Puff pastry is hardly what comes to mind when thinking about strengthening high-pressure PVC water pipes. But there you have it. Researchers thinking like bakers have been able to develop an innovative way to improve the mechanical behaviour of PVC.
The dilemma Sirci Gresintex sought to crack: how to increase the physical strength and impact resistance of the material without using chemicals. Very often, improving one property will reduce another and the use of additives is generally more costly than plain PVC.
The solution: orient molecular chains of PVC so they are parallel to each other in order to form layers, very much like a puff pastry. Sirci Gresintex spokesman Alessio Bazzurri has more formal jargon for it:
"Biaxially-oriented PVC is state-of-the-art, leading-edge plastic pipe technology,’’ Bazzurri says. ‘’PVC has been used for many years in the manufacture of pipelines for fluids; the bi-orientation process enhances its qualities to an amazing degree, ensuring a high level of reliability.’’
To make it, a moderately thick pipe of standard PVC is first extruded by bringing it to a temperature where the material is rather soft (close to 100°C). It is then stretched in order to double approximately the diameter of the pipe. At this point, the molecular chains are now oriented parallel to the surface of the pipe. The pipe is then cooled down to normal temperature to freeze this molecular orientation.
A key to that is using air instead of water as a heating medium -- says the developer Ignacio Munoz of Molecor.
"A drastic change to air was a full challenge in terms of engineering,’’ says Munoz. ‘’When the equipment was ready to start up, we realized that to program the machine more than 70 parameters were required. But after all this hard R&D job, benefits of a dry technology highly rewarded the effort.’’
The resulting material has extraordinary properties: not only is its impact resistance much better but also the pressure strength and the stiffness of the pipe which becomes practically unbreakable!
Expensive additives need not be added to the PVC pipe which has a thickness of approximately half of a standard PVC pipe. It is also much lighter and fewer natural resources are used to produce it.
This type of pipe is particularly useful for drinking water under high pressure because of its excellent long-term resistance and low cost per meter.
Sirci Gresintex considered this technology as an excellent alternative to traditional piping materials for Italy. These lightweight pipes are easy to install and are highly durable since no corrosion will occur.
