Effect of coagulating agent viscosity on the kinetics of formation, morphology, and transport properties of cellulose nanofiltration membranes
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Low-viscous coagulating agents are tradionally used to precipitate polymers from their solutions and obtain films and fibers from them; they represent, as a rule, the combinations of solvent and nonsolvent of the polymer used. At the same time, since the structure of the precipitated polymer is formed under non-equilibrium conditions, the influence of the coagulant viscosity can be quite substantial. The influence of the viscosity of the medium on the formation of structure, morphology, and transport characteristics of the precipitated polymer is studied by example of forming of the cellulose membranes from solution in N-methyl-morpholine N-oxide using some proton-donor coagulants. In this regard, the interdiffusion processes proceeding at the contact of cellulose solutions and coagulating agents (water, propylene glycol, glycerin) are explored using the laser interferometry method. Varying the precipitator viscosity allows one to change the rate of formation and correspondingly the morphology of the cellulose films. In turn, the membrane structure determines its transport characteristics, which were assessed by the filtration of aprotic media with anionic dyes—Orange II and Remazol Brilliant Blue R. The application of the low-viscous precipitator provides the formation of a uniform film structure in the bulk, but leads to development of defects close to the surface, while a viscous medium promotes the formation of a relatively thin dense shell on the films.
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