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

Xiaozhen He, Ilkka Rytöluoto, Paolo Seri, Rafal Anyszka, Amirhossein Mahtabani, Hadi Naderiallaf, Minna Niittymäki, Eetta Saarimäki, Christelle Mazel, Gabriele Perego, Kari Lahti, Mika Paajanen, Wilma Dierkes (Corresponding Author), Anke Blume

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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 temperature 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 concentration. 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
    JournalPolymer Testing
    Volume98
    DOIs
    Publication statusPublished - Jun 2021
    MoE publication typeA1 Journal article-refereed

    Keywords

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

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