Plasma degradation of contaminated PPE: an energy-efficient method to treat contaminated plastic waste

The massive increase in personal protective equipment (PPE) use during the COVID-19 pandemic, particularly disposable surgical masks made from non-biodegradable polypropylene (PP), has created a global waste management crisis. The World Health Organization estimated healthcare professionals alone used ~89 million masks monthly by March 2020, and daily global disposal reached an estimated 3.4 billion single-use masks in 2020. This waste is problematic due to the risk of handling infectious materials and the slow degradation of PP in the environment. Current disposal methods, such as incineration, present environmental challenges including air pollution and high costs. Incineration also presents a linear usage model, incompatible with circular economy goals. Therefore, safe, energy-efficient, and sustainable alternatives are crucial. This study explores the use of cold plasma technology as a potential solution, leveraging its known effectiveness in sterilization and surface modification of various materials, including inactivation of pathogens and viruses. The research focuses on evaluating the viability of cold plasma for degrading commercially sourced surgical masks, quantifying mass loss, and analyzing morphological and chemical changes in the mask components.

The literature extensively documents the use of plasma technologies for diverse applications, including plastics degradation, surface etching, and sterilization. Studies have shown plasma treatment effectively decontaminates surfaces by inactivating various pathogens, including ESKAPE pathogens, *E. coli*, MRSA, and various viruses. Plasma's ability to generate UV radiation further enhances its disinfection capabilities. The advantages of using plasma for PPE sterilization include its speed, safety, and environmental friendliness, making it a promising alternative to incineration. Previous research has demonstrated the relationship between plasma power and degradation rate, suggesting that increased power could accelerate the process. Studies on polymer surface modification using plasma have also established the use of combined IR and XPS analysis for identifying chemical changes at the polymer surface.

Commercially sourced surgical masks were cut into strips and segments. Bulk PP sheets served as controls. Samples were irradiated using a Henniker HPT-200 cold plasma unit (200 W, 40 kHz) for various time intervals (up to 4 hours). Mass loss was monitored using a microbalance. Scanning electron microscopy (SEM) examined morphological changes in the PP fibers. Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS) analyzed surface chemistry changes. Thermogravimetric analysis/differential scanning calorimetry (TGA/DSC) and wide-angle X-ray scattering (WAXS) investigated changes in crystallinity. The plasma unit’s operation involved evacuation, gas filling (ambient air at 15 sccm), and plasma irradiation. Samples were handled with gloves and tweezers to prevent contamination. SEM samples were sputter-coated with Pd/Au. For XPS, a PHI Quantera II scanning XPS microprobe with monochromatic Al Kα radiation was used, maintaining charge neutralization using low-energy electrons. Survey and high-resolution spectra of O 1s, N 1s, and C 1s core levels were collected. TGA/DSC was performed using a TA Instrument SDT Q600, heating samples to 300 °C at 5 °C/min under N₂ flow. WAXS employed a Panalytical Empyrean diffractometer with a Cu anode source. Crystallinity was determined from WAXS data by fitting amorphous and crystalline components.

Plasma irradiation induced significant mass loss in the surgical masks. The unfolded 3-ply mask showed the fastest degradation rate (0.26 ± 0.03% mass loss/minute), achieving a total mass loss of 63.34 ± 7.76% after 4 hours. The folded mask showed a slower rate (0.20 ± 0.02% mass loss/minute) due to reduced surface area. Bulk PP degraded much slower (0.01 ± 0.01% mass loss/minute). The different layers of the mask exhibited varied degradation rates, with the middle filter layer showing the highest mass loss (99.0 ± 1.5% after 4 hours), followed by the outer blue layer (87.4 ± 6.7%), and the inner white layer. SEM images revealed morphological changes, including fiber length reduction, localized melting, and surface pitting with increasing irradiation time, particularly pronounced in the middle filter layer. ATR-IR spectroscopy showed the growth of peaks corresponding to C=O and O-H groups, indicating the formation of carboxyl and hydroxyl groups due to oxygen incorporation from the plasma. XPS confirmed the surface chemical modification, observing oxidized carbon species, C–OH, and O–CO groups. The appearance of nitrogen-containing species (N–(C=O)– and C–NR2) was also noted, likely originating from nitrogen in the air plasma. TGA/DSC and WAXS analysis revealed a decrease in the degree of crystallinity and melting temperature after plasma irradiation, consistent with polymer chain fragmentation. The elasticated ear loops showed significantly slower degradation compared to the mask fabric.

The results demonstrate the effectiveness of cold plasma in degrading PP microfibers in non-woven textiles, particularly the melt-blown middle layer of the surgical masks. The variation in degradation rates among the different layers highlights the influence of manufacturing processes (melt-blown vs. spun-bond) on plasma interaction. The observed surface oxidation, indicated by the formation of C=O and O-H groups, suggests a degradation mechanism similar to cool-flame oxidation of hydrocarbons. While the study used a low-power system (200 W), the results are promising, showing substantial degradation in a relatively short time. This suggests that increasing power could further enhance the degradation rate. The energy consumption of cold plasma is significantly lower compared to conventional incineration, making it a more sustainable alternative. The generation of oxygenated small organic molecules during degradation offers potential for producing value-added chemicals, though further investigation is needed. The controlled degradation via plasma minimizes the release of microplastics into the environment compared to uncontrolled degradation or incineration.

Cold plasma treatment provides a rapid, energy-efficient, and environmentally friendly method for degrading contaminated PPE. The significant mass loss and surface modification observed in the study support this conclusion. Future research should focus on optimizing the process (e.g., increasing plasma power, investigating different gas compositions) and characterizing the gaseous byproducts for potential value-added applications. The integration of this method into healthcare waste management could significantly reduce environmental burdens associated with disposable PPE.

The study used a laboratory-scale plasma unit with limited capacity. Scaling up the process for large-scale waste treatment requires further development. A more detailed analysis of the gaseous byproducts generated during the degradation process is also needed to fully assess the potential for recovering value-added chemicals. The impact of minor components (dyes, plasticizers) in the mask materials on the degradation process was not explicitly investigated.