Cellulose acetate (CA), cellulose acetate propionate (CAP), and cellulose acetate butyrate (CAB) were fabricated as membrane via nonsolvent induced phase separation process. N,N-Dimethylformamide (DMF) and N,N-Dimethylacetamide (DMAc) as solvents and water as nonsolvent were employed. Ternary phase diagrams for all six ternary systems were constructed using Flory-Huggins theory. In this way, cloud points as well as Berghman's points were determined. Modulus of polymers steepened in various concentration of solvent/nonsolvent mixtures were measured to find the weight fraction of polymer (w(p)) in which vitrification takes place. W-P values for CA, CAP, and CAB were obtained 0.59, 0.67, and 0.74 in presence of DMF while those were 0.69, 0.74, and 0.84 in presence of DMAc; whereas glass transition temperatures (T-g) for three polymers were determined 180 degrees C, 142 degrees C, and 101 degrees C correspondingly. Pure water flux for CA, CAP, and CAB membrane increased from 75.7 to 83.4 and 290.3 and from 109.6 to 116.1 and 400.3 L/m(2) h bar when DMF and DMAc were used as solvents, respectively. Results revealed that as T-g of polymer decreases, the membrane structure vitrifies at higher polymer concentration with more porous structure, bigger pores, higher permeate flux followed by decrease in mechanical strength. POLYM. ENG. SCI., 58:1135-1145, 2018. (c) 2017 Society of Plastics Engineers