Recycled plastic pipe co-extrusion molding method

Abstract

The invention relates to the technical field of high polymer materials, in particular to a reprocessed plastic pipe co-extrusion molding method, which comprises the following components by mass: 80-90 parts of reprocessed plastic particles; 5 to 10 parts of a bio-based toughening agent; 3 to 5 parts of a self-repairing nano filler; 1 to 2 parts of graphene coated carbon black; 2-3 parts of a dynamic vulcanization cross-linking agent; 15 to 20 parts of ultraviolet curing resin; 4 to 6 parts of titanium dioxide / silver composite nanoparticles; and 1-3 parts of a nano titanium dioxide whitening agent. Through collaborative design of the regenerated plastic base material and the functional components, multi-dimensional improvement of the material performance is achieved, the pipe is endowed with the composite functions of self-repairing, static electricity resistance, bacterium resistance and the like, and the application potential of regenerated plastic in the field of high-end engineering is remarkably expanded. In addition, a multi-stage co-extrusion process and a gradient temperature control technology are adopted, and a reliable technical path is provided for large-scale production of environment-friendly high polymer materials.

Description

Technical Field

[0001] The invention relates to the technical field of polymer materials, in particular to a co-extrusion molding method of recycled plastic pipes. Background Art

[0002] Recycled plastic pipes are widely used in drainage, gas transmission, and industrial piping. Core requirements include high mechanical strength, antistatic properties, corrosion resistance, and long-lasting antimicrobial properties. With increasingly stringent environmental protection requirements, materials must meet resource recycling requirements while also balancing production efficiency and cost control. Complex operating conditions place higher demands on pipe interfacial strength, dimensional stability, and functional layer synergy. Multi-layer composite processes are urgently needed to achieve precise molding and performance integration of multi-component materials.

[0003] In response to the above needs, the following targeted solutions have been proposed in the current technical field:

[0004] Injection molding technology: a mixture of recycled plastic and additives is injected into a mold, suitable for small-batch customized pipe production;

[0005] Blow molding process: using gas pressure to blow the molten recycled material into a tube, suitable for hollow structural parts;

[0006] Surface coating technology: Form a functional coating on the pipe surface by spraying or dipping, such as a conductive layer or antibacterial layer.

[0007] Although the above method has achieved the preparation of recycled plastic pipes to a certain extent, there are still some shortcomings:

[0008] Insufficient production efficiency and continuous production capacity: Injection molding technology is suitable for small-batch production, but it is difficult to achieve continuous production of long-length pipes, resulting in high energy consumption and low equipment utilization;

[0009] Difficulty in controlling structural uniformity: The blow molding process requires extremely high mold precision. Bubbles or wall thickness deviations are prone to occur during the molding process, affecting the overall quality stability of the pipe.

[0010] Weak bonding of the functional layer: Surface coating technology relies on physical adhesion, and the coating is easily detached due to mechanical friction or environmental erosion, resulting in functional failure and a high risk of construction pollution. Summary of the Invention

[0011] In view of the deficiencies of the prior art, the present invention provides a co-extrusion molding method for recycled plastic pipes, which solves the problems of the above-mentioned background technology.

[0012] According to a first aspect of the present invention, there is provided a recycled plastic pipe material comprising the following components in parts by mass:

[0013] Recycled plastic particles: 80-90 parts;

[0014] Bio-based toughening agent: 5-10 parts;

[0015] Self-repairing nanofiller: 3-5 parts;

[0016] Graphene coated carbon black: 1-2 parts;

[0017] Dynamic vulcanization crosslinking agent: 2-3 parts;

[0018] UV curing resin: 15-20 parts;

[0019] Titanium dioxide / silver composite nanoparticles: 4-6 parts;

[0020] Nano titanium dioxide whitening agent: 1 to 3 parts.

[0021] Regenerated Plastic Particles (RPP) are used to provide basic mechanical properties and resource recycling capabilities. Through physical recycling processes, waste plastics are converted into recycled particles, reducing raw material costs and minimizing environmental pollution.

[0022] Dynamic Sulfur Curing Agent (DSCA) is used to increase the crosslink density of the material. The dynamically reversible covalent bonds in the DSCA reconstruct the crosslink network in the molten state, improving the thermal stability and fatigue resistance of the recycled plastic pipe.

[0023] Ultraviolet Curable Resin (UCR) is used to form a wear-resistant decorative layer. A photoinitiator triggers free radical polymerization of acrylate groups under UV light, creating a dense cross-linked structure and increasing the surface hardness of the recycled plastic pipe.

[0024] Nano-titanium dioxide whitening agent (n-TiO2WTA) is used to improve the whiteness of the material. The high-refractive-index nanoparticles in nano-titanium dioxide scatter visible light, enhancing the gloss of the pipe surface and shielding it from UV aging.

[0025] According to an embodiment of the present invention, recycled plastic particles serve as a substrate to provide basic mechanical properties and resource recycling capabilities, and the dynamic vulcanization crosslinker reconstructs the crosslinking network through dynamic reversible covalent bonds. The synergistic effect of the two components significantly improves the mechanical strength, thermal stability and fatigue resistance of the material.

[0026] According to an embodiment of the present invention, the recycled plastic particles are recycled particles obtained by crushing, screening and drying recycled polyethylene materials; the bio-based toughening agent is a viscous dispersion formed by mixing polylactic acid and epoxidized soybean oil; and the self-healing nanofiller is a nanoscale suspension formed by mixing graphene oxide with azobenzene molecules grafted on its surface and polycaprolactone microcapsules.

[0027] Wherein, the mass ratio of the polylactic acid to the epoxidized soybean oil is 3:2-4:3;

[0028] The mass ratio of the graphene oxide to the polycaprolactone microcapsules is 1:2-1:3, wherein the polycaprolactone microcapsules are microcapsule solutions formed by polymerizing polycaprolactone and polyvinyl alcohol, and the mass ratio of the polycaprolactone to the polyvinyl alcohol is 1:1-1:2.

[0029] Bio-based toughening agent (BTA) is used to improve the toughness of materials. It uses molecular chain entanglement or compatibility optimization to form energy dissipation paths in stress concentration areas, thereby delaying crack propagation in recycled plastic pipes.

[0030] Self-healing nanofillers (SHNFs) endow materials with light- or heat-responsive self-healing capabilities. Their surface functional groups undergo reversible chemical bond recombination under external stimuli, enabling the automatic closure of microcracks.

[0031] According to an embodiment of the present invention, the specific preparation process of the recycled plastic particles includes:

[0032] The recycled polyethylene material is placed in a pulverizer and crushed to a particle size of ≤2 mm. The crushed plastic particles of 80-100 mesh are then screened out by a vibrating screen. Finally, the crushed plastic particles are hot-air dried at 80-90° C. for 2-3 hours to remove moisture and volatiles, thereby obtaining the recycled plastic particles.

[0033] According to an embodiment of the present invention, the graphene-coated carbon black is a conductive particle prepared by a high-temperature melt grafting method of carbon black and graphene oxide; the dynamic vulcanization crosslinking agent is a composite white powder obtained by blending dicumyl peroxide and vinyltriethoxysilane; and the UV-curable resin is a solid resin obtained by copolymerizing butyl acrylate and polyurethane acrylate and irradiating with UV light.

[0034] Wherein, the mass ratio of the carbon black to the graphene oxide is 1:1-1:3;

[0035] The mass ratio of the dicumyl peroxide to the vinyltriethoxysilane is 2:1-4:1;

[0036] The mass ratio of the butyl acrylate to the polyurethane acrylate is 3:1-4:1.

[0037] Graphene-coated carbon black (GC-CB) is used to construct a conductive network. The graphene layer enhances the efficiency of electron transfer between carbon black particles, forming a continuous conductive path and reducing volume resistivity.

[0038] According to an embodiment of the present invention, butyl acrylate provides excellent flexibility and film-forming properties, while polyurethane acrylate imparts high wear resistance and adhesion. After copolymerization, free radical polymerization occurs under the action of a UV light initiator, forming a three-dimensional cross-linked network structure that significantly enhances the hardness and weather resistance of the resin layer. Simultaneously, the polar groups of the polyurethane segments form synergistic hydrogen bonds with the ester groups of the acrylate, enhancing intermolecular forces and imparting both impact and chemical resistance to the cured resin layer. Ultimately, this results in a high-gloss, wear-resistant, and long-term stable decorative layer on the surface of the recycled plastic pipe.

[0039] According to an embodiment of the present invention, the titanium dioxide / silver composite nanoparticles are yellow powders obtained by reacting nano-titanium dioxide with silver nitrate; the nano-titanium dioxide whitening agent is the nano-titanium dioxide modified with a silane coupling agent;

[0040] Wherein, the mass ratio of the nano titanium dioxide to the silver nitrate is 1:0.1-1:0.5;

[0041] The mass ratio of the nano titanium dioxide to the silane coupling agent is 20:1-20:3.

[0042] Titanium dioxide / silver composite nanoparticles (TiO2 / Ag CNP) are used to achieve long-lasting antibacterial properties. Nano-titanium dioxide generates reactive oxygen free radicals under light, which damage microbial cell membranes. Meanwhile, silver ions interfere with the activity of bacterial metabolic enzymes. This dual antibacterial effect gives the recycled plastic pipe a highly effective antibacterial property.

[0043] According to the embodiments of the present invention, the silane coupling agent-modified nano-titanium dioxide not only optimizes the dispersion of antimicrobial particles but also enhances the stability of silver ions through surface chemical bonding, extending the duration of the antimicrobial function. Ultimately, the whitening agent and the antimicrobial component complement each other, simultaneously improving the material's whiteness retention, weather resistance, and antimicrobial durability.

[0044] According to a second aspect of the present invention, a co-extrusion method for recycled plastic pipes is provided. Figure 1 As shown, the following steps are included:

[0045] S1: mixing the recycled plastic particles, the bio-based toughening agent, the self-repairing nanofiller and the dynamic vulcanization crosslinking agent, and placing the mixture in a twin-screw extruder for melt blending to prepare substrate layer particles;

[0046] S2: mixing the UV-curable resin and the nano-titanium dioxide brightener, placing the mixture in a high-speed disperser and stirring the mixture to prepare decorative layer particles;

[0047] S3: mixing the graphene-coated carbon black and the dynamic vulcanization crosslinking agent, placing the mixture in a single-screw extruder for melt blending to prepare conductive layer particles;

[0048] S4: depositing the titanium dioxide / silver composite nanoparticles on the surface of the conductive layer particles to prepare antibacterial layer particles;

[0049] S5: adding the substrate layer particles, the decorative layer particles, the conductive layer particles and the antibacterial layer particles into the four single-screw extruders respectively, and performing gradient temperature-controlled co-extrusion through a multi-stage co-extrusion die to prepare a four-layer composite structure;

[0050] S6: performing gradient cooling and shaping on the four-layer composite structure, and irradiating the antibacterial layer particles in the four-layer composite structure with ultraviolet light to prepare the recycled plastic pipe.

[0051] According to an embodiment of the present invention, the step of mixing the UV-curable resin and the nano-titanium dioxide brightener and then placing the mixture in a high-speed disperser and stirring the mixture uniformly to prepare the decorative layer particles comprises:

[0052] The ultraviolet curable resin and the nano titanium dioxide brightener are mixed in a mass ratio of 15:1-20:3, and the mixture is fed into the high-speed disperser and stirred at a speed of 3000-5000 rpm / min for 30-40 minutes to obtain a homogeneous white slurry;

[0053] The homogeneous white slurry is placed in a spray dryer and dried at 80-90° C. for 5-8 minutes to obtain the decorative layer particles with a particle size of 200-300 μm.

[0054] According to an embodiment of the present invention, after the UV-curable resin and the nano-titanium dioxide whitening agent are mixed in a mass ratio, the nano-titanium dioxide whitening agent is uniformly coated in the resin matrix, which not only improves the whiteness and glossiness of the resin system, but also enhances the surface hardness and weather resistance after UV curing through its high refractive index.

[0055] According to an embodiment of the present invention, the base material layer particles, the decorative layer particles, the conductive layer particles, and the antibacterial layer particles are respectively added to the four single-screw extruders, and gradient temperature-controlled co-extrusion is performed through a multi-stage co-extrusion die to prepare a four-layer composite structure, which includes:

[0056] placing the substrate layer particles, the decorative layer particles, the conductive layer particles, and the antibacterial layer particles in four of the single-screw extruders, respectively, to obtain substrate layer extrudates, decorative layer extrudates, conductive layer extrudates, and antibacterial layer extrudates in sequence;

[0057] The process parameters of the four single-screw extruders are respectively set as follows:

[0058] Substrate layer extruder: screw speed 40-50rpm / min, temperature 120-140℃, pressure 5-8MPa;

[0059] Decorative layer extruder: screw speed 30-40rpm / min, temperature 130-150℃, pressure 4-6MPa;

[0060] Conductive layer extruder: screw speed 20-30rpm / min, temperature 150-170℃, pressure 3-5MPa;

[0061] Antibacterial layer extruder: screw speed 15-25rpm / min, temperature 140-160℃, pressure 2-4MPa;

[0062] Placing the substrate layer extrudate, the decorative layer extrudate, the conductive layer extrudate, and the antibacterial layer extrudate in the gradient temperature control zone of the multi-stage co-extrusion die head, and sequentially superimposing them during the co-extrusion process, while providing an overlap zone of 10-15 mm in the transition zone between each layer to prepare the four-layer composite structure;

[0063] The gradient temperature control zones are set as follows: the base material layer temperature control zone is 120-140°C, the decorative layer temperature control zone is 130-150°C, the conductive layer temperature control zone is 150-170°C, and the antibacterial layer temperature control zone is 140-160°C.

[0064] According to an embodiment of the present invention, the thickness of the four-layer composite structure is 2.0-3.5 mm, wherein the thickness of the conductive layer in the four-layer composite structure is 0.1-0.3 mm, the thickness of the antibacterial layer is 0.1-0.2 mm, the thickness of the decorative layer is 0.2-0.5 mm, and the thickness of the substrate layer is 1.5-2.5 mm.

[0065] According to an embodiment of the present invention, performing gradient cooling and shaping on the four-layer composite structure includes:

[0066] The four-layer composite structure is sequentially passed through a three-stage gradient cooling water tank for cooling and shaping, with a water flow rate of 3-5 m / s and an outlet temperature of 40-50° C.

[0067] The cooling water temperature gradient of the three-level gradient cooling water tank is:

[0068] The first stage: 25-40℃, cooling time 30-40 seconds;

[0069] The second stage: 15-20℃, cooling time 40-50 seconds;

[0070] The third stage: 10-15℃, cooling time 50-60 seconds.

[0071] According to an embodiment of the present invention, the gradient cooling process achieves uniform cooling and stress release for the four-layer composite structure through the synergistic effect of a three-level water temperature gradient and flow rate control. The first stage involves slow cooling to avoid internal stress concentration, the second stage accelerates crystallization to enhance interfacial bonding strength, and the third stage locks in molecular chain orientation at low temperatures, simultaneously ensuring dimensional stability and functional layer activity.

[0072] According to an embodiment of the present invention, the step of irradiating the antibacterial layer particles in the four-layer composite structure with ultraviolet light to prepare the recycled plastic pipe includes:

[0073] Use 120-150W / cm 2 The antibacterial layer particles in the four-layer composite structure are irradiated with ultraviolet light for 5-8 seconds with a mercury lamp at a irradiation distance of 10-15 cm and a wavelength of 365 nm to obtain the recycled plastic pipe.

[0074] According to an embodiment of the present invention, ultraviolet light energy activates the surface of nano-titanium dioxide to produce electron-hole pairs, generating highly oxidizing hydroxyl radicals and superoxide anions, which directly destroy the cell membrane structure of microorganisms, so that the antibacterial layer remains continuously active after the recycled plastic pipe is formed, achieving the dual effects of physical barrier and chemical antibacterial, and ultimately giving the pipe broad-spectrum and long-lasting antibacterial properties.

[0075] The present invention has the following beneficial effects:

[0076] The present invention significantly enhances the mechanical strength, weather resistance and functional integration capability of recycled plastic pipes through the synergistic effect of the four components of the substrate layer, the decorative layer, the conductive layer and the antibacterial layer. The substrate layer is based on recycled plastic particles and combines bio-based toughening agents and self-repairing nanofillers to form a dynamic cross-linking network, which effectively alleviates the risk of material fatigue cracking. The conductive layer relies on graphene-coated carbon black to construct a continuous conductive path and reduce the volume resistivity. The antibacterial layer is provided with continuous bactericidal ability by titanium dioxide / silver composite nanoparticles. The four-layer structure achieves strong interface bonding under the gradient temperature control co-extrusion process, simultaneously meeting the structural load-bearing, appearance durability and functional requirements.

[0077] The specialized design of each layer of material imparts multi-dimensional functional properties to the tubing. Self-healing nanofillers repair microcracks under thermal or light stimulation, extending service life. The conductive network formed by graphene-encapsulated carbon black effectively inhibits static electricity accumulation, making it suitable for high-risk explosion-proof environments. Titanium dioxide / silver composite nanoparticles achieve broad-spectrum antimicrobial properties and inhibit biofilm formation through a dual mechanism of photocatalysis and ion release.

[0078] This invention uses recycled plastic particles as its core raw material and transforms waste plastic into high-performance materials through a physical recycling process, reducing primary resource consumption and lowering carbon emissions. The introduction of bio-based toughening agents and biodegradable components further enhances the material's eco-friendliness, enabling clean production with low energy consumption and low pollution, in line with the development of a circular economy and green manufacturing.

[0079] This invention utilizes a multi-stage co-extrusion die head with a gradient temperature control design to precisely match the melting characteristics and flow behavior of each material layer, eliminating interfacial stress concentration and thickness deviation. High-speed dispersion and spray drying processes ensure uniform particle size in the decorative layer, while a gradient cooling water tank utilizes a phased temperature control strategy to achieve stress release and dimensional stability in the four-layer structure. Ultraviolet light irradiation activates the active ingredients in the antibacterial layer, simultaneously achieving functional curing and performance activation, ultimately achieving highly consistent and reliable material performance in mass production.

[0080] Through systematic innovation in materials and processes, this invention enables recycled plastic pipes to combine high strength, self-healing properties, electrical conductivity, antibacterial properties, wear resistance, and UV resistance, making them suitable for harsh environments such as drainage, gas transmission, and industrial piping. Its structural design and functional configuration allow for flexible adaptation to diverse application scenarios, such as the corrosion resistance requirements of wet underground environments, antistatic requirements in the chemical industry, and the long-term antibacterial needs of hospital systems. This provides an innovative paradigm for the multifunctional development of polymer materials.

[0081] Of course, any product implementing the present invention does not necessarily need to achieve all of the advantages described above at the same time. BRIEF DESCRIPTION OF THE DRAWINGS

[0082] Figure 1 Flowchart of a method according to an embodiment of the present invention. DETAILED DESCRIPTION

[0083] The embodiment of the present application provides a co-extrusion molding method for recycled plastic pipes through the present invention.

[0084] Example 1: Standard formula recycled plastic pipe

[0085] Recycled plastic particles: 85 parts;

[0086] Bio-based toughening agent: 7.5 parts;

[0087] Self-repairing nanofiller: 4 parts;

[0088] Graphene-coated carbon black: 1.5 parts;

[0089] Dynamic vulcanization crosslinking agent: 2.5 parts;

[0090] UV curing resin: 17.5 parts;

[0091] Titanium dioxide / silver composite nanoparticles: 5 parts; nano titanium dioxide whitening agent: 2 parts.

[0092] Example 2: Increasing the content of bio-based toughening agent Recycled plastic particles: 85 parts;

[0093] Bio-based toughening agent: 10 parts;

[0094] Self-repairing nanofiller: 4 parts;

[0095] Graphene-coated carbon black: 1.5 parts;

[0096] Dynamic vulcanization crosslinking agent: 2.5 parts;

[0097] UV curing resin: 17.5 parts;

[0098] Titanium dioxide / silver composite nanoparticles: 5 parts; nano titanium dioxide whitening agent: 2 parts.

[0099] Example 3: Reducing the content of self-repairing nanofiller Recycled plastic particles: 85 parts;

[0100] Bio-based toughening agent: 7.5 parts;

[0101] Self-repairing nanofiller: 3 parts;

[0102] Graphene-coated carbon black: 1.5 parts;

[0103] Dynamic vulcanization crosslinking agent: 2.5 parts;

[0104] UV curing resin: 17.5 parts;

[0105] Titanium dioxide / silver composite nanoparticles: 5 parts; nano titanium dioxide whitening agent: 2 parts.

[0106] Example 4: Enhanced antibacterial properties

[0107] Recycled plastic particles: 85 parts;

[0108] Bio-based toughening agent: 7.5 parts;

[0109] Self-repairing nanofiller: 4 parts;

[0110] Graphene-coated carbon black: 1.5 parts;

[0111] Dynamic vulcanization crosslinking agent: 2.5 parts;

[0112] UV curing resin: 17.5 parts;

[0113] Titanium dioxide / silver composite nanoparticles: 6 parts; nano titanium dioxide whitening agent: 2 parts.

[0114] Example 5: Optimizing the appearance of whiteness Recycled plastic particles: 85 parts;

[0115] Bio-based toughening agent: 7.5 parts;

[0116] Self-repairing nanofiller: 4 parts;

[0117] Graphene-coated carbon black: 1.5 parts;

[0118] Dynamic vulcanization crosslinking agent: 2.5 parts;

[0119] UV curing resin: 17.5 parts;

[0120] Titanium dioxide / silver composite nanoparticles: 5 parts; nano titanium dioxide whitening agent: 3 parts.

[0121] Example 6: Improving electrical conductivity

[0122] Recycled plastic particles: 85 parts;

[0123] Bio-based toughening agent: 7.5 parts;

[0124] Self-repairing nanofiller: 4 parts;

[0125] Graphene coated carbon black: 2 parts;

[0126] Dynamic vulcanization crosslinking agent: 2.5 parts;

[0127] UV curing resin: 17.5 parts;

[0128] Titanium dioxide / silver composite nanoparticles: 5 parts; nano titanium dioxide whitening agent: 2 parts. Comparative Example 1: Recycled plastic particles without self-repairing nanofiller: 85 parts;

[0129] Bio-based toughening agent: 7.5 parts;

[0130] Graphene-coated carbon black: 1.5 parts;

[0131] Dynamic vulcanization crosslinking agent: 2.5 parts;

[0132] UV curing resin: 17.5 parts;

[0133] Titanium dioxide / silver composite nanoparticles: 5 parts; nano titanium dioxide whitening agent: 2 parts.

[0134] Comparative Example 2: Recycled plastic particles without dynamic vulcanization crosslinking agent: 85 parts;

[0135] Bio-based toughening agent: 7.5 parts;

[0136] Self-repairing nanofiller: 4 parts;

[0137] Graphene-coated carbon black: 1.5 parts;

[0138] UV curing resin: 17.5 parts;

[0139] Titanium dioxide / silver composite nanoparticles: 5 parts; nano titanium dioxide whitening agent: 2 parts.

[0140] Comparative Example 3: Recycled plastic particles without titanium dioxide / silver composite nanoparticles: 85 parts;

[0141] Bio-based toughening agent: 7.5 parts;

[0142] Self-repairing nanofiller: 4 parts;

[0143] Graphene-coated carbon black: 1.5 parts;

[0144] Dynamic vulcanization crosslinking agent: 2.5 parts;

[0145] UV curing resin: 17.5 parts;

[0146] Nano titanium dioxide whitening agent: 2 parts.

[0147] Comparative Example 4: No nano titanium dioxide whitening agent

[0148] Recycled plastic particles: 85 parts;

[0149] Bio-based toughening agent: 7.5 parts;

[0150] Self-repairing nanofiller: 4 parts;

[0151] Graphene-coated carbon black: 1.5 parts;

[0152] Dynamic vulcanization crosslinking agent: 2.5 parts;

[0153] UV curing resin: 17.5 parts;

[0154] Titanium dioxide / silver composite nanoparticles: 5 parts.

[0155] Experimental example:

[0156] The performance of the above examples 1-6 and comparative examples 1-4 was measured, and the results are shown in Table 1.

[0157] 1. Mechanical properties test

[0158] The tensile strength was determined using a universal material testing machine with a sample size of 100 mm × 10 mm × 2.5 mm, a tensile rate of 5 mm / min, and the maximum load was recorded.

[0159] 2. Conductivity test

[0160] The volume resistivity was measured by the four-probe method with a current density of 10 mA / cm 2 The sample size is 100mm×10mm×2.5mm, and the test environment is 25℃ and humidity 50%.

[0161] 3. Antibacterial performance test

[0162] The agar diffusion method was used to evaluate the antibacterial effect. Escherichia coli and Staphylococcus aureus were used as test strains. The diameter of the inhibition zone was measured after the pipe samples were immersed in the bacterial suspension and cultured for 24 hours.

[0163] 4. Self-repair performance test

[0164] The self-repair ability was evaluated through scratch repair experiments. Microcracks were created on the sample surface using laser cutting. After heating in a constant temperature box at 60°C for 1 hour, the degree of crack closure was observed and the repair rate was calculated.

[0165] 5. Whiteness and glossiness test

[0166] The surface whiteness value and glossiness (60° angle reflectance) were measured using a spectrophotometer and quantitatively analyzed by comparison with a standard white board.

[0167] Table 1. Experimental data of Examples 1-6 and Comparative Examples 1-4 of the present invention

[0168]

[0169]

[0170] From Table 1 we can see that the mechanical properties are:

[0171] The tensile strengths of Example 2 (adding a bio-based toughening agent) and Example 6 (improving conductivity) were significantly higher than those of the standard formulation (Example 1), indicating that the toughening agent and the conductive component synergistically optimized the toughness of the material.

[0172] The tensile strength of Comparative Example 1 (without self-repairing filler) and Comparative Example 2 (without cross-linking agent) decreased significantly, verifying the key role of self-repairing filler and cross-linking agent in structural stability.

[0173] Conductivity:

[0174] The volume resistivity of Example 6 is the lowest at 7.2×10 5 Ω·cm, the graphene-coated carbon black content increases to effectively construct a conductive path;

[0175] Comparative Example 2 (without crosslinking agent) has a maximum resistivity of 2.4×10 6 Ω·cm, highlighting the necessity of cross-linking agent for the stability of the conductive layer.

[0176] Antimicrobial properties:

[0177] The diameter of the inhibition zone of Example 4 (enhanced antibacterial performance) reached 16 mm, and the increase in the content of titanium dioxide / silver composite nanoparticles significantly improved the antibacterial activity;

[0178] Comparative Example 3 (without antibacterial particles) only formed a 6 mm inhibition zone, indicating the decisive role of the antibacterial component in inhibiting microorganisms.

[0179] Self-healing performance:

[0180] The self-repair rates of Examples 1 and 5 both exceeded 75%, and the synergistic effect of the self-repairing filler and the cross-linking agent caused the microcracks to close quickly;

[0181] The repair rate of comparative example 1 (without self-repairing filler) is only 50%, indicating the core contribution of the self-repairing component to damage recovery.

[0182] Appearance performance:

[0183] The whiteness value of Example 5 (optimized whiteness) reaches 92, and the increase in the content of nano-titanium dioxide whitening agent significantly improves the surface whiteness;

[0184] The whiteness value of Comparative Example 4 (without brightener) dropped to 80 and the gloss dropped to 75 GU, indicating the direct effect of the brightener on the appearance of the material.

[0185] Based on the above integrated experimental data, the recycled plastic pipe produced by co-extrusion achieves comprehensive optimization of mechanical properties, conductivity, antibacterial properties, and appearance. Its mechanical strength and self-healing capabilities meet the requirements of complex working conditions. The conductive and antibacterial functional layers are suitable for anti-static and anti-biological contamination scenarios. The improved whiteness and glossiness broaden decorative applications. This pipe is suitable for drainage, industrial piping, medical equipment, and other fields. In the future, the dynamic cross-linking system can be upgraded to further enhance its high-temperature and chemical corrosion resistance, promoting the development of recycled plastics towards high-performance and functionalization.

[0186] Although the preferred embodiments of the present invention have been described, those skilled in the art may make additional changes and modifications to these embodiments once they have learned the basic creative concept. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments and all changes and modifications that fall within the scope of the present invention.

[0187] Obviously, those skilled in the art may make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, if such changes and modifications fall within the scope of the claims and their equivalents, the present invention is intended to include such changes and modifications.

Claims

1. A co-extruded recycled plastic pipe, characterized in that: The composition is as follows in parts by mass: Recycled plastic particles: 80-90 parts; Bio-based toughening agent: 5-10 parts; Self-repairing nanofiller: 3-5 parts; Graphene coated carbon black: 1-2 parts; Dynamic vulcanization crosslinking agent: 2-3 parts; UV curing resin: 15-20 parts; Titanium dioxide / silver composite nanoparticles: 4-6 parts; Nano titanium dioxide whitening agent: 1 to 3 parts.

2. The recycled plastic pipe according to claim 1, characterized in that: The recycled plastic particles are recycled particles obtained by crushing, screening and drying recycled polyethylene materials; the bio-based toughening agent is a viscous dispersion formed by mixing polylactic acid and epoxy soybean oil; the self-healing nanofiller is a nanoscale suspension formed by mixing graphene oxide with azobenzene molecules grafted on its surface and polycaprolactone microcapsules; Wherein, the mass ratio of the polylactic acid to the epoxidized soybean oil is 3:2-4:3; The mass ratio of the graphene oxide to the polycaprolactone microcapsules is 1:2-1:3, wherein the polycaprolactone microcapsules are microcapsule solutions formed by polymerizing polycaprolactone and polyvinyl alcohol, and the mass ratio of the polycaprolactone to the polyvinyl alcohol is 1:1-1:

2.

3. The recycled plastic pipe according to claim 1, characterized in that: The graphene-coated carbon black is a conductive particle prepared by high-temperature melt grafting of carbon black and graphene oxide; the dynamic vulcanization crosslinking agent is a composite white powder obtained by blending dicumyl peroxide and vinyltriethoxysilane; and the UV-curable resin is a solid resin obtained by copolymerizing butyl acrylate and polyurethane acrylate and irradiating with UV light. Wherein, the mass ratio of the carbon black to the graphene oxide is 1:1-1:3; The mass ratio of the dicumyl peroxide to the vinyltriethoxysilane is 2:1-4:1; The mass ratio of the butyl acrylate to the polyurethane acrylate is 3:1-4:

1.

4. The recycled plastic pipe according to claim 1, characterized in that: The titanium dioxide / silver composite nanoparticles are yellow powders obtained by reacting nano titanium dioxide with silver nitrate; the nano titanium dioxide whitening agent is the nano titanium dioxide modified with a silane coupling agent; Wherein, the mass ratio of the nano titanium dioxide to the silver nitrate is 1:0.1-1:0.5; The mass ratio of the nano titanium dioxide to the silane coupling agent is 20:1-20:

3.

5. A co-extrusion method for recycled plastic pipes according to any one of claims 1 to 4, characterized in that: The steps include: The recycled plastic particles, the bio-based toughening agent, the self-repairing nanofiller and the dynamic vulcanization crosslinking agent are mixed and placed in a twin-screw extruder for melt blending to prepare substrate layer particles; The ultraviolet curable resin and the nano titanium dioxide brightener are mixed and placed in a high-speed disperser for uniform stirring to prepare decorative layer particles; The graphene-coated carbon black and the dynamic vulcanization crosslinking agent are mixed and placed in a single-screw extruder for melt blending to prepare conductive layer particles; Depositing the titanium dioxide / silver composite nanoparticles on the surface of the conductive layer particles to prepare antibacterial layer particles; The substrate layer particles, the decorative layer particles, the conductive layer particles, and the antibacterial layer particles are respectively added into the four single-screw extruders, and gradient temperature-controlled co-extrusion is performed through a multi-stage co-extrusion die to prepare a four-layer composite structure; The four-layer composite structure is subjected to gradient cooling and shaping, and the antibacterial layer particles in the four-layer composite structure are irradiated with ultraviolet light to prepare the recycled plastic pipe.

6. The co-extrusion molding method of recycled plastic pipe according to claim 5, characterized in that: The step of mixing the ultraviolet curable resin and the nano titanium dioxide brightener and stirring the mixture in a high-speed disperser to prepare the decorative layer particles comprises: The ultraviolet curable resin and the nano titanium dioxide brightener are mixed in a mass ratio of 15:1-20:3, and the mixture is fed into the high-speed disperser and stirred at a speed of 3000-5000 rpm / min for 30-40 minutes to obtain a homogeneous white slurry; The homogeneous white slurry is placed in a spray dryer and dried at 80-90° C. for 5-8 minutes to obtain the decorative layer particles with a particle size of 200-300 μm.

7. The co-extrusion molding method of recycled plastic pipe according to claim 5, characterized in that: The step of adding the substrate layer particles, the decorative layer particles, the conductive layer particles, and the antibacterial layer particles into four single-screw extruders, and performing gradient temperature-controlled co-extrusion through a multi-stage co-extrusion die to prepare a four-layer composite structure comprises: placing the substrate layer particles, the decorative layer particles, the conductive layer particles, and the antibacterial layer particles in four of the single-screw extruders, respectively, to obtain substrate layer extrudates, decorative layer extrudates, conductive layer extrudates, and antibacterial layer extrudates in sequence; The process parameters of the four single-screw extruders are respectively set as follows: Substrate layer extruder: screw speed 40-50rpm / min, temperature 120-140℃, pressure 5-8MPa; Decorative layer extruder: screw speed 30-40rpm / min, temperature 130-150℃, pressure 4-6MPa; Conductive layer extruder: screw speed 20-30rpm / min, temperature 150-170℃, pressure 3-5MPa; Antibacterial layer extruder: screw speed 15-25rpm / min, temperature 140-160℃, pressure 2-4MPa; Placing the substrate layer extrudate, the decorative layer extrudate, the conductive layer extrudate, and the antibacterial layer extrudate in the gradient temperature control zone of the multi-stage co-extrusion die head, and sequentially superimposing them during the co-extrusion process, while providing an overlap zone of 10-15 mm in the transition zone between each layer to prepare the four-layer composite structure; The gradient temperature control zones are set as follows: the base material layer temperature control zone is 120-140°C, the decorative layer temperature control zone is 130-150°C, the conductive layer temperature control zone is 150-170°C, and the antibacterial layer temperature control zone is 140-160°C.

8. The co-extrusion molding method of recycled plastic pipe according to claim 5, characterized in that: The step of performing gradient cooling and shaping on the four-layer composite structure comprises: The four-layer composite structure is sequentially passed through a three-stage gradient cooling water tank for cooling and shaping, with a water flow rate of 3-5 m / s and an outlet temperature of 40-50° C. The cooling water temperature gradient of the three-level gradient cooling water tank is: The first stage: 25-40℃, cooling time 30-40 seconds; The second stage: 15-20℃, cooling time 40-50 seconds; The third stage: 10-15℃, cooling time 50-60 seconds.

9. The co-extrusion molding method of recycled plastic pipe according to claim 5, characterized in that: The step of irradiating the antibacterial layer particles in the four-layer composite structure with ultraviolet light to prepare the recycled plastic pipe comprises: Use 120-150W / cm 2 The antibacterial layer particles in the four-layer composite structure are irradiated with ultraviolet light for 5-8 seconds with a mercury lamp at a irradiation distance of 10-15 cm and a wavelength of 365 nm to obtain the recycled plastic pipe.

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