Chemistry Reference
In-Depth Information
4.6 Applications of Chitosan and Modified Chitosan
4.6.1 As Superabsorbent Materials
Yu et al. [
121
] have synthesized a novel superabsorbent polymer by graft copoly-
merization of sodium acrylate and 1-vinyl-2-pyrrolidone onto the chain of
N
-
O
-
CMCh. They found that the water absorption properties of the superabsorbent
polymer are greatly affected by the reaction temperature and time as well as by
the ratios of the reagents including the amounts of the cross-linking agent, the
initiator, the monomer, the molar ratio of the two monomers, and the volume of the
water in the reaction system. Superabsorbent polymers are defined as polymers with
a network structure and an appropriate degree of cross-linking [
122
] which can
absorb a large amount of water. Ch-based superabsorbent polymers could be
prepared by graft copolymerization with vinyl monomers along the Ch chains and
cross-linking [
123
]. Because of its very good biocompatibility and antibacterial
property, Ch-based superabsorbent polymers are expected to be widely used in
many applications [
124
] such as medical materials, sanitary materials, controlled
release devices, and matrices for enzyme immobilization. The same was found to
be true for CMCh [
125
].
Graft copolymerization of acrylonitrile (AN) and its amidoxime derivative onto
Ch and CMCh has been investigated by Sabaa et al. [
109
,
110
]. The obtained results
clearly showed the great improvement of the water uptake behavior of Ch in basic
medium, as both the grafted Ch and its corresponding amidoxime derivative swell
more than the parent ungrafted polymer and that the swell ability increased only for
the amidoxime derivative in neutral medium more than the parent Ch. While in the
case of CMCh [
110
], the results indicated that the parent polymer had the greatest
ability to swell in different pH values in comparison to the different graft
copolymers and their amidoxime derivatives. Huacai et al. [
111
] synthesized a
superabsorbent Ch resin by a graft copolymerization reaction of Ch with the
partially neutralized acrylic acid under microwave radiation. Under the optimum
conditions, they attained a grafting degree and a grafting efficiency equal to 0.896
and 0.865, respectively, which approached the ones obtained by the traditional
heating method. However, the reaction rate under this microwave irradiation
method was increased by eight times that obtained by the conventional method,
and the resin can absorb water 704 times its own dry weight, which indicates that
the prepared resin can be considered as an effective superabsorbent material.
4.6.2 As Metals Ions Adsorption and as Ion Exchangers
Environmental contamination is a serious problem that is related to possible serious
consequences, including heavy metals contamination of water from various
sources. The traditional methods for heavy metals removal from wastewater
