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Accepted Manuscript
Preparation and characterization of cellulose nanofibers and nanocrystals from
liquefied banana pseudo-stem residue
Fanrong Meng, Guoqing Wang, Xueyu Du, Zhifen Wang, Shuying Xu, Yucang Zhang
PII:
S1359-8368(18)32451-X
DOI:
10.1016/j.compositesb.2018.08.048
Reference:
JCOMB 5878
To appear in:
Composites Part B
Received Date: 3 August 2018
Accepted Date: 13 August 2018
Please cite this article as: Meng F, Wang G, Du X, Wang Z, Xu S, Zhang Y, Preparation and
characterization of cellulose nanofibers and nanocrystals from liquefied banana pseudo-stem residue,
Composites Part B (2018), doi: 10.1016/j.compositesb.2018.08.048.
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ACCEPTED MANUSCRIPT
Preparation and Characterization of Cellulose Nanofibers and Nanocrystals from
liquefied Banana Pseudo-stem Residue
Fanrong Meng, Guoqing Wang, Xueyu Du, Zhifen Wang, Shuying Xu, Yucang Zhang∗
Key Laboratory of Ministry of Education for Advanced Materials in Tropical Island Resources,
Hainan University, Haikou 570228, Hainan, China
Chemical Engineering, Hainan University, Haikou 570228, China
Abstract
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State Key Laboratory of Marine Resource Utilization in South China Sea, College of Materials &
This work aimed to extraction of nanocellulose from banana pseudo-stems (BPs)
via energy-saving method for reinforcing polymeric matrix materials. BPs was
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initially subjected to an atmospheric liquefaction process to remove waxes, pectin,
hemicellulose and partly lignin. Bleaching treatment was further conducted to
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eliminate residual lignin and polycondensate in the liquefied residues. Cellulose
nanofibers (CNF) were subsequently obtained by a two-stage TEMPO-mediated
oxidation and high-intensity ultrasonic treatment. TEMPO-oxidized cellulose (TOC)
thus produced were acid hydrolyzed into nanocrystals (CNC). Results show that
liquefied residue content as well as its constituent varied with respect to liquefaction
time. Scanning electron microscopy (SEM) and fourier transform infrared (FTIR)
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demonstrate that the progressive removal of non-cellulosic impurities. Results of
transmission electron microscopy (TEM) and atomic force microscopy (AFM) exhibit
that CNF present a range of 3~5 nm in diameter and 400~500 nm in length, while
CNC have average diameter of 2.24 ± 0.57 nm and a length of 125 ± 28 nm. X-ray
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diffraction (XRD) analysis indicates that the cellulose crystal type of TOC would stay
unchanged and the CNCs have a high crystallinity (75%). Thermogravimetric analysis
(TGA) was also used to investigate the thermal stability of the residues and
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nanocelluloses.
Keywords: Banana pseudo-stem;
Nanofibers; Cellulose Nanocrystals
1. Introduction
Liquefaction;
TEMPO-oxidized
Cellulose
Given the growing concern of environmental conservation and dwindling
exhaustion of petroleum resources, exploitation of new materials has been the object
for academic and industrial researchers. Renewables are by far the fastest-growing
fuel source, increasing five-fold and providing around 14% of primary energy [1].
Cellulose, produced from plants, animals or bacteria, has been the most popular
∗
Corresponding author.
E-mail address: yczhang@hainu.edu.cn (Y. Zhang)
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natural resource among various renewables materials [2]. Annually, about 7.5 × 1010
tons of cellulose are processed [3]. Plants are uppermost industrial source of cellulose
[4, 5]. Currently, pulping process [6], steam explosion [7], and alkaline treatment [8, 9]
have been taken to remove hemicellulose, lignin and a comparably small amount of
extractives and inorganic salts in lignocellulosic biomass to extraction cellulose.
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Moreover, liquefaction is usually an effective method for converting solid biomass
into bio-polyols [10], the liquefied residue collected and evaluated has been
successfully used in the preparation of nanocellulose [11, 12].
Nanocellulose as reinforcing agent in polymer matrixes warrants a tremendous
level of attention in the materials community because of its availability, abundant, low
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cost, and the related physicochemical characteristics such as unique optical,
rheological and mechanical properties, large surface area and aspect ratio, and
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favorable thermal conductivity compared with other commercial fibers [13, 14].
Typically, nano-scale structural cellulose can be distinguished as three types of
materials: cellulose nanocrystals (CNC), cellulose nanofibrils (CNF) and bacterial
cellulose (BC). However, CNC and CNF are much more common [15]. Different
biosynthesis conditions, techniques of extraction from respective sources, give rise to
cellulose nanoparticles with varied crystal structure, morphology, surface chemistries,
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and specific properties [16].
CNC are mainly fabricated by acid hydrolysis/heat controlled methods
employing sulfuric acid, hydrochloric acid, phosphoric acid, hydrobromic acid, etc
[17]. However, sulfuric acid is more frequently-used due to its versatile tuning the
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surface charge density that endow NCC suspensions higher colloidal stabilities [18].
CNC with rod, sphere, and network morphologies were prepared by acid hydrolysis of
cotton cellulose, followed by freeze-drying [19]. CNF preparation methods can be
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summarized as three kinds of processes: (i) mechanical disintegration (e.g.
homogenization, grinding, and ball milling), (ii) biological and chemical
pretreatments (e.g. enzymatic hydrolysis, TEMPO oxidation, and quaternization), and
(iii) combination of chemical and mechanical treatments [15]. The main distinctions
between CNC and CNF are their dimension and crystallinity. CNFs contain both
amorphous and crystalline cellulose domains with length of up to few micrometers,
while CNCs are highly crystalline (90% crystallinity) with length typically less than
500 nm. Many researchers have shown that CNC and CNF can be used as follows
applications, for example, as strength additives to reinforce polymer in heavy metal
adsorbent [20]; combining with inorganic nanoparticles or polymers for antimicrobial
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applications [21]; Moreover, modifications of nanocellulose are guide to help in
designing polymer/nanocellulose composites through the utilization of nanocellulose
properties and the selection of functional polymers, paving the way to specific
polymer–filler interaction [22].
Banana Pseudo-stem (BPs) is the by-product obtained after the banana harvested.
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Bananas worldwide production is approximately 113.28 million tons per year, with
China accounting for around 11.76% [23]. Instead of being discarded, large amount of
BPs offers an ideal opportunity for producing value-added cellulose [24, 25].
Therefore, the main goal of this study is to develop simple and energy saving method
to isolate nanocellulose from BPs. Initially, BPs feedstocks were given to an
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atmospheric liquefaction; the liquid products can be used for further applications [26].
Then, the remaining residue was collected and bleached. Finally, the residues were
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subjected to TEMPO-mediated oxidation before ultrasonic fibrillation process to
extract NFC and acidolysis process to produce CNC. The obtained samples were
characterized for understanding their morphological, structural and thermal properties.
2. Materials and methods
2.1 Materials and chemicals
Banana pseudo-stem harvested in Haikou, China was dried, milled and sieved to
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50 meshes. Polyethylene glycol 400 (PEG 400) and glycerol were used as the
liquefaction reagents, sulfuric acid acted as the acid catalyst as well as used for
hydrolysis. Sodium chlorite and citric acid were used as bleaching agents. Sodium
hypochlorite was come from Guangzhou Chemical Reagent Co., China. Chlorous acid
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sodium and TEMPO was purchased from Aladdin Co., China. The other chemicals
were of reagent grade and were used without further purification.
2.2 Liquefaction of BPs
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25 g of liquefaction solvents (PEG 400: glycerol= 4:1, w/w), 0.49 g of 98%
sulfuric acid were added to a three-necked glass flask and preheated to 150 °C. 5 g of
BPs was added to the mixture to start the reaction. After reacting for a specified time
under continuous stirring and reflux condition, the flask was immersed into cold water
to quench the reaction. The black precipitate was diluted with excess ethanol. The
liquefied residue (LR) was collected by filtration and dried at 105 °C. Residue yield
was equivalent to the weight percentage of the residue to the pristine mass of BPs, as
defined with the following equation:
Liquefactionyield % = 1 −
× 100%
(1)
Liquefied products were obtained after evaporation of ethanol for the other
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applications.
2.3 Chemical composition
The chemical compositions of BPs and LR were determined as follows.
Acid-insoluble lignin was determined according to the ASTM D1106-1996 (2001),
Cellulose content was determined by the nitrate method [27]. The holocellulose
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(cellulose + hemicellulose) content was measured by the acid chlorite method. The
hemicellulose content was estimated by difference. An average of three replicates was
calculated for each sample.
2.4 Preparation of CNF and CNC
2.4.1 Bleaching process of LR
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The bleaching process of LR was conducted by adding acidified sodium chlorite
solution (6 wt%, pH 3.8~4.5) at 75 °C for 1h to remove residual lignin and
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polycondensate. This treatment was repeated 3~4 times until the residue became
colorless. The reaction mixture was cooled, rinsed and filtered using excess deionized
water. Finally, bleached LR (BLR) was obtained after freeze drying.
2.4.2 TEMPO-mediated oxidation of liquefied residue
According to literatures reported by Saito & Isogai [28] and Hirota [29]. 1 g of
BLR were suspended in 100 mL of acetate-sodium acetate buffer (pH=4.8). 16 mg of
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TEMPO and 100 mg of NaClO2 were added to the mixture under magnetic stirring at
60 °C. Immediately, 0.5 mL 1 wt% NaClO solution was added dropwise and the
reaction was carried out on an airtight shade reactor for 24 h. The oxidation was
terminated with 100 mL ethanol. Oxidized BLR (OBLP) were filtered, washed and
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freeze-dried.
2.4.3 Preparation of CNF
To isolation individual CNF, 50 g of 0.5 wt% OBLP suspensions were subjected
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to 1 h cycles of sonication using an Ultrasonic Processor (Dekelaier JY98-ⅢL, 20
kHz, 1000 W). A double wall glass crushing cup attached to a recirculating cooling
system was used to keep the solution temperature at 4 °C. Finally, the OBLP
suspension was centrifuged at 10000 rpm for 25 min to remove non-fibrillated
cellulose; a transparent suspension of CNF was collected for characterization.
2.4.4 Preparation of CNC
1 g of the OBLR was soaked in 20 mL of sulfuric acid (64 wt%) under stirring.
Hydrolysis was last for 30 min at 50 °C and quenched by adding 10-fold cold water.
The mixture were subjected to ultrasonic fibrillation (25 kHz, 750 W) followed by
centrifugation (10000 rpm at 4 °C for 15 min). CNC uniform distributed in the
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translucent supernatant was dialyzed for 5 days with deionized water and freeze dried.
The precipitate was also dried and weighed.
2.5 Characterization
2.5.1 Scanning electron microscopy (SEM)
The Scanning electron microscopy (SEM) photographs of dried samples were
were coated with platinum using the sputtering technique.
2.5.2 Fourier transform infrared spectroscopy (FTIR)
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taken on a Hitachi S3000N scanning electron micro-scope (10 KV). All the samples
Fourier transform infrared spectroscope (FTIR) analysis of samples was
conducted on a TENSOR27 spectrometer (Bruker) using the KBr disk technique. 4
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cm-1 resolution and 16 scans were accumulated for each spectrum in a range of
500~4000cm-1.
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2.5.3 X-ray diffraction (XRD)
XRD profiles of the samples were performed on a Bruker AXS diffractometer,
Model D8 Advance, using Cu Kα radiation source (30 kV and 20 mA). The
diffraction intensities were recorded between 5 and 50° (2θ angle range) with a scan
rate of 0.4°min-1. The relative crystallinity index (Cr.I.) of the sample was calculated
following Eq. 2 [30]. I002 is the maximum diffraction intensity of the (002) plane, and
#$. &. % =
'(() *'+,
'(()
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Iam represents the diffraction intensity of the amorphous part [31].
× 100
(2)
The average thickness of cellulose crystallites was estimated from the X-ray
-./0 = 3
12
4/) 6
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diffraction patterns by using Scherrer’s Eq. (3) [32].
7
(3)
where Dhkl is the crystallite dimension in the direction normal to the h k l family of
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lattice planes, K is the correction factor and usually taken to be 0.9, λ is the radiation
wavelength, θ is the diffraction angle and β1/2 is the peak width at half maximum
intensity. The crystal size was determined perpendicular to the (002) planes. Before
plotting, data were smoothed over 35 adjacent points and then normalized, so that the
main peaks had the same y-axis values and could be compared directly.
2.5.4 Transmission electron microscopy (TEM)
TEM photographs of nanocellulose were carried out on a transmission electron
microscope (JEOL JEM-1200EX, Japan) with an accelerating voltage of 120 kV. A
droplet of the diluted suspension (0.2 wt% to 0.01 wt%) was deposited on the surface
of carbon-coated copper grids.
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2.5.5 Atomic force microscopy (AFM)
The morphologies of NFC and CNC were confirmed using the AFM
measurements, which were performed with Dimension Icon equipment (Bruker,
America). AFM images were obtained at room temperature in the dynamic mode with
a scan rate of 1 Hz and using Si tips with a curvature radius of less than 10 nm and a
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spring constant of 42 N m-1. The thicknesses of nanocellulose were determined using
the Vector Scan software (software for Shimadzu’s SPM-9600).
2.5.6 Thermogravimetric analysis
Thermogravimetric analysis (TGA) of fibers were studied using the NETZSCH5
209F3 thermogravimetric analyzer over a temperature range of 40~800 °C at a
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heating rate of 10 °C/min under a nitrogen flow rate of 20 mL/min.
3 Results and discussions
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3.1. Effect of liquefaction time
Fig. 1. The effect of the reaction time on the liquefaction yield and chemical constituent of LR.
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(T=150 °C, charge ratio 5:1, 1mmol/g BPs)
The composition of the three major constituents of the BPs powder was 23.8%
cellulose, 25.7% hemicellulose, 8.6% acid-insoluble lignin. According to our previous
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study [33], cellulose fibers can be obtained by selectively liquefied holocellulose. As
shown in Fig. 1, the whole liquefaction could be divided into two stages. Pectin and
wax were easy dissolved in liquefying agent; at the same time, the amorphous regions
in the BPs, including hemicellulose, lignin and disordered inter-crystalline regions of
cellulose, could be hydrolyzed [34, 35], so both the liquefaction yield and the content
of hemicellulose and lignin from the LR changed a lot during the first fast stage.
About 68% of the BPs components were liquefied and converted into soluble products
within 30 min. Cellulose crystallites were difficult to be depolymerized, and the
liquefaction yield tended to remain almost constant in the second stage. When the
reaction time extended to 75 min, the content of lignin demonstrated a slight increase
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in the LR, which could be ascribed to the lignin condensation reaction [36]. The
content of cellulose from the LR decreased first due to the depolymerization of
amorphous region, and then increased as the liquefaction time increased. 79.06% of
lignin and 98.53% of hemicellulose were degraded during the acidolysis and
alcoholysis in liquefaction process, so the relative cellulose content increased.
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Accordingly, 90 min is optimal reaction time for liquefaction with the maximum
cellulose content of 91.33%.
Liquefaction was conducted to solubilize the extractives, lignin and
hemicelluloses, while the bleaching process was applied to remove the residual lignin
[37]. The evolution of macroscopic appearance for the BPs fibres after two stages of
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treatment is presented in Fig. 2. Brown BPs changed to brownish-black because of the
creation of chromophore during liquefaction, such as lignin derivatives. The bleached
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material appears completely white colored, indicating that a majority of the initial
non-cellulosic components and impurities were removed by purification process;
consequently the final product is almost pure cellulosic material.
(b)
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(a)
Fig. 2. Photographs of raw materials: (a) BPs, (b) LR and (c) BLR
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3.2 Microstructure morphology of LR
(c)
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Fig. 3. SEM images of BPs (a, b), LR (c, d) and BLR (e, f).
Both wax and
The microstructure of the BPs fibers was imaged by SEM (Fig. 3). As shown in
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Fig. 3a and b, rough surface and long wrapped fiber bundles are observed for the raw
materials of BPs. Those outer non-cellulosic layer consist of hemicellulose, lignin,
wax, pectin and other impurities, which are known to surround the surface of cellulose
fibers acting as "natural binders". After liquefaction (Fig. 3c and d), the fiber bundles
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tend loose and some individual micro fibrils exposed due to the partial removal of
non-cellulosic impurities. Many small pieces and granules appeared on the surface of
residue are probably lignin polycondensate and deposits of inorganic minerals. With
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bleaching treatment, residues show relative glossy fiber-shaped texture and the
surface is relatively smooth (Fig. 3e and f). Moreover, it is worth noting that the
residue size is significantly smaller compared to the raw materials of BPs. This is
attributed to the rigid fiber bundles cracked into small irregular fragments during
delignification.
3.3 Morphology of NFC and NCC
The morphological features of NFC and CNC produced from BPs leaves and
balls were assessed by TEM observations (Fig. 4). The observation revealed
nanosized fibrils with wide heterogeneous distribution both in width and in length
(Fig. 4a, b). The dimensions of the corresponding nanofibrils were evaluated by
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digital image analysis (Image J) of TEM micrographs using a minimum of 90
nanofibrils. Data indicated broad width distribution of the nanofibrils ranging from 5
up to 21 nm. The individual fibrils with width lower than 5 nm corresponded
presumably to elementary cellulose fibrils composed of altering crystalline and
amorphous domains. On the other hand, the larger fibrils are likely composed of
(a)
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(b)
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bundles of elementary fibrils blinded together through hydrogen bonding.
(d)
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(c)
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Fig. 4. TEM images of CNF (a, b) and CNC (c, d) extracted from liquefied BPs residues.
Fig. 4 (c), (d) shows TEM micrographs of CNC, which presents needle-like
nanoparticles. These images show individual nanocrystals and some aggregates. The
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appearance of laterally aggregated elementary crystallites in TEM images is expected
due to the high specific area and strong hydrogen bonds established between the
whiskers. These aggregates may exist even in suspension but, when the dispersing
medium is removed, as in the case of the TEM sample preparation, bundles of
whiskers can be even more numerous than individualized needle.
3.4 X-ray diffraction
The X-ray diffraction patterns of BPs, BLR, OBLR, CNF and CNC are depicted
in Fig. 5. They are typical of cellulose I with an amorphous broad hump and
crystalline peaks around 2θ = 16°, 22°, and 35° [38]. The Cr.I. was determined for the
various samples using the formula (2) and the results for the BPs, BLR, OBLR, CNF
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and CNC are 8.7, 26.3, 67.2, 64.4 and 73.5%, respectively. A continuous increase of
the Cr.I. value was observed upon the successive chemical treatments.
The higher crystallinity of BLR with respect to BPs can be ascribed to the
progressive removal of hemicellulose, lignin and other amorphous non-cellulosic
compounds induced by the liquefaction and bleaching treatments. Cellulose has a
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crystalline structure because of hydrogen bonding interactions and Van der Waals
forces between adjacent molecules [39]. The lightly decrease in Cr.I. of OBLR
compared to BLR was observed maybe attributed to the surface carboxylation
consumed partly hydrogen bond and reduced intermolecular forces; thus the oxidation
process not only modified surface chemical group of cellulose but also partly
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destroyed the crystalline ones. A similar effect of a hydrolysis time in excess was
observed in a previous study. The subsequent highly increase in crystallinity of CNF,
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CNC in relation to BLR was found, owing to ultrasonic cavitation and hydronium
ions can have access to amorphous regions of cellulose and trigger the cleavage of
glycosidic bonds, which eventually releases more individual crystallites. In Fig. 5,
CNC displayed narrowest and sharpest peaks at 2θ = 22° due to their higher
crystallinity compared to other samples. It's reported that the growth and realignment
of monocrystals may occur simultaneously during the generation of CNC and further
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improve the cellulose crystallinity [40].
This raise in the cellulose fibres crystallinity was also expected to enhance their
rigidity and strength. Accordingly, it was supposed that the potential mechanical
behaviors and reinforcing capability of nanocellulose increased [41]. The average
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cross-sectional dimension of the elementary cellulose crystallites was calculated from
XRD by employing Scherrer’s equation. Scherrer’s expression is limited to suitable
for samples of high crystallinity, therefore this determination was made only for CNF
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and CNC, and the values found were 2.73 nm.
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Fig. 5. X-ray diffraction patterns of BPs materials, liquefied residues and TEMPO-oxidized
residues
3.5 FTIR characterization
Fig. 6 exhibits infrared spectra of BPs, BLR, OBLR and CNC. Wide band
between 3440 to 3400 cm-1 is ascribed to O-H stretching vibrations. The peak near
2900~2925 in all spectra is corresponding to stretching vibration of the aliphatic
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saturated C-H group. Band around 1640 cm-1 is assigned to the absorption of water.
The peak at 1599 cm-1 in BPs may be from the water, but it was mainly regarded as
the aromatic C-C stretch of aromatic ring in the lignin (Sun et al., 2005). The bands at
1735 and 1253 cm-1 corresponds to carbonyl units (C=O) stretching vibration
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representative of lignin and hemicellulose and C-O-C vibrations of aromatic ether
linkages in lignin [42, 43], respectively, are remarkable reduced or not present at all in
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the BLR sample. This observation suggests the removal of lignin and hemicellulose
after the liquefaction and bleaching treatment [44]. After oxidation, the hydroxyl
group of OBLR decreased obviously, while C=O carbonyl stretching vibrations at
1700 cm-1 was overlapped by the band 1640 cm-1 which is assigned to the absorption
of water. In addition, typical cellulose signals are found prevalent to all spectra,
including the rock vibration of the C1-H around 897 cm-1, the characteristic C-O
stretching (from C2, C3 and C6) at 1052~1032 cm-1; the C-O-C stretching vibration
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of pyranose ring skeletal at 1161 cm-1, and the C6-H2 flexion between 1428 and 1317
cm-1 [45]. These results suggest that the overall cellulose molecular structure was not
changed following the oxidation conducted on the BLR fibres. No significant
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differences accept for a tiny peak at 1238 cm-1 were observed between the spectra
corresponding to oxidized and acid hydrolyzed fibers. The band which is attributed to
S=O vibration appeared due to the esterification reaction [19]. The results indicate
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that the cellulose molecular structure remains unchanged following acid hydrolysis.
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Fig. 6. FT-IR transmittances of (a) BPs, (b) LR, (c) BLR, (d) OBLR and (e) CNC
3.6 Thermogravimetric analysis (TGA)
As reported in previous studies, the treatment with sulfuric acid leads to a
significantly decrease in thermal stability of cellulose whiskers. Since typical
processing temperatures for thermoplastics rise above 200 °C, the thermal stability of
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these crystals is a key factor in order for them to be used as effective reinforcing
materials. The TG and differential thermogravimetry (DTG) curves of the BPs, BLR,
OBLR and CNC are presented in Fig. 7 (a) and (b), respectively. The corresponding
data are listed in Table 1. In all cases, a small weight loss was found in the range of
weight compounds (present in BPs).
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35~150 ◦C, due to the evaporation of the water of the materials or low molecular
The first degradation step corresponds basically to cellulose degradation
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processes such as depolymerization, dehydration and decomposition of glycosyl units.
Due to the low decomposition temperature of hemicellulose, lignin and pectin, the
DTG curve of untreated soy hulls showed a small broadening or shoulder on the left
side of the main peak, which accounts for the pyrolysis of cellulose (about 340 ◦C).
On the other hand at the same step, the thermal degradation of OBLR also proceeded
at lower temperatures than BLR, but this behavior was expected given that the
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introduction of sulfate groups diminishes the thermostability in the cellulose whiskers
because of the dehydration reaction of cellulose crystals as reported elsewhere.
The second degradation step (DTG peak above 425 ◦C) was attributed to the
oxidation and breakdown of the charred residue to lower molecular weight gaseous
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products . In this step, less charred residue of BLR than that of BPs is due to that fact
that the non-cellulosic could induce higher char formation, while the increased
charred residue of OBLR is because of the sulfate groups acting as the flame
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retardants [46]. These results are very consistent with results obtained from the
chemical composition, XRD and FTIR measurements.
Fig. 7. TG and DTG curves of BPs materials, liquefied residues and TEMPO-oxidized residue
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Table 1
Detailed DTG data of CG-PVA composite films as obtained from TGA measurements under N2
T10% (°C)
T25% (°C)
T50% (°C)
TDTAmax (°C)
R700 (%)
BPs
207.5
268.3
319
208.9/311.2
27.5
LR
274.3
296.8
314.3
308.2
20.5
BLR
315.5
341.5
356.5
357.3
12.3
OBLR
260.2
291.9
328.4
332
19.5
CNC
319.7
334.8
345.7
347.9
4.0
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Sample
4. Conclusions
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The present work shows that nanocellulose can be isolated from banana
pseudostem. Liquefaction and chemical treatment with sodium chlorite removed the
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non-cellulosic constituents resulting in fibers with high content of α-cellulose, hence
suitable for extracting CNF and CNC. CNF present a range of 3~5 nm in diameter and
400~500 nm in length. The hydrolysis conditions used led to obtaining stable aqueous
suspensions of OBLR which are negatively charged, due the presence of sulfate
groups. Through the X-ray diffraction was possible to observe that there was
formation of cellulose type II in the CNC due to the hydrolysis conditions used permit
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re-precipitation of cellulose. CNC presented a needle-shaped nature, high crystallinity
(75%), good thermal stability (around 200 ◦C), an average length (L) of 125 ± 28 nm,
diameter (D) of 2.24 ± 0.57 nm, giving an aspect ratio (L/D) around 44. It can be
concluded from these results that the nanocellulose obtained from banana pseudostem
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have great potential to be used as reinforcement agents for the manufacture of
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nanocomposites.
Acknowledgements
This study was supported by the National Natural Science Foundation of China
(No. 51263006), the Hainan Province of Key Project (ZDYF2017005), Natural
Science Foundation of Hainan Province (217008), the Ministry of PhD Education and
the
Hainan
International
Science
and
Technology
Cooperation
Specific
(KJHZ2014-02). The authors wish to thank the Analytical and Testing Center of
Hainan University.
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