Cellular electrets -from polymer granules to electromechanically active films

The paper describes how to study, develop and manufacture cellular electret films for ingenious applications. In order to create a cellular film, the polymer has to be equipped with fillers. These can be foam nucleating agents, where chemical reaction takes place or fillers, which produce cracks during film stretching. The third method to expand the film into a porous structure is to use the gas diffusion expansion method. The most critical things in determining the final porous structure are the material choice, additives and production method of the film. When porous film has been achieved the film has to be charged to get a permanent electric charge inside the film. The aim is to have electric charge on every single surface level of the porous film. Charging circumstances (charging pressure, charging in different gases, corona level) affect the electret. The electrical properties of the polymer itself is the most impressive element to define the final electret level. The principle of measuring the permanent electric charge at different temperature and the sensitivity levels of the porous film are also described in this study.