Direct Fluorination Induced Variation in Interface Discharge Behavior Between Polypropylene and Silicone Rubber Under AC Voltage

This paper reports on the effect of direct fluorination on interface discharge characteristics between isotactic polypropylene (PP) and silicone rubber under AC voltage. The influence of fluorination time on discharge initiation and propagation stages has been estimated by measuring phase resolved partial discharge pattern and relationship between discharge rate ( N ) and discharge magnitude ( Q ). Attenuated total reflection Fourier transform infrared spectrum, water contact angle and surface roughness were also measured to gain a better understanding of the fluorination effect on surface chemical and physical structures of sample. Obtained results showed that with the increase of fluorination time from 0 to 15 min, the average surface roughness of PP increased from ~42 to ~65 nm, whereas the water contact angle decreased from ~88° to ~58°. In addition, the discharge initiation time increased from ~2 to ~4 s but the discharge propagation time decreased from ~14 to ~2 s, leading to the reduction in overall time of interface breakdown from ~16 to ~6 s. It is suggested that at the initiation stage the C-F bond introduced by direct fluorination with higher bond energy and deeper trap depth should be responsible for the alleviation of polymer degradation, while at the propagation stage the formation of larger void at the surface tends to accelerate the degradation of polymer. It could be concluded that although the direct fluorination has positive effect by delaying the appearance of discharge channel, it possesses negative effect by shortening the propagation process.