Cellulose chemical modification

Kouznetsov, D. A., A. A. Ivanov, and P. R. Veletsky (1996), Analysis of cellulose chemical modification A potentially promising technique for characterizing cellulose archaeological textiles, /. Archaeol. Sci. 23, 23-34,109-121. 

Keywords Applications Cellulose Chemical modification Hemicelluloses TEMPO... 

Cellulose Derivatives. Chemical modification markedly alters the physical properties of ceUulose. Common derivatives iaclude methylceUulose ethylceUulose [9004-57-3] ptopylceUulose /7(9(93 -/ -7/, hydroxyethjlceUulose /7(9(94- 52-(97, hydtoxyptopylceUulose [9004-64-2],... 

It may also be mentioned that a number of commercial polymers are produced by chemical modification of other polymers, either natural or synthetic. Examples are cellulose acetate from the naturally occurring polymer cellulose, poly(vinyl alcohol) from polyfvinyl acetate) and chlorosulphonated polyethylene (Hypalon) from polyethylene. 

Grafting reactions alter the physical and mechanical properties of the polymer used as a substrate. Grafting differs from normal chemical modification (e.g., functionalization of polymers) in the possibility of tailoring material properties to a specific end use. For example, cellulose derivatization improves various properties of the original cellulose, but these derivatives cannot compete with many of the petrochemically derived synthetic polymers. Thus, in order to provide a better market position for cellulose derivatives, there is little doubt that further chemical modification is required. Accordingly, grafting of vinyl monomers onto cellulose or cellulose derivatives may improve the intrinsic properties of these polymers. 

The xanthate method [62] is considered as one of the most promising methods for industrial chemical modification. The principal involved in the xanthate method of grafting is that cellulosic xanthate either ferrated or in acidic conditions reacts with hydrogen peroxide to produce macroradicals. The following reaction mechanism has been proposed ... 

An effective method of NVF chemical modification is graft copolymerization [34,35]. This reaction is initiated by free radicals of the cellulose molecule. The cellulose is treated with an aqueous solution with selected ions and is exposed to a high-energy radiation. Then, the cellulose molecule cracks and radicals are formed. Afterwards, the radical sites of the cellulose are treated with a suitable solution (compatible with the polymer matrix), for example vinyl monomer [35] acrylonitrile [34], methyl methacrylate [47], polystyrene [41]. The resulting copolymer possesses properties characteristic of both fibrous cellulose and grafted polymer. 

When used as substitutes for asbestos fibers, plant fibers and manmade cellulose fibers show comparable characteristic values in a cement matrix, but at lower costs. As with plastic composites, these values are essentially dependent on the properties of the fiber and the adhesion between fiber and matrix. Distinctly higher values for strength and. stiffness of the composites can be achieved by a chemical modification of the fiber surface (acrylic and polystyrene treatment [74]), usually produced by the Hatschek-process 75-77J. Tests by Coutts et al. [76] and Coutts [77,78] on wood fiber cement (soft-, and hardwood fibers) show that already at a fiber content of 8-10 wt%, a maximum of strengthening is achieved (Fig. 22). 

Due to the lack of a commercial supply, as well as their usually low molecular weight and poor solubility, xylans have found little industrial utility and interest in their modification has been rather low in comparison to commercially available polysaccharides such as cellulose or starch. With the aim of improving the functional properties of xylans and/or imparting new functionalities to them, various chemical modifications have been investigated during the past decade. Most of them were presented in recent reviews [3,399]. 

Figure 17-5. Amylose, cellulose. Amylose consists of a water-soluble portion, a linear polymer of glucose, the amylose and a water-insoluble portion, the amylopectin. The difference between amylose and cellulose is the way in which the glucose units are linked. In amylose, a-linkages are present, whereas in cellulose, p-linkages are present. Because of this difference, amylose is soluble in water and cellulose is not. Chemical modification allows cellulose to become water soluble.

The objective of this work is to determine the surface concentration of the hydroxyl groups of cellulose and PVA films utilizing their chemical modification. We chose these polymers mainly because the hydroxyl group is their sole functional group. Recently we have reported that a cellulose film is more excellent in wettability towards water than PVA, though cellulose is insoluble in water, in contrast to PVA(4). Since only the chemical composition of the surface must be responsible for water... 

Surface Modification of Cellulose and PVA Films. Cellulose, as well as PVA,is known to be a typical non-ionic, hydrophilic polymer possessing hydroxyl groups. As this group has a high reactivity,chemical modification of these polymers is relatively easy and, in fact, has been the subject of extensive research. However, so far as we know, no work has been reported concerned with reactions occurring only at the surface of films or fibers from these polymers. 

Rowell etal. (1987b) produced PF-bonded flakeboard from acetylated southern pine (21.6 % WPG) or aspen (17.6 % WPG) flakes. This was not completely resistant to attack by termites Reticulitermes flavipes) in a 4-week test. It was thought that acetylation was less effective in preventing termite attack than other chemical modifications because cellulose decomposition in the intestines of termites leads to acetic acid formation in any case. 

Rowell, R.M. (1983a). Chemical modification of wood. Forest Products Abstracts, 6(12), 363-382. Rowell, R.M. (1983b). Chemical modification of wood. In Wood and Cellulosic Chemistry, Hon, D.N.S., and Shiraishi, N. (Eds.). Marcel Dekker, New York, USA, pp. 703-756. 

Cost sensitivity studies have shown that the successful commercialization of cellulase-based processes, such as the conversion of cellulose to fermentable sugars, is highly dependent on the cost of enzyme production (i). Because fungal -D-glucosidase (EC 3.2.1.21) is the most labile enzyme in this system under process conditions (2), and k to efficient saccharification of cellulose, this enzyme was targeted for application of stabilization technology, both through chemical modification and immobilization to solid supports. 

This paper will also assume that the reader has basic starch and cellulose knowledge and that it is not necessary to review the structure of the molecules. It is, however, important to know that starch from native, non-genetically selected sources, is a mixture of two molecules and not simply one compound. Amylose is an essentially linear molecule and differs from amylopectin, which has about 4-6%oC-(l—>6) branches, even though both molecules are mainly o4 -(1—>4) linked D -glucose. The differences in these two molecules and their chemical modifications are the basis of application technology and the reason for the growing importance of specialty starches. 

Arthur, J. C., Jr., Chemical Modification of Cellulose and its Derivatives, Chap. 2 in Comprehensive Polymer Science, Vol. 6, G. C. Eastmond, A. Ledwith, S. Russo, and P. Sigwalt, eds., Pergamon Press, Oxford, 1989. 

Cellophane is, after chemical modification, obtained from the cellulose in wood, just as paper (from cellulose and lignin), cellulose fibres ( rayon ), and cellulose plastics. Leather is made from animal hides in a tanning process. 

Treatments with Chemicals or Resins. Resin treatments are divided into topical or chemical modifications of the fiber itself. Most chemical treatments of synthetic fibers are topical because of the inert character of the fiber itself and the general resistance of the fiber to penetration by reagents. By contrast, cellulosics and wool possess chemical functionality that makes them reactive with reagents containing groups designed for such purchases. Natural fibers also provide a better substrate for nonreactive topical treatments because they permit better penetration of the reagents. 

Hcinzc. T. and W.G. Glasser Cellulose Derivatives Modification. Characterization, and Nanostructures. American Chemical Society. Washington. DC. 1998. Kennedy. J l, P.A. Williams, and G.O. Phillips Cellulose and Cellulose Derivatives, Tcchnomic Publishing Company. Inc., Lancaster. PA. 1999. 

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