High-temperature Breakdown Performance Improvement of Polypropylene Films Based on Micromorphology Control

• Published in: IEEE transactions on dielectrics and electrical insulation Vol. 28; no. 5; pp. 1547 - 1554
• Main Authors: Ran, Z. Y., Du, B. X., Xiao, Meng
• Format: Journal Article
• Language: English
• Published: New York IEEE 01.10.2021; The Institute of Electrical and Electronics Engineers, Inc. (IEEE)
• Subjects: Acicular structure; ambient temperature; Breakdown; breakdown strength; Carrier mobility; Carrier transport; Conduction losses; Conductivity; Crystallization; Crystals; Dielectric loss; Dielectric losses; dielectric properties; Doping; Electric breakdown; Entanglement; High temperature; metallized film capacitor; micromorphology; Molecular chains; Nanocrystals; Polypropylene; PP film; Temperature; Thermodynamic properties
• ISSN: 1070-9878; 1558-4135
• DOI: 10.1109/TDEI.2021.009583

In this paper, a modification method of polypropylene (PP) films is proposed for capacitors by micro doping of carboxylated cellulose nanocrystals (C-CNCs). Results prove that crystallization process of films is promoted, due to the entanglement effect of acicular ultra-structures of C-CNCs on PP molecular chains. With a proper doping content (0.01 wt%), the thermal properties are elevated, and the DC conductivity decreases by raising crystallinity and limiting carrier movement. Modified films possess a restricted dielectric loss at low frequencies because of regular microstructures and decreased conduction loss. Based on DC experiments at different temperatures, the breakdown strength of C-CNC/PP films shows an increase by approximately 51% at 85 °C, basically equaled to the level of pure PP at 25 °C. The mechanism is attributed to deep trap sites, which are introduced by the large crystal region and result in short free path in carrier transport. This novel PP film shows a great potential for application under thermal-electrical compound field in power systems.