POLYETHYLENE COMPOSITION HAVING HIGH MECHANICAL PROPERTIES

摘要

Polyethylene composition with improved balance of environmental stress cracking resistance (FNCT) and impact resistance (Charpy), particularly suited for preparing pipes, said composition having the following features:
1) density from 0.945 to 0.955 g/cm3;2) ratio MIF/MIP from more than 30 to 45;3) Shear-Induced Crystallization Index SIC from 1.0 to 2.5;4) Long Chain Branching index equal to or greater than 0.85.

主权项

1. A polyethylene composition having:
1) a density from 0.945 to 0.955 g/cm3, determined according to ISO 1183 at 23° C.; 2) a ratio MIF/MIP from more than 30 to 45, wherein the MIF is the melt flow index at 190° C. with a load of 21.60 kg, and the MIP is the melt flow index at 190° C. with a load of 5 kg, both determined according to ISO 1133; 3) a SIC Index from 1.0 to 2.5; and 4) a Long Chain Branching index equal to or greater than 0.85; wherein the SIC Index is the Shear-Induced Crystallization Index, determined according to the following relation:
SIC Index=(tonset,SIC@1000×tonset,quiescent)/(HLMI) where tonset,SIC@1000 is measured in seconds and is the time required for crystallization onset under shear rate of 1000 s−1, the tonset, quiescent is measured in seconds and is the crystallization onset time at temperature of 125° C. under no shear, determined in isothermal mode by differential scanning calorimetry; HLMI is the melt flow index determined at 190° C. with a load of 21.6 kg, according to ISO 1133.