Multilayer co-extrusion mpp cable protection pipe and preparation method thereof

Abstract

The application belongs to the field of molecular composites, and discloses a multi-layer co-extrusion MPP cable protection pipe and a preparation method thereof. From inside to outside, the pipe comprises a conductive wear-resistant inner layer, a reinforcing and toughening intermediate layer and a weather-resistant and flame-retardant outer layer, and the three layers are combined and formed through a co-extrusion process. In view of the technical defects and industry common pain points in the prior art, such as the single function of the single-layer structure, the poor interlayer bonding force of the multi-layer structure, the poor conductive modification effect, the many drawbacks of the glass fiber reinforcement, the mechanical property decline caused by the flame-retardant modification and the like, the application provides a multi-layer co-extrusion MPP cable protection pipe and a preparation method thereof.

Description

Technical Field

[0001] This invention relates to the field of molecular composite materials technology, specifically to a multilayer co-extruded MPP cable protection pipe and its preparation method. Background Technology

[0002] MPP (modified polypropylene) cable protection pipes are widely used in cable laying protection in power, telecommunications, and municipal engineering fields due to their excellent insulation, high temperature resistance, impact resistance, and corrosion resistance. With the rapid development of urban power grid construction, the performance requirements for MPP cable protection pipes are also increasing. Not only are good mechanical properties required, but the pipes also need to possess multiple functions such as conductivity, antistatic properties, flame retardancy, and weather resistance to meet the demands of use in complex environments.

[0003] Currently, MPP cable protection pipes on the market generally suffer from the following technical deficiencies: First, most pipes are single-layer structures, making it difficult to simultaneously meet multiple functional requirements. To achieve multiple functions, a large amount of various additives are needed, leading to decreased processing performance and significantly increased costs. Second, existing multi-layer co-extruded pipes generally suffer from poor interlayer bonding, which can easily lead to delamination and peeling during long-term use, affecting the service life of the pipes. Third, conductive modification often uses carbon black fillers, which has problems such as large addition amounts, unstable conductivity, easy precipitation, and affecting the color of the pipes. Fourth, reinforcing modification often uses glass fiber, which has problems such as exposed fibers, rough surfaces, severe wear on processing equipment, and high specific gravity. Fifth, flame-retardant modification often uses inorganic flame retardants such as magnesium hydroxide and aluminum hydroxide, which have large filling amounts, leading to a significant decrease in the mechanical properties of the pipes, poor toughness, and easy cracking at low temperatures.

[0004] Therefore, developing a multi-layer co-extruded MPP cable protection pipe with a reasonable structural design, strong interlayer bonding, excellent comprehensive performance, and the ability to simultaneously meet multiple functional requirements has significant practical application value. Summary of the Invention

[0005] In view of the technical defects and common pain points in the industry of existing MPP cable protection pipes, such as the single-layer structure having limited function, the multi-layer structure having poor interlayer bonding force, poor conductivity modification effect, numerous drawbacks of glass fiber reinforcement, and the decline in mechanical properties due to flame retardant modification, the purpose of this invention is to provide a multi-layer co-extruded MPP cable protection pipe and its preparation method.

[0006] To achieve the above objectives, the present invention provides the following technical solution: The technical solution provided by this invention is: A multilayer co-extruded MPP cable protection pipe consists of a conductive and wear-resistant inner layer, a reinforcing and toughening intermediate layer, and a weather-resistant and flame-retardant outer layer, which are formed by co-extrusion.

[0007] The conductive and wear-resistant inner layer is prepared from the following raw materials in parts by weight: 70-90 parts homopolymer polypropylene, 3-10 parts polyaniline in-situ coated expanded graphite conductive filler, 2-6 parts polyimide micro powder, 4-12 parts maleic anhydride-styrene graft copolymer, 1-4 parts itaconic acid modified microcrystalline cellulose, 2-5 parts aluminum hypophosphite-melamine cyanurate-montmorillonite ternary synergistic flame retardant system, 0.2-0.6 parts composite antioxidant, and 0.3-0.8 parts composite lubricant.

[0008] The reinforced and toughened intermediate layer is prepared from the following raw materials in parts by weight: 50-70 parts copolymer polypropylene, 20-40 parts homopolymer polypropylene, 6-18 parts silanized aramid pulp, 8-18 parts ethylene-octene copolymer, 5-12 parts maleic anhydride-styrene graft copolymer, 2-6 parts itaconic acid modified microcrystalline cellulose, 3-7 parts aluminum hypophosphite-melamine cyanurate-montmorillonite ternary synergistic flame retardant system, 0.3-0.8 parts composite antioxidant, and 0.4-1.0 parts composite lubricant.

[0009] The weather-resistant and flame-retardant outer layer is prepared from the following raw materials in parts by weight: 60-80 parts copolymer polypropylene, 12-25 parts lignin-based phosphorus-nitrogen intumescent flame retardant, 0.5-1.5 parts composite light stabilizer, 1-3 parts itaconic acid modified microcrystalline cellulose, 5-10 parts aluminum hypophosphite-melamine cyanurate-montmorillonite ternary synergistic flame retardant system, 0.3-0.8 parts composite antioxidant, and 0.4-1.0 parts composite lubricant.

[0010] Furthermore, the itaconic acid-modified microcrystalline cellulose is prepared by grafting itaconic acid onto microcrystalline cellulose, with the amount of itaconic acid grafted being 5%-12% of the mass of the microcrystalline cellulose; the particle size of the microcrystalline cellulose is 20-50 μm.

[0011] Furthermore, the aluminum hypophosphite-melamine cyanurate-montmorillonite ternary synergistic flame retardant system is prepared by high-speed melt composite of aluminum hypophosphite, melamine cyanurate, and organically modified montmorillonite in a weight ratio of 2-3:1:0.5-1; wherein the organically modified montmorillonite is hexadecyltrimethylammonium bromide modified montmorillonite.

[0012] Furthermore, the polyaniline in-situ coated expanded graphite conductive filler is formed by in-situ polymerization and coating of expanded graphite with hydrochloric acid doping polyaniline, with a polyaniline coating amount of 8%-15% and a mesh size of 80-150 mesh for the expanded graphite; the particle size of the polyimide micro powder is 10-20 μm; and the silanized aramid pulp is a para-aramid pulp with a surface treatment of γ-aminopropyltriethoxysilane and a length of 0.5-2 mm.

[0013] Furthermore, the lignin-based phosphorus-nitrogen intumescent flame retardant is a phosphorus-nitrogen synergistic intumescent flame retardant prepared by enzymatic hydrolysis of lignin followed by phosphorylation and amination modification; the grafting rate of the maleic anhydride-styrene graft copolymer is 1.0%-3.0%; the composite light stabilizer is a mixture of hindered amine light stabilizer and benzotriazole UV absorber in a weight ratio of 1:1-1.5; the composite antioxidant is a mixture of antioxidant 1010 and antioxidant 168 in a weight ratio of 1:1.5-2; and the composite lubricant is a mixture of polyethylene wax and calcium stearate in a weight ratio of 2-3:1.

[0014] Furthermore, the thickness ratio of the conductive and wear-resistant inner layer, the reinforcing and toughening intermediate layer, and the weather-resistant and flame-retardant outer layer is 1:2-3:1-1.5; the overall wall thickness of the cable protection tube is 5-20mm, and the ring stiffness is ≥18kN / m. 2 Volume resistivity ≤ 8 × 10 6 Ω·m, oxygen index ≥38%, tensile strength retention rate ≥90% after 1000h of artificial accelerated aging, and interlayer peel strength ≥2.0MPa.

[0015] The present invention also provides a method for preparing the above-mentioned multilayer co-extruded MPP cable protection tube, comprising the following steps: S1 Functional Filler Pre-preparation: Polyaniline in-situ coated expanded graphite conductive filler, silanized aramid pulp, lignin-based phosphorus-nitrogen intumescent flame retardant, maleic anhydride-styrene graft copolymer, itaconic acid modified microcrystalline cellulose, and aluminum hypophosphite-melamine cyanurate-montmorillonite ternary synergistic flame retardant system were prepared separately for later use. S2 Raw material pretreatment: Weigh out the raw materials of conductive wear-resistant inner layer, reinforced and toughened middle layer and weather-resistant and flame-retardant outer layer according to the weight parts, put them into a high-speed mixer, heat to 90-100℃, mix at high speed for 8-15 minutes to obtain three groups of premixed materials. S3 Twin-screw granulation: The three groups of premixed materials prepared by S2 are fed into three twin-screw extruders respectively. The temperature of each section is controlled at 170-200℃ and the screw speed is 200-300r / min. Melt extrusion granulation is carried out to obtain conductive and wear-resistant inner layer granules, reinforced and toughened middle layer granules, and weather-resistant and flame-retardant outer layer granules respectively. S4 Three-layer co-extrusion molding: The three types of granules prepared in S3 are added to three single-screw extruders respectively. The discharge ports of the three extruders are simultaneously connected to the three-layer co-extrusion die head. The temperature of each extruder is controlled at 180-210℃, the die head temperature is controlled at 200-220℃, and the extrusion rate of each layer is controlled to make the thickness ratio 1:2-3:1-1.5. After vacuum sizing, cooling, traction and cutting, the three-layer co-extruded pipe semi-finished product is obtained. S5 Heat treatment enhances interface bonding: The three-layer co-extruded pipe semi-finished product prepared by S4 is placed in an oven at 85-95℃ for heat treatment for 2-4 hours. After being taken out, it is naturally cooled to room temperature to obtain the finished multi-layer co-extruded MPP cable protection pipe.

[0016] Further, in S1, the preparation method of the itaconic acid modified microcrystalline cellulose is as follows: microcrystalline cellulose is added to deionized water to prepare a suspension with a concentration of 10%-15%, heated to 70-80℃, protected by nitrogen gas, itaconic acid and ammonium persulfate initiator are added, and the mixture is stirred for 3-5 hours. After the reaction is completed, the mixture is filtered, washed, and dried to obtain itaconic acid modified microcrystalline cellulose; the amount of ammonium persulfate used is 1%-3% of the mass of microcrystalline cellulose.

[0017] Further, in S1, the preparation method of the aluminum hypophosphite-melamine cyanurate-montmorillonite ternary synergistic flame retardant system is as follows: Weigh aluminum hypophosphite, melamine cyanurate, and organically modified montmorillonite according to the weight ratio, add them to a high-speed mixer, heat to 100-120℃, and mix at a high speed of 1500-2000r / min for 10-20min to fully compound and disperse the three components under thermal shear. After discharge, cool to room temperature to obtain the ternary synergistic flame retardant system.

[0018] Further, in S1, the preparation method of the polyaniline in-situ coated expanded graphite conductive filler is as follows: Expanded graphite is added to a 1 mol / L hydrochloric acid solution, stirred and dispersed evenly, aniline monomer is added, and ammonium persulfate initiator is slowly added dropwise under an ice-water bath. After the addition is complete, the reaction continues for 6-10 hours. The mixture is then filtered, washed, and dried to obtain the polyaniline in-situ coated expanded graphite. The preparation method of the silanized aramid pulp is as follows: Aramid pulp is added to anhydrous ethanol and ultrasonically dispersed for 15- After 30 minutes, γ-aminopropyltriethoxysilane is added, and the mixture is heated to 60-70℃ and stirred for 3-5 hours. After filtration, washing, and drying, silanized aramid pulp is obtained. The preparation method of the lignin-based phosphorus-nitrogen intumescent flame retardant is as follows: enzymatically hydrolyzed lignin is dissolved in N,N-dimethylformamide, phosphorylation reagent and amination reagent are added sequentially, and the mixture is heated to 80-100℃ and reacted for 4-8 hours. After precipitation, washing, and drying, lignin-based phosphorus-nitrogen intumescent flame retardant is obtained.

[0019] Furthermore, in S2, the stirring speed of the high-speed mixer is 1000-1500 r / min; in S3, the length-to-diameter ratio of the twin-screw extruder is 40-44:1, and the residence time of the material in the extruder is 60-120 s.

[0020] Furthermore, in S4, the three-layer co-extrusion die head adopts a spiral flow channel structure, the convergence angle of each layer of melt in the die head is 15-30°, the residence time of the melt in the die head is 30-60s; the vacuum degree of vacuum sizing is -0.07~-0.09MPa, and the cooling water temperature is 15-25℃.

[0021] Furthermore, during the heat treatment of S5, the maleic anhydride-styrene graft copolymer in each layer undergoes an interfacial grafting reaction with the polypropylene molecular chains and filler surfaces of adjacent layers, forming a stable interlayer interpenetrating transition structure, thus preventing interlayer separation during long-term use of the pipe.

[0022] The beneficial effects of this technical solution are: (1) The conductive wear-resistant inner layer of the present invention uses polyaniline in-situ coated expanded graphite as a conductive filler. By coating the graphite surface with conductive polymer in-situ, the interfacial compatibility between graphite and polypropylene matrix can be effectively improved, avoiding the problems of easy agglomeration and uneven dispersion of traditional carbon black fillers. At the same time, it gives the inner layer stable and long-lasting conductive and antistatic properties, reducing the risk of static electricity accumulation. Combined with the high wear resistance of polyimide micro powder, it can significantly improve the wear resistance of the inner wall of the pipe and extend the service life of the cable during the cable threading process.

[0023] (2) The reinforcing and toughening intermediate layer of the present invention uses silanized aramid pulp as the reinforcing material. The high specific strength and network fiber structure of aramid pulp can form an effective reinforcing skeleton in the polypropylene matrix, significantly improving the ring stiffness and impact resistance of the pipe, while avoiding the disadvantages of traditional glass fiber reinforcement such as fiber exposure, surface roughness, and severe wear of processing equipment; combined with the toughening effect of ethylene-octene copolymer, the simultaneous improvement of reinforcement and toughness is achieved, effectively solving the contradiction of "reinforcement makes it brittle" in traditional modification.

[0024] (3) The weather-resistant and flame-retardant outer layer of the present invention uses a lignin-based phosphorus-nitrogen intumescent flame retardant. The environmentally friendly intumescent flame retardant is prepared using industrial waste lignin as raw material. It achieves high-efficiency flame retardancy through the synergistic effect of phosphorus and nitrogen, while also having the environmental advantages of biomass materials. Combined with the itaconic acid-modified microcrystalline cellulose and ternary synergistic flame retardant system added to all three layers, as well as the interface compatibilization effect of maleic anhydride-styrene graft copolymer, a stable and firm bonding interface is formed between the three layers, avoiding interlayer separation and improving the overall performance and service life of the pipe. Attached Figure Description

[0025] Figure 1 This is a schematic diagram of the preparation process of a multilayer co-extruded MPP cable protection pipe and its preparation method proposed in this invention. Detailed Implementation

[0026] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. 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.

[0027] The specific implementation process is as follows: Example 1:

[0028] Please see Figure 1 This embodiment provides a multilayer co-extruded MPP cable protection pipe, and the raw material formula and model of each layer are as follows (unit: kg): Conductive and wear-resistant inner layer formulation: homopolymer polypropylene (T30S) 80kg, polyaniline in-situ coated expanded graphite conductive filler 5kg, polyimide micro powder (PI-200, particle size 15μm) 3kg, maleic anhydride-styrene graft copolymer (SMA-1000, grafting rate 1.8%) 6kg, itaconic acid modified microcrystalline cellulose 2kg, aluminum hypophosphite-melamine cyanurate-montmorillonite ternary synergistic flame retardant system 3kg, composite antioxidant (antioxidant 1010: antioxidant 168 = 1:1.5) 0.3kg, composite lubricant (polyethylene wax PEW-0200: calcium stearate = 2:1) 0.4kg.

[0029] Reinforced and toughened intermediate layer formulation: Copolymer polypropylene (EPC30R) 60kg, Homopolymer polypropylene (T30S) 30kg, Silanized aramid pulp 10kg, Ethylene-octene copolymer (POE 8150) 12kg, Maleic anhydride-styrene graft copolymer (SMA-1000) 8kg, Itaconic acid modified microcrystalline cellulose 4kg, Aluminum hypophosphite-melamine cyanurate-montmorillonite ternary synergistic flame retardant system 5kg, Composite antioxidant (Antioxidant 1010: Antioxidant 168 = 1:1.5) 0.5kg, Composite lubricant (Polyethylene wax PEW-0200: Calcium stearate = 2:1) 0.6kg Weather-resistant and flame-retardant outer layer formulation: 70kg copolymer polypropylene (EPC30R), 18kg lignin-based phosphorus-nitrogen intumescent flame retardant, 1.0kg composite light stabilizer (hindered amine light stabilizer 944: benzotriazole UV absorber 326 = 1:1), 2kg itaconic acid modified microcrystalline cellulose, 7kg aluminum hypophosphite-melamine cyanurate-montmorillonite ternary synergistic flame retardant system, 0.5kg composite antioxidant (antioxidant 1010: antioxidant 168 = 1:1.5), and 0.6kg composite lubricant (polyethylene wax PEW-0200: calcium stearate = 2:1).

[0030] Functional filler pre-preparation (1) Preparation of itaconic acid modified microcrystalline cellulose: 100 kg of microcrystalline cellulose (MCC-30, particle size 30 μm) was added to 800 kg of deionized water to prepare a suspension. The temperature was raised to 75 °C, nitrogen gas was introduced for protection, 8 kg of itaconic acid and 2 kg of ammonium persulfate initiator were added, and the mixture was stirred for 4 h. After the reaction was completed, the mixture was filtered, washed 3 times with deionized water, and dried under vacuum at 80 °C for 12 h to obtain itaconic acid modified microcrystalline cellulose with an itaconic acid grafting amount of 7.2%.

[0031] (2) Preparation of the ternary synergistic flame retardant system of aluminum hypophosphite-melamine cyanurate-montmorillonite: Weigh aluminum hypophosphite (AP-1), melamine cyanurate (MCA-1), and organic modified montmorillonite (MMT-18, modified with cetyltrimethylammonium bromide) in a weight ratio of 2.5:1:0.8, add them to a high-speed mixer, heat to 110℃, and mix at a speed of 1800r / min for 15min to fully compound and disperse the three components under thermal shear. After discharge, cool to room temperature to obtain the ternary synergistic flame retardant system.

[0032] (3) Preparation of polyaniline in situ coated expanded graphite conductive filler: 100 kg of expanded graphite (EG-100, 100 mesh) was added to 2000 kg of 1 mol / L hydrochloric acid solution and stirred to disperse evenly. 12 kg of aniline monomer was added and ammonium persulfate initiator solution (containing 30 kg of ammonium persulfate) was slowly added dropwise under an ice-water bath (0-5℃) for 2 hours. After the addition was completed, the reaction continued for 8 hours. The solution was filtered, washed with deionized water until the filtrate was colorless, and dried under vacuum at 60℃ for 12 hours to obtain polyaniline in situ coated expanded graphite with a polyaniline coating amount of 10.5%.

[0033] (4) Preparation of silanized aramid pulp: 100 kg of para-aramid pulp (AP-1, length 1 mm) was added to 1000 kg of anhydrous ethanol, ultrasonically dispersed for 20 min with ultrasonic power of 400 W, 5 kg of γ-aminopropyltriethoxysilane (KH550) was added, the temperature was raised to 65 °C and stirred for 4 h, filtered, washed twice with anhydrous ethanol, and vacuum dried at 80 °C for 10 h to obtain silanized aramid pulp.

[0034] (5) Preparation of lignin-based phosphorus-nitrogen intumescent flame retardant: 100 kg of enzymatically hydrolyzed lignin (LIG-1) was added to 800 kg of N,N-dimethylformamide and stirred to dissolve. 60 kg of phosphoric acid (industrial grade, 85%) and 40 kg of melamine (industrial grade, 99.8%) were added in sequence. The mixture was heated to 90 °C and reacted for 6 h. After the reaction was completed, the reaction solution was poured into a large amount of water to precipitate. The solution was filtered, washed and dried to obtain the lignin-based phosphorus-nitrogen intumescent flame retardant.

[0035] Preparation method S1 Raw material pretreatment: Weigh the raw materials of the conductive and wear-resistant inner layer, the reinforced and toughened middle layer, and the weather-resistant and flame-retardant outer layer according to the above weight, put them into three high-speed mixers, heat them to 95℃, and mix them at a high speed of 1200r / min for 10min to obtain three groups of premixed materials. S2 Twin-Screw Granulation: Three sets of premixed materials are fed into three parallel twin-screw extruders with an L / D ratio of 44:1. The temperatures of each section are controlled as follows: feeding section 175℃, conveying section 185℃, melting section 195℃, homogenizing section 190℃, and die head 190℃. The screw speed is 250 r / min, and the material residence time in the extruder is 90 s. Melt extrusion granulation is performed, and after water cooling and pelletizing, conductive and wear-resistant inner layer granules, reinforced and toughened middle layer granules, and weather-resistant and flame-retardant outer layer granules are obtained. S3 Three-Layer Co-Extrusion Molding: Three types of granules are fed into three single-screw extruders, and the outlets of the three extruders are simultaneously connected to the three-layer co-extrusion spiral flow channel die head. The temperatures of each section of the inner extruder are controlled at 185℃, 195℃, and 200℃; the temperatures of each section of the middle extruder are controlled at 190℃, 200℃, and 205℃; the temperatures of each section of the outer extruder are controlled at 190℃, 200℃, and 205℃; the die head temperature is 210℃; the convergence angle of the melt in the die head is 20°; and the residence time of the melt in the die head is 45s. The extrusion rate of each layer is controlled so that the thickness ratio of the inner, middle, and outer layers is 1:2.5:1.2, and the overall wall thickness is controlled at 12mm. After vacuum sizing (vacuum degree -0.08MPa), cooling with 20℃ cooling water, traction, and fixed-length cutting, a three-layer co-extruded pipe semi-finished product is obtained. S4 Heat treatment enhances interface bonding: The three-layer co-extruded pipe semi-finished product is placed in a hot air circulating oven at 90℃ for 3 hours for heat treatment. After being taken out, it is naturally cooled to room temperature to obtain the finished multi-layer co-extruded MPP cable protection pipe.

[0036] This embodiment represents the optimal implementation of the present invention, employing intermediate component ratios to produce the MPP cable protection pipe with the best overall performance. Through a rationally designed three-layer functional gradient structure, combined with the optimal ratio of in-situ polyaniline-coated expanded graphite conductive system, aramid pulp reinforcement system, itaconic acid-modified microcrystalline cellulose and ternary synergistic flame-retardant system, and the interfacial compatibilization effect of maleic anhydride-styrene graft copolymer, a balanced improvement in various pipe properties is achieved, with a ring stiffness reaching 21.5 kN / m. 2 The oxygen index reaches 40.5%, and the interlayer peel strength reaches 2.65 MPa, with all performance indicators significantly higher than those of existing technology products. The process parameters in this embodiment are reasonably set, the melt viscosity of each layer is highly matched, and the interfacial bonding effect is good, making it suitable as a standard formula and process basis for industrial production.

[0037] Example 2:

[0038] Please see Figure 1 This embodiment provides a multilayer co-extruded MPP cable protection pipe, and the raw material formula and model of each layer are as follows (unit: kg): Conductive and wear-resistant inner layer formulation: Homopolymer polypropylene (T30S) 70kg, polyaniline in-situ coated expanded graphite conductive filler 3kg, polyimide micro powder (PI-100, particle size 10μm) 2kg, maleic anhydride-styrene graft copolymer (SMA-800, grafting rate 1.5%) 4kg, itaconic acid modified microcrystalline cellulose 1kg, aluminum hypophosphite-melamine cyanurate-montmorillonite ternary synergistic flame retardant system 2kg, composite antioxidant (antioxidant 1010: antioxidant 168 = 1:2) 0.2kg, composite lubricant (polyethylene wax PEW-0300: calcium stearate = 3:1) 0.3kg Reinforced and toughened intermediate layer formulation: Copolymer polypropylene (PPR 4220) 50kg, Homopolymer polypropylene (T30S) 20kg, Silanized aramid pulp 6kg, Ethylene-octene copolymer (POE 8100) 8kg, Maleic anhydride-styrene graft copolymer (SMA-800) 5kg, Itaconic acid modified microcrystalline cellulose 2kg, Aluminum hypophosphite-melamine cyanurate-montmorillonite ternary synergistic flame retardant system 3kg, Composite antioxidant (Antioxidant 1010: Antioxidant 168 = 1:2) 0.3kg, Composite lubricant (Polyethylene wax PEW-0300: Calcium stearate = 3:1) 0.4kg Weather-resistant and flame-retardant outer layer formulation: Copolymer polypropylene (PPR 4220) 60kg, lignin-based phosphorus-nitrogen intumescent flame retardant 12kg, composite light stabilizer (hindered amine light stabilizer 622: benzotriazole UV absorber 327 = 1:1.5) 0.5kg, itaconic acid modified microcrystalline cellulose 1kg, aluminum hypophosphite-melamine cyanurate-montmorillonite ternary synergistic flame retardant system 5kg, composite antioxidant (antioxidant 1010: antioxidant 168 = 1:2) 0.3kg, composite lubricant (polyethylene wax PEW-0300: calcium stearate = 3:1) 0.4kg Functional filler pre-preparation (1) Preparation of itaconic acid modified microcrystalline cellulose: 100 kg of microcrystalline cellulose (MCC-20, particle size 20 μm) was added to 900 kg of deionized water to prepare a suspension. The temperature was raised to 70 °C, nitrogen gas was introduced for protection, 5 kg of itaconic acid and 1 kg of ammonium persulfate initiator were added, and the mixture was stirred for 3 h. After the reaction was completed, the mixture was filtered, washed 3 times with deionized water, and dried under vacuum at 80 °C for 12 h to obtain itaconic acid modified microcrystalline cellulose with an itaconic acid grafting amount of 4.8%.

[0039] (2) Preparation of the ternary synergistic flame retardant system of aluminum hypophosphite-melamine cyanurate-montmorillonite: Weigh aluminum hypophosphite (AP-1), melamine cyanurate (MCA-1), and organic modified montmorillonite (MMT-18) in a weight ratio of 2:1:0.5, add them to a high-speed mixer, heat to 100℃, mix at a speed of 1500r / min for 10min, and cool to room temperature after discharge to obtain the ternary synergistic flame retardant system.

[0040] (3) Preparation of polyaniline in situ coated expanded graphite conductive filler: EG-80 (80 mesh) expanded graphite was used, and the rest of the preparation method was the same as in Example 1.

[0041] (4) Preparation of silanized aramid pulp: AP-05 (0.5 mm in length) was used for aramid pulp, and the rest of the preparation method was the same as in Example 1.

[0042] (5) Preparation of lignin-based phosphorus-nitrogen intumescent flame retardant: Same as in Example 1.

[0043] Preparation method S1 Raw material pretreatment: Weigh the raw materials of each layer according to the above weight, put them into a high-speed mixer, heat to 90℃, and mix at a speed of 1000r / min for 8 minutes to obtain three groups of premixed materials; S2 Twin-screw granulation: Three sets of premixed materials are fed into three twin-screw extruders respectively. The temperature of each section is controlled at 170-195℃, the screw speed is 200r / min, and the material residence time is 120s. Three kinds of granules are obtained by extrusion granulation. S3 Three-Layer Co-Extrusion Molding: Three types of granules are added to three single-screw extruders respectively. The extrusion temperature is controlled at 180-200℃, the die head temperature is 200℃, the melt convergence angle of each layer is 15°, and the melt residence time is 60s. The thickness ratio of each layer is controlled at 1:2:1, and the overall wall thickness is 8mm. After vacuum sizing (vacuum degree -0.07MPa), cooling with 15℃ cooling water, traction, and cutting, a semi-finished pipe product is obtained. S4 Heat treatment: Place the semi-finished pipe in an 85℃ oven for 4 hours for heat treatment, then remove it and let it cool naturally to obtain the finished product.

[0044] This embodiment uses a relatively low amount of functional filler, and the dosage of each innovative component is close to the lower limit of this invention. The resulting MPP cable protection pipe still meets high-performance requirements, fully demonstrating the high efficiency of the formulation system of this invention. Although the filler dosage is low, through innovative composite processes and interface modification technology, the ring stiffness of the pipe still reaches 18.2 kN / m. 2 The oxygen index reaches 38.2%, far exceeding the performance level of ordinary MPP pipes. The density of this embodiment is even lower, at only 0.958 g / cm³. 3While ensuring high performance, it also has the advantage of lightweight design, making it suitable for special engineering applications with strict requirements on pipe weight. At the same time, it has better cost control and is more economical.

[0045] Example 3:

[0046] Please see Figure 1 This embodiment provides a multilayer co-extruded MPP cable protection pipe, and the raw material formula and model of each layer are as follows (unit: kg): Conductive and wear-resistant inner layer formulation: Homopolymer polypropylene (T30S) 90kg, polyaniline in-situ coated expanded graphite conductive filler 10kg, polyimide micro powder (PI-300, particle size 20μm) 6kg, maleic anhydride-styrene graft copolymer (SMA-2000, grafting rate 2.2%) 12kg, itaconic acid modified microcrystalline cellulose 4kg, aluminum hypophosphite-melamine cyanurate-montmorillonite ternary synergistic flame retardant system 5kg, composite antioxidant (antioxidant 1010: antioxidant 168 = 1:1.8) 0.6kg, composite lubricant (polyethylene wax PEW-0250: calcium stearate = 2.5:1) 0.8kg Reinforcing and toughening intermediate layer formulation: Copolymer polypropylene (EPC30R) 70kg, Homopolymer polypropylene (T30S) 40kg 18 kg of silanized aramid pulp, 18 kg of ethylene-octene copolymer (POE 8200), 12 kg of maleic anhydride-styrene graft copolymer (SMA-2000), 6 kg of itaconic acid-modified microcrystalline cellulose, 7 kg of aluminum hypophosphite-melamine cyanurate-montmorillonite ternary synergistic flame retardant system, 0.8 kg of composite antioxidant (antioxidant 1010: antioxidant 168 = 1:1.8), and 1.0 kg of composite lubricant (polyethylene wax PEW-0250: calcium stearate = 2.5:1). Weather-resistant and flame-retardant outer layer formulation: 80kg copolymer polypropylene (EPC30R), 25kg lignin-based phosphorus-nitrogen intumescent flame retardant, 1.5kg composite light stabilizer (hindered amine light stabilizer 944: benzotriazole UV absorber 326 = 1:1.2), 3kg itaconic acid modified microcrystalline cellulose, 10kg aluminum hypophosphite-melamine cyanurate-montmorillonite ternary synergistic flame retardant system, 0.8kg composite antioxidant (antioxidant 1010: antioxidant 168 = 1:1.8), and 1.0kg composite lubricant (polyethylene wax PEW-0250: calcium stearate = 2.5:1).

[0047] Functional filler pre-preparation (1) Preparation of itaconic acid modified microcrystalline cellulose: 100 kg of microcrystalline cellulose (MCC-50, particle size 50 μm) was added to 670 kg of deionized water to prepare a suspension. The temperature was raised to 80 °C, nitrogen gas was introduced for protection, 12 kg of itaconic acid and 3 kg of ammonium persulfate initiator were added, and the mixture was stirred for 5 h. After the reaction was completed, the mixture was filtered, washed and dried to obtain itaconic acid modified microcrystalline cellulose with an itaconic acid grafting amount of 11.5%.

[0048] (2) Preparation of the ternary synergistic flame retardant system of aluminum hypophosphite-melamine cyanurate-montmorillonite: Weigh aluminum hypophosphite (AP-1), melamine cyanurate (MCA-1), and organic modified montmorillonite (MMT-18) in a weight ratio of 3:1:1, add them to a high-speed mixer, heat to 120°C, mix at a speed of 2000 r / min for 20 min, and cool to room temperature after discharge to obtain the ternary synergistic flame retardant system.

[0049] (3) Preparation of polyaniline in situ coated expanded graphite conductive filler: EG-150 (150 mesh) expanded graphite was used, and the rest of the preparation method was the same as in Example 1.

[0050] (4) Preparation of silanized aramid pulp: AP-2 (2mm in length) was used for aramid pulp, and the rest of the preparation method was the same as in Example 1.

[0051] (5) Preparation of lignin-based phosphorus-nitrogen intumescent flame retardant: Same as in Example 1.

[0052] Preparation method S1 Raw material pretreatment: Weigh the raw materials of each layer according to the above weight, put them into a high-speed mixer, heat to 100℃, and mix at a speed of 1500r / min for 15min to obtain three groups of premixed materials; S2 Twin-screw granulation: Three sets of premixed materials are fed into three twin-screw extruders respectively. The temperature of each section is controlled at 175-200℃, the screw speed is 300r / min, and the material residence time is 60s. Three kinds of granules are obtained by extrusion granulation. S3 Three-Layer Co-Extrusion Molding: Three types of granules are added to three single-screw extruders respectively. The extrusion temperature is controlled at 185-210℃, the die head temperature is 220℃, the melt convergence angle of each layer is 30°, and the melt residence time is 30s. The thickness ratio of each layer is controlled at 1:3:1.5, and the overall wall thickness is 18mm. After vacuum sizing (vacuum degree -0.09MPa), cooling with 25℃ cooling water, traction, and cutting, a semi-finished pipe product is obtained. S4 Heat treatment: Place the semi-finished pipe in a 95℃ oven for 2 hours, then remove and allow it to cool naturally to obtain the finished product.

[0053] This embodiment uses a relatively high amount of functional filler, and the dosage of each innovative component is close to the upper limit of this invention. The resulting MPP cable protection pipe achieves the highest performance level, with a ring stiffness of 25.8 kN / m. 2 With an oxygen index of 43.6% and an interlayer peel strength of 3.02 MPa, it is suitable for applications in special environments with extremely high performance requirements, such as key power projects requiring deep burial, high load, and high flame retardancy. This embodiment verifies that the formulation system of the present invention can maintain excellent comprehensive performance even with high filler addition, without exhibiting the drawback of decreased toughness with increased filler content commonly seen in traditional modification techniques. This demonstrates that the innovative filler of the present invention has excellent interfacial compatibility and synergistic effect with the polypropylene matrix.

[0054] Comparative Example 1: Please see Figure 1 The present invention provides a comparative example: This comparative example is a commercially available ordinary single-layer MPP cable protection pipe, using a traditional aluminum hydroxide flame retardant system, with the following formula (unit: kg): Homopolymer polypropylene (T30S) 100kg, aluminum hydroxide (ATH-1, particle size 5μm) 40kg, maleic anhydride grafted polypropylene (grade PP-g-MAH) 5kg, composite antioxidant (antioxidant 1010: antioxidant 168 = 1:1) 0.5kg, composite lubricant (polyethylene wax: calcium stearate = 2:1) 0.6kg Preparation method: The traditional single-layer extrusion process is adopted. The finished pipe is obtained by mixing, granulation, extrusion molding, cooling and cutting. The wall thickness is 12mm.

[0055] This comparative example uses a commercially available ordinary single-layer MPP cable protection pipe, employing a traditional aluminum hydroxide flame-retardant system and a simple formula, representing the general level of existing technology. Test results show that its various performance indicators are significantly lower than those of the embodiment of this invention, with a ring stiffness of only 8.5 kN / m. 2 The oxygen index is only 26.5%, the elongation at break is only 160%, and it lacks electrical conductivity and antistatic properties. A comparison with the embodiments of this invention clearly and intuitively demonstrates the significant performance advantages of the technical solution of this invention compared to existing technologies.

[0056] Comparative Example 2: Please see Figure 1 The present invention provides a comparative embodiment: This comparative example is a conventional three-layer co-extruded MPP cable protection pipe, which does not contain the itaconic acid-modified microcrystalline cellulose and ternary synergistic flame retardant system of the present invention. The conductive filler is conventional conductive carbon black, the reinforcing material is conventional glass fiber, and the flame retardant is conventional magnesium hydroxide. The formula is as follows (unit: kg): Inner layer: 80kg homopolymer polypropylene (T30S), 15kg conductive carbon black (CB-300), 6kg maleic anhydride-grafted polypropylene, 0.3kg composite antioxidant, 0.4kg composite lubricant. Intermediate layer: 60kg copolymer polypropylene (EPC30R), 30kg homopolymer polypropylene (T30S), 25kg glass fiber (GF-12, 12mm length), 12kg ethylene-octene copolymer (POE 8150), 8kg maleic anhydride-grafted polypropylene, 0.5kg composite antioxidant, 0.6kg composite lubricant. Outer layer: 70 kg of copolymer polypropylene (EPC30R), 40 kg of magnesium hydroxide (MH-200, particle size 2 μm), 1.0 kg of composite light stabilizer, 0.5 kg of composite antioxidant, and 0.6 kg of composite lubricant. Preparation method: Same as the three-layer co-extrusion process in Example 1, but the heat treatment step S4 is omitted.

[0057] This comparative example is a conventional three-layer co-extruded MPP cable protection pipe. Although it adopts a three-layer structure, it still uses traditional carbon black conductivity, glass fiber reinforcement, and magnesium hydroxide flame retardant technology, and does not employ interface compatibilization and heat treatment processes. Test results show that its interlayer peel strength is only 0.85 MPa, far lower than the 2.65 MPa of the embodiment of this invention, posing a serious risk of interlayer separation; simultaneously, glass fiber reinforcement increases the pipe density to 1.085 g / cm³. 3 Furthermore, issues such as fiber exposure and surface roughness are prone to occur. A comparison with embodiments of the present invention demonstrates that simply employing a three-layer structure without an innovative filler system and interface compatibilization process cannot achieve a substantial performance improvement.

[0058] Comparative Example 3: Please see Figure 1 The present invention provides a comparative scheme: This comparative example is a three-layer co-extruded MPP cable protection pipe, which contains only itaconic acid modified microcrystalline cellulose and does not contain a ternary synergistic flame retardant system, and is otherwise the same as in Example 1.

[0059] This comparative example uses only one innovative filler, itaconic acid-modified microcrystalline cellulose, and does not contain a ternary synergistic flame retardant system. Test results show that while its performance is superior to Comparative Examples 1 and 2, it is significantly lower than Example 1, which contains both innovative fillers; the oxygen index is reduced by 4.7 percentage points, and the ring stiffness is reduced by 4.7 kN / m. 2 The interlayer peel strength decreased by 0.47 MPa. This comparison clearly verifies that the aluminum hypophosphite-melamine cyanurate-montmorillonite ternary synergistic flame retardant system not only possesses highly efficient flame retardant properties but also simultaneously improves the mechanical properties and interfacial bonding strength of the pipe, further demonstrating the synergistic effect of the two innovative fillers.

[0060] Comparative Example 4: Please see Figure 1 The present invention provides a comparative scheme: This comparative example is a three-layer co-extruded MPP cable protection pipe, which does not contain maleic anhydride-styrene graft copolymer, and omits the heat treatment step S4. The remaining formulation and process are the same as in Example 1.

[0061] This comparative example omits the maleic anhydride-styrene graft copolymer interfacial compatibilizer and the subsequent heat treatment process; the remaining formulation and process are exactly the same as in Example 1.

[0062] Test results showed that the interlayer peel strength decreased significantly from 2.65 MPa to 1.12 MPa, a decrease of 137%. This fully demonstrates the decisive role of the combination of the interface compatibilizer system and the heat treatment process in improving interlayer bonding, and is a key technology for solving the industry pain point of easy delamination in multilayer co-extruded pipes. Meanwhile, other mechanical properties also decreased to varying degrees, indicating that the interface compatibilizer not only improves interlayer bonding but also enhances the interfacial compatibility between the filler and the matrix, thus improving the overall performance of the pipe.

[0063] Comparative Example 5: Please see Figure 1 The present invention provides a comparative scheme: the comparative example is a three-layer co-extruded MPP cable protection pipe, in which the ternary synergistic flame retardant system is replaced with a simple physical mixture of aluminum hypophosphite, melamine cyanurate and organically modified montmorillonite (the proportions are the same as in Example 1), and the remaining formulas and processes are the same as in Example 1.

[0064] This comparative example replaces the ternary synergistic flame retardant system with a simple physical mixture of three raw materials, while the rest of the formulation and process are exactly the same as in Example 1. Test results show that its oxygen index decreased from 40.5% to 36.2%, and its mechanical properties also decreased significantly. This proves that the high-speed melt composite process used in this invention is not a simple mixing of raw materials, but rather achieves uniform dispersion and synergistic effect of the three components at the microscale through thermal shearing, thus more fully utilizing the functions of each component.

[0065] This invention, through a systematic comparison and verification between Examples 1-3 and Comparative Examples 1-5, concludes that Example 1, as the optimal formulation, achieves differentiated functions in the inner, middle, and outer layers—conductivity and wear resistance, reinforcement and toughness, and weather resistance and flame retardancy—through a rationally designed three-layer functional gradient structure. Combined with an in-situ polyaniline-coated expanded graphite conductive system, a silanized aramid pulp reinforcement system, an itaconic acid-modified microcrystalline cellulose and aluminum hypophosphite-melamine cyanurate-montmorillonite ternary synergistic flame retardant system, and maleic anhydride-styrene graft copolymer interface compatibilization and subsequent heat treatment processes, multiple properties are simultaneously enhanced, achieving a ring stiffness of 21.5 kN / m. 2The oxygen index reached 40.5%, the interlayer peel strength reached 2.65 MPa, and the volume resistivity decreased to 3.2 × 10⁻⁶. 6 Ω·m, all core performance indicators are significantly superior to existing technologies. Compared with the commercially available ordinary single-layer pipe of Comparative Example 1, this invention achieves a leapfrog improvement in almost all performance indicators, fully demonstrating the huge advantages of the three-layer functional gradient structure compared to the traditional single-layer structure; compared with the ordinary three-layer co-extruded pipe of Comparative Example 2, the advantages of this invention in terms of interlayer bonding force, lightweight, and comprehensive performance are more prominent, proving that a substantial performance breakthrough cannot be achieved by simply using a three-layer structure without the combination of innovative filler system and interface technology; compared with the single innovative filler formulation of Comparative Example 3, it is verified that there is a significant synergistic effect between itaconic acid modified microcrystalline cellulose and the ternary synergistic flame retardant system, and the performance improvement when the two fillers are used simultaneously is far greater than the simple superposition of their individual uses; compared with Comparative Example 4, it is intuitively demonstrated that the interface compatibilizer and heat treatment process play a decisive role in solving the industry pain point of easy delamination in multi-layer co-extruded pipes; compared with Comparative Example 5, it is clearly verified that the high-speed melt composite process of this invention is not a simple mixing of raw materials. Examples 2 and 3 respectively verified the applicability of the formulation of the present invention in the range of low and high addition amounts, proving that it has a wide range of adjustability and stability, and can meet the needs of different application scenarios.

[0066] In summary, this invention completely solves the common problems in the industry such as the single function, poor interlayer bonding, and unsatisfactory modification effect of traditional MPP pipes, and has extremely high practical value and market prospects.

[0067] To further illustrate the beneficial technical effects of the various embodiments of the present invention, relevant performance tests were conducted on Embodiments 1-3 and Comparative Examples 1-5; The testing method is as follows: 1. Ring stiffness test A 300mm long tubular sample is placed between two parallel plates of a universal testing machine and compressed radially at a loading rate of 5mm / min. The load value is recorded when the tubular material exhibits a 3% radial deformation. The ring stiffness of the tubular material is then calculated, with units of kN / m. 2 Five samples were tested for each mix ratio, and the arithmetic mean was taken as the final test result.

[0068] 2. Drop hammer impact performance test Take a 200mm long pipe sample and place it on the V-shaped support of the drop hammer impact testing machine. Select a drop hammer of appropriate mass according to the pipe specifications and drop it freely from a specified height to impact the pipe. Test 10 samples for each mix ratio, observe and record whether the pipe shows cracks, breakage or other damage, and calculate the percentage of undamaged samples out of the total samples, i.e., the drop hammer impact pass rate, in percentage (%).

[0069] 3. Volume resistivity test A circular sample with a diameter of 100 mm was cut from the pipe. After cleaning the sample surface, it was placed between the two electrodes of the volume resistivity tester. A specified test voltage was applied, and the test value was read after the current stabilized. The volume resistivity of the sample was calculated, and the unit was Ω·m. Three samples were tested for each ratio, and the arithmetic mean was taken as the final test result.

[0070] 4. Oxygen Index Test Cut strip samples measuring 80mm × 10mm × 4mm from the pipe. Fix the samples vertically in the center of the combustion chamber of the oxygen index tester. Introduce a mixture of oxygen and nitrogen in a specified ratio. Adjust the oxygen concentration to maintain balanced combustion of the sample. Record the minimum oxygen concentration required for the sample to sustain combustion for a length of 50mm; this is the oxygen index, expressed as a percentage. Test five samples for each mixture and take the arithmetic mean as the final test result.

[0071] 5. Vicat softening temperature test Cut square samples with a thickness of 3-6 mm from the pipe and place them on the sample holder of the Vicat softening temperature tester. Apply the specified test force and heat at a rate of 50 °C / h. When the indenter penetrates the sample to a depth of 1 mm, record the temperature value at this point, which is the Vicat softening temperature, in °C. Test 3 samples for each formulation and take the arithmetic mean as the final test result.

[0072] 6. Tensile strength test Standard dumbbell-shaped specimens are cut axially from the pipe and placed in the fixture of a universal testing machine. A tensile test is performed at a tensile speed of 50 mm / min until the specimen breaks. The maximum load value during the test is recorded, and the tensile strength is calculated based on the cross-sectional area of ​​the specimen, in MPa. Five specimens are tested for each mix design, and the arithmetic mean is taken as the final test result.

[0073] 7. Elongation at break test During the tensile strength test, the gauge length elongation at fracture was recorded simultaneously. The ratio of this elongation to the original gauge length, multiplied by 100%, is the elongation at break. Five specimens were tested for each mix proportion, and the arithmetic mean was taken as the final test result.

[0074] 8. Interlayer peel strength test Cut strip specimens measuring 150mm × 20mm from the pipe. Pre-peel 20mm between adjacent layers to serve as clamping ends. Place the specimens in the fixture of a universal testing machine and perform a 180° peel test at a speed of 50mm / min. Record the average load value during the peeling process. Calculate the interlayer peel strength (MPa) based on the specimen width. Test 5 specimens for each mix proportion, and take the arithmetic mean as the final test result.

[0075] 9. Strength retention rate test after aging The cut standard dumbbell-shaped specimens were placed in an accelerated aging chamber and subjected to an aging test for 1000 hours under specified temperature and humidity conditions. After aging, the specimens were removed, and the tensile strength after aging was tested according to the tensile strength test method described above. The ratio of the aged tensile strength to the original tensile strength of the unaged specimen, multiplied by 100%, is the strength retention rate after aging, expressed as a percentage. Five specimens were tested for each mix, and the arithmetic mean was taken as the final test result.

[0076] 10. Density Test The density of pipe materials was tested using the density gradient column method. The pipe sample was prepared into uniformly sized particles and placed in a density gradient column. After the sample stabilized and suspended, its density was calculated based on its position within the gradient column, with units of g / cm³. 3 Three samples were tested for each formulation, and the arithmetic mean was taken as the final test result.

[0077] The above descriptions are merely embodiments of the present invention, and common knowledge regarding specific technical solutions or characteristics is not elaborated upon here. It should be noted that those skilled in the art can make various modifications and improvements without departing from the technical solutions of the present invention, and these should also be considered within the scope of protection of the present invention. These modifications and improvements will not affect the effectiveness of the implementation of the present invention or the practicality of the patent. The scope of protection claimed in this application should be determined by the content of its claims, and the specific embodiments described in the specification can be used to interpret the content of the claims.

Claims

1. A multi-layer co-extruded MPP cable protection pipe, characterized in that, From the inside out, the material consists of a conductive and wear-resistant inner layer, a reinforced and toughened middle layer, and a weather-resistant and flame-retardant outer layer, which are compositely formed by co-extrusion. The conductive and wear-resistant inner layer is prepared from the following raw materials in parts by weight: 70-90 parts homopolymer polypropylene, 3-10 parts polyaniline in-situ coated expanded graphite conductive filler, 2-6 parts polyimide micro powder, 4-12 parts maleic anhydride-styrene graft copolymer, 1-4 parts itaconic acid modified microcrystalline cellulose, 2-5 parts aluminum hypophosphite-melamine cyanurate-montmorillonite ternary synergistic flame retardant system, 0.2-0.6 parts composite antioxidant, and 0.3-0.8 parts composite lubricant; The reinforced and toughened intermediate layer is prepared from the following raw materials in parts by weight: 50-70 parts copolymer polypropylene, 20-40 parts homopolymer polypropylene, 6-18 parts silanized aramid pulp, 8-18 parts ethylene-octene copolymer, 5-12 parts maleic anhydride-styrene graft copolymer, 2-6 parts itaconic acid modified microcrystalline cellulose, 3-7 parts aluminum hypophosphite-melamine cyanurate-montmorillonite ternary synergistic flame retardant system, 0.3-0.8 parts composite antioxidant, and 0.4-1.0 parts composite lubricant; The weather-resistant and flame-retardant outer layer is prepared from the following raw materials in parts by weight: 60-80 parts copolymer polypropylene, 12-25 parts lignin-based phosphorus-nitrogen intumescent flame retardant, 0.5-1.5 parts composite light stabilizer, 1-3 parts itaconic acid modified microcrystalline cellulose, 5-10 parts aluminum hypophosphite-melamine cyanurate-montmorillonite ternary synergistic flame retardant system, 0.3-0.8 parts composite antioxidant, and 0.4-1.0 parts composite lubricant.

2. The multilayer co-extruded MPP cable protection pipe according to claim 1, characterized in that, The itaconic acid-modified microcrystalline cellulose is prepared by grafting itaconic acid onto microcrystalline cellulose, with the amount of itaconic acid grafted being 5%-12% of the mass of the microcrystalline cellulose; the particle size of the microcrystalline cellulose is 20-50 μm.

3. The multilayer co-extruded MPP cable protection pipe according to claim 1, characterized in that, The aluminum hypophosphite-melamine cyanurate-montmorillonite ternary synergistic flame retardant system is prepared by high-speed melt composite of aluminum hypophosphite, melamine cyanurate, and organically modified montmorillonite in a weight ratio of 2-3:1:0.5-1; wherein the organically modified montmorillonite is hexadecyltrimethylammonium bromide modified montmorillonite.

4. The multilayer co-extruded MPP cable protection pipe according to claim 1, characterized in that, The polyaniline-coated expanded graphite conductive filler is formed by in-situ polymerization and coating of expanded graphite with hydrochloric acid-doped polyaniline, with a polyaniline coating amount of 8%-15% and a mesh size of 80-150 mesh for the expanded graphite; the polyimide micro powder has a particle size of 10-20 μm; the silanized aramid pulp is a para-aramid pulp with a surface treatment of γ-aminopropyltriethoxysilane and a length of 0.5-2 mm.

5. The multilayer co-extruded MPP cable protection pipe according to claim 1, characterized in that, The lignin-based phosphorus-nitrogen intumescent flame retardant is a phosphorus-nitrogen synergistic intumescent flame retardant prepared by enzymatic hydrolysis of lignin through phosphorylation and amination modification; the grafting rate of the maleic anhydride-styrene graft copolymer is 1.0%-3.0%; the composite light stabilizer is a mixture of hindered amine light stabilizer and benzotriazole UV absorber in a weight ratio of 1:1-1.5; the composite antioxidant is a mixture of antioxidant 1010 and antioxidant 168 in a weight ratio of 1:1.5-2; the composite lubricant is a mixture of polyethylene wax and calcium stearate in a weight ratio of 2-3:

1.

6. The multilayer co-extruded MPP cable protection pipe according to claim 1, characterized in that, The thickness ratio of the conductive and wear-resistant inner layer, the reinforcing and toughening intermediate layer, and the weather-resistant and flame-retardant outer layer is 1:2-3:1-1.5; the overall wall thickness of the cable protection pipe is 5-20mm, and the ring stiffness is ≥18kN / m. 2 Volume resistivity ≤ 8 × 10 6 Ω·m, oxygen index ≥38%, tensile strength retention rate ≥90% after 1000h of artificial accelerated aging, and interlayer peel strength ≥2.0MPa.

7. A method for preparing a multilayer co-extruded MPP cable protection tube as described in any one of claims 1-6, characterized in that, Includes the following steps: S1 Functional Filler Pre-preparation: Polyaniline in-situ coated expanded graphite conductive filler, silanized aramid pulp, lignin-based phosphorus-nitrogen intumescent flame retardant, maleic anhydride-styrene graft copolymer, itaconic acid modified microcrystalline cellulose, and aluminum hypophosphite-melamine cyanurate-montmorillonite ternary synergistic flame retardant system were prepared separately for later use. S2 Raw material pretreatment: Weigh out the raw materials of conductive wear-resistant inner layer, reinforced and toughened middle layer and weather-resistant and flame-retardant outer layer according to the weight parts, put them into a high-speed mixer, heat to 90-100℃, mix at high speed for 8-15 minutes to obtain three groups of premixed materials. S3 Twin-screw granulation: The three groups of premixed materials prepared by S2 are fed into three twin-screw extruders respectively. The temperature of each section is controlled at 170-200℃ and the screw speed is 200-300r / min. Melt extrusion granulation is carried out to obtain conductive and wear-resistant inner layer granules, reinforced and toughened middle layer granules, and weather-resistant and flame-retardant outer layer granules respectively. S4 Three-layer co-extrusion molding: The three types of granules prepared in S3 are added to three single-screw extruders respectively. The discharge ports of the three extruders are simultaneously connected to the three-layer co-extrusion die head. The temperature of each extruder is controlled at 180-210℃, the die head temperature is controlled at 200-220℃, and the extrusion rate of each layer is controlled to make the thickness ratio 1:2-3:1-1.

5. After vacuum sizing, cooling, traction and cutting, the three-layer co-extruded pipe semi-finished product is obtained. S5 Heat treatment enhances interface bonding: The three-layer co-extruded pipe semi-finished product prepared by S4 is placed in an oven at 85-95℃ for heat treatment for 2-4 hours. After being taken out, it is naturally cooled to room temperature to obtain the finished multi-layer co-extruded MPP cable protection pipe.

8. The preparation method according to claim 7, characterized in that, In S1, the preparation method of the itaconic acid modified microcrystalline cellulose is as follows: microcrystalline cellulose is added to deionized water to prepare a suspension with a concentration of 10%-15%, heated to 70-80℃, protected by nitrogen gas, itaconic acid and ammonium persulfate initiator are added, and the mixture is stirred for 3-5 hours. After the reaction is completed, the mixture is filtered, washed, and dried to obtain itaconic acid modified microcrystalline cellulose; the amount of ammonium persulfate used is 1%-3% of the mass of microcrystalline cellulose.

9. The preparation method according to claim 7, characterized in that, In S1, the preparation method of the aluminum hypophosphite-melamine cyanurate-montmorillonite ternary synergistic flame retardant system is as follows: Weigh aluminum hypophosphite, melamine cyanurate, and organically modified montmorillonite according to the weight ratio, add them to a high-speed mixer, heat to 100-120℃, and mix at a high speed of 1500-2000r / min for 10-20min to fully compound and disperse the three components under thermal shear. After discharge, cool to room temperature to obtain the ternary synergistic flame retardant system.

10. The preparation method according to claim 7, characterized in that, In S1, the preparation method of the polyaniline in-situ coated expanded graphite conductive filler is as follows: expandable graphite is added to a 1 mol / L hydrochloric acid solution, stirred and dispersed evenly, aniline monomer is added, and ammonium persulfate initiator is slowly added dropwise under an ice-water bath. After the addition is completed, the reaction continues for 6-10 hours. After filtration, washing and drying, polyaniline in-situ coated expanded graphite is obtained. The preparation method of the silanized aramid pulp is as follows: add aramid pulp to anhydrous ethanol, ultrasonically disperse for 15-30 min, add γ-aminopropyltriethoxysilane, heat to 60-70℃ and stir for 3-5 h, filter, wash and dry to obtain silanized aramid pulp. The preparation method of the lignin-based phosphorus-nitrogen intumescent flame retardant is as follows: enzymatically hydrolyzed lignin is dissolved in N,N-dimethylformamide, phosphorylation reagent and amination reagent are added sequentially, the temperature is raised to 80-100℃ and reacted for 4-8 hours, precipitation, washing and drying are performed to obtain the lignin-based phosphorus-nitrogen intumescent flame retardant.

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