High-strength steel-plastic composite pipe and preparation method thereof

Abstract

The invention relates to the technical field of pipes, and provides a high-strength steel-plastic composite pipe and a preparation method thereof. The high-strength steel-plastic composite pipe sequentially comprises a plastic pipe and a steel pipe from inside to outside, and the plastic pipe is prepared from, by weight, 70-84 parts of polyethylene, 20-25 parts of ethylene-vinyl acetate copolymer, 1-3 parts of antioxidant, 3-5 parts of plasticizer, 8-10 parts of filler, 1-2 parts of lubricant and 9-15 parts of palygorskite composite polytetrafluoroethylene fiber. The palygorskite composite polytetrafluoroethylene fiber is prepared from the following raw materials: palygorskite, polytetrafluoroethylene fiber and ethylene-vinyl alcohol copolymer in a mass ratio of (20-40): 10: (2-6). By means of the technical scheme, the problem that the steel-plastic composite pipe is poor in low temperature resistance in the related technology is solved.

Description

Technical Field

[0001] The present invention relates to the technical field of pipe materials, and specifically, to a high-strength steel-plastic composite pipe and a preparation method thereof. Background Art

[0002] Steel-plastic composite pipes are generally composed of steel pipes and plastic pipes. Steel-plastic composite pipes combine the advantages of high strength of steel and corrosion resistance of plastics, and are widely used in the market. However, the plastic inner pipes in existing steel-plastic composite pipes generally use polyethylene materials. In actual use, the plastic inner pipes are prone to becoming brittle and hard in low-temperature environments, and phenomena such as cracking occur, reducing the service life of the pipes. To solve this problem, polytetrafluoroethylene is usually added to the plastic pipes to improve the low-temperature resistance of the plastic pipes. However, due to the poor compatibility of polytetrafluoroethylene with the substrate, the improvement of the low-temperature performance of the plastic pipes is very limited. Therefore, it is of great significance to develop a high-strength steel-plastic composite pipe with low-temperature resistance. Summary of the Invention

[0003] The present invention provides a high-strength steel-plastic composite pipe and a preparation method thereof, which solve the problem of poor low-temperature resistance of steel-plastic composite pipes in related technologies.

[0004] The technical solution of the present invention is as follows: The present invention provides a high-strength steel-plastic composite pipe, which sequentially includes a plastic pipe and a steel pipe from the inside to the outside. The raw materials of the plastic pipe include the following components in parts by weight: 70-84 parts of polyethylene, 20-25 parts of ethylene-vinyl acetate copolymer, 1-3 parts of antioxidant, 3-5 parts of plasticizer, 8-10 parts of filler, 1-2 parts of lubricant, and 9-15 parts of palygorskite composite polytetrafluoroethylene fiber. The raw materials of the palygorskite composite polytetrafluoroethylene fiber include palygorskite, polytetrafluoroethylene fiber, and ethylene-vinyl alcohol copolymer with a mass ratio of 20-40:10:2-6.

[0005] As a further technical solution, the mass ratio of the palygorskite, the polytetrafluoroethylene fiber, and the ethylene-vinyl alcohol copolymer is 30:10:2.4-3.6.

[0006] In the present invention, the mass ratio of palygorskite, polytetrafluoroethylene fiber, and ethylene-vinyl alcohol copolymer is 30:10:2.4-3.6. The ethylene-vinyl alcohol copolymer molecules can just right combine with palygorskite and polytetrafluoroethylene fiber to form a stable and uniform coating layer, which can ensure good interfacial bonding between palygorskite, polytetrafluoroethylene fiber and the plastic matrix, make stress transfer more efficient, and effectively improve the tensile strength and impact resistance. As a further technical solution, the ethylene content in the ethylene-vinyl alcohol copolymer is 32-44 mol%.

[0007] In the present invention, when the ethylene content in the ethylene-vinyl alcohol copolymer is 32-44 mol%, the tensile strength of the plastic inner tube of the high-strength steel-plastic composite pipe can be significantly enhanced. When the ethylene content in the ethylene-vinyl alcohol copolymer is less than 32 mol%, the proportion of vinyl alcohol units is relatively high. A large number of hydroxyl groups cause strong hydrogen bonding between molecules, enhancing the rigidity of the molecular chain. Although the intermolecular force is large, the segmental movement is restricted. When subjected to external tensile force, the molecular chain is difficult to disperse stress through slip and orientation, resulting in easy brittle fracture of the material and difficult improvement of the tensile strength. When the ethylene content exceeds 44 mol%, too many ethylene units will reduce the regularity of the molecular chain, and at the same time reduce the number of hydroxyl groups, weakening the hydrogen bonding between molecules, resulting in insufficient intermolecular interaction force. During the stretching process, the molecular chain is prone to relative sliding and cannot effectively transmit stress, which is also not conducive to the improvement of the tensile strength.

[0008] As a further technical solution, the preparation method of the palygorskite composite polytetrafluoroethylene fiber includes the following steps: A1. Immerse the polytetrafluoroethylene fiber in a sodium naphthalene solution, wash and dry it to obtain a pretreated polytetrafluoroethylene fiber; A2. Add palygorskite and ethylene-vinyl alcohol copolymer to N,N-dimethylformamide and mix to obtain a mixed solution; A3. Immerse the pretreated polytetrafluoroethylene fiber in the mixed solution and dry it to obtain palygorskite composite polytetrafluoroethylene fiber.

[0009] As a further technical solution, in step A1, the polytetrafluoroethylene fiber is immersed in a sodium naphthalene solution and then in an acetone solution, washed with water and dried to obtain a pretreated polytetrafluoroethylene fiber.

[0010] As a further technical solution, the soaking time in the sodium naphthalene solution is 5-10 min, and the soaking time in the acetone solution is 3-5 min.

[0011] As a further technical solution, in step A2, the mixing temperature is 60-80 °C and the mixing time is 2-3 h.

[0012] As a further technical solution, in step A3, the impregnation time is 4-6 h.

[0013] As a further technical solution, in step A3, the mass-volume ratio of palygorskite to N,N-dimethylformamide is 1 g:8-10 mL.

[0014] As a further technical solution, the plasticizer includes one or more of dibutyl phthalate, triphenyl phosphate, and butyl epoxy fatty acid ester; and / or, The antioxidant includes a hindered phenol antioxidant; and / or, The lubricant includes one or more of stearic acid, calcium stearate, and paraffin wax; and / or, The filler includes one or more of silica, talc powder, and calcium carbonate.

[0015] As a further technical solution, the hindered phenol antioxidant includes one or more of antioxidant BHT, antioxidant 1010, and antioxidant 1076.

[0016] As a further technical solution, the polyethylene includes high-density polyethylene and linear low-density polyethylene, and the mass ratio of the high-density polyethylene to the linear low-density polyethylene is 1:3 to 5.

[0017] The high-density polyethylene has a high molecular chain regularity, and a large number of crystalline regions endow the pipe with high rigidity and strength. However, in a low-temperature environment, the molecular chain segments have poor mobility, and the crystalline regions limit the deformation of the chain segments, resulting in the material being prone to embrittlement. The linear low-density polyethylene molecular chain contains more short branches, which reduces the regularity of the molecular chain, has good flexibility and low-temperature resistance. At low temperatures, the short branches on the linear low-density polyethylene molecular chain can buffer external stress to a certain extent, reduce the mutual restraint between molecular chains, and enable the chain segments to still perform limited movement, avoiding the material from quickly becoming hard and brittle. By limiting the mass ratio of high-density polyethylene to linear low-density polyethylene to 1:3 to 5, the proportion of linear low-density polyethylene is relatively high, and its large number of short branches are interspersed between the crystalline regions and amorphous regions of high-density polyethylene, reducing the overall crystallinity and the increase in material brittleness caused by too high crystallinity; at the same time, the compounding of the two makes the inner plastic pipe of the plastic form a more uniform micro-phase structure, enhancing the interaction between different chain segments, and ensuring the overall flexibility and impact resistance of the material at low temperatures.

[0018] As a further technical solution, an adhesive is further included between the plastic pipe and the steel pipe.

[0019] The present invention also provides a method for preparing a high-strength steel-plastic composite pipe for preparing the high-strength steel-plastic composite pipe described above, which is characterized by including the following steps: S1. After mixing the raw materials of the plastic pipe, extrude and mold to obtain the plastic pipe; S2. After coating the adhesive on the outer side of the plastic pipe, sleeving it on the inner side of the steel pipe, and subjecting it to pressure compounding to obtain the high-strength steel-plastic composite pipe.

[0020] The working principle and beneficial effects of the present invention are: In the present invention, by adding palygorskite composite polytetrafluoroethylene fibers into the plastic pipe of the steel-plastic composite pipe, the low-temperature resistance of the plastic pipe is improved, and the service life of the steel-plastic composite pipe in a low-temperature environment is extended. To solve the problem in the prior art that due to the poor compatibility between polytetrafluoroethylene and polyethylene, the improvement of the low-temperature resistance of the plastic pipe by polytetrafluoroethylene is very limited. In the present invention, by adding palygorskite composite polytetrafluoroethylene fibers into the plastic pipe, its low-temperature toughness can be effectively improved. Polytetrafluoroethylene fibers have excellent low-temperature resistance and can still maintain good flexibility and mechanical properties in extremely cold environments; ethylene-vinyl alcohol copolymer, as a polymer with good adhesiveness and compatibility, can play a bridging role between palygorskite and polytetrafluoroethylene fibers; the hydroxyl groups in the ethylene-vinyl alcohol copolymer molecules can interact with the hydroxyl groups on the surface of palygorskite and the carboxyl groups on the surface of polytetrafluoroethylene through hydrogen bonds, enabling palygorskite to adhere to the surface of polytetrafluoroethylene fibers, increasing the surface roughness of the polytetrafluoroethylene fibers. This not only makes the polytetrafluoroethylene fibers more easily dispersed in the plastic matrixes of polyethylene and ethylene-vinyl acetate copolymer, but also improves the compatibility between the polytetrafluoroethylene fibers and the plastic pipe matrix, enabling the polytetrafluoroethylene fibers to better play their role at low temperatures and improving the overall low-temperature resistance of the plastic pipe; at the same time, the layer-chain structure of palygorskite helps to disperse the stress generated in a low-temperature environment, reducing the risk of material brittle fracture caused by temperature changes and further improving the low-temperature resistance of the plastic pipe. Specific embodiments

[0021] The following will describe the technical solutions in the embodiments of the present invention clearly and completely in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without making creative efforts fall within the scope of protection of the present invention.

[0022] In the following examples and comparative examples: Ethylene-vinyl alcohol copolymer of model L171B, ethylene content: 27 mol%; ethylene-vinyl alcohol copolymer of model G156B, ethylene content: 48 mol%; ethylene-vinyl alcohol copolymer of model F104B, ethylene content: 32 mol%; ethylene-vinyl alcohol copolymer of model E171B, ethylene content: 44 mol%; high-density polyethylene, model: 5502; linear low-density polyethylene, model: 7042; ethylene-vinyl acetate copolymer, model: EA28025; polytetrafluoroethylene fibers, diameter: 10 - 20 μm, length 1 - 3 mm; palygorskite, particle size: 325 mesh; white carbon black, particle size: 800 mesh; talc powder, particle size: 600 mesh; calcium carbonate, particle size: 1250 mesh; polyamic acid, solid content: 15%; Preparation of sodium naphthalene solution: Add 20 g of metallic sodium into 1 L of naphthalene tetrahydrofuran solution (the mass concentration of naphthalene tetrahydrofuran solution is 12%), and stir at room temperature until the solution turns black.

[0023] Example 1 A preparation method of a high-strength steel-plastic composite pipe, comprising the following steps: S1. Mix 14 parts of high-density polyethylene, 56 parts of linear low-density polyethylene, 20 parts of ethylene-vinyl acetate copolymer, 1 part of antioxidant BHT, 3 parts of dibutyl phthalate, 8 parts of white carbon black, 1 part of stearic acid, and 9 parts of palygorskite composite polytetrafluoroethylene fiber, and then extrude and mold to obtain a plastic pipe; S2. After coating the outer side of the plastic pipe with an adhesive, sleeve it inside the steel pipe, and perform pressure compounding to obtain a high-strength steel-plastic composite pipe; A preparation method of palygorskite composite polytetrafluoroethylene fiber, comprising the following steps: A1. Immerse 10 g of polytetrafluoroethylene fiber in 150 mL of sodium naphthalene solution for 5 min, and then immerse it in 100 mL of acetone solution for 3 min. Wash the polytetrafluoroethylene fiber with water and dry it to obtain pretreated polytetrafluoroethylene fiber; A2. Add 20 g of palygorskite and 2 g of ethylene-vinyl alcohol copolymer L171B into 160 mL of N,N-dimethylformamide, and stir at 60 °C for 3 h to obtain a mixed solution; A3. Immerse the pretreated polytetrafluoroethylene fiber in the mixed solution for 4 h, and dry it to obtain palygorskite composite polytetrafluoroethylene fiber.

[0024] Example 2 A preparation method of a high-strength steel-plastic composite pipe, comprising the following steps: S1. Mix 19 parts of high-density polyethylene, 57 parts of linear low-density polyethylene, 22 parts of ethylene-vinyl acetate copolymer, 2 parts of antioxidant 1010, 4 parts of triphenyl phosphate, 9 parts of talc powder, 1 part of calcium stearate, and 13 parts of palygorskite composite polytetrafluoroethylene fiber, and then extrude and mold to obtain a plastic pipe; S2. After coating the outer side of the plastic pipe with an adhesive, sleeve it inside the steel pipe, and perform pressure compounding to obtain a high-strength steel-plastic composite pipe; A preparation method of palygorskite composite polytetrafluoroethylene fiber, comprising the following steps: A1. Immerse 10 g of polytetrafluoroethylene fiber in 150 mL of sodium naphthalene solution for 7 min, and then immerse it in 100 mL of acetone solution for 4 min. Wash the polytetrafluoroethylene fiber with water and dry it to obtain pretreated polytetrafluoroethylene fiber; A2. Add 30 g of palygorskite and 2 g of ethylene-vinyl alcohol copolymer L171B to 270 mL of N,N-dimethylformamide, and stir for 3 h at 70 °C to obtain a mixed solution; A3. Immerse the pretreated polytetrafluoroethylene fiber in the mixed solution for 5 h, and obtain palygorskite composite polytetrafluoroethylene fiber after drying.

[0025] Example 3 A method for preparing a high-strength steel-plastic composite pipe, comprising the following steps: S1. Mix 14 parts of high-density polyethylene, 70 parts of linear low-density polyethylene, 25 parts of ethylene-vinyl acetate copolymer, 3 parts of antioxidant 1076, 5 parts of epoxy fatty acid butyl ester, 10 parts of calcium carbonate, 2 parts of paraffin, and 15 parts of palygorskite composite polytetrafluoroethylene fiber, and then extrude and mold to obtain a plastic pipe; S2. After coating the outer side of the plastic pipe with an adhesive, sleeve it inside the steel pipe, and obtain a high-strength steel-plastic composite pipe through pressure compounding; A method for preparing palygorskite composite polytetrafluoroethylene fiber, comprising the following steps: A1. Add 10 g of polytetrafluoroethylene fiber to 150 mL of sodium naphthalene solution and soak for 10 min, then soak in 100 mL of acetone solution for 5 min. Wash the polytetrafluoroethylene fiber with water and dry it to obtain pretreated polytetrafluoroethylene fiber; A2. Add 40 g of palygorskite and 2 g of ethylene-vinyl alcohol copolymer L171B to 400 mL of N,N-dimethylformamide, and stir for 2 h at 80 °C to obtain a mixed solution; A3. Immerse the pretreated polytetrafluoroethylene fiber in the mixed solution for 6 h, and obtain palygorskite composite polytetrafluoroethylene fiber after drying.

[0026] Example 4 This example is different from Example 2 only in that the addition amount of ethylene-vinyl alcohol copolymer L171B is 6 g.

[0027] Example 5 This example is different from Example 2 only in that the addition amount of ethylene-vinyl alcohol copolymer L171B is 2.4 g.

[0028] Example 6 This example is different from Example 2 only in that the addition amount of ethylene-vinyl alcohol copolymer L171B is 3 g.

[0029] Example 7 This example is different from Example 2 only in that the addition amount of ethylene-vinyl alcohol copolymer L171B is 3.6 g.

[0030] Example 8 Compared with Example 6, this example is only different in that ethylene-vinyl alcohol copolymer L171B is replaced with an equal amount of ethylene-vinyl alcohol copolymer G156B.

[0031] Example 9 Compared with Example 6, this example is only different in that ethylene-vinyl alcohol copolymer L171B is replaced with an equal amount of ethylene-vinyl alcohol copolymer F104B.

[0032] Example 10 Compared with Example 6, this example is only different in that ethylene-vinyl alcohol copolymer L171B is replaced with an equal amount of ethylene-vinyl alcohol copolymer E171B.

[0033] Comparative Example 1 Compared with Example 1, this comparative example is only different in that palygorskite composite polytetrafluoroethylene fiber is replaced with an equal amount of palygorskite.

[0034] Comparative Example 2 Compared with Example 1, this comparative example is only different in that palygorskite composite polytetrafluoroethylene fiber is replaced with an equal amount of polytetrafluoroethylene fiber.

[0035] Comparative Example 3 A preparation method of a high-strength steel-plastic composite pipe includes the following steps: S1. Mix 14 parts of high-density polyethylene, 56 parts of linear low-density polyethylene, 20 parts of ethylene-vinyl acetate copolymer, 0.5625 part of ethylene-vinyl alcohol copolymer L171B, 1 part of antioxidant BHT, 3 parts of dibutyl phthalate, 8 parts of silica, 1 part of stearic acid, 2.8125 parts of polytetrafluoroethylene fiber, and 5.625 parts of palygorskite, and then extrude and mold to obtain a plastic pipe; S2. After coating an adhesive on the outer side of the plastic pipe, sleeving it on the inner side of a steel pipe, and subjecting it to pressure compounding to obtain a high-strength steel-plastic composite pipe.

[0036] Experimental Example 1 Test the Charpy impact strength of the plastic pipes prepared in Examples 1 to 7 and Comparative Examples 1 to 3 at 23°C and -20°C according to the method of B.1 in GB / T 18743.1-2022 "Plastics pipes for thermoplastics - Determination of Charpy impact strength - Part 1: General test method". The thickness of the plastic pipe is 2.5 mm, and the test results are shown in Table 1.

[0037] Table 1 Test results of low-temperature resistance of plastic pipes

[0038] As can be seen from Table 1, the variation range of the simply supported beam impact strength of the plastic pipes prepared in Examples 1 to 7 at -20°C is lower than that of Comparative Examples 1 to 3, indicating that adding palygorskite and composite polytetrafluoroethylene fibers to polyethylene can improve the low-temperature resistance of plastic pipes.

[0039] Experimental Example 2 The plastic pipes prepared in Examples 7 to 10 were tested for tensile strength according to the method in GB / T 8804.1-2003 "Plastics pipes for thermoplastics - Determination of tensile properties - Part 1: General test method". The thickness of the plastic pipes was 2.5 mm, and the test results are shown in Table 2.

[0040] Table 2 Tensile strength test results of plastic pipes

[0041] As can be seen from Table 2, the tensile strength of the plastic pipes prepared in Examples 9 to 10 is higher than that in Examples 7 to 8, indicating that when ethylene-vinyl alcohol copolymer modifies palygorskite and the ethylene content in the ethylene-vinyl alcohol copolymer is 32 to 44 mol / %, the tensile strength of the plastic pipes can be improved.

[0042] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A high-strength steel-plastic composite pipe, characterized in that, It successively includes a plastic pipe and a steel pipe from the inside to the outside. The raw materials of the plastic pipe include the following components in parts by weight: 70 - 84 parts of polyethylene, 20 - 25 parts of ethylene-vinyl acetate copolymer, 1 - 3 parts of antioxidant, 3 - 5 parts of plasticizer, 8 - 10 parts of filler, 1 - 2 parts of lubricant, and 9 - 15 parts of palygorskite composite polytetrafluoroethylene fiber. The raw materials of the palygorskite composite polytetrafluoroethylene fiber include palygorskite, polytetrafluoroethylene fiber, and ethylene-vinyl alcohol copolymer with a mass ratio of 20 - 40:10:2 - 6.

2. The high-strength steel-plastic composite pipe according to claim 1, characterized in that, The mass ratio of the palygorskite, the polytetrafluoroethylene fiber, and the ethylene-vinyl alcohol copolymer is 30:10:2.4 - 3.

6.

3. The high-strength steel-plastic composite pipe according to claim 1, characterized in that, The content of ethylene in the ethylene-vinyl alcohol copolymer is 32 - 44 mol%.

4. The high-strength steel-plastic composite pipe according to claim 1, characterized in that, The preparation method of the palygorskite composite polytetrafluoroethylene fiber includes the following steps: A1. Immerse the polytetrafluoroethylene fiber in a sodium naphthalene solution, and obtain pretreated polytetrafluoroethylene fiber after washing and drying. A2. Add palygorskite and ethylene-vinyl alcohol copolymer to N,N-dimethylformamide and mix to obtain a mixed solution. A3. Immerse the pretreated polytetrafluoroethylene fiber in the mixed solution and obtain palygorskite composite polytetrafluoroethylene fiber after drying.

5. The high-strength steel-plastic composite pipe according to claim 4, characterized in that, The mass-volume ratio of the palygorskite to N,N-dimethylformamide is 1 g:8 - 10 mL.

6. The high-strength steel-plastic composite pipe according to claim 1, characterized in that, The plasticizer includes one or more of dibutyl phthalate, triphenyl phosphate, and butyl epoxy fatty acid ester; and / or, The antioxidant includes hindered phenol antioxidants.

7. The high-strength steel-plastic composite pipe according to claim 1, characterized in that, The lubricant includes one or more of stearic acid, calcium stearate, and paraffin; and / or, The filler includes one or more of silica, talc powder, and calcium carbonate.

8. The high-strength steel-plastic composite pipe according to claim 1, characterized in that, The polyethylene includes high-density polyethylene and linear low-density polyethylene, and the mass ratio of the high-density polyethylene to the linear low-density polyethylene is 1:3 - 5.

9. The high-strength steel-plastic composite pipe according to claim 1, characterized in that, There is also an adhesive between the plastic pipe and the steel pipe.

10. A preparation method of a high-strength steel-plastic composite pipe for preparing the high-strength steel-plastic composite pipe according to any one of claims 1 to 9, characterized in that, It includes the following steps: S1. Mix the raw materials of the plastic pipe and extrude to form a plastic pipe. S2. Coat the outside of the plastic pipe with an adhesive, then sleeve it inside the steel pipe, and obtain a high-strength steel-plastic composite pipe after pressure compounding.

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