Civil Engineering Reference
In-Depth Information
5.2.5
Extraction of Cellulose Nanoi llers
Many studies have been done on isolation and characterization of cellulose nanoi -
bers from various sources. Cellulose nanoi bers can be extracted from the cell walls
by simple mechanical shearing or by a combination of both chemical and mechanical
routes [10] .
Alemdar and Sain [19] have extracted cellulose nanoi bers from wheat straw by a
chemical treatment followed by a mechanical treatment (cryocrushing, disintegration,
and dei brillation steps) to individualize the nanoi bers from the cell walls.
Zimmermann
et al.
[20] separated nanoi brillated cellulose (NFC) from dif erent
cellulosic precursors by mechanical dispersion and high pressure homogenization
processes (up to 1500 bar). h e diameter was below 100 nm. Cellulose nanoi bers
were extracted by Wang and Sain [21] from soybean stock by chemomechanical treat-
ments ( Figure 5.2 ). h ese were bundles of cellulose nanoi bers with a diameter ranging
between 50 and 100 nm and lengths of thousands of nanometers.
In some cases the isolation of cellulose micro/nanoi brils involves enzymatic pre-
treatment followed by mechanical treatments [22, 23]. h e morphology and aspect ratio
of the extracted nanoi bers may vary depending upon the raw materials and extraction
techniques [24]. Examples of various cellulose nanoi ber extraction methods, including
microi brillar cellulose (MFC) are shown in Table 5.1.
h ere are basically two families of nanosized cellulosic particles. h e i rst one con-
sists of cellulose nanocrystals and the second one is microi brillated cellulose (MFC)
[17] . However, dif erent terminologies are used to describe these cellulose nanopar-
ticles, leading to some misunderstanding and ambiguities. Currently, the isolation,
characterization, and search for applications of novel forms of cellulose, variously
termed crystallites, nanocrystals, whiskers, nanoi brils, and nanoi bers, is generating
Pretreated with 17.5%
NaOH solution, for 2 hr.
Soybean stock
used as the raw
materials
NaOH treated
mass
Acid hydrolysis with
1M HCl, at 70-80°C,
for 2 hr.
2% w/w NaOH
solution, at 70-80°C,
for 2 hr.
Acid hydrolyzed
mass
Alkali treated
mass
Cryocruhing using
liquid Nitrogen
Isolated
cellulose
nanoiber
Deibrillation
Cryocrushed
mass
With High pressure
homogenizer
Figure 5.2
Isolation of cellulose nanoi bers by chemomechanical treatment [10].
