High-strength sag-resistant polyethylene pipe composition as well as preparation method and application thereof

Abstract

The invention discloses a high-strength sag-resistant polyethylene pipe composition as well as a preparation method and application thereof, and belongs to the technical field of polyethylene modification. The problems that a polyethylene pipe in the prior art is low in density, low in strength, poor in sag resistance and incapable of being applied to the field of large-diameter thermal pipes are solved. The polyethylene pipe composition disclosed by the invention is prepared from the following components in parts by weight: 100 parts of high-density polyethylene, 3 to 10 parts of polyisobutene, 0.18 to 0.35 part of liquid crystal polymer, 0.06 to 0.15 part of composite compatilizer, 0.03 to 0.1 part of acid acceptor, 0.05 to 0.12 part of antioxidant 1, 0.04 to 0.12 part of antioxidant 2 and 0.03 to 0.1 part of antioxidant 3. According to the polyethylene pipe composition, a small amount of polyisobutene and a liquid crystal polymer are added into high-density polyethylene, and after cross-linking compatibility and blending melting, the crystallization behavior of polyethylene can be changed, and the processability, compression strength, melt strength and rapid crack resistance of polyethylene are improved.

Description

Technical Field

[0001] The invention relates to a high-strength anti-sag polyethylene pipe composition and a preparation method and application thereof. Liquid crystal polymer powder and polyisobutylene are used to synergistically perform composite modification on high-density polyethylene (HDPE), belonging to the technical field of polyethylene modification. Background Art

[0002] At present, domestic water pipes, gas pipes and thermal pipes mainly use two types of high-pressure grade pipe materials, PE100 and PE-RTⅡ. The demand is expected to be around 3.8 million tons by 2025. Among them, the raw materials in the field of large-diameter thermal pipes basically rely on imported resins, which are more than 500 yuan / ton higher than PE80 grade polyethylene pipe materials and have higher economic benefits. At the same time, with the advancement of urban transformation and the replacement of steel with plastic, the demand for high-pressure grade pipes will also increase year by year. Domestic polyethylene pressure-resistant pipes are mostly low-grade PE60 and PE80, with a large range of applications. The molded pipes have low density, low strength, and poor anti-sag properties, and cannot be used in the field of large-diameter thermal pipes.

[0003] An important reason for the difference in the performance of HDPE resin for pipes is the different distribution of comonomers (such as α-olefins such as 1-butene and 1-hexene) on polyethylene molecular chains of different lengths. Due to the presence of comonomers, the molecular chain of HDPE for pipes contains 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, which in turn affects the crystallization behavior and macroscopic properties of HDPE. In actual application, it was found that the ethylene polymer prepared by metallocene catalyst has low melt viscosity when extruding a larger diameter pipe, and sag is prone to occur during the extrusion process. During molding or hot melt welding after molding, sag causes uneven welding wall thickness, affecting the quality of the pipe. Therefore, ethylene polymers prepared by metallocene catalysts can only be used to mold small-diameter pipes (such as pipes with a diameter of less than 32mm), and pipes should not be melt welded.

[0004] In the prior art, some improvements have been made to the current HDPE pipe material, but they are mainly aimed at how to improve the environmental stress cracking resistance of HDPE, such as:

[0005] CN 102924774B discloses a polyethylene resin composition for pipes, which uses HDPE resin as a base material and improves the environmental stress cracking resistance of the resin through ultra-low density polyethylene (ULDPE) weathering masterbatch and organic peroxide micro-crosslinking modification. However, the process is processed by three-screw extrusion, which has high processing costs.

[0006] CN 106232638A discloses a polyolefin with excellent environmental stress cracking resistance, and prepares a polyolefin with high molecular weight, wide molecular weight distribution and high long chain branch content through polymerization reaction, which has excellent environmental cracking resistance and processability. However, the polymerization process requires a large amount of investment, high cost and great difficulty.

[0007] CN 105924584A discloses a long-chain branched high-density polyethylene material resistant to environmental stress cracking. The high-density polyethylene is modified by adding a difunctional grafting monomer to the material through a melt reaction processing method to improve its environmental stress cracking resistance. However, the processing fluidity is reduced and the reaction is difficult to control.

[0008] With the advancement of technology and the continuous improvement of the long-term pressure resistance and safety of pipes, it is necessary to improve the strength and anti-sag performance of pipes and explore higher standard pipe application areas. Summary of the invention

[0009] One of the purposes of the present invention is to provide a polyethylene pipe composition, and further to provide a polyethylene pipe prepared from the polyethylene pipe composition, wherein the polyethylene pipe has the advantages of excellent processability and good anti-sag property, is suitable for high-speed processing, and has significantly improved compressive strength and melt strength, which is conducive to ensuring that the pipe meets the performance requirements and service life requirements under different use environments.

[0010] The second object of the present invention is to provide a method for preparing a polyethylene pipe composition, which is simple, easy to operate, energy-saving and environmentally friendly.

[0011] The technical solutions adopted by the present invention to achieve the above-mentioned purpose are as follows.

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

[0013]

[0014]

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

[0016] Preferably, the HDPE has a density of 0.936-0.948 g / cm 3; Under the conditions of 190°C and 2.16kg, the melt flow rate (MFR) is 0.1-1.0g / 10min; the relative content of lamellae with a thickness of more than 10nm is between 72-80%, and the relative content of lamellae with a thickness of less than 6.2nm is between 4.1-5.2%; the weight average molecular weight (Mw) is greater than 170,000, of which the content of the part with a molecular weight of more than 1 million is greater than 0.38%, and the molecular weight distribution is 15-25; the comonomer is α-olefin, and the molar percentage of the comonomer is 0.71-0.96mol%, and the number of branches / 1000C is 3.42-5.49; more preferably, the density of the HDPE is 0.940-0.945g / cm 3 ; More preferably, the MFR of the HDPE is 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 18-22; More preferably, the number of branches / 1000C of the HDPE is 4.62-5.23.

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

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

[0019] Preferably, the weight average molecular weight of the polyisobutylene is between 75,000 and 105,000.

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

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

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

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

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

[0025] Preferably, the antioxidant 1 includes one or more of tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] pentaerythritol ester, 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, and 1,3,5-tris(3,5-di-tert-butyl-4-hydroxybenzyl)-1,3,5-triazine-2,4,6(1H,3H,5H)-trione; more preferably, tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] pentaerythritol ester.

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

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

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

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

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

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

[0032] Step 1, weigh each raw material by weight;

[0033] Step 2: first dissolve the composite compatibilizer and liquid crystal polymer into an organic solvent, then mix them evenly with polyisobutylene, and after the organic solvent is completely evaporated, mix them evenly with high-density polyethylene, acid absorber, antioxidant 1, antioxidant 2 and antioxidant 3, and let stand at 60-70° C. for 5-10 minutes to obtain a polyethylene pipe composition.

[0034] Preferably, the conditions for uniform mixing with polyisobutylene are: mixing temperature 45-52° C., mixing time 21-25 min.

[0035] Preferably, the conditions for uniformly mixing with high-density polyethylene, acid absorber, antioxidant 1, antioxidant 2 and antioxidant 3 are: first stirring at 300-500 r / min for 2-3 min, then stirring at 1300-16500 r / min for 5-10 min, and the stirring temperature is 60-70°C.

[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 invention also provides a polyethylene pipe prepared from the polyethylene pipe composition.

[0038] Preferably, the polyethylene pipe composition is extruded and pelletized to obtain the polyethylene pipe.

[0039] More preferably, the extrusion granulation conditions are: the screw aspect ratio is 50-58, the gap between the screw and the barrel is between 0.25-0.4 mm, the screw speed is 200-250 r / min, the feeding rate 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 granulation cooling water temperature is below 30°C.

[0040] Compared with the prior art, the present invention has the following beneficial effects:

[0041] The polyethylene pipe material composition of the invention is based on HDPE. By defining the molecular structure of HDPE and various added components, a small amount of polyisobutylene and LCP are added to HDPE by a specific preparation method, and after cross-linking and compatibility and blending and melting, the molecular chains of the main chain and the side chain of different lengths influence and act on each other, so as to achieve a balance between the entanglement of the molecular chains and the crystallinity, change the crystallization behavior of the polymer, improve the processability, compressive strength, melt strength and rapid crack resistance of the polyethylene pipe prepared by the composition, and can be used to produce pressure pipes of different specifications with a diameter of 10-120 mm, and the surface of the pipe is smooth and has no crystal points.

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

[0043] In order to further understand the present invention, preferred embodiments of the present invention are described below. However, it should be understood that these descriptions are only for further illustrating the features and advantages of the present invention, rather than limiting the claims of the present invention.

[0044] The polyethylene pipe composition of the present invention 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 composite compatibilizer, 0.03-0.1 parts of acid absorber, 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 may also consist of the above components alone.

[0045] In this embodiment, HDPE adopts a suitable density to ensure that the pipe has a high strength. The density of HDPE used in this embodiment is 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 the test is conducted after boiling for 30 minutes. The processing of large-diameter pipes requires the pipe to have a higher anti-sag performance. The lower the MFR of the polymer, the better its anti-sag performance is relatively speaking. Too high MFR will reduce its anti-sag performance, but too low MFR will affect its processing performance. The MFR of HDPE used in this embodiment is 0.1-1.0g / 10min, preferably 0.15-0.22g / 10min. MFR can be tested according to GB / T 3682-2000, with the test conditions of 190°C and a load of 2.16kg. The molecular weight distribution is wide and the weight-average molecular weight is large, which is conducive to making the pipe have higher compressive strength and mechanical properties, and can also ensure that the pipe has good processing performance; the HDPE Mw used in this embodiment is greater than 170,000, wherein the content of the part with a molecular weight of more than 1 million is greater than 0.38%, and the higher the molecular weight and the higher the content of the high molecular weight part, the better the mechanical properties of the pipe; the molecular weight distribution is 15-25, preferably 18-22, and the molecular weight distribution can ensure the processability of the pipe. In this way, the comprehensive molecular weight and component distribution ensure that the pipe has a certain mechanical strength and good processing performance; the molecular weight and its distribution can be determined by gel permeation chromatography (GPC), with two chromatographic 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°C, the dissolution is 4h, the flow rate is 1.0ml / min, and a narrow distribution polystyrene standard is used for universal calibration. In addition, melt strength is related to the degree of entanglement of molecular chains. The higher the number of branches, the higher the degree of entanglement of molecular chains and the higher the melt strength. A higher melt strength is required during pipe extrusion to meet the needs of high-speed traction and large-diameter pipe molding. The comonomer of HDPE used in this embodiment is α-olefin, preferably 1-hexene, the molar percentage of the comonomer is 0.71-0.96 mol%, the number of branches / 1000C is 3.42-5.49, preferably 4.62-5.23, and the comonomer and terminal methyl content of HDPE can be analyzed by carbon spectrum nuclear magnetic resonance, and the specific analysis method is the existing technology; branching point statistical test: using nuclear magnetic resonance method, first put 75 mg of sample into a 5 mm sample tube, add 0.5 mL of deuterated o-dichlorobenzene solvent, and keep the sample tube in a constant temperature bath at 140°C for 3-4 hours to make it evenly dispersed. Then put the prepared sample tube into the NMR spectrometer and scan the sample (pulse angle 90 °, pulse interval 5s, spectral width 220ppm, combined pulse decoupling); after the scan is completed, the spectrum is processed and the peaks in the range of 5-50ppm are accurately integrated (based on the isolated -CH 2 -peak calibration is 30ppm). Mw and the number of branches affect the reaction effect and synergy of the additives in the formula, and then affect the chain structure of the polymer. In addition, the HDPE with a thickness of more than 10nm has a relative content of 72-80% of lamellae, and the relative content of lamellae with a thickness of less than 6.2nm is between 4.1-5.2%. It is preferred to use DSC to perform crystallization thermal fractionation analysis on HDPE, and the specific analysis method is the existing technology.

[0046] In this embodiment, the Unipol gas phase process can be used to prepare HDPE, which is a prior art. This embodiment provides a method, but is not limited thereto: ethylene, hydrogen and comonomer are introduced into a gas phase fluidized bed reactor, and react under the action of a catalyst to generate a 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 rate of the polymerization reaction, and has a significant effect on the hydrogen adjustment sensitivity of the catalyst, thereby affecting the molecular weight of the product. When the reaction temperature is increased, the molecular weight of the product is reduced, and the melt mass flow rate will increase. Preferably, the reaction temperature is controlled at 92-94°C. Hydrogen, as a chain transfer agent, must have a certain concentration in the reactor to adjust the melt flow rate of the product. The preferred hydrogen / ethylene molar ratio of the present invention is 0.0025-0.015. The product density 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 ratio is the main factor affecting the product density, and the hexene / ethylene molar ratio is preferably 0.003-0.015. The catalyst is a metallocene catalyst supported on a carrier, and the carrier is preferably SiO 2 The average particle size of the carrier is 30 μm, and the surface area of ​​the carrier is 3-420 m 2 / g, the average diameter of the pores of the carrier is between 0.01-3μm, and the metallocene is aluminum and zirconium. The preparation method of the metallocene catalyst is: first activate the carrier at 200-300°C, then add benzene, n-pentane, isopentane or hexane, after 2-3h, add methylaluminoxane (MAO) and stir for 2-2.5h, then add di(n-butylcyclopentadienyl) zirconium dichloride and stir for 2-2.5h to obtain the metallocene catalyst; wherein the aluminum / zirconium ratio will affect the molecular weight distribution of the product, and the preferred aluminum / zirconium molar ratio is (3-8):1, preferably (3.2-6.5):1.

[0047] In this embodiment, LCP is a white solid powder that can be obtained commercially. The amount of LCP added is preferably 0.21-0.28 parts. LCP plays the role of a nucleating agent in the HDPE matrix, promotes the crystallization process of HDPE, narrows the grain size distribution, makes the crystals more perfect, and makes the crystals more regular, and has better mechanical strength. While effectively reducing the sag effect, it also ensures a smooth surface of the pipe product. The reduction of the [2 0 0] crystal plane size and the [1 1 0] crystal plane size of the polyethylene pipe measured by X-ray diffraction is more beneficial to the improvement of strength.

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

[0049] In the present embodiment, the addition amount of the composite compatibilizer is preferably 0.07-0.1 parts. The composite compatibilizer is a mixture of EVA-G-MAH and hexahydrophthalic acid metal salt compounds in a mass ratio of (1.5-2.8): 1. In the composite compatibilizer, the simultaneous use of EVA-G-MAH and hexahydrophthalic acid metal salt compounds can bring a good synergistic effect, has a high reactivity, has excellent coupling compatibility, can increase the compatibility between various components, increase the number of side chains in the polyethylene molecule, improve the molecular chain entanglement effect, the anhydride group of EVA-G-MAH and the terminal hydroxyl group of LCP undergo esterification reaction, and a volume expansion effect is generated in situ, which enhances the bonding strength between the pipe phase interfaces. In the present embodiment, the grafting rate of EVA-G-MAH is 1.5-18%, preferably 1.6%, the MFR is 2.1-2.6 g / lOmin, preferably 2.4 g / lOmin, the VA content is 18-22%, preferably 20%, and it can be obtained commercially. The hexahydrophthalic acid metal salt compound is preferably calcium hexahydrophthalate, which can be obtained commercially.

[0050] When the pipe is in contact with air, it will chemically react with oxygen in the air and be oxidized, which is a typical free radical reaction. In this embodiment, the compound antioxidant is added to the pipe, which can react with the oxidative free radicals R. and ROO. generated by oxidation in the pipe, interrupting the growth of the active chain, thereby effectively inhibiting or reducing the degradation and aging process of the pipe and extending the service life of the pipe. The three antioxidants in this embodiment have good synergistic effects and better antioxidant effects. Among them, antioxidant 1 is a symmetrical hindered phenol compound, and one or more of tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] pentaerythritol ester, β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate n-octadecyl 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 can be selected, preferably tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] pentaerythritol ester, and the addition amount is preferably 0.06-0.1 parts. 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, distearyl diphosphite of pentaerythritol, 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. Antioxidant 3 is a semi-hindered phenol antioxidant, preferably semi-hindered phenol antioxidant 1790, and the addition amount is preferably 0.06-0.08 parts.

[0051] The acid scavenger of this embodiment is preferably zinc stearate, and the added amount is preferably 0.05-0.08 parts.

[0052] The method for preparing the polyethylene pipe composition of the present invention comprises the following steps:

[0053] Step 1, weigh each raw material by weight;

[0054] Step 2: first dissolve the composite compatibilizer and LCP in an organic solvent, then add the mixture to a high-speed mixer and mix with polyisobutylene at a mixing temperature of 45-52°C for a mixing time of 21-25 min. After the organic solvent is completely volatilized, high-density polyethylene, acid absorber, antioxidant 1, antioxidant 2 and antioxidant 3 are added to the high-speed mixer for mixing. 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°C. After stopping stirring, stand at 60-70°C for 5-10 min, preferably 6 min, to obtain a polyethylene pipe composition.

[0055] In this embodiment, the preferred organic solvent is 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 invention can be used to prepare polyethylene pipes. Preferably, the polyethylene pipe composition is added into an extruder for extrusion granulation, and then cooled to obtain the polyethylene pipe. The extrusion conditions are as follows: the aspect ratio of the extruder screw is 50-58, the gap between the screw and the barrel is between 0.25-0.4 mm, the screw speed is 200-250 r / min, the feeding speed is 120-130 r / min, the minimum granulation temperature is 190-200° C., the maximum granulation temperature is 250-260° C., and the residence time of the polyethylene pipe composition in the screw is 6-7 minutes, so as to facilitate various additives to give full play to the synergistic effect; and the granulation cooling water temperature is below 30° C.

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

[0058] The terms used in the present invention generally have the meanings commonly understood by those of ordinary skill in the art, unless otherwise specified.

[0059] In order to enable those skilled in the art to better understand the technical solution of the present invention, the present invention will be further described in detail below in conjunction with embodiments.

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

[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 composite compatibilizer (a mixture of DuPont 30E868EVA-G-MAH and calcium hexahydrophthalate at a ratio of 2.8:1, with a grafting rate of EVA-G-MAH of 1.6%, an MFR of 2.4 g / lOmin, and a VA content of 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] Among them, the density of HDPE is 0.942g / cm 3 , MFR is 0.20g / 10min (under the conditions of 190℃ and 2.16kg), the content of the part with molecular weight above 1 million is 0.40, Mw is 195,000, molecular weight distribution is 20, number of branches / 1000C is 4.75, the content of platelets with thickness above 10nm is 76%, the content of platelets with thickness below 6.2nm is 5.2%, and the molar percentage of hexene is 0.96mol%. It is prepared by gas phase process with metallocene catalyst, reaction temperature is controlled at 94℃, reaction pressure is controlled at 2.3MPa, ethylene partial pressure is 80%, and the molar ratio of aluminum / zirconium in the metallocene catalyst is 3.2:1.

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

[0065] Step 1, weigh each raw material by weight;

[0066] Step 2: first dissolve the composite compatibilizer and LCP in dibutoxymethane (the added amount is 25-30 times the total weight of the composite compatibilizer), and then add it to a high-speed mixer to mix with polyisobutylene, the mixing temperature is 45-52°C, the mixing time is 21-25min, after the dibutoxymethane is completely volatilized, HDPE, acid absorber, antioxidant 1, antioxidant 2 and antioxidant 3 are added to the high-speed mixer, first stirred at 300-500r / min for 2-3min, then stirred at 1300-16500r / min for 5-10min, the stirring temperature is 60-70°C, after stopping stirring, let it stand at 60-70°C for 6min to obtain a polyethylene pipe composition.

[0067] Method for preparing polyethylene pipe using the polyethylene pipe composition:

[0068] The polyethylene pipe composition is added into an extruder for extrusion granulation to obtain a polyethylene pipe; the aspect ratio of the extruder screw 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 speed is 200-250 r / min, the feeding speed is 120-130 r / min, and the residence time of the polyethylene pipe composition in the screw is 6-7 minutes; the granulation cooling water temperature is below 30° C.

[0069] Example 2

[0070] The polyethylene pipe composition comprises, 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 composite compatibilizer (a mixture of DuPont 30E868EVA-G-MAH and calcium hexahydrophthalate at a ratio of 1.5:1, with a grafting rate of EVA-G-MAH of 1.6%, an MFR of 2.4 g / lOmin, and a VA content of 20%), 0.06 parts of zinc stearate, 0.08 parts of antioxidant 1010, 0.05 parts of antioxidant 168, and 0.07 parts of antioxidant 1790;

[0071] Among them, the density of HDPE is 0.941g / cm 3 , MFR is 0.22g / 10min (under the conditions of 190℃ and 2.16kg), the content of the part with molecular weight above 1 million is 0.39, Mw is 190,000, molecular weight distribution is 18, number of branches / 1000C is 5.23, the content of platelets with thickness above 10nm is 80%, and the content of platelets with thickness below 6.2nm is 4.1%. The molar percentage of comonomer is 0.83mol%. It is prepared by gas phase process with metallocene catalyst, reaction temperature is controlled at 94℃, reaction pressure is controlled at 2.3MPa, ethylene partial pressure is 80%, and the molar ratio of aluminum / zirconium in the metallocene catalyst is 6.1:1.

[0072] The preparation method of the polyethylene pipe composition is the same as that of Example 1.

[0073] The method for preparing a polyethylene pipe from the polyethylene pipe composition is the same as that in Example 1.

[0074] Example 3

[0075] The polyethylene pipe composition comprises, by weight, 100 parts of HDPE, 8 parts of polyisobutylene (weight average molecular weight 85,000), 0.24 parts of DuPont 6130LX (LCP), 0.09 parts of composite compatibilizer (a mixture of DuPont 30E868EVA-G-MAH and calcium hexahydrophthalate at a ratio of 2.8:1, with a grafting rate of EVA-G-MAH of 1.6%, an MFR of 2.4 g / lOmin, and a VA content of 20%), 0.07 parts of zinc stearate, 0.07 parts of antioxidant 1010, 0.06 parts of antioxidant 168, and 0.06 parts of antioxidant 1790;

[0076] Among them, the density of HDPE is 0.940g / cm 3, MFR is 0.15g / 10min (190℃, 2.16kg), the content of molecular weight above 1 million is 0.42, Mw is 175,000, molecular weight distribution is 21, the content of platelets with thickness above 10nm is 72%, the content of platelets with thickness below 6.2nm is 4.5%, and the number of branches / 1000C is 4.62. The molar percentage of comonomer is 0.71mol%. It is prepared by gas phase process with metallocene catalyst, reaction temperature is controlled at 94℃, reaction pressure is controlled at 2.3MPa, ethylene partial pressure is 80%, and the molar ratio of aluminum / zirconium in the metallocene catalyst is 4.5:1.

[0077] The preparation method of the polyethylene pipe composition is the same as that of Example 1.

[0078] The method for preparing a polyethylene pipe from the polyethylene pipe composition is the same as that in 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 parts of composite compatibilizer (a mixture of DuPont 30E868EVA-G-MAH and calcium hexahydrophthalate at a ratio of 2.5:1, with a grafting rate of EVA-G-MAH of 1.6%, an MFR of 2.4 g / lOmin, and a VA content of 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] Among them, the density of 100 parts of HDPE is 0.945g / cm 3 , MFR is 0.18g / 10min (under the conditions of 190℃ and 2.16kg), the content of molecular weight above 1 million is 0.41, Mw is 185,000, molecular weight distribution is 22, the content of platelets with thickness above 10nm is 78%, the content of platelets with thickness below 6.2nm is 5.0%, and the number of branches / 1000C is 5.01. The molar percentage of comonomer is 0.90mol%. It is prepared by gas phase process with metallocene catalyst, the reaction temperature is controlled at 94℃, the reaction pressure is controlled at 2.3MPa, the ethylene partial pressure is 80%, and the molar ratio of aluminum / zirconium in the metallocene catalyst is 6.5:1.

[0082] The preparation method of the polyethylene pipe composition is the same as that of Example 1.

[0083] The method for preparing a polyethylene pipe from the polyethylene pipe composition is the same as that in Example 1.

[0084] Example 5

[0085] The polyethylene pipe composition comprises, 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 composite compatibilizer (a mixture of DuPont 30E868EVA-G-MAH and calcium hexahydrophthalate at a ratio of 2.1:1, with a grafting rate of EVA-G-MAH of 1.6%, an MFR of 2.4 g / lOmin, and a VA content of 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;

[0086] Among them, the density of HDPE is 0.943g / cm 3 , MFR is 0.19g / 10min (under the conditions of 190℃ and 2.16kg), the content of the part with molecular weight above 1 million is 0.43, Mw is 180,000, molecular weight distribution is 19, the content of platelets with thickness above 10nm is 75%, the content of platelets with thickness below 6.2nm is 4.8%, and the number of branches / 1000C is 4.89. The molar percentage of comonomer is 0.75mol%. It is prepared by gas phase process with metallocene catalyst, the reaction temperature is controlled at 94℃, the reaction pressure is controlled at 2.3MPa, the ethylene partial pressure is 80%, and the molar ratio of aluminum / zirconium in the metallocene catalyst is 4.0:1.

[0087] The preparation method of the polyethylene pipe composition is the same as that of Example 1.

[0088] The method for preparing a polyethylene pipe from the polyethylene pipe composition is the same as that in Example 1.

[0089] Comparative Example 1

[0090] The raw materials used are the same as those in Example 1, and the method for preparing the polyethylene pipe composition is the same as that in Example 1, except that 7.5 parts of polyisobutylene are not added. The method for preparing the polyethylene pipe from the polyethylene pipe composition is the same as that in Example 1.

[0091] Comparative Example 2

[0092] The raw materials used are the same as those in Example 1, and the method for preparing the polyethylene pipe composition is the same as that in Example 1, except that 0.25 parts of liquid crystal polymer (LCP) is not added. The method for preparing the polyethylene pipe from the polyethylene pipe composition is the same as that in Example 1.

[0093] Comparative Example 3

[0094] The raw materials used are the same as those in Example 1, and the method for preparing the polyethylene pipe composition is the same as that in Example 1, except that 0.1 parts of the composite compatibilizer is replaced by 0.1 parts of liquid oil. The method for preparing the polyethylene pipe from the polyethylene pipe composition is the same as that in Example 1.

[0095] Comparative Example 4

[0096] The raw materials used are the same as those in Example 2, and the method for preparing the polyethylene pipe composition is the same as that in Example 2, except that the composite compatibilizer and LCP in step 2 are directly mixed with polyisobutylene without dissolving dibutoxymethane. The method for preparing the polyethylene pipe from the polyethylene pipe composition is the same as that in Example 1.

[0097] Comparative Example 5

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

[0099] The performance of the samples of Examples 1-5 and Comparative Examples 1-5 was tested.

[0100] The detection method is:

[0101] Rapid crack propagation (RCP) is a type of failure associated with rapid and unstable expansion of longitudinal cracks in pressurized plastic pipes. If rapid crack propagation occurs, the crack in the pipe can extend to several hundred meters in an instant, causing serious safety accidents. Therefore, resistance to rapid crack propagation is an important property of pipes. ASTM F2231 specifies a test method for evaluating the resistance to rapid crack propagation of pipes using the PAC method, i.e., the Charpy simply supported beam impact test.

[0102] The melt strength test temperature is 190℃, the screw speed is 20r / min, the tensile acceleration is 20mm / s2, and the force at the time of melt fracture is 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] The simply supported beam notched impact strength is tested according to GB / T 1043.1-2008, A-type notch, 23°C;

[0105] The load deformation temperature is tested according to GB / T 1634.2-2004. A high load deformation temperature is beneficial to the application of pipes under high temperature conditions (above 60°C);

[0106] The short-term hydrostatic strength is tested according to GB / T 18252-2000.

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

[0108] Appearance: Polyethylene pipes are used to prepare pipes with specifications of 110*10mm.

[0109] Extrusion processing current refers to the extrusion current generated under the same process conditions when polyethylene pipes are used to prepare pipes with a specification of 110*10mm.

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

[0111]

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

[0113]

[0114] Table 3 Appearance of pipes prepared 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 Crystal point Comparative Example 3 Crystal point Comparative Example 4 smooth Comparative Example 5 Crystal point

[0116] Obviously, the above embodiments are merely examples for clear explanation, and are not intended to limit the embodiments. For those skilled in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all the embodiments here. The obvious changes or modifications derived from them are still within the protection scope of the invention.

Claims

1. A polyethylene pipe composition, characterized in that: In parts by weight, it includes: The composite compatibilizer is a mixture of EVA-G-MAH and hexahydrophthalic acid metal salt compounds in a mass ratio of (1.5-2.8):1; antioxidant 1 is a symmetrical hindered phenol antioxidant, antioxidant 2 is a phosphite antioxidant, and antioxidant 3 is a semi-hindered phenol antioxidant.

2. The polyethylene pipe composition according to claim 1, characterized in that: The high-density polyethylene has a density of 0.936-0.948 g / cm 3 ; Under the conditions of 190°C and 2.16kg, the melt flow rate is 0.1-1.0g / 10min; the relative content of platelets with a thickness of more than 10nm is between 72-80%, and the relative content of platelets with a thickness of less than 6.2nm is between 4.1-5.2%; the weight-average molecular weight is greater than 170,000, of which the content of the part with a molecular weight of more than 1 million is greater than 0.38%, and the molecular weight distribution is 15-25; the comonomer is α-olefin, and the molar percentage of the comonomer is 0.71-0.96mol%, and the number of branches / 1000C is 3.42-5.

49.

3. The polyethylene pipe composition according to claim 1, characterized in that: The high-density polyethylene is prepared by a gas phase process using a metallocene catalyst, the reaction temperature is 92-94° C., the reaction pressure is 2.2-2.4 MPa, and the molar ratio of aluminum to zirconium in the metallocene catalyst is (3-8):

1.

4. The polyethylene pipe composition according to claim 1, characterized in that: The weight average molecular weight of the polyisobutylene is between 75,000 and 105,000; In the composite compatibilizer, the grafting rate of EVA-G-MAH is 1.5-1.8%, the melt flow rate is 2.1-2.6 g / lOmin, and the VA content is 18-22%; The hexahydrophthalic acid metal salt compound is calcium hexahydrophthalate; The acid absorber is zinc stearate.

5. The polyethylene pipe composition according to claim 1, characterized in that: The antioxidant 1 includes one or more of tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate]pentaerythritol, 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, 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, distearyl pentaerythritol diphosphite, and bis(2,4-tert-butylphenyl)pentaerythritol diphosphite; The antioxidant 3 is semi-hindered phenol antioxidant 1790.

6. The method for preparing the polyethylene pipe composition according to any one of claims 1 to 5, characterized in that: The following steps are involved: Step 1, weigh each raw material by weight; Step 2: first dissolve the composite compatibilizer and liquid crystal polymer into an organic solvent, then mix them evenly with polyisobutylene, and after the organic solvent is completely evaporated, mix them evenly with high-density polyethylene, acid absorber, antioxidant 1, antioxidant 2 and antioxidant 3, and let stand at 60-70° C. for 5-10 minutes to obtain a polyethylene pipe composition.

7. The method for preparing the polyethylene pipe composition according to claim 6, characterized in that: The conditions for uniform mixing with polyisobutylene are: mixing temperature 45-52°C, mixing time 21-25min; The conditions for uniformly mixing with high-density polyethylene, acid absorber, antioxidant 1, antioxidant 2 and antioxidant 3 are: first stirring at 300-500 r / min for 2-3 min, then stirring at 1300-16500 r / min for 5-10 min, and the stirring temperature is 60-70°C; The organic solvent is dibutoxymethane, and the added amount of the organic solvent is 25-30 times the total weight of the composite compatibilizer.

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

9. The method for preparing a polyethylene pipe according to claim 8, characterized in that: The polyethylene pipe composition according to any one of claims 1 to 5 is extruded and granulated to obtain a polyethylene pipe.

10. The method for preparing a polyethylene pipe according to claim 9, characterized in that: The extrusion granulation conditions are as follows: the screw aspect ratio is 50-58, the clearance between the screw and the barrel is between 0.25-0.4 mm, the screw 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° C., the maximum granulation temperature is 250-260° C., and the granulation cooling water temperature is below 30° C.

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