Phenomenological Effects of Solvent-Casting Conditions on Pore Characteristics of Regenerated Cellulose Membranes

Abstract

ABSTRACT:An attempt was made (1) to prepare porous regenerated cellulose membranes by casting cellulose cuprammonium solutions and then immersing them into aqueous acetone solutions as coagulant, and (2) to investigate membrane characteristics such as radius of secondary particles S2 on the surfaces of the membranes, mean pore diameter measured by the water-flow-rate method 2rr, membrane porosity by apparent density method Pr(d3), and membrane thickness of dry membrane La, and (3) to clarify phenomenological effects of solvent-casting conditions on pore characteristics of the membrane formed and to explain the effect in terms of the particle growth theory proposed previously by Kamide-Iijima et al. (Kl). 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 faster; ammonia was one of the most important factors dominating the size of polymer particles, composing the membranes. Ld was in proportion to the cellulose weight fraction Ween of cast solutions; on the contrary, Pr(d3) and 2rr were inversely proportional to Ween· These experimental findings suggest strongly that density of dried polymer particles increases in proportion to Ween in the solutions. Pore shape in a whole body of a membrane changed drastically from noncircular pores to circular pores when w Acetone in coagulation solutions exceeded 0.30, indicating that wAcetone dominates phase separation conditions such as phase volume ratio R(= V 0 ,/ V< 2 >; v 0 , and V< 2 > are volumes of polymer-lean and -rich phases, respectively), compositions of phase separation points.Changes in Pr(d 3 ), 2rr and tensile strength TS of the membranes, prepared by using coagulation solutions having different wAcetone, coincide fairly well with that of pore shape. Membranes constructed by larger cellulose particles have larger pores, and this tendency agreed well with results obtained by Ki's lattice theory on pore size distribution proposed before.

Poly(L‐lactide‐co‐glycolide) microporous membranes for medical applications produced with the use of polyethylene glycol as a pore former

“…When PEG concentration was higher, e.g., 60% or more, higher number of PEG‐rich domains had the possibility to collide and agglomerate resulting in lower number of domains but of bigger size. Our observation is in agreement with Kamide's theory on particle growth during membrane formation 38, 39. The PEG‐rich domains sediment resulting in their preferable accumulation near the surface of glass Petri dish.…”

Preparation and characterization of dense cellulose film for membrane application

“…(2), and thickness of dry membrane, L d (m), into eq. (4), that was derived based on the straight through cylindrical pore model20: \font\abc=cmmib10\def\bi#1{\hbox{\abc #1}} $${\bi r} {\bi f}. = \sqrt {{{8\eta_{{\rm{H}}_{{2}} {\rm{O}}} JL_d}\over {{\bi P}_{\bi r} \Delta {\bi P}}}}$$ in which η H2O (N s m −2 ) is the viscosity of water, and Δ P (N m −2 ) is the load pressure.…”

Formation and Characterization of Cellulose Membranes fromN-Methylmorpholine-N-oxide Solution

“…The mean pore radius, r f (m), was evaluated by means of the water-flow-rate method by substituting the experimentally determined values of porosity, P r , permeation flux, J (m 3 N m -2 N s -1 ), and thickness of dry membrane, L d (m), into Equation (4), that was derived on the basis of the straightthrough cylindrical pore model: [10] …”