The relationship between chitin and chitosan

Chitin is an important marine biological resource. The chitin produced in nature is more than 10 billion tons per year, mainly from the shells of arthropods such as shrimp, crab, insects and microorganisms. Carboxymethyl chitosan is the second largest renewable resource after cellulose on the earth, and the only basic polysaccharide containing nitrogen. It is a white or gray white amorphous, translucent solid, insoluble in water, dilute acid, dilute alkali and general organic solvents, soluble in concentrated alkali, concentrated hydrochloric acid, concentrated sulfuric acid and anhydrous formic acid, but at the same time the main chain is degraded.

Chitosan is the product of deacetylation of chitin. It is a white or gray amorphous, translucent solid with a slight pearl luster. It is insoluble in water, alkali solution, dilute phosphoric acid, dilute sulfuric acid, dilute hydrochloric acid, dilute nitric acid and other inorganic acids as well as most organic acids. In dilute acid, the main chain of chitosan will degrade slowly.

Deacetylation degree and molecular weight are two main indexes of chitosan. In general, viscosity method is used to determine the molecular weight of chitosan, which needs to be calculated from the intrinsic viscosity. Viscosity is also affected by many factors, including deacetylation degree, molecular weight, ionic strength, pH and temperature. The degree of deacetylation of chitosan is directly related to the solubility, viscosity, ion exchange capacity, flocculation performance, chemical reaction capacity related to amino group of chitosan in dilute acid. Chitosan is the product of deacetylation of chitin. Generally speaking, it can be called chitosan when more than 55% of chitin is deacetylated. According to the degree of deacetylation, the chitosan with low degree of deacetylation is 55% - 70%, medium degree of deacetylation is 70% - 85%, high degree of deacetylation is 85% - 95%, while the chitosan with 100% degree of deacetylation is difficult to prepare.

Gold chitosan carboxymethyl chitosan has good chemical and physical properties. It can combine with many substances (such as cholesterol, fat, protein, tumor cells, metal ions). Its physical and chemical properties can be further improved by chemical methods. Chitosan materials can be made by drawing, film-forming, granulating and other methods, which can be widely used in food packaging, medical material water treatment, textile industry, agriculture, environmental protection, cosmetics and other daily chemical industries. Chitin, chitosan and their derivatives have the functions of promoting wound healing, antibacterial and antiviral. The research and application of chitin, chitosan and their derivatives in biomedical fields such as drug carrier, medical dressing, tissue engineering materials and antibacterial materials have attracted more and more attention.

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