PE-based nano high-thermal-conductivity composite material and pipe preparation process

Abstract

The invention relates to the technical field of high-molecular polyethylene, and particularly discloses a PE-based nano high-thermal-conductivity composite material and a pipe preparation process, the PE-based nano high-thermal-conductivity composite material is prepared from the following raw materials: high-density polyethylene, linear low-density polyethylene, an ethylene-octylene copolymer, a modified carbon nanotube, a core-shell oxide, a graphene nanosheet, an interface compatilizer, an antioxidant and a cross-linking agent; the modified carbon nano tube is obtained by depositing a SiO2 layer on the surface of a carbon nano tube and then grafting vinyltriethoxysilane; a core layer of the core-shell oxide is zirconium oxide, a shell layer of the core-shell oxide is aluminum oxide, the surface of the zirconium oxide of the core layer is coated with a zinc stearate hydrophobic layer, and the surface of the aluminum oxide of the shell layer is grafted with methacryloxypropyltrimethoxysilane. According to the invention, through compounding of the modified carbon nanotubes, the core-shell structure zirconium oxide-aluminum oxide and the graphene nanosheets, a three-dimensional heat-conducting network is constructed in a core layer, filler agglomeration is inhibited, and interface thermal resistance is reduced.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of high molecular polyethylene, in particular to a PE-based nanometer high-thermal-conductivity composite material and a pipe preparation process. BACKGROUND

[0002] In the fields of building heating, industrial heat conduction and electronic heat dissipation, polyethylene-based composite materials are widely used due to their excellent corrosion resistance, processability and cost advantage, but their inherent low thermal conductivity (about 0.4 W / m·K for pure PE) seriously restricts their application in high-thermal-conductivity scenarios. Traditional methods for improving the thermal conductivity of PE mostly involve adding high-thermal-conductivity fillers (such as carbon nanotubes, graphene, metal oxides, etc.) to build a thermal conduction network, but the nanofillers tend to agglomerate in the non-polar PE matrix, resulting in a significant increase in interfacial thermal resistance and a limited improvement in thermal conductivity (the thermal conductivity of traditional filler systems is usually <2.0 W / m·K). In addition, the introduction of rigid fillers can damage the flexibility of the PE matrix, leading to a decrease in tensile strength and elongation at break, especially in pipe applications, where stress concentration can cause cracking.

[0003] Most high-thermal-conductivity PE pipes in the prior art use a single filler system, which cannot balance the improvement in thermal conductivity and the maintenance of mechanical properties. For example, when the thermal conductivity of pure carbon nanotube-filled PE reaches 3.0 W / m·K, the elongation at break often decreases to less than 200%, which cannot meet the impact resistance requirements of pipes. Moreover, the π-π stacking effect of carbon nanotubes and the energy mismatched interface between the polar surface of metal oxides and the non-polar PE matrix result in severe agglomeration of fillers, interruption of thermal conduction pathways, and deterioration of mechanical properties due to interfacial stress concentration. In addition, the existing crosslinking process mostly uses a fixed ratio, without dynamic adjustment according to the filler content, resulting in uneven crosslinking density and skin layer that is prone to brittle overcrosslinking or insufficient crosslinking, leading to a decrease in wear resistance.

[0004] Furthermore, in terms of preparation process, traditional extrusion molding cannot achieve uniform dispersion of nanofillers, and lacks means to control the orientation of fillers, resulting in significant anisotropy of thermal conductivity and inability to meet the demand for efficient axial heat conduction of pipes. Therefore, there is an urgent need in the market to develop PE-based composite material pipes with high thermal conductivity, high toughness and good interfacial compatibility. SUMMARY

[0005] The present application aims to overcome the shortcomings of the prior art and provide a PE-based nanometer high-thermal-conductivity composite material and a pipe preparation process for the same, to solve the problems raised in the background.

[0006] The PE-based nanometer high-thermal-conductivity composite material comprises component A and component B, component A is the core layer, and component B is the skin layer,

[0007] Component A is composed of the following raw materials by mass fraction: high density polyethylene 58-62 parts, linear low density polyethylene 7-9 parts, ethylene-octene copolymer 4-6 parts, modified carbon nanotube 4-6 parts, core-shell oxide 14-16 parts, graphene nanosheet 2.5-3.5 parts, interfacial compatibilizer 2-4 parts, antioxidant 0.4-0.6 parts, crosslinking agent 0.4-0.6 parts;

[0008] Component B is composed of the following raw materials by mass fraction: high density polyethylene 66-70 parts, linear low density polyethylene 5-7 parts, ethylene-octene copolymer 2-4 parts, modified carbon nanotube 2-4 parts, core-shell oxide 11-13 parts, graphene nanosheet 1.5-2.5 parts, interfacial compatibilizer 4-6 parts, antioxidant 0.6-0.8 parts, crosslinking agent 2.0-2.6 parts;

[0009] The modified carbon nanotube is obtained by grafting vinyltriethoxysilane after depositing a SiO2 layer on the surface of the carbon nanotube;

[0010] The core layer of the core-shell oxide is zirconium oxide, and the shell layer is aluminum oxide, wherein the surface of the core layer zirconium oxide is coated with a zinc stearate hydrophobic layer, and the surface of the shell layer aluminum oxide is grafted with methacryloyloxypropyltrimethoxysilane.

[0011] Further, the crosslinking agent of component A is di-t-butyl peroxide, and the crosslinking agent of component B is a mixture of vinyltrimethoxysilane and dibutyl dilaurate in a mass ratio of 1.7-1.9:0.15-0.25.

[0012] Further, the interfacial compatibilizer of component A and component B is both maleic anhydride grafted polyethylene.

[0013] Further, the antioxidant of component A is a mixture of antioxidant 1076 and antioxidant 168 in a mass ratio of 0.25-0.35:0.15-0.25, and the antioxidant of component B is a mixture of antioxidant 1076 and antioxidant 168 in a mass ratio of 0.35-0.45:0.25-0.35.

[0014] Further, the preparation of the core layer zirconium oxide includes:

[0015] First, Zr(NO3)4·5H2O is dissolved in an ethanol-water solution, and ammonia water is added dropwise under stirring until the pH is 8.8-9.2, and the sol is continuously stirred to form a sol, then the sol is loaded into a dialysis bag with a molecular weight cut-off of 1000-1200, and dialyzed in deionized water until the conductivity of the dialysate is <5 μS / cm, and the nitrate ions are removed;

[0016] The sol after dialysis is added to zinc stearate, the amount of zinc stearate is 10%-15% of the mass of the target zirconia, and the reaction is refluxed in an oil bath to make the zinc stearate coat the surface of the zirconia to form a hydrophobic layer. After the reaction is completed, the product is washed by centrifugation three times and calcined in a muffle furnace to obtain the core-shell zirconia particle.

[0017] Further, the preparation of the core-shell alumina-coated zirconia particle comprises:

[0018] The zirconia core is dispersed in isopropanol, and methacryloxypropyl trimethoxysilane is added, the amount of methacryloxypropyl trimethoxysilane is 6%-9% of the mass of the target alumina. After ultrasonic dispersion for 30-50 minutes, the isopropanol solution of aluminum isopropanol salt is slowly added dropwise, and the hydrolysis reaction is carried out in a 70-80℃ water bath for 5-6 hours, during which continuous stirring is carried out. After the reaction is completed, the product is collected by reduced pressure filtration, washed with isopropanol, and dried in a vacuum drying oven to obtain the core-shell structure zirconia-alumina metal oxide particle.

[0019] Further, the preparation of the modified carbon nanotube comprises:

[0020] The carbon nanotube is placed in a tube furnace, and tetraethoxysilane vapor is introduced, and argon gas is introduced as a protective gas at the same time. The SiO2 coating layer is formed on the surface of the carbon nanotube by deposition for 8-12 minutes. The SiO2-coated carbon nanotube is added to an ethanol-water solution, and then 20%-25% of the mass of the carbon nanotube is added to the solution. Vinyltriethoxysilane is added, the pH is adjusted to 4.3-4.7 with hydrochloric acid, and then ultrasonic treatment is carried out, the ultrasonic frequency is 35-45 kHz, and the ultrasonic treatment time is 160-190 minutes. The vinyltriethoxysilane is grafted to the surface of the SiO2 coating layer. After the grafting is completed, the modified carbon nanotube is obtained by drying treatment by spray drying.

[0021] The pipe material preparation process of the PE-based nanometer high-thermal-conductivity composite material comprises the following steps:

[0022] The calculated amount of high-density polyethylene, linear low-density polyethylene, and ethylene-octene copolymer of component A is put into a high-speed mixer, and pre-mixed at 75-85℃ and a rotation speed of 2300-2700r / min for 4-6 minutes. Then, the modified carbon nanotube, core-shell oxide, graphene nanosheet, interfacial compatibilizer, antioxidant, and crosslinking agent are added and pre-mixed for 8-12 minutes to form a uniform dispersion. The pre-mixed material is melt-extruded through a double-screw extruder with a length-diameter ratio of 38-42:1. An alternating electric field is applied in the 3rd-5th zone of the extruder, and an ultrasonic wave is applied synchronously. The homogenization section of the double-screw extruder is configured with a high-shear module, and the screw rotation speed is 270-310r / min. The residence time of component A in the temperature range of 190-210℃ is controlled to be 30-60 seconds. The core layer pipe blank is extruded from the pipe opening of the double-screw extruder.

[0023] The high-density polyethylene, linear low-density polyethylene and ethylene-octene copolymer in component B are premixed at 75-85 DEG C and 2300-2700 r / min for 4-6 min, then the modified carbon nanotube, core-shell oxide, graphene nanosheet and interfacial compatibilizer are premixed for 8-12 min, and finally the crosslinking agent is added, and ultrasonic dispersion is started for 10-15 min, the ultrasonic frequency is 35-45 kHz, and the power is 300-400 W, to obtain the premix of component B;

[0024] The core layer pipe blank enters the co-extrusion die, the premix of component B passes through the independent flow channel to coat the core layer, and the composite pipe material formed by co-extrusion enters the vacuum sizing sleeve, and the pipe material is prepared after water bath and spray cooling and shaping.

[0025] Further, the amount of the crosslinking agent vinyltrimethoxysilane in component B accounts for 2.0% of the total mass of the raw materials of component B

[0026] ~2.6%, the amount of dibutyldilaurate accounts for 0.15%~0.25% of the total mass of the raw materials of component B, the mass ratio of vinyltrimethoxysilane to dibutyldilaurate is linearly adjusted from 1.9:0.15 to 1.7:0.25 when the content of the modified carbon nanotube in component B increases by 1 part, and the mass ratio of vinyltrimethoxysilane to dibutyldilaurate is inversely adjusted from 1.9:0.15 to 1.7:0.25 when the content of the core-shell oxide increases by 1 part.

[0027] Further, in the extrusion of component A, the temperature of each zone of the screw is set as follows: zone 1, 155-165 DEG C; zone 2, 170-180 DEG C; zone 3, 180-190 DEG C; zone 4, 190-200 DEG C; zone 5, 195-205 DEG C; zone 6, 200-210 DEG C; zone 7, 200-210 DEG C; zone 8, 195-205 DEG C; die, 200-210 DEG C; the strength of the alternating electric field is 7.5-8.5 kV / cm, the frequency is 75-85 Hz, and the frequency of the ultrasonic wave is 40-50 kHz, and the power is 180-220 W.

[0028] The beneficial effects of the present application are as follows:

[0029] 1. By compounding the modified carbon nanotube, core-shell structured zirconium oxide-aluminum oxide and graphene nanosheet, a three-dimensional heat conduction network is constructed in the core layer, filler aggregation is inhibited, and the interfacial thermal resistance is reduced. The longitudinal thermal conductivity of the pipe material reaches 4.2-4.8 W / m·K, and the transverse thermal conductivity reaches 1.7-1.9 W / m·K, meeting the demand for efficient axial heat conduction.

[0030] 2. The core layer adopts high-density PE and linear low-density PE, ethylene-octene copolymer to form a “rigid-flexible” matrix, and is properly cross-linked (di-tert-butyl peroxide is used as an initiator), so that the elongation at break reaches 330%-370% and the tensile strength reaches 26-30 MPa; the skin layer uses high-crystallinity PE and a dynamic cross-linking system (vinyl trimethoxysilane / dibutyl dilaurate is used in a dynamic ratio) to improve the surface hardness, and at the same time, forms a modulus gradient (150-200 MPa for the core layer and 200-250 MPa for the skin layer) with the core layer, so as to reduce the interface stress concentration, and the interface peeling strength reaches 23-27 N / cm.

[0031] 3. The modified carbon nanotube, inorganic SiO2 and organic vinyl amphiphilic interface layer and the double interface modification of the core-shell oxide (a zinc stearate hydrophobic layer / methacryloxy silane grafting layer) make the dispersivity of the filler in the PE matrix improved and the interface thermal resistance reduced. The antioxidant compound system enhances the outdoor aging resistance.

[0032] 4. In the double screw extrusion process, an alternating electric field is applied to induce the axial orientation of the carbon nanotube, and at the same time, an ultrasonic wave is used to disperse and destroy the filler aggregation, and gradient temperature cross-linking and online infrared monitoring are combined to realize the matching of the cross-linking density and the melt viscosity.

[0033] 5. The proportion of the cross-linking agent in component B is dynamically adjusted according to the content of the filler, so as to avoid the skin layer from being excessively cross-linked and brittle, and to ensure the uniformity of the cross-linking density. The dual-component structure of the core layer toughening and the skin layer modulus gradient solves the contradiction between the traditional single component thermal conductivity and mechanical properties, and meets the application requirements of the pipe axial thermal conductivity. BRIEF DESCRIPTION OF DRAWINGS

[0034] Figure 1 It is a flow chart of the pipe preparation process of the PE-based nanometer high-thermal-conductivity composite material. DETAILED DESCRIPTION

[0035] The PE-based nanometer high-thermal-conductivity composite material provided by the application comprises component A and component B, component A is a core layer, and component B is a skin layer. Component A is composed of the following raw materials in parts by mass: high-density polyethylene 58-62 parts, linear low-density polyethylene 7-9 parts, ethylene-octene copolymer 4-6 parts, modified carbon nanotube 4-6 parts, core-shell oxide 14-16 parts, graphene nanosheet 2.5-3.5 parts, maleic anhydride grafted polyethylene (Eastman G-3003) 2-4 parts, antioxidant 1076 0.25-0.35 parts, antioxidant 168 0.15-0.25 parts, and di-tert-butyl peroxide 0.4-0.6 parts.

[0036] Component B is composed of the following raw materials in parts by mass: high density polyethylene 66-70 parts, linear low density polyethylene 5-7 parts, ethylene-octene copolymer 2-4 parts, modified carbon nanotube 2-4 parts, core-shell oxide 11-13 parts, graphene nanosheet 1.5-2.5 parts, maleic anhydride grafted polyethylene (Eastman G-3003) 4-6 parts, antioxidant 1076 0.35-0.45 parts, antioxidant 168 0.25-0.35 parts, vinyl trimethoxysilane 1.7-1.9 parts, dibutyl dilaurate 0.15-0.25 parts.

[0037] The ratio of component A is centered on toughening, wherein the high density polyethylene (58-62 parts) of component A provides a rigid skeleton, the linear low density polyethylene (7-9 parts) and the ethylene-octene copolymer (4-6 parts) improve the ductility of the matrix through flexible segments, and the three form a "rigid and flexible" resin matrix, so that the core layer has impact toughness. The modified carbon nanotube (4-6 parts) and the graphene nanosheet (2.5-3.5 parts) are compounded to construct a three-dimensional heat conduction network, the axial heat conduction advantage of the carbon nanotube and the in-plane heat conduction characteristics of the graphene are synergistic, and the heat conduction efficiency is improved; the core-shell oxide (14-16 parts) reduces filler agglomeration through the high thermal conductivity of the zirconium oxide core and the interface modification of the aluminum oxide shell, and at the same time, the zinc stearate hydrophobic layer and the silane grafting layer improve the compatibility with the polyethylene matrix. The maleic anhydride grafted polyethylene (2-4 parts) as an interfacial compatibilizer, the polar anhydride groups react with the filler surface hydroxyl groups, and the non-polar polyethylene segments are entangled with the matrix, reducing the interfacial stress concentration. The di-t-butyl peroxide (0.4-0.6 parts) initiates mild crosslinking to form an elastic network structure, further enhancing the anti-creep performance of the core layer, while controlling the crosslinking degree to avoid material embrittlement.

[0038] The proportioning of component B is mainly centered on "reducing the overall elastic modulus difference, wear resistance, and environmental resistance". Among them, the content of high-density polyethylene (66-70 parts) of component B is increased compared with component A, and low proportion of linear low-density polyethylene (5-7 parts) and ethylene-octene copolymer (2-4 parts) is matched to improve the crystallinity and rigidity of the skin layer, form a gradient with the core layer, and reduce the interface stress concentration. The amount of modified carbon nanotubes (2-4 parts) and core-shell oxides (11-13 parts) is reduced to reduce the influence of fillers on the flexibility of the skin layer, while retaining moderate thermal conductivity; graphene nanosheets (1.5-2.5 parts) are dispersed in the skin layer to assist in forming a thermal conduction path and improving surface hardness. High proportion of maleic anhydride grafted polyethylene (4-6 parts) strengthens the interface adhesion between the skin layer and the core layer, and the anhydride groups react with the surface active sites of the core layer fillers to form a chemical anchoring effect. Ethyl trimethoxysilane (1.7-1.9 parts) and dibutyl dilauryl acid (0.15-0.25 parts) form a dynamic crosslinking system, silane hydrolysis condensation forms a network structure, improves the wear resistance and environmental stress cracking resistance of the skin layer (≥1000h), and the catalyst dosage is dynamically adjusted with the filler content to avoid excessive brittle increase; high proportion of antioxidants (0.6-0.8 parts) enhances the outdoor aging resistance of the skin layer.

[0039] The carbon nanotubes are placed in a tube furnace, and tetraethoxysilane vapor is introduced, and argon gas is introduced as a protective gas, and a uniform SiO2 coating layer is formed on the surface of the carbon nanotubes after 8-12 min. The SiO2 coated carbon nanotubes are added to an ethanol-water solution, then 20%-25% of the mass of the carbon nanotubes is added to the solution, and the pH is adjusted to 4.3-4.7 with hydrochloric acid, and then ultrasonic treatment is performed, the ultrasonic frequency is 35-45 kHz, and the ultrasonic treatment time is 160-190 min. The vinyl triethoxysilane is grafted to the surface of the SiO2 coating layer, and after the grafting is completed, the modified carbon nanotubes are obtained by spray drying.

[0040] The preparation of the modified carbon nanotube includes the following steps: placing the carbon nanotube in a tube furnace, introducing a tetraethoxysilane vapor with a flow rate of 5 sccm at 700°C, introducing argon with a flow rate of 50 sccm as a protective gas, depositing for 8-12 min, and forming a uniform SiO2 coating layer on the surface of the carbon nanotube with a thickness of 4-8 nm. The modified carbon nanotube is added to an ethanol-water (volume ratio 3:1) solution, 20%-25% of the mass of the carbon nanotube is added as vinyltriethoxysilane, hydrochloric acid is used to adjust the pH to 4.3-4.7, ultrasonic treatment is performed at 60°C, the ultrasonic frequency is 35-45 kHz, the power is 400-450 W, and the treatment time is 3 h, so that the vinyltriethoxysilane is grafted to the surface of the SiO2 coating layer. After the grafting is completed, drying treatment is performed by a spray drying method, the inlet temperature is set to 190°C during drying, and the modified carbon nanotube with a surface grafting rate of 2.5%-3.0% is obtained.

[0041] The 4-8 nm thick SiO2 coating layer is deposited on the surface of the carbon nanotube by tetraethoxysilane, the inorganic rigid barrier of SiO2 is used to destroy the π-π stacking force between the carbon nanotubes, and the agglomeration phenomenon is fundamentally inhibited. When the vinyltriethoxysilane is subsequently grafted, the ethoxyl groups of the silane molecules are hydrolyzed to form silanol, which is condensed with the SiO2 surface hydroxyl groups to form Si-O-Si covalent bonds, so that the vinyl functional groups are directionally anchored on the surface of the coating layer, and a dual amphiphilic interface layer of the inorganic SiO2 layer and the organic vinyl segment is constructed. The ethanol-water solvent system can control the hydrolysis rate of the silane, the acidic environment can optimize the hydrolysis balance of the silane, and the ultrasonic treatment (40 kHz, 400 W) at 60°C promotes the migration of the silane molecules to the surface of the coating layer and uniform grafting through the cavitation effect, and finally a modified structure with a grafting rate of 2.5%-3.0% is formed.

[0042] The modified carbon nanotube is converted from the original hydrophobic agglomerated state to a dual amphiphilic dispersed state through the gradient affinity of the inorganic-organic interface layer, the dispersion degree in the PE matrix is improved, the interruption of the heat conduction path caused by the accumulation of fillers is effectively avoided, the interfacial shear strength between the carbon nanotube and the matrix is improved through the chemical compatibility of the vinyl functional groups with the PE matrix, and the stress concentration phenomenon is reduced. In addition, the 4-8 nm ultra-thin SiO2 layer retains the advantages of the axial thermal conductivity of the carbon nanotube, reduces the interfacial thermal resistance through interface phonon scattering regulation, and cooperates with the graphene nanosheet to construct a continuous heat conduction network.

[0043] Overall, the modified carbon nanotubes provide a high-efficiency heat-conducting skeleton for the core layer, and form a three-dimensional heat-conducting network with the core-shell oxide and graphene to improve the thermal conductivity of the core layer and meet the high-thermal-conductivity requirement; in the skin layer, the amount of modified carbon nanotubes is reduced and the interface modification is optimized to avoid the rigidity mutation of the skin layer caused by excessive addition of fillers, while retaining the thermal conductivity of 1.2-1.5 W / m·K, and cooperating with the high-crystallinity PE matrix of the skin layer to realize the gradient matching of the elastic modulus with the core layer; in addition, the synergistic effect of the modified carbon nanotubes and the maleic anhydride grafted polyethylene can enhance the chemical anchoring of the interface between the core layer and the skin layer, improve the interlayer peeling strength, and ensure the structural stability of the composite pipe under cold and hot cycle conditions.

[0044] The preparation of the core-shell oxide includes the preparation of the core layer zirconium oxide and the coating of the shell layer aluminum oxide. In the preparation of the core layer, Zr(NO3)4·5H2O is dissolved in an ethanol-water (volume ratio 2:1) solution, 25% ammonia water is added dropwise under stirring until the pH is 8.8-9.2, the sol is continuously stirred at 60°C for 2 hours to form a sol, then the sol is loaded into a dialysis bag (molecular weight cut-off 1000-1200) and dialyzed in deionized water for 72 hours until the conductivity of the dialysate is <5 μS / cm to completely remove nitrate ions. The sol after dialysis is added with zinc stearate (the amount is 10%-15% of the mass of the target zirconium oxide), and refluxed at 80°C for 4 hours to make the zinc stearate physically adsorbed and chemically bonded on the surface of the zirconium oxide to form a 5 nm thick hydrophobic layer. After the reaction, the product is washed by centrifugation (ethanol / water mixture, volume ratio 1:1) three times, and calcined at 500°C for 3 hours in a muffle furnace to obtain core layer zirconium oxide particles with a particle size of 50-80 nm.

[0045] In the coating of the shell layer, the above-mentioned zirconium oxide core is dispersed in isopropanol (solid content 5%), and methacryloxypropyltrimethoxysilane (the amount is 6%-9% of the mass of the target aluminum oxide) is added, and ultrasonic dispersion is performed for 30-50 minutes, then aluminum isopropyl alcohol salt isopropanol solution (concentration 0.2 mol / L) is slowly added dropwise, and hydrolysis reaction is performed at 70°C-80°C water bath for 5-6 hours, during which continuous stirring is performed. After the reaction is completed, the product is collected by reduced pressure filtration, washed twice with isopropanol to remove unreacted methacryloxypropyltrimethoxysilane, and dried in a 60°C vacuum drying oven for 12 hours to obtain core-shell structure zirconium oxide-aluminum oxide particles. The shell layer aluminum oxide has a thickness of 20-30 nm and a surface grafting rate of 1.5%-2.0%, and the silane bond of the methacryloxypropyltrimethoxysilane forms a covalent connection with the shell layer aluminum oxide, while the organic group of the methacryloxypropyltrimethoxysilane forms a physical entanglement with the polyethylene matrix, effectively improving the interface compatibility of the filler and the matrix. The preparation process solves the problem of the polarity difference between the metal oxide and the polyethylene through the hydrophobic modification of the core layer and the silane grafting of the shell layer.

[0046] In the preparation of the core layer zirconia, zirconium nitrate reacts with ammonia in an ethanol-water system to form amorphous zirconium hydroxide sol, and after dialysis to completely remove nitrate ions, zinc stearate is formed on the surface of zirconia by esterification of carboxylate with zirconia surface hydroxyl and physical adsorption of hydrophobic alkyl chains, forming a hydrophobic layer on the surface of zirconia. During calcination, zinc stearate decomposes to leave only the chemically bonded hydrophobic groups, converting hydrophilic zirconia into a hydrophobic core, solving the compatibility problem of high-thermal-conductivity zirconia with non-polar PE matrix. During shell coating, aluminum isopropyl alcohol salt hydrolyzes to form aluminum hydroxide precursor, which grows on the surface of the zirconia core to form a 20-30 nm thick aluminum oxide shell. After hydrolysis of the methoxy group of methacryloyloxypropyl trimethoxysilane, it condenses with the surface hydroxyl group of aluminum oxide to form Si-O-Al covalent bonds, and its methacryloyloxy group copolymerizes with the free radicals of the PE matrix, forming an interface transition layer of inorganic core, silane bridge, and organic chain, which improves the dispersion of the core-shell oxide in the PE matrix and reduces the size of the agglomerates.

[0047] The core-shell oxide process has the following advantages: first, the synergistic effect of core layer hydrophobic modification and shell layer silane grafting reduces the surface energy of high-thermal-conductivity zirconia through the dual mechanisms of polarity neutralization and interface bridging, forming an energy match with the PE matrix and reducing the interfacial tension. At the same time, the interfacial thermal resistance between the filler and the matrix is reduced. Second, the gradient structure of the 50-80 nm core layer particle size and the 20-30 nm shell thickness not only retains the intrinsic high thermal conductivity of zirconia, but also inhibits the growth of zirconia grains (crystallinity controlled at 75%-85%) through the nano-limiting effect of the aluminum oxide shell, avoiding interface defects caused by excessive grain growth. Third, the shell surface grafting rate of 1.5%-2.0% allows the organic chain segments (about 15 nm in length) of silane molecules to form a 10-15 nm winding layer with PE molecular chains, improving the interfacial shear strength and reducing stress concentration between the filler and the matrix.

[0048] Overall, in the core layer, 14-16 parts of core-shell oxides form a three-dimensional heat conduction network with 4-6 parts of modified carbon nanotubes and 2.5-3.5 parts of graphene nanosheets. The high thermal conductivity of zirconium oxide core and the in-plane thermal conductivity of graphene and the axial thermal conductivity of carbon nanotubes are synergistic, which improves the thermal conductivity of the core layer. At the same time, the hydrophobic modification reduces the agglomeration of fillers, and the flexible segment of ethylene-octene copolymer is combined to improve the elongation at break and impact strength of the core layer. In the skin layer, the amount of core-shell oxides is reduced to 11-13 parts to avoid the rigidity mutation of the skin layer caused by excessive addition of fillers. The surface silane grafting layer and high proportion of maleic anhydride grafted polyethylene (4%-6%) form a "silane bond-anhydride group" double chemical anchoring, which improves the interfacial peeling strength of the core-skin, and the hardness of the aluminum oxide shell improves the surface wear resistance of the skin layer. In combination with the dynamic crosslinking system, the environmental stress cracking resistance time of the skin layer is prolonged. In addition, the double interface modification of core-shell oxides and the amphiphilic interface layer of modified carbon nanotubes form a synergistic effect, which reduces the overall interfacial thermal resistance of the composite material, and the longitudinal thermal conductivity of the pipe is 8 times that of pure PE, while the transverse thermal conductivity is maintained, meeting the high-efficiency heat conduction demand.

[0049] As Figure 1As shown, the high-density polyethylene, linear low-density polyethylene, and ethylene-octene copolymer of component A are put into a high-speed mixer, and pre-mixed at 75-85°C and 2300-2700 r / min for 4-6 minutes to make the base resin preliminarily mixed uniformly. Then the modified carbon nanotube, core-shell oxide, graphene nanosheet, interfacial compatibilizer, antioxidant, and crosslinking agent (dibutyl peroxide, with a dosage of 0.4%-0.6% of the mass of component A) are added and continue to be pre-mixed for 8-12 minutes to form a uniform dispersion, ensuring that the nanofiller and crosslinking agent are fully dispersed in the resin matrix. The pre-mixed material is melt-extruded through a double-screw extruder with a length-diameter ratio of 38-42:1, and the temperature of each zone of the screw is set as follows: zone 1, 155-165°C; zone 2, 170-180°C; zone 3, 180-190°C; zone 4, 190-200°C; zone 5, 195-205°C; zone 6, 200-210°C; zone 7, 200-210°C; zone 8, 195-205°C; and the die head, 200-210°C. This temperature distribution ensures that the material is fully melted and the crosslinking agent is not decomposed prematurely. An alternating electric field (intensity 7.5-8.5 kV / cm, frequency 75-85 Hz) is applied in the 3rd-5th zones of the extruder to induce the carbon nanotube to be oriented along the axial direction of the pipe, forming a heat conduction path; at the same time, an ultrasonic wave (40-50 kHz, power 180-220 W) is applied to break the filler agglomerates and improve the dispersion uniformity. The homogenization section is configured with a high-shear module (kneading block angle 40°-50°, thickness 1.8-2.2 mm) and a screw rotating at 270-310 r / min, and a melt gear pump (pressure 15-20 MPa) is used to further refine the dispersion of the nanofiller, while the residence time of component A in the temperature range of 190-210°C is controlled to be 30-60 seconds to ensure that the dibutyl peroxide fully initiates the crosslinking reaction, and the core layer pipe blank with a moderate crosslinking structure is extruded.

[0050] After the raw materials of component B (high-density polyethylene, linear low-density polyethylene, ethylene-octene copolymer, modified carbon nanotube, core-shell oxide, graphene nanosheet, interfacial compatibilizer, antioxidant, and crosslinking agent) are pre-mixed in the same way, the core layer pipe blank enters the co-extrusion die, and the skin layer material coats the core layer through an independent flow channel. The temperature of the die is controlled in zones: the core layer flow channel, 190-200°C; and the skin layer flow channel, 180-190°C, to ensure that the melt viscosity of the core layer (100-150 Pa·s) matches that of the skin layer (150-200 Pa·s), realizing seamless bonding at the core-skin interface. During the co-extrusion process, the vinyl trimethoxysilane crosslinking agent (mixed with dibutyl dilaurate at a mass ratio of 1.7-1.9:0.15-0.25) in the skin layer flow channel triggers a hydrolysis condensation reaction at 180-190°C at a heating rate of 0.5-1.0°C / s, combined with the melt pressure of 20-30 MPa in the die, to form a skin layer structure with a crosslinking density of 8%-12%, improving the surface hardness and environmental stress cracking resistance of the pipe.

[0051] The composite pipe enters a vacuum sizing sleeve (water temperature 15-20 °C, vacuum degree -0.06 to -0.08 MPa), and the pipe wall is adhered to the sizing mold by negative pressure adsorption, so as to control the outer diameter tolerance ±0.1 mm and simultaneously inhibit the core-skin delamination. Two-stage cooling is adopted: primary water bath (60-70 °C, water flow speed 0.5-1.0 m / s) slow cooling for 30-60 seconds to reduce internal stress; secondary spray cooling (20-25 °C, spray pressure 0.2-0.3 MPa) rapid sizing, and the total cooling time is controlled within 90-120 seconds. The cooling water adopts reverse flow design, and the temperature difference between the inlet water temperature and the primary water bath temperature is ≤5 °C, so as to improve the heat exchange efficiency. After the pipe is cooled, the pipe is stably pulled by a pulling machine at 1.2-1.5 times the extrusion line speed, so as to ensure that the core layer and the skin layer maintain the interfacial bonding force under dynamic stress, and finally the pipe is cut by a cutting machine according to the set length, and the pipe end is polished after cutting, so as to ensure that the pipe end is perpendicular to the axis within an angle of ≤0.5°.

[0052] During the crosslinking of component B, a gradient temperature zone (170-180 °C preheating section → 180-190 °C crosslinking trigger section) is arranged at the front end of the skin layer flow channel, the residence time of the melt in the crosslinking trigger section is controlled within 40-60 seconds, the temperature rising rate is 0.5-1.0 °C / s, so as to make the vinyl trimethoxysilane gradually hydrolyze and condense under the catalysis of dibutyl dilaurate. At the same time, the pressure in the die is monitored in real time by a melt pressure sensor (20-30 MPa), and when the pressure fluctuation exceeds ±5%, the screw speed (250-300 r / min) is automatically adjusted, so as to ensure that the crosslinking reaction is carried out in a stable shear field, and a uniform network crosslinking structure (target crosslinking density 10%-12%) is formed.

[0053] The amount of dibutyl dilaurate as a hydrolysis catalyst needs to be dynamically matched with the amount of vinyl trimethoxysilane: when the content of the modified carbon nanotube in the skin layer material is taken as the upper limit (4 parts), the mass ratio of the crosslinking agent is adjusted to 1.7:0.25 (silane:catalyst), so as to enhance the catalytic efficiency of the polar interface; if the content of the core-shell oxide is taken as the lower limit (11 parts), the mass ratio is adjusted to 1.9:0.15, so as to avoid the increase of the skin layer brittleness caused by the excessive amount of the catalyst. At the same time, a coating containing a silane coupling agent is coated on the inner wall of the co-extrusion die, so as to reduce the melt retention and promote the interfacial crosslinking reaction.

[0054] Specifically, the content of the modified carbon nanotubes in the skin material is 2-4 parts, and the mass ratio of vinyltrimethoxysilane to dibutyldilaurate is dynamically matched according to the following rules: for every 1 part increase in the content of the modified carbon nanotubes, the mass ratio of vinyltrimethoxysilane to dibutyldilaurate is linearly adjusted from 1.9:0.15 to 1.7:0.25. For example, when the content of the modified carbon nanotubes is 2 parts, the mass ratio of vinyltrimethoxysilane to dibutyldilaurate is 1.9:0.15; when the content of the modified carbon nanotubes is 3 parts, the mass ratio of vinyltrimethoxysilane to dibutyldilaurate is adjusted to 1.8:0.20; and when the content of the modified carbon nanotubes reaches 4 parts, the mass ratio of vinyltrimethoxysilane to dibutyldilaurate is 1.7:0.25.

[0055] The content of the core-shell oxide in the skin material is 11-13 parts, and the mass ratio of vinyltrimethoxysilane to dibutyldilaurate is dynamically matched: for every 1 part increase in the content of the core-shell oxide, the mass ratio of silane to catalyst is inversely adjusted from 1.9:0.15 to 1.7:0.25. For example, when the content of the core-shell oxide is 11 parts, the mass ratio is 1.9:0.15; when the content is 12 parts, the mass ratio is adjusted to 1.8:0.20; and when the content is 13 parts, the mass ratio is 1.7:0.25.

[0056] The above mass ratio adjustment needs to satisfy that the amount of vinyltrimethoxysilane in component B is 1.7-1.9 parts, the amount of dibutyldilaurate is 0.15-0.25 parts, and the mass ratio of silane to catalyst is always maintained in the range of 1.7-1.9:0.15-0.25, in order to balance the catalytic efficiency of the polar interface and the demand for skin brittleness resistance.

[0057] In the gradient cooling stage, humid hot air with a humidity of 50%-60% is introduced into the primary water bath (60-70°C), and the residual dibutyldilaurate is used to catalyze the subsequent crosslinking reaction of vinyltrimethoxysilane and water molecules, so as to increase the crosslinking density of the skin by 10%-15%. After cooling, the pipe material is placed in an environment with a temperature of 40-50°C and a humidity of 60%-70% for 24-48 hours to complete the "post-crosslinking" process, and to ensure that the skin hardness (Shore D 65-70) and the environmental stress cracking resistance time (≥1000h) meet the standards.

[0058] An online infrared spectrometer is arranged at the outlet of the co-extrusion die head to detect the conversion rate of silane groups in the skin melt in real time (target 85%-90%). If the conversion rate is less than 80%, the die head temperature is automatically increased by 2-3°C or the residence time is extended by 10 seconds; if it is higher than 95%, the screw speed is reduced by 5-10 r / min to avoid abnormal increase of the elastic modulus caused by excessive crosslinking (the skin elastic modulus is controlled to be 200-250 MPa, which is gradient-matched with the core layer (150-200 MPa)).

[0059] Example 1

[0060] The PE-based nanometer high-thermal-conductivity composite pipe material is prepared from the following raw materials by mass fraction:

[0061] Component A: 60 parts of high-density polyethylene, 8 parts of linear low-density polyethylene, 5 parts of ethylene-octene copolymer, 5 parts of modified carbon nanotube, 15 parts of core-shell oxide, 3 parts of graphene nanosheet, 3 parts of maleic anhydride grafted polyethylene, 0.3 part of antioxidant 1076, 0.2 part of antioxidant 168, and 0.5 part of di-t-butyl peroxide;

[0062] Component B: 68 parts of high-density polyethylene, 6 parts of linear low-density polyethylene, 3 parts of ethylene-octene copolymer, 3 parts of modified carbon nanotube, 12 parts of core-shell oxide, 2 parts of graphene nanosheet, 5 parts of maleic anhydride grafted polyethylene, 0.4 part of antioxidant 1076, 0.3 part of antioxidant 168, 1.8 parts of vinyl trimethoxysilane, and 0.2 part of dibutyl dilaurate;

[0063] The preparation of the modified carbon nanotube includes the following steps:

[0064] The carbon nanotube is subjected to 5 sccm of tetraethoxysilane vapor (50 sccm of argon protection) deposition for 10 minutes in a 700℃ tube furnace to form a 6nm SiO2 coating layer. An ethanol-water (volume ratio 3:1) solution is added, 22.5 parts of vinyl triethoxysilane is added, the pH is adjusted to 4.5, and ultrasonic treatment is performed at 60℃ for 3 hours at a frequency of 40 kHz and a power of 425W. Spray drying (inlet temperature 190℃) is performed to obtain the modified carbon nanotube.

[0065] The preparation of the core-shell oxide includes the following steps:

[0066] Zr(NO3)4·5H2O is dissolved in 300mL of ethanol-water (volume ratio 2:1) solution, and 25% ammonia water is added dropwise under stirring at 60℃ until the pH reaches 9.0. The stirring is continued for 2 hours to form a sol. The sol is loaded into a dialysis bag with a molecular weight cutoff of 1000, and dialyzed in deionized water for 72 hours until the conductivity of the dialysate is <5μS / cm. After dialysis, 18g of zinc stearate (12% of the mass of the target zirconium oxide) is added to the sol, and refluxed at 80℃ for 4 hours to form a 5nm hydrophobic layer. After the reaction, the product is washed three times by centrifugation with ethanol-water (1:1) mixture, and calcined at 500℃ in a muffle furnace for 3 hours to obtain core-shell zirconia particles with a particle size of 50-80nm.

[0067] 50 g of zirconium oxide core was dispersed in 1000 mL of isopropyl alcohol (solid content 5%), 4.5 g of methacryloxypropyl trimethoxysilane (7.5% of the target aluminum oxide mass) was added, and ultrasonic dispersion was performed for 40 minutes. 500 mL of an aluminum isopropyl alcohol salt isopropyl alcohol solution with a concentration of 0.2 mol / L was slowly added, and the hydrolysis reaction was performed in a 75°C water bath for 5.5 hours with continuous stirring. After the reaction was completed, filtration was performed under reduced pressure, and washing was performed twice with isopropyl alcohol, and drying was performed in a 60°C vacuum drying oven for 12 hours, thereby obtaining core-shell structure particles with an aluminum oxide shell thickness of 20-30 nm and a surface grafting rate of 1.8%.

[0068] The pipe material preparation includes the following steps:

[0069] The high-density polyethylene, linear low-density polyethylene, and ethylene-octene copolymer of component A were put into a high-speed mixer, pre-mixed at 80°C and 2500 r / min for 5 minutes, and then the modified carbon nanotubes, core-shell oxide, graphene nanosheet, interfacial compatibilizer, antioxidant, and crosslinking agent were added and pre-mixed for another 10 minutes. The pre-mixed material was melt-extruded through a double-screw extruder with a length-diameter ratio of 40:1, and the screw zone temperatures were as follows: zone 1, 160°C; zone 2, 175°C; zone 3, 185°C; zone 4, 195°C; zone 5, 200°C; zone 6, 205°C; zone 7, 205°C; zone 8, 200°C; and the die head, 205°C. An alternating electric field with a strength of 8 kV / cm and a frequency of 80 Hz was applied to the 3rd-5th zones of the extruder, and an ultrasonic wave with a frequency of 45 kHz and a power of 200 W was synchronously applied. The screw rotation speed was 290 r / min, the temperature of component A was controlled to be in the range of 190-210°C for 45 seconds, and the core layer pipe blank was extruded.

[0070] The high-density polyethylene, linear low-density polyethylene, and ethylene-octene copolymer of component B were pre-mixed at 80°C and 2500 r / min for 5 minutes, and then the modified carbon nanotubes, core-shell oxide, graphene nanosheet, and interfacial compatibilizer were added and pre-mixed for another 10 minutes. Finally, the crosslinking agent was added, and ultrasonic dispersion was started simultaneously for 12 minutes (frequency 40 kHz, power 350 W). The core layer pipe blank entered the co-extrusion die head, the core layer channel temperature was 195°C, and the skin layer channel temperature was 185°C. The composite pipe material passed through a vacuum sizing sleeve (water temperature 18°C, vacuum degree -0.07 MPa), a first-stage water bath (65°C, water flow speed 0.8 m / s) for slow cooling for 45 seconds, and a second-stage spraying (22°C, pressure 0.25 MPa) for shaping. The total cooling time was 100 seconds, and the traction machine was operated at 1.3 times the extrusion line speed.

[0071] Comparative Example 1

[0072] Different from example 1, the modified carbon nanotubes in component A and component B are replaced by unmodified carbon nanotubes (without deposition of SiO2 and grafting of vinyl triethoxysilane), and the dosages of the other components are consistent with those in example 1, the preparation process is consistent with that in example 1, and the proportion of the crosslinking agent is 3 parts of modified carbon nanotubes to 1.8 parts of vinyl trimethoxysilane to 0.2 parts of dibutyl dilaurate.

[0073] The pipe performance test method and performance test data of example 1 and comparative example 1 are shown in Table 1 below.

[0074]

[0075] Table 1 Pipe performance test table of example 1 and comparative example 1

[0076] The test results in Table 1 show that the unmodified carbon nanotubes cause discontinuity of the heat conduction path due to agglomeration, poor interfacial compatibility, a decrease of 33.3% in the longitudinal thermal conductivity of the pipe, a decrease of 10.7% in the tensile strength, and a decrease of 40% in the interfacial peeling strength, verifying the key role of the modified carbon nanotubes in improving the dispersibility, thermal conductivity, and interfacial bonding force.

[0077] Comparative example 2

[0078] Different from example 1, the core-shell oxide in component A and component B is replaced by an unmodified physical mixture of zirconia and alumina (zirconia: alumina = 1:1, without forming a core-shell structure and without surface modification), and the unmodified zirconia (particle size 50-80 nm) and alumina (particle size 20-30 nm) are directly mixed in a mass ratio of 1:1 during preparation without core-shell coating and surface treatment.

[0079] The pipe performance test method and performance test data of example 1 and comparative example 2 are shown in Table 2 below.

[0080]

[0081] Table 2 Pipe performance test table of example 1 and comparative example 2

[0082] The test data in Table 2 show that, due to the use of unmodified physical mixture in comparative example 2, the lack of core-shell structure and interfacial modification leads to discontinuity of the heat conduction path and interfacial stress concentration, a decrease of 28.9% in the longitudinal thermal conductivity of the pipe, a decrease of 14.3% in the tensile strength, and a decrease of 28% in the interfacial peeling strength, verifying the advantage of the modified core-shell oxide in improving the thermal and mechanical properties through gradient interfacial design.

[0083] Comparative example 3

[0084] Different from example 1, the core-skin bi-component structure was cancelled, and a single component was used: high density polyethylene 64 parts, linear low density polyethylene 7 parts, ethylene-octene copolymer 4 parts, modified carbon nanotube 4 parts, core-shell oxide 13.5 parts, graphene nanosheet 2.5 parts, maleic anhydride grafted polyethylene 4 parts, antioxidant 1076 0.35 parts, antioxidant 168 0.25 parts, vinyl trimethoxysilane 1.8 parts, dibutyl dilauryl acid 0.2 parts. Single screw extrusion was used in preparation, no alternating electric field was applied, and the rest of the temperature and ultrasonic parameters were the same as those in example 3.

[0085] The pipe performance test method and performance test data of example 1 and comparative example 3 are shown in table 2.

[0086]

[0087]

[0088] Table 3 pipe performance test table of example 1 and comparative example 3

[0089] The test data in table 3 shows that the bi-component structure improves the longitudinal thermal conductivity by 25%, the tensile strength by 7.7%, and the environmental resistance by 33.3% through core layer toughening and skin layer modulus gradient design, verifying the advantage of bi-component design in the synergistic optimization of thermal and mechanical properties. The single component lacks gradient structure, resulting in performance decline due to interface stress concentration.

[0090] Example 2

[0091] Different from example 1, the preparation of the PE-based nanometer high thermal conductivity composite pipe includes the following mass parts of raw materials:

[0092] Component A: high density polyethylene 58 parts, linear low density polyethylene 7 parts, ethylene-octene copolymer 4 parts, modified carbon nanotube 4 parts, core-shell oxide 14 parts, graphene nanosheet 2.5 parts, maleic anhydride grafted polyethylene 2 parts, antioxidant 1076 0.25 parts, antioxidant 168 0.15 parts, di-t-butyl peroxide 0.4 parts;

[0093] Component B: high density polyethylene 66 parts, linear low density polyethylene 5 parts, ethylene-octene copolymer 2 parts, modified carbon nanotube 2 parts, core-shell oxide 13 parts, graphene nanosheet 1.5 parts, maleic anhydride grafted polyethylene 4 parts, antioxidant 1076 0.35 parts, antioxidant 168 0.25 parts, vinyl trimethoxysilane 1.9 parts, dibutyl dilauryl acid 0.15 parts;

[0094] Among them, the modified carbon nanotube, core-shell oxide, and pipe preparation process are the same as those in example 1.

[0095] Example 3

[0096] Different from example 1, the PE-based nanometer high-thermal-conductivity composite pipe material preparation includes the following mass parts of raw materials:

[0097] Component A: high-density polyethylene 62 parts, linear low-density polyethylene 9 parts, ethylene-octene copolymer 6 parts, modified carbon nanotube 6 parts, core-shell oxide 16 parts, graphene nanosheet 3.5 parts, maleic anhydride grafted polyethylene 4 parts, antioxidant 1076 0.35 parts, antioxidant 168 0.25 parts, di-t-butyl peroxide 0.6 parts;

[0098] Component B: high-density polyethylene 70 parts, linear low-density polyethylene 7 parts, ethylene-octene copolymer 4 parts, modified carbon nanotube 4 parts, core-shell oxide 11 parts, graphene nanosheet 2.5 parts, maleic anhydride grafted polyethylene 6 parts, antioxidant 1076 0.45 parts, antioxidant 168 0.35 parts, vinyl trimethoxysilane 1.7 parts, dibutyl dilaurate 0.25 parts;

[0099] Among them, the modified carbon nanotube, the core-shell oxide, and the pipe material preparation process are the same as example 1.

[0100] Example 4

[0101] Different from example 1, the PE-based nanometer high-thermal-conductivity composite pipe material preparation includes the following mass parts of raw materials:

[0102] Component A: high-density polyethylene 60 parts, linear low-density polyethylene 8 parts, ethylene-octene copolymer 5 parts, modified carbon nanotube 5 parts, core-shell oxide 15 parts, graphene nanosheet 3 parts, maleic anhydride grafted polyethylene 3 parts, antioxidant 1076 0.3 parts, antioxidant 168 0.2 parts, di-t-butyl peroxide 0.5 parts;

[0103] Component B: high-density polyethylene 67 parts, linear low-density polyethylene 6 parts, ethylene-octene copolymer 3 parts, modified carbon nanotube 3 parts, core-shell oxide 11 parts, graphene nanosheet 2 parts, maleic anhydride grafted polyethylene 5 parts, antioxidant 1076 0.4 parts, antioxidant 168 0.3 parts, vinyl trimethoxysilane 1.7 parts, dibutyl dilaurate 0.25 parts;

[0104] Among them, the modified carbon nanotube, the core-shell oxide, and the pipe material preparation process are the same as example 1.

[0105] Comparative example 4

[0106] Different from example 1, the PE-based nanometer high-thermal-conductivity composite pipe material preparation includes the following mass parts of raw materials (the raw material usage is lower than the lower limit):

[0107] Component A: high density polyethylene 57 parts, linear low density polyethylene 6 parts, ethylene-octene copolymer 3 parts, modified carbon nanotube 3 parts, core-shell oxide 13 parts, graphene nanosheet 2 parts, maleic anhydride grafted polyethylene 1 part, antioxidant 1076 0.2 parts, antioxidant 168 0.1 part, di-t-butyl peroxide 0.3 parts;

[0108] Component B: high density polyethylene 65 parts, linear low density polyethylene 4 parts, ethylene-octene copolymer 1 part, modified carbon nanotube 1 part, core-shell oxide 10 parts, graphene nanosheet 1 part, maleic anhydride grafted polyethylene 3 parts, antioxidant 1076 0.3 parts, antioxidant 168 0.2 part, vinyl trimethoxysilane 1.6 parts, dibutyl dilauryl acid 0.1 parts;

[0109] Among them, the modified carbon nanotube, the core-shell oxide, and the preparation process of the pipe are the same as those in Example 1.

[0110] Comparative Example 5

[0111] Different from Example 1, the preparation of the PE-based nanometer high-thermal-conductivity composite pipe includes the following raw materials (the amount of raw materials is higher than the upper limit):

[0112] Component A: high density polyethylene 63 parts, linear low density polyethylene 10 parts, ethylene-octene copolymer 7 parts, modified carbon nanotube 7 parts, core-shell oxide 17 parts, graphene nanosheet 4 parts, maleic anhydride grafted polyethylene 5 parts, antioxidant 1076 0.4 parts, antioxidant 168 0.3 part, di-t-butyl peroxide 0.7 parts;

[0113] Component B: high density polyethylene 71 parts, linear low density polyethylene 8 parts, ethylene-octene copolymer 5 parts, modified carbon nanotube 5 parts, core-shell oxide 14 parts, graphene nanosheet 3 parts, maleic anhydride grafted polyethylene 7 parts, antioxidant 1076 0.5 parts, antioxidant 168 0.4 part, vinyl trimethoxysilane 2.0 parts, dibutyl dilauryl acid 0.3 parts;

[0114] Among them, the modified carbon nanotube, the core-shell oxide, and the preparation process of the pipe are the same as those in Example 1.

[0115] Comparative Example 6 (the proportion of crosslinking agent is not adjusted according to the rules)

[0116] Different from Example 1, the preparation of the PE-based nanometer high-thermal-conductivity composite pipe includes the following raw materials (the proportion of crosslinking agent is not adjusted according to the rules):

[0117] Component A: high density polyethylene 60 parts, linear low density polyethylene 8 parts, ethylene-octene copolymer 5 parts, modified carbon nanotube 5 parts, core-shell oxide 15 parts, graphene nanosheet 3 parts, maleic anhydride grafted polyethylene 3 parts, antioxidant 1076 0.3 parts, antioxidant 168 0.2 parts, di-t-butyl peroxide 0.5 parts;

[0118] Component B: high density polyethylene 65 parts, linear low density polyethylene 4 parts, ethylene-octene copolymer 1 part, modified carbon nanotube 5 parts (exceeding the upper limit), core-shell oxide 10 parts (below the lower limit), graphene nanosheet 1 part, maleic anhydride grafted polyethylene 3 parts, antioxidant 1076 0.3 parts, antioxidant 168 0.2 parts, vinyl trimethoxysilane 1.6 parts, dibutyldilaurate 0.1 part (not adjusted in proportion according to the increase of modified carbon nanotube).

[0119] Among them, the preparation process of modified carbon nanotubes, core-shell oxides and pipes is the same as that of Example 1.

[0120] The performance test data of Examples 2-4 and Comparative Examples 4-6 are shown in Table 4.

[0121]

[0122]

[0123] Table 4 Performance test data of Examples 2-4 and Comparative Examples 4-6

[0124] Test results show that: in Examples 2-4, the core layer forms a "rigid-flexible" matrix with high density polyethylene and elastomer, and is combined with modified carbon nanotubes, core-shell oxides and graphene to build a three-dimensional heat conduction network. The SiO2 coating layer of the modified carbon nanotube inhibits agglomeration, and the hydrophobic core and silane grafted shell layer of the core-shell oxide reduce the interfacial thermal resistance, so that the longitudinal thermal conductivity coefficient reaches 4.2-4.8 W / m·K. The skin layer forms a modulus gradient through a high crystallinity PE matrix and a dynamic crosslinking system (vinyl trimethoxysilane and dibutyldilaurate in a regular ratio), and the interfacial peeling strength is 23-27 N / cm, and the environmental stress cracking resistance time is ≥1100 h.

[0125] The core layer filler in Comparative Example 4 was insufficient, resulting in the fracture of the heat conduction network, and the longitudinal thermal conductivity decreased to 2.8 W / m·K; the crosslinking agent in the skin layer was insufficient, the crosslinking density was low, and the environmental resistance time was shortened to 700 h. The core layer filler in Comparative Example 5 was excessive (e.g., 17 parts of core-shell oxide), which caused agglomeration and destroyed the continuity of the matrix, and the tensile strength decreased to 24 MPa; the skin layer PE had too high crystallinity, which caused the toughness to decrease, and the elongation at break was only 290%. In Comparative Example 6, the modified carbon nanotubes in component B were excessive (5 parts), but the crosslinking agent was not adjusted according to the rules, the silane hydrolysis was not complete, the crosslinking density of the skin layer was uneven, the thermal conductivity and the environmental resistance time decreased to 3.0 W / m·K and 720 h, respectively, which verified the necessity of dynamic matching of the crosslinking agent.

[0126] Therefore, when the raw material usage is within the limited range, the performance can be synergistically improved through the design of “core layer toughening-skin layer modulus gradient” and interface modification; exceeding the range or incorrect proportion of the crosslinking agent will cause the destruction of the heat conduction path, interface stress concentration and crosslinking defects, and the performance will significantly decrease.

Claims

1. PE-based nano high thermal conductivity composite material, characterized in that: It includes component A and component B, component A is the core layer, and component B is the skin layer; Component A is composed of the following raw materials in parts by mass: 58-62 parts of high-density polyethylene, 7-9 parts of linear low-density polyethylene, 4-6 parts of ethylene-octene copolymer, 4-6 parts of modified carbon nanotubes, 14-16 parts of core-shell oxide, 2.5-3.5 parts of graphene nanosheets, 2-4 parts of interfacial compatibilizer, 0.4-0.6 parts of antioxidant, and 0.4-0.6 parts of crosslinking agent; Component B is composed of the following raw materials in parts by mass: 66-70 parts of high-density polyethylene, 5-7 parts of linear low-density polyethylene, 2-4 parts of ethylene-octene copolymer, 2-4 parts of modified carbon nanotubes, 11-13 parts of core-shell oxide, 1.5-2.5 parts of graphene nanosheets, 4-6 parts of interfacial compatibilizer, 0.6-0.8 parts of antioxidant, and 2.0-2.6 parts of crosslinking agent; The modified carbon nanotubes are obtained by depositing a SiO2 layer on the surface of the carbon nanotubes and then grafting vinyltriethoxysilane; The core layer of the core-shell oxide is zirconium oxide, and the shell layer is aluminum oxide. The surface of the core zirconium oxide is coated with a zinc stearate hydrophobic layer, and the surface of the shell aluminum oxide is grafted with methacryloxypropyltrimethoxysilane.

2. The PE-based nano-high thermal conductivity composite material according to claim 1, characterized in that: The crosslinking agent of component A is di-tert-butyl peroxide, and the crosslinking agent of component B is a mixture of vinyltrimethoxysilane and dibutyl dilauric acid in a mass ratio of 1.7-1.9:0.15-0.

25.

3. The PE-based nano-high thermal conductivity composite material according to claim 1, characterized in that: The interfacial compatibilizers of component A and component B are both maleic anhydride grafted polyethylene.

4. The PE-based nano-high thermal conductivity composite material according to claim 1, characterized in that: The antioxidant of component A is a mixture of antioxidant 1076 and antioxidant 168 at a mass ratio of 0.25-0.35:0.15-0.25, and the antioxidant of component B is a mixture of antioxidant 1076 and antioxidant 168 at a mass ratio of 0.35-0.45:0.25-0.

35.

5. The PE-based nano-high thermal conductivity composite material according to claim 1, characterized in that: The preparation of core layer zirconia includes: First, Zr(NO3)4·5H2O was dissolved in an ethanol-water solution. Ammonia was added dropwise while stirring until the pH was 8.8-9.

2. Stirring was continued to form a sol. The sol was then placed in a dialysis bag with a molecular weight cutoff of 1000-1200 and dialyzed in deionized water until the dialysate conductivity was less than 5μS / cm to remove nitrate ions. The dialyzed sol is added with zinc stearate in an amount of 10%-15% of the target zirconium oxide mass, and refluxed in an oil bath to form a hydrophobic layer on the surface of the zirconium oxide. After the reaction is completed, the sol is centrifuged and washed three times, and calcined in a muffle furnace to obtain core layer zirconium oxide particles.

6. The PE-based nano-high thermal conductivity composite material according to claim 5, characterized in that: The preparation of the core zirconium oxide particles coated with alumina shell includes: The zirconium oxide core is dispersed in isopropanol, and methacryloxypropyltrimethoxysilane is added in an amount of 6%-9% of the target alumina mass. After ultrasonic dispersion for 30-50 minutes, an isopropanol solution of aluminum isopropoxide is slowly added dropwise, and a hydrolysis reaction is carried out in a water bath at 70°C-80°C for 5-6 hours with continuous stirring. After the reaction is completed, the product is collected by reduced pressure filtration, washed with isopropanol, and dried in a vacuum drying oven to obtain core-shell structured zirconium oxide-alumina metal oxide particles.

7. The PE-based nano-high thermal conductivity composite material according to claim 1, characterized in that: The preparation of modified carbon nanotubes includes: The carbon nanotubes are placed in a tube furnace, and tetraethoxysilane vapor is introduced, and argon is introduced as a protective gas at the same time. The deposition is carried out for 8-12 minutes to form a uniform SiO2 coating layer on the surface of the carbon nanotubes. The SiO2-coated carbon nanotubes are added to an ethanol-water solution, and then vinyltriethoxysilane accounting for 20% to 25% of the mass of the carbon nanotubes is added. The pH is adjusted to 4.3-4.7 with hydrochloric acid, and then ultrasonic treatment is carried out. The ultrasonic frequency is 35-45kHz and the ultrasonic treatment time is 160-190 minutes to graft the vinyltriethoxysilane to the surface of the SiO2 coating layer. After the grafting is completed, the modified carbon nanotubes are dried by spray drying to obtain the modified carbon nanotubes.

8. A process for preparing a pipe using the PE-based nano-high thermal conductivity composite material according to any one of claims 1 to 7, comprising the steps of: The high-density polyethylene, linear low-density polyethylene, and ethylene-octene copolymer of component A are put into a high-speed mixer according to the calculated amount, premixed at 75-85° C. and a rotation speed of 2300-2700 r / min for 4-6 minutes, and then modified carbon nanotubes, core-shell oxides, graphene nanosheets, interfacial compatibilizers, antioxidants, and crosslinking agents are added and premixed for another 8-12 minutes to form a uniform dispersion. The premix is ​​melt-extruded through a twin-screw extruder with an aspect ratio of 38-42:1, an alternating electric field is applied in zones 3-5 of the extruder, and ultrasonic waves are applied simultaneously. The homogenizing section of the twin-screw extruder is equipped with a high shear module, the screw speed is 270-310 r / min, and the residence time of component A in the temperature range of 190-210° C. is controlled to be 30-60 seconds. A core layer tube billet is extruded from the nozzle of the twin-screw extruder; Premixing high-density polyethylene, linear low-density polyethylene, and ethylene-octene copolymer of component B according to the calculated amount at 75-85° C. and 2300-2700 r / min for 4-6 minutes, then adding modified carbon nanotubes, core-shell oxides, graphene nanosheets, and an interfacial compatibilizer and premixing for 8-12 minutes, and finally adding a crosslinking agent, and simultaneously starting ultrasonic dispersion for 10-15 minutes at an ultrasonic frequency of 35-45 kHz and a power of 300-400 W to prepare a premix of component B; The skin layer is co-extruded and coated, the core layer tube billet enters the co-extrusion die head, the premix of component B is coated with the core layer through an independent flow channel, the co-extruded composite pipe enters the vacuum sizing sleeve, and is cooled and shaped by a water bath and spray to obtain the pipe.

9. The process for preparing a pipe made of a PE-based nano-composite material with high thermal conductivity according to claim 8, characterized in that: The amount of the crosslinking agent vinyltrimethoxysilane in component B accounts for 2.0% to 2.6% of the total mass of the raw materials of component B, and the amount of dibutyl dilauric acid accounts for 0.15% to 0.25% of the total mass of the raw materials of component B. With each increase of 1 part of the modified carbon nanotube content in component B within the dosage range, the mass ratio of vinyltrimethoxysilane to dibutyl dilauric acid is linearly adjusted from 1.9:0.15 to 1.7:0.

25. With each increase of 1 part of the core-shell oxide content in component B, the mass ratio of vinyltrimethoxysilane to dibutyl dilauric acid is reversely adjusted from 1.9:0.15 to 1.7:0.

25.

10. The process for preparing a pipe made of a PE-based nano-composite material with high thermal conductivity according to claim 8, characterized in that: During the extrusion of component A, the temperatures of each zone of the screw are set as follows: 155-165°C in zone 1, 170-180°C in zone 2, 180-190°C in zone 3, 190-200°C in zone 4, 195-205°C in zone 5, 200-210°C in zone 6, 200-210°C in zone 7, 195-205°C in zone 8, and 200-210°C in the die head; the intensity of the alternating electric field is 7.5-8.5 kV / cm, the frequency is 75-85 Hz, the frequency of the ultrasonic wave is 40-50 kHz, and the power is 180-220 W.

Images