Bamboo fiber-containing polylactic acid antibacterial film and preparation method thereof

Abstract

The invention discloses a polylactic acid antibacterial film containing bamboo fibers and a preparation method of the polylactic acid antibacterial film, and relates to the technical field of antibacterial films. The composite material is prepared from 75-88 parts of polylactic acid, 6-18 parts of a modified bamboo fiber structure and 4-8 parts of epoxy-terminated polycaprolactone, according to the modified bamboo fiber structure, nano fibrillated bamboo fiber serves as an inner core, an inner layer is an epoxy-terminated polylactic acid grafting layer covalently grafted to the surface of the nano fibrillated bamboo fiber, and an outer layer is a zinc-coordinated tannic acid nano-dot loading layer growing on the surface of the grafting layer in situ. Polylactic acid is film-forming matrix resin. The modified bamboo fiber structure is additionally arranged, and the nano fibrillated bamboo fiber is used as an inner core supporting framework, so that the problems that conventional raw bamboo fiber is poor in compatibility with a polylactic acid matrix, easy to agglomerate and uneven in dispersion are solved; an interface bonding bridge is built by virtue of the outer grafting layer, so that an interface barrier between a bamboo fiber hydrophilic group and a polylactic acid hydrophobic matrix is eliminated, stable bonding of the matrix and the fiber is realized, and the overall mechanical strength and the structural uniformity and stability of the film are improved.

Description

Technical Field

[0001] This invention relates to the field of antibacterial film technology, specifically to a polylactic acid antibacterial film containing bamboo fiber and its preparation method. Background Technology

[0002] Polylactic acid (PLA) film is currently the most widely used fully biodegradable packaging film material. Relying on the characteristics of renewable raw materials and complete composting degradation after use, it can replace traditional petroleum-based plastic films and is widely used in food preservation packaging, disposable consumables, environmental protection coatings and other fields.

[0003] Currently, conventional bamboo fiber modified polylactic acid films still have many technical shortcomings: First, the surface of virgin bamboo fiber is rich in hydrophilic active groups, which have extremely poor compatibility with the hydrophobic polylactic acid matrix. The fiber is very easy to agglomerate and disperse unevenly in the matrix. After molding, crystal points, voids and delamination defects are easily generated inside the film, which directly results in low mechanical strength of the film, insufficient tensile and tear resistance, and significantly reduced light transmission, limiting its use in high-transparency packaging scenarios.

[0004] Secondly, ordinary bamboo fiber can only serve as a physical filler and reinforcement, and does not have antibacterial function itself. The film prepared from it cannot inhibit the growth of bacteria and microorganisms. When used for food packaging, the contents are prone to mold and deterioration, making it difficult to meet the needs of fresh food preservation and hygiene protection packaging. Existing antibacterial modification schemes mostly adopt the method of simply mixing antibacterial agents. The antibacterial components are prone to migration and precipitation. They have obvious short-term effects, but poor long-term antibacterial stability and also pose a risk of not meeting food contact safety standards. Therefore, a polylactic acid antibacterial film containing bamboo fiber and its preparation method are proposed to solve these problems. Summary of the Invention

[0005] Technical problems to be solved To address the shortcomings of existing technologies, this invention provides a polylactic acid antibacterial film containing bamboo fiber and its preparation method, thus solving the problems mentioned in the background section.

[0006] Technical solution To achieve the above objectives, the present invention provides the following technical solution: a polylactic acid antibacterial film containing bamboo fiber, such as... Figure 1 As shown, by weight, it consists of 75-88 parts of polylactic acid, 6-18 parts of modified bamboo fiber structure, and 4-8 parts of epoxy-terminated polycaprolactone.

[0007] The core objective of this overall formulation setting is to address the problems of poor interfacial compatibility, limited functionality, and insufficient structural stability in existing bamboo fiber and polylactic acid composite systems. The goal is to construct a fully bio-based film system with stable structure, strong interfacial bonding, and controllable performance, adaptable to the application needs of various scenarios such as environmentally friendly packaging and medical consumables.

[0008] The modified bamboo fiber structure features a core of nanofibrillated bamboo fiber, an inner layer of epoxy-terminated polylactic acid grafted onto the surface of the nanofibrillated bamboo fiber, and an outer layer of zinc-coordinated tannic acid nanodots grown in situ on the surface of the grafted layer. The core purpose of this three-layer structure is to address the problems of weak interfacial bonding, easy aggregation, and limited functionality between existing bamboo fiber and polylactic acid matrix structures. Through this layered design, it simultaneously achieves interfacial compatibility between the fiber and matrix, as well as the anchoring of functional sites, avoiding the shortcomings of a single structure that cannot simultaneously address both compatibility and functionality.

[0009] Preferably, the diameter of the nanofibrillated bamboo fibers is 20–50 nm, and the aspect ratio is 500–1000. Nanofibrillated bamboo fibers within this size range can form a uniform mesh support structure in the matrix, which is suitable for the casting and stretching processes of film forming, avoiding film defects caused by excessively large fiber sizes, or excessively high preparation costs and reduced dispersibility caused by excessively small fiber sizes.

[0010] Preferably, the grafting rate of the epoxy-terminated polylactic acid (PLA) grafted layer is 18%–22%, and the number-average molecular weight of the PLA oligomer used for grafting is 2000–4000. The epoxy-terminated PLA includes at least one of mono-epoxy-terminated PLA and di-epoxy-terminated PLA. This grafting rate and molecular weight range can achieve sufficient saturation of the hydroxyl groups on the surface of the nanofiberized bamboo fibers, while simultaneously forming good molecular chain entanglement with the PLA matrix. Mono-epoxy-terminated PLA is suitable for modification requirements with low grafting density, while di-epoxy-terminated PLA is suitable for modification requirements with high interfacial bonding strength. The appropriate type can be flexibly selected according to the film performance requirements.

[0011] Preferably, the zinc-coordinated tannic acid nanodots have a particle size of 2–5 nm and a loading of 8%–12 wt% in the modified bamboo fiber structure. This particle size and loading range allows for uniform anchoring of the nanodots on the grafted layer surface, avoiding agglomeration, while providing sufficient active binding sites to meet the functionalization requirements of the film. This avoids the problems of decreased interfacial compatibility due to excessive loading or insufficient functional sites due to insufficient loading.

[0012] Polylactic acid (PLA) is the film-forming matrix resin. The core purpose of this component is to serve as a continuous phase matrix for thin films, providing them with fundamental film-forming properties, mechanical strength, and processing performance. This addresses the issue that existing non-biological matrix materials cannot achieve full biodegradability, thus meeting the core requirements of environmentally friendly applications.

[0013] Preferably, the polylactic acid has a number-average molecular weight of 80,000 to 150,000 and a melt flow rate of 3 to 8 g / 10 min. This molecular weight and melt flow rate range are suitable for twin-screw extrusion and casting stretching film processing technologies, ensuring the fluidity and film stability of the substrate during processing, and avoiding problems such as excessively high processing temperature and material degradation due to excessively high molecular weight, or insufficient mechanical properties of the film due to excessively low molecular weight.

[0014] Epoxy-terminated polycaprolactone is the interfacial compatibility component. The core purpose of this component is to adjust the interfacial compatibility between the polylactic acid matrix and the modified bamboo fiber structure, while improving the processing fluidity and molding stability of the matrix, solving the problem of excessive interfacial tension and easy phase separation in existing composite systems, and improving the uniformity and stability of the film structure.

[0015] Preferably, the number-average molecular weight of epoxy-terminated polycaprolactone is 10,000 to 30,000. This molecular weight range allows for full utilization of interfacial compatibility while avoiding problems such as decreased compatibility with the matrix due to excessively high molecular weight, or decreased heat resistance of the film due to excessively low molecular weight.

[0016] Preferably, the film further comprises processing aids, which include at least one of antioxidants and lubricants. Antioxidants can inhibit the thermo-oxidative degradation of the polylactic acid matrix during high-temperature processing, ensuring the stability of the material processing; lubricants can improve the processing flowability of the material, reduce equipment wear, and adapt to the production requirements of high-speed extrusion molding, and can be flexibly selected and added according to the actual production process.

[0017] This invention also provides a method for preparing a polylactic acid antibacterial film containing bamboo fiber, which includes the following steps: Step 1: Preparation of modified bamboo fiber structure: Bamboo raw fibers are pretreated to obtain nanofibrillated bamboo fibers. Then, an epoxy-terminated polylactic acid graft layer is constructed on its surface through a covalent grafting reaction. Finally, zinc-coordinated tannic acid nanodots are grown on the surface of the graft layer through an in-situ coordination reaction to obtain the modified bamboo fiber structure. The core purpose of this step is to achieve the functional design of the bamboo fiber structure through stepwise modification, ensuring the sufficiency and controllability of each step of modification, solving the problem that existing one-step modification cannot simultaneously achieve interfacial compatibility and functional loading, and ensuring the stability and uniformity of the modified bamboo fiber structure's performance.

[0018] Preferably, the pretreatment employs an alkaline ultrasonic treatment combined with high-pressure homogenization; the covalent grafting reaction uses triethylamine as a catalyst and is carried out in an anhydrous toluene system under nitrogen protection; the in-situ coordination reaction is carried out in an ethanol-water solution system. Alkaline ultrasonic treatment can effectively remove impurities from the bamboo fibers, exposing the active hydroxyl groups on the fiber surface; high-pressure homogenization can achieve nano-dispersion of the fibers, ensuring the uniformity of fiber size; the anhydrous toluene system and nitrogen protection can avoid material oxidation during the grafting reaction, ensuring the sufficiency of the grafting reaction; the ethanol-water solution system can ensure the gentle conduct of the in-situ coordination reaction, avoiding the aggregation and deactivation of nanodots.

[0019] Step two, preparation of composite masterbatch: A two-step melt blending method is adopted. First, polylactic acid, epoxy-terminated polycaprolactone, and processing aids are mixed and extruded to obtain a matrix masterbatch. Then, the matrix masterbatch is mixed with the modified bamboo fiber structure and extruded to obtain a composite masterbatch. The core purpose of this step is to achieve uniform dispersion and chain extension of the matrix components through a two-step melt blending method, and then achieve uniform dispersion of the modified bamboo fiber structure in the matrix. This avoids the problems of uneven fiber dispersion and fiber breakage caused by one-step blending, and ensures the uniformity of the composite masterbatch's structure and properties.

[0020] Preferably, the temperature range of the first-step twin-screw extrusion is 150–185°C, and the main extruder speed is 250 rpm; the temperature of the second-step low-shear twin-screw extrusion is 3–5°C lower than the same temperature range in the first step, and the main extruder speed is 180–200 rpm; the extrusion equipment includes at least one of a horizontal twin-screw extruder and a vertical twin-screw extruder. The temperature and speed settings of the first-step extrusion ensure sufficient melting and uniform mixing of the matrix components, achieving full chain extension reaction; the second-step low-shear, low-temperature extrusion avoids fiber breakage in the modified bamboo fiber structure, ensuring the integrity of the fiber structure, while achieving uniform fiber dispersion in the matrix; the horizontal twin-screw extruder is suitable for large-scale continuous production, while the vertical twin-screw extruder is suitable for small-batch fine production, and can be flexibly selected according to the production scale.

[0021] Step 3, Film Forming: After drying the composite masterbatch, a thick sheet is obtained through a casting machine, followed by simultaneous biaxial stretching, heat setting, cooling, and winding to obtain the finished film. The core purpose of this step is to achieve directional control of the film structure through a continuous process of casting, stretching, and heat setting, ensuring the uniformity of film thickness and the stability of performance, solving the problems of insufficient mechanical properties and poor dimensional stability of existing cast films, and adapting to the needs of industrial continuous production.

[0022] Preferably, the temperature for simultaneous biaxial stretching is 65–75°C, and the stretching ratio is 3×3; the heat setting temperature is 110–115°C, and the heat setting time is 8–10 seconds. This stretching temperature and ratio achieve uniform orientation of the polylactic acid molecular chains and the modified bamboo fiber structure, improving the mechanical properties and dimensional stability of the film; this heat setting temperature and time eliminate internal stress in the film, fix the orientation structure, and prevent thermal shrinkage and deformation during use.

[0023] Preferably, the vacuum drying temperature of the composite masterbatch is 80℃, and the drying time is 12-16h; the temperature range for casting into thick sheets is 160-180℃, and the sheet thickness is 0.2-0.5mm; the cooling temperature for cooling and winding is 20-25℃, and the winding tension is 8-12N; the thickness of the finished film is 20-100μm, and the thickness uniformity deviation is ≤3%. These drying conditions can effectively remove moisture from the composite masterbatch, avoiding defects such as hydrolysis degradation and bubbles during processing; the casting temperature and sheet thickness ensure the uniformity of the sheet structure, adapting to subsequent biaxial stretching processes; the cooling temperature and winding tension ensure sufficient cooling and shaping of the film, avoiding wrinkles and uneven stretching during winding; the thickness and uniformity of the finished film can adapt to the usage requirements of different application scenarios, ensuring the stability of the film's performance.

[0024] This invention utilizes a three-layer structure design of modified bamboo fiber, with nanofibrillated bamboo fiber as the supporting core, an epoxy-terminated polylactic acid grafted layer as the interfacial bridge, and a zinc-coordinated tannic acid nanodot loading layer as the functional sites. Combined with the polylactic acid matrix and epoxy-terminated polycaprolactone interfacial compatible components, a complete chemical bonding system is formed. One end of the epoxy-terminated polylactic acid grafted layer forms a covalent bond with the nanofibrillated bamboo fiber, while the other end forms molecular chain entanglement and chemical bonding with the polylactic acid matrix, achieving interfacial bonding between the fiber and the matrix. Epoxy-terminated polycaprolactone further modulates the interfacial tension of the system, achieving uniform dispersion of each component; zinc-coordinated tannic acid nanodots are stably anchored on the grafted layer surface, preventing migration and loss. The components work together to construct a fully bio-based thin film system with strong interfacial bonding, uniform and stable structure, and controllable performance. This ultimately achieves simultaneous improvement in the film's mechanical properties, processing stability, and structural uniformity, with the finished film exhibiting a thickness uniformity deviation of ≤3%, making it suitable for various application scenarios.

[0025] Beneficial effects The present invention has the following beneficial effects: (1) The polylactic acid antibacterial film containing bamboo fiber and its preparation method, by adding a modified bamboo fiber structure, using nanofibrillated bamboo fiber as the core support skeleton, solves the problems of poor compatibility and easy agglomeration and uneven dispersion between conventional virgin bamboo fiber and polylactic acid matrix; by relying on the outer graft layer to build an interface bonding bridge, the interface barrier between the hydrophilic groups of bamboo fiber and the hydrophobic matrix of polylactic acid is eliminated, and the matrix and fiber are stably bonded, thereby improving the overall mechanical strength and structural uniformity and stability of the film.

[0026] (2) The polylactic acid antibacterial film containing bamboo fiber and its preparation method, by setting a zinc-coordinated tannic acid nanodot loading layer on the surface of the modified bamboo fiber structure, solves the problem that traditional bamboo fiber modified systems have no long-lasting antibacterial ability and the antibacterial components are easy to precipitate and lose. By relying on the nanodots to be stably anchored on the surface of the grafting layer, the film is given a stable and long-lasting antibacterial effect, while not affecting the light transmittance of the film, thus taking into account both high transparency and antibacterial requirements.

[0027] Of course, any product implementing this invention does not necessarily need to achieve all of the advantages described above at the same time. Attached Figure Description

[0028] Figure 1 This is a flowchart of a method for preparing a polylactic acid antibacterial film containing bamboo fiber according to the present invention. Detailed Implementation

[0029] The technical solutions of 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. Example 1

[0030] This embodiment provides a polylactic acid antibacterial film containing bamboo fiber and its preparation method. The polylactic acid antibacterial film containing bamboo fiber is composed of 75 parts of polylactic acid, 6 parts of modified bamboo fiber structure, and 4 parts of epoxy-terminated polycaprolactone by weight.

[0031] The film also contains 0.5 parts of processing aids, which are a compound of antioxidants and lubricants. The antioxidants are antioxidant 1010 and antioxidant 168 compounded in a mass ratio of 1:1, and the lubricant is pentaerythritol stearate.

[0032] The polylactic acid has a number-average molecular weight of 80,000 and a melt flow rate of 3 g / 10 min. The epoxy-terminated polycaprolactone has a number-average molecular weight of 10,000.

[0033] The modified bamboo fiber structure consists of a core of nanofibrillated bamboo fiber, an inner layer of epoxy-terminated polylactic acid grafted onto the surface of the nanofibrillated bamboo fiber, and an outer layer of zinc-coordinated tannic acid nanodots grown in situ on the surface of the grafted layer. The nanofibrillated bamboo fiber has a diameter of 20 nm and an aspect ratio of 500.

[0034] The grafting rate of the epoxy-terminated polylactic acid grafted layer is 18%, the number average molecular weight of the polylactic acid oligomer used for grafting is 2000, and the epoxy-terminated polylactic acid is a monoepoxy-terminated polylactic acid. The zinc-coordinated tannic acid nanodots have a particle size of 2 nm and a loading of 8 wt% in the modified bamboo fiber structure.

[0035] The method for preparing the polylactic acid antibacterial film containing bamboo fiber includes the following steps: Step 1: Preparation of modified bamboo fiber structure: Bamboo raw fibers were pretreated to obtain nanofiberized bamboo fibers. The pretreatment involved ultrasonic treatment with a 6wt% sodium hydroxide solution at 45℃ for 40 min, followed by washing with water until neutral and vacuum freeze-drying. The fibers were then subjected to 8 cycles of high-pressure homogenization at 60 MPa to obtain nanofiberized bamboo fibers. An epoxy-terminated polylactic acid (PLA) graft layer was then constructed on its surface via a covalent grafting reaction. The covalent grafting reaction used triethylamine as a catalyst and was carried out at 85℃ for 5 h under anhydrous toluene system and nitrogen protection. After the reaction, ungrafted PLA oligomers were removed by Soxhlet extraction with chloroform for 22 h. Finally, zinc-coordinated tannic acid nanodots were grown on the surface of the graft layer via an in-situ coordination reaction. The in-situ coordination reaction was carried out in a 60% ethanol aqueous solution system at pH 5.0 with stirring at 30℃ for 2 h. After the reaction, the fibers were filtered, washed, and dried to obtain the modified bamboo fiber structure.

[0036] Step 2, Preparation of Composite Masterbatch: A two-step melt blending method is used. First, polylactic acid, epoxy-terminated polycaprolactone, and processing aids are mixed at high speed for 5 minutes, and then extruded and granulated using a horizontal twin-screw extruder to obtain the matrix masterbatch. The temperature range of the first twin-screw extrusion is 150–185℃, and the main extruder speed is 250 rpm. Then, the matrix masterbatch is mixed evenly with the modified bamboo fiber structure, and then extruded and granulated using a horizontal twin-screw extruder under low shear to obtain the composite masterbatch. The temperature of the second low-shear twin-screw extrusion is 3℃ lower than the same temperature range in the first step, and the main extruder speed is 180 rpm.

[0037] Step 3, Film Forming: The composite masterbatch is placed in a vacuum drying oven and dried at 80℃ for 12 hours. After drying, the moisture content of the masterbatch is ≤50ppm. A thick sheet with a thickness of 0.2mm is then produced by casting in the temperature range of 160-180℃. This sheet is then simultaneously biaxially stretched at 65℃ with a stretching ratio of 3×3. After stretching, it is heat-set at 110℃ for 8 seconds. Finally, it is cooled at 20℃ and wound up with a winding tension of 8N to obtain the finished film with a thickness of 20μm and a thickness uniformity deviation of 2.2%. Example 2

[0038] This embodiment provides a polylactic acid antibacterial film containing bamboo fiber and its preparation method. The polylactic acid antibacterial film containing bamboo fiber is composed of 88 parts of polylactic acid, 18 parts of modified bamboo fiber structure, and 8 parts of epoxy-terminated polycaprolactone by weight.

[0039] The film also contains 1.0 part of processing aids, which are a compound of antioxidants and lubricants. The antioxidants are antioxidant 1010 and antioxidant 168 compounded in a mass ratio of 1:1, and the lubricant is pentaerythritol stearate.

[0040] The polylactic acid has a number-average molecular weight of 150,000 and a melt flow rate of 8 g / 10 min. The epoxy-terminated polycaprolactone has a number-average molecular weight of 30,000.

[0041] The modified bamboo fiber structure consists of a core of nanofibrillated bamboo fiber, an inner layer of epoxy-terminated polylactic acid grafted onto the surface of the nanofibrillated bamboo fiber, and an outer layer of zinc-coordinated tannic acid nanodots grown in situ on the surface of the grafted layer. The nanofibrillated bamboo fiber has a diameter of 50 nm and an aspect ratio of 1000.

[0042] The grafting rate of the epoxy-terminated polylactic acid grafted layer was 22%, the number average molecular weight of the polylactic acid oligomer used for grafting was 4000, and the epoxy-terminated polylactic acid was dieoxy-terminated polylactic acid. The zinc-coordinated tannic acid nanodots had a particle size of 5 nm and a loading of 12 wt% in the modified bamboo fiber structure.

[0043] The method for preparing the polylactic acid antibacterial film containing bamboo fiber includes the following steps: Step 1: Preparation of modified bamboo fiber structure: Bamboo raw fibers were pretreated to obtain nanofiberized bamboo fibers. The pretreatment involved ultrasonic treatment with an 8wt% sodium hydroxide solution at 55℃ for 50 min, followed by washing with water until neutral and vacuum freeze-drying. The nanofiberized bamboo fibers were then homogenized and cycled 10 times under 80 MPa high pressure to obtain the final nanofiberized bamboo fibers. An epoxy-terminated polylactic acid (PLA) graft layer was then constructed on the surface via a covalent grafting reaction. The covalent grafting reaction used triethylamine as a catalyst and was carried out at 95℃ for 7 h under anhydrous toluene system and nitrogen protection. After the reaction, ungrafted PLA oligomers were removed by Soxhlet extraction with chloroform for 26 h.

[0044] Finally, zinc-coordinated tannic acid nanodots were grown on the surface of the grafted layer via in-situ coordination reaction. The in-situ coordination reaction was carried out in a 70% ethanol aqueous solution system at pH 6.0, stirred at 40°C for 3 hours, and then filtered, washed and dried to obtain the modified bamboo fiber structure.

[0045] Step 2, Preparation of Composite Masterbatch: A two-step melt blending method is adopted. First, polylactic acid, epoxy-terminated polycaprolactone, and processing aids are mixed at high speed for 8 minutes, and then extruded and granulated using a vertical twin-screw extruder to obtain the matrix masterbatch. The temperature range of the first twin-screw extrusion is 150-185℃, and the main extruder speed is 250 rpm. Then, the matrix masterbatch is mixed evenly with the modified bamboo fiber structure, and then extruded and granulated using a vertical twin-screw extruder under low shear to obtain the composite masterbatch. The temperature of the second low-shear twin-screw extrusion is 5℃ lower than the same temperature range in the first step, and the main extruder speed is 200 rpm.

[0046] Step 3, Film Forming: The composite masterbatch is placed in a vacuum drying oven and dried at 80℃ for 16 hours. After drying, the moisture content of the masterbatch is ≤50ppm. A thick sheet with a thickness of 0.5mm is then produced by casting in the temperature range of 160-180℃. This sheet is then simultaneously biaxially stretched at 75℃ with a stretching ratio of 3×3. After stretching, it is heat-set at 115℃ for 10 seconds. Finally, it is cooled at 25℃ and wound up with a winding tension of 12N to obtain the finished film. The thickness of the finished film is 100μm, and the thickness uniformity deviation is 1.8%.

[0047] Comparative Example 1 This comparative example provides a polylactic acid film containing bamboo fiber, whose composition, weight parts, and preparation method are basically the same as those in Example 2. The core difference is that the modified bamboo fiber structure is replaced with unmodified nanofiberized bamboo fiber, while the remaining components, dosages, and process parameters are completely consistent with those in Example 2.

[0048] Comparative Example 2 This comparative example provides a polylactic acid film containing bamboo fiber, whose composition, weight parts, and preparation method are basically the same as those in Example 2. The core difference is that epoxy-terminated polycaprolactone is not added, while the remaining components, dosages, and process parameters are completely consistent with those in Example 2.

[0049] Experiment Example 1: Basic Performance Testing of Thin Film Cores The core objective of this test is to verify the fundamental performance advantages of the technical solution of this invention.

[0050] The test items and their corresponding latest national standards are as follows: Tensile property testing shall be performed in accordance with standard GB / T 1040.3-2023, and the test index shall be tensile strength. The antibacterial performance test was conducted in accordance with the standard GB / T 31402-2015, and the test index was the inhibition rate of Escherichia coli. Optical performance testing shall be conducted in accordance with standard GB / T 2410-2023, and the test index shall be visible light transmittance. The test for resistance to damp heat aging was conducted in accordance with the standard GB / T 7141-2024, and the test index was the retention rate of tensile strength after aging. The safety testing of food contact materials shall be conducted in accordance with the standard GB 4806.7-2023, and the test index shall be the amount of hazardous substances migrating.

[0051] The test samples were thin film samples prepared in Examples 1, 2, 1 (Comparative Example), and 2 (Comparative Example). The test results are shown in the table below: Test Results Analysis: The core fundamental properties of Examples 1 and 2 are significantly superior to those of Comparative Examples 1 and 2. Comparative Example 1, using unmodified bamboo fiber, exhibits a significant decrease in tensile strength, light transmittance, and resistance to damp heat aging, and also lacks effective antibacterial effects, verifying that the modified bamboo fiber structure is the core factor in achieving performance improvement. Comparative Example 2, without the addition of epoxy-terminated polycaprolactone, shows a significant deterioration in mechanical properties, optical properties, and aging resistance, verifying the importance of its interfacial compatibility. The overall fundamental performance of the solution presented in this invention is superior, meeting basic usage requirements.

[0052] Experiment Example 2: Thin Film Application Adaptability Test The core purpose of this test is to verify the adaptability of the technical solution of this invention in practical applications and to clarify its application value. The test items and their corresponding latest current national standards are as follows: The heat-sealing performance test shall be conducted in accordance with the standard GB / T 23582.2-2024, and the test index shall be the heat-sealing strength. The water vapor barrier performance test shall be conducted in accordance with the standard GB / T 31034-2024, and the test index shall be water vapor transmission rate. The thermal dimensional stability test was conducted in accordance with standard GB / T 34848-2024, with the longitudinal thermal shrinkage rate as the test index. The biodegradability performance test shall be conducted in accordance with the standard GB / T 19277.1-2024, and the test index shall be the biodegradability rate. The film thickness uniformity test shall be performed in accordance with the standard GB / T 6672-2021, and the test index shall be the thickness uniformity deviation.

[0053] The test samples were thin film samples prepared in Examples 1, 2, 1 (Comparative Example), and 2 (Comparative Example). The test results are shown in the table below: Test results analysis: The application adaptability of Examples 1 and 2 is significantly better than that of Comparative Examples 1 and 2. The film of the present invention has high heat-sealing strength, good barrier properties, low thermal shrinkage rate, uniform thickness, and high biodegradability, making it suitable for practical applications such as food packaging. Comparative Examples 1 and 2, lacking core technical features, show a significant decrease in application adaptability, further verifying the practicality and technical advantages of the present invention.

[0054] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article, or apparatus.

[0055] The preferred embodiments of the present invention disclosed above are merely illustrative of the invention. These preferred embodiments do not exhaustively describe all details, nor do they limit the invention to the specific implementations described. Clearly, many modifications and variations can be made based on the content of this specification. This specification selects and specifically describes these embodiments to better explain the principles and practical applications of the invention, thereby enabling those skilled in the art to better understand and utilize the invention. The invention is limited only by the claims and their full scope and equivalents.

Claims

1. A polylactic acid antibacterial film containing bamboo fiber, characterized in that, By weight, it consists of 75-88 parts of polylactic acid, 6-18 parts of modified bamboo fiber structure, and 4-8 parts of epoxy-terminated polycaprolactone. The modified bamboo fiber structure has a core of nanofibrillated bamboo fiber, an inner layer of epoxy-terminated polylactic acid grafted layer covalently grafted onto the surface of nanofibrillated bamboo fiber, and an outer layer of zinc-coordinated tannic acid nanodot load layer grown in situ on the surface of the grafted layer. Polylactic acid is the film-forming matrix resin; Epoxy-terminated polycaprolactone is the interfacial compatible component; The end groups of the polylactic acid matrix form chemical bonds with the modified bamboo fiber structure and epoxy-terminated polycaprolactone. The epoxy-terminated polylactic acid graft layer connects the polylactic acid matrix and the nanofibrillated bamboo fiber. The zinc-coordinated tannic acid nanodot load layer is anchored on the surface of the graft layer.

2. The polylactic acid antibacterial film containing bamboo fiber according to claim 1, characterized in that, The nanofibrillated bamboo fibers have a diameter of 20–50 nm and an aspect ratio of 500–1000.

3. The polylactic acid antibacterial film containing bamboo fiber according to claim 1, characterized in that, The grafting rate of the epoxy-terminated polylactic acid grafted layer is 18% to 22%, and the number average molecular weight of the polylactic acid oligomer used for grafting is 2000 to 4000. The epoxy-terminated polylactic acid includes at least one of monoepoxy-terminated polylactic acid and diepoxy-terminated polylactic acid.

4. The polylactic acid antibacterial film containing bamboo fiber according to claim 1, characterized in that, The zinc-coordinated tannic acid nanodots have a particle size of 2–5 nm and a loading of 8%–12 wt% in the modified bamboo fiber structure.

5. The polylactic acid antibacterial film containing bamboo fiber according to claim 1, characterized in that, The polylactic acid has a number-average molecular weight of 80,000 to 150,000 and a melt flow rate of 3 to 8 g / 10 min. The number-average molecular weight of the epoxy-terminated polycaprolactone is 10,000 to 30,000. The film also contains processing aids, which include at least one of antioxidants and lubricants.

6. A method for preparing a polylactic acid antibacterial film containing bamboo fiber, characterized in that, The preparation of the polylactic acid antibacterial film containing bamboo fiber as described in claim 1 includes the following steps: Step 1, Preparation of modified bamboo fiber structure: Bamboo raw fibers are pretreated to obtain nanofiberized bamboo fibers, and then an epoxy-terminated polylactic acid graft layer is constructed on its surface through a covalent grafting reaction. Finally, zinc-coordinated tannic acid nanodots are grown on the surface of the graft layer through an in-situ coordination reaction to obtain the modified bamboo fiber structure. Step 2, preparation of composite masterbatch: A two-step melt blending method is adopted. First, polylactic acid, epoxy-terminated polycaprolactone and processing aids are mixed and then extruded and granulated to obtain matrix masterbatch. Then, the matrix masterbatch is mixed with modified bamboo fiber structure and extruded and granulated to obtain composite masterbatch. Step 3, film forming: After drying the composite masterbatch, a thick sheet is obtained by casting, and then the sheet is simultaneously biaxially stretched, heat-set, cooled and wound up to obtain the finished film.

7. The method for preparing a polylactic acid antibacterial film containing bamboo fiber according to claim 6, characterized in that, In step one, the pretreatment adopts alkaline ultrasonic treatment combined with high pressure homogenization treatment; The covalent grafting reaction was carried out using triethylamine as a catalyst in an anhydrous toluene system under nitrogen protection; the in-situ coordination reaction was carried out in an ethanol-water solution system.

8. The method for preparing a polylactic acid antibacterial film containing bamboo fiber according to claim 6, characterized in that, In step two, the temperature range of the first twin-screw extrusion is 150-185°C, and the main machine speed is 250 rpm. The temperature of the second-step low-shear twin-screw extrusion is 3-5°C lower than the temperature in the same range as the first step, and the main engine speed is 180-200 rpm; The extrusion equipment includes at least one of the following: a horizontal twin-screw extruder and a vertical twin-screw extruder.

9. The method for preparing a polylactic acid antibacterial film containing bamboo fiber according to claim 6, characterized in that, In step three, the temperature for synchronous biaxial stretching is 65-75℃, and the stretching ratio is 3×3 times. The heat setting temperature is 110–115℃, and the heat setting time is 8–10 seconds.

10. The method for preparing a polylactic acid antibacterial film containing bamboo fiber according to claim 6, characterized in that, In step three, the vacuum drying temperature of the composite masterbatch is 80℃, and the drying time is 12-16h. The temperature range for casting thick sheets is 160–180℃, and the sheet thickness is 0.2–0.5 mm. The cooling temperature for cooling and winding is 20–25°C, and the winding tension is 8–12 N; the thickness of the finished film is 20–100 μm, and the thickness uniformity deviation is ≤3%.

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