Polypropylene modified plastic pipe and method for manufacturing the same

Abstract

The application discloses a kind of polypropylene modified plastic pipe and preparation method thereof, it is related to pipeline material technical field.The plastic pipe includes inner layer and outer layer structure: inner layer is by fiber powder, interface modifier (coupling agent 50%-60%, dispersing agent 30%-40%, defoaming agent 5%-10%) and random copolymer polypropylene mixed extrusion molding;Outer layer is by glass fiber or basalt fiber axial uniform distribution on the surface of inner tube through separating plate, with fiber powder, interface modifier and polypropylene co-extrusion coating molding.Preparation when using double extruder co-extrusion process, inner layer extrusion temperature 180-200 DEG C, outer layer 190-210 DEG C, cooling rate ≥10 DEG C / min.The application is reinforced by axial continuous fiber through interface optimization, significantly improves pipeline axial tensile strength (≥45MPa) and ring stiffness (≥50kPa), solves the problem of traditional pipeline delamination deformation and cracking.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of pipe materials, and particularly relates to a polypropylene modified plastic pipe and a preparation method thereof. BACKGROUND

[0002] Polypropylene (PP) pipes are widely used in municipal and chemical fields due to their corrosion resistance, light weight and low cost. However, the traditional PP pipes have defects of low longitudinal tensile strength and insufficient hoop stiffness, and are prone to deformation and cracking under high pressure or large temperature difference. The existing technology modifies the pipes by adding short fibers or fillers, but the random distribution of the fibers leads to uneven enhancement effect, limited axial bearing capacity, and easy delamination failure due to insufficient interfacial bonding force.

[0003] Some studies attempt to use a multi-layer composite structure or a surface treatment process to improve the performance of the pipes. For example, a plasma treatment layer and an adhesive layer are added to the surface of the core pipe to enhance the bonding force of the fiber winding layer, but such a process requires multiple post-processing procedures, has low production efficiency and high cost. Another solution introduces elastomers or nanofibers to improve toughness, but the elastomers are prone to degradation at high temperatures, and the uneven dispersion of nanofibers leads to stress concentration, which poses a risk of leakage during long-term use.

[0004] In view of the above problems, it is urgent to develop a new type of reinforcing structure that simultaneously improves the longitudinal tensile strength and hoop stiffness through the directional arrangement of axial continuous fibers, and designs a composite interfacial agent to optimize the interlayer bonding. At the same time, an efficient preparation process is needed to avoid interfacial failure caused by high-temperature processing, and fundamentally solve the problems of pipe delamination, deformation and cracking. SUMMARY

[0005] The technical problem to be solved by the application is to overcome the above-mentioned defects of the prior art and provide a preparation method of a polypropylene modified plastic pipe with high strength, high production efficiency and excellent interlayer bonding.

[0006] The technical solution adopted by the application to solve the technical problem is as follows:

[0007] A polypropylene modified plastic pipe, characterized in that: an inner layer is formed by mixing and extruding fiber powder, an interfacial improvement agent and random copolymerized polypropylene; and an outer layer is an axial continuous fiber reinforced layer that covers the inner layer and is formed by co-extrusion of continuous fibers, fiber powder, an interfacial improvement agent and random copolymerized polypropylene.

[0008] Preferably, the interfacial improvement agent is composed of a coupling agent, a dispersing agent and a defoaming agent, and the addition amount is 1%-3% of the weight of the matrix.

[0009] Preferably, the components in the interfacial improvement agent are as follows in terms of weight percentage: the coupling agent is 50%-60%, the dispersing agent is 30%-40%, and the defoaming agent is 5%-10%.

[0010] Preferably, the axial continuous fibers are glass fibers or basalt, and the fiber content is 15%-25%.

[0011] Preferably, the continuous fibers are uniformly distributed in the axial direction by a yarn distributing plate, and the aperture of the yarn distributing plate is 5-8 mm.

[0012] A preparation method of a polypropylene modified plastic pipe, characterized in that the method comprises the following steps:

[0013] S1: mixing raw materials for an inner layer, melting and extruding the raw materials through a first extruder, and forming an inner pipe through an annular die;

[0014] S2: distributing continuous fibers on the inner pipe in the axial direction through a yarn distributing plate, and injecting outer layer mixed materials into a second extruder perpendicular to the inner pipe to coat the continuous fibers;

[0015] S3: cooling and shaping the co-extrusion body, and cutting the co-extrusion body to obtain a finished product.

[0016] Preferably, the stirring speed of the raw material mixing in the step S1 is 200-500 rpm.

[0017] Preferably, the temperature of the first extruder is 180-200℃, and the temperature of the second extruder is 190-210℃.

[0018] Preferably, the cooling in the step S3 adopts a spray water tank, the water temperature is 15-20℃, and the cooling rate is ≥10℃ / min.

[0019] Preferably, the pulling speed in the step S3 is 2-3 m / min.

[0020] The present application has the following beneficial effects:

[0021] (1) The axial tensile strength of the present application is improved, and the axial continuous fibers are arranged in a skeleton structure (Example 2: axial tensile strength 48.3 MPa vs. Comparative Example 32.1 MPa);

[0022] (2) The ring stiffness of the present application is improved, and the outer layer co-extrusion coating process makes the fiber and the matrix closely combined (Example 2 ring stiffness 51.7 kPa), and the pipe roundness retention rate is >99%;

[0023] (3) The anti-delamination performance of the present application is excellent, and the coupling agent / dispersant / defoaming agent in the interface improver has a synergistic effect (Example 1 interlayer bonding force 4.8 MPa), and there is no delamination after being boiled in water at 95℃ for 72 hours;

[0024] (4) The thermal stability of the present application is enhanced, and the thermal decomposition temperature of the composite interface agent is >200℃ (Example 2 heat distortion temperature 152℃), which is higher than that of pure polypropylene pipe;

[0025] (5) The production efficiency is improved, and the double-extruder co-extrusion process realizes continuous production (traction speed 2.5 m / min), which is faster than the traditional winding process. DETAILED DESCRIPTION

[0026] The application will be further described below in combination with examples.

[0027] The raw materials or chemical reagents used in the examples and comparative examples of the application are obtained through conventional commercial channels unless otherwise specified; the experimental equipment used in the examples and comparative examples of the application is a double-screw extruder (length-diameter ratio 40:1), a yarn separating plate (pore diameter 6 mm), and a spraying water tank.

[0028] A polypropylene modified plastic pipe raw material example 1

[0029] The polypropylene modified plastic pipe raw material comprises 100 parts of random copolymerized polypropylene (melt index 2.0 g / 10 min), 15 parts of glass fiber powder (particle size 20 μm), and 2 parts of interface modifier (55% coupling agent KH-550, 35% polyethylene wax dispersant, and 10% BYK-065 defoaming agent).

[0030] A polypropylene modified plastic pipe preparation method example 1

[0031] According to the components and weight parts of the polypropylene modified plastic pipe raw material example 1, first, 100 parts of random copolymerized polypropylene (melt index 2.0 g / 10 min), 15 parts of glass fiber powder (particle size 20 μm), and 2 parts of interface modifier (containing 55% KH-550 coupling agent, 35% polyethylene wax dispersant, and 10% BYK-065 defoaming agent) are added to a mixing device and stirred at a speed of 300 rpm for 10 minutes to achieve uniform mixing; then the mixture is melt-extruded at a temperature of 190°C through a first extruder to form a Φ50×3 mm inner tube through an annular die; next, 24 bundles of Tex 2400 glass fibers are evenly distributed on the surface of the inner tube through a yarn separating plate with a pore diameter of 6 mm, and the same formula outer layer mixture is injected into a second extruder (200°C) for synchronous coating; finally, the co-extruded body enters an 18°C spraying water tank for cooling for 12 seconds (cooling rate 12°C / min), and is cut and shaped at a traction speed of 2.2 m / min to complete the preparation of the pipe.

[0032] In order to evaluate the effects of the polypropylene modified plastic pipe preparation method example 1 of the application in enhancing interlayer bonding force, axial tensile strength, roundness deviation, and heat aging test, the following standard test methods are used for comprehensive evaluation:

[0033] Interfacial bonding strength: Adopt ASTM D1876 standard (lap shear strength test method), cut the prepared pipe into 25mm x 100mm strip-shaped sample, and preform a 10mm long standard notch at the interface between the inner and outer layers; install the sample in the clamps of an electronic universal testing machine (such as Instron 5967), apply a vertical peeling force at a crosshead speed of 10mm / min, and record the load-displacement curve in real time until the interlayer is completely separated; the interfacial bonding strength (unit: MPa) is obtained by dividing the peak shear force (unit: kN) by the bonding area (calculated as 25mm x 10mm).

[0034] Axial tensile strength: Adopt GB / T 8804.2-2003 standard (tensile properties test of plastic pipes). Use a microcomputer-controlled electronic tensile testing machine (such as MTS Criterion), cut a dumbbell-shaped sample (gauge length 50mm, width 10mm) along the axial direction of the pipe at a rate of 50mm / min, and apply a uniaxial tensile load to fracture. Real-time record the maximum load (kN) through the sensor, and calculate the tensile strength (unit: MPa) combined with the original cross-sectional area of the sample.

[0035] Roundness deviation: Adopt laser scanning method, use a non-contact roundness instrument (such as Taylor Hobson Talyrond565), place the cross section of the pipe on a rotating table, and scan the surface profile at a speed of 60r / min. Calculate the difference between the maximum diameter and the minimum diameter (unit: mm) by collecting 1000 radial coordinate data, as the roundness deviation value.

[0036] Heat aging test: According to ISO 2578, immerse the sample in 95℃ distilled water for 72 hours, observe the interlayer peeling after taking out and measure the weight change rate (precision ±0.01%), simulate the long-term stability in high temperature environment.

[0037] After the application example 1 of the application is treated by the preparation method of the polypropylene modified plastic pipe, the interfacial bonding strength reaches 4.8MPa. Due to the 55% KH-550 coupling agent in the interfacial modifier forms chemical bond bridge with the polypropylene carboxyl group and the glass fiber silanol group during the melting process; the 35% polyethylene wax dispersant eliminates fiber powder agglomeration by reducing the melt viscosity, and increases the effective bonding area; the 10% BYK-065 defoaming agent inhibits the aggregation of processing bubbles at the interface, avoids the formation of stress concentration micro defects, and the three synergistically realize the dense interface transition layer.

[0038] After the application is detected, the polypropylene modified plastic pipe prepared by the preparation method of the application has no delamination phenomenon after being boiled in 95℃ water for 72 hours. The result is due to the elimination of micro-holes by the defoaming agent, and the thermal stability of the isocyanate group in the molecular chain of the coupling agent maintains the chemical bond strength in a high temperature and humid environment; the uniform interface layer formed by the dispersing agent blocks the water penetration path, and the triple protection mechanism effectively resists the interlayer peeling caused by thermal expansion stress.

[0039] After the application is detected, the polypropylene modified plastic pipe prepared by the preparation method of the application has an axial tensile strength of 42.6MPa. Because the interface improver optimizes the stress transfer efficiency of the fiber / matrix: the coupling agent improves the interfacial compatibility to improve the load transfer rate; the dispersing agent ensures that the fiber powder is uniformly distributed in the matrix, eliminating local weak areas; the defoaming agent reduces the interfacial micro-holes to make the stress distribution more uniform, avoiding early fracture.

[0040] After the application is detected, the polypropylene modified plastic pipe prepared by the preparation method of the application has a pipe roundness deviation of only 0.21mm after cooling. This is due to the elimination of local shrinkage differences caused by bubbles by the defoaming agent, and the promotion of uniform crystallization of the melt by the dispersing agent; the coupling agent enhances the interfacial bonding force to inhibit the deformation caused by cooling shrinkage stress, and cooperates with a cooling rate of 12℃ / min to achieve rapid shaping.

[0041] A polypropylene modified plastic pipe raw material example 2

[0042] The polypropylene modified plastic pipe raw material example 2 includes: the inner layer is the same as example 1, and the outer layer glass fiber content varies (15% / 20% / 25%).

[0043] A polypropylene modified plastic pipe preparation method example 2

[0044] According to the components and weight parts of the polypropylene modified plastic pipe raw material example 2, the inner layer is prepared in the same way as example one, the interface improver is fixed at 2.5 parts (60% coupling agent, 35% dispersing agent, 5% defoaming agent), and the outer layer varies with 15%, 20% or 25% glass fiber content; in the specific operation, the inner layer raw material is stirred at 300rpm for 10 minutes, then extruded into an inner tube through a 190℃ first extruder, then a continuous glass fiber bundle with a preset content is distributed axially on the inner tube through a 6mm yarn distributor, and the outer layer mixture is melted in a 200℃ second extruder and wrapped around the fiber layer; the co-extrusion body is then cooled in a 18℃ spray water tank for 12 seconds (rate 12℃ / min), finally cut at 2.2m / min, and the optimal value is determined by comparing the performance of samples with different fiber contents.

[0045] In order to evaluate the effect of the polypropylene modified plastic pipe preparation method example 2 on the axial tensile strength and ring stiffness, the following standard test methods are used for comprehensive evaluation:

[0046] Axial tensile strength: same as example 1;

[0047] Ring stiffness: according to GB / T 9647-2015 standard (plastic pipe ring stiffness test), a 300mm long pipe segment is placed under a ring pressure plate, with a 3% deformation of the pipe diameter as the target, a radial load is applied at a rate of 2mm / min, the load-deformation curve is recorded, and the ring stiffness is calculated according to the formula S=(F×1000) / (ΔY×L) (unit: kPa, where F is the load, ΔY is the deformation, and L is the sample length).

[0048] After detection, the axial tensile strength of the polypropylene modified plastic pipe prepared by the method of example 2 is 42.6MPa and the ring stiffness is 46.8kPa when the fiber content is 15%. This result is due to the low stress transfer efficiency caused by insufficient fiber content: the proportion of glass fiber as the reinforcing framework is low, the main tensile load is borne by the polypropylene matrix, and the fiber dispersion uniformity is insufficient, resulting in uneven ring stress distribution; at the same time, the fiber content does not reach the critical value, the interfacial shear strength is not fully activated, and the coupling agent effect is limited, resulting in limited strength and stiffness improvement.

[0049] After detection, the axial tensile strength of the polypropylene modified plastic pipe prepared by the method of example 2 is significantly improved to 48.3MPa and the ring stiffness is 51.7kPa when the fiber content is 20%. This is due to the synergistic optimization of fiber / matrix: continuous fiber axial distribution forms an efficient load-bearing network, coupling agent forms a chemical bond bridge at the fiber-polypropylene interface, and dispersant ensures melt flowability, so that the fiber is uniformly infiltrated; the load increases linearly without stress concentration mutation point, and the ring stiffness is improved because the fiber framework effectively inhibits radial deformation.

[0050] After detection, the axial tensile strength of the polypropylene modified plastic pipe prepared by the method of example 2 is reduced to 45.1MPa and the ring stiffness is 50.2kPa when the fiber content is 25%. The main reason is that excessive fiber causes melt coating defects: high fiber ratio leads to a sharp increase in melt viscosity, insufficient flow during outer layer co-extrusion, and increased porosity; at the same time, fiber accumulation weakens the effect of interfacial modifier, and the stress transfer path is interrupted, so that the increase in ring stiffness is narrowed due to the weakening of the overall structure by porosity.

[0051] A polypropylene modified plastic pipe raw material example 3

[0052] The polypropylene modified plastic pipe raw material example 3 comprises: same as example 2 (fiber 20%).

[0053] A polypropylene modified plastic pipe preparation method example 3

[0054] According to the components and weight parts of the polypropylene modified plastic pipe raw material example 3, the raw material ratio is consistent with example 2 (20% fiber content), the inner layer is constant at 190℃ extrusion temperature, and the outer layer temperature is set at 190℃, 200℃ and 210℃ respectively; during operation, the inner layer mixture is formed into an inner pipe after stirring by the first extruder, the continuous fibers are distributed axially after passing through the yarn distributor, and the outer layer mixture is melt coated in the second extruder with variable temperature; the co-extrusion body then enters the 18℃ spray water tank for cooling for 12 seconds (rate 12℃ / min), and the cutting is completed at a pulling speed of 2.2m / min, and the process window is optimized by analyzing the thermal deformation and roundness data at different temperatures.

[0055] In order to evaluate the effect of the polypropylene modified plastic pipe preparation method example 3 on the heat distortion temperature and roundness deviation, the following standard test methods are used for comprehensive evaluation:

[0056] Heat distortion temperature: follow the ISO 75-2:2013 standard (plastic heat distortion temperature test method). Use a heat distortion instrument (such as Ceast HDT 3 VICAT), process the pipe sample into a 120mm×10mm×4mm cuboid sample, place it in a silicone oil bath, and apply a constant bending stress of 0.45MPa. Heat at a rate of 120℃ / h, record the temperature when the center deformation of the sample reaches 0.2mm as the heat distortion temperature (unit: ℃);

[0057] Roundness deviation: same as example 1.

[0058] After detection, the polypropylene modified plastic pipe preparation method example 3 treated by the application has a heat distortion temperature of 143℃ at an outer layer temperature of 190℃, and a roundness deviation of 0.38mm. 190℃ is lower than the best melting window of atactic polypropylene, the outer layer resin has poor flowability, and cannot completely coat the axial continuous fibers, forming local dry spots. At the same time, the interface improver is not fully activated, the coupling agent reaction efficiency is reduced, the fiber / matrix combination is weakened, causing non-uniform shrinkage, which ultimately increases the roundness deviation and reduces the thermal stability.

[0059] After detection, the polypropylene modified plastic pipe preparation method example 3 treated by the application has a heat distortion temperature of 152℃ at an outer layer temperature of 200℃, and a roundness deviation of 0.21mm. This is due to the precise matching of temperature to material characteristics: 200℃ is close to the polypropylene melting peak, ensuring that the melt flows fully and the fibers are fully infiltrated. The interface improver works efficiently, forming a dense chemical bond network to inhibit cooling shrinkage stress; combined with a cooling rate of 12℃ / min (18℃ spray water tank), rapid setting reduces crystallization defects, achieving ultra-high roundness accuracy and thermal stability.

[0060] After the treatment of the application, the outer layer temperature of the polypropylene modified plastic pipe prepared by the method of Example 3 is 210℃, and the heat distortion temperature is reduced to 148℃, and the roundness deviation is increased to 0.45mm. The main reason is that high temperature causes thermal degradation: 210℃ exceeds the heat resistance limit of the interfacial modifier, and the decomposition of the defoaming agent produces micropores, which weakens the interlayer bonding force. At the same time, the over-heating of the melt leads to viscosity fluctuation, and the fiber distribution is disordered, resulting in uneven shrinkage during cooling, and finally the roundness deviation is large, and the heat distortion temperature is reduced due to the rupture of the molecular chain of the matrix.

[0061] A traditional polypropylene modified plastic pipe raw material comparative example 1

[0062] The traditional polypropylene modified plastic pipe raw material comparative example 1 includes: the inner layer is the same as example 1, and the outer layer cancels the fiber and only uses polypropylene + fiber powder mixture.

[0063] A traditional polypropylene modified plastic pipe preparation method comparative example 1

[0064] According to the components and weight parts of the traditional polypropylene modified plastic pipe raw material comparative example 1, first, the inner layer raw material - 100 parts of random copolymerized polypropylene (melt index 2.0g / 10min), 15 parts of glass fiber powder (particle size 20μm) and 2 parts of interfacial modifier (containing 55% KH-550 coupling agent, 35% polyethylene wax dispersant and 10% BYK-065 defoaming agent) are put into a mixer to stir for 10 minutes at a speed of 300rpm; then a Φ50×3mm inner tube is extruded by a first extruder at a temperature of 190℃; then, the fiber separation and coating process is cancelled, and the mixture (without continuous fiber) is directly injected into a second extruder at a temperature of 200℃ to extrude a single material outer layer; the co-extrusion body enters a 18℃ spray water tank for cooling for 12 seconds (cooling rate 12℃ / min), and finally is cut and shaped at a pulling speed of 2.2m / min to obtain a comparative pipeline sample without axial fiber reinforced structure.

[0065] In order to evaluate the effect of the traditional polypropylene modified plastic pipe preparation method comparative example 1 on axial tensile strength, heat aging test and ring stiffness, the following standard test methods are used for comprehensive evaluation:

[0066] The axial tensile strength and heat aging test are the same as example 1;

[0067] Ring stiffness: the same as example 2.

[0068] After the application of the application to the preparation method of a traditional polypropylene modified plastic pipe of Comparative Example 1, the axial tensile strength is only 32.1 MPa. The result is due to the cancellation of the axial continuous fiber reinforced layer, resulting in the failure of the stress transfer mechanism: the polypropylene matrix alone bears all the load, lacking the load sharing of the fiber skeleton; at the same time, although the interface improver exists, there is no fiber anchoring point, and it cannot form an effective chemical bond bridge, and the stress is concentrated in the weak area of the matrix, causing early fracture. The addition of fiber powder only provides limited reinforcement and cannot make up for the axial load advantage of continuous fibers, and the final strength is much lower than the reinforced structure.

[0069] After the application of the application to the preparation method of a traditional polypropylene modified plastic pipe of Comparative Example 1, the interlayer completely peels off after 24 hours of boiling in water at 95°C. The main reason is that the mismatch of the thermal expansion coefficient causes the interface shear failure: the inner layer and the outer layer are both homogeneous polypropylene mixtures, but the cooling shrinkage stress is not inhibited by the fiber skeleton; in a hot and humid environment, the thermal stability of the coupling agent of the interface improver is insufficient, and the chemical bond degradation weakens the bonding force. Water penetrates along the fiber-free interface, exacerbating interlayer sliding, and micro-cracks expand to through defects, and the thermal stress far exceeds the interface tolerance limit, resulting in irreversible delamination.

[0070] After the application of the application to the preparation method of a traditional polypropylene modified plastic pipe of Comparative Example 1, the ring stiffness is only 28.9 kPa. Due to the lack of radial bearing structure: no three-dimensional skeleton formed by continuous fibers, the deformation resistance of the pipe under pressure is insufficient; although the fiber powder is dispersed in the matrix, it cannot establish a continuous reinforcing network. The shrinkage stress is uniform during the cooling process, but there is no inhibition mechanism (roundness deviation 0.6 mm), the structural integrity is weakened, the elastic modulus decays, and the radial stiffness decreases. This result confirms the necessity of the axial fiber reinforced layer for improving the ring stiffness.

[0071] In summary, after the application of the application to the preparation method of a traditional polypropylene modified plastic pipe of Comparative Example 1, the Comparative Example cancels the axial continuous fiber reinforced layer and only uses homogeneous polypropylene mixture to extrude, resulting in a sharp drop in axial tensile strength to 32.1 MPa, ring stiffness only 28.9 kPa, and interlayer peeling after 24 hours of boiling in water at 95°C. In Example 1, by optimizing the ratio of the interface improver (coupling agent 55%, dispersant 35%, defoaming agent 10%), using a double extruder co-extrusion process (inner layer 190°C, outer layer 200°C) to prepare a polypropylene modified plastic pipe, the interlayer bonding force is improved to 4.8 MPa and the axial tensile strength is improved to 42.6 MPa, due to the synergistic effect of coupling agent enhanced chemical bond, dispersant eliminated fiber agglomeration and defoaming agent inhibited defects, highlighting the necessity of fiber skeleton and interface optimization in Example 1, verifying the core advantages of the application in improving the mechanical properties and thermal stability of the pipe.

Claims

1. A polypropylene modified plastic pipe, characterized in that: The product comprises an inner layer extruded from a mixture of fiber powder, an interface modifier, and random copolymer polypropylene; and an outer layer coated with an axially continuous fiber reinforcement layer, co-extruded from fiber powder, an interface modifier, and random copolymer polypropylene. The interface modifier consists of a coupling agent, a dispersant, and a defoamer, added at 1%-3% of the base weight. The components of the interface modifier, by weight percentage, are: coupling agent 50%-60%, dispersant 30%-40%, and defoamer 5%-10%. The coupling agent is KH-550, the dispersant is polyethylene wax, and the defoamer is BYK-065. The preparation method of the polypropylene modified plastic pipe includes the following steps. S1: The inner layer raw materials are mixed and then melted and extruded through the first extruder, and the inner tube is formed through the ring die; S2: The continuous fibers are axially distributed on the inner tube through the yarn splitter, while the outer layer mixture is injected into the second extruder perpendicular to the inner tube to coat the continuous fibers. S3: The co-extruded material is cooled, shaped, and then cut to obtain the finished product.

2. The polypropylene modified plastic pipe according to claim 1, characterized in that: The axial continuous fiber is glass fiber or basalt, with a fiber content of 15%-25%.

3. The polypropylene modified plastic pipe according to claim 2, characterized in that: The continuous fibers are axially uniformly distributed through a yarn separating plate with a hole diameter of 5-8 mm.

4. The polypropylene modified plastic pipe according to claim 1, characterized in that: The stirring speed for mixing the raw materials in step S1 is 200-500 rpm.

5. The polypropylene modified plastic pipe according to claim 1, characterized in that: The temperature of the first extruder is 180-200℃, and the temperature of the second extruder is 190-210℃.

6. The polypropylene modified plastic pipe according to claim 1, characterized in that: In step S3, cooling is achieved using a spray water tank with a water temperature of 15-20℃ and a cooling rate of ≥10℃ / min.

7. A polypropylene modified plastic pipe according to claim 1, characterized in that: The traction speed in step S3 is 2-3 m / min.