High strength sag-resistant polyethylene pipe composition and method of making and use thereof

Abstract

High-strength anti-sagging polyethylene pipe composition and its preparation method and application belong to the technical field of polyethylene modification. The problems of low density, low strength, poor anti-sagging property and inability to be applied to the field of large-diameter heat pipe in the prior art are solved. The polyethylene pipe composition includes 100 parts of high-density polyethylene, 3-10 parts of polyisobutylene, 0.18-0.35 parts of liquid crystal polymer, 0.06-0.15 parts of composite compatibilizer, 0.03-0.1 parts of acid absorbent, 0.05-0.12 parts of antioxidant 1, 0.04-0.12 parts of antioxidant 2 and 0.03-0.1 parts of antioxidant 3 by weight. After a small amount of polyisobutylene and liquid crystal polymer are added to the high-density polyethylene and cross-linking and blending are carried out, the crystallization behavior of the polyethylene can be changed, and the processability, pressure strength, melt strength and fast crack resistance of the polyethylene are improved.

Description

TECHNICAL FIELD

[0001] The present application relates to a high-strength anti-sagging polyethylene pipe composition and its preparation method and application, which utilizes liquid crystal polymer powder and polyisobutylene to synergistically modify high-density polyethylene (HDPE), and belongs to the technical field of polyethylene modification. BACKGROUND

[0002] At present, PE100 grade and PE-RT II type two high-pressure resistant pipe materials are mainly used for domestic water supply pipes, gas pipes and heat pipes, and the demand is expected to be about 3.8 million tons by 2025. The raw materials for large-diameter heat pipes basically rely on imported resins, and their prices are more than 500 yuan / ton higher than those of PE80 grade polyethylene pipe materials, which have high economic benefits. At the same time, with the promotion of city reconstruction and plastic replacing steel, the demand for high-pressure resistant pipe materials will also increase year by year. Domestic polyethylene pressure-resistant pipe materials are mainly PE60 grade and PE80 grade, which have great limitations in application scope, and the formed pipe materials have low density, low strength and poor anti-sagging property, which cannot be applied to large-diameter heat pipe field.

[0003] The main reason for the difference in the performance of pipe special-purpose HDPE resins is the different distribution of comonomers (such as 1-butene, 1-hexene and other alpha-olefins) on polyethylene molecular chains of different lengths. Due to the existence of comonomers, the molecular chains of pipe special-purpose HDPE contain a small amount of short branches, and there are differences in the distribution within and between molecules, which leads to different lengths of crystallizable methylene sequences, and further affects the crystallization behavior and macroscopic properties of HDPE. It is found in practical application that the ethylene polymer prepared by using a metallocene catalyst has low melt viscosity and is prone to sagging during extrusion molding of large-diameter pipes. The sagging causes uneven wall thickness during welding after molding or during molding, which affects the quality of the pipe. Therefore, the ethylene polymer prepared by using a metallocene catalyst can only be used for molding small-diameter pipes (such as pipes with a diameter of 32 mm or less), and the pipe should not be welded by melting.

[0004] In the prior art, some improvements have been made for the pipe special-purpose HDPE, but mainly for how to improve the environmental stress cracking resistance of HDPE, such as:

[0005] CN 102924774B discloses a pipe special-purpose polyethylene resin composition, which is based on HDPE resin, and the environmental stress cracking resistance of the resin is improved by using ultra-low-density polyethylene (ULDPE) weather-resistant masterbatch and organic peroxide micro-crosslinking modification. However, three times of screw extrusion processing is required, which has high processing cost.

[0006] CN 106232638A discloses a polyolefin with excellent environmental stress cracking resistance, a high molecular weight, wide molecular weight distribution and high long chain branching content polyolefin is prepared by polymerization reaction, which has excellent environmental cracking resistance and processability. But the polymerization process needs a lot of investment, high cost, difficulty.

[0007] CN 105924584A discloses a long-chain branched high-density polyethylene material with environmental stress cracking resistance, which is modified by long-chain branching of high-density polyethylene by adding a di-functional grafting monomer by melt reaction processing to improve its environmental stress cracking resistance, but the processing fluidity is reduced, and the reaction is not easy to control.

[0008] With the progress of technology and the continuous improvement of the long-term pressure performance and safety of the pipe material, it is necessary to improve the strength and anti-sag performance of the pipe material, and to open up the application field of higher standard pipe material. SUMMARY

[0009] One of the purposes of the present application is to provide a polyethylene pipe material composition, and further to provide a polyethylene pipe prepared from the polyethylene pipe material composition, which has the advantages of excellent processability, good anti-sag performance, is suitable for high-speed processing, and the pressure strength and melt strength are significantly improved, which is beneficial to ensure that the pipe material meets the performance requirements and service life requirements in different use environments.

[0010] The second purpose of the present application is to provide a preparation method of a polyethylene pipe material composition, which is simple, easy to operate, energy-saving and environment-friendly.

[0011] The technical scheme adopted by the present application to achieve the above purposes is as follows.

[0012] The polyethylene pipe material composition of the present application comprises, by weight:

[0013]

[0014]

[0015] The composite compatibilizer is a mixture of EVA-G-MAH and metal salt of hexahydrophthalic acid in a mass ratio of (1.5-2.8):1; antioxidant 1 is a symmetrical hindered phenolic antioxidant, antioxidant 2 is a phosphite antioxidant, and antioxidant 3 is a semi-hindered phenolic antioxidant.

[0016] Preferably, the HDPE has a density of 0.936-0.948 g / cm 3; 190°C, 2.16 kg, melt flow rate (MFR) of 0.1-1.0 g / 10 min; relative content of lamellae having a thickness of 10 nm or more is between 72-80%, relative content of lamellae having a thickness of 6.2 nm or less is between 4.1-5.2%; weight average molecular weight (Mw) is greater than 170,000, content of molecular weight of 1,000,000 or more is greater than 0.38%, molecular weight distribution is between 15-25; comonomer is an α-olefin, comonomer content is between 0.71-0.96 mol%, number of branches / 1,000 C is between 3.42-5.49; more preferably, the density of the HDPE is between 0.940-0.945 g / cm 3 ; more preferably, the MFR of the HDPE is between 0.15-0.22 g / 10 min; more preferably, the comonomer of the HDPE is 1-hexene; more preferably, the molecular weight distribution of the HDPE is between 18-22; more preferably, the number of branches / 1,000 C of the HDPE is between 4.62-5.23.

[0017] Preferably, the HDPE is produced using a gas phase process, a metallocene catalyst, a reaction temperature of 92-94°C, a reaction pressure of 2.2-2.4 MPa, and a molar ratio of aluminum to zirconium in the metallocene catalyst of (3-8): 1; more preferably, the molar ratio of aluminum to zirconium is (3.2-6.5): 1.

[0018] Preferably, the liquid crystal polymer is added in an amount of 0.21-0.28 parts.

[0019] Preferably, the polyisobutylene has a weight average molecular weight of between 7.5-10.5 million.

[0020] Preferably, the polyisobutylene is added in an amount of 4-8 parts.

[0021] Preferably, in the composite compatibilizer, the grafting rate of EVA-G-MAH is between 1.5-1.8%, the MFR is between 2.1-2.6 g / 10 min, the VA content is between 18-22%, and the metal salt of hexahydrophthalic acid is calcium hexahydrophthalate.

[0022] Preferably, the composite compatibilizer is added in an amount of 0.07-0.1 parts.

[0023] Preferably, the acid absorbent is zinc stearate.

[0024] Preferably, the acid absorbent is added in an amount of 0.05-0.08 parts.

[0025] Preferably, the antioxidant 1 comprises one or more of tetra[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionic acid]pentaerythritol ester, n-octadecyl β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate, 1,3,5-trimethyl-2,4,6-tris(3,5-di-tert-butyl-4-hydroxybenzyl)benzene, 1,3,5-tris(3,5-di-tert-butyl-4-hydroxybenzyl)-1,3,5-triazine-2,4,6(1H,3H,5H)-trione; more preferably, tetra[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionic acid]pentaerythritol ester.

[0026] Preferably, the antioxidant 1 is added in an amount of 0.06-0.1 parts.

[0027] Preferably, the antioxidant 2 comprises one or more of tris[2.4-di-tert-butylphenyl]phosphite, bis(2,4-di-tert-butylphenyl)pentaerythritol diphosphite, pentaerythritol di-stearyl diphosphite, bis(2,4-tert-butylphenyl)pentaerythritol diphosphite; more preferably, tris[2.4-di-tert-butylphenyl]phosphite.

[0028] Preferably, the antioxidant 2 is added in an amount of 0.05-0.08 parts.

[0029] Preferably, the antioxidant 3 is a semi-hindered phenolic antioxidant 1790.

[0030] Preferably, the antioxidant 3 is added in an amount of 0.06-0.08 parts.

[0031] The method for preparing the polyethylene pipe composition of the present application comprises the following steps:

[0032] Step one, respectively take each raw material by weight parts;

[0033] Step two, first dissolve the composite compatibilizer and the liquid crystal polymer in the organic solvent, then mix with polyisobutylene uniformly, after the organic solvent is completely volatilized, mix with high-density polyethylene, acid absorbent, antioxidant 1, antioxidant 2 and antioxidant 3 uniformly, and then stand for 5-10 min under the condition of 60-70℃, to obtain the polyethylene pipe composition.

[0034] Preferably, the mixing condition of polyisobutylene uniformly is that the mixing temperature is 45-52℃ and the mixing time is 21-25 min.

[0035] Preferably, the mixing condition of high-density polyethylene, acid absorbent, antioxidant 1, antioxidant 2 and antioxidant 3 uniformly is that first stir at 300-500 r / min for 2-3 min, then stir at 1300-16500 r / min for 5-10 min, and the stirring temperature is 60-70℃.

[0036] Preferably, the organic solvent is dibutoxymethane, and the amount of the organic solvent added is 25-30 times the total weight of the composite compatibilizer.

[0037] The present application also provides a polyethylene pipe prepared from the polyethylene pipe composition.

[0038] Preferably, the polyethylene pipe composition is extrusion granulated to obtain the polyethylene pipe.

[0039] More preferably, the extrusion granulation is performed under the following conditions: the screw length-diameter ratio is 50-58, the gap between the screw and the barrel is 0.25-0.4 mm, the screw rotation speed is 200-250 r / min, the feeding speed is 120-130 r / min, the residence time of the polyethylene pipe composition in the screw is 6-7 min, the minimum granulation temperature is 190-200℃, the maximum granulation temperature is 250-260℃, and the cooling water temperature is below 30℃.

[0040] Compared with the prior art, the present application has the following advantages:

[0041] The polyethylene pipe composition of the present application is based on HDPE, and a small amount of polyisobutylene and LCP are added to the HDPE by limiting the molecular structure of the HDPE and the components, and then the mixture is compatibilized and blended by a specific preparation method. The molecular chains of different lengths and side chains interact with each other, and the balance between the molecular chain entanglement and the crystallinity is achieved. The crystallization behavior of the polymer is changed, and the processability, pressure strength, melt strength, and rapid crack resistance of the polyethylene pipe prepared therefrom are improved. The polyethylene pipe composition can be used to produce pressure pipes with different specifications of 10-120 mm in diameter, and the surface of the pipe is smooth without crystal points.

[0042] The preparation method of the polyethylene pipe composition and the preparation method of the polyethylene pipe are simple, easy to implement, energy-saving, and environmentally friendly. DETAILED DESCRIPTION

[0043] In order to further understand the present application, the preferred embodiments of the present application are described below, but it should be understood that these descriptions are only for further illustrating the features and advantages of the present application, and are not limitations of the claims of the present application.

[0044] The polyethylene pipe composition of the present application comprises, by weight, 100 parts of HDPE, 3-10 parts of polyisobutylene, 0.18-0.35 parts of liquid crystal polymer (LCP), 0.06-0.15 parts of a composite compatibilizer, 0.03-0.1 parts of an acid absorbent, 0.05-0.12 parts of antioxidant 1, 0.04-0.12 parts of antioxidant 2, and 0.03-0.1 parts of antioxidant 3. The composition can also consist only of the above components.

[0045] In the embodiment, the HDPE has a suitable density to ensure that the pipe has high strength. The HDPE used in the embodiment has a density of 0.936-0.948 g / cm 3 , preferably 0.940-0.945 g / cm 3 . The density is tested according to GB / T 1033.2-2010, using the D method, and is tested after boiling for 30 min. Large-diameter pipes require pipe materials with high sag resistance. The lower the MFR of the polymer, the better the sag resistance. However, too high MFR will reduce the sag resistance, and too low MFR will affect the processability. The HDPE used in the embodiment has an MFR of 0.1-1.0 g / 10 min, preferably 0.15-0.22 g / 10 min. The MFR can be tested according to GB / T 3682-2000, under the conditions of 190℃ and a load of 2.16 kg. A wide molecular weight distribution and a large weight average molecular weight are beneficial to the pipe having high pressure strength and mechanical properties, and can also ensure that the pipe has good processability. The HDPE used in the embodiment has a Mw of greater than 170,000, and the content of the portion with a molecular weight of greater than 1,000,000 is greater than 0.38%. A high molecular weight and a high content of the high molecular weight portion are beneficial to improving the mechanical properties of the pipe. The molecular weight distribution is 15-25, preferably 18-22. The molecular weight distribution can ensure the processability of the pipe. In this way, the molecular weight and the molecular weight distribution ensure that the pipe has certain mechanical strength and good processability. The molecular weight and the molecular weight distribution can be determined by gel permeation chromatography (GPC). The chromatographic column is two columns connected in series. The solvent and the mobile phase are both 1,2,4-trichlorobenzene containing 0.1% antioxidant 2,6-dibutyl-p-cresol. The column temperature is 150℃. The dissolution time is 4 h. The flow rate is 1.0 ml / min. A narrow-distribution polystyrene standard is used for universal calibration. In addition, the melt strength is related to the degree of entanglement of the molecular chain. The higher the number of branches, the higher the degree of entanglement of the molecular chain, and the higher the melt strength. The pipe requires high melt strength to meet the needs of high-speed traction and large-diameter pipe forming during extrusion. The comonomer of the HDPE used in the embodiment is an α-olefin, preferably 1-hexene. The molar percentage content of the comonomer is 0.71-0.96 mol%. The number of branches per 1,000 C is 3.42-5.49, preferably 4.62-5.23. The comonomer and the end-methyl content of the HDPE can be analyzed by carbon spectrum nuclear magnetic resonance. The specific analysis method is known in the art. The number of branching points is tested by nuclear magnetic resonance. First, 75 mg of the sample is placed in a 5 mm sample tube, 0.5 mL of deuterated o-dichlorobenzene solvent is added, and the sample tube is kept in a 140℃ constant temperature bath for 3-4 h to make it uniformly dispersed. Then, the prepared sample tube is placed in a nuclear magnetic resonance spectrometer. After being stabilized at a test temperature of 125℃ for 30 min, the sample is scanned (pulse angle 90 °, pulse interval 5 s, spectral width 220 ppm, combined pulse decoupling); after the scan is completed, the spectrum is processed and the spectral peaks in the range 5-50 ppm are accurately integrated (with the isolated -CH2- peak in the polymer being scaled to 30 ppm). The Mw and the number of branches affect the reaction effect and synergy of the auxiliary in the formula, and then affect the chain structure of the polymer. In addition, the HDPE used in the embodiment has a lamella content of 72-80% at a thickness of 10 nm or more, and a relative lamella content of 4.1-5.2% at a thickness of 6.2 nm or less. Preferably, the HDPE is subjected to crystallization heat fractionation analysis by DSC, and the specific analysis method is a prior art.

[0046] In the embodiment, the HDPE can be prepared by a Unipol gas phase process, which is a prior art. The embodiment provides a method, but is not limited thereto: ethylene, hydrogen and comonomer are introduced into a gas phase fluidized bed reactor to react under the action of a catalyst to generate high-density polyethylene resin; the reaction pressure in the gas phase fluidized bed is controlled at 2.2-2.4 MPa, and the ethylene partial pressure is 80-90%; the reaction temperature affects the speed of the polymerization reaction, and has a significant influence on the hydrogen sensitivity of the catalyst, thereby affecting the molecular weight of the product. The higher the reaction temperature, the lower the molecular weight of the product, and the higher the melt mass flow rate. Preferably, the reaction temperature is controlled at 92-94°C. Hydrogen, as a chain transfer agent, must occupy a certain concentration in the reactor to adjust the melt flow rate of the product. The hydrogen / ethylene molar ratio of the present application is preferably 0.0025-0.015. The density of the product decreases with the increase of the comonomer content in the reactor. The comonomer is preferably an α-olefin, such as 1-butene, 1-hexene, etc., preferably 1-hexene. The hexene / ethylene molar ratio is the main factor affecting the density of the product, and the hexene / ethylene molar ratio is preferably 0.003-0.015. The catalyst is a metallocene catalyst supported on a carrier. The carrier is preferably SiO2. The average particle size of the carrier is 30 μm. The surface area of the carrier is between 3-420 m 2 / g. The average diameter of the pores of the carrier is between 0.01-3 μm. The metallocene is aluminum and zirconium. The preparation method of the metallocene catalyst is as follows: first, activate the carrier at 200-300°C, then add benzene, n-pentane, isopentane or hexane, after 2-3 h, add methylaluminoxane (MAO) and stir for 2-2.5 h, then add di(n-butylcyclopentadienyl)zirconium dichloride and stir for 2-2.5 h to obtain the metallocene catalyst. The aluminum / zirconium ratio will affect the molecular weight distribution of the product. The molar ratio of aluminum / zirconium is preferably (3-8):1, and more preferably (3.2-6.5):1.

[0047] In the embodiment, the LCP is a white solid powder, which can be commercially available. The LCP is preferably added in an amount of 0.21-0.28 parts. The LCP functions as a nucleating agent in the HDPE matrix, promotes the crystallization process of the HDPE, narrows the grain size distribution, makes the crystal more perfect and regular, and improves the mechanical strength. The reduction of the [2 0 0] and [1 1 0] crystal plane sizes of the polyethylene pipe is more beneficial to the improvement of the strength.

[0048] In the embodiment, the polyisobutylene can be commercially available. The weight average molecular weight of the polyisobutylene is between 75,000 and 105,000. The polyisobutylene is preferably added in an amount of 4-8 parts. A small amount of the polyisobutylene added to the polyethylene can improve the melt strength and impact strength of the polyethylene pipe.

[0049] In the embodiment, the composite compatibilizer is preferably added in an amount of 0.07-0.1 parts. The composite compatibilizer is a mixture of EVA-G-MAH and a metal salt of hexahydrophthalic acid in a mass ratio of (1.5-2.8):1. In the composite compatibilizer, the two compounds of EVA-G-MAH and the metal salt of hexahydrophthalic acid are used simultaneously to bring a better synergistic effect, have a higher reactivity, have excellent coupling compatibility, can increase the compatibility between various components, increase the number of branches in the polyethylene molecules, and improve the entanglement effect of the molecular chain. The anhydride groups of the EVA-G-MAH react with the terminal hydroxyl groups of the LCP to produce a compatibilization effect in situ, and enhance the bonding strength between the pipe interfaces. In the embodiment, the grafting rate of the EVA-G-MAH is 1.5-18%, preferably 1.6%, the MFR is 2.1-2.6 g / 10 min, preferably 2.4 g / 10 min, and the VA content is 18-22%, preferably 20%. The EVA-G-MAH can be commercially available, and the metal salt of hexahydrophthalic acid is preferably calcium hexahydrophthalate, which can be commercially available.

[0050] When the pipe material is in contact with air, it will be oxidized by the oxygen in the air, which is a typical free radical reaction. The present embodiment adds a compounded antioxidant to the pipe material, which can react with the oxidation free radicals R. and ROO. generated by oxidation in the pipe material, interrupt the growth of active chains, thereby effectively inhibiting or reducing the degradation and aging process of the pipe material, and prolonging the service life of the pipe material. The three antioxidants of the present embodiment have good synergistic effect, and the antioxidant effect is better. Among them, the antioxidant 1 is a symmetrical hindered phenolic compound, which can be selected from one or more of tetra[β-(3,5-di-tert-butyl-4-hydroxyphenyl) propionic acid] pentaerythritol ester, β-(3,5-di-tert-butyl-4-hydroxyphenyl) propionic acid n-octadecyl ester, 1,3,5-trimethyl-2,4,6-tris(3,5-di-tert-butyl-4-hydroxybenzyl) benzene, 1,3,5-tris(3,5-di-tert-butyl-4-hydroxybenzyl)-1,3,5-triazine-2,4,6(1H,3H,5H)-trione, preferably tetra[β-(3,5-di-tert-butyl-4-hydroxyphenyl) propionic acid] pentaerythritol ester, and the addition amount is preferably 0.06-0.1 parts. The antioxidant 2 is a phosphite compound, which can be selected from one or more of tris[2.4-di-tert-butylphenyl] phosphite, bis(2,4-di-tert-butylphenol) pentaerythritol diphosphite, pentaerythritol distearyl diphosphite, bis(2,4-tert-butylphenyl) pentaerythritol diphosphite, etc., preferably tris[2.4-di-tert-butylphenyl] phosphite, and the addition amount is preferably 0.05-0.08 parts. The antioxidant 3 is a semi-hindered phenolic antioxidant, preferably semi-hindered phenolic antioxidant 1790, and the addition amount is preferably 0.06-0.08 parts.

[0051] The acid absorber of the present embodiment is preferably zinc stearate, and the addition amount is preferably 0.05-0.08 parts.

[0052] The preparation method of the polyethylene pipe material composition of the present application comprises the following steps:

[0053] Step one, respectively weigh each raw material by parts;

[0054] Step two, first dissolve the composite compatibilizer and LCP in the organic solvent, then add it into the high-speed mixer and mix with polyisobutylene, the mixing temperature is 45-52℃, the mixing time is 21-25min, after the organic solvent is completely volatilized, then add high-density polyethylene, acid absorber, antioxidant 1, antioxidant 2 and antioxidant 3 into the high-speed mixer and mix, first stir at 300-500r / min for 2-3min, then stir at 1300-16500r / min for 5-10min, the stirring temperature is 60-70℃, after stopping stirring, stand for 5-10min at 60-70℃, preferably 6min, to obtain the polyethylene pipe material composition.

[0055] In the embodiment, the organic solvent is preferably dibutoxymethane, and the amount of the organic solvent added is 25-30 times the total weight of the composite compatibilizer.

[0056] The polyethylene pipe composition of the present application can be used to prepare a polyethylene pipe. Preferably, the polyethylene pipe composition is added to an extruder for extrusion granulation, and after cooling, a polyethylene pipe is obtained. The extrusion conditions are as follows: the length-diameter ratio of the screw of the extruder is 50-58, the gap between the screw and the barrel is 0.25-0.4 mm, the screw rotation speed is 200-250 r / min, the feeding speed is 120-130 r / min, the lowest granulation temperature is 190-200 °C, the highest granulation temperature is 250-260 °C, and the residence time of the polyethylene pipe composition in the screw is 6-7 min, so as to facilitate the full play of the synergistic effect of various additives; and the cooling water temperature is below 30 °C.

[0057] The polyethylene pipe of the embodiment has good processability and high melt strength. The melt strength reflects the extension resistance and melt sag resistance of the polymer melt. The high melt strength can meet the needs of high-speed traction and large-diameter pipe forming. At the same time, the pipe has excellent resistance to rapid crack propagation. The excellent resistance to rapid crack propagation can effectively solve the problems caused by scratches and scratches during pipe construction and use. In addition, the pipe still has high heat-oxidative aging resistance under long-term use conditions, and the pipe surface is smooth and free of crystal points.

[0058] In the present application, the terms used generally have the meanings commonly understood by those of ordinary skill in the art, unless otherwise defined.

[0059] In order for those skilled in the art to better understand the technical solutions of the present application, the present application will be further described in detail below with reference to the embodiments.

[0060] In the following examples, various processes and methods that are not described in detail are conventional methods known in the art. The materials, reagents, devices, instruments, equipment, etc. used in the following examples can be obtained from commercial channels unless otherwise specified.

[0061] Example 1

[0062] The polyethylene pipe composition comprises, by weight, 100 parts of HDPE, 7.5 parts of polyisobutylene (weight average molecular weight 100,000), 0.25 parts of DuPont 6130LX (LCP), 0.1 parts of a composite compatibilizer (a mixture of DuPont 30E868 EVA-G-MAH and calcium hexahydrophthalate at a ratio of 2.8:1, the grafting rate of EVA-G-MAH being 1.6%, the MFR being 2.4 g / 10 min, and the VA content being 20%), 0.06 parts of zinc stearate, 0.1 parts of antioxidant 1010, 0.08 parts of antioxidant 168, and 0.08 parts of antioxidant 1790.

[0063] wherein the HDPE has a density of 0.942 g / cm 3 , MFR of 0.20 g / 10 min (190°C, 2.16 kg), content of molecular weight 100 million or more of 0.40, Mw of 19.5 million, molecular weight distribution of 20, number of branches per 1000C of 4.75, content of lamella of 10 nm or more of 76%, content of lamella of 6.2 nm or less of 5.2%, and hexene molar content of 0.96 mol%. The polyethylene pipe composition is prepared by a gas phase process using a metallocene catalyst, with the reaction temperature controlled at 94°C, the reaction pressure controlled at 2.3 MPa, the ethylene partial pressure at 80%, and the molar ratio of aluminum to zirconium in the metallocene catalyst at 3.2:1.

[0064] The method for preparing the polyethylene pipe composition comprises the following steps:

[0065] Step one, each raw material is weighed by weight parts;

[0066] Step two, the composite compatibilizer and LCP are first dissolved in dibutoxymethane (the addition amount is 25-30 times the total weight of the composite compatibilizer), and then mixed with polyisobutylene in a high-speed mixer, the mixing temperature is 45-52°C, and the mixing time is 21-25 min; after the dibutoxymethane is completely volatilized, the HDPE, the acid absorbent, the antioxidant 1, the antioxidant 2, and the antioxidant 3 are added into the high-speed mixer, and stirred at 300-500 r / min for 2-3 min, and then stirred at 1300-16500 r / min for 5-10 min, the stirring temperature is 60-70°C, and after stopping stirring, the polyethylene pipe composition is obtained by standing at 60-70°C for 6 min.

[0067] The method for preparing the polyethylene pipe using the polyethylene pipe composition comprises the following steps:

[0068] The polyethylene pipe composition is added into an extruder for extrusion and granulation to obtain the polyethylene pipe; the length-diameter ratio of the screw of the extruder is 50-58, the gap between the screw and the barrel is between 0.25-0.4 mm, the lowest granulation temperature is 190-200°C, the highest granulation temperature is 250-260°C, the screw rotation speed is 200-250 r / min, the feeding speed is 120-130 r / min, the residence time of the polyethylene pipe composition in the screw is 6-7 min, and the cooling water temperature is below 30°C.

[0069] Example 2

[0070] A polyethylene pipe composition comprising, in parts by weight, 100 parts of HDPE, 8 parts of polyisobutylene (weight average molecular weight 75,000), 0.28 parts of DuPont 6130LX (LCP), 0.1 parts of a composite compatibilizer (a mixture of DuPont 30E868 EVA-G-MAH and calcium hexahydrophthalate at a ratio of 1.5:1, the grafting rate of EVA-G-MAH being 1.6%, MFR being 2.4 g / 10 min, VA content being 20%), 0.06 parts of zinc stearate, 0.08 parts of antioxidant 1010, 0.05 parts of antioxidant 168, 0.07 parts of antioxidant 1790;

[0071] wherein the HDPE has a density of 0.941 g / cm 3 MFR of 0.22 g / 10 min (at 190°C, 2.16 kg), a molecular weight of 1 million or more, a content of 0.39, Mw of 190,000, a molecular weight distribution of 18, a number of branches per 1,000 C of 5.23, a content of lamellae of 80% or more in thickness of 10 nm, a content of lamellae of 4.1% or less in thickness of 6.2 nm, and a comonomer content of 0.83 mol%. The polyethylene pipe composition is prepared by a gas phase process using a metallocene catalyst, the reaction temperature being controlled at 94°C, the reaction pressure being controlled at 2.3 MPa, the ethylene partial pressure being 80%, and the molar ratio of aluminum to zirconium in the metallocene catalyst being 6.1:1.

[0072] The polyethylene pipe composition is prepared by the method of Example 1.

[0073] The polyethylene pipe composition is prepared by the method of Example 1.

[0074] Example 3

[0075] A polyethylene pipe composition comprising, in parts by weight, 100 parts of HDPE, 8 parts of polyisobutylene (weight average molecular weight 75,000), 0.28 parts of DuPont 6130LX (LCP), 0.1 parts of a composite compatibilizer (a mixture of DuPont 30E868 EVA-G-MAH and calcium hexahydrophthalate at a ratio of 1.5:1, the grafting rate of EVA-G-MAH being 1.6%, MFR being 2.4 g / 10 min, VA content being 20%), 0.06 parts of zinc stearate, 0.08 parts of antioxidant 1010, 0.05 parts of antioxidant 168, 0.07 parts of antioxidant 1790;

[0076] wherein the HDPE has a density of 0.941 g / cm 3, MFR is 0.15 g / 10 min (190°C, 2.16 kg), the content of the fraction with a molecular weight of 1 million or more is 0.42, Mw is 175,000, the molecular weight distribution is 21, the content of the lamella with a thickness of 10 nm or more is 72%, the content of the lamella with a thickness of 6.2 nm or less is 4.5%, the number of branches per 1,000 C is 4.62. The comonomer content is 0.71 mol%. The polyethylene pipe composition is prepared by a gas phase process using a metallocene catalyst, the reaction temperature is controlled at 94°C, the reaction pressure is controlled at 2.3 MPa, the ethylene partial pressure is 80%, and the molar ratio of aluminum to zirconium in the metallocene catalyst is 4.5:1.

[0077] The polyethylene pipe composition is prepared according to the method of Example 1.

[0078] The polyethylene pipe is prepared according to the method of Example 1.

[0079] Example 4

[0080] The polyethylene pipe composition comprises, by weight, 100 parts of HDPE, 7.5 parts of polyisobutylene (weight average molecular weight 90,000), 0.26 parts of DuPont 6130LX (LCP), 0.1 part of a composite compatibilizer (a mixture of DuPont 30E868 EVA-G-MAH and calcium hexahydrophthalate at a ratio of 2.5:1, the grafting rate of EVA-G-MAH being 1.6%, MFR being 2.4 g / 10 min, VA content being 20%), 0.07 parts of zinc stearate, 0.06 parts of antioxidant 1010, 0.07 parts of antioxidant 168, and 0.06 parts of antioxidant 1790.

[0081] The HDPE has a density of 0.945 g / cm 3 , MFR is 0.18 g / 10 min (190°C, 2.16 kg), the content of the fraction with a molecular weight of 1 million or more is 0.41, Mw is 185,000, the molecular weight distribution is 22, the content of the lamella with a thickness of 10 nm or more is 78%, the content of the lamella with a thickness of 6.2 nm or less is 5.0%, and the number of branches per 1,000 C is 5.01. The comonomer content is 0.90 mol%. The polyethylene pipe composition is prepared by a gas phase process using a metallocene catalyst, the reaction temperature is controlled at 94°C, the reaction pressure is controlled at 2.3 MPa, the ethylene partial pressure is 80%, and the molar ratio of aluminum to zirconium in the metallocene catalyst is 6.5:1.

[0082] The polyethylene pipe composition is prepared according to the method of Example 1.

[0083] The polyethylene pipe is prepared according to the method of Example 1.

[0084] Example 5

[0085] A polyethylene pipe composition comprising, in parts by weight, 100 parts of HDPE, 8 parts of polyisobutylene (weight average molecular weight 80,000), 0.21 parts of DuPont 6130LX (LCP), 0.1 parts of a composite compatibilizer (a mixture of DuPont 30E868 EVA-G-MAH and calcium hexahydrophthalate in a ratio of 2.1:1, the grafting rate of EVA-G-MAH being 1.6%, MFR being 2.4 g / 10 min, and VA content being 20%), 0.055 parts of zinc stearate, 0.09 parts of antioxidant 1010, 0.075 parts of antioxidant 168, and 0.075 parts of antioxidant 1790 is prepared.

[0086] The HDPE has a density of 0.943 g / cm 3 MFR of 0.19 g / 10 min (at 190°C and 2.16 kg), a molecular weight of 1 million or more, a content of 0.43, a Mw of 180,000, a molecular weight distribution of 19, a content of lamellar crystals of 75% or more in thickness of 10 nm, a content of lamellar crystals of 4.8% or less in thickness of 6.2 nm, a number of branches per 1,000 C of 4.89, and a comonomer content of 0.75 mol%. The polyethylene is prepared by a gas phase process using a metallocene catalyst, the reaction temperature is controlled at 94°C, the reaction pressure is controlled at 2.3 MPa, the ethylene partial pressure is 80%, and the molar ratio of aluminum to zirconium in the metallocene catalyst is 4.0:1.

[0087] The polyethylene pipe composition is prepared according to the method of Example 1.

[0088] The polyethylene pipe is prepared according to the method of Example 1.

[0089] Comparative Example 1

[0090] The polyethylene pipe composition is prepared according to the method of Example 1 using the same raw materials as in Example 1, except that 7.5 parts of polyisobutylene is not added. The polyethylene pipe is prepared according to the method of Example 1.

[0091] Comparative Example 2

[0092] The polyethylene pipe composition is prepared according to the method of Example 1 using the same raw materials as in Example 1, except that 0.25 parts of liquid crystal polymer (LCP) is not added. The polyethylene pipe is prepared according to the method of Example 1.

[0093] Comparative Example 3

[0094] The polyethylene pipe composition is prepared according to the method of Example 1 using the same raw materials as in Example 1, except that 0.1 parts of the composite compatibilizer is replaced by 0.1 parts of liquid oil. The polyethylene pipe is prepared according to the method of Example 1.

[0095] Comparative Example 4

[0096] The polyethylene pipe composition was prepared in the same way as in Example 2, except that the compatibilizer and LCP in Step 2 were mixed directly with the polyisobutylene without dissolving in dibutoxymethane. The polyethylene pipe composition was prepared into a polyethylene pipe in the same way as in Example 1.

[0097] Comparative Example 5

[0098] Commercially available heat-resistant polyethylene pipe, 4731B, from Basell USA.

[0099] The samples of Examples 1-5 and Comparative Examples 1-5 were subjected to performance testing.

[0100] The testing methods were as follows:

[0101] Rapid crack propagation (RCP) is a type of failure related to rapid unstable propagation of a longitudinal crack in a pressurized plastic pipe. If RCP occurs, the crack in the pipe can propagate several hundred meters instantaneously, causing a serious safety accident. Therefore, the RCP resistance is an important property of a pipe. ASTM F2231 provides a test method for evaluating the RCP resistance of a pipe by PAC method, i.e. Charpy simple supported beam impact test.

[0102] The melt strength test temperature was 190°C, the screw rotation speed was 20 r / min, the tensile acceleration was 20 mm / s2, and the force at the time of melt fracture was taken as the melt strength value.

[0103] Oxidation induction time (OIT) was tested according to GB / T 19466.6-2009, using an aluminum cup at 210°C.

[0104] Notched Charpy impact strength was tested according to GB / T 1043.1-2008, using a type A notch at 23°C.

[0105] Load deflection temperature was tested according to GB / T 1634.2-2004. A high load deflection temperature is beneficial to the application of a pipe at high temperatures (above 60°C).

[0106] Short-term hydrostatic strength was tested according to GB / T 18252-2000.

[0107] Grain size test: X-ray diffraction method.

[0108] Appearance: A pipe with a specification of 110*10 mm was prepared using the polyethylene pipe.

[0109] Extrusion processing current refers to the extrusion current generated under the same process conditions when a pipe with a specification of 110*10 mm is prepared using the polyethylene pipe.

[0110] Table 1 Grain size of samples of Examples 1-5 and Comparative Examples 1-5

[0111]

[0112] Table 2 Overall performance of samples of Examples 1-5 and Comparative Examples 1-5

[0113]

[0114] Table 3 Appearance of pipes produced from samples of Examples 1-5 and Comparative Examples 1-5

[0115] Sample Pipe surface Example 1 Smooth Example 2 Smooth Example 3 Smooth Example 4 Smooth Example 5 Smooth Comparative Example 1 Slightly smooth Comparative Example 2 With crystals Comparative Example 3 With crystals Comparative Example 4 Smooth Comparative Example 5 With crystals

[0116] Obviously, the above examples are merely illustrative in nature and are not intended to limit the examples. Other variations and modifications of the examples can occur to those skilled in the art upon consideration of the foregoing description. It is intended that the following claims be interpreted as encompassing all such variations and modifications.

Claims

1. A polyethylene pipe composition, characterized in that, By weight, comprising: High density polyethylene 100 parts; Polyisobutylene 3-10 parts; Liquid crystal polymer 0.18-0.35 parts; Composite compatibilizer 0.06-0.15 parts; Acid absorbent 0.03-0.1 parts; Antioxidant 10.05-0.12 parts; Antioxidant 20.04-0.12 parts; Antioxidant 30.03-0.1 parts; The composite compatibilizer is a mixture of EVA-G-MAH and metal salt of hexahydrophthalic acid in a mass ratio of (1.5-2.8):1; antioxidant 1 is a symmetrical hindered phenolic antioxidant, antioxidant 2 is a phosphite antioxidant, and antioxidant 3 is a semi-hindered phenolic antioxidant; said high density polyethylene: density 0.936-0.948 g / cm 3 ; melt flow rate at 190°C, 2.16 kg 0.1-1.0 g / 10 min; weight average molecular weight greater than 170,000; fraction of molecular weight above 1 million greater than 0.38%, molecular weight distribution 15-25; number of branches per 1000C 3.42-5.49; The weight average molecular weight of the polyisobutylene is between 75,000 and 105,000; The preparation method of the polyethylene pipe composition comprises the following steps: Step one, respectively weigh each raw material by weight parts; Step two, first dissolve the composite compatibilizer and the liquid crystal polymer in the organic solvent, the organic solvent is dibutoxymethane, then mix with polyisobutylene uniformly, after the organic solvent is completely volatilized, mix with high density polyethylene, acid absorbent, antioxidant 1, antioxidant 2 and antioxidant 3 uniformly, stand for 5-10 min under the condition of 60-70℃, get the polyethylene pipe composition.

2. The polyethylene pipe composition of claim 1, wherein The high density polyethylene: the relative content of lamellar phase with thickness of more than 10 nm is between 72-80%, and the relative content of lamellar phase with thickness of less than 6.2 nm is between 4.1-5.2%; the comonomer is alpha-olefin, and the comonomer molar percentage content is 0.71-0.96mol%.

3. The polyethylene pipe composition of claim 1, wherein The high density polyethylene is prepared by gas phase process with metallocene catalyst, the reaction temperature is 92-94℃, the reaction pressure is 2.2-2.4MPa, and the molar ratio of aluminum and zirconium in the metallocene catalyst is (3-8):1; In the composite compatibilizer, the grafting rate of EVA-G-MAH is 1.5-1.8%, the melt flow rate is 2.1-2.6g / 10min, and the VA content is 18-22%; The metal salt of hexahydrophthalic acid is calcium hexahydrophthalate; The acid absorbent is zinc stearate.

4. The polyethylene pipe composition according to claim 1, wherein The antioxidant 1 includes one or more of tetra[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate]pentaerythritol ester, β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate n-octadecyl alcohol ester, 1,3,5-trimethyl-2,4,6-tris(3,5-di-tert-butyl-4-hydroxybenzyl)benzene, and 1,3,5-tris(3,5-di-tert-butyl-4-hydroxybenzyl)-1,3,5-triazine-2,4,6(1H,3H,5H)-trione; The antioxidant 2 includes one or more of tris[2.4-di-tert-butylphenyl]phosphite, bis(2,4-di-tert-butylphenol)pentaerythritol diphosphite, pentaerythritol distearyl diphosphite, and bis(2,4-tert-butylphenyl)pentaerythritol diphosphite; The antioxidant 3 is semi-hindered phenolic antioxidant 1790.

5. The polyethylene pipe composition according to claim 1, wherein the polyethylene pipe composition is prepared by mixing the polyethylene, the polyisobutylene, the high density polyethylene, the acid absorbent, the antioxidant 1, the antioxidant 2, the antioxidant 3 and the organic solvent under the following conditions: the polyethylene, the polyisobutylene, the high density polyethylene, the acid absorbent, the antioxidant 1, the antioxidant 2 and the antioxidant 3 are mixed at a temperature of 45-52°C for 21-25 minutes; and the organic solvent is added in an amount of 25-30 times the total weight of the composite compatibilizer.

6. A polyethylene pipe prepared from the polyethylene pipe composition according to any one of claims 1-5.

7. The polyethylene pipe according to claim 6, wherein the polyethylene pipe is prepared by extruding and granulating the polyethylene pipe composition according to any one of claims 1-5.

8. The polyethylene pipe according to claim 7, wherein the polyethylene pipe is prepared by extruding and granulating the polyethylene pipe composition according to any one of claims 1-5 under the following conditions: the length-diameter ratio of the screw is 50-58; the gap between the screw and the barrel is 0.25-0.4 mm; the rotation speed of the screw is 200-250 r / min; the feeding speed is 120-130 r / min; the residence time of the polyethylene pipe composition in the screw is 6-7 min; the minimum granulation temperature is 190-200°C; the maximum granulation temperature is 250-260°C; and the cooling water temperature is below 30°C.

9. The polyethylene pipe according to claim 7, wherein the polyethylene pipe is prepared by extruding and granulating the polyethylene pipe composition according to any one of claims 1-5 under the following conditions: the length-diameter ratio of the screw is 50-58; the gap between the screw and the barrel is 0.25-0.4 mm; the rotation speed of the screw is 200-250 r / min; the feeding speed is 120-130 r / min; the residence time of the polyethylene pipe composition in the screw is 6-7 min; the minimum granulation temperature is 190-200°C; the maximum granulation temperature is 250-260°C; and the cooling water temperature is below 30°C.

7. The method of producing a polyethylene pipe according to claim 6, characterized by, ​ 8. The method of producing a polyethylene pipe according to claim 7, characterized by, ​

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