Blend of bimodal polyethylene with unimodal ultra high molecular weight polyethylene with improved mechanical properties

1. High density polyethylene blend, comprising:

(A) 55 to 99 wt % of a high density multimodal polyethylene component having a density of at least 930 kg/m 3 , and

(B) 1 to 45 wt % of an ultra-high molecular weight polyethylene homopolymer component having

(i) an intrinsic viscosity of at least 15.0 dl/g

(ii) a nominal viscosity molecular weight (M v ) of at least 2.0*10 6 g/mol and

(iii) a molecular weight of (M w ) of at least 0.7*10 6 g/mol,

wherein component (B) is a disentangled ultra-high molecular weight polyethylene homopolymer, which is further characterized by a factor for the normalized elastic modulus G′ 0 /G′ p in the range of 0.20 to 0.95 determined in a dynamic time sweep measurement at 180° C. with constant strain of 0.5% at fixed frequency of 10 rad/s for at least 3600 s, whereby G′ 0 is the elastic shear modulus measured at t 0 directly after melting the sample and G′ p is the maximum plateau modulus; and

wherein said blend has an MFR 21 of 0.05 to 10.0 g/10 min and a density of at least 925 kg/m 3 .

2. A blend as defined in claim 1 , wherein component (A) is a bimodal HDPE having 0.1 to 2 mol % comonomer and an MFR 21 of 1-20 g/10 min.

3. A blend as defined in claim 1 , wherein component (A) comprises an ethylene homopolymer component and a butene or hexene ethylene copolymer component.

4. A blend as defined in claim 1 , wherein component (A) is present in an amount of 80 to 93 wt %.

5. A blend as claimed in claim 1 , wherein the density of the blend is 935 to 970 kg/m 3 .

6. A blend as claimed in claim 1 , wherein the UHMW polyethylene homopolymer component has a complex viscosity η* 0.05 at a shear stress of 0.05 rad/s at 190° C. in the range of 1,000,000 Pa·s to 30,000,000 Pa·s.

7. A blend as claimed in claim 1 , wherein the UHMW polyethylene homopolymer is further characterized by the factor G′ 0 /G′ p in the range of 0.30 to 0.94 in a dynamic time sweep measurement.

8. A blend as claimed in claim 1 , wherein the UHMW polyethylene homopolymer component is an unimodal UHMW polyethylene.

9. A blend as claimed in claim 1 , wherein the UHMW polyethylene homopolymer component is prepared in a slurry polymerization process at 30 to 100° C. by using a Ziegler-Natta catalyst.

10. A blend as claimed in claim 1 , wherein the blend further comprises carbon black in an amount of 1.0 to 10 wt %, based on the total amount of the composition, whereby the carbon black is added in its original form or in the form of a master batch, in which carbon black, and optionally further additives are contained in concentrated form in a carrier polymer.

11. A process for the preparation of a blend as defined in claim 1 comprising mixing

(A) 55 to 99 wt % of a high density multimodal polyethylene component having a density of at least 930 kg/m 3 , and

(B) 1 to 45 wt % of an ultra-high molecular weight polyethylene homopolymer having

(i) an intrinsic viscosity of at least 15.0 dl/g

(ii) a nominal viscosity molecular weight (M v ) of at least 2.0*10 6 g/mol and

(iii) a molecular weight of (M w ) of at least 0.7*10 6 g/mol,

and extruding or kneading the same so as to form a blend having an MFR 21 of 0.05 to 10.0 g/10 min and a density of at least 925 kg/m 3 ;

wherein component (B) is a disentangled ultra-high molecular weight polyethylene homopolymer, which is further characterized by a factor for the normalized elastic modulus G′ 0 /G′ p in the range of 0.20 to 0.95 determined in a dynamic time sweep measurement at 180° C. with constant strain of 0.5% at fixed frequency of 10 rad/s for at least 3600 s, whereby G′ 0 is the elastic shear modulus measured at t 0 directly after melting the sample and G′ p is the maximum plateau modulus.

12. An article made from the polyethylene blend as defined in claim 1 .

13. Method for the production of an article comprising the use of the polyethylene blend according to claim 1 .