Flexible hydrogen transport PE composite pipe and preparation method thereof

Abstract

The invention discloses a flexible hydrogen transport PE composite pipe. The flexible hydrogen transport PE composite pipe is of a three-layer structure, raw material selection, carbon fiber pretreatment, filler pulping, coating treatment and co-extrusion forming. The method solves the problems that an existing preparation method is uneven in material mixing and poor in pipe size precision. The invention further discloses the flexible hydrogen transport PE composite pipe, the flexible hydrogen transport PE composite pipe is prepared by the preparation method of the flexible hydrogen transport PE composite pipe, and the mechanical property is also improved while the flame-retardant, antistatic and compact properties are improved.

Description

Technical Field

[0001] The invention belongs to the technical field of polymer materials, relates to a flexible hydrogen-transmitting PE composite pipe, and also relates to a preparation method of the flexible hydrogen-transmitting PE composite pipe. Background Art

[0002] With the rapid development of science and technology and industrialization, the demand for resources is becoming increasingly tight, leading people to look underground. To obtain various means of production, such as coal, ore, and oil, deep tunnels and extensive lines are needed. New alternative energy sources, such as hydrogen, are also being developed. However, transporting hydrogen, which is flammable and explosive and has a very small atomic radius, from its source over long distances is a significant challenge. Polyethylene (PE) pipe, a key piping material, is used effectively in mining operations for water supply and drainage, shotcrete pipes, and vacuum ventilation and gas extraction pipes due to its excellent corrosion resistance, aging resistance, and mechanical properties. However, traditional PE pipe materials lack performance in high-temperature, high-pressure, and flame-retardant environments. To address this, PE pipes are modified by adding various fillers and adjusting manufacturing process parameters to achieve wear resistance, pressure resistance, thermal stability, and antistatic properties, making them more adaptable to complex environments and more demanding operating conditions.

[0003] In terms of the selection of flame retardants and antistatic agents, patent CN114044997B uses high-density polyethylene and linear low-density polyethylene as the base materials, adds unsaturated silane coupling agent modified glass fiber as reinforcing filler, and the impact strength of the prepared composite material is as high as 37.8KJ / m 2 Wang Suna used super molecular weight polyethylene as the base material, added an IFR system intumescent flame retardant and 3% carbon black as an antistatic agent, and hot-pressed it to produce a flame-retardant and antistatic PE composite pipe for mining. The volume resistivity was 2.0×10 8 Ω, oxygen index is 30.1%. Patent CN102010540B uses linear low-density polyethylene as the base material, adds auxiliary components such as monoglyceride and ethylene diacylamide to graphite to make an antistatic composition, and then mixes it with coated red phosphorus. The surface resistivity of the prepared flame-retardant polyethylene antistatic composition for mining is 4.1×10 4 Ω, good flame retardant properties. Patent CN112574489A uses high-density polyethylene as the base material, selects graphene and carbon nanotubes as conductive agents, and then adds at least one of phosphorus-based flame retardants, metal hydroxides, nitrogen-based flame retardants, and intumescent flame retardants as flame retardants, antioxidant 168, and polyethylene wax as a surface treatment agent to prepare a polyethylene composite pipe for mining with a surface resistivity of 3.3×10 5Ω, and flame retardancy is V0 grade. Patent CN109575398A uses high-density polyethylene as the base material, graphene and carbon black as conductive fillers, and then adds at least one of red phosphorus, magnesium hydroxide, aluminum hydroxide, hexabromocyclododecane or antimony trioxide as a flame retardant, PE wax as a dispersant, and at least one of calcium stearate, barium sulfate, silicate or titanium dioxide as a nucleating agent to prepare a mining-grade graphene, carbon black, polyethylene composite pipe. It has good flame retardancy and a surface resistivity of 8.9×10 5 Zhang Wei and his colleagues used ultra-high molecular weight polyethylene as the base material, added nano-carbon antistatic filler black and nano-composite flame retardant, and mixed them at high speed. The mixture was finally extruded to prepare nano-antistatic halogen-free flame-retardant PE composite pipe. The addition of nano-carbon black formed a double conductive grid, which can meet the antistatic performance requirements at a low carbon black content.

[0004] In terms of molding preparation, patent CN117534894B uses a twin-screw extruder to mix ammonium polyphosphate and nano-montmorillonite as the main flame retardants, aluminum hydroxide and magnesium oxide as auxiliary flame retardants, with linear low-density polyethylene in a specific proportion, and then extrudes and granulates them. The resulting extruded pipe exhibits excellent flame retardancy and mechanical properties. Mao Qianchao used PE fiber cloth as reinforcement and high-density polyethylene as the matrix through injection molding to prepare a PE single-polymer composite. The results showed that at an injection temperature of 300°C, an injection pressure of 120.8 MPa, an injection rate of 0.23 m / s, and a dwell time of 15 seconds, the PE single-polymer composite achieved a tensile strength of 151 MPa, 7.6 times that of unreinforced PE resin. Li Huilan used an in-mold winding method for ultra-high molecular weight polyethylene pipes. At a rotation speed of 20 r / min, she produced ultra-high molecular weight polyethylene composite pipes with a yield strength of approximately 20 MPa, a tensile strength of approximately 34 MPa, and an elongation at break of approximately 450%. Patent CN105650367A uses 1.0-3.5mm steel wire to weave two layers of steel mesh skeletons with different mesh sizes and steel wire diameters on the polyethylene surface. The composite pipe prepared by winding and forming using a winding machine has high strength and low manufacturing cost.

[0005] It can be seen that the addition of inorganic flame retardants containing nitrogen and phosphorus has improved the flame retardant performance to a certain extent, but it still cannot meet the needs of high fire resistance and antistatic hydrogen transmission pipes. Although inorganic flame retardants have the advantages of being non-toxic and smokeless, they are all achieved by adding a large amount of flame retardants to improve the fire resistance and antistatic ability of polyethylene, which inevitably reduces the mechanical properties of polyethylene. In terms of preparation technology, injection molding is expensive and requires precision molds, which wastes a lot of raw materials. The pipes prepared by blow molding may have problems such as insufficient dimensional accuracy or poor surface quality. In order to solve the problems existing in the prior art, the present invention prepares a mixed filler with ammonium polyphosphate, mullite powder and carbon black, which combines the advantages of inorganic flame retardants, such as good smoke suppression, high flame retardant efficiency, and excellent electrical conductivity and low cost of phosphorus flame retardants. The composite material with a "core-shell" structure greatly enhances the compatibility and dispersion uniformity of the filler in the composite pipe. The pipe molding adopts multi-layer co-extrusion to overcome the problems of uneven mixing, low density, poor pipe dimensional accuracy and high cost in the previous preparation methods. Summary of the Invention

[0006] The purpose of the present invention is to provide a method for preparing a flexible hydrogen transport PE composite pipe, which overcomes the problems of uneven mixing, low density and poor pipe dimensional accuracy in existing preparation methods.

[0007] Another object of the present invention is to provide a flexible PE composite pipe for hydrogen transport, which improves the flame retardant and antistatic properties while also improving the mechanical properties.

[0008] The first technical solution adopted by the present invention is a method for preparing a flexible hydrogen transport PE composite pipe, which specifically includes: designing a three-layer flexible hydrogen transport PE composite pipe, raw material selection, carbon fiber pretreatment, filler pulping, coating treatment and co-extrusion molding.

[0009] The first technical solution of the present invention is also characterized in that:

[0010] Please follow the steps below to implement it:

[0011] Step 1: Design a three-layer flexible hydrogen transport PE composite pipe consisting of an inner lining layer, a reinforcement layer, and an outer protective layer from the inside out;

[0012] Step 2: Select the raw materials. The inner lining and outer protective layer are made of the same raw materials, including high-density polyethylene, antistatic agent, flame retardant and other additives. The reinforcing layer is made of carbon fiber.

[0013] Step 3: Debonding and roughening the carbon fiber surface to obtain pretreated carbon fiber;

[0014] Step 4: ball milling, dissolving, ultrasonically dispersing, and filtering part of the raw materials of the inner lining layer and the outer protective layer in sequence to obtain a slurry;

[0015] Step 5: coating the other raw materials of the inner lining layer and the outer protective layer with the slurry obtained in step 4 to obtain raw material particles of the inner lining layer and the outer protective layer;

[0016] Step 6: Extrude the raw material particles obtained in step 5 to form an inner lining pipe, weave a carbon fiber mesh on the surface of the inner lining pipe with pretreated carbon fiber, and then extrude the raw material particles into an outer protective layer and wrap it on the surface of the carbon fiber mesh pipe. After cooling, a flexible hydrogen transport PE composite pipe is obtained.

[0017] In step 2, the grade of high-density polyethylene is 8800J, the antistatic agent is conductive carbon black, the flame retardant includes a main flame retardant and an auxiliary flame retardant, the main flame retardant is ammonium polyphosphate, the auxiliary flame retardant is mullite powder, other additives include silane coupling agent KH560 and ethylene-octene copolymer, and the diameter of the carbon fiber is 0.5 to 1.5 μm;

[0018] The polymerization degree of ammonium polyphosphate is greater than 1000, and the particle size is 50 to 150 μm; the particle size of mullite powder is 50 to 150 μm; and the conductive carbon black is used as an antistatic filler, and the particle size is 50 to 150 μm.

[0019] Specifically, step 3 is as follows: first, the carbon fiber to be treated is placed in a heating furnace and burned at 480°C for 60 minutes to burn out the organic binder on its surface, and then soaked in acetone for 60 minutes to dissolve the coke and clean the carbon fiber surface, washed with water several times, dried, and set aside, and then the carbon fiber after degumming is placed in concentrated nitric acid and heated to 90°C for coarsening for 60 minutes, neutralized with a dilute NaOH solution to neutrality, washed with water, and dried to obtain the pretreated carbon fiber.

[0020] Specifically, step 4 comprises mixing ammonium polyphosphate, mullite, and carbon black in a mass ratio of 4:1:5, and then placing them in a ball mill for 24 hours to obtain a mixed filler powder with a particle size of less than 1 μm. The prepared filler powder is added to a container with KH560 hydrolyzate as a solvent, and the mass ratio of the mixed filler powder to the KH560 hydrolyzate is 1:4. The powder suspension is obtained by ultrasonic dispersion for 2 hours. The mixture to be separated is poured into a Buchner funnel, and the vacuum pump is turned on to form a negative pressure in the funnel. The liquid in the mixture is extracted through the filter paper, and the solid slurry remains on the filter paper. The vacuum pump is turned off and the filter paper is removed to obtain a filtered slurry with a viscosity of 500 to 3000 mPa·s.

[0021] In step 4, during ball milling, the ball-to-material mass ratio is 15:1, the ball milling medium is steel balls or zirconia beads, and the ball milling medium, i.e., the grinding ball, has a diameter of 3 to 5 mm;

[0022] The ultrasonic frequency of the ultrasonic dispersion in step 4 is 100 kHz.

[0023] Step 5 is specifically as follows: first, open the mixing bin door of the fluidized bed coater, add the slurry into the closed drum of the fluidized bed coater, and then add high-density polyethylene particles and ethylene-octene copolymer particles thereto to perform complex trajectory motion. The mass ratio of the high-density polyethylene particles to the ethylene-octene copolymer particles is 10:1, and the mass ratio of the sum of the mass of the high-density polyethylene particles and the ethylene-octene copolymer particles to the slurry is 1:1 to 1:3. Stir repeatedly for 1 to 5 hours, and finally open the bin door to obtain a core-shell structure with high-density polyethylene particles and ethylene-octene copolymer particles as the core and the slurry as the outer shell. The shell thickness is greater than or equal to 10 μm, and the volume ratio of the particles to the slurry is 1:1.2 to 1:1.5, and finally obtain the raw material particles of the inner liner and the outer protective layer.

[0024] Specifically, step 6 is to add the raw material particles prepared in step 5 into the first extruder to prepare the inner lining molded pipe. The inner lining molded pipe extruded by the first extruder continues to be pulled forward and enters the first winding machine. The turntable of the first winding machine rotates clockwise at a constant speed to wind the first layer of carbon fiber mesh, and then enters the second winding machine. The turntable of the second winding machine rotates counterclockwise at a constant speed to wind the second layer of carbon fiber mesh. The inner lining molded pipe wrapped with two layers of carbon fiber mesh enters the second extruder, and the raw material particles are added to the feeding port of the second extruder. The second extruder extrudes the outer protective layer and wraps it on the surface of the carbon fiber mesh pipe. Finally, after cooling, a three-layer PE composite pipe, i.e., a flexible hydrogen transport PE composite pipe, is obtained.

[0025] In step 6, the first layer of carbon fiber mesh and the second layer of carbon fiber mesh are both pretreated carbon fibers wound crosswise into a mesh, the winding angle θ is set to 45° to 55°, the grids of the first layer of carbon fiber mesh and the second layer of carbon fiber mesh are both diamond-shaped, and the spacing d between each two carbon fibers in the grid is 1 to 3 cm;

[0026] The temperature of the IV interval of the first extruder and the second extruder is controlled at 160-210°C;

[0027] The thickness of the carbon fiber reinforcement layer of the inner lining formed pipe wound with two layers of carbon fiber mesh is 2-6 μm.

[0028] The second technical solution adopted by the present invention is that the flexible hydrogen-transporting PE composite pipe is prepared by the preparation method of the flexible hydrogen-transporting PE composite pipe of the present invention.

[0029] The beneficial effects of the present invention are:

[0030] 1) The preparation method of the flexible hydrogen transport PE composite pipe of the present invention designs the pipe structure into three layers. Under the premise of meeting the anti-static and flame retardant properties, it also has excellent mechanical properties. From the outside to the inside, it is an outer protective layer, a reinforcement layer and an inner lining layer. The raw materials of the inner lining layer are high-density polyethylene, flame retardants, antistatic agents and other additives. The main flame retardant is ammonium polyphosphate. When the material is heated, ammonium polyphosphate can decompose to produce phosphoric acid and ammonia. Phosphoric acid can promote the formation of a carbon layer on the surface of polyethylene to isolate heat and oxygen. Ammonia can dilute the surrounding oxygen concentration, thereby inhibiting the combustion process. In addition, the thermal decomposition of ammonium polyphosphate is an endothermic process, which can absorb part of the heat generated during combustion to slow down or stop the combustion process. The auxiliary flame retardant is mullite powder. Mullite powder has a high specific surface area, which helps to form an intercalated network structure in the carbon layer and can enhance the thermal stability of the carbon layer. Its good thermal stability will promote the decomposition process of ammonium polyphosphate, thereby achieving higher flame retardant efficiency. The addition of mullite powder can form a protective film covering the surface of the material to isolate oxygen from direct contact with combustible substances. In addition, the addition of mullite powder can also effectively improve the mechanical properties of polyethylene. The smaller particle size of the mixed filler can provide a larger specific surface area and form a denser protective layer.

[0031] 2) The preparation method of the present invention can not only improve the mechanical properties of high-density polyethylene by adding ethylene-octene copolymer (POE), but also enhance the compatibility of inorganic fillers in polyethylene. Its chemical structure is very similar to that of polyethylene and has excellent compatibility with the polyethylene matrix, which helps to form a more uniform microstructure, thereby further improving the performance of the composite material.

[0032] 3) The reinforcement layer designed in the preparation method of the present invention is to wrap two layers of modified carbon fiber mesh on the outer surface of the inner lining molded pipe to enhance the mechanical properties of the pipe. The use of carbon fiber mesh to wrap and reinforce polyethylene pipes can improve its mechanical properties by more than 100 times compared to steel mesh winding. The flexibility is also higher than that of metal mesh, which is convenient for the later construction and installation of the pipe. The fiber itself is also a carbon material, which is conducive to fusion with PE polymer materials, avoiding cracking and affecting the service life. It has good corrosion resistance. The outer protective layer uses the same raw material composition as the inner lining layer. The raw material particles of the inner lining layer and the outer protective layer are made by wrapping the filler into a slurry on the surface of the particles, thereby further improving the dispersion uniformity of each filler in the polyethylene and the interface compatibility between the filler and the polyethylene.

[0033] 4) The flexible hydrogen transport PE composite pipe of the present invention is a composite pipe with a three-layer structure. The compound flame retardant of the inner lining layer and the outer protective layer achieves high flame retardant performance under the premise of a small amount of addition, and the added filler meets environmental protection requirements. While improving the flame retardant and antistatic properties, other additives are added to ensure that the mechanical properties of the PE composite pipe itself are improved while ensuring performance improvement. The reinforcement layer adopts carbon fiber winding to enhance the impact strength and tensile strength of the polyethylene material itself. The use of slurry for coating treatment is not only conducive to the dispersion of the filler, but also can improve the density of the pipe and prevent the leakage of hydrogen during transportation. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 This is a schematic structural diagram of the flexible hydrogen transport PE composite pipe of the present invention;

[0035] Figure 2 shows the surface morphology of carbon fibers before and after pretreatment, where Figure 2(a) shows the original carbon fibers, Figure 2(b) shows the carbon fibers after thermal degreasing, and Figure 2(c) shows the roughened carbon fibers.

[0036] Figure 3 is a diagram of the coating process of raw material particles, Figure 3(a) is a diagram of the coating process, and Figure 3(b) is a diagram of the interface of the raw material particles;

[0037] Figure 4 This is the working principle diagram of fluidized bed coating machine;

[0038] Figure 5 This is a schematic diagram of the co-extrusion molding of flexible hydrogen transport PE composite pipes;

[0039] Figure 6 Schematic diagram of carbon fiber woven mesh;

[0040] Figure 7 is a microscopic morphology of the flexible hydrogen transport PE composite pipe in Example 13 of the present invention, wherein Figure 7(a) and Figure 7(b) are microscopic morphology at two locations on the surface of the flexible hydrogen transport PE composite pipe, Figure 7(c) and Figure 7(d) are microscopic morphology at two locations on the cross section of the flexible hydrogen transport PE composite pipe, and Figure 7(e) and Figure 7(f) are microscopic morphology at two locations on the tensile fracture of the flexible hydrogen transport PE composite pipe.

[0041] In the figure, 1. Inner lining layer, 2. Reinforcement layer, 3. Outer protective layer, 4. Drum, 5. Raw material particles, 6. Slurry tank, 7. Mixing bin door switch, 8. First extruder, 9. First winding machine, 10. Pretreated carbon fiber, 11. Second winding machine, 12. Second extruder, 13. Three-layer PE composite pipe, 14. Control panel. DETAILED DESCRIPTION

[0042] The present invention will be described in detail below with reference to the accompanying drawings and specific embodiments.

[0043] Example 1

[0044] This embodiment provides a method for preparing a flexible PE composite pipe for hydrogen transmission, which is specifically implemented according to the following steps:

[0045] Step 1: Design a three-layer flexible PE composite pipe for hydrogen transmission;

[0046] like Figure 1 As shown, the design is a three-layer flexible hydrogen transport PE composite pipe consisting of an inner lining layer 1, a reinforcement layer 2 and an outer protective layer 3 from the inside to the outside;

[0047] Step 2: Raw material selection

[0048] The inner lining layer 1 and the outer protective layer 3 are made of the same raw materials, including high-density polyethylene, antistatic agent, flame retardant and other additives, and the reinforcing layer 2 is made of carbon fiber;

[0049] Step 3: Carbon fiber pretreatment

[0050] In order to protect the carbon fiber during winding, weaving and transportation, it is often treated with glue, resulting in a smooth organic adhesive covering the surface of the carbon fiber. Therefore, the carbon fiber surface is debonded and roughened before use to obtain pretreated carbon fiber 10. The purpose of debonding is to obtain a carbon fiber with a clean surface, and the purpose of roughening is to increase the surface roughness of the fiber and increase the number of polar groups, thereby enhancing the activity of the surface, increasing the surface energy and improving the affinity.

[0051] Step 4: Filler pulping

[0052] Part of the raw materials of the inner lining layer 1 and the outer protective layer 3 are subjected to ball milling, dissolution, ultrasonic dispersion, and suction filtration in sequence to obtain a slurry;

[0053] Step 5: Coating

[0054] The other raw materials of the inner lining layer 1 and the outer protective layer 3 are coated with the slurry obtained in step 4 to obtain raw material particles 5 of the inner lining layer 1 and the outer protective layer 3;

[0055] Step 6: Co-extrusion

[0056] The raw material particles 5 obtained in step 5 are extruded to form an inner lining pipe, and a carbon fiber mesh is woven on the surface of the inner lining pipe with pretreated carbon fibers 10. The raw material particles 5 are then extruded to form an outer protective layer 3 which is wrapped on the surface of the carbon fiber mesh pipe. After cooling, a flexible hydrogen transport PE composite pipe is obtained.

[0057] This embodiment provides a flexible hydrogen-transporting PE composite pipe, which is prepared using the method for preparing the flexible hydrogen-transporting PE composite pipe of this embodiment.

[0058] Example 2

[0059] This embodiment provides a method for preparing a flexible hydrogen transport PE composite pipe. Based on Example 1, in step 2, the grade of high-density polyethylene is 8800J, the antistatic agent is conductive carbon black with a particle size of 50 μm, the flame retardant includes a main flame retardant and an auxiliary flame retardant, the main flame retardant is ammonium polyphosphate with a degree of polymerization of >1000 and a particle size of 50 μm, the auxiliary flame retardant is mullite powder with a particle size of 50 μm; other additives include silane coupling agent KH560 and ethylene-octene copolymer, and the diameter of the carbon fiber is 0.5 μm.

[0060] Conductive carbon black is used as an antistatic filler. Since the outer protective layer 3 and the inner lining layer 1 are made of the same raw materials, the antistatic filler can form a complete conductive network system in the entire pipe, which can achieve excellent flame retardant properties regardless of whether it is transporting flammable substances or exposed to harsh environments with high temperatures.

[0061] Example 3

[0062] This embodiment provides a method for preparing a flexible hydrogen transport PE composite pipe. Based on Example 1, in step 2, the grade of high-density polyethylene is 8800J, the antistatic agent is conductive carbon black with a particle size of 150 μm, the flame retardant includes a main flame retardant and an auxiliary flame retardant, the main flame retardant is ammonium polyphosphate with a degree of polymerization of >1000 and a particle size of 150 μm, the auxiliary flame retardant is mullite powder with a particle size of 150 μm; other additives include silane coupling agent KH560 and ethylene-octene copolymer, and the diameter of the carbon fiber is 1.5 μm.

[0063] Example 4

[0064] This embodiment provides a method for preparing a flexible hydrogen transport PE composite pipe. Based on Example 1, in step 2, the grade of high-density polyethylene is 8800J, the antistatic agent is conductive carbon black with a particle size of 120 μm, the flame retardant includes a main flame retardant and an auxiliary flame retardant, the main flame retardant is ammonium polyphosphate with a degree of polymerization of >1000 and a particle size of 12 μm, the auxiliary flame retardant is mullite powder with a particle size of 12 μm; other additives include silane coupling agent KH560 and ethylene-octene copolymer, and the diameter of the carbon fiber is 1.1 μm.

[0065] Example 5

[0066] This embodiment provides a preparation method for a flexible hydrogen transport PE composite pipe. Based on Example 4, step 3 is specifically as follows: first, the carbon fiber to be treated is placed in a heating furnace and burned at 480°C for 60 minutes to burn out the organic binder on its surface; then, it is soaked in acetone for 60 minutes to dissolve the coke and clean the surface of the carbon fiber; then, it is washed with water multiple times, dried, and set aside; then, the carbon fiber after debonding is placed in concentrated nitric acid and heated to 90°C for coarsening for 60 minutes; then, it is neutralized to neutrality with a dilute NaOH solution; and after washing and drying, the pretreated carbon fiber 10 is obtained.

[0067] Figure 2 shows the surface morphology of carbon fiber before and after pretreatment. It can be seen that the surface of commercial carbon fiber is very smooth, but shallow grooves can still be observed along the axial direction. These grooves are actually caused by drawing during the preparation process of carbon fiber. The surface of carbon fiber after thermal degreasing is shown in Figure 2(b). Compared with Figure 2(a), the grooves on the surface of carbon fiber are deepened, and grooves can be clearly seen. This is the surface morphology of carbon fiber itself. In addition, small white spots and granularity can be seen. This is because some organic adhesives are not removed and coke carbon is attached to its surface. Therefore, after thermal degreasing, it is necessary to soak in acetone for 60 minutes and ultrasonically clean. The ridges of the roughened carbon fiber grooves are not as sharp as those after thermal degreasing, are discontinuous, and have more small corrosion points. The increased roughness of the carbon fiber surface blunts the sharp angles.

[0068] Example 6

[0069] This embodiment provides a method for preparing a flexible hydrogen transport PE composite pipe. Based on Example 5, step 4 specifically comprises: mixing ammonium polyphosphate, mullite, and carbon black in a mass ratio of 4:1:5, and then placing the mixture in a ball mill for ball milling. During ball milling, the ball-to-material mass ratio is 15:1, the ball milling medium is steel balls or zirconia beads, the ball milling medium, i.e., the grinding ball diameter is 3 mm, and the ball milling time is 24 h. Finally, a mixed filler powder with a particle size of less than 1 μm is obtained. The prepared filler powder is added to a container with KH560 hydrolyzate as a solvent, and the mass ratio of the mixed filler powder to the KH560 hydrolyzate is 1:4. Ultrasonic dispersion is performed for 2 h at an ultrasonic frequency of 100 kHz to obtain a powder suspension. The mixture to be separated is poured into a Buchner funnel, and the vacuum pump is turned on to form a negative pressure in the funnel. The liquid in the mixture is extracted through the filter paper, and the solid slurry remains on the filter paper. The vacuum pump is turned off, and the filter paper is removed to finally obtain a filtered slurry with a slurry viscosity of 500 mPa·s.

[0070] Example 7

[0071] This embodiment provides a preparation method of a flexible hydrogen transport PE composite pipe. Based on Example 5, step 4 is specifically as follows: ammonium polyphosphate, mullite, and carbon black are mixed in a mass ratio of 4:1:5, and then put into a ball mill for ball milling. During ball milling, the ball-to-material mass ratio is 15:1, the ball milling medium is steel balls or zirconium oxide beads, the ball milling medium, i.e., the grinding ball diameter is 5 mm, the ball milling time is 24 hours, and finally a mixed filler powder with a particle size of less than 1 μm is obtained. The prepared filler powder is added to In a container with KH560 hydrolyzate as solvent, the mass ratio of the mixed filler powder and KH560 hydrolyzate is 1:4, and ultrasonic dispersion is carried out for 2 hours at an ultrasonic frequency of 100 kHz to obtain a powder suspension. The mixture to be separated is poured into a Buchner funnel, and the vacuum pump is turned on to form a negative pressure in the funnel. The liquid in the mixture is sucked away through the filter paper, and the solid slurry remains on the filter paper. The vacuum pump is turned off and the filter paper is removed to finally obtain a filtered slurry with a slurry viscosity of 3000 mPa·s.

[0072] Example 8

[0073] This embodiment provides a preparation method of a flexible hydrogen transport PE composite pipe. Based on Example 5, step 4 is specifically as follows: ammonium polyphosphate, mullite, and carbon black are mixed in a mass ratio of 4:1:5, and then put into a ball mill for ball milling. During ball milling, the ball-to-material mass ratio is 15:1, the ball milling medium is steel balls or zirconium oxide beads, the ball milling medium, i.e., the grinding ball diameter is 4 mm, the ball milling time is 24 hours, and finally a mixed filler powder with a particle size of less than 1 μm is obtained. The prepared filler powder is added to In a container with KH560 hydrolyzate as solvent, the mass ratio of the mixed filler powder and KH560 hydrolyzate is 1:4, and ultrasonic dispersion is carried out for 2 hours at an ultrasonic frequency of 100 kHz to obtain a powder suspension. The mixture to be separated is poured into a Buchner funnel, and the vacuum pump is turned on to form a negative pressure in the funnel. The liquid in the mixture is sucked away through the filter paper, and the solid slurry remains on the filter paper. The vacuum pump is turned off and the filter paper is removed to finally obtain a filtered slurry with a slurry viscosity of 1800 mPa·s.

[0074] Example 9

[0075] This embodiment provides a preparation method of a flexible hydrogen transport PE composite pipe. Based on Example 6, step 5 is specifically as shown in Figure 3(a). First, the mixing chamber door switch 7 of the fluidized bed coating machine is opened, and the slurry is added to the slurry pool 6 of the closed drum 4 of the fluidized bed coating machine. Then, high-density polyethylene particles (HDPE particles) and ethylene-octene copolymer particles (POE particles) are added thereto to perform complex trajectory motion. The mass ratio of the high-density polyethylene particles to the ethylene-octene copolymer particles is 10:1, and the mass ratio of the sum of the high-density polyethylene particles and the ethylene-octene copolymer particles to the slurry is 1:1. The mixture is repeatedly stirred for 1 hour. Figure 4The working principle of the fluidized bed coater is shown, and finally the door is opened to obtain a core-shell structure with high-density polyethylene particles and ethylene octene copolymer particles as the core and the slurry as the shell, the shell thickness is 10 μm, the volume ratio of particles to slurry is 1:1.2, and finally the raw material particles 5 of the inner lining layer 1 and the outer protective layer 3 as shown in Figure 3(b) are obtained, where A is the HDPE particle and B is the slurry shell.

[0076] Wherein, the mass M of the required slurry is calculated as follows:

[0077] M = p · (A x T)

[0078] In the formula, p is the density of the slurry, about 1.3 g / cm 3 ; A is the surface area of a single polyethylene particle, about 1.1-1.5 cm 2 ; T is the thickness of the slurry, about 10 μm.

[0079] Example 10

[0080] This embodiment provides a preparation method of flexible hydrogen conveying PE composite pipe, based on example 7, step 5 is specifically, first open the mixing door of the fluidized bed coater, add the slurry into the closed drum 4 of the fluidized bed coater, then add high-density polyethylene particles (HDPE particles) and ethylene octene copolymer particles (POE particles) to make complex trajectory motion, the mass ratio of high-density polyethylene particles to ethylene octene copolymer particles is 10:1, the mass ratio of high-density polyethylene particles to ethylene octene copolymer particles to the mass of the slurry is 1:3, and the stirring is repeated for 5 h, finally the door is opened to obtain a core-shell structure with high-density polyethylene particles and ethylene octene copolymer particles as the core and the slurry as the shell, the shell thickness is 12 μm, the volume ratio of particles to slurry is 1:1.5, and finally the raw material particles 5 of the inner lining layer 1 and the outer protective layer 3 are obtained.

[0081] Example 11

[0082] This embodiment provides a preparation method of a flexible hydrogen transport PE composite pipe. Based on Example 8, step 5 is specifically as follows: first, open the mixing bin door of the fluidized bed coating machine, add the slurry into the closed drum 4 of the fluidized bed coating machine, and then add high-density polyethylene particles (HDPE particles) and ethylene-octene copolymer particles (POE particles) thereto to perform complex trajectory motion. The mass ratio of the high-density polyethylene particles to the ethylene-octene copolymer particles is 10:1, and the mass ratio of the sum of the mass of the high-density polyethylene particles and the ethylene-octene copolymer particles to the slurry is 1:2. Stir repeatedly for 3 hours, and finally open the bin door to obtain a core-shell structure with high-density polyethylene particles and ethylene-octene copolymer particles as the core and the slurry as the outer shell. The shell thickness is 11 μm, and the volume ratio of the particles to the slurry is 1:1.3. Finally, raw material particles 5 of the inner lining layer 1 and the outer protective layer 3 are obtained.

[0083] The filler slurry coating method solves the problems of uneven dispersion of fillers in polyethylene composite materials, low interface bonding, low production efficiency and high cost produced by raw material blending and extrusion granulation.

[0084] Example 11

[0085] This embodiment provides a method for preparing a flexible hydrogen transport PE composite pipe. Based on Example 9, step 6 is specifically as follows: Figure 5 As shown, the raw material particles 5 prepared in step 5 are added to the first extruder 8 to prepare the inner lining layer 1 formed pipe. The inner lining layer 1 formed pipe extruded by the first extruder 8 continues to be pulled forward and enters the first winding machine 9. The turntable of the first winding machine 9 rotates clockwise at a constant speed to wind the first layer of carbon fiber mesh, and then enters the second winding machine 11. The turntable of the second winding machine 11 rotates counterclockwise at a constant speed to wind the second layer of carbon fiber mesh. The inner lining layer 1 formed pipe wound with two layers of carbon fiber mesh enters the second extruder 12, and the raw material particles 5 are added to the feeding port of the second extruder 12. The second extruder 12 extrudes the outer protective layer 3 and wraps it on the surface of the carbon fiber mesh pipe. Finally, after cooling, a three-layer PE composite pipe 13, i.e., a flexible hydrogen transport PE composite pipe, is obtained.

[0086] like Figure 6 As shown, in step 6, the first layer of carbon fiber mesh and the second layer of carbon fiber mesh are both pretreated carbon fibers 10 cross-wound into a mesh, the winding angle θ is set to 45°, the grids of the first layer of carbon fiber mesh and the second layer of carbon fiber mesh are both diamond-shaped, and the spacing d between each two carbon fibers in the grid is 1 cm; the control panel 14 is used to control the IV zone temperature of the first extruder 8 and the second extruder 12 at 160°C;

[0087] The thickness of the carbon fiber reinforced layer 2 of the inner lining forming tube wound with two layers of carbon fiber mesh is 2 μm.

[0088] After the inner liner 1 is extruded, the winding machine is used to weave on the surface of the inner liner 1, and the pretreated carbon fibers 10 are embedded in the matrix of the inner liner 1 and the outer protective layer 3, and the thickness of the carbon fibers 10 is only a few microns. Therefore, the good interfacial compatibility between the polyethylene matrix and the carbon fibers can be effectively ensured, and the antistatic filler is added in the inner liner 1 and the outer protective layer 3. Therefore, the carbon fiber mesh and the inner and outer pipes form a complete conductive grid, and the risk of static accumulation can be effectively prevented.

[0089] Example 12

[0090] In this embodiment, a preparation method of a flexible hydrogen transport PE composite pipe is provided. On the basis of the embodiments 10 and 6, step 6 is specifically as shown in Figure 5 The prepared raw material particles 5 in step 5 are added into the first extruder 8 to prepare the inner liner 1 forming pipe. The inner liner 1 forming pipe extruded by the first extruder 8 is continuously pulled forward into the first winding machine 9. The rotating disc of the first winding machine 9 rotates at a uniform speed in a clockwise direction to wind the first layer of carbon fiber mesh. Then, the inner liner 1 forming pipe is introduced into the second winding machine 11. The rotating disc of the second winding machine 11 rotates at a uniform speed in a counterclockwise direction to wind the second layer of carbon fiber mesh. The inner liner 1 forming pipe with the two layers of carbon fiber mesh is introduced into the second extruder 12. The raw material particles 5 are added into the feeding port of the second extruder 12. The outer protective layer 3 is extruded by the second extruder 12 and wrapped on the surface of the carbon fiber mesh pipe. Finally, the three-layer PE composite pipe 13, i.e., the flexible hydrogen transport PE composite pipe, is prepared after cooling.

[0091] As shown in Figure 6 In step 6, the first layer of carbon fiber mesh and the second layer of carbon fiber mesh are both the pretreated carbon fibers 10 which are interlaced to form a mesh shape. The winding angle θ is set to 55°. The mesh of the first layer of carbon fiber mesh and the second layer of carbon fiber mesh is in a rhombus shape. The distance d between every two carbon fibers of the mesh is 3 cm. The I-V interval temperature of the first extruder 8 and the second extruder 12 is controlled to 210°C by using the control panel 14.

[0092] The thickness of the carbon fiber reinforced layer 2 of the inner liner forming pipe with the two layers of carbon fiber mesh is 6 μm.

[0093] Example 13

[0094] In this embodiment, a preparation method of a flexible hydrogen transport PE composite pipe is provided. On the basis of the embodiments 11 and 7, step 6 is specifically as shown in Figure 5As shown, the raw material particles 5 prepared in step 5 are added into the first extruder 8 to prepare the inner liner layer 1 forming pipe, and the inner liner layer 1 forming pipe extruded by the first extruder 8 is continuously pulled forward into the first winding machine 9, the rotating disc of the first winding machine 9 rotates at a uniform speed in a clockwise direction to wind the first layer of carbon fiber mesh, and then enters the second winding machine 11, the rotating disc of the second winding machine 11 rotates at a uniform speed in a counterclockwise direction to wind the second layer of carbon fiber mesh, the inner liner layer 1 forming pipe with the two layers of carbon fiber mesh is wound is pulled into the second extruder 12, raw material particles 5 are added into the feeding port of the second extruder 12, and the outer protective layer 3 is extruded by the second extruder 12 and wrapped on the surface of the carbon fiber mesh pipe, and finally the three-layer PE composite pipe 13, i.e., the flexible hydrogen transport PE composite pipe, is prepared after cooling.

[0095] As shown in Figure 6 step 6, the first layer of carbon fiber mesh and the second layer of carbon fiber mesh are both pretreated carbon fibers 10, and the two layers of carbon fiber mesh are wound into a mesh shape with an intersection angle θ of 50°, and the grid of the first layer of carbon fiber mesh and the second layer of carbon fiber mesh is in a diamond shape, and the distance d between every two carbon fibers of the grid is 2 cm; the I-V interval temperature of the first extruder 8 and the second extruder 12 is controlled to be 180℃ by using the control panel 14.

[0096] The carbon fiber reinforced layer 2 of the inner liner layer forming pipe with the two layers of carbon fiber mesh has a thickness of 4 μm.

[0097] The embodiment also provides a flexible hydrogen transport PE composite pipe, which is prepared by using the preparation method of the flexible hydrogen transport PE composite pipe of the embodiment, i.e., the three-layer PE composite pipe 13, as shown in FIGS. 7(a)-(b), which are both surface micro-morphologies, FIGS. 7(c)-(d) are both cross-sectional micro-morphologies, and FIGS. 7(e)-(f) are both tensile fracture micro-morphologies.

[0098] Compared with ordinary single-layer pipes, the three-layer PE composite pipe 13 of the embodiment is more compact, which can effectively reduce the leakage problem during hydrogen energy transportation, and in addition, each layer of the multi-layer pipe is provided with different performance functions, and can exhibit more excellent comprehensive performance in hydrogen transport work applications.

[0099] As known from the above content, the preparation method of the flexible hydrogen transport PE composite pipe of the embodiment uses co-extrusion molding to prepare the flexible hydrogen transport PE composite pipe with a three-layer structure, the compounded flame retardant of the inner liner layer 1 and the outer protective layer 3 has high flame retardant performance under the premise of a small amount of addition, and the added filler meets the environmental protection requirements. While improving the flame-retardant and anti-static performance, other additives are added to ensure performance improvement and also improve the mechanical properties of the PE composite pipe itself, and the reinforcing layer 2 uses carbon fiber winding to enhance the impact strength and tensile strength of the polyethylene material itself. The surface resistivity of the flexible hydrogen transport PE composite pipe of the embodiment is less than 1 x 10 6Ω, and the flame retardant performance is V-0 level, both of which meet and exceed the use standards of mining pipes, and the comprehensive mechanical properties are excellent. Table 1 shows the performance comparison of Example 13 and the comparative example.

[0100] Table 1 Performance comparison of flexible hydrogen transport PE composite pipes and other mining PE pipes

[0101]

[0102] As can be seen from Table 1, the flexible hydrogen transport PE composite pipe prepared by the preparation method of the flexible hydrogen transport PE composite pipe of the present invention has high flame retardant properties, can effectively prevent static electricity accumulation, and has the properties of being light weight and having good flexibility.

[0103] In summary, the preparation method of the flexible hydrogen transport PE composite pipe of the present invention abandons the problems of uneven dispersion of fillers caused by simple high-speed mixing of raw materials in the past, complex extrusion granulation process, high energy consumption, etc. The flame retardant raw materials of the present invention are ammonium polyphosphate and mullite powder. On the basis of low cost, their synergistic flame retardant properties in polyethylene composite materials are also deeply explored, and a more accurate compounding ratio is given. In terms of raw material preparation, the method of filler slurry coating is adopted to solve the problems of uneven dispersion of fillers prepared by raw material blending and extrusion granulation in polyethylene composite materials, low interface bonding, low production efficiency and high cost in the past. The filler can be evenly dispersed in the polyethylene matrix. At the same time, the nanofiller can be filled between the links or segments of the polymer material to play a role in densification. The prepared raw materials greatly improve the production efficiency. The prepared three-layer composite pipe has a tight interface bonding and excellent comprehensive mechanical properties.

[0104] In terms of structural design, the pipe structure designed by the present invention is composed of an outer protective layer, a reinforcement layer and an inner lining layer from the outside to the inside. The reinforcement layer is woven with carbon fiber. After the inner lining layer is extruded, it is woven on its surface using a braiding machine. The carbon fiber is embedded in the matrix of the inner lining layer and the outer protective layer, and its thickness is only a few microns. This not only effectively ensures good interface compatibility between the polyethylene matrix and the carbon fiber, but also adds antistatic fillers to the inner lining layer and the outer protective layer. Such a structural design can form a complete conductive grid between the carbon fiber mesh and the inner and outer pipes, which can effectively prevent the risks caused by static electricity accumulation. The pipe structure of the present invention not only brings excellent mechanical properties, but also makes the composite pipe have the characteristics of light weight and good flexibility. It can adapt to complex laying environments and is easy to transport and install, meeting the different application requirements of PE composite pipes in complex environments.

Claims

1. A method for preparing a flexible hydrogen transport PE composite pipe, characterized in that: Specifically, it includes: designing a three-layer flexible hydrogen transmission PE composite pipe, raw material selection, carbon fiber pretreatment, filler pulping, coating treatment and co-extrusion molding.

2. The method for preparing a flexible PE composite pipe for hydrogen transport according to claim 1, characterized in that: Please follow the steps below to implement: Step 1: Design a three-layer flexible hydrogen transport PE composite pipe comprising, from inside to outside, an inner lining layer (1), a reinforcement layer (2), and an outer protective layer (3); Step 2: Selecting raw materials. The inner lining layer (1) and the outer protective layer (3) are made of the same raw materials, including high-density polyethylene, antistatic agent, flame retardant and other additives. The reinforcing layer (2) is made of carbon fiber. Step 3, performing degumming and roughening treatment on the surface of the carbon fiber to obtain pretreated carbon fiber (10); Step 4: ball milling, dissolving, ultrasonically dispersing, and filtering part of the raw materials of the inner lining layer (1) and the outer protective layer (3) in sequence to obtain a slurry; Step 5: coating the other raw materials of the inner lining layer (1) and the outer protective layer (3) with the slurry obtained in step 4 to obtain raw material particles of the inner lining layer (1) and the outer protective layer (3); Step 6: Extrude the raw material particles obtained in step 5 to form an inner lining pipe, weave a carbon fiber mesh on the surface of the inner lining pipe with pretreated carbon fiber, and then extrude the raw material particles to form an outer protective layer (3) wrapped on the surface of the carbon fiber mesh pipe, and obtain a flexible hydrogen transport PE composite pipe after cooling.

3. The method for preparing a flexible PE composite pipe for hydrogen transportation according to claim 2, characterized in that: In step 2, the grade of high-density polyethylene is 8800J, the antistatic agent is conductive carbon black, the flame retardant includes a main flame retardant and an auxiliary flame retardant, the main flame retardant is ammonium polyphosphate, the auxiliary flame retardant is mullite powder, other additives include silane coupling agent KH560 and ethylene-octene copolymer, and the diameter of the carbon fiber is 0.5 to 1.5 μm; The polymerization degree of the ammonium polyphosphate is greater than 1000, and the particle size is 50 to 150 μm; the particle size of the mullite powder is 50 to 150 μm; and the conductive carbon black is used as an antistatic filler, and the particle size is 50 to 150 μm.

4. The method for preparing a flexible PE composite pipe for hydrogen transport according to claim 2, characterized in that: Specifically, the step 3 is as follows: first, the carbon fiber to be treated is placed in a heating furnace and burned at 480° C. for 60 minutes to burn out the organic binder on its surface; then, it is soaked in acetone for 60 minutes to dissolve the coke and clean the surface of the carbon fiber; then, it is washed with water for multiple times, dried, and set aside; then, the carbon fiber after debonding is placed in concentrated nitric acid and heated to 90° C. for coarsening for 60 minutes; then, it is neutralized to neutrality with a dilute NaOH solution; and then, after washing with water and drying, the pretreated carbon fiber (10) is obtained.

5. The method for preparing the flexible hydrogen transport PE composite pipe according to claim 3, characterized in that: Specifically, step 4 comprises mixing ammonium polyphosphate, mullite, and carbon black in a mass ratio of 4:1:5, and then placing the mixture in a ball mill for ball milling for 24 hours to obtain a mixed filler powder with a particle size of less than 1 μm. The prepared filler powder is added to a container with KH560 hydrolyzate as a solvent, wherein the mass ratio of the mixed filler powder to the KH560 hydrolyzate is 1:4, and ultrasonically dispersed for 2 hours to obtain a powder suspension. The mixture to be separated is poured into a Büchner funnel, and the vacuum pump is turned on to form a negative pressure in the funnel. The liquid in the mixture is extracted through the filter paper, and the solid slurry remains on the filter paper. The vacuum pump is turned off, and the filter paper is removed to finally obtain a filtered slurry, wherein the viscosity of the slurry is 500 to 3000 mPa·s.

6. The method for preparing a flexible PE composite pipe for hydrogen transportation according to claim 5, characterized in that: In step 4, during ball milling, the ball-to-material mass ratio is 15:1, the ball milling medium is steel balls or zirconia beads, and the ball milling medium, i.e., the grinding ball, has a diameter of 3 to 5 mm; The ultrasonic frequency of the ultrasonic dispersion in step 4 is 100 kHz.

7. The method for preparing a flexible PE composite pipe for hydrogen transportation according to claim 3, characterized in that: Specifically, step 5 comprises the following steps: first, opening the mixing chamber door of the fluidized bed coater, adding the slurry into the closed drum (4) of the fluidized bed coater, and then adding high-density polyethylene particles and ethylene-octene copolymer particles thereto to perform complex trajectory motion, wherein the mass ratio of the high-density polyethylene particles to the ethylene-octene copolymer particles is 10:1, and the mass ratio of the sum of the mass of the high-density polyethylene particles and the ethylene-octene copolymer particles to the slurry is 1:1 to 1:3, repeatedly stirring for 1 to 5 hours, and finally opening the chamber door to obtain a core-shell structure with the high-density polyethylene particles and the ethylene-octene copolymer particles as the core and the slurry as the shell, wherein the shell thickness is greater than or equal to 10 μm, and the volume ratio of the particles to the slurry is 1:1.2 to 1:1.5, thereby finally obtaining raw material particles of the inner lining layer (1) and the outer protective layer (3).

8. The method for preparing a flexible PE composite pipe for hydrogen transportation according to claim 3, characterized in that: Specifically, step 6 comprises adding the raw material particles prepared in step 5 into the first extruder (8) to prepare an inner lining formed pipe, the inner lining formed pipe extruded by the first extruder (8) continues to be pulled forward and enters the first winding machine (9), the turntable of the first winding machine (9) rotates clockwise at a constant speed to wind the first layer of carbon fiber mesh, and then enters the second winding machine (11), the turntable of the second winding machine (11) rotates counterclockwise at a constant speed to wind the second layer of carbon fiber mesh, the inner lining formed pipe wound with two layers of carbon fiber mesh enters the second extruder (12), the raw material particles are added to the feeding port of the second extruder (12), the second extruder extrude the outer protective layer (3) and wrap it on the surface of the carbon fiber mesh pipe, and finally, after cooling, a three-layer PE composite pipe, i.e., a flexible hydrogen transport PE composite pipe, is obtained.

9. The method for preparing a flexible PE composite pipe for hydrogen transportation according to claim 8, characterized in that: In step 6, the first layer of carbon fiber mesh and the second layer of carbon fiber mesh are both pretreated carbon fibers wound crosswise into a mesh, the winding angle θ is set to 45° to 55°, the grids of the first layer of carbon fiber mesh and the second layer of carbon fiber mesh are both diamond-shaped, and the spacing d between each two carbon fibers in the grid is 1 to 3 cm; The IV interval temperature of the first extruder (8) and the second extruder (12) is controlled at 160-210°C; The thickness of the carbon fiber reinforcement layer (2) of the inner lining forming pipe wound with two layers of carbon fiber mesh is 2-6 μm.

10. Flexible hydrogen transport PE composite pipe, characterized in that: The flexible hydrogen transport PE composite pipe is prepared by the preparation method of any one of claims 1 to 9.

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