Oriented PVC | materials feature
Oriented PVC (PVC-O) is growing in importance as a pipe material – with adherents claiming it is the ‘greenest’ way to make pipe. Lou Reade reports
oriented PVC pipe
Just as the barrier properties of polypropylene fi lm can be improved by stretching it in two directions – to make BOPP – so pipe can be pulled and stretched to boost its properties. Oriented PVC (PVC-O) has existed for around 40
years, but it is only in the last decade that production technology has become sophisticated enough to make commercial pipe that meets acceptable standards, according to Rob Spekreijse, CEO of PVC-O machinery manufacturer Rollepaal. “The advantages of PVC-O, compared to non-poly-
mer pipe solutions, is fabulous,” he said. “And, for water pipe, it is a better solution than polyolefi ns like PE100.” And while ductile iron has far higher mechanical
properties – such as tensile strength, stiffness and impact strength – these are only necessary to counter- act the material’s greatest weakness: corrosion. “These [mechanical] requirements are not necessary
for the pipe to transport water,” said Spekreijse. He cited studies that showed failure rates for
different types of pipe in the US and Canada. Those for standard UPVC were much better than cast or ductile
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iron, or asbestos cement. “UPVC is by far the best material for use in water
transport, which means that PVC-O is even better,” he said.
Production methods PVC-O pipe is made by extruding PVC pipe in the normal way, and then stretching it – in either one or two directions – above its glass transition temperature. PVC-O will return to its original size if exposed to temperatures above 75˚C, he said, and it should not be used beyond temperatures of 45-50˚C. There are four main methods for doing this, though one is no longer used commercially, said Spekreisje. The methods are ‘inline’ (or ‘die drawn’) and ‘offl ine’ (or ‘pipe mould’). Another key difference between methods is whether the pipe is stretched by air or water. The preform pipe – from which the fi nal PVC-O pipe
is produced – must be of excellent quality, with the lowest possible waviness, be as close as possible to minimum diameter and have very low eccentricity. An early production method – no longer available
October 2014 | PIPE & PROFILE EXTRUSION 11
Lining up:
When PVC’s amorphous structure (bottom section) is
subjected to the orientation
process, it takes on a laminate structure (top section)
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