Hemodialysis Membrane Prepared from Cellulose/N-Methylmorpholine-N-oxide Solution. IV. Comparative Studies on the Surface Morphology of Membranes Prepared from N-Methylmorpholine-N-oxide and Cuprammonium Solutions

The surface morphology of regenerated cellulose membranes prepared by casting cellulose/N-methylmorpholine-N-oxide (NMMO) and cuprammonium solutions onto a glass plate (denoted NMMO membrane and cuprammonium membrane, respectively) were studied by using scanning electron microscopy (SEM) and atomic force microscopy (AFM). The concentration of cellulose in the casting solution was 8 wt %. The SEM images of the surfaces of both membranes indicated that they had aggregate structures formed by cellulose particles (10-150 nm in diameter). In the NMMO membrane, the glass-side surface was composed of larger particles and was rougher than the air-side surface. However, in the cuprammonium membrane there was little structural difference between air-side and glass-side surfaces. The AFM images showed that all surfaces were rough due to the cellulose particles. As for the NMMO membrane, the difference in the surface structure between the air-side and the glass-side was the same as observed by SEM. AFM also indicated that the order of the surface roughness was as follows: glass-side of NMMO membrane > air-side of NMMO membrane > air-side of cuprammonium membrane congruent to glass-side of cuprammonium membrane. On the basis of these results observed for both membranes, the reason for the difference in the performances of NMMO and cuprammonium membranes is discussed from the viewpoint of surface structure. (C) 2010 Wiley Periodicals, Inc. J Appl Polym Sci 116: 3040-3046, 2010