Title: Effect of Reaction Conditions on the Formation and Thermal Behavior of Cellulose Nanocrystals
1Effect of Reaction Conditions on the Formation
and Thermal Behavior of Cellulose Nanocrystals
Ilari Filpponen, Xingwu Wang, Lucian A. Lucia
Dimitris S. Argyropoulos
Organic Chemistry of Wood Components
Laboratory Department of Forest Biomaterials
Science Engineering North Carolina State
University Raleigh, North Carolina, USA
2007 International Conference on
Nanotechnology For the Forest Products
Industry 13 15 June 2007 ? Knoxville,
Tennessee, USA
2Outline
- Brief Introduction/Background
- Objectives
- Production and Thermal Analysis of Cellulose
Nanocrystals - Structural Analysis
- Summary
3From Bulk Cellulose to Cell-Nanocrystals
- Cellulose is one of the most abundant natural
biopolymers which upon acid hydrolysis yields
highly crystalline rod-like rigid hydrophilic
particles having nanoscale dimensions
Glucose
Acid hydrolysis of cellulose to form cellulose
nanocrystals
Revol et al., Int. J. Biol. Macromol. 14,
170-172, 1992
4Experimental-Overall Objectives
- Optimization of the manufacturing process and
utilization of thermal analysis for the
characterization of cellulose nanocrystals - Understanding the size and uniformity of
nanocrystals in relation to the manufacturing
process
5Preparation of Cellulose Nanocrystals
- The cellulose pulp obtained from Whatman no.1
(98 a-cellulose, 80 crystallinity) filter paper
was used as starting material - In this study hydrobromic acid was used in
different concentrations (1.5M, 2.5M and 4.0M),
respectively - The effect of reaction times, temperatures and
applied external energy (ultrasonication during
or after the hydrolysis) to the yields were
investigated
6Hydrolysis Reaction
HBr (50ml)
Solution
Cellulose Pulp (1 gram)
Acid Hydrolysis (oil bath, stirring)
Centrifugation
(1,500g)
Ultrasonication
Cellulose Suspension
7Purification Steps
Centrifug.
Supernatant off
5 cycles
contains cellulose nanocrystals
pH 1-2
pH 4-5
Centrifugated Suspension
Turbid Supernatant
Centrifugation (15,000g)
Collected Supernatant
Freeze drying
Remaining Sediment
Cellulose Nanocrystals
8The Effect of Reaction Time and Temperature (2.5M
HBr)
Ultrasonication During the Reaction
Ultrasonication After the Reaction
100C
100C
80C
80C
Yields increases along the reaction time in all
conditions applied.
9The Effect of Ultrasonication (2.5M HBr)
Reaction at 100ºC
Reaction at 80ºC
100
SC During
SC During
80
60
Yield ()
40
SC After
20
SC After
0
0
1
2
3
4
5
Time (hr)
At 80ºC ultrasonication, when applied during,
increased yields but at 100ºC the effect was not
significant (SC Ultrasonication).
10Yields with Different HBr Concentrations
The yields were seen to increase significantly
when acid concentration was Increased from 1.5M
to 2.5M. With 4.0 M HBr unwanted reactions were
observed.
11Optimized HBr Hydrolysis Conditions (2.5M)
Reaction at 100ºC
Optimal Conditions
68
SC During
SC After
Typical yields from hydrolysis with either HCl or
H2SO4 are around 40-45
12Thermal Analysis
Thermal analysis may provide a convenient and
rapid tool for the determination and correlation
of various physicochemical properties of
cellulose nanocrystals (crystallinity, crystal
dimensions)
13Thermal Analysis
Thermogravimetric analyses (TGA)Information
provided Thermal degradation, total amount of
water ().
Differential Scanning Calorimetry (DSC)
Information provided endothermic water
evaporation peak (J/g), apparent maximum at
around 120-130ºC
Samples were kept in constant humidity (69)
before analysis and measurements were duplicated
14Differential Scanning Calorimetry (DSC)
Loss of absorbed water
Cellulose nanocrystals
Sediment
Starting Cellulose
Tg was observed for cellulose powder and
unreacted cellulose but not for cellulose
nanocrystals
15Cellulose Crystallinity and ?Hvap of H2O
- Bertran et al. studied the correlation between
the cellulose crystallinity and enthalpy of
evaporation of absorbed water by using DSC - Higher crystallinity decreased the energy needed
for water removal. Results were in good
agreement with X-ray diffraction measurements
6
5
O (kJ/g)
4
2
3
2
Heat of Evaporation H
1
0
0
10
20
30
40
50
60
70
80
Crystallinity Index ()
Bertran et al. J. Appl. Pol. Sci., 32, 4241-53,
1986
16Cellulose Nanocrystals and ?Hvap of H2O
100C SC during (2.5M HBr)
Cellulose Nanocrystals
Cellulose Sediment
The crystallinity of dispersed nanoparticles seem
to increase during the hydrolysis. Measurements
showed good reproducibility.
17X-ray Diffraction of Cell-Nanocrystals
- Crystallinities were calculated according to
Segal et al. - Cr.I. () ((I002 Iam) / I002) x 100
- where I002 is the maximum intensity from (002)
plane at 2? 22.8 and - Iam is the intensity of the background scatter
measured at 2? 18 - The average crystallite size, in nm, was
determined by the Debye-Scherrer formula - D k ?Cu/ß cos?
- here k 0.9, ?Cu 0.154056 nm, ß FWHM (full
width at half maximum, or half-width) in radians,
? the position of the maximum of diffraction.
18X-Ray Diffraction (XRD)
80 crystallinity (Cr.I.)
91 crystallinity (Cr.I.)
Count rate (cps) x103
Count rate (cps) x103
2? angle
2? angle
Starting Cellulose Cellulose
Nanocrystals
Acid hydrolysis increased the crystallinity of
cellulose particles
19Transmission Electron Microscopy
- The length distribution of
- cellulose nanocrystals were
- estimated from TEM images.
- Aggregation of cellulose
- whiskers hindered the
- determination of transverse dimensions
200 nm
XRD
3hr, 100ºC, HBr (2.5M) SC during
20Average sizes of Cellulose Nanocrystals
Transverse dimensions are based on XRD analysis.
Lengths were estimated from TEM images. Cr.I.
Crystallinity Index
21Summary
- Reaction conditions play a significant role in
determining the yield of cellulose nanocrystals - Ultrasonication during the hydrolysis reaction
improved the yields of cellulose nanocrystals and
allowed lower reaction temperatures - Thermal analysis is seen to provide information
that currently is attempted to be correlated with
various physicochemical properties of the
cellulose nanocrystals (work in progress)