The Types of Water in
Cellulosic Fibers: DSC
and NMR Spectroscopy
Outline
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Types of water
Differential Scanning Calorimetry
Nuclear Magnetic Resonance Spectroscopy
Analytical determination of types of water
Summary
Purpose
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Types of water are removed in different ways
Water removal huge component of papermaking
costs
Trend towards use of non-wood fibers
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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
Types of water
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Free/Bulk water
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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
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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. 2006. vol. 100. p. 937-945.
Types of water
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Non-freezing bound water
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“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. 2006. vol. 100. p. 937-945.
Differential Scanning
Calorimetry (DSC)
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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
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Exothermic
Endothermic
DSC
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Temperature range
about -100°C to 900°C
Major applications
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Determination of drug
purity, reaction time for
enzyme degradation,
degree of crystallization
at a particular
temperature
Two modes:
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Heat flux
Power compensated
TA Instruments Q100
http://www.tainstruments.com/product.asp?n=1&id=16
Lucia, L. “DSC: A bulk analytical technique.” Lecture notes: WPS 595b Biomaterials Characterization. North Carolina State University. 9 February 2006.
Heat flux DSC
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Sample and reference heated
or cooled by separate heating
units
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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
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. 2002.
Power-compensation DSC
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Same heat energy transferred to sample and
reference
Transported heat carefully controlled
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Temperature difference is
monitored
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. 2002.
Nuclear Magnetic Resonance
(NMR) Spectroscopy
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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
NMR
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Spin and charge of the nuclei cause behavior
similar to bar magnets
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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.
NMR
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Placing nuclei in strong magnetic field, can monitor
energy transition when photon is absorbed
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When nuclei then subjected to radio waves some
absorb radiation and are raised to higher energy
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The excess of lower energy spin is essential for monitoring
of the energy adsorption later
Difference in energy between low and high energy states
provides signal
Signal sensitivity is directly proportional to magnetic
field
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.
NMR
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Distinguish between nuclei of different elements
because of chemical shifts in peaks
Fourier transform
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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)
http://www.chemistry.adelaide.edu.au/external/soc-rel/content/ftnmr.htm
Analytical determination
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DSC: Detect different types of water using
procedures analogous to paper drying
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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
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Proton-NMR well-suited for study of
water/cellulose interactions, relaxation times, and
for distribution of moisture within paper sheet
Ogiwara et al- NMR
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Level of bound water
strongly dependent on
type and condition of
fibers
Temperaturedependence of
experimental readings
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Amount of detectable
bound water was more
accurate as experimental
temperature decreased
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. 1970. vol. 14 p.303-309.
Ogiwara et al- NMR
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Determined boundary temperature, Tc, where
water molecules become bound to cellulose
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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
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 6168% 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
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
Summary
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Three types of water
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Analyze using
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Each treated differently to maximize efficiency
DSC
NMR
Combination
Movement towards utilization of non-wood
fibers for papermaking