| Membrane separation technology is widely used in various industries,especially in recent decades,due to the rapid development of quality membranes.At present,membrane materials are mainly based on petrochemical organic polymers.With its widespread applications,the disposal of used membranes is enevitable,and their potental impact to the environment has become a concern.In addition,fossil resources inlcuding petroleum are non-renewable.It is therefore desirable to search for membrane materials that are abundantly available at a low price and are environmentally friendly.In this study,a widely available natural polymer,cellulose,was used to fabribate membranes by immersion precipitation phase transformation method.The cellulose membrane was characterized by triple flat membrane test system,scanning electron microscopy(SEM),molecular weight cut-off,porosity test and tensile strength assessment.The study focused on examining the influence of the molecular weight of the cellulose polymer,the concentration of the cellulose polymer in the casting solution,and the thickness of the cellulose film on the pure water flux and mechanical strength of the membrane.Additionally,the effects of coagulation bath conditions on the morphology and structure of the cellulose membrane were investigated.The main results from this study are sumamrised below.The results show that cotton linter pulp board with an average cellulose molecular weight of 10.1×10~4 daltons was found to be a good raw material for the membrane preparation.A membrane of high quality was abtained by casting the membraene at a thichness of 250?m when casting solution contained 4wt%cellulose.The cellulose membrane prepared under these conditions belongs to an ultrafiltration membrane with a water flux of 76.66 LMH and a maximal tensile stress of 1.85 MPa.Membrane film formation mechanism:In the coagulation bath,the uniform and stable aqueous cellulose system is destroyed by the mass transfer,leading to a phase change and formation of a sponge-like celloluse membrane.The morphology and porous structure depend on the mass transfer rate of meterials in the process.Three types of coagulation baths were tested:deionized water,ethanol,and isooctane;only the first two could result in phase inversion and membrane formation.No film formation occurred when isooctane was used as coagulation bath because of its non-polar nature.Between water and ethenol used as a coagulation bath,the rate of membrane formation in deionized water is faster than that in ethanol.The SEM imaging showed that water as the coagulation bath helped to create a denser membrane structure with less pores.This was consistent with the water flux measurement results showing a flux of 21.72 LMH for membrane formed with water as the floculation bath versus 76.66 LMH for the membrane formed with the ethanol coagulation bath.The components of the coagulation bath were adjusted to investigate their effect on the morphology and structure of the cellulose membrane.Membrane preparation was carried out using different ratios of ethanol and deionized water as a coagulation bath.Pure water flux,molecular weight cutoff and porosity of the membrane were characterized.When the ethanol content of the coagulation bath component is 40%,the pure water flux of the cellulose membrane is the largest(266 LMH).Porosity test:the membrane regenerated in pure water was 2.95%,the peak value was 3.46%when the ethanol content was 40%,and the membrane regenerated in ethanol was 2.51%.The molecular weight cut-off showed that the coagulation bath conditions of the cellulose membrane changed,the water flux changed significantly,but the membrane retention performance was almost the same.Therefore,changes in water flux may be caused by membrane porosity. |
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