Vanillin quaternary phosphonium salt grafted chitosan antibacterial preservative film and synthesis method thereof

Abstract

This invention relates to a vanillin quaternary phosphonium salt grafted chitosan antibacterial food preservation film, the material of which has the following structure: ; wherein: R is butyl or phenyl; X ‑ For F ‑ Cl ‑ ,Br ‑ or I ‑ One of the following is provided: y is 1~5; n is 50~3100. The invention also discloses a method for synthesizing this preservation film. The preservation film of this invention is biodegradable, can block ultraviolet light, and has good biocompatibility, showing promising application prospects in fruit preservation and other fields.

Description

Technical Field

[0001] This invention relates to the field of functional polymer material synthesis technology, and in particular to a vanillin quaternary phosphonium salt grafted chitosan antibacterial preservation film and its synthesis method. Background Technology

[0002] With the global food security issue becoming increasingly severe, the development of food preservation technologies has become a key topic of international concern. According to the FAO's "2022 State of Food Security and Nutrition in the World" report, approximately 828 million people worldwide face the threat of hunger, while about 1.3 billion tons of food are wasted annually; among these, the loss rate of fruits and vegetables is as high as 40% to 50%. Achieving "zero hunger" by 2030 is one of the UN's Sustainable Development Goals. However, due to factors such as population growth, climate change, and the scarcity of natural resources, achieving this goal is fraught with challenges, and a large number of people worldwide still suffer from famine. It is reported that about one-third of the world's food is contaminated and spoiled each year, resulting in significant waste; perishable foods often lose their edible value due to mold and rot during harvesting, transportation, storage, and processing, with the loss of fresh produce such as fruits and vegetables being particularly prominent. According to statistics from the FAO, fruit and vegetable waste accounts for more than half of the total food waste globally each year, and fruit waste mainly originates from spoilage during storage and transportation. Fresh fruits and vegetables suffer from extremely high losses during storage and transportation, making post-harvest preservation a global challenge. Rotten fruit often contains putrefactive bacteria (molds, yeasts, etc.) and foodborne pathogens (E. coli, Staphylococcus aureus, etc.), which can easily cause discomfort or even illness in humans. Fruit rot not only causes enormous economic losses and resource waste but can also induce foodborne illnesses, posing a threat to public health and safety. Therefore, developing preservation technologies that can effectively extend the shelf life of fruits is of significant practical importance, helping to improve corporate economic efficiency, conserve natural resources, and protect public health.

[0003] Currently, chemically synthesized preservatives have become the main means of controlling post-harvest microbial diseases in fruits and vegetables due to their excellent preservation and anti-corrosion properties. Fruit spoilage is a complex physiological and biochemical process involving multiple factors such as water loss, respiratory metabolism, oxidation reactions, aging, and microbial infection. Extending shelf life is one of the key ways to reduce fruit loss. To this end, various preservation technologies have been developed, including waxing, adding preservatives, low-temperature storage, irradiation treatment, heat treatment, and controlled atmosphere storage. Waxing is a commonly used method, usually involving coating the surface of the fruit with weak organic acids and their derivatives. However, fruit wax is difficult to completely wash off, and long-term ingestion of residual substances can accumulate in the human body, posing potential health hazards. In contrast, while refrigeration, irradiation, heat treatment, and controlled atmosphere storage each have their advantages, they often alter the appearance and flavor of the fruit and generally suffer from high costs and long processing times, limiting their widespread application. Among many preservation materials, petroleum-based synthetic waxes are widely used in post-harvest fruit preservation due to their excellent preservation effects. However, their negative impacts on the ecological environment and human health cannot be ignored. Some synthetic waxes release harmful substances such as heavy metal ions, volatile organic compounds, organic solvents, and carcinogens during their production and use. Ingestion of these waxes may lead to poisoning, nervous system damage, and respiratory irritation; long-term exposure may also increase the risk of cancer. Furthermore, most synthetic waxes are difficult to biodegrade, causing adverse effects on water bodies, soil, and biological communities, leading to environmental pollution. Petroleum-based components cannot be digested and metabolized by the human body, further highlighting their environmental unsustainability and safety hazards in the food industry. Therefore, developing economical, efficient, non-toxic, antibacterial, and environmentally sustainable new preservation technologies, especially natural green coating materials that can replace petroleum-based synthetic waxes, has become a current research hotspot. This not only helps extend the shelf life of fruits but also provides an important direction for achieving green and safe fruit preservation.

[0004] Chitosan (CS) is a natural polymer compound, a polysaccharide composed of N-acetyl-D-glucosamine and diglucosamine units. It primarily originates from the partial deacetylation of chitin, resulting in N-acetyl-D-glucosamine copolymers. CS possesses excellent biodegradability and biocompatibility, is widely available, inexpensive, readily available, environmentally friendly, and easily forms films, making it widely considered one of the most promising green packaging materials and a potential replacement for traditional petroleum-based plastics. Its molecular structure contains amino groups (Chit-NH3). +Chitosan possesses polycationic and chelating properties, giving it unique antibacterial properties that inhibit the growth and reproduction of microorganisms. These properties effectively prevent fruit spoilage during storage, maintaining its quality, and it has become a commonly used material for researching perishable food components and food plastic films. However, the inherent defects of polymer materials, such as insufficient mechanical strength, limited flexibility, poor barrier properties, and limited functionality, severely restrict the large-scale application of CS (carbon dioxide) in practice, especially in the food packaging field.

[0005] To overcome the above shortcomings, compatible polymers with similar structures and properties to chitosan (CS) can be selectively introduced, or the material can be chemically / physically modified, thereby improving the overall performance and practical application value of composite bio-coatings. For example, Zhao P et al. (Maillard reaction based chitosan-monosaccharide films and the application in fruit preservation, Food Hydrocolloids, 2025, 166: 111269.) prepared a bioactive packaging film by combining chitosan-monosaccharide complex (CG / CM) with polyvinyl alcohol (PVA) through hydrogen bonding. The CG / CM composite film has excellent antioxidant and antibacterial properties and showed good results in the preservation of strawberries and cherry tomatoes, effectively extending the shelf life by at least 3 to 6 days. Zhao J et al. (Preparation of chitosan / Enokimushroom foot polysaccharide composite cling film and its application in blueberry preservation. International Journal of Biological Macromolecules, 246: 125567.) prepared a composite preservation film using chitosan and enoki mushroom foot polysaccharide as substrates via solution casting. The film showed significantly better preservation than the control group and exhibited superior antibacterial and antioxidant properties, effectively delaying fruit spoilage and extending shelf life. Gao N et al. (Chitosan / nanoclusters membrane-based sensors with antibacterial properties for rapid detection of bacterial viability and foodpreservation. Food Hydrocolloids, 2024, 154: 110144.) enhanced the peroxidase activity of CuNCs using chitosan. This composite material exhibited high biocompatibility and excellent broad-spectrum antibacterial activity against both Gram-positive and Gram-negative bacteria, thus achieving fruit preservation and storage.Liu X, et al. (A transparent p-coumaric acid-grafted-chitosan coating with antimicrobial, antioxidant and antifogging properties for fruit packaging applications. CarbohydratePolymers, 2024, 339: 122238.) synthesized β-coumaric acid via a carbodiimide coupling reaction and then prepared a CS-PCA coating using a casting method. This coating exhibited good antioxidant and antibacterial properties. The coating was further applied to polyethylene cling film, and its effectiveness was confirmed through strawberry preservation tests. Invention patent CN120623537 A discloses a chitosan food packaging film containing MBene, its preparation method, and its application. First, a layered MBene material is prepared, and a dispersion is obtained by modifying MBene with polyethyleneimine. This dispersion is then mixed with a chitosan solution, glycerol is added, and the mixture is poured and dried to finally obtain a chitosan food packaging film containing MBene. It was found that adding MBene not only enhances the mechanical properties of the chitosan composite film, but also, as a nano-antibacterial agent, enhances the composite packaging film's ability to inhibit microbial growth and extend food shelf life. Invention patent CN 117024810 A discloses a preservation film and its preparation method. First, acrolein is added to a chitosan solution, then resveratrol is added, followed by solid cysteine ​​and glycerol, ultimately obtaining a composite chitosan hydrogel-sodium alginate bilayer film. Using acrolein as a crosslinking agent not only increases the resveratrol loading of the chitosan film but also improves the film's antioxidant and antibacterial capabilities. Zhu Z, et al. (Synergistic enhancement of gelatin-chitosan films with vanillin Schiff base and ZnO for effective strawberry preservation, Food Control, 2025, 180: 111647.) utilized vanillin to react with chitosan and gelatin via a Schiff base reaction, and then introduced Zn. 2+ Through complexation, CGV-Zn for food packaging was produced. 2+Composite membranes improve the mechanical properties of the film; vanillin molecules contain aldehyde and phenolic hydroxyl groups, exhibiting excellent UV absorption characteristics, which can endow the composite membrane with superior UV resistance. Yuan S, et al. (The characterization of antimicrobial nanocomposites based on chitosan, cinnamon essential oil, and TiO2 for fruit preservation, Food Chemistry, 2023, 413: 135446.) mixed cinnamon essential oil (CEO), TiO2, and chitosan (CS). The results showed that treatment with CS-TC nanocomposites could double the shelf life of strawberries compared to the control group, while also exhibiting good light transmittance and antibacterial activity. However, effectively improving the activity of antibacterial groups while avoiding bacterial resistance remains a challenge.

[0006] The World Health Organization (WHO) has declared the situation of bacterial infections caused by antibiotic resistance a major public health emergency: facing increasingly complex infectious diseases, some of which are no longer treatable, the efficacy of existing antibiotics and antimicrobial drugs continues to decline. Furthermore, data from the US Centers for Disease Control and Prevention (CDC) shows a sharp increase in the infection rate of drug-resistant Candida species, with the domestic bacterial resistance rate in the United States surging from 12% to 60% between 2019 and 2020. This underscores the urgent need to accelerate the development of novel antimicrobial drugs with entirely new molecular mechanisms of action to inhibit and block microbial proliferation. Among these, heterocyclic quaternary salts (QHSs), mainly comprising quaternary ammonium salts and quaternary phosphonium salts, represent a highly promising research direction for overcoming bacterial resistance and developing novel antimicrobial therapeutics. Quaternary phosphonium salts (QPSs), with structures and biological activities similar to quaternary ammonium salts, were developed and reported in the mid-20th century and possess good antimicrobial activity. With the increasingly widespread application of quaternary phosphonium salts in the scientific and technological field, related research has continued to deepen, confirming that quaternary phosphonium salts possess superior thermal stability and antibacterial activity compared to quaternary ammonium salts. For example, invention patent CN121537566A discloses a cyclodextrin-grafted polyquaternary phosphonium salt eugenol ester antibacterial material. Through chemical modification of cyclodextrin as a biocompatible cyclodextrin-based macromolecular chain transfer agent, and using quaternary phosphonium salt eugenol ester monomer as the antibacterial monomer, the material prepared using RAFT polymerization technology exhibits excellent antibacterial properties. Invention patent CN119039517A discloses a quaternary phosphonium salt eugenol ester polymer antibacterial material, using quaternary phosphonium salt as the main antibacterial component, different hydrophilic and hydrophobic monomers as regulatory comonomers, and haloacetyl halide as a connecting bridge, using RAFT polymerization technology to prepare antibacterial nanomaterials with excellent activity. Wang L, et al. (Effect of the structure of chitosan quaternary phosphonium salt and chitosan quaternary ammonium salt on the antibacterial and antibiofilm activity. International Journal of Biological Macromolecules, 2023, 242(2): 124877.) synthesized N-(4-N′,N′,N′-trimethylphosphine chloride)benzoylchitosan (TMPCS), N-(4-N′,N′,N′-triphenylphosphine chloride)benzoylchitosan (TPPCS) and N-(4-N′,N′,N′-trimethylmethylamine chloride)benzoylchitosan (TMACS), and studied their antibacterial activities against Escherichia coli and Staphylococcus aureus. The activity of the membrane was studied by crystal violet method. The antibacterial evaluation showed that the structurally similar chitosan quaternary phosphonium salt had superior antibacterial activity compared with the chitosan quaternary ammonium salt.SunXB, et al. (Poly(phosphonium)-Functionalized Double-Armed β-CD Antimicrobial Material via RAFT. Macromolecules, 2023, 56(23): 9498-9508.) synthesized a series of double-armed antimicrobial polymers (CD-QPS) via Steglich esterification and reversible addition-fragmentation chain transfer polymerization (RAFT), which exhibited excellent antimicrobial activity against Escherichia coli and Staphylococcus aureus. Lu J, et al. (Antibacterial performance of cationicquaternary phosphonium-modified chitosan polymer in water. Chinese Chemical Letters, 2024, 35(9): 109406.) prepared a chitosan-based antibacterial agent PCC by self-assembly of quaternary phosphonium salt (QPS). PCC is positively charged over a wide pH range, overcoming the limitation of antibacterial properties under acidic conditions. It has an antibacterial rate of 95% against Escherichia coli and 100% against Staphylococcus aureus. Shi LW et al. (Synthetic antibacterial Quaternary phosphorus salts promote methicillin-resistant Staphylococcus aureus-infected wound healing, International Journal of Nanomedicine, 2023, 18: 1145-1158.) synthesized three alkyl-bis(triphenyl)quaternary phosphorus bromides: (1,2-DBTPP)Br2, (1,4-DBTPP)Br2, and (1,6-DBTPP)Br2 via a one-step method. They also synthesized alkyl bis(triphenyl)phosphine bromides (1,2-DBTPP)Br2, (1,4-DBTPP)Br2, and (1,6-DBTPP)Br2, and evaluated their antibacterial activity against four pathogens using the minimum inhibitory concentration method. The results showed that (1,4-DBTPP)Br2 exhibited good solubility, low toxicity, and low hemolytic activity, and showed strong antibacterial activity against MRSA cells. Invention patent CN 121698905 A discloses a structurally stable quaternary phosphonium salt antibacterial agent, which is obtained by esterification of borneol and halogen to obtain borneol halopropionate; borneol halopropionate is then nucleophilically substituted with tertiary phosphine to obtain quaternary phosphonium salt of borneol halopropionate. This quaternary phosphonium salt has a highly effective inhibitory effect on a variety of bacteria (such as Escherichia coli and Staphylococcus aureus).Invention patent CN119391099 A discloses an antibacterial graphene-modified polystyrene plastic. The method involves a nucleophilic substitution reaction between the bromine atom of brominated butyltriphenylphosphonium bromide and a hydroxyl group of a polyol to obtain a terminal hydroxyl-terminated triphenylphosphonium bromide. This bromide is then used as a quaternary phosphonium salt antibacterial monomer to obtain functionalized graphene with high antibacterial activity. Furthermore, the triphenylphosphonium bromide modified on the graphene surface contains numerous benzene ring structures, similar in polarity to styrene, which can improve the interfacial affinity and compatibility between graphene and polystyrene, promoting graphene dispersion and reducing agglomeration, thereby endowing polystyrene with excellent antibacterial properties. Quaternary phosphonium salt antibacterial materials have been extensively reported, demonstrating their excellent antibacterial properties and low tendency to induce drug resistance. However, existing research mainly focuses on the antibacterial properties of quaternary phosphonium salts, resulting in limited functionality. In addition, the high cytotoxicity of quaternary phosphonium salt materials has hindered further research. Therefore, it is particularly important to design and synthesize novel quaternary phosphonium salt antibacterial monomers with multiple functions; secondly, combining them with bio-based materials such as chitosan can endow them with biocompatibility and environmental friendliness, thus achieving a "win-win" goal. Summary of the Invention

[0007] The technical problem to be solved by the present invention is to provide a degradable, ultraviolet-shielding, and biocompatible vanillin quaternary phosphonium salt grafted chitosan antibacterial preservation film.

[0008] The technical problem to be solved by the present invention is to provide a method for synthesizing the vanillin quaternary phosphonium salt grafted chitosan antibacterial preservation film.

[0009] To address the aforementioned problems, the present invention provides a vanillin quaternary phosphonium salt grafted chitosan antibacterial food preservation film, characterized in that the material of the food preservation film has the following structure: ; Wherein: R is butyl or phenyl; X - For F - Cl - ,Br - or I - One of them; y is 1 ~ 5; n is 50 ~ 3100.

[0010] The method for synthesizing a vanillin quaternary phosphonium salt grafted chitosan antibacterial food preservation film as described above includes the following steps: (1) Preparation of halogenated acylated vanillin: In container A equipped with a stirrer, vanillin, an organic base, and reaction solvent A are added sequentially and magnetically stirred in an ice-water bath at 0-5°C for 5-30 min. Then, a haloacyl halide reagent is dissolved in reaction solvent B and slowly added dropwise to the above system. The ice-water bath is removed, and stirring continues at room temperature for 8-24 h. After the reaction is complete, a quencher is slowly added, and the mixture is stirred for 30 min. The organic phase is collected after liquid-liquid extraction, and the filtrate is rotary evaporated to obtain a dark brown crude product. The crude product is purified by column chromatography, and the resulting dark brown liquid is haloacylated vanillin. (2) Synthesis of active compounds of vanillin quaternary phosphonium salt: Halogenated vanillin, organophosphorus ligand, and reaction solvent C were added sequentially to container B, which was equipped with a stirring and heating device. Under inert gas protection, the mixture was refluxed and stirred at 30-70 °C for 12-48 h. Subsequently, the reaction system was cooled to room temperature, and the reaction solution was rotary evaporated under reduced pressure to obtain a crude product. A precipitant was slowly added dropwise to the crude product to precipitate the product. The precipitate was filtered, washed, and then vacuum dried to obtain an orange powder product, which is the active compound of vanillin quaternary phosphonium salt. (3) Synthetic vanillin quaternary phosphonium salt grafted chitosan antibacterial food preservation film: In container C equipped with a stirring device, chitosan is added to an organic acid solution and magnetically stirred at room temperature for 1-6 h to form a clear and transparent solution. Then, vanillin quaternary phosphonium salt active compound is dissolved in reaction solvent D and slowly added dropwise to the above system. The mixture is stirred at room temperature for 30 min to ensure uniform mixing. The system is then transferred to an oil bath and reacted at 40-70 °C for 5-12 h. After the reaction is complete, the solution is poured into a mold and dried at room temperature to form a film, thus obtaining a light brown vanillin quaternary phosphonium salt grafted chitosan antibacterial preservation film.

[0011] In step (1), the ratio of vanillin, organic base, and reaction solvent A is 3.5-10.0 g: 4.5-10.0 g: 10-70 mL; the mass ratio of vanillin to haloacyl halide reagent is 3.5-10.0 g: 5.1-20.5 g; the ratio of reaction solvent B to haloacyl halide reagent is 15-60 mL: 5.1-20.5 g; and the ratio of vanillin to quencher is 3.5-10.0 g: 20-150 mL.

[0012] In step (1), the organic base refers to one of trimethylamine, pyridine, or triethylamine; the haloacyl halogen reagent refers to one of chloroacetyl chloride, chlorobutyryl chloride, or bromopropionyl chloride; the quencher refers to one of distilled water, methanol, or dilute hydrochloric acid; and the column chromatography uses neutral silica or neutral alumina as the stationary phase and two of petroleum ether, ethyl acetate, chloroform, n-hexane, tetrahydrofuran, and methanol mixed uniformly in a volume ratio of 2:1 to 10:1 as the eluent.

[0013] The structural formula of the vanillin quaternary phosphonium salt active compound in step (2) is as follows: ; Wherein: R is butyl or phenyl; X - For F - Cl - ,Br - or I - One of them; y is 1 to 5.

[0014] In step (2), the ratio of halogenated vanillin, organophosphine ligand, and reaction solvent C is 4.0 ~ 15.5 g: 5.0 ~ 20.5 g: 50 ~ 120 mL; the ratio of halogenated vanillin and precipitant is 4.0 ~ 15.5 g: 100 ~ 250 mL.

[0015] In step (2), the organophosphorus ligand refers to triphenylphosphine or tributylphosphine; the inert gas refers to one of nitrogen, argon or carbon dioxide; and the precipitant refers to one or a mixture of two of anhydrous diethyl ether, acetone or petroleum ether.

[0016] In step (3), the organic acid solution refers to one of glacial acetic acid, citric acid, or lactic acid with a mass concentration of 0.5% to 5.5%; the mold is one of glass petri dish, polypropylene plastic, or polytetrafluoroethylene mold.

[0017] In step (3), the ratio of chitosan to organic acid solution is 1 ~ 10 g: 60 ~ 120 mL; the mass ratio of chitosan to vanillin quaternary phosphonium salt active compound is 1.5 ~ 8.0 g: 0.01 ~ 0.20 g; and the ratio of vanillin quaternary phosphonium salt active compound to reaction solvent D is 0.01 ~ 0.20 g: 2 mL.

[0018] In steps (1) to (3), reaction solvent A, reaction solvent B, reaction solvent C, and reaction solvent D are all one or a mixture of two of the following: acetonitrile, dichloromethane, dimethyl sulfoxide, anhydrous ethanol, chloroform, N,N-dimethylformamide, 1,4-dioxane, tetrahydrofuran, and acetone.

[0019] Compared with the prior art, the present invention has the following advantages: 1. This invention combines the active compound of vanillin quaternary phosphonium salt with chitosan through Schiff base bonding, making full use of the easy film-forming and non-toxic properties of chitosan and the excellent broad-spectrum antibacterial properties of quaternary phosphonium salt. This not only improves the antibacterial performance of chitosan but also reduces the toxicity of quaternary phosphonium salt itself, giving the material good biocompatibility and achieving a "1+1>2" effect.

[0020] 2. This invention utilizes the Schiff base reaction to enable the chitosan and vanillin quaternary phosphonium salt active compounds to work synergistically, thereby enhancing the overall ultraviolet shielding capability of the membrane material and giving it excellent ultraviolet shielding effect.

[0021] 3. The method for synthesizing vanillin quaternary phosphonium salt grafted chitosan antibacterial preservation film of the present invention has the characteristics of high reaction selectivity and conversion rate, simple reaction steps, high efficiency, and good substrate tolerance. It can provide a novel strategy for developing new chitosan-based antibacterial materials.

[0022] 4. The vanillin quaternary phosphonium salt grafted chitosan antibacterial preservation film of the present invention can be applied to packaging materials, fruit preservation, and agricultural antibacterial agents. Attached Figure Description

[0023] The specific embodiments of the present invention will be described in further detail below with reference to the accompanying drawings.

[0024] Figure 1 The nuclear magnetic resonance hydrogen spectrum of the vanillin quaternary phosphonium salt active compound prepared in Example 1 of this invention.

[0025] Figure 2 The infrared spectra of the vanillin quaternary phosphonium salt grafted chitosan antibacterial preservation film and the vanillin quaternary phosphonium salt active compound prepared in Example 1 of the present invention are shown.

[0026] Figure 3 Photograph (a) and scanning electron microscope image (b) of the vanillin quaternary phosphonium salt grafted chitosan antibacterial preservation film prepared in Example 1 of the present invention.

[0027] Figure 4 The UV-Vis spectra of the vanillin quaternary phosphonium salt grafted chitosan antibacterial preservation film and the chitosan film prepared in Example 1 of this invention are shown.

[0028] Figure 5 The effect of the vanillin quaternary phosphonium salt grafted chitosan antibacterial preservation film prepared in Example 1 of the present invention on the antibacterial rate of Escherichia coli and Staphylococcus aureus at a specific concentration. Detailed Implementation

[0029] A vanillin quaternary phosphonium salt grafted chitosan antibacterial food preservation film, the material of which has the following structure: ; Wherein: R is butyl or phenyl; X - For F - Cl - ,Br - or I - One of them; y is 1 ~ 5; n is 50 ~ 3100.

[0030] Its synthesis method includes the following steps: (1) Preparation of halogenated acylated vanillin: In container A equipped with a stirring device, vanillin, an organic base, and reaction solvent A are added sequentially. The organic base is one of trimethylamine, pyridine, or triethylamine. The ratio of vanillin, organic base, and reaction solvent A is 3.5–10.0 g : 4.5–10.0 g : 10–70 mL. Then, the container is placed in an ice-water bath at 0–5 °C and magnetically stirred for 5–30 min.

[0031] The haloacyl halide reagent is then dissolved in reaction solvent B and transferred to a constant-pressure dropping funnel. The haloacyl halide reagent refers to one of chloroacetyl chloride, chlorobutyryl chloride, or bromopropionyl chloride. The mass ratio of vanillin to haloacyl halide reagent is 3.5–10.0 g: 5.1–20.5 g; the ratio of reaction solvent B to haloacyl halide reagent is 15–60 mL: 5.1–20.5 g. The solution is slowly added dropwise to the above system (if white fumes are produced, it indicates the release of hydrogen chloride gas). After removing the ice-water bath, the mixture is stirred at room temperature for 8–24 h. During the reaction, the solution color gradually deepens from pale yellow to dark brown.

[0032] After the reaction is complete, a quencher is slowly added. The quencher is one of distilled water, methanol, or dilute hydrochloric acid. The ratio of vanillin to quencher is 3.5–10.0 g: 20–150 mL. The mixture is stirred for 30 min to quench excess haloacyl halides. After separation and extraction, the organic phase is collected. The filtrate is rotary evaporated to obtain a dark brown crude product. The crude product is purified by column chromatography using neutral silica or neutral alumina as the stationary phase. The eluent is a homogeneous mixture of two of the following: petroleum ether, ethyl acetate, chloroform, n-hexane, tetrahydrofuran, and methanol, in a volume ratio of 2:1 to 10:1 (mL / mL). The dark brown liquid obtained after purification is haloacylated vanillin.

[0033] (2) Synthesis of active compounds of vanillin quaternary phosphonium salt: In container B equipped with a stirrer and a heating device, halogenated vanillin, an organophosphorus ligand, and reaction solvent C are added sequentially. The organophosphorus ligand refers to triphenylphosphine or tributylphosphine. The ratio of halogenated vanillin, organophosphorus ligand, and reaction solvent C is 4.0–15.5 g: 5.0–20.5 g: 50–120 mL. Under the protection of an inert gas, either nitrogen, argon, or carbon dioxide, the reaction is carried out under reflux and stirred at 30–70 °C for 12–48 h. Subsequently, the reaction system is cooled to room temperature, and the reaction solution is evaporated under reduced pressure to obtain a crude product. A precipitant, which is one or a mixture of two of anhydrous diethyl ether, acetone, and petroleum ether, is slowly added dropwise to the crude product. The precipitant is 4.0–15.5 g: 100–250 mL. A precipitate is formed. After filtration, washing, and vacuum drying, the resulting orange powder is the active compound of vanillin quaternary phosphonium salt.

[0034] The structural formula of the active compound, vanillin quaternary phosphonium salt, is as follows: Wherein: R is butyl or phenyl; X - For F - Cl - ,Br - or I - One of them; y is 1 to 5.

[0035] (3) Synthetic vanillin quaternary phosphonium salt grafted chitosan antibacterial food preservation film: In container C equipped with a stirring device, chitosan is added to an organic acid solution and magnetically stirred at room temperature for 1 to 6 hours to form a clear and transparent solution. The organic acid solution refers to one of glacial acetic acid, citric acid, or lactic acid with a mass concentration of 0.5% to 5.5%. The ratio of chitosan to organic acid solution is 1 to 10 g: 60 to 120 mL.

[0036] The vanillin quaternary phosphonium salt active compound was dissolved in reaction solvent D and then slowly added dropwise to the above system. The mass ratio of chitosan to vanillin quaternary phosphonium salt active compound was 1.5~8.0 g:0.01~0.20 g; the ratio of vanillin quaternary phosphonium salt active compound to reaction solvent D was 0.01~0.20 g:2 mL. The mixture was stirred at room temperature for 30 min to ensure uniform mixing. The system was then transferred to an oil bath and reacted at 40~70 ℃ for 5~12 h. After the reaction was completed, the solution was poured into a glass petri dish, a polypropylene plastic mold, or a polytetrafluoroethylene mold and allowed to air dry at room temperature to form a film, thus obtaining a light brown vanillin quaternary phosphonium salt grafted chitosan antibacterial preservation film.

[0037] Throughout the entire reaction process described above, reaction solvents A, B, C, and D are all one or a mixture of two of the following: acetonitrile, dichloromethane, dimethyl sulfoxide, anhydrous ethanol, chloroform, N,N-dimethylformamide, 1,4-dioxane, tetrahydrofuran, and acetone.

[0038] Example 1 (1) Preparation of halogenated acylated vanillin: In a round-bottom flask equipped with a stirrer, 3.8 g vanillin, 5.5 g triethylamine, and 35 mL dichloromethane were added sequentially. The flask was then placed in an ice-water bath at 0–5 °C and magnetically stirred for 20 min. Next, 7.4 g of chloroacetyl chloride was dissolved in 30 mL of dichloromethane and transferred to a constant-pressure dropping funnel. This solution was then slowly added dropwise to the above system (white fumes indicate the release of hydrogen chloride gas). The ice-water bath was removed, and the mixture was stirred at room temperature for 12 h. During the reaction, the solution color gradually deepened from pale yellow to dark brown. After the reaction was complete, 60 mL of distilled water was slowly added, and the mixture was stirred for 30 min to quench excess chloroacetyl chloride. The organic phase was collected after separation and extraction. The filtrate was rotary evaporated to obtain a dark brown crude product. The crude product was purified by column chromatography using ethyl acetate:methanol at a volume ratio of 4:1 (mL / mL). The dark brown liquid obtained after purification was chloroacetylated vanillin.

[0039] (2) Synthesis of active compounds of vanillin quaternary phosphonium salt: In a round-bottom flask equipped with a stirrer and heating device, 5.3 g of chloroacetylated vanillin, 6.2 g of triphenylphosphine, and 80 mL of dichloromethane were added sequentially. Under nitrogen protection, the mixture was refluxed at 40 °C with stirring for 24 h. Subsequently, the reaction system was cooled to room temperature, and the reaction solution was rotary evaporated under reduced pressure to obtain a crude product. 150 mL of anhydrous diethyl ether was slowly added dropwise to the crude product, causing a precipitate to form. The precipitate was filtered, washed, and dried under vacuum to obtain an orange powder, which is the active compound of vanillin quaternary phosphonium salt.

[0040] (3) Synthetic vanillin quaternary phosphonium salt grafted chitosan antibacterial food preservation film: In a round-bottom flask equipped with a stirrer, 3.5 g of chitosan was added to 120 mL of a 4.5% acetic acid solution and magnetically stirred at room temperature for 2 h to form a clear and transparent solution. Then, 0.06 g of vanillin quaternary phosphonium salt active compound was weighed, dissolved in 2 mL of anhydrous ethanol, and slowly added dropwise to the above system. The mixture was stirred at room temperature for 30 min to ensure uniform mixing. The system was then transferred to an oil bath and reacted at 60 °C for 8 h. After the reaction was completed, the solution was poured into a polypropylene plastic mold and dried at room temperature to form a film, thus obtaining a light brown vanillin quaternary phosphonium salt grafted chitosan antibacterial preservation film.

[0041] The present invention characterized and tested the products of vanillin quaternary phosphonium salt grafted chitosan antibacterial preservative film and vanillin quaternary phosphonium salt active compound synthesized in Example 1 using the following methods.

[0042] [Hydrogen NMR Spectroscopy] Figure 1 The proton NMR spectrum of the active compound of vanillin quaternary phosphonium salt ( 1 H NMR) (DMSO-d6, 400 MHz, δ ppm). 1 The positions and splitting of the peaks in the H NMR spectrum are as follows: 9.77 (s, 1H), 7.92 (d, 1H), 7.91 (d, 1H), 7.89 (s, 1H), 7.85 (t, 3H), 7.84 (t, 6H), 7.80 (d, 6H), 3.83 (s, 3H). 1 The H NMR results showed that the chemical shifts and integral ratios of the obtained characteristic peaks corresponded to the chemical structure of the vanillin quaternary phosphonium salt active compound, proving that the obtained structure was correct and indicating that the vanillin quaternary phosphonium salt active compound was successfully prepared.

[0043] Infrared spectrum Figure 2 The Fourier Transform Infrared (FT-IR) spectra of the active compound of vanillin quaternary phosphonium salt and its product (vanillin quaternary phosphonium salt grafted chitosan antibacterial food preservation film). The FT-IR spectrum of the active compound of vanillin quaternary phosphonium salt shows a depth of 3053 cm⁻¹. -1 1113 cm -1 996cm -1 The absorption peaks at 1172 cm⁻¹ are attributed to characteristic peaks of the benzene ring (-Ph), CP, and phosphorus-benzene ring (P-Ph), respectively; -1 The absorption peak at 1440 cm⁻¹ corresponds to the stretching vibration absorption peak of COC; -1 The characteristic peaks appearing at 1422 ~ 1516 cm⁻¹ are attributed to the stretching vibration absorption peaks of PC in the phenyl-phosphorus (Ph-P) structure. -1 The absorption peaks within the range are attributed to the stretching vibrations of the aromatic ring C-C skeleton. The FT-IR spectrum of the product (aldehyde-quaternary phosphonium salt grafted chitosan antibacterial film) shows a peak at 3391 cm⁻¹. -1 The broad peaks of stretching vibrations attributable to OH and NH shift to lower wavenumbers, attributed to the steric hindrance effect resulting from the condensation reaction of benzaldehyde and chitosan; 1660 ~ 1730 cm⁻¹ -1 No characteristic absorption peaks of aldehyde groups were observed within the range, indicating that no detectable free aldehyde residues were found in the system; 1634 cm⁻¹ -1 A new absorption peak appears at 1400 ~ 1500 cm⁻¹, attributed to the stretching vibration absorption peak of the imine bond (C=N);-1 The absorption peaks within the range are attributed to the skeletal stretching vibrations of the aromatic ring CC. In summary, the infrared absorption peaks of the product correspond to its expected functional group structure, thus confirming the successful synthesis of the aldehyde-based quaternary phosphonium salt-grafted chitosan antibacterial film.

[0044] [morphological analysis] Figure 3 Photograph (a) and scanning electron microscope (SEM, b) of the antibacterial and preservative film grafted with vanillin quaternary phosphonium salt onto chitosan. Image (a) shows a smooth and highly transparent film surface. The SEM reveals a highly uniform, dense microstructure without significant defects; no phase separation or porous structures were observed, and no obvious cracks or fine wrinkles were found. This result indicates that the active compound of vanillin quaternary phosphonium salt, after being successfully grafted onto the chitosan backbone via Schiff base dynamic bonds (C=N), did not disrupt the homogeneity of the chitosan matrix. Instead, it promoted the orderly arrangement of polymer chains through intermolecular interactions (such as hydrogen bonds and electrostatic interactions), forming a dense and continuous film structure. From the perspective of antibacterial and fruit preservation performance, this uniform and dense morphology has multiple advantages: First, the dense film structure can significantly reduce the permeability of water vapor and oxygen, forming a stable physical barrier on the fruit surface, effectively inhibiting water loss and oxygen penetration, thereby slowing down the fruit's respiration rate and oxidative browning process, and extending shelf life. Secondly, the quaternary phosphonium salt groups are uniformly distributed in the membrane matrix without local aggregation, ensuring uniform exposure of antibacterial active sites and avoiding performance inconsistencies caused by insufficient or excessive local antibacterial concentrations. The strong positive charge of the quaternary phosphonium salt can efficiently adsorb and disrupt bacterial cell membranes through electrostatic interactions, while the continuous membrane structure can stably fix the active groups on the material surface, achieving long-lasting antibacterial effects while preventing rapid loss of active substances. In addition, the defect-free microstructure of the membrane surface can reduce the attachment sites of microorganisms, lowering the risk of pathogenic bacteria colonizing the membrane surface and further improving the hygiene and safety of the preservation system. In summary, the grafting modification of chitosan and aldehyde-based quaternary phosphonium salts not only maintains the excellent film-forming properties and uniformity of the membrane material, but also endows the composite membrane with excellent physical barrier properties and antibacterial activity through synergistic optimization of structure and function, providing a reliable microstructural basis for its application in the field of food preservation.

[0045] UV shielding performance By using ultraviolet-visible spectroscopy (200 ~ 1100 nm, Figure 4In comparison, the optical properties of pure chitosan film and vanillin quaternary phosphonium salt grafted chitosan antibacterial preservation film (sample) were compared. It was found that the introduction of vanillin quaternary phosphonium salt active compound improved the ultraviolet shielding performance of the film in the range of 200 ~ 400 nm. The film material has a blocking rate of 99.73% for long-wave ultraviolet (UV-A) and 99.90% for medium-wave ultraviolet (UV-B) and short-wave ultraviolet (UV-C).

[0046] First, the achievement of ultraviolet shielding performance is attributed to the following structural features: (1) Schiff base contains unsaturated conjugated C=N, which can pass through π→π * (2) The aldehyde quaternary phosphonium salt molecule contains multiple sets of cyclic conjugated systems, which can undergo π→π transition absorption in the UV-A and UV-B bands; * It absorbs high-energy ultraviolet photons through a transition, and the auxochrome methoxy group can undergo an n→π transition with the benzene ring. * The two effects work together to enhance the membrane's UV shielding capability.

[0047] Secondly, combined with scanning electron microscopy images, the uniform binding of vanillin quaternary phosphonium salt active compound with chitosan matrix increases the interaction interface between aldehyde quaternary phosphonium salt and ultraviolet light, forming the structural basis for ultraviolet shielding performance.

[0048] Therefore, this film can be used to protect photosensitive fruits (such as strawberries and blueberries) and fruits that are prone to oxidative browning (such as apples and bananas), inhibiting photo-oxidation reactions caused by ultraviolet light, thereby delaying spoilage, discoloration and nutrient loss, and extending the shelf life of food.

[0049] [Antibacterial properties] Choose Escherichia coli ( E. coli ) and Staphylococcus aureus ( S. aureus Using representative test strains, solid culture media were prepared, and the antibacterial properties of the vanillin quaternary phosphonium salt grafted chitosan antibacterial film were determined by colony counting method (semi-quantitative). Figure 5 This film shows the effect of E. coli and S. aureus The antibacterial rate. The film is prepared by Schiff base condensation reaction of aldehyde-functionalized quaternary phosphonium salt and amino groups on the chitosan molecular chain, forming a cross-linked composite film containing C=N, which is effective against Gram-negative bacteria (…). E. coli ) and Gram-positive bacteria ( S. aureus All of them have broad-spectrum antibacterial activity; they are effective against... S. aureus Its antibacterial rate is 99.91%, and it has a high antibacterial rate. E. coli The antibacterial rate is 95.87%.

[0050] Its antibacterial mechanism is as follows: 1) Chitosan itself has polycationic properties, which can interact with bacterial cell membranes and disrupt the integrity of the membrane structure. After chitosan condenses with aldehydes to form Schiff bases, the antibacterial performance is further enhanced. This is because the formation of imine bonds (C=N) can more effectively interfere with bacterial enzyme activity and metabolic processes. At the same time, Schiff bases can complex with metal ions essential for bacterial growth, inhibiting bacterial proliferation. 2) After modification with quaternary phosphonium salts, the positive charge density on the surface of chitosan molecules increases. The positively charged groups of cationic chitosan derivatives can interact electrostatically with the negatively charged components on the surface of bacterial cell membranes. After the polycations are adsorbed onto the bacterial outer membrane, they disrupt the surface structure of microbial cells, hinder the transport of nutrients into the cell and cause leakage of intracellular substances, ultimately leading to bacterial death. 3) This composite membrane retains the biocompatibility and biodegradability of chitosan, and has higher safety in use compared to traditional quaternary phosphonium salt antibacterial agents with higher toxicity.

[0051] Therefore, vanillin quaternary phosphonium salt grafted chitosan antibacterial preservation film has potential application prospects in the field of novel antibacterial preservation materials.

[0052] Example 2 (1) Preparation of halogenated acylated vanillin: In a round-bottom flask equipped with a stirrer, 5.2 g vanillin, 7.3 g trimethylamine, and 20 mL dimethyl sulfoxide were added sequentially. The flask was then placed in an ice-water bath at 0–5 °C and magnetically stirred for 8 min. Next, 10.4 g bromopropionyl chloride was dissolved in 15 mL of dimethyl sulfoxide and transferred to a constant-pressure dropping funnel. This solution was then slowly added dropwise to the above system (white fumes indicate the release of hydrogen chloride gas). The ice-water bath was removed, and the mixture was stirred at room temperature for 9 h. During the reaction, the solution color gradually deepened from pale yellow to dark brown. After the reaction was complete, 30 mL of methanol was slowly added, and the mixture was stirred for 30 min to quench excess bromopropionyl chloride. The organic phase was collected after liquid-liquid extraction, and the filtrate was rotary evaporated to obtain a dark brown crude product. The crude product was purified by column chromatography using ethyl acetate:petroleum ether at a volume ratio of 5:1 (mL / mL). The dark brown liquid obtained after purification was bromopropionyl vanillin.

[0053] (2) Synthesis of active compounds of vanillin quaternary phosphonium salt: In a round-bottom flask equipped with a stirrer and heater, 10.3 g of bromopropionyl vanillin, 11.4 g of tributylphosphine, and 80 mL of dimethyl sulfoxide were added sequentially. Under argon protection, the mixture was refluxed at 65 °C with stirring for 36 h. The reaction system was then cooled to room temperature, and the reaction solution was rotary evaporated under reduced pressure to obtain a crude product. 100 mL of petroleum ether was slowly added dropwise to the crude product, causing a precipitate to form. The precipitate was filtered, washed, and then vacuum dried to obtain an orange powder, which is the active compound of vanillin quaternary phosphonium salt.

[0054] (3) Synthetic vanillin quaternary phosphonium salt grafted chitosan antibacterial food preservation film: In a round-bottom flask equipped with a stirrer, 2.5 g of chitosan was added to 100 mL of a 2.0% acetic acid solution and magnetically stirred at room temperature for 4 h to form a clear and transparent solution. Then, 0.10 g of vanillin quaternary phosphonium salt active compound was weighed, dissolved in 2 mL of acetonitrile, and slowly added dropwise to the above system. The mixture was stirred at room temperature for 30 min to ensure uniform mixing. The system was then transferred to an oil bath and reacted at 45 °C for 10 h. After the reaction was completed, the solution was poured into a polypropylene plastic mold and dried at room temperature to form a film, thus obtaining a light brown vanillin quaternary phosphonium salt grafted chitosan antibacterial preservation film.

[0055] Example 3 (1) Preparation of halogenated acylated vanillin: In a round-bottom flask equipped with a stirrer, 9.5 g vanillin, 8.8 g pyridine, and 65 mL tetrahydrofuran were added sequentially, and the mixture was then magnetically stirred in an ice-water bath at 0–5 °C for 25 min. Next, 18.5 g chlorobutyryl chloride was dissolved in 55 mL tetrahydrofuran and transferred to a constant-pressure dropping funnel. This solution was then slowly added dropwise to the above system (white fumes indicate the release of hydrogen chloride gas). The ice-water bath was removed, and the mixture was stirred at room temperature for 15 h. During the reaction, the solution color gradually deepened from pale yellow to dark brown. After the reaction was complete, 125 mL distilled water was slowly added, and the mixture was stirred for 30 min to quench excess chlorobutyryl chloride. The organic phase was collected after separation and extraction. The filtrate was rotary evaporated to obtain a dark brown crude product. The crude product was purified by column chromatography using a hexane:methanol eluent with a volume ratio of 6:1 (mL / mL). The dark brown liquid obtained after purification was chlorobutyrylated vanillin.

[0056] (2) Synthesis of active compounds of vanillin quaternary phosphonium salt: In a round-bottom flask equipped with a stirrer and heating device, 14.3 g of chlorobutyrylated vanillin, 18.2 g of triphenylphosphine, and 100 mL of tetrahydrofuran were added sequentially. Under argon protection, the mixture was refluxed at 45 °C with stirring for 24 h. Subsequently, the reaction system was cooled to room temperature, and the reaction solution was rotary evaporated under reduced pressure to obtain a crude product. 80 mL of anhydrous diethyl ether was slowly added dropwise to the crude product, causing a precipitate to form. The precipitate was filtered, washed, and dried under vacuum to obtain an orange powder, which is the active compound of vanillin quaternary phosphonium salt.

[0057] (3) Synthetic vanillin quaternary phosphonium salt grafted chitosan antibacterial food preservation film: In a round-bottom flask equipped with a stirrer, 8.0 g of chitosan was added to 80 mL of a 4.0% lactic acid solution and magnetically stirred at room temperature for 1 h to form a clear and transparent solution. Then, 0.20 g of vanillin quaternary phosphonium salt active compound was weighed, dissolved in 2 mL of dimethyl sulfoxide, and slowly added dropwise to the above system. The mixture was stirred at room temperature for 30 min to ensure uniform mixing. The system was then transferred to an oil bath and reacted at 65 °C for 6 h. After the reaction was completed, the solution was poured into a glass petri dish and dried at room temperature to form a film, thus obtaining a light brown vanillin quaternary phosphonium salt grafted chitosan antibacterial preservation film.

Claims

1. A vanillin quaternary phosphonium salt grafted chitosan antibacterial food preservation film, characterized in that: The material of this plastic wrap has the following structure: ； Wherein: R is butyl or phenyl; X - For F - Cl - ,Br - or I - One of them; y is 1 ~ 5; n is 50 ~ 3100.

2. The method for synthesizing a vanillin quaternary phosphonium salt grafted chitosan antibacterial preservative film as described in claim 1, comprising the following steps: (1) Preparation of halogenated acylated vanillin: In container A equipped with a stirrer, vanillin, an organic base, and reaction solvent A are added sequentially and magnetically stirred in an ice-water bath at 0–5 °C for 5–30 min. Then, a haloacyl halide reagent is dissolved in reaction solvent B and slowly added dropwise to the above system. The ice-water bath is removed, and stirring continues at room temperature for 8–24 h. After the reaction is complete, a quencher is slowly added, and the mixture is stirred for 30 min. The organic phase is collected after liquid-liquid extraction, and the filtrate is rotary evaporated to obtain a dark brown crude product. The crude product is purified by column chromatography, and the resulting dark brown liquid is haloacylated vanillin. (2) Synthesis of active compounds of vanillin quaternary phosphonium salt: Halogenated vanillin, organophosphorus ligand, and reaction solvent C were added sequentially to container B, which was equipped with a stirring and heating device. Under inert gas protection, the mixture was refluxed and stirred at 30-70 °C for 12-48 h. Subsequently, the reaction system was cooled to room temperature, and the reaction solution was rotary evaporated under reduced pressure to obtain a crude product. A precipitant was slowly added dropwise to the crude product to precipitate the product. The precipitate was filtered, washed, and then vacuum dried to obtain an orange powder, which is the active compound of vanillin quaternary phosphonium salt. (3) Synthetic vanillin quaternary phosphonium salt grafted chitosan antibacterial food preservation film: In container C equipped with a stirring device, chitosan is added to an organic acid solution and magnetically stirred at room temperature for 1 to 6 hours to form a clear and transparent solution; then, vanillin quaternary phosphonium salt active compound is dissolved in reaction solvent D and slowly added dropwise to the above system, and stirred at room temperature for 30 minutes to mix the two evenly. The system was then transferred to an oil bath and reacted at 40-70 °C for 5-12 h. After the reaction was completed, the solution was poured into a mold and dried at room temperature to form a film, which yielded a light brown vanillin quaternary phosphonium salt grafted chitosan antibacterial preservation film.

3. The method for synthesizing a vanillin quaternary phosphonium salt grafted chitosan antibacterial preservative film as described in claim 2, characterized in that: In step (1), the ratio of vanillin, organic base, and reaction solvent A is 3.5-10.0 g: 4.5-10.0 g: 10-70 mL; the mass ratio of vanillin to haloacyl halide reagent is 3.5-10.0 g: 5.1-20.5 g; the ratio of reaction solvent B to haloacyl halide reagent is 15-60 mL: 5.1-20.5 g; and the ratio of vanillin to quencher is 3.5-10.0 g: 20-150 mL.

4. The method for synthesizing a vanillin quaternary phosphonium salt grafted chitosan antibacterial preservative film as described in claim 2, characterized in that: In step (1), the organic base refers to one of trimethylamine, pyridine, or triethylamine; the haloacyl halogen reagent refers to one of chloroacetyl chloride, chlorobutyryl chloride, or bromopropionyl chloride; the quencher refers to one of distilled water, methanol, or dilute hydrochloric acid; and the column chromatography uses neutral silica or neutral alumina as the stationary phase and two of petroleum ether, ethyl acetate, chloroform, n-hexane, tetrahydrofuran, and methanol mixed uniformly in a volume ratio of 2:1 to 10:1 as the eluent.

5. The method for synthesizing a vanillin quaternary phosphonium salt grafted chitosan antibacterial preservative film as described in claim 2, characterized in that: The structural formula of the vanillin quaternary phosphonium salt active compound in step (2) is as follows: ； Wherein: R is butyl or phenyl; X - For F - Cl - ,Br - or I - One of them; y is 1 to 5.

6. The method for synthesizing a vanillin quaternary phosphonium salt grafted chitosan antibacterial preservative film as described in claim 2, characterized in that: In step (2), the ratio of halogenated vanillin, organophosphine ligand, and reaction solvent C is 4.0 ~ 15.5 g: 5.0 ~ 20.5 g: 50 ~ 120 mL; the ratio of halogenated vanillin and precipitant is 4.0 ~ 15.5 g: 100 ~ 250 mL.

7. The method for synthesizing a vanillin quaternary phosphonium salt grafted chitosan antibacterial preservative film as described in claim 2, characterized in that: In step (2), the organophosphorus ligand refers to triphenylphosphine or tributylphosphine; the inert gas refers to one of nitrogen, argon or carbon dioxide; and the precipitant refers to one or a mixture of two of anhydrous diethyl ether, acetone or petroleum ether.

8. The method for synthesizing a vanillin quaternary phosphonium salt grafted chitosan antibacterial preservative film as described in claim 2, characterized in that: In step (3), the organic acid solution refers to one of glacial acetic acid, citric acid, or lactic acid with a mass concentration of 0.5% to 5.5%; the mold is one of glass petri dish, polypropylene plastic, or polytetrafluoroethylene mold.

9. The method for synthesizing a vanillin quaternary phosphonium salt grafted chitosan antibacterial preservative film as described in claim 2, characterized in that: In step (3), the ratio of chitosan to organic acid solution is 1 ~ 10 g: 60 ~ 120 mL; the mass ratio of chitosan to vanillin quaternary phosphonium salt active compound is 1.5 ~ 8.0 g: 0.01 ~ 0.20 g; and the ratio of vanillin quaternary phosphonium salt active compound to reaction solvent D is 0.01 ~ 0.20 g: 2 mL.

10. The method for synthesizing a vanillin quaternary phosphonium salt grafted chitosan antibacterial preservative film as described in claim 2, characterized in that: In steps (1) to (3), reaction solvent A, reaction solvent B, reaction solvent C, and reaction solvent D are all one or a mixture of two of the following: acetonitrile, dichloromethane, dimethyl sulfoxide, anhydrous ethanol, chloroform, N,N-dimethylformamide, 1,4-dioxane, tetrahydrofuran, and acetone.

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