  The use of cold atmospheric plasmas (CAP) to sterilize sensitive surfaces is
an interesting new field of applied plasma physics. Motivated by the shortages
of face masks and safety clothing at the beginning of the corona pandemic, we
conducted studies on the sterilization of FF3 face masks with CAP and the
resulting material effects. Therefore, the bactericidal and sporicidal efficacy
of CAP afterglow sterilization 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 (15h) 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 kVpp, 5 kHz). For B. atrophaeus inactivation of
more than 4-log was achieved after 30 minutes. E. coli population could be
reduced by 5-log within one minute of CAP treatment and after five minutes 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 but only to a limited extent, as otherwise the
permeability levels no longer meet the DIN EN 149 specifications.
