1. Effect 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

2. Outline Brief Introduction/Background Objectives
Production and Thermal Analysis of Cellulose Nanocrystals
Structural Analysis
Summary

3. From 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, , 1992

4. Experimental-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

5. Preparation of Cellulose Nanocrystals
The cellulose pulp obtained from Whatman no.1 (98% α-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

6. Acid Hydrolysis (oil bath, stirring)
Hydrolysis Reaction
HBr (50ml)
Solution
Cellulose Pulp (1 gram)
Acid Hydrolysis (oil bath, stirring)
Centrifugation
(1,500g)
Ultrasonication
Cellulose Suspension

7. Centrifugated Suspension Cellulose Nanocrystals
Purification 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

8. The Effect of Reaction Time and Temperature (2.5M HBr)
Ultrasonication After the Reaction
Ultrasonication During the Reaction 20 40 60 80
100 1 2 3 4 5
Time (hr)
Yield (%) 20 40 60 80
100 1 2 3 4 5
Time (hr)
Yield (%)
100°C
100°C
80°C
80°C
Yields increases along the reaction time in all conditions applied.

9. The Effect of Ultrasonication (2.5M HBr)
Reaction at 80ºC
Reaction at 100ºC 20 40 60 80
100 1 2 3 4 5
Time (hr)
Yield (%)
100
SC During
SC During 80 60
Yield (%) 40
SC After 20
SC After 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).

10. Yields with Different HBr Concentrations
1.5 M
2.5 M
4.0 M 10 20 30 40 50 60 70 80
2hr, 100ºC SC
During
After
4hr, 100ºC SC
Hydrolysis Conditions
Yields (%)
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.

11. Optimized HBr Hydrolysis Conditions (2.5M)
Reaction at 100ºC
Optimal Conditions
0.00
20.00
40.00
60.00
80.00
100.00 1 2 3 4 5
Time (hr)
Yield (%)
68%
SC During
SC After
Typical yields from hydrolysis with either HCl or H2SO4 are around 40-45%

12. Thermal Analysis Hypothesis:
Thermal analysis may provide a convenient and rapid tool for the determination and correlation of various physicochemical properties of cellulose nanocrystals (crystallinity, crystal dimensions)

13. Thermal 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 ºC
Samples were kept in constant humidity (69%) before
analysis and measurements were duplicated

14. Differential 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

15. Cellulose Crystallinity and ΔHvap of H2O6
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 5
O (kJ/g) 2 4 3 2
Heat of Evaporation H 1 10 20 30 40 50 60 70 80
Crystallinity Index (%)
Bertran et al. J. Appl. Pol. Sci., 32, , 1986

16. Cellulose Nanocrystals and ΔHvap of H2O
100°C SC during (2.5M HBr) 1 2 3 4 5 6 7 8
Time (hr)
Heat of Evaporation H2O (kJ/g)
0.5 1
1.5 2
2.5 3
3.5 4
4.5 5
Time (hr)
Heat of Evaporation H2O (kJ/g)
Cellulose Nanocrystals
Cellulose Sediment
The crystallinity of dispersed nanoparticles seem to increase during the hydrolysis. Measurements showed good reproducibility.

17. X-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 2θ = 22.8° and
Iam is the intensity of the background scatter measured at 2θ = 18°
The average crystallite size, in nm, was determined by the Debye-Scherrer formula:
D = k λCu/β cosθ
here k = 0.9, λCu = nm, β = FWHM (full width at half maximum, or half-width) in radians, θ = the position of the maximum of diffraction.

18. X-Ray Diffraction (XRD)
80% crystallinity (Cr.I.)
91% crystallinity (Cr.I.)
Count rate (cps) x103
Count rate (cps) x103
2θ angle
2θ angle
Starting Cellulose Cellulose Nanocrystals
Acid hydrolysis increased the crystallinity of cellulose particles

19. Transmission 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

20. Average sizes of Cellulose Nanocrystals
n.d.
8.3
8.2 91
100°C, SC during, 3hr
(sediment)
7.7
8.6
7.6 89
100°C, SC during, 2hr
7.0 88
100°C, SC during, 1hr
Length
(nm)
Transverse 2
Transverse 1
Cr.I.
Sample
Transverse dimensions are based on XRD analysis. Lengths were estimated
from TEM images. Cr.I. = Crystallinity Index

21. Summary
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)