PEX-A pipe as well as preparation method and application thereof

Abstract

The invention discloses a PEX-A pipe as well as a preparation method and application thereof, and relates to the technical field of high polymer materials. The PEX-A pipe comprises the following raw material components in percentage by weight: 60-75% of high-density polyethylene; 5-15% of ultra-high molecular weight polyethylene; 3-8% of linear low density polyethylene; 5-12% of an ethylene-octylene copolymer; 1-3% of clay; 0.5-2% of a thermo-sensitive shape memory microcapsule; 0.05 to 0.1 percent of composite peroxide; the thermo-sensitive shape memory microcapsule comprises at least one of paraffin / polymer composite microspheres, stearic acid / polylactic acid composite microspheres and a silicon dioxide coated n-eicosane phase change material; the composite peroxide comprises di-tert-butyl peroxide and dicumyl peroxide. The PEX-A pipe provided by the invention has excellent antistatic capability, fatigue resistance, penetration resistance, deformation resistance, low temperature resistance and corrosion resistance.

Description

Technical Field

[0001] The present invention relates to the technical field of polymer materials, and particularly relates to a PEX-A pipe and its preparation method and application. Background Art

[0002] Traditional peroxide-crosslinked polyethylene (PEX-A) pipes use peroxides to initiate crosslinking. Although they have high heat resistance, their shape memory function is limited by the uniformity of the crosslinking network. Currently, the blending system of HDPE and a small amount of LLDPE has limited effect in improving flexibility, and the yield point elongation rate is difficult to exceed 20%, resulting in local plastic deformation during the cold expansion process, which affects the sealing performance of the pipe connection. In addition, a single crosslinking network is prone to stress relaxation after repeated deformation, resulting in a decrease in the shape recovery rate. Moreover, when transporting flammable and explosive media in chemical pipelines, traditional pipes lack effective antistatic performance, posing safety hazards. At the same time, in extreme environments such as deep sea high pressure and ultra-low temperature, the performance of traditional PEX-A pipes cannot meet the engineering requirements. Furthermore, the existing pipes have relatively single functions and mostly rely on external mechanical forces to achieve shape changes, and it is difficult to actively respond to environmental changes. Summary of the Invention

[0003] The purpose of the present invention is to overcome the deficiencies of the prior art and provide a PEX-A pipe and its preparation method and application. The PEX-A pipe of the present invention has excellent antistatic ability, fatigue resistance, impermeability, deformation resistance, low temperature resistance, and corrosion resistance.

[0004] To achieve the above purpose, the technical solution adopted by the present invention is as follows: In the first aspect, the present invention provides a PEX-A pipe, which comprises the following raw material components in weight percentage: High-density polyethylene (HDPE) 60-75%; ultra-high molecular weight polyethylene (UHMWPE) 5-15%; linear low-density polyethylene (LLDPE) 3-8%; ethylene-octene copolymer (POE) 5-12%; clay 1-3%; thermosensitive shape memory microcapsules 0.5-2%; compound peroxide 0.05-0.1%; the clay includes at least one of nano-clay and modified nano-clay; The thermosensitive shape memory microcapsules include at least one of paraffin / polymer composite microspheres, stearic acid / polylactic acid (PLA) composite microspheres, and silica-coated n-eicosane phase change materials; The compound peroxide includes di-tert-butyl peroxide (DTBP) and dicumyl peroxide (DCP), and the mass ratio of the di-tert-butyl peroxide to the dicumyl peroxide is 1:(0.5-2).

[0005] The present invention uses high-density polyethylene and ultra-high molecular weight polyethylene as the main chain, and is combined with linear low-density polyethylene and ethylene-octene copolymer to form a matrix with both rigidity and flexibility. Then, clay is added to the pipe to enhance the mechanical properties of the pipe. At the same time, thermosensitive shape memory microcapsules are added, which can achieve precise deformation response triggered by temperature, enabling the pipe to automatically shrink at high temperatures to compensate for thermal expansion and avoid pipeline deformation and cracking. Moreover, the present invention selects paraffin / polymer composite microspheres, stearic acid / polylactic acid composite microspheres, and silica-coated n-eicosane phase change materials as thermosensitive shape memory microcapsules, and realizes a multi-response mechanism (such as photo / thermal dual response) through a core-shell structure, which can better achieve precise deformation response triggered by temperature and improve the deformation resistance of the pipe.

[0006] The paraffin / polymer composite microspheres described in the present invention are composite microspheres with paraffin as the core and polymer as the shell; the stearic acid / polylactic acid composite microspheres are composite microspheres with stearic acid as the core and polylactic acid as the shell; the silica-coated n-eicosane phase change material is a microcapsule with n-eicosane as the core and silica as the shell.

[0007] The present invention uses a specific ratio of DTBP and DCP for compounding, which has a synergistic effect and can achieve "slow first and then fast" crosslinking kinetics, thereby improving the long-term stability of the pipe. Therefore, the PEX-A pipe described in the present invention has excellent antistatic ability, fatigue resistance, impermeability, deformation resistance, low temperature resistance, and corrosion resistance.

[0008] By controlling the mass ratio of di-tert-butyl peroxide and dicumyl peroxide within the above range, the present invention is beneficial to balance the crosslinking density and processing performance, and avoid the increase in brittleness caused by excessive crosslinking, thereby improving the performance of the pipe.

[0009] Preferably, the molecular weight of the high-density polyethylene is 200,000 - 350,000 g / mol, and the melt index under the test conditions of 190 °C / 2.16 kg is 0.3 - 1.0 g / 10 min (ASTM D1238-23a). The molecular weight detection standard of high-density polyethylene is ASTM D6474-20 (GPC method).

[0010] Preferably, the molecular weight of the ultra-high molecular weight polyethylene is 3,000,000 - 6,000,000 g / mol, and the melt index under the test conditions of 190 °C / 2.16 kg is 0 - 0.1 g / 10 min (ASTM D1238-23a). The molecular weight detection standard of ultra-high molecular weight polyethylene is ASTM D4020-18.

[0011] Preferably, the linear low-density polyethylene has a molecular weight of 100,000 - 200,000 g / mol and a melt index of 1.0 - 5.0 g / 10 min (ASTM D1238-23a) under the test conditions of 190 °C / 2.16 kg. The detection standard for the molecular weight of linear low-density polyethylene is ASTM D6474-20 (GPC method).

[0012] Preferably, the mass content of octene in the ethylene-octene copolymer is 20% - 30%. The mass content of octene is determined by nuclear magnetic resonance (NMR).

[0013] By controlling the content of octene in the present invention, the compatibility between the ethylene-octene copolymer and the matrix can be improved, thereby enhancing the flexibility of the pipe.

[0014] Preferably, the ethylene-octene copolymer has a molecular weight of 100,000 - 300,000 g / mol (determined by ASTM D6474-20 GPC method) and a melt index of 0.5 - 3.0 g / 10 min (ASTM D1238-23a) under the test conditions of 190 °C / 2.16 kg.

[0015] By controlling the molecular weights and melt indices of high-density polyethylene, ultra-high molecular weight polyethylene, linear low-density polyethylene, and ethylene-octene copolymer in the present invention, a dynamic balance between rigidity and flexibility can be achieved, breaking through the compatibility limitations of traditional blending systems, thereby improving the comprehensive performance of the pipe.

[0016] Preferably, the nano-clay includes at least one of nano-organically modified montmorillonite (OMMT), nano-lithium saponite, and nano-kaolin.

[0017] Preferably, the nano-clay has a lamellar thickness of 1 - 5 nm, a lateral dimension of 50 - 200 nm, and a specific surface area of 700 - 1000 m 2 / g. The specific surface area is determined by the BET method.

[0018] It should be noted that the lateral dimension refers to the maximum projection length of the lamella in the two-dimensional plane, and the lateral dimension is measured by atomic force microscopy (AFM).

[0019] The high specific surface area and oriented arrangement of the nano-clay form a "nano-spring" structure, which is beneficial to enhancing the stress dispersion ability, inhibiting crack propagation, and thus improving the mechanical properties of the pipe.

[0020] Preferably, the modified nano-clay is obtained by modifying with carbon nanotubes or graphene.

[0021] Preferably, the modified nano-clay is obtained by modifying with carbon nanotubes, and the modification method is as follows: Disperse carboxylated carbon nanotubes (CNT) and nanoclay in a solvent. After mixing evenly, dry and grind to obtain modified nanoclay.

[0022] The nanoclay is modified by carbon nanotubes to obtain a carbon nanotube-clay composite. Moreover, the carbon nanotubes and the nanoclay form a composite through hydrogen bonding or electrostatic adsorption.

[0023] Preferably, the mass of the nanoclay is 1-3% of the total mass of the raw materials; the mass of the carboxylated carbon nanotubes is 3-8% of the mass of the nanoclay; the mass of the solvent is 10-30 times the mass of the nanoclay.

[0024] Preferably, the diameter of the carbon nanotubes is 10-30 nm and the length is 1-10 μm.

[0025] Preferably, the modified nanoclay is obtained by modifying with graphene, and the modification method is as follows: Mix graphene oxide (GO), nanoclay and water evenly, and then add a reducing agent for treatment to obtain modified nanoclay.

[0026] The nanoclay is modified by graphene to obtain a graphene-clay composite. Moreover, the graphene and the nanoclay enhance the interfacial bonding through van der Waals forces.

[0027] Preferably, the mass of the nanoclay is 1-3% of the total mass of the raw materials; the mass of the graphene oxide is 2-5% of the mass of the nanoclay; the mass of the water is 50-100 times the mass of the nanoclay; the mass of the reducing agent is 10-20% of the mass of the graphene oxide.

[0028] It should be noted that the "total mass of the raw materials" in the above "the mass of the nanoclay is 1-3% of the total mass of the raw materials" refers to the sum of the masses of each raw material component in the PEX-A pipe.

[0029] Preferably, the sheet thickness of the graphene is 1-5 layers and the lateral dimension is 0.5-5 μm.

[0030] It should be noted that the sheet thickness of the graphene is 1-5 layers, the single-layer thickness is 0.34 nm, and the total sheet thickness of the graphene is 0.34-1.7 nm.

[0031] By controlling the size of the carbon nanotubes or graphene, the present invention can form a conductive network, cooperate with the nanoclay to construct a "clay-carbon-based" two-phase reinforcement structure, and significantly improve the antistatic performance of the pipe.

[0032] Preferably, the preparation method of the paraffin / polymer composite microspheres is as follows: The paraffin and the monomer mixture are mixed and heated to melting, and the monomer mixture includes styrene monomers and acrylate monomers; then an emulsifier is added and high-speed shearing is carried out to form a microemulsion; then an initiator is added to initiate polymerization, and paraffin / polymer composite microspheres are obtained after curing.

[0033] The paraffin / polymer composite microspheres prepared by the present invention have a core-shell structure, with paraffin as the core and polymer as the shell, and can achieve a precise deformation response triggered by temperature (response temperature 55-65 °C), thereby improving the deformation resistance of the pipe.

[0034] Preferably, the mass ratio of the paraffin to the monomer mixture is 1:(1-2), preferably 1:2.

[0035] Preferably, the mass ratio of the styrene monomer to the acrylate monomer is 1:(1-2), preferably 1:1.

[0036] Preferably, the melting point of the paraffin is 50-60 °C.

[0037] Preferably, the emulsifier includes at least one of sodium dodecyl sulfate, Tween-80, Span-60, polyethylene glycol (PEG), cetyltrimethylammonium bromide (CTAB).

[0038] Preferably, the speed of the high-speed shearing is 8000-12000 rpm.

[0039] Preferably, the initiator includes at least one of ammonium persulfate, azobisisobutyronitrile (AIBN), benzoyl peroxide (BPO), ferrous sulfate / potassium persulfate.

[0040] Preferably, the D50 particle size of the thermosensitive shape memory microcapsules is 1-10 μm. The particle size is measured by a laser particle size analyzer.

[0041] Preferably, the PEX-A pipe further includes 0.1-0.8% by weight of an antioxidant and 1-10% by weight of a color masterbatch.

[0042] Preferably, the antioxidant includes at least one of Irganox 1010, Irgafos 168, and antioxidant DSTDP.

[0043] In a second aspect, the present invention also provides a method for preparing a PEX-A pipe, including the following steps: (1) Mix high-density polyethylene, ultra-high molecular weight polyethylene, linear low-density polyethylene, ethylene-octene copolymer, and thermosensitive shape memory microcapsules evenly, and then add clay and mix evenly to obtain a mixture. (2) Melt and blend the mixture in an extruder, then inject the compound peroxide at the die head of the extruder, preheat at 90 - 100 °C for 28 - 30 min, and then cure at 120 - 125 °C for 1 - 2 h to obtain PEX-A pipes.

[0044] In the present invention, the decomposition of di-tert-butyl peroxide is triggered first at 90 - 100 °C, and then the decomposition of dicumyl peroxide is activated at 120 - 125 °C. The spatial distribution of the crosslinked network can be optimized by injecting in stages. Moreover, by adopting the dynamic crosslinking process combined with the method of injecting peroxide at the die head, the gradient regulation of the crosslinking degree can be realized, and the pressure resistance of the pipes can be significantly improved.

[0045] Preferably, a photoinitiator is added after curing in step (2) and irradiated under ultraviolet light.

[0046] The present invention adopts a three-stage crosslinking process. On the basis of the existing two-stage peroxide crosslinking, an ultraviolet light-assisted crosslinking step is added. A high-density crosslinked layer is formed on the pipe surface by using the photoinitiator, further improving the corrosion resistance and surface hardness of the pipes.

[0047] Preferably, the photoinitiator includes at least one of benzophenone (BP), 1-hydroxycyclohexyl phenyl ketone (184), Irgacure 250, and bis(2,4,6-trimethylbenzoyl)phenylphosphine oxide (Irgacure 819).

[0048] More preferably, the initiator is bis(2,4,6-trimethylbenzoyl)phenylphosphine oxide (Irgacure 819), whose absorption wavelength matches that of the ultraviolet light source (365 nm) and has a high initiation efficiency.

[0049] It should be noted that the wavelength of the ultraviolet light needs to match the photoinitiator (such as the absorption peak of Irgacure 819 at 365 nm), the light intensity is 50 - 200 mW / cm 2 , and the irradiation time is 5 - 10 minutes.

[0050] Preferably, the shear rate during the addition of clay and mixing in step (1) is 5000 - 10000 s -1 .

[0051] By controlling the shear rate during the addition of clay and mixing in the present invention, it can ensure the uniform dispersion of the clay in the matrix and avoid agglomeration. Moreover, through the high shear rate, the oriented arrangement of the nano-fillers can be realized to form a "stress buffer layer", which is beneficial to improving the deformation resistance of the pipes.

[0052] Preferably, the temperature during the melt blending in step (2) is 160 - 190 °C.

[0053] Thirdly, the present invention also provides an application of PEX-A pipes in floor heating, chemical pipelines, offshore engineering, and polar facilities.

[0054] Compared with the prior art, the beneficial effects of the present invention are as follows: (1) By introducing carbon nanotubes or graphene into the clay, a "clay-carbon-based" composite reinforcement phase is formed in the present invention. The high electrical conductivity and mechanical properties of the carbon material can synergistically improve the antistatic ability and fatigue resistance of the pipes.

[0055] (2) Thermosensitive shape memory microcapsules are added to the pipes in the present invention, enabling a temperature-triggered deformation response function. For example, it automatically shrinks at high temperatures to compensate for thermal expansion and prevent pipeline deformation and cracking. This design combines passive shape memory with active response for the first time, breaking through the limitations of the prior art that only relies on external mechanical forces.

[0056] (3) The PEX-A pipes described in the present invention can be stably applied under harsh working conditions. For example, they have antistatic ability when transporting flammable and explosive media in chemical pipelines and can still maintain excellent performance in extreme environments such as deep sea high pressure and ultra-low temperature. At the same time, intelligent functions are integrated, enabling the pipes to actively respond to temperature changes, compensate for thermal expansion, and prevent pipeline deformation and cracking. Detailed implementation manners

[0057] To better illustrate the purpose, technical solution, and advantages of the present invention, the present invention will be further described below in conjunction with specific embodiments. However, the protection scope and implementation manners of the present invention are not limited thereto.

[0058] The materials, reagents, etc. used in the following embodiments are commercially available reagents and materials unless otherwise specified.

[0059] Embodiment 1 The present invention discloses a PEX-A pipe, which comprises the following raw material components in weight percentage: High-density polyethylene 62%; ultra-high molecular weight polyethylene 12%; linear low-density polyethylene 6%; ethylene-octene copolymer 11%; nano-clay 3%; thermosensitive shape memory microcapsules 1%; compound peroxide 0.1%; antioxidant 0.6%; color masterbatch 4.3%.

[0060] The high-density polyethylene has a molecular weight of 200,000 g / mol, a melt index of 1.0 g / 10 min, and the manufacturer is ExxonMobil™ HD6704.56 (MI 1.0, molecular weight 200,000).

[0061] The ultra-high molecular weight polyethylene has a molecular weight of 3,000,000 g / mol, a melt index of 0.1 g / 10 min, and the manufacturer is Ticona GUR® 4120 (MI 0.1, molecular weight 3,000,000).

[0062] The linear low density polyethylene has a molecular weight of 100,000 g / mol and a melt index of 5.0 g / 10 min, and the manufacturer is Dowlex™ 2045G (MI 5.0, molecular weight 100,000).

[0063] The mass content of octene in the ethylene-octene copolymer is 20%, the melt index is 0.5 g / 10 min, and it is DowEngage™ 8180 (octene 20%, MI 0.5).

[0064] The nano clay is nano organically modified montmorillonite (Nanocor® I.30P). The lamellar thickness of the nano clay is 1 - 5 nm, the lateral dimension is 50 - 200 nm, and the specific surface area is 750 m 2 / g.

[0065] The thermosensitive shape memory microcapsule is a paraffin / polymer composite microsphere, and the preparation method of the paraffin / polymer composite microsphere is as follows: Mix paraffin and the monomer mixture evenly at a mass ratio of 1:2 and heat to melting; the monomer mixture includes styrene monomer and acrylate monomer at a mass ratio of 1:1; then add an emulsifier (sodium dodecyl sulfate), and form a microemulsion by high-speed shearing under the action of the emulsifier, and the shearing speed is 8000 rpm; then add an initiator (ammonium persulfate) to initiate polymerization, and obtain paraffin / polymer composite microspheres after curing. The particle size of the paraffin / polymer composite microspheres is 1 - 10 μm. The mass of the emulsifier is 2% of the mass of the paraffin / polymer composite microspheres. The mass of the initiator is 0.5% of the total mass of the monomer mixture.

[0066] The composite peroxide includes di-tert-butyl peroxide and dicumyl peroxide, and the mass ratio of di-tert-butyl peroxide to dicumyl peroxide is 1:1.

[0067] The antioxidant is antioxidant DSTDP.

[0068] The masterbatch is Cabot Monarch® 880, polyethylene-based carrier + 2% carbon black.

[0069] The present invention also discloses a preparation method of a PEX-A pipe, which includes the following steps: (1) Mix high density polyethylene, ultra-high molecular weight polyethylene, linear low density polyethylene, ethylene-octene copolymer, thermosensitive shape memory microcapsule, antioxidant, and masterbatch for 2 h, then add nano clay and perform high-speed shear dispersion, and the shear rate is 5000 s -1 , and obtain a mixed material after mixing evenly.

[0070] (2) The mixture is melt-blended in an extruder at a temperature of 160 - 190 °C during melt-blending; then di-tert-butyl peroxide and dicumyl peroxide are injected at the die head of the extruder, and a three-stage cross-linking process is adopted: first preheat at 90 °C for 30 min, then cure at 120 °C for 2 h, and finally add a photoinitiator (Irgacure 819) under ultraviolet light with a light intensity of 100 mW / cm 2 , irradiate for 10 min to obtain PEX-A pipes.

[0071] Example 2 The present invention discloses a PEX-A pipe, which comprises the following raw material components by weight percentage: High-density polyethylene 60%; ultra-high molecular weight polyethylene 15%; linear low-density polyethylene 8%; ethylene-octene copolymer 5%; nano-clay 1%; thermosensitive shape memory microcapsules 0.5%; compound peroxide 0.05%; antioxidant 0.8%; color masterbatch 9.65%.

[0072] The high-density polyethylene has a molecular weight of 350,000 g / mol, a melt index of 0.3 g / 10 min, and the manufacturer is BasellLupolen 4261AG (MI 0.3, molecular weight 350,000).

[0073] The ultra-high molecular weight polyethylene has a molecular weight of 6,000,000 g / mol, a melt index of 0.1 g / 10 min, and the manufacturer is Celanese GUR®4150 (MI 0.1, molecular weight 6,000,000).

[0074] The linear low-density polyethylene has a molecular weight of 200,000 g / mol, a melt index of 1.0 g / 10 min, and the manufacturer is ExxonMobil™LL3004.32 (MI 1.0, molecular weight 200,000).

[0075] The ethylene-octene copolymer has an octene mass content of 30% and a melt index of 3.0 g / 10 min, and the manufacturer is Dow Engage™8450 (octene 30%, MI 3.0).

[0076] The nano-clay is nano-organically modified montmorillonite (Nanocor®I.30P), the nano-clay has a lamellar thickness of 1 - 5 nm, a lateral size of 50 - 200 nm, and a specific surface area of 750 m 2 / g.

[0077] The thermosensitive shape memory microcapsules are paraffin / polymer composite microspheres, and the preparation method of the paraffin / polymer composite microspheres is as follows: Mix paraffin wax and the monomer mixture evenly at a mass ratio of 1:2 and heat to melting; the monomer mixture includes styrene monomer and acrylate monomer at a mass ratio of 1:1; then add an emulsifier (sodium dodecyl sulfate), and form a microemulsion by high-speed shearing under the action of the emulsifier, with a shearing speed of 12,000 rpm; then add an initiator (ammonium persulfate) to initiate polymerization, and obtain paraffin / polymer composite microspheres after curing. The particle size of the paraffin / polymer composite microspheres is 1 - 10 μm. The mass of the emulsifier is 5% of the mass of the paraffin / polymer composite microspheres. The mass of the initiator is 1.5% of the total mass of the monomer mixture.

[0078] The composite peroxide includes di-tert-butyl peroxide and dicumyl peroxide, and the mass ratio of the di-tert-butyl peroxide to the dicumyl peroxide is 1:1.

[0079] The antioxidant is antioxidant DSTDP.

[0080] The color masterbatch is Cabot Monarch® 880, polyethylene-based carrier + 2% carbon black.

[0081] The present invention also discloses a preparation method of a PEX-A pipe, comprising the following steps: (1) Mix high-density polyethylene, ultra-high molecular weight polyethylene, linear low-density polyethylene, ethylene-octene copolymer, temperature-sensitive shape memory microcapsules, antioxidant, and color masterbatch for 2 h, then add nano-clay and conduct high-speed shear dispersion, with a shear rate of 10,000 s -1 , and obtain a mixed material after mixing evenly.

[0082] (2) Melt and blend the mixed material in an extruder, and the temperature during melt blending is 160 - 190 °C; then inject di-tert-butyl peroxide and dicumyl peroxide at the die head of the extruder, and adopt a three-stage cross-linking process: first preheat at 90 °C for 30 min, then cure at 120 °C for 2 h, and finally add a photoinitiator (Irgacure 819) under ultraviolet light, with a light intensity of 100 mW / cm 2 , irradiate for 10 min, and obtain a PEX-A pipe.

[0083] Example 3 A PEX-A pipe, which is different from that in Example 1 in that the PEX-A pipe includes the following raw material components in weight percentages: High-density polyethylene 73.8%; ultra-high molecular weight polyethylene 5%; linear low-density polyethylene 3%; ethylene-octene copolymer 12%; nano-clay 3%; temperature-sensitive shape memory microcapsules 2%; composite peroxide 0.1%; antioxidant 0.1%; color masterbatch 1%.

[0084] Example 4 A PEX-A pipe, which is different from that in Example 1 in that the mass ratio of di-tert-butyl peroxide to dicumyl peroxide is 1:0.5.

[0085] Example 5 A PEX-A pipe, which is different from that in Example 1 in that the mass ratio of di-tert-butyl peroxide to dicumyl peroxide is 1:2.

[0086] Example 6 A PEX-A pipe, which is different from that in Example 1 in that the nano-clay is modified by carbon nanotubes, and the modification method is as follows: Disperse carboxylated carbon nanotubes and nano-clay in ethanol, ultrasonic treat for 2 hours, dry and then grind to obtain modified nano-clay, that is, carbon nanotube-clay composite. The mass of carboxylated carbon nanotubes is 3% of the mass of nano-clay, the mass of nano-clay is 3% of the total raw material mass, and the mass of ethanol is 30 times the mass of nano-clay.

[0087] The diameter of the carboxylated carbon nanotubes is 10 - 30 nm, and the length is 1 - 10 μm.

[0088] Example 7 A PEX-A pipe, which is different from that in Example 1 in that the nano-clay is modified by graphene, and the modification method is as follows: Mix graphene oxide and nano-clay aqueous solution evenly, and then add hydrazine hydrate for reduction treatment to obtain modified nano-clay, that is, graphene-clay composite. The mass of graphene oxide is 3% of the mass of nano-clay, the mass of nano-clay is 3% of the total raw material mass, the mass of water is 100 times the mass of nano-clay, and the mass of hydrazine hydrate is 15% of the mass of graphene oxide.

[0089] The sheet thickness of graphene oxide is 0.34 - 1.7 nm, and the lateral size is 0.5 - 5 μm.

[0090] Example 8 A PEX-A pipe, which is different from that in Example 1 in that an equal mass of stearic acid / polylactic acid composite microspheres is used to replace the paraffin / polymer composite microspheres.

[0091] The preparation method of the stearic acid / polylactic acid composite microspheres is as follows: Melt and blend stearic acid and PLA in an extruder at a mass ratio of 1:1, the extrusion temperature is 160 - 190 °C, and then spray drying (inlet temperature 120 °C, outlet temperature 60 °C) to obtain the stearic acid / polylactic acid composite microspheres.

[0092] Example 9 <x A PEX-A pipe, which is different from that of Example 1 in that silica-coated n-eicosane phase change material with equal mass is used to replace the paraffin / polymer composite microspheres.

[0093] The silica-coated n-eicosane phase change material is prepared by the sol-gel method. The method is as follows: n-eicosane is added to Span-80 for emulsification. After emulsification, it reacts with TEOS (the molar ratio of n-eicosane to TEOS is 1:2). Then ammonia water is added for catalysis. After curing at 60 °C, the silica-coated n-eicosane phase change material is obtained.

[0094] The mass of Span-80 is 5% of the mass of n-eicosane; the molar ratio of ammonia water to TEOS is 0.1:1.

[0095] Comparative Example 1 A PEX-A pipe, which is different from that of Example 1 in that high-density polyethylene with equal mass is used to replace the nanoclay.

[0096] Comparative Example 2 A PEX-A pipe, which is different from that of Example 1 in that high-density polyethylene with equal mass is used to replace the ethylene-octene copolymer.

[0097] Comparative Example 3 A PEX-A pipe, which is different from that of Example 1 in that high-density polyethylene with equal mass is used to replace the paraffin / polymer composite microspheres.

[0098] Comparative Example 4 A PEX-A pipe, which is different from that of Example 1 in that dicumyl peroxide is not added to the composite peroxide.

[0099] Comparative Example 5 A PEX-A pipe, which is different from that of Example 1 in that di-tert-butyl peroxide is not added to the composite peroxide.

[0100] Comparative Example 6 A PEX-A pipe, which is different from that of Example 1 in that the mass ratio of di-tert-butyl peroxide to dicumyl peroxide is 1:0.2.

[0101] Comparative Example 7 A PEX-A pipe, which is different from that of Example 1 in that the mass ratio of di-tert-butyl peroxide to dicumyl peroxide is 1:5.

[0102] Comparative Example 8 A PEX-A pipe, which is different from Example 1 in that the weight ratio of high-density polyethylene, ultra-high molecular weight polyethylene, linear low-density polyethylene, and ethylene-octene copolymer is different from that of Example 1. Specifically, the PEX-A pipe comprises the following raw material components in weight percentages: High-density polyethylene 57%; ultra-high molecular weight polyethylene 18%; linear low-density polyethylene 1%; ethylene-octene copolymer 15%; nano-clay 3%; thermosensitive shape memory microcapsules 1%; compound peroxide 0.1%; antioxidant 0.6%; color masterbatch 4.3%.

[0103] Comparative Example 9 A PEX-A pipe, which is different from Example 1 in that the weight ratio of high-density polyethylene, ultra-high molecular weight polyethylene, linear low-density polyethylene, and ethylene-octene copolymer is different from that of Example 1. Specifically, the PEX-A pipe comprises the following raw material components in weight percentages: High-density polyethylene 76%; ultra-high molecular weight polyethylene 4%; linear low-density polyethylene 10%; ethylene-octene copolymer 3%; nano-clay 1%; thermosensitive shape memory microcapsules 1%; compound peroxide 0.1%; antioxidant 0.6%; color masterbatch 4.3%.

[0104] Performance testing 1. Yield point elongation rate (%): Refer to ASTM D638-22 Standard Test Method for Tensile Properties of Plastics.

[0105] 2. Shape recovery rate (95°C, %): Through dynamic mechanical analysis (DMA) combined with a custom temperature control program (heating to 95°C and then cooling, recording the deformation recovery rate). Test conditions: Deformation amount 50%, heating rate 5°C / min, holding for 30 min, cooling to 25°C for measurement.

[0106] 3. Hydrostatic strength (95°C, MPa): Refer to ISO 1167-1:2006 Plastics piping systems - Determination of resistance to internal pressure - Part 1: General method for long-term hydrostatic strength (in a 95°C water pressure environment).

[0107] 4. Crosslinking degree (%): Refer to ASTM D2765-16(2024), xylene extraction method, and calculate the crosslinking degree through the content of insoluble matter.

[0108] 5. Surface resistivity (Ω·cm): Refer to ASTM D257-14(2021)e1 Standard Test Method for Surface Resistivity of Electrical Insulating Materials, with electrode spacing and voltage conditions: Electrode spacing 10 mm, voltage 500 V, humidity 50 ± 5%.

[0109] 6. Impact Strength (Improvement Ratio): Refer to ASTM D256-24 (Izod Impact), with unmodified PEX-A as the reference, and the reference value is 15 kJ / m 2 , and calculate the improvement ratio of impact strength.

[0110] 7. Tensile Strength (MPa): Refer to the standard tensile test of ASTM D638-22, with a tensile rate of 50 mm / min.

[0111] 8. Shore D Hardness: Refer to the ASTM D2240-15(2021) Shore D durometer indentation method, with a test time of 15 seconds.

[0112] 9. Volume Swelling Ratio after Immersion in Xylene for 24 Hours (%): Refer to ASTM D570-22, replace distilled water with xylene solvent, and measure the volume change rate after immersion for 24 hours.

[0113] 10. Deep-Sea High-Pressure Deformation Recovery Rate (10 MPa, %): Refer to ISO 6259-3:2015, simulate the deep-sea high-pressure (10 MPa water pressure) environment, and conduct the recovery rate test after applying deformation. The test conditions are: deep-sea high pressure: 10 MPa / 24h, deformation 50%, recovery 2h.

[0114] 11. Ultra-Low Temperature Deformation Recovery Rate (-60°C, %): Refer to ISO 6259-3:2015, apply deformation in a -60°C low-temperature chamber, and measure the recovery rate after returning to room temperature. The test conditions are: -60°C / 4h, deformation 30%, recovery to room temperature.

[0115] 12. Deep-Sea High-Pressure Hydrostatic Strength (10 MPa, MPa): Refer to ISO 1167-1:2006, and test the long-term hydrostatic strength (95°C) of the pipe under 10 MPa water pressure.

[0116] 13. Ultra-Low Temperature Hydrostatic Strength (-60°C, MPa): Refer to ISO 1167-1:2006, and test the short-term hydrostatic strength (1 h) of the pipe in a -60°C low-temperature environment.

[0117] 14. Tensile Strength Decay Rate after Aging Experiment (5000 hours, %): Refer to ASTM D3045-18, 5000-hour thermo-oxidative aging (95°C air environment), with unmodified PEX-A as the reference (the decay rate after 5000 hours is 35%), and compare the change in tensile strength before and after aging.

[0118] 15. Sealing Performance after Cold Expansion Recovery Cycle Times: Refer to ISO 1167-1:2006, after cold expansion-recovery cycle (1000 times), pressurize to 1.5 times the working pressure and observe the leakage situation.

[0119] The above test results are shown in Table 1 and Table 2.

[0120] Table 1 Table 2 As can be seen from Table 1, the PEX-A pipe described in the present invention has excellent antistatic ability, fatigue resistance, impermeability, deformation resistance, low temperature resistance and corrosion resistance.

[0121] From Examples 6-7 and Example 1, it can be seen that after the nano-clay is modified by carbon nanotubes or graphene, the hydrostatic strength, impact strength, tensile strength and hardness are improved compared with Example 1, indicating that the modification treatment of the nano-clay can improve the mechanical properties of the PEX-A pipe. Moreover, after the nano-clay is modified with carbon nanotubes or graphene, the corrosion resistance, antistatic ability, low temperature resistance and deformation resistance of the PEX-A pipe are all improved.

[0122] From Comparative Examples 1-3 and Example 1, it can be seen that in Comparative Example 1, no nano-clay is added, in Comparative Example 2, no ethylene-octene copolymer is added, and in Comparative Example 3, no paraffin / polymer composite microspheres are added. The yield point elongation and shape recovery rate in Comparative Examples 1-3 are lower than those in Example 1, indicating that the simultaneous addition of nano-clay, ethylene-octene copolymer and paraffin / polymer composite microspheres in the matrix is beneficial to improving the deformation resistance of the PEX-A pipe. Moreover, the surface resistivity and xylene immersion swelling rate in Comparative Examples 1-3 are higher than those in Example 1, indicating that the simultaneous addition of nano-clay, ethylene-octene copolymer and paraffin / polymer composite microspheres in the matrix is also beneficial to improving the antistatic ability and corrosion resistance of the PEX-A pipe.

[0123] From Comparative Examples 4-5 and Example 1, it can be seen that in Comparative Example 4, the composite peroxide only includes di-tert-butyl peroxide, and in Comparative Example 5, it only includes diisopropylbenzene peroxide. The crosslinking degree of the PEX-A pipe in Comparative Examples 4-5 is lower than that in Example 1, and moreover, the mechanical properties, corrosion resistance, deformation resistance and antistatic ability are all inferior to those in Example 1, indicating that the compounding of di-tert-butyl peroxide and diisopropylbenzene peroxide used in the present invention has a synergistic effect and is beneficial to improving the comprehensive performance of the pipe.

[0124] From Comparative Examples 6-7 and Example 1, it can be seen that if the mass ratio of di-tert-butyl peroxide and diisopropylbenzene peroxide is too large or too small, it will affect the performance of the PEX-A pipe. By controlling the mass ratio of di-tert-butyl peroxide and diisopropylbenzene peroxide to be 1:(0.5-2), the present invention can balance the crosslinking density and processing performance, avoid the increase in brittleness caused by excessive crosslinking, and thus improve the comprehensive performance of the pipe.

[0125] It can be seen from Comparative Examples 8-9 and Example 1 that if the contents of high-density polyethylene, ultra-high molecular weight polyethylene, linear low-density polyethylene, and ethylene-octene copolymer are too low or too high, the performance of the PEX-A pipe will be greatly affected. By controlling the component ratios of high-density polyethylene, ultra-high molecular weight polyethylene, linear low-density polyethylene, and ethylene-octene copolymer, the present invention can achieve a "dual-phase reinforcement" structure that combines rigidity and flexibility, enabling the PEX-A pipe to have excellent electrostatic resistance, fatigue resistance, impermeability, deformation resistance, low-temperature resistance, and corrosion resistance.

[0126] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit the protection scope of the present invention. Although the present invention has been described in detail with reference to the preferred embodiments, those of ordinary skill in the art should understand that the technical solutions of the present invention can be modified or equivalently replaced without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A PEX-A pipe, characterized in that, It comprises raw material components with the following weight percentages: High-density polyethylene 60 - 75%; Ultra-high molecular weight polyethylene 5 - 15%; Linear low-density polyethylene 3 - 8%; Ethylene-octene copolymer 5 - 12%; Clay 1 - 3%; Thermosensitive shape memory microcapsules 0.5 - 2%; Compound peroxide 0.05 - 0.1%; The clay includes at least one of nano-clay and modified nano-clay; The thermosensitive shape memory microcapsules include at least one of paraffin / polymer composite microspheres, stearic acid / polylactic acid composite microspheres, and silica-coated n-eicosane phase change materials; The compound peroxide includes di-tert-butyl peroxide and dicumyl peroxide, and the mass ratio of di-tert-butyl peroxide to dicumyl peroxide is 1:(0.5 - 2).

2. The PEX-A pipe according to claim 1, wherein The high-density polyethylene has a molecular weight of 200,000 - 350,000 g / mol and a melt index of 0.3 - 1.0 g / 10min under the test conditions of 190°C / 2.16 kg; And / or, the ultra-high molecular weight polyethylene has a molecular weight of 3,000,000 - 6,000,000 g / mol and a melt index of 0 - 0.1 g / 10min under the test conditions of 190°C / 2.16 kg; And / or, the linear low-density polyethylene has a molecular weight of 100,000 - 200,000 g / mol and a melt index of 1.0 - 5.0 g / 10min under the test conditions of 190°C / 2.16 kg; And / or, the ethylene-octene copolymer has a molecular weight of 100,000 - 300,000 g / mol and a melt index of 0.5 - 3.0 g / 10min under the test conditions of 190°C / 2.16 kg.

3. The PEX-A pipe according to claim 1, wherein, The nano-clay includes at least one of nano-organically modified montmorillonite, nano-lithium saponite, and nano-kaolin; And / or, the nano-clay has a thickness of 0.34 - 1.7 nm, a lateral size of 50 - 200 nm, and a specific surface area of 700 - 1000 m 2 / g.

4. The PEX-A pipe according to claim 1, wherein The modified nano-clay is obtained by modifying with carbon nanotubes or graphene.

5. The PEX-A pipe according to claim 4, wherein The modified nano-clay is obtained by modifying with carbon nanotubes, and the modification method is as follows: Disperse carboxylated carbon nanotubes and nano-clay in a solvent, mix evenly, and then obtain the modified nano-clay through drying and grinding.

6. The PEX-A pipe according to claim 4, wherein The modified nano-clay is obtained by modifying with graphene, and the modification method is as follows: Mix graphene oxide, nano-clay, and water evenly, and then add a reducing agent for treatment to obtain the modified nano-clay.

7. The PEX-A pipe according to claim 1, characterized in that, The preparation method of the paraffin / polymer composite microspheres is as follows: Mix paraffin and a monomer mixture and heat to melting. The monomer mixture includes styrene monomer and acrylate monomer; then add an emulsifier and perform high-speed shearing to form a microemulsion; then add an initiator to initiate polymerization, and obtain paraffin / polymer composite microspheres after curing.

8. A method for preparing a PEX-A pipe according to any one of claims 1-7, characterized in that, It includes the following steps: (1) Mix high-density polyethylene, ultra-high molecular weight polyethylene, linear low-density polyethylene, ethylene-octene copolymer, and thermosensitive shape memory microcapsules evenly, and then add clay and mix evenly to obtain a mixed material; (2) Melt and blend the mixed material in an extruder, then inject the compound peroxide at the die head of the extruder, preheat at 90 - 100°C for 28 - 30 min, and then cure at 120 - 125°C for 1 - 2 h to obtain PEX-A pipes.

9. The preparation method of the PEX-A pipe according to claim 8, characterized in that, The shear rate during the addition of clay and mixing in step (1) is 5000 - 10000 s -1 ; And / or, the temperature during melt blending in step (2) is 160-190°C.

10. Application of a PEX-A pipe as described in any one of claims 1-7 in floor heating, chemical pipelines, offshore engineering, and polar facilities.

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