Composite polyamide membranes chemical structure

The membranes under study are thin-film composite membranes composed of two layers as illustrated in Fig. 3 a thin polyamide film as active layer and a large mesoporous polysulphone as the support layer. The three studied membranes are 2 NF membranes, noted NF90, NF270 and a low-polarization reverse osmosis (LPRO) membrane, noted BW30. All membranes were purchased from Filmtec (DOW, USA) the specifications of the membranes are given in Table 2. The chemical structures of the support and active layer materials are reported in Fig. 4 [86], Polyamide material is the more used but some authors have reported results... 

Figure 4.10 Chemical structure of the Dow Water Solutions FT30 polyamide composite RO membrane.

Some hydrolysis of the trimesoyl chloride takes place during membrane fabrication. ESCA studies indicated that approximately one-sixth of the carboxyl groups ere present as ionic carboxylate and five-sixths of the carboxyl groups are present as amides, leading to the above structure. The FT-30 barrier layer is insoluble in sulfuric acid and in all organic solvents, in agreement with the crosslinked nature indicated above. Its chemical structure is somewhat similar to the composition of the duPont Permasep B-9 hollow fiber polyamide, believed to be approximately as follows ... 

In reverse osmosis membranes, we tried to introduce high amide linkage into polyamide membrane to realize better salt rejection and better water flux. Consequently, crosslinked fully aromatic polyamide membrane from 1,3,5-Triaminobenzene has found to have excellent separation performance and durability. Moreover, based on "UTC-70", fully aromatic polyamide membrane from 1,3,5-Triaminobenzene commercialized by Toray, various types of membrane have developed to satisfy different requirements in wide ranges of application. In such membranes, controlling membrane performance is accomplished through composition of membrane materials, control of polycondensation reaction, physical treatment and chemical treatment, which are closely related to chemical and physical structures of membranes. 

Figure 6.15 (a) Cross-section of a thin-film composite polyamide RO membrane (FT-30), (b) chemical structure of FT-30 polymer, and (c) Micrograph of a thin-film composite membrane-polyamide layer on polysulphone support. Source P.A. Pacheo et al, J. Memb. Sci. 358 (2010), 51-59. Copyright (2010), with permission from Elsevier. 

Gas permeation through a polymer membrane is not only a function of the chemical structure of the polymer chains, but is also determined by a morphology inside the film with typical domain dimensions of several nanometers. Membranes from commercial polyether- -polyamide (PEBA) polymers with varying chemical composition, cast from both n-butanol and cyclohexanol are studied by SAXS, in dry form and water-swollen, and as a function of strain. The nanostructure from soft and hard domains is determined [681. 

IS measurements were performed to determine the membrane variations associated with (i) Dense and porous layers of a commercial RO membrane (ii) Different PEG concentrations in the top dense layer of a polyamide/polysulfone experimental membrane (iii) Hydrophobic character of one layer in a composite or multilayer structure (iv) Membrane matrix material modification and (v) Protein (BSA) fouling of a porous commercial membrane. The results obtained with other characterization techniques, such as morphological, chemical, and adsorption analyses, have validated the information obtained from the IS results. 

In order to solve the problems that occurred with unmodified cellulosic membranes, synthetic membranes were developed. The first synthetic polymeric membrane was produced in the early 1970s. Since that time, various synthetic polymers such as poly-sulfone, polyamide, poly(methyl methacrylate), polyethersulfone, polyethersulfone/ polyamide have been used in the production of synthetic hemodialysis membranes [20,21]. Synthetic membranes have large mean pore size and thick wall structure. These properties provide high ultrafiltration rate, which is necessary for hemodialysis to be achieved with relatively low transmembrane pressures [20]. The main difference in synthetic and cellulosic membranes is the chemical composition of the membrane. Synthetic membranes are made from manufactured thermoplastics, while both modified and unmodified cellulosic membranes are prepared from natural polymers [20]. 

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