Polyethylene composite material for manufacturing food packaging box and preparation method of polyethylene composite material

Abstract

The invention relates to the technical field of composite materials, and discloses a polyethylene composite material for manufacturing a food packaging box and a preparation method thereof.The polyethylene composite material is prepared from polyethylene, an antioxidant, a lubricant, a compatilizer, a composite reinforcing material and a functional additive. According to the present invention, by adding the functional additive into the polyethylene matrix, the effective stress dispersion point can be formed in the polyethylene matrix, the toughness of the composite material can be improved, and the mechanical property of the composite material can be effectively improved; the antibacterial substance is introduced in a chemical bonding manner, and the antibacterial property of the composite material is improved, so that the polyethylene composite material prepared by the invention is excellent in mechanical property, toughness and antibacterial property, and can be used for manufacturing food packaging boxes.

Description

Technical Field

[0001] The invention relates to the technical field of composite materials, and in particular to a polyethylene composite material for making food packaging boxes and a preparation method thereof. Background Art

[0002] Food packaging boxes play a very important role in the food industry. They can ensure the quality and safety of food, effectively isolate harmful factors such as air, moisture, dust, and maintain the quality of food. Packaging boxes can also prevent food from being squeezed and collided during transportation, which is conducive to the subsequent sales of food. With the continuous advancement of science and technology, the materials of food packaging boxes tend to be diverse, including plastic materials, paper materials, metal materials, glass materials, etc. Plastic materials have become one of the mainstream materials for food packaging boxes because of their light weight, good chemical stability, easy processing and molding, good barrier properties, and low cost. They are widely used. Common plastic materials include: polypropylene (PP), polyethylene (PE), polystyrene (PS), polyvinyl chloride (PVC), polycarbonate (PC), etc. Polyethylene materials can be selected as the material for making food packaging boxes because of their advantages such as good water and moisture resistance, good low temperature resistance, and low price.

[0003] However, there are shortcomings in polyethylene materials. The strength and toughness of polyethylene materials are insufficient. When impacted by external forces, they are easily damaged, resulting in damage to food packaging boxes. The antibacterial properties of polyethylene materials are poor, and food is easily contaminated by microorganisms such as bacteria and molds, which reduces the shelf life of food and causes food waste. The patent with publication number CN112694658B discloses a polyethylene composition and a polyethylene film and a preparation method and application thereof. The polyethylene film does not use a nucleating agent and a metallocene linear low-density polyethylene. By mixing linear low-density polyethylene and long-chain branched polyethylene, a film material with higher transparency, lower haze and higher mechanical properties can be obtained by melt extrusion and granulation. The film material is suitable for daily necessities packaging materials, cosmetic packaging materials, detergent packaging materials, food packaging materials and pharmaceutical packaging materials. Higher transparency improves the visualization of the product in the package, and can ensure the shape of the product, reducing the risk of product packaging breaking during transportation. However, the patent does not take into account the importance of antibacterial properties in food packaging materials. Therefore, the present invention provides a polyethylene composite material for making food packaging boxes, which has excellent mechanical properties, toughness and antibacterial properties and has broad application prospects. Summary of the invention

[0004] In order to solve the problems mentioned in the background technology, the object of the present invention is to provide a polyethylene composite material for making food packaging boxes and a preparation method thereof.

[0005] The purpose of the present invention can be achieved by the following technical solutions:

[0006] A polyethylene composite material for making food packaging boxes comprises the following raw materials in parts by weight: 75-90 parts of low-density polyethylene, 0.5-2 parts of antioxidant, 1-4 parts of lubricant, 1-4 parts of compatibilizer, 3-5 parts of composite reinforcing material, and 4-6 parts of functional additive.

[0007] Furthermore, the antioxidant is antioxidant 1010 or antioxidant 168; the lubricant is any one of calcium stearate, polyethylene wax or ethylene bisstearamide; and the compatibilizer is maleic anhydride grafted polyethylene.

[0008] Furthermore, the preparation method of the composite reinforcement material comprises the following steps:

[0009] Step A: adding serpentine to dimethyl sulfoxide, dispersing it evenly, introducing nitrogen protection, adding a diacyl chloride modifier and a catalyst, raising the temperature to 90-100° C., reacting for 2-4 hours, filtering, washing, and drying to obtain modified serpentine;

[0010] Step B: Add modified serpentine into N,N-dimethylformamide, disperse evenly, add amino polycaprolactone and composite catalyst, stir and react for 3-5 hours, filter, wash and dry to obtain composite reinforcement material.

[0011] By adopting the above technical scheme, the serpentine surface contains hydroxyl groups, which can react with the acyl chloride at one end of the diacyl chloride modifier structure under the action of a catalyst, thereby introducing acyl chloride groups on the serpentine surface to obtain modified serpentine, and the acyl chloride groups on the surface of the modified serpentine can react with aminopolycaprolactone under the action of a composite catalyst to obtain a composite reinforcing material. The composite reinforcing material prepared by the present invention uses serpentine as a matrix, and by grafting serpentine with aminopolycaprolactone, the compatibilizer problem between serpentine and a polyethylene matrix can be effectively improved, and the agglomeration of serpentine in the matrix is ​​also avoided. Serpentine can be uniformly dispersed in the polyethylene matrix, and the skeleton support effect of serpentine in the polyethylene matrix is ​​utilized to enhance the mechanical properties. In addition, under the action of the compatibilizer, it can interact with the polyethylene molecular chain, significantly improve the interface bonding force between the composite reinforcing material and the polyethylene matrix, and help to improve the mechanical properties of the polyethylene composite material.

[0012] Furthermore, in step A, the diacyl chloride modifier is any one of terephthaloyl chloride, malonyl chloride, succinyl chloride, glutaryl chloride or adipoyl chloride.

[0013] Furthermore, in step A, the catalyst is p-toluenesulfonic acid.

[0014] Furthermore, in step B, the composite catalyst is dicyclohexylcarbodiimide and N-hydroxysuccinimide in a mass ratio of 0.8-0.9:0.2-0.3.

[0015] Furthermore, the preparation method of the functional additive comprises the following steps:

[0016] Step S1: adding eucommia gum to tetrahydrofuran, mixing and stirring evenly, adding dithiothreitol and a photoinitiator, irradiating with ultraviolet light for 3-5 hours at room temperature, evaporating to remove the solvent, washing, and drying to obtain modified eucommia gum;

[0017] Step S2: Add the modified eucommia gum to N,N-dimethylformamide, mix and stir evenly, then add vanillic acid and trifluoromethanesulfonic acid, raise the temperature to 95-100°C, react for 4-6 hours, cool to room temperature, separate the product, wash and dry to obtain a functional additive.

[0018] By adopting the above technical scheme, the olefinic group in the structure of eucommia gum can undergo a thiol-ene click reaction with the thiol group in the dithiothreitol structure, thereby introducing a hydroxyl group into the eucommia gum to obtain modified eucommia gum. The hydroxyl group in the structure of the modified eucommia gum can undergo an esterification reaction with the carboxyl group in the vanillic acid structure under the action of trifluoromethanesulfonic acid to obtain a functional additive. The functional additive prepared by the present invention combines eucommia gum and vanillic acid by chemical bonding. Eucommia gum is a natural polymer material with flexible segments. When added to a polyethylene matrix, it can form an effective stress dispersion point, absorb and disperse energy when the polyethylene composite material is impacted by external force, and prevent the composite material from breaking. Vanillic acid is a natural antibacterial small molecule with a broad-spectrum antibacterial effect. Vanillic acid is introduced into eucommia gum by chemical bonding, which can effectively prevent the small molecule antibacterial substance vanillic acid from precipitating from the material during long-term use, causing the antibacterial property of the composite material to decrease and be corroded by bacteria and mold. The functional additive can be cross-linked with the polyethylene material under the action of a compatibilizer, further enhancing the toughness of the composite material, and a small amount of the functional additive can have a long-lasting and effective antibacterial effect.

[0019] Furthermore, in S1, the photoinitiator is any one of benzoin dimethyl ether, benzoin isopropyl ether or benzoin isobutyl ether.

[0020] A method for preparing a polyethylene composite material for making a food packaging box comprises the following steps:

[0021] Step 1: Add low-density polyethylene, antioxidant, lubricant, compatibilizer, composite reinforcement and functional additive into a high-speed mixer, stir and mix them evenly at a speed of 300-500 r / min to obtain a mixed base material;

[0022] Step 2: Add the mixed base material into a twin-screw extruder, and perform extrusion granulation at a screw speed of 200-400 r / min and an extrusion section temperature of 180-210° C. to obtain a polyethylene composite material.

[0023] Beneficial effects of the present invention:

[0024] The present invention adds composite reinforcing materials and functional additives to a polyethylene matrix so that the prepared polyethylene composite material has excellent mechanical properties, toughness and antibacterial properties. The tensile strength can reach up to 29.6 MPa, the elongation at break can reach up to 162.6%, and the antibacterial rate can reach up to 99.5%. Therefore, the food packaging box prepared using the polyethylene composite material has a longer service life, is less susceptible to contamination and erosion by microorganisms such as bacteria, and is safer and more hygienic.

[0025] Of course, any product implementing the present invention does not necessarily need to achieve all of the advantages described above at the same time. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings required for describing the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other accompanying drawings can be obtained based on these accompanying drawings without paying creative work.

[0027] Figure 1 This is an infrared spectrum of the composite reinforcement material prepared by the present invention;

[0028] Figure 2 This is the infrared spectrum of the functional additive prepared by the present invention. DETAILED DESCRIPTION

[0029] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of 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.

[0030] The preparation methods of the composite reinforcing materials and functional additives in the following examples and comparative examples are as follows:

[0031] 1. Preparation of composite reinforcement materials

[0032] Step A: 2.8 g of serpentine was added to dimethyl sulfoxide, and after being evenly dispersed, nitrogen was introduced for protection, 1.6 g of terephthaloyl chloride and 0.5 g of p-toluenesulfonic acid were added, the temperature was raised to 95° C., and after reacting for 3 h, the mixture was filtered, washed, and dried to obtain modified serpentine;

[0033] Step B: Add 2.6 g of modified serpentine to N,N-dimethylformamide, and after uniform dispersion, add 1.2 g of aminopolycaprolactone, 0.4 g of dicyclohexylcarbodiimide and 0.1 g of N-hydroxysuccinimide, stir and react for 4 hours, filter, wash and dry to obtain a composite reinforcement material.

[0034] The sample was prepared by potassium bromide tableting method, and the composite reinforcement was tested by infrared using Nicolet 8700 Fourier transform infrared spectrometer. Figure 1 As shown, 3032cm -1 The absorption peak of CH in the benzene ring appears at 1742 cm -1 The absorption peak of C=O in the ester group appeared at 1665 cm -1 The absorption peak of C=O in amide appeared at 1558 cm -1 The absorption peak of NH in amide appeared at 1054 cm -1 The absorption peak of S iOS i in serpentine appeared.

[0035] 2. Preparation of functional additives

[0036] Step S1: adding 3 g of eucommia gum to tetrahydrofuran, mixing and stirring evenly, adding 2 g of dithiothreitol and 0.2 g of benzoin dimethyl ether, irradiating with ultraviolet light at room temperature for 4 h, evaporating and removing the solvent, washing, and drying to obtain modified eucommia gum;

[0037] Step S2: Add 3 g of modified eucommia gum to N,N-dimethylformamide, mix and stir evenly, then add 2.2 g of vanillic acid and 0.5 g of trifluoromethanesulfonic acid, raise the temperature to 98°C, react for 5 hours, cool to room temperature, separate the product, wash and dry to obtain a functional additive.

[0038] The samples were prepared by potassium bromide tableting method, and the functional additives were tested by infrared using Nicolet 8700 Fourier transform infrared spectrometer. Figure 2 As shown, 3411cm -1 The absorption peak of OH appeared at 3056 cm -1 The absorption peak of CH in the carbon-carbon double bond appears at 3028 cm -1 The absorption peak of CH in the benzene ring appeared at 1733 cm -1 The absorption peak of C=O in the ester group appeared at 1172 cm-1 The absorption peak of CSC appears at .

[0039] Example 1

[0040] Preparation of polyethylene composites

[0041] Step 1: Add 75g of low-density polyethylene, 0.5g of antioxidant 1010, 1g of calcium stearate lubricant, 1g of maleic anhydride grafted polyethylene compatibilizer, 3g of composite reinforcement material and 4g of functional additive into a high-speed mixer, stir and mix evenly at a speed of 300r / min to obtain a mixed base material;

[0042] Step 2: Add the mixed base material into a twin-screw extruder, and perform extrusion granulation at a screw speed of 200 r / min and an extrusion section temperature of 180° C. to obtain a polyethylene composite material.

[0043] Example 2

[0044] Preparation of polyethylene composites

[0045] Step 1: Add 78g of low-density polyethylene, 0.5g of antioxidant 1010, 1g of calcium stearate lubricant, 2g of maleic anhydride grafted polyethylene compatibilizer, 4.5g of composite reinforcement material and 5g of functional additive into a high-speed mixer, stir and mix evenly at a speed of 400r / min to obtain a mixed base material;

[0046] Step 2: Add the mixed base material into a twin-screw extruder, and perform extrusion granulation at a screw speed of 300 r / min and an extrusion section temperature of 200° C. to obtain a polyethylene composite material.

[0047] Example 3

[0048] Preparation of polyethylene composites

[0049] Step 1: Add 90g of low-density polyethylene, 2g of antioxidant, 4g of calcium stearate lubricant, 4g of maleic anhydride grafted polyethylene compatibilizer, 5g of composite reinforcement material and 6g of functional additive into a high-speed mixer, stir and mix evenly at a speed of 500r / min to obtain a mixed base material;

[0050] Step 2: Add the mixed base material into a twin-screw extruder, and perform extrusion granulation at a screw speed of 400 r / min and an extrusion section temperature of 210° C. to obtain a polyethylene composite material.

[0051] Comparative Example 1

[0052] Preparation of polyethylene composites

[0053] Step 1: Add 78g polyethylene, 0.5g antioxidant 1010, 1g calcium stearate lubricant, 2g maleic anhydride grafted polyethylene compatibilizer, and 4.5g composite reinforcement material into a high-speed mixer, and stir and mix them evenly at a speed of 400r / min to obtain a mixed base material;

[0054] Step 2: Add the mixed base material into a twin-screw extruder, and perform extrusion granulation at a screw speed of 300 r / min and an extrusion section temperature of 200° C. to obtain a polyethylene composite material.

[0055] Comparative Example 2

[0056] Preparation of polyethylene composites

[0057] Step 1: Add 78g of low-density polyethylene, 0.5g of antioxidant 1010, 1g of calcium stearate lubricant, 2g of maleic anhydride grafted polyethylene compatibilizer, and 5g of functional additive into a high-speed mixer, and stir and mix them evenly at a speed of 400r / min to obtain a mixed base material;

[0058] Step 2: Add the mixed base material into a twin-screw extruder, and perform extrusion granulation at a screw speed of 300 r / min and an extrusion section temperature of 200° C. to obtain a polyethylene composite material.

[0059] Comparative Example 3

[0060] Preparation of polyethylene composites

[0061] Step 1: Add 78g of low-density polyethylene, 0.5g of antioxidant 1010, 1g of calcium stearate lubricant, 2g of maleic anhydride grafted polyethylene compatibilizer, 4.5g of serpentine and 5g of functional additive into a high-speed mixer, stir and mix evenly at a speed of 400r / min to obtain a mixed base material;

[0062] Step 2: Add the mixed base material into a twin-screw extruder, and perform extrusion granulation at a screw speed of 300 r / min and an extrusion section temperature of 200° C. to obtain a polyethylene composite material.

[0063] Comparative Example 4

[0064] Preparation of polyethylene composites

[0065] Step 1: Add 78g of low-density polyethylene, 0.5g of antioxidant 1010, 1g of calcium stearate lubricant, 2g of maleic anhydride grafted polyethylene compatibilizer, 4.5g of composite reinforcing material and 5g of eucommia gum into a high-speed mixer, stir and mix evenly at a speed of 400r / min to obtain a mixed base material;

[0066] Step 2: Add the mixed base material into a twin-screw extruder, and perform extrusion granulation at a screw speed of 300 r / min and an extrusion section temperature of 200° C. to obtain a polyethylene composite material.

[0067] Performance Testing

[0068] The polyethylene composite materials prepared in Examples 1 to 3 and Comparative Examples 1 to 4 were prepared into samples that met the test requirements. The tensile properties and elongation at break were tested in accordance with GB / T 1040.3-2006 standard to determine the mechanical properties and toughness of the samples. In accordance with GB / T 31402-2023 standard, Escherichia coli was used as the test strain, and the antibacterial rate was calculated to determine the antibacterial properties of the samples. The test results are shown in the following table:

[0069] Tensile strength(MPa) Elongation at break (%) Antibacterial rate (%) Example 1 26.8 159.4 99.2 Example 2 29.6 162.6 99.5 Example 3 27.9 160.5 99.3 Comparative Example 1 25.3 119.7 58.4 Comparative Example 2 17.9 154.2 98.6 Comparative Example 3 20.2 157.3 98.9 Comparative Example 4 26.1 138.8 59.1

[0070] It can be seen from the above table that the polyethylene composite materials prepared in Examples 1 to 3 of the present invention have excellent mechanical properties, toughness and antibacterial properties. Comparative Example 1 adds a composite reinforcement material but does not add a functional additive. The mechanical properties are excellent, but it is impossible to use eucommia gum to graft vanillic acid to improve the toughness and antibacterial properties of the polyethylene composite material, so the toughness and antibacterial properties are poor; Comparative Example 2 adds a functional additive but does not add a composite reinforcement material. The toughness and antibacterial properties are excellent, but serpentine cannot be used to graft aminopolycaprolactone, so the mechanical properties are poor; Comparative Example 3 adds serpentine and functional additives, and the toughness and antibacterial properties are excellent. Serpentine may agglomerate in the polyethylene matrix without modification, which has a negative impact on the mechanical properties of the polyethylene composite material, so the mechanical properties are poor; Comparative Example 4 adds a composite reinforcement material and eucommia gum, and the mechanical properties are excellent, but vanillic acid is not grafted, so the antibacterial properties are poor.

[0071] The above contents are merely examples and explanations of the concept of the present invention. The technicians in this technical field may make various modifications or additions to the specific embodiments described or replace them in a similar manner. As long as they do not deviate from the concept of the invention or exceed the scope defined by the claims, they should all fall within the protection scope of the present invention.

Claims

1. A polyethylene composite material for making food packaging boxes, characterized in that: The invention comprises the following raw materials in parts by weight: 75-90 parts of low-density polyethylene, 0.5-2 parts of antioxidant, 1-4 parts of lubricant, 1-4 parts of compatibilizer, 3-5 parts of composite reinforcing material and 4-6 parts of functional additive.

2. The polyethylene composite material for making food packaging boxes according to claim 1, characterized in that: The antioxidant is antioxidant 1010 or antioxidant 168; the lubricant is any one of calcium stearate, polyethylene wax or ethylene bisstearamide; and the compatibilizer is maleic anhydride grafted polyethylene.

3. The polyethylene composite material for making food packaging boxes according to claim 1, characterized in that: The preparation method of the composite reinforcement material comprises the following steps: Step A: adding serpentine to dimethyl sulfoxide, dispersing it evenly, introducing nitrogen protection, adding a diacyl chloride modifier and a catalyst, raising the temperature to 90-100° C., reacting for 2-4 hours, filtering, washing, and drying to obtain modified serpentine; Step B: Add modified serpentine into N,N-dimethylformamide, disperse evenly, add amino polycaprolactone and composite catalyst, stir and react for 3-5 hours, filter, wash and dry to obtain composite reinforcement material.

4. The polyethylene composite material for making food packaging boxes according to claim 3, characterized in that: In step A, the diacyl chloride modifier is any one of terephthaloyl chloride, malonyl chloride, succinyl chloride, glutaryl chloride or adipoyl chloride.

5. The polyethylene composite material for making food packaging boxes according to claim 3, characterized in that: In step A, the catalyst is p-toluenesulfonic acid.

6. The polyethylene composite material for making food packaging boxes according to claim 3, characterized in that: In step B, the composite catalyst is dicyclohexylcarbodiimide and N-hydroxysuccinimide in a mass ratio of 0.8-0.9:0.2-0.

3.

7. The polyethylene composite material for making food packaging boxes according to claim 1, characterized in that: The preparation method of the functional additive comprises the following steps: Step S1: adding eucommia gum to tetrahydrofuran, mixing and stirring evenly, adding dithiothreitol and a photoinitiator, irradiating with ultraviolet light for 3-5 hours at room temperature, evaporating to remove the solvent, washing, and drying to obtain modified eucommia gum; Step S2: Add the modified eucommia gum to N,N-dimethylformamide, mix and stir evenly, then add vanillic acid and trifluoromethanesulfonic acid, raise the temperature to 95-100°C, react for 4-6 hours, cool to room temperature, separate the product, wash and dry to obtain a functional additive.

8. The polyethylene composite material for making food packaging boxes according to claim 7, characterized in that: In S1, the photoinitiator is any one of benzoin dimethyl ether, benzoin isopropyl ether or benzoin isobutyl ether.

9. A method for preparing a polyethylene composite material for making a food packaging box as claimed in claim 1, characterized in that: The following steps are involved: Step 1: Add low-density polyethylene, antioxidant, lubricant, compatibilizer, composite reinforcement and functional additive into a high-speed mixer, stir and mix them evenly at a speed of 300-500 r / min to obtain a mixed base material; Step 2: Add the mixed base material into a twin-screw extruder, and perform extrusion granulation at a screw speed of 200-400 r / min and an extrusion section temperature of 180-210° C. to obtain a polyethylene composite material.

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