Significantly enhanced surface electrical conduction of poly(butylene terephthalate) insulators by direct fluorination

Commercialization of cyclic butylene terephthalate oligomers has opened the door to bulky poly(butylene terephthalate) (PBT) matrix composite parts. In view of the potential applications of PBT in high voltage insulation or other sectors, where surface charge can play an unwanted role, PBT sheets were surface fluorinated in a laboratory vessel using a F₂/N₂ mixture with 12.5% F₂ by volume at the different temperatures of 25, 55, and 85 ° C for the same time of 30 min, to enhance surface electrical conduction and to investigate the effect of fluorination temperature. Conductivity measurements reveal that the fluorinated samples have a much higher surface conductivity than the unfluorinated sample, and surface conductivity significantly increases with fluorination temperature. In accordance with the conductivity measurements, surface potential measurements after corona charging show that the fluorinated samples have a lower or much lower initial surface potential or even no surface potential, strongly depending on fluorination temperature and ambient humidity, compared with a high surface potential of the unfluorinated sample. ATR-IR analyses indicate that fluorination led to substantial changes in surface composition and structure, depending on fluorination temperature. SEM cross section and surface images show an increase of the fluorinated layer thickness with fluorination temperature and a modification of the surface morphology. Contact angle measurements of water show that fluorination also led to a significant increase in surface hydrophilicity, especially at higher fluorination temperatures. The intrinsic increase in surface electrical conduction is considered to be a result of competition between surface compositional changes and surface structural changes or the chemical traps and the physical traps.