Antibacterial degradable composite material and preparation method and application thereof

Abstract

This invention belongs to the field of functional polymer nanocomposite materials technology, specifically relating to an antibacterial and biodegradable composite material, its preparation method, and its applications. This invention achieves synergistic antibacterial effects through a core-shell structure design, combining photocatalytic sterilization with controlled, sustained release of silver ions. The gold shell stabilizes the silver bromide core and promotes the separation of photogenerated carriers. The surface treatment agent system addresses the issues of nanoparticle aggregation and interfacial compatibility. The final product possesses advantages such as highly efficient, broad-spectrum, and long-lasting antibacterial properties, stable mechanical properties, and green biodegradability. The process is mild and controllable, easily scalable for industrial application, and can be widely used in the production of antibacterial and biodegradable plastic products such as food packaging films, medical dressings, and daily necessities.

Description

Technical Field

[0001] This invention belongs to the field of functional polymer nanocomposite materials technology, specifically relating to an antibacterial and biodegradable composite material, its preparation method, and its application. Background Technology

[0002] With the deepening of the concept of sustainable development, the problem of "white pollution" urgently needs to be solved. Biodegradable plastics (such as polylactic acid and polyhydroxyalkanoates) have become a focus of industry and research as green alternatives to traditional plastics. At the same time, in the fields of food preservation, medical protection, and daily hygiene, plastic products not only need to meet environmental protection requirements, but are also endowed with the important function of actively inhibiting or killing pathogenic microorganisms to ensure public health and safety.

[0003] Currently, the mainstream method for imparting antibacterial properties to biodegradable plastics is to blend inorganic antibacterial agents, especially nano-silver (Ag) and its complexes, into the polymer matrix. Silver-based antibacterial agents are widely used due to their broad-spectrum and high-efficiency characteristics; however, in the actual industrialization process, especially for high-performance and long-life applications, a series of key technical bottlenecks remain unresolved. Imbalance between antibacterial long-lasting effect and safety: Traditional nano-silver or silver ion antibacterial agents mainly rely on silver ions (Ag) + The process involves the dissolution and release of silver ions. This process typically exhibits a rapid "burst release effect," leading to excessively high silver ion concentrations in the short term. This can trigger cytotoxicity risks and cause the antibacterial activity to rapidly decline due to the depletion of the active components, making it difficult to meet the antibacterial requirements of the product throughout its entire life cycle.

[0004] Limitations and environmental dependence of single antibacterial mechanisms: The effectiveness of contact bactericidal mechanisms that rely solely on the release of silver ions is limited by factors such as ion migration rate and environmental humidity. The antibacterial effect will decrease significantly on dry surfaces or when the release of silver ions is hindered.

[0005] The instability of the antibacterial agent itself leads to its failure: Silver bromide (AgBr), as a classic photocatalytic antibacterial material, has catalytic activity far exceeding that of conventional nano-silver. However, pure AgBr is prone to self-decomposition under light irradiation (AgBr→Ag+Br), leading to structural disintegration and the destruction of the catalytic active center (Ag). + It is irreversibly lost and has poor antibacterial durability.

[0006] The challenges of nanoparticle dispersion and interfacial compatibility: The inherent high surface energy of nanoparticles makes them prone to agglomeration during polymer melt processing, leading to uneven dispersion. This not only significantly reduces the effective specific surface area of ​​antibacterial agents, affecting antibacterial efficiency, but also creates defects within the material, impairing mechanical properties. Poor interfacial compatibility between inorganic nanoparticles and the organic polymer matrix further exacerbates these problems.

[0007] To overcome the limitations of single antibacterial agents, researchers have attempted to construct nanocomposite structures. For example, they have combined silver with materials such as titanium dioxide and graphene to enhance photocatalytic performance. However, challenges remain regarding how to simultaneously stabilize AgBr and regulate Ag... + Systematic solutions that address release kinetics and introduce multiple synergistic antimicrobial mechanisms remain insufficient. In particular, the core challenge currently facing the technology lies in how to construct an efficient catalytic system capable of generating multiple reactive oxygen species (ROS) in situ through ingenious structural design, while simultaneously suppressing AgBr photolysis and achieving perfect integration with the polymer matrix. Therefore, there is an urgent need in this field for innovative antimicrobial agent design and compounding technologies to develop antimicrobial biodegradable plastic masterbatches that combine the advantages of high efficiency, long-lasting effect, safety, stability, and ease of processing. Summary of the Invention

[0008] To address the technical bottlenecks encountered in the application of silver-based antibacterial agents to biodegradable plastics, such as uneven dispersion of antibacterial agents, uncontrollable release of silver ions leading to a contradiction between long-term effectiveness and safety, and poor interfacial compatibility between inorganic nanoparticles and organic polymer matrices, the present invention aims to provide an antibacterial biodegradable composite material, its preparation method, and its application, thereby solving the above-mentioned problems.

[0009] To achieve the above objectives, the present invention provides the following technical solution: The present invention provides an antibacterial and biodegradable composite material, which, based on a mass percentage of 100%, comprises: 0.1-5% antibacterial agent, 0.5-5% surface treatment agent, and the balance being a biodegradable polymer matrix; The antibacterial agent has a core-shell structure, wherein the core is silver bromide nanoparticles and the shell is a layer of gold nanoparticles. The surface treatment agent includes dispersants, coupling agents, and polymer compatibilizers.

[0010] Preferably, the silver bromide nanoparticles have a particle size of 10~100 nm; The thickness of the gold nanoparticle layer is 1~10 nm.

[0011] Preferably, the method for preparing the antibacterial agent includes the following steps: Under light-protected or low-light conditions, a solution containing silver ions and a solution containing bromide ions are reacted in the presence of a protective agent to obtain silver bromide nanoparticle colloids. A reducing agent and chloroauric acid solution were added to the silver bromide nanoparticle colloid to carry out an in-situ reduction reaction, thereby obtaining the antibacterial agent.

[0012] Preferably, the protective agent includes at least one of polyvinylpyrrolidone, gelatin, and sodium citrate; the silver ion-containing solution includes silver nitrate solution; the bromide ion-containing solution includes sodium bromide solution or potassium bromide solution; the reaction temperature is 20~60℃, and the time is 0.5~2h.

[0013] Preferably, the reducing agent includes ascorbic acid, sodium borohydride, or hydrazine hydrate; the molar ratio of gold to silver bromide in the chloroauric acid solution is 1:2~10; the temperature of the in-situ reduction reaction is 30~70℃, and the reaction time is 1~4h.

[0014] Preferably, the biodegradable polymer matrix includes at least one of polylactic acid, polybutylene succinate, polyhydroxyalkanoate, polypropylene carbonate, and starch-based plastics.

[0015] Preferably, the dispersant comprises at least one of zinc stearate, calcium stearate, and ethylene bis-stearamide; The coupling agent includes silane coupling agents and / or titanate coupling agents; The polymeric compatibilizer includes maleic anhydride-grafted polyolefin or maleic anhydride-grafted biodegradable polymer. The mass ratio of the dispersant, coupling agent, and polymer compatibilizer is 1:0.5~2:1~4.

[0016] This invention also provides a method for preparing the antibacterial and biodegradable composite material described in the above technical solution, comprising the following steps: The antibacterial and biodegradable composite material is obtained by melt-blending and extruding the contained components.

[0017] Preferably, the melt blending temperature is 140~200℃ and the screw speed is 100~300rpm.

[0018] The present invention also provides the application of the antibacterial degradable composite material described in the above technical solution or the antibacterial degradable composite material prepared by the preparation method described in the above technical solution in food packaging films, medical dressings or daily necessities.

[0019] Compared with the prior art, the technical solution provided by the present invention has the following significant advantages: (1) Synergistic antibacterial effect, high efficiency and long duration: This invention creatively uses core-shell structured silver bromide@gold nanoparticles as the antibacterial core. This structure has multiple synergistic effects: ① The gold shell effectively stabilizes the silver bromide core, inhibits its photodegradation and inactivation, and ensures the durability of antibacterial activity. ② The heterojunction formed between gold and silver bromide greatly promotes the separation efficiency of photogenerated carriers, enabling the generation of reactive oxygen species under visible light / indoor light, achieving highly efficient photocatalytic sterilization. ③ The gold shell, as an intelligent control layer, can achieve controlled and sustained release of silver ions, avoiding the toxicity risk and subsequent efficacy decay caused by initial "burst release". The synergistic mechanism of photocatalytic sterilization and sustained-release sterilization results in a broader antibacterial spectrum, higher efficiency, and longer duration of action.

[0020] (2) Excellent dispersion and stable performance: By using dispersants, coupling agents, and polymer compatibilizers as surface treatment agents, the agglomeration problem of nanoparticles in polymer melts is fundamentally solved through the synergistic effects of physical lubrication, chemical bonding, and thermodynamic compatibility, ensuring uniform nanoscale dispersion and strong interfacial bonding in the matrix. This not only maximizes the effective specific surface area of ​​the antibacterial agent and improves the antibacterial efficiency, but also effectively avoids the decline in material mechanical properties caused by agglomerates.

[0021] (3) Mature process and easy to promote: The preparation method of the present invention has clear steps and mild and controllable conditions. The synthesis of silver bromide@gold nanoparticles adopts a mature liquid phase chemical method, and the morphology and size are easy to control; the preparation of masterbatch adopts a common plastic melt extrusion blending process, which is fully compatible with the existing plastic processing industry chain, requires no special equipment, has a low technical threshold, and is very suitable for large-scale industrial production.

[0022] (4) Green and safe, with wide applications: The final product uses biodegradable polymers as the matrix, which solves the problem of "white pollution" at the source; at the same time, the antibacterial function is long-lasting and controllable through structural design, which improves the hygiene and safety level of the product. This masterbatch can be conveniently used to prepare various food packaging, medical supplies and daily consumer products, meeting the market's urgent demand for green, healthy and functional materials, and has broad application prospects. Detailed Implementation

[0023] The present invention provides an antibacterial and biodegradable composite material, which, based on a mass percentage of 100%, comprises: 0.1-5% antibacterial agent, 0.5-5% surface treatment agent, and the balance being a biodegradable polymer matrix; The antibacterial agent has a core-shell structure, wherein the core is silver bromide nanoparticles and the shell is a layer of gold nanoparticles. The surface treatment agent includes dispersants, coupling agents, and polymer compatibilizers.

[0024] The antibacterial and biodegradable composite material provided by this invention comprises 0.1-5% antibacterial agent by weight percentage, specifically 0.1%, 0.5%, 1.0%, 1.5%, 2.0%, 2.5%, 3.0%, 3.5%, 4.0%, 4.5%, and 5.0%. In this invention, the particle size of the silver bromide nanoparticles is preferably 10-100 nm; the thickness of the gold nanoparticle layer is preferably 1-10 nm, specifically 1 nm, 2 nm, 3 nm, 4 nm, 5 nm, 6 nm, 7 nm, 8 nm, 9 nm, and 10 nm.

[0025] In this invention, the method for preparing the antibacterial agent preferably includes the following steps: Under light-protected or low-light conditions, a solution containing silver ions and a solution containing bromide ions are reacted in the presence of a protective agent to obtain silver bromide nanoparticle colloids. A reducing agent and chloroauric acid solution were added to the silver bromide nanoparticle colloid to carry out an in-situ reduction reaction, thereby obtaining the antibacterial agent.

[0026] In this invention, the protective agent preferably includes at least one of polyvinylpyrrolidone, gelatin, and sodium citrate; the silver ion-containing solution preferably includes silver nitrate solution, and the concentration of the silver ion-containing solution is preferably 0.1 mol / L; the bromide ion-containing solution preferably includes sodium bromide solution or potassium bromide solution; the concentration of the bromide ion-containing solution is preferably 0.1 mol / L; the volume ratio of the silver ion-containing solution to the bromide ion-containing solution is preferably 1:1; the volume ratio of the protective agent to the silver ion-containing solution is preferably 0.05~0.2 g:1 mL; the reaction system preferably also includes deionized water; the reaction temperature is preferably 20~60℃, specifically 20℃, 30℃, 40℃, 50℃, or 60℃; the reaction time is preferably 0.5~2 h (referring to the reaction time after adding the bromide ion-containing solution), specifically 0.5 h, 1 h, 1.5 h, or 2 h. In this invention, the reaction process is preferably as follows: under conditions of light protection or weak light and stirring, the protective agent is dissolved in deionized water, a solution containing silver ions is added dropwise to the system, and then the mixture is stirred again, followed by the addition of a solution containing bromide ions to carry out the reaction; the dissolution temperature is preferably the same as the reaction temperature; and the stirring time is preferably 20-30 minutes.

[0027] In this invention, the reducing agent preferably includes ascorbic acid, sodium borohydride, or hydrazine hydrate; the molar ratio of gold to silver bromide in the chloroauric acid solution is 1:2 to 10, specifically 1:2, 1:3, 1:4, 1:5, 1:6, 1:7, 1:8, 1:9, or 1:10; the concentration of the chloroauric acid solution is preferably 0.01 mol / L; the preferred ratio of the chloroauric acid solution to the reducing agent is 1-5 mL: 0.01-0.1 g. In this invention, the sodium borohydride is preferably added dropwise in solution form, and the concentration of the solution is preferably 0.1 mol / L; the hydrazine hydrate is preferably added dropwise after dilution, and the dilution factor is preferably 10 times.

[0028] In this invention, the preferred temperature for the in-situ reduction reaction is 30-70℃, specifically 30℃, 40℃, 50℃, 60℃, or 70℃; the preferred time is 1-4 hours, specifically 1 hour, 2 hours, 3 hours, or 4 hours; the in-situ reduction reaction is preferably carried out under stirring conditions. The preferred process of the in-situ reduction reaction includes: adding a reducing agent to the silver bromide nanoparticle colloid, stirring to dissolve, and then adding chloroauric acid solution to carry out the in-situ reduction reaction. After the in-situ reduction reaction, the invention also preferably includes post-treatment, which preferably includes: centrifuging the obtained system, washing the resulting precipitate three times with water and once with anhydrous ethanol, and then drying; the preferred centrifugation speed is 10000-12000 rpm, and the preferred time is 15-20 minutes; the preferred drying temperature is 60℃, and the preferred time is 8 hours.

[0029] This invention utilizes the synergistic effect of gold (Au) nanoshells and AgBr cores, effectively stabilizing the AgBr structure and suppressing its photolysis. Furthermore, by constructing a Schottky barrier, it significantly enhances the separation efficiency of photogenerated carriers, thereby evoking a powerful photocatalytic sterilization effect under visible light and even indoor light. This photocatalytic sterilization and Ag... + The synergistic mechanism of slow-release sterilization achieves an antibacterial effect of "1+1>2". At the same time, the gold shell layer acts as a "barrier" and "buffer layer", realizing intelligent regulation of the release rate of silver ions, ensuring the long-lasting antibacterial effect and biosafety.

[0030] The antibacterial and biodegradable composite material provided by the present invention, by weight percentage, comprises a balance of biodegradable polymer matrix. In the present invention, the biodegradable polymer matrix preferably comprises at least one of polylactic acid, polybutylene succinate, polyhydroxyalkanoate, polypropylene carbonate, and starch-based plastics. In the present invention, the number-average molecular weight of the polylactic acid is preferably 100,000; the number-average molecular weight of the polybutylene succinate is preferably 80,000. In a specific embodiment of the present invention, the biodegradable polymer matrix is ​​specifically polylactic acid and a polylactic acid and polybutylene succinate resin in a mass ratio of 60:35.

[0031] The antibacterial and biodegradable composite material provided by the present invention comprises 0.5-5% surface treatment agent by weight percentage, specifically 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, and 5%.

[0032] In this invention, the dispersant preferably comprises at least one of zinc stearate, calcium stearate, and ethylene bis-stearamide; the coupling agent preferably comprises a silane coupling agent and / or a titanate coupling agent; the silane coupling agent preferably comprises at least one of γ-aminopropyltriethoxysilane (KH550), γ-glycidoxypropyltrimethoxysilane (KH560), and γ-methacryloyloxypropyltrimethoxysilane (KH570); the titanate coupling agent preferably comprises... The polymer compatibilizer is selected from at least one of isopropyl tris(dioctyl pyrophosphonoyloxy)titanate (NDZ-201), isopropyl tris(isostearoyl)titanate (NDZ-101), and tetraisopropyl di(dioctyl phosphite)titanate (NDZ-102); the polymer compatibilizer preferably comprises maleic anhydride-grafted polyolefin or maleic anhydride-grafted biodegradable polymer; the biodegradable polymer in the maleic anhydride-grafted biodegradable polymer is the biodegradable polymer matrix described in the above scheme. In this invention, the grafting rate of maleic anhydride-grafted polylactic acid is preferably 1.2%; the grafting rate of maleic anhydride-grafted polybutylene succinate is preferably 1.2%. In this invention, the mass ratio of the dispersant, coupling agent, and polymer compatibilizer is preferably 1:0.5~2:1~4, specifically 1:0.5:1.5, 1.5:1.0:1.5, or 2:1:2. The present invention uses the above-mentioned surface treatment agent to ensure good dispersion and interfacial bonding of nanoparticles in the matrix.

[0033] This invention also provides a method for preparing the antibacterial and biodegradable composite material described in the above technical solution, comprising the following steps: The antibacterial and biodegradable composite material is obtained by melt-blending and extruding the contained components.

[0034] In this invention, prior to melt blending, mechanical blending is preferably performed. The mechanical blending speed is preferably 500-1500 rpm, specifically 500 rpm, 900 rpm, 1000 rpm, or 1500 rpm; the temperature is preferably 20-40℃, more preferably 30℃; and the time is preferably 5-15 min, more preferably 10 min. In this invention, the melt blending temperature is preferably 140-200℃, preferably including three temperature zones: a first temperature zone preferably 140-160℃, a second temperature zone preferably 160-180℃, and a third temperature zone preferably 180-200℃; the die head temperature is preferably 170-190℃; and the screw speed is preferably 100-300 rpm, more preferably 200 rpm. After extrusion, the invention also preferably involves water cooling and pelletizing.

[0035] The present invention also provides the application of the antibacterial degradable composite material described in the above technical solution or the antibacterial degradable composite material prepared by the preparation method described in the above technical solution in food packaging films, medical dressings or daily necessities.

[0036] Unless otherwise specified, the materials and equipment used in this invention are all commercially available products in the field.

[0037] The technical solutions of this invention will be clearly and completely described below with reference to the embodiments thereof. Obviously, the described embodiments are only a part of the embodiments of this invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0038] Example 1 Preparation of antibacterial and biodegradable composite materials based on PLA: (1) Synthesis of silver bromide nanoparticles: Under light-protected conditions, 200 mL of deionized water was added to a three-necked flask, and 0.5 g of polyvinylpyrrolidone (PVP, a protective agent) was added while stirring. The temperature was raised to 40 °C and stirred until completely dissolved. Then, 10 mL of 0.1 mol / L silver nitrate solution was slowly added dropwise to the flask, and stirring was continued for 30 min. Next, 10 mL of 0.1 mol / L sodium bromide solution was slowly added dropwise. After the addition was completed, the reaction was maintained at 40 °C for 1 h to obtain pale yellow silver bromide nanoparticle colloids. (2) Preparation of core-shell silver bromide@gold nanoparticles: Add 0.3g of ascorbic acid (reducing agent) to the colloid obtained in step 1, stir to dissolve, and then slowly add 20mL of 0.01mol / L chloroauric acid (HAuCl4) solution (molar ratio of gold to silver bromide is 1:5). Heat to 50℃ for in-situ reduction reaction and keep warm and stir for 2h. After the reaction is completed, centrifuge the colloid (10000rpm, 20min), wash the precipitate 3 times with deionized water and 1 time with anhydrous ethanol, and then dry in a vacuum drying oven at 60℃ for 8h to obtain gray-black silver bromide@gold nanoparticle solid powder (gold shell thickness is about 3nm, silver bromide particle size is 30~50nm). (3) Preparation of composite materials: Weigh the raw materials according to the following mass ratio: 0.5wt% silver bromide@gold nanoparticles, 96.5wt% polylactic acid resin (PLA, number average molecular weight 100,000), 1wt% zinc stearate, 0.5wt% silane coupling agent (KH550), and 1.5wt% maleic anhydride-grafted polylactic acid (MAH-g-PLA, grafting rate 1.2%) (total content of surface treatment agent 3wt%). Add all raw materials to a high-speed mixer and premix for 15 minutes at 30℃ and 800 rpm. Then add the mixture to a twin-screw extruder and set the extrusion temperature to 160~180℃ (zone 1 160℃, zone 2 170℃, zone 3 180℃, die head 175℃) and screw speed to 200 rpm. After melt blending, extrusion, water cooling, and pelletizing, an antibacterial and biodegradable composite material (denoted as M1) is obtained. Example 2 Preparation using an antibacterial and biodegradable masterbatch based on a PLA / PBS blend matrix: (1) Synthesis of silver bromide nanoparticles: Under light-protected conditions, 200 mL of deionized water and 0.6 g of sodium citrate (protectant) were added to a three-necked flask, and the mixture was heated to 30 °C and stirred to dissolve. 10 mL of 0.1 mol / L silver nitrate solution was added dropwise, and after stirring for 20 min, 10 mL of 0.1 mol / L sodium bromide solution was added dropwise. The mixture was reacted at 30 °C for 0.8 h to obtain silver bromide nanoparticle colloids. (2) Preparation of core-shell silver bromide@gold nanoparticles: Add 0.2 g of sodium borohydride (reducing agent, prepared as a 0.1 mol / L solution with deionized water) to the above colloid, stir well, and then add 15 mL of 0.01 mol / L chloroauric acid (HAuCl4) solution (molar ratio of gold to silver bromide is 1:7). Heat to 40 °C and react for 1.5 h. After the reaction is complete, centrifuge the colloid (12000 rpm, 15 min), wash the precipitate three times with deionized water and once with anhydrous ethanol, and then dry it in a vacuum drying oven at 60 °C for 6 h to obtain silver bromide@gold nanoparticle powder (gold shell thickness is about 2 nm, silver bromide particle size is 20~40 nm). (3) Preparation of composite materials: Mass ratio: silver bromide@gold nanoparticles 1.0wt%, polylactic acid resin (PLA, number average molecular weight 100,000) 60wt%, polybutylene succinate resin (PBS, number average molecular weight 80,000) 35wt%, calcium stearate 1.5wt%, isopropyl tris(dioctyl pyrophosphoryloxy)titanate coupling agent (NDZ-201) 1.0wt%, maleic anhydride-grafted polybutylene succinate (MAH-g-PBS, grafting rate 1.2%) 1.5wt% (total content of surface treatment agent 4wt%); premixed for 15min at 30℃ and 700rpm in a high-speed mixer; melt-blended, extruded, and pelletized in a twin-screw extruder at 150~170℃ (zone 1 150℃, zone 2 165℃, zone 3 180℃, die head 175℃) and screw speed 180rpm to obtain an antibacterial and biodegradable composite material (denoted as M2). Example 3 Preparation of high-content antibacterial composite materials (1) Synthesis of silver bromide nanoparticles: Under low light conditions, 200 mL of deionized water and 1 g of gelatin (protectant) were added to a three-necked flask, and the mixture was heated to 50 °C and stirred to dissolve. 10 mL of 0.1 mol / L silver nitrate solution was added dropwise, and the mixture was stirred for 30 min. Then, 15 mL of 0.1 mol / L sodium bromide solution was added dropwise, and the mixture was reacted at 50 °C for 1.5 h to obtain silver bromide nanoparticle colloids. (2) Preparation of core-shell silver bromide@gold nanoparticles: Add 0.5 g of hydrazine hydrate (reducing agent, diluted 10 times before addition) to the colloid, stir, and then add 30 mL of 0.01 mol / L chloroauric acid (HAuCl4) solution (molar ratio of gold to silver bromide is 1:3). Heat to 60 °C and react for 3 h. After the reaction is complete, centrifuge the colloid (12000 rpm, 18 min). Wash the precipitate three times with deionized water and once with anhydrous ethanol, and then dry it in a vacuum drying oven at 60 °C for 10 h to obtain silver bromide@gold nanoparticle powder (gold shell thickness is about 5 nm, silver bromide particle size is 50~80 nm). (3) Preparation of composite materials: Mass ratio: 3.0 wt% silver bromide@gold nanoparticles, 92 wt% polylactic acid resin (PLA, number average molecular weight 100,000), 2 wt% ethylene bis-stearamide (EBS), 1 wt% silane coupling agent (KH560), 2 wt% maleic anhydride-grafted polylactic acid (MAH-g-PLA, grafting rate 1.2%) (total content of surface treatment agent 5 wt%); premixed for 10 min at 40℃ and 900 rpm in a high-speed mixer; melt-blended, extruded, and pelletized in a twin-screw extruder at 170~190℃ (zone 1 160℃, zone 2 180℃, zone 3 190℃, die head 185℃) and screw speed 250 rpm to obtain an antibacterial and biodegradable composite material (denoted as M3). Comparative Example 1 AgBr antibacterial masterbatch without gold shell: Except for the antibacterial agent being single silver bromide nanoparticles (without gold coating, particle size 30~50 nm), the other raw material ratios and preparation processes were completely consistent with those in Example 1, resulting in a composite material (denoted as D1).

[0039] Comparative Example 2 Traditional nano-silver antibacterial masterbatch: Except for the antibacterial agent being nano-silver (particle size 20~40nm), the other raw material ratios and preparation processes were completely consistent with those in Example 1, resulting in a composite material (denoted as D2).

[0040] Comparative Example 3 Antibacterial masterbatch without surface treatment agent Except for the absence of zinc stearate, silane coupling agent (KH550), maleic anhydride-grafted polylactic acid (MAH-g-PLA) (with 0% surface treatment agent content), and 99.5% polylactic acid resin, the other raw material ratios and preparation processes were completely consistent with those in Example 1, resulting in a composite material (denoted as D3).

[0041] Performance testing The composite materials from Examples 1-3 and Comparative Examples 1-3 were mixed with PLA resin at a mass ratio of 1:10, and thin films with a thickness of 50 μm were prepared using a blown film machine (as test samples). The antibacterial properties, dispersibility, mechanical properties, and degradation properties of the samples were tested. The test methods and results are as follows: Test method: Antibacterial performance test: According to GB / T 31402-2015 "Test method for antibacterial properties of plastic surfaces", Escherichia coli (ATCC 25922) and Staphylococcus aureus (ATCC 6538) were used as test strains to test the antibacterial rate of the samples against the two bacteria in 24 hours; after 50 accelerated aging cycles (simulating a 1-year use environment), the antibacterial rate was tested again to evaluate the long-term antibacterial effect. Dispersion test: The dispersion state of antibacterial particles and the particle size of aggregates in the film were observed using transmission electron microscopy (TEM); Mechanical property testing: According to GB / T 1040.3-2006 "Determination of tensile properties of plastics - Part 3: Test conditions for films and sheets", the tensile strength and elongation at break of the samples were tested. Degradation performance test: According to GB / T 19277.1-2011 "Determination of final aerobic biodegradability of materials under controlled composting conditions by means of determination of carbon dioxide released - Part 1: General method", the biodegradation rate of the sample under composting conditions (58℃, 55% humidity) for 60 days was tested. The test results are shown in Table 1: Table 1 Performance test results of the examples and comparative examples

[0042] Results Analysis (1) Antibacterial properties: Highly effective and long-lasting The initial antibacterial rates of the samples in Examples 1-3 against Escherichia coli and Staphylococcus aureus were all ≥99.7%, which were significantly better than those of Comparative Example 1 (single AgBr) and Comparative Example 2 (traditional nano silver), demonstrating the synergistic antibacterial advantages of the silver bromide@gold core-shell structure (photocatalysis + ion slow release). After 50 aging cycles, the antibacterial rate of the sample in the example remained above 99.4%, while the antibacterial rate of Comparative Example 1 and Comparative Example 2 dropped to 83-88%, indicating that the gold shell effectively inhibited the photolysis inactivation of AgBr and significantly improved the long-term antibacterial effect; at the same time, it avoided the "burst release effect" of traditional nano silver and ensured the antibacterial stability during long-term use.

[0043] (2) Dispersion performance: Uniformly dispersed with no obvious agglomeration In the samples of Examples 1-3, the particle size of the antibacterial particle aggregates was ≤100nm. TEM observation showed that the particles were uniformly dispersed at the nanoscale. This was due to the synergistic effect of dispersant, coupling agent and polymer compatibilizer: zinc stearate (dispersant) reduced the friction between particles, silane coupling agent (KH550 / KH560) achieved chemical bonding between particles and matrix, and MAH-g-PLA / MAH-g-PBS (compatibility) improved thermodynamic compatibility. All three inhibited aggregation together. Comparative Example 3 (without surface treatment agent) has an agglomerate particle size of over 500 nm. The large-scale agglomeration of particles not only reduces the effective antibacterial area (initial antibacterial rate is only 94%~95%), but also leads to internal defects in the material and a significant decrease in mechanical properties.

[0044] (3) Mechanical properties: stable and excellent The tensile strength of the samples in Examples 1-3 was ≥48.7MPa and the elongation at break was ≥3.8%. Among them, the elongation at break of Example 2 (PLA / PBS blend matrix) reached 12.5%, which reflects the synergistic effect of matrix blending and surface treatment agent, ensuring good interfacial bonding between antibacterial particles and matrix, and avoiding mechanical property degradation caused by particle agglomeration. The tensile strength of Comparative Example 3 was only 42.1 MPa and the elongation at break was 2.1%, which was significantly lower than that of the Example, demonstrating the key role of the surface treatment agent system in ensuring the mechanical properties of the material. (4) Degradation performance: Green and environmentally friendly The biodegradation rate of the samples in Examples 1-3 was ≥66.8% after 60 days, with Example 2 (PLA / PBS blend matrix) reaching 72.3%, which was not significantly different from the comparative example. This indicates that the addition of antibacterial particles and surface treatment agents did not affect the biodegradability of the biodegradable polymer. The product solves the problem of "white pollution" from the source and meets the requirements of green environmental protection.

[0045] Although the above embodiments have provided a detailed description of the present invention, they are only some embodiments of the present invention, and not all embodiments. Other embodiments can be obtained based on these embodiments without creative effort, and these embodiments all fall within the protection scope of the present invention.

Claims

1. An antibacterial and biodegradable composite material, characterized in that, Based on a mass percentage of 100%, its components include: 0.1-5% antibacterial agent, 0.5-5% surface treatment agent, and the balance being a biodegradable polymer matrix; The antibacterial agent has a core-shell structure, wherein the core is silver bromide nanoparticles and the shell is a layer of gold nanoparticles. The surface treatment agent includes dispersants, coupling agents, and polymer compatibilizers.

2. The antibacterial and biodegradable composite material according to claim 1, characterized in that, The silver bromide nanoparticles have a particle size of 10~100 nm; The thickness of the gold nanoparticle layer is 1~10 nm.

3. The antibacterial and biodegradable composite material according to claim 1, characterized in that, The method for preparing the antibacterial agent includes the following steps: Under light-protected or low-light conditions, a solution containing silver ions and a solution containing bromide ions are reacted in the presence of a protective agent to obtain silver bromide nanoparticle colloids. A reducing agent and chloroauric acid solution were added to the silver bromide nanoparticle colloid to carry out an in-situ reduction reaction, thereby obtaining the antibacterial agent.

4. The antibacterial and biodegradable composite material according to claim 3, characterized in that, The protective agent includes at least one of polyvinylpyrrolidone, gelatin, and sodium citrate; the silver ion-containing solution includes silver nitrate solution; the bromide ion-containing solution includes sodium bromide solution or potassium bromide solution; the reaction temperature is 20~60℃, and the time is 0.5~2h.

5. The antibacterial and biodegradable composite material according to claim 3, characterized in that, The reducing agent includes ascorbic acid, sodium borohydride, or hydrazine hydrate; the molar ratio of gold to silver bromide in the chloroauric acid solution is 1:2~10; the temperature of the in-situ reduction reaction is 30~70℃, and the reaction time is 1~4h.

6. The antibacterial and biodegradable composite material according to claim 1, characterized in that, The biodegradable polymer matrix includes at least one of polylactic acid, polybutylene succinate, polyhydroxyalkanoate, polypropylene carbonate, and starch-based plastics.

7. The antibacterial and biodegradable composite material according to claim 1, characterized in that, The dispersant includes at least one of zinc stearate, calcium stearate, and ethylene bis-stearamide; The coupling agent includes silane coupling agents and / or titanate coupling agents; The polymeric compatibilizer includes maleic anhydride-grafted polyolefin or maleic anhydride-grafted biodegradable polymer. The mass ratio of the dispersant, coupling agent, and polymer compatibilizer is 1:0.5~2:1~4.

8. A method for preparing the antibacterial biodegradable composite material according to any one of claims 1 to 7, characterized in that, Includes the following steps: The antibacterial and biodegradable composite material is obtained by melt-blending and extruding the contained components.

9. The preparation method according to claim 8, characterized in that, The melt blending temperature is 140~200℃, and the screw speed is 100~300rpm.

10. The application of the antibacterial degradable composite material according to any one of claims 1 to 7 or the antibacterial degradable composite material prepared by the preparation method according to claims 8 or 9 in food packaging films, medical dressings or daily necessities.

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