Composite polyethylene and its use

Abstract

The application discloses a kind of composite polyethylene and its application, the composite polyethylene includes the following raw materials: high-density polyethylene 30-40 parts, low-density polyethylene 30-40 parts, linear low-density polyethylene 15-25 parts, functional agent 10-16 parts, antioxidant 1-3 parts, plasticizer 1-2 parts, coupling agent 0.5-1.5 parts, by the raw materials of reasonable proportioning and mixing high temperature preparation obtains composite polyethylene.The composite polyethylene provided in the application has excellent barrier property, antibacterial property, extrusion resistance and ultraviolet light aging resistance, and can be widely applied in the preparation of hose packaging material.

Description

Technical Field

[0001] This invention relates to the field of packaging materials technology, and in particular to a composite polyethylene and its applications. Background Technology

[0002] Toothpaste tubes, a type of flexible packaging material developed after 1960, are the fourth generation of products following tin, tin-lead, and tin-aluminum tubes. Toothpaste tubes primarily use polyethylene as the resin, which boasts relatively stable chemical properties, good corrosion resistance, and the dual characteristics of plastic and aluminum tubes. It is widely used in the packaging of daily chemical products such as toothpaste, cosmetics, and pharmaceuticals. With advancements in technology, the demand for daily chemical product packaging is increasing, leading to increasingly stringent requirements for packaging materials. In the toothpaste packaging field, toothpaste tubes are prone to deformation and damage due to repeated compression during use, resulting in leakage of contents or long-term infiltration of water vapor and oxygen in humid environments, affecting the quality of the contents. Furthermore, interpenetration occurs between oxygen molecules in the air outside the tube and molecules of the contents inside. Therefore, toothpaste tubes not only need high barrier properties but also excellent antibacterial, anti-deformation, and UV aging resistance. Thus, there is a strong need for a high-performance composite polyethylene material for the manufacture of toothpaste tubes.

[0003] CN118388865A discloses a high heat-resistant and antibacterial cosmetic packaging tube and its preparation method. The raw materials for preparing the cosmetic packaging tube, by weight, include: 50-55 parts high-density polyethylene, 8-12 parts low-density polyethylene, 15-18 parts metallocene polyethylene, 30-35 parts modified nano-calcium sulfate, 10-15 parts modified nano-calcium carbonate, 3-5 parts antioxidant, 4-6 parts plasticizer, 2-3 parts coupling agent, and 0.5-0.8 parts antibacterial agent, wherein the antibacterial agent is modified silver-zinc doped silica. This invention's high heat-resistant and antibacterial cosmetic packaging tube has good antibacterial properties, heat resistance, and barrier properties; however, its extrusion resistance and UV aging resistance are poor, which is not conducive to extending its service life. Summary of the Invention

[0004] In view of the above-mentioned deficiencies of the prior art, the present invention provides a composite polyethylene with excellent barrier properties, antibacterial properties, tensile strength and UV aging resistance, making it a high-performance polymer material, which is beneficial for the application of composite polyethylene in the preparation of hoses.

[0005] To achieve the above objectives, the present invention provides a composite polyethylene, wherein the raw materials for preparing the composite polyethylene include the following components in parts by weight: 30-40 parts of high-density polyethylene, 30-40 parts of low-density polyethylene, 15-25 parts of linear low-density polyethylene, 10-16 parts of functional agent, 1-3 parts of antioxidant, 1-2 parts of plasticizer, and 0.5-1.5 parts of coupling agent.

[0006] Preferably, the functional agent is selected from composite modified cellulose nanocrystals, or a mixture of composite modified cellulose nanocrystals and chitosan; the composite modified cellulose nanocrystals and chitosan are mixed in a mass ratio of 4-6:1-3.

[0007] More preferably, the chitosan material is selected from one of chitosan, hydroxypropyl chitosan, and carboxymethyl chitosan.

[0008] Preferably, the preparation method of the composite modified cellulose nanocrystals includes the following steps, in parts by weight:

[0009] Mix 2-5 parts of microcrystalline cellulose with 80-120 parts of 0.5-2 mol / L ammonium persulfate aqueous solution, sonicate at 55-65℃ for 3-5 h, then centrifuge and wash with water to obtain a colloidal solution; mix the obtained colloidal solution with 80-120 parts of 0.5-2 mol / L citric acid aqueous solution at 600-800 rpm, then sonicate at 55-65℃ for 1-3 h to obtain a white suspension; centrifuge the obtained white suspension at 8000-10000 rpm for 10-15 min, wash with water 2-3 times, and then use... The suspension was dialyzed through a cellulose dialysis membrane until the solution was neutral to obtain a modified suspension. 40-60 parts of the modified suspension were ultrasonically treated for 1-2 hours, and then 40-60 parts of a 1:1 mixture of water and ethanol containing 2-5 mg / mL of modifier were added. The mixture was stirred and refluxed at 85-90℃ for 22-25 hours to obtain a mixed solution. The mixed solution was centrifuged at 10000-12000 rpm for 20-30 minutes, the precipitate was collected and washed 2-3 times with water and ethanol, then washed 1-2 times with anhydrous acetone, and dried to obtain composite modified cellulose nanocrystals.

[0010] Preferably, the modifier is a mixture of ε-polylysine and cashew phenol in a mass ratio of 1:1.

[0011] This invention involves mixing microcrystalline cellulose with ammonium persulfate solution and introducing carboxyl functional groups onto the surface of cellulose nanocrystals through an oxidation reaction to form oxidized cellulose nanocrystals. The oxidized cellulose nanocrystals are then mixed with citric acid solution and subjected to esterification under acidic conditions to introduce carboxyl groups from the citric acid, forming carboxylated cellulose nanocrystals. An aqueous suspension of the carboxylated cellulose nanocrystals is then reacted with ε-polylysine and cashew nut shell extract. The amine groups of ε-polylysine attack the carbon atoms of the carboxyl groups on the surface of the carboxylated cellulose nanocrystals, forming a tetrahedral intermediate. Hydrolysis removes the hydroxyl groups, forming stable amide bonds, thus grafting ε-polylysine onto the surface of the carboxylated cellulose nanocrystals. Simultaneously, the phenolic hydroxyl groups of cashew nut shell extract can undergo esterification with the carboxyl groups on the carboxylated cellulose nanocrystals, forming ester bonds, and thus grafting onto the surface of the cellulose nanocrystals, or grafting onto the surface of the cellulose nanocrystals through physical adsorption and hydrogen bonding, resulting in composite modified cellulose nanocrystals.

[0012] The inventors have discovered that using composite polyethylene prepared with the addition of composite modified cellulose nanocrystals to prepare composite polyethylene sheets significantly improves the barrier properties, antibacterial properties, tensile strength, and UV aging resistance of the composite polyethylene sheets. The reasons for this are likely as follows: Firstly, regarding barrier properties, the nanoscale effect of the composite modified cellulose nanocrystals forms a dense microstructure within the polyethylene matrix, effectively increasing the path length for water vapor and oxygen to penetrate the material, thereby reducing water vapor and oxygen permeability. This physical barrier effect is the direct cause of the improved barrier properties. Simultaneously, the grafting of ε-polylysine increases the surface polarity of the cellulose nanocrystals, improving their compatibility with polyethylene and resulting in more uniform dispersion of the cellulose nanocrystals within the polyethylene matrix. This further reduces the free volume in the polymer, lowering the permeability of gases and water vapor.

[0013] In terms of antibacterial properties, ε-polylysine and cashew phenol exhibit certain antibacterial and antifungal activities, capable of disrupting bacterial cell walls and inhibiting bacterial growth. When ε-polylysine and cashew phenol are grafted onto the surface of cellulose nanocrystals, this antibacterial property is imparted to the composite polyethylene sheet, giving the sheet a long-lasting antibacterial effect. Furthermore, the composite-modified cellulose nanocrystals may further enhance the antibacterial properties of the sheet by physically interfering with bacterial attachment and reproduction on the sheet surface, reducing biofilm formation.

[0014] The addition of composite modified cellulose nanocrystals significantly improved the tensile strength of composite polyethylene sheets. As a nanoscale reinforcement, the interfacial interaction between the composite modified cellulose nanocrystals and the polyethylene matrix enhanced the material's mechanical properties. Under tensile force, the composite modified cellulose nanocrystals effectively transferred and dispersed stress, reducing stress concentration and thus improving the material's tensile strength. Furthermore, the composite modified cellulose nanocrystals may influence the crystallization behavior of polyethylene, leading to a more uniform crystalline structure, which is also an important factor in improving tensile strength.

[0015] Regarding UV aging resistance, cashew phenol can absorb ultraviolet light. Its grafting onto the surface of composite modified cellulose nanocrystals reduces direct UV exposure to polyethylene, lowers the photodegradation rate, and improves the light stability of the composite polyethylene sheet. Simultaneously, ε-polylysine grafting enhances the chemical stability of the cellulose nanocrystals, making them less prone to decomposition under UV irradiation and preserving the material's properties. Furthermore, the composite modified cellulose nanocrystals may capture free radicals generated in polyethylene under UV irradiation, slowing down the aging process and thus improving the sheet's UV aging resistance.

[0016] Preferably, the antioxidant is selected from at least one of butylated hydroxyanisole, butylated hydroxytoluene, and propyl gallate.

[0017] Preferably, the plasticizer is selected from at least one of diisononyl phthalate, dioctyl adipate, and dioctyl sebacate.

[0018] Preferably, the coupling agent is selected from one of isopropyl tristearate titanate, γ-aminopropyltriethoxysilane, and γ-methacryloyloxypropyltrimethoxysilane.

[0019] The present invention also provides a method for preparing the above-mentioned composite polyethylene, comprising the following steps:

[0020] High-density polyethylene (HDPE), low-density polyethylene (LDPE), and linear low-density polyethylene (LLDPE) are placed in a dryer and dried at 65-85℃ for 1-3 hours. The dried HDPE, LLDPE, and LLDPE are then mixed in a high-speed mixer at 700-900 rpm for 3-8 minutes. Functional agents, antioxidants, plasticizers, and coupling agents are then added and the mixture is continued for 8-15 minutes. The mixture is then placed in a twin-screw extruder and melted at 160-220℃. The melt is then conveyed and fed into a blown film die at a temperature of 180-230℃. After extrusion through the die, the film is blown up, cooled, shaped, trimmed, and wound to obtain a sheet, i.e., composite polyethylene.

[0021] The present invention also provides applications of the above-mentioned composite polyethylene, which can be used to prepare tubes for product packaging of daily chemical products and food; the tubes may be toothpaste tubes.

[0022] High-density polyethylene (HDPE) has high density and crystallinity, resulting in excellent mechanical strength, hardness, chemical resistance, and heat resistance. The high crystallinity of HDPE promotes the formation of a compact structure, reducing the diffusion paths of gas molecules and helping to lower the permeability of water vapor and oxygen. The high strength properties of HDPE contribute to improving the overall tensile strength of composite polyethylene.

[0023] Low-density polyethylene has good flexibility, extensibility, transparency, cold resistance and processability, which can give composite polyethylene good flexibility and processing performance; the addition of linear low-density polyethylene can improve the strength and heat resistance of composite polyethylene, and further enhance its physical properties.

[0024] Propyl gallate is a natural phenolic compound widely found in the fruits and leaves of certain plants. It possesses antioxidant and antibacterial properties, which can enhance the antibacterial properties and UV aging resistance of composite polyethylene. Furthermore, the phenolic hydroxyl groups of propyl gallate can form hydrogen bonds with polyethylene chains, potentially increasing the interactions between polymer chains in composite polyethylene, thereby increasing its density and uniformity and improving its barrier properties.

[0025] As a plasticizer, dioctyl sebacate can significantly improve the flexibility and plasticity of composite polyethylene, making it easier to process and mold.

[0026] γ-aminopropyltriethoxysilane is a coupling agent that can improve the interfacial bonding between the raw material components and the polymer matrix, thereby enhancing the mechanical properties and thermal stability of the composite material. γ-aminopropyltriethoxysilane can also improve the UV aging resistance of composite polyethylene by forming a siloxane network, reducing direct UV damage to polyethylene, and simultaneously increasing its tensile strength, thus contributing to a longer service life for composite polyethylene.

[0027] The beneficial effects of this invention are:

[0028] 1. Compared with existing technologies, by using a specific weight proportion of high-density polyethylene, low-density polyethylene and linear low-density polyethylene as the polyethylene matrix, the mixed use can achieve complementary and balanced performance, improve the overall performance, and then add functional agents, antioxidants, plasticizers and coupling agents to mix with the polyethylene matrix at high temperature to prepare composite polyethylene with excellent barrier properties, extrusion resistance, antibacterial properties and UV aging resistance, thereby ensuring the service life and stability of the hoses made using composite polyethylene.

[0029] 2. Compared with the existing technology, the present invention introduces a composite modified cellulose nanocrystal and carboxymethyl chitosan mixed composition functional agent. During the preparation of composite polyethylene, the two can improve the barrier properties, antibacterial properties, tensile strength and UV aging resistance of composite polyethylene through chemical cross-linking and physical action, making it a high-performance polymer material, which is beneficial to the application of composite polyethylene in the preparation of hoses. Detailed Implementation

[0030] The parameters for using specific chemical substances, and their sources.

[0031] High-density polyethylene, brand: Yanshan Petrochemical, grade: 8100M;

[0032] Linear low-density polyethylene, brand: Priman, grade: SP1520;

[0033] Low-density polyethylene, brand: Lanzhou Petrochemical, grade: 1810D;

[0034] ε-polylysine, molecular weight: 4000;

[0035] Microcrystalline cellulose, particle size: 25μm, brand: Kramar;

[0036] Cellulose nanocrystals, length: 100 nm, diameter: 20 nm;

[0037] Cashew phenol, product number: PCS2356, is sourced from Chengdu Zhibiao Chemical Pure Biotechnology Co., Ltd.

[0038] Example 1

[0039] A composite polyethylene, the preparation method of which includes the following steps:

[0040] 38 parts by weight of high-density polyethylene, 38 parts by weight of low-density polyethylene, and 20 parts by weight of linear low-density polyethylene were put into a dryer and dried at 75°C for 2 hours. The dried high-density polyethylene, low-density polyethylene, and linear low-density polyethylene were mixed in a high-speed mixer at 800 rpm for 5 minutes. Then, 12 parts by weight of functional agent, 2 parts by weight of propyl gallate, 1.5 parts by weight of dioctyl sebacate, and 1 part by weight of γ-aminopropyltriethoxysilane were added and mixed for another 10 minutes. The mixture was then placed in a twin-screw extruder and melted at 190°C. The melt was then conveyed and flowed to a blown film die at a temperature of 220°C. After extrusion through the die, the film was blown up, cooled and shaped, trimmed, and wound to obtain a sheet, i.e., composite polyethylene.

[0041] The functional agent is a composite modified cellulose nanocrystal, and its preparation method includes the following steps:

[0042] Three parts by weight of microcrystalline cellulose and 100 parts by weight of a 1 mol / L ammonium persulfate aqueous solution were mixed and sonicated at 62°C (ultrasonic frequency 20 kHz, ultrasonic power 50 W) for 4.5 h. The mixture was then centrifuged and washed with water to obtain a colloidal solution. This colloidal solution was mixed with 100 parts by weight of a 1 mol / L citric acid aqueous solution at 700 rpm and stirred. The mixture was then sonicated at 62°C for 2.5 h to obtain a white suspension. This white suspension was centrifuged at 9000 rpm for 13 min and washed three times with water. The solution was then dialyzed using a regenerated cellulose dialysis membrane (14 kDa). The suspension was dialyzed until the solution was neutral to obtain a modified suspension. 50 parts by weight of the modified suspension were sonicated (ultrasonic frequency 20 kHz, ultrasonic power 50 W) for 1.5 h. Then, 50 parts by weight of a mixed solution of water and ethanol containing 2 mg / mL ε-polylysine and 2 mg / mL cashew phenol at a volume ratio of 1:1 were added. The mixture was stirred and refluxed at 88 °C for 24 h to obtain a mixed solution. The mixed solution was centrifuged at 11000 rpm for 25 min, the precipitate was collected and washed three times with water and ethanol, then washed twice with anhydrous acetone, and dried to obtain composite modified cellulose nanocrystals.

[0043] Example 2

[0044] A composite polyethylene differs from Example 1 in that the functional agent is a mixture of composite modified cellulose nanocrystals and chitosan in a mass ratio of 5:2.

[0045] The preparation method of the composite modified cellulose nanocrystals is the same as that in Example 1.

[0046] Example 3

[0047] A composite polyethylene differs from Example 1 in that the functional agent is a mixture of composite modified cellulose nanocrystals and hydroxypropyl chitosan in a mass ratio of 5:2.

[0048] The preparation method of the composite modified cellulose nanocrystals is the same as that in Example 1.

[0049] Example 4

[0050] A composite polyethylene differs from Example 1 in that the functional agent is a mixture of composite modified cellulose nanocrystals and carboxymethyl chitosan in a mass ratio of 5:2.

[0051] The preparation method of the composite modified cellulose nanocrystals is the same as that in Example 1.

[0052] Comparative Example 1

[0053] A composite polyethylene, differing from Example 1 in that the preparation method of the composite modified cellulose nanocrystals includes the following steps:

[0054] Three parts by weight of microcrystalline cellulose and 100 parts by weight of a 1 mol / L ammonium persulfate aqueous solution were mixed and sonicated at 62°C (ultrasonic frequency 20 kHz, ultrasonic power 50 W) for 4.5 h. The mixture was then centrifuged and washed with water to obtain a colloidal solution. The obtained colloidal solution was mixed with 100 parts by weight of a 1 mol / L citric acid aqueous solution at 700 rpm and stirred. The mixture was then sonicated at 62°C (ultrasonic frequency 20 kHz, ultrasonic power 50 W) for 2.5 h to obtain a white suspension. The obtained white suspension was centrifuged at 9000 rpm for 13 min and washed three times with water. Then, it was reused... The suspension was dialyzed through a 14 kDa cellulose dialysis membrane until the solution was neutral to obtain a modified suspension. 50 parts by weight of the modified suspension were ultrasonically treated (ultrasonic frequency 20 kHz, ultrasonic power 50 W) for 1.5 h. Then, 50 parts by weight of a 1:1 mixture of water and ethanol containing 4 mg / mL ε-polylysine were added, and the mixture was stirred and refluxed at 88 °C for 24 h to obtain a mixed solution. The mixed solution was centrifuged at 11000 rpm for 25 min, the precipitate was collected, and washed three times with water and ethanol, then twice with anhydrous acetone, and dried to obtain composite modified cellulose nanocrystals.

[0055] Comparative Example 2

[0056] A composite polyethylene, differing from Example 1 in that the preparation method of the composite modified cellulose nanocrystals includes the following steps:

[0057] Three parts by weight of microcrystalline cellulose and 100 parts by weight of a 1 mol / L ammonium persulfate aqueous solution were mixed and sonicated at 62°C (ultrasonic frequency 20 kHz, ultrasonic power 50 W) for 4.5 h. The mixture was then centrifuged and washed with water to obtain a colloidal solution. The obtained colloidal solution was mixed with 100 parts by weight of a 1 mol / L citric acid aqueous solution at 700 rpm and stirred. The mixture was then sonicated at 62°C (ultrasonic frequency 20 kHz, ultrasonic power 50 W) for 2.5 h to obtain a white suspension. The obtained white suspension was centrifuged at 9000 rpm for 13 min and washed three times with water. The suspension was dialyzed using a regenerated cellulose dialysis membrane (14 kDa) until the solution was neutral to obtain a modified suspension. 50 parts by weight of the modified suspension were ultrasonically treated (ultrasonic frequency 20 kHz, ultrasonic power 50 W) for 1.5 h. Then, 50 parts by weight of a 1:1 mixture of water and ethanol containing 4 mg / mL cashew phenol were added. The mixture was stirred and refluxed at 88 °C for 24 h to obtain a mixed solution. The mixed solution was centrifuged at 11,000 rpm for 25 min, the precipitate was collected, and washed three times with water and ethanol, then washed twice with anhydrous acetone, and dried to obtain composite modified cellulose nanocrystals.

[0058] Comparative Example 3

[0059] A composite polyethylene differs from Example 1 in that the functional agent is a mixture of cellulose nanocrystals and carboxymethyl chitosan in a mass ratio of 5:2.

[0060] Comparative Example 4

[0061] A composite polyethylene, which differs from Example 1 in that the functional agent is carboxymethyl chitosan.

[0062] Comparative Example 5

[0063] A composite polyethylene, which differs from Example 1 in that the functional agent is cellulose nanocrystals.

[0064] Test Example 1

[0065] Performance testing

[0066] Composite polyethylene prepared in Examples 1-4 and Comparative Examples 1-5 of this invention were taken as test plastic sheet samples for later use; then, samples were taken according to the following test standards, and performance tests were performed:

[0067] Barrier performance: The oxygen transmission rate (cm²) of the plastic film was tested according to the standard GB / T1038.2-2022 "Test Method for Gas Permeability of Plastic Films and Sheets - Part 2: Isobaric Method". 3 / m 2 ·24h·0.1Mpa);

[0068] Water vapor transmission rate: The water vapor transmission rate of the plastic film was tested according to the standard GB / T1037-2021 "Determination of Water Vapor Transmission Performance of Plastic Films and Sheets - Cup Method for Weight Gain and Loss" (g / (m²)). 2 ·24h));

[0069] Antibacterial rate: The antibacterial rate (%) of the plastic film was tested according to the standard GB / T31402-2015 "Test Method for Antibacterial Properties of Plastic Surfaces". The test bacteria were: Escherichia coli (ATCC8739) and Staphylococcus aureus (ATCC6538P).

[0070] Tensile strength: The tensile strength (MPa) of the plastic film was tested in accordance with the standard GB / T1040.1-2018 Determination of tensile properties of plastics Part 1: General Rules;

[0071] Light aging resistance: The plastic film samples of each embodiment and comparative example were placed under an irradiance of 1W / m². 2 The plastic film samples were subjected to photoaging tests by irradiating them with ultraviolet light for 500 hours. After the test, the tensile strength of the plastic film samples was tested again.

[0072] The test results are shown in Table 1.

[0073] Table 1

[0074]

[0075] Table 1 shows that, comparing Examples 1-4 and Comparative Examples 1-5, the oxygen permeability, water vapor permeability, and tensile strength after aging of Examples 1-4 decreased less than those of Comparative Examples 1-5, while the antibacterial rate against Escherichia coli and Staphylococcus aureus and the tensile strength of Examples 1-4 were higher than those of Comparative Examples 1-5. Comparing Examples 1-4, the oxygen permeability, water vapor permeability, and tensile strength after aging of Examples 2-4 decreased less than those of Example 1, while the antibacterial rate against Escherichia coli and Staphylococcus aureus and the tensile strength of Examples 2-4 were higher than those of Example 1, with Example 4 showing the best performance. This indicates that the simultaneous addition of composite modified cellulose nanocrystals and chitosan is beneficial for improving the barrier properties, antibacterial properties, tensile strength, and UV aging resistance of composite polyethylene. Furthermore, the composite modified cellulose nanocrystals obtained by introducing cashew phenol and / or ε-polylysine modification have a significant impact on the barrier properties, antibacterial properties, tensile strength, and UV aging resistance of composite polyethylene. The reason for this may be that during the preparation of composite polyethylene, chitosan, as a natural polysaccharide, possesses excellent film-forming properties and water vapor barrier properties. Its synergistic effect with composite modified cellulose nanocrystals enhances the barrier effect of the sheet. Simultaneously, the introduction of cashew phenol into the composite modified cellulose nanocrystals improves the sheet's antioxidant capacity and further reduces the gas diffusion rate through interaction with the polymer chains. Furthermore, chitosan can undergo esterification with the phenolic hydroxyl groups of cashew phenol on the composite modified cellulose nanocrystals, forming hydrogen bonds with its grafted ε-polylysine to create a cross-linked structure, further enhancing the sheet's barrier properties.

[0076] The enhanced antibacterial properties may be attributed to the positive charge of ε-polylysine grafted onto the composite modified cellulose nanocrystals, which interacts with the negative charge of the bacterial cell membrane, disrupting its integrity and leading to bacterial death. This enhances the antibacterial performance of the composite polyethylene. Chitosan, with its broad-spectrum antibacterial properties, effectively inhibits the growth of various microorganisms. When the composite modified cellulose nanocrystals and chitosan are combined, their antibacterial effects complement each other. Furthermore, the antibacterial properties of cashew phenol grafted onto the composite modified cellulose nanocrystals synergistically enhance the effects of ε-polylysine and chitosan, forming an effective antibacterial barrier on the sheet surface and inhibiting the growth of bacteria and fungi. Simultaneously, chitosan can form hydrogen bonds with the composite modified cellulose nanocrystals, strengthening intermolecular interactions and providing an even stronger antibacterial effect.

[0077] The improvement in tensile strength is likely due to the introduction of cashew phenol into the composite modified cellulose nanocrystals in the composite polyethylene sheet, which improves the sheet's toughness, resulting in better ductility and tear resistance under external forces. During the preparation of the composite polyethylene, chitosan can cross-link with cashew phenol and ε-polylysine in the composite modified cellulose nanocrystals, forming additional cross-linking points. This makes the polymer chains more tightly connected, reducing stress concentration during tensile testing. Furthermore, the composite modified cellulose nanocrystals and chitosan may enhance the interaction between polymer chains through esterification and hydrogen bonding, thereby increasing the tensile strength of the sheet.

[0078] The improved UV aging resistance is likely due to the introduction of cashew nutshell protein (CFPP) into the composite modified cellulose nanocrystals, which provides photostability to the composite polyethylene sheet. CFPP effectively absorbs UV rays and reduces direct exposure to polyethylene, thus slowing down the photoaging process. The antioxidant properties of CFPP neutralize UV-induced free radicals, reducing polymer oxidative degradation. Simultaneously, the addition of composite modified cellulose nanocrystals and chitosan enhances the sheet's chemical stability, allowing it to maintain its properties under UV irradiation and extending its service life.

[0079] Comparing Examples 2-4, it can be found that Example 4, which simultaneously adds composite modified cellulose nanocrystals and carboxymethyl chitosan, exhibits superior barrier properties, antibacterial properties, tensile strength, and UV aging resistance compared to Examples 2 and 3, which simultaneously add composite modified cellulose nanocrystals and chitosan. This may be because carboxymethyl chitosan possesses more carboxyl functional groups, which can form more hydrogen or ionic bonds with the polyethylene matrix, improving the interaction between polymer chains, enhancing the cohesiveness and mechanical properties of the sheet, thereby reducing water vapor and oxygen permeability and increasing tensile strength. The carboxyl groups of carboxymethyl chitosan may increase the negative charge density of the sheet, enhancing the interaction with the positively charged ε-polylysine in the composite modified cellulose nanocrystals, improving dispersibility and compatibility, and facilitating the formation of a more stable network structure in the sheet, thus improving antibacterial properties and UV aging resistance.

[0080] In summary, the synergistic use of composite modified cellulose nanocrystals and carboxymethyl chitosan can enhance the barrier properties, antibacterial properties, tensile strength, and UV aging resistance of composite polyethylene through chemical cross-linking and physical interactions, making it a high-performance polymer material.

Claims

1. A composite polyethylene, characterized in that, The raw materials for preparing the composite polyethylene include the following components in parts by weight: 30-40 parts of high-density polyethylene, 30-40 parts of low-density polyethylene, 15-25 parts of linear low-density polyethylene, 10-16 parts of functional agent, 1-3 parts of antioxidant, 1-2 parts of plasticizer, and 0.5-1.5 parts of coupling agent. The functional agent is selected from composite modified cellulose nanocrystals, and a mixture of composite modified cellulose nanocrystals and chitosan; the composite modified cellulose nanocrystals and chitosan are mixed in a mass ratio of 4-6:1-3. The preparation method of the composite modified cellulose nanocrystals includes the following steps, in parts by weight: Mix 2-5 parts of microcrystalline cellulose with 80-120 parts of 0.5-2 mol / L ammonium persulfate aqueous solution, sonicate at 55-65℃ for 3-5 h, then centrifuge and wash with water to obtain a colloidal solution; mix the obtained colloidal solution with 80-120 parts of 0.5-2 mol / L citric acid aqueous solution at 600-800 rpm, then sonicate at 55-65℃ for 1-3 h to obtain a white suspension; centrifuge the obtained white suspension at 8000-10000 rpm for 10-15 min, wash with water 2-3 times, then dialyze the suspension using a regenerated cellulose dialysis membrane until the solution is neutral to obtain a modified suspension; 40-60 parts of the modified suspension were ultrasonically treated for 1-2 hours, and then 40-60 parts of a mixed solution of water and ethanol containing 2-5 mg / mL of modifier at a volume ratio of 1:1 were added. The mixture was stirred and refluxed at 85-90℃ for 22-25 hours to obtain a mixed solution. The mixed solution was centrifuged at 10000-12000 rpm for 20-30 minutes, the precipitate was collected and washed 2-3 times with water and ethanol, then washed 1-2 times with anhydrous acetone, and dried to obtain composite modified cellulose nanocrystals. The modifier is a mixture of ε-polylysine and cashew phenol in a mass ratio of 1:

1.

2. The composite polyethylene as described in claim 1, characterized in that: The chitosan material is selected from one of chitosan, hydroxypropyl chitosan, and carboxymethyl chitosan.

3. The composite polyethylene as described in claim 1, characterized in that: The antioxidant is selected from at least one of butylated hydroxyanisole, butylated hydroxytoluene, and propyl gallate.

4. The composite polyethylene as described in claim 1, characterized in that: The plasticizer is selected from at least one of diisononyl phthalate, dioctyl adipate, and dioctyl sebacate.

5. The composite polyethylene as described in claim 1, characterized in that: The coupling agent is selected from one of isopropyl tristearate titanate, γ-aminopropyltriethoxysilane, and γ-methacryloyloxypropyltrimethoxysilane.

6. The method for preparing composite polyethylene according to any one of claims 1-5, characterized in that, The steps are as follows: High-density polyethylene (HDPE), low-density polyethylene (LDPE), and linear low-density polyethylene (LLDPE) are placed in a dryer and dried at 65-85℃ for 1-3 hours. The dried HDPE, LLDPE, and LLDPE are then mixed in a high-speed mixer at 700-900 rpm for 3-8 minutes. Functional agents, antioxidants, plasticizers, and coupling agents are then added and the mixture is continued for 8-15 minutes. The mixture is then placed in a twin-screw extruder and melted at 160-220℃. The melt is then conveyed and fed into a blown film die at a temperature of 180-230℃. After extrusion through the die, the film is blown up, cooled, shaped, trimmed, and wound to obtain a sheet, i.e., composite polyethylene.

7. The application of the composite polyethylene as described in any one of claims 1-5, characterized in that: The composite polyethylene is used to manufacture flexible tubes for product packaging of daily chemical products and food.

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