Preparation And Properties Of Dopamine Modified Cellulose Acetate Ultrafiltration Membrane

Membrane separation technology,especially ultrafiltration membrane separation,as an emerging separation technology,has the advantages of simple equipment,environmentally friendly,low use and maintenance costs,etc.,and has been widely used in biopharmaceuticals,sewage treatment,food processing and other fields.However,in practical applications,the use of ultrafiltration membranes is bound to accompany the problem of membrane fouling.Membrane fouling is the deposition of macromolecular pollutants on the membrane surface and in the pores during the ultrafiltration process.Because the polluting substance is a hydrophobic substance,in order to solve the problem of membrane pollution,we chemically modify the membrane material to improve its hydrophilic properties,thereby enhancing its anti-pollution ability.First,an oxidation reaction and a Schiff base reaction were used to prepare a membranematerial with antifouling properties.Cellulose acetate was prepared by the oxidation of sodium periodate to obtain cellulose acetate dialdehyde.After reacting with dopamine by Schiff base,cellulose acetate 2,3-modified dopamine(CA-2,3-DA)material was prepared and phase-converted.A hydrophilic CA-2,3-DA anti-fouling ultrafiltration membrane was prepared by the method.The chemical composition and structure of CA-2,3-DA were determined using Fourier transform infrared spectroscopy FTIR and nuclear magnetic resonance hydrogen spectroscopy 1H NMR analysis.Thermogravimetric analysis TGA was used to test its thermal stability,and Ubbelohde viscometer was used to test its film-forming performance.For the CA-2,3-DA ultrafiltration membrane,the microscopic morphology was characterized by scanning electron microscope SEM,and the ultrafiltration performance was tested using static protein adsorption and cyclic ultrafiltration experiments.The specific results are as follows.The protein adsorption amount of CA-2,3-DA membrane is only 21.5μg/cm2,which is about half that of CA membrane.The water flux was 167.3L/m2h,and the protein retention rate was 92.5%.In the cyclic ultrafiltration experiment,after the water flux stabilized,in the third ultrafiltration,the water flux recovery rate of the CA-2,3-DA membrane was as high as 96.0%.These results indicate that the CA-2,3-DA membrane has good hydrophilic properties and anti-fouling ability,and has maintained good stability in long-term ultrafiltration experiments.Due to the oxidation reaction,the mechanical properties of cellulose acetate will decrease.Therefore,two steps of chlorination reaction and substitution reaction were used to prepare dopamine modified cellulose acetate material.A chlorination reaction occurs between cellulose acetate and p-toluenesulfonyl chloride to generate p-toluenesulfonyl cellulose acetate.The obtained product is then reacted with dopamine to prepare cellulose acetate 6-modified dopamine(CA-6-DA).CA-6-DA membrane was prepared using a non-solvent induced phase separation(NIPS)process.The chemical structure of CA-6-DA material was confirmed by FTIR and 1H NMR.The heat resistance was verified by TGA.Through SEM,the CA-6-DA membrane exhibits a typical ultrafiltration membrane structure,a dense surface layer and a support layer with large fingers,and the support layer is more coarse.The water contact angle test shows that the surface energy of CA-6-DA film is higher and it has better hydrophilic properties.The results of separation experiment and ultrafiltration experiment show that CA-6-DA membrane has good separation and anti-pollution performance,its water flux is 181.2 L/m2h,and the water flux recovery rate can still reach 115.7 L/m2h after three cycles.These results indicate that most of the pollutants attached in the ultrafiltration process are reversible pollutants,which can be cleaned by hydraulic power and have good flux recovery performance.The above results show that CA-2,3-DA and CA-6-DA ultrafiltration membranes have excellent performance.It proved the feasibility of using chemical modification to prepare high-performance membrane materials,and provided a new idea for large-scale preparation of anti-fouling ultrafiltration membranes.It has extensive application prospects.