Polyethylene stretching wrapping film and preparation method thereof

Abstract

The invention discloses a polyethylene stretching and wrapping film and a preparation method thereof. The polyethylene stretching and wrapping film comprises an upper film layer, a middle film layer and a lower film layer, the upper film layer and the lower film layer are prepared from the following components in parts by weight: 20-40 parts of high-density polyethylene, 25-45 parts of low-density polyethylene, 20-40 parts of linear low-density polyethylene, 5-15 parts of polyethylene glycol 4000, 3-8 parts of nano cellulose and 1-4 parts of an anti-aging agent; the middle film layer is prepared from the following components in parts by weight: 40 to 60 parts of linear low density polyethylene, 5 to 10 parts of ethylene-vinyl acetate copolymer, 0.2 to 0.8 part of LLDPE grafted maleic anhydride, 1 to 3 parts of plasticizer, 1 to 2 parts of coupling agent, 0.5 to 2 parts of antioxidant and 1 to 5 parts of functional agent. The polyethylene stretching and wrapping film provided by the invention has relatively good tensile property, barrier property and long-term antibacterial property.

Description

Technical Field

[0001] The present invention relates to the technical field of stretch films, and in particular to a polyethylene stretch stretch film and a preparation method thereof. Background Art

[0002] Stretch film, also known as "stretch film", is a new type of self-adhesive wrapping packaging material. It is widely used in combined wrapping packaging of industrial products due to its excellent properties such as high tensile strength, large elongation, good self-adhesion, high transparency, strong protection and good cleanliness.

[0003] Stretch film is primarily made of PVC, EVA, and PE. Polyethylene (PE) stretch film is widely used in stretch film production due to its high production efficiency, environmental adaptability, high quality, low price, and non-toxicity and odorlessness. Polyethylene stretch film is widely used in packaging various goods and logistics packaging due to its excellent flexibility and oil and moisture resistance. However, due to the relatively simple composition of conventional polyethylene stretch film, its tensile properties are insufficient. This results in insufficient tension when wrapping goods, causing them to loosen during transportation and failing to effectively secure them. Furthermore, it is easily punctured or torn when wrapping large and heavy items, as well as sharp objects, resulting in packaging failure and unsuitable for large-scale applications. The specific mechanical strength of polyethylene stretch film varies depending on the raw material formula and production process. Multi-layer co-extrusion, combined with a certain proportion of functional additives and other auxiliary materials, is an effective way to improve the film's tensile properties.

[0004] CN119749019A discloses a stretch film and its preparation method. The stretch film comprises an upper film and a lower film. The upper film comprises 28-35 parts MLLDPE and 3-6 parts LMDPE; the lower film comprises 30-40 parts LLDPE, 5-8 parts MDPE, and 55-70 parts functional masterbatch. The functional masterbatch comprises metallocene polyethylene, an elastomer, sodium polyacrylate-modified talc, and a maleic anhydride-grafted elastomer. This invention utilizes specific raw materials and a specific ratio to produce the stretch film, improving its stretchability, processing performance, mechanical properties, and thermal stability. However, the barrier properties of the stretch film provided by this invention are poor, resulting in reduced quality of the packaged contents or a shortened shelf life.

[0005] CN112848585A discloses a PE stretch film and its preparation process. The invention provides a PE stretch film co-extruded from three layers: an outer layer, a middle layer, and an inner layer. The outer layer comprises the following components by weight: 60-80 parts linear low-density polyethylene, 3-8 parts linear medium-density polyethylene, and 6-12 parts metallocene; the middle layer comprises the following components by weight: 55-70 parts linear low-density polyethylene, 2-6 parts linear medium-density polyethylene, and 5-10 parts metallocene; and the inner layer comprises the following components by weight: 50-70 parts linear low-density polyethylene, 2-8 parts metallocene, and 1-5 parts tackifier. The PE stretch film provided by this invention exhibits high uniformity, smoothness, and transparency, as well as excellent puncture and tear resistance. However, the PE stretch film has poor antibacterial properties, making the packaging susceptible to bacterial damage and failing to effectively guarantee the quality of the goods. Summary of the Invention

[0006] In view of the above-mentioned defects of the prior art, the present invention provides a polyethylene stretch wrap film and a preparation method thereof. The polyethylene stretch wrap film prepared by the method provided by the present invention not only has good tensile properties, but also the barrier properties and long-term antibacterial properties of the wrap film are greatly improved, thereby expanding the application range of the polyethylene stretch wrap film.

[0007] To achieve the above-mentioned object, the present invention provides a polyethylene stretch wrap film, comprising an upper film layer, a middle film layer and a lower film layer; the middle film layer is arranged between the upper film layer and the lower film layer and is fixedly connected to the upper film layer and the lower film layer respectively;

[0008] The upper and lower film layer materials include the following components in parts by weight: 20-40 parts of high-density polyethylene, 25-45 parts of low-density polyethylene, 20-40 parts of linear low-density polyethylene, 5-15 parts of polyethylene glycol 4000, 3-8 parts of nanocellulose, and 1-4 parts of antioxidant;

[0009] The middle film layer comprises the following components in parts by weight: 40-60 parts of linear low-density polyethylene, 5-10 parts of ethylene-vinyl acetate copolymer, 0.2-0.8 parts of LLDPE grafted maleic anhydride, 1-3 parts of a plasticizer, 1-2 parts of a coupling agent, 0.5-2 parts of an antioxidant, and 1-5 parts of a functional agent; the functional agent is prepared by using methacrylate linseed gum as a carrier to load a plant extract; or, by using methacrylate linseed gum modified with a polythiol compound as a carrier to load a plant extract;

[0010] Preferably, the mass ratio of the upper film layer material, the middle film layer material and the lower film layer material is 1:(1-3):(1-2);

[0011] Preferably, the polyethylene stretch wrap film has a thickness of 20-30 μm.

[0012] Preferably, the antioxidant is selected from one of antioxidant 2246, antioxidant A and antioxidant NDBC.

[0013] Preferably, the plasticizer is selected from at least one of diisononyl phthalate, dioctyl adipate, and dioctyl sebacate.

[0014] Preferably, the coupling agent is selected from one of isopropyl tristearate titanate, γ-aminopropyl triethoxysilane, and γ-methacryloxypropyl trimethoxysilane.

[0015] Preferably, the antioxidant is selected from one of antioxidant 1010, antioxidant 1076, and antioxidant CA.

[0016] Preferably, the preparation method of the functional agent comprises the following steps, calculated by weight:

[0017] S1. Add 1-3 parts of flaxseed gum to 100-300 parts of water, heat to 45-55° C. and stir until completely dissolved, then add 1-3 parts of methacrylic anhydride dropwise while continuously stirring, and react at 45-55° C. for 2-4 hours; filter the reaction solution through a microfiltration membrane, and then ultrafilter using a tangential flow ultrafiltration system. The retentate is concentrated by rotary evaporation and vacuum dried to obtain modified flaxseed gum;

[0018] S2. Add 0.5-1.5 parts of modified flaxseed gum to 80-120 parts of water, heat to 45-55° C. and stir until completely dissolved, then add 0.1-0.3 parts of plant extract, and ultrasonically treat at an ultrasonic power of 200-600 W and 45-55° C. for 10-30 minutes to obtain a mixture; then vacuum-dry the mixture, grind it into powder, and pass it through an 80-100 mesh sieve to obtain modified flaxseed gum loaded with plant extract, i.e., a functional agent.

[0019] Preferably, the step S2 may also be, by weight:

[0020] 0.5-1.5 parts of modified linseed gum are added to 50-150 parts of water, heated to 45-55°C and stirred until completely dissolved, then 0.5-1 parts of polythiol compound are added dropwise under stirring, mixed and stirred for 20-30 minutes, and then 0.001-0.002 parts of Eosin Y photoinitiator are added and stirred evenly to obtain a mixed solution 1; the mixed solution 1 is exposed to an intensity of 10-20 mW / cm 2The composite modified linseed gum is irradiated under visible light until gelation occurs, and then soaked in water for 2-3 times, each time for 1-3 hours, and then dried to obtain a composite modified linseed gum; 0.5-1.5 parts of the composite modified linseed gum and 0.1-0.3 parts of the plant extract are added to 80-120 parts of water, mixed, and ultrasonically treated at an ultrasonic power of 200-600 W and 45-55° C. for 10-30 minutes to obtain a mixture; the mixture is then vacuum-dried, and then ground into powder and passed through an 80-100 mesh sieve to obtain a composite modified linseed gum loaded with the plant extract, i.e., a functional agent.

[0021] More preferably, the plant extract is selected from one of ginkgo extract and neem extract.

[0022] More preferably, the polythiol compound is selected from one of 3,6-dioxo-1,8-octanedithiol and trimethylolpropane tris(3-mercaptopropionate).

[0023] Further explaining the present invention, during the preparation process of the functional agent, the carboxylic acid anhydride groups in methacrylic anhydride react with the hydroxyl groups in the flaxseed gum structure to form ester bonds, thereby preparing methacrylate flaxseed gum, i.e., modified flaxseed gum. Plant extracts are then introduced and mixed with the methacrylate flaxseed gum and ultrasonically treated. During the reaction, the plant extracts are effectively promoted to be uniformly loaded onto the mesoporous methacrylate flaxseed gum, thereby obtaining modified flaxseed gum loaded with plant extracts. The present invention finds that the modified flaxseed gum has good thermal stability, and loading the plant extracts onto the modified flaxseed gum can better protect the activity of the active ingredients of the plant extracts, so that the prepared polyethylene stretch wrap film has good tensile properties, barrier properties, and antibacterial properties.

[0024] To further explore the effect of the functional agent prepared by the present invention on polyethylene stretch wrap film, based on the above, the present invention further modifies methacrylate linseed gum to prepare a composite modified linseed gum. During the reaction, EosinY absorbs visible light to generate free radicals. The free radicals trigger the thiol group in the structure of the polythiol compound 3,6-dioxo-1,8-octanedithiol or trimethylolpropane tris(3-mercaptopropionate) to attack the allylic double bond of the methacrylate linseed gum, forming a thioether bond, thereby further modifying the methacrylate linseed gum to obtain a composite modified linseed gum. Then, a plant extract is introduced into the composite modified linseed gum, mixed, and ultrasonically reacted. The plant extract is effectively promoted to be uniformly loaded onto the composite modified linseed gum with mesopores, thereby obtaining a composite modified linseed gum loaded with plant extracts. The inventors found that compared with the modified linseed gum loaded with plant extracts, the composite modified linseed gum loaded with plant extracts has a better improvement effect on the tensile properties, barrier properties and antibacterial properties of polyethylene stretch wrap film.

[0025] The application also provides a preparation method of the polyethylene stretch wrapping film, comprising the following steps:

[0026] (1) adding each component in the upper film layer material, the middle layer material and the lower film layer material into three stirring containers respectively according to the corresponding ratio and stirring and mixing uniformly;

[0027] (2) high-temperature extruding the mixture obtained in the three stirring containers in step S1 through a screw extruder to obtain upper layer, middle layer and lower layer plastic particles;

[0028] (3) adding the upper layer, middle layer and lower layer plastic particles obtained in step S2 into the corresponding cavities of a casting machine respectively, and forming films through casting, wherein the casting temperature is 220-250℃, the temperature of the casting cooling roller is 30-40℃, and then the polyethylene stretch wrapping film is obtained through winding and packaging, and the winding tension is not more than 15 Kg.

[0029] The application has the following beneficial effects:

[0030] 1. Compared with the prior art, the application adopts a multi-layer co-extrusion production process, uses high-density polyethylene, low-density polyethylene and linear low-density polyethylene as main raw materials, and simultaneously uses polyethylene glycol 4000, nanocellulose, an antioxidant, an ethylene-vinyl acetate copolymer, LLDPE grafted maleic anhydride, a plasticizer, a silane coupling agent and a functional agent in a certain proportion to prepare the polyethylene stretch wrapping film, which not only effectively improves the tensile properties of the polyethylene stretch wrapping film, but also improves the barrier properties and long-term antibacterial properties of the wrapping film, and expands the application range of the polyethylene stretch wrapping film.

[0031] 2. Compared with the prior art, the application selects methacrylate flaxseed gum as a carrier to load plant extracts to prepare modified flaxseed gum loaded with plant extracts or uses 3,6-diox-1,8-octanedithiol or trimethylolpropane tris(3-mercaptopropionate) to modify the methacrylate flaxseed gum as a carrier to load plant extracts to prepare a composite modified flaxseed gum of plant extracts as a functional agent, and introduces the functional agent into the preparation process of the polyethylene stretch wrapping film, so that the prepared polyethylene stretch wrapping film has good tensile properties and barrier properties. In addition, the modified methacrylate flaxseed gum as a carrier to load plant extracts can effectively protect the heat-sensitive components in the plant extracts from decomposition under high temperature in the preparation process of the polyethylene stretch wrapping film, so as to reduce the activity of the effective components in the plant extracts, so that the prepared polyethylene stretch wrapping film has good antibacterial properties and can exert the antibacterial effect for a long time. DETAILED DESCRIPTION

[0032] Parameters for specific chemical substances used, sources.

[0033] High-density polyethylene, brand, Yanshan Petrochemical, grade: 1620J;

[0034] Linear low-density polyethylene, brand: Priman, grade: SP1520;

[0035] Low-density polyethylene, brand: CNOOC Shell, grade: 2420M;

[0036] Polyethylene glycol 4000, molecular weight: 4000;

[0037] Nanocellulose, diameter: 60 nm, length: 20 μm, product number: TL-020, from Nanjing Tianlu Nanotechnology Co., Ltd.;

[0038] Ethylene-vinyl acetate copolymer, brand: Taiwan Yaju, grade: EV302;

[0039] LLDPE grafted with maleic anhydride, brand: Coase, model: W1L;

[0040] Preparation of flaxseed gum: Weigh 10 g of flax seeds (commercially available), add them to 40 mL of water, heat and stir until the solution becomes a viscous hot solution; after the hot solution is allowed to stand and separate, pour out the supernatant, filter and dry to obtain flaxseed gum.

[0041] Preparation of Ginkgo Extract: Fresh Ginkgo Leaves (commercially available) were washed, dried, crushed, and passed through a 60-mesh sieve for later use; the Ginkgo Leaves were mixed with water at a solid-liquid ratio of 1:15 and then extracted with water using a two-extraction method. The first extraction was performed at 85°C for 2 hours. After filtering, the leaf residue was added with an equal amount of water and extracted at 80°C for 1 hour. The two filtrates were combined; the filtrate was centrifuged at 8000 rpm for 10 minutes, and the clarified filtrate was collected. The filtrate was then placed on a rotary evaporator (45°C, vacuum degree 0.08 MPa) and concentrated under reduced pressure to 1 / 5 of the original volume, and then placed at 45°C for vacuum drying for 24 hours to obtain the Ginkgo Extract.

[0042] Preparation of neem extract: Fresh neem leaves (commercially available) were washed, dried, crushed, and passed through an 80-mesh sieve for later use; neem leaves were mixed with water at a solid-liquid ratio of 1:15 and then extracted. Ultrasonic extraction was performed at an ultrasonic power of 50 kHz and a temperature of 50°C for 40 minutes; the filtrate was then filtered through a 0.22 μm microporous membrane, and the filtrate was concentrated under reduced pressure (40°C, vacuum degree 0.08 MPa) to 1 / 4 of the original volume, and then vacuum dried at 65°C for 24 hours to obtain the neem extract.

[0043] Example 1

[0044] A polyethylene stretch wrap film is composed of an upper film layer, a middle film layer, and a lower film layer in a mass ratio of 1:2.5:1.5; the middle film layer is arranged between the upper film layer and the lower film layer and is fixedly connected to the upper film layer and the lower film layer respectively; the thickness of the polyethylene stretch wrap film is 25 μm.

[0045] The upper film layer material is composed of the following components: 33 parts by weight of high-density polyethylene, 36 parts by weight of low-density polyethylene, 30 parts by weight of linear low-density polyethylene, 8 parts by weight of polyethylene glycol 4000, 5 parts by weight of nanocellulose, and 3 parts by weight of antioxidant 2246;

[0046] The middle film layer material is composed of the following components: 45 parts by weight of linear low-density polyethylene, 10 parts by weight of ethylene-vinyl acetate copolymer, 0.5 parts by weight of LLDPE grafted maleic anhydride, 2 parts by weight of diisononyl phthalate, 1.5 parts by weight of γ-aminopropyltriethoxysilane, 1 part by weight of antioxidant 1076, and 3 parts by weight of functional agent;

[0047] The lower film layer material is composed of the following components: 35 parts by weight of high-density polyethylene, 32 parts by weight of low-density polyethylene, 28 parts by weight of linear low-density polyethylene, 15 parts by weight of polyethylene glycol 4000, 5 parts by weight of nanocellulose, and 3 parts by weight of antioxidant 2246;

[0048] The preparation method of the functional agent comprises the following steps:

[0049] S1. Add 2 g of flaxseed gum to 200 mL of water, heat to 50° C. and stir until completely dissolved, then add 2 g of methacrylic anhydride dropwise while continuously stirring, and react at 50° C. for 3 h; filter the reaction solution through a 0.45 μm microfiltration membrane, and then ultrafilter using a tangential flow ultrafiltration system (installed with an ultrafiltration membrane with a molecular weight cutoff of 10 kDa); concentrate the retentate by rotary evaporation, and dry in vacuo to obtain modified flaxseed gum;

[0050] S2. Add 1 g of modified flaxseed gum to 100 mL of water, heat to 50° C. and stir until completely dissolved, then add 0.2 g of ginkgo extract, and ultrasonically treat at an ultrasonic power of 400 W and 50° C. for 20 min to obtain a mixture; then place the mixture at 45° C. and vacuum dry for 24 h, then grind it into powder and pass it through an 80-mesh sieve to obtain modified flaxseed gum loaded with ginkgo extract, i.e., a functional agent.

[0051] The method for preparing the polyethylene stretch wrap film comprises the following steps:

[0052] (1) Add the components of the upper film layer material, the middle film layer material and the lower film layer material into three stirring containers according to the corresponding proportions and stir to mix evenly;

[0053] (2) Extruding the mixtures obtained in the three stirring containers in step S1 at high temperature through screw extruders to obtain upper, middle and lower plastic particles;

[0054] (3) The upper layer, middle layer and lower layer plastic particles obtained in step S2 are respectively added into the corresponding chambers of the casting machine, and cast into films, wherein the casting temperature is 250°C, the temperature of the casting cooling roller is 35°C, and then the polyethylene stretch wrap film is obtained by winding and packaging, and the winding tension is not more than 15 kg.

[0055] Example 2

[0056] A polyethylene stretch wrap film, which differs from Example 1 only in that the preparation method of the functional agent comprises the following steps:

[0057] S1. Add 2 g of flaxseed gum to 200 mL of water, heat to 50° C. and stir until completely dissolved, then add 2 g of methacrylic anhydride dropwise while continuously stirring, and react at 50° C. for 3 h; filter the reaction solution through a 0.45 μm microfiltration membrane, and then ultrafilter using a tangential flow ultrafiltration system (installed with an ultrafiltration membrane with a molecular weight cutoff of 10 kDa); concentrate the retentate by rotary evaporation, and dry in vacuo to obtain modified flaxseed gum;

[0058] S2. Add 1 g of modified linseed gum to 100 mL of water, heat to 50° C. and stir until completely dissolved, then add 0.2 g of neem extract, and ultrasonically treat at an ultrasonic power of 400 W and 50° C. for 20 min to obtain a mixture; then place the mixture at 45° C. and vacuum dry for 24 h, then grind it into powder and pass it through an 80-mesh sieve to obtain modified linseed gum loaded with neem leaf extract, i.e., a functional agent.

[0059] The preparation method of the above polyethylene stretch wrap film is consistent with that of Example 1.

[0060] Example 3

[0061] A polyethylene stretch wrap film, which differs from Example 1 only in that the preparation method of the functional agent comprises the following steps:

[0062] S1. Add 2 g of flaxseed gum to 200 mL of water, heat to 50° C. and stir until completely dissolved, then add 2 g of methacrylic anhydride dropwise while continuously stirring, and react at 50° C. for 3 h; filter the reaction solution through a 0.45 μm microfiltration membrane, and then ultrafilter using a tangential flow ultrafiltration system (installed with an ultrafiltration membrane with a molecular weight cutoff of 10 kDa); concentrate the retentate by rotary evaporation, and dry in vacuo to obtain modified flaxseed gum;

[0063] S2. Add 1 g of modified linseed gum to 100 mL of water, heat to 50 °C and stir until completely dissolved, then add 0.8 g of 3,6-dioxo-1,8-octanedithiol dropwise under stirring, and mix and stir for 30 min, then add 0.001 g of EosinY photoinitiator and stir evenly to obtain a mixed solution 1; expose the mixed solution 1 to an intensity of 15 mW / cm 2 The mixture was irradiated with visible light until gelation, and then soaked in water for 3 times, each time for 2 hours, and then dried to obtain a composite modified linseed gum; 1 g of the composite modified linseed gum and 0.2 g of neem extract were added to 100 mL of water and mixed, and ultrasonically treated at an ultrasonic power of 400 W and 50° C. for 20 minutes to obtain a mixture; the mixture was then placed at 45° C. and vacuum dried for 24 hours, and then ground into powder and passed through an 80-mesh sieve to obtain a composite modified linseed gum loaded with neem leaf extract, i.e., a functional agent.

[0064] The preparation method of the above polyethylene stretch wrap film is consistent with that of Example 1.

[0065] Example 4

[0066] A polyethylene stretch wrap film, which differs from Example 1 only in that the preparation method of the functional agent comprises the following steps:

[0067] S1. Add 2 g of flaxseed gum to 200 mL of water, heat to 50° C. and stir until completely dissolved, then add 2 g of methacrylic anhydride dropwise while continuously stirring, and react at 50° C. for 3 h; filter the reaction solution through a 0.45 μm microfiltration membrane, and then ultrafilter using a tangential flow ultrafiltration system (installed with an ultrafiltration membrane with a molecular weight cutoff of 10 kDa); concentrate the retentate by rotary evaporation, and dry in vacuo to obtain modified flaxseed gum;

[0068] S2. Add 1 g of modified linseed gum to 100 mL of water, heat to 50 ° C and stir until completely dissolved, then add 0.8 g of trimethylolpropane tris (3-mercaptopropionate) dropwise under stirring, and then mix and stir for 30 minutes, then add 0.001 g of EosinY photoinitiator and stir evenly to obtain a mixed solution 1; expose the mixed solution 1 to an intensity of 15 mW / cm 2 The mixture was irradiated with visible light until gelation, and then soaked in water for 3 times, each time for 2 hours, and then dried to obtain a composite modified linseed gum; 1 g of the composite modified linseed gum and 0.2 g of neem extract were added to 100 mL of water and mixed, and ultrasonically treated at an ultrasonic power of 400 W and 50° C. for 20 minutes to obtain a mixture; the mixture was then placed at 45° C. and vacuum dried for 24 hours, and then ground into powder and passed through an 80-mesh sieve to obtain a composite modified linseed gum loaded with neem leaf extract, i.e., a functional agent.

[0069] The preparation method of the above polyethylene stretch wrap film is consistent with that of Example 1.

[0070] Comparative Example 1

[0071] A polyethylene stretch wrap film, which differs from Example 1 only in that the preparation method of the functional agent comprises the following steps:

[0072] S1. Add 2 g of flaxseed gum to 200 mL of water, heat to 50° C. and stir until completely dissolved, then add 2 g of methacrylic anhydride dropwise while continuously stirring, and react at 50° C. for 3 h; filter the reaction solution through a 0.45 μm microfiltration membrane, and then ultrafilter using a tangential flow ultrafiltration system (installed with an ultrafiltration membrane with a molecular weight cutoff of 10 kDa); concentrate the retentate by rotary evaporation, and dry in vacuo to obtain modified flaxseed gum;

[0073] S2. Add 1 g of modified linseed gum to 100 mL of water, heat to 50 ° C and stir until completely dissolved, then add 0.8 g of trimethylolpropane tris (3-mercaptopropionate) dropwise under stirring, and then mix and stir for 30 minutes, then add 0.001 g of EosinY photoinitiator and stir evenly to obtain a mixed solution 1; expose the mixed solution 1 to an intensity of 15 mW / cm 2 The mixture was irradiated with visible light until gelation, and then soaked in water for 3 times, each time for 2 hours, and then dried, ground into powder and passed through an 80-mesh sieve to obtain a composite modified flaxseed gum, i.e., a functional agent.

[0074] The preparation method of the above polyethylene stretch wrap film is consistent with that of Example 1.

[0075] Comparative Example 2

[0076] A polyethylene stretch wrap film, which differs from Example 1 only in that the preparation method of the functional agent comprises the following steps:

[0077] 2 g of flaxseed gum was added to 200 mL of water, heated to 50° C. and stirred until completely dissolved, 2 g of methacrylic anhydride was added dropwise while continuously stirring, and the mixture was reacted at 50° C. for 3 h; the reaction solution was filtered with a 0.45 μm microfiltration membrane, and then ultrafiltration was performed using a tangential flow ultrafiltration system (installed with an ultrafiltration membrane with a molecular weight cutoff of 10 kDa). The retentate was concentrated by rotary evaporation and vacuum dried to obtain the modified flaxseed gum, i.e., the functional agent.

[0078] The preparation method of the above polyethylene stretch wrap film is consistent with that of Example 1.

[0079] Comparative Example 3

[0080] A polyethylene stretch wrap film, which differs from Example 1 only in that the preparation method of the functional agent comprises the following steps:

[0081] 1 g of flaxseed gum was added to 100 mL of water, heated to 50°C and stirred until completely dissolved, then 0.2 g of neem extract was added, and ultrasonic treatment was performed at an ultrasonic power of 400 W and 50°C for 20 minutes to obtain a mixture; the mixture was then placed at 45°C and vacuum dried for 24 hours, and then ground into powder and passed through an 80-mesh sieve to obtain flaxseed gum loaded with neem leaf extract, i.e., a functional agent.

[0082] The preparation method of the above polyethylene stretch wrap film is consistent with that of Example 1.

[0083] Comparative Example 4

[0084] A polyethylene stretch wrap film, which differs from Example 1 only in that the functional agent is neem extract;

[0085] Comparative Example 5

[0086] A polyethylene stretch wrap film is composed of an upper film layer, a middle film layer, and a lower film layer in a mass ratio of 1:2.5:1.5; the middle film layer is arranged between the upper film layer and the lower film layer and is fixedly connected to the upper film layer and the lower film layer respectively; the thickness of the polyethylene stretch wrap film is 25 μm.

[0087] The upper film layer material is composed of the following components: 33 parts by weight of high-density polyethylene, 36 parts by weight of low-density polyethylene, 30 parts by weight of linear low-density polyethylene, 8 parts by weight of polyethylene glycol 4000, 5 parts by weight of nanocellulose, and 3 parts by weight of antioxidant 2246;

[0088] The middle film layer material is composed of the following components: 45 parts by weight of linear low-density polyethylene, 10 parts by weight of ethylene-vinyl acetate copolymer, 0.5 parts by weight of LLDPE grafted maleic anhydride, 2 parts by weight of diisononyl phthalate, 1.5 parts by weight of γ-aminopropyltriethoxysilane, and 1 part by weight of antioxidant 1076;

[0089] The lower film layer material is composed of the following components: 35 parts by weight of high-density polyethylene, 32 parts by weight of low-density polyethylene, 28 parts by weight of linear low-density polyethylene, 15 parts by weight of polyethylene glycol 4000, 5 parts by weight of nanocellulose, and 3 parts by weight of antioxidant 2246.

[0090] The preparation method of the above polyethylene stretch wrap film is consistent with that of Example 1.

[0091] Test Example 1

[0092] Performance testing

[0093] The polyethylene stretch wrap films prepared in Examples 1-4 of the present invention and Comparative Examples 1-5 were respectively taken as test plastic film samples for later use; and then samples were taken and performance tests were performed according to the following test standards:

[0094] Tensile strength: Refer to the standard "GB / T1040.1-2018 Determination of tensile properties of plastics Part 1: General principles" to test the tensile strength (MPa) of plastic films;

[0095] Barrier performance: Refer to the standard "GB / T 19789-2021 Packaging materials plastic film and sheet oxygen permeability test coulometer test method" to test the oxygen permeability of plastic film (cm 3 / m 2 ·24h·0.1Mpa);

[0096] The test results are shown in Table 1;

[0097] Table 1

[0098]

[0099]

[0100] As shown in Table 1, a comparison of Examples 1-4 and Comparative Examples 1-5 reveals that the tensile strength of Example 1-4 is higher than that of Comparative Examples 1-5, indicating that the polyethylene stretch wrap films prepared according to the present invention possess superior tensile and barrier properties. A comparison of Examples 1-4 reveals that the tensile strength of Examples 3-4 is higher than that of Example 1-2, with Example 4 having the highest tensile strength and exhibiting the best tensile properties. This may be due to the introduction of modified flaxseed gum loaded with plant extracts as a functional agent, which improves the tensile strength of the polyethylene stretch wrap film. The composite modified flaxseed gum has a cross-linked network structure, enabling good interfacial bonding with the polyethylene matrix, thereby enhancing the tensile properties of the polyethylene stretch wrap film. Compared to Comparative Examples 1-2, Examples 1-4 incorporate plant extracts during the functional agent preparation process, which helps increase the compatibility of the composite modified flaxseed gum with the polyethylene matrix, further enhancing the tensile strength of the film. Compared with 3,6-dioxo-1,8-octanedithiol as a polythiol compound for further modification of flaxseed gum, trimethylolpropane tris(3-mercaptopropionate) has more thiol groups in its structure, which can provide a higher cross-linking density and is conducive to the formation of a highly cross-linked network structure. In addition, the thiol activity of trimethylolpropane tris(3-mercaptopropionate) is higher than that of 3,6-dioxo-1,8-octanedithiol, and it can react more quickly with methacrylated flaxseed gum to form a more stable cross-linked network, so the improvement effect on tensile properties is more obvious.

[0101] As shown in Table 1, a comparison of Examples 1-4 and Comparative Examples 1-5 reveals that the oxygen transmission rate of Example 1-4 is lower than that of Comparative Examples 1-5, indicating that the polyethylene stretch film prepared in accordance with the present invention possesses superior barrier properties. Comparative Examples 1-4 reveal that the oxygen transmission rates of Examples 3-4 are lower than those of Example 1-2, with Example 4 having the lowest oxygen transmission rate, demonstrating the best barrier performance. This may be due to the inclusion of modified flaxseed gum loaded with plant extracts as a functional agent, which helps reduce the oxygen transmission rate of the polyethylene stretch film. The mesoporous structure and cross-linked network of the composite modified flaxseed gum may form tiny pores within the polyethylene matrix, which can hinder oxygen transmission and thus improve the film's oxygen barrier properties. Compared to Comparative Examples 1-2, Examples 1-4 incorporate plant extracts during the functional agent preparation process. These plant extracts contain natural components with certain barrier properties that react chemically with oxygen, reducing its transmission rate and further improving the film's oxygen barrier properties. Compared with further modification of flaxseed gum with 3,6-dioxo-1,8-octanedithiol, the high-density cross-linked network formed by the composite modified flaxseed gum loaded with plant extracts prepared by modification with trimethylolpropane tris(3-mercaptopropionate) can more effectively load the plant extracts and ensure that the plant extracts are evenly distributed in the flaxseed gum matrix. This uniform distribution helps to further improve the barrier properties of the stretch film.

[0102] Test Example 2

[0103] Antibacterial performance test

[0104] The polyethylene stretch wrap films prepared in Examples 1-4 of the present invention and Comparative Examples 3-4 were respectively taken as test plastic film samples for later use; then, samples were taken according to the following test standards, and each test plastic film sample was subjected to an accelerated test (placed in an environment with a temperature of 50° C. and a humidity of 85%). The antibacterial rates of the samples at 5h, 50h, and 100h were tested. The antibacterial performance test was performed according to the following method:

[0105] Antibacterial rate: The antibacterial rate (%) of the plastic film was tested according to the standard "GB / T 31402-2023 Determination of antibacterial activity on the surface of plastics and other non-porous materials". The experimental bacteria were Escherichia coli (ATCC8739) and Staphylococcus aureus (ATCC6538P).

[0106] The specific test results are shown in Table 2.

[0107] Table 2

[0108]

[0109]

[0110] As can be seen from Table 2, by comparing Examples 1-4 and Comparative Examples 3-4, it was found that at the 5th hour, the antibacterial rates of Examples 1-4 were all higher than 99%, and all had good antibacterial properties, while the antibacterial rates of Comparative Examples 3-4 were lower and the antibacterial properties were poorer; with the extension of the storage time, the decrease in the antibacterial rates of Examples 1-4 was significantly lower than that of Comparative Examples 3-4. At the 100th hour, the antibacterial rates of Examples 1-4 were significantly higher than those of Comparative Examples 3-4, indicating that the polyethylene stretch wrap film prepared by the embodiments of the present invention has good long-term antibacterial properties; by comparing Examples 1-4, it was found that the decrease in the antibacterial rates of Examples 3-4 was significantly lower than that of Examples 1-2, among which the decrease in Example 4 was the smallest, showing a good long-term antibacterial effect. Analysis shows that the reason may be that the introduction of modified flaxseed gum loaded with plant extracts as a functional agent is beneficial to improving the antibacterial properties of the polyethylene stretch wrap film. Plant extracts are introduced during the preparation of the modified flaxseed gum loaded with plant extracts. The plant extracts contain natural antibacterial ingredients such as phenolic compounds and alkaloids. These ingredients can destroy bacterial cell membranes and inhibit bacterial growth and reproduction, thereby giving the film antibacterial properties. At the same time, the mesoporous structure of the composite modified flaxseed gum can be used as a sustained-release carrier for antibacterial ingredients, slowly releasing the antibacterial ingredients, thereby prolonging the duration of the antibacterial effect. Compared with further modification of flaxseed gum using 3,6-dioxo-1,8-octanedithiol, the high-density cross-linked network formed by the composite modified flaxseed gum loaded with plant extracts prepared using trimethylolpropane tris (3-mercaptopropionate) can load plant extracts more effectively and evenly, thereby helping to further improve the antibacterial properties of the stretch film, and has better sustained-release properties, which can slowly release the antibacterial ingredients in the plant extracts, thereby further prolonging the duration of the antibacterial effect.

Claims

1. A polyethylene stretch film, characterized in that: The invention comprises an upper film layer, a middle film layer and a lower film layer; the middle film layer is arranged between the upper film layer and the lower film layer and is fixedly connected to the upper film layer and the lower film layer respectively; the materials of the upper film layer and the lower film layer comprise the following components in parts by weight: 20-40 parts of high-density polyethylene, 25-45 parts of low-density polyethylene, 20-40 parts of linear low-density polyethylene, 5-15 parts of polyethylene glycol 4000, 3-8 parts of nanocellulose, and 1-4 parts of an antioxidant; the middle film layer comprises the following components in parts by weight: 40-60 parts of linear low-density polyethylene, 5-10 parts of ethylene-vinyl acetate copolymer, 0.2-0.8 parts of LLDPE grafted maleic anhydride, 1-3 parts of a plasticizer, 1-2 parts of a coupling agent, 0.5-2 parts of an antioxidant, and 1-5 parts of a functional agent; The functional agent is prepared by using methacrylate linseed gum as a carrier to load the plant extract; or, it is prepared by using methacrylate linseed gum modified with a polythiol compound as a carrier to load the plant extract; The polythiol compound is 3,6-dioxo-1,8-octanedithiol or trimethylolpropane tris(3-mercaptopropionate); The plant extract is ginkgo extract or neem leaf extract; The mass ratio of the upper film layer material, the middle film layer material and the lower film layer material is 1:1-3:1-2; The polyethylene stretch wrap film has a thickness of 20-30 μm.

2. The polyethylene stretch wrap film according to claim 1, wherein: The antioxidant is selected from one of antioxidant 2246, antioxidant A and antioxidant NDBC.

3. The polyethylene stretch wrap film according to claim 1, wherein: The plasticizer is selected from at least one of diisononyl phthalate, dioctyl adipate, and dioctyl sebacate.

4. The polyethylene stretch wrap film according to claim 1, wherein: The coupling agent is selected from one of isopropyl tristearate titanate, γ-aminopropyl triethoxysilane, and γ-methacryloxypropyl trimethoxysilane.

5. The polyethylene stretch wrap film according to claim 1, wherein: The antioxidant is selected from one of antioxidant 1010, antioxidant 1076, and antioxidant CA.

6. The polyethylene stretch wrap film according to claim 1, characterized in that: The preparation method of the functional agent comprises the following steps, calculated by weight: S1. Add 1-3 parts of flaxseed gum to 100-300 parts of water, heat to 45-55° C. and stir until completely dissolved, then add 1-3 parts of methacrylic anhydride dropwise while continuously stirring, and react at 45-55° C. for 2-4 hours; filter the reaction solution through a microfiltration membrane, and then ultrafilter using a tangential flow ultrafiltration system. The retentate is concentrated by rotary evaporation and vacuum dried to obtain modified flaxseed gum; S2. Add 0.5-1.5 parts of modified flaxseed gum to 80-120 parts of water, heat to 45-55° C. and stir until completely dissolved, then add 0.1-0.3 parts of plant extract, and ultrasonically treat at an ultrasonic power of 200-600 W and 45-55° C. for 10-30 minutes to obtain a mixture; then vacuum-dry the mixture, grind it into powder, and pass it through an 80-100 mesh sieve to obtain modified flaxseed gum loaded with plant extract, i.e., a functional agent.

7. The polyethylene stretch wrap film according to claim 6, characterized in that: The step S2 may also be, by weight: 0.5-1.5 parts of modified linseed gum are added to 50-150 parts of water, heated to 45-55°C and stirred until completely dissolved, then 0.5-1 parts of polythiol compound are added dropwise under stirring, mixed and stirred for 20-30 minutes, and then 0.001-0.002 parts of Eosin Y photoinitiator are added and stirred evenly to obtain a mixed solution 1; the mixed solution 1 is exposed to an intensity of 10-20 mW / cm 2 The composite modified linseed gum is irradiated under visible light until gelation occurs, and then soaked in water for 2-3 times, each time for 1-3 hours, and then dried to obtain a composite modified linseed gum; 0.5-1.5 parts of the composite modified linseed gum and 0.1-0.3 parts of the plant extract are added to 80-120 parts of water, mixed, and ultrasonically treated at an ultrasonic power of 200-600 W and 45-55° C. for 10-30 minutes to obtain a mixture; the mixture is then vacuum-dried, and then ground into powder and passed through an 80-100 mesh sieve to obtain a composite modified linseed gum loaded with the plant extract, i.e., a functional agent.

8. The polyethylene stretch wrap film according to claim 6 or 7, characterized in that: The plant extract is selected from one of ginkgo extract and neem extract.

9. The polyethylene stretch wrap film according to claim 7, characterized in that: The polythiol compound is selected from one of 3,6-dioxo-1,8-octanedithiol and trimethylolpropane tris(3-mercaptopropionate).

10. The method for preparing a polyethylene stretch wrap film according to any one of claims 1 to 9, characterized in that: The following steps are involved: (1) Add the components of the upper film layer material, the middle film layer material and the lower film layer material into three stirring containers according to the corresponding proportions and stir to mix evenly; (2) Extruding the mixtures obtained in the three stirring containers in step S1 at high temperature through screw extruders to obtain upper, middle and lower plastic particles; (3) The upper layer, middle layer and lower layer plastic particles obtained in step S2 are respectively added to the corresponding chambers in the casting machine, and cast into films, wherein the casting temperature is 220-250°C, the temperature of the casting cooling roller is 30-40°C, and then the polyethylene stretch wrap film is obtained by winding and packaging, and the winding tension is not more than 15Kg.

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