Thermal instability of electromechanical films of cellular polypropylene

Taylor, D.M.; Fernández, Óscar Fernández

doi:10.1109/tdei.2005.1511102

Cited by 24 publications

(15 citation statements)

References 18 publications

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“…[19,20] Within this range of electric fields, however, the microplasma discharges inside the voids may be strongly influenced by means of a suitable gas atmosphere, as reported in the literature, [3] where, for example, nitrogen gas was kept inside the voids during charging. On relatively soft foams, electric charging in gases with high electric breakdown fields such as SF 6 can enhance the internal charging, as previously demonstrated for cellular PP films. [21] Consequently, electric charging of our PETP samples was always performed in SF 6 .…”

Section: Internal Bipolar Electric Charging and Resulting Piezoelectrsupporting

confidence: 55%

“…On relatively soft foams, electric charging in gases with high electric breakdown fields such as SF 6 can enhance the internal charging, as previously demonstrated for cellular PP films. [21] Consequently, electric charging of our PETP samples was always performed in SF 6 . With SF 6 in the cellular voids and around the sample, charging under corona-tip voltages of -60 kV (the limit of our experimental equipment) was possible.…”

Section: Internal Bipolar Electric Charging and Resulting Piezoelectrsupporting

confidence: 55%

“…[3][4][5] Their industrial applications are, however, still relatively scarce because of several limitations, the most severe of which is a low thermal stability. [6] Consequently, several novel or improved ferroelectret materials have been proposed and investigated during the last few years. Among the more promising ferroelectret polymers are suitably foamed poly(ethylene terephthalate) (PETP) films [7,8] as well as blends and copolymers of cyclo-olefin polymers (COPs).…”

Section: Introductionmentioning

confidence: 99%

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Optimized Preparation of Elastically Soft, Highly Piezoelectric, Cellular Ferroelectrets from Nonvoided Poly(ethylene Terephthalate) Films

Wirges

Wegener

Voronina

et al. 2007

Adv Funct Materials

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Electrically charged cellular polymer films can exhibit very high piezoelectric activity and are therefore more and more often employed in advanced electromechanical and electro‐acoustical transducers. In this paper, we report an optimized sequence of steps for preparing such ferroelectrets from commercial nonvoided poly(ethylene terephthalate) (PETP) films by means of foaming with CO2, biaxial mechanical stretching, controlled void inflation, and bipolar electric charging. The nonvoided PETP films were foamed with supercritical CO2 at a suitably high pressure and subsequently annealed for stabilization. The cellular foam structure was further optimized by means of well‐controlled biaxial stretching in a commercial stretcher and sometimes subsequent inflation in a pressure chamber. Bipolar electric charging of the internal voids was achieved through the application of high electric fields in an SF6 atmosphere. The new optimized PETP ferroelectrets exhibit quite large piezoelectric coefficients up to almost 500 pC N–1, for which unusually low elastic stiffnesses of only around 0.3 MPa are essential. The PETP‐foam ferroelectrets possess unclamped thickness‐extension resonance frequencies between approximately 120 and 250 kHz, and are thus highly suitable for several established as well as novel ultrasonic‐transducer applications.

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Section: Internal Bipolar Electric Charging and Resulting Piezoelectrsupporting

confidence: 55%

Section: Internal Bipolar Electric Charging and Resulting Piezoelectrsupporting

confidence: 55%

Section: Introductionmentioning

confidence: 99%

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Optimized Preparation of Elastically Soft, Highly Piezoelectric, Cellular Ferroelectrets from Nonvoided Poly(ethylene Terephthalate) Films

Wirges

Wegener

Voronina

et al. 2007

Adv Funct Materials

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“…[3][4][5] One of the most studied materials in this field is cellular polypropylene (PP). [6][7][8][9][10][11][12][13] The piezoelectric d 33 coefficients that can be obtained in this material are often much larger than those of conventional piezoelectric polymers such as polyvinylidene fluoride and its copolymers. 14-17 However, ferroelectrets made of cellular PP films exhibit rather low thermal stability of piezoelectricity.…”

mentioning

confidence: 99%

“…At 50 C piezoelectric coefficients in cellular PP films start to decay rapidly, and already at 100 C, these coefficients are lower than those observed in conventional ferroelectric polymers. 7,9,11,12 In order to improve the thermal stability of piezoelectricity, several other material with better charge-storage properties have been investigated. As already mentioned above, those include mostly fluorocarbon polymers-namely polytetrafluoroethylene (PTFE) and its copolymers.…”

mentioning

confidence: 99%

Treatment with orthophosphoric acid enhances the thermal stability of the piezoelectricity in low-density polyethylene ferroelectrets

Rychkov

Altafim

Qiu

et al. 2012

Journal of Applied Physics

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Ferroelectrets have been fabricated from low-density polyethylene (LDPE) films by means of a template-based lamination. The temperature dependence of the piezoelectric d33 coefficient has been investigated. It was found that low-density polyethylene ferroelectrets have rather low thermal stability with the piezoelectric coefficient decaying almost to zero already at 100 °C. This behavior is attributed to the poor electret properties of the polyethylene films used for the fabrication of the ferroelectrets. In order to improve the charge trapping and the thermal stability of electret charge and piezoelectricity, LDPE ferroelectrets were treated with orthophosphoric acid. The treatment resulted in considerable improvements of the charge stability in LDPE films and in ferroelectret systems made from them. For example, the charge and piezoelectric-coefficient decay curves shifted to higher temperatures by 60 K and 40 K, respectively. It is shown that the decay of the piezoelectric coefficient in LDPE ferroelectrets is governed by the relaxation of less stable positive charges. The treatment also leads to noticeable changes in the chemical composition of the LDPE surface. Infrared spectroscopy reveals absorption bands attributed to phosphorus-containing structures, while scanning electron microscopy shows new island-like structures, 50–200 nm in diameter, on the modified surface.

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