Biomedical Engineering Reference
In-Depth Information
Tree
Transverse Section
Growth Ring
Cellular Structure
m
mm
cm
500
µ
m
(a)
(b)
(c)
(d)
Cellulose
Fibril Structure
Micro-Fibril
Fibril-Matrix
Structure
Cell Wall Structure
O
H
H H
O
OH
H
CH 2 OH
S3
S2
S1
P
ML
OH
H
OH
H
HO
O
H
Amorphous
H
H
CH 2 OH
OH
H
H
O
Crystalline
O
OH
H
H
CH 2 OH
Elementary
Fibrils
OH
H
O
H
25
µ
m
HO
O
H
H
CH 2 OH
OH
H
1 nm
10 nm
300 nm
O
(h)
(g)
(f)
(e)
Figure1.3 Woodhierarchicalstructure:fromtreetocellulose(Moon2006).
of 100-300 nm long. Nanocrystalline cellulose is anywhere from a tenth to a quarter
of the strength of carbon nanotubes (Xanthos 2005, Samir et al . 2005). Nanocrystalline
cellulose can also be referred to as nanowhiskers.
The hierarchical structure of wood, based on its elementary nanofibrilar components,
leads to the unique strength and high performance properties of different species of wood.
While a great deal of valuable study has led to an understanding of many mechanisms
relating to the properties of wood and paper, the overall complexity of wood's structure
has limited discovery. Today we have the tools used in other areas of nanotechnology
to look at structures down to the atomic scale. While this is fueling discovery in a
wide range of biomimetic materials, studies on wood are only now beginning. Simpler
structures found in seashells, insect cuticles and bones are being understood as relating
to their hierarchical structures. (Aizenberg et al . 2005) and we are poised for these
techniques to be applied to lignocellulosic-based products.
1.7
Nanomanufacturing
The value chain for lignocellulosic-based nanomaterials (Figure 1.4) is the same as for
any other materials - regardless of dimension (Hollman 2007, Langsner 2005). It is
based upon being able to profitably produce and sell products in the marketplace. While
the focus of nanotechnology-related research may seem to be on nanoscale properties
of materials, it is the nanotechnology-enabled macroscale end products that are most
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