Sustainable utilization of waste expanded polystyrene in cellulose acetate polymer blend membranes for CO ₂ /CH ₄ separation

Expanded polystyrene (EPS) commonly called thermocol is a widely used packaging material that poses serious environmental challenges due to its poor biodegradability and low recycling. This study investigates the use of waste EPS to develop sustainable polymer blend membranes using cellulose acetate (CA) <i>via</i> solution casting and solvent evaporation technique for carbon dioxide (CO₂) separation. The membranes were characterized using fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), differential scanning calorimetry (DSC), and field-emission scanning electron microscopy (FESEM) techniques. Model biogas having CO₂/CH₄ composition of 40 : 60 was used to test blend membranes at 1.5 and 3 bars. A significant enhancement in the CO₂ permeability was observed after the incorporation of EPS due to increased chain flexibility and free volume. The 5 wt% EPS/CA blend membrane showed the highest CO₂ permeability of 105.83 Barrer with 15.98 CO₂/CH₄ selectivity at 3 bar. 10 wt% EPS loaded blend membrane achieved the highest CO₂/CH₄ selectivity of 21.25 with 47.63 Barrer CO₂ permeability at 1.5 bar. The results have demonstrated that blending of CA with waste EPS is an effective strategy that can upcycle plastic waste into value added membrane material which can be used for efficient CO₂ separation and sustainable biogas upgrading.