Polyolefinic molding composition having improved resistance to thermooxidative degradation and its use for the production of pipes
A molding composition is suitable for the production of pipes having improved resistance to thermooxidative degradation when these pipes are in long-term contact with liquids comprising disinfectants having an oxidizing effect. Such molding composition comprises, in addition to thermoplastic polyolefins, a polyoxy compound and/or a polyhydroxy compound as additive in an amount of from 0.01 to 1.0% by weight. In addition, the molding composition can further comprise an unsaturated aliphatic hydrocarbon in an amount of up to 5% by weight. The invention also relates to a process for improving the long-term resistance of water pipes to damage caused by oxidizing disinfectants from the water by use of this molding composition.
1. A process for forming a pipe comprising the steps of:
(i) forming a molding composition by admixing:
(a) a thermoplastic polyolefin;
(b) 0.01 to 1.0% by weight, based on the total weight of the molding composition, of an organic polyoxy compound having the chemical formula:
R—[(CH 2 ) n —O] m —H
wherein
n is an integer in the range from 1 to 10,
m is an integer in the range from 3 to 500 and
R is a hydrogen atom, an OH group or an alkyl group wherein the alkyl group has from 1 to 10 carbon atoms and may bear further substituents selected from the group consisting of —OH, —COOH, —OCH 3 and —OC 2 H 5 ,
wherein the organic polyoxy compound has a mean molar mass in a range from 400 to 9000 g/mol; and
(c) 0.1 to 5.0% by weight, based on the total weight of the molding composition, of an unsaturated aliphatic hydrocarbon compound selected from the group consisting of a polyisoprene, polyoctenamer and a polydecenamer;
(ii) pelletizing the molding composition to form pellets;
(iii) extruding the pellets in the form of a pipe; and
(iv) crosslinking the pipe.
2. The process according to claim 1 , wherein the organic polyoxy compound is polyethylene glycol, methoxypolyethylene glycol or polypropylene glycol.
3. The process according to claim 1 , wherein the organic polyoxy compound has a mean molar mass of 400 g/mol or 9000 g/mol.
4. The process according to claim 1 , wherein the organic polyoxy compound is present in an amount from 0.01 to 0.5% by weight.
5. The process according to claim 1 , wherein the thermoplastic polyolefin comprises polyethylene, polypropylene or copolymers of polyethylene or polypropylene with olefinically unsaturated monomers having from 4 to 10 carbon atoms.
6. The process according to claim 1 , wherein the molding composition further comprises:
up to 10% by weight, based on the total weight of the molding composition of an additive wherein the additive is selected from the group consisting of a heat stabilizer, an antioxidant, a UV absorber, a light stabilizer, a metal deactivator, a peroxide-destroying compound, a basic costabilizer and combinations thereof.