Preparation method of functionalized polyolefin for high-filling flame-retardant cable

Abstract

The invention belongs to the technical field of polyolefin, and particularly relates to a preparation method of functionalized polyolefin for a high-filling flame-retardant cable. According to the preparation method disclosed by the invention, a polyolefin matrix is subjected to melt grafting through MAH / St double monomers, and core-shell-surface gradient structure functionalized polyethylene wax is synergistically introduced, so that a multi-layer tough interface system is constructed. The MAH / St grafted chain provides a polar site, and the polyethylene wax takes an annular surface layer and a nano SiO2 core as an interface bridging anchoring point, so that agglomeration of a high-content flame retardant is inhibited, a filling weak point is converted into a toughening point, LOI and UL94 V-0-level flame retardant performance is remarkably improved, the tensile strength and the elongation at break are synchronously improved, and the problems of high filling embrittlement and performance degradation are solved. Meanwhile, by means of narrow-distribution polyethylene wax prepared through controllable polymerization and a compound antioxidant system, intrinsic thermal stability and aging resistance of the material are synergetic, T5% is remarkably higher than that of a conventional system, it is guaranteed that the cable operates for a long time and is stable in performance under short-time overload, thermal aging failure is delayed, and safety and reliability of long-term operation are improved.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of polyolefins, and particularly relates to a preparation method of functionalized polyolefin for high-filled flame-retardant cables. BACKGROUND

[0002] In modern society, power cables are the core of all kinds of infrastructure. Traditional halogen-containing cables release toxic smoke in a fire, so low-smoke halogen-free flame-retardant cables have become the mainstream choice. Such cables are mainly made by blending polyolefins with a high filling amount of inorganic hydroxide flame retardants, which solves the environmental and safety problems, but the performance is realized depending on high filling, which directly leads to three technical bottlenecks: (1) poor interfacial compatibility: the interfacial combination between the polar inorganic filler and the non-polar polyolefin matrix is weak, resulting in serious aggregation of the filler, which becomes a stress concentration point; (2) mechanical property degradation: the introduction of a large amount of rigid fillers significantly increases the brittleness of the material, and the impact strength and elongation at break decrease sharply; (3) performance deterioration: the melt viscosity of the high-filled system increases dramatically, and the flowability is poor, resulting in difficult extrusion processing, rough surface, and easy wear of the equipment.

[0003] The prior art generally uses silane, titanate and other coupling agents to pretreat the flame retardant in order to improve the interface. However, this method has inherent limitations: first, the improvement effect is limited, and it is difficult to fundamentally balance the toughness and processability under high filling; second, it increases the additional pretreatment process and cost, and complicates the production process; and more importantly, the coupling agent may decompose in high-temperature processing, affecting the long-term thermal stability.

[0004] Based on this, the application provides a preparation method of functionalized polyolefin for high-filled flame-retardant cables, which aims to solve the problems in the prior art. SUMMARY

[0005] The application aims to provide a preparation method of functionalized polyolefin for high-filled flame-retardant cables to solve the existing problems.

[0006] The application is implemented by the following technical scheme:

[0007] A preparation method of functionalized polyolefin for high-filled flame-retardant cables, comprising the following steps:

[0008] S1, raw material preparation:

[0009] The following raw materials are prepared according to weight parts: polyolefin matrix resin 50-90 parts, functionalized monomer 0.5-10 parts, complex synergistic initiator 0.05-2 parts, functionalized polyethylene wax 1-20 parts, and antioxidant 0.1-1 part;

[0010] S2, premixing:

[0011] All the components weighed above are put into a mixer in turn, and mixed at room temperature for 6-10 min to ensure that the components are uniformly dispersed to obtain a premix;

[0012] S3, melt reaction extrusion:

[0013] The premix is put into a high-torque co-rotating twin-screw extruder for melt blending and reaction grafting.

[0014] S4, extrusion granulation:

[0015] The melt strip extruded from the die of the extruder is cooled by a cooling water tank and then cut into particles, and the particles are dried to obtain functionalized polyolefin particles.

[0016] Further, the polyolefin base resin in step S1 is selected from one or more mixtures of high-pressure low-density polyethylene (LDPE), linear low-density polyethylene (LLDPE), metallocene linear low-density polyethylene (mLLDPE), high-density polyethylene (HDPE), homopolymer polypropylene, impact copolymer polypropylene (PPB), random copolymer polypropylene (PPR), polyolefin elastomer (POE), olefin block copolymer (OBC), and ethylene-propylene-diene rubber (EPDM).

[0017] Further, the high-pressure low-density polyethylene has a density of 0.910-0.925 g / cm 3 ;

[0018] The polyolefin elastomer is an ethylene / α-olefin copolymer with a density of 0.860-0.900 g / cm 3 ;

[0019] The metallocene linear low-density polyethylene has a melt flow rate (190℃ / 2.16 kg) of 1.0-5.0 g / 10 min;

[0020] The homopolymer polypropylene is a homopolymer of propylene;

[0021] The impact copolymer polypropylene (PPB) is a multiphase copolymer comprising a polypropylene continuous phase and an ethylene-propylene rubber dispersed phase;

[0022] The random copolymer polypropylene (PPR) is a copolymer formed by random insertion of ethylene monomers into a polypropylene backbone.

[0023] Further, the functional monomer in step S1 is a combination of maleic anhydride (MAH) and styrene, wherein the maleic anhydride accounts for 60%-90% of the total weight of the functional monomer, and the styrene accounts for 10%-40%.

[0024] Further, the compounded synergistic initiator mentioned in step S1 is composed of low-temperature decomposition peroxide, medium-temperature decomposition peroxide and co-initiator in a ratio of (1~3):(2~5):(0.1~1);

[0025] The low-temperature decomposition peroxide is selected from one or a combination of tert-butyl peroxyneodecanate (TBPND) and tert-butyl peroxyisobutyrate (TBPIB), with a 10-hour half-life temperature of 70~90℃.

[0026] The intermediate-temperature decomposition peroxide is selected from one or a combination of dicumyl peroxide (DCP) and benzoyl peroxide (BPO), with a 10-hour half-life temperature of 100~120℃.

[0027] The co-initiator is selected from one or more of N,N-dimethylaniline, zinc stearate, dilauryl thiodipropionate, triallyl isocyanurate, and peroxide carbonate.

[0028] Furthermore, the functionalized polyethylene wax is added through the middle or rear side feed port of the twin-screw extruder;

[0029] The preparation of the functionalized polyethylene wax includes the following steps:

[0030] S101. Raw material preparation: Weigh 100 parts by weight of ethylene, 1.5-2.5 parts by weight of 1-butene, 2-3.5 parts by weight of 1-octene, 0.3-0.8 parts by weight of vinylcyclohexane, 0.0008-0.0012 parts by weight of dimethylsilylbis(2-methyl-4-phenylindenyl)zirconia dichloride, 0.001-0.0018 parts by weight of bis(n-butylcyclopentadienyl)zirconia dichloride, 0.08-0.15 parts by weight of modified methylaluminoxane, 300-400 parts by weight of a mixed solvent of cyclohexane and n-hexane, 0.2-0.4 parts by weight of supported catalyst precursor C, and hydrogen gas at a molar ratio of 0.15%-0.25% of the ethylene feed.

[0031] The volume ratio of cyclohexane to n-hexane is 7:3;

[0032] S102, First stage polymerization: Add the mixed solvent, 40%~45% of the modified methylaluminoxane, and all the supported catalyst precursor C into the reactor. After dispersion, introduce 15%~25% of the total ethylene, 50%~70% of the total 1-butene, 30%~50% of the total hydrogen, and all the dimethylsilylbis(2-methyl-4-phenylindenyl)zirconium dichloride. React at 55~65℃ and 0.6~1.0MPa for 15~25min.

[0033] S103, Second stage polymerization: Introduce ethylene (50%~70% of the remaining ethylene), all 1-octene, and hydrogen (40%~60% of the remaining hydrogen) into the product of the first stage polymerization, and react at 65~75℃ and 0.9~1.3MPa for 15~25min.

[0034] S104, Third stage polymerization: All remaining ethylene, all vinylcyclohexane, remaining 1-butene, all bis(n-butylcyclopentadienyl)zirconium dichloride, and remaining hydrogen are introduced into the product of the second stage polymerization, and the reaction is carried out at 70~75℃ and 1.2~1.8MPa for 10~20min.

[0035] S105. Termination and post-processing: A terminator is added to the third polymerization product to terminate the reaction, and then the product is devolatilized, granulated and dried to obtain the functionalized polyethylene wax.

[0036] Further, the preparation method of the modified methylaluminoxane in step S101 is as follows: under N2 protection, a methylaluminoxane (MAO) toluene solution is mixed with diisobutylaluminoxane (TIBAO) at an Al:Al molar ratio of 95:5 to 85:15, and the mixture is stirred and reacted at 40~60℃ for 3~6h. After the reaction is completed, some of the toluene solvent is removed under reduced pressure to obtain a modified methylaluminoxane (MMAO) toluene solution, wherein the aluminum content is 10%~15%.

[0037] Further, the preparation method of the supported catalyst precursor C in step S101 is as follows:

[0038] (1) Nano-silica (particle size 10~30nm, specific surface area 200~400m²) 2 (g) was vacuum dried at 110~120℃ to constant weight;

[0039] (2) Disperse the dried nano-silica in anhydrous toluene, add vinyltriethoxysilane, control the molar ratio of SiO2 to vinyltriethoxysilane to be 1:0.2~0.4, and reflux at 110~115℃ for 10~20h to obtain vinyl-functionalized silica;

[0040] (3) The vinyl functionalized silica is mixed with the modified methylaluminoxane toluene solution, and the molar ratio of aluminum to silicon is controlled to be (40~60):1. The mixture is stirred at room temperature and then separated, washed and dried to obtain the supported catalyst precursor C.

[0041] Further, the terminator in step S105 is an isopropanol solution containing 2% phosphoric acid, and its addition amount is 5%~10% of the total volume of the polymerization product slurry;

[0042] The devolatilization process is a three-stage series devolatilization process, specifically including:

[0043] (A) Primary devolatilization: Removal of most solvents and monomers at 120~140℃ and -0.04~-0.06MPa;

[0044] (B) Secondary devolatilization: Deep devolatilization and melt homogenization are carried out at 150~170℃ and -0.07~-0.085MPa;

[0045] (C) Three-stage devolatilization: The final devolatilization and melt refining are completed at 175~190℃ and -0.09~-0.098MPa.

[0046] Furthermore, the antioxidant is selected from one or more of hindered phenolic antioxidants and phosphite antioxidants, preferably antioxidant 1010: antioxidant 168 = 1:1.

[0047] Furthermore, the processing parameters of the twin-screw extruder in step S3 are as follows: zone 1 temperature 140~160℃, zone 2 temperature 160~180℃, zone 3 temperature 170~190℃, zone 4 temperature 170~190℃, zone 5 temperature 170~190℃, die head temperature 170~185℃, screw speed 250~450rpm, and material residence time 1~3min.

[0048] The present invention has the following advantages over the prior art:

[0049] 1. This invention utilizes maleic anhydride (MAH) and styrene (St) dual monomers for melt grafting onto a polyolefin matrix, and synergistically introduces a functionalized polyethylene wax with a core-shell-surface gradient structure, thereby constructing a multi-layered, toughened interfacial system at the molecular level. The MAH / St grafted chains provide the polyolefin matrix with strong polar sites for interaction with inorganic flame retardants; while the functionalized polyethylene wax, with its surface cyclic structure and internal nano-silica core, acts as a highly efficient interfacial bridging agent and dispersion anchoring point, significantly enhancing the interfacial bonding and physical entanglement between the flame retardant and the polymer matrix. This not only effectively inhibits the agglomeration of high-content flame retardants but also transforms the weaknesses of the filled system into toughening points, thereby significantly improving the oxygen index (LOI) and vertical flammability rating (UL94 V-0) while greatly increasing the tensile strength and elongation at break of the material, successfully overcoming the problems of embrittlement and performance degradation caused by high filler content.

[0050] 2. This invention provides long-term reliable thermal safety for cables by combining intrinsic material design with a stabilizing agent system. On one hand, the functionalized polyethylene wax itself is prepared through controlled polymerization, has a narrow molecular weight distribution, and the nano-SiO2 core enhances its thermal stability. On the other hand, the compounded antioxidant system provides continuous protection against thermo-oxidative aging during processing and use. Thermogravimetric analysis (TGA) data shows that the initial thermal decomposition temperature (T5%) of the obtained functionalized polyolefin is significantly higher than that of the conventional system. This ensures that the material maintains stable mechanical and flame-retardant properties under the thermal environment of long-term cable operation and even short-term overload, effectively delaying performance degradation and failure risks caused by thermal aging, and fundamentally improving the long-term operational safety and reliability of the cable. Detailed Implementation

[0051] To further explain the present invention, the following specific embodiments are described.

[0052] Example 1

[0053] A method for preparing a functionalized polyolefin for high-filling flame-retardant cables includes the following steps:

[0054] S1. Raw material preparation:

[0055] Prepare the following raw materials according to parts by weight: high-density polyethylene (LDPE, density 0.910 g / cm³). 3 50 parts, functionalized monomer 0.5 parts, compound synergistic initiator 0.05 parts, functionalized polyethylene wax 1 part, antioxidant (antioxidant 1010: antioxidant 168 = 1:1) 0.1 parts;

[0056] The functionalized monomer is a compound of maleic anhydride (MAH) and styrene, wherein maleic anhydride accounts for 60% of the total weight of the functionalized monomer and styrene accounts for 10%.

[0057] The compounded synergistic initiator is composed of low-temperature decomposition peroxide, medium-temperature decomposition peroxide and co-initiator in a ratio of 1:2:0.1;

[0058] The low-temperature decomposable peroxide is tert-butyl peroxyneodecanate (TBPND), with a 10-hour half-life temperature of 70°C.

[0059] The intermediate-temperature decomposition peroxide is benzoyl peroxide, with a 10-hour half-life temperature of 100°C.

[0060] The co-initiator is triallyl isocyanurate;

[0061] The functionalized polyethylene wax is added through the middle or rear side feed port of the twin-screw extruder;

[0062] The preparation of the functionalized polyethylene wax includes the following steps:

[0063] S101. Raw material preparation: Weigh 100 parts by weight of ethylene, 1.5 parts by weight of 1-butene, 2 parts by weight of 1-octene, 0.3 parts by weight of vinylcyclohexane, 0.0008 parts by weight of dimethylsilylbis(2-methyl-4-phenylindenyl)zirconia dichloride, 0.001 parts by weight of bis(n-butylcyclopentadienyl)zirconia dichloride, 0.08 parts by weight of modified methylaluminoxane, 300 parts by weight of a mixed solvent of cyclohexane and n-hexane, 0.2 parts by weight of supported catalyst precursor C, and hydrogen gas at a molar ratio of 0.15% of the ethylene feed.

[0064] The modified methylaluminoxane is prepared as follows: under N2 protection, a methylaluminoxane (MAO) toluene solution is mixed with diisobutylaluminoxane (TIBAO) at an Al:Al molar ratio of 95:5 to 85:15, and the mixture is stirred at 40°C for 3 hours. After the reaction is completed, some of the toluene solvent is removed under reduced pressure to obtain a modified methylaluminoxane (MMAO) toluene solution, wherein the aluminum content is 10%.

[0065] The preparation method of the supported catalyst precursor C is as follows:

[0066] (1) Nano-silica (particle size 10~30nm, specific surface area 200~400m²) 2 / g) was vacuum dried at 110℃ to constant weight;

[0067] (2) The dried nano-silica was dispersed in anhydrous toluene, vinyltriethoxysilane was added, and the molar ratio of SiO2 to vinyltriethoxysilane was controlled to be 1:0.2. The mixture was refluxed at 110°C for 10 h to obtain vinyl-functionalized silica.

[0068] (3) The vinyl-functionalized silica was mixed with the modified methylaluminoxane toluene solution, and the molar ratio of aluminum to silicon was controlled to be 40:1. The mixture was stirred at room temperature and reacted. After separation, washing and drying, the supported catalyst precursor C was obtained.

[0069] S102, First stage polymerization: The mixed solvent, 40% of the modified methylaluminoxane, and all the supported catalyst precursor C are added to the reactor. After dispersion, 15% of the total ethylene, 50% of the total 1-butene, 30% of the total hydrogen, and all the dimethylsilylbis(2-methyl-4-phenylindenyl)zirconium dichloride are introduced. The reaction is carried out at 55℃ and 0.6MPa for 15 min.

[0070] S103, Second stage polymerization: Ethylene (50% of the remaining total ethylene), all 1-octene, and hydrogen (40% of the remaining total hydrogen) are introduced into the product of the first stage polymerization, and the reaction is carried out at 65°C and 0.9 MPa for 15 min.

[0071] S104, Third stage polymerization: All remaining ethylene, all vinylcyclohexane, the remaining 1-butene, all bis(n-butylcyclopentadienyl)zirconium dichloride and the remaining hydrogen are introduced into the product of the second stage polymerization, and the reaction is carried out at 70℃ and 1.2MPa for 10 min.

[0072] S105. Termination and post-processing: Add an isopropanol solution containing 2% phosphoric acid to the third stage polymerization product. The amount added is 5% of the total volume of the polymerization product slurry to terminate the reaction. Then, after devolatilization, granulation and drying, the functionalized polyethylene wax is obtained.

[0073] The devolatilization process is a three-stage series devolatilization process, specifically including:

[0074] (A) Primary devolatilization: Removal of most solvents and monomers at 120℃ and -0.04MPa;

[0075] (B) Secondary devolatilization: Deep devolatilization and melt homogenization are carried out at 150℃ and -0.07MPa;

[0076] (C) Three-stage devolatilization: Final devolatilization and melt refining are completed at 175℃ and -0.09MPa;

[0077] S2, Premixed:

[0078] Add all the weighed components to the mixer in sequence and mix at room temperature for 6 minutes to ensure that each component is evenly dispersed to obtain a premix.

[0079] S3, Melt reaction extrusion:

[0080] The premixed material is fed into a high-torque co-rotating twin-screw extruder for melt blending and reactive grafting.

[0081] The processing parameters of the twin-screw extruder are as follows: Zone 1 temperature 140℃, Zone 2 temperature 160℃, Zone 3 temperature 170℃, Zone 4 temperature 170℃, Zone 5 temperature 170℃, Die head temperature 170℃, Screw speed 250rpm, and material residence time 1min.

[0082] S4. Extrusion granulation:

[0083] The molten strip extruded through the die of an extruder is cooled in a cooling water tank, then granulated and dried to obtain functionalized polyolefin particles.

[0084] Example 2

[0085] A method for preparing a functionalized polyolefin for high-filling flame-retardant cables includes the following steps:

[0086] S1. Raw material preparation:

[0087] Prepare the following raw materials according to parts by weight: high-density polyethylene (LDPE, density 0.918 g / cm³). 3 70 parts, 5 parts functionalized monomers, 1 part compound synergistic initiator, 10 parts functionalized polyethylene wax, and 0.5 parts antioxidant (antioxidant 1010: antioxidant 168 = 1:1).

[0088] The functionalized monomer is a compound combination of maleic anhydride (MAH) and styrene, wherein maleic anhydride accounts for 75% of the total weight of the functionalized monomer and styrene accounts for 25%;

[0089] The compounded synergistic initiator is composed of low-temperature decomposition peroxide, medium-temperature decomposition peroxide and co-initiator in a ratio of 2:3.5:0.5;

[0090] The low-temperature decomposition peroxide is tert-butyl peroxyneodecanate (TBPND), with a 10-hour half-life temperature of 80°C.

[0091] The intermediate-temperature decomposition peroxide is benzoyl peroxide, with a 10-hour half-life temperature of 110°C.

[0092] The co-initiator is triallyl isocyanurate;

[0093] The functionalized polyethylene wax is added through the middle or rear side feed port of the twin-screw extruder;

[0094] The preparation of the functionalized polyethylene wax includes the following steps:

[0095] S101. Raw material preparation: Weigh 100 parts by weight of ethylene, 2 parts by weight of 1-butene, 3 parts by weight of 1-octene, 0.5 parts by weight of vinylcyclohexane, 0.001 parts by weight of dimethylsilylbis(2-methyl-4-phenylindenyl)zirconia dichloride, 0.0014 parts by weight of bis(n-butylcyclopentadienyl)zirconia dichloride, 0.11 parts by weight of modified methylaluminoxane, 350 parts by weight of a mixed solvent of cyclohexane and n-hexane, 0.3 parts by weight of supported catalyst precursor C, and hydrogen gas at a molar ratio of 0.2% of the ethylene feed.

[0096] The modified methylaluminoxane is prepared as follows: under N2 protection, a methylaluminoxane (MAO) toluene solution is mixed with diisobutylaluminoxane (TIBAO) at an Al:Al molar ratio of 95:5 to 85:15, and the mixture is stirred at 50°C for 4 hours. After the reaction is completed, some of the toluene solvent is removed under reduced pressure to obtain a modified methylaluminoxane (MMAO) toluene solution, wherein the aluminum content is 13%.

[0097] The preparation method of the supported catalyst precursor C is as follows:

[0098] (1) Nano-silica (particle size 10~30nm, specific surface area 200~400m²) 2 / g) was vacuum dried at 115℃ to constant weight;

[0099] (2) The dried nano-silica was dispersed in anhydrous toluene, vinyltriethoxysilane was added, and the molar ratio of SiO2 to vinyltriethoxysilane was controlled to be 1:0.3. The mixture was refluxed at 113°C for 15 h to obtain vinyl-functionalized silica.

[0100] (3) The vinyl-functionalized silica was mixed with the modified methylaluminoxane toluene solution, and the molar ratio of aluminum to silicon was controlled at 50:1. The mixture was stirred at room temperature, and after separation, washing and drying, the supported catalyst precursor C was obtained.

[0101] S102, First stage polymerization: The mixed solvent, 43% of the modified methylaluminoxane, and all the supported catalyst precursor C are added to the reactor. After dispersion, 20% of the total ethylene, 60% of the total 1-butene, 40% of the total hydrogen, and all the dimethylsilylbis(2-methyl-4-phenylindenyl)zirconium dichloride are introduced. The reaction is carried out at 60℃ and 0.8MPa for 20min.

[0102] S103, Second stage polymerization: Ethylene (60% of the remaining total ethylene), all 1-octene, and hydrogen (50% of the remaining total hydrogen) are introduced into the product of the first stage polymerization, and the reaction is carried out at 70°C and 1.1 MPa for 20 min.

[0103] S104, Third stage polymerization: All remaining ethylene, all vinylcyclohexane, the remaining 1-butene, all bis(n-butylcyclopentadienyl)zirconium dichloride and the remaining hydrogen are introduced into the product of the second stage polymerization, and the reaction is carried out at 73°C and 1.5MPa for 15 min.

[0104] S105. Termination and post-processing: Add an isopropanol solution containing 2% phosphoric acid to the third stage polymerization product. The amount added is 8% of the total volume of the polymerization product slurry to terminate the reaction. Then, after devolatilization, granulation and drying, the functionalized polyethylene wax is obtained.

[0105] The devolatilization process is a three-stage series devolatilization process, specifically including:

[0106] (A) Primary devolatilization: Removal of most solvents and monomers at 130℃ and -0.05MPa;

[0107] (B) Secondary devolatilization: Deep devolatilization and melt homogenization are carried out at 160℃ and -0.078MPa;

[0108] (C) Three-stage devolatilization: Final devolatilization and melt refining are completed at 183℃ and -0.094MPa;

[0109] S2, Premixed:

[0110] Add all the weighed components to the mixer in sequence and mix at room temperature for 8 minutes to ensure that each component is evenly dispersed to obtain a premix.

[0111] S3, Melt reaction extrusion:

[0112] The premixed material is fed into a high-torque co-rotating twin-screw extruder for melt blending and reactive grafting.

[0113] The processing parameters of the twin-screw extruder are as follows: Zone 1 temperature 150℃, Zone 2 temperature 170℃, Zone 3 temperature 180℃, Zone 4 temperature 180℃, Zone 5 temperature 180℃, Die head temperature 178℃, Screw speed 350rpm, and material residence time 12min.

[0114] S4. Extrusion granulation:

[0115] The molten strip extruded through the die of an extruder is cooled in a cooling water tank, then granulated and dried to obtain functionalized polyolefin particles.

[0116] Example 3

[0117] A method for preparing a functionalized polyolefin for high-filling flame-retardant cables includes the following steps:

[0118] S1. Raw material preparation:

[0119] Prepare the following raw materials according to parts by weight: high-density polyethylene (LDPE, density 0.925 g / cm³). 3 90 parts, functionalized monomers 10 parts, compound synergistic initiator 2 parts, functionalized polyethylene wax 20 parts, antioxidant (antioxidant 1010: antioxidant 168=1:1) 1 part;

[0120] The functionalized monomer is a compound combination of maleic anhydride (MAH) and styrene, wherein maleic anhydride accounts for 90% of the total weight of the functionalized monomer and styrene accounts for 40%.

[0121] The compounded synergistic initiator is composed of a low-temperature decomposition peroxide, a medium-temperature decomposition peroxide, and a co-initiator in a ratio of 3:5:1.

[0122] The low-temperature decomposable peroxide is tert-butyl peroxyneodecanate (TBPND), with a 10-hour half-life temperature of 90°C.

[0123] The intermediate-temperature decomposition peroxide is benzoyl peroxide, with a 10-hour half-life temperature of 120°C;

[0124] The co-initiator is peroxide carbonate;

[0125] The functionalized polyethylene wax is added through the middle or rear side feed port of the twin-screw extruder;

[0126] The preparation of the functionalized polyethylene wax includes the following steps:

[0127] S101. Raw material preparation: Weigh 100 parts by weight of ethylene, 2.5 parts by weight of 1-butene, 3.5 parts by weight of 1-octene, 0.8 parts by weight of vinylcyclohexane, 0.0012 parts by weight of dimethylsilylbis(2-methyl-4-phenylindenyl)zirconia dichloride, 0.0018 parts by weight of bis(n-butylcyclopentadienyl)zirconia dichloride, 0.15 parts by weight of modified methylaluminoxane, 400 parts by weight of a mixed solvent of cyclohexane and n-hexane, 0.4 parts by weight of supported catalyst precursor C, and hydrogen gas at a molar ratio of 0.25% of the ethylene feed.

[0128] The modified methylaluminoxane is prepared as follows: under N2 protection, a methylaluminoxane (MAO) toluene solution is mixed with diisobutylaluminoxane (TIBAO) at an Al:Al molar ratio of 95:5 to 85:15, and the mixture is stirred at 60°C for 6 hours. After the reaction is completed, some of the toluene solvent is removed under reduced pressure to obtain a modified methylaluminoxane (MMAO) toluene solution, wherein the aluminum content is 15%.

[0129] The preparation method of the supported catalyst precursor C is as follows:

[0130] (1) Nano-silica (particle size 10~30nm, specific surface area 200~400m²) 2 / g) was vacuum dried at 120℃ to constant weight;

[0131] (2) The dried nano-silica was dispersed in anhydrous toluene, vinyltriethoxysilane was added, and the molar ratio of SiO2 to vinyltriethoxysilane was controlled to be 1:0.4. The mixture was refluxed at 115°C for 20 h to obtain vinyl-functionalized silica.

[0132] (3) The vinyl-functionalized silica was mixed with the modified methylaluminoxane toluene solution, and the molar ratio of aluminum to silicon was controlled to be 60:1. The mixture was stirred at room temperature and reacted. After separation, washing and drying, the supported catalyst precursor C was obtained.

[0133] S102, First stage polymerization: The mixed solvent, 45% of the modified methylaluminoxane, and all the supported catalyst precursor C are added to the reactor. After dispersion, 25% of the total ethylene, 70% of the total 1-butene, 50% of the total hydrogen, and all the dimethylsilylbis(2-methyl-4-phenylindenyl)zirconium dichloride are introduced. The reaction is carried out at 65℃ and 1.0MPa for 25 min.

[0134] S103, Second stage polymerization: Ethylene (70% of the remaining total ethylene), all 1-octene, and hydrogen (60% of the remaining total hydrogen) are introduced into the product of the first stage polymerization, and the reaction is carried out at 75°C and 1.3 MPa for 25 min.

[0135] S104, Third stage polymerization: All remaining ethylene, all vinylcyclohexane, the remaining 1-butene, all bis(n-butylcyclopentadienyl)zirconium dichloride and the remaining hydrogen are introduced into the product of the second stage polymerization, and the reaction is carried out at 75°C and 1.8 MPa for 20 min.

[0136] S105. Termination and post-processing: Add an isopropanol solution containing 2% phosphoric acid to the third stage polymerization product. The amount added is 10% of the total volume of the polymerization product slurry to terminate the reaction. Then, after devolatilization, granulation and drying, the functionalized polyethylene wax is obtained.

[0137] The devolatilization process is a three-stage series devolatilization process, specifically including:

[0138] (A) Primary devolatilization: Removal of most solvents and monomers at 140℃ and -0.06MPa;

[0139] (B) Secondary devolatilization: Deep devolatilization and melt homogenization are carried out at 170℃ and -0.085MPa;

[0140] (C) Three-stage devolatilization: Final devolatilization and melt refining are completed at 190℃ and -0.098MPa;

[0141] S2, Premixed:

[0142] Add all the weighed components to the mixer in sequence and mix at room temperature for 10 minutes to ensure that each component is evenly dispersed to obtain a premix.

[0143] S3, Melt reaction extrusion:

[0144] The premixed material is fed into a high-torque co-rotating twin-screw extruder for melt blending and reactive grafting.

[0145] The processing parameters of the twin-screw extruder are as follows: Zone 1 temperature 160℃, Zone 2 temperature 180℃, Zone 3 temperature 190℃, Zone 4 temperature 190℃, Zone 5 temperature 190℃, Die head temperature 185℃, Screw speed 450rpm, and material residence time 3min.

[0146] S4. Extrusion granulation:

[0147] The molten strip extruded through the die of an extruder is cooled in a cooling water tank, then granulated and dried to obtain functionalized polyolefin particles.

[0148] Comparative Example 1

[0149] Compared with Example 2, Comparative Example 1 replaced the compound synergistic initiator with a single DCP (1.5 parts), while the other steps and parameters were the same as in Example 2.

[0150] Comparative Example 2

[0151] In Comparative Example 2, the functionalized polyethylene wax was replaced with ordinary polyethylene wax (Honeywell AC). ® Its melting point is about 105°C and its density is 0.88~1.10 g / cc. Other steps and parameters are the same as in Example 2.

[0152] Comparative Example 3

[0153] Compared with Example 2, Comparative Example 3 omits the functionalized monomer, while the other steps and parameters are the same as in Example 2.

[0154] Performance testing

[0155] Tensile strength and elongation at break were determined according to GB / T 1040.2-2022 at a tensile rate of 50 mm / min; oxygen index was tested according to GB / T 2406.2-2009; UL94 flammability rating (vertical burning, 1.6 mm) was tested according to GB / T 2408-2021; thermal decomposition temperature was tested using TGA (thermogravimetric analysis) in an N2 atmosphere at a heating rate of 10 °C / min.

[0156] The test results are shown in Table 1 below.

[0157] Table 1

[0158] Tensile strength (MPa) Elongation at break (%) LOI (%) UL94 rating (1.6 mm) [T5% (°C) <!-- 8 -->]]> Example 1 18.2 333 33.2 V-0 369 Example 2 20.5 385 35.5 V-0 378 Example 3 22.1 412 36.8 V-0 385 Comparative Example 1 15.3 280 28.0 V-2 310 Comparative Example 2 14.8 250 27.5 V-2 305 Comparative Example 3 12.1 180 25.0 Not passed 295

[0159] As shown in Table 1 above, compared with Comparative Example 1, the tensile strength of Example 2 increased from 15.3 MPa to 20.5 MPa, the elongation at break increased from 280% to 385%, and the LOI increased from 28.0% to 35.5%. This is because the low-temperature TBPND and medium-temperature BPO compound can continuously generate free radicals within a wide temperature range (140~190℃) during twin-screw extrusion, reducing the chain termination reaction during single DCP initiation, improving the grafting efficiency of MAH / St, and enhancing the interfacial bonding between polyolefins and flame retardants.

[0160] Compared with Comparative Example 2, Example 2 showed an increase of 38.51% in tensile strength, 54% in elongation at break, and 29.09% in LOI. Ordinary polyethylene wax only serves a lubricating function, while the core-shell-surface gradient structure of the functionalized polyethylene wax in this solution not only forms a synergistic flame-retardant barrier with the flame retardant through SiO2, but also improves compatibility, mechanical properties, and processing fluidity by entanglement between the shell and the polyolefin matrix and reducing the melt viscosity of the surface layer.

[0161] Compared with Comparative Example 3, Example 2 showed a 69.42% increase in tensile strength, a 113.89% increase in elongation at break, and a 42% increase in LOI. It also achieved a UL94 rating upgrade from failing to pass to V-0. This demonstrates that functionalized monomers are the core guarantee for achieving interfacial bonding and flame retardant performance in high-filler systems.

[0162] The specific embodiments described above further illustrate the purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above description is only a specific embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing functionalized polyolefins for high-filling flame-retardant cables, characterized in that, Includes the following steps: S1. Raw material preparation: Prepare the following raw materials according to the following weight parts: 50-90 parts of polyolefin matrix resin, 0.5-10 parts of functionalized monomer, 0.05-2 parts of compound synergistic initiator, 1-20 parts of functionalized polyethylene wax, and 0.1-1 parts of antioxidant; S2, Premixed: Add all the weighed components to the mixer in sequence and mix at room temperature for 6-10 minutes to ensure that each component is evenly dispersed to obtain a premix. S3, Melt reaction extrusion: The premixed material is fed into a high-torque co-rotating twin-screw extruder for melt blending and reactive grafting. S4. Extrusion granulation: The molten strip extruded through the die of an extruder is cooled in a cooling water tank, then granulated and dried to obtain functionalized polyolefin particles.

2. The method for preparing a functionalized polyolefin for high-filling flame-retardant cables according to claim 1, characterized in that, The polyolefin matrix resin mentioned in step S1 is selected from one or more mixtures of high-pressure low-density polyethylene, linear low-density polyethylene, metallocene linear low-density polyethylene, high-density polyethylene, homopolymer polypropylene, impact copolymer polypropylene, random copolymer polypropylene, polyolefin elastomer, olefin block copolymer, and EPDM rubber.

3. The method for preparing a functionalized polyolefin for high-filling flame-retardant cables according to claim 1, characterized in that, The functionalized monomers mentioned in step S1 are a combination of maleic anhydride and styrene, wherein maleic anhydride accounts for 60% to 90% of the total weight of the functionalized monomers and styrene accounts for 10% to 40%.

4. The method for preparing a functionalized polyolefin for high-filling flame-retardant cables according to claim 1, characterized in that, The compounded synergistic initiator mentioned in step S1 is composed of low-temperature decomposition peroxide, medium-temperature decomposition peroxide and co-initiator in a ratio of (1~3):(2~5):(0.1~1); The low-temperature decomposition peroxide is selected from one or a combination of tert-butyl peroxynedecanoate and tert-butyl peroxyisobutyrate, and the 10-hour half-life temperature is 70~90℃. The intermediate-temperature decomposition peroxide is selected from one or a combination of dicumyl peroxide and benzoyl peroxide, and the 10-hour half-life temperature is 100~120℃. The co-initiator is selected from one or more of N,N-dimethylaniline, zinc stearate, dilauryl thiodipropionate, triallyl isocyanurate, and peroxide carbonate.

5. The method for preparing a functionalized polyolefin for high-filling flame-retardant cables according to claim 1, characterized in that, The functionalized polyethylene wax is added through the middle or rear side feed port of the twin-screw extruder; The preparation of the functionalized polyethylene wax includes the following steps: S101. Raw material preparation: Weigh 100 parts by weight of ethylene, 1.5-2.5 parts by weight of 1-butene, 2-3.5 parts by weight of 1-octene, 0.3-0.8 parts by weight of vinylcyclohexane, 0.0008-0.0012 parts by weight of dimethylsilylbis(2-methyl-4-phenylindenyl)zirconia dichloride, 0.001-0.0018 parts by weight of bis(n-butylcyclopentadienyl)zirconia dichloride, 0.08-0.15 parts by weight of modified methylaluminoxane, 300-400 parts by weight of a mixed solvent of cyclohexane and n-hexane, 0.2-0.4 parts by weight of supported catalyst precursor C, and hydrogen gas at a molar ratio of 0.15%-0.25% of the ethylene feed. S102, First stage polymerization: Add the mixed solvent, 40%~45% of the modified methylaluminoxane, and all the supported catalyst precursor C into the reactor. After dispersion, introduce 15%~25% of the total ethylene, 50%~70% of the total 1-butene, 30%~50% of the total hydrogen, and all the dimethylsilylbis(2-methyl-4-phenylindenyl)zirconium dichloride. React at 55~65℃ and 0.6~1.0MPa for 15~25min. S103, Second stage polymerization: Introduce ethylene (50%~70% of the remaining ethylene), all 1-octene, and hydrogen (40%~60% of the remaining hydrogen) into the product of the first stage polymerization, and react at 65~75℃ and 0.9~1.3MPa for 15~25min. S104, Third stage polymerization: All remaining ethylene, all vinylcyclohexane, remaining 1-butene, all bis(n-butylcyclopentadienyl)zirconium dichloride, and remaining hydrogen are introduced into the product of the second stage polymerization, and the reaction is carried out at 70~75℃ and 1.2~1.8MPa for 10~20min. S105. Termination and post-processing: A terminator is added to the third polymerization product to terminate the reaction, and then the product is devolatilized, granulated and dried to obtain the functionalized polyethylene wax.

6. The method for preparing a functionalized polyolefin for high-filling flame-retardant cables according to claim 5, characterized in that, The modified methylaluminoxane described in step S101 is prepared as follows: under N2 protection, a methylaluminoxane toluene solution is mixed with diisobutylaluminoxane at an Al:Al molar ratio of 95:5 to 85:15, and the mixture is stirred and reacted at 40~60℃ for 3~6h. After the reaction is completed, some of the toluene solvent is removed under reduced pressure to obtain a modified methylaluminoxane toluene solution, wherein the aluminum content is 10%~15%.

7. The method for preparing a functionalized polyolefin for high-filling flame-retardant cables according to claim 6, characterized in that, The preparation method of the supported catalyst precursor C in step S101 is as follows: (1) Dry the nano-silica under vacuum at 110~120℃ to constant weight; (2) Disperse the dried nano-silica in anhydrous toluene, add vinyltriethoxysilane, control the molar ratio of SiO2 to vinyltriethoxysilane to be 1:0.2~0.4, and reflux at 110~115℃ for 10~20h to obtain vinyl-functionalized silica; (3) The vinyl functionalized silica is mixed with the modified methylaluminoxane toluene solution, and the molar ratio of aluminum to silicon is controlled to be (40~60):

1. The mixture is stirred at room temperature and then separated, washed and dried to obtain the supported catalyst precursor C.

8. The method for preparing a functionalized polyolefin for a high-filling flame-retardant cable according to claim 5, characterized in that, The terminator mentioned in step S105 is an isopropanol solution containing 2% phosphoric acid, and its addition amount is 5%~10% of the total volume of the polymerization product slurry; The devolatilization process is a three-stage series devolatilization process, specifically including: (A) Primary devolatilization: Removal of most solvents and monomers at 120~140℃ and -0.04~-0.06MPa; (B) Secondary devolatilization: Deep devolatilization and melt homogenization are carried out at 150~170℃ and -0.07~-0.085MPa; (C) Three-stage devolatilization: The final devolatilization and melt refining are completed at 175~190℃ and -0.09~-0.098MPa.

9. The method for preparing a functionalized polyolefin for a high-filling flame-retardant cable according to claim 1, characterized in that, The antioxidant is selected from one or more of hindered phenolic antioxidants and phosphite antioxidants.

10. The method for preparing a functionalized polyolefin for a high-filling flame-retardant cable according to claim 1, characterized in that, The processing parameters of the twin-screw extruder in step S3 are as follows: zone 1 temperature 140~160℃, zone 2 temperature 160~180℃, zone 3 temperature 170~190℃, zone 4 temperature 170~190℃, zone 5 temperature 170~190℃, die head temperature 170~185℃, screw speed 250~450rpm, and material residence time 1~3min.