Effects of coagulants on porous structure of membranes prepared from cellulose in NaOH/urea aqueous solution

A series of regenerated cellulose membranes was prepared from cellulose in NaOH/urea aqueous solution by coagulating with various coagulants including H2SO4, HOAc, H2SO4/Na2SO4, Na2SO4, (NH4)2SO4, H2O, C2H5OH and (CH3)2CO, respectively. The morphology, water permeability and physical properties of the membranes were investigated by scanning electron micrograph, atom force micrograph, flow rate method, tensile test, etc. The membranes prepared from various coagulants possessed a pore size range from 265 to 730 nm in the free surface, and relatively uniform structure having pore size from 173 to 266 nm in the inner. The membranes coagulated with acidic coagulant exhibited the relatively small pore size and narrow distribution. On the contrary, the membranes coagulated with organic coagulant possessed the relatively large pore size and wide distribution. All of the membranes coagulated with acidic and salt aqueous solution exhibited the better tensile strength and elongation at break than that with organic coagulant. The membranes in this work possessed larger mean pore size and higher water permeability than those prepared from the cuoxam and viscose. The nucleation and growth of the cellulose-lean phase in the cellulose gel resulted in the formation of porous structure in the cellulose matrix, and the pore size was mainly related to the diffusion rate between nonsolvent and solvent. This work provided a promising way to prepare porous membranes having different pore size and physical properties by choosing the proper coagulants.