Electric hot melting connection treatment process for PE pipes for municipal pipelines

Abstract

The invention relates to the technical field of municipal pipeline construction, and discloses an electric hot melting connection treatment process of a PE pipe for municipal pipelines, interface reconstruction paste is prepared from the following components in parts by weight: 35-45 parts of a matrix conversion component, 15-25 parts of a rheology locking component, 20-30 parts of a phase change distance component and 5-10 parts of a thermal latent crosslinking component; wherein the matrix conversion component is selected from maleic anhydride grafted polyethylene wax, the grafting rate is 0.8%-1.2%, the melting point is 105-115 DEG C, and the number-average molecular weight is 2000-4000. The physical gap is forcibly maintained in the initial stage of heating, reaction time and space are provided for component conversion of a matrix, an oxide layer on the surface of the pipe can be converted in situ, and therefore dependence on manual scraping operation precision is reduced, and effective fusion of a connection interface is guaranteed.

Description

Technical Field

[0001] This invention relates to the field of municipal pipeline construction technology, specifically to an electrofusion connection process for PE pipes used in municipal pipelines. Background Technology

[0002] Polyethylene (PE) pipes are widely used in municipal water supply and drainage and gas transmission pipeline projects due to their excellent corrosion resistance, flexibility, and hygienic properties. Electrofusion connection is the mainstream connection method in PE pipe construction. Its principle is to heat the polyethylene material on the inner wall of the fitting by passing an electric current through a resistance wire embedded in the inner wall of the fitting, so that the polyethylene material on the inner wall of the fitting and the outer wall of the pipe melts and forms an integral connection after cooling and solidification.

[0003] However, when polyethylene is exposed to air for a long time, its surface will naturally oxidize to form a polar oxide layer. This oxide layer has high thermal stability and poor compatibility with the matrix. If it exists in the welding interface, it will seriously hinder the cross-interface diffusion and entanglement of polyethylene molecular chains, becoming a structural weakness that leads to joint failure.

[0004] Currently, industry standards primarily rely on construction workers mechanically scraping the pipe ends before welding to remove the oxide layer. However, in actual construction sites, due to limitations such as pipe ovality deviation, wear and tear on scraping tools, and the instability of manual operation, mechanical scraping often fails to thoroughly and evenly remove the oxide layer from all areas to be welded, easily leaving localized oxide spots at the welding interface.

[0005] More importantly, the fit between standard electrofusion fittings and the pipe is relatively small. During the initial heating phase, as the polyethylene material expands due to heat, the fit quickly disappears, creating contact pressure. Under conventional processes, this physical closure process often occurs before the interface temperature reaches a level sufficient to cause the oxide layer to crack or be carried away by the shear force of the melt flow. Due to the lack of sufficient reaction time and overflow channels, the residual oxide layer is directly sealed inside the fusion interface, hindering the effective fusion of the molten material and forming defects such as false welds or cold joints that are difficult to detect through visual inspection. Summary of the Invention

[0006] To address the shortcomings of existing technologies, this invention provides an electrofusion connection process for PE pipes used in municipal pipelines, which solves the problem that in existing technologies, molten material easily covers the fusion interface, leading to incomplete fusion.

[0007] The first aspect of the present invention provides an interface reconstruction paste for electrofusion bonding of PE pipes for municipal pipelines, the interface reconstruction paste being made of the following components in parts by weight: 35 to 45 parts of matrix conversion component, 15 to 25 parts of rheology locking component, 20 to 30 parts of phase change spacing component, and 5 to 10 parts of thermal latent crosslinking component.

[0008] The matrix conversion component is maleic anhydride-grafted polyethylene wax with a grafting rate of 0.8% to 1.2%, a melting point of 105°C to 115°C, a number-average molecular weight of 2000 to 4000, and a melt viscosity of 200 mPa·s to 500 mPa·s at 140°C.

[0009] The rheology-locking component is a surface-modified wollastonite whisker or potassium titanate whisker with an aspect ratio of 20 to 40, which is pretreated with 1.0% to 1.5% by mass of γ-methacryloyloxypropyltrimethoxysilane coupling agent. When subjected to the shearing action of the melt flow during electrothermal melting, the whiskers collide with each other to form a locking network, thereby locking the interface and reconstructing the position of the paste.

[0010] The phase change spacer component is composed of isotactic polypropylene microspheres with a particle size of 150 to 200 micrometers and a melting point of 160 to 168 degrees Celsius. These isotactic polypropylene microspheres maintain a solid spherical structure during the preparation process.

[0011] The thermally latent crosslinking component includes an organic peroxide master initiator with a 1-minute half-life temperature of 190°C to 200°C. The organic peroxide master initiator is 2,5-dimethyl-2,5-bis-tert-butylperoxyhexyne-3, and further comprises 30% to 50% by weight of triallyl isocyanurate as a co-crosslinking agent.

[0012] In this interface reconstruction paste, the melting point of the phase change spacer component, the melting point of the PE pipe to be connected, and the initial decomposition temperature of the thermally latent crosslinking component satisfy a specific thermodynamic relationship: the melting point of the PE pipe to be connected is lower than the melting point of the phase change spacer component, and the melting point of the phase change spacer component is lower than the initial decomposition temperature of the thermally latent crosslinking component. The interface reconstruction paste is a solid paste prepared by mixing in a temperature-controlled planetary mixer under conditions below the melting point of the phase change spacer component and below the initial decomposition temperature of the thermally latent crosslinking component.

[0013] A second aspect of this invention provides a process for electrofusion connection of PE pipes for municipal pipelines. This process uses the interface reconstruction paste described in the first aspect above and includes the following steps: Step S1: Clean the area of ​​the PE pipe to be welded, heat the interface reconstruction paste to 40 to 50 degrees Celsius to soften it, and then apply it to the outer surface of the pipe insertion end. The coating thickness is controlled between 0.25 mm and 0.35 mm.

[0014] Step S2: Insert the PE pipe coated with interface reconstruction paste into the electrofusion fitting. The phase change spacer component in the paste forces a physical gap between the outer wall of the pipe and the inner wall of the fitting. The physical gap is determined by the particle size of the phase change spacer component. During the insertion process, the rigidity of the phase change spacer component prevents the interface reconstruction paste from being scraped off.

[0015] Step S3: Turn on the power supply and control the voltage output and heating temperature of the electrofusion welding machine according to the three consecutive stages: activation and conversion stage, rheological locking and phase change stage, and cross-linking fusion stage.

[0016] Specifically, during the activation and conversion stage, the output voltage is 40% to 50% of the rated voltage for 60 to 90 seconds, and the interface temperature is controlled at 130 to 150 degrees Celsius. During this stage, the phase change spacer component maintains a solid support physical gap, and the matrix conversion component melts and undergoes an esterification reaction with the oxide layer on the surface of the pipe.

[0017] During the rheological locking and phase change stages, the output voltage linearly increases from 50% to 80% of the rated voltage over a period of 40 to 60 seconds, while the interface temperature is controlled between 150 and 180 degrees Celsius. During this stage, as the PE pipe melt expands and generates shear flow, the rheological locking component undergoes a shear thickening effect to resist melt erosion. When the temperature exceeds 165 degrees Celsius, the phase change spacing component softens and melts, causing the physical gap to collapse.

[0018] During the crosslinking and fusion stage, the rated voltage is output at 100% for 100 to 120 seconds, and the interface temperature is controlled at 200 to 220 degrees Celsius. During this stage, the physical gaps completely disappear, the thermal latent crosslinking components decompose and trigger free radical reactions, forming a chemical crosslinking network at the connection interface.

[0019] Step S4: Stop heating and keep the clamp fixed until the joint cools down naturally. The natural cooling time should be at least 20 minutes, and the ambient temperature should be 23 degrees Celsius ± 2 degrees Celsius.

[0020] This invention provides a process for electrofusion connection of PE pipes used in municipal pipelines. It has the following beneficial effects: 1. This invention utilizes the melting point difference and rigid support of phase-change spaced components to solve the technical problems of incomplete oxide layer removal and premature interface closure leading to false welds in electrofusion bonding. By forcibly maintaining a physical gap in the early stage of heating, sufficient reaction time and space are provided for the matrix conversion components, enabling them to convert the oxide layer on the pipe surface in situ. This reduces the dependence on the precision of manual scraping operations and ensures effective fusion of the connection interface.

[0021] 2. This invention utilizes the shear thickening mechanism of rheologically locked components to solve the technical problem of easy loss of functional coatings under high-temperature and high-pressure melt flow. When the pipe melts and expands to generate shear flow, the whisker filler forms a capillary network to significantly increase the local viscosity, locking the active components at the welding interface. This avoids modification failure caused by material extrusion and ensures the effective retention of modified materials in the joint area.

[0022] 3. This invention solves the technical problems of residual stress and microporosity caused by crystallization shrinkage during the welding of thick-walled PE pipes by synergistic effect of chemical cross-linking of thermally latent cross-linking components and physical reinforcement of inorganic whiskers. The chemical cross-linking network formed at the end of the welding process improves the interfacial strength, and the physical pinning effect of whiskers effectively suppresses the volume shrinkage of polyethylene during cooling, thereby improving the sealing performance and long-term mechanical stability of the joint. Attached Figure Description

[0023] Figure 1 This is a schematic diagram of the processing technology of the present invention. Detailed Implementation

[0024] The technical solution of the present invention will now be clearly and completely described with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0025] The main raw materials and reagents used in the following examples and comparative examples have the following sources and specifications. Reagents not specifically mentioned are all commercially available analytical grade or higher grade products.

[0026] Maleic anhydride-grafted polyethylene wax: CAS No. 9006-26-2, grafting rate 1.0% by mass, melting point 110°C, number-average molecular weight (Mn) 3000, melt viscosity at 140°C 350 mPa·s; Wollastonite whiskers: CAS No. 13983-17-0, needle-like crystals, average length 20 μm, aspect ratio 30; Potassium titanate whiskers: CAS No. 12030-97-6, average length 15 μm, aspect ratio 25; Silane coupling agent KH-570: chemical name γ-methacryloyloxypropyltrimethoxysilane, CAS No. 2530-85-0, purity ≥98.0%; Isotactic polypropylene microspheres: CAS No. 9003-07-0, isotacticity ≥96%, melting point 164 degrees Celsius, particle size controlled between 150μm and 200μm by standard sieve screening; Organic peroxide main initiator: chemical name 2,5-dimethyl-2,5-bis(tert-butylperoxy)hexyne-3, CAS No. 1068-27-5, purity ≥95%, 1-minute half-life temperature 193 degrees Celsius; Co-crosslinking agent TAIC: chemical name triallyl isocyanurate, CAS No. 1025-15-6, purity ≥98%; PE100 pipes and fittings: Pipe specifications DN110SDR11, electrofusion fitting specifications DN110SDR11, both made of PE100 grade polyethylene.

[0027] Example 1: Please refer to the appendix Figure 1 This embodiment provides an interface reconstruction paste for electrofusion bonding of PE pipes for municipal pipelines, which is made of the following components in parts by weight: 40 parts of matrix conversion component maleic anhydride grafted polyethylene wax, 20 parts of rheology locking component wollastonite whiskers, 25 parts of phase change spacing component isotactic polypropylene microspheres, and 8 parts of thermal latent crosslinking component, of which 5.6 parts are organic peroxide main initiator and 2.4 parts are co-crosslinking agent TAIC.

[0028] The preparation method of this interface reconstruction paste is as follows: First, place wollastonite whiskers in a high-speed mixer, add 1.2% (by weight of whiskers) of silane coupling agent KH-570, and mix at 60 degrees Celsius for 30 minutes. Discharge and set aside. Heat a temperature-controlled planetary mixer to 120 degrees Celsius, add maleic anhydride-grafted polyethylene wax, and stir until completely melted. Add the pretreated wollastonite whiskers, evacuate to -0.08 MPa, and stir to disperse for 15 minutes. Reduce the temperature to 100 degrees Celsius, add isotactic polypropylene microspheres, organic peroxide main initiator, and crosslinking agent TAIC, and stir for 10 minutes. Discharge and allow to cool naturally to room temperature to obtain a solid paste.

[0029] This embodiment also provides a process for electrofusion connection of PE pipes for municipal pipelines using the above-mentioned interface reconstruction paste, selecting PE100 pipes of DN110SDR11 specification and electrofusion sleeves, including the following steps: Step S1: Clean the area of ​​the pipe to be welded, heat the interface reconstruction paste to 45 degrees Celsius to soften it, and apply it to the outer surface of the pipe insertion end. The coating thickness is controlled to be 0.30 mm.

[0030] Step S2: Insert the pipe into the electrofusion sleeve to the positioning mark, and the paste provides physical support in the gap.

[0031] Step S3: Connect the electrofusion welding machine and control the output in the following three stages: Activation and conversion stage: Output 45% of the rated voltage for 75 seconds, and control the interface temperature at 140 degrees Celsius. Rheological lockout and phase transition stage: The output voltage linearly increases from 50% to 80% of the rated voltage for 50 seconds, while the interface temperature is controlled at 165 degrees Celsius. Crosslinking and fusion stage: output 100% of the rated voltage for 110 seconds, and control the interface temperature at 210 degrees Celsius.

[0032] Step S4: Stop heating, keep the clamp fixed, and allow it to cool naturally for 30 minutes at an ambient temperature of 23 degrees Celsius.

[0033] Example 2: The interface reconstruction paste of this example is made of the following components in parts by weight: 35 parts of matrix conversion component maleic anhydride grafted polyethylene wax, 25 parts of rheology locking component wollastonite whiskers, 20 parts of phase change spacing component isotactic polypropylene microspheres, and 10 parts of thermal latent crosslinking component, of which 7.0 parts are organic peroxide main initiator and 3.0 parts are co-crosslinking agent TAIC.

[0034] The wollastonite whiskers were pretreated with 1.0% by mass of silane coupling agent KH-570, and the treatment process was the same as in Example 1; the paste preparation process was the same as in Example 1.

[0035] The connection process uses the same pipes and fittings as in Example 1. The paste is softened by heating and then applied to a thickness of 0.25 mm. The welding parameters are set as follows: Activation and conversion stage: output 40% of the rated voltage for 90 seconds, and control the interface temperature at 130 degrees Celsius; Rheological lockout and phase transition stage: The output voltage linearly increases from 50% to 80% of the rated voltage for 40 seconds, while the interface temperature is controlled at 150 degrees Celsius. Crosslinking and fusion stage: output 100% of the rated voltage for 120 seconds, and control the interface temperature at 200 degrees Celsius.

[0036] The cooling conditions in step S4 are the same as in Example 1.

[0037] Example 3: The interface reconstruction paste of this example is made of the following components in parts by weight: 45 parts of matrix conversion component maleic anhydride grafted polyethylene wax, 15 parts of rheology locking component potassium titanate whiskers, 30 parts of phase change spacing component isotactic polypropylene microspheres, and 5 parts of thermal latent crosslinking component, of which 3.5 parts are organic peroxide main initiator and 1.5 parts are co-crosslinking agent TAIC.

[0038] Potassium titanate whiskers were pretreated with 1.5% by mass of silane coupling agent KH-570, and the treatment process was the same as in Example 1; the paste preparation process was the same as in Example 1.

[0039] The connection process uses the same pipes and fittings as in Example 1. The paste is softened by heating and then applied to a thickness of 0.35 mm. The welding parameters are set as follows: Activation and conversion stage: Output 50% of the rated voltage for 60 seconds, and control the interface temperature at 150 degrees Celsius. Rheological lockout and phase transition stage: The output voltage rises linearly from 50% to 80% of the rated voltage for 60 seconds, while the interface temperature is controlled at 180 degrees Celsius. Crosslinking and fusion stage: output 100% of the rated voltage for 100 seconds, and control the interface temperature at 220 degrees Celsius.

[0040] The cooling conditions in step S4 are the same as in Example 1.

[0041] Comparative Example 1 This comparative example does not use interface reconstruction paste. Clean the area of ​​the pipe to be welded, and use a mechanical scraper to remove the oxide layer on the pipe surface to a depth of 0.2 mm. Insert the pipe into the electrofusion sleeve and use the standard electrofusion welding procedure, i.e., constant heating at 100% of the rated voltage for 235 seconds. Cooling conditions are the same as in Example 1.

[0042] Comparative Example 2 This comparative example prepared a paste without phase change spacing components. Isotactic polypropylene microspheres were removed from the formulation, and the amount of maleic anhydride-grafted polyethylene wax was adjusted to 65 parts to maintain the total amount. The types and amounts of the remaining components were the same as in Example 1, and the preparation and bonding processes were also the same as in Example 1.

[0043] Comparative Example 3 This comparative example prepared a paste without rheology-locking components. Wollastonite whiskers were removed from the formulation, and the amount of maleic anhydride-grafted polyethylene wax was adjusted to 60 parts to maintain the total amount. The types and amounts of the remaining components were the same as in Example 1, and the preparation and bonding processes were also the same as in Example 1.

[0044] Comparative Example 4 This comparative example uses the interface reconstruction paste prepared in Example 1, and the coating process is the same as in Example 1. However, the connection process adopts the standard electrofusion welding procedure, the same as in Comparative Example 1, that is, constant heating at 100% of the rated output voltage for 235 seconds, and cooling conditions are the same as in Example 1.

[0045] Peel strength and hydrostatic strength test instructions The electrofusion joints prepared in Examples 1 to 3 and Comparative Examples 1 to 4 were tested according to ISO 13954 "Plastic pipes and fittings - Peel test of polyethylene electrofusion assemblies" and ISO 1167 "Thermoplastic pipes, fittings and assemblies for fluid transport - Determination of resistance to internal pressure".

[0046] The specific testing steps are as follows: First, a peel strength test is performed. After the electrofusion joint has cooled naturally, it is cut axially to prepare no less than four strip-shaped specimens evenly distributed along the circumference. The specimens are fixed in the upper and lower clamps of a universal testing machine, and the tensile speed is set to 25 mm / min. The testing machine is started until the specimen fails, the maximum tensile load is recorded, and the effective width of the weld surface is measured using vernier calipers. The peel strength (Newtons / mm) is calculated. At the same time, the failure interface is observed with the naked eye and a low-magnification magnifying glass to distinguish between ductile failure areas (fracture occurring in the pipe or fitting body, with a tearing interface) and brittle failure areas (fracture occurring at the weld interface, with a smooth and bright surface). The percentage of the ductile failure area to the total weld area is calculated, which is the complement of the brittle debonding rate.

[0047] Next, a hydrostatic strength test is conducted. A complete electrofusion joint assembly is taken, sealing caps are installed at both ends, tap water is injected, and air inside the pipe is removed. The assembly is placed in a constant-temperature water tank at 80 degrees Celsius for conditioning for at least 24 hours. Based on the characteristics of PE100 material and SDR11 specifications, the ring stress is set to 5.5 MPa, and the corresponding test pressure is calculated. The pressure pump is started to raise the pressure to the set value, the pressure is maintained, and the time it takes for the pipe or fitting to rupture and leak is recorded. If no rupture occurs within the specified time, the test is stopped and recorded as passed.

[0048] The specific data obtained from the test are shown in the table below: Table 1 Summary of Mechanical Performance Test Data for Interface Reconstruction Paste and Processing Joints

[0049] The data in Table 1 show that the joint peel strength of Examples 1 to 3 is all higher than 135 N / mm and exhibits an extremely high proportion of toughness failure, which is attributed to the physical support effect of the phase change spacer component in the early stage of heating. During the activation and conversion stage, the isotactic polypropylene microspheres maintained the physical gap between the pipe and the fitting, preventing premature interface closure. The existence of this gap ensures that the maleic anhydride-grafted polyethylene wax can fully wet and undergo esterification reaction with the oxide layer on the pipe surface, completing the in-situ chemical modification. Comparative Example 2 lacks this microsphere component, causing the interface to close before the oxide layer conversion is complete, and the residual oxide layer causes local brittle failure; although Comparative Example 4 contains microspheres, due to the use of continuous rapid heating, the microspheres melted and collapsed before the end of the reaction time window, also failing to achieve effective oxide layer conversion, resulting in a significant decrease in the proportion of toughness failure.

[0050] The example groups all exhibited a pressure resistance life exceeding 1000 hours in hydrostatic testing, while Comparative Example 3 showed a failure time of only 160 hours, confirming the necessity of the rheological locking component for the retention of active materials. During the rheological locking and phase change stages of electrofusion bonding, the polyethylene melt expands, generating shear flow. In the examples, the whiskers treated with coupling agent collide with each other in the shear field and form a stuck network, producing a shear thickening effect that locks the interface reconstruction paste in the bonding region. Comparative Example 3 lacks the whisker component; the low-viscosity paste is squeezed out of the welding zone under melt pressure, resulting in a lack of cross-linking modification material at the interface, failing to form an effective bonding layer, and thus failing rapidly under long-term hydrostatic load.

[0051] Furthermore, the high peel strength and long service life of Examples 1 to 3 also benefit from the synergistic enhancement of the thermally latent crosslinking component and the inorganic whiskers. During the crosslinking fusion stage, the increase in temperature triggers the decomposition of organic peroxides, forming chemical crosslinking bonds between polyethylene molecular chains, transforming the physical melt interface into a chemically bonded interface. Simultaneously, the whiskers remaining at the interface restrict the contraction movement of the polyethylene chain segments during cooling, reducing the accumulation of residual stress. Comparative Example 1, using a traditional mechanical scraping method, relies solely on physical melting and is limited by the inhomogeneity of manual operation, resulting in a large standard deviation, indicating significant fluctuations in bond quality, and failing to achieve the high-temperature creep resistance improvement brought about by chemical crosslinking.

[0052] Crosslinking Degree and Interfacial Component Retention Test Instructions For the electrofusion joints prepared in Examples 1 to 3 and Comparative Examples 1 to 4, the degree of crosslinking was characterized by gel content test and the retention rate of functional materials was characterized by interface ash content test.

[0053] The specific testing steps are as follows: First, the gel content was tested. According to ISO 10147, "Determination of gel content in cross-linked polyethylene (PE-X) pipes and fittings," a thin sample was cut from the center of the fusion zone of the electrofusion joint. The sample thickness was controlled between 0.1 mm and 0.2 mm, and the mass was approximately 0.2 g. The sample was wrapped in a 120-mesh stainless steel wire mesh bag, weighed, and then placed in a Soxhlet extractor. Xylene was used as the solvent, and the mixture was heated to boiling and refluxed for 8 hours. After extraction, the mesh bag was removed and placed in a vacuum oven to dry at 140°C to constant weight. The ratio of the residual mass of the sample after extraction to the mass of the sample before extraction was calculated to determine the gel content.

[0054] Next, the interface ash content was tested. Following ISO 3451-1 "Determination of ash content in plastics – Part 1: General methods", the electrofusion joint was dissected to expose the fusion interface. A fine scraper was used to scrape powder from the fusion interface layer, with the sampling depth controlled within 0.5 mm to ensure the sample primarily originated from the mixing area between the interface reconstruction layer and the surface of the pipe / fitting. Approximately 2 grams of the scraped sample was weighed and placed in a pre-weighed porcelain crucible, which was then placed in a muffle furnace. The heating program was set, and the crucible was calcined at 600°C ± 25°C for 6 hours until the carbides were completely oxidized and decomposed. The crucible was removed, cooled to room temperature in a desiccator, and weighed. The percentage of residual inorganic matter to the total sample mass was calculated, which is the ash content (%).

[0055] The specific data obtained from the test are shown in the table below: Table 2 Summary of Microstructure and Component Analysis Data of Electrofusion Joint Interface

[0056] The gel content data in Table 2 directly confirms the chemical action mechanism of the thermally latent crosslinking component at the joint interface. The gel content in Examples 1 to 3 remained consistently above 70%, indicating that during the crosslinking and fusion stage, when the interface temperature reached the decomposition temperature of the organic peroxide, the initiator successfully induced free radical reactions between polyethylene molecular chains, forming a dense three-dimensional network structure. In contrast, Comparative Example 1, without any crosslinking agent, had a gel content close to zero, confirming that conventional electrofusion bonding relies solely on the physical mechanism of molecular chain diffusion entanglement. The high degree of crosslinking in these examples endowed the joints with higher resistance to thermal creep and environmental stress cracking, which corroborates the excellent hydrostatic strength performance in Test Example 1.

[0057] The results of the interfacial ash content test quantitatively verified the shear thickening effect of the rheology-locked component. The interfacial ash content of the example group remained between 11% and 14%, indicating that the inorganic whisker filler was effectively trapped at the welding interface during electrofusion. When the pipe melt expands due to heat and generates shear flow, the whiskers treated with coupling agent quickly respond to the shear field change, forming a rigid locking network, which significantly increases the local viscosity of the paste. This rheology-locking mechanism not only prevents the whiskers themselves from being lost, but also anchors the crosslinking agent and matrix conversion components dispersed in the paste to the reaction area. In contrast, Comparative Example 3, due to the removal of the rheology-locking component, had an interfacial ash content of only 0.5%, and the gel content also decreased significantly to 18.2%, indicating that in the absence of whisker locking, most of the functional paste was washed away and squeezed out to the welding cold zone with the melt flow, resulting in the failure of interfacial modification.

[0058] The compatibility between the phase change spaced components and the multi-stage temperature control process directly determines the final reaction efficiency. Comparative Example 2 lacked microsphere support, and Comparative Example 4 had a mismatched heating program; both had significantly lower gel content and ash content than the examples. This is because, in the absence of physical gap support or premature microsphere collapse, the welding interface closes prematurely, and the scouring effect of melt flow occurs before the chemical network forms, causing some unreacted or unlocked paste to be mechanically extruded. The examples maintained a stable reaction space during the activation stage through the rigid support of microspheres and used segmented heating to ensure that the rheological locking network was formed before entering the stage of intense melt flow, thereby maximizing the retention and transformation of functional materials.

[0059] Impact performance and fracture energy dissipation test instructions For the electrofusion joints prepared in Examples 1 to 3 and Comparative Examples 1 to 4, the impact performance of the joint interface was tested according to ISO 9854-1 "Determination of impact strength of simply supported beams for fluid transport" and GB / T 1043.1 standard, in order to evaluate the resistance to brittle fracture and energy dissipation characteristics of the joint interface under high-speed impact load.

[0060] The specific testing steps are as follows: First, sample preparation is performed. A rectangular strip sample is cut along the axial direction of the pipe in the fusion zone of the electrofusion joint, with dimensions set at 80 mm long, 10 mm wide, and 4 mm thick. Ensure the fusion interface is centered along the sample's length. Using a notching tool, a type A notch is machined at the fusion interface with a depth of 2 mm and a bottom radius of 0.25 mm. The notch direction is perpendicular to the fusion surface to guide crack propagation along the joint interface.

[0061] Impact testing was then conducted. The prepared specimen was placed on the support of a pendulum impact testing machine, with the span adjusted to 62 mm. A pendulum with an energy range of 50 joules was selected, and the impact velocity was set to 2.9 m / s. The pendulum was released to impact the back of the notch in the specimen, and the impact energy absorbed when the specimen fractured was recorded. The impact strength was calculated based on the cross-sectional area at the notch. Ten valid specimens were tested in each group, and the mean and standard deviation were calculated.

[0062] The specific data obtained from the test are shown in the table below: Table 3 Summary of interfacial notched impact strength test data for electrofusion joints

[0063] The impact strength data in Table 3 reveal the mechanism by which the interface reconstruction paste eliminates microscopic defects at the interface. The impact strength values ​​of Examples 1 to 3 range from 39.8 to 44.1 kJ / m², and the fracture surfaces exhibit obvious plastic deformation characteristics, which is directly related to the effective treatment of the oxide layer by the matrix conversion component. Within the physical gaps constructed by the phase change spacing component, maleic anhydride-grafted polyethylene wax transforms the polar oxide layer, which could have been a crack initiation point, into an ester-based interface compatible with the polyethylene matrix. In Comparative Example 2, due to the lack of microsphere support, the oxide layer was not converted and was sealed by the melt, forming a continuous weak interface layer. This caused cracks to propagate rapidly along the oxide layer at extremely low energy, exhibiting typical brittle fracture.

[0064] The high energy dissipation characteristics of the example group also confirm the toughening effect of the rheologically locked component at the microscale. When a crack attempts to penetrate the weld interface under impact load, the whiskers dispersed at the interface force the crack tip to deflect, bifurcate, or detour, prolonging the crack propagation path. Furthermore, the process of whiskers being pulled out of the matrix or breaking absorbs a significant amount of impact kinetic energy. In contrast, Comparative Example 3, lacking the rheological locking and physical reinforcement of whiskers, experienced paste loss during welding, leaving only ordinary polyethylene matrix at the interface, which could not prevent the straight propagation of cracks. Its impact strength was only 12.7 kJ / m², significantly lower than that of the examples.

[0065] The degree of matching between the multi-stage temperature-controlled process and the thermally latent crosslinking components determines the network uniformity of the final joint. Although Comparative Example 4 possessed a complete formulation, the use of constant-pressure rapid heating caused the microspheres to melt before the oxide layer transformation was complete, and the crosslinking reaction was initiated too quickly, failing to form a homogeneous interpenetrating network structure. This mismatch between the process and material properties resulted in stress concentration points at the interface, leading to lower fracture energy in impact tests. The embodiment, through staged temperature control, ensured the strict execution of the sequence of physical gap maintenance, chemical transformation completion, rheological network locking, and final crosslinking curing, thereby constructing a strong and tough interface capable of withstanding high impact loads.

[0066] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. An interface reconstruction paste for electrofusion bonding of PE pipes used in municipal pipelines, characterized in that, It is made from the following components in parts by weight: The matrix conversion component consists of 35-45 parts, the rheology locking component consists of 15-25 parts, the phase change spacing component consists of 20-30 parts, and the thermal latent crosslinking component consists of 5-10 parts. The matrix conversion component is maleic anhydride-grafted polyethylene wax with a grafting rate of 0.8%–1.2% and a melting point of 105°C–115°C; the rheology locking component is surface-modified wollastonite whiskers or potassium titanate whiskers with an aspect ratio of 20–40; the phase change spacing component is isotactic polypropylene microspheres with a particle size of 150 μm–200 μm and a melting point of 160°C–168°C; and the thermal latent crosslinking component includes an organic peroxide main initiator with a 1-minute half-life temperature of 190°C–200°C.

2. The interface reconstruction paste for electrofusion bonding of PE pipes for municipal pipelines according to claim 1, characterized in that: The isotactic polypropylene microspheres of the phase change spacing component maintain a solid spherical structure during the preparation process, and the melting point of the isotactic polypropylene microspheres, the melting point of the PE pipe to be connected, and the initial decomposition temperature of the thermal latent crosslinking component satisfy the following thermodynamic relationship: the melting point of the PE pipe to be connected is less than the melting point of the isotactic polypropylene microspheres, and the melting point of the isotactic polypropylene microspheres is less than the initial decomposition temperature of the thermal latent crosslinking component. The organic peroxide main initiator in the thermal latent crosslinking component is 2,5-dimethyl-2,5-bis(tert-butylperoxy)hexyne-3, and it also contains 30% to 50% by weight of triallyl isocyanurate as a co-crosslinking agent.

3. The interface reconstruction paste for electrofusion bonding of PE pipes for municipal pipelines according to claim 1, characterized in that: The rheology-locked component is pretreated with 1.0% to 1.5% by mass of γ-methacryloyloxypropyltrimethoxysilane coupling agent.

4. The interface reconstruction paste for electrofusion bonding of PE pipes for municipal pipelines according to claim 1, characterized in that: The matrix conversion component has a number average molecular weight of 2000-4000 and a melt viscosity of 200-500 mPa·s at 140 degrees Celsius.

5. A process for electrofusion connection of PE pipes for municipal pipelines, comprising an interface reconstruction paste for electrofusion connection of PE pipes for municipal pipelines according to any one of claims 1-4, characterized in that, Includes the following steps: Step S1: Clean the area of ​​the PE pipe to be welded, and apply the interface reconstruction paste to the outer surface of the pipe insertion end after heating and softening. Step S2: Insert the PE pipe coated with interface reconstruction paste into the electrofusion fitting, and use the phase change spacing component in the paste to force a physical gap between the outer wall of the pipe and the inner wall of the fitting. Step S3: Turn on the power supply and control the voltage output and heating temperature of the electrofusion welding machine according to the three consecutive stages of activation and conversion stage, rheological locking and phase change stage, and cross-linking fusion stage. Step S4: Stop heating and keep the clamp in place until the joint cools down naturally.

6. The electrofusion connection process for PE pipes used in municipal pipelines according to claim 5, characterized in that: In step S1, the heating and softening temperature of the interface reconstruction paste is 40 degrees Celsius to 50 degrees Celsius, and the coating thickness is controlled between 0.25 mm and 0.35 mm. In step S2, the physical gap is determined by the particle size of the phase change spacing component, and the rigidity of the phase change spacing component is used during insertion to prevent the interface reconstruction paste from being scraped off.

7. The electrofusion connection process for PE pipes used in municipal pipelines according to claim 5, characterized in that: The specific parameters for the activation and conversion stage in step S3 are: 40% to 50% of the rated output voltage, duration of 60 to 90 seconds, and control of the interface temperature at 130 to 150 degrees Celsius.

8. The electrofusion connection process for PE pipes used in municipal pipelines according to claim 5, characterized in that: The specific parameters for the rheological locking and phase transition stage in step S3 are as follows: the output voltage linearly increases from 50% to 80% of the rated voltage for 40 to 60 seconds, and the interface temperature is controlled between 150 and 180 degrees Celsius. During this stage, as the PE pipe melt expands and generates shear flow, the rheological locking component undergoes a shear thickening effect to resist melt erosion, and when the temperature exceeds 165 degrees Celsius, the phase change spacer component softens and melts, causing the physical gap to collapse.

9. The electrofusion connection process for PE pipes used in municipal pipelines according to claim 5, characterized in that: The specific parameters for the cross-linking and fusion stage in step S3 are: 100% of the rated voltage output, duration of 100-120 seconds, and interface temperature controlled at 200-220 degrees Celsius.

10. The electrofusion connection process for PE pipes used in municipal pipelines according to claim 5, characterized in that: In step S4, the natural cooling time is at least 20 minutes, and the cooling ambient temperature is 23±2 degrees Celsius.

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