CN111234348B - Special material for buried polyethylene structural wall pipeline and preparation method thereof - Google Patents

Abstract

The invention discloses a special material for buried polyethylene structural wall pipes, comprising the following preparation raw materials in parts by weight: 10-40 parts of pipe-grade polyethylene, 10-30 parts of hollow-grade polyethylene, and 3-10 parts of injection-molded polyethylene , 20-45 parts of film-grade linear polyethylene, 4-6 parts of carbon black masterbatch, 1-3 parts of appearance improving agent and 4-10 parts of environmental stress cracking regulator. The special material for the buried polyethylene structural wall pipeline of the present invention is selected from four different grades of polyethylene: pipe grade polyethylene, hollow grade polyethylene, injection grade polyethylene and film grade linear polyethylene, which can be prepared with excellent mechanical properties and Appearance properties of recycled buried polyethylene structural wall pipes. The invention also discloses a preparation method of the special material for the buried polyethylene structure wall pipeline, and the method can prepare the special material for the buried polyethylene structure wall pipeline with uniform performance.

Description

Special material for buried polyethylene structural wall pipeline and preparation method thereof

technical field

The invention relates to the technical field of polymer materials, in particular to a special material for buried polyethylene structural wall pipes and a preparation method thereof.

Background technique

Among the production and manufacturing technologies of various pipes, the development of high-density polyethylene (HDPE) buried drainage pipes is the most rapid. According to the classification of existing production technologies, there are mainly two processes: direct extrusion molding and winding-welding molding, while The most widely used is the structural pipe made by the direct extrusion molding process. This type of structural pipe is made of HDPE as the main raw material, which is co-extruded by the inner and outer extruders at one time. It has the advantages of light weight, high pressure resistance, high ring stiffness, good toughness, low temperature resistance, corrosion resistance, fast construction and long life.

As a structural pipe, the buried polyethylene structural wall pipe has high requirements on the strength, stiffness, service life and molding of the material, so it must have an appropriate melt flow rate, high mechanical properties, and resistance to environmental stress cracking. and thermal oxidation resistance. The national standard GB/T 19472.1-2004 provides detailed regulations for buried polyethylene structural wall pipes.

In order to prepare special materials for buried polyethylene structural wall pipes whose performance meets the national standard, most of the domestic use is based on pipe-grade polyethylene resin, and a small amount of HDPE pipe material, linear low-density polyethylene, linear low-density polyethylene, etc. are added to the base material. Reinforced masterbatch, carbon black, antioxidants, modifiers, etc. are kneaded, such as the published patent CN 102494203 A, the resins used are all new polyethylene materials, and the use of waste polyethylene materials to produce buried polyethylene There are few reports and patents on special materials for structural wall pipes. The patent publication number CN 106832528 A discloses a production method of HDPE regenerated modified material, but the waste plastics involved have no specific physical property requirements.

However, in the process of national scientific and technological progress and the rapid development of economy, there are many kinds of waste polyethylene products, and the total amount is huge. How to recycle these waste polyethylene is not only one of the policy directions encouraged and advocated by the state, but also one of the social responsibilities of plastic modification enterprises. According to long-term production experience, if all the raw materials of the special materials for buried polyethylene structural wall pipes are made of waste polyethylene materials, extrusion defects such as pockmarks, bulges, and air bubbles are prone to occur during the extrusion process. At the same time, many manufacturers of plastic pipes are in order to reduce costs. Adding recycled materials and ignoring the product quality, when using recycled materials for production, the bottom material, source, physical properties, etc. of recycled materials are not fully understood, and there is a lack of experimental verification. There are phenomena such as insufficient ring stiffness, insufficient toughness, and environmental stress cracking resistance. Accidents such as project rework and delay were caused. Therefore, it is urgent to develop a new technology for the special material for buried polyethylene structural wall pipes that uses waste polyethylene materials as raw materials, whose performance meets the national standard and whose extrusion appearance is qualified.

SUMMARY OF THE INVENTION

The purpose of the present invention is to overcome the deficiencies existing in the prior art and provide a special material for buried polyethylene structural wall pipes and a preparation method thereof.

In order to achieve the above purpose, the technical solution adopted in the present invention is: a special material for buried polyethylene structural wall pipeline, comprising the following preparation raw materials in parts by weight: 10-40 parts of pipe-grade polyethylene and 10-30 parts of hollow-grade polyethylene , 3-10 parts of injection-molded polyethylene, 20-45 parts of film-grade linear polyethylene, 4-6 parts of carbon black masterbatch, 1-3 parts of appearance improver and 4-10 parts of environmental stress cracking regulator.

Four different grades of polyethylene are selected for the special material for the buried polyethylene structural wall pipeline of the present invention, and the regenerated buried polyethylene structural wall pipeline with excellent mechanical properties and appearance properties can be prepared with the above ratio.

Preferably, the pipe-grade polyethylene, hollow-grade polyethylene, injection-molding-grade polyethylene and film-grade linear polyethylene are all recycled resins. The raw materials of pipe-grade polyethylene, hollow-grade polyethylene, injection-molding-grade polyethylene, and film-grade linear polyethylene can be new resins, recycled resins, or a mixture of new resins and recycled resins, preferably recycled resins. The cost can be greatly reduced, and the buried polyethylene structural wall pipeline prepared by using the formula of the special material of the present invention can still maintain good mechanical properties under the condition that all raw materials are used waste recycled materials, and all meet the requirements of the national standard. , and the extrusion process has no appearance defects, such as bubbles, bulging, pockmarks, shrinkage holes, etc.

Pipe-grade polyethylene recycling waste mainly refers to a type of crushed material obtained from high-density polyethylene pipes, such as gas pipes, high-density polyethylene corrugated pipes, drip irrigation pipes, anti-corrosion layers of buried steel pipes, and a volume of 100L. The above polyethylene vats, etc. Its source is relatively pure, its performance is excellent, and it has high resistance to environmental stress cracking.

Hollow-grade polyethylene recycling waste mainly refers to a type of crushed material obtained by crushing high-density polyethylene hollow parts, such as polyethylene hollow barrels with a volume of less than 100L, polyethylene milk bottles, daily miscellaneous polyethylene bottles, etc. It has good mechanical properties and contains a very small amount of PP miscellaneous materials.

Injection-grade polyethylene recycling waste is mainly broken by high-density polyethylene bottle caps or other injection-molded parts (such as beer boxes, turnover baskets, etc.), which have less impurities, better particle gloss and excellent performance.

Film-grade linear polyethylene recycling waste is mainly a type of film-based recycled granulation material with LLDPE as the main body. Since the tensile properties of LLDPE are much higher than that of LDPE, the main resin of this type of film can be judged by testing its tensile properties.

Preferably, the special material for buried polyethylene structural wall pipeline comprises the following raw materials by weight: 15-30 parts of pipe-grade polyethylene, 10-20 parts of hollow-grade polyethylene, 5-8 parts of injection-molded polyethylene, film 20-40 parts of grade linear polyethylene, 4-6 parts of carbon black masterbatch, 1-3 parts of appearance improver and 5-8 parts of environmental stress cracking resistance regulator.

Preferably, the melt flow rate of the pipe grade polyethylene is 0.1˜0.5 g/10min, and the melt flow rate of the pipe grade polyethylene is measured at 190° C. according to GB/T 3682 using a weight of 5 kg.

Preferably, the melt flow rate of the hollow grade polyethylene is 0.5˜2.0 g/10min, and the melt flow rate of the hollow grade polyethylene is measured at 190° C. according to GB/T 368 2 using a weight of 5 kg.

Preferably, the melt flow rate of the injection molding grade polyethylene is 0.5˜2.0 g/10min, and the melt flow rate of the injection molding grade polyethylene is measured at 190° C. according to GB/T 3682 using a weight of 2.16 kg.

Preferably, the melt flow rate of the film-grade linear polyethylene is 2.0˜4.0 g/10min, and the film-grade linear polyethylene is measured at 190° C. according to GB/T 3682 using a weight of 2.16 kg.

Preferably, the density of the pipe-grade polyethylene is 0.95-0.97 g/cm ³ . According to GB/T 1040.2, the tensile properties are tested by extruding 1BA type splines, with a thickness of 2 mm and a tensile speed of 50 mm/min: stretching The strength is greater than 25MPa, and the elongation is greater than 600%.

Preferably, the density of the hollow-grade polyethylene is 0.95-0.97g/cm ³ . According to GB/T 1040.2, the tensile properties are tested by extruding a 1BA type spline, a thickness of 2 mm, and a tensile speed of 50 mm/min: stretching The strength is greater than 22MPa, and the elongation is greater than 350%.

Preferably, the density of the injection-molded polyethylene is 0.95-0.97 g/cm ³ , and the tensile properties are tested according to GB/T 1040.2 molding 1A-type splines, thickness 4 mm, and tensile speed 50 mm/min: tensile strength Greater than 20MPa, the elongation is greater than 50%; the flexural modulus tested according to GB/T 9341-2008 is greater than 750MPa.

Preferably, the density of the film-grade linear polyethylene is 0.915-0.955g/cm ³ , and the tensile properties are tested according to GB/T 1040.2 using extruded 1BA type splines, thickness 2mm, and tensile speed 50mm/min: The tensile strength is greater than 22MPa, and the elongation is greater than 500%.

The ash content of the pipe-grade polyethylene, hollow-grade polyethylene, injection-molding-grade polyethylene and film-grade linear polyethylene is less than 2%, and the ash content test conditions are burning in a muffle furnace at 650±50° C. for 2 hours.

Preferably, the carbon black masterbatch contains the following components in parts by weight: 30-50 parts of film-grade linear polyethylene, 40-45 parts of carbon black, 15-20 parts of antioxidant, 1-3 parts of dispersant and weather resistance The antioxidant is a hindered phenolic antioxidant and/or a phosphite antioxidant, the dispersing agent is PE wax, and the weathering agent is an ultraviolet light absorber and a hindered amine light Mixture of stabilizers.

The film-grade linear polyethylene can be a new resin or a recycled resin, preferably a recycled resin, and its melt flow rate is 2.0-4.0g/10min. The film-grade linear polyethylene uses 2.16kg according to GB/T 3682 The weight is measured at 190°C, the density is 0.915～0.955g/cm ³ , and the tensile strength is tested according to GB/T 1040.2 using extruded 1BA type splines, thickness 2mm, and tensile speed 50mm/min: the tensile strength is greater than 22MPa, the elongation is greater than 500%. In the carbon black masterbatch, film grade linear polyethylene is preferably the pelletizing material.

Preferably, the appearance improving agent is PE-based calcium oxide masterbatch.

Preferably, the environmental stress crack resistance improving agent is an ethylene-butene polymer and/or an ethylene-octene polymer.

Preferably, the antioxidant is a mixture of hindered phenolic antioxidant and phosphite antioxidant, and the weight ratio of the hindered phenolic antioxidant to phosphite antioxidant is 3:2 ; and/or the weathering agent is that the weight ratio of the UV absorber and the hindered amine light stabilizer is 1:1.

The object of the present invention is also to provide a preparation method of the special material for the buried polyethylene structural wall pipeline, comprising the following steps:

(1) mixing and granulating pipe-grade polyethylene, hollow-grade polyethylene and injection-molding-grade polyethylene to obtain crushed material;

(2) granulating film grade linear polyethylene to obtain film granulation material;

(3) Mix the crushed material, film granulation material, carbon black masterbatch, appearance improver and environmental stress cracking resistance regulator evenly and put it into the upper-stage single-screw extruder. After melt extrusion, it flows into the lower-stage extruder to melt. Extrusion, water cooling, pelletizing, sieving and drying to obtain the special material for the buried polyethylene structural wall pipeline.

Since the density, particle size and size of the pipe-grade polyethylene, hollow-grade polyethylene and injection-molded polyethylene in step (1) are quite different from those of the film-grade linear polyethylene in step (2), if the traditional "one-pot polyethylene" The blending process can cause broken flakes and particles to delaminate, affecting uniformity, resulting in fluctuations in finished product performance and even substandard results. Therefore, the performance of the finished product can be achieved by granulating the pipe-grade polyethylene, hollow-grade polyethylene and injection-molding-grade polyethylene in the step (1) and the film-grade linear polyethylene in the step (2), respectively, and then mixing and melt extrusion. uniformity.

The two-stage extruder is used to produce the special material for buried polyethylene structural wall pipes. The upper-stage single-screw extruder can effectively plasticize, remove impurities and naturally exhaust the waste polyethylene crushed materials. The lower-stage extruder can pass The design of the screw combination can improve the dispersibility and compatibility of each component, and the vacuum system can be set up to further devolatilize, so as to obtain the special material for regenerated buried polyethylene structural wall pipes with high gloss and no pores on the cut surface.

Preferably, the preparation method of the carbon black masterbatch is as follows: after the film-grade polyethylene, carbon black, antioxidant, dispersant and weathering agent are uniformly mixed in a high-speed mixer at a low speed, put into an internal mixer, and dense The mixing temperature is 160~175℃, and the mixing time is 10~15 minutes; then the mixed material mass is fed into the single-screw extruder through the conical twin-screw for grinding and air-cooling granulation. The temperature of the single-screw extruder is 170 ~190°C.

Preferably, in step (1), the extruder used for granulation is a single-screw melt extrusion granulator, the temperature of each temperature zone is 160-200°C, and the temperature of the single-screw screen changer and the head is The temperature is 200～210℃, and the mesh number of the screen changer is 60+80 mesh.

Preferably, in step (3), the equipment used for the mixing is a vertical mixer or a horizontal mixer with a volume greater than 5 m ³ to improve the uniformity of mixing.

Preferably, in step (3), the upper-stage single-screw extruder has at least one exhaust port, and the conveying section of the single-screw adopts a deep screw groove design to increase the feeding amount; the melt-compression section first adopts a separate screw design to achieve solidification. The liquid separation improves the plasticizing capacity, and then a chute barrier section (1-2D in length) is set near the exhaust section to increase the melting and mixing effect; the exhaust section adopts a deep screw groove design in order to improve the devolatilization efficiency; In the metering section, a deeper screw groove and a shorter lead are set to increase the annular mixing effect of the melt.

Preferably, the temperature of each section of the first-stage single-screw machine is: 180°C for the solid conveying section, 220-240°C for the melt-compression section, 225°C for the exhaust section, 215-225°C for the homogenization section, 220°C for the filter plate, and 220°C for the discharge. Tube 220℃;

In the step (3), the lower-stage extruder is a single-screw extruder or a twin-screw extruder. If it is a single-screw, the screw structure should be a deeper screw and a shorter lead to improve the melting point. The annular mixing effect of the body; if it is a twin screw, the screw combination of the multi-stage 45° meshing area is designed to improve the dispersion and compatibility of each component. The exhaust port is equipped with vacuum equipment, the vacuum degree is -0.08MPa, the temperature of each temperature zone is 190-200℃, and the die head is 210℃.

The beneficial effects of the present invention are as follows: the present invention provides a special material for buried polyethylene structural wall pipes and a preparation method thereof. The special material for the buried polyethylene structural wall pipeline of the present invention is selected from four different grades of polyethylene: pipe grade polyethylene, hollow grade polyethylene, injection grade polyethylene and film grade linear polyethylene, which can be prepared with excellent mechanical properties and Appearance properties of recycled buried polyethylene structural wall pipes.

Detailed ways

In order to better illustrate the purpose, technical solutions and advantages of the present invention, the present invention will be further described below with reference to specific embodiments.

The preparation raw material formulations of the special materials for buried polyethylene structural wall pipes described in Examples and Comparative Examples are shown in Table 2 and Table 3.

In the examples and comparative examples, the pipe-grade polyethylene crushed material, hollow-grade polyethylene crushed material, and injection-molded polyethylene crushed material are all recycled resins, obtained after sorting, crushing, cleaning, and dehydration, and film-grade linear polyethylene is obtained. The granulation material is obtained by sorting, crushing, cleaning and dehydrating the recovered linear polyethylene film.

The pipe-grade polyethylene crushed materials are all selected from polyethylene materials with the following characteristics: the melt flow rate is 0.1-0.5g/10min (according to GB/T 3682, using a weight of 5kg and measuring at 190°C), and the density is 0.95 ～0.97g/cm ³ , according to GB/T 1040.2, using extruded 1BA type splines, thickness 2mm, tensile speed 50mm/min for tensile property test: tensile strength is greater than 25MPa, elongation is greater than 600%.

The hollow-grade polyethylenes are all selected from polyethylene materials with the following characteristics: a melt flow rate of 0.5 to 2.0 g/10min (according to GB/T 368 2 using a 5 kg weight and measured at 190°C), and a density of 0.95 to 0.95 0.97g/cm ³ , according to GB/T 1040.2, using extruded 1BA spline, thickness 2mm, tensile speed 50mm/min for tensile property test: tensile strength is greater than 22MPa, elongation is greater than 350%.

The injection-molding polyethylene is selected from polyethylene materials with the following characteristics: melt flow rate of 0.5～2.0g/10min (according to GB/T 3682 using 2.16kg weight and measured at 190°C), density of 0.95～ 0.97g/cm ³ , according to GB/T 1040.2 molding 1A spline, tensile speed 50mm/min for tensile property test: tensile strength greater than 20MPa, elongation greater than 50%; according to GB/T 9341-2008 The tested flexural modulus was greater than 750 MPa.

The film-grade linear polyethylenes are all selected from polyethylene materials with the following characteristics: a melt flow rate of 2.0 to 4.0 g/10min (according to GB/T 3682 using a weight of 2.16 kg and measured at 190°C), and a density of 0.915 ～0.955g/cm ³ , according to GB/T 1040.2, using extruded 1BA spline, thickness 2mm, tensile speed 50mm/min for tensile property test: tensile strength is greater than 22MPa, elongation is greater than 500%.

The carbon black masterbatch comprises the following components in parts by weight: 40 parts of film-grade linear polyethylene, 43 parts of carbon black, 18 parts of antioxidant, 2 parts of dispersant and 2 parts of weathering agent; the film-grade linear polyethylene All are selected from polyethylene materials with the following characteristics: melt flow rate is 2.0～4.0g/10min (according to GB/T 3682 using 2.16kg weight and measured at 190℃), density is 0.915～0.955g/cm ³ , According to GB/T 1040.2, extruded 1BA type splines, thickness 2mm, tensile speed 50mm/min are used for tensile property test: tensile strength is greater than 22MPa, elongation is greater than 500%.

The preparation method of the carbon black master batch is as follows: after the film grade polyethylene, carbon black, antioxidant, dispersant and weather resistance agent are uniformly mixed in a high mixer at a low speed, then put into an internal mixer, and the internal mixing temperature is 160 °C. ～175℃, the mixing time is 10～15 minutes; then the mixed material mass is fed into the single-screw extruder through the conical twin-screw for grinding and air-cooling granulation. The temperature of the single-screw extruder is 170～190℃ . The antioxidant is a mixture of a hindered phenolic antioxidant and a phosphite antioxidant, and the weight ratio of the hindered phenolic antioxidant to the phosphite antioxidant is 3:2, and the The dispersing agent is PE wax, the weathering agent is a mixture of an ultraviolet light absorber and a hindered amine light stabilizer, and the weight ratio of the ultraviolet light absorber and the hindered amine light stabilizer is 1:1. Among them, hindered phenolic antioxidants were purchased from Tianjin Rianlong New Materials Co., Ltd., model RIANOX 1010; phosphite antioxidants were purchased from Tianjin Rianlong New Materials Co., Ltd., model RIANOX 168; PE wax was purchased from from Guangzhou Hengshi Import and Export Trading Co., Ltd., model CS-12N; UV absorber purchased from Cytec Engineering Materials (Shanghai) Co., Ltd., model UV-531; hindered amine light stabilizer purchased from Adico (China) ) Investment Co., Ltd., model LA-402AF.

The appearance improving agent is PE-based calcium oxide masterbatch, which was purchased from Guangzhou Lvxin Environmental Protection Technology Co., Ltd., and the commodity model is NDM-1008.

The environmental stress cracking resistance improver is ethylene-butene polymer and/or ethylene-octene polymer, purchased from Ningbo Nengzhiguang New Material Technology Co., Ltd., and the commodity model is MC218.

The preparation method of the special material for the buried polyethylene structural wall pipeline described in the embodiment and the comparative example comprises the following steps:

(1) The pipe-grade polyethylene crushed material, hollow-grade polyethylene crushed material and injection-molded polyethylene crushed material are cleaned, dehydrated and then bagged for use. After sorting, crushing, cleaning and dehydration of the low-density polyethylene film, the The temperature of each temperature zone of the single-screw melt extrusion and granulation is 160-200°C, and the temperature of the screen changer and the head of the single-screw is 200-210°C. The mesh number of the filter is 60+80 mesh;

(2) The treated pipe grade polyethylene crushed material, hollow grade polyethylene crushed material and injection-molded polyethylene crushed material are weighed according to the formula proportions, put into a vertical mixing tank with a volume of ⁵ m after mixing for 30 minutes, and then put into In the silo of the vibrating unloading weighing scale; weigh the film-grade polyethylene granules, the special functional carbon black masterbatch, the appearance improver and the environmental stress cracking resistance improver according to the formula proportions, and put them into a ^2m3 horizontal container. After 20 minutes of mixing in the type mixing tank, put it into the silo of another weighing scale (which can be a vibrating feeding weighing scale or a screw feeding weighing scale). Set the feeding ratio or weight of the two weighing scales according to the formula ratio, and the material will be accurately fed into the feeding port of the upper-stage single-screw extruder according to the proportion;

(3) The material enters the upper-stage single-screw extruder and undergoes four processes: solid conveying, melt plasticization, melt mixing and melt impurity removal and filtration. The number is 80+100 mesh; the melt after removal of impurities flows into the feeding port of the next-stage single-screw or twin-screw extruder. The surface is eagerly cut, then sieved, dried online, and packaged to obtain the special material for buried polyethylene structural wall pipes.

The performance testing method of embodiment and comparative example is shown in Table 1:

Table 1

The test results are shown in Table 2 and Table 3.

Table 2

table 3

It can be seen from Tables 2 and 3 that the special materials for buried polyethylene structural wall pipes described in Examples 1 to 7 have the special material indexes that meet GB/T19472.1-2004.

Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit the protection scope of the present invention. Although the present invention is described in detail with reference to the preferred embodiments, those of ordinary skill in the art should understand that, The technical solutions of the present invention may be modified or equivalently replaced without departing from the spirit and scope of the technical solutions of the present invention.

Claims (3)

1. The special material for the buried polyethylene structure wall pipeline is characterized by comprising the following preparation raw materials in parts by weight: 10-40 parts of pipe grade polyethylene, 10-30 parts of hollow grade polyethylene, 3-10 parts of injection grade polyethylene, 20-45 parts of film grade linear polyethylene, 4-6 parts of carbon black master batch, 1-3 parts of appearance improver and 4-10 parts of environmental stress cracking resistance regulator;

the melt flow rate of the pipe grade polyethylene is 0.1-0.5 g/10min, the melt flow rate of the pipe grade polyethylene is measured at 190 ℃ according to GB/T3682 with the weight of 5kg, and the density of the pipe grade polyethylene is 0.95-0.97 g/cm ³ According to GB/T1040.2, an extrusion molding 1BA type sample strip, the thickness of the sample strip is 2mm, and the tensile speed is 50mm/min is adopted for carrying out tensile property test: the tensile strength is more than 25MPa, and the elongation is more than 600 percent;

the melt flow rate of the hollow-grade polyethylene is 0.5-2.0 g/10min, and the hollow-grade polyethyleneThe melt flow rate of the ethylene is measured according to GB/T3682 using a weight of 5kg and at 190 ℃, and the density of the hollow-grade polyethylene is 0.95-0.97 g/cm ³ According to GB/T1040.2, an extrusion molding 1BA type sample strip, the thickness of the sample strip is 2mm, and the tensile speed is 50mm/min is adopted for carrying out tensile property test: the tensile strength is more than 22MPa, and the elongation is more than 350 percent;

the melt flow rate of the injection-grade polyethylene is 0.5-2.0 g/10min, the melt flow rate of the injection-grade polyethylene is measured at 190 ℃ by using 2.16kg of weight according to GB/T3682, and the density of the injection-grade polyethylene is 0.95-0.97 g/cm ³ Tensile properties were measured according to GB/T1040.2 moulding of 1A type bars, thickness 4mm, tensile speed 50 mm/min: the tensile strength is more than 20MPa, and the elongation is more than 50 percent; the flexural modulus tested according to GB/T9341-2008 is more than 750 MPa;

the melt flow rate of the film-grade linear polyethylene is 2.0-4.0 g/10min, the film-grade linear polyethylene is measured at 190 ℃ according to GB/T3682 with a weight of 2.16kg, and the density of the film-grade linear polyethylene is 0.915-0.955 g/cm ³ According to GB/T1040.2, an extrusion molding 1BA type sample strip, the thickness of the sample strip is 2mm, and the tensile speed is 50mm/min is adopted for carrying out tensile property test: the tensile strength is more than 22MPa, and the elongation is more than 500 percent;

the carbon black master batch comprises the following components in parts by weight: 30-50 parts of film-grade linear polyethylene, 40-45 parts of carbon black, 15-20 parts of antioxidant, 1-3 parts of dispersant and 1-3 parts of weather resistant agent; the antioxidant is hindered phenol antioxidant and/or phosphite antioxidant, the dispersing agent is PE wax, and the weather-resistant agent is a mixture of an ultraviolet light absorber and a hindered amine light stabilizer;

the appearance improver is PE-based calcium oxide master batch;

the environmental stress cracking resistance improver is an ethylene-butene high polymer and/or an ethylene-octene high polymer.

2. The special material for the buried polyethylene structure wall pipeline as claimed in claim 1, wherein the antioxidant is a mixture of hindered phenol antioxidant and phosphite antioxidant, and the weight ratio of the hindered phenol antioxidant to the phosphite antioxidant is 3: 2; and/or the weather resisting agent is an ultraviolet absorbent and the hindered amine light stabilizer with the weight ratio of 1: 1.

3. The method for preparing the special material for the buried polyethylene structure wall pipeline as claimed in claim 1 or 2, is characterized by comprising the following steps:

(1) mixing and granulating the pipe-grade polyethylene, the hollow-grade polyethylene and the injection-grade polyethylene to obtain a crushed material;

(2) granulating the film-grade linear polyethylene to obtain film granulating materials;

(3) uniformly mixing the crushed material, the film granulating material, the carbon black master batch, the appearance improver and the environmental stress cracking resistance regulator, then putting the mixture into an upper-stage single-screw extruder, and flowing the mixture into a lower-stage extruder after melt extrusion for melt extrusion, water cooling, granulating, sieving and drying to obtain the special material for the buried polyethylene structural wall pipeline.