Borealis Technology Oy

Borealis A/s

Elisabeth Ribarits

Ola Fagrell

Jarmo Lindroos

Solveig Johansson

Marja Ora

Arja Lehtinen

Jussi Laurell

Eeva-Leena Heino

Teija Sihvonen

Jari Aaril&auml;

Lars Isaksson

Bernt-ANGke Sultan

Mats B&auml;ckman

Gustav Kermark

A multimodal polymer composition for pipes is disclosed as well as a pipes made thereof. The polymer is a multimodal polyethylene with a density of 0.930-0.965 g/cm , and a viscosity at a shear stress of 747 Pa of at least 650 Pa.s, said multimodal polyethylene comprising a low molecular weight (LMW) ethylene homopolymer fraction and a high molecular weight (HMW) ethylene copolymer fraction, said HMW fraction having a weight ratio of the LMW fraction to the HMW fraction of (35-55):(65-45). Preferably, the multimodal polyethylene has a viscosity at a shear stress of 2.7 kPa of 260-450 kPa.s; and a shear thinning index (SHI) defined as the ratio of the viscosities at shear stresses of 2.7 and 210 kPa, respectively, of SHI &equals;50-150, and a storage modulus (G&prime;) at a loss modulus (G&Prime;) of 5 kPa, of G&prime; &gE;3000 Pa. The pipe is made of the multimodal polymer composition and withstands a stress of 8.0 MPa gauge during 50 years at 20&deg; C. (MRS8.0). Preferably, the pipe has a rapid crack propagation (RCP) S4-value, determined according to ISO 13477:1997(E), of &minus;5&deg; C. or lower and a slow crack propagation resistance, determined according to ISO 13479:1997, of at least 500 hrs at 4.6 MPa/80&deg; C. The polymer composition affords good non-sagging properties to pipe made thereof.

Polymer composition for pipes

A semiconducting, cross-linkable and silane-containing polymer composition is disclosed, as is a cable sheathing for an electric cable which, as semiconducting layer, includes the cross-linked polymer composition. The composition is based on ethylene and contains carbon black. Preferably, the polymer is a terpolymer of ethylene, a (meth)acrylate of an alcohol having 1-8 carbon atoms, such as methyl, ethyl or butyl acrylate, and an unsaturated silane compound, such as vinyltrimethoxy silane. The polymer composition is distinguished by the fact that the carbon black has a specific surface area of approximately 30-80 m.sup.2 /g, which reduces the problems associated with undesirable cross-linking of the polymer composition, for instance in extrusion.

Semiconducting polymer composition and cable sheathing comprising the

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Spekeröd, Sweden

Elisabeth Ribarits