Multimodal polyethylene composition with high pressure resistance
View Patent ↗The present invention relates to a multimodal polyethylene composition which can be manufactured into pipes showing improved pressure resistance comprising a high density multimodal ethylene polymer component (A) having a density of at least 930 kg/m 3 , and a MFR 21 of not more than 15 g/10 min, wherein said composition exhibits a LAOS-NLF defined as L A O S - N L F = G 1 ′ G 3 ′ where G 1 ′—first order Fourier Coefficient G 3 ′—third order Fourier Coefficient of at least 1.7. Such a polyethylene composition is useful for the manufacture of pressure pipes that exhibit improved pressure resistance and creep resistance and do not undergo sagging. Further disclosed is a process for the production of a pipe using such a multimodal polyethylene composition and a pipe comprising such a multimodal polyethylene composition.
1. A multimodal polyethylene composition comprising a high density multimodal ethylene polymer component (A) having a density of at least 930 kg/m 3 , and a MFR 21 of not more than 15 g/10 min,
wherein said composition exhibits a LAOS-NLF defined as
L
A
O
S
-
N
L
F
=
G
1
′
G
3
′
where G′ 1 —first order Fourier Coefficient
G′ 3 —third order Fourier Coefficient
of at least 1.7.
2. The multimodal ethylene polymer composition according to claim 1 , which has a viscosity at a shear stress of 747 Pa (eta747) of 1,000 kPa·s or higher.
3. The multimodal polyethylene composition according to claim 1 whereby the polypropylene base resin has a F30 melt strength of 10 cN or higher at 200° C. measured according to ISO 16790:2005.
4. The multimodal polyethylene composition according to claim 1 having a ratio (eta 0.05 )/(eta 300 ) of the complex viscosity, in Pa·s, at a frequency of 0.05 rad/s (eta 0.05 ), to the complex viscosity, in Pa·s, at a frequency of 300 rad/s (eta 300 ) of at least 190.
5. The multimodal polyethylene composition according to claim 1 obtainable by melt-mixing a high density multimodal ethylene polymer component (A) having a density of at least 930 kg/m 3 , and a MFR 21 of not more than 15 g/10 min, and extruding said high density multimodal ethylene polymer component (A) in the presence of up to 10 wt. % of additives, based on the weight of the mixture so as to form said multimodal polyethylene composition.
6. The multimodal polyethylene composition according to claim 1 further comprising an ultrahigh molecular weight ethylene polymer component (B).
7. The multimodal polyethylene composition according to claim 6 , wherein the ultrahigh molecular weight ethylene polymer component (B) has a nominal viscosity molecular weight (Mv) according to ASTM D 4020-05 in the range of from 1,000,000 to 6,000,000 g/mol.
8. Process for the production of a pipe comprising the steps of
(a) melt-mixing a high density multimodal ethylene polymer component (A) having a density of at least 930 kg/m 3 , and a MFR 21 of not more than 15 g/10 min,
(b) extruding the high density multimodal ethylene polymer component (A) so as to form a multimodal polyethylene composition in the presence of up to 10 wt. % of additives, based on the extruded mixture, the multimodal polyethylene composition having an MFR 21 of not more than 15 g/10 min, a density of at least 925 kg/m 3 and a LAOS-NLF defined as
L
A
O
S
-
N
L
F
=
G
1
′
G
3
′
where G′ 1 —first order Fourier Coefficient
G′ 3 —third order Fourier Coefficient
of at least 1.7, and
(c) forming said multimodal ethylene polymer composition into a pipe.
9. The process according to claim 8 , wherein an ultrahigh molecular weight polymer component (B) is added to the melt-mixing step (a).
10. The process according to claim 8 , wherein at least a part of the additives is added in step (b) at a position situated with 50% of the length from the downstream end of the extruder.
11. The process according to claim 8 , wherein at least an antioxidant and/or an acid scavenger is added at a position situated within 50% of the length from the downstream end of the extruder.
12. A pipe comprising the multimodal polyethylene composition according to claim 1 .
13. The pipe according to claim 12 having a hydrostatic pressure resistance according to ISO 1167-1:2006 with a failure time at 13.9 MPa stress and at 20° C. of at least 30 h.
14. A method for the production of a pipe wherein a multimodal polyethylene composition as defined in claim 1 is extruded and cooled.