Civil Engineering Reference
In-Depth Information
Figure 15.2
Atomic arrangement of (a) cellulose I
a
with hydrogen bonding network; (b) cellulose I
ß
with
hydrogen bonding. Hydrogen bonding is shown by dotted lines [27].
der Waals interactions, with parallel shear, whereas cellulose I
ß
is comprised of mono-
clinic two-chain unit cell having stacking of parallel cellulose chains with alternating
shear [21]. However, cellulose I
a
can be transformed into cellulose I
ß
by hydrothermal
treatment without losing its crystallinity [22-24] or by treatments with various solvents
[25] . h e atomic arrangement of cellulose I
a
and cellulose I
ß
with hydrogen bonding
network, however, where conformation of chains is similar but hydrogen bonding pat-
tern is dif erent [26, 27], is shown in Figure 15.2.
Overall, cellulose I is mainly responsible for the mechanical properties of reinforced
polymer composites due to its high elastic modulus and crystallinity. h e elastic modu-
lus of perfect cellulose crystals has been calculated and estimated between 130 GPa to
250 GPa, whereas the tensile strength is approximately between 0.8 GPa to 10 GPa [28].
In previous studies cellulose has already been processed into i lms, gels, i bers, microi -
bers, nanoi bers and nanocrystals for dif erent applications [29-32]. Actually, cellulose
i ber is the bundle of microi brils comprising nanocrystalline domains linking through
amorphous domains [33].
15.3
Nanocellulose
Nanocellulose can broadly be dei ned as a set of particles having at least one dimen-
sion in nanoscale obtained by dif erent mechanical/chemical, or only chemical, or acid-
hydrolysis methods. According to a survey of the literature, there is no standardized
nomenclature for cellulose-based nanoparticles, while various terms have been used
to describe a particular set of cellulose nanoparticles. Because of inconsistency in use
of these terms, there are some particle types depending on source materials of cellu-
lose and method of extraction. However, depending on their aspect ratio, nanocellu-
loses have already been characterized with dif erent terms like microi brillated cellulose
(MFC-diameter: 10-100 nm) [34] , nanoi brillated cellulose (NFC-diameter: 4-20 nm)
[35], CNCs (CNCs-diameter: 3-5 nm) [34, 36], tunicate CNCs (t-CNCs-diameter: 20
nm) [34, 37], algae cellulose particles (AC-diameter: 20 nm) [38, 39], bacterial cellulose
particles (BC-diameter: 6-50 nm) [40, 41]. It can commonly be called "nanocellulose,"
