Fig. 3.

Chemical composition and physical morphology of a surgical mask before and after heat treatment. The chemical morphology of the disposable mask before and after heat treatment was observed. (A) Survey XPS spectra and detailed O 1s and C 1s spectra were obtained for both the unheated and heated mask filter layers (all vertical scalings are identical). The survey spectra show the same elemental composition for unheated and heated mask filter layers. No oxidation is observed after heat treatment, as evidenced by the detailed O 1s spectra. The detailed C 1s spectra indicate that some sp² carbon was converted to sp³ carbon during heating. (B) Scanning electron microscope (SEM) images show the physical morphology of the meltblown filter layer before and after application of heat treatment at 70 °C for a period of 30 min. (C) Representative images of a droplet advancing and receding on the hydrophobic outer layer of the 3-ply disposable mask and the average contact angle measurements before and after heat treatment at 70 °C for 30 min.