Method of compounding a multimodal polyethylene composition

1. A method of compounding a multimodal polyethylene composition in a compounding device, comprising:

a) compounding a multimodal polyethylene composition in a compounding device for a total residence time of at least 1.5 minutes,

b) applying a total drive specific energy (SEC) on the polyethylene composition of from 0.270 to 0.460 kWh/kg, and

c) optionally, applying a specific cooling energy (SCC) of at most 0.200 kWh/kg on the polyethylene composition,

wherein the total specific energy, which is the difference between the total drive specific energy (SEC) and any specific cooling energy (SCC), applied on the polyethylene composition is from 0.220 to 0.330 kWh/kg.

2. Method according to claim 1 , wherein the total residence time of the polyethylene composition in the compounding device is at least 2 minutes.

3. Method according to claim 2 , wherein the total residence time of the polyethylene composition in the compounding device is at least 3 minutes.

4. Method according to claim 3 , wherein the total residence time of the polyethylene composition in the compounding device is between 4.5 and 10 minutes.

5. Method according to any one of claims 1 - 4 , wherein the total drive specific energy (SEC) applied on the polyethylene composition is from 0.305 to 0.415 kWh/kg and wherein the specific cooling energy (SCC) applied on the polyethylene composition is from 0.045 to 0.145 kWh/kg.

6. Method according to claim 1 , wherein the compounding drive comprises at least one melting zone preceding at least one homogenizing zone.

7. Method according to claim 6 , wherein the drive specific energy applied to the composition in the melting zone (SEC melting ) is from 0.190 to 0.260 kWh/kg.

8. Method according to claim 6 or 7 , wherein the temperature of the composition coming out of the melting zone and entering the homogenizing zone is from 220 to 300° C.

9. Method according to claim 6 , wherein the residence time of the polyethylene composition in the homogenizing zone is at least 2 minutes.

10. Method according to claim 6 , wherein the drive specific energy applied to the polyethylene composition in the homogenizing zone (SEC homogenizing ) is from 0.080 to 0.200 kWh/kg and wherein a specific cooling energy (SCC homogenizing ) from 0.045 to 1.45 kWh/kg is applied on the polyethylene composition in the homogenizing zone.

11. Method according to claim 6 , wherein the temperature of the composition coming out of the homogenizing zone is from 265 to 310° C.

12. Method according to claim 6 , wherein the homogenizing zone comprises a single screw extruder.

13. Method according to claim 12 , wherein the single screw extruder comprises mixing elements developing shear and/or elongation stress.

14. Method according to claim 1 , wherein from 0.005 to 1 part, per 100 parts of the multimodal polyethylene composition, of a antioxidant additive comprising a compound of formula:

wherein R represents an alkyl or an alkenyl chain comprising from 8 to 35 carbon atoms, is added to the multimodal polyethylene composition.

15. Method according to claim 1 wherein the multimodal polyethylene composition has a melt flow rate MI 5 from 0.01 to 10.0 g/10 min and a density of 930 to 965 kg/m 3 and comprises from 30 to 70% by weight of a low molecular weight ethylene polymer having a melt flow rate MI 2 from 1 to 5000 g/10 mm and a density of at least 960 kg/m 3 , and from 30 to 70% by weight of a high molecular weight ethylene polymer having a melt flow rate HLMI from 0.001 to 10.0 g/10 mm and a density of 910 to 940 kg/m 3 .