A method for preparing MPP power pipe material with improved tensile strength

Abstract

This invention discloses a method for preparing MPP power pipes with improved tensile strength. The method includes: providing multiple raw materials for forming multiple layers of the MPP power pipe, and feeding the raw materials into multiple extruders; forming the MPP power pipe through co-extrusion, wherein the MPP power pipe comprises, from the outside to the inside, a first MPP layer, a first composite PET layer, a second MPP layer, a second composite PET layer, and a third MPP layer. The MPP power pipes manufactured by this invention exhibit high tensile strength, high impact strength, and good retention of impact strength at low temperatures.

Description

Technical Field

[0001] This invention relates to the field of layered materials technology, and in particular to a method for preparing an MPP power pipe with improved tensile strength. Background Technology

[0002] MPP pipe, also known as MPP power cable protection pipe, is divided into open-cut and trenchless types. Trenchless MPP pipe is also called MPP jacking pipe or drag pipe. MPP pipe uses modified polypropylene as the main raw material. It has the characteristics of high temperature resistance and external pressure resistance, and is suitable for medium and low voltage power transmission cable laying pipes below 10KV. The trenchless construction characteristics of MPP pipe can reduce environmental damage, making it a new type of power infrastructure material. The Ministry of Housing and Urban-Rural Development's "Design Standard for Urban Power Cable Lines" (GB 51218-2016) advocates the use of recyclable, low-environmental-impact cable protection pipes, and the proportion of trenchless construction should be increased to over 60%.

[0003] MPP pipes are a type of high-performance polypropylene pipe, but they may still have shortcomings under certain high-load or special working conditions (such as high-stress environments or deep burial environments). Existing technologies have conducted extensive research on this type of material. For example, the main improvement of MPP pipes in existing technology CN111961253A is the addition of modified calcium sulfate whiskers to polypropylene resin. Because this existing technology modifies the calcium sulfate whiskers, it enhances the dispersion of inorganic whiskers in the organic polymer, thereby improving the tensile strength and flame resistance of the MPP pipe. However, this existing technology is a single-layer polymer, which cannot fully utilize the advantages of layered composite materials.

[0004] For example, the main improvement of existing technology CN119264557A for MPP pipes is the addition of graphene-modified polypropylene to traditional polypropylene. This existing technology can improve the thermal conductivity of polypropylene materials. The problem with this existing technology is that it fails to address the main shortcomings of current MPP. In fact, the main technical challenge currently facing MPP power pipes is not their insufficient thermal conductivity, but rather how to improve their tensile strength and low-temperature toughness. This is the key to enhancing the market position of MPP power pipes. Summary of the Invention

[0005] To improve the tensile strength and low-temperature toughness of MPP power pipes, this invention provides a method for preparing MPP power pipes with improved tensile strength. This invention designs a new structure for MPP power pipes, improving the existing single-layer MPP power pipes into a composite MPP power pipe with multiple MPP layers by co-extrusion. In addition, this invention adds multiple PET layers between the MPP layers. Experimental results show that the PET layers can not only improve the tensile properties of the MPP power pipes, but also help improve the flowability of the polymer in the MPP layers, thereby obtaining MPP power pipes with high tensile strength.

[0006] This invention provides a method for preparing MPP power pipes with improved tensile strength, the method comprising:

[0007] Multiple raw materials are provided for forming multiple layers of MPP power tubing, and the multiple raw materials are fed into multiple extruders respectively;

[0008] MPP power pipes are formed by co-extrusion, wherein the MPP power pipes consist of a first MPP layer, a first composite PET layer, a second MPP layer, a second composite PET layer, and a third MPP layer from the outside to the inside.

[0009] In a preferred embodiment, the first composite PET layer comprises, from the outside to the inside, a first PET layer and a second PET layer; the second composite PET layer comprises, from the outside to the inside, a third PET layer and a fourth PET layer.

[0010] In a preferred embodiment, the weight-average molecular weight of the polypropylene constituting the first MPP layer is 1,100,000-1,400,000 g / mol.

[0011] In a preferred embodiment, the polypropylene constituting the second MPP layer has a weight-average molecular weight of 600,000-800,000 g / mol.

[0012] In a preferred embodiment, the polypropylene constituting the third MPP layer has a weight-average molecular weight of 80,000-100,000 g / mol.

[0013] In a preferred embodiment, the weight-average molecular weight of PET in the first PET layer is 170,000-180,000 g / mol; wherein the weight-average molecular weight of PET in the second PET layer is 200,000-220,000 g / mol.

[0014] In a preferred embodiment, the weight-average molecular weight of PET in the third PET layer is 90,000-100,000 g / mol; wherein the weight-average molecular weight of PET in the fourth PET layer is 110,000-130,000 g / mol.

[0015] In a preferred embodiment, the thickness of the first MPP layer is at least three times the thickness of the second MPP layer, and the thickness of the first MPP layer is at least three times the thickness of the third MPP layer.

[0016] In a preferred embodiment, the thickness of the first composite PET layer is at least three times the thickness of the second composite PET layer, wherein the first PET layer and the second PET layer have the same thickness; and the third PET layer and the fourth PET layer have the same thickness.

[0017] Compared with the prior art, the present invention has the following advantages: The present invention designs a new structure for MPP power pipes, and improves the existing single-layer MPP power pipes into composite MPP power pipes with multiple MPP layers by co-extrusion method. In addition, the present invention adds multiple PET layers between the MPP layers. Experimental results show that the PET layers can not only improve the tensile properties of the MPP power pipes, but also help improve the flowability of the polymer in the MPP layers, thereby achieving high tensile strength MPP power pipes. Attached Figure Description

[0018] Figure 1 This is a flowchart of a method according to an embodiment of the present invention.

[0019] Figure 2 This is a structural schematic diagram of an embodiment of the present invention.

[0020] Figure 3 This is a view showing the change in impact strength with temperature according to an embodiment of the present invention.

[0021] Figure 4 This is a view showing the impact strength as a function of temperature, according to another embodiment of the present invention.

[0022] Figure 5 This is a view showing the impact strength of existing MPP power pipe materials as a function of temperature. Detailed Implementation

[0023] The specific embodiments of the present invention will now be described in detail with reference to the accompanying drawings, but it should be understood that the scope of protection of the present invention is not limited to the specific embodiments.

[0024] Figure 1 This is a flowchart of a method according to an embodiment of the present invention. As shown in the figure, the preparation method of the present invention includes the following steps:

[0025] Step 1: Provide various raw materials for forming multiple layers of MPP power pipes, and feed the various raw materials into multiple extruders respectively. It should be understood that the raw materials used to form the various layers of this invention are not pure polymers, because other additives must be added to the polymer for processing and molding. Taking the raw material for forming the PET layer as an example, referring to the composition formulation of prior art CN104031304A, the composition formulation of the raw materials for forming each PET layer in this invention is: 100 parts by weight of polyethylene terephthalate (PET), 2 parts of ultraviolet crosslinking agent methyl benzoylformate (MBF), 1 part of ultraviolet crosslinking agent 1173 (2-hydroxy-2-methyl-1-phenylpropanone), 0.5 parts of antioxidant 168, 20 parts of micron-sized ZrO2 powder, and 5 parts of molybdenum chromium orange. It should also be understood that the difference between the raw materials for each PET layer lies in the different weight-average molecular weights of the pure PET used to form each PET layer. It should be understood that this invention only uses this PET formulation as an example; other PET formulations are also applicable to the improved concepts proposed in this invention. Similarly, the proportions of the raw materials forming each MPP layer can be referenced in the prior art CN111961253A, specifically: 100 parts polypropylene, 35 parts modified calcium sulfate whiskers, 5 parts flame retardant, and 1 part modified montmorillonite. The difference between the raw materials for each MPP layer lies in the different weight-average molecular weights of the pure polypropylene used to form each MPP layer. Furthermore, a detailed description of co-extrusion can be found in prior art CN107405845B (specifically, paragraphs 0062-0065 of its specification). This invention briefly extracts a portion of this prior art to facilitate understanding by those skilled in the art: In the co-extrusion step, the raw materials for each layer are fed into multiple extruders (for example, if this invention has 7 layers, then 7 extruders are needed, each extruder extruding the polymer for one layer) to form a multilayer structure. This invention employs the multi-manifold die described in the aforementioned prior art. The components of a multi-manifold die head can be: (a) similar to a single-layer die head, except that it has more than one feed channel; (b) each melt channel has its own regulating channel for flow control; and (c) the melt stream converges inside the die head near the outlet and appears as a unique multi-layer extrusion. Co-extrusion technology is already a mature technology, and there are currently many factories on the market that can customize multi-manifold dies. Our company provides the thickness and number of layers required for the product, and these factories can manufacture suitable dies accordingly. Since the technical content of co-extrusion is common knowledge, this invention will not elaborate further.

[0026] Step 2: MPP power pipe is formed by co-extrusion, wherein the MPP power pipe comprises, from the outside to the inside, a first MPP layer, a first composite PET layer, a second MPP layer, a second composite PET layer, and a third MPP layer. In one example, the process of extruding the PET polymer can be referred to in the prior art. As an example, the PET extrusion process used in this invention refers to CN104031304A, specifically: a single-screw extruder is used, the screw diameter of the single-screw extruder is 70mm, the length-to-diameter ratio is 20:1, and the extruder temperature is set sequentially as follows: 185-195℃, 190-200℃, 195-205℃, 200-210℃, 195-205℃. The extrusion process for MPP can be referenced in CN111961253A. Specifically, the extrusion is performed using a twin-screw extruder, with the barrel temperature set at 180-200℃ in zone 1, 190-210℃ in zone 2, 200-220℃ in zone 3, and 210-230℃ in zone 4. The extruder screw speed is 120-150 r / min. Finally, all polymer layers pass through a multi-manifold die and enter the mold for plasticization and shaping, ultimately yielding the finished product.

[0027] Figure 2 This is a structural schematic diagram of an embodiment of the present invention. As shown in the figure, the MPP power conduit of the present invention includes, from the outside to the inside: a first MPP layer, a first PET layer, a second PET layer, a second MPP layer, a third PET layer, a fourth PET layer, and a third MPP layer. In the present invention, "inner" refers to the side of the MPP power conduit facing the cable, and "outer" refers to the side opposite to "inner".

[0028] Example 1

[0029] MPP power pipes are formed by the following preparation method: providing multiple raw materials for forming multiple layers of the MPP power pipe, and feeding the multiple raw materials into multiple extruders respectively; forming the MPP power pipe by co-extrusion, wherein the MPP power pipe comprises, from the outside to the inside, a first MPP layer, a first composite PET layer, a second MPP layer, a second composite PET layer, and a third MPP layer. The first composite PET layer comprises, from the outside to the inside, a first PET layer and a second PET layer; the second composite PET layer comprises, from the outside to the inside, a third PET layer and a fourth PET layer.

[0030] The weight-average molecular weight of the polypropylene constituting the first MPP layer is 1,100,000 g / mol.

[0031] The polypropylene constituting the second MPP layer has a weight-average molecular weight of 600,000 g / mol.

[0032] The polypropylene constituting the third MPP layer has a weight-average molecular weight of 80,000 g / mol.

[0033] The weight-average molecular weight of PET in the first PET layer is 170,000 g / mol; the weight-average molecular weight of PET in the second PET layer is 200,000 g / mol.

[0034] The weight-average molecular weight of PET in the third PET layer is 90,000 g / mol; while the weight-average molecular weight of PET in the fourth PET layer is 110,000 g / mol.

[0035] The thickness of the first MPP layer is three times that of the second MPP layer, and the thickness of the first MPP layer is three times that of the third MPP layer.

[0036] The thickness of the first composite PET layer is three times that of the second composite PET layer, wherein the first PET layer and the second PET layer have the same thickness; the third PET layer and the fourth PET layer have the same thickness. It should be understood that the embodiments of the present invention do not limit the specific thickness of each layer. The specific thickness of each layer should be deduced from the requirements of the user or the testing standard. For example, the tensile strength of each embodiment of the present invention is tested according to GB / T 1040, which has dimensional requirements for the specimen. Therefore, the thickness of the finished product follows this standard when conducting tensile tests. When selling the product, the buyer can specify their thickness requirements for the MPP power pipe, and our company can then design the thickness of each layer according to the buyer's requirements. After testing, the tensile strength of Example 1 is 40 MPa. The reason why the tensile strength of Example 1 is significantly improved compared to the prior art CN111961253A is as follows: During the co-extrusion process, limited thermal diffusion occurs at the interface of different polymer melts, and the molecular chains interpenetrate, forming a physical entanglement network. This entanglement can effectively transfer stress and prevent the interface from becoming a weak point. The molecular chain entanglement density in the interface region is higher than that inside the single material, enhancing the local mechanical strength. The difference in modulus between layers in a multilayer structure results in a more uniform stress distribution during tension. Furthermore, when a crack propagates to the interface, the crack path may deflect (e.g., turn parallel to the interface) due to the differences in mechanical properties between layers, lengthening the propagation path; simultaneously, the high-modulus layer may form a "bridging" effect, hindering crack opening. Local defects (such as bubbles and impurities) in a single material layer are prone to becoming fracture initiation points; the multilayer structure isolates defects through layering, reducing the synergistic effect of defects and improving statistical strength. Another reason is that traditional high-molecular-weight polypropylene has poor flowability, making processing and molding difficult, resulting in numerous defects and poor mechanical properties in the molded high-molecular-weight MPP materials. However, in the multilayer co-extrusion process, the flowability combination structure formed by the high-flowability layer and the low-flowability layer (e.g., in this invention, the first MPP layer is a low-flowability layer and the first PET layer is a high-flowability layer) can redistribute flow energy through interfacial shear stress. In addition, the high-flowability layer flows preferentially, forming a "lubricating layer," reducing overall flow resistance and thus promoting the flow of the low-flowability layer. The high-flowability layer withstands a higher shear rate at the interface, reducing local viscosity (shear thinning), further optimizing the flow field distribution. Finally, the multilayer structure can suppress the viscoelastic instability when a single material flows.It should be noted that the weight-average molecular weight design of each layer in this invention is not a simple gradient descent. For example, the first PET layer is outside the second PET layer, but the weight-average molecular weight of the first PET layer is lower than that of the second PET layer. This is because our researchers found that the PET layer has a greater ability to promote the flow of different types of low-flow polymers than to promote the flow of the same type of low-flow polymers. Furthermore, the PET layer with this molecular weight has a stronger ability to form a better interface and physical entanglement network with the first MPP layer. Therefore, the weight-average molecular weight of the first PET layer is designed to be lower than that of the second PET layer. After implementing this design, we found that maintaining a larger difference in the weight-average molecular weight between the first and third MPP layers is beneficial for improving the mechanical properties of the material. This may be related to the modulus differences among the three layers with significantly different molecular weights. Subsequently, the impact strength of the finished product of Example 1 was tested according to GB / T 1843-2008, and the impact strength of Example 1 was 49 kJ / m. 2 The reasons why the impact strength of Example 1 is significantly improved compared to the prior art CN111961253A are as follows: 1. When the crack propagates from the relatively rigid layer to the relatively tough layer, the crack path is deflected due to the difference in modulus (e.g., turning towards the interface or propagating along the tough layer), lengthening the propagation path and consuming more energy. 2. During co-extrusion, the molecular chains of different polymers undergo limited diffusion at the interface, forming an interpenetrating network and enhancing the interfacial bonding force. Interfacial entanglement enables more efficient stress transfer from the rigid layer to the tough layer, avoiding interruption of energy dissipation caused by interfacial peeling. 3. Local defects (such as bubbles and impurities) in single-layer materials are prone to become crack initiation points. Multilayer structures confine defects to local areas through boundaries, reducing the risk of overall failure. In addition, this invention tested the impact strength of Example 1 with temperature (25℃-minus 40℃), and the results are shown in [reference missing]. Figure 3It can be seen that the impact strength of Example 1 remained basically unchanged from 25℃ to -20℃. The lower value at -5℃ may be due to the inherent properties of the material (i.e., the material properties at different locations in the same batch of products cannot be completely consistent due to molecular inhomogeneity and varying degrees of defects). The reason for this conclusion is that the impact strength rebounded at even lower temperatures of -10℃ and -15℃. Only below -20℃ did the impact strength of Example 1 decrease slowly, which should be due to the reduction in material toughness. Only below -30℃ did the impact strength of Example 1 decrease more rapidly, but the impact strength still remained at a relatively high value. The reasons for this phenomenon are: 1. Impact energy is dissipated through the plastic deformation of the tough layer (such as crazes and shear bands) and the elastic response gradient of the rigid layer; at low temperatures, the brittle-dominated rigid layer is "wrapped" by the tough layer, avoiding rapid brittle failure of a single material. 2. In the multilayer structure, the relaxation peaks of different layers superimpose, broadening the frequency domain of low-temperature energy absorption. 3. The limited diffusion of molecular chains at the co-extrusion interface forms physical entanglement. At low temperatures, the thermal motion of molecular chains is restricted, and the entanglement points become "anchor points" for stress transfer. The entanglement density in the interface region is higher than that in the bulk, which improves the interfacial bonding strength at low temperatures (avoiding delamination).

[0037] Example 2

[0038] MPP power pipes are formed by the following preparation method: providing multiple raw materials for forming multiple layers of MPP power pipes, and feeding the multiple raw materials into multiple extruders respectively;

[0039] MPP power pipes are formed by co-extrusion, wherein the MPP power pipes, from the outside to the inside, sequentially include a first MPP layer, a first composite PET layer, a second MPP layer, a second composite PET layer, and a third MPP layer. The first composite PET layer, from the outside to the inside, sequentially includes a first PET layer and a second PET layer; the second composite PET layer, from the outside to the inside, sequentially includes a third PET layer and a fourth PET layer.

[0040] The weight-average molecular weight of the polypropylene constituting the first MPP layer is 1,400,000 g / mol.

[0041] The polypropylene constituting the second MPP layer has a weight-average molecular weight of 800,000 g / mol.

[0042] The polypropylene constituting the third MPP layer has a weight-average molecular weight of 100,000 g / mol.

[0043] The weight-average molecular weight of PET in the first PET layer is 180,000 g / mol; the weight-average molecular weight of PET in the second PET layer is 220,000 g / mol.

[0044] The weight-average molecular weight of PET in the third PET layer is 100,000 g / mol; while the weight-average molecular weight of PET in the fourth PET layer is 130,000 g / mol.

[0045] The thickness of the first MPP layer is four times that of the second MPP layer, and the thickness of the first MPP layer is four times that of the third MPP layer.

[0046] The thickness of the first composite PET layer is four times that of the second composite PET layer, wherein the first PET layer and the second PET layer have the same thickness; the third PET layer and the fourth PET layer have the same thickness. The testing standards are the same as in Example 1. The tensile strength of Example 2 is 43 MPa, and the impact strength is 50 kJ / m. 2 The variation of impact strength with temperature in Example 2 can be found in [reference needed]. Figure 4 .

[0047] Example 3

[0048] MPP power pipes are formed by the following preparation method: providing multiple raw materials for forming multiple layers of MPP power pipes, and feeding the multiple raw materials into multiple extruders respectively;

[0049] MPP power pipes are formed by co-extrusion, wherein the MPP power pipes, from the outside to the inside, sequentially include a first MPP layer, a first composite PET layer, a second MPP layer, a second composite PET layer, and a third MPP layer. The first composite PET layer, from the outside to the inside, sequentially includes a first PET layer and a second PET layer; the second composite PET layer, from the outside to the inside, sequentially includes a third PET layer and a fourth PET layer.

[0050] The polypropylene constituting the first MPP layer has a weight-average molecular weight of 1,200,000 g / mol.

[0051] The polypropylene constituting the second MPP layer has a weight-average molecular weight of 700,000 g / mol.

[0052] The polypropylene constituting the third MPP layer has a weight-average molecular weight of 90,000 g / mol.

[0053] The weight-average molecular weight of PET in the first PET layer is 175,000 g / mol; the weight-average molecular weight of PET in the second PET layer is 210,000 g / mol.

[0054] The weight-average molecular weight of PET in the third PET layer is 80,000 g / mol; while the weight-average molecular weight of PET in the fourth PET layer is 120,000 g / mol.

[0055] The thickness of the first MPP layer is four times that of the second MPP layer, and the thickness of the first MPP layer is four times that of the third MPP layer.

[0056] The thickness of the first composite PET layer is four times that of the second composite PET layer, wherein the first PET layer and the second PET layer have the same thickness; the third PET layer and the fourth PET layer have the same thickness. The testing standards are the same as in Example 1. The tensile strength of Example 3 is 40 MPa, and the impact strength is 48 kJ / m. 2 .

[0057] Comparative Example 1

[0058] MPP samples were prepared according to the formulation and method described in Example 1 of CN111961253A. Since CN111961253A does not specify the molecular weight of polypropylene, this invention uses polypropylene with a molecular weight of 1200000 g / mol. The testing standards were consistent with those of Example 1. The tensile strength of Comparative Example 1 was 29.5 MPa, and the impact strength was 39 kJ / m². 2 The numerical values ​​differ from those in Example 1 of CN111961253A. This difference is mainly due to the fact that the process cannot be completely consistent with CN111961253A, as the prior art does not disclose all process details, and the polypropylene used in the prior art is different from that of this invention. For the impact strength variation with temperature in Comparative Example 1, please refer to [link to relevant documentation]. Figure 5 .

[0059] Comparative Example 2

[0060] MPP power pipes are formed by the following preparation method: providing multiple raw materials for forming multiple layers of MPP power pipes, and feeding the multiple raw materials into multiple extruders respectively;

[0061] MPP power tubing was formed by co-extrusion, wherein the MPP power tubing comprises, from the outside to the inside, a first MPP layer, a first PET layer, a second MPP layer, a third PET layer, and a third MPP layer. The remaining process parameters are the same as in Example 1. The testing standards are the same as in Example 1. The tensile strength of Comparative Example 2 is 34 MPa, and the impact strength is 42 kJ / m. 2The decrease in the numerical value of Comparative Example 2 can be attributed to poor layer structure design. Several key effects present in Example 1 are absent. For instance, during co-extrusion, limited thermal diffusion occurs at the interface between different polymer melts, leading to interpenetration of molecular chains and the formation of a physically entangled network. Many factors influence this network, such as the molecular weight distribution of the polymers (since molecular chain morphology and length are related to molecular weight) and the release of interfacial stress between layers. Poor layer structure design can result in poor formation of this physically entangled network. Furthermore, while differences in mechanical properties between layers can indeed promote crack path deflection, excessive differences can cause a material to break instantly, potentially leading to the breakage of a layer before the crack has a chance to deflect. Finally, layer design must also consider flowability.

[0062] Comparative Example 3

[0063] The weight-average molecular weight of the polypropylene constituting the second MPP layer is 900,000 g / mol. The weight-average molecular weight of the polypropylene constituting the third MPP layer is 200,000 g / mol. The remaining process parameters are the same as in Example 1. The testing standards are the same as in Example 1. The tensile strength of Comparative Example 3 is 34 MPa, and the impact strength is 43 kJ / m. 2 .

[0064] Comparative Example 4

[0065] The weight-average molecular weight of the PET in the first PET layer is 220,000 g / mol; the weight-average molecular weight of the PET in the second PET layer is 180,000 g / mol. The remaining process parameters are the same as in Example 1. The testing standards are the same as in Example 1. The tensile strength of Comparative Example 4 is 37 MPa, and the impact strength is 45 kJ / m. 2 .

[0066] Comparative Example 5

[0067] The weight-average molecular weight of the PET in the third PET layer is 130,000 g / mol; the weight-average molecular weight of the PET in the fourth PET layer is 100,000 g / mol. The remaining process parameters are the same as in Example 1. The testing standards are the same as in Example 1. The tensile strength of Comparative Example 4 is 36 MPa, and the impact strength is 45 kJ / m. 2 .

[0068] Comparative Example 6

[0069] The thickness of the first MPP layer is the same as the thickness of the second MPP layer, and the thickness of the first MPP layer is the same as the thickness of the third MPP layer. The remaining process parameters are the same as in Example 1. The testing standards are the same as in Example 1. The tensile strength of Comparative Example 6 is 29 MPa, and the impact strength is 30 kJ / m. 2The poor mechanical properties of Comparative Example 6 are mainly due to the excessive thickness and high proportion of low molecular weight layers, as well as the mismatch between interlayer interfaces and stress.

[0070] It should be understood that the specific embodiments described above are merely illustrative or explanatory of the principles of the invention and do not constitute a limitation thereof. Therefore, any modifications, equivalent substitutions, improvements, etc., made without departing from the spirit and scope of the invention should be included within the protection scope of the invention. Furthermore, the appended claims are intended to cover all variations and modifications falling within the scope and boundaries of the appended claims, or equivalent forms of such scope and boundaries.

Claims

1. A method for preparing an MPP power pipe with improved tensile strength, the method comprising: Multiple raw materials are provided for forming multiple layers of the MPP power tubing, and the multiple raw materials are respectively fed into multiple extruders; The MPP power pipe is formed by co-extrusion, wherein the MPP power pipe comprises, from the outside to the inside, a first MPP layer, a first composite PET layer, a second MPP layer, a second composite PET layer, and a third MPP layer. The first composite PET layer comprises, from the outside to the inside, a first PET layer and a second PET layer; the second composite PET layer comprises, from the outside to the inside, a third PET layer and a fourth PET layer; the weight-average molecular weight of the polypropylene constituting the first MPP layer is 1,100,000-1,400,000 g / mol; the weight-average molecular weight of the polypropylene constituting the second MPP layer is 600,000-800,000 g / mol; the weight-average molecular weight of the polypropylene constituting the third MPP layer is 80,000-100,000 g / mol; in the first PET layer... The weight-average molecular weight of the PET in the first layer is 170,000-180,000 g / mol; the weight-average molecular weight of the PET in the second layer is 200,000-220,000 g / mol; the weight-average molecular weight of the PET in the third layer is 90,000-100,000 g / mol; the weight-average molecular weight of the PET in the fourth layer is 110,000-130,000 g / mol; the thickness of the first MPP layer is at least three times the thickness of the second MPP layer, and the thickness of the first MPP layer is at least three times the thickness of the third MPP layer.

2. The preparation method according to claim 1, wherein, The thickness of the first composite PET layer is at least three times the thickness of the second composite PET layer, wherein the first PET layer and the second PET layer have the same thickness; and the third PET layer and the fourth PET layer have the same thickness.

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