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US-12624200-B2 - Density and chemical composition control for polymer with good stress crack properties

US12624200B2US 12624200 B2US12624200 B2US 12624200B2US-12624200-B2

Abstract

Provided are polyethylene copolymers with improved stress crack resistance, methods for making such copolymers, and films made from the same. The polyethylene copolymers include at least 95 wt % ethylene and at most 5 wt % of at least one comonomer having 3 to 18 carbon atoms; and further have a 30% single point notched constant tensile load of at least 1,000 hours, a density of 0.931 to 0.936 g/cm 3 , a melt index (I 2 ) of 0.1 to 0.5 g/10 min, and a 25-75 chemical composition distribution index of 0.3 or more.

Inventors

  • Martin ANTENSTEINER
  • Nathaniel B. Guy
  • Porter C. Shannon
  • Richard E. Pequeno

Assignees

  • EXXONMOBIL CHEMICAL PATENTS INC.

Dates

Publication Date
20260512
Application Date
20210413

Claims (9)

  1. 1 . A polyethylene copolymer with improved stress crack resistance, comprising: at least 95 wt % ethylene-derived units; and at most 5 wt % of units derived from at least one comonomer having 3 to 18 carbon atoms, wherein the polyethylene copolymer has a 30% single point notched constant tensile load of at least 1,000 hours, a density of 0.931 to 0.936 g/cm 3 , a melt index (I2) of 0.1 to 0.5 g/10 min, and a 25-75 chemical composition distribution index (25-75 CCDI) of 0.3 or more.
  2. 2 . The polyethylene copolymer of claim 1 , further having a melt index ratio (MIR) of 30 to 70.
  3. 3 . The polyethylene copolymer of claim 1 , further having a 36% single point notched constant tensile load of at least 600 hours.
  4. 4 . The polyethylene copolymer of claim 1 , further having one or more of the following properties: (a) a molecular weight distribution (MWD) of 3 to 6; (b) a Composition Distribution Breadth Index (CDBI) of 85% or more; and (c) a branching index (g'vis) of 0.85 to 0.95.
  5. 5 . The polyethylene copolymer of claim 4 , having all of the properties (a)-(c).
  6. 6 . The polyethylene copolymer of claim 1 , wherein the comonomer is selected from the group consisting of propylene, 1-butene, 1-pentene, 1-hexene, 1-heptene, 1-octene, 4-methylpent-1-ene, 1-decene, 1-dodecene, 1-hexadecene, 1,3-hexadiene, 1,4-hexadiene, cyclopentadiene, dicyclopentadiene, 4-vinylcyclohex-1-ene, methyloctadiene, 1-methyl-1,6-octadiene, 7-methyl-1,6-octadiene, 1,5-cyclooctadiene, norbornadiene, ethylidene norbornene, 5-vinylidene-2-norbornene, 5-vinyl-2-norbornene, isoprene, styrene, butadiene, isobutylene, chloroprene, acrylonitrile, and a cyclic olefin.
  7. 7 . The polyethylene copolymer of claim 1 , wherein the comonomer is selected from the group consisting of 1-butene, 1-hexene, and 1-octene.
  8. 8 . The polyethylene copolymer of claim 1 , wherein the comonomer is 1-hexene.
  9. 9 . A film made of the polyethylene copolymer of claim 1 .

Description

CROSS-REFERENCE TO RELATED APPLICATIONS This application is a National Phase Application claiming priority to PCT Application Serial No. PCT/US2021/027063, filed Apr. 13, 2021, which claims the benefit of U.S. Provisional Application 63/016,889 filed Apr. 28, 2020 entitled “Polymer Chemical Composition and Process for Producing Same” and U.S. Provisional Application 63/167,937 filed Mar. 30, 2021 entitled “Density and Chemical Composition Control for Polymer with Good Stress Crack Properties”, the entireties of which are incorporated by reference herein. FIELD OF THE INVENTION This disclosure relates to polyethylene polymers, polymerization processes for making such polyethylene polymers, and geomembranes and films made therefrom. BACKGROUND OF THE INVENTION Geomembranes are very low permeability synthetic membranes, liners, or barriers used to control gas or liquid migration in a project, structure, or system. In many instances, geomembranes are made from continuous polymeric sheets or geotextiles (impregnated with asphalt, elastomer, or polymer sprays). In some instances, geomembranes involve multilayered bitumen geocomposites. In some instances, geomembranes are prepared by melt-blown or cast film processes. Because the films tend to be relatively thick, the polymer composition should have sufficient melt strength to yield a commercially-viable, blown film. As such, a polymer having a density greater than 0.925 g/cm3 yields appropriate tensile strength for geomembrane applications. Unfortunately, crack resistance suffers as density increases. A balance is sought between tensile strength and crack resistance. In a gas-phase copolymerization process, an alkene and a comonomer yield a polyolefin. In some instances, the process also includes hydrogen and other raw materials. The gas-phase reactor may include a fluidized-bed reactor, a compressor, and heat exchanger. In some instances, fluidizing gas (which is passed through a distributor plate near the bottom of the reactor vessel) maintains the copolymerization reaction in a two-phase fluidized bed of gaseous reactants and granular polyolefin. Catalyst is added to the fluidized bed, and the heat of the exothermic reaction is transferred to the circulating gas stream. The gas stream is compressed, cooled in an external recycle line, and reintroduced through the distributor plate. Reactant concentrations are managed by make-up feed streams. Several operating conditions affect the gas-phase copolymerization process and the resulting copolymer. Examples include operating temperature, comonomer type and amount, and type and quantity of catalyst. Polyolefin properties subject to process influences include molecular weight, molecular weight distribution, polymer density, melt index, impact resistance, environmental stress cracking resistance (ESCR), single point notched constant tensile load (“SP-NCTL” or simply “NCTL”), and others. Depending upon properties, some polyolefins are better suited for geomembrane applications. BRIEF SUMMARY OF THE INVENTION The present disclosure provides a polyethylene copolymer made from or containing ethylene and an olefin comonomer having 3 to 18 carbon atoms, wherein the polyethylene copolymer has a density in the range of 0.931 to 0.936 g/cm3, a melt index (I2) in the range of 0.1 to 0.5 g/10 min, and a 25%-75% chemical composition distribution index (25-75 CCDI), described in more detail herein, of greater than 0.3, all of which can be independently adjusted by reactor conditions. The polyethylene copolymer may include at least 95 wt % ethylene and at most 5 wt % of at least one comonomer having 3 to 18 carbon atoms, said wt % s based on the total mass of all monomers in the comonomer. The polyethylene copolymer can have a 30% single point notched constant tensile load of at least 1,000 hours, a density of 0.931 to 0.936 g/cm3, a melt index (I2) of 0.1 to 0.5 g/10 min, and a 25-75 chemical composition distribution index of 0.3 or more. It has been surprisingly and unexpected discovered that polyethylene copolymers having a unique combination of density, melt index (I2), and chemical composition distribution can exhibit significantly improved stress crack performance over similar polyethylene copolymers of the same density and MI. Indeed, it was nothing short of surprising and unexpected to observe such a significant difference in stress crack performance in polyethylene copolymers having a density in the range of 0.931 to 0.936 g/cm3 and a melt index (I2) in the range of 0.1 to 0.5 g/10 min. As such, the polyethylene copolymers provided in various embodiments herein are particularly suitable for the geomembrane market. BRIEF DESCRIPTION OF THE DRAWINGS So that the manner in which the above recited features of the present invention can be understood in detail, a more particular description of the invention, briefly summarized above, may be had by reference to embodiments, some of which are illustrated in the appended drawings. I