Fig. 2.

SEM images of nonwoven composite structures in surgical face mask applications; the approximate scale bar added for better comparison. a) PP spunbond (S) (Nanjundappa and Bhat, 2005), b) PBT meltblown (M) (Ellison et al., 2007), c) PVA electrospun (E) (Oktay et al., 2014), d) PVA/SAP spunbond-electrospun (SE) (Sivri, 2018), e) PCL meltblown-electrospun (ME) (Erben et al., 2016), and f) Hydroentangled spunbond-meltblown-spunbond (SMS) (Mukhopadhyay, 2014), g) Schematic example of commercial face masks structure: surgical face masks and respirators.