Biomedical Engineering Reference
In-Depth Information
A new chitosan derivative has been synthesized by cross-linking a metal com-
plexing agent, [6, 6´-piperazine-1, 4 diyl dimethylene bis (4-methyl-2-formyl) phenol]
with chitosan. Adsorption towards various metal ions such as Mn(II), Fe(II), Co(II),
Cu(II), Ni(II), Cd(II), and Pb(II) were carried out at 25°C. The maximum adsorption
capacity was 1.21 mmol/g for Cu (II) and the order of adsorption capacities for the
metal ions studied was found to be Cu(II) > Ni(II) > Cd(II) > Co(II) > Mn(II) > Fe (II)
> Pb(II) (Krishnapriya and Kandaswamy, 2009).
Grafted Chitosan
Among the various methods of modifications, graft copolymerization has been mostly
used method. Grafting of chitosan allows the formation of functional derivatives by
covalent binding of a molecule, the graft, on to the chitosan backbone. Chitosan has
two types of reactive groups that can be grafted. First, the free amine groups on deacet-
ylated units and secondly, the hydroxyl groups on the C
3
and C
6
carbons on acetylated
(or) deacetylated units. Recently researches have shown that after primary derivation
followed by graft modification, chitosan would obtain much improved water solu-
bility, antibacterial and antioxidant properties (Xie et al., 2001, 2002) and enhanced
adsorption properties (Thanou et al., 2001).
Grafting is a method wherein monomers are covalently bonded onto the polymer
chain. Two major types of grafting may be considered as
(i) Grafting with a single monomer.
(ii) Grafting with a mixture of two monomers. (Bhattacharya and Misra, 2004)
The grafting of carboxylic functions has frequently been regarded as an interest-
ing process for increasing the sorption properties of chitosan (Holme and Hall, 1991).
Carboxylic acids have also been grafted on chitosan through Schiff's base reactions
(Guillen et al., 1992; Muzzarelli, 1985; Muzarelli et al., 1985; Saucedo et al., 1992). A
Schiff's base reaction was used for the grafting of methyl pyridine on chitosan in order
to prepare a sorbent for precious metal recovery (Baba and Hirakawa, 1992), and also
for copper uptake (Rodrigues et al., 1998).
Becker prepared a sulfur derivative by a two step procedure consisting of pre-
reaction of chitosan with glutaraldehyde followed by reaction with a mixture of form-
aldehyde and thioglycolic acid .These sulfur derivatives have been successfully tested
for the recovery of mercury and the uptake of precious metals, owing to the chelating
affinity of sulfur compounds for metal ions (Becker et al., 2000). Sulfonic groups have
been also grafted on chitosan to improve sorption capacity for metal ions on acidic
solutions (Weltrowski et al., 1996).
Chitosan grafted with poly (acrylonitrile) has been further modified to yield ami-
doximated chitosan, a derivative having a higher adsorption for Cu
2+
, Pb
2+
compared
to cross-linked chitosan (Kang et al., 1996). Recently, a great deal of attention has
been paid to the grafting of crown ether on chitosan for manufacturing new metal ion
sorbents using a Schiff's base reaction (Peng et al., 1998; Tan et al., 2000). Azacrown
ether grafted with chitosan and mesocyclic diamine grafted with chitosan crown ether
showed high selectivity for Cu
2+
in presence of Pb
2+
( Yang et al., 2000).
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