Highly corrosion resistant polyolefin drain pipe material and method of making same

Abstract

The application provides a kind of high corrosion-resistant polyolefin drainage pipeline material and its preparation method, belong to high polymer composite material technical field, to solve the problem that existing polyolefin pipeline material cannot overcome the irreversible accumulation of multilayer pipeline interface micro-damage, resulting in delamination failure. The intermediate layer material is an adhesive layer formed by a polymer composition containing a dynamic covalent cross-linking network. The dynamic covalent cross-linking network is a thermally reversible cross-linking network based on Diels-Alder reaction. The dynamic covalent cross-linking network contains covalent bonds that can undergo reversible cleavage and recombination under thermal stimulation, thereby imparting self-healing function to the intermediate layer material. The present application has high corrosion resistance, excellent mechanical properties and wide temperature range long-term service reliability while maintaining the overall thermoplastic recyclability of the material.

Description

Technical Field

[0001] This application belongs to the field of polymer composite materials technology, specifically relating to a highly corrosion-resistant polyolefin drainage pipe material and its preparation method. Background Technology

[0002] Existing drainage pipe materials mainly include cast iron pipes, concrete pipes, clay pipes, and polyvinyl chloride (PVC) pipes. Cast iron and concrete pipes are heavy, inconvenient to construct, and have rough inner walls that easily accumulate scale. Although PVC pipes are widely used, they have poor thermal stability, significant low-temperature brittleness, and pose environmental hazards during production, use, and disposal. Polyolefin materials, represented by polyethylene and polypropylene, are gradually becoming the mainstream choice in the drainage pipe field due to their significant advantages such as light weight, good toughness, relatively good chemical corrosion resistance, smooth inner walls that do not accumulate scale, excellent hydraulic properties, easy connection, and recyclability. However, with the development of industrial sophistication and increasingly stringent environmental protection requirements, the media transported by drainage pipes are becoming increasingly complex. Many industrial wastewaters, laboratory waste liquids, hospital sewage, and certain commercial wastewaters often contain high concentrations of acids and alkalis, strong oxidants, organic solvents, animal and vegetable oils, and various chemical agents—non-typical corrosive components. When ordinary polyolefin pipes are in contact with such media for a long time, their polymer chains are prone to oxidative degradation, swelling, dissolution, or environmental stress cracking, which leads to a decrease in pipe strength, leakage, or even rupture, greatly shortening the effective service life of the system.

[0003] To improve the corrosion resistance of polyolefin pipes, several improvement routes have been proposed in existing technologies. One approach is to use high molecular weight, high-density polyethylene or special copolymer polypropylene to improve resistance to slow crack propagation. However, this method offers limited improvement in resistance to strong oxidizing acids and organic solvents and cannot address the problem of a sharp drop in corrosion resistance at high temperatures. Another approach involves a multi-layer composite structure, with ordinary polyolefin as the outer layer and fluoroplastics such as polyvinylidene fluoride, perfluoroethylene propylene, or cross-linked polyethylene as the inner corrosion-resistant barrier layer. However, the interlayer bonding strength is prone to deterioration under temperature fluctuations and media penetration, leading to delamination. Furthermore, fluoropolymers are extremely expensive, hindering widespread adoption. A third approach involves adding inorganic fillers such as glass fiber, carbon fiber, and mica to improve the pipe's rigidity and heat resistance. However, the interface between the filler and the matrix is ​​prone to peeling under corrosive media, causing microcracks and accelerating failure. Additionally, high filler content significantly reduces the material's toughness. Fourth, cross-linking polyolefins with silanes, peroxides, or radiation to form a three-dimensional network structure improves their chemical resistance and stress cracking resistance. However, the cross-linked material loses its thermoplasticity and cannot be remelted and recycled, which is inconsistent with the policy orientation of a circular economy. Fifth, coating the inner wall of pipes with anti-corrosion coatings such as epoxy resin and polyurethane is difficult to achieve uniform coating on the narrow inner wall of drainage pipes. Problems such as pinholes and uneven thickness are hard to avoid, and the adhesion between organic coatings and polyolefin substrates is not easy to maintain in the long term.

[0004] Therefore, there is an urgent need for a polyolefin drainage pipe material that can combine high corrosion resistance and long-term service reliability in a wide temperature range and complex chemical media environment, while maintaining good mechanical properties, overall recyclability and economic processability. Summary of the Invention

[0005] In view of this, this application provides a highly corrosion-resistant polyolefin drainage pipe material and its preparation method to solve the problem of delamination failure caused by the irreversible accumulation of micro-damage at the interface of multi-layer pipes, which is impossible for existing polyolefin pipe materials.

[0006] To solve the above problems, the technical solution adopted in this application is as follows:

[0007] In a first aspect, this application proposes a highly corrosion-resistant polyolefin drainage pipe material, which is a multilayer composite material comprising an inner layer material, an intermediate layer material, and an outer layer material. The intermediate layer material is an adhesive layer formed by a polymer composition containing a dynamic covalent crosslinking network. The dynamic covalent crosslinking network is a thermally reversible crosslinking network based on the Diels-Alder reaction. The dynamic covalent crosslinking network contains covalent bonds that can undergo reversible breakage and recombination under thermal stimulation, thereby endowing the intermediate layer material with self-healing function.

[0008] Furthermore, the inner layer material is a nano-barrier and anti-corrosion material, comprising 100 parts by weight of bimodal high-density polyolefin matrix, 1-10 parts by weight of two-dimensional nanosheet filler and 2-15 parts by weight of reactive compatibilizer; the two-dimensional nanosheet filler is montmorillonite and / or layered double hydroxide, and its surface is treated with a coupling agent; the reactive compatibilizer is maleic anhydride-grafted polyolefin.

[0009] Furthermore, by weight, the inner layer material also contains 0.5-3 parts of grafted polyolefin oligomers containing thymine or ureidinone tetrahydrobonded units to form a supramolecular physical crosslinking network in the inner layer material, which constitutes an interpenetrating dual physical network structure with the crystalline region of the bimodal high-density polyethylene matrix.

[0010] Further, the polymer composition forming the interlayer material comprises, by weight, 100 parts of maleic anhydride-grafted ethylene-octene copolymer, 10-80 parts of a polyolefin containing furan side groups, and 1-20 parts of a bismaleimide crosslinking agent; the maleic anhydride-grafted ethylene-octene copolymer serves as an elastic skeleton; the polyolefin containing furan side groups and the bismaleimide crosslinking agent form the thermally reversible crosslinking network through a Diels-Alder reaction; the thermally reversible crosslinking network endows the interlayer material with thermally activated self-healing ability; and the elastic skeleton of the maleic anhydride-grafted ethylene-octene copolymer endows the interlayer material with a shape memory effect, which shrinks under thermal stimulation to assist in crack closure.

[0011] Furthermore, the maleic anhydride grafting rate of the maleic anhydride-grafted ethylene-octene copolymer is 1.5-3.0%.

[0012] Furthermore, the outer layer material comprises, by weight, 100 parts of polyolefin matrix, 10-35 parts of reinforcing fiber and 3-12 parts of elastomer toughening agent; the reinforcing fiber is chopped glass fiber or basalt fiber; the elastomer toughening agent is maleic anhydride-grafted ethylene-octene copolymer or maleic anhydride-grafted ethylene propylene diene monomer (EPDM) rubber.

[0013] Furthermore, the thickness of the inner layer material accounts for 15-25% of the total thickness of the multilayer composite material, the thickness of the middle layer material accounts for 3-8%, and the thickness of the outer layer material accounts for 67-82%.

[0014] Secondly, this application also proposes a method for preparing the high corrosion-resistant polyolefin drainage pipe material described in the first aspect, characterized by employing a three-layer co-extrusion molding process, comprising the following steps: Step 1: feeding the inner layer material, intermediate layer material, and outer layer material into three extruders respectively; Step 2: during the co-extrusion process, meteringly adding a bismaleimide crosslinking agent to the melt of the intermediate layer material, causing it to undergo a Diels-Alder reaction with the premixed polyolefin containing furan side groups in the intermediate layer material, generating a thermally reversible dynamic covalent crosslinking network in situ; Step 3: compounding and extruding the three-layer melt through a layered spiral die head, followed by vacuum sizing, cooling, traction, and cutting to obtain the pipe material.

[0015] Furthermore, in step 2, the amount of bismaleimide crosslinking agent added is 1-20% of the total weight of the intermediate layer material, so that the formed dynamic covalent crosslinking network has a suitable crosslinking density, thereby giving the intermediate layer material a self-healing function; in step 2, the melt temperature of the intermediate layer material is controlled at 160-200℃ to ensure that the crosslinking agent reacts fully to form a dynamic crosslinking network, while avoiding excessive crosslinking.

[0016] Further, the preparation method of the inner layer material in step 1 includes: firstly, melting and granulating two-dimensional nanosheet filler, reactive compatibilizer and part of bimodal high-density polyethylene matrix through a twin-screw extruder to prepare nano masterbatch, wherein the screw speed of the twin-screw extruder is 300-600 rpm and the processing temperature is 180-230℃; then, mixing the nano masterbatch with the remaining bimodal high-density polyethylene matrix, stabilizer and optional supramolecular reinforcing agent evenly to obtain inner layer special material.

[0017] Furthermore, in step 3, the composite temperature of the three-layer melt in the layered spiral die head is controlled to be 190-230℃, so that the intermediate layer material undergoes interfacial chemical bonding with the inner and outer layer materials during the melt composite process, forming an integrated multilayer composite material.

[0018] In summary, due to the adoption of the above technical solution, the beneficial effects of this application are:

[0019] The elastic skeleton within the interlayer material contracts under thermal stimulation through shape memory effect, driving the physical closure of microcracks and creating conditions for crack-face contact in chemical repair. Subsequently, the dynamic covalent cross-linked network undergoes reversible fracture and recombination at the closed crack interface, with the broken molecular chains redistributing and bonding at the interface to complete the chemical repair. This synergistic mechanism enables the continuous dynamic repair of interfacial micro-damage generated in multilayer composite pipelines under long-term thermal cycling and mechanical vibration conditions, fundamentally overcoming the problem of delamination failure caused by irreversible accumulation of micro-damage. Attached Figure Description

[0020] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort. Wherein:

[0021] Figure 1 This is a schematic flowchart illustrating the preparation method of the high corrosion-resistant polyolefin drainage pipe material provided in the embodiments of this application. Detailed Implementation

[0022] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of them. The components of the embodiments of this application described and shown in the accompanying drawings can be arranged and designed in various different configurations.

[0023] Therefore, the following detailed description of the embodiments of this application provided in the accompanying drawings is not intended to limit the scope of the claimed application, but merely to illustrate selected embodiments of the application. All other embodiments obtained by those skilled in the art based on the embodiments in this application without inventive effort are within the scope of protection of this application.

[0024] It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other.

[0025] It should be noted that similar labels and letters in the following figures indicate similar items. Therefore, once an item is defined in one figure, it does not need to be further defined and explained in subsequent figures.

[0026] In this application, unless otherwise expressly specified and limited, "above" or "below" a second feature can include direct contact between the first and second features, or contact between the first and second features through another feature between them. Furthermore, "above," "over," and "on top" of a second feature includes the first feature directly above or diagonally above the second feature, or simply indicates that the first feature is at a higher horizontal level than the second feature. "Below," "below," and "under" a second feature includes the first feature directly below or diagonally below the second feature, or simply indicates that the first feature is at a lower horizontal level than the second feature. The terms "first," "second," etc., used in the specification and claims of this application are used to distinguish similar objects and are not used to describe a specific order or sequence. It should be understood that such data can be interchanged where appropriate so that embodiments of this application can be implemented in orders other than those illustrated or described herein, and the objects distinguished by "first," "second," etc., are generally of the same class and do not limit the number of objects; for example, a first object can be one or more. Furthermore, "and / or" in the specification and claims indicates at least one of the connected objects, and the character " / " generally indicates that the preceding and following objects are in an "or" relationship.

[0027] Existing drainage pipe materials mainly include cast iron pipes, concrete pipes, clay pipes, and polyvinyl chloride (PVC) pipes. Cast iron and concrete pipes are heavy, inconvenient to construct, and have rough inner walls that easily accumulate scale. Although PVC pipes are widely used, they have poor thermal stability, significant low-temperature brittleness, and pose environmental hazards during production, use, and disposal. Polyolefin materials, represented by polyethylene and polypropylene, are gradually becoming the mainstream choice in the drainage pipe field due to their significant advantages such as light weight, good toughness, relatively good chemical corrosion resistance, smooth inner walls that do not accumulate scale, excellent hydraulic properties, easy connection, and recyclability. However, with the development of industrial sophistication and increasingly stringent environmental protection requirements, the media transported by drainage pipes are becoming increasingly complex. Many industrial wastewaters, laboratory waste liquids, hospital sewage, and certain commercial wastewaters often contain high concentrations of acids and alkalis, strong oxidants, organic solvents, animal and vegetable oils, and various chemical agents—non-typical corrosive components. When ordinary polyolefin pipes are in prolonged contact with such media, their polymer chains are prone to oxidative degradation, swelling, dissolution, or environmental stress cracking, leading to decreased pipe strength, leakage, and even rupture, significantly shortening the effective service life of the system. To improve the corrosion resistance of polyolefin pipes, several improvement routes have been proposed in existing technologies. One approach is to use high molecular weight, high-density polyethylene or special copolymer polypropylene to improve resistance to slow crack propagation. However, this method offers limited improvement in resistance to strong oxidizing acids and organic solvents and cannot solve the problem of a sharp drop in corrosion resistance at high temperatures. Another approach is to adopt a multi-layer composite structure, with ordinary polyolefin as the outer layer and fluoroplastics such as polyvinylidene fluoride, perfluoroethylene propylene, or cross-linked polyethylene as the inner corrosion-resistant barrier layer. However, the interlayer bonding strength is easily deteriorated under temperature fluctuations and media penetration, leading to delamination. Furthermore, fluoropolymers are extremely expensive, hindering widespread adoption. Thirdly, inorganic fillers such as glass fiber, carbon fiber, and mica are added to improve the rigidity and heat resistance of the pipes. However, the interface between the filler and the matrix is ​​prone to peeling under corrosive media, causing microcracks and accelerating failure. At the same time, high filler content can significantly reduce the toughness of the material. Fourthly, polyolefins are cross-linked using silanes, peroxides, or radiation to form a three-dimensional network structure, which improves chemical resistance and stress cracking resistance. However, after cross-linking, the material loses its thermoplasticity and cannot be remelted and recycled, which is inconsistent with the policy orientation of a circular economy. Fifthly, epoxy resin, polyurethane, and other anti-corrosion coatings are applied to the inner wall of the pipe. However, uniform application to the narrow inner wall of drainage pipes is difficult, and problems such as pinholes and uneven thickness are hard to avoid. Furthermore, the adhesion between the organic coating and the polyolefin substrate is not easy to maintain in the long term.

[0028] This application reconstructs the intermediate layer in traditional multilayer composite pipes, which only serves a physical bonding function, into a self-healing functional layer with active damage management capabilities. This concept is achieved by introducing a dynamic covalent cross-linking network based on the Diels-Alder reaction, containing covalent bonds that can undergo reversible breakage and recombination under thermal stimulation. Unlike the static bonding layer design commonly used in existing technologies, this application creatively applies dynamic reversible covalent bonds, typically considered heat-sensitive, to the interface of multilayer polyolefin pipes requiring long-term heat resistance, achieving a reverse design that turns a disadvantage into an advantage. The inherent thermal stimulation in pipe operating conditions is no longer a negative factor leading to material performance degradation, but rather a positive driving force triggering interface self-healing. The elastic skeleton in the intermediate layer material contracts under thermal stimulation through shape memory effect, driving the physical closure of microcracks and creating crack-face contact conditions for chemical repair. Subsequently, the dynamic covalent cross-linking network undergoes reversible breakage and recombination at the closed crack interface, and the broken molecular chains redistribute and bond at the interface, completing the chemical repair. This synergistic mechanism enables the continuous and dynamic repair of interfacial micro-damage generated in multi-layer composite pipelines under long-term hot and cold cycles and mechanical vibration conditions, fundamentally overcoming the problem of delamination failure caused by irreversible accumulation of micro-damage.

[0029] The following is in conjunction with the appendix Figure 1 The technical solutions provided in this application will be described in detail through specific embodiments and application scenarios.

[0030] In a first aspect, this application proposes a highly corrosion-resistant polyolefin drainage pipe material, which is a multilayer composite material comprising an inner layer material, an intermediate layer material, and an outer layer material. The intermediate layer material is an adhesive layer formed by a polymer composition containing a dynamic covalent crosslinking network. The dynamic covalent crosslinking network is a thermally reversible crosslinking network based on the Diels-Alder reaction. The dynamic covalent crosslinking network contains covalent bonds that can undergo reversible breakage and recombination under thermal stimulation, thereby endowing the intermediate layer material with self-healing function.

[0031] First, this application employs a three-layer composite structure consisting of an inner layer, a middle layer, and an outer layer, achieving the different functions required by the pipeline in different layers. The inner layer provides corrosion protection and barrier function, directly contacting corrosive media. The middle layer provides interlayer adhesion and interface self-healing function. The outer layer provides structural load-bearing and resistance to external impacts. This functional design allows each layer to be independently optimized for its specific function, without having to accommodate multiple conflicting performance requirements in a single material, thus achieving a balance between corrosion resistance, mechanical properties, and recyclability.

[0032] Secondly, the intermediate layer material is an adhesive layer formed from a polymer composition containing a dynamic covalent cross-linked network. This adhesive layer achieves strong interfacial bonding between the three layers through chemical bonding with the inner and outer layers via reactive groups in its components. Furthermore, its internal dynamic covalent cross-linked network endows the intermediate layer material with a unique self-healing function. This self-healing function refers to the ability of microcracks to spontaneously heal under specific stimuli when they develop within the intermediate layer material or at the interlayer interface due to long-term thermal stress, mechanical vibration, or media penetration, restoring the material's integrity and adhesive strength.

[0033] Third, regarding the specific selection of the dynamic covalent crosslinking network. This application selects a thermally reversible crosslinking network based on the Diels-Alder reaction as the chemical realization of the dynamic covalent crosslinking network. The Diels-Alder reaction is a cycloaddition reaction between a conjugated diene and a dienophile, and its important characteristic is the thermal reversibility of the reaction. At lower temperatures, the furan group, as a conjugated diene, undergoes a forward Diels-Alder reaction with bismaleimide, as a dienophile, to form stable cyclic covalent crosslinks, constructing a three-dimensional crosslinking network that endows the material with good mechanical strength and dimensional stability. When the temperature rises to a certain range, the reverse Diels-Alder reaction is triggered, the formed covalent crosslinks break, the network topology rearranges, and the material undergoes local decrosslinking, gaining molecular chain mobility. When the temperature drops again, the forward Diels-Alder reaction restarts, the broken covalent bonds re-bond at new positions, and the crosslinking network is reconstructed.

[0034] The heat inherent in the pipeline's operating environment is no longer simply a negative factor leading to material degradation, but is transformed into energy that triggers interface self-repair. When microcracks develop within the interlayer material or at the interlayer interface due to thermal stress, mechanical fatigue, or aging, the high-temperature medium transported by the pipeline or the ambient heat provides the thermal stimulus needed to trigger the reversible fracture and recombination of Diels-Alder dynamic covalent bonds. Driven by the shape memory effect of the elastic framework, the microcracks physically close, and subsequently, under thermal stimulation, the dynamic covalent bonds at the crack interface undergo reversible recombination, completing chemical repair. The entire process requires no external intervention or maintenance shutdown; it can be spontaneously completed using the thermal energy generated during normal pipeline operation, achieving true online self-repair.

[0035] The polymer composition of the interlayer material contains maleic anhydride-grafted ethylene-octene copolymer as an elastic backbone. This elastic backbone exhibits a shape memory effect. When the pipeline is heated or experiences temperature changes, the shrinkage stress of the elastic backbone drives the two surfaces of the microcrack to physically close, creating conditions for subsequent chemical repair. After crack closure, the furan-side-group-containing polyolefin exposed at the crack interface undergoes dynamic reverse and forward Diels-Alder reactions with the bismaleimide crosslinking agent under the thermal stimulation of the pipeline's operating temperature. The broken molecular chains redistribute, recombine, and bond at the crack interface, achieving chemical repair of the crack and restoring the adhesive strength and interfacial integrity of the interlayer material. This self-healing process requires no external intervention and can proceed spontaneously using only the thermal stimulation of the pipeline's operating environment, endowing the pipeline material with autonomous damage management capabilities throughout its entire life cycle.

[0036] The synergistic effect of the aforementioned multilayer composite structure and dynamic covalent cross-linked network produces technical effects far exceeding the simple superposition of the components. First, the inner layer material constructs a physical barrier against corrosive media, significantly reducing the rate at which corrosive media penetrates to the interface between the intermediate and outer layers, providing a stable chemical environment for the self-healing mechanism of the intermediate layer. Second, the intermediate layer material not only provides initial interlayer adhesion but also continuously repairs micro-damage generated at the interface during long-term service through its self-healing function, eliminating the delamination failure mechanism at its root and completely solving the core durability problem of multilayer composite pipelines. Finally, the outer layer material bears the main mechanical load, protecting the inner and intermediate layers from external mechanical damage. Its design, combining fiber reinforcement and elastomer toughening, provides high ring stiffness and high impact resistance. The synergistic function of these three layers achieves a comprehensive technical effect of high corrosion resistance, high long-term reliability, high mechanical properties, and overall thermoplastic recyclability.

[0037] In some embodiments, the inner layer material is a nano-barrier and corrosion-resistant material, comprising, by weight, 100 parts of bimodal high-density polyolefin matrix, 1-10 parts of two-dimensional nanosheet filler, and 2-15 parts of reactive compatibilizer; the two-dimensional nanosheet filler is montmorillonite and / or layered double hydroxide, and its surface is treated with a coupling agent; the reactive compatibilizer is maleic anhydride-grafted polyolefin.

[0038] The choice of bimodal high-density polyethylene matrix is ​​based on its unique molecular weight distribution. The high molecular weight fraction provides excellent resistance to slow crack propagation, while the low molecular weight fraction ensures good melt processing fluidity. This allows the inner layer material to form a dense barrier layer when molded into a pipe, while also possessing long-term resistance to media penetration and crack propagation. Two-dimensional nanosheet fillers are uniformly dispersed in the matrix in an exfoliated or intercalated form. Their high aspect ratio sheet structure forms a tortuous labyrinthine penetration path within the matrix, reducing the diffusion coefficient of corrosive media molecules by one to two orders of magnitude, and producing excellent physical barrier effects against various solvents, oxidizing acids, and halogenated hydrocarbons. The unique lamellar structure of the layered double hydroxide gives it a specific ability to capture and exchange corrosive anions such as chloride ions. It can actively capture corrosive anions that penetrate into the matrix, further reducing the chemical activity of the medium, complementing the physical barrier properties of montmorillonite. The filler surface treated with coupling agent achieves strong interfacial bonding with the matrix through reactive compatibilizer, which avoids preferential penetration of corrosive media along the interface between the filler and the matrix. At the same time, the nanosheets can effectively passivate the microcrack tips when subjected to stress, maintaining the material's high elongation at break and impact strength.

[0039] In some embodiments, the inner layer material further comprises, by weight, 0.5-3 parts of a grafted polyolefin oligomer containing thymine or ureidinone tetrahydrobonded units to form a supramolecular physical crosslinking network in the inner layer material, which, together with the crystalline region of the bimodal high-density polyethylene matrix, constitutes an interpenetrating dual physical network structure.

[0040] The thymine and ureidinone groups can form a quadruple hydrogen bond array through self-recognition. Their dimer binding constant is much higher than that of ordinary hydrogen bonds, allowing them to form a stable and dynamically reversible supramolecular physical cross-linked network at room temperature. This supramolecular network is uniformly dispersed in the inner layer material matrix, interpenetrating with the crystalline regions of the bimodal high-density polyethylene matrix to form an interpenetrating dual-physical network structure. When the inner layer material is subjected to external stress or microcracks, the crystalline network provides the overall rigidity and strength of the material, while the quadruple hydrogen bond network efficiently dissipates energy at the crack tip. Due to the reversible breakage and recombination characteristics of the quadruple hydrogen bonds, the hydrogen bond array breaks and absorbs energy under stress, and rebonds to restore structural integrity after the stress is removed, thereby actively inhibiting the initiation and propagation of microcracks. The interpenetrating dual physical network structure works synergistically with the aforementioned nanomaze barrier structure. On the one hand, the nanosheets block corrosive media by extending the penetration path. On the other hand, the dual network structure inhibits the propagation of microcracks caused by the penetration of corrosive media or mechanical stress through energy dissipation mechanism. The two work together to ensure the long-term integrity of the inner layer material from the two dimensions of passive barrier and active protection.

[0041] In some embodiments, the polymer composition forming the interlayer material comprises, by weight, 100 parts of maleic anhydride-grafted ethylene-octene copolymer, 10-80 parts of a polyolefin containing furan side groups, and 1-20 parts of a bismaleimide crosslinking agent; the maleic anhydride-grafted ethylene-octene copolymer serves as an elastic backbone; the polyolefin containing furan side groups and the bismaleimide crosslinking agent form the thermally reversible crosslinking network through a Diels-Alder reaction; the thermally reversible crosslinking network endows the interlayer material with thermally activated self-healing capability; and the elastic backbone of the maleic anhydride-grafted ethylene-octene copolymer endows the interlayer material with a shape memory effect, which shrinks under thermal stimulation to assist in crack closure.

[0042] Maleic anhydride-grafted ethylene-octene copolymer serves as the elastic backbone component. Its ethylene-octene copolymer backbone possesses an extremely low glass transition temperature and excellent elastic recovery properties, endowing the intermediate layer material with an entropic elastically driven shape memory effect. When the pipe experiences thermal stress due to temperature changes or microcracks appear at the interface, the elastic strain energy stored in the elastic backbone is released, driving the material to contract and recover, causing the two surfaces of the crack to physically close. The maleic anhydride grafting groups in this component provide reaction sites for interfacial chemical bonding with the inner and outer layer materials, achieving chemical bonding between the three layers. The furan-side-group-containing polyolefin and the bismaleimide crosslinking agent together constitute the precursor of the dynamic covalent crosslinking network. The furan-side-group-containing polyolefin introduces furan groups into the side groups of the polyolefin molecular chain through copolymerization, giving it good compatibility with the polyolefin system. Simultaneously, the furan ring, as a conjugated diene, exhibits activity in the Diels-Alder reaction with bismaleimide. Bismaleimide crosslinking agents, as dienophiles, contain a maleimide group at each end, enabling them to crosslink with two different polyolefin molecular chains containing furan side groups to construct a three-dimensional network. The dosage is between 1 and 20 parts. Insufficient crosslinking agent dosage results in insufficient crosslinking density, preventing the dynamic crosslinking network from forming effective mechanical support and sufficient reversible bonds required for self-repair. Excessive crosslinking agent dosage leads to excessive crosslinking density, restricting the movement of molecular chains, hindering the reverse Diels-Alder reaction and the diffusion and recombination of molecular chains at the crack interface, thus reducing self-repair efficiency. The thermally reversible crosslinking network endows the intermediate layer material with thermally activated self-repair capabilities, while the elastic framework imparts a shape memory effect. These two mechanisms work synergistically in time and space. The shape memory effect first drives the physical closure of the crack under thermal stimulation, creating the geometric conditions for crack-face contact in chemical repair. The thermally reversible crosslinking network then undergoes dynamic exchange between reverse and forward Diels-Alder reactions at the closed crack interface, allowing broken molecular chains to redistribute and re-bond at the interface, completing the chemical repair. This spatiotemporal synergistic mechanism of closure and repair enables the intermediate layer material to autonomously cope with interfacial micro-damage caused by long-term thermal cycling and mechanical vibration conditions, thereby eliminating the hidden danger of delamination failure from the root.

[0043] In some embodiments, the maleic anhydride grafting rate of the maleic anhydride-grafted ethylene-octene copolymer is 1.5-3.0%. The grafting rate refers to the mass percentage of maleic anhydride groups grafted onto the polymer backbone. The lower limit of the grafting rate is 1.5% because when the grafting rate is too low, the number of maleic anhydride groups is insufficient to provide enough interfacial chemical bonding reaction sites, resulting in insufficient chemical bond density between the intermediate layer material and the inner and outer layers. The interlayer bonding force still mainly relies on physical thermal fusion adhesion, failing to achieve the goal of chemical bonding integration. Simultaneously, an excessively low grafting rate also results in insufficient crosslinking point density in the elastic skeleton, reducing the fixation and recovery rates of the shape memory effect, and failing to provide sufficient shrinkage driving force to assist crack closure. The upper limit of the grafting rate is 3% because when the grafting rate is too high, the excessive number of maleic anhydride groups leads to an overall high crosslinking density in the intermediate layer material, severely restricting molecular chain movement, reducing the material's elongation at break and elastic recovery performance, and weakening the molecular chain diffusion ability required for the shape memory effect and self-healing process. Furthermore, excessively high grafting rates can significantly increase the melt viscosity of the interlayer material, leading to poor viscosity matching with the inner and outer layers during three-layer co-extrusion molding, thus affecting the uniformity of the interlayer interface and the composite quality. Within a grafting rate range of 1.5-3.0%, maleic anhydride-grafted ethylene-octene copolymers can simultaneously satisfy the requirements of sufficient interfacial chemical bonding ability, good shape memory effect, suitable molecular chain mobility, and melt rheological properties matched with the co-extrusion process, achieving an optimal balance between the interlayer material's adhesive function, self-healing function, and process adaptability.

[0044] In some embodiments, the outer layer material comprises, by weight, 100 parts of polyolefin matrix, 10-35 parts of reinforcing fiber and 3-12 parts of elastomer toughening agent; the reinforcing fiber is chopped glass fiber or basalt fiber; the elastomer toughening agent is maleic anhydride-grafted ethylene-octene copolymer or maleic anhydride-grafted EPDM rubber.

[0045] The reinforcing fibers are uniformly dispersed in the polyolefin matrix, forming a fiber skeleton network that provides the necessary ring stiffness and creep resistance for the pipeline. This allows the pipeline to withstand external soil pressure and traffic loads without excessive deformation when buried or laid overhead, protecting the inner and intermediate layers from external mechanical damage. The elastomer toughening agent forms a dispersed island structure in the matrix. Its elastomeric phase can undergo cavitation and shear yielding under external impact, absorbing a large amount of impact energy and significantly improving the material's low-temperature impact resistance, preventing brittle cracking during handling, laying, and uneven foundation settlement. The maleic anhydride grafts used in the elastomer toughening agent carry reactive anhydride groups that can participate in the interfacial chemical bonding system of the intermediate layer material during co-extrusion. These groups chemically bond with reactive components in the intermediate layer material, making the bond between the outer and intermediate layers not only rely on physical thermal fusion adhesion but also form chemical covalent bonds, further enhancing the integrity of the three-layer structure. The reinforcing fibers and elastomer toughening agents of the outer material work together to achieve a balance between high stiffness and high toughness, so that the pipeline has sufficient ring stiffness without losing its ability to resist impact and deformation due to excessive rigidity.

[0046] In some embodiments, the thickness of the inner layer material accounts for 15-25% of the total thickness of the multilayer composite material, the thickness of the intermediate layer material accounts for 3-8%, and the thickness of the outer layer material accounts for 67-82%.

[0047] The inner layer, serving as a corrosion-resistant barrier, is designed to be as thin as possible while still meeting labyrinth barrier and anti-permeability requirements. This reduces the amount of expensive nanofillers and reactive compatibilizers used, thus controlling material costs. The middle layer, acting as an adhesive and self-healing layer, is designed to be thin enough to adequately cover the interface and provide sufficient reaction sites for effective chemical bonding and self-healing. Excessive thickness would lead to material waste and potentially create new weak points due to the relatively low strength of the middle layer itself. Insufficient thickness would fail to provide enough dynamic covalent bonds and elastic framework contraction driving force to complete the self-healing process. The outer layer, serving as the structural load-bearing layer, occupies the majority of the wall thickness, fully utilizing its low cost, high stiffness, and high toughness to bear the main mechanical loads. This proportional configuration of the three layers reflects the core concept of functional decoupling: high-cost functional materials used in small quantities are concentrated in thin layers performing specific functions, while low-cost structural materials used in large quantities dominate, achieving excellent overall performance while maintaining economic feasibility. The appropriate matching of the thickness of each layer is also coordinated with the functional requirements of each layer and the thermal expansion characteristics of each layer material. This helps to reduce the stress difference between the layers when the temperature changes, and works in synergy with the stress relaxation and self-healing function of the intermediate layer material to jointly ensure the structural integrity of the pipeline under long-term hot and cold cycle conditions.

[0048] Secondly, this application also proposes a method for preparing the high corrosion-resistant polyolefin drainage pipe material described in the first aspect, characterized by employing a three-layer co-extrusion molding process, comprising the following steps: Step 1: feeding the inner layer material, intermediate layer material, and outer layer material into three extruders respectively; Step 2: during the co-extrusion process, meteringly adding a bismaleimide crosslinking agent to the melt of the intermediate layer material, causing it to undergo a Diels-Alder reaction with the premixed polyolefin containing furan side groups in the intermediate layer material, generating a thermally reversible dynamic covalent crosslinking network in situ; Step 3: compounding and extruding the three-layer melt through a layered spiral die head, followed by vacuum sizing, cooling, traction, and cutting to obtain the pipe material.

[0049] Specifically, this application employs a three-layer co-extrusion molding process to prepare the high corrosion-resistant polyolefin drainage pipe material. The key to this process design lies in integrating the chemical synthesis of the material with the structural forming of the pipe into a single, continuous co-extrusion process. Traditional multilayer composite pipe preparation methods typically involve preparing each layer separately and then combining them via hot-melt bonding or adhesive bonding. This process is complex, time-consuming, and the interlayer bonding strength is significantly affected by secondary processing. The three-layer co-extrusion molding process of this application simultaneously completes the construction of the inner layer nano-barrier structure, the in-situ generation of the intermediate layer dynamic covalent cross-linked network, and the integrated molding of the interfacial chemical bonds between the three layers in a single continuous step. This simultaneous process design reduces the degradation impact of processing thermal history on the material, ensures direct contact between the fresh interfaces of each layer in the molten state, and facilitates the full diffusion and entanglement of molecular chains, providing a technological foundation for forming a high-quality multilayer integrated structure.

[0050] In the co-extrusion process, a bismaleimide crosslinking agent is metered into the melt of the interlayer material, causing it to undergo a Diels-Alder reaction with the premixed furan-side-group-containing polyolefin in the interlayer material, generating a thermally reversible dynamic covalent crosslinked network in situ. The core innovation of this step lies in controlling the formation of the dynamic covalent crosslinked network during the co-extrusion stage of pipe forming. When the interlayer material is fed into the extruder, its components consist only of a premix of maleic anhydride-grafted ethylene-octene copolymer and furan-side-group-containing polyolefin. At this point, no crosslinked network has formed, and the melt viscosity is relatively low, exhibiting good flowability, which is beneficial for uniform melt transport and distribution in the extruder and the layered screw die. The bismaleimide crosslinking agent is injected into the interlayer material melt during co-extrusion using a side-line metering method. This method ensures that the crosslinking reaction occurs in situ before or during the melt's entry into the layered screw die. In-situ generation means that the crosslinked network is formed simultaneously with the three-layer composite material, rather than being pre-prepared and then composited. When a dynamic covalent cross-linked network is first formed, the molecular chains are still in a highly mobile state. The dynamic reversibility of the cross-linking bonds allows the cross-linked network to fully adapt to the contact surface shape with the inner and outer layers at the interface, achieving close interfacial contact at the molecular level. Simultaneously, the reactive groups in the newly formed cross-linked network exhibit the highest reactivity with the reactive groups on the surfaces of the inner and outer layers under high-temperature molten conditions, which is beneficial for maximizing interfacial chemical bonding. If a pre-cross-linked intermediate layer material is used for further composite bonding, the cross-linked network has already fully solidified, the molecular chain mobility decreases, and the efficiency of interfacial contact and chemical bonding will be significantly reduced.

[0051] In some embodiments, the amount of bismaleimide crosslinking agent added in step 2 is 1-20% of the total weight of the intermediate layer material, so that the formed dynamic covalent crosslinking network has a suitable crosslinking density, thereby giving the intermediate layer material a self-healing function; in step 2, the melt temperature of the intermediate layer material is controlled at 160-200°C to ensure that the crosslinking agent reacts fully to form a dynamic crosslinking network, while avoiding over-crosslinking.

[0052] The selection of the crosslinking agent dosage is based on the following considerations: When the dosage is less than 1%, the number of bismaleimide molecules is too small, resulting in a low density of crosslinking bonds. The dynamic crosslinking network cannot form an effective three-dimensional through-structure, leading to insufficient self-healing ability and mechanical strength of the intermediate layer material. When the dosage is greater than 20%, the crosslinking density is too high, severely restricting molecular chain movement. Even if the reverse Diels-Alder reaction is thermally triggered, the molecular chains cannot complete diffusion and recombination within a limited time, resulting in a sharp decrease in self-healing efficiency. The melt temperature window of 160-200℃ is determined based on the thermodynamic and kinetic characteristics of the Diels-Alder reaction. Above 160℃, the forward Diels-Alder reaction rate is relatively fast, achieving the required degree of crosslinking within the limited residence time of co-extrusion. Simultaneously, this temperature range does not reach the temperature region where the reverse Diels-Alder reaction occurs significantly, avoiding excessive competition between crosslinking and de-crosslinking that prevents effective network formation. When the temperature exceeds 200℃, the reverse Diels-Alder reaction rate increases significantly, and a large amount of de-crosslinking occurs simultaneously with the formation of the crosslinked network, making it impossible to establish a stable crosslinked structure. Furthermore, excessively high temperatures may lead to thermal degradation of the polyolefin matrix. The amount of crosslinking agent added is coordinated with the melt temperature to ensure that the dynamic crosslinking network reaches the optimal crosslinking density for self-healing within a given extrusion residence time. This ensures that the network has sufficient mechanical integrity and elastic recovery driving force while retaining the mobility of molecular chains to achieve efficient self-healing.

[0053] In some embodiments, the preparation method of the inner layer material in step 1 includes: firstly, melting and granulating two-dimensional nanosheet filler, reactive compatibilizer and part of bimodal high-density polyethylene matrix through a twin-screw extruder to prepare nano masterbatch, wherein the screw speed of the twin-screw extruder is 300-600 rpm and the processing temperature is 180-230℃; then, mixing the nano masterbatch with the remaining bimodal high-density polyethylene matrix, stabilizer and optional supramolecular reinforcing agent uniformly to obtain inner layer special material.

[0054] Nano-montmorillonite and layered double hydroxides exist in a multi-layered, aggregated state in their original state. If directly mixed and extruded with the entire matrix resin in one step, the filler particles can only achieve macroscopic dispersion in the matrix and cannot achieve nanoscale intercalation or exfoliation. A large number of sheets still exist in the form of aggregates, significantly reducing the labyrinth barrier effect. Using a masterbatch method, high-concentration nanofillers and reactive compatibilizers are first subjected to high-shear melt blending in a portion of the matrix. The high shear rate of 300-6 rpm provided by the twin-screw extruder, combined with a processing temperature of 180-230℃, allows the maleic anhydride groups in the reactive compatibilizer to react in situ with the hydroxyl groups on the surface of the nanofiller. The compatibilizer molecular chains insert into the spaces between the filler sheets, expanding the interlayer spacing. Under the action of a strong shear field, intercalation and even exfoliation of the sheets are achieved. Due to the high filler concentration in the masterbatch, the contact frequency between the filler particles and the screw is high, resulting in a dispersion efficiency far superior to direct mixing with low concentrations. In the prepared nano-masterbatch, the nanofillers are already dispersed in the carrier resin in a pre-intercalated or pre-exfoliated form. During subsequent mixing with the remaining matrix resin and extrusion molding, these nano-dispersed layers are further uniformly distributed in the melt, ultimately forming a uniform, highly oriented labyrinth barrier structure in the inner layer material. A processing temperature of 180-230℃ ensures that the bimodal high-density polyethylene melts fully, providing a suitable melt viscosity to transfer shear force, while allowing the grafting reaction to proceed smoothly. Excessive temperature may lead to resin degradation or compatibilizer decomposition, while excessively low temperature results in excessively high melt viscosity and poor shear dispersion.

[0055] In some embodiments, in step 3, the composite temperature of the three-layer melt in the layered spiral die head is controlled to be 190-230°C, so that the intermediate layer material undergoes interfacial chemical bonding with the inner and outer layer materials during the melt composite process, forming an integrated multilayer composite material.

[0056] The layered spiral die head is the core component of multilayer co-extrusion. It merges three independent melt streams from three extruders in the order of inner, middle, and outer layers, forming a concentric ring-shaped composite melt stream within the die head. First, the merging temperature is 190-230℃. Within this temperature range, the polyolefin material is completely molten, and the melt viscosity is moderate. When the three melt layers merge within the die head, a clear interlayer interface is formed without interlayer disorder or interpenetration. Second, at this temperature, the ongoing Diels-Alder reaction in the middle layer melt maintains a suitable rate. When the dynamic crosslinking network comes into contact with the inner and outer layers at the interface, the maleic anhydride groups on the maleic anhydride-grafted ethylene-octene copolymer react chemically or undergo strong physical interactions with the reactive compatibilizer residual reactive groups in the inner layer material and the maleic anhydride groups carried by the elastomer toughening agent in the outer layer material, forming cross-interface chemical bonds. Finally, the composite temperature is higher than the forward crosslinking temperature of the Diels-Alder reaction of the intermediate layer material, allowing the newly formed crosslinked network to retain a certain degree of dynamic reversible activity. Crosslinking bonds can undergo local rearrangement at the interface to adapt to the microscopic geometry of the interface, achieving close molecular-level contact. If the composite temperature is too low, the melt viscosity of each layer is too high, the interlayer interfaces cannot fully contact, the chemical bonding efficiency is low, and the interlayer bonding force relies solely on physical adhesion, making delamination likely during long-term service. If the composite temperature is too high, it may trigger excessive reverse Diels-Alder reaction, resulting in severe dissociation of the crosslinked network and the intermediate layer material losing its proper mechanical strength and self-healing function. The composite temperature window of 190-230℃, combined with the melt temperature control in step 2 and the amount of crosslinking agent, achieves optimal temporal and spatial matching for the generation of the dynamic crosslinked network, the establishment of interfacial chemical bonds, and the formation of the three-layer composite structure, ultimately producing a highly corrosion-resistant polyolefin drainage pipe material with an integrated structure.

[0057] Example 1

[0058] The inner layer material, by weight, comprises the following components: 100 parts of bimodal high-density polyethylene matrix, 2.5 parts of montmorillonite surface-treated with a silane coupling agent, 2.5 parts of layered double hydroxide surface-treated with a silane coupling agent, 8 parts of maleic anhydride-grafted high-density polyethylene as a reactive compatibilizer, 1.5 parts of grafted polyethylene oligomer containing ureidopyrimidinone tetrahydrobonds as a supramolecular reinforcing agent, and 0.3 parts of antioxidant 1010, 0.3 parts of antioxidant 168, and 0.2 parts of calcium stearate. The total amount of montmorillonite and layered double hydroxide is 5 parts; the reactive compatibilizer is 8 parts, falling within the range of 2 to 15 parts; and the supramolecular reinforcing agent is 1.5 parts.

[0059] The intermediate layer material, by weight, comprises the following components: 100 parts of maleic anhydride-grafted ethylene-octene copolymer, 45 parts of polyethylene containing furan side groups, and 10 parts of bismaleimide crosslinking agent. The maleic anhydride grafting rate of the maleic anhydride-grafted ethylene-octene copolymer is 2.0%. The polyethylene containing furan side groups comprises 45 parts. The bismaleimide crosslinking agent comprises 10 parts.

[0060] The outer layer material, by weight, comprises the following components: 100 parts of copolymer polypropylene matrix, 22 parts of chopped glass fibers treated with a silane coupling agent, and 8 parts of maleic anhydride-grafted ethylene-octene copolymer as an elastomer toughening agent. The chopped glass fibers comprise 22 parts, and the elastomer toughening agent comprises 8 parts. The average length of the chopped glass fibers is 4.5 mm, and the average diameter is 13 micrometers.

[0061] The thickness of the inner layer material accounts for 20% of the total thickness of the multilayer composite material, the thickness of the middle layer material accounts for 5%, and the thickness of the outer layer material accounts for 75%.

[0062] The preparation method of the above-mentioned high corrosion-resistant polyolefin drainage pipe material adopts a three-layer co-extrusion molding process, and the specific steps are as follows.

[0063] Step 1: Preparation of Inner Layer Material. First, 2.5 parts of montmorillonite, 2.5 parts of layered double hydroxide, 8 parts of maleic anhydride-grafted high-density polyethylene, and 20 parts of bimodal high-density polyethylene matrix are melt-blended and granulated in a twin-screw extruder to prepare nano-masterbatch. The screw speed of the twin-screw extruder is set to 450 rpm; the processing temperature is set to 205℃, with temperatures at each stage from the feeding section to the die being 180, 195, 205, 210, 210, and 205℃ respectively. Then, the prepared nano-masterbatch is mixed evenly with the remaining 80 parts of bimodal high-density polyethylene matrix, 1.5 parts of grafted polyethylene oligomer containing ureidopyrimidinone tetrahydrobonded units, 0.3 parts of antioxidant 1010, 0.3 parts of antioxidant 168, and 0.2 parts of calcium stearate in a high-speed mixer to obtain the inner layer material.

[0064] Step 2: Premixing and Co-extrusion of the Intermediate Layer Material. 100 parts of maleic anhydride-grafted ethylene-octene copolymer and 45 parts of polyethylene containing furan side groups are mixed evenly in a high-speed mixer to obtain an intermediate layer premix. The intermediate layer premix is ​​then fed into an intermediate layer extruder. During co-extrusion, 10 parts of bismaleimide crosslinking agent are injected into the melt of the intermediate layer extruder through a side-stream metering feeding system, causing a Diels-Alder reaction with the furan-side-group-containing polyethylene in the intermediate layer premix to generate a thermally reversible dynamic covalent crosslinked network in situ. The temperature of each section of the intermediate layer extruder is controlled to maintain the melt temperature at 180°C, within the intermediate range of 160-200°C.

[0065] Step 3: Preparation of the outer layer material and three-layer co-extrusion. 100 parts of copolymer polypropylene matrix, 22 parts of chopped glass fiber treated with a silane coupling agent, and 8 parts of maleic anhydride-grafted ethylene-octene copolymer were mixed evenly in a high-speed mixer to obtain the outer layer material. The inner layer material obtained in Step 1, the intermediate layer melt containing a dynamic cross-linked network obtained in Step 2, and the outer layer material obtained in this step were respectively fed into three extruders. The temperature of each section of the inner layer extruder was set to 180-210℃, and the temperature of each section of the outer layer extruder was set to 190-220℃. The three-layer melt was compounded and extruded through a layered spiral die head. The compounding temperature of the layered spiral die head was controlled at 210℃, within the middle range of 190-230℃, so that the intermediate layer material could undergo interfacial chemical bonding with the inner and outer layer materials during the melt compounding process, forming an integrated multilayer composite material. Subsequently, through vacuum sizing, cooling in a cooling water tank, traction by a tracked traction machine, and cutting by a planetary cutting machine, a high corrosion-resistant polyolefin drainage pipe material with an outer diameter of 110 mm and a total wall thickness of 3.2 mm was produced. The inner layer material thickness is 0.64 mm, the middle layer material thickness is 0.16 mm, and the outer layer material thickness is 2.40 mm.

[0066] Example 2

[0067] The only difference between this embodiment and Example 1 is that the amount of polyethylene containing furan side groups in the polymer composition of the intermediate layer material is adjusted from 45 parts to 80 parts. In step 2, the intermediate layer premix is ​​prepared by mixing 100 parts of maleic anhydride-grafted ethylene-octene copolymer with 80 parts of polyethylene containing furan side groups. The amount of bismaleimide crosslinking agent added in step 2 remains unchanged at 10 parts.

[0068] Example 3

[0069] The only difference between this embodiment and Example 1 is that the amount of polyethylene containing furan side groups in the polymer composition of the intermediate layer material is adjusted from 45 parts to 10 parts. In step 2, the intermediate layer premix is ​​prepared by mixing 100 parts of maleic anhydride-grafted ethylene-octene copolymer with 10 parts of polyethylene containing furan side groups. The amount of bismaleimide crosslinking agent added in step 2 remains unchanged at 10 parts.

[0070] Example 4

[0071] The only difference between this embodiment and Example 1 is that the amount of bismaleimide crosslinking agent in the polymer composition of the intermediate layer material is adjusted from 10 parts to 20 parts. In step 2, the amount of bismaleimide crosslinking agent injected into the melt of the intermediate layer extruder through the side-line metering feeding system is correspondingly adjusted to 20 parts.

[0072] Example 5

[0073] The only difference between this embodiment and Example 1 is that the amount of bismaleimide crosslinking agent in the polymer composition of the intermediate layer material is adjusted from 10 parts to 1 part. In step 2, the amount of bismaleimide crosslinking agent injected into the intermediate layer extruder melt through the side-line metering feeding system is correspondingly adjusted to 1 part.

[0074] Example 6

[0075] The only difference between this embodiment and Example 1 is that the amount of grafted polyethylene oligomer containing ureidopyrimidinone tetrahydrobonded units in the inner layer material is adjusted from 1.5 parts to 3 parts. In step 1, when mixing the nanomasterbatch with the remaining bimodal high-density polyethylene matrix and other components, the amount of supramolecular reinforcing agent added is adjusted accordingly to 3 parts.

[0076] Example 7

[0077] The only difference between this embodiment and Example 1 is that the amount of grafted polyethylene oligomer containing ureidopyrimidinone tetrahydrobonded units in the inner layer material is adjusted from 1.5 parts to 0.5 parts. In step 1, when mixing the nanomasterbatch with the remaining bimodal high-density polyethylene matrix and other components, the amount of supramolecular reinforcing agent added is adjusted accordingly to 0.5 parts.

[0078] Example 8

[0079] The only difference between this embodiment and Example 1 is that the maleic anhydride grafting rate of the maleic anhydride-grafted ethylene-octene copolymer used in the intermediate layer material is adjusted from 2.0% to 3.0%. The remaining components and amounts remain unchanged, as does the preparation method.

[0080] Example 9

[0081] The only difference between this embodiment and Example 1 is that the maleic anhydride grafting rate of the maleic anhydride-grafted ethylene-octene copolymer used in the intermediate layer material is adjusted from 2.0% to 1.5%. The remaining components and amounts remain unchanged, as does the preparation method.

[0082] Comparative Example 1

[0083] The only difference between this comparative example and Example 1 is that the polymer composition of the interlayer material does not contain polyethylene with furan side groups, i.e., its amount is 0 parts. In step 2, the interlayer material is only 100 parts of maleic anhydride-grafted ethylene-octene copolymer, without the addition of polyethylene with furan side groups. In step 2, 10 parts of bismaleimide crosslinking agent are still added, but due to the lack of furan groups, the Diels-Alder reaction cannot occur, and a dynamic covalent crosslinking network cannot be formed.

[0084] Comparative Example 2

[0085] The only difference between this comparative example and Example 1 is that no bismaleimide crosslinking agent is added to the polymer composition of the interlayer material; that is, its amount is 0 parts. In step 2, no bismaleimide crosslinking agent is injected into the melt of the interlayer material. The interlayer material consists only of maleic anhydride-grafted ethylene-octene copolymer and polyethylene containing furan side groups, and cannot form a crosslinked network.

[0086] Comparative Example 3

[0087] The only difference between this comparative example and Example 1 is that the inner layer material does not contain grafted polyethylene oligomers with ureidopyrimidinone tetrahydrobonding units; that is, its amount is 0 parts. In step 1, when mixing the nanomasterbatch with the remaining bimodal high-density polyethylene matrix and stabilizer, no supramolecular reinforcing agent is added, and the inner layer material cannot form a supramolecular physical cross-linked network.

[0088] Comparative Example 4

[0089] The only difference between this comparative example and Example 1 is that the interlayer material uses ungrafted ethylene-octene copolymer instead of maleic anhydride-grafted ethylene-octene copolymer, i.e., the maleic anhydride grafting rate is 0. All other components and amounts remain unchanged, as does the preparation method. Due to the lack of maleic anhydride groups, the interlayer material cannot form effective chemical bonds with the inner and outer layers, and the shape memory elastic framework also lacks chemical sites for connection to the crosslinking network.

[0090] Test method:

[0091] Self-healing efficiency: After the intermediate layer material is cured, scratches about 10 mm long and 0.2 mm deep are made on the surface with a blade. The sample is placed in an 80℃ oven for 2 hours for heat treatment. After being taken out and cooled to room temperature, the interlaminar shear strength before and after scratch repair is tested using an electronic universal testing machine. The self-healing efficiency is the percentage of the repaired strength to the original strength.

[0092] Interlaminar shear strength retention rate after thermal cycling aging: The pipe sample was placed in a high and low temperature alternating test chamber, and a cycle was performed by holding it at -20℃ for 1 hour and at 90℃ for 1 hour. A total of 1000 cycles were performed. After removal, the interlaminar shear strength was tested according to ISO 16965 standard, and the retention rate was calculated based on the strength of the original sample without aging.

[0093] Chemical resistance (tensile strength retention): The pipe sample was immersed in a 60% sulfuric acid solution at 80°C for 30 days. After removal, the tensile strength was tested according to ISO 527 standard, and the retention rate was calculated based on the strength of the original sample before immersion.

[0094] The high corrosion-resistant polyolefin drainage pipe materials prepared in Examples 1-9 and Comparative Examples 4 were tested according to the above test methods, and the relevant test data are shown in Table 1.

[0095] Table 1. Test data of drainage pipe materials in Examples 1-9 and Comparative Examples 4

[0096] serial number Polyethylene containing furan side groups (parts) Bismaleimide crosslinking agent (parts) Supramolecular reinforcing agent (parts) MAH grafting rate (%) Self-repair efficiency (%) Interlaminar shear strength retention rate after 1000 thermal cycles (%) Tensile strength retention rate (%) after 30 days at 80℃ and 60% sulfuric acid Example 1 45 10 1.5 2.0 88 96 89 Example 2 80 10 1.5 2.0 72 85 86 Example 3 10 10 1.5 2.0 65 78 87 Example 4 45 20 1.5 2.0 61 81 85 Example 5 45 1 1.5 2.0 58 73 87 Example 6 45 10 3 2.0 86 94 92 Example 7 45 10 0.5 2.0 87 92 85 Example 8 45 10 1.5 3.0 82 90 87 Example 9 45 10 1.5 1.5 78 86 85 Comparative Example 1 0 10 1.5 2.0 5 41 83 Comparative Example 2 45 0 1.5 2.0 3 35 82 Comparative Example 3 45 10 0 2.0 85 88 78 Comparative Example 4 45 10 1.5 0 10 28 76

[0097] In Comparative Example 1, after removing the furan-containing polyethylene side group, the self-healing efficiency plummeted from 88% in Example 1 to 5%, and the interlaminar shear strength retention rate after thermal cycling plummeted from 96% to 41%. In Comparative Example 2, after removing the bismaleimide crosslinking agent, the self-healing efficiency decreased to 3%, and the interlaminar shear strength retention rate after thermal cycling decreased to 35%. These two comparative examples fully demonstrate that both components of the dynamic covalent crosslinking network are indispensable; the absence of either component leads to the complete loss of interfacial self-healing ability and long-term durability.

[0098] In Comparative Example 3, after removing the supramolecular reinforcing agent, the tensile strength retention rate after long-term immersion in 60% sulfuric acid at 80°C decreased from 89% in Example 1 to 78%, while the decrease in self-healing efficiency and thermal cycling retention rate was relatively small. This indicates that the supramolecular network makes a unique contribution to the suppression of microcracks under long-term chemical erosion.

[0099] In Comparative Example 4, after replacing the grafted POE with ungrafted POE, the self-healing efficiency plummeted to 10%, the interlaminar shear strength retention rate after thermal cycling dropped sharply to 28%, and the chemical corrosion resistance decreased to 76%, with all three properties deteriorating significantly. This indicates that the maleic anhydride group is not only key to achieving interlaminar chemical bonding but also a chemical anchor point for establishing mechanical connections between the elastic framework and the dynamic cross-linked network; its presence is a fundamental prerequisite for achieving self-healing functionality.

[0100] It should be noted that, in this document, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Unless otherwise specified, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes that element.

[0101] The various embodiments in this specification are described in a progressive manner, with each embodiment focusing on the differences from other embodiments. The same or similar parts between the various embodiments can be referred to each other.

[0102] The above description of the disclosed embodiments enables those skilled in the art to make or use this application. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of this application. Therefore, this application is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

[0103] Furthermore, it should be noted that the scope of the methods and apparatus in the embodiments of this application is not limited to performing functions in the order shown or discussed, but may also include performing functions substantially simultaneously or in the reverse order, depending on the functions involved. For example, the described methods may be performed in a different order than described, and various steps may be added, omitted, or combined. In addition, features described with reference to certain examples may be combined in other examples.

Claims

1. A highly corrosion-resistant polyolefin drainage pipe material, characterized in that, It is a multilayer composite material comprising an inner layer material, an intermediate layer material, and an outer layer material. The intermediate layer material is an adhesive layer formed by a polymer composition containing a dynamic covalent crosslinking network. The dynamic covalent crosslinking network is a thermally reversible crosslinking network based on the Diels-Alder reaction. The dynamic covalent crosslinking network contains covalent bonds that can undergo reversible breakage and recombination under thermal stimulation, thereby endowing the intermediate layer material with self-healing function.

2. The high corrosion-resistant polyolefin drainage pipe material according to claim 1, characterized in that, The inner layer material is a nano-barrier and anti-corrosion material, comprising 100 parts by weight of bimodal high-density polyolefin matrix, 1-10 parts by weight of two-dimensional nanosheet filler and 2-15 parts by weight of reactive compatibilizer; the two-dimensional nanosheet filler is montmorillonite and / or layered double hydroxide, and its surface is treated with a coupling agent; the reactive compatibilizer is maleic anhydride-grafted polyolefin.

3. The high corrosion-resistant polyolefin drainage pipe material according to claim 2, characterized in that, By weight, the inner layer material further comprises 0.5-3 parts of grafted polyolefin oligomers containing thymine or ureidinone tetrahydrobonded units to form a supramolecular physical crosslinking network in the inner layer material, which constitutes an interpenetrating dual physical network structure with the crystalline region of the bimodal high-density polyethylene matrix.

4. The high corrosion-resistant polyolefin drainage pipe material according to claim 1, characterized in that, The polymer composition forming the interlayer material comprises, by weight, 100 parts of maleic anhydride-grafted ethylene-octene copolymer, 10-80 parts of a polyolefin containing furan side groups, and 1-20 parts of a bismaleimide crosslinking agent; the maleic anhydride-grafted ethylene-octene copolymer serves as an elastic backbone; the polyolefin containing furan side groups and the bismaleimide crosslinking agent form the thermally reversible crosslinking network through a Diels-Alder reaction; the thermally reversible crosslinking network endows the interlayer material with thermally activated self-healing ability; and the elastic backbone of the maleic anhydride-grafted ethylene-octene copolymer endows the interlayer material with a shape memory effect, which shrinks under thermal stimulation to assist in crack closure.

5. The high corrosion-resistant polyolefin drainage pipe material according to claim 4, characterized in that, The maleic anhydride grafting rate of the maleic anhydride-grafted ethylene-octene copolymer is 1.5-3.0%.

6. The high corrosion-resistant polyolefin drainage pipe material according to claim 1, characterized in that, The outer layer material comprises, by weight, 100 parts of polyolefin matrix, 10-35 parts of reinforcing fiber and 3-12 parts of elastomer toughening agent; the reinforcing fiber is chopped glass fiber or basalt fiber; the elastomer toughening agent is maleic anhydride-grafted ethylene-octene copolymer or maleic anhydride-grafted ethylene propylene diene monomer (EPDM) rubber.

7. The high corrosion-resistant polyolefin drainage pipe material according to any one of claims 1 to 6, characterized in that, The thickness of the inner layer material accounts for 15-25% of the total thickness of the multilayer composite material, the thickness of the middle layer material accounts for 3-8%, and the thickness of the outer layer material accounts for 67-82%.

8. A method for preparing the high corrosion-resistant polyolefin drainage pipe material according to any one of claims 1 to 7, characterized in that, The three-layer co-extrusion molding process includes the following steps: Step 1: Feed the inner layer material, intermediate layer material and outer layer material into three extruders respectively; Step 2: During the co-extrusion process, bismaleimide crosslinking agent is metered and added to the melt of the intermediate layer material, so that it undergoes a Diels-Alder reaction with the premixed polyolefin containing furan side groups in the intermediate layer material to generate a thermally reversible dynamic covalent crosslinking network in situ. Step 3: The three-layer melt is compounded and extruded through a layered spiral die head, and then vacuum sizing, cooling, traction and cutting are performed to obtain the pipe material.

9. The method according to claim 8, characterized in that, In step 2, the amount of bismaleimide crosslinking agent added is 1-20% of the total weight of the intermediate layer material, so that the formed dynamic covalent crosslinking network has a suitable crosslinking density, thereby giving the intermediate layer material a self-healing function; in step 2, the melt temperature of the intermediate layer material is controlled at 160-200℃ to ensure that the crosslinking agent reacts fully to form a dynamic crosslinking network, while avoiding over-crosslinking.

10. The method according to claim 8, characterized in that, The preparation method of the inner layer material in step 1 includes: firstly, melting and granulating two-dimensional nanosheet filler, reactive compatibilizer and part of bimodal high-density polyethylene matrix through a twin-screw extruder to prepare nano masterbatch, wherein the screw speed of the twin-screw extruder is 300-600 rpm and the processing temperature is 180-230℃; then, mixing the nano masterbatch with the remaining bimodal high-density polyethylene matrix, stabilizer and optional supramolecular reinforcing agent evenly to obtain the inner layer special material; And / or, in step 3, the composite temperature of the three-layer melt in the layered spiral die head is controlled to be 190-230°C, so that the intermediate layer material undergoes interfacial chemical bonding with the inner and outer layer materials during the melt composite process, forming an integrated multilayer composite material.

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