High-strength polyethylene milk bottle cap and preparation process thereof

Abstract

The invention relates to the technical field of milk bottle caps, in particular to a high-strength polyethylene milk bottle cap and a preparation process thereof. The preparation method comprises the following steps: 1, preparing a functional additive: S1, adding polylysine into a nano-montmorillonite dispersion liquid, carrying out intercalation reaction at 60-65 DEG C for 2-3 hours, centrifuging, and drying to obtain modified nano-montmorillonite; s2, in a nitrogen atmosphere, adding caffeic acid into a PBS buffer solution, adding EDC and NHS, and stirring for 15-30 minutes in an ice bath; adding a modified nano montmorillonite-PBS buffer solution, continuously stirring for 24 hours, washing and drying to obtain a functional additive; and 2, mixing the high-density polyethylene, the functional additive, the compatilizer, the aldehyde polyolefin elastomer, palm oil and color master batch, and carrying out melt extrusion and injection molding to obtain the high-strength polyethylene milk bottle cap. In the scheme, the prepared high-strength polyethylene milk bottle cap has excellent mechanical strength and oxygen barrier property.

Description

Technical Field

[0001] The invention relates to the technical field of milk bottle caps, in particular to a high-strength polyethylene milk bottle cap and a preparation process thereof. Background Art

[0002] In recent years, as consumers have higher requirements for food safety and packaging quality, the market demand for high strength and high sealing performance has continued to grow. Among them, polyethylene is a widely used thermoplastic material; due to its light weight, durability and high chemical stability, it has become an ideal material for making milk bottle caps. However, traditional polyethylene bottle caps lack rigidity and toughness; at the same time, they have poor antioxidant and barrier properties, and will cause aging and deformation under high temperature or light, which will lead to a decrease in the sealing performance of the bottle cap, affecting the storage and transportation of milk.

[0003] In order to ensure the quality of milk and extend its shelf life, the antioxidant and barrier properties of polyethylene bottle caps need to be comprehensively improved. In the existing technology, antioxidants such as butylated hydroxyanisole and barrier agents such as montmorillonite are usually introduced; first, there are problems with migration and dispersion, which poses a safety hazard; second, there are compatibility issues, resulting in excessive introduction of the amount of polyethylene bottle caps, which affects the mechanical properties.

[0004] In summary, solving the above problems and preparing a high-strength polyethylene milk bottle cap are of great significance. Summary of the invention

[0005] The object of the present invention is to provide a high-strength polyethylene milk bottle cap and a preparation process thereof to solve the problems raised in the above-mentioned background technology.

[0006] In order to solve the above technical problems, the present invention provides the following technical solutions: A preparation process of a high-strength polyethylene milk bottle cap comprises the following steps: Step 1: Preparation of functional additives: S1: adding polylysine to the nano-montmorillonite dispersion, performing intercalation reaction at 60-65°C for 2-3 hours, centrifuging and drying to obtain modified nano-montmorillonite; S2: Under nitrogen atmosphere, caffeic acid was added to PBS buffer solution, EDC and NHS were added, and the mixture was stirred for 15 to 30 minutes in an ice bath; modified nano-montmorillonite-PBS buffer solution was added, and the mixture was stirred for 24 hours, and then washed and dried to obtain a functional additive; Step 2: High-density polyethylene, functional additives, compatibilizers, formaldehyde-modified polyolefin elastomers, palm oil, and masterbatches are mixed, melt-extruded, and injection molded to obtain high-strength polyethylene milk bottle caps.

[0007] More optimally, the raw materials of the high-strength polyethylene milk bottle cap include the following components: by weight, 100 parts of high-density polyethylene, 4 to 8 parts of functional additives, 2 to 5 parts of compatibilizers, 1.5 to 3 parts of formaldehyde-modified polyolefin elastomers, 1 to 1.5 parts of palm oil, and 1 to 2 parts of masterbatch.

[0008] More optimally, the compatibilizer includes maleic anhydride grafted polyethylene and maleic anhydride grafted polyolefin elastomer in a mass ratio of 2:3.

[0009] More optimally, the modified nano-montmorillonite comprises polylysine and nano-montmorillonite in a mass ratio of 4:3.2-3.5; and the functional additive comprises modified nano-montmorillonite and caffeic acid in a mass ratio of 1:0.2-0.3.

[0010] More optimally, the preparation method of the modified polyolefin elastomer is: S1: melt-extrude a polyolefin elastomer, 4-vinylbenzyl alcohol, and a peroxidation initiator in a twin-screw extruder, grind the components, and obtain a hydroxylated modified polyolefin elastomer; S2: Adding the hydroxylated modified polyolefin elastomer and the molybdenum catalyst into DMF in sequence, reacting at 50-55° C. for 2-3 hours, washing and drying, to obtain the aldehyde-modified polyolefin elastomer.

[0011] More optimally, the hydroxylated modified polyolefin elastomer comprises a polyolefin elastomer, 4-vinyl benzyl alcohol, and a peroxidation initiator in a mass ratio of 90:5-10:0.1-0.5; The aldehyde-modified polyolefin elastomer comprises a hydroxylated modified polyolefin elastomer and a molybdenum catalyst in a mass ratio of 1:0.02-0.05.

[0012] The preparation method of the molybdenum catalyst is as follows: molybdenum dioxide dichloride and carbon black in a mass ratio of 1:1 are sequentially added into DMF, reacted at 115-120° C. for 24 hours, washed and dried to obtain the molybdenum catalyst.

[0013] Preferably, the functional additive is pre-compounded with the aldehyde-modified polyolefin elastomer; the process of step 2 is as follows: S1: Dispersing the functional additive and the aldehyde-modified polyolefin elastomer in ethanol in sequence, stirring and heating at 60-65° C. for 4-6 hours, removing the solvent, and drying to obtain raw material A; S2: Mix raw material A with high-density polyethylene, compatibilizer, palm oil and masterbatch, melt extrude and injection mold to obtain a high-strength polyethylene milk bottle cap.

[0014] More optimally, the process parameters of the melt extrusion are: feed rate of 10~15r / min, screw speed of 30~40r / min, temperature of each temperature zone of 165~170℃, 165~170℃, 165~170℃, 175~180℃, 185~190℃, 185~190℃, 185~190℃, 175~180℃; the process parameters of the injection molding are: injection pressure of 80~100bar, temperature of each temperature zone of 200~205℃, 210~215℃, 215~220℃, 215~220℃.

[0015] More optimally, a high-strength polyethylene milk bottle cap is prepared by a preparation process of a high-strength polyethylene milk bottle cap.

[0016] Compared with the prior art, the present application has the following beneficial effects: the functional additives prepared in the scheme significantly enhance the antioxidant and barrier properties of the polyethylene milk bottle cap; two compatibilizers are used at the same time for the dispersion and compatibility of the functional additives in the polyethylene milk bottle cap. In addition, by introducing the aldehyde-modified polyolefin elastomer to modify the functional additive, the interface properties of the functional additive are further enhanced, the amount of the functional additive introduced is increased, the migration is inhibited, and the mechanical properties and barrier properties of the polyethylene milk bottle cap are improved.

[0017] In the scheme, the functional additive is based on nano-montmorillonite. Polylysine is loaded on the nano-montmorillonite through intercalation reaction. And further, caffeic acid is attached to polylysine through the reaction between carboxyl and amino groups to obtain the functional additives in turn.

[0018] Among them, nano-montmorillonite is a natural layered silicate with antibacterial properties. It has a high aspect ratio and an impermeable layered structure, which can effectively reduce the diffusion path of molecules, thereby improving antibacterial and oxygen barrier properties. At the same time, its introduction can promote the crystallization of the polymer, thereby effectively enhancing the strength of the polyethylene Newmai bottle cap. Polylysine is a safe material with antibacterial and antioxidant properties. Its introduction further improves the antibacterial and barrier properties of functional additives and increases antioxidant properties. In addition, it also contains amino groups as functional sites, which are further grafted with caffeic acid. Caffeic acid is a polyphenol compound with limited antioxidant activity, which can inhibit oxidation reactions and extend the shelf life of milk. At the same time, caffeic acid contains vinyl groups that can be cross-linked with high-density polyethylene.

[0019] In the scheme, in order to further improve the dispersibility of functional additives in high-density polyethylene and improve the mechanical properties of milk bottle caps, one of the schemes is to use the amino sites contained in the functional additives to further react and graft with the aldehyde-modified polyolefin elastomer, and use the polyolefin elastomer segments in the aldehyde-modified polyolefin elastomer to effectively disperse in high-density polyethylene, further improving the interfacial effect. At the same time, the aldehyde-modified polyolefin elastomer has toughening effects on high-density polyethylene, and it is prepared by first grafting 4-vinylbenzyl alcohol and then using a catalyst to convert the alcohol group into an aldehyde group. The benzene ring in 4-vinylbenzyl alcohol has rigidity, and its introduction can improve the tensile strength of the polyethylene bottle cap.

[0020] Among them, since the functional additives in this application reach 5%~7%; in the scheme, in order to further improve the performance, a compound compatibilizer is further introduced, which includes maleic anhydride grafted polyethylene and maleic anhydride grafted polyolefin elastomer, among which maleic anhydride grafted polyolefin elastomer can further improve the dispersibility of functional additives, and at the same time cooperate with aldehyde-modified polyolefin elastomer to effectively ensure the interface of elastomer; and the introduction of maleic anhydride grafted polyethylene ensures the interface strength of the composite material; compared with a single compatibilizer, the introduction of a specific ratio of maleic anhydride grafted polyethylene and maleic anhydride grafted polyolefin elastomer makes the polyethylene milk bottle cap have higher mechanical strength. In addition, the introduction of palm oil is used as a plasticizer to improve the processing performance of high-strength polyethylene milk bottle caps. DETAILED DESCRIPTION

[0021] Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in the field without making any creative work shall fall within the scope of protection of the present invention.

[0022] It should be noted that the following parts are by mass; the purchase manufacturers of all raw materials involved in the present invention are not subject to any special restrictions and exemplarily include: the brand of high-density polyethylene is HD2200JP, and the manufacturer is PTT; the model of maleic anhydride grafted polyethylene is XH6050MGXTTR; the brand of maleic anhydride grafted polyolefin elastomer is VA-1202, and the manufacturer is Exxon; the grade of palm oil is food grade, and the brand is Tengyun Chemical; the brand of masterbatch is 8001, and the brand is Dude Plastics; the brand of polyolefin elastomer is 8003, and the brand is Dow of the United States; the pH of PBS buffer solution is 7.2; the model of nano-montmorillonite is food grade, and the brand is Kanos; polylysine is food grade, and the brand is Bainafo; the CAS number of caffeic acid is 331-39-5, and the CAS number of 4-vinylbenzyl alcohol is 1074-61-9.

[0023] Preparation of molybdenum catalyst: Molybdenum dioxide dichloride and carbon black in a mass ratio of 1:1 are added to DMF in sequence, reacted at 120° C. for 24 hours, washed and dried to obtain a molybdenum catalyst.

[0024] Embodiment 1: A process for preparing a high-strength polyethylene milk bottle cap, comprising the following steps: Step 1: Preparation of functional additives: S1: Add 4 parts of polylysine to 3.2 g / L nano-montmorillonite dispersion (containing 3.2 parts of nano-montmorillonite, the solvent is deionized water), intercalate at 65°C for 2 hours, centrifuge and dry to obtain modified nano-montmorillonite; S2: Under a nitrogen atmosphere, add 0.3 parts of caffeic acid to 30 parts of PBS buffer solution, add 0.3 parts of EDC and 0.18 parts of NHS, and stir for 30 minutes in an ice bath; add modified nano-montmorillonite-PBS buffer solution (1 part of modified nano-montmorillonite, 30 parts of PBS buffer solution), continue stirring for 24 hours, wash and dry to obtain a functional additive; Step 2: Preparation of high-strength polyethylene milk bottle cap: S1: (1) melt-extrude 9 parts of polyolefin elastomer, 1 part of 4-vinylbenzyl alcohol, and 0.3 parts of peroxidation initiator BPO in a twin-screw base, grind the components, and obtain a hydroxylated modified polyolefin elastomer; (2) add the hydroxylated modified polyolefin elastomer and a molybdenum catalyst in a mass ratio of 1:0.04 to DMF in sequence, react at 55°C for 2 hours, wash, and dry to obtain an aldehyde-modified polyolefin elastomer; S2: Weigh 100 parts of high-density polyethylene, 6 parts of functional additives, 3 parts of compatibilizer (maleic anhydride grafted polyethylene and maleic anhydride grafted polyolefin elastomer in a mass ratio of 2:3), 3 parts of aldehyde-modified polyolefin elastomer, 1.5 parts of palm oil, and 1.5 parts of masterbatch as raw materials; S3: (1) dispersing the functional additive and the aldehyde-modified polyolefin elastomer in 100 parts of ethanol in sequence, stirring and heating at 65° C. for 6 hours, removing the solvent, and drying to obtain a raw material A; (2) Mix raw material A with high-density polyethylene, compatibilizer, palm oil and masterbatch, and set the process parameters as follows: feed rate of 10 r / min, screw speed of 35 r / min, and temperatures in each temperature zone of 165°C, 170°C, 170°C, 175°C, 185°C, 185°C, 185°C, and 175°C for melt extrusion; set the process parameters as follows: injection pressure of 80 bar, and temperatures in each temperature zone of 200°C, 210°C, 215°C, and 220°C for injection molding to obtain high-strength polyethylene milk bottle caps.

[0025] Embodiment 2: A process for preparing a high-strength polyethylene milk bottle cap, comprising the following steps: Step 1: Preparation of functional additives: S1: Add 4 parts of polylysine to 3.2 g / L nano-montmorillonite dispersion (containing 3.2 parts of nano-montmorillonite, the solvent is deionized water), intercalate at 65°C for 2 hours, centrifuge and dry to obtain modified nano-montmorillonite; S2: Under a nitrogen atmosphere, add 0.3 parts of caffeic acid to 30 parts of PBS buffer solution, add 0.3 parts of EDC and 0.18 parts of NHS, and stir for 30 minutes in an ice bath; add modified nano-montmorillonite-PBS buffer solution (1 part of modified nano-montmorillonite, 30 parts of PBS buffer solution), continue stirring for 24 hours, wash and dry to obtain a functional additive; Step 2: Preparation of high-strength polyethylene milk bottle cap: S1: (1) melt-extrude 9 parts of polyolefin elastomer, 1 part of 4-vinylbenzyl alcohol, and 0.3 parts of peroxidation initiator BPO in a twin-screw base, grind the components, and obtain a hydroxylated modified polyolefin elastomer; (2) add the hydroxylated modified polyolefin elastomer and a molybdenum catalyst in a mass ratio of 1:0.04 to DMF in sequence, react at 55°C for 2 hours, wash, and dry to obtain an aldehyde-modified polyolefin elastomer; S2: Weigh 100 parts of high-density polyethylene, 4 parts of functional additives, 2 parts of compatibilizer (maleic anhydride grafted polyethylene and maleic anhydride grafted polyolefin elastomer in a mass ratio of 2:3), 1.5 parts of formaldehyde-modified polyolefin elastomer, 1.5 parts of palm oil, and 1 part of masterbatch as raw materials; S3: (1) dispersing the functional additive and the aldehyde-modified polyolefin elastomer in 100 parts of ethanol in sequence, stirring and heating at 65° C. for 6 hours, removing the solvent, and drying to obtain a raw material A; (2) Mix raw material A with high-density polyethylene, compatibilizer, palm oil and masterbatch, and set the process parameters as follows: feed rate of 10 r / min, screw speed of 30 r / min, temperatures in each temperature zone of 165°C, 170°C, 170°C, 175°C, 185°C, 185°C, 185°C, and 175°C for melt extrusion; set the process parameters as follows: injection pressure of 80 bar, temperatures in each temperature zone of 200°C, 210°C, 215°C, and 220°C for injection molding to obtain high-strength polyethylene milk bottle caps.

[0026] Embodiment 3: A process for preparing a high-strength polyethylene milk bottle cap, comprising the following steps: Step 1: Preparation of functional additives: S1: Add 4 parts of polylysine to 3.2 g / L nano-montmorillonite dispersion (containing 3.2 parts of nano-montmorillonite, the solvent is deionized water), intercalate at 65°C for 2 hours, centrifuge and dry to obtain modified nano-montmorillonite; S2: Under a nitrogen atmosphere, add 0.3 parts of caffeic acid to 30 parts of PBS buffer solution, add 0.3 parts of EDC and 0.18 parts of NHS, and stir for 30 minutes in an ice bath; add modified nano-montmorillonite-PBS buffer solution (1 part of modified nano-montmorillonite, 30 parts of PBS buffer solution), continue stirring for 24 hours, wash and dry to obtain a functional additive; Step 2: Preparation of high-strength polyethylene milk bottle cap: S1: (1) melt-extrude 9 parts of polyolefin elastomer, 1 part of 4-vinylbenzyl alcohol, and 0.3 parts of peroxidation initiator BPO in a twin-screw base, grind the components, and obtain a hydroxylated modified polyolefin elastomer; (2) add the hydroxylated modified polyolefin elastomer and a molybdenum catalyst in a mass ratio of 1:0.04 to DMF in sequence, react at 55°C for 2 hours, wash, and dry to obtain an aldehyde-modified polyolefin elastomer; S2: Weigh 100 parts of high-density polyethylene, 8 parts of functional additives, 5 parts of compatibilizer (maleic anhydride grafted polyethylene and maleic anhydride grafted polyolefin elastomer in a mass ratio of 2:3), 3 parts of formaldehyde-modified polyolefin elastomer, 1 part of palm oil, and 2 parts of masterbatch as raw materials; S3: (1) dispersing the functional additive and the aldehyde-modified polyolefin elastomer in 100 parts of ethanol in sequence, stirring and heating at 65° C. for 6 hours, removing the solvent, and drying to obtain a raw material A; (2) Mix raw material A with high-density polyethylene, compatibilizer, palm oil and masterbatch, and set the process parameters as follows: feed rate of 10 r / min, screw speed of 40 r / min, and temperatures in each temperature zone of 165°C, 170°C, 170°C, 175°C, 185°C, 185°C, 185°C, and 175°C for melt extrusion; set the process parameters as follows: injection pressure of 100 bar, and temperatures in each temperature zone of 200°C, 210°C, 215°C, and 220°C for injection molding to obtain high-strength polyethylene milk bottle caps.

[0027] Comparative Example 1: Based on Example 1, polyolefin elastomer was used to replace the aldehyde-modified polyolefin elastomer, and the rest was the same as Example 1; Step 1: Preparation of functional additives: S1: Add 4 parts of polylysine to 3.2 g / L nano-montmorillonite dispersion (containing 3.2 parts of nano-montmorillonite, the solvent is deionized water), intercalate at 65°C for 2 hours, centrifuge and dry to obtain modified nano-montmorillonite; S2: Under a nitrogen atmosphere, add 0.3 parts of caffeic acid to 30 parts of PBS buffer solution, add 0.3 parts of EDC and 0.18 parts of NHS, and stir for 30 minutes in an ice bath; add modified nano-montmorillonite-PBS buffer solution (1 part of modified nano-montmorillonite, 30 parts of PBS buffer solution), continue stirring for 24 hours, wash and dry to obtain a functional additive; Step 2: Preparation of high-strength polyethylene milk bottle cap: S1: Weigh 100 parts of high-density polyethylene, 6 parts of functional additives, 3 parts of compatibilizer (maleic anhydride grafted polyethylene and maleic anhydride grafted polyolefin elastomer in a mass ratio of 2:3), 3 parts of polyolefin elastomer, 1.5 parts of palm oil, and 1.5 parts of masterbatch as raw materials; S2: Mix high-density polyethylene, functional additives, polyolefin elastomer, compatibilizer, palm oil and masterbatch, and set the process parameters as follows: feed rate of 10r / min, screw speed of 35r / min, temperatures in each temperature zone of 165℃, 170℃, 170℃, 175℃, 185℃, 185℃, 185℃, and 175℃ for melt extrusion; set the process parameters as follows: injection pressure of 80bar, temperatures in each temperature zone of 200℃, 210℃, 215℃, and 220℃ for injection molding to obtain high-strength polyethylene milk bottle caps.

[0028] Comparative Example 2: Based on Example 1, maleic anhydride grafted polyolefin elastomer is used alone as a compatibilizer, and the rest is the same as Example 1; Step 1: Preparation of functional additives: S1: Add 4 parts of polylysine to 3.2 g / L nano-montmorillonite dispersion (containing 3.2 parts of nano-montmorillonite, the solvent is deionized water), intercalate at 65°C for 2 hours, centrifuge and dry to obtain modified nano-montmorillonite; S2: Under a nitrogen atmosphere, add 0.3 parts of caffeic acid to 30 parts of PBS buffer solution, add 0.3 parts of EDC and 0.18 parts of NHS, and stir for 30 minutes in an ice bath; add modified nano-montmorillonite-PBS buffer solution (1 part of modified nano-montmorillonite, 30 parts of PBS buffer solution), continue stirring for 24 hours, wash and dry to obtain a functional additive; Step 2: Preparation of high-strength polyethylene milk bottle cap: S1: (1) melt-extrude 9 parts of polyolefin elastomer, 1 part of 4-vinylbenzyl alcohol, and 0.3 parts of peroxidation initiator BPO in a twin-screw base, grind the components, and obtain a hydroxylated modified polyolefin elastomer; (2) add the hydroxylated modified polyolefin elastomer and a molybdenum catalyst in a mass ratio of 1:0.04 to DMF in sequence, react at 55°C for 2 hours, wash, and dry to obtain an aldehyde-modified polyolefin elastomer; S2: Weigh 100 parts of high-density polyethylene, 6 parts of functional additives, 3 parts of maleic anhydride grafted polyolefin elastomer, 3 parts of aldehyde-modified polyolefin elastomer, 1.5 parts of palm oil, and 1.5 parts of masterbatch as raw materials; S3: (1) dispersing the functional additive and the aldehyde-modified polyolefin elastomer in 100 parts of ethanol in sequence, stirring and heating at 65° C. for 6 hours, removing the solvent, and drying to obtain a raw material A; (2) Mix raw material A with high-density polyethylene, maleic anhydride grafted polyolefin elastomer, palm oil and masterbatch, and set the process parameters as follows: feed rate of 10 r / min, screw speed of 35 r / min, and temperatures in each temperature zone of 165°C, 170°C, 170°C, 175°C, 185°C, 185°C, 185°C, and 175°C for melt extrusion; set the process parameters as follows: injection molding pressure of 80 bar, and temperatures in each temperature zone of 200°C, 210°C, 215°C, and 220°C for injection molding to obtain high-strength polyethylene milk bottle caps.

[0029] Comparative Example 3: Based on Example 1, the functional additive is caffeic acid modified nano-montmorillonite, and the rest is the same as Example 1; Step 1: Preparation of functional additives: 0.3 parts of caffeic acid are added to 3.2 g / L nano-montmorillonite dispersion (containing 3.2 parts of nano-montmorillonite, the solvent is deionized water), intercalation reaction is carried out at 65°C for 2 hours, centrifuged and dried to obtain caffeic acid-modified nano-montmorillonite as a functional additive; Step 2: Preparation of high-strength polyethylene milk bottle cap: S1: (1) melt-extrude 9 parts of polyolefin elastomer, 1 part of 4-vinylbenzyl alcohol, and 0.3 parts of peroxidation initiator BPO in a twin-screw base, grind the components, and obtain a hydroxylated modified polyolefin elastomer; (2) add the hydroxylated modified polyolefin elastomer and a molybdenum catalyst in a mass ratio of 1:0.04 to DMF in sequence, react at 55°C for 2 hours, wash, and dry to obtain an aldehyde-modified polyolefin elastomer; S2: Weigh 100 parts of high-density polyethylene, 6 parts of functional additives, 3 parts of compatibilizer (maleic anhydride grafted polyethylene and maleic anhydride grafted polyolefin elastomer in a mass ratio of 2:3), 3 parts of aldehyde-modified polyolefin elastomer, 1.5 parts of palm oil, and 1.5 parts of masterbatch as raw materials; S3: Mix high-density polyethylene, functional additives, formaldehyde-modified polyolefin elastomer, compatibilizer, palm oil and masterbatch, and set the process parameters as follows: feed rate of 10r / min, screw speed of 35r / min, temperatures in each temperature zone of 165℃, 170℃, 170℃, 175℃, 185℃, 185℃, 185℃, and 175℃ for melt extrusion; set the process parameters as follows: injection pressure of 80bar, temperatures in each temperature zone of 200℃, 210℃, 215℃, and 220℃ for injection molding to obtain high-strength polyethylene milk bottle caps.

[0030] Comparative Example 4: Based on Example 1, the amount of functional additive introduced was increased, and the rest was the same as Example 1; Step 1: Preparation of functional additives: S1: Add 4 parts of polylysine to 3.2 g / L nano-montmorillonite dispersion (containing 3.2 parts of nano-montmorillonite, the solvent is deionized water), intercalate at 65°C for 2 hours, centrifuge and dry to obtain modified nano-montmorillonite; S2: Under a nitrogen atmosphere, add 0.3 parts of caffeic acid to 30 parts of PBS buffer solution, add 0.3 parts of EDC and 0.18 parts of NHS, and stir for 30 minutes in an ice bath; add modified nano-montmorillonite-PBS buffer solution (1 part of modified nano-montmorillonite, 30 parts of PBS buffer solution), continue stirring for 24 hours, wash and dry to obtain a functional additive; Step 2: Preparation of high-strength polyethylene milk bottle cap: S1: (1) melt-extrude 9 parts of polyolefin elastomer, 1 part of 4-vinylbenzyl alcohol, and 0.3 parts of peroxidation initiator BPO in a twin-screw base, grind the components, and obtain a hydroxylated modified polyolefin elastomer; (2) add the hydroxylated modified polyolefin elastomer and a molybdenum catalyst in a mass ratio of 1:0.04 to DMF in sequence, react at 55°C for 2 hours, wash, and dry to obtain an aldehyde-modified polyolefin elastomer; S2: Weigh 100 parts of high-density polyethylene, 10 parts of functional additives, 3 parts of compatibilizer (maleic anhydride grafted polyethylene and maleic anhydride grafted polyolefin elastomer in a mass ratio of 2:3), 3 parts of formaldehyde-modified polyolefin elastomer, 1.5 parts of palm oil, and 1.5 parts of masterbatch as raw materials; S3: (1) dispersing the functional additive and the aldehyde-modified polyolefin elastomer in 100 parts of ethanol in sequence, stirring and heating at 65° C. for 6 hours, removing the solvent, and drying to obtain a raw material A; (2) Mix raw material A with high-density polyethylene, compatibilizer, palm oil and masterbatch, and set the process parameters as follows: feed rate of 10 r / min, screw speed of 35 r / min, and temperatures in each temperature zone of 165°C, 170°C, 170°C, 175°C, 185°C, 185°C, 185°C, and 175°C for melt extrusion; set the process parameters as follows: injection pressure of 80 bar, and temperatures in each temperature zone of 200°C, 210°C, 215°C, and 220°C for injection molding to obtain high-strength polyethylene milk bottle caps.

[0031] Performance test: The high-strength polyethylene milk bottle caps prepared in the examples and comparative examples were subjected to relevant performance tests. (1) Referring to GB / T10004-2008, the tensile strength was tested at a tensile rate of 200 m / min; (2) Referring to GB / T1038-2000, the oxygen permeability was tested after pre-permeation for 0.5 hours and 3 cycles; (3) Antioxidant (caffeic acid) migration test, the bottle caps were placed in a 95% ethanol solution, treated at 70°C for 2 hours, and the migration amount was tested; the obtained data are shown in the following table:

[0032] Conclusion: From the data in the above table, it can be seen that the present application prepares a polyethylene milk bottle cap with high strength and high barrier properties; by comparing the data of Comparative Examples 1 to Comparative Examples 4 with Example 1, it can be seen that in Comparative Example 1, polyolefin elastomer is used to replace the aldehyde-modified polyolefin elastomer, which reduces the interface effect and compatibility of the functional additives, resulting in a decrease in performance; in Comparative Example 2, due to the use of a single maleic anhydride grafted polyolefin elastomer as a compatibilizer, the mechanical properties are reduced; in Comparative Example 3, since the functional additive is caffeic acid-modified nano-montmorillonite, the interface effect and oxygen barrier properties are reduced; in Comparative Example 4, due to the excessive amount of functional additives introduced, the mechanical properties and barrier properties are reduced.

[0033] Finally, it should be noted that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art can still modify the technical solutions described in the aforementioned embodiments or replace some of the technical features therein by equivalents. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A process for preparing a high-strength polyethylene milk bottle cap, characterized in that: The following steps are involved: Step 1: Preparation of functional additives: S1: adding polylysine to the nano-montmorillonite dispersion, performing intercalation reaction at 60-65°C for 2-3 hours, centrifuging and drying to obtain modified nano-montmorillonite; S2: Under nitrogen atmosphere, caffeic acid was added to PBS buffer solution, EDC and NHS were added, and the mixture was stirred for 15 to 30 minutes in an ice bath; modified nano-montmorillonite-PBS buffer solution was added, and the mixture was stirred for 24 hours, and then washed and dried to obtain a functional additive; Step 2: High-density polyethylene, functional additives, compatibilizers, formaldehyde-modified polyolefin elastomers, palm oil, and masterbatches are mixed, melt-extruded, and injection molded to obtain high-strength polyethylene milk bottle caps.

2. The preparation process of a high-strength polyethylene milk bottle cap according to claim 1, characterized in that: The raw materials of the high-strength polyethylene milk bottle cap include the following components: by weight, 100 parts of high-density polyethylene, 4 to 8 parts of functional additives, 2 to 5 parts of compatibilizers, 1.5 to 3 parts of formaldehyde-modified polyolefin elastomers, 1 to 1.5 parts of palm oil, and 1 to 2 parts of masterbatch.

3. The preparation process of a high-strength polyethylene milk bottle cap according to claim 1, characterized in that: The compatibilizer includes maleic anhydride grafted polyethylene and maleic anhydride grafted polyolefin elastomer in a mass ratio of 2:

3.

4. The process for preparing a high-strength polyethylene milk bottle cap according to claim 1, characterized in that: The modified nano-montmorillonite comprises polylysine and nano-montmorillonite in a mass ratio of 4:3.2-3.5; and the functional additive comprises modified nano-montmorillonite and caffeic acid in a mass ratio of 1:0.2-0.

3.

5. The process for preparing a high-strength polyethylene milk bottle cap according to claim 1, characterized in that: The preparation method of the modified polyolefin elastomer is: S1: melt-extrude a polyolefin elastomer, 4-vinylbenzyl alcohol, and a peroxidation initiator in a twin-screw extruder, grind the components, and obtain a hydroxylated modified polyolefin elastomer; S2: Adding the hydroxylated modified polyolefin elastomer and the molybdenum catalyst into DMF in sequence, reacting at 50-55° C. for 2-3 hours, washing and drying, to obtain the aldehyde-modified polyolefin elastomer.

6. The process for preparing a high-strength polyethylene milk bottle cap according to claim 5, characterized in that: The hydroxylated modified polyolefin elastomer comprises a polyolefin elastomer, 4-vinyl benzyl alcohol, and a peroxidation initiator in a mass ratio of 90:5-10:0.1-0.5; The aldehyde-modified polyolefin elastomer comprises a hydroxylated modified polyolefin elastomer and a molybdenum catalyst in a mass ratio of 1:0.02-0.

05.

7. The process for preparing a high-strength polyethylene milk bottle cap according to claim 1, characterized in that: The functional additive is pre-compounded with the aldehyde-modified polyolefin elastomer; the process of step 2 is as follows: S1: Dispersing the functional additive and the aldehyde-modified polyolefin elastomer in ethanol in sequence, stirring and heating at 60-65° C. for 4-6 hours, removing the solvent, and drying to obtain raw material A; S2: Mix raw material A with high-density polyethylene, compatibilizer, palm oil and masterbatch, melt extrude and injection mold to obtain a high-strength polyethylene milk bottle cap.

8. The process for preparing a high-strength polyethylene milk bottle cap according to claim 1, characterized in that: The process parameters of the melt extrusion are: a feed rate of 10-15 r / min, a screw speed of 30-40 r / min, and temperatures in each temperature zone of 165-170°C, 165-170°C, 165-170°C, 175-180°C, 185-190°C, 185-190°C, 185-190°C, and 175-180°C; the process parameters of the injection molding are: an injection pressure of 80-100 bar, and temperatures in each temperature zone of 200-205°C, 210-215°C, 215-220°C, and 215-220°C.

9. A high-strength polyethylene milk bottle cap prepared according to the preparation process of a high-strength polyethylene milk bottle cap according to any one of claims 1 to 8.

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