Supporting Information

Transcription

1 Copyright WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim, Germany, 14. Supporting Information for Adv. Mater., DOI: 1.1/adma A New Application Area for Fullerenes: Voltage Stabilizers for Power Cable Insulation Markus Jarvid, Anette Johansson, Renee Kroon, Jonas M. Bjuggren, Harald Wutzel, Villgot Englund, Stanislaw Gubanski, Mats R. Andersson,* and Christian Müller*

2 Supporting Information A New Application Area for Fullerenes: Voltage Stabilizers for Power Cable Insulation Markus Jarvid, Anette Johansson, Renee Kroon, Jonas M. Bjuggren, Harald Wutzel, Villgot Englund, Stanislaw Gubanski, Mats R. Andersson, * and Christian Müller * Markus Jarvid, Dr. Renee Kroon, J. M. Bjuggren, Dr. H. Wutzel, Prof. M. R. Andersson, Dr. C. Müller Department of Chemical and Biological Engineering/Polymer Technology, Chalmers University of Technology, 4196 Göteborg, Sweden * christian.muller@chalmers.se Dr. Renee Kroon, Prof. M. R. Andersson Ian Wark Research Institute, University of South Australia, Mawson Lakes, South Australia 595, Australia * mats.andersson@unisa.edu.au A. Johansson, Prof. S. Gubanski Department of Materials and Manufacturing Technology/High Voltage Engineering, Chalmers University of Technology, 4196 Göteborg, Sweden Dr. V. Englund Innovation & Technology, Borealis AB, Stenungsund, Sweden 1 / 6

3 Relative intensity / a.u. XLPE + 1 wt% PCBM XLPE + 5 wt% PCBM XLPE LDPE + 1 wt% PCBM LDPE + 5 wt% PCBM LDPE Wavenumber / cm -1 PCBM Figure S1. FTIR spectra of neat PCBM, LDPE and XLPE, as well as LDPE PCBM and XLPE PCBM containing a PCBM concentration of c ~ 5 and 1 wt%. Note the decrease of the FTIR signal at 54 cm -1, which is associated with the fullerene cage, upon cross-linking. / 6

4 Probability / % ln-ln(1-f) N tree / - ln-ln(1-f) N tree / - f / % f / % a XLPE XLPE PCBM* b c ln (E tree - E ) XLPE E tree / kv mm XLPE PCBM* E tree / kv mm -1 Figure S. (a) Left panel: Linearized 3-parameter cumulative Weibull distribution describing the number of electrical tree-initiation events as a function of electric field for neat XLPE (red diamonds) and diffusion loaded-xlpe PCBM* with a PCBM concentration of c ~.5 mmol kg -1 (blue circles); (b) corresponding 3-parameter Weibull probability density function (PDF), as well as number of samples observed at different tree-initiation fields ; (c) 3-parameter cumulative Weibull distribution function,, of neat XLPE (red diamonds), and diffusion-loaded XLPE PCBM* (blue circles). 3 / 6

5 Experimental Section Materials. PCBM and C 6 were used as purchased from Solenne BV (purity > 99%). LDPE compound with the trade name Borlink TM LS41S, containing dicumyl peroxide and the antioxidant 6,6'-di-tert-butyl-4,4'- thiodi-m-cresol, was obtained from Borealis AB (typical meltflow index ~ g/1 min at 19 C and.16 kg, density ~.9 g cm -3 ). This compound has a low level of contaminants that may influence electrical measurements and is recommended for use in high voltage applications up to kv. [1] Sample preparation. Peroxide containing LDPE pellets were ground to a fine powder with a Retsch grinder equipped with a 5 micrometer sieve. Unless stated otherwise the powder was subsequently impregnated with either C 6 toluene solution or PCBM dichloromethane solution (1 ml g -1 solvent with respect to LDPE). The solvent was removed by rotary evaporation followed by drying in vacuum. For electrical treeing tests the impregnated LDPE compound was melt-pressed at 13 C to form two separate parts, which were molded together to enclose a 1 µm thin tungsten wire, followed by cross-linking of LDPE at 18 C to form the final test object (cf. Ref. [] for detailed description). Cross-linking by-products were removed by degassing samples in vacuum (.1 mbar) at 8 C for 4 days. To ensure a comparable thermal history cross-linked and degassed samples were cooled from 13 C at a rate of. to.5 C min -1. Diffusion-loaded samples were prepared by deposition of PCBM powder on XLPE-treeing test objects, followed by heat treatment at 18 C under nitrogen atmosphere for seven days and finally cooling from 13 C at a rate of. to.5 C min -1. Already after 3 min clear diffusion of PCBM into XLPE was visible and after seven days the samples had adopted a homogeneous color. The PCBM concentration of the ~3 mm thick samples was determined with transmission UV-vis spectroscopy (Perkin Elmer Lambda 9 spectrophotometer equipped with an integrating sphere) at 435 nm relative to neat XLPE and calibrated with a ~1.8 g l -1 PCBM solution in CHCl 3 (1 mm path length). 4 / 6

6 Gel content. The gel-content of cross-linked samples was determined gravimetrically using a solvent extraction technique. Soluble material was extracted by placing samples (~.1 g) in stainless steel net pouches (1 mesh) for 8 h in ~1 dm 3 boiling decalin that contained 1 wt% of the antioxidant Irganox 176 from BASF to prevent degradation (decalin was exchanged after 6 h). Samples were dried at ambient for two days and then under vacuum (< 1 mbar) and 8 C for two days. The remaining weight of the non-soluble fraction was used to calculate the gel-content (cf. Ref. [3]). FTIR spectroscopy. Measurements were performed with a Perkin Elmer FTIR, on ~1 µm thick films containing wt% of PCBM or C 6 that were prepared in the same way as the treeing samples. Transmission spectra were collected for films melt-pressed at 13 C and after crosslinking at 18 C. The spectra were normalized against the cm -1 methyl peak. Thermal analysis. Differential scanning calorimetry (DSC) was performed under nitrogen at a scan rate of 1 C min -1 with a Perkin Elmer Pyris 1 equipped with a Perkin Elmer Intra cooler 1P. Calculation of crystallinity. We carried out DSC to estimate the crystallinity X of XLPE according to the total enthalpy method: [4] (1) where is the enthalpy of fusion calculated from the integrated area of the DSC melting endotherm in first heating thermograms (Figure 1d), ~ 9 J g -1 is the enthalpy of fusion of 1% crystalline polyethylene, and and are the heat capacity of the amorphous and crystalline phase, respectively. [5] The integration limits were chosen to be ~ C and ~ 1 C. 5 / 6

7 Calculation of peak lamellar thickness. We used the Gibbs-Thomson equation to estimate the peak lamellar thickness from DSC measurements according to: () where = 9.4 mj m - is the fold surface energy and = K denotes the equilibrium melting temperature of polyethylene. Small-angle X-ray scattering (SAXS). Measurements were carried out using synchrotron radiation (λ =.91 Å) at the I911-SAXS beamline of the MAX IV Laboratory, Lund, Sweden. [6] A Pilatus 1M D-detector from Dectris placed at a distance of 1.9 m from the sample was used to record transmission SAXS patterns of 3 mm thick solid samples within a q range of.1-4 nm -1. The D SAXS patterns were radially averaged after correction for background radiation and calibrated with silver behenate. Electrical treeing tests. The electrical treeing measurement setup and analysis is described in detail in Ref. []. An AC voltage applied at the tungsten wire electrode (contacted with aluminum tape) was increased at a rate of V s -1 (root mean square value). The formation of electrical trees was observed in-situ with an optical microscope. For each sample the first four trees growing from nondeformed segments of the tungsten wire electrode are considered to form independent of each other and are used for data analysis. [1] J. O. Boström, E. Marsden, R. N. Hampton, U. Nilsson, IEEE. Elect. Insul. Mag. 3, 6. [] E. M. Jarvid, A. B. Johansson, J. H. M. Blennow, M. R. Andersson, S. M. Gubanski, IEEE Trans. Dielectr. Electr. Insul. 13,, 171. [3] L. H. U. Andersson, B. Gustafsson, T. Hjertberg, Polymer 4, 45, 577. [4] U. W. Gedde, Polymer Physics, Kluwer Academic Publishers, [5] B. Wunderlich, H. Bauer, Heat Capacity of Linear High Polymers, Springer Verlag, 197. [6] A. Labrador, Y. Cerenius, C. Svensson, K. Theodor, T. Plivelic, J. Phys. Conf. Ser. 13, 45, / 6