Electrical properties of polypropylene-bonded hindered phenol blends

Polypropylene (PP) film is the most commonly used dielectric film in power capacitor applications, thanks to its high breakdown strength combined with low dielectric losses. Today, antioxidants based on hindered phenol (HP) are mixed into the PP resin during manufacturing to provide thermal-oxidative protection during melt processing, however they increase the dielectric losses. Recently, a new PP-HP copolymer has been synthesized containing a few comonomer units with HP moieties, which are homogeneously distributed along the PP polymer chain. Addition of new PP-HP copolymer to PP dramatically improve the thermal-oxidative stability under elevated temperatures compared to neat PP. In the current study the electrical properties of this novel PP-HP copolymer and PP/PP-HP blends are investigated using dielectric spectroscopy and direct current (DC) breakdown strength. By adding lower amounts (2-5 wt%) of the PP-HP copolymer in PP, the dielectric constant and loss remains similar to that of neat PP. The short-term DC breakdown strength of the PP/PP-HP blends is equal or higher than the neat PP reference, combined with a reduced scatter in breakdown data. As a next step, long-term ageing tests of the PP/PP-HP blends are required. These findings may bring an advanced PP dielectric material into the market which is highly beneficial for high voltage power capacitor applications.