Pressure effect on the polymer electret films

Polypropylene (PP), poly(lactic acid) (PLA) and poly(ethylene terephthalate) (PET) samples, charged in a positive or in a negative corona were studied. The charging of the samples in a corona discharge was carried out by means of a conventional corona triode system. After charging the surface potentials were measured using the method of the vibrating electrode with compensation and then the electrets were placed into a vacuum chamber under different low pressures from 10 Pa to 10⁵ Pa for 30 minutes. The effect of lower pressure on the surface potential of charged samples was investigated. It was established that the reduced pressure led to the surface potential decay of the electrets. The results obtained of polypropylene, poly(ethylene terephthalate) and poly(lactic acid) electrets show that charge decay is different for different polarity of the corona voltage and for different materials. The same effect was earlier observed for other polymer films. Processes of desorption from the electrets surface accompanied with surface diffusion are supposed to occur.