Polypropylene modified plastic pipe and preparation method thereof

Abstract

The invention discloses a polypropylene modified plastic pipe and a preparation method thereof and relates to the technical field of pipeline materials. The plastic pipe comprises an inner-layer structure and an outer-layer structure, wherein the inner layer is formed by mixing and extruding fiber powder, an interface improving agent (50-60% of a coupling agent, 30-40% of a dispersing agent and 5-10% of a defoaming agent) and polypropylene random copolymer; and the outer layer is formed by axially and uniformly distributing glass fibers or basalt fibers on the surface of the inner pipe through a yarn splitting plate, and co-extruding and coating the glass fibers or basalt fibers with fiber powder, an interface improver and polypropylene. During preparation, a double-extruder co-extrusion process is adopted, the extrusion temperature of the inner layer is 180-200 DEG C, the extrusion temperature of the outer layer is 190-210 DEG C, and the cooling rate is greater than or equal to 10 DEG C / min. Through optimization of the axial continuous fiber reinforced layer and the interface, the axial tensile strength (larger than or equal to 45 MPa) and the ring stiffness (larger than or equal to 50 kPa) of the pipeline are remarkably improved, and the problems of layering deformation and cracking of a traditional pipeline are solved.

Description

Technical Field

[0001] This invention belongs to the field of pipeline materials technology, specifically relating to a polypropylene modified plastic pipe and its preparation method. Background Technology

[0002] Polypropylene (PP) pipes are widely used in municipal and chemical industries due to their advantages such as corrosion resistance, lightweight, and low cost. However, traditional PP pipes suffer from low longitudinal tensile strength and insufficient circumferential stiffness, making them prone to deformation and cracking under high pressure or large temperature variations. Existing technologies modify PP pipes by adding short fibers or fillers, but the random distribution of fibers leads to uneven reinforcement, limited improvement in axial load-bearing capacity, and susceptibility to delamination failure due to insufficient interfacial bonding.

[0003] Some studies have attempted to improve pipe performance using multi-layered composite structures or surface treatment processes. For example, adding a plasma treatment layer and an adhesive layer to the core tube surface can enhance the bonding strength of the fiber winding layer. However, such processes require multiple post-processing steps, resulting in low production efficiency and high costs. Another approach involves introducing elastomers or nanofibers to improve toughness, but elastomers are prone to degradation at high temperatures, and uneven dispersion of nanofibers can lead to stress concentration, posing a risk of leakage with long-term use.

[0004] To address the aforementioned issues, there is an urgent need to develop a novel reinforcement structure: axially continuous fiber orientation arrangement to simultaneously enhance longitudinal tensile strength and circumferential stiffness, and a composite interface agent to optimize interlayer bonding. Simultaneously, an efficient manufacturing process is required to avoid interface failure caused by high-temperature processing, fundamentally solving the problems of pipe delamination deformation and cracking. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to overcome the above-mentioned defects of the prior art and provide a method for preparing polypropylene modified plastic pipe that takes into account high strength, high production efficiency and excellent interlayer bonding.

[0006] The technical solution adopted by this invention to solve its technical problem is as follows: A modified polypropylene plastic pipe, characterized in that: it comprises an inner layer formed by extrusion of a mixture of fiber powder, interface modifier and random copolymer polypropylene; and an outer layer covering the inner layer with an axially continuous fiber reinforcement layer formed by co-extrusion of continuous fiber, fiber powder, interface modifier and random copolymer polypropylene.

[0007] Preferably, the interface improver is composed of a coupling agent, a dispersant, and an antifoaming agent, and the amount added is 1%-3% of the weight of the base material.

[0008] Preferably, the components of the interface improver are, by weight percentage: 50%-60% coupling agent, 30%-40% dispersant, and 5%-10% defoamer.

[0009] Preferably, the axial continuous fiber is glass fiber or basalt, and the fiber content is 15%-25%.

[0010] Preferably, the continuous fibers are axially uniformly distributed by a yarn separating plate, and the diameter of the yarn separating plate is 5-8 mm.

[0011] A method for preparing a polypropylene modified plastic pipe, characterized by comprising 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.

[0012] Preferably, the stirring speed for mixing the raw materials in step S1 is 200-500 rpm.

[0013] Preferably, the temperature of the first extruder is 180-200℃, and the temperature of the second extruder is 190-210℃.

[0014] Preferably, 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.

[0015] Preferably, the traction speed in S3 is 2-3 m / min.

[0016] The beneficial effects of this invention are as follows: (1) The present invention improves the axial tensile strength and forms a skeleton structure by axial continuous fiber orientation arrangement (Example 2: axial tensile strength 48.3MPa vs Comparative Example 32.1MPa). (2) The ring stiffness of the present invention is improved, and the co-extrusion coating process of the outer layer makes the fiber and the matrix tightly bonded (ring stiffness of 51.7 kPa in Example 2), and the pipe roundness retention rate is >99%; (3) The present invention has excellent anti-delamination performance. The coupling agent / dispersant / defoamer in the interface improver have a synergistic effect (interlayer bonding force of 4.8MPa in Example 1), and no delamination occurs after boiling in water at 95°C for 72 hours; (4) The present invention has enhanced thermal stability, and the composite interface agent has a thermal decomposition temperature >200℃ (heat distortion temperature of 152℃ in Example 2), which is higher than that of pure polypropylene pipes; (5) The present invention improves production efficiency and achieves continuous production through dual extruder co-extrusion process (traction speed 2.5m / min), which is faster than the traditional winding process. Detailed Implementation

[0017] The present invention will be further described below with reference to the embodiments.

[0018] Unless otherwise specified, the raw materials or chemical reagents used in the embodiments and comparative examples of this invention were obtained through conventional commercial channels. The experimental equipment used in the embodiments and comparative examples of this invention is a twin-screw extruder (length-to-diameter ratio 40:1), a yarn separating plate (orifice diameter 6mm), and a spray tank.

[0019] Example 1 of a raw material for modified polypropylene plastic pipes The raw material for the modified polypropylene plastic pipe includes: 100 parts of random copolymer polypropylene (melt index 2.0 g / 10 min), 15 parts of glass fiber powder (particle size 20 μm), and 2 parts of interface improver (coupling agent KH-550 55%, dispersant polyethylene wax 35%, defoamer BYK-065 10%).

[0020] Example 1: A method for preparing a polypropylene modified plastic pipe According to the components and weight parts of Example 1 of a polypropylene modified plastic pipe raw material, firstly, 100 parts of random copolymer polypropylene (melt index 2.0 g / 10 min), 15 parts of glass fiber powder (particle size 20 μm), and 2 parts of interface improver (containing 55% KH-550 coupling agent, 35% polyethylene wax dispersant, and 10% BYK-065 defoamer) were added to a mixing device and stirred at 300 rpm for 10 minutes to achieve uniform mixing. Then, the mixture was melt-extruded through a first extruder at 190°C and formed into a Φ50×3 mm inner tube through a ring die. Next, 24 bundles of Tex 2400 glass fibers were axially and evenly distributed on the surface of the inner tube through a 6 mm aperture yarn separator. At the same time, the outer layer mixture of the same formula was injected into a second extruder (200°C) for synchronous coating. Finally, the co-extrusion was cooled in an 18°C ​​spray water tank for 12 seconds (cooling rate 12°C / min) and cut and shaped at a traction speed of 2.2 m / min to complete the pipe preparation.

[0021] To evaluate the effectiveness of Example 1 of the preparation method for the modified polypropylene plastic pipe of the present invention in terms of enhanced interlayer bonding, axial tensile strength, roundness deviation, and thermal aging test, the following standard test methods were used for comprehensive evaluation: Interlayer bond strength: Using ASTM D1876 standard (lap shear strength test method), the prepared pipe was cut into 25mm×100mm strip specimens, and a 10mm long standard notch was pre-made at the interface between the inner and outer layers. The specimens were installed in the fixture of an electronic universal testing machine (such as Instron 5967), and a vertical peel force was applied at a crosshead speed of 10mm / min. The load-displacement curve was recorded in real time until the interlayers were completely separated. The interlayer bond strength (unit: kN) was obtained by dividing the peak shear force (unit: kN) by the bonded area (calculated as 25mm×10mm).

[0022] Axial tensile strength: Compliance with GB / T 8804.2-2003 standard (Tensile properties test of plastic pipes). A computer-controlled electronic tensile testing machine (such as MTS Criterion) was used. Dumbbell-shaped specimens (50 mm gauge length, 10 mm width) were cut along the pipe axis, and a uniaxial tensile load was applied at a rate of 50 mm / min until fracture. The maximum load (kN) was recorded in real time using sensors, and the tensile strength (unit: MPa) was calculated based on the original cross-sectional area of ​​the specimen.

[0023] Roundness deviation: A laser scanning method is used, employing a non-contact roundness meter (such as Taylor Hobson Talyrond 565). The pipe cross-section is placed on a rotary table, and the surface profile is scanned at a speed of 60 r / min. By collecting radial coordinate data from 1000 points, the difference between the maximum and minimum diameters (unit: mm) is calculated as the roundness deviation value.

[0024] Thermal aging test: According to ISO 2578, the sample was immersed in distilled water at 95°C for 72 hours. After removal, the interlayer peeling was observed and the weight change rate was measured (accuracy ±0.01%) to simulate the long-term stability under high temperature environment.

[0025] Testing revealed that, after treatment with a method for preparing modified polypropylene plastic pipes according to Example 1 of this invention, the interlayer bonding strength reached 4.8 MPa. This is attributed to the fact that the 55% KH-550 coupling agent in the interface improver forms chemical bridges with the polypropylene carboxyl groups and glass fiber silanol groups during the melting process; the 35% polyethylene wax dispersant eliminates fiber powder agglomeration by reducing melt viscosity, increasing the effective bonding area; and the 10% BYK-065 defoamer inhibits the aggregation of processing bubbles at the interface, avoiding the formation of stress concentration micro-defects. The three components work synergistically to achieve a dense interface transition layer.

[0026] Testing revealed that, after treatment with a polypropylene modified plastic pipe prepared according to Example 1 of this invention, no stratification occurred after boiling in water at 95°C for 72 hours. This result is attributed to the defoamer's ability to eliminate micropores, the coupling agent's molecular chain containing heat-stable isocyanate groups which maintain chemical bond strength under high temperature and humidity conditions, and the dispersant forming a uniform interface layer that blocks moisture penetration pathways. This triple protection mechanism effectively resists interlayer delamination caused by thermal expansion stress.

[0027] Testing revealed that, after treatment with a method for preparing a modified polypropylene plastic pipe according to Example 1 of this invention, the axial tensile strength reached 42.6 MPa. This was achieved because the interface modifier optimized the fiber / matrix stress transfer efficiency: the coupling agent improved interfacial compatibility, thus increasing the load transfer rate; the dispersant ensured uniform distribution of fiber powder in the matrix, eliminating localized weak areas; and the defoamer reduced interfacial micropores, resulting in a more balanced stress distribution and preventing premature fracture.

[0028] Testing revealed that, after processing with a method for preparing a modified polypropylene plastic pipe according to Example 1 of this invention, the pipe roundness deviation after cooling was only 0.21 mm. This is attributed to the defoamer eliminating local shrinkage differences caused by air bubbles, the dispersant promoting uniform melt crystallization, and the coupling agent enhancing interfacial bonding to suppress deformation caused by cooling shrinkage stress, combined with a cooling rate of 12℃ / min to achieve rapid shaping.

[0029] Example 2 of a raw material for modified polypropylene plastic pipes Example 2 of the polypropylene modified plastic pipe raw material includes: the inner layer is the same as in Example 1, and the glass fiber content of the outer layer varies (15% / 20% / 25%).

[0030] Example 2: A method for preparing a polypropylene modified plastic pipe According to the components and weight parts of a polypropylene modified plastic pipe raw material in Example 2, the inner layer preparation is the same as in Example 1, with a fixed interface improver of 2.5 parts (60% coupling agent, 35% dispersant, and 5% defoamer). The outer layer variable uses 15%, 20%, or 25% glass fiber content. In specific operation, the inner layer raw material is first stirred at 300 rpm for 10 minutes and then extruded into an inner tube through a first extruder at 190°C. Then, a set amount of continuous glass fiber bundles is axially distributed on the inner tube through a 6mm yarn divider. The outer layer mixture is melted in a second extruder at 200°C and coated with the fiber layer. The co-extrusion is then cooled in a 18°C ​​spray water tank for 12 seconds (rate 12°C / min) and finally cut at 2.2 m / min. The optimal value is determined by comparing the performance of samples with different fiber contents.

[0031] To evaluate the effect of Example 2 of the preparation method of the polypropylene modified plastic pipe of the present invention on axial tensile strength and ring stiffness, the following standard test methods were used for comprehensive evaluation: Axial tensile strength: Same as in Example 1; Ring stiffness: According to GB / T 9647-2015 standard (test of ring stiffness of plastic pipe), a 300mm long pipe section is placed under an annular pressure plate. With a target deformation of 3% of the pipe diameter, 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 specimen length).

[0032] Testing revealed that, after treatment with a polypropylene modified plastic pipe prepared according to Example 2 of this invention, the axial tensile strength reached 42.6 MPa and the ring stiffness reached 46.8 kPa when the fiber content was 15%. This result is attributed to the low stress transfer efficiency caused by insufficient fiber content: the proportion of glass fiber as a reinforcing skeleton is low, the matrix polypropylene bears the main tensile load, and the fiber dispersion is insufficient, resulting in uneven circumferential stress distribution; at the same time, the fiber content did not reach the critical value, and the interfacial shear strength did not fully activate the coupling agent, resulting in limited improvement in strength and stiffness.

[0033] Testing revealed that, after treatment with a polypropylene modified plastic pipe preparation method according to Example 2 of this invention, the axial tensile strength significantly increased to 48.3 MPa and the ring stiffness reached 51.7 kPa when the fiber content was 20%. This is attributed to the synergistic optimization of the fiber / matrix: the continuous axial distribution of fibers forms a highly efficient load-bearing network, the coupling agent forms chemical bond bridges at the fiber-polypropylene interface, the dispersant ensures melt flowability, and the fibers are uniformly wetted; the load increases linearly without stress concentration abrupt changes, and the ring stiffness is improved because the fiber skeleton effectively suppresses radial deformation.

[0034] Testing revealed that, after treatment with a modified polypropylene plastic pipe according to Example 2 of this invention, the axial tensile strength decreased to 45.1 MPa and the ring stiffness to 50.2 kPa when the fiber content was 25%. This was mainly due to melt coating defects caused by excessive fiber: the high fiber content led to a sharp increase in melt viscosity, insufficient flow during co-extrusion of the outer layer, and increased porosity; at the same time, fiber accumulation weakened the effect of the interface improver, interrupted the stress transmission path, and narrowed the increase in ring stiffness due to reduced structural integrity caused by porosity.

[0035] Example 3 of a raw material for modified polypropylene plastic pipes Example 3 of the polypropylene modified plastic pipe raw material includes: the same as in Example 2 (20% fiber).

[0036] Example 3: A method for preparing a polypropylene modified plastic pipe According to Example 3 of a polypropylene modified plastic pipe raw material, the components and weight parts are the same as in Example 2 (20% fiber content). The inner layer is kept at a constant extrusion temperature of 190°C, and the outer layer temperatures are set to 190°C, 200°C and 210°C respectively. During operation, the inner layer mixture is stirred and then formed into an inner tube by the first extruder. After the continuous fibers are axially distributed through the yarn separator, the outer layer mixture is melt-coated in the second extruder with a variable temperature. The co-extrusion is then cooled in an 18°C ​​spray water tank for 12 seconds (rate 12°C / min) and cut at a traction speed of 2.2m / min. The process window is optimized by analyzing the heat deformation and roundness data at different temperatures.

[0037] To evaluate the effect of Example 3 of the preparation method of the polypropylene modified plastic pipe of the present invention on heat distortion temperature and roundness deviation, the following standard test methods were used for comprehensive evaluation: Heat distortion temperature: Follow ISO 75-2:2013 standard (Plastics heat distortion temperature test method). Using a heat distortion tester (such as Ceast HDT 3 VICAT), process the pipe sample into a 120mm × 10mm × 4mm cuboid specimen, place it in a silicone oil bath, and apply a constant bending stress of 0.45MPa. Heat at a heating rate of 120℃ / h, and record the temperature at which the deformation at the center of the specimen reaches 0.2mm as the heat distortion temperature (unit:℃). Roundness deviation: Same as in Example 1.

[0038] Testing revealed that, after treatment with a polypropylene modified plastic pipe method according to Example 3 of this invention, the heat distortion temperature at an outer layer temperature of 190℃ was 143℃, and the roundness deviation reached 0.38mm. 190℃ is below the optimal melting window for random copolymer polypropylene, resulting in poor resin flowability in the outer layer, failing to completely coat the axially continuous fibers and forming localized dry spots. Simultaneously, the interface improver was not fully activated, the coupling agent's reaction efficiency decreased, and the weakened fiber / matrix bond led to uneven shrinkage, ultimately increasing the roundness deviation and reducing thermal stability.

[0039] Testing revealed that, after treatment with a polypropylene modified plastic pipe preparation method as described in Example 3 of this invention, the heat distortion temperature at an outer layer temperature of 200℃ increased to 152℃, and the roundness deviation was optimized to 0.21mm. This is attributed to the precise temperature matching of material characteristics: 200℃ is close to the melting peak of polypropylene, ensuring sufficient melt flow and complete fiber wetting. The interface improver effectively forms a dense chemical bond network, suppressing cooling shrinkage stress; combined with a cooling rate of 12℃ / min (18℃ in the spray tank), rapid shaping reduces crystallization defects, achieving ultra-high roundness accuracy and thermal stability.

[0040] Testing revealed that, after treatment with a polypropylene modified plastic pipe preparation method as described in Example 3 of this invention, the heat distortion temperature at an outer layer temperature of 210℃ decreased to 148℃, and the roundness deviation increased to 0.45mm. This was mainly due to thermal degradation caused by high temperature: 210℃ exceeded the heat resistance limit of the interface improver, and the defoamer decomposed to produce micropores, weakening the interlayer bonding force. Simultaneously, melt overheating led to viscosity fluctuations, disordered fiber distribution, and uneven shrinkage during cooling, ultimately resulting in a large roundness deviation and a decrease in heat distortion temperature due to the breakage of the matrix molecular chains.

[0041] Comparative Example 1: A Traditional Polypropylene Modified Plastic Pipe Raw Material The aforementioned comparative example 1 of a traditional polypropylene modified plastic pipe raw material includes: the inner layer is the same as in Example 1, but the outer layer omits fibers and uses only a mixture of polypropylene and fiber powder.

[0042] Comparative Example 1: A method for preparing a traditional polypropylene modified plastic pipe According to the components and weight parts of a traditional polypropylene modified plastic pipe raw material comparative example 1, the inner layer raw material—100 parts of random copolymer 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 defoamer)—was first put into a mixer and stirred at 300 rpm for 10 minutes. Then, the inner tube of Φ50×3 mm was melt-extruded through the first extruder at 190℃. Next, the fiber separation and coating process was eliminated, and the same formula mixture (excluding continuous fibers) was directly injected into the second extruder and the outer layer of a single material was extruded at 200℃. The co-extrusion was cooled in a 18℃ spray water tank for 12 seconds (cooling rate 12℃ / min), and finally cut and shaped at a traction speed of 2.2 m / min to obtain a comparative pipe sample with a non-axial fiber reinforced structure.

[0043] To evaluate the effectiveness of a traditional polypropylene modified plastic pipe preparation method in Comparative Example 1 in terms of axial tensile strength, heat aging test, and ring stiffness, the following standard test methods were used for comprehensive evaluation: Axial tensile strength and thermal aging tests are the same as in Example 1; Ring stiffness: Same as in Example 2.

[0044] Testing revealed that the axial tensile strength of Comparative Example 1, after treatment using a traditional method for preparing modified polypropylene plastic pipes, was only 32.1 MPa. This result stems from the removal of the outer axial continuous fiber reinforcement layer, leading to the failure of the stress transfer mechanism: the polypropylene matrix bears the entire load alone, lacking the load-bearing capacity of the fiber skeleton; simultaneously, although the interface modifier is present, there are no fiber anchoring points, preventing the formation of effective chemical bonds, causing stress concentration in the weak areas of the matrix and triggering early fracture. The addition of fiber powder provides only limited reinforcement and cannot compensate for the axial load-bearing advantage of continuous fibers, resulting in a final strength far lower than that of the reinforced structure.

[0045] Testing revealed that, in Comparative Example 1 of this invention, after treatment with a traditional method for preparing modified polypropylene plastic pipes, complete delamination occurred after boiling in water at 95°C for 24 hours. The main cause was interfacial shear failure due to a mismatch in thermal expansion coefficients: both the inner and outer layers were homogeneous polypropylene mixtures, but the cooling shrinkage stress was not suppressed by a fiber skeleton; under humid and hot conditions, the coupling agent in the interface improver lacked thermal stability, and chemical bond degradation weakened the bonding force. Moisture penetrated along the fiberless interface, exacerbating interfacial slippage, causing microcracks to propagate into penetrating defects, and thermal stress far exceeding the interface tolerance limit, leading to irreversible delamination.

[0046] Testing revealed that the ring stiffness of Comparative Example 1, after treatment using a conventional method for preparing modified polypropylene plastic pipes, was only 28.9 kPa. This was attributed to the lack of a radial load-bearing structure: the absence of a continuous fiber-formed three-dimensional skeleton resulted in insufficient deformation resistance under pressure; although the fiber powder was dispersed in the matrix, it could not establish a continuous reinforcing network. During cooling, the shrinkage stress was uniform but lacked an inhibition mechanism (roundness deviation of 0.6 mm), weakening the overall structural integrity, reducing the elastic modulus, and decreasing the radial stiffness. This result confirms the necessity of an axial fiber reinforcement layer for improving ring stiffness.

[0047] In summary, Comparative Example 1, after being processed using a traditional method for preparing modified polypropylene pipes, suffered a sharp drop in axial tensile strength to 32.1 MPa and ring stiffness to only 28.9 kPa due to the elimination of the axial continuous fiber reinforcement layer and the use of only homogeneous polypropylene mixture extrusion. This resulted in interlayer delamination after boiling in water at 95°C for 24 hours. In contrast, Example 1, by optimizing the interface improver ratio (55% coupling agent, 35% dispersant, and 10% defoamer) and using a dual-extrusion co-extrusion process (inner layer 190°C, outer layer 200°C) to prepare the modified polypropylene pipe, achieved a significant improvement in interlayer bonding strength to 4.8 MPa and axial tensile strength to 42.6 MPa. This improvement is attributed to the synergistic effect of the coupling agent enhancing chemical bonding, the dispersant eliminating fiber agglomeration, and the defoamer suppressing defects. This highlights the necessity of optimizing the fiber skeleton and interface in Example 1 and verifies the core advantages of this invention in improving the mechanical properties and thermal stability of pipes.

Claims

1. A polypropylene modified plastic pipe, characterized in that: The inner layer is formed by extrusion of a mixture of fiber powder, interface modifier and random copolymer polypropylene; the outer layer is an axially continuous fiber reinforcement layer covering the inner layer, which is formed by co-extrusion of continuous fiber, fiber powder, interface modifier and random copolymer polypropylene.

2. The polypropylene modified plastic pipe according to claim 1, characterized in that: The interface improver consists of coupling agent, dispersant and defoamer, and the amount added is 1%-3% of the weight of the base material.

3. The polypropylene modified plastic pipe according to claim 2, characterized in that: The components of the interface improver, by weight percentage, are: coupling agent 50%-60%, dispersant 30%-40%, and defoamer 5%-10%.

4. 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%.

5. The polypropylene modified plastic pipe according to claim 4, characterized in that: The continuous fibers are axially uniformly distributed through a yarn separating plate with a hole diameter of 5-8 mm.

6. A method for preparing a polypropylene modified plastic pipe, characterized in that: 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.

7. The method for preparing a polypropylene modified plastic pipe according to claim 6, characterized in that: The stirring speed for mixing the raw materials in step S1 is 200-500 rpm.

8. The method for preparing a polypropylene modified plastic pipe according to claim 6, characterized in that: The temperature of the first extruder is 180-200℃, and the temperature of the second extruder is 190-210℃.

9. The method for preparing a polypropylene modified plastic pipe according to claim 6, characterized in that: The cooling in S3 uses a spray water tank with a water temperature of 15-20℃ and a cooling rate of ≥10℃ / min.

10. The method for preparing a polypropylene modified plastic pipe according to claim 6, characterized in that: The traction speed in S3 is 2-3 m / min.