Cellulose acetate membranes chemical structure

Deterioration of Asymmetric Cellulose Acetate Membranes with NaOCl -------Structural and Chemical Change... 

It is important to note that the chemical structures of the membranes are proprietary and local variations can occur due to the nature of membrane manufacturing processes. In order to avoid possible misinterpretation of membrane chemieal structure due to local variations, ESCA analysis was repeated for selected membranes. The XPS analysis revealed that CALP was a cellulose acetate membrane represented for the most part by tri-acetate species (acetate (O—C=0)be 289.7 eV) (Fig. 27). The LFCl membrane showed a polyamide active layer apparently crosslinked to a polysulfone (S (2p)be 170-168 eV) infrastructure as suggested by the XPS surface scan. 

These types of separators consist of a solid matrix and a liquid phase, which is retained in the microporous structure by capillary forces. To be effective for batteries, the liquid in the microporous separator, which generally contains an organic phase, must be insoluble in the electrolyte, chemically stable, and still provide adequate ionic conductivity. Several types of polymers, such as polypropylene, polysulfone, poly(tetrafluoroethylene), and cellulose acetate, have been used for porous substrates for supported-liquid membranes. The PVdF coated polyolefin-based microporous membranes used in gel—polymer lithium-ion battery fall into this category. Gel polymer... 

Figure 4.4 Chemical structure of cellulose acetate RO membranes.

Membrane and Membrane Design Most membranes are polymers in nature, but some inorganic membranes have become available. The most common membranes are based on polysulfone, cellulose acetate, polyamide, fluoropolymers, and other compounds. Formation of a symmetric membrane structure is an important element in the success of UF/NF membrane separation (16). The other considerations for membrane separation are as follows (1) separation capabilities (retention or selectivity), (2) separation rate (flux), (3) chemical and mechanical stabilities, and (4) membrane material cost. 

Modification of Polymers. One way to solve the problem of finding good polymers for membranes is to make modifications of the chemical structure of the polymer. Sulphonation for instance of polysulphone (19) is a well known example of how a hydrophobic polymer can be modified to a hydrophilic polymer with charged groups. Other attemps have been made, for instance to modify cellulose acetate by putting charged positive groups in the form of quaternary ammonium into the polymer (20). 

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