Process for treatment of an initial polyethylene-containing material to produce a polyethylene composition for injection molding

Process for treatment of an initial polyethylene-containing material to produce a polyethylene composition characterized in that it comprises the following steps:

• a) providing a twin-screw extruder with thermal regulation devices;
• b) providing an initial polyethylene-containing material comprising at least 50 wt. % of polyethylene based on the total weight of the initial polyethylene-containing material;
• c) extruding the initial polyethylene-containing material to obtain a polyethylene composition;
• wherein extrusion is performed with a residence time of less than 20 min;
• and
• d) recovering a polyethylene composition;
• wherein step (c) of extruding comprises a thermal treatment of the initial polyethylene-containing material at a temperature of at least 300° C. in one or more hot zones of the twin-screw extruder by self-heating of the material wherein the one or more hot zones have a total length equal to or greater than 6 D with D being a screw diameter, wherein the extrusion is performed with mechanical specific energy greater than or equal to 0.4 kWh/kg, wherein the screw profile comprises at least one hot zone with successive kneading blocks elements over a length of at least 4 D followed by a left-handed element with D being the screw diameter, wherein the thermal regulation devices, are set to initial imposed barrel temperatures ranging between 24° and 320° C., and are switched off when the barrel temperature in the zone spontaneously exceeds the imposed barrel temperature by at least 3° C. without the need of external heat application;
• and
• wherein the polyethylene composition recovered in step (d) has:
• a density of at least 0.910 g/cm3 as determined according to ISO 1183-1:2012 at 23° C.;
• a melt index MI2 T ranging from 3.0 to 60.0 g/10 min as determined according to ISO 1133-2011 at 190° C. under a load of 2.16 kg;
• an unsaturation index higher than 2,000 wherein the unsaturation index is the product of the average molecular weight (Mn) in Dalton and the vinyl unsaturation units per 1,000 carbon atoms as determined by ASTM D6248-98:2004;
• and a complex viscosity at 0.1 rad/sec at 190° C. of at most 20,000 Pa·s.