Cellulose acetate membranes preparation

The wet cellulose acetate membranes prepared for reverse osmosis purposes can be used for gas separation when they are dried. The water in the cellulose acetate membrane cannot be evaporated in air, however, because the asymmetric structure of the membrane will collapse. Instead, the multistage solvent exchange and the evaporation method is applied. In this method, the water in the membrane is first replaced by a water-miscible solvent such as ethanol. Then, the first solvent is replaced by a second volatile solvent such as hexane. The second solvent is subsequently air-evaporated to obtain a dry membrane. 

Lui, A. Talbot, F.D.F Sourirajan, S. Fouda, A.E. Matsuura, T. Studies on gas transport through dry cellulose acetate membranes prepared by solvent exchange technique. Sep. Sci. Technol. 1988, 23, 1839. 

Figure 1.25 Rejection of a cellulose acetate membrane prepared from a casting solution containing 25% cellulose acetate, 45% acetone and 30% formamide by precipitation in a water bath at 0°C as a function of the evaporation time prior to the precipitation, (Test condition 1% NaCI-solution, 100 bar hydrostatic pressure).

Murphy D., de Pinho M.N. (1995), An ATR-FTIR study of water in cellulose acetate membranes prepared by phase inversion, Journal of Membrane Science, 106, 245-257. 

MA3 Matsuyama, H., Ohga, K., Maid, T., Teiamoto, M., and Nakatsuka, S., Porous cellulose acetate membrane prepared by thermally induced phase separation, J. Appl. Polym. Sci., 89, 3951, 2003. 

Cellulose acetate membrane was studied because of its past use in concentrate preparation and the need to better define its performance for specific organic recovery. Cellulose acetate continues to be widely used for a variety of industrial and commercial water purification applications. Cellulose acetate was not expected to perform at the level of the more highly cross-linked and inert thin-film composite membrane. 

Since Loeb and Sourirajan 8) found how to cast asymmetric cellulose acetate membranes, which consist of a very thin surface layer, supported by a more porous thick layer in 1962, many workers have investigated the preparation and performance of cellulose acetate membranes. 

H. Strathmann, P. Scheible and R.W. Baker, A Rationale for the Preparation of Loeb-Sourirajan-type Cellulose Acetate Membranes, J. Appl. Polym. Sci. 15, 811 (1971). 

The first commercial brackish water RO(BWRO) was on line at the Raintree facility in Coalinga, California. Tubular cellulose acetate membranes developed and prepared at UCLA were used in the facility. Additionally, the hardware for the system was fabricated at UCLA and transported piecemeal to the facility.9... 

Cellulose acetate is the material for the first-generation reverse osmosis (RO) membranes. The announcement of cellulose acetate membranes for seawater desalination by Loeb and Sourirajan in 1960 triggered the applications of membrane separation processes in many industrial sectors. Cellulose acetate membranes are prepared by the dry-wet phase inversion technique. 

The functional stability of GOD membranes has also been enhanced by coupling with an asymmetric ultrafiltration membrane (Koyama et al., 1980). The GOD-cellulose acetate membrane used was prepared as follows 250 mg cellulose triacetate was dissolved in 5 ml dichloro-methane, the solution was mixed with 0.2 ml 50% glutaraldehyde and 1 ml l,8-diamino-4-amino methyl octane and sprayed onto a glass plate. After three days the membrane was removed from the support and immersed in 1% glutaraldehyde solution for 1 h at 35°C, rinsed with water and exposed for 2-3 h to phosphate buffer, pH 7.7, containing 1 mg/ml GOD. The membrane was then treated with sodium tetraborate, rinsed with water and stored at 4-lO°C until use. It was combined with the ultrafiltration membrane in the following way 20 mg cellulose diacetate was dissolved in 35 g formamide and 45 g acetone and cast on a glass plate. At room temperature the solvents evaporated within a few seconds and a membrane of about 30 pm thickness remained, which was kept in ice water for 1 h before application in the sensor. 

In order to exclude disturbing substances, Newman (1976), Tsuchida and Yoda (1981), and Palleschi et al. (1986) covered the platinum electrode by a H2O2 selective asymmetric cellulose acetate membrane. The membrane (thickness, 15.3 pm) was prepared from acetyl cellulose... 

Osmotic phenomena have been observed since the middle of the eighteenth century. The first experiments were conducted with animal membranes and it wasn t unitl 1867 that artificial membranes were employed. In the early 1950 s, research workers at the University of Florida demonstrated, with thick films, that cellulose acetate possessed unique salt and water transport properties which made it potentially attractive as a reverse osmosis desalination membrane. During the 1960 s, Loeb and others at the University of California at Los Angeles developed techniques to prepare cellulose acetate membranes with an economical water flux and salt rejection at moderate driving pressures. With this development, reverse osmosis became a practical possibility. 

Because of unfavorable sorption effects on paper that cause tailing, materials with lower adsorptivity were sought. Thus, cellulose acetate [35] and nitrocellulose [36,37] membranes were introduced. Cellulose acetate can be either prepared in the laboratory by treating cellulose with acetic anhydride, or it may be purchased from commercial sources. Cellulose acetate membranes are readily soluble in phenol, glacial acetic acid, dichloromethane and acetone. In part they can be solubilized in several solvent mixtures e.g., chloroform/ethanol (9 1 v/v). For detection (optical scanning) the foil can be made translucent by immersion in cottonseed oil, decalin, liquid paraffin or Whitemore oil 120. 

Benosmane, N., Guedioura, B., Hamdi, S. M., Hamdi, M., and Boutemeur, B. 2010. Preparation, characterization and thermal studies of polymer inclusion cellulose acetate membrane with calix 4 resorcinarenes as carriers. Materials Science Engineering C-Materials for Biological Applications 30 860-867. 

S.P. Nunes, F. Galembeck, N. Barelu, Cellulose Acetate Membranes for Osmo-sedimentation Performance and Morphological Dependence on Preparation Conditions. Pdymer 27 (1986) 937 943. 

The studies of membrane morphology by SEM have produced a large number of cross-sectional pictures for polymeric membranes since the onset of asymmetric cellulose acetate membranes by Loeb and Sourirajan. The contribution of those pictures to the design of novel membranes with improved performance was truly phenomenal. SEM requires cumbersome sample preparation, which may hinder true images. AFM does not need such sample preparation, and the pictures taken by AFM are considered to reflect the true nature of membrane morphology. 

Cellulose acetate membranes with superior properties could be prepared by phase inversion technique using high performance thermoplastic PAI as the modification agent [82,83]. An improvement of surface porosity due to the addition of PAI and a decrease in mean pore size was found. The membranes were checked for the separation of metal ions from aqueous solutions by polymer enhanced ultrafiltration. 

Rajesh S, Maheswari P, Senthilkumar S, Jayalakshmi A, Mohan D. Preparation and characterisation of poly(anude-imide) incorporated cellulose acetate membranes for polymer enhanced ultrafiltrafion of metal ions. Chem EngJ2011 171(l) 33. ... 

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