Download Review Paper on Characterization of Chitin and

Review Paper on Characterization of Chitin and Chitosan and Importance of
Cationizing Cotton Fiber for Dye Uptake.
Rajeev Rajbhandari
Plant and Soil Science, Texas Tech University
For chitosan, the band at 1590 cm-1 has a larger intensity than at 1655 cm-1,
because of effective deacetylation and when chitin deacetylation occurs, the band
observed at 1655 cm-1 decreases, while a growth at 1590 cm-1 occurs, indicating
the prevalence of NH2 groups. Hence, the reaction of chitosan is considerably
more versatile than cellulose due to the presence of - NH2 groups. TGA for chitin
showed the first peak in the range of 50–1100C, and is attributed to water
evaporation. The second occurs in the range of 300–4000C which attributed to the
degradation of the saccharide structure of the molecule, including the dehydration
of saccharide rings. In chitosan three peaks occurred in which two peaks were
same as chitin but third peak that appears around 3000C could be due to the
degradation of part of the molecule that was deacetylated. Adsorption of heavy
metals is higher in cellulose and chitin blended than in pure chitin. Dyeability is
increased with chitin presence in cellulosic fiber without use of salt.
Keywords: Cellulose, Chitin, Salt, FTIR, TGA, XRD, Cationization
INTRODUCTION
Cellulose, the most abundant renewable polymer, is produced by nature at an annual rate of
1011–1012 tons. Cellulose is a polymer consisting of unbranched β (1 → 4) D- glucopyranosyl
units. The cellulose chains have a strong tendency to aggregate to highly order structural entities
due to their chemical constitution and spatial conformation (Zhao et al., 2006). In other hand
Chitin is the second most ubiquitous natural polysaccharide after cellulose on earth and is
composed of β (1→4)-linked 2-acetamido-2-deoxy-β- D-glucose (N-acetylglucosamine). It is
often considered as cellulose derivative, even though it does not occur in organisms producing
cellulose. It is structurally identical to cellulose, but it has acetamide groups (-NHCOCH3) at the
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C-2 positions. Similarly the principle derivative of chitin, chitosan is a linear polymer of α
(1→4)-linked 2-amino-2-deoxy- β-D-glucopyranose and is easily derived by N- deacetylation, to
a varying extent that is characterized by the degree of deacetylation, and is consequently a
copolymer of N-acetylglucosamine and glucosamine.
Fig 1: Structural difference between Cellulose (Source: Ilharco et al., 1996) and Chitin (Source:
Datta et al., 2004)
Fig 2: Structure of Chitosan (Source: Paulino et al., 2005)
Chitin and chitosan the naturally abundant and renewable polymers have excellent properties
such as, biodegradability, bio-compatibility, non-toxicity, and adsorption. The reaction of
chitosan is considerably more versatile than cellulose due to the presence of - NH2 groups (Dutta
et al., 2004).
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MATERIALS and METHODS
Various papers were reviewed to understand cellulose, chitin, chitosan and its characterization
which is very much important to increase dye uptake efficiency in salt free condition.
REVIEW
Chitin and Chitosan processing
The crustacean shells mainly involve the removal of proteins (deproteinization) and the
dissolution of calcium carbonate (demineralization) that is present in crab shells in high
concentrations. The resulting chitin is deacetylated in 40 percent sodium hydroxide (NaOH) with
NaBH4 (0.83g L-1) as reducing and protecting reagent at 120 0C for 1 to 3 hours. This treatment
produces 70% deacetylated chitosan.
Flow diagram for chitin and chitosan production:
Crustacean shells → Size reduction → Protein separation → (NaOH) → Washing and
Demineralization (HCl) → washing and dewatering → Decolouration → Chitin →
Deacetylation (NaOH) → Washing and Dewatering →Chitosan (Dutta et al., 2004).
Fig 3: General mechanism of Chitosan production from chitin (Source: Paulino et al., 2005)
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FTIR (Fourier Transform Infrared)
FTIR detects the vibration characteristics of chemical functional groups in a sample. When an
infrared light interacts with the matter, chemical bonds will stretch, contract and bend. As a
result, a chemical functional group tends to adsorb infrared radiation in a specific wave number
range regardless of the structure of the rest of the molecule. For example, the C=O stretch of a
carbonyl group appears at around 1700 cm-1 in a variety of molecules. Hence, the correlation of
the band wave number position with the chemical structure is used to identify a functional group
in a sample.
Paulino et al., (2006) stated that chitin in the crystalline state shows only one intense peak at
1626 cm-1 but when the peak is seen in 1656 cm-1, it might be an indication of amorphous state
which is supported by Cardenas et al., (2004), stated that two absorption are obtained at 1660
and 1627 cm-1 in α-chitin whereas in β-chitin only one band at 1656 cm-1 is found.
The bands at 1626 cm-1 and 1656 cm-1 are attributed to the vibrations of the amide I band, and
the band at 1656 cm-1 corresponds to the amide I stretching of C=O. The band could be attributed
to the stretching of C-N vibration of the superimposed C=O group, linked to OH group by H
bonding.
The bands observed at 3474 and 3434 cm-1 correspond to the vibrational stretching of the
hydroxyl groups. When these two peaks appeared with certain intensity, two bands were
observed at 1626 and 1656 cm-1. The wide peak at 3500 and 1650 cm-1 is the indication of less
accentuated hydrogen interactions, or the presence of free hydroxyl groups (Paulino et al., 2006).
Cardenas et al., (2004) also stated that vibration at 3479 cm-1 corresponds to the intra-molecular
hydrogen bond involving the OH (6)...O=C that is missing in β chitin.
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The band at 1345 cm-1 corresponds to a CO–NH deformation and to the CH2 group (amide III),
due to the formation of CO–NH group. The sharp band at 1377 cm-1 corresponds to a
symmetrical deformation of the CH3 group, and at 1557 cm-1 corresponds to the stretching or N–
H deformation of amine II (Paulino et al., 2006).
Fig 4: FTIR spectra for Chitin and Chitosan (Source: Paulino et al., 2005)
Chitosan FTIR: For chitosan, the band at 1590 cm-1 has a larger intensity than at 1655 cm-1,
which suggests effective deacetylation. When chitin deacetylation occurs, the band observed at
1655 cm-1 decreases, while a growth at 1590 cm-1
occurs, indicating the prevalence of NH2
groups. When the same spectrum is observed, in which the band from 1500 to 1700 cm-1 is
stressed, indicated that there was an intensification of the peak at 1590 and a decrease at 1655
cm-1, that suggests the occurrence of deacetylation. Fig. 5 shows the spectrum of chitosan
obtained with different times of deacetylation, and was observed that even after 4 hours of
reaction, the deacetylation was very small. After 5 hours of reaction, an intensification of the
peak at 1590 cm-1 occurs, indicating the efficiency of deacetylation (Paulino et al., 2006).
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Fig 5: Chitosan FTIR of samples with different times of deacetylation (Source: Paulino et al.,
2005)
Thermogravimetric analysis (TGA): In the thermogram of chitin (Fig. 6) two decomposition
steps were observed, the first occurs in the range of 50–110 0C, and is attributed to water
evaporation. The second occurs in the range of 300–400 0C and could be attributed to the
degradation of the saccharide structure of the molecule, including the dehydration of saccharide
rings and the polymerization and decomposition of the acetylated and deacetylated units of
chitin. The percentage of residual mass after heating at 1000 0C was 36%, and could suggest the
presence of minerals that were not extracted in the acidic stage (Paulino et al., 2006).
Fig 6: TGA of chitin (Source: Paulino et al., 2005)
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In the chitosan thermogram (Fig. 7), three decomposition steps were observed, and the first and
the third peaks were similar to chitin, occurring in the range of 50–110 0C and 300–400 0C,
respectively. The second decomposition step occurred at a lower temperature than observed for
the chitin decomposition. It suggests that chitosan has poor thermal stability. The peak that
appears around 3000C could be due to the degradation of part of the molecule that was
deacetylated (Paulino et al., 2006).
Fig 7: TGA of chitosan (Source: Paulino et al., 2005)
X-Ray Diffraction (XRD)
According to Kamel et al., (2009) the decreased in crystallinity measured by XRD indicates
increase in amorphous region and increase in d-spacing values which indicate the increase in
dye- uptake via dyeing.
Zhao et al., (2007) observed that ordered structure of the crystalline region is not disrupted by
hydrolysis and the crystallinity of cellulose after hydrolysis does not increase although it is well
known that amorphous cellulose is more reactive.
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The crystallinity of the cellulose/chitin beads is lower than that of chitin flakes which suggests
that the cellulose crystalline in blending beads is more easily destroyed because of the effect of
interaction between chitin and NaOH in aqueous solution and the metal ions more easily to
penetrate into the blend beads on account of the adsorption mainly taking place on the
amorphous regions. As a result, the adsorption ability of heavy metals on cellulose/chitin beads
is higher than that of pure chitin flakes (Zhou et al., 2005).
Dyeing stages and impact of dyeing in environment
Dyeing is a traditional way to impart color onto cloth. The color of dyed cloth is the result of the
physical characteristics of both the dye and the fabric. Dyeing process consist of three major
stages which may have influence on the control and on the rate of transfer of dye molecules form
solution to the fibers (Trotman, 1984) . These stages are:
1. Migration of dye molecules from the solution to the interface between dyebath and
polymer molecules in the fiber followed by the migration of dye molecules to the
surface of the fiber.
2. Diffusion of the dye molecules from the surface towards the center of the fiber.
3. Immobilization of dye molecules in the fiber through physical forces, hydrogen bonds
or covalent bonds.
The impacts of conventional dyeing are adverse in environment. Some of the important issues
are as follows:
Color
With the increased demand of textile products, the textile industry and its wastewaters have been
increasing proportionally (Santos, Cervantes, & Lier, 2007). Pollution of communal water bodies
by waste dyestuff released from textile plants is a major environmental pollution (Kandelbauer,
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Paulo, & Gubitz, 2007). Reactive dye has a problem of high colored dye effluent because of high
levels of hydrolysis of dye. On an average 10-40% dye is hydrolyzed (Blackburn & Burkinshaw,
2002a). The release of colored effluents in the water bodies is undesirable because of their color
and many dyes from wastewater and their breakdown products are toxic and mutagenic to life.
The colored effluent not only mars the natural beauty of the rivers but also extremely toxic to
aquatic life because it interfere the transmission of sunlight and thus reduction the action of
photosynthesis (Longhinotti et al., 1998).
Electrolyte
Reactive dyes are widely used in dyeing process because of high wash fastness on cotton. The
high wash fastness comes from the formation of covalent bond between reactive group of dye
and nucleophiles in the fiber (Blackburn & Burkinshaw, 2002a). But reactive dyes have
disadvantage to some extent. It needs high concentration of salt. (Montazer, Malek, & Rahimi,
2007) reported that when cellulosic fibers come in contact with water produce slightly negative
charge due to ionization of hydroxyl groups and dyes such as reactive and direct dyes are anionic
(negative in charge). Large quantities of salt (30-150 g/l) are needed to overcome the static
repulsion between cotton fibers and reactive dyes to promote dyeability (Zhang, Chen, Lin,
Wang, & Zhao, 2008). Higher electrolyte concentration in the effluents is not desirable and
(Kanana et al., 2006) had reported that it may impair the delicate biochemistry of aquatic
organism, evolution of hydrogen sulphide gas under anaerobic conditions when sodium sulphate
is used as electrolyte, dissolution of such sulphides and subsequent bacterial oxidation to harmful
sulphuric acid.
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Alkali
Alkali is added in dyeing process to achieve pH of around 11 to generate sufficient cellulosate
anions (cell-O-) for dye fixation. The neutral species (cell-OH) is not sufficient to occur
nucleophilic reaction between dye and fiber (Blackburn & Burkinshaw, 2002b), this alkali must
be neutralized at the end of dyeing process which adds extra cost and salt concentration.
Importance of cationization of cellulosic fiber
Cellulose fibers when come in contact with water produce slightly negative charge due to the
ionization of hydroxyl groups, whereas most of the dye for cotton are anionic (such as reactive
and direct dyes) in solution. The slightly negative charge on the fibers results in repulsion of
anionic dyestuffs and thus the exhaustion of the bath is limited. Therefore in dyeing of cotton
with anionic dyes, a large amount of electrolyte, such as Glauber’s salt or sodium chloride is
required in order to reduce the charge repulsion between the negatively charged cotton and the
anionic dyes (Montezar et al., 2007). Traditionally, large quantities of salt (30-150g/l) are
needed to overcome the static repulsion between cotton fibers and reactive dyes in order to
promote dye-ability (Zhang et al., 2008)
Normally not all the dye in the dye bath is exhausted, thus causing environmental problems due
to the discharge of effluent that is colored as well as having a high salt concentration. Chemical
modification of cotton is generally performed by reaction with the functional groups (hydroxyl
groups) already present in the fiber. Many studies devoted to improving the dye-ability of cotton
fibers have used quaternary cationic agents having various reactive groups. The most common
approach is via reaction of various types of fiber- reactive substituted amino compounds. By
introducing amino groups, the cellulose fiber will be cationized giving high substantivity for
anionic dyes due to columbic attraction between the positive charge on the fiber and the negative
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charge on the anionic dyes. This cationized cotton could be dye-able with reactive dyes under
neutral or mild acidic conditions in the absence of electrolyte in the dye bath (Montezar et al.,
2007). Chitosan being natural fiber, biocompatibility and biodegradable it is widely used in
textile industries. Chitosan can easily absorb anionic dyes namely direct, acid and reactive dyes
because of electrostatic attraction due to its cationic nature in acidic condition.
Fig 8: Schematic presentation of chitin and dye interaction
(Shimizu, Nakajima, Yoshikawa, & Takagishi, 2002) also reported that high concentration of
chitin showed the higher dye absorption. They compare chitin/cellulose composite fiber known
as crabyon, crabyon having lower concentration of chitin, silk and wool. The higher absorption
of dye is due to electrostatic interaction of the anionic dye with the protonated amino group of
partially deacetylated chitin in crabyon. Crabyon fibers have high water regain capacity and
metal ions adsorption ability and these properties depend upon the content of amino groups in
the fibers.
Thus, most researchers focus on introducing cationic groups like amino or ammonium groups
into cotton fabrics for interactions with anionic dyes (Zhang et al., 2008).
Effect of cationization on environment
The effluent load is very low from the cationized cotton fabric in comparison to conventional
method. Hence the dyeing effluent needs not to be sent to the effluent treatment plant which
reduces the needs of plant capacity and investment. It leads to a substantial reduction in dyeing
cost. The effluent of cationized cotton dyeing poses lesser loads than that of conventional dyeing
because of no addition of salt and alkali in the dye bath. The wash water effluent consists of
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negligible effluent load as the maximum fixation of dye through cationization (Kannan et al.,
2006).
Effect of cationization on effluent load
The most beneficial part of the cationization technique is the reduction of Total Dissolved Solids
(TDS) in the effluent which cannot be removed from the effluent easily, which need capital
intensive and cost consuming treatments like reverse osmosis, nano filtration and ion exchange
(Kannan et al., 2006).
Conclusion
From the review of different papers, it is concluded that when cotton fiber is treated by
chitin/chitosan, the presence of amino functional group (cationic in nature) increases the dye
uptake and the electrolyte (salt) could be minimized during dyeing process, which is very
detrimental to delicate biochemistry of aquatic organism and environment.
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