PHENOMENOLOGICAL EFFECTS OF SOLVENT-CASTING CONDITIONS ON PORE CHARACTERISTICS OF REGENERATED CELLULOSE MEMBRANES

An attempt was made (1) to prepare porous regenerated cellulose membra nes by casting cellulose cuprammonium solutions and then immersing the m into aqueous acetone solutions as coagulant, and (2) to investigate membrane characteristics such as radius of secondary particles S-2 on the surfaces of the membranes, mean pore diameter measured by the wate r-flow-rate method 2r(f), membrane porosity by apparent density method Pr(d(3)), and membrane thickness of dry membrane L(d), and (3) to cla rify phenomenological effects of solvent-casting conditions on pore ch aracteristics of the membrane formed and to explain the effect in term s of the particle growth theory proposed previously by Kamide-Iijima e t al. (KI). Surfaces of membranes prepared by immersing cast solutions in coagulation solution having weight fraction of acetone w(Acetone) below 0.30 consisted of the secondary particles of polymer-rich phase (referred to as ''polymer particle''). As the ammonia concentration in the system was higher, polymer particles of polymer-rich phase grow f aster; ammonia was one of the most important factors dominating the si ze of polymer particles, composing the membranes. L(d) was in proporti on to the cellulose weight fraction w(Cell) of cast solutions; on the contrary, Pr(d(3)) and 2r(f) were inversely proportional to w(Cell). T hese experimental findings suggest strongly that density of dried poly mer particles increases in proportion to w(Cell) in the solutions. Por e shape in a whole body of a membrane changed drastically from noncirc ular pores to circular pores when w(Acetone) in coagulation solutions exceeded 0.30, indicating that w(Acetone) dominates phase separation c onditions such as phase volume ratio R(= V-(1)/V-(2); V-(1) and V-(2) are volumes of polymer-lean and -rich phases, respectively), compositi ons of phase separation points. Changes in Pr(d(3)), 2r(f) and tensile strength TS of the membranes, prepared by using coagulation solutions having different w(Acetone), coincide fairly well with that of pore s hape. Membranes constructed by larger cellulose particles have larger pores, and this tendency agreed well with results obtained by KI's lat tice theory on pore size distribution proposed before.