Corrosion-resistant buried polyolefin drainage pipe and preparation method thereof

Abstract

The invention belongs to the technical field of high polymer materials, and discloses a corrosion-resistant buried polyolefin drainage pipe and a preparation method thereof.The corrosion-resistant buried polyolefin drainage pipe is prepared from, by mass, 100-120 parts of high-density polyethylene, 20-30 parts of ABS resin, 5-10 parts of plasticizer, 10-15 parts of modified boron nitride, 0.5-2 parts of composite flame retardant, 0.1-0.5 part of antioxidant, 3-5 parts of calcium stearate and 1-3 parts of PE wax; the modified boron nitride is a triazine derivative which is grafted on the surface of hexagonal boron nitride and contains a plurality of benzisothiazolinone units; the composite flame retardant is compounded by a phosphorus-containing Schiff base flame retardant and DOPO according to the mass ratio of 1: (2-4); the high-density polyethylene is used as a matrix, the modified boron nitride is added, so that the corrosion resistance of the material is improved, the phosphorus-containing Schiff base flame retardant is compounded with DOPO, the flame retardance of the material is improved, and meanwhile, the dosage of DOPO is reduced.

Description

Technical Field

[0001] The invention belongs to the technical field of polymer materials, and in particular relates to a corrosion-resistant buried polyolefin drainage pipe and a preparation method thereof. Background Art

[0002] Polyethylene is a highly crystalline, non-polar thermoplastic resin with excellent resistance to most household and industrial chemicals, such as chemical corrosion caused by certain types of chemicals, such as corrosive oxidants (concentrated nitric acid), aromatic hydrocarbons (xylene) and halogenated hydrocarbons (carbon tetrachloride), etc. It is lightweight and non-toxic. Therefore, polyethylene is widely used in pipes, such as rainwater drainage pipes and other sewer pipes. Among them, polyethylene drainage pipes are widely used in drainage fields such as roads, railway subgrades, subway projects, waste landfills, tunnels, green belts, sports fields, and slope protection caused by high water content, as well as irrigation and drainage systems in agriculture and horticulture.

[0003] The wastewater discharged from the drainage pipe is generally industrial wastewater or domestic sewage, which will cause a certain degree of corrosion to the water pipe. As time goes by, the pipe will be corroded more and more seriously, which will cause the pipe wall to become thinner and cracks to appear, which will cause water leakage problems and damage the surrounding environment. After the pipe is corroded, the service life of the pipe will be shortened. At the same time, the existing PE drainage pipes are generally single-layer structures, and most of them are white, with poor shading effect. If used outdoors for a long time, it will provide a good environment for the growth of bacteria, often causing a large number of microorganisms to breed and multiply on the inside of the pipe body. The microorganisms will directly degrade the pipe, indirectly degrade it, and have surface effects, thereby shortening the service life of the pipe. Therefore, there is an urgent need for a corrosion-resistant polyolefin material to meet the needs of drainage pipes. Summary of the invention

[0004] In order to solve the deficiencies mentioned in the above background technology, the purpose of the present invention is to provide a corrosion-resistant buried polyolefin drainage pipe and a preparation method thereof, which takes high-density polyethylene as the matrix and improves the corrosion resistance of the material by adding modified boron nitride. In addition, by compounding a phosphorus-containing Schiff base flame retardant with DOPO, the flame retardant performance of the material is improved, while reducing the amount of DOPO used.

[0005] The purpose of the present invention can be achieved through the following technical solutions: A corrosion-resistant buried polyolefin drainage pipe, comprising the following components by weight: 100-120 parts of high-density polyethylene, 20-30 parts of ABS resin, 5-10 parts of plasticizer, 10-15 parts of modified boron nitride, 0.5-2 parts of composite flame retardant, 0.1-0.5 parts of antioxidant, 3-5 parts of calcium stearate, and 1-3 parts of PE wax; The modified boron nitride is a hexagonal boron nitride surface grafted with a triazine derivative containing multiple benzisothiazolinone units; The composite flame retardant is compounded by a phosphorus-containing Schiff base flame retardant and DOPO in a mass ratio of 1:2-4. The phosphorus-containing Schiff base flame retardant is based on 5-hydroxyisophthalaldehyde as a basic functional unit, and introduces phosphorus elements and Schiff base structures with flame retardant functions.

[0006] More preferably, the plasticizer is one or more of dioctyl phthalate, triethylene glycol di(2-ethylbutyrate), tricresyl phosphate, diisobutyl phthalate, and diisodecyl phthalate.

[0007] More preferably, the antioxidant is one or more of antioxidant 1010, antioxidant 168, and antioxidant 1024. Further preferably, the preparation method of modified boron nitride comprises the following steps: (1) 1,2-benzisothiazol-3-one, potassium carbonate and N,N-dimethylformamide were mixed, and then 1,3-dibromo-2-propanol was slowly added at room temperature, and the mixture was heated to 70°C and stirred for 10-12 hours. After the reaction, deionized water was added to dissolve the product, and the mixed solution was extracted with ethyl acetate. Anhydrous magnesium sulfate was added to the extract to dehydrate it, and then it was filtered. The filtrate was evaporated to remove ethyl acetate, and finally purified by a chromatographic column to obtain intermediate A; (2) Add cyanuric chloride to tetrahydrofuran and triethylamine under nitrogen atmosphere, stir to dissolve cyanuric chloride, then uniformly add 3-aminopropyltriethoxysilane dropwise, react in an ice bath for 2-3 hours after the addition is complete, then add intermediate A to the reaction system, then heat at a rate of 2-4°C / min to 50-70°C, keep warm for 5-6 hours, cool after the reaction is complete, remove triethylamine hydrochloride by suction filtration, and remove tetrahydrofuran by reduced pressure distillation to obtain a triazine derivative; (3) Add hexagonal boron nitride to 90 vol% ethanol aqueous solution, ultrasonically disperse for 10-15 min, adjust the solution pH to 4 with hydrochloric acid aqueous solution, then slowly add the triazine derivative to the above dispersion, continue ultrasonically dispersing for 5-10 min, heat to 80 °C and keep the reaction for 3-5 h, filter after cooling, wash and dry to obtain modified boron nitride.

[0008] More preferably, the molar ratio of 1,2-benzisothiazol-3-one to 1,3-dibromo-2-propanol is 2:1.

[0009] More preferably, the molar ratio of cyanuric chloride, 3-aminopropyltriethoxysilane and intermediate A is 1:1:2.

[0010] Further preferably, the preparation method of the phosphorus-containing Schiff base flame retardant comprises the following steps: A. Dissolve 5-hydroxyisophthalaldehyde and triethylamine in ethyl acetate, dissolve phenylphosphoryl dichloride in ethyl acetate, slowly drop the phenylphosphoryl dichloride solution into the mixed solution of 5-hydroxyisophthalaldehyde and triethylamine under nitrogen protection at 0 °C, after the dropwise addition is completed, react at 55-65 °C for 20-24 h, filter after the reaction is completed, wash the filtrate with saturated brine three times, concentrate and recrystallize to obtain intermediate B; B. Dissolve intermediate B and p-aminophenol in anhydrous ethanol respectively. Slowly drip the intermediate B solution into the p-aminophenol solution under nitrogen protection. After the dropwise addition is completed, keep the temperature at 45-50°C to react for 4-6 hours. After the reaction is completed, remove the anhydrous ethanol by rotary evaporation to obtain a phosphorus-containing Schiff base flame retardant.

[0011] More preferably, the molar ratio of 5-hydroxyisophthalaldehyde to phenylphosphoryl dichloride is 2:1.

[0012] More preferably, the molar ratio of intermediate B to p-aminophenol is 1:4.

[0013] A method for preparing a corrosion-resistant buried polyolefin drainage pipe comprises the following steps: S1. Mixing ingredients: mixing high-density polyethylene, ABS resin, plasticizer, modified boron nitride, composite flame retardant, antioxidant, calcium stearate and PE wax, and using a high-speed mixer to stir the above materials to obtain a uniformly dispersed mixture; S2. Extrusion molding: The mixed material is fed into the extruder from the hopper, compressed and plasticized by the screw to be converted into a high-viscosity elastic body, and continuously extruded through the mold. The hot pipe embryo enters the cooling and sizing device, and is cut to a fixed length after cooling to room temperature.

[0014] Beneficial effects of the present invention: The present invention synthesizes a triazine derivative having a benzisothiazolinone structure and a siloxane structure through a nucleophilic substitution reaction, and then grafts hexagonal boron nitride after hydrolysis of siloxane, which can significantly improve the dispersibility of boron nitride in a polymer matrix, thereby better exerting its effect of blocking chemical corrosion. At the same time, the triazine derivative contains multiple benzisothiazolinone units in the molecular structure, which also makes the material have good antibacterial properties, effectively inhibits the growth of microorganisms, and prevents the direct degradation of microorganisms, indirect degradation and surface effects on the material, thereby exerting a corrosion-resistant effect. The present invention uses 5-hydroxyisophthalaldehyde as a basic functional unit, introduces a phosphorus element and a Schiff base structure with a flame retardant function, prepares a flame retardant with a phosphorus-nitrogen synergistic flame retardant effect, and adds it and DOPO as a composite flame retardant to a polymer matrix, which can effectively improve the flame retardant properties of the material and reduce the amount of DOPO used. DETAILED DESCRIPTION

[0015] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0016] Example 1 A method for preparing modified boron nitride comprises the following steps: (1) 3.02 g 1,2-benzisothiazol-3-one (0.02 mol), 2.05 g potassium carbonate and 50 ml N,N-dimethylformamide were mixed, and then 2.18 g 1,3-dibromo-2-propanol (0.01 mol) was slowly added at room temperature, and the mixture was heated to 70°C and stirred for 12 h. After the reaction, deionized water was added to dissolve the product, and the mixed solution was extracted with ethyl acetate. Anhydrous magnesium sulfate was added to the extract for dehydration, and then filtered. The filtrate was evaporated to remove the ethyl acetate, and finally purified by a chromatographic column to obtain intermediate A; (2) Under nitrogen atmosphere, 1.84 g of cyanuric chloride (0.01 mol) was added to 30 ml of tetrahydrofuran and 20 ml of triethylamine, and the cyanuric chloride was dissolved by stirring. Then, 2.21 g of 3-aminopropyltriethoxysilane (0.01 mol) was added dropwise at a uniform rate. After the addition was completed, the reaction was carried out in an ice bath for 3 h. Then, 7.16 g of intermediate A (0.02 mol) was added to the reaction system. The temperature was then raised at a rate of 3 °C / min to 60 °C. The temperature was kept for 6 h. After the reaction was completed, the system was cooled, the triethylamine hydrochloride was removed by suction filtration, and the tetrahydrofuran was removed by vacuum distillation to obtain a triazine derivative. (3) Add 3.51 g of hexagonal boron nitride to 50 ml of 90 Vol% ethanol aqueous solution, and ultrasonically disperse for 12 min. Adjust the pH of the solution to 4 with hydrochloric acid aqueous solution, and then slowly add 1.8 g of triazine derivative to the above dispersion, continue ultrasonically dispersing for 8 min, heat to 80 ° C and keep the reaction for 4 h. After cooling, filter, wash and dry to obtain the modified boron nitride.

[0017] Example 2 A method for preparing a phosphorus-containing Schiff base flame retardant comprises the following steps: A. Dissolve 3.0g 5-hydroxyisophthalaldehyde (0.02mol) and 20ml triethylamine in 30ml ethyl acetate, and dissolve 1.95g phenylphosphoryl dichloride (0.01mol) in 20ml ethyl acetate. Slowly drop the phenylphosphoryl dichloride solution into the mixed solution of 5-hydroxyisophthalaldehyde and triethylamine under nitrogen protection at 0℃. After the dropwise addition, react at 60℃ for 24h. After the reaction is completed, filter, wash the filtrate with saturated brine 3 times, and concentrate and recrystallize to obtain intermediate B. B. Dissolve 4.23 g of intermediate B (0.01 mol) and 4.36 g of p-aminophenol (0.04 mol) in anhydrous ethanol respectively. Slowly drip the intermediate B solution into the p-aminophenol solution under nitrogen protection. After the dropwise addition is completed, keep the temperature at 50° C. for 5 hours. After the reaction is completed, remove the anhydrous ethanol by rotary evaporation to obtain the phosphorus-containing Schiff base flame retardant.

[0018] Example 3 A corrosion-resistant buried polyolefin drainage pipe comprises the following components in parts by mass: 120 parts of high-density polyethylene, 20 parts of ABS resin, 6 parts of dioctyl phthalate, 4 parts of diisodecyl phthalate, 10 parts of modified boron nitride, 2 parts of composite flame retardant, 0.1 parts of antioxidant, 5 parts of calcium stearate, and 1 part of PE wax, wherein the modified boron nitride is triazine derivative grafted hexagonal boron nitride prepared in Example 1, and the composite flame retardant is a compound of the phosphorus-containing Schiff base flame retardant prepared in Example 2 and DOPO in a mass ratio of 1:4.

[0019] The method for preparing the above-mentioned corrosion-resistant buried polyolefin drainage pipe comprises the following steps: S1. Mixing ingredients: mixing high-density polyethylene, ABS resin, plasticizer, modified boron nitride, composite flame retardant, antioxidant, calcium stearate and PE wax, and using a high-speed mixer to stir the above materials to obtain a uniformly dispersed mixture; S2. Extrusion molding: The mixed material is fed into the extruder from the hopper, compressed and plasticized by the screw to be converted into a high-viscosity elastic body, and continuously extruded through the mold. The hot pipe embryo enters the cooling and sizing device, and is cut to a fixed length after cooling to room temperature.

[0020] Example 4 A corrosion-resistant buried polyolefin drainage pipe comprises the following components in parts by mass: 100 parts of high-density polyethylene, 30 parts of ABS resin, 3 parts of dioctyl phthalate, 2 parts of diisobutyl phthalate, 15 parts of modified boron nitride, 0.5 parts of composite flame retardant, 0.5 parts of antioxidant, 3 parts of calcium stearate, and 3 parts of PE wax, wherein the modified boron nitride is triazine derivative grafted hexagonal boron nitride prepared in Example 1, and the composite flame retardant is a compound of the phosphorus-containing Schiff base flame retardant prepared in Example 2 and DOPO in a mass ratio of 1:2.

[0021] The preparation method of the above-mentioned corrosion-resistant buried polyolefin drainage pipe is the same as that of Example 3.

[0022] Example 5 A corrosion-resistant buried polyolefin drainage pipe comprises the following components in parts by weight: 110 parts of high-density polyethylene, 25 parts of ABS resin, 4 parts of dioctyl phthalate, 4 parts of di(2-ethylbutyrate) triethylene glycol ester, 12 parts of modified boron nitride, 1.2 parts of a composite flame retardant, 0.3 parts of an antioxidant, 4 parts of calcium stearate, and 2 parts of PE wax. The modified boron nitride is a triazine derivative grafted hexagonal boron nitride prepared in Example 1, and the composite flame retardant is a compound of the phosphorus-containing Schiff base flame retardant prepared in Example 2 and DOPO in a mass ratio of 1:3.

[0023] The preparation method of the above-mentioned corrosion-resistant buried polyolefin drainage pipe is the same as that of Example 3.

[0024] Comparative Example 1 A corrosion-resistant buried polyolefin drainage pipe comprises the following components in parts by weight: 110 parts of high-density polyethylene, 25 parts of ABS resin, 4 parts of dioctyl phthalate, 4 parts of di(2-ethylbutyrate) triethylene glycol ester, 1.2 parts of a composite flame retardant, 0.3 parts of an antioxidant, 4 parts of calcium stearate, and 2 parts of PE wax. The modified boron nitride is a triazine derivative grafted hexagonal boron nitride prepared in Example 1, and the composite flame retardant is a compound of the phosphorus-containing Schiff base flame retardant prepared in Example 2 and DOPO in a mass ratio of 1:3.

[0025] The preparation method of the above-mentioned corrosion-resistant buried polyolefin drainage pipe is the same as that of Example 3.

[0026] Comparative Example 2 A corrosion-resistant buried polyolefin drainage pipe comprises the following components in parts by mass: 110 parts of high-density polyethylene, 25 parts of ABS resin, 4 parts of dioctyl phthalate, 4 parts of di(2-ethylbutyrate) triethylene glycol ester, 12 parts of modified boron nitride, 1.2 parts of DOPO, 0.3 parts of antioxidant, 4 parts of calcium stearate, and 2 parts of PE wax. The modified boron nitride is the triazine derivative grafted hexagonal boron nitride prepared in Example 1.

[0027] The preparation method of the above-mentioned corrosion-resistant buried polyolefin drainage pipe is the same as that of Example 3 Performance Testing 1. Corrosion resistance Prepare 1.00 L of 20% concentrated nitric acid solution, add 10.00 g of copper nitrate, and fully dissolve at 60° C. Put the corrosion-resistant buried polyolefin drainage pipe prepared in Examples 3 to 5 and Comparative Examples 1 to 2 into the concentrated nitric acid-copper nitrate mixed solution, treat at 60° C. for 2 hours, then take out and wash the corrosion-resistant buried polyolefin drainage pipe with deionized water.

[0028] Gloss test: Tested according to ASTM D2457-2013. Corrosion-resistant buried polyolefin drainage pipe color change test: Tested according to ASTM D2244-2011. The sample color is characterized under the Lab color model, and the calculation formula for color change (ΔE) is: ΔE=|ΔL|+|Δa|+|Δb|, where: ΔE is the color change; ΔL is the depth change; Δa is the red-green change; Δb is the yellow-blue change. The data is shown in Table 1 below.

[0029] Table 1 Corrosion resistance test results of buried polyolefin drainage pipe

[0030] From the data in Table 1, it can be seen that the corrosion resistance of the corrosion-resistant buried polyolefin drainage pipe in Comparative Example 1 is significantly worse than that of other groups. The difference between Comparative Example 1 and other groups is that the modified boron nitride of the present invention is not added. The crystal structure of boron nitride is similar to that of graphene, which gives it excellent mechanical and chemical stability. In particular, the oxide layer formed on its surface not only makes the surface smoother, but also effectively blocks the erosion of chemical reactions and corrosion. When it is used as a polymer filler, the material can obtain excellent corrosion resistance. However, the difference in the electronegativity of P and N leads to the so-called "lip-lip" interaction between adjacent layers, making it difficult for a large amount of hexagonal boron nitride to be peeled off and easy to re-agglomerate, making it difficult to evenly disperse it in the polymer matrix. The invention synthesizes a triazine derivative having a benzisothiazolinone structure and a siloxane structure through a nucleophilic substitution reaction, and then grafts hexagonal boron nitride after hydrolysis of the siloxane, thereby significantly improving the dispersibility of the boron nitride in a polymer matrix, thereby better exerting its effect of blocking chemical corrosion; at the same time, the triazine derivative contains a plurality of benzisothiazolinone units in the molecular structure, which also enables the material to have good antibacterial properties, effectively inhibits the growth of microorganisms, and prevents the influence of direct degradation, indirect degradation and surface effects of microorganisms on the material, thereby exerting a corrosion-resistant effect.

[0031] 2. Flame retardant performance test The corrosion-resistant buried polyolefin drainage pipes in Examples 3 to 5 and Comparative Examples 1 to 2 were made into 127×12.7×3.2 mm standard specimens, and horizontal and vertical (UL-94) combustion tests were performed according to ASTM D3801-1996 standard. At the same time, an oxygen index test (LOI) was performed according to ASTM D2863-70 standard to obtain the data shown in Table 2 below.

[0032] Table 2 Performance test results of corrosion-resistant buried polyolefin drainage pipe

[0033] It can be seen from the data in Table 2 that the flame retardant effect of the comparative example 2, in which the phosphorus-containing Schiff base flame retardant prepared by the present invention is not added, is significantly lower than that of other groups. The present invention uses 5-hydroxyisophthalaldehyde as the basic functional unit, introduces phosphorus elements and Schiff base structures with flame retardant functions, prepares a flame retardant with phosphorus-nitrogen synergistic flame retardant effects, and adds it and DOPO as a compound flame retardant to the polymer matrix, which can effectively improve the flame retardant properties of the material while reducing the amount of DOPO used.

[0034] In the description of this specification, the description with reference to the terms "one embodiment", "example", "specific example", etc. means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representation of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments or examples in a suitable manner.

[0035] The above shows and describes the basic principles, main features and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments, and the above embodiments and descriptions are only for explaining the principles of the present invention. Without departing from the spirit and scope of the present invention, the present invention may have various changes and improvements, and these changes and improvements all fall within the scope of the present invention to be protected.

Claims

1. A corrosion-resistant buried polyolefin drainage pipe, characterized in that: The invention comprises the following components by weight: 100-120 parts of high-density polyethylene, 20-30 parts of ABS resin, 5-10 parts of plasticizer, 10-15 parts of modified boron nitride, 0.5-2 parts of composite flame retardant, 0.1-0.5 parts of antioxidant, 3-5 parts of calcium stearate and 1-3 parts of PE wax; The modified boron nitride is a hexagonal boron nitride surface grafted with a triazine derivative containing multiple benzisothiazolinone units; The composite flame retardant is compounded by a phosphorus-containing Schiff base flame retardant and DOPO in a mass ratio of 1:2-4. The phosphorus-containing Schiff base flame retardant is composed of 5-hydroxyisophthalaldehyde as a basic functional unit, and a phosphorus element and a Schiff base structure with flame retardant function are introduced.

2. The corrosion-resistant buried polyolefin drainage pipe according to claim 1, characterized in that: The plasticizer is one or more of dioctyl phthalate, di(2-ethylbutyrate) triethylene glycol ester, tricresyl phosphate, diisobutyl phthalate and diisodecyl phthalate.

3. The corrosion-resistant buried polyolefin drainage pipe according to claim 1, characterized in that: The antioxidant is one or more of antioxidant 1010, antioxidant 168, and antioxidant 1024.

4. The corrosion-resistant buried polyolefin drainage pipe according to claim 1, characterized in that: The preparation method of the modified boron nitride comprises the following steps: (1) 1,2-benzisothiazol-3-one, potassium carbonate and N,N-dimethylformamide were mixed, and then 1,3-dibromo-2-propanol was slowly added at room temperature, and the mixture was heated to 70°C and stirred for 10-12 hours. After the reaction, deionized water was added to dissolve the product, and the mixed solution was extracted with ethyl acetate. Anhydrous magnesium sulfate was added to the extract to dehydrate it, and then it was filtered. The filtrate was evaporated to remove ethyl acetate, and finally purified by a chromatographic column to obtain intermediate A; (2) Add cyanuric chloride to tetrahydrofuran and triethylamine under nitrogen atmosphere, stir to dissolve cyanuric chloride, then uniformly add 3-aminopropyltriethoxysilane dropwise, react in an ice bath for 2-3 hours after the addition is complete, then add intermediate A to the reaction system, then heat at a rate of 2-4°C / min to 50-70°C, keep warm for 5-6 hours, cool after the reaction is complete, remove triethylamine hydrochloride by suction filtration, and remove tetrahydrofuran by reduced pressure distillation to obtain a triazine derivative; (3) adding hexagonal boron nitride to 90 vol% ethanol aqueous solution, ultrasonically dispersing for 10-15 min, adjusting the pH value of the solution to 4 with hydrochloric acid aqueous solution, and then slowly adding the triazine derivative to the above dispersion, continuing ultrasonically dispersing for 5-10 min, heating to 80° C. and keeping the temperature for reaction for 3-5 h, and filtering after cooling, washing, and drying to obtain the modified boron nitride.

5. The corrosion-resistant buried polyolefin drainage pipe according to claim 4, characterized in that: The molar ratio of the 1,2-benzisothiazol-3-one to 1,3-dibromo-2-propanol is 2:

1.

6. The corrosion-resistant buried polyolefin drainage pipe according to claim 4, characterized in that: The molar ratio of the cyanuric chloride, 3-aminopropyltriethoxysilane and intermediate A is 1:1:

2.

7. The corrosion-resistant buried polyolefin drainage pipe according to claim 1, characterized in that: The preparation method of the phosphorus-containing Schiff base flame retardant comprises the following steps: A. Dissolve 5-hydroxyisophthalaldehyde and triethylamine in ethyl acetate, dissolve phenylphosphoryl dichloride in ethyl acetate, slowly drop the phenylphosphoryl dichloride solution into the mixed solution of 5-hydroxyisophthalaldehyde and triethylamine under nitrogen protection at 0 °C, after the dropwise addition is completed, react at 55-65 °C for 20-24 h, filter after the reaction is completed, wash the filtrate with saturated brine three times, concentrate and recrystallize to obtain intermediate B; B. Dissolve the intermediate B and p-aminophenol in anhydrous ethanol respectively, slowly drip the intermediate B solution into the p-aminophenol solution under nitrogen protection, keep the temperature at 45-50° C. for 4-6 hours after the dropwise addition, and remove the anhydrous ethanol by rotary evaporation after the reaction to obtain the phosphorus-containing Schiff base flame retardant.

8. The corrosion-resistant buried polyolefin drainage pipe according to claim 7, characterized in that: The molar ratio of the 5-hydroxyisophthalaldehyde to phenylphosphoryl dichloride is 2:

1.

9. The corrosion-resistant buried polyolefin drainage pipe according to claim 7, characterized in that: The molar ratio of the intermediate B to p-aminophenol is 1:

4.

10. The method for preparing the corrosion-resistant buried polyolefin drainage pipe according to any one of claims 1 to 8, characterized in that: The following steps are involved: S1. Mixing ingredients: mixing high-density polyethylene, ABS resin, plasticizer, modified boron nitride, composite flame retardant, antioxidant, calcium stearate and PE wax, and using a high-speed mixer to stir the above materials to obtain a uniformly dispersed mixture; S2. Extrusion molding: The mixed material is fed into the extruder from the hopper, compressed and plasticized by the screw to be converted into a high-viscosity elastic body, and continuously extruded through the mold. The hot pipe embryo enters the cooling and sizing device, and is cut to a fixed length after cooling to room temperature.

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