Although the peak of the COVID-19 pandemic has now almost passed, people are encouraged and even required to wear facemasks in particular conditions and in many countries around the world. Masks built with natural or synthetic fibers may include different layers, and the fibers can be submitted to different treatments before manufacturing. Once they reach their usage limit, masks should be collected for further processing or valorization, which are complicated tasks due to their significant quantities, dispersion and composition [
1,
2]. In [
3,
4], the authors explored different potential solutions to valorize used masks, sometimes treated as medical waste. The main route for the valorization of used masks is thermal degradation, which should be carried out without undesirable impacts on people and the environment. It is therefore necessary to analyze the thermal degradations of masks and the resulting gaseous emissions. Different pyrolysis techniques that are applicable to masks built with polypropylene fibers and pyrolysis products were analyzed in the review [
5]. The analysis of the available literature suggests that fast and catalytic pyrolysis significantly increases the quantity and quality of pyrolytic oil, but slow pyrolysis maximizes the yield of solid products (carbonaceous char and coke). In [
6], the authors performed different pyrolysis techniques on the layers of surgical masks and characterized the resulting char and products. They observed that liquid fuel obtained after slow or medium pyrolysis was carbon- and hydrogen-rich, with a higher heating value of 43.5 MJ/kg. In [
2], the authors analyzed the combustion characteristics of a surgical mask and an extra protective mask with a zeolite layer and silver ions. They performed combustion experiments on new and used masks under temperature ramps of 5, 10, 20, and 30 °C/min. They measured the emitted gases using mass spectrometry. Non-catalytic and catalytic pyrolysis experiments were performed in [
7] on a complete surgical mask to determine the gaseous products. The pyrolysis and combustion of five masks (including tissue and surgical masks) used in France at the beginning of the COVID-19 pandemic were analyzed and compared in [
8]. The main gaseous emissions occurring during combustion experiments were also determined in that study. In [
9], the authors performed pyrolysis experiments on a surgical mask under temperature ramps of 15, 20, 25, and 30 °C/min. They determined the kinetic parameters associated with these pyrolysis experiments and analyzed the pyrolysis products using an online FTIR-MS technique. The values of the kinetic parameters and the main gaseous emissions determined in these papers are compared to those of the present study. In [
10,
11], the authors performed pyrolysis experiments on a surgical mask and on its layers, which were all built with polypropylene fibers. They performed a kinetic analysis and analyzed the pyrolysis products using the GC-MS technique. They found that propene, furan, 2,4-dimethyl-1-heptene, and isopropylcyclobutane were the major compounds. Thermal conversions of masks were also explored with other medical waste in [
12,
13], for example. This medical waste can be characterized by strong heterogeneity. Their thermal degradation can lead to emissions of toxic gases such as polycyclic aromatic hydrocarbons and hydrochloric acid. In [
14], the authors performed hydrothermal liquefaction on surgical three-ply masks built with polypropylene and polyester. They observed that this thermal degradation simultaneously destroyed pathogens and recycled the different polymers present in the masks.
In the present study, two facemasks commonly used in the Russian Federation are first characterized. The results of the proximate and ultimate analyses, the higher and lower heating values, and the amounts of the main minerals and metals highly differ between the two masks. Pyrolysis and combustion experiments were performed on these two masks in a thermobalance under the temperature ramps of 5, 10, 15, and 20 °C/min. The thermogravimetric profiles slightly differ between the two masks, but also from those of quite similar masks previously analyzed in the literature. Kinetic modeling was performed on the pyrolysis and combustion of these two masks. The extended independent parallel reaction model was used to determine the pre-exponential factor and activation energy values related to the thermal degradation of these masks, together with the associated reaction functions. This model involves as many differential equations as the number of constituents to be degraded and is based on characterizations of the material. Its efficiency in simulating the mass and mass rate curves was already proven for different materials in [
8,
15], for example. Further pyrolysis experiments were performed on these two masks under isothermal temperatures of 300, 400, and 500 °C. The pyrolysis products were analyzed using the gas chromatography technique and assembled according to the IUPAC classes. The by-products obtained applying pyrolysis experiments performed under three isothermal temperatures highly differ between the two masks, and slightly differ from those obtained in the literature for quite similar masks. Finally, combustion experiments were performed on the two masks in a horizontal oven under a temperature ramp approximately equal to 5 °C/min to determine the main gaseous emissions (CO, CO
2, NO, NO
2, and total hydrocarbons (THCs)) occurring during such combustion experiments. The main gaseous emissions are CO
2 for the Tissue mask and total hydrocarbons for the Surgical mask. The results obtained in this study highly differ between the two masks due to the fibers (natural or synthetic) used for their fabrication. The present study thus gives a complete overview of the thermal degradations of the two Russian facemasks and proposes routes for their valorization by direct production of energy through combustion, with control of the associated gaseous emissions, or the production of valuable by-products with pyrolysis under appropriate isothermal temperature.