PP/PP-HI/silica nanocomposites for HVDC cable insulation: Are silica clusters beneficial for space charge accumulation?

Xiaozhen He, Ilkka Rytoluoto, Paolo Seri, Rafal Anyszka, Amirhossein Mahtabani, Hadi Naderiallaf, Minna Niittymaki, Eetta Saarimaki, Christelle Mazel, Gabriele Perego, Kari Lahti, Mika Paajanen, Wilma Dierkes*, Anke Blume

*Corresponding author for this work

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Abstract

New potential High Voltage Direct Current (HVDC) cable insulation materials based on nanocomposites are developed in this study. The nanocomposites are produced by blending of polypropylene (PP), propylene- ethylene copolymer (PP–HI) and a modified fumed silica (A-silica) in a concentration of 1 and 2 wt %. The A- silica is successfully modified with (3-aminopropyl)triethoxysilane (APTES) via a solvent-free method, as proven by infrared spectroscopy, thermogravimetry and transmission electron microscope mapping.
A-silica in the polymer matrix acts as a nucleating agent resulting in an increase of the crystallization tem-perature of the polymers and a smaller crystal size. Moreover, the silica addition modified the crystals morphology of the unfilled PP/PP-HI blend. The composite containing A-silica with 2 wt% contains bigger-size silica clusters than the composite filled with 1 wt%. The composite with the higher A-silica concentration shows lower space charge accumulation and a lower charge current value. Besides, much deeper traps and lower trap density are observed in the composite with 2 wt% A-silica addition compared to the one with a lower concen-tration. Surprisingly, the presence of silica clusters with dimensions of more than 200 nm exhibit a positive effect on reducing the space charge accumulation. However, the real cause of this improvement might be due to change of the electron distribution stemming from the amine-amine hydrogen bond formation, or the change of the chain mobility due to the presence of occluded polymer macromolecules constrained inside the high structure silica clusters. Both phenomena may lead to a higher energetic barrier of charge de-trapping, thus increasing the depth of the charge traps.
Original languageEnglish
Article number107186
Number of pages14
JournalPolymer testing
Volume98
Early online date30 Mar 2021
DOIs
Publication statusPublished - Jun 2021

Keywords

  • HVDC insulation
  • PP/PP-HI blend
  • Space charge accumulation
  • Nanocomposites
  • Fumed silica

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