Charge Protection in Electret Air Filtration Nonwoven Materials

Nonwoven media used as electret air filters are often embedded with charges to improve particle capture efficiency. These charged filters are invariably exposed to low surface tension fluids such as oils and alcohols leading to charge loss. In this study, filtration media are endowed with charge protection through increased surface repellency using melt additives that can migrate to the surface during processing. Nonwovens containing fluorochemical melt additives are produced, and examined to determine the relationship between surface chemistry, isopropyl alcohol (IPA) repellency, resultant charge retention, and filtration characteristics. Surface fluorine/carbon (F/C) ratios of approximate to 0.2 are sufficient to protect filtration performance from vapor discharging methods. Samples with bulk additive loadings of 1.2% or higher are found to achieve the necessary repellency to resist discharging independent of the migration state of the sample, while samples loaded at the 0.6% level required sufficient migration to achieve the requisite F/C ratio of 0.2 in order to be protected. Samples that achieved the necessary surface chemistry to provide significant IPA repellency retained > 80% of electret charge and corresponding filtration performance. These results have special significance in the design of filtration media relevant in global healthcare and other industrial settings. Polypropylene nonwovens are used to develop electret/charged filtration media for filtration applications such as HEPA filters and masks. These filters are exposed to alcohol or oil aerosols leading to discharging and efficacy loss. The use of fluorochemical melt additives that migrate to the surface provides repellency and charge retention. image