Solution for Plastic Pollution: Upcycling Waste Polypropylene Masks for Effective Oil-Spill Management

Global plastic production has surged from 2 million tons to 360 million tons in 60 years, with significant portions becoming single-use waste due to high collection costs and limited infrastructure. The COVID-19 pandemic further increased PP waste from single-use PPE such as masks and gloves, intensifying pressure on waste management systems and contributing to micro/nanoplastics. Oil spills are a major source of water pollution; effective sorbents require high selectivity, fast uptake kinetics, high capacity and retention, and mechanical robustness. While various synthetic sorbents (polymers, graphene, CNTs) have been explored, many are costly, have limited recyclability, or require complex processing. PP is abundant in plastic waste (~20%), low-cost, and hydrophobic, making it a promising oil-sorbent candidate. This work proposes upcycling PP waste from single-use face masks into a layered oil-sorbent pouch with enhanced sorption capacity, selectivity, and reusability, while following precautions to mitigate pathogen risks during processing.

- Polymer sorbents such as polyurethane (PU) can achieve ~100 g/g uptake with ~70% residual sorption after 15 sorption-squeezing cycles, but PU is expensive and represents <3% of plastic waste compared to PP (~20%). - Reported polymer aerogels (PP, PVDF, PC, HDPE, PU) typically show uptake capacities of ~6–25 g/g. - Graphene aerogels can have high oil uptake but suffer from low mechanical strength and poor recyclability, often requiring chemical extraction of absorbed oil; graphene production also increases cost. CNT-based sorbents utilize high surface area but are expensive. - Facemask-derived sorbents: (i) Heptane-treated KF94 PP masks (90 °C, 1 h) achieved up to 21 g/g oil removal on water surfaces; (ii) PP fabric from disposable masks coated with fluorine-free MAF-6 showed ~14 g/g for unbranched/cyclic alkanes with lower affinity for low-weight alkanes. These gaps motivate a simple, low-cost, and reusable PP-waste-derived sorbent with higher capacity and simpler regeneration.

Materials and characterization: Waste PP masks were collected locally, washed with detergent and water, and quarantined for 14 days to mitigate pathogen risk. Xylene (isomeric mixture) served as solvent. Substrates were 5 cm × 4 cm glass plates. Characterization tools included SEM (FEI Quanta650FEG), XRD (PANalytical Empyrean), XPS (Thermo Fisher Escalab 250XI, Al Kα 1486.6 eV), FTIR (PerkinElmer Frontier), profilometry (Leica DCM8), contact angle (OCA 35), micrometer and Deflesko FS3 PosiTector 6000 for thickness, and AFM (Oxford Instruments). Synthesis of porous and fibrous thin films and pouch assembly: - Dissolution/spin coating: 1.2 g PP waste dissolved in 10 mL xylene at 130 °C for ~20 min to obtain a clear solution. A glass plate on the spin coater was heated to 120 °C. The hot solution was dispensed and spin-coated in three steps: 400 rpm for 10 s, 1000 rpm for 60 s, and 3000 rpm for 120 s. The coated substrate was annealed in a hot-air oven at 160 °C for 20 min to yield a PP porous-thin film. Operations were performed in a fume hood. - Fibrous film: A PP non-woven sheet was heated at 80 °C for 5 min to enhance flexibility and compatibility, yielding a PP fibrous-thin film. - Pouch construction: Superposed films (five layers: layers 1, 3, 5 porous PP thin films; layers 2, 4 fibrous PP films) each of 20 cm² were placed in a pouch made from PP fibrous-thin film and heat-sealed on three sides. One side immobilized the film stack; a thread was attached for handling. The pouch was made slightly larger than the films to prevent damage during sorption/desorption studies. Porosity measurement: Sorbent mass was recorded dry, then after immersion in N-methyl-2-pyrrolidone (or ethanol) to saturation. After wiping surface solvent, wet mass was recorded. Porosity was approximated from the mass difference accounting for solvent and sorbent densities. Contact angle: 2–6 μL droplets were used; values reported as averages of five measurements for toluene, sunflower oil, engine oil, and paraffin oil. Morphology and surface analysis: SEM to assess pore size, distribution, and shape; AFM for surface roughness; optical microscopy for fibrous film network. Chemical/structural analysis: XPS to detect residual solvent and surface composition; FTIR for polymer functional groups; DSC for melting point and enthalpy/crystallinity; XRD for crystalline peaks and crystallinity. Sorption testing: - Saturation kinetics: Sorbent immersed in oil for set times (0.5–15 min), removed, and weighed for immediate uptake capacity; equilibrium capacity measured after 5 min dripping. - Dripping kinetics: Oil retained versus dripping time (0–15 min) post-saturation. - Oil comparison: Uptake assessed for toluene, sunflower, paraffin, crude, and engine oils, both immediate and equilibrium. - Oil-water separation: Selectivity tested by placing the pouch on engine oil films on water with 1–10% oil-in-water; measured separation efficiency and co-absorption. Recyclability: A 20 cm² pouch was cycled in engine oil to saturation, weighed (immediate and equilibrium after 5 min drip), regenerated by mechanical squeezing (hand pressing) or hexane washing, and reused; oil recovery percentages were calculated.

- Morphology/porosity: Porous PP thin film exhibited ~40% porosity with elliptical pores of 0.5–5 μm interconnected through polymer chain interactions. AFM RMS roughness was 749 nm, facilitating oil sorption. - Surface/chemistry: XPS showed C 1s (~285 eV) and O 1s (~532 eV) peaks; absence of a 292 eV π–π* shake-up peak indicated complete removal of xylene solvent; minor oxygen (~<2%) suggested slight surface oxidation without affecting overall hydrophobicity. FTIR confirmed PP signatures (CH bending at 1456 and 1376 cm−1; CH rocking at 728 cm−1; CH stretching 2950–2850 cm−1) and indicated C–O stretching at 1235 cm−1 (ether linkages) associated with intermolecular interactions. - Thermal/crystallinity: DSC melting point 168 °C; enthalpy change 118 J/g corresponding to ~57% crystallinity. XRD showed PP peaks at 14°, 16.9°, 18.4°, 21.7° with ~60% crystallinity, consistent with DSC. - Wetting/oleophilicity: Contact angles (°): toluene ~0.7 ± 0.2 (spreads immediately), sunflower oil 19.9 ± 2.3, engine oil 14.2 ± 1.3, paraffin oil 11.0 ± 2.6; crude oil not measured due to viscosity; overall superoleophilic behavior. - Uptake capacity and kinetics: Saturation reached within 5 min. Immediate uptake (g/g) at 5 min: engine oil 85 ± 4; crude oil 84 ± 7. Equilibrium uptake after 5 min drip (g/g): engine oil 55 ± 4; crude oil 57 ± 5. Time profiles showed rapid increase by 2 min (engine oil 68 ± 4 immediate; 43 ± 4 equilibrium) and plateau by 5 min. - Dripping/retention: Post-saturation dripping decreased to negligible after 5 min, stabilizing at ~55 ± 4 g/g (engine) and ~57 ± 3 g/g (crude). - Oil selectivity in water: Fixed co-absorption of ~0.5 g/g water across 1–10% oil-in-water. Above 8% oil, the pouch absorbed oil exclusively; below 8%, it absorbed a few water droplets which were displaced by oil. Separation efficiency was ~99.5% at 1–7% oil and ~100% at 8–10%. - Reusability/regeneration: Immediate/equilibrium uptake were 85 and 55 g/g, respectively. Mechanical squeezing recovered ~91% of oil (≈8 g/g retained in pores), enabling reuse; hexane washing achieved 100% oil recovery and full reuse efficiency. The pouch effectively absorbed oil up to seven reuse cycles with mechanical squeezing between cycles. - Comparative context: The PP-waste pouch delivers higher capacity and faster kinetics than many reported polymer aerogels (6–25 g/g) and provides simple mechanical regeneration unlike graphene aerogels that require chemical extraction.

The study demonstrates that waste PP (particularly from non-woven face masks) can be upcycled into a layered oil-sorbent pouch with high oil uptake (up to 85 g/g), rapid saturation (<5 min), strong oil/water selectivity (~99.5–100% separation at 1–10% oil-in-water), and practical reusability through mechanical squeezing (91% oil recovery) or solvent washing (100% recovery). The porous-fibrous architecture combines high surface roughness and interconnected micron-scale pores with a permeable fibrous support, driving capillary/oleophilic uptake and fast transport. Analytical characterization confirms an appropriate semi-crystalline PP structure, solvent-free films, and robust morphology to sustain multiple sorption–desorption cycles. These results directly address the research goal of converting abundant, low-cost PP waste into effective, reusable oil-spill sorbents, offering advantages over costly specialty polymers (e.g., PU), low-capacity polymer aerogels, and high-cost nanocarbon sorbents that often require chemical regeneration. The oil-only uptake at ≥8% oil-in-water and minimal water co-absorption highlight selectivity relevant to spill scenarios. The workflow incorporates pathogen risk mitigation and indicates a potential route for circular economy solutions that reduce environmental plastic burdens while enabling emergency-response materials.

An oil-sorbent pouch fabricated from upcycled waste PP face masks was developed and shown to be highly effective for oil-spill management. The pouch exhibits super-fast sorption kinetics, high uptake capacity (85 g/g immediate; 55 g/g equilibrium), superoleophilicity, and robust reusability (up to seven cycles with mechanical squeezing; complete recovery with hexane washing). Structural analyses confirmed porous, interconnected microstructures (0.5–5 μm pores), semi-crystalline PP, and solvent-free films. The approach transforms problematic PP waste into a value-added product, supporting circular economy goals and providing a practical, low-cost alternative to existing sorbents. Future work could scale fabrication, broaden testing across more oil types and environmental conditions, and further optimize pouch architecture for selectivity and durability.

- Contact angle for crude oil could not be measured due to its viscous, sticky nature; performance was inferred from uptake tests rather than direct wetting data. - At oil-in-water concentrations below 8%, the pouch co-absorbed small amounts of water (fixed ~0.5 g/g), indicating limited selectivity at very low oil contents; exclusive oil absorption occurred only at ≥8% oil. - Mechanical regeneration recovered ~91% of absorbed oil, leaving ~8 g/g within the pores; full recovery required hexane washing. - Reported tests used sample areas of 20 cm² and selected oils; broader validation across varied scales and oil chemistries was not presented.