Cellulose is a kind of natural high molecular polymer and it is the smallest
physical structure unit of cellulose. When it is converted into superfine fiber
it will have excellent properties including high crystallinity, high purity,
high Young modulus, high strength, high hydrophilic, high fine structure and
high transparency, etc. As a kind of natural fiber it is widely applied in varies
aspects for its outstanding properties of light, degradability, great biocompatibility
and renewability. It has attracted the attentions of many scholars. Turbak
et al. (1983) used 4% prehydrolysis wood pulp as the raw material
and made up the melamine faced chipboard. Dufresne (Li
et al., 2010) purified beet fiber through high-pressure homogenization
treatment and produced the MFC (Melamine Faced Chipboard). MFC is also adopted
here to ensure the destruction of all its cell walls. When dried, MFC is put
for the preparation of high strength fiber sheet. Zimmermann
et al. (2010) adopts different raw materials and through using mechanical
dispersion and high pressure homogenization, MFC with maximum length and diameter
smaller than 100 nm was obtained. Analysis shows that agglomeration in the micron
size of cellulose has poor uniformity of network structure. Using sulfuric acid
hydrolyzed cotton, wood pulp and other raw materials. They also studied the
self-assembly properties and the synthesis conditions of cellulose liquid crystal.
In 2006, (Bondeson et al., 2006) optimized the
conditions of the sulfuric acid hydrolysis of Norway spruce preparation Nano
fibers and found the rapidly and high yields method of preparing Nano cellulose
Ding Enyong (Qin et al., 2011) used cotton
fiber as raw material to produce spherical or ellipsoidal Nano fibers, in size
range of 5-100 nm, through ultrasonic dispersion and acid hydrolysis. N crystal
type of cellulose was identified on the particles out layers. Zhong-Yan
Qin (Bai et al., 2009) adopted the cotton pulps
as raw material, fabricated Nano fibers NCC with diameter of 5-10 nm and length
of the 100-400 nm, through the ultrasonic treatment. Nano fibers synthesized
by this method have particular properties of both high crystallinity and yield
MATERIALS AND METHODS
Preparation of nitrocellulose: Salix wood power and nitric acid-ethanol
(1:4) with a liquid ratio of 1:25 are mixed in a reactor equipping with a reflux-condensing
device. The mixture is put in the water 100°C for about one hour, then repeat
above operations for three to five times, till cellulose turns white. Then residue
is washed by ethanol nitrate and then hot water, until its pH value reached
neutral. The finally use anhydrous ethanol washing for twice and then drains
Preparation of MCC: Salix psammophila cellulose is divided on 6% hydrochloric
acid, (Salix cellulose): (hydrochloric acid) =1:20, hydrolyzing temperature
is 95 degrees Celsius. The time of hydrolysis is set to 25 min. After though
rinsing and washing to neutral pH value, samples are dried at low temperature.
Preparation of nanometer cellulose: The Microcrystalline Cellulose (MCC)
is dissolved into a quantity of 64% H2SO4 solution. Then
microcrystalline cellulose solution is dispersed by microwave analyzer and then
subject it in 45centigrade water bath for 2 h. The solution is transferred to
a dialysis bag for dialysis until it reached neutral. The bag containing Nan-crystalline
cellulose is put for drying in the freezes dryer.
TESTS OF SAMPLES PROPERTIES
Measurement of ATR-FTIR: ATR-FTIR means Attenuated total reflectance-Fourier
transform infrared spectrometry. The infrared spectrums of nitrocellulose, microcrystalline
cellulose and cellulose Nanowhiskers are tested by Pekin-Elmer Fourier transform
total reflection infrared spectroscopy. Each sample is scanned for 16 times.
Middle infrared spectral region is refined to 650 ~ 4000 cm-1 with
the resolution of 2 cm-1.
Measurement of X-ray diffraction: The X-ray diffract meter is applied
in the test, Cu-Ka radiographic source is 40 kV and 250 mA. The scan rate is
5° min-1, the scanning range is 20 between 5 to 60°.
Thermo-gravimetric analysis: Differential thermal scanning calorimeter
was employed here to measure the fibers Thermo Gravimetric (TG) curves. The
tests are conducted in nitrogen atmosphere, the nitrogen flow printed mUmin,
heating rate of 10°C min-1. The test temperature is ranged from
25 to 600°C.
RESULTS AND DISCUSSION
From Fig. 1 it can be seen that cellulose molecules of the
H and the adjacent hydroxyl groups of the O are linked to the formation of hydrogen
bonds on the cellulose. These hydrogen bonds stretching vibrations, however,
are concentrated at about 3400 cm-1. The hydrogen bonding found among
molecules are included but not limited to HO (3) O (2) HO (6), O (3) HO (5)
O (6). The vibration peak of both microcrystalline cellulose and Nano-cellulose
are observed to be with the trend of moving to the lower wave number. The absorbance
of Nanocellulose and microcrystalline cellulose are significantly greater than
that of the nitrocellulose, indicating that both intermolecular and intermolecular
hydrogen bonds are strengthened. It is caused by the existence of alcohol hydroxyl
groups of cellulose during the preparation the microcrystalline cellulose and
nanometer cellulose. The cellulose of the alcohol hydroxyl groups is in a pattern
of acid-oxidized. Smaller absorption peaks at 1710 cm-1 are only
found in nitrocellulose samples, produced by the ester group. For the micro-nano
sample of cellulose, the corresponding peak is not found in the spectrum. The
stretching vibration of C = O fell in the band of 1598 cm-1. It is
easy to find the band of nitrated cellulose, microcrystalline cellulose in Fig.
1 without much change. The absorption peaks of Nano-cellulose are broadened,
as the result of the oxidation, during the preparation of Nano -ellulose by
sulfuric acid. The characteristic peaks of cellulose fell with in 1368-1361
cm-1. The other peaks between 1160-1000 cm-1 are corresponding
to a cyclic C-O-C asymmetric plane stretching vibrations. 11060 cm-1
stood for the circular C-O-C's C-C's stretching vibration. All C-C bonds are
obviously oxidized through the nanometer of the cellulose. Other peaks found
on the spectrum include the cyclic C-O-C asymmetric plane stretching vibration/CH2
(CH2OH) on 898 cm-1 and the OH surface deformation vibration
on 700-666 cm-1.
|| Nitrocellulose, microcrystalline cellulose, nano cellulose
||Nitrocellulose, microcrystalline cellulose, nano cellulose
X-ray spectrum diagram
Figure 2 is the X-ray patterns of nitrated cellulose, microcrystalline
cellulose and cellulose Nanocrystal. From the figure, one can conclude that
the difference between their each individual characteristic peaks remains mainly
consistent. The strongest peak located at 14.8, 16.1 and 22.4°, respectively.
Each of them is in correspondence to the cellulose crystal of 101, 10T and 002.
So from this phenomenon it is quite sure that the cellulose maintains itself
in the form of type I during the process of micro-Nano preparation. Compared
to the cellulose samples, crystallinity is increased from 76.2 to 87.6%. The
diffraction peak represents for a mixture with the process of micro Nano cellulose,
is located at 22.4° and is sharper and higher in relative peak strength.
However, the dispersion of non-crystalline is decreased, as in the opposite
zone of crystalline. In the process of acid-hydrolyzation, hydrogen ions entered
the amorphous regions of cellulose and accelerate the hydrolysis of the glycoside
bond cleavage. Thus the cellulose crystal is finally obtained. For the amorphous
regions of cellulose, reactivity activity is scored higher than the crystallization
zone. In the hydrolysis reaction, amorphous regions of cellulose reacted quickly
while the crystal fiber zone restricted its own reactions to the surface areas.
Therefore, crystallization among nitrocellulose, microcrystalline cellulose
and cellulose Nano-crystal comparison of Nano-crystalline Cellulose are all
The polymers such as Cellulose will start its degradation as dehydrated and
aromatized when heated. From Fig. 3 and 4,
they show the identical distribution of the decomposition temperature of nitrated
cellulose and microcrystalline cellulose. The pyrogenation temperature of the
nitrocellulose is obviously higher, when compared with the Nanocrystalline Cellulose.
||Nitrocellulose, microcrystalline cellulose, Nano-cellulose
thermal analysis curve
||Nitrocellulose, microcrystalline cellulose, Nano cellulose
thermal gravity analysis curve
Seen from the figure, a smaller absorption peak will appeared when the temperature
is among 25-150°C. When the temperature is added to 300-400°C, another
strong absorption peak is appeared. As to the nitration cellulose and microcrystalline
cellulose, there are no obvious absorption peaks at 150-240°C while Nano
cellulose produces an opposite peak under the effects from thermal behavior.
A strong absorption peak is found at about 240°C and later is verified to
be the Nano cellulose. Figure 3 and 4 show
the smaller absorption peak of Nano-cellulose and indicated by the figures,
the heat of Nanocrystalline Cellulose is considerably smaller than nitrocellulose,
thus has worse in thermal stability. Due to the small sizes, Nano cellulose
absorbs heat faster than nitrocellulose molecules with increasing temperature.
It also show that the Nano-cellulose possess a good heat dissipation effect,
due to the exposure of Nano cellulose molecular chain function groups, followed
by activity strengthening and carbonization under lower temperature. The Nanocrystalline
celluloses como water and C2, C4 hydroxyl are removed at the same time.
The emerging regions of both vibration peak of microcrystalline cellulose and
cellulose Nanocrystal have the trend of moving towards lower wave numbers. The
absorption of Nano cellulose and microcrystalline cellulose are greater than
that of nitrocellulose. Intermolecular hydrogen bond is strengthened while at
the same time the cellulose of hydroxyl is oxidized.
During the process of preparing micro-nano cellulose its crystal structure
remains keep to type I. Compared with the nitrocellulose, the crystalinity of
cellulose is increased from 76.2-87.6%. In the same process, the diffraction
peak at 22.4° is sharpened while the relative peak strength is increased
significantly but the non-crystal zones are decreased.
Nano cellulose has a better dissipation effect than the microcrystalline cellulose,
or cellulose in the process of micro nanometer. When the section group of cellulose
molecular chain is exposed, activity intensity will be increased. The carbonization
is then achieved under low temperature. Celluloses
combo water and C2, C4 hydroxyl are removed at the same time.
We gratefully acknowledge the financial support from Introduction of Advanced
International Forestry Science and Technology Project (No. 2011-4-07) and Inner
Mongolia Natural Science Fund Major Projects (No. 2011ZD007).