PAULOWNIA ELONGATA S. Y. HU - ANATOMICAL AND CHEMICAL
PROPERTIES OF WOOD FIBERS
Jasmina Popović , Gordana Radošević
[email protected]
Faculty of Forestry, Kneza Višeslava 1 , Belgrade/Serbia
Abstract: Shortage of wood raw material strengthens the ever growing interest for the
cultivation of fast growing species in short rotation plantations. In recent years in the
whole world species of the Paulowniа genus have been drawing a lot of attention.
Paulowniа elongata S.Y.Hu was introduced into Serbia from tissue culture and it is
cultivated on a sample plot in the vicinity of Bela Crkva. This paper presents the results
of the research of both anatomy and chemical constitution of the species Paulowniа
elongata S.Y.H, aged 11 years, from the area of Bela Crkva in the aim of getting an
insight into the quality characteristics of wood and its applicability as a raw material in
the wood processing industry.
Key words: Paulowniа elongata, growth rings, wood fibers, lignin, cellulose,
extractives
1. INTRODUCTION
Taking into account the ever growing trend of consumption of wood as a raw
material, there is an ever growing interest in the cultivation of fast growing species in
short rotation plantations, particularlyy in areas with the soil of unsatisfactory quality
in terms of agriculture (Vilotić, 2004 et.al.).
In the past few decades, species of the Paulowniа genus have been grown in
plantations in many areas worldwide.
About ten species and several varieties of the Paulowniа genus are known.
Those are fast growing species originating from China, with short rotation periods,
which makes them attractive for plantation cultivation aimed at the production of raw
material for wood processing industry. They are relatively undemanding regarding the
quality of soil. In favourable conditions, a tree aged 5-7 years reaches the hight of 15
– 20 m. The Paulowniа genus is characterized by: resistance to rot, dimensional
stability and high ignition point, which makes it very popular on the world market
(Ber gma nn, 1998). The colour of the wood is fair, and the wood is soft and easy to
process. Its specific weight is217-274 kg/m3 (Јun-Qing, et al., 1983). It is used in the
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production of OSB (oriented strand board) panels and veneers (Bergmann, 1998), for
the production of musical instruments but also for pulping processes (Olson, Carpenter,
1985).
In this paper, anatomical and chemical characteristics of the tree Paulownia
elongata, grown in the area of Bela Crkva were studied, as well as important indicators
of the quality of wood as a raw material in chemo-mechanical wood processing.
2. MATERIALS AND METHODS
In 1996 in the area of Bela Crkva in Serbia, an experimental plot was established in
which two species of the genus Paulownia are grown: Paulowniа fortunei and
Paulowniа elongata. In June of 2008 three representative trees of each P. elongata
were cut in order to obtain samples for testing.
From all three cut trees of P. Elongata, 3 cm thick disks were taken at breast
height (1,3m). From each disk samples of standard dimensions were cut from core to
bark. One half of the sample was used for chemical composition analysis, whereas the
second half was used for the analysis of anatomical characteristics.
2.1. Anatomical analysis
By using Franklin's reagent for maceration, and by decomposition of
intercellular substance, individual cells of tissue suitable for measuring were extracted.
Maceration solution consisted of 30% hydrogen peroxide and glacial acetic acid in a
1:1 ratio. The prepared reagent was applied to wood samples (fragmented to the size
of the matches) in the glass tubes, after which the tubes were corked. The material in
test tubes was transformed into pulp in the oven at a temperature of 65ofor the period of
24 hours. After rinsing with distilled water and shaking individual cells of xylem tissue
suitable for measuring were obtained. Macerated wood fragments are transported to the
glass slide with a dissecting needle and they are observed with a microscope.
Fiber length, thickness of cell walls and lumen diameters nad trachea width
were measured using the system consisting of Leica DMLS microscope, and a camera:
Leica DC 300 supported by Leica IM 1000 software which enabled digital recording of
prepared preparations, and very precise electronic measurement of the mentioned
anatomical elements.
From each sample the length of 100 fibers was measured with microscopic
magnification of 50 X. These values were then expressed as the Mean numerical fiber
length (Clar k, 1985) calculated with the formula:
Mn =  LN
N
(1)
and Mean mass fibre length with the formula:
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Mm =
3
L N
L N
(2)
2
Quality of wood fibers is expressed by Ranke coefficient (RR3), as one of the
frequently used indicators of fiber quality, which characterizes the morphology of
fibers' cross-section, and is calculated as the ratio of the double cell wall thickness and
the lumen diameter (W a g e n f u r , R., 1984). Ranke coefficient value was obtained by
measuring 50 fibers from each sample (thickness of cell wall and lumen diameter) with
a microscope magnification of 200 X.
2.2. Chemical analysis
Analysis of the chemical composition included: determination of moisture
content, cellulose, the Klason lignin, ash, substances extracted from wood dissolved in
organic solvent mixture, and in hot water.
Preparation of samples for the analysis of chemical composition was
performed using standard TAPPI T 11 WD-76 method. After cutting the standard
samples from the core to the bark, the tubes were chipped, and grinded using Willey
mill (Culatti), and then sieved on a series of vibration sieves. Wood fractions ranging
from 0.5 to 1.0mm in size were used for chemical analysis.
Moisture content was determined using the method of wood raw material
drying at a temperature of 103±20C according to TAPPI T 12 wd-82 method (also
Br owning, B.L., 1967a).
Wood ash content was determined as a residue after annealing at the
temperature of 575 ± 250C for a period of 3h according to standard methods of TAPPI
15 WD -80 (also Br owning, BL, 1967).
Cellulose content was determined by Kurschner-Hoffer's method, which is
treating the wood raw material with a concentrated mixture of HNO3 and C2H5OH with
a total duration of 4h (B r o w n i n g , B.L., 1967b).
Lignin content was determined using a modified Klason's method. Wood raw
materials previously extracted in the mixture of toluole and ethanol were first treated
with 72% H2SO4, and then with diluted 3% H2SO4 (Solar Ener gy R es ear ch
I nstitut e, 1991).
The content of extracted components was determined using the mixture of
toluene: ethanol = 2:1 in Soxlet apparatus, according to standard TAPPI T 6 os-50
method.
Determination of the content of components extracted in hot water was done
using standard TAPPI T1 os-50 method (also Br owning, BL, 1967a).
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The obtained results of the analysis of chemical composition refer to the oven
dry wood substance.
3. RESULTS AND DISCUSSION
mm
The analysis of annual growth rings gives us an insight into the macrostructure
of wood mass, which makes previous estimation of its features possible. The width of
annual growth rings is in direct correlation with the favourability of growing
conditions. The analyzed trees show maximum values of ring growth width in the
second year, which is in accordance with the above mentioned data on the short
rotation of this species (C a p a r r o s et al., 2007).
40
1
2
3
35
30
25
20
15
10
5
2008
2007
2006
2005
2004
2003
2002
2001
2000
1999
1998
1997
0
year
Figure 1- Growth ring width
Mechanical elements contained in the wood tissue of Paulownia are wood
fibers. Those are prosenchymal elements with pointed ends belonging to very lignified
cell walls.
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Image 1 - Radial section
Image 2 - Tangential section
Image 3 - Wood fibers (macerate)
Image 4 - Macerate
Measurement results of the mean numerical (Mn) and mean mass ( Mm) fiber
length and the Ranke coefficient (RR3) are shown in table. 1.
Таble1 - Paulownia elongata – anatomical characteristics
Tree 1
Mn, mm
0,938
Mm, mm
0,979
r, (µm)
31,187
d, (µm)
3,935
3
RR
0,248
r - libriform cell diameter
d - thickness of librifom cells
Tree 2
Tree 3
0,979
1,018
29,174
3,877
0,267
1,038
1,069
30,817
3,905
0,257
Average
values
0,985
1,022
30,393
3,906
0,257
The measured values are: Mean numerical – 0.985mm and Mean mass fiber
length – 1.022mm, which is in accordance with the values ranging from 0.96-1.19mm
(Ј u n - Q i n g , et al., 1983) for the Paulownia genus, and their values are slightly
higher than for P. fortunei: 0.783mm and 0.818mm (P op ović et al. , 2008).
However, these values are lower than the ones for the fast growing broadleaves
(Populus x euramericana cv. Robusta i cl. I-214, Populus deltoides cl. 618 and cl. 450
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aged 9-16 years), which are grown as a raw material for fiber production, 1.078-1.116
mm (K l a š n j a et al., 2006).
The 0.257 Ranke coefficient value is a higher value than the one for P.
Fortunei, which is 0.134 (Pop ović et a l. , 2008 ). For the polars (Populus x
euramericana cv. Robusta i cl. I-214, Populus deltoides cl. 618 i cl. 450) the value of
the Ranke coefficient is slightly higher: 0.29 – 0.46 ( Klašnja et al., 1991).
Table 2 shows the values of the basic chemical constituents content in the
wood tissue: cellulose (C), lignin (L), as well as ash content (P) and extractives in the
organic solvent (E) and hot water (F) for each tree, as well as their average values.
Тable 2 - Paulownia elongata – chemical composition
C, %
L, %
P, %
E, %
F, %
Tree 1
Tree 2
Tree 3
48,13
19,35
0,51
7,79
5,94
47,23
19,43
0,49
7,97
6,28
48,18
19,25
0,45
8,20
5,92
Average
values
47,85
19,34
0,48
7,99
6,05
The avearge content of cellulose of 47.85% in the studied samples was
relatively high, which was somewhat higher than the value of 43.61% mentioned by
Аtes et al., (2008) for this species aged two years, as well as for the species Paulownia
fortunei aged 12 years from the same locality(Popović et al., 2008). Celulose content
is significantly different from the literature values for the species of the Paulownia
genus.: 38.50 – 41.46% (Јun-Qing, et al., 1983), but it is necessary to keep in mind a
large number of factors which can affect the variations of the chemical composition of
the wood of the same species, primarily the site, climatic conditions, growing
conditions, etc.
I n compar is on t o t he p op lar s (Populus x euramericana cv. robusta, and
cl. I-214, Populus deltoides cl. 618 and cl. 450, age 9-16 years) which have been
grown as fast-growing species in Serbia, the cellulose content was somewhat lower and
it ranged from 50.27-52.05% (Klašnja et al. , 2006).
However the average lignin content in the tested samples was 19.34%, which
was a significantly higher value than the value of 18.52% for the species P. Fortunei
(Pop ović et al. , 2008) fr om t he sa me localit y, but a lower valu e t han
the valu e of 20.5% qu ot ed f or t his sp ecies by Аt es et al. ( 2008) and
21.24 – 24.28%, for the Paulownia genus (Ј u n - Q i n g , et al., 1983).
In comparison to poplars, lignin content is also lower for this species ranging
from 21.21 to 23.16% (Klašnja et al. , 2006).
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The average inorganic matter content (ash) of 0.48% is slightly higher than the
literature values for this species of 0.21% (Аt es et al., 2008), and 0.27% for P.
Fortunei (Pop ović et al. , 2008), but complies with the other authors' findings for
the Paulownia genus: 0.21 – 0.74% (Ј u n - Q i n g , et al., 1983 and also with the
values for the mentioned poplar clones: 0.31-0.37% (Klašnja et al. , 2006).
The average content of extracts of the samples in hot water is 6.05%, and the
content of extracted matters in the mixture of organic solvents (toluol/ethanol) is
7.99%, which are lower values compared to P. fortunei values of 9.85% и 11.48%
(Pop ović et al. , 2008).
The obtained results of the content of extractives are significantly different
from literature values for this species: 10.5%, for the extract in hot water and 3.76%
for the benzol/ethanol extract (Аt es et al., 2008), but such values can be expected
with regard to the great difference in age between the investigated samples.
The values of the exractives content are in compliance with the results
obtained by other authors for the Paulownia genus: 6.2-11.3% in hot water and 4.4-10
in organic solvents (ethanol) (Ј u n - Q i n g , et al., 1983), and they are significantly
higher than the values in poplars: 3.30-3.60% in the toluol/ethanol mixture and 0.811.39% in hot water (K l a š n j a et al., 2006).
4.CONCLUSION
The analysis of anatomical and chemical content of the wood of the species
Paulowniа elongata, aged 11 years from the area of Bela Crkva was carried out. The
results of the chemical analysis reveal relatively high cellulose content. The content of
extractives in hot water is also relatively high, particularly in the ethanol/toulol
mixture.
With regard to the facts that Paulowniа elongata is known as a fast growing
species with short rotation, and that relatively high cellulose content was determined,
the application of Paulowniа elongata wood, as a raw material in the chemical wood
processing industry can be taken into consideration.
Paulownia elongata has slightly higher cellulose content and a lower content
of extractives, compared to P. fortunei, so from the aspect of chemical composition it
could be considered a more suitable raw material for fiber production. Likewise, the
values of Mean numerical and mean mass fiber length as well as the value of the Ranke
coefficient show slightly higher values compared to the ones in P. fortunei aged 12
years, grown in the same locality.
Deviation in chemical constituents content from the results obtained by other
authors for this species can be explained for by different growing conditions, primarily
quality of the soil and climatic factors, which were undoubtedly present, although not
compared in this paper.
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Summary
The material for this research originates from the area of Bela Crkva in Serbia.
The samples of Paulowniа elongata aged 11 years for the purposes of this research
were taken at the (1,3m) breast height of the trees, in the form of 3cm-thick disks, and
standard samples were cut from them. One half of the wood specimens (from the pit to
the bark), were used for the analysis of the following anatomic characters: growth ring
width, mean numerical fiber length and mean mass fiber length and Ranke coefficient.
The second half of the specimens was used for the analysis of the chemical
composition: the content of cellulose, lignin, ash, the extractives in organic solution
(T/E) and hot water.
The average value of the mean numerical fiber length is 0.985 mm, of the
mean mass fiber length 1.022mm, and of the Ranke coefficient 0.257.
Cellulose content was relativelly high - 47.85%, while the lignin content which
amounted to 19.34% and the ash content of 0.48% were within the limits of common
values.The extractives content in the toulol/ethanol mixture was relatively high 7.99% and - 6.05% in hot water.
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