This document discusses various methods for chemically characterizing pulp. It describes techniques for determining dry matter content, carbohydrate composition through hydrolysis and chromatography, pentosan content, alkali solubility of carbohydrates, carbohydrate molecular weight and degree of polymerization. Methods are also presented for analyzing lignin content and degree of delignification, extractives, fiber surface composition, dirt/shives, color reversion, inorganic matter, and properties important for dissolving pulps. The document provides detailed information on standardized procedures for characterizing various chemical components and properties of pulp.

1. By Audrey Zahra
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Chemical analysis of pulp

2. Introduction
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 The purpose of chemical characterization of pulp is to obtain information about
quality aspects and special properties of the pulp
 Methods for chemical characterization of chemical pulp have been standardized
for example by ISO, TAPPI, and SCAN standardizing organisations
 Most chemical methods for characterizing pulps give information about the total
composition of the pulp but not about the distribution of different chemical
components in the fiber wall.
 Besides quantitative determinations of lignin, extractives, and carbohydrate
content, pulp analysis can also be qualitative. The molecular weight distribution of
lignin and the degree of polymerization of cellulose (often indicated by the
viscosity measurement) are examples of qualitative determinations.

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 Dry matter content
― Dry matter content is defined as the ratio of the mass of the test piece
after drying under specified conditions to its mass at the time of sampling.
― Common dry matter determination: oven at 105℃ to constant weight
― ISO 638 (lab procedures) / ISO 801 (on-line)

4. Carbohydrates
• Carbohydrates composition
• General method : use quantitative determination of monosaccharides
released during hydrolysis usually with H2SO4 → Chromatography methods
• Gas chromatography – TMS (trimethylsilyl)
• Monosaccharides require conversion into volatile derivatives
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Gas chromatography method - etherification
TAPPI 249 - esterification

5. • Liquid chromatography
• Advantages: no need conversion of monosaccharides, high
resolution, sensitivity and selectivity of detection
• Refractometer and UV detectors used with different
seperation columns
• Caution
• Converting the monosaccharide composition into a
polysaccharide composition by formulas in the literature.
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6. Pentosans
• TAPPI T 223
• The pentosan content in pulp indicates the remaining fraction of
xylan after pulping and bleaching. Xylan can be determined by
treating the sample with boiling HCl.
• furfural formed from xylose and arabinose is removed from the
reaction mixture by distillation and determined
spectrophotometrically.
• This by-products interfere with the determination of xylan
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7. • Division of carbohydrates according to alkali solubility
• Cellulose was separated by solubility of sodium hydroxide
• α-cellulose : 17.8% NaOH- solubles
• β-cellulose : Alkali soluble → Neutralization → Precipitated part
• γ-cellulose : Alkali soluble → Neutralization → Soluble part
• Performing the dilution and washing stages in different ways
therefore affects the result
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8. • Determination of carbohydrate molecular mass and degree of
polymerization(DP)
• DP is an indication of the extent to which carbohydrates and especially
cellulose have degraded during cooking and bleaching.
• Method: cellulose may be converted to a derivative such as its nitrate or
carbanilate in organic solvent
• Cellulose soluble solvents
• Cuoxam (Copper oxide-ammonia solution)
• CED or Cuene (Copper ethylenediamine)
• Cadoxen (Cadium oxide in ethylene diamine-water solution)
• EWNN (Iron and sodium tartrate)
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9. • Different molecular masses, polydispersity
• The mixtures for analysis are always polydisperse.
• Different methods for determination of molecular mass
• Number-average molecular mass (Mn)
• Osmometric methods or chemical determination of terminal groups
• Weight-average molecular mass (Mw)
• Light scattering
• Viscosity-average molecular mass (Mv)
• Viscosity of the solution
• Sedimentation-average molecular mass (Mz)
• Ultra centrifugation
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10. • Different molecular masses, polydispersity
• Number-average molecular mass (Mn)
• Weight-average molecular mass (Mw)
• A polymer mixture has 20 molecules. Half the molecules have a
molecular mass of 1 000. The other half have a molecular mass of 10 000.
• Mn = (10 x 1000 + 10 x 10000) / 20 = 5500
• Mw = (10x10002 +10x100002) / 110000
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12. Carbohydrates
• Viscosity measurements
• Use capillary methods
• Velocity gradients can result from measuring the viscosities of
solutions with the same mass concentration using capillaries of
different diameters
• Pulp solution is a non-Newtonian liquid
• viscosity fomula
• V.N. = reduced viscosity, n = intrinsic viscosity, n0 = viscosity of net solvent, c = solution
concentration
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Relationship between
viscosity and DP

13. Carbohydrates
• Gel permeation chromatography
• Gel polymer composed of Polystylene-type as a stationary phase
• Mainly used for water-insoluble polymers (cellulose is insoluble)
• Using the pore size of the packing material inside the column, the larger the
molecule (the larger the molecular weight), the faster it passes through the
column; Doesn't get stuck in pores
• The smaller the size of a molecule (smaller molecular weight), the slower it
passes through the column; caught in the pore
• It is possible to calculate the molecular weight distribution of an unknown
substance by drawing a calibration curve using a standard substance with
known molecular weight.
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14. Carbohydrates
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16. • Functional groups present in carbohydrates
• Carbonyl group
• Using copper number (TAPPI T 430)
• After treating the pulp with a soluble copper salt solution, oxidation of
terminal groups and precipitation of carbonyl groups by the amount of copper
oxide occur. At this time, the content of carbonyl groups in the pulp is
measured by quantifying the carbonyl groups that have undergone the
precipitation reaction.
• Using the forms (oximes and hydrazones) → colorimetric
determination
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17. • Carboxyl groups
• Measurement method using MgCl(aq)
• After treating the pulp with MgCl(aq) to change the pulp into an acid form, the
excess drug is removed by washing, and magnesium ions ionically bound to the
carboxyl group are dropped with hydrochloric acid solution, and the magnesium
ions are analyzed by atomic absorption spectroscopy.
• Assay by HCl (TAPPI T 237)
• After converting the pulp to acid form with dilute hydrochloric acid, add NaHCO3
or NaCl to react, filter, and collect the filtrate. Na+ ions are attached to the
carboxyl group. At this time, the amount of Na+ lost by neutralizing the filtrate is
titrated to obtain inversely.
• Electrical conductivity measurement method
• Disadvantages: In the case of sulfite pulp, sulfonic acids are formed, so there is
also a disadvantage that these sulfonic acids are quantified together with carboxyl
groups.
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18. Carbohydrates
• Uronic acids
• Uronic acid produced by acid decomposition decomposes
carbon dioxide. At this time, the amount of decomposed
carbon dioxide is measured and quantitatively analyzed.
• Enzymatic hydrolysis and LC determination
Measurement of uronic acid generated after enzymatic digestion
by anion exchange chromatography
• Can be measured using UV spectrophotometer or LC
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19. Carbohydrates
• Carbohydrate studies using FTIR spectroscopy
• Infrared(IR) spectroscopy →using pellets compressed from a
ground sample and KBr
• Diffuse reflectance infrared Fourier transform spectroscopy
(DRIFTS) – only neat samples
• ATR(Attenuated total reflectance), PA(Photoacoustic)
spectroscopy → nondestructive, reproducible, rapid
• Cellulose crystallinity was determined by IR spectroscopy
• Caution: affect of lignin on the area of crystallinity cellulose
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20. Lignin
• Quantitative determination of lignin
• Lignin: acid soluble + acid insoluble (somewhat uncertain)
• Acid insoluble lignin (Klason lignin): 72% acid decomposition residue,
TAPPI T 222
• Acid soluble lignin: soluble lignin remaining in solution after 72% acid
decomposition
• Wave length: UV spectrascopy use at about 205 nm and 280 nm
• Caution: The peaks at 280 nm overlap with the furan system.
• Determination of small amounts of lignin (less than 0.05%)
• A small amount of lignin is quantified by measuring the absorbance at
280 nm after immersing the dissolving pulp in Cadoxen solvent. However,
this method can be inaccurate.
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21. Lignin
• Degree of delignification
• Roe number
• Moist pulp + chlorine gas
• Kappa number
• This number of mL of 0.2M KMnO4 solution consumed by 1 g of
dry pulp in 10min during treatment with KMnO4 in H2SO4 solution
• Kappa number range from 5 to 100
• All compounds oxidized by permanganate (not only lignin) will
increase the consumption of MnO4 and increase kappa number
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22. Lignin
• Characterization of lignin
• Methoxyl groups
• Methoxyl group determination by hydrogen iodide (HI)
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23. Lignin
• Sulfonic acid groups
• Phenolic hydroxyl groups
• Molecular mass distribution
• Spectroscopic methods
• Pyrolysis
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24. Liginin
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26. Lignin
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27. Organic extractives
• Besides cellulose, hemicelluloses, and lignin, pulp also contains
many other components that are soluble in neutral organic
solvents or water.
• Non-polar extractives: fatty acids, resin acids, waxes, alcohols,
terpenes, sterols, steryl esters and glycerides
• Polar extractives: lignans
• Total extractives
• Soxhlet extraction
• Acetone -
• Dichloromethane – unsaponified resins, fats, and waxes
• Ethanol – free and saponified resin acids, waxes, fats
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28. Organic extractives
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29. Organic extractives
• Analysis of extractives
• The extracts are susceptible to oxidation and are dried in the
presence of an inert gas prior to analysis.MTBE(methyl-t-butyl
ether)
• Supercritical fluid extraction
• A fluid at a point in time where liquid and gas cannot be
distinguished under constant high temperature and pressure is
called supercritical fluid. Therefore, it has a great effect on
extracting the extract.
• GC-MS available, but poor separation dfficiency
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30. Fiber surface composition
• Analysis of the chemical structure of the fiber surface is
important when examining the influence of constituents in
the pulp fiber surface layer on delignification reactions.
• Electron spectroscopy for chemical analysis (ESCA) is the
appropriate way.
• The method essentially measures the ratio between oxygen
and carbon (O/C)
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31. Dirt and shives in pulp
• A contrary in pulp is any unwanted foreign particle that is
visible in the sheet and has a markedly contrasting opacity or
color compared with the remainder of the sheet
• Such particles are often wood bark although pitch, slime,
plastic, or small particles of iron may be present
• EN ISO 5350-1 and EN ISO 5350-2 (using transmitting and
reflecting light)
• TAPPI T 213
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32. Color reversion
• Color reversion
• It is a phenomenon in which the whiteness of the pulp
automatically drops after bleaching. It depends on the
type of fiber material, pulping method, and bleaching
method.
• PC number
• Uses measurement of the brightness of a sample before and
after a 1h exposure to 100% RH and 100℃
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33. Inorganic matter
• Ash and its components
• Ash values obtained after ignition at 525, 575, 925 ℃
• Chlorine compounds
• Originate from the wood or form during the bleaching process using
chlorine chemicals
• TotCl
• Oxidation by combution during Cl2 → Cl-
• By microcoulometric titration of HCl formed
• Other elements
• Properties and components of water extracts
• pH and conductivity of water extracts of pulp
• Water soluble sulfates and chlorides
• Estimation of washing efficiency
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34. Analysis of dissolving pulps
• Chemical analysis of dissolving pulps includes analyzing
those pulp components that may prevent complete
dissolution of the pulp or cause other problems in
processing of final product
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