Semi-permeable membran cellulose acetate

This technique has been applied to the concentration of organochlorine and organophosphorus insecticide [7,8] and various ethers, glycols amines, nitriles, hydrocarbons, and chlorinated hydrocarbons. Although this work was concerned with drinking water, it is a useful technique which may have application in seawater analysis. Cellulose acetate [9], ethyl cellulose acetate [6], and crosslinked polyethyleneinine [8] have been used as semi-permeable membranes. 

Proteins can be separated from small molecules by dialysis through a semi-permeable membrane such as cellophane (cellulose acetate). Pores in the membrane allow molecules up to approximately 10 kDa to pass through, whereas larger molecules are retained inside the dialysis bag (Fig. 1). As most proteins have molecular masses greater than 10 kDa, this technique is not suitable for fractionating proteins, but is often used to remove small molecules such... 

Figure 2. Schematic diagram of an ITP-apparatus. a = PT-electrode b = terminating electrolyte c = drain d = silicone septum e = UV-detector f = conductivity (potential gradient) detector g = silicone septum h = semi-permeable membrane (e.g. cellulose acetate) i = Pt-electrode. p and q lead to a current-stabilized power supply (20 kV). The separation compartment is a PTFE-capi1lary (I.D. =...

In order to eliminate the disadvantages following from the use of flexible membranes, Giddings et al. [50] designed a new channel in which both of the semi-permeable membranes of cellulose acetate were carried by polyethylene frist,... 

Cellulose acetate (CA), the acetate ester of cellulose, is one of the most commonly used biocompatible materials for the preparation of semi-permeable membranes to be used for dialysis, ultrafiltration, and reverse osmosis. CA membranes have very low absorption characteristics and thermal stability with high flow rates. Cellulose-based materials are also widely used in the bio-pharmaceutical industry as the matrix for adsorbent beads and membranes. Moreover, CA nanofibers can be used as carrier for delivery of vitamins or pharmaceutical products [15]. 

Cellulose acetate butyrate is insoluble in water and is available in several viscosity grades depending on their molecular weight. This pol)nner has been used to obtain sustained-release matrices prepared by direct compression technique as well as in obtaining semi-permeable membranes for osmotic pump systems [16]. Cellulose acetate butyrate microparticles (Figure 19.3) for the sustained release of drugs can be obtained by the emulsion-solvent evaporation method [17]. 

From Equations 28 and 29 it may be concluded that zero-order release may be obtained if the permeability characteristics of the semi-permeable membrane are controlled, namely the area, thickness, the diffusion coefficient of water across the membrane, and a saturated concentration of drug is maintained within the tablet core (by the correct choice of drug salt and inclusion of excipients). In the original OROS system the semi-pcrmcable membrane was composed of cellulose acetate and the osmotic pressure of the core was controlled by the inclusion of salts. If a non-saturaled drug solution is present in the tablet core non zero-order release occurs (a.47, a. 159). 

Semi-permeable membrane coating (cellulose acetate butyrate)... 

Acetylation rates have also been studied by Centola37 who treated natural and mercerized ramie fibers for varying times with acetic anhydride and sodium acetate and examined the reaction products chemically and by X-ray diffraction. The reagent was considered to penetrate into the interior of fibers. A heterogeneous micellar reaction was believed to occur that converted a semi-permeable elastic membrane around the micelles into the triacetate. The rate of acetylation of mercerized ramie was observed to be faster than that of unmercerized fiber. Centola concluded that about 40 % of the cellulose in native ramie is amorphous and acetylates rapidly. 

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