Polymer composition

Abstract

A high-strength multimodal polyethylene composition useful for the manufacture of plastic articles therefrom; a process for making the above-mentioned composition; and a pipe article made from the above-mentioned composition, the composition comprising a mixture of: (a) at least one first polymeric resin comprising a high molecular weight copolymer resin having a molecular weight greater than 350,000 g / mol; (b) at least one second polymeric resin comprising a low molecular weight homopolymer resin having a molecular weight less than 30,000 g / mol; and (c) at least one third polymeric resin comprising a medium molecular weight copolymer resin having a molecular weight of from 50,000 g / mol to 150,000 g / mol; wherein the high-strength multimodal polyethylene composition has a minimum required strength greater than 11.3 MPa.

Description

Technical Field

[0001] This invention relates to polymer compositions; and more specifically, to high-strength polyethylene polymer compositions comprising a combination of at least three different polyethylene polymers having three different molecular weights. These high-strength polyethylene polymer compositions can be used in a variety of applications, such as for water and gas transmission pipelines. Background Technology

[0002] To date, various polymer compositions have been used to manufacture a wide range of articles / products requiring high mechanical properties. For example, plastic pipes are articles that require high strength (e.g., a high-pressure stress level greater than 10 MPa in terms of minimum required strength (MRS)) for certain high-pressure applications.

[0003] In the plastic pipe industry, the “PE 100” pipe grade, which is readily available in the plastic pipe industry, is commonly used. “PE 100” is pipe grade polyethylene (PE); and typically has an optimal balance of the following three key properties: (1) Minimum Required Strength (MRS), which is typically 10 MPa for PE 100, as defined in EN ISO 12162; wherein MRS provides the pipe with long-term strength and creep resistance; (2) Resistance to stress cracking (sometimes referred to as resistance to slow crack growth [SCGR]), which is typically >500 hours when tested on notched pipes at 80°C and 9.2 bar; and (3) Resistance to rapid crack propagation, which is typically measured by crack arrest at 0°C and 10 bar pressure.

[0004] Polyethylene polymer resins with higher strength (i.e., higher MRS) than PE 100 are referred to in the art as "PE112" pipe-grade resins. Typically, such PE 112 resins have a pressure rating of 11.2 MPa, or MRS. However, even though three commercial PE 112 pipe-grade resins are currently available from suppliers such as SCG Polymer, SABIC, and Sinopec, PE 112 resin has not yet achieved widespread and common use in the plastic pipe manufacturing industry. Furthermore, an MRS of 11.2 MPa or possibly higher is not a common value achieved by pressure pipe resins used in the plastic pipe manufacturing industry, because any increase in MRS in increments of 0.1 MPa is very difficult to achieve for pipe resins. This is because producing PE polymer resin materials with increased MRS requires appropriate molecular design and an increase in the linkage chain density of the PE material to a level where the long-term creep resistance is significantly higher than that of pressure pipe resins with an MRS of 10.0 MPa (e.g., PE 100 resin) or even higher than that of pressure pipe resins with an MRS of 11.2 MPa (e.g., PE 112 resin).

[0005] The desired result is achieved with popular polymeric resins possessing the highest possible MRS (e.g., 11.2 MPa or higher), such as PE 112 resin used in the manufacture of plastic pipes. The higher MRS allows such high-pressure pipe resins to be used in applications requiring an MRS greater than that of standard PE 100 resin. For example, pipes made from PE 112 resin can be used in underwater applications. Additionally, PE 112 pipe resin offers the advantage of providing options for reducing the wall thickness of the pipe to be used.

[0006] Previous progress has been made in modifying PE pipe resins used to manufacture pipes, enabling the resulting pipes to be used in high-performance applications. For example, patent application publication WO 2020 / 232006A1 discloses the use of high-density polyethylene (HDPE) resin in the manufacture of pressure pipes, wherein one or more variables of the HDPE base polymer and / or its masterbatch are optimized to improve strength and performance for the production of next-generation pressure pipes. The aforementioned publication discloses that such optimization can improve the MRS and creep properties of pipes made from such HDPE resins.

[0007] The aforementioned references also disclose the formulation of base polymers and / or carbon black masterbatches (masterbatches having a carrier resin and carbon black) to produce tube resins. The aforementioned references disclose methods for improving the physical properties and performance of the tube resins by: (1) increasing the density and / or molecular weight of the base polymer used with a standard masterbatch to achieve PE 112 designation; and / or (2) increasing the density and / or molecular weight of the carrier resin in the masterbatch without altering the carbon black properties, so that the masterbatch can be used with a standard base polymer to achieve PE 112 designation. Once modified, the base polymer and masterbatch are blended together to form a resulting polymer resin that can be extruded as a next-generation tube. The polymer resin obtained by blending a base polymer and carbon black masterbatch, disclosed in WO 2020 / 232006A1, is a high-strength resin with an MRS of at least 11.2 MPa and at most 11.3 MPa. In addition, the high-strength resin described in the above references is a blend of a bimodal, high molecular weight, high-density polyethylene base polymer with a density between 0.947 g / cm3 and 0.952 g / cm3 and a masterbatch containing a carrier resin and carbon black, wherein the density of the masterbatch is between 1.1 g / cm3 and 1.4 g / cm3 and the carbon black particle size range is less than 55 nm.

[0008] Other references, including, for example, U.S. Patent Nos. 7,989,549; 7,416,686B2; 9,234,061B2; 7,868,092; and U.S. Patent Application Publication US20090252910A1, disclose various polyethylene-based polymer compositions having various MRS values ​​from 9.0 MPa to 11.2 MPa for the manufacture of pipes. However, none of the aforementioned references provide improved multi-peak (at least three-peak) polymer resin compositions with improved properties (e.g., molecular weight and density) to enhance the pressure performance (e.g., design stress exceeding 11.2 MPa) of pipe articles made from such polymer compositions.

[0009] Therefore, it is desirable to provide multi-peak (e.g., at least three-peak) polyethylene polymer resin compositions that, according to the plastic pipe industry, are higher than the standard “PE 100” pipe grade resin and equal to or higher than the “PE 112” pipe grade resin, with an MRS increase even higher than the 11.2 MPa MRS disclosed in WO 2020 / 232006A1. Summary of the Invention

[0010] This invention relates to high-strength multimodal polyethylene polymer compositions that can be used to manufacture plastic products such as pipe fittings.

[0011] In one embodiment, the invention includes a high-strength multimodal (e.g., at least three-modal) polyethylene polymer composition for use in manufacturing plastic articles such as pipe fittings, the composition comprising a mixture of: (a) at least one first polymer resin comprising a high molecular weight (HMW) copolymer resin with a molecular weight greater than 350,000 g / mol; (b) at least one second polymer resin comprising a low molecular weight (LMW) homopolymer resin with a molecular weight less than 30,000 g / mol; and (c) at least one third polymer resin comprising a medium molecular weight (MMW) copolymer resin having a molecular weight of 50,000 g / mol to 150,000 g / mol; wherein in a general embodiment, the high-strength multimodal polyethylene composition has a minimum desired strength (MRS) greater than 11.3 MPa, and in another embodiment greater than or equal to 11.5 MPa.

[0012] In another embodiment, the present invention includes a method for preparing the above-described high-strength polyethylene composition.

[0013] In another embodiment, the invention includes pipe fittings made from the above-described high-strength polyethylene composition.

[0014] One object of the present invention is to provide a novel trimodal high-strength polyethylene composition for use in the production of pipe fittings, wherein the MRS of the composition is at least greater than 11.3 MPa in one embodiment and at least greater than or equal to 11.5 MPa in another embodiment. According to the present invention, pipe fittings can be manufactured using the novel composition described above, wherein, after taking into account a C of 1.25 for performance in high-pressure applications, the fittings have an applicable design stress greater than 9.0 MPa. Detailed Implementation

[0015] Temperatures in this article are in degrees Celsius (°C).

[0016] Unless otherwise stated, “room temperature (RT)” and / or “ambient temperature” in this document mean a temperature between 20°C and 26°C.

[0017] A "polymer" is a polymeric compound prepared by polymerizing monomers (whether of the same or different types). Therefore, the general term "polymer" encompasses the term homopolymer (used to refer to polymers prepared from only one type of monomer, where it should be understood that trace impurities may be incorporated into the polymer structure) and the term "interpolymer," which includes copolymers (used to refer to polymers prepared from two or more different types of monomers), terpolymers (used to refer to polymers prepared from three different types of monomers), and polymers prepared from more than three different types of monomers. Trace impurities (e.g., catalyst residues) may be incorporated into and / or within the polymer. It also encompasses all forms of copolymers, such as random, block, etc. It should be noted that although polymers are often referred to as being "made from" one or more specified monomers, "based on" a specified monomer or monomer type, "containing" a specified monomer content, etc., in this context, the term "monomer" should be understood to refer to the polymeric residue of the specified monomer rather than the unpolymerized material. Generally, polymers are referred to herein as "units" based on the polymeric form of the corresponding monomer.

[0018] In this article, "tube-forming composition" refers to a composition that can be processed into tubular products, components, or structures.

[0019] In this paper, "Minimum Required Strength (MRS)" refers to the predicted hydrostatic strength at 20°C and over a 50-year period, with a lower confidence limit of 97.5%. The MRS was determined by regression analysis of test data from long-term pressure tests according to ISO 9080. Regression analysis allows for the prediction of the minimum strength for a specific service life. Extrapolation of the data was performed to predict the minimum strength at 20°C and a specified 50-year design life.

[0020] "PE 100" is a designation used to classify pipe-grade polyethylene (PE) resin. The designation PE 100 is based on the long-term strength of polyethylene, referred to as the minimum required strength (MRS) according to ISO 12162-1; and the designation PE 100 refers to pipe-grade PE resin with an extrapolated minimum MRS of 10 MPa for a 50-year service life at room temperature. In addition to the MRS of 10 MPa (1450 psi), some other properties of the pipe designated PE100 (according to the PE4710 pipe category which meets the ASTM D3350 unit classification) include, for example: (1) Hydrostatic Design Basis (HDB) pressure: 1600 psi (11 MPa); (2) Permissible compressive strength: 7.93 MPa; (3) Yield tensile strength: 23 MPa; (4) Elongation at break >600%; (5) Modulus of elasticity (50 years): 200 MPa; (6) Flexural modulus: 1,000 MPa; (7) Poisson's ratio: 0.45; (8) Coefficient of thermal expansion (CTE): 1.3 × 10⁻⁴ °C⁻¹; and (9) Temperature resistance up to 60 °C.

[0021] The term "design stress" used in this document for pipe fittings refers to the allowable stress for a given application at 20°C, derived from the MRS by dividing the design stress (C). A typical design stress (C) for pressure pipes conveying water is 1.25 for polyethylene pipe resin, as defined in EN ISO 12162.

[0022] In this document, the term "single peak" for polyethylene polymers refers to a polymer having a single polyethylene component that exhibits a single peak in the molecular weight distribution measured in GPC analysis.

[0023] In this article, the term "bimodal" for polyethylene polymers refers to a polymer having two polyethylene components, which have two molecular weight peaks in the molecular weight distribution measured in GPC analysis.

[0024] In this article, the term "triple peak" for polyethylene polymers refers to a polymer having three polyethylene components, which exhibit three molecular weight peaks in the molecular weight distribution measured in GPC analysis.

[0025] In this document, the term "multimodal" for polyethylene polymers refers to a polymer having at least three or more polyethylene components that exhibit molecular weight peaks in the molecular weight distribution measured in GPC analysis.

[0026] In this article, "high strength" for pipe fittings typically refers to a high pressure (or high MRS) rating greater than 11.2 MPa.

[0027] The term "composition" refers to a mixture of materials comprising the composition, as well as reaction products and decomposition products formed from the materials of the composition.

[0028] The numerical ranges disclosed herein include all values ​​from the lower limit to the upper limit, and include both the lower limit and the upper limit. For a range containing exact values ​​(e.g., a range from 1 or 2 or 3 to 5 or 6 or 7), any subrange between any two exact values ​​is included (e.g., the range 1 to 7 above includes subranges of 1 to 2; 2 to 6; 5 to 7; 3 to 7; 5 to 6, etc.).

[0029] The terms “comprising,” “including,” “having,” and their derivatives are not intended to exclude the presence of any additional components, steps, or procedures, whether or not such components, steps, or procedures are specifically disclosed. For the avoidance of any doubt, unless stated otherwise, all compositions claimed using the term “comprising” may include any additional additives, adjuvants, or compounds, whether polymerized or otherwise. Conversely, the term “consisting of” excludes any other components, steps, or procedures from any subsequently listed scope, except those that are not essential for operability. The term “consisting of” excludes any components, steps, or procedures not specifically described or listed. Unless otherwise stated, the term “or” refers to members listed individually and in any combination. Use of the singular includes use of the plural, and vice versa.

[0030] As used throughout this specification, the abbreviations given below have the following meanings unless the context clearly indicates otherwise: "=" means "equal to" or "equal to"; "<" means "less than"; ">" means "greater than"; "≤" means "less than or equal to"; "≥" means "greater than or equal to"; "~" means "approximately"; @ means "at"; μm = micrometer, nm = nanometer; g = gram; mg = milligram; kg = kilogram; mW / mK = milliwatt per meter Kelvin; L = liter; mL = milliliter; g / mL = gram per milliliter; g / L = gram per milliliter. Liter; kg / m³ = kilograms per cubic meter; g / m³ = grams per cubic meter; g / cm³ = grams per cubic centimeter; ppm = parts per million weight; pbw = parts by weight; rpm = revolutions per minute; m = meter; m / min = meters per minute; mm = millimeter; cm = centimeter; μm = micrometer; min = minute; s = second; ms = millisecond; hr = hour; kPa-s = kilopascal-second; MPa = megapascal; Pa-s = pascal-second; mPa-s = millipascal-second; g / mol = grams per mole; g / eq = grams per equivalent; mg KOH / g = milligrams of potassium hydroxide per gram; Mn = number-average molecular weight; Mw = weight-average molecular weight; pts = parts by weight; 1 / s or s-1 = reciprocal seconds [s-1]; ℃ = degrees Celsius; mmHg = millimeters of mercury; psig = pounds per square inch; kPa = kilopascal; % = percentage; vol% = volume percentage; mol% = mole percentage; dg / min = gram per minute; g / 10min = gram per 10 minutes; MHz = megahertz; wt% = weight percentage; 1 / min or min-1 = reciprocal of minutes; and M or mol / L = mole.

[0031] Unless otherwise stated, all percentages, parts, ratios and similar quantities are defined by weight. For example, unless otherwise indicated, all percentages mentioned herein are weight percentages (wt%).

[0032] In one general embodiment, the present invention includes a high-strength multimodal polyethylene composition comprising: (a) at least one first polymer resin comprising a high molecular weight (HMW) polyethylene copolymer having an HMW greater than 350,000 g / mol; and (b) at least one second polymer resin comprising a low molecular weight (LMW) polyethylene homopolymer having an LMW less than 30,000 g / mol; and (c) at least one third polymer resin comprising a medium molecular weight (MMW) polyethylene copolymer having an MMW of 50,000 g / mol to 150,000 g / mol. Other optional compounds may be added to the above composition if desired, such as (d) carbon black material provided by carbon black masterbatch.

[0033] The first HMW ethylene copolymer, i.e., component (a) of the high-strength polyethylene composition of the present invention, may include one or more polyethylene copolymers of different molecular weights. Typically, the molecular weight of the first HMW polyethylene copolymer is from 300,000 g / mol to 10,000,000 g / mol in one embodiment, from 300,000 g / mol to 5,000,000 g / mol in another embodiment, and from 300,000 g / mol to 1,000,000 g / mol in yet another embodiment.

[0034] In a preferred embodiment, the first HMW ethylene copolymer that can be used in the present invention may be an ethylene-hexene copolymer, an ethylene-butene copolymer, an ethylene-octene copolymer, or a mixture thereof polymerized in a first reactor.

[0035] In addition to having a high molecular weight, the first HMW ethylene copolymer also has a density greater than 0.920 g / cm³ in one embodiment, from 0.920 g / cm³ to 0.935 g / cm³ in another embodiment, and from 0.920 g / cm³ to 0.931 g / cm³ in yet another embodiment. Furthermore, the first HMW ethylene copolymer has an I₂I greater than 0.30 dg / min in one embodiment and from 0.30 dg / min to 0.50 dg / min in another embodiment. In a preferred embodiment, the second HMW copolymer used in the present invention may have a density greater than 0.920 g / cm³ and an I₂I greater than 0.30 dg / min.

[0036] An example of an advantageous property exhibited by the first HMW polyethylene copolymer of the present invention includes providing resistance to slow crack growth, which depends on the linker chain density, a function of the presence of comonomers.

[0037] The concentration of the first HMW polyethylene copolymer in this invention includes, for example, 50 wt% to 65 wt% in one embodiment, 50 wt% to 60 wt% in another embodiment, and 50 wt% to 57 wt% in yet another embodiment.

[0038] The second LMW ethylene homopolymer, i.e., component (b) of the high-strength polyethylene composition of the present invention, may include one or more ethylene homopolymers of different molecular weights. Typically, the molecular weight of the second LMW ethylene homopolymer is from 1,000 g / mol to 60,000 g / mol in one embodiment, from 1,000 g / mol to 40,000 g / mol in another embodiment, and from 1,000 g / mol to 30,000 g / mol in yet another embodiment.

[0039] In addition to having a low molecular weight, the second LMW ethylene homopolymer has a high density greater than 0.960 g / cm³ in one embodiment, a high density of 0.960 g / cm³ to 0.972 g / cm³ in another embodiment, and a high density of 0.965 g / cm³ to 0.972 g / cm³ in yet another embodiment. Furthermore, the I₂ of the second LMW ethylene homopolymer is greater than 100 dg / min in one embodiment, 100 dg / min to 1,000 dg / min in another embodiment, and 300 dg / min to 1,000 dg / min in yet another embodiment. In a preferred embodiment, the second LMW high-density ethylene homopolymer used in the present invention may have a density greater than 0.960 g / cm³ and an I₂ greater than 100 dg / min.

[0040] The concentration of the second LMW polyethylene homopolymer that can be used in this invention includes, for example, 35 wt% to 50 wt% in one embodiment, 35 wt% to 45 wt% in another embodiment, and 35 wt% to 40 wt% in yet another embodiment.

[0041] The third MMW polyethylene copolymer, i.e., component (c) of the high-strength polyethylene composition of the present invention, may include one or more polyethylene copolymers of different molecular weights. Typically, the molecular weight of the third MMW polyethylene copolymer is from 60,000 g / mol to 500,000 g / mol in one embodiment, from 60,000 g / mol to 400,000 g / mol in another embodiment, and from 60,000 g / mol to 300,000 g / mol in yet another embodiment.

[0042] In addition to having a medium molecular weight, the third MMW ethylene copolymer also has a density greater than 0.915 g / cm³ in one embodiment, from 0.915 g / cm³ to 930 g / cm³ in another embodiment, and from 0.915 g / cm³ to 0.925 g / cm³ in yet another embodiment. Furthermore, the I₂ content of the third MMW ethylene copolymer is greater than 0.5 dg / min in one embodiment, from 0.5 dg / min to 2.5 dg / min in another embodiment, and from 0.5 dg / min to 1.5 dg / min in yet another embodiment. In a preferred embodiment, the third MMW copolymer used in the present invention may have a density greater than 0.915 g / cm³ and an I₂ content greater than 0.5 dg / min.

[0043] In a preferred embodiment, the third MMW polyethylene copolymer used in this invention may be linear low-density polyethylene. The third MMW polyethylene copolymer of this invention comprises a 1-octene comonomer, and the presence of a combination of 1-octene and other comonomers (1-hexene) provides the advantageous properties described in the embodiments.

[0044] The concentration of the third MMW polyethylene copolymer that can be used in this invention includes, for example, 2 wt% to 6 wt% in one embodiment, 2 wt% to 5 wt% in another embodiment, and 2 wt% to 4 wt% in yet another embodiment.

[0045] In other embodiments, the high-strength polyethylene composition of the present invention may include one or more different optional compounds as component (d) of the high-strength polyethylene composition of the present invention. For example, optional compounds that can be used in the present invention may include carbon black; primary antioxidants and secondary antioxidants; and mixtures thereof.

[0046] When used in this invention, the concentration of the optional compound may, for example, be 0 wt% to 5 wt% in one embodiment, 1 wt% to 4 wt% in another embodiment, and 2 wt% to 3 wt% in yet another embodiment.

[0047] In a preferred embodiment, the high-strength polyethylene composition of the present invention may include, for example, carbon black material as optional component (d). Carbon black is used to prevent ultraviolet (UV) degradation of the polymer. For polyethylene pipes, the average particle size of the carbon black may be less than 60 nm in one embodiment and less than 30 nm in another embodiment. In other embodiments, according to the requirements described in EN12201-1, the average particle size of the carbon black is less than 25 nm in one embodiment and 10 nm to 25 nm in another embodiment.

[0048] In another preferred embodiment, the carbon black used in the high-strength polyethylene composition can be obtained from carbon black masterbatch. Carbon black masterbatch is a blend of carbon black and a carrier resin. The carrier resin can be, for example, high-density polyethylene, linear low-density polyethylene, and mixtures thereof. The carrier resin can have a unimodal or bimodal molecular weight distribution. The carbon black masterbatch may also contain a primary antioxidant and / or a secondary antioxidant to prevent thermal oxidation.

[0049] Typically, the carrier resin used in this invention has a lower density and lower molecular weight compared to the base resin in high-strength multimodal polyethylene compositions, which is contrary to some prior art, such as WO 2020 / 232006A1, which discloses increasing the density and / or molecular weight of the carrier resin in the masterbatch.

[0050] Typically, masterbatches are produced by blending a carrier compound with carbon black. For example, 60 wt% of carrier resin is blended with 40 wt% of carbon black. Blending can be performed using conventional equipment and methods, including, for example, extruders, such as twin-screw extruders, or batch mixers.

[0051] When used in this invention, the concentration of carbon black compound from the carbon black masterbatch includes, for example, 2 wt% to 5 wt% in one embodiment, 2 wt% to 3 wt% in another embodiment, and 2 wt% to 2.5 wt% in yet another embodiment. If the carbon black content is less than 2 wt%, UV degradation of the polymer used in pipe applications cannot be prevented. Higher than 5 wt% carbon black content may lead to premature failure during long-term hydrostatic testing on pipes.

[0052] The polymerization method of the present invention provides a high-strength multi-peak polyethylene composition having properties equal to or greater than those of polyethylene compositions classified as PE 100 or PE 112 without inflection points, and outperforming current conventional polyethylene compositions classified as PE 100 or PE 112.

[0053] Some advantageous properties and / or benefits of the high-strength polyethylene compositions of the present invention include, for example, ease of processing during pipe extrusion for manufacturing pipe fittings due to a higher MFR5, resulting in lower extruder and die pressures compared to commercial PE 112 products. For example, using known processing equipment and parameters, such as known pipe extrusion methods for processing conventional PE 100 resin, the composition provides higher yields and throughput. In one embodiment, for example, the polyethylene compositions of the present invention provide efficient processing and better productivity because the polyethylene compositions have a viscosity that allows for the use of a single-screw extruder, where melting occurs primarily due to viscous dissipation (or shear) of the polymer. Furthermore, in terms of the procedure for processing the polyethylene compositions of the present invention, the processing of the polyethylene compositions is more similar to that of conventional PE 100 resin; however, compared to currently available resins classified as PE 112, the polyethylene compositions of the present invention are processed at lower die pressures with higher yields and throughputs.

[0054] Typically, polyethylene compositions exhibit an MFR of, for example, 0.2 dg / min to 0.5 dg / min in one embodiment, 0.25 dg / min to 0.5 dg / min in another embodiment, and 0.3 dg / min to 0.5 dg / min in yet another embodiment, as measured at 190°C and 5 kg. In a preferred embodiment, the composition has an MFR of 0.31 dg / min at 190°C and 5 kg. The flowability and processability of the composition of the present invention with an MFR of 0.31 dg / min at 190°C and 5 kg are significantly better than those of the prior art resins described in Example Table I with an MFR of 0.20 g / 10 min.

[0055] Furthermore, the compositions of the present invention can be used to manufacture pipe products with a much higher MRS than that required to meet the PE 112 rating. For example, in one general embodiment, the composition provides an increase in MRS strength of at least 15% compared to PE100, and up to 25% from ≥15%. The strength of the polyethylene compositions of the present invention can be determined from regression curves; and no inflection point is observed on the regression curves for each temperature test, with a testing period of up to 10,000 hours. Therefore, the polyethylene compositions of the present invention have an MRS rating of, for example, >11.3 MPa@50 years in one embodiment and ≥11.5 MPa@50 years in another embodiment. The results of long-term circumferential stress testing of the material are used. At pressures 17% higher than PE100, the polyethylene compositions of the present invention provide an additional safety factor and extended service life.

[0056] Polyethylene (PE) is a thermoplastic material and is typically produced by the polymerization of ethylene. A general method for preparing the high-strength multimodal (e.g., trimodal) polyethylene composition of the present invention includes compounding: (a) at least one first polymer resin comprising a polyethylene copolymer resin with an HMW greater than 350,000 g / mol; (b) at least one second homopolymer resin comprising a polyethylene homopolymer resin with an LMW less than 30,000 g / mol; and (c) at least one third polymer resin comprising a polyethylene copolymer resin with an MMW of 50,000 g / mol to 150,000 g / mol; and (d) optionally, carbon black material from a carbon black masterbatch; wherein the mixture is processed to form a high-strength multimodal polyethylene composition; wherein the resulting high-strength multimodal polyethylene composition can be used to manufacture pipe fittings with an MRS greater than or equal to 11.2 MPa. Typically, components (a) to (c) and optionally (d) are mixed at temperatures ranging from 170°C to 260°C in one general embodiment; from 180°C to 250°C in another embodiment; and from 190°C to 240°C in yet another embodiment. Conventional mixing equipment can be used to form high-strength multimodal polyethylene compositions.

[0057] In a preferred embodiment, the method for preparing a high-strength multimodal polyethylene composition includes the following steps:

[0058] (I) Mixing components (a) to (c) and optional (d); and

[0059] (II) The mixture from step (I) is formed into granules; wherein the granules may be further processed into articles, such as pipe products.

[0060] In another preferred embodiment, the method includes, for example, the following steps: (i) mixing components (a) and (b) separated from components (c) and (d) in a conventional reactor to form a first mixture; (ii) mixing components (c) and (d) using various compounding equipment known in the art, including a granulation device, to form a blend of components (c) and (d) or a second mixture; (iii) compounding the first mixture of components (a) and (b) with the second mixture of components (c) and (d) using known compounding equipment having a granulation step; and (iv) granulating the compounded components (a) to (d) using conventional pellet forming equipment to form pellets of a high-strength polyethylene composition. The resulting pellets of the high-strength multi-peak polyethylene composition formed in step (iv) can then be processed using conventional equipment to convert the pellets into pipe fittings. For example, the resulting PE pellets can be extruded using an extruder with a suitable die to form pipe fittings; or the resulting PE pellets can be formed into other desired articles using conventional co-extrusion methods and equipment.

[0061] One of the advantages of using the above-described method for preparing the compositions of the present invention includes, for example, that the method allows the introduction of the third polymer resin component by blending a third polymer resin, such as component (c), and optionally a component such as carbon black, i.e., component (d), via a carbon black masterbatch, instead of using a third reactor in series. The aforementioned advantage of using this method is that trimodality is achieved without the need for three reactors. Furthermore, the final product can be prepared on a conventional pellet forming unit.

[0062] Typically, a method for producing articles of the present invention, such as pipe fittings, includes, for example, the following steps: (i) providing a high-strength multimodal polyethylene composition, such as a trimodal polyethylene composition, suitable for manufacturing plastic articles such as pipe fittings, the composition comprising a mixture of: (a) at least one first polymer resin comprising a copolymer resin with a molecular weight greater than 350,000 g / mol; (b) at least one second polymer resin comprising a homopolymer resin with a molecular weight less than 30,000 g / mol; and (c) at least one third polymer resin comprising a copolymer resin with a molecular weight of 50,000 g / mol to 150,000 g / mol; wherein the high-strength trimodal polyethylene composition has a minimum desired strength greater than 10 MPa; and (ii) processing the composition of step (i) into articles, such as pipe fittings, using an extrusion process to form articles; wherein the articles, such as pipe fittings, have a minimum desired strength greater than 10 MPa. The processing step (ii) for manufacturing high-strength PE plastic pipes includes, for example, forming granules from the composition using a granulation unit; and then processing the granules using an extruder using the extrusion method described above.

[0063] The high-strength multimodal polyethylene polymer composition of the present invention described above can be used to manufacture various articles or products for which increased MRS is required in applications. In a preferred embodiment, articles produced from the above composition are, for example, pipe fittings. Compared with some previously known pipe products, pipe fittings produced using the above composition and method have several advantageous and beneficial properties after undergoing the manufacturing process. For example, pipe fittings manufactured from the high-strength polyethylene composition of the present invention have: (1) a much higher MRS than required to meet PE 112 grade, particularly pipe fittings having an MRS of at least greater than 11.2 MPa; (2) high SHM; and (3) resistance to slow crack growth that is close to or meets the requirements for trenchless installation pipe products.

[0064] The PE pressure pipe of the present invention has the general benefits of being lightweight, flexible, and having high strength; that is, the pipe has improved pressure resistance and can operate at higher pressures. For example, the MRS of the pipe fitting is ≥11.3 MPa in one general embodiment, ≥3 MPa in another embodiment, ≥12 MPa in another embodiment, ≥13 MPa in another embodiment, and ≥14 MPa in another embodiment. In other embodiments, the MRS of the pipe fitting is in the range of, for example, 11.2 MPa to 13.99 MPa (e.g., similar to PE125 category) in one general embodiment, in the range of 11.2 MPa to 12 MPa in another embodiment, and in the range of 11.2 MPa (e.g., similar to PE112 category) to 11.7 MPa in yet another embodiment.

[0065] Due to their higher MRS, the polyethylene compositions of the present invention perform as well as or better than PE 100 and PE 112. Therefore, if desired, the maximum permissible operating pressure (MAOP) of pipes made from the compositions of the present invention can be increased and the pipe wall thickness can be reduced. In one embodiment, the pipe product may have thick walls and a large diameter, for example, a wall thickness of 3 mm to 147 mm and a diameter of 16 mm to 2,500 mm.

[0066] In another embodiment, the pipe product made from the composition of the present invention has a high strain hardening modulus (SHM) and resistance to slow crack growth approaching the requirements for trenchless installation pipe products. For example, the SHM of the pipe fitting is greater than 45 MPa in one general embodiment, greater than 53 MPa in another embodiment, and greater than 60 MPa in yet another embodiment. In other embodiments, the SHM of the pipe fitting is from 45 MPa to 70 MPa in one general embodiment, from 45 MPa to 60 MPa in another embodiment, and from 45 MPa to 55 MPa in yet another embodiment.

[0067] For example, the pipe fittings made from the composition exhibit resistance to slow crack growth greater than 1,000 hours in one general embodiment, greater than 5,000 hours in another embodiment, and greater than 8,760 hours in yet another embodiment. In a preferred embodiment, the resin may advantageously exceed a test time of 8,760 hours. In other embodiments, the pipe fittings exhibit resistance to slow crack growth of 1,000 to 8,760 hours in one general embodiment, 5,000 to 8,760 hours in another embodiment, and 6,000 to 8,760 hours in yet another embodiment; and in yet another embodiment, the resin exceeds a test time of 8,760 hours.

[0068] Theoretically, a denser linker chain in the final high-strength polyethylene composition is achieved by introducing 1-octene into the composition via a carbon black masterbatch, which is added to the existing linker chain due to the presence of 1-hexene in the base resin of the composition. As a result, pipe products manufactured using the inventive composition containing 1-octene exhibit significantly higher long-term creep performance than pipe products manufactured using compositions without 1-octene. For example, pipe products manufactured using the same base resin formulation without 1-octene fail in <8,000 hours under an applied circumferential stress of 5.66 MPa, while pipe products manufactured using the inventive composition containing both 1-octene and 1-hexene can maintain their integrity for more than >12,186 hours under an applied circumferential stress of 5.91 MPa.

[0069] Other characteristics of the fitting include, for example, a density of 0.955 g / cm³ to 0.966 g / cm³ in one embodiment, a density of 0.955 g / cm³ to 0.963 g / cm³ in another embodiment, and a density of 0.955 g / cm³ to 0.960 g / cm³ in yet another embodiment.

[0070] The yield tensile strength of the pipe fitting may be, for example, 21 MPa to 35 MPa in one embodiment, 21 MPa to 31 MPa in another embodiment, and 21 MPa to 26 MPa in yet another embodiment.

[0071] The resistance of the pipe fitting to slow crack growth can be, for example, >500 hours in one embodiment, 1,000 hours to 8,760 hours in another embodiment, and 5,000 hours to 8,760 hours in yet another embodiment.

[0072] The resistance to rapid crack propagation (RCP) of pipe fittings may be, for example, >10 bar at 0°C in one embodiment, 10 to 25 bar in another embodiment, and 10 to 40 bar in yet another embodiment. As described in ISO 13477, RCP resistance refers to “no crack propagation” or “crack arrest” under applied pressure and impact loads.

[0073] In combination with the above-described characteristics of the fitting, the fitting may also have a notched tube strength of >500 hours in one general embodiment and >8,760 hours in another embodiment. In other embodiments, the notched tube strength may be from 1,000 hours to 8,760 hours in one embodiment and from 5,000 hours to 8,760 hours in another embodiment.

[0074] In a preferred embodiment, the pipe fittings of the present invention exhibit a density of 0.958 g / cm³, a yield tensile strength of ~25 MPa, resistance to slow crack growth for >500 hours, resistance to rapid crack propagation (RCP) of >10 bar at 0°C, and notched pipe strength for >500 hours.

[0075] As described above, the resulting PE plastic pipe is manufactured by extrusion and can be made in various sizes. For example, the pipe diameter can be from 1.6 cm to 250 cm; and the pipe wall thickness can be from 2.3 mm to 14.7 cm. PE pipes can be made into coils of various lengths or straight lengths up to 12 m. Typically, smaller diameters (e.g., <15.2 cm OD) are coiled, and larger diameters (e.g., >15.2 cm OD) are straight.

[0076] In addition, PE pipes can be made in a variety of forms and colors, such as (1) monochrome extrusions such as black pipes; (2) black pipes with co-extruded colored stripes; or (3) black or natural pipes with co-extruded colored layers. Some common colors used in the plastic pipe industry to classify PE pipes include, for example, (1) all black for drinking water or industrial applications; (2) all blue for drinking water, or black with blue stripes; and (3) all yellow for gas pipelines or black with yellow stripes.

[0077] As described above, the compositions of the present invention can be used to produce various PE articles. Furthermore, in a preferred embodiment, the article is a pipe fitting with a high MRS and can be used in high-pressure applications. For example, pipes with high MRS can be used in underwater applications. The PE pipes of the present invention are easy to install, lightweight, non-corrosive, and have a service life of up to 100 years. For example, the resin composition of the present invention maintains an MRS greater than 11.3 MPa in an extrapolated range of 50 to 100 years at 20°C. In a preferred embodiment, the resin maintains an MRS greater than or equal to 11.5 MPa and retains this MRS over an extrapolated life of 50 to 100 years at 20°C.

[0078] In other embodiments, the pipe can be used to transport various types of flowing substances, including drinking water, gas (fluid) and slurry applications; another embodiment includes compression-molded or extruded sheets assembled onto a container by thermoplastic welding.

[0079] Example

[0080] The following embodiments (Inv.Ex.) and comparative embodiments (Comp.Ex.) (collectively, “Examples”) are given to further illustrate the invention in detail, but should not be construed as limiting the scope of the claims. Unless otherwise specified, all parts and percentages are by weight.

[0081] The various terms and symbols used in the embodiments are explained as follows:

[0082] “MRS” stands for Minimum Required Strength.

[0083] “MFR” stands for melt flow rate.

[0084] “I2” or MFR2 is the MFR measured at 190°C with a load of 2.16 kg.

[0085] “I5” or MFR5 is the MFR measured at 190°C with a 5.0 kg load.

[0086] “I21” or MFR21 is the MFR measured at 190°C with a 21.6 kg load.

[0087] "BK" represents black resin.

[0088] “NT” stands for natural resin (i.e., non-black resin).

[0089] “SHM” represents strain hardening modulus.

[0090] “CB MB” represents carbon black masterbatch.

[0091] "CM in CB MB" represents the comonomer in carbon black masterbatch.

[0092] “NA” means not applicable.

[0093] “CB content” represents the carbon black content.

[0094] “OIT” represents oxidation induction time.

[0095] "ISO" stands for International Organization for Standardization.

[0096] Test methods

[0097] The testing methods used in this embodiment are as follows:

[0098] density

[0099] The density of the polymer is measured according to the procedure described in ASTM D792. The density is measured by displacement (Archimedes) method. The sample is weighed in air (dry weight) and then immersed in a fluid (wet weight). The density of the immersion fluid is known, and the weight loss of the sample during immersion allows for the calculation of the sample density. The immersion fluid can be water (Method A) or other liquids (Method B).

[0100] Molding of material sheets is performed according to the method described in ASTM D4703, Annex A.1, Procedure C. Three specimens (~38 mm × ~12.7 mm × ~3 mm) are cut from the sheet upon removal from the press. Density can be measured as “rapid” density (within 1 hour of molding) or annealed density (conditioned for 40+ hours after molding at 23 ± 2 °C and 50 ± 10% RH). All densities reported in the examples were measured using Method B on annealed samples.

[0101] Melt flow rates (I2, I5 and I) 21 )

[0102] The melt flow rate of the resin was determined according to the procedure described in ASTM D1238. This test method involves determining the extrusion rate of the molten thermoplastic resin using an extruder. After a specific preheating time of 7 (+ / - 0.5) minutes, the resin was extruded through a die with a specific length and orifice diameter under specified temperature, load, and piston position in the barrel. Method B of ASTM D1238 was used. Method B is an automated timing method. Here, the sample is extruded from the melt indexer, and the piston stroke is timed over a predetermined distance, which is automated by the position of a movable arm located below the load frame. For I2 up to 10 g / 10 min, the predetermined distance is 6.35 mm; for I2 > 10 g / 10 min, the predetermined distance is 25.4 mm. The weight of the extrudate was determined by volume (distance × orifice area) and melt density. The melt density of polyethylene was taken as 0.7636 g / cm³. Data were reported as MFR in g / 10 min or dg / min. The samples can be run under loads of 21.6 kg, 5.0 kg, or 2.16 kg (i.e., I21, I5, or I2, respectively).

[0103] Gel permeation chromatography (GPC)

[0104] The chromatographic system used consisted of a PolymerChar GPC-IR high-temperature GPC chromatograph equipped with an internal IR5 infrared detector (IR5). The autosampler chamber was set to 160°C, and the column chamber to 150°C. Four Agilent "Mix A" 30 cm 20 μm linear mixed-bed columns were used. The chromatographic solvent used was 1,2,4-trichlorobenzene containing 200 ppm butylated hydroxytoluene (BHT). The solvent source was nitrogen bubbling. The injection volume was 200 μL, and the flow rate was 1.0 mL / min.

[0105] The GPC column setup was calibrated using 21 narrow molecular weight polystyrene standards ranging from 580 g / mol to 8,400,000 g / mol, arranged in six “cocktail” mixtures, with each individual molecular weight spaced at least ten times apart. A “ten-fold interval” refers to the interval between two quantities in a 10:1 ratio. For example, 1.8 and 18, or 25 and 250, have a ten-fold interval. These standards were purchased from Agilent Technologies. The polystyrene standards were prepared as follows: 0.025 g in 50 mL of solvent for molecular weights equal to or greater than 1,000,000 g / mol, and 0.05 g in 50 mL of solvent for molecular weights less than 1,000,000 g / mol. The polystyrene standards were dissolved at 80°C with gentle stirring for 30 minutes. The molecular weight of polystyrene standard peaks was converted to polystyrene molecular weight using equation (EQ1) (as described in Williams and Ward, J. Polym. Sci., Polym. Let.), 6, 621 (1968):

[0106] M 聚乙烯 =A×(M) 聚苯乙烯 ) B (Equation 1)

[0107] Where M is the molecular weight, A has a value of 0.4315, and B equals 1.0.

[0108] A fifth-order polynomial was used to fit the calibration point for the corresponding polyethylene equivalent. A small adjustment to A (approximately 0.375 to 0.445) was made to correct for column resolution and band broadening effects, resulting in a linear homopolymer polyethylene standard with a molecular weight of 120,000 g / mol.

[0109] Total plate counts were performed on the GPC column assembly using decane (prepared in 50 mL of trichlorobenzene (TCB) at a dose of 0.04 g, dissolved under slow stirring for 20 min). Plate counts and symmetry were measured by injection at 200 μL according to the following equations (Equation (EQ2)) and (Equation (EQ3)):

[0110]

[0111] Where RV is the retention volume in milliliters, peak width is in milliliters, peak maximum is the maximum height of the peak, and 1 / 2 height is 1 / 2 the height of the peak maximum.

[0112]

[0113] Where RV is the retention volume in milliliters, and peak width is in milliliters, peak maximum is the position of the peak value, one-tenth height is 1 / 10 of the height of the peak maximum, and a subsequent peak refers to the tail of a peak whose retention volume is later than the peak maximum, while a preceding peak refers to the front of a peak whose retention volume is earlier than the peak maximum. The plate count of the chromatographic system should be greater than 18,000, and the symmetry should be between 0.98 and 1.22.

[0114] Samples were prepared semi-automatically using PolymerChar Instrument Control software, with a target sample weight of 2 mg / mL. Solvent (containing 200 ppm BHT) was added to a pre-bubbled, diaphragm-capped vial via a PolymerChar high-temperature autosampler. The sample was then dissolved at 160°C for 2 hours with low-speed shaking.

[0115] Based on the GPC results, using the internal IR5 detector (measurement channel) of the PolymerChar GPC-IR chromatograph, according to equations (EQ4) to (EQ5), using the PolymerChar GPCOne... TM The software calculates Mn(GPC) and Mw(GPC) based on the baseline-subtracted IR chromatograms at each equidistant data collection point (i) and the polypropylene equivalent molecular weight obtained from the narrow standard calibration curve at point (i) according to equation (EQ1).

[0116]

[0117]

[0118] The polydispersity index is defined as Mw / Mn.

[0119] Comonomer content was determined using nuclear magnetic resonance (NMR).

[0120] Sample preparation

[0121] Samples were prepared by adding ~100 mg of sample to 3.25 g of 1,1,2,2-tetrachloroethane (TCE) in a Norell 1001-7 10 mm NMR tube, wherein 25 wt% was TCE-d2. The solvent contained 0.025 mol (M) of Cr(AcAc)3 as a relaxant. The sample tube was purged with N2, capped, and sealed with Teflon tape, then heated and vortexed at 145 °C to obtain a homogeneous solution.

[0122] Data acquisition parameters

[0123] 13CNMR was performed on a Bruker AVANCE 600MHz spectrometer equipped with a 10mm extended temperature freezer. Data were acquired at a sample temperature of 120°C using a 7.8-second pulse repetition delay, a 90-degree tilt angle, and inverse gating decoupling. All measurements were performed on non-spin samples in lock-up mode. Samples were allowed to equilibrate for seven minutes before data acquisition. The 13CNMR chemical shift internal reference is the EEE terpolymer at 30.0 ppm. EEE refers to the sequence of three ethylene units.

[0124] Data Analysis

[0125] For hexene, use the average of the two peaks, then examine the three other peaks shared by hexene and octene. Subtract the contribution of hexene, then average the differences.

[0126] C13 NMR comonomer content (general description + references)

[0127] The determination of polymer composition using NMR spectroscopy is well known. ASTM D 5017-96, J.C. Crandall et al., “NMR and Macromolecules”, ACS Symposium series 247, ed. J.C. Crandall, Am. Chem. Soc., Washington, DC, 1984, Chapter 9; and J.C. Crandall, “Polymer Sequence Determination”, Academic Press, New York (1977) provide general methods for analyzing polymers by NMR spectroscopy.

[0128] Strain hardening modulus (SHM)

[0129] Strain hardening modulus was determined according to ISO 18488. Resin granules were compressed and molded, then conditioned at 120°C for one hour, followed by controlled cooling to room temperature at a rate of 2°C / min. Tensile bars (dog-bone shaped) were punched from the compression-molded sheet. Tensile tests were performed at 80°C, and strain was recorded using a non-contact elongation meter. The slope between stretch ratios of 8 and 12 was calculated using Neo-Hookean strain measurement (NHSM) and a true stress diagram, as specified in ISO 18488. If failure occurred before the stretch ratio reached 12, the stretch ratio corresponding to the failure strain was considered the upper limit of the slope. If failure occurred before the stretch ratio reached 8.5, the test was considered invalid. In this example, no samples failed before the stretch ratio reached 8.5.

[0130] Various commercially available polyethylene resin products are described in Table I.

[0131] Table I - Characteristics of Polyethylene Products

[0132]

[0133] Notes to Table I: (1) Similar characteristics to PE100 grade.

[0134] (2) No black compounds were found; MRS 11.2; an inflection point was observed.

[0135] (3) Element's MRS 11.2 list has no inflection point.

[0136] Example 1 and Comparative Examples A to C: Compositions

[0137] General procedure for preparing compositions

[0138] The base resin used in the examples and described in Table II comprises bimodal HDPE having high molecular weight (HMW) and low molecular weight (LMW) components. The HMW component is present in the base resin at a concentration ranging from 55 wt% to 65 wt%. The HMW component is prepared in a first reactor, and the LMW component is prepared in a second reactor connected in series with the first reactor. An antioxidant is added to the reactor-grade resin collected from the second reactor; then, the compound made with the antioxidant and the reactor-grade resin is granulated.

[0139] The masterbatch is based on a polyethylene component that serves as a carrier, wherein the polyethylene is an ethylene copolymer with C8 carbon atom groups.

[0140] A final tube resin composition for extrusion is prepared by mixing a base resin and a masterbatch on a continuous mixer typically used for polyolefin processing.

[0141] As described in Table II, Comparative Example A is the base resin and is used as is from the production line. The “base resin” is a bimodal HDPE resin with HMW and LMW components, exhibiting two molecular weight peaks in the molecular weight distribution measured by GPC analysis.

[0142] Comparative Example B uses the same base resin as Comparative Example A, except that the resin is passed through an extruder to intentionally subject it to an additional thermal history. This thermal history is identical when preparing black compounds, as in Comparative Example C and Example 1 of the present invention. "Thermal history" herein refers to the compounding conditions on the extruder used in the examples.

[0143] Comparative Examples A and B contain no carbon black in their compositions. Similarly, Comparative Examples A and B contain a 1-hexene comonomer present in the compositions, but no 1-octene.

[0144] Comparative Example C contains carbon black; and the composition contains 1-hexene and 1-butene comonomers, while Example 1 of the present invention contains carbon black; and the composition contains 1-hexene and 1-octene comonomers.

[0145] Table II: Components of the Examples

[0146] <![CDATA[ Example number ]]> <![CDATA[ formula ]]> <![CDATA[ CM in CB MB ]]> <![CDATA[ CB content (wt%) ]]> Comparative Example A base resin <![CDATA[NA (3) ]]> NA Comparative Example B base resin NA NA Comparative Example C <![CDATA[Base resin + CB MB#1 (1) > 1-Butene 2.25 Embodiment 1 of the present invention <![CDATA[Base resin + CB MB#2 (2) > 1-Octenene 2.25

[0147] Notes to Table II: (1) The carrier resin used in CB MB#1 has a 1-butene comonomer.

[0148] (2) The carrier resin used in CB MB#2 has a 1-octene comonomer.

[0149] (3) NA = Not applicable.

[0150] As described above, Comparative Example C contains 1-butene and 1-hexene comonomers, while Example 1 of the present invention contains 1-hexene and 1-octene comonomers. The comonomer contents of these two examples are described in Table III. The comonomer contents of the compositions were measured using NMR (nuclear magnetic resonance) spectroscopy.

[0151] Table III - Comonomer Content of Examples

[0152]

[0153] The MFR21 and MFR2 of all three components (a) through (c) of the composition were measured using ASTM D1238. Similarly, the density of the components was measured using ASTM D792. These two properties are described in Table IV. The final formulation of Example 1 of the present invention was subjected to triple detector compositional GPC and deconvolution to determine the average molecular weight and polydispersity index of each component.

[0154] Table IV - Characteristics of the polyethylene component in the formulation

[0155]

[0156] Note to Table IV: The final formulation contains 2.25 wt% carbon black.

[0157] The MFR2 and density of the final formulation were measured using ASTM standards D1238 and D792, respectively. Average molecular weight and polydispersity index characteristics were obtained using gel permeation chromatography (GPC). These characteristics of the final formulation of Example 1 of this invention are described in Table V.

[0158] Table V - Characteristics of the final formulation of Example 1 of the present invention

[0159]

[0160] Example 2 and Comparative Examples D to F: Tensile bar samples

[0161] According to ISO 18488, the strain hardening modulus (SHM) of several tensile bar specimens made from the compositions described in Table VI was measured using the procedures described in the Test Methods section above.

[0162] Table VI - Performance of Tensile Bar Test Samples

[0163]

[0164] The results described in Table VI show that adding carbon black to the composition of Example 1 of the present invention did not decrease the SHM compared to the composition of Comparative Example B, where both compositions have the same thermal history. However, adding carbon black to Comparative Example C resulted in a ~10% decrease in SHM. This decrease in SHM is due to the difference in the combination of comonomers and the resulting difference in the chain density. The composition and comonomer content of the examples are described in Table II.

[0165] Example 3 and Comparative Examples H to I: Tube

[0166] General procedure for preparing tube test samples

[0167] The resin composition prepared by the above procedure and described in Table VII is extruded by tube extrusion to form a tube sample for testing. The extrusion method for manufacturing the tube is a well-known method in the field of tube manufacturing. For MRS determination, the extrusion size is... The pipe. Dimensions This is the outer diameter of the pipe, and the dimension "3mm" is the wall thickness. This pipe size is typical for pipe testing and is tested according to EN standard 12201-2 (European standard).

[0168] In having General-purpose HDPE pipes are extruded on an extrusion line with a screw and L / D ratio of 28. The extruder temperature settings are: 200°C for all four extruder zones, 200°C for the adapter flange, and 200°C for the extruder head. A water-cooled hopper zone is used during extrusion. The extruder head used is a support-type head; and the die geometry is a 38.4mm diameter die with a 30.9mm needle diameter. The tube was calibrated using a standard disc calibration unit and a vacuum chamber in which a vacuum of 0.3 bar was applied.

[0169] The linear velocity was 3.5 m / min, the screw rpm was 70 (min⁻¹), the resulting extruder pressure was 194 bar, and the material temperature was 190°C. The downstream equipment consisted of one vacuum tank and two cooling tanks with spray cooling. The tubes were cut using Graewe tube cutting units and Graewe tracks.

[0170] For the slow crack growth (SCG) test on the tube sample, the tube sample is extruded using an extruder as described above, wherein the tool is adjusted and a device with... The calibration unit for the diameter is equipped with a device that accommodates an outer diameter of [missing information]. The water tank contains pipes with a wall thickness of 10 mm. It is known to those skilled in the art that, according to EN 12201, it is possible to manufacture water tanks with an outer diameter smaller than... The tube used for testing has a wall thickness of 10mm.

[0171] General procedure for testing tube samples

[0172] Pipe samples were tested at Element, a widely recognized testing organization in the pipe industry, to determine the long-term circumferential stress properties of the resin. Testing was conducted according to ISO 1167 (Parts 1 and 2). Regressions were performed at three temperatures: 20°C, 60°C, and 80°C. At each selected temperature, the resin was tested for 10,000 hours and beyond without exhibiting brittle fracture or an inflection point. The MRS value of the resin was calculated according to the procedures in ISO 9080.

[0173] Slow crack growth was induced in the tube sample according to the notched tube test procedure of ISO 13479. The pre-notched tube was subjected to a pressure of 9.2 bar in a water tank at 80°C. According to ISO 13479, the wall thickness of the tube sample at the notched portion used for testing was between 0.78 and 0.82 times the minimum wall thickness of the unnotched portion of the tube sample.

[0174] The MRS of the compositions described in Table VII were measured using a 32 mm tube according to the procedure described in ISO 9080-2012.

[0175] Table VII - Performance of Test Tube Samples

[0176]

[0177] Table VIII describes the various physical properties measured on the test samples, where density, OIT, I2, I5, I21, and CB content were measured on the resin composition of Example 1 of the present invention, and SHM properties were measured on plate test specimens made from the composition of Example 1 of the present invention. Both ASTM and ISO standards are used to determine density, oxidation induction time (OIT), melt flow rate at various loads (e.g., at 2.16 kg, 5.0 kg, and 21.6 kg), and carbon black content. SHM, which represents the polymer's resistance to slow crack growth, was measured according to the procedure described in ISO 18488.

[0178] Table VIII - Physical Properties of Embodiment 1 of the Invention

[0179]

[0180] The I5 measurement of 0.31 dg / min described in Table VIII indicates that the composition of Example 1 of the present invention has better flowability compared to the other PE 112 resins described in Table I. All commercial PE 112 grades have an I5 of less than 0.31 dg / min.

[0181] The composition of Example 1 of this invention has an SHM measurement of 54 MPa, indicating that the composition belongs to the ISO standard product category suitable for trenchless installation. Other commercial PE 112 resins, such as El-Lene HDPE H112 PC, have an SHM of 48 MPa, which is at least 10% lower than that of Example 1 of this invention.

Claims

1. A high-strength multimodal polyethylene composition that can be used to manufacture plastic articles therefrom, said composition comprising a mixture of the following substances: (a) at least one first polymer resin, said first polymer resin having a molecular weight greater than 350,000 g / mol and a density of 0.920 g / cm³. 3 Up to 0.935 g / cm 3 The high molecular weight copolymer resin, wherein the first polymer resin is a reaction product of ethylene and a first comonomer; (b) at least one second polymer resin, said at least one second polymer resin having a molecular weight of less than 30,000 g / mol and a density greater than 0.965 g / cm³. 3 Low molecular weight homopolymer resins; and (c) At least one third polymer resin, said at least one third polymer resin having a molecular weight of 50,000 g / mol to 150,000 g / mol and a density of 0.915 g / cm³. 3 Up to 0.925 g / cm 3 A medium molecular weight copolymer resin, wherein the third polymer is a reaction product of ethylene and a second comonomer different from the first comonomer; and The second comonomer has short-chain branches with carbon atoms longer than C4 than the first comonomer; and the high-strength multimodal polyethylene composition has a minimum required strength greater than 11.3 MPa.

2. The composition according to claim 1, wherein the first comonomer is 1-hexene, and wherein the second comonomer is 1-octene.

3. The composition according to claim 1, wherein the high-strength multimodal polyethylene composition has a minimum required strength of 11.3 MPa to 13 MPa.

4. The composition according to claim 1, wherein the high-strength multimodal polyethylene composition has a minimum required strength of 11.3 MPa to 11.7 MPa.

5. The composition according to claim 1, wherein the high-strength multimodal polyethylene composition is a trimodal polyethylene composition.

6. The composition according to claim 1 further comprises (d) a carbon black material; wherein the carbon black material is derived from a carbon black masterbatch comprising a blend of carbon black and a carrier polymer resin, wherein the carrier polymer resin is the at least one third polymer resin, i.e., component (c).

7. The composition according to claim 1, wherein the at least one first polymer resin is an ethylene copolymer; wherein the at least one second polymer resin is an ethylene homopolymer; and wherein the at least one third polymer resin is an ethylene copolymer.

8. The composition according to claim 1, wherein the concentration of the at least one first polymer resin is 50% to 60% by weight; wherein the concentration of the at least one second polymer resin is 35% to 45% by weight; and wherein the concentration of the at least one third polymer resin is 2% to 5% by weight.

9. The composition according to claim 6, wherein the concentration of the carbon black material is 2% to 2.5% by weight.

10. A method for preparing a high-strength multimodal polyethylene composition suitable for manufacturing plastic articles, the method comprising: compounding: (a) at least one first polymer resin, said at least one first polymer resin comprising a copolymer resin with a molecular weight greater than 350,000 g / mol; (b) at least one second polymer resin, said at least one second polymer resin comprising a homopolymer resin with a molecular weight of less than 30,000 g / mol; as well as (c) at least one third polymer resin, said at least one third polymer resin comprising a copolymer resin having a molecular weight of 50,000 g / mol to 150,000 g / mol; The high-strength multi-peak polyethylene composition described herein has a minimum required strength greater than 11.3 MPa.

11. A method for producing controlled articles, the method comprising the following steps: (i) Provides a high-strength trimodal polyethylene composition that can be used to manufacture the tubular articles therefrom, the composition comprising a mixture of the following substances: (a) at least one first polymer resin, said at least one first polymer resin comprising a copolymer resin with a molecular weight greater than 350,000 g / mol; (b) at least one second polymer resin, said at least one second polymer resin comprising a homopolymer resin with a molecular weight of less than 30,000 g / mol; as well as (c) at least one third polymer resin, said at least one third polymer resin comprising a copolymer resin with a molecular weight of 50,000 g / mol to 150,000 g / mol; wherein said high-strength multimodal polyethylene composition has a minimum required strength greater than 10 MPa; and (ii) Using an extrusion method, the composition of step (i) is processed into a tube to form the tube article; The tubular material described therein has a minimum required strength of greater than 11.3 MPa.

12. A tubular product manufactured by the method according to claim 11.

13. The pipe product of claim 12, wherein the pipe product exhibits a slow crack growth performance exceeding 6,000 hours as tested according to ISO 13479.

14. The tubular product of claim 13, wherein the slow crack growth performance is greater than or equal to 8,760 hours.

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