Regeneration of an electret filter by contact electrification

Contact electrification restores the surface potential of a polypropylene electret filter for face masks and regenerates its filtration efficiency.

Corona Virus Nanoparticles and Enhanced Respiratory Protection for Outpatient Ophthalmic Practice

The Covid-19 pandemic has emerged rapidly and is now part of our everyday life and work. At the time of writing this editorial all routine clinical activity and surgery that had previously been stopped is set for a phased reopening over the next 6 weeks to 6 months. Ophthalmic examination includes close working distance to our patients at the slit lamp (<20 cm). Many nasolacrimal outpatient procedures can easily convert into droplet infection and even aerosol i.e reflux from lacrimal washout. In addition, many slit lamp based procedures and examinations can lead to prolonged exposure and in some cases even aerosol generation. Thus loosely fitted surgical masks, despite their electret filter to trap nanoparticles may offer little or no protection at all. Evidence is overwhelming that ophthalmologists need enhanced PPEs including surgical cap, gown, fit tested mask, gloves and goggles for all ophthalmic examinations. Hesitation in implementing new PPE guidance for ophthalmology will probably cost lives. An overview of the use of PPE is discussed in the following paragraphs.

Effects of solid particles with various charging states and oil aerosols on the filtration characteristics of electret media

In this study, electret media were loaded with neutralized and charged potassium chloride (KCl) to examine the effect of charged solid particles on loading behaviour. The media were then loaded with diethylhexyl sebacate (DEHS), dipropylene glycol (DPG) and glycerol to obtain a correlation between the efficiency degradation and liquid aerosol. The results indicated that the efficiency of electret media decreased from 72% to 46% under the neutralized KCl loading whilst the efficiency decreased from 96% to 82% under the positively charged KCl loading. Particle charging increased the initial efficiency and also effectively minimized the efficiency degradation. Given the increase in efficiency via chargers, the deposition morphology of the solid particles on the fibres was changed to mitigate the efficiency degradation. With respect to electret media loaded with DEHS, DPG and glycerol, the decrease in efficiency was associated with the solubility difference between the fibres and oil aerosols. Given sufficient affinity between the oil particles and fibres, oil molecules permeated the chain segments of the fibres and produced swelling that damaged the charge traps and decreased efficiency. The results of this study can guide practical electret filter operations and provide a better indoor environment.