A highly heat-resistant, high-toughness silane-crosslinked polyethylene composition and a method for producing the same

Abstract

The application discloses a kind of high heat resistance high toughness silane crosslinking polyethylene composition and preparation method thereof, it is related to high polymer material modification technical field, including the following steps: base resin, double active gradient crosslinking system and other materials are mixed, by gradient temperature control grafting and devolatilization, grafting premix is prepared;With catalytic system, chain extender and other second-order segmented blending, devolatilization is cut after granulation drying, and composition finished product is obtained;Mould pressing is formed and constant-temperature water bath crosslinking, and high heat resistance high toughness silane crosslinking polyethylene composition is prepared.The application is completed by using double-stage engagement type double-screw extruder, and silane grafting reaction and melt blending are completed in stages, and gradient temperature control is used in grafting section and blending section, combined with the synergistic cooperation of base resin, double active gradient crosslinking system, dynamic lock and unlock type tin-free catalytic system and other components, the problem that silane grafting reaction is not sufficient in prior art, component mixing is not uniform, resulting in that the core performance such as product heat resistance, toughness fluctuates greatly, and the controllability of preparation process is poor.

Description

Technical Field

[0001] This invention relates to the field of polymer material modification technology, specifically to a high heat-resistant and high-toughness silane crosslinked polyethylene composition and its preparation method. Background Technology

[0002] Silane crosslinked polyethylene compositions transform the linear molecular structure of ordinary polyethylene into a three-dimensional network structure through a silane crosslinking reaction, thereby significantly improving the material's heat resistance, creep resistance, tensile strength, resistance to environmental stress cracking, and chemical resistance. This improvement enables it to meet the requirements of high temperature, pressure, and long-term use conditions, and it is widely used in the manufacture of medium and low voltage wire and cable insulation layers, hot and cold water conveying pipes, heat shrink films, and large hollow containers.

[0003] In existing technologies, organotin catalytic systems are commonly used for silane crosslinked polyethylene compositions and their preparation methods. This often leads to the precipitation of heavy metal tin and poor environmental compliance. Conventional tin-free catalysts cannot simultaneously ensure material storage stability and crosslinking efficiency. Furthermore, the combination of a single matrix resin and a single-component crosslinking system presents a trade-off between heat resistance and toughness. Traditional one-step preparation processes are also prone to insufficient silane grafting and uneven component mixing, resulting in large fluctuations in the core properties of the product, poor process controllability, and difficulty in adapting to high-end applications. Therefore, this invention provides a high-heat-resistant and high-toughness silane crosslinked polyethylene composition and its preparation method. Summary of the Invention

[0004] The purpose of this invention is to provide a high heat-resistant and high-toughness silane crosslinked polyethylene composition and its preparation method. This invention utilizes a two-stage interlocking twin-screw gradient temperature-controlled extrusion process, combined with the synergistic design of a compound matrix resin, a dual-active gradient crosslinking system, and a dynamically locked-unlocking tin-free catalytic system, to optimize the silane grafting and melt blending processes. While ensuring environmental friendliness and the absence of heavy metal precipitation, this invention simultaneously improves storage stability, crosslinking efficiency, heat resistance, and toughness, thus solving the problems existing in the prior art.

[0005] To achieve the above objectives, the present invention provides the following technical solution: A method for preparing a high heat-resistant and high-toughness silane crosslinked polyethylene composition includes the following steps: Bimodal metallocene linear low-density polyethylene, vinyl-terminated hyperbranched polyolefin, dual-active gradient crosslinking system, initiation system, and processing stabilizer are mixed in proportion and the silane grafting reaction is completed in the first stage near-melting point strong shear grafting section of a two-stage interlocking twin-screw extruder. The grafting section adopts gradient temperature control and vacuum removal of unreacted volatiles to obtain the grafted premix. The grafted premix, chain extender, dynamic lock-and-unlock Wuxi catalytic system, and functional additives are uniformly mixed in the second stage of the segmented melt blending section of a twin-screw extruder. The blending section adopts gradient temperature control. After removing residual volatiles, the product is obtained by water cooling, pelletizing and drying. After the finished granules are molded, they are placed in a constant temperature water bath to complete cross-linking, resulting in high heat resistance and high toughness cross-linked polyethylene products.

[0006] Preferably, the matrix resin is composed of bimodal metallocene linear low-density polyethylene and vinyl-terminated hyperbranched polyolefin, with a mass ratio of 80:20 to 95:5.

[0007] Preferably, the melt flow rate (190°C, 2.16 kg) of the bimodal metallocene linear low-density polyethylene is 1.0-2.0 g / 10 min, and the molecular weight distribution index is <3.0. The terminal vinyl hyperbranched polyolefin has a branching degree ≥60%, a melt flow rate (190℃, 2.16kg) of 5.0~8.0g / 10min, and a terminal vinyl content ≥0.8mmol / g.

[0008] Preferably, the dual-active gradient crosslinking system is a compound of vinyltriisopropoxysilane and 1,3-divinyl-1,1,3,3-tetramethyldisiloxane, with a mass ratio of 3:1 to 9:1, and the total amount added is 1.5 to 3.0 parts of the matrix resin mass.

[0009] Preferably, the dynamic lock-and-unlock type Wuxi catalytic system is a compound of hydrophobic β-cyclodextrin-ethylenediaminetetraacetic acid chelated zinc main catalyst and lanthanum isooctanoate co-catalyst, with a molar ratio of 8:1 to 12:1, and the total addition amount is 0.10 to 0.25 parts by mass of the matrix resin.

[0010] Preferably, the initiation system is a compound of bis(tert-butylperoxyisopropyl)benzene as the main initiator and bis(2-ethylhexyl) peroxydicarbonate as the auxiliary initiator, and the total amount added is 0.035 to 0.10 parts by mass of the matrix resin.

[0011] Preferably, the chain extender is one or more of glycidyl methacrylate and hydroxyethyl methacrylate, and the amount added is 0.10 to 0.25 parts by weight of the matrix resin.

[0012] Preferably, the functional additives include processing stabilizers, long-lasting antioxidants, and reactive metal passivators, with a total addition amount of 0.35 to 0.72 parts by mass of the matrix resin; wherein the processing stabilizer is one or more of antioxidant 168 and antioxidant 626, the long-lasting antioxidant is one or more of thioester-bridged hindered phenol intramolecular complex antioxidant and antioxidant 1010, and the reactive metal passivator is 3-(N-salicyloyl)aminopropyltriethoxysilane.

[0013] Preferably, the temperature of each zone in the first stage near-melting point high-shear grafting section of the dual-stage interlocking twin-screw extruder is 105℃~120℃, and the temperature of the second stage segmented melt blending section is 115℃~140℃.

[0014] Preferably, a high heat-resistant and high-toughness silane cross-linked polyethylene composition is prepared by a method for preparing a high heat-resistant and high-toughness silane cross-linked polyethylene composition.

[0015] Compared with the prior art, the beneficial effects of the present invention are: 1. This invention employs a two-stage meshing twin-screw extruder to complete the silane grafting reaction and melt blending in stages. Both the grafting and blending stages utilize gradient temperature control. Combined with the synergistic effects of the matrix resin, the dual-active gradient crosslinking system, and the dynamically locked / unlocked tin-free catalytic system, precise temperature control and uniform reaction are achieved in the preparation process of the silane crosslinked polyethylene composition. Compared with existing technologies, this invention can significantly improve grafting efficiency, blending uniformity, and product performance stability. Therefore, it can solve the problems of insufficient silane grafting reaction and uneven component mixing in existing technologies, which lead to large fluctuations in core properties such as heat resistance and toughness, and poor controllability of the preparation process.

[0016] 2. This invention employs a dynamic lock-and-unlock type tin-free catalytic system, using hydrophobic β-cyclodextrin-ethylenediaminetetraacetic acid chelated zinc as the main catalyst and lanthanum isooctanoate as the co-catalyst, to replace existing organotin catalysts or conventional tin-free catalysts. This achieves a dual improvement in catalytic efficiency and storage stability. Compared with existing technologies, it avoids the precipitation of heavy metal tin, improves the environmental compliance of the product, and extends the shelf life of the finished product while ensuring cross-linking efficiency. Therefore, it can solve the problems of existing organotin catalysts failing to meet environmental standards and conventional tin-free catalysts being unable to balance storage stability and cross-linking efficiency.

[0017] 3. This invention uses a matrix resin formed by compounding bimodal metallocene linear low-density polyethylene with vinyl-terminated hyperbranched polyolefins, and combines the synergistic effect of a dual-active gradient crosslinking system to achieve a synergistic improvement in the heat resistance and toughness of the product. Compared with the prior art, it can break the inherent law of the inverse constraint between the heat resistance and toughness of silane crosslinked polyethylene, and improve the comprehensive mechanical properties and heat resistance of the product. Therefore, it can solve the problem that silane crosslinked polyethylene products in the prior art cannot simultaneously meet the requirements of high heat resistance and high toughness, and cannot be adapted to high-end application scenarios. Detailed Implementation

[0018] The technical solutions in the embodiments of the present invention have been clearly and completely described. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0019] This embodiment provides a method for preparing a high heat-resistant and high-toughness silane crosslinked polyethylene composition, comprising the following steps: Bimodal metallocene linear low-density polyethylene, vinyl-terminated hyperbranched polyolefin, dual-active gradient crosslinking system, initiation system, and processing stabilizer are mixed in proportion and the silane grafting reaction is completed in the first stage near-melting point strong shear grafting section of a two-stage interlocking twin-screw extruder. The grafting section adopts gradient temperature control and vacuum removal of unreacted volatiles to obtain the grafted premix. The grafted premix, chain extender, dynamic lock-and-unlock Wuxi catalytic system, and functional additives are uniformly mixed in the second stage of the segmented melt blending section of a twin-screw extruder. The blending section adopts gradient temperature control. After removing residual volatiles, the product is obtained by water cooling, pelletizing and drying. After the finished granules are molded, they are placed in a constant temperature water bath to complete cross-linking, resulting in high heat resistance and high toughness cross-linked polyethylene products.

[0020] In some embodiments, the bimodal metallocene linear low-density polyethylene and the vinyl-terminated hyperbranched polyolefin constitute the matrix resin, with a mass ratio of 80:20 to 95:5.

[0021] In some embodiments, the melt flow rate (190°C, 2.16 kg) of the bimodal metallocene linear low-density polyethylene is 1.0–2.0 g / 10 min, and the molecular weight distribution index is <3.0; the degree of branching of the end-vinyl hyperbranched polyolefin is ≥60%, the melt flow rate (190°C, 2.16 kg) is 5.0–8.0 g / 10 min, and the end-vinyl content is ≥0.8 mmol / g.

[0022] In some embodiments, the dual-active gradient crosslinking system is a compound of vinyltriisopropoxysilane and 1,3-divinyl-1,1,3,3-tetramethyldisiloxane, with a mass ratio of 3:1 to 9:1, and the total amount added is 1.5 to 3.0 parts by mass of the matrix resin.

[0023] In some embodiments, the dynamically locked-unlocking Wuxi catalytic system is a compound of hydrophobic β-cyclodextrin-ethylenediaminetetraacetic acid chelated zinc main catalyst and lanthanum isooctanoate co-catalyst, with a molar ratio of 8:1 to 12:1, and the total addition amount is 0.10 to 0.25 parts by mass of the matrix resin.

[0024] In some embodiments, the initiation system is a compound of bis(tert-butylperoxyisopropyl)benzene as the main initiator and bis(2-ethylhexyl) peroxydicarbonate as the auxiliary initiator, with a total addition amount of 0.035 to 0.10 parts by mass of the matrix resin.

[0025] In some embodiments, the chain extender is one or more of glycidyl methacrylate and hydroxyethyl methacrylate, and the amount added is 0.10 to 0.25 parts by weight of the matrix resin.

[0026] In some embodiments, the functional additives include processing stabilizers, long-lasting antioxidants, and reactive metal passivators, with a total addition amount of 0.35 to 0.72 parts by mass of the matrix resin; wherein the processing stabilizer is one or more of antioxidant 168 and antioxidant 626, the long-lasting antioxidant is one or more of thioester-bridged hindered phenol intramolecular complex antioxidant and antioxidant 1010, and the reactive metal passivator is 3-(N-salicyloyl)aminopropyltriethoxysilane.

[0027] In some embodiments, the temperature of each zone in the first stage near-melting point high-shear grafting section of the two-stage interlocking twin-screw extruder is 105℃~120℃, and the temperature of the second stage segmented melt blending section is 115℃~140℃.

[0028] In some embodiments, the preparation method of the hydrophobic β-cyclodextrin-ethylenediaminetetraacetic acid chelated zinc main catalyst is as follows: β-cyclodextrin is vacuum dried at -0.098 MPa and 80 °C for 12 h, anhydrous N,N-dimethylformamide is added at a solid-liquid ratio of 1 g:15 mL, and the mixture is stirred and dissolved at 25 °C under nitrogen protection. Triethylamine with a molar amount of 7 times that of β-cyclodextrin is added, and trimethylchlorosilane with a molar amount of 6.5 times that of β-cyclodextrin is added dropwise at a rate of 1 mL / min to 2 mL / min. The mixture is kept at 60 °C for 8 h, and the reaction is carried out by filtration, distillation, washing, and drying to obtain 6-trimethylsilanized hydrophobic β-cyclodextrin. Hydrophobic β-cyclodextrin was added to anhydrous tetrahydrofuran at a solid-liquid ratio of 1 g: 20 mL, along with 3 molar amounts of 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride and 2 molar amounts of N-hydroxysuccinimide. The pH was adjusted to 5.5–6.0, and the mixture was activated in the dark for 2 h. Then, 1.2 molar amounts of ethylenediaminetetraacetic acid disodium salt aqueous solution were added dropwise, and the mixture was kept at 50 °C for 12 h. The mixture was then dialyzed and freeze-dried to obtain ethylenediaminetetraacetic acid-grafted hydrophobic β-cyclodextrin. The product was added to a 1:1 volume ratio ethanol-water solution, followed by the dropwise addition of an equimolar amount of zinc chloride ethanol solution. The reaction was carried out at room temperature for 4 hours. After filtration, washing, and drying, the target catalyst was obtained, with a coordination stability constant ≥10. 18 Moisture content ≤0.05%, particle size D50 ≤50μm.

[0029] In some embodiments, the finished pellets are cylindrical pellets with a diameter of 2 mm to 4 mm and a length of 2 mm to 4 mm, and the pellets are vacuum dried at 35°C to 45°C for 1 h to 3 h. The molding process parameters for finished granules are as follows: molding temperature 135℃~145℃, molding pressure 8MPa~12MPa, holding time 3min~8min, venting 3 times during molding, holding pressure for 10s and releasing pressure for 5s each time, and demolding after cold pressing and cooling to room temperature. The crosslinking process for finished products uses a 90℃ constant temperature water bath. The crosslinking time is adjusted according to the product type: for performance testing, the molded samples are crosslinked for 3 to 5 hours; for actual application products, the time is adjusted according to the wall thickness: products with a wall thickness ≤ 2 mm are crosslinked for 2 hours, products with a wall thickness of 2 mm to 5 mm are crosslinked for 4 hours, and products with a wall thickness of 5 mm to 10 mm are crosslinked for 6 hours.

[0030] In some embodiments, the finished composition exhibits a crosslinking degree of ≥70% after being subjected to a 90°C water bath for 2 hours, a room temperature sealed storage period of ≥12 months, a heat distortion temperature (0.45MPa) of ≥135°C, a Vicat softening temperature of ≥138°C, and a room temperature unnotched impact strength of a simply supported beam of ≥25kJ / m. 2 The unnotched impact strength of a simply supported beam at -20℃ is ≥16kJ / m. 2 Tensile strength ≥18MPa, elongation at break ≥450%, tensile strength retention rate ≥90% after 168h of heat aging at 150℃, thermal elongation ≤40% after 15min at 200℃, no heavy metal tin precipitation, and complies with EU RoHS standards and GB4806.7-2016 food contact standards.

[0031] Based on the foregoing embodiments, the following sets of experiments were conducted: It should be noted that the raw materials used in the following embodiments are all commercially available industrial-grade raw materials, and all raw material ratios and process parameters fall completely within the aforementioned corresponding general range. In the following embodiments, the raw material ratios are all parts by weight.

[0032] Example 1: A method for preparing a high heat-resistant and high-toughness silane crosslinked polyethylene composition, comprising the following steps: 88 parts of bimodal metallocene linear low-density polyethylene (commercially available brand: ExxonMobil Exceed 1018, melt index 1.5 g / 10 min, molecular weight distribution index 2.8), 12 parts of vinyl-terminated hyperbranched polyolefin (commercially available brand: Dow Affinity GA1900, degree of branching 68%, melt index 6.5 g / 10 min, vinyl-terminated content 0.92 mmol / g), 1.98 parts of vinyltriisopropoxysilane, and 0.2 Two parts of 1,3-divinyl-1,1,3,3-tetramethyldisiloxane, 0.05 parts of bis(tert-butylperoxyisopropyl)benzene, 0.01 parts of bis(2-ethylhexyl) peroxydicarbonate, and 0.08 parts of antioxidant 168 were mixed evenly and the silane grafting reaction was completed in the first stage near-melting point high-shear grafting section of a two-stage interlocking twin-screw extruder. The temperature of each temperature zone in the entire grafting section was 108℃~118℃. Unreacted volatiles were removed under vacuum to obtain the grafted premix. The grafted premix was uniformly mixed with 0.18 parts glycidyl methacrylate, 0.164 parts hydrophobic β-cyclodextrin-ethylenediaminetetraacetic acid chelated zinc main catalyst, 0.016 parts lanthanum isooctanoate co-catalyst, 0.3 parts thioester-bridged hindered phenol intramolecular complex antioxidant, and 0.15 parts 3-(N-salicyloyl)aminopropyltriethoxysilane in the second stage of a twin-screw extruder. The temperature of each zone in the blending section was 120℃~135℃. After removing residual volatiles, the mixture was water-cooled, pelletized, and dried to obtain the finished silane crosslinked polyethylene composition. After the finished granules are molded, they are placed in a 90℃ constant temperature water bath for 4 hours to crosslink, resulting in high heat resistance and high toughness crosslinked polyethylene products.

[0033] Example 2: A method for preparing a high heat-resistant and high-toughness silane crosslinked polyethylene composition, comprising the following steps: 95 parts of bimodal metallocene linear low-density polyethylene, 5 parts of vinyl-terminated hyperbranched polyolefin, 1.98 parts of vinyltriisopropoxysilane, 0.22 parts of 1,3-divinyl-1,1,3,3-tetramethyldisiloxane, 0.05 parts of bis(tert-butylperoxyisopropyl)benzene, 0.01 parts of bis(2-ethylhexyl) peroxydicarbonate, and 0.08 parts of antioxidant 168 were mixed evenly and the silane grafting reaction was completed in the first stage near-melting point high-shear grafting section of a two-stage interlocking twin-screw extruder. The temperature of each temperature zone in the entire grafting section was 108℃~118℃. Unreacted volatiles were removed under vacuum to obtain the grafted premix. The grafted premix was uniformly mixed with 0.18 parts glycidyl methacrylate, 0.164 parts hydrophobic β-cyclodextrin-ethylenediaminetetraacetic acid chelated zinc main catalyst, 0.016 parts lanthanum isooctanoate co-catalyst, 0.3 parts thioester-bridged hindered phenol intramolecular complex antioxidant, and 0.15 parts 3-(N-salicyloyl)aminopropyltriethoxysilane in the second stage of a twin-screw extruder. The temperature of each zone in the blending section was 120℃~135℃. After removing residual volatiles, the mixture was water-cooled, pelletized, and dried to obtain the finished silane crosslinked polyethylene composition. After the finished granules are molded, they are placed in a 90℃ constant temperature water bath for 4 hours to crosslink, resulting in high heat resistance and high toughness crosslinked polyethylene products.

[0034] Example 3: A method for preparing a high heat-resistant and high-toughness silane crosslinked polyethylene composition, comprising the following steps: 80 parts of bimodal metallocene linear low-density polyethylene, 20 parts of vinyl-terminated hyperbranched polyolefin, 1.98 parts of vinyltriisopropoxysilane, 0.22 parts of 1,3-divinyl-1,1,3,3-tetramethyldisiloxane, 0.05 parts of bis(tert-butylperoxyisopropyl)benzene, 0.01 parts of bis(2-ethylhexyl) peroxydicarbonate, and 0.08 parts of antioxidant 168 were mixed evenly and the silane grafting reaction was completed in the first stage near-melting point high-shear grafting section of a two-stage interlocking twin-screw extruder. The temperature of each temperature zone in the entire grafting section was 108℃~118℃. Unreacted volatiles were removed under vacuum to obtain the grafted premix. The grafted premix was uniformly mixed with 0.18 parts glycidyl methacrylate, 0.164 parts hydrophobic β-cyclodextrin-ethylenediaminetetraacetic acid chelated zinc main catalyst, 0.016 parts lanthanum isooctanoate co-catalyst, 0.3 parts thioester-bridged hindered phenol intramolecular complex antioxidant, and 0.15 parts 3-(N-salicyloyl)aminopropyltriethoxysilane in the second stage of a twin-screw extruder. The temperature of each zone in the blending section was 120℃~135℃. After removing residual volatiles, the mixture was water-cooled, pelletized, and dried to obtain the finished silane crosslinked polyethylene composition. After the finished granules are molded, they are placed in a 90℃ constant temperature water bath for 4 hours to crosslink, resulting in high heat resistance and high toughness crosslinked polyethylene products.

[0035] Example 4: A method for preparing a high heat-resistant and high-toughness silane crosslinked polyethylene composition, comprising the following steps: 88 parts of bimodal metallocene linear low-density polyethylene, 12 parts of vinyl-terminated hyperbranched polyolefin, 1.65 parts of vinyltriisopropoxysilane, 0.55 parts of 1,3-divinyl-1,1,3,3-tetramethyldisiloxane, 0.05 parts of bis(tert-butylperoxyisopropyl)benzene, 0.01 parts of bis(2-ethylhexyl) peroxydicarbonate, and 0.08 parts of antioxidant 168 were mixed evenly and the silane grafting reaction was completed in the first stage near-melting point high-shear grafting section of a two-stage interlocking twin-screw extruder. The temperature of each temperature zone in the entire grafting section was 108℃~118℃. Unreacted volatiles were removed under vacuum to obtain the grafted premix. The grafted premix was uniformly mixed with 0.18 parts glycidyl methacrylate, 0.164 parts hydrophobic β-cyclodextrin-ethylenediaminetetraacetic acid chelated zinc main catalyst, 0.016 parts lanthanum isooctanoate co-catalyst, 0.3 parts thioester-bridged hindered phenol intramolecular complex antioxidant, and 0.15 parts 3-(N-salicyloyl)aminopropyltriethoxysilane in the second stage of a twin-screw extruder. The temperature of each zone in the blending section was 120℃~135℃. After removing residual volatiles, the mixture was water-cooled, pelletized, and dried to obtain the finished silane crosslinked polyethylene composition. After the finished granules are molded, they are placed in a 90℃ constant temperature water bath for 4 hours to crosslink, resulting in high heat resistance and high toughness crosslinked polyethylene products.

[0036] Example 5: A method for preparing a high heat-resistant and high-toughness silane crosslinked polyethylene composition, comprising the following steps: 88 parts of bimodal metallocene linear low-density polyethylene, 12 parts of vinyl-terminated hyperbranched polyolefin, 1.98 parts of vinyltriisopropoxysilane, 0.22 parts of 1,3-divinyl-1,1,3,3-tetramethyldisiloxane, 0.05 parts of bis(tert-butylperoxyisopropyl)benzene, 0.01 parts of bis(2-ethylhexyl) peroxydicarbonate, and 0.08 parts of antioxidant 168 were mixed evenly and the silane grafting reaction was completed in the first stage near-melting point high-shear grafting section of a two-stage interlocking twin-screw extruder. The temperature of each temperature zone in the entire grafting section was 108℃~118℃. Unreacted volatiles were removed under vacuum to obtain the grafted premix. The grafted premix was uniformly mixed with 0.18 parts glycidyl methacrylate, 0.228 parts hydrophobic β-cyclodextrin-ethylenediaminetetraacetic acid chelated zinc main catalyst, 0.022 parts lanthanum isooctanoate co-catalyst, 0.3 parts thioester-bridged hindered phenol intramolecular complex antioxidant, and 0.15 parts 3-(N-salicyloyl)aminopropyltriethoxysilane in the second stage of a twin-screw extruder. The temperature of each zone in the blending section was 120℃~135℃. After removing residual volatiles, the mixture was water-cooled, pelletized, and dried to obtain the finished silane crosslinked polyethylene composition. After the finished granules are molded, they are placed in a 90℃ constant temperature water bath for 4 hours to crosslink, resulting in high heat resistance and high toughness crosslinked polyethylene products.

[0037] Example 6: A method for preparing a high heat-resistant and high-toughness silane crosslinked polyethylene composition, comprising the following steps: 88 parts of bimodal metallocene linear low-density polyethylene, 12 parts of vinyl-terminated hyperbranched polyolefin, 1.98 parts of vinyltriisopropoxysilane, 0.22 parts of 1,3-divinyl-1,1,3,3-tetramethyldisiloxane, 0.05 parts of bis(tert-butylperoxyisopropyl)benzene, 0.01 parts of bis(2-ethylhexyl) peroxydicarbonate, and 0.08 parts of antioxidant 168 were mixed evenly and the silane grafting reaction was completed in the first stage near-melting point high-shear grafting section of a two-stage interlocking twin-screw extruder. The temperature of each temperature zone in the entire grafting section was 108℃~118℃. Unreacted volatiles were removed under vacuum to obtain the grafted premix. The grafted premix was uniformly mixed with 0.18 parts glycidyl methacrylate, 0.091 parts hydrophobic β-cyclodextrin-ethylenediaminetetraacetic acid chelated zinc main catalyst, 0.009 parts lanthanum isooctanoate co-catalyst, 0.3 parts thioester-bridged hindered phenol intramolecular complex antioxidant, and 0.15 parts 3-(N-salicyloyl)aminopropyltriethoxysilane in the second stage of a twin-screw extruder. The temperature of each zone in the blending section was 120℃~135℃. After removing residual volatiles, the mixture was water-cooled, pelletized, and dried to obtain the finished silane crosslinked polyethylene composition. After the finished granules are molded, they are placed in a 90℃ constant temperature water bath for 4 hours to crosslink, resulting in high heat resistance and high toughness crosslinked polyethylene products.

[0038] Example 7: A method for preparing a high heat-resistant and high-toughness silane crosslinked polyethylene composition, comprising the following steps: 88 parts of bimodal metallocene linear low-density polyethylene, 12 parts of vinyl-terminated hyperbranched polyolefin, 1.98 parts of vinyltriisopropoxysilane, 0.22 parts of 1,3-divinyl-1,1,3,3-tetramethyldisiloxane, 0.05 parts of bis(tert-butylperoxyisopropyl)benzene, 0.01 parts of bis(2-ethylhexyl) peroxydicarbonate, and 0.08 parts of antioxidant 168 were mixed evenly and the silane grafting reaction was completed in the first stage near-melting point high-shear grafting section of a two-stage interlocking twin-screw extruder. The temperature of each temperature zone in the entire grafting section was 105℃~120℃. Unreacted volatiles were removed under vacuum to obtain the grafted premix. The grafted premix was uniformly mixed with 0.18 parts glycidyl methacrylate, 0.164 parts hydrophobic β-cyclodextrin-ethylenediaminetetraacetic acid chelated zinc main catalyst, 0.016 parts lanthanum isooctanoate co-catalyst, 0.3 parts thioester-bridged hindered phenol intramolecular complex antioxidant, and 0.15 parts 3-(N-salicyloyl)aminopropyltriethoxysilane in the second stage of a twin-screw extruder. The temperature of each zone in the blending section was 115℃~140℃. After removing residual volatiles, the mixture was water-cooled, pelletized, and dried to obtain the finished silane crosslinked polyethylene composition. After the finished granules are molded, they are placed in a 90℃ constant temperature water bath for 4 hours to crosslink, resulting in high heat resistance and high toughness crosslinked polyethylene products.

[0039] Comparative Example 1 differs from Example 1 in that: dibutyltin dilaurate is used instead of the dynamically locked-unlocking tin-free catalytic system, with an addition amount of 0.18 parts, and the other steps are the same as in Example 1.

[0040] Comparative Example 2 differs from Example 1 in that zinc stearate is used instead of the dynamically locked-unlocking Wuxi catalytic system, with an addition amount of 0.18 parts. Other steps are the same as in Example 1.

[0041] Comparative Example 3 differs from Example 1 in that it uses a single vinyltriisopropoxysilane as a crosslinking agent, with a total addition amount of 2.2 parts, and does not contain 1,3-divinyl-1,1,3,3-tetramethyldisiloxane. The other steps are the same as in Example 1. This example is used to verify the technical effect of the dual-activity gradient crosslinking system.

[0042] Comparative Example 4 differs from Example 1 in that it uses 100 parts of bimodal metallocene linear low-density polyethylene as the single matrix resin and unterminated vinyl hyperbranched polyolefin. The other steps are the same as in Example 1. This example is used to verify the technical effect of the matrix compound system.

[0043] The performance of the silane crosslinked polyethylene materials prepared in Examples 1 to 7 and Comparative Examples 1 to 4 were tested. All tests were conducted in a standard environment of 23℃±2℃ and 50%±5%RH. Three parallel samples were set up for each test group, and the arithmetic mean of the results was taken. The standards and methods used for the tests are as follows: Crosslinking degree test: GB / T18474-2022 "Determination of crosslinking degree of crosslinked polyethylene (PE-X) pipes and fittings" was performed, using the xylene reflux extraction method with a reflux time of 6 hours; Room temperature storage period test: Based on GB / T18474-2022, the uncrosslinked finished granules were stored in a sealed environment at 25℃ and 50%RH, and the gel rate was tested monthly. The longest sealed storage time with a gel rate ≤0.5% was taken as the effective storage period. Heat distortion temperature test: GB / T1634.2-2019 "Determination of load distortion temperature of plastics - Part 2: Plastics, hard rubber and long fiber reinforced composites" was performed, with a test load of 0.45 MPa and a sample size of 80 mm × 10 mm × 4 mm. Vicat softening temperature test: GB / T1633-2022 "Determination of Vicat softening temperature (VST) of thermoplastics" was performed, using the B50 method, with a test load of 50N, a heating rate of 50℃ / h, and a sample thickness of 4mm. Simply supported beam impact strength test: GB / T1043.1-2008 "Determination of impact properties of simply supported plastic beams - Part 1: Non-instrumental impact test" was performed. The unnotched impact strength was tested at room temperature (23℃) and low temperature (-20℃). The sample size was 80mm×10mm×4mm. Tensile property test: GB / T1040.2-2006 "Determination of tensile properties of plastics - Part 2: Test conditions for molded and extruded plastics" was performed, using type I specimens with a thickness of 4 mm and a tensile rate of 50 mm / min. Thermal aging performance test: GB / T7141-2008 "Test Method for Thermal Aging of Plastics" was performed. After thermal aging at 150℃ for 168h, the tensile strength retention rate was tested. Thermal elongation test: Perform GB / T2951.32-2008 "General test methods for insulation and sheathing materials of cables and optical cables - Part 32: Test methods for rubber and plastic mixtures - Thermal elongation test", test temperature 200℃, load 0.2MPa, test thermal elongation rate for 15min; Heavy metal tin precipitation test: IEC62321-4:2013 "Determination of certain substances in electrical and electronic products - Part 4: Determination of cadmium, lead and metallic chromium", instrument detection limit 0.1 ppm.

[0044] The standard properties of commercially available ordinary silane cross-linked polyethylene cable material (domestic mainstream industrial grade) are as follows: room temperature sealed storage period ≤6 months, cross-linking degree ≤68% after 2 hours in a 90℃ water bath, heat distortion temperature ≤126℃, room temperature simply supported beam unnotched impact strength ≤22kJ / m², and thermal elongation ≥45% at 200℃, which serves as an industry benchmark.

[0045] The obtained test data are recorded in Table 1 below: Example 1 demonstrated the best performance across all aspects, verifying the feasibility of the basic process of this invention. Through the synergistic effect of the dynamically locked and unlocked Wuxi catalytic system and the dual-activity gradient crosslinking system, it simultaneously achieved an ultra-long storage period of 12 months, rapid crosslinking in 2 hours, and a balance between high heat resistance and high toughness, thus completely solving the core pain points of the existing technology.

[0046] Examples 2 and 3, using the upper and lower limits of the matrix resin ratio, respectively, can stably achieve the core performance indicators of the present invention, verifying the stability of the matrix ratio across the entire range. At the same time, it proves that end-vinyl hyperbranched polyolefins can significantly improve the toughness of materials without significantly sacrificing heat resistance, breaking the inherent law that heat resistance and toughness of silane crosslinked polyethylene are inversely constrained.

[0047] Example 4 uses the lower limit of the dual-active gradient crosslinking system ratio, which still stably achieves the core performance target, fully covers the protection range, and ensures the stability of the protection range.

[0048] Examples 5 and 6, using the upper and lower limits of the molar ratio of the catalytic system respectively, both met the preset performance requirements, verifying the high efficiency of the catalytic system across the entire range and providing flexibility for cost control in industrial production.

[0049] Example 7 uses the upper and lower limits of the twin-screw temperature range, yet still manages to stably achieve the core performance target, verifying the stability of the process temperature across the entire range.

[0050] Comparative Example 1 uses a traditional organotin catalytic system. Although the crosslinking efficiency is close to that of the present invention, the storage period is only 6 months, the precipitation of heavy metal tin exceeds the standard, and it does not meet the environmental protection compliance requirements. Its overall performance is significantly inferior to that of the present invention, which verifies the dual advantages of the present invention in terms of environmental protection and performance.

[0051] Comparative Example 2 uses the existing conventional zinc stearate tin-free catalytic system, which has a storage period of only 3 months at room temperature and a crosslinking degree of only 38.2% after 2 hours. It cannot balance storage stability and crosslinking efficiency, thus verifying the breakthrough solution of the dynamic lock-and-unlock type tin-free catalytic system of the present invention to the core pain points of the industry.

[0052] Comparative Examples 3 and 4 removed the dual-active gradient crosslinking system and the terminal vinyl hyperbranched polyolefin, respectively. The crosslinking uniformity, heat resistance, and toughness of the materials were significantly deteriorated, which verified the synergistic effect of the two core technical features of the present invention and is the key to achieving performance breakthrough.

[0053] Comparative analysis reveals that this invention achieves a comprehensive breakthrough in the environmental friendliness, storage stability, crosslinking efficiency, heat resistance, and toughness of silane crosslinked polyethylene through the synergistic effect of a dynamically locked / unlocked Wuxi catalytic system, a dual-activity gradient crosslinking system, a matrix compounding system, and a two-stage gradient temperature control process. This effectively addresses the three core pain points of existing technologies. All raw materials used in this invention are industrially mass-produced general-purpose materials, and the process can be directly adapted to existing general-purpose production lines without customized equipment requirements. It possesses outstanding novelty, inventiveness, and industrial applicability, and can be widely applied in high-end scenarios such as high-temperature resistant environmentally friendly cables and food-contact grade fluid pipes.

[0054] In the description of this specification, references to terms such as "an experiment," "example," "specific example," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that experiment or example is included in at least one experiment or example of the invention. In this specification, illustrative expressions of the above terms do not necessarily refer to the same experiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more experiments or examples.

[0055] The preferred experiments disclosed above are merely illustrative of the invention. These preferred experiments do not exhaustively describe all details, nor do they limit the invention to the specific embodiments described. Clearly, many modifications and variations can be made based on the content of this specification. This specification selects and specifically describes these experiments to better explain the principles and practical applications of the invention, thereby enabling those skilled in the art to better understand and utilize it. The invention is limited only by the claims and their full scope and equivalents.

Claims

1. A method for preparing a high heat-resistant and high-toughness silane crosslinked polyethylene composition, characterized in that, Includes the following steps: Bimodal metallocene linear low-density polyethylene, vinyl-terminated hyperbranched polyolefin, dual-active gradient crosslinking system, initiation system, and processing stabilizer are mixed in proportion and the silane grafting reaction is completed in the first stage near-melting point strong shear grafting section of a two-stage interlocking twin-screw extruder. The grafting section adopts gradient temperature control and vacuum removal of unreacted volatiles to obtain the grafted premix. The grafted premix, chain extender, dynamic lock-and-unlock Wuxi catalytic system, and functional additives are uniformly mixed in the second stage of the segmented melt blending section of a twin-screw extruder. The blending section adopts gradient temperature control. After removing residual volatiles, the product is obtained by water cooling, pelletizing and drying. After the finished granules are molded, they are placed in a constant temperature water bath to complete cross-linking, resulting in high heat resistance and high toughness cross-linked polyethylene products.

2. The method for preparing a high heat-resistant and high-toughness silane crosslinked polyethylene composition according to claim 1, characterized in that, The matrix resin is composed of bimodal metallocene linear low-density polyethylene and vinyl-terminated hyperbranched polyolefin, with a mass ratio of 80:20 to 95:

5.

3. The method for preparing a high heat-resistant and high-toughness silane crosslinked polyethylene composition according to claim 2, characterized in that, The melt flow rate (190℃, 2.16kg) of the bimodal metallocene linear low-density polyethylene is 1.0~2.0g / 10min, and the molecular weight distribution index is <3.

0. The terminal vinyl hyperbranched polyolefin has a branching degree ≥60%, a melt flow rate (190℃, 2.16kg) of 5.0~8.0g / 10min, and a terminal vinyl content ≥0.8mmol / g.

4. The method for preparing a high heat-resistant and high-toughness silane crosslinked polyethylene composition according to claim 1, characterized in that, The dual-active gradient crosslinking system is a compound of vinyltriisopropoxysilane and 1,3-divinyl-1,1,3,3-tetramethyldisiloxane, with a mass ratio of 3:1 to 9:1, and the total amount added is 1.5 to 3.0 parts of the matrix resin mass.

5. The method for preparing a high heat-resistant and high-toughness silane crosslinked polyethylene composition according to claim 1, characterized in that, The dynamic lock-and-unlock type Wuxi catalytic system is a compound of hydrophobic β-cyclodextrin-ethylenediaminetetraacetic acid chelated zinc main catalyst and lanthanum isooctanoate co-catalyst, with a molar ratio of 8:1 to 12:1, and the total addition amount is 0.10 to 0.25 parts by mass of the matrix resin.

6. The method for preparing a high heat-resistant and high-toughness silane crosslinked polyethylene composition according to claim 1, characterized in that, The initiation system is a compound of bis(tert-butylperoxyisopropyl)benzene as the main initiator and bis(2-ethylhexyl) peroxydicarbonate as the auxiliary initiator, with a total addition amount of 0.035 to 0.10 parts by mass of the matrix resin.

7. The method for preparing a high heat-resistant and high-toughness silane crosslinked polyethylene composition according to claim 1, characterized in that, The chain extender is one or more of glycidyl methacrylate and hydroxyethyl methacrylate, and the amount added is 0.10 to 0.25 parts by weight of the matrix resin.

8. The method for preparing a high heat-resistant and high-toughness silane crosslinked polyethylene composition according to claim 1, characterized in that, The functional additives include processing stabilizers, long-lasting antioxidants, and reactive metal passivators, with a total addition amount of 0.35 to 0.72 parts by mass of the matrix resin; wherein the processing stabilizer is one or more of antioxidant 168 and antioxidant 626, the long-lasting antioxidant is one or more of thioester-bridged hindered phenol intramolecular complex antioxidant and antioxidant 1010, and the reactive metal passivator is 3-(N-salicyloyl)aminopropyltriethoxysilane.

9. The method for preparing a high heat-resistant and high-toughness silane crosslinked polyethylene composition according to claim 1, characterized in that, The first-stage near-melting-point high-shear grafting section of the dual-stage interlocking twin-screw extruder has a temperature range of 105℃ to 120℃, and the second-stage segmented melt blending section has a temperature range of 115℃ to 140℃.

10. A high heat-resistant and high-toughness silane crosslinked polyethylene composition, characterized in that, The high heat-resistant and high toughness silane crosslinked polyethylene composition is prepared by the preparation method of the high heat-resistant and high toughness silane crosslinked polyethylene composition according to any one of claims 1-9.

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