Anti-aging polyethylene composite material for electric melting pipe fittings and preparation method thereof
By chemically bonding antioxidant monomers to a hydrotalcite carrier, and combining the layered structure and amide bonds of hydrotalcite, the problem of antioxidant migration at high temperatures is solved, thereby improving the heat and oxygen aging resistance and mechanical stability of electrofusion fittings.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- ANHUI WANDA PIPE TECHNOLOGY CO LTD
- Filing Date
- 2026-03-06
- Publication Date
- 2026-05-12
AI Technical Summary
In the existing technology, antioxidants have low molecular weight and are added to the polyethylene matrix through physical mixing, which makes them easy to migrate and volatilize under high temperature thermal fields. This cannot effectively improve the heat and oxygen aging resistance of electrofusion fittings, resulting in the material becoming brittle and reducing its strength during use.
By immobilizing antioxidant monomers on a hydrotalcite carrier through chemical bonding, the antioxidant components are in situ anchored in high-temperature welding hot zones and chlorinated water flow environments. The layered structure of the hydrotalcite is used to construct a physical barrier, and combined with the chemical stability of the amide bonds, the long-term aging resistance of the material is improved.
During high-temperature welding, antioxidants remain stably at the molten interface, reducing thermal oxidation fracture, constructing an anti-permeability barrier, and extending the service safety and mechanical stability of electrofusion fittings in complex water environments.
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Abstract
Description
Technical Field
[0001] This invention belongs to the field of polyethylene composite material technology, specifically an aging-resistant polyethylene composite material for electrofusion fittings and its preparation method. Background Technology
[0002] Polyethylene pipes, with their excellent toughness and reliable connection, have been widely used in urban water supply network systems. Among them, electrofusion fittings, as a special type of connector with embedded resistance wires, work by heating the inner wall of the fitting with electricity to melt the polyethylene resin on the outer wall of the pipe at high temperature, forming an integrated connection interface. This means that electrofusion fittings not only have to be in direct contact with tap water for a long time, but also have to withstand the severe high-temperature thermo-oxidative shock at the beginning of installation.
[0003] To improve the heat and oxygen aging resistance of polyethylene materials, the current industrial practice is to add antioxidants to the polyethylene matrix to form an anti-aging system. Among existing technologies, Chinese patent application CN110467769A discloses an antioxidant high-density polyethylene composite material and its preparation method. This method involves compounding phenolic antioxidant 1010 with phosphite antioxidant 168 to form a small-molecule composite antioxidant system, which is then added to the high-density polyethylene matrix through physical mixing with inorganic fillers to enhance the material's antioxidant properties.
[0004] In the above technical solution, because the antioxidant has a low molecular weight and is dispersed in the matrix only through physical action, its bonding force with the matrix is weak. Under the action of the high temperature thermal field of electrofusion welding, the small molecule antioxidant obtains extremely high thermal motion energy, which easily overcomes the intermolecular forces and undergoes violent thermal migration and volatilization to the surface of the melt. This irreversible physical migration can easily lead to the loss of antioxidant components at the key welding interface. The polyethylene molecular chains that are not protected are prone to oxidation, breakage and degradation under thermal and oxygen attack, which makes the pipe fitting material easy to become brittle and significantly reduce its strength during use, making it difficult to meet the requirements of long-term safe service of electrofusion pipe fittings. Summary of the Invention
[0005] The purpose of this invention is to provide an aging-resistant polyethylene composite material for electrofusion fittings and its preparation method. By chemically bonding antioxidant monomers onto a hydrotalcite carrier, the antioxidant components are in-situ anchored and chemically stabilized in the high-temperature welding thermal field and chlorinated water flow environment, thereby improving the long-term aging resistance of the material.
[0006] The objective of this invention can be achieved through the following technical solutions:
[0007] This invention provides an aging-resistant polyethylene composite material for electrofusion fittings, prepared through the following steps:
[0008] Step 1: Using thionyl chloride as an acyl chloride reagent, the carboxyl group of 3,5-di-tert-butyl-4-hydroxyphenylpropionic acid is activated to obtain an active acylation intermediate. Subsequently, the active acylation intermediate undergoes a nucleophilic substitution reaction with 4-aminostyrene to form an amide bond, thereby obtaining a polymerizable antioxidant monomer containing an amide group.
[0009] Step 2: Sodium dodecyl sulfonate containing long-chain alkyl groups and acrylic acid containing reactive double bonds are introduced into the interlayer structure of hydrotalcite through ion exchange to obtain hydrophobically modified hydrotalcite containing double bonds. Subsequently, using azobisisobutyronitrile as an initiator, polymerizable antioxidant monomers containing amide groups undergo in-situ free radical grafting polymerization with hydrophobically modified hydrotalcite containing double bonds to obtain hydrotalcite-based macromolecular antioxidants.
[0010] Step 3: Using high-density polyethylene as the matrix, mix it with hydrotalcite-based macromolecular antioxidant and polyethylene wax, melt extrude and granulate it in a twin-screw extruder to obtain an aging-resistant polyethylene composite material for electrofusion fittings.
[0011] This invention also provides a method for preparing an aging-resistant polyethylene composite material for electrofusion fittings, comprising the following steps:
[0012] High-density polyethylene, hydrotalcite-based macromolecular antioxidant, and polyethylene wax (lubricant) are placed in a high-speed mixer and mixed at 800-1000 r / min for 4-8 min. The mixed material is then melt-extruded and granulated in a twin-screw extruder to obtain an aging-resistant polyethylene composite material for electrofusion fittings.
[0013] Furthermore, the twin-screw extruder has processing temperatures of 160-170℃, 180-200℃, and 190-210℃, a die temperature of 190-210℃, and a screw speed of 200-300 r / min.
[0014] Furthermore, the mass ratio of high-density polyethylene, hydrotalcite-based macromolecular antioxidant, and polyethylene wax is 300-500:10-20:3-5.
[0015] Furthermore, the preparation process of the hydrotalcite-based macromolecular antioxidant is as follows:
[0016] Hydrophobically modified hydrotalcite containing double bonds and toluene were placed in a reactor under nitrogen atmosphere and stirred at 25-35℃ for 10-20 min. Polymerizable antioxidant monomers containing amide groups and azobisisobutyronitrile were added, and the reaction was carried out at 70-80℃ for 6-8 h. The mixture was filtered, washed, and vacuum dried to constant weight to obtain hydrotalcite-based macromolecular antioxidant.
[0017] This step involves in-situ free radical polymerization under an inert atmosphere. In a nitrogen-protected system, the antioxidant activity of the hindered phenolic structure is suppressed. Furthermore, due to the steric hindrance of the ortho-tert-butyl group, the phenolic hydroxyl group is unlikely to react with the carbon center free radical generated by the initiator. Therefore, under the thermal excitation of the initiator azobisisobutyronitrile, the reaction mainly manifests as highly active polymerization of the vinyl double bond: the primary free radicals generated by the initiator preferentially attack the double bonds in the monomer and the hydrotalcite, initiating the chain growth reaction. Under anaerobic and high-concentration monomer conditions, the polymerization rate is much greater than the inhibition rate, thus ensuring that the antioxidant monomer can polymerize smoothly and be anchored to the hydrotalcite layer by covalent bonds, achieving chemical immobilization of the antioxidant component.
[0018] Furthermore, the ratio of hydrophobically modified hydrotalcite containing double bonds, polymerizable antioxidant monomers containing amide groups, azobisisobutyronitrile, and toluene is 40-60g: 15-20g: 0.2-0.4g: 300-500mL.
[0019] Furthermore, the preparation process of hydrophobically modified hydrotalcite containing double bonds is as follows:
[0020] Hydrotalcite, sodium dodecyl sulfonate, acrylic acid, and deionized water were placed in a reaction vessel and stirred at 25-35℃ for 20-40 min. A 0.1 mol / L nitric acid solution was added to adjust the pH of the reaction solution to 5-6. The reaction was carried out at 60-80℃ for 2-4 h. The mixture was filtered, washed, and vacuum dried to constant weight. It was then ground and sieved to obtain hydrophobically modified hydrotalcite containing double bonds.
[0021] This step involves anion exchange between the layers of hydrotalcite. Under acidic and heated conditions, carbonate ions between the hydrotalcite layers are dissociated. Sodium dodecyl sulfonate and acrylic acid in the reaction solution enter the hydrotalcite interlayer or adsorb onto the layer surface through electrostatic attraction, displacing the original inorganic anions. The long-chain alkyl group of sodium dodecyl sulfonate lowers the surface energy of the hydrotalcite through a covering effect, changing it from hydrophilic to hydrophobic. Meanwhile, the acrylate ions interact with the metal cations (Mg²⁺) in the layer through their carboxyl ends. 2+ / Al 3+ Coordination or electrostatic bonding occurs, successfully introducing carbon-carbon double bonds with polymerization activity, providing reaction sites for subsequent chemical grafting.
[0022] Furthermore, the ratio of hydrotalcite, sodium dodecyl sulfonate, acrylic acid, and deionized water is 50-70g: 6-8g: 10-14g: 600-800mL.
[0023] Furthermore, the preparation process of polymerizable amide-containing antioxidant monomers is as follows:
[0024] 4-Aminostyrene, N,N-diisopropylethylamine, and dichloromethane were placed in a reaction vessel and stirred at 25-35°C for 10-20 min. After cooling to 0-5°C, an active acylation intermediate was added, and the mixture was heated to 25-35°C for 2-4 h. The reaction solution was extracted and washed, and the lower dichloromethane organic phase was collected. Anhydrous magnesium sulfate was added for drying, and the mixture was filtered to remove impurities. The solvent was then removed by rotary evaporation to obtain a polymerizable amide-containing antioxidant monomer. The reaction process is shown below:
[0025]
[0026] This step involves an amidation reaction between an amine and an acyl chloride. The amino group in 4-aminostyrene is used to nucleophilically substitute the active acylation intermediate, forming a stable amide bond structure. At the same time, the organic base N,N-diisopropylethylamine added to the system acts as an acid-binding agent, rapidly neutralizing the hydrogen chloride generated in the reaction and forming a hydrochloride precipitate, thus disrupting the reversible equilibrium of the reaction and pushing the reaction to proceed to the end, completing the construction of a polymerizable amide-containing antioxidant monomer.
[0027] Furthermore, the ratio of 4-aminostyrene, N,N-diisopropylethylamine, active acylation intermediate, and dichloromethane is 10-20g: 20-40g: 30-50g: 300-500mL.
[0028] Furthermore, the preparation process of the active acylation intermediate is as follows:
[0029] 3,5-Di-tert-butyl-4-hydroxyphenylpropionic acid and dichloromethane were placed in a reaction vessel under a nitrogen atmosphere and stirred at 25-35°C for 20-40 min. Thionyl chloride was then added, and the reaction was carried out at 40-60°C for 4-6 h. The mixture was then distilled under reduced pressure to obtain the active acylated intermediate. The reaction process is shown below:
[0030]
[0031] This step utilizes thionyl chloride as a highly efficient acylation reagent to convert the terminal carboxyl group (-COOH) of 3,5-di-tert-butyl-4-hydroxyphenylpropionic acid into a more chemically active acyl chloride group (-COCl) through a nucleophilic substitution process. In this process, the hindered phenolic hydroxyl group in the starting material structure is much less active than the carboxyl group due to the huge steric hindrance of the two adjacent tert-butyl groups. Therefore, the reaction mainly occurs at the carboxyl site, achieving highly selective conversion of functional groups.
[0032] Furthermore, the ratio of 3,5-di-tert-butyl-4-hydroxyphenylpropionic acid, sulfoxide, and dichloromethane is 50-100g:40-60g:200-300mL.
[0033] The beneficial effects of this invention are:
[0034] 1. The aging-resistant polyethylene composite material for electrofusion fittings prepared by this invention utilizes hydrotalcite as a carrier to graft small-molecule antioxidants onto it through chemical bonds, thereby increasing the molecular weight and volume of the antioxidant components and effectively inhibiting their thermal mobility. During high-temperature welding of electrofusion fittings, this macromolecular antioxidant can remain stably at the molten interface, ensuring improved anti-aging ability of the fittings in the connection area. At the same time, the unique layered structure of the hydrotalcite layer plays a crucial role in thermal buffering and thermal barrier at high temperatures. During the welding process, the inorganic skeleton blocks the rapid conduction of heat, avoiding local overheating and significantly reducing the thermal oxidation and breakage of polyethylene polymer chains at high welding temperatures.
[0035] 2. The aging-resistant polyethylene composite material for electrofusion fittings prepared in this invention utilizes the long-chain alkyl groups of sodium dodecyl sulfonate to hydrophobize hydrophilic hydrotalcite, enabling the hydrotalcite-based macromolecular antioxidant to be uniformly dispersed in the non-polar polyethylene matrix. Simultaneously, the hierarchical structure of hydrotalcite constructs a multi-layered, interwoven physical barrier. Under specific service scenarios where electrofusion fittings are subjected to long-term internal water pressure and contact with tap water, this forces the permeating water and chloride ions to bypass these layers of barriers, significantly extending the diffusion path of corrosive media. Furthermore, the introduction of highly stable amide bonds into the antioxidant monomers effectively resists the chemical attack and hydrolytic breakage of residual chloride ions in tap water, ensuring the integrity of the antioxidant molecular structure. This synergistic effect of macroscopic physical barrier and microscopic chemical resistance not only constructs a tight anti-permeation barrier for the polyethylene matrix but also prevents the propagation of microcracks induced by media erosion during long-term service, significantly improving the long-term service safety of electrofusion fittings in complex water environments. Detailed Implementation
[0036] 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.
[0037] Example 1: This example provides an aging-resistant polyethylene composite material for electrofusion fittings, prepared through the following steps:
[0038] S1: 50g of 3,5-di-tert-butyl-4-hydroxyphenylpropionic acid and 200mL of dichloromethane were placed in a reaction vessel under nitrogen atmosphere protection. The mixture was stirred at 200r / min for 20min at 25℃. 40g of thionyl chloride was added, and the reaction was continued at 40℃ with the same stirring rate for 4h. After the reaction was completed, the mixture was cooled to room temperature and distilled under reduced pressure to obtain the active acylated intermediate.
[0039] S2: Place 10g of 4-aminostyrene, 20g of N,N-diisopropylethylamine and 300mL of dichloromethane in a reaction vessel, stir at 200r / min for 10min at 25℃, cool to 0℃, add 30g of active acylation intermediate, raise the temperature to 25℃ and continue the reaction at the same stirring rate for 2h. After the reaction is completed, transfer the reaction solution to a separatory funnel, and extract and wash it successively with 0.5mol / L dilute hydrochloric acid, saturated sodium bicarbonate solution and saturated brine. Collect the lower dichloromethane organic phase, add anhydrous magnesium sulfate to dry, filter to remove impurities, and rotary evaporate the filtrate under reduced pressure at 30℃ until the solvent is completely removed to obtain a polymerizable amide-containing antioxidant monomer.
[0040] S3: Place 50g of hydrotalcite, 6g of sodium dodecyl sulfonate, 10g of acrylic acid and 600mL of deionized water in a reaction vessel, stir at 200r / min for 20min at 25℃, add 0.1mol / L nitric acid solution to adjust the pH of the reaction solution to 5, and continue to react at 60℃ with the same stirring rate for 2h. After the reaction is completed, cool to room temperature, filter, wash the filter cake twice with deionized water, vacuum dry at 60℃ to constant weight, grind, and sieve through a 300-mesh sieve to obtain hydrophobically modified hydrotalcite containing double bonds.
[0041] S4: 40g of hydrophobically modified hydrotalcite containing double bonds and 300mL of toluene were placed in a reactor under nitrogen atmosphere protection. The mixture was stirred at 200r / min for 10min at 25℃. 15g of polymerizable amide-containing antioxidant monomer and 0.2g of azobisisobutyronitrile were added. The mixture was reacted at 70℃ with the same stirring rate for 6h. After the reaction was completed, the mixture was cooled to room temperature, filtered, and the filter cake was washed with deionized water until the last washing liquid was neutral. The mixture was then vacuum dried at 60℃ to constant weight to obtain the hydrotalcite-based macromolecular antioxidant.
[0042] S5: Place 300g of high-density polyethylene, 10g of hydrotalcite-based macromolecular antioxidant and 3g of polyethylene wax (lubricant) in a high-speed mixer and mix at 800r / min for 4min. Place the mixed material in a twin-screw extruder with processing temperatures of 160℃, 180℃ and 190℃, a die temperature of 190℃ and a screw speed of 200r / min. After melt blending and extrusion, the material is cooled and pelletized to obtain an aging-resistant polyethylene composite material for electrofusion fittings.
[0043] Example 2: This example provides an aging-resistant polyethylene composite material for electrofusion fittings, prepared through the following steps:
[0044] S1: Place 75g of 3,5-di-tert-butyl-4-hydroxyphenylpropionic acid and 250mL of dichloromethane in a reaction vessel under nitrogen atmosphere protection, stir at 200-300r / min for 20-40min at 25-35℃, add 50g of thionyl chloride, and continue the reaction at 50℃ with the same stirring rate for 5h. After the reaction is completed, cool to room temperature and distill under reduced pressure to obtain the active acylated intermediate.
[0045] S2: 15g of 4-aminostyrene, 30g of N,N-diisopropylethylamine and 400mL of dichloromethane were placed in a reaction vessel and stirred at 250r / min for 15min at 30℃. After cooling to 3℃, 40g of active acylation intermediate was added. After the addition was completed, the temperature was raised to 30℃ and the reaction was continued for 3h with the same stirring rate. After the reaction was completed, the reaction solution was transferred to a separatory funnel and extracted and washed successively with 0.5mol / L dilute hydrochloric acid, saturated sodium bicarbonate solution and saturated brine. The lower dichloromethane organic phase was collected, dried with anhydrous magnesium sulfate, filtered to remove impurities, and the filtrate was rotary evaporated under reduced pressure at 35℃ until the solvent was completely removed to obtain a polymerizable amide-containing antioxidant monomer.
[0046] S3: 60g of hydrotalcite, 7g of sodium dodecyl sulfonate, 12g of acrylic acid and 700mL of deionized water were placed in a reaction vessel and stirred at 250r / min for 30min at 30℃. The pH of the reaction solution was adjusted to 5.5 by adding 0.1mol / L nitric acid solution. The reaction was continued at 70℃ with the same stirring rate for 3h. After the reaction was completed, the mixture was cooled to room temperature, filtered, and the filter cake was washed with deionized water until the last washing liquid was neutral. The mixture was then vacuum dried at 70℃ to constant weight, ground, and sieved through a 350-mesh sieve to obtain hydrophobically modified hydrotalcite containing double bonds.
[0047] S4: 50g of hydrophobically modified hydrotalcite containing double bonds and 400mL of toluene were placed in a reactor under nitrogen atmosphere protection. The mixture was stirred at 250r / min for 15min at 30℃. 18g of polymerizable amide-containing antioxidant monomer and 0.3g of azobisisobutyronitrile were added. The mixture was reacted at 75℃ with the same stirring rate for 7h. After the reaction was completed, the mixture was cooled to room temperature, filtered, and the filter cake was washed three times with anhydrous ethanol. The cake was then vacuum dried at 70℃ to constant weight to obtain the hydrotalcite-based macromolecular antioxidant.
[0048] S5: Place 400g of high-density polyethylene, 15g of hydrotalcite-based macromolecular antioxidant and 4g of polyethylene wax in a high-speed mixer and mix at 900r / min for 4-8min. Place the mixed material in a twin-screw extruder with processing temperatures of 165℃, 190℃ and 200℃, a die temperature of 200℃ and a screw speed of 250r / min. After melt blending and extrusion, the material is cooled and pelletized to obtain an aging-resistant polyethylene composite material for electrofusion fittings.
[0049] Example 3: This example provides an aging-resistant polyethylene composite material for electrofusion fittings, prepared through the following steps:
[0050] S1: 100g of 3,5-di-tert-butyl-4-hydroxyphenylpropionic acid and 300mL of dichloromethane were placed in a reaction vessel under nitrogen atmosphere protection. The mixture was stirred at 300r / min for 40min at 35℃. 60g of thionyl chloride was added, and the reaction was continued at 60℃ with the same stirring rate for 6h. After the reaction was completed, the mixture was cooled to room temperature and distilled under reduced pressure to obtain the active acylated intermediate.
[0051] S2: 20g of 4-aminostyrene, 40g of N,N-diisopropylethylamine and 500mL of dichloromethane were placed in a reaction vessel and stirred at 300r / min for 20min at 35℃. After cooling to 5℃, 50g of active acylation intermediate was added. After the addition was completed, the temperature was raised to 35℃ and the reaction was continued at the same stirring rate for 4h. After the reaction was completed, the reaction solution was transferred to a separatory funnel and extracted and washed successively with 0.5mol / L dilute hydrochloric acid, saturated sodium bicarbonate solution and saturated brine. The lower dichloromethane organic phase was collected, dried with anhydrous magnesium sulfate, filtered to remove impurities, and the filtrate was rotary evaporated under reduced pressure at 40℃ until the solvent was completely removed to obtain a polymerizable amide-containing antioxidant monomer.
[0052] S3: 70g of hydrotalcite, 8g of sodium dodecyl sulfonate, 14g of acrylic acid and 800mL of deionized water were placed in a reaction vessel and stirred at 300r / min for 40min at 35℃. The pH of the reaction solution was adjusted to 6 by adding 0.1mol / L nitric acid solution. The reaction was continued at 80℃ with the same stirring rate for 4h. After the reaction was completed, the mixture was cooled to room temperature, filtered, and the filter cake was washed with deionized water until the last washing liquid was neutral. The mixture was then vacuum dried at 80℃ to constant weight, ground, and sieved through a 400-mesh sieve to obtain hydrophobically modified hydrotalcite containing double bonds.
[0053] S4: 60g of hydrophobically modified hydrotalcite containing double bonds and 500mL of toluene were placed in a reactor under nitrogen atmosphere protection. The mixture was stirred at 300r / min for 20min at 35℃. 20g of polymerizable amide-containing antioxidant monomer and 0.4g of azobisisobutyronitrile were added. The mixture was reacted at 80℃ with the same stirring rate for 8h. After the reaction was completed, the mixture was cooled to room temperature, filtered, and the filter cake was washed 4 times with anhydrous ethanol. The cake was then vacuum dried at 80℃ to constant weight to obtain the hydrotalcite-based macromolecular antioxidant.
[0054] S5: Place 500g of high-density polyethylene, 20g of hydrotalcite-based macromolecular antioxidant and 5g of polyethylene wax (lubricant) in a high-speed mixer and mix at 1000r / min for 8min. Place the mixed material in a twin-screw extruder with processing temperatures of 170℃, 200℃ and 210℃, a die temperature of 210℃ and a screw speed of 300r / min. After melt blending and extrusion, the material is cooled and pelletized to obtain an aging-resistant polyethylene composite material for electrofusion fittings.
[0055] Comparative Example 1: The difference from Example 2 is that commercially available hydrotalcite was used instead of the hydrophobic modified hydrotalcite containing double bonds prepared in step S3, while the other steps remained unchanged, to prepare an aging-resistant polyethylene composite material for electrofusion fittings.
[0056] Comparative Example 2: The difference from Example 2 is that a commercially available antioxidant was used instead of the hydrotalcite-based macromolecular antioxidant prepared in step S4, while the other steps remained unchanged, to prepare an aging-resistant polyethylene composite material for electrofusion fittings.
[0057] Comparative Example 3: The difference from Example 2 is that the hydrophobic modified hydrotalcite containing double bonds prepared in step S3 is not added in step S4, while the other steps remain unchanged, and an aging-resistant polyethylene composite material for electrofusion fittings is prepared.
[0058] The high-density polyethylene purchased in the above embodiments and comparative examples was produced by Maoming Branch of China Petroleum & Chemical Corporation, model TR-480. The melt flow rate was 0.15-0.25 g / 10 min (190℃, 5 kg); the hydrotalcite was produced by Shanghai Maclean Biochemical Technology Co., Ltd., CAS number 11097-59-9, which is a magnesium-aluminum type hydrotalcite with a magnesium-aluminum molar ratio of 3:1 and an average flake diameter ≤2 μm; the antioxidant was produced by Tianjin Lianlong New Materials Co., Ltd., model Antioxidant 1010, CAS number 6683-19-8, which is a phenolic antioxidant containing hindered ester bonds.
[0059] The aging-resistant polyethylene composite materials for electrofusion fittings prepared in Examples 1-3 and Comparative Examples 1-3 were subjected to performance tests, and the test results are shown in Table 1.
[0060] Sample preparation: The polyethylene composite material granules prepared in the above examples and comparative examples were injection molded in an injection molding machine to prepare type 1A dumbbell-shaped tensile specimens conforming to GB / T 1040.2 standard. These specimens were used as pre-aging specimens for mechanical property testing.
[0061] Accelerated corrosion aging test: Simulating the long-term service scenario of electrofusion fittings in a chloride-containing tap water network, all samples were subjected to accelerated corrosion aging treatment. The samples were completely immersed in an aqueous solution of sodium hypochlorite at 80°C with an effective chlorine concentration of 10 ppm, and continuously soaked for 168 hours under constant temperature conditions to obtain the aged samples.
[0062] Mechanical properties: Referring to standard GB / T 1040.2-2006, the specimens before and after aging were placed on a universal testing machine for tensile testing. The tensile speed was set to 50 mm / min until the specimen broke. The tensile strength and elongation at break of the material were recorded. The higher the tensile strength and elongation at break of the specimen, the better the mechanical properties of the material.
[0063] Table 1. Performance Test Table of Aging-Resistant Polyethylene Composite Materials Used in Electrofusion Fittings
[0064]
[0065] As shown in Table 1, the performance of the aging-resistant polyethylene composite materials for electrofusion fittings prepared in Examples 1-3 is superior to that in Comparative Examples 1-3. Furthermore, the mechanical properties of the materials did not change significantly after accelerated corrosion aging tests. This indicates that the hydrotalcite-based macromolecular antioxidant prepared in this invention provides rigid support in the polyethylene matrix by utilizing a uniformly dispersed hydrotalcite skeleton, while firmly anchoring the chlorination-resistant amide groups through chemical bonding. This effectively overcomes the dual defects of small molecule antioxidants, such as easy physical migration and easy chemical failure, ensuring that the electrofusion fittings maintain excellent anti-aging ability and mechanical stability even under long-term chlorine-containing high-temperature water flow.
[0066] The elongation at break and tensile strength of the sample before aging in Comparative Example 1 were significantly reduced. This may be because the commercially available hydrotalcite is highly polar and causes severe agglomeration in the non-polar polyethylene matrix, forming stress concentration points, which in turn disrupts the continuity of the matrix and reduces the mechanical properties of the material.
[0067] The decrease in elongation at break and tensile strength of the sample in Comparative Example 2 before and after aging was significantly greater than that in Comparative Example 3. This may be because commercially available small molecule antioxidants contain ester bonds that are prone to hydrolysis and failure in high-temperature water containing chloride ions. This indicates that the antioxidant monomer containing amide bonds synthesized in this invention has high stability under water conditions containing chloride ions.
[0068] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention.
Claims
1. A method for preparing an aging-resistant polyethylene composite material for electrofusion fittings, characterized in that, Includes the following steps: Step 1: Using thionyl chloride as an acyl chloride reagent, the carboxyl group of 3,5-di-tert-butyl-4-hydroxyphenylpropionic acid is activated to obtain an active acylation intermediate. Subsequently, the active acylation intermediate undergoes a nucleophilic substitution reaction with 4-aminostyrene to form an amide bond, thereby obtaining a polymerizable antioxidant monomer containing an amide group. Step 2: Sodium dodecyl sulfonate containing long-chain alkyl groups and acrylic acid containing reactive double bonds are introduced into the interlayer structure of hydrotalcite through ion exchange to obtain hydrophobically modified hydrotalcite containing double bonds. Subsequently, using azobisisobutyronitrile as an initiator, polymerizable antioxidant monomers containing amide groups undergo in-situ free radical grafting polymerization with hydrophobically modified hydrotalcite containing double bonds to obtain hydrotalcite-based macromolecular antioxidants. Step 3: Using high-density polyethylene as the matrix, mix it with hydrotalcite-based macromolecular antioxidant and polyethylene wax, melt extrude and granulate it in a twin-screw extruder to obtain an aging-resistant polyethylene composite material for electrofusion fittings.
2. The method for preparing an aging-resistant polyethylene composite material for electrofusion fittings according to claim 1, characterized in that, The hydrotalcite-based macromolecular antioxidant described in step two is prepared through the following steps: Hydrophobically modified hydrotalcite containing double bonds and toluene were placed in a reactor under nitrogen atmosphere and stirred at 25-35℃ for 10-20 min. Polymerizable antioxidant monomers containing amide groups and azobisisobutyronitrile were added, and the reaction was carried out at 70-80℃ for 6-8 h. The mixture was filtered, washed, and vacuum dried to constant weight to obtain hydrotalcite-based macromolecular antioxidant.
3. The method for preparing an aging-resistant polyethylene composite material for electrofusion fittings according to claim 2, characterized in that, The ratio of the hydrophobically modified hydrotalcite containing double bonds, the polymerizable amide-containing antioxidant monomer, azobisisobutyronitrile, and toluene is 40-60g: 15-20g: 0.2-0.4g: 300-500mL.
4. The method for preparing an aging-resistant polyethylene composite material for electrofusion fittings according to claim 3, characterized in that, The hydrophobically modified hydrotalcite containing double bonds is prepared through the following steps: Hydrotalcite, sodium dodecyl sulfonate, acrylic acid, and deionized water were placed in a reaction vessel and stirred at 25-35℃ for 20-40 min. A 0.1 mol / L nitric acid solution was added to adjust the pH of the reaction solution to 5-6. The reaction was carried out at 60-80℃ for 2-4 h. The mixture was filtered, washed, and vacuum dried to constant weight. It was then ground and sieved to obtain hydrophobically modified hydrotalcite containing double bonds.
5. The method for preparing an aging-resistant polyethylene composite material for electrofusion fittings according to claim 4, characterized in that, The ratio of hydrotalcite, sodium dodecyl sulfonate, acrylic acid, and deionized water is 50-70g: 6-8g: 10-14g: 600-800mL.
6. The method for preparing an aging-resistant polyethylene composite material for electrofusion fittings according to claim 3, characterized in that, The polymerizable amide-containing antioxidant monomer is prepared by the following steps: 4-Aminostyrene, N,N-diisopropylethylamine and dichloromethane were placed in a reaction vessel and stirred at 25-35℃ for 10-20 min. After cooling to 0-5℃, an active acylation intermediate was added, and the mixture was heated to 25-35℃ and reacted for 2-4 h. The reaction solution was extracted and washed, and the lower dichloromethane organic phase was collected. Anhydrous magnesium sulfate was added for drying, and the mixture was filtered to remove impurities. The solvent was then rotary evaporated until completely removed to obtain a polymerizable amide-containing antioxidant monomer. The ratio of 4-aminostyrene, N,N-diisopropylethylamine, active acylation intermediate, and dichloromethane is 10-20g: 20-40g: 30-50g: 300-500mL.
7. The method for preparing an aging-resistant polyethylene composite material for electrofusion fittings according to claim 6, characterized in that, The preparation process of the active acylation intermediate is as follows: 3,5-Di-tert-butyl-4-hydroxyphenylpropionic acid and dichloromethane were placed in a reaction vessel under a nitrogen atmosphere and stirred at 25-35°C for 20-40 min. Then, thionyl chloride was added and reacted at 40-60°C for 4-6 h. The reaction was then carried out by vacuum distillation to obtain the active acylated intermediate. The ratio of 3,5-di-tert-butyl-4-hydroxyphenylpropionic acid, sulfoxide, and dichloromethane is 50-100g:40-60g:200-300mL.
8. The method for preparing an aging-resistant polyethylene composite material for electrofusion fittings according to claim 1, characterized in that, The mass ratio of high-density polyethylene, hydrotalcite-based macromolecular antioxidant, and polyethylene wax in step three is 300-500:10-20:3-5.
9. A method for preparing an aging-resistant polyethylene composite material for electrofusion fittings according to claim 1, characterized in that, The twin-screw extruder described in step three has processing temperatures of 160-170℃, 180-200℃, and 190-210℃, a die temperature of 190-210℃, and a screw speed of 200-300 r / min.
10. An aging-resistant polyethylene composite material for electrofusion fittings, characterized in that, The aging-resistant polyethylene composite material for electrofusion fittings, as described in any one of claims 1-9, is prepared by a method for preparing such a material.