Chitin properties

Definition Deacylated derivative of chitin Properties M.w. 70,000 Toxicology TSCA listed Storage Hygroscopic... 

Last years the concern of the scientists and contributors to chitin, chitosan and chitincontaining connections has increased. It is connected to their widespread occurrence in the nature, paiticulai properties, and also feasibility in many areas of a national economy. The raw sources for obtaining chitincontaining of products are the testas of crabs, lobsters, shrimps, and also cabbage-weeds, funguses. 

Chitosan, having a similar chemical backbone as cellulose, is a linear polymer composed of a partially deacety-lated material of chitin [(l-4)-2-acetamide-2-deoxy-/3-D-glucan]. Grafting copolymer chains onto chitosan can improve some properties of the resulting copolymers [48-50]. Yang et al. [16] reported the grafting reaction of chitosan using the Ce(IV) ion as an initiator, but no detailed mechanism of this initiation has been published so far. 

Amino-sugars and Related Compounds. Part IV. Isolation and Properties of Oligosaccharides Obtained by Controlled Fragmentation of Chitin, S. A. Barker, A. B. Foster, M. Stacey, and J. M. Webber, J. Chem. Soc., (1958) 2218 - 2227. 

The solubility of chitin is remarkably poorer than that of cellulose, because of the high crystallinity of chitin, supported by hydrogen bonds mainly through the acetamido group. Dimethylacetamide containing 5-9% liCl (DMAc/IiCl), and N-methyl-2-pyrrohdinone/LiCl are systems where chitin can be dissolved up to 5%. The main chain of chitin is rigid at room temperature, so that mesomorphic properties may be expected at a sufficiently high concentration [67,68]. 

Nontoxic and noncorrosive solvent systems can be used when chitosan is considered instead of chitin for the manufacture of fibers. Improvements of the fiber quality rely mostly on technical shrewdness for instance the use of potassium hydrogen phthalate at pH 4-5 imparted better mechanical properties [255]. 

Cross-linking agents have been proposed for the improvement of chitin fibres in the wet state. Epichlorohydrin is a convenient base-catalysed crosslinker to be used in 0.067 M NaOH (pH 10) at 40 °C. The wet strength of the fibres was considerably improved, whereas cross-hnking had neghgible effect on the dry fibre properties. Of course, the more extended the chemical modification, the more unpredictable the biochemical characteristics and effects in vivo. Every modified chitin or modified chitosan fibre should be studied in terms of biocompatibiUty, biodegradabiUty and overall effects on the wounded tissues. 

The mechanistic properties are clearly improved by the incorporation of proteins. Insects and crustaceans have a shell made of chitin, a chain molecule (polymer) based on chemically modified (acetylamino-) glucose. 

Figure 22.11. Cellulose is a structural and rather chemically inert component of terrestrial plants. Alginic acid is synthesized by marine algae and has medicinal properties. Some polysaccharides contain nitrogen in the form of amino sugars. The primary example of this is chitin, which composes the exoskeletons of Crustacea. An amino sugar contains an amine in place of a hydroxyl group. In other polysaccharides, sugars combine with lipids and proteins. These form glycoUpids and glycoproteins, respectively.

Natural and synthetic aminopolysaccharides have recently attracted much attention because of their unique stmctures and properties that are generally different from those of normal polysaccharides such as cellulose. For example, chitin is the most abundant aminopolysaccharide among the naturally occurring polysaccharides and has been of great interest in numerous scientific and application field (Scheme 1) [3]. 

More complex polysaccharides play important roles in connective tissues and elsewhere. For example, hyaluronic acid is universally present in connective tissues of animals, as well as in their vitreous and synovial fluids. It helps to provide the fluids present in joints with shock-absorbing and lubricating properties. Unlike cellulose, chitin, starch, and glycogen, hyaluronic acid contains two different monomers glucose and N-acetylglucosamine alternate in the structure. Thus, hyaluronic acid is a regular alternating copolymer ABABABA —... 

Chitin and Chitosan Sources, Chemistry, Biochemistry, Biochemistry, Physical Properties and Applications Skjak-Braek, G. Anthousen, T. Sanford, P., Eds. Elsevier Applied Science New York, NY, 1989 835 pp. 

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