Preparation method of MPP electric pipe with improved tensile strength

Abstract

The invention discloses a preparation method of an MPP electric pipe with improved tensile strength, and the preparation method comprises the following steps: providing a plurality of raw materials for forming a plurality of layers of the MPP electric pipe, and respectively putting the plurality of raw materials into a plurality of extruders; the MPP electric power pipe is formed through a co-extrusion method, and the MPP electric power pipe sequentially comprises a first MPP layer, a first composite PET layer, a second MPP layer, a second composite PET layer and a third MPP layer from outside to inside. The MPP electric power pipe manufactured by the invention is high in tensile strength and high in impact strength, and the impact strength is good in retentivity at low temperature.

Description

Technical Field

[0001] The present invention relates to the technical field of layered materials, and in particular to a method for preparing an MPP electric power pipe with improved tensile strength. Background Art

[0002] MPP pipe, also known as MPP power cable protection pipe, is divided into trenchless and trenchless types. MPP trenchless pipe is also called MPP jacking pipe or dragging pipe. MPP pipe uses modified polypropylene as its main raw material. It is resistant to high temperatures and external pressures and is suitable for medium and low voltage transmission line cable conduit below 10kV. The trenchless construction feature 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 "Urban Power Cable Line Design Standard" (GB 51218-2016) advocates the use of recyclable, low-environmental-load cable protection pipe, and the proportion of trenchless construction must be increased to more than 60%.

[0003] MPP pipes are a type of high-performance polypropylene pipe, but they may still have shortcomings under certain high-load or special operating conditions (such as high-stress environments and deep burial environments). Extensive research has been conducted on this type of material. For example, the main improvement to MPP pipes in CN111961253A is the addition of modified calcium sulfate whiskers to the polypropylene resin. Because this prior art modifies the calcium sulfate whiskers, the dispersion of the inorganic whiskers in the organic polymer is enhanced, thereby improving the tensile strength and flame retardancy of the MPP pipes. However, this prior art is a single-layer polymer, which does not leverage the advantages of layered composite materials.

[0004] For example, the prior art CN119264557A primarily improves MPP pipes by adding graphene-modified polypropylene to traditional polypropylene, which improves the thermal conductivity of the polypropylene material. However, this prior art fails to address the primary shortcomings of current MPP pipes. In fact, the primary technical challenge facing MPP power pipes is not their insufficient thermal conductivity, but rather improving their tensile strength and low-temperature toughness, which are the key to enhancing their market position. Summary of the Invention

[0005] In order to improve the tensile strength and low-temperature toughness of MPP power pipes, the present invention provides a method for preparing MPP power pipes with improved tensile strength. The present invention designs a new structure of MPP power pipes, and improves the existing single-layer MPP power pipes into composite MPP power pipes with multiple MPP layers of the present invention through a 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 fluidity of the polymer in the MPP layer, thereby obtaining MPP power pipes with high tensile strength.

[0006] The present invention provides a method for preparing an MPP electric power pipe with improved tensile strength, the preparation method comprising:

[0007] Providing a plurality of raw materials for forming a plurality of layers of an MPP power pipe, and respectively placing the plurality of raw materials into a plurality of extruders;

[0008] The MPP electric pipe is formed by a co-extrusion method, wherein the MPP electric pipe includes 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 includes a first PET layer and a second PET layer in sequence from the outside to the inside; the second composite PET layer includes a third PET layer and a fourth PET layer in sequence from the outside to the inside.

[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 weight average molecular weight of the polypropylene constituting the second MPP layer is 600,000-800,000 g / mol.

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

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

[0014] In a preferred embodiment, the weight average molecular weight of the PET in the third PET layer is 90,000-100,000 g / mol; wherein the weight average molecular weight of the 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 of MPP power pipes, and improves the existing single-layer MPP power pipes into composite MPP power pipes of multiple MPP layers of the present invention through a 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 fluidity of the polymer in the MPP layer, thereby realizing MPP power pipes with high tensile strength. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 It is a method flow chart of an embodiment of the present invention.

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

[0020] Figure 3 FIG. 1 is a graph showing the change in impact strength with temperature according to an embodiment of the present invention.

[0021] Figure 4 FIG. 4 is a graph showing the change in impact strength with temperature according to another embodiment of the present invention.

[0022] Figure 5 This is a graph showing how the impact strength of the existing MPP power pipe material changes with temperature. DETAILED DESCRIPTION

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

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

[0025] Step 1: Provide multiple raw materials for forming multiple layers of MPP power pipe and place them into multiple extruders. It should be understood that the raw materials used to form each layer of the present invention are not pure polymers, as additives must be added to the polymer for processing and molding. Taking the raw materials for forming the PET layer as an example, referring to the composition of the prior art CN104031304A, the raw materials for forming each PET layer in the present invention are formulated as follows: 100 parts by weight of polyethylene terephthalate (PET), 2 parts of the UV crosslinker methyl benzoylformate (MBF), 1 part of the UV crosslinker 1173 (2-hydroxy-2-methyl-1-phenylpropanone), 0.5 parts of the antioxidant 168, 20 parts of micronized ZrO2 powder, and 5 parts of molybdenum chrome orange. It should also be understood that the raw materials for each PET layer differ in the weight-average molecular weight of the pure PET used to form each PET layer. It should be understood that this invention uses this PET formulation as an example; other PET formulations are also applicable to the improved concepts proposed in this invention. Similarly, the ratio of the raw materials forming each MPP layer can refer to the background art CN111961253A, specifically: 100 parts of polypropylene, 35 parts of modified calcium sulfate whiskers, 5 parts of flame retardant, and 1 part of modified montmorillonite. The difference between the raw materials of each MPP layer is that the weight-average molecular weight of the pure polypropylene in the raw materials used to form each MPP layer is different. In addition, the detailed introduction of co-extrusion can be found in the prior art CN107405845B (specifically refer to its specification sections 0062-0065). The present invention briefly excerpts part of the content of this prior art to facilitate those skilled in the art to understand the present invention: in the co-extrusion step, the raw materials of each layer are fed into multiple extruders respectively (for example, the present invention has 7 layers, so 7 extruders are required, each extruder is used to extrude the polymer of one layer) to form a multilayer structure. The present invention adopts the multi-manifold die head introduced in the aforementioned prior art. The components of a multi-manifold die can be: (a) similar to a single-layer die, except that there is more than one feed channel; (b) each melt channel has its own regulating row for flow control; and (c) the melt streams converge inside the die near the outlet and emerge as a unique multi-layer extrudate. Coextrusion technology is already mature, and there are a large number of factories on the market that can customize multi-manifold dies. We provide the product thickness and number of layers required, and these factories can manufacture the appropriate die accordingly. Since the relevant technical content of coextrusion is common knowledge, it will not be further described in this invention.

[0026] Step 2: Form an MPP power pipe by co-extrusion, wherein the MPP power pipe includes, 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 for extruding the PET polymer can be referred to the prior art. As an example, the PET extrusion process used in the present invention refers to CN104031304A, specifically: a single-screw extruder is used, the screw diameter of the single-screw extruder is 70 mm, the aspect ratio is 20:1, and the extruder temperatures are set to: 185-195°C, 190-200°C, 195-205°C, 200-210°C, and 195-205°C, respectively. The extrusion process of MPP can refer to CN111961253A. Specifically, extrusion is performed using a twin-screw extruder, with the barrel temperature set at 180-200°C in zone 1, 190-210°C in zone 2, 200-220°C in zone 3, and 210-230°C in zone 4. The extruder screw speed is 120-150 r / min. Finally, all polymer layers pass through a multi-manifold die head and enter the mold for plasticization and shaping to obtain the finished product.

[0027] Figure 2 This is a schematic diagram of the structure of an embodiment of the present invention. As shown, the MPP power pipe of the present invention comprises, from outside to 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 this invention, "inside" refers to the side of the MPP power pipe facing the cable, and "outside" refers to the side opposite the "inside."

[0028] Example 1

[0029] The MPP power pipe is formed by the following manufacturing method: providing multiple raw materials for forming multiple layers of the MPP power pipe and introducing the multiple raw materials into multiple extruders; forming the MPP power pipe by co-extrusion, wherein the MPP power pipe includes, 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 includes, from the outside to the inside, a first PET layer and a second PET layer; the second composite PET layer includes, 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 was 1,100,000 g / mol.

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

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

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

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

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

[0036] The thickness of the first composite PET layer is three times that of the second composite PET layer. The first and second PET layers have the same thickness, and the third and fourth PET layers 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 determined based on the requirements of the user or testing standards. For example, the tensile strength of each embodiment of the present invention is tested in accordance with GB / T 1040, which has dimension requirements for specimens. Therefore, when conducting tensile tests, the thickness of the finished product complies with this standard. When selling the product, the buyer can specify the thickness requirements for the MPP power pipe, and our company can then design the thickness of each layer according to the buyer's requirements. Testing showed that the tensile strength of Example 1 was 40 MPa. The reason for this significant improvement in tensile strength compared to the prior art CN111961253A is as follows: During the coextrusion process, limited thermal diffusion occurs at the interface between the different polymer melts, causing the molecular chains to interpenetrate and form a physically entangled network. This entanglement effectively transfers stress, preventing the interface from becoming a weak point. The molecular chain entanglement density at the interface is higher than within the individual materials, enhancing local mechanical strength. The modulus of each layer in a multilayer structure varies, which makes the stress distribution more uniform during stretching. 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 the layers, extending the propagation path. Simultaneously, the high-modulus layer may create a "bridging" effect, hindering crack opening. Local defects (e.g., bubbles, impurities) in a single material layer can easily become fracture initiation points; a multilayer structure isolates defects by layering, reducing the synergistic effect of defects and improving statistical strength. Another reason is that traditional high-molecular-weight polypropylene has poor fluidity and is difficult to process and mold, resulting in high-molecular-weight MPP materials with many defects and poor mechanical properties. However, during multilayer coextrusion, the high-fluidity layer and the low-fluidity layer form a fluidity coordination structure (for example, in the present invention, the first MPP layer is a low-fluidity layer and the first PET layer is a high-fluidity layer), which can redistribute flow energy through interfacial shear stress. Furthermore, the high-fluidity layer flows preferentially, forming a "lubricating layer" that reduces overall flow resistance and promotes flow in the low-fluidity layer. The high-flowability layer experiences higher shear rates at the interface, reducing local viscosity (shear thinning) and further optimizing the flow field distribution. Finally, the multilayer structure suppresses viscoelastic instabilities in the flow of a single material.It should be noted that the weight-average molecular weight of each layer in the present invention is not designed to be a simple gradient. For example, the first PET layer is positioned outside the second PET layer, but its weight-average molecular weight is lower than that of the second PET layer. This is because our researchers have discovered that PET layers promote the flow of different low-flow polymers more effectively than they promote the flow of similar low-flow polymers. Furthermore, PET with this molecular weight is more capable of forming 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. Following this design, we discovered that maintaining a larger difference in weight-average molecular weight between the first and third MPP layers improves the mechanical properties of the material, likely due to the difference in modulus between the three layers with distinct molecular weights. The finished product of Example 1 was subsequently subjected to impact strength testing 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 greatly improved compared with the prior art CN111961253A are as follows: 1. When the crack extends from the relatively rigid layer to the relatively tough layer, due to the difference in modulus, the crack path is deflected (such as turning to the interface or extending along the tough layer), extending the extension path and consuming more energy. 2. During the co-extrusion process, different polymer molecular chains undergo limited diffusion at the interface to form an interpenetrating network, which enhances the interfacial bonding force. Interface entanglement enables stress to be transferred more efficiently from the rigid layer to the tough layer, avoiding energy dissipation interruption caused by interface peeling. 3. Local defects in single-layer materials (such as bubbles, impurities) can easily become the starting point of cracks. The multi-layer structure limits the defects to local areas through boundaries, reducing the risk of overall failure. In addition, the present invention tested the impact strength of Example 1 as a function of temperature (25°C-minus 40°C), and the results are shown in Figure 2. Figure 3. It can be seen that from 25℃ to minus 20℃, the impact strength of Example 1 has basically not changed. The lower value at minus 5 degrees may be due to the decrease in the value caused by the inherent characteristics of the material (that is, the materials at different positions of the same batch of products are not uniform due to molecular uniformity and the number of defects, resulting in the performance of the materials at two positions cannot be completely consistent). The reason for this conclusion is that at lower temperatures of minus 10 and 15 degrees, the impact strength of the test rebounded. Only below minus 20 degrees does the impact strength of Example 1 slowly decrease. The decrease in impact strength here should be due to the decrease in material toughness. Only below minus 30 degrees does the impact strength of Example 1 decrease rapidly, but the impact strength still remains at a higher value. The reasons for this phenomenon are: 1. The impact energy is dissipated through the plastic deformation of the toughness layer (such as silver streaks, shear bands) and the elastic response gradient of the rigid layer; the brittle-dominated rigid layer at low temperatures is "wrapped" by the toughness layer to avoid rapid brittle failure of a single material. 2. In the multi-layer structure, the relaxation peaks of different layers are superimposed to broaden the low-temperature energy absorption frequency domain. 3. The limited diffusion of molecular chains at the co-extrusion interface forms physical entanglements. The thermal motion of the molecular chains is restricted at low temperatures, and the entanglement points become "anchor points" for stress transfer. The entanglement density in the interface area is higher than that in the bulk, which improves the interface bonding strength at low temperatures (avoiding delamination).

[0037] Example 2

[0038] The MPP power pipe is formed by the following preparation method: providing a plurality of raw materials for forming a plurality of layers of the MPP power pipe, and respectively placing the plurality of raw materials into a plurality of extruders;

[0039] The MPP electrical pipe is formed by co-extrusion and comprises, from the outside in, 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 in, the first PET layer and the second PET layer; the second composite PET layer comprises, from the outside in, the third PET layer and the fourth PET layer.

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

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

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

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

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

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

[0046] The thickness of the first composite PET layer is four times the thickness of the second composite PET layer, wherein the first PET layer is the same thickness as the second PET layer; the third PET layer is the same thickness as the fourth PET layer. The test standard is the same as that of Example 1. The tensile strength of Example 2 is 43MPa and the impact strength is 50kJ / m 2 The impact strength of Example 2 varies with temperature. Figure 4 .

[0047] Example 3

[0048] The MPP power pipe is formed by the following preparation method: providing a plurality of raw materials for forming a plurality of layers of the MPP power pipe, and respectively placing the plurality of raw materials into a plurality of extruders;

[0049] The MPP electrical pipe is formed by co-extrusion and comprises, from the outside in, 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 in, the first PET layer and the second PET layer; the second composite PET layer comprises, from the outside in, the third PET layer and the fourth PET layer.

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

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

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

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

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

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

[0056] The thickness of the first composite PET layer is four times the thickness of the second composite PET layer, wherein the first PET layer is the same thickness as the second PET layer; the third PET layer is the same thickness as the fourth PET layer. The test standard is the same as that of 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] The MPP sample was prepared according to the ratio and method of Example 1 of CN111961253A. Since the molecular weight of polypropylene is not given in CN111961253A, the present invention selected 1200000 g / mol polypropylene. The test standard is consistent with that of Example 1. The tensile strength of Comparative Example 1 is 29.5 MPa and the impact strength is 39 kJ / m 2 The values ​​are different from those of Example 1 of CN111961253A. The main reason for the difference is that the process is not completely consistent with that of CN111961253A, because the prior art does not disclose all the process details and the polypropylene used in the prior art is different from that of the present invention. Figure 5 .

[0059] Comparative Example 2

[0060] The MPP power pipe is formed by the following preparation method: providing a plurality of raw materials for forming a plurality of layers of the MPP power pipe, and respectively placing the plurality of raw materials into a plurality of extruders;

[0061] The MPP power pipe is formed by a co-extrusion method, wherein the MPP power pipe includes, 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 those in Example 1. The test standards are the same as those in Example 1. The tensile strength of Comparative Example 2 is 34 MPa and the impact strength is 42 kJ / m 2. The reason for the decrease in the numerical value of Comparative Example 2 can be attributed to the fact that due to the poor layer structure design, multiple powerful effects in Example 1 do not exist. For example, during the co-extrusion process, different polymer melts undergo limited heat diffusion at the interface, and the molecular chains penetrate each other to form a physical entanglement network. There are many factors that affect this network, such as the matching relationship of polymer molecular weight (because the molecular chain morphology and length are related to the molecular weight), the release of interfacial stress between layers, etc. Due to the poor layer structure design, the physical entanglement network may not be well formed. For example, the difference in mechanical properties between the layers can indeed promote the deflection of the crack path, but the difference in mechanical properties between the layers is too large, which may cause a material to be broken instantly, which may cause the crack to break a certain material layer before it has a chance to deflect. For another example, the layer design must also consider the matching of fluidity.

[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 those in Example 1. The test standards are the same as those 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; wherein, 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 those in Example 1. The test standards are the same as those 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; wherein, 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 those in Example 1. The test standards are the same as those 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 that of the second MPP layer, and the thickness of the first MPP layer is the same as that of the third MPP layer. The remaining process parameters are the same as those in Example 1. The test standards are the same as those in Example 1. The tensile strength of Comparative Example 6 is 29 MPa, and the impact strength is 30 kJ / m 2The main reason for the poor mechanical properties of Comparative Example 6 is that the thickness of the low molecular weight layer is too large, accounting for a large proportion, and the interface between the layers and the stress mismatch are caused.

[0070] It should be understood that the above-described specific embodiments of the present invention are merely illustrative or illustrative of the principles of the present invention and do not constitute limitations of the present invention. Therefore, any modifications, equivalent substitutions, improvements, etc. made without departing from the spirit and scope of the present invention should be included within the scope of protection of the present invention. In addition, the appended claims are intended to cover all variations and modifications that fall within the scope and metes and bounds of the appended claims, or equivalents thereof.

Claims

1. A method for preparing an MPP electric power pipe with improved tensile strength, the method comprising: Providing a plurality of raw materials for forming a plurality of layers of the MPP power pipe, and respectively placing the plurality of raw materials into a plurality of extruders; The MPP power pipe is formed by a co-extrusion method, wherein the MPP power pipe includes, 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.

2. The preparation method according to claim 1, wherein The first composite PET layer includes a first PET layer and a second PET layer in sequence from the outside to the inside; the second composite PET layer includes a third PET layer and a fourth PET layer in sequence from the outside to the inside.

3. The preparation method according to claim 2, wherein The weight average molecular weight of the polypropylene constituting the first MPP layer is 1,100,000-1,400,000 g / mol.

4. The preparation method according to claim 3, wherein The weight average molecular weight of the polypropylene constituting the second MPP layer is 600,000-800,000 g / mol.

5. The preparation method according to claim 4, wherein The weight average molecular weight of the polypropylene constituting the third MPP layer is 80,000-100,000 g / mol.

6. The preparation method according to claim 5, wherein The weight average molecular weight of the PET in the first PET layer is 170,000-180,000 g / mol; wherein the weight average molecular weight of the PET in the second PET layer is 200,000-220,000 g / mol.

7. The preparation method according to claim 6, wherein The weight average molecular weight of the PET in the third PET layer is 90,000-100,000 g / mol; wherein the weight average molecular weight of the PET in the fourth PET layer is 110,000-130,000 g / mol.

8. The preparation method according to claim 7, wherein The first MPP layer is at least three times thicker than the second MPP layer, and the first MPP layer is at least three times thicker than the third MPP layer.

9. The preparation method according to claim 8, 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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