Amorphous Silk Fibroin Membranes for Separation of CO<sub>2</sub>

Amorphous silk fibroin has shown promise as a polymeric material derivable from natural sources for making membranes for use in removing CO2 from mixed-gas streams. For most applications of silk fibroin, for purposes other than gas separation, this material is used in its highly crystalline, nearly natural form because this form has uncommonly high tensile strength. However, the crystalline phase of silk fibroin is impermeable, making it necessary to convert the material to amorphous form to obtain the high permeability needed for gas separation.

Accordingly, one aspect of the present development is a process for generating amorphous silk fibroin by treating native silk fibroin in an aqueous methanol/salt solution. The resulting material remains self-standing and can be prepared as thin film suitable for permeation testing. The permeability of this material by pure CO2 has been found to be highly improved, and its mixed-gas permeability has been found to exceed the mixed-gas permeabilities of several ultrahigh-CO2-permeable synthetic polymers. Only one of the synthetic polymers — poly(trimethylsilylpropyne) [PTMSP] — may be more highly permeable by CO2. PTMSP becomes unstable with time, whereas amorphous silk should not, although at the time of this reporting this has not been conclusively proven.

This work was done by Christopher M. Aberg, Anand K. Patel, Eun Seok Gil, and Richard J. Spontak of North Carolina State University and May-Britt Hagg of Norwegian University of Science and Technology for Johnson Space Center.

For further information, contact the JSC Innovation Partnerships Office at (281) 483- 3809. MSC-24032-1

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