High-Loading Poly(ethylene glycol)-Blended Poly(acrylic acid) Membranes for CO₂ Separation

Poly(ethylene glycol) (PEG) is an amorphous material of interest owing to its high CO₂ affinity and potential usage in CO₂ separation applications. However, amorphous PEG often has a low molecular weight, making it challenging to form into the membrane. The crystalline high average molar mass poly(ethylene oxide) (PEO) cannot exhibit CO₂ separation characteristics. Thus, it is crucial to employ low molecular weight PEG in high molecular weight polymers to increase the CO₂ affinity for CO₂ separation membranes. In this work, poly(acrylic acid) (PAA)/PEG blend membranes with a PEG-rich phase were simply fabricated by physical mixing with an ethanol solvent. The carbonyl group of the PAA and the hydroxyl group of the PEG formed a hydrogen bond. Furthermore, the thermal stability, glass transition temperature, and surface hydrophilicity of PAA/PEG blend membranes with various PEG concentrations were further characterized. The PAA/PEG(1:9) blend membrane exhibited an improved CO₂ permeability of 51 Barrer with high selectivities relative to the other gas species (H₂, N₂, and CH₄; CO₂/H₂ = 6, CO₂/N₂ = 63, CO₂/CH₄ = 21) at 35 °C and 150 psi owing to the enhanced CO₂ affinity with the amorphous PEG-rich phase. These PAA/PEG blend membrane permeation characteristics indicate a promising prospect for CO₂ capture applications.