The Preparation Of Hydrophilic PAN Ultrafiltration Membrane And The Separation Of Astragalus Polysaccharides

Polyacrylonitrile possess good chemical stability, thermostability and fine mechanical function, therefor, it is widely used for preparation of the ultrafiltration membranes. However, in the practical application,because the surface of the polyacrylonitrile displays certain hydrophobicity, it is easy to yied to membranes fouling ,and it will make the flux obviously lower and useful life shorten ,this situation is not only increasing procreative cost, but also severely affecting its separation efficiency.We will carry out the modification study of acrylonitrile in order to overcome its shortcoming.Blending is a small investment and quick method of membranes modification. It will effectively improve the hydrophilicity of membranes and membranes fouling,polyacrylonitrile and acrylonitrile copolymer with polyurethane are blending to produce ultrafiltration membranes. Besides, this text is also researching the separate of the effective ingredients from the astragalus,through determining the membrane performance on three membranes,and choosing the suitable membranes.First,PAN ultrafiltration membranes and PAN/PU blend ultrafiltration membranes are prepared by phase inversion processes,and we determine the membranes performance concluding the water flux and retentivity and so on , The experimental results show that water flux of the membranes after modification are improved,resulting in decreasing the time of filtration; Rejection of the membranes are adding; we find that contact angles are minishing after blending PU through determining contact angles of the membranes, so this method can increase hydrophilicity and anti fouling properties of the membranes.Membrane materials are P(AN-MMA)/PU copolymer and ulrtafiltration membranes are prepared by phase inversion processes.We find that membrane performances are best when the blend proportion of the P(AN-MMA)/PU membrane is 8:2,mass fraction is 14%.When the water flux is 719.1L/m2·h, it has higher water flux contract with the same proportion PAN/PU.We conclude through researching the P(AN-MMA-VAC)/PU blend membrane performances that water flux is decreasing and rejection is raising with increasing the content of the PU; membrane contact angle has not obviously changing when the content of the PU is 20%-30%.Contracting with three membranes, we conclude that hydrophilicity of the P(AN-MMA) /PU ultrafiltration membrane is the highest and rejection of the PAN / PU membrane is the best.We should consider the problem of polysaccharides yield at first when we studied the separation of astragalus polysaccharides, so this text chose PAN and PU blend membranes which the blend ratio is 8:2 and the content is 14% to separate the effective ingredients from astragalus, water flux is 634.9L/m2·h, retentivity is 90.2%under this ratio, we calculated that the average rejection of the membranes are achieving 99.8% for astragalus polysaccharides after separation. The experiment shows that this membrane is fit for separating ingredients from astragalus polysaccharides.