40 Introduction to Renewable Biomaterials
easily implementable product known as petroleum (literally, “rock oil”). At that time,
a famous entrepreneur and industrialist, Mr. Henry T. Ford, opined that it behooved
mankind to foster the exploitation and use of natural materials (such as wood) for
their use as fuels; for example, he planned to power his Model Ts with ethanol while
early diesel engines were run with peanut oil. The ability to use wood, plants, and their
by-products for energy and other valuable products was important at that time, and it
continues to be even more paramount now with the specter of the scarcity of petroleum
reserves looming and the concomitant ever-increasing price of gasoline. However,
efficient use of such raw materials demands a keen and in-depth understanding of their
constituents and the processes in place to unlock their fuel and material value. A good
understanding of these materials is key to their future use.
Wood is a raw material that has served humankind very well over its history. Locked
within its macrostructure are three significant polymers (biopolymers) whose utility
can rival that of petroleum and its by-products. The principal building blocks of
wood (and hence nearly all lignocellulosics) are cellulose, heteropolysaccharides (or
“hemicelluloses”), and lignin. These raw polymers are among the most abundant
materials in the biosphere. They are only rivaled by chitin, another polysaccharide
like cellulose that is found in the exoskeletons of marine and terrestrial life forms, as
to their dominance in the material world. The symmetry found in the natural world
is extraordinary especially when comparing the exquisite twofold screw structure of
cellulose, the most dominant biomaterial on land, to its analogue, chitin, and the most
dominant biomaterial in the sea. Figure 2.1 demonstrates this awesome symmetry.
2.2.1 Cellulose
Cellulose, the major constituent of lignocellulosics, occupies up to 50% or more of the
overall composition of the matter [1]. In general, it is considered to be the most abun-
dant renewable material on the planet, with annual cellulosic biomass production in the
order of approximately 2 teratons (or 2× 1012 tons). Although it has the same structural
motif in each material that it comprises (i.e., the same corkscrew twofold symmetry),
its degree of polymerization (DP or “n” shown in Figure 2.1) and crystallinity (degree of
packing order as evidenced by X-ray crystallography) can vary widely. Estimates of the
DP found in the literature show that it can vary from aboutn=300 (in wood) to upward
of 10,000 (cotton and bacterial cellulose, BC). It can also show wide trends in the overall
crystalline morphology; for example, it can show a relatively low crystallinity in wood,
OH
OH
O
O O
O
n n
OH
(a) (b)
OH
NH HO
HO
HO
O O
OH
OH
CH 3
O
O
HO
NH
CH 3
O
O
Figure 2.1The archetypal structures of the most abundant biomaterials on the planet.
(a) The repeating unit (N-acetylglucosamine) of the biopolymer chitin. (b) The repeating unit (glucose)
of the biopolymer cellulose.
