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BR-112023007506-B1 - Polyethylene composition, process for the production of a polyethylene composition, article, tube and use of a polyethylene composition.

BR112023007506B1BR 112023007506 B1BR112023007506 B1BR 112023007506B1BR-112023007506-B1

Abstract

POLYETHYLENE COMPOSITION, PROCESS FOR PRODUCING A POLYETHYLENE COMPOSITION, ARTICLE, TUBE AND USE OF A POLYETHYLENE COMPOSITION. The invention relates to a polyethylene (PE) composition comprising a base resin comprising (A) a first fraction of ethylene homo- or copolymer, wherein fraction (A) has a melt flow index, MFR 2, of 100 to 600 g/10 minutes; and (B) a second fraction of ethylene 1-hexene copolymer, wherein fraction (A) has a lower molecular weight than fraction (B) and wherein fraction (B) is present in an amount of 50.0 to 58.0% by weight, based on the total weight of the base resin; wherein the base resin has a content of 1-hexene-derived units of 0.44 to 0.79 molar percent, based on the total amount of base resin; wherein the base resin has a molecular weight distribution, with the ratio Mw/Mn, of 32 to 40 and the base resin has an average molecular weight Z, Mz, of more than 1,500 kg/mol; wherein the polyethylene composition has a melt flow index MFR 5 of 0.10 to 0.25 g/10 minutes; and a melt flow index ratio, FRR 21/5, of 30 to 42; and wherein the composition (...).

Inventors

  • Qizheng Dou
  • Victor SUMERIN
  • Elena Pomakhina
  • Jari Äärilä

Assignees

  • BOREALIS AG

Dates

Publication Date
20260310
Application Date
20211025
Priority Date
20201026

Claims (12)

  1. 1. Polyethylene composition CHARACTERIZED in that it comprises a base resin comprising: (A) a first fraction of ethylene homopolymer or copolymer, wherein fraction (A) has a melt flow index, MFR2, as measured in accordance with ISO 1133, of 115 to 450 g/10 minutes; and (B) a second ethylene-1-hexene copolymer fraction, wherein fraction (A) has a lower molecular weight than fraction (B) and fraction (B) is present in an amount of 53.0 to 58.0% by weight, based on the total weight of the base resin; wherein the base resin has a content of 1-hexene derived units of 0.44 to 0.79% molar, based on the total amount of base resin; wherein the base resin has a molecular weight distribution, with the ratio Mw/Mn, of 32 to 40 and the base resin has an average molecular weight Z, Mz, greater than 1,500 kg/mol; wherein the polyethylene composition has a melt flow index MFR5 of 0.10 to 0.25 g/10 minutes; and a melt flow index ratio, FRR21/5, of 30 to 42; in which the polyethylene composition has a critical temperature, Tc, in the rapid crack propagation test equal to or less than -10°C and not less than -25°C.
  2. 2. Polyethylene composition, according to claim 1, CHARACTERIZED in that the polyethylene composition has a hardening modulus of 75 to 110 MPa; and/or in that the polyethylene composition has a failure time in the accelerated creep test (ACT) of more than 1500 h; and/or in that the polyethylene composition has a failure time in the short-duration pressure resistance test (STPR) at a stress level of 5.4 MPa at 80°C of at least 200 h; and/or in that the polyethylene composition has a failure time in the short-duration pressure resistance test (STPR) at a stress level of 12.0 MPa at 20°C of at least 130 h; and/or in that the polyethylene composition has a yield strength at 80°C of 6.0 to 7.0 MPa; and/or where the base resin has a viscosity at a shear stress of 747 Pa (eta747) of more than 700 kPa*s and not more than 1400 kPa*s.
  3. 3. Polyethylene composition, according to any one of claims 1 to 2, CHARACTERIZED in that fraction (A) has a melt flow index, MFR2, as measured according to ISO 1133, of 100 to 230 g/10 minutes or in that fraction (A) has a melt flow index, MFR2, as measured according to ISO 1133, of 270 to 380 g/10 minutes.
  4. 4. Polyethylene composition, according to any one of claims 1 to 3, CHARACTERIZED in that fraction (B) of the base resin has a content of 1-hexene derived units of 0.85 to 1.58 molar percent based on the total amount of fraction (B); and/or in that fraction (B) is present in an amount of 53.0 to 55.0 percent by weight based on the total weight of the base resin.
  5. 5. Polyethylene composition, according to any one of claims 1 to 4, CHARACTERIZED in that the base resin has a number average molecular weight, Mn, equal to or greater than 7,300 g/mol; and/or in that the base resin has a number average molecular weight, Mn, equal to or less than 9,150 g/mol; and/or in that the base resin has a molecular weight distribution, with the ratio Mw/Mn, from 32.5 to 39.5; and/or in that the base resin has a number average molecular weight Z, Mz, greater than 1,700 kg/mol.
  6. 6. Polyethylene composition, according to any one of claims 1 to 5, CHARACTERIZED in that the base resin has a density of 945.5 to 948.5 kg/m3; and/or in that the polyethylene composition has a density of 955 to 961 kg/m3; and/or in that the base resin has a content of 1-hexene derived units of 0.46 to 0.76 mol% based on the total amount of base resin.
  7. 7. Polyethylene composition, according to any one of claims 1 to 6, CHARACTERIZED in that the polyethylene composition has a melt flow index, MFR5, of 0.14 to 0.20 g/10 minutes; and/or in that the polyethylene composition has a critical temperature, Tc, in the rapid crack propagation test equal to or less than -12°C and/or not less than -23°C.
  8. 8. Process for producing a polyethylene composition as defined in any one of claims 1 to 7, CHARACTERIZED in that the base resin is produced in a multi-stage polymerization process in the presence of a Ziegler-Natta catalyst.
  9. 9. Article CHARACTERIZED by the fact that it comprises a polyethylene composition as defined in any one of claims 1 to 7.
  10. 10. Article according to claim 9, CHARACTERIZED by being a pipe or pipe fitting.
  11. 11. Pipe, according to claim 10, CHARACTERIZED in that: the pipe has a critical temperature, Tc, in the rapid crack propagation test equal to or less than -10°C and not less than -25°C; and/or the pipe has a failure time in the accelerated creep test (ACT) of more than 3000h; and/or the pipe has a failure time in the short-duration pressure resistance test (STPR) at a stress level of 5.4 MPa at 80°C of at least 200h; and/or the pipe has a failure time in the short-duration pressure resistance test (STPR) at a stress level of 12.0 MPa at 20°C of at least 200h.
  12. 12. Use of a polyethylene composition as defined in any one of claims 1 to 7 CHARACTERIZED by the fact that it is for producing an article.

Description

[0001] The present invention relates to a polyethylene composition comprising a base resin, a polyethylene composition that can be obtained by a multi-stage process, an article comprising a polyethylene composition, a tube, and the use of a polyethylene composition comprising a base resin to produce an article. [0002] Polyolefin pipes and especially polyethylene pipes are conventionally used for transporting water, gas, as well as industrial liquids and suspensions. Due to their versatility, ease of production and installation, as well as their non-corrosiveness, their use is constantly increasing. [0003] The fluids transported may have varying temperatures, typically within the temperature range of around 0°C to around 50°C. According to ISO 9080, polyethylene pipes are classified by their minimum required strength, i.e., their ability to withstand different circumferential stresses for 50 years at 20°C without fracturing. Thus, pipes that withstand a circumferential stress of 8.0 MPa (MRS8.0) are classified as PE80 pipes, and pipes that withstand a circumferential stress of 10.0 MPa (MRS10.0) are classified as PE100 pipes. The service temperature for PE100 is typically within the temperature range of around 0°C to around 50°C. [0004] To meet PE80 requirements with multimodal resins manufactured by conventional Ziegler-Natta catalysts, the density needs to be at least 940 kg/m3, and to meet PE100 requirements, the density needs to be above 945 kg/m3. However, the density of a polyethylene resin is directly connected to its crystallinity. The higher the crystallinity of a polyethylene resin, the lower its resistance to slow crack growth. In other words, all polyethylene materials for pipe pressure resistance suffer from both crystallinity dependence and density dependence on slow crack growth. When density is increased, resistance to slow crack growth (SCG) decreases. [0005] The manufacture of polyethylene materials to be used in pressure pipes is discussed, for example, in an article by Scheirs et al. (Scheirs, Bohm, Boot and Leevers: PE100 Resins for Pipe Applications, TRIP Vol. 4, No. 12 (1996) pp. 408-415). [0006] Pipes designed for transporting pressurized fluids (so-called pressure pipes) to withstand higher design and internal stresses require both greater creep resistance and greater stiffness. On the other hand, pressure pipes must also meet demanding requirements regarding their resistance to slow crack propagation, low friability, and high impact resistance. However, these properties are contradictory, making it difficult to provide a pipe composition that excels in all these properties simultaneously. Furthermore, since polymer pipes are generally manufactured by extrusion or, to a lesser extent, injection molding, the polyethylene composition must also have good processability. Finally, the polymeric composition used for the pipe must also exhibit good weldability, because piping systems are normally constructed by welding or fusion, either as a general method of joining parts of the system or joining layers, for example, in multilayer piping structures, such as butt welding, electrofusion, spin welding (friction welding), and manual or automated welding with additional welding materials. Therefore, it is important that the composition used exhibits a certain minimum weld strength. It is known that, especially for polymeric compositions with fillers, weld strength is typically low. [0007] It is known that, in order to meet the opposing requirements for a piping material, bimodal polyethylene compositions can be used. Such compositions are described, for example, in EP 0 739 937 and WO 02/102891. The bimodal polyethylene compositions described in these documents typically comprise a low molecular weight polyethylene fraction and a high molecular weight fraction of an ethylene copolymer comprising one or more alpha-olefin comonomers. [0008] EP 1 987 097, on behalf of Chevron Phillips Chemical Company, describes a polyethylene suitable for pipes with a pellet density of 947 kg/m3 to 954 kg/m3 and MFR21 (ASTM D1238, 21.6 kg load) of 1 to 30 g/10 minutes. The exemplified resins show a weighted average molecular weight of 278 to 346 kg/mol in Mw/Mn of 30.5 to 35.1. [0009] EP 1 781 712, on behalf of Univation Tech LLC [US], describes several compositions, including, among others, a high-strength bimodal polyethylene composition with a density of 0.940 g/cc or more, the composition comprising a high molecular weight polyethylene component with a higher weighted average molecular weight (HwHMW) and a low molecular weight polyethylene component with a lower weighted average molecular weight (HwLMW), wherein the ratio of the higher weighted average molecular weight to the lower weighted average molecular weight (MwHMW:MwLMW) is 30 or more; and the composition qualifies as a PE100 material such that, according to ISO 1167, a pipe formed from the composition that is subjected to the internal strength of the