Regulating phase inversion behavior in cellulose acetate membranes using hydroxyethyl cellulose: Suppression of macrovoids and development of uniform sponge-like porous structures.

Porous cellulose acetate (CA) membranes fabricated via the nonsolvent-induced phase separation (NIPS) process often exhibit finger-like macrovoids and heterogeneous pore structures arising from rapid solvent-nonsolvent exchange. In this study, hydroxyethyl cellulose (HEC), a water-affinity cellulose derivative, was introduced at low concentration as a functional additive to regulate phase inversion behavior during the NIPS process. The incorporation of HEC transformed the conventional macrovoid-containing morphology of Porous_CA into a uniform sponge-like porous structure while increasing membrane porosity from 77.3 ± 5.1% to 87.3 ± 3.1% and reducing the Gurley value from 120.1 ± 17 to 72.6 ± 17 s/100 cc. Despite the suppression of macrovoid formation, the CA/HEC membranes exhibited enhanced gas transport performance, indicating the effectiveness of the interconnected porous network. FT-IR, XRD, and DSC analyses revealed that HEC incorporation modified the intermolecular interaction environment and molecular packing of the CA matrix without inducing the formation of new chemical bonds or crystalline phases. In addition, the membranes maintained acceptable thermal stability despite their highly porous structures.