A multilayer composite pipe and a method for producing the same

Abstract

This invention discloses a multilayer composite pipe and its preparation method, belonging to the field of polymer materials technology. The multilayer composite pipe includes an inner layer, a middle layer, and an outer layer arranged sequentially from the inside out. The inner layer is random copolymer polypropylene, the middle layer is 2-amino-2-methyl-1,3-propanediol, and the outer layer is modified polyvinyl chloride. The thickness ratio of the inner, middle, and outer layers is 1:(0.6-1.3):(0.6-0.8). This multilayer composite pipe utilizes the phase change of 2-amino-2-methyl-1,3-propanediol for energy storage, providing the function of storing energy at high temperatures and releasing energy at low temperatures, thus achieving heat preservation and energy saving. The use of modified polyvinyl chloride in the outer layer increases the pipe's weather resistance and resistance to environmental stress cracking, while also further improving the pipe's thermal insulation performance.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of high polymer materials, and more particularly to a multi-layer composite pipe and a preparation method thereof. BACKGROUND

[0002] Traditional plastic pipe materials mainly include polyethylene (PE), polypropylene (PP), polyvinyl chloride (PVC), and polybutylene succinate (PBS), etc. Plastic pipes have low cost, light weight, and are widely used. For plastic pipes used in a long-term high-temperature environment, on the one hand, the pipes themselves need to have good high-temperature resistance, and on the other hand, the pipes also have high requirements for heat preservation. Traditional heat preservation methods generally wrap the pipes with heat preservation cotton. This heat preservation method has discontinuous heat preservation cotton, and the pipes have exposed parts. After a long time, the heat preservation cotton will also age and fall off, and the heat preservation capacity is limited. Moreover, not all pipes will be wrapped with heat preservation cotton. The heat preservation capacity of most pipes is generally low, which makes it difficult to achieve the purpose of heat preservation and constant temperature control. In a continuous high-temperature environment, only the pipes themselves and the outer wrapping are not enough to meet the special use environment. The process of continuous external heating for temperature maintenance has high energy consumption and poor heat preservation effect, is not suitable for long-distance transportation, and causes excessive waste of social energy such as electricity and heat, which needs to be solved.

[0003] In addition, the use environment of high-temperature pipes is also complex and changeable. Some pipes need to be used all year round and cannot be replaced, some pipes need to withstand special production process environments, and some pipes are exposed to the outdoors and subjected to wind, rain, and sunlight. Therefore, the high-low temperature resistance, environmental stress cracking resistance, and weather resistance of the pipes need to be tested, and the comprehensive performance requirements of the pipes are also increasing. It is difficult for a single layer pipe to meet many performance requirements through a specific formula design. For example, a pipe with high tensile strength has reduced toughness and weather resistance, a high-temperature resistant pipe has insufficient heat preservation performance, and an ordinary pipe cannot withstand environmental stress cracking for a long time.

[0004] The prior art discloses a phase change heat preservation double-flow composite pipe containing a TPU layer. A heat preservation layer is wrapped outside a random copolymer polypropylene plastic pipe, and the heat preservation layer is an extrusion molding of a random copolymer polypropylene modified by a mixture of paraffin and n-dodecane. A heat insulation layer is extrusion molded by a thermoplastic polyurethane elastomer rubber outside the heat preservation layer. A plastic layer is wrapped outside the heat insulation layer. The phase change temperature of the composite pipe is between 28-39℃. However, this composite pipe is only suitable for fluids with a temperature of 20-60℃ in the pipe. When the temperature of the fluid in the pipe exceeds 60℃, the composite pipe cannot have a good heat preservation effect. SUMMARY

[0005] The technical problem to be solved by the present invention is to overcome the defects and shortcomings of existing phase change thermal insulation composite pipes that are not suitable for fluids with a temperature above 60°C. The present invention provides a multi-layer composite pipe that has excellent energy storage and thermal insulation performance, as well as weather resistance and environmental stress cracking resistance for fluids with a temperature above 60°C inside the pipe.

[0006] Another objective of this invention is to provide a method for preparing multilayer composite pipes.

[0007] The above-mentioned objective of this invention is achieved through the following technical solution:

[0008] A multilayer composite pipe includes an inner layer, a middle layer, and an outer layer arranged sequentially from the inside out. The inner layer is random copolymer polypropylene, the middle layer is 2-amino-2-methyl-1,3-propanediol, and the outer layer is modified polyvinyl chloride. The thickness ratio of the inner layer, the middle layer, and the outer layer is 1:(0.6-1.3):(0.6-0.8).

[0009] The phase transition temperature of amino-2-methyl-1,3-propanediol is 50-80℃, and the latent heat of phase transition is 105-120 J / g.

[0010] In the multi-layer composite pipe of the present invention, the middle layer is 2-amino-2-methyl-1,3-propanediol, which stores energy through the phase change of 2-amino-2-methyl-1,3-propanediol. Compared with existing pipes, it provides the function of storing energy at high temperature and releasing energy at low temperature, thus playing a role in heat preservation and energy saving.

[0011] The outer layer of this invention uses modified polyvinyl chloride, which increases the pipe's weather resistance and resistance to environmental stress cracking. At the same time, the modified polyvinyl chloride in the outer layer further improves the pipe's thermal insulation performance.

[0012] This invention employs a multi-layer composite structure, which enhances the energy storage, heat preservation, and wear resistance of the pipeline.

[0013] The pipe described in this invention can be used at fluid temperatures of 50-80℃, and has good energy storage and heat preservation effects. It can also be used for fluids below 50℃. The fluid can be water or common alkaline solutions, inorganic or organic solvents. The pipe can be used at external ambient temperatures of -10-100℃, and the external ambient humidity is not limited. The external environment can also be water, alkaline solutions, inorganic or organic solvents.

[0014] Preferably, the modified polyvinyl chloride is obtained by modifying polyvinyl chloride with chlorinated rubber and chlorinated paraffin; in the modified polyvinyl chloride, the mass ratio of polyvinyl chloride, chlorinated paraffin and chlorinated rubber is 100:(10-30):(50-100).

[0015] Preferably, the method for preparing the modified polyvinyl chloride includes the following steps:

[0016] Chlorinated paraffin and a portion of chlorinated rubber are mixed to obtain plasticized chlorinated rubber; the plasticized chlorinated rubber, polyvinyl chloride and the remaining chlorinated rubber are mixed, extruded and granulated through a twin-screw extruder to obtain modified polyvinyl chloride.

[0017] Preferably, in the method for preparing modified polyvinyl chloride, the temperature of the feeding section of the extruder is 120-135℃, the temperature of the compression section is 130-150℃, and the temperature of the homogenization section is 140-160℃.

[0018] More preferably, the preparation method of the modified polyvinyl chloride may specifically include the following steps:

[0019] S1: Weigh the raw materials according to the mass ratio of polyvinyl chloride powder, chlorinated paraffin and chlorinated rubber powder of 100:(10-30):(50-100, weigh the heat stabilizer according to the total mass percentage (3%-10%), and weigh the other additives according to the total mass percentage (1%-10%).

[0020] S2: Weigh out chlorinated rubber (1.6-3.3 times the mass of chlorinated paraffin) and mix it evenly in a high-speed mixer. Let it stand in a cool environment for 10 minutes to obtain a chlorinated rubber mixture that has been fully plasticized by chlorinated paraffin.

[0021] S3: Polyvinyl chloride powder, plasticized chlorinated rubber mixture, remaining chlorinated rubber powder, and other components are thoroughly mixed in a high-speed mixer, and then extruded and granulated through a conical twin-screw extruder. The temperature of the conical twin-screw extruder is controlled as follows: feeding section temperature 120-135℃, compression section temperature 130-150℃, and homogenization section temperature 140-160℃ to obtain modified polyvinyl chloride.

[0022] The heat stabilizer is one or more of calcium-zinc composite stabilizer and magnesium-aluminum intercalated hydrotalcite. Other additives may be plasticizers and antioxidants. The plasticizer may be one or more of dibutyl phthalate and dioctyl phthalate. The antioxidant may be antioxidant 1010.

[0023] The outer layer of the pipe in this invention is made of polyvinyl chloride modified with chlorinated rubber and chlorinated paraffin. By utilizing the toughness, plasticizing and cross-linking capabilities of chlorinated rubber and chlorinated paraffin, the toughness of the outer layer of the pipe is improved, and the weather resistance and environmental stress cracking resistance of the pipe are further improved.

[0024] Preferably, the melt index of the random copolymer polypropylene is 0.22-0.35 g / 10 min, the test conditions are a temperature of 230℃, a load of 2.16 kg, and the test standard is ASTM D1238-2013.

[0025] This invention also protects a method for preparing the multilayer composite pipe according to any one of the above claims, comprising the following steps:

[0026] Step (1): Random copolymer polypropylene, 2-amino-2-methyl-1,3-propanediol and modified polyvinyl chloride are added to an extruder and extruded.

[0027] Step (2): The random copolymer polypropylene, 2-amino-2-methyl-1,3-propanediol and modified polyvinyl chloride extruded in step (1) are extruded together through a multi-stage temperature-controlled co-extrusion pipe die at a temperature of 150-190℃.

[0028] Step (3): Cool and shape the multilayer material after co-extrusion in step (2) at 15-30℃ to obtain the multilayer composite pipe.

[0029] This invention prepares a phase change energy storage composite pipe through a co-extrusion process of random copolymer polypropylene, 2-amino-2-methyl-1,3-propanediol, and modified polyvinyl chloride. Under high temperature conditions, an expansion and compression effect occurs at the contact surfaces between the inner layer of random copolymer polypropylene and the intermediate layer of 2-amino-2-methyl-1,3-propanediol, and between the intermediate layer of 2-amino-2-methyl-1,3-propanediol and the outer layer of modified polyvinyl chloride. This eliminates thermal stress and is accompanied by a certain diffusion effect, which improves the interlayer adhesion of the multilayer composite pipe material, the mechanical strength, peel strength, and ring stiffness of the composite pipe, prevents the pipe from cracking and wearing out under high-intensity working conditions, and improves the durability of the pipe.

[0030] Preferably, in step (1), a co-rotating twin-screw extruder is used for extrusion; in step (2), a three-layer co-extrusion co-rotating twin-screw extruder is used for extrusion.

[0031] Preferably, in step (1), the extrusion processing temperature of the random copolymer polypropylene material is: 160-175℃ in the feeding section, 170-185℃ in the compression section, and 190-200℃ in the homogenization section.

[0032] Preferably, in step (1), the extrusion processing temperature of the 2-amino-2-methyl-1,3-propanediol material is: 60-75℃ in the feeding section, 75-90℃ in the compression section, and 90-105℃ in the homogenization section.

[0033] Preferably, in step (2), the temperature of the feeding section of the extruder is 150-165℃, the temperature of the compression section of the extruder is 170-180℃, and the temperature of the homogenization section of the extruder is 180-190℃.

[0034] Preferably, the flow channel length of the co-extrusion pipe die in step (2) is 0.2-1 meter.

[0035] Compared with the prior art, the beneficial effects of the present invention are:

[0036] This invention discloses a multi-layer composite pipe. The middle layer is 2-amino-2-methyl-1,3-propanediol, which stores energy through a phase change. Compared with existing pipes, it provides the function of storing energy at high temperatures and releasing energy at low temperatures, thus achieving heat preservation and energy saving. The outer layer of this invention uses modified polyvinyl chloride, which increases the pipe's weather resistance and resistance to environmental stress cracking. Simultaneously, the modified polyvinyl chloride in the outer layer further improves the pipe's heat preservation performance. This invention employs a multi-layer composite structure, enhancing the pipe's energy storage, heat preservation, wear resistance, and weather resistance. Detailed Implementation

[0037] The present invention will be further described below with reference to specific embodiments, but the embodiments do not limit the present invention in any way. Unless otherwise stated, the raw materials and reagents used in the embodiments of the present invention are conventionally purchased raw materials and reagents.

[0038] Single-layer PPR pipe, "Liansu" brand, pipe model DN50, pipe inner diameter 50mm, pipe wall thickness 3mm.

[0039] Example 1

[0040] A multi-layer composite pipe comprises an inner layer, a middle layer, and an outer layer. The inner layer is random copolymer polypropylene with a melt index of 0.23 g / 10 min. The middle layer is 2-amino-2-methyl-1,3-propanediol. The outer layer is polyvinyl chloride modified based on chlorinated rubber and chlorinated paraffin. The thickness ratio of the inner, middle, and outer layers is 1:0.6:0.8. The inner diameter of the pipe is 50 mm, and the overall wall thickness of the pipe is 3 mm.

[0041] Modified polyvinyl chloride (PVC) is produced by modifying PVC with chlorinated rubber and chlorinated paraffin, specifically through the following steps:

[0042] Step 1: Weigh the raw materials according to the mass ratio of polyvinyl chloride powder, chlorinated paraffin and chlorinated rubber powder of 100:30:100, weigh the calcium zinc composite stabilizer according to 5% of the total mass, weigh the dibutyl phthalate according to 10% of the total mass, and weigh the antioxidant 1010 according to 8% of the total mass.

[0043] Step 2: Weigh 3.0 times the mass of chlorinated paraffin into chlorinated rubber and mix them evenly in a high-speed mixer. Let it stand in a cool environment for 10 minutes to obtain a chlorinated rubber mixture that has been fully plasticized by chlorinated paraffin.

[0044] Step 3: After fully mixing the polyvinyl chloride powder, the plasticized chlorinated rubber mixture, the remaining chlorinated rubber powder, and other components in a high-speed mixer, the mixture is extruded and granulated through a conical twin-screw extruder. The temperature of the conical twin-screw extruder is controlled as follows: feeding section 120℃, compression section 135℃, homogenization section 150℃, to obtain modified polyvinyl chloride particles.

[0045] The multi-layer composite pipe is prepared by a co-extrusion process, specifically including the following steps:

[0046] Step (1): Random copolymer polypropylene, 2-amino-2-methyl-1,3-propanediol, and modified polyvinyl chloride are respectively added to a co-rotating twin-screw extruder for extrusion. The extrusion temperature of polypropylene is: 160℃ in the feeding section, 180℃ in the compression section, and 190℃ in the homogenization section. The extrusion temperature of 2-amino-2-methyl-1,3-propanediol is: 60℃ in the feeding section, 75℃ in the compression section, and 95℃ in the homogenization section. Modified polyvinyl chloride is directly processed in Step (2) after Step 3.

[0047] Step (2): The random copolymer polypropylene, 2-amino-2-methyl-1,3-propanediol and modified polyvinyl chloride extruded in step (1) are extruded together through the co-extrusion die of a three-layer co-extrusion twin-screw extruder with multi-stage temperature control. The working temperature of the extruder is: 150℃ in the feeding section, 170℃ in the compression section and 180℃ in the homogenization section. The temperature of the co-extrusion die is controlled at 180℃ and the flow channel length is 0.6 meters.

[0048] Step (3): Cool and shape the multilayer material after co-extrusion in step (2) at 25°C to obtain a phase change energy storage multilayer composite weather-resistant pipe comprising a random copolymer polypropylene inner layer, a 2-amino-2-methyl-1,3-propanediol intermediate layer and a modified polyvinyl chloride outer layer.

[0049] Example 2

[0050] A multi-layer composite pipe, which differs from Example 1,

[0051] The thickness ratio of the inner layer, the middle layer, and the outer layer is 1:1.3:0.8.

[0052] The rest is the same as in Example 1, and will not be repeated here.

[0053] Example 3

[0054] A multi-layer composite pipe, differing from Example 1 in the method of preparing modified polyvinyl chloride:

[0055] Step 1: Weigh the raw materials according to the mass ratio of polyvinyl chloride powder, chlorinated paraffin and chlorinated rubber powder of 100:30:50, weigh the calcium-zinc composite stabilizer according to 5% of the total mass, weigh the dibutyl phthalate according to 5% of the total mass, and weigh the antioxidant 1010 according to 8% of the total mass.

[0056] Step 2: Weigh 1.6 times the mass of chlorinated paraffin into chlorinated rubber and mix them evenly in a high-speed mixer. Let it stand in a cool environment for 10 minutes to obtain a chlorinated rubber mixture that has been fully plasticized by chlorinated paraffin.

[0057] The rest is the same as in Example 1, and will not be repeated here.

[0058] Example 4

[0059] A multi-layer composite pipe, differing from Example 1 in the method of preparing modified polyvinyl chloride:

[0060] Step 3: After fully mixing the polyvinyl chloride powder, the plasticized chlorinated rubber mixture, the remaining chlorinated rubber powder, and other components in a high-speed mixer, the mixture is extruded and granulated through a conical twin-screw extruder. The temperature of the conical twin-screw extruder is controlled as follows: feeding section 135℃, compression section 150℃, homogenization section 160℃, to obtain modified polyvinyl chloride particles.

[0061] The rest is the same as in Example 1, and will not be repeated here.

[0062] Example 5

[0063] A multi-layer composite pipe, differing from Example 1 in its preparation method:

[0064] Step (2): The random copolymer polypropylene, 2-amino-2-methyl-1,3-propanediol and modified polyvinyl chloride extruded in step (1) are extruded together through the co-extrusion die of a three-layer co-extrusion twin-screw extruder with multi-stage temperature control. The working temperature of the extruder is: 160℃ in the feeding section, 180℃ in the compression section and 190℃ in the homogenization section. The temperature of the co-extrusion die is controlled at 180℃ and the flow channel length is 0.6 meters.

[0065] The rest is the same as in Example 1, and will not be repeated here.

[0066] Example 6

[0067] A multi-layer composite pipe, differing from Example 1 in its preparation method:

[0068] Step (2): The random copolymer polypropylene, 2-amino-2-methyl-1,3-propanediol and modified polyvinyl chloride extruded in step (1) are extruded together through the co-extrusion die of a three-layer co-extrusion twin-screw extruder with multi-stage temperature control. The working temperature of the extruder is: 150℃ in the feeding section, 170℃ in the compression section and 180℃ in the homogenization section. The temperature of the co-extrusion die is controlled at 150℃ and the flow channel length is 0.6 meters.

[0069] The rest is the same as in Example 1, and will not be repeated here.

[0070] Example 7

[0071] A multi-layer composite pipe, differing from Example 1 in its preparation method:

[0072] Step (3): Cool and shape the multilayer material after co-extrusion in step (2) at 15°C to obtain a phase change energy storage multilayer composite weather-resistant pipe comprising a random copolymer polypropylene inner layer, a 2-amino-2-methyl-1,3-propanediol intermediate layer and a modified polyvinyl chloride outer layer.

[0073] The rest is the same as in Example 1, and will not be repeated here.

[0074] Example 8

[0075] A multi-layer composite pipe, differing from Example 1 in the method of preparing modified polyvinyl chloride:

[0076] Weigh the raw materials according to the mass ratio of polyvinyl chloride powder, chlorinated paraffin and chlorinated rubber powder of 100:30:100, weigh the calcium-zinc composite stabilizer according to 5% of the total mass, weigh the dibutyl phthalate according to 10% of the total mass, and weigh the antioxidant 1010 according to 8% of the total mass.

[0077] Polyvinyl chloride powder, chlorinated paraffin, chlorinated rubber powder, and other components are thoroughly mixed in a high-speed mixer and then extruded and granulated through a conical twin-screw extruder. The temperature of the conical twin-screw extruder is controlled as follows: 120°C in the feeding section, 135°C in the compression section, and 150°C in the homogenization section to obtain modified polyvinyl chloride particles.

[0078] The rest is the same as in Example 1, and will not be repeated here.

[0079] Comparative Example 1

[0080] A multi-layer composite pipe, which differs from Example 1,

[0081] Excluding the intermediate layer. The thickness ratio of the inner layer to the outer layer is 1.3:1.1.

[0082] The multi-layer composite pipe is prepared by a co-extrusion process, specifically including the following steps:

[0083] Step (1): Random copolymer polypropylene and modified polyvinyl chloride are respectively added to a co-rotating twin-screw extruder for extrusion. The extrusion temperature of polypropylene material is: 160℃ in the feeding section, 180℃ in the compression section, and 190℃ in the homogenization section. Modified polyvinyl chloride is directly processed in Step (2) after Step 3.

[0084] Step (2): The random copolymer polypropylene and modified polyvinyl chloride extruded in step (1) are extruded together through the co-extrusion pipe die of a multi-stage temperature-controlled twin-screw extruder. The working temperature of the extruder is: 160℃ in the feeding section, 180℃ in the compression section, and 190℃ in the homogenization section. The temperature of the co-extrusion pipe die is controlled at 180℃, and the flow channel length is 0.6 meters.

[0085] The rest is the same as in Example 1, and will not be repeated here.

[0086] Comparative Example 2

[0087] A multi-layer composite pipe, which differs from Example 1,

[0088] The thickness ratio of the inner layer, middle layer, and outer layer is 1:0.5:0.5.

[0089] The rest is the same as in Example 1, and will not be repeated here.

[0090] Comparative Example 3

[0091] A multi-layer composite pipe, which differs from Example 1 in that modified polyvinyl chloride is replaced with polyvinyl chloride.

[0092] The rest is the same as in Example 1, and will not be repeated here.

[0093] Comparative Example 4

[0094] A multi-layer composite pipe, differing from Example 1 in the method of preparing modified polyvinyl chloride:

[0095] Step 3: After fully mixing the polyvinyl chloride powder, the plasticized chlorinated rubber mixture, the remaining chlorinated rubber powder, and other components in a high-speed mixer, the mixture is extruded and granulated through a conical twin-screw extruder. The temperature of the conical twin-screw extruder is controlled as follows: 150°C in the feeding section, 165°C in the compression section, and 175°C in the homogenization section to obtain modified polyvinyl chloride particles.

[0096] The rest is the same as in Example 1, and will not be repeated here.

[0097] Comparative Example 5

[0098] A multi-layer composite pipe, differing from Example 1 in its preparation method:

[0099] Step (2): The random copolymer polypropylene, 2-amino-2-methyl-1,3-propanediol and modified polyvinyl chloride extruded in step (1) are extruded together through the co-extrusion die of a three-layer co-extrusion twin-screw extruder with multi-stage temperature control. The working temperature of the extruder is: 180℃ in the feeding section, 195℃ in the compression section and 205℃ in the homogenization section. The temperature of the co-extrusion die is controlled at 180℃ and the flow channel length is 0.6 meters.

[0100] The rest is the same as in Example 1, and will not be repeated here.

[0101] Comparative Example 6

[0102] A multi-layer composite pipe, differing from Example 1 in its preparation method:

[0103] Step (2): The random copolymer polypropylene, 2-amino-2-methyl-1,3-propanediol and modified polyvinyl chloride extruded in step (1) are extruded together through the co-extrusion die of a three-layer co-extrusion twin-screw extruder with multi-stage temperature control. The working temperature of the extruder is: 150℃ in the feeding section, 170℃ in the compression section and 180℃ in the homogenization section. The temperature of the co-extrusion die is controlled at 200℃ and the flow channel length is 0.6 meters.

[0104] The rest is the same as in Example 1, and will not be repeated here.

[0105] Comparative Example 7

[0106] A multi-layer composite pipe, differing from Example 1 in its preparation method:

[0107] Step (3): Cool and shape the multilayer material after co-extrusion in step (2) at 10°C to obtain a phase change energy storage multilayer composite weather-resistant pipe comprising a polypropylene inner layer, a 2-amino-2-methyl-1,3-propanediol intermediate layer and a modified polyvinyl chloride outer layer.

[0108] The rest is the same as in Example 1, and will not be repeated here.

[0109] Result detection

[0110] The multilayer composite pipes of the above embodiments and comparative examples were tested using the following performance testing methods:

[0111] Tensile strength: Tested at 20℃ according to national standard GB / T 8804.3-2003.

[0112] Impact strength: Tested at 20℃ according to national standard GB / T 18743-2022.

[0113] Apparent thermal conductivity: Tested according to national standard GB / T 29046-2012, with the liquid temperature inside the pipe at 80℃ and the ambient temperature at 20-25℃.

[0114] Aging test: The pipe provided by this invention has an operating temperature of 50-80℃, not exceeding 110℃. Therefore, referring to the test methods for the thermal insulation performance and shear strength of pipes after artificial accelerated aging treatment in the national standard GB / T 29046-2012, the sample was subjected to tensile strength test after being kept at 90℃ for 3600h. The sample length during the aging process was 2m.

[0115] Environmental stress cracking test: The test was conducted according to the provisions of standard ISO 16770, using a dumbbell-shaped stamped specimen with a notch depth of 0.5 mm. The specimen was continuously tested in a 2.0% nonylphenol polyethylene glycol ether (TX-10) aqueous solution at 80℃ for 300 hours, and the specimen was continuously checked for failure. The test was terminated if specimen failure occurred during the test.

[0116] The specific test results are shown in Table 1 below:

[0117] Table 1

[0118]

[0119] As can be seen from the above data, the multi-layer composite pipe material of the present invention has high tensile strength, impact strength and environmental stress cracking time, while having a low apparent thermal conductivity. After aging resistance test treatment, the overall tensile strength of the material decreases less, indicating that the multi-layer composite pipe provided by the present invention has good mechanical properties, weather resistance and environmental adaptability, and can be applied to the fields of liquid transportation and energy storage insulation at higher temperatures and over longer distances.

[0120] The data above also shows that, as demonstrated by Examples 1 and 3 and Comparative Example 3, unmodified PVC leads to an increase in apparent thermal conductivity, reducing the energy storage effect of the pipeline. Comparative Example 1, lacking an intermediate phase change layer, exhibits significantly inferior insulation and energy storage performance compared to the Examples. Commercially available single-layer PPR pipes also exhibit similar issues, with all performance characteristics falling short of the Examples.

[0121] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not intended to limit the implementation of the present invention. Those skilled in the art can make other variations or modifications based on the above description. It is neither necessary nor possible to exhaustively describe all embodiments here. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the claims of the present invention.

Claims

1. A multi-layer composite pipe, characterized in that, It comprises an inner layer, a middle layer, and an outer layer arranged sequentially from the inside out. The inner layer is random copolymer polypropylene, the middle layer is 2-amino-2-methyl-1,3-propanediol, and the outer layer is modified polyvinyl chloride. The thickness ratio of the inner layer, the middle layer, and the outer layer is 1:(0.6-1.3):(0.6-0.8). The modified polyvinyl chloride is obtained by modifying polyvinyl chloride with chlorinated rubber and chlorinated paraffin; in the modified polyvinyl chloride, the mass ratio of polyvinyl chloride, chlorinated paraffin and chlorinated rubber is 100:(10-30):(50-100). The preparation method of the modified polyvinyl chloride includes the following steps: Chlorinated rubber, in an amount of 1.6-3.3 times the mass of chlorinated paraffin, is mixed with chlorinated paraffin to obtain plasticized chlorinated rubber; the plasticized chlorinated rubber, polyvinyl chloride, and the remaining chlorinated rubber are mixed, extruded and granulated using a twin-screw extruder to obtain modified polyvinyl chloride; In the preparation method of the modified polyvinyl chloride, the temperature of the feeding section of the extruder is 120-135℃, the temperature of the compression section is 130-150℃, and the temperature of the homogenization section is 140-160℃.

2. The multi-layer composite pipe as described in claim 1, characterized in that, The random copolymer polypropylene has a melt index of 0.22-0.35 g / 10 min, and the test conditions are a temperature of 230℃, a load of 2.16 kg, and the test standard is ASTM D1238-2013.

3. The method for preparing the multilayer composite pipe according to claim 1 or 2, characterized in that, Includes the following steps: Step (1): Random copolymer polypropylene, 2-amino-2-methyl-1,3-propanediol and modified polyvinyl chloride are added to an extruder and extruded. Step (2): The random copolymer polypropylene, 2-amino-2-methyl-1,3-propanediol and modified polyvinyl chloride extruded from step (1) are extruded together through a multi-stage temperature-controlled co-extrusion pipe die at a temperature of 150-190℃. Step (3): Cool and shape the multilayer material after co-extrusion in step (2) at 15-30℃ to obtain the multilayer composite pipe.

4. The method for preparing the multilayer composite pipe as described in claim 3, characterized in that, In step (1), a co-rotating twin-screw extruder is used for extrusion; in step (2), a three-layer co-extrusion co-rotating twin-screw extruder is used for extrusion.

5. The method for preparing the multilayer composite pipe as described in claim 3, characterized in that, In step (1), the extrusion processing temperature of the random copolymer polypropylene material is: 160-175℃ in the feeding section, 170-185℃ in the compression section, and 190-200℃ in the homogenization section.

6. The method for preparing the multilayer composite pipe as described in claim 3, characterized in that, In step (1), the extrusion processing temperature of the 2-amino-2-methyl-1,3-propanediol material is: 60-75℃ in the feeding section, 75-90℃ in the compression section, and 90-105℃ in the homogenization section.

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