Development of a desktop mask charger

Abstract

Polypropylene mesh, integrated in N95 respirators and surgical masks that are widely used in the current crisis of COVID-19, filters aerosols via electrostatics in addition to the physical block. However, any contact to water such as storage under high humidity, exposure to exhaling breath, and washing in water removes its charges and thus compromises its filtering efficiency. We developed a desk top device based on a Cockcroft-Walton's voltage multiplier that can restore the electrostatic charge of surgical masks within 1 min and recover the filtering efficiency of the polypropylene mesh from 87% to 97%. The device is easy to operate and safe, thus may be applied for the reuse of surgical masks towards reducing the plastic wastes.

Keywords: COVID-19; Mask; Polypropylene; Static electricity.

Fig. 1

Cockcroft-Walton's voltage multiplier used in the static electricity generator.

Fig. 2

a, A scheme showing the setup used to measure the voltages of PET or PET/aluminum double layer electrode. b, Measured voltage vs the position of the electrode (n = 3). Inset shows the position numbers. c, A scheme showing the setup used to measure the voltages of double layer electrodes with different insulators as a covering material. d, The measured voltages of the double layer electrodes with different insulators (n = 31); polyethylene terephthalate (PET), polycarbonates (PC), polypropylene (PP).

Fig. 3

a, A font view of the setup used to measure the voltages of the tip of static electricity generator at different heights between 6 cm and 25 cm b, Measured voltage vs the distance of the electrode from the ground (n = 3). Note that only relative values should be considered in Fig. 3b as the measurement was performed at a larger distance from the tip of the gun than the one that is used to read accurate values for avoiding breaking the probe (see materials and methods for the details). c, A scheme showing the setup used to measure voltages with a double layer electrode with or without ceramic legs. d, The measured voltages with or without legs vs time.

Fig. 4

a, A scheme showing the setup with different types of lids. b, Electrostatics of polypropylene sheets before charging, after charging with no lid, with a non-grounded lid, with grounded lids made of different materials (n = 3–8). c, Charging time dependence on the polypropylene electrostatics (n = 3–4).

Fig. 5

Functional prototype of a desk-top mask charger. a, The cross section, and b, the operation of the device. c, Polypropylene sheet electrostatics before and after charging (n = 10). In “polypropylene sheet”, the polypropylene sheet was extracted from surgical masks and the sheet was charged with the device. In “surgical mask”, the entire mask was charged. d, Examples of data used in c before averaging. e, The results from the Particle Filtration Efficiency (PFE) Test (n = 9).