Chitin/chitosan chemically modified

Chitin is known to be biodegradable, biocompatible, and nontoxic. It is used in dmg delivery and bio medical applications. It also used in the purification of water especially for the absorption of toxic dyes. Chitin has limited solubility in solvents but chitosan is readily soluble in acidic aqueous solutions and has more tendency to be chemically modified. Chitosan can readily be spun into fibers, cast into films, or precipitated in a variety of micromorphologies from acidic solutions. Min and Kim have reported on the adsorption of acid dyes from wastewater using composites of PAN/chitosan [52]. Shin et al. has reported on copolymers composed of PVA and poly dimethyl siloxanes cross-linked with chitosan to prepare semi IPN hydrogels for application as biomedical materials... 

Sashiwa H, Aiba SI (2004) Chemically modified chitin and chitosan as biomaterials. Prog Polym Sci 29 887-908... 

Sun, L., Du, Y., Chen, X. et al., 2005. Qnartemized carboxymethyl chitosan A new approach to chemically modified chitosan III Antimicrobial activity and apphcation as pulp-cup. Asian Chitin Journal, 1 39-48. 

Polysaccharides are natural polymers that are highly diverse and used widely as they are or after modification in the biomedical and pharmaceutical fields. Among the polysaccharides, cellulose is the most abundant, as it represents about one-third of all plant matter. Cellulose fibres have been used for centuries without major modification, but for many uses cellulose has been chemically modified to be easily manufactured. Chitin, the major constituent of crab shells, is probably the second most abundant polysaccharide. Before being used, chitin has to be de-acetylated, resulting in chitosan, as shown in Figure 3.11. Chitin de-acetylated over 70% is water-soluble. 

A bio-derived plastic on the other hand is biopolymer that is chemically modified to improve its properties. Cellulose from plants can be acetylated to yield cellulose acetate, the bio-derived plastic used in cigarette filters. It can also be xanthated and extruded into cellophane (or Rayon), a bio-derived plastic. Chitin, a biopolymer from crab shells, can be processed (by converting the amide functionalities into amine functionalities) into its amine analog to obtain a bio-derived plastic, chitosan. 

Kamble et al (2007) reported on the applicability of chitin, chitosan and chemically modified chitosan (20%-lanthanum chitosan) as adsorbents for the removal of excess F from drinking water. Chitosan which is derived from chitin is one of the main components of crustacean shells of prawn, crab, shrimp or lobster, has the ability to coordinate metal ions because of its high concentration of amine functional groups (Li et al, 1992). It is also a non-toxic, biodegradable and biocompatible material. Furthermore, the effects of various physico-chemical parameters such as pH, adsorbent dose, initial F concentration and the presence of interfering ions on adsorption of F were assessed by Kamble et al (2007). The authors concluded that lanthanum chitosan adsorbents were better at removal of F from water than plain chitosan and chitin (Fig. 6.2). 

The applicability of chitin, chitosan and chemically modified chitosan as adsorbents should also be investigated further for the removal of F, As and U from drinking water. We can expect this to be one area of rapid development. Chitosan which is derived from chitin one of the mainly components of crustacean shells of prawn, crab, shrimp or lobster, is inexpensive and versatile and has the ability to coordinate various metal ions. 

Sashiwa, H., Aiba, S. Chemically modified chitin and chitosan as Biomaterials. Progress in Polymer Science. 2004,29, 887-908. 

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. 

In order to improve the properties of these unique polysaccharides and to develop new advanced materials, much attention has been paid to their chemical modification. These polymers have two reactive groups suitable for this purpose, namely, primary (C6) and secondary (C3) hydroxyl groups in the case of chitin whereas chitosan has additionally the amino (C2) group on each deacetylated unit. All these functions are susceptible to a variety of classical reactions which can be applied here in a controlled fashion to obtain a vast array of novel materials based on the two polysaccharides which can also be modified by either crosslinking or graft copolymerization. This topic has been extensively studied and thoroughly documented [5-7]. 

The poor solubility, low surface area, and porosity of chitin and chitosan are the major limiting factors in their utilization. Chitosan can be modified by physical or chemical processes in order to improve the mechanical and chemical properties. Chemical modification of chitosan has two main aims (a) to improve the metal adsorption properties and (b) to change the solubility properties of chitosan in water or acidic medium. The substitution chemical reactions involve the NH2 group in the C2 position or the OH groups in the C3 and Cg positions of acetylated and deacetylated units. Chitosan membrane is swollen in water the amino groups may be protonated and leave the hydroxide ions free in water, which may contribute to the ionic conduction in the membrane. 

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