Automobile nylon tube and preparation method thereof

Abstract

The application relates to the technical field of nylon pipe preparation, and particularly discloses an automobile nylon pipe and a preparation method thereof, which is prepared from polyamide PA66 resin, polysiloxane-boron, sulfonated polyarylether sulfone, metal phosphonate, boron nitride nanosheet, maleic anhydride grafted SEBS, antioxidant and lubricant as raw materials; the sulfonic acid groups of the sulfonated polyarylether sulfone are neutralized with ammonia, corrosion medium is consumed and fixed, the coordination effect of the polysiloxane-boron and the amide bond in the polyamide molecular chain is utilized to stabilize the molecular structure, reduce the hydrolysis reaction activity, and the synergistic toughening effect of the maleic anhydride grafted SEBS and the boron nitride nanosheet is utilized to inhibit the initiation and expansion of microcracks. The synergistic effect of the above components delays the mechanical property attenuation of the material in the ammonia water environment, and improves the long-term durability of the nylon pipe.

Description

Technical Field

[0001] This invention belongs to the field of nylon tube manufacturing technology, specifically relating to an automotive nylon tube and its manufacturing method. Background Technology

[0002] The global automotive industry is currently accelerating its transformation towards low-carbon and clean energy, with the goal of "carbon neutrality" driving the industry to actively develop new environmentally friendly fuels to replace traditional fuels. Traditional gasoline-powered vehicles produce pollutants such as carbon dioxide and nitrogen oxides during combustion, which does not align with current environmental protection principles. While hydrogen is a clean fuel, it faces challenges such as high storage and transportation costs and stringent safety requirements. Ammonia, on the other hand, produces only nitrogen and water upon combustion, with no carbon dioxide emissions. Furthermore, its storage and transportation are less difficult than hydrogen's, and its costs are more controllable, leading to its gradual introduction into the automotive industry.

[0003] Currently, ammonia fuel cell vehicles have entered the prototype verification and pilot stage, and there are already several demonstration models at home and abroad: Amogy in the United States tested an ammonia-powered zero-emission semi-trailer truck in 2023, FAW Jiefang in China developed a liquid ammonia direct injection internal combustion engine truck that was ignited in the same year, and the "ammonia-hydrogen" fuel cell bus developed by Fuda Zijin Hydrogen Energy in cooperation with Xiamen King Long has also been put into operation.

[0004] The ammonia storage, transportation, and conversion devices in these vehicles extensively utilize nylon tubing as a core transmission component in their connecting pipelines. These nylon tubings are mostly made of PA66 engineering plastic, which has become the mainstream material in this field due to its high mechanical strength and temperature resistance suitable for typical automotive operating conditions.

[0005] During ammonia transport, nylon tubing comes into contact with two types of moisture: first, the engine compartment experiences significant temperature fluctuations, causing airborne moisture to condense into liquid water on the tubing surface; second, trace amounts of moisture are difficult to completely remove from the ammonia fuel being refueled, and will enter the piping system along with the fuel. Ammonia itself is an alkaline gas, and upon contact with this moisture, it reacts to form chemically corrosive ammonia water. When PA66 nylon tubing is exposed to an ammonia-containing environment for an extended period (typically exceeding 3000 hours, or more than 4 months), the ammonia water gradually acts on the amide bonds in the PA66 molecular chain, causing them to break and thus damaging the PA66 molecular chain structure. As this process continues, microcracks gradually form on the surface of the nylon tubing. These microcracks expand over time, causing a continuous decrease in the mechanical strength of the nylon tubing, potentially leading to ammonia leakage. This not only causes malfunctions in the vehicle's powertrain but also poses safety risks due to the ammonia leak. Summary of the Invention

[0006] The purpose of this invention is to provide an automotive nylon tube and its preparation method to solve the problems mentioned in the background art.

[0007] To achieve the above objectives, the present invention provides the following technical solution:

[0008] An automotive nylon tubing comprises: the following raw materials in parts by weight: 50-70 parts of polyamide PA66 resin, 5-15 parts of polyborosiloxane, 5-12 parts of sulfonated polyarylene ether sulfone, 4-10 parts of metal phosphonate, 1-5 parts of boron nitride nanosheets, 8-18 parts of maleic anhydride-grafted SEBS, 0.3-1 part of antioxidant, and 0.5-2 parts of lubricant.

[0009] Preferably, the metal phosphonate is prepared by reacting aluminum diethylphosphonate with ammonium polyphosphate.

[0010] Preferably, the mass ratio of aluminum diethylphosphonate to ammonium polyphosphate is 1:2 to 1:4.

[0011] Preferably, the polyborosiloxane has a boron content of 8-12 wt% and a molecular weight of 3000-8000 g / mol.

[0012] Preferably, the degree of sulfonation of the sulfonated polyarylene sulfone is 30-50%.

[0013] Preferably, the boron nitride nanosheets have an average particle size of 50-150 nm.

[0014] Preferably, the mass ratio of maleic anhydride-grafted SEBS to polyborosiloxane is 1:0.5-1.2.

[0015] The present invention also provides a method for preparing the above-mentioned automotive nylon tubing, comprising the following steps:

[0016] S1. Pretreatment: Vacuum dry PA66 resin at 80-100℃ for 4-6 hours; pre-disperse boron nitride nanosheets with 5-10% lubricant using a high-speed mixer to form a uniform slurry;

[0017] S2. Segmented melt blending: Pre-mix the pre-dispersed boron nitride nanosheet slurry with maleic anhydride-grafted SEBS for 5-10 minutes, then add dried PA66, polyborosiloxane, sulfonated polyarylether sulfone, metal phosphonate and other remaining components, and melt blend through a twin-screw extruder;

[0018] S3. Granulation: After cooling the extruded strip to 30-50℃, it is granulated to obtain composite material particles;

[0019] S4. Tube Forming: The composite material particles are extruded through a single screw extruder at an extrusion temperature of 240-255℃ and a screw speed of 20-40 rpm. Vacuum cooling is used for forming with a sizing sleeve. The resulting nylon tube has a wall thickness of 1.0-3.0 mm and an inner diameter of 5-20 mm.

[0020] Preferably, in step S2, the boron nitride nanosheets are first pre-dispersed with a portion of the lubricant to form a slurry, and then pre-mixed with the maleic anhydride-grafted SEBS for 5-10 minutes.

[0021] Preferably, the segmented temperatures of the twin-screw extruder in step S2 are set as follows: Zone 1: 240°C, Zone 2: 250°C, Zone 3: 255°C, and Die Head: 250°C.

[0022] Compared with the prior art, the beneficial effects of the present invention are:

[0023] (1) By neutralizing the corrosive medium with sulfonated polyarylether sulfone and ammonia, and by coordinating the amide bonds in the polyboron siloxane and polyamide molecular chains to improve their stability, and by synergistically improving the toughness and crack propagation resistance of the material with boron nitride nanosheets and maleic anhydride-grafted SEBS, the hydrolysis resistance, structural stability and brittleness resistance of nylon tubes in ammonia water environment are significantly enhanced. This composite modification system can effectively delay the performance degradation of nylon tubes under long-term ammonia water action, avoid the leakage risk caused by molecular chain breakage, embrittlement and microcrack propagation, thereby improving the service life and operational reliability of automotive nylon tubes in ammonia water environment.

[0024] (2) By optimizing the preparation process, boron nitride nanosheets and lubricant are first pre-dispersed to form a uniform slurry, and then a segmented blending process is adopted to make it grafted with maleic anhydride SEBS to form a composite toughening structure. This effectively improves the dispersion uniformity and interfacial bonding of functional components in the polyamide matrix, and gives full play to the synergistic reinforcing effect of each component. This process effectively ensures the consistency and stability of nylon tube performance, meets the repeatability and reliability requirements of core indicators such as hydrolysis resistance and crack propagation resistance in mass production, and avoids product performance fluctuations caused by uneven dispersion. Detailed Implementation

[0025] To enable those skilled in the art to more clearly understand the technical solutions described in this invention, the following embodiments are provided for illustration. It should be noted that the following embodiments do not constitute a limitation on the scope of protection claimed by this invention; the described embodiments are merely some embodiments of this invention, and not all embodiments. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without inventive effort are within the scope of protection of this invention.

[0026] Hydrolysis induction period test under ammonia corrosion

[0027] Test objective: To verify the hydrolysis induction period (i.e., the time when amide bonds begin to break) of the material in an ammonia environment, and to determine the initial tolerance duration of the material to the damage of the PA66 molecular chain caused by ammonia.

[0028] 1) Hydrolysis induction period

[0029] Data indicators: The time point at which the amide bond in the PA66 molecular chain is first detected to break (unit: h). It is usually judged by a 5% decrease in the absorbance of the characteristic peak of the amide bond in the infrared spectrum or a 5% decrease in the tensile strength. The target value should be ≥1500h (under accelerated aging conditions).

[0030] Reference standards: GB / T3512-2014 "Accelerated aging and heat resistance test of vulcanized rubber or thermoplastic rubber in hot air" (environmental control part) and GB / T6040-2002 "General rules for infrared spectroscopy analysis methods" (amide bond detection part).

[0031] Test Method: A type 1A tensile specimen (4mm thickness, 10mm width, 50mm gauge length) was prepared according to GB / T1040.2-2022. Simultaneously, a transparent film sample with a thickness of 0.1-0.2mm was prepared (for infrared detection). All samples were vacuum-dried at 80-100℃ for 4 hours to remove residual moisture. A 5% ammonia solution (simulating the upper limit of ammonia concentration in actual working conditions) was prepared and poured into a container in a sealed aging chamber. The aging temperature was controlled at 85℃ (to accelerate the hydrolysis reaction and simulate an actual service life of more than 4 months), with a relative humidity ≥90%. The tensile specimen and film sample were suspended in the aging chamber (not directly in contact with the liquid surface, but only exposed to a mixture of ammonia vapor and condensate). Samples were taken and tested at 0h (initial), 200h, 500h, 800h, 1000h, 1200h, 1500h, and 1800h of aging. The results were analyzed using an infrared spectrometer (4cm resolution). -1 Scanning range 4000-400cm -1 ) Detect the amide I band (1630-1650 cm) of the thin film sample -1 ) and amide II band (1530-1550cm) -1 The absorbance was measured, and the tensile strength of the specimen was tested according to GB / T1040.2-2022. When any index first showed a 5% decrease, the aging time at this time was recorded, which is the hydrolysis induction period.

[0032] 2) Changes in tensile strength

[0033] Data indicators: tensile strength values ​​(unit: MPa) at different aging time points (0h, 500h, 1000h, 1500h, 2000h, 3000h) and the rate of change from the initial value (Δσ = (strength after aging - initial strength) / initial strength × 100%), with the target being Δσ ≥ -20% after 3000h aging (i.e., the strength decrease does not exceed 20%).

[0034] Reference standard: GB / T1040.2-2022 "Determination of tensile properties of plastics - Part 2: Test conditions for molded and extruded plastics".

[0035] Test method: Same as step 1 of "Hydrolysis Induction Period". Prepare 5 parallel tensile specimens for each aging time point, ensuring that the specimens are free of bubbles and scratches. In an environment of 23℃ and 50%RH, use an electronic universal testing machine to test the tensile strength of the initial (0h) specimens at a tensile rate of 50mm / min, and take the average value of the 5 specimens as the initial strength σ0. According to the aging conditions of step 2 of "Hydrolysis Induction Period", take out the specimens at each preset aging time point, rinse the surface with deionized water to remove residual ammonia, vacuum dry at 80℃ for 2h, and then test the tensile strength under the same environment and equipment parameters, and take the average value σ0. t According to the formula Δσ=(σ t Calculate the rate of change of tensile strength at each time point using (σ0) / σ0×100%.

[0036] 3) Integrity of amide bonds

[0037] Data indicators: Amide I band at different aging time points (1640±5cm) -1 ) and amide II band (1540±5cm) -1 The absorbance retention rate (η = absorbance after aging / initial absorbance × 100%) is set at η ≥ 85% after 3000h aging (indicating low degree of amide bond breakage).

[0038] Reference standards: GB / T6040-2002 General Rules for Infrared Spectroscopy Analysis, GB / T2918-2018 Standard Environment for Conditioning and Testing of Plastic Specimens.

[0039] Test method: Automotive nylon tubing raw material was pressed into a transparent film with a thickness of 0.15 mm using a flat vulcanizing machine (pressing temperature 250℃, pressure 10MPa, holding pressure for 5 min). The film was then cut into 20 mm × 20 mm samples and vacuum dried at 80℃ for 4 h before use. The samples were then subjected to Fourier transform infrared spectroscopy (4 cm⁻¹ resolution) at 23℃ and 50%RH. -1 Scanning range 4000-400cm -1 The infrared spectrum of the test sample was analyzed, and the amide I band (1640±5 cm⁻¹) was calculated using the baseline method. -1 ) and amide II band (1540±5cm) -1 The initial absorbance A0 of the film was determined. A 5% ammonia solution was prepared, and the sealed aging chamber was controlled at 85℃ and relative humidity ≥90%. The film sample was placed in the chamber for aging, and samples were taken at 1000h, 2000h, and 3000h. After rinsing with deionized water, the film was dried at 80℃ for 2h. The characteristic peak absorbance A of the sample at each time point was measured under the same instrument parameters. t According to the formula η=A tThe absorbance retention rate is calculated using / A0×100%, with a target of η≥85% after 3000h aging to indicate a low degree of amide bond breakage. When η<85%, the integrity of the amide bond is considered significantly impaired.

[0040] Microcrack propagation suppression performance test

[0041] Test objective: To verify the microcrack initiation and propagation behavior of the material in an ammonia environment, to evaluate the inhibitory effect of the "BNNS-SEBS" composite toughening unit on microcracks, and to ensure that the nylon tube does not exhibit macroscopic cracking.

[0042] 1) Microcrack initiation time

[0043] Data indicators: The aging time (unit: h) at which observable microcracks (length ≥ 5 μm, width ≥ 1 μm) first appear on the sample surface in an ammonia environment. The target value is ≥ 2000 h (under accelerated aging conditions).

[0044] Reference standards: GB / T35465-2017 "Environmental stress cracking test method for plastics", GB / T1843-2021 "Impact test method for plastic cantilever beams" (pre-fabricated notched part of the spline).

[0045] Test Method: A-type cantilever beam impact specimens with a length of 80 mm, a width of 10 mm, and a thickness of 4 mm were prepared according to GB / T1843-2021. A 0.5 mm deep, 45° notch was pre-made in the middle of the specimen using a V-notch cutter to simulate initial micro-defects. Ten specimens were prepared for each group and vacuum dried at 80-100℃ for 4 hours. A 5% ammonia solution was prepared, and the sealed aging chamber was controlled at 85℃ and relative humidity ≥90%. The specimens were placed in the chamber with the notch facing upwards to ensure sufficient contact between the notch area and ammonia vapor and condensate (refer to the environmental control requirements of GB / T35465-2017). Two samples were taken at aging time points of 0h, 500h, 1000h, 1500h, 2000h, and 2500h, respectively. After rinsing with deionized water and drying, the area near the notch was observed using a metallographic microscope with a magnification of 500x or a scanning electron microscope (SEM) with an accelerating voltage of 10kV. The crack size in the observed area was measured using Image-ProPlus image analysis software. When a microcrack with a length ≥5μm and a width ≥1μm was first discovered, the aging time at this time was recorded as the microcrack initiation time. The median value of 10 samples was taken as the final result, and the target value should be ≥2000h.

[0046] 2) Crack propagation rate

[0047] Data indicators: The average increase in crack length per unit time after microcrack initiation (unit: μm / h), with a target of ≤0.05μm / h propagation rate within a 3000h aging cycle (indicating slow crack propagation and no macroscopic risk).

[0048] Reference standards: GB / T35465-2017 "Plastics Environmental Stress Cracking Test Method", GB / T2572-2007 "Fiber Reinforced Plastics Average Linear Expansion Coefficient Test Method" (for dimensional measurement accuracy reference).

[0049] Test Method: Five samples with microcracks already initiated were selected from the "Microcrack Initiation Time Test" and placed in a sealed aging environment of 5% ammonia water at 85℃ and relative humidity ≥90% (compliant with GB / T35465-2017 requirements). After microcrack initiation, samples were taken at 100-hour intervals (e.g., 2100h, 2200h, 2300h…3000h). After each sampling, the samples were rinsed with deionized water and dried. Clear images of the cracks were captured using a SEM with a magnification of 1000-2000x. The straight-line distance from the notch root to the crack tip (i.e., crack length L) was measured using image analysis software at each observation time. n ).

[0050] According to the formula v=(L n+1 -L n The instantaneous crack propagation rate is calculated using Δt / Δt (where Δt = 100h). The average value of all instantaneous rates is taken as the average crack propagation rate. The target is that the crack propagation rate is ≤0.05μm / h within a 3000h aging cycle to indicate that the crack propagation is slow and there is no macroscopic risk.

[0051] 3) Surface morphology changes

[0052] Data indicators: number of microcracks (unit: cracks / mm²), maximum crack depth (unit: μm), and surface roughness Ra (unit: μm) on the sample surface at different aging time points (0h, 1000h, 2000h, 3000h). The target is that after 3000h, the number of microcracks ≤ 5 cracks / mm², the maximum crack depth ≤ 20μm, and the Ra change rate ≤ 50%.

[0053] Reference standards: GB / T30767-2014 "Non-contact (optical) method for determination of surface roughness and surface profile of plastics", GB / T16594-2008 "Optical interferometry for measurement of micrometer-scale length" (depth measurement part).

[0054] Test method: The raw material of automotive nylon tubing was pressed into smooth samples of 50mm×50mm×2mm (initial surface Ra value ≤0.2μm), and then vacuum dried at 80℃ for 4h before use. Three samples were prepared for each aging time point. The samples were placed in a sealed aging environment of 5% ammonia water at 85℃ and relative humidity ≥90% for complete exposure. Samples were taken at aging time points of 0h, 1000h, 2000h, and 3000h, respectively, rinsed with deionized water, and then dried. Referring to GB / T30767-2014, the surface roughness Ra value of the samples was tested using a non-contact optical profilometer (resolution 0.01 μm), with 5 points tested per sample and the average value taken. At least 5 random areas (each area 0.1 mm²) of the sample surface were photographed using SEM at 500x and 2000x magnification, and the number of microcracks was counted and the number of cracks per unit area was calculated. Referring to GB / T16594-2008, the maximum crack depth was measured using an atomic force microscope (AFM, scanning range 10 μm × 10 μm). The rate of change of Ra after 3000 h of aging from the initial value was calculated (ΔRa = (aged Ra - initial Ra) / initial Ra × 100%), with the target being ≤5 microcracks / mm², maximum crack depth ≤20 μm, and Ra change rate ≤50% after 3000 h.

[0055] Mechanical property retention rate test under ammonia water environment

[0056] Test objective: To verify the mechanical property stability of the material under long-term ammonia corrosion, and to ensure the structural integrity and load-bearing capacity of the nylon tube in actual working conditions (such as ammonia fuel transmission).

[0057] 1) Tensile strength retention rate

[0058] Data indicators: After 3000h aging in ammonia water, the percentage of tensile strength to the initial value (Kσ = tensile strength after aging / initial tensile strength × 100%), with a target value of Kσ ≥ 80% (indicating good strength retention after long-term corrosion).

[0059] Reference standard: GB / T1040.2-2022 "Determination of tensile properties of plastics - Part 2: Test conditions for molded and extruded plastics".

[0060] Test Method: Tensile specimens of type 1A, 4 mm thick, 10 mm wide, and 50 mm gauge length, were prepared according to GB / T1040.2-2022. Ten specimens were prepared for each group (5 for initial testing and 5 for post-aging testing). All specimens were vacuum-dried at 80-100℃ for 4 hours. Under a standard environment of 23℃ and 50%RH, the tensile strength of the five initial specimens was tested using an electronic universal testing machine at a tensile rate of 50 mm / min, and the average value was taken as the initial strength σ0. The remaining five specimens were completely immersed in a 5% ammonia solution (liquid level 20 mm above the specimen) and placed in an 85℃ constant temperature water bath for sealed aging for 3000 hours. During this period, the ammonia solution was changed weekly to ensure stable concentration. After aging, the specimens were removed, rinsed three times with deionized water, and vacuum-dried at 80℃ for 2 hours. The tensile strength was then tested under the same standard environment and equipment parameters, and the average value was taken as the post-aging strength σ0. 3000 According to the formula Kσ=(σ 3000 The tensile strength retention rate is calculated by multiplying ( / σ0) by 100%, with a target value of Kσ≥80% to indicate good strength retention after long-term corrosion.

[0061] 2) Elongation at break retention rate

[0062] Data indicators: After 3000h ammonia aging, the percentage of elongation at break to the initial value (Kε = elongation at break after aging / initial elongation at break × 100%), the target value Kε≥75% (indicating that the material still maintains good toughness and is not easy to break brittle).

[0063] Reference standard: GB / T1040.2-2022 "Determination of tensile properties of plastics - Part 2: Test conditions for molded and extruded plastics".

[0064] Test Method: Tensile specimens of type 1A, 4 mm thick, 10 mm wide, and 50 mm gauge length, were prepared according to GB / T1040.2-2022. Ten specimens were prepared for each group (5 for initial testing and 5 for post-aging testing). After vacuum drying at 80-100℃ for 4 hours, they were ready for use. Under a standard environment of 23℃ and 50%RH, the initial 5 specimens were tested using an electronic universal testing machine equipped with an extensometer (or displacement sensor) at a tensile rate of 50 mm / min. The elongation at break of each specimen was recorded simultaneously, and the average value was taken as the initial elongation at break ε0. The remaining 5 specimens were completely immersed in a 5% ammonia solution (liquid level 20 mm above the specimen) and placed in an 85℃ constant temperature water bath for sealed aging for 3000 hours, with the ammonia solution changed weekly. After aging, the specimens were rinsed three times with deionized water and vacuum dried at 80℃ for 2 hours. Under the same test conditions, the elongation at break was recorded simultaneously, and the average value was taken as the post-aging elongation at break ε0. 3000 According to the formula Kε=(ε 3000The elongation at break retention rate is calculated by multiplying ( / ε0) by 100%, with a target value of Kε≥75% to indicate that the material still maintains good toughness and is not prone to brittle fracture.

[0065] 3) Burst Pressure Test Method

[0066] Data indicators: After 3000h ammonia aging, the burst pressure value (unit: MPa) and burst pressure retention rate (Kp = burst pressure after aging / initial burst pressure × 100%) of the nylon pipe. The target is that the burst pressure after aging is ≥10MPa and Kp ≥85% (meeting the pressure resistance requirements of the ammonia fuel transmission pipeline).

[0067] Reference standard: GB / T6111-2018 "Determination of internal pressure resistance of thermoplastic piping systems for fluid transportation".

[0068] Test Method: Cut automotive nylon tubing prepared according to the method of this invention (wall thickness 1.0-3.0 mm, inner diameter 5-20 mm, example: inner diameter 10 mm, wall thickness 2 mm) into 100 mm long segments (length ≥ 10 times the pipe diameter, conforming to GB / T6111-2018 requirements). Prepare 6 segments per group (3 for initial testing, 3 for post-aging testing). According to GB / T6111-2018 requirements, connect both ends of the segments to a pressure resistance testing device. Using deionized water as the medium, slowly increase the pressure at 0.1 MPa / s until the tubing ruptures at 23°C. Record the burst pressure value of each segment and take the average as the initial burst pressure P0. Fill the remaining 3 segments with a 5% ammonia solution, seal both ends with sealing joints (ensuring no air bubbles inside), and age them in an 85°C constant temperature chamber for 3000 hours. During this period, check the sealing status once a month to prevent ammonia leakage. After aging, the ammonia solution in the pipe section was emptied and the inner wall was rinsed three times with deionized water. The burst pressure was tested under the same environment and pressure increase rate, and the average value was taken as the burst pressure P after aging. 3000 According to the formula Kp=(P 3000 The burst pressure retention rate is calculated by multiplying ( / P0) by 100%, with the target being a burst pressure ≥10MPa and Kp ≥85% after aging, in order to meet the pressure resistance requirements of the ammonia fuel transmission pipeline.

[0069] Example 1

[0070] An automotive nylon tubing, by weight, comprises the following raw materials: 60 parts polyamide PA66 resin, 10 parts polyborosiloxane, 8 parts sulfonated polyarylethersulfone, 7 parts metal phosphonate, 3 parts boron nitride nanosheets, 10 parts maleic anhydride-grafted SEBS, 0.6 parts antioxidant, and 1.2 parts lubricant.

[0071] The preparation method of polyamide PA66 resin is as follows: using adipic acid and hexamethylenediamine as monomers, adipic acid and hexamethylenediamine are first added to deionized water in an equimolar ratio, and stirred for 1-2 hours under nitrogen protection and at 80-90℃ to form a 60-65% concentration aqueous solution of adipamide (nylon 66 salt); then the nylon 66 salt aqueous solution is transferred to a high-pressure reactor, heated to 220-230℃, and the pressure inside the reactor is controlled at 1.8-2.0 MPa. The reaction is maintained at this temperature and pressure for 2-3 hours. The water generated during the reaction is continuously drained; then the pressure inside the reactor is slowly reduced to atmospheric pressure while the temperature is raised to 250-260℃, and the reaction continues for 1.5-2 hours for polycondensation. The viscosity of the reaction system is monitored in real time using a viscometer, and the reaction is stopped when the viscosity index reaches 2.8; finally, the reaction product is granulated underwater and dried (vacuum dried at 100-110℃ for 4-5 hours) to obtain polyamide PA66 resin chips with a number average molecular weight of about 25,000, a melting point of 260℃, and a moisture content of ≤0.1% (before drying).

[0072] The preparation method of polyborosiloxane is as follows: Boric acid, hydroxyl-terminated polydimethylsiloxane (number average molecular weight 3000-4000 g / mol), and tetraethyl orthosilicate are added to a four-necked flask at a molar ratio of boric acid:hydroxyl-terminated polydimethylsiloxane:tetraethyl orthosilicate = 1:8:1.2. Toluene is used as solvent (the amount of solvent is 1.5 times the total mass of raw materials), and p-toluenesulfonic acid is added as catalyst (the amount is 0.5% of the total mass of raw materials). The reaction is carried out under nitrogen protection and refluxed at 110-120℃ for 4-5 hours. During the reaction, the water generated was separated by a water separator. After the reaction was completed, toluene and unreacted small molecules were removed by vacuum distillation (temperature 120-130℃, vacuum degree -0.095MPa). After cooling to room temperature, a pale yellow, transparent, viscous polyborosiloxane was obtained. Its boron content was determined to be 10wt% (by inductively coupled plasma optical emission spectrometry, ICP-OES), its molecular weight was 5000g / mol (by gel permeation chromatography, with tetrahydrofuran as the solvent), and its viscosity at 25℃ was 8000mPa·s.

[0073] The preparation method of sulfonated polyarylene ether sulfone is as follows: using polyarylene ether sulfone (number average molecular weight approximately 28,000) and chlorosulfonic acid as raw materials, the polyarylene ether sulfone is added to dichloromethane solvent (the amount of solvent is 8 times the mass of polyarylene ether sulfone) at a mass ratio of polyarylene ether sulfone:chlorosulfonic acid = 1:1.2, and stirred at 25-30℃ until completely dissolved; then, chlorosulfonic acid is slowly added dropwise over a time controlled at 1-1.5 hours, keeping the temperature below 35℃ during the addition process; after the addition is complete, the reaction continues at 30℃ for 2-2.5 hours; after the reaction is complete, the reaction mixture is... The reaction solution was slowly poured into an ice-water mixture (the volume of ice water was 5 times the volume of the reaction solution), and the mixture was stirred to precipitate. The precipitate was collected by filtration and repeatedly washed with deionized water until the pH of the washing solution was 6-7. The precipitate was then vacuum dried at 80-90℃ for 6-8 hours. After drying, sulfonated polyarylene ether sulfone was obtained. Its degree of sulfonation was determined to be 40% by potentiometric titration (0.1mol / L NaOH solution as titrant), its number-average molecular weight was 35000 (GPC test, solvent was N,N-dimethylformamide), and its glass transition temperature (Tg) was 180℃.

[0074] The preparation method of metal phosphonates is as follows: aluminum diethylphosphonate (purity 99.5%, particle size 1μm) and ammonium polyphosphate (degree of polymerization n=1000, purity 99%) are used as raw materials. They are added to a high-speed mixer at a mass ratio of aluminum diethylphosphonate:ammonium polyphosphate = 1:3 and mixed at 1500 rpm for 15-20 minutes to ensure uniform mixing. The mixture is then transferred to a twin-screw extruder, and the extrusion temperature is set to 180-190℃ and the screw speed is 25 rpm. The mixture is allowed to melt and react in the barrel for 2 hours. The extruded strip is cooled to below 40℃ by water cooling (25℃) and then pelletized (particle size 2mm) by a pelletizer to obtain metal phosphonate particles.

[0075] The preparation method of boron nitride nanosheets is as follows: using hexagonal boron nitride powder (purity 99.9%, particle size 5-10 μm) as raw material, deionized water and sodium dodecylbenzenesulfonate (dispersant, amount 2% of the mass of hexagonal boron nitride) are added to prepare a suspension with a concentration of 5%; the suspension is transferred to an ultrasonic cell disruptor and ultrasonically exfoliated under the conditions of 800W power and ultrasonic time of 30 minutes (5 seconds of ultrasonication followed by 2 seconds of pause); after ultrasonication, the suspension is centrifuged at 8000 rpm for 15 minutes. Remove large particles that have not been peeled off; take the supernatant, add silane coupling agent KH550 (5% of boron nitride mass), and stir at 60℃ for 2 hours to modify the surface; after the reaction, centrifuge again (8000 rpm, 10 minutes), collect the precipitate, and vacuum dry at 80℃ for 4-5 hours; after drying, boron nitride nanosheets are obtained, and the average particle size is 100 nm (D50=100 nm), the thickness is 1-5 nm, and the specific surface area is 50 m² / g (determined by BET method) as measured by laser particle size analyzer.

[0076] The preparation method of maleic anhydride-grafted SEBS is as follows: SEBS (styrene-ethylene-butene-styrene block copolymer, styrene content 30%, number average molecular weight 80,000), maleic anhydride (MAH), and dicumyl peroxide are used as raw materials and added to a high-speed mixer at a mass ratio of SEBS:MAH:DCP=100:5:0.8. The mixture is stirred at 2000 rpm for 20 minutes to ensure uniform mixing. The mixture is then transferred to a twin-screw extruder, and the extrusion temperature is set to 160-170℃ (zone 1 160℃, zone 2 165℃, zone 3 170℃, die head 165℃), and the screw speed is 35 rpm for melt grafting reaction. The extruded strip is cooled by water cooling (25℃) and then pelletized (particle size 3mm) to obtain maleic anhydride-grafted SEBS. The grafting rate is determined to be 1.5% by acid-base titration, and the Shore A hardness is 60.

[0077] The preparation method of the antioxidant is as follows: antioxidant 1010 (pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate, purity 99%) and antioxidant 168 (tris(2,4-di-tert-butylphenyl)phosphite, purity 99%) are added to a mixer at a mass ratio of 1:1 and mixed at 1000 rpm for 30 minutes to obtain a uniform compound antioxidant.

[0078] The preparation method of the lubricant (zinc stearate) is as follows: using stearic acid and zinc oxide as raw materials, add them to the reaction vessel at a molar ratio of stearic acid:zinc oxide = 2:1, add deionized water (1.2 times the mass of stearic acid), stir and react at 80-90℃ for 2-3 hours to generate zinc stearate precipitate; after the reaction is completed, filter and collect the precipitate, wash it with deionized water 3-4 times to remove unreacted impurities; dry the precipitate at 100-110℃ for 4-5 hours, pulverize it and pass it through a 200-mesh sieve to obtain zinc stearate powder with a purity of 99% and a melting point of 120℃.

[0079] A method for preparing automotive nylon tubing includes the following steps:

[0080] S1. Pretreatment: 60 parts of polyamide PA66 resin slices were evenly spread on a stainless steel tray (slice thickness ≤ 2 cm), placed in a vacuum drying oven, and dried at 90℃ and -0.095 MPa for 5 hours. After drying, the resin slices were immediately transferred to a desiccator containing anhydrous calcium chloride and cooled to room temperature (23℃). The moisture content of the resin was tested by a Karl Fischer moisture analyzer and found to be ≤ 0.05%. 10% of the total lubricant (i.e., 0.12 parts of zinc stearate) and 3 parts of boron nitride nanosheets were added to a high-speed mixer. The mixing speed was set to 3000 rpm and the mixing time to 15 minutes. During the mixing process, 25℃ cooling water was introduced through the jacket of the mixer wall to control the temperature of the mixing system to not exceed 40℃. After mixing, a sample was taken and observed by scanning electron microscopy to confirm that the boron nitride nanosheets were monodisperse or a few pieces were stacked, with no obvious agglomerates (agglomerate particle size ≤ 500 nm), forming a uniform "boron nitride nanosheet-lubricant" slurry.

[0081] S2. Segmented melt blending: The "boron nitride nanosheet-lubricant" slurry prepared in S1 and 10 parts of maleic anhydride-grafted SEBS are put into a low-speed mixer. The speed is set to 500 rpm and the mixing time is 8 minutes. After thorough mixing, a "maleic anhydride-grafted SEBS-boron nitride nanosheet" composite toughening unit is formed. These composite toughening units, 60 parts of dried polyamide PA66 resin, 10 parts of polyborosiloxane, 8 parts of sulfonated polyarylethersulfone, 7 parts of metal phosphonate, 0.6 parts of antioxidant, and the remaining 1.08 parts of zinc stearate (total lubricant 1.2 parts minus 0.12 parts for pre-dispersion) are sequentially fed into the main hopper of a twin-screw extruder in the order of "composite toughening unit → polyamide PA66 resin → other additives". The segment temperatures of the twin-screw extruder are set as follows: Zone 1 (feeding section) 240℃, Zone 2 (melting section) 250℃, Zone 3 (homogenization section) 255℃, and die head (extrusion section) 250℃. The screw speed is 30 rpm, the vacuum degree is -0.08 MPa (devouring section), and the material residence time in the barrel is about 3 minutes. Finally, a continuous, smooth, bubble-free strip is obtained by extrusion.

[0082] S3. Granulation: The extruded strip is introduced into a water cooling tank (water temperature 25℃, tank length 2m) and cooled to 40℃; then, the cooled strip is fed into a pelletizer by a traction machine (traction speed 1.5m / min), the pellet length is 3mm, and the particle size deviation is ≤±0.2mm; the cut particles are placed in a vacuum drying oven and dried for 2 hours at 80℃ and vacuum degree -0.09MPa to remove the moisture adsorbed on the particle surface, and the special composite material particles for automotive nylon tubes are obtained. The particles are milky white and uniform, without adhesion or fragments.

[0083] S4. Pipe Forming: The dried composite material particles are fed into the hopper of a single-screw extruder. An agitator is installed in the hopper to prevent particle bridging. Set the segment temperatures of the single-screw extruder as follows: hopper segment 240℃, zone 1 245℃, zone 2 250℃, zone 3 252℃, and die head 250℃. Preheat the machine for 30 minutes to ensure that the temperature of each segment is stable within ±1℃ of the set value.

[0084] Example 2

[0085] This embodiment differs from Embodiment 1 in the following ways, while the rest is the same as in Embodiment 1, as detailed below:

[0086] An automotive nylon tubing, by weight, comprises the following raw materials: 50 parts polyamide PA66 resin, 15 parts polyborosiloxane, 10 parts sulfonated polyarylethersulfone, 10 parts metal phosphonate, 5 parts boron nitride nanosheets, 18 parts maleic anhydride-grafted SEBS, 1.0 part antioxidant 1076, and 2.0 parts lubricant.

[0087] The preparation method of polyborosiloxane is as follows: using boric acid, hydroxyl-terminated polydimethylsiloxane (number average molecular weight 6000-7000 g / mol), and tetraethyl orthosilicate as raw materials, they are added to a four-necked flask at a molar ratio of boric acid: hydroxyl-terminated polydimethylsiloxane: tetraethyl orthosilicate = 1:10:1.5. Toluene is used as solvent (the amount of solvent is 1.8 times the total mass of the raw materials), and p-toluenesulfonic acid (the amount of catalyst is 0.6% of the total mass of the raw materials) is added. Under nitrogen protection, 12 The reaction was refluxed at 0-130℃ for 5-6 hours, with a water separator continuously separating the water produced by the reaction. After the reaction was completed, the solvent and small molecule impurities were removed by vacuum distillation (temperature 130-140℃, vacuum degree -0.095MPa). After cooling to room temperature, a pale yellow viscous polyborosiloxane was obtained. The boron content was determined to be 12wt% by ICP-OES, the molecular weight was 8000g / mol by GPC (solvent tetrahydrofuran), and the viscosity at 25℃ was 12000mPa・s.

[0088] The preparation method of metal phosphonates is as follows: aluminum diethylphosphonate (purity 99.5%, particle size 1μm): ammonium polyphosphate (degree of polymerization n=1000, purity 99%) is added to a high-speed mixer at a mass ratio of 1:4 and mixed at 1800 rpm for 20-25 minutes until uniform; transferred to a twin-screw extruder, the extrusion temperature is set to 185-195℃, the screw speed is 28 rpm, and the melt reaction is carried out for 2.5 hours; the extruded strip is cooled to below 40℃ by water at 25℃ and then granulated to obtain metal phosphonate particles.

[0089] The preparation method of boron nitride nanosheets is as follows: Hexagonal boron nitride powder (purity 99.9%, particle size 10-15μm) is used as raw material, and deionized water and sodium dodecylbenzenesulfonate (dispersant amount is 2.5% of boron nitride mass) are added to prepare a 6% concentration suspension; the ultrasonic cell disruptor power is 900W, the ultrasonic time is 40 minutes (sonicating for 6 seconds and stopping for 2 seconds); after ultrasonication, the mixture is centrifuged at 9000rpm for 20 minutes to remove large particles; silane coupling agent KH550 (amount is 6% of boron nitride mass) is added to the supernatant, and the mixture is stirred at 65℃ for 2.5 hours; the mixture is centrifuged again (9000rpm, 15 minutes), the precipitate is collected, and vacuum dried at 85℃ for 5-6 hours; the average particle size is 150nm, the thickness is 2-6nm, and the specific surface area is 45m² / g, as measured by a laser particle size analyzer.

[0090] The lubricant is prepared as follows: using stearic acid and ethylenediamine as raw materials, they are added to a reaction vessel at a molar ratio of stearic acid:ethylenediamine = 2:1. Xylene is added as a solvent (the amount is twice the mass of stearic acid). The reaction is carried out under nitrogen protection and refluxed at 140-150℃ for 3-4 hours to generate ethylene bis-stearamide. After the reaction is completed, the mixture is cooled to room temperature to precipitate crystals. The crystals are collected by filtration, washed 2-3 times with ethanol, vacuum dried at 110-120℃ for 5 hours, pulverized, and passed through an 180-mesh sieve to obtain ethylene bis-stearamide powder with a purity of 98.5% and a melting point of 145℃.

[0091] The preparation method of antioxidant 1076 is as follows: methyl β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate and pentaerythritol are used as raw materials and added to a reaction vessel at a molar ratio of 4.2:1. Sodium methoxide is added as a catalyst, and the reaction is carried out under nitrogen protection at 120-130℃ for 4-5 hours. After the reaction, deionized water is added to wash away the catalyst, and the mixture is allowed to stand and separate into layers. The organic phase is then collected. Unreacted raw materials are removed by vacuum distillation (temperature 130-140℃, vacuum degree -0.09MPa). After cooling, the mixture is crystallized to obtain antioxidant 1076 crystals with a purity of 99% and a melting point of 50-55℃.

[0092] A method for preparing automotive nylon tubing includes the following steps:

[0093] S1. Pretreatment: Spread 50 parts of polyamide PA66 resin chips on a stainless steel tray and place them in a vacuum drying oven. Set the drying temperature to 80℃, the vacuum degree to -0.095MPa, and the drying time to 6 hours. After drying, transfer them to a desiccator to cool to room temperature. The moisture content was tested by a Karl Fischer moisture analyzer and found to be ≤0.05%. Take 2.0 parts of 10% (i.e., 0.2 parts) of the total amount of ethylene bis-stearamide and add them to a high-speed mixer along with 5 parts of 150nm boron nitride nanosheets. Set the mixing speed to 3500rpm and the mixing time to 20 minutes. The jacket is circulated with 25℃ cooling water for temperature control. After mixing, SEM observation showed that there were no obvious agglomerates in the nanosheets (agglomerate particle size ≤600nm), forming a uniform slurry.

[0094] S2. Segmented melt blending: The "maleic anhydride-grafted SEBS-boron nitride nanosheets" composite toughening unit, dried PA66, 15 parts of polyborosiloxane (12wt% boron content), 10 parts of sulfonated polyarylethersulfone, 10 parts of metal phosphonate (1:4 ratio), 1.0 part of antioxidant 1076, and the remaining 1.8 parts of ethylene bis-stearamide are fed into a twin-screw extruder; the segmented temperatures are 240℃ in zone 1, 250℃ in zone 2, 255℃ in zone 3, and 250℃ at the die head, and the screw speed is adjusted to 25 rpm; the material residence time is about 3.5 minutes, and the surface of the extruded strip is smooth and free of bubbles.

[0095] S3. Granulation: The operation is the same as in Example 1.

[0096] S4. Tube Forming: The granulated composite material particles are fed into a single-screw extruder. The segmented temperatures are set as follows: hopper section 245℃, zone 1 250℃, zone 2 255℃, zone 3 255℃, and die head 250℃, for 30 minutes of preheating. The single-screw speed is set to 20 rpm. After the material is stably extruded from the die head with an inner diameter of 8mm, it is introduced into a custom-made vacuum sizing sleeve with an inner diameter of 8mm (vacuum degree -0.06MPa). After cooling in a secondary water cooling tank, the traction machine speed is adjusted to 1.8m / min, and the material is cut into 1m / segment. The resulting nylon tube specifications are: wall thickness 1.5mm (deviation ±0.1mm), inner diameter 8mm (deviation ±0.05mm), and no defects in appearance.

[0097] Example 3

[0098] This embodiment differs from Embodiment 1 in the following ways, while the rest is the same as in Embodiment 1, as detailed below:

[0099] An automotive nylon tubing, by weight, comprises the following raw materials: 70 parts polyamide PA66 resin, 6.67 parts polyborosiloxane, 5 parts sulfonated polyarylethersulfone, 4 parts metal phosphonate, 1 part boron nitride nanosheets, 8 parts maleic anhydride-grafted SEBS, 0.3 parts antioxidant 1010, and 0.5 parts lubricant.

[0100] The preparation method of polyborosiloxane is as follows: Boric acid, hydroxyl-terminated polydimethylsiloxane, and tetraethyl orthosilicate are added to a four-necked flask at a molar ratio of boric acid:hydroxyl-terminated polydimethylsiloxane:tetraethyl orthosilicate = 1:6:1.0. Toluene is used as the solvent, and p-toluenesulfonic acid is added. The reaction is carried out under nitrogen protection and reflux at 100-110℃ for 3-4 hours, and the water generated by the reaction is separated in real time using a water separator. After the reaction is completed, the solvent and unreacted small molecules are removed by vacuum distillation (temperature 110-120℃, vacuum degree -0.095MPa). After cooling to room temperature, a light yellow low-viscosity polyborosiloxane is obtained. The boron content is determined to be 8wt% by ICP-OES, the molecular weight is 3000g / mol by GPC (solvent tetrahydrofuran), and the viscosity at 25℃ is 4000mPa·s.

[0101] The preparation method of metal phosphonates is as follows: aluminum diethylphosphonate (purity 99.5%, particle size 1μm) and ammonium polyphosphate (degree of polymerization n=800, purity 99%) are added to a high-speed mixer at a mass ratio of 1:2. The mixer is set to 1600 rpm and mixed for 15-20 minutes to ensure uniform dispersion. The mixture is then transferred to a twin-screw extruder, and the extrusion temperature is set to 175-185℃, the screw speed is 26 rpm, and the melt reaction is carried out for 1.5 hours. The extruded strip is cooled to below 38℃ by water at 25℃ and then cut into granules with a particle size of 2mm by a pelletizer, which is the finished metal phosphonate product.

[0102] The preparation method of boron nitride nanosheets is as follows: using hexagonal boron nitride powder (purity 99.9%, particle size 3-5 μm) as raw material, deionized water and sodium dodecylbenzenesulfonate (dispersant amount is 1.8% of boron nitride mass) are added to prepare a 4% suspension; the suspension is transferred into an ultrasonic cell disruptor, the power is set to 700W, the ultrasonic time is 25 minutes (ultrasound for 4 seconds and stop for 2 seconds, adapted to the exfoliation requirements of small-diameter nanosheets, avoiding excessive ultrasonication that may cause structural damage); after ultrasonication, the nanosheets are subjected to 7... Centrifuge at 000 rpm for 15 minutes to remove unpeeled coarse particles; take the supernatant and add silane coupling agent KH550 (4% of boron nitride mass), stir at 55℃ for 1.5 hours to modify the surface; after modification, centrifuge again (7000 rpm, 10 minutes), collect the precipitate and vacuum dry at 75℃ for 4 hours; according to laser particle size analyzer, the average particle size of the nanosheets is 50 nm (D50=50 nm), the thickness is 1-3 nm, and the specific surface area is 60 m² / g.

[0103] The preparation method of the lubricant (calcium stearate) is as follows: using stearic acid and calcium chloride as raw materials, they are added to a reaction vessel at a molar ratio of stearic acid:calcium chloride = 2:1, and an ethanol-water mixed solvent (ethanol:water = 1:1, the amount of which is 1.5 times the mass of stearic acid) is added. The mixture is stirred and reacted at 75-85℃ for 2-2.5 hours to generate calcium stearate precipitate. After the reaction is completed, the precipitate is collected by filtration and repeatedly washed with deionized water until the washing liquid is free of chloride ions (no white precipitate is detected by silver nitrate solution). The precipitate is dried at 90-100℃ for 3-4 hours, pulverized, and passed through a 200-mesh sieve to obtain calcium stearate powder with a purity of 99% and a melting point of 150℃.

[0104] The preparation method of antioxidant 1010 is as follows: methyl β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate and pentaerythritol are used as raw materials and added to a reaction vessel at a molar ratio of methyl β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate: pentaerythritol = 4.1:1. Sodium hydroxide is added as a catalyst (0.6% of the total mass of raw materials), and the reaction is carried out under nitrogen protection at 115-125℃ for 3.5-4 hours. After the reaction is completed, dilute hydrochloric acid is added to neutralize the catalyst to pH=7, and the organic phase is collected after standing and separating. The residual raw materials and solvents are removed by vacuum distillation (temperature 125-135℃, vacuum degree -0.09MPa), and white crystals are precipitated after cooling. The crystals are recrystallized once with ethanol to obtain high-purity antioxidant 1010 with a purity of 99.2% and a melting point of 52-54℃.

[0105] A method for preparing automotive nylon tubing includes the following steps:

[0106] S1. Pretreatment: 70 parts of polyamide PA66 resin chips were evenly spread on a stainless steel tray and placed in a vacuum drying oven. The drying temperature was set to 100℃, the vacuum degree to -0.095MPa, and the drying time to 4 hours. After drying, the chips were immediately transferred to a desiccator containing anhydrous calcium chloride and cooled to room temperature (23℃). The moisture content was tested by a Karl Fischer moisture analyzer and found to be ≤0.04%. 0.5 parts of calcium stearate (5% of the total amount) were added together with 1 part of 50nm boron nitride nanosheets into a high-speed mixer. The mixing speed was set to 2800rpm and the mixing time to 10 minutes. During the mixing process, 25℃ cooling water was circulated through the jacket to control the temperature. After mixing, SEM observation showed that the nanosheets were monodisperse and the aggregate particle size was ≤300nm, forming a uniform "boron nitride nanosheet-calcium stearate" slurry.

[0107] S2. Segmented melt blending: The "boron nitride nanosheets-calcium stearate" slurry prepared in S1 and 8 parts of maleic anhydride-grafted SEBS were fed into a low-speed mixer. The speed was set to 500 rpm and the mixing time was 5 minutes to form a "SEBS-boron nitride" composite toughening unit. Subsequently, this unit, along with 70 parts of dried PA66, 6.67 parts of polyborosiloxane (8wt% boron content), 5 parts of sulfonated polyarylethersulfone, 4 parts of metal phosphonate (1:2 ratio), 0.3 parts of antioxidant 1010, and the remaining 0.475 parts of calcium stearate, were fed into a twin-screw extruder. The segmented temperatures were 240℃ in zone 1, 250℃ in zone 2, 255℃ in zone 3, and 250℃ at the die head. The screw speed was adjusted to 35 rpm. The material residence time in the barrel was about 2.8 minutes. The extruded strip had a smooth surface, no bubbles or carbonization points, and a stable melt state.

[0108] S3. Granulation: The operation is the same as in Example 1.

[0109] S4. Tube Forming: The composite material particles prepared in S3 are fed into a single-screw extruder, and the segmented temperatures are set as follows: hopper section 235℃, zone 1 240℃, zone 2 245℃, zone 3 245℃, and die head 240℃. The machine is preheated for 30 minutes to ensure that the temperature of each section is stable within ±1℃ of the set value. The single screw speed is set to 40 rpm. After the material is stably extruded from the die head with an inner diameter of 20mm, it is introduced into a custom-made vacuum sizing sleeve with an inner diameter of 20mm. The extruded tube is sent to a secondary water cooling tank and cooled to below 35℃. The tube is then pulled by a traction machine and finally cut into 1m sections using a tube cutter. The finished automotive nylon tube specifications are: wall thickness 3.0mm, inner diameter 20mm. Visual inspection shows that the tube wall is free of eccentricity, scratches, and dents, and the dimensional accuracy meets the requirements for automotive piping applications.

[0110] Example 4

[0111] This embodiment differs from Embodiment 1 in the following ways, while the rest is the same as in Embodiment 1, as detailed below:

[0112] An automotive nylon tubing, by weight, comprises the following raw materials: 55 parts polyamide PA66 resin, 12 parts polyborosiloxane, 12 parts sulfurized polyarylether sulfone, 8 parts metal phosphonate, 4 parts boron nitride nanosheets, 14.4 parts maleic anhydride-grafted SEBS, 0.8 parts antioxidant, and 1.5 parts lubricant.

[0113] The preparation method of sulfonated polyarylene ether sulfone is as follows: using polyarylene ether sulfone and chlorosulfonic acid as raw materials, polyarylene ether sulfone:chlorosulfonic acid = 1:0.9 mass ratio, polyarylene ether sulfone is added to dichloromethane solvent, and stirred at 22-25℃ until completely dissolved; chlorosulfonic acid is slowly added dropwise, with the addition time controlled at 1.5-2 hours, and the temperature is controlled by an ice bath during the addition process to ensure that the system temperature does not exceed 28℃; after the addition is completed, the reaction is continued at 25℃ for 1.5-2 hours; after the reaction is completed, the reaction solution is slowly poured into an ice-water mixture, stirred to precipitate; the precipitate is collected by filtration, and repeatedly washed with deionized water until the pH of the washing solution is 6.5-7, and then the precipitate is vacuum dried at 85℃ for 7 hours; the degree of sulfonation is determined by potentiometric titration to be 30%, the number average molecular weight is 32000, and the glass transition temperature (Tg) is 175℃.

[0114] The preparation method of metal phosphonates is as follows: aluminum diethylphosphonate and ammonium polyphosphate are added to a high-speed mixer at a mass ratio of 1:2, and the mixture is mixed for 18-22 minutes at a speed of 1700 rpm. The mixture is then transferred to a twin-screw extruder, and the extrusion temperature is set to 180-190℃, the screw speed is set to 27 rpm, and the melt reaction is carried out for 2 hours. The extruded strip is cooled to below 40℃ by water at 25℃ and then granulated to obtain metal phosphonate particles.

[0115] The preparation method of boron nitride nanosheets is as follows: hexagonal boron nitride powder is used as raw material, and deionized water and sodium dodecylbenzenesulfonate are added to prepare a suspension with a concentration of 5.5%; the suspension is transferred into an ultrasonic cell disruptor, the power is set to 850W, and the ultrasonic time is 35 minutes; after ultrasonication, the nanosheets are centrifuged at 8500rpm for 18 minutes to remove unpeeled coarse particles; the supernatant is taken and silane coupling agent KH550 is added, and the mixture is stirred at 62℃ for 2.2 hours; after modification, the nanosheets are centrifuged again (8500rpm, 12 minutes), the precipitate is collected and vacuum dried at 82℃ for 4.5 hours; the nanosheets have an average particle size of 80nm, a thickness of 1-4nm, and a specific surface area of ​​55m² / g, as measured by a laser particle size analyzer.

[0116] The preparation method of the antioxidant is as follows: antioxidant 1010 and antioxidant 168 are added to a mixer at a mass ratio of 1:1 and the speed is set to 1200 rpm for 35 minutes; after mixing, a sample is taken for testing, and the mixture is analyzed by high performance liquid chromatography (HPLC). The uniformity deviation of the two is ≤2%, which ensures the stable antioxidant effect.

[0117] A method for preparing automotive nylon tubing includes the following steps:

[0118] S1. Pretreatment: 55 parts of polyamide PA66 resin chips were evenly spread on a stainless steel tray and placed in a vacuum drying oven. The drying temperature was set to 95℃, the vacuum degree to -0.095MPa, and the drying time to 4.5 hours. After drying, the chips were transferred to a desiccator and cooled to room temperature (23℃). The moisture content was tested by a Karl Fischer moisture analyzer and found to be ≤0.045%. 1.5 parts of zinc stearate (10% of the total amount) were added together with 4 parts of 80nm boron nitride nanosheets into a high-speed mixer. The mixing speed was set to 3200rpm and the mixing time to 18 minutes. During the mixing process, 25℃ cooling water was circulated through the jacket to control the system temperature to ≤42℃. After mixing, SEM observation showed that the nanosheets were in a small-scale stacked dispersion state, with agglomerate particle size ≤400nm, forming a uniform "boron nitride nanosheet-zinc stearate" slurry.

[0119] S2. Segmented melt blending: The slurry prepared in S1 and 14.4 parts of maleic anhydride-grafted SEBS were fed into a low-speed mixer. The speed was set to 500 rpm and the mixing time was 7 minutes to form a "SEBS-boron nitride" composite toughening unit. Subsequently, this unit, along with 55 parts of dried PA66, 12 parts of polyborosiloxane (10wt% boron content), 12 parts of sulfonated polyarylene ether sulfone (30% sulfonation degree), 8 parts of metal phosphonate (1:2 ratio), 0.8 parts of compound antioxidant, and the remaining 1.35 parts of zinc stearate, were fed into a twin-screw extruder. The segmented temperatures were 240℃ in zone 1, 250℃ in zone 2, 255℃ in zone 3, and 250℃ at the die head. The screw speed was adjusted to 32 rpm. The material residence time in the barrel was about 3.2 minutes. The extruded strip had a smooth surface and no bubbles. The melt flow rate (260℃ / 2.16kg) was 12g / 10min as measured by a melt flow rate meter (MFR).

[0120] S3. Granulation: The operation is the same as in Example 1.

[0121] S4. Pipe Forming: The composite material granules produced in S3 are fed into a single-screw extruder, with the following segment temperatures set: hopper section 242℃, zone 1 246℃, zone 2 250℃, zone 3 252℃, and die head 248℃. The machine is preheated for 30 minutes, and the temperature of each segment stabilizes within ±1℃ of the set value. The single-screw speed is set to 28 rpm. The pipe is fed into a secondary water cooling tank and cooled to below 42℃. It is then pulled by a traction machine and cut into 1m / segment. The resulting automotive nylon pipe specifications are: wall thickness 2.5mm (deviation ±0.1mm), inner diameter 12mm (deviation ±0.05mm). Laser diameter measurement shows an inner diameter roundness error ≤0.03mm and a surface roughness Ra ≤0.2μm, meeting the dimensional and appearance requirements for automotive ammonia fuel lines.

[0122] Example 5

[0123] This embodiment differs from Embodiment 1 in the following ways, while the rest is the same as in Embodiment 1, as detailed below:

[0124] An automotive nylon tubing, by weight, comprises the following raw materials: 65 parts polyamide PA66 resin, 8 parts polyborosiloxane, 6 parts sulfurized polyarylether sulfone, 6 parts metal phosphonate, 2 parts boron nitride nanosheets, 9.6 parts maleic anhydride-grafted SEBS, 0.5 parts antioxidant, and 1.0 part lubricant.

[0125] The preparation method of sulfided polyarylene ether sulfone is as follows: using polyarylene ether sulfone and chlorosulfonic acid as raw materials, polyarylene ether sulfone:chlorosulfonic acid = 1:1.5 mass ratio, polyarylene ether sulfone is added to dichloromethane solvent, and stirred at 28-32℃ until completely dissolved; chlorosulfonic acid is slowly added dropwise, with the addition time controlled at 2-2.5 hours, and the temperature is controlled by water bath during the addition process to ensure that the system temperature does not exceed 35℃; after the addition is completed, the reaction continues at 32℃ for 3-3.5 hours; after the reaction is completed, the reaction solution is slowly poured into an ice-water mixture, and the precipitate is precipitated by rapid stirring; the precipitate is collected by filtration, and washed repeatedly with deionized water until the pH of the washing solution is 6-7, and then the precipitate is vacuum dried at 90℃ for 8 hours; the degree of sulfonation is determined by potentiometric titration to be 50%, the number average molecular weight is 38000, and the glass transition temperature (Tg) is 185℃.

[0126] The preparation method of metal phosphonates is as follows: aluminum diethylphosphonate and ammonium polyphosphate are added to a high-speed mixer at a mass ratio of 1:4, and the mixture is mixed for 22-25 minutes at a speed of 1900 rpm. The mixture is then transferred to a twin-screw extruder, and the extrusion temperature is set to 190-200℃, the screw speed is set to 29 rpm, and the melt reaction is carried out for 2.5 hours. The extruded strip is cooled to below 40℃ by water at 25℃ and then granulated to obtain metal phosphonate particles. X-ray diffraction (XRD) test shows that the characteristic peaks of the product are free of impurities, proving that the reaction is complete.

[0127] The preparation method of boron nitride nanosheets is as follows: hexagonal boron nitride powder is used as raw material, and deionized water and sodium dodecylbenzenesulfonate are added to prepare a suspension with a concentration of 5.8%; the suspension is transferred into an ultrasonic cell disruptor, the power is set to 950W, and the ultrasonic time is 45 minutes; after ultrasonication, it is centrifuged at 9500rpm for 22 minutes; the supernatant is taken and silane coupling agent KH550 is added, and the mixture is stirred at 68℃ for 2.8 hours; after modification, it is centrifuged again (9500rpm, 18 minutes), the precipitate is collected and vacuum dried at 88℃ for 5.5 hours; the average particle size of the nanosheets is 120nm, the thickness is 2-5nm, and the specific surface area is 48m² / g, as measured by a laser particle size analyzer.

[0128] The lubricant is prepared as follows: using stearic acid and ethylenediamine as raw materials, they are added to a reaction vessel at a molar ratio of stearic acid:ethylenediamine = 2:1, with xylene as solvent. The reaction is carried out under nitrogen protection and refluxed at 145-155℃ for 3.5-4.5 hours. After the reaction is completed, the mixture is cooled to room temperature to precipitate crystals. The crystals are collected by filtration, washed 3-4 times with anhydrous ethanol, dried under vacuum at 115-125℃ for 6 hours, pulverized, and passed through a 180-mesh sieve to obtain ethylene bis-stearamide powder with a purity of 99% and a melting point of 148℃.

[0129] A method for preparing automotive nylon tubing includes the following steps:

[0130] S1. Pretreatment: Spread 65 polyamide PA66 resin slices evenly on a stainless steel tray, place them in a vacuum drying oven, set the drying temperature to 85℃, vacuum degree to -0.095MPa, and drying time to 5.5 hours; immediately after drying, transfer them to a desiccator containing anhydrous calcium chloride, cool to room temperature (23℃), and test the moisture content using a Karl Fischer moisture analyzer, which is ≤0.048%.

[0131] S2. Segmented melt blending: The slurry prepared in S1 and 9.6 parts of maleic anhydride-grafted SEBS were added to a low-speed mixer. The speed was set to 500 rpm and the mixing time was 9 minutes. After thorough mixing, a "SEBS-boron nitride" composite toughening unit was formed. Subsequently, this unit was combined with 65 parts of dried PA66, 8 parts of polyborosiloxane (11 wt% boron content), 6 parts of sulfonated polyarylene ether sulfone (50% sulfonation degree), 6 parts of metal phosphonate (1:4 ratio), and 0.5 parts of antioxidant. Agent 1076 and the remaining 0.92 parts of ethylene bis-stearamide were fed into a twin-screw extruder; the segmented temperatures were 240℃ in zone 1, 250℃ in zone 2, 255℃ in zone 3, and 250℃ at the die head, and the screw speed was adjusted to 28 rpm; the material residence time in the barrel was about 3.4 minutes, and the extruded strip had a smooth surface without bubbles or carbonization points. The melting point of the strip was tested by differential scanning calorimetry (DSC) and found to be 258℃, which is ≤2℃ different from the melting point of PA66 matrix, proving that the components are compatible.

[0132] S3. Granulation: The operation is the same as in Example 1.

[0133] S4. Pipe Forming: The granulated composite material particles are fed into a single-screw extruder, and the segmented temperatures are set as follows: hopper section 245℃, zone 1 248℃, zone 2 253℃, zone 3 253℃, and die head 250℃. The machine is preheated for 30 minutes, and the temperature of each segment stabilizes within ±1℃ of the set value. An infrared thermometer confirms that the die head temperature does not fluctuate. The single-screw speed is set to 35 rpm. After the material is stably extruded from the die head with an inner diameter of 15mm, it is introduced into a custom-made vacuum sizing sleeve with an inner diameter of 15mm. The extruded pipe is sent to a secondary water cooling tank and cooled to below 38℃. The pipe is then pulled by a traction machine and finally cut into 1m segments using a pipe cutter. The finished automotive nylon pipe specifications are: wall thickness 1.8mm (deviation ±0.1mm), inner diameter 15mm (deviation ±0.05mm). Visual inspection shows no eccentricity of the pipe wall, no scratches or dents on the surface, and no leakage is detected through a pressure test.

[0134] Comparative Example 1

[0135] Compared with Example 1, this comparative example does not add sulfonated polyarylether sulfone during the preparation of nylon tubes, while the types, amounts, specifications and preparation steps of other raw materials are the same as in Example 1.

[0136] An automotive nylon tubing, by weight, comprises the following raw materials: 60 parts polyamide PA66 resin, 10 parts polyborosiloxane, 7 parts metal phosphonate, 3 parts boron nitride nanosheets, 10 parts maleic anhydride-grafted SEBS, 0.6 parts antioxidant, and 1.2 parts lubricant, wherein the mass ratio of maleic anhydride-grafted SEBS to polyborosiloxane is 1:1, and the specifications of the remaining raw materials are completely consistent with those in Example 1.

[0137] Comparative Example 2

[0138] Compared with Example 1, this comparative example only lacks the raw material polyborosiloxane, without adding any substitutes. The types, weight parts, specifications, and preparation steps of the other raw materials are completely the same as in Example 1.

[0139] An automotive nylon tubing, by weight, comprises the following raw materials: 60 parts polyamide PA66 resin, 7 parts metal phosphonate, 8 parts sulfonated polyarylene ether sulfone, 3 parts boron nitride nanosheets, 10 parts maleic anhydride-grafted SEBS, 0.6 parts antioxidant, and 1.2 parts lubricant. Since polyborosiloxane is not included, there is no requirement for the "mass ratio of maleic anhydride-grafted SEBS to polyborosiloxane." The specifications of the remaining raw materials are completely consistent with those in Example 1.

[0140] Comparative Example 3

[0141] Compared with Example 1, this comparative example only changed the processing method of boron nitride nanosheets, which were directly fed in dry powder form. The types, weight parts, specifications, and other steps of the preparation process of the other raw materials were completely the same as in Example 1.

[0142] An automotive nylon tubing, by weight, comprises the following raw materials: 60 parts polyamide PA66 resin, 10 parts polyborosiloxane, 8 parts sulfonated polyarylethersulfone, 7 parts metal phosphonate, 3 parts boron nitride nanosheets, 10 parts maleic anhydride-grafted SEBS, 0.6 parts antioxidant, and 1.2 parts lubricant, wherein the mass ratio of maleic anhydride-grafted SEBS to polyborosiloxane is 1:1, and the specifications of the remaining raw materials are completely consistent with those in Example 1.

[0143] The preparation steps of this automotive nylon tube differ from those in Example 1 only in the "boron nitride nanosheet treatment" step; the remaining steps are identical, as detailed below:

[0144] S1. Pretreatment: PA66 resin is vacuum dried at 90℃ for 5 hours. Boron nitride nanosheets are not pre-dispersed with lubricant and are used directly as dry powder.

[0145] S2. Segmented melt blending: Boron nitride nanosheet powder and 10 parts of maleic anhydride-grafted SEBS are directly added to a low-speed mixer for premixing for 8 minutes, and then the remaining raw materials are added and melt blended in a twin-screw extruder. The remaining steps are the same as in Example 1.

[0146] Comparative Example 4

[0147] Compared with Example 1, this comparative example only changed the proportion of metal phosphonates as raw materials, while the types, weight parts, specifications and preparation steps of the other raw materials were completely the same as in Example 1.

[0148] An automotive nylon tubing, by weight, comprises the following raw materials: 60 parts polyamide PA66 resin, 10 parts polyborosiloxane, 8 parts sulfonated polyarylethersulfone, 7 parts metal phosphonate, 3 parts boron nitride nanosheets, 10 parts maleic anhydride-grafted SEBS, 0.6 parts antioxidant, and 1.2 parts lubricant, wherein the mass ratio of maleic anhydride-grafted SEBS to polyborosiloxane is 1:1, and the specifications of the remaining raw materials are completely consistent with those in Example 1.

[0149] The preparation method of metal phosphonates is as follows: aluminum diethylphosphonate and ammonium polyphosphate are used as raw materials. They are added to a high-speed mixer at a mass ratio of aluminum diethylphosphonate to ammonium polyphosphate of 1:5. The mixing speed is set to 1500 rpm and the mixing time is 15 minutes to ensure that the two raw materials are evenly dispersed. The mixture is then transferred to a twin-screw extruder. The extrusion temperature is set to 180-190℃ and the screw speed is set to 25 rpm. The mixture is melted and reacted in the barrel for 2 hours. The extruded strip is cooled to below 40℃ in a 25℃ water cooling tank and then fed into a pelletizer to be cut into particles with a particle size of 2μm.

[0150] Comparative Example 5

[0151] Compared with Example 1, this comparative example only adjusts the mass ratio of maleic anhydride-grafted SEBS to polyborosiloxane. The types, weight parts, specifications, and preparation steps of the other raw materials are completely the same as in Example 1.

[0152] An automotive nylon tubing, by weight, comprises the following raw materials: 60 parts polyamide PA66 resin, 10 parts polyborosiloxane, 8 parts sulfonated polyarylethersulfone, 7 parts metal phosphonate, 3 parts boron nitride nanosheets, 6.67 parts maleic anhydride-grafted SEBS, 0.6 parts antioxidant, and 1.2 parts lubricant, wherein the mass ratio of maleic anhydride-grafted SEBS to polyborosiloxane is 1:1.5, and the specifications of the remaining raw materials are completely consistent with those in Example 1.

[0153] The nylon tube samples prepared using the raw materials and steps described in Examples 1, 2, 3, 4, and 5, and Comparative Examples 1, 2, 3, 4, and 5 were subjected to performance tests, and the results are categorized into the following three tables based on the testing objectives:

[0154] Table 1 Hydrolysis induction period test under ammonia corrosion

[0155]

[0156] Hydrolysis induction period: This reflects the delay time it takes for a material to begin hydrolysis in an ammonia environment. The longer the time, the stronger the material's "initial protection" against ammonia-induced hydrolysis. The target value was set at ≥1500h (based on accelerated aging conversion of 3-5 years of service life for automotive nylon tubing, and significantly better than the hydrolysis resistance level of ordinary PA66). Examples 1 to 5 all met the target, with Example 2 reaching 2000h, thanks to the ammonia capture effect of sulfonated polyarylene ether sulfone and the molecular stabilizing effect of polyborosiloxane. Comparative Examples 1 to 5 did not meet the target, especially Comparative Example 1 (lacking sulfonated polyarylene ether sulfone), which only reached 800h, indicating that the absence of key components significantly shortens the hydrolysis initiation time.

[0157] Tensile strength change: This reflects the degree to which the tensile strength of the material is retained after aging in ammonia water for 3000 hours (a negative number indicates a decrease in strength; the smaller the absolute value, the better the strength retention). The target value is set at ≥-20%, meaning the strength decrease does not exceed 20% (ensuring that the material can maintain its basic structural strength even after long-term use in an ammonia water environment, meeting the mechanical safety requirements of automotive pipelines). Examples 1 to 5 all met the target, while Example 2 only decreased by 11%, demonstrating the compatibility modification effect of SEBS and polyborosiloxane. Comparative Examples 1 to 5 did not meet the target, with Comparative Example 1 (lacking sulfonated polyarylethersulfone) decreasing by 40%, indicating that the absence of key components leads to rapid strength loss.

[0158] Amide bond integrity: The amide bond is the core structure of the nylon molecule, and its absorbance retention rate reflects the integrity of the molecular chain (the higher the retention rate, the less amide bond breakage). The target value was set at ≥85% (to ensure that the nylon molecular chain does not undergo severe breakage and maintain the basic physicochemical properties of the material). Examples 1 to 5 all met the target, and Example 2 reached 95%, confirming that the capture of ammonia molecules by sulfonated polyarylene ether sulfone can protect the amide bond. Most of the comparative examples 1 to 5 did not meet the target, and Comparative example 1 (lacking sulfonated polyarylene ether sulfone) only reached 65%, indicating that the lack of an ammonia capture mechanism will accelerate the breakage of the amide bond.

[0159] Table 2 Microcrack propagation suppression performance test

[0160]

[0161] Microcrack initiation time: Based on the long-term service requirements of automotive pipelines, it is necessary to delay the "first appearance" time of microcracks, with a target value set at ≥2000h (after accelerating aging and correlating with actual working conditions, ensuring no risk of initial cracks for 3-5 years). The initiation times of Examples 1 to 5 are 2200-2600h (such as Example 2 reaching 2600h), all far exceeding the target. This is because the pre-dispersion of boron nitride and sulfonated polyarylene ether sulfone in the formulation work together to resist corrosion, which can significantly delay the "initiation" of cracks. Comparative Examples 1 to 5 are only 1200-2000h (such as Comparative Example 1 only 1200h), mostly below the target. The absence of key components (or process deviation) allows ammonia water to corrode the surface more quickly, leading to the premature initiation of microcracks.

[0162] Crack propagation rate: To avoid rapid crack propagation leading to leakage, the rate needs to be controlled to ≤0.05 μm / h (based on the "safe leakage risk threshold" from engineering experience). Examples 1 to 5 showed rates of 0.02-0.04 μm / h (Example 2 was only 0.02 μm / h), all superior to the target. This is due to the toughening effect of SEBS and the "locking" effect of polyborosiloxane molecules, which effectively hinder crack propagation. Comparative Examples 1 to 5 reached 0.06-0.15 μm / h (Comparative Example 1 reached 0.15 μm / h, 7.5 times that of Example 2). The absence of key components caused the crack to grow rapidly in ammonia water, resulting in a sharp decrease in its resistance to propagation.

[0163] Surface morphology changes: From the perspective of pipeline sealing and leakage resistance, it is necessary to control the number of microcracks to ≤5 / mm², the maximum crack depth to ≤20μm, and the Ra change rate to ≤50% (ensuring the impact of surface integrity on pipeline function). Examples 1 to 5 have 2-4 microcracks / mm², a depth of 12-18μm, and a Ra change rate of 35%-45% (e.g., Example 2 has only 2 microcracks / mm² and a depth of 12μm), all of which meet the targets. This is because the components such as metal phosphonates and boron nitride synergistically stabilize the surface and inhibit ammonia water corrosion. Comparative Examples 1 to 5 have 6-12 microcracks / mm², a depth of 25-45μm, and a Ra change rate of 58%-85% (e.g., Comparative Example 1 has 12 microcracks / mm² and a depth of 45μm), which far exceed the targets. The lack of core anti-corrosion components leads to severe damage to the surface by ammonia water, resulting in significant morphological deterioration.

[0164] Table 3 Mechanical property retention rate test under ammonia water environment

[0165]

[0166] Tensile strength retention rate: This mainly reflects the degree to which the tensile strength of the material is retained after aging in an ammonia environment for 3000 hours (the higher the value, the smaller the strength loss and the better the long-term mechanical stability). Based on the long-term load-bearing requirements of automotive nylon tubing, a strength retention rate of ≥80% must be ensured (to ensure that the pipeline does not fail due to excessive strength loss during its service life). The retention rates of Examples 1 to 5 are 82%-89% (such as Example 2 reaching 89%), all of which meet the target. This is because sulfonated polyarylene ether sulfone, polyborosiloxane, etc. in the formulation synergistically resist hydrolysis, protect the molecular chains and interface bonding, and reduce strength loss. Comparative Examples 1 to 5 are only 60%-73% (such as Comparative Example 1 only 60%), and the absence of key components (or deviation in proportion / process) leads to easy breakage of molecular chains, easy peeling of interfaces, and rapid loss of strength.

[0167] Elongation at break retention rate: This mainly reflects the material's ability to retain toughness after aging in an ammonia environment (the higher the value, the smaller the toughness loss, and the stronger the resistance to cracking and deformation). To ensure the pipeline's resistance to embrittlement under vibration and pressure fluctuations, the elongation at break retention rate needs to be ≥75% (to prevent the material from cracking under stress after becoming brittle). Examples 1 to 5 show retention rates of 78%-85% (Example 2 reaches 85%), all meeting the target. This is due to the toughening effect of maleic anhydride-grafted SEBS and the synergistic effect with other components, which inhibits the toughness degradation caused by ammonia. Comparative Examples 1 to 5 show only 55%-71% (Comparative Example 1 only 55%), indicating the loss of key toughening or anti-hydrolysis components, leading to rapid embrittlement and a significant decrease in toughness.

[0168] Burst pressure test method: It is mainly used to simulate the ultimate pressure resistance of pipelines (referencing standards such as GB / T6111, by gradually increasing the pressure to the point of pipeline rupture and recording the pressure; "3000h burst pressure" is the test result after ammonia aging, and "retention rate" is the ratio of the burst pressure after aging to the initial value). Automotive nylon hoses need to withstand fluid pressure for a long time, therefore the 3000h burst pressure must be ≥10MPa, and the retention rate ≥85% (ensuring sufficient pressure resistance after aging). Examples 1 to 5 exhibited burst pressures of 11.8-13.2 MPa over 3000 hours (13.2 MPa in Example 2), with a retention rate of 86%-92% (92% in Example 2), all meeting the target. This was due to the excellent overall hydrolysis and crack resistance of the formulation, resulting in good pipeline structural integrity even after aging. Comparative Examples 1 to 5 exhibited burst pressures of 7.8-10.2 MPa over 3000 hours (only Comparative Example 5 reached 10 MPa), with a retention rate of 65%-79% (all below 85%). The absence of key components made the pipeline prone to microcracks and molecular chain deterioration in ammonia water, significantly reducing pressure resistance and retention rate.

[0169] The test results from five examples and five comparative examples show that the nylon tubes prepared in the examples exhibit a hydrolysis induction period of 1600 hours or more under ammonia corrosion, effectively delaying the initiation of hydrolysis. They also demonstrate good microcrack suppression, with a long microcrack initiation time and a low crack propagation rate within 3000 hours, effectively controlling surface morphology degradation. Furthermore, after aging in an ammonia environment for 3000 hours, the tensile strength, elongation at break, and other mechanical properties are well preserved, and the burst pressure and retention rate meet expectations. In contrast, the comparative examples, due to the absence of key components or deviations in process and proportions from the design range, did not achieve the same performance as the examples.

[0170] The foregoing has only described certain exemplary embodiments of the present invention by way of illustration. Undoubtedly, those skilled in the art can modify the described embodiments in various ways without departing from the spirit and scope of the present invention. Therefore, the above description is illustrative in nature and should not be construed as limiting the scope of protection of the claims of the present invention.

Claims

1. A type of automotive nylon tubing, characterized in that, By weight, it includes the following ingredients: 50-70 parts of polyamide PA66 resin, 5-15 parts of polyborosiloxane, 5-12 parts of sulfonated polyarylether sulfone, 4-10 parts of metal phosphonate, 1-5 parts of boron nitride nanosheets, 8-18 parts of maleic anhydride grafted SEBS, 0.3-1 part of antioxidant, and 0.5-2 parts of lubricant. The metal phosphonate is prepared by reacting aluminum diethylphosphonate with ammonium polyphosphate. The degree of sulfonation of the sulfonated polyarylene sulfone is 30-50%; The method for preparing the automotive nylon tubing includes the following steps: S1. Pretreatment: Vacuum dry PA66 resin at 80-100℃ for 4-6 hours; pre-disperse boron nitride nanosheets with 5-10% lubricant using a high-speed mixer to form a uniform slurry; S2. Segmented melt blending: Pre-mix the pre-dispersed boron nitride nanosheet slurry with maleic anhydride-grafted SEBS for 5-10 minutes, then add dried PA66, polyborosiloxane, sulfonated polyarylether sulfone, metal phosphonate and other remaining components, and melt blend through a twin-screw extruder; S3. Granulation: After cooling the extruded strip to 30-50℃, it is granulated to obtain composite material particles; S4. Tube Forming: The composite material particles are extruded through a single screw extruder at an extrusion temperature of 240-255℃ and a screw speed of 20-40 rpm. Vacuum cooling is used for forming with a sizing sleeve. The resulting nylon tube has a wall thickness of 1.0-3.0 mm and an inner diameter of 5-20 mm.

2. The automotive nylon tubing according to claim 1, characterized in that: The mass ratio of aluminum diethylphosphonate to ammonium polyphosphate is 1:2-1:

4.

3. The automotive nylon tubing according to claim 1, characterized in that: The polyborosiloxane has a boron content of 8-12 wt% and a molecular weight of 3000-8000 g / mol.

4. The automotive nylon tubing according to claim 1, characterized in that: The boron nitride nanosheets have an average particle size of 50-150 nm.

5. The automotive nylon tubing according to claim 1, characterized in that: The mass ratio of maleic anhydride-grafted SEBS to polyborosiloxane is 1:0.5-1.

2.

6. A method for preparing an automotive nylon tube as described in any one of claims 1-5, characterized in that, Includes the following steps: S1. Pretreatment: Vacuum dry PA66 resin at 80-100℃ for 4-6 hours; pre-disperse boron nitride nanosheets with 5-10% lubricant using a high-speed mixer to form a uniform slurry; S2. Segmented melt blending: Pre-mix the pre-dispersed boron nitride nanosheet slurry with maleic anhydride-grafted SEBS for 5-10 minutes, then add dried PA66, polyborosiloxane, sulfonated polyarylether sulfone, metal phosphonate and other remaining components, and melt blend through a twin-screw extruder; S3. Granulation: After cooling the extruded strip to 30-50℃, it is granulated to obtain composite material particles; S4. Tube Forming: The composite material particles are extruded through a single screw extruder at an extrusion temperature of 240-255℃ and a screw speed of 20-40 rpm. Vacuum cooling is used for forming with a sizing sleeve. The resulting nylon tube has a wall thickness of 1.0-3.0 mm and an inner diameter of 5-20 mm.

7. The method according to claim 6, characterized in that: In step S2, the boron nitride nanosheets are first pre-dispersed with a portion of the lubricant to form a slurry, and then pre-mixed with the maleic anhydride-grafted SEBS for 5-10 minutes.

8. The method according to claim 6, characterized in that: The segmented temperatures of the twin-screw extruder in step S2 are set as follows: Zone 1: 240°C, Zone 2: 250°C, Zone 3: 255°C, and Die Head: 250°C.

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