The thermoplastic resins most often used to make pipes for water and heating systems are:

• PE-X cross linked polyethylene
• PP-C copolymer polypropylene
• PB polibutene

All the above- mentioned resins belong to the polyolephine family, a group of plastic materials obtained by polymerization of unsaturated hydrocarbons, which have one or more double links. In a conventional polymer the molecular chains are irregularly placed: they have fairly good mobility, heat causes oscillation in these chains until they break, resulting in alteration of material’s characteristics. Two ways of preventing this problem have been tested.

Researchers have selected polymers with long molecular chains because, as molecular rate increases, the mechanical characteristics of manufactured item improve; these chains must be as linear as possible, i.e. they must show a low number of ramifications and a high degree of crystallization by extrusion these chains are submitted to stretch, allowing crystallization of a further percentage.

Isotactic polymers show much better mechanical characteristics as compared to their correspondent amorphous polymers; they maintain their properties up to temperatures close to melting point. Thus describes the nature of polypropylene techno-polymers in a simple way.

The other way tested by researchers is creation of chemical links among molecular chains in order to make them much steadier and avoid their sliding. This procedure has been adopted for the cross linking of polyethylene-PE-X.

There is a very big production of PP copolymers it is therefore important that fitness of raw material used be proven; it must be suitable to bear the thermo mechanical stresses required of it in operation for a long time (50 years).

Thus it guaranteed that goods manufactured have high mechanical properties; it has been stabilized with appropriate anti-oxidants to postpone the combined effects of pressure and temperature for a very long time.