A polyethylene composite material for hot-melt butt-jointed polyethylene structured-wall double-flat-winding pipe and a preparation method thereof

Abstract

The application discloses a kind of polyethylene composite materials for hot-melt butt joint polyethylene structural wall double-flat winding pipe, belong to high polymer material technical field. Including following component: polyethylene resin 100 parts;Carbon black master batch 2~4 parts;Polydopamine coated zinc oxide nanowire 0.5~2 parts;Phase change microcapsule 0.2~1 parts;The phase change microcapsule has with phenolic resin as shell, with n-hexadecane as core material structure.The polyethylene structural wall double-flat winding pipe prepared by the synergistic effect of polydopamine coated zinc oxide nanowire and phase change microcapsule in the application is not easy to produce bubble and pore when port hot-melt butt joint, can also shorten the pipe length that needs to be cut off, reduce cooling demoulding time, improve joint tensile strength and ring stiffness, improve hot-melt welding joint quality.

Description

Technical Field

[0001] This invention relates to the field of polymer materials technology, and more specifically, to a polyethylene composite material for double-flat spiral wound pipes with heat-melt butt-welded polyethylene structural walls, its preparation method, and its application. Background Technology

[0002] Polyethylene structural wall double-flat spiral wound pipe is a type A structural wall pipe in Part 2 of the national standard GB / T19472.2-2004 Buried Polyethylene (PE) Structural Wall Piping System.

[0003] High-density polyethylene (HDPE) spiral wound structured wall pipes have achieved a breakthrough in hot-winding molding technology, maintaining ring stiffness performance standards while optimizing both lightweight construction and economic efficiency. Through three-dimensional reinforced structural design and fusion joint quality control, this technology demonstrates superior performance in key areas such as resistance to geological subsidence, ocean current disturbance, and chemical corrosion, making it particularly suitable for marine water intake and drainage projects with high standards for material durability and life-cycle cost. Currently, this technology system has become a core solution for large-diameter pipeline projects in fields such as cross-sea passages, island and reef development, and coastal nuclear power plants.

[0004] Conventional high-density polyethylene (HDPE) spiral wound pipes typically employ an electrofusion socket connection with an inner solid wall and outer ribbed pipe structure. For example, existing technology discloses a stepped socket electrofusion connection for Krah pipes, where the electrofusion socket and electrofusion spigot are arranged in a stepped structure, resulting in a thick and reliable wall at the interface, suitable for curved submerged pipe applications in marine engineering and long-haul offshore pipeline transportation. This connection method involves completing the electrofusion socket connection on land before submerging to the seabed. However, under the combined conditions of dynamic ocean loads, continuous ocean current impacts, and long-term tidal effects, the structural adaptability and connection reliability of electrofusion socket connections become problematic.

[0005] Using hot-melt butt welding at the ends of ultra-large diameter spiral wound pipes can improve connection strength and durability. High-density polyethylene (HDPE) spiral wound structured pipes are formed by hot-winding on a steel roller mold heated to a predetermined temperature. Both the pipe body and the hot-melt butt welded ends require multiple layers of film winding; the thicker the pipe wall, the more winding layers are needed. Since HDPE resin naturally contains some residual moisture, and low molecular weight segments and unpolymerized monomers also volatilize, especially when the relative humidity is high, a condensation film will form on the pipe surface. In multi-layer winding, residual moisture and volatiles at the film overlap cannot escape, leading to internal air bubbles inside the pipe body and at the hot-melt weld at the pipe ends. If these moisture and volatiles remain in the weld seam, during subsequent cooling and curing, the decreasing temperature leads to a decrease in gas solubility, causing these residual gases to precipitate and form bubbles (such as...). Figure 1As shown in (a)). Bubbles, as a common defect in welds, can seriously affect weld quality, specifically by reducing weld strength and sealing performance. The presence of bubbles disrupts the continuity and density of the weld, making it prone to stress concentration points under external forces, leading to weld cracking. Simultaneously, the presence of bubbles prevents the weld from forming a completely sealed structure, affecting its sealing performance.

[0006] Meanwhile, during the winding process, the melt exhibits a unique heat exchange environment: one side is in close contact with the metal of the steel roller mold, and due to the high thermal conductivity of metal, heat can be conducted rapidly; while the other side is directly exposed to the air, whose thermal conductivity is extremely low, resulting in very slow heat transfer. This significant difference in thermal conductivity leads to a large temperature difference between the two sides of the melt, and the inner and outer walls of the tube, as well as the thick-walled welded tube section, experience severe temperature unevenness during the cooling process, resulting in high concentration of internal stress and ultimately the formation of pores (such as...). Figure 1 (as shown in (b)) and delamination are among the defects. These defects not only seriously affect the quality and performance of the pipes, but also reduce the strength of the hot-melt butt joint, threatening the safety and stability of the project.

[0007] Furthermore, in the winding process, uneven melt solidification shrinkage and unstable tension control during winding lead to a large shrinkage rate at the solid wall end and a tendency to produce a large end face taper (e.g., Figure 1 As shown in (c), secondary processing is required to cut off the tapered part of the end face. The length of pipe that needs to be cut off from one end face reaches 20mm. Summary of the Invention

[0008] To address the technical problems of bubbles, pores, and large end-face tapers that easily occur during the hot-melt welding of polyethylene structural wall double-flat spiral pipes, resulting in a long length of pipe that needs to be cut off, this invention provides a polyethylene composite material for hot-melt weldable polyethylene structural wall double-flat spiral pipes. Through the synergistic effect of polydopamine-coated zinc oxide nanowires and phase change microcapsules, the prepared polyethylene structural wall double-flat spiral pipe is less prone to generating bubbles and pores during the hot-melt welding of the ends, and can also shorten the length of pipe that needs to be cut off.

[0009] Another objective of this invention is to provide a double-flat spiral wound pipe with a thermomeltable butt-welded polyethylene structural wall.

[0010] Another objective of this invention is to provide an application of a double-flat spiral wound pipe with a thermomeltable butt-welded polyethylene structural wall.

[0011] The above-mentioned objective of this invention is achieved through the following technical solution: A polyethylene composite material for double-flat spiral wound pipes with heat-melt butt-welded polyethylene structural walls, comprising the following components by weight: 100 parts of polyethylene resin; 2-4 parts carbon black masterbatch; Polydopamine-coated zinc oxide nanowires, 0.5-2 parts; Phase change microcapsules, 0.2-1 part; The phase change microcapsules have a structure with phenolic resin as the outer shell and n-hexadecane as the core material.

[0012] The polyethylene resin is a high-density polyethylene resin.

[0013] Zinc oxide nanowires possess high thermal conductivity. Polydopamine can increase the surface activity of zinc oxide nanowires. After being coated with polydopamine, zinc oxide nanowires can be uniformly dispersed in polyethylene resin, constructing continuous and interconnected thermally conductive pathways within the resin. This also reduces the interfacial thermal resistance between the zinc oxide nanowires and polyethylene resin, ensuring even heat conduction, improving cooling efficiency, and shortening demolding time. Furthermore, the high thermal conductivity and dispersibility of polydopamine-coated zinc oxide nanowires ensure synchronized radial and axial temperature fields in the pipe, reducing internal stress defects and preventing porosity.

[0014] The phase change microcapsules of this invention can serve as nano-connectors anchored within a polydopamine-coated zinc oxide nanowire network. The microcapsules utilize phenolic resin as the outer shell, with molecules containing numerous phenolic hydroxyl and methylene groups. The terminal amino groups in the polydopamine-coated zinc oxide nanowires exhibit high reactivity. Under high-temperature conditions, the phenolic hydroxyl groups of the phenolic resin undergo dehydration condensation with the terminal amino groups in the polydopamine-coated zinc oxide nanowires, while the methylene groups also react chemically with the active sites on the polyethylene chains, resulting in in-situ cross-linking. Within a short time, CN,COC covalent bonds are formed. These CN,COC covalent bonds tightly connect the polydopamine-coated zinc oxide nanowires and polyethylene chains together through chemical bonds. Due to the higher binding energy and stability of chemical bonds, these covalent bonds can more effectively transfer and disperse stress under external forces, preventing relative sliding or separation between materials and thus resulting in a stronger bond. High chemical bonding energy and strong stability enable more effective stress transfer and dispersion, preventing relative sliding or separation of materials and enhancing the bonding performance between layers, tensile strength of seams, and butt joint strength. The cross-linking and curing of phenolic resin forms hard nodes that permanently anchor the three-dimensional network of polydopamine-coated zinc oxide nanowires. This complements the chemical stability and heat resistance of polyethylene, enhancing local strength, improving ring stiffness and resistance to circumferential deformation, making it suitable for applications such as pipelines that require withstanding internal and external pressures.

[0015] The phase change microcapsule of this invention is a self-driven micro-explosion phase change microcapsule. The core material of the phase change microcapsule, n-hexadecane, has a melting point of 18.2°C. During the tube body forming and welding process, the bonding layer between the tube body and the end film, or the end face of the heat-fused tube material, is heated to above 58°C. Therefore, n-hexadecane will rapidly vaporize to form high-pressure gas. When the internal gas pressure exceeds the critical pressure that the phenolic resin shell can withstand, local rupture will occur at the weak points of the phenolic resin shell. After the phenolic resin shell ruptures, n-hexadecane will escape from the low-pressure discontinuities in the structure caused by microcracks or interface defects present in the film during the winding and overlapping process. This will carry away residual moisture and volatiles from the material welding process, preventing these impurities from forming bubbles during the cooling and solidification of the weld joint, thus improving the quality and reliability of the weld joint.

[0016] Even if there is unvaporized hexadecane, it can cool and solidify to form a flexible micro-buffer pad. When the pipeline is subjected to local impact or vibration, it absorbs deformation energy, alleviates stress concentration caused by external impact, prevents pipeline cracking, and thus ensures reliable operation of the pipeline under complex working conditions.

[0017] This invention precisely controls the coefficient of thermal expansion of HDPE pipes through a composite modification system of polydopamine-coated zinc oxide nanowires and phase change microcapsules, achieving synergistic shrinkage of the inner and outer walls during cooling. The interfacial bonding effect of polydopamine enhances the compatibility between the filler and the resin matrix, eliminating uneven shrinkage caused by modulus differences. Zinc oxide nanowires, by introducing micro-nano structures, restrict molecular chain movement, reducing the material's coefficient of thermal expansion. The hexadecane phase change microcapsules utilize their vaporization endothermic properties to alleviate localized temperature differences during cooling and balance the shrinkage rate. This invention addresses the industry challenge of large shrinkage rates at the solid wall ends and the resulting end-face taper requiring secondary processing and cutting in the winding molding process.

[0018] Furthermore, the high thermal conductivity of polydopamine-coated zinc oxide nanowires significantly reduces heat accumulation within the material, mitigating thermal aging damage to the resin matrix caused by high temperatures. The polydopamine molecule is rich in catechol groups, which possess excellent free radical scavenging capabilities. By providing active hydrogen atoms, these groups effectively terminate the free radical chain reaction generated during polyethylene oxidation, thereby delaying the onset of oxidative degradation and directly extending the material's oxidation induction period. The phase change endothermic effect of the phase change microcapsules precisely regulates the local temperature field within the material, preventing localized overheating from damaging the polydopamine coating and zinc oxide nanowire structure, thus maintaining their antioxidant activity for a long time and further enhancing the material's thermal stability and service life.

[0019] Preferably, the polydopamine-coated zinc oxide nanowires and the phase change microcapsules are added in the form of masterbatch, and the carrier resin of the masterbatch is polyethylene resin.

[0020] Preferably, the preparation method of the masterbatch includes the following steps: mixing the polydopamine-coated zinc oxide nanowires, the phase change microcapsules, the polyethylene resin and antioxidant, and then feeding them into a single-screw extruder for extrusion and granulation to obtain the masterbatch; wherein the mixing temperature is 160-180℃ and the mixing time is 10-20 min.

[0021] The addition of the polydopamine-coated zinc oxide nanowires and the phase change microcapsules in masterbatch form facilitates their uniform dispersion in the composite material. During masterbatch preparation, the mixing time is short, and heat has not yet been fully conducted to the microcapsule core, preventing the core material from responding prematurely and thus preventing premature rupture of the phase change microcapsules.

[0022] Preferably, the preparation method of the polydopamine-coated modified zinc oxide nanowires includes the following steps: mixing and stirring a tris(hydroxymethyl)aminomethane hydrochloride buffer solution containing dopamine hydrochloride with an anhydrous ethanol suspension of zinc oxide nanowires to obtain polydopamine-coated modified zinc oxide nanowires; wherein, the mass ratio of dopamine hydrochloride to zinc oxide nanowires is (0.1~0.5):1.

[0023] The method for preparing polydopamine-coated modified zinc oxide nanowires utilizes the self-polymerization properties of dopamine to form a polydopamine coating on the surface of zinc oxide nanowires.

[0024] In a specific embodiment, the preparation method of the polydopamine-coated modified zinc oxide nanowires includes the following steps: Zinc oxide nanowires are ultrasonically dispersed in anhydrous ethanol to obtain an anhydrous ethanol suspension of zinc oxide nanowires. Tris(hydroxymethyl)aminomethane is dissolved in water, and hydrochloric acid is added to adjust the pH to 8-9 to obtain a tris-HCl buffer solution. Dopamine hydrochloride is added to the tris-HCl buffer solution, and then poured into the anhydrous ethanol suspension of zinc oxide nanowires. The mixture is stirred for 4-20 hours, and after drying, polydopamine-coated modified zinc oxide nanowires are obtained.

[0025] Preferably, the zinc oxide nanowires have a diameter of 70~250nm and a length of 1~10um.

[0026] Preferably, the shell thickness of the phase change microcapsule is 0.2~0.5 μm.

[0027] Preferably, the preparation method of the phase change microcapsules includes the following steps: dissolving phenolic resin and n-hexadecane in an organic solvent to form an organic solution; dispersing the organic solution in water with added surfactant and stirring to form an emulsion; heating and solidifying the emulsion, and drying to obtain the phase change microcapsules; wherein the mass ratio of phenolic resin to n-hexadecane is (5~20):1. The organic solvent can be one or more of ethyl acetate and acetone. The surfactant can be sodium dodecyl sulfate. The heating temperature can be 140~160℃, and the heating time can be 5~7h.

[0028] The phase change microcapsules have an average particle size of 1~5 μm and a phase change enthalpy value ≥180 J / g.

[0029] This invention also protects a double-flat spiral wound pipe with a heat-fusion butt joint for polyethylene structural walls, comprising a pipe body, ribs, and a protective layer. The pipe body includes a main pipe portion and a heat-fusion butt joint portion at the pipe end. The ribs are spirally wound at equal intervals along the outer wall of the main pipe portion to form a corrugated pipe structure. The protective layer covers the outer wall of the ribs and the heat-fusion butt joint portion at the pipe end. The material of the protective layer is any of the polyethylene composite materials described above.

[0030] Preferably, the inner diameter of the heat-fusible butt-welded polyethylene structural wall double-flat spiral wound tube is greater than or equal to 1600 mm.

[0031] When the diameter of a polyethylene structural wall double-smooth spiral wound pipe is too large, the difficulty of melt flow control increases geometrically with the increase of pipe diameter, making the aforementioned technical problems more likely to occur. The polyethylene composite material for the thermofusion-welded polyethylene structural wall double-smooth spiral wound pipe of the present invention is particularly suitable for the preparation of the protective layer of large-diameter polyethylene structural wall double-smooth spiral wound pipes with an inner diameter of 1600 mm or greater.

[0032] More preferably, the inner diameter of the heat-fusible butt-welded polyethylene structural wall double-flat spiral wound tube is 1600~4000mm.

[0033] More preferably, the inner diameter of the heat-fusible butt-welded polyethylene structural wall double-flat spiral wound tube is 2400~4000mm.

[0034] Preferably, the ribbed tube is a PP tube.

[0035] This invention also protects the application of the thermofusion-welded polyethylene structural wall double-flat spiral wound pipe described in any of the above claims in marine water intake and drainage.

[0036] Compared with the prior art, the beneficial effects of the present invention are: This invention discloses a polyethylene composite material for hot-melt butt-welded polyethylene structural wall double-flat spiral wound pipe. Through the synergistic effect of polydopamine-coated zinc oxide nanowires and phase change microcapsules, the thermal conductivity of the hot-melt butt-welded polyethylene structural wall double-flat spiral wound pipe is improved, reducing the likelihood of air bubbles and pores during end-to-end hot-melt welding. Furthermore, it reduces cooling and demolding time, decreases shrinkage, shortens the length of pipe that needs to be cut, improves joint tensile strength and ring stiffness, and enhances the quality of the hot-melt welded joint. Attached Figure Description

[0037] Figure 1 Image (a) is a photograph of a double-flat spiral wound pipe with a polyethylene structural wall containing air bubbles. Figure 1 (b) in the image is a picture of a porous polyethylene structured wall double-flat spiral wound pipe. Figure 1 (c) in the image is a picture of a double-flat spiral wound pipe with a tapered end face and a polyethylene structural wall.

[0038] Figure 2 This is a physical image of the heat-fusible butt-welded reinforced polyethylene structural wall double-flat spiral wound pipe prepared in Example 1 of the present invention.

[0039] Figure 3 This is a front view of the heat-fusible butt-welded reinforced polyethylene structural wall double-flat spiral wound pipe prepared in Example 1 of the present invention.

[0040] Figure 4 This is a cross-sectional view of the heat-fusible butt-welded reinforced polyethylene structural wall double-flat spiral wound pipe prepared in Example 1 of the present invention. Detailed Implementation

[0041] The present invention will be further described below with reference to specific embodiments, but the embodiments do not limit the present invention in any way. Unless otherwise stated, the raw materials and reagents used in the embodiments of the present invention are conventionally purchased raw materials and reagents.

[0042] Zinc oxide nanowire 1: Diameter 70-250nm, length 1-10um, manufacturer is Xianfeng Nano, grade is 105480.

[0043] Zinc oxide 2, nano-particles, manufactured by Xianfeng Nano, grade 100368, particle size 30-80nm. Ethylene-based phenolic resin, manufactured by Kaixuan Plastics Technology Co., Ltd., grade 2Y-658.

[0044] PE resin: Manufacturer: Hainan Refining & Chemical Co., Ltd.; Melt index: 0.17-0.29 g / 10 min; Test conditions: 190℃, 5 kg; Grade: 23050.

[0045] Carbon black masterbatch: manufactured by Chongqing Aocai, grade C4153L.

[0046] Example 1 A heat-fusible butt-welded polyethylene structural wall double-flat spiral wound pipe polyethylene composite material, by weight, comprises the following components: 100 parts polyethylene resin; 3 parts carbon black masterbatch; 1 part polydopamine-coated zinc oxide nanowires; and 0.4 parts phase change microcapsules. The phase change microcapsules have a structure with a phenolic resin shell and n-hexadecane as the core material. The polydopamine-coated zinc oxide nanowires and the phase change microcapsules are added in the form of masterbatch, and the carrier resin of the masterbatch is polyethylene resin.

[0047] The preparation method of polydopamine-coated zinc oxide nanowires is as follows: 2g of zinc oxide nanowires were added to an appropriate amount of anhydrous ethanol and sonicated in a high-energy cell disruptor for 30 minutes to disperse them, resulting in a milky white ZnONWs anhydrous ethanol solution. 0.484g and 0.004mol of tris(hydroxymethyl)aminomethane were dissolved in 400ml of deionized water, and the pH of the solution was adjusted to between 8 and 9 with 1mol / L HCl solution to obtain a Tris buffer solution. 0.8g of dopamine hydrochloride (the mass ratio of dopamine hydrochloride to zinc oxide nanowires was 0.4:1) was added to the Tris buffer solution, stirred and sonicated, and then slowly poured into the ZnONWs anhydrous ethanol solution. The mixture was magnetically stirred at room temperature for 18h, and dried to obtain polydopamine-coated zinc oxide nanowires.

[0048] The preparation method of the phase change microcapsules is as follows: 10 parts of ethyl phenolic resin, 24 parts of ethyl acetate, 6 parts of acetone, 1 part of n-hexadecane (the mass ratio of phenolic resin to n-hexadecane is 10:1), 3 parts of sodium dodecyl sulfate, and 20 parts of deionized water are stirred in a reaction vessel at room temperature for 1 hour to form an emulsion at a stirring speed of 5000 rpm. The emulsion is heated to 150℃ and reacted for 6 hours. After cooling to room temperature, it is centrifuged at 5000 rpm and then dried at 60℃ to obtain core-shell structured phase change microcapsules.

[0049] The preparation method of polydopamine-coated zinc oxide nanowires / phase change microcapsules masterbatch is as follows: polydopamine-coated zinc oxide nanowires, phase change microcapsules, PE resin, and antioxidant 1010 are mixed at a mass ratio of 5:2:92.5:0.5 at 160-180℃ for 10 minutes; after mixing, the mixture is fed into a single-screw extruder for extrusion granulation to obtain polydopamine-coated zinc oxide nanowires / phase change microcapsules masterbatch.

[0050] like Figure 2 , Figure 3 and Figure 4As shown, a heat-fusion butt-welded polyethylene structural wall double-flat spiral wound pipe includes a pipe body, ribs, and a protective layer. The pipe body includes a main pipe section and a heat-fusion butt-welded pipe end section. The ribs are spirally wound at equal intervals along the outer wall of the main pipe section to form a corrugated pipe structure. The protective layer covers the outer wall of the ribs and the heat-fusion butt-welded pipe end section. The material of the protective layer is the aforementioned heat-fusion butt-welded polyethylene structural wall double-flat spiral wound pipe polyethylene composite material.

[0051] The preparation method of the heat-fusible butt-welded polyethylene structural wall double-flat spiral wound pipe is as follows: The above-mentioned polydopamine-coated zinc oxide nanowire / phase change microcapsule masterbatch, carbon black masterbatch, and PE resin are mixed in a mass ratio of 20:3:81.5 to prepare a sheet film. On a preheated 210℃ integral steel roller mold, equidistantly spirally wound ribs onto the outer wall of the main body of the pipe to form a corrugated pipe structure. The sheet film is then applied to the outer wall of the ribs and the heat-fusible butt-welded joint at the pipe ends for integral winding molding, producing a pipe as shown in the image. Figure 2 The product shown is a heat-fusion butt-welded reinforced polyethylene structural wall double-smooth spiral wound pipe with a specification of DN / ID2400mm. The heat-fusion butt-welded joint of the pipe ends features a thick wall of 80mm. The main body of the pipe is a hollow ribbed tube structure, supported by a 100mm specification PP single-wall corrugated pipe. The outer surface features spiral "O" shaped ribs with a protective layer. The inner layer is a single-layer solid wall pipe. Both the inner and outer surfaces of the pipe are smooth and flat.

[0052] Example 2 A polyethylene composite material for double-flat spiral wound pipes with heat-melt butt-welded polyethylene structural walls, comprising the following components by weight: 100 parts polyethylene resin; 4 parts carbon black masterbatch; 2 parts polydopamine-coated zinc oxide nanowires; and 1 part phase change microcapsule. The phase change microcapsule has a structure with phenolic resin as the outer shell and n-hexadecane as the core material.

[0053] The preparation method differs from that in Example 1 in that: In the preparation of polydopamine-coated zinc oxide nanowires / phase change microcapsules masterbatch, the mass ratio of polydopamine-coated zinc oxide nanowires, phase change microcapsules, PE100 resin, and antioxidant 1010 is 10:5:84.5:0.5.

[0054] In the preparation of the heat-fusible butt-welded polyethylene structural wall double-flat spiral wound pipe, the above-mentioned polydopamine-coated zinc oxide nanowire / phase change microcapsule masterbatch, carbon black masterbatch and PE resin are mixed in a mass ratio of 20:4:83.1.

[0055] A heat-melt butt-welded polyethylene structural wall double-flat spiral wound pipe differs from Example 1 in that the protective layer material is the aforementioned heat-melt butt-welded polyethylene structural wall double-flat spiral wound pipe polyethylene composite material.

[0056] Example 3 A polyethylene composite material for double-flat wound pipes with heat-melt butt-welded polyethylene structural walls, differing from Example 1 in the preparation of polydopamine-coated zinc oxide nanowires: 0.2g of dopamine hydrochloride was added to a Tris buffer solution.

[0057] That is, the mass ratio of dopamine hydrochloride to zinc oxide nanowires is 0.1:1.

[0058] A heat-melt butt-welded polyethylene structural wall double-flat spiral wound pipe differs from Example 1 in that the protective layer material is the aforementioned heat-melt butt-welded polyethylene structural wall double-flat spiral wound pipe polyethylene composite material.

[0059] Example 4 A polyethylene composite material for double-flat wound pipes with heat-melt butt-welded polyethylene structural walls, differing from Example 1 in the preparation of polydopamine-coated zinc oxide nanowires: 1g of dopamine hydrochloride was added to a Tris buffer solution.

[0060] That is, the mass ratio of dopamine hydrochloride to zinc oxide nanowires is 0.5:1.

[0061] A heat-melt butt-welded polyethylene structural wall double-flat spiral wound pipe differs from Example 1 in that the protective layer material is the aforementioned heat-melt butt-welded polyethylene structural wall double-flat spiral wound pipe polyethylene composite material.

[0062] Example 5 A polyethylene composite material for double-flat wound pipes with heat-melt butt-welded polyethylene structural walls, differing from Example 1 in the preparation of phase change microcapsules: 5 parts of ethyl phenolic resin and 1 part of n-hexadecane.

[0063] That is, the mass ratio of phenolic resin to n-hexadecane is 5:1.

[0064] A heat-melt butt-welded polyethylene structural wall double-flat spiral wound pipe differs from Example 1 in that the protective layer material is the aforementioned heat-melt butt-welded polyethylene structural wall double-flat spiral wound pipe polyethylene composite material.

[0065] Example 6 A polyethylene composite material for double-flat wound pipes with heat-melt butt-welded polyethylene structural walls, differing from Example 1 in the preparation of phase change microcapsules: 20 parts of ethyl phenolic resin and 1 part of n-hexadecane.

[0066] That is, the mass ratio of phenolic resin to n-hexadecane is 20:1.

[0067] A heat-melt butt-welded polyethylene structural wall double-flat spiral wound pipe differs from Example 1 in that the protective layer material is the aforementioned heat-melt butt-welded polyethylene structural wall double-flat spiral wound pipe polyethylene composite material.

[0068] Comparative Example 1 A polyethylene composite material, which differs from Example 1 in that zinc oxide nanowires 1 are replaced with zinc oxide 2.

[0069] A polyethylene structural wall double-flat spiral wound pipe differs from Example 1 in that the protective layer is made of the aforementioned polyethylene composite material.

[0070] Comparative Example 2 A polyethylene composite material, which differs from Example 1 in that the zinc oxide nanowires 1 are not coated with polydopamine.

[0071] A polyethylene structural wall double-flat spiral wound pipe differs from Example 1 in that the protective layer is made of the aforementioned polyethylene composite material.

[0072] Comparative Example 3 A polyethylene composite material comprises the following components: 100 parts polyethylene resin; 3 parts carbon black masterbatch; and 1 part polydopamine-coated zinc oxide nanowires.

[0073] The difference from Example 1 is that it does not include phase change microcapsules.

[0074] A polyethylene structural wall double-flat spiral wound pipe differs from Example 1 in that the protective layer is made of the aforementioned polyethylene composite material.

[0075] Comparative Example 4 A polyethylene composite material, by weight, comprises 100 parts of polyethylene resin and 3 parts of carbon black masterbatch.

[0076] A polyethylene structural wall double-flat spiral wound pipe differs from Example 1 in that the protective layer is made of the aforementioned polyethylene composite material.

[0077] Result detection The polyethylene structural wall double-flat spiral wound pipes of Examples 1-6 and Comparative Examples 1-4 were connected by end heat fusion butt welding, and the following tests were conducted: (1) End face appearance: Use a hot melt butt welding machine with a matching milling cutter to mill the butt face for at least 5 turns, and then observe whether there are bubbles or delamination on the end face. If bubbles or delamination appear, mark NG; if no bubbles or delamination appear, mark OK.

[0078] (2) The length of pipe material that needs to be cut off at the end face.

[0079] (3) Demolding cycle: the time required for the outer wall of the pipe to reach 45°C after the pipe is wound and formed using the same cooling process.

[0080] (4) Ring stiffness: Tested according to GB / T 9647-2015.

[0081] (5) Oxidation induction time (inner wall): Tested according to GB / T19466.6-2009, test temperature 200℃. The longer the oxidation induction time, the better the antioxidant performance.

[0082] (6) Hot-melt joint GB / T19810-2005 "Determination of tensile strength and failure mode of hot-melt butt joints of polyethylene (PE) pipes and fittings": ductile failure. (maximum tensile force), joint welding temperature 200~210℃.

[0083] (7) Tensile strength of the weld: Tested according to GB / T 8804.3-2003.

[0084] The specific detection results for each embodiment are shown in Table 1 below: Table 1

[0085] The specific test results for each comparative example are shown in Table 2 below: Table 2

[0086] As can be seen from Tables 1 and 2 above, the DN / ID2400mm large-diameter thermofusion-welded polyethylene structural wall double-flat spiral wound pipe prepared by the polyethylene composite material in this embodiment of the invention does not produce bubbles or delamination on the end face during thermofusion welding. Furthermore, the length of pipe that needs to be cut off from one end face can be as low as 0~0.8mm, eliminating the need for subsequent cutting processes and improving the overall yield. Moreover, the synergistic effect of polydopamine-coated zinc oxide nanowires and phase change microcapsules increases the tensile strength of the joint to 23.5~26.4MPa and the ring stiffness to 8.6~10.2kN / m. 2 The tensile strength at the hot-melt weld joint is increased to 4528~4823N. Data on the demolding cycle shows that the pipe prepared from the material of this invention can shorten the cooling time, with a demolding cycle as low as 4~6.6 hours. The steel roller located in the middle of the pipe can be pulled out within a shorter cooling time to complete the demolding process, thus shortening the production cycle.

[0087] In Examples 1 and 2, Comparative Example 4, the polyethylene composite material does not contain polydopamine-coated zinc oxide nanowires and phase change microcapsules. The resulting polyethylene structural wall double-flat wound pipe is prone to bubbles and delamination at the end face. Moreover, the solid wall end has a large shrinkage rate and a large end face taper. Secondary processing is required to cut off the taper part of the end face. The length of pipe that needs to be cut off at one end face reaches 20 mm.

[0088] As can be seen from the examples and Comparative Example 1, when zinc oxide nanowire 1 is replaced with zinc oxide 2, since zinc oxide 2 is in nanoparticle form and does not form a thermally conductive path, the melt solidification shrinkage is uneven and the tension control is unstable during the winding process, resulting in a large shrinkage rate at the solid wall end. Secondary processing is required to cut off the tapered part of the end face. The length of the tube that needs to be cut off at one end face is still 6 mm.

[0089] As can be seen from Examples and Comparative Example 2, the zinc oxide nanowires 1, without polydopamine coating, exhibited brittle fracture due to excessively low joint strength.

[0090] As can be seen from the examples and Comparative Example 3, the polyethylene composite material of Comparative Example 3 does not include phase change microcapsules, which will form bubbles and the tensile strength at the weld is too low.

[0091] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not intended to limit the implementation of the present invention. Those skilled in the art can make other variations or modifications based on the above description. It is neither necessary nor possible to exhaustively describe all embodiments here. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the claims of the present invention.

Claims

1. A polyethylene composite material for use in double-flat spiral wound pipes with heat-melt butt-welded polyethylene structural walls, characterized in that, By weight, it includes the following components: 100 parts of polyethylene resin; 2-4 parts carbon black masterbatch; Polydopamine-coated zinc oxide nanowires, 0.5-2 parts; Phase change microcapsules, 0.2-1 part; The phase change microcapsules have a structure with phenolic resin as the outer shell and n-hexadecane as the core material.

2. The polyethylene composite material as described in claim 1, characterized in that, The polydopamine-coated zinc oxide nanowires and the phase change microcapsules are added in the form of masterbatch, and the carrier resin of the masterbatch is polyethylene resin.

3. The polyethylene composite material as described in claim 2, characterized in that, The preparation method of the masterbatch includes the following steps: the polydopamine-coated zinc oxide nanowires, the phase change microcapsules, the polyethylene resin and antioxidant are mixed and then fed into a single screw extruder for extrusion and granulation to obtain the masterbatch; wherein, the mixing temperature is 160-180℃ and the mixing time is 10-20min.

4. The polyethylene composite material as described in claim 1, characterized in that, The preparation method of the polydopamine-coated modified zinc oxide nanowires includes the following steps: mixing and stirring a tris(hydroxymethyl)aminomethane hydrochloride buffer solution containing dopamine hydrochloride with an anhydrous ethanol suspension of zinc oxide nanowires to obtain polydopamine-coated modified zinc oxide nanowires; wherein, the mass ratio of dopamine hydrochloride to zinc oxide nanowires is (0.1~0.5):

1.

5. The polyethylene composite material as described in claim 4, characterized in that, The zinc oxide nanowires have a diameter of 70~250nm and a length of 1~10um.

6. The polyethylene composite material as described in claim 1, characterized in that, The preparation method of the phase change microcapsules includes the following steps: dissolving phenolic resin and n-hexadecane in an organic solvent to form an organic solution; dispersing the organic solution in water with added surfactant and stirring to form an emulsion; heating and curing the emulsion and drying it to obtain the phase change microcapsules; wherein the mass ratio of phenolic resin to n-hexadecane is (5~20):

1.

7. A double-flat spiral wound pipe with a heat-fusion butt-welded polyethylene structural wall, characterized in that, The device includes a pipe body, ribs, and a protective layer. The pipe body includes a main pipe section and a hot-melt joint section at the pipe end. The ribs are spirally wound at equal intervals along the outer wall of the main pipe section to form a corrugated pipe structure. The protective layer covers the outer wall of the ribs and the hot-melt joint section at the pipe end. The material of the protective layer is the polyethylene composite material according to any one of claims 1 to 6.

8. The double-flat spiral wound pipe with a heat-fusion butt-welded polyethylene structural wall as described in claim 7, characterized in that, The inner diameter of the heat-melt butt-welded polyethylene structural wall double-flat spiral wound tube is 1600~4000mm.

9. The double-flat spiral wound pipe with a heat-fusion butt-welded polyethylene structural wall as described in claim 7, characterized in that, The ribbed tube is a PP tube.

10. The application of the thermofusion-welded polyethylene structural wall double-flat spiral wound pipe according to any one of claims 7 to 9 in marine water intake and drainage.

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