Antibacterial food packaging bag and preparation method thereof

Abstract

The invention relates to the technical field of plastics, in particular to an antibacterial food packaging bag and a preparation method thereof.The antibacterial food packaging bag is prepared by blending polylactic acid and polypropylene carbonate as a base film raw material, selecting a food-grade ADR chain extender as a chain extender, selecting one of butyl titanate and a titanate coupling agent as a compatibilizer and selecting composite hybrid cellulose as a broad-spectrum antibacterial agent; carrying out extrusion granulation and blow molding to obtain a base film; the preparation method comprises the following steps: taking microcrystalline cellulose-nano zinc oxide hybrid particles as hybrid cellulose, performing epoxidation on the hybrid cellulose by using epoxy chloropropane, and then grafting an amino acid-based Schiff base antibacterial agent by using epoxy-hydroxyl reaction; composite hybrid cellulose and modified castor oil-based waterborne polyurethane are used for preparing a protective coating, the surface of a base membrane is coated with the protective coating, and a green, environment-friendly, durable, antibacterial, hydrophobic and antifouling self-repairing surface is constructed.

Description

Technical Field

[0001] The invention relates to the technical field of plastics, in particular to an antibacterial food packaging bag and a preparation method thereof. Background Art

[0002] In modern society, people often use plastic as packaging materials in daily life and industrial and agricultural production. Traditional food plastic packaging bags generally have poor antibacterial ability. Using them to hold foods such as fruits and vegetables for a long time can easily accelerate the decay of food. As the concepts of green, healthy and safe are deeply rooted in people's minds, degradable and antibacterial food plastic packaging has gradually come into the consumer's field of vision.

[0003] Existing biodegradable antibacterial food plastics are mostly made of biodegradable raw materials such as polylactic acid and polypropylene carbonate as the base material with the addition of antibacterial agents. Although polylactic acid has the advantages of high mechanical strength and good thermal stability, it has problems such as brittleness, poor barrier properties, and difficulty in blowing film alone; and although polypropylene carbonate has good gas barrier properties, it still has disadvantages such as low heat resistance temperature and poor mechanical strength. In addition, most of them have problems such as short-lived antibacterial effect and poor water resistance. Summary of the invention

[0004] The object of the present invention is to provide an antibacterial food packaging bag and a preparation method thereof to solve the problems in the prior art.

[0005] In order to solve the above technical problems, the present invention provides the following technical solutions: A method for preparing an antibacterial food packaging bag comprises the following steps: S1: polylactic acid, polypropylene carbonate, chain extender, compatibilizer and composite hybrid cellulose are mixed and extruded, granulated and blow-molded to obtain a base film; S2: Preparation of protective coatings using composite hybrid cellulose and modified castor oil-based waterborne polyurethane; S3: The protective coating is coated on the surface of the base film, dried, and then transferred to a bag making machine, and cut, heat-sealed, and punched in sequence to obtain an antibacterial food packaging bag.

[0006] Furthermore, the working conditions of mixed extrusion are: using a twin-screw extruder for extrusion, wherein the temperature of zone 1 of the twin-screw extruder is 153°C, the temperature of zone 2 is 163°C, the temperature of zone 3 is 185°C, the temperature of zone 4 is 153°C, and the screw speed is 12.5rpm; the working conditions of blow molding are: using an extrusion film blowing machine for molding, wherein the temperature of zone 1 of the extrusion film blowing machine is 145°C, the temperature of zone 2 is 170°C, the temperature of zone 3 is 175°C, the temperature of zone 4 is 145°C, the screw speed is 12rpm, and the traction speed is 4m / min.

[0007] Furthermore, the chain extender is a food-grade ADR chain extender, and the compatibilizer is one of butyl titanate and a titanate coupling agent or a combination thereof.

[0008] Furthermore, the raw material composition of the base film is, by weight: 55-65 parts of polylactic acid, 35-45 parts of polypropylene carbonate, 0.5-1 parts of chain extender, 5-10 parts of compatibilizer, and 0.8-1.3 parts of composite hybrid cellulose.

[0009] Furthermore, the mass ratio of the composite hybrid cellulose and the modified castor oil-based waterborne polyurethane in the protective coating is 9.5-12.5%.

[0010] Further, the preparation of the composite hybrid cellulose comprises the following steps: (1) Mix microcrystalline cellulose, sodium hydroxide solution and ethanol solution, keep warm at 18-30°C for 3-4 hours, filter and dry, add ethanol, stir for 8-10 minutes, add zinc acetate dihydrate and ethanol mixture, keep warm in a water bath at 70-80°C for 60-70 minutes, adjust the pH to 10.9-11.1, keep warm for 30-40 minutes, filter and dry to obtain hybrid cellulose; (2) Mixing hybrid cellulose, NaOH solution and epichlorohydrin, stirring at 18-25° C. for 18-20 hours, filtering, washing and drying to obtain epoxidized hybrid cellulose; (3) The amino acid-based Schiff base antibacterial agent, epoxidized hybrid cellulose, Amberlyst-15 ion exchange resin, and N,N-dimethylformamide are mixed, ultrasonically treated for 30-40 minutes, heated to 60-70°C and kept warm for 1-2 hours, filtered, and rotary evaporated to obtain composite hybrid cellulose.

[0011] Further, the preparation of modified castor oil-based waterborne polyurethane comprises the following steps: Under a nitrogen atmosphere, isophorone diisocyanate, castor oil and glyceryl monostearate are mixed, a mixed solution of dibutyltin dilaurate and acetone is added, the temperature is raised to 53-57°C and kept warm for 30-40 minutes, the temperature is lowered to 18-25°C, a mixed solution of 2,2-dihydroxymethylpropionic acid and acetone is added, the temperature is raised to 53-57°C and kept warm for 2-3 hours, a mixed solution of 3-dimethylamino-1,2-propylene glycol and acetone is added, the temperature is raised to 68-72°C and kept warm for 2-3 hours, an amino acid-based Schiff base antibacterial agent is added, the temperature is continued to be kept warm for 1-2 hours, the temperature is lowered to 18-35°C, syringic acid is added, the mixture is stirred for 25-30 minutes, deionized water is added for emulsification, and rotary evaporation is performed to obtain a modified castor oil-based waterborne polyurethane.

[0012] Furthermore, the mass ratio of isophorone diisocyanate, castor oil, glyceryl monostearate, 2,2-bis(hydroxymethyl)propionic acid, 3-dimethylamino-1,2-propylene glycol, amino acid-based Schiff base antibacterial agent, and syringic acid is 8:3.4:0.8:0.6:1.2:1.8:2.6.

[0013] Further, the preparation of the amino acid-based Schiff base antibacterial agent comprises the following steps: Phenylalanine, potassium hydroxide and ethanol are mixed, the temperature is raised to 58-62°C, a mixture of syringaldehyde and ethanol is added, the temperature is kept for 2-3 hours, cooled, rotary evaporated, ethyl acetate is added, filtered under reduced pressure, rinsed and dried to obtain an amino acid-based Schiff base antibacterial agent.

[0014] Compared with the prior art, the present invention has the following beneficial effects: The present invention provides an antibacterial food packaging bag and a preparation method thereof. By optimizing components and processes, an antibacterial food packaging bag with good mechanical strength, strong barrier properties and a self-repairing hydrophobic surface is prepared.

[0015] In the present invention, biodegradable high molecular polymer polylactic acid and polypropylene carbonate are blended as the raw material of the base film of the food packaging bag, which is helpful to improve the mechanical properties and thermal stability of polypropylene carbonate, overcome the inherent brittleness of polylactic acid, and synergistically improve the comprehensive performance of the packaging bag. A food-grade ADR chain extender is selected as the chain extender, and one of butyl titanate and titanate coupling agent is selected as the compatibilizer to accelerate the ester exchange reaction process of polylactic acid and polypropylene carbonate in a molten state and improve the compatibility of the two. In order to give the food packaging bag excellent antibacterial and barrier properties, zinc acetate is used as a precursor to prepare microcrystalline cellulose-nano zinc oxide hybrid particles as hybrid cellulose. In order to improve the uniformity of the dispersion of the hybrid cellulose in the base film, epichlorohydrin is used to epoxidize the hybrid cellulose to obtain epoxidized hybrid cellulose, and then an amino acid-based Schiff base antibacterial agent is grafted by epoxy-hydroxyl reaction to prepare a composite hybrid cellulose with multiple active sites as a broad-spectrum antibacterial agent, thereby enhancing its bonding strength with the base material and greatly improving the antibacterial performance of the packaging bag; wherein the amino acid-based Schiff base antibacterial agent is prepared by Schiff base reaction of phenylalanine and bio-based aldehyde syringaldehyde, and the amino acid-based Schiff base antibacterial agent also reacts with zinc ions in the epoxidized hybrid cellulose to generate a Schiff base metal complex, thereby improving the thermal stability of the composite hybrid cellulose and improving various properties of the base film.

[0016] In order to give the surface of the packaging bag excellent resistance to mechanical damage, barrier properties and antibacterial durability, a protective coating was prepared using composite hybrid cellulose and modified castor oil-based waterborne polyurethane and coated on the surface of the base film to construct a green, environmentally friendly, durable antibacterial, hydrophobic and antifouling self-repairing surface.

[0017] The invention relates to a method for preparing a modified castor oil-based waterborne polyurethane by using isophorone diisocyanate and castor oil as raw materials, glyceryl monostearate as a modifier, and dibutyltin dilaurate as a catalyzer to obtain a prepolymer, using 2,2-bis(hydroxymethyl)propionic acid as a hydrophilic chain extender, using 3-dimethylamino-1,2-propylene glycol containing a tertiary amine group as a chain extender, using an amino acid-based Schiff base antibacterial agent as a capping agent, using syringic acid as a neutralizing agent, and adding water for emulsification. The introduction of glyceryl monostearate can improve the waterproofness and heat resistance of the coating; 3-dimethylamino-1,2-propylene glycol can improve the water resistance and heat resistance of the coating; Diol is used as a chain extender to react with syringic acid to undergo quaternization reaction, and the amino acid-based Schiff base antibacterial agent cooperates with the amino acid-based Schiff base antibacterial agent to enhance the broad-spectrum antibacterial effect. At the same time, the introduction of dynamic Schiff base bonds gives the coating formed by the coating good self-healing properties. Composite hybrid cellulose is introduced as a filler in the protective coating. While improving the barrier properties of the coating, by controlling the mass ratio of composite hybrid cellulose and modified castor oil-based water-based polyurethane, the base film is given a green, broad-spectrum antibacterial, hydrophobic and antifouling self-healing surface, thereby greatly extending the use range and life of the packaging bag. DETAILED DESCRIPTION

[0018] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0019] It should be noted that if the embodiments of the present invention involve directional indications such as up, down, left, right, front, and back, the directional indication is only used to explain a specific posture such as the relative position relationship between the components, the movement status, etc. If the specific posture changes, the directional indication will also change accordingly. In addition, the technical solutions between the various embodiments can be combined with each other, but it must be based on the ability of ordinary technicians in this field to implement. When the combination of technical solutions is contradictory or cannot be implemented, it should be considered that such a combination of technical solutions does not exist and is not within the protection scope required by the present invention.

[0020] The technical solution of the present invention is further described in detail below in conjunction with specific embodiments. It should be understood that the following embodiments are only used to explain the present invention and are not used to limit the present invention.

[0021] Embodiment 1: A method for preparing an antibacterial food packaging bag, comprising the following steps: S1: polylactic acid, polypropylene carbonate, chain extender, compatibilizer and composite hybrid cellulose are mixed and extruded, granulated and blow-molded to obtain a base film; The working conditions of mixed extrusion are: using a twin-screw extruder for extrusion, wherein the temperature of the first zone of the twin-screw extruder is 153°C, the temperature of the second zone is 163°C, the temperature of the third zone is 185°C, the temperature of the fourth zone is 153°C, and the screw speed is 12.5rpm; the working conditions of blow molding are: using an extrusion film blowing machine for molding, wherein the temperature of the first zone of the extrusion film blowing machine is 145°C, the temperature of the second zone is 170°C, the temperature of the third zone is 185°C, the temperature of the fourth zone is 145°C, the screw speed is 12rpm, and the traction speed is 4m / min; The chain extender is a food grade ADR chain extender, and the compatibilizer is butyl titanate; The raw material composition of the base film is as follows: 55 parts of polylactic acid, 35 parts of polypropylene carbonate, 0.5 parts of chain extender, 5 parts of compatibilizer, and 0.8 parts of composite hybrid cellulose, in terms of mass fractions; The preparation of the composite hybrid cellulose comprises the following steps: (1) 10 g of microcrystalline cellulose, 50 mL of 8% wt sodium hydroxide solution, and 25 mL of ethanol solution were mixed, kept at 18 °C for 4 h, filtered, dried, 50 mL of ethanol was added, stirred for 8 min, 2.5 g of zinc acetate dihydrate and 75 mL of ethanol were added, kept in a 70 °C water bath for 70 min, the pH was adjusted to 10.9, kept warm for 30 min, filtered, and dried to obtain hybrid cellulose; (2) Mix 1 g of hybrid cellulose, 20 mL of 2 mol / L NaOH solution, and 6 mL of epichlorohydrin, stir at 18 °C for 20 h, filter, wash, and dry to obtain epoxidized hybrid cellulose; (3) 3.2 g of amino acid-based Schiff base antibacterial agent, 6.5 g of epoxidized hybrid cellulose, 1 g of Amberlyst-15 ion exchange resin, and 25 mL of N,N-dimethylformamide were mixed, ultrasonically treated for 30 min, heated to 60 °C and kept warm for 2 h, filtered, and rotary evaporated to obtain composite hybrid cellulose; The preparation of the amino acid Schiff base antibacterial agent comprises the following steps: 5mmol phenylalanine, 0.28g potassium hydroxide and 100mL ethanol were mixed, heated to 58°C, a mixture of 7.5mmol syringaldehyde and 75mL ethanol was added, kept warm for 2h, cooled, rotary evaporated, 75mL ethyl acetate was added, filtered under reduced pressure, rinsed and dried to obtain an amino acid-based Schiff base antibacterial agent; S2: Preparation of protective coatings using composite hybrid cellulose and modified castor oil-based waterborne polyurethane; The mass ratio of composite hybrid cellulose and modified castor oil-based waterborne polyurethane in the protective coating is 9.5%; The preparation of the modified castor oil-based waterborne polyurethane comprises the following steps: Under a nitrogen atmosphere, 8 g of isophorone diisocyanate, 3.4 g of castor oil, and 0.8 g of glyceryl monostearate were mixed, 100 μL of dibutyltin dilaurate and 10 mL of acetone were added, the temperature was raised to 53 ° C and kept for 40 min, the temperature was lowered to 18 ° C, 0.6 g of 2,2-bis(hydroxymethyl)propionic acid and 2 mL of acetone were added, the temperature was raised to 53 ° C and kept for 3 h, 1.2 g of 3-dimethylamino-1,2-propylene glycol and a mixed solution of 5 mL of acetone were added, the temperature was raised to 68 ° C and kept for 3 h, 1.8 g of amino acid-based Schiff base antibacterial agent was added and kept for 1 h, the temperature was lowered to 18 ° C, 2.6 g of syringic acid was added, stirred for 25 min, deionized water was added for emulsification for 1 h, and a modified castor oil-based waterborne polyurethane with a solid content of 25% was obtained; S3: The protective coating is coated on the surface of the base film, dried, and then transferred to a bag making machine, and cut, heat-sealed, and punched in sequence to obtain an antibacterial food packaging bag.

[0022] Embodiment 2: A method for preparing an antibacterial food packaging bag, comprising the following steps: S1: polylactic acid, polypropylene carbonate, chain extender, compatibilizer and composite hybrid cellulose are mixed and extruded, granulated and blow-molded to obtain a base film; The working conditions of mixed extrusion are: using a twin-screw extruder for extrusion, wherein the temperature of the first zone of the twin-screw extruder is 153°C, the temperature of the second zone is 163°C, the temperature of the third zone is 185°C, the temperature of the fourth zone is 153°C, and the screw speed is 12.5rpm; the working conditions of blow molding are: using an extrusion film blowing machine for molding, wherein the temperature of the first zone of the extrusion film blowing machine is 145°C, the temperature of the second zone is 170°C, the temperature of the third zone is 185°C, the temperature of the fourth zone is 145°C, the screw speed is 12rpm, and the traction speed is 4m / min; The chain extender is a food grade ADR chain extender, and the compatibilizer is butyl titanate; The raw material composition of the base film is as follows: 60 parts of polylactic acid, 40 parts of polypropylene carbonate, 0.7 parts of chain extender, 7 parts of compatibilizer, and 1 part of composite hybrid cellulose. The preparation of the composite hybrid cellulose comprises the following steps: (1) 10 g of microcrystalline cellulose, 50 mL of 8% wt sodium hydroxide solution, and 25 mL of ethanol solution were mixed, kept at 25 °C for 3.5 h, filtered, dried, 50 mL of ethanol was added, stirred for 9 min, 2.5 g of zinc acetate dihydrate and 75 mL of ethanol were added, kept in a 75 °C water bath for 65 min, the pH was adjusted to 11, kept warm for 35 min, filtered, and dried to obtain hybrid cellulose; (2) Mix 1 g of hybrid cellulose, 20 mL of 2 mol / L NaOH solution, and 6 mL of epichlorohydrin, stir at 20 °C for 19 h, filter, wash, and dry to obtain epoxidized hybrid cellulose; (3) 3.2 g of amino acid-based Schiff base antibacterial agent, 6.5 g of epoxidized hybrid cellulose, 1 g of Amberlyst-15 ion exchange resin, and 25 mL of N,N-dimethylformamide were mixed, ultrasonically treated for 35 min, heated to 65 °C and kept warm for 1.5 h, filtered, and rotary evaporated to obtain composite hybrid cellulose; The preparation of the amino acid Schiff base antibacterial agent comprises the following steps: 5mmol phenylalanine, 0.28g potassium hydroxide and 100mL ethanol were mixed, heated to 60°C, a mixture of 7.5mmol syringaldehyde and 75mL ethanol was added, kept warm for 2.5h, cooled, rotary evaporated, 75mL ethyl acetate was added, filtered under reduced pressure, rinsed and dried to obtain an amino acid-based Schiff base antibacterial agent; S2: Preparation of protective coatings using composite hybrid cellulose and modified castor oil-based waterborne polyurethane; The mass ratio of composite hybrid cellulose and modified castor oil-based waterborne polyurethane in the protective coating is 11%; The preparation of the modified castor oil-based waterborne polyurethane comprises the following steps: Under a nitrogen atmosphere, 8 g of isophorone diisocyanate, 3.4 g of castor oil, and 0.8 g of glyceryl monostearate were mixed, 100 μL of dibutyltin dilaurate and 10 mL of acetone were added, the temperature was raised to 53-57 ° C and kept for 35 min, the temperature was lowered to 20 ° C, 0.6 g of 2,2-bishydroxymethylpropionic acid and 2 mL of acetone were added, the temperature was raised to 55 ° C and kept for 2.5 h, 1.2 g of 3-dimethylamino-1,2-propylene glycol and a mixed solution of 5 mL of acetone were added, the temperature was raised to 70 ° C and kept for 2.5 h, 1.8 g of amino acid Schiff base antibacterial agent was added and kept for 1.5 h, the temperature was lowered to 25 ° C, 2.6 g of syringic acid was added, stirred for 28 min, deionized water was added for emulsification for 1 h, and rotary evaporation was performed to obtain a modified castor oil-based waterborne polyurethane with a solid content of 25%; S3: The protective coating is coated on the surface of the base film, dried, and then transferred to a bag making machine, and cut, heat-sealed, and punched in sequence to obtain an antibacterial food packaging bag.

[0023] Embodiment 3: A method for preparing an antibacterial food packaging bag, comprising the following steps: S1: polylactic acid, polypropylene carbonate, chain extender, compatibilizer and composite hybrid cellulose are mixed and extruded, granulated and blow-molded to obtain a base film; The working conditions of mixed extrusion are: using a twin-screw extruder for extrusion, wherein the temperature of the first zone of the twin-screw extruder is 153°C, the temperature of the second zone is 163°C, the temperature of the third zone is 185°C, the temperature of the fourth zone is 153°C, and the screw speed is 12.5rpm; the working conditions of blow molding are: using an extrusion film blowing machine for molding, wherein the temperature of the first zone of the extrusion film blowing machine is 145°C, the temperature of the second zone is 170°C, the temperature of the third zone is 185°C, the temperature of the fourth zone is 145°C, the screw speed is 12rpm, and the traction speed is 4m / min; The chain extender is a food grade ADR chain extender, and the compatibilizer is butyl titanate; The raw material composition of the base film is as follows: 65 parts of polylactic acid, 45 parts of polypropylene carbonate, 1 part of chain extender, 10 parts of compatibilizer, and 1.3 parts of composite hybrid cellulose, in terms of mass fractions; The preparation of the composite hybrid cellulose comprises the following steps: (1) 10 g of microcrystalline cellulose, 50 mL of 8% wt sodium hydroxide solution, and 25 mL of ethanol solution were mixed, kept at 30 °C for 3 h, filtered, dried, 50 mL of ethanol was added, stirred for 10 min, 2.5 g of zinc acetate dihydrate and 75 mL of ethanol were added, kept in a water bath at 80 °C for 70 min, the pH was adjusted to 11.1, kept warm for 40 min, filtered, and dried to obtain hybrid cellulose; (2) Mix 1 g of hybrid cellulose, 20 mL of 2 mol / L NaOH solution, and 6 mL of epichlorohydrin, stir at 25 °C for 18 h, filter, wash, and dry to obtain epoxidized hybrid cellulose; (3) 3.2 g of amino acid Schiff base antibacterial agent, 6.5 g of epoxidized hybrid cellulose, 1 g of Amberlyst-15 ion exchange resin, and 25 mL of N,N-dimethylformamide were mixed, ultrasonically treated for 40 min, heated to 70 °C and kept warm for 1 h, filtered, and rotary evaporated to obtain composite hybrid cellulose; The preparation of the amino acid Schiff base antibacterial agent comprises the following steps: 5mmol phenylalanine, 0.28g potassium hydroxide and 100mL ethanol were mixed, heated to 62°C, a mixture of 7.5mmol syringaldehyde and 75mL ethanol was added, kept warm for 3h, cooled, rotary evaporated, 75mL ethyl acetate was added, filtered under reduced pressure, rinsed and dried to obtain an amino acid-based Schiff base antibacterial agent; S2: Preparation of protective coatings using composite hybrid cellulose and modified castor oil-based waterborne polyurethane; The mass ratio of composite hybrid cellulose and modified castor oil-based waterborne polyurethane in the protective coating is 12.5%; The preparation of the modified castor oil-based waterborne polyurethane comprises the following steps: Under a nitrogen atmosphere, 8 g of isophorone diisocyanate, 3.4 g of castor oil, and 0.8 g of glyceryl monostearate were mixed, 100 μL of dibutyltin dilaurate and 10 mL of acetone were added, the temperature was raised to 57 ° C and kept for 30 min, the temperature was lowered to 25 ° C, 0.6 g of 2,2-bis(hydroxymethyl)propionic acid and 2 mL of acetone were added, the temperature was raised to 57 ° C and kept for 2 h, 1.2 g of 3-dimethylamino-1,2-propylene glycol and a mixed solution of 5 mL of acetone were added, the temperature was raised to 72 ° C and kept for 2 h, 1.8 g of amino acid Schiff base antibacterial agent was added and kept for 2 h, the temperature was lowered to 35 ° C, 2.6 g of syringic acid was added, stirred for 30 min, deionized water was added for emulsification for 1 h, and a modified castor oil-based waterborne polyurethane with a solid content of 25% was obtained; S3: The protective coating is coated on the surface of the base film, dried, and then transferred to a bag making machine, and cut, heat-sealed, and punched in sequence to obtain an antibacterial food packaging bag.

[0024] Comparative Example 1: Taking Example 3 as the control group, microcrystalline cellulose was used to replace the composite hybrid cellulose, and other processes were normal.

[0025] Comparative Example 2: Taking Example 3 as the control group, the modified castor oil-based water-based polyurethane was replaced with water-based polyurethane (BZ-7: Changzhou Baichang Coatings Technology Co., Ltd.), and the other processes were normal.

[0026] Comparative Example 3: Example 3 was used as the control group, and no amino acid Schiff base antibacterial agent was prepared, and other processes were normal.

[0027] In the examples and comparative examples, the thickness of the base film is 0.1 mm, and the thickness of the protective coating after being coated on the surface of the base film and cured is 0.05 mm.

[0028] Sources of raw materials used (for demonstration purposes only): Polylactic acid 032563: Hubei Shiteng Chemical Technology Co., Ltd.; Amberlyst-15 ion exchange resin Y52434: Shanghai Yuanye Biotechnology Co., Ltd.; Polypropylene carbonate PA92354: Guangdong Wengjiang Chemical Reagent Co., Ltd.; Food-grade ADR chain extender (ADR-4368): BASF Joncryl; Phenylalanine (98%): Wuhan Xingzhongcheng Technology Co., Ltd.; Butyl titanate T104105, microcrystalline cellulose C434461, zinc acetate dihydrate Z110777, epichlorohydrin E108182, syringaldehyde S106250, isophorone diisocyanate I109582, dibutyltin dilaurate D100274, castor oil C110663, glyceryl monostearate S112705, N,N-dimethylformamide D111999, 2,2-bis(hydroxymethyl)propionic acid B104539, 3-dimethylamino-1,2-propylene glycol D135042, syringic acid S104156: Aladdin reagent; sodium hydroxide, ethanol, potassium hydroxide, ethyl acetate, acetone, analytical grade: Sinopharm reagent.

[0029] Performance test: The food packaging bags prepared in the embodiments and comparative examples were tested: Tensile strength: tested by electronic universal testing machine, sample length 100mm, width 20mm, test temperature 28℃, tensile rate 10mm / min; Hydrophobicity: Characterized by water contact angle, tested with a 2µL deionized water droplet; Antibacterial property: refer to ISO22196:2007, use plate counting method, and the detected bacteria is ATCC6538 Staphylococcus aureus; Self-healing property: scratch the surface of the sample with a length of 2mm, a width of 2µm and a depth of 0.05mm, keep it at 60℃ for 12h, and then measure the tensile strength again. If the change rate of tensile strength is less than 1% including 1%, it is excellent, otherwise it is unqualified. The results are shown in Table 1. Table 1

[0030] The present invention provides an antibacterial food packaging bag and a preparation method thereof. By optimizing components and processes, an antibacterial food packaging bag with good mechanical strength, strong barrier properties and a self-repairing hydrophobic surface is prepared.

[0031] By comparing Example 3 with Comparative Examples 1 and 3, it can be seen that in order to give the food packaging bag excellent antibacterial and barrier properties, zinc acetate is used as a precursor in the present invention to prepare microcrystalline cellulose-nano zinc oxide hybrid particles as hybrid cellulose. In order to improve the uniformity of the dispersion of the hybrid cellulose in the base film, epichlorohydrin is used to epoxidize the hybrid cellulose to obtain epoxidized hybrid cellulose, and then the amino acid-based Schiff base antibacterial agent is grafted by epoxy-hydroxyl reaction to prepare a composite hybrid cellulose with multiple active sites as a broad-spectrum antibacterial agent, thereby enhancing its bonding strength with the base material and greatly improving the antibacterial performance of the packaging bag; wherein the amino acid-based Schiff base antibacterial agent is prepared by Schiff base reaction of phenylalanine and bio-based aldehyde syringaldehyde, and the amino acid-based Schiff base antibacterial agent also reacts with zinc ions in the epoxidized hybrid cellulose to generate Schiff base metal complexes, thereby improving the thermal stability of the composite hybrid cellulose and improving various properties of the base film.

[0032] By comparing Example 3 with Comparative Examples 2 and 3, it can be seen that in order to give the packaging bag surface excellent resistance to mechanical damage, barrier properties and antibacterial durability, a protective coating is prepared using composite hybrid cellulose and modified castor oil-based waterborne polyurethane, and coated on the surface of the base film to construct a green, environmentally friendly, durable antibacterial, hydrophobic and antifouling self-repairing surface; The invention adopts isophorone diisocyanate and castor oil as raw materials, glyceryl monostearate as modifier, dibutyltin dilaurate as catalysis to obtain a prepolymer, 2,2-bis(hydroxymethyl)propionic acid as a hydrophilic chain extender, 3-dimethylamino-1,2-propylene glycol containing a tertiary amine group as a chain extender, an amino acid-based Schiff base antibacterial agent as a capping agent, syringic acid as a neutralizing agent, and water is added for emulsification to synthesize a modified castor oil-based waterborne polyurethane; the introduction of glyceryl monostearate can improve the waterproofness and heat resistance of the coating; 3-dimethylamino-1,2-propylene glycol as a neutralizing agent Alcohol is used as a chain extender to react with syringic acid to undergo quaternization reaction, and the amino acid-based Schiff base antibacterial agent cooperates with the amino acid-based Schiff base antibacterial agent to enhance the broad-spectrum antibacterial effect. At the same time, the introduction of dynamic Schiff base bonds gives the coating formed by the coating good self-healing properties. Composite hybrid cellulose is introduced as a filler in the protective coating. While improving the barrier properties of the coating, by controlling the mass ratio of composite hybrid cellulose and modified castor oil-based water-based polyurethane, the base film is given a green, broad-spectrum antibacterial, hydrophobic and antifouling self-healing surface, thereby greatly extending the use range and service life of the packaging bag.

[0033] The above descriptions are only embodiments of the present invention and are not intended to limit the patent scope of the present invention. All equivalent structural changes made using the present invention specification under the inventive concept of the present invention, or direct / indirect applications in other related technical fields, are included in the patent protection scope of the present invention.

Claims

1. A method for preparing an antibacterial food packaging bag, characterized in that: The following steps are involved: S1: polylactic acid, polypropylene carbonate, chain extender, compatibilizer and composite hybrid cellulose are mixed and extruded, granulated and blow-molded to obtain a base film; S2: Preparation of protective coatings using composite hybrid cellulose and modified castor oil-based waterborne polyurethane; S3: The protective coating is coated on the surface of the base film, dried, and then transferred to a bag making machine, and cut, heat-sealed, and punched in sequence to obtain an antibacterial food packaging bag.

2. The method for preparing an antibacterial food packaging bag according to claim 1, characterized in that: The working conditions for mixed extrusion are: using a twin-screw extruder for extrusion, wherein the temperature of zone 1 of the twin-screw extruder is 153°C, the temperature of zone 2 is 163°C, the temperature of zone 3 is 185°C, the temperature of zone 4 is 153°C, and the screw speed is 12.5rpm; the working conditions for blow molding are: using an extrusion film blowing machine for molding, wherein the temperature of zone 1 of the extrusion film blowing machine is 145°C, the temperature of zone 2 is 170°C, the temperature of zone 3 is 185°C, the temperature of zone 4 is 145°C, the screw speed is 12rpm, and the traction speed is 4m / min.

3. The method for preparing an antibacterial food packaging bag according to claim 1, characterized in that: The chain extender is a food-grade ADR chain extender, and the compatibilizer is one of butyl titanate and a titanate coupling agent or a combination thereof.

4. The method for preparing an antibacterial food packaging bag according to claim 1, characterized in that: The raw material composition of the base film is as follows, by weight: 55-65 parts of polylactic acid, 35-45 parts of polypropylene carbonate, 0.5-1 parts of chain extender, 5-10 parts of compatibilizer, and 0.8-1.3 parts of composite hybrid cellulose.

5. The method for preparing an antibacterial food packaging bag according to claim 1, characterized in that: The mass ratio of the composite hybrid cellulose and the modified castor oil-based waterborne polyurethane in the protective coating is 9.5-12.5%.

6. The method for preparing an antibacterial food packaging bag according to claim 1, characterized in that: The preparation of the composite hybrid cellulose comprises the following steps: (1) Mix microcrystalline cellulose, sodium hydroxide solution and ethanol solution, keep warm at 18-30°C for 3-4 hours, filter and dry, add ethanol, stir for 8-10 minutes, add zinc acetate dihydrate and ethanol mixture, keep warm in a water bath at 70-80°C for 60-70 minutes, adjust the pH to 10.9-11.1, keep warm for 30-40 minutes, filter and dry to obtain hybrid cellulose; (2) Mixing hybrid cellulose, NaOH solution and epichlorohydrin, stirring at 18-25° C. for 18-20 hours, filtering, washing and drying to obtain epoxidized hybrid cellulose; (3) The amino acid-based Schiff base antibacterial agent, epoxidized hybrid cellulose, Amberlyst-15 ion exchange resin, and N,N-dimethylformamide are mixed, ultrasonically treated for 30-40 minutes, heated to 60-70°C and kept warm for 1-2 hours, filtered, and rotary evaporated to obtain composite hybrid cellulose.

7. The method for preparing an antibacterial food packaging bag according to claim 1, characterized in that: The preparation of the modified castor oil-based waterborne polyurethane comprises the following steps: Under a nitrogen atmosphere, isophorone diisocyanate, castor oil and glyceryl monostearate are mixed, a mixed solution of dibutyltin dilaurate and acetone is added, the temperature is raised to 53-57°C and kept warm for 30-40 minutes, the temperature is lowered to 18-25°C, a mixed solution of 2,2-dihydroxymethylpropionic acid and acetone is added, the temperature is raised to 53-57°C and kept warm for 2-3 hours, a mixed solution of 3-dimethylamino-1,2-propylene glycol and acetone is added, the temperature is raised to 68-72°C and kept warm for 2-3 hours, an amino acid-based Schiff base antibacterial agent is added, the temperature is continued to be kept warm for 1-2 hours, the temperature is lowered to 18-35°C, syringic acid is added, the mixture is stirred for 25-30 minutes, deionized water is added for emulsification, and rotary evaporation is performed to obtain a modified castor oil-based waterborne polyurethane.

8. The method for preparing an antibacterial food packaging bag according to claim 7, characterized in that: The mass ratio of isophorone diisocyanate, castor oil, glyceryl monostearate, 2,2-bis(hydroxymethyl)propionic acid, 3-dimethylamino-1,2-propylene glycol, amino acid-based Schiff base antibacterial agent, and syringic acid is 8:3.4:0.8:0.6:1.2:1.8:2.

6.

9. The method for preparing an antibacterial food packaging bag according to claim 6 or 7, characterized in that: The preparation of the amino acid Schiff base antibacterial agent comprises the following steps: Phenylalanine, potassium hydroxide and ethanol are mixed, the temperature is raised to 58-62°C, a mixture of syringaldehyde and ethanol is added, the temperature is kept for 2-3 hours, cooled, rotary evaporated, ethyl acetate is added, filtered under reduced pressure, rinsed and dried to obtain an amino acid-based Schiff base antibacterial agent.

10. An antibacterial food packaging bag, characterized in that: The compound is prepared by the preparation method according to any one of claims 1 to 8.

Images