Preparation Of Modified Cellulose Acetate Ultrafiltration Membrane And Study Of Its Separation Performance

As a green and energy-efficient separation technology, ultrafiltration has been widely applied in bioseparation. However, the adsorption and precipitation of biomacromolecule on the ultrafiltration membrane surface causes membrane fouling. Membrane fouling constitutes a bottleneck of ultrafiltration development. Major approaches, such as developing novel hydrophilic membrane materials and hydrophilic modification of membrane materials have been carried out for fouling reduction. In this dissertation, cellulose acetate (CA), a hydrophilic membrane material, was selected to prepare ulreafiltration membrane for the aim of reducing membrane fouling during biosepration.CA ultrafiltration membranes were prepared via the phase inversion process. Since the lower water flux and lower protein rejection retio, Pluronic F127 block copolymer was added to fabricate modified CA membranes. The water content of modified CA membranes increased with an increase of Pluronic F127 content in the casting solutions. The decreased of static water contact angle with an increase in the Pluronic F127 content indicated an increase of surface hydrophilicity. The results of Fourier transform infrared spectrometer (FT-IR) analysis confirmed that most of Pluronic F127 has been leached out from the modified CA membranes. The scanning electron microscopy (SEM) photographs showed that the modified CA membranes had thinner top layer and bigger pore volume in the porous sub-layer compared to the CA control membrane. The ultrafiltration experiments revealed that the addition of Pluronic F127 influenced the permeation performance of the membranes, all the modified CA membranes exhibited higher water flux and higher bovine serum albumin (BSA) rejection ratio than those of the CA control membrane. Pluronic F127 block copolymer was as both pore forming agent and surface modification agent during Modified CA ultrafiltration membranes.Multi-walled carbon nanotubes (MWNTs) were blended with CA to fabricate CA/MWNTs blend membranes, and the membranes were characterized and evaluated. The membrane surface became rougher than control CA membrane and membrane structure had no significant changes according to SEM. The mechanical property of CA/MWNTs blend membranes was improved compared with control CA membrane. Ultrafiltration results showed that the pure water flux was enhanced when MWNTs/CA ratio reached 3.0wt% and 5.0wt%, and when MWNTs/CA ratio was 1.0wt% the pure water flux was not enhanced. BSA rejection ratio was lower due to the blend membranes surface was rougher with increased pore size.SiO₂ nanoparticles were blended with CA to fabricate CA/SiO₂ blend membranes, and the membranes were characterized and evaluated. The membrane surface had a lot of particles formed by SiO₂ reuniting and membrane structure had no significant changes according to SEM. The mechanical property of CA/SiO₂ blend membranes was decreased with an increase in SiO₂ content, which was due to SiO₂ reuniting. Ultrafiltration results showed that the pure water flux was similar to CA membranes modified by Pluronic F127. BSA rejection ratio decreased due to the blend membranes surface was rougher with increased pore size and SiO₂ reuniting.