Preparation And Properties Of Antibacterial Cellulose Acetate Reverse Osmosis Membrane

Sea water or brackish water desalination is regarded as the major solution alleviating the shortage of clean water supplies.Among the exsiting technique,reverse osmosis(RO)shows the advantages of high separation efficiency,simple process and environmental friendly.Compared with polyamide,the most common conventional membrane material used in reverse osmosis membranes,cellulose acetate and its derivatives have attracted much attention due to their advantages of natural renewable and unique chloride resistance and so on.However,the bad microbial degradability resistance limits their purification efficiency and service life when applied in the field of complex water such as sea water or brackish water and so on.To solve this problem,the optimum technological conditions for preparing reverse osmosis membrane were obtained by parameter adjustment and rheological analysis in this research.Then,the antibacterial modification of cellulose acetate reverse osmosis membrane was designed and adopted by chemical modification and physical blending based on its structure characteristics.(1)In detail,cellulose acetate reverse osmosis membranes(CDA-RO and CTA-RO)were respectively prepared via the non-solvent induced phase separation(NIPS)process with cellulose diacetate and cellulose triacetate.The process parameters such as cellulose acetate concentration,solvent proportioning,additive content and evaporation time were optimized by using the testing results of flux and salt rejection,namely the cellulose acetate concentration was 13 wt%,the mass ratio of 1,4-dioxane and acetone was 2.5,the content of maleic acid was 4.8 wt%and the solvent evaporation time was 40 s.The rheological analysis showed that the CDA casting solution belonged to the Newton fluid and its rheological behavior was similar to the dilute solution.Whilst the CTA casting solution belonged to the pseudoplastic fluid(shear thinning)and its rheological behavior was similar to the gel.Nevertheless,the casting solution with a concentration of 13 wt%was approximated to the Newton fluid in the range of low shear rate.The research of parameter regulation and rheology behavior analysis respectively provided basis for preparation and optimization of cellulose acetate reverse osmosis membrane.(2)CTA-RO membrane was partially hydrolyzed to form more active hydroxyl groups and then underwent etherification process with 3-chloro-2-hydroxypropyl-trimethyl ammonium chloride(CHPTAC)to covalently bond quaternary amine group which had antibacterial property.When the membrane was modified for 2 or 3 h the structure of the quaternized CTA-RO membranes maintained the membrane structures without significant impaction on crystalline,mechanical property and thermal stability.The flux and hydrophilicity increased with the salt rejection higher than 92%.Moreover,the modified CTA-RO membranes showed highter antibacterial activity against both E.coli(Gram negative)and S.aureus(Gram positive)with a bactericidal rate of 78.7%-89.0%for E.coli and 64.4%-76.6%for S.aureus,respectively.(3)Bromoacetyl bromide with structure similar to acetyl group and high reactivity was chosen to react with the few hydroxyl groups in CDA through esterification process and NIPS technic forming antibacterial CDA-RO membrane(Br-CA-RO).The results showed that owing to the increased esterification degree and molecular chain regularity the structure and performance of Br-CA-RO was approximated to CTA-RO which showed higher density and separation efficiency.The flux and salt rejection were 14.1 L m-2 h-1 and 95.6%,respectively.Both the modified powder and the resulting Br-CA-RO membrane had good antibacterial property.The relative bactericidal rate of Br-CA-RO membrane against E.coli and S.aureus were higher than 70%and 93%?respectively.(4)To combine the high antibacterial activity of quaternary ammonium salt to E.coli and the high antibacterial activity of bromoacetyl to S.aureus,a series of tertiary amines were used to modified Br-CA-RO through the reaction of haloalkane and tertiary amine forming quaternary ammonium salt.The results showed that stable quaternary ammonium salt can be obtained under mild reaction conditions.The resulting RO membrane modified with N,N-dimethyloctylamine which had 8 carbon atoms in its alkyl chain had the best performances,namely the flux was 17.41 L m-2 h-1 and the salt rejection was 96.7%.Additionally,its bactericidal rate against to E.coli and S.aureus were close to or reached 100%,better than those only modified with either quaternary ammonium or bromoacetyl bromide.(5)Chitosan(CS)was blended with CTA to form CTA/CS-RO membrane via liquid-liquid blend and NIPS technic.The salt rejection was 90%at optimized conditions and its bactericidal rate against to E.coli and S.aureus were 72.5%and 51%,respectively.In addition,the leakage of CS particles occurred during long term operation due to the weak intermolecular force between CS and CTA,thus decreasing its antibacterial activity.Hence,chemical modification had the advantages of high antibacterial efficiency,separation performances and application stability than blending method for cellulose acetate reverse osmosis membranes.