Chitosan is a well known derivative of chitin, the major difference being the degree of deacetylation (DAC),which is the same as the relative amount of free amine .DAC refers to the relative amount of acetyl groups removed from the molecule ,expressed as a percentage . Chitosan is obtained when chitin is subjected to strong caustic soda and heat which removes the N-acetyl group. (11) The production of chitosan is currently based on crab and shrimp shells discarded by the canning industries. (25) The production of chitosan from crustacean shells obtained, as a food industry waste is economically feasible, especially if it includes the recovery of carotenoids. (28) Chitosan derivatives are easily obtained under mild conditions and can be considered as substituted glucans.(34) Recently, the gel forms ability of chitosan in N-methyl morpholine N-oxide .(32)Chitosan molecular weight distributions have obtain using HPLC .(46)The weight average molecular weight (Mw) of chitosan has been determined by light scattering .(47)
Properties of chitosan
Chitosan is capable of undergoing many chemical modifications because it is an amino polysaccharide. The amino group (-NH2) is a useful functional group to alter chemically to produce new polymers. (1)Chitosan degrade before melting, which is typical for polysaccharides with extensive hydrogen bonding. (75)Chitosan is insoluble in water and most common solvents but it is soluble without degradation in weak acids such as 5% formic and acetic acids, and it is thermally stable up to 150ºC. (30)Chitosan is non-toxic and easily bio-absorbable . (74) Moreover, chitosan has antacid and antinuclear activities which prevent weaken drug irritation in the stomach . . (133)Also ,chitosan matrix formulations appear to float and gradually swell in an acid medium. (4)besides chitosan is the only natural cationic gum that becomes viscous on being neutralized with acid . (78)Chitosan used in creames ,lotions ,permanent waving lotions ,nail lacqueres, artificial skin ,dressing sutures ,also chitosan used as coating material and crosslinking agent in fabric used in medical textiles specially fabrics used in heart prostheses.
Chitin is white flaky ,hard ,inelastic ,nitrogenous polysaccharide and the major source of surface pollution in coastal areas .Chitin is of commercial interest due to their high percentage of nitrogen (6.89)compared with synthetically substituted cellulose (1,25).Chitin is recommended as suitable functional materials because these natural polymers have excellent properties such as biocompatibility ,biodegradability, non-toxicity, adsorption properties …etc Chitin has been known to form microfibrillar arrangements in living organisms. Theses fibrils are usually embedded in protein matrix have diameters from 2.5 to 2.8 nm. Fibers made of chitin are useful as absorbable sutures and wound dressing materials