Preparation process of bamboo fiber graft modified full-biodegradable composite membrane material

Abstract

The invention relates to the technical field of high polymer material preparation, and discloses a bamboo fiber graft modified full-biodegradable composite membrane material preparation process which comprises the following steps: firstly, performing hot mixing and cooling on dried bamboo fiber powder, anhydrous citric acid, choline chloride, activated zinc oxide and pentaerythritol to prepare a bamboo fiber modified premix; then mixing the biodegradable polyester resin with the premix; adding the mixture into an extruder, injecting epoxidized soybean oil into a barrel through a liquid metering device, and performing melt extrusion granulation under a vacuum exhaust condition; and finally carrying out blow molding to form the film. Through in-situ reaction extrusion of multi-component synergism, surface grafting of bamboo fibers, chain extension of a polyester matrix and interface chemical bonding of the bamboo fibers and the polyester matrix are achieved, interface compatibility is effectively improved, degradation of the material in the processing process is inhibited, and the mechanical property and thermal stability of the composite film material are remarkably improved; the process is efficient and environment-friendly, and the cost is controllable.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of high polymer material preparation, in particular to a preparation process of a bamboo fiber grafted and modified full-biodegradable composite film material. BACKGROUND

[0002] With the enhancement of environmental protection consciousness and the implementation of the "ban plastic" policy, full-biodegradable plastics represented by polybutylene adipate terephthalate (PBAT) and polylactic acid (PLA) have become an important alternative material for treating white pollution. In order to reduce the raw material cost and endow the material with higher rigidity and heat resistance, it has become an important technical direction in the industry to introduce natural plant fibers such as bamboo fibers into the biodegradable polyester matrix to prepare full-biodegradable composite materials. Bamboo fiber, as a renewable biomass resource, has the advantages of wide source, high specific strength and complete biodegradability, and is an ideal reinforcing filler.

[0003] However, the application of bamboo fiber in the preparation of biodegradable polyester film always faces the technical bottleneck of poor interfacial compatibility between components. The biodegradable polyester matrix usually shows hydrophobicity, while the bamboo fiber surface is rich in a large number of hydroxyl groups, showing strong hydrophilicity. This essential difference in polarity makes it difficult for the two to form a close interface bond during melt blending, and phase separation is easily generated. This defect in the microstructure directly leads to a significant decrease in the macroscopic mechanical properties of the composite material, especially in the film blowing process, which is prone to film breaking, insufficient strength and other problems, seriously limiting its commercial application range.

[0004] In addition, the thermal stability of bamboo fiber is relatively low, and it is easy to be thermally degraded or release a small amount of water during high-temperature melt extrusion. These water and acidic degradation products can accelerate the hydrolysis reaction of the polyester matrix, leading to the breakage of the polyester molecular chain, the decrease of the molecular weight, and then causing the decrease of the melt strength and the instability of the processing fluidity. The existing modification technology mainly adopts alkali immersion, silane coupling agent wet treatment and other methods for pretreatment of bamboo fiber. Although these traditional methods can improve the interface bonding to a certain extent, the process flow is complicated, involving immersion, washing, dehydration and long-time drying and other processes, which not only has low production efficiency and huge energy consumption, but also produces a large amount of industrial wastewater, which does not meet the needs of green manufacturing and low-cost industrial production. Therefore, developing a preparation process capable of realizing online synchronous modification of bamboo fiber, interface compatibilization and inhibition of polyester matrix degradation is a technical problem to be solved in the current field. SUMMARY

[0005] The technical problem solved by the present application is that in the existing biodegradable composite film material, the interface compatibility of plant fibers (such as bamboo fibers) and the polyester matrix is poor, which leads to the decrease of the mechanical properties of the material and the narrow processing window; at the same time, the introduction of plant fibers easily leads to the degradation of the material during the melt processing process, which affects the quality of the final product. The present application aims to provide a preparation process, which improves the interface compatibility and enhances the comprehensive performance of the composite film material by in-situ grafting modification of bamboo fibers and optimizing the reaction extrusion process of the composite material.

[0006] To solve the above problems, the present application provides the following technical solutions: The present application provides a preparation process of bamboo fiber grafting modified fully biodegradable composite film material, comprising 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 the bamboo fiber modified premix is obtained after cooling; (2) Mixing: the biodegradable polyester resin is uniformly mixed with the bamboo fiber modified premix to obtain a mixture; (3) Reaction extrusion: the mixture is added to the extruder, and liquid metering device is used to inject epoxy soybean oil into the extruder barrel, and melt extrusion granulation is carried out under vacuum exhaust condition to obtain modified composite material master batch; (4) Blown film: the modified composite material master batch is blown into a film in a film blowing machine to obtain a composite film material.

[0007] By adopting the above technical solutions, the present application has obtained significant technical effects: In the premix preparation stage, the surface of the bamboo fiber is treated by anhydrous citric acid, choline chloride, active zinc oxide and pentaerythritol. Then, in the reaction extrusion stage, the above modified system cooperates with the epoxy soybean oil to initiate a series of in-situ reactions in the biodegradable polyester melt. In the melt extrusion process, the following reactions mainly occur: Grafting of citric acid and introduction of active sites: under the action of high temperature and shear of the extruder, the carboxyl group in the anhydrous citric acid molecule reacts with the hydroxyl group on the surface of the bamboo fiber to graft the citric acid molecule onto the surface of the bamboo fiber. This step preliminarily 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.

[0008] Interface bridging of epoxy soybean oil: the epoxy groups on the molecules of the injected epoxy soybean oil are activated under the catalysis of choline chloride and active zinc oxide. The activated epoxy groups can simultaneously react with the remaining carboxyl groups of the grafted citric acid on the bamboo fibers and the terminal carboxyl or hydroxyl groups of the biodegradable polyester resin (such as PBAT). In this way, the epoxy soybean oil molecules form a chemical bond between the bamboo fibers and the polyester matrix, building a stable "bamboo fiber-epoxy soybean oil-polyester" interface layer, which significantly improves the interface bonding between the two.

[0009] Synergistic chain extension and network construction of pentaerythritol: as a polyhydroxyl compound, the four hydroxyl groups on the molecules of pentaerythritol can esterify with the carboxyl groups (from citric acid or polyester end groups) present in the system. This reaction consumes the small molecules of polyester produced by hydrolysis or thermal degradation, effectively improving the melt viscosity, and at the same time forming a light crosslinking network locally. This network structure further enhances the melt strength of the composite material.

[0010] Effective removal of by-products: the small molecular by-products such as water produced in the above esterification reaction will accelerate the hydrolysis of the polyester if they remain in the melt. The process sets up a vacuum exhaust in a specific area of the extruder, which can timely extract these small molecular by-products, promote the reaction equilibrium to move in the direction conducive to chain extension and grafting, and thus inhibit the degradation of the polyester matrix.

[0011] In summary, the present application realizes the grafting of bamboo fibers, the chain extension of polyester matrix and the chemical bridging of the interface layer in the molten state through a multi-component synergistic in-situ reaction extrusion strategy, effectively improves the interfacial bonding force between bamboo fibers and polyester matrix, and inhibits the thermal degradation of the material during processing. Therefore, the prepared composite film material exhibits good mechanical properties, thermal stability and processing fluidity.

[0012] As a preferred embodiment of the present application, the bamboo fiber modification premix is made from raw materials containing the following weight parts: 100 parts of dry bamboo fiber powder; 2.5-10 parts of anhydrous citric acid; 2.5-10 parts of choline chloride; 0.5-2.5 parts of active zinc oxide; 2.5-10 parts of pentaerythritol.

[0013] As another preferred embodiment of the present application, the specific steps for preparing the bamboo fiber modification premix are: S1: Mix the dry bamboo fiber powder, anhydrous citric acid and choline chloride, and heat to 85-95℃ for first-stage mixing treatment; S2: Keep the temperature unchanged, add active zinc oxide, and perform second-stage mixing treatment; S3: Keep the temperature unchanged, add pentaerythritol, and perform third-stage mixing treatment; S4: after mixing, cooling to 40℃ or below and discharging. By using the above technical scheme, the components are added in stages, which can make the catalyst system and the reactants more uniformly dispersed, avoid local reaction too fast or uneven, and help to ensure the quality of the premix and the stability of the subsequent reaction extrusion.

[0014] As another preferred scheme of the present application, the weight ratio of the components in steps (2) and (3) is: biodegradable polyester resin 100 parts; bamboo fiber modified premix 13.25-43.2 parts; epoxy soybean oil 2.0-5.0 parts.

[0015] By using the above technical scheme, the components in this ratio range can achieve better synergistic effect, ensure that the reaction proceeds fully, while maintaining good processing performance and cost-effectiveness of the material.

[0016] As another preferred scheme of the present application, the biodegradable polyester resin is polybutylene adipate terephthalate (PBAT), or a mixture of PBAT and polylactic acid (PLA).

[0017] By using the above technical scheme, the type of base resin can be flexibly adjusted according to the application requirements of the final product, to obtain different balance of rigidity and toughness and degradation rates.

[0018] As another preferred scheme of the present application, the temperature zoning of the barrel of the extruder and the position of the vacuum exhaust are specifically optimized.

[0019] By using the above technical scheme, the precisely controlled temperature curve provides suitable reaction conditions for different regions (such as esterification, ring opening, chain extension), and the vacuum exhaust at specific positions ensures.

[0020] The present application provides a preparation process for bamboo fiber grafted and modified full-biodegradable composite film material. It has the following beneficial effects: 1、The present application uses the synergistic effect of anhydrous citric acid, epoxy soybean oil and other components to build a chemical bond between the bamboo fiber and the polyester matrix during the extrusion process. This in-situ generated interfacial layer replaces the weak van der Waals force in traditional physical blending, allowing stress to be effectively transferred from the polyester matrix to the reinforcing bamboo fiber, resulting in a composite film material with higher tensile strength and elongation at break.

[0021] 2、The process of the present application uses pentaerythritol and epoxy soybean oil to in-situ chain extend and repair polyester molecules that are broken due to heat, shear or a small amount of moisture, improving the melt strength. At the same time, the vacuum exhaust port set at a specific area of the extruder can timely remove small molecular by-products such as water produced by esterification reaction, reducing the hydrolytic degradation of the polyester. The combination of these two aspects ensures the stability of the material performance during processing.

[0022] 3、The application integrates the graft modification of bamboo fiber, the chain extension of polyester matrix and the composite process of the two in the core step of reaction extrusion. Compared with the traditional process which needs independent and complex pretreatment of the fiber, the application eliminates the cumbersome steps such as washing and drying of the modified fiber, shortens the production cycle, reduces the equipment and energy consumption, and makes the whole preparation process more economical and valuable for industrial application. DETAILED DESCRIPTION

[0023] The technical solutions in the embodiments of the application will be described below in combination with the examples and test examples of the application. Obviously, the described embodiments are only part of the embodiments of the application, rather than all the embodiments. Based on the embodiments in the application, all other embodiments obtained by those skilled in the art without creative labor fall within the protection scope of the application.

[0024] Preparation Examples 1-3: Preparation Example 1: The preparation example provides a bamboo fiber modification premix, including the following steps: 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 are put into a high-speed mixer with a heating jacket, the temperature is raised to 90℃, and mixing is carried out at a speed of 900rpm for 10 minutes; Then the speed is reduced to 500rpm, the temperature is kept at 90℃, 15g (i.e. 1.5 parts by weight) of active zinc oxide is added, and mixing is continued for 4 minutes; Finally, the speed is restored to 900rpm, 50g (i.e. 5 parts by weight) of pentaerythritol is added, and mixing is continued for 4 minutes; After mixing, the material is discharged into a cold mixer and cooled to below 40℃ for discharge, and a bamboo fiber modification premix A1 is obtained.

[0025] Preparation Example 2: The preparation example provides a bamboo fiber modification premix, including the following steps: 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 are put into a high-speed mixer with a heating jacket, the temperature is raised to 85℃, and mixing is carried out at a speed of 800rpm for 8 minutes; Then the speed is reduced to 400rpm, the temperature is kept at 85℃, 5g (i.e. 0.5 parts by weight) of active zinc oxide is added, and mixing is continued for 3 minutes; Finally, the speed is restored to 800rpm, 25g (i.e. 2.5 parts by weight) of pentaerythritol is added, and mixing is continued for 3 minutes; After mixing, the material is discharged into a cold mixer and cooled to below 40℃ to discharge, obtaining the bamboo fiber modified premix A2.

[0026] Preparation Example 3: This preparation example provides a bamboo fiber modified premix, comprising the following steps: 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 are put into a high-speed mixer with a heating jacket, heated to 95℃, and mixed at a speed of 1000rpm for 12 minutes; Then the speed is reduced to 600rpm, the temperature is kept at 95℃, 25g (i.e. 2.5 parts by weight) of active zinc oxide is added, and the mixing is continued for 5 minutes; Finally, the speed is restored to 1000rpm, 100g (i.e. 10 parts by weight) of pentaerythritol is added, and the mixing is continued for 5 minutes; After mixing, the material is discharged into a cold mixer and cooled to below 40℃ to discharge, obtaining the bamboo fiber modified premix A2.

[0027] Examples 1-4: Example 1: This example provides a preparation process of bamboo fiber grafting modified fully biodegradable composite film material, comprising the following steps: (1) 100 parts of polybutylene adipate terephthalate (PBAT) resin, 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) are weighed and uniformly mixed, and then added to the main feeding hopper of the twin-screw extruder; (2) 3.5 parts of epoxy soybean oil is injected into the first cylinder of the twin-screw extruder through a liquid metering pump; (3) The screw speed of the twin-screw extruder is controlled at 300rpm, and the barrel temperature is set as follows: 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℃, and die head: 150℃; The material is extruded, water-cooled, pelletized and dried to obtain a modified composite material master batch; (4) The obtained master batch is added to a single-screw film blowing machine, and a composite film with a thickness of 30μm is obtained under the conditions of machine body temperature 150-165℃, die head temperature 160℃, and blow ratio 3.0:1.

[0028] Example 2: This example provides a preparation process of bamboo fiber grafting modified fully biodegradable composite film material, comprising the following steps: (1) Take 100 parts of PBAT resin, 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, 1 part of pentaerythritol), mix uniformly and add to the main feeding hopper of the twin-screw extruder; (2) Inject 2.0 parts of epoxy soybean oil into the main feeding port of the twin-screw extruder through a liquid metering pump; (3) Control the screw speed of the twin-screw extruder at 250 rpm, and set the barrel temperature zones as follows: 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℃, die head 145℃; The material is extruded, water-cooled, pelletized and dried to obtain modified composite material masterbatch; (4) Add the obtained masterbatch to a single-screw film blowing machine, and blow film under the conditions of machine body temperature 145-160℃, die head temperature 155℃, and blow-up ratio 2.5:1 to obtain a composite film with a thickness of 20μm.

[0029] Example 3: This example provides a preparation process of bamboo fiber graft modified fully biodegradable composite film material, including the following steps: (1) Take 100 parts of PBAT resin, 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, 1 part of pentaerythritol), mix uniformly and add to the main feeding hopper of the twin-screw extruder; (2) Inject 5.0 parts of epoxy soybean oil into the first barrel of the twin-screw extruder through a liquid metering pump; (3) Control the screw speed of the twin-screw extruder at 400 rpm, and set the barrel temperature zones as follows: 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℃, die head 155℃; The material is extruded, water-cooled, pelletized and dried to obtain modified composite material masterbatch; (4) Add the obtained masterbatch to a single-screw film blowing machine, and blow film under the conditions of machine body temperature 155-170℃, die head temperature 165℃, and blow-up ratio 3.5:1 to obtain a composite film with a thickness of 50μm.

[0030] Example 4: This example provides a preparation process of bamboo fiber graft modified fully biodegradable composite film material, including the following steps: (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; (2) 4.0 parts of epoxidized soybean oil were injected into the first section of the twin-screw extruder using a liquid metering pump; (3) The screw speed of the twin-screw extruder is controlled at 350 rpm, and the barrel temperature zones are set as follows: 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℃; The material is extruded, water-cooled, pelletized and dried to obtain modified composite material masterbatch; (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.

[0031] Comparative Examples 1-7: Comparative Example 1: This comparative example provides a bamboo fiber / PBAT composite material, which differs from Example 1 in that: 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.

[0032] Comparative Example 2: This comparative example provides a modified composite membrane material, which differs from Example 1 in that: 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.

[0033] Comparative Example 3: This comparative example provides a modified composite membrane material, which differs from Example 1 in that: In the preparation of bamboo fiber modified premix, no active zinc oxide was added, and the other 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.

[0034] Comparative Example 4: This comparative example provides a modified composite membrane material, which differs from Example 1 in that: 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.

[0035] Comparative Example 5: This comparative example provides a modified composite membrane material, which differs from Example 1 in that: 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: 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.

[0036] 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: 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.

[0037] Comparative Example 7: This comparative example provides a conventional free radical grafting modified composite membrane material, which differs from Example 1 in that: 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.

[0038] Test Example 1-2: Test Example 1: Processing Rheological Stability and Thermal Degradation Characteristics Test Experimental method description: 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: 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.

[0039] Results Analysis and Conclusions: The test results for each group of samples are summarized in Table 1.

[0040] Table 1: Rheological stability and appearance color test data of the examples and comparative examples

[0041] 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.

[0042] Results Analysis and Conclusions: 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.

[0043] 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.

[0044] 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.

[0045] Test Example 2: Mechanical Properties and Interface Bonding Effect Test Experimental methods: 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.

[0046] Experimental data: The mechanical property test results of each group of samples are summarized in Table 2.

[0047] Table 2: Test data of thin film mechanical properties of the examples and comparative examples

[0048] Results Analysis and Conclusions: 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: 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.

[0049] 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.

[0050] 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.

[0051] 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. Bamboo fiber grafting modification of full biodegradable composite film material preparation process, characterized in that, The method comprises the following steps: (1) preparing a bamboo fiber modified premix: mixing dry bamboo fiber powder, anhydrous citric acid, choline chloride, active zinc oxide and pentaerythritol under heating conditions, and obtaining a bamboo fiber modified premix after cooling; (2) mixing: uniformly mixing a biodegradable polyester resin with the bamboo fiber modified premix to obtain a mixture; (3) reaction extrusion: adding the mixture into an extruder, and injecting epoxy soybean oil into the barrel of the extruder through a liquid metering device, and performing melt extrusion granulation under vacuum exhaust conditions to obtain a modified composite material master batch; (4) blow film forming: blow molding the modified composite material master batch in a film blowing machine to obtain a composite film material.

2. The bamboo fiber grafting modification full-biodegradable composite film material preparation process according to claim 1, characterized in that, The bamboo fiber modified premix in step (1) is prepared from raw materials comprising the following weight parts: dry bamboo fiber powder 100 parts; anhydrous citric acid 2.5-10 parts; choline chloride 2.5-10 parts; active zinc oxide 0.5-2.5 parts; pentaerythritol 2.5-10 parts.

3. The process for the preparation of bamboo fiber grafted biodegradable composite film material as claimed in claim 1 wherein, The specific steps for preparing the bamboo fiber modified premix in step (1) are as follows: S1: mixing dry bamboo fiber powder, anhydrous citric acid and choline chloride, and heating to 85-95℃ for first-stage mixing treatment; S2: keeping the temperature unchanged, adding active zinc oxide for second-stage mixing treatment; S3: keeping the temperature unchanged, adding pentaerythritol for third-stage mixing treatment; S4: after mixing, cooling to below 40℃ for discharging.

4. The process for the preparation of bamboo fiber grafted biodegradable composite film material as claimed in claim 1, wherein, The weight ratio of each component in steps (2) and (3) is as follows: biodegradable polyester resin 100 parts; bamboo fiber modified premix 13.25-43.2 parts; epoxy soybean oil 2.0-5.0 parts.

5. The process for the preparation of bamboo fiber grafted biodegradable composite film material as claimed in claim 1, wherein, The biodegradable polyester resin is polybutylene adipate terephthalate, or a mixture of polybutylene adipate terephthalate and polylactic acid; when it is a mixture of polybutylene adipate terephthalate and polylactic acid, the weight ratio of polybutylene adipate terephthalate to polylactic acid is 7:

3.

6. The process for the preparation of bamboo fiber grafted biodegradable composite film material as claimed in claim 1, wherein, In step (3), the position of injecting the epoxy soybean oil is the first barrel of the extruder or the main feeding port, wherein the epoxy soybean oil is injected into the first barrel of the extruder through a liquid metering pump.

7. The process for the preparation of bamboo fiber grafted biodegradable composite film material as claimed in claim 1, wherein, In step (3), the screw rotation speed of the extruder is 250-400 rpm, and the barrel temperature setting range is 130-170℃; the vacuum degree of the vacuum exhaust is controlled between -0.06MPa and -0.08MPa.

8. The process for the preparation of bamboo fiber grafted biodegradable composite film material as claimed in claim 1, wherein, In step (4), the conditions for blow film forming are as follows: machine body temperature 145-170℃, die temperature 155-165℃, and blow ratio 2.5:1 to 3.5:

1.

9. The process for the preparation of bamboo fiber grafted biodegradable composite film material as claimed in claim 3, wherein, In the S1 step, the rotation speed is 800-1000 rpm, and the mixing time is 8-12 minutes; in the S2 step, the rotation speed is reduced to 400-600 rpm, and the mixing time is 3-5 minutes; in the S3 step, the rotation speed is restored to 800-1000 rpm, and the mixing time is 3-5 minutes.

10. The process for the preparation of bamboo fiber grafted biodegradable composite film material as claimed in claim 1 wherein, In step (3), the barrel temperature zoning is set as follows: Zone 1 130-140°C, Zone 2 145-155°C, Zone 3 155-165°C, Zone 4 160-170°C, Zone 5 160-170°C, Zone 6 155-165°C, Zone 7 150-160°C, Die 145-155°C; The vacuum exhaust is performed in the sixth zone.

Images