Influence of corona poling on the electrostrictive behavior of cellular polypropylene films
Résumé
In this study, a quadratic electric field dependence of the strain on the −30 kV corona-charged cellular polypropylene (PP) was observed, which was found to mainly originate from electrostriction after evaluation of Maxwell stress effect. The −30 kV-charged sample presented a maximal strain twice as high as that of the non-charged sample for the same applied electric field. Both the dielectric constant and apparent electrostrictive coefficient of cellular PP were also seen to increase after corona poling treatment. We investigated such higher electrostrictive response from the behavior of surface potential decay, the TSC current and the thermal properties. From TSC current curves, it was found that a certain amount of charges became injected into the film. And then, the total charge within the PP was calculated by integrating the TSC current, which provided a convincing evidence for enhanced electrostriction of studied polymer. In addition, from DSC analysis, it was demonstrated that the corona treatment increased the crystallinity of the cellular PP, which was also highly desirable for enhancing the electrostrictive response. Increase in the permittivity and strain was explained experimentally and mathematically by using the space-charge theory and a simplified model.