Dairy product easy-tear composite packaging material

Abstract

The application relates to the technical field of dairy product packaging material research and development, and discloses a dairy product easy-to-tear composite packaging material, which comprises the following steps: preparing a composite antibacterial agent; preparing a BOPE surface layer by taking low-density polyethylene resin and the composite antibacterial agent as raw materials; preparing a barrier intermediate layer by taking ethylene-vinyl alcohol copolymer resin and low-density polyethylene resin as raw materials; preparing a PE inner layer by taking low-density polyethylene resin and the composite antibacterial agent as raw materials; and bonding the BOPE surface layer, the barrier intermediate layer and the PE inner layer by adopting a high-speed solvent-free compounding process to obtain a composite film. The application provides a preparation method of the antibacterial dairy product packaging material, and the antibacterial dairy product packaging material prepared by the application has practical application value and can be used in dairy product packaging.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of dairy product packaging material research and development, in particular to a dairy product easy-to-tear composite packaging material. BACKGROUND

[0002] Dairy products contain rich nutrients such as protein, milk fat, carbohydrates, vitamins, etc., and are prone to microbial contamination during storage and transportation. Therefore, it is urgent to seek a natural, effective and safe method to inhibit the growth of harmful microorganisms.

[0003] Adding antibacterial agents is the main means to improve the antibacterial performance of food packaging materials. For example, the patent with publication number CN116082732A discloses an antibacterial polyethylene food-grade packaging film and a preparation method thereof. By introducing a composite antibacterial agent (composed of modified nano-zirconium phosphate silver antibacterial agent and nano-zinc oxide antibacterial agent) into the polyethylene material, the overall antibacterial ability of the plastic packaging bag can be effectively improved.

[0004] Searches have found that nano-zinc oxide is an inorganic antibacterial material with safety, long-term effectiveness and heat resistance, and has been widely used in food and drug packaging fields. Schiff bases have biological activities such as antibacterial, bactericidal, antitumor, and antiviral, and are often used as organic antibacterial agents. Coumarin is a natural antioxidant widely present in plants and has excellent antioxidant activity.

[0005] In addition, traditional plastic films have defects such as difficulty in opening the bag mouth, difficulty in tearing by hand, and irregular or jagged tearing after tearing, which can easily lead to leakage of the contents of the package, which limits their actual use in the field of dairy product packaging. Bi-directional stretch films such as bi-directional stretch nylon film (BOPA), bi-directional stretch polyester film (BOPET), bi-directional stretch polypropylene film (BOPP), and bi-directional stretch polyethylene film (BOPE) have excellent easy-to-tear properties, can be torn vertically and horizontally in a straight line, and the tearing edge is neat. By dry or solvent-free compounding of traditional plastic films with bi-directional stretch films, a composite material can be prepared to meet the easy-to-tear requirement of the packaging product. SUMMARY

[0006] The present application provides a dairy product easy-to-tear composite packaging material. Schiff base type coupling agents and Schiff base type crosslinking agents are synthesized and used to modify nano-zinc oxide, which enhances the interfacial compatibility of nano-zinc oxide with the polyethylene matrix and also synergistically imparts antibacterial properties to the polyethylene. A high-speed solvent-free compounding process is then used to prepare a dairy product packaging material with antibacterial properties.

[0007] A method for preparing a dairy product easy-to-tear composite packaging material, comprising the following steps:

[0008] Step one, the preparation method of the composite antibacterial agent is as follows: a Schiff base type coupling agent is synthesized, and hydroxylated nano zinc oxide particles are surface modified by using the Schiff base type coupling agent to obtain the composite antibacterial agent;

[0009] Step two, the low-density polyethylene resin and the composite antibacterial agent are used as raw materials, and the raw materials are blended, melted, extruded by a double-screw extruder, and subjected to longitudinal stretching and then transverse stretching, and then hot-pressed to obtain a BOPE surface layer.

[0010] The ethylene-vinyl alcohol copolymer resin and the low-density polyethylene resin are used as raw materials, and the raw materials are blended, melted, extruded and pelletized by a double-screw extruder, and then cast into a film to obtain a barrier intermediate layer.

[0011] The low-density polyethylene resin and the composite antibacterial agent are used as raw materials, and the raw materials are blended, melted, extruded and pelletized by a double-screw extruder, and then cast into a film to obtain a PE inner layer.

[0012] Step three, the BOPE surface layer, the barrier intermediate layer and the PE inner layer are bonded by using a high-speed solvent-free compounding process to obtain a composite film, and the composite film is a dairy product easy-to-tear composite packaging material.

[0013] Preferably, the preparation method of the composite antibacterial agent is as follows: a Schiff base type coupling agent and a Schiff base type crosslinking agent are synthesized, and hydroxylated nano zinc oxide particles are surface modified by using the Schiff base type coupling agent and the Schiff base type crosslinking agent.

[0014] Preferably, the preparation method of the Schiff base type coupling agent is as follows:

[0015] Step S3-1: 7-hydroxycoumarin is used as a nucleophile, a nucleophilic substitution reaction occurs between the bromine functional group of 2-bromoacetaldehyde and the hydroxyl functional group of 7-hydroxycoumarin, and a coumarin aldehyde monomer is generated;

[0016] Step S3-2: a Schiff base reaction mechanism is used, a condensation reaction occurs between the amino functional group of 3-aminopropyltrimethoxysilane and the carbonyl functional group of the coumarin aldehyde monomer, and a Schiff base type coupling agent is generated.

[0017] Preferably, the preparation method of the Schiff base type crosslinking agent is as follows:

[0018] Step S4-1: 5,7-dihydroxycoumarin is used as a nucleophile, a nucleophilic substitution reaction occurs between the bromine functional group of 2-bromoacetaldehyde and the hydroxyl functional group of 5,7-dihydroxycoumarin, and a coumarin dialdehyde monomer is generated;

[0019] Step S4-2: a Schiff base reaction mechanism is used, a condensation reaction occurs between the amino functional group of 3-aminopropyltrimethoxysilane and the carbonyl functional group of the coumarin dialdehyde monomer, and a Schiff base type crosslinking agent is generated.

[0020] Preferably, the preparation process parameters of the composite film in step three are set as follows: the composite speed is 300-500 m / min, the composite temperature is 40-50 DEG C, the cooling temperature is 20-30 DEG C, the composite pressure is 0.3-0.5 Mpa, and the gluing pressure is 0.4-0.6 Mpa.

[0021] The thickness of the dairy product easy-tear composite packaging material prepared according to the above method is 80-200 mu m.

[0022] Preferably, the average tear strength of the dairy product easy-tear composite packaging material is 0.9-1.2 N.

[0023] Preferably, the dairy product easy-tear composite packaging material has antibacterial effect, and the bacteria are Escherichia coli or Staphylococcus aureus.

[0024] Advantages

[0025] The application first synthesizes a Schiff base type coupling agent and a crosslinking agent, modifies the surface of nano zinc oxide particles to obtain a composite antibacterial agent by using the coupling agent and the crosslinking agent, then modifies the surface layer and the inner layer of the composite film by using the composite antibacterial agent, and finally prepares the composite film by using a high-speed solvent-free compounding process.

[0026] The experimental results show that the composite film has antibacterial performance, meets the easy-tear performance requirements, has excellent comprehensive performance, has practical application value, and can be used in dairy product packaging. BRIEF DESCRIPTION OF DRAWINGS

[0027] Figure 1 The synthesis route of the Schiff base type coupling agent is shown in the following figure:

[0028] Figure 2 The synthesis route of the Schiff base type crosslinking agent is shown in the following figure:

[0029] Figure 3 The antibacterial performance experimental results of the composite film are shown in the following figure: DETAILED DESCRIPTION

[0030] Example 1:

[0031] The synthesis process of the Schiff base type coupling agent is as follows: Figure 1

[0032] ​(1) Synthesis of coumarin aldehyde monomer, the specific synthesis method is: taking 7-hydroxycoumarin as a nucleophile, a nucleophilic substitution reaction occurs between the bromine functional group of 2-bromoacetaldehyde and the hydroxyl functional group of 7-hydroxycoumarin to generate a coumarin aldehyde monomer, and the specific experimental steps are: 3.2 g of 7-hydroxycoumarin and 50 mL of N,N-dimethylformamide are added to a three-necked flask, under the protection of nitrogen and mechanical stirring, the temperature is raised to 30°C for 30 min, then 1.5 mL of 2-bromoacetaldehyde and 10 mL of potassium carbonate solution (prepared from 2.7 g of potassium carbonate and 20 mL of N,N-dimethylformamide) are sequentially added to the three-necked flask, the temperature is raised to 70°C and stirred for 10 h, after cooling, filtration, washing with ethanol and deionized water in sequence, and vacuum drying, a coumarin aldehyde monomer is obtained;

[0033] (2) Synthesis of Schiff base type coupling agent, the specific synthesis method is: using the Schiff base reaction mechanism, a condensation reaction occurs between the amino functional group of 3-aminopropyltrimethoxysilane and the carbonyl functional group of the coumarin aldehyde monomer to generate a Schiff base type coupling agent, and the specific experimental steps are: 2.1 g of the coumarin aldehyde monomer and 50 mL of anhydrous ethanol are added to a two-necked flask, under mechanical stirring, the temperature is raised to 30°C and stirred until complete dissolution, then the flask is cooled to room temperature, 2 mL of glacial acetic acid and 10 mL of 3-aminopropyltrimethoxysilane solution (prepared from 1.8 g of 3-aminopropyltrimethoxysilane and 10 mL of anhydrous ethanol) are added dropwise to the flask, the temperature is raised to 85°C and refluxed for 3 h, after cooling, suction filtration is performed, recrystallization is performed using anhydrous ethanol, and vacuum drying is performed to obtain a Schiff base type coupling agent;

[0034] The nuclear magnetic resonance hydrogen spectrum of the Schiff base type coupling agent is characterized as: 1 H NMR (DMSO d6, 400 MHz) δ: 0.80-0.83 (t, 2H), 1.68-1.74 (m, 2H), 3.14-3.16 (t, 2H), 3.57 (s, 9H), 4.73-4.74 (d, 2H), 6.29-6.94 (m, 3H), 7.43-7.45 (t, 1H, -N=CH-), 7.58-7.99 (m, 2H).

[0035] Example 2:

[0036] The preparation of the Schiff base type crosslinking agent is shown as follows: Figure 2

[0037] ​(1) Synthesis of coumarin dialdehyde monomer, the specific synthesis method is: using 5, 7-dihydroxycoumarin as a nucleophile, through the nucleophilic substitution reaction of the bromine function group of 2-bromoacetaldehyde and the hydroxyl function group of 5, 7-dihydroxycoumarin, to generate coumarin dialdehyde monomer, the specific synthesis steps and synthesis reaction conditions are referred to the synthesis experiment of coumarin aldehyde monomer, and the difference between the synthesis experiment of coumarin aldehyde monomer and the synthesis experiment of coumarin dialdehyde monomer is that 1.8g 5, 7-dihydroxycoumarin is used to replace 3.2g 7-hydroxycoumarin;

[0038] (2) Synthesis of Schiff base type crosslinking agent, the specific synthesis method is: using Schiff base reaction mechanism, through the condensation reaction of the amino function group of 3-aminopropyltrimethoxysilane and the carbonyl function group of coumarin dialdehyde monomer, to generate Schiff base type crosslinking agent, the specific synthesis steps and synthesis reaction conditions are referred to the synthesis experiment of Schiff base type coupling agent, and the difference between the synthesis experiment of Schiff base type coupling agent and the synthesis experiment of Schiff base type crosslinking agent is that 2.6g coumarin dialdehyde monomer is used to replace 2.1g coumarin aldehyde monomer;

[0039] The nuclear magnetic resonance hydrogen spectrum of the Schiff base type crosslinking agent is characterized as: 1 H NMR (DMSO d6, 400MHz) δ: 0.80-0.83 (t, 4H), 1.68-1.74 (m, 4H), 3.10-3.13 (t, 4H), 3.57 (s, 18H), 4.76-4.77 (dd, 4H), 6.32-6.55 (m, 3H), 7.43-7.48 (dt, 2H, -N=CH-), 8.10-8.12 (d, 1H).

[0040] Example 3:

[0041] (1) Preparation of antibacterial agent I, the preparation method is: using the Schiff base type coupling agent to modify the hydroxylated nano zinc oxide to obtain the antibacterial agent I, the specific experimental steps are: under the action of nitrogen protection and mechanical stirring, 1g Schiff base type coupling agent, 3g hydroxylated nano zinc oxide and 50mL isopropyl alcohol are added into a round bottom flask, the temperature is increased to 25℃, and the stirring reaction is carried out for 6h, then 1mL ammonia water is added into the flask, and the stirring reaction is continued for 18h, and then the antibacterial agent I is obtained by using anhydrous ethanol washing, filtration, rotary evaporation and vacuum drying;

[0042] (2) Preparation of antibacterial agent II, the preparation method is: using Schiff base type coupling agent and Schiff base type crosslinking agent to modify hydroxylated nano zinc oxide, to obtain antibacterial agent II, the specific experimental steps are: under the action of nitrogen protection and mechanical stirring, 0.5g Schiff base type coupling agent, 0.5g Schiff base type crosslinking agent, 3g hydroxylated nano zinc oxide and 50mL isopropyl alcohol are added into a round-bottom flask, the temperature is raised to 25℃ and stirred for 6h, then 1mL ammonia water is added dropwise into the flask, and the stirring reaction is continued for 18h, washed with anhydrous ethanol, filtered, rotary evaporated and vacuum dried to obtain antibacterial agent II;

[0043] The preparation method of the hydroxylated nano zinc oxide is: 20g zinc oxide nanoparticles and 200mL hydrogen peroxide aqueous solution (30wt%) are added into a round-bottom flask, ultrasonic dispersion is performed for 10min, under the action of mechanical stirring, the temperature is raised to 105℃ and refluxed for 6h, after cooling, centrifugation is performed at 5000rpm for 5min, then deionized water is used for washing for 3 times, and finally vacuum drying is performed at 80℃ for 5h to obtain the hydroxylated nano zinc oxide.

[0044] The zinc oxide nanoparticles are purchased from Changzhou Kenada New Material Technology Co., Ltd., and the model number is KND-NX10 nano zinc oxide.

[0045] Example 4:

[0046] (1) Preparation of composite film I, including the following steps:

[0047] Step one, preparation of BOPE surface layer: 45g low density polyethylene resin and 3g antibacterial agent I are added into a double screw extruder which has been preheated to 140℃, and then blended, melted and extruded through the double screw extruder, after that, the BOPE surface layer is obtained by sequentially stretching it in the longitudinal direction and then in the transverse direction, the temperature is 80℃ during the longitudinal stretching, the stretching multiple is 5 times, the temperature is 150℃ during the transverse stretching, the stretching multiple is 6 times, and finally heat setting is performed at 140℃.

[0048] The process parameter settings of the double screw extruder corresponding to the BOPE surface layer are as follows: the temperatures of the first to third zones are 110℃, 140℃ and 160℃ respectively, and the rotating speed is 30r / min.

[0049] Step two, preparation of barrier intermediate layer: 10g ethylene-vinyl alcohol copolymer resin and 15g low density polyethylene resin are added into a double screw extruder which has been preheated to 170℃, and then blended, melted and extruded through the double screw extruder, and then 1-5mm particles are obtained by cutting with a pelletizer, after that, the particles are directly added into a casting machine which has been preheated to 170℃, and then a film is obtained by casting.

[0050] The process parameters of the double-screw extruder corresponding to the barrier intermediate layer are set as follows: the temperatures of zones 1-3 are 160℃, 185℃, and 200℃ respectively, and the rotating speed is 40r / min.

[0051] Step three, preparation of the PE inner layer: 45g of low-density polyethylene resin and 3g of antibacterial agent I are added into a double-screw extruder preheated to 140℃, and then blended, melted and extruded by the double-screw extruder, and cut into 1-5mm particles by a pelletizer, which is then directly added into a casting machine preheated to 140℃ to be cast into a film to obtain the PE inner layer.

[0052] The process parameters of the double-screw extruder corresponding to the PE inner layer are set as follows: the temperatures of zones 1-3 are 110℃, 140℃, and 160℃ respectively, and the rotating speed is 30r / min.

[0053] Step four, preparation of the composite film I: the BOPE surface layer, the barrier intermediate layer and the PE inner layer are bonded together by using a high-speed solvent-free laminator, and the bonding speed is 400m / min, the bonding temperature is 45℃, the cooling temperature is 25℃, the bonding pressure is 0.4Mpa, and the gluing pressure is 0.5Mpa, to obtain a composite film I with a thickness of 100μm.

[0054] The low-density polyethylene resin is purchased from China Offshore Shell Petrochemical Co., Ltd., and its specifications are 2420H, Mn is 180000, and MFR is 2.0-2.5g / 10min; the ethylene-vinyl alcohol copolymer resin is purchased from Dongguan Kaisil Plastic Raw Material Co., Ltd., and its specifications are E105B, Mn is 10000, and the ethylene content is 44%.

[0055] (2) Preparation of the composite film II: antibacterial agent II is used to replace the above antibacterial agent I, and the composite film II is prepared according to the preparation steps and experimental conditions of the composite film I.

[0056] Performance test:

[0057] (1) The trouser tear method is selected, and the tear strength of the sample is tested according to GB / T 16578.1-2008, and the specific test steps are as follows: a 150mm×50mm sample is cut in the middle of the 50mm dimension to form a 75mm long straight incision, and then clamped on an Instron 5565 material testing machine, and the tear strength test item is selected for testing, and the longitudinal and transverse tear strengths of the sample are recorded, and the average tear strength of the sample is calculated;

[0058] (2) The tensile strength of the sample was tested using an Instron 5565 universal material testing machine, and the specific test steps were as follows: the sample of 150mm x 20mm was fixed on the material testing machine, and the tensile test was carried out at a tensile rate of 5mm / min, and the longitudinal and transverse tensile strength of the sample was recorded;

[0059] (3) The antibacterial performance test was carried out using MJ-250I type mold incubator, and the specific test steps were as follows: the sample was cut into a disc with a diameter of 6mm, and was sterilized by irradiation with ultraviolet lamp for 2h, then 100μL of bacterial solution (concentration of 1.0x10 6 CFU / mL) was coated on the culture medium, the sterile sample was pasted in the culture medium, and was placed in a 37℃ incubator for 24h, and the diameter of the bacteriostatic ring was observed;

[0060] Among them, the bacterial solution was ATCC6538 type Staphylococcus aureus and ATCC25922 type Escherichia coli purchased from Shanghai Luwei Technology Co., Ltd.;

[0061] (4) The oxygen transmission performance of the sample was tested according to GB / T 1038-2000, and the specific test steps were as follows: a 30cm circular sample was placed in a glass desiccator with environmental temperature of 25℃ and anhydrous calcium chloride as desiccant, and was kept for 72h, then the sample was tested using Y110 type oxygen transmission tester;

[0062] (5) The hygiene performance of the sample was tested according to GB / T 5009.60-2003 "Analysis method of polyethylene, polystyrene and polypropylene forming products for food packaging";

[0063] The above experimental results are shown in Tables 1-3.

[0064] Table 1 Experimental results of tear resistance and mechanical properties of composite film

[0065]

[0066] Table 2 Experimental results of antibacterial and barrier properties of composite film

[0067]

[0068]

[0069] Table 3 Experimental results of hygiene performance of composite film

[0070]

[0071] Note: The experimental results of physical and chemical indicators are based on GB / T 5009.58-2003 "Analysis method of polyethylene resin for food packaging";

[0072] According to the antibacterial performance test data in Table 2 Figure 3 , the following conclusions can be drawn by comprehensively analyzing the above experimental results:

[0073] (1) According to the national standard and the use requirements of enterprise users, the tear strength of the sample detected by the trouser method should be ≤2N, and from the test results in Table 1, it can be known that the composite films prepared by the present application all meet the easy tearing performance requirements;

[0074] (2) Composite film I and composite film II both show obvious inhibitory effect on Staphylococcus aureus and Escherichia coli, that is, composite film I and composite film II have antibacterial properties;

[0075] (3) The oxygen transmission rate of the three-layer film used for dairy product packaging is required to be less than 2.47×10 -2 cm 3 / (m 2 ·24h·Pa), and from the test results in Table 2, it can be known that the composite films prepared by the present application all meet the use requirements of dairy product packaging;

[0076] (4) The hygienic of the composite film I and the composite film II prepared by the present application meets the national standard requirements and can be used in dairy product packaging.

Claims

1. A method for the preparation of a dairy easy-tear composite packaging material, characterized by, The method comprises the following steps: Step 1, preparing a composite antibacterial agent, the preparation method of which is as follows: The surface of the hydroxylated nano zinc oxide particles is modified by using a Schiff base type coupling agent to obtain the modified product; Or the surface of the hydroxylated nano zinc oxide particles is modified by using a Schiff base type coupling agent and a Schiff base type crosslinking agent to obtain the modified product; The chemical structural formula of the Schiff base type coupling agent is as follows: ； The chemical structural formula of the Schiff base type crosslinking agent is as follows: ； Step 2, using low-density polyethylene resin and the composite antibacterial agent as raw materials, the raw materials are blended, melted, extruded by a double-screw extruder, and then subjected to longitudinal stretching and transverse stretching, and finally hot-pressed to obtain a BOPE surface layer; Using ethylene-vinyl alcohol copolymer resin and low-density polyethylene resin as raw materials, the raw materials are blended, melted, extruded and pelletized by a double-screw extruder, and then a film is obtained by casting, thereby obtaining a barrier intermediate layer; Using low-density polyethylene resin and the composite antibacterial agent as raw materials, the raw materials are blended, melted, extruded and pelletized by a double-screw extruder, and then a film is obtained by casting, thereby obtaining a PE inner layer; Step 3, using a high-speed solvent-free compounding process to bond the BOPE surface layer, the barrier intermediate layer and the PE inner layer to obtain a composite film, which is a dairy product easy-to-tear composite packaging material.

2. A process for the preparation of a dairy easy-tear composite packaging material according to claim 1, characterized in that, The preparation method of the Schiff base type coupling agent is as follows: Using 7-hydroxycoumarin as a nucleophile, a nucleophilic substitution reaction is performed between the bromine functional group of 2-bromoacetaldehyde and the hydroxyl functional group of 7-hydroxycoumarin to obtain a coumarin aldehyde monomer; Using the Schiff base reaction mechanism, a condensation reaction is performed between the amino functional group of 3-aminopropyltrimethoxysilane and the carbonyl functional group of the coumarin aldehyde monomer to obtain the Schiff base type coupling agent.

3. A method of producing a dairy product easy-tear composite packaging material according to claim 1, characterized in that, The preparation method of the Schiff base type crosslinking agent is as follows: Using 5,7-dihydroxycoumarin as a nucleophile, a nucleophilic substitution reaction is performed between the bromine functional group of 2-bromoacetaldehyde and the hydroxyl functional group of 5,7-dihydroxycoumarin to obtain a coumarin dialdehyde monomer; Using the Schiff base reaction mechanism, a condensation reaction is performed between the amino functional group of 3-aminopropyltrimethoxysilane and the carbonyl functional group of the coumarin dialdehyde monomer to obtain the Schiff base type crosslinking agent.

4. A method of producing a dairy product easy-tear composite packaging material according to claim 1, characterized in that, In step 3, the preparation process parameters of the composite film are as follows: the compounding speed is 300-500 m / min, the compounding temperature is 40-50℃, the cooling temperature is 20-30℃, the compounding pressure is 0.3-0.5 Mpa, and the gluing pressure is 0.4-0.6 Mpa.

5. A dairy easy-tear composite packaging material prepared according to the method of any one of claims 1-4, characterized in that, The thickness of the dairy product easy-to-tear composite packaging material is 80-200 μm.

6. A dairy product easy-tear composite packaging material according to claim 5, characterized in that, The average tear strength of the dairy product easy-to-tear composite packaging material is 0.9-1.2 N.

7. A dairy product easy-tear composite packaging material according to claim 5, characterized in that, The dairy product easy-to-tear composite packaging material has antibacterial effect, and the bacteria are Escherichia coli or Staphylococcus aureus.

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