A composite material for food packaging with sustainable utilization and its preparation process

Abstract

The present invention relates to the field of packaging materials, and particularly to a composite material for food packaging that can be sustainably utilized and its preparation process. The process includes the following steps: preparation of a high-barrier coating for oxygen and moisture; preparation of a high-strength film material solution; surface treatment and film layer coating of a PET substrate. Through the synergistic effect of rice bran wax and cinnamaldehyde, the hydrophilicity of polyvinyl alcohol is inhibited and a dense film structure is formed, enhancing the mechanical strength of the film layer and its barrier properties against moisture and oxygen. Moreover, cinnamyl alcohol can also provide good antioxidant and antibacterial properties for the film layer, and ZnO can be embedded in the coating structure to fill micropores and defects, improving the denseness and mechanical strength of the film layer. In summary, the barrier ability of the composite material for food packaging that can be sustainably utilized against oxygen and moisture is significantly improved, and it has good antibacterial and antioxidant properties.

Description

Technical Field

[0001] The present invention relates to the field of packaging materials, and particularly to a sustainable composite material for food packaging and a preparation process thereof. Background Art

[0002] With the enhancement of people's environmental protection awareness, the demand for sustainable packaging materials in the food packaging industry is increasing day by day. Traditional food packaging materials, especially plastic materials, although having good airtightness and moisture resistance, often have problems such as being difficult to reuse and easy to pollute the environment. In recent years, how to develop sustainable packaging materials on the premise of ensuring food safety has become the focus of attention in the academic and industrial fields.

[0003] Polyethylene terephthalate (PET), as a widely used food packaging material, has high transparency and good gas barrier properties. However, since the main raw material of PET material comes from petroleum, which is a non-renewable resource and difficult to degrade in the natural environment, it results in high energy consumption during the recycling process, easy material waste and generation of harmful chemical substances, increasing the burden on the environment. At the same time, in some high-demand packaging applications, the gas and moisture barrier properties of PET materials still do not meet the requirements, restricting the application range of polyethylene terephthalate. Summary of the Invention

[0004] In order to solve the above technical defects, the present invention has developed a sustainable composite material for food packaging and a preparation process thereof. The prepared sustainable composite material for food packaging has good antibacterial properties and can maintain excellent mechanical properties during the recycling process, enabling it to be continuously utilized, avoiding the problem of frequent recycling, saving energy, and having high gas and moisture barrier properties, meeting the needs of most food packaging.

[0005] A preparation process of a sustainable composite material for food packaging includes the following steps:

[0006] S1: Preparation of high gas and moisture barrier coating

[0007] The rice bran wax is melted and filtered, and then coated on the surface of the carrier. After cooling, a rice bran wax film is obtained. 3-aminopropyltriethoxysilane is mixed with absolute ethanol, and then an acid reagent is added, and stirred to obtain a 3-aminopropyltriethoxysilane solution. The rice bran wax film is immersed in the 3-aminopropyltriethoxysilane solution, stirred and then allowed to stand, and filtered to obtain a solid. After the solid is washed and dried, a modified rice bran wax is obtained. The modified rice bran wax and cinnamaldehyde are added to deionized water, and the temperature is raised for water bath stirring to obtain a premixed solution. Polyvinyl alcohol is dissolved in hot deionized water to obtain polyvinyl alcohol solution I. Nano-ZnO is ultrasonically dispersed in deionized water to obtain a ZnO dispersion. Then, polyvinyl alcohol solution I and the ZnO dispersion are mixed evenly to obtain a suspension. The suspension and the premixed solution are mixed and stirred evenly, the pH is adjusted, and then water bath heating is carried out, and then ultrasonic treatment is carried out to obtain an oxygen and moisture high-barrier coating;

[0008] S2: Preparation of high-strength film material solution

[0009] The silk is placed in an aqueous solution of Na2CO3 for heat treatment, washed and dried to obtain degummed silk. The degummed silk is added to the dissolution solution, and the temperature is raised and stirred until completely dissolved to obtain a silk fibroin mixed solution. The silk fibroin mixed solution is dialyzed with deionized water to obtain a silk fibroin aqueous solution. Polyvinyl alcohol is dissolved in deionized water to prepare polyvinyl alcohol solution II. Then, corn starch nanocrystals are ultrasonically dispersed in deionized water to prepare a corn starch nanocrystal dispersion. The silk fibroin aqueous solution and polyvinyl alcohol solution II are mixed evenly, fumaric acid is added and stirred, and then glycerol and the corn starch nanocrystal dispersion are added for high-speed shearing, and after standing, a high-strength film material solution is obtained;

[0010] S3: Surface treatment of PET substrate and film coating

[0011] The PET substrate is washed and then subjected to hierarchical corona treatment to obtain a surface-treated PET substrate. The high-strength film material solution is evenly coated on the surface of the surface-treated PET substrate using a coating rod, and after drying, a coated PET substrate is obtained. Then, the oxygen and moisture high-barrier coating is evenly coated on the surface of the coated PET substrate using a coating rod, and drying is continued to obtain a sustainable food packaging composite material.

[0012] Furthermore, the preparation of the oxygen and moisture high-barrier coating in step S1 includes the following steps:

[0013] S1.1: Heat the rice bran wax until it is completely melted, filter to remove impurities, and then uniformly coat it on the surface of the carrier by roll coating, controlling the coating thickness to be 1-2 mm. After cooling to room temperature, a rice bran wax film is obtained. 3-aminopropyltriethoxysilane and absolute ethanol are mixed in a volume ratio of 1:(20-30) and placed in a container, and then 1-2 wt% of an acid reagent is added and stirred evenly to obtain a 3-aminopropyltriethoxysilane solution;

[0014] S1.2: Immerse the rice bran wax film in a 3-aminopropyltriethoxysilane solution, stir for 20 - 30 minutes, then let it stand for 1 - 1.5 hours, and then filter to obtain a solid. Rinse the solid with absolute ethanol for 1 - 2 minutes, then rinse it 2 - 3 times with deionized water, and then place it in a drying oven to dry at a temperature of 40 - 45 °C for 2 - 3 hours to obtain modified rice bran wax. Add 1 - 2 parts by weight of the modified rice bran wax and 0.4 - 0.5 parts by weight of cinnamaldehyde to 30 - 40 parts by weight of deionized water, and stir at 50 - 55 °C in a water bath for 50 - 60 minutes to obtain a premixed solution;

[0015] S1.3: Dissolve 12 - 15 parts by weight of polyvinyl alcohol in deionized water at 95 - 98 °C to prepare a polyvinyl alcohol solution I with a mass fraction of 20 - 25%. Mix 1 - 1.5 parts by weight of nano-ZnO and 50 - 60 parts by weight of deionized water and place them in an ultrasonic cleaner, and ultrasonicate at an ultrasonic frequency of 25 - 30 kHz for 10 - 12 minutes to obtain a ZnO dispersion. Then mix the polyvinyl alcohol solution I and the ZnO dispersion in a mass ratio of 1:(0.8 - 1) in a container, stir for 25 - 30 minutes to obtain a suspension. Stir the premixed solution prepared in step S1.2 and the suspension evenly at high speed, adjust the pH to 2 - 3, then place it in a water bath pot, heat it at a water bath temperature of 60 - 65 °C for 1 - 2 hours, and then ultrasonicate at an ultrasonic frequency of 25 - 30 kHz for 20 - 30 minutes to obtain an oxygen and moisture high-barrier coating.

[0016] Further, step S2 for preparing a high-strength film material solution includes the following steps:

[0017] S2.1: Place silk in an aqueous solution of Na2CO3 with a concentration of 0.05 - 0.06%, heat it at 98 - 100 °C for 30 - 35 minutes, repeat 2 - 3 times, wash it clean with deionized water and then dry it to obtain degummed silk. Add the degummed silk to a dissolution solution, stir at 70 - 75 °C until the degummed silk is completely dissolved to obtain a silk fibroin mixed solution. Load the silk fibroin mixed solution into a dialysis bag and dialyze it with deionized water for 4 - 5 days to obtain a silk fibroin aqueous solution;

[0018] S2.2: Dissolve polyvinyl alcohol in deionized water at 95 - 98 °C to prepare a 5 - 6 wt% polyvinyl alcohol solution II. Then place corn starch nanocrystals and deionized water in an ultrasonic disperser and ultrasonically disperse them at an ultrasonic frequency of 25 - 30 kHz for 10 - 15 minutes to prepare a 0.6 - 0.8 wt% corn starch nanocrystal dispersion;

[0019] S2.3: Mix the aqueous solution of silk fibroin and the polyvinyl alcohol solution II in a volume ratio of 1: (0.8 - 1) in a container. After stirring evenly, add fumaric acid. After stirring for 1 - 2 hours, add glycerol and the corn starch nanocrystal dispersion liquid. Then, perform high - speed shearing at a rotational speed of 2000 - 3000 rpm for 40 - 45 minutes and let it stand for 2 - 3 hours to obtain a high - strength film - forming solution.

[0020] Further, the surface treatment and film - layer coating of the PET substrate in step S3 include the following steps:

[0021] S3.1: Clean the surface of the PET substrate, and then place it in a corona machine. Set the distance between the corona blade and the PET substrate to 4 - 5 mm, the voltage to 6 - 8 kV, and the pulse frequency to 32 - 35 kHz. Start the corona machine for corona treatment for 10 - 15 minutes. Then, change the distance between the corona blade and the PET substrate to 6 - 8 mm, the voltage to 8.5 - 9 kV, and the pulse frequency to 20 - 25 kHz. Start the corona machine for corona treatment for 10 - 12 minutes. Then, change the distance between the corona blade and the PET substrate to 10 - 12 mm, the voltage to 9.5 - 11 kV, and the pulse frequency to 18 - 20 kHz. Start the corona machine for corona treatment for 15 - 20 minutes to obtain a surface - treated PET substrate;

[0022] S3.2: Use a coating rod with a wet film thickness of 8 - 10 μm to evenly coat the high - strength film - forming solution on the surface of the surface - treated PET substrate. Then, place it in a blast dryer and dry for 12 - 15 hours to obtain a PET substrate with a film. Then, use a coating rod with a thickness of 6 - 8 μm to evenly coat the high - oxygen - and - moisture - barrier coating on the surface of the PET substrate with a film. Continue to place it in a blast dryer and dry for 10 - 12 hours to obtain a sustainable food - packaging composite material.

[0023] Further, the acid reagent in step S1.1 is acetic acid.

[0024] Further, the stirring speed of the high - speed stirring in step S1.3 is 1200 - 1500 rpm.

[0025] Further, the method of adjusting the pH in step S1.3 is to add a hydrochloric acid solution with a concentration of 20 - 25%.

[0026] Further, the dissolution solution in step S2.1 is prepared from CaCl2, ethanol, and water in a molar ratio of 1: (2 - 3): (8 - 10).

[0027] Further, in step S2.3, fumaric acid accounts for 0.5-1% of the total mass of the silk fibroin aqueous solution and the polyvinyl alcohol solution, glycerol accounts for 25-30% of the total volume of the silk fibroin aqueous solution and the polyvinyl alcohol solution, and the corn starch nanocrystal dispersion accounts for 40-50% of the total volume of the silk fibroin aqueous solution and the polyvinyl alcohol solution.

[0028] A sustainable composite material for food packaging is prepared by the preparation process of the above-mentioned sustainable composite material for food packaging.

[0029] The beneficial effects are as follows: 1. In the present invention, rice bran wax is immersed in 3-aminopropyltriethoxysilane solution to introduce amino groups on the surface, and after obtaining the modified rice bran wax, it is stirred with cinnamaldehyde in a water bath at an elevated temperature. During this process, a Schiff base reaction occurs between the aldehyde group and the amino group to obtain a premixed solution, which improves the binding ability of rice bran wax and subsequent polyvinyl alcohol. Then, it is mixed with polyvinyl alcohol solution I and ZnO dispersion, and subjected to a water bath at an elevated temperature and ultrasonic treatment to prepare an oxygen and moisture high-barrier coating. Among them, the imine formed after the Schiff base reaction between rice bran wax and cinnamaldehyde can crosslink with polyvinyl alcohol. The two synergistically inhibit the hydrophilicity of polyvinyl alcohol and form a dense membrane structure, enhancing the mechanical strength of the membrane layer and the barrier properties against moisture and oxygen. Moreover, cinnamyl alcohol can also provide good antioxidant and antibacterial properties for the membrane layer, and ZnO can be embedded in the coating structure to fill micropores and defects, improving the denseness and mechanical strength of the membrane layer. In summary, when coated on the PET substrate, it greatly improves the barrier ability of the sustainable composite material for food packaging against oxygen and moisture, and endows it with good antibacterial and antioxidant properties.

[0030] In the present invention, using silk fibroin as the main raw material and fumaric acid as the crosslinking agent, a pre-crosslinking reaction is first carried out with polyvinyl alcohol, and then glycerol and corn starch nanocrystals are added to introduce a crystallization domain. Fumaric acid reacts with a large number of hydroxyl and amino groups present in each component to form a large number of hydrogen bonds. Among them, the crystallization domain and hydrogen bonds can act as sacrificial bonds to dissipate energy in the high-strength film material, endowing the high-strength film material with excellent mechanical properties. And because the crystallization domain and hydrogen bonds have dynamic recoverability, when the high-strength film material is coated on the PET substrate, the prepared composite material for food packaging can still maintain excellent mechanical properties after being recycled, enabling it to be continuously utilized and avoiding the frequent recycling of PET materials.

[0031] In the present invention, by subjecting the PET substrate to hierarchical corona treatment, the surface tension of the PET substrate is greatly increased, and the surface tension of the PET substrate can be evenly distributed, reducing the decrease in the mechanical strength of the PET substrate after corona treatment, and greatly improving the adhesion between the high-strength film material solution and the PET substrate, enhancing the overall strength and stability of the sustainable composite material for food packaging. Description of the Drawings

[0032] Figure 1 The process flow chart for the preparation of a sustainable food packaging composite material adopted in the embodiments of the present invention. Specific embodiments

[0033] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without making creative efforts belong to the scope of protection of the present invention.

[0034] Embodiment 1: A sustainable food packaging composite material and its preparation process, as Figure 1 shown, including the following steps:

[0035] S1: Preparation of oxygen and moisture high-barrier coating

[0036] S1.1: Heat rice bran wax until it is completely melted, filter to remove impurities, and then evenly coat it on the surface of the carrier by the roll coating method, control the coating thickness to be 1 mm, and obtain a rice bran wax film after cooling to room temperature. Mix 3-aminopropyltriethoxysilane and absolute ethanol in a volume ratio of 1:20 and place them in a container, then add 1 wt% acetic acid and stir evenly to obtain a 3-aminopropyltriethoxysilane solution;

[0037] S1.2: Immerse the rice bran wax film in the 3-aminopropyltriethoxysilane solution, stir for 20 minutes and then let it stand for 1 hour, then filter to obtain a solid, rinse the solid with absolute ethanol for 1 minute, then rinse it twice with deionized water, and then place it in a drying oven and dry it at a temperature of 40 °C for 2 hours to obtain modified rice bran wax. Add 1 part by weight of modified rice bran wax and 0.4 part by weight of cinnamaldehyde to 30 parts by weight of deionized water, and stir in a water bath at 50 °C for 50 minutes to obtain a premixed solution;

[0038] S1.3: Dissolve 12 parts by weight of polyvinyl alcohol in deionized water at 95 °C to prepare a polyvinyl alcohol solution I with a mass fraction of 20%. Mix 1 part by weight of nano-ZnO and 50 parts by weight of deionized water and place them in an ultrasonic cleaner, and ultrasonicate at an ultrasonic frequency of 25 kHz for 10 minutes to obtain a ZnO dispersion. Then mix the polyvinyl alcohol solution I and the ZnO dispersion in a mass ratio of 1:0.8 and place them in a container, stir for 25 minutes to obtain a suspension. Stir the premixed solution prepared in step S1.2 and the suspension evenly at a stirring speed of 1200 rpm, add a hydrochloric acid solution with a concentration of 25% to adjust the pH to 2, then place it in a water bath pot, heat it at a water bath temperature of 60 °C for 1 hour, and then ultrasonicate at an ultrasonic frequency of 25 kHz for 20 minutes to obtain an oxygen and moisture high-barrier coating.

[0039] S2: Prepare a high-strength film material solution

[0040] S2.1: Place silk in an aqueous Na2CO3 solution with a concentration of 0.05%, heat at 98 °C for 30 minutes, repeat 2 times, wash thoroughly with deionized water and then dry to obtain degummed silk. Add the degummed silk to a dissolution solution, which is prepared from CaCl2, ethanol, and water in a molar ratio of 1:2:8. Stir at 70 °C until the degummed silk is completely dissolved to obtain a silk fibroin mixture. Load the silk fibroin mixture into a dialysis bag and dialyze with deionized water for 4 days to obtain a silk fibroin aqueous solution;

[0041] S2.2: Dissolve polyvinyl alcohol in deionized water at 95 °C to prepare a 5 wt% polyvinyl alcohol solution II. Then place corn starch nanocrystals and deionized water in an ultrasonic disperser and ultrasonically disperse at an ultrasonic frequency of 25 kHz for 10 minutes to prepare a 0.6 wt% corn starch nanocrystal dispersion;

[0042] S2.3: Mix the silk fibroin aqueous solution and polyvinyl alcohol solution II in a volume ratio of 1:0.8 in a container. After stirring evenly, add 0.5% of fumaric acid based on the total mass of the silk fibroin aqueous solution and polyvinyl alcohol solution. Stir for 1 hour, then add glycerol accounting for 25% of the total volume of the silk fibroin aqueous solution and polyvinyl alcohol solution and 40% of the corn starch nanocrystal dispersion. High-speed shear at a speed of 2000 rpm for 40 minutes and then let it stand for 2 hours to obtain a high-strength film material solution.

[0043] S3: Surface treatment of the PET substrate and film coating

[0044] S3.1: Clean the surface of the PET substrate, then place it in a corona machine. Set the distance between the corona blade and the PET substrate to 4 mm, the voltage to 6 kV, and the pulse frequency to 32 kHz. Start the corona machine for 15 minutes of corona treatment. Then change the distance between the corona blade and the PET substrate to 6 mm, the voltage to 8.5 kV, and the pulse frequency to 20 kHz. Start the corona machine for 12 minutes of corona treatment. Then change the distance between the corona blade and the PET substrate to 10 mm, the voltage to 9.5 kV, and the pulse frequency to 18 kHz. Start the corona machine for 20 minutes of corona treatment to obtain a surface-treated PET substrate;

[0045] S3.2: Use a coating rod with a wet film thickness of 8 μm to evenly coat the high-strength film material solution on the surface of the surface-treated PET substrate, then place it in a forced-air dryer and dry for 12 hours to obtain a PET substrate with a film. Then use a 6-μm coating rod to evenly coat an oxygen and moisture high-barrier coating on the surface of the PET substrate with a film, and continue to place it in a forced-air dryer and dry for 10 hours to obtain a sustainable food packaging composite material.

[0046] Example 2: A composite material for food packaging with sustainable utilization and its preparation process, as Figure 1 shown, including the following steps:

[0047] S1: Preparation of oxygen and moisture high-barrier coating

[0048] S1.1: Heat rice bran wax until it is completely melted, filter to remove impurities, then use the roll coating method to evenly coat it on the surface of the carrier, control the coating thickness to be 1 mm, and obtain a rice bran wax film after cooling to room temperature. Mix 3-aminopropyltriethoxysilane and absolute ethanol in a volume ratio of 1:20 and place them in a container, then add 1 wt% acetic acid and stir evenly to obtain a 3-aminopropyltriethoxysilane solution;

[0049] S1.2: Immerse the rice bran wax film in the 3-aminopropyltriethoxysilane solution, stir for 20 minutes and then let it stand for 1 hour, then filter to obtain a solid substance. Rinse the solid substance with absolute ethanol for 1 minute, then rinse it twice with deionized water, and then place it in a drying oven to dry at a temperature of 40 °C for 2 hours to obtain modified rice bran wax. Add 2 parts by weight of the modified rice bran wax and 0.5 part by weight of cinnamaldehyde to 40 parts by weight of deionized water, and stir at 50 °C in a water bath for 50 minutes to obtain a premixed solution;

[0050] S1.3: Dissolve 15 parts by weight of polyvinyl alcohol in deionized water at 95 °C to prepare a polyvinyl alcohol solution I with a mass fraction of 25%. Mix 1.5 parts by weight of nano-ZnO and 60 parts by weight of deionized water and place them in an ultrasonic cleaner, and ultrasonicate for 10 minutes at an ultrasonic frequency of 25 kHz to obtain a ZnO dispersion liquid. Then mix the polyvinyl alcohol solution I and the ZnO dispersion liquid in a mass ratio of 1:1 and place them in a container, stir for 25 minutes to obtain a suspension. Stir the premixed solution prepared in step S1.2 and the suspension evenly at a stirring speed of 1200 rpm, add a hydrochloric acid solution with a concentration of 25% to adjust the pH to 2, then place it in a water bath pot and heat at a water bath temperature of 60 °C for 1 hour, and then ultrasonicate at an ultrasonic frequency of 25 kHz for 20 minutes to obtain an oxygen and moisture high-barrier coating.

[0051] S2: Preparation of high-strength film material solution

[0052] S2.1: Place silk in an aqueous solution of Na2CO3 with a concentration of 0.05%, heat at 98 °C for 30 minutes, repeat 2 times, wash it clean with deionized water and then dry it to obtain degummed silk. Add the degummed silk to the dissolution solution, and the dissolution solution is prepared from CaCl2, ethanol and water in a molar ratio of 1:2:8. Stir at 70 °C until the degummed silk is completely dissolved to obtain a silk fibroin mixed solution. Put the silk fibroin mixed solution into a dialysis bag and dialyze it with deionized water for 4 days to obtain a silk fibroin aqueous solution;

[0053] S2.2: Dissolve polyvinyl alcohol in deionized water at 95 °C to prepare a 6 wt% polyvinyl alcohol solution II. Then, place corn starch nanocrystals and deionized water in an ultrasonic disperser and disperse them ultrasonically at a frequency of 25 kHz for 10 minutes to obtain a 0.8 wt% corn starch nanocrystal dispersion.

[0054] S2.3: Mix the aqueous silk fibroin solution and polyvinyl alcohol solution II in a volume ratio of 1:1 in a container. After stirring evenly, add 1% of fumaric acid based on the total mass of the aqueous silk fibroin solution and polyvinyl alcohol solution. After stirring for 1 hour, add glycerol accounting for 30% of the total volume of the aqueous silk fibroin solution and polyvinyl alcohol solution and 50% of the corn starch nanocrystal dispersion. High-speed shear at a speed of 2000 rpm for 40 minutes and then let it stand for 2 hours to obtain a high-strength film material solution.

[0055] S3: Surface treatment of PET substrate and film coating

[0056] S3.1: Clean the surface of the PET substrate, and then place it in a corona machine. Set the distance between the corona blade and the PET substrate to 4 mm, the voltage to 6 kV, and the pulse frequency to 32 kHz. Start the corona machine for 15 minutes of corona treatment. Then, change the distance between the corona blade and the PET substrate to 6 mm, the voltage to 8.5 kV, and the pulse frequency to 20 kHz. Start the corona machine for 12 minutes of corona treatment. Then, change the distance between the corona blade and the PET substrate to 10 mm, the voltage to 9.5 kV, and the pulse frequency to 18 kHz. Start the corona machine for 20 minutes of corona treatment to obtain a surface-treated PET substrate.

[0057] S3.2: Use a coating rod with a wet film thickness of 8 μm to evenly coat the high-strength film material solution on the surface of the surface-treated PET substrate, and then place it in a hot air dryer and dry for 12 hours to obtain a PET substrate with a film. Then, use a 6-μm coating rod to evenly coat the oxygen and moisture high-barrier coating on the surface of the PET substrate with a film, and continue to place it in a hot air dryer and dry for 10 hours to obtain a sustainable food packaging composite material.

[0058] Example 3: A sustainable food packaging composite material and its preparation process, as Figure 1 shown, including the following steps:

[0059] S1: Preparation of oxygen and moisture high-barrier coating

[0060] S1.1: Heat rice bran wax until it is completely melted, filter to remove impurities, then evenly coat it on the surface of the carrier by the roll coating method, control the coating thickness to be 2 mm, and obtain a rice bran wax film after cooling to room temperature. Mix 3-aminopropyltriethoxysilane and absolute ethanol in a volume ratio of 1:30 and place them in a container, then add 2 wt% acetic acid and stir evenly to obtain a 3-aminopropyltriethoxysilane solution;

[0061] S1.2: Immerse the rice bran wax film in the 3-aminopropyltriethoxysilane solution, stir for 30 minutes and then let it stand for 1.5 hours, then filter to obtain a solid. Rinse the solid with absolute ethanol for 2 minutes, then rinse it 3 times with deionized water, and then place it in a drying oven to dry at a temperature of 45 °C for 3 hours to obtain modified rice bran wax. Add 1 part by weight of the modified rice bran wax and 0.4 part by weight of cinnamaldehyde to 30 parts by weight of deionized water, and stir at 55 °C in a water bath for 60 minutes to obtain a premixed solution;

[0062] S1.3: Dissolve 12 parts by weight of polyvinyl alcohol in deionized water at 98 °C to prepare a polyvinyl alcohol solution I with a mass fraction of 20%. Mix 1 part by weight of nano-ZnO and 50 parts by weight of deionized water and place them in an ultrasonic cleaner, and ultrasonically clean for 12 minutes at an ultrasonic frequency of 30 kHz to obtain a ZnO dispersion. Then mix the polyvinyl alcohol solution I and the ZnO dispersion in a mass ratio of 1:0.8 and place them in a container, stir for 30 minutes to obtain a suspension. Stir the premixed solution prepared in step S1.2 and the suspension evenly at a stirring speed of 1500 rpm, add a 20% hydrochloric acid solution to adjust the pH to 3, then place it in a water bath pot and heat at a water bath temperature of 65 °C for 2 hours, and then ultrasonically clean for 30 minutes at an ultrasonic frequency of 30 kHz to obtain an oxygen and moisture high-barrier coating.

[0063] S2: Prepare a high-strength film material solution

[0064] S2.1: Place silk in an aqueous solution of Na2CO3 with a concentration of 0.06%, heat at 100 °C for 35 minutes, repeat 3 times, wash it clean with deionized water and then dry it to obtain degummed silk. Add the degummed silk to the dissolution solution, and the dissolution solution is prepared from CaCl2, ethanol and water in a molar ratio of 1:3:10. Stir at 75 °C until the degummed silk is completely dissolved to obtain a silk fibroin mixed solution. Put the silk fibroin mixed solution into a dialysis bag and dialyze it with deionized water for 5 days to obtain a silk fibroin aqueous solution;

[0065] S2.2: Dissolve polyvinyl alcohol in deionized water at 98 °C to prepare a 6 wt% polyvinyl alcohol solution II. Then place corn starch nanocrystals and deionized water in an ultrasonic disperser and ultrasonically disperse them for 15 minutes at an ultrasonic frequency of 30 kHz to prepare a 0.6 wt% corn starch nanocrystal dispersion;

[0066] S2.3: Mix the aqueous solution of silk fibroin and the polyvinyl alcohol solution II in a volume ratio of 1:0.8 in a container. After stirring evenly, add 0.5% of fumaric acid based on the total mass of the aqueous solution of silk fibroin and the polyvinyl alcohol solution. After stirring for 2 hours, add glycerol accounting for 25% of the total volume of the aqueous solution of silk fibroin and the polyvinyl alcohol solution and 40% of the corn starch nanocrystal dispersion. High-speed shear at a speed of 3000 rpm for 45 minutes and then let it stand for 3 hours to obtain a high-strength film material solution.

[0067] S3: Surface treatment of the PET substrate and film layer coating

[0068] S3.1: Clean the surface of the PET substrate, and then place it in a corona machine. Set the distance between the corona blade and the PET substrate to 5 mm, the voltage to 8 kV, and the pulse frequency to 35 kHz. Start the corona machine for 10 minutes of corona treatment. Then change the distance between the corona blade and the PET substrate to 8 mm, the voltage to 9 kV, and the pulse frequency to 25 kHz. Start the corona machine for 10 minutes of corona treatment. Then change the distance between the corona blade and the PET substrate to 12 mm, the voltage to 11 kV, and the pulse frequency to 20 kHz. Start the corona machine for 15 minutes of corona treatment to obtain a surface-treated PET substrate;

[0069] S3.2: Use a coating rod with a wet film thickness of 10 μm to evenly coat the high-strength film material solution on the surface of the surface-treated PET substrate, and then place it in a blast dryer for 15 hours to obtain a PET substrate with a film. Then use an 8-μm coating rod to evenly coat the high oxygen and moisture barrier coating on the surface of the PET substrate with a film, and continue to place it in a blast dryer for 12 hours to obtain a sustainable food packaging composite material.

[0070] Comparative Example 1: The difference between Comparative Example 1 and Example 1 is that Comparative Example 1 removes steps S1.1 and S1.2 and does not add the premixed solution in step S1.3. The remaining steps are the same as those in Example 1, and a sustainable food packaging composite material is prepared, denoted as Comparative Example 1.

[0071] Comparative Example 2: The difference between Comparative Example 2 and Example 1 is that Comparative Example 2 removes step S1.1 and does not add modified rice bran wax in step S1.2. The remaining steps are the same as those in Example 1, and a sustainable food packaging composite material is prepared, denoted as Comparative Example 2.

[0072] Comparative Example 3: The difference between Comparative Example 3 and Example 1 is that Comparative Example 3 does not add cinnamaldehyde in step S1.2. The remaining steps are the same as those in Example 1, and a sustainable food packaging composite material is prepared, denoted as Comparative Example 3.

[0073] Comparative Example 4: The difference between Comparative Example 4 and Example 1 is that in Comparative Example 4, step S2 is removed, and the high-strength film material solution is not coated on the surface-treated PET substrate in step S3.2. The remaining steps are the same as those in Example 1, and a sustainable food packaging composite material is prepared, denoted as Comparative Example 4.

[0074] Experiment 1: Take the sustainable food packaging composite materials prepared in the examples and Comparative Examples 1-3. Refer to "GB / T 1034—2008 Test Method for Water Absorption of Plastics", conduct a 12-hour water absorption treatment on the sustainable food packaging composite materials, and calculate the water absorption rate according to the formula water absorption rate = (m2 - m1) / m1 × 100%, where m2 is the weight after water absorption and m1 is the weight before water absorption. According to the determination of "GB / T 26253-2010 Plastics - Film and Sheeting - Water Vapor Transmission Rate", test its water vapor barrier performance, and then according to "GB / T 1038-2000 Plastics - Film and Sheeting - Gas Permeability Test Method - Differential Pressure Method", test its oxygen barrier performance. Each group of experiments is carried out three times, and the average value is taken, and the data is recorded and made into a table, as shown in Table 1.

[0075] Table 1: Water Absorption Rate, Water Vapor and Oxygen Permeation Rates of Sustainable Food Packaging Composite Materials

[0076] Water Absorption Rate / % <![CDATA[Water vapor transmission rate g / (m 2 ·day)]]> <![CDATA[Oxygen transmission rate g / (m 2 ·day)]]> Example 1 5.3 2.2 1.2 Example 2 5.1 2.1 1.2 Example 3 4.8 1.8 1 Comparative Example 1 26.3 42.3 81.4 Comparative Example 2 18.6 25.6 47.9 Comparative Example 3 15.3 20.1 44.3

[0077] As can be seen from Table 1, the sustainable food packaging composite materials prepared in the examples have lower water absorption rate, water vapor transmission rate and oxygen transmission rate than Comparative Examples 1-3. It can be proved that combining modified rice bran wax and cinnamaldehyde and preparing an oxygen and moisture high-barrier coating with polyvinyl alcohol can greatly improve the barrier ability of the sustainable food packaging composite materials to oxygen and moisture. And it can be seen that the increased values of the water absorption rate, water vapor transmission rate and oxygen transmission rate of Comparative Example 1 relative to Example 1 are less than the sum of the increased values of the water absorption rate, water vapor transmission rate and oxygen transmission rate of Comparative Example 2 and Comparative Example 3, which can prove that modified rice bran wax and cinnamaldehyde synergistically improve the barrier performance of the sustainable food packaging composite materials to moisture and oxygen.

[0078] Experiment 2: Take the sustainable food packaging composite materials prepared in the examples and Comparative Examples 1-4 with the same shape and size respectively, clamp them on the film material electronic universal testing machine, with a tensile force of 30 N, the initial fixture setting is 20 mm, the gauge length setting is 10 mm, and the tensile rate setting is 30 mm / min. Test the tensile distance at break under normal temperature conditions. The longer the tensile distance, the better the tensile strength. Each test is carried out three times, and the data is recorded and made into a table, as shown in Table 2.

[0079] Table 2: Tensile Distance of Sustainable Food Packaging Composite Materials under 30 N Tensile Force

[0080] Tensile Distance / mm First Second Third Example 1 14.5 14.3 14.6 Example 2 14.8 14.9 14.7 Example 3 15.1 14.9 15.2 Comparative Example 1 13.2 13.1 13.3 Comparative Example 2 13.9 14.1 13.8 Comparative Example 3 13.6 13.7 13.6 Comparative Example 4 10.1 10.3 10.5

[0081] As can be seen from Table 2, the tensile strengths of the sustainable food packaging composite materials prepared in the examples are all greater than those of Comparative Examples 1-4. It can be proved that combining modified rice bran wax and cinnamaldehyde and preparing an oxygen and moisture high-barrier coating with polyvinyl alcohol can also improve the mechanical properties of the sustainable food packaging composite materials. At the same time, it can be proved that using silk fibroin as the main raw material, fumaric acid as the cross-linking agent, polyvinyl alcohol and corn starch nanocrystals, the prepared high-strength film solution can greatly improve the mechanical properties of the sustainable food packaging composite materials.

[0082] Experiment 3: Take the surface-treated PET substrates and PET substrates prepared in the examples, and use a surface tension tester to test the surface tension. Test three times respectively, record the data and make a table as shown in Table 3. It can be seen that the surface tension of the surface-treated PET substrates prepared in the examples is much higher than that of the PET substrates, and all are higher than 55 dyn / cm, fully meeting the requirements of film coating adhesion.

[0083] Table 3: Surface Tension of Surface-Treated PET Substrates

[0084] Surface Tension dyn / cm First Second Third Example 1 54 56 53 Example 2 55 57 56 Example 3 57 58 56 PET Substrate 40 42 41

[0085] The above examples are only illustrative of the principles and effects of the present invention, and are not intended to limit the present invention. Any person familiar with this technology can modify or change the above examples without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or changes completed by those with ordinary knowledge in the technical field without departing from the spirit and technical idea disclosed by the present invention should still be covered by the claims of the present invention.

Claims

1. A process for preparing a composite material for food packaging that can be used sustainably, characterized in that: The following steps are involved: S1: Preparation of high oxygen and moisture barrier coatings The rice bran wax is melted and filtered, and then coated on the surface of the carrier, and then cooled to obtain a rice bran wax film, 3-aminopropyl triethoxysilane is mixed with anhydrous ethanol, an acid reagent is added, and stirred to obtain a 3-aminopropyl triethoxysilane solution, the rice bran wax film is immersed in the 3-aminopropyl triethoxysilane solution, stirred and then allowed to stand, and a solid is obtained by filtering, and the solid is washed and dried to obtain a modified rice bran wax, the modified rice bran wax and cinnamaldehyde are added to deionized water, the temperature is increased and stirred in a water bath to obtain a premixed liquid, polyvinyl alcohol is dissolved in hot deionized water to obtain a polyvinyl alcohol solution I, nano ZnO is ultrasonically dispersed in deionized water to obtain a ZnO dispersion, and then the polyvinyl alcohol solution I and the ZnO dispersion are uniformly mixed to obtain a suspension, the suspension and the premixed liquid are uniformly mixed and stirred, the pH is adjusted, the water bath is heated, and then ultrasonic treatment is performed to obtain a high oxygen and moisture barrier coating; S2: Preparation of high-strength membrane solution The silk is placed in a Na2CO3 aqueous solution for heating treatment, washed and dried to obtain degummed silk, the degummed silk is added to a dissolving solution, heated and stirred until completely dissolved to obtain a silk fibroin mixed solution, the silk fibroin mixed solution is dialyzed with deionized water to obtain a silk fibroin aqueous solution, polyvinyl alcohol is dissolved in deionized water to obtain a polyvinyl alcohol solution II, corn starch nanocrystals are ultrasonically dispersed in deionized water to obtain a corn starch nanocrystal dispersion, the silk fibroin aqueous solution and the polyvinyl alcohol solution II are uniformly mixed, fumaric acid is added and stirred, and then glycerol and the corn starch nanocrystal dispersion are added for high-speed shearing, and a high-strength membrane material solution is obtained after standing. S3: Surface treatment and film coating of PET substrate The PET substrate is cleaned and subjected to graded corona treatment to obtain a surface-treated PET substrate. A high-strength film material solution is evenly coated on the surface of the surface-treated PET substrate using a coating rod. After drying, a film-coated PET substrate is obtained. A coating rod is then used to evenly coat the oxygen and moisture high barrier coating on the surface of the film-coated PET substrate. Drying is continued to obtain a sustainable composite material for food packaging.

2. The process for preparing a composite material for sustainable food packaging according to claim 1, characterized in that: Step S1: Preparation of oxygen and moisture high barrier coating, comprising the following steps: S1.1: Heat the rice bran wax until it is completely melted, filter to remove impurities, and then evenly coat the wax on the surface of the carrier by roller coating, controlling the coating thickness to be 1-2 mm, and obtain a rice bran wax film after cooling to room temperature, and place 3-aminopropyltriethoxysilane and anhydrous ethanol in a volume ratio of 1: (20-30) in a container, then add 1-2wt% of an acid reagent, and stir evenly to obtain a 3-aminopropyltriethoxysilane solution; S1.2: Immerse the rice bran wax film in a 3-aminopropyltriethoxysilane solution, stir for 20-30 minutes, let stand for 1-1.5 hours, and then filter to obtain a solid, rinse the solid with anhydrous ethanol for 1-2 minutes, rinse it in deionized water for 2-3 times, and then dry it in a drying oven at a temperature of 40-45° C. for 2-3 hours to obtain a modified rice bran wax, add 1-2 parts by weight of the modified rice bran wax and 0.4-0.5 parts by weight of cinnamaldehyde to 30-40 parts by weight of deionized water, and stir it in a water bath at 50-55° C. for 50-60 minutes to obtain a premix; S1.3: Dissolve 12-15 parts by weight of polyvinyl alcohol in deionized water at 95-98°C to prepare a polyvinyl alcohol solution I with a mass fraction of 20-25%, mix 1-1.5 parts by weight of nano ZnO and 50-60 parts by weight of deionized water and place them in an ultrasonic cleaning machine, ultrasonicate at an ultrasonic frequency of 25-30kHz for 10-12 minutes to obtain a ZnO dispersion, then mix the polyvinyl alcohol solution I and the ZnO dispersion in a mass ratio of 1: (0.8-1) in a container, stir for 25-30 minutes to obtain a suspension, stir the premixed solution and the suspension obtained in step S1.2 at high speed to uniformly mix, adjust the pH to 2-3, place in a water bath, heat at a water bath temperature of 60-65°C for 1-2 hours, and then ultrasonicate at an ultrasonic frequency of 25-30kHz for 20-30 minutes to obtain a high oxygen and moisture barrier coating.

3. The process for preparing a composite material for sustainable food packaging according to claim 2, characterized in that: Step S2 prepares a high-strength membrane material solution, comprising the following steps: S2.1: placing silk in a 0.05-0.06% Na2CO3 aqueous solution, heating at 98-100°C for 30-35 minutes, repeating 2-3 times, washing with deionized water and drying to obtain degummed silk, adding the degummed silk to the dissolving solution, stirring at 70-75°C until the degummed silk is completely dissolved, obtaining a silk fibroin mixed solution, placing the silk fibroin mixed solution into a dialysis bag, dialyzing with deionized water for 4-5 days, obtaining a silk fibroin aqueous solution; S2.2: dissolving polyvinyl alcohol in deionized water at 95-98° C. to prepare a 5-6 wt % polyvinyl alcohol solution II, and then placing corn starch nanocrystals and deionized water in an ultrasonic disperser, and ultrasonically dispersing at an ultrasonic frequency of 25-30 kHz for 10-15 minutes to prepare a 0.6-0.8 wt % corn starch nanocrystal dispersion; S2.3: Mix the silk fibroin aqueous solution and polyvinyl alcohol solution II in a volume ratio of 1: (0.8-1) in a container, stir evenly and add fumaric acid. After stirring for 1-2 hours, add glycerol and corn starch nanocrystal dispersion, shear at a speed of 2000-3000 rpm for 40-45 minutes, and then let it stand for 2-3 hours to obtain a high-strength membrane solution.

4. The process for preparing a composite material for sustainable food packaging according to claim 3, characterized in that: Step S3: Surface treatment of PET substrate and film coating, including the following steps: S3.1: Clean the surface of the PET substrate, then place it in a corona machine, set the distance between the electric blade and the PET substrate to 4-5mm, the voltage to 6-8kV, the pulse frequency to 32-35kHz, start the corona machine for 10-15 minutes of corona treatment, then change the distance between the electric blade and the PET substrate to 6-8mm, the voltage to 8.5-9kV, the pulse frequency to 20-25kHz, start the corona machine for 10-12 minutes of corona treatment, then change the distance between the electric blade and the PET substrate to 10-12mm, the voltage to 9.5-11kV, the pulse frequency to 18-20kHz, start the corona machine for 15-20 minutes of corona treatment, and obtain a surface-treated PET substrate; S3.2: Use a coating rod with a wet film thickness of 8-10μm to evenly coat the high-strength film material solution on the surface of the surface-treated PET substrate, and then place it in a blower dryer for drying for 12-15 hours to obtain a coated PET substrate. Then use a 6-8μm coating rod to evenly coat the oxygen and moisture high barrier coating on the surface of the coated PET substrate, and continue to place it in a blower dryer for drying for 10-12 hours to obtain a sustainable composite material for food packaging.

5. The process for preparing a composite material for sustainable food packaging according to claim 2, characterized in that: The acid reagent in step S1.1 is acetic acid.

6. The process for preparing a composite material for sustainable food packaging according to claim 2, characterized in that: The stirring speed of the high-speed stirring in step S1.3 is 1200-1500 rpm.

7. The process for preparing a composite material for sustainable food packaging according to claim 2, characterized in that: In step S1.3, the pH is adjusted by adding a hydrochloric acid solution with a concentration of 20-25%.

8. The process for preparing a composite material for sustainable food packaging according to claim 3, characterized in that: The dissolving solution in step S2.1 is prepared from CaCl2, ethanol and water in a molar ratio of 1:(2-3):(8-10).

9. The process for preparing a composite material for sustainable food packaging according to claim 3, characterized in that: In step S2.3, the fumaric acid accounts for 0.5-1% of the total mass of the silk fibroin aqueous solution and the polyvinyl alcohol solution, the glycerol accounts for 25-30% of the total volume of the silk fibroin aqueous solution and the polyvinyl alcohol solution, and the corn starch nanocrystal dispersion accounts for 40-50% of the total volume of the silk fibroin aqueous solution and the polyvinyl alcohol solution.

10. A sustainable composite material for food packaging, characterized in that: The food packaging composite material is prepared by the preparation process of a sustainable composite material for food packaging according to any one of claims 1 to 9.

Images