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Annals of Warsaw University of Life Sciences - SGGW Forestry and
Wood Technology № 88, 2014: 157-161 (Ann. WULS - SGGW, For. and
Wood Technol. 88, 2014) The activation energy of swelling beech
wood (Fagus sylvatica L.) in water WALDEMAR MOLIŃSKI, JAN
KUCZYŃSKI, JAKUB PUSZYŃSKI, EDWARD ROSZYK Department of Wood
Science, Poznań University of Life Sciences Abstract: The
activation energy of swelling beech wood (Fagus sylvatica L.) in
water. This paper shows the results of the activation energy of
swelling beech wood in water. The results showed that activation
energy depends on the density. Increasing that values increase
activation energy of swelling. Keywords: activation energy,
swelling, beech wood INTRODUCTION
Swelling of wood is considered to be its disadvantage. To
minimize this effect, solid wood is processed into many kinds of
wood based materials. Those types of materials characterized by a
lower swelling in water values, witch increase activation energy.
For OSB its 54.1, plywood 62.8 (Sinha et al. 2011) and for the
wood-polymer composite (WPC) the activation energy is 590 kJ/mol
(Ou et al. 2011). For wood, linear function of swelling in wetting
time in initial period (after induction) of those process is used
to mark activation energy. Carrying out this process at various
temperatures allows to determine the initial swelling rate. Already
in 1872, Svante Arrhenius, a Swedish scientist showed that the
dependence of the reaction rate of the natural logarithm (ln k) as
a function of the inverse absolute temperature (1/T) is a straight
line. The directional factor of this compound is characteristic to
a given reaction. According to West (1988) and Banks and West
(1989) swelling of the wood is results of collisions of a particle
solution with a wood and their binding to the active centres of
wood substance. They have shown that kinetics of wood swelling
strongly depends on temperature, and this relationship is
subordinated classical Arrhenius equation. Recognizing wood
swelling as a bimolecular chemical reaction that takes place only
by colliding liquid molecules with the wood molecules, they
proposed a model for illustrating the movement of the liquid into
the wood of the zipper-like effect. React may, however, only
molecules whose energy level exceeds the value of the activation
energy (Bala 1997). The activation energy of the process of wood
swelling in water test is relatively new, and this is due to the
very high kinetics of the swelling even at room temperature. Only
in 1994 Mantanis et al. (1994b) using a linear deflection sensor
connected to the computer determined the activation energy of the
four species of wood in the water. In this work, it was found that
the value of activation energy of wood swelling in water depends,
among others: from the species, content of the compounds extraction
and wood density. Sahin (2010) studying the Castanea sativa Mill.
wood also demonstrated that measured value of the wood swelling
energy in water is partly depends from the direction of moisture
deformation measurements. Resuming, the wood swelling is a complex
process influenced by many factors (Mantanis et al. 1994a and b;
Morisato et al. 2002; Ishimaru and Sakai 1998; Ishimaru and Iida
2001), the results may vary. No information about the activation
energy of wood swelling beech (Fagus sylvatica L.) in water was the
cause of these study.
MATERIALS
Determination of the swelling beech wood was carried out on
samples with dimensions of 25 (R) x 25 (T) x 10 (L) mm. Samples
were obtained from a single, central
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plank, with 60 mm thickness and 3 m length. Plank was obtained
from close to stump zone of tree and was seasoned by two years
under the roof. To prepare the samples only defect-free, straight
grain wood was used. In next step, plank was sawed longitudinally
through the pith. From both elements, two boards were handling with
dimensions slightly larger than the size of the final samples.
After conditioning in laboratory for two weeks, elements were cut
using a planer. Rings were tangential to one of the edges.
Subsequently, each planks were cut in half of its length, which
gives a samples with 10 mm length. All samples like those were
treated as a twin. A scheme of preparation of the samples is shown
in Figure 1.
Figure 1. Scheme of preparation of the samples
Samples were properly described to permit their origin
identification. Then, they were
laboratory kiln dried at 103±2°C to completely dry condition.
After the seasoning to room temperature, their linear dimensions
(±0.001 mm) and their mass (±0.001 g) were measured. Density of
each sample were calculated. Its values were very similar to twin
samples.
The method of determination kinetics of the wood swelling in
water was similar to that used in the Mantanis′a et al. (1994a)
work. This value was determine for the tangential direction.
Samples were moistened in water with varying temperature: 20, 40,
60 and 80°C. KEST ELECTRONICS displacement meter with special
software were used to measure kinetics of swelling. It allows for
automatic registration of displacement inductive sensor in time
with an accuracy of 0.001 mm. Moistening in water has been done on
the triple water bath LWR RS-485. It allows maintaining the water
temperature at the desired level during the experiment with
accuracy of 0.5°C. The registration process of wood swelling
continued out for 8 hours. The value of maximum swelling were
taking after 24 hours of soaking in water. RESULTS
The results of the average wood swelling measurements in water
with varying temperature are shown in Figure 2. Each average values
were calculated from six reps for samples obtained from two planks
located on opposite sides of the pith. Figure shows only the
initial period of swelling process. It shows that increasing
temperature of the water increase swelling process, and further,
equilibrium of swelling establishes quicker. This fact should be
associated with the kinetics of wetting samples (Figure 3), samples
at higher temperatures
25
1025
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moisturize faster. Increase maximum value of swelling with
increasing temperature (Table 1) should be associated with leaching
some of a extraction compounds of cell walls (Stamm and
Loughborough 1942; Boiciuc and Petrician 1970; Mantanis et al.
1994a i b; Ishimaru and Iida 2001). An important aspect of the
increase wood swelling as the temperature of immersion liquid
increases is also softening the cellulose matrix, which facilitates
swelling (e.g. Eriksson et al. 1991, Engelund et al. 2013).
Furthermore, Mantanis et al. (1994a) found that a higher value for
the maximum swelling of wood at increased temperatures may be the
result of small changes in the structure of the cell wall.
Figure 2. Initial period of wood swelling in the tangential
direction for the beech samples in varying
temperatures
Figure 3. Kinetics of changes in moisture content of wood
Swelling rate, calculated for the six samples (3 on each side, L
and P), in the initial
linear range are summarized in Table 2. Table data shows a clear
increase in the initial rate of wood swelling (in linear zone) with
increased temperature of the process. The results of this study
fully agree with Mantanisa et al. (1994a) results (on Sitka spruce,
Douglas fir, sugar maple and aspen wood). They have shown a
dramatic increase in the swelling kinetics of these species of wood
in the water as the temperature increases. It should be noted that
those study were modelled on the methodology developed by these
authors and the obtained results confirmed earlier expectations in
this regard. Activation energy of swelling in water (Table 2)
ranged from 25.5 kJ/mol (L3/P4 samplers with the lowest average
density) to 29.8 kJ/mol
0
2
4
6
8
10
12
14
16
0 50 100 150 200 250 300 350
Swel
ling,
α [%
]
Time, t [min]
20°C 40°C 60°C 80°C
0
10
20
30
40
50
60
70
0 20 40 60 80 100 120
Moi
stur
e co
nten
t, M
C [%
]
Time, t [min]
20°C 40°C 60°C 80°C
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(L1/P2 with highest density). Those results confirm earlier
observations (Mantanis et al. 1994a and b) that increasing wood
density increase activation energy of swelling. Table 1. Average
maximum values of swelling beech wood samples in a tangential
direction, humidified in the water of different temperatures and
different positions of the samples within the tree
Temperature, T [°C]
Samples mark L1/P2 L2/P3 L3/P4
Density, ρ0 [kg/m3] 730 695-720 645-660
Maximum values of swelling [%] 20 14.22 13.84 13.08 40 15.84
15.34 13.71 60 16.36 16.01 14.26 80 16.57 16.13 14.43
Table 2. Initial swelling kinetics of beech wood samples in
water at different temperatures and position
Samples mark
Density, ρ0 [kg/m3]
Kinetics of swelling [%/min] 20°C 40°C 60°C 80°C
L1/P2 730 0.260 0.570 1.119 2.072 L2/P3 710 0.239 0.478 0.911
1.776 L3/P4 650 0.306 0.598 1.068 1.815
Correlation between activation energy of swelling wood in water
with density is
shown at Figure 4. The data in this figure show that the
correlation can be approximated by a straight line with a
relatively high coefficient of determination (R2 > 0.85). In the
range of wood density from 650 to 730 kg/m3, density increase of 10
kg/m3 gives activation energy increases about 0.5 kJ/mol.
Figure 4. Correlation between activation energy of swelling wood
in water with density
CONCLUSIONS On the grounds of the results, it can be concluded
that:
1. As temperatures increase, the swelling of beech wood in the
water and its maximum values increases, equilibrium time of
swelling establishes is dramatically shorten.
2. The activation energy of beech wood swelling in water range
from 25.5 to 29.8 kJ/mol.
3. The value of activation energy of beech wood swelling is a
linear function of its density.
Ea = 0.0514ρ0 - 7.8985 R² = 0.8544
24
26
28
30
32
630 650 670 690 710 730 750
Ea
[kJ/
mol
]
Density, ρ0 [kg/m3]
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Streszczenie: Energia aktywacji pęcznienia drewna buka (Fagus
sylvatica L.) w wodzie. W pracy przedstawiono wyniki oznaczeń
energii aktywacji procesu pęcznienia drewna w wodzie. Uzyskane
rezultaty wykazały, że wartość tej wielkości zależy od gęstości.
Wraz ze wzrostem gęstości drewna buka wzrasta energia aktywacji
jego pęcznienia. Corresponding author: Edward Roszyk Department of
Wood Science Poznań University of Life Sciences Wojska Polskiego
38/42 60-627 Poznań, Poland e-mail: [email protected]