Piezoelectric d33 coefficient of cellular polypropylene subjected to expansion by pressure treatment

The piezoelectric activity of charged cellular polypropylene films of originally 40 and 50μm thickness can be significantly increased by thickness expansion due to an exposure to high pressure for time periods of the order of hours. After such a treatment, the d33 coefficient, measured by quasistatic and interferometric methods, is found to be as high as 1200pC∕N at 0.001Hz, decreasing to 350pC∕N just below resonance. At the resonance, which is located in the range of 150–400kHz for differently treated samples, d33 coefficients up to 1400pC∕N are found. The high d33 coefficients result from a decrease of Young’s modulus Y and an increase of the chargeability of the material due to the expansion, while the decrease of d33 with frequency up to resonance is related to a corresponding increase of Y. Static pressures up to 10kPa have little influence on d33, but higher pressures result in a reversible decrease.

[1]  Mika Paajanen,et al.  Gas diffusion expansion-increased thickness and enhanced electromechanical response of cellular polymer electret films , 2002, Proceedings. 11th International Symposium on Electrets.

[2]  Michael Wegener,et al.  Understanding the role of the gas in the voids during corona charging of cellular electret films - a way to enhance their piezoelectricity , 2001 .

[3]  J. H. Cole,et al.  Frequency and temperature dependence of elastic moduli of polymers , 1986 .

[4]  R. Kressmann,et al.  Linear and nonlinear piezoelectric response of charged cellular polypropylene , 2001 .

[5]  Jukka Lekkala,et al.  ElectroMechanical Film (EMFi) — a new multipurpose electret material , 2000 .

[6]  M. Paajanen,et al.  Determination of the actuator sensitivity of electromechanical polypropylene films by atomic force microscopy , 2000 .

[7]  Reimund Gerhard-Multhaupt,et al.  Less can be more. Holes in polymers lead to a new paradigm of piezoelectric materials for electret transducers , 2002 .

[8]  Gerhard M. Sessler,et al.  Piezoelectricity in cellular electret films , 2000 .

[9]  J. Hillenbrand,et al.  Pressure-treated cellular polypropylene with large piezoelectric coefficients , 2003, 2003 Annual Report Conference on Electrical Insulation and Dielectric Phenomena.

[10]  Gerhard M. Sessler,et al.  Electromechanical response of cellular electret films , 1999 .

[11]  Jukka Lekkala,et al.  Large and broadband piezoelectricity in smart polymer-foam space-charge electrets , 2000 .

[12]  M. Paajanen,et al.  Enhancing the cellular structure and the electromechanical response of ferroelectrets - gas diffusion expansion of voided polypropylene films , 2003, 2003 Annual Report Conference on Electrical Insulation and Dielectric Phenomena.

[13]  J. Hillenbrand,et al.  Quasistatic and dynamic piezoelectric coefficients of polymer foams and polymer film systems , 2004, IEEE Transactions on Dielectrics and Electrical Insulation.