Organic extractives in wood and
paper pulp:
Occurence, properties and analyses.
Examination in Wood Chemistry course
21. December 2005
Jon Reino Heum
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Outline
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Basic facts on extractives
•
Occurence in wood
•
Oleoresin vs parenchyma resin
•
Phenolic extractives
•
Heartwood
•
Cross sectional chemical composition in common softwoods
•
Methods for characterization of extractives:
-chromatographic techniques
-spectroscopic techniques
-other methods
Extractives
• Group of non-structural components in wood
• Consists of both hydrophilic and lipophilic
compounds
• Dissolves in either water or organic solvents
• Different amounts and distribution of extractives
from tree to tree, dependent on:
- wood species
- growing site (latitude, altitude, wind exposure etc)
- position within the tree
- genetic factors
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Extractives continued
• No economically feasible way of removing the
extractives
• Gives the colour and odour to the trees
• Protects the tree from microbic and insect attacks
• The energy stock of the living cells of trees
• The heartwood of pine is filled with extractives
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General distribution in the tree
•
Most extractives are located in resin canals and/or parenchyma cells
•
High extractives content in heartwood of pine
•
Extractives level decreases higher up in the tree
• The general composition of the extractives
varies over the stem cross section of wood
•
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20-40 % extractives in bark
Resin canals
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•
Exclusive for softwoods and some tropical hardwoods
•
Located in the latewood or the transition wood between early- and
latewood
•
Built up of living epithelial cells in the sapwood. In heartwood these
cells are dead
•
Both axial and radial canals
Schematic
Vertical resin canal
Horizontal resin canal
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Resin canals
• In the resin canals oleoresin dominates, consisting of an amorpheus
mixture of cyclic terpenes and terpenoids
• The living epithelial cells of the sapwood creates a osmotic pressure
(5-10 bars) in the resin canals
• This pressure push the oleoresin to areas where the tree has been
traumatised and the bark has been removed
• This transportation of oleoresin goes through the original resin canal
system (schizogenic), and/or by a traumatic resin canal system
(lysogenic) made in the cambium at the traumatised areas
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Oleoresin
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•
Located in resin canals
•
Consists of terpenes and terpenoids
•
Protects the tree from microbic attack
•
Secretes out where traumas to the tree has damaged the bark.
•
Exclusive for softwood and tropical hardwoods with resin canals
•
Non-volatile components are dissolved in a mixture of volatile
components
•
The volatile components evaporate in contact with air, and the nonvolatil components dries. This creates the caracteristic resin deposits on
the tree steems
Structure of oleoresins
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•
Monoterpenoids and diterpenoids (resin acids) are dominating
•
All built up by different amounts of isopren-units (C5H8)
Classification of Terpenes
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Prefix
# C-atoms
# Isoprene units
Occurence
Hemi
5
1
Mono
10
2
Softwood oleoresin
Sesqui
15
3
Hardwood resin
Di
20
4
Resin acids
Sester
25
5
Tri
30
6
Tetra
40
8
Poly
>40
>8
In many plants
Leaves
Monoterpenoids
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Volatile components in softwood oleoresin, built up of two Isoprene units
•
Gives wood the characteristic odour
•
Can be divided into acyclic, monocyclic, bicyclic and tricyclic
Acyclic
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Monocyclic
Bicyclic
Diterpenoids
•
One of the most
important group of
extractives in softwood
•
The most important
group of diterpenoids is
resin acids
•
acyclic
tricyclic
Can be divided into
acyclic, mono-, bi-, tri,
tetra and macrocyclic
macrocyclic
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Sesquiterpenoids
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•
More than 2500 sesquiterpenoids
have been identified
•
Wide variety of skeleton types
from acyclic to tetracyclic systems
•
Occur only in small amounts in
tropical wood species
cadinene
Resin acids
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Mainly carboxylic derivates of neutral tricyclic diterpenoids
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Classified in pimarane and abietane acids
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One lipophilic and one hydrophilic end
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Some less important resin acids are bicyclic and are classified as labdane acids
Sandaracopimarsyre
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Levopimarsyre
Common acids in common species
Norway spruce
Pimaric
8.1
6.2
Sandaracopimaric
1.6
6.4
Isopimaric
3.5
13.3
Sum (pimaric)
13.2
25.9
Levopimaric
30.0
16.2
Palustric
15.1
13.5
Abietic
15.8
11.2
Neoabietic
11.1
10.2
Dehydroabietic
14.4
22.6
Sum (abietic)
86.4
73.7
Abietane
Scots pine
Pimarane
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Resin acid
Triterpenoids and stereoids
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•
Widely distributed in plants
•
Triterpenoids and stereoids are
closely related
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Occure mainly as fatty acid esters
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Betulinol gives the white colour to
Birch bark
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Other important is Sitosterol and
Campesterol
Polyterpenoids
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•
Acyclic primary alcohols of
polyisoprenoids
•
Most common in leaves and not in
wood
•
One special type of polyterpenoids,
betulaprenol, occur as fatty acid
esters in Silver birch
•
Some trees produce rubber from
polyterpenoids
Parenchyma cells
• Living cell. Essential to the wood metabolism
• Both vertical and axial cells
• More than 95% of the parenchyma cells in softwood are located in the
wood rays
• In spruce wood most of the ray cells are parenchyma cells, whereas in
pine wood the ray tracheids dominate
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Parenchyma resin
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•
Located in the parenchyma cells of
the tree
•
Mainly composed of fats and
waxes
•
Important in the trees metabolism
•
Parenchyma resin is virtually the
only resin type in hardwoods
Chemical composition
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•
In fresh wood free fatty acids are present practically only in heartwood. Fatty
acids are partially liberated during wood storage
•
The waxes are esters of higher fatty alkohols (C18-C24), terpene alcohols and
sterols.
•
Waxy components are free fatty alcohols.
•
Fats and waxes are hydrolized during kraft pulping. The liberated fatty acids
can be recovered together with resin acids as soap skimmings from the black
liquor
Fatty acids and glycerol esters
• Most fatty acids in sapwood is esterified with glycerol, predominantly
as triglycerides
• The free fatty acids are almost only present in heartwood, and exists as
both unsaturated and saturated acids
• More than 30 fatty acids has been identified in hardwoods and
softwoods. Mainly the fatty acids appear in both hardwoods and
softwoods
• The C18-fatty acids dominates in the wood
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Abundant fatty acid components
Saturated
Palmitic
Hexadecanoic
C16
Stearic
Octadecanoic
C18
Arachidic
Eicosanoic
C20
Behenic
Docosanoic
C22
Lignoceric
Tetracosanoic
C24
Oleic
cis-9-Octadecanoic
C18
Linoleic
cis, cis-9,12-Octadecadienoic
C18
Linolenic (pine)
cis, cis, cis-9,12,15-Octadesatrienoic
C18
Pinolenic (Picea)
cis, cis, cis-5,9,12-Octadesatrienoic
C18
Eicosatrienoic
cis, cis, cis-5,11,14-Eicosatrienoic
C20
Unsaturated
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Linoleic acid
Oleic acid
Triolein
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Waxes
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Ester of a long chained fatty alcohol and a fatty acid
R1= fatty acid chain
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Steryl esters and triterpenyl esters
•
Steryl esters are a fatty acid esterified with a sterol
•
Triterpenyl are a fatty acid esterified with a triterpenyl alcohol
R2-fatty acid chains
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Phenolic constituents
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•
Especially heartwood and bark contain a large variety of complex
aromatic extractives. Most of them are phenolic compounds and many are
derived from the phenyl propanoid structure
•
Thousands of phenolic compounds have been identified
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Have fungicidal properties and protect the tree from microbic attacks
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Contribute to the natural colour of wood
Phenolic constituents
Stilbenes:
- Derivatives of 1,2-diphenylethylene
- Conjugated double bond system
- Reactive components in acidic sulphite pulping inhibiting the
delignification
- Typical member is pinosylvin, present in pines
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Phenolic constituents
Lignans:
- Formed by oxidative coupling of two phenylpropane units
- Most usual in spruce wood
- Commercially attractive products
Pinoresinol
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Phenolic constituents
Hydrolyzable tannins
Condensed tannins
Flavonoids
- small amounts
Tannins
Taxifolin (Flavonoids)
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Extractives distribution – cross sectional
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•
The amount and composition of extractives vary over the log cross
section
•
Most significant for softwoods
•
Biggest difference between heartwood and sapwood
Extractives distribution – cross sectional
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Scots pine
Norway spruce
Formation of heartwood
• Heartwood is the phenomenon that the trees close the inner part of the
log.
• Hardwoods close the structure by tylosis or secretion. Spruce also
closes its structure while pine heartwood is filled up with extractives.
• The dead, closed structure prevents microbic attacks
• The high amounts of resin acids and stilbenes gives heartwood of pine
the characteristic colour.
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Properties of heartwood
• Enzymatic hydrolyses of fatty acid esters, predominantly triglycerides
gives heartwood (especially spruce) a higher amount of free fatty
acids.
• Pine heartwood is rich in resin acids and phenolic compounds
• Isomerization of resin acids to dehydroabietic acid increases the
amount of this resin acid in heartwood.
• Autooxidation of unsaturated fatty acids
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Extractives in bleaching
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•
Chlorine dioxide will mainly oxidize the extractives and
make them hydrophilic
•
Mainly sterols and unsaturated fatty acids are degraded by
chlorine dioxide
•
Unsaturated fatty acids is aldo degraded by hydrogen
peroxide, but not to the same extent
•
A higher extractives content will demand a higher
bleaching chemicals consumption
Extractives in kraft pulping
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•
A high number of the fatty acid esters are hydrolised
•
Resin acids may react with the cooking liquor
•
The free fatty acids and the resin acids are dissolved as sodium salts in the
black liquor
•
These acids are often skimmed off the black liqour as a bi-product
•
High usage of defoamers may cause pitch problems
Extractives in sulphite pulping
• Fatty acids are hydrolised
• Some resin acids are sulfonated
• Fatty acids and resin acids formes insoluble Ca-soaps at pH above 6-7,
in the presence of Ca-ions
• Some phenolic components like pinosylvin and taxifolin inhibits
delignification
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Extractives analysis
• Analysis of extractives can be made at three levels
- gravimetric of total
- determination of different component groups
- analysis of different components (sometimes preceded by a group
separation)
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Extraction
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In order to separate the extractives from the wood, they
must be extracted by an organic solvent.
•
Extraction can be made on wood, pulp or paper, and
liquid-liquid extraction on process water is also
widespread.
Soxhlet
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For solid phase extractions the most used techniques are
Soxhlet and Soxtech extraction.
•
Soxtech extraction is the fastest, but the amount of
material is limited
Soxtech
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Choice of solvent
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Critical for the extraction.
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Aceton – polar solvent with the highest yield. Also solves some simple
carbohydrates and phenols.
•
Cyclohexane – non-polar and solves only lipophilic extractives
•
Diethyl eter (DEE) – also high yield (not as much as aceton), and
solves simple carbohydrates and phenols. Intermediate polarity
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Dichloromethane (DCM) – Intermediate polarity, out of use due to
health risk
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Methyl tertiary-butyl ether (MTBE) – used for process water analysis
-The present SCAN-standard on solid-phase extraction uses a mix of
Aceton and Cyclohexane
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Analysis of wood resin
• Can be determined by several chromatographic techniques:
- Gas chromatography (GC)
- High performance liquid chromatography (HPLC)
- Supercritical fluic chromatography (SFC)
- Thin layer chromatography (TLC)
• Spectroscopic analysis using NMR and IR is also applied
• Other direct methods
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Gas Chromatography
• The best method for extractives analysis
• Give high resolution on the chromatography distribution
• Component group analysis with short coloumn GC
• Individual component analysis with long coloumn GC
• Together with a mass spectroscopy (GC-MS) it is a powerful tool for
extractives identification
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High performance liquid chromatography
• Liquid chromatography technique
• Gives a good group separation
• Sterols and fatty acids are co-eluted
• Size exclusion - classifies molecules on the size on the molecules
• Reverse fase - the surface of the coloumn material is hydrophobic,
retaining lipophilic material
• Normal fase - the surface is polar retaining the polar molecules
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Supercritical fluid chromatography
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Analyse on component groups
•
Direct characterization without
preceding derivatization
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Steryl esters and triglycerides are not
separated
Thin layer chromatography
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•
Inexpensive and convenient technique for resin
analysis
•
Good visual image of the resin group composition
•
However quantitative analyses is not accurate
•
Well suited for preparativ separation of resin
group, e.g., for further detailed analysis by GC
Nuclear Magnetic Resonance
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•
NMR is a phenomenon which occurs when the nuclei of certain atoms in a
static magnetic field are exposed to a second oscillating magnetic field. This
happens with the nuclei have a property called spin (e.g. 1H, 2H, 13C, 31P ).
•
The electron density around each nucleus in a molecule varies according to the
types of nuclei and bonds in the molecule  chemical shift.
•
Component group determination
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Non-destructive technique
•
Time consuming and expensive but accurate technique
Infrared spectroscopy
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•
Uses infrared radiation
•
Determines compounds from which specific frequencies chemical
bonds vibrate
•
Used for characterization of deposits
•
Gives structural information, but is no quantitative analysis
Other methods
• Pyrolysis-GC: Quick and efficient way of analysis of spots in papir
• FTIR: non-destructive characterization of spots in paper and pulp
• ESCA: Non-destructive fiber surface (3-9nm) analysis
• SIMS: Fiber surface (0,2-20nm) analysis. Determination of detailed
chemical structure, but slow and expensive.
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Summary
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•
•
•
•
•
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The amount and composition of extractives varies with position in the wood
log
Two main types of extractives is the oleoresin in resin canals in softwood, and
fat and wax in the parenchyma cells
The main groups of extractives is: resin acids, fatty acids (either free or
esterified) and alchohols and phenolic compounds
Pine heartwood is rich in resin acids, because they fill up the dead resin canals
Spruce heartwood is richer in free fatty acids than spruce sapwood, due to
slow hydrolysis
Chromatography seems to be the best methods of extractives analysis available
today, efficient and not too expensive method
Other direct methods may be presise and non destructive, but they are in
general expensive and slower