A highly breathable, light-proof, antibacterial and fresh-keeping film and its preparation method

Abstract

The present invention relates to the field of multifunctional film technology, and discloses a highly breathable, light-proof, antibacterial, fresh-keeping film and preparation method, based on epoxy-hydroxyl ring-opening mechanism and ion exchange, using sodium citrate, allyl glycidyl ether and compatibilized long fatty chain quaternary ammonium salt as raw materials, prepare alkenyl compatibilized linker; Based on mercapto-ene click reaction mechanism: alkenyl compatibilized linker is modified to silver-loaded or non-silver-loaded mercaptolated nano zinc oxide surface to prepare silver-loaded or non-silver-loaded organic-inorganic hybrid composite functional component; Using low-density polyethylene resin and organic-inorganic hybrid composite functional component (or silver-loaded organic-inorganic hybrid composite functional component) as raw materials, through extrusion granulation, film blowing and stretching process, prepare highly breathable, light-proof, antibacterial, fresh-keeping film. The film product prepared by the present invention has both high breathability, light-proof and antibacterial capabilities, and can be used as fruit and vegetable fresh-keeping packaging material.

Description

Technical Field

[0001] The invention relates to the technical field of fruit and vegetable fresh-keeping packaging materials, and in particular to a highly breathable, light-proof and antibacterial fresh-keeping film and a preparation method thereof. Background Art

[0002] Packaging is crucial for preserving the freshness of fruits and vegetables, and plastic film is one of the most commonly used packaging materials. Fruits and vegetables are still active after being picked, and the water vapor generated by their physiological processes easily forms droplets on the inner surface of ordinary packaging films with poor air permeability. Microorganisms thrive on these droplets, causing biochemical reactions that cause the fruits and vegetables to spoil.

[0003] Antimicrobial film is a packaging material made by adding antimicrobial agents to food packaging. It effectively kills bacteria and other microorganisms on the surface of food, ensuring food safety. Nano-zinc oxide, due to its excellent heat resistance and strong antimicrobial properties, is often used as an antimicrobial agent in the preparation of antimicrobial films. Research has found that storing fruits and vegetables in the dark can help reduce metabolic levels, maintaining good sensory and nutritional quality. Nano-zinc oxide is also a UV screener. Furthermore, nano-zinc oxide can be used as a porogen, combined with the stretching process, to effectively control the microporous structure of the film.

[0004] With the continuous improvement of food safety, the requirements for the preservation of high-value fruits and vegetables are getting higher and higher. The preservation of fresh fruits and vegetables requires light-proof, breathable and antibacterial properties. However, there is currently no film material on the market that is highly breathable, light-proof and has antibacterial properties specifically for fruits and vegetables. Summary of the Invention

[0005] The present invention uses nano zinc oxide with both light-shielding and antibacterial functions as a modifier for polyethylene resin. In order to effectively overcome the interface effect between inorganic nano zinc oxide and organic polyethylene resin, an olefinic compatibilizer is designed and synthesized. The interface bonding condition between nano zinc oxide and polyethylene resin matrix is improved by the homemade olefinic compatibilizer, and further combined with the preparation process of blow molding and stretching, a highly breathable, light-shielding and antibacterial fresh-keeping film is prepared.

[0006] In order to achieve the above object, the present invention adopts the following technical solutions:

[0007] A method for preparing a highly breathable, light-proof, antibacterial, fresh-keeping film comprises the following steps:

[0008] Step 1: Based on the epoxy-hydroxyl ring-opening mechanism, sodium citrate and allyl glycidyl ether are used as raw materials to prepare sodium propylene citrate intermediate;

[0009] The alkylated compatibilized linker is prepared by ion exchange between the intermediate sodium propylene citrate and the compatibilized long fatty chain quaternary ammonium salt;

[0010] Based on the thiol-ene click reaction mechanism: the ene-type compatibilizing linker is modified onto the surface of silver-loaded or non-silver-loaded thiol-modified nano-zinc oxide to prepare silver-loaded or non-silver-loaded organic-inorganic hybrid composite functional components;

[0011] Step 2: Adding silver-loaded or non-silver-loaded organic-inorganic hybrid composite functional components according to 1wt%-10wt% of the polyethylene resin, and preparing a highly breathable, light-proof and antibacterial fresh-keeping film through extrusion granulation, film blowing and stretching processes.

[0012] Furthermore, the volume-expanding long fatty chain quaternary ammonium salt is one of hexadecyltrimethylammonium chloride, octadecyltrimethylammonium chloride, and tetradecyltrimethylammonium chloride.

[0013] Furthermore, the preparation method of the alkenyl compatibilizing linker is as follows:

[0014] Under the catalysis of boron trifluoride ether complex, an epoxy-hydroxyl ring-opening reaction was carried out between 1 molar equivalent of sodium citrate and 1 molar equivalent of allyl glycidyl ether to prepare an allyl sodium citrate intermediate. Subsequently, the alkenyl sodium citrate intermediate was ion-exchanged with hexadecyltrimethylammonium chloride at a molar ratio of 1:3 to prepare an alkenyl compatibilizing linker.

[0015] Furthermore, the preparation method of the silver-loaded organic-inorganic hybrid composite functional component is:

[0016] Silver ions coordinate with the thiol groups in the thiol-zinc oxide nanoparticles to prepare silver-loaded thiol-zinc oxide nanoparticles;

[0017] Silver-loaded thiolated nano-zinc oxide and olefinic compatibilizing linker undergo thiol-olefin click reaction to prepare silver-loaded organic-inorganic hybrid composite functional component.

[0018] Furthermore, the blow molding process parameters are: temperatures in zones 1-4 are: 90-110°C, 130-140°C, 150-170°C, and 175-185°C.

[0019] Furthermore, the stretching process is a longitudinal stretching process, and its process parameters are: stretching temperature is 80-100° C., and stretching ratio is 1-5 times.

[0020] Furthermore, the particle size of the nano zinc oxide used in the thiolated nano zinc oxide is 20-50 nm.

[0021] Furthermore, the thickness of the highly breathable, light-proof, antibacterial and fresh-keeping film is 10-20 μm.

[0022] Furthermore, the highly breathable, light-proof and antibacterial fresh-keeping film can be used as a packaging material for fruits and vegetables.

[0023] The beneficial effects of the present invention are as follows:

[0024] Based on the epoxy ring-opening and ion exchange mechanism, an olefinic compatibilizing linker was synthesized using sodium citrate, allyl glycidyl ether and hexadecyltrimethylammonium chloride as raw materials.

[0025] Based on the thiol-ene click chemistry mechanism, an olefinic compatibilizing linker is grafted onto the surface of thiol-modified nano-zinc oxide (or silver-loaded thiol-modified nano-zinc oxide) to prepare an organic-inorganic hybrid composite functional component (or silver-loaded organic-inorganic hybrid composite functional component);

[0026] Using low-density polyethylene resin and organic-inorganic hybrid composite functional components (or silver-loaded organic-inorganic hybrid composite functional components) as raw materials, a highly breathable, light-proof, antibacterial and fresh-keeping film product is produced through blow molding and stretching processes;

[0027] The experimental results show that the membrane product prepared by the present invention has the excellent properties of high air permeability, light protection and antibacterial properties. DETAILED DESCRIPTION

[0028] Experimental Example 1:

[0029] The preparation of an organic-inorganic hybrid composite functional component comprises the following steps:

[0030] (1) Preparation of sodium propylene citrate intermediate. The preparation mechanism is as follows: under the catalytic action of boron trifluoride ether complex, the hydroxyl group in sodium citrate and the epoxy group in allyl glycidyl ether undergo a ring-opening reaction to obtain sodium propylene citrate intermediate. The specific experimental steps are as follows: under nitrogen protection, 3g sodium citrate and 0.05g boron trifluoride ether complex are added to 50mL of 70% ethanol aqueous solution, stirred evenly, and then 1.4g allyl glycidyl ether is added and mixed evenly. The system temperature is raised to 50℃, stirred for 6h, and then the pH value of the system is adjusted to 7 with ammonia water. The solvent is removed by rotary evaporation, filtered, the product is collected, and vacuum dried at 60℃ for 5h to obtain sodium propylene citrate intermediate.

[0031] The chemical structural formula of the intermediate sodium propylene citrate is:

[0032] ;

[0033] (2) Preparation of an olefinic compatibilizing linker. The preparation mechanism is as follows: Based on the ion exchange mechanism, hexadecyltrimethylammonium chloride and sodium propylene citrate intermediate undergo ion exchange to prepare an olefinic compatibilizing linker. The specific experimental steps are as follows: 2.6 g of hexadecyltrimethylammonium chloride is dissolved in 100 mL of deionized water at a temperature of 60°C to obtain a hot solution a; 1 g of sodium propylene citrate intermediate is dissolved in 50 mL of deionized water at a temperature of 60°C to obtain a hot solution b; the two hot solutions are then mixed to precipitate sodium chloride, cooled to room temperature under stirring, separated and filtered, washed with deionized water, and vacuum dried at 50°C for 6 hours to prepare an olefinic compatibilizing linker.

[0034] The chemical structure of the olefin-type compatibilizing linker is:

[0035] ;

[0036] The nuclear magnetic resonance hydrogen spectrum of the alkenyl compatibilizing linker is characterized as follows:

[0037] 1 H NMR (DMSO-d6, 400MHz) δ: 0.88-0.90 (t, 9H), 1.27-1.35 (m, 78H), 1.37-1.48 (m, 6H), 1.62 (s, 18H), 1.66 (s, 9H), 1.84-2.00 (m, 6H), 2. 75-2.87 (m, 4H), 3.44-3.57 (m, 4H), 3.90-3.96 (m, 1H), 4.01-4.02 (d, 2H), 4.38-4.39 (d, 1H), 5.15-5.27 (dd, 2H), 5.83-5.93 (m, 1H);

[0038] (3) Preparation of thiolated nano zinc oxide. The specific experimental steps are as follows: 2 g of nano zinc oxide (particle size 30 nm) was placed in 50 mL of anhydrous ethanol, ultrasonically dispersed for 20 min, 1.3 g of 3-mercaptopropyltriethoxysilane was added, mixed, and the temperature was raised to 60 ° C. The mixture was stirred for 6 h, and then the obtained mixture was separated by suction filtration, washed, and placed in a vacuum drying oven at 60 ° C for 8 h to obtain thiolated nano zinc oxide.

[0039] The chemical structure of mercapto zinc oxide is:

[0040] ;

[0041] (4) Preparation of organic-inorganic hybrid composite functional components. The preparation mechanism is as follows: under the action of benzoin dimethyl ether initiator, the alkenyl functional group in the alkenyl compatibilizer linker and the thiol group in the thiol nano-zinc oxide undergo a thiol-ene click chemical reaction to prepare an organic-inorganic hybrid composite functional component. The specific experimental steps are as follows: 2g of thiol nano-zinc oxide and 3.8g of alkenyl compatibilizer linker are added to 100mL of acetone, stirred and mixed evenly, 0.1g of benzoin dimethyl ether initiator is added, and the reaction is stirred for 3h under ultraviolet lamp (365nm, 25w), the acetone is removed by rotary evaporation, the product is filtered, and the product is collected and vacuum dried at 60℃ for 3h to prepare an organic-inorganic hybrid composite functional component.

[0042] Experimental Example 2:

[0043] Since the photocatalytic band gap of nano-zinc oxide is relatively wide, it can only be excited in the ultraviolet region with a relatively short wavelength (about 375nm). Therefore, under conditions that do not meet the excitation wavelength or insufficient lighting conditions, the antibacterial effect of nano-zinc oxide will be limited or unable to be exerted, and the purpose of anti-biological pollution cannot be achieved. Silver ions have a strong inhibitory and killing effect on microorganisms. Therefore, the present invention conceives a silver-loaded thiolated nano-zinc oxide antibacterial agent. In the absence of light or ultraviolet rays, silver ions can still exert an antibacterial effect alone. When light or ultraviolet rays are present, nano-zinc oxide and silver ions can synergistically exert an antibacterial effect, which not only effectively supplements the antibacterial deficiency of nano-zinc oxide, but also solves the problem of the high price of silver ions.

[0044] The silver-loaded thiolated nano-zinc oxide was replaced with the thiolated nano-zinc oxide in Experimental Example 1 to prepare a silver-loaded organic-inorganic hybrid composite functional component. The preparation method of the silver-loaded thiolated nano-zinc oxide is as follows: silver is loaded on the surface of the nano-zinc oxide through the strong coordination effect between some thiol groups in the thiolated nano-zinc oxide and silver ions to prepare the silver-loaded thiolated nano-zinc oxide. The specific experimental steps are as follows: 2.5 g of thiolated nano-zinc oxide was placed in 50 mL of deionized water and stirred evenly, and then 2 mL of a 1 mol / L AgNO3 solution was added. After stirring for 2 hours, the mixture was centrifuged and washed. The washing liquid was collected for silver ion loading detection and vacuum dried at 60°C for 4 hours to prepare the silver-loaded thiolated nano-zinc oxide.

[0045] According to the color development reaction of 1,10-phenanthroline-bromopyrogallol red and silver ions to form a ternary complex, the mass concentration of silver ions in the silver-loaded thiolated nano-zinc oxide washing solution was determined by spectrophotometry, and the silver ion loading capacity was calculated according to the following formula: Q=(1.50-cV)×63.5% / m0, Q is the amount of silver ions loaded per gram of silver-loaded thiolated nano-zinc oxide, g / g; c is the mass concentration of silver nitrate in the washing solution, g / mL; V is the volume of the silver nitrate solution, mL; m0 is the mass of the thiolated nano-zinc oxide, g; after testing, the silver ion loading capacity was 86 mg / g. Example 1:

[0046] A highly breathable, light-proof, antibacterial, fresh-keeping film A, comprising the following raw materials in parts by weight:

[0047] 100 parts of low-density polyethylene resin (brand: DFDJ4960);

[0048] 6 parts of organic-inorganic hybrid composite functional components;

[0049] The preparation method of the highly breathable, light-proof and antibacterial fresh-keeping film comprises the following steps:

[0050] Step 1, according to the formula of highly breathable, light-proof and antibacterial fresh-keeping film a, the ingredients are prepared, the low-density polyethylene resin and the organic-inorganic hybrid composite functional component are added to the mixer, and after stirring and mixing, the mixed material is poured into a twin-screw extruder for extrusion granulation, wherein the screw speed is 30r / min, and the temperatures of zones 1-4 are: 125°C, 165°C, 175°C, and 175°C, and then the pellets are placed in a vacuum drying oven at 80°C and dried for 4h to obtain a mixed masterbatch;

[0051] Step 2: Using a single-screw extruder, the obtained mixed masterbatch was blown into a film by an upward blowing method, wherein the screw speed during the blown film forming was 35 r / min, and the temperatures in zones 1-4 were: 100° C., 135° C., 160° C., and 180° C., to obtain a film with a thickness of 80 μm;

[0052] Step 3: longitudinally stretch the film with a thickness of 80 μm, set the stretching temperature to 90°C, the stretching ratio to 5 times, the initial speed to 0.5 m / min, and maintain the deformation heat treatment at 200°C for 5 seconds after stretching to prepare a highly breathable, light-proof and antibacterial fresh-keeping film a. Example 2:

[0053] A highly breathable, light-proof, antibacterial fresh-keeping film b was prepared, which differed from the highly breathable, light-proof, antibacterial fresh-keeping film a only in that the amount of the organic-inorganic hybrid composite functional component was 1 part by weight. Example 3:

[0054] A highly breathable, light-proof, antibacterial fresh-keeping film c was prepared, which differed from the highly breathable, light-proof, antibacterial fresh-keeping film a only in that the amount of the organic-inorganic hybrid composite functional component used was 10 parts by weight. Example 4:

[0055] A highly breathable, light-proof, antibacterial fresh-keeping film d was prepared, which differed from the highly breathable, light-proof, antibacterial fresh-keeping film a only in that a silver-loaded organic-inorganic hybrid composite functional component was used to replace the organic-inorganic hybrid composite functional component.

[0056] Comparative Example:

[0057] The polyethylene film is prepared, and the difference between the polyethylene film and the highly breathable, light-proof and antibacterial fresh-keeping film a is that the polyethylene film does not use an organic-inorganic hybrid composite functional component.

[0058] Performance testing:

[0059] 1. Antibacterial Performance Test: Escherichia coli and Staphylococcus aureus were used as test bacteria. Escherichia coli and Staphylococcus aureus were cultured at 37°C for 24 hours and diluted to 106 colony-forming units (CFU) per milliliter. 0.1g of sample was added to 10mL of bacterial dilution solution and irradiated at room temperature under 120W white light for 2 hours. Then, 0.1mL of the solution was dropped onto an AGAR plate and evenly spread, and placed at 37°C for 12 hours. The relative inhibition rate was then calculated and the average value was taken. The calculation formula is: Relative inhibition rate = (PM) / P × 100%, where P and M are the average number of bacteria in the control and experimental group samples, respectively.

[0060] Among them, the model of Escherichia coli is ATCC 25922; the model of Staphylococcus aureus is ATCC 6538;

[0061] The above test results are shown in Table 1 below;

[0062] Table 1 Test results of antibacterial properties of highly breathable, light-proof and antibacterial fresh-keeping films

[0063]

[0064] 2. Light-shielding performance test: According to GB / T 2410-2008 "Determination of light transmittance and haze of transparent plastics", the sample is tested for ultraviolet light transmittance, the test wavelength range is 250-800nm, and the transmittance of the sample at 380nm is recorded;

[0065] 3. Air Permeability Test: The oxygen transmission rate (OTR) of the sample was calculated according to GB / T 1038.1-2022 "Plastic Film and Sheeting - Gas Permeability Test Method - Part 1: Differential Pressure Method"; the water vapor transmission rate (WVP) of the sample was calculated according to GB / T 1037-2021 "Plastic Film and Sheeting - Determination of Water Vapor Permeability - Cup Weight Gain and Weight Loss Method". The test conditions were temperature 23°C and relative humidity 50%. Each group of samples was measured three times and the average value was taken.

[0066] 4. Mechanical properties test: The mechanical properties test was conducted according to GB / T 1040.3-2006. The specific test steps are as follows: a 20mm×150mm sample was fixed on a tensile testing machine, and a tensile test was performed at a tensile rate of 50mm / min, and the tensile strength of the sample was recorded;

[0067] The above test results are shown in Table 2 below;

[0068] Table 2 Performance test results of high-breathable, light-proof and antibacterial fresh-keeping film

[0069]

[0070] The following conclusions can be drawn from the experimental data in Table 1 and Table 2:

[0071] Compared with the prior art, the highly breathable, light-proof, antibacterial and fresh-keeping film prepared by the present invention has achieved beneficial technical effects of significantly improving breathability, light-proof performance, antibacterial ability and mechanical properties.

Claims

1. A method for preparing a highly breathable, light-proof, antibacterial, fresh-keeping film, characterized in that: The following steps are involved: Step 1: Based on the epoxy-hydroxyl ring-opening mechanism, sodium citrate and allyl glycidyl ether are used as raw materials to prepare sodium propylene citrate intermediate; The alkylated compatibilized linker is prepared by ion exchange between the intermediate sodium propylene citrate and the compatibilized long fatty chain quaternary ammonium salt; The chemical structural formula of the alkenyl compatibilizing linker is: ； Based on the thiol-ene click reaction mechanism: the ene-type compatibilizing linker is modified onto the surface of silver-loaded or non-silver-loaded thiol-modified nano-zinc oxide to prepare silver-loaded or non-silver-loaded organic-inorganic hybrid composite functional components; Step 2: Adding silver-loaded or non-silver-loaded organic-inorganic hybrid composite functional components according to 1wt%-10wt% of the polyethylene resin, and preparing a highly breathable, light-proof and antibacterial fresh-keeping film through extrusion granulation, film blowing and stretching processes.

2. The method for preparing a highly breathable, light-proof, antibacterial fresh-keeping film according to claim 1, characterized in that: The preparation method of the alkenyl compatibilizing linker is as follows: Under the catalysis of boron trifluoride etherate complex, an epoxy-hydroxyl ring-opening reaction is carried out between 1 molar equivalent of sodium citrate and 1 molar equivalent of allyl glycidyl ether to prepare an allyl sodium citrate intermediate, and then an ion exchange reaction is carried out between the alkenyl sodium citrate intermediate and a compatibilizing long fatty chain quaternary ammonium salt at a molar ratio of 1:3 to prepare an alkenyl compatibilizing linker; The volume-expanding long fatty chain quaternary ammonium salt is one of hexadecyltrimethylammonium chloride, octadecyltrimethylammonium chloride and tetradecyltrimethylammonium chloride.

3. The method for preparing a highly breathable, light-proof, antibacterial and fresh-keeping film according to claim 1, wherein: The preparation method of the silver-carrying organic-inorganic hybrid composite functional component is as follows: Silver ions coordinate with the thiol groups in the thiol-zinc oxide nanoparticles to prepare silver-loaded thiol-zinc oxide nanoparticles; Silver-loaded thiolated nano-zinc oxide and olefinic compatibilizing linker undergo thiol-olefin click reaction to prepare silver-loaded organic-inorganic hybrid composite functional component.

4. The method for preparing a highly breathable, light-proof, antibacterial fresh-keeping film according to claim 1, characterized in that: The blow molding process parameters are as follows: the temperatures of zones 1-4 are: 90-110°C, 130-140°C, 150-170°C, and 175-185°C.

5. The method for preparing a highly breathable, light-proof, antibacterial fresh-keeping film according to claim 1, characterized in that: The stretching process is a longitudinal stretching process, and its process parameters are: stretching temperature is 80-100° C., and stretching ratio is 1-5 times.

6. The method for preparing a highly breathable, light-proof, antibacterial fresh-keeping film according to claim 1, characterized in that: The particle size of the nano zinc oxide used in the mercaptolated nano zinc oxide is 20-50 nm.

7. A highly breathable, light-proof, antibacterial fresh-keeping film prepared according to the method according to any one of claims 1 to 6, characterized in that: The thickness of the highly breathable, light-proof, antibacterial and fresh-keeping film is 10-20 μm.

8. The use of a highly breathable, light-proof, antibacterial fresh-keeping film according to claim 7, characterized in that: The highly breathable, light-proof and antibacterial fresh-keeping film can be used as a fresh-keeping packaging material for fruits and vegetables.

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