molding machine to obtain a composite film material.

2. The preparation process of the bamboo fiber grafted modified fully biodegradable composite membrane material according to claim 1, characterized in that, The bamboo fiber modified premix described in step (1) is made from the following raw materials in parts by weight: 100 parts of dried bamboo fiber powder; Anhydrous citric acid 2.5-10 parts; Choline chloride 2.5-10 parts; 0.5-2.5 parts of active zinc oxide; Pentaerythritol 2.5-10 parts.

3. The preparation process of the bamboo fiber grafted modified fully biodegradable composite membrane material according to claim 1, characterized in that, The weight ratios of the components in steps (2) and (3) are as follows: 100 parts of biodegradable polyester resin; Bamboo fiber modified premix: 13.25-43.2 parts; Epoxidized soybean oil 2.0-5.0 parts.

4. The preparation process of the bamboo fiber grafted modified fully biodegradable composite membrane material according to claim 1, characterized in that, The biodegradable polyester resin is poly(butylene adipate) terephthalate (PAT) or a mixture of PAT and polylactic acid (PLA); wherein, when it is a mixture of PAT and PLA, the weight ratio of PAT to PLA is 7:

3.

5. The preparation process of the bamboo fiber grafted modified fully biodegradable composite membrane material according to claim 1, characterized in that, In step (3), the epoxidized soybean oil is injected into the first section of the extruder or the main feed port, wherein the epoxidized soybean oil is injected into the first section of the extruder through a liquid metering pump.

6. The preparation process of the bamboo fiber grafted modified fully biodegradable composite membrane material according to claim 1, characterized in that, In step (3), the screw speed of the extruder is 250-400 rpm, and the barrel temperature is set within the range of 130-170℃; the vacuum degree of the vacuum exhaust is controlled between -0.06MPa and -0.08MPa.

7. The preparation process of the bamboo fiber grafted modified fully biodegradable composite membrane material according to claim 1, characterized in that, In step (4), the conditions for blow molding are: machine body temperature 145-170℃, die head temperature 155-165℃, and blow ratio 2.5:1 to 3.5:

1.

8. The preparation process of the bamboo fiber grafted modified fully biodegradable composite membrane material according to claim 1, characterized in that, In step S1, the rotation speed is 800-1000 rpm and the mixing time is 8-12 minutes; in step S2, the rotation speed is reduced to 400-600 rpm and the mixing time is 3-5 minutes; in step S3, the rotation speed is restored to 800-1000 rpm and the mixing time is 3-5 minutes.

9. The preparation process of the bamboo fiber grafted modified fully biodegradable composite membrane material according to claim 1, characterized in that, In step (3), the barrel temperature zoning is set as follows: Zone 1: 130-140℃, Zone 2: 145-155℃, Zone 3: 155-165℃, Zone 4: 160-170℃, Zone 5: 160-170℃, Zone 6: 155-165℃, Zone 7: 150-160℃, Machine head: 145-155℃; The vacuum exhaust is carried out in zone six.

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