Chitin and chitosan: Properties and applications

doi:10.1016/j.progpolymsci.2006.06.001

Elsevier

Progress in Polymer Science

Volume 31, Issue 7, July 2006, Pages 603-632

Progress in Polymer Science

https://doi.org/10.1016/j.progpolymsci.200606001 Get rights and content

Abstract

Chitin is the second most important natural polymer in the world. The main sources exploited are two marine crustaceans, shrimp and crabs. Our objective is to appraise the state of the art concerning this polysaccharide: its morphology in the native solid state, methods of identification and characterization and chemical modifications, as well as the difficulties in utilizing and processing it for selected applications. We note the important work of P. Austin, S. Tokura and S. Hirano, who have contributed to the applications development of chitin, especially in fiber form. Then, we discuss chitosan, the most important derivative of chitin, outlining the best techniques to characterize it and the main problems encountered in its utilization. Chitosan, which is soluble in acidic aqueous media, is used in many applications (food, cosmetics, biomedical and pharmaceutical applications). We briefly describe the chemical modifications of chitosan—an area in which a variety of syntheses have been proposed tentatively, but are not yet developed on an industrial scale. This review emphasizes recent papers on the high value-added applications of these materials in medicine and cosmetics.

Introduction

Chitin, poly (β-(1→4)-N-acetyl-d-glucosamine), is a natural polysaccharide of major importance, first identified in 1884 (Fig. 1). This biopolymer is synthesized by an enormous number of living organisms; and considering the amount of chitin produced annually in the world, it is the most abundant polymer after cellulose. Chitin occurs in nature as ordered crystalline microfibrils forming structural components in the exoskeleton of arthropods or in the cell walls of fungi and yeast. It is also produced by a number of other living organisms in the lower plant and animal kingdoms, serving in many functions where reinforcement and strength are required.

Despite the widespread occurrence of chitin, up to now the main commercial sources of chitin have been crab and shrimp shells. In industrial processing, chitin is extracted from crustaceans by acid treatment to dissolve calcium carbonate followed by alkaline extraction to solubilize proteins. In addition a decolorization step is often added to remove leftover pigments and obtain a colorless product. These treatments must be adapted to each chitin source, owing to differences in the ultrastructure of the initial materials (the extraction and pre-treatment of chitin are not described in this paper). The resulting chitin needs to be graded in terms of purity and color since residual protein and pigment can cause problems for further utilization, especially for biomedical products. By partial deacetylation under alkaline conditions, one obtains chitosan, which is the most important chitin derivative in terms of applications.

This review aims to present state-of-the-art knowledge of the morphology of chitin and chitosan and to indicate the best methods for characterization in solution or solid state. The last decade of development will be discussed, as well as recent chemical modifications solution the uses of chitin to be expanded.

Section snippets

Chitin structure in the solid state

Depending on its source, chitin occurs as two allomorphs, namely the α and β forms [1], [2], which can be differentiated by infrared and solid-state NMR spectroscopy together with X-ray diffraction. A third allomorph γ-chitin has also been described [1], [3], but from a detailed analysis, it seems that it is just a variant of the α family [4]. α-Chitin is by far the most abundant; it occurs in fungal and yeast cell walls, in krill, in lobster and crab tendons and shells, and in shrimp shells,

Chitosan

When the degree of deacetylation of chitin reaches about 50% (depending on the origin of the polymer), it becomes soluble in aqueous acidic media and is called chitosan. The solubilization occurs by protonation of the –NH₂ function on the C-2 position of the d-glucosamine repeat unit, whereby the polysaccharide is converted to a polyelectrolyte in acidic media. Chitosan is the only pseudonatural cationic polymer and thus, it finds many applications that follow from its unique character

Conclusion

In this review we aim to present an overview of the state of art in the knowledge and technical applications of chitin and chitosan. We include an extensive bibliography of recent studies, both basic and applied. Nevertheless, this is an ambitious project; and the very large number of papers published on a wide range of properties and applications forces us to make a selection from the most significant results obtained by the many groups working around the world.

Chitin is a natural polymer for

Acknowledgments

The author thanks Henri Chanzy (CERMAV-Grenoble) for valuable information regarding the solid-state structure of chitin and Karim Mazeau (CERMAV-Grenoble) for the molecular modelling of chitin and chitosan.

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Chitin and chitosan: Properties and applications

Abstract

Introduction

Section snippets

Chitin structure in the solid state

Chitosan

Conclusion

Acknowledgments

TIBTECH

Int J Biol Macromol

J Struct Biol

Arch Biochem Biophys

J Struct Biol

J Mol Biol

Adv Insect Physiol

Int J Biol Macromol

Carbohydr Polym

Makromol Chem

Makromol Chem

Makromol Chem

J Appl Polym Sci

Process Biochem

J Nucl Sci Technol

J Biomed Mater Res A

Int J Biol Macromol

The chitin system

Biol Rev

Chitin

Chitin and its association with other molecules

J Polym Sci Part C

Conformation in polysaccharides and complex carbohydrates

J Biosci

Chitin crystals

The chitinous nature of filament ejected by Phaeocystis (Prymnesiophycae)

J Phycol

Molecular structure in arthropod cuticles

Single crystals of α-chitin

Int J Biol Macromol

High-resolution electron microscopy on cellulose II and α-chitin single crystals

Cellulose

Microfibril assembly by granules of chitin synthetase

Proc Nat Acad Sci USA

Artificial chitin spherulites composed of single crystalline ribbons of α-chitin via enzymatic polymerization

Macromolecules

Chitin in pogonophore tubes

J Mar Biol Assoc UK

A new crystallographic modification of chitin and its distribution

Experientia

chitinous fibrils in the lorica of the flagellate chrysophyte Poterioochromonas stipitata (syn. Ochromonas malhamensis)

J Cell Biol

Comparison of chitin fibril structure and assembly in three unicellular organisms

Studies on chitin (β-(1→4)-linked 2-acetamido-2-deoxy-d-glucan) fibers from the diatom Thalassiosira fluviatilis, Hustedt. III. The structure of chitin from X-ray diffraction and electron microscope observations

Can J Chem

High-resolution electron microscopy of β-chitin microfibrils

Biopolymers

Rötgenographische studien an chitin

Z Physiol Chem

X-ray studies of chitin, chitosan, and derivatives

J Phys Chem

Refinement of the structure of β-chitin

Biopolymers

Structure of β-chitin or parallel chain systems of poly-β-(1→4)-N-acetyl-d-glucosamine

Biopolymers

Fast intracrystalline hydration of β-chitin revealed by combined microdrop generation and on-line synchrotron radiation microdiffraction

Biomacromolecules

Crystallosolvates of β-chitin and alcohols

Inclusion complexes of β-chitin an aliphatic amines

Biomacromolecules

Guest selectivity in complexation of β-chitin

Macromolecules

Complexation of α-chitin with aliphatic amines

Biomacromolecules

Structural aspects of the swelling of β-chitin in HCl and its conversion into α-chitin

Macromolecules

Infra-red and X-ray studies of chitin

Disc Faraday Soc

Infrared spectra of crystalline polysaccharides. V. Chitin

J Polym Sci

Studies on chitin (β-(1→4)-linked 2-acetamido-2-deoxy-d-glucan) fibers of the diatom Thalassiosira fluviatilis Hustedt. II. Proton magnetic resonance, infrared, and X-ray studies

Can J Chem