Fundamental Science and Applications for Biomaterials 55
in 1975 to over 160 MMT today. Starch is inexpensive, widely available, and one of
the most abundant biomass products in nature. It is produced in many different plant
organs including roots, leaves, seeds, and stems. However, the hydrophilic nature of
starch and its tendency to embrittle with age do not make it suitable as a replacement for
plastics – hence, the importance of adding lignocellulose to the starch matrix system.
2.4.2 Starch-Based Materials
The development and production of biodegradable starch-based materials have been
spurred by oil shortages and the growing interest in easing the environmental burden
of petrochemically derived polymers. Starch is one of the most studied and promising
raw materials for the production of biodegradable plastics, which is a natural renewable
carbohydrate polymer obtained from a great variety of crops (Figure 2.10). Starch is low
cost material in comparison to most synthetic plastics and is readily available. Starch has
been investigated widely for the potential manufacture of products such as water-soluble
pouches for detergents and insecticides, flushable liners and bags, and medical delivery
systems and devices. Native starch commonly exists in a granular structure, which can
be processed into thermoplastic starch (TPS) under the action of high temperature and
shear by melt extrusion. Unfortunately, the properties of TPSs are not satisfactory for
some applications such as packaging materials and composites engineering products.
One of the unique characteristics of starch-based polymers is their processing prop-
erties, which are much more complex than conventional polymers. The processing of
starch-based polymers involves multiple reactions, for example, water diffusion, granule
expansion, gelatinization, decomposition, melting, and crystallization (Figure 2.11).
Figure 2.10Chemical structures and
physical schematic representation of
(a) amylose starch and (b) amylopectin
starch.
HO
OH OH OH
OH OH
OH OH
OH OH OH
O
OOO
O
O
O O O
O
CH 2 O
CH 2 O CH 2 CH 2 O
O
O
(a)
(b)
OO
CH 2 O
O
CH 2 O
