Chemically modified cellulose

Oil Gator is a chemically modified cellulosic fiber that promotes in sitn biodegradation of hydrocarbons. According to the manufacturer, when the fiber is moistened, the bacteria reproduce and adapt to the available hydrocarbon food source. Oil Gator also extracts hydrocarbons by adsorption. 

Regioselective enzymatic acylation of large, insoluble polysaccharides is still a quite difficult task and therefore it is not surprising that only scant data have been reported up to now, most of them describing reaction outcomes which met with limited success. Nevertheless, enzymatic derivatization of polysaccharides has been performed in nonpolar organic solvents using insoluble polysaccharides with soluble [51] or suspended enzymes [52]. Chemically modified celluloses with either enhanced solubility or more readily accessible hydroxyl groups, like cellulose acetate or hydroxypropyl cellulose, were acylated by CalB, as reported by Sereti and coworkers [53]. However, the same authors failed to modify crystalline cellulose under the same reaction conditions. 

Chemically modified cellulose supports are also used in TLC, either as fibres or a crystalline powder. The most widely known of these is DEAE-cellulose, a basic phase containing diethylaminoethyl groups. The hydrophilic character of other polar phases with ion exchange properties can be used for the separation of ampholytes. 

Gunasingham H, Teo P, Lai Y, Tan S. Chemically modified cellulose acetate membrane for biosensor applications. Biosensors 1989, 4, 349-359. 

When examined with a scanning electron microscope, none of the exposed chemically modified celluloses exhibited any significant changes in morphology beyond the appearance of fractured fiber ends and fibrillar cracks. Such damage was also detected in the exposed nonoxidized control. 

Fig. 1. HgCl, adsorption kinetics by chemically modified cellulose.

Fig. 6. Equilibrium pH variation as a function of initial pH for HgCl,. Solutions chemically modified cellulose systems.

Several functional groups have been used to obtain cellulose anion exchangers [aminoethyl (AE), diethyl-aminoethyl (DEAE)], or cation exchangers [car-boxymethyl (CM), phosphate (P)] for thin-layer chromatography. PEI cellulose is not a chemically modified cellulose, but a complex of cellulose with polyethyleneimine. These cellulose exchangers are particularly useful for the separation of proteins, aminoacids, enzymes, nucleobases, nucleosides, nucleotides, and nucleic acids. 

The present book is a follow-up of a previous one with the title Analytical Pyrolysis of Natural Organic Polymers published by Elsevier as vol. 20 in the series Techniques and Instrumentation in Analytical Chemistry. In addition to the discussion on pyrolysis of various natural polymers, the previous book contains information on chemically modified celluloses, modified starches, etc. For this reason, the present book does not include synthetically modified natural polymers. Information on the pyrolysis process and pyrolytic techniques in general also can be found in the book on natural polymers. 

Chemically modified cellulose in the form of cellulose nitrate or nitrocellulose was made and tested for commercial applications in Britain in the 1855-1860 period without much success. The discovery by Hyatt, in 1863, that cellulose nitrate could be plasticized with camphor to give moldability to the blend, made this material much more useful. By 1870, celluloid (plasticized cellulose nitrate) was being produced into a variety of commercial products such as billiard balls, decorative boxes, and combs. Nitrocellulose was also soluble in organic solvents, unlike cellulose, and so could be applied to surfaces in solution to form a coating, as in airplane dopes and automobile lacquers. It could also be solution spun into fibers (synthetic silk) and formed into photographic film, or used as a laminating layer in early auto safety glass. It was also used as an explosive. The hazard introduced to many of these uses of nitrocellulose by its extremely flammable nature resulted in an interest to discover other cellulose derivatives that could still be easily formed, like nitrocellulose, but without its extreme fire hazard. 

Basically, the methods for determining the relative reactivities of the hydroxyl groups of the n-glucose residues of cellulose all depend upon measuring the distribution of substituents between the C-2, C-3, and C-6 positions in chemically modified cellulose. It is thus to be expected that the relative reactivities will differ from one class of reaction to the next, and that they will also depend upon the way in which a particular modification, such as etherification, is carried out. Hence, it is important that relative reactivity be defined in terms of the set of experimental conditions under consideration. 

Cellulosic substances have been used in various fields from commodities to industrial materials after mechanical and chemical modifications. Especially because chemically modified cellulosics have some unique functional properties, and also because of their biodegradability in most instances, the chemistry of cellulose has become one of the major areas in cellulose science. Figure 12 illustrates the chemical structure of cellulose in terms of chemical modifications. "" Three hydroxyl groups in the glucose residue, one primary and the other two secondary, are the sites for substitution reactions, which are the most common in cellulose derivatizations. The (1 4)-/3-glycoside bonds and other functional groups such as carboxyls and aldehydes present in most cellulosic material as minor groups are also possible sites for chemical modifications. 

Chemically reactive systems are those in which a special effect, in addition to partition and/or adsorption, lends added selectivity to the system. Examples include use of chemically modified cellulose (carboxyl paper), ion-exchange papers [34], or papers impregnated with a selective reagent (e.g., boric acid [35] for separation of various hydroxyl compounds), or the mobile phase may contain a reactive or complexing reagent in combination with normal or modified cellulose [21]. 

There are a variety of chemically modified celluloses each of which behaves as an ion exchange medium. 

Table 17.5 Maximum adsorbed amounts (mg.g ) of adsorbed organic solutes onto chemically modified cellulose fibers. ...

Boufi Sami, is Professor at the Department of Chemistry of the University of Sfax (FSS). His research activities include chemical modification of cellulose and carbohydrate materials, the synthesis of functional polymer for colloidal chemistry, and the exploitation of chemically modified cellulose fibres as reusable adsorbent for dissolved organic pollutants. 

G. M. Nabar and V. A. Shenai, Chemically modified celluloses. III. Estimation of free carboxylic acid groups in oxycellulose, J. Appl. Polym. Sci., 14 (1970) 1215-1226 Chem. Abstr., I i... 

Chemically modified celluloses have been analyzed by conventional wet methods and by various Instrumental methods designed to differentiate bulk and surface properties. Electron emission spectroscopy for chemical analyses (ESCA) used alone and In combination with radiofrequency cold plasmas yielded elemental analyses, oxidative states of the element, and distribution of the element. Techniques of electron paramagnetic resonance (EPR), chemiluminescence, reflectance infrared spectroscopy, electron microscopy, and energy dispersive X-ray analyses were also used to detect species on surfaces and to obtain depth profiles of a given reagent in chemically modified cottons. 

In a recent communication (22), we described the fabrication and preliminary evaluation of a chemically modified cellulose acetate film as an optical sensor for the selective determination of pH. This sensor was fabricated by the immobilization of Congo Red at a porous cellulosic film. Advantageous features of this design... 

Schwenker RF, Pacsu E, Chemically modifying cellulose for flame resistance, Ind Eng Chem, 50(1),... 

Chemically modified cellulose (e.g., cellulose acetate (CA) and cellulose acetate butyrate (CAB)) Organically modified nanoclay (quaternary ammonium modified MMT, Ag-zeolite)... 

Both rayon and acetate rayon are made from chemically modified cellulose and were the first commercially important synthetic textile fibers. In the production of rayon, cellulose fibers are treated with carbon disulfide, CSg, in aqueous sodium hydroxide. In this reaction, some of the —OH groups on a ceUulose fiber are converted to the sodium... 

Regeneration Physically or chemically modified cellulose can be regenerated in suitable solvents (for instance xanthates in sulfuric acid) leading to pure cellulose Relative density (pr) The ratio between the aerogel bulk density and the bulk glass density (e.g., for silica 2.2 g/cm )... 

Cellulose is not thermoplastic but can be chemically modified to produce a wide variety of cellulosic plastics—some of which are thermoplastic—and fibers. Before 1950 cellulosics were the most important group of thermoplastics today, cellulosic fibers still make up about 8% of the fiber market. Some chemically modified celluloses do not have the biodegradability of cellulose. 

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