Klason lignin of four different types of tropical hardwoods and rattan was studied using rT-IR spectroscopy. There

were observable differences in the rT-IR spectra of the lignin studied. Lignin from the more durable and more

resistant wood were found to contain less guaiacyl groups than that from the softer and less resistant wood. 77re

strength and resistance of the wood might be related to its lignin content

Ibrahim, Ramli

Lau, S

Universiti Putra Malaysia Institutional Repository

Pertanika 14(1), 75-81 (1992)COMMUNICATION VFf-IR Spectroscopic Studies on Lignin from Some TropicalWoods and Rattan.ABSTRAKKajian ke atas lignin Klason dari empat jenis Iwyu keras tropika dan rotan dengan menggunakan spekrtroskopiFT-inJra merah telah dijalankan. Ketahanan dan kekuatan sesuatu jenis kayu berhubung rapat dengan kandunganligninnya. Terdapat perbezaan pada spektra rT-infra merah di antara lignin-lignin yang dikaji. Kayu yang mudahreput mengandungi lebih kumpulan guaisil di dalam lignin berbanding dengan yang lebih tahan reput.ABSTRACTKlason lignin ojJour different types oj tropical hardwoods and raLtan was studied using rT-IR sj)ectroscopy. Therewere observable differences in the rT-IR spectra oj the lignin studied. Lignin Jrom the more durable and moreresistant wood were Jound to contain less guaiacyl groups than that from the softer and less resistant wood. 77restrength and resistance oj the wood might be related to its lignin content.INTRODUCTIONLignin in wood fibres has been associated withthe mechanical strength of the wood and itsresistance towards microorganism attack (Higuchi1981). The elucidation of the structure of ligninhas been difficult, giving rise to controversies asto the actual roles played by lignin. Moreover, thestructure of lignin has not been completely un-derstood. However, lignins are generally classifiedinto three major groups (Higuchi 1981). They are(i) the gymnosperm lignin which is adehydrogenated polymer of coniferyl alcohol, (ii)the angiosperm lignin which is a mixeddehydrogenated polymer of coniferyl and sinapylalcohols and (iii) grass lignin which is composedof a mixed dehydrogenated polymer of coniferyl,sinapyl and p-coumaryl alcohols.Alllignins that have been isolated were foundto have undergone a certain amount of structuralmodification either chemically or physically(Harkin 1969). As lignin is a complex polymer,there is bound to be some structural deformationduring extraction.There has been considerable work on theapplication of FT-IR spectroscopy in lignin analy-sis. FT-IR spectroscopy has been used to monitorthe degradation of lignin in wheat straw andsignificant differences were found in the FT-IRspectra of the lignin in the region of 1400 - 1750em'! (Buta et al. 1989). The absorption band at1510 cm-! has been used as an internal standardfor quantitative analysis of lignin content (Roy etal. 1987). Pioneering work on this aspect wascarried out by Morton and Sparkes in 1967. Thedeconvolution of FT-IR spectra of lignin has en-hanced the fine structures and resolutions mak-ing it possible to elucidate the differences be-tween two lignin samples using FT-IR spectroscopy(Faix and Beonhoff 1988).Belian (Eusideroxylon zwageri) which is foundonly in Borneo is one of the most valuable woodsin Sarawak and Sabah. Belian wood is very dura-ble and resistant to microorganism attack. It iscommonly used as tiles for roofs, bridges, andsupports for pepper vines. The wood is able towithstand weathering for at least ten years withoutmuch deterioration. On the other hand, woodfrom rubber trees (Hevea brasiliensis) is non-du-rable and offers very little resistance to microor-ganism attack. If these properties of wood arerelated to its lignin composition, then there shouldbe significant differences between the lignin fromwood of the belian and that of the rubber tree.This research was carried out to study thedifferences between the lignin from some tropicalhardwoods and rattan (Calamus sp.). The findingsof this project will be useful for developing amethod of wood preservation.CHfiHICH/ICHoY~3OHConiferyI alcohol (1)I~CH30AAoCH3OHSyringyl grouo (4)S. LAU & RAMLI IBRAHIMSinaoyl alcohol (2)Guaiacyl grouo (5)C~OHICH11CH¢o-eounary I alcohol (3)MATERIALS AND METHODSLignin is known to consist of polymeric substancesthat differ in composition from one species ofplant to another as well as from tree to tree withinindividual species. Factors affecting this differenceare local climatic conditions, soil composition,pH, the nature of the surrounding vegetation(Harkin 1969). Wood samples of belian(Eusideroxylon zwageri) , selangan batu (Shorea sp.)and kapur (Dryobalanops sp.) were collected as sawntimber from a sawmill at Bintulu. The species ofselangan batu and kapur were not identified.Rattan cuttings were obtained from a furnitureshop at Bintulu and the species was not deter-mined. Rubberwood was obtained from the rub-ber plantation at Universiti Pertanian Malaysia,Kampus Bintulu. In this study, the differenceswithin the individual species were not consideredand were assumed to be less significant comparedto the variations observed between the differenttypes of plant species.Isolation of LigninLignin was isolated using the established Klasonmethod (Ritter et al. 1932). Sawdust from the woodsamples was ground to pass a 40-mesh sieve anddried in an oven at 500 e for 24 h. One gram ofthe dried sample was weighed into a celluloseextraction thimble. The thimble was placed in aSoxhlet extraction apparatus and the wood wasextracted with 95% ethanol-benzene, 1 : 2 (v/v),for 8 h. The solvent was removed and air dried ina fume-cupboard. The wood was then digested ina beaker with hot distilled water (400 ml) at aboutlOOoe for 3 h, filtered and washed with hotdistilled water (100 ml), then rinsed with ethanol(50 ml) before being air dried.The partially digested wood was placed in asmall beaker and 72% sulphuric acid (I5ml) wasadded slowly with stirring. The mixture was al-lowed to stand for 2 h in a water bath at 300 e withfrequent stirring. The mixture was then transferredinto alL flask and 560 ml of water was added todilute the sulphuric acid to a concentration of3%. The mixture was boiled under reflux for 4 h.The insoluble lignin was allowed to settle beforebeing filtered into a pre-weighed filtering crucible(porosity no.3), and washed free of acid with hotdistilled water (500 ml). The crucible and itscontents were dried in an oven at 105°e for 12 h,cooled in a desiccator and weighed. The dryingand weighing were repeated until the weight wasconstant.The lignin content was calculated as a per-centage of the oven-dry unextracted wood. Thislignin is also known as Klason lignin. Analyseswere carried out in 5 replicates for type of woodsample.FT-IR Analysis of LigninLignin samples were made into KBr discs. Ap-proximately 2 mg of lignins were ground with 200mg of KBr. The FT-IR spectra were taken usingPerkin Elmer 1600 FT-IR Spectrometer.Analysis of lignin in the wood was carried outusing the multiple internal reflectance technique(MIR). Pieces of wood to be analysed were cutinto thin strips ca. 35 x 15 mm and a thickness ofapproximately 1 mm. The MIR technique enabledthe studies on untreated lignin to be carried out.76 PERTANIKA VOL. 15 NO. I, 1992FT-IR SPECfROSCOPIC STUDIES ON LIGNIN FROM SOME TROPICAL WOODS AND RATTATABLE 1Percentages of Klason lignin in some tropicalwoods and rattan.RESULTS AND DISCUSSIONKlason lignin contents of four different hardwoodsand a species of rattan were determined and aretabulated in Table 1. Belian, selangan batu andkapur are among the tropical hardwoods that arerelatively durable and have high resistance to-wards decay with belian being the most durableand kapur the least durable of the three Uantanand Tam 1987). The Kalson lignin contents ofthese three types of wood were very similar withbelian having a slightly higher percentage ofligninthan selangan batu and kapur. Rubberwood, whichis known to decay easily, was found to containonly 18% lignin. This result indicates that a pos-sible relationship between the lignin content of awood and its strength might exist.FT-IR spectra of the Klason lignins were takenfor each of the wood and rattan samples (Fig. 1a, b, c). The spectra of the lignins in the regionfrom 1800 cm·1 to 4000 cm-l did not provide muchinformation other than broad hydroxyl andaliphatic GH absorptions. This observation wasalso noted by others (Buta et at. 1989; Roy et at.1987). This region of the FT-IR spectra will not beconsidered further. The aromatic absorption re-TABLE 2FT-IR absorption bands for Klason lignin.Type of wood % Ligninmean ± s.dev_Wave number(em-I)1700 - 17441600 - 16151505 - 15151455 - 14901420 - 14301320 - 13301270 - 12801220116011201030Significance of bands.C=O in acetyl, aliphatic ester or alde-hyde groups.aromatic skeletal vibrations.aromatic skeletal vibrations.C-H deformation asymmetric.aromatic skeletal vibrations.syringyl ring (4) breathing with c-ostretching.guaiacyl ring (5) breathing with C-Ostretching.syringyl ring (4) breathing_aromatic C-H in plane deformation,guaiacyl type (5).aromatic C-H plane deformation ofsyringyl type (4).aromatic C-H in plane deformationguaiacyl type (5) and C-O deforma-tion of primary alcohoLBelian (Eusideroxylon zwageri)Selangan bam (Shorea sp.)Kapur (Dl),obalanops sp.)Rubber (Hevea lJrasiliensis)Rattan (Calamus sp.)32.5 ± 0.4231.2 ± 0.2929.6 ± 0.9218.2 ± 0.16?6.3 ± 1.68woods and rattan show similar absorption bandsas that of the Klason lignin. In addition to theabsorption bands of lignin, there are extra bandsobserved. These bands, (1010 'cm- I ), are mostlikely to be due to the presence of cellulosecomponents of the wood. In the MIR spectra,there are two absorption bands that showed sig-TABLE 3FT-IR absorption band shifts between 1612and 1400 em-I.* band shifts of significant differenceBelian 1612* 1510* 1457Selangan batu 1609 1498 1458 1424Kapur 1609 1499 1459 1424Rubberwood 1604* 1499 1458 shoulderRattan 1608 1500 1462* 1425gion of the spectra contains bands assigned tolignin (Hergert 1971; Roy el at. 1987). Bandassignment of the spectra between regions 1000and 1800 cm- I is shown in Table 2. The FT-IRspectra of Klason lignin from the samples show ashift in the absorption bands between 1612 and1500 cm- l . Table 3 shows the corresponding bandshifts in the five samples studied.The spectra of wood strips using multipleinternal reflectance (MIR) technique are shownin Figure 2 a, b, c. The MIR spectra of the variousWood Absorption Bands (em-I)PERTAl lKA VOL 15 NO.1, 1992 77S. LAD & RAMLI IBRAHIM92.75iTBOO em-I1600 1400 1200 1000Fig. 1 (a) FT-IR spectra of lignin from kapUT obtained using KBr pellet cell.69.70+------,----------r------"'T------,-------,----180092.91lI:T,I\,\\\\\\\ rJ\I ' \\ ' ,\ ' 1\ I I\ ' I, : I 1\I I I I \\ ' \ !"I : 1 '\ I \\ I ~: I ,'v' \\ \. I I' I I I\\ \ , , I I " r,\ \! '-' \,1 \, ,tIJ \1\ \,1" \i '''\ / V \.\ I, r· \ I I'1/\. \: I \ \ ",,) \,\. I \ \1\. \. IVA/', .... ,.... \,.v \ I \\" I'• I ,IIVBOO cm-\100012001400160060.B2+-----.----.lI.--r------,---.lL..---,-----~-­180078 PERTANIKA VOL. 15 NO.1, 1992FT-IR SPECTROSCOPIC STUDIES ON LIGNIN FROM SOME TROPICAL WOODS AND RATTAN90.94:nFig. I(b)and I(c)80.08:n1600 1400 1200 1000Comparison FT-m spectra of lignin obtained using the KBr pellet cell.(C) - Rubberwood; (D) - Selangan Batu and (E) - Belian.~~".:r-- m I~cD If) ~ ~'f (\J toOJ ....'f .... ~If) ~ 0 m.... C\J C\I~ ~E800 em-I(A) - Rattan; (B) Kapur;1600 1400 1200 1000 800 cm-JFT-IR spectrum of Selangan Batu wood strip obtained using the MIR technique.63. 18+-----r-------,r------,-----.I.....,-----,---1800Fig. 2 (a) :PERTANIKA VOL. 15 NO.1, 1992 79s. LAU & RAMLI IBRAHI [,,\\\BOO cm-\,,V[Jc1000,,I, ,, /",\ '\ • 1\/ \ 1\ 'I II "\ ,I II I" 'V'"" :, I, I, II I, I\ I, ,\ ,, ,\ I, I"12001400\I t' /\\ J\ I \ /\ J \'.II \.1 " \ J\11600~,\\\ ,'\164.72-+--------.-------,r---------,-----~,__------r_--1BOO94.40:nE1600 1400 1200 1000 BOO em-IComparison FT-IR spectra of wood st1ips obtained using the MIR technique. (A) - Rattan; (B)- Selangan Batu; (C) - RubbelWood; (D) - KapuT and (E) - Belian./,~, \,1"",/ \/'.1\ f, 1 \I , I , B , \-" ,. (t (.... ,f I /"', "\ ,,, ...."'\4...... .... I 1 I\ r '( 1\,' \ /'\ (\ l' I I\ ",/\..' \ ( ,,\ 1\ t \.1 ", ,'" " \/\ "... \ I \...1 \ / \'\r.\ ') f\ 'v \/ -" I .\ \ ,/. j· ...d\i iJV.~'J\ /. \ ,: /",r--'-----...'\.\.--- . '--J ~ ~ I'! /. D \V \\.... \ ,,I;. \"", " I,\\ ,J!\\/~/\.62.19+-------,-------,------,------'''--,------,---1800Fig. 2 (b) and 2 (c)90.66Xl80 PERTANIKA VOL. 15 NO. I, 1992FT-IR SPECTROSCOPIC STUDIES ON LIGNIN FROM SOME TROPICAL WOODS AND RATTANnificant differences among the various wood sam-ples. The first was the absorption band of wavenumber between 1500 and 1515 cml. Belian woodshowed a relatively strong absorption at 1510 em'I while the wood showed a doublet at 1503 and1512 cm'l. This absorption band is assigned to thearomatic skeletal vibration. This indicates thatbelian has almost a single type of aromatic ringwhile the other wood contains at least two typeswith a more or less similar concentration. Thesecond absorption band is at the region between1000 and 1030 cm'l. Belian and selangan batushowed a single absorption band at 1013 cmlwhile kapur showed a wider band which wasunresolved at 1007 cm'l. Rubberwood showeddistinctly t:\vo equally strong bands at 1013 and1030 cm,l, while rattan also showed the \:\vo simi-lar bands, with the band at 1030 cml being muchstronger than that of 1013 cm,l. The absorptionband at 1030 cm,l is assigned to the aromatic C-Bin plane deformation of the guaiacyl type (5).This indicates that lignins in rubberwood andrattan contain a higher proportion of guaiacylgroup than those from belian, selangan batu andkapur.CONCLUSIONThis study has shown that there are detectabledifferences in the IT-IR spectra of the extractedlignins as well as in the untreated wood strips ofvarious types of wood. Further studies should be:carried out to elucidate the specific differencesbetween the lignins of various woods. Separationof lignin components will be necessary to charac-terise the exact nature of each type of lignin inplants. Further work is being done in our labora-tory.ACKNO~DGEMENTSThe authors wish to thank IRPA for funding theproject and Encik Mohd Afandi bin Mat Sani andEncik Sidem Nogep for assistance.S. LAD & RAMLI IBRAHIMCentre of Basis Science StudiesUniversiti Pertanian Malaysia, Kampus BintuluPO. Box 396, 97008 BintuluSarawak Malaysia..REFERENCESBUTA, j.G., F. ZADRAZIL, and G.C. GALLETTI. 1989. IT-IR Determination of Lignin Degradation inWheat Straw by White Rot Fungus Strophariamgosoannulata with Different Oxygen Concen-trations. J Agric. Food Chem. 37: 1382-1384.FAlX, O. and O. BEONHOFF. 1988. IT-IR Spectra ofMilled Wood Lignins and Lignin Polymer Mod-els (DHP's) with Enhanced Resolution Obtainedby Deconvolution. J Wood Chem. Technol. 8(4):505-523.HARKIN, j. M. 1969. Methods of Attacking the Prob-lems of Lignin Structure. In Recent Advances inPhytochemistry, vol.II, ed. M. K. Seikel and V.C. Runeckles, p 35-75, N. Y.: Appleton-Century-Crofts.HERGERT, H. L. 1971. In LIGNINS ed. K. V. SARKAl'iENand C. H. LUDWIG, P 267-293 N. Y. : Wiley-Interscience.HIGUCHI, T. 1981. Lignin Structure and Morphologi-cal Distribution in Plant Cell Wall. In LigninBiodegradation: Microbiology, Chemistry andPotential Applications, vol.1,pl-19 ed. T. K. Kirk,T. Higuchi and H. M. Chang. Florida: CRCPress,JANTfu'l, M. D. and M. K. TAiYL 1987. Natural Dura-bility of Malaysian Timbers, Timber Trade Leaf-let No. 28, FRlM, K. L.MORTON, j. and H.E. SPARKEs. 1967. Tappi, 50: 363.RITTER, G. j., R. M. SEBORG and R. L. MITCHELL. 1932,Ind. Eng. Chem., Anal. Ed., 4: 202.RoY, A.K., S.c. BAG and S.K. SEN. 1987. Studies onthe Chemical Nature of Milled Wood Lignin ofJute Stick, Cellu. Chem. Technol. 21: 343-348.(Received. 2 September 1991)PERTANIKA VOL. 15 NO. 1,1992 81

Ff-IR Spectroscopic Studies on Lignin from Some Tropical

Woods and Rattan

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Ff-IR Spectroscopic Studies on Lignin from Some Tropical Woods and Rattan

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