Preparation method of high-performance HDPE (high-density polyethylene) pipeline material

Abstract

The invention discloses a preparation method of a high-performance HDPE (high-density polyethylene) pipeline material, which is characterized in that a cross-linking agent and a cross-linking aid are pretreated by a solvent method and are blended and internally mixed with a polyethylene material and coated activated calcium carbonate microcapsules, and a synergistic effect of low-temperature impurity removal and high-temperature plasticizing is realized by combining a two-stage single-screw extrusion process. A high-temperature physical odor removal technology is adopted to remove small-molecule odor substances. Compared with a traditional physical blending method, chemical crosslinking is used for replacing a high-cost reinforcing material, a composite coating technology of the nano silica sol and the titanate coupling agent is used for achieving self-repairing of micro cracks on the surface of the material, the mechanical property is guaranteed, meanwhile, the raw material cost is reduced, the impact strength of the product is improved, and the melt flow stability is remarkably improved.

Description

Technical Field

[0001] The invention belongs to the technical field of polymer materials, and in particular relates to a method for preparing high-performance HDPE pipe material. Background Art

[0002] HDPE pipes are increasingly popular for their outstanding corrosion resistance, heat resistance, wear resistance, non-polluting properties, long service life, and low manufacturing and installation costs. They are widely used in gas transmission, water supply, heating, building water supply and drainage, and their usage has grown rapidly in recent years. Currently, HDPE pipes are the second most widely used plastic pipe, second only to PVC pipes.

[0003] HDPE granules for pipe manufacturing are typically extruded at high temperatures. HDPE pipe molding requires a melt index (MI) of 190°C (0.8-1.2 g / 10 min at 5 kg). Physical blending is typically performed by adding low-MI materials from blue drums, large white drums, or ton drums to lower the MI. However, physical blending is inefficient, requiring large amounts of material to lower the MI to the desired value, resulting in high material costs. Furthermore, the Izod impact strength of HDPE pipe produced by physical blending is generally less than 30 kJ / m². Furthermore, residual levels of small volatile molecules (such as aldehydes and ketones) in recycled materials often exceed 200 ppm, potentially posing a health risk to production personnel. Summary of the Invention

[0004] In view of the defects of conventional HDPE pipe material preparation process, such as high energy consumption and poor product quality, this application provides a preparation method of high-performance HDPE pipe material, which improves the tensile strength of HDPE while reducing the amount of volatile residues, and effectively avoids thermal oxidation of the material caused by high-temperature treatment.

[0005] The present invention is achieved through the following technical solutions: A method for preparing high-performance HDPE pipe material comprises the following steps: (a) Elemental silicon powder with a purity of ≥99.9%, caustic soda flakes, and pure water are uniformly mixed in a mass ratio of (0.8-1.2):(0.1-0.2):(8-12), followed by constant temperature stirring at 65-90°C for 12 hours to prepare a silica sol with a particle size of 20-50 nm. Finally, the silica sol is purified by ultrafiltration through a filter press with a 1 μm pore size to obtain a nano-silica sol with a concentration of 25-30 wt%; (b) mixing 800-1250 mesh calcium carbonate and nano-silica sol in a mass ratio of 100:(1-1.5), then adding a titanate coupling agent in a mass ratio of calcium carbonate to titanate coupling agent of 100:(0.5-0.8), and stirring at 800-1200 rpm at 50-90°C for 15-20 minutes to prepare coated composite particles having a specific surface area of ≥18 m² / g; (c) Pretreatment of the crosslinking system solvent: A high-temperature crosslinking agent and a crosslinking aid are mixed in a mass ratio of 1:(2-3), dissolved in 6 times the mass of ethylene glycol to obtain a mixed solution, and 0.2% of the mass of the mixed solution of antioxidant 1010 is added. Finally, ultrasonic vibration is carried out at 33-37°C for 15-30 minutes until the system transmittance is greater than 95%. The solvent is one or a combination of ethanol, ethylene glycol, and butanol. The high-temperature crosslinking agent is one or a combination of 2,4-di-tert-butyl peroxide isopropyl benzene, diisopropyl benzene peroxide, and 2,5-dimethyl-2,5-di(tert-butyl peroxy)hexane; The crosslinking aid is one or a combination of two of maleic anhydride, vinyltrimethoxysilane, allylsiloxane, vinyl propyl phthalate, and vinyl propyl terephthalate; (d) Banburying: Mixing, by weight, 100 parts of recycled HDPE bottle flakes, 70-100 parts of coated composite particles, 1.5-2.5 parts of a pre-treated crosslinking system, 1-2 parts of a lubricant, and 2 parts of a black masterbatch, and banburying the mixture at a temperature of 170-200° C. for 15-20 minutes; the lubricant is one or a combination of PE wax, stearic acid, and pentaerythritol ester; (e) the material obtained by the internal mixing treatment in step (d) is subjected to dynamic shearing by a screw extruder, and the aspect ratio is (28-32):1; (f) High-temperature vacuum deodorization: The material obtained by the screw extruder in step (e) is underwater pelletized and dried to obtain pellets, which are then vacuum-dried by heating to 90-110°C at a rate of 5°C / min and maintaining a vacuum degree of -0.06 to -0.08 MPa for 2-3 hours. The residual volatile matter content is ≤50 ppm, thereby obtaining a HDPE pipe material.

[0006] During the calcium carbonate activation stage, the present invention introduces nano-silica sol and titanate coupling agent to form a composite coating layer. The shell layer remains stable during the processing process. When microcracks appear in the pipeline, the microcapsules rupture to release the repair agent and react with the ambient moisture to form a siloxane network, thereby achieving self-repair of the cracks. The synergistic effect of the silanol group and the coupling agent significantly improves the calcium carbonate-HDPE interface bonding strength. The nano-filling effect of the silica sol and the synergistic effect of the cross-linking agent achieve dual enhancement of chemical bonding and physical anchoring at the inorganic filler-polymer interface.

[0007] Preferably, the crosslinking aid is prepared by mixing maleic anhydride and vinyltrimethoxysilane in a ratio of 3:1, and a nano-silica dispersant is added to the crosslinking aid at a mass ratio of 0.1-0.3% during the pretreatment of the crosslinking system solvent.

[0008] Preferably, in step (e), the material obtained by the banburying treatment in step (d) is sent to a first-stage single-screw extruder for treatment at 180-190° C., then filtered through a filter, sent to a second-stage single-screw extruder for treatment at 200-220° C., and then filtered through a filter before underwater pelletizing.

[0009] Preferably, the single-screw extruder in the first stage adopts a φ65mm single screw, a die head temperature of 170-180°C, a filter mesh number of 200-250 mesh after the single-screw extruder in the first stage, and a screw speed of 35-45 rpm.

[0010] Preferably, the two-stage screw extruder adopts a φ90mm single screw, a die head temperature of 180-190°C, a filter mesh size of 80-100 meshes, and a screw speed of 25-35 rpm.

[0011] The first-stage extrusion adopts a low-temperature + high-mesh filter design, which can effectively intercept high-temperature impurities in the HDPE material (impurities are solid rather than molten at low temperatures and will not penetrate the filter), thereby improving impurity removal efficiency; the second-stage extrusion adopts a high-temperature + low-mesh filter design. The high temperature can fully melt and plasticize the raw materials with stable performance, and the low-mesh filter can supplement the interception of the first-stage high-mesh filter. Because the filter plate aperture is relatively large, the pressure fluctuation of the melt passing through will not be too large. There is no need to reduce the screw speed to ensure that the melt pressure is within a safe range, thereby not reducing the output of HDPE pipe materials.

[0012] The gradient parameters of molecular sieve adsorption and vacuum devolatilization realize online deodorization in the process section for the first time, shortening the process cycle.

[0013] Preferably, the initial vacuum degree of the vacuum drying is -0.06 MPa, which is increased to -0.08 MPa after the temperature is raised to 105° C. and maintained for 2.5 hours.

[0014] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. The present invention uses a composite coating technology of nano-silica sol and titanate coupling agent to form a stable shell layer on the surface of calcium carbonate, so that the composite particles and HDPE form a dual reinforcement of chemical bonding (hydrogen bonding) and physical anchoring (nano-filling effect); when microcracks occur on the surface of HDPE pipe material, the coating layer ruptures and releases silica sol, which reacts with environmental moisture to form a siloxane network, achieving self-repair.

[0015] 2. The present invention integrates a molecular sieve in a two-stage extrusion die head, combines a gradient vacuum devolatilization process, and adds an antioxidant 1010 for pretreatment of the cross-linking system to jointly treat volatile residues. The molecular sieve adsorbs volatile substances in real time, and the vacuum devolatilization removes the residues in stages. The antioxidant inhibits the formation of high-temperature thermal oxidation by-products, thereby greatly reducing the amount of volatile residues in the final product of the present invention and improving production safety.

[0016] 3. The present invention optimizes the two-stage extrusion process. The first-stage extrusion adopts low temperature + high mesh filter to intercept solid impurities and improve the impurity removal efficiency; the second-stage extrusion adopts high temperature + low mesh filter to ensure sufficient plasticization of the melt, combined with the resonant shear section to achieve dynamic dispersion and reduce screw speed fluctuations. The molecular sieve online adsorption replaces the traditional post-processing process, shortening the process cycle by 30%, thereby greatly reducing production energy consumption. DETAILED DESCRIPTION

[0017] The present invention will be further described below with reference to the examples. In the examples, unless otherwise specified, the technical means used are conventional technical means in the art.

[0018] Example 1: A method for preparing high-performance HDPE pipe material, comprising the following steps: (a) Elemental silicon powder with a purity of ≥99.9%, caustic soda flakes, and pure water were mixed in a mass ratio of 0.8:0.1:8, and then stirred at 65°C for 12 hours to prepare a silica sol with a particle size of 20 nm. Finally, the silica sol was purified by ultrafiltration through a filter press with a 1 μm pore size to obtain a nano-silica sol with a concentration of 25 wt%; (b) 800-mesh calcium carbonate and nano-silica sol were mixed in a mass ratio of 100:1, and then a titanate coupling agent was added in a mass ratio of calcium carbonate to titanate coupling agent of 100:0.5, and the mixture was stirred at 800 rpm for 15 minutes at 50°C to prepare coated composite particles having a specific surface area of ≥18 m² / g; (c) Solvent pretreatment of the crosslinking system: A high-temperature crosslinker and a crosslinking aid were mixed in a mass ratio of 1:2, dissolved in 6 times the mass of ethanol to obtain a mixed solution, and 0.2% of the mass of the mixed solution was added with antioxidant 1010. Finally, the solution was ultrasonically shaken at 33°C for 15 min until the system transmittance was >95%. The high temperature crosslinking agent is 2,4-di-tert-butyl cumene peroxide; the crosslinking aid is maleic anhydride; (d) Banburying: 100 parts of recycled HDPE bottle flakes, 70 parts of coated composite particles, 1.5 parts of pre-treated cross-linking system, 1 part of PE wax, and 2 parts of black masterbatch were mixed by weight, and then banburying was performed at a banburying temperature of 170°C for 15 minutes; (e) the material obtained by the internal mixing treatment in step (d) is subjected to dynamic shearing by a screw extruder, with an aspect ratio of 28:1; (f) High-temperature vacuum deodorization: The material obtained by the screw extruder in step (e) is underwater pelletized and dried to obtain pellets, which are then vacuum-dried. The temperature is increased at 5°C / min, the initial vacuum degree is -0.06 MPa, the temperature is increased to 110°C, and then increased to -0.08 MPa, and maintained for 2 hours. The residual volatile matter content is ≤50 ppm, thereby obtaining HDPE pipe material.

[0019] The HDPE pipe material prepared in this embodiment has a melt index of 0.75 g / 10 min at 190°C and 5 kg, a tensile strength of 18.6 MPa, an elongation at break of 55%, a flexural strength of 22.8 MPa, a flexural modulus of 1923.8 MPa, and a cantilever notched impact strength of 38.1 KJ / m 2 .

[0020] Example 2: A method for preparing a high-performance HDPE pipe material, comprising the following steps: (a) Elemental silicon powder with a purity of ≥99.9%, caustic soda flakes, and pure water were mixed in a mass ratio of 1.2:0.2:12, and then stirred at 90°C for 12 hours to prepare a silica sol with a particle size of 50 nm. Finally, the silica sol was purified by ultrafiltration through a filter press with a 1 μm pore size to obtain a nano-silica sol with a concentration of 30 wt%; (b) 1250 mesh calcium carbonate and nano-silica sol were mixed in a mass ratio of 100:1.5, and then titanate coupling agent was added in a mass ratio of calcium carbonate to titanate coupling agent of 100:0.8, and the mixture was stirred at 1200 rpm at 90°C for 20 minutes to prepare coated composite particles with a specific surface area of ≥18 m² / g; (c) Solvent pretreatment of the crosslinking system: The high-temperature crosslinker and the crosslinking aid were dissolved in 6x ethylene glycol solvent at a mass ratio of 1:3, and 0.2% of antioxidant 1010 was added. Finally, ultrasonic vibration was performed at 37°C for 30 min until the system transmittance was >95%; The high-temperature crosslinking agent is dicumyl peroxide; the crosslinking auxiliary agent is obtained by compounding maleic anhydride and vinyltrimethoxysilane in a ratio of 3:1, and 0.3% nano-silica dispersant is added and mixed during the pretreatment of the crosslinking system solvent.

[0021] (d) Banburying: 100 parts of recycled HDPE bottle flakes, 100 parts of coated composite particles, 2.5 parts of pre-treated cross-linking system, 2 parts of stearic acid, and 2 parts of black masterbatch were mixed by weight, and then banburying was performed at a banburying temperature of 200°C for 20 minutes; (e) The material obtained by the internal mixing treatment in step (d) is subjected to dynamic shearing in a screw extruder, first sent to a first-stage single-screw extruder for processing, then filtered through a filter, sent to a second-stage single-screw extruder for processing, and then filtered through a filter before underwater pelletizing; the aspect ratios of the first-stage and second-stage extruders are 28:1 and 32:1, respectively; The first-stage single-screw extruder adopts a φ65mm single screw, a die head temperature of 170°C, a filter mesh of 200 mesh, and a screw speed of 35rpm; the second-stage screw extruder adopts a φ90mm single screw, a die head temperature of 180°C, a filter mesh of 80 mesh, and a screw speed of 25rpm.

[0022] (f) High-temperature vacuum deodorization: The material obtained by the screw extruder in step (e) is underwater pelletized and dried to obtain pellets, which are then vacuum-dried. The temperature is increased at 5°C / min, the initial vacuum degree is -0.08 MPa, the temperature is increased to 90°C, and then increased to -0.1 MPa, and maintained for 3 hours. The residual volatile matter content is ≤50 ppm, thereby obtaining HDPE pipe material.

[0023] The HDPE pipe material prepared in this embodiment has a melt index of 0.78 g / 10 min at 190°C and 5 kg, a tensile strength of 18.8 MPa, an elongation at break of 52%, a flexural strength of 23.5 MPa, a flexural modulus of 1949.5 MPa, and a cantilever notched impact strength of 37.3 KJ / m 2 .

[0024] Example 3: A method for preparing a high-performance HDPE pipe material, comprising the following steps: (a) Elemental silicon powder with a purity of ≥99.9%, caustic soda flakes, and pure water were mixed in a mass ratio of 1:0.15:10, and then stirred at 75°C for 12 hours to prepare a silica sol with a particle size of 40 nm. Finally, the silica sol was purified by ultrafiltration through a filter press with a 1 μm pore size to obtain a nano-silica sol with a concentration of 28 wt%; (b) 800-1250 mesh calcium carbonate and nano-silica sol were mixed in a mass ratio of 100:1.2, and then titanate coupling agent was added in a mass ratio of calcium carbonate to titanate coupling agent of 100:0.7, and the mixture was stirred at 1000 rpm at 65°C for 18 minutes to prepare coated composite particles with a specific surface area of ≥18 m² / g; (c) Solvent pretreatment of the crosslinking system: The high-temperature crosslinker and the crosslinking aid were dissolved in 6-fold butanol solvent at a mass ratio of 1:2, and 0.2% of antioxidant 1010 was added. Finally, ultrasonic vibration was performed at 35°C for 20 min until the system transmittance was greater than 95%; The high-temperature crosslinking agent is a mixture of 2,4-di-tert-butyl peroxide isopropyl benzene and 2,5-dimethyl-2,5-di(tert-butyl peroxy)hexane in equal proportions; The cross-linking aid is a mixture of maleic anhydride and vinyl propyl terephthalate in equal proportions; (d) Banburying: 100 parts of recycled HDPE bottle flakes, 80 parts of coated composite particles, 2.0 parts of pre-treated cross-linking system, 1 part of pentaerythritol ester, 1 part of PE wax, and 2 parts of black masterbatch were mixed by weight, and then banburying was performed at a banburying temperature of 190°C for 18 minutes; (e) The material obtained by the internal mixing treatment in step (d) is subjected to dynamic shearing by a screw extruder, first sent to a first-stage single-screw extruder for processing, then filtered through a filter, sent to a second-stage single-screw extruder for processing, and then filtered through a filter and subjected to underwater pelletizing; the aspect ratio is 30:1; The first-stage single-screw extruder adopts a φ65mm single screw, a die head temperature of 180°C, a filter mesh of 250 mesh after the first-stage single-screw extruder, and a screw speed of 45rpm; the second-stage screw extruder adopts a φ90mm single screw, a die head temperature of 190°C, a filter mesh of 100 mesh, and a screw speed of 35rpm.

[0025] (f) High-temperature vacuum deodorization: The material obtained by the screw extruder in step (e) is underwater pelletized and dried to obtain pellets, which are then vacuum-dried. The temperature is increased at 5°C / min, the initial vacuum degree is -0.06 MPa, the temperature is increased to 105°C, and then increased to -0.08 MPa, and maintained for 3 hours. The residual volatile matter content is ≤50 ppm, thereby obtaining HDPE pipe material.

[0026] The HDPE pipe material prepared in this embodiment has a melt index of 0.81 g / 10 min at 190°C and 5 kg, a tensile strength of 19.6 MPa, an elongation at break of 50%, a flexural strength of 24.7 MPa, a flexural modulus of 1956.7 MPa, and a cantilever notched impact strength of 38.5 KJ / m 2 The production cost per ton is about 3,500 yuan. At the same time, the performance of HDPE masterbatch used in the production of plastic pipes on the market was tested. Its melt index at 190°C and 5kg is 0.84g / 10min, the tensile strength is 18.4MPa, the elongation at break is 45%, the flexural strength is 25.79MPa, the flexural modulus is 1885.8MPa, and the cantilever notched impact strength is 30.4KJ / m 2 , the production cost per ton is about 4,000 yuan.

[0027] It can be seen that the performance indicators of the HDPE pipe material prepared by the process of the present invention in terms of melt index, flexural modulus, flexural strength and tensile strength are basically unchanged compared with ordinary materials, and the impact resistance is significantly improved and the cost is significantly reduced.

[0028] The above embodiments are merely exemplary embodiments of the present invention and are not intended to limit the scope of the present invention. The scope of protection of the present invention is defined by the claims. Persons skilled in the art may make various modifications or equivalent substitutions to the present invention within the spirit and scope of protection of the present invention, and such modifications or equivalent substitutions shall also be deemed to fall within the scope of protection of the present invention.

Claims

1. A method for preparing high-performance HDPE pipe material, characterized in that: The following steps are involved: (a) Elemental silicon powder with a purity of ≥99.9%, caustic soda flakes, and pure water are uniformly mixed in a mass ratio of (0.8-1.2):(0.1-0.2):(8-12), followed by constant temperature stirring at 65-90°C for 12 hours to prepare a silica sol with a particle size of 20-50 nm. Finally, the silica sol is purified by ultrafiltration through a filter press with a 1 μm pore size to obtain a nano-silica sol with a concentration of 25-30 wt%; (b) mixing 800-1250 mesh calcium carbonate and nano-silica sol in a mass ratio of 100:(1-1.5), then adding a titanate coupling agent in a mass ratio of calcium carbonate to titanate coupling agent of 100:(0.5-0.8), and stirring at 800-1200 rpm at 50-90°C for 15-20 minutes to prepare coated composite particles having a specific surface area of ≥18 m² / g; (c) Pretreatment of the crosslinking system solvent: The high-temperature crosslinker and the crosslinking aid were mixed in a mass ratio of 1:(2-3), dissolved in 6 times the mass of the solvent to obtain a mixed solution, and 0.2% of the mass of the mixed solution of antioxidant 1010 was added. Finally, ultrasonic vibration was performed at 33-37°C for 15-30 minutes until the system transmittance was greater than 95%; The high-temperature crosslinking agent is one or a combination of 2,4-di-tert-butyl peroxide isopropyl benzene, diisopropyl benzene peroxide, and 2,5-dimethyl-2,5-di(tert-butyl peroxy)hexane; The crosslinking aid is one or a combination of two of maleic anhydride, vinyltrimethoxysilane, allylsiloxane, vinyl propyl phthalate, and vinyl propyl terephthalate; (d) Banburying: Mix 100 parts of recycled HDPE bottle flakes, 70-100 parts of coated composite particles, 1.5-2.5 parts of pre-treated cross-linking system, 1-2 parts of lubricant, and 2 parts of black masterbatch by weight, and then banbury at a temperature of 170-200°C for 15-20 minutes. (e) the material obtained by the internal mixing treatment in step (d) is subjected to dynamic shearing by a screw extruder, and the aspect ratio is (28-32):1; (f) High-temperature vacuum deodorization: The material obtained by the screw extruder in step (e) is underwater pelletized and dried to obtain pellets, which are then vacuum-dried by heating to 90-110°C at a rate of 5°C / min and maintaining a vacuum degree of -0.06 to -0.08 MPa for 2-3 hours. The residual volatile matter content is ≤50 ppm, thereby obtaining a HDPE pipe material.

2. The method for preparing high-performance HDPE pipe material according to claim 1, characterized in that The crosslinking aid is obtained by compounding maleic anhydride and vinyltrimethoxysilane in a ratio of 3:

1. During the pretreatment of the crosslinking system solvent, a nano-silica dispersant with a mass of 0.1-0.3% of the crosslinking aid is added and mixed.

3. The method for preparing high performance HDPE pipe material according to claim 1, characterized in that In step (e), the material obtained by the banburying treatment in step (d) is sent to a first-stage single-screw extruder for treatment at 180-190°C, then filtered through a filter, sent to a second-stage single-screw extruder for treatment at 200-220°C, and then filtered through a filter before underwater pelletizing.

4. The method for preparing high performance HDPE pipe material according to claim 3, characterized in that The single-screw extruder in the first stage adopts a φ65mm single screw, a die head temperature of 170-180°C, a filter mesh number of 200-250 meshes after the single-screw extruder in the first stage, and a screw speed of 35-45rpm.

5. The method for preparing high performance HDPE pipe material according to claim 3, characterized in that The two-stage screw extruder adopts a φ90mm single screw, a die head temperature of 180-190°C, a filter mesh size of 80-100 mesh, and a screw speed of 25-35rpm.

6. The method for preparing high performance HDPE pipe material according to claim 1, characterized in that The initial vacuum degree of the vacuum drying was -0.06 MPa, which was increased to -0.08 MPa after heating to 105°C and maintained for 2.5 hours.

7. The method for preparing high-performance HDPE pipe material according to claim 1, characterized in that: The solvent in step (c) is one or a combination of two of ethanol, ethylene glycol, and butanol.

8. The method for preparing high-performance HDPE pipe material according to claim 1, characterized in that: The lubricant in step (d) is one or a combination of two of PE wax, stearic acid, and pentaerythritol ester.