(2006) Influence of Raw

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Industrial Crops and Products 24 (2006) 160–165

Influence of raw-material and process variables in the kraftpulping of Cynara cardunculus L.

Jorge Gominho ∗, Helena Pereira

Centro de Estudos Florestais, Instituto Superior de Agronomia, Tapada da Ajuda, 1349-017 Lisboa, Portugal

Received 18 May 2005; accepted 8 March 2006

Abstract

Wholestalks andmanuallydepithedstalks of the thistle Cynara cardunculus L.werestudied at 150,160 and 170 ◦C regarding their

kraft pulping kinetics. Three pulping phases were observed: initial, bulk and residual, corresponding to the removal of approximately

25, 15 and 5% of the material, respectively. The rate constants of the initial phase were approximately 10 times higher than that of

the bulk phase (5.3× 10−2 min−1 versus 5.9× 10−3 min−1 for the whole stalks pulping at 160 ◦C). The activation energy was 74,

45 and 24 kJ mol−1, respectively, for the initial, bulk and final delignification phases. The pulp yields from depithed stalks were

somewhat higher (57% versus 54% at 160 ◦C, 120 min). The presence of pith was related to lower yields and to higher diffusion

resistance of parenchyma cells. Depithing of stalks should be included as a raw-material preparation before pulping

© 2006 Elsevier B.V. All rights reserved.

Keywords: Annual crops; Cynara cardunculus L.; Kraft pulping; Kinetics; Activation energy; Depithing

1. Introduction

The European Union has supported research on sev-

eral non-wood species with high biomass production,

that can be planted in areas made available from agricul-

ture and that are adequate for different industrial uses

(van Dam et al., 1994). One of the interesting fibre

crops is the thistle Cynara cardunculus L., a perennial

plant, with annual growth cycles, that can attain high

productivities above 20 tonnes ha−1 and grows in dry

conditions (Fernandez and Manzanares, 1990; Gominho

et al., 2001). Approximately 40% of thetotaldrybiomass

is concentrated in the stalk at the time of harvest in

September and it is practically dry with a moisture con-

∗ Corresponding author. Tel.: +351 213634662;

fax: +351 213645000.

E-mail address: [email protected] (J. Gominho).

tent under 14% (Gominho et al., 2001; Dalianis et al.,

1996; Fernandez, 1992).

One of the possible uses for the Cynara biomass is as

a fibre source for paper pulp production (Dalianis et al.,

1996; Villar et al., 1999; Gominho and Pereira, 2000;

Antunes et al., 2000). Annual plants represent approxi-

mately 10% of the world pulp production, with China as

the most important producer with more than two-third

of the total (Sadawarte, 1995). The most frequent raw-

materials are straw, in particular wheat and rice straw,

and sugar cane bagasse (MacLeod, 1988). The E.U. con-

sumption of pulps from annual plants is around 400,000

tonnes of which about one-fourth is imported (van Dam

et al., 1994).

The pulping of annual plants differs substantially

from wood pulping. In most cases, delignification pro-

ceeds very fast andthe resultingpulpshave a low residual

lignin content. However, the few reports on the activa-

tion energy for the bulk delignification of annual plants

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J. Gominho, H. Pereira / Industrial Crops and Products 24 (2006) 160–165 161

are not very different from the values obtained for wood

(Laith et al., 1995; Gonzalo et al., 1998). In general,

the papermaking properties of annual plant pulps are

inferior to those of wood pulps (Grace and Malcolm,

1989; Sadawarte, 1995). The main reason is the differ-

ent anatomy of these raw-materials, since most annual

plants have a particularly high content of parenchymacells which have no interest for paper properties and

cause problems in the paper machine (Biermann, 1993).

The pulping behaviour of Cynara is closer to wood

than to annual plants, probably due to a lignin con-

tent somewhat similar to hardwoods (Gominho et al.,

2001). The research on the pulping aptitude of Cynara

has shown that stalks can be pulped with different

processes for paper production (Gominho and Pereira,

2000) and that pulps can be produced with high resis-

tance and a favourable refining behaviour (Villar et al.,

1999; Gominho et al., 2001). The stalks of Cynaraplants are structurally and anatomically heterogeneous

(Quilho et al., 2004) and the presence of the central

pith may make the pulping difficult and advise a post-

harvest depithing operation (Gominho et al., 2001).

Considering that knowledge on reaction kinetics is an

important tool to control and optimize the pulping pro-

cess, we present in this paper the kinetics of the kraft

pulping of Cynara stalks and determined the reaction

rate constants and activation energies for the different

delignification phases, in whole and depithed mate-

rial. The influence of other process parameters (par-ticle size, impregnation and alkali charge) was also

tested.

2. Materials and methods

Thematerial used in this study wascollected from one

trial of C. cardunculus established in the experimental

fieldsof Instituto Superior de Agronomia (Lisbon, Portu-

gal) and harvested in September, at the end of the annual

rotation cycle. The leaves and the capitula were removed

and only the stalks were used. At the time of harvest, the

moisture content of the stalks was 14%. The samplesincluded the whole stalks and depithed stalks obtained

by the manual separation of the pith with the help of

knives. The chemical composition of the raw-material

was: 14.6% total extractives (extracted with a sequence

of dichloromethane, ethanol and water), 17.0% lignin

(Klason and acid soluble lignin) and 53.0% polysaccha-

rides for the whole stalks, and 13.8, 13.6 and 54.7%,

respectively, for the depithed stalks (Gominho et al.,

2001).

The kraft pulping of Cynara stalks was made in

micro-pulpers using 10 g of raw-material (o.d.) in 10 mL

stainless steel autoclaves in a thermostated rotating oil

bath. Temperatures of 150, 160 and 170 ◦C were used

under the following pulping conditions: ratio liquor,

biomass 7:1; total alkali, 20% (as Na2O); and sulfid-

ity, 30%. The reaction time at temperature varied from

5 to 120 min. After reaction the reactors were cooled

in an ice bath. The resulting pulp (or remaining solids)were thoroughly washed with water, the suspension was

suction filtered and the solids air-dried over night at

room temperature,followedby 48 h at 70 ◦C. Yieldswere

determined based on the oven-dry mass of chips charged

to the reactor.

For kinetic modelling, the rate of mass loss in each

pulping phase was described mathematically by a first-

order reaction with respect to the remaining solids in the

lignocellulose matrix, calculated as:

M M 0

=

i=3i=1

ai exp(−kit )

where M / M 0 is the fraction of the material remaining

in the residue, M 0 the initial material, ai (experimental

values) the fraction of the material susceptible to solu-

bilization by the process and k i is the corresponding rate

constant, with i representing the reaction phase (i = 1, 2,

3). The values of ai were calculated from the M / M 0 val-

ues for the beginning and the end of the corresponding i

phase. Therefore, a plot of residual solidsas ln M / M 0 ver-

sus time gives a straight line with the slope representing

the value of k i (min−1).

The experimental activation energy of the pulping

reaction was determined using the Arrhenius equation:

ki = (A)exp

−

Eai

RT

where k i is the rate constant for phase i, A the Arrhe-

nius constant, E ai the activation energy (kJ mol−1), R

the gas constant (8.314 kJ K−1 mol−1) and T is the abso-

lute temperature (K). A plot of ln(k i) versus 1/T should

be a straight line with the slope equal to E ai / R.

Pulping using 100 mL digesters was used for experi-ments to study the effect of total alkali (18, 20 and 22%

as Na2O), chip dimension (large, 2 cm× 2 cm; medium,

1 cm× 1 cm; small, 0.5 cm× 0.5 cm) and impregnation

(with overnight impregnation with the liquor and with-

out impregnation). Total yields, residual lignin (Klason

lignin and acid soluble lignin) were determined for dif-

ferent reaction times (30, 60, 90 and 120 min) according

to TAPPI standard methods.

The average fibre length in chips of different dimen-

sions was determined by measuring 500 fibres for each

sample in a semi-automated system (Leitz-ASM 68 K),



162 J. Gominho, H. Pereira / Industrial Crops and Products 24 (2006) 160–165

Fig. 1. Mass fraction of material remaining during pulping of Cynara

cardunculus L. whole stalks and depithed stalks at 160 ◦C.

after cell dissociation with acetic acid: 20% hydrogen

peroxide 1:1 at 60 ◦C during 48 h.

3. Results and discussion

The kraft pulping of C. cardunculus stalks showed a

time dependent mass loss rate, where three phases could

be distinguished: initial, bulk and residual (Fig. 1). At

160 ◦C, the initial phase corresponded to a quick and

substantial mass loss of approximately 25% in the first

5 min of reaction; in the bulk phase, further 15% mass

loss occured at a slower rate until 45 min; in the final

phase, there was a very slow mass loss when further 5%of the material was removed after 120 min total pulping

time.

Gonzalo et al. (1998) also reported three phases for

the pulping of wheat straw by the kraft and soda pro-

cesses and De Groot et al. (1994, 1995) f or the alkaline

delignification of hemp. For wood, a similar behaviour

was referred by Oliet et al. (2000) f or the organosolv

delignification and Santos et al. (1997) f or the kraft pulp-

ing of Eucalyptus globulus and by Labidi and Pla (1992)

for the kraft, soda and soda-AQ of Populus trichocarpa.

In some cases only two successive pulping phases were

recorded as in the kraft and ASAM pulping of Eucalyp-tus globulus wood (Miranda and Pereira, 2002).

The pulping of whole stalks and of depithed stalks

showed a similar behaviour (Fig. 1). The mass loss in the

first phase was coincident, and the bulk phase showed

only a slightly lower mass loss rate for the depithed

stalks. After 120 min, the pulping yield was 54% for the

whole stalks and 57% for the depithed stalks.

The lower yield obtained with the whole stalks should

result from the effect of pith. Pith differs significantly in

anatomy from the rest of the surrounding tissues; it has

only small isodiametric parenchyma cells (Gominho et


cardunculus L. whole stalks at 150, 160 and 170 ◦C.

al., 2001) which will be washed out to a large extent

in the process of pulp washing. In the Cynara plant the

mass proportion of pith in relation to the total stalk cross

section is approximately 10% and pith shows some dif-

ferences in chemical composition (higher lignin and less

polysaccharides) in relation to whole stalks (Gominho

et al., 2001).

The effect of temperature on pulping kinetics is shown

in Fig.2 f or whole stalks and in Fig. 3 f or depithed stalks.

The pulping curves have a similar shape for the tested

temperatures, and in all cases the three reaction phases

were present. At the highest temperature tested (170 ◦C)

the mass loss was larger, even if the difference in relation

to the 160 ◦C pulping was small at the end of the process,e.g. 52 and 54% yield, respectively, for 170 and 160 ◦C

after 120 min pulping of whole stalks. The mass loss

occurring at 150 ◦C was always smaller and at the end,

the yield was clearly higher (60% in comparison to 54%

at 160 ◦C) for whole stalks pulping.

In relation to the fraction of the initial material

that was solubilized into the pulping liquor, the results

showed that it was higher in the initial pulping phase and


cardunculus L. depithed stalks at 150, 160 and 170◦

C.




Table 1

Rate constants and activation energies for the kraft pulping of the Cynara cardunculus whole stalks and depithed stalks, considering three reaction

phases: initial, bulk and residual

Phase Rate constant, k (min−1) Activation energy (kJ mol−1)

150 ◦C 160 ◦C 170 ◦C

Whole stalksInitial 25.3× 10−3 53.3× 10−3 64.8×10−3 74

Bulk 4.7× 10−3 5.9× 10−3 7.5×10−3 45

Residual 1.1× 10−3 1.3× 10−3 1.5×10−3 24

Depithed stalks

Initial 30.5× 10−3 49.0× 10−3 54.7×10−3 46

Bulk 4.3× 10−3 4.5× 10−3 6.5×10−3 32

Residual 1.1× 10−3 1.2× 10−3 0.7×10−3 13

lowest in the residual phase, and rather independent of

pulping temperature. For the pulping of whole stalks the

fraction was, respectively, at 150, 160 and 170◦

C: in theinitial phase, 0.22, 0.23 and 0.28; in the bulk phase; 0.14,

0.17 and 0.12; in the residual phase, 0.06, 0.04 and 0.08.

For the pulping of depithed stalks the fraction of the ini-

tial material that was solubilized in the different phases

was similar: 0.14, 0.22 and 0.24 for the initial phase,

0.20, 0.17 and 0.22 for the bulk phase and 0.04, 0.04

and 0.02 for the residual phase at 150, 160 and 170 ◦C,

respectively.

The different phases in pulping correspond to the

selective reaction of the lignocellulosic structural com-

ponents. During the initial phase in alkaline deligni-

fication hemicelluloses are deacetylated and dissolved

and a small quantity of lignin is removed mainly corre-

sponding to cleavage of phenolic -O-4-linkages and of

some -O-4-phenolic linkages; in the bulk phase occurs

the cleavage of non-phenolic -O-4-linkages and in the

residual phase the cleavage of carbon–carbon bonds in

lignin and-degradation (Gierer, 1970, 1985; Gierer and

Noren, 1980; Gellerstedt and Lindfors, 1984).

In the case of Cynara pulping, a considerable mass

loss occurred very quickly in the initial phase and should

be related to the material chemical composition, namely

the high content of polar extractives and hemicellu-loses (12.9% polar extractives and 15.1% pentosans)

(Gominho et al., 2001). Therefore, most of the initial

mass loss should correspond to the solubilization of

extractives and hemicelluloses and this explains why the

highest mass loss did not occur in the bulk delignification

phase, as it is usual with wood pulping.

A first-order reaction could be applied to the pulp-

ing, allowing the calculation of rate constants from the

ln M / M 0 plots. Table 1 shows the obtained rate con-

stants from the three successive pulping phases. The

mass loss rate constant in the initial phase was approx-

imately 10 times the rate constant in the bulk phase

(5.3× 10−2 min−1 versus 5.9× 10−3 min−1 at 160 ◦C),

while the residual phase was approximately four-timesslower than the bulk phase (1.3× 10−3 min−1 versus

5.9× 10−3 min−1 at 160 ◦C). No significant differ-

ences were obtained between whole stalks and depithed

stalks, therefore supporting the idea that the lower yield

obtained with whole stalks resulted from the loss of pith

cells in the pulp washing phase.

As regards the activation energies (Table 1), higher

values were found for the initial pulping phase, decreas-

ing successively until very low values for the final

pulping period (i.e. 74, 45 and 24 kJ mol−1 for whole

stalks pulping). The effect of temperature was therefore

diminute regarding the final mass loss rate. The activa-

tion energy values for the pulping of depithed stalks were

lower than for the whole stalks.

The values obtained for the activation energy of

Cynara pulping were lower than the reported 93 and

131 kJ mol−1for straw (Laith et al., 1995; Gonzalo et al.,

1998), 110 kJ mol−1 for hemp (Laith et al., 1995) and

for wood, i.e. 129 kJ mol−1 for western hemlock (Dolk

et al., 1989) and 143 kJ mol−1 for poplar (Labidi and

Pla, 1992). However, a kinetic study on the delignifica-

tionand polysaccharide solubilizationduring organosolv

pulping of giant reed ( Arundo donax ) indicated simi-lar values of 74 and 64 kJ mol−1 for xylan and lignin

loss (Shatalov and Pereira, 2005). The removal of lignin

during the kraft pulping of eucalypt wood also showed

similar activation energies (87.3 and 74.6 kJ mol−1 for

two successive phases) (Miranda and Pereira, 2002).

The low values obtained for the activation energy of Cynara indicates a strong effect of diffusion processes,

to which largely contribute the presence of parenchyma

cells in the material. It should be noted that the Cynara

stalks contain parenchyma cells not only in the inner

circular pith (which is removed when the material is



164 J. Gominho, H. Pereira / Industrial Crops and Products 24 (2006) 160–165

Table 2

Yields (percent of o.d. raw-material) and residual lignin (percent of pulp) for the kraft pulping of Cynara cardunculus whole stalks with different

total alkali reaction charges (18, 20 and 22% as Na 2O)

Time (h) 18% 20% 22%

Total yield

(%)

Klason

lignin (%)

Soluble

lignin (%)

Total yield

(%)

Klason

lignin (%)

Soluble

lignin (%)

Total yield

(%)

Klason

lignin (%)

Soluble

lignin (%)

0.5 49.6 2.9 1.9 47.2 2.8 1.9 46.3 1.5 1.9

1 47.8 2.9 1.8 47.7 2.5 1.9 46.7 1.6 1.8

1.5 46.8 1.7 2.1 45.2 1.2 1.9 43.1 1.7 1.9

2 46.7 1.9 2.1 45.9 1.6 2.1 44.4 1.6 1.9

Table 3

The influence of chip dimensions in pulping yields and residual lignin

for depithed stalks of Cynara cardunculus L. pulping at 170 ◦C, 2 h

and total alkali 20%

Chips dimensions Pulping

yield (%)

Klason

lignin (%)

Soluble

lignin (%)

With impregnation (24 h)

Large 46.8 1.4 1.7

Medium 45.7 1.7 1.6

Small 46.2 1.2 1.5

Without impregnation

Large 47.0 3.6 1.9

Medium 45.6 2.5 1.9

Small 45.7 1.3 1.9

depithed) but also as a matrix where the fibro-vascular

bundles are embedded (Gominho et al., 2001; Quilh´o etal.,2004). Therefore, the effect of parenchyma occurs not

only in the whole stalks but also in the depithed stalks.

The influence of alkali charge on yield and delignifi-

cation degree is shown in Table 2. The increase of alkali

concentration shortens the pulping time fora given delig-

nification, e.g. 46.3 with 3.4% residual total lignin were

obtained with only 0.5 h pulping times with 22% alkali,

while 1.5 h were neededfor 46.8% yield with 3.8% resid-

ual lignin with 18% alkali.

Table 3 shows yields and delignification degrees for

pulpings carried out with chips with different dimen-

sions, and with and without a pre-impregnation withthe pulping liquor. When the chips were previously

soaked in the liquor, yield and delignification were sim-

ilar for all chips dimensions. Without pre-impregnation,

an effect of chip dimension could be observed with a

small decrease of delignification for the larger chips

showing the importance of liquor diffusion within the

solid matrix: residual lignin was 5.5, 4.4 and 3.2%,

respectively, for the large, medium and smaller chips.

The delignification in the small chips was the same with

and without impregnations, as a result of their higher

external surface.

It should be noted that reduction of chip dimension

negatively impacts on the pulp quality parameters that

are influenced by fibre length. In fact, the average fibre

length of thechips used here decreased from 2.03, 1.91 to

1.78 mm, respectively, in large, medium and small chips.

The results obtained confirmed that pulping of theannual plant C. cardunculus resembles hardwood pulp-

ing in relation to overall reaction duration and chemical

charge, however with a much faster initial phase with a

substantial mass loss. Specificities of this raw-material

include the heterogeneous anatomy with the presence of

parenchyma cells, namely in thepith. In addition to being

cells with no paper value, due to their small dimensions

and isodiametric shape (Quilhoetal.,2004), parenchyma

cells decrease delignification and pulp yield and increase

diffusion resistance. Removal of pith should therefore be

included in the pre-pulping raw-material preparation.

Also the overall low activation energies that wereobtained for all phases of the pulping, and especially for

the final stage, point out to the importance of improving

diffusion in and out of the solid lignocellulosic matrix.

4. Conclusions

The pulping of whole stalksof C. cardunculus yielded

over 46% pulp with a low residual Klason lignin content.

Mass loss rates in Cynara kraft pulping were strongly

time dependent, with a very fast solubilization in the ini-

tial period, anda very slow final pulping phase. Diffusionprocesses playedan importantrole in the Cynara pulping

and temperature had only a moderate effect in increasing

reaction rates. The presence of pith was related to lower

yields and a higher diffusion resistance and depithing of

stalks should be included as a raw-material preparation

before pulping.

Acknowledgements

Financial support was given to the first author by a

scholarship from “Fundacao para a Ciencia e Tecnolo-




gia” (Portugal). The work was supported by the research

projects AIR3-CT93-1089 (EU, DGVI, programme

AIR) and PRAXIS XXI 3/3.2/Papel 2311/95 (Fundacao

para a Ciencia e Tecnologia, Portugal).

References

Antunes, A., Amaral, M., Belgacem, N., 2000. Cynara cardunculus L.

Chemical composition and soda-antraquinone cooking. Ind. Crop

Prod. 12 (2), 85–91.

Biermann,C., 1993.Essentialsof Pulping and Papermaking. Academic

Press, New York.

Dalianis, C., Panoutsou, C., Dercas, N.,1996. Spanish thistle artichoke,

Cynara cardunculus L. under Greek conditions. In: Proceedings of

theNineth European Conference, Biomass for Energy, Industry and

Environment. Elsevier Applied Science, London, pp. 663–668.

De Groot, B., van Dam, J.E.G., Riet, K., 1995. Alkaline pulping of

hemp woody core: kinetic modelling of lignin, xylan and cellulose

extraction and degradation. Holzforschung 49, 332–342.

De Groot, B., van Dam, J.E.G., van der Zwan, R.P., Riet, K., 1994.Simplified kinetic modelling of alkaline delignification of hemp

woody core. Holzforschung 48, 207–214.

Dolk, M., Yan, J.F., McCarty, J.L., 1989. Lignin 25. Kinetics of west-

ern hemlock in flow-through reactors under alkaline conditions.

Holzforschung 43 (2), 91–98.

Fernandez,J., 1992. Production and utilisation of Cynara Cardunculus

L. biomass for energy, paper–pulp and food industry. In: Proceed-

ings of the Sixth European Conference on Biomass for Energy

Industry and Environment. Elsevier Applied Science, London, pp.

312–316.

Fernandez, J., Manzanares, P., 1990. Cynara cardunculus L., a new

crop for oil, paper–pulp and energy. In: Proceedings of the Fifth

European Conference on Biomass for Energy and Industry. Else-

vier Applied Science, London, pp. 1184–1189.Gellerstedt, G., Lindfors, E.L., 1984. Structural changes in lignin dur-

ing kraft pulping. Holzforschung 38 (3), 151–158.

Gierer, J., 1970. The reactions of lignin during pulping. A description

and comparison of conventional pulping process. Sven. Papper-

stidn. 73 (18), 571–596.

Gierer, J., 1985. Chemistry of delignification. Part I. General concept

and reactions during pulping. Wood Sci. Technol. 19 (4), 289–312.

Gierer, J., Noren, I.,1980. On the course of delignification during kraft

pulping. Holzforschung 34 (6), 197–200.

Gominho, J., Fernandez, J., Pereira, H., 2001. Cynara cardunculus

L.—a new fibre crop for pulp and paper production. Ind. Crop

Prod. 13, 1–10.

Gominho, J., Pereira, H., 2000. An overview of the research on pulp-

ing aptitude of Cynara cardunculus L. In: Kyritsis, S., Beenackers,

A.A.C.M., Helm, P., Grassi, A., Chiaramonti, D. (Eds.), Proceed-

ings of First World Conference and Exhibition on Biomass for

Energy and Industry, vol. 2. Science Publishers Ltd., UK, pp.1187–1190.

Gonzalo, E.I., Lindgren, C.T., Lindstrom, M.E., 1998. Kinetics of

wheat straw delignification in soda and kraft pulping. J. Wood

Chem. Technol. 18 (1), 69–82.

Grace, T.M.,Malcolm,E.W., 1989.Pulp and Paper Manufacture. Alka-

line Pulping, vol. 5., third ed. TAPPI and CPPA, Atlanta.

Labidi, A.,Pla, F., 1992. Delignification en milieu alcalin de bois feuil-

lus a l’aided’unreacteur alitfixeet a faible temps de passage. Partie

II. Developpemeents cinetiques. Holzforschung 46 (2), 155–161.

Laith, A.K., Attila, R., Polyanszky, E., Istvan, R., 1995. Kinetics of

delignification in kraft pulping of wheat straw and hemp. Tappi J.

78 (8), 161–164.

MacLeod, M., 1988. Nonwood fiber: number 2, and trying harder.

Tappi J. 74 (6), 50–54.

Miranda, I., Pereira, H., 2002. Kinetics of ASAM and kraft pulping of

eucalyptwood ( Eucalypus globulus). Holzforschung 56 (1), 85–90.

Oliet, M., Francisco, R., Aurora, S., Miguel, A.G., Tijero, J., 2000.

Organosolv delignification of Eucalyptus globules. Kinetic study

of autocatalyzed ethanol pulping. Ind. Eng. Chem. Res. 39, 34–39.

Quilho, T., Gominho, J.,Pereira,H., 2004.Anatomical characterisation

of a new fibre crop: the thistle Cynara cardunculus L. Iawa J. 25

(2), 217–230.

Sadawarte, S., 1995. Better technology needed to clean up nonwood

fiber. Pulp Paper Int. 37 (6), 84–95.

Santos, A., Francisco, R., Miguel, A.G., Daniel, M., Felix, G., 1997.

Kinetic modelling of kraft delignification of Eucalyptus globulus.

Eng. Chem. Res. 36, 4114–4120.Shatalov, A.A., Pereira, H., 2005. Kinetics of polysaccharide degra-

dation during ethanol–alkali delignification of giant reed. Part 1.

Cellulose and xylan. Carbohydr. Polym. 59 (4), 435–442.

van Dam, J., Vilsteren, G., Zomers, F., Shannom, W., Hamilton, I.,

1994. Industrial Fibre Crops, ATO-DLO, Wageningen.

Villar, J., Poveda, P., Tagle, L., 1999. Obtencion de pastas al sulfato a

partir del cardo (Cynara cardunculus L.). Influencia del troceado

sobre la calidad de las pastas. Invest. Agric. Sist. Recur. For. 8 (2),

305–317.

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(2006) Influence of Raw