Conference Paper
To read the full-text of this research, you can request a copy directly from the authors.


This paper investigates the evolution of electrical and physico-chemical properties of low-voltage power cables for nuclear application subjected to both temperature and radiation aging. Electrical response is evaluated by the means of the dielectric spectroscopy technique while the physico-chemical and mechanical changes are analysed at different structural scales by five complementary techniques (FTIR spectroscopy, DSC, OIT, swelling measurement and micro-indentation). All these techniques are shown to be appropriate for the evaluation of the radiochemical aging development on LV cables, suggesting the effectiveness of dielectric spectroscopy as a non-destructive technique for on-site cable diagnosis.

No full-text available

Request Full-text Paper PDF

To read the full-text of this research,
you can request a copy directly from the authors.

... As showed and widely known in literature [5][6][7][8], aging can significantly change the physical-chemical properties of organic species, including polymers. ...
... This process yields to the formation of higher dipolar oxygen-bonded chains, whose electrical response (dipolar polarization) is placed in the highest frequency range here considered. For this reason, this frequency range is usually reported as sensitive to degradation [6][7][8]. Among the high frequencies of the analyzed spectra, 100 kHz showed in literature to be representative of this frequency range and highly related to both the dipolar polarization and the aging of the polymer [4,5,7]. ...
... Previous studies [8] showed that during aging the primary antioxidant can move from the inner part of the polymer to the outer part changing its shape into needles (polymorphism of the antioxidant). Oxidation, indeed, occurs primarily in the outer layers of the polymer due to the interaction of the surface with the environment; this activates the antioxidants which act like an oxygen-proof layer, localizing the degradation only in the outer layer of the polymer. ...
Conference Paper
This paper investigates the evolution of electrical properties with aging for two XLPE based materials having different chemical compositions. It is shown that aging and material composition can significantly affect the electrical response, suggesting the suitability of dielectric spectroscopy for polymer diagnostics. Furthermore, the dielectric response is correlated with the evolution of mechanical properties, in particular elongation at break (EaB), in order to evaluate the possible scaling-up of the current cable qualification standard.
... To do so, a correlation among these various properties was performed. In particular, a relationship between the high frequency dielectric response and the total esters absorbance peaks obtained by the FT-IR spectra is possible and was shown to be consistent in previous works [12,27]. Unfortunately, since the material analyzed here shows no ester peak in the base material (lack of external antioxidants, e.g., phenol-based molecules), the total absorbance peak ( Figure 4) is almost zero and the dielectric losses (Figure 1d) in the high frequency region show very little variation with aging (inside the same order of magnitude) until the last aging period (1500 h) in air. ...
Full-text available
The usability of any material hinges upon its stability over time. One of the major concerns, focusing on polymeric materials, is the degradation they face during their service life. The degradation mechanisms are deeply influenced by the aging temperature to which the material is subjected. In this paper, low-density polyethylene (LDPE) flat specimens were thermally aged under two different temperatures (90 °C and 110 °C) and analyzed. Specimens were characterized through both the most common mechanical and chemical measurements techniques (e.g., tensile stress, thermal analyses, oxidation induction time) and electrical measurements (dielectric spectroscopy, in particular), which are examples of non-destructive techniques. As a result, a very spread characterization of the polyethylene-based materials was obtained and a very good correlation was found to exist between these different techniques, highlighting the possibility of following the aging degradation development of polymers through electrical non-destructive techniques.
Full-text available
This paper describes a study of the surface plasticization and antiplasticization of an amorphous and a semicrystalline poly(ether ether ketone) (PEEK) in solvent environments using nanohardness method. A range of solvents (octane, chloroform, tetrachloroethane, acetone, dichlorobenzene, polyethyleneglycol (PEG), methanol and water) based on the Hilderbrand’s Solubility Parameter were selected as solvent environments. The results of the nanoindentation hardness experiments performed on the virgin and the solvent immersed polymeric surfaces are reported. The surface plasticization or antiplasticization is reported on the basis of the softening or the hardening of the near surface layers (⩽1μm) after immersion of the polymeric surfaces in the solvent environments. Surface plasticization of the amorphous PEEK has been observed in organic solvents. The chlorine containing solvents have severely degraded the hardness of the amorphous polymer. A surface hardening of the amorphous PEEK has been observed after immersion in water. Semicrystalline PEEK was seen to exhibit a considerable inert behaviour to common organic solvents but chlorinated organic solvents and water have caused a decrease in the surface mechanical properties.
Full-text available
Degree of crosslinking in silane-water crosslinked ethylene–octene copolymer and its blends with low-density polyethylene was investigated, using three different techniques: the conventional gel content determination, solvent uptake factor method and infrared analysis. The results from those techniques show a similar trend in which the degree of crosslinking increases with increase of crosslinking time, and decreases with increase of crystalline portion in the materials. The measurement of gel content, although it is a direct way to yield results on degree of crosslinking, is time consuming and uses a large amount of solvent for extraction. Also, good care must be taken when analysing the gel content of samples with low degree of crosslinking. Analysis of FTIR data has shown potential for the determination of crosslink variations in the silane crosslinked materials and gives meaningful information on the progress of the silane-water crosslinking reaction.
This paper focuses on the electrical and mechanical properties of irradiated and thermally-stressed NPP cables used for instrumentation and control (I&C). These cables show some noteworthy changes after few years of uncontrolled environment conditions due to a phenomenon called post-irradiation effect. Strong post-irradiation effects, e.g. reduction of mechanical properties, raise of crosslinking and oxidation grade, were found on XLPE cable insulation years after irradiation. These degradation mechanisms can be correlated with electrical measurements in which imaginary permittivity values raise, in particular at low-frequencies where interfacial phenomena take place. This behavior can be linked to the increase of interfacial area between amorphous and crystalline region of polymer, supporting the evidence that post-irradiation effects can lead to polymer crosslinking during a storage period even at room temperature.
The thermal degradation of PEI has been studied in wide ranges of temperature (between 180 and 250 °C) and oxygen partial pressure (between 0.21 and 50 bars). On one hand, the chemical ageing mechanisms have been analysed and elucidated by FTIR spectrophotometry and by differential calorimetry (DSC) on sufficiently thin PEI films (between 10 and 60 μm thickness) to be totally free of the effects of oxygen diffusion. As expected, and by analogy with other aromatic polymers of similar chemical structure, oxidation occurs preferentially on the methyl groups of the isopropylidene unit of the bisphenol A part, thus causing the disappearance of their characteristic IR absorption band at 2970 cm⁻¹ and the growth of a new IR absorption band at 3350 cm⁻¹, attributed to alcohols. In addition, oxidation leads successively to a relative predominance of chain scissions and crosslinking, resulting in a non-monotonic change of Tg. On the other hand, the consequences of oxidation on the elastic properties have been analysed and elucidated by micro-indentation on polished cross-sections of PEI plates of 3 mm thickness. The diffusion control of oxidation leads to the development of profiles of Young's modulus within the sample thickness, which correlate perfectly with the changes in chemical structure determined by FTIR spectrophotometry. However, the increase in Young's modulus in the superficial oxidized layer is not the direct consequence of oxidation but of a physical ageing.
EPDM elastomer is widely used as the insulation of low to medium voltage electrical cables used in power plants, for which the life-time prediction has been hampered by the lack of knowledge on structure/mechanical properties, and the nonexistence of pertinent criteria of structural failure. In an attempt to fill this gap, three EPDM matrices filled with 0, 33 and 100 phr of pristine and surface treated ATH were crosslinked by dicumyl peroxide at 170°C and, subsequently, aged thermally at 90,110 and 130°C, and radiochemically under 0.1, 1 and 10 kGy.h-1, in air. A multi-scale approach was employed to analyze the oxidation of EPDM at molecular scale, and to determine its consequences at macromolecular and macroscopic scales by using several complementary characterization techniques: FTIR spectrophotometry, differential calorimetry, rheometry in melt state, swelling test, uniaxial tensile testing, etc. The structure/properties relationships established in this study are capable to explain, in particular, the alteration of elastic and fracture properties of the EPDM matrices due to chain scissions, and the reinforcement of the filler/matrix interphases induced by the specific conditions of oxidation.
Dielectric spectroscopy was evaluated as a condition monitoring technique for aged polyethylene electrical insulation in nuclear power plants. Bare core insulations of crosslinked polyethylene were aged at 55 and 85 °C under exposure to 60Co γ-radiation at different dose rates (0.42, 0.76 and 1.06 kGy h-1) to different total doses. The samples were studied by dielectric spectroscopy and tensile testing, and the crystallinity, mass fraction of soluble component and density were determined. The oxidation profiles along the depth of the insulations were assessed by infrared microscopy. The aged samples showed an increase in both the real and imaginary parts of the dielectric permittivity over the whole frequency range studied, an increase in the mass fraction of soluble component and in the material density, and a decrease in the strain-at-break. The imaginary part of the dielectric permittivity at 100 kHz increased in a linear fashion with increasing material density, the latter being strictly related to the extent of oxidation of the material according to infrared spectroscopy and differential scanning calorimetry. The generic relationship between the imaginary part of the permittivity and the density included all the data obtained under different ageing conditions. The results suggest that dielectric spectroscopy can be used for in-situ measurements of the degree of oxidation of polyethylene cables, in order to obtain information about the condition of the cable insulation to enable the remaining lifetime to be predicted.
Ethylene-octene copolymers prepared by Dow's INSITE™ constrained geometry catalyst technology present a broad range of solid-state structures from highly crystalline, lamellar morphologies to the granular morphology of low crystallinity copolymers. As the comonomer content increases, the accompanying tensile behavior changes from necking and cold drawing typical of a semicrystalline thermoplastic to uniform drawing and high recovery characteristic of an elastomer. Although changes in morphological features and tensile properties occur gradually with increasing comonomer content, the combined body of observations from melting behavior, morphology, dynamic mechanical response, yielding, and large-scale deformation suggest a classification scheme with four distinct categories. Materials with densities higher than 0.93 g/cc, type IV, exhibit a lamellar morphology with well-developed spherulitic superstructure. Type III polymers with densities between 0.93 and 0.91 g/cc have thinner lamellae and smaller spherulites. Type II materials with densities between 0.91 and 0.89 g/cc have a mixed morphology of small lamellae and bundled crystals. These materials can form very small spherulites. Type I copolymers with densities less than 0.89 g/cc have no lamellae or spherulites. Fringed micellar or bundled crystals are inferred from the low degree of crystallinity, the low melting temperature, and the granular, nonlamellar morphology. © 1996 John Wiley & Sons, Inc.
Irganox 1076(R) (octadecyl-3,5-di-tert-butyl-4-hydroxyhydrocinnamate) is a common phenolic antioxidant used in many polymer-based medical devices. As with many organic compounds, several polymorphs exist. However, in literature, only two forms of Irganox 1076(R) have been mentioned. In this study, we were able to produce, by crystallization in different solvents, three distinct polymorphs, which were characterized by DSC, FTIR and PXRD. Moreover, the three polymorphs have long-time stability at ambient pressure and temperature, meaning that they can potentially be present in or on polymeric devices. During DSC measurements, a fourth polymorph, which was only stable at low temperature, was evidenced. Thanks to Raman microspectroscopy, Irganox 1076(R) was identified directly on commercial polyurethane catheters which exhibited a blooming phenomenon. This study proves that the polymorph identified on the surface is different from the commercially available Irganox 1076(R). These results emphasize the importance of the screening of polymorphs before any study of the biocompatibility of antioxidants used in medical devices.
Aging of nuclear power plant cables: in search of non-destructive diagnostic quantities
  • L Verardi
L. Verardi, "Aging of nuclear power plant cables: in search of non-destructive diagnostic quantities", PhD Thesis, University of Bologna, 2014.
Thermal analysis of polymers
  • J D Menczel
  • R B Prime
J.D. Menczel, R.B. Prime, "Thermal analysis of polymers", Wiley, 2009.
Characterization of polymer materials using FT-IR and DSC techniques
  • P Pagès
P. Pagès, Characterization of polymer materials using FT-IR and DSC techniques. Universidade da Coruña, 2005.
Investigation on Thermal Degradation Phenomena on Low Density Polyethylene (LDPE) through Dielectric Spectroscopy
  • S V Suraci
  • D Fabiani
  • L Mazzocchetti
  • V Maceratesi
  • S Merighi
S.V. Suraci, D. Fabiani, L. Mazzocchetti, V. Maceratesi, S. Merighi, "Investigation on Thermal Degradation Phenomena on Low Density Polyethylene (LDPE) through Dielectric Spectroscopy", IEEE Conference on Electrical Insulation and Dielectric Phenomena, CEIDP, 2018, pp. 434 -437.