Biopolymers - Food and Industrial Bioproducts and Bioprocessing - page 270

(Figure 11.6). Chitin is insoluble in aqueous solutions at neutral pH, but N-deacetylation
increases the aqueous solubility of the polymer also providing reactive primary amines for
chemical modification as the molecular weight reduces from 1000-2500 to 100-500 kDa
during the deacetylation process.
The improved solubility of chitosan enables the synthesis of biomaterial conjugates by
grafting of synthetic hydrophobic polymers, which induce amphiphilic pH sensitive and
thermally sensitive properties (Baldwin and Kiick, 2009).
Preparation methods, physicochemical properties, and applications of chitosan have been
reviewed by Wani and co-workers (2010). Moreover, chitooligosaccharides, which are
chemically or enzymatically derived chitosan oligomers, have been found to exhibit various
bioactivities, although the mechanisms remain poorly understood (Aam et al ., 2010 ). Chitin
is degraded into its monomer, N-acetyl glucosamine, by chitinase enzymes derived from
plants, fungi, bacteria, insects, and fish (Flieger et al ., 2003 ). The production of microbial
chitinases, for example the production of chitinases by genetically engineered organisms
and by incorporating modern fermentation techniques, were summarized by Felse and
Panda (2000). More recently Sahoo and co-workers (2009) reviewed the chemical
modification, depolymerization processes, and the use of chitin and chitosan in biomedical,
food/nutritional, material, microbiological, immunological, and other miscellaneous
applications. In addition, just like the aforementioned carbohydrates, chitosan films also
show electro-activity when doped with NaClO 4 , NaI, LiCF 3 SO 3 , and LiCH 3 CO 2 at varying
concentrations depending on salt type and amount, and hydrated films with 10 -4 S/cm
conductance (Finkenstadt, 2005). On the other hand, the potential of chitin and chitosan for
arsenic removal from groundwater and the use of these natural polymers for arsenic trioxide
delivery in tumor therapy were described. The efficacy was attributed to the hydroxyl and
amine functionalities acting as metal scavengers (Da Sacco and Masotti 2010).
11.3 FAT- AND OIL-BASED POLYMERS
The relatively low cost, ready availability, renewability, and the potential biodegradability of
materials derived from plant oils make vegetable oils advantageous starting materials for
many applications. This class of renewable raw materials possesses great potential as a
sustainable resource for the polymer industry, since naturally occurring fatty acids can be
exploited for monomer and polymer synthesis without many reaction steps. The direct use
of plant oils without chemical modification or further functionalization most often leads to
cross-linked structures (thermosets, coatings, resins). Moreover, thermoplastic materials
can be prepared from fatty acids and their derivatives (obtained by transesterification of the
triglycerides) having linear and hyperbranched architectures and resulting in polymers with
tunable properties.
11.3.1 Polymers from triglycerides
Plant oils mainly comprise triacylglycerides that can be directly used for the synthesis of a
variety of polymers. For instance, they have been used in the synthesis of coatings, often
avoiding additional costs and time associated with the modification of the starting materials
(Derksen et al ., 1995). A wide range of polymerization methods, including condensation,
radical, cationic, and metathesis procedures, have been investigated. The scope, limitations,
and possibility of utilizing these methods for polymer production from triacylglycerides
have been reviewed by Güner and co-workers (2006).