Variation of Lignin Monomeric Composition During Kraft Pulping of Eucalyptus globulus Heartwood and Sapwood

Journal of Wood Chemistry and Technology, 33:1–18, 2013Copyright © Taylor & Francis Group, LLCISSN: 0277-3813 print / 1532-2319 onlineDOI: 10.1080/02773813.2012.703284

Variation of Lignin Monomeric Composition DuringKraft Pulping of Eucalyptus globulus Heartwood

and Sapwood

ANA LOURENCO,1 JORGE GOMINHO,1 ANTONIO VELEZMARQUES,2 AND HELENA PEREIRA1

1Forest Research Center, School of Agriculture, Technical University of Lisbon,Lisbon, Portugal2Research Center for Chemical Engineering and Biotechnology, SuperiorInstitute of Engineering of Lisbon, Lisbon, Portugal

Abstract: Heartwood and sapwood samples from Eucalyptus globulus were char-acterized by Py-GC/MS and GC-FID in respect to composition and content oflignin. The pyrolysis lignin-derived compounds were assembled by groups: “syringol,”“S-aldehydes,” “S-ketones,” “S-alcohols,” and “C11H12O3” (S-units); “guaiacol,”“eugenol,” “G-aldehydes,” “G-ketones,” “G-alcohols,” and “others” (G-units); “phe-nol” and “H-aldehydes” (H-units). Heartwood and sapwood had similar lignin contentin an extractive-free basis (23.7% and 23.0%, respectively) and in lignin composition(S-units, 76.0% vs. 76.3%; G-units, 22.0% vs. 21.0%; H-units, 1.9% vs. 2.7%; S/Gratio 3.5 and 3.6). The wood samples were kraft pulped under isothermal conditions at130◦C, 150◦C and 170◦C and several cooking times. Heartwood and sapwood behavedsimilarly. At 130◦C the delignification was slow with no significant selectivity in respectto lignin composition. At 150◦C and 170◦C the S-units were more susceptible to reactionand comparatively more removed, inducing a decrease of S/G ratio to 0.6. The main prod-ucts to be extracted belong to “syringol” and “S-aldehydes,” while the residual ligninin pulps was enriched in “guaiacol,” “eugenol” (G-units), and “phenol” (H-units).

Keywords Eucalyptus globulus, heartwood, pyrolysis, S/G ratio, lignin composition

Introduction

Eucalyptus globulus has excellent wood quality for pulping with very good technicalpulp properties[1] and high pulp yield[2] due to its chemical composition: low extractivescontent,[3] total lignin ranging from 15.4% to 27.0%,[2,3,4] with high range of S/G values

This work was funded in part by the Portuguese Science Foundation (FCT), through a Ph.D.scholarship granted to the first author (SFRH/BD/40060/2007), an R&D project PTDC/AGR-CFL/110419/2009, through the base funding to the Forest Research Center (CEF) under theFEDER/POCI 2010 Programme, and by PEst-OE/AGR/UI0239/2011. The authors thank Clara Araujoand ALTRI, who supplied the wood material.

Address correspondence to Ana Lourenco, Forest Research Center, School of Agricul-ture, Technical University of Lisbon, Tapada da Ajuda 1349 017, Lisbon, Portugal. E-mail:[email protected]

1

2 A. Lourenco et al.

(1.9–6.4[2,5,6] using Py-GC/MS), and high cellulose content at 40.1%–53.6%.[3,7] A reviewof E. globulus wood chemical composition and pulping was published recently.[8]

The lignin structural composition in Eucalyptus globulus has been investigated, specif-ically the syringyl/guaiacyl ratio (S/G), since it is considered an important characteristicin wood selection for pulping.[2,6,9] A high S/G ratio impacts positively on delignifica-tion, since S-lignin degrades more easily during pulping,[10] thereby leading to low alkaliconsumption and high pulp yield.[2,11] In this context it has been suggested[2] that lignincomposition might be more important than lignin content, although this is still a contro-versial subject, as discussed by Bose et al.[12] due to the absence of an accurate method todetermine the S/G ratio.

Py-GC/MS is a very useful technique for wood characterization and especially forlignin determination because it needs small amounts of sample with no pre-treatmentexcept extraction and grinding.[13] Lignin degrades at a wide range of pyrolysis temperatures(100◦C-900◦C),[14] involving dehydration, producing phenolic compounds with unsaturatedside chains and low molecular mass products and gases.[14,15] In fact, the major productsfrom lignin pyrolysis are its derivatives guaiacol and syringol,[13,15] while the minor productsare low molecular mass compounds (such as methanol, formaldehyde, acetaldehyde, aceticacid, and water) and gases (CO, CO2, CH4).[14]

Wood pyrolysis products and in particular those derived from lignin degradation havebeen reviewed,[16] but no studies were found in the literature comparing heartwood andsapwood. Heartwood has more extractives compared to sapwood, which will have a neg-ative impact during pulping by increasing chemical consumption, reducing pulp yields,and affecting process performance (for example, pitch deposits). Heartwood content inpulpwoods is therefore an important pulping quality property, and its impact on pulping ofE. globulus has been the subject of recent studies.[17–19]

This paper presents the results of an evaluation of lignin degradation of heartwood andsapwood of E. globulus during isothermal pulping at three temperatures (130◦C, 150◦C, and170◦C) at several cooking times, ranging from 0 to 180 min, using Py-CG/MS(FID) as theanalytical tool. Some kinetic studies were already performed using E. globulus wood,[20,21]

but few differentiated heartwood and sapwood[18] and none considered the kinetics oflignin structural variation. It is therefore the aim of this paper to better understand thekinetics of lignin degradation of heartwood and sapwood, thereby contributing to potentialimprovements in eucalyptus wood pulping.

Material and Methods

Samples

Heartwood and sapwood of Eucalyptus globulus Labill. were used as raw material forthis study. A disc was removed at 1.3 m of tree height, and sapwood and heartwood weremanually separated, milled, sieved, and characterized as described elsewhere (Lourencoet al.[17]). Kraft pulping was performed using 5 g (20–40 mesh fraction) of the sapwood andheartwood samples in stainless-steel rotating autoclaves in an oil-temperature-controlledbath under the following conditions: sulfidity 30% (as Na2O); active alkali 20% (as Na2O);liquor-to-wood ratio 4:1 (mL/g), under isothermal conditions. Three cooking temperatureswere used (130◦C, 150◦C, and 170◦C) with a combination of cooking times between 0and 180 min. The time 0 refers to the first delignification point, when the delignificationtemperature was attained; a 5 min heating period was necessary to reach the temperature.

Lignin Monomeric Composition 3

After each pulping time, the autoclaves were removed and cooled in ice to stop the reaction.The samples were defibrated in a blender and thoroughly washed with de-ionized hot waterif they were pulps, or otherwise just washed. The total yield was determined for all thesamples, as presented by Lourenco et al.[17]

Before chemical analysis, the samples were extracted in a Soxhlet; wood was extractedwith a sequence of dichloromethane, ethanol, and water during respectively 6h, 12h, 12h,and pulps with ethanol and water (70:30) during several hours, to remove extractableresidues present after delignification.

Py-GC-MS(FID) Analysis

Heartwood and sapwood samples and their respective pulps were analyzed by pyrolysis-gas chromatography. A CDS platinum coil Pyroprobe 2000 apparatus with a CDS 1500valved interface was coupled to the split/splitless injector of a GC-MS(FID) Thermo TraceUltra Polaris Ion Trap apparatus from Thermo Finnigan (Austin, TX), equipped with afused-silica capillary column Equity-1701 (60m × 0.25mm × 0.25 µm) from Supelco.

Identification and quantification of pyrolysis products were performed separately byPy-GC/MS and Py-GC/FID analysis, respectively. For identification of analytes, the Na-tional Institute of Standards and Technology (NIST) mass spectral search program for theNIST/EPA/NIH Mass Spectral Library version 2.0a, September 2001, was used as well asdata from Faix et al.[22,23] The identification process was made using the wood samplesand the pulps obtained with the longest cooking time for the three temperatures in order tomaximize the number of products identified. For quantification, the FID response factorsof pyrolysis products were considered to be all equal to 1.0. To the best of our knowledge,Faix and Meier[24] were the only authors to apply different response factors.

The samples were dried and powdered in a Retsch MM200 mixer ball mill during60 min (as determined experimentally for several samples). The range of the sample massused in this work was 95 to 105 µg as usual for this type of analysis. The sample waspyrolyzed in a quartz boat at 650◦C for 10 s with a temperature rise time of ca. 20◦C/ms(ramp-off) with the interface kept at 260◦C. The pyrolysates were purged from the pyrolysisinterface into the GC injector with a helium gas flow programmed as follows: 2.0 mL/min(1 min hold), decrease to 1.5 mL/min using a rate reduction of 0.5 mL/min2 and thento 1.0 mL/min at a rate reduction of 0.2 mL/min2, held for the remaining time. The GCinjector, FID detector, and GC-MS interface temperatures were 240◦C, 280◦C, and 280◦C,respectively. The GC oven program was: 40◦C, held for 4 min, 10◦C/min to 70◦C, 5◦C/minto 100◦C, 3◦C/min to 265◦C, held for 3 min, 5◦C/min to 270◦C, held for 9 min. For massspectra analysis, electronic ionization at 70 eV, 220◦C for ion source temperature and0.3 mL of damping helium gas were used.

The following considerations were taken before calculation procedures: i) not all ofthe pyrolysis products were completely separated (a few overlapping peaks occurred), butin most cases they could be identified; if the peak represented two compounds, one derivedfrom carbohydrates and the other from lignin, the peak area was only considered for totalarea calculation and not included for quantification of total lignin or total polysaccharides;ii) the small areas of contaminant phthalates (from plastic containers and caps) and silicones(from column bleeding) were not considered.

The total area of the pyrogram was obtained by automatic integration (Thermo Ex-calibur software) and manually corrected in some peaks for all the samples. The manualcorrection was performed because the software did not ensure adequate peak integrationsince: i) there were large differences between samples in the shape and density of the peaks;


ii) some peaks presented shoulders that were not properly integrated. The lignin pyrolysisderived products were summed up corresponding to total lignin (TL), and were classifiedas S-lignin, G-lignin, and H-lignin units, and their corresponding percentages calculatedin relation to total lignin. The S/G ratio was calculated using the sum of the areas fromsyringyl and guaiacyl derivatives.

To facilitate the analysis of results, the S-, G-, and H-lignin derivatives were grouped.The S-lignin compounds were grouped as: “syringol” (syringol; 4-methylsyringol;4-ethylsyringol; 4-vinylsyringol; 4-allylsyringol; 4-propenylsyringol cis and trans);“S-aldehydes” (syringaldehyde; homosyringaldehyde; sinapinaldehyde), S-ketones (ace-tosyringone; syringyl acetone; propiosyringone); “S-alcohols” (sinapyl alcohol isomers);and “C11H12O3.” The G-lignin derivatives were grouped as: “guaiacol” (methylguaiacol; 3-ethylguaiacol; 4-vinylguaiacol; 4-propylguaiacol); “eugenol” (eugenol; isoeugenol, cis andtrans); “G-aldehydes” (vanillin; homovanillin); “G-ketones” (acetoguaiacone; guaiacyl ace-tone; propioguaiacone); “G-alcohols” (coniferyl alcohol isomers). The area of the unknowncompounds and of the C10H10O2 was summed and designated as “others.” The H-lignin wasgrouped into “phenol” (cresol; phenol; dimethylphenol) and “H-aldehyde” (benzaldehyde).

Results and Discussion

Wood Lignin Characterization

The pyrograms obtained for sapwood and heartwood for the lignin-derived products arepresented in Figure 1 and the peak assignments in Table 1. The relative area of eachcompound reported to total lignin area is presented in Table 2.

A total of 43 compounds derived from pyrolysis of lignin were identified, from which17 were syringyl (S), 21 guaiacyl (G), and 5 hydroxyphenyl (H) derivatives. The peakswere well resolved with the exception of an overlap with carbohydrates and guaiacol, andtwo guaiacol derivatives: peak 35 (guaiacol and 2,3-dihydro-5-hydroxy-6-methyl-(4H)-pyran-4-one), peak 44 (4-methylguaiacol and an unidentified anhydrosugar), and peak 48(4-ethylguaiacol and 4-hydroxy-3-methyl-(5H)-furanone).

The estimated lignin content in sapwood and heartwood, based on the lignin productsobtained by pyrolysis, was 23.0% and 23.7%, respectively. These values are similar toother determinations using pyrolysis such as the 21.6% obtained by Oudia et al. [25] Theseresults are comparable to total lignin, determined as Klason and soluble lignin, in the samematerial, respectively, 24.3% and 23.5% (% o.d. wood), referred to by Lourenco et al.[17]

The pyrolysis products from sapwood and heartwood were the same compounds aspreviously reported for the wood as a whole.[2,6] As expected for a hardwood,[26] the syringyl(76.3% vs. 76.0%) and guaiacyl units (21.0% vs. 22.0%) prevailed over hydroxyphenyl

Figure 1. Py-GC/FID chromatograms of heartwood and sapwood from E. globulus wood. The peakassignments of lignin derived products are given in Table 1.

Tabl

e1

Peak

assi

gnm

enti

nth

epy

rogr

amof

hear

twoo

dan

dsa

pwoo

dfr

omE

ucal

yptu

sgl

obul

us

Peak

Peak

no.

RT

Com

poun

dO

rigi

n∗M

Wno

.R

TC

ompo

und

Ori

gin∗

MW

2520

.18

Ben

zald

ehyd

eH

106

6944

.43

4-E

thyl

syri

ngol

S18

234

24.6

5Ph

enol

H94

7045

.05

Ace

togu

aiac

one

G16

635

#25

.65

2,3-

Dih

ydro

-5-h

ydro

xy-6

-m

ethy

l-(4

H)-

pyra

n-4-

one/

guai

acol

cH/G

128/

124

7146

.63

4-V

inyl

syri

ngol

S18

0

3626

.66

o-C

reso

lH

108

7246

.99

Gua

iacy

lace

tone

G18

040

28.3

6m

-/p-

Cre

sol

H10

873

47.3

44-

Ally

lsyr

ingo

lS

194

4128

.61

Met

hylg

uaia

col

G13

874

48.2

1Pr

opio

guai

acon

eG

180

44#

29.9

14-

Met

hylg

uaia

col/A

nhyd

rosu

gar

G/C

138/

-75

48.6

9C

onif

eryl

alco

hol(

cis)

G18

045

30.2

7D

imet

hylp

heno

lH

122

7649

.23

4-Pr

open

ylsy

ring

ol(c

is)

S19

447

32.6

33-

Eth

ylgu

aiac

olG

152

78,7

950

.62/

50.9

5C

11H

12O

3S

192

48#

33.3

54-

Eth

ylgu

aiac

ol/4

-Hyd

roxy

-3-

met

hyl-

(5H

)-fu

rano

neG

/C15

2/14

480

51.4

44-

Prop

enyl

syri

ngol

(tra

ns)

S19

4

5235

.72

4-V

inyl

guai

acol

G15

081

52.4

5Sy

ring

alde

hyde

S18

253

36.7

5E

ugen

olG

164

8253

.99

Hom

osyr

inga

ldeh

yde

S19

654

36.8

54-

Prop

ylgu

aiac

olG

166

8454

.81

Ace

tosy

ring

one

S19

656

37.8

4Sy

ring

olS

154

8555

.44

Con

ifer

ylal

coho

l(tr

ans)

G18

058

,59

38.4

9/38

.65

Isoe

ugen

olis

omer

G16

486

56.1

0C

onif

eral

dehy

deG

178

6039

.00

Isoe

ugen

ol(c

is)

G16

487

56.2

5Sy

ring

ylac

eton

eS

210

6139

.32

unkn

own

(M/Z

107,

109,

138)

G-

8857

.36

Prop

iosy

ring

one

S21

063

41.0

9Is

oeug

enol

(tra

ns)

G16

489

57.9

1Si

napy

lalc

ohol

isom

erS

210

6441

.54

4-M

ethy

lsyr

ingo

lS

168

9060

.38

Dih

ydro

sina

pyla

lcoh

olS

212

6541

.88

Van

illin

G15

291

61.1

7Si

napy

lalc

ohol

(cis

)S

210

66,6

742

.52/

42.9

6C

10H

10O

2G

162

9264

.42

Sina

pina

ldeh

yde

S20

868

44.2

0H

omov

anill

inG

166

#,co

mpo

unds

over

lapp

ed;

RT,

rete

ntio

ntim

e;M

W,

mol

arm

ass;

∗L

igni

nde

riva

tive

prod

ucts

:H

-H-l

igni

nun

it;G

-G-l

igni

nun

its;

S-S-

ligni

nun

its;

carb

ohyd

rate

sde

riva

tive

prod

uct:

cH-f

rom

hexo

ses;

c-fr

omhe

xose

sor

pent

oses

.

5


Table 2Lignin Py-derived products (% of area of total lignin peaks) and total lignin (% of totalidentified peaks area) of heartwood and sapwood from Eucalyptus globulus determined by

Py-GC/FID

% of total lignin

Group Peak nº Compounds Sapwood Heartwood

Syringol 56 Syringol 10.14 7.3364 4-Methylsyringol 5.47 6.5169 4-Ethylsyringol 1.28 1.1871 4-Vinylsyringol 12.07 11.4773 4-Allylsyringol 4.09 3.8176 4-Propenylsyringol (cis) 2.16 1.8580 4-Propenylsyringol (trans) 10.32 10.47

Total 45.5 42.6S-aldehydes 81 Syringaldehyde 7.50 7.39

82 Homosyringaldehyde 5.47 6.4692 Sinapinaldehyde 2.80 3.15

Total 15.8 17.0S-ketones 84 Acetosyringone 3.46 3.58

87 Syringyl acetone 1.48 1.7988 Propiosyringone 0.28 0.27

Total 5.2 5.6S-alcohols 89 Sinapyl alcohol isomer 1.85 1.84

90 Dihydrosinapyl alcohol 0.35 0.3491 Sinapyl alcohol (cis) 0.55 0.59

Total 2.7 2.878, 79 C11H12O3 7.04 8.00

Total S-type ligninunits

76.3 76.0

Guaiacol 41 Methylguaiacol 0.15 0.1847 3-Ethylguaiacol 0.43 0.6152 4-Vinylguaiacol 3.54 3.8954 4-Propylguaiacol 0.25 0.28

Total 4.4 5.0Eugenol 53 Eugenol 2.49 2.12

58, 59 Isoeugenol isomer 0.84 0.7660 Isoeugenol (cis) 0.37 0.3663 Isoeugenol (trans) 2.45 2.63

Total 6.2 5.9G-aldehydes 65 Vanillin 1.50 1.62

68 Homovanillin 2.29 2.4786 Coniferaldehyde 0.81 0.74

Total 4.6 4.8G-ketones 70 Acetoguaiacone 0.68 0.70

72 Guaiacyl acetone 0.69 0.7374 Propioguaiacone 0.34 0.19

Total 1.7 1.6


Table 2Lignin Py-derived products (% of area of total lignin peaks) and total lignin (% of totalidentified peaks area) of heartwood and sapwood from Eucalyptus globulus determined by

Py-GC/FID (Continued)

% of total lignin

Group Peak nº Compounds Sapwood Heartwood

G-alcohols 75 Coniferyl alcohol (cis) 1.03 1.1385 Coniferyl alcohol (trans) 0.14 0.13

Total 1.2 1.3Others 61 unknown (M/Z 107,109,138) 0.70 1.07

66, 67 C10H10O2 2.31 2.41Total 3.0 3.5Total G-type lignin

units21.0 22.0

Phenol 34 Phenol 0.73 0.6236 o-Cresol 0.38 0.3140 m-/ p-Cresol 0.57 0.4245 Dimethylphenol 0.23 0.02

Total 1.9 1.4H-aldehyde 25 Benzaldehyde 0.77 0.57Total H-type lignin

units2.7 1.9

Total lignin (TL, %identified area)

23.0 23.7

units (2.7% and 1.9%). The main lignin products obtained from S-units were (Table 2):syringol, 4-methylsyringol, 4-vinylsyringol, 4-allylsyringol, 4-propenylsyringol (trans), sy-ringaldehyde, homosyringaldehyde, sinapinaldehyde, acetosyringone, and C11H12O3. Theproducts derived from G-units were: 4-vinylguaiacol, eugenol, isoeugenol (trans), vanillin,homovanillin, coniferyl alcohol (cis), and C10H10O2. These compounds were also de-scribed by del Rio et al.[2] for E. globulus wood pyrolysis, and the majority of them werealso obtained by Lima et al.[27] for other eucalypts, but with lower values of 4-allylsyringolcompared to E. globulus (1% vs. 4%).

Syringol derivatives represented the major group in the lignin pyrolysis products(around 45% of total lignin), where 4-vinylsyringol (peak 71), syringol (peak 56), and4-propensyringol (trans) (peak 80) represented from 10% to 12%. The group of aldehydescorresponded to a mean 17% of lignin with syringaldehyde (peak 92) representing about8%. The ketones and alcohols characterized less than 6%, but acetosyringone (peak 84)was relatively important with 3.6%.

The G-units included similar percentages of guaiacol, eugenol, and aldehydes com-pounds, representing 5–6% of the lignin. The most important individual compounds were4-vinylguaiacol (peak 52) representing almost 4%, eugenol (peak 53) and isoeugenol (trans)(peak 63) with 2–3%, and homovanillin (peak 63) with 2.5%. The H-units included mainlyphenols.


Heartwood and sapwood did not show large differences in lignin content (23.7% and23.0%) or lignin units composition, since the same pyrolysis products were present in bothsamples (Table 2). In the “syringol” group, syringol (peak 56) was the only compound witha larger difference between sapwood and heartwood (7.3 % vs. 10.1 %).

The S/G ratios obtained from sapwood and heartwood pyrolysis were identical (3.6 vs.3.5, Table 3). To the best of our knowledge no one studied the S/G ratio of E. globulussapwood and heartwood.

For E. globulus wood the results for S/G obtained by different authors are quite diverse:4.3 was obtained by Oudia et al.,[25] 4.1 by Rencoret et al.,[28] 3.0 by Ibarra et al.,[29] and1.9–2.3 by Rodrigues et al.[6] The comparison of S/G values obtained by different authorsis difficult due to differences in the conditions used for the analysis (e.g. the pyrolysistemperature[30,31]) or calculations (e.g. if only some of the lignin-derived products areused[27,30]). The origin of the tree[6] or its heterogeneity[32] may also play a role. Overall,the S/G ratio is difficult to calculate with accuracy by any method,[12] because the S units,which are less condensed, are easier to quantify than the more condensed G units.

The fact that no differences were found between sapwood and heartwood in this sampleis only indicative of the possibility that no variation of lignin composition and content willbe found related to cambial age in E. globulus trees at pulping age. In consequence, nodifferences in delignification should be expected from different stem components of suchtrees, a fact that is of practical importance in industrial pulping. This was proved in thisstudy, as discussed below.

Previous works[17,18] had already shown that the pulping and delignification kineticsof E. globulus sapwood and heartwood were similar. Therefore the differences in pulpyield that are obtained with heartwood (respectively 46.5 and 50.4% at 170◦C)[17] arederived from the higher content in extractives in heartwood in relation to sapwood.[17]

The distinctive feature of heartwood is the accumulation of extractives[19] together withthe anatomical difference of tyloses that may cause difficult impregnation. In this study,we used extractive-free wood for the pyrolysis analysis similar to other authors.[12,31]

Since the pulping was carried out on milled wood (20–40 mesh), the differences in liquorimpregnation were minimized and are not addressed here.

Delignified Samples Characterization

The physical structure of the samples was maintained in early stages of delignification, i.e.with short reaction times, as apparently similar to wood. This is why the samples weremilled prior to analysis for homogenization, which is an important factor as pointed out byMeier and Faix.[13] The characterization of pulps by pyrolysis is summarized in Table 3,regarding total lignin, the proportion of S, G and H units, S/G and S/G/H ratios. Heartwoodand sapwood showed similar results concerning the amount and composition of the ligninremaining in the pulps. No studies were found in the literature regarding pyrolysis of pulpsobtained from E. globulus heartwood, so our results will be compared to those of wood asa whole.

There was a very slight increase of lignin content in the samples in the first fourpoints of delignification at 130◦C, and in the two points at 150◦C, which may be explainedby the removal of hemicelluloses during the initial phase of pulping,[33] the natural sam-ple diversity, and the error associated with the method. This was not noticed at 170◦Cbecause the reaction is faster and the effect on lignin removal is therefore more noticeable.After this, the lignin content decreased along time and the rate of decrease was temperature-dependent: the lignin content of samples after 10 min at 130◦C, 150◦C, and 170◦C was

Tabl

e3

Val

ues

ofto

tall

igni

n(%

ofto

tali

dent

ified

area

,ID

obta

ined

from

pyro

lysi

s),t

hepr

opor

tion

ofS-

,G-,

and

H-l

igni

nun

its(%

ofto

tall

igni

n),a

ndth

era

tios

S/G

and

S/G

/Hof

sapw

ood

and

hear

twoo

dof

Euc

alyp

tus

glob

ulus

atse

vera

ldel

igni

ficat

ion

times

(min

)an

dat

130◦ C

,150

◦ C,a

nd17

0◦ C

Tota

lLig

nin

G-u

nits

S-un

itsH

-uni

ts(%

ID)

(%to

tall

igni

n)(%

tota

llig

nin)

(%to

tall

igni

n)S/

GS/

G/H

Rea

ctio

nco

nditi

ons

Sapw

ood

Hea

rtw

ood

Sapw

ood

Hea

rtw

ood

Sapw

ood

Hea

rtw

ood

Sapw

ood

Hea

rtw

ood

Sapw

ood

Hea

rtw

ood

Sapw

ood

Hea

rtw

ood

◦ Cm

inw

ood

23.0

23.7

21.0

22.0

76.3

76.0

2.7

1.9

3.63

3.45

29/8

/139

/11/

113

0◦C

025

.728

.319

.619

.177

.277

.33.

23.

63.

944.

0624

/6/1

22/5

/11

24.2

24.9

17.8

20.7

78.5

75.5

3.7

3.9

4.40

3.65

21/5

/120

/5/1

323

.926

.520

.019

.276

.476

.53.

54.

33.

813.

9822

/6/1

18/5

/15

24.3

27.1

20.4

19.1

76.4

76.9

3.2

3.9

3.75

4.02

24/6

/120

/5/1

1023

.324

.819

.119

.677

.275

.73.

74.

74.

043.

8621

/5/1

16/4

/120

22.0

22.9

19.9

19.5

75.9

76.5

4.2

4.1

3.82

3.93

18/5

/119

/5/1

6519

.019

.220

.920

.673

.274

.35.

95.

03.

503.

6012

/4/1

15/4

/195

15.2

14.7

20.3

24.1

73.3

71.1

6.4

4.8

3.61

2.95

11/3

/115

/5/1

180

10.5

11.6

25.6

24.8

68.0

70.2

6.4

5.0

2.65

2.83

11/4

/114

/5/1

150◦ C

025

.026

.719

.918

.976

.377

.63.

83.

53.

834.

1120

/5/1

22/5

/11

24.0

25.7

19.7

18.1

76.3

77.4

4.0

4.4

3.87

4.27

19/5

/118

/4/1

322

.826

.619

.018

.077

.177

.73.

94.

44.

054.

3320

/5/1

18/4

/15

20.9

25.3

20.3

18.1

75.9

77.3

3.8

4.6

3.74

4.26

20/5

/117

/4/1

1019

.319

.819

.220

.176

.275

.14.

64.

83.

973.

7417

/4/1

16/4

/120

15.3

17.1

21.8

20.2

73.4

75.5

4.8

4.3

3.37

3.74

15/5

/117

/5/1

653.

95.

339

.632

.339

.954

.620

.513

.11.

011.

692/

2/1

4/3/

195

2.8

3.1

45.1

46.1

31.1

34.0

23.8

19.9

0.69

0.74

1/2/

12/

2/1

180

2.8

2.5

44.6

41.9

25.0

25.9

30.4

32.2

0.56

0.62

1/2/

11/

2/1

170◦ C

022

.822

.818

.921

.177

.475

.63.

73.

34.

103.

5821

/5/1

23/6

/1(C

onti

nued

onne

xtpa

ge)

9

Tabl

e3

Val

ues

ofto

tall

igni

n(%

ofto

tali

dent

ified

area

,ID

obta

ined

from

pyro

lysi

s),t

hepr

opor

tion

ofS-

,G-,

and

H-l

igni

nun

its(%

ofto

tall

igni

n),a

ndth

era

tios

S/G

and

S/G

/Hof

sapw

ood

and

hear

twoo

dof

Euc

alyp

tus

glob

ulus

atse

vera

ldel

igni

ficat

ion

times

(min

)an

dat

130◦ C

,150

◦ C,a

nd17

0◦ C(C

onti

nued

)

Tota

lLig

nin

G-u

nits

S-un

itsH

-uni

ts(%

ID)

(%to

tall

igni

n)(%

tota

llig

nin)

(%to

tall

igni

n)S/

GS/

G/H

Rea

ctio

nco

nditi

ons

Sapw

ood

Hea

rtw

ood

Sapw

ood

Hea

rtw

ood

Sapw

ood

Hea

rtw

ood

Sapw

ood

Hea

rtw

ood

Sapw

ood

Hea

rtw

ood

Sapw

ood

Hea

rtw

ood

117

.318

.819

.619

.875

.374

.25.

16.

03.

853.

7515

/4/1

12/3

/13

15.9

18.8

23.2

19.4

73.3

74.9

3.5

5.6

3.16

3.86

21/7

/113

/3/1

512

.513

.223

.621

.769

.472

.17.

06.

22.

943.

3310

/3/1

12/4

/110

6.6

8.2

28.2

25.3

62.5

64.6

9.3

10.2

2.22

2.56

7/3/

16/

3/1

202.

93.

137

.240

.229

.741

.133

.118

.70.

801.

021/

1/1

2/2/

165

2.7

2.3

38.3

45.3

24.0

23.0

37.7

31.7

0.63

0.51

1/1/

11/

1/1

952.

42.

339

.744

.621

.521

.338

.834

.10.

540.

481/

1/1

1/1/

118

02.

22.

346

.047

.426

.724

.227

.228

.40.

580.

511/

2/1

1/2/

1

10


Figure 2. Py-GC/FID chromatograms of sapwood and heartwood from E. globulus pulps after180min of delignification at 170◦C. The peak assignments of lignin-derived products are given inTable 1.

on average, respectively, 24.1%, 19.5%, and 7.4%; and after 65 min it was 19.1%, 4.6%,and 2.5%, respectively. After 180 min lignin content was 3% at 150◦C and 2% at 170◦C(Table 3). These are values comparable to the 4% in E. globulus pulps, also determined bypyrolysis by Oudia et al.[34] Lourenco et al.[17] characterized these sapwood and heartwoodsamples by determination of total lignin (% o.d. wood) using standard wet chemistry meth-ods and obtained similar, although somewhat lower, values to those obtained by pyrolysis(after 180 min, 1.8% and 2.4% at 150◦C; and 1.1% and 2.0% at 170◦C). For E. globuluswood pulps obtained at 170◦C, Miranda and Pereira[21] reported 2.7% residual lignin.

The pyrograms for pulps produced after 180min at 170◦C are presented in Figure 2,where the reduction of the lignin-derived peaks is notorious when compared to woodpyrograms (Figure 1).

The composition of residual lignin in the pulps changed significantly in the later stagesof pulping, especially when the content of residual lignin was low, and its evolution withpulping time depended on the temperature, as shown in Table 3. The delignification at130◦C was characterized by a constant removal of lignin that was independent of the typeof lignin moities, e.g. there was no selectivity in lignin removal in these conditions: forexample, the content of S-lignin represented 77% and 69%, and of G-units 19% and 25%,respectively, for the first and last points of delignification (Table 3). This did not happen inthe delignification at the other temperatures, where a selective removal of different ligninmoieties occurred. At 150◦C and 170◦C, there was an increase of G and H-type units inlignin (respectively, 19% and 3% to 47% and 28%), as well as a decrease of S-units (77%to 25%). This is consistent with Pinto et al.[20] and Xie and Yasuda.[35] Pulps at the end ofthe cooking present therefore a higher content of G and H-type of lignin.[36]

A slight decrease of G-units occurred in the very first point of delignification (0 min,Table 3), as also mentioned by Chiang and Funaoka[37] and Pimenta et al.[38] This shouldbe due to their linkages to carbohydrates,[39] and it was shown that in E. globulus pulpingglucose and xylose are removed during the initial impregnation phase.[33]

Table 4 shows the lignin composition as regards the individual pyrolysis productsfor a few selected cases of wood pulped at 170◦C in order to understand what kind ofstructural moities are preferentially removed along delignification. The easiest groups tobe removed were the “S-alcohols” and C11H12O3 that were near zero in the pulp producedat 180 min. “S-ketones” were the following, representing in average only 5% of total S-lignin after 20 min of cooking. In this group, the easiest component to be removed waspropiosyringone (peak 88). Although the decrease in the “syringol” group was notorious,since in the beginning it represented 46.3% of lignin and in the end 17.7% (due to removalof 4-vynylsyringol and trans-4-propenylsyringol), it still represented the major group inthe residual lignin, as also referred by del Rio et al.[2]

Tabl

e4

Prop

ortio

nof

ligni

nPy

-der

ived

prod

ucts

(%of

tota

llig

nin

peak

sar

ea)

and

tota

llig

nin

(%of

tota

lide

ntifi

edpe

aks

area

)of

sapw

ood

and

hear

twoo

dpu

lps

at17

0◦ C

Coo

king

time

(min

)0

1020

180

Gro

ups

Com

poun

dsSa

pwoo

dH

eart

woo

dSa

pwoo

dH

eart

woo

dSa

pwoo

dH

eart

woo

dSa

pwoo

dH

eart

woo

d

Syri

ngol

Syri

ngol

9.21

7.76

6.83

8.83

6.59

8.87

6.30

7.76

4-M

ethy

lsyr

ingo

l4.

454.

353.

494.

202.

203.

101.

171.

484-

Eth

ylsy

ring

ol0.

950.

930.

611.

040.

000.

000.

000.

004-

Vin

ylsy

ring

ol12

.68

12.4

07.

4311

.32

5.12

7.45

2.51

3.04

4-A

llyls

yrin

gol

4.42

4.47

2.77

3.39

1.91

2.67

1.96

1.94

4-Pr

open

ylsy

ring

ol(c

is)

1.98

1.97

1.52

1.49

0.91

0.00

0.00

0.00

4-Pr

open

ylsy

ring

ol(t

rans

)12

.60

12.4

49.

019.

904.

818.

346.

483.

17

Tota

l46

.344

.331

.740

.221

.530

.418

.417

.4S-

alde

hyde

sSy

ring

alde

hyde

7.00

6.71

2.39

3.02

1.18

1.96

1.81

1.55

Hom

osyr

inga

ldeh

yde

5.23

5.05

3.08

2.94

2.73

3.12

2.77

2.31

Sina

pina

ldeh

yde

2.20

2.61

0.94

1.18

0.00

0.00

0.00

0.00

Tota

l14

.414

.46.

47.

13.

95.

14.

63.

9S-

keto

nes

Ace

tosy

ring

one

4.66

4.95

4.16

3.64

2.58

4.20

3.74

2.98

Syri

ngyl

acet

one

2.07

2.20

2.04

2.15

1.29

1.45

0.00

0.00

Prop

iosy

ring

one

0.34

0.38

0.22

0.25

0.00

0.00

0.00

0.00

Tota

l7.

17.

56.

46.

03.

95.

63.

73.

0S-

alco

hols

Sina

pyla

lcoh

olis

omer

1.17

0.98

0.50

0.40

0.42

0.00

0.00

0.00

Dih

ydro

sina

pyla

lcoh

ol0.

190.

510.

180.

220.

000.

000.

000.

00Si

napy

lalc

ohol

(cis

)0.

771.

000.

390.

390.

000.

000.

000.

00To

tal

2.1

2.5

1.1

1.0

0.4

0.0

0.0

0.0

12

C11

H12

O3

7.5

6.9

16.9

10.2

0.0

0.0

0.0

0.0

Tota

lS-t

ype

oflig

nin

77.4

75.6

62.5

64.6

29.7

41.1

26.7

24.2

Gua

iaco

lM

ethy

lgua

iaco

l0.

100.

180.

000.

000.

000.

000.

000.

003-

Eth

ylgu

aiac

ol0.

470.

652.

681.

714.

315.

026.

807.

544-

Vin

ylgu

aiac

ol,

3.22

3.26

2.70

3.62

3.44

3.10

2.81

2.74

4-Pr

opyl

guai

acol

0.15

0.25

0.00

0.00

0.00

0.00

0.00

0.00

Tota

l3.

94.

35.

45.

37.

88.

19.

610

.3E

ugen

olE

ugen

ol2.

021.

977.

685.

3615

.43

15.0

021

.01

20.6

8Is

oeug

enol

isom

er0.

881.

101.

150.

871.

893.

184.

944.

92Is

oeug

enol

(cis

)0.

340.

380.

400.

450.

280.

610.

000.

00Is

oeug

enol

(tra

ns)

2.24

2.43

1.65

2.21

0.69

1.49

0.00

0.30

Tota

l5.

55.

910

.98.

918

.320

.325

.925

.9G

-ald

ehyd

esV

anill

in1.

541.

901.

721.

871.

891.

420.

000.

56H

omov

anill

in1.

962.

222.

702.

680.

000.

000.

000.

00C

onif

eral

dehy

de0.

640.

700.

450.

230.

520.

480.

740.

00To

tal

4.1

4.8

4.9

4.8

2.4

1.9

0.7

0.6

G-k

eton

esA

ceto

guai

acon

e0.

840.

870.

620.

880.

000.

000.

000.

00G

uaia

cyla

ceto

ne0.

860.

821.

241.

151.

511.

872.

382.

49Pr

opio

guai

acon

e0.

150.

150.

210.

180.

000.

000.

000.

00To

tal

1.9

1.8

2.1

2.2

1.5

1.9

2.4

2.5

(Con

tinu

edon

next

page

)

13

Tabl

e4

Prop

ortio

nof

ligni

nPy

-der

ived

prod

ucts

(%of

tota

llig

nin

peak

sar

ea)

and

tota

llig

nin

(%of

tota

lide

ntifi

edpe

aks

area

)of

sapw

ood

and

hear

twoo

dpu

lps

at17

0◦ C(C

onti

nued

)

Coo

king

time

(min

)0

1020

180

Gro

ups

Com

poun

dsSa

pwoo

dH

eart

woo

dSa

pwoo

dH

eart

woo

dSa

pwoo

dH

eart

woo

dSa

pwoo

dH

eart

woo

d

G-a

lcoh

ols

Con

ifer

ylal

coho

l(ci

s)0.

420.

540.

960.

621.

251.

602.

192.

32C

onif

eryl

alco

hol

(tra

ns)

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

Tota

l0.

40.

51.

00.

61.

21.

62.

22.

3O

ther

sun

know

n(M

/Z10

7,10

9,13

8)0.

320.

601.

960.

833.

164.

065.

154.

49

C10

H10

O2

2.75

3.07

2.03

2.62

2.79

2.37

0.00

1.34

Tota

l3.

13.

74.

03.

56.

06.

45.

15.

8To

talG

-typ

eof

ligni

n18

.921

.128

.225

.337

.240

.246

.047

.4Ph

enol

Phen

ol0.

790.

792.

002.

076.

914.

485.

055.

99o-

Cre

sol

0.41

0.34

0.67

0.80

2.19

1.46

1.99

2.31

m-/

p-C

reso

l0.

940.

893.

273.

198.

945.

899.

9510

.16

Dim

ethy

lphe

nol

0.60

0.51

0.90

2.19

6.09

2.52

2.37

3.56

Tota

l2.

72.

56.

88.

224

.114

.419

.422

.0H

-ald

ehyd

eB

enza

ldeh

yde

0.9

0.8

2.5

1.9

9.0

4.3

7.9

6.4

Tota

lH-t

ype

oflig

nin

3.7

3.3

9.3

10.2

33.1

18.7

27.2

28.4

Tota

llig

nin

(TL

,%id

enti

fied

area

)22

.822

.86.

68.

22.

93.

12.

22.

3

14


Sapwood

Time (min)

0 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150 160 170 180 190

% o

f lig

nin

0

10

20

30

40

50

60Syringol S-aldehydes Guaiacol Eugenol Phenol

Heartwood

Time (min)

0 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150 160 170 180 190

% o

f lig

nin

0

10

20

30

40

50


Figure 3. Variation along pulping time of the proportion of the main chemical groups (Syringol,S-aldehydes, Guaiacol, Eugenol, and Phenol) in the residual lignin the samples of sapwood (left) andheartwood (right) pulped at 150◦C.

In G-units the major contributor was the “eugenol” group, where eugenol (peak 53)increased greatly in the last point (21%), as also reported by del Rio et al.[40] The decreasein G- and “S-aldehydes” while the “G-ketones” increased was also observed by Oudiaet al.,[25,34] who suggested that the C3-side group of syringol and guaiacol are preferentiallyattacked by the alkaline medium. The phenolic compounds (peaks 34, 36, 40 and 41) werethe major contributors to the increase of H-units in the pulps, representing on average 3%and 21%, respectively, at 0 and 180 min cooking time.

A similar behavior of lignin composition in pulps obtained at 150◦C is shownin Figure 3, where the main chemical groups (“syringol,” “S-aldehydes,” “guaiacol,”“eugenol,” and “phenol”) are represented. It is clear that most of the compositional varia-tion occurred before 65 min of pulping, a step later than in the 170◦C where most changesoccurred until 20 min. “syringol” and “S-aldehydes” groups decreased, “guaiacol” and“eugenol” increased, while the “phenol” group was maintained during delignification.

The changes were much less notorious at 130◦C (Figure 4), since lignin was moreslowly removed at this temperature, including all the groups selected for presentation inFigure 4.

The S/G ratio of the pulps decreased during delignification: at 130◦C, the decrease wason average from 4.00 to 2.74, showing a weaker selectivity in the type of lignin removedat this temperature when compared to the behavior at 150◦C (where the decrease was from

Sapwood

Time (min)

0 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150 160 170 180 190

% o

f lig

nin

0

10

20

30

40

50


Heartwood

Time (min)

0 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150 160 170 180 19

% o

f lig

nin

0

10

20

30

40

50


Figure 4. Variation along pulping time of the proportion of the main chemical clusters (Syringol,S-aldehydes, Guaiacol, Eugenol, and Phenol) in the residual lignin in the samples of sapwood (left)and heartwood (right) pulped at 130◦C.


3.97 to 0.59). The S/G decrease at 170◦C started earlier, e.g. after 10 min of cookingrepresented 2.39, and after 180 min, 0.55. Oudia et al.[25] obtained 1.4. This is indicative ofthe higher extraction of syringyl units during delignification in relation to guaiacyl units.Although H-lignin has only a minor importance in eucalypt wood lignin, this was changedduring delignification and it was quite clear that temperature and time contributed to anincrease of H units in the residual lignin of the samples. For instance, the ratio S/G/H forsapwood and heartwood was 11:4:1 (sapwood) and 14:5:1 (heartwood) after pulping at130◦C for 180 min, and 1:2:1 when increasing temperature to 150◦C or 170◦C.

The results obtained clearly showed that the lignin composition is important in pulping.In particular, a high percentage of S-units in wood lignin is important for the pulping athigh temperatures similar to that of industrial pulping, because the units can be extractedmore easily by the kraft liquor. In this way, the selection of species or of genotypes withhigh S/G ratios can be seen as advantageous for the pulping process.

Conclusions

The major conclusions of this work are: i) for this particular study, sapwood and heartwoodof Eucalyptus globulus are similar in respect to lignin content (on an extractive-free base)and lignin monomeric composition; E. globulus wood lignin is characterized by an averageof 76%, 22%, and 3% of, respectively, S-, G-, and H-units; ii) the pulping temperatureinfluences the removal of lignin and the composition of the residual lignin; the removalof S-, G-, and H-units was equal for sapwood and heartwood; iii) during delignification at150◦C and 170◦C, the S-units of lignin are more susceptible to reaction and preferentiallyremoved, in particular the “syringol” and “S-aldehydes” groups; iv) the residual lignin inpulps in the last stages of delignification is enriched in G- and H-units, respectively, in“eugenol” and “phenol” groups.

References

1. Patt, R.; Kordsachia, O.; Fehr, J. European hardwoods versus Eucalyptus globulus as a rawmaterial for pulping. J Wood Sci Technol 2006, 40, 39–48.

2. del Rio, J.C.; Gutierrez, A.; Hernando, M.; Landin, P.; Romero, J.; Martinez, A.T. Determiningthe influence of eucalypt lignin composition in paper pulp yield using Py-GC/MS. J Anal ApplPyrolysis 2005, 74, 110–115.

3. Kojima, Y.; Isaji, S.; Yoon, S.; Ona, T. Selection criteria of Eucalyptus globulus Labill. forproduction of chemithermomechanical pulps (CTMP). Holzforschung 2008, 62, 71–76.

4. Miranda, I.; Pereira, P. Variation of pulpwood quality with provenances and site in Eucalyptusglobulus Labill. Ann for Sci 2002, 59(3), 283–291.

5. Rodrigues, J.; Meier, D.; Faix, O.; Pereira, H. Determination of tree to tree variation in sy-ringyl:guaiacyl ratio of Eucalyptus globulus wood lignin by analytical pyrolysis. J Anal ApplPyrolysis 1999, 48, 121–128.

6. Pinto, P.C.; Evtuguin, D.V.; Neto, C.P. 2005. Effects of structural features of wood biopolymerson hardwood pulping and bleaching performances. Ind Eng Chem Res 2005, 44, 9777–9784.

7. Pereira, H.; Sardinha, R. Chemical composition of Eucalyptus globulus Lab. Appita 1984, 37(8),661–664.

8. Pereira, H.; Miranda, I.; Gominho, J.; Tavares, F.; Quilho, T.; Graca, J.; Rodrigues, J.; Shatalov,A.; Knapic, S. Qualidade Tecnologica do Eucalipto Eucalyptus globulus; Centro de EstudosFlorestais; Instituto Superior de Agronomia: Universidade Tecnica de Lisboa, Lisboa, 2010.

9. Rodrigues, J.; Graca, J.; Pereira, H. Influence of tree eccentric growth on syringyl/guaiacyl ratioof Eucalyptus globulus wood lignin accessed by analytical pyrolysis. J Anal Appl Pyrolysis 2001,58–59, 481–489.


10. Gonzalez-Vila, F.J.; Almendros, G.; del Rio, J.C.; Martın, F.; Gutierrez, A.; Romero, J.Ease of delignification assessment of wood from different eucalyptus species by pyrolysis(TMAH)-GC/MS and CP/MAS 13C-NMR spectrometry. J Anal Appl Pyrolysis 1999, 49, 295–305.

11. Collins, D.J.; Pilotti, C.A.; Wallis, A.F.A. Correlation of chemical composition and kraft pulp-ing properties of some Papua New Guinea reforestation woods. Appita 1990, 43(3), 193–195.

12. Bose, S.K.; Francis, R.C.; Govender, M.; Bush, T.; Spark, A. Lignin content versus syringyl toguaiacyl ratio amongst poplars. Bioresour Technol 2009, 100, 1628–1633.

13. Meier, D.; Faix, O. Pyrolysis-gas-chromatography-mass spectroscopy. In Methods in LigninChemistry; Lin, S.Y.; Dence, C.W., Eds.; Springer Series in Wood Science: New York, 1992,177–199.

14. Yang, H.; Yan, R.; Chen, H.; Lee, D.H.; Zheng, C. Characteristics of hemicelluloses, celluloseand lignin pyrolysis. Fuel 2007, 86, 1781–1788.

15. Meier, D.; Faix, O. State of the art of applied fast pyrolysis of lignocellulosic materials – a review.Bioresour Technol 1999, 68, 71–77.

16. Amen-Chen, C.; Pakdel, H.; Roy, C. Production of monomeric phenols by thermochemicalconversion of biomass: A review. Bioresour Technol 2001, 79, 277–299.

17. Lourenco, A.; Gominho, J.; Pereira, H. Pulping and delignification of sapwood and heartwoodfrom Eucalyptus globulus. J Pulp Pap Sci 2010, 36(3–4), 63–69.

18. Lourenco, A.; Gominho, J.; Pereira, H. Modelling of sapwood and heartwood delignificationkinetics of Eucalyptus globulus using consecutive and simultaneous approaches. J Wood Sci2011, 57, 20–26.

19. Miranda, I.; Gominho, J.; Lourenco, A.; Pereira, H. Heartwood extractives and pulp yield ofthree Eucalyptus globulus clones grown in two sites. Appita J 2007, 60(6), 485–488, 500.

20. Pinto, P.C.; Evtuguin, D.V.; Neto, C.P.; Silvestre, A.J.D.; Amado, F.M.L. Behavior of Eucalyptusglobulus lignin during kraft pulping: II. Analysis by NMR, ESI/MS, and GPC. J Wood ChemTechnol 2002, 22(2–3), 109–125.

21. Miranda, I.; Pereira, H. Kinetics of ASAM and kraft pulping of eucalyptus wood (Eucalyptusglobulus). Holzforschung 2002, 56, 85–90.

22. Faix, O.; Meier, D.; Fortman, I. Thermal degradation products of wood: A collection of electron-impact (EI) mass spectra of monomeric lignin derived products. Holz als Roh-und Werkstoff1990, 48, 351–354.

23. Faix, O.; Meier, D.; Fortman, I. Thermal degradation products of wood: Gas chromatographicseparation and mass spectrometric characterization of monomeric lignin derived products. Holzals Roh-und Werkstoff 1990, 48, 281–285.

24. Faix, O.; Meier, D. Pyrolytic and hydrogenolytic degradation studies on lignocellulosics, pulpsand lignins. Holz als Roh-und Werkstoff 1989, 47, 67–72.

25. Oudia, A.; Meszaros, E.; Jakab, E.; Simoes, R.; Queiroz, J.; Ragauskas, A.; Novak, L. Analyticalpyrolysis study of biodelignification of cloned Eucalyptus globulus (EG) clone and Pinus pinasterAiton kraft pulp and residual lignins. J Anal Appl Pyrolysis 2009, 85, 19–29.

26. Rowell, R.M.; LeVan-Green, S.L. Cell wall chemistry. In Handbook of Wood Chemistry andWood Composites; Rowell, R.M., Ed.; CRC Press: Boca Raton, Florida, 2005, 37–74.

27. Lima, C.F.; Barbosa, L.C.A.; Marcelo, C.R.; Silverio, F.O.; Colodette, J.L. Comparison betweenanalytical pyrolysis and nitrobenzene oxidation for determination of syringyl/guaiacyl ration inEucalyptus spp. lignin. BioResour 2008, 3(3), 701–712.

28. Rencoret, J.; Gutierrez, A.; Ibarra, D.; del Rio, J.C. Lipid and lignin composition of wood fromdifferent eucalypt species. Holzforschung 2007, 61, 165–174.

29. Ibarra, D.; Chavez, M.I.; Rencoret, J.; del Rio, J.C.; Gutierrez, A.; Romero, J.; Camarero, S.;Martınez, M.J.; Jimenez-Barbero, J.; Martınez, A.T. Lignin modification during Eucalyptusglobulus kraft pulping followed by totally chlorine-free bleaching: A two-dimensional nuclearmagnetic resonance, Fourier transformed infrared, and pyrolysis-gas chromatography/mass spec-trometry study. J Agric Food Chem 2007, 55, 3477–3490.


30. Nunes, C.A.; Lima, C.F.; Barbosa, L.C.A.; Colodette, J.L.; Gouveia, A.F.G. Determination ofEucalyptus spp lignin S/G ratio: A comparison between methods. Bioresour Technol 2010, 101,4056–4061.

31. Barbosa, L.C.A.; Maltha, C.R.A.; Silva, VL.; Collodette, JL. Determination of the sy-ringyl/guaiacyl ratio in eucalyptus wood by pyrolysis-gas-chromatography/mass spectrometry(Py-GC/MS). Quim Nova 2008, 31, 2035–2041.

32. Yokoi, H.; Ishida, Y.; Ohtani, H.; Tsuge, S.; Sonoda, T.; Ona, T. Charaterization of within-treevariation of lignin components in Eucalyptus camaldulensis by pyrolysis-gas chromatography.Analyst 1999, 124, 669–674.

33. Santiago, A.S.; Neto, C.P. Impact of kraft modifications on Eucalyptus globulus pulping perfor-mance and polysaccharide retention. Ind Eng Chem Res 2008, 47(19), 7433–7440.

34. Oudia, A.; Meszaros, E.; Simoes, R.; Queiroz, J.; Jakab, E. Pyrolysis-GC/MS and TG/MS studyof mediated laccase biodelignification of Eucalyptus globulus kraft pulp. J Anal Appl Pyrolysis2007, 78, 233–242.

35. Xie, Y.; Yasuda, S. Difference of condensed lignin structures in eucalyptus species. Nordic PulpPap Res J 2004, 19, 18–21.

36. Tsutsumi, Y.; Kondo, R.; Sakai, K.; Imamura, H. The difference of reactivity between syringyllignin and guaiacyl lignin in alkaline systems. Holzforschung 1995, 49(5), 423–428.

37. Chiang, V.L.; Funaoka, M. The dissolution and condensation reactions of guaiacyl and sy-ringyl units in residual lignin during kraft delignification of sweetgum. Holzforschung 1990, 44,147–155.

38. Pimenta, L.R.; Gomide, J.L.; Colodette, J.L.; Shin, N.H. Comportamento das constituintesquımicos da madeira de eucalipto na polpacao lo-solids. In: 3rd ICEP - International Collo-quium on Eucalyptus Pulp, Belo Horizonte, Brazil, 2007.

39. Ishii, T.; Shimizu, K. Chemistry of cell wall polysaccharides. In Wood and Cellulosic Chemistry;Hon, D.N.S.; Shiraishi, N., Eds.; Marcel Dekker: New York, 2001, 175–212.

40. del Rio, J.C.; Gutierrez, A.; Romero, J.; Martınez, M.J.; Martınez, A.T. Identification of residuallignin markers in eucalypt kraft pulps by Py-GC/MS. J Anal Appl Pyrolysis 2001, 58–59,425–439.

Documents

Variation of Lignin Monomeric Composition During Kraft Pulping of Eucalyptus globulus Heartwood and Sapwood