WO2020025317A1 - Polyethylene with ionomeric groups for increased environmental stress cracking resistance - Google Patents

Abstract

A polyethylene composition having increased environmental stress crack resistance comprises a polymer blend of a multimodal high density polyethylene (HOPE) and an ionomeric polyethylene. In a method of forming a polyethylene composition having increased environmental stress crack resistance, a multimodal high density polyethylene (HOPE) is modified by combining the multimodal HOPE with an ionomeric polyethylene.

Description

POLYETHYLENE WITH IONOMERIC GROUPS FOR INCREASED ENVIRONMENTAL

STRESS CRACKING RESISTANCE

TECHNICAL FIELD

[0001 ] The invention relates to high density polyethylene compositions that have improved environmental stress crack resistance.

BACKGROUND

[0002] Synthetic polymeric materials, particularly thermoplastic resins, are widely used in the manufacturing of a variety of end-use articles ranging from medical devices to food containers. Conventional propylene based polymeric materials have long been used in processes like thermoforming, blow molding, coating, etc., requiring high melt strength which could be achieved by increasing molecular weight and broadening of molecular weight distribution. Molecular weight and molecular weight distribution can be modified in the polymerization process itself by choosing particular process conditions and catalysts.

[0003] Polypropylene (PP) has widely been used to produce caps and closures. To achieve a necessary cap strength, however, an inner liner (e.g., made from ethylene vinyl acetate (EVA), polyvinylchloride (PVC), butyl rubber, or the like) is typically required to achieve the requisite seal properties and organoleptic properties. Such two-layer caps are costly. On the other hand, high density polyethylene (HDPE) typically possesses requisite stiffness, flow properties, and better organoleptic properties for making one-piece closures, such as screw caps. HDPE, however, mostly lacks in its ability to resist cracking over time (as measured by environmental stress cracking resistance (ESCR) testing). Hence, there is a need to improve ESCR performance of HDPE compositions.

[0004] Attempts have been made to improve such performance. These include the incorporation of C₄, O_Q, and/or Cs comonomers used during polymerization, which may be carried out in the vapor phase or in solution. Fine-tuning the molecular weight distribution (bi- or multi-modal) has also been used, as well as blending the polyethylene with other polymers. Cross-linking of silane grafted of polyethylene has also been used.

[0005] Given the growing trend of down-gauging of the plastic parts (for example, caps and closure, bottles and containers) and the use of plastic containers for storing aggressive chemicals (bleach bottles), an enhanced ESCR performance of plastics even at a lower thickness becomes more vital. For instance, a weight reduction of bottle caps from 3 g to 1.8 - 2.0 g, as currently demanded by many brand-owners, while still keeping its ESCR performance, is an emerging challenge.

[0006] While various methods exist to increase ESCR properties of polyethylene, many of these suffer in that they are cost prohibitive or applicable only to the method of making the starting polyethylene materials instead of to existing polyethylene materials. Thus, there is a continuing need for polyethylene-based compositions having increased ESCR, particularly for those that are suitable for cap and closure applications.

SUMMARY

[0007] A polyethylene composition having increased environmental stress crack resistance comprises a polymer blend of a multimodal high density polyethylene (HDPE) and an ionomeric polyethylene.

[0008] In particular embodiments, the ionomeric polyethylene may be present in an amount of from 0.1 wt.% to 15 wt.% by weight of the polymer blend. In some instances, the ionomeric polyethylene may be present in an amount of from 2 wt.% or less by weight of the polymer blend.

[0009] The ionomeric polyethylene may have an average molecular weight (Mw) of from 5000 to 60,000 g/mol.

[0010] The ionomeric polyethylene may comprise a copolymer of ethylene and at least one of a carboxylic acid and a sulphonic acid. The carboxylic acid may be at least one of acrylic acid, methylacrylic acid, and ethylacrylic acid

[001 1] The ionomeric polyethylene may have an ionic group content of from 0.5 mol% to 20 mol% of the ionomeric polyethylene. In certain embodiments, the ionomeric polyethylene may contain metal counter ions comprising at least one of a mono and a divalent metal salt. The metal counter ions may comprise Li, Na, K, Zn, Ca, Mg, Pb and Sn.

[0012] In certain applications, the polymer blend provides a molded article having an ESCR of at least 25 or 40 hours as determined by ASTM D1693-15B. In others, the polymer blend provides a molded article having an ESCR of from 25 or 40 hours to 1000 hours as determined by ASTM D1693-15B. [0013] The HDPE may be a copolymer with comonomers selected from C3 to C10 olefin monomers, the comonomers being present in the HDPE copolymer in an amount of from 2 wt.% or less. In certain instances, the HDPE may be a copolymer with comonomers selected from C3 to C10 olefin monomers, the comonomers being present in the HDPE copolymer in an amount of from 1 wt.% or less. In other cases, the HDPE is a neat HDPE.

[0014] In particular embodiments, the HDPE has a melt flow rate at 190 °C and 2.16 kg or 21 .6 kg of 0.2 dg/min to 50 dg/min and/or a density of 945 kg/m³ to 965 kg/m³. Preferably, the density of the HDPE is determined in accordance with ISO 1 183-1 (2012), method A, and the melt flow rate in accordance with ISO 1 133-1 (201 1 ).

[0015] The HDPE may for example have a melt flow rate at 2.16 kg / 190°C of 0.2 dg/min to 50 dg/min, preferably 0.2 to 25 dg/min, or 0.4 to 15 dg/min, more preferably 0.5 to 15 dg/min, or 0.6 to 10.0 dg/min, even more preferably 1.0 to 10.0 dg/min, or 0.8 to 5.0 dg/min, even more preferably 1 .0 to 5.0 dg/min.

[0016] The HDPE may further include an additive of at least one of a nucleating agent, a heat conductive agent, a tie agent, an antiblocking agent, an antistatic agent, an antioxidant, a neutralizing agent, an acid scavenger, a blowing agent, a crystallization aid, a dye, a flame retardant agent, a filler, an impact modifier, a mold release agent, an oil, another polymer, a pigment, a processing agent, a reinforcing agent, a stabilizer, an UV resistance agent, a clarifying agent, a slip agent, a flow modifying agent, ionic additive and combinations thereof.

[0017] The polymer blend may be formed into an article of manufacture. This may include at least one of a film, a molded part, a container, a beverage container cap, a lid, a sheet, a pipe, a pipe coupling, a bottle, a cup, a tray, a pallet, and a toy. The article may be formed by at least one of injection molding, blow molding, compression molding, sheet extrusion, film blowing, pipe extrusion, profile extrusion, calendaring, and thermoforming.

[0018] In a method forming a polyethylene composition having increased environmental stress crack resistance, a multimodal high density polyethylene (HDPE) is modified by combining the multimodal HDPE with an ionomeric polyethylene.

BRIEF DESCRIPTION OF THE DRAWINGS

[0019] For a more complete understanding of the embodiments described herein, and the advantages thereof, reference is now made to the following descriptions taken in conjunction with the accompanying figures, in which: [0020] FIG. 1 is a scanning electron microscope (SEM) image of a polymer blend of HDPE incorporated with 10 wt.% of ionomeric additive;

[0021 ] FIG. 2 is an unstained transmission electron microscope (TEM) image of a polymer blend of HDPE incorporated with 10 wt.% of ionomeric additive;

[0022] FIG. 3 is an unstained transmission electron microscope (TEM) image of a polymer blend of HDPE incorporated with 5 wt.% (A) of ionomeric additive;

[0023] FIG. 4 is an unstained transmission electron microscope (TEM) image of a polymer blend of HDPE incorporated with 15wt.% (B) of ionomeric additive; and

[0024] FIG. 5 is an unstained transmission electron microscope (TEM) image of a polymer blend of HDPE incorporated with 20 wt.% (C) of ionomeric additive.

DETAILED DESCRIPTION

[0025] It has been discovered that the environmental stress crack resistance (ESCR) of high density polyethylene (HDPE) can be increased by incorporating an additive of an ionomeric polyethylene. The ionomeric polyethylene is incorporated into the HDPE by polymer melt blending the ionomeric polyethylene with the HDPE or by grafting ionic compounds onto polyethylene chains during processing of the HDPE. The amount and the type of the ionomeric polyethylene incorporated into the HDPE is selected so that the processability of the HDPE remains relatively unaffected while its ESCR performance is enhanced.

[0026] The HDPE polymers used in the polymer blend can include those prepared by any of the polymerization processes, which are in commercial use (e.g., a“high pressure” process, a slurry process, a solution process and/or a gas phase process) and with the use of any of the known catalysts (e.g., multisite catalysts such as Ziegler Natta catalysts, and/or single site catalysts such as chromium or Phillips catalysts, metallocene catalysts, and the like).

[0027] The HDPE can be unimodal, bimodal, multimodal HDPE or a combination of these. As used herein, where the phrase or term“high density polyethylene” or“HDPE” are used without characterization as unimodal, bimodal or multimodal HDPE, the phrase or term should be construed as referring to any or all of them. Bimodal and/or multimodal HDPE can be made using an advance cascade process. HDPE can be obtained from a commercial vendor. Non- limiting examples of suitable commercially available HDPE include those HDPE polymers marketed as SABIC^® HDPE CC253 and SABIC^® HDPE CC254 (SABIC^®, Kingdom of Saudi Arabia). In certain aspects, the polymer blends of the present invention do not include polypropylene. In some embodiments, the polymer blends do not include linear low density polyethylene (LLDPE).

[0028] The HDPE can be characterized by various properties such as a melt flow rate (MFR) at 190 °C and 2.16 kg and / or 21.6 kg, a density, ESCR, tensile strength at yield tensile modulus, tensile elongation at yield, Charpy notched impact strength (-30 °C), hardness or combinations thereof. The density of the unimodal, bimodal or multimodal HDPE can be from 945 kg/m³ to 965 kg/m³, or at least, equal to, and/or between any two of 945 kg/m³, 950 kg/m³, 955 kg/m³, 960 kg/m³, and 965 kg/m³.

[0029] It should be noted in the description, if a numerical value, concentration or range is presented, each numerical value should be read once as modified by the term "about" (unless already expressly so modified), and then read again as not so modified unless otherwise indicated in context. Also, in the description, it should be understood that an amount range listed or described as being useful, suitable, or the like, is intended that any and every value within the range, including the end points, is to be considered as having been stated. For example,“a range of from 1 to 10” is to be read as indicating each and every possible number along the continuum between about 1 and about 10. Thus, even if specific points within the range, or even no point within the range, are explicitly identified or referred to, it is to be understood that the inventor appreciates and understands that any and all points within the range are to be considered to have been specified, and that inventor possesses the entire range and all points within the range.

[0030] In some embodiments, all or a portion of the HDPE component is unimodal. A MFR of unimodal HDPE at 190 °C and 2.16 kg and/or 21 .6 kg can be from 0.2 dg/min to 50 dg/min or at least, equal to, and/or between any two of 0.2 dg/min, 0.3 dg/min, 0.4 dg/min, 0.5 dg/min, 0.75 dg/min, 1 dg/min, 1.25 dg/min, 1.5 dg/min, 1 .75 dg/min, 2 dg/min, 3 dg/min, 4 dg/min, and 5 dg/min, 6 dg/min, 7 dg/min, 8 dg/min, 9 dg/min, 10 dg/min, 1 1 dg/min, 12 dg/min, 13 dg/min, 14 dg/min, 15 dg/min, 16 dg/min, 17 dg/min, 18 dg/min, 19 dg/min, and 20 dg/min, 21 dg/min, 22 dg/min, 23 dg/min, 24 dg/min, 25 dg/min, 26 dg/min, 27 dg/min, 28 dg/min, 29 dg/min, 30 dg/min, 31 dg/min, 32 dg/min, 33 dg/min, 34 dg/min, 35 dg/min, 36 dg/min, 37 dg/min, 38 dg/min, 39 dg/min, 40 dg/min. 41 dg/min, 42 dg/min, 43 dg/min, 44 dg/min, 45 dg/min, 46 dg/min, 47 dg/min, 48 dg/min, 49 dg/min and 50 dg/min. In particular embodiments, the MFR is from 0.5 dg/min to 5 dg/min at 190 °C and with a 2.16 kg load. [0031 ] Tensile modulus and/or flexural modulus of unimodal HDPE can be from 1000 MPa to 1300 MPa, or at least, equal to, and/or between any two of 1000 MPa, 1050 MPa, 1 100 MPa, 1 150 MPa, 1200 MPa, 1250 MPa, and 1300 MPa, as measured by ISO 527-2. Tensile and/or flexural strength at yield of unimodal HDPE can be from 20 MPa to 40 MPa, or at least, equal to, and/or between any two of 20 MPa, 25 MPa, 30 MPa, 35 MPa, and 40 MPa, as measured by ISO 527-2.

[0032] In some embodiments, all or a portion of the HDPE component is bimodal and/or multimodal. Bimodal or multimodal HDPE can have a MFR at 190 °C and 2.16 kg and/or 21 kg of from 0.2 dg/min to 20 dg/min or at least, equal to, and/or between any two of 0.2 dg/min to 20 dg/min or at least, equal to, and/or between any two of 0.2 dg/min, 0.3 dg/min, 0.4 dg/min, 0.5 dg/min, 0.75 dg/min, 1 dg/min, 1.25 dg/min, 1.5 dg/min, 1.75 dg/min, 2 dg/min, 3 dg/min, 4 dg/min, and 5 dg/min, 6 dg/min, 7 dg/min, 8 dg/min, 9 dg/min, 10 dg/min, 1 1 dg/min, 12 dg/min, 13 dg/min, 14 dg/min, 15 dg/min, 16 dg/min, 17 dg/min, 18 dg/min, 19 dg/min, and 20 dg/min. In particular embodiments, the MFR is from 0.5 dg/min to 5 dg/min.

[0033] Tensile modulus of bimodal or multimodal HDPE can be from 1000 MPa to 1300 MPa, or at least, equal to, and/or between any two of 1000 MPa, 1050 MPa, 1 100 MPa, 1 150 MPa, 1200 MPa, 1250 MPa and 1300 MPa, as measured by ASTM D638. Tensile strength at yield of bimodal and multimodal HDPE can be from 20 MPa to 40 MPa, or at least, equal to, and/or between any two of 20 MPa, 25 MPa, 30 MPa, 35 MPa, and 40 MPa, as measured by ASTM D638.

[0034] The Charpy notched impact strength of the HDPE component at -30 °C can be from 3 kJ/m² to 6 kJ/m² or at least, equal to, and/or between any two of 3 kJ/m², 4 kJ/m², 5 kJ/m², and 6 kJ/m².

[0035] In certain embodiments, the HDPE component of the polymer blend will constitute homopolymers of ethylene. These may include homopolymers solely of neat HDPE. In other embodiments, however, the HDPE may include a polymer blend with non-HDPE polyethylene. These may include low density polyethylene (LDPE), linear low density polyethylene (LLDPE), and medium density polyethylene (MDPE). When such non-HDPE polyethylene is used it may be present in the HDPE polymer component in an amount of from 2 wt.%, 1.5 wt.%, 1 wt.%, 0.5 wt.%, 0.1 wt.% or less. [0036] In other embodiments, the HDPE component can include copolymers of ethylene with at least one C₃ to C10 alpha olefin. Typically, this will be at least one of the alpha olefins of butene, hexene, and/or octene. In some embodiments the HDPE is a copolymer with 1-butene (polyethylene-1 -butene) or 1 -hexene (polyethylene-1 -hexene). When such copolymers are used, the non-ethylene comonomer may be present in the HDPE copolymer in an amount of from 2 wt.%, 1.5 wt.%, 1 wt.%, 0.5 wt.%, 0.1 wt.% or less. In particular embodiments, there is no butene or no C₃ to C10 alpha olefin comonomer.

[0037] In certain embodiments, the HDPE may be an un-functionalized neat HDPE with no functional groups along the polymer chain. In particular embodiments, the HDPE polyethylene does not include any anhydride modified HDPE.

[0038] The HDPE component, as described above, is used as a polymer blend in combination with an ionomeric polyethylene. The ionomeric polyethylene used may be comprised of copolymers of ethylene and ionic compounds of carboxylic acid and/or sulphonic acid monomers. The carboxylic acid monomer may be those a, b-ethylenically unsaturated carboxylic acid group containing monomers having from 3 to 8 carbon atoms, and their combinations. Such ionomeric polyethylene materials incorporating such carboxylic acid monomers include those described in U.S. Patent No. 3,264,272, which is hereby incorporated herein by reference for all purposes. In particular, those carboxylic acid monomers of acrylic acid, methylacrylic acid, and/or an ethylacrylic acid, and combinations of these and others, may be particularly useful.

[0039] The ionic groups are distributed throughout the ionomeric polyethylene copolymer and may be randomly distributed along the polymer chain. The ionic groups (e.g., carboxylic acid and/or sulphonic acid groups) may be present in the ionomeric polyethylene in an amount of from 50 mol%, 45 mol%, 40 mol%, 35 mol%, 30 mol%, 25 mol%, 20 mol%, 15 mol%, 10 mol%, 5 mol%, 1 mol%, 0.5 mol % or less. In particular embodiments, the ionic groups may be present in the ionomeric polyethylene in an amount at least, equal to, and/or between any two of 0.2 mol%, 0.3 mol%, 0.4 mol%, 0.5 mol%, 1 mol%, 5 mol%, 10 mol%, 15 mol%, 20 mol%, 25 mol%, 30 mol%, 35 mol%, 40 mol%, 45 mol%, and 50 mol%. In more particular embodiments, the ionic groups are present in the ionomeric polyethylene in an amount at least, equal to, and/or between any two of 0.2 mol%, 0.3 mol%, 0.4 mol%, 0.5 mol%, 1 mol%, 5 mol%, 10 mol%, 15 mol%, 20 mol%, and 25 mol%. And still more particularly, the ionic groups may be present in the ionomeric polyethylene in an amount at least, equal to, and/or between any two of 1 mol%, 2 mol%, 3 mol%, 4 mol%, 5 mol%, 6 mol%, 7 mol%, 8 mol%, 9 mol%, 10 mol%, 1 1 mol%, 12 mol%, 13 mol%, 14 mol% and 15 mol%.

[0040] The ionomeric polyethylene will typically contain metal counter ions that neutralize all or some portion of the ionic groups of carboxylic and/or sulphonic acid. The metal counter ions may comprise at least one of mono or divalent metal salts that may be distributed throughout the polymer. Non-limiting examples of such metal counter ions include Li, Na, K, Zn, Ca, Mg, Pb and Sn, and combinations of these. These may be used in an amount to provide from 10%, 20%, 30%, 40%, 50% or more neutralization of the carboxylic acid and/or sulphonic acid groups of the ionomeric polyethylene. In particular embodiments, the metal counter ions may be used in an amount at least, equal to, and/or between any two of 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, and 100% neutralization of the carboxylic acid and/or sulphonic acid groups of the ionomeric polyethylene.

[0041 ] The ionomeric polyethylene component of the polymer blend may have a weight average molecular weight (Mw) of from 3000 to 60,000 g/mol with respect to polystyrene standard or at least, equal to, and/or between any two molecular weights of, 3000, 4000, 5000, 6000, 7000, 8000, 9000, 10,000, 1 1 ,000, 12,000, 13,000, 14,000, 15,000, 16,000,

17,000, 18,000, 19,000, 20,000, 21 ,000, 22,000, 23,000, 24,000, 25,000, 26,000, 27,000,

28,000, 29,000, 30,000, 31 ,000, 32,000, 33,000, 34,000, 35,000, 36,000, 37,000, 38,000,

39,000, 40,000, 41 ,000, 42,000, 43,000, 44,000, 45,000, 46,000, 47,000, 48,000, 49,000,

50,000, 51 ,000, 52,000, 53,000, 54,000, 55,000, 56,000, 57,000, 58,000, 59,000 and 60,000. In certain embodiments, the weight average Mw of the ionomeric polyethylene is from 5,000 to 20,000, 30,000, or 40,000.

[0042] The ionomeric polyethylene component of the polymer blend may have a density from 945 kg/m³ to 965 kg/m³, or at least, equal to, and/or between any two of 945 kg/m³, 950 kg/m³, 955 kg/m³, 960 kg/m³, and 965 kg/m³. The ionomeric polyethylene component of the polymer blend may have a melt flow rate at 190 °C and with a load of 2.16 Kg from 0.5 dg/min to 10 dg/min.

[0043] The ionomeric polyethylene used in the polymer blend may be a preformed ionomeric polyethylene, with or without neutralization by metal counter ions. Such ionomeric polyethylene may be that prepared in a reactor by copolymerizing ethylene with the ionic groups or ionic group precursors through conventional polymerization techniques. A non- limiting example of a suitable commercially available ionomeric polyethylene is that available as SURLYN^®-PC350, from E.l. du Pont de Nemours and Company, Inc., Wilmington, DE.

[0044] In other instances, the ionomeric polyethylene may be formed by grafting ionic compounds, such as carboxylic acid and/or sulphonic acid, to preexisting polyethylene polymers. Such ionomeric polyethylene formed by grafting techniques may be pre-formed, as well, and used in a polymer blend in conjunction with non-ionomeric HDPE of the polymer blend. Graft polymerization may be carried out by ionizing radiation, UV radiation, and chemical initiators. In certain applications, grafting may be carried out in situ during extrusion of non-ionomeric HDPE to form the desired ionomeric polyethylene content of the final HDPE product.

[0045] The ionic groups may be the same or different for the ionomeric polyethylene used (e.g., ethylene copolymerized with carboxylic acid and sulphonic acid, ethylene copolymerized with acrylic acid and methacrylic acid, etc.). In some embodiments, different ionomeric polyethylene copolymers having different ionic groups may be used in combination with one another (e.g., mixture of ethylene/carboxylic acid copolymers and ethylene/sulphonic acid copolymers).

[0046] To impart the desired ESCR characteristics of the final product, the ionomeric polyethylene is used in combination with the HDPE in an amount of from 0.1 wt.% to 15 wt.% by total weight of the polymer blend. In particular embodiments, the ionomeric polyethylene is used in an amount at least, equal to, and/or between any two of 0.1 wt.%, 0.2 wt.%, 0.3 wt.%, 0.4 wt.%, 0.5 wt.%, 0.6 wt.%, 0.7 wt.%, 0.8 wt.%, 0.9 wt.%, 1 wt.%, 1 .5 wt.%, 2 wt.%, 3 wt.%, 4 wt.%, 5 wt.%, 6 wt.%, 7 wt.%, 8 wt.%, 9 wt.%, 10 wt.%, 1 1 wt.%, 12 wt.%, 13 wt.%, 14 wt.%, and 15 wt.% by total weight of the polymer blend, with from 0.5 wt.% to 15 wt.% being particularly useful.

[0047] In other embodiments, lesser amounts of the ionomeric polyethylene may be used, with the ionomeric polyethylene being used in an amount of from 2 wt.% or less by weight of the polymer blend. In such instances, the ionomeric polyethylene may be at least, equal to, and/or between any two of 0.10 wt%, 0.15 wt%, 0.20 wt.%, 0.25 wt%, 0.30 wt.%, 0.35 wt%, 0.40 wt.%, 0.45 wt%, 0.50 wt.%, 0.55 wt%, 0.60 wt%, 0.65 wt.%, 0.70 wt.%, 0.75 wt%, 0.80 wt.%, 0.85 wt%, 0.90 wt.%, 0.95 wt%, 1 .00 wt.%, 1.10 wt%, 1.15, 1.20 wt%, 1.25 wt%, 1.30 wt%, 1.35 wt%, 1.40 wt%, 1 .45 wt%, 1.50 wt%, 1.55 wt%, 1.60 wt%, 1 .65 wt%, 1.70 wt%, 1.75 wt%, 1.80 wt%, 1.85 wt%, 1.90 wt%, 1.95 wt%. and 2.0 wt.%. [0048] Such lesser amounts (e.g., from 0.10 wt.% to 2. O wt.%) of ionomeric polyethylene, may be particularly useful when used in combination with multimodal HDPE. When lesser amounts of ionomeric polyethylene are used they may be used in combination with multimodal HDPE, without any unimodal and/or bimodal HDPE being present in the polymer blend. Where such unimodal and/or bimodal HDPE are present in the multimodal HDPE polymer blend, these may be present in the polymer blend in a total amount of from 50 wt.%, 45 wt.%, 40 wt.%, 35 wt.%, 30 wt.%, 25 wt.%, 20 wt.%, 15 wt.%, 10 wt.%, 5 wt.%, 1 wt.%, 0.5 wt.%, 0.1 wt.% or less by total weight of the polymer blend.

[0049] The polyethylene compositions can further include at least one additive. Non-limiting examples of additives include a nucleating agent, a heat conductive agent, a tie agent, an antiblocking agent, an antistatic agent, an antioxidant, a neutralizing agent, an acid scavenger, a blowing agent, a crystallization aid, a dye, a flame retardant agent, a filler (hard or soft), an impact modifier, a mold release agent, an oil, another polymer, a pigment, a processing agent, a reinforcing agent, a stabilizer (including light stabilizers), an UV resistance agent, a clarifying agent, a slip agent, a flow modifying agent, and combinations thereof. In certain embodiments, no carbon black is present in the HDPE composition.

[0050] Non-limiting examples of nucleating agents include calcium carbonate (CaCC>3), barium sulfate (BaS0₄), silica (S1O2), kaolin, talc, mica, titania (T1O2), alumina (AI2O3), a zeolite, mono-or polycarboxylic aromatic acid, a dye, a pigment, metal carboxylates, metal aromatic carboxylate, hexahydrophthalic acid metal salts, stearates, organic phosphates, bisamides, sorbitols, or a combination thereof. A non-limiting example of metal aromatic carboxylate includes sodium benzoate.

[0051 ] In some instances, a heat conductive additive is present in the polymer blend in an amount of at least, equal to, and/or between any two of 0.01 wt.%, 0.2 wt.%, 0.3 wt.%, 0.4 wt.%, 0.5 wt.%, 0.6 wt.%, 0.7 wt.%, 0.8 wt.%, 0.9 wt.%, and 1.0 wt. % by total weight of the polymer blend. Non-limiting examples of heat conductive additive include, aluminum oxide, titanium dioxide, graphitic compounds, graphenes, boron nitride, aluminum nitride, zinc oxide

[0052] In certain aspects, a tie molecule is present in the polymer blend in amount of at least, equal to, and/or between any two of 0.01 wt.%, 0.2 wt.%, 0.3 wt.%, 0.4 wt.%, 0.5 wt.%, 0.6 wt.%, 0.7 wt.%, 0.8 wt.%, 0.9 wt.%, and 1.0 wt. % by total weight of the polymer blend. Non- limiting examples of tie molecules include, linear low density polyethylene, low density polyethylene, medium density polyethylene.

[0053] In some embodiments, a filler is present in the polymer blend in amount of at least, equal to, and/or between any two of 0.01 wt.%, 0.2 wt.%, 0.3 wt.%, 0.4 wt.%, 0.5 wt.%, 0.6 wt.%, 0.7 wt.%, 0.8 wt.%, 0.9 wt.%, 1 .0 wt. %, 2.0 wt. %, 3.0 wt. %, 4.0 wt. %, 5.0 wt. %, 6.0 wt. %, 7.0 wt. %, 8.0 wt. %, 9.0 wt. %, 10.0 wt. %, 20.0 wt. %, 30.0 wt. % by total weight of the polymer blend. The filler can be a hard filler. Non-limiting examples of hard filler include, inorganic particulate fillers such as silica, calcium carbonate, inorganic layered fillers such as clays, mica. The filler can be a soft filler. Non-limiting examples of soft filler include, immiscible particulate elastomeric/polymeric resins. The filler can also be a hollow filler. Non-limiting examples of hollow filler include, glass microspheres, plastic microspheres, ceramic microspheres such as cenospheres made up of alumino silicate microspheres, metallic microspheres made up of aluminum and copper/silver microspheres, phenolic microspheres.

[0054] In certain aspects, a light stabilizer is present in the polymer blend in an amount of at least, equal to, and/or between any two of 0.01 wt.%, 0.2 wt.%, 0.3 wt.%, 0.4 wt.%, 0.5 wt.%, 0.6 wt.%, 0.7 wt.%, 0.8 wt.%, 0.9 wt.%, and 1.0 wt. % by total weight of the polymer blend. The light stabilizer can be a hindered amine light stabilizer. The term“hindered amine light stabilizer” refers to a class of amine compounds having certain light stabilizing properties. Non-limiting examples, of hindered amine light stabilizers (HALS) include 1 -cyclohexyloxy- 2,2,6,6-tetramethyl-4-octadecylaminopiperidine; bis(2,2,6,6-tetramethylpiperidin-4-yl) sebacate; bis(1 -acetoxy-2,2,6,6-tetramethylpiperidin-4-yl) sebacate; bis(1 ,2,2,6,6- pentamethylpiperidin-4-yl) sebacate; bis(1 -cyclohexyloxy-2,2,6,6-tetramethylpiperidin-4-yl) sebacate; bis(1-octyloxy-2,2,6,6-tetramethylpiperidin-4-yl) sebacate; bis(1 -acyl-2, 2,6,6- tetramethylpiperidin-4-yl) sebacate; bis(1 ,2,2,6,6-pentamethyl-4-piperidyl) n-butyl-3,5-di-tert- butyl-4-hydroxybenzyl malonate; 2,4-bis[(1-cyclohexyloxy-2,2,6,6-tetramethylpiperidin-4- yl)butylamino]-6-(2-hydroxyethyl amino-s-triazine; bis(1-cyclohexyloxy-2, 2,6,6- tetramethylpiperidin-4-yl) adipate; 2,4-bis[(1-cyclohexyloxy-2,2,6,6-piperidin-4-yl)butylamino]- 6-chloro-s-triazine; 1-(2-hydroxy-2-methylpropoxy)-4-hydroxy-2,2,6,6-tetramethylpiperidine; 1-(2-hydroxy-2-methylpropoxy)-4-oxo-2,2,6,6-tetramethylpiperidine; 1 -(2-hydroxy-2-methyl propoxy)-4-octadecanoyloxy-2,2,6,6-tetramethyl piperidine; bis(1 -(2-hydroxy-2- methylpropoxy)-2,2,6,6-tetramethylpiperidin-4-yl) sebacate;bis(1-(2-hydroxy-2- methylpropoxy)-2,2,6,6-tetramethylpiperidin-4-yl) adipate; 2,4-bis{N-[1 -(2-hydroxy-2-methyl propoxy)-2,2,6,6-tetramethylpiperidin-4-yl]-N-butylamino}-6-(2-hydroxyethylamino)-s-triazine; 4-benzoyl-2,2,6,6-tetramethylpiperidine; di-(1 ,2,2,6,6-pentamethylpiperidin-4-yl) p- methoxybenzylidenemalonate; 2,2,6,6-tetramethylpiperidin-4-yl octadecanoate; bis(1- octyloxy-2,2,6,6-tetramethylpiperidyl) succinate; 1 ,2,2,6,6-pentamethyl-4-aminopiperidine; 2- undecyl-7,7,9,9-tetramethyl-1-oxa-3,8-diaza-4-oxo-spiro[4,5]decane; tris(2,2,6,6-tetramethyl- 4-piperidyl) nitrilotriacetate; tris(2-hydroxy-3-(amino-(2,2,6,6-tetramethylpiperidin-4-yl)propyl) nitrilotriacetate; tetrakis(2,2,6,6-tetramethyl-4-piperidyl)-1 ,2,3,4-butane-tetracarboxylate; tetrakis(1 ,2,2,6,6-pentamethyl-4-piperidyl)-1 ,2,3,4-butane-tetracarboxylate; 1 , 1 '-(1 ,2- ethanediyl)-bis(3,3,5,5-tetramethylpiperazinone); 3-n-octyl-7,7,9,9-tetramethyl-1 ,3,8- triazaspiro[4.5]decan-2,4-dione; 8-acetyl-3-dodecyl-7,7,9,9-tetramethyl-1 ,3,8- triazaspiro[4.5]decane-2,4-dione; 3-dodecyl-1-(2,2,6,6-tetramethyl-4-piperidyl)pyrrolidin-2,5- dione; 3-dodecyl-1-(1 ,2,2,6,6-pentamethyl-4-piperidyl)pyrrolidine-2,5-dione; N,N'-bis-formyl- N,N'-bis(2,2,6,6-tetramethyl-4-piperidyl)hexamethylenediamine; reaction product of 2,4- bis[(1-cyclohexyloxy-2,2,6,6-piperidin-4-yl)butylamino]-6-chloro-s-triazine with N,N'-bis(3- aminopropyl)ethylenediamine);condensate of 1-(2-hydroxyethyl)-2,2,6,6-tetramethyl-4- hydroxypiperidine and succinic acid; condensate of N,N'-bis(2,2,6,6-tetramethyl-4-piperidyl)- hexamethylenediamine and 4-tert-octylamino-2,6-dichloro-1 ,3,5-triazine; condensate of N,N'- bis(2,2,6,6-tetramethyl-4-piperidyl)-hexamethylenediamine and 4-cyclohexylamino-2,6- dichloro-1 ,3,5-triazine; condensate of N,N'-bis-(2,2,6,6-tetramethyl-4- piperidyl)hexamethylenediamine and 4-morpholino-2,6-dichloro-1 ,3,5-triazine; condensate of N,N'-bis-(1 ,2,2,6,6-pentamethyl-4-piperidyl)hexamethylenediamine and 4-morpholino-2,6- dichloro-1 ,3,5-triazine; condensate of 2-chloro-4,6-bis(4-n-butylamino-2,2,6,6-tetramethyl piperidyl)-1 ,3,5-triazine and 1 ,2-bis(3-aminopropylamino)ethane; condensate of 2-chloro-4,6- di-(4-n-butylamino-1 ,2,2,6,6-pentamethylpiperidyl)-1 ,3,5-triazine and 1 ,2-bis-(3- aminopropylamino)ethane; a reaction product of 7,7,9,9-tetramethyl-2-cycloundecyl-1-oxa- 3,8-diaza-4-oxospiro[4,5]decane and epichlorohydrin; poly[methyl, (3-oxy-(2, 2,6,6- tetramethylpiperidin-4-yl)propyl)]siloxane, CAS#182635-99-0; reaction product of maleic acid anhydride-CI 8-C22-oolefin-copolymer with 2,2,6,6-tetramethyl-4-aminopiperidine; oligomeric condensate of 4,4'-hexamethylenebis(amino-2,2,6,6-tetramethylpiperidine) and 2,4-dichloro-6-[(2,2,6,6-tetramethylpiperidin-4-yl)butylamino]-s-triazine end-capped with 2- chloro-4,6-bis(dibutylamino)-s-triazine; oligomeric condensate of 4,4'- hexamethylenebis(amino-1 ,2,2,6,6-pentaamethylpiperidine) and 2,4-dichloro-6-[(1 , 2, 2,6,6- pentaamethylpiperidin-4-yl)butylamino]-s-triazine end-capped with 2-chloro-4,6- bis(dibutylamino)-s-triazine; oligomeric condensate of 4,4'-hexamethylenebis(amino-1- propoxy-2,2,6,6-tetramethyl piperidine) and 2,4-dichloro-6-[(1-propoxy-2,2,6,6- tetramethylpiperidin-4-yl)butylamino]-s-triazine end-capped with 2-chloro-4,6- bis(dibutylamino)-s-triazine; oligomeric condensate of 4,4'-hexamethylenebis(amino-1- acyloxy-2,2,6,6-tetramethyl piperidine) and 2,4-dichloro-6-[(1-acyloxy-2,2,6,6- tetramethylpiperidin-4-yl)butylamino]-s-triazine end-capped with 2-chloro-4,6- bis(dibutylamino)-s-triazine; and product obtained by reacting (a) with (b) where (a) is product obtained by reacting 1 ,2-bis(3-aminopropylamino)ethane with cyanuric chloride and (b) is (2,2,6,6-tetramethyl piperidin-4-yl)butylamine. Also included are the sterically hindered N-H, N-methyl, N-methoxy, N-hydroxy, N-propoxy, N-octyloxy, N-cyclohexyloxy, N-acyloxy and N- (2-hydroxy-2-methylpropoxy) analogues of any of the above mentioned compounds. Non- limiting examples of commercial light stabilizer are available from BASF under the trade name Uvinul® 4050H, 4077H, 4092H, 5062H, 5050H, 4092H, 4077H, 3026, 3027, 3028, 3029, 3033P, and 3034 or Tinuvin® 622.

[0055] Anti-static agents can be used to inhibit accumulation of dust on plastic articles. Antistatic agents can improve the electrical conductivity of the plastic compositions, and thus dissipate any surface charges, which develop during production and use. Thus, dust particles are less attracted to the surface of the plastic article, and dust accumulation is consequently reduced. In certain aspects of the present invention, the antistatic agent can be a glycerol monostearate. The polymer blend can include an anti-static agent in an amount of at least, equal to, and/or between any two 0.01 wt.%, 0.2 wt.%, 0.3 wt.%, 0.4 wt.%, 0.5 wt.%, 0.6 wt.%, 0.7 wt.%, 0.8 wt.%, 0.9 wt.%, and 1 wt. % by total weight of the polymer blend.

[0056] A lubricant can be added to a polymer blend to improve the mold-making characteristics. The lubricant can be a low molecular compound from a group of fatty acids, fatty acid esters, wax ester, fatty alcohol ester, amide waxes, metal carboxylate, montanic acids, montanic acid ester, or such high molecular compounds, as paraffins or polyethylene waxes. In certain aspects of the present invention, the lubricant is a metal stearate. Non- limiting examples of metal stearates include zinc stearate, calcium stearate, lithium stearate or a combination thereof, preferably calcium stearate. The polymer blend can include a lubricant in an amount of at least, equal to, and/or between any two of 0.01 wt.%, 0.2 wt.%, 0.3 wt.%, 0.4 wt.%, 0.5 wt.%, 0.6 wt.%, 0.7 wt.%, 0.8 wt.%, 0.9 wt.%, and 1 wt. % by total weight of the polymer blend.

[0057] An antioxidant can provide protection against polymer degradation during processing. Phosphites are known thermal oxidative stabilizing agents for polymers and other organic materials. The antioxidant can be a phosphite-based antioxidant. In certain aspects phosphite-antioxidants include, but are not limited to, triphenyl phosphite, diphenylalkyl phosphites, phenyldialkyl phosphites, tris(nonylphenyl)phosphite, trilauryl phosphite, trioctadecyl phosphite, distearyl pentaerythritol diphosphite, tris(2,4-di-tert- butylphenyl)phosphite, diisodecyl pentaerythritol diphosphite, bis(2,4-di-tert- butylphenyl)pentaerythritol diphosphite tristearyl sorbitol triphosphite, and tetrakis(2,4-di- tertbutylphenyl)-4,4'-biphenylene diphosphonite, bis(2,4-dicumylphenyl)pentaerythritol diphosphite. The polymer blend can include an antioxidant in an amount of at least, equal to, and/or between any two of 0.01 wt.%, 02 wt.%, 0.3 wt.%, 0.4 wt.%, 0.5 wt.%, 0.6 wt.%, 0.7 wt.%, 0.8 wt.%, 0.9 wt.%, and 0.1 wt. % by total weight of the polymer blend. Non-limiting examples of commercially available antioxidants include Irganox 1010 available from BASF, or Doverphos S9228T available from Dover Chemical Company.

[0058] In forming the composition, the various components of the HDPE and ionomeric polyethylene, which may be in the form of pellets, powder, flakes or fluff, along with any additives, can be dry blended. These materials combined in a customary mixing machine, in which the HDPE and ionomeric polyethylene are mixed with the optional additives. The optional additives can be added at the end or during the processing steps to produce the polymer blend. Suitable machines for such mixing are known to those skilled in the art. Non- limiting examples include mixers, kneaders and extruders. These materials are then fed directly into the feed zone of an extruder. In certain cases, the process can be carried out in an extruder and introduction of the additives may occur during processing. Non-limiting examples of suitable extruders include single-screw extruders, counter-rotating and co- rotating twin-screw extruders, planetary-gear extruders, ring extruders, or co-kneaders. The process can be performed at a temperature from 160 °C to 300 °C.

[0059] In some embodiments, the HDPE and ionomeric polyethylene, and optionally one or more additives, used to produce the polymer blend of the present invention can be melt- extruded by following typical procedures of weighing the required amounts of the HDPE, ionomeric polyethylene and other additives, followed by dry blending, and then feeding the mixture into a main feeder of a twin-screw co-rotating extruder (length/diameter (L/D) ratio of 25:1 or 40:1 ) to obtain the final composition. The HDPE, ionomeric polyethylene, or blend thereof can be subjected to an elevated temperature for a sufficient period of time during blending. The blending temperature can be above the softening point of the polymers. In certain aspects, the extrusion process can be performed at a temperature from 160 °C to 300 °C. The ionomeric polyethylene can be added along with other additives in-line and prior to pelletization of the HDPE resin during the production process. The amounts of ionomeric polyethylene combined with the HDPE can be adjusted to provide those weight amounts previously discussed. [0060] Additives can be premixed or added individually to the polymer blend or the different components thereof. By way of example, the additives of the present invention can be premixed such that the blend is formed prior to adding it to the HDPE or the ionomeric polyethylene. The additive-containing blend thereof can be subjected to an elevated temperature for a sufficient period of time during blending and/or incorporation of additives. Incorporation of additives into the polymer resin can be carried out, for example, by mixing the above-described components using methods customary in process technology. The blending temperature can be above the softening point of the polymers. In certain aspects, a process can be performed at a temperature from 160 °C to 300 °C. Such“melt mixing” or“melt compounding” results in uniform dispersion of the present additives in the HDPE and/or ionomeric polyethylene.

[0061 ] Where ionomeric polyethylene component is formed in situ by grafting during extrusion of the HDPE, any additives, such as the ionic groups, metal ions, and chemical initiators needed to facilitate such grafting of the ionic groups to the polyethylene may be premixed or added individually to the HDPE polymer or the other additives prior to or during extrusion.

[0062] Articles (e.g., caps) that manufactured from the blend of HDPE and ionomeric polyethylene can have a higher ESCR than articles of manufacture made from HDPE without the ionomeric polyethylene (i.e., the HDPE used to prepare the blend). In some embodiments, the articles of manufacture of the present invention have an ESCR that is 200% to 1000% greater than the ESCR values of HDPE articles of manufacture with the same configuration using the same HDPE without the use of the ionomeric polyethylene. The ESCR values can be at least, equal to, and/or between any two of 200%, 300%, 400%, 500%, 600%, 700%, 800%, 900%, 1000% and 2000% greater than the ESCR HDPE values without the use of ionomeric polyethylene. As exemplified in the Examples section and throughout the specification, polymer blend containing articles of manufacture of the present invention can have an ESCR values from at least 20 hours to 1000 hours (e.g., 20, 30, 40, 50, 60, 70, 80, 90, 100, 1 10, 120, 130, 140, 150, 160, 170, 180, 190, 200, 300, 400, 500, 600, 700, 800, 900, 1000, and 2000 and any range or value there between and including the endpoints). In contrast HDPE articles of manufacture without the ionomeric polyethylene, can have an ESCR values of less than but not equal to 20 hours.

[0063] The polymer blend compositions formed as described are normally collected as pellets, which can be stored for a time or employed immediately in a forming process. The forming processes can include injection molding, blow molding, compression molding, sheet extrusion, film blowing, pipe extrusion, profile extrusion, calendaring, thermoforming, rotomolding, or combinations thereof. The final formed articles can be, for instance, molded parts, sheets, films, or fibers. Examples of molded parts include a cap, a bottle cap, a container, a lid, a sheet, a pipe, a pipe coupling, a bottle, a cup, a tray, a pallet, or a toy, or combinations thereof. Caps can be injection and/or compression molded. The caps may be threaded or non- threaded caps for selectively closing off openings to bottles or other containers. Such caps can be used in a variety of food and non-food applications. By way of example, caps that include the polymer blend of the present invention can be used with containers for storing carbonated beverages, pressurized beverages, or the like.

[0064] The following examples serve to further illustrate various embodiments and applications.

EXAMPLES

EXAMPLE 1

[0065] An ionomeric polyethylene, available as SURLYN^®-PC350, which is an ionomer of ethylene acid copolymer with sodium metal ions, having melt flow rate (190 °C/2.16 Kg) of 4.5 g/10 min and a melting point of 88 °C was dry mixed as powder or flakes in different amounts of from 5 wt.% to 10 wt.% with commercially available HDPE. The HDPE used were SABIC^® HDPE CC254 and an experimental grade multimodal HDPE. SABIC^® HDPE CC254 is an HDPE having a MFR at 190 °C and 2.16 kg of 2.1 dg/min and a density of 953 kg/m³. The MFR of multimodal HDPE at 190 °C and 2.16 kg of 0.8 dg/min and a density of 953 Kg/m³. For comparison purposes, neat HDPEs without any ionomeric polyethylene were also tested. The different mixtures were fed into a hopper of a ZSK- 25 mm 6 barrel twin-screw extruder with an L/D ratio of 25:1 . The operating parameters used are set forth in Table 1 below:

Table 1

[0066] The torque measured during the melt extrusion of the neat and formulated HDPE with the ionomeric polyethylene was in the range of 28-34%, indicating that the processibility of HDPE was not hampered significantly with the addition of the ionomeric polyethylene.

EXAMPLE 2

[0067] The pellets obtained after the melt extrusion of Example 1 were compressed molded into 1.85 mm to 1.95 mm thick sheets at a temperature of 195 °C to 210 °C, with a holding time of 5 min and a cooling time of 5 min. No visual inhomogeneity was evident in the compression molded sheets. The compression molded sheets, both the neat and formulated HDPE, were then evaluated for ESCR performance according to ASTM D1693-15B method (Bell Test).

[0068] The compression molded sheets were cut into test specimens having a length of 38 mm and width of 13 mm. A notch of 0.5 mm depth was created at the center of each test specimen prior to storing it in a conditioned environment of 23 °C and humidity of 55% RH. The conditioned specimens were U-bent with the aid of a jig. Ten of the bent specimens for each neat and formulated HDPE materials were placed in an aluminum sample holder and subsequently placed inside a test tube filled with 10% v/v aqueous solution of Igepol CO-630 (nonylphenoxy poly(ethyleneoxy) ethanol, CAS 68412-54-4). The mouth of the test tube was closed with a rubber cork wrapped with an aluminum foil. The test specimens placed in the test tube filled with Igepol CO-630 aqueous solution were immersed in a silicone oil bath maintained at 50 °C. The time it took to observe the formation of cracks in the test specimens were regularly noted. The time taken for 50% of the specimens (i.e., 5 out of the 10 specimens) to fail (i.e., crack) were reported to infer the ESCR performance of the given composition.

[0069] The ESCR performance of the neat HDPE and formulated HDPE incorporating the ionomeric polyethylene is presented in Table 2 below:

Table 2

[0070] As can be seen from Table 2, the observed time for 50% of the samples to fail for HDPE (CC254) was 16 hrs. A more than 2 fold increase of time for 50% of the specimens to fail was found for those HDPE compositions incorporating ionomeric polyethylene at 15 wt.% loading.

[0071] Melt mass flow rate (MFR) of neat HDPE (CC254) resin measured at 190 °C with a load of 2.16 Kg by ISO 1133-1 :2011 method, along with that of blends of bimodal HDPE and different loading of ionomeric additive are depicted in the Table 3 below. The standard deviation observed during the MFR measurements was 0.1 g/10 min.

Table 3

[0072] As can be seen from Table 3, the observed MFR value for neat HDPE CC254 and multimodal HDPE were 2.0 and 0.8 g/10 min, respectively. In comparison, the MFR value for the HDPE compositions incorporated with ionomeric additive increases with increasing loading of ionomeric additive. This result indicates that the melt viscosity/flow characteristics of HDPE resins have increased with the incorporation of ionomeric additive. This is in addition to the superior ESCR performance of such ionomeric additive incorporated HDPE compositions.

[0073] The scanning electron microscope (SEM) image of a blend of HDPE (CC254) incorporated with 10 wt.% ionomer additive is depicted in FIG. 1. The ionomeric additive is dispersed as spherical domains with size varying from 0.3 to 3 microns. The unstained transmission electron microscope (TEM) image of a blend of HDPE (CC254) incorporated with 10 wt.% ionomer additive is depicted in FIG. 2. TEM samples were prepared by cryo- microtoming the ESCR test specimen at -120 °C. At a higher magnification, the nearly spherical ionomer domains with sizes ranging from 50 to 500 nanometers are seen as white patches. The unstained transmission electron microscope (TEM) images of a blend of HDPE (CC254) incorporated with different amounts of ionomeric additive at 5 wt. % (A), 10 wt.% (B) and 20 wt.% (C) are depicted in FIGS. 3-5, respectively. As seen from these images, the domain size of ionomeric additive is the range of 50 - 500 nanometers, with a slight increase of domain sizes with increasing loading of ionomeric additive in the HDPE. .

[0074] While the invention has been shown in some of its forms, it should be apparent to those skilled in the art that it is not so limited, but is susceptible to various changes and modifications without departing from the scope of the invention based on experimental data or other optimizations considering the overall economics of the process. Accordingly, it is appropriate that the appended claims be construed broadly and in a manner consistent with the scope of the invention.

Claims

1. A polyethylene composition having increased environmental stress crack resistance, the composition comprising a polymer blend of a multimodal high density polyethylene (HDPE) and an ionomeric polyethylene, preferably wherein the HDPE has a melt flow rate at 190 °C and 2.16 kg or 21.6 kg of 0.2 dg/min to 50 dg/min and/or a density of 945 kg/m³ to 965 kg/m³, wherein the density of the HDPE is determined in accordance with ISO 1 183-1 (2012), method A, and the melt flow rate in accordance with ISO 1 133-1 (201 1 ).

2. The composition of claim 1 , wherein the ionomeric polyethylene is present in an amount of from 0.1 wt.% to 15 wt.% by weight of the polymer blend, or from 2 wt.% or less by weight of the polymer blend.

3. The composition of any one of claims 1-2, wherein the ionomeric polyethylene has an average molecular weight (Mw) of from 5000 to 60,000 g/mol.

4. The composition of any one of claims 1-3, wherein the ionomeric polyethylene comprises a copolymer of ethylene and at least one of a carboxylic acid and a sulphonic acid, preferably wherein the carboxylic acid is at least one of acrylic acid, methylacrylic acid, and ethylacrylic acid.

5. The composition of any one of claims 1-4, wherein the ionomeric polyethylene has an ionic group content of from 0.5 mol% to 25 mol% of the ionomeric polyethylene.

6. The composition of any one of claims 1-5, wherein the ionomeric polyethylene contains metal counter ions comprising at least one of a mono and a divalent metal salt.

7. The composition of any one of claims 1-6, wherein the ionomeric polyethylene contains metal counter ions comprising Li, Na, K, Zn, Ca, Mg, Pb and Sn.

8. The composition of any one of claims 1-7, wherein the polymer blend provides a molded article having an ESCR of at least 40 hours as determined by ASTM D1693-15B, preferably of from 40 hours to 1000 hours.

9. The composition of any one of claims 1-8, wherein the HDPE is a copolymer with comonomers selected from C₃ to C10 olefin monomers, the comonomers being present in the HDPE copolymer in an amount of from 2 wt.% or less.

10. The composition of any one of claims 1-9, wherein the HDPE is a copolymer with comonomers selected from C₃ to C10 olefin monomers, the comonomers being present in the HDPE copolymer in an amount of from 1 wt.% or less.

11. The composition of any one of claims 1-10, further comprising an additive of at least one of a nucleating agent, a heat conductive agent, a tie agent, an antiblocking agent, an antistatic agent, an antioxidant, a neutralizing agent, an acid scavenger, a blowing agent, a crystallization aid, a dye, a flame retardant agent, a filler, an impact modifier, a mold release agent, an oil, another polymer, a pigment, a processing agent, a reinforcing agent, a stabilizer, an UV resistance agent, a clarifying agent, a slip agent, a flow modifying agent, ionic additive and combinations thereof.

12. The composition of any one of claims 1-1 1 , wherein the polymer blend is formed into an article of manufacture, preferably wherein the article is at least one of a film, a molded part, a container, a beverage container cap, a lid, a sheet, a pipe, a pipe coupling, a bottle, a cup, a tray, a pallet, and a toy.

13. The composition of claim 12, wherein the article is formed by at least one of injection molding, blow molding, compression molding, sheet extrusion, film blowing, pipe extrusion, profile extrusion, calendaring, and thermoforming.

14. A method of forming a polyethylene composition having increased environmental stress crack resistance, the method comprising modifying a multimodal high density polyethylene (HDPE) by combining the multimodal HDPE with an ionomeric polyethylene.

15. Use in a polymer blend comprising multimodal high-density polyethylene of an ionic polyethylene, present in an amount of from 0.1 wt.% to 15 wt.% by total weight of the polymer blend, preferably of from 5.0 wt.% to 15 wt.%, for increase of the

environmental stress crack resistance of a polymer composition comprising the blend.