Presentation on theme: "The Types of Water in Cellulosic Fibers: DSC and NMR Spectroscopy"— Presentation transcript:
1 The Types of Water in Cellulosic Fibers: DSC and NMR Spectroscopy
2 Outline Types of water Differential Scanning Calorimetry Nuclear Magnetic Resonance SpectroscopyAnalytical determination of types of waterSummary
3 Purpose Types of water are removed in different ways Water removal huge component of papermaking costsTrend towards use of non-wood fibersHas become increasingly important to understand how cellulosic materials behave in paper drying processBehavior should be known for wood fibers for effective comparisonsDifferential Scanning Calorimetry (DSC) and Nuclear Magnetic Resonance (NMR) spectroscopyIf you know what kind of water is in the fiber and how much, it is easier to remove it efficientlyStudy the water using DSC and NMRDSC can evaluate the fractions of water determine concentration and drying rateNMR can determine location of fractions and drying rate
4 Types of water Free/Bulk water Freezing bound water Found in large poresMakes up inter-fiber free water in pores and intra-fiber water in lumenRemoved by centrifugation, melting point similar to bulk waterFreezing bound waterMelting and freezing temperature depressed by about 2°C due to small size of micropores and presence of polymers like hemicelluloseLoss causes most detrimental irreversible pore closureHubbe, 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 surfacesHydrogen-bonded to hydroxyl and carboxylic acid groups in microporesAmount calculated by subtracting total freezing water from the moisture ratio of the sampleHubbe, 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 measurementsMeasure difference in heat flow rate between a sample and an inert reference material as a function of time and temperatureTwo typesExothermicEndothermicExothermic: Heat flows out of sample as result of cooling, crystallization, or oxidationEndothermic: 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 temperatureTwo modes:Heat fluxPower compensatedTA Instruments Q100Lucia, L. “DSC: A bulk analytical technique.” Lecture notes: WPS 595b Biomaterials Characterization. North Carolina State University. 9 February 2006.
8 Heat flux DSCSample and reference heated or cooled by separate heating unitsFurnaces 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 linearlyPower being sent to heaters is adjusted so that the same temperature is maintained for both sample and referenceDifference in power to keep temperatures the same is used to generate curveSample and reference positioned above their heatersAverage temperature control circuit used to monitor the progress of the temperature control programCircuit insures that assigned temperature is actual average temperature of the sample and referenceSkoog, 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 referenceTransported heat carefully controlledTemperature difference ismonitoredThermocouple below sample and reference platforms sends a measurement of the relative temperatures which are then converted to a differential heat flow between the two materialsSkoog, 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 compoundBased on measurement of adsorption of electro-magnetic radiation in the radio frequency range 60 to 800 MHzConcept that certain atomic nuclei have magnetic and spin moments1H, 13C, 19F, and 31P
11 NMRSpin and charge of the nuclei cause behavior similar to bar magnetsEnergy levels split causing nuclei to possess one of two magnetic forcesEach nucleus is able to switch between energy states through the absorption of a photon.
12 NMRPlacing nuclei in strong magnetic field, can monitor energy transition when photon is absorbedThe excess of lower energy spin is essential for monitoring of the energy adsorption laterWhen nuclei then subjected to radio waves some absorb radiation and are raised to higher energyDifference in energy between low and high energy states provides signalSignal sensitivity is directly proportional to magnetic fieldWhen 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 stateOnce subjected to radio waves, some are then aligned against magnetic fieldAs new machines are developed, the magnetic fields increase in strength and sensitivity increasesSkoog, 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 NMRDistinguish between nuclei of different elements because of chemical shifts in peaksFourier transformTwo-dimensionalTwo different pulse frequencies bombard samplePulsedRadiofrequency (RF) radiation 90-degrees to magnetic field causes nuclei to jump into higher-energy alignmentPulse simultaneously excites nuclei in all local environmentsNuclei re-emit RF radiation and create interference pattern known as a free-induction decay (FID)Chemical shifts due to electron environment surrounding nucleiFrequencies 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 dryingTemperature fluctuations help determine which type of water is present and in what quantityNMR: Observe effects of drying because protons in each type of water give off specific signalProton-NMR well-suited for study of water/cellulose interactions, relaxation times, and for distribution of moisture within paper sheet
15 Ogiwara et al- NMRLevel of bound water strongly dependent on type and condition of fibersTemperature-dependence of experimental readingsAmount of detectable bound water was more accurate as experimental temperature decreasedThis boundary temperature is specific for each cellulose sample and a given water content and corresponded well with the glass transition temperature of the systemBelow 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 ofCellulose Studied by a High-Resolution NMR Spectrometer.” Journal of Applied Polymer Science vol. 14 p
16 Ogiwara et al- NMRDetermined boundary temperature, Tc, where water molecules become bound to celluloseThe lower the water content became, the greater the changes in TcSimilar DSC studies agreed that glass transition temperature was lower for moist cellulose than for an air-dried sampleThese 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 timeDrying rates used during the imaging processWater content decreased rapidly to an inflection point around 61-68% water by weightDecreased again to a point just below 37-45% weightRemaining moisture tightly bound to fibers and was hard to removeNarrowest lines and highest intensities matched with highest water contentIncreases in line widths with time correspond to decreases in water content and matched two inflection pointsWater distribution measured using two-dimensional NMR imaging before and after dryingThere 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 sampleExplain method brieflyGraphsThere will be graphs and further explanation
19 Summary Three types of water Analyze using Each treated differently to maximize efficiencyAnalyze usingDSCNMRCombinationMovement towards utilization of non-wood fibers for papermakingWill elaborate on these more