High-thermal-conductivity PERT floor heating pipe and preparation method thereof

Abstract

The application provides a high-thermal-conductivity PERT floor heating pipe and a preparation method thereof, and belongs to the technical field of floor heating pipe materials. The PERT floor heating pipe comprises a thermal-conductivity outer layer and an anti-fouling inner layer, wherein the thermal-conductivity outer layer is prepared from the following raw materials in parts by weight: 200-500 parts of PERT resin, 5-15 parts of thermal-conductivity composite filler, 1-5 parts of plasticizer, 0.5-3.5 parts of antioxidant and 2-5 parts of compatilizer, and the thermal-conductivity composite filler is prepared from graphite nanosheets and surface-treated aluminum nitride; the anti-fouling inner layer is prepared from the following raw materials in parts by weight: 100-200 parts of PERT resin, 3-8 parts of anti-fouling auxiliary agent, 1-2 parts of plasticizer, 0.5-1.5 parts of antioxidant and 1-2 parts of compatilizer, and the anti-fouling auxiliary agent is prepared from carbon nanotubes after modification, modification and halogenation. The PERT floor heating pipe prepared by the application not only has excellent thermal-conductivity and mechanical properties, but also has antibacterial and anti-fouling properties, and can maintain good properties in a long-term use process.

Description

Technical Field

[0001] This invention belongs to the field of underfloor heating pipe technology, specifically relating to a high thermal conductivity PERT underfloor heating pipe and its preparation method. Background Technology

[0002] Many cities experience cold winters, often necessitating home heating to maintain comfortable indoor temperatures. Underfloor heating, also known as radiant floor heating, is commonly used in homes. It involves burying hot water pipes or heating cables under the floor to heat the entire floor, distributing the heat evenly throughout the room through radiation. As a common heating method, underfloor heating is widely used in new buildings. Traditional underfloor heating pipes typically use PERT resin, a heat-resistant polyethylene resin with good toughness, low-temperature impact resistance, and water pressure resistance, making it suitable as a primary material in heating systems. However, PERT resin itself has relatively low thermal conductivity (compared to metal pipes), and friction or static electricity can further affect its thermal conductivity. Furthermore, over long-term use, it is susceptible to scale buildup due to oxygen and bacteria in the water, severely impacting the heat dissipation efficiency and lifespan of the underfloor heating pipes, as well as the hygiene of the indoor environment.

[0003] To address the aforementioned issues, existing technologies utilize antifouling or thermally conductive fillers, such as silanes, to improve the hydrophobicity of the pipe's inner wall by adding antifouling or thermally conductive fillers to the PERT resin. This prevents impurities and bacteria in the water from adhering to the pipe's inner wall, reducing fouling deposits. Thermally conductive agents can increase the pipe's thermal conductivity, accelerating heat transfer to improve floor heating efficiency and make heating more uniform. Chinese patent CN106589547A discloses a PERT underfloor heating pipe, its preparation method, and its applications. This underfloor heating pipe uses type II or type I heat-resistant polyethylene as the main material, and adds fillers such as graphite and carbon fiber to improve the pipe's thermal conductivity and thermal conductivity, reducing the pipe's expansion coefficient and contraction rate. It can be widely used in underfloor heating. However, these fillers often have poor compatibility with the main material, PERT resin, negatively impacting the overall performance and stability of the underfloor heating pipe. Therefore, the present invention aims to prepare a new type of high thermal conductivity PERT underfloor heating pipe to solve the problems of insufficient stain resistance and thermal conductivity in the existing technology, thereby providing a more efficient heating experience and maintaining good performance and reliability during long-term use, further meeting people's needs for a comfortable indoor environment. Summary of the Invention

[0004] In view of the shortcomings of existing technologies, this invention provides a high thermal conductivity PERT underfloor heating pipe, comprising a thermally conductive outer layer and an anti-fouling inner layer. By adding a thermally conductive composite filler made of graphite nanosheets and surface-treated aluminum nitride to the thermally conductive outer layer material, and adding an anti-fouling additive made of modified and halogenated carbon nanotubes to the anti-fouling inner layer material, the PERT underfloor heating pipe not only maintains excellent thermal conductivity and mechanical properties but also has antibacterial and anti-scaling properties, maintaining good performance during long-term use. This invention also provides a method for preparing the aforementioned high thermal conductivity PERT underfloor heating pipe.

[0005] A high thermal conductivity PERT underfloor heating pipe includes a thermally conductive outer layer and a stain-resistant inner layer;

[0006] Preferably, the thermally conductive outer layer is made of the following raw materials in parts by weight: 200-500 parts PERT resin, 5-15 parts thermally conductive composite filler, 1-5 parts plasticizer, 0.5-3.5 parts antioxidant, and 2-5 parts compatibilizer.

[0007] Preferably, the antifouling inner layer is made of the following raw materials in parts by weight: 100-200 parts PERT resin, 3-8 parts antifouling additive, 1-2 parts plasticizer, 0.5-1.5 parts antioxidant, and 1-2 parts compatibilizer.

[0008] Preferably, the thickness of the thermally conductive outer layer is 1-3 mm and the thickness of the anti-fouling inner layer is 0.5-2 mm.

[0009] Preferably, the plasticizer is one or a mixture of two or more of polyethylene wax, chlorinated paraffin, dioctyl phthalate, tributyl acetyl citrate, and di(2-ethylhexyl) adipate.

[0010] Preferably, the antioxidant is one or a mixture of two or more of the following antioxidants: DSTP, 1076, 1010, 1098, and 636.

[0011] Preferably, the compatibilizer is one or a mixture of two or more of the following: polyethylene grafted with maleic anhydride, polypropylene grafted with maleic anhydride, and polyolefin elastomer grafted with maleic anhydride.

[0012] Preferably, the preparation method of the thermally conductive composite filler is as follows:

[0013] 0.1-0.5 parts by weight of 3-(2,3-epoxypropoxy)propyltrimethoxysilane, 0.1-0.5 parts by weight of 3-diethylenetriaminopropylmethyldimethoxysilane, 1-3 parts by weight of ammonium stearate, and 3-6 parts by weight of acetic acid are added to methanol and water and mixed evenly. Then, 10-30 parts by weight of aluminum nitride are added, heated and stirred, centrifuged, washed, and dried to obtain surface-treated aluminum nitride. 15-20 parts by weight of graphite nanosheets and 5-10 parts by weight of surface-treated aluminum nitride are added to N,N-dimethylformamide and mixed evenly. The mixture is heated and stirred, centrifuged, washed, and dried, and then calcined under nitrogen protection to obtain a thermally conductive composite filler.

[0014] The thermally conductive composite filler prepared in this invention is based on the precise control and regulation of graphite nanosheets and surface-treated aluminum nitride. During the preparation of the composite filler, a surface treatment liquid composed of 3-(2,3-epoxypropoxy)propyltrimethoxysilane and 3-diethylenetriaminopropylmethyldimethoxysilane is used to modify the surface of the aluminum nitride, giving it a positive charge. This positive charge attracts the negative charge on the surface of the graphite nanosheets, promoting self-assembly between the two through electrostatic interactions and chemical bonding. Therefore, the graphite nanosheets are uniformly coated in a covering layer formed on the surface of the aluminum nitride. This self-assembly process not only improves the compatibility and dispersibility of the graphite nanosheets with the matrix but also enhances the stability of the filler. Furthermore, the graphite nanosheets themselves possess high thermal conductivity; therefore, after being combined with surface-treated aluminum nitride, the overall thermal conductivity of the filler is significantly improved. The aluminum nitride, as part of the matrix, not only maintains high strength and high thermal conductivity but also undergoes further improvement through surface treatment to ensure its effective bonding with the graphite nanosheets. In summary, this composite filler not only possesses the advantage of high thermal conductivity of graphite nanosheets, but also overcomes problems such as dispersibility and poor compatibility with the matrix. The components in the filler achieve synergistic effects, making the filler structure more stable, thereby improving the overall thermal conductivity.

[0015] Preferably, the preparation method of the thermally conductive composite filler is as follows:

[0016] 0.1-0.5 parts by weight of 3-(2,3-epoxypropoxy)propyltrimethoxysilane, 0.1-0.5 parts by weight of 3-diethylenetriaminopropylmethyldimethoxysilane, 1-3 parts by weight of ammonium stearate, and 3-6 parts by weight of acetic acid are added to 50-80 parts by weight of methanol and 30-50 parts by weight of water and mixed evenly. Then, 10-30 parts by weight of aluminum nitride are added and stirred at 75-85℃ for 5-10 hours. After centrifugation, washing, and drying, surface-treated aluminum nitride is obtained. 15-20 parts by weight of graphite nanosheets and 5-10 parts by weight of surface-treated aluminum nitride are added to 100-300 parts by weight of N,N-dimethylformamide and mixed evenly. After stirring at 40-50℃ for 2-5 hours, centrifugation, washing, and drying are carried out. Then, the mixture is calcined at 1100-1300℃ under nitrogen protection for 1-3 hours to obtain a thermally conductive composite filler.

[0017] Preferably, the aluminum nitride is composed of aluminum nitride with a particle size of 2-10 μm and aluminum nitride with a particle size of 40-50 μm in a weight ratio of 1:1-2.

[0018] Preferably, the antifouling additive is prepared as follows:

[0019] 1-5 parts by weight of carbon nanotubes are added to N,N-dimethylformamide and mixed evenly. Then, 10-15 parts by weight of vinyltriethoxysilane are added, heated and stirred, centrifuged, washed, and dried to obtain vinyl carbon nanotubes. 0.2-0.5 parts by weight of sodium dodecylbenzenesulfonate and 1-2 parts by weight of vinyl carbon nanotubes are added to water and mixed evenly. Then, 0.5-1.5 parts by weight of 4-vinylpiperidine hydrochloride, 1-1.5 parts by weight of butyl methacrylate, and 0.1-0.3 parts by weight of azobisisobutyronitrile are added, and the mixture is heated under nitrogen protection. After centrifugation, washing, and drying, piperidine-modified carbon nanotubes are obtained. 0.5-2 parts by weight of piperidine-modified carbon nanotubes and 0.5-2 parts by weight of sodium hypochlorite are added to water and mixed evenly. After stirring at room temperature, centrifugation, washing, and drying, an antifouling agent is obtained. Preferably, the carbon nanotubes are hydroxylated multi-walled carbon nanotubes.

[0020] This invention first introduces ethylene into the carbon nanotube surface through a grafting reaction between vinyltriethoxysilane and hydroxyl groups, thereby introducing vinyl groups. This step chemically modifies the carbon nanotube surface, providing a foundation for subsequent modifications. Then, under the initiator of azobisisobutyronitrile (AIBN), 4-vinylpiperidine hydrochloride and butyl methacrylate monomers undergo in-situ graft polymerization on the carbon nanotube surface to obtain piperidine-modified carbon nanotubes, further improving the surface properties and compatibility of the carbon nanotubes. Finally, halogenation treatment with sodium hypochlorite yields halogenated amine antibacterial carbon nanotubes, which are used as an antifouling additive in the inner layer of PERT underfloor heating pipes. On the one hand, the grafted halogenated amine antibacterial structure possesses excellent antibacterial capabilities, ensuring no bacterial residue on the inner wall of the underfloor heating pipe and significantly improving the antibacterial and antiscaling performance of the pipe material. On the other hand, through this series of treatment steps, the aggregation and dispersion of carbon nanotubes are improved, enhancing interfacial compatibility with the matrix and avoiding adverse effects on the overall mechanical and other properties of the pipe material from direct addition. Furthermore, this invention utilizes the interaction of two aluminum nitride particles of different sizes to better increase the thermal conductivity of the thermally conductive filler. This may be because using two aluminum nitride particles of different sizes helps to form a denser network structure in the system, thereby improving the overall thermal conductivity of the pipe.

[0021] Preferably, the antifouling additive is prepared as follows:

[0022] Add 1-5 parts by weight of carbon nanotubes to 100-200 parts by weight of N,N-dimethylformamide and mix thoroughly. Then add 10-15 parts by weight of vinyltriethoxysilane and stir at 125-135℃ for 50-70 hours. Centrifuge, wash, and dry to obtain vinyl carbon nanotubes. Add 0.2-0.5 parts by weight of sodium dodecylbenzenesulfonate and 1-2 parts by weight of vinyl carbon nanotubes to 80-120 parts by weight of water and mix thoroughly. Then add 0.5-1.5 parts by weight of sodium dodecylbenzenesulfonate. 4-Vinylpiperidine hydrochloride (parts by weight), 1-1.5 parts by weight of butyl methacrylate, and 0.1-0.3 parts by weight of azobisisobutyronitrile (azobisisobutyronitrile) are reacted at 85-95°C under nitrogen protection for 2-5 hours. After centrifugation, washing, and drying, piperidine-modified carbon nanotubes are obtained. 0.5-2 parts by weight of piperidine-modified carbon nanotubes and 0.5-2 parts by weight of sodium hypochlorite are added to 50-100 parts by weight of water and mixed evenly. The mixture is stirred at room temperature for 5-10 hours, centrifuged, washed, and dried to obtain an antifouling agent.

[0023] This invention also provides a method for preparing the above-mentioned high thermal conductivity PERT underfloor heating pipe, comprising the following steps:

[0024] According to the raw material formula, the raw materials for the thermally conductive outer layer and the anti-fouling inner layer are mixed separately to obtain a thermally conductive outer layer mixture and an anti-fouling inner layer mixture. Then, the thermally conductive outer layer mixture and the anti-fouling inner layer mixture are extruded in two layers, sized, shaped, and traction-cut to obtain the high thermal conductivity PERT underfloor heating pipe. The extrusion temperature is 190-210℃.

[0025] The beneficial effects of this invention are:

[0026] This invention provides a method for preparing PERT underfloor heating pipes. By adding a thermally conductive composite filler made of graphite nanosheets and surface-treated aluminum nitride to the thermally conductive outer layer material, and adding an anti-fouling additive made of modified and halogenated carbon nanotubes to the anti-fouling inner layer material, the PERT underfloor heating pipes not only have excellent thermal conductivity and mechanical properties, but also antibacterial and anti-scaling properties, and can maintain good performance during long-term use. Detailed Implementation

[0027] The technical solutions of the present invention will be clearly and completely described below with reference to specific embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0028] Example 1

[0029] A high thermal conductivity PERT underfloor heating pipe includes a thermally conductive outer layer and a stain-resistant inner layer;

[0030] The thermally conductive outer layer is made from the following raw materials in parts by weight: 300 parts by weight of PERT resin (density 0.937 g / cm³). 3 8.5 parts by weight of thermally conductive composite filler (melt index 0.6 g / 10 min), 2.6 parts by weight of plasticizer tributyl acetylacetic acid, 2 parts by weight of antioxidant 1010, and 3 parts by weight of compatibilizer polyethylene grafted maleic anhydride (CAS: 9006-26-2).

[0031] The preparation method of the thermally conductive composite filler is as follows:

[0032] 0.2 parts by weight of 3-(2,3-epoxypropoxy)propyltrimethoxysilane (CAS: 2530-83-8), 0.3 parts by weight of 3-diethylenetriaminopropylmethyldimethoxysilane (CAS: 99740-64-4), 2 parts by weight of ammonium stearate (CAS: 1002-89-7), and 5 parts by weight of acetic acid were added to 60 parts by weight of methanol and 40 parts by weight of water and mixed thoroughly. Then, 20 parts by weight of aluminum nitride (composed of aluminum nitride with a particle size of 5 μm and a particle size of...) were added. Aluminum nitride with a thickness of 45 μm was prepared by mixing aluminum nitride in a weight ratio of 1:1.5 at 82 °C for 7 h, centrifuging, washing, and drying to obtain surface-treated aluminum nitride. 18 parts by weight of graphite nanosheets (GNP thickness ≤15 nm) and 7.5 parts by weight of surface-treated aluminum nitride were added to 200 parts by weight of N,N-dimethylformamide and mixed evenly. The mixture was stirred at 45 °C for 3 h, centrifuged, washed, and dried, and then calcined at 1250 °C under nitrogen protection for 2 h to obtain a thermally conductive composite filler.

[0033] The antifouling inner layer is made from the following raw materials in parts by weight: 150 parts by weight of PERT resin (density 0.937 g / cm³). 3 6 parts by weight of antifouling agent (melt index 0.6 g / 10 min), 1.3 parts by weight of plasticizer tributyl acetylacetic acid, 1 part by weight of antioxidant 1010, and 1.5 parts by weight of compatibilizer polyethylene grafted maleic anhydride (CAS: 9006-26-2).

[0034] The method for preparing the antifouling additive is as follows:

[0035] 2.5 parts by weight of carbon nanotubes were added to 150 parts by weight of N,N-dimethylformamide and mixed thoroughly. Then, 12 parts by weight of vinyltriethoxysilane were added, and the mixture was stirred at 130°C for 60 h. After centrifugation, washing, and drying, vinyl carbon nanotubes were obtained. The carbon nanotubes were hydroxylated multi-walled carbon nanotubes with a length of 0.5-2 μm, an inner diameter of 2-5 nm, an outer diameter of 5-15 nm, and a hydroxyl content of 5.6 wt%. 0.4 parts by weight of sodium dodecylbenzenesulfonate and 1.5 parts by weight of vinyl carbon nanotubes were added to 10... Mix 0 parts by weight of water thoroughly, then add 1 part by weight of 4-vinylpiperidine hydrochloride (CAS: 1311316-95-6), 1.2 parts by weight of butyl methacrylate and 0.25 parts by weight of azobisisobutyronitrile, react at 90°C under nitrogen protection for 3 h, centrifuge, wash and dry to obtain piperidine-modified carbon nanotubes; add 0.85 parts by weight of piperidine-modified carbon nanotubes and 1 part by weight of sodium hypochlorite to 60 parts by weight of water and mix thoroughly, stir at room temperature for 6 h, centrifuge, wash and dry to obtain antifouling additive.

[0036] A method for preparing a high thermal conductivity PERT underfloor heating pipe includes the following steps:

[0037] According to the raw material formula, the raw materials for the thermally conductive outer layer and the anti-fouling inner layer are mixed separately to obtain a thermally conductive outer layer mixture and an anti-fouling inner layer mixture. Then, the thermally conductive outer layer mixture and the anti-fouling inner layer mixture are extruded in two layers, sized, shaped, and traction-cut to obtain the high thermal conductivity PERT underfloor heating pipe. The extrusion temperature is 190-210℃, the thickness of the thermally conductive outer layer is 2mm, and the thickness of the anti-fouling inner layer is 1mm.

[0038] Example 2

[0039] A high thermal conductivity PERT underfloor heating pipe includes a thermally conductive outer layer and a stain-resistant inner layer;

[0040] The thermally conductive outer layer is made from the following raw materials in parts by weight: 300 parts by weight of PERT resin (density 0.937 g / cm³). 3 8.5 parts by weight of thermally conductive composite filler (melt index 0.6 g / 10 min), 2.6 parts by weight of plasticizer tributyl acetylacetic acid, 2 parts by weight of antioxidant 1010, and 3 parts by weight of compatibilizer polyethylene grafted maleic anhydride (CAS: 9006-26-2).

[0041] The preparation method of the thermally conductive composite filler is as follows:

[0042] 18 parts by weight of graphite nanosheets (GNP thickness ≤ 15 nm) and 7.5 parts by weight of aluminum nitride (composed of aluminum nitride with a particle size of 5 μm and aluminum nitride with a particle size of 45 μm in a weight ratio of 1:1.5) were added to 200 parts by weight of N,N-dimethylformamide and mixed evenly. The mixture was stirred at 45 °C for 3 h, centrifuged, washed, dried, and then calcined at 1250 °C under nitrogen protection for 2 h to obtain a thermally conductive composite filler.

[0043] The antifouling inner layer is made from the following raw materials in parts by weight: 150 parts by weight of PERT resin (density 0.937 g / cm³). 3 6 parts by weight of antifouling agent (melt index 0.6 g / 10 min), 1.3 parts by weight of plasticizer tributyl acetylacetic acid, 1 part by weight of antioxidant 1010, and 1.5 parts by weight of compatibilizer polyethylene grafted maleic anhydride (CAS: 9006-26-2).

[0044] The method for preparing the antifouling additive is as follows:

[0045] 2.5 parts by weight of carbon nanotubes were added to 150 parts by weight of N,N-dimethylformamide and mixed thoroughly. Then, 12 parts by weight of vinyltriethoxysilane were added, and the mixture was stirred at 130°C for 60 h. After centrifugation, washing, and drying, vinyl carbon nanotubes were obtained. The carbon nanotubes were hydroxylated multi-walled carbon nanotubes with a length of 0.5-2 μm, an inner diameter of 2-5 nm, an outer diameter of 5-15 nm, and a hydroxyl content of 5.6 wt%. 0.4 parts by weight of sodium dodecylbenzenesulfonate and 1.5 parts by weight of vinyl carbon nanotubes were added to 10... Mix 0 parts by weight of water thoroughly, then add 1 part by weight of 4-vinylpiperidine hydrochloride (CAS: 1311316-95-6), 1.2 parts by weight of butyl methacrylate and 0.25 parts by weight of azobisisobutyronitrile, react at 90°C under nitrogen protection for 3 h, centrifuge, wash and dry to obtain piperidine-modified carbon nanotubes; add 0.85 parts by weight of piperidine-modified carbon nanotubes and 1 part by weight of sodium hypochlorite to 60 parts by weight of water and mix thoroughly, stir at room temperature for 6 h, centrifuge, wash and dry to obtain antifouling additive.

[0046] A method for preparing a high thermal conductivity PERT underfloor heating pipe includes the following steps:

[0047] According to the raw material formula, the raw materials for the thermally conductive outer layer and the anti-fouling inner layer are mixed separately to obtain a thermally conductive outer layer mixture and an anti-fouling inner layer mixture. Then, the thermally conductive outer layer mixture and the anti-fouling inner layer mixture are extruded in two layers, sized, shaped, and traction-cut to obtain the high thermal conductivity PERT underfloor heating pipe. The extrusion temperature is 190-210℃, the thickness of the thermally conductive outer layer is 2mm, and the thickness of the anti-fouling inner layer is 1mm.

[0048] Example 3

[0049] A high thermal conductivity PERT underfloor heating pipe includes a thermally conductive outer layer and a stain-resistant inner layer;

[0050] The thermally conductive outer layer is made from the following raw materials in parts by weight: 300 parts by weight of PERT resin (density 0.937 g / cm³). 3 8.5 parts by weight of thermally conductive composite filler (melt index 0.6 g / 10 min), 2.6 parts by weight of plasticizer tributyl acetylacetic acid, 2 parts by weight of antioxidant 1010, and 3 parts by weight of compatibilizer polyethylene grafted maleic anhydride (CAS: 9006-26-2).

[0051] The preparation method of the thermally conductive composite filler is as follows:

[0052] 0.2 parts by weight of 3-(2,3-epoxypropoxy)propyltrimethoxysilane (CAS: 2530-83-8), 0.3 parts by weight of 3-diethylenetriaminopropylmethyldimethoxysilane (CAS: 99740-64-4), 2 parts by weight of ammonium stearate (CAS: 1002-89-7), and 5 parts by weight of acetic acid were added to 60 parts by weight of methanol and 40 parts by weight of water and mixed evenly. Then, 20 parts by weight of aluminum nitride (aluminum nitride with a particle size of 5 μm) were added, and the mixture was stirred at 82 °C for 7 h. After centrifugation, washing, and drying, surface-treated aluminum nitride was obtained. 18 parts by weight of graphite nanosheets (GNP thickness ≤ 15 nm) and 7.5 parts by weight of surface-treated aluminum nitride were added to 200 parts by weight of N,N-dimethylformamide and mixed evenly. After stirring at 45 °C for 3 h, the mixture was centrifuged, washed, and dried. Then, it was calcined at 1250 °C under nitrogen protection for 2 h to obtain a thermally conductive composite filler.

[0053] The antifouling inner layer is made from the following raw materials in parts by weight: 150 parts by weight of PERT resin (density 0.937 g / cm³). 3 6 parts by weight of antifouling agent (melt index 0.6 g / 10 min), 1.3 parts by weight of plasticizer tributyl acetylacetic acid, 1 part by weight of antioxidant 1010, and 1.5 parts by weight of compatibilizer polyethylene grafted maleic anhydride (CAS: 9006-26-2).

[0054] The method for preparing the antifouling additive is as follows:

[0055] 2.5 parts by weight of carbon nanotubes were added to 150 parts by weight of N,N-dimethylformamide and mixed thoroughly. Then, 12 parts by weight of vinyltriethoxysilane were added, and the mixture was stirred at 130°C for 60 h. After centrifugation, washing, and drying, vinyl carbon nanotubes were obtained. The carbon nanotubes were hydroxylated multi-walled carbon nanotubes with a length of 0.5-2 μm, an inner diameter of 2-5 nm, an outer diameter of 5-15 nm, and a hydroxyl content of 5.6 wt%. 0.4 parts by weight of sodium dodecylbenzenesulfonate and 1.5 parts by weight of vinyl carbon nanotubes were added to 10... Mix 0 parts by weight of water thoroughly, then add 1 part by weight of 4-vinylpiperidine hydrochloride (CAS: 1311316-95-6), 1.2 parts by weight of butyl methacrylate and 0.25 parts by weight of azobisisobutyronitrile, react at 90°C under nitrogen protection for 3 h, centrifuge, wash and dry to obtain piperidine-modified carbon nanotubes; add 0.85 parts by weight of piperidine-modified carbon nanotubes and 1 part by weight of sodium hypochlorite to 60 parts by weight of water and mix thoroughly, stir at room temperature for 6 h, centrifuge, wash and dry to obtain antifouling additive.

[0056] A method for preparing a high thermal conductivity PERT underfloor heating pipe includes the following steps:

[0057] According to the raw material formula, the raw materials for the thermally conductive outer layer and the anti-fouling inner layer are mixed separately to obtain a thermally conductive outer layer mixture and an anti-fouling inner layer mixture. Then, the thermally conductive outer layer mixture and the anti-fouling inner layer mixture are extruded in two layers, sized, shaped, and traction-cut to obtain the high thermal conductivity PERT underfloor heating pipe. The extrusion temperature is 190-210℃, the thickness of the thermally conductive outer layer is 2mm, and the thickness of the anti-fouling inner layer is 1mm.

[0058] Example 4

[0059] A high thermal conductivity PERT underfloor heating pipe includes a thermally conductive outer layer and a stain-resistant inner layer;

[0060] The thermally conductive outer layer is made from the following raw materials in parts by weight: 300 parts by weight of PERT resin (density 0.937 g / cm³). 3 8.5 parts by weight of thermally conductive composite filler (melt index 0.6 g / 10 min), 2.6 parts by weight of plasticizer tributyl acetylacetic acid, 2 parts by weight of antioxidant 1010, and 3 parts by weight of compatibilizer polyethylene grafted maleic anhydride (CAS: 9006-26-2).

[0061] The preparation method of the thermally conductive composite filler is as follows:

[0062] 0.2 parts by weight of 3-(2,3-epoxypropoxy)propyltrimethoxysilane (CAS: 2530-83-8), 0.3 parts by weight of 3-diethylenetriaminopropylmethyldimethoxysilane (CAS: 99740-64-4), 2 parts by weight of ammonium stearate (CAS: 1002-89-7), and 5 parts by weight of acetic acid were added to 60 parts by weight of methanol and 40 parts by weight of water and mixed thoroughly. Then, 20 parts by weight of aluminum nitride (composed of aluminum nitride with a particle size of 5 μm and a particle size of...) were added. Aluminum nitride with a thickness of 45 μm was prepared by mixing aluminum nitride in a weight ratio of 1:1.5 at 82 °C for 7 h, centrifuging, washing, and drying to obtain surface-treated aluminum nitride. 18 parts by weight of graphite nanosheets (GNP thickness ≤15 nm) and 7.5 parts by weight of surface-treated aluminum nitride were added to 200 parts by weight of N,N-dimethylformamide and mixed evenly. The mixture was stirred at 45 °C for 3 h, centrifuged, washed, and dried, and then calcined at 1250 °C under nitrogen protection for 2 h to obtain a thermally conductive composite filler.

[0063] The antifouling inner layer is made from the following raw materials in parts by weight: 150 parts by weight of PERT resin (density 0.937 g / cm³). 3 6 parts by weight of antifouling agent (melt index 0.6 g / 10 min), 1.3 parts by weight of plasticizer tributyl acetylacetic acid, 1 part by weight of antioxidant 1010, and 1.5 parts by weight of compatibilizer polyethylene grafted maleic anhydride (CAS: 9006-26-2).

[0064] The method for preparing the antifouling additive is as follows:

[0065] 0.85 parts by weight of carbon nanotubes and 1 part by weight of sodium hypochlorite were added to 60 parts by weight of water and mixed thoroughly. The mixture was stirred at room temperature for 6 hours, centrifuged, washed, and dried to obtain an antifouling agent. The carbon nanotubes were hydroxylated multi-walled carbon nanotubes with a length of 0.5-2 μm, an inner diameter of 2-5 nm, an outer diameter of 5-15 nm, and a hydroxyl content of 5.6 wt%.

[0066] A method for preparing a high thermal conductivity PERT underfloor heating pipe includes the following steps:

[0067] According to the raw material formula, the raw materials for the thermally conductive outer layer and the anti-fouling inner layer are mixed separately to obtain a thermally conductive outer layer mixture and an anti-fouling inner layer mixture. Then, the thermally conductive outer layer mixture and the anti-fouling inner layer mixture are extruded in two layers, sized, shaped, and traction-cut to obtain the high thermal conductivity PERT underfloor heating pipe. The extrusion temperature is 190-210℃, the thickness of the thermally conductive outer layer is 2mm, and the thickness of the anti-fouling inner layer is 1mm.

[0068] Example 5

[0069] A high thermal conductivity PERT underfloor heating pipe includes a thermally conductive outer layer and a stain-resistant inner layer;

[0070] The thermally conductive outer layer is made from the following raw materials in parts by weight: 300 parts by weight of PERT resin (density 0.937 g / cm³). 3 8.5 parts by weight of thermally conductive composite filler (melt index 0.6 g / 10 min), 2.6 parts by weight of plasticizer tributyl acetylacetic acid, 2 parts by weight of antioxidant 1010, and 3 parts by weight of compatibilizer polyethylene grafted maleic anhydride (CAS: 9006-26-2).

[0071] The preparation method of the thermally conductive composite filler is as follows:

[0072] 0.2 parts by weight of 3-(2,3-epoxypropoxy)propyltrimethoxysilane (CAS: 2530-83-8), 0.3 parts by weight of 3-diethylenetriaminopropylmethyldimethoxysilane (CAS: 99740-64-4), 2 parts by weight of ammonium stearate (CAS: 1002-89-7), and 5 parts by weight of acetic acid were added to 60 parts by weight of methanol and 40 parts by weight of water and mixed thoroughly. Then, 20 parts by weight of aluminum nitride (composed of aluminum nitride with a particle size of 5 μm and a particle size of...) were added. Aluminum nitride with a thickness of 45 μm was prepared by mixing aluminum nitride in a weight ratio of 1:1.5 at 82 °C for 7 h, centrifuging, washing, and drying to obtain surface-treated aluminum nitride. 18 parts by weight of graphite nanosheets (GNP thickness ≤15 nm) and 7.5 parts by weight of surface-treated aluminum nitride were added to 200 parts by weight of N,N-dimethylformamide and mixed evenly. The mixture was stirred at 45 °C for 3 h, centrifuged, washed, and dried, and then calcined at 1250 °C under nitrogen protection for 2 h to obtain a thermally conductive composite filler.

[0073] The antifouling inner layer is made from the following raw materials in parts by weight: 150 parts by weight of PERT resin (density 0.937 g / cm³). 3 6 parts by weight of antifouling agent (melt index 0.6 g / 10 min), 1.3 parts by weight of plasticizer tributyl acetylacetic acid, 1 part by weight of antioxidant 1010, and 1.5 parts by weight of compatibilizer polyethylene grafted maleic anhydride (CAS: 9006-26-2).

[0074] The method for preparing the antifouling additive is as follows:

[0075] 2.5 parts by weight of carbon nanotubes were added to 150 parts by weight of N,N-dimethylformamide and mixed evenly. Then, 12 parts by weight of vinyltriethoxysilane were added, and the mixture was stirred at 130°C for 60 h. After centrifugation, washing, and drying, vinyl carbon nanotubes were obtained. The carbon nanotubes were hydroxylated multi-walled carbon nanotubes with a length of 0.5-2 μm, an inner diameter of 2-5 nm, an outer diameter of 5-15 nm, and a hydroxyl content of 5.6 wt%. 0.85 parts by weight of vinyl carbon nanotubes and 1 part by weight of sodium hypochlorite were added to 60 parts by weight of water and mixed evenly. The mixture was stirred at room temperature for 6 h, and then centrifuged, washed, and dried to obtain an antifouling agent.

[0076] A method for preparing a high thermal conductivity PERT underfloor heating pipe includes the following steps:

[0077] According to the raw material formula, the raw materials for the thermally conductive outer layer and the anti-fouling inner layer are mixed separately to obtain a thermally conductive outer layer mixture and an anti-fouling inner layer mixture. Then, the thermally conductive outer layer mixture and the anti-fouling inner layer mixture are extruded in two layers, sized, shaped, and traction-cut to obtain the high thermal conductivity PERT underfloor heating pipe. The extrusion temperature is 190-210℃, the thickness of the thermally conductive outer layer is 2mm, and the thickness of the anti-fouling inner layer is 1mm.

[0078] Test Example 1

[0079] The thermal conductivity of the above examples was determined according to GB / T3399-1982 "Test Method for Thermal Conductivity of Plastics - Heat-Protected Plate Method"; the tensile strength of the above examples was determined according to GB / T1040.2-2022 "Determination of Tensile Properties of Plastics - Part 2: Test Conditions for Molded and Extruded Plastics".

[0080] Table 1. Tensile strength and thermal conductivity of underfloor heating pipes

[0081] Tensile strength (MPa) Thermal conductivity (W / m·K) Example 1 30.8 1.60 Example 2 26.5 1.12 Example 3 29.0 1.38

[0082] Test Example 2

[0083] The anti-fouling performance and hydrostatic resistance of the above examples were tested in accordance with GB / T28799.2-2020 "Heat-resistant polyethylene (PE-RT) piping systems for hot and cold water - Part 2: Pipes".

[0084] Table 2. Anti-fouling and hydrostatic resistance properties of underfloor heating pipes

[0085]

[0086] It can be seen that the PERT floor heating pipe prepared by this invention not only has excellent mechanical properties and high thermal conductivity, but also good antibacterial and anti-scaling capabilities, keeping the inner wall free of dirt and preventing leakage and rupture during long-term use. Compared with Examples 2-3, the thermally conductive composite filler used in Example 1 is based on the precise control and regulation of graphite nanosheets and surface-treated aluminum nitride. A surface treatment liquid composed of 3-(2,3-epoxypropoxy)propyltrimethoxysilane and 3-diethylenetriaminopropylmethyldimethoxysilane is used to modify the surface of aluminum nitride, giving it a positive charge. This positive charge attracts the negative charge on the surface of the graphite nanosheets, promoting self-assembly between the two through electrostatic interaction and chemical bonding. The graphite nanosheets are uniformly coated in the covering layer formed on the surface of the aluminum nitride, which not only improves the compatibility and dispersibility of the graphite nanosheets with the matrix, but also enhances the stability of the filler. This composite filler combines the high thermal conductivity of graphite nanosheets with the advantages of dispersibility and poor compatibility with the matrix. The components in the filler work synergistically, making the filler structure more stable and thus improving the overall thermal conductivity. Compared with Examples 4-5, the antifouling additive used in Example 1 first involves grafting vinyl groups onto the hydroxyl groups on the surface of carbon nanotubes via vinyltriethoxysilane, introducing vinyl groups into the surface of the carbon nanotubes. Then, under the action of the initiator azobisisobutyronitrile, monomers 4-vinylpiperidine hydrochloride and butyl methacrylate undergo in-situ graft polymerization on the surface of the carbon nanotubes to obtain piperidine-modified carbon nanotubes, further improving the surface properties and compatibility of the carbon nanotubes. Finally, after halogenation treatment with sodium hypochlorite, haloamine antibacterial carbon nanotubes are obtained, which are used as antifouling additives in the inner layer of PERT underfloor heating pipes. On the one hand, the grafted haloamine antibacterial structure has excellent antibacterial ability, which can prevent bacterial residues on the inner wall of the underfloor heating pipe, significantly improving the antibacterial and antiscaling performance of the pipe material. On the other hand, through this series of treatment steps, the aggregation and dispersion of carbon nanotubes are improved, and the interfacial compatibility with the matrix is ​​enhanced, avoiding the adverse effects of direct addition on the comprehensive mechanical properties of the pipe material. Furthermore, this invention utilizes the interaction of two aluminum nitride particles of different sizes to better increase the thermal conductivity of the thermally conductive filler. This may be because using two aluminum nitride particles of different sizes helps to form a denser network structure in the system, thereby improving the overall thermal conductivity.

[0087] The preferred embodiments of the present invention have been described in detail above. It should be understood that those skilled in the art can make numerous modifications and variations based on the concept of the present invention without creative effort. Therefore, all technical solutions that can be obtained by those skilled in the art based on the concept of the present invention through logical analysis, reasoning, or limited experimentation on the basis of existing technology should be within the scope of protection defined by the claims.

Claims

1. A high thermal conductivity PERT underfloor heating pipe, characterized in that: It includes a thermally conductive outer layer and an anti-fouling inner layer; the thermally conductive outer layer is made of the following raw materials in parts by weight: 200-500 parts PERT resin, 5-15 parts thermally conductive composite filler, 1-5 parts plasticizer, 0.5-3.5 parts antioxidant, and 2-5 parts compatibilizer; The preparation method of the thermally conductive composite filler is as follows: By weight, 0.1-0.5 parts of 3-(2,3-epoxypropoxy)propyltrimethoxysilane, 0.1-0.5 parts of 3-diethylenetriaminopropylmethyldimethoxysilane, 1-3 parts of ammonium stearate, and 3-6 parts of acetic acid are added to methanol and water and mixed evenly. Then, 10-30 parts of aluminum nitride are added, heated and stirred, centrifuged, washed, and dried to obtain surface-treated aluminum nitride. 15-20 parts of graphite nanosheets and 5-10 parts of surface-treated aluminum nitride are added to N,N-dimethylformamide and mixed evenly. The mixture is heated and stirred, centrifuged, washed, and dried, and then calcined under nitrogen protection to obtain a thermally conductive composite filler. The aluminum nitride is composed of aluminum nitride with a particle size of 2-10 μm and aluminum nitride with a particle size of 40-50 μm in a weight ratio of 1:1-2. The antifouling inner layer is made of the following raw materials in parts by weight: 100-200 parts PERT resin, 3-8 parts antifouling additive, 1-2 parts plasticizer, 0.5-1.5 parts antioxidant, and 1-2 parts compatibilizer; The method for preparing the antifouling additive is as follows: By weight, 1-5 parts of carbon nanotubes are added to N,N-dimethylformamide and mixed evenly. Then, 10-15 parts of vinyltriethoxysilane are added, heated and stirred, centrifuged, washed, and dried to obtain vinyl carbon nanotubes. 0.2-0.5 parts of sodium dodecylbenzenesulfonate and 1-2 parts of vinyl carbon nanotubes are added to water and mixed evenly. Then, 0.5-1.5 parts of 4-vinylpiperidine hydrochloride, 1-1.5 parts of butyl methacrylate, and 0.1-0.3 parts of azobisisobutyronitrile are added. The mixture is heated under nitrogen protection, centrifuged, washed, and dried to obtain piperidine-modified carbon nanotubes. 0.5-2 parts of piperidine-modified carbon nanotubes and 0.5-2 parts of sodium hypochlorite are added to water and mixed evenly. The mixture is stirred at room temperature, centrifuged, washed, and dried to obtain an antifouling agent.

2. The high thermal conductivity PERT underfloor heating pipe as described in claim 1, characterized in that: The carbon nanotubes are hydroxylated multi-walled carbon nanotubes.

3. The high thermal conductivity PERT underfloor heating pipe as described in claim 1, characterized in that: The plasticizer is one or a mixture of two or more of the following: polyethylene wax, chlorinated paraffin, dioctyl phthalate, tributyl acetyl citrate, and di(2-ethylhexyl) adipate.

4. The high thermal conductivity PERT underfloor heating pipe as described in claim 1, characterized in that: The antioxidant is one or a mixture of two or more of the following antioxidants: DSTP, 1076, 1010, 1098, and 636.

5. The high thermal conductivity PERT underfloor heating pipe as described in claim 1, characterized in that: The compatibilizer is one or a mixture of two or more of the following: polyethylene grafted with maleic anhydride, polypropylene grafted with maleic anhydride, and polyolefin elastomer grafted with maleic anhydride.

6. The method for preparing the high thermal conductivity PERT underfloor heating pipe according to any one of claims 1-5, characterized in that: Includes the following steps: According to the raw material formula, the raw materials for the heat-conducting outer layer and the anti-fouling inner layer are mixed separately to obtain the heat-conducting outer layer mixture and the anti-fouling inner layer mixture; then the heat-conducting outer layer mixture and the anti-fouling inner layer mixture are extruded in two layers, sized, shaped, and traction-cut to obtain the high thermal conductivity PERT floor heating pipe.

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