PE pipe resistant to low-temperature embrittlement impact and preparation method thereof

Abstract

The application relates to the technical field of C08L, in particular to a PE pipe resistant to low-temperature embrittlement impact and a preparation method thereof. The PE pipe comprises a base layer and an impact-resistant layer from inside to outside. The base layer is made of melt blending of ultrahigh molecular weight polyethylene, a toughening agent, a photoinitiator, a nano-silica aerogel modifier and a graphene-carbon nanotube composite modifier. The impact-resistant layer is made of melt blending of a thermoplastic polyurethane elastomer, a liquid nitrile rubber, an ethylene-vinyl acetate copolymer and nano-calcium carbonate and then is extruded into a shape. The PE pipe resistant to low-temperature embrittlement impact provided by the application is improved on the basis of the prior art, and the performance is comprehensively improved, especially the low-temperature resistance and the impact resistance. The base layer of the technical scheme takes ultrahigh molecular weight polyethylene as a matrix, adds the toughening agent, the photoinitiator, the nano-silica aerogel modifier and the graphene-carbon nanotube composite modifier, forms a multi-component synergistic system, and jointly enhances the performance of the PE pipe.

Description

Technical Field

[0001] This invention relates to the field of CO8L technology, specifically to a PE pipe resistant to low-temperature embrittlement impact and its preparation method. Background Technology

[0002] Polyethylene (PE) pipes, as a typical thermoplastic pipe material, are widely used in water supply and drainage systems, gas transmission, agricultural irrigation, and municipal engineering due to their excellent chemical corrosion resistance, good flexibility, convenient construction performance, and relatively economical cost. With the continuous advancement of infrastructure construction, the application scenarios of PE pipes are gradually expanding to complex environments, especially in cold regions or working conditions requiring dynamic loads, where their performance faces severe challenges.

[0003] In existing technologies, the molecular chain structure of traditional PE pipes is predominantly linear. At low temperatures, the mobility of these molecular chain segments significantly decreases, leading to a marked brittle transition and a sharp decline in impact resistance. When subjected to external impact or sudden temperature changes, PE pipes are highly susceptible to embrittlement and cracking, severely impacting the safety and service life of the piping system. Furthermore, the impact resistance of conventional PE pipes primarily depends on the toughness of the matrix resin; however, the performance improvement potential of a single resin is limited, making it difficult to simultaneously meet the requirements for embrittlement resistance and high strength at low temperatures. Summary of the Invention

[0004] The purpose of this invention is to provide a PE pipe that is resistant to low-temperature embrittlement impact.

[0005] To achieve the above objectives, the present invention provides the following technical solution:

[0006] A PE pipe resistant to low-temperature embrittlement impact, the PE pipe comprising a base layer and an impact-resistant layer from the inside out;

[0007] The base layer is made by melt blending 100 parts by weight of ultra-high molecular weight polyethylene, 8-12 parts by weight of toughening agent, 1.6-2 parts by weight of photoinitiator, 2-4 parts by weight of nano-silica aerogel modifier, and 1-3 parts by weight of graphene-carbon nanotube composite modifier; the impact-resistant layer is made by melt blending thermoplastic polyurethane elastomer, liquid nitrile rubber, ethylene-vinyl acetate copolymer, and nano-calcium carbonate in a mass ratio of 60-70:15-18:10-14:5-6 and then extruding.

[0008] As a further technical solution, the toughening agent is EPDM rubber;

[0009] The photoinitiator is 2-hydroxy-2-methyl-1-phenylpropanone and benzoin dimethyl ether.

[0010] As a further technical solution, the nano-silica aerogel modifier is prepared by the following method:

[0011] Tetraethyl orthosilicate, anhydrous ethanol, and deionized water were mixed in a volume ratio of 1:3-5:1-3. Hydrochloric acid (0.5%-1.5% by mass) was added as a catalyst, and the mixture was stirred at room temperature for 2-4 hours to form a homogeneous sol. The sol was then transferred to a mold and gelled at 60-80°C for 6-10 hours. After gelation, the gel was immersed in a 10%-20% ethylene glycol solution for solvent replacement for 12-15 hours. Finally, supercritical drying was performed using carbon dioxide as the medium at 38-45°C and 12-15 MPa for 3-5 hours to obtain nano-silica aerogel. The obtained nano-silica aerogel was added to a 2%-5% silane coupling agent KH-550 ethanol solution and stirred at 58-70°C for 3-5 hours. After the reaction, the mixture was filtered and dried to obtain the nano-silica aerogel modifier with an average particle size of 10 nm.

[0012] As a further technical solution, the graphene-carbon nanotube composite modifier is prepared by the following method:

[0013] Graphene and carbon nanotubes in a mass ratio of 1-2:1 were added to a 4%-4.5% (w / w) aqueous solution of polyacrylamide and ultrasonically dispersed for 30-60 min at a power of 300-500 W. Then, coupling agent KH-560 was added at a mass of 0.5%-0.7% of the total mass of graphene and carbon nanotubes, and the mixture was stirred at 60-80℃ for 2-4 h. After the reaction, the mixture was freeze-dried at -40℃ under a vacuum of 1-2 Pa. Finally, the dried product was placed in a microwave reactor and treated at a power of 300-400 W for 8-10 min to obtain the graphene-carbon nanotube composite modifier.

[0014] As a further technical solution, the thickness of the base layer is 2-4mm, and the thickness of the impact-resistant layer is 2-3mm.

[0015] As a further technical solution, the impact-resistant layer also contains 0.6%-0.7% antioxidant 1010 and 0.3%-0.4% ultraviolet absorber UV-531 by mass fraction.

[0016] A method for developing PE pipes resistant to low-temperature embrittlement impact includes the following steps:

[0017] (1) Raw material pretreatment: ultra-high molecular weight polyethylene was dried at 80℃ for 4h, nano silica aerogel modifier was dried at 60℃ for 2h, and graphene-carbon nanotube composite modifier was dried at 50℃ for 3h.

[0018] (2) Base layer mixing: toughening agent, photoinitiator, nano silica aerogel modifier, graphene-carbon nanotube composite modifier and ultra-high molecular weight polyethylene are mixed at 180℃ for 15-18min, and the mixing speed is 60-80r / min. During mixing, ultra-high molecular weight polyethylene, nano silica aerogel modifier and graphene-carbon nanotube composite modifier are premixed at 160-165℃ for 5-8min, and then toughening agent, antifreeze agent and photoinitiator are added.

[0019] (3) Impact layer mixing: thermoplastic polyurethane elastomer, liquid nitrile rubber, ethylene-vinyl acetate copolymer, nano calcium carbonate, antioxidant 1010 and ultraviolet absorber UV-531 are mixed at 160-170℃ for 10-15 min.

[0020] (4) Double-layer co-extrusion: The base layer and the impact-resistant layer are extruded separately by two single-screw extruders equipped with screws of different length-to-diameter ratios. The length-to-diameter ratio of the screws of the extruder used for extruding the base layer is 30-35:1, and the length-to-diameter ratio of the screws of the extruder used for extruding the impact-resistant layer is 28-32:1. The temperature of the base layer extruder is set to a three-stage temperature control: the temperature of the feeding section is 160-170℃, the temperature of the compression section is 180-190℃, and the temperature of the metering section is 190-200℃, with a screw speed of 20-30 r / min. The temperature of the impact-resistant layer extruder is also set to a three-stage temperature control: the temperature of the feeding section is 150-160℃, the temperature of the compression section is 170-180℃, and the temperature of the metering section is 180-190℃, with a screw speed of 15-25 r / min. The temperature of the composite die is controlled at 190-210℃. By adjusting the extrusion speed of the two extruders to be consistent with the traction speed of the traction machine, the base layer and the impact-resistant layer are uniformly composited in the composite die.

[0021] (5) Ultraviolet crosslinking: Irradiation is carried out using ultraviolet light with a wavelength of 360-420nm under nitrogen protection;

[0022] (6) Gradient cooling: First, air cool to 80℃ at a rate of ≤5℃ / min, then water cool to 25℃ at a rate of ≤10℃ / min;

[0023] (7) Post-treatment: After water cooling, place the PE pipe at room temperature for 24-28 hours for aging treatment.

[0024] As a further technical solution, the mixing equipment mentioned in step (3) is an open mill, and the roller temperature of the open mill is controlled at 160-165℃ for the front roller and 165-170℃ for the rear roller.

[0025] As a further technical solution, in step (4), the irradiation distance is 10-20cm and the irradiation intensity is 200-300mW / cm. 2 The irradiation time is 2-3 hours.

[0026] As a further technical solution, after water cooling in step (6), the PE pipe is subjected to surface grinding treatment, and the grinding roughness Ra is 0.8-1.6μm.

[0027] Compared with the prior art, the beneficial effects of the present invention are:

[0028] The low-temperature embrittlement impact-resistant PE pipe provided by this invention improves upon existing technical solutions, achieving a comprehensive performance enhancement, especially in terms of low-temperature resistance and impact resistance.

[0029] The technical solution of this invention uses ultra-high molecular weight polyethylene (UHMWPE) as the base material. By adding toughening agents, photoinitiators, nano-silica aerogel modifiers, and graphene-carbon nanotube composite modifiers, a multi-component synergistic system is formed, collectively enhancing the performance of the PE pipe. UHMWPE provides a high-strength matrix framework, and its long molecular chain structure endows the material with basic mechanical properties. The EPDM rubber toughening agent, through physical blending, forms an elastomer network within the matrix. When the material is impacted, the elastomer particles can induce crazing and shear yielding, absorbing impact energy and reducing the tendency for embrittlement. The introduced photoinitiator generates active free radicals under ultraviolet irradiation, initiating cross-linking of the matrix molecular chains to form a three-dimensional network structure, increasing the intermolecular forces, thereby enhancing the material's structural stability and low-temperature resistance.

[0030] By introducing nano-silica aerogel modifier, its nano-porous structure can be uniformly dispersed in the matrix. On the one hand, it acts as a physical reinforcing filler, improving tensile strength and elastic modulus through interfacial forces. On the other hand, the low thermal conductivity of the aerogel can inhibit heat loss in low-temperature environments and delay the freezing of molecular chains, thereby improving low-temperature toughness.

[0031] Graphene-carbon nanotube composite modifiers function through a synergistic mechanism of nano-reinforcement and thermal conductivity. The sheet structure of graphene and the one-dimensional network of carbon nanotubes form an interconnected reinforcing framework, significantly improving the mechanical strength and impact resistance of the material. At the same time, the high thermal conductivity of both can uniformly disperse local stress, avoiding embrittlement caused by stress concentration, and forming a synergistic reinforcing system with nano-silica aerogel.

[0032] The impact-resistant layer of this invention uses a compound system of thermoplastic polyurethane elastomer, liquid nitrile rubber, ethylene-vinyl acetate copolymer and nano-calcium carbonate to achieve efficient buffering against external impacts.

[0033] TPU as the matrix: It has a molecular structure with alternating hard and soft segments. The hard segments provide strength, while the soft segments impart elasticity, maintaining good flexibility even at low temperatures. Liquid NBR toughening: Its polar groups form good interfacial compatibility with TPU, and it is uniformly dispersed in the TPU matrix. When subjected to impact, NBR particles can induce multiple crazing, further absorbing energy and improving impact resistance. EVA synergistic toughening: The vinyl acetate groups in its molecular chain can lower the glass transition temperature of the system, improve low-temperature elasticity, and form a multi-elastomer synergistic toughening network with TPU and NBR, significantly improving the resistance to embrittlement at low temperatures. Nano-calcium carbonate: As a rigid filler, after uniform dispersion, it can act as a physical cross-linking point, adjusting the hardness and elastic modulus of the material, avoiding insufficient strength caused by excessive softness of the impact-resistant layer, and forming a balanced system with the elastomer.

[0034] This invention achieves this by using a composite of a base layer and an impact-resistant layer:

[0035] Complementary structure: The base layer provides high-strength and low-temperature resistant main support, while the impact-resistant layer forms a buffer barrier on the outer layer. The two are combined through the interface to form a composite structure, which ensures both strength and impact resistance.

[0036] Functional Synergy: The cross-linked network of the base layer and the elastic network of the impact-resistant layer form a gradient structure that is strong inside and tough outside. When the PE pipe is subjected to low-temperature impact, the impact-resistant layer absorbs most of the energy first, while the base layer inhibits crack propagation through the cross-linked structure, thus avoiding embrittlement and breakage. Attached Figure Description

[0037] Figure 1 This is a process flow diagram for a PE pipe resistant to low-temperature embrittlement and impact. Detailed Implementation

[0038] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0039] This invention provides a PE pipe resistant to low-temperature embrittlement impact, the PE pipe comprising, from the inside out, a base layer and an impact-resistant layer:

[0040] The base layer is made by melt blending 100 parts by weight of ultra-high molecular weight polyethylene, 8-12 parts of toughening agent, 1.6-2.0 parts of photoinitiator, 2-4 parts of nano-silica aerogel modifier and 1-3 parts of graphene-carbon nanotube composite modifier.

[0041] Impact-resistant layer: It is formed by extrusion molding after melt blending of thermoplastic polyurethane elastomer, liquid nitrile rubber, ethylene-vinyl acetate copolymer and nano calcium carbonate in a mass ratio of 60-70:15-18:10-14:5-6.

[0042] Key Component Description

[0043] Toughening agent: EPDM rubber is preferred, which can improve the flexibility and impact resistance of the substrate.

[0044] Photoinitiator: Composed of 2-hydroxy-2-methyl-1-phenylpropanone and benzoin dimethyl ether, it promotes the ultraviolet crosslinking reaction of the base material.

[0045] Nano-silica aerogel modifier: Prepared via a sol-gel method combined with supercritical drying, with an average particle size of 10 nm, it can improve the strength and low-temperature resistance of the substrate. The preparation method is as follows:

[0046] Tetraethyl orthosilicate, anhydrous ethanol, and deionized water were mixed in a volume ratio of 1:3-5:1-3, and hydrochloric acid with a mass fraction of 0.5%-1.5% was added as a catalyst. The mixture was stirred at room temperature for 2-4 hours to form a sol.

[0047] Transfer the sol to a mold and gel at 60-80℃ for 6-10 hours.

[0048] The gel was soaked in a 10%-20% ethylene glycol solution for 12-15 hours to replace the solvent.

[0049] Nano-silica aerogels were obtained by supercritical drying at 38-45℃ and 12-15MPa for 3-5 hours using carbon dioxide as a medium.

[0050] The aerogel was added to an ethanol solution of silane coupling agent KH-550 with a mass fraction of 2%-5%, and stirred at 58-70℃ for 3-5 hours. After filtration and drying, the modifier was obtained.

[0051] Graphene-carbon nanotube composite modifier: Prepared via ultrasonic dispersion-coupling reaction-microwave treatment, it enhances the mechanical properties and thermal conductivity of the substrate. The preparation method is as follows:

[0052] Add graphene and carbon nanotubes in a mass ratio of 1-2:1 to a 4%-4.5% polyacrylamide aqueous solution and ultrasonically disperse at 300-500W for 30-60 minutes.

[0053] Add 0.5%-0.7% of the total mass of graphene and carbon nanotubes of coupling agent KH-560, and stir at 60-80℃ for 2-4 hours.

[0054] The product is obtained by freeze-drying (-40℃, 1-2Pa) and then processing in a 300-400W microwave reactor for 8-10 minutes.

[0055] Impact-resistant layer additives: contain 0.6%-0.7% antioxidant 1010 and 0.3%-0.4% UV absorber UV-531 by mass fraction to improve anti-aging performance.

[0056] PE pipe structural parameters

[0057] The base layer thickness is 2-4mm, and the impact-resistant layer thickness is 2-3mm.

[0058] Preparation method

[0059] Raw material pretreatment: Ultra-high molecular weight polyethylene was dried at 80℃ for 4 hours, nano-silica aerogel modifier was dried at 60℃ for 2 hours, and graphene-carbon nanotube composite modifier was dried at 50℃ for 3 hours.

[0060] Base layer mixing: Toughening agent, photoinitiator, nano-silica aerogel modifier, graphene-carbon nanotube composite modifier, and ultra-high molecular weight polyethylene are mixed at 180℃ for 15-18 minutes at a mixing speed of 60-80 r / min. First, ultra-high molecular weight polyethylene, nano-silica aerogel modifier, and graphene-carbon nanotube composite modifier are premixed at 160-165℃ for 5-8 minutes, then the toughening agent and photoinitiator are added.

[0061] Impact-resistant layer compound: Thermoplastic polyurethane elastomer, liquid nitrile rubber, ethylene-vinyl acetate copolymer, nano calcium carbonate, antioxidant 1010 and ultraviolet absorber UV-531 are mixed in a two-roll mill at 160-170℃ for 10-15 minutes. The roller temperature of the two-roll mill is 160-165℃ for the front roller and 165-170℃ for the rear roller.

[0062] Double-layer co-extrusion: The base layer and impact-resistant layer are extruded separately using two single-screw extruders.

[0063] The screw length-to-diameter ratio of the base extruder is 30-35:1, with three-stage temperature control: 160-170℃ for the feeding section, 180-190℃ for the compression section, and 190-200℃ for the metering section. The screw speed is 20-30 r / min.

[0064] The impact-resistant extruder screw has a length-to-diameter ratio of 28-32:1 and a three-stage temperature control: 150-160℃ for the feeding section, 170-180℃ for the compression section, and 180-190℃ for the metering section. The screw speed is 15-25 r / min.

[0065] The temperature of the composite die head should be 190-210℃. Adjust the extrusion speed to match the traction speed to ensure uniform compounding.

[0066] UV crosslinking: Irradiation is performed using ultraviolet light with a wavelength of 360-420nm under nitrogen protection, at a distance of 10-20cm and an intensity of 200-300mW / cm. 2 The time is 2-3 hours.

[0067] Gradient cooling: First, air cool to 80℃ at a rate of ≤5℃ / min, then water cool to 25℃ at a rate of ≤10℃ / min.

[0068] Post-treatment: After water cooling, allow to stand at room temperature for 24-28 hours for aging treatment, and then grind the surface until the roughness Ra is 0.8-1.6μm.

[0069] The following are specific embodiments.

[0070] Example 1

[0071] Raw material composition

[0072] Base layer (parts by weight): 100 parts ultra-high molecular weight polyethylene, 10 parts EPDM rubber, 1.8 parts 2-hydroxy-2-methyl-1-phenylpropanone and benzoin dimethyl ether (mass ratio 1:1), 3 parts nano-silica aerogel modifier, and 2 parts graphene-carbon nanotube composite modifier (graphene:carbon nanotube ratio 1.5:1).

[0073] Impact-resistant layer (by mass): 65 parts thermoplastic polyurethane elastomer, 16 parts liquid nitrile rubber, 12 parts ethylene-vinyl acetate copolymer, 5.5 parts nano calcium carbonate, 0.65% antioxidant 1010, and 0.35% UV absorber UV-531.

[0074] Preparation steps, such as Figure 1 As shown.

[0075] The raw materials were pretreated according to the preparation method described above.

[0076] Base mixing: First, premix ultra-high molecular weight polyethylene, nano-silica aerogel modifier, and graphene-carbon nanotube composite modifier at 162℃ for 6 minutes, then add EPDM rubber and photoinitiator, and mix at 180℃ for 16 minutes at a speed of 70 r / min.

[0077] Impact-resistant layer mixing: mix at 163°C for the front roller and 167°C for the rear roller of the open mill for 12 minutes.

[0078] Double-layer co-extrusion: The temperatures of the three sections of the base layer extruder are 165℃, 185℃, and 195℃, and the rotation speed is 25r / min; the temperatures of the three sections of the impact layer extruder are 155℃, 175℃, and 185℃, and the rotation speed is 20r / min, with a composite die temperature of 200℃.

[0079] UV crosslinking: irradiation distance 15cm, intensity 250mW / cm 2 The time is 2.5 hours.

[0080] After gradient cooling, the surface was aged for 26 hours and then polished to Ra 1.2 μm.

[0081] Example 2

[0082] The difference from Example 1 is as follows:

[0083] The amount of toughening agent used in the base layer is 8 parts of EPDM rubber.

[0084] The amount of nano-silica aerogel modifier used is 2 parts.

[0085] The impact-resistant layer consists of 60 parts thermoplastic polyurethane elastomer, 18 parts liquid nitrile rubber, 14 parts ethylene-vinyl acetate copolymer, and 6 parts nano-calcium carbonate.

[0086] Example 3

[0087] The difference from Example 1 is as follows:

[0088] The amount of graphene-carbon nanotube composite modifier used at the base layer is 1 part (graphene:carbon nanotube ratio is 1:1).

[0089] The amount of photoinitiator used was 1.6 parts.

[0090] The impact-resistant layer consists of 70 parts thermoplastic polyurethane elastomer, 15 parts liquid nitrile rubber, 10 parts ethylene-vinyl acetate copolymer, and 5 parts nano-calcium carbonate.

[0091] Example 4

[0092] The difference from Example 1 is as follows:

[0093] The amount of base layer nano-silica aerogel modifier is 4 parts, and the amount of graphene-carbon nanotube composite modifier is 3 parts (graphene:carbon nanotube ratio is 2:1).

[0094] The amount of liquid nitrile rubber in the impact-resistant layer is 17 parts, and the amount of ethylene-vinyl acetate copolymer is 13 parts.

[0095] Example 5

[0096] The difference from Example 1 is as follows:

[0097] The amount of toughening agent used in the base layer is 12 parts of EPDM rubber.

[0098] The amount of photoinitiator used is 2.0 parts.

[0099] The impact-resistant layer contains 5.8 parts of nano-calcium carbonate, 0.7% of antioxidant 1010, and 0.4% of ultraviolet absorber UV-531.

[0100] The following is a comparative example.

[0101] Comparative Example 1

[0102] The difference from Example 1 is that no graphene-carbon nanotube composite modifier was added to the base layer, while the other raw materials and processes were the same as in Example 1.

[0103] Comparative Example 2

[0104] The difference from Example 1 is that liquid nitrile rubber was not added to the impact-resistant layer, but was replaced with an equal mass of thermoplastic polyurethane elastomer. Other raw materials and processes are the same as in Example 1.

[0105] Comparative Example 3

[0106] The difference from Example 1 is that no ultraviolet crosslinking treatment was performed during the preparation process, while the other raw materials and processes were the same as in Example 1.

[0107] Experimental verification

[0108] Experiment 1: Low-temperature embrittlement temperature test

[0109] Experimental methods

[0110] Referring to GB / T5470-2008 "Determination of Low-Temperature Impact Embrittlement Temperature of Plastics", PE pipe samples of 50mm×6mm×2mm were prepared and placed in an environment of -40℃ for 2 hours. The samples were then impacted from a height of 1m with a 10kg hammer, and the temperatures at which 50% of the samples did not become embrittled were recorded. The results are as follows:

[0111] Table 1

[0112]

[0113] As shown in Table 1, the low-temperature embrittlement temperatures of Examples 1-5 were all below -39℃, indicating that the bilayer structure combined with the modifier significantly improved the low-temperature resistance. Among them, Example 4 exhibited the best low-temperature performance due to its higher content of nano-silica aerogel and graphene-carbon nanotube composite modifier.

[0114] Comparative Example 1, without the addition of graphene-carbon nanotube composite modifier, had insufficient base layer strength and toughness, and was prone to embrittlement at low temperatures.

[0115] Comparative Example 2 lacks liquid nitrile rubber in its impact-resistant layer, resulting in reduced elasticity and decreased low-temperature embrittlement resistance.

[0116] Comparative Example 3 was not subjected to UV crosslinking, resulting in insufficient crosslinking degree of the base molecular chain, poor structural stability, and deteriorated low-temperature performance.

[0117] Experiment 2: Impact Strength Test of Simply Supported Beam

[0118] Experimental methods

[0119] Referring to GB / T1843-2008 "Determination of Impact Strength of Simply Supported Plastic Beams", the sample size was 80mm×10mm×4mm, the span was 64mm, the impact velocity was 3.5m / s, and the test temperatures were 23℃ and -20℃. The results are as follows:

[0120] Table 2

[0121]

[0122] As shown in Table 2, the impact strength of the examples at both room temperature and low temperature is significantly higher than that of the comparative examples. Example 4 exhibits the best impact performance due to optimized modifier dosage, maintaining 30.1 kJ / m² at -20°C. 2 .

[0123] Comparative Example 1 lacks a graphene-carbon nanotube composite modifier, resulting in the inability of the base layer to form an effective reinforcing network and a decrease in impact energy absorption capacity.

[0124] In Comparative Example 2, the impact-resistant layer lacks the toughening effect of liquid nitrile rubber, resulting in poor molecular chain mobility at low temperatures and reduced impact strength.

[0125] In Comparative Example 3, the uncrosslinked base layer molecular chains have weak intermolecular forces, making them prone to relative slippage during impact, which leads to a decrease in strength.

[0126] Experiment 3: Tensile property test

[0127] Experimental methods

[0128] Referring to GB / T1040.2-2006 "Determination of tensile properties of plastics - Part 2: Test conditions for molded and extruded plastics", the specimen was a type I dumbbell shape, the tensile speed was 50 mm / min, and the test temperature was 23℃. The results are as follows:

[0129] Table 3

[0130]

[0131] As shown in Table 3, the tensile strength and elongation at break of the examples are superior to those of the comparative examples. Due to the synergistic effect of the modifier, Example 4 achieved a tensile strength of 48.3 MPa and an elongation at break of 395%.

[0132] In Comparative Example 1, the lack of graphene-carbon nanotube composite modifier in the base layer affected the dispersibility of the nano-silica aerogel, resulting in a decrease in strength and elongation.

[0133] In Comparative Example 2, the composition of the impact-resistant layer was unbalanced, resulting in poor interfacial compatibility with the base layer and reduced overall tensile properties.

[0134] In Comparative Example 3, the uncrosslinked base layer molecular chains had insufficient orientation, making them prone to breakage during stretching and resulting in performance degradation.

[0135] Test 4: Weather Resistance Test

[0136] Experimental methods

[0137] Referring to GB / T3512-2014 "Plastics Hot Air Aging Test Method", the samples were placed in an 80℃ hot air aging chamber for 1000 hours, and the tensile strength retention rate and impact strength retention rate before and after aging were tested. The results are as follows:

[0138] Table 4

[0139]

[0140] As can be seen from Table 4, the aging resistance of the examples is significantly better than that of the comparative examples. Example 4 has the highest retention rate due to the reasonable amount of impact-resistant layer additives.

[0141] Comparative Example 1 lacks a graphene-carbon nanotube composite modifier in its base layer, which cannot effectively inhibit free radical oxidation, resulting in severe performance degradation after aging.

[0142] Comparative Example 2 lacked liquid nitrile rubber in its impact-resistant layer, resulting in uneven distribution of antioxidants and reduced aging protection.

[0143] In Comparative Example 3, the uncrosslinked base layer molecular chains are susceptible to oxidative attack, leading to a decrease in performance retention.

[0144] Test 5: Resistance to External Pressure

[0145] Experimental methods

[0146] Referring to GB / T9647-2015 "Determination of Ring Stiffness of Thermoplastic Pipes", the three-point bending method was used. The specimen length was 300 mm, the span was 200 mm, and the loading speed was 5 mm / min. The external pressure load when the specimen deformation was 3% was recorded. The results are as follows:

[0147] Table 5

[0148]

[0149] As can be seen from Table 5, the external pressure resistance of the embodiments is significantly higher than that of the comparative examples. Due to the optimization of the base layer and impact-resistant layer structure, the external pressure load of Embodiment 4 reaches 9.1 kN / m.

[0150] Comparative Example 1 shows that the base layer has insufficient strength and cannot effectively resist external pressure, resulting in a decrease in load-bearing capacity.

[0151] Comparative Example 2 shows that the impact-resistant layer has sufficient rigidity but insufficient toughness, and is prone to local deformation under pressure.

[0152] In Comparative Example 3, the uncrosslinked base layer has weak intermolecular bonding, making its structure prone to collapse under pressure and exhibiting poor resistance to external pressure.

[0153] The preferred embodiments of the present invention disclosed above are merely illustrative of the invention. These preferred embodiments do not exhaustively describe all details, nor do they limit the invention to the specific implementations described. Clearly, many modifications and variations can be made based on the content of this specification. This specification selects and specifically describes these embodiments to better explain the principles and practical applications of the invention, thereby enabling those skilled in the art to better understand and utilize the invention. The invention is limited only by the claims and their full scope and equivalents.

Claims

1. A PE pipe resistant to low-temperature embrittlement impact, characterized in that, The PE pipe comprises a base layer and an impact-resistant layer from the inside out; The base layer is made by melt blending 100 parts by weight of ultra-high molecular weight polyethylene, 8-12 parts by weight of toughening agent, 1.6-2 parts by weight of photoinitiator, 2-4 parts by weight of nano-silica aerogel modifier, and 1-3 parts by weight of graphene-carbon nanotube composite modifier; the impact-resistant layer is made by melt blending thermoplastic polyurethane elastomer, liquid nitrile rubber, ethylene-vinyl acetate copolymer, and nano-calcium carbonate in a mass ratio of 60-70:15-18:10-14:5-6 and then extruding it. The nano-silica aerogel modifier is prepared by the following method: Tetraethyl orthosilicate, anhydrous ethanol, and deionized water were mixed in a volume ratio of 1:3-5:1-3. Hydrochloric acid (0.5%-1.5% by mass) was added as a catalyst, and the mixture was stirred at room temperature for 2-4 hours to form a homogeneous sol. The sol was then transferred to a mold and gelled at 60-80°C for 6-10 hours. After gelation, the gel was immersed in a 10%-20% ethylene glycol solution for solvent replacement for 12-15 hours. Finally, supercritical drying was performed using carbon dioxide as the medium at 38-45°C and 12-15 MPa for 3-5 hours to obtain nano-silica aerogel. The obtained nano-silica aerogel was added to a 2%-5% silane coupling agent KH-550 ethanol solution and stirred at 58-70°C for 3-5 hours. After the reaction, the mixture was filtered and dried to obtain the nano-silica aerogel modifier with an average particle size of 10 nm. The graphene-carbon nanotube composite modifier is prepared by the following method: Graphene and carbon nanotubes in a mass ratio of 1-2:1 were added to a 4%-4.5% (w / w) aqueous solution of polyacrylamide and ultrasonically dispersed for 30-60 min at a power of 300-500 W. Then, coupling agent KH-560 was added at a mass of 0.5%-0.7% of the total mass of graphene and carbon nanotubes, and the mixture was stirred at 60-80℃ for 2-4 h. After the reaction, the mixture was freeze-dried at -40℃ under a vacuum of 1-2 Pa. Finally, the dried product was placed in a microwave reactor and treated at a power of 300-400 W for 8-10 min to obtain the graphene-carbon nanotube composite modifier.

2. The PE pipe resistant to low-temperature embrittlement impact according to claim 1, characterized in that, The toughening agent is EPDM rubber; The photoinitiator is 2-hydroxy-2-methyl-1-phenylpropanone and benzoin dimethyl ether.

3. The PE pipe resistant to low-temperature embrittlement impact according to claim 1, characterized in that, The thickness of the base layer is 2-4 mm, and the thickness of the impact-resistant layer is 2-3 mm.

4. The PE pipe resistant to low-temperature embrittlement impact according to claim 1, characterized in that, The impact-resistant layer also contains 0.6%-0.7% antioxidant 1010 and 0.3%-0.4% ultraviolet absorber UV-531 by mass.

5. A method for preparing a PE pipe resistant to low-temperature embrittlement impact as described in any one of claims 1-4, characterized in that, Includes the following steps: (1) Raw material pretreatment: ultra-high molecular weight polyethylene was dried at 80℃ for 4h, nano silica aerogel modifier was dried at 60℃ for 2h, and graphene-carbon nanotube composite modifier was dried at 50℃ for 3h. (2) Base layer mixing: toughening agent, photoinitiator, nano silica aerogel modifier, graphene-carbon nanotube composite modifier and ultra-high molecular weight polyethylene are mixed at 180℃ for 15-18min, and the mixing speed is 60-80r / min. During mixing, ultra-high molecular weight polyethylene, nano silica aerogel modifier and graphene-carbon nanotube composite modifier are premixed at 160-165℃ for 5-8min, and then toughening agent, antifreeze agent and photoinitiator are added. (3) Impact layer mixing: thermoplastic polyurethane elastomer, liquid nitrile rubber, ethylene-vinyl acetate copolymer, nano calcium carbonate, antioxidant 1010 and ultraviolet absorber UV-531 are mixed at 160-170℃ for 10-15 min. (4) Double-layer co-extrusion: The base layer and the impact-resistant layer are extruded separately by two single-screw extruders equipped with screws of different length-to-diameter ratios. The length-to-diameter ratio of the screws of the extruder used for extruding the base layer is 30-35:1, and the length-to-diameter ratio of the screws of the extruder used for extruding the impact-resistant layer is 28-32:

1. The temperature of the base layer extruder is set to a three-stage temperature control: the temperature of the feeding section is 160-170℃, the temperature of the compression section is 180-190℃, and the temperature of the metering section is 190-200℃, with a screw speed of 20-30 r / min. The temperature of the impact-resistant layer extruder is also set to a three-stage temperature control: the temperature of the feeding section is 150-160℃, the temperature of the compression section is 170-180℃, and the temperature of the metering section is 180-190℃, with a screw speed of 15-25 r / min. The temperature of the composite die is controlled at 190-210℃. By adjusting the extrusion speed of the two extruders to be consistent with the traction speed of the traction machine, the base layer and the impact-resistant layer are uniformly composited in the composite die. (5) Ultraviolet crosslinking: Irradiation is carried out using ultraviolet light with a wavelength of 360-420nm under nitrogen protection; (6) Gradient cooling: First, air cool to 80℃ at a rate of ≤5℃ / min, then water cool to 25℃ at a rate of ≤10℃ / min; (7) Post-treatment: After water cooling, place the PE pipe at room temperature for 24-28 hours for aging treatment.

6. The preparation method according to claim 5, characterized in that, The mixing equipment mentioned in step (3) is an open mill, and the roller temperature of the open mill is controlled at 160-165℃ for the front roller and 165-170℃ for the rear roller.

7. 根据权利要求5所述的制备方法，其特征在于， 步骤（4）中辐照距离为10-20cm，辐照强度为200-300mW / cm2，辐照时间为2-3h。 8. The preparation method according to claim 5, characterized in that, After water cooling in step (6), the PE pipe is surface polished with a roughness Ra of 0.8-1.6μm.

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