High-oxidation-resistance long-life polyethylene cable sheath material and preparation method thereof

Abstract

The invention discloses a high-oxidation-resistance long-life polyethylene cable sheath material and a preparation method thereof, and relates to the technical field of high polymer materials. Comprising the following components: high-molecular-weight high-density polyethylene, surface-modified nano-dioxide, furan-maleimide grafted polyethylene, a Schiff base dynamic cross-linking agent, tea polyphenol grafted polyethylene, a temperature-responsive oxygen-blocking microcapsule, a main antioxidant, an auxiliary antioxidant, an emergency antioxidant, a light stabilizer, a halogen-free flame retardant, a processing aid and an acid absorbent. According to the invention, the main antioxidant, the auxiliary antioxidant and the tea polyphenol grafted polyethylene form a chemically synthesized and naturally modified composite antioxidant system, the designed service life of the material is greatly prolonged, the temperature-responsive oxygen-blocking microcapsule automatically cracks to release the core material when the operating temperature of the cable is greater than or equal to 90 DEG C, a dynamic oxygen-blocking layer is formed, and the service life of the cable is prolonged. The defect that the effect of traditional physical oxygen barrier is attenuated at high temperature is overcome, and the oxygen permeability at high temperature is reduced compared with that of a single nano barrier scheme.

Description

Technical Field

[0001] This invention relates to the field of polymer materials technology, and in particular to high-oxidation-resistant, long-life polyethylene cable sheath material and its preparation method. Background Technology

[0002] Polyethylene is the mainstream matrix material for cable sheathing due to its excellent electrical insulation, mechanical strength, and processing fluidity. As cable applications expand to harsher environments, such as offshore wind power, photovoltaic power stations, and nuclear power plants, higher requirements are placed on the service life, oxidation resistance, and weather resistance of sheathing materials. Conventional polyethylene cable sheathing materials are gradually revealing several technical shortcomings.

[0003] First, existing antioxidant systems for polyethylene sheathing materials mostly rely on a simple combination of primary and secondary antioxidants. This system is prone to activity decay under long-term high temperature, strong ultraviolet radiation, or high shear conditions, failing to continuously capture free radicals or decompose hydrogen peroxides. This leads to accelerated oxidative aging of the material, with an actual service life typically only 20-25 years, making it difficult to meet the demand for a long service life of over 40 years. Meanwhile, some solutions attempt to introduce natural antioxidants to improve longevity, but natural antioxidants have poor compatibility with the polyethylene matrix, are prone to migration and loss, and cannot fully exert their antioxidant effect.

[0004] Secondly, oxygen barrier protection often adopts a single physical barrier method, such as adding nanoparticles to form a maze effect. However, when the cable operating temperature increases, the oxygen permeation rate will increase significantly, and the oxygen barrier effect will decrease with the increase of temperature. It cannot achieve dynamic and adaptive oxygen barrier protection, which further accelerates the internal oxidation of the material.

[0005] Furthermore, polyethylene materials are prone to micro-cracks during processing and use. Existing sheath materials lack effective micro-repair mechanisms. These micro-cracks will gradually expand and become channels for oxygen and moisture penetration, accelerating material aging and causing a decline in mechanical properties, thus affecting the safety of cable operation.

[0006] Existing preparation processes mostly employ a single-feed, fixed-temperature-range melt blending method. For heat-sensitive functional components, this method is prone to decomposition and failure due to prolonged exposure to high temperatures. It is also difficult to ensure the uniform dispersion of components such as nanoparticles and microcapsules, resulting in large fluctuations in the performance of the final product and an inability to stably achieve the design specifications.

[0007] In summary, there is an urgent need to develop a polyethylene cable sheath material that possesses long-lasting antioxidant properties, dynamic oxygen barrier properties, microscopic self-healing capabilities, and also takes into account flame retardancy and mechanical properties, in order to overcome the shortcomings of existing technologies. Summary of the Invention

[0008] To address the aforementioned technical problems, this invention provides a high-oxidation-resistant, long-life polyethylene cable sheath material and its preparation method. The technical solution is as follows:

[0009] High-oxidation-resistant, long-life polyethylene cable sheath material, by weight percentage, comprises the following components:

[0010] High molecular weight high-density polyethylene 78.0wt%-84.0wt%, surface-modified nano-silica 0.8wt%-2.5wt%, furan-maleimide grafted polyethylene 1.6wt%-4.2wt%, Schiff base dynamic crosslinking agent 0.3wt%-0.6wt%, tea polyphenol grafted polyethylene 0.5wt%-1.0wt%, temperature-responsive oxygen-barrier microcapsules 0.4wt%-0.8wt%, main antioxidant 0.2wt%-0.4wt%, auxiliary antioxidant 0.3wt%-0.5wt%, emergency antioxidant 0.1wt%-0.2wt%, light stabilizer 0.2wt%-0.4wt%, halogen-free flame retardant 12.0wt%-21.0wt%, processing aid 0.4wt%-0.8wt%, acid absorbent 0.1wt%-0.2wt%;

[0011] The Schiff base dynamic crosslinking agent is a bis(salicylaldehyde) ethylenediamine Schiff base, which forms a double dynamic bond network with the DA bonds of furan-maleimide grafted polyethylene.

[0012] The temperature-responsive oxygen barrier microcapsules have a core-wall structure. The core material is a hindered amine oxygen barrier agent, and the wall material is polycaprolactone. The core-wall material weight ratio is 3:2, and the particle size is 1μm-3μm. When the material operating temperature is greater than or equal to 90℃, the core material is automatically ruptured and released to form an oxygen barrier layer.

[0013] Optionally, the tea polyphenol-grafted polyethylene is prepared by melt grafting with a grafting rate of 8%-12%, using dicumyl peroxide as an initiator, and the amount of initiator is 0.3 wt% of the total weight of tea polyphenols and polyethylene. The grafted product is subjected to Soxhlet extraction to remove ungrafted tea polyphenols.

[0014] Optionally, the temperature-responsive oxygen-barrier microcapsules are prepared by interfacial polymerization, and the number-average molecular weight of the wall material polycaprolactone is 10,000-20,000.

[0015] Optionally, the primary antioxidant is antioxidant 1010, and the secondary antioxidant is antioxidant 168. The primary antioxidant, the secondary antioxidant, and tea polyphenols grafted onto polyethylene form a composite antioxidant system that combines chemical synthesis and natural modification.

[0016] Optionally, the halogen-free flame retardant is magnesium hydroxide coated with stearic acid, with a particle size of 1μm-5μm, which synergistically enhances the flame retardant and smoke-suppressing performance of the material with surface-modified nano-silica; the processing aid is a compound of polyethylene wax and fluoroelastomer with a molecular weight of 1000-3000, and the weight ratio of polyethylene wax to fluoroelastomer is (1.8-2.2):1.

[0017] A method for preparing a high-oxidation-resistant, long-life polyethylene cable sheath material includes the following steps:

[0018] Step 1: Dry the surface-modified nano-silica, high molecular weight high-density polyethylene, halogen-free flame retardant and temperature-responsive oxygen-barrier microcapsules respectively to remove moisture from the raw materials or prevent the functional components from prematurely degrading.

[0019] Step 2: Using a high-speed mixer, the base resin, processing aids, small molecule additives, dynamic functional additives, and solid particulate additives are added in stages in that order. By adjusting the mixing speed and time, the components are evenly dispersed to obtain the initial mixture.

[0020] Step 3: Add the initial mixture to a co-rotating twin-screw extruder, control the extruder temperature zones, screw speed and vacuum exhaust conditions to ensure that the material is fully melted and the functional components do not decompose. After the extruded material is cooled, it is granulated to obtain granules.

[0021] Step 4: Dry the granulated material, control the moisture content to a preset range, and then seal it in packaging and store it under specific conditions.

[0022] Optionally, the raw material pretreatment in step 1 specifically includes:

[0023] Step 11: The surface-modified nano-silica is dried in a vacuum oven at 80℃-100℃ for 3.5-4 hours;

[0024] Step 12: Place the high molecular weight high density polyethylene in a hot air dryer at 70℃-80℃ for 2-3 hours. After drying, the moisture content should be less than or equal to 0.05%.

[0025] Step 13: Dry the halogen-free flame retardant at 98℃-100℃ for 2-3 hours;

[0026] Step 14: The temperature-responsive oxygen-barrier microcapsules are placed in a vacuum dryer at 58℃-65℃ for 1.5-2 hours.

[0027] Step 15: Place the primary antioxidant, secondary antioxidant, emergency antioxidant, light stabilizer, acid absorber, and processing aid in a vacuum drying oven at 40℃-50℃ and dry for 1-1.5 hours.

[0028] Optionally, the method for preparing the temperature-responsive oxygen-barrier microcapsules includes the following steps:

[0029] Step a: Mix the hindered amine oxygen inhibitor with ethanol at a mass ratio of 1:4 and stir magnetically for 10-15 min to obtain a core material solution; add 2.5-3 wt% sodium dodecylbenzenesulfonate of the core material mass to the core material solution and continue stirring for 8-10 min to obtain a core material pre-dispersion.

[0030] Step b: Dissolve polycaprolactone in dichloromethane to prepare a wall material solution, and stir magnetically until completely dissolved;

[0031] Step c: Drop the core material pre-dispersion liquid from step a into the wall material solution from step b, and emulsify it for 30-40 minutes at 28℃-25℃ using a high-speed disperser at a speed of 2500rpm-3500rpm to form an oil-in-water emulsion.

[0032] Step d: Add deionized water dropwise to the oil-in-water emulsion, the amount of water added being twice the volume of the oil-in-water emulsion. At the same time, raise the temperature to 40℃-42℃ and stir at 400rpm-600rpm for 2-2.5h to allow the dichloromethane to fully evaporate and the PCL wall material to solidify and encapsulate the core material.

[0033] Step e: Centrifuge the solidified microcapsule suspension at 7000rpm-9000rpm for 10-12min and collect the lower layer of microcapsule particles.

[0034] Step f: Wash with deionized water 2-3 times to remove residual emulsifier on the surface; finally, dry in a vacuum drying oven at 55℃-60℃ for 3-4 hours to obtain particle size temperature-responsive oxygen barrier microcapsules.

[0035] Optionally, the initial mixing in step 2 can be performed as follows: Using a high-speed mixer, first add the pretreated high molecular weight high-density polyethylene and processing aids, and mix at 450 rpm-550 rpm for 1-1.5 min; then add the main antioxidant, auxiliary antioxidant, emergency antioxidant, light stabilizer, and acid absorber, and mix at 800 rpm-900 rpm for 2-2.5 min; next, add the Schiff base dynamic crosslinking agent and tea polyphenol grafted polyethylene, and mix at 1100 rpm-1200 rpm for 3-4 min; finally, add the pretreated surface-modified nano silica, furan-maleimide grafted polyethylene, temperature-responsive oxygen-barrier microcapsules, and halogen-free flame retardant, and mix at 1500 rpm-2000 rpm for 5-8 min until the material temperature reaches 60-70℃ to obtain the initial mixture.

[0036] Optionally, in step 3, the melt blending and granulation process uses a co-rotating twin-screw extruder, and the temperatures of the extruder's feeding zone, melting zone, mixing zone, homogenizing zone, and die head are set to: 140℃-150℃, 160℃-170℃, 175℃-185℃, 170℃-175℃, and 165℃-170℃, respectively.

[0037] The screw speed is controlled at 220-280 rpm, and a two-stage vacuum exhaust system is installed in the middle section of the extruder, with a vacuum degree of -0.08 to -0.09 MPa.

[0038] After being cooled by cooling water at 40℃-50℃, the extruded material is cut into cylindrical pellets of a set size by a pelletizer.

[0039] In summary, the present invention has at least one of the following beneficial technical effects:

[0040] This invention provides a high-antioxidant, long-life polyethylene cable sheath material and its preparation method. It utilizes a chemically synthesized and naturally modified composite antioxidant system formed by a primary antioxidant, an auxiliary antioxidant, and tea polyphenol-grafted polyethylene. The tea polyphenol-grafted polyethylene exhibits excellent compatibility with the matrix and can effectively capture free radicals over a long period. Combined with the replenishing effect of an emergency antioxidant under extreme conditions, the material's oxidation induction period is significantly extended compared to traditional methods. Simultaneously, the microscopic repair capability of the dual dynamic bond network effectively blocks the aging chain reaction initiated by microcracks, resulting in a significantly improved material design life and meeting the long-life requirements under harsh environments.

[0041] Temperature-responsive oxygen barrier microcapsules automatically rupture and release the core material when the cable operating temperature is greater than or equal to 90°C, forming a dynamic oxygen barrier layer. This compensates for the shortcomings of traditional physical oxygen barrier in terms of effectiveness at high temperatures, reducing oxygen permeability at high temperatures compared to single nano barrier solutions. It achieves dual protection of physical barrier at room temperature and chemical oxygen barrier at high temperature, dynamically adapting to oxygen barrier requirements at different temperatures.

[0042] Schiff base-based dynamic crosslinking agents form a double dynamic bond network with furan-maleimide grafted polyethylene, which can achieve molecular chain breakage and reconnection in the 80-120℃ range, repairing micro-cracks during processing and use. At the same time, the surface-modified nano-silica and halogen-free flame retardant work synergistically to avoid excessive degradation of mechanical properties, thus balancing flame retardancy and mechanical strength. Attached Figure Description

[0043] Figure 1 This is a schematic flowchart of the preparation method of the high oxidation resistance and long life polyethylene cable sheath material of the present invention. Detailed Implementation

[0044] The present invention will be further described in detail below with reference to the accompanying drawings.

[0045] This invention discloses a high-oxidation-resistant, long-life polyethylene cable sheath material and its preparation method.

[0046] Reference Figure 1 Example 1, High-oxidation-resistant, long-life polyethylene cable sheath material, comprises the following components by weight percentage:

[0047] High molecular weight high-density polyethylene 78.0wt%-84.0wt%, surface-modified nano-silica 0.8wt%-2.5wt%, furan-maleimide grafted polyethylene 1.6wt%-4.2wt%, Schiff base dynamic crosslinking agent 0.3wt%-0.6wt%, tea polyphenol grafted polyethylene 0.5wt%-1.0wt%, temperature-responsive oxygen-barrier microcapsules 0.4wt%-0.8wt%, main antioxidant 0.2wt%-0.4wt%, auxiliary antioxidant 0.3wt%-0.5wt%, emergency antioxidant 0.1wt%-0.2wt%, light stabilizer 0.2wt%-0.4wt%, halogen-free flame retardant 12.0wt%-21.0wt%, processing aid 0.4wt%-0.8wt%, acid absorbent 0.1wt%-0.2wt%;

[0048] The Schiff base dynamic crosslinking agent is a bis(salicylaldehyde) ethylenediamine Schiff base, which forms a double dynamic bond network with the DA bonds of furan-maleimide grafted polyethylene.

[0049] The temperature-responsive oxygen barrier microcapsules have a core-wall structure. The core material is a hindered amine oxygen barrier agent, and the wall material is polycaprolactone. The core-wall material weight ratio is 3:2, and the particle size is 1μm-3μm. When the material operating temperature is greater than or equal to 90℃, the core material is automatically ruptured and released to form an oxygen barrier layer.

[0050] By adopting the above technical solution, high molecular weight high-density polyethylene is used as the matrix. Its polymer chain structure is regular and its molecular weight is high. The melt flow rate is 0.1-0.3 g / 10 min. On the one hand, it can provide excellent mechanical strength and electrical insulation through strong interactions between molecular chains, which can meet the basic requirements of cable sheath for structural support and insulation protection. On the other hand, its linear molecular chain structure provides a uniformly dispersed carrier framework for other functional components, ensuring that each functional component can be stably combined and play its role, and avoiding performance stratification caused by poor matrix compatibility.

[0051] Schiff base-based dynamic crosslinking agents synergistically form a double dynamic bond network with the DA bonds (Diels-Alder bonds) of furan-maleimide-grafted polyethylene. The core principle is as follows:

[0052] Dynamic bond function of Schiff base: The imine bond (-C=N-) in the bis(salicylic) ethylenediamine Schiff base molecule is reversible. When the material is heated (80-120℃) or subjected to external force to generate microcracks, the imine bond can break and recombine, filling the micro-defects through local reconstruction of the molecular chain. At the same time, the hydroxyl group in its molecule can form hydrogen bonds with the polyethylene molecular chain and other components, further enhancing the network bonding force.

[0053] The furan ring and maleimide group on the furan-maleimide grafted polyethylene molecular chain can form a stable DA addition bond at room temperature. When heated, the addition bond breaks and reforms after cooling, realizing the cycle of molecular chain breakage and reconnection. This process can actively repair microcracks caused by shearing and stretching during processing or use, and prevent the cracks from expanding into channels for oxygen and moisture penetration.

[0054] The hydrogen bonding of Schiff base dynamic bonds and the reversible addition of DA bonds intertwine to form a dynamic network with higher density and more sensitive response: Schiff base bonds can quickly respond to the local stress generated by microcracks and achieve instant repair; while DA bonds enhance the repair stability through long-range reconstruction of molecular chains. The combined effect of the two enables the material to maintain stable mechanical properties under repeated thermal cycling or external force, while delaying oxidative aging caused by cracks.

[0055] This solution utilizes the synergy of primary antioxidants, secondary antioxidants, tea polyphenol-grafted polyethylene, and emergency antioxidants to construct comprehensive antioxidant protection for all scenarios.

[0056] The free radical capture principle of primary antioxidants: The molecules of primary antioxidants (such as antioxidant 1010) contain multiple hindered phenolic hydroxyl groups, which can actively combine with alkyl free radicals (・R) and peroxy free radicals (・OOR) generated during the oxidation process of materials to form stable phenolic oxygen free radicals, terminate the propagation of the oxidation chain reaction, and block the "initiation-diffusion" link of oxidation.

[0057] The principle of hydroperoxide decomposition by auxiliary antioxidants: Auxiliary antioxidants (such as antioxidant 168) are phosphite compounds that can react with hydroperoxides (ROOH) generated during oxidation, decomposing them into stable alcohols and esters. This prevents further decomposition of hydroperoxides to generate new free radicals (such as ·OH and ·OOR), thus reducing the "secondary initiation" of oxidation reactions from the source.

[0058] The long-lasting antioxidant principle of tea polyphenol-grafted polyethylene: Tea polyphenol-grafted polyethylene binds tea polyphenols (natural compounds containing multiple phenolic hydroxyl groups) to the polyethylene molecular chain through melt grafting. On the one hand, this solves the compatibility problem between tea polyphenols and the polyethylene matrix, preventing their migration and loss. On the other hand, the phenolic hydroxyl groups of tea polyphenols can capture free radicals for a long time, and the conjugated system in its molecular structure can stabilize the captured free radicals, prolonging the antioxidant cycle. At the same time, the antioxidant activity of natural phenolic hydroxyl groups can be sustained, compensating for the activity decay of traditional synthetic antioxidants after long-term use.

[0059] The principle of emergency antioxidants in extreme conditions: Under extreme conditions such as high temperature (≥130℃) and high shear, the molecular structure of emergency antioxidants (such as hydroxylamine ethers) can be rapidly activated. Through nucleophilic reactions with peroxy free radicals, they can efficiently capture highly active free radicals that traditional antioxidants cannot handle. This process can "fill the gap" when the activity of primary and secondary antioxidants is insufficient, avoid "oxidative bursts" in extreme environments, and form the "last line of defense" for antioxidant protection.

[0060] It achieves full-scenario antioxidant coverage, including free radical capture, hydrogen peroxide decomposition, long-term antioxidant effect, and extreme replenishment, which significantly reduces the oxidation rate of materials and extends the antioxidant life.

[0061] The oxygen barrier function is achieved through the synergistic effect of physical barrier properties of surface-modified nano-silica and chemical oxygen barrier properties of temperature-responsive oxygen barrier microcapsules, as follows:

[0062] After being modified with a silane coupling agent (such as KH550), nano-silica's surface lipophilic groups can tightly bind with polyethylene molecular chains, forming a uniformly dispersed nanoparticle barrier within the matrix. When oxygen molecules diffuse within the material, they must navigate through the labyrinthine path formed by the nanoparticles, significantly increasing the diffusion distance and thus reducing the oxygen permeation rate, achieving physical oxygen barrier at room temperature. Simultaneously, the high specific surface area of ​​the nanoparticles enhances the bonding force with the matrix, further improving the material's mechanical strength.

[0063] The microcapsules adopt a core-shell structure with a core material and a wall material. The glass transition temperature and melting temperature of the polycaprolactone wall material are adapted to the cable operating temperature: when the material operating temperature is ≥90℃, the polycaprolactone wall material softens and cracks, releasing the internal core material; the core material reacts with oxygen that has penetrated into the material, forming a chemical oxygen barrier layer by capturing oxygen molecules or inhibiting the combination of oxygen and free radicals, thus compensating for the weakening of the maze effect of nanoparticles at high temperatures.

[0064] It achieves dynamic adaptation between physical oxygen barrier at room temperature and chemical oxygen barrier at high temperature, covering the oxygen barrier requirements of cables under all operating conditions from room temperature storage to high temperature operation, and reducing oxygen-induced oxidation aging.

[0065] When heated, halogen-free flame retardants decompose and absorb heat, releasing water vapor. On the one hand, this heat absorption lowers the surface temperature of the material, inhibiting the combustion reaction; on the other hand, the water vapor dilutes the oxygen concentration in the combustion zone, and the decomposition products (magnesium oxide) form a dense inorganic coating layer on the material surface, blocking heat and oxygen transfer, thus achieving flame retardancy and smoke suppression. At the same time, the stearic acid coating on the surface can improve its compatibility with the polyethylene matrix, avoiding the decrease in mechanical properties caused by flame retardant agglomeration.

[0066] Example 2: The tea polyphenol grafted polyethylene was prepared by melt grafting with a grafting rate of 8%-12%. Diisopropylbenzene peroxide was used as an initiator, and the amount of initiator was 0.3 wt% of the total weight of tea polyphenols and polyethylene. The grafted product was subjected to Soxhlet extraction to remove ungrafted tea polyphenols.

[0067] Example 3: The temperature-responsive oxygen-barrier microcapsules were prepared by interfacial polymerization, and the number-average molecular weight of the wall material polycaprolactone was 10,000-20,000.

[0068] Example 4: The primary antioxidant is antioxidant 1010, and the secondary antioxidant is antioxidant 168. The primary antioxidant, the secondary antioxidant, and tea polyphenols are grafted onto polyethylene to form a chemically synthesized and naturally modified composite antioxidant system.

[0069] Example 5: The halogen-free flame retardant is magnesium hydroxide coated with stearic acid, with a particle size of 1μm-5μm, which synergistically enhances the flame retardant and smoke-suppressing performance of the material with surface-modified nano-silica; the processing aid is a compound of polyethylene wax and fluoroelastomer with a molecular weight of 1000-3000, and the weight ratio of polyethylene wax to fluoroelastomer is (1.8-2.2):1.

[0070] By employing the above technical solution, in the melt grafting method, dicumyl peroxide decomposes upon heating to generate free radicals, which initiate the formation of active sites on the polyethylene molecular chains. These sites then undergo a grafting reaction with the phenolic hydroxyl groups in the tea polyphenol molecules, bonding the tea polyphenols to the polyethylene chains. Controlling the initiator dosage to 0.3 wt% of the total weight of tea polyphenols and polyethylene balances grafting efficiency with the risk of polyethylene degradation, ensuring a stable grafting rate of 8%-12%. Soxhlet extraction involves repeated rinsing with organic solvents to remove ungrafted free tea polyphenols, preventing their migration and loss during subsequent processing. This ensures the long-term stable binding of tea polyphenols to the matrix, allowing them to continuously exert their antioxidant effects.

[0071] Interfacial polymerization utilizes the polymerization reaction between the core material (hindered amine oxygen barrier) and the wall material (polycaprolactone) at the oil-water interface to form core-shell microcapsules. The number-average molecular weight of the polycaprolactone wall material is controlled between 10,000 and 20,000, allowing for precise control of its melting temperature and mechanical properties: excessively high molecular weight results in an overly hard wall material that is difficult to rupture at 90°C; excessively low molecular weight leads to premature softening of the wall material and premature release of the core material. This structure allows the microcapsules to stably encapsulate the core material at room temperature. When the temperature is ≥90°C, the polycaprolactone wall material softens and ruptures, releasing the core material as needed to form an oxygen barrier layer, adapting to changes in cable operating temperature.

[0072] The primary antioxidant 1010 captures alkyl and peroxide free radicals through hindered phenolic hydroxyl groups, terminating the oxidation chain reaction; the auxiliary antioxidant 168 decomposes hydrogen peroxide, preventing the generation of new free radicals, and the two form a basic antioxidant synergy. In tea polyphenol-grafted polyethylene, the grafted tea polyphenols capture free radicals for a long time through natural phenolic hydroxyl groups, and the conjugated system of its molecular structure can stabilize the captured free radicals, compensating for the activity decay of 1010 and 168 after long-term use. The combination of the three forms a composite antioxidant system of "immediate blocking - source inhibition - long-term replenishment", broadening the antioxidant scenarios and extending the antioxidant cycle.

[0073] The halogen-free flame retardant is magnesium hydroxide coated with stearic acid. Stearic acid reduces the interfacial tension between magnesium hydroxide and the polyethylene matrix, reduces agglomeration, and improves compatibility. When heated, magnesium hydroxide decomposes, absorbs heat, and releases water vapor. This, combined with the physical barrier formed by the surface-modified nano-silica, enhances the flame retardant and smoke-suppressing effects through cooling, oxygen isolation, and covering. Among the processing aids, polyethylene wax with a molecular weight of 1000-3000 reduces melt viscosity and improves fluidity; fluoroelastomer improves interfacial compatibility and promotes the dispersion of nanoparticles and microcapsules. The two are compounded at a ratio of (1.8-2.2):1 to balance fluidity and dispersibility, ensuring processing stability and uniform distribution of functional components.

[0074] Example 6: A method for preparing a high-oxidation-resistant, long-life polyethylene cable sheath material, comprising the following steps:

[0075] Step 1: Dry the surface-modified nano-silica, high molecular weight high-density polyethylene, halogen-free flame retardant and temperature-responsive oxygen-barrier microcapsules respectively to remove moisture from the raw materials or prevent the functional components from prematurely degrading.

[0076] Step 2: Using a high-speed mixer, the base resin, processing aids, small molecule additives, dynamic functional additives, and solid particulate additives are added in stages in that order. By adjusting the mixing speed and time, the components are evenly dispersed to obtain the initial mixture.

[0077] Step 3: Add the initial mixture to a co-rotating twin-screw extruder, control the extruder temperature zones, screw speed and vacuum exhaust conditions to ensure that the material is fully melted and the functional components do not decompose. After the extruded material is cooled, it is granulated to obtain granules.

[0078] Step 4: Dry the granulated material, control the moisture content to a preset range, and then seal it in packaging and store it under specific conditions.

[0079] Example 7, the raw material pretreatment in step 1 specifically includes:

[0080] Step 11: The surface-modified nano-silica is dried in a vacuum oven at 80℃-100℃ for 3.5-4 hours;

[0081] Step 12: Place the high molecular weight high density polyethylene in a hot air dryer at 70℃-80℃ for 2-3 hours. After drying, the moisture content should be less than or equal to 0.05%.

[0082] Step 13: Dry the halogen-free flame retardant at 98℃-100℃ for 2-3 hours;

[0083] Step 14: The temperature-responsive oxygen-barrier microcapsules are placed in a vacuum dryer at 58℃-65℃ for 1.5-2 hours.

[0084] Step 15: Place the primary antioxidant, secondary antioxidant, emergency antioxidant, light stabilizer, acid absorber, and processing aid in a vacuum drying oven at 40℃-50℃ and dry for 1-1.5 hours.

[0085] Example 8, the method for preparing the temperature-responsive oxygen-barrier microcapsules includes the following steps:

[0086] Step a: Mix the hindered amine oxygen inhibitor with ethanol at a mass ratio of 1:4 and stir magnetically for 10-15 min to obtain a core material solution; add 2.5-3 wt% sodium dodecylbenzenesulfonate of the core material mass to the core material solution and continue stirring for 8-10 min to obtain a core material pre-dispersion.

[0087] Step b: Dissolve polycaprolactone in dichloromethane to prepare a wall material solution, and stir magnetically until completely dissolved;

[0088] Step c: Drop the core material pre-dispersion liquid from step a into the wall material solution from step b, and emulsify it for 30-40 minutes at 28℃-25℃ using a high-speed disperser at a speed of 2500rpm-3500rpm to form an oil-in-water emulsion.

[0089] Step d: Add deionized water dropwise to the oil-in-water emulsion, the amount of water added being twice the volume of the oil-in-water emulsion. At the same time, raise the temperature to 40℃-42℃ and stir at 400rpm-600rpm for 2-2.5h to allow the dichloromethane to fully evaporate and the PCL wall material to solidify and encapsulate the core material.

[0090] Step e: Centrifuge the solidified microcapsule suspension at 7000rpm-9000rpm for 10-12min and collect the lower layer of microcapsule particles.

[0091] Step f: Wash with deionized water 2-3 times to remove residual emulsifier on the surface; finally, dry in a vacuum drying oven at 55℃-60℃ for 3-4 hours to obtain particle size temperature-responsive oxygen barrier microcapsules.

[0092] Example 9, the specific operation of the initial mixing in step 2 is as follows: Using a high-speed mixer, first add the pretreated high molecular weight high-density polyethylene and processing aids, and mix at 450rpm-550rpm for 1-1.5min; then add the main antioxidant, auxiliary antioxidant, emergency antioxidant, light stabilizer and acid absorber, and mix at 800rpm-900rpm for 2-2.5min; next add Schiff base dynamic crosslinking agent and tea polyphenol grafted polyethylene, and mix at 1100rpm-1200rpm for 3-4min; finally add the pretreated surface-modified nano silica, furan-maleimide grafted polyethylene, temperature-responsive oxygen barrier microcapsules and halogen-free flame retardant, and mix at 1500rpm-2000rpm for 5-8min until the material temperature rises to 60-70℃ to obtain the initial mixture.

[0093] In Example 10, during the melt blending and granulation in step 3, a co-rotating twin-screw extruder was used. The temperatures of the extruder's feeding zone, melting zone, mixing zone, homogenizing zone, and die head were set to 140℃-150℃, 160℃-170℃, 175℃-185℃, 170℃-175℃, and 165℃-170℃, respectively.

[0094] The screw speed is controlled at 220-280 rpm, and a two-stage vacuum exhaust system is installed in the middle section of the extruder, with a vacuum degree of -0.08 to -0.09 MPa.

[0095] After being cooled by cooling water at 40℃-50℃, the extruded material is cut into cylindrical pellets of a set size by a pelletizer.

[0096] By adopting the above technical solution, different drying parameters are used for different raw materials. The core is to match the characteristics of the raw materials and avoid functional damage or performance defects.

[0097] Surface-modified nano-silica is vacuum dried at 80-100℃ for 3.5-4 hours to remove adsorbed water from the particle surface and prevent particle agglomeration due to moisture during melting, which would affect the oxygen barrier and reinforcement effects.

[0098] High molecular weight high density polyethylene is dried with hot air at 70-80℃ for 2-3 hours until the moisture content is less than or equal to 0.05%. This is to avoid the resin softening and clumping due to excessive drying temperature, and to remove moisture to prevent air bubbles from being generated during extrusion.

[0099] The halogen-free flame retardant is dried at 98-100℃ for 2-3 hours to remove surface free water, improve its compatibility with the polyethylene matrix, and reduce the decrease in mechanical properties caused by flame retardant agglomeration.

[0100] Temperature-responsive oxygen-barrier microcapsules are vacuum dried at 58-65℃ for 1.5-2 hours. Low-temperature drying can prevent the wall material (polycaprolactone) from softening in advance, prevent core material leakage, and ensure temperature-responsive function.

[0101] Small molecule additives (main antioxidants, processing aids, etc.) are vacuum dried at 40-50℃ for 1-1.5 hours to remove trace amounts of moisture to prevent clumping and ensure uniform dispersion during subsequent initial mixing.

[0102] The interface polymerization method achieves core material coating, wall material curing, and particle size control through multi-step control. The core principle is as follows:

[0103] Step a involves dissolving the hindered amine oxygen barrier in ethanol and adding sodium dodecylbenzene sulfonate (emulsifier) ​​to ensure uniform dispersion of the core material and form a stable pre-dispersion, laying the foundation for subsequent coating.

[0104] Step b involves dissolving polycaprolactone in dichloromethane to form a homogeneous wall material solution, ensuring that the wall material can fully encapsulate the core material.

[0105] Step c involves emulsifying at 25-28℃ and 2500-3500 rpm for 30-40 minutes. The droplet size of the emulsion is adjusted by the rotation speed, thereby controlling the final particle size of the microcapsules (1-3 μm) to form a stable oil-in-water emulsion.

[0106] Step d involves adding deionized water and heating to 40-42℃, which accelerates the volatilization of dichloromethane, allowing the polycaprolactone wall material to gradually solidify and tightly wrap the core material to form a core-shell structure. Low-speed stirring at 400-600 rpm avoids emulsion stratification and ensures uniform coating of the wall material.

[0107] Step e involves centrifuging at 7000-9000 rpm for 10-12 minutes to quickly separate the microcapsule particles; step f involves washing to remove residual emulsifier and vacuum drying at 55-60℃ for 3-4 hours to avoid high-temperature damage to the wall material, ultimately yielding microcapsules with stable structure and sensitive temperature response.

[0108] The core of staged feeding and gradient rotation speed design is to optimize dispersion efficiency based on component characteristics and avoid agglomeration or functional damage.

[0109] First, add the base resin and processing aids, and mix at a low speed of 450-550 rpm for 1-1.5 min to allow the processing aids to uniformly coat the resin particles and reduce the dispersion resistance of subsequent small molecule aids and solid particles.

[0110] Add small molecule additives (main antioxidants, light stabilizers, etc.) and mix at a medium speed of 800-900 rpm for 2-2.5 minutes. This ensures that the small molecule additives are evenly attached to the resin surface and avoids the additives from scattering and being lost due to high speed.

[0111] Add dynamic functional additives (Schiff base crosslinking agent, tea polyphenol grafted polyethylene), mix at a high speed of 1100-1200 rpm for 3-4 minutes, and use appropriate shear force to initially disperse the dynamic additives, while avoiding excessive speed to avoid damaging the dynamic bond structure.

[0112] Finally, add solid particle additives (nano silica, microcapsules, flame retardants) and mix at high speed of 1500-2000 rpm for 5-8 minutes until the material temperature reaches 60-70℃. High temperature can promote the initial bonding between particles and matrix, and high-speed shear force breaks up particle agglomeration, ensuring uniform dispersion of solid components and finally obtaining a homogeneous initial mixture.

[0113] By employing temperature zoning, rotation speed control, and vacuum degassing, a balance is struck between sufficient melting and functional protection. The core principle is as follows:

[0114] Temperature zone design: feeding zone 140-150℃ low temperature to prevent resin bridging; melting zone 160-170℃ gradually increases temperature to melt the resin; mixing zone 175-185℃ ensures that the material is fully mixed and does not exceed the decomposition temperature of Schiff base dynamic bonds and microcapsules; homogenization zone 170-175℃ and die head 165-170℃ cool down to avoid excessive melting of material and failure of functional components;

[0115] Screw speed 220-280 rpm: Moderate speed can provide sufficient shear force to promote secondary dispersion of components such as nanoparticles and microcapsules, while avoiding excessive shear heat caused by excessive speed, which may lead to resin degradation or dynamic bond breakage.

[0116] Level 2 vacuum exhaust (vacuum degree -0.08 to -0.09 MPa): can remove low molecular weight volatiles generated during the melting process (such as antioxidant decomposition products and residual solvents), avoid bubbles in the granulated material, and improve the density and mechanical properties of the product.

[0117] The following specific embodiments illustrate the implementation principle of the present invention:

[0118] High-oxidation-resistant, long-life polyethylene cable sheath material, by weight percentage, comprises the following components:

[0119] High molecular weight high-density polyethylene: melt flow rate of 0.2 g / 10 min, content of 80.0 wt%;

[0120] Surface-modified nano-silica: KH550 was used for surface modification, with a particle size of 20 nm and a content of 1.5 wt%.

[0121] Furan-maleimide grafted polyethylene: grafting rate 7%, content 2.8 wt%;

[0122] Schiff base-based dynamic crosslinking agent: specifically, bis(salicylic acid) ethylenediamine Schiff base, with a content of 0.4 wt%;

[0123] Tea polyphenols grafted onto polyethylene: prepared by melt grafting method, with a grafting rate of 10% and a content of 0.7 wt%;

[0124] Temperature-responsive oxygen-barrier microcapsules: The core material is the hindered amine oxygen barrier UV-3808PP5, and the wall material is polycaprolactone with a number-average molecular weight of 15,000, a particle size of 2 μm, and a content of 0.6 wt%.

[0125] Main antioxidant: Specifically, antioxidant 1010, with a content of 0.3 wt%;

[0126] Co-antioxidant: Specifically, antioxidant 168, with a content of 0.4 wt%;

[0127] Emergency antioxidant: specifically, hydroxylamine ether compounds, at a content of 0.15 wt%;

[0128] Light stabilizer: It is a compound of light stabilizer 770 and ultraviolet absorber UV-531 in a 1:1 weight ratio, with a content of 0.3 wt%.

[0129] Halogen-free flame retardant: specifically, magnesium hydroxide coated with stearic acid, with a particle size of 3μm and a content of 12.85wt%;

[0130] Processing aids: composed of polyethylene wax with a molecular weight of 2000 and fluoroelastomer in a weight ratio of 2:1, with a content of 0.6 wt%.

[0131] Acid absorbent: specifically zinc stearate, with a content of 0.15 wt%.

[0132] Preparation process:

[0133] Raw material pretreatment: Surface-modified nano-silica was dried in a vacuum oven at 90℃ for 4 hours; high molecular weight high-density polyethylene was dried in a hot air dryer at 75℃ for 2.5 hours, and the moisture content after drying was controlled at 0.04%; halogen-free flame retardant was dried in a dryer at 99℃ for 2.5 hours; temperature-responsive oxygen-barrier microcapsules were dried in a vacuum dryer at 60℃ for 1.8 hours; main antioxidant, auxiliary antioxidant, emergency antioxidant, light stabilizer, acid absorber and processing aid were all dried in a vacuum dryer at 45℃ for 1.2 hours.

[0134] Initial mixing: Using a 100L high-speed mixer, first add pretreated high molecular weight high-density polyethylene and processing aids, and mix at 500 rpm for 1.2 min; then add pretreated primary antioxidant, secondary antioxidant, emergency antioxidant, light stabilizer and acid absorber, and adjust the speed to 850 rpm and mix for 2.2 min; next add Schiff base dynamic crosslinking agent and tea polyphenol grafted polyethylene, and increase the speed to 1150 rpm and mix for 3.5 min; finally add pretreated surface-modified nano silica, furan-maleimide grafted polyethylene, temperature-responsive oxygen barrier microcapsules and halogen-free flame retardant, and adjust the speed to 1800 rpm and mix for 6 min until the material temperature rises to 65℃ to obtain the initial mixture.

[0135] Melt blending and granulation: A co-rotating twin-screw extruder with a screw diameter of 65mm was selected. The extruder temperature was set by zone as follows: feeding zone 145℃, melting zone 165℃, mixing zone 180℃, homogenizing zone 172℃, and die head 168℃. The screw speed was controlled at 250rpm. Two-stage vacuum exhaust was set in the middle section of the extruder, and the vacuum degree was maintained at -0.085MPa. The strip material formed by extrusion was cooled by cooling water at 45℃ and then cut into 3×3mm cylindrical pellets by a pelletizer.

[0136] Post-processing and packaging: The cut granules are placed in a fluidized bed dryer and dried for 35 minutes at 55℃ and 1.5m / s wind speed. The moisture content of the dried granules is controlled at 0.04%. They are sealed in aluminum foil composite bags at a specification of 25kg per bag and stored in a cool and dry environment at 28℃ after packaging.

[0137] The product performance test results are shown in Table 1:

[0138] Table 1

[0139] Performance testing items Test Standards Test Results Oxidation induction period (OIT) at 135℃ GB / T19466.6 38.5min Tensile strength (23℃) GB / T1040.3 22.8MPa Elongation at break (23℃) GB / T1040.3 650% Oxygen permeability at 100℃ GB / T1038 <![CDATA[0.85cm 3 ·mm / (m 2 ·d·atm)]]> Oxygen Index (LOI) GB / T2406 29.5% Tensile strength retention rate after 10 cycles of thermal cycling at 100℃ Test after 10 cycles of heating at 100°C and cooling to room temperature 92.3% Elongation at break retention rate after 10 cycles of thermal cycling at 100℃ Homemade method 90.5% Predicted lifespan after accelerated aging (135℃ thermo-oxidation) Derivation of Arrhenius's formula 45 years Smoke Density Rating (SDR) GB / T8627 48

[0140] The performance comparison results with traditional polyethylene cable sheath materials are shown in Table 2:

[0141] Table 2

[0142] Performance testing items Test Standards Traditional products (standard formula) Product in this embodiment Performance improvement Oxidation induction period (OIT) at 135℃ GB / T19466.6 15.2min 38.5min +153.3% Tensile strength (23℃) GB / T1040.3 19.5MPa 22.8MPa +16.9% Elongation at break (23℃) GB / T1040.3 520% 650% +25.0% Oxygen permeability at 100℃ GB / T1038 <![CDATA[2.3cm 3 ·mm / (m 2 ·d·atm)]]> <![CDATA[0.85cm 3 ·mm / (m 2 ·d·atm)]]> -63.0% Oxygen Index (LOI) GB / T2406 26.0% 29.5% +13.5% Tensile strength retention rate after 10 cycles of thermal cycling at 100℃ Test after 10 cycles of heating at 100°C and cooling to room temperature 75.1% 92.3% +22.9% Elongation at break retention rate after 10 cycles of thermal cycling at 100℃ Test after 10 cycles of heating at 100°C and cooling to room temperature 68.3% 90.5% +32.5% Predicted lifespan after accelerated aging (135℃ thermo-oxidation) Arrhenius formula 22 years 45 years +104.5% Smoke Density Rating (SDR) GB / T8627 65 48 -26.2%

[0143] The traditional product formula consists of 92wt% ordinary HDPE, 0.2wt% antioxidant 1010, 0.3wt% antioxidant 168, 0.2wt% light stabilizer UV-531, 7wt% uncoated magnesium hydroxide, and 0.3wt% polyethylene wax. It does not contain dynamic crosslinking agent, tea polyphenol grafted PE, temperature-responsive microcapsules, or surface-modified nano-SiO2.

[0144] The above are all preferred embodiments of the present invention and are not intended to limit the scope of protection of the present invention. Therefore, all equivalent changes made in accordance with the structure, shape and principle of the present invention should be covered within the scope of protection of the present invention.

Claims

1. A high-oxidation-resistant, long-life polyethylene cable sheath material, characterized in that, It includes the following components as a percentage of the total weight: High molecular weight high-density polyethylene 78.0wt%-84.0wt%, surface-modified nano-silica 0.8wt%-2.5wt%, furan-maleimide grafted polyethylene 1.6wt%-4.2wt%, Schiff base dynamic crosslinking agent 0.3wt%-0.6wt%, tea polyphenol grafted polyethylene 0.5wt%-1.0wt%, temperature-responsive oxygen-barrier microcapsules 0.4wt%-0.8wt%, main antioxidant 0.2wt%-0.4wt%, auxiliary antioxidant 0.3wt%-0.5wt%, emergency antioxidant 0.1wt%-0.2wt%, light stabilizer 0.2wt%-0.4wt%, halogen-free flame retardant 12.0wt%-21.0wt%, processing aid 0.4wt%-0.8wt%, acid absorbent 0.1wt%-0.2wt%; The Schiff base dynamic crosslinking agent is a bis(salicylaldehyde) ethylenediamine Schiff base, which forms a double dynamic bond network with the DA bonds of furan-maleimide grafted polyethylene. The temperature-responsive oxygen barrier microcapsules have a core-wall structure. The core material is a hindered amine oxygen barrier agent, and the wall material is polycaprolactone. The core-wall material weight ratio is 3:2, and the particle size is 1μm-3μm. When the material operating temperature is greater than or equal to 90℃, the core material is automatically ruptured and released to form an oxygen barrier layer.

2. The high oxidation resistance and long service life polyethylene cable sheath material according to claim 1, characterized in that, The tea polyphenol-grafted polyethylene was prepared by melt grafting with a grafting rate of 8%-12%. Diisopropylbenzene peroxide was used as an initiator, and the amount of initiator was 0.3 wt% of the total weight of tea polyphenols and polyethylene. The grafted product was subjected to Soxhlet extraction to remove ungrafted tea polyphenols.

3. The high oxidation resistance and long life polyethylene cable sheath material according to claim 2, characterized in that, The temperature-responsive oxygen-barrier microcapsules were prepared by interfacial polymerization, and the wall material, polycaprolactone, had a number-average molecular weight of 10,000-20,000.

4. The high oxidation resistance and long life polyethylene cable sheath material according to claim 3, characterized in that, The primary antioxidant is antioxidant 1010, and the secondary antioxidant is antioxidant 168. The primary antioxidant, secondary antioxidant, and tea polyphenols grafted onto polyethylene form a composite antioxidant system that combines chemical synthesis and natural modification.

5. The high oxidation resistance and long service life polyethylene cable sheath material according to claim 4, characterized in that, The halogen-free flame retardant is magnesium hydroxide coated with stearic acid, with a particle size of 1μm-5μm, which synergistically enhances the flame retardant and smoke-suppressing performance of the material with surface-modified nano-silica; the processing aid is a compound of polyethylene wax and fluoroelastomer with a molecular weight of 1000-3000, with a weight ratio of polyethylene wax to fluoroelastomer of (1.8-2.2):

1.

6. A method for preparing the high oxidation resistance and long life polyethylene cable sheath material as described in claim 5, characterized in that, Includes the following steps: Step 1: Dry the surface-modified nano-silica, high molecular weight high-density polyethylene, halogen-free flame retardant and temperature-responsive oxygen-barrier microcapsules respectively to remove moisture from the raw materials or prevent the functional components from prematurely degrading. Step 2: Using a high-speed mixer, the base resin, processing aids, small molecule additives, dynamic functional additives, and solid particulate additives are added in stages in that order. By adjusting the mixing speed and time, the components are evenly dispersed to obtain the initial mixture. Step 3: Add the initial mixture to a co-rotating twin-screw extruder, control the extruder temperature zones, screw speed and vacuum exhaust conditions to ensure that the material is fully melted and the functional components do not decompose. After the extruded material is cooled, it is granulated to obtain granules. Step 4: Dry the granulated material, control the moisture content to a preset range, and then seal it in packaging and store it under specific conditions.

7. The preparation method according to claim 6, characterized in that, Step 1, the raw material pretreatment, specifically includes: Step 11: The surface-modified nano-silica is dried in a vacuum oven at 80℃-100℃ for 3.5-4 hours; Step 12: Place the high molecular weight high density polyethylene in a hot air dryer at 70℃-80℃ for 2-3 hours. After drying, the moisture content should be less than or equal to 0.05%. Step 13: Dry the halogen-free flame retardant at 98℃-100℃ for 2-3 hours; Step 14: The temperature-responsive oxygen-barrier microcapsules are vacuum dried at 58℃-65℃ for 1.5-2 hours. Step 15: Place the primary antioxidant, secondary antioxidant, emergency antioxidant, light stabilizer, acid absorber, and processing aid in a vacuum drying oven at 40℃-50℃ and dry for 1-1.5 hours.

8. The preparation method according to claim 7, characterized in that, The method for preparing the temperature-responsive oxygen-barrier microcapsules includes the following steps: Step a: Mix the hindered amine oxygen inhibitor with ethanol at a mass ratio of 1:4 and stir magnetically for 10-15 min to obtain a core material solution; add 2.5-3 wt% sodium dodecylbenzenesulfonate of the core material mass to the core material solution and continue stirring for 8-10 min to obtain a core material pre-dispersion. Step b: Dissolve polycaprolactone in dichloromethane to prepare a wall material solution, and stir magnetically until completely dissolved; Step c: Drop the core material pre-dispersion liquid from step a into the wall material solution from step b, and emulsify it for 30-40 minutes at 28℃-25℃ using a high-speed disperser at a speed of 2500rpm-3500rpm to form an oil-in-water emulsion. Step d: Add deionized water dropwise to the oil-in-water emulsion, the amount of water added being twice the volume of the oil-in-water emulsion. At the same time, raise the temperature to 40℃-42℃ and stir at 400rpm-600rpm for 2-2.5h to allow the dichloromethane to fully evaporate and the PCL wall material to solidify and encapsulate the core material. Step e: Centrifuge the solidified microcapsule suspension at 7000rpm-9000rpm for 10-12min and collect the lower layer of microcapsule particles. Step f: Wash with deionized water 2-3 times to remove residual emulsifier on the surface; finally, dry in a vacuum drying oven at 55℃-60℃ for 3-4 hours to obtain particle size temperature-responsive oxygen barrier microcapsules.

9. The preparation method according to claim 8, characterized in that, The specific operation of the initial mixing in step 2 is as follows: Using a high-speed mixer, first add the pretreated high molecular weight high-density polyethylene and processing aids, and mix at 450rpm-550rpm for 1-1.5min; then add the main antioxidant, auxiliary antioxidant, emergency antioxidant, light stabilizer and acid absorber, and mix at 800rpm-900rpm for 2-2.5min; next add Schiff base dynamic crosslinking agent and tea polyphenol grafted polyethylene, and mix at 1100rpm-1200rpm for 3-4min; finally add the pretreated surface-modified nano silica, furan-maleimide grafted polyethylene, temperature-responsive oxygen barrier microcapsules and halogen-free flame retardant, and mix at 1500rpm-2000rpm for 5-8min until the material temperature rises to 60-70℃ to obtain the initial mixture.

10. The preparation method according to claim 9, characterized in that, In step 3, melt blending and granulation, a co-rotating twin-screw extruder is used. The temperatures of the extruder's feeding zone, melting zone, mixing zone, homogenizing zone, and die head are set to 140℃-150℃, 160℃-170℃, 175℃-185℃, 170℃-175℃, and 165℃-170℃, respectively. The screw speed is controlled at 220-280 rpm, and a two-stage vacuum exhaust system is installed in the middle section of the extruder, with a vacuum degree of -0.08 to -0.09 MPa. After the extruded material is cooled by cooling water at 40℃-50℃, it is cut into cylindrical pellets of a set size by a pelletizer.

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