Charge Storage Performance of Polyetherimide Ultem®1000-Influence of Secondary Antioxidants and Purification

The performance of a polymeric electret material depends on many parameters, and besides chemical structure, charging conditions, and application temperature, other factors, such as grade, manufacturer, processing history, and additive package, are critical. Commercial polyetherimide (PEI) Ultem (R) 1000 films exhibited satisfying electret properties as revealed by an isothermal potential decay (ITPD) to 75% of the initial surface charge after 24 h at 90 degrees C. It was found that after purification by reprecipitation this value drops to 34% and that the same PEI synthesized by two different methods revealed to be a very poor electret with charge retention of almost zero. Assuming that an additive in the commercial material might be responsible for this behavior, we identified an organophosphonite which is commonly used as antioxidant in high-temperature polymers. We incorporated this additive by melt compounding into purified PEI and found a dramatic increase in charge retention to 79% of the initial charge at an additive load level of 0.5 wt %. By immersing Ultem (R) 1000 films in water, the electret behavior was further improved and almost 100% charge retention was achieved. (C) 2009 Wiley Periodicals, Inc. J Appl Polym Sci 115:1247-1255, 2010