Microporous membranes prepared from cellulose in NaOH/thiourea aqueous solution

We successfully prepared novel microporous membranes from cellulose in NaOH/thiourea aqueous solution by coagulating with ammonium sulphate [(NH4)2SO4] aqueous solution with different concentration for 1–20 min. The structure, morphology, water permeability and mechanical properties of the regenerated cellulose (RC) membranes were measured, and the effects of the coagulant concentration and coagulating time on the microporous formation and pore size of the membranes were investigated. The results from Fourier transfer infrared spectroscopy, wide angle X-ray diffraction, scanning electron microscopy (SEM) revealed that the membranes possess homogeneous porous structure on the surface and relatively dense microporous structure in the inner. By changing the coagulation condition, the different apparent average pore diameters (2re) observed by SEM were obtained, ranged from 312 to 523 nm for the surface, and from 187 to 320 nm for the cross-section. With an increase of (NH4)2SO4 concentration from 1 to 10 wt.%, the 2re, the mean pore diameters (2rf) measured by flow rate method and water permeability decreased, and then increased as the (NH4)2SO4 content was higher than 10 wt.%. The mean pore size and water permeability of the membranes are significantly larger than those from viscose and cuprammonium rayon process as well as NaOH/urea aqueous solution. Interestingly, the RC microporous membranes coagulated, respectively, with 1 and 10 wt.% (NH4)2SO4 for 5 min exhibited the maximum values of pore size (2re = 514 nm, 2rf = 43.3 nm), as well as the smallest pore size (2re = 312 nm, 2rf = 26.6 nm). This work provides promising potential way to prepare biodegradable membrane materials in the separation technique field.