Homogeneous Isolation of Nanocellulose from Cotton Cellulose by High Pressure Homogenization

doi:10.4236/msce.2013.15010

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Journal of Materials Science and Chemical Engineering, 2013, 1, 49-52

http://dx.doi.org/10.4236/msce.2013.15010 Published Online October 2013 (http://www.scirp.org/journal/msce)

Homogeneous Isolation of Nanocellulos e from Cotton

Cellulose by High Pressure Homogenization

Yihong Wang1,2, Xiaoyi Wei1, Jihua Li1,3*, Fei Wang1, Qinghuang Wang1,3*, Lingxue Kong4

1Agriculture Products Processing Research Institute, Chinese Academy of

Tropical Agricultural Sciences, Zhanjiang, China

2College of Food Science and Technology of Huazhong Agricultural University, Wuhan, China

3National Center of Important Tropical Crops Engineering and Technology Research, Haikou, China

4Institute for Frontier Materials, Deakin University, Waurn Ponds, Vic, Australia

Email: *[email protected]

Received July 2013

ABSTRACT

Nano-cellulose materials are widely believed to have the potential to push polymer mechanical properties. The cotton

cellulose was dissolved in ionic liquid (1-butyl-3-methylimidazolium chloride ([Bmim]Cl)), and then was isolated by

high pressure homogenization in a homogeneous media. The nano-cellulose was obtained at 80 MPa for 30 cycles. The

geometry and microstructure of the cellulose nano-fibres were observed by SEM and their particle size analysis. FTIR,

XRD and TGA were used to characterize changes to chemical functionality. Particular emphasis is given to the physical

and chemical characterization of these nano-fibres together w ith their thermal stability and crystallinity, in order to de-

velop their suitability.

Keywords: Ionic Liquid; Particle Size; High Pressure Homogenization; Thermal Stability; Crystallin ity

1. Introduction

Science and technology continue to move toward re-

newable raw materials and more env ironmentally friend-

ly and sustainable resources and processes [2]. Cellulose,

as a whole is of growing importance in the development

and application of polymer materials, represents a pote n-

tially sustainable source to create fuels, chemicals, com-

posites, and a host of other products to replace fossil-

based products [8]. The nanomaterial landscape is vast,

which is widely believed to have the potential to push

polymer mechanical properties to extreme values [6].

Production of nanocellulose has different methods, such

as acid hydrolysis [9] alkali hydrolysis ball milling and

so on. And the weakness of these methods limit the de-

velopment.

Homogeneous isolation of nanocellulose by high pres-

sure homogenization is a new and comparatively green

method due to without pretreatment by adding catalytic

amount of sulfuric acid and cellulose solution under mild

condition [5].

We report the structural and physicochemical proper-

ties of the nanocellulose caused by the whole process,

using Four ier transform infrared (FT-IR) spectroscopy,

transmission electron microscopy, and XPS measure-

ments.

2. Experimental

2.1. Materials

Cotton cellulose was purchased by local factory in Zhan-

jiang, China. The ionic liquid 1-butyl-3-methylimidazo-

lium chloride ([Bmim]Cl) was synthesized according to

the previous work [4]. All other chemicals were of ana-

lytical grade, come from Guangzhou Chemical Reagent

Factory (Guangzhou, China).

2.2. Preparation of Nanocellulose

Cotton cellulose was pretreated by 1% (w/v) sodium hy-

droxyl solution to remove hemicellulose and lignin, re-

spectively. It was washed with distilled water until the

solution was neutral, and then air dried. Pretreated cotton

cellulose was dissolved in [Bmim]Cl by microwave

(Qpro-M, Questron Inc., Canada) heating until it formed

a clear and viscous solution after completely dissolved in

ILs. Then it was homogenized by a high pressure homo-

genizer (AH100D, ATS Engineering Inc., Canada) at

pressure levels ranging from 40 to 120 MPa and for up to

50 HPH cycles. Fin a lly, the regenerated SBC was dried

in a vacuum freeze drying equipment.

*Corresponding a uthor.

Y. H. WANG ET AL.

2.3. Characterization

2.3.1. TEM Analysis

The morphology of the nanocellulose was studied by

TEM (JEM-100, JEOL, Tokyo, Japan), operated at 100

keV.

2.3.2. Infrar ed Spectroscopy (IR) Analysis

The FTIR spectra of original cellulose, IL pretreated cel-

lulose and nanocellulose was measured in the range from

4000 to 400 cm−1 (Spectrum GX-1, PerkinElmer, USA).

2.3.3. Thermal Analysis

Thermal analysis measurements (TG) were carried out

with a Synchronous Thermal Analysis (STA449C/4/G,

Netzsch, Germany). Original cellulose, IL treated cellu-

lose, and nanocellulose were heated from 50˚C to 700˚C

at a heating rate of 10˚C min−1. Under a nitrogen atmos-

phere with a gas flow of 20 ml·min−1.

2.3.4. X-Ray Diffraction (XRD) Analysis

X-ray diffractometry in reflection mode was carried out

using a diffractometer (DLMAX-2550, Japan), with mo-

nochromatic Cu Kα radiation (λ = 0.15418 nm), gener-

ated at 40 kV and 40 mA , at room temperature. The

samples were scanned within 5.00 - 45.00˚ 2θ in step

mode with a step of 0.01˚ and a rate of 1 min−1. The

crystallite index of cellulose was calculated using the

kim’s empirical method [1].

3. Results and Discussion

Dissolution process was performed at 110˚C, 120˚C,

130˚C, 140˚C and 150˚C. As expected, the dissolution

time of cellulose decreased with increasing temperature.

However, the yield of cellulose always increased with

increasing temperature. Finally, we found experimentally

that the best solub ilisation could be achieved in 1% (g/g)

cellulose/[Bmim]Cl during 150˚C for 6mins at 400 W of

microwave.

The pretreated cotton cellulose was dissolved in

[Bmim] Cl to form a homogeneous solution. And the

mixed solution was passed through high pressure homo-

genizer to gain the nanocellulose. Considered the par ticle

sizes and economical factor, the optimum of HPH

process condition was at a pressure of 80MPa with 30

cycles.

3.1. TEM Analysis

The TEM micrograph of a dilute suspension of nanocel-

lulose was shown in Figure 1. The particles of nanocel-

lulose was about 20 nm. This result indicates that the

diameter of cellulose treated by HPH could be reached

on the scale of a nanometer.

3.2. Infrared S pectroscopy (IR) Anal ysis

FT-IR spectra of original cellulose, IL treated cellulose

and nanocellulose was carried out in Figure 2. We ob-

served between 3700 cm−1 and 3000 cm−1 corresponding

to O-H stretching, decrease and become broader after

treated with ILs, which can be correlated with a disrup-

tion of int ra-molecular and intermolecular hydrogen

bonds. The absorption band at 1452 cm−1 in cotton cel-

lulose, assigned to CH2 motion [11], became very weak

and shifted to a low wave number after treated with ILs

in different temperature , resp onding to the breaking of an

intra-molecular hydrogen bond involving O6 [13]. The

band at 880 cm−1 belongs to β-glucosidic bond, and the

absorption peak in regeneration cotton cellulose shifted

to a high wave number than the corresponding one in the

cotton cellulose, which is a characteristic of transition

from cellulose I to cellulose II [3].

Significantly, no difference was found between the

spectrum of nanocellulose and IL treated cellulose. The

result indicates that no other derivational reaction oc-

curred during the processes of dissolutio n and refining.

3.3. Thermal Analysis

The TGA and DTG curves of three kinds of cellulose

were shown in Figure 3. The onset decomposition tem-

perature of original cellulose was about 339˚C. Whereas

IL treated cellulose and homogenized cellulose was

Figure 1. TEM of nanocellulose.

5001000 1500 2000 2500 3000 3500

Transmittan ce(%)

Wavenumber(cm-1)

Figure 2. IR spectra of original cellulose (a), IL treated cel-

lulose (b) an d nan ocellulose (c).

Y. H. WANG ET AL.

326˚C and 286˚C respectively. It implied that the nano-

cellulose exhibited the lowest thermal stability. Possible

explain was that crystal region between cellulose were

destroyed in the process.

3.4. X-Ray Diffraction (XRD) Analysis

The X-ray diffraction patterns of original cellulose, IL

treated cellulose as well as nanocellulose was shown in

Figure 4. shown in ˚C. The diffraction peaks on about

10 20 30 40

1000

2000

3000

4000

5000

6000

7000

8000

9000

Inst ensi ty

2θ

Figure 3. X-ray diffraction patterns of original cellulose (a),

IL treated cellulose (b) and nanocellulose (c).

100 200 300 400 500 600 700

100

Ma ss(%)

Temperature(°C)

100 200 300 400 500 600 700

- 25

- 20

- 15

- 10

-5

DTG(%min )

Temperature(°C)

Figure 4. TG and DTG curves of original cellulose (a), IL

treated cellulose (b) and nanocellulose (c).

15.1˚ (11̅0), 16.9˚ (110), and 23.0˚ (200), confirmed that

only cellulose I was present in it [12]. During the disso-

lution process, the cellulose chains are separated and

became random [7], which are indicated by the crystal-

line form of regenerated cotton cellulose II [10]. The

crystallinity index of original cellulose, IL treated cellu-

lose and homogenized cellulose was 4 3.1%, 15 .8% and

14.66% respectively. The crystallinity index decreased

because the intermolecular and intra-molecular h ydrogen

bonds of cellulose were broken by ionic liquids and HPH

[7]. It was suggested that the hydrogen bonds of cellulose

were broken, which cause the collapse of crystal struc-

ture duri n g the whole process .

4. Conclusion

The present work has demonstrated that nano-cellulose

could be prepared by high pressure homogenization.

Nanocellulose with dimension s o f 20 nm in diameter was

served under TEM. The FTIR spectra confirmed that the

basic structure of cellulose nanocrystals was maintained

and no derivative was formed. The nanocellulose had a

lower thermal stability and crystallinity index. These

results showed significant modifications in the structure

and the texture treated by HPH. A possible explanation

was that numbers of hydrogen bonds decreased by HPH.

The applications of n ano -ellulose will be explored .

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