Two-stage phase separation of cellulose acetate membranes modified with plasma-treated natural zeolite: Response surface modeling

Cellulose acetate (CA) microfiltration membranes were prepared by two-stage vapor-induced phase separation (VIPS) and immersion precipitation. To improve the hydrophilicity and permeability of the membranes at low operating pressures, plasma-treated natural zeolite was incorporated into the membranes. A response surface methodology based on the three-level central composite design (CCD) was used to model and optimize the casting solution composition of the membranes with the aim of maximizing membranes permeability. Three independent variables for CCD optimization were concentration of CA, polyvinylpyrrolidone (PVP) pore former, and plasma-treated zeolite additive. The results showed that a second-order polynomial model could properly predict the response (pure water flux) at any input variable values with a satisfying determination coefficient (R ² ) of 0.954. Also, analysis of variance (ANOVA) confirmed the adequacy of the obtained model. The permeability of the prepared membranes increased by increasing zeolite loading from 0.10 to 0.50 wt%, which was related to the membranes morphology and porosity and confirmed by scanning electron microscopy (SEM) images. Pure water flux of the membranes decreased by increasing CA concentration while an optimum PVP amount was required to reach the maximum flux. The result of the bubble point analysis well matched with surface SEM images of the membranes and permeability trend predicted by CCD model. Also, the prepared CA membranes with different compositions showed no toxicity for mouse L929 fibroblast, which indicated their nontoxic and biocompatible nature.