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A. Frank, I Berger, M Messiha, C.-G. Ek, N. Schuler, J.-M. Storheil, E. Mayrbäurl, S. Heeley, F. Krause, L. Niemöller, P. Gabriels, Y.S. Deshmukh, F. Arbeiter, T. Koch, G. Pinter:
"Slow crack growth resistance of non-virgin polymers";
Talk: Plastic Pipes XIX, Las Vegas; 09-24-2018 - 09-26-2018; in: "Proceedings of the 19th Plastic Pipes Conference PPXIX", Plastic Pipes Conference Association, (2018), Paper ID ID192, 11 pages.

For economic and ecological reasons, the use of non-virgin polymeric materials for
structural applications becomes more and more important. The dominating polymers
for manufacturing of piping systems are polyethylene (PE), polypropylene (PP) and polyvinylchloride
(PVC). Especially in the field of non-pressure applications, during the past
years the international piping industry has put additional attention to an in-creased
use of non-virgin reprocessed or recycled materials. For non-pressure pipes a minimum
lifetime of 100 years will be required in future. Resistance against slow crack growth
(SCG) is known as the most critical failure mechanism for long term pressure pipes.
Compared to virgin materials, in non-virgin materials different effects are responsible
for reduced SCG resistance such as impurities, polymer inhomogeneity or material degradation.
Hence, a detailed knowledge about the SCG resistance of the used material
is of essential importance for lifetime assessment. The current paper investigates the
SCG resistance of different non-virgin PE , PP and PV C grades with the Cracked Round
Bar (CRB) Test according ISO 18489. It is demonstrated that the SCG resistance is clearly
lower than compared to virgin materials. These results are accompanied by optical
fracture surface analysis in order to identify polymeric and inorganic impurities as two
of the main reasons for decreased SCG resistance. To investigate effects of polymeric
impurities in more detail, in a second step laboratory material were designed by a welldefined
mixing of a PE-HD and a PP pipe grade in nine different ratios. The data show
that already a very low amount of PE in PP and vice versa reduces the SCG resistance
significantly. The current paper demonstrates that the CRB Test is a quick and sensitive
method for the characterization of the SCG resistance not only for PE but also for PP and
PVC. Moreover, it shows that already a small amount of a polymeric impurity has a big
impact on the long-term relevant resistance against SCG.