Influence of physical aging on the performance of corona‐charged amorphous polymer electrets

Abstract

The influence of physical aging on the electret properties before corona charging of three amorphous polymers, polyetherimide (PEI), poly(phenylene ether) (PPE), and polystyrene (PS), as well as with blends of PPE and PS, was investigated. The degree of aging was monitored by determining the enthalpy relaxation Δh using differential scanning calorimetry (DSC). The electret performance was evaluated by isothermal potential decay (ITPD) at elevated temperatures and by thermal stimulated discharge (TSD) measurements. It was demonstrated that physical aging below the glass transition temperature substantially improves the electret performance of amorphous polymers by reducing the free volume and thus hindering charge motion. As an example, the performance of nonaged PEI was improved by physical aging at 200 °C for 4 days from 18 to 95% retained charge after 24 h at 120 °C. A similar beneficial influence of physical aging on the charge storage capability was achieved using blends of PPE with PS. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 990–997, 2010

Tailored Additives to Improve the Electret Performance of Polycarbonates

“…The enthalpy relaxation Dh was calculated by subtracting the DSC output power traces from the first heating of an aged and a non-aged film (also called the area subtraction method) according to Hutchinson. [21,24] A compression molded film without thermal aging served as the non-aged reference. This reference film was kept at above T g for 6 min and subsequently quenched to room temperature with a cooling rate of about 70 K Á h À1 during the compression molding step, which is considered a thermal erase treatment.…”

“…This reference film was kept at above T g for 6 min and subsequently quenched to room temperature with a cooling rate of about 70 K Á h À1 during the compression molding step, which is considered a thermal erase treatment. [24] Isothermal Surface Potential Decay (ITPD) Measurements Squares (40 Â 40 mm 2 ) of polycarbonate films were carefully pressed onto conductive double-sided adhesive tape, which was prior adhered to aluminum plates. With this procedure, air bubbles could be avoided and we experienced that this method gives the same results as evaporated metal electrodes.…”

“…The films were charged for 30 s in a standard point-to-plate corona triode employing a grid voltage of þ400 V (grid size: 0.2 mm) and a corona voltage of þ12.5 kV. [15][16][17][18]24,29,[32][33][34] The grid ensures uniform film surface potentials between 400 V and 420 V. [35] The charge storage characteristics of the obtained electret films were evaluated by the ITPD method. Here the surface potential of the electrets films is determined as a function of the exposed time at elevated isothermal temperatures, which was the standard temperature of T ITPD ¼ 90 8C unless otherwise noted.…”

“…[37,38] In previous studies, the beneficial influence of physical aging on the charge storage capabilities of many amorphous polymers was reported. [22][23][24][25]39] Although the physical aging behavior of polycarbonate is well documented in the literature, [40][41][42][43] the effect of such a treatment on the electret properties on polycarbonate was not the subject of an investigation up to now. Therefore, we compare the electret performance of compression molded Makrolon 1 3108 films physically aged at 140 8C (i.e., 8 8C below T g ) to non-aged films.…”

“…In previous studies, a beneficial influence of annealing on the charge storage properties of amorphous polymers was shown. [22][23][24][25] The engineering plastic polycarbonate is an amorphous polymer and is especially noted for its excellent light transmission, high toughness and high creep modulus, in combination with high heat resistance, high dimensional stability and good electrical insulation properties. Perlman and Reedyk reported in 1968 on the charge decay of different polycarbonate films as heterocharge electrets.…”