HDPE double-wall corrugated pipe and preparation method and application thereof

Abstract

This invention discloses an HDPE double-wall corrugated pipe, its preparation method, and its application, belonging to the field of plastic pipe technology. The HDPE double-wall corrugated pipe of this invention includes an HDPE double-wall corrugated pipe body and a composite material layer covering its outer wall. The composite material layer, from the outside to the inside, consists of inner and outer layers of ethylene-ethyl acrylate copolymer and an intermediate layer of styrene-based thermoplastic elastomer. Adding a specific composite material layer to the outside of a traditional pipe significantly improves the pipe's toughness, impact resistance, low-temperature resistance, and aging resistance. It is particularly suitable for pipe production using environmentally friendly recycled PE materials, effectively overcoming the problem of balancing ring stiffness and toughness in existing technologies, and extending the service life of the pipe.

Description

Technical Field

[0001] This application belongs to the field of plastic pipe technology, and in particular relates to an HDPE double-wall corrugated pipe, its preparation method and application. Background Technology

[0002] High-density polyethylene (HDPE) double-wall corrugated pipes are widely used in municipal drainage, sewage, and cable protection due to their advantages such as light weight, high ring stiffness, and convenient construction. However, current HDPE double-wall corrugated pipes on the market, especially those designed for high ring stiffness, generally suffer from a technical weakness: the corrugated crests are relatively brittle. Under external pressure, heavy loads, or impacts, they are prone to denting or even cracking, and once plastic deformation occurs, they are difficult to recover. This structural defect seriously affects the pipe's durability and actual service life.

[0003] The causes of this problem are multifaceted. Firstly, there is a tendency within the industry to prioritize ring stiffness in product design, neglecting the pipe's wall thickness, strength, and toughness. In recent years, with increasingly stringent environmental requirements, the proportion of environmentally friendly recycled PE materials used in pipe production has gradually increased, even becoming a primary raw material. Although pipes produced using recycled materials can easily achieve the high international standard of 8.0 kN / m ring stiffness by adding stiffening filler masterbatch, the underlying issues remain. 2 However, this usually comes at the cost of sacrificing the toughness and strength of the material. The anti-aging properties, oxidation induction time (OIT), ash content, and impact resistance of recycled materials are far inferior to those of pure PE raw materials, resulting in inherent defects in the final product, such as high brittleness, weak impact resistance, and poor aging resistance.

[0004] In practical applications, these pipes are exposed to complex and variable working conditions, such as diurnal temperature variations, seasonal freeze-thaw cycles, impacts from drops during loading and unloading, and pressure from backfill soil and rocks. Under the combined influence of these external forces and environmental factors, stress concentration is easily generated at the corrugated sections and pressure points of the pipe body, leading to damage and cracking, thus posing a potential safety hazard to the project.

[0005] Existing technology discloses an HDPE double-wall corrugated pipe comprising high-density polyethylene, modified carbon nanotubes, functionalized nano-titanium dioxide, POE elastomer, lubricant, and benzoyl peroxide. By modifying the carbon nanotubes and functionalized nano-silica, the poor compatibility of inorganic fillers in HDPE double-wall corrugated pipes is addressed, improving ring stiffness and creep resistance while ensuring the overall mechanical properties and aging resistance of the material remain unaffected. However, the preparation of the modified filler is complex, hindering the industrialization of the product. Although ring stiffness is improved, toughness needs further enhancement, and its applicability to environmentally friendly recycled materials is unknown.

[0006] Therefore, developing a double-walled HDPE corrugated pipe that can balance ring stiffness and toughness, strength and impact resistance is of great research significance and application value. Summary of the Invention

[0007] To address the technical problems existing in the prior art, the primary objective of this invention is to provide an HDPE double-wall corrugated pipe.

[0008] Another object of the present invention is to provide a method for preparing the above-mentioned HDPE double-wall corrugated pipe.

[0009] Another object of the present invention is to provide the application of the above-mentioned HDPE double-wall corrugated pipe in the preparation of environmentally friendly recycled pipe.

[0010] To achieve the above-mentioned objectives, the present invention adopts the following technical solution: This invention protects an HDPE double-wall corrugated pipe, wherein the outer wall of the HDPE double-wall corrugated pipe is covered with a composite material layer. The composite material layer comprises, from the outside to the inside, an outer layer, a middle layer, and an inner layer; The outer and inner layers are made of ethylene-ethyl acrylate copolymer, and the middle layer is made of styrene-based thermoplastic elastomer. The thickness of the composite material layer is 3 mm or more; The thickness of the intermediate layer is less than 40% of the thickness of the composite material layer.

[0011] This invention provides an HDPE double-wall corrugated pipe, wherein the composite material layer covering the pipe provides protection outside the crests of the corrugations, enhances the surface elasticity of the pipe, resists low-temperature impact and flexibility, and maintains the specified ring stiffness.

[0012] The intermediate layer of the composite material uses a styrene-based thermoplastic elastomer, which possesses the high elasticity, large deformation recovery ability, and outstanding aging resistance of traditional vulcanized rubber. When external extrusion or impact energy is transferred to this elastomer layer, its molecular chain segments can undergo reversible extension and slippage, dissipating mechanical energy into internal frictional heat. This significantly suppresses the indentation and cracking of the wave crest, providing the composite material layer with flexibility and elastic strength. The outer ethylene-ethyl acrylate copolymer protects the intermediate styrene-based thermoplastic elastomer from direct contact with the outside environment. Furthermore, the inner ethylene-ethyl acrylate copolymer is compatible with the PE material of the outer wave crest of the pipe, achieving a good plasticizing effect and providing the product with certain low-temperature impact resistance, high toughness, and high-temperature resistance.

[0013] By controlling the total thickness of the composite material layer to be above 3 mm and the thickness of the intermediate layer to be no more than 40%, the elastomer layer can effectively absorb impact energy without excessively weakening the pipe's resistance to external pressure deformation, thus achieving the best balance between ring stiffness and toughness.

[0014] Preferably, the thickness of the intermediate layer accounts for 34% to 40% of the thickness of the composite material layer.

[0015] Preferably, the number-average molecular weight of the ethylene-ethyl acrylate copolymer is 50,000 to 100,000.

[0016] Preferably, the melt flow rate (MFR) of the ethylene-ethyl acrylate copolymer is 5~10 g / 10 min at 190°C and 2.16 kg.

[0017] When the MFR is in the moderate range of 5~10 g / 10min, the ethylene-ethyl acrylate copolymer melt maintains good spreadability and wettability, achieving tight molecular chain entanglement with the pipe body and elastomer layer, while also possessing sufficient melt strength to maintain clear interfaces and uniform thickness between layers. This ensures that the composite material layer forms a continuous, dense, and strongly adherent gradient buffer structure after co-extrusion, ultimately maximizing the synergistic effect of the high toughness of the ethylene-ethyl acrylate copolymer and the high resilience of the elastomer, significantly improving the pipe's resistance to low-temperature impact, aging resistance, and overall durability.

[0018] Preferably, the styrene-based thermoplastic elastomer is at least one of a block copolymer of styrene and a diene or a hydrogenated styrene-based thermoplastic elastomer; wherein the diene is at least one of butadiene or isoprene.

[0019] Preferably, the melt flow rate of the styrene-based thermoplastic elastomer is 3~4 g / 10 min at 190°C and 2.16 kg.

[0020] Preferably, the total thickness of the composite material layer is 3~5mm.

[0021] The present invention also protects the preparation method of the above-mentioned HDPE double-wall corrugated pipe, which includes the following steps: co-extruding an ethylene-ethyl acrylate copolymer and a styrene thermoplastic elastomer to form a composite material layer, and then heating and extruding it to cover the outer layer of the HDPE double-wall corrugated pipe.

[0022] The application of the aforementioned HDPE double-wall corrugated pipe in the preparation of environmentally friendly recycled pipes is also within the scope of protection of this invention.

[0023] Compared with the prior art, the present invention has the following beneficial effects: The HDPE double-wall corrugated pipe of the present invention includes an HDPE double-wall corrugated pipe body and a composite material layer covering its outer wall; the composite material layer consists of an outer layer of ethylene-ethyl acrylate copolymer, an intermediate layer of styrene-based thermoplastic elastomer, and an inner layer of ethylene-ethyl acrylate copolymer from the outside to the inside. By adding a specific composite material layer to the outside of the traditional pipe, the toughness, impact resistance, low-temperature resistance and aging resistance of the pipe are significantly improved. It is especially suitable for the production of pipes based on environmentally friendly recycled PE materials, effectively overcoming the problem of difficulty in balancing ring stiffness and toughness in the prior art, and extending the service life of the pipe. Attached Figure Description

[0024] Figure 1 This is a schematic diagram of HDPE double-wall corrugated pipe. Detailed Implementation

[0025] The present invention is further illustrated below with reference to specific embodiments. These embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Experimental methods in the following embodiments that do not specify specific conditions are generally performed under conventional conditions in the art or as recommended by the manufacturer; the raw materials and reagents used, unless otherwise specified, are all commercially available from the conventional market. Any non-substantial changes and substitutions made by those skilled in the art based on the present invention are within the scope of protection claimed by the present invention.

[0026] I. The reagents used in the various embodiments and comparative examples of this invention are described below: Double-wall corrugated pipe: Liansu, 70 series double-wall corrugated pipe SN8 300 specification product, made from recycled materials.

[0027] Ethylene-ethyl acrylate copolymer #1: Arkema 4700 (France), melt flow rate (190 ℃ / 2.16 kg) is 7.6 g / 10 min, ethyl acrylate content: 30 % wt; Ethylene-ethyl acrylate copolymer #2: Dow 5012, ethyl acrylate content 15%wt, melt flow rate (190 ℃ / 2.16 kg) is 3.9 g / 10min; Ethylene-ethyl acrylate copolymer #3: Arkema 5500 (France), ethyl acrylate content 20%wt, melt flow rate (190 ℃ / 2.16 kg) is 4.5 g / 10min; Styrene-based thermoplastic elastomer #1: Dushanzi Petrochemical T6302H (styrene-butadiene-styrene block copolymer), melt flow rate (190 ℃ / 2.16 kg) is 3.58 g / 10 min; Styrene-based thermoplastic elastomer #2: Baling Petrochemical SIS1105 (styrene-isoprene-styrene block copolymer), melt flow rate (190 ℃ / 2.16 kg) is 3.46 g / 10 min; Styrene-based thermoplastic elastomer #3: Baling Petrochemical YH-502 (hydrogenated styrene-butadiene-styrene block copolymer), melt flow rate (190 ℃ / 2.16 kg) is 3.29 g / 10 min; Ethylene-vinyl acetate copolymer EVA: Ningxia Coal Industry UL2528, melt flow rate (190 ℃ / 2.16 kg) is 6.7 g / 10 min, vinyl acetate content: 27.5 %wt.

[0028] II. Experimental Methods Example 1 Ethylene-ethyl acrylate copolymer 1# and styrene thermoplastic elastomer 1# are co-extruded at 195~205℃ to form a composite material layer, which is then heated and extruded to cover the outer layer of HDPE double-wall corrugated pipe. The material ratio of the middle layer is 40%, and the material ratio of the inner and outer layers is 30% each. The thickness of the composite material layer is 4mm.

[0029] Example 2 The experimental method is the same as in Example 1, except that the thickness of the composite material layer is 3 mm.

[0030] Example 3 The experimental method is the same as in Example 1, except that the thickness of the composite material layer is 5 mm.

[0031] Example 4 The experimental method is the same as in Example 1, except that the thickness of the composite material layer is 10 mm.

[0032] Example 5 The experimental method is the same as in Example 1, except that the thickness of the intermediate layer accounts for 30% of the thickness of the composite material layer, and the thicknesses of the inner and outer layers are 35% respectively.

[0033] Example 6 The experimental method is the same as in Example 1, except that the thickness of the intermediate layer accounts for 34% of the thickness of the composite material layer, and the thicknesses of the inner and outer layers are 33% respectively.

[0034] Example 7 The experimental method is the same as in Example 1, except that the outer and inner layers are different in thickness. The material ratio of the middle layer is 40%, the inner layer is 20%, and the outer layer is 40%.

[0035] Example 8 The experimental method was the same as in Example 1, except that styrene-based thermoplastic elastomer 2# was used as the intermediate layer material.

[0036] Example 9 The experimental method was the same as in Example 1, except that styrene-based thermoplastic elastomer 3# was used as the intermediate layer material.

[0037] Example 10 The experimental method is the same as in Example 1, except that the thickness of the intermediate layer accounts for 50% of the thickness of the composite material layer, and the thicknesses of the inner and outer layers are 25% respectively.

[0038] Example 11 The experimental method was the same as in Example 1, except that the ethylene-ethyl acrylate copolymer 2# was used.

[0039] Example 12 The experimental method was the same as in Example 1, except that the ethylene-ethyl acrylate copolymer 3# was used.

[0040] Comparative Example 1 Double-wall corrugated pipe: Liansu, double-wall corrugated pipe 70 series SN8 300 specification product, without the composite material layer of Example 1.

[0041] Comparative Example 2 The experimental method was the same as in Example 1, except that the outer and inner layers were made of equal amounts of ethylene-vinyl acetate copolymer (EVA) instead of ethylene-ethyl acrylate copolymer (EEA).

[0042] Comparative Example 3 The experimental method was the same as in Example 1, except that the intermediate layer was made of a polyurethane thermoplastic elastomer.

[0043] Comparative Example 4 The experimental method was the same as in Example 1, except that the intermediate layer was made of a polyolefin thermoplastic elastomer.

[0044] Comparative Example 5 The experimental method is the same as in Example 1, except that the thickness of the composite material layer is 2 mm.

[0045] III. Test Indicators (1) Low temperature impact: 0℃; Refer to GB / T 14152-2001 for testing, 400SN8 specification, double wall corrugated pipe with nominal inner diameter of 400 mm and ring stiffness grade of SN8; inner diameter > 315 mm, drop weight of 3.2 kg, drop height of 2000 mm.

[0046] (2) Tensile yield stress; tested according to GB / T 1040.2-2006.

[0047] (3) Oxidation induction time; Refer to GB / T 19466.6-2009 for testing. Place the product sample in a device at 200℃ and continuously supply oxygen for combustion. Set the time to 60 minutes and observe whether the curve shows a turning point within 60 minutes.

[0048] (4) Ring flexibility; tested according to ISO 13968:2008.

[0049] (5) Forklift simulation loading and unloading drop test: Use a forklift to lift the pipe to a height of 6 meters and let the pipe fall naturally to the ground to see if the pipe body is broken, in order to test the toughness and strength of the product.

[0050] IV. Test Results Table 1. Test Results of Examples / Comparative Examples

[0051] Note: Impact result 21 / 28 means 21 samples did not break under 28 impacts; ring flexibility 33% mold line cracking means that the mold line cracked when the sample reached 33% of the deformation under constant force.

[0052] Comparative Example 1 shows a double-walled HDPE corrugated pipe made from recycled material. Lacking a three-layer composite material layer, it exhibits poor low-temperature impact resistance, very low tensile yield stress, short oxidation induction time, and poor ring flexibility. At 18%, the mold line cracks, and the drop test results in wave crest fracture. This indicates that although the ring stiffness is high, the material is brittle and has poor toughness. This is because without the protection of the composite material layer, the pipe directly bears the impact.

[0053] In Comparative Example 2, EVA was used instead of EEA, resulting in significantly poorer low-temperature impact toughness, tensile yield stress, and ring flexibility. The EEA used in this invention has higher adhesion to PE than EVA, and can better bond with the crests of PE double-wall pipes; it also has stronger heat resistance and low-temperature toughness, and is superior in low-temperature impact performance.

[0054] Comparative Example 3, which used TPU instead of styrene-based elastomers, produced an overall product with poor hand softness and poor dimensional shrinkage.

[0055] Comparative Example 4, which replaced styrene-based elastomers with POE, showed significantly poorer low-temperature impact toughness and a shorter oxidation induction time. POE is an ethylene-octene copolymer, which has good compatibility with HDPE, but it lacks a benzene ring structure, has lower molecular chain rigidity, and its anti-aging properties are not as good as those of hydrogenated styrene-based elastomers.

[0056] Comparative Example 5 has a composite material layer thickness of 2mm, which has significantly poor low-temperature impact toughness and poor ring flexibility (30% of the mold line cracks). Insufficient thickness means that the energy absorption capacity is not enough, and the impact energy is easily transferred to the pipe body, leading to damage.

[0057] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A type of HDPE double-wall corrugated pipe, characterized in that, The outer wall of the HDPE double-wall corrugated pipe is covered with a composite material layer. The composite material layer comprises, from the outside to the inside, an outer layer, a middle layer, and an inner layer; The outer and inner layers are made of ethylene-ethyl acrylate copolymer, and the middle layer is made of styrene-based thermoplastic elastomer. The thickness of the composite material layer is 3 mm or more.

2. The HDPE double-wall corrugated pipe according to claim 1, characterized in that, The thickness of the intermediate layer is less than 40% of the thickness of the composite material layer.

3. The HDPE double-wall corrugated pipe according to claim 1, characterized in that, The ethyl acrylate content of the ethylene-ethyl acrylate copolymer is 15-20%.

4. The HDPE double-wall corrugated pipe according to claim 1, characterized in that, The styrene-based thermoplastic elastomer is at least one of a block copolymer of styrene and a diene or a hydrogenated styrene-based thermoplastic elastomer; wherein the diene is at least one of butadiene or isoprene.

5. The HDPE double-wall corrugated pipe according to claim 1, characterized in that, The total thickness of the composite material layer is 3~5mm.

6. The HDPE double-wall corrugated pipe according to claim 1, characterized in that, The inner and outer layers have the same thickness.

7. The HDPE double-wall corrugated pipe according to claim 1, characterized in that, The melt flow rate of the ethylene-ethyl acrylate copolymer at 190°C and a load of 2.16 kg is 5~10 g / 10 min.

8. The method for preparing the HDPE double-wall corrugated pipe according to any one of claims 1 to 7, characterized in that, Includes the following steps: The composite material layer is formed by co-extruding ethylene-ethyl acrylate copolymer and styrene thermoplastic elastomer, and then heated and extruded to cover the outer layer of HDPE double-wall corrugated pipe.

9. The preparation method according to claim 8, characterized in that, The temperature of the heated extrusion covering is 195℃~205℃.

10. The application of the HDPE double-wall corrugated pipe according to any one of claims 1 to 7 in the preparation of municipal drainage pipes, sewage pipes or cable protection pipes.

Images