MATERIAL | PVC-O
Right: C-PVC-O (right) retained its dimensional properties at higher temperatures than PVC-O, says Molecor
same way as does to standard PVC pipes. An existing orientation machine (Molecor model M-OR- P-1640) was adapted to work at temperatures up to 150°C (although this was ultimately too high). The tests were done on DN160mm pipe, which is a popular size for PVC-O. The raw material, TempRite 88708, was supplied by Lubrizol, and the pipe was made on a Battenfeld Cincin- nati Argo 93 extrusion line. The main changes had to be made in the orientation stage. Temperature was increased, in steps of 5°C, until the ideal tempera- ture for orientation was obtained. Other param- eters such as pressure and expansion speed were also adjusted. After fixing these, a set of pipes was made under standard conditions, which proved that the line could be used to produce C-PVC-O. Once the pipe samples had been produced,
Below: C-PVC-O pipe underwent pressure failure in tests, but not significantly
they were tested according to the ISO 16422 Standard for PVC-O pipes – allowing a comparison between PVC-U, PVC-O, CPVC and CPVC-O. Two stress-strain tests were done on the preform and on the final oriented pipe. Both results were above standard PVC-U and its oriented couple. It seemed to match well with the test requirements for CPVC and PVC-U for stress test (50 vs 48 MPa), where a higher stress value is expected for PVC-O, said Molecor.
In an axial sample test, oriented C-PVC-O showed a pipe stress of 54.78MPa, and a pipe strain of 94.6%. These results are in line with those of PVC-O, showing a higher stress samples after orientation than standard as it happens in PVC-O.
From a requirement of 50MPa for standard CPVC-O there is an increase of properties, said Molecor. Strain also shows a behaviour in line with the orientation of PVC-U, as it is less than in standard CPVC – usually exceeding 100%, said Molecor.
Hoop testing The corresponding values for a hoop sample test were: stress, 94.8MPa; and strain, 28.6%. The stress value for CPVC-O is quite similar to that obtained for
PVC-O. Taking into account that the
preform value is a little higher for CPVC, it seems that orientation effect is less than the one in PVC-U. “Another significant consideration is how much
the strain value is reduced in C-PVC after orienta- tion,” said Muñoz. A value of 28.6 % is smaller than that for PVC-O in the hoop direction – which is usually above 80% – or even the standard CPVC before orientation, with values above 100%. This reduced capability to deform has also been shown in pressure tests, where pipes failed – but not with significant deformations, he said. Testing also revealed that the impact resistance
of C-PVC-O is far greater than that of normal C-PVC, though it has a lower improvement com- pared with PVC-O. For instance, in impact tests designed for PVC-O, C-PVC-O failed three out of 25 tests – then, in a repeat, failed four out of eight. “I have never seen PVC-O fail this kind of test,” said Muñoz. However, in thermal tests, C-PVC-O proved
more resilient: it retained its dimensions up to around 110°C, while PVC-O began to shrink at about 80°C. This pattern follows the trend of the original (unoriented) materials. Molecor says it has shown that orientation can boost the mechanical properties of standard C-PVC, in a similar way PVC-U. This could be done by adapting existing mould-based lines. “Compared with PVC-O, C-PVC-O behaves worse in impact test – and has a lower young modulus in the ring stiffness test – but when compared with C-PVC it is superior,” said Muñoz. The Minimum Required Strength (MRS) of
C-PVC-O is similar to PVC-O at ambient tempera- ture, but as temperature increases its performance
22 PIPE & PROFILE EXTRUSION | October 2018
www.pipeandprofile.com
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