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RU-2861713-C2 - HIGH-DENSITY POLYETHYLENE FOR USE IN PIPES WITH IMPROVED PRESSURE CHARACTERISTICS AND MECHANICAL PROPERTIES

RU2861713C2RU 2861713 C2RU2861713 C2RU 2861713C2RU-2861713-C2

Abstract

FIELD: polyethylene compositions. SUBSTANCE: proposed are a multimodal polyethylene composition for manufacturing an article, comprising a base resin containing a copolymer of ethylene and at least one comonomer selected from alpha-olefins having from 3 to 10 carbon atoms, and optionally additives in an amount of 10 mas.% or less, where the base resin comprises a first homopolymer ethylene component (A) and a second copolymer ethylene component (B), which is a copolymer of ethylene and at least one alpha-olefin comonomer with 3-10 carbon atoms, component (B) has a higher weight average molecular weight than component (A), and the weight ratio of the first homopolymer ethylene component (A) to the second copolymer ethylene component (B) is from 45:55 to 55:45; a method for producing the proposed multimodal polyethylene composition; a pipe or fitting and use of the proposed composition for improving pressure resistance and/or resistance to slow crack growth of a pipe. EFFECT: obtaining multimodal polyethylene compositions that demonstrate an improved balance of properties with respect to resistance to slow crack growth, resistance to hydrostatic pressure at room temperature and at elevated temperatures, tensile properties, strain hardening modulus, impact characteristics and processing characteristics. 13 dep cl, 3 dwg, 6 tbl, 5 ex

Inventors

  • KUMAR ASHISH
  • ANTONY NISHA
  • KALIAPPAN SENTHIL KUMAR

Dates

Publication Date
20260508
Application Date
20231221
Priority Date
20221222

Claims (20)

  1. 1. A multimodal polyethylene composition for the manufacture of an article, comprising a base resin containing a copolymer of ethylene and at least one comonomer selected from alpha-olefins having from 3 to 10 carbon atoms, and optionally additives in an amount of 10 wt.% or less,
  2. wherein the base resin comprises a first homopolymer ethylene component (A) and a second copolymer ethylene component (B), which is a copolymer of ethylene and at least one alpha-olefin comonomer with 3-10 carbon atoms,
  3. component (B) has a higher weight average molecular weight than component (A), and
  4. the mass ratio of the first homopolymer ethylene component (A) to the second copolymer ethylene component (B) is from 45:55 to 55:45,
  5. and the base resin has:
  6. (a) a density of at least 945.0 kg/ m3 and not more than 955.0 kg/ m3 , determined in accordance with ISO 1183-1,
  7. (b) a melt flow rate MFR 5 measured at 190 °C, 5 kg, as determined according to ISO 1133, of 0.15 to 0.25 g/10 min,
  8. (c) a comonomer content of not more than 1.2% by weight, based on the total weight of the base resin, as determined by quantitative analysis using the 13 C{ 1 H} NMR (nuclear magnetic resonance) method,
  9. and where the polyethylene composition has:
  10. (d) a molecular chain length, determined by quantitative 13C { 1 H} NMR (nuclear magnetic resonance) analysis, of at least 850 and not more than 1200.
  11. 2. A multimodal polyethylene composition according to claim 1, having:
  12. (e) a tensile modulus of elasticity of at least 900 MPa and not more than 1200 MPa, determined in accordance with ISO 527-2.
  13. 3. A multimodal polyethylene composition according to claim 1 or 2, having:
  14. (f) a strain hardening modulus of at least 45 MPa and not more than 85 MPa.
  15. 4. A multimodal polyethylene composition according to any one of paragraphs 1-3, having:
  16. (g) a content of lamellar fraction having a lamellar thickness greater than 21.7 nm, determined in accordance with the self-nucleation annealing (SSA) technique, amounting to from 28 to 52 wt.%, based on the total crystalline fraction.
  17. 5. A multimodal polyethylene composition according to any one of paragraphs 1-4, having:
  18. (h) a content of lamellar fraction having a lamellar thickness in the range of more than 11.8 to 21.7 nm, determined in accordance with the self-nucleation annealing (SSA) technique, amounting to from 33.0 to 52 wt.%, based on the total crystalline fraction.
  19. 6. A multimodal polyethylene composition according to any one of paragraphs 1-5, having:
  20. (i-1) hydrostatic pressure resistance (HPT) at 80 °C and 5.6 MPa, determined in accordance with ISO 1167-1:2006, of at least 2000 hours to failure time, and/or

Description

The present invention relates to a multimodal polyethylene composition suitable for use in pipes, with an improved balance of pressure resistance and resistance to slow crack growth, along with improved mechanical properties. The present invention also relates to a method for producing such a multimodal polyethylene composition and to a pipe or fitting containing such a multimodal polyethylene composition. Prior art Pipes made of polymeric materials have a variety of applications, including fluid transport, i.e., the transportation of liquids, suspensions, and gases, such as water or natural gas. During transport, it is normal for the liquid to be under pressure. In addition, the transported liquid may have varying temperatures, typically ranging from approximately 0°C to approximately 50°C. Such pressure pipes are preferably made of polyolefin plastics, typically unimodal or bimodal ethylene plastics, such as medium-density polyethylene (MDPE; density: 930-942 kg/ m3 ) and high-density polyethylene (HDPE; density: 942-965 kg/ m3 ), or polypropylene compounds. The term "pressure pipe" as used in this document refers to a pipe that, when in use, is subject to positive pressure, i.e., the pressure inside the pipe is greater than the pressure outside the pipe. Polymer pipes are typically manufactured using extrusion or, to a lesser extent, injection molding. A typical polymer pipe extrusion system includes an extruder, a die head, a sizing unit, a cooling unit, a haul-off unit, and a cutting and/or winding unit. The production of polyethylene materials for use in pressure pipes is discussed, for example, in the article by Scheirs et al (Scheirs, Bohm, Boot and Leevers: PE100 Resins for Pipe Applications, TRIP Vol. 4, No. 12 (1996) pp. 408-415). Pressure pipe materials are classified according to the long-term hydrostatic strength of thermoplastic materials on pipe-shaped specimens using extrapolation from ISO 9080 and ISO 12162, for example, PE80 or PE100. Classification based on the minimum long-term strength (MRS) of ISO 9080 specifies that PE100 material will have a service life of at least 50 years at 20°C with an internal hoop stress of 10 MPa. Higher MRS for PE100 material is typically achieved using higher-density polyethylene compounds. Compounds based on multimodal high-density polyethylene (HDPE) are well known for use in pipes, particularly as PE100 pressure pipes. PE100 materials are commonly used for applications such as pressurized gas pipes, potable water pipes, sewer pipes, and industrial pipes. EP 2743305 A1 discloses a pipe comprising a high density polyethylene based mixture comprising (A) from 55 to 95 wt.% of a multimodal high density polyethylene component having a density of at least 940 kg/ m3 , and (B) from 5 to 45 wt.% of an ultra high molecular weight polyethylene homopolymer having a nominal viscosity molecular weight Mv of from 1,000,000 to 4,000,000 g/mol; and wherein said mixture has an MFR 21 of 10.0 g/10 min or less and a density of at least 940 kg/ m3 . The pipe may have a pressure resistance of at least 100 h at a stress of 14.5 MPa and/or at least 1000 h at 13.9 MPa. In addition, such pipes demonstrate resistance to sagging, and the mixture demonstrates good homogeneity. EP 3293208 A1 discloses a bimodal polyethylene composition comprising a low molecular weight polyethylene homopolymer fraction and a high molecular weight polyethylene copolymer fraction, wherein the high molecular weight polyethylene fraction has a C4-C10 alpha-olefin, preferably 1-butene, comonomer content of from 0.25 to 3 mol%, wherein the low molecular weight polyethylene content relative to the total amount of the bimodal polyethylene composition is from 40 to 65 wt%; and the bimodal polyethylene composition has a MWD 2 /1 (molecular weight distribution) of more than 0.7 and a Mw 2 /1 (weight average molecular weight) of more than 15. Such a bimodal polyethylene composition has an improved balance between pressure resistance corresponding to PE112 and resistance to slow crack growth for more than 3500 hours. New installation methods, such as trenchless and sand-bedded installations, require the use of polyethylene resin pipes with higher slow crack growth resistance. Requirements for slow crack growth resistance are becoming increasingly stringent, and many existing products fail to meet these requirements, along with the required pressure ratings. These applications require the pipe material to meet a wide range of rheological, mechanical, and pressure-response properties. Many of these properties are conflicting, difficult to achieve simultaneously, as improving one property degrades another. For example, attempting to improve hydrostatic pressure (HPT) performance, typically by increasing material density, results in decreased slow crack growth resistance or notched pipe test (NPT) performance. Improving NPT performance typically requires increasing the comonomer content or the degree of linking cha