A silane-modified antioxidant with anti-precipitation and anti-migration and a preparation method and application thereof

Abstract

The application discloses a silane-modified antioxidant with anti-precipitation and anti-migration, a preparation method and application thereof, and belongs to the technical field of polyethylene pipe materials. The antioxidant is obtained by optimizing and modifying a composite antioxidant, and three different types of antioxidants, namely, hindered phenol, aromatic amine and tocopherol, are chemically bonded to a molecular skeleton to form a composite and multi-mechanism antioxidant active end, so that the antioxidant has the advantages of excellent migration resistance and precipitation resistance, and the durability of the antioxidant is ensured. In addition, the modified antioxidant is applied to the preparation of a silane cross-linked polyethylene pipe material, has better compatibility, and is firmly fixed in a polymer network through covalent bond anchoring, so that the antioxidant molecule provides stable, durable and reliable antioxidant protection for the pipe material, the service life of the pipe material is greatly prolonged, and the total cost of replacement and maintenance is reduced.

Description

Technical Field

[0001] This invention relates to the field of polyethylene pipe technology, and more specifically, to a silane-modified antioxidant that resists precipitation and migration, its preparation method, and its application. Background Technology

[0002] Silane cross-linked polyethylene (PEX) pipes are widely used in building hot and cold water systems, underfloor heating pipes, and fluid transportation in the food industry due to their excellent heat resistance, chemical corrosion resistance, and mechanical strength. To ensure the service life of PEX pipes in long-term high-temperature and oxygen-containing environments, antioxidants are usually added to the polyethylene matrix to slow down its thermal oxidative degradation process.

[0003] Currently, commonly used antioxidants in industry are mainly small-molecule hindered phenolic or phosphite compounds. However, these small-molecule antioxidants are prone to migrating and precipitating from the polyethylene matrix during long-term use of PEX pipes, especially under the influence of high-temperature water flow. This loss of antioxidants not only leads to premature aging and failure of the pipes due to decreased antioxidant protection, but more seriously, the precipitated antioxidants may enter the transported medium (such as drinking water), causing water pollution and posing health and safety risks. For example, Chinese patent application number CN202310723567.0 discloses a silane crosslinked polyethylene material. This application discloses a silane crosslinked polyethylene material, mainly composed of the following components in parts by weight: 240-300 parts of polyethylene composite resin, 20-28 parts of modified silane crosslinking agent, 12-16 parts of stabilizer, 10-16 parts of initiator, 12-14 parts of antioxidant, 20-24 parts of catalyst, 50-70 parts of reinforcing agent, 26-30 parts of elastomer, 6-8 parts of water-absorbing agent, and 60-70 parts of auxiliary agent carrier. This method improves the crosslinking transition strength of the cable material by adding a modified silane crosslinking agent, and improves the electrical properties of the cable material by adding a stabilizer; however, the compatibility with oxidation and migration issues still need further improvement. Summary of the Invention

[0004] Based on this, in order to solve one of the above-mentioned technical problems, the present invention provides a silane-modified antioxidant that resists precipitation and migration, its preparation method, and its application. The specific technical solution is as follows:

[0005] A silane-modified antioxidant that resists precipitation and migration, wherein the general molecular structure of the silane-modified antioxidant is: AO-L-SiX3; Wherein, AO is a functional group with antioxidant activity; L is a linking group; SiX3 is a hydrolyzable silane group, and X is a hydrolyzable group.

[0006] Furthermore, the antioxidant functional group is obtained from 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionic acid, 4,4'-bis(phenylisopropyl)diphenylamine, and tocopherol.

[0007] Further, the mass ratio of 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionic acid, 4,4'-bis(phenylisopropyl)diphenylamine and tocopherol is (3~7):(1~3):(1~2).

[0008] Furthermore, the linking group is at least one of short-chain alkyl, ester, and amide bonds.

[0009] Furthermore, the hydrolyzable group X is selected from at least one of methoxy, ethoxy, and chloro groups.

[0010] In addition, the present invention also provides a method for preparing a silane-modified antioxidant that resists precipitation and migration, the preparation method comprising the following steps: Under the protection of an inert gas, an antioxidant containing antioxidant functional groups is dispersed in a solvent, then a catalyst is added and stirred until homogeneous. Silane coupling agent is then slowly added dropwise. The reaction is carried out under reflux at a temperature of 80℃~120℃ for 4h~8h. After the reaction is completed, the solvent and byproducts are removed by vacuum distillation. After washing and purification, a silane-modified antioxidant is obtained.

[0011] Furthermore, the silane coupling agent is at least one selected from vinyltriethoxysilane, vinyldimethylethoxysilane, allyltrichlorosilane, and allyltrimethoxysilane.

[0012] Furthermore, the solvent is at least one of ethanol and toluene; the catalyst is dibutyltin dilaurate.

[0013] In addition, the present invention also provides an application of the silane-modified antioxidant, wherein the application is the use of the silane-modified antioxidant in the preparation of silane cross-linked polyethylene pipes.

[0014] Furthermore, the preparation of the silane cross-linked polyethylene pipe includes the following steps: S1. High-density polyethylene and linear low-density polyethylene are blended to obtain a base resin; S2. The base resin, modified antioxidant, silane coupling agent, peroxide initiator and crosslinking catalyst are melt-blended and extruded at 180℃~200℃ to obtain a tube blank; S3. The tube blank is placed in hot water at 90℃~95℃ for 30h~40h to complete the crosslinking process and obtain the tube.

[0015] Compared with the prior art, the present invention has the following beneficial effects: 1. This invention optimizes and modifies a composite antioxidant by chemically bonding three different types of antioxidants—hindered phenols, aromatic amines, and tocopherols—to a molecular backbone, forming a composite and multi-mechanism antioxidant active end. Compared with traditional physical composite antioxidants, this invention has superior resistance to migration and precipitation, thereby ensuring the durability of the antioxidant.

[0016] 2. The modified antioxidant groups of the present invention contain antioxidant groups of 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionic acid, 4,4'-bis(phenylisopropyl)diphenylamine, and tocopherol. Among them, 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionic acid can capture alkyl free radicals, 4,4'-bis(phenylisopropyl)diphenylamine can capture alkyl free radicals and peroxide free radicals, and tocopherol can scavenge free radicals and inhibit oxidation reactions, reduce oxidative stress reactions, and achieve a synergistic effect to achieve better antioxidant performance.

[0017] 3. The modified antioxidant of the present invention, when applied in the preparation of silane crosslinked polyethylene pipes, exhibits better compatibility, solves the phase separation problem that may be caused by physical mixing, and is more uniformly dispersed in the polymer matrix. Through covalent bond anchoring, the antioxidant molecules are firmly fixed in the polymer network, providing stable, long-lasting, and reliable antioxidant protection for the pipes, significantly improving the service life of the pipes and reducing the total cost of replacement and maintenance. Detailed Implementation

[0018] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to its embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and do not limit the scope of protection of the invention.

[0019] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used herein in the description of the invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0020] An embodiment of the present invention provides a silane-modified antioxidant that resists precipitation and migration, wherein the general molecular structure of the silane-modified antioxidant is: AO-L-SiX3; Wherein, AO is a functional group with antioxidant activity; L is a linking group; SiX3 is a hydrolyzable silane group, and X is a hydrolyzable group.

[0021] In one embodiment, the antioxidant functional group is derived from 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionic acid, 4,4'-bis(phenylisopropyl)diphenylamine, and tocopherol.

[0022] In one embodiment, the mass ratio of 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionic acid, 4,4'-bis(phenylisopropyl)diphenylamine and tocopherol is (3~7):(1~3):(1~2).

[0023] In one embodiment, the linking group is at least one of short-chain alkyl, ester, and amide bonds.

[0024] In one embodiment, the hydrolyzable group X is selected from at least one of methoxy, ethoxy, and chloro groups.

[0025] In addition, the present invention also provides a method for preparing a silane-modified antioxidant that resists precipitation and migration, the preparation method comprising the following steps: Under the protection of an inert gas, an antioxidant containing antioxidant functional groups is dispersed in a solvent, then a catalyst is added and stirred until homogeneous. Silane coupling agent is then slowly added dropwise. The reaction is carried out under reflux at a temperature of 80℃~120℃ for 4h~8h. After the reaction is completed, the solvent and byproducts are removed by vacuum distillation. After washing and purification, a silane-modified antioxidant is obtained.

[0026] In one embodiment, the inert gas is nitrogen.

[0027] In one embodiment, the silane coupling agent is at least one of vinyltriethoxysilane, vinyldimethylethoxysilane, allyltrichlorosilane, and allyltrimethoxysilane.

[0028] In one embodiment, the solvent is at least one of ethanol and toluene; the catalyst is dibutyltin dilaurate.

[0029] In one embodiment, in the preparation of the silane-modified antioxidant, the weight ratio of the antioxidant containing antioxidant active functional groups, solvent, catalyst and silane coupling agent is (1~5):(10~15):(0.1~0.5):(3~8).

[0030] In addition, the present invention also provides an application of the silane-modified antioxidant, wherein the application is the use of the silane-modified antioxidant in the preparation of silane cross-linked polyethylene pipes.

[0031] In one embodiment, the preparation of the silane cross-linked polyethylene pipe includes the following steps: S1. High-density polyethylene and linear low-density polyethylene are blended to obtain a base resin; S2. The base resin, modified antioxidant, silane coupling agent, peroxide initiator and crosslinking catalyst are melt-blended and extruded at 180℃~200℃ to obtain a tube blank; S3. The tube blank is placed in hot water at 90℃~95℃ for 30h~40h to complete the crosslinking process and obtain the tube.

[0032] In one embodiment, the melt blending is performed using a twin-screw extruder.

[0033] In one embodiment, the twin screws have a length-to-diameter ratio of 30:1 and a screw rotation speed of 40 r / min.

[0034] In one embodiment, the weight ratio of the high-density polyethylene to the linear low-density polyethylene is (6~7):(3~4).

[0035] In one embodiment, the melt index of the high-density polyethylene is 0.6-1.8 g / 10 min.

[0036] In one embodiment, the linear low-density polyethylene has a melt index of 1.2-3.5 g / 10 min.

[0037] In one embodiment, the weight ratio of the base resin, modified antioxidant, silane coupling agent, peroxide initiator and crosslinking catalyst is 100:(0.1~3):(0.1~5):(0.1~3):(0.1~5).

[0038] In one embodiment, the silane coupling agent is at least one of vinyltrimethoxysilane and vinyldimethylethoxysilane.

[0039] In one embodiment, the peroxide initiator is at least one selected from di(2-ethylhexyl) peroxydicarbonate, tert-butyl peroxyneodecanate, tert-amyl peroxyneodecanate, tert-amyl peroxynevalerate, and tert-butyl peroxynevalerate.

[0040] The modified antioxidant obtained by the above scheme has excellent and stable antioxidant properties, and when applied to silane cross-linked polyethylene pipes, it can achieve excellent antioxidant effect and extend the service life of the pipes.

[0041] In one embodiment, the crosslinking catalyst is dibutyltin dilaurate.

[0042] The implementation schemes of the present invention will now be described in detail with reference to specific embodiments.

[0043] Example 1: A method for preparing a silane cross-linked polyethylene pipe includes the following steps: S1. A base resin is obtained by blending high-density polyethylene and linear low-density polyethylene in a weight ratio of 7:3. S2. By weight ratio, 100 parts of the base resin, 1 part of the modified antioxidant, 0.3 parts of vinyltrimethoxysilane, 1 part of tert-butyl peroxypentanoate and 2 parts of crosslinking catalyst are melt-blended and extruded at 180℃~200℃, with the length-to-diameter ratio of the twin screw being 30:1 and the screw speed being 40 r / min, to obtain a tube blank; The modified antioxidant is prepared as follows: under nitrogen protection, 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionic acid, 4,4'-di(phenylisopropyl)diphenylamine and tocopherol are mixed in a mass ratio of 5:3:2 to obtain an antioxidant containing antioxidant functional groups; 5 parts of the antioxidant containing antioxidant functional groups are dispersed in 10 parts of ethanol by weight, and then 0.1 parts of dibutyltin dilaurate are added. After stirring evenly, 5 parts of vinyltriethoxysilane are slowly added dropwise. The mixture is stirred and refluxed at 85°C for 6 hours. After the reaction is completed, the solvent and byproducts are removed by vacuum distillation. After washing and purification, the silane-modified antioxidant is obtained. S3. The tube blank is placed in hot water at 90°C for 35 hours to complete the crosslinking process and obtain the tube.

[0044] Example 2: A method for preparing a silane cross-linked polyethylene pipe includes the following steps: S1. A base resin is obtained by blending high-density polyethylene and linear low-density polyethylene in a weight ratio of 7:3. S2. By weight ratio, 100 parts of the base resin, 0.9 parts of modified antioxidant, 0.3 parts of vinyltrimethoxysilane, 1.2 parts of tert-butyl peroxypentanoate and 2 parts of crosslinking catalyst are melt-blended and extruded at 180℃~200℃, with the twin screw having a length-to-diameter ratio of 30:1 and a screw speed of 40 r / min to obtain a tube blank; The modified antioxidant is prepared as follows: under nitrogen protection, 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionic acid, 4,4'-di(phenylisopropyl)diphenylamine and tocopherol are mixed in a mass ratio of 6:2:2 to obtain an antioxidant containing antioxidant functional groups; 5 parts of the antioxidant containing antioxidant functional groups are dispersed in 10 parts of ethanol by weight, and then 0.1 parts of dibutyltin dilaurate are added. After stirring evenly, 4 parts of vinyltriethoxysilane are slowly added dropwise. The mixture is stirred and refluxed at 100°C for 5 hours. After the reaction is completed, the solvent and byproducts are removed by vacuum distillation. After washing and purification, the silane-modified antioxidant is obtained. S3. The tube blank is placed in hot water at 90°C for 35 hours to complete the crosslinking process and obtain the tube.

[0045] Example 3: A method for preparing a silane cross-linked polyethylene pipe includes the following steps: S1. A base resin is obtained by blending high-density polyethylene and linear low-density polyethylene in a weight ratio of 7:3. S2. By weight ratio, 100 parts of the base resin, 1 part of the modified antioxidant, 0.4 parts of vinyltrimethoxysilane, 1.1 parts of tert-butyl peroxypentanoate and 2 parts of crosslinking catalyst are melt-blended and extruded at 180℃~200℃, with the length-to-diameter ratio of the twin screws being 30:1 and the screw speed being 40 r / min, to obtain a tube blank; The modified antioxidant is prepared as follows: under nitrogen protection, 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionic acid, 4,4'-bis(phenylisopropyl)diphenylamine and tocopherol are mixed in a mass ratio of 6:3:1 to obtain an antioxidant containing antioxidant functional groups; 5 parts of the antioxidant containing antioxidant functional groups are dispersed in 10 parts of ethanol by weight, and then 0.1 parts of dibutyltin dilaurate are added. After stirring evenly, 4 parts of vinyltriethoxysilane are slowly added dropwise. The mixture is stirred and refluxed at 95°C for 7 hours. After the reaction is completed, the solvent and byproducts are removed by vacuum distillation. After washing and purification, the silane-modified antioxidant is obtained. S3. The tube blank is placed in hot water at 90°C for 35 hours to complete the crosslinking process and obtain the tube.

[0046] Comparative Example 1: Compared with Example 3, the difference between Comparative Example 1 and Example 3 is that the modified antioxidant in Comparative Example 1 only contains 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionic acid, while the rest is the same as in Example 3.

[0047] Comparative Example 2: The difference between Comparative Example 2 and Example 3 is that only 4,4'-bis(phenylisopropyl)diphenylamine was added to the modified antioxidant of Comparative Example 2, while the rest was the same as in Example 1.

[0048] Comparative Example 3: The difference between Comparative Example 3 and Example 3 is that the modified antioxidant in Comparative Example 3 only contains a single tocopherol, while the rest is the same as in Example 1.

[0049] Comparative Example 4: The difference between Comparative Example 4 and Example 3 is that the modified antioxidant in Comparative Example 4 is obtained by modifying a mixture of 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionic acid and 4,4'-bis(phenylisopropyl)diphenylamine in a mass ratio of 1:1. Otherwise, it is the same as Example 1.

[0050] Comparative Example 5: The difference between Comparative Example 5 and Example 3 is that the antioxidant in Comparative Example 5 was not modified, but otherwise it was the same as Example 3.

[0051] Comparative Example 6: The difference between Comparative Example 6 and Example 3 is that the silane cross-linked polyethylene pipe in Comparative Example 6 did not contain any modified antioxidants, while the rest was the same as in Example 3.

[0052] The performance of the silane cross-linked polyethylene pipe samples prepared in Examples 1-3 and the silane cross-linked polyethylene pipe samples prepared in Comparative Examples 1-6 was tested, and the results are shown in Table 1 below. 1. Crosslinking degree: Each sample was tested according to the test method for crosslinking degree of crosslinked polyethylene (PE-X) pipes and fittings in GB / T18474-2001.

[0053] 2. Tensile strength: ISO6529-2:2020, test speed 50mm / min, dumbbell-shaped specimen.

[0054] 3. Environmental stress cracking time: ASTM D1693-15, polyoxyethylene (9) nonylphenyl ether (CAS No. 68412-54-4) solution with a mass-volume concentration of 50 g / mL, type A specimen, notch depth of 0.3 mm, cracking time recorded at 80°C.

[0055] 4. Antioxidant properties: ISO11346:2014 (Oxidation Induction Time Method, OIT), test conditions: 200℃, oxygen flow rate 50mL / min, record oxidation induction time (min) to reflect the material's antioxidant capacity.

[0056] Table 1: Performance Test Results

[0057] As can be seen from the data analysis in Table 1, the present invention, through optimization of the oxidant, compounding and then modification treatment, has better antioxidant properties, and the degree of crosslinking in the silane crosslinked polyethylene pipe is uniform, the structure is stable, the overall compatibility is excellent, the antioxidant stability is excellent, and the long-term durability is excellent. Compared to Example 3, Comparative Example 1, which added only 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionic acid, Comparative Example 2, which added only 4,4'-bis(phenylisopropyl)diphenylamine, and Comparative Example 3, which added only tocopherol, not only had a slight impact on the strength of the pipe, but also showed a significant decrease in its environmental stress cracking resistance and antioxidant performance. This indicates that a single antioxidant component cannot achieve a synergistic effect, resulting in insufficient antioxidant capacity of the pipe and affecting its long-term durability. Comparative Example 4 used a mixture of 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionic acid and 4,4'-bis(phenylisopropyl)diphenylamine in a mass ratio of 1:1. The modified product obtained after compounding, although its antioxidant performance is higher than that of the single component in Comparative Examples 1-3, is still worse than that in Example 3, indicating that there is a synergistic effect among the antioxidants of the present invention, and the compounding can promote the antioxidant activity of the pipe. The antioxidant in Comparative Example 5 was not modified, and its compatibility in the pipe was poor, and the degree of crosslinking decreased significantly, indicating that the unmodified antioxidant has a certain inhibitory effect on crosslinking, and that the unmodified antioxidant is easy to migrate and precipitate, with poor antioxidant durability and significantly worse antioxidant aging resistance than that in Example 3. No antioxidant was added in Comparative Example 6. The lack of antioxidant seriously affected the antioxidant aging resistance of the pipe and made the stress cracking resistance poor. Overall, this invention demonstrates a synergistic effect among the antioxidants present invention. By chemically bonding and fixing them within the polymer network, it effectively solves the problems of migration and precipitation. Single antioxidants, unmodified antioxidants, or the absence of antioxidants all lead to a significant decline in material performance. In contrast, the silane-modified composite antioxidant of this invention exhibits significant advantages in terms of crosslinking degree, mechanical properties, resistance to environmental stress cracking, and antioxidant properties.

[0058] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0059] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this invention patent should be determined by the appended claims.

Claims

1. A silane-modified antioxidant with anti-precipitation and anti-migration properties, characterized in that, The general molecular structure formula of the silane-modified antioxidant is: AO-L-SiX3; Wherein, AO is a functional group with antioxidant activity; L is a linking group; SiX3 is a hydrolyzable silane group, and X is a hydrolyzable group.

2. The silane-modified antioxidant according to claim 1, characterized in that, The antioxidant functional group is derived from 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionic acid, 4,4'-bis(phenylisopropyl)diphenylamine, and tocopherol.

3. The silane-modified antioxidant according to claim 1, characterized in that, The mass ratio of 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionic acid, 4,4'-bis(phenylisopropyl)diphenylamine and tocopherol is (3~7):(1~3):(1~2).

4. The silane-modified antioxidant according to claim 1, characterized in that, The linking group is at least one of short-chain alkyl, ester, and amide bonds.

5. The silane-modified antioxidant according to claim 1, characterized in that, The hydrolyzable group X is selected from at least one of methoxy, ethoxy, and chlorin.

6. A method for preparing a silane-modified antioxidant that resists precipitation and migration, characterized in that, The preparation method is used to prepare the silane-modified antioxidant with anti-precipitation and anti-migration properties as described in any one of claims 1 to 5, and the preparation method includes the following steps: Under the protection of an inert gas, an antioxidant containing antioxidant functional groups is dispersed in a solvent, then a catalyst is added and stirred until homogeneous. Silane coupling agent is then slowly added dropwise. The reaction is carried out under reflux at a temperature of 80℃~120℃ for 4h~8h. After the reaction is completed, the solvent and byproducts are removed by vacuum distillation. After washing and purification, a silane-modified antioxidant is obtained.

7. The preparation method according to claim 6, characterized in that, The silane coupling agent is at least one of vinyltriethoxysilane, vinyldimethylethoxysilane, allyltrichlorosilane, and allyltrimethoxysilane.

8. The preparation method according to claim 6, characterized in that, The solvent is at least one of ethanol and toluene; the catalyst is dibutyltin dilaurate.

9. The application of a silane-modified antioxidant, characterized in that, The application is the use of the silane-modified antioxidant as described in any one of claims 1 to 5 in the preparation of silane cross-linked polyethylene pipes.

10. The application according to claim 9, characterized in that, The preparation of the silane cross-linked polyethylene pipe includes the following steps: S1. High-density polyethylene and linear low-density polyethylene are blended to obtain a base resin; S2. The base resin, modified antioxidant, silane coupling agent, peroxide initiator and crosslinking catalyst are melt-blended and extruded at 180℃~200℃ to obtain a tube blank; S3. The tube blank is placed in hot water at 90℃~95℃ for 30h~40h to complete the crosslinking process and obtain the tube.

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