Heat-oxidative aging resistant single-layer MPP power tube and preparation method thereof

Abstract

This invention belongs to the technical field of cable protection pipe materials, and discloses a heat- and oxygen-aging-resistant single-layer MPP power pipe and its preparation method. It employs MPP resin, reaction-compatible hindered phenol-intercalated LDH functional masterbatch, toughening agent, β-crystal nucleating agent, and additives, all co-extruded together. The functional masterbatch forms an interfacial graft structure through in-situ reaction between hindered phenol-intercalated LDH and PP-g-MAH, and combined with a moisture content control process, achieves a synergistic effect of low antioxidant migration, oxygen barrier, and interfacial reinforcement. This single-layer pipe improves oxidation induction time and mechanical retention after heat and oxygen aging while reducing processing defects, exhibiting excellent long-term service stability.

Description

Technical Field

[0001] This invention belongs to the technical field of cable protection pipe materials, specifically relating to a heat-resistant and oxygen-aging-resistant single-layer MPP power pipe and its preparation method. Background Technology

[0002] MPP power cable conduits are cable protection pipes made primarily of modified polypropylene. They possess good heat resistance, insulation, corrosion resistance, and construction adaptability, and are widely used in power cable protection projects such as direct burial, pipe jacking, and directional drilling. Because cables continuously generate heat during long-term operation, MPP power cable conduits are often exposed to high-temperature environments during their underground service. Furthermore, throughout their entire lifecycle—from production and processing to transportation, storage, construction, and underground service—the conduits are subject to the combined effects of oxygen, moisture, mechanical stress, and localized thermal history, easily leading to problems such as thermo-oxidative aging, decreased toughness, reduced ring stiffness retention, and weld embrittlement, severely impacting the long-term reliability and service life of the conduits. Existing modification schemes for aging-resistant MPP conduits typically employ the following technical routes: 1) directly adding hindered phenolic primary antioxidants, phosphite auxiliary antioxidants, and thioester antioxidants; 2) adding hindered amine light stabilizers; and 3) adding inorganic fillers such as carbon black, talc, and mica powder. However, these technical routes have significant limitations. Firstly, small molecule hindered phenolic antioxidants have a certain degree of migration in the polypropylene matrix. During long-term high-temperature service, water immersion or thermal cycling, the effective antioxidant components will continue to migrate, precipitate and be consumed, resulting in a significant decrease in the pipe's resistance to thermo-oxidative aging as the service time increases. Secondly, although ordinary inorganic fillers can improve the rigidity and dimensional stability of pipes, they have poor compatibility with non-polar polypropylene matrix and are prone to agglomeration in the matrix, causing stress concentration at the interface, which leads to a decrease in the impact toughness and elongation at break of the pipe, which is not conducive to the long-term mechanical reliability of the pipe.

[0003] Layered double hydroxides (LDHs, also known as hydrotalcites) are a class of inorganic nanomaterials with a layered anionic clay structure. They are characterized by a positively charged metal hydroxide master layer and intercalable exchangeable interlayer anions. The exchangeable interlayer anions of LDH allow functional organic anions to be inserted into the LDH interlayer via ion exchange, forming an organic-inorganic intercalated composite structure and reducing the free migration of guest molecules. When LDH nanosheets are uniformly dispersed in a polymer matrix, they can extend the diffusion path of small gas molecules, reduce oxygen permeation rates, and create a barrier effect. Simultaneously, LDH possesses certain acid-base buffering and free radical scavenging capabilities, which can help improve the thermal stability of the material.

[0004] Currently, the approach of directly using antioxidant-intercalated LDH or ordinary LDH in modified MPP pipes still faces the following unresolved technical issues: First, the LDH surface is highly hydrophilic and has poor interfacial compatibility with the non-polar polypropylene matrix, making it difficult for the nanosheets to be fully peeled off and uniformly dispersed during the extrusion process. Second, LDH material has strong hygroscopicity. The interlayer structural water and surface adsorbed water are easily vaporized during high-temperature extrusion processing, resulting in bubbles, silver streaks and interface defects in the pipe. Third, the LDH sheets lack a stable chemical interface bond with the polypropylene matrix, and interface debonding will still occur during long-term thermo-oxidative aging. Fourth, when LDH powder is directly added to the pipe extrusion system, the dispersion process is difficult to control, and the stability of industrial production is poor.

[0005] Therefore, it is necessary to develop a more comprehensive heat- and oxygen-resistant single-layer MPP power pipe modification technology. Summary of the Invention

[0006] The purpose of this invention is to provide a heat- and oxygen-resistant single-layer MPP power pipe and its preparation method, so as to solve the technical problems of existing MPP power pipes during long-term service, such as serious antioxidant migration and consumption, significant decrease in toughness after heat and oxygen aging, poor dispersion of inorganic fillers, extrusion processing bubble defects, and insufficient retention of ring stiffness and impact performance after pipe aging.

[0007] To achieve the above objectives, the present invention adopts the following technical solution: This invention provides a heat-resistant and oxygen-aging resistant single-layer MPP power pipe, which, by weight, comprises: 100 parts of MPP resin, 2-8 parts of reaction-compatible hindered phenolic intercalation LDH functional masterbatch, 3-8 parts of toughening agent, 0.05-0.3 parts of β-crystal nucleating agent, 0.1-0.3 parts of processing antioxidant, and 0.2-1.0 parts of lubricant.

[0008] By weight percentage, the functional masterbatch comprises: 20-40 wt% reaction-compatible hindered phenolic intercalation LDH, 45-75 wt% PP-g-MAH compatibilizer, 0-10 wt% plasticizer and dispersant, 0.2-2.0 wt% lubricant, 0.1-0.8 wt% processing antioxidant, and 0-3 wt% dispersant, with the total content of all components being 100 wt%.

[0009] Preferably, the content of reaction-compatible hindered phenolic intercalation LDH is 25~35 wt%; and the content of PP-g-MAH compatibilizer is 55~70 wt%.

[0010] Preferably, the host of the reaction-compatible hindered phenolic intercalation LDH is one or more of Mg / Al-LDH, Zn / Al-LDH, and Ca / Al-LDH.

[0011] More preferably, the host of the reaction-compatible hindered phenolic intercalation LDH is Mg / Al-LDH.

[0012] Preferably, the molar ratio of divalent metal elements to trivalent metal elements in the LDH matrix is ​​(2~4):1.

[0013] More preferably, the molar ratio of divalent metal elements to trivalent metal elements in the LDH matrix is ​​(2.5~3.5):1.

[0014] Preferably, the LDH interlayer contains a hindered phenolic derivative, which simultaneously contains an intercalation group, a hindered phenolic antioxidant structure, and a reactive end group that can chemically react with the maleic anhydride group of PP-g-MAH.

[0015] Preferably, the intercalation group is one or more of carboxylates, sulfonates, and phosphonates; the hindered phenolic antioxidant structure contains a 3,5-di-tert-butyl-4-hydroxyphenyl structure; and the reaction terminal group is selected from one or more of amino, hydroxyl, epoxy, alkenyl, or silaneoxy groups.

[0016] Preferably, the surface or edge of the reaction-compatible hindered phenolic intercalated LDH is further modified with an aminosilane, epoxysilane or hydroxysilane coupling agent to introduce or strengthen end groups that can react with PP-g-MAH; more preferably, γ-aminopropyltriethoxysilane is used for amination modification.

[0017] Preferably, the maleic anhydride grafting rate of PP-g-MAH is 0.5~2.5 wt%, and the melt index is 30~200 g / 10min, so as to ensure that it has both flowability and reactivity during melt blending.

[0018] Preferably, in the functional masterbatch, the plasticizer and dispersant is one of polypropylene wax and polyethylene wax; the lubricant is one of calcium stearate and zinc stearate; and the dispersant is one of stearamide and ethylene bis-stearamide.

[0019] During the melt blending stage of the functional masterbatch preparation process, the amino, hydroxyl, or epoxy groups on the surface of the reaction-compatible hindered phenol-intercalated LDH undergo ring-opening amidation, esterification, or ring-opening addition reactions with the maleic anhydride groups on the PP-g-MAH chain, forming a polypropylene-compatible graft layer in situ on the LDH sheet surface. This graft layer imparts good compatibility between LDH and the MPP matrix, while simultaneously inhibiting the migration and precipitation of the hindered phenolic antioxidant structure through chemical bonding and intercalation confinement.

[0020] Preferably, the amount of reaction-compatible hindered phenol intercalation LDH functional masterbatch is 4-6 parts; More preferably, the amount of reaction-compatible hindered phenol intercalation LDH functional masterbatch is 5 parts.

[0021] Preferably, the toughening agent is one or more of POE, EPDM or SEBS.

[0022] More preferably, the toughening agent is POE, and the amount used is 4 to 6 parts.

[0023] Preferably, the β-crystal nucleating agent is one or more of amide-based, rare earth-based, or organic acid salt-based β-crystal nucleating agents.

[0024] The β-crystal nucleating agent is an N,N'-dicyclohexyl-2,6-naphthalenediamide type nucleating agent.

[0025] Preferably, the processing antioxidant is a compound system of hindered phenolic antioxidant and phosphite antioxidant.

[0026] More preferably, hindered phenolic antioxidant 1010 and phosphite antioxidant 168 are compounded at a mass ratio of 1:(1~3).

[0027] Preferably, the lubricant is selected from one or more of calcium stearate, zinc stearate, polyethylene wax, polypropylene wax, and stearamide; more preferably, it is a compound system of calcium stearate and polyethylene wax.

[0028] The mechanism of this invention is as follows: First, hindered phenolic antioxidant derivatives are ionicly bonded to the LDH interlayer via carboxylates, sulfonates, or phosphonates. Furthermore, the chemical binding of the PP-g-MAH graft layer significantly restricts the free migration pathways of antioxidant molecules within the polypropylene matrix, effectively inhibiting thermal migration and water leaching of the antioxidants. Additionally, the hindered phenolic groups are distributed near the LDH sheets, allowing oxygen or free radicals to be captured nearby when diffusing along the filler interface, improving the antioxidant utilization efficiency of the hindered phenolic groups. Simultaneously, the intercalated antioxidants exhibit a slow-release function in the early stages of aging, extending the effective antioxidant activity period.

[0029] Secondly, the amino, hydroxyl, or epoxy groups on the surface of the reaction-compatible hindered phenol-intercalated LDH undergo a ring-opening chemical reaction with the maleic anhydride groups of PP-g-MAH during melt blending, forming a graft layer compatible with the PP matrix in situ on the LDH surface. This graft layer improves the exfoliation degree and uniform dispersion of the LDH nanosheets, reducing stress concentration caused by agglomeration. Furthermore, it maintains the chemical bonding stability of the LDH interface during thermo-oxidative aging, inhibiting interfacial debonding. After uniform exfoliation and dispersion in the MPP matrix, the LDH nanosheets form tortuous diffusion channels, extending the path of oxygen diffusion into the material interior, reducing the oxygen permeation rate, and slowing down the oxidative degradation of the polypropylene chains from the source.

[0030] Furthermore, the combination of functional masterbatch pre-dispersion and moisture content control ensures that the hydrophilic LDH has undergone surface reaction, melt coating, and dehydration treatment before entering the pipe extrusion system, thereby significantly reducing processing defects such as nanoparticle agglomeration, bubbles, silver streaks, and interface voids.

[0031] On the other hand, the present invention also provides a method for preparing a heat- and oxygen-resistant single-layer MPP power tube, comprising the following steps: S1, LDH pretreatment: LDH is added to deionized water or a water / alcohol mixture and dispersed thoroughly. The pH of the system is adjusted to 8-11, and the mixture is stirred for 0.5-2 hours to allow the LDH sheets to fully swell and disperse. Preferably, the LDH is first dried at 80-120°C for 4-12 hours to reduce the free water content.

[0032] S2, hindered phenolic derivative intercalation: Hindered phenolic derivatives containing carboxylate, sulfonate, or phosphonate intercalation groups are added to the above LDH dispersion and stirred at 50–90°C for 4–12 h. The hindered phenolic derivatives are introduced into the LDH interlayer through ion exchange to obtain reaction-compatible hindered phenolic intercalated LDH. After the reaction, the product is sequentially filtered, thoroughly washed, and dried; preferably, the drying conditions are vacuum drying at 80–110°C for 6–12 h.

[0033] S3. Modification of surface reactive groups of reaction-compatible hindered phenol-intercalated LDH: Disperse reaction-compatible hindered phenol intercalated LDH in ethanol, water or toluene, add aminosilane, epoxysilane or hydroxysilane coupling agent, and react at 50~90℃ for 2~8h to introduce amino, hydroxy or epoxy groups that can chemically react with PP-g-MAH onto the surface or edge of the reaction-compatible hindered phenol intercalated LDH, thus obtaining reaction-compatible hindered phenol intercalated LDH.

[0034] S4. Drying and moisture content control of reaction-compatible hindered phenol intercalation LDH: The reaction-compatible hindered phenol intercalated LDH was vacuum dried at 90~120℃ for 4~12h to control its moisture content to be lower than 0.2 wt%; preferably lower than 0.1 wt%.

[0035] S5. Preparation of functional masterbatch: The reaction-compatible hindered phenolic intercalated LDH, PP-g-MAH, processing antioxidant, lubricant, and optional dispersant are added to a high-speed mixer and mixed for 5-15 min. Then, the mixture is melt-extruded and granulated using a twin-screw extruder. Preferably, the twin-screw extrusion temperature is 170-205℃, and vacuum exhaust is turned on during extrusion, with a vacuum degree of -0.06 to -0.09 MPa and a screw speed of 100-300 rpm. After extrusion, the resulting functional masterbatch is dried at 80-100℃ for 2-6 h to reduce the moisture content of the masterbatch to less than 0.1 wt%.

[0036] S6 and MPP pipes are mixed: MPP resin, reaction-compatible hindered phenolic intercalation LDH functional masterbatch, toughening agent, β-crystal nucleating agent, processing antioxidant and lubricant are added to a high-speed mixing device according to the formula ratio and mixed evenly to obtain MPP pipe material mixture.

[0037] S7, Single-layer pipe extrusion molding: The pipe mixture is added to a pipe extruder, and after melting and plasticizing, molding, vacuum sizing, cooling, traction and cutting, a heat-resistant and oxygen-aging-resistant single-layer MPP power pipe is obtained; preferably, the pipe extrusion temperature is 180~210℃.

[0038] Preferably, the moisture content control in S4 and S5 is carried out throughout the pretreatment process of functional masterbatch and pipe extrusion to remove interlayer water and surface adsorbed water of LDH, and avoid bubbles, silver streaks and interface defects caused by moisture vaporization during subsequent melt extrusion.

[0039] Compared with the prior art, the present invention has the following beneficial effects: 1. Through the dual effects of ionic bonding fixation of hindered phenol derivative intercalated LDH and chemical binding of PP-g-MAH grafted layer, the amount of antioxidant migration is reduced compared with ordinary small molecule antioxidant system, significantly extending the effective antioxidant cycle of pipe.

[0040] 2. After LDH nanosheets are uniformly dispersed in the matrix, they form tortuous barrier paths, which reduce the oxygen permeation rate, thereby improving the oxidation induction time and performance retention rate after thermo-oxidative aging of the material.

[0041] 3. By using reaction-compatible hindered phenol intercalation LDH and PP-g-MAH in situ grafting reaction, the average agglomeration size of LDH in the MPP matrix is ​​reduced, significantly improving the dispersion uniformity.

[0042] 4. LDH dispersion is pre-completed through functional masterbatch, reducing the risk of direct agglomeration of nanofillers during pipe extrusion.

[0043] 5. By employing strict drying, vacuum degassing, and moisture content control processes, processing defects caused by LDH moisture absorption are eliminated or significantly reduced, thereby improving the industrial production stability of single-layer MPP power pipes.

[0044] 6. While improving the thermo-oxidative aging performance, the synergistic effect of low-dosage LDH with toughening agents and nucleating agents enables the initial drop hammer impact performance and ring stiffness of the pipe to meet the requirements of engineering applications. The impact strength retention rate and ring stiffness retention rate are significantly improved after thermo-oxidative aging.

[0045] 7. This invention focuses on a single-layer MPP power pipe structure, which can achieve excellent heat and oxygen aging resistance, low migration and processing stability without relying on multi-layer co-extrusion, which is conducive to simplifying production equipment and process control. Detailed Implementation

[0046] To enable those skilled in the art to better understand the present application, the technical solutions in the specific embodiments of the present application will be clearly and completely described below. Unless otherwise defined, the technical or scientific terms used in this invention should have the ordinary meaning understood by those skilled in the art to which this invention pertains.

[0047] The specifications of the raw materials used in the examples and comparative examples are as follows: MPP resin is a commercially available modified polypropylene pipe material with an MFR (230℃ / 2.16kg) of 0.4 g / 10min; the Mg / Al molar ratio of Mg / Al-LDH is 3:1, and the average particle size is approximately 5 μm; the grafting rate of PP-g-MAH is 1.2 wt%, and the MFR (230℃ / 2.16kg) is 80 g / 10min; the POE toughening agent is an ethylene / octene copolymer with an MFR (190℃ / 2.16kg) of 5 g / min. g / 10min; the β-crystal nucleating agent is an N,N'-dicyclohexyl-2,6-naphthalenediamide nucleating agent; the processing antioxidant is a complex of hindered phenolic antioxidant 1010 and phosphite antioxidant 168 in a 1:2 mass ratio; the lubricant is a complex of calcium stearate and polyethylene wax in a 1:1 mass ratio; the hindered phenolic derivative is a 3,5-di-tert-butyl-4-hydroxyphenylpropionic acid derivative containing carboxylate intercalation groups and hydroxyl reactive terminal groups, with a relative molecular weight of approximately 680; the silane coupling agent is γ-aminopropyltriethoxysilane (KH-550).

[0048] The general preparation process is as follows: Weigh Mg / Al-LDH, dry it at 105℃ for 8 hours, then add it to deionized water and disperse it by mechanical stirring. Adjust the pH to 9.5 with 10 wt% Na₂CO₃ solution and stir for 1 hour. Dissolve the hindered phenolic derivative containing sodium carboxylate intercalation groups and β-hydroxy reactive terminal groups in a 4:1 volume ratio of deionized water / ethanol mixture, and slowly add it to the above LDH dispersion. Stir and react at 70℃ for 8 hours to allow the hindered phenolic derivative anions to enter the LDH interlayer through ion exchange. After the reaction is complete, filter and wash thoroughly with deionized water until the pH of the filtrate is 7.0-7.5 to obtain hindered phenolic intercalated LDH.

[0049] Reaction-compatible hindered phenol-intercalated LDH was added to a 9:1 volume ratio of ethanol and water, ultrasonically dispersed for 30 min, then KH-550 was added, and the mixture was stirred and refluxed at 75 °C for 4 h to introduce amino groups onto the surface of the reaction-compatible hindered phenol-intercalated LDH sheets. After the reaction, the mixture was filtered, washed with ethanol, and vacuum dried at 105 °C for 8 h to obtain NH2-AO-LDH. In the examples, the water content of NH2-AO-LDH was controlled to be less than 0.1 wt%.

[0050] NH2-AO-LDH, PP-g-MAH, polypropylene wax, processing antioxidant, calcium stearate, and stearamide were mixed in a high-speed mixer at 800 rpm for 10 min according to the formula ratio, and then transferred to a co-rotating twin-screw extruder for melt extrusion granulation. The extrusion temperature was set sequentially from the feeding section to the die head as 170℃, 180℃, 190℃, 195℃, 200℃, 200℃, and 195℃; the screw speed was 180 rpm; and the vacuum degree at the vacuum exhaust port was -0.08 MPa. The extruded strip was water-cooled, air-dried, and then pelletized. The resulting functional masterbatch was dried at 90℃ for 4 h to reduce the moisture content of the masterbatch to below 0.1 wt%.

[0051] MPP resin, functional masterbatch or comparative modification system, POE toughening agent, β-crystal nucleating agent, processing antioxidant, and lubricant are added to a high-speed mixer according to the formula ratio and mixed at 600 rpm for 10 min to obtain MPP pipe material. The mixture is then fed into a single-screw pipe extruder (screw diameter 65mm, L / D=32), with extrusion temperatures set as follows: feeding section 185℃, compression section 195℃, metering section 200℃, and die head 195℃. The material is then extruded through a die, vacuum sizing, spray cooling, traction, and cutting to obtain the inner diameter... A single-layer MPP power conduit with a diameter of 110 mm and a wall thickness of 6.5 mm.

[0052] Example 1 Functional masterbatch A was prepared according to a general preparation process. In functional masterbatch A, the content of NH2-AO-LDH was 25 wt%, the content of PP-g-MAH was 70 wt%, the content of polypropylene wax was 2.5 wt%, the content of processing antioxidant was 0.5 wt%, the content of calcium stearate was 0.5 wt%, and the content of stearamide was 1.5 wt%. The amount of KH-550 used was 3 wt% of the mass of the reaction-compatible hindered phenolic intercalated LDH.

[0053] The following pipe components were weighed according to weight: 100 parts MPP resin, 4 parts functional masterbatch A, 5 parts POE toughening agent, 0.1 parts β-crystal nucleating agent, 0.2 parts processing antioxidant, 0.3 parts calcium stearate, and 0.2 parts polyethylene wax. The sample of Example 1 was prepared according to the general single-layer pipe manufacturing process.

[0054] Example 2 Functional masterbatch B was prepared according to a general preparation process. In functional masterbatch B, the content of NH2-AO-LDH was 30 wt%, PP-g-MAH was 65 wt%, polypropylene wax was 3 wt%, processing antioxidant was 0.5 wt%, calcium stearate was 0.5 wt%, stearamide was 1.0 wt%, and KH-550 was used at 5 wt% of the mass of AO-LDH.

[0055] The following pipe components were weighed according to weight: 100 parts MPP resin, 5 parts functional masterbatch B, 5 parts POE toughening agent, 0.1 parts β-crystal nucleating agent, 0.2 parts processing antioxidant, 0.3 parts calcium stearate, and 0.2 parts polyethylene wax. The sample of Example 2 was prepared according to the general single-layer pipe manufacturing process.

[0056] Example 3 Functional masterbatch C was prepared according to a general preparation process. In functional masterbatch C, the content of NH2-AO-LDH was 35 wt%, the content of PP-g-MAH was 60 wt%, the content of polypropylene wax was 3.5 wt%, the content of processing antioxidant was 0.5 wt%, the content of calcium stearate was 0.5 wt%, and the content of stearamide was 0.5 wt%; the amount of KH-550 was 7 wt% of the mass of AO-LDH.

[0057] The following pipe components were weighed according to weight: 100 parts MPP resin, 6 parts functional masterbatch C, 5 parts POE toughening agent, 0.1 parts β crystal nucleating agent, 0.2 parts processing antioxidant, 0.3 parts calcium stearate, and 0.2 parts polyethylene wax. The sample of Example 3 was prepared according to the general single-layer pipe manufacturing process.

[0058] To ensure comparability, except for the differences in modified systems or moisture content control explicitly stated in each comparative example, the comparative examples all adopted the same single-layer pipe mixing, extrusion, sizing, cooling, traction and cutting processes as the examples.

[0059] Comparative Example 1 This comparative example is a blank ordinary MPP power pipe. It is formulated with 100 parts of MPP resin, 0.2 parts of processing antioxidant, and 0.5 parts of lubricant, without the addition of LDH or additional antioxidant modification system. The remaining molding process is the same as in the example.

[0060] Comparative Example 2 This comparative example is an MPP power pipe with directly added small molecule antioxidant 1010 / 168. It was formulated with 100 parts MPP resin, 5 parts POE toughening agent, 0.1 parts β-crystal nucleating agent, 0.3 parts hindered phenolic antioxidant 1010, 0.5 parts phosphite antioxidant 168, and 0.5 parts lubricant, without the addition of LDH. The remaining molding process was the same as in the example.

[0061] Comparative Example 3 This comparative example is an MPP power pipe directly blended with ordinary LDH and 1010 / 168. It was formulated with 100 parts MPP resin, 5 parts POE toughening agent, 0.1 parts β-crystal nucleating agent, 1.5 parts unintercalated ordinary Mg / Al-LDH, 0.3 parts antioxidant 1010, 0.5 parts antioxidant 168, and 0.5 parts lubricant. Hindered phenol intercalation treatment and reaction compatibility treatment were not performed; the remaining molding process was the same as in the example.

[0062] Comparative Example 4 This comparative example involves hindered phenolic intercalated LDH added directly to MPP pipes without undergoing PP-g-MAH compatibility treatment. The mixture was prepared with 100 parts MPP resin, 5 parts POE toughening agent, 0.1 parts β-crystal nucleating agent, 1.5 parts unmodified AO-LDH direct powder, 0.2 parts processing antioxidant, and 0.5 parts lubricant. No PP-g-MAH was added, and no functional masterbatch was prepared. The remaining molding processes were the same as in the previous examples.

[0063] Comparative Example 5 This comparative example compares conventional organic-modified LDH with 1010 / 168 MPP pipes. Mg / Al-LDH was modified by intercalation with sodium dodecyl sulfate (SDS) to obtain conventional organic LDH (SDS-LDH). It was formulated with 100 parts MPP resin, 5 parts POE toughening agent, 0.1 parts β-crystal nucleating agent, 1.5 parts SDS-LDH, 0.3 parts antioxidant 1010, 0.5 parts antioxidant 168, and 0.5 parts lubricant. Reactive hindered phenolic intercalation LDH was not used; the remaining molding process was the same as in the previous example.

[0064] Comparative Example 6 This comparative example uses reaction-compatible hindered phenolic intercalated LDH direct powder without preparing functional masterbatch. It is formulated with 100 parts MPP resin, 5 parts POE toughening agent, 0.1 parts β-crystal nucleating agent, 1.5 parts NH2-AO-LDH direct powder, 3 parts PP-g-MAH, 0.2 parts processing antioxidant, and 0.5 parts lubricant. The components are directly added to the pipe compounding system without first preparing functional masterbatch; the remaining molding process is the same as in the example.

[0065] Comparative Example 7 This comparative example describes the preparation of MPP pipes modified with a reaction-compatible hindered phenol-intercalated LDH functional masterbatch without moisture content control during preparation. This comparative example uses the same functional masterbatch B formulation and pipe formulation as Example 2, but without 105°C vacuum drying for moisture content control after surface modification of the reaction-compatible hindered phenol-intercalated LDH, and without 90°C drying after extrusion granulation of the functional masterbatch. Measurements showed that the moisture content of NH2-AO-LDH before entering the extruder was approximately 0.65 wt%, and the moisture content of the functional masterbatch was approximately 0.42 wt%. Except for the absence of the aforementioned moisture content control, the remaining melt extrusion granulation and single-layer pipe forming processes were the same as in Example 2.

[0066] Test case The test items and methods for this test are as follows: Oxidation induction time (OIT): According to GB / T 17391, the oxidation induction time of the sample in a pure oxygen atmosphere is determined by differential scanning calorimetry (DSC) at 200℃, expressed in minutes. The larger the value, the stronger the resistance to heat and oxygen aging.

[0067] Antioxidant migration: A sheet with dimensions of 50mm×50mm×3mm was soaked in distilled water at 80℃ for 1000h. The concentration of hindered phenolic antioxidants in the leachate was determined by UV-Vis spectrophotometry and converted into a percentage of migration relative to Comparative Example 2. The migration amount of Comparative Example 2 was normalized to 100%.

[0068] Notched impact strength retention rate after thermo-oxidative aging: Cut test pieces from the pipe and thermo-oxidative age them in an oven at (120±2)℃ for 1000h. Determine the notched impact strength of the cantilever beam before and after aging according to GB / T 1843, and calculate the retention rate (after aging / before aging × 100%).

[0069] Ring stiffness retention rate after thermo-oxidative aging: After thermo-oxidative aging in an oven at (120±2)℃ for 1000h, the ring stiffness before and after aging was measured in accordance with GB / T 9647, and the retention rate was calculated.

[0070] Average aggregation size of LDH in the matrix: Take the cross section of the pipe and observe the dispersion morphology of LDH in the PP matrix using transmission electron microscopy (TEM). Count at least 50 LDH particles / aggregates and take the number-average equivalent diameter as the average aggregation size, in μm.

[0071] Pipe surface defect rate: The length of visible bubbles or silver streaks in a single batch of pipes (50 pipes, 6 m in length / pipe, total inspection length 300 m) is counted, and the surface defect rate is calculated as defect length / total inspection length × 100%.

[0072] Initial drop hammer impact pass rate (0℃): Refer to GB / T 14152, conduct drop hammer impact test under 0℃ conditions, and calculate the pass rate (number of pipes that do not break / total number of pipes tested × 100%). The number of pipes tested shall not be less than 20.

[0073] The test results are shown in the table below: Table 1: Comparison of Initial Mechanical Properties and Engineering Requirements of Pipes in Various Examples

[0074] Table 2: Summary of Overall Performance of Pipes in Each Example and Comparative Example

[0075] "—" indicates that the sample did not contain LDH or that this item is not applicable. Antioxidant migration was normalized to 100% baseline with Comparative Example 2 as the baseline; Comparative Example 1 only contained the processing antioxidant dosage level and did not contain the additional hindered phenol antioxidant modification system, so the migration was not comparable and was marked with "—".

[0076] Table 3: Key Factor Analysis of the Contribution of Key Factors in the LDH Addition System to Pipe Performance

[0077] Table 4: Evolution of antioxidant migration with soaking time

[0078] The migration amount of Comparative Example 2 at 1000h was normalized to 100%. Comparative Example 2 exceeded the 100% baseline at 2000h, indicating that the small molecule antioxidant continued to precipitate under long-term immersion conditions; the intercalation fixation + grafting layer dual constraint of Examples 1-3 significantly reduced the cumulative migration amount.

[0079] Test results show that the thermo-oxidative aging resistance of Examples 1-3 of this invention is significantly better than that of all comparative examples. Example 2 achieved an OIT of 78 min, approximately 73% higher than the ordinary 1010 / 168 system (Comparative Example 2, 45 min); after 1000 h of thermo-oxidative aging, the impact strength retention rate was 83%, 28 percentage points higher than Comparative Example 2; the ring stiffness retention rate was 89%, 17 percentage points higher than Comparative Example 2. Example 3 achieved an OIT of 82 min with a higher actual content of reaction-compatible hindered phenolic intercalated LDH, further demonstrating that increasing the content of reaction-compatible hindered phenolic intercalated LDH within the formulation range of this invention can further improve the thermo-oxidative aging resistance.

[0080] Examples 1-3 all employed the same single-layer pipe forming process, differing only in the amounts of NH2-AO-LDH, PP-g-MAH, and silane in the functional masterbatch, as well as the amount of masterbatch added. All three examples exhibited high OIT (Optimal Inert Temperature), low antioxidant migration, low apparent defect rate, and initial mechanical properties meeting engineering requirements. This demonstrates that the scope of protection of this invention does not depend on a single optimal point, but rather that stable technical effects can be achieved within a certain range of masterbatch parameters.

[0081] In Comparative Example 4, the introduction of hindered phenolic intercalated LDH alone could reduce antioxidant migration and improve OIT to some extent. However, due to the lack of a PP-g-MAH compatible layer, the average LDH agglomeration size still reached 5.1 μm. The impact strength retention rate and ring stiffness retention rate after thermo-oxidative aging were significantly lower than those in Example 2, and the apparent defect rate of the pipe was significantly higher. This demonstrates that the construction of the PP-g-MAH reactive compatibility interface is one of the key factors in the technical effectiveness of this invention.

[0082] Comparative Example 6 used reaction-compatible hindered phenol-intercalated LDH as direct powder feed without preparing functional masterbatch. Although its performance was better than that of ordinary LDH system, the average LDH agglomeration size was 3.0 μm, and the apparent defect rate of the pipe was as high as 11.5%, significantly higher than the 1.5% in Example 2. This indicates that the functional masterbatch step can significantly reduce agglomeration and improve processing stability, which plays an important role in industrial continuous extrusion.

[0083] Comparative Example 7 used the same functional masterbatch and tubing formulation as Example 2, but did not perform reaction-compatible hindered phenolic intercalation LDH and did not control the moisture content of the functional masterbatch. The OIT, impact strength retention, and ring stiffness retention of Comparative Example 7 were all lower than those of Example 2, and the apparent defect rate increased to 11.8%. This indicates that even with the same formulation and extrusion process, uncontrolled LDH moisture content can still cause bubbles, streaks, and interfacial voids, thereby weakening aging resistance and mechanical properties; moisture content control is a crucial process feature for achieving stable industrial-scale production in this invention.

[0084] Long-term water immersion antioxidant migration test showed that the cumulative migration amount of Example 2 at 2000h was only about 27% of the migration amount of Comparative Example 2 at the same point. The migration amount of Example 3 was further reduced, proving that the dual constraint mechanism of intercalation fixation and grafting layer can effectively maintain the antioxidant structure function over a long service life, fundamentally extending the heat and oxygen aging resistance life of single-layer MPP power tubes.

[0085] Finally, it should be noted that the described embodiments are merely some, not all, of the embodiments of the present invention. Those skilled in the art will understand that various changes, modifications, substitutions, and variations can be made to these embodiments without departing from the principles and spirit of the present invention. The scope of the present invention is defined by the claims and their equivalents; that is, all other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

Claims

1. A heat- and oxygen-resistant single-layer MPP power pipe, characterized in that, It comprises the following components by weight: 100 parts MPP resin, 2-8 parts reaction-compatible hindered phenolic intercalation LDH functional masterbatch, 3-8 parts toughening agent, 0.05-0.3 parts β-crystal nucleating agent, 0.1-0.3 parts processing antioxidant, and 0.2-1.0 parts lubricant; The reaction-compatible hindered phenol intercalation LDH functional masterbatch comprises: 20-40 wt% reaction-compatible hindered phenol intercalation LDH, 45-75 wt% PP-g-MAH compatibilizer, 0-10 wt% plasticizer and dispersant, 0.2-2.0 wt% lubricant, 0.1-0.8 wt% processing antioxidant, and 0-3 wt% dispersant, with the total content of all components being 100 wt%.

2. The power pipe according to claim 1, characterized in that, The reaction-compatible hindered phenol intercalation LDH content is 25~35wt%, and the PP-g-MAH compatibilizer content is 55~70wt%.

3. The power pipe according to claim 1, characterized in that, LDH can be one or more of Mg / Al-LDH, Zn / Al-LDH, or Ca / Al-LDH.

4. The power pipe according to claim 1, characterized in that, The molar ratio of divalent to trivalent metals in LDH is (2~4):

1.

5. The power conduit according to claim 1, characterized in that, The hindered phenol derivatives in hindered phenol intercalated LDH simultaneously contain intercalation groups, hindered phenol antioxidant structures, and reactive end groups that can react with PP-g-MAH.

6. The power pipe according to claim 5, characterized in that, The intercalating group is one or more combinations of carboxylates, sulfonates, or phosphonates; the hindered phenolic antioxidant structure includes a 3,5-di-tert-butyl-4-hydroxyphenyl structure; the reactive terminal group is one or more combinations of amino, hydroxyl, epoxy, alkenyl, or silanoxy groups.

7. The power pipe according to claim 1, characterized in that, The PP-g-MAH grafting rate is 0.5~2.5 wt%, and the melt index is 30~200 g / 10min.

8. The power pipe according to claim 1, characterized in that, The toughening agent is one or more of the following: ethylene-octene copolymer, ethylene-propylene-diene monomer copolymer, or styrene-based thermoplastic elastomer.

9. The power pipe according to claim 1, characterized in that, The tube body has a single-layer structure and is formed by melt extrusion. The tube wall material is a homogeneous MPP composite system.

10. A method for preparing a power tube as described in any one of claims 1-9, characterized in that, Includes the following steps: S1. After drying LDH at 80~120℃, disperse it in an aqueous system and adjust the pH to 8~11; S2. Hindered phenolic derivatives are added to the dispersion system and intercalated into the LDH interlayer through ion exchange to form intercalated LDH. S3. Surface modification of intercalated LDH is carried out using silane coupling agents to introduce functional groups that can react with PP-g-MAH; S4. The modified LDH is subjected to vacuum drying treatment to reduce the moisture content to below 0.2 wt%. S5. Modified LDH, PP-g-MAH, processed antioxidants, and lubricants are melt-blended and granulated to obtain functional masterbatch. S6 prepares pipe material by mixing MPP resin, functional masterbatch, toughening agent, β-crystal nucleating agent and additives; S7. The mixture is melt-extruded into shape by a single screw extruder, and then sized, cooled and cut to obtain a single-layer MPP power pipe.

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