Organic extractives in wood and paper pulp:

1. Organic extractives in wood and paper pulp: Occurence, properties and analyses. Examination in Wood Chemistry course 21. December 2005 Jon Reino Heum

2. Outline • 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

3. 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

4. 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

5. 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 • 20-40 % extractives in bark

6. Resin canals • 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

7. Schematic Vertical resin canal Horizontal resin canal

8. 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

9. Oleoresin • 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 non-volatil components dries. This creates the caracteristic resin deposits on the tree steems

10. Structure of oleoresins • Monoterpenoids and diterpenoids (resin acids) are dominating • All built up by different amounts of isopren-units (C5H8)

11. Classification of Terpenes

12. Monoterpenoids • 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 Monocyclic Bicyclic

13. Diterpenoids acyclic • One of the most important group of extractives in softwood • The most important group of diterpenoids is resin acids • Can be divided into acyclic, mono-, bi-, tri, tetra and macrocyclic tricyclic macrocyclic

14. Sesquiterpenoids • 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

15. Resin acids • Mainly carboxylic derivates of neutral tricyclic diterpenoids • Classified in pimarane and abietane acids • One lipophilic and one hydrophilic end • Some less important resin acids are bicyclic and are classified as labdane acids Sandaracopimarsyre Levopimarsyre

16. Common acids in common species Pimarane Abietane

17. Triterpenoids and stereoids • Widely distributed in plants • Triterpenoids and stereoids are closely related • Occure mainly as fatty acid esters • Betulinol gives the white colour to Birch bark • Other important is Sitosterol and Campesterol

18. Polyterpenoids • 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

19. 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

20. Parenchyma resin • 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

21. Chemical composition • 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

22. 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

23. Abundant fatty acid components

24. Oleic acid Linoleic acid Triolein

25. Waxes • Ester of a long chained fatty alcohol and a fatty acid R1= fatty acid chain

26. 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

27. Phenolic constituents • 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 • Have fungicidal properties and protect the tree from microbic attacks • Contribute to the natural colour of wood

28. 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

29. Phenolic constituents Lignans:- Formed by oxidative coupling of two phenylpropane units- Most usual in spruce wood- Commercially attractive products Pinoresinol

30. Phenolic constituents Hydrolyzable tannins Condensed tannins Flavonoids - small amounts Tannins Taxifolin (Flavonoids)

31. Extractives distribution – cross sectional • The amount and composition of extractives vary over the log cross section • Most significant for softwoods • Biggest difference between heartwood and sapwood

32. Extractives distribution – cross sectional Scots pine Norway spruce

33. 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.

34. 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

35. Extractives in bleaching • 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

36. Extractives in kraft pulping • 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

37. 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

38. 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)

39. Extraction • 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. • 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 Soxhlet Soxtech

40. Choice of solvent • Critical for the extraction. • 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 • Dichloromethane (DCM) – Intermediate polarity, out of use due to health risk • 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

41. 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

42. 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

43. 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

44. Supercritical fluid chromatography • Analyse on component groups • Direct characterization without preceding derivatization • Steryl esters and triglycerides are not separated

45. Thin layer chromatography • 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

46. Nuclear Magnetic Resonance • 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 • Non-destructive technique • Time consuming and expensive but accurate technique

47. Infrared spectroscopy • 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

48. 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.

49. Summary • 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