Polyolefin composition with increased resistance to ClO2-containing water

1. A method for increasing the resistance of a polyolefin composition comprising a polyolefin base resin against degradation caused by contact with ClO 2 -containing water, by adding to said polyolefin composition 100 ppm to 1000 ppm of one or more antioxidant selected from the group consisting of:

a) phenols according to formula I:

wherein

R is a non-substituted or substituted aliphatic or aromatic hydrocarbyl radical which may comprise heteroatoms or R is a heteroatom,

R′ and R″ independently are a non-substituted or substituted hydrocarbyl radical which may comprise heteroatoms or H,

X 1 , X 2 and X 3 independently are a non-substituted or substituted hydrocarbyl radical which may comprise heteroatoms or H or OH, with at least X 1 , X 2 or X 3 being OH,

n is 1 to 4, and

at least one of the substituents R, R′ and/or R″ of the phenol comprises at least one sulphur, phosphorus and/or nitrogen heteroatom(s),

b) amine compounds according to formula II:

wherein R 1 , R 2 , R 3 , R 4 and R 5 independently are hydrogen or an aliphatic or aromatic hydrocarbyl radical, optionally comprising heteroatoms, and R 6 is hydrogen, and

c) sulphur-containing compounds according to formula III:

R a —S—R b ,

wherein R a and R b independently are an aliphatic or aromatic hydrocarbyl radical, optionally comprising heteroatoms, and

contacting said polyolefin composition with ClO 2 -containing water,

wherein said polyolefin composition has a lifetime of at least 200 h in a test measuring the resistance against ClO 2 -containing water at 90° C. and at a concentration of ClO 2 of 4 ppm wherein the equipment used is according to ASTM F2263-03.

2. The method according claim 1 , wherein the polyolefin composition comprises an ethylene homo- or copolymer base resin.

3. The method according to claim 1 , wherein the increased resistance is imparted to a pipe comprised of the polyolefin composition.

4. The method according to claim 1 , wherein the heteroatom of at least one of substituents R, R′ and R″ is a sulphur atom.

5. The method according to claim 1 , further comprising forming a pipe from said polyolefin composition and transporting drinking water through the pipe.

6. The method according to claim 5 , wherein the drinking water contains ClO 2 .

7. The method according to claim 1 , wherein the base resin has a density from 930 to 960 kg/m 3 .