Correlating gas permeability and morphology of bio-based polyether-block-amide copolymer membranes by IR nanospectroscopy

• Published in: Journal of membrane science 2024-08, Vol.708, p.123001, Article 123001
• Main Authors: David, Oana, Etxeberria Benavides, Miren, Amenabar Altuna, Iban, Fernandez Carretero, Francisco Jose, Diaz De Guereñu Zabarte, Maria del Mar, Flat, Jean Jaques, Pineau, Quentin, Goikoetxea Larruskain, Monika, Hillenbrand, Rainer
• Format: Article
• Language: English
• Subjects: atomic force microscopy; calorimetry; carbon dioxide; composite polymers; extrusion; Gas separation; infrared spectroscopy; IR nanospectroscopy; Membrane; permeability; Polyether-block-amides; Polymer segregation; solvents
• ISSN: 0376-7388; 1873-3123
• DOI: 10.1016/j.memsci.2024.123001

The gas permeability of polymer membranes is determined by their nanoscale morphology, which strongly depends on the membrane fabrication. Here, we demonstrate how the correlation between gas permeability and fabrication-dependent nanoscale morphology of polymer membranes can be elucidated by infrared (IR) nanospectroscopy based on elastic IR scattering at an atomic force microscope tip. Specifically, we fabricated membranes of PEBAX® RNEW – a bio-based polyether-block-amide copolymer – by solvent casting and extrusion, achieving unprecedented CO2 permeability and CO2/N2 selectivity for the solvent-cast membranes. For the extruded membranes, however, we found an about 50 % reduced CO2 permeability, which could not be explained by differential scanning calorimetry and conventional IR spectroscopy. In contrast, IR nanospectroscopy revealed a highly crystalline polyether oxide (PEO) surface layer on the extruded membranes, not observed for the solvent-cast membranes. Annealing of the extruded membranes at 110 °C transformed the crystalline into amorphous PEO layers, as confirmed by IR nanospectroscopy, yielding a gas permeability close to that of the solvent-cast membranes. We thus attribute the dramatic gas reduction of the extruded membranes to their highly crystalline surface layers. Generally, studying polymer morphology by IR nanospectroscopy provides valuable information for better understanding the local gas permeability properties of polymer membranes. [Display omitted] •Poly(ether-block-amide11) copolymer membranes for unmatched CO2 separation.•Compared to solvent casting, extrusion reduces CO2 permeability by 50 %.•Morphology of polymer membranes was elucidated by infrared (IR) nanospectroscopy.•Extruded membranes show 50 nm thin crystalline polyether oxide (PEO) surface layer.•Annealing transformed the crystalline PEO layers into amorphous layers.