Antibacterial composite material of nanometer silver / chitosan nanofiller doped polymer and preparation method thereof

Abstract

This invention discloses an antibacterial composite material of nano-silver / chitosan nanofiller doped with polymer and its preparation method, belonging to the field of antibacterial composite material technology. This invention modifies chitosan through amphiphilic grafting, simultaneously grafting hydrophobic segments compatible with the polymer matrix and hydrophilic groups with strong coordination ability to silver ions, forming a "molecular bridge" structure. Subsequently, the amphiphilic grafted chitosan is uniformly dispersed with plasma-pretreated polymer resin and silver precursor in a deep eutectic solvent, and nano-silver is generated by in-situ reduction, effectively solving the problems of nanoparticle aggregation and interfacial compatibility. Based on this, an antibacterial composite material with both long-lasting antibacterial effect and excellent mechanical properties is obtained through melt blending and injection molding.

Description

Technical Field

[0001] This invention relates to the field of antibacterial composite materials technology, specifically to antibacterial composite materials doped with nano-silver / chitosan nanofillers and their preparation methods. Background Technology

[0002] In fields such as food preservation, medical packaging, and aquatic product transportation, material contamination and functional failure caused by microbial growth have always been core issues that urgently need to be addressed. This is especially true in the transportation of live aquatic products, where the imbalance of the microecology in the transport water leads to the proliferation of bacteria and fungi, significantly reducing the survival rate of aquatic products and causing serious economic losses. Therefore, developing composite materials that combine long-lasting antibacterial properties with excellent mechanical stability has become a key direction for meeting the high-end needs of these fields.

[0003] Currently, the preparation of antibacterial composite materials mostly uses polymers as the matrix, achieving functionalization through the doping of nano-antibacterial agents (such as nano-silver and zinc oxide). Among them, nano-silver has become one of the most widely used antibacterial components due to its broad antibacterial spectrum and high bactericidal efficiency; while chitosan, as a natural polysaccharide material, not only possesses certain antibacterial activity and biocompatibility, but its amino and hydroxyl groups on its molecular chain can also coordinate with metal ions, making it regarded as an ideal carrier for nano-silver. However, existing nano-silver / chitosan-polymer composite systems still face two major bottlenecks in practical applications:

[0004] Firstly, nanoparticles exhibit poor agglomeration and interfacial compatibility. Chitosan molecules have strong hydrogen bonds, and their hydrophilicity differs significantly from the polarity of most hydrophobic polymer matrices (such as polyethylene and polylactic acid), leading to easy agglomeration during direct blending. Simultaneously, nanosilver has high surface energy; without an effective dispersion mechanism, it easily forms large aggregates during the composite process, reducing antibacterial efficiency and disrupting the continuity of the polymer matrix, resulting in a significant decrease in the material's mechanical properties. To improve compatibility, existing technologies often employ surfactant modification or coupling agent treatment; however, these methods suffer from problems such as easy precipitation of the modifier and weak interfacial bonding, making it difficult to achieve long-term stable dispersion effects.

[0005] Secondly, its antibacterial properties are short-lived and pose high environmental risks. In traditional composite processes, nano-silver is mostly added to the system through physical mixing, lacking a strong bond with the carrier and matrix. It is easily lost during use through dissolution and detachment. On the one hand, the rapid release of nano-silver leads to a sharp drop in antibacterial activity in the short term, failing to meet the requirements for long-term use; on the other hand, excessive release of nano-silver into the environment may pose potential risks to aquatic ecosystems and human health, which is inconsistent with the development trend of green materials.

[0006] In summary, the current technical shortcomings of nano-silver / chitosan-polymer antibacterial composites in terms of dispersibility, interfacial bonding strength, and long-lasting antibacterial properties limit their application in high-end fields. Therefore, developing a preparation method that can simultaneously solve the problems of nanoparticle agglomeration, poor interfacial compatibility, and short-term antibacterial effect, and achieving synergistic optimization of the composite material in terms of "long-lasting antibacterial effect, excellent mechanical properties, and environmental safety" has become an urgent need in this field. Summary of the Invention

[0007] The technical problem this invention aims to solve is to overcome the shortcomings of existing technologies and provide an antibacterial composite material of nano-silver / chitosan nanofiller doped with polymer and its preparation method. This is achieved by amphiphilic grafting modification of chitosan, simultaneously grafting hydrophobic segments compatible with the polymer matrix and hydrophilic groups with strong coordination ability to silver ions, forming a "molecular bridge" structure. Subsequently, the amphiphilic grafted chitosan is uniformly dispersed with plasma-pretreated polymer resin and a silver precursor in a deep eutectic solvent, and nano-silver is generated through in-situ reduction, effectively solving the problems of nanoparticle aggregation and interfacial compatibility. Based on this, an antibacterial composite material with both long-lasting antibacterial effect and excellent mechanical properties is obtained through melt blending and injection molding.

[0008] The technical solution of this invention is as follows:

[0009] On one hand, the present invention provides a method for preparing an antibacterial composite material of a nano-silver / chitosan nanofiller-doped polymer, comprising the following steps:

[0010] S1 Preparation of amphiphilic grafted modified chitosan;

[0011] S2 disperses amphiphilic grafted modified chitosan and silver nitrate in a deep eutectic solvent to form a uniform suspension. Then, a reducing agent is added to carry out an in-situ reduction reaction. After the reaction is completed, solid-liquid separation and drying are performed, and the powder is ground to obtain nano-silver / chitosan nanofiller powder.

[0012] S3 pre-treats the polymer resin by plasma etching, mixes it evenly with nano silver / chitosan nanofiller powder, then melt-blends and extrudes to granulate, to obtain antibacterial composite material masterbatch;

[0013] S4 mixes antibacterial composite material masterbatch with polymer resin and then injection molds it to obtain an antibacterial composite material doped with nano-silver / chitosan nanofiller.

[0014] Preferably, step S1 specifically includes the following steps:

[0015] (1) Grafting of hydrophobic segments of chitosan

[0016] (1-1) Prepare chitosan solution;

[0017] (1-2) Add the initiator to the chitosan solution under a nitrogen atmosphere, heat to 60-70℃, and stir for 60-80 min;

[0018] (1-3) Prepare a PEO ethanol solution and add it dropwise to the solution obtained in step (1-2). After the addition is complete, maintain the reaction at 60-70℃ under a nitrogen atmosphere for 6-8 hours.

[0019] (1-4) After the reaction is complete, the reaction solution is cooled to room temperature and the pH is adjusted to 6.5-7 to precipitate the grafted product; the precipitate is collected by suction filtration, washed, and vacuum dried to obtain the hydrophobic modified chitosan intermediate;

[0020] (2) Grafting of hydrophilic chelate segments

[0021] (2-1) The hydrophobically modified chitosan intermediate was uniformly dispersed in deionized water to obtain a dispersion. The pH was adjusted to 9-9.5, and then a crosslinking agent was added. The temperature was raised to 55-65℃ and stirred for 2-3 hours.

[0022] (2-2) Dissolve iminodiacetic acid (IDA) in deionized water, adjust the pH to 8.5-9, and prepare an iminodiacetic acid salt solution; add the iminodiacetic acid salt solution dropwise to the reaction solution in step (2-1), and after the addition is complete, raise the temperature to 60-65℃ and stir the reaction for 6-8 hours, maintaining the pH at 8.5-9 during the process;

[0023] (2-3) After the reaction is complete, the reaction solution is cooled to room temperature, the precipitate is collected by filtration, washed and dried under vacuum to obtain amphiphilic grafted modified chitosan.

[0024] Preferably, in step (1-1), the concentration of the chitosan solution is 0.05-0.1 g / mL; in step (1-2), the initiator is potassium persulfate, which is 5-8% of the mass of chitosan in the chitosan solution; in step (1-3), the mass ratio of PEO in the PEO ethanol solution to chitosan in the chitosan solution is (1.5-1.8):1, and the concentration of the PEO ethanol solution is 0.3-0.5 g / mL.

[0025] Preferably, in step (2-1), the concentration of the hydrophobic modified chitosan intermediate in the dispersion is 0.05-0.1 g / mL; the crosslinking agent is epichlorohydrin, and the mass ratio of the crosslinking agent to the hydrophobic modified chitosan intermediate is (0.75-1):1; in step (2-2), the mass ratio of iminodiacetic acid to the hydrophobic modified chitosan intermediate is (1.25-1.5):1; and the mass-volume ratio of iminodiacetic acid to deionized water is (10-15) g:80 mL.

[0026] Preferably, in step S2, the mass ratio of amphiphilic grafted modified chitosan to silver nitrate is (10-12):1; the eutectic solvent includes ethylene glycol and choline chloride in a volume ratio of (1-2):1; the reducing agent is ascorbic acid, and the molar ratio of ascorbic acid to silver nitrate is (1.5-2):1.

[0027] Preferably, in steps S3 and S4, the polymer resin is polyethylene (PE); in step S3, the specific operation of plasma etching pretreatment of the polymer resin is as follows: using argon-oxygen mixed plasma with a volume ratio of (3-4):1, and treating for 3-5 minutes under the conditions of power 80-100W and pressure 5-8Pa.

[0028] Preferably, in step S3, the mass ratio of polymer resin to nano-silver / chitosan nanofiller powder is (90-95):(5-10).

[0029] Preferably, in step S3, a twin-screw extruder is used to perform melt blending at extrusion temperatures of 145°C, 150°C, and 155°C and a screw speed of 350-400 r / min.

[0030] Preferably, in step S4, the amount of antibacterial composite material masterbatch added is 1-5 wt.%; the injection molding temperature is 140℃, 145℃, and 150℃ respectively; the injection pressure is 65-70 MPa; and the screw speed is 300-400 r / min.

[0031] On the other hand, the present invention provides an antibacterial composite material of nano-silver / chitosan nanofiller doped polymer, which is prepared by the above-mentioned preparation method of the antibacterial composite material of nano-silver / chitosan nanofiller doped polymer.

[0032] Compared with the prior art, the present invention has the following advantages:

[0033] This invention first modifies chitosan through amphiphilic grafting, simultaneously grafting hydrophobic segments compatible with the polymer matrix and hydrophilic groups with strong coordination ability for silver ions, forming a "molecular bridge" structure. Then, the amphiphilic grafted chitosan is uniformly dispersed with plasma-pretreated polymer resin and a silver precursor in a deep eutectic solvent, and nano-silver is generated through in-situ reduction, effectively solving the problems of nanoparticle aggregation and interfacial compatibility. Based on this, an antibacterial composite material with both long-lasting antibacterial effect and excellent mechanical properties is obtained through melt blending and injection molding. This material achieves a strong bond between nano-silver, chitosan, and the polymer matrix at the molecular level through the stable coordination of nano-silver and amphiphilic grafted chitosan. This not only effectively inhibits the aggregation of nano-silver and its precipitation during later use, but also enables the controllable and long-lasting release of silver ions through its coordination groups, thus providing excellent and long-lasting antibacterial performance, extending the antibacterial period, and reducing environmental risks. When applied to live aquatic product transport packaging (such as high-transparency PE film), it can significantly inhibit the growth of microorganisms in the transport water while maintaining the necessary mechanical properties and sealing strength of the material, thereby improving the survival rate and health of live fish and meeting the clear requirements of high-end logistics packaging for long-term safety and functional integration. Attached Figure Description

[0034] Figure 1 This is a schematic diagram of the preparation method of the antibacterial composite material of nano-silver / chitosan nanofiller doped polymer of the present invention.

[0035] Figure 2 These are SEM (a) and TEM (b) images of the antibacterial composite material of nano-silver / chitosan nanofiller-doped polymer prepared in Example 5 of this invention.

[0036] Figure 3 The thermogravimetric analysis curve is shown for the antibacterial composite material of nano-silver / chitosan nanofiller doped with polymer prepared in Example 5 of this invention.

[0037] Figure 4 The DSC heating curves (a) and cooling curves (b) are of the antibacterial composite materials of pure PE resin in Comparative Example 1 and the nano-silver / chitosan nanofiller-doped polymers in Examples 1-7 of this invention.

[0038] Figure 5These are antibacterial composite materials of nano-silver / chitosan nanofiller-doped polymers from Examples 1 and 5 of the present invention, and pure PE resin from Comparative Example 1, showing their antibacterial effects against Candida albicans, Escherichia coli, and Staphylococcus aureus. Figures (a), (b), and (c) show the colony counts of Candida albicans at the start of the experiment, 3 days after the start of the experiment, and 6 days after the start of the experiment, respectively. Figures (d), (e), and (f) show the colony counts of Escherichia coli at the start of the experiment, 3 days after the start of the experiment, and 6 days after the start of the experiment, respectively. Figures (g), (h), and (i) show the colony counts of Staphylococcus aureus at the start of the experiment, 3 days after the start of the experiment, and 6 days after the start of the experiment, respectively. Detailed Implementation

[0039] To enable those skilled in the art to better understand the technical solutions of this invention, the technical solutions of this invention will be clearly and completely described below in conjunction with the embodiments of this invention.

[0040] Example 1

[0041] The method for preparing the antibacterial composite material of nano-silver / chitosan nanofiller-doped polymer in this embodiment includes the following steps:

[0042] S1 Preparation of Amphiphilic Grafted Modified Chitosan

[0043] (1) Grafting of hydrophobic segments of chitosan

[0044] (1-1) Preparation of chitosan solution: Weigh 10g of chitosan powder, add it to a 500mL four-necked flask, add 200mL of deionized water, stir well, add 1mol / L HCl solution dropwise, adjust the pH to 4, stir in a 30℃ water bath for 30min to completely dissolve the chitosan and obtain the chitosan solution.

[0045] (1-2) Introduce nitrogen gas (flow rate 50 mL / min) and purge for 30 min to remove oxygen from the system; add 0.5 g potassium persulfate to the chitosan solution, heat to 70 °C, and stir for 60 min to oxidize the amino / hydroxyl groups on the chitosan molecular chain and generate active free radical sites.

[0046] (1-3) Dissolve 15g of PEO in 50mL of anhydrous ethanol to prepare a homogeneous solution. Add the solution dropwise into a four-necked flask through a constant pressure dropping funnel (dropping rate 1mL / min). After the addition is complete, maintain the reaction at 70℃ under a nitrogen atmosphere for 6h. During this period, maintain the stirring rate at 300r / min to ensure that the PEO and chitosan active free radical sites undergo an addition reaction to form hydrophobic segments.

[0047] (1-4) After the reaction is completed, the reaction solution is cooled to room temperature, and 1 mol / L NaOH solution is added to adjust the pH to 7 so that the grafted product precipitates out. The precipitate is collected by suction filtration and washed three times with deionized water (100 mL each time) to remove unreacted chitosan and salt impurities. The precipitate is placed in a vacuum drying oven and dried at 60 °C for 12 h to obtain the hydrophobic modified chitosan intermediate (denoted as CS-PEO-1).

[0048] (2) Grafting of hydrophilic chelate segments

[0049] (2-1) Add 8g of CS-PEO-1 to a 500mL four-necked flask, add 150mL of deionized water, stir at 30℃ for 30min to make it uniformly dispersed in deionized water to obtain a dispersion; add 1mol / L HCl solution dropwise to adjust the pH to 9, then add 6g of epichlorohydrin, heat to 55℃, stir for 2h, so that the epoxy group of epichlorohydrin reacts with the remaining hydroxyl group on the CS-PEO-1 molecular chain to undergo a ring-opening reaction, introducing an active chloromethyl site (-CH2Cl).

[0050] (2-2) Dissolve 10g of IDA in 80mL of deionized water and adjust the pH to 9 with 1mol / L NaOH solution to prepare an IDA sodium salt solution. Add the IDA sodium salt solution dropwise into a four-necked flask through a constant pressure dropping funnel (dropping rate 1.5mL / min). After the addition is complete, heat to 65℃ and stir for 8h, maintaining the pH at 9 during the reaction. This allows the amino group of IDA to undergo a nucleophilic substitution reaction with the active chloromethyl site on CS-PEO-1, grafting to form a -N(CH2COOH)2 hydrophilic chelating group.

[0051] (2-3) After the reaction is completed, the reaction solution is cooled to room temperature, the precipitate is collected by filtration, and the precipitate is washed twice with 1 mol / L HCl solution (80 mL each time) to remove excess IDA. Then it is washed with deionized water until the conductivity of the washing solution is ≤50 μS / cm. The precipitate is placed in a vacuum drying oven and dried at 50℃ for 16 h to obtain amphiphilic grafted modified chitosan (denoted as CS-PEO-IDA-1).

[0052] S2 Preparation of Nano-Silver / Chitosan Nanofiller Powder

[0053] 1 g of CS-PEO-IDA-1 and 0.1 g of silver nitrate were dispersed in a deep eutectic solvent composed of ethylene glycol and choline chloride in a volume ratio of 2:1. The mixture was stirred in a water bath at 60 °C for 2 h to form a homogeneous suspension. Then, 0.17 g of ascorbic acid was added, and the mixture was stirred at 60 °C for 1 h to carry out an in-situ reduction reaction. After the reaction was completed, the solvent was removed by rotary evaporation. The resulting solid was vacuum dried at 50 °C and ground to obtain nano-silver / chitosan nanofiller powder.

[0054] S3 Preparation of Antibacterial Composite Material Masterbatch

[0055] Under conditions of 100W power and 5Pa pressure, 20g of low-density polyethylene (LDPE) powder was subjected to plasma etching pretreatment using an argon-oxygen mixed plasma with a volume ratio of 3:1 for 3 minutes, resulting in the formation of active groups such as hydroxyl and carboxyl groups on the LDPE surface. The plasma-etched LDPE powder was then uniformly mixed with 1.06g of nano-silver / chitosan nanofiller powder. The mixture was melt-blended using a twin-screw extruder at extrusion temperatures of 145℃, 150℃, and 155℃, and a screw speed of 350r / min. After extrusion, water cooling, and pelletizing, antibacterial composite masterbatch was obtained.

[0056] S4 Preparation of Antibacterial Composites of Nano-Silver / Chitosan Nanofiller Doped Polymers

[0057] Using a DSMXplore 5&15 micro-blender, 1g of antibacterial composite masterbatch was fully melt-blended with 99g of PE resin, and then injection molded in a DSMXplore 10cc micro-injection molding machine. The injection temperatures were 140℃, 145℃, and 150℃, the injection pressure was 70MPa, and the screw speed was 350r / min, to obtain an antibacterial composite material of nano-silver / chitosan nanofiller-doped polymer.

[0058] Example 2

[0059] The difference from Example 1 is that in step S4, the amount of antibacterial composite material masterbatch added is 2g and the amount of PE resin added is 98g.

[0060] Example 3

[0061] The difference from Example 1 is that in step S4, the amount of antibacterial composite material masterbatch added is 3g and the amount of PE resin added is 97g.

[0062] Example 4

[0063] The difference from Example 1 is that in step S4, the amount of antibacterial composite material masterbatch added is 4g and the amount of PE resin added is 96g.

[0064] Example 5

[0065] The difference from Example 1 is that in step S4, the amount of antibacterial composite material masterbatch added is 5g and the amount of PE resin added is 95g.

[0066] Example 6

[0067] The method for preparing the antibacterial composite material of nano-silver / chitosan nanofiller-doped polymer in this embodiment includes the following steps:

[0068] S1 Preparation of Amphiphilic Grafted Modified Chitosan

[0069] (1) Grafting of hydrophobic segments of chitosan

[0070] (1-1) Preparation of chitosan solution: Weigh 20g of chitosan powder, add it to a 500mL four-necked flask, add 200mL of deionized water, stir well, add 1mol / L HCl solution dropwise, adjust the pH to 4, stir in a 30℃ water bath for 30min to completely dissolve the chitosan and obtain the chitosan solution.

[0071] (1-2) Introduce nitrogen gas (flow rate 50 mL / min) and purge for 30 min to remove oxygen from the system; add 1.2 g potassium persulfate to the chitosan solution, heat to 60 °C, and stir for 80 min to oxidize the amino / hydroxyl groups on the chitosan molecular chain and generate active free radical sites.

[0072] (1-3) Dissolve 36g of PEO in 100mL of anhydrous ethanol to prepare a homogeneous solution. Add the solution dropwise into a four-necked flask through a constant pressure dropping funnel (dropping rate 1mL / min). After the addition is complete, maintain the reaction at 60℃ under a nitrogen atmosphere for 8h. During this period, maintain the stirring rate at 300r / min to ensure that the PEO and chitosan active free radical sites undergo an addition reaction to form hydrophobic segments.

[0073] (1-4) After the reaction is completed, the reaction solution is cooled to room temperature, and 1 mol / L NaOH solution is added to adjust the pH to 6.5 so that the grafted product precipitates out. The precipitate is collected by vacuum filtration and washed three times with deionized water (100 mL each time) to remove unreacted chitosan and salt impurities. The precipitate is placed in a vacuum drying oven and dried at 60℃ for 12 h to obtain the hydrophobic modified chitosan intermediate (denoted as CS-PEO-2).

[0074] (2) Grafting of hydrophilic chelate segments

[0075] (2-1) Add 8g of CS-PEO-2 to a 500mL four-necked flask, add 80mL of deionized water, stir at 30℃ for 30min to make it uniformly dispersed in deionized water to obtain a dispersion; add 1mol / L HCl solution dropwise to adjust the pH to 9.5, then add 8g of epichlorohydrin, heat to 65℃, stir for 2h, so that the epoxy group of epichlorohydrin reacts with the remaining hydroxyl group on the CS-PEO-2 molecular chain to undergo a ring-opening reaction, introducing an active chloromethyl site (-CH2Cl).

[0076] (2-2) Dissolve 12g of IDA in 80mL of deionized water and adjust the pH to 8.5 with 1mol / L NaOH solution to prepare an IDA sodium salt solution. Add the IDA sodium salt solution dropwise into a four-necked flask through a constant pressure dropping funnel (dropping rate 1.5mL / min). After the addition is complete, heat to 60℃ and stir the reaction for 7h, maintaining the pH at 8.5 during the reaction. This allows the amino group of IDA to undergo a nucleophilic substitution reaction with the active chloromethyl site on CS-PEO-2, grafting to form a -N(CH2COOH)2 hydrophilic chelating group.

[0077] (2-3) After the reaction is completed, the reaction solution is cooled to room temperature, the precipitate is collected by filtration, and the precipitate is washed twice with 1 mol / L HCl solution (80 mL each time) to remove excess IDA. Then it is washed with deionized water until the conductivity of the washing solution is ≤50 μS / cm. The precipitate is placed in a vacuum drying oven and dried at 50℃ for 16 h to obtain amphiphilic grafted modified chitosan (denoted as CS-PEO-IDA-2).

[0078] S2 Preparation of Nano-Silver / Chitosan Nanofiller Powder

[0079] 1 g of CS-PEO-IDA-2 and 0.1 g of silver nitrate were dispersed in a deep eutectic solvent composed of ethylene glycol and choline chloride in a volume ratio of 1:1. The mixture was stirred in a water bath at 60 °C for 2 h to form a homogeneous suspension. Then, 0.16 g of ascorbic acid was added, and the mixture was stirred at 60 °C for 1 h to carry out an in-situ reduction reaction. After the reaction was completed, the solvent was removed by rotary evaporation. The resulting solid was vacuum dried at 50 °C and ground to obtain nano-silver / chitosan nanofiller powder.

[0080] S3 Preparation of Antibacterial Composite Material Masterbatch

[0081] Under conditions of 80W power and 8Pa pressure, 20g of low-density polyethylene (LDPE) powder was subjected to plasma etching pretreatment using an argon-oxygen mixed plasma with a volume ratio of 3:1 for 4 minutes, resulting in the formation of active groups such as hydroxyl and carboxyl groups on the LDPE surface. The plasma-etched LDPE powder was then uniformly mixed with 1.1g of nano-silver / chitosan nanofiller powder. The mixture was melt-blended using a twin-screw extruder at extrusion temperatures of 145℃, 150℃, and 155℃, and a screw speed of 380r / min. After extrusion, water cooling, and pelletizing, antibacterial composite masterbatch was obtained.

[0082] S4 Preparation of Antibacterial Composites of Nano-Silver / Chitosan Nanofiller Doped Polymers

[0083] Using a DSMXplore 5&15 micro-blender, 1g of antibacterial composite masterbatch was fully melt-blended with 99g of PE resin, and then injection-molded in a DSMXplore 10cc micro-injection molding machine. The injection temperatures were 140℃, 145℃, and 150℃, the injection pressure was 68MPa, and the screw speed was 300r / min, resulting in an antibacterial composite material of nano-silver / chitosan nanofiller-doped polymer.

[0084] Example 7

[0085] The method for preparing the antibacterial composite material of nano-silver / chitosan nanofiller-doped polymer in this embodiment includes the following steps:

[0086] S1 Preparation of Amphiphilic Grafted Modified Chitosan

[0087] (1) Grafting of hydrophobic segments of chitosan

[0088] (1-1) Preparation of chitosan solution: Weigh 10g of chitosan powder, add it to a 500mL four-necked flask, add 200mL of deionized water, stir well, add 1mol / L HCl solution dropwise, adjust the pH to 4, stir in a 30℃ water bath for 30min to completely dissolve the chitosan and obtain the chitosan solution.

[0089] (1-2) Introduce nitrogen gas (flow rate 50 mL / min) and purge for 30 min to remove oxygen from the system; add 0.8 g potassium persulfate to the chitosan solution, heat to 65 °C, and stir for 70 min to oxidize the amino / hydroxyl groups on the chitosan molecular chain and generate active free radical sites.

[0090] (1-3) Dissolve 16g of PEO in 35mL of anhydrous ethanol to prepare a homogeneous solution. Then, drop the solution into a four-necked flask through a constant pressure dropping funnel (dropping rate 1mL / min). After the addition is complete, maintain the reaction at 65℃ under a nitrogen atmosphere for 7h. During this period, the stirring rate is maintained at 300r / min to ensure that the PEO and the active free radical sites of chitosan undergo an addition reaction to form hydrophobic segments.

[0091] (1-4) After the reaction is completed, the reaction solution is cooled to room temperature, and 1 mol / L NaOH solution is added to adjust the pH to 7 so that the grafted product precipitates out. The precipitate is collected by suction filtration and washed three times with deionized water (100 mL each time) to remove unreacted chitosan and salt impurities. The precipitate is placed in a vacuum drying oven and dried at 60 °C for 12 h to obtain the hydrophobic modified chitosan intermediate (denoted as CS-PEO-3).

[0092] (2) Grafting of hydrophilic chelate segments

[0093] (2-1) Add 8g of CS-PEO-3 to a 500mL four-necked flask, add 150mL of deionized water, stir at 30℃ for 30min to make it uniformly dispersed in deionized water to obtain a dispersion; add 1mol / L HCl solution dropwise to adjust the pH to 9, then add 6g of epichlorohydrin, heat to 60℃, stir for 3h, so that the epoxy group of epichlorohydrin reacts with the remaining hydroxyl group on the CS-PEO-3 molecular chain to undergo a ring-opening reaction, introducing an active chloromethyl site (-CH2Cl).

[0094] (2-2) Dissolve 10g of IDA in 80mL of deionized water and adjust the pH to 9 with 1mol / L NaOH solution to prepare an IDA sodium salt solution. Add the IDA sodium salt solution dropwise into a four-necked flask through a constant pressure dropping funnel (dropping rate 1.5mL / min). After the addition is complete, heat to 62℃ and stir for 6h, maintaining the pH at 9 during the reaction. This allows the amino group of IDA to undergo a nucleophilic substitution reaction with the active chloromethyl site on CS-PEO-3, grafting to form a -N(CH2COOH)2 hydrophilic chelating group.

[0095] (2-3) After the reaction is completed, the reaction solution is cooled to room temperature, the precipitate is collected by filtration, and the precipitate is washed twice with 1 mol / L HCl solution (80 mL each time) to remove excess IDA. Then it is washed with deionized water until the conductivity of the washing solution is ≤50 μS / cm. The precipitate is placed in a vacuum drying oven and dried at 50℃ for 16 h to obtain amphiphilic grafted modified chitosan (denoted as CS-PEO-IDA-3).

[0096] S2 Preparation of Nano-Silver / Chitosan Nanofiller Powder

[0097] 1.2 g of CS-PEO-IDA-3 and 0.1 g of silver nitrate were dispersed in a deep eutectic solvent composed of ethylene glycol and choline chloride in a volume ratio of 1.5:1. The mixture was stirred in a water bath at 60 °C for 2 h to form a homogeneous suspension. Then, 0.21 g of ascorbic acid was added, and the mixture was stirred at 60 °C for 1.5 h to carry out an in-situ reduction reaction. After the reaction was completed, the solvent was removed by rotary evaporation. The resulting solid was vacuum dried at 50 °C and ground to obtain nano-silver / chitosan nanofiller powder.

[0098] S3 Preparation of Antibacterial Composite Material Masterbatch

[0099] Under conditions of 90W power and 6Pa pressure, 20g of low-density polyethylene (LDPE) powder was subjected to plasma etching pretreatment using an argon-oxygen mixed plasma with a volume ratio of 4:1 for 5 minutes, resulting in the formation of active groups such as hydroxyl and carboxyl groups on the LDPE surface. The plasma-etched LDPE powder was then uniformly mixed with 2.22g of nano-silver / chitosan nanofiller powder. The mixture was melt-blended using a twin-screw extruder at extrusion temperatures of 145℃, 150℃, and 155℃, and a screw speed of 400r / min. After extrusion, water cooling, and pelletizing, the antibacterial composite masterbatch was obtained.

[0100] S4 Preparation of Antibacterial Composites of Nano-Silver / Chitosan Nanofiller Doped Polymers

[0101] Using a DSMXplore 5&15 micro-blender, 1g of antibacterial composite masterbatch was fully melt-blended with 99g of PE resin, and then injection-molded in a DSMXplore 10cc micro-injection molding machine. The injection temperatures were 140℃, 145℃, and 150℃, the injection pressure was 65MPa, and the screw speed was 400r / min, resulting in an antibacterial composite material of nano-silver / chitosan nanofiller-doped polymer.

[0102] Comparative Example 1

[0103] Comparative Example 1 used pure PE resin.

[0104] Comparative Example 2

[0105] The difference from Example 1 is that step S1 is omitted, and in step S2, an equal amount of chitosan powder is used instead of CS-PEO-IDA-1.

[0106] Comparative Example 3

[0107] The difference from Example 1 is that step S2 is omitted, and in step S3, an equal amount of CS-PEO-IDA-1 is used instead of the nano silver / chitosan nanofiller powder.

[0108] Comparative Example 4

[0109] The difference from Example 1 is that in step S3, the LDPE powder is not subjected to plasma etching pretreatment.

[0110] Examples 1-7 and Comparative Examples 1-4 were injection molded into dumbbell-shaped specimens with a length of 75 mm, a width of 4 mm, and a thickness of 2 mm, with a narrow central section of 25 mm. The crystallinity, mechanical properties, and antibacterial properties of each specimen were tested. Crystallinity was tested using differential scanning calorimetry (DSC), which yielded parameters such as melt temperature (Tm), crystallization temperature (Tc), enthalpy of melt (ΔHm), and enthalpy of crystallization (ΔHc). Based on these parameters, the degree of crystallinity (Xt), half-crystallization time (T1 / 2), Avrami exponent (n), and crystallization rate constant (Kc) were calculated. Mechanical properties were tested according to GB / T 1040.2-2022 "Determination of tensile properties of plastics—Part 2: Test conditions for molded and extruded plastics". Antibacterial properties were tested according to GB / T 21510-2024 "Test method for antibacterial properties of nano-inorganic materials" and ISO 22196:2011 "Measurement of antibacterial activity of plastics and other non-porous surfaces". The test results are shown in Table 1-3:

[0111] Table 1. Crystallization performance test results of injection-molded specimens from Examples 1-7 and Comparative Examples 1-4

[0112]

[0113] Table 2. Mechanical property test results of injection-molded specimens from Examples 1-7 and Comparative Examples 1-4

[0114]

[0115] Table 3. Antibacterial performance test results of injection-molded specimens from Examples 1-7 and Comparative Examples 1-4

[0116]

[0117] As can be seen from the data in the table, the antibacterial composite material of nano-silver / chitosan nanofiller doped with polymer prepared in this invention exhibits excellent antibacterial efficacy. All examples demonstrate highly efficient immediate antibacterial activity (≥97%) and good antibacterial durability, with antibacterial performance retention generally exceeding 94% after aging. Their antibacterial rate far exceeds the effectiveness standard (≥90%), confirming that the material possesses long-lasting antibacterial properties. Among them, Example 5 achieved the best synergistic balance in antibacterial performance, mechanical strength, and crystallinity: its immediate antibacterial rate reached 99.6%, maintaining 98.5% after aging, while also possessing optimal tensile strength (70.00 MPa) and crystallinity. This confirms that under the optimized process parameters of this invention, the material successfully achieved synergistic enhancement of both structure and function.

[0118] The data in the table also shows that Comparative Example 1, using unmodified pure PE resin, exhibits performance at the baseline level and lacks any antibacterial function. Comparative Example 2 uses ordinary chitosan; due to the poor compatibility between unmodified chitosan and PE resin, and its lack of effective complexation and sustained-release ability for silver ions, the antibacterial components are unevenly dispersed and easily lost, resulting in low and short-lasting antibacterial performance. Comparative Example 3 lacks nano-silver as a core antibacterial substance, relying solely on the weak antibacterial properties of chitosan itself; therefore, the antibacterial effect of the resulting composite material falls far short of the standards for high efficiency and long-lasting effectiveness. In Comparative Example 4, the LDPE was not pretreated by plasma etching. Because the LDPE matrix surface was not activated, the interfacial bonding force between the nanofiller and the matrix was very weak, directly leading to easy detachment of the antibacterial components and poor long-lasting effectiveness. Simultaneously, the material's mechanical properties were also impaired due to interfacial defects.

[0119] In summary, the failures of Comparative Examples 1-4 demonstrate, from the opposite perspective, that the complete process of this invention is interconnected. Among these, amphiphilic grafted modified chitosan is the key carrier for solving compatibility and sustained release, nano-silver is the core substance providing highly efficient antibacterial properties, and plasma etching pretreatment is a necessary prerequisite for achieving a strong interfacial bond. These three elements work synergistically and are indispensable, collectively forming the technical foundation for obtaining composite materials that possess both highly efficient and long-lasting antibacterial properties and excellent mechanical properties.

[0120] Figure 2 The SEM and TEM characterization results of the antibacterial composite material of nano-silver / chitosan nanofiller-doped polymer prepared in Example 5 of this invention are shown. Figure 2 As shown in (a), the nano-silver / chitosan nanofiller exhibits a uniform spherical morphology with a diameter of 200-300 nm, indicating that the high dispersion and stable loading of nano-silver in the chitosan carrier were successfully achieved through amphiphilic grafting modification and in-situ reduction process. Figure 2 (b) Further, it is shown that the silver / chitosan nanofiller is uniformly embedded in the polymer matrix without obvious agglomeration or phase separation, proving that the "molecular bridge" design and plasma etching pretreatment process effectively improve interfacial compatibility and form a structurally stable composite material system. This uniformly dispersed composite structure not only provides the material with durable and efficient antibacterial properties, but also helps to maintain and improve the mechanical integrity and overall performance of the matrix.

[0121] Figure 3Thermogravimetric analysis (TGA) curves of the antibacterial composite material prepared in Example 5, doped with 5 wt.% antibacterial composite masterbatch, are shown. It can be seen that the thermal decomposition curves of this antibacterial composite material and pure PE resin exhibit similar characteristic trends, with minimal residual weight change. The antibacterial composite material maintains a temperature exceeding 325°C even with a 5% weight loss, indicating good thermal stability at high temperatures. This analysis demonstrates that the incorporation of nano-silver / chitosan nanofillers improves and enhances the thermal stability of the polymer matrix. The presence of nano-silver particles helps disperse heat and improve the material's heat resistance, while the biocompatibility and heat resistance of chitosan further enhance the overall thermal stability of the material. This allows the antibacterial composite material to maintain high thermal stability even at high temperatures, making it suitable for a wider range of applications.

[0122] Figure 4 Figures (a) and (b) compare the DSC curves of pure PE resin in Comparative Example 1 with the antibacterial composites with different contents of antibacterial composite masterbatch in Examples 1-7. As shown in the figures, the melting peak and crystallization peak of pure PE resin are located at 125.2℃ and 149.5℃, respectively. After incorporating nano-silver / chitosan nanofiller, the crystallization peak is significantly enhanced, and the crystallization temperature (Tc) shows a trend of first increasing and then decreasing with the increase of the amount of nano-silver / chitosan nanofiller: increasing from 153.3℃ in Example 1 to 154.3℃ in Example 2, and then gradually decreasing to 152.2℃ in Example 5. This result indicates that an appropriate amount of nanofiller can act as an effective heterogeneous nucleating agent, increasing the crystallization temperature.

[0123] However, the peak macroscopic mechanical properties of the material do not coincide with the optimal crystallization temperature. As shown in Table 2, the tensile strength and tensile modulus of the material show a continuous upward trend with increasing filler content, increasing from 61.81 MPa and 473.21 MPa in Example 1 to 70.00 MPa and 590.00 MPa in Example 5. This phenomenon is attributed to the contribution of the dual effect of the nanofiller: the lower addition amount (2 wt.%) mainly optimizes crystallization nucleation (increasing Tc), while the higher addition amount (5 wt.%) dominates the improvement of the final mechanical properties through a more significant interfacial reinforcement effect. Meanwhile, the highest crystallinity (Xt=38.5%) and the shortest half-crystallization period (T1 / 2=62.0 s) in Example 5 provide the structural basis for its excellent mechanical properties.

[0124] The above results confirm that the process of this invention can impart long-lasting antibacterial function to materials while precisely controlling crystallization kinetics and significantly improving mechanical properties, achieving synergistic enhancement among the three. In particular, Example 5 achieved the best balance in terms of crystallinity, crystallization rate, and overall mechanical properties.

[0125] The antibacterial properties of the nano-silver / chitosan nanofiller-doped polymer antibacterial composites in Examples 1 and 5, and the pure PE resin in Comparative Example 1, were evaluated through inhibition experiments against Staphylococcus aureus, Escherichia coli, and Candida albicans. The inhibition experiments were conducted using a combination of shaking co-culture and plate count method. The specific procedures were as follows: First, potato dextrose broth (PDB) liquid medium and potato dextrose agar (PDA) solid medium were prepared and sterilized under high temperature and high pressure (PDB liquid medium 121℃, 20 min; PDA solid medium 115℃, 20 min) for later use. Single colonies of each test bacterium were picked from fresh plates and inoculated into PDB liquid medium. The culture was carried out in a constant temperature shaker (bacteria 37℃, fungi 28℃, 200 rpm) until the logarithmic growth phase. The bacterial suspension concentration was adjusted to 1×10⁻⁶ with sterile PBS solution. 6 CFU / mL. Samples from Examples 1, 5, and Comparative Example 1 were sterilized by UV irradiation for at least 30 minutes. The experiment was divided into Comparative Example 1, Example 1, and Example 5 groups, with three parallel experiments in each group. The sterilized samples were transferred to sterile Erlenmeyer flasks, and 70 mL of sterile PBS solution and 5 mL of the above bacterial suspension were added sequentially. The flasks were then incubated in a constant temperature incubator with shaking for 18 hours (37°C for bacteria, 28°C for fungi). After incubation, the bacterial suspension in the sterile Erlenmeyer flasks was taken and serially diluted 10-fold with sterile PBS. 100 µL of the appropriately diluted bacterial suspension was evenly spread onto the corresponding PDA plates and incubated at constant temperature (37°C for bacteria, 24 hours; 28°C for fungi, 48 hours). The colonies were then photographed and counted, and the inhibition rate of each group was calculated.

[0126] The results are as follows Figure 5As shown, the pure PE resin in Comparative Example 1 had no significant inhibitory effect on the three tested microorganisms. However, the PE samples in Examples 1 and 5, doped with silver / chitosan nanofillers, exhibited significant antibacterial activity, and the effect increased with increasing doping concentration. Specifically, when the doping concentration was 1 wt.%, the inhibition rate of the samples against the three bacterial colonies reached 30-40%; when the doping concentration was increased to 5 wt.%, the antibacterial effect was most prominent, with the inhibition rate further increasing to 70-80%. This result confirms that the antibacterial composite material of silver / chitosan nanofiller-doped polymer prepared by the present invention through amphiphilic grafting modification and in-situ reduction process can effectively exert the potent antibacterial effect of silver nanofillers. From the perspective of its mechanism of action, its excellent antibacterial properties mainly stem from two synergistic effects: first, the silver ions released by the nano-silver can disrupt the integrity of microbial cell membranes and interfere with the normal function of their internal DNA and proteins; second, the amphiphilic grafted modified chitosan can not only regulate the sustained release of silver ions through coordination, but its own positive charge can also generate electrostatic adsorption with the negatively charged bacterial surface, further enhancing the antibacterial effect. Therefore, the nano-silver / chitosan nanofiller-doped polymer antibacterial composite material of this invention provides a reliable solution for achieving long-lasting and highly efficient antibacterial function.

[0127] In summary, this invention, based on an amphiphilic interface design and functional integration strategy, firstly, designs the molecular structure of chitosan, simultaneously grafting hydrophobic segments compatible with the polymer matrix and hydrophilic groups with strong coordination ability for silver ions, constructing an amphiphilic "molecular bridge"; subsequently, it is uniformly dispersed with plasma-pretreated polymer resin and silver precursor in a deep eutectic solvent, and highly dispersed nano-silver is generated by in-situ reduction, effectively solving the problems of nanoparticle aggregation and interface compatibility; through melt blending and injection molding processes, a multifunctional composite material integrating long-lasting antibacterial properties and mechanical reinforcement is finally obtained (e.g., ...). Figure 1 (As shown). When this material is applied to the packaging for transporting live aquatic products and ornamental fish, its amphiphilic interface design and controlled slow-release mechanism ensure continuous inhibition of aquatic microorganisms during long-distance transportation, significantly reducing the risk of infection in fish. Simultaneously, its excellent mechanical properties give the packaging film good air permeability, puncture resistance, and flexibility. This invention, through material design and process innovation, provides a safe, reliable, and monitorable packaging solution for high-end live biological logistics, demonstrating clear application prospects and market potential.

Claims

1. A method for preparing an antibacterial composite material of a nanosilver / chitosan nanofiller doped polymer, characterized in that, The method comprises the following steps: S1: preparing amphiphilic graft-modified chitosan; S2: dispersing the amphiphilic graft-modified chitosan and silver nitrate in a deep eutectic solvent to form a uniform suspension, adding a reducing agent to perform an in-situ reduction reaction, performing solid-liquid separation and drying after the reaction is completed, and grinding to obtain a nano-silver / chitosan nanofiller powder; S3: performing plasma etching pretreatment on a polymer resin, uniformly mixing the nano-silver / chitosan nanofiller powder with the polymer resin, and then performing melt blending and extrusion granulation to obtain antibacterial composite material master batches; S4: mixing the antibacterial composite material master batches with the polymer resin, and performing injection molding to obtain an antibacterial composite material of a nano-silver / chitosan nanofiller doped polymer; Step S1 specifically comprises the following steps: (1) hydrophobic chain segment grafting of chitosan (1-1) preparing a chitosan solution; (1-2) adding an initiator to the chitosan solution under a nitrogen atmosphere, and heating to 60-70 DEG C and stirring for 60-80 min; (1-3) preparing a PEO ethanol solution, and dropping the solution into the solution obtained in step (1-2); after the dropping is completed, the reaction is maintained at 60-70 DEG C and under a nitrogen atmosphere for 6-8 h; (1-4) after the reaction is completed, the reaction liquid is cooled to room temperature, the pH is adjusted to 6.5-7, and the graft product is precipitated; the precipitate is collected by suction filtration and washed and vacuum dried to obtain a hydrophobically modified chitosan intermediate; (2) hydrophilic chelating chain segment grafting (2-1) uniformly dispersing the hydrophobically modified chitosan intermediate in deionized water to obtain a dispersion, adjusting the pH to 9-9.5, and then adding a crosslinking agent and heating to 55-65 DEG C and stirring for 2-3 h; (2-2) dissolving iminodiacetic acid in deionized water, adjusting the pH to 8.5-9, and preparing an iminodiacetic acid salt solution; the iminodiacetic acid salt solution is dropped into the reaction liquid of step (2-1), and after the dropping is completed, the temperature is raised to 60-65 DEG C and the reaction is stirred for 6-8 h, during which the pH is maintained at 8.5-9; (2-3) after the reaction is completed, the reaction liquid is cooled to room temperature, the precipitate is collected by suction filtration and washed and vacuum dried to obtain amphiphilic graft-modified chitosan; In steps S3 and S4, the polymer resin is polyethylene; in step S3, the specific operation of performing plasma etching pretreatment on the polymer resin is as follows: an argon-oxygen mixed plasma with a volume ratio of (3-4):1 is used, and the treatment is performed at a power of 80-100 W and a pressure of 5-8 Pa for 3-5 min.

2. The method for preparing the antibacterial composite material of nano-silver / chitosan nanofiller doped with polymer as described in claim 1, characterized in that, In step (1-1), the concentration of the chitosan solution is 0.05-0.1 g / mL; in step (1-2), the initiator is potassium persulfate, which accounts for 5-8% of the mass of chitosan in the chitosan solution; in step (1-3), the mass ratio of PEO in the PEO ethanol solution to chitosan in the chitosan solution is (1.5-1.8):1, and the concentration of the PEO ethanol solution is 0.3-0.5 g / mL.

3. The method of claim 1, wherein the method is characterized by the steps of: (a) mixing silver nanoparticles and chitosan to form a mixture; (b) adding the mixture to a polymer solution; (c) stirring the mixture and the polymer solution; (d) drying the mixture and the polymer solution; and (e) obtaining the antibacterial composite material. In step (2-1), the concentration of the hydrophobically modified chitosan intermediate in the dispersion is 0.05-0.1 g / mL; the crosslinking agent is epichlorohydrin, and the mass ratio of the hydrophobically modified chitosan intermediate to the crosslinking agent is (0.75-1):1; in step (2-2), the mass ratio of iminodiacetic acid to the hydrophobically modified chitosan intermediate is (1.25-1.5):1; and the mass-volume ratio of iminodiacetic acid to deionized water is (10-15) g:80 mL.

4. The method of claim 1, wherein the method is characterized by the steps of: (a) mixing silver nanoparticles and chitosan to form a mixture; (b) adding the mixture to a polymer solution; (c) stirring the mixture and the polymer solution; (d) drying the mixture and the polymer solution; and (e) obtaining the antibacterial composite material. In step S2, the mass ratio of the amphiphilic graft-modified chitosan to silver nitrate is (10-12):1; the deep eutectic solvent comprises ethylene glycol and choline chloride in a volume ratio of (1-2):1; and the molar ratio of the reducing agent ascorbic acid to silver nitrate is (1.5-2):

1.

5. The method of claim 1, wherein the method is characterized by the steps of: (a) mixing silver nanoparticles and chitosan to form a mixture; (b) adding the mixture to a polymer solution; (c) stirring the mixture and the polymer solution; (d) drying the mixture and the polymer solution; and (e) obtaining the antibacterial composite material. In step S3, the mass ratio of the polymer resin to the nano-silver / chitosan nano-filler powder is (90-95):(5-10).

6. The method for preparing the antibacterial composite material of nano-silver / chitosan nanofiller doped with polymer as described in claim 1, characterized in that, In step S3, a twin-screw extruder is used for melt blending at an extrusion temperature of 145℃, 150℃, or 155℃, and a screw rotation speed of 350-400 r / min.

7. The method for preparing the antibacterial composite material of nano-silver / chitosan nanofiller doped with polymer as described in claim 1, characterized in that, In step S4, the addition amount of the antibacterial composite material master batch is 1-5 wt.%; the injection molding temperature is 140℃, 145℃, or 150℃, the injection pressure is 65-70 MPa, and the screw rotation speed is 300-400 r / min.

8. An antibacterial composite material of a nanosilver / chitosan nanofiller doped polymer, characterized in that, The antibacterial composite material doped with the nano-silver / chitosan nano-filler is prepared by the method as claimed in any one of claims 1-7. In step S2, the mass ratio of the amphiphilic graft-modified chitosan to silver nitrate is (10-12):1; the deep eutectic solvent comprises ethylene glycol and choline chloride in a volume ratio of (1-2):1; and the molar ratio of the reducing agent ascorbic acid to silver nitrate is (1.5-2):

1. In step S3, the mass ratio of the polymer resin to the nano-silver / chitosan nano-filler powder is (90-95):(5-10). In step S3, a twin-screw extruder is used for melt blending at an extrusion temperature of 145℃, 150℃, or 155℃, and a screw rotation speed of 350-400 r / min. In step S4, the addition amount of the antibacterial composite material master batch is 1-5 wt.%; the injection molding temperature is 140℃, 145℃, or 150℃, the injection pressure is 65-70 MPa, and the screw rotation speed is 300-400 r / min. The antibacterial composite material doped with the nano-silver / chitosan nano-filler is prepared by the method as claimed in any one of claims 1-7.

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