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Chlorinated Water Induced Aging of Pipe Grade Polypropylene Random Copolymers

1
Johannes Kepler University Linz, Altenberger Strasse 69, 4040 Linz, Austria
2
Department of Mechanical Engineering, University of Minnesota, 111 Church Street SE, Minneapolis, MN 55455, USA
*
Author to whom correspondence should be addressed.
Polymers 2019, 11(6), 996; https://doi.org/10.3390/polym11060996
Received: 10 May 2019 / Revised: 29 May 2019 / Accepted: 30 May 2019 / Published: 4 June 2019
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Abstract

Polypropylene random copolymers (PP-R) are common materials for pressurized hot water pipes. In many pipe systems, potable water is disinfected by chlorine to prevent waterborne diseases. This paper deals with hot chlorinated water induced aging of two PP-R grades with varying morphology. One material had a conventional monoclinic α crystal form (PP-Rα), whereas the other was explicitly beta-nucleated resulting in a trigonal β crystal form with a fine spherulite structure (PP-Rβ). Micro-sized specimens with a thickness of 100 µm were used for aging experiments at 60 °C in chlorinated water with 5 mg/L free chlorine, and aging indicators were monitored for exposure times of up to 2000 h. On the other hand, superimposed mechanical-environmental tests were carried out by using cracked round bar specimens with a diameter of 14 mm to determine the fatigue crack growth (FCG) resistance of both PP-R grades at 60 °C in non-chlorinated and chlorinated water. PP-Rβ was found to outperform PP-Rα with an about 30% higher time-to-embrittlement value of 2000 h. Furthermore, PP-Rβ exhibited an enhanced FCG resistance in both non-chlorinated and chlorinated water. The effect of chlorine content on the deterioration of the FCG resistances was significantly more pronounced for PP-Rα. View Full-Text
Keywords: polypropylene; pipe grades; chlorinated water; aging; fatigue crack growth resistance; superimposed mechanical-environmental testing polypropylene; pipe grades; chlorinated water; aging; fatigue crack growth resistance; superimposed mechanical-environmental testing
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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited (CC BY 4.0).
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Fischer, J.; Freudenthaler, P.J.; Lang, R.W.; Buchberger, W.; Mantell, S.C. Chlorinated Water Induced Aging of Pipe Grade Polypropylene Random Copolymers. Polymers 2019, 11, 996.

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