A composite additive for improving the high-transparency, weather resistance and recyclability of linear polyethylene film and a preparation method thereof

Abstract

The application relates to a composite additive for improving the high-transparency, weather resistance and recyclability of linear polyethylene film material and a preparation method thereof, and belongs to the technical field of polymer material processing additives.The application synchronously realizes high-transparency and long-acting weather resistance of linear polyethylene film by designing a compatibility and transparency nucleation system, a yellowing-resistant and weather-resistant stable system and a polyolefin-based dynamic covalent bond chain repair system, and the three systems are matched, and the triple requirements of high value and cyclic recycling are met, and the application has extremely strong industrialization popularization value.

Description

Technical Field

[0001] This invention relates to the field of polymer processing aids, and more particularly to linear polyethylene films. Specifically, it relates to a multifunctional composite aid that simultaneously improves the high transparency, weather resistance, and recyclability of linear polyethylene films, and its preparation method. Background Technology

[0002] Linear polyethylene (LLDPE / LDPE / mLLDPE) films are widely used in agricultural coverings, food packaging, and everyday commodity packaging due to their excellent mechanical properties, good heat-sealing properties, and low content. With rising consumer demand and increasingly stringent environmental requirements, the market is placing higher demands on film performance: firstly, better transparency and visual appeal (high transparency and low fogging); secondly, longer outdoor service life, especially resistance to UV aging; and thirdly, compliance with circular economy policies, requiring easy recycling and reuse to reduce "white pollution."

[0003] Currently, the industry typically uses single-function additives to improve a specific property. For example, nucleating agents (such as sorbitol derivatives) are added to improve transparency and gloss; UV absorbers and hindered amine light stabilizers are added to enhance weather resistance. However, these additives often present intractable technical problems. Poor compatibility and dispersibility: When multiple small-molecule powder additives are directly mixed with resin, the large differences in polarity can easily lead to agglomeration and uneven dispersion. This not only fails to achieve the expected function but also affects the uniformity of film performance and even increases film haze. Mutual constraints on performance: Simple compounding of multiple additives can easily produce antagonistic effects. Some additives may have a negative impact on another property. For example, some ultraviolet absorbers may yellow under long-term light exposure, directly affecting the initial transparency and long-term optical properties of the film. Some nucleating agents may change the crystal morphology of polyethylene, resulting in uneven spherulite size, which in turn affects the toughness and processing stability of the film. Damage to recyclability: After outdoor aging or multiple heat processing, the molecular chains of the film break, the molecular weight decreases, and the mechanical properties are severely reduced, losing their recycling value. Traditional additive systems can only delay aging and cannot repair the molecular chain damage caused by aging or processing, resulting in a sharp drop in the performance of recycled materials. They can usually only be used in a downgraded manner and cannot achieve high-value recycling.

[0004] In the prior art, CN114773699A discloses a composite additive for improving the weather resistance and tensile properties of linear polyethylene film materials, which only solves the problems of weather resistance and mechanical properties. In order to balance high transparency and recyclability, CN107987321A discloses a composite additive for high-gloss transparent linear low-density polyethylene film, which only focuses on transparency modification and does not solve the problems of weather resistance and recycling. Existing self-healing polyethylene related technologies mostly involve grafting modification of the resin matrix to introduce dynamic covalent bonds, which is complex and costly. Moreover, it does not consider the synergistic compatibility between self-healing components and anti-reflective and weather-resistant components, which can easily lead to a decline in the optical properties of the film. Therefore, it cannot be directly used as a general-purpose additive in the existing film processing technology.

[0005] Therefore, developing an integrated composite additive that can synergistically improve the transparency and weather resistance of linear polyethylene films, actively repair molecular chains, and ensure the material's ability to be processed multiple times has become a pressing technical challenge in this field. Summary of the Invention

[0006] To address the shortcomings of existing technologies, this invention proposes a composite additive and its preparation method for improving the high permeability, weather resistance, and recyclability of linear polyethylene film materials. This additive can solve the above three requirements at once, and the functional components have synergistic effects, good dispersibility, and are easy to use.

[0007] The technical problem to be solved by the present invention is achieved through the following technical solution: A composite additive for improving the high transparency, weather resistance and recyclability of linear polyethylene film materials, comprising the following components by weight: 0.5-15 parts of a transparency-enhancing and nucleating component, 1-20 parts of a weather-stabilizing component, 2-25 parts of a dynamic covalent bond repair component, 50-95 parts of a carrier resin, and 0.1-8 parts of a dispersing agent.

[0008] The dynamic covalent bond repair component is a polyolefin-based polymer grafted with reversible dynamic covalent bonds. The polyolefin backbone is homologous to the polyethylene matrix, ensuring complete compatibility with the matrix and eliminating precipitation and haze effects. The grafted reversible dynamic covalent bonds can undergo reversible breakage and reconstruction within the conventional heat treatment temperature range of polyethylene (120-220℃). During film processing and recycling, it actively bridges the broken polyolefin molecular chains, repairing molecular chain damage caused by aging and heat treatment, effectively solving the problem of sudden performance degradation in recycled materials. It can also synergize with the weather resistance system to delay molecular chain breakage and further improve long-term weather resistance.

[0009] The antireflective nucleating component is an organic nucleating agent system compatible with the linear polyethylene matrix. It can efficiently induce the formation of uniform and fine spherulites in polyethylene, reduce light scattering, and achieve high transparency and low haze. At the same time, through compatibility design, it avoids antagonism with weather-resistant components and chain repair components, and does not damage the weather resistance and mechanical properties of the film.

[0010] The weather-resistant stabilizing component is a yellowing-resistant composite stabilizing system containing light stabilizers and antioxidants. Through the design of yellowing-resistant and non-migratory components, a triple protection system of ultraviolet shielding, free radical capture, and heat aging resistance is constructed, which effectively delays the photo-oxidative aging of the film. At the same time, it does not yellow or affect the transparency of the film after long-term use. It has a synergistic effect with antireflective nucleating components and chain repair components, and there is no performance mutual exclusion.

[0011] The reversible dynamic covalent bond includes at least one of the following: DA dynamic covalent bond, disulfide bond, diselenide bond, transesterification bond, and acylhydrazone bond. All of these are types of dynamic covalent bonds that can achieve reversible reactions at the heat treatment temperature of polyethylene.

[0012] Furthermore, the dynamic covalent bond repair component is at least one of furan-maleimide DA dynamically covalently modified polyethylene wax and disulfide bond modified hyperbranched polyethylene. Both are polyolefin skeleton modifications, have excellent compatibility with the polyethylene matrix, and the dynamic bond reversible reaction temperature is completely matched with the polyethylene processing temperature, resulting in high repair efficiency.

[0013] Furthermore, the dynamic covalent bond repair component is a compound of furan-maleimide dynamically covalently modified polyethylene wax and disulfide-modified hyperbranched polyethylene in a mass ratio of (1-10):(1-8). The furan-maleimide dynamically covalently modified polyethylene wax is a modified polyethylene wax containing DA covalent bonds, obtained by grafting maleic acid glycosides, furanylamine, and bismaleimide crosslinking. The disulfide-modified hyperbranched polyethylene is obtained by end-capping hydroxyl-terminated hyperbranched polyethylene with carboxylic acid containing disulfide bonds, with a number average molecular weight of 2000-8000 g / mol and a disulfide bond content ≥0.5 mmol / g.

[0014] In this invention, the anti-reflective nucleating component is at least one of sorbitol derivative nucleating agents, organophosphate nucleating agents, hyperbranched polymer nucleating agents, and rosin ester nucleating agents, all of which are types of organic nucleating agents that can be used in polyethylene.

[0015] Furthermore, the antireflective nucleating component is a compound of hydrophobically modified sorbitol derivative and hyperbranched polyester nucleating agent in a mass ratio of (1-8):(1-5). The hydrophobically modified sorbitol derivative is a 1,3:2,4-dibenzyl sorbitol nucleating agent obtained by hydrophobic modification with long alkyl silanes, and the modified powder has a water contact angle ≥100°. The hyperbranched polyester nucleating agent is a hydroxyl-terminated hyperbranched polyester obtained by end-capping modification with long-chain fatty acids, with a molecular weight of 1000-8000 g / mol and a branching degree ≥0.7.

[0016] In this invention, the weather-resistant stabilizing component is a compound of at least two of the following: hindered amine light stabilizers, benzotriazole UV absorbers, benzophenone UV absorbers, hindered phenolic antioxidants, and phosphite antioxidants, to meet the weather resistance requirements of different scenarios.

[0017] Furthermore, the weather-stabilizing component is a high molecular weight hindered amine light stabilizer, a long-chain alkyl-modified benzotriazole UV absorber, and a composite antioxidant compounded in a mass ratio of (1-10):(1-8):(0.2-5). The high molecular weight hindered amine light stabilizer is a non-migratory hindered amine light stabilizer with a number average molecular weight ≥2000 g / mol. The long-chain alkyl-modified benzotriazole UV absorber is a benzotriazole derivative containing C4-C18 alkyl groups. The composite antioxidant is a hindered phenolic primary antioxidant and a phosphite secondary antioxidant compounded in a mass ratio of 1:(0.5-2).

[0018] In this invention, the carrier resin is at least one of linear low-density polyethylene (LLDPE), low-density polyethylene (LDPE), and metallocene linear low-density polyethylene (mLLDPE), with a melt flow rate of 0.5-10 g / 10 min (190℃ / 2.16 kg). It is homologous to the film matrix resin, has no interface problems, and does not affect the optical and mechanical properties of the film. The dispersing agent is at least one of polyethylene wax, polypropylene wax, stearate, silane coupling agent, and titanate coupling agent, used to improve the dispersibility and compatibility of the powder additives and avoid agglomeration.

[0019] Preferably, the composite additive comprises the following components by weight: 2-8 parts of a penetration-enhancing and nucleating component, 3-12 parts of a weather-stabilizing component, 5-15 parts of a dynamic covalent bond repair component, 60-85 parts of a carrier resin, and 1-5 parts of a dispersing agent.

[0020] Based on the above raw materials, a method for preparing a composite additive to improve the high transparency, weather resistance, and recyclability of linear polyethylene film includes the following steps: S1 Powder Surface Modification: Powder raw materials containing anti-reflective nucleating components and weather-resistant stabilizing components are mixed with dispersants, heated to 60-120℃, and mixed at high speed to complete in-situ coating modification of the powder surface, thus obtaining modified composite powder. This solves the compatibility problem between powder additives and resins and avoids agglomeration. S2 Premix: Modified composite powder, dynamic covalent bond repair component and carrier resin are uniformly mixed to obtain premix; S3 Melt Molding: The premixed material is melt-blended, extruded, and granulated to obtain the composite additive. The final product is a masterbatch type additive, which is free of dust pollution, easy to use, and compatible with existing industrial production processes.

[0021] In step S1, the high-speed mixing speed is 1000-2000 r / min and the mixing time is 5-30 min; in step S2, the mixing speed is 500-1200 r / min and the mixing time is 3-15 min; in step S3, a twin-screw extruder is used for melt extrusion, with an extrusion temperature of 150-200℃ and a main extruder speed of 200-500 r / min.

[0022] Based on the above raw materials and preparation process, the obtained composite additive is applied to the processing modification of linear polyethylene materials, wherein the linear polyethylene materials include at least one of linear low-density polyethylene (LLDPE), low-density polyethylene (LDPE), and metallocene linear low-density polyethylene (mLLDPE). The amount of composite additive added is 0.5%-10% of the total mass of the linear polyethylene material. It can be widely used in the processing of various polyethylene products such as films, sheets, and injection molding, and is especially suitable for blown film and casting processing of film products.

[0023] This invention combines dynamic covalent chemistry with the principles of Norish photodegradation of polyolefins, proposing a dispersed dynamic bond repair approach. It selects thermoresponsive dynamic covalent bonds such as DA bonds and disulfide bonds, whose reversible reaction temperatures perfectly match the conventional processing range of polyethylene. This allows for bridging broken molecular chains during processing, while the weather-resistant system blocks the UV-induced Norish degradation chain reaction, reducing the source of molecular chain breakage. The two work together to achieve simultaneous repair and protection, thus realizing active and reversible repair of aging damage. Furthermore, because these dynamic bond components are modified using a polyolefin homologous backbone graft, their solubility is almost identical to that of the low-density polyethylene matrix, achieving molecular-level compatibility without affecting film transparency or causing performance antagonism.

[0024] In addition, the core reason for the sharp drop in mechanical properties of polyethylene after aging and multiple processing is the decrease in number-average molecular weight and the widening of molecular weight distribution caused by molecular chain breakage. Only by repairing the broken molecular chains and maintaining molecular weight stability can the performance of recycled materials be fundamentally guaranteed. Based on the above principle, the dynamic covalent bond of this solution can re-bridge the broken molecular chain ends through a reversible reaction during the hot processing, maintain the molecular weight stability of the matrix, and thus achieve a high retention rate of mechanical properties after multiple cycles of processing.

[0025] Moreover, UV absorbers can convert UV light energy into harmless heat energy through intramolecular proton transfer, avoiding photodegradation. Light stabilizers, through recycling, continuously capture and degrade free radicals generated by the Norish photodegradation reaction, decompose hydrogen peroxide, and work in conjunction with antioxidants to inhibit thermo-oxidative aging, forming a more comprehensive protective effect.

[0026] In this invention, based on the theory of polymer crystallization, polyethylene crystallization is divided into homogeneous nucleation and heterogeneous nucleation. Homogeneous nucleation requires high supercooling, resulting in large and unevenly distributed spherulites. When visible light passes through, strong light scattering occurs, directly leading to high film haze and low transmittance. In contrast, efficient heterogeneous nucleating agents can significantly reduce the nucleation barrier, forming a large number of uniform crystal nuclei at low supercooling, inducing the formation of fine spherulites smaller than the wavelength of visible light. This significantly reduces light scattering while improving crystallinity, achieving high transmittance and low haze. The sorbitol derivatives, organophosphates, and hyperbranched polymer nucleating agents selected in this application are all efficient heterogeneous nucleating agents for linear polyethylene, which can stably improve film transmittance and reduce haze. Meanwhile, by modifying the nucleating agent with long alkyl hydrophobicity and using the long-chain fatty acid-terminated hyperbranched nucleating agent, the polarity of the nucleating agent is greatly reduced, making its solubility parameters highly matched with the polyethylene matrix. This avoids the agglomeration of small molecule nucleating agents and their poor compatibility with the matrix, while also avoiding the side effects of traditional nucleating agents that increase transparency and reduce toughness, thus ensuring the stability of nucleation efficiency and optical performance.

[0027] Compared with the prior art, the present invention has the following advantages: (1) This application achieves simultaneous improvement of three properties: high transparency, UV aging resistance, and recyclability through the design of homologous polyolefin chain repair components, compatibility anti-reflection system, and yellowing and weather resistance system. It can make the light transmittance of linear polyethylene film ≥94%, haze ≤3%, mechanical property retention rate ≥90% after 1000 h UV aging, and mechanical property retention rate ≥85% after 3 cycles of processing; (2) This application introduces a polyolefin-based dynamic covalent bond chain repair system into a multifunctional composite additive for polyethylene. Without modifying the base resin, the active repair of molecular chain damage can be achieved in the conventional processing process simply by adding the additive. This solves the problem of the sudden drop in performance of traditional polyethylene recycled materials, realizes the multiple high-value recycling of polyethylene film, and greatly reduces white pollution. (3) This application makes the composite additive into a masterbatch formulation with an addition amount of only 0.5%-10%, which can be directly mixed with polyethylene resin without changing the existing production equipment and processing technology. There is no dust pollution or precipitation risk. It can be widely used in almost all polyethylene film application scenarios such as food packaging, agricultural greenhouse film, and outdoor packaging, and has extremely strong industrial promotion value. Attached Figure Description

[0028] Figure 1 Comparison diagrams of the optical performance of embodiments in this application (Example 1 and Comparative Examples 5-7); Figure 2 The diagram shows a comparison of the weather resistance, recyclability, and yellowing performance of the embodiments in this application (Example 1 and Comparative Examples 5-7). Detailed Implementation

[0029] The present invention will be further described below with reference to the accompanying drawings and specific preferred embodiments, but this does not limit the scope of protection of the present invention. Example 1

[0030] This embodiment provides a composite additive to improve the high transparency, weather resistance, and recyclability of linear polyethylene film materials. The raw material components, by weight, are: Four parts of the anti-reflection nucleating component: 2.5 parts of octadecyltrimethoxysilane hydrophobically modified sorbitol derivative and 1.5 parts of stearic acid-terminated hyperbranched polyester nucleating agent; Weather-stabilizing components (7 parts): hindered amine light stabilizer HALS 944 (3.5 parts), ultraviolet absorber UV-329 (2.5 parts), and a compound of hindered phenolic antioxidant 1010 and phosphite antioxidant 168 (1 part by mass ratio 1:1). 10 parts of dynamic covalent bond repair components: 6 parts of furan-maleimide DA dynamically covalent bond modified polyethylene wax, and 4 parts of disulfide bond modified hyperbranched polyethylene; 76 parts of carrier resin: linear low-density polyethylene (LLDPE) (film grade, melt flow rate 2 g / 10 min, 190℃ / 2.16 kg). Dispersing agent 3 parts: polyethylene wax 1.5 parts, zinc stearate 0.8 parts, vinyltriethoxysilane 0.7 parts.

[0031] Of the aforementioned raw materials, some can be purchased directly, while others are prepared using commercially available raw materials.

[0032] 1.1 Preparation methods of some core raw materials 1.1.1 Preparation of octadecyltrimethoxysilane hydrophobically modified sorbitol derivatives ① Raw material pretreatment: Place commercially available 1,3:2,4-di(3,4-dimethylbenzyl)sorbitol (DMDBS, nucleating agent 3988) in a vacuum drying oven and dry it at 80℃ for 4 h to remove the adsorbed moisture on the powder surface and set it aside for later use. ② Dry in-situ modification: Add the dried DMDBS powder to a high-speed mixer, start stirring at low speed (300 r / min), and simultaneously spray in 2% by weight of DMDBS powder octadecyltrimethoxysilane and 0.5% by weight of deionized water. ③ Heating reaction: At the feed inlet of the variable ratio high-speed mixer, the temperature is raised to 105℃, the speed is adjusted to 1500 r / min, and the high-speed mixing reaction is carried out for 15 min to complete the grafting modification of silane coupling agent on the surface of DMDBS powder. ④ Post-processing: After discharge, the material is naturally cooled to room temperature and passed through a 2000-mesh sieve to obtain octadecyltrimethoxysilane hydrophobically modified sorbitol derivative; ⑤ Performance testing: The modified powder has a water contact angle of 108° and a grafting rate of 1.72%.

[0033] 1.1.2 Preparation of stearic acid-terminated hyperbranched polyester nucleating agent ①Raw material ratio: Prepare 100 parts of third-generation hydroxyl-terminated hyperbranched polyester with a hydroxyl value of 520 mgKOH / g and a branching degree of 0.88, 120 parts of stearic acid, and 0.8 parts of p-toluenesulfonic acid catalyst by mass ratio; ② Melt esterification reaction: Add all the above raw materials into a reactor equipped with nitrogen protection and a condensation and water separation device, turn on the nitrogen protection, raise the temperature to 140°C, and after the raw materials are completely melted, turn on the stirring at 300 r / min, continue to raise the temperature to 160°C, and keep the reaction at this temperature for 4 hours, continuously draining the condensate generated during the reaction. ③ Vacuum devolatilization: After the reaction is complete, turn on the vacuum system and keep it at -0.095 MPa vacuum and 160℃ for 30 min to remove unreacted free stearic acid and low molecular weight byproducts. ④ Discharge and granulation: Stop heating, purge with nitrogen to cool down to 120℃, discharge the material, cool, crush, and sieve to obtain stearic acid-terminated hyperbranched polyester nucleating agent; ⑤ Performance testing: molecular weight 3500 g / mol, branching degree 0.85, end-capping rate 96.2%.

[0034] 1.1.3 Preparation of furan-maleimide (DA) dynamically covalently modified polyethylene wax (1) Preparation of maleic acid-grafted polyethylene wax ①Raw material ratio: Prepare 100 parts of polyethylene wax, 15 parts of maleic acid glycoside, and 0.3 parts of initiator DCP dicumyl peroxide by mass ratio; ② Melt grafting reaction: Add polyethylene wax to a mixer, heat to 170℃, and after it is completely melted, start stirring at 60 r / min. Add the premix of maleic acid and DCP in 3 portions, with an interval of 30 min between each addition. After all the additions are completed, continue to keep the mixture warm for 3 h. ③ Purification: After the reaction is completed, the product is discharged while hot, xylene is added and heated to reflux to dissolve, and then acetone is added to precipitate and purify. This process is repeated 3 times to remove unreacted maleic acid and DCP byproducts. The product is then dried under vacuum at 80°C for 6 h to obtain maleic acid-grafted polyethylene wax with a grafting rate of 4.2%.

[0035] (2) Preparation of furan-modified polyethylene wax ①Raw material ratio: Weigh 100 parts of the above maleic acid-grafted polyethylene wax and 8.5 parts of furanyl methylamine according to the molar ratio of carboxyl to amino groups of 1:1.2, and add them to a reaction vessel protected by nitrogen. ②Imidization reaction: turn on nitrogen protection, heat to 150℃, stir at 300 r / min, and keep the reaction at this temperature for 4 hours to complete the grafting of furan groups; ③ Vacuum devolatilization: After the reaction is completed, the product is kept at a vacuum of -0.095 MPa for 20 min to remove unreacted furanylamine. The product is then discharged and cooled to obtain furan-modified polyethylene wax.

[0036] (3) DA dynamic covalent crosslinking modification ①Raw material ratio: Weigh 100 parts of the above-mentioned furan modified polyethylene wax and 6.2 parts of bismaleimide according to the molar ratio of furan group to maleimide group of 2:1, and add them to the reaction vessel; ②D-A addition reaction: turn on nitrogen protection, heat to 160℃, stir at 300 r / min, and keep the reaction at this temperature for 2 h to complete the construction of the dynamic covalent bond of furan-maleimide DA; ③ Discharge: After the reaction is completed, the material is discharged, cooled, and crushed to obtain furan-maleimide DA dynamically covalently modified polyethylene wax.

[0037] 1.1.4 Preparation of disulfide bond modified hyperbranched polyethylene ①Raw material ratio: Weigh 100 parts of terminal hydroxyl hyperbranched polyethylene with a number average molecular weight of 4000 g / mol and a hydroxyl value of 380 mgKOH / g, 22 parts of 3,3'-dithiodipropionic acid, and 0.6 parts of p-toluenesulfonic acid catalyst according to the molar ratio of hydroxyl to carboxyl groups of 1:1.1. ② Esterification end-capping reaction: Add the above raw materials to a reactor equipped with nitrogen protection and a condensation and water separation device, turn on the nitrogen protection, raise the temperature to 130°C, and after the raw materials are completely melted, turn on the stirring at 300 r / min, continue to raise the temperature to 150°C, keep the reaction at the temperature for 5 h, and continuously discharge the condensate generated in the reaction. ③ Vacuum devolatilization: After the reaction is completed, the mixture is kept at a vacuum of -0.095 MPa and 150℃ for 30 min to remove unreacted raw materials and low molecular weight byproducts. ④ Discharge: Discharge the material at 120℃, cool, crush, and sieve to obtain disulfide bond modified hyperbranched polyethylene; ⑤ Performance testing: molecular weight 4500 g / mol, disulfide bond content 0.9 mmol / g.

[0038] 1.2 Preparation method of composite additives ① In-situ coating modification of powder: The hydrophobic modified sorbitol derivative, stearic acid-terminated hyperbranched polyester nucleating agent, and HALS 944, UV-329, and composite antioxidant powder raw materials prepared above are added to a high-speed mixer, and then the prescribed amount of dispersing agent is added. The mixture is heated to 90℃ and mixed at a high speed of 1300 r / min for 15 min to complete the in-situ coating modification of the powder surface and obtain the modified composite powder. ② Premixing treatment: Add the modified composite powder, the furan-maleimide dynamically covalently modified polyethylene wax prepared above, the disulfide bond modified hyperbranched polyethylene, and the formulated amount of LLDPE carrier resin to a high-speed mixer and mix at 900 r / min for 8 min at room temperature to obtain a uniform premix. ③ Melt extrusion granulation: The premixed material is added to a twin-screw extruder with an extrusion temperature range of 165℃-175℃-185℃-185℃-180℃-175℃ and a main machine speed of 350 r / min. After melt blending, extrusion, water cooling, air drying and pelletizing, the composite additive masterbatch is obtained. Example 2

[0039] This embodiment uses the raw materials obtained in Example 1, and by adjusting the raw material composition and ratio, a new implementation case is formed for preparation.

[0040] The raw material components, by weight, are as follows: Two parts of the antireflective nucleating component: one part of the hydrophobically modified sorbitol derivative and one part of the hyperbranched polyester nucleating agent; Weather-stabilizing components (3 parts): HALS 622 (2 parts), UV-328 (0.5 parts), and composite antioxidant (0.5 parts); Five parts of dynamic covalent bond repair components: three parts of furan-maleimide dynamically covalent bond modified polyethylene wax, and two parts of disulfide bond modified hyperbranched polyethylene; 85 parts of carrier resin: LLDPE (melt flow rate 5 g / 10 min, 190℃ / 2.16 kg). Dispersing agent 5 parts: polyethylene wax 3 parts, zinc stearate 1 part, vinyltriethoxysilane 1 part.

[0041] The preparation method of the composite additive is the same as in Example 1, except that the extrusion temperature range is adjusted to 160℃-170℃-180℃-180℃-175℃-170℃ and the main machine speed is 300 r / min. Example 3

[0042] This embodiment uses the raw materials obtained in Example 1, and by adjusting the raw material composition and ratio, a new implementation case is formed for preparation.

[0043] The raw material components, by weight, are as follows: Eight parts of the anti-reflective nucleating component: five parts of hydrophobically modified sorbitol derivative and three parts of hyperbranched polyester nucleating agent; Weather-stabilizing components (12 parts): HALS 944 (6 parts), UV-329 (4 parts), and composite antioxidant (2 parts); 15 parts of dynamic covalent bond repair components: 9 parts of furan-maleimide dynamically covalent bond modified polyethylene wax, and 6 parts of disulfide bond modified hyperbranched polyethylene. 60 parts of carrier resin: LLDPE (melt flow rate 3 g / 10 min, 190℃ / 2.16 kg). Dispersing agent 5 parts: polyethylene wax 2.5 parts, zinc stearate 1.2 parts, vinyltriethoxysilane 1.3 parts.

[0044] The preparation method of the composite additive is the same as in Example 1, except that the extrusion temperature range is adjusted to 170℃-180℃-190℃-190℃-185℃-180℃ and the main machine speed is 400 r / min. Example 4

[0045] This embodiment sets up a control experiment to compare Examples 1-3 with comparative cases that lack key components and existing technologies, thereby verifying the technical effect of this application.

[0046] (1) Scheme design Comparative Example 1 served as a blank control group, using pure LLDPE resin (melt flow rate 2 g / 10 min, 190℃ / 2.16 kg) without any additives. Comparative Example 2 only added the antireflection nucleating component from Example 1, with the same amount added as in Example 1, and directly blended it with LLDPE resin for blown film production; Comparative Example 3 only added the weather-resistant stabilizing component from Example 1, with the same amount added as in Example 1, and directly blended it with LLDPE resin for blown film production; Comparative Example 4 only added the dynamic covalent bond repair component from Example 1, with the same amount added as in Example 1, and directly blended it with LLDPE resin for blown film production; Comparative Example 5 was prepared with commercially available polyethylene antireflective and weather-resistant composite additives at a dosage of 3%. The main components were unmodified sorbitol nucleating agent, UV-326, and HALS 770, with no chain repair components. Comparative Example 6 uses a composite additive prepared with the formula in the existing technology (CN114773699A), with an addition amount of 3%. The main components include (parts by weight): 70 parts LLDPE carrier, 8 parts HALS 944, 5 parts UV-327, 2 parts antioxidant 1010, 3 parts calcium stearate, and 12 parts polyethylene wax. The masterbatch was prepared using a twin-screw extrusion process according to the preparation method, with an extrusion temperature of 160-190℃. Comparative Example 7 uses a composite additive prepared with the formula in the existing technology (CN107987321A), with an addition amount of 3%. The main components include (parts by mass): 30 parts of sorbitol nucleating agent, 40 parts of polyethylene wax, 20 parts of zinc stearate, and 10 parts of ethylene bis-stearamide. The masterbatch was prepared according to the preparation method using a high-speed mixing and melt extrusion process, with an extrusion temperature of 150-180℃.

[0047] (2) Performance testing All samples from the examples and comparative examples were mixed with LLDPE resin (melt flow rate 2 g / 10 min) according to the corresponding addition amounts, and films with a thickness of 25 μm were prepared using the same single-screw blown film machine. All processing parameters were completely consistent, and performance tests were conducted according to national standards, as follows.

[0048] Optical properties: GB / T 2410-2008 "Determination of transmittance and haze of transparent plastics"; Weather resistance: GB / T 16422.3-2014 "Laboratory Light Source Exposure Test Methods for Plastics - Part 3: Fluorescent Ultraviolet Lamps" (UVB-313 lamp tube, irradiance 0.71 W / m²) 2 (Aging time 1000 h), and the retention rate of tensile strength and elongation at break before and after aging were tested; Recyclability: After the film is crushed, it is processed three times under the same blown film process. The tensile strength and elongation at break retention rate are tested after three cycles. Yellowing performance: The yellowing index ΔYI after 1000 h of UV aging was tested according to GB / T 2409-1989 "Test Method for Yellow Index of Plastics".

[0049] (3) Test results The test results are shown in Table 1 after the samples of Examples 1-3 and the comparative examples were added to the same resin and made into films.

[0050] Table 1 shows a comparison of the thin film performance test results. As shown in the table: 1) The embodiments of the present invention simultaneously achieve five core indicators for low-density polyethylene resin: high light transmittance (≥93.5%), low haze (≤4.2), long-lasting weather resistance (mechanical retention rate after 1000 h aging ≥87.6%), high cycle retention rate (mechanical retention rate after 3 cycles ≥82.1%), and low yellowing (ΔYI≤1.5), while also meeting the triple requirements of high transmittance, weather resistance, and recyclability; 2) Comparative Example 6 only solved the weather resistance problem, completely neglecting transparency and recyclability; Comparative Example 7 only solved the transparency problem, with extremely poor weather resistance and recyclability. Existing technologies can only achieve improvement in a single performance aspect, failing to comprehensively address all three aspects; 3) Although commercially available ordinary anti-reflective and weather-resistant additives (Comparative Example 5) While both added anti-reflective and weather-resistant components, significant performance antagonism exists due to the simple compounding process: haze (5.9%) is 2.8% higher than that of the present invention, weather resistance (82.5%) is 10% lower than that of the present invention, and there is no chain repair function at all. After 3 cycles, the mechanical property retention rate is only 67.9%, making it impossible to achieve multiple recycling. 4) The comprehensive performance of Example 1 of the present invention is far superior to the sum of the performance of Comparative Example 2 + Comparative Example 3 + Comparative Example 4, which shows that the anti-reflective, weather-resistant, and chain repair functions of the present invention have a significant positive synergistic effect.

[0051] Figure 1 and Figure 2 The performance comparison between Example 1 and Comparative Examples 5-7 is presented visually.

Claims

1. A composite additive for improving the high transparency, weather resistance, and recyclability of linear polyethylene film materials, characterized in that, By weight, the raw materials include the following components: 0.5-15 parts of antireflective and nucleating component, 1-20 parts of weather-resistant and stabilizing component, 2-25 parts of dynamic covalent bond repair component, 50-95 parts of carrier resin, and 0.1-8 parts of dispersant. The dynamic covalent bond repair component is a polyolefin-based polymer grafted with reversible dynamic covalent bonds; the grafted reversible dynamic covalent bonds can undergo reversible breakage and reconstruction within the conventional heat treatment temperature range of polyethylene (120-220℃). The antireflective nucleating component is an organic nucleating agent system compatible with the linear polyethylene matrix, and the weather-resistant stabilizing component is a yellowing-resistant composite stabilizing system containing light stabilizers and antioxidants.

2. The composite additive according to claim 1, characterized in that, The reversible dynamic covalent bond includes at least one of DA dynamic covalent bond, disulfide bond, diselenide bond, transesterification bond, and acylhydrazone bond, and the dynamic covalent bond chain repair component is at least one of furan-maleimide DA dynamic covalent bond modified polyethylene wax and disulfide bond modified hyperbranched polyethylene.

3. The composite additive according to claim 2, characterized in that, The dynamic covalent bond repair component is a compound of furan-maleimide dynamically covalently modified polyethylene wax and disulfide-modified hyperbranched polyethylene in a mass ratio of (1-10):(1-8). The furan-maleimide dynamically covalently modified polyethylene wax is a modified polyethylene wax containing DA covalent bonds, obtained by grafting maleic acid glycosides, furanylamine, and bismaleimide crosslinking. The disulfide-modified hyperbranched polyethylene is obtained by end-capping hydroxyl-terminated hyperbranched polyethylene with carboxylic acid containing disulfide bonds, with a number average molecular weight of 2000-8000 g / mol and a disulfide bond content ≥0.5 mmol / g.

4. The composite additive according to claim 1, characterized in that, The enhanced penetration nucleating component is at least one of the following: sorbitol derivative nucleating agents, organophosphate nucleating agents, hyperbranched polymer nucleating agents, and rosin ester nucleating agents.

5. The composite additive according to claim 4, characterized in that: The enhanced-reflection nucleating component is a mixture of hydrophobically modified sorbitol derivative and hyperbranched polyester nucleating agent in a mass ratio of (1-8):(1-5). The hydrophobically modified sorbitol derivative is a 1,3:2,4-dibenzyl sorbitol nucleating agent obtained by hydrophobic modification with long alkyl silanes, and the modified powder has a water contact angle ≥100°. The hyperbranched polyester nucleating agent is a hydroxyl-terminated hyperbranched polyester obtained by end-capping modification with long-chain fatty acids, with a molecular weight of 1000-8000 g / mol and a branching degree ≥0.

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6. The composite additive according to claim 1, characterized in that, The weather-stabilizing component is a compound of at least two of the following: hindered amine light stabilizers, benzotriazole UV absorbers, benzophenone UV absorbers, hindered phenolic antioxidants, and phosphite antioxidants.

7. The composite additive according to claim 6, characterized in that, The weather-resistant stabilizing component is a mixture of a high molecular weight hindered amine light stabilizer, a long-chain alkyl-modified benzotriazole UV absorber, and a composite antioxidant in a mass ratio of (1-10):(1-8):(0.2-5). The high molecular weight hindered amine light stabilizer is a non-migratory hindered amine light stabilizer with a number average molecular weight ≥2000 g / mol. The long-chain alkyl-modified benzotriazole UV absorber is a benzotriazole derivative containing C4-C18 alkyl groups. The composite antioxidant is a mixture of a hindered phenolic primary antioxidant and a phosphite secondary antioxidant in a mass ratio of 1:(0.5-2).

8. The composite additive according to claim 1, characterized in that, The carrier resin is at least one of linear low-density polyethylene (LLDPE), low-density polyethylene (LDPE), and metallocene linear low-density polyethylene (mLLDPE), with a melt flow rate of 0.5-10 g / 10 min (190℃ / 2.16 kg); the dispersing agent is at least one of polyethylene wax, polypropylene wax, stearate, silane coupling agent, and titanate coupling agent.

9. A method for preparing a composite additive as described in any one of claims 1-8, characterized in that, Includes the following steps: S1 Powder Surface Modification: Powder raw materials containing penetrating and nucleating components and weather-resistant stabilizing components are mixed with dispersing agents, heated to 60-120℃, and mixed at high speed to complete in-situ coating modification of the powder surface, thus obtaining modified composite powder; S2 Premix: Modified composite powder, dynamic covalent bond repair component and carrier resin are uniformly mixed to obtain premix; S3 Melt Molding: The premixed material is melt-blended, extruded, and granulated to obtain the composite additive. The final product is a masterbatch type additive.

10. The application of the composite additive according to any one of claims 1-8, characterized in that, The composite additive is applied to the processing modification of linear polyethylene materials, wherein the linear polyethylene materials include at least one of linear low-density polyethylene (LLDPE), low-density polyethylene (LDPE), and metallocene linear low-density polyethylene (mLLDPE), and the amount of composite additive added is 0.5%-10% of the total mass of the linear polyethylene materials.

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