Cellulose derivative membranes

Membrane Filters. The cellulose-derivative membrane filters, as we know them, have been available since 1927 and are now commonplace [29,32,35-38]. The classic membrane filters are prepared by means of a colloid chemical process gelation of concentrated colloidal solutions of polymers and removal of solvent to leave pores. Although porous, in practice they differ from the capillary model of a pore in that their stmcture is not regular. A classic membrane filter has three different structures the upper surface structure, the inner structure, and the lower surface stmcture [29,35-38]. These filters contain tortuous channels, and the pore sizes inside the filter are larger than those on the surface of a membrane filter. The diameters of these channels can be closely controlled during manufacture. The mechanisms involved in the capture of... 

NOTE The above applies to composite polyamide and polyvinyl derivative membranes. Do NOT use chlorine, which is suitable only for cellulose acetate membranes. 

Polymeric pH indicators, phenolphthalein-formaldehyde (PPF) and o-cresolphthalein-formaldehyde (CPF) were synthesized with phenolphthalein and o-cresolphthalein reacted by formaldehyde under alkaline conditions, respectively. They can be immobilized in hydrolyzed cellulose diacetate membranes (HCDA) mainly due to macromolecular entrapment, and can be covalently bound to poly(vinyl alcohol) (PVA) via the considerable newly produced hydroxylmethyl groups [168,169], Phenol red (phenolsulfonphthalein) and its derivatives are commonly used for pH determination. 

Relationship Between Nodular and Rejecting Layers. Nodular formation was conceived by Maler and Scheuerman (14) and was shown to exist in the skin structure of anisotropic cellulose acetate membranes by Schultz and Asunmaa ( ), who ion etched the skin to discover an assembly of close-packed, 188 A in diameter spheres. Resting (15) has identified this kind of micellar structure in dry cellulose ester reverse osmosis membranes, and Panar, et al. (16) has identified their existence in the polyamide derivatives. Our work has shown that nodules exist in most polymeric membranes cast into a nonsolvent bath, where gelation at the interface is caused by initial depletion of solvent, as shown in Case B, which follows restricted Inward contraction of the interfacial zone. This leads to a dispersed phase of micelles within a continuous phase (designated as "polymer-poor phase") composed of a mixture of solvents, coagulant, and a dissolved fraction of the polymer. The formation of such a skin is delineated in the scheme shown in Figure 11. 

As an example of hybridization of zeolites with cellulose derivatives, self-supporting zeolite membranes with a sponge-like architecture and zeolite microtubes were prepared by using CA filter membranes as a template [154]. The hierarchical structure with sub-nanometer- to micrometer-sized pores is a characteristic of great promise for a wide range of applications such as catalysis, adsorption, and separation. There was also an attempt to prepare alginate membranes incorporated with zeolites, e.g., for pervaporation separation of water/acetic acid mixtures [155]. 

Polymers for membrane preparation can be classified into natural and synthetic ones. Polysaccharides and rubbers are important examples of natural membrane materials, but only cellulose derivatives are still used in large scale for technical membranes. By far the majority of current membranes are made from synthetic polymers (which, however, originally had been developed for many other engineering applications). Macromolecular structure is crucial for membrane barrier and other properties main factors include the chemical structure of the chain segments, molar mass (chain length), chain flexibility as well as intra- and intermolecular interactions. 

Figure 14 shows the plots of the ratio Mw/Mn of the CA fractions prepared by the SSF method 39 42), as a function of their Mw. Mw and Mn values were determined by light scattering and membrane osmometry, respectively. Except for a few fractions of CA(2.46) and CA(2.92), Mw/Mn values of CA fractions lie between 1.2 and 1.5, independently of their Mw values. Most of the fractions of cellulose derivatives reported in the literature were prepared by the SPF method 44) their Mw/Mn values range roughly from 1.2 to 3.7 (most of them 1.5-2.0) and moreover depend markedly on Mw. This indicates clearly that the SSF method is superior to SPF for cellulose derivatives, as it is also the case for synthetic polymers such as polystyrene 38). A computer simulation for a quasi-temary system carried out by K amide and Matsuda also showed the inconditional superiority of the SSF method 34 - 36 ... 

Unconventional routes of drug administration by using gels and jellies are also being explored. Thus, two nasal jellies were developed and marketed. The intranasal vitamin B-12 gel, Nascobal (Schwarz Pharma), is used as a dietary supplement. The gel base is composed of a hydrophilic cellulose derivative, the exact nature of which is not disclosed. However, the gel is apparently odorless and non-iriitating, and adheres well to the mucous membrane. Neo-Synephrine Viscous (Sanofi Winthrop) is a water-soluble nasal jelly formulated with methylcellulose it contains the decongestant phenylephrine hydrochloride. 

It is seen that at temperature in the 20-50 °C region both membranes showed substantially the same performance in terms of provided flux. However, the polybenzimidazole film performed increasingly better as the temperature was raised fiuther, the flux increasing from 693 1 m day at 49 °C to 1019 I m" at 90 °C. In contrast, the cellulose derivative standard showed a sharp drop in flux to about one-half over this temperature span and turned out to be entirely impermeable at 90 °C. A similarly outstanding performance at the even higher test pressure of 6.89 MN was observed with... 

Kokta, B. Luner, P. Suen, R. In "Membranes From Cellulose and Cellulose Derivatives" A. F, Turbak, Ed. J. Appl. Polym. Sci., Appl. Polym. Symp. 1970, 169-179. 

C. R. In "Membranes from Cellulose and Cellulose Derivatives" Turbak, A. F., Ed. Ibidem. 

Among the successful membrane matrices arc collagen, various cellulose derivatives, polyamides (such as Nylon and polyacrylonitrile) and urethane. In the following paragraphs, a brief discussion of each of those membrane materials Is presented. 

Cellulose Derivative Matrix. Four possible methods for preparing cellulosic, enzyme membranes are presented ... 

Mascini and Mazzei (1986) succeeded in the covalent immobilization of PyOD to a Biodyne Immunoaffinity Membrane (Pall Biodyne, USA) containing carboxylic groups on the surface. The membrane was preactivated with a carbodiimide derivative. The enzyme membrane was fixed on the tip of a hydrogen peroxide-indicating Pt electrode between a cellulose acetate membrane and a further dialysis membrane. This pyruvate sensor has been applied to serum measurement. Over 30 days the sensitivity dropped by only 13%. 

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