A Fundamental Review of the Relationships between Nanotechnology and Lignocellulosic Biomass - The Nanoscience and Technology of Renewable Biomaterials - page 10

used as an electrical wire (Ye et al . 2006). Nanocomposites for self-cleaning textiles
as well as solar cell applications have also been proposed. CdS nanowire has been
made using a nanocellulose derivative. Other applications could be possible if one were
able to combine other inorganics with cellulose (Venkataramanan and Kawanami 2006).
Cellulose has also been used for electrical devices (including artificial muscles), due
to its piezoelectric nature (Kim and Yun 2006). Termed smart cellulose, 'electroactive
paper' (EAPap) is a chemically treated paper with thin electrodes on both sides. When
electrical voltage is applied on the electrodes, the EAPap bends. Natural nanocellu-
lose has also been found to form layer by layer films with antireflective properties.
Multiwalled nanoribbon cellulose has also been used for wound dressing (Brown Jr.
et al . 2007).

1.6 Wood Nanodimensional Structure and Composition

Wood is a cellular hierarchical biocomposite (Figure 1.3) made up of cellulose, hemicel-
lulose, lignin, extractives and trace elements. Wood like many other biological tissues
including bones and teeth are hierarchically structured composites in order to provide
maximum strength with a minimum of material. At the nanoscale level, wood is a
cellulosic fibrillar composite. Wood is approximately 30-40% cellulose by weight
with about half of the cellulose in nanocrystalline form and half in amorphous form
(Figure 1.3g).
Cellulose (Figure 1.3h) is the most common organic polymer in the world representing
about 1 . 5 10 12 tons of the total annual biomass production. Cellulose is the major

carbohydrate component of wood along with the hemicelluloses (20-35% by weight).
Lignin, extractives, and trace amounts of other materials make up the remaining portion
of wood. Cellulose is expressed from enzyme rosettes as 3-5 nm diameter fibrils that
aggregate into larger microfibrils up to 20 nm in diameter (Figure 1.3g and 1.3f; see also
Chapter 2 of this topic for more information on the cellulose biomachine). These fibrils
self-assemble in a manner similar to liquid crystals leading to nanodimensional and larger
structures seen in typical plant cell walls (Neville 1993, de Rodriguez et al . 2006). The
theoretical modulus of a cellulose molecule is around 250 GPa, but measurements for
the stiffness of cellulose in the cell wall are around 130 GPa. This means that cellulose
is a high performance material comparable with the best fibers technology can produce
(Vincent 2002).
Because wood has a hierarchical structure, advances in separation techniques are
goaled at leading to the commercial production and use of multiple nanoscale architec-
tures namely nanocrystalline cellulose, nanofibrils, and nanoscale cell wall architectures
(Figure 1.3g and 1.3f) (Cash 2003). Nanofibrils in their simplest form are the elemen-
tary cellulosic fibrils shown in Figure 1.3g containing both crystalline and amorphous
segments and can be hundreds to a thousand or more nanometers long. Nanoscale cell
wall architectures are the larger nanodimensional structures depicted in Figures 1.3g
and 1.3f that are composed of multiple elementary nanofibril arrangements. Nanocrys-
talline cellulose is the liberated crystalline segments of elementary nanofibril crystalline
cellulose fibrils after the amorphous segments have been removed - usually via treat-
ment with strong acids at elevated temperature. Nanocrystalline cellulose is in the range

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