Cold Atmospheric Plasma Decontamination of FFP3 Face Masks and Long-Term Material Effects

The use of cold atmospheric plasmas (CAPs) to decontaminate sensitive surfaces is an interesting field of applied plasma physics. Motivated by the shortages of face masks and safety clothing in the beginning of the corona pandemic, we conducted studies on the decontamination of FF3 face masks with CAP and the resulting material effects. Therefore, the bactericidal and sporicidal efficacy of CAP afterglow decontamination of FFP3 mask material was investigated by inoculating fabric samples with test germs
Escherichia coli
(
E. coli
) and
Bacillus atrophaeus
(
B. atrophaeus
) and subsequent CAP afterglow treatment in a surface micro discharge (SMD) plasma device. In addition, a detailed analysis of the changes in long-term plasma treated (15 h) mask material and its individual components—ethylene vinyl acetate (EVA) and polypropylene (PP)—was carried out using surface analysis methods, such as laser microscopy, contact angle measurements, X-ray photoelectron spectroscopy (XPS) as well as fabric permeability and resistance measurements. The experiments showed that
E. coli
and
B. atrophaeus
could both be effectively inactivated by plasma treatment in nitrogen mode (12 kV
_pp
, 5 kHz).
For B. atrophaeus
inactivation of more than 4-log was achieved after 30 min.
E. coli
population could be reduced by 5-log within 1 min of CAP treatment and after 5 min a complete inactivation (> 6 log) was achieved. Material analysis showed that long-term (> 5 h) plasma treatment affects the electrostatic properties of the fabric. From this, it can be deduced that the plasma treatment of FFP3 face masks with the CAP afterglow of an SMD device effectively inactivates microorganisms on the fabric. FFP3 masks can be plasma decontaminated and reused multiple times (up to 5 h of CAP treatment time) but only to a limited extent, as otherwise the permeability levels no longer meet the DIN EN 149 specifications.