Chitin and Chitosan for Versatile Applications

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CHITIN AND CHITOSAN FOR VERSATILEAPPLICATIONSPradip Kumar Dutta a; M. N. V. Ravikumar b; Joydeep Dutta ca Chemistry Section, Department of Applied Sciences & Humanities, Motilal NehruRegional Engineering College, Allahabad, Indiab Department of Preventive Medicine & Environmental Health, University ofKentucky Medical Center, Lexington, KY, U.S.A.c School of Chemical Sciences, D. A. University, Indore, India

Online Publication Date: 19 August 2002

To cite this Article: Dutta, Pradip Kumar, Ravikumar, M. N. V. and Dutta, Joydeep(2002) 'CHITIN AND CHITOSAN FOR VERSATILE APPLICATIONS', PolymerReviews, 42:3, 307 — 354

To link to this article: DOI: 10.1081/MC-120006451URL: http://dx.doi.org/10.1081/MC-120006451

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©2002 Marcel Dekker, Inc. All rights reserved. This material may not be used or reproduced in any form without the express written permission of Marcel Dekker, Inc.

MARCEL DEKKER, INC. • 270 MADISON AVENUE • NEW YORK, NY 10016

CHITIN AND CHITOSAN FOR VERSATILE

APPLICATIONS

Pradip Kumar Dutta,1,* M. N. V. Ravikumar,2,y

and Joydeep Dutta3

1Chemistry Section, Department of Applied Sciences & Humanities,Motilal Nehru Regional Engineering College, Allahabad 211004, India

2Department of Applied Chemistry, Shri G. S. Institute ofTechnology & Science, Indore 452 003, India

3School of Chemical Sciences, D. A. University,Indore 452 001, India

CONTENTS

1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 308

2. Processing of Chitin and Chitosan . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 309

3. Economic Aspects . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 311

4. Properties of Chitin and Chitosan . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 311

5. Derivatives of Chitin and Chitosan . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 312

5.1. Chitin Derivatives of Polysaccharides and Polypeptides . . . . . . . . 315

5.2. Tosyl and Iodo Chitins . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 315

5.3. Ether-Type Chitin Derivatives . . . . . . . . . . . . . . . . . . . . . . . . . . 316

5.4. Mixed Ester-Type Chitin Derivatives . . . . . . . . . . . . . . . . . . . . . 317

5.5. Regioselective Chlorination of Chitin . . . . . . . . . . . . . . . . . . . . . 318

5.6. N-Acyl, N-Arylidene, and N-Alkylidene Chitosan Gels . . . . . . . . 318

5.7. Maleilated Chitosan and Acrylamide Copolymers . . . . . . . . . . . . 319

5.8. Chitosan/Calcium Alginate Beads . . . . . . . . . . . . . . . . . . . . . . . 320

5.9. Calcium Carbonate–Chitosan Composites . . . . . . . . . . . . . . . . . 321

307

DOI: 10.1081/MC-120006451 1532-1797 (Print); 1532-9038 (Online)Copyright # 2002 by Marcel Dekker, Inc. www.dekker.com

*Corresponding author. E-mail: [email protected] address: Department of Preventive Medicine & Environmental Health, University ofKentucky, Medical Center, Lexington, KY 40507.

JOURNAL OF MACROMOLECULAR SCIENCEPart C—Polymer Reviews

Vol. C42, No. 3, pp. 307–354, 2002

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5.10. Chitosan/Polyether Hydrogels . . . . . . . . . . . . . . . . . . . . . . . . . . 321

5.11. Polysaccharide Chitosan/PEO–PPO Nanoparticles . . . . . . . . . . . 321

6. Applications of Chitin and Chitosan . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 322

6.1. Biomedical Applications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 322

6.2. Applications in Chromatographic Separations. . . . . . . . . . . . . . . 331

6.3. Photography . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 331

6.4. Food and Nutrition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 332

6.5. Water Engineering . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 332

6.6. Textile Industry . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 334

6.7. Cosmetics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 344

6.8. Paper Industry . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 345

6.9. Engineering Applications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 345

7. Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 345

References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 345

ABSTRACT

Chitin and chitosan are versatile polymers, where the interest in chitosanis due to the large variety of useful forms that are commercially availableor can be made available. Chitin basically is obtained from prawn/crabshells; chemical treatment of chitin produces chitosan. This articlesurveys applications of chitin and chitosan in various industrial andbiomedical fields.

Key Words: Chitin; Chitosan; Industrial; Biomedical; Applications

1. INTRODUCTION

Chitin is a white, hard, inelastic, nitrogenous polysaccharide found inthe outer skeleton of insects, crabs, shrimps, and lobsters, and in the internalstructure of other invertebrates. The waste of these natural polymers is amajor source of surface pollution in coastal areas. Chitin is the most abun-dant natural and acetylamino polysaccharide and estimated to be producedannually almost as much as cellulose.[1] It has become of great interest notonly as an under-utilized resource, but also as a new functional material ofhigh potential in various fields, and the recent progress in chitin chemistry isquite noteworthy.

Chitin (I) is a cellulose (II)-like polysaccharide of b-linked 2-acet-amido-2-deoxy-D-glucose residues, which exhibits various different propertiesfrom cellulose, whose hydroxyl groups in the C2 position are substitutedwith acetamide groups (–NH–CO–CH3) in chitin. Similarly, chitosan (III) isa linear polymer of a (1!4)-linked 2-amino-2-deoxy-D-glucopyranose,easily derived from chitin (I) by deacetylation (Eq. 1).

308 DUTTA, RAVIKUMAR, AND DUTTA

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ð1Þ

As most polymers are synthetic materials, their biocompatibility andbiodegradability are much more limited than those of natural polymerssuch as cellulose, chitin, chitosan, and their derivatives. While they arenaturally abundant and renewable, a limitation exists in their reactivityand processability.[2,3] In this respect, chitin and chitosan are recommendedas suitable resource materials, since these natural polymers have excellentproperties such as biodegradability, biocompatibility, non-toxicity, andadsorption. The reaction of chitosan is considerably more versatile thancellulose due to the presence of NH2 groups.

Today much attention is paid to chitosan as a potential polysaccharideresource.[4] Various efforts have been made to prepare functional derivativesof chitosan by chemical modifications,[5–8] and only few of them are found todissolve in conventional organic solvents.[9,10] Chitosan is only soluble inaqueous solutions of some acids, and some selective N-alkylidinations[5,6]

and N-acylations[7,8] have also been attempted. Although several water-soluble[11,12] or highly swelling[8,13] derivatives are obtained, it is difficult todevelop the solubility in common organic solvents by these methods.Modification of the chemical structure of chitin and chitosan to improvethe solubility in conventional organic solvents has been reviewed by manyauthors.[1–4,14–23] On the other hand, only a few reviews have been reportedon biomedical applications of chitin/chitosan,[24–33] and no comprehensivereview has yet been published covering the entire range of applications. Thisreview covers the literature from 1926 to 2000 dealing with properties,processing, and applications of chitin and chitosan.

2. PROCESSING OF CHITIN AND CHITOSAN

Chitin is easily obtained from crab or shrimp shells and fungal mycelia.Chitin production is associated with food industries such as shrimp canning.

CHITIN AND CHITOSAN 309

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The production of chitosan–glucan complexes is associated with fermentationprocesses, such as those for the production of citric acid fromAspergillus niger.The processing of the fungal waste from A. niger,Mucor rouxii, and strepto-myces consists of an alkali treatment that yields chitosan–glucan complexes.The alkali removes the protein and deacetylates chitin simultaneously.Depending on the alkali concentration, some alkali-soluble glucans are alsoremoved.[34]

The processing of crustacean shells mainly involves the removal of pro-teins and the dissolution of calcium carbonate that is present in crab shells inhigh concentrations. The resulting chitin is deacetylated in 40% sodiumhydroxide at 120�C for 1–3 hr. This treatment produces 70% deacetylatedchitosan. Complete deacetylation can be obtained by repeating the steps, asshown in Fig. 1.


Figure 1. Conversion of chitin to chitosan.

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3. ECONOMIC ASPECTS

The production of chitin and chitosan is currently based on crab andshrimp shells discarded by the canning industries in Oregon, Washington,Virginia, and Japan, and by various finishing fleets in the Antarctic. Severalcountries possess large unexploited crustacean resources, e.g., Norway,Mexico, and Chile.[35] The production of chitosan from crustacean shellsobtained as a food industry waste is economically feasible, especially if itincludes the recovery of carotenoids. The shells contain considerable quanti-ties of astaxanthin, a carotenoid that has so far not been synthesized, andwhich is marketed as a fish food additive in aquaculture, especially for salmon.

To produce 1 kg of 70% deacetylated chitosan from shrimp shells,6.3 kg of HCl and 1.8 kg of NaOH are required in addition to nitrogen,process water (0.5 t), and cooling water (0.9 t). Important items in estimatingthe production cost include transportation, which varies depending on laborand location. In 1984 the worldwide price of chitosan was ca. US$ 10.00/kg,and the current price is ca. US$ 6.00/kg.

During the past decades, the Central Institute of Fisheries Technology,Kerala, India initiated research on chitin and chitosan. In 1978, Madhavanand Nair[36] were the first to report that dry prawn waste and dry squillacontained 23% and 15% chitin, respectively. In 1986, Madhavan et al.[37]

reported that the chitinous solid waste fraction of the average Indian landingof shellfish ranged from 60,000 to 80,000 tons. Chitin and chitosan are nowproduced[38] commercially in India, Poland, Japan, the United States,Norway, and Australia. A considerable amount of research is in progresson chitin/chitosan all over the world, including India, to tailor and impart therequired functionalities to maximize its utility.

4. PROPERTIES OF CHITIN AND CHITOSAN

Most of the naturally occurring polysaccharides, e.g., cellulose,dextrin, pectin, alginic acid, agar, agarose and carragenas, are natural andacidic in nature, whereas chitin and chitosan are examples of highly basicpolysaccharides. Their properties include solubility in various media, solu-tion, viscosity, polyelectrolyte behavior, polyoxysalt formation, ability toform films, metal chelations, optical, and structural characteristics.[39]

Although the b(1!4)-anhydroglucosidic bond of chitin is also present incellulose, the characteristic properties of chitin/chitosan are not shared bycellulose.[40] Chitin is highly hydrophobic and is insoluble in water and mostorganic solvents. It is soluble in hexafluoroisopropanol, hexafluoroace-tone,[41] and chloroalcohols in conjunction with aqueous solutions of mineralacids[39] and dimethylacetamide (DMAc) containing 5% lithium chloride


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(LiCl).[42] Recently, the dissolution of chitosan in N-methyl morpholine-N-oxide (NMMO)/H2O has been reported by Dutta et al.[43a,b] The hydrolysisof chitin with concentrated acids under drastic conditions produces the rela-tively pure amino sugar, D-glucosamine.

Depending on the extent of deacetylation, chitin contains 5% to 8%(w/v) nitrogen, which is mostly in the form of primary aliphatic aminogroups as found in chitosan. Chitosan undergoes the reactions typical ofamines, of which N-acylation and Schiff reactions are the most important.Chitosan glucans are easily obtained under mild conditions, but it is difficultto obtain cellulose glucans.

N-Acylation with acid anhydrides or acyl halides introducesamido groups at the chitosan nitrogen. Acetic anhydride affords fullyacetylated chitins. Linear aliphatic N-acyl groups higher than propionylpermit rapid acetylation of the hydroxyl groups in chitosan. Highlybenzoylated chitin is soluble in benzyl alcohol, dimethyl sulfoxide (DMSO),formic acid, and dichloroacetic acid. The N-hexanoyl, N-decanoyl, andN-dodecanoyl derivatives have been obtained in methanesulfonic acid.[44,45]

Chitosan forms aldimines and ketimines with aldehydes and ketones,respectively, at room temperature. Reaction with ketoacids followed byreduction with sodium borohydride produces glucans carrying proteic andnon-proteic amino acid groups. N-Carboxymethyl chitosan is obtained fromglyoxylic acid. Examples of non-proteic amino acid glucans derived fromchitosan are the N-carboxybenzyl chitosans obtained from o- and p-phthal-aldehydic acids.[46,47]

Chitosan and simple aldehydes produce N-alkyl chitosan upon hydro-genation. The presence of the more or less bulky substituent weakens thehydrogen bonds of chitosan; therefore, N-alkyl chitosans swell in water inspite of the hydrophobicity of alkyl chains. They retain the film-formingproperty of chitosan.[48]

5. DERIVATIVES OF CHITIN AND CHITOSAN

Chitosan may readily be derivatized by utilizing the reactivity of theprimary amino group and the primary and secondary hydroxyl groups.Glycol chitin, a partially o-hydroxyethylated chitin, was the first derivativeof practical importance; other derivatives[49] are as shown in Table 1.

Derivatives of chitin may be classified into two categories; in each case,the N-acetyl groups are removed, and the exposed amino function then reactseither with acyl chlorides or anhydrides to give the group NHCOR, or ismodified by reductive amination to NHCH2COOH. Of greatest potentialimportance are derivatives of both types formed by reaction with bi- orpolyfunctional reagents, thus carrying sites for further chemical reac-tion.[50,51] In practice, such reactions are carried out on native chitin or on


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Table 1. Chitin Derivatives and Their Uses[49]

Derivatives Examples Potential Uses

N-Acylchitosans Formyl, acetyl, propionyl butyryl, hexa-noyl, acetanoyl, decanoyl, dodecanoyl,tetradecanoyl, lauroyl, myristoyl, palmi-toyl, stearoyl, benzoyl, monochloroacetoyl,

dichloroacetyl, trifluoroacetyl, carbamoyl,succinyl, acetoxybenzoyl, 5-methyl pyrroli-dinone

Textiles, membranes, andmedical aids like wounddressings

N-Carboxyalkyl

(aryl) chitosans

N-Carboxybenzyl, glycine glucan (N-car-

boxymethyl chitosan), alanine glucan, phe-nylalanine glucan, tyrosine glucan, serineglucan, glutamic acid glucan, methionine

glucan, leucine glucan

Chromatographic media

and metal ion collection,functional cosmetics ingre-dient in hydrating creams

N-Carboxyacylchitosans

From anhydrides such as maleic, itaconic,acetylthiosuccinic, glutaric, cyclohexane1,2-dicarboxylic, phthalic, cis-tetra hydro-

phthalic, 5-norbornene, 2,3-dicarboxylicdiphenic, salicylic, trimellitic, pyromelliticanhydride, N,N-dicarboxymethyl

Use for collection of tracetransition metal ions toform films or membranes

and to prepare cosmeticproducts

O-Carboxyalkyl

chitosans

O-Carboxymethyl, crosslinked O-carboxy-

methyl

Molecular sieves, viscosity

builders, and metal ioncollection

Sugar derivatives 1-Deoxygalactic-1-yl-, 1-deoxyglucit-1-yl-,1-deoxymelibiit-1-yl, 1-deoxylactit-1-yl, 1-deoxylactit-1-yl-4(2,2,6,6-tetramethyl-pipe-

ridine-1-oxyl)-, 1-deoxy-60-aldehydolactit-1-yl-, 1-deoxy-60-aldehydomelibiit-1-yl, cel-lobiit-1-yl-chitosans, products obtained

from ascorbic acid

Expected to be useful as anovel type of antimicro-bial agent

Metal ion chelates Palladium, copper, silver, iodine Catalyst, photography,health products, andinsecticides

Semisynthetic

resins of chitosan

Copolymer of chitosan with methyl

methacrylate, polyureaurethane, poly(amideester) acrylamide–maleic anhydride

Textiles

Naturalpolysaccharide

complexes,quaternarychitosan salts

Chitosan glucans from various organisms Flocculation and metalion chelation

Miscellaneous Alkyl chitin, benzyl chitin, di-O-butyryl

chitin

Intermediate serine pro-

tease purification, used asdrug carrier, textiles, pre-cursor of various chitinbiomaterials

(continued )

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incompletely de-N-acetylated chitosan, so that the resulting polymer containsthree types of monomeric units (IV).

These polyampholytes are particularly effective in removing metalcations from dilute solutions. Chitosan itself chelates metal ions, especiallythose of transition metals, and also finds application as a matrix for immo-bilization of enzymes.[49]

Special attention has been given to the chemical modification of chitin,since it has the greatest potential to be fully exploited. Reactions with purechitin have been carried out mostly in the solid state, owing to the lack of


Table 1. Continued

Derivatives Examples Potential Uses

Hydroxybutyl chitin, hydroxyalkyl chito-sans, cyanoethyl chitosan

Desalting, filtration, dialy-sis, and insulating papers

Glycol chitosan Enzymology, dialysis, andspecial papers

Glutaraldehyde chitosan Enzyme immobilization

Linoleic acid–chitosan complex Food additive and anti-

cholesterolemic

Uracylchitosan, theophylline chitosan,adenine chitosan, chitosan salts of acid,polysaccharides, chitosan streptomycin,N-cyclohexane chitosan, 2-amido-2,6-

diaminoheptanoic acid chitosan

Chemically crosslinked glycine glucan Suitable for collection ofcarrier-free radioisotopes

Chitosan ascorbate ketimine and itsreduced form

Used to treat parodonto-pathies

Imidazole chitosan Proposed for treatment of

bone lesions

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solubility in ordinary solvents. A 50% deacetylated chitin has been found tobe soluble in water.[52,53]. This water-soluble form of chitin is a useful startingmaterial for its smooth modifications, through various reactions in solutionphase.

5.1. Chitin Derivatives of Polysaccharides and Polypeptides

Polysaccharide/polypeptide hybrid materials, chitin derivatives havingpolypeptide side chains, were prepared by the graft copolymerization ofg-methyl L-glutamate N-carboxy anhydride (NCA) onto the water-solubleform of chitin in water/ethyl acetate.[1] Although NCA is very susceptibleto hydrolysis, the N-acetyl groups of chitin react with NCA smoothly insolution, producing the resultant graft copolymer (V), (Eq. 2). After freeze-drying, and hydrolysis in the presence of Na2CO3, the white powdery graftcopolymer (VI) was obtained (Eq. 3).

ð2Þ

ð3Þ

5.2. Tosyl and Iodo Chitins

Derivatives with tosyl and iodo groups add reactivity and bulkinessto the chitin macromolecules. The resulting derivatives are soluble reactiveprecursors for further regioselective modifications, which can be carriedout exclusively in homogeneous solution.[15]

Chitin dissolved in aqueous sodium hydroxide was treated with chloro-form solution of tosyl chloride, where the reaction was interfacial betweenthe two immiscible solutions and depends on the rate of stirring. With vigor-ous stirring, the substitution was quite efficient and reproducible at 0�C.


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The tosyl chitins (VII) thus obtained were soluble and reactive precursorswere subjected to the conversion to iodo chitins. The iodo substitution in thepresence of excess sodium iodide in DMSO takes place easily due to the highsolubility of both tosyl and iodo chitins. The resulting iodo chitins (VIII)were isolated by pouring the mixtures into acetone (Eq. 4). When the reac-tions were carried out above 100�C, the products were light tan to brown.At relatively low temperatures, e.g., at 75–85�C, colorless products couldbe prepared in high yield.[14,15]

ð4Þ

5.3. Ether-Type Chitin Derivatives

Novel ether-type chitin derivatives were synthesized by reacting alkalisalts of chitin with 1-chloropropane, propylene oxide, and 3-chloro-1,2-pro-panediol to prepare propyl chitin (PPC) (IX), hydroxypropyl chitin (HPC)(X), and dihydroxypropyl chitin (DHPC) (XI), respectively (Eqs. 5–7). Thesubstituents were introduced primarily at the C6 position of the glucosamineunit in chitin, with a degree of substitution of approximately 0.3–0.5. Thethree chitin derivatives are soluble in weakly acidic aqueous solutions andDHPC even in pure water.[54–60]


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ð5Þ

ð6Þ

ð7Þ

5.4. Mixed Ester-Type Chitin Derivatives

One of the ways of enhancing the solubility of chitin was the introduc-tion of bulky acyl residues into the polymer.[16] One part powdered chitin wasadded to a mixture of four parts methanesulfonic acid and six partscarboxylic acid anhydrides.

In the case of mixed esters, the products were obtained by varying theamount of butyric anhydride and acetic anhydride. The reaction mixture wasstirred for 2–3 hr at 0–5�C and stored at 20�C overnight to complete thereaction. The products were precipitated in large quantities of crushed ice,


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filtered off, and washed with distilled water (Eq. 8). The samples were sub-sequently suspended in distilled water, neutralized with ammonia water, andboiled for a few minutes to neutralize any traces of remaining acids. The acylchitins or mixed esters (XII) were filtered, washed with distilled water, anddried in vacuum. The acetyl chitin is soluble only in acidic solvents, such asformic acid, dichloroacetic acid, and methanesulfonic acid, while butyrylchitin is reported to be soluble in methanol, ethanol, dimethylformamide(DMF), dioxin, acetone, tetrahydrofuran, and in acidic solvents such asformic acid.[16]

ð8Þ

5.5. Regioselective Chlorination of Chitin

Sakamoto et al.[61] reported chlorination of chitin with equimolarmixtures of N-chlorosuccinimide and triphenyl phosphine under homo-geneous conditions in a 5% (w/v) solution of LiCl in DMAc at 70–85�C.The report reveals that polymer chain scission took place to some extent,especially when the chlorination was carried out at higher temperatures withhigher concentrations of reagents Carbon-13 nuclear magnetic resonance.(13C-NMR) spectroscopy of the chlorinated products and gas chromato-graphic-mass spectrometric (GC-MS) analysis of their hydrolyzates, bothas trifluoroacetyl derivatives, showed that the chlorine substitution tookplace regioselectively at C6. Tseng et al.[62] reported the possibility of bromi-nation of regenerated chitin in a similar fashion.

5.6. N-Acyl, N-Arylidene, and N-Alkylidene Chitosan Gels

Hirano[20] reported that the amino group at C2 is more reactive towardselectrophiles than are the hydroxyl groups at C3 and C6 in the amino-2-deoxy-D-glucoside residue of chitosan. Chitosan is soluble in aqueous aceticacid solution, and the solution is miscible with methanol. In this solution,N-substitution occurs selectively in reaction with carboxylic acids and


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aldehydes, to produce N-acyl, N-arylidene, and N-alkylidene derivatives(XIII), respectively.

5.7. Maleilated Chitosan and Acrylamide Copolymers

The synthesis of crosslinked copolymers of maleilated chitosan andacrylamide was reported by Berkovich et al.[54] Hydrophilic three-dimen-sional polymers find application as column-packing material for gel andbiospecific chromatography, as well as in the immobilization of enzymes.Typical polymers used for these purposes are acrylamide, glycolmethacrylate,agar and its derivatives, dextrans, and gels based on cellulose. The three-dimensional structures and gels based on chitosan are obtained either bycrosslinking chitosan with bifunctional aldehydes and anhydrides of acids,or as a result of the formation of hydrogen bonds and the physical interac-tions between substituents in chitosan chains.[13,53,55] Recently, Sridhari andDutta[63] used this copolymer for color removal from textile effluents.

An efficient procedure for the preparation of network polymers of chi-tosan (XIV) is achieved by copolymerizing the double bonds of substituentsin chitosan chains and vinyl monomer. The double bonds were introducedinto the chitosan molecule by acylating it with maleic anhydride, and acry-lamide was used as the vinyl comonomer.


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5.8. Chitosan/Calcium Alginate Beads

Huguet et al.[64] reported the use of chitosan and calcium alginate forthe mild encapsulation of hemoglobin. The first procedure consisted ofadding dropwise a hemoglobin-containing sodium alginate mixture in a chi-tosan solution, then hardening the interior of capsules thus formed, in thepresence of CaCl2. In the second method, the droplets were directly pulled offin a chitosan–CaCl2 mixture. Both procedures led to beads containing a highconcentration in entrapped hemoglobin, as more than 90% of the initialconcentration was retained inside the beads provided that the chitosan con-centration was great enough. The molecular weight of chitosan and the pH ofits solution (2, 4, or 5.4) had only a slight effect, the best retention beingobtained with beads prepared at pH5.4. The best retention during storage inwater was obtained with beads prepared with high molecular weight chitosansolution at pH2. Ionic interactions existing between alginate and chitosan atpH5.4 and 2.0 are shown as (XV) and (XVI), respectively.


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5.9. Calcium Carbonate–Chitosan Composites

Zhang and Gonsalves[65] reported the crystal growth of calcium carbo-nate on a chitosan substrate using a supersaturated calcium carbonate solu-tion at different concentrations of polyacrylic acid (PAA) as an additive viabiomimetic processing. Polyacrylic acid was introduced to the system forbiomimetic growth of calcium carbonate crystals on the chitosan film surface,and protonated nitrogen and carboxylate anions were created on the chitosanfilm surface. Nucleation was initiated from these charges. Nucleation andcrystallization occurred at low concentrations of PAA, and crystals coveredthe whole film with a spherical morphology.

5.10. Chitosan/Polyether Hydrogels

Hydrogels have been widely used in controlled-release systems.[66a,b]

Hydrogels which swell and contract in response to external pH are beingexplored.[67–69] Peng et al.[70,71] reported the pH sensitivity, swelling kinetics,and modeling drug release properties of semi-IPN hydrogels from chitosanand polyether N330.

5.11. Polysaccharide Chitosan/PEO–PPO Nanoparticles

Hydrophilic nanoparticle carriers have important potential applicationsfor the administration of therapeutic molecules. These recently developedhydrophobic–hydrophilic carriers require the use of organic solvents fortheir preparation and have a limited protein-loading capacity. To overcomethese limitations, a new approach was described for the preparation ofnanoparticles (XVII) solely from hydrophilic polymers[72] (Eq. 9). The pre-paration technique, based on an ionic gelation process, is extremely mild andinvolves the mixture of two aqueous phases at room temperature. One phasecontains the polysaccharide chitosan (XVIII) and a diblock copolymer ofethylene dioxide and propylene oxide (PEO–PPO) (XIX), and the other con-tains the polyanion sodium triphosphate (TPP) (XX) of nanoparticles. Themixture can be conveniently modulated by varying the ratio chitosan(CS)/PEO–PPO.

ð9Þ


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In order to explore fully the high potential of chitin it is necessary toestablish efficient modification methods. Chemical modifications of chitin are,however, generally difficult owing to the lack of solubility, and the reactionsunder heterogeneous conditions are accompanied by various problems such asa low extent of reaction, difficulty in regioselective substitution, structuralambiguity of the products, and partial degradation due to severe reactionconditions. Recently, Kurita[73] has developed novel modes of modificationreactions of chitin to make possible sophisticated molecular designs, includingbiodegradability and bioactivity relations of the derivatives, and applications.

6. APPLICATIONS OF CHITIN AND CHITOSAN

The interest in chitin originates from the study of the behavior andchemical characteristics of lysozyme, an enzyme present in human bodyfluids. It dissolves certain bacteria by cleaving the chitinous material of thecell walls.[74] A wide variety of medical applications for chitin and chitinderivatives have been reported over the last three decades.[75–78] It has beensuggested that chitosan may be used to inhibit fibroplasia in wound healingand to promote tissue growth and differentiation in tissue culture.[79]

The poor solubility of chitin is the major limiting factor in its utilization,and the investigation of its properties and structure. Despite these limita-tions, various applications of chitin and modified chitins have been reportedin the literature, e.g., as raw material for man-made fibers.[80] Fibers made ofchitin and chitosan have been useful as absorbable sutures and wound-dres-sing materials.[81–85] These chitin sutures resist attack in bile, urine, andpancreatic juice, which are difficult with other absorbable sutures.[85] It hasbeen claimed that wound dressings made of chitin and chitosan fibers[82]

accelerate the healing of wounds by up to 75%. Apart from their applicationsin the medical field, chitin and chitosan fibers have potential applicationsin waste water treatment, where the removal of heavy metal ions bychitosan through chelation has received much attention.[81,86–89] Their usein the apparel industry, with much larger scope, could be a long-termpossibility.[90–93]

6.1. Biomedical Applications

The design of artificial kidney systems has made possible repetitivehemodialysis and sustaining the life of chronic kidney failure patients.Chitosan membranes have been proposed as an artificial kidney membranebecause of their suitable permeability and high tensile strength.[94–97] Themost important part of the artificial kidney is the semipermeable membrane,so far made from commercial regenerated cellulose and cuprophane. Since


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the primary action of the cellulose membrane is that of a sieve, there is littleselectivity in the separation of two closely related molecules.[98] These novelmembranes need to be developed for better control of transport, ease offormability, and inherent blood compatibility.

A series of membranes prepared from chitin and its derivativesimproved dialysis properties.[99,100] One of the most serious problems ofusing these artificial membranes is surface-induced thrombosis, where hepar-ization of blood is needed to prevent clotting, and people who are liable tointernal hemorrhage can be dialyzed only at great risk. Hence the mostchallenging problem still to be solved is the development of membraneswhich are inherently blood compatible. From this point of view, chitosanis hemostatic, i.e., causes clots.

6.1.1. Blended Chitosan Membranes

Albumin, gelatin, and collagen are being widely used for modifying thepolymeric substrates to improve their blood compatibility due to their pas-sive nature in attaching platelets.[99–101] It appears that these protein-blendedmembranes improve permeability to small molecules like urea, creatinine,uric acid, and glucose, compared to the standard membrane of bare chitosan.These membranes also inhibit the passage of large molecules like albumin(Mw�69 000). Albumin-blended membranes have similar permeability as thatof other protein blended membranes for small molecules when dialyzed for6 hr from various isolated permeants.[102]

Collagen is easily degraded in biological media, and depending on thecircumstances, this can be considered either as an advantage or a drawback.A method often chosen to slow down the biodegradation of natural polymersconsists of crosslinking them by various processes[103,104] in order to hinderthe mechanism of recognition by the hydrolytic enzymes specific to thesepolymers. Chitosan in interaction with collagen can affect the mechanismof hydrolysis by collagenase in two ways: by inhibition of the process ofrecognition, or by direct interaction with the enzyme. Chitosan is indeedknown to inhibit some proteases.[105]

In 1993, Taravel and Domard[106] were the first to report the interactionbetween atelocollagen and fully deacetylated chitosan. Their investigationshowed that a purely electrostatic complex is formed in which all the chitosancharges are involved. The process is largely hindered by gel formation incollagen solutions at high pH, and an encapsulation of microgels of collagenis suggested. The conformation of collagen in the complex is largely modifiedin the solid state. Further studies show that in some circumstances anothertype of complex can be obtained.[106]

Zhang et al.[107] reported on the properties of collagen and chitosancomposites using formaldehyde as crosslinking agent. From their studies it


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was clear that the chitosan network can interpenetrate into the collagen net-work, and that the mechanical and swelling properties were enhanced. Theyreported that the crosslinking conditions, such as time, concentration, andpH, can affect the swelling degree and tensile strength of these composites.

Fibrinogen adsorption kinetics and platelet attachment to variousprotein-blended chitosan membranes were also investigated to demonstratetheir blood compatibility.[30] The adhesion of platelets to protein-blendedchitosans can be modified to variable degrees when tyrode-washed calf plate-lets are exposed to those membranes. Albumin-blended membrane demon-strates a maximum reduction in platelet adhesion in comparison to othermembranes studied.[30]

It is well understood that the nature of the surface-bound protein canalter the subsequent platelet adhesion and thrombosis.[99] Hence, reducedfibrinogen binding to certain protein-blended membranes may be one ofthe parameters for reduced platelet–surface binding via the modulation offibrinogen receptors. Thus, it appears, albumin-blended chitosan membraneshave superior permeability and blood compatibility compared to chitosan orstandard cellulose membranes.

6.1.2. Enzyme Immobilization

One of the most important applications of chitin is the immobilizationof enzymes and whole cells.[108] A limited number of enzymes are of practicalinterest for industrial needs,[109] and some of the enzymes that have beenimmobilized are given in Table 2.

There are many methods of immobilization of enzymes, such asentrapment and absorption, fixing by crosslinking chitosan solutions and


Table 2. Enzymes/Cell Immobilized on Chitin and Its Derivatives and ProposedUses[38]

Enzyme/Cells Proposed Uses

AMP deaminase AMP to IMPAmylase diastase and glucoamylase Starch and glycogen to D-glucose

a-Chymotripsin Plastein synthesisb-D-Galactosidase Hydrolysis of lactoseD-Glucose isomerase D-glucose to D-fructose, preparation of

D-gluconic acid

b-D-Glucosidase Hydrolysis of cellobioseLysozyme, Pronase, Subtilisin, andTripsin

Preparation of pharmaceuticals, cosmetics,and food protein

Urease Urea to ammonia and CO2

E. coli cells, Nitrosomonaseuropea cells

Synthesis of L-tryptophan, nitrification ofwaste water

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crosslinking insolubilized chitosan.[110] The most common method of fixingenzymes to chitosan is by using crosslinking reagents such as dialdehydes(e.g., glyoxal and glutaraldehyde). The amino group of chitosan and theenzyme forms aldimine bonds with the dialdehyde and is reduced bysodium borohydride or sodium cyanoborohydride to form stable gels ofactive immobilized enzymes.[110–112]

In order to improve the mechanical stability and density with highresistance to attrition and compression, an inorganic support such as silicagel is coated with chitosan and subsequently used for the immobilization ofenzymes. Such a system has all the advantages of support, such as flexibility,elasticity, and high coupling efficiency. Enzyme immobilization can also bedone on porous surfaces of chitosan beads, giving good cell carriers, becausesurface area, density, and compressive strength are not changed during ster-ilization of these beads.[113]

The advantages of using immobilized enzymes are: the enzymic reactioncan be stopped at any desired time, a small amount of enzyme is sufficient forlarge amounts of substrates, the enzyme is not lost in the product, there is noinhibition to limit the extent of the reaction, there is no self-digestion of theenzyme, enzymes from pathogenic organisms can be used, and a batch pro-cess can be made into a continuous process.

In recent years the practice of using non-growing whole or lysed micro-bial cells, rather than purified enzymes, has gained in popularity. Advantagesof immobilized cells are simple product isolation and repeated use in a con-tinuous process.[114]

6.1.2.1. Bioactive Complex Immobilized Albumin-BlendedChitosan Membranes

While chitosan membrane is thrombogenic, N-acetyl and N-hexanoylchitosan membranes are more non-thrombogenic. So attempts were made toimprove the blood compatibility of chitosan membranes via surface modifi-cations with least interference to their permeability properties.[115–118]

A complex having fibrinolytic, anticoagulant, and antiplatelet activitieswas prepared by the modification of urokinase with antithrombin-III,methyldopa, and polyglycolethylene. A non-thrombogenic, albumin-blendedchitosan membrane was derived by immobilizing this bioactive complex viacarbodiimide.[119] This novel membrane demonstrated good permeability forsmall molecules and showed a dramatic reduction in platelet attachment.

It appears that membranes carrying immobilized drug complexes mayhave wider applications, such as in the hemodialysis of patients with hyper-tension, as well as for improved permeability and blood compatibility. Thismay also be useful for patients who are liable to internal hemorrhage onheparinization, which may reduce or prevent the use of heparin during


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dialysis. These membranes have to be sterilized before clinical use. So, thevariation in permeability, mechanical, and surface properties was studied dueto different sterilization techniques on chitosan membranes.[30]

Reports are available regarding the permeability of various moleculesthrough chitosan membranes[30,120,121] which contain different immobilizedand modified biomolecules, such as:

1. Bioactive molecules immobilized to liposome-modified, albumin-blended chitosan membrane.

2. Phosphoryl choline bilayer immobilized on albumin-blendedchitosan membrane.

3. Chondratin sulfate and phosphoryl choline immobilized onchitosan surfaces treated with glow discharge and albumin.

Various modifications are suggested to dramatically improve theblood compatibility of chitosan membrane without altering its superiorpermeability. The development of a smaller artificial kidney may be possibleif these approaches are successful.

6.1.3. Chitosan as an Artificial Skin

Individuals who suffer extensive losses of skin are acutely ill and areexposed to massive infection or to severe fluid loss. Patients who survive theseearly symptoms must often cope with problems of rehabilitation arising fromdeep, disfiguring scars and crippling contractures. Malette et al.[122] studiedthe effect of treatment with chitosan and saline solution on healing andfibroplasia of wounds made by scalpel insersions in skin and subcutaneoustissue in the abdominal surface of dogs. Yannas and Burke[123] proposed adesign for artificial skin, applicable to long-term chronic use, and focused ona non-antigenic membrane which performs as a biodegradable template forthe synthesis of neodermal tissue. It appears that chitosan polysaccharideshaving structural characteristics similar to glycosamino glycans can beconsidered for developing such a substratum for skin replacement.[123–126]

6.1.4. Chitin and Chitosan-Based Dressings

Chitin and chitosan have many distinctive biomedical properties andhave been applied in many different industrial areas. However, chitin-basedwound-healing products are still at the early stage of research.[127]

A dressingmade of a chitosan–gelatin complex was developed by Sparkesand Murray.[128] The procedure involves dissolving chitosan in water in thepresence of a suitable acid, maintaining the pH of the solution at about 2–3,followed by addition of gelatin dissolved in water. The weight ratio of chitosan


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and gelatin is 3:1 to 1:3. To reduce the stiffness of the resulting dressing,plasticizers such as glycerol and sorbitol are added into themixture. A dressingfilm was cast from this solution on a flat plate and dried at room temperature.It was claimed that, in contrast to conventional biological dressings, thisexperimental dressing, displayed excellent adhesion to subcutaneous fat.

Nara et al.[129] patented a wound dressing comprising a non-woven fabriccomposed of chitin fibers made by a wet spinning technique. In one of theexamples, chitin powder was ground to 100 mesh and treated in 1N HCl for1 hr at 4�C. It was then heated to 90�C where it was treated for 3 hr in a 3%NaOH solution to remove calcium and protein in the chitin powder, and rinsedrepeatedly followed by drying. The resultant chitin had a viscosity of 256 cP at30�C when it was dissolved in a DMAc solution containing 8% LiCl (w/v) toform a 0.2% solution (w/v). After filtering and holding to allow defoamingto occur, the dope was transported to a nozzle under pressure and extrudedinto butanol at 60�C. The chitin was coagulated, collected, and the resultantstrand was rinsed with water and dried to obtain a filament of 0.74 dtex with astrength of 2.8 g/d. The filaments were then cut into staple fibers. Non-wovendressings were made by using polyvinyl alcohol as a fibrous binder.

In 1988, Kifune et al.[130] developed a new wound dressing, composed ofchitin non-woven fabric, which has been proved to be beneficial in clinicalpractice. Kim and Min[131] have developed a wound covering material frompolyelectrolyte complexes of chitosan with sulfonated chitosan. It isproposed that wound healing is accelerated by the oligomers of degradedchitosan by tissue enzymes, and this material was found to be effective inregeneration of the skin tissue in the wound area.

Biagini et al.[132] developed a chitosan derivative, N-carboxybutylchitosan, used in dressings to treat plastic surgery donor sites. The solutionof N-carboxybutyl chitosan was dialyzed and freeze-dried to produce a softand flexible pad, which was sterilized and applied to the wound. Theyreported that this dressing could promote ordered tissue regenerationcompared to control donor sites. Further, the dressing may show betterhistoarchitectural order and better vascularization. While the absence ofinflammatory cells was observed at the dermal level, fewer aspects ofproliferation of the malpigihan layer were reported at the epidermal level.

Researchers at the British Textile Technology Group (BTTG) patenteda procedure for making chitin-based fibrous dressing.[133–136] In their methodthe chitin/chitosan fibers were not made by the traditional fiber-spinningtechnique, and the raw materials were not derived from shrimp shell, butinstead from microfungi. Their procedure can be summarized as follows:

I. Microfungal mycelia preparation from culture of Mucor mucedogrowing in a nutrient solution.

II. Culture washing and treatment with NaOH to remove protein andprecipitate chitin/chitosan.


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III. Bleaching and further washing.IV. Preparation of the dispersion of the fibers using paper-making

equipment.V. Filtration and wet-laid matt preparation; mixing with other fibers

to give mechanical strength.

This is a novel method which uses non-animal sources as the rawmaterial, and the resulting microfungal fibers are totally different from thenormal spun fibers. They have highly branched and irregular structures.The fibers are unmanageably brittle when they are allowed to dry, and aplasticizer has to be associated with the whole process. A wet-laid matt isthe basic product.

Muzzarelli[137] recently introduced another chitosan derivative whichwas believed to be very promising in medical applications. This derivativeis 5-methylpyrrolidinone chitosan, which was made by a series of chemicalreactions. It was claimed that this polymer is compatible with other polymersolutions, including gelatin, poly(vinyl alcohol), poly(vinyl pyrrolidone), andhyaluronic acid. The advantages claimed by the inventor include healing ofwounded mensical tissues, healing of decubitus ulcers, depression of capsuleformation around prostheses, limitation of scar formation, and retractionduring healing. Some wound dressing samples were also prepared from theaqueous solution of this 5-methylpyrrolidinone chitosan, which was dialyzedand laminated between stainless steel plates and freeze-dried to yield fleeces.It was also claimed that this material could be fabricated into many differentforms, such as filaments, non-woven fabrics, etc. Once applied to a wound,5-methylpyrrolidinone chitosan becomes immediately available in the formof oligomers produced under the action of lysozyme.

Another chitin derivative, dibutyrylchitin, was spun into a fiber recentlyby a research group[138] at the University of Leeds. Dibutyryl chitin wasprepared by treatment of krill chitin with butyric anhydride at 25–30�C inthe presence of perchloric acid as a catalyst. Samples of polymers with themolecular weights high enough to form fibers were obtained, and dibutyrylchitin fibers were made by a simple method of dry-spinning in acetone. Theresults showed that the fibers had tensile properties similar to or better thanthose of chitin and some chitin derivatives. An attempt to convert dibutyrylchitin fibers to chitin fibers was made. It was claimed that chitin fibers withgood tensile properties could be obtained by alkaline hydrolysis of dibutyrylchitin fibers without destroying the fiber structure. However, no moreinformation was given about the uses of this fiber.

As far as chitin-based commercial wound dressings are concerned, oneproduct (Beschitin�, Unitika) is commerically available in Japan. This is anon-woven fabric manufactured from chitin filaments. At present, very fewcommercial dressings based on chitin or chitosan fiber are available in themarket.


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6.1.5. Opthalmology

Chitosan possesses all the characteristics required for an ideal contactlens: optical clarity, mechanical stability, sufficient optical correction, gaspermeability, partially towards oxygen, wettability, and immunologicalcompatibility. Contact lenses are made from partially depolymerized andpurified squid pen chitosan by spin-casting technology, and these contactlenses are clear, tough, and possess other required physical properties suchas modulus, tensile strength, tear strength, elongation, water content, andoxygen permeability. Antimicrobial and wound-healing properties of chi-tosan, along with excellent film-forming capability, make chitosan suitablefor the development of an ocular bandage lens.[139]

6.1.6. Biodegradable Drug Delivery Systems

The efficiency of drugs would increase enormously if they were directedselectively to their cellular targets, a concept first introduced by Paul Ehrichat the beginning of the twentieth century. However, it is only for the last 30years that the development of natural science has initiated projects in severallaboratories to try to translate this dream into reality. There are several waysof approaching this problem.[140–146]

The applicability of natural polysaccharides such as agar, konjac, andpectin in the design of dosage forms for sustained release has beenreported.[147–149] Despite the medical applications of chitin/chitosan describedabove, they are still utilized in the pharmaceutical field.[41] It is known thatcompounds having a molecular weight lower than 2900 pass through mem-branes derived from chitosan.[150] Since chitin and chitosan do not cause anybiological hazard and are inexpensive, these polymers might be suitable for usein the preparation of dosage forms of commercial drugs.[151–155]

Controlled-release technology emerged during the 1980s as a commer-cially sound methodology (Fig. 2). The achievement of predictable and repro-ducible release of an agent into a specific environment over an extendedperiod of time has many significant merits. The most significant meritwould be to create a desired environment with optimal response, minimumside effect, and prolonged efficacy. This is a relatively new technology andrequires an interdisciplinary scientific approach. Chitin/chitosan controlleddelivery systems are being developed further, and used for a wide variety ofreagents in a number of environments.[72,156–158]

Draget et al.[104] described a procedure for preparing homogeneous chit-osan gels by in situmolybdate crosslinking. The gels are obtained by dispersingsolid MoO3 in a buffered chitosan solution, and the polymer is crosslinked byformation of heavily negatively chargedmolybdate polyoxyanions. The result-ing ionic gels are transparent, thermoirreversible, and can be made at low


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polymer concentrations. Depending on the ionic strength, these gels are able toswell to several times their original size in aqueous solutions.

Chandy and Sharma[159] showed the possibility of modifying the for-mulation to obtain the desired controlled release of the drug in an oralsustained-delivery system. They prepared chitosan beads for oral sustaineddelivery in 2% acetic acid, blowing through nozzles into NaOH–methanolsolution by compressed air. The regenerated porous beads were washed withhot, and then cold, water. Nishimura et al.[160] reported the properties ofthese beads. The in vitro evaluations of nifedipine-loaded chitosan beadswere monitored by ultraviolet (UV) spectrophotometer.

Thacharodi and Rao[161] have developed transdermal propranololhydrochloride (prop-HCl) delivery systems which are controlled by mem-brane permeation. Various chitosan membranes with different crosslink den-sities were used as drug release controlling membranes, and chitosan gel asthe drug reservoir. The physicochemical properties of the membranes havebeen well characterized, and the permeability characteristics of these mem-branes to both lipophilic and hydrophilic drugs have been reported.[162a,b]

A procedure for preparing a homogeneous chitosan gel in NMMO/H2Ohas been developed in the authors’ laboratory for sustained dosages.[43]

Chitosan gel was obtained at 120oC in NMMO/H2O, which is transparentand suitable for sustained dosages. (Caution! NMMO detonates readily at130�C.) The swelling and thermal behavior of the new gelling system havealso been studied by the authors.[163a,b]

6.1.7. Microcapsules/Microspheres Related to Chitosan

Since the introduction of microcapsules by Green et al.[164] in the1950s, interest in the preparation, characterization, and application of


Figure 2. Repeated dose vs. controlled delivery: (a) repeated dose delivery, (b) controlleddelivery.

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microcapsules/microspheres has increased immensely. Syntheses of micro-capsules/microspheres have been widely reviewed.[164–167] Due to the attrac-tive properties and wide applications of chitosan-based microcapsules andmicrospheres, a survey of their preparation, characteristics, and applicationsis very useful.[168–171]

Natural polymeric microcapsules/microspheres are generally manufac-tured via different microencapsulation processes, e.g., polymerization techni-ques. The choice of technique is largely dependent on the nature of thestarting materials and the desired compositional and morphological charac-teristics of the resultant microcapsules/microspheres. It is not easy, for exam-ple, to use the solvent evaporation and the polymer melt solidificationmethods to prepare chitosan microcapsules due to difficulties in obtainingcomplete solvent evaporation and due to the lack of a melting point forchitosan. Yao et al.[165] reviewed microencapsulating methods employedfor chitosan microcapsules/microspheres.

All types of chitosan microcapsules/microspheres have a wide range ofapplications. They may be employed, for example, to solve numerous pro-blems in environmental and biomedical engineering. Chitosan microcapsules/microspheres are being studied for the controlled release of drugs.[165]

6.2. Applications in Chromatographic Separations

The characteristics of chitin and chitosan make them of great value forchromatographic supports. They can interact with organic substances likeproteins and act as electron donors toward transition metal ions.Townsley,[172a] and Takeda and Tomida[172b] used chitin powder as a chroma-tographic support in thin layer chromatography for the separation of nucleicderivatives. Chitin thin layers have higher Rf than for cellulose layers. Thesuperiority of chitin to silica gel and polyamide for the thin layer chromato-graphy of some phenols and amino acids has also been reported elsewhere.[173]

Chitosan has also been used byMuzzarelli and Rocchetti[174a] for the determi-nation of molybdenum and vanadium in sea water. Thus, several fields ofchromatography are open to industrial applications of chitin, chitosan, andtheir derivatives,[174b,c] like ion exchange chromatography, chelation chroma-tography, ligand exchange chromatography, affinity chromatography, highpressure chromatography, and gel chromatography.

6.3. Photography

Chitosan plays an important role in the field of photography due toits resistance to abrasion, optical characteristics, film-forming ability, andbehavior with silver complexes, which are easily carried from one to another


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layer of a film. Furthermore, due to the presence of regular amino groups,chitosan can easily form mixtures with gelation and thus prevent lateraldiffusion of acidic dyes.[175]

6.4. Food and Nutrition[176–188]

Chitosan has been used as an effective agent for coagulation ofsuspended solids from various food processing waste, and the potentialfood application of chitin and chitosan and some of their functional proper-ties have been presented in recent years. The use of chitinous material toimprove nutritional value has been well studied by different workers. Thepresence of chitin in marine invertebrates, insects, fungi, yeast, and in cellwalls of certain plants, and of chitosan in various fungi, indicates that chitinand chitosan are already part of our food supply. Furthermore, the toxicitystudies have showed that chitosan is as safe as salt and sugar. According tothe U.S. Environmental Protection Agency, chitosan is acceptable forportable water applications. Chitosan also has hypolipidemic and hypo-cholersterolemic activity.

6.5. Water Engineering

As environmental protection is becoming an important global issue, therelevant industries should pay attention to developing such a technologywhich would be free from all sorts of environmental problems.[189,190]

Nair et al.[191] used chitosan obtained from prawn waste for removal ofmercury from solutions. In order to find the effect of particle size of chitosanon adsorption of Hg2þ, chitosan of two different particle sizes, namely,10–20mesh and 40mesh, was employed. The results of their investigationare given in Fig. 3, which clearly indicates that the efficiency of adsorptionof chitosan depends upon the period of treatment, particle size, initial con-centration of the Hg2þ, and quantity of the chitosan used. The study onadsorption of metal ions using chitosan as an adsorbent by various workersis listed in Table 3. Recently, Bhavani and Dutta[193] reported the removal ofcolor from dyehouse effluents using chitosan as an adsorbent.

Hydroxymethyl chitin and other water-soluble derivatives are usefulflocculants for anionic waste streams.[74] Chitosan N-benzyl sulfonate deri-vatives are used as sorbents for removal of metal ions in acidic medium byWeltrowski et al.[194] The selective adsorption capacity for metal ions ofamidoximated chitosan bead-g-PAN copolymer has been studied byKang et al.[195] These investigations have clearly indicated that chitosanhas a natural selectivity for the heavy metal ions and is useful for thetreatment of waste water. Maleilated chitosan and chitosan fibers in


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Figure 3. Influence of quantity of chitosan on the adsorption of mercury from lower andhigher concentrations.

Table 3. Waste Water Treatment from Chitosan as an Adsorbent by Various Workers

Removal ofMetal Ions

Conc. Range(ppm)

Parameters forAdsorption

ResearchGroup Ref.

Cd2þ 1–10 Particle size ofadsorbent

Jha et al. [192a]

Cd2þ — Rower et al. [192b]Cu2þ, Hg2þ,Ni2þ, Zn2þ

— Temperature variation,pH7

Makay et al. [192c]

— — Yang et al. [192d]Cr3þ — Particle size 0.4–4 Maruce et al. [192e]Cr6þ — — Udayshankar et al. [192f]

Hg2þ — Kinetics study Peniche-covas et al. [192g]

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various forms have been used for the removal of dyes from the effluent oftextile industries.[196a,b]

6.6. Textile Industry

6.6.1. Introduction to Chitin and Chitosan Fibers

Utilization of chitin as a resource is extremely limited because of thepoor solubility and poor reactivity, which are due to the strong micellestructure which was formed through hydrogen bonds between aminoacetylgroups. The spinnability and film-forming ability, like those in cellulose, areobtained in chitin when it dissolves at high concentrations without degrada-tion of the molecules. The polyamide-type micelle should be broken up priorto solubilization of chitin into a solvent or prior to being subjected tochemical reactions. The preparation of chitin viscose was reported previouslythrough the xanthation of alkali chitin by the application of a freezingprocedure.[197]

Chitin fiber was obtained from chitin viscose using the spinning condi-tions of rayon fiber at a lower temperature, but it was not suitable for practicaluse because of the weakness of both its tenacity and its knot strength in the wetstate. However, the freezing procedure would seem to be useful to break up themicelle structure of a chitin molecule. On this basis several solvents for poly-amides were applied to dissolve the chitin. The formic acid–dichloroacetic acidsystem was found to be a suitable solvent for obtaining a viscous chitin solu-tion when the freezing procedure was employed.[197]

Chitosan fibers were made by wet spinning of the polymer’s solution in2% aqueous acetic acid.[198] The fiber properties were affected by processingconditions, such as spin strength ratio, coagulation bath composition, anddrying conditions. The chitosan fibers were acetylated with acetic anhydridein methanol, producing regenerated chitin fibers. The acetylation process wasaffected by the reaction temperature, treatment time, and the molar ratio ofanhydride of amine groups. The properties of the acetylated chitosan fiberswere studied in terms of thermal stability, solubility, and mechanical proper-ties. It was found that, after acetylation, the fibers had an improved thermalstability and tensile strength.

There have been many attempts to produce chitin and chitosanfibers.[197,199–205] In the case of chitin, the major problem has been to find asuitable solvent. Although a number of solvents, such as formic acid,[197] con-centratedmineral acid,[201] trichloroacetic acid (TCA),[205]DMAc–LiCl,[200,205]

and a 40/40/20 mixture of TCA, chloral hydrate, and dichloromethane[204]

can dissolve chitin, the solvents are not convenient and in some cases degrada-tion of the polymer is unavoidable. Nonetheless, chitin fibers with a tenacity ofup to 0.44N/tex (4.5 g/dtex) have been reported.[204,206,207]


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6.6.1.1. Solvent and Solution Properties

Chitin and chitosan degrade before melting, which is typical for poly-saccharides with extensive hydrogen bonding. This makes it necessary todissolve chitin and chitosan in an appropriate solvent system to spin fibers.Residual solvent must then be either leached or evaporated out of thefiber. Solvent systems for chitin and chitosan have been studied extensively.Although many solvents have been used, only a handful are practical forindustrial applications due to lack of toxicity, corrosiveness, or mutagenicproperties.[208] Potentially useful solvents include certain acids [aqueousacetic acid, formic acid (FA)], halogenated solvents, amides with Li com-plexes, and combinations thereof.

Solution properties of chitin and chitosan have also been studied exten-sively. For fiber spinning, the objective is to obtain a homogeneous non-gelsolution with a maximum polymer-to-solvent ratio. For each solvent system,polymer concentration, pH, counterion concentration, and temperatureeffects on the solution viscosity must be known. Examples of these are mea-sured mostly for chitosan and reported by various workers elsewhere.[209–220]

In the case of fibers, comparative data from solvent to solvent are unavail-able. As a general rule, researchers dissolve the maximum amount of polymerin a given solvent system that still retains homogeneity and then spin fiberswithout any further characterization of the solution. To spin fibers out ofsolution requires a coagulant to allow for polymer regeneration or solidifica-tion. The nature of the coagulant is also highly dependent on the solvent andsolution properties as well as the polymer used.

6.6.1.2. Natural Microfibrillar Arrangement

Chitin has been known to form microfibrillar arrangements in livingorganisms. These fibrils are usually embedded in a protein matrix and havediameters from 2.5 to 2.8 nm. Crustacean cuticles possess chitin microfibrilswith diameters as large as 25 nm. These microfibrillar arrangements werereviewed by Muzzarelli,[221] and by Brine and Austin.[222]

6.6.1.3. Fiber Formation—in Retrospection

Von Weimarn[223,224] reported the first solution of chitin that could beformed into a ‘‘ropy-plastic’’ state in 1926. These solutions were using readilysoluble salts capable of strong hydration. In the order of ease of solubility ofchitin, they are:

LiCN > CaðCNSÞ2> CaI2> CaBr2> CaCl2


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No tensile evaluations were formed on these ropy materials. Kunike[225]

pointed out as early as 1926 the problems in dissolving chitin. To help in thedissolution of chitin, it was N-deacetylated in 5% caustic at 60oC for 14 days.Another procedure for N-deacetylation was to place the chitin in an auto-clave for 3 hr at 180oC and 10 atm pressure. He also pointed out that 6% to10% solids of N-deacetylated chitin can be brought into acidic solutions atroom temperature. Aqueous acetic acid was found to be suitable for thispurpose.

Fibers were spun by removing impurities of these acidic solutionsthrough filter presses. Chemicals incompatible with chitin were suggestedas coagulants. The resultant fibers were washed and dried under tension.The final product fibers had a round to heart-shaped cross-section with atensile breaking load of 35 kg/mm2 (345 Pa). The fibers possessed a dull lustersimilar to natural silk, leading to the suggestion that the N-deacetylatedchitin fibers would make good artificial hair. The collection and recyclingof chitin from small-scale consumers was also suggested. An early patentapplication on plastic masses of chitin was made on this procedure byKunike[225] at the Kaiser Wilhem Institute fuer Fasertoffchemie in 1926.

Clark and Smith[226] produced fibers by dissolving chitin at 95�C inpresaturated solutions of lithium thiocyanate (saturated at 60�C).Their investigation showed no tensile properties or solution concentrations,however, x-ray analysis showed a high degree of orientation. Solventremoval was not successful, even at 200�C. Lithium iodide was impliedto have behaved in the same manner. A ratio of five molecules lithiumthiocyanate per mole and hydroglucose unit was found to exist. This iscomparable to the cellulose–lithium thiocyanate compound, and the roleof solvent/salt complexes in terms of cellulose solubility has been reviewedin detail.[227,228]

6.6.2. Novel Solvent Spin Systems

6.6.2.1. Halogenated Solvent Spin System

In 1975, Austin[229] suggested organic solvents containing acids for thedirect dissolution of chitin. Such a system was chloroethanol and sulfuricacid, where the precipitation of chitin in fibrillar form in water, methanol, oraqueous ammonium hydroxides was mentioned, but no fiber tensile datawere presented.

In 1975, Brine and Austin[222] suggested TCA as a chitin solvent. Chitinwas pulverized and two parts by weight were added to 87 parts by weight of asolvent mixture containing 40% TCA, 40% chloral hydrate, and 20% methy-lene chloride over a period of 30–45min. A filament was extruded fromthis solution using a hypodermic needle and acetone as the coagulant.


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The filament was then neutralized with potassium hydroxide (KOH) in2-propanol followed by washing in deionized water. The filaments werethen cold drawn. Two tensile breaks were taken at 60% relative humidityand room temperature. The first break was from a filament with a cross-section of 0.08� 0.10mm2, yielding a tensile strength of 72 kg/mm2 (710Pa)and a breaking elongation of 13%. The second filament had a cross-sectionof 0.014� 0.740mm2, indicating a collapsed core structure. It had a tensilestrength of 104 kg/mm2 (1026 Pa) and a breaking elongation of44%.[185,203,230] Syringing a filament should not be interpreted as conclusiveevidence for a possible wet-spinning process. While syringe extrusion mightindicate the selection of a coagulant, it would be surprising to obtain mean-ingful tensile data. Shear forces in a spinneret are much greater than thoseexperienced in a syringe tip.

Kifune et al.[231] suggested dissolving chitin in TCA and a chlorinatedhydrocarbon such as chloromethane, dichloromethane, 1,1,2-trichloro-ethane. The TCA concentration should be kept between 2.5% and 75% byweight. A concentration range between 1% and 10% chitin was suggested, aswell as dissolution below room temperature. Fiber extrusion occurredthrough a spinneret of between 0.04 and 0.06mm diameter into an acetonecoagulation bath followed by a methanol bath. The dried filaments ranged intensile strength from 1.67 to 3.1 g/d and an elongation from 8.7% to 20%,respectively. The strength of the fibers was improved by leaving them in0.5 g/L aqueous caustic solution for 1 h. The resultant tensile strengthswere 2.25 to 3.20 g/d with elongations of 19.2% to 27.3%, respectively.Kifune et al.[83,232] further suggested that these chitin filaments were suitableas adsorbable surgical sutures. However, TCA is very corrosive and degradesthe polymer molecular weight. The breaking elongations suggest that thehalogenated solvents act as plasticizers.

Fuji Spinning Company[233] dissolved chitosan in a mixture of waterand dichloroacetic acid (DCA). The 6.44% chitosan acetate salt solutionviscosity was 410 poise. The dope was extruded through a platinum nozzleinto basic CuCO3/NH4OH solution to form fibers. Denier and tensile proper-ties were unavailable.

Capozza[94,234–236] suggested hexafluoroisopropanol and hexafluoro-acetone sesquihydrate as a solvent system. Chitin was spun into fibersusing this system. Dry spinning was accomplished by heating a solutioncontaining chitin and 97 parts hexafluoroisopropanol at 55�C and extrudingthrough a spinneret. The fibers were autoclaved by steam but no tensileproperties were given. Wet spinning was accomplished by extruding a 3%solution of chitin in hexafluoroacetone sesquihydrate into an acetone coagu-lation bath. The solution was further washed with acetone and then dried anddrawn. Comparative tensile strengths were not reported. Solvents used bythese systems were highly toxic,[237] which made complete solvent recoveryimperative.


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Tokura et al.[198] used a combination of FA, DCA, and isopropyletheras a solvent system. Chitin was cycled several times from �20�C to roomtemperature in FA, after which a small amount of DCA was added.Isopropylether was then added to reduce the solution viscosity to below199 poise. Different coagulation systems were used. The filament tensileproperties[198] show that dry tenacities were below 1.59 g/d and no elonga-tions above 4.3%. It is noteworthy that the wet strength drops to below0.50 g/d, but that the elongation increases to as high as 13%.

A TCA/dichloromethane spin system[238] is also described by UnitikaCo. Ltd. Three parts chitin were dissolved in 50 parts TCA and 50 partsdichloromethane by weight. The defoamed dope was extruded into acetonebefore wind-up. The bobbins were neutralized with KOH, washed withwater, and dried. The fibers had a tensile strength of 2 g/d and 0.5–20 denier.

Unitika Co. Ltd. also used the TCA–chloral hydrate dichloroethanesolvent system[239] for chitin. Five parts chitin were dissolved in 100 partsof a 4:4:2 TCA:chloral hydrate:dichloroethane solvent mixture and extrudedthrough a 0.06-mm nozzle into acetone. The fibers were treated with metha-nolic NaOH. The fiber gave optimum tenacity of 3.2 g/d with an elongationof 20%. Unitika Co. Ltd. followed this up with another patent using a 60:40TCA:trichloroethylene spin dope mixture.[240] Tensile properties were una-vailable. In 1983, Unitika Co. Ltd.[241] showed that a dope consisting of threeparts chitin, 50 parts TCA, and 50 parts dichloromethane could be spun at arate of 1.7 mL/min under 25 kg/cm2 pressure into acetone to form filaments.The extrusion die had 50 holes of 0.07mm diameter each. This indicates ajet velocity of 8.8m/min and a take-up of 5m/min. The coagulation bath wasmaintained at 18�C. The filaments were washed with acetone at 18�C for10min, rewound at 4.5m/min, then neutralized, washed, and dried.The multifilament product had a total denier of 150 with a tenacity of2.65 g/d. A similar system using four parts of chitin in the same solvent,but a 40-hole die of 0.08mm diameter each, was also used.[242] The jet velo-city was 10.4m/min into a 25�C acetone bath. The first take-up roll at5m/min was followed by a rewinding at 7m/min. The total denier was175; however, no tensile properties were reported.

Some of the halogenated solvent systems approached dry tenacities ofabove 3 g/d; however, the low wet tenacities were still undesirable. Althoughthe fiber characterization was much better for these systems, the polymercharacterization lacked molecular weight as well as degree of N-acetylationformation. Solution properties would be hard to obtain due to rapid chitindegradation in these solvents. Although anhydrous coagulation baths wereused and compared, fibers were neutralized in aqueous media. A study incompletely anhydrous systems would be of interest, since it may lead to moredensely consolidated fibers. The implementation of these spin systemsrepresents a problem due to the nature of the solvents: TCA and DCA arecorrosive and degrade the polymer upon short exposures.


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6.6.2.2. Amide–LiCl System

In 1977, Rutherford and Austin[42] published marine chitin propertiesand solvents. This summarized the problems encountered in finding a solventsystem for chitin. Austin[243] suggested DMAc and 5% LiCl or N-methyl-2-pyrrolidone (NMP) and 5% LiCl as solvents for chitin. A solution of 5% w/vwas obtained within 2 hr with these systems. A filament was extruded fromthe solution using a 15-gauge needle into an acetone coagulation bath. Thiswas followed by more washing and drawing in acetone. The final filamentwas washed in deionized water. Tensile properties were obtained at 60%relative humidity and room temperature at an applied stress of 0.1 cm/min.The resultant dry tensile strengths for different crab and shrimp speciesranged from 24 to 60 kg/mm2 (236–592Pa). Austin[244] published anothercomprehensive paper in which he elaborated on chitin solvents, but notfibers.

Nakajima et al.[83] also dissolved chitin in an amide–LiCl solution. Thesolution was extruded through a 0.05-mm spinneret into a butylalcohol coa-gulant. The dry tensile strength of the fibers was 50 kg/mm2 (493Pa). Kifuneet al.[245,246] elaborated on this spin system. A spin dope concentration of 1%to 10% in NMP and DMAc–LiCl is suggested, with an alcohol coagulationbath followed by a draw bath and further washing.

Several other Japanese patents[247,248] also used the DMAc–LiCl spinsystem. Unitika Co. Ltd. claimed fibers spun from a solution containing 0.5 gchitin, 8 g LiCl, and 100 g DMF. The viscosity of the solution was 50–600 cPat 30�C depending on the chitin concentration. A 3% chitin dope in a 20:1DMF:LiCl solvent was spun through a die of 50 holes of 0.08mm diametereach into an isobutanol coagulation bath at 10m/min. This gave 61-denierfibers with tenacities of 3.81 g/d after washing and drying. This was followedby spinning a 3.5% chitin solution dissolved in a 25:3 NMP:LiCl solutioninto 70�C isobutanol. No tensile properties were reported. Unitika Co.Ltd.[248] also reported a 58-denier filament with a tenacity of 4.25 g/d byspinning a dope consisting of 11 g chitin and 200 g of 8% LiCl in NMPsolution. The coagulant was isobutanol. Along the same lines,[249] a dopewas prepared containing 3 g chitin and 200 g of saturated LiCl in DMAcsolution. To this dope, another 0.5 g LiCl was added before spinning intoisobutanol. The final 65-denier filament had a tenacity of 4.18 g/d. It is notclear if this high denier was for fibers or multifilaments; in general, high-denier fibers result in poor tensile properties.

A group of Russian researchers[250] spun chitin fibers out of DMAc/NMP solutions containing 5% chitin and 5% LiCl (based on chitin content).The fibers were drawn in a 50:50 ethanol:ethylene glycol bath, giving anaverage yield strength of 390MPa with 3% elongation. An initial modulusof 2GPa was also reported. Scanning electron microscopy showed fibers witha round fibrillar cross-section. A follow-up study showed that as the degree


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of N-acetylation increased (12–30%), the modulus of elasticity and relativeelongation decreased. X-ray analysis showed that as the degree of acetylationincreased, the amount of amorphous regions also increased.[251]

The amide–lithium systems showed some of the best dry tenacities,although they still lack adequate wet tenacities. The low wet tenacities areprobably due to low crystallinity and poor consolidation of the fiber. Thefibers and spin dopes were well characterized, but the polymers used toprepare these dopes were not properly characterized. Some coagulation stu-dies were carried out, but a clear comparison could not be made. A very realproblem with this spin system is the removal and recovery of lithium from thefiber. The lithium acts as a Lewis acid by solvating the chitin amide group.

6.6.2.3. NMMO/H2O System

Attempts have been made by the authors[252] to develop a process forchitosan fibers by direct dissolution using a novel solvent system (NMMO/H2O). In this process, a mixture of 5% chitosan to NMMO/H2O was keptfor 48 hr at room temperature and then heated to elevated temperature untilgel formation is complete.[163] The resulting chitosan gel was then allowed tocool to the ambient temperature. The almost transparent and brownish gelobtained was insoluble in water and in common organic solvents. The Tg ofthe gel was observed about 6�C higher than that of chitosan, i.e., 150�C, andthe increased Tg of the gel was due to the restricted molecular movement,owing to formation of N¼O bonding at the C2 position of chitosan. Thethermal behavior of chitosan and gel is confirmed by evaluation of enthalpychanges, from 163 to 169 cal/g. The fiber was made from the gel followingmelt spinning. The precipitation of chitosan in fibrillar form in water wasobtained.

6.6.3. Fiber Summary

Early recognition of chitin’s microfibrillar arrangement pointed to fiber-forming possibilities. Chitin was found to be intractable in common organicsolvents. This led to the parallel development of the xanthate process as itwas established for cellulose. Resultant fiber properties were below 2 g/d intensile strength. The low tensile strength values and environmental concernswith the xanthate process led to the development of novel halogenated andamide–Li(halide) solvent systems in the 1970s. Breaking strengths of4.25 g/dMPa for fibers were reported.[253] A combination of solvent removalrepresents some of the major obstacles with these systems. To avoid thesesolvent problems, chitosan can be dissolved with ease in dilute non-corrosiveaqueous acids such as formic and acetic acids. Fibers obtained from these


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aqueous acid solutions exhibited breaking strength of 3.81 g/dMPa. A widerange of chitosan derivatives has also been synthesized, of which mixed esterderivatives gave the most promising results.[44,253–257] Fiber properties of7.1 g/d are found from liquid crystal solutions.[257] Each of these chitosanderivatives still had a 10-fold loss of wet tensile strength. Several attempts atcrosslinking chitosan improved the wet strength slightly, while sacrificingelongation. Careful attention should be paid to differentiate the effects ofdegree of N-acetylation, molecular weight, casting solution, thermal drying,coagulation, and solvent removal. In this respect, the direct dissolution ofchitosan in NMMO/H2O may give a promising prospect for new-generationfibers.[252]

6.6.4. Chitosan in Degree of Polymerization (DP)Finishing for Improved Dyeability

The applicability of chitin and chitosan has been investigated in variousareas of the textile industries. In the textile finishing field, they are used toimprove the soil release property, shrink-proofing of wool, and dyeability ofimmature cotton. Shin and Dong[258] reported the effect of molecular weightof chitosan on dyeability of DP finished cotton. They treated cotton fabricswith a mixture of chitosan and DMDHEU (dimethylol dihydroxyethyleneurea) or DMeDHEU (dimethyl dihydroxyethylene urea) in one step. Treatedfabrics were dyed with direct, acid, and reactive dyes, and their performanceproperties and color fastness were studied.

6.6.4.1. Effect of Molecular Weight of Chitosan onPerformance Properties

Chitosan of higher molecular weight, i.e., higher DP, causes a decreasein wrinkle recovery angle (WRA) of DMDHEU or DMeDHEU/chitosan-treated samples.[258] However, as the molecular weight of chitosan decreases,the WRA increases to a similar level as for DMDHEU or DMeDHEU-treated samples, as shown in Table 4. Also, higher molecular weight chitosangives higher breaking strength retention (BS, Rtn.) due to the binding effectof the fabric structure.

6.6.4.2. Effect of Molecular Weight of Chitosan on theUptake of Direct, Acid, and Reactive Dyes[258]

All the DMDHEU/chitosan-treated samples give higher coloryields than DMDHEU-treated samples. Direct dye uptakes of the


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DMDHEU-treated samples were negligible. Except for the samples treatedwith chitosan of molecular weight below 1.4� 104, all the DMDHEU/chitosan-treated samples give higher color yields than the untreated samples.As shown in Table 4, the dye uptake of direct dye increases as the molecularweight of chitosan increases.

Uptake of acid dyes of the untreated, DMDHEU/chitosan-treated, andDMeDHEU/chitosan-treated samples showed higher dye uptake than theuntreated as well as DMDHEU or DMeDHEU-treated samples. Again thedye uptake of acid dyes increases as the molecular weight of chitosandecreases.

The results showed that reactive dye uptakes of DMDHEU orDMeDHEU/chitosan-treated samples are much lower than those of theuntreated. Dye uptake of CI reactive red 183 is higher than that ofDMDHEU-treated sample, regardless of chitosan molecular weight. Inthe case of DMeDHEU/chitosan-treated samples, dye uptakes are higherthan those of DMDHEU-treated sample, regardless of chitosan molecularweight.

The dye uptake of DMDHEU or DMeDHEU-treated samples tends toincrease as the molecular weight of chitosan decreases, though the differencein dye uptake is small and just opposite when compared with the results ofdirect and acid dyes.


Table 4. Properties of DMDHEU/Chitosan (DMeDHEU/Chitosan)-Treated Fabrics[258]

Color Strength Values (K/S)

Sample

Add-on

(%)

WRAa

(oWþf )

BS Rtn.b

(%)

Direct

Red 81

Acid

Red 266

Reactive

Red 183

Reactive

Red 183*

Untreated 176 100 41 0.2 6.6 0.3DMDHEU-treated

(DMeDHEU-treated)

4.4 ( 4.8 ) 294 (271) 56 (76) 0.3 (3.3) 0.3 (0.4) 0.4 (2.2) 1.1 (3.0)

DMDHEU/

chitosan(DMeDHEU/chitosan)-treated

F (185,300) 7.3 (7.4) 257 (207) 80 (91) 9.1 (11.2) 5.8 (5.7) 0.4 (5.2) 2.3 (9.1)A (73,200) 7.2 (7.2) 289 (219) 73 (101) 7.2 (13.2) 6.1 (7.4) 0.4 (4.8) 2.1 (9.0)B (59,000) 7.8 (8.1) 285 (215) 64 (97) 6.2 (11.0) 4.5 (5.6) 0.4 (4.9) 2.4 (10.4)

C (21,000) 8.6 (8.2) 306 (252) 62 (89) 6.0 (10.8) 4.0 (4.0) 0.5 (5.3) 3.0 (12.4)D (14,000) 7.0 (7.4) 305 (269) 68 (94) 3.7 (9.0) 2.7 (2.3) 0.5 (5.4) 2.4 (9.7)E (3,800) 7.7 (6.7) 302 (264) 61 (82) 1.9 (5.8) 1.3 (0.8) 1.2 (6.3) 2.5 (5.2)

aWRA: wrinkle recovery angle.bBS Rtn.: binding strength retention.

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6.6.5. Color Removal from Textile Mill Effluents

Color, which contributes so much to the beauty of nature, is essentialto the attractiveness and acceptability of most products used by modernsociety.[259] Textile wet-processing operations produce high volumes ofeffluent waste water of varied composition, often containing salts plusorganic surfactants, solvents, and dyes. Color pollution regulations havebeen ‘‘on the books’’ in the United States since the mid 1970s, but untilrecently have not been enforced. The textile industry’s continuing concernfor the environment, and desire to be better corporate citizens, has broughtreviewed emphasis on environmentally friendly products and productionusing technologies focusing on either source reduction or improved wastetreatment.[260]

Much can still be done on both fronts, and no single technique is likelyto solve all problems, especially in the area of color pollution control.[261]

Mounting pressure on the textile industry to treat dyehouse effluents has ledto a host of new and old technologies competing to provide cost-effectivesolutions. Among the oldest of methods for treatment of waste water is theuse of adsorbents derived from biological matter or biomass. Because of itslow-cost, widespread availability, biomass has often been investigated withsome promising results.[262–271]

6.6.5.1. Dye Binding and Water Uptake

In 1982, Knorr[272] examined dye binding and water uptake propertiesof chitin and chitosan followed by Sosulski’s method.[273] The absorbance ofthe supernatant was measured at 505 nm using deionized water as blank. Theweight of supernatant was used as a basis for the calculation of the totalamount of dye bound or released. The pH adjustment was carried out byusing either 10mL of a commercial buffer solution or by adding 0.1 N HCl toa slurry of 0.5 g chitin/chitosan and 10 mL of dye solution. After stirring for15min the pH was readjusted and deionized water added to reach 20.5 g oftotal weight. Chitosan gels were formed at pH values below 5.5, and no dyebinding measurements could be performed.

The effects of dye concentration in chitin/chitosan dye solutionratios on dye binding capacity and water uptake of chitin and chitosanhave been studied.[272] A marked difference between water uptake ofchitin and chitosan was found, with chitosan having higher water uptakethan chitin. This difference can be due to differences in the crystallinity ofthe products or differences in the amount of salt-forming groups.Differences in the amount of covalently bound protein residues mightalso affect water uptake.[39]


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An effect of chitin/chitosan dye solution ratio on water uptake was alsoobserved as being higher at a 0.5 g : 20mL ratio than at a 2.0 g : 20mL ratio.Similar trends were found with dye binding capacity. This difference could becaused by differences in rate of water uptake (wettability) at different chitinto aqueous dye solution ratios.

Dye concentration had no marked effect on water uptake, but signifi-cantly affected the dye binding capacity of chitin and chitosan. The results ofregression and correlation analyses examined the dye binding capacity ofchitin and chitosan as a function of dye concentration.[274] The results indi-cate that the dye binding capacity of both chitin and chitosan correlatedsignificantly with dye concentration.

The effect of pH on the dye binding capacity of chitin and chitosan isalso reported.[274] These data indicate a decline in the dye binding capacity ofchitin and chitosan above pH7.0. Within a pH range of 2.0–7.0 the dyebinding capacity of chitin was shown to be stable, while chitosan formedgels below pH5.5 and could not be evaluated. With the exception of chitinat pH9, the dye binding capacity was not affected by adjusting the pH eitherwith hydrochloric acid or with a buffer solution. The authors’ physicochem-ical study[193] of the adsorption on chitosan is also noteworthy in this context.

It is important to consider the methods of containing the solid adsor-bent and the waste water when applying the adsorption system to large-scaletreatment. Two major classes of contacting systems exist, namely, the batch-type process and the bed or column systems. The bed-type processes may befixed-bed or fluidized-bed systems; the detailed procedure is described else-where.[275]

Chitosan can be spun into fibers,[276] which apparently have muchimproved adsorption kinetics. Chemically crosslinking the chitosan fibersallows the fibers to be used at low pH, which improves their dye bindingcapacity, without solubilizing the chitosan.[196]

Chitosan can also be cast into membranes and then crosslinked toproduce filters with excellent physical and chemical stability and highwater permeability.[277] Chitosan membranes would thus be expected tohave very rapid dye adsorption kinetics, in addition to high capacity,although no reports are found in the literature on this effect.

6.7. Cosmetics

Organic acids are usually good solvents for cosmetic applications.Chitin and chitosan have fungicidal and fungistatic properties. Chitosanis the only natural cationic gum that becomes viscous on being neutralizedwith acid. These materials are used in creams, lotions, and permanentwaving lotions, and several derivatives have also been reported as naillacquers.[278]


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6.8. Paper Industry

6.8.1. Paper Finishing

Chitosan has been reported to impart wet strength to paper.[279]

Hydroxymethyl chitin and other water-soluble derivatives are useful endadditives in paper making. This polymer, although potentially available inlarge quantities, has never become a commercially significant product.

6.9. Engineering Applications

6.9.1. Solid State Batteries

Chitosan is insoluble in water, which poses a problem in the fabricationof solid state proton-conducting polymer batteries. A lack of water present inthe chitosan obviates the presence of hydrogen ions. Consequently, theproton-conducting polymer needed for solid state battery applicationcannot be obtained from chitosan alone. Chitosan is a biopolymer whichcan provide some ionic conductivity when dissolved in acetic acid. The con-ductivity is due to the presence of proton from the acetic acid solution. Thetransport of these protons is thought to occur through the many microvoids inthe polymer, since the dielectric constants from piezoelectric studies are small,suggesting the polymer structures to contain many microvoids. The choice ofa more suitable electrode material may produce a better battery system.[280]

7. CONCLUSION

From the foregoing sections it is clear that chitin and chitosan canreadily be derivatized by utilizing the reactivity of the primary aminogroup and the primary and secondary hydroxyl groups to find applicationsin diversified areas. In this review various aspects, including the properties,processing, and applications, have been critically emphasized. Further, inthis review an attempt has been made to increase the understanding of theimportance and characteristics of chitin and chitosan. In view of this, thisreview will be of great interest both for industrial and academic institutions.

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