Extraction, chemical modification and characterization of chitin and chitosan.

Chitin is the second most common polymer after cellulose in earth, existing in the shells of crustaceans like crab and shrimp. Chitosan is a natural amino-polysaccharide derived from chitin, known as one of the most abundant organic materials in nature, it has been widely used in several applications due to its natural origin and exceptional properties such as biocompatibility, biodegradability, non-toxicity, and chelating of metal ions. Chitin and chitosan are characterized by deacetylation degree, one of the most important chemical characteristics that can influence the performance of chitosan in many applications. Chitosan is usually prepared by a thermochemical method, consuming time, energy and reagents. In this review, various methods of chitosan extraction will be approached and compared; the importance of a new method of ecological extraction will be emphasized. Moreover, in order to improve the chitosan functionality, and better control these physicochemical properties, several chemical modifications have been reported. These chemical modifications lead to a broad range of derivatives with a wide range of applications in many fields. Recent examples of the distinct applications, with particular emphasis on environmental applications, have been presented.