Multi-layer composite pipe as well as preparation method and application thereof

Abstract

The invention discloses a multi-layer composite pipe as well as a preparation method and application thereof, and relates to the technical field of high polymer materials. The multi-layer composite pipe sequentially comprises a PEXB layer, a composite coating, a PTFE layer and a self-repairing layer from outside to inside, the composite coating comprises graphene, silver nanoparticles loaded on the surface of the graphene and a bio-based material crosslinked with the silver nanoparticles, and the self-repairing layer comprises polyurethane / epoxy resin microcapsules; the mass ratio of the graphene to the bio-based material to the silver nanoparticles in the composite coating is (85-89): 10: (1-5); the bio-based material is selected from one of carboxymethyl chitosan and sodium alginate. The multi-layer composite pipe has excellent chlorine resistance, antibacterial property, corrosion resistance and self-repairing function.

Description

Technical Field

[0001] The present invention relates to the technical field of polymer materials, and particularly relates to a multi-layer composite pipe and its preparation method and application. Background Art

[0002] Polyethylene (PE) pipes are widely used due to their corrosion resistance and easy processing, etc., but they are prone to oxidative degradation in a chlorine-containing environment. Traditional chlorine-resistant coatings lack antibacterial functions and have poor stability. In the prior art, although graphene coatings can improve chlorine resistance, they have a single function and rely on chemical exfoliation processes, with insufficient environmental friendliness. In addition, antibacterial functions usually require the addition of silver ions or organic antibacterial agents, which have problems such as easy migration and poor stability. Summary of the Invention

[0003] The purpose of the present invention is to overcome the deficiencies of the prior art and provide a multi-layer composite pipe and its preparation method and application. The multi-layer composite pipe of the present invention has excellent chlorine resistance, antibacterial property, corrosion resistance and self-healing function.

[0004] To achieve the above purpose, the technical solution adopted by the present invention is as follows: In the first aspect, the present invention provides a multi-layer composite pipe, which sequentially includes a cross-linked polyethylene (PEXB) layer, a composite coating, a polytetrafluoroethylene (PTFE) layer, and a self-healing layer from the outside to the inside. The components of the composite coating include graphene, silver nanoparticles (AgNPs) loaded on the surface of graphene, and a bio-based material cross-linked with the silver nanoparticles. The component of the self-healing layer is a polyurethane / epoxy resin microcapsule; The mass ratio of graphene, bio-based material, and silver nanoparticles in the composite coating is (85 - 89):10:(1 - 5); the bio-based material is selected from one of carboxymethyl chitosan and sodium alginate.

[0005] In the composite coating, the silver nanoparticles are loaded on the surface of graphene and cross-linked with carboxymethyl chitosan or sodium alginate. The carboxyl or sulfate group in carboxymethyl chitosan or sodium alginate can form a stable coordination with the silver nanoparticles, which is beneficial to improving the durability of the composite coating. The polyurethane / epoxy resin microcapsule is formed by polyurethane encapsulating epoxy resin. The microcapsule wall material (polyurethane) ruptures under stress, releasing the core material (epoxy resin), which undergoes a click chemical reaction with the free amino groups on the pipe surface to form a covalent cross-linked network to repair cracks and achieve the dynamic repair function.

[0006] The PEXB layer serves as a mechanical support, which can improve the mechanical strength and temperature resistance of the pipe. The composite coating provides antibacterial and chlorine resistance properties. The PTFE layer provides super corrosion resistance and a low friction coefficient. The self-healing layer can achieve the function of dynamically repairing microcracks. Therefore, through the mutual cooperation of each layer, the multi-layer composite pipe of the present invention has excellent chlorine resistance, antibacterial property, corrosion resistance and self-healing function.

[0007] By controlling the mass ratio of graphene, bio-based materials, and silver nanoparticles within the above range, the present invention is beneficial to improving the electrical conductivity and antibacterial properties of the composite coating.

[0008] It should be noted that through experimental verification of the present invention, other bio-based materials (such as chitosan, cellulose derivatives) lack carboxyl or sulfate groups and cannot stably coordinate with silver nanoparticles, resulting in a decline in the coating performance.

[0009] Preferably, the mass ratio of graphene, bio-based materials, and silver nanoparticles in the composite coating is 85:10:5.

[0010] Preferably, the thickness of the PEXB layer is 2 - 5 mm.

[0011] If the thickness of the PEXB layer is less than 2 mm, the creep resistance of the multi-layer composite pipe decreases, and the upper temperature limit also decreases; if the thickness of the PEXB layer is greater than 5 mm, the flexibility of the pipe is lost, and the bending radius increases. Therefore, by controlling the thickness of the PEXB layer within the range of 2 - 5 mm, it is beneficial to improve the heat resistance, creep resistance, and impact resistance of the multi-layer composite pipe.

[0012] More preferably, the thickness of the PEXB layer is any one or the range value of two of 2 mm, 3 mm, 4 mm, and 5 mm.

[0013] The cross-linked polyethylene of the present invention can be self-made by the silane grafting method as follows: Mix high-density polyethylene and a silane coupling agent evenly according to a mass ratio of (97 - 99):(1 - 3), and extrude and pelletize; then hydrolyze the pellets in a water bath at 80 - 90 °C for 20 - 24 hours to form silanol groups; place the hydrolyzed pellets in a cross-linking furnace, introduce nitrogen protection at 110 - 120 °C, and obtain cross-linked polyethylene after catalytic condensation reaction, with a cross-linking degree ≥ 75%.

[0014] Adopting the silane cross-linking process is beneficial to environmental protection and can avoid the decline in coating adhesion caused by silane residue, which is beneficial to improving the mechanical strength and heat resistance of the pipe.

[0015] Preferably, the molecular weight of the cross-linked polyethylene is 200 - 500 kDa, and the melt index is 0.3 - 1.5 g / 10min (ASTM D1238 - 23a). The molecular weight is measured according to the ASTM D6474 - 20 standard.

[0016] If the molecular weight of the cross-linked polyethylene is too low, it is easy to cause poor impact resistance of the pipe; if the molecular weight of the cross-linked polyethylene is too high, it makes processing difficult. Therefore, by controlling the molecular weight of the cross-linked polyethylene, the impact resistance of the multi-layer composite pipe can be improved.

[0017] Preferably, the thickness of the composite coating is 0.5 - 1.5 μm.

[0018] More preferably, the thickness of the composite coating is any one or the range value of two of 0.5 μm, 0.6 μm, 0.7 μm, 0.8 μm, 0.9 μm, 1.0 μm, 1.1 μm, 1.2 μm, 1.3 μm, 1.4 μm, 1.5 μm.

[0019] Preferably, the average particle size of the silver nanoparticles is 10 - 50 nm, and the specific surface area is 20 - 50 m 2 / g. By controlling the size of the silver nanoparticles, agglomeration of the silver nanoparticles can be avoided, which is beneficial to improving the antibacterial efficiency of the composite coating.

[0020] Preferably, the crosslinking degree of the bio - based material is 80 - 90%. If the crosslinking degree of the bio - based material exceeds 90%, the bio - based material will become brittle and the coating is prone to cracking. Therefore, controlling the crosslinking degree within 80 - 90% can balance durability and mechanical properties.

[0021] Preferably, the molecular weight of the carboxymethyl chitosan is 40 - 50 kDa, and the degree of deacetylation is ≥85%.

[0022] Preferably, the thickness of the PTFE layer is 50 - 200 μm.

[0023] If the thickness of the PTFE layer is less than 50 μm, the corrosion resistance decreases; if the thickness of the PTFE layer is greater than 200 μm, the fluid resistance increases and the friction coefficient increases. Therefore, by controlling the thickness of the PTFE layer within the range of 50 - 200 μm, it is beneficial to improve the corrosion resistance of the multi - layer composite pipe.

[0024] More preferably, the thickness of the PTFE layer is any one or the range value of two of 50 μm, 60 μm, 70 μm, 80 μm, 90 μm, 100 μm, 110 μm, 120 μm, 130 μm, 140 μm, 150 μm, 160 μm, 170 μm, 180 μm, 190 μm, 200 μm.

[0025] Preferably, the molecular weight of the PTFE is 1×10 6 ~5×10 6 Da, and the melt index is 0 - 0.1 g / 10min (ASTMD4894 - 19(2024)). High - molecular - weight PTFE has a high crystallinity and a reduced friction coefficient, resulting in an increase in the surface smoothness of the PTFE layer.

[0026] Preferably, the thickness of the self - healing layer is 5 - 10 μm (single - layer spraying thickness).

[0027] More preferably, the thickness of the self-healing layer is any one or the range value of two of 5μm, 6μm, 7μm, 8μm, 9μm, 10μm.

[0028] Preferably, the particle size of the polyurethane / epoxy resin microcapsules is 2-10μm.

[0029] If the particle size of the polyurethane / epoxy resin microcapsules is less than 2μm, the storage repair dose is insufficient and the repair efficiency is reduced; if the particle size is greater than 10μm, the surface roughness of the coating increases, the friction coefficient rises, and the surface smoothness decreases. Therefore, by controlling the particle size of the polyurethane / epoxy resin microcapsules, it is beneficial to improve the performance of the multi-layer composite pipe.

[0030] Preferably, the polyurethane / epoxy resin microcapsules include polyurethane / epoxy resin microcapsules A with a particle size of 2-5μm and polyurethane / epoxy resin microcapsules B with a particle size of 5-8μm. The mass ratio of the polyurethane / epoxy resin microcapsules A to the polyurethane / epoxy resin microcapsules B is (70-80):(20-30), preferably 70:30. The present invention adopts bimodal distribution polyurethane / epoxy resin microcapsules, enabling the multi-layer composite pipe to take into account both the repair efficiency and the surface smoothness.

[0031] Preferably, the rupture threshold of the polyurethane / epoxy resin microcapsules is 3-5 MPa.

[0032] If the rupture threshold of the polyurethane / epoxy resin microcapsules is greater than 5MPa, the microcapsules need to rupture under higher stress, resulting in the inability to repair microcracks in a timely manner and reducing the repair efficiency of the multi-layer composite pipe. If the rupture threshold of the polyurethane / epoxy resin microcapsules is lower than 3MPa, the microcapsules are easily mis-triggered due to mechanical vibration or slight stress during transportation or installation, resulting in premature release of the repair agent and reducing the repair efficiency. Therefore, the present invention first proposes the concept of "dynamic threshold matching". By precisely regulating the rupture threshold (3-5 MPa), it is ensured that the microcapsules are only triggered when real cracks appear, solving the contradiction between misresponse and delayed repair of self-healing materials.

[0033] Preferably, the molecular weight of the polyurethane is 5-10 kDa.

[0034] Preferably, the viscosity of the epoxy resin is 100-200 cP.

[0035] In the second aspect, the present invention also provides a method for preparing a multi-layer composite pipe, comprising the following steps: (1) Add silver nitrate solution and bio-based materials to the graphene oxide dispersion, irradiate under ultraviolet light, centrifuge and wash to obtain a graphene / AgNPs-bio-based dispersion; mix polyurethane and epoxy resin evenly, then add an emulsifier, emulsify and disperse in ethanol to obtain a microcapsule dispersion. (2) Spray the graphene / AgNPs-bio-based dispersion on the surface of the PEXB layer to obtain a composite coating, then spray the polytetrafluoroethylene dispersion on the surface of the composite coating, cure to obtain a PTFE layer, and finally spray the microcapsule dispersion on the surface of the PTFE layer, cure to obtain a self-healing layer, thus obtaining a multi-layer composite pipe.

[0036] Preferably, in the step (1), the purity of the graphene oxide is greater than 99%, the sheet thickness is 1 - 5 layers, the lateral size is 1 - 10 μm, and the specific surface area is 800 - 1200 m 2 / g. By controlling the size of the graphene oxide, it is beneficial to improve the uniformity of the composite coating, thereby improving the antibacterial performance and coating adhesion of the cross-linked polyethylene pipe.

[0037] It should be noted that the sheet thickness of the graphene oxide is 1 - 5 layers, the single-layer thickness is 0.34 nm, and the total thickness range is 0.34 - 1.7 nm.

[0038] The lateral size refers to the maximum diameter of the graphene oxide sheet in the two-dimensional plane, which is measured by atomic force microscopy (AFM).

[0039] Preferably, in the step (1), the concentration of the graphene oxide dispersion is 0.5 - 1.0 wt%.

[0040] Preferably, in the step (1), the emulsifier is sodium dodecyl sulfate, the concentration is 0.1 - 0.5 wt%, preferably 0.5 wt%.

[0041] Preferably, in the step (1), the wavelength of the ultraviolet light is 365 nm and the power is 30 - 50 W. When the wavelength of the ultraviolet light is 365 nm, the reduction efficiency of AgNO 3 is the highest.

[0042] If the power of the ultraviolet light is less than 30 W, the reduction of AgNO 3 is incomplete, the particle size of AgNPs increases, resulting in a decrease in the antibacterial rate of the composite coating. If the power of the ultraviolet light is greater than 50 W, a local thermal effect will occur, causing chain breakage of carboxymethyl chitosan or sodium alginate, resulting in a decrease in the adhesion of the composite coating.

[0043] More preferably, in the step (1), the ultraviolet light source is a high-pressure mercury lamp with a wavelength of 365 nm, a power of 50 W, and a vertical irradiation distance of 10 cm from the liquid surface. The reaction vessel is made of quartz to avoid ultraviolet absorption.

[0044] Preferably, in the step (1), the mass ratio of polyurethane to epoxy resin is 1:(1 - 4), preferably 1:3.

[0045] Preferably, in the step (2), electrospraying and pulsed laser irradiation are used to spray the graphene / AgNPs - bio - based dispersion liquid on the surface of the PEXB layer.

[0046] The present invention adopts the combination of electrospraying and pulsed laser irradiation, which can accurately control the cross - linking degree between silver nanoparticles and bio - based materials, realize uniform loading of the coating and interface strengthening, and avoid damage to the substrate by traditional high - temperature processes.

[0047] Preferably, the parameters of the electrospraying are: voltage 14 - 15 kv, flow rate 0.1 - 0.2 mL / min, and spraying distance 18 - 20 cm.

[0048] Preferably, the parameters of the pulsed laser irradiation are: wavelength 532 nm, energy density 1 - 1.5 J / cm 2 . By controlling the parameters of the pulsed laser irradiation, it is beneficial to promote the cross - linking between bio - based materials and silver nanoparticles.

[0049] Preferably, in the step (2), the concentration of the polytetrafluoroethylene dispersion liquid is 5 - 10 wt%, preferably 10 wt%.

[0050] In the third aspect, the present invention also provides an application of the multi - layer composite pipe in drinking water transportation and high - temperature and high - pressure fluid transportation.

[0051] Compared with the prior art, the beneficial effects of the present invention are as follows: (1) In the present invention, the PEXB layer provides high - strength support, which can improve the mechanical strength and heat resistance of the pipe. The composite coating provides antibacterial and chlorine - resistant properties. The PTFE layer provides super corrosion resistance and low friction coefficient. The self - repair layer can realize the function of dynamically repairing micro - cracks. Therefore, through the mutual cooperation of each layer, the multi - layer composite pipe of the present invention has excellent chlorine resistance, antibacterial property, corrosion resistance and self - repair function.

[0052] (2) For the first time, the present invention integrates PEXB, PTFE with self - healing function, breaking through the limitation of single function. Moreover, by setting the PTFE layer and optimizing the cross - linking process, the corrosion resistance and coating adhesion can be significantly improved. At the same time, it also breaks through the single chlorine - resistant function, innovatively integrating antibacterial and self - healing functions, and adopting bio - based materials and green processes. Furthermore, for the first time, the present invention combines pulsed laser interface strengthening with electro - spraying to solve the problems of adhesion and uniformity of the composite coating. BRIEF DESCRIPTION OF THE DRAWINGS

[0053] Figure 1 is a schematic structural diagram of the multi - layer composite pipe described in the present invention. 1 is the self - healing layer, 2 is the PTFE layer, 3 is the composite coating, and 4 is the PEXB layer. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0054] To better illustrate the purpose, technical solutions and advantages of the present invention, the present invention will be further described below in conjunction with specific embodiments, but the protection scope and implementation manners of the present invention are not limited thereto.

[0055] The materials, reagents, etc. used in the following embodiments are, unless otherwise specified, reagents and materials that can be obtained from commercial channels.

[0056] Example 1 The present invention discloses a multi - layer composite pipe, as Figure 1 shown, from the outside to the inside, it sequentially includes a PEXB layer 4, a composite coating 3, a PTFE layer 2, and a self - healing layer 1.

[0057] The thicknesses of the PEXB layer, the composite coating, the PTFE layer, and the self - healing layer are 2 mm, 1.5 μm, 100 μm, and 5 μm respectively.

[0058] The component of the PEXB layer is PEXB, the molecular weight of PEXB is 200 kDa, and the melt index is 1.5 g / 10 min (ASTM D1238 - 23a).

[0059] The preparation method of the PEXB is as follows: Mix high - density polyethylene and vinyltrimethoxysilane evenly at a mass ratio of 97:3, and extrude and pelletize; then hydrolyze the pellets in a 90 °C water bath for 24 hours to form silanol groups; place the hydrolyzed pellets in a cross - linking furnace, introduce nitrogen protection at 120 °C, and carry out a catalytic condensation reaction for 4 hours to obtain PEXB.

[0060] The components of the composite coating include graphene, silver nanoparticles loaded on the surface of graphene, and carboxymethyl chitosan cross - linked with silver nanoparticles. The mass ratio of graphene, carboxymethyl chitosan, and silver nanoparticles is 85:10:5; the average particle size of the silver nanoparticles is 50 nm, and the specific surface area is 20 m 2 / g; The molecular weight of the carboxymethyl chitosan is 50 kDa, and the degree of deacetylation is 85%; the crosslinking degree of the carboxymethyl chitosan is 80%.

[0061] The component of the PTFE layer is PTFE, and the molecular weight of PTFE is 1×10 6 Da, and the melt index is 0.1 g / 10 min (ASTM D4894-19(2024)).

[0062] The component of the self-healing layer is polyurethane / epoxy resin microcapsules, and the rupture threshold of the polyurethane / epoxy resin microcapsules is 5 MPa; the polyurethane / epoxy resin microcapsules include polyurethane / epoxy resin microcapsule A with a particle size of 2-5 μm and polyurethane / epoxy resin microcapsule B with a particle size of 5-8 μm, and the mass ratio of the polyurethane / epoxy resin microcapsule A to the polyurethane / epoxy resin microcapsule B is 70:30; The molecular weight of the polyurethane is 10 kDa, and the viscosity of the epoxy resin is 200 cP.

[0063] The present invention also discloses a preparation method of a multi-layer composite pipe, comprising the following steps: (1) Add graphene oxide to an acetic acid solution, and ultrasonically treat for 30 min to obtain a graphene oxide dispersion with a concentration of 0.5 wt%, then add a silver nitrate solution and carboxymethyl chitosan, and continuously irradiate with ultraviolet light for 30 min. The wavelength of the ultraviolet light is 365 nm, the power is 50 W, the vertical irradiation distance from the liquid surface is 10 cm, and the reaction vessel is made of quartz material; finally, centrifuge and wash 3 times to obtain a graphene / AgNPs-CS dispersion; wherein, the purity of the graphene oxide is greater than 99%, the number of lamellar layers is 5, the lateral dimension is 10 μm, and the specific surface area is 800 m 2 / g; Adopt the interfacial polymerization method, mix polyurethane and epoxy resin evenly at 50 °C according to a mass ratio of 1:3, then add sodium dodecyl sulfate with a concentration of 0.5 wt%, emulsify and disperse in ethanol to obtain a microcapsule dispersion.

[0064] (2) Spray the graphene / AgNPs-CS dispersion on the surface of the PEXB layer by electrospraying and pulsed laser irradiation to obtain a composite coating. The parameters of electrospraying are: voltage 15 kv, flow rate 0.2 mL / min, spraying distance 20 cm; the parameters of pulsed laser irradiation are: wavelength 532 nm, energy density 1.5 J / cm 2 ; Then spray a 10 wt% polytetrafluoroethylene dispersion on the surface of the composite coating and cure at room temperature for 24 h to obtain a PTFE layer; Finally, the microcapsule dispersion is sprayed on the surface of the PTFE layer and cured at room temperature for 12 h to obtain a self-healing layer, thus obtaining a multi-layer composite pipe.

[0065] Example 2 The present invention discloses a multi-layer composite pipe, as Figure 1 shown, which sequentially includes a PEXB layer 4, a composite coating 3, a PTFE layer 2, and a self-healing layer 1 from outside to inside.

[0066] The thicknesses of the PEXB layer, the composite coating, the PTFE layer, and the self-healing layer are 5 mm, 0.5 μm, 200 μm, and 10 μm respectively.

[0067] The component of the PEXB layer is PEXB, the molecular weight of PEXB is 500 kDa, and the melt index is 0.3 g / 10 min (ASTM D1238-23a). The preparation method of the PEXB is the same as that in Example 1.

[0068] The components of the composite coating include graphene, silver nanoparticles loaded on the surface of graphene, and carboxymethyl chitosan crosslinked with the silver nanoparticles. The mass ratio of graphene, carboxymethyl chitosan, and silver nanoparticles is 85:10:5; the average particle size of the silver nanoparticles is 50 nm, and the specific surface area is 20 m 2 / g; the molecular weight of the carboxymethyl chitosan is 50 kDa, and the degree of deacetylation is 85%; the crosslinking degree of the carboxymethyl chitosan is 80%.

[0069] The component of the PTFE layer is PTFE, the molecular weight of PTFE is 1×10 6 Da, and the melt index is 0.1 g / 10 min (ASTM D4894-19(2024)).

[0070] The component of the self-healing layer is polyurethane / epoxy resin microcapsules, and the rupture threshold of the polyurethane / epoxy resin microcapsules is 5 MPa; the polyurethane / epoxy resin microcapsules include polyurethane / epoxy resin microcapsules A with a particle size of 2-5 μm and polyurethane / epoxy resin microcapsules B with a particle size of 5-8 μm, and the mass ratio of the polyurethane / epoxy resin microcapsules A and the polyurethane / epoxy resin microcapsules B is 70:30; The molecular weight of the polyurethane is 10 kDa, and the viscosity of the epoxy resin is 200 cP.

[0071] The present invention also discloses a preparation method of a multi-layer composite pipe, which includes the following steps: (1) Add graphene oxide to acetic acid solution and ultrasonically treat it for 30 min to obtain a graphene oxide dispersion with a concentration of 1.0 wt%. Then add silver nitrate solution and carboxymethyl chitosan, and continuously irradiate it under ultraviolet light for 30 min. The wavelength of the ultraviolet light is 365 nm, the power is 50 W, and the vertical irradiation distance from the liquid surface is 10 cm. The reaction vessel is made of quartz material; finally, centrifuge and wash it 3 times to obtain a graphene / AgNPs-CS dispersion; among them, the purity of graphene oxide is greater than 99%, the lamellar thickness is 5 layers, the lateral size is 10 μm, and the specific surface area is 800 m 2 / g; Using the interfacial polymerization method, mix polyurethane and epoxy resin evenly at 50 °C according to a mass ratio of 1:3, then add sodium dodecyl sulfate with a concentration of 0.5 wt%, emulsify and disperse it in ethanol to obtain a microcapsule dispersion.

[0072] (2) Spray the graphene / AgNPs-CS dispersion on the surface of the PEXB layer by electrospraying and pulsed laser irradiation to obtain a composite coating. The parameters of electrospraying are: voltage 15 kv, flow rate 0.2 mL / min, spraying distance 20 cm; the parameters of pulsed laser irradiation are: wavelength 532 nm, energy density 1.5 J / cm 2 ; Then spray a polytetrafluoroethylene dispersion with a concentration of 10 wt% on the surface of the composite coating and cure it at room temperature for 24 h to obtain a PTFE layer; Finally, spray the microcapsule dispersion on the surface of the PTFE layer and cure it at room temperature for 12 h to obtain a self-healing layer, that is, a multi-layer composite pipe is obtained.

[0073] Example 3 A multi-layer composite pipe, different from Example 1 in that the mass ratio of graphene, carboxymethyl chitosan, and silver nanoparticles in the composite coating is 89:10:1.

[0074] Example 4 A multi-layer composite pipe, different from Example 1 in that the mass ratio of graphene, carboxymethyl chitosan, and silver nanoparticles in the composite coating is 87:10:3.

[0075] Example 5 A multi-layer composite pipe, different from Example 1 in that the crosslinking degree of carboxymethyl chitosan in the composite coating is 85%.

[0076] Example 6 A multi-layer composite pipe, different from Example 1 in that the crosslinking degree of carboxymethyl chitosan in the composite coating is 90%.

[0077] Example 7 A multi-layer composite pipe, which is different from that of Example 1 in that sodium alginate of equal mass is used to replace carboxymethyl chitosan.

[0078] Example 8 A multi-layer composite pipe, which is different from that of Example 1 in that the mass ratio of graphene, carboxymethyl chitosan, and silver nanoparticles in the composite coating is 88:10:2.

[0079] Example 9 A multi-layer composite pipe, which is different from that of Example 1 in that the mass ratio of graphene, carboxymethyl chitosan, and silver nanoparticles in the composite coating is 86:10:4.

[0080] Example 10 A multi-layer composite pipe, which is different from that of Example 1 in that the rupture threshold of the polyurethane / epoxy resin microcapsule is 3 MPa.

[0081] Example 11 A multi-layer composite pipe, which is different from that of Example 1 in that the thickness of the PTFE layer is different from that of Example 1, that is, the thicknesses of the PEXB layer, the composite coating, the PTFE layer, and the self-healing layer are 2 mm, 1.5 μm, 50 μm, and 5 μm, respectively.

[0082] Example 12 A multi-layer composite pipe, which is different from that of Example 1 in that the thickness of the PTFE layer is different from that of Example 1, that is, the thicknesses of the PEXB layer, the composite coating, the PTFE layer, and the self-healing layer are 2 mm, 1.5 μm, 200 μm, and 5 μm, respectively.

[0083] Comparative Example 1 A multi-layer composite pipe, which is different from that of Example 1 in that polyethylene of equal mass is used to replace cross-linked polyethylene, that is, the PEXB layer is replaced with a polyethylene layer.

[0084] Comparative Example 2 A multi-layer composite pipe, which is different from that of Example 1 in that starch of equal mass is used to replace carboxymethyl chitosan.

[0085] Comparative Example 3 A multi-layer composite pipe, which is different from that of Example 1 in that the mass ratio of graphene, carboxymethyl chitosan, and silver nanoparticles in the composite coating is 70:20:10.

[0086] Comparative Example 4 A multi-layer composite pipe, which is different from that of Example 1 in that the mass ratio of graphene, carboxymethyl chitosan, and silver nanoparticles in the composite coating is 95.5:4:0.5.

[0087] Comparative Example 5 A method for preparing a multi-layer composite pipe, which is different from Example 1 in that step (2) is different: first, a polytetrafluoroethylene dispersion with a concentration of 10 wt% is sprayed on the surface of the PEXB layer and cured at room temperature for 24 h to obtain a PTFE layer; Then, the graphene / AgNPs-CS dispersion is sprayed on the surface of the PTFE layer by electrospraying and pulsed laser irradiation to obtain a composite coating. The parameters of electrospraying are: voltage 15 kv, flow rate 0.2 mL / min, spraying distance 20 cm; the parameters of pulsed laser irradiation are: wavelength 532 nm, energy density 1.5 J / cm 2 ; Finally, the microcapsule dispersion is sprayed on the surface of the composite coating and cured at room temperature for 12 h to obtain a self-healing layer, thus obtaining a multi-layer composite pipe.

[0088] Performance testing 1. Antibacterial rate (Escherichia coli): Obtained by testing according to the GB / T 31402-2015 standard.

[0089] 2. Chlorine oxidation induction period: Obtained by testing according to the ASTM F2023-21 standard, and the test is carried out at 25 °C and a Cl - concentration of 15 mg / L.

[0090] 3. Microcrack repair efficiency: Hydraulic cycle test (5 MPa), and the test principle is: under a stress of 5 MPa, microcracks are generated on the surface of the pipe, the polyurethane microcapsules rupture, and the released epoxy resin reacts with the free amino groups on the surface of the pipe through a click reaction (such as a thiol-ene reaction) to form a covalent cross-linking network within 30 seconds to fill the cracks. The crack closure rate measured after the hydraulic cycle test is the microcrack repair efficiency.

[0091] 4. Friction coefficient: Obtained by testing according to the ASTM D1894-24 standard.

[0092] 5. Corrosion resistance: Tested according to the ASTM D543-21 standard. The pipe is immersed in a 10% HCl solution (70 °C) for 240 hours, and a mass loss rate ≤ 0.5% is considered qualified.

[0093] 6. Adhesion grade: Tested according to the ASTM D903-98(2021) standard, and tested by the cross-cut method (spacing 1 mm), and the adhesion grade ≥ 4B (no peeling).

[0094] 7. Elongation at break: Obtained by testing according to the ASTM D638-22 standard.

[0095] The above test results are shown in Table 1.

[0096] Table 1 Note: All data in Table 1 are the average value ± standard deviation of three independent experiments (such as antibacterial rate 99.8% ± 0.2%).

[0097] As can be seen from Table 1, the multi-layer composite pipe described in the present invention has excellent chlorine resistance, antibacterial property, corrosion resistance and self-healing function.

[0098] From Examples 1, 3, 4, 8, and 9, it can be seen that by controlling the mass ratio of graphene, carboxymethyl chitosan, and silver nanoparticles to be (85-89):10:(1-5), the antibacterial function failure of the composite coating can be avoided, and the problem of agglomeration of silver nanoparticles can be inhibited, breaking through the technical bottleneck of silver ion migration in traditional coatings, making the composite coating have excellent comprehensive performance.

[0099] From Examples 1, 5, and 6, it can be seen that when the crosslinking degree of carboxymethyl chitosan is controlled at 80-90%, not only the stability and repair efficiency of the composite coating can be improved, but also the composite coating has both flexibility and durability. The adhesion grade in Example 6 is still 5B, but the repair efficiency decreases slightly because the increased crosslinking degree makes it more difficult for microcapsules to embed.

[0100] Comparing Example 7 with Example 1, it can be obtained that the chlorine oxidation induction period in Example 7 is slightly lower because the coordination ability of the sulfate group of sodium alginate is slightly weaker than that of carboxymethyl chitosan.

[0101] From Examples 1 and 10, it can be seen that when the rupture threshold of polyurethane / epoxy resin microcapsules is 3 MPa or 5 MPa, the microcrack repair efficiency is greater than 85%, indicating that by controlling the rupture threshold of polyurethane / epoxy resin microcapsules to be 3-5 MPa, it is beneficial to improve the repair efficiency of the self-healing layer.

[0102] Comparing Examples 11 and 12 with Example 1, it can be obtained that when the thickness of the PTFE layer increases from 50 μm to 200 μm, the friction coefficient slightly increases (0.02 → 0.03), which is because the microprotrusions on the coating surface increase, resulting in an increase in fluid resistance. Therefore, by controlling the thickness of the PTFE layer to be 50-200 μm, the corrosion resistance and fluid transmission efficiency can be balanced, improving the performance of the pipe.

[0103] Comparing Comparative Example 1 with Example 1, it can be obtained that using polyethylene to replace crosslinked polyethylene will reduce the antibacterial property, corrosion resistance and self-healing function of the multi-layer composite pipe, because ordinary polyethylene has a low crosslinking degree and low heat resistance, resulting in a decrease in the performance of the pipe. While the present invention uses irradiated crosslinked polyethylene with a crosslinking degree ≥ 75%, which is beneficial to improving the antibacterial property, corrosion resistance and self-healing function of the pipe.

[0104] It can be seen from the comparison between Comparative Example 2 and Example 1 that when starch is used to replace carboxymethyl chitosan, the performance of the multi-layer composite pipe is affected. This is because starch does not contain carboxyl or sulfate groups and cannot form a stable coordination with silver nanoparticles, resulting in easy migration of silver ions and a decrease in the antibacterial performance of the pipe. Moreover, since starch is prone to moisture absorption, it easily accelerates the degradation of the coating, shortening the chlorine oxidation induction period. In contrast, in the present invention, silver nanoparticles are loaded on the surface of graphene and crosslinked with carboxymethyl chitosan. The carboxyl groups in carboxymethyl chitosan can form a stable coordination with silver nanoparticles, improving the performance of the composite coating.

[0105] It can be seen from the comparison between Comparative Examples 3-4 and Example 1 that when the content of silver nanoparticles is less than 1%, the antibacterial efficiency decreases significantly. When the content of silver nanoparticles is greater than 5%, they are prone to agglomeration, leading to a decrease in the performance of the pipe. Therefore, by controlling the mass ratio of graphene, carboxymethyl chitosan, and silver nanoparticles to be (85-89):10:(1-5), it is beneficial to improve the performance of the composite coating.

[0106] It can be seen from the comparison between Comparative Example 5 and Example 1 that if the positions of the composite coating and the PTFE layer are interchanged, due to the low surface energy of the PTFE layer, it hinders the contact between the composite coating and the fluid medium, and silver nanoparticles cannot be released into the medium, resulting in a decrease in the antibacterial function. At the same time, the interfacial adhesion between the composite coating and the PTFE layer decreases, accelerating the peeling of the coating, thereby reducing the chlorine resistance and antibacterial performance of the multi-layer composite pipe. Therefore, in the multi-layer composite pipe of the present invention, a PEXB layer, a composite coating, a PTFE layer, and a self-healing layer are sequentially arranged from the outside to the inside. The PTFE layer is in direct contact with the corrosive medium, and the self-healing layer is placed in the innermost layer of the pipe to trigger repair at the initial stage of cracks, preventing the medium from penetrating into the intermediate layer and enabling the multi-layer composite pipe to achieve the best performance.

[0107] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit the protection scope of the present invention. Although the present invention has been described in detail with reference to the preferred embodiments, those of ordinary skill in the art should understand that the technical solutions of the present invention can be modified or equivalently replaced without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A multi-layer composite pipe, characterized in that: From the outside to the inside, it includes a PEXB layer, a composite coating, a PTFE layer, and a self-repairing layer. The composite coating includes graphene, silver nanoparticles loaded on the surface of the graphene, and a bio-based material cross-linked with the silver nanoparticles. The self-repairing layer includes polyurethane / epoxy resin microcapsules. The mass ratio of graphene, bio-based material and silver nanoparticles in the composite coating is (85-89):10:(1-5); the bio-based material is selected from one of carboxymethyl chitosan and sodium alginate.

2. The multi-layer composite pipe according to claim 1, characterized in that: The thickness of the PEXB layer is 2-5 mm; And / or, the thickness of the composite coating is 0.5-1.5 μm; And / or, the thickness of the PTFE layer is 50-200 μm; And / or, the thickness of the self-repairing layer is 5-10 μm.

3. The multi-layer composite pipe according to claim 1, characterized in that: The bio-based material has a cross-linking degree of 80-90%.

4. The multi-layer composite pipe according to claim 1, characterized in that: The silver nanoparticles have an average particle size of 10-50 nm and a specific surface area of ​​20-50 m 2 / g.

5. The multi-layer composite pipe according to claim 1, characterized in that: The molecular weight of the PEXB is 200-500 kDa and the melt index is 0.3-1.5 g / 10min; and / or, The molecular weight of the PTFE is 1×10 6 ~5×10 6 Da, melt index is 0-0.1 g / 10min.

6. The multi-layer composite pipe according to claim 1, characterized in that: The particle size of the polyurethane / epoxy resin microcapsules is 2-10 μm; and / or, The rupture threshold of the polyurethane / epoxy resin microcapsule is 3-5 MPa.

7. The multi-layer composite pipe according to claim 6, characterized in that: The polyurethane / epoxy resin microcapsules include polyurethane / epoxy resin microcapsules A with a particle size of 2-5 μm and polyurethane / epoxy resin microcapsules B with a particle size of 5-8 μm, and the mass ratio of the polyurethane / epoxy resin microcapsules A to the polyurethane / epoxy resin microcapsules B is (70-80):(20-30).

8. The method for preparing a multi-layer composite pipe according to any one of claims 1 to 7, characterized in that: The following steps are involved: (1) adding silver nitrate solution and bio-based materials to a graphene oxide dispersion, irradiating the dispersion under ultraviolet light, and washing the dispersion by centrifugation to obtain a graphene / AgNPs-bio-based dispersion; mixing polyurethane and epoxy resin evenly, and then adding an emulsifier, emulsifying and dispersing the mixture in ethanol to obtain a microcapsule dispersion; (2) Spraying the graphene / AgNPs-biobased dispersion on the surface of the PEXB layer to obtain a composite coating, then spraying the polytetrafluoroethylene dispersion on the surface of the composite coating, and obtaining a PTFE layer after curing, and finally spraying the microcapsule dispersion on the surface of the PTFE layer, and obtaining a self-healing layer after curing, thereby obtaining a multilayer composite pipe.

9. The method for preparing a multi-layer composite pipe according to claim 8, characterized in that: In step (1), the wavelength of the ultraviolet light is 365 nm and the power is 30-50 W; and / or, In the step (2), the graphene / AgNPs-biobased dispersion is sprayed on the surface of the PEXB layer by electrospraying and pulsed laser irradiation.

10. Application of the multilayer composite pipe according to any one of claims 1 to 7 in drinking water transportation and high-temperature and high-pressure fluid transportation.

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