A high-strength steel-plastic composite pipe and its preparation method

Abstract

This invention relates to the field of pipe technology and proposes a high-strength steel-plastic composite pipe and its preparation method. A high-strength steel-plastic composite pipe comprises, from the inside out, a plastic pipe and a steel pipe. 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 in a mass ratio of 20-40:10:2-6. This technical solution solves the problem of poor low-temperature resistance in related technologies for steel-plastic composite pipes.

Description

Technical Field

[0001] This invention relates to the field of pipe technology, specifically to a high-strength steel-plastic composite pipe and its preparation method. Background Technology

[0002] Steel-plastic composite pipes are generally composed of steel and plastic pipes. They combine the high strength of steel with the corrosion resistance of plastics, making them widely used in the market. However, the plastic inner tube in existing steel-plastic composite pipes is generally made of polyethylene. In actual use, the plastic inner tube easily becomes brittle and cracked in low-temperature environments, reducing the pipe's service life. To solve this problem, polytetrafluoroethylene (PTFE) is usually added to the plastic tube to improve its low-temperature resistance. However, due to the poor compatibility of PTFE with the substrate, the improvement in the low-temperature resistance of the plastic tube is very limited. Therefore, developing a high-strength steel-plastic composite pipe with low-temperature resistance is of great significance. Summary of the Invention

[0003] This invention proposes a high-strength steel-plastic composite pipe and its preparation method, which solves 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:

[0005] This invention proposes a high-strength steel-plastic composite pipe, which comprises a plastic pipe and a steel pipe from the inside out. 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 in a mass ratio of 20-40:10:2-6.

[0006] As a further technical solution, the mass ratio of palygorskite, polytetrafluoroethylene fiber, and ethylene-vinyl alcohol copolymer is 30:10:2.4~3.6.

[0007] In this 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 combine with palygorskite and polytetrafluoroethylene fiber in a just right way to form a stable and uniform coating layer, which can ensure good interfacial bonding between palygorskite, polytetrafluoroethylene fiber and plastic matrix, making stress transfer more efficient and effectively improving tensile strength and impact resistance.

[0008] As a further technical solution, the ethylene content in the ethylene-vinyl alcohol copolymer is 32~44 mol.

[0009] In this invention, when the ethylene content in the ethylene-vinyl alcohol copolymer is 32-44 mol%, the tensile strength of the inner plastic 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, and the large number of hydroxyl groups leads to strong hydrogen bonding between molecules, which increases the rigidity of the molecular chain. Although the intermolecular forces are large, the movement of chain segments is restricted. When subjected to external tensile force, the molecular chain is difficult to disperse stress through slip and orientation, which makes the material prone to brittle fracture and makes it difficult to improve the tensile strength. When the ethylene content exceeds 44 mol%, the excessive number of ethylene units will reduce the regularity of the molecular chain and reduce the number of hydroxyl groups, weakening the hydrogen bonding between molecules. This results in insufficient interaction between molecular chains, and the molecular chains are prone to relative sliding during the stretching process, which cannot effectively transfer stress and is also not conducive to improving the tensile strength.

[0010] As a further technical solution, the preparation method of the palygorskite composite polytetrafluoroethylene fiber includes the following steps:

[0011] A1. Polytetrafluoroethylene (PTFE) fibers are soaked in sodium naphthalene solution, and then washed and dried to obtain pretreated PTFE fibers.

[0012] A2. Add palygorskite and ethylene-vinyl alcohol copolymer to N,N-dimethylformamide and mix to obtain a mixed solution;

[0013] A3. The pretreated polytetrafluoroethylene fiber is impregnated in the mixed solution and dried to obtain palygorskite composite polytetrafluoroethylene fiber.

[0014] As a further technical solution, in step A1, the polytetrafluoroethylene fiber is soaked in a sodium naphthalene solution, then soaked in an acetone solution, and after being washed with water and dried, pretreated polytetrafluoroethylene fiber is obtained.

[0015] As a further technical solution, the soaking time in sodium naphthalene solution is 5-10 minutes, and the soaking time in acetone solution is 3-5 minutes.

[0016] As a further technical solution, in step A2, the mixing temperature is 60~80℃ and the mixing time is 2~3h.

[0017] As a further technical solution, in step A3, the soaking time is 4~6 hours.

[0018] As a further technical solution, in step A3, the mass-to-volume ratio of palygorskite and N,N-dimethylformamide is 1g:8~10mL.

[0019] As a further technical solution, the plasticizer includes one or more of dibutyl phthalate, triphenyl phosphate, and butyl epoxide fatty acid ester; and / or,

[0020] The antioxidants include hindered phenolic antioxidants; and / or,

[0021] The lubricant includes one or more of stearic acid, calcium stearate, and paraffin wax; and / or,

[0022] The filler includes one or more of silica, talc, and calcium carbonate.

[0023] As a further technical solution, the hindered phenolic antioxidant includes one or more of antioxidant BHT, antioxidant 1010, and antioxidant 1076.

[0024] 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 1:3~5.

[0025] High-density polyethylene (HDPE) has a high degree of molecular chain regularity, and its numerous crystalline regions give the pipe high rigidity and strength. However, at low temperatures, its molecular chain segments have poor mobility, and the crystalline regions restrict chain segment deformation, leading to embrittlement. Linear low-density polyethylene (LLDPE), on the other hand, contains more short branches, reducing the regularity of the molecular chain and providing good flexibility and low-temperature resistance. At low temperatures, the short branches on the LLDPE molecular chains can buffer external stress to some extent, reducing the mutual binding between molecular chains and allowing the chain segments to still move within a limited range, preventing the material from rapidly hardening and becoming brittle. By limiting the mass ratio of HDPE to LLDPE to 1:3~5, the higher proportion of LLDPE, with its numerous short branches interspersed between the crystalline and amorphous regions of HDPE, reduces the overall crystallinity and minimizes the increase in brittleness caused by excessive crystallinity. Simultaneously, the combination of the two results in a more uniform microstructure in the plastic inner tube, enhancing the interaction between different chain segments and ensuring the overall flexibility and impact resistance of the material at low temperatures.

[0026] As a further technical solution, an adhesive is also included between the plastic pipe and the steel pipe.

[0027] This invention also proposes a method for preparing a high-strength steel-plastic composite pipe, characterized by comprising the following steps:

[0028] S1. After mixing the raw materials for plastic pipes, the plastic pipes are extruded and molded to obtain plastic pipes;

[0029] S2. After coating the outside of the plastic pipe with adhesive, it is fitted onto the inside of the steel pipe and then pressurized to obtain a high-strength steel-plastic composite pipe.

[0030] The working principle and beneficial effects of this invention are as follows:

[0031] This invention improves the low-temperature resistance of steel-plastic composite pipes by adding palygorskite-composite polytetrafluoroethylene (PTFE) fibers to the plastic pipe, thus extending the service life of the steel-plastic composite pipe in low-temperature environments. To address the problem in existing technologies where the poor compatibility between PTFE and polyethylene limits the improvement of low-temperature resistance of plastic pipes, this invention effectively improves their low-temperature toughness by adding palygorskite-composite PTFE fibers to the plastic pipe. Polytetrafluoroethylene (PTFE) fibers possess excellent low-temperature resistance, maintaining good flexibility and mechanical properties even in extremely cold environments. Ethylene-vinyl alcohol copolymers, as polymers with good adhesion and compatibility, can form a bridging effect between palygorskite and PTFE 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 PTFE through hydrogen bonds, allowing palygorskite to adhere to the surface of PTFE fibers. This increases the surface roughness of the PTFE fibers, making them easier to disperse in the polyethylene and ethylene-vinyl acetate copolymer plastic matrices. It also improves the compatibility of PTFE fibers with the plastic pipe matrix, enabling the PTFE fibers to function better at low temperatures and enhancing the overall low-temperature resistance of the plastic pipe. Simultaneously, the layered chain structure of palygorskite helps disperse stress generated in low-temperature environments, reducing the risk of material brittleness due to temperature changes, further improving the low-temperature resistance of the plastic pipe. Detailed Implementation

[0032] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. 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 of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0033] In the following embodiments and comparative examples:

[0034] The following materials are listed: Ethylene-vinyl alcohol copolymer, model L171B, with an ethylene content of 27 mol%; Ethylene-vinyl alcohol copolymer, model G156B, with an ethylene content of 48 mol%; Ethylene-vinyl alcohol copolymer, model F104B, with an ethylene content of 32 mol%; Ethylene-vinyl alcohol copolymer, model E171B, with an ethylene content of 44 mol%; High-density polyethylene, model: 5502; Linear low-density polyethylene, model: 7042; Ethylene-vinyl acetate copolymer, model: EA28025; Polytetrafluoroethylene fiber, diameter: 10~20 μm, length: 1~3 mm; Pallasic acid, particle size: 325 mesh; Silica, particle size: 800 mesh; Talc, particle size: 600 mesh; Calcium carbonate, particle size: 1250 mesh; Polyamic acid, solid content: 15%.

[0035] Preparation of sodium naphthalene solution: Add 20g of metallic sodium to 1L of tetrahydrofuran solution of naphthalene (the mass concentration of tetrahydrofuran solution of naphthalene is 12%), and stir at room temperature until the solution turns black.

[0036] Example 1

[0037] A method for preparing a high-strength steel-plastic composite pipe includes the following steps:

[0038] 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 silica, 1 part of stearic acid, and 9 parts of palygorskite composite polytetrafluoroethylene fiber, and then extrude them to obtain plastic pipes.

[0039] S2. After coating the outside of the plastic pipe with adhesive, it is fitted onto the inside of the steel pipe and then pressurized to obtain a high-strength steel-plastic composite pipe.

[0040] The preparation method of palygorskite composite polytetrafluoroethylene fiber includes the following steps:

[0041] A1. Soak 10g of polytetrafluoroethylene fiber in 150mL of sodium naphthalene solution for 5min, then soak it in 100mL of acetone solution for 3min. After washing and drying the polytetrafluoroethylene fiber, pretreated polytetrafluoroethylene fiber is obtained.

[0042] A2. Add 20g of palygorskite and 2g of ethylene-vinyl alcohol copolymer L171B to 160mL of N,N-dimethylformamide, and stir at 60℃ for 3h to obtain a mixed solution.

[0043] A3. The pretreated polytetrafluoroethylene fiber was impregnated in the mixed solution for 4 hours and then dried to obtain palygorskite composite polytetrafluoroethylene fiber.

[0044] Example 2

[0045] A method for preparing a high-strength steel-plastic composite pipe includes the following steps:

[0046] 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, 1 part of calcium stearate, and 13 parts of palygorskite composite polytetrafluoroethylene fiber, and then extrude them to obtain plastic pipes.

[0047] S2. After coating the outside of the plastic pipe with adhesive, it is fitted onto the inside of the steel pipe and then pressurized to obtain a high-strength steel-plastic composite pipe.

[0048] The preparation method of palygorskite composite polytetrafluoroethylene fiber includes the following steps:

[0049] A1. Soak 10g of polytetrafluoroethylene fiber in 150mL of sodium naphthalene solution for 7min, then soak it in 100mL of acetone solution for 4min. After washing and drying the polytetrafluoroethylene fiber, pretreated polytetrafluoroethylene fiber is obtained.

[0050] A2. Add 30g of palygorskite and 2g of ethylene-vinyl alcohol copolymer L171B to 270mL of N,N-dimethylformamide, and stir at 70℃ for 3h to obtain a mixed solution.

[0051] A3. The pretreated polytetrafluoroethylene fibers were immersed in a mixed solution for 5 hours and then dried to obtain palygorskite composite polytetrafluoroethylene fibers.

[0052] Example 3

[0053] A method for preparing a high-strength steel-plastic composite pipe includes the following steps:

[0054] 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 wax, and 15 parts of palygorskite composite polytetrafluoroethylene fiber, and then extrude them to obtain plastic pipes.

[0055] S2. After coating the outside of the plastic pipe with adhesive, it is fitted onto the inside of the steel pipe and then pressurized to obtain a high-strength steel-plastic composite pipe.

[0056] The preparation method of palygorskite composite polytetrafluoroethylene fiber includes the following steps:

[0057] A1. Soak 10g of polytetrafluoroethylene fiber in 150mL of sodium naphthalene solution for 10min, then soak it in 100mL of acetone solution for 5min. After washing and drying the polytetrafluoroethylene fiber, pretreated polytetrafluoroethylene fiber is obtained.

[0058] A2. Add 40g of palygorskite and 2g of ethylene-vinyl alcohol copolymer L171B to 400mL of N,N-dimethylformamide, and stir at 80℃ for 2h to obtain a mixed solution.

[0059] A3. The pretreated polytetrafluoroethylene fibers were impregnated in the mixed solution for 6 hours and then dried to obtain palygorskite composite polytetrafluoroethylene fibers.

[0060] Example 4

[0061] The only difference between this embodiment and Example 2 is that the amount of ethylene-vinyl alcohol copolymer L171B added is 6g.

[0062] Example 5

[0063] The only difference between this embodiment and Example 2 is that the amount of ethylene-vinyl alcohol copolymer L171B added is 2.4g.

[0064] Example 6

[0065] The only difference between this embodiment and Example 2 is that the amount of ethylene-vinyl alcohol copolymer L171B added is 3g.

[0066] Example 7

[0067] The only difference between this embodiment and Example 2 is that the amount of ethylene-vinyl alcohol copolymer L171B added is 3.6g.

[0068] Example 8

[0069] The only difference between this embodiment and Example 6 is that the ethylene-vinyl alcohol copolymer L171B is replaced with an equal amount of ethylene-vinyl alcohol copolymer G156B.

[0070] Example 9

[0071] The only difference between this embodiment and Example 6 is that the ethylene-vinyl alcohol copolymer L171B is replaced with an equal amount of ethylene-vinyl alcohol copolymer F104B.

[0072] Example 10

[0073] The only difference between this embodiment and Example 6 is that the ethylene-vinyl alcohol copolymer L171B is replaced with an equal amount of ethylene-vinyl alcohol copolymer E171B.

[0074] Comparative Example 1

[0075] The only difference between this comparative example and Example 1 is that the palygorskite composite polytetrafluoroethylene fiber is replaced with an equal amount of palygorskite.

[0076] Comparative Example 2

[0077] The only difference between this comparative example and Example 1 is that the palygorskite composite polytetrafluoroethylene fiber is replaced with an equal amount of polytetrafluoroethylene fiber.

[0078] Comparative Example 3

[0079] A method for preparing a high-strength steel-plastic composite pipe includes the following steps:

[0080] S1. Mix 14 parts high-density polyethylene, 56 parts linear low-density polyethylene, 20 parts ethylene-vinyl acetate copolymer, 0.5625 parts ethylene-vinyl alcohol copolymer L171B, 1 part antioxidant BHT, 3 parts dibutyl phthalate, 8 parts silica, 1 part stearic acid, 2.8125 parts polytetrafluoroethylene fiber, and 5.625 parts palygorskite, and then extrude the mixture to obtain a plastic pipe.

[0081] S2. After coating the outside of the plastic pipe with adhesive, it is fitted onto the inside of the steel pipe and then pressurized to obtain a high-strength steel-plastic composite pipe.

[0082] Experimental Example 1

[0083] The plastic pipes prepared in Examples 1-7 and Comparative Examples 1-3 were tested for their simple beam impact strength at 23℃ and -20℃ according to method B.1 of GB / T 18743.1-2022 "Determination of impact strength of simply supported beams for thermoplastic pipes - Part 1: General test methods". The thickness of the plastic pipe was 2.5mm. The test results are shown in Table 1.

[0084] Table 1. Low-temperature resistance test results of plastic pipes

[0085]

[0086] As shown in Table 1, the plastic pipes prepared in Examples 1-7 exhibited a lower variation in the impact strength of simply supported beams at -20℃ compared to Comparative Examples 1-3, indicating that adding palygorskite composite polytetrafluoroethylene fiber to polyethylene can improve the low-temperature resistance of the plastic pipes.

[0087] Experiment Example 2

[0088] The plastic pipes prepared in Examples 7 to 10 were tested for tensile strength according to the method in GB / T 8804.1-2003 "Determination of tensile properties of thermoplastic pipes - Part 1: General test methods". The thickness of the plastic pipe was 2.5 mm. The test results are shown in Table 2.

[0089] Table 2 Tensile strength test results of plastic pipes

[0090]

[0091] As shown in Table 2, the tensile strength of the plastic pipes prepared in Examples 9-10 is higher than that in Examples 7-8, indicating that when the ethylene-vinyl alcohol copolymer modifies palygorskite and the ethylene content in the ethylene-vinyl alcohol copolymer is 32-44 mol / % it can improve the tensile strength of the plastic pipe.

[0092] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A high-strength steel-plastic composite pipe, characterized in that, From the inside out, it includes a plastic pipe and a steel pipe. 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 in a mass ratio of 20-40:10:2-6. The mass ratio of palygorskite, polytetrafluoroethylene fiber, and ethylene-vinyl alcohol copolymer is 30:10:2.4~3.6; The preparation method of the palygorskite composite polytetrafluoroethylene fiber includes the following steps: A1. Polytetrafluoroethylene (PTFE) fibers are soaked in sodium naphthalene solution, and then washed and dried to obtain pretreated PTFE fibers. A2. Papyrrolidone and ethylene-vinyl alcohol copolymer are added to N,N-dimethylformamide and mixed to obtain a mixed solution; A3. The pretreated polytetrafluoroethylene fiber is impregnated in the mixed solution and dried to obtain palygorskite composite polytetrafluoroethylene fiber.

2. The high-strength steel-plastic composite pipe according to claim 1, characterized in that, The ethylene-vinyl alcohol copolymer contains 32-44 mol of ethylene.

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

4. A 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 antioxidants include hindered phenolic antioxidants.

5. A 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 wax; and / or, The filler includes one or more of silica, talc, and calcium carbonate.

6. A 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.

7. A high-strength steel-plastic composite pipe according to claim 1, characterized in that, An adhesive is also included between the plastic pipe and the steel pipe.

8. A method for preparing a high-strength steel-plastic composite pipe, used to prepare the high-strength steel-plastic composite pipe according to any one of claims 1 to 7, characterized in that, Includes the following steps: S1. After mixing the raw materials for plastic pipes, the plastic pipes are extruded and molded to obtain plastic pipes; S2. After coating the outside of the plastic pipe with adhesive, it is fitted onto the inside of the steel pipe and then pressurized to obtain a high-strength steel-plastic composite pipe.

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