Bio-Based Materials - Introduction to Chemicals from Biomass - page 230

chemical modifications are required to overcome this issue and turn starch into a
material that can be perfectly thermally processed [30].

6.3.4 Starch Derivatives

The oxidation of starch leads to the formation of carbonyl and carboxyl groups in
the polymer chain. Depolymerisation also occurs and starch turns yellowish.
Advantageously, the viscosity and the gelatinisation temperature of oxidised
starches are lower than that of native starch. They are used in the paper industry
for coating and glues.
Non-ionic starch ethers are used in the food industry to avoid the water release
from frozen food and in the paper industry as a coating agent.
Cationic starch ethers are used in the paper industry to increase the cohesion
and the rigidity of cellulose fibres and as a flocculant for the selective separation
of negatively charged particles.
Reticulated starch , obtained by reaction with bifunctional reagents, increases
the water retention capacity and diminishes the swelling of starch grains, thus
increasing their mechanical and thermal resistance. This is particularly important
for the production of highly absorbent diapers.
Starch esters are thermoplastic materials with properties that are similar but not
exactly the same as those of cellulose esters. In particular, starch acetate (DS < 0.2)
is used as a coating agent in the paper industry and as a food or detergent
additive.

6.3.5 Chitin and Chitosan

Chitin is a polysaccharide comprising N -acetylglucosamine that forms a hard,
semi-transparent biomaterial found throughout the natural world. Chitin is the
main component of the exoskeletons of crab, lobster and shrimp. Chitin is also
found in insects (e.g. ants, beetles, and butterflies), cephalopods (e.g. squids and
octopus) and even in fungi. Nevertheless, the main industrial source of chitin by
far is crustaceans.
Because of its similarity to cellulose in terms of structure, chitin may be
described as cellulose with one hydroxyl group on each monomer replaced by an
acetylamine group. This allows for increased hydrogen bonding between adjacent
polymers, giving the polymer improved strength.
The properties of chitin as a tough and strong material make it an interesting
material for surgical thread. Additionally, its biodegradability means it wears
away with time as the wound heals. Moreover, chitin has some unusual properties
that accelerate healing of wounds in humans. Chitin has even been used as a
stand-alone wound-healing agent.
Industrial separation membranes and ion-exchange resins can also be made
from chitin, especially for water purification. Chitin is also used industrially as an