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Plasticizer migration from PVC cable insulation - The challenges of extrapolation methods
KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Polymeric Materials.
KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Polymeric Materials.
2014 (English)In: Polymer degradation and stability, ISSN 0141-3910, E-ISSN 1873-2321, Vol. 101, no 1, 24-31 p.Article in journal (Refereed) Published
Abstract [en]

A single strand PVC-P insulation including an internal metal conductor removed from the jacketed assemblies of a signal cable showed brittleness after 30 years service at 25 +/- 3 degrees C in air. The PVC compound contained diisodecyl phthalate (DIDP), di(2-ethylhexyl) phthalate (DEHP) and a sizeable fraction of filler. Single strand insulation samples with internal metal conductor were aged in air at elevated temperatures for different periods of time after which the strain at break, the Young's modulus and the plasticizer content were assessed by tensile testing and liquid chromatography. Isothermal evaporation rates from pristine DIDP and DEHP and solutions of the two plasticizers were obtained by thermogravimetry. Data for Young's modulus, strain at break and plasticizer contents were extrapolated to service temperature using two different extrapolation methods, Arrhenius extrapolation (constant activation energy) and a method based on models by Langmuir, Clausius-Clapeyron and Kirchhoff. These methods assume that evaporation of plasticizers to the surrounding gas phase is the dominant deterioration mechanism. Both methods predicted only a minor decrease in plasticizer content after 30 years of ageing at 28 degrees C and thus a material with adequate mechanical properties. Liquid chromatography showed that the single strand cable samples contained a very low DIDP content (4 wt.%) and an anomalously high DEHP content; a finding that cannot be explained by the expected evaporative loss mechanism. It is suggested that DIDP was efficiently extracted by contact with a DEHP-rich interface at the insulation surface, a process which is active during plant operation, but could not be simulated by controlled laboratory accelerated ageing studies.

Place, publisher, year, edition, pages
2014. Vol. 101, no 1, 24-31 p.
Keyword [en]
Poly(vinyl chloride), Di(2-ethylhexyl)phthalate, Diisodecyl phthalate, Ageing
National Category
Polymer Technologies
URN: urn:nbn:se:kth:diva-145081DOI: 10.1016/j.polymdegradstab.2014.01.021ISI: 000334000400004ScopusID: 2-s2.0-84896317790OAI: diva2:716327
Swedish Radiation Safety Authority

QC 20140509

Available from: 2014-05-09 Created: 2014-05-08 Last updated: 2015-05-29Bibliographically approved
In thesis
1. Polymeric materials in nuclear power plants: Lifetime prediction, condition monitoring and simulation of ageing
Open this publication in new window or tab >>Polymeric materials in nuclear power plants: Lifetime prediction, condition monitoring and simulation of ageing
2015 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Nuclear power plants generate a significant part of the world’s electrical power consumption. However, many plants are nearing the end of their designed lifetime, and to extend the lifetime it is important to verify that every component can withstand the added service time. This includes polymeric materials, which become brittle with time. By predicting their lifetime and monitoring their condition, unnecessary downtime of the plant can be avoided, and secure operation can be ensured. The lifetime can be predicted by extrapolating results from accelerated ageing to service conditions, or by simulation of the degradation process.

In this study, lifetime predictions through extrapolation were performed on samples of a polyvinyl chloride (PVC) core insulation and an acrylonitrile butadiene rubber (NBR) membrane, which were thermally aged in air. The lifetime of the PVC cable was predicted using Arrhenius extrapolation, and using a method based on Langmuir, Clausius-Clapeyron, and Kirchhoff’s equations.

The lifetime of the NBR membrane was predicted using extrapolation in the temperature domain using an Arrhenius approach coupled with an extrapolation in pressure-domain, yielding realistic lifetimes.

Two cable insulations, one made from crosslinked polyethylene (XLPE) and the other from ethylene propylene rubber (EPR) were aged under the simultaneous effect of elevated temperature and γ-radiation investigated using several condition monitoring techniques. In particular, two non-destructive techniques, dielectric spectroscopy and nuclear magnetic resonance, showed promising results be developed and used in situ.

Finally, a computer model simulating the diffusion and consumption of oxygen in XLPE was developed, based on assumptions that diffusion, consumption and solubility were dependent on the total degree of oxidation. The model showed promise for further development.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2015. 75 p.
TRITA-CHE-Report, ISSN 1654-1081 ; 2015:29
National Category
Textile, Rubber and Polymeric Materials
urn:nbn:se:kth:diva-168193 (URN)978-91-7595-587-2 (ISBN)
Public defence
2015-06-11, K2, Teknikringen 28, KTH, Stockholm, 13:00 (English)

QC 20150529

Available from: 2015-05-29 Created: 2015-05-27 Last updated: 2015-05-29Bibliographically approved

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Linde, ErikGedde, Ulf W.
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