African Journal of Biotechnology Vol. 7 (22), pp. 4153-4158, 19 November, 2008
Available online at http://www.academicjournals.org/AJB
ISSN 1684–5315 © 2008 Academic Journals
Full Length Research Paper
Characterization and evaluation of Paulownia elongota
as a raw material for paper production
Saim Ates1*, Yonghao Ni 2, Mehmet Akgul3, Ayhan Tozluoglu3
1Kastamonu University, Forestry Faculty, 37100, Kastamonu, Turkey.
2Limerick Pulp and Paper Centre, UNB, Fredericton, NB, E3B6C2, Canada.
3Duzce University, Forestry Faculty, 81100, Duzce, Turkey.
Accepted 23 September, 2008
Paulownia elongota, one of the most fast growing species of the world, was evaluated as raw material
for pulp and paper production. The chemical, morphological and anatomical aspects of paulownia wood
were determined. The lignin, holocellulose and -cellulose contents in P. elongota wood were
comparable to those of some common non-wood and hardwood raw materials. Different chemical
pulping procedures were applied to P. elongota wood to evaluate its pulping potential. Paper strength
properties and acidic group content bound to the cell wall were determined. The alkali solubility, water
solubility and alcohol-benzene extractive content were higher than those from wood and most non-
woods. The fiber length of 0.83 mm was observed, which is close to low end of the hardwoods but fiber
diameter was very wide, similar to that of softwoods. The pulpability of paulownia wood was also
studied. The pulp yield and viscosity were very low and the kappa numbers were high. The strength
properties were comparable to those of some wood and non-wood pulps. Although, paulownia pulps
are considered as low quality materials, it can be used for paper production when mixed with long
Key words: Paulownia elongota, chemical, morphological, anatomical properties, pulping.
Pulp and paper industry is facing ever-increasing demand
of quality paper and paperboard that is causing search for
new and hitherto unexploited sources of cellulosic fibers.
However, out of nearly 600 known species, less than a
dozen are in commercial use for pulp production. These
species, most frequently found in plantations in the diffe-
rent regions of the world, may not always be favorable
with regard to fiber quality and wood composition as well
as natural evolution and ease of hybridization (Khristova
et al., 2006).
Paulownia is a genus of about 20 native species in
China and South-East Asia and cultivated since as early
as 1000 BC. Its characteristics of rot resistance, dimen-
sional stability and a very high ignition point ensure the
popularity of this timber in the world market (Bergmann,
1998). Most species of paulownia are extremely fast
growing and can be harvested in 15 years for valuable
Corresponding author: E-mail: email@example.com,
Tel: +90-5052243173; Fax: +90-3662152316
timber. Low quality lumber can easily be produced from 6-
7 years old tree. A full grown paulownia can reach a
height of 10 to 20 m and grows up to 3 m in one year
under ideal conditions. A 10-year old tree can measure
30-40 cm diameter at breast height (DBH) and can have
a timber volume of 0.3-0.5 m3 (Flynn and Holder, 2001).
The wood of paulownia is soft, lightweight, ring porous
straight grained, and mostly knot free wood with a satiny
luster. Average specific gravity of the wood is reported as
0.35 g cm-3 (Kalaycioglu et al., 2005).
Paulownia is also known as a fast growing tree. It can be
used for several applications; one of them is its use as
source for pulp (Virginia et al., 2008; Rai et al., 2000). It can
be characterized by a fast development and a uniform and
regular growth. Each paulownia tree could produce a cubic
meter of wood at the age of 5–7 years; it may grow in
intensive plantations with about 2000 trees ha-1. Based on
the above one can calculate that an annual production
would be 330 ton ha-1, a more conservative number would
be about 150 ton ha-1 (Caparro et al., 2008).
The main objective of this study was to establish the
suitability of Paulownia elongata as a potential source of
4154 Afr. J. Biotechnol.
lignocellulosic fibers for paper and composites materials.
In the present study, anatomical, morphological and
chemical characteristics were evaluated in order to obtain
more information about their suitability for pulp
MATERIALS AND METHODS
For this study, a wood sample of the hybrid P. elongota (2 years-old
tree) was harvested from a plantation in the west of Turkey
(plantation of Bragfor Fidancılık). Several trees of about 6.0–7.5 m
high and 27-33 cm diameter at breast height were felt and the
stems were cut into 0.5-2.0 m wood logs that were air-dried and
used to make 2–3 cm chips in length for the pulping trials. A repre-
sentative part of the chips were also ground into 40–60 mesh wood
mills, 10 g of which were used for the chemical analyses.
Characterization of raw materials
The raw materials were analyzed for holocellulose, -cellulose,
lignin, ash, alcohol–benzene extractable, cold and hot water and
1% soda soluble, in accordance with the applicable TAPPI
standards: T-203-0S-61, T-222, T-221, T-204, T-257 and T-212,
respectively. Five replicates were done for each experiment.
Morphological and anatomical properties
For the measurements of fiber length, fiber width, lumen width and
cell wall width, P. elongota wood (after removing barks) was mace-
rated in a solution containing 1:1 HNO3 and KClO3. For maceration,
wood samples taken from three parts of each P. elongota wood
were chosen. A drop of macerated sample was taken on a slide and
fiber length, fiber width, lumen width and cell wall thickness were
measured under a microscope. For measuring fiber length and
diameter, 200 fibers were measured from 10 slides and average
reading was taken.
For anatomical properties, paulownia wood chips of about 1 cm
was autoclaved followed by immediate storage in a mixture of equal
volume of glycerin, ethyl alcohol and water till sectioning with sliding
microtome. Then permanent slide was prepared and analyzed on a
microscope. The percentage of vascular bundles was calculated
from the vascular bundle area divided by total area.
Three different pulping processes were conducted: kraft-
antraqhinon (AQ), soda-AQ and ethanol (ALCELL). Pulping
experiments were carried out in 15 L electrically heated laboratory
type rotary digester and governed with digital temperature control
system. At the end of pulping, pressure was relieved to atmospheric
pressure then pulps were washed, disintegrated in a laboratory type
pulp mixer with 2 L capacity and screened on a Noram type pulp
screen with 0.15 mm slotted plate. Pulp yield was determined as
dry matter obtained on the basis of oven dried (od) raw material.
Kappa number and viscosity were determined in accordance with T
236 cm-85 and T 230 om-94, respectively. Hand sheets of un-
bleached pulps with a grammage of ~60 g m-2 were prepared
according to Tappi T 272 om-92. Before the ethanol pulp sample
was used in this study, displacement washing was performed with a
70% ethanol solution at 70°C a 10% pulp consistency, a superficial
velocity of 100 ml min-1 and a dilution factor of 4.5 ml g-1. The kappa
number of the washed pulp thus obtained was 42.06.
Paulownia wood sample was mechanically refined, then extracted
following TAPPI T-264-88 with the substitution of acetone before
determination of acid groups. The extracted sample and three
different P. elongota pulps were alternately soaked and rinsed two
times in 0.1 N HCl for 45 min. The pulp samples were dispersed
450 ml of 0,001 M sodium chloride and titrated with 0.1 M sodium
hydroxide. The alkali was added at a rate of 0.5 ml every 5 min so
as to allow sufficient time for equilibrium to be reached between
readings. Following titration, the pulp was washed and oven-dried
at 105oC. All titrations were followed both potentiometrically and
conductometrically (Katz et al., 1984).
RESULTS AND DISCUSSION
Table 1 shows the chemical properties of P. elongota
wood and their comparison with bamboo, eucalyptus,
some annual plants, coniferous and deciduous wood
which are the main fibrous raw materials. As shown in
Table 1, lignin content of P. elongota was found as
20.5%, which is comparable with all annual plants and
hardwoods (17-26%) especially with eucalyptus (23.3%);
it is however, substantially lower than softwoods (25-
32%). The average holocellulose content of P. elongota
was found as 75.74% and it is fairly acceptable ratio when
compared with bamboo (70.5%), most annual plant and
coniferous (68-74%). The -cellulose in P. elongota wood
(43.61%) is higher than wheat straw, corn stalk, tobacco
stalk, sunflower stalk and kenaf (38.2, 35.6, 37.5, 37.5
and 37.4%, respectively) When compared with hard-
woods and softwoods, P. elongota have substantially
higher water, alkali and alcohol-benzene solubility, which
means lower pulp yield probably higher biological oxygen
demand (BOD) load in the effluent. P. elongota wood also
showed similar solubility with bamboo and eucalyptus and
better solubility values than wheat straw and than most
annual plants (Table 1).
The anatomical structure of P. elongota wood was
studied on transverse and tangential sections (Figure
1a,b). The light microscopy observation revealed the
prevalence of four distinct tissue systems: vessels,
parenchyma, rays and fibers. It can be seen from cross
section (Figure 1a) that the difference in vessel size
between early and late wood is three or five times.
Solitary vessels, simple perforation and tyloses in vessels
can be seen. Each vessel was surrounded by a large
number of paratracheal. Parenchyma can be seen mostly
clear around the vessels of late wood and wide strip-
shaped in early wood. Fiber cells are more in late wood
than in early wood. Rays are multiseriate, usually homo-
geneous and 1-40 cells high and 1-5 cells wide (Figure
1b). These anatomical properties are closely similar to
Paulownia fortunei wood studied by Hua et al. (1986).
The average content of parenchyma cells of P. elongo-
ta is about 53.8%. The percentage of parenchyma cells
for P. elongota differs from wood species (7 and 30% for
soft and hardwood, respectively) (Rydholm, 1976), but
resembles other non-wood like corn stalks, straw etc.
Ates et al. 4155
Table 1. Chemical analysis of Paulownia elongota wood
1 % NaOH (%)
Cold water (%)
Eucalyptus 80.42 50.17 23.30 0.47 3.29 23.56 5.62 9.91 Ayata 2008
Bamboo 70.5 43.3 24.5 1.35 3.94 25.1 - 6.47 Deniz,and Ates
Wheat straw 74.5 38.2 15.3 4.7 7.8 40.59 10.75 13.99 Deniz et al.2004
Rye straw 74.1 44.4 15.4 3.2 9.2 39.2 10.2 13.0 Usta and Eroglu
Corn stalk 64.8 35.6 17.4 7.5 9.5 47.1 - 14.8 Usta et al. 1990
67.6 37.5 19.5 7.3 6.5 42.9 15.8 19.1
74.9 37.5 18.2 8.2 7.0 29.8 15.5 16.5
Cotton stalk 77.6 - 21.4 4.2 3.0 21.9 - -
Erolu et al. 1992
Reed 77.9 47.5 18.7 3.9 4.0 28.3 3.3 3.8 Kirci et al. 1998
Kenaf 81.2 37.4 14.5 4.1 5.0 34.9 11.7 12.8 Atchison
Hemp 86.77 63.77 6.59 - 4.23 29.55 7.75 9.06 Gumuskaya and
Coniferous 68-74 40-45 25-32 <1 - - 2-6 2-5 Eroglu 1998
Deciduous 70-81 38-49 17-26 <1 - - 3-6 3-6
S.d. Standart deviation.
Figure 1. Transversal (a) and tangential (b) sections and macerated sample (c) of Paulownia
elongota wood. F: Fibers, P: parenchyma, R: rays, and T: trachea cells.
(Atchison, 1993). The similar ratio of tissue systems was
found by Jahan et al. (2006) for golpata fronds (Nypa
fruticans). The proportion of vascular tissues and fibers in
P. elongota (9.71 and 39.04%, respectively) are also
different from woods (30 and 50%), but close to other
materials like wheat straw (13.5 and 37.5%) and bamboo
(11 and 38%) (Shatalov and Pereira, 2006). When com-
pared with woody materials, P. elongota wood has lower
amount of fiber and higher content of short parenchyma
4156 Afr. J. Biotechnol.
Table 2. Morphological analyses of Paulownia elongota wood
(E. globulus) 1.28 18.0 - 7.0 Teresa et al.
Bamboo 2.30 15.1 6.9 4.17 Deniz,and Ates
(T. durum L) 0.74 13.2 4.0 4.6 Deniz et
Rye straw 1.15 14.7 4.2 1.1 Usta and
Corn stalk 1.32 24.3 10.7 6.8 Usta et al.
Cotton stalk I.32 29.3 23.0 3.6
Tobacco straw 1.07 26.8 16..3 5.3
stalk 128 22.1 15.6 3.3
Erolu et al.
Reed 1.39 13.5 7.0 3.2 Kirci et al.
Kenaf 2.60 20.0 Atchison 1993
Coniferous 2.7-4.6 32-43 - -
Deciduous 0.7-1.6 20-40 - - Atchison 1987
Table 2 shows the morphological characteristics of P.
elongota and its comparison with other fibrous materials.
The image of the fibers can be shown in Figure 1c. The
average fiber length of P. elongota wood is 0.82 mm,
which is shorter than softwoods (2.7-4.6 mm) and close to
minimum value of hardwood fibers (0.7- 1.6 mm) and
almost the same with wheat straw fibers (0.74 mm).
However, the fiber lengths of eucalyptus, rye, and tobacco
stalk are 1.28, 1.15 and 1.07, mm respectively (Table 2).
The fiber width of P. elongota was found as about 36.3
m which was in normal range when compared to
hardwoods fiber (approximately 20.0–40.0 m) (Atchison,
1987). The fiber wall thickness of P. elongota is also
higher than the other fibrous materials. The physical
properties of a pulp sheet are closely related to morpho-
logical properties of pulp fiber (Young, 1981).
The strength properties of the papers were found to
positively correlate with the felting coefficient (fiber
length/fiber diameter). It is stated that if felting coefficient
of a fibrous material is lower than 70, it is invaluable for
quality pulp and paper production (Young, 1981; Bektas
et al., 1999). The felting coefficient of P. elongota fibers
was found as 22.7. Whatsoever high felting coefficient
means lower strength properties. Some authors have a
different opinion because not only strength properties
depend on felting coefficient, but also cell wall thickness
(Erolu, 1998). As depend on the cell-wall thickness,
rigidity coefficient (cell wall thickness x 100/fiber width) is
one of the important parameter. Rigidity coefficient was
calculated as 23.7 for P. elongota wood. Higher rigidity
ratio gives lower paper strength properties especially
lower burst, tear and tensile indexes (Bektas et al., 1999).
Strength properties of P. elongota obtained from three
different chemical pulping processes confirms these
results (Table 3).
Related with this expression, another criterion is
elasticity coefficient (Istas et al., 1954) for evaluating fiber
quality (lumen width x 100/fiber width). We calculated the
elasticity coefficient as 52.9 for P. elongota fibers. Ac-
cording to Istas et al. (1954), if the elasticity coefficient is
between 50 and 70, this kind of fibers easily can be flat
and give good paper with high strength properties. So, P.
elongota fibers with short fiber length, thick cell wall and
large lumen width can be used for paper production after
mixing with long fibrous materials.
P. elongota wood was cooked by kraft-AQ, soda-AQ
and ethanol processes. Pulping conditions and results of
the characterization of unbleached pulp samples obtained
using three different methods, and of paper sheets made
from them are presented in Table 3. The conditions were
selected a series of pre-trial, just to evaluate P. elongota
wood as pulping raw material.
Ates et al. 4157
Table 3. Operation conditions used in the pulping of Paulownia elongota and results of the
characterization of unbleached pulp samples using three different methods and of paper sheets
made from them.
Parameter Kraft-AQ Soda-AQ Ethanol
Active alkali charge (%) 18 18 -
Sulphidity charge (%) 20 - -
Ethanol charge (%) - - 50
AQ (%) 0.1 0.1 -
Liquor to wood 6/1 6/1 8/1
Pulping time (Min.) 90 90 120
Pulping temp (oC) 160 160 180
Yield (%) 38.3 37.8 38.4
Kappa no 28.2 27.8 42.06
Viscosity (cP) 12.08 10.38 13.92
CSF 670 665 725
Bulk (cm³·g-¹) 2.15 2.13 1.90
Breaking length (km) 1.66 1.53 2.59
Brightness (%ISO) 21.83 24.03 32.86
Burst (kPa·m²·g-¹) 1.15 1.09 0.90
Tear (mN·m²·g-¹) 2.10 1.96 3.36
Coarseness (mg 100m-1) 10.5 10.5 14.6
Percent fines (0-0.2mm) 17.45 25.00 16.62
Curl Index 0.059 0.052 0.044
Kink Index 0.83 0.74 0.75
Fiber Length (mm) 0.450 0.427 0.508
Uncooked wood Kraft and Soda pulps E-OH Pulp
Strong acid (mmol·kg-¹) 370.1 356.7 333.3
Weak acid (mmol·kg-¹) 170.0 173.3 106.7
Total acid (mmol·kg-¹) 540.1 530.0 440.0
Table 3 showed that pulp yield in three processes were
lower for kraft-AQ, soda-AQ and ethanol pulps as 38.3,
37.8 and 38.4%, respectively, and kappa numbers were
little higher than other non-wood fibers. It can be ex-
plained with high amount of water and alkali solubility of
P. elongota wood (Table 1). At similar cooking conditions,
golpata fronds showed similar pulp yield and kappa
number (Jahan et al., 2006). Viscosity values were found
for kraft-AQ, soda-AQ and ethanol pulps as 12.08, 10.38
and 13.92 cp, respectively. The strength properties of P.
elongota wood for unbleached alkaline pulps are also
given in Table 3. The breaking length was higher than
that of pine and olive pulps (Jimenez et al., 1992). Burst
index for the kraft-AQ, soda-AQ and ethanol P. elongota
pulps (1.15, 1.09 and 0.90 kPa·m² g-1 respectively) are
comparable with the giant reed pulps obtained from
ethanol soda, ASAM, organacell and kraft pulping pro-
cess (1.42, 1.31, 1.08 and 0.96 kPa m2g-1 respectively).
Similar results for optimum P. fortunei organosolv pulp
were obtained by Caparro et al. (2008) as 38.4% yield,
46.9 kappa number, 27.4% ISO brightness, 28.87 Nm g-1
tensile index, 1.22 kPa m2 g-1 burst index and 1.23 kN m2
g-1 tear index.
Due to its higher content of fines and shorter average
fiber length, the soda-AQ pulp had lower breaking length
and tear index than the ethanol pulp. The reason is
probably the carbohydrates are being protected more
effectively against hydrolysis reactions in high alcoholic
environment (Akgul and Kirci, 2002) coupled with the
effect of the alkali in white liquor. Kraft-AQ pulp showed
similar characteristics with soda-AQ pulp. There is no
significant difference between the two alkaline pulps.
Table 3 also shows the acid groups bound to cell wall of
the P. elongota wood. The amount of acid groups on pulp
samples decreased after pulping process, decreasing
values for both soda-AQ and kraft-AQ pulps (from 540.1
to 530.0 mmol kg-1) obtained were the same. But in
ethanol pulping, the acid groups reduced rapidly after
pulping (from 540.1 to 440). The freeness (CSF) values of
the samples correct it. Acid groups in P. elongota wood
and pulp samples are extremely higher than wood (Hunt
et al., 2002). It can be concluded that, high amount of
total acid groups for P. elongota pulps do not significantly
affect the strength properties.
4158 Afr. J. Biotechnol.
The following conclusions may be drawn from this
investigation: The lignin, holocellulose and -cellulose in
P. elongota wood are comparable to hardwood and
common non-wood. P. elongota have substantially higher
water, alkali and alcohol-benzene solubility than that of
softwoods and hardwoods, which caused lower pulp yield.
P. elongota wood has lower amount of fiber and higher
content of short parenchyma cells. The pulp yields and
viscosities are lower and kappa numbers are higher than
some common wood and non wood raw materials. The
acid groups bound to cell wall decreased with chemical
pulping process. Ethanol process caused maximum
decrease on acid groups. P. elongota fibers have lower
felting coefficient and elasticity coefficient. Although these
kinds of fibers are considered as low quality materials, it
can be used for paper production when mixed with long
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