Investigation of the electret properties of PDLA/PEC porous composite films

In the present paper the influence of both time and low pressure on the surface potential decay of porous composite films of poly(D-lactic acid) and poly(ε-caprolactone) was investigated. The samples were charged in a corona discharge by means of a corona triode system under room conditions. Positive or negative voltage was applied to the corona electrode and voltage of the same polarity as that of the corona electrode was applied to the grid. After charging, the initial surface potential was measured using the method of the vibrating electrode with compensation. Two groups of tests were performed. In the first group, after charging, the electrets were placed into a vacuum chamber where the pressure was reduced step by step in the range from 1000 mbar to 0.1 mbar. At each step the samples were stored for 1 minute. After that the electrets were removed from the vacuum chamber, their surface potential was measured again and the normalized surface potential was calculated. The influence of low pressure was analyzed by the equation that describes processes of desorption from the electret’s surface. In the second group, after charging, the electret surface potential was measured by the time of storage. The possible surface potential decay mechanisms responsible for the electret’s behavior were discussed. It was established that the surface potential decay depends on both corona polarity and type of films. It was shown that the samples charged in a positive corona are more stable than those charged in a negative corona.