Modified calcium carbonate applied to filling of HDPE (high-density polyethylene) pressure-bearing pipeline

Abstract

The invention discloses modified calcium carbonate applied to filling of an HDPE (high-density polyethylene) pressure-bearing pipeline, and relates to the technical field of calcium carbonate powder modification, and the modified calcium carbonate is prepared from the following components in parts by mass: 100 parts of calcium carbonate, 1.5-2.0 parts of a modifier, 0.25-0.35 part of a dispersing agent, 0.2-0.4 part of an antioxidant and 0.1-0.15 part of Caster 2, the modifier is one of dimethyl methoxy silane terminated telechelic polybutadiene, a polyethylene-b-polyethylene glycol block copolymer and polysiloxane with a side chain containing an epoxy group. The HDPE pressure-bearing pipeline filling material is good in dispersity, compatibility and binding force, high-proportion filling can be achieved in HDPE pressure-bearing pipeline production, the mechanical property and aging resistance of a pipeline can be improved, the hydrostatic strength is guaranteed, and the cost of the pressure-bearing pipeline is reduced.

Description

Technical Field

[0001] The invention relates to the technical field of calcium carbonate powder modification, in particular to modified calcium carbonate used for filling HDPE pressure pipes. Background Art

[0002] PE 100 material is the highest grade material among PE materials at present. Its price is higher than other PE materials. It is mainly used in the production of pressure pipes such as water supply pipes and gas pipes. Due to the particularity of the application field and extremely harsh test conditions (such as 20℃, 100h hydrostatic strength test, 80℃, 165h hydrostatic strength test, 80℃, 1000h hydrostatic strength test, etc.), it is extremely difficult to add fillers when PE 100 material is used to produce pressure pipes. For example, in the filling of water supply and gas pipes, relevant tests show that when the filler exceeds 5%, the produced pipe will not pass the hydrostatic strength test. As a result, the price of HDPE (high-density polyethylene) pressure pipes has remained high. Summary of the invention

[0003] The technical problem to be solved by the present invention is to provide a modified calcium carbonate used for filling HDPE pressure pipes, which has good dispersibility, compatibility and bonding strength, can achieve high-proportion filling in the production of HDPE pressure pipes, and can improve the mechanical properties and aging resistance of the pipes, ensure the hydrostatic strength, and help reduce the cost of pressure pipes.

[0004] In order to solve the above technical problems, the technical solution of the present invention is: modified calcium carbonate used for filling HDPE pressure pipes, comprising the following components: by mass, 100 parts of calcium carbonate, 1.5-2.0 parts of modifier, 0.25-0.35 parts of dispersant, 0.2-0.4 parts of antioxidant, and 0.1-0.15 parts of Cast2; the modifier is one of dimethylmethoxysilane-terminated telechelic polybutadiene, polyethylene-b-polyethylene glycol block copolymer, and polysiloxane containing epoxy groups on the side chain; Wherein, the dimethylmethoxysilane-terminated telechelic polybutadiene has the structural formula , where n is 16 to 46; The polyethylene-b-polyethylene glycol block copolymer has the structural formula: , where n is 41 to 500, and m is 17 to 120; The polysiloxane structural formula containing epoxy groups in the side chains is .

[0005] As a preferred technical solution, the calcium carbonate is heavy calcium carbonate, and the particle size of the calcium carbonate is D 50 ≤1.35μm, D 97≤8.31μm, and the water content in the calcium carbonate is 0.5-1% of the mass of the calcium carbonate.

[0006] As a preferred technical solution, the dispersant is one of a polyolefin type hyperdispersant, a polyacrylate type hyperdispersant, and a polyether type hyperdispersant.

[0007] As a preferred technical solution, the antioxidant is compounded by a main antioxidant and an auxiliary antioxidant, and the compounding ratio of the main antioxidant and the auxiliary antioxidant is 1:1 or 1:2; Wherein, the primary antioxidant is one of 2, 2′-methylenebis(4-methyl-6-tert-butylphenol), N,N′-bis-(3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionyl)hexanediamine, β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate, pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate, 1,1,3-tris(2-methyl-4-hydroxy-5-tert-butylphenyl)butane, and 4,4′-methylenebis(2,6-di-tert-butylphenol); The auxiliary antioxidant is one of tris(2,4-di-tert-butylbenzene) phosphite, dilauryl thiodipropionate, distearyl thiodipropionate, distearyl pentaerythritol diphosphite, and 3-(dodecylthio)propionic acid-2,2-bis[[3-(dodecylthio)-propionyloxy]methyl]-1,3-propylene glycol ester.

[0008] The modified calcium carbonate used for filling HDPE pressure pipes is prepared by using two high-speed and low-speed dual-speed mixers with heating functions, a low-speed mixer with cooling function and a set of metering pump metering feeding devices with heating function; the preparation method includes a low-temperature process and a high-temperature process.

[0009] As a preferred technical solution, the low temperature process comprises the following steps: SP A1 , adding the modifier into the heater of the metering pump metering feeding device and heating it, and controlling the heating temperature of the heater to be 85-95° C.; SP A2 1. Heat one of the high-speed and low-speed dual-speed mixers to 50-60°C and keep the temperature constant for 30 minutes; SP A3 , add the measured calcium carbonate into SP A2 The high-speed and low-speed dual-speed mixer of the step, under low-speed stirring, uniformly add the proportioned dispersant to the high-speed and low-speed dual-speed mixer, the dispersant addition time is controlled at 30 to 45 seconds, and continue to stir at low speed until the temperature of the calcium carbonate is not less than 50° C.; SP A4, spray the modifier uniformly to SP through the metering pump metering feeding device A3 The step is to add the modifier to the calcium carbonate in the high-speed and low-speed dual-speed mixer for 30 to 45 seconds, continue stirring for 3 to 5 minutes, then stop stirring and keep static, stirring at a low speed for 1 minute every 5 minutes during the static period; SP A5 , keep static for 15 to 20 minutes and then release the mixed powder.

[0010] As a preferred technical solution, the high temperature process includes the following steps: SP B1 , raising the temperature of the other high-speed and low-speed dual-speed mixer to 100-110° C. and keeping the temperature constant for 30 minutes; SP B2 , SP A5 Add the mixed powder released in step 1 into SP B1 In the high-speed and low-speed dual-speed mixer of the step, stirring at a low speed until the temperature of the mixed powder is not less than 100° C.; SP B3 , Stir the mixed powder for 15 to 20 minutes when the temperature is 100 to 110°C; SP B4 , add the antioxidant and Cast2 in the ratio, and stir at high speed for 3 to 5 minutes; SP B5 , SP B4 The mixed material obtained by stirring in the step is transferred into a low-speed mixer with a cooling function, and the temperature is reduced to room temperature under low-speed stirring to obtain modified calcium carbonate.

[0011] Due to the adoption of the above technical solution, the present invention achieves the following beneficial effects: (1) The dispersant in the present invention is a hyperdispersant. The anchoring groups in the hyperdispersant are combined with the surface of the powder particles through ionic bonds, hydrogen bonds and van der Waals forces, adsorbed on the surface of the particles, and form an adsorption layer around the particles. It is not easy to desorb, and the solvation chain forms a coating layer on the surface of the particles. According to the three-dimensional (spatial) stability mechanism, when two particles adsorbed with hyperdispersant molecules are close to each other and the distance between them is less than 2 times the thickness of the adsorption layer, the steric hindrance generated by the extended solvation chain causes the particles to bounce off, preventing them from agglomerating, thereby ensuring the dispersibility of the calcium carbonate powder.

[0012] (2) The modifier in the present invention is selected from dimethylmethoxysilane-terminated telechelic polybutadiene, polyethylene-b-polyethylene glycol block copolymer or polysiloxane containing epoxy groups in the side chain, which respectively contain highly active methoxy groups (-OCH3) or epoxy groups ( ), these active groups are hydrolyzed into hydroxyl groups (-OH) and combined with the hydroxyl groups (-OH) on the surface of calcium carbonate to form a stable structure. At the same time, the three modifiers are all long-chain modifiers. When applied to HDPE matrix materials, they can be entangled with the HDPE molecular chain, thereby achieving good compatibility and bonding between calcium carbonate and HDPE when filling HDPE. When the pressure pipe is damaged, it takes more energy to disentangle. Therefore, in the case of high-ratio filling, the performance of the HDPE pipe can still be improved and meet the requirements of the static hydraulic strength test.

[0013] (3) The addition of antioxidant and Cast2 (calcium stearate) in the present invention utilizes the antioxidant's anti-thermal oxidative aging function and Cast2's ability to eliminate residual catalysts in polyolefins. The combined effect of the two improves the aging resistance of HDPE after filling.

[0014] (4) In the present invention, calcium carbonate is used as a cheap filling material in HDPE pressure pipes, and the cost reduction effect is obvious. DETAILED DESCRIPTION

[0015] The present invention is further described below in conjunction with Examples. In the following detailed description, certain exemplary embodiments of the present invention are described only by way of illustration. Needless to say, those of ordinary skill in the art will recognize that the described embodiments may be modified in a variety of ways without departing from the spirit and scope of the present invention. Therefore, the description is illustrative in nature and is not intended to limit the scope of protection of the claims.

[0016] The modified calcium carbonate used for filling HDPE pressure pipes includes the following components: by mass, 100 parts of calcium carbonate, 1.5-2.0 parts of a modifier, 0.25-0.35 parts of a dispersant, 0.2-0.4 parts of an antioxidant, and 0.1-0.15 parts of Cast2; the modifier is one of dimethylmethoxysilane-terminated telechelic polybutadiene, polyethylene-b-polyethylene glycol block copolymer, and polysiloxane containing epoxy groups on the side chains.

[0017] Wherein, the dimethylmethoxysilane-terminated telechelic polybutadiene has the structural formula , where n is 16 to 46.

[0018] The polyethylene-b-polyethylene glycol block copolymer has the structural formula: , where n is 41~500 and m is 17~120.

[0019] The polysiloxane structural formula containing epoxy groups in the side chains is .

[0020] The end groups of the dimethylmethoxysilane-terminated telechelic polybutadiene and the polyethylene-b-polyethylene glycol block copolymer both have highly active methoxy groups (-OCH3), and the side chains of the polysiloxane containing epoxy groups contain highly active epoxy groups ( Since calcium carbonate itself is alkaline, its pH value is about 10, the methoxy group (-OCH3) or epoxy group ( ) is hydrolyzed in an alkaline environment with water contained in calcium carbonate to produce hydroxyl groups (-OH), and then the hydroxyl groups (-OH) produced by hydrolysis combine with the hydroxyl groups (-OH) on the surface of calcium carbonate under high temperature and shear force to form a stable structure. At the same time, the dimethylmethoxysilane-terminated telechelic polybutadiene, the polyethylene-b-polyethylene glycol block copolymer, and the polysiloxane with epoxy groups on the side chain are all long-chain structures. When the modified calcium carbonate is filled with HDPE, the long-chain structure is entangled with the HDPE molecular chain to achieve compatibility and combination of calcium carbonate and HDPE. When the pressure-bearing pipeline is damaged, more energy is consumed for disentanglement. Even in the case of high-ratio filling, the performance of the HDPE blending system can be improved and meet the requirements of the hydrostatic strength test.

[0021] Preferably, the calcium carbonate is heavy calcium carbonate, and the particle size of the calcium carbonate is D 50 ≤1.35μm, D 97 ≤8.31μm, the water content in the calcium carbonate is 0.5-1% of the mass of the calcium carbonate. This kind of calcium carbonate is cheap, and when it is used to fill a high proportion of HDPE pressure pipes, it has a significant effect on reducing the cost of HDPE pressure pipes.

[0022] Preferably, the dispersant is one of a polyolefin-type hyperdispersant, a polyacrylate-type hyperdispersant, and a polyether-type hyperdispersant.

[0023] The dispersant of the present invention adopts a super dispersant, and the dispersing mechanism of the super dispersant is as follows: the anchoring groups in the super dispersant, such as -R2N, -R3N+, -COOH, -COO, -SO3H, -SO 2- ,-PO4 2-, polyamines, polyols and polyethers, etc., which can be tightly adsorbed on the surface of solid particles through interactions such as ionic bonds, covalent bonds, hydrogen bonds and van der Waals forces, forming an adsorption layer around the particles, and are not prone to desorption. The solvated chains in hyperdispersants, such as polyesters, polyethers, polyolefins and polyacrylates, can be divided into three types according to their polarity: low-polarity polyolefin chains, medium-polarity polyester chains or polyacrylate chains, and strong-polarity polyether chains. In a polarity-matched dispersion medium, the solvated chains have good compatibility with the dispersion medium and adopt a relatively extended conformation in the dispersion medium. According to the three-dimensional (spatial) stability mechanism, when two particles adsorbed with hyperdispersant molecules are close to each other and the distance between them is less than 2 times the thickness of the adsorption layer, the steric hindrance generated by the extended solvated chains causes the particles to bounce off, preventing them from agglomerating, thus ensuring the dispersibility of the calcium carbonate powder.

[0024] The antioxidant is compounded by a main antioxidant and an auxiliary antioxidant, and the compounding ratio of the main antioxidant to the auxiliary antioxidant is 1:1 or 1:2.

[0025] Wherein, the main antioxidant is one of 2,2′-methylenebis(4-methyl-6-tert-butylphenol), N,N′-bis-(3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionyl)hexanediamine, β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate, pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate, 1,1,3-tris(2-methyl-4-hydroxy-5-tert-butylphenyl)butane, and 4,4′-methylenebis(2,6-di-tert-butylphenol).

[0026] The auxiliary antioxidant is one of tris(2,4-di-tert-butylbenzene) phosphite, dilauryl thiodipropionate, distearyl thiodipropionate, distearyl pentaerythritol diphosphite, and 3-(dodecylthio)propionic acid-2,2-bis[[3-(dodecylthio)-propionyloxy]methyl]-1,3-propylene glycol ester.

[0027] The antioxidant mechanism of the antioxidant is a well-known technology and will not be described in detail here.

[0028] Cast2 is used as a halogen absorber in PE and PP to eliminate the adverse effects of residual catalysts in the resin on the color and stability of the resin. Antioxidants and Cast2 are used in combination to improve the aging resistance of filled HDPE.

[0029] The modified calcium carbonate used for filling HDPE pressure pipes is prepared by using two high-speed and low-speed dual-speed mixers with heating functions, a low-speed mixer with cooling function and a set of metering pump metering feeding devices with heating function; the preparation method includes a low-temperature process and a high-temperature process.

[0030] The low temperature process comprises the following steps: SP A1 , adding the modifier into the heater of the metering pump metering feeding device and heating it, and controlling the heating temperature of the heater to be 85-95° C.; SP A2 1. Heat one of the high-speed and low-speed dual-speed mixers to 50-60°C and keep the temperature constant for 30 minutes; SP A3 , add the measured calcium carbonate into SP A2 The high-speed and low-speed dual-speed mixer of the step, under low-speed stirring, uniformly add the proportioned dispersant to the high-speed and low-speed dual-speed mixer, the dispersant addition time is controlled at 30 to 45 seconds, and continue to stir at low speed until the temperature of the calcium carbonate is not less than 50° C.; SP A4 , spray the modifier uniformly to SP through the metering pump metering feeding device A3 The step is to add the modifier to the calcium carbonate in the high-speed and low-speed dual-speed mixer for 30 to 45 seconds, continue stirring for 3 to 5 minutes, then stop stirring and keep static, stirring at a low speed for 1 minute every 5 minutes during the static period; SP A5 , keep static for 15 to 20 minutes and then release the mixed powder.

[0031] The purpose of heating the modifier is to reduce the viscosity of the dimethylmethoxysilane-terminated telechelic polybutadiene and the polysiloxane containing epoxy groups on the side chains or to melt them, and to reduce the viscosity of the polyethylene-b-polyethylene glycol block copolymer in the modifier, so as to facilitate uniform spraying onto the surface of the calcium carbonate.

[0032] The purpose of keeping it static is to promote the high-activity methoxy group (-OCH3) at the end of the dimethylmethoxysilane-terminated telechelic polybutadiene and the polyethylene-b-polyethylene glycol block copolymer, and the high-activity epoxy group ( ) is hydrolyzed in an alkaline environment (pH of about 10) of the calcium carbonate. The purpose of heating the calcium carbonate is to increase the movement activity of the calcium carbonate containing water and promote the hydrolysis of the active groups of the modifier.

[0033] The high temperature process comprises the following steps: SP B1 , raising the temperature of the other high-speed and low-speed dual-speed mixer to 100-110° C. and keeping the temperature constant for 30 minutes; SP B2 , SP A5 Add the mixed powder released in step 1 into SP B1In the high-speed and low-speed dual-speed mixer of the step, stirring at a low speed until the temperature of the mixed powder is not less than 100° C.; SP B3 , Stir the mixed powder for 15 to 20 minutes when the temperature is 100 to 110°C; SP B4 , add the antioxidant and Cast2 in the ratio, and stir at high speed for 3 to 5 minutes; SP B5 , SP B4 The mixed material obtained by stirring in the step is transferred into a low-speed mixer with a cooling function, and the temperature is reduced to room temperature under low-speed stirring to obtain modified calcium carbonate.

[0034] At high temperature, the highly active methoxy groups (-OCH3) at the end groups of the dimethylmethoxysilane-terminated telechelic polybutadiene and the polyethylene-b-polyethylene glycol block copolymer, and the highly active epoxy groups ( ) The hydroxyl groups (-OH) produced by hydrolysis are more likely to react with the hydroxyl groups (-OH) on the surface of calcium carbonate to form a strong -O- bond.

[0035] For the sake of simplicity, in the following examples: (1) Calcium carbonate is selected as D 50 =1.10μm, D 97 =5.83 μm, heavy calcium carbonate having a moisture content of 0.8% of the mass of the calcium carbonate; (2) The antioxidant is selected as the main antioxidant 2, 2′-methylenebis(4-methyl-6-tert-butylphenol) and the auxiliary antioxidant tris(2,4-di-tert-butylphenyl) phosphite, and the compounding ratio is 1:1; (3) In the methylmethoxysilane-terminated telechelic polybutadiene, n is 16; (4) In the polyethylene-b-polyethylene glycol block copolymer, n is 100 and m is 50; (5) The material of the HDPE pressure pipe used in the embodiment is PE 100, with a grade of 049; (6) The modified calcium carbonate powder was filled with HDPE to produce φ110 and SDR11 pressure-bearing pipes for testing. The production used a conical twin-screw extruder equipped with a φ110 and SDR11 pipe head. The extruder temperature (including the head) was controlled at 85-225°C, the sizing vacuum was 0.35-0.4MPa, and the cooling length was 18 meters. The average outer diameter of the produced pipe was 110.1-110.3mm, and the wall thickness was 10.1-10.3mm. The modified calcium carbonate powder and HDPE were fed into the silo of the conical twin-screw extruder using a loss-in-weight scale, and the wall thickness deviation caused by the extrusion process was controlled by a meter weight machine; (7) Since the technical requirements and test methods of GB / T 13663.2-2018 "Polyethylene (PE) Pipe Systems for Water Supply Part 2: Pipes" and GB / T15558.2-2023 "Buried Polyethylene (PE) Pipe Systems for Gas Part 2: Pipes" are consistent, the embodiments of the present invention and the comparative examples are state regulated and tested according to the test methods given in GB / T 13663.2-2018; the hydrostatic strength test is carried out using the hydrostatic strength test under the water medium of 80°C and 165h as required by the factory inspection.

[0036] Embodiment 1: 100 parts of calcium carbonate, 2 parts of polyethylene-b-polyethylene glycol block copolymer, 0.35 parts of polyolefin hyperdispersant, 0.4 parts of antioxidant, and 0.15 parts of Cast2.

[0037] By mass, 95 parts of HDPE, 5 parts of modified calcium carbonate, and 5 parts of black masterbatch (carbon black content not less than 42%) were used to produce pipes, which were marked as Examples 1-5.

[0038] By mass, 90 parts of HDPE, 10 parts of modified calcium carbonate, and 5 parts of black masterbatch (with a carbon black content of not less than 42%) were used to produce pipes, which were marked as Examples 1-10.

[0039] By mass, 85 parts of HDPE, 15 parts of modified calcium carbonate, and 5 parts of black masterbatch (carbon black content not less than 42%) were used to produce pipes, which were marked as Examples 1-15.

[0040] By mass, 80 parts of HDPE, 20 parts of modified calcium carbonate, and 5 parts of black masterbatch (with a carbon black content of not less than 42%) were used to produce pipes, which were marked as Examples 1-20.

[0041] Embodiment 2: 100 parts of calcium carbonate, 1.7 parts of polyethylene-b-polyethylene glycol block copolymer, 0.3 parts of polyolefin hyperdispersant, 0.3 parts of antioxidant, and 0.12 parts of Cast2.

[0042] By mass, 85 parts of HDPE, 15 parts of modified calcium carbonate, and 5 parts of black masterbatch (carbon black content not less than 42%) were used to produce a pipe marked as Example 2-15.

[0043] Embodiment 3: 100 parts of calcium carbonate, 1.5 parts of polyethylene-b-polyethylene glycol block copolymer, 0.25 parts of polyolefin hyperdispersant, 0.2 parts of antioxidant, and 0.1 parts of Cast2.

[0044] By mass, 85 parts of HDPE, 15 parts of modified calcium carbonate, and 5 parts of black masterbatch (carbon black content not less than 42%) were used to produce a pipe marked as Example 3-15.

[0045] Embodiment 4: 100 parts of calcium carbonate, 2 parts of dimethylmethoxysilane-terminated telechelic polybutadiene, 0.35 parts of polyolefin hyperdispersant, 0.4 parts of antioxidant, and 0.15 parts of Cast2.

[0046] By mass, 85 parts of HDPE, 15 parts of modified calcium carbonate, and 5 parts of black masterbatch (carbon black content not less than 42%) were used to produce pipes, which were marked as Examples 4-15.

[0047] Embodiment 5: 100 parts of calcium carbonate, 2 parts of polysiloxane containing epoxy groups in the side chain, 0.35 parts of polyolefin hyperdispersant, 0.4 parts of antioxidant, and 0.15 parts of Cast2.

[0048] By mass, 85 parts of HDPE, 15 parts of modified calcium carbonate, and 5 parts of black masterbatch (carbon black content not less than 42%) were used to produce pipes, which were marked as Examples 5-15.

[0049] Embodiment 6: 100 parts of calcium carbonate, 2 parts of polyethylene-b-polyethylene glycol block copolymer, 0.35 parts of polyacrylate type hyperdispersant, 0.4 parts of antioxidant, and 0.15 parts of Cast2.

[0050] By mass, 85 parts of HDPE, 15 parts of modified calcium carbonate, and 5 parts of black masterbatch (carbon black content not less than 42%) were used to produce pipes, which were marked as Examples 6-15.

[0051] Embodiment 7: 100 parts of calcium carbonate, 2 parts of polyethylene-b-polyethylene glycol block copolymer, 0.35 parts of polyether type hyperdispersant, 0.4 parts of antioxidant, and 0.15 parts of Cast2.

[0052] By mass, 85 parts of HDPE, 15 parts of modified calcium carbonate, and 5 parts of black masterbatch (carbon black content not less than 42%) were used to produce pipes, which were marked as Examples 7-15.

[0053] Comparative Example: Calcium carbonate uses commercially available calcium carbonate masterbatch, the calcium carbonate content in the masterbatch is 88%, the calcium carbonate used is 3000 mesh calcium carbonate, which is consistent with the calcium carbonate used in the embodiment, and the additives used in the masterbatch are aluminum-titanium composite coupling agent and stearic acid, and the amount used is unknown.

[0054] By mass, 5 parts of calcium carbonate masterbatch, 95 parts of HDPE, and 5 parts of black masterbatch (carbon black content not less than 42%) were used to produce a pipe marked as Comparative Example-5.

[0055] By mass, 10 parts of calcium carbonate masterbatch, 90 parts of HDPE, and 5 parts of black masterbatch (carbon black content not less than 42%) were used to produce a pipe marked as Comparative Example-10.

[0056] By mass, 15 parts of calcium carbonate masterbatch, 85 parts of HDPE, and 5 parts of black masterbatch (carbon black content not less than 42%) were used to produce a pipe marked as Comparative Example-15.

[0057] Calcium carbonate masterbatch 20 parts, HDPE 80 parts, black masterbatch (carbon black content not less than 42%) 5 parts were used to produce pipes, which were marked as Comparative Example 20.

[0058] The test results of Examples 1 to 7 and the comparative examples and the comparison with the national standard are shown in Table 1.

[0059] Table 1 Test data of embodiments and comparative examples Table 1 (Continued) Test data of examples and comparative examples Note: The national standard requirements are GB / T 13663.2-2018 "Polyethylene (PE) Pipe Systems for Water Supply Part 2: Pipes" and GB / T 15558.2-2023 "Buried Polyethylene (PE) Pipe Systems for Gas Part 2: Pipes".

[0060] It can be seen from Table 1 that the pressure-bearing pipes produced by HDPE filled with modified calcium carbonate in Examples 1 to 7 have various properties that are better than those of the comparative examples with the same filling amount. In Example 1, when the modified calcium carbonate filling amount is 5 parts, 10 parts, 15 parts, and 20 parts, respectively, the pipes are in a good state without damage or leakage in the 165h hydrostatic strength test under 80°C water medium, while in the comparative example, when only the calcium carbonate masterbatch filling amount is 5 parts, the pipes are in a good state without damage or leakage in the 165h hydrostatic strength test under 80°C water medium, and when the calcium carbonate masterbatch filling amount is 10 parts, 15 parts, and 20 parts, respectively, the pipes burst in the 165h hydrostatic strength test under 80°C water medium. In addition, the mechanical properties and oxidation induction time of the HDPE pipe filled with 5, 10, 15, and 20 parts of modified calcium carbonate in Example 1 are significantly higher than those of the HDPE pipe filled with 5, 10, 15, and 20 parts of calcium carbonate masterbatch in the comparative example. When the filling amount is not less than 10 parts, the performance gap becomes more obvious, especially the oxidation induction time of the comparative example drops sharply. These differences can be more intuitively seen from the comparison of Examples 1-15, Examples 2 to 7 in Example 1 with the same addition amount of 15 parts and the comparative example-15 in the comparative example. Since the oxidation induction time characterizes the aging resistance of the pipe, the improvement of the aging resistance of Examples 1 to 7 is obvious.

[0061] The reason for the outstanding performance of the embodiments is that: on the one hand, in the embodiments, the dimethylmethoxysilane-terminated telechelic polybutadiene, polyethylene-b-polyethylene glycol block copolymer, and polysiloxane containing epoxy groups in the side chain are respectively provided with highly active methoxy groups (-OCH3) or epoxy groups ( ) is hydrolyzed into hydroxyl (-OH), and then reacts with the hydroxyl (-OH) on the surface of the calcium carbonate to form a stable -O- structure. At the same time, the long chains of the dimethylmethoxysilane-terminated telechelic polybutadiene, polyethylene-b-polyethylene glycol block copolymer, and polysiloxane with epoxy groups on the side chains are entangled with the molecular chains of the HDPE matrix material to achieve compatibility between calcium carbonate and HDPE. The use of superdispersants makes the calcium carbonate more evenly dispersed, thereby improving the mechanical properties and hydrostatic properties of HDPE pipes. On the other hand, although the addition of calcium carbonate provides oxidation active points to the blending system (Wang Aidong, Yu Haiou, Yang Xiaoyun, et al. Study on the thermal oxidation aging properties of filled polypropylene [J]. Plastics Industry, 2013, 41 (7): 68-72; Cheng Wei, Wen Haoyu, Xu Gang. Effect of inorganic fillers on the oxidation induction period of HDPE [J]. Materials Science, 2018, 8(5):509~514), reducing the oxidation induction time of HDPE, but the consumption of hydroxyl groups (-OH) on the surface of calcium carbonate by the dimethylmethoxysilane-terminated telechelic polybutadiene, polyethylene-b-polyethylene glycol block copolymer, and the polysiloxane containing epoxy groups on the side chain, as well as the use of antioxidants and Cast2 offset the effect of calcium carbonate on the aging resistance of HDPE.

[0062] The description of the present invention is given for the purpose of illustration and description, and is not intended to be exhaustive or to limit the invention to the disclosed form. Many modifications and variations will be apparent to those of ordinary skill in the art. The embodiments are selected and described in order to better illustrate the principles and practical applications of the present invention and to enable those of ordinary skill in the art to understand the present invention and thereby design various embodiments with various modifications suitable for particular uses.

Claims

1. Modified calcium carbonate used for filling HDPE pressure pipes, characterized in that: The invention comprises the following components: by weight, 100 parts of calcium carbonate, 1.5-2.0 parts of a modifier, 0.25-0.35 parts of a dispersant, 0.2-0.4 parts of an antioxidant, and 0.1-0.15 parts of Cast2; the modifier is one of dimethylmethoxysilane-terminated telechelic polybutadiene, polyethylene-b-polyethylene glycol block copolymer, and polysiloxane containing epoxy groups on the side chain; Wherein, the dimethylmethoxysilane-terminated telechelic polybutadiene has the structural formula , where n is 16 to 46; The polyethylene-b-polyethylene glycol block copolymer has the structural formula: , where n is 41 to 500, and m is 17 to 120; The polysiloxane structure containing epoxy groups in the side chain is .

2. The modified calcium carbonate used for filling HDPE pressure pipes according to claim 1, characterized in that: The calcium carbonate is heavy calcium carbonate, and the particle size of the calcium carbonate is D 50 ≤1.35μm, D 97 ≤8.31μm, and the water content in the calcium carbonate is 0.5-1% of the mass of the calcium carbonate.

3. The modified calcium carbonate used for filling HDPE pressure pipes according to claim 1, characterized in that: The dispersant is one of a polyolefin type hyperdispersant, a polyacrylate type hyperdispersant and a polyether type hyperdispersant.

4. The modified calcium carbonate for filling HDPE pressure pipes according to claim 1, characterized in that: The antioxidant is compounded by a main antioxidant and an auxiliary antioxidant, and the compounding ratio of the main antioxidant to the auxiliary antioxidant is 1:1 or 1:2; Wherein, the primary antioxidant is one of 2, 2′-methylenebis(4-methyl-6-tert-butylphenol), N,N′-bis-(3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionyl)hexanediamine, β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate, pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate, 1,1,3-tris(2-methyl-4-hydroxy-5-tert-butylphenyl)butane, and 4,4′-methylenebis(2,6-di-tert-butylphenol); The auxiliary antioxidant is one of tris(2,4-di-tert-butylbenzene) phosphite, dilauryl thiodipropionate, distearyl thiodipropionate, distearyl pentaerythritol diphosphite, and 3-(dodecylthio)propionic acid-2,2-bis[[3-(dodecylthio)-propionyloxy]methyl]-1,3-propylene glycol ester.

5. The modified calcium carbonate used for filling HDPE pressure pipes according to any one of claims 1 to 4, characterized in that: Its preparation adopts two high-speed and low-speed dual-speed mixers with heating function, a low-speed mixer with cooling function and a set of metering pump metering feeding device with heating function; the preparation method includes low-temperature process and high-temperature process.

6. The modified calcium carbonate for filling HDPE pressure pipes according to claim 5, characterized in that: The low temperature process comprises the following steps: SP A1 , adding the modifier into the heater of the metering pump metering feeding device and heating it, and controlling the heating temperature of the heater to be 85-95° C.; SP A2 1. Heat one of the high-speed and low-speed dual-speed mixers to 50-60°C and keep the temperature constant for 30 minutes; SP A3 , add the measured calcium carbonate into SP A2 The high-speed and low-speed dual-speed mixer of the step, under low-speed stirring, uniformly add the proportioned dispersant to the high-speed and low-speed dual-speed mixer, the dispersant addition time is controlled at 30 to 45 seconds, and continue to stir at low speed until the temperature of the calcium carbonate is not less than 50° C.; SP A4 , spray the modifier uniformly to SP through the metering pump metering feeding device A3 The step is to add the modifier to the calcium carbonate in the high-speed and low-speed dual-speed mixer for 30 to 45 seconds, continue stirring for 3 to 5 minutes, then stop stirring and keep static, stirring at a low speed for 1 minute every 5 minutes during the static period; SP A5 , keep static for 15 to 20 minutes and then release the mixed powder.

7. The modified calcium carbonate used for filling HDPE pressure pipes according to claim 6, characterized in that: The high temperature process comprises the following steps: SP B1 , raising the temperature of the other high-speed and low-speed dual-speed mixer to 100-110° C. and keeping the temperature constant for 30 minutes; SP B2 , SP A5 Add the mixed powder released in step 1 into SP B1 In the high-speed and low-speed dual-speed mixer of the step, stirring at a low speed until the temperature of the mixed powder is not less than 100° C.; SP B3 , Stir the mixed powder for 15 to 20 minutes when the temperature is 100 to 110°C; SP B4 , add the antioxidant and Cast2 in the ratio, and stir at high speed for 3 to 5 minutes; SP B5 , SP B4 The mixed material obtained by stirring in the step is transferred into a low-speed mixer with a cooling function, and the temperature is reduced to room temperature under low-speed stirring to obtain modified calcium carbonate.

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