TY  - JOUR
A1  - Qiu, Xunlin
A1  - Groth, Frederick
A1  - Wirges, Werner
A1  - Gerhard, Reimund
T1  - Cellular polypropylene foam films as DC voltage insulation and as piezoelectrets
BT  - a comparison
JF  - IEEE transactions on dielectrics and electrical insulation
N2  - Polymer foams are in industrial use for several decades. More recently, non-polar polymer foams were found to be piezoelectric (so-called piezoelectrets) after internal electrical charging of the cavities. So far, few studies have been carried out on the electrical-insulation properties of polymer foams. Here, we compare the piezoelectric and the DC-voltage electrical-insulation properties of cellular polypropylene (PP) foams. Their cavity microstructure can be adjusted via inflation in high-pressure nitrogen gas in combination with a subsequent thermal treatment. While inflation is effective for improving the piezoelectricity, it is detrimental for the electrical-insulation properties. The original cellular PP foam shows a breakdown strength of approximately 230 MV/m, within the same range as that of solid PP. The breakdown strength decreases with increasing degree of inflation, and the dependence on the foam thickness follows an inverse power law with an exponent of 1.2. Nevertheless, up to a thickness of 140 mu m (3.5 times the original thickness), the breakdown strength of cellular-foam PP films is at least 7 times that of an air gap with the same thickness. In addition, the influence of high temperatures and high humidities on the piezoelectricity and the breakdown strength of cellular PP was studied. It was found that the piezoelectric d(33) coefficient decays rapidly already at 70 degrees C, while the breakdown strength slightly increases during storage at 70 or 90 degrees C. Under a relative humidity of 95%, the breakdown strength increases with storage time, while the piezoelectric d(33) coefficient slightly decreases.
KW  - Cellular polypropylene (PP)
KW  - polymer-foam films
KW  - ferro- and piezoelectrets
KW  - charge storage
KW  - electrical breakdown
KW  - dielectric barrier discharges
Y1  - 2018
U6  - https://doi.org/10.1109/TDEI.2018.007192
SN  - 1070-9878
SN  - 1558-4135
VL  - 25
IS  - 3
SP  - 829
EP  - 834
PB  - Institut of Electr. and Electronics Engineers
CY  - Piscataway
ER  -