Multi-feed twin-screw extrusion conduit and method for preparing high-temperature-resistant polyethylene glycol adipate

Abstract

The application relates to the technical field of high-temperature-resistant pipeline production, in particular to a multi-end-feeding double-screw extrusion pipeline and a preparation method of high-temperature-resistant polyethylene glycol adipate. The pipeline comprises a corrosion-resistant layer, a pipeline layer and a heat-insulating layer; the corrosion-resistant layer is made of vinyl ester resin, the vinyl ester resin is sprayed on the inner surface of the pipeline layer; the pipeline layer is made of high-temperature-resistant polyethylene glycol adipate, the particles are softened at high temperature, and the pipeline layer is formed by extrusion through a mold; the heat-insulating layer is made of ceramic fiber felt, the outer surface of the pipeline layer is uniformly brushed with a high-temperature adhesive binder, and the ceramic fiber felt is adhered to the outer surface of the pipeline layer. Carbon nanotubes are uniformly grafted on polyethylene glycol adipate to form a uniform heat-conducting net, the high-heat-resistance of polyether ether ketone is used to improve the heat-resistance of polyethylene glycol adipate, and the heat of a locally overheated position is guided to the surroundings through the heat-conducting net, so that decomposition caused by excessively high temperature is avoided. On the basis of improving the heat-resistance of the pipeline, the ability of the pipeline to resist uneven heat is improved.

Description

Technical Field

[0001] This invention relates to the field of high-temperature resistant pipe manufacturing technology, specifically to multi-end feeding twin-screw extrusion pipes and a method for preparing high-temperature resistant polyethylene glycol ester. Background Technology

[0002] Mixing rapidly mixable liquid chemicals in pipelines before subsequent reactions is a common process. However, during this mixing process, the temperature of the chemicals is often unevenly distributed. If the pipeline material is selected based on the average temperature, a small amount of liquid at locations with temperatures above the average may exceed the pipeline's high-temperature tolerance, causing small-area burns. Over time, these small burns can accumulate and lead to leaks. Existing pipelines made from polyethylene glycol (PEG) suffer from this problem.

[0003] Polyethylene glycol (PEG), as an organic material, is used in membrane materials, shell materials, and engineering plastics, exhibiting good toughness and plasticity. However, PEG's heat resistance is not very good, with a thermal decomposition temperature typically around 250℃, making it unsuitable for high-temperature environments. Therefore, heat resistance of PEG is improved by copolymerizing high-temperature resistant materials with PEG through grafting, copolymerization, and physical bonding.

[0004] However, in practical applications, traditional mixing methods (such as mechanical stirring and ordinary ultrasound) are insufficient to achieve uniform dispersion of nanoscale materials (such as carbon nanotubes). This easily leads to agglomeration and dispersion dead zones, affecting subsequent grafting reactions and causing large fluctuations in the product's heat resistance and thermal conductivity, failing to meet the requirements of high-temperature pipeline materials. Furthermore, material heating is not uniform, unlike uniform heating in a laboratory setting; the heating of materials is uneven, with localized temperatures exceeding the average. In such cases, even if most of the heat generated does not reach the decomposition temperature of polyethylene ethylene glycol (PEG), PEG will still decompose due to heat. Even increasing the decomposition temperature of PEG does not solve the problem of PE decomposition occurring before reaching the decomposition temperature. Summary of the Invention

[0005] In view of the shortcomings of the prior art, the purpose of this invention is to provide a multi-end feeding twin-screw extrusion pipe that improves the pipe's heat resistance and its ability to withstand uneven heat distribution.

[0006] Another objective of this invention is to provide a method for preparing high-temperature resistant polyethylene glycol ester for multi-ended feeding twin-screw extrusion pipes. This method involves using a two-step grafting process, altering the polarity of carbon nanotubes with a strong acid, dispersing the carbon nanotubes with a silane coupling agent, treating polyetheretherketone (PEEK) to break the benzene rings on its surface and make it polar, and then allowing the fully dispersed carbon nanotubes to undergo an esterification reaction with their polar groups on the PEEK surface, thus significantly improving the material's performance.

[0007] The multi-end feeding twin-screw extrusion pipe of the present invention includes a corrosion-resistant layer, a pipe layer and an insulation layer;

[0008] The corrosion-resistant layer is made of vinyl ester resin, and a topcoat slurry containing glass flakes is prepared and sprayed in 2-3 coats, each coat being 80-100μm thick, with a total thickness of 160-300μm, and cured at room temperature for 24 hours.

[0009] The pipe layer uses high-temperature resistant polyethylene glycol ester. The high temperature softens the particles and extrudes them to form the pipe layer. The twin-screw extruder temperature is 240-260℃, and the die temperature is 230-250℃. The vacuum sizing method is adopted, with a vacuum degree of -0.05~-0.08MPa, a cooling water tank temperature of 15-25℃, and a traction speed of 0.5-1.0m / min.

[0010] The insulation layer uses ceramic fiber felt, and the surface of the pipe layer is uniformly coated with a high-temperature adhesive with a thickness of 0.2-0.5mm to avoid air bubbles.

[0011] Pre-cut the ceramic fiber felt to the pipe circumference plus 5% overlap, and wrap it around the pipe while the adhesive is still hot-melted at high temperature. Apply 0.1-0.3MPa pressure to ensure a tight fit.

[0012] After bonding, cure at room temperature for 24 hours or heat to cure. After curing, the high-temperature adhesive forms a continuous transition layer, filling the micropores at the interface.

[0013] The method for preparing high-temperature resistant polyethylene glycol ester according to the present invention includes the following steps:

[0014] (1) Sonicate carbon nanotubes in a mixed acid;

[0015] (2) The ultrasonically treated carbon nanotubes were modified by adding a silane coupling agent;

[0016] (3) The modified carbon nanotubes were added to an NMP solution containing polyetherimide and mixed and dispersed to form a CNTs-PEI-NMP suspension;

[0017] (4) Add polyetheretherketone powder to CNTs-PEI-NMP suspension for mixing and dispersion;

[0018] (5) The ultrasonicated CNTs-PEI-NMP suspension was reacted with polyether ether ketone in hexafluoroisopropanol for 6 hours. After the reaction was completed, the CNTs / PEEK polymer was obtained by filtration.

[0019] (6) The CNTs / PEEK polymer is reacted with trifluoromethanesulfonic acid to introduce sulfonic acid groups (-SO3H) onto the surface of polyetheretherketone (PEEK), forming a CNTs / PEEK copolymer. Sulfonic acid groups are strong acidic groups with high chemical reactivity. In grafting reactions, sulfonic acid groups can act as electrophiles or nucleophiles, providing additional reaction sites. During grafting with polyethylene glycol (PEG), sulfonic acid groups can undergo esterification with the hydroxyl or carboxyl groups in the PEG molecule, thereby promoting the grafting reaction. Sulfonic acid groups (-SO3H) are introduced onto the surface of PEG. As a strongly polar group, sulfonic acid groups can significantly improve the interfacial compatibility between the CNTs / PEEK copolymer and the PEG matrix, and may also serve as auxiliary reaction sites.

[0020] (7) The CNTs / PEEK copolymer was double-grafted with polyethylene glycol ester under the catalysis of tetrabutyl titanate; a large number of carboxyl and hydroxyl groups were introduced on the surface of CNTs by acid treatment, and PEEK was polymerized by using specific monomers to ensure that the PEEK chain ends also had active groups.

[0021] (8) After grafting is completed, the high-temperature resistant polyethylene glycol ester is obtained by cooling.

[0022] In step (3), the mixing and dispersion of materials is carried out by ultrasonic treatment or by a material mixing and dispersion device. The specific method of the material mixing and dispersion device is as follows: the NMP solution of polyetherimide is used as the main fluid and pumped into the Venturi mixer at a flow rate of 8-15 m / s by a circulating pump; the slurry premixed with modified carbon nanotubes and a small amount of NMP is drawn into the main fluid by the negative pressure generated at the throat of the Venturi tube and circulated and dispersed for 30-120 min.

[0023] In step (4), the mixing and dispersion of materials is carried out by ultrasonic treatment or by a material mixing and dispersion device. The specific method of the material mixing and dispersion device is as follows: the CNTs-PEI-NMP suspension is used as the main fluid and pumped into the Venturi mixer at a flow rate of 8-15 m / s by a circulating pump; the slurry premixed with polyether ether ketone powder and a small amount of NMP is drawn into the main fluid by the negative pressure generated at the throat of the Venturi tube and circulated and dispersed for 30-120 min.

[0024] The material mixing and dispersion device includes a reactor, which is connected to a circulating pump via a pipeline. The circulating pump is connected to the top of the reactor via a circulating pipeline, which is connected to the bottom of the reactor via a Venturi mixer. A valve is installed between the Venturi mixer and the reactor. The Venturi mixer has an outer wall and includes a contraction angle and a diffusion angle. A storage tank is connected to the contraction angle. The top of the storage tank is connected to a nitrogen pressurized mixing tank via a feed pipeline. A vacuum pump is connected to the reactor, and a stirrer is installed inside the reactor. The storage tank is always kept at a slightly positive pressure by nitrogen. After the raw materials in the storage tank are added, nitrogen can be dispersed into the reactor through the Venturi mixer, while ensuring that air does not enter, to enhance mixing. Then, the vacuum pump is turned on to expel the nitrogen.

[0025] The method for preparing the high-temperature resistant polyethylene glycol ester involves ultrasonically treating 1-3g of carbon nanotubes in a mixture of 50-150mL sulfuric acid and nitric acid (volume ratio of sulfuric acid to nitric acid: 1:3) for 2 hours. The ultrasonic treatment of carbon nanotubes in a strong acid oxidizes them: CNTs + HNO3 / H2SO4 → CNTs-COOH + CNTs-OH + other oxygen-containing groups. This forms polar groups such as carboxyl and hydroxyl groups, increasing the polarity of the carbon nanotubes. Simultaneously, the mixed acid treatment effectively removes amorphous carbon, residual metal catalysts, and other impurities from the carbon nanotube surface. The increased surface charge of the oxidized carbon nanotubes inhibits aggregation through electrostatic repulsion and steric hindrance, promoting uniform dispersion in the polyetheretherketone matrix.

[0026] The method for preparing the high-temperature resistant polyethylene glycol ester involves modifying carbon nanotubes using a 2 wt.% silane coupling agent ethanol solution. Carbon nanotubes are prone to aggregation due to van der Waals forces, which affects their application in composite materials. Silane coupling agents contain hydrolyzable groups (such as alkoxy groups) and organic functional groups. During the modification process, the alkoxy groups of the silane coupling agent hydrolyze to generate silanol groups. These silanol groups can undergo condensation reactions with hydroxyl groups and other groups on the surface of carbon nanotubes, thereby attaching to the surface of the carbon nanotubes. Meanwhile, the organic functional groups face outwards, increasing the steric hindrance on the surface of the carbon nanotubes and reducing the mutual attraction between carbon nanotubes, making them easier to disperse in solvents or matrix materials.

[0027] The method for preparing the high-temperature resistant polyethylene glycol ester involves adding N-methylpyrrolidone as a solvent to a container, first adding polyetherimide and stirring at a reaction temperature of 60°C for 1 hour to form a polyetherimide solution, then adding 1-3g of modified carbon nanotubes to the solution, placing the container containing the mixed solution into an ultrasonic cleaner, setting the ultrasonic frequency to 20kHz and the ultrasonic power density to 5W / cm². 2After ultrasonic treatment for 30 minutes, a CNTs-PEI-NMP suspension was obtained. The physical adsorption or coating of polyetherimide on the surface of carbon nanotubes can form steric hindrance and inhibit CNT aggregation.

[0028] The method for preparing the high-temperature resistant polyethylene glycol ester involves adding 0.5g of polyetheretherketone (PEEK) powder to a CNTs-PEI-NMP suspension. Intermittent sonication is performed for 20 minutes, with a 3-second working cycle followed by a 2-second pause, at a power of 300W, to obtain the CNTs / PEEK polymer. The polar groups in the PEEK molecular chain, such as carbonyl (-C=O) and ether bonds (-O-), interact weakly with the oxygen-containing groups on the surface of carbon nanotubes, such as hydroxyl (-OH) and carboxyl (-COOH), through hydrogen bonds or van der Waals forces.

[0029] A CNTs-PEI-NMP suspension with a volume ratio of (5-6):(6-7) was mixed with hexafluoroisopropanol, and sulfonic acid groups were introduced for copolymerization. Copolymerization of polyetheretherketone (PEEK) with fluorinated monomers can reduce the melt viscosity of PEEK, enhance interfacial compatibility, and significantly improve the interfacial compatibility between the CNTs / PEEK copolymer and polyethylene glycol ester by introducing sulfonic acid groups (-SO3H) as strongly polar groups, while also providing additional reaction sites for grafting reactions.

[0030] CNTs / PEEK copolymer was grafted with polyethylene glycol ester under the catalysis of tetrabutyl titanate, and double grafting was achieved through esterification reaction.

[0031] Polyetheretherketone (PEEK) segment: The terminal carboxyl group of PEEK reacts with the hydroxyl group of polyethylene glycol ester to form an ester bond (-COO-).

[0032] On the surface of carbon nanotubes: the carboxyl groups of carbon nanotubes undergo condensation polymerization with the hydroxyl groups of polyethylene glycol ester, forming covalent bonds for anchoring.

[0033] The reaction formula is:

[0034] PEEK-COOH+HO-EGO→PEEK-COO-EGO+H2OnCNTs-COOH+nEGO-OH→[CNTs-COO-EGO] n +nH2O.

[0035] This invention forms a dense protective layer by spraying 2-3 coats of a glass flake-containing topcoat slurry (total thickness 160-300μm), significantly enhancing the pipeline's resistance to chemical solvent corrosion. Addressing the issue of corrosive liquids eroding pipelines during chemical mixing mentioned in the background art, this coating effectively delays corrosion of the pipeline's inner wall, preventing thermal failure caused by localized weak points resulting from corrosion.

[0036] By introducing polyetheretherketone (PEEK) and carbon nanotubes (CNTs) through a double grafting technique, the thermal decomposition temperature of polyethylene glycol (PEG) was increased from 250℃ to 340-368℃, while the thermal conductivity was improved to 0.68-0.85 W / m·K. This improvement directly solves the core problem of "local temperatures exceeding the material decomposition threshold" in the prior art. It rapidly dissipates heat through a uniform heat-conducting network, preventing decomposition of the pipe's inner wall due to localized overheating in contact with high-temperature liquids.

[0037] The process employs pre-cutting and overlapping, along with hot-pressing bonding at a pressure of 0.1-0.3 MPa, ensuring a tight bond between the insulation layer and the pipe layer. The low thermal conductivity of the ceramic fiber felt (<0.1 W / m·K), combined with the interfacial filling effect of the high-temperature adhesive, reduces external heat loss and prevents excessive internal heat accumulation, achieving bidirectional heat management.

[0038] The pipe layer is prepared by twin-screw extrusion at a temperature of 240-260℃, which is fully compatible with the processing temperature of the modified polyethylene glycol material of this invention, which is 130-280℃. This proves that the material can be directly applied to existing pipe production lines without additional equipment investment.

[0039] Traditional polyethylene glycol (PEG) pipes require frequent replacement due to insufficient heat resistance. However, the pipes of this invention significantly reduce maintenance costs by improving material lifespan (carbon residue rate from 5.2% to 22.3%) and thermal conductivity, making them particularly suitable for chemical production environments requiring long-term resistance to high temperatures and corrosive media. This invention also comprehensively addresses the problem of uneven heat generation.

[0040] This invention utilizes a synergistic design of a "thermal conductive network + insulation layer":

[0041] Thermal conductive network: Carbon nanotubes form continuous pathways in the polyethylene glycol matrix, rapidly transferring localized heat from the inner wall of the pipe in contact with the high-temperature liquid to low-temperature areas (such as the outer wall of the pipe or adjacent pipe sections), thus avoiding temperature concentration.

[0042] Insulation layer: When the external ambient temperature fluctuates, ceramic fiber felt can stabilize the internal temperature field of the pipe, reduce the damage of thermal stress to the material structure, and further extend the service life.

[0043] Compared with the prior art, the beneficial effects of the present invention are:

[0044] (1) This invention does not directly utilize the high-temperature resistance of carbon nanotubes to copolymerize with polyethylene glycol ester, but instead uses a very small amount of carbon nanotubes for grafting. A two-step grafting process is employed: first, a strong acid is used to alter the polarity of the carbon nanotubes; then, a silane coupling agent is used to disperse the carbon nanotubes; and finally, the polyetheretherketone (PEEK) is treated to break the benzene rings on its surface, making it polar. The fully dispersed carbon nanotubes then undergo an esterification reaction with their polar groups on the PEEK surface, thus fully dispersing onto the PEEK. This forms a bond between the carbon nanotubes and the PEEK.

[0045] (2) The second step is grafting. Carbon nanotubes and polyether ether ketone are grafted onto the carboxyl or hydroxyl groups at both ends of polyethylene glycol ester through a catalyst to form a three-dimensional cross-linked structure. Since the carbon nanotubes are fully dispersed on the surface of polyether ether ketone, when the sheet-like polyether ether ketone is grafted onto polyethylene glycol ester, the carbon nanotubes will be uniformly dispersed on the polyethylene glycol ester to form a uniform heat-conducting network. The high heat resistance of polyether ether ketone is used to improve the heat resistance of polyethylene glycol ester, and the heat is directed to the surrounding area through the heat-conducting network to avoid decomposition caused by excessive temperature. The heat resistance is truly improved, and the damage caused by local heating is effectively overcome.

[0046] (3) This invention introduces both high-heat-resistant PEEK molecular chains and high-thermal-conductivity CNTs networks into the polyethylene glycol matrix through chemical grafting. This synergistic structure of 'heat-resistant skeleton + thermally conductive network' not only increases the overall thermal decomposition temperature of the material, but more importantly, it solves the problem of local overheating that existing technologies cannot address. When hot spots appear inside the pipe, the uniformly dispersed CNTs network can quickly conduct heat away, avoiding local degradation, thereby achieving a leap from 'high-temperature resistance' to 'resistance to uneven high temperatures'.

[0047] (4) The negative pressure and turbulence generated by the high flow rate of the Venturi mixer, combined with the circulation dispersion, break the agglomeration of carbon nanotubes and form a uniform heat conduction network to solve the problem of local overheating; enhance reaction efficiency: the design of the contraction angle and diffusion angle promotes full contact of components, improves the double grafting reaction conversion rate, and significantly improves heat resistance. Attached Figure Description

[0048] Figure 1 This is a schematic diagram of the material mixing and dispersing device of the present invention;

[0049] Figure 2 This is a schematic diagram of the structure of the Venturi mixer of the present invention;

[0050] In the diagram: 1. Reactor; 2. Circulation pump; 3. Vacuum pump; 4. Venturi mixer; 5. Valve; 6. Circulation pipeline; 7. Mixer outer wall; 8. Contraction angle; 9. Diffusion angle; 10. Storage tank; 11. Nitrogen pressurized mixing tank; 12. Feed pipeline. Detailed Implementation

[0051] To make the objectives and technical solutions of this invention clearer, this invention will be further described in detail.

[0052] like Figure 1-2 As shown, the material mixing and dispersing device includes a reactor 1. The reactor 1 is connected to a circulating pump 2 via a pipeline. The circulating pump 2 is connected to the top of the reactor 1 via a circulating pipeline 6. The circulating pipeline 6 is connected to the bottom of the reactor 1 via a Venturi mixer 4. A valve 5 is provided between the Venturi mixer 4 and the reactor 1. A mixer outer wall 7 is provided on the outside of the Venturi mixer 4. The Venturi mixer 4 includes a contraction angle 8 and a diffusion angle 9. A storage tank 10 is connected at the contraction angle 8. The top of the storage tank 10 is connected to a nitrogen pressurized mixing tank 11 via a feed pipeline 12. A vacuum pump 3 is connected to the reactor 1. A stirrer is provided inside the reactor 1.

[0053] The preparation method of high-temperature resistant polyethylene glycol ester is further explained below with reference to embodiments of the present invention:

[0054] Test method:

[0055] Tensile strength: GB / T1040.1-2018;

[0056] Bending strength: GB / T9341-2008;

[0057] Impact strength: GB / T1043.1-2008;

[0058] Heat distortion temperature: GB / T1634.1-2021;

[0059] Acid and alkali resistance tensile strength retention rate: GB / T11547-2008;

[0060] Melt flow rate: GB / T3682.1-2018;

[0061] Extrusion shrinkage rate: GB / T15585-1995;

[0062] Thermal stability test:

[0063] Thermogravimetric analysis (TGA) was used for analysis. In a TA Instruments Q500 thermogravimetric analyzer, 10 mg of sample was placed in an alumina crucible and heated in an air atmosphere using a heating source. The heating rate was controlled at 10 °C / min. The thermal decomposition (Td) of the test material was observed and recorded for comparison. A higher Td indicates better thermal stability.

[0064] Carbon residue test:

[0065] 15 mg of sample was ground into powder, passed through an 80-mesh sieve to remove large particles, and then placed in a thermogravimetric analyzer. The sample was heated from room temperature to 800 °C in air, with a temperature increase rate controlled at 10 °C / min. The sample was then calcined at 600 °C, and the residual mass was extracted. The char yield was calculated as: char yield = residual mass / initial sample mass × 100. A higher char yield indicates better thermal stability.

[0066] Thermal conductivity: Tested using the laser flash method, the product was hot-pressed into a 1mm film and coated with graphite on both sides. Calibration was performed using a sapphire calibrator. The product was then placed in a Netzsch LFA457 MicroFlash tester, and a laser pulse was triggered to record the temperature response curve. The thermal diffusivity α was calculated by fitting the temperature rise curve using the instrument software.

[0067] Density ρ was determined by Archimedes' displacement method, and specific heat capacity C p Measured by DSC (differential scanning calorimetry).

[0068] The final thermal conductivity λ = α·ρ·C p A higher thermal conductivity coefficient indicates better thermal conductivity of the product.

[0069] Pipeline mechanical properties:

[0070] Tensile strength: According to GB / T8804.2-2003 "Determination of tensile properties of thermoplastic pipes - Part 2: Rigid polyvinyl chloride (PVC-U), chlorinated polyvinyl chloride (PVC-C) and high-impact polyvinyl chloride (PVC-HI) pipes".

[0071] Bending strength: According to GB / T9341-2008 "Determination of bending properties of plastics".

[0072] Impact strength (simply supported beam): According to GB / T1043.1-2008 "Determination of impact properties of simply supported beams of plastic".

[0073] Pipeline heat resistance:

[0074] Heat distortion temperature (HDT): Based on GB / T1634.1-2021, material test data are directly adopted.

[0075] Resistance to localized overheating: A localized area (2cm in diameter) of the inner wall of the prepared pipe was continuously exposed to a heat source at 280℃ for 10 minutes. The pipe's inner wall was then observed for signs of charring, softening, bulging, or decomposition. This test aims to simulate a working condition where the localized temperature is higher than the average temperature.

[0076] Pipeline chemical corrosion resistance:

[0077] Acid and alkali resistance tensile strength retention rate: According to GB / T11547-2008, the pipe sample was immersed in 10% H2SO4 and 10% NaOH solution at 60℃ for 72h, and its tensile strength was tested and the retention rate was calculated.

[0078] Pipe extrusion molding performance:

[0079] Extrusion shrinkage: Based on GB / T15585-1995, material test data were directly adopted.

[0080] Carbon nanotubes, FT7000, average diameter 7-11nm, length 5-20μm, Jiangsu Tiannai Technology Co., Ltd.

[0081] Silane coupling agent, KH-550 (γ-aminopropyltriethoxysilane), Nanjing Shuguang Chemical Group Co., Ltd.;

[0082] Polyetherimide, Ultem® 1000, Saudi Basic Industries Corporation (SABIC).

[0083] Polyetheretherketone (PEEK), Victrex® PEEK 450G, Vigus Ltd., UK;

[0084] Polyethylene glycol resin, XK7228, Hubei Xinkang Pharmaceutical Chemical Co., Ltd.;

[0085] High-temperature adhesive: HC1015, heat resistance temperature: 1400℃, Langfang Hengcheng Insulation Materials Co., Ltd.

[0086] Example 1

[0087] A method for preparing high-temperature resistant polyethylene glycol ester includes the following steps:

[0088] (1) 1 g of carbon nanotubes with a diameter of 15 nm, a length of 3 μm, and a purity of 97% were ultrasonically treated in a mixture of 50 mL of sulfuric acid and nitric acid. The ratio of 98% concentrated sulfuric acid to 65% concentrated nitric acid was 1:3. The ultrasonic treatment lasted for 2 h, with an ultrasonic frequency of 30 kHz and an ultrasonic power of 250 W. The temperature was controlled to not exceed 45 °C.

[0089] (2) Dissolve 0.01g of KH-550 silane coupling agent in 0.5mL of ethanol solution with a concentration of 95%. Use the KH-550 silane coupling agent solution to modify the filtered and cleaned carbon nanotubes. The reaction time is 1h and the reaction temperature is 120℃. After the reaction is complete, wash until neutral and dry.

[0090] (3) Add 50 mL of N-methylpyrrolidone as a solvent to a container, add 0.5 g of polyetherimide, stir for 1 h at a reaction temperature of 60 °C to form a polyetherimide solution, then add 1 g of modified carbon nanotubes to the solution. Place the container containing the mixed solution into an ultrasonic cleaner, set the ultrasonic frequency to 20 kHz and the ultrasonic power density to 5 W / cm². 2 After sonication for 30 minutes, a CNTs-PEI-NMP suspension was obtained.

[0091] (4) Add 0.5g of polyetheretherketone powder to the CNTs-PEI-NMP suspension. Perform intermittent ultrasound for 20min, with a cycle of 3s working and 2s pausing, and an ultrasound power of 300W.

[0092] (5) 50 mL of the sonicated suspension was directly poured into 60 mL of hexafluoroisopropanol, and 0.1 g of p-toluenesulfonic acid was added as a catalyst. The mixture was stirred at 90 °C for 30 min, and then the temperature was raised to 120 °C and sonicated at 200 W for 10 min. Under nitrogen protection, the temperature was raised to 280 °C and reacted for 6 h. After the reaction was completed, the product was poured into a large amount of methanol to precipitate, filtered and dried to obtain the CNTs / PEEK polymer. Copolymerization of polyetheretherketone with fluorinated monomers can reduce the melt viscosity of polyetheretherketone and enhance interfacial compatibility.

[0093] (6) The CNTs / PEEK polymer was added to 15 mL of dichloromethane solvent, and 2.5 mL of 98% trifluoromethanesulfonic acid was added dropwise to the solution. The mixture was stirred at 300 rpm for 2 h at a reaction temperature of 60 °C. Sulfonic acid groups (-SO3H) were introduced onto the surface of polyetheretherketone. The solution was then separated and purified to obtain the CNTs / PEEK polymer with sulfonic acid groups.

[0094] (7) Take 0.3g of oxalic acid and 0.625mL of ethylene glycol and esterify them at 130℃ for 2h to obtain polyethylene glycol ester prepolymer.

[0095] (8) Take 0.3g of polyethylene glycol prepolymer obtained in step (7) and add it to 15mL of methanol solution. Then add 1.5g of CNTs / PEEK polymer powder evenly to the methanol solution within 10min. Stir continuously during the addition process. Finally, add 0.01g of tetrabutyl titanate for catalysis. Stir continuously for 4h and react at 130℃. Use a water separator to remove the water generated during the reaction.

[0096] (9) After the reaction is complete, cool, filter, wash with methanol 4 times, and then dry in a vacuum drying oven at 58°C for 16 h. High-temperature resistant polyethylene glycol ester is obtained.

[0097] Multi-end feeding twin-screw extrusion pipe, including a corrosion-resistant layer, a pipe layer and an insulation layer;

[0098] The corrosion-resistant layer is made of vinyl ester resin (commercially available MFE-2 type), and a topcoat slurry containing glass flakes (particle size 40μm, thickness 3μm) is prepared and sprayed in 3 coats, each coat being 90μm thick, for a total thickness of 200μm. It is then cured at room temperature for 24 hours.

[0099] The pipe layer uses the high-temperature resistant polyethylene glycol ester obtained in Example 1. The high temperature softens the particles and extrudes them to form the pipe layer. The twin-screw extruder temperatures (feed port - die head) are 240℃, 245℃, 250℃, 255℃, 255℃, 250℃, and the die temperature is 240℃. The vacuum sizing method is used with a vacuum degree of -0.05MPa, a cooling water tank temperature of 20℃, and a traction speed of 0.8m / min.

[0100] The insulation layer uses ceramic fiber felt, and the surface of the pipe layer is uniformly coated with a 0.4mm thick high-temperature adhesive to avoid air bubbles.

[0101] Ceramic fiber felt (density 128 kg / m³) 3 (The thermal conductivity is 0.08 W / m·K). The pre-cut adhesive is the pipe circumference plus 5% overlap. While the adhesive is still hot-melt at high temperature, it is wrapped around the pipe and 0.2 MPa pressure is applied to ensure a tight fit.

[0102] After bonding, cure at room temperature for 24 hours or heat to cure. After curing, the high-temperature adhesive forms a continuous transition layer, filling the micropores at the interface.

[0103] Example 2

[0104] A method for preparing high-temperature resistant polyethylene glycol ester includes the following steps:

[0105] (1) 1.2 g of carbon nanotubes with a diameter of 15 nm, a length of 3 μm, and a purity of 97% were ultrasonically treated in a mixture of 60 mL of sulfuric acid and nitric acid. The ratio of 98% concentrated sulfuric acid to 65% concentrated nitric acid was 1:3. The ultrasonic treatment lasted for 2 h, with an ultrasonic frequency of 30 kHz and an ultrasonic power of 250 W. The temperature was controlled to not exceed 45 °C.

[0106] (2) Dissolve 0.012 g of KH-550 silane coupling agent in 0.6 mL of ethanol solution with a concentration of 95%. Use the KH-550 silane coupling agent solution to modify the filtered and cleaned carbon nanotubes. The reaction time is 1 h and the reaction temperature is 120 °C. After the reaction is complete, wash until neutral and dry.

[0107] (3) Add 60 mL of N-methylpyrrolidone as a solvent to a container, add 0.5 g of polyetherimide, stir at 60 °C for 1 h to form a polyetherimide solution, then add 1.2 g of modified carbon nanotubes to the solution. Place the container containing the mixed solution into an ultrasonic cleaner, set the ultrasonic frequency to 20 kHz and the ultrasonic power density to 5 W / cm². 2 The mixture was sonicated for 30 minutes to obtain a CNTs-PEI-NMP suspension.

[0108] (4) Add 0.5g of polyetheretherketone powder to the CNTs-PEI-NMP suspension. Perform intermittent ultrasound for 20min, with a cycle of 3s working and 2s pausing, and an ultrasound power of 300W.

[0109] (5) 60 mL of the sonicated suspension was directly poured into 70 mL of hexafluoroisopropanol and 0.12 g of p-toluenesulfonic acid was added as a catalyst. The mixture was stirred at 90 °C for 30 min, then the temperature was raised to 120 °C and the power was increased to 200 W. The mixture was sonicated for 10 min. Under nitrogen protection, the reaction was carried out at 280 °C for 6 h. After the reaction was completed, the product was poured into a large amount of methanol to precipitate, filtered, and dried to obtain the CNTs / PEEK polymer. Copolymerization of polyetheretherketone with fluorinated monomers can reduce the melt viscosity of polyetheretherketone and enhance interfacial compatibility.

[0110] (6) Add 1.7 g of CNTs / PEEK polymer to 18 mL of dichloromethane solvent, and add 3 mL of 98% trifluoromethanesulfonic acid dropwise to the solution. Stir the mixture at 300 rpm for 2 h at a reaction temperature of 60 °C. Sulfonic acid groups (-SO3H) are introduced onto the surface of polyetheretherketone. The solution is then separated and purified to obtain CNTs / PEEK polymer with sulfonic acid groups.

[0111] (7) Take 0.34g of oxalic acid and 0.71mL of ethylene glycol and esterify them at 130℃ for 2h to obtain polyethylene glycol ester prepolymer.

[0112] (8) Take 0.34g of polyethylene glycol prepolymer obtained in step (7) and add it to 18mL of methanol solution. Then add 1.7g of CNTs / PEEK polymer powder evenly to the methanol solution within 10min. Stir continuously during the addition process. Finally, add 0.01g of tetrabutyl titanate for catalysis. Stir continuously for 4h at a reaction temperature of 130℃. Use a water separator to remove the water generated during the reaction.

[0113] (9) After the reaction is complete, cool, filter, wash with methanol 4 times, and then dry in a vacuum drying oven at 58°C for 16 h. High-temperature resistant polyethylene glycol ester is obtained.

[0114] The high-temperature resistant polyethylene glycol ester obtained in Example 2 was used to prepare a multi-end feeding twin-screw extrusion pipe with the traction speed increased to 0.9 m / min. Other steps were the same as in Example 1.

[0115] Example 3

[0116] A method for preparing high-temperature resistant polyethylene glycol ester includes the following steps:

[0117] (1) 3g of carbon nanotubes with a diameter of 15nm, a length of 3μm and a purity of 97% were ultrasonically treated in a mixture of sulfuric acid and nitric acid in 150mL. The ratio of 98% concentrated sulfuric acid to 65% concentrated nitric acid was 1:3. The ultrasonic treatment lasted for 2h, with an ultrasonic frequency of 30kHz and an ultrasonic power of 250W. The temperature was controlled to not exceed 45℃.

[0118] (2) Dissolve 0.03g of KH-550 silane coupling agent in 1.5mL of ethanol solution with a concentration of 95%. Use the KH-550 silane coupling agent solution to modify the filtered and cleaned carbon nanotubes. The reaction time is 1h and the reaction temperature is 120℃. After the reaction is complete, wash until neutral and dry.

[0119] (3) Add 150 mL of N-methylpyrrolidone as a solvent to a container, add 1.5 g of polyetherimide, stir at 60 °C for 1 h to form a polyetherimide solution, then add 3 g of modified carbon nanotubes to the solution. Place the container containing the mixed solution into an ultrasonic cleaner, set the ultrasonic frequency to 20 kHz and the ultrasonic power density to 5 W / cm². 2 The mixture was sonicated for 30 minutes to obtain a CNTs-PEI-NMP suspension.

[0120] (4) Add 0.5g of polyetheretherketone powder to the CNTs-PEI-NMP suspension. Perform intermittent ultrasound for 20min, with a cycle of 3s working and 2s pausing, and an ultrasound power of 300W.

[0121] (5) 150 mL of the sonicated suspension was directly poured into 180 mL of hexafluoroisopropanol and 0.3 g of p-toluenesulfonic acid was added as a catalyst. The mixture was stirred at 90 °C for 30 min, and then the temperature was raised to 120 °C and sonicated at 200 W for 10 min. The reaction was carried out at 280 °C for 6 h under nitrogen protection. After the reaction was completed, the product was poured into a large amount of methanol to precipitate, filtered and dried to obtain the CNTs / PEEK polymer. Copolymerization of polyetheretherketone with fluorinated monomers can reduce the melt viscosity of polyetheretherketone and enhance interfacial compatibility.

[0122] (6) Add 3.5 g of CNTs / PEEK polymer to 35 mL of dichloromethane solvent, and add 7 mL of 98% trifluoromethanesulfonic acid dropwise to the solution. Stir the mixture at 300 rpm for 2 h at a reaction temperature of 60 °C. Sulfonic acid groups (-SO3H) are introduced onto the surface of polyetheretherketone. The solution is then separated and purified to obtain CNTs / PEEK polymer with sulfonic acid groups.

[0123] (7) Take 0.34g of oxalic acid and 0.71mL of ethylene glycol and esterify them at 130℃ for 2h to obtain polyethylene glycol ester prepolymer.

[0124] (8) Take 0.5g of polyethylene glycol prepolymer obtained in step (7) and add it to 18mL of methanol solution. Then add 3.5g of CNTs / PEEK polymer powder evenly to the methanol solution within 10min. Stir continuously during the addition process. Finally, add 0.01g of tetrabutyl titanate for catalysis. Stir continuously for 4h at a reaction temperature of 130℃. Use a water separator to remove the water generated during the reaction.

[0125] (9) After the reaction is complete, cool, filter, wash with methanol 4 times, and then dry in a vacuum drying oven at 58°C for 16 h. High-temperature resistant polyethylene glycol ester is obtained.

[0126] The high-temperature resistant polyethylene glycol ester obtained in Example 3 was used to prepare a multi-ended feeding twin-screw extrusion pipe. The extruder die head temperature was 260°C, and the other steps were the same as in Example 1.

[0127] Example 4

[0128] A method for preparing high-temperature resistant polyethylene glycol ester includes the following steps:

[0129] (1) Prepare modified CNTs by following steps (1)-(2) of Example 1.

[0130] (2) Add 1.5L NMP to the reactor of the material mixing and dispersing device, start the stirring and heating system, raise the temperature to 60°C, add 15g PEI, and stir for 1h until completely dissolved.

[0131] (3) The 3g modified CNTs obtained in step 1 are premixed with 200mL NMP to form a slurry, which is then added to the storage tank of the material mixing and dispersing device.

[0132] (4) Start the circulation pump and pump the PEI-NMP solution into the Venturi mixer (throat diameter: pipe diameter = 1:4, material: Hastelloy C-276) at a flow rate of 10 m / s. Adjust the Venturi suction inlet valve to uniformly draw the CNTs slurry into the main fluid within 20 min.

[0133] (5) Continue to circulate and disperse for 60 minutes to obtain a CNTs-PEI-NMP suspension with extremely uniform dispersion.

[0134] (6) 20g of PEEK powder and 100mL of NMP are premixed into a slurry and then aspirated into the suspension of step 5 in the same manner within 30min through a material mixing and dispersing device. The mixture is then circulated for another 40min to obtain a uniform mixture of CNTs-PEEK-PEI-NMP.

[0135] (7) The subsequent steps are the same as steps (5)-(9) in Example 1, including copolymerization, sulfonation and grafting reaction with polyethylene glycol ester to obtain high temperature resistant polyethylene glycol ester.

[0136] The high-temperature resistant polyethylene glycol ester obtained in Example 4 was used to prepare a multi-end feeding twin-screw extrusion pipe. The extruder die head temperature was 250°C, the traction speed was 1.0 m / min, and the other steps were the same as in Example 1.

[0137] Comparative Example 1: Ungrafted carbon nanotubes and polyetheretherketone compared to Example 1:

[0138] (1) Take 0.3g of polyethylene glycol ester and add it to 15mL of methanol solution.

[0139] (2) No CNTs / PEEK or catalysts are added.

[0140] (3) Stir the reaction with a water separator at a reaction temperature of 130℃ for 4 hours.

[0141] (4) After cooling, filter, wash with methanol 3 times, and vacuum dry at 60°C for 12 hours.

[0142] Multi-ended feeding twin-screw extrusion pipes were prepared using the polyethylene glycol ester obtained in Comparative Example 1. The extruder die head temperature was 230°C, and other steps were the same as in Example 1.

[0143] Comparative Example 2: Compared with Example 1, only carbon nanotubes were grafted without polyetheretherketone. The specific steps were as follows:

[0144] (1) 1.2 g of carbon nanotubes with a diameter of 15 nm, a length of 3 μm, and a purity of 97% were ultrasonically treated in a mixture of 60 mL of sulfuric acid and nitric acid. The ratio of 98% concentrated sulfuric acid to 65% concentrated nitric acid was 1:3. The ultrasonic treatment lasted for 2 h, with an ultrasonic frequency of 30 kHz and an ultrasonic power of 250 W. The temperature was controlled to not exceed 45 °C.

[0145] (2) Dissolve 0.012 g of KH-550 silane coupling agent in 0.6 mL of ethanol solution with a concentration of 95%. Use the KH-550 silane coupling agent solution to modify the filtered and cleaned carbon nanotubes. The reaction time is 1 h and the reaction temperature is 120 °C. After the reaction is complete, wash until neutral and dry.

[0146] (3) Take 0.3g of polyethylene glycol ester and add it to 18mL of methanol solution. Then add 1.2g of CNTs powder evenly to the methanol solution within 10min. Stir continuously during the addition process. Finally, add 0.01g of tetrabutyl titanate for catalysis. Stir continuously for 4h and react at 130℃. Use a water separator to remove the water generated during the reaction.

[0147] (4) After the reaction is complete, cool, filter, wash with methanol 4 times, and then dry in a vacuum drying oven at 58°C for 16 h. High-temperature resistant polyethylene glycol ester is obtained.

[0148] The polyethylene glycol ester obtained in Comparative Example 2 was used to prepare a multi-ended feeding twin-screw extrusion pipe, and the other steps were the same as in Example 1.

[0149] Comparative Example 3: Copolymerization process of polyethylene glycol ester and polyetheretherketone. Specific steps are as follows:

[0150] (1) 0.5 g of polyetheretherketone powder was added to 30 mL of hexafluoroisopropanol and 0.06 g of p-toluenesulfonic acid was added as a catalyst. The mixture was stirred at 90 °C for 30 min, and then the temperature was raised to 120 °C and ultrasonicated at 200 W for 10 min. The reaction was carried out at 280 °C for 6 h under nitrogen protection. After the reaction was completed, the product was poured into a large amount of methanol to precipitate, filtered and dried to obtain the PEEK polymer. Copolymerization of polyetheretherketone with fluorinated monomers can reduce the melt viscosity of polyetheretherketone and enhance interfacial compatibility.

[0151] (2) Add 0.5g of PEEK polymer to 10mL of dichloromethane solvent, and add 2mL of 98% trifluoromethanesulfonic acid dropwise to the solution. Stir the mixture at 300rpm for 2h and the reaction temperature is 60℃. Sulfonic acid groups (-SO3H) are introduced onto the surface of polyetheretherketone. The solution is then separated and purified to obtain PEEK polymer with sulfonic acid groups.

[0152] (3) Take 0.3g of polyethylene glycol ester and add it to 18mL of methanol solution. Then add 0.5g of PEEK polymer powder evenly to the methanol solution within 10min. Stir continuously during the addition process. Finally, add 0.01g of tetrabutyl titanate for catalysis. Stir continuously for 4h and react at 130℃. Use a water separator to remove the water generated during the reaction.

[0153] (4) After the reaction is complete, cool, filter, wash with methanol 4 times, and then dry in a vacuum drying oven at 58°C for 16 h. High-temperature resistant polyethylene glycol ester is obtained.

[0154] The polyethylene glycol ester obtained in Comparative Example 3 was used to prepare a multi-ended feeding twin-screw extrusion pipe, and the other steps were the same as in Example 1.

[0155] The performance test data of the polyethylene glycol esters obtained in Examples 1-4 and Comparative Examples 1-3 are shown in Table 1.

[0156] The performance test data of the multi-ended feeding twin-screw extrusion pipes obtained in Examples 1-4 and Comparative Examples 1-3 are shown in Table 2.

[0157] Table 1: Performance test data of polyethylene glycol esters obtained in Examples 1-4 and Comparative Examples 1-3

[0158]

[0159] Test conditions for retention of acid and alkali tensile strength: 10% H2SO4 / 10% NaOH, soaked at 60℃ for 72h.

[0160] As shown in Table 1, Examples 1-4 are superior to Comparative Examples 1-3 in all aspects, including thermal decomposition temperature, char residue, thermal conductivity, mechanical properties, heat distortion temperature, acid and alkali resistance, and molding performance. Examples 2 and 4 exhibit the best performance, with thermal decomposition temperatures of 365℃ and 368℃, tensile strengths of 42MPa and 45MPa, acid and alkali resistance tensile strength retention rates of 92 / 89% and 95 / 91%, and extrusion shrinkage rates of 1.3% and 1.2%, demonstrating the synergistic enhancement effect of double grafting and efficient dispersion. Example 3 shows a slight decline in performance due to some agglomeration of CNTs due to excessive CNTs, but it is still superior to the comparative examples. Comparative Example 1 has the worst performance in all aspects, while Comparative Examples 2 and 3 show limited performance improvement, proving that double grafting modification is the key to balancing the material's heat resistance, mechanical properties, corrosion resistance, and molding performance.

[0161] Table 2: Performance test data of multi-feed twin-screw extrusion tubing obtained from Examples 1-4 and Comparative Examples 1-3

[0162]

[0163] As shown in Table 2, the pipes prepared in the examples exhibit performance far exceeding that of all comparative examples. This strongly demonstrates the effectiveness of the proposed dual-grafting synergistic enhancement strategy of "heat-resistant skeleton (PEEK) + thermally conductive network (CNT)". Introducing PEEK or CNT alone (as in Comparative Examples 2 and 3) cannot comprehensively solve the problem of high-temperature resistance, especially resistance to uneven high temperatures.

Claims

1. A multi-end feeding twin-screw extrusion pipe, characterized in that, Includes a corrosion-resistant layer, a pipe layer, and an insulation layer; The corrosion-resistant layer is made of vinyl ester resin, which is sprayed onto the inner surface of the pipe layer. The pipe layer is made of high-temperature resistant polyethylene glycol ester. The particles are softened by heating and then extruded through a die to form the pipe layer. The insulation layer uses ceramic fiber felt, and a high-temperature adhesive is evenly applied to the outer surface of the pipe layer, and the ceramic fiber felt is then bonded to the outer surface of the pipe layer. The high-temperature resistant polyethylene glycol ester is prepared by double grafting. First, fully dispersed carbon nanotubes are esterified with their polar groups on the surface of polyether ether ketone (PEEK) to fully disperse them on PEEK. Second, carbon nanotubes and PEEK are simultaneously grafted onto the carboxyl or hydroxyl groups at both ends of the polyethylene glycol ester through a catalyst to form a three-dimensional cross-linked structure.

2. A method for preparing high-temperature resistant polyethylene glycol ester for use in the multi-end feeding twin-screw extrusion pipe of claim 1, characterized in that, Includes the following steps: (1) Sonicate carbon nanotubes in a mixed acid; (2) The ultrasonically treated carbon nanotubes were modified by adding a silane coupling agent; (3) The modified carbon nanotubes were added to an NMP solution containing polyetherimide and mixed and dispersed to form a CNTs-PEI-NMP suspension; (4) Add polyetheretherketone powder to CNTs-PEI-NMP suspension for mixing and dispersion; (5) The CNTs-PEI-NMP suspension after sonication was reacted with polyetheretherketone in hexafluoroisopropanol. After the reaction was completed, the CNTs / PEEK polymer was obtained by filtration. (6) React the CNTs / PEEK polymer with trifluoromethanesulfonic acid to introduce sulfonic acid groups -SO3H on the surface of polyetheretherketone to form a CNTs / PEEK copolymer; (7) The CNTs / PEEK copolymer was double-grafted with polyethylene glycol ester under the catalysis of tetrabutyl titanate; (8) After grafting is completed, the high-temperature resistant polyethylene glycol ester is obtained by cooling.

3. The method for preparing high-temperature resistant polyethylene glycol ester according to claim 2, characterized in that, In step (3), the mixing and dispersion of materials is carried out by ultrasonic treatment or by a material mixing and dispersion device. The specific method of the material mixing and dispersion device is as follows: the NMP solution of polyetherimide is used as the main fluid and pumped into the Venturi mixer at a flow rate of 8-15 m / s by a circulating pump; the slurry premixed with modified carbon nanotubes and a small amount of NMP is drawn into the main fluid by the negative pressure generated at the throat of the Venturi tube and circulated and dispersed for 30-120 min.

4. The method for preparing high-temperature resistant polyethylene glycol ester according to claim 2, characterized in that, In step (4), the mixing and dispersion of materials is carried out by ultrasonic treatment or by a material mixing and dispersion device. The specific method of the material mixing and dispersion device is as follows: the CNTs-PEI-NMP suspension is used as the main fluid and pumped into the Venturi mixer at a flow rate of 8-15 m / s by a circulating pump; the slurry premixed with polyether ether ketone powder and a small amount of NMP is drawn into the main fluid by the negative pressure generated at the throat of the Venturi tube and circulated and dispersed for 30-120 min.

5. The method for preparing high-temperature resistant polyethylene glycol ester according to claim 2, characterized in that, Carbon nanotubes are subjected to ultrasonic treatment in a mixture of sulfuric acid and nitric acid.

6. The method for preparing high-temperature resistant polyethylene glycol ester according to claim 2, characterized in that, Carbon nanotubes were modified using a 2 wt.% silane coupling agent ethanol solution.

7. The method for preparing high-temperature resistant polyethylene glycol ester according to claim 2, characterized in that, Carbon nanotubes were dissolved in a polyetherimide solution and subjected to ultrasonic treatment to form a uniform suspension.

8. The method for preparing high-temperature resistant polyethylene glycol ester according to claim 2, characterized in that, Polyetheretherketone (PEEK) powder was added to a CNTs-PEI-NMP suspension and subjected to intermittent sonication to form a CNTs / PEEK polymer.

9. The method for preparing high-temperature resistant polyethylene glycol ester according to claim 2, characterized in that, A CNTs-PEI-NMP suspension with a volume ratio of (5-6):(6-7) was copolymerized with hexafluoroisopropanol.

10. The method for preparing high-temperature resistant polyethylene glycol ester according to claim 2, characterized in that, The copolymerized CNTs / PEEK polymer reacts with 98% trifluoromethanesulfonic acid to introduce sulfonic acid groups onto the surface of polyetheretherketone.

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