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

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

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, 170-172, 1992

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

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

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

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

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.

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).

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.

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%

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)

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 120-130ºC Samples were kept in constant humidity (69%) before analysis and measurements were duplicated

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

Cellulose Crystallinity and ΔHvap of H2O 6 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, 4241-53, 1986

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.

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 = 0.154056 nm, β = FWHM (full width at half maximum, or half-width) in radians, θ = the position of the maximum of diffraction.

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

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

Average sizes of Cellulose Nanocrystals n.d. 8.3 8.2 91 100°C, SC during, 3hr (sediment) 100-400 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

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)