1. The Types of Water in Cellulosic Fibers: DSC and NMR Spectroscopy

2. Outline Types of water Differential Scanning Calorimetry
Nuclear Magnetic Resonance Spectroscopy
Analytical determination of types of water
Summary

3. Purpose Types of water are removed in different ways
Water removal huge component of papermaking costs
Trend towards use of non-wood fibers
Has become increasingly important to understand how cellulosic materials behave in paper drying process
Behavior should be known for wood fibers for effective comparisons
Differential Scanning Calorimetry (DSC) and Nuclear Magnetic Resonance (NMR) spectroscopy
If you know what kind of water is in the fiber and how much, it is easier to remove it efficiently
Study the water using DSC and NMR
DSC can evaluate the fractions of water determine concentration and drying rate
NMR can determine location of fractions and drying rate

4. Types of water Free/Bulk water Freezing bound water
Found in large pores
Makes up inter-fiber free water in pores and intra-fiber water in lumen
Removed by centrifugation, melting point similar to bulk water
Freezing bound water
Melting and freezing temperature depressed by about 2°C due to small size of micropores and presence of polymers like hemicellulose
Loss causes most detrimental irreversible pore closure
Hubbe, M. A. WPS 527 Coursepack. North Carolina State University.
Heikkinen, S. et al. “NMR Imaging and Differential Scanning Calorimetry Study on Drying Pine, Birch, and Reed Pulps and Their Mixtures.” Journal of Applied Polymer Science vol p

5. Types of water Non-freezing bound water
“Water of hydration” associated with various surfaces
Hydrogen-bonded to hydroxyl and carboxylic acid groups in micropores
Amount calculated by subtracting total freezing water from the moisture ratio of the sample
Hubbe, M. A. WPS 527 Coursepack. North Carolina State University.
Heikkinen, S. et al. “NMR Imaging and Differential Scanning Calorimetry Study on Drying Pine, Birch, and Reed Pulps and Their Mixtures.” Journal of Applied Polymer Science vol p

6. Differential Scanning Calorimetry (DSC)
Most common analytical method for bulk surface measurements
Measure difference in heat flow rate between a sample and an inert reference material as a function of time and temperature
Two types
Exothermic
Endothermic
Exothermic: Heat flows out of sample as result of cooling, crystallization, or oxidation
Endothermic: Heat flows into sample due to heating or process like melting, evaporation, or a glass transition

7. DSC Temperature range about -100°C to 900°C Major applications
Determination of drug purity, reaction time for enzyme degradation, degree of crystallization at a particular temperature
Two modes:
Heat flux
Power compensated
TA Instruments Q100
Lucia, L. “DSC: A bulk analytical technique.” Lecture notes: WPS 595b Biomaterials Characterization. North Carolina State University. 9 February 2006.

8. Heat flux DSC
Sample and reference heated or cooled by separate heating units
Furnaces keep temperatures isothermal to one another throughout the test.
Objective is to monitor electrical power used by heaters as temperatures are either increased or decreased linearly
Power being sent to heaters is adjusted so that the same temperature is maintained for both sample and reference
Difference in power to keep temperatures the same is used to generate curve
Sample and reference positioned above their heaters
Average temperature control circuit used to monitor the progress of the temperature control program
Circuit insures that assigned temperature is actual average temperature of the sample and reference
Skoog, D. A., Holler, F. J., & Nieman, T. A. (1998). Principles of Instrumental Analysis. 5th edition. Thomson Learning Inc.
Bhadeshia, H. K. D. H. “Differential Scanning Calorimetry.” University of Cambridge, Materials Science & Metallurgy

9. Power-compensation DSC
Same heat energy transferred to sample and reference
Transported heat carefully controlled
Temperature difference is
monitored
Thermocouple below sample and reference platforms sends a measurement of the relative temperatures which are then converted to a differential heat flow between the two materials
Skoog, D. A., Holler, F. J., & Nieman, T. A. (1998). Principles of Instrumental Analysis. 5th edition. Thomson Learning Inc.
Bhadeshia, H. K. D. H. “Differential Scanning Calorimetry.” University of Cambridge, Materials Science & Metallurgy

10. Nuclear Magnetic Resonance (NMR) Spectroscopy
Determination of molecular structure for organic and inorganic compound
Based on measurement of adsorption of electro-magnetic radiation in the radio frequency range 60 to 800 MHz
Concept that certain atomic nuclei have magnetic and spin moments
1H, 13C, 19F, and 31P

11. NMR
Spin and charge of the nuclei cause behavior similar to bar magnets
Energy levels split causing nuclei to possess one of two magnetic forces
Each nucleus is able to switch between energy states through the absorption of a photon.

12. NMR
Placing nuclei in strong magnetic field, can monitor energy transition when photon is absorbed
The excess of lower energy spin is essential for monitoring of the energy adsorption later
When nuclei then subjected to radio waves some absorb radiation and are raised to higher energy
Difference in energy between low and high energy states provides signal
Signal sensitivity is directly proportional to magnetic field
When no magnetic field is present, sample contain an identical number of nuclei for each spin state.
They align with the magnetic field because it is a lower energy state
Once subjected to radio waves, some are then aligned against magnetic field
As new machines are developed, the magnetic fields increase in strength and sensitivity increases
Skoog, D. A., Holler, F. J., & Nieman, T. A. (1998). Principles of Instrumental Analysis. 5th edition. Thomson Learning Inc.
Argyropoulos, D.S. “NMR Spectroscopy.” Lecture notes: WPS 595b Biomaterials Characterization. North Carolina State University. 24 January 2006.

13. NMR
Distinguish between nuclei of different elements because of chemical shifts in peaks
Fourier transform
Two-dimensional
Two different pulse frequencies bombard sample
Pulsed
Radiofrequency (RF) radiation 90-degrees to magnetic field causes nuclei to jump into higher-energy alignment
Pulse simultaneously excites nuclei in all local environments
Nuclei re-emit RF radiation and create interference pattern known as a free-induction decay (FID)
Chemical shifts due to electron environment surrounding nuclei
Frequencies are extracted from the FID by a Fourier transform of the time-based data.

14. Analytical determination
DSC: Detect different types of water using procedures analogous to paper drying
Temperature fluctuations help determine which type of water is present and in what quantity
NMR: Observe effects of drying because protons in each type of water give off specific signal
Proton-NMR well-suited for study of water/cellulose interactions, relaxation times, and for distribution of moisture within paper sheet

15. Ogiwara et al- NMR
Level of bound water strongly dependent on type and condition of fibers
Temperature-dependence of experimental readings
Amount of detectable bound water was more accurate as experimental temperature decreased
This boundary temperature is specific for each cellulose sample and a given water content and corresponded well with the glass transition temperature of the system
Below the Tc value, water molecules trying to force their way into cellulose actually destroy the cellulose-cellulose hydrogen bonds and form new water-cellulose hydrogen bonds. The water in that region is therefore without the ability to move. This causes the proton relaxation time in NMR to become longer than that for free water.
Above the boundary temperature however, the cellulose-cellulose bonds are easily broken to form water-cellulose ones and the water therefore has a large freedom of motion.
Ogiwara, Y., Kubota, H., & Hayashi, S. “Temperature Dependency of Bound Water of
Cellulose Studied by a High-Resolution NMR Spectrometer.” Journal of Applied Polymer Science vol. 14 p

16. Ogiwara et al- NMR
Determined boundary temperature, Tc, where water molecules become bound to cellulose
The lower the water content became, the greater the changes in Tc
Similar DSC studies agreed that glass transition temperature was lower for moist cellulose than for an air-dried sample
These results showed that Tc represents the glass transition temperature for a given compound

17. Heikkinen- DSC and NMR NMR
Drying setup for NMR imaging probe used to measure water contents of pulps gravimetrically as a function of drying time
Drying rates used during the imaging process
Water content decreased rapidly to an inflection point around 61-68% water by weight
Decreased again to a point just below 37-45% weight
Remaining moisture tightly bound to fibers and was hard to remove
Narrowest lines and highest intensities matched with highest water content
Increases in line widths with time correspond to decreases in water content and matched two inflection points
Water distribution measured using two-dimensional NMR imaging before and after drying
There will be graphs from this paper

18. Heikkinen- DSC and NMR DSC
Used to determine fraction of each type of water and rate at which it disappeared from the sample
Explain method briefly
Graphs
There will be graphs and further explanation

19. Summary Three types of water Analyze using
Each treated differently to maximize efficiency
Analyze using
DSC
NMR
Combination
Movement towards utilization of non-wood fibers for papermaking
Will elaborate on these more