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Long-term performance of poly(vinyl chloride) cables, Part 2: Migration of plasticizer
KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
2008 (English)In: Polymer degradation and stability, ISSN 0141-3910, E-ISSN 1873-2321, Vol. 93, no 9, 1704-1710 p.Article in journal (Refereed) Published
Abstract [en]

Cable samples with plasticized poly(vinyl chloride) insulations were aged in air at temperatures between 80 and 155 degrees C. The concentrations of the plasticizer (di-(2-ethylhexyl) phthalate, DEHP) in the insulations of the aged cables were determined by extraction of samples in tetrahydrofuran followed by analysis of the extract by liquid chromatography. The plasticizer concentration data for different ageing times were analysed by numerical methods, fitting Fick's second law with a concentration-dependent diffusivity. The analysis showed that the transport of the plasticizer to the surrounding air phase was controlled by diffusion at 120 and 155 degrees C with an activation energy of 89 kJ mol(-1). The evaporation of the plasticizer from the outer boundary was rate controlling at lower temperatures (<= 100 degrees C), The rate of evaporation was initially constant and independent of the plasticizer concentration at both 80 and 100 degrees C. The activation energy for the initial DEHP loss rate from PVC at these temperatures was the same as that obtained for evaporation of pure DEHP on a glass plate at 60-100 degrees C measured by thermogravimetry, 98 2 kJ mol-1. Furthermore, the evaporation rate of pure DEHP on a glass plate was also of the same order of magnitude as the rate of plasticizer loss from the cable insulation. Extrapolation of the plasticizer loss rate data (from the cable at 80 degrees C and from pure liquid DEHP at temperatures between 60 and 100 IQ to 25 degrees C predicted a maximum loss of plasticizer of 1% over 25 years. This is in accordance with earlier presented data and with the data presented in this report.

Place, publisher, year, edition, pages
[Ekelund, M.; Azhdar, B.; Hedenqvist, M. S.; Gedde, U. W.] Royal Inst Technol, Sch Chem Sci & Engn, SE-10044 Stockholm, Sweden., 2008. Vol. 93, no 9, 1704-1710 p.
Keyword [en]
long-term prediction, evaporation, plasticizer migration, poly(vinyl chloride), BRANCHED POLYETHYLENE, PHTHALATE, POLYMERS, PVC, PARAMETERS, TRANSPORT, PRESSURE, KINETICS, HPLC
National Category
Chemical Engineering
Identifiers
URN: urn:nbn:se:kth:diva-14089DOI: 10.1016/j.polymdegradstab.2008.05.030ISI: 000259795600013Scopus ID: 2-s2.0-50849127815OAI: oai:DiVA.org:kth-14089DiVA: diva2:329635
Note
QC 20100713Available from: 2010-07-13 Created: 2010-07-13 Last updated: 2017-12-12Bibliographically approved
In thesis
1. Long-term Performance of PVC and CSPE Cables used in Nuclear Power Plants: the Effect of Degradation and Plasticizer migration
Open this publication in new window or tab >>Long-term Performance of PVC and CSPE Cables used in Nuclear Power Plants: the Effect of Degradation and Plasticizer migration
2009 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Enormous amounts of low voltage cables installed in a Swedish nuclear power plant are reaching their expected lifetimes. Since the cables are crucial to operational safety, it is of great importance that the actual condition of the installed cables is determined. In this study, cables based on poly(vinyl chloride) plasticized with di(2-ethylhexyl)phthalate (DEHP) were examined with respect to the degradation mechanisms responsible for the ageing of the insulation. This was achieved by studying samples that underwent accelerated ageing by different analytical methods, such as indenter modulus measurements, tensile testing, infrared spectroscopy, differential scanning calorimetry and liquid chromatography, to assess the condition of the cables. The results were unambiguous; the main deterioration mechanism differed for the jacket and the core insulation. The immediate increase in stiffness of the jacket insulation suggests that loss of plasticizer was the dominant cause for degradation. The core insulation on the other hand showed much smaller changes in the mechanical properties due to thermal ageing with an activation energy of the change in the   indenter modulus matching that of the dehydrochlorination process. The electrical functionality during high-energy line break accident was correlated to the mechanical properties of the cable and this correlation was used to establish a lifetime criterion. The mechanical data showed Arrhenius temperature dependence with activation energies of 80 kJmol-1 and 100 kJmol-1 for the jacketing and 130 kJmol-1 for the core insulation. These activation energies were used to extrapolate the lifetimes to service temperatures (20 °C to 50 °C). Plasticizer migration was determined as the lifetime controlling mechanism at the service temperatures. Experimental data, obtained by extraction of DEHP followed by liquid chromatography, were analysed by numerical methods to gain a better understanding of the migration. The analysis showed that the transport of DEHP to the surrounding environment was diffusion controlled at temperatures between 120 °C and 150 °C, with an activation energy of 89 kJmol-1. At lower temperatures, HTML clipboard ≤100 °C, the loss of plasticizer was controlled by evaporation, with an activation energy of 99 kJmol-1. Under the latter conditions, the rate of plasticizer loss from the PVC cable was very similar to that from the pure plasticizer, suggesting that a film of plasticizer was formed on the PVC surface. The evaporation of DEHP showed a clear dependence on the rate of ventilation of the gas phase surrounding the cable. The ability to monitor the condition of the installed cables is dependent on good techniques for the remaining lifetime assessment. The condition monitoring technique, Line Resonance Analysis, was applied to chlorosulfonated polyethylene cables. A clear correlation between LIRA and indenter modulus data obtained and LIRA and tensile testing results was found. This is of interest since existing lifetime criteria used in the nuclear plants are based on these two testing techniques.

 

Place, publisher, year, edition, pages
Stockholm: KTH, 2009. 59 p.
Series
Trita-CHE-Report, ISSN 1654-1081 ; 2009:53
Keyword
PCV, CSPE, cables, ageing, mechanical properties, plasticizer migratio, LIRA, life time prediction
National Category
Chemical Sciences
Identifiers
urn:nbn:se:kth:diva-11286 (URN)978-91-7415-452-8 (ISBN)
Public defence
2009-10-29, E1, Lindstedtsvägen 3, KTH, Stockholm, 10:00 (English)
Opponent
Supervisors
Note
QC 20100713Available from: 2009-10-14 Created: 2009-10-14 Last updated: 2010-07-16Bibliographically approved
2. Long-term performance of poly(vinyl chloride) cables: mechanical and electrical performances and the effect of plasticizer migration
Open this publication in new window or tab >>Long-term performance of poly(vinyl chloride) cables: mechanical and electrical performances and the effect of plasticizer migration
2007 (English)Licentiate thesis, comprehensive summary (Other scientific)
Abstract [en]

Cables insulated with plasticized poly(vinyl chloride) were aged at temperatures between 80 and 180 °C in air and their conditions were assessed by indenter modulus measurements, tensile testing, infrared (IR) spectroscopy, differential scanning calorimetry (DSC) and liquid chromatography (HPLC). Electrical testing of oven-aged cable samples was performed in order to relate the electrical functionality during a high-energy line break accident to the mechanical properties and to establish a lifetime criterion. The mechanical data taken at room temperature after ageing could be superimposed with regard to ageing time and temperature. The ageing-temperature shift factor showed Arrhenius temperature dependence. The jacketing material showed an immediate increase in stiffness (indenter and Young’s modulus) and a decrease in the strain at break on ageing; these changes were dominated by loss of plasticizer by migration also confirmed by IR spectroscopy, DSC and HPLC. The core insulation showed smaller and also delayed changes in these mechanical parameters; the loss of plasticizer by migration was retarded by the closed environment and the changes in the mechanical parameters were due to chemical degradation (dehydrochlorination). Comparison with data obtained from this study and from other studies indicates that extrapolation of data for the jacketing insulation can be performed according to the Arrhenius equation even down to service temperatures (20-40 °C). Extraction of plasticizer of samples from cables that have been exposed to service for 25 years showed a minor decrease (within the margin of error) in plasticizer content with reference to that of unexposed cable samples. The low temperature deterioration of the jacketing is according to this scheme dominated by loss of plasticizer by migration.

Numerical analysis were performed on desorption data obtained by liquid chromatography. The fitting of the data to Fick’s law showed a transition between 100 and 120 ºC. This was interpreted as a change from evaporation-control of migration at low temperatures to a diffusion-control of migration at the higher temperatures.

Place, publisher, year, edition, pages
Stockholm: KTH, 2007. 47 p.
Series
Trita-CHE-Report, ISSN 1654-1081 ; 2007:38
Keyword
Poly(vinyl chloride) cables, ageing, mechanical properties, plasticizer migration
National Category
Polymer Chemistry
Identifiers
urn:nbn:se:kth:diva-4405 (URN)978-91-7178-712-5 (ISBN)
Presentation
2007-06-05, E3, Osquars backe 14, 10044 Stockholm, 10:00
Opponent
Supervisors
Note
QC 20101104Available from: 2007-05-29 Created: 2007-05-29 Last updated: 2010-11-04Bibliographically approved

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