A high flame-retardant HPPM double-wall corrugated pipe and its preparation method

Abstract

This invention discloses a high flame-retardant HPPM double-wall corrugated pipe and its preparation method, relating to the field of double-wall corrugated pipe technology. The invention discloses a method for preparing a high flame-retardant HPPM double-wall corrugated pipe, comprising the following steps: feeding inner layer raw material into an inner layer extruder and extruding it through the inner layer flow channel of a co-extrusion die to form an inner layer; feeding outer layer raw material into an outer layer extruder and extruding it through the outer layer flow channel of a co-extrusion die to form an outer layer; combining the inner and outer layers, corrugating, and cooling to obtain a high flame-retardant HPPM double-wall corrugated pipe; the HPPM double-wall corrugated pipe prepared in this application has the characteristics of good flame retardant effect and excellent mechanical properties.

Description

Technical Field

[0001] This invention relates to the field of double-wall corrugated pipe technology, specifically to a high flame-retardant HPPM double-wall corrugated pipe and its preparation method. Background Technology

[0002] Double-wall corrugated pipes have a smooth inner wall and a corrugated outer wall (the corrugation shape can be right angle, trapezoid, sine, etc.). They are formed by simultaneously extruding two concentric tubes and fusing them with the corrugated outer surface onto the inner tube. Utilizing its unique annular hollow structure, with a smooth inner wall and a corrugated outer wall, the double-wall corrugated pipe forms a scientifically sound mechanical system, exhibiting high strength and toughness compared to traditional rigid plastic pipes. Furthermore, the connection of this type of pipe is relatively convenient; a rubber sealing ring is added at the annular joint, greatly reducing construction and installation difficulty and saving manpower and material costs. Double-wall corrugated pipes can be classified according to different materials, such as high-density polyethylene, polypropylene, and rigid polyvinyl chloride. Among general-purpose resins, polypropylene, a major resin variety, is widely used due to its good processing performance, high strength, and good heat resistance. However, polypropylene's flammability and low-temperature brittleness limit its application in some fields.

[0003] In existing technologies, elastomers are commonly used to modify polypropylene through blending, thereby improving its physical properties. However, when the elastomer content exceeds 20%, although low-temperature toughness is significantly improved (impact strength at -30℃ can be increased by 300%), tensile strength decreases by 30%-40%, and the ring stiffness of the pipe may fall below 8 kN / m. 2 (The standard requires a lower limit), affecting the pressure-bearing capacity. Furthermore, adding halogen-free flame retardants such as magnesium hydroxide requires a high filler content of 60%, leading to decreased melt flowability (MFR decreases from 15g / 10min to 2g / 10min), increasing the difference in flow rate between the inner and outer layers during extrusion, and making delamination more likely. Flame retardants and elastomers also compete for the dispersed phase, worsening interfacial compatibility and potentially causing a "wick effect" during combustion, accelerating flame spread. Summary of the Invention

[0004] The purpose of this invention is to provide a high flame-retardant HPPM double-wall corrugated pipe and its preparation method, thereby solving the following technical problems: The addition of existing elastomers and halogen-free flame retardants to polypropylene resins results in high levels of flame retardants affecting melt flowability, and elastomers causing a decrease in the mechanical properties of the material. Furthermore, flame retardants and elastomers compete for the dispersed phase, leading to deterioration of interfacial compatibility and potentially producing a "wick effect" during combustion, which accelerates the spread of flames.

[0005] The objective of this invention can be achieved through the following technical solutions: A method for preparing a high flame-retardant HPPM double-wall corrugated pipe includes the following steps: The inner layer material is fed into the inner layer extruder and extruded through the inner layer flow channel of the co-extrusion die to form the inner layer; the outer layer material is fed into the outer layer extruder and extruded through the outer layer flow channel of the co-extrusion die to form the outer layer; the inner layer and the outer layer are combined, corrugated, and cooled to obtain a high flame retardant HPPM double-wall corrugated pipe. The inner layer raw materials include the following parts by weight: 60-65 parts PP resin, 20-25 parts composite flame retardant, 3-4 parts nano modifier, 3.5-5 parts compatibilizer, and 1.5-2.5 parts additive composition one; The outer layer raw materials include the following parts by weight: 55-60 parts PP resin, 25-30 parts composite flame retardant, 4-5 parts nano modifier, 3.5-5 parts compatibilizer, and 1.5-2.5 parts additive composition two; The preparation method of the nano-modifier includes the following steps: S1: Add MgCl2·6H2O, AlCl3·6H2O and deionized water to the reactor and disperse them. Control the temperature at 50-60℃, add precipitant, keep warm and age for 12-15h, centrifuge and wash to obtain slurry; S2: Add the slurry and KH550 into the reaction flask, control the temperature at 60-70℃, and keep it warm for 2-4 hours to hydrolyze and obtain the pretreated slurry; S3: Add the pretreated slurry, ethanol, water, and tetraethyl orthosilicate to the reaction vessel and disperse them. Add ammonia water dropwise to adjust the pH to 9.5. Control the temperature at 40-45℃ and keep the reaction at this temperature for 3-6 hours. Collect the particles by centrifugation, wash with ethanol, and dry to obtain the nano-modifier.

[0006] As a further aspect of the present invention: the precipitant in S1 is composed of sodium carbonate and sodium hydroxide in a mass ratio of 6:1-1.1; the addition ratio of MgCl2·6H2O, AlCl3·6H2O, deionized water and precipitant is 60-90g: 24-36g: 800-1200mL: 35-38g.

[0007] As a further aspect of the present invention: the addition ratio of slurry and KH550 in S2 is 100g:1-2g.

[0008] As a further aspect of the present invention: the addition ratio of pretreated slurry, ethanol, water and tetraethyl orthosilicate in S3 is 100g: 400-500mL: 20-30mL: 45-55g.

[0009] As a further aspect of the present invention: the compatibilizer is composed of maleic anhydride-grafted polypropylene and DOPO-grafted PP in a mass ratio of 2-3:1.5-2; The preparation method of DOPO-grafted PP includes the following steps: 0.2-0.4g of dicumyl peroxide, 1-2g of DOPO, and 0.3-0.5g of acetone are added to a reaction flask and stirred and dissolved in a water bath at 85-90℃ to obtain a mixture; 96-98g of PP and 0.3-0.5g of ethylene bis-stearamide are added to a high-speed mixer and mixed; the mixture is added, mixed, extruded and granulated, cooled, and dried to obtain DOPO-grafted PP.

[0010] As a further aspect of the present invention: Inner layer raw material preparation: Each component of the inner layer raw material is fed into a high-speed mixer at 1000-1200 r / min and 110-120℃ for 8-10 min to obtain an inner layer mixture; the inner layer mixture is fed into a twin-screw extruder for granulation at a temperature of 170-190℃, a screw speed of 300-400 r / min, and a die head pressure of 12-15 MPa. After pelleting, the pellets are air-cooled to room temperature with a particle size of 3-5 mm to obtain the inner layer raw material.

[0011] Preparation of outer layer raw materials: Each component of the outer layer raw materials is fed into a high-speed mixer at 1000-1200 r / min and 110-120℃ for 8-10 min to obtain the outer layer mixture; the outer layer mixture is fed into a twin-screw extruder for granulation at a temperature of 170-190℃, a screw speed of 300-400 r / min, and a die head pressure of 12-15 MPa. After pelleting, the pellets are air-cooled to room temperature with a particle size of 3-5 mm to obtain the outer layer raw materials.

[0012] As a further aspect of the present invention: the composite flame retardant is composed of ammonium polyphosphate, magnesium hydroxide, and melamine cyanurate in a mass ratio of 12-15:8-10:5-7.

[0013] As a further aspect of the present invention: the auxiliary composition consists of an antioxidant, a light stabilizer, and a lubricant in a mass ratio of 0.3-0.5:0.5-1:0.5-1; The second additive composition consists of antioxidants, lubricants, and light stabilizers in a mass ratio of 0.3-0.5:0.8-1.2:0.5-1.

[0014] As a further aspect of the present invention: the antioxidant is antioxidant 1010; the light stabilizer is composed of ultraviolet light absorber UV-531 and light stabilizer 770; and the lubricant is composed of calcium stearate and PE wax.

[0015] As a further aspect of the present invention: the temperature settings of the inner extruder are as follows: feeding zone 160-170℃, melting zone 175-185℃, homogenization zone 185-195℃, and die head 190-200℃; the die head pressure of the inner extruder is 5-10MPa. Temperature settings for the outer extruder: feeding zone 165-175℃, melting zone 180-190℃, homogenization zone 190-200℃, die head 195-205℃; die head pressure for the outer extruder 10-15MPa; The screw speed of the inner extruder is 40-50 rpm, and the screw speed of the outer extruder is 30-40 rpm. The ratio of the inner layer to the outer layer wall thickness is 1.2-1.5:1.

[0016] As a further aspect of the present invention: the corrugation forming is a composite tube blank formed in a corrugated mold; the mold temperature is 210-220℃; The specific process for cooling and shaping is vacuum adsorption shaping under a vacuum degree of 0.05-0.08MPa, followed by cooling with cooling water.

[0017] A high flame-retardant HPPM double-wall corrugated pipe is made by any of the above preparation methods.

[0018] The beneficial effects of this invention are: (1) Nano-modifiers improve interfacial compatibility, optimize processing fluidity and enhance mechanical stability The nano-modifier prepared in this invention is a core-shell particle with a layered bimetallic hydroxide core, which is pretreated with KH550 and then coated with a silicon layer on the core surface. The layered structure of the nanoparticle core prepared in this application inherently possesses a certain flame-retardant effect. After KH550 pretreatment, the amino groups in its molecules react with the hydroxyl groups on the surface of the hydrotalcite to form chemical bonds, while organic groups are exposed on the particle surface, significantly reducing the particle surface energy. The third step, silicon coating, forms a dense siloxane layer on the particle surface, further improving the particle dispersion stability. The nano-modifier forms a strong interfacial bond with the polypropylene substrate, avoiding the problem of easy agglomeration of traditional inorganic particles. Simultaneously, the siloxane layer reduces melt flow resistance, improves melt flowability during processing, reduces the difference in flow rate between inner and outer layers, and inhibits delamination. Furthermore, the layered nanoparticles can form a "physical support network" in the polypropylene matrix, enhancing the mechanical load-bearing capacity of the matrix and effectively mitigating the tendency for brittle fracture at low temperatures.

[0019] (2) DOPO grafted PP imparts high flame retardant properties to polypropylene while taking into account its compatibility with the matrix. The phosphaphenanthrene structure in the DOPO (9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide) molecule is a key flame-retardant group. After a grafting reaction initiated by dicumyl peroxide, the DOPO molecule is chemically bonded to the PP molecular chain. Compared with physical addition of DOPO, this significantly improves the compatibility with the PP matrix and avoids the problem of flame retardant migration and loss. During combustion, the phosphaphenanthrene structure can decompose to produce phosphoric acid substances. These substances can catalyze the dehydration and char formation of the polypropylene matrix, forming a dense char layer covering the material surface, isolating oxygen from contact with combustible gases, thereby inhibiting flame spread. At the same time, the grafted PP molecular chain structure does not undergo excessive degradation, which can reduce the damage to the mechanical properties of the matrix while ensuring flame retardant performance.

[0020] (3) The synergistic effect of nano-modifier and DOPO-grafted PP achieves the superposition effect of "flame retardant performance enhancement + mechanical property balance + processing stability improvement". First, the layered structure of the nano-modifier and the char layer formed by the decomposition of DOPO-grafted PP can construct a "dual barrier system". The layered nanoparticles can fill the pores of the char layer, making the char layer denser and further enhancing its ability to isolate oxygen and heat. Compared with using only one modifier, it can improve the flame retardant rating.

[0021] Secondly, while DOPO-grafted PP improves flame retardancy, it may slightly reduce the toughness of the matrix. The "physical support network" of the nano-modifier can make up for this defect. At the same time, the good interfacial compatibility between the two can avoid the mechanical property degradation caused by the aggregation of the dispersed phase, and ultimately achieve the improvement of low-temperature toughness. Finally, the silicon coating of the nano-modifier can reduce melt flow resistance, alleviate the slight increase in melt viscosity caused by DOPO grafting, keep the overall melt flowability stable, ensure uniform flow rate of inner and outer layers during extrusion, and avoid delamination.

[0022] (4) A multi-component synergistic system is formed by nano-modifiers, DOPO-grafted PP and composite flame retardants. First, the nano-modifier, DOPO-grafted PP and composite flame retardant work synergistically. The phosphoric acid produced by the decomposition of ammonium polyphosphate can react with the hydroxyl groups on the surface of the nano-modifier to further promote the formation of the char layer. While magnesium hydroxide decomposes and absorbs heat to cool down, its decomposition product MgO can combine with the siloxane layer to enhance the strength of the char layer. The three work synergistically to reduce the amount of flame retardant added and avoid the deterioration of melt fluidity caused by high filling.

[0023] Secondly, the synergistic effect of nano-modifiers, DOPO-grafted PP and compatibilizers allows the anhydride groups of maleic anhydride-grafted polypropylene to react chemically with the amino groups on the surface of nano-modifiers and DOPO-grafted PP, forming stronger chemical bonds. This further enhances the interfacial compatibility between the components and avoids the problem of flame retardants and elastomers (this invention does not add a large amount of elastomer, a small amount of compatibilizer is sufficient to achieve compatibility) competing for the dispersed phase.

[0024] Finally, the synergistic effect of nano-modifiers, DOPO-grafted PP and lubricant, the silicon coating of nano-modifiers can reduce the migration of lubricant, so that the lubricant is evenly distributed in the melt, further optimizing the processing fluidity, while avoiding surface defects caused by lubricant precipitation. Detailed Implementation

[0025] The technical solutions in the embodiments of the present invention will be clearly and completely described below. 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.

[0026] Example 1: The preparation method of the nano-modifier includes the following steps: S1: Add 60g MgCl2·6H2O, 24g AlCl3·6H2O and 800mL deionized water to the reaction vessel and disperse them. Control the temperature at 50℃, add 30g sodium carbonate and 5g sodium hydroxide, keep warm and age for 12h, centrifuge and wash to obtain slurry; S2: Add 100g of slurry and 1g of KH550 to the reaction flask, control the temperature at 60℃, and keep it at the temperature for 2 hours to hydrolyze and obtain the pretreated slurry; S3: Add 100g of pretreated slurry, 400mL of ethanol, 20mL of water, and 45g of tetraethyl orthosilicate to a reaction vessel and disperse. Add 28wt% ammonia water dropwise to adjust the pH to 9.5. Control the temperature at 40℃ and keep the reaction at this temperature for 3h. Collect the particles by centrifugation, wash with ethanol, and dry (vacuum dry at 60℃ for 2h and cure at 120℃ for 1h) to obtain the nano-modifier.

[0027] The preparation method of DOPO-grafted PP includes the following steps: 0.2g of dicumyl peroxide, 1g of DOPO, and 0.3g of acetone were added to a reaction flask and stirred and dissolved in an 85℃ water bath to obtain a mixture. 96g of PP and 0.3g of ethylene bis-stearamide were added to a high-speed mixer and mixed. The mixture was added and mixed at high speed (300 rpm for 90 seconds). The mixture was then extruded and granulated (feed zone 180℃ → melt zone 200℃ → homogenization zone 220℃ → die head 210℃, screw speed: 200 rpm), cooled, and dried (vacuum drying at 80℃ for 2 hours) to obtain DOPO-grafted PP.

[0028] Example 2: The preparation method of the nano-modifier includes the following steps: S1: 70g MgCl2·6H2O, 30g AlCl3·6H2O and 1000mL deionized water were added to the reaction vessel and dispersed. The temperature was controlled at 55℃. 30g sodium carbonate and 5.5g sodium hydroxide were added. The mixture was kept at this temperature and aged for 13.5h. After centrifugation and washing, the slurry was obtained. S2: Add 100g of slurry and 1.5g of KH550 to the reaction flask, control the temperature at 65℃, and keep it warm for 3 hours to hydrolyze and obtain the pretreated slurry; S3: Add 100g of pretreated slurry, 400mL of ethanol, 25mL of water and 50g of tetraethyl orthosilicate to the reaction vessel and disperse. Add 28wt% ammonia water dropwise to adjust the pH to 9.5. Control the temperature at 40℃ and keep the reaction at this temperature for 4.5h. Collect the particles by centrifugation, wash with ethanol and dry (vacuum dry at 60℃ for 2h and cure at 120℃ for 1h) to obtain the nano-modifier.

[0029] The preparation method of DOPO-grafted PP includes the following steps: 0.3g of dicumyl peroxide, 1.5g of DOPO, and 0.5g of acetone were added to a reaction flask and stirred and dissolved in a 90℃ water bath to obtain a mixture. 96g of PP and 0.4g of ethylene bis-stearamide were added to a high-speed mixer and mixed. The mixture was added and mixed at high speed (300 rpm for 90 seconds). The mixture was then extruded and granulated (feed zone 180℃ → melt zone 200℃ → homogenization zone 220℃ → die head 210℃, screw speed: 200 rpm), cooled, and dried (vacuum drying at 80℃ for 2 hours) to obtain DOPO-grafted PP.

[0030] Example 3: The preparation method of the nano-modifier includes the following steps: S1: Add 90g MgCl2·6H2O, 36g AlCl3·6H2O and 1200mL deionized water to the reaction vessel and disperse them. Control the temperature at 60℃, add 32g sodium carbonate and 5.5g sodium hydroxide, keep warm and age for 15h, centrifuge and wash to obtain slurry; S2: Add 100g of slurry and 2g of KH550 to a reaction flask, control the temperature at 70℃, and keep it warm for 4 hours to hydrolyze and obtain the pretreated slurry; S3: Add 100g of pretreated slurry, 500mL of ethanol, 30mL of water, and 55g of tetraethyl orthosilicate to a reaction vessel and disperse them. Add 28wt% ammonia water dropwise to adjust the pH to 9.5. Control the temperature at 45℃ and keep the reaction at this temperature for 6 hours. Collect the particles by centrifugation, wash with ethanol, and dry (vacuum dry at 60℃ for 2 hours and cure at 120℃ for 1 hour) to obtain the nano-modifier.

[0031] The preparation method of DOPO-grafted PP includes the following steps: 0.4g of dicumyl peroxide, 2g of DOPO, and 0.5g of acetone were added to a reaction flask and stirred and dissolved in a 90℃ water bath to obtain a mixture. 98g of PP and 0.5g of ethylene bis-stearamide were added to a high-speed mixer and mixed. The mixture was added and mixed at high speed (300 rpm for 90 seconds). The mixture was then extruded and granulated (feed zone 180℃ → melt zone 200℃ → homogenization zone 220℃ → die head 210℃, screw speed: 250 rpm), cooled, and dried (vacuum drying at 80℃ for 2 hours) to obtain DOPO-grafted PP.

[0032] Example 4: A method for preparing a high flame-retardant HPPM double-wall corrugated pipe, comprising the following steps: 65g of PP resin (Hyosung B240P from South Korea), 9.6g of ammonium polyphosphate, 6.4g of magnesium hydroxide, 4g of melamine cyanurate, 4g of the nano-modifier prepared in Example 1, 2.5g of maleic anhydride-grafted polypropylene, 1.5g of DOPO-grafted PP prepared in Example 1, 0.4g of antioxidant 1010, 0.2g of UV absorber UV-531, 0.4g of light stabilizer 770, 0.4g of calcium stearate, and 0.6g of PE wax were added to a high-speed mixer and mixed at 1200r / min and 115℃ for 10min to obtain an inner layer mixture. The inner layer mixture was then fed into a twin-screw extruder for granulation at 180℃, a screw speed of 350r / min, and a die head pressure of 13MPa. After pelleting, the pellets were air-cooled to room temperature, with a particle size of 3-5mm, to obtain the inner layer raw material. 60g of PP resin (Hyosung B240P from South Korea), 9.6g of ammonium polyphosphate, 6.4g of magnesium hydroxide, 4g of melamine cyanurate, 5g of the nano-modifier prepared in Example 1, 2.5g of maleic anhydride-grafted polypropylene, 1.5g of DOPO-grafted PP prepared in Example 1, 0.4g of antioxidant 1010, 0.4g of UV absorber UV-531, 0.5g of light stabilizer 770, 0.3g of calcium stearate, and 0.4g of PE wax were added to a high-speed mixer and mixed at 1200r / min and 114℃ for 10min to obtain an outer layer mixture. The outer layer mixture was then fed into a twin-screw extruder for granulation at 180℃, a screw speed of 350r / min, and a die head pressure of 13MPa. After pelleting, the pellets were air-cooled to room temperature, with a particle size of 3-5mm, to obtain the outer layer raw material. The inner layer material is fed into the inner layer extruder and extruded through the inner layer flow channel of the co-extrusion die to form the inner layer. The temperature settings of the inner layer extruder are: feeding zone 166℃, melting zone 180℃, homogenization zone 190℃, and die head 195℃. The die head pressure of the inner layer extruder is 8MPa. The screw speed of the inner layer extruder is 45rpm. The outer layer raw material is fed into the outer layer extruder and extruded through the outer layer flow channel of the co-extrusion die to form the outer layer; the temperature settings of the outer layer extruder are: feed zone 170℃, melting zone 185℃, homogenization zone 195℃, and die head 200℃; the die head pressure of the outer layer extruder is 12MPa; the screw speed of the outer layer extruder is 35rpm; The inner and outer layers are combined to obtain a tube blank, which is then corrugated in a corrugated mold (mold temperature 210℃), vacuum adsorption and shaping under a vacuum degree of 0.06MPa, and rapidly cooled in a cooling water tank (water temperature 15℃) to obtain a high flame retardant HPPM double-wall corrugated pipe.

[0033] Example 5: A method for preparing a high flame-retardant HPPM double-wall corrugated pipe, comprising the following steps: 65g of PP resin (Hyosung B240P from South Korea), 9.6g of ammonium polyphosphate, 6.4g of magnesium hydroxide, 4g of melamine cyanurate, 4g of the nano-modifier prepared in Example 2, 2.5g of maleic anhydride-grafted polypropylene, 1.5g of DOPO-grafted PP prepared in Example 2, 0.4g of antioxidant 1010, 0.2g of UV absorber UV-531, 0.4g of light stabilizer 770, 0.4g of calcium stearate, and 0.6g of PE wax were added to a high-speed mixer and mixed at 1200r / min and 115℃ for 10min to obtain an inner layer mixture. The inner layer mixture was then fed into a twin-screw extruder for granulation at 180℃, screw speed 350r / min, and die head pressure 13MPa. After pelleting, the pellets were air-cooled to room temperature, with a particle size of 3-5mm, to obtain the inner layer raw material. 60g of PP resin (Hyosung B240P from South Korea), 9.6g of ammonium polyphosphate, 6.4g of magnesium hydroxide, 4g of melamine cyanurate, 5g of the nano-modifier prepared in Example 2, 2.5g of maleic anhydride-grafted polypropylene, 1.5g of DOPO-grafted PP prepared in Example 2, 0.4g of antioxidant 1010, 0.4g of UV absorber UV-531, 0.5g of light stabilizer 770, 0.3g of calcium stearate, and 0.4g of PE wax were added to a high-speed mixer and mixed at 1200r / min and 114℃ for 10min to obtain an outer layer mixture. The outer layer mixture was then fed into a twin-screw extruder for granulation at 180℃, screw speed 350r / min, and die head pressure 13MPa. After pelleting, the pellets were air-cooled to room temperature, with a particle size of 3-5mm, to obtain the outer layer raw material. The inner layer material is fed into the inner layer extruder and extruded through the inner layer flow channel of the co-extrusion die to form the inner layer. The temperature settings of the inner layer extruder are: feeding zone 166℃, melting zone 180℃, homogenization zone 190℃, and die head 195℃. The die head pressure of the inner layer extruder is 8MPa. The screw speed of the inner layer extruder is 45rpm. The outer layer raw material is fed into the outer layer extruder and extruded through the outer layer flow channel of the co-extrusion die to form the outer layer; the temperature settings of the outer layer extruder are: feed zone 170℃, melting zone 185℃, homogenization zone 195℃, and die head 200℃; the die head pressure of the outer layer extruder is 12MPa; the screw speed of the outer layer extruder is 35rpm; The inner and outer layers are combined to obtain a tube blank, which is then corrugated in a corrugated mold (mold temperature 210℃), vacuum adsorption and shaping under a vacuum degree of 0.06MPa, and rapidly cooled in a cooling water tank (water temperature 15℃) to obtain a high flame retardant HPPM double-wall corrugated pipe.

[0034] Example 6: A method for preparing a high flame-retardant HPPM double-wall corrugated pipe, comprising the following steps: 65g of PP resin (Hyosung B240P from South Korea), 9.6g of ammonium polyphosphate, 6.4g of magnesium hydroxide, 4g of melamine cyanurate, 4g of the nano-modifier prepared in Example 3, 2.5g of maleic anhydride-grafted polypropylene, 1.5g of DOPO-grafted PP prepared in Example 3, 0.4g of antioxidant 1010, 0.2g of UV absorber UV-531, 0.4g of light stabilizer 770, 0.4g of calcium stearate, and 0.6g of PE wax were added to a high-speed mixer and mixed at 1200r / min and 115℃ for 10min to obtain an inner layer mixture. The inner layer mixture was then fed into a twin-screw extruder for granulation at 180℃, screw speed 350r / min, and die head pressure 13MPa. After pelleting, the pellets were air-cooled to room temperature, with a particle size of 3-5mm, to obtain the inner layer raw material. 60g of PP resin (Hyosung B240P from Korea), 9.6g of ammonium polyphosphate, 6.4g of magnesium hydroxide, 4g of melamine cyanurate, 5g of the nano-modifier prepared in Example 3, 2.5g of maleic anhydride-grafted polypropylene, 1.5g of DOPO-grafted PP prepared in Example 3, 0.4g of antioxidant 1010, 0.4g of UV absorber UV-531, 0.5g of light stabilizer 770, 0.3g of calcium stearate, and 0.4g of PE wax were added to a high-speed mixer and mixed at 1200r / min and 114℃ for 10min to obtain an outer layer mixture. The outer layer mixture was then fed into a twin-screw extruder for granulation at 180℃, screw speed 350r / min, and die head pressure 13MPa. After pelleting, the pellets were air-cooled to room temperature, with a particle size of 3-5mm, to obtain the outer layer raw material. The inner layer material is fed into the inner layer extruder and extruded through the inner layer flow channel of the co-extrusion die to form the inner layer. The temperature settings of the inner layer extruder are: feeding zone 166℃, melting zone 180℃, homogenization zone 190℃, and die head 195℃. The die head pressure of the inner layer extruder is 8MPa. The screw speed of the inner layer extruder is 45rpm. The outer layer raw material is fed into the outer layer extruder and extruded through the outer layer flow channel of the co-extrusion die to form the outer layer; the temperature settings of the outer layer extruder are: feed zone 170℃, melting zone 185℃, homogenization zone 195℃, and die head 200℃; the die head pressure of the outer layer extruder is 12MPa; the screw speed of the outer layer extruder is 35rpm; The inner and outer layers are combined to obtain a tube blank, which is then corrugated in a corrugated mold (mold temperature 210℃), vacuum adsorption and shaping under a vacuum degree of 0.06MPa, and rapidly cooled in a cooling water tank (water temperature 15℃) to obtain a high flame retardant HPPM double-wall corrugated pipe.

[0035] Comparative Example 1: The preparation method of the nano-modifier includes the following steps: S1: 70g MgCl2·6H2O, 30g AlCl3·6H2O and 1000mL deionized water were added to the reaction vessel and dispersed. The temperature was controlled at 55℃. 30g sodium carbonate and 5.5g sodium hydroxide were added. The mixture was kept at this temperature and aged for 13.5h. After centrifugation and washing, the slurry was obtained. S2: 100g of pretreated slurry, 400mL of ethanol, 25mL of water and 50g of tetraethyl orthosilicate were added to the reaction vessel and dispersed. 28wt% ammonia was added dropwise to adjust the pH to 9.5. The temperature was controlled at 40℃ and the reaction was kept at this temperature for 4.5h. The particles were collected by centrifugation, washed with ethanol and dried (vacuum dried at 60℃ for 2h and cured at 120℃ for 1h) to obtain the nano-modifier.

[0036] Comparative Example 2: The preparation method of the nano-modifier includes the following steps: S1: 70g MgCl2·6H2O, 30g AlCl3·6H2O and 1000mL deionized water were added to the reaction vessel and dispersed. The temperature was controlled at 55℃. 30g sodium carbonate and 5.5g sodium hydroxide were added. The mixture was kept at this temperature and aged for 13.5h. After centrifugation and washing, the slurry was obtained. S2: Add 100g of slurry and 1.5g of KH550 to a reaction flask, control the temperature at 65℃, and keep it warm for 3h to hydrolyze and obtain a pretreated slurry. Collect the particles by centrifugation, wash with ethanol, and dry (vacuum dry at 60℃ for 2h, and cure at 120℃ for 1h) to obtain a nano-modifier.

[0037] Comparative Example 3: A method for preparing a high flame-retardant HPPM double-wall corrugated pipe, comprising the following steps: 65g of PP resin (Hyosung B240P from South Korea), 9.6g of ammonium polyphosphate, 6.4g of magnesium hydroxide, 4g of melamine cyanurate, 4g of the nano-modifier prepared in Comparative Example 1, 2.5g of maleic anhydride-grafted polypropylene, 1.5g of DOPO-grafted PP prepared in Example 2, 0.4g of antioxidant 1010, 0.2g of UV absorber UV-531, 0.4g of light stabilizer 770, 0.4g of calcium stearate, and 0.6g of PE wax were added to a high-speed mixer and mixed at 1200r / min and 115℃ for 10min to obtain an inner layer mixture. The inner layer mixture was then fed into a twin-screw extruder for granulation at 180℃, screw speed 350r / min, and die head pressure 13MPa. After pelleting, the pellets were air-cooled to room temperature, with a particle size of 3-5mm, to obtain the inner layer raw material. 60g of PP resin (Hyosung B240P from South Korea), 9.6g of ammonium polyphosphate, 6.4g of magnesium hydroxide, 4g of melamine cyanurate, 5g of the nano-modifier prepared in Comparative Example 1, 2.5g of maleic anhydride-grafted polypropylene, 1.5g of DOPO-grafted PP prepared in Example 2, 0.4g of antioxidant 1010, 0.4g of UV absorber UV-531, 0.5g of light stabilizer 770, 0.3g of calcium stearate, and 0.4g of PE wax were added to a high-speed mixer and mixed at 1200r / min and 114℃ for 10min to obtain an outer layer mixture. The outer layer mixture was then fed into a twin-screw extruder for granulation at 180℃, screw speed 350r / min, and die head pressure 13MPa. After pelleting, the pellets were air-cooled to room temperature, with a particle size of 3-5mm, to obtain the outer layer raw material. The inner layer material is fed into the inner layer extruder and extruded through the inner layer flow channel of the co-extrusion die to form the inner layer. The temperature settings of the inner layer extruder are: feeding zone 166℃, melting zone 180℃, homogenization zone 190℃, and die head 195℃. The die head pressure of the inner layer extruder is 8MPa. The screw speed of the inner layer extruder is 45rpm. The outer layer raw material is fed into the outer layer extruder and extruded through the outer layer flow channel of the co-extrusion die to form the outer layer; the temperature settings of the outer layer extruder are: feed zone 170℃, melting zone 185℃, homogenization zone 195℃, and die head 200℃; the die head pressure of the outer layer extruder is 12MPa; the screw speed of the outer layer extruder is 35rpm; The inner and outer layers are combined to obtain a tube blank, which is then corrugated in a corrugated mold (mold temperature 210℃), vacuum adsorption and shaping under a vacuum degree of 0.06MPa, and rapidly cooled in a cooling water tank (water temperature 15℃) to obtain a high flame retardant HPPM double-wall corrugated pipe.

[0038] Comparative Example 4: A method for preparing a high flame-retardant HPPM double-wall corrugated pipe, comprising the following steps: 65g of PP resin (Hyosung B240P from South Korea), 9.6g of ammonium polyphosphate, 6.4g of magnesium hydroxide, 4g of melamine cyanurate, 4g of the nano-modifier prepared in Comparative Example 2, 2.5g of maleic anhydride-grafted polypropylene, 1.5g of DOPO-grafted PP prepared in Example 2, 0.4g of antioxidant 1010, 0.2g of UV absorber UV-531, 0.4g of light stabilizer 770, 0.4g of calcium stearate, and 0.6g of PE wax were added to a high-speed mixer and mixed at 1200r / min and 115℃ for 10min to obtain an inner layer mixture. The inner layer mixture was then fed into a twin-screw extruder for granulation at 180℃, screw speed 350r / min, and die head pressure 13MPa. After pelleting, the pellets were air-cooled to room temperature, with a particle size of 3-5mm, to obtain the inner layer raw material. 60g of PP resin (Hyosung B240P from Korea), 9.6g of ammonium polyphosphate, 6.4g of magnesium hydroxide, 4g of melamine cyanurate, 5g of the nano-modifier prepared in Comparative Example 2, 2.5g of maleic anhydride-grafted polypropylene, 1.5g of DOPO-grafted PP prepared in Example 2, 0.4g of antioxidant 1010, 0.4g of UV absorber UV-531, 0.5g of light stabilizer 770, 0.3g of calcium stearate, and 0.4g of PE wax were added to a high-speed mixer and mixed at 1200r / min and 114℃ for 10min to obtain an outer layer mixture. The outer layer mixture was then fed into a twin-screw extruder for granulation at 180℃, screw speed 350r / min, and die head pressure 13MPa. After pelleting, the pellets were air-cooled to room temperature, with a particle size of 3-5mm, to obtain the outer layer raw material. The inner layer material is fed into the inner layer extruder and extruded through the inner layer flow channel of the co-extrusion die to form the inner layer. The temperature settings of the inner layer extruder are: feeding zone 166℃, melting zone 180℃, homogenization zone 190℃, and die head 195℃. The die head pressure of the inner layer extruder is 8MPa. The screw speed of the inner layer extruder is 45rpm. The outer layer raw material is fed into the outer layer extruder and extruded through the outer layer flow channel of the co-extrusion die to form the outer layer; the temperature settings of the outer layer extruder are: feed zone 170℃, melting zone 185℃, homogenization zone 195℃, and die head 200℃; the die head pressure of the outer layer extruder is 12MPa; the screw speed of the outer layer extruder is 35rpm; The inner and outer layers are combined to obtain a tube blank, which is then corrugated in a corrugated mold (mold temperature 210℃), vacuum adsorption and shaping under a vacuum degree of 0.06MPa, and rapidly cooled in a cooling water tank (water temperature 15℃) to obtain a high flame retardant HPPM double-wall corrugated pipe.

[0039] Comparative Example 5: A method for preparing a high flame-retardant HPPM double-wall corrugated pipe, comprising the following steps: 65g of PP resin (Hyosung B240P from South Korea), 9.6g of ammonium polyphosphate, 6.4g of magnesium hydroxide, 4g of melamine cyanurate, 4g of the nano-modifier prepared in Example 3, 2.5g of maleic anhydride-grafted polypropylene, 1.5g of DOPO, 0.4g of antioxidant 1010, 0.2g of UV absorber UV-531, 0.4g of light stabilizer 770, 0.4g of calcium stearate, and 0.6g of PE wax were added to a high-speed mixer and mixed at 1200r / min and 115℃ for 10min to obtain an inner layer mixture. The inner layer mixture was then fed into a twin-screw extruder for granulation at 180℃, a screw speed of 350r / min, and a die head pressure of 13MPa. After pelleting, the pellets were air-cooled to room temperature, with a particle size of 3-5mm, to obtain the inner layer raw material. 60g of PP resin (Hyosung B240P from Korea), 9.6g of ammonium polyphosphate, 6.4g of magnesium hydroxide, 4g of melamine cyanurate, 5g of the nano-modifier prepared in Example 3, 2.5g of maleic anhydride-grafted polypropylene, 1.5g of DOPO, 0.4g of antioxidant 1010, 0.4g of UV absorber UV-531, 0.5g of light stabilizer 770, 0.3g of calcium stearate, and 0.4g of PE wax were added to a high-speed mixer and mixed at 1200r / min and 114℃ for 10min to obtain an outer layer mixture. The outer layer mixture was then fed into a twin-screw extruder for granulation at 180℃, a screw speed of 350r / min, and a die head pressure of 13MPa. After pelleting, the pellets were air-cooled to room temperature, with a particle size of 3-5mm, to obtain the outer layer raw material. The inner layer material is fed into the inner layer extruder and extruded through the inner layer flow channel of the co-extrusion die to form the inner layer. The temperature settings of the inner layer extruder are: feeding zone 166℃, melting zone 180℃, homogenization zone 190℃, and die head 195℃. The die head pressure of the inner layer extruder is 8MPa. The screw speed of the inner layer extruder is 45rpm. The outer layer raw material is fed into the outer layer extruder and extruded through the outer layer flow channel of the co-extrusion die to form the outer layer; the temperature settings of the outer layer extruder are: feed zone 170℃, melting zone 185℃, homogenization zone 195℃, and die head 200℃; the die head pressure of the outer layer extruder is 12MPa; the screw speed of the outer layer extruder is 35rpm; The inner and outer layers are combined to obtain a tube blank, which is then corrugated in a corrugated mold (mold temperature 210℃), vacuum adsorption and shaping under a vacuum degree of 0.06MPa, and rapidly cooled in a cooling water tank (water temperature 15℃) to obtain a high flame retardant HPPM double-wall corrugated pipe.

[0040] Performance testing (1) Ring stiffness: The ring stiffness of thermoplastic pipes was tested according to GB / T 9647-2003 "Determination of ring stiffness of thermoplastic pipes". The test results are shown in Table 1. (2) Impact resistance: The impact resistance of double-wall corrugated pipe at -30℃ was tested according to GB / T 14152-2015 "Test method for external impact resistance of thermoplastic pipes - clockwise rotation method". The test results are shown in Table 1. (3) Tensile strength: The test was conducted according to GB / T 1040.2-2006 "Determination of tensile properties of plastics - Part 2: Test conditions for molded and extruded plastics". The test results are shown in Table 1. Table 1: Statistical Table of Mechanical Property Test Data for Examples 4-6 and Comparative Examples 3-5 As shown in Table 1, when the nano-modifier prepared in this application and DOPO-grafted PP are added to the polypropylene resin matrix, the physical support network formed by the nano-modifier and the synergistic effect of DOPO-grafted PP compensate for the negative impact of a single component on mechanical properties. However, in Comparative Examples 3-4, the poor interfacial compatibility due to incomplete nano-modification and Comparative Example 5, the destruction of the matrix structure by DOPO agglomeration both lead to deterioration of mechanical properties.

[0041] Table 2: Statistical Table of Flame Retardant Performance Test Data for Examples 4-6 and Comparative Examples 3-5 As shown in Table 2, this application utilizes the synergistic effect of nano-modifiers, DOPO-grafted PP and composite flame retardants to achieve a vertical combustion rating of V-0 and an oxygen index of over 30% for the pipes prepared in Examples 5-6, which is significantly better than Comparative Examples 3-5 (Comparative Examples 3-4 are V-1 and Comparative Example 5 is V-2).

[0042] (4) Melt Flow Rate (MFR): The test was conducted according to GB / T 3682.1-2018 "Determination of Melt Mass Flow Rate (MFR) and Melt Volume Flow Rate (MVR) of Thermoplastic Plastics - Part 1: Standard Methods", with a test temperature of 230℃ and a load of 2.16kg. At the same time, the bonding state of the inner and outer layers of the pipe after molding was observed to evaluate whether there were any delamination defects. The test results are shown in Table 3. Table 3: Statistical Table of Processability Test Data for Examples 4-6 and Comparative Examples 3-5 As shown in Table 3, the MFR of the pipes prepared in Examples 5-6 of this application is above 11 g / 10 min, and the inner and outer layers of the pipes are tightly bonded without delamination. The MFR of the pipes prepared in Comparative Examples 3-5 is all below 8 g / 10 min, and delamination exists to varying degrees. The silicon coating layer of the nano-modifier in this scheme reduces the melt flow resistance and synergistically optimizes the processing fluidity with DOPO grafted PP. In contrast, the melt resistance of Comparative Examples 3-4 is increased due to defects in nano-modification, and Comparative Example 5 suffers from poor compatibility due to the lack of DOPO grafting, both of which lead to deterioration in processing performance.

[0043] The foregoing has provided a detailed description of one embodiment of the present invention, but this description is merely a preferred embodiment and should not be construed as limiting the scope of the invention. All equivalent variations and modifications made within the scope of the claims of this invention should still fall within the patent coverage of this invention.

Claims

1. A method for preparing a high flame-retardant HPPM double-wall corrugated pipe, characterized in that, Includes the following steps: The inner layer raw material is fed into the inner layer extruder and extruded through the inner layer flow channel of the co-extrusion die to form the inner layer; the outer layer raw material is fed into the outer layer extruder and extruded through the outer layer flow channel of the co-extrusion die to form the outer layer; the inner layer and the outer layer are combined, corrugated, and cooled to obtain a high flame retardant HPPM double-wall corrugated pipe. The inner layer raw material comprises the following parts by weight: 60-65 parts PP resin, 20-25 parts composite flame retardant, 3-4 parts nano modifier, 3.5-5 parts compatibilizer, and 1.5-2.5 parts additive composition one; The outer layer raw material comprises the following parts by weight: 55-60 parts PP resin, 25-30 parts composite flame retardant, 4-5 parts nano modifier, 3.5-5 parts compatibilizer, and 1.5-2.5 parts additive composition two. The preparation method of the nano-modifier includes the following steps: S1: Add MgCl2·6H2O, AlCl3·6H2O and deionized water to the reactor and disperse them. Control the temperature at 50-60℃, add precipitant, keep warm and age for 12-15h, centrifuge and wash to obtain slurry; S2: Add the slurry and KH550 into the reaction flask, control the temperature at 60-70℃, and keep it warm for 2-4 hours to hydrolyze and obtain the pretreated slurry; S3: Add the pretreated slurry, ethanol, water, and tetraethyl orthosilicate to the reaction vessel and disperse them. Add ammonia water dropwise to adjust the pH to 9.

5. Control the temperature at 40-45℃ and keep the reaction at this temperature for 3-6 hours. Collect the particles by centrifugation, wash with ethanol, and dry to obtain the nano-modifier.

2. The method for preparing a high flame-retardant HPPM double-wall corrugated pipe according to claim 1, characterized in that, The precipitant described in S1 is composed of sodium carbonate and sodium hydroxide in a mass ratio of 6:1-1.1; the addition ratio of MgCl2·6H2O, AlCl3·6H2O, deionized water, and precipitant is 60-90g: 24-36g: 800-1200mL: 35-38g.

3. The method for preparing a high flame-retardant HPPM double-wall corrugated pipe according to claim 1, characterized in that, The addition ratio of slurry and KH550 in S2 is 100g: 1-2g.

4. The method for preparing a high flame-retardant HPPM double-wall corrugated pipe according to claim 1, characterized in that, The addition ratio of pretreated slurry, ethanol, water, and tetraethyl orthosilicate in S3 is 100g: 400-500mL: 20-30mL: 45-55g.

5. The method for preparing a high flame-retardant HPPM double-wall corrugated pipe according to claim 1, characterized in that, The compatibilizer is composed of maleic anhydride-grafted polypropylene and DOPO-grafted PP in a mass ratio of 2-3:1.5-2. The preparation method of DOPO-grafted PP includes the following steps: 0.2-0.4g of dicumyl peroxide, 1-2g of DOPO, and 0.3-0.5g of acetone are added to a reaction flask and stirred and dissolved in a water bath at 85-90℃ to obtain a mixture; 96-98g of PP and 0.3-0.5g of ethylene bis-stearamide are added to a high-speed mixer and mixed; the mixture is added, mixed, extruded and granulated, cooled, and dried to obtain DOPO-grafted PP.

6. The method for preparing a high flame-retardant HPPM double-wall corrugated pipe according to claim 5, characterized in that, The composite flame retardant is composed of ammonium polyphosphate, magnesium hydroxide, and melamine cyanurate in a mass ratio of 12-15:8-10:5-7.

7. The method for preparing a high flame-retardant HPPM double-wall corrugated pipe according to claim 5, characterized in that, The additive composition consists of an antioxidant, a light stabilizer, and a lubricant in a mass ratio of 0.3-0.5:0.5-1:0.5-1. The second auxiliary agent composition consists of an antioxidant, a lubricant, and a light stabilizer in a mass ratio of 0.3-0.5:0.8-1.2:0.5-1.

8. The method for preparing a high flame-retardant HPPM double-wall corrugated pipe according to claim 1, characterized in that, The temperature settings for the inner extruder are as follows: feeding zone 160-170℃, melting zone 175-185℃, homogenization zone 185-195℃, and die head 190-200℃; the die head pressure of the inner extruder is 5-10MPa. The temperature settings for the outer extruder are as follows: feeding zone 165-175℃, melting zone 180-190℃, homogenization zone 190-200℃, and die head 195-205℃; the die head pressure of the outer extruder is 10-15MPa. The screw speed of the inner extruder is 40-50 rpm, and the screw speed of the outer extruder is 30-40 rpm. The ratio of the inner layer to the outer layer wall thickness is 1.2-1.5:

1.

9. The method for preparing a high flame-retardant HPPM double-wall corrugated pipe according to claim 1, characterized in that, The corrugating process involves forming a composite tube blank in a corrugated mold; the mold temperature is 210-220℃. The specific process for cooling and shaping is vacuum adsorption shaping under a vacuum degree of 0.05-0.08MPa, followed by cooling with cooling water.

10. A high flame-retardant HPPM double-wall corrugated pipe, characterized in that, It is prepared by the preparation method described in any one of claims 1-9.

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