PEX Pipes – Basic Informations

PEX Pipes = Pipes of cross linked polyethylene
In order to crosslink the molecular chains of a polyethylene, the following methods are used today:

PE-Xa: Use of organic peroxides (Chemical cross linking)
PE-Xb: With Silane compounds (Chemical cross linking)
PE-Xc: By electron beam (Physical cross linking)

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Cross Linking of Polyethylene – the Principle
Simplified the principle of the molecular linking of polyethylene is describable as follows:

The long molecular chains consist of carbon atoms (C) and hydrogen atoms (H). By use of special chemicals, i.e. temperature related decomposition of organic peroxides or by using high energy rays, e.g. electron beam, hydrogen atoms can be separated out of the molecular chain, which is generating reactive spots (free radicals) in the chain. Across those reactive spots adjacent chains direct carbon – carbon bonds could be formed what leads to a three dimensional network.

The linking mechanism of the silane cross linking method is quite different – after creating free radicals the linking of the molecular chains is generated by grafted silane bonds under the treatment of heat and humidity. The peroxide cross linking will be performed at temperatures above 130°C in the so-called amorphous phase. At cooling down a changed semi-crystalline structure is forming back within the new molecular network. This causes the characteristic lowered density and the outstanding flexibility of the peroxide cross linked pipes. The cross linking processes of the silane or the irradiation methods however are running at temperatures below the crystallite melting temperature. Thus both cross linked materials are retaining the properties of the basic raw material here.

Areas of application
PEX pipes can be used in domestic installations for surface heating and cooling, radiator connection as well as in drinking water installations.
However, by far the largest part of PEX pipes can be found in panel heating.