Cellulose microporous membranes prepared from NaOH/urea aqueous solution

A series of regenerated cellulose (RC) microporous membranes was prepared from cotton linters in 6 wt.% NaOH/4 wt.% urea aqueous solution by coagulating with 1–10 wt.% CaCl2 aqueous solution for 1–20 min, and then treating with 3 wt.% HCl for 2 min. The crystallinity, morphology, water permeability and mechanical properties of the membranes were investigated by X-ray diffraction, 13C NMR, scanning electron micrograph (SEM), flow rate method, miniature ultrafiltration equipment and tensile test. RC membranes have the Cellulose II crystalline form, and the values of their crystallinity degree lay in the range of 58–64%. All of the RC membranes exhibited homogenous porous structure on the surface and relatively dense microporous structure in the inner, and the pore size 2rSEM for the surface and the cross-section determined by SEM are 180–380 and 120–140 nm, respectively. An increase of coagulation time resulted in the relatively small pore size and narrow pore size distribution of the membranes. The pore size (2rf) values determined by flow rate method were in the range from 26 to 43 nm, and much smaller than the 2rSEM of inner section. The mean pore size and water permeability of the membranes prepared from cellulose in 6 wt.% NaOH/4 wt.% urea aqueous solution were significantly larger than those of the RC membranes prepared from cuoxam. The RC microporous membranes coagulated with 5 wt.% CaCl2 for 1–2 min possessed excellent tensile strength and breaking elongation (σb=108 MPa and εb=11%), and relatively large pore size.