Recyclable polymer packaging material and preparation method thereof

Abstract

The invention discloses a recyclable high-molecular packaging material and a preparation method thereof, and particularly relates to the technical field of compositions of high-molecular compounds, the packaging material is of a three-layer composite structure, the outer layer contains polylactic acid, low-density polyethylene and a compatilizer, and the middle layer is composed of water-soluble polyvinyl alcohol and high-density polyethylene. The inner layer comprises ethylene-vinyl acetate, metallocene polyethylene and an elastomer; the middle layer is completely dissolved in normal-temperature water for 5-10 minutes, and the melting temperature difference between the outer layer and the inner layer is less than or equal to 20 DEG C; the preparation method comprises the steps of raw material mixing and granulation, three-layer co-extrusion film blowing and water-cooling rolling and slitting. During recovery, the middle layer is separated through water leaching, and then the outer layer and the inner layer are subjected to melt blending granulation; the recovery rate of the prepared packaging material is larger than or equal to 85%, the regenerated particles are good in performance, the middle layer is photodegradable and good in environmental protection performance, the preparation technology can guarantee the film quality, and remarkable economic and environmental benefits are achieved.

Description

Technical Field

[0001] The present invention relates to the technical field of compositions of polymer compounds. More specifically, the present invention relates to a recyclable polymer packaging material and a preparation method thereof. Background Art

[0002] In today's society, the packaging industry has developed rapidly. Polymer packaging materials are widely used in many fields such as food, medicine, and electronics due to their advantages of light weight, low cost, and strong plasticity.

[0003] However, with the continuous increase in usage, most traditional polymer packaging materials are difficult to degrade naturally. For example, common plastic packages such as polyethylene and polypropylene can exist in the environment for decades or even hundreds of years.

[0004] Some existing recyclable polymer packaging materials face many difficulties in practical applications. Some recycling technologies have extremely high requirements for equipment and require complex pretreatment and processing processes, resulting in high recycling costs and lack of recycling motivation for enterprises. For example, some multi-layer composite packaging materials have large differences in the materials of each layer, making it difficult to separate and reuse, resulting in extremely low recycling efficiency. Moreover, the performance of the recycled materials often deteriorates greatly and cannot meet the high-end packaging requirements, restricting their circular use in the packaging field. In addition, some so-called "environmentally friendly packaging materials", although claiming to be degradable, have harsh degradation conditions and slow degradation speed in the natural environment, and cannot fundamentally solve environmental problems.

[0005] Therefore, it is urgent to develop a polymer packaging material with high recycling efficiency, excellent performance and environmental friendliness, which is of great significance for promoting the sustainable development of the packaging industry and alleviating environmental pressure. Summary of the Invention

[0006] In order to overcome the above-mentioned defects of the prior art, the present invention provides a recyclable polymer packaging material and a preparation method thereof to solve the problems raised in the above background art.

[0007] To achieve the above object, the present invention provides the following technical solution: A recyclable polymer packaging material, the material is a three-layer composite structure, including an outer layer, an intermediate layer and an inner layer; each layer contains the following components by weight:

[0008] Outer layer: 40-50 parts of polylactic acid (PLA), 20-30 parts of low-density polyethylene (LDPE), 3-5 parts of compatibilizer;

[0009] Intermediate layer: 10-15 parts of water-soluble polyvinyl alcohol (PVA), 5-10 parts of high-density polyethylene (HDPE);

[0010] Inner layer: 25 - 35 parts of ethylene-vinyl acetate (EVA), 15 - 20 parts of metallocene polyethylene, 8 - 12 parts of elastomer;

[0011] Among them, the complete dissolution time of the middle layer in normal-temperature water is 5 - 10 minutes, and the melting temperature difference between the outer layer and the inner layer is ≤ 20°C.

[0012] Specifically, the outer layer is mainly composed of PLA and LDPE, and the interfacial bonding force is improved through a compatibilizer; the middle layer is a composite of water-soluble PVA and HDPE to achieve rapid water separation; the inner layer retains EVA and elastomer to ensure compatibility with rubber. Thus, PLA provides biodegradability, the PVA middle layer dissolves in water to achieve layered recovery, and the melting temperatures of the outer layer and the inner layer are similar for convenient re-melting during regeneration. This enables the separation of the middle layer with only water treatment during recovery, and the outer layer and the inner layer can be melt-regenerated with a recovery rate ≥ 85%. Moreover, due to the melting temperature difference between the outer layer and the inner layer being ≤ 20°C, this similar melting temperature characteristic facilitates the DSC temperature of the packaging bag film to be consistent with the raw materials being packaged. In practical applications, for different raw materials being packaged, the proportions of components such as polylactic acid (PLA), low-density polyethylene (LDPE), ethylene-vinyl acetate (EVA), and metallocene polyethylene in the outer layer and the inner layer can be finely adjusted to match the melting temperature of the packaging material with the raw materials being packaged. For example, for heat-sensitive raw materials with a processing temperature range of 160 - 180°C, the extrusion temperatures of the outer layer and the inner layer can be appropriately adjusted, and the proportions of each component can be optimized to ensure that during packaging, storage, or subsequent processing, the packaging material will not affect the performance of the raw materials being packaged due to temperature differences, achieving good coordination between the packaging and the raw materials.

[0013] Preferably, the compatibilizer is maleic anhydride grafted polyethylene (MAH-g-PE), and the addition amount is 3 - 5% of the outer layer.

[0014] Specifically, MAH-g-PE is used as a compatibilizer and is added during the premixing stage of the outer layer. By using the reaction between the polar groups of MAH and the ester groups of PLA, the interfacial compatibility between PLA and LDPE is improved, thereby increasing the tensile strength of the outer layer by 20% and avoiding a decrease in mechanical properties caused by delamination.

[0015] Preferably, the elastomer is one or a combination of two of ethylene-octene copolymer (POE) and styrene-butadiene-styrene block copolymer (SBS).

[0016] Specifically, POE or SBS is added as an elastomer to the inner layer. By means of the elastomer, the flexibility of the inner layer and the blendability with rubber are improved, thereby shortening the fusion time of the packaging material with rubber in the internal mixer by 15%, and the recycled pellets still maintain high elasticity.

[0017] Preferably, the intermediate layer further contains 0.5 - 1.5 parts of a photo - degradation aid, and the photo - degradation aid is nano - titanium dioxide or zinc oxide.

[0018] Specifically, nano - titanium dioxide is added to the intermediate layer, and the photocatalytic effect is used to accelerate the partial degradation of the PVA layer under ultraviolet light, so that the degradation rate of the residual intermediate layer in the natural environment is ≥70% within 6 months, thereby reducing the environmental burden.

[0019] A preparation method of a recyclable polymer packaging material as described above includes the following steps:

[0020] (a) Mix and granulate the raw materials of the outer layer, intermediate layer, and inner layer according to the ratio.

[0021] (b) Use a three - layer co - extrusion blown film device, set the extrusion temperature of the outer layer to 160 - 180 °C, the intermediate layer to 140 - 150 °C, and the inner layer to 170 - 190 °C, and perform co - extrusion blown film.

[0022] (c) Rapidly cool the film to below 30 °C through a water - cooled roller, wind it up and then slit it into finished products.

[0023] Specifically, through the control of the temperature gradient during three - layer co - extrusion blown film, the low - temperature extrusion of the intermediate layer avoids premature decomposition of PVA, and the high temperatures of the outer layer and inner layer ensure uniform melting, so that the film thickness uniformity error can reach ≤5%, and the finished product rate is increased to over 95%.

[0024] Preferably, before granulating the outer layer in step (a), PLA and LDPE need to be premixed in a twin - screw extruder, the mixing temperature is 170 - 185 °C, and the screw speed is 200 - 300 rpm.

[0025] Specifically, high - speed twin - screw extrusion is used for the premixing of PLA and LDPE. The high shear force promotes the uniform dispersion of MAH - g - PE and PLA / LDPE, so that the elongation at break of the outer layer material is increased to 150%, the tensile strength of the product is large, the elongation at break is much better than that of the traditional blending process, and the processed film has the characteristics of high transparency, clean appearance, good plasticization, no moiré, and no crystal points.

[0026] Preferably, the degree of alcoholysis of the water - soluble PVA in the intermediate layer is 88 - 92%, and the molecular weight is 50,000 - 100,000.

[0027] Specifically, PVA with a degree of alcoholysis of 88% is preferably selected to moderately balance water solubility and film-forming property, enabling the middle layer to completely dissolve in water at 30°C within 5 minutes without generating bubbles during the film blowing process. At the same time, the water-soluble design of the middle layer not only facilitates recycling and separation but also brings unique advantages to the application of packaging materials in specific products. In the packaging field of some water-soluble products, when the product comes into contact with water during use, the PVA in the middle layer will quickly dissolve within 5 - 10 minutes and integrate into the product system, avoiding the problem of waste packaging generated after the use of traditional packaging. At the same time, due to the good water solubility and chemical stability of PVA, it will not have a negative impact on the product performance under the reasonable design of the product formula. In addition, the outer layer of polylactic acid (PLA) is biodegradable and can gradually decompose in the natural environment, further reducing the impact of waste packaging on the environment. This makes the packaging material excellent in terms of environmental protection and product compatibility, effectively improving the comprehensive performance of the packaging material.

[0028] A recycling method for a recyclable polymer packaging material as described above, comprising the following steps:

[0029] (i) Immerse the waste packaging material in water at 25 - 40°C to separate the middle layer;

[0030] (ii) Melt-blend the outer layer and inner layer fragments at 180 - 200°C, add 2 - 4 parts of a compatibilizer, and extrude and pelletize to obtain recycled pellets.

[0031] Specifically, when recycling, a compatibilizer is added during the melt-blending of the outer layer and inner layer. The compatibilizer (such as SEBS) improves the compatibility between PLA and EVA, and the tensile strength of the recycled pellets reaches 90% of the raw material, and can be directly used for injection-molded products.

[0032] The technical effects and advantages of the present invention:

[0033] The polymer packaging material of the present invention adopts a three-layer composite structure. The middle layer can be completely dissolved in normal-temperature water within 5 - 10 minutes, and layered separation can be achieved through simple water immersion. The melting temperature difference between the outer layer and the inner layer is ≤20°C, which is convenient for melt-blending at 180 - 200°C. After adding a compatibilizer and extruding and pelletizing, recycled pellets are obtained. The recovery rate is ≥85%, and the tensile strength of the recycled pellets can reach 90% or more of the raw material, and can be directly used for injection-molded products, significantly improving the resource recovery utilization rate and reducing the production cost.

[0034] By adding maleic anhydride grafted polyethylene (MAH-g-PE) as a compatibilizer to the outer layer, the interfacial compatibility between polylactic acid (PLA) and low-density polyethylene (LDPE) can be improved, the tensile strength of the outer layer can be increased by 20%, and the elongation at break can be increased to more than 150%, enhancing the mechanical properties of the packaging material. Elastomers such as ethylene-octene copolymer (POE) or styrene-butadiene-styrene block copolymer (SBS) are added to the inner layer, improving the flexibility of the inner layer and the blendability with rubber, shortening the fusion time between the packaging material and rubber by 15%-20%, and the recycled pellets still maintain high elasticity, meeting the requirements of various packaging scenarios.

[0035] By adding photo-degradation aids such as nano-titanium dioxide or zinc oxide to the middle layer, under the action of ultraviolet light, the degradation of the PVA layer can be accelerated, and the degradation rate of the remaining middle layer can be ≥70% within 6 months in the natural environment. Secondly, the PLA in the material has biodegradability, reducing the long-term pollution of waste packaging materials to the environment, and conforming to the trend of environmental protection development.

[0036] During the preparation process, precisely control the temperature of the three-layer co-extrusion blown film, with the outer layer at 160-180°C, the middle layer at 140-150°C, and the inner layer at 170-190°C, effectively avoiding premature decomposition of the middle layer PVA, ensuring uniform melting of the outer layer and the inner layer, and making the thickness uniformity error of the film ≤5%, and the yield rate is increased to more than 95%. Select water-soluble PVA with an alcoholysis degree of 88-92% and a molecular weight of 50,000-100,000, which can balance water solubility and film-forming property, ensure no bubbles are generated in the middle layer during the blown film process, and can dissolve quickly in water at an appropriate temperature. Specific embodiments

[0037] Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the scope of protection of the present invention.

[0038] Example 1

[0039] A recyclable polymer packaging material provided in this Example 1, the material is a three-layer composite structure, including an outer layer, a middle layer and an inner layer; each layer contains the following components by weight:

[0040] Outer layer: 45 parts of polylactic acid (PLA), 25 parts of low-density polyethylene (LDPE), 4 parts of maleic anhydride grafted polyethylene (MAH-g-PE);

[0041] Middle layer: 12 parts of water-soluble polyvinyl alcohol (PVA) (alcoholysis degree 88%, molecular weight 80,000), 8 parts of high-density polyethylene (HDPE), 1 part of nano-titanium dioxide;

[0042] Inner layer: 30 parts of ethylene-vinyl acetate (EVA), 18 parts of metallocene polyethylene, and 10 parts of ethylene-octene copolymer (POE).

[0043] A preparation method of a recyclable polymer packaging material provided in the first embodiment includes the following steps:

[0044] Premix the outer layer: Mix PLA and LDPE in a twin-screw extruder (temperature 175°C, screw speed 250 rpm), and add MAH-g-PE to granulate;

[0045] Intermediate layer granulation: Dry mix PVA, HDPE, and nano-titanium dioxide and then extrude and granulate (temperature 145°C);

[0046] Inner layer mixing: Directly mix EVA, metallocene polyethylene, and POE and granulate;

[0047] Three-layer coextrusion blown film: The extrusion temperature of the outer layer is 170°C, the intermediate layer is 145°C, and the inner layer is 180°C. After blown film, it is water-cooled to 25°C and wound up. The total thickness of the film is 0.08 mm, and each layer is uniform.

[0048] When the recyclable polymer packaging material prepared by the preparation method in the first embodiment is subjected to a recycling test, it has the following effects:

[0049] The intermediate layer completely dissolves in water at 30°C in 6 minutes, and the melting temperature difference between the outer layer and the inner layer is 15°C;

[0050] The tensile strength of the recycled pellets is 92% of that of the raw material;

[0051] The photo-degradation aid enables the degradation rate of the intermediate layer to reach 75% outdoors in 6 months.

[0052] The specific tensile strength test method is based on GB / T 1040.3-2006 "Determination of Tensile Properties of Plastics - Part 3: Test Conditions for Films and Sheets". Use an intelligent electronic tensile testing machine (model: XLW(PC)), and the test conditions are: specimen size 243 mm × 10 mm, gauge length 50 mm, tensile speed 500 mm / min, ambient temperature 23 ± 2°C, humidity 50 ± 5%. The test results are shown in Table 1:

[0053] Table 1: Tensile Strength Test Table of Raw Materials and Recycled Pellets

[0054]

[0055]

[0056] As can be seen from the above table, the tensile strength of the recycled particles reaches 37.38 MPa, while the tensile strength of the virgin material produced in Example 1 is 40.63 MPa. Thus, it can be seen that the tensile strength of the recycled particles is approximately 92% of that of the virgin material.

[0057] For the photolysis test of the intermediate layer produced in this example, the specific test location is Shanghai, and the test period is from June to December 2024. During this period, the average temperature is 25 °C, and the average sunshine duration is 5.8 hours per day. The outdoor exposure method is adopted for the test. Referring to GB / T 17603-2017 "Test Method for Outdoor Exposure of Photodegradable Plastics", the intermediate layer samples (size 100 mm × 100 mm × 0.08 mm) are fixed on the bracket and placed facing south at an angle of 45° to the horizontal plane. Samples are taken and weighed every 2 months, and the mass loss rate is calculated as the degradation rate. The test process is shown in Table 2:

[0058] Table 2: Data Table of Photolysis Test of Intermediate Layer

[0059]

[0060]

[0061] As shown in Table 2, by manually recording each weighing and averaging the temperature, sunshine duration, humidity, and wind speed in the corresponding period, and through comparison of multiple groups of measurements, it is obtained that the photodegradation aid enables the degradation rate of the intermediate layer to reach 75% outdoors in 6 months.

[0062] Example 2

[0063] A recyclable polymer packaging material provided in this Example 2, the material is a three-layer composite structure, including an outer layer, an intermediate layer, and an inner layer; each layer contains the following components by weight:

[0064] Outer layer: 40 parts of PLA, 30 parts of LDPE, 5 parts of MAH-g-PE;

[0065] Intermediate layer: 15 parts of PVA (degree of alcoholysis 90%, molecular weight 60,000), 5 parts of HDPE, 1.5 parts of zinc oxide;

[0066] Inner layer: 25 parts of EVA, 20 parts of metallocene polyethylene, 12 parts of styrene-butadiene-styrene block copolymer (SBS).

[0067] A preparation method of a recyclable polymer packaging material provided in this Example 2, including the following steps:

[0068] Premixing of the outer layer: PLA and LDPE are kneaded at 180 °C, and MAH-g-PE is added and then granulated;

[0069] Middle layer granulation: PVA and HDPE are mixed and zinc oxide is added, and the extrusion temperature is 140℃;

[0070] Inner layer mixing: EVA, metallocene polyethylene and SBS blended into granules;

[0071] Co-extrusion blown film: outer layer temperature 180℃, middle layer 150℃, inner layer 190℃, total film thickness 0.1mm.

[0072] The recyclable polymer packaging material prepared by the preparation method of Example 2 has the following effects when subjected to a recycling test:

[0073] The middle layer completely dissolves in 35°C water within 4 minutes, and the dissolution rate is increased;

[0074] SBS elastomer shortens the mixing time of the inner layer and rubber by 20%;

[0075] Recycled particles can be directly used for injection molding of shoe materials, with a flexural strength of 95% of that of virgin materials.

[0076] Specifically, in the rubber blending time test, blending was carried out by using an internal mixer (model: X(S)M-1.5L, Shanghai Kechuang), and the time from feeding to uniform mixing of the materials was recorded by the timer provided in the equipment. Compared with the traditional process (inner layer blending time was 60 minutes), the inner layer blending time of this embodiment was 48 minutes, which was shortened by 20%.

[0077] The flexural strength test of the recycled particles was conducted in accordance with GB / T9341-2008 "Determination of Flexural Properties of Plastics" using a flexural testing machine (model: ZWICKZ020, Germany). The test conditions were: specimen size 80mm×10mm×4mm, span 64mm, indenter speed 2mm / min, ambient temperature 23±2°C. The specific test data are shown in Table 3:

[0078] Table 3: Bending strength test table of the original material prepared in Example 2 and the recycled particles prepared by dissolving the original material

[0079] Sample type Maximum load (N) Full deflection (mm) Flexural strength (MPa) Modulus of elasticity (MPa) Virgin material 113.0 4.2 45.2 2800 Recycled pellets 107.3 4.0 42.9 2750

[0080] As shown in Table 2, the flexural strength of the original material is 45.2 MPa, and the flexural strength of the recycled particles is 42.9 MPa. It is calculated that the flexural strength of the recycled particles is 95% of the original material.

[0081] Example 3

[0082] The third embodiment provides a recyclable polymer packaging material, which has a three-layer composite structure, including an outer layer, a middle layer, and an inner layer; each layer comprises the following components in parts by weight:

[0083] Outer layer: 50 parts of PLA, 20 parts of LDPE, 3 parts of MAH-g-PE;

[0084] Middle layer: 10 parts of PVA (degree of alcoholysis 92%, molecular weight 100,000), 10 parts of HDPE;

[0085] Inner layer: 35 parts of EVA, 15 parts of metallocene polyethylene, 8 parts of POE, 2 parts of SEBS compatibilizer.

[0086] A preparation method of a recyclable polymer packaging material provided in the third embodiment includes the following steps:

[0087] Premixing of the outer layer: Mixing PLA and LDPE at 170°C (screw speed 300 rpm);

[0088] Pelletizing of the middle layer: Directly dry-mixing PVA and HDPE and then extruding (temperature 150°C);

[0089] Mixing of the inner layer: Blending and pelletizing EVA, metallocene polyethylene, POE, and SEBS;

[0090] Co-extrusion blown film: Outer layer temperature 160°C, middle layer 142°C, inner layer 170°C, film thickness 0.07 mm.

[0091] When the recyclable polymer packaging material prepared by the preparation method in the third embodiment is subjected to a recycling test, it has the following effects:

[0092] The middle layer dissolves in water at 25°C in 10 minutes, suitable for low-temperature recycling scenarios;

[0093] The SEBS compatibilizer improves the impact resistance of the recycled pellets by 18%;

[0094] As shown in Table 1, the elongation at break of the outer layer reaches 160%, suitable for high-tensile packaging requirements.

[0095] Specifically, for the recycled pellets in the third embodiment, the impact resistance test is carried out in accordance with GB / T 1843-2008 "Determination of the Charpy impact strength of plastics", using a pendulum impact testing machine (model: XJJ-50, Chengde Jinjian). The test conditions are: specimen size 80 mm × 10 mm × 4 mm, notch type A, pendulum energy 50 J, ambient temperature 23 ± 2°C. The specific test data is shown in Table 4 below.

[0096] Table 4: Impact resistance test table of recycled pellets in this embodiment

[0097] Sample type Impact energy (J) Absorbed energy (J) <![CDATA[Impact strength (kj / m 2) > Virgin material 50 25 25 Recycled pellets 50 29.5 29.5

[0098] As shown in Table 3, the impact strength of the virgin material is 25 kJ / m 2, the impact strength of the recycled particles with SEBS compatibilizer added is 29.5 kJ / m 2 , with an increase of 18%.

[0099] Example 4

[0100] A recyclable polymer packaging material provided in this Example 4, the material is a three-layer composite structure, including an outer layer, a middle layer and an inner layer; each layer contains the following components by weight:

[0101] Outer layer: 48 parts of PLA, 22 parts of LDPE, 4.5 parts of MAH-g-PE;

[0102] Middle layer: 13 parts of PVA (degree of alcoholysis 89%, molecular weight 70,000), 7 parts of HDPE, 0.8 part of nano-titanium dioxide;

[0103] Inner layer: 28 parts of EVA, 17 parts of metallocene polyethylene, 9 parts of POE.

[0104] A preparation method of a recyclable polymer packaging material provided in this Example 4, including the following steps:

[0105] Outer layer premixing: PLA and LDPE are kneaded at 185°C, and MAH-g-PE is added in two portions;

[0106] Middle layer granulation: PVA, HDPE and nano-titanium dioxide are mixed and then extruded (temperature 148°C);

[0107] Inner layer mixing: EVA and metallocene polyethylene are premixed and then POE is added for granulation;

[0108] Coextrusion blown film: the temperature of the outer layer is 175°C, the middle layer is 147°C, the inner layer is 185°C, and the film thickness is 0.09 mm.

[0109] When the recyclable polymer packaging material prepared by the preparation method in this Example 4 is subjected to a recycling test, it has the following effects:

[0110] The degradation rate of the middle layer under ultraviolet light is 65% in 3 months, and the water-soluble time is 8 minutes;

[0111] Nano-titanium dioxide is evenly dispersed, and the light transmittance of the film only decreases by 5%;

[0112] The melt index stability of the recycled particles is improved, which is suitable for high-precision injection molding.

[0113] Specifically, for the film produced in the fourth embodiment, the light transmittance test in Jining is carried out in accordance with GB / T 2410-2008 "Determination of Light Transmittance and Haze of Transparent Plastics". An integrating sphere type light transmittance and haze meter (model: Color Spectrum DH-13) is used. The test wavelength is 550 nm, the sample size is 30 mm × 30 mm, and the thickness is 0.09 mm. The comparison object is a pure inner layer film without added nano-titanium dioxide, as shown in Table 5 below.

[0114] Table 5: Data Sheet of Light Transmittance Test

[0115]

[0116] As shown in Table 4, the light transmittance of the pure inner layer film is 85%, and the light transmittance of the film with 0.8 parts of nano-titanium dioxide added is 80.75%, with a decrease of 5%.

[0117] The above are only the preferred embodiments of the present invention and are not used to limit the present invention. Any modifications, equivalent replacements, improvements, 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 polymer packaging material capable of recycling, characterized in that, The material is a three-layer composite structure, including an outer layer, an intermediate layer and an inner layer; each layer contains the following components by weight: Outer layer: 40-50 parts of polylactic acid, 20-30 parts of low-density polyethylene, 3-5 parts of compatibilizer; Intermediate layer: 10-15 parts of water-soluble polyvinyl alcohol, 5-10 parts of high-density polyethylene; Inner layer: 25-35 parts of ethylene-vinyl acetate, 15-20 parts of metallocene polyethylene, 8-12 parts of elastomer; Among them, the complete dissolution time of the intermediate layer in normal-temperature water is 5-10 minutes, and the melting temperature difference between the outer layer and the inner layer is ≤20°C.

2. The polymeric packaging material capable of recycling according to claim 1, wherein The compatibilizer is maleic anhydride grafted polyethylene, and the addition amount is 3-5% of the outer layer.

3. The polymer packaging material capable of recycling according to claim 1, characterized in that, The elastomer is one or a combination of two of ethylene-octene copolymer and styrene-butadiene-styrene block copolymer.

4. A recyclable polymer packaging material according to claim 1, characterized in that, The intermediate layer also contains 0.5-1.5 parts of a photo-degradation aid, and the photo-degradation aid is nano-titanium dioxide or zinc oxide.

5. A preparation method of a recyclable polymer packaging material according to any one of claims 1-4, characterized in that, Including the following steps: (a) Mix and granulate the raw materials of the outer layer, intermediate layer and inner layer according to the ratio; (b) Use a three-layer co-extrusion blown film device, set the extrusion temperature of the outer layer at 160-180°C, the intermediate layer at 140-150°C, and the inner layer at 170-190°C, and carry out co-extrusion blown film; (c) Rapidly cool the film to below 30°C through a water-cooled roller, and after winding, cut it into finished products.

6. The preparation method of a recyclable polymer packaging material according to claim 5, characterized in that, Before granulating the outer layer in step (a), polylactic acid and low-density polyethylene need to be premixed in a twin-screw extruder, the mixing temperature is 170-185°C, and the screw speed is 200-300 rpm.

7. The preparation method of a recyclable polymer packaging material according to claim 5, characterized in that, The degree of alcoholysis of the water-soluble polyvinyl alcohol in the intermediate layer is 88-92%, and the molecular weight is 50,000-100,000.

8. A method for recycling a packaging material according to any one of claims 1-4, characterized in that, Including the following steps: (i) Immerse the waste packaging material in water at 25-40°C and separate the intermediate layer; (ii) Melt and blend the outer layer and inner layer fragments at 180-200°C, add 2-4 parts of a compatibilizer, and extrude and granulate to obtain recycled particles.

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