Lipophilic extractives from several nonwoody lignocellulosic crops (flax, hemp, sisal, abaca) and their fate during alkaline pulping and TCF/ECF bleaching.

Abstract

The fate of lipophilic extractives from several nonwoody species (flax, hemp, sisal and abaca) used for the manufacturing of cellulose pulps, was studied during soda/anthraquinone (AQ) pulping and totally chorine free (TCF) and elemental chlorine free (ECF) bleaching. With this purpose, the lipophilic extracts from the raw materials and their unbleached and bleached industrial pulps, were analyzed by gas chromatography-mass spectrometry. Aldehydes, hydroxyfatty acids and esterified compounds such as ester waxes, sterol esters and alkylferulates strongly decreased after soda/AQ pulping while alkanes, alcohols, free sterols and sterol glycosides survived the cooking process. Among the lipophilic extractives that remained in the unbleached pulps, some amounts of free sterols were still present in the TCF pulps whereas they were practically absent in the ECF pulps. Sterol glycosides were also removed after both TCF and ECF bleaching. By contrast, saturated fatty acids, fatty alcohols and alkanes were still present in both bleached pulps.

Full text

Page 1

Lipophilic extractives from several nonwoody lignocellulosic crops (flax, hemp,
sisal, abaca) and their fate during alkaline pulping and TCF/ECF bleaching
Gisela Marques, José C. del Río, Ana Gutiérrez*
Instituto de Recursos Naturales y Agrobiología, CSIC, P.O. Box 1052, E-41080 Seville, Spain
a r t i c l e i n f o
Article history:
Received 20 May 2009
Received in revised form 6 August 2009
Accepted 7 August 2009
Available online 3 September 2009
Keywords:
Pitch
Lipophilic extractives
Paper pulp
Nonwoody fibers
a b s t r a c t
The fate of lipophilic extractives from several nonwoody species (flax, hemp, sisal and abaca) used for the
manufacturing of cellulose pulps, was studied during soda/anthraquinone (AQ) pulping and totally cho-
rine free (TCF) and elemental chlorine free (ECF) bleaching. With this purpose, the lipophilic extracts from
the raw materials and their unbleached and bleached industrial pulps, were analyzed by gas chromatog-
raphy–mass spectrometry. Aldehydes, hydroxyfatty acids and esterified compounds such as ester waxes,
sterol esters and alkylferulates strongly decreased after soda/AQ pulping while alkanes, alcohols, free
sterols and sterol glycosides survived the cooking process. Among the lipophilic extractives that
remained in the unbleached pulps, some amounts of free sterols were still present in the TCF pulps
whereas they were practically absent in the ECF pulps. Sterol glycosides were also removed after both
TCF and ECF bleaching. By contrast, saturated fatty acids, fatty alcohols and alkanes were still present
in both bleached pulps.
? 2009 Elsevier Ltd. All rights reserved.
1. Introduction
Lipophilic extractives, i.e., the non-polar extractable fraction
from wood and other lignocellulosic crops, include different classes
of compounds, such as alkanes, fatty alcohols, fatty acids, free and
conjugated sterols, terpenoids, triglycerides and waxes. These lipo-
philic compounds, even when present in low amounts in the raw
material, may play an important role in industrial wood processing
for bleached pulp and paper production since they are at the origin
of the so-called pitch deposits along the pulp and paper manufac-
turing processes. Pitch deposition is a serious problem in the pulp
and paper industry since it is responsible for reduced production
levels, higher equipment maintenance costs, higher operating
costs, and an increased incidence of defects in the finished prod-
ucts, which reduces quality and benefits (Back and Allen, 2000).
The nature and severity of pitch deposition depend not only on
the raw materials used (and hence on the nature of the lipophilic
compounds), but also on the industrial processes of pulping and
bleaching applied at the mill. In the manufacture of alkaline pulps,
a large part of the lipids originally present in the raw material is
removed during the cooking and bleaching stages. However, some
chemical species survive these processes and are found as pulp
extractives (Bergelin and Holmbom, 2003; Freire et al., 2005,
2006; Gutiérrez et al., 2001a), suspended in process waters
(Gutiérrez et al., 2001b) or forming the so-called pitch deposits
in circuits, equipments and final product (Bergelin et al., 2005;
del Río et al., 1998, 2000; Gutiérrez and del Río, 2005; Silvestre
et al., 1999). Growing pressure for closing water loops in pulp
and paper mills leads to increasing build up of lipophilic com-
pounds in the processes and therefore, to an increasing number
of severe and costly pitch related problems.
The different classes of lipids havedifferent behavior during pul-
ping and bleaching. Several studies have provided information on
the behavior of wood lipids, such as fatty and resin acids, triglycer-
idesandsterolsandtriterpenolsduringpulpingandbleaching(Back
and Allen, 2000; Bergelin and Holmbom, 2003, 2008; Freire et al.,
2005, 2006; Gutiérrez et al., 2001a; Shin and Kim, 2006). However,
thechemistryoflipidsfromnonwoodypulpsinpulpingandbleach-
ing has not been examined much so far (Gutiérrez et al., 2004; Gut-
iérrez and del Río, 2003a,b). Likewise, to the best of our knowledge,
there is very little information available dealing with pitch prob-
lems on nonwoody pulps (Gutiérrez and del Río, 2005). In this con-
text, the aim of this work was to identify the specific lipophilic
constituents of different nonwoody fibers, which are used for the
manufacturing of cellulose pulps for specialty papers, and to study
their behavior during soda/anthraquinone (AQ) pulping and totally
chorine free (TCF) and elemental chlorine free (ECF) bleaching. For
this, a series of pulps (crude pulps taken after soda/AQ pulping
and bleached pulps taken after TCF and ECF bleaching) from differ-
entnonwoodyrawmaterials(flax,hemp,sisal,abaca)wereselected
for this study. The composition of the lipophilic compounds in the
fibers and their respective pulps was analyzed by gas chromatogra-
phy (GC) and gas chromatography–mass spectrometry (GC–MS)
0960-8524/$ - see front matter ? 2009 Elsevier Ltd. All rights reserved.
doi:10.1016/j.biortech.2009.08.036
* Corresponding author. Tel.: +34 95 462 4711; fax: +34 95 462 4002.
E-mail address: anagu@irnase.csic.es (A. Gutiérrez).
Bioresource Technology 101 (2010) 260–267
Contents lists available at ScienceDirect
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journal homepage: www.elsevier.com/locate/biortech

Page 2

using short- and medium-length high temperature capillary col-
umns, respectively, with thin films, which enables the elution and
analysis of intact high molecular weight lipids such as waxes or ste-
rol glycosides (Gutiérrez et al., 1998; Gutiérrez and del Río, 2001).
The knowledge of the behavior of lipophilic extractives during pul-
ping and bleaching is an important step towards understanding and
predicting the pitch problems and designing effective solutions for
its control.
2. Methods
2.1. Samples
Two bast fibers, flax (Linum usitatissimum) and hemp (Cannabis
sativa), and two leaf fibers, sisal (Agave sisalana) and abaca (Musa
textilis), were selected for this study. The raw materials and their
respective crude (unbleached) pulps (pulps taken after soda/AQ
pulping), as well as pulp samples after TCF and ECF bleaching, were
supplied by CELESA pulp mill (Tortosa, Spain). General conditions
of soda/AQ pulping included the use of sodium hydroxide and
anthraquinone (up to 0.05%) as cooking chemicals, and 2–4 h of
cooking time at a temperature of about 160–170 ?C. The TCF
bleaching sequence used (QPo) included a quelating stage (Q)
and a hydrogen peroxide stage under pressurized oxygen (Po).
The ECF bleaching sequence used (DPo) included a chlorine dioxide
stage (D) followed by a hydrogen peroxide stage under pressurized
oxygen (Po).
2.2. Lipid extraction
Raw materials and pulps were air-dried until constant weight
and the samples were Soxhlet-extracted with acetone for 8 h. All
the extracts were evaporated to dryness and redissolved in chloro-
form for chromatographic analysis of the lipophilic fraction as de-
scribed below.
2.3. GC and GC–MS analyses
The GC analyses of the lipids from the raw materials and pulps
were performed in an Agilent 6890N Network GC system using a
short fused-silica DB-5HT capillary column (5 m ? 0.25 mm inter-
nal diameter, 0.1 lm film thickness) from J&W Scientific, enabling
simultaneous elution of the different lipid classes (Gutiérrez et al.,
1998). The temperature program was started at 100 ?C with 1 min
hold, and then raised to 350 ?C at 15 ?C/min, and held for 3 min.
The injector and flame-ionization detector (FID) temperatures
were set at 300 and 350 ?C, respectively. Helium (5 ml/min) was
used as carrier gas, and the injection was performed in splitless
mode.
The GC–MS analyses were performed with a Varian 3800 chro-
matograph coupled to an ion-trap detector (Varian 4000) using a
medium-length (12 m) capillary column of the same characteris-
tics described above for GC/FID. The oven was heated from
120 ?C (1 min) to 380 ?C at 10 ?C/min, and held for 5 min. The
transfer line was kept at 300 ?C, the injector was programmed from
120 ?C (0.1 min) to 380 ?C at 200 ?C/min and held until the end of
the analysis, and helium was used as carrier gas at a rate of 2 ml/
min. The compounds were identified by mass fragmentography,
and by comparing their mass spectra with those of the Wiley
and NIST libraries and standards.
Both underivatized and derivatized samples were analyzed by
GC and GC–MS. Two derivatized samples, silylated samples and
methylated and silylated samples, were analyzed. The silylation
was performed using bis(trimethylsilyl)trifluoroacetamide (BSTFA)
in the presence of pyridine at 80 ?C for 90 min (Gutiérrez and del
Río, 2001). Trimethylsilyl-diazomethane methylation, in the pres-
ence of methanol (at room temperature for 10 min) followed by
BSTFA silylation, in the presence of pyridine, were also performed.
Fatty alcohols, fatty acids and sterol glycosides were determined as
silylated derivatives in the derivatized samples. Hydroxyfatty acids
were determined in the samples after methylation followed by
silylation. The rest of compounds were determined in the underiv-
atized samples. Peaks were quantified by area and a mixture of
standards (octadecane, palmitic acid, sitosterol, cholesteryl oleate,
and sitosteryl 3b-D-glucopyranoside) with a concentration range
between 0.1 and 1 mg/ml was used to elaborate calibration curves.
The data from two replicates were averaged.
3. Results and discussion
The lipid content of the nonwoody fibers used in this study and
their corresponding crude and TCF and ECF bleached pulps is
shown in Table 1. Flax fibers have the highest content on lipophilic
extractives followed by hemp, sisal and abaca fibers. Regardless the
higher lipid content of flax fibers, the content of lipophilic extrac-
tives of its crude pulp was similar or even lower than in the other
fibers. On the other hand, the lipid content of the pulps decreased
further after TCF or ECF bleaching, ranging from 0.03% to 0.18%. The
differences observed in the lipid content among the different crude
and bleached pulps of the nonwoody fibers is related to the behav-
ior of lipophilic extractives present in the raw materials in alkaline
pulping and to their reactivity towards the bleaching agents used
as described below.
3.1. Composition of lipophilic extractives in the nonwoody fibers
selected for this study
With the aim of studying the fate of the different lipophilic
extractives during soda/AQ pulping, the lipid extracts from the dif-
ferent nonwoody fibers selected for this study were analyzed by
GC and GC–MS and then compared with those in the crude pulps.
The composition of the lipophilic extractives of the selected raw
materials is listed in Table 2 and the chemical structures of the
main compounds identified are represented in Fig. 1.
The main lipid classes present in the nonwoody fibers selected
for this study were series of alkanes (I), fatty alcohols (II), alde-
hydes (III), fatty acids (IV), steroids, including free (V) and conju-
gated sterols (VI–VII), triterpenoids (VIII) and ester waxes (IX).
The detailed composition of the lipophilic compounds present in
these fibers have been previously addressed (del Río et al., 2004;
del Río and Gutiérrez, 2006; Gutiérrez et al., 2006b, 2008; Gut-
iérrez and del Río, 2003a,b).
In the case of flax bast fibers the predominant lipophilic com-
pounds present were series of fatty acids and aldehydes, account-
ing for 34% and 23% of total extract, respectively, followed by ester
waxes (18%), and fatty alcohols (13%). Fatty acids were also the
predominant compounds (27% of total extract) in hemp bast fibers,
followed by alkanes (15%), free sterols (12%) and steroid hydrocar-
bons (12%). Among the selected leaf fibers, free sterols predomi-
nated in both sisal (20%) and abaca (45%), followed by alkanes
Table 1
Lipophilic extractives content (%) in the selected nonwoody raw materials and pulps.
Flax HempSisal Abaca
Fiber
Crude pulp
TCF pulp
ECF pulp
1.70
0.21
0.05
0.13
0.88
0.26
0.18
0.18
0.68
0.30
0.09
0.14
0.51
0.20
0.04
0.03
G. Marques et al./Bioresource Technology 101 (2010) 260–267
261

Page 3

Table 2
Composition of lipophilic extractives (mg/100 g) in nonwoody raw materials (M) and crude (C), TCF (T) and ECF (E) pulps.
CompoundFlaxHempSisalAbaca
MCTEMCTEMCTEMCTE
Fatty acids
n-Hexadecanoic acid
9,12-Octadecadienoic acid
9-Octadecenoic acid
n-Octadecanoic acid
n-Nonadecanoic acid
n-Eicosanoic acid
n-Heneicosanoic acid
n-Docosanoic acid
n-Tricosanoic acid
n-Tetracosanoic acid
n-Pentacosanoic acid
n-Hexacosanoic acid
n-Octacosanoic acid
552
121
1
235
52
tr
20
4
36
16
40
8
19
–
96
27
tr
39
22
3
2
tr
2
tr
1
tr
–
–
29
4
–
2
8
tr
4
tr
4
tr
4
tr
3
–
39
18
–
1
12
tr
4
tr
2
tr
2
tr
tr
–
78
34
3
15
6
tr
4
tr
5
2
4
2
3
–
60
15
1
1
10
5
6
1
7
3
7
1
3
–
12
4
1
tr
3
1
<1
1
1
1
<1
<1
tr
tr
80
29
–
1
20
tr
6
1
8
4
6
1
1
3
9
4
–
–
<1
–
tr
–
tr
1
1
<1
1
2
50
24
–
–
6
–
1
–
tr
tr
1
2
10
17
10
8
–
–
7
–
<1
–
1
<1
1
tr
1
tr
42
27
–
–
16
–
2
–
2
1
3
–
2
tr
9
4
1
2
1
tr
<1
tr
<1
tr
1
tr
tr
–
57
20
3
6
21
–
2
–
tr
tr
3
–
2
–
19
9
–
–
11
tr
tr
–
tr
tr
<1
tr
–
–
28
10
–
–
16
tr
1
tr
tr
tr
1
tr
1
–
a-Hydroxyfatty acids
2-Hydroxydocosanoic acid
2-Hydroxytricosanoic acid
2-Hydroxytetracosanoic acid
2-Hydroxypentacosanoic acid
11
3
2
6
tr
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
9
–
–
5
4
tr
–
–
tr
–
–
–
–
–
–
–
–
–
–
–
7
1
1
4
1
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
1
–
–
1
tr
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
x-Hydroxyfatty acids
22-Hydroxydocosanoic acid
26-Hydroxyhexacosanoic acid
28-Hydroxyoctacosanoic acid
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
6
1
2
3
–
–
–
–
–
–
–
–
–
–
–
–
1
1
tr
–
–
–
–
–
–
–
–
–
–
–
–
–
Fatty alcohols
n-Docosanol
n-Tetracosanol
n-Hexacosanol
n-Octacosanol
n-Triacontanol
220
–
4
49
116
51
68
–
2
15
38
13
1
–
tr
<1
1
<1
52
–
–
11
29
12
2
–
<1
<1
1
1
44
4
3
8
21
8
13
1
1
2
6
3
59
4
4
12
28
11
8
–
–
2
5
1
74
5
6
20
35
8
18
2
1
5
9
1
51
3
5
14
25
4
tr
tr
tr
tr
tr
tr
6
2
1
1
2
<1
1
<1
<1
<1
<1
–
<1
<1
tr
tr
tr
–
Alkanes
n-Heneicosane
n-Docosane
n-Tricosane
n-Tetracosane
n-Pentacosane
n-Hexacosane
n-Heptacosane
n-Nonacosane
n-Hentriacontane
27
–
–
–
–
2
–
5
20
–
22
–
–
–
–
2
–
3
17
–
1
–
–
–
–
<1
–
<1
<1
–
3
–
–
–
–
tr
–
1
2
–
43
–
–
–
–
<1
–
3
38
2
44
–
–
–
–
1
–
5
31
7
14
–
–
–
–
–
–
1
12
1
23
–
–
–
–
–
–
2
19
2
15
2
1
2
1
5
1
3
<1
–
18
–
–
–
tr
5
tr
3
10
tr
4
–
–
<1
–
2
tr
1
1
tr
22
–
–
1
tr
5
tr
4
12
tr
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
Aldehydes
n-Hexacosanal
n-Octacosanal
n-Triacontanal
371
58
174
139
3
tr
3
tr
<1
tr
<1
tr
8
1
5
2
25
3
9
13
<1
–
<1
tr
tr
–
tr
–
6
1
3
2
1
tr
1
tr
tr
tr
tr
tr
tr
tr
1
1
2
–
2
4
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
Steroid hydrocarbons
Stigmasta-3,5,22-triene
Stigmasta-3,5-diene
14
5
9
3
3
<1
1
1
tr
2
2
tr
30
12
18
5
4
1
1
1
<1
1
1
tr
14
10
4
11
11
tr
1
1
–
3
3
–
3
2
1
4
3
1
1
1
<1
<1
<1
tr
Steroid ketones
Cycloartenone
b-Amirenone
Stigmasta-3,5-dien-7-one
Stigmast-4-en-3-one
Stigmastadienone isomer
Friedelan-3-one
Ergostane-3,6-dione
Stigmastane-3,6-dione
33
–
–
5
9
3
–
6
10
6
–
–
3
1
1
–
tr
1
<1
–
–
<1
tr
–
–
–
–
tr
–
–
tr
–
–
–
–
–
27
–
tr
3
5
2
15
–
2
6
–
1
1
–
<1
4
–
–
3
–
tr
1
–
<1
2
–
–
9
–
–
<1
–
2
7
–
–
3
–
–
2
1
<1
–
–
<1
5
–
–
3
1
tr
–
–
1
1
–
–
1
tr
<1
–
–
tr
7
–
–
5
tr
2
–
–
–
4
2
–
1
1
<1
–
–
–
6
1
–
3
1
1
–
–
–
5
<1
–
3
1
1
–
–
–
1
–
–
1
<1
tr
–
–
–
Free sterols/triterpenols
Campesterol
Stigmasterol
Sitosterol
Stigmastanol
b-Amyrin
a-Amyrin
7-Oxositosterol
Hecogenin
92
27
23
36
6
–
–
–
–
33
8
5
17
3
–
–
–
–
3
1
<1
2
<1
–
–
–
–
–
–
–
–
–
–
–
–
–
36
3
3
18
2
9
1
–
–
78
9
9
37
6
15
2
–
–
15
2
2
7
1
3
<1
–
–
6
–
–
–
–
5
1
–
–
20
<1
3
11
1
1
tr
2
2
107
9
15
56
6
6
1
2
12
14
tr
2
8
1
tr
tr
1
2
14
–
2
8
1
tr
tr
tr
2
25
2
2
10
tr
–
–
11
–
20
3
3
11
1
–
–
2
–
5
1
1
3
<1
–
–
<1
–
<1
tr
<1
<1
<1
–
–
tr
–
Sterol glycosidesa
Campesterol 3b-D-Glcp
Stigmasterol 3b-D-Glcp
Sitosterol 3b-D-Glcp
5
tr
tr
5
8
2
1
5
1
<1
tr
1
tr
tr
tr
tr
13
2
1
10
16
3
2
11
<1
tr
tr
<1
tr
–
–
tr
2
tr
<1
2
25
6
3
16
2
<1
<1
2
1
tr
tr
1
2
<1
tr
2
8
3
1
4
<1
<1
tr
<1
tr
tr
tr
tr
Sterol/triterpenol esters6–––7–––<1–––1–––
262
G. Marques et al./Bioresource Technology 101 (2010) 260–267

Page 4

(14%) and fatty acids (10%) in sisal, and by fatty acids (16%) in aba-
ca fibers.
These lipophilic compounds can be classified into two principal
groups, namely organic acids and neutral components. Organic
acids include fatty acids, and the neutrals include alkanes, alde-
hydes, fatty alcohols, and free sterols as well as esterified and con-
jugatedcompoundssuchas
alkylferulates and sterol glycosides. Organic acids and neutral
compounds, the latter including saponifiable and unsaponifiable
compounds, present different behavior during alkaline pulping,
as shown below.
ester waxes,sterol esters,
3.2. Fate of lipophilic extractives during soda/AQ pulping
The fate of the different lipophilic extractives during soda/AQ
pulping was studied by analyzing the respective crude pulps. This
is exemplified in Figs. 2 and 3 for the hemp bast fibers and the sisal
leaf fibers, respectively. The composition of main lipids present in
the crude pulps of the studied fibers is listed in Table 2. It can be
observed that the lipophilic compounds from the raw materials
are modified to a different extent during alkaline (soda/AQ) pul-
ping depending of their chemical nature. Fatty acids, which are
among the main lipophilic extractives predominating in all these
Table 2 (continued)
CompoundFlaxHempSisalAbaca
MCTEMCTEMCTEMCTE
b-Amyrin acetate
Sitosterol esters
–
6
–
–
–
–
–
–
6
1
–
–
–
–
–
–
–
<1
–
–
–
–
–
–
–
1
–
–
–
–
–
–
Ester waxesa
C40
C42
C44
C46
C48
C50
284
8
19
68
130
56
4
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
17
tr
4
5
4
2
2
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
<1
–
tr
<1
tr
<1
<1
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
Ferulates
t-Tetracosanil ferulate
t-Hexacosanil ferulate
t-Octacosanil ferulate
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
5
1
2
2
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
aAbbreviations: Glcp, glucopyranoside; C(n), n denotes the total carbon atom number; tr: traces.
OH
O
I II
III
IV
HO
V
O
O
VI
IX
O
O
VII
O
OH
O
OH
HO
CH2OH
OH
H
O
HO
VIII
Fig. 1. Chemical structures of compounds representing the main classes of lipophilic extractives found in lignocellulosic fibers: (I) pentacosane; (II) octacosanol; (III)
octacosanal; (IV) palmitic acid; (V) sitosterol; (VI) sitosteryl linoleate; (VII) sitosteryl 3b-D-glucopyranoside; (VIII) b-amyrin; and (IX) octacosyl hexadecanoate.
G. Marques et al./Bioresource Technology 101 (2010) 260–267
263

Page 5

fibers, were also present in significant amounts in the crude pulps.
The content of fatty acids decreased significantly after soda/AQ
pulping of flax fibers whereas an increase in fatty acids content
was produced after pulping of the other fibers, being especially evi-
dent in the case of sisal and abaca. In contrast, a-hydroxyfatty
acids present in all the fibers, and x-hydroxyfatty acids present
in sisal and abaca, were completely absent in crude pulps.
On the other hand, esterified compounds such as ester waxes,
sterols esters and ferulic acid esters, were completely hydrolyzed
during soda/AQ pulping. This is especially evident in the case of
flax fibers where ester waxes predominate. In contrast, other con-
jugated compounds, namely sterol glycosides, which are present in
all nonwoody fibers studied here, resisted the alkaline cooking
conditions and were present intact in the crude pulps, as already
reported in the pulping of woody (Gutiérrez and del Río, 2001;
Nilvebrant and Byström, 1995) and nonwoody plants (Gutiérrez
and del Río, 2003a,b; Gutiérrez et al., 2004). The importance of
the presence of sterol glycosides after alkaline pulping is due to
their high hydrophilic–lipophilic balance, high melting point and
very low solubility in water, alkali and the usual organic solvents
(Hillis and Sumimoto, 1989). Due to these properties, sterol glyco-
sides constitute a part of protecting layers that prevent the cooking
510 1520 25
AQ
Fa16
Fa18
5+6+7
4
3
Defoamer
11
1
Fa16
Fa18
AQ
1
7
Al30
11
TCF pulp
ECF pulp
Fa16
Fa18:1
+
Fa18:2
Fa18
1
2
5+6+7
4
3
11
12
W42
W44W46W48
SE
Hemp bast fibers
Ak27
+
Al24
AQ
Fa18
Fa16
1
5+6+7
4
3
11
Al30
Crude pulp
Ak29
+
Al26
9
+
10
8
Fa18:1
+
Fa18:2
Ak27
+
Al24
Ak29
+
Al26
Ak31
+
Al28
Ak27
+
Al24
Ak29
+
Al26
Ak31
+
Al28
Al30
Ak27
+
Al24
Al22
Ak29
+
Al26
Ak31
+
Al28
W50
Fig. 2. GC–MS chromatograms of underivatized lipophilic extractives from hemp fibers (raw material), and their crude, TCF and ECF pulps. Peak identification, 1: stigmasta-
3,5,22-triene; 2: stigmasta-3,5-diene; 3: campesterol; 4: stigmasterol; 5: sitosterol; 6: stigmastanol; 7: b-amyrin; 8: stigmasta-3,5-dien-7-one; 9: b-amyrin acetate; 10:
stigmast-4-en-3-one; 11: friedelan-3-one; 12: stigmastane-3,6-dione; AQ: anthraquinone; Fa(n): fatty acids; Ak(n): alkanes; Al(n): fatty alcohols; SE: sterol esters; W(n):
ester waxes; n denotes the total carbon atom number.
264
G. Marques et al./Bioresource Technology 101 (2010) 260–267

Page 6

and bleaching chemicals to reach the resin and thereby keep them
and other extractives in the pulp. Other neutral compounds, such
as aldehydes, which were present in significant amounts in flax
and hemp fibers, decreased largely during pulping and therefore
were practically absent in the crude pulps. The content of steroid
hydrocarbons and steroid ketones also decreased after soda/AQ
cooking. Finally, alkanes, fatty alcohols and free sterols and trite-
rpenols survived the alkaline conditions and therefore were the
main lipophilic constituents in crude pulps.
The behavior of the fatty acids in an aqueous environment is
quite different from that of the neutrals. At alkaline pH, the acids
dissociate and can dissolve in water to quite a high extent forming
fatty acid soaps that can form micelles. Fatty acid soaps are effec-
tive solubilizing agents facilitating the removal from pulp of spar-
ingly soluble neutral substances (Back, 2000). The ratio of
saponifiables-to-unsaponifiables has been suggested to be a better
index for predicting pitch problems than the total amount of lipids
(Back and Allen, 2000). In fact, the higher abundances of unsapon-
ifiable compounds with respect to the saponifiable ones is the
main cause for pitch problems during pulping of some woods, such
as aspen or eucalypt (Chen et al., 1995; del Río et al., 1998, 2000).
This fact can explain why the lipid content of crude flax pulps is
similar or even lower than the other pulps regardless flax fibers
had the highest extractive content. As mentioned above, fatty acids
5+6+7
4
3
Al28
1
2
Ak27
F24
Ak25
Ak23
Fa16
Ak21
8
Fe24
Fe26 Fe28
5+6+7
8
AQ
Fa16
Al28
1
4
3
Fa18
9
AQ
Fa18
Fa16
5+6
9
1
4
AQ
Fa18
Fa16
5+6
9
1
4
3
Defoamer
TCF pulp
ECF pulp
Sisal leaf fibers
Crude pulp
Ak29
+
Al26
Ak25
+
Al22
Ak25
+
Al22
Ak27
+
Al24
Ak29
+
Al26
Ak27
+
Al24
Ak29
+
Al26
Al28
Ak25
+
Al22
Ak27
+
Al24
Ak29
+
Al26
Al28
5 10 15 20 25
9
Al30
Al30
Al30
Fig. 3. GC–MS chromatograms of underivatized lipophilic extractives from sisal fibers (raw material), and their crude pulp, TCF and ECF pulps. Peak identification, 1:
stigmasta-3,5,22-triene; 2: stigmasta-3,5-diene; 3: campesterol; 4: stigmasterol; 5: sitosterol; 6: stigmastanol; 7: b-amyrin; 8: stigmasta-3,5-dien-7-one; 9: hecogenin; AQ:
anthraquinone; Fa(n): fatty acids; Ak(n): alkanes; Al(n): fatty alcohols; Fe(n): n-alkylferulates; n denotes the total carbon atom number.
G. Marques et al./Bioresource Technology 101 (2010) 260–267
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are the predominant lipids in flax fibers and can help to solubilize
other water-insoluble components such as fatty alcohols and ster-
ols. In contrast, the lipid content of crude sisal pulp is higher than
the other three pulps regardless the relatively low content of lipo-
philic extractives in the raw material. Sisal fibers have low fatty
acid content whereas the content in neutrals such as alkanes, fatty
alcohols and steroids is relatively high. Particularly, the high abun-
dances of free sterols, which have a high propensity to form pitch
deposits (del Río et al., 1998, 2000), in the crude pulps from hemp
and sisal, would point to a high pitch deposition tendency of the
lipophilics from these fibers.
3.3. Fate of lipophilic extractives during TCF and ECF bleaching
The lipophilic extractives remaining in the crude pulp are car-
ried over to the bleach plant, where they react with the bleaching
agents used (Björklund-Jansson et al., 1995; Holmbom, 2000). Pulp
bleaching technology radically changed in the 1990s when the pre-
viously used chlorine was replaced by several new bleaching
chemicals (Sjöström, 1993) and ECF and TCF sequences were
adopted. As a consequence, new pitch problems arose due to the
different reactivity of pulp lipids with the new bleaching agents.
With the aim of studying the behavior of the different classes of
lipophilic extractives under different bleaching conditions, both
TCF and ECF bleached pulps were analyzed and compared with
their respective crude pulps.
In general terms, the qualitative composition of the lipophilic
extractives from the TCF pulps was very similar to that of their
respective crude pulps (Figs. 2 and 3) although the lipid content
was significantly lower (Table 2). Fatty alcohols, alkanes, free ster-
ols and triterpenols, and fatty acids were the main lipophilic com-
pounds present in the TCF bleached pulps, although in lower
amount than in their respective crude pulps. The low reactivity
of most pulp lipids in TCF bleaching sequences (using hydrogen
peroxide as a bleaching agent) has been reported (Freire et al.,
2003; Gutiérrez et al., 2001a). The decrease in the content of these
lipophilic compounds in the TCF pulps, regardless the low reactiv-
ity of hydrogen peroxide towards them, might be due to the exten-
sive washing in alkaline conditions carried out in the industrial TCF
bleaching sequences used. Moreover, it is interesting to note that
sterol glycosides, which resisted soda/AQ pulping conditions, were
removed to a high extent under the industrial TCF bleaching con-
ditions used in this work. The high efficiency of hydrogen peroxide
in degrading sterol glycosides was previously reported using mod-
el compounds (Nilvebrant and Byström, 1995). However, a lower
extent in the removal of sterol glycosides were observed during
TCF bleaching of eucalypt pulps (Gutiérrez et al., 2006a). In addi-
tion to the lipophilic extractives arising from the raw materials,
several non-resolved peaks corresponding to the defoamers used
in the process could also be observed in TCF pulps (Figs. 2 and
3). The excessive use of defoamers can also produce problems of
pitch deposition (Allen, 2000). The presence of defoamer in pitch
deposits produced during manufacturing of paper pulp from hemp
fibers has been reported (Gutiérrez and del Río, 2005).
On the other hand, the composition of the lipophilic extractives
from ECF pulps was somewhat different compared to that from
their respective crude pulps (Figs. 2 and 3). The main difference ob-
served was the large removal of free sterols in all the ECF pulps,
although some minor amounts of free sterols still remained in sisal
ECF pulp. The complete degradation of unsaturated sterols, such as
sitosterol, during ECF bleaching has been previously reported in
pitch deposits, pulps and in reactions with pure compounds (Freire
et al., 2003; Gutiérrez et al., 2001a; Björklund-Jansson et al., 1995).
On the other hand, sterol glycosides were largely removed during
the ECF bleaching and were practically absent in these pulps. A less
reactivity of these compounds with chlorine dioxide compared to
hydrogen peroxide has been reported (Nilvebrant and Byström,
1995). Therefore, the complete removal of sterol glycosides in
the ECF pulps studied here may have been due to the use of hydro-
gen peroxide in the ECF sequence.
The removal of lipophilic extractives in bleaching can be mainly
achieved by two mechanisms. The first one includes the dispersion
and desorption of pulp lipids followed by removal with washing li-
quors, and the second mechanism includes the chemical degrada-
tion/modification of lipids, mainly by oxidative action of bleaching
chemicals resulting in more hydrophilic compounds, which may
be subsequently removed in washing (Holmbom, 2000). The de-
crease in the content of the lipophilic compounds in the TCF pulps
studied here might be due to the first mechanism as mentioned
above, taking into account the low reactivity of these lipids towards
hydrogen peroxide. In contrast, the removal of unsaturated com-
pounds during ECF bleaching was due to the second mechanism
(Holmbom, 2000). The lower reactivity of pulp lipids in TCF bleach-
ing sequences using hydrogen peroxide as a bleaching agent com-
pared to ECF bleaching using chlorine dioxide (Back and Allen,
2000;Gutiérrezetal.,2009)maycausepitchproblemstobe,inprin-
ciple, more severe in the former bleaching sequences. This is spe-
cially evident in the case of unsaturated steroids and triterpenoids
as well as unsaturated fatty acids, which are strongly modified by
chlorine dioxide but remain practically unaltered by oxygen and
hydrogen peroxide (Holmbom, 2000; Bergelin and Holmbom,
2003; Freire et al., 2005, 2006; Gutiérrez et al., 2001a). However, in
the nonwoody pulps studied here, the major lipophilic compounds
present are saturated fatty acids, fatty alcohols and alkanes, which
donotshowreactivitytowardschlorinedioxide,andthereforethere
are not great differences in the composition of the lipophilic extrac-
tives between ECF and TCF bleached pulps, with the exception of
abaca pulp which lacks fatty alcohols and alkanes and where unsat-
uratedsterolsarethepredominantlipophiliccompounds.Therefore,
both ECF and TCF bleached pulps will undergo similar pitch prob-
lems. Fatty acids, fatty alcohols and alkanes have been reported to
bethecompoundsresponsibleforpitchdepositsformedduringpul-
ping of nonwoody plants (Gutiérrez and del Río, 2005).
4. Conclusions
A thorough chemical characterization of the lipophilic extrac-
tives from different nonwoody fibers (flax, hemp, sisal and abaca)
at different stages of pulp production (soda/AQ pulping and TCF/
ECF bleaching) has been carried out. This study provides useful
information into the extent of their removal along the cooking
and bleaching processes. The soda/AQ pulping stage led to the re-
moval of aldehydes, hydroxyfatty acids and the complete hydroly-
sis of esterified compounds such as ester waxes, sterol esters and
alkyl ferulates. Among the bleaching processes, ECF bleaching
showed high reactivity towards unsaturated sterols and both ECF
and TCF bleaching were very effective in removing sterol glyco-
sides from nonwoody pulps. In contrast, saturated fatty acids, fatty
alcohols and alkanes, which are the main lipophilic compounds in
most of the studied fibers, survived pulping and bleaching condi-
tions and were the predominating compounds in both TCF and
ECF bleached pulps.
Acknowledgements
This study has been supported by the Spanish Projects
BIO2007-28719-E and AGL2008-00709 and the EU Project BIORE-
NEW (NMP2-CT-2006-026456). We thank CELESA pulp mill (Torto-
sa, Spain) for providing the samples. G.M. thanks the Spanish MEC
for a FPI fellowship.
266
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