Title :
Model for the inflation process of cellular space-charge electrets
Author :
Leonhartsberger, J.G. ; Camacho-Gonzalez, F. ; Dansachmüller, M. ; Bauer-Gogonea, S. ; Schwödiauer, R. ; Bauer, S. ; Forstner, R. ; Eder, G.
Author_Institution :
Soft Matter Phys., Johannes Kepler Univ., Linz, Austria
Abstract :
Ferroelectrets are closed-cell polymer foams that behave like ferroelectric materials during and after internally charging the voids of the cellular structure. In order to optimize the electromechanical properties of ferroelectrets, the voids within the cellular polymer are expanded in a controlled manner in a high pressure gas chamber. Thereby, the gas pressure is first increased, subsequently released and finally the expanded structure is stabilized by a heat setting treatment at elevated temperatures. Dielectric dilatometry provides an easy means for the in-situ monitoring of the multi-step foaming process, and therefore allows for the control of the degree of foaming. The mechanical stabilization of the expanded cellular polymer structure is explained in terms of the enhanced crystallinity as a result of the heat setting process. A simple model for the gas exchange process between the gas in the voids and the gas in the high pressure gas chamber is developed. For the model a simplification of the cellular structure is used, where an air-gap is separated from the electrodes by two polymer layers. The gas transport through the polymer is modelled by Fick´s law with permeabilities taken from the solution diffusion gas transport model. Good agreement between model calculations and experiment is obtained for the diffusion expansion of cellular polypropylene with CO2 and He as blowing agents.
Keywords :
diffusion; electrets; electromechanical effects; ferroelectric materials; polymer foams; polymer structure; space charge; voids (solid); Fick law; blowing agents; cellular polymer structure; cellular space-charge electrets; closed-cell polymer foams; dielectric dilatometry; diffusion expansion; electromechanical properties; ferroelectrets; ferroelectric materials; gas exchange process; gas transport model; heat setting treatment; inflation process; mechanical stabilization; multistep foaming process; permeability; voids; Air gaps; Crystallization; Dielectrics; Electrets; Ferroelectric materials; Heat treatment; Monitoring; Polymer foams; Pressure control; Temperature;
Conference_Titel :
Electrets, 2005. ISE-12. 2005 12th International Symposium on
Print_ISBN :
0-7803-9116-0
DOI :
10.1109/ISE.2005.1612323