Polyethylene composition having environmental stress cracking resistance

A polyethylene composition comprising:

• A)30 to 70% by weight of an ethylene homopolymer or copolymer with density equal to or greater than 0.960 g/cm3 and melt flow index MIE at 190° C. with a load of 2.16 kg, according to ISO 1133, of 2 to 20 g/10 min;
• and
• B) 30 to 70% by weight of an ethylene copolymer having a MIE value lower than the MIE value the ethylene homopolymer or copolymer of A),
• wherein the polyethylene composition has the following features:
• 1) a density from 0.940 to 0.955 g/cm3, determined according to ISO 1183 at 23° C.;
• 2) a ratio MIF/MIP from 12 to 40, where MIF is melt flow index at 190° C. with a load of 21.60 kg, and MIP is melt flow index at 190° C. with a load of 5 kg, both determined according to ISO 1133-1;
• 3) a Mz from 500,000 to 3,500,000 g/mol, where Mz is z-average molecular weight, measured by GPC;
• 4) η0.02 from 80,000 to 300,000 Pa·s, wherein η0.02 is complex shear viscosity at an angular frequency of 0.02 rad/s, measured with dynamic oscillatory shear in a plate-plate rotational rheometer at a temperature of 190° C.;
• 5) a HMWcopo index from 1 to 15,
• wherein the HMWcopo index is determined according to the following formula:
• HMWcopo=(η0.02×tmaxDSC)/(10{circumflex over ( )}5)
• where η0.02 is complex shear viscosity of a melt in Pa·s, measured at a temperature of 190° C., in a parallel-plate rheometer under dynamic oscillatory shear mode with an applied angular frequency of 0.02 rad/s;
• the tmaxDSC is time, in minutes, to reach maximum value of heat flow of crystallization at a temperature of 124° C. under quiescent conditions, measured in isothermal mode in a differential scanning calorimetry apparatus;
• and
• 6) Mz/Mw*LCBI lower than 6.4, wherein Mw is weight average molecular weight and LCBI is a ratio of a measured mean-square radius of gyration Rg, measured by GPC-MALLS, to a mean-square radius of gyration for a linear PE having a same molecular weight at a molecular weight of 1,000,000 g/mol.