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ORI GIN AL
Nondestructive evaluation of heat-treated Eucalyptusgrandis Hill ex Maiden wood using stress wave method
Rosilei A. Garcia • Alexandre Monteiro de Carvalho •
Joao Vicente de Figueiredo Latorraca • Jorge Luis Monteiro de Matos •
Wanessa A. Santos • Rafael Fonseca de Medeiros Silva
Received: 14 April 2009 / Published online: 21 October 2010
� Springer-Verlag 2010
Abstract The objectives of this study were to evaluate the effect of heat treatment
of eucalypt wood (Eucalyptus grandis Hill ex Maiden) on the dynamic modulus of
elasticity by using the stress wave nondestructive method and also to determine the
air-dry density variation, weight loss and equilibrium moisture content following
treatment. Heat treatments were performed at four different temperatures (180, 200,
215 and 230�C) and for three different durations (15 min, 2 and 4 h). The results
revealed a significant reduction in air-dry density following heat treatment inde-
pendent of temperature and time. A significant weight loss was observed between
and within treatments. The treatment at 230�C for 2 and 4 h produced a weight loss
of 20.5 and 26.5%, respectively, which was statistically different from other
treatment conditions. The dynamic modulus of elasticity decreased by about 13% in
the most severe treatment (230�C for 4 h). Depending on the temperature and time,
the equilibrium moisture content was significantly reduced within the range of
40–74%.
R. A. Garcia (&) � A. M. de Carvalho � J. V. de Figueiredo Latorraca
Departamento de Produtos Florestais (DPF)/Instituto de Florestas (IF),
Universidade Federal Rural do Rio de Janeiro (UFRRJ), BR 465 km 07,
Seropedica, Rio de Janeiro 23890-000, Brazil
e-mail: [email protected]
J. L. M. de Matos
Laboratorio de Tecnologia da Madeira/Departamento de Engenharia e Tecnologia Florestal/Setor
de Ciencias Agrarias/Universidade Federal do Parana (UFPR), Rua Lothario Meissner 3400,
Jardim Botanico, Curitiba, Parana 80210-170, Brazil
W. A. Santos � R. F. de Medeiros Silva
Departamento de Produtos Florestais (DPF)/Instituto de Florestas (IF),
Universidade Federal Rural do Rio de Janeiro (UFRRJ), BR 465 km 07,
Seropedica, Rio de Janeiro 23890-000, Brazil
123
Wood Sci Technol (2012) 46:41–52
DOI 10.1007/s00226-010-0387-6
Introduction
Eucalypt is largely used in Brazilian paper and wood-based composite industries
because it is a fast-growing, productive and easily adaptable tree species. However,
its solid wood presents some disadvantages such as low durability, high swelling
rate, low dimensional stability and serious drying problems, which cause limitations
on use (Unsal and Ayrilmis 2005). Environmental pressures concerning the use of
native timber tree species and Amazon Forest preservation in Brazil have motivated
research studies on eucalypt solid wood and the use of environmentally friendly
treatments.
Heat treatment has been extensively studied in recent years because it aggregates
some desirable properties to the wood and can be a desirable alternative for wood
preservation because it does not use chemical components. It is well known that
heat-treated wood has improved dimensional stability and natural durability as well
as decreased equilibrium moisture content. Nevertheless, the heat treatment
performance depends on the wood species and their properties, specifically the
chemical and anatomical characteristics, initial moisture content and processing
parameters, i.e., temperature and time. Despite these advantages, heat treatment can
also change the wood’s surface characteristics (wettability, gluing quality, surface
hardness, roughness and color) and mechanical properties (Brunetti et al. 2007;
Esteves et al. 2007; Garcia et al. 2008; Kamdem et al. 2002; Korkut and Guller
2008; Unsal and Ayrilmis 2005).
In general, the values of all mechanical properties are reduced following heat
treatment. Korkut and Hiziroglu (2008) studied the effect of heat treatment on the
mechanical properties of hazelnut wood. They observed a drastic reduction in the
Janka hardness and tension strength parallel to grain values while modulus of
elasticity (MOE) loss was between 10 and 27% depending on treatment conditions.
Yildiz et al. (2002) evaluated the MOE of beech wood (Fagus orientalis Lipsky)
heat-treated at different conditions (130, 150, 180 and 200�C for 2, 6 and 10 h). In
general, the MOE decreased between 3 and 45% with increasing temperature and
time, except for the treatment at 200�C for 10 h, which showed an increase by about
17% when compared to untreated wood. Also, Santos (2000) observed an increase
in MOE of heat-treated Eucalyptus globulus Labill. wood ranging from 57 to 71%
depending on annual ring directions, when compared to untreated wood. Another
study by Vital et al. (1983) reported a decrease in MOE of Eucalyptus saligna Smith
wood heat-treated at 105–155�C for 10–160 h. Shi et al. (2007) found a decrease in
MOE of heat-treated spruce and pine ranging from 4 to 28% and an increase in
MOE of heat-treated fir, aspen and birch wood ranging from 15 to 30% when treated
within temperature sets of 200 and 212�C for 3 h. These different results on MOE
can be explained by different conditions employed during heat treatment (initial
moisture content, time and temperature of treatment, nitrogen or oxygen
atmosphere) and by intrinsic characteristics of each wood. Although there are
innumerable studies on heat-treated woods properties, generally the mechanical and
physical properties following treatment are compared between different wood
pieces (untreated vs. treated samples), which can give inaccurate results due to
extreme wood heterogeneity.
42 Wood Sci Technol (2012) 46:41–52
123
In this study, it was proposed to evaluate the dynamic modulus of elasticity
(MOEd) of heat-treated eucalypt wood by a nondestructive method. Nondestructive
evaluation methods (NDE) have been applied at different approaches for several
material categories, i.e., standing tree, solid wood, laminates and wood-based
composites, in order to determine their properties and characteristics by a simple
and fast way (Bodij 2000). Repellin and Guyonnet (2003) used NDE to determine
the MOEd of heat-treated beech wood with success. One of the principal advantages
of NDE is the possibility to measure the wood properties before and after treatment
on the same sample, which improves the sensibility of the test.
In this context, the objectives of this study were (1) to evaluate the effect of heat
treatment of eucalypt wood (Eucalyptus grandis Hill ex Maiden) on the MOEd in
order to understand the heat-treated wood mechanical behavior and (2) to determine
the air-dry density variation, weight loss following treatment and equilibrium
moisture content of the wood under untreated and heat-treated conditions.
Materials and methods
Material and heat treatment
Six trees of 23-year-old Eucalyptus grandis Hill ex Maiden, planted with spacing of
2 9 3 m between trees and not subjected to silvicultural treatments, were obtained
from Quimvale Florestal Ltda plantations located at South Region of Rio de Janeiro
State, Brazil. Boards of dimensions 2 9 0.12 9 0.05 m3 (length 9 width 9
thickness) were prepared from the logs by LPZ Artefatos de Madeira Ltda sawmill
and air-dried for 2 months at the Wood Drying Laboratory of the Department of
Forest Products at Rural Federal University of Rio de Janeiro-UFRRJ (Seropedica,
Rio de Janeiro State, Brazil).
Samples measuring 0.40 9 0.12 9 0.05 m3 (length 9 width 9 thickness) were
then cut from the boards and heat-treated at a variety of high-temperature settings
and different time periods. The heat treatment was performed in an ELETROlab�
oven, model 403, with 0.1 m3 capacity, and external and internal dimensions of
0.90 9 0.98 9 0.55 m3 and 0.50 9 0.50 9 0.40 m3, respectively, available at the
Wood Drying Laboratory (Department of Forest Products, UFRRJ). The samples
were heat-treated at 180, 200, 215 and 230�C for 15 min, 2 and 4 h. The initial
moisture content of the samples before heat treatment was between 12 and 14%.
Before and after heat treatment, samples were conditioned at 20�C and 65% relative
humidity in a conditioning room until equilibrium moisture content was reached,
and then stress wave measurements were made. The moisture content of samples
was determined by using a moisture meter, Model M51 from MARRARI
Automation (Curitiba, Parana State, Brazil) at three equidistant points along the
sample length. The dimensions and weights of the samples were also measured
before and after heat treatment in order to determine the sample air-dry density
variation and weight loss (in percentage of initial weight).
Wood Sci Technol (2012) 46:41–52 43
123
Stress wave time measurements
A Model 239A Stress Wave Timer Electronic Unit from METRIGUARD Inc.,
Pullman WA, USA, available at the Wood Technology Laboratory of the
Department of Forest Technology and Engineering at Federal University of
Parana-UFPR (Curitiba, Parana State, Brazil) was used to perform the sonic
propagation time measurements on the eucalypt wood before and after heat
treatment. The stress wave timer (SWT) presents two accelerometers: the first
includes an impact device (pendulum ball-hammer) for initiating stress waves,
while the second one is secured to the sample and detects the final stress wave signal
as shown in Fig. 1. To conduct the measurements, each wood sample was attached
by start and stop clamps at a distance of 36 cm between the two accelerometers,
then the impact device was started, and the stress wave time was read in
microseconds (ls). Three replicated stress wave time measurements were performed
on each sample in the longitudinal direction (along the wood fibers). Finally, the
MOEd was obtained using the following equations:
MOEd ¼ SWS2 � q�g� 10�5; ð1Þ
and
SWS ¼ L�t � 10�6; ð2Þ
where MOEd = dynamic modulus of elasticity, kgf m-2; SWS = stress wave speed
through the wood sample, cm s-1; q = wood sample air-dry density at the
equilibrium moisture content, g cm-3; g = acceleration of gravity, 9,804 m s-2;
L = distance between the two accelerometers, cm; and t = measured stress wave
transmission time, ls.
For solid wood, the NDE can be sometimes complicated due to some growth
characteristics such as density, knots, irregular grains, reaction wood and cracks,
Fig. 1 Stress wave timer, Model 239A, from METRIGUARD Inc. (Pullman, WA, USA). Details ofmeasurement device: A: start clamp; B: pendulum ball-hammer; C: stop clamp; D: stress wave timer, inmicroseconds; and E: wood sample
44 Wood Sci Technol (2012) 46:41–52
123
which require some care before testing. Hence, a wood classification was performed
before heat treatment in order to minimize the effect of these factors.
Experimental design and statistical analysis
The experimental design used in this study resulted in a total of 12 treatment
combinations with two independent variables: temperature (four levels) and time
(three levels), as shown in Table 1. Each treatment had six replicates resulting in 72
observations under each condition (untreated and heat-treated) for a total of 144
observations.
Statistical analysis of repeated measures using the MIXED procedure of the SAS
Institute Inc. (2003) was performed to observe the differences between dependent
variables: sample air-dry density, weight loss (Wloss), dynamic modulus of elasticity
(MOEd) and equilibrium moisture content (EMC) of the wood before and after heat
treatment. Repeated measures analyses are applied to response outcomes measured
on the same experimental unit under different conditions, such as in the
experimental design of this study. This statistical analysis provides tests between
treatments and within treatments and their interaction effects. The between-
treatments factor corresponds to a set of conditions (groups), where a dependent
variable is measured on independent groups of samples, where each group is
exposed to a different condition. The within-treatments factor corresponds to a set
of conditions where a dependent variable is measured repeatedly for all samples
across a set of conditions or trials. Therefore, in this study, 12 groups (12 different
conditions of heat treatment) and two trials (before and after heat treatment) were
used.
Table 1 Experimental design
used
Number of replicates by
treatment = 6. Number of
observations by condition
(untreated vs. heat-
treated) = 72. Total number of
observations = 144
Independent variables of heat treatment Treatment
combinationTemperature (oC) Time
180 15 min 180oC (15 min)
2 h 180oC (2 h)
4 h 180oC (4 h)
200 15 min 200oC (15 min)
2 h 200oC (2 h)
4 h 200oC (4 h)
215 15 min 215oC (15 min)
2 h 215oC (2 h)
4 h 215oC (4 h)
230 15 min 230oC (15 min)
2 h 230oC (2 h)
4 h 230oC (4 h)
Wood Sci Technol (2012) 46:41–52 45
123
Results and discussion
Table 2 presents the descriptive statistics (means and standard deviations) obtained
for air-dry density, Wloss, MOEd and EMC of eucalypt wood under untreated and
heat-treated conditions. Table 3 presents the results (F-values) of repeated
measurements analysis of variance (ANOVA) for all variables. Table 4 presents
the results (F-values) obtained for contrasts between two conditions (untreated vs.
heat-treated) for each treatment.
Statistical analysis revealed significant effect within treatments, i.e., a reduction
in air-dry density following heat treatment independent of temperature and time, as
shown in Fig. 2. Previous studies also reported significant decreases in wood density
following heat treatment. For example, Unsal and Ayrilmis (2005) reported air-dry
density decreases of 7 and 10% for Eucalyptus camaldulensis Dehn. wood treated at
150 and 180�C for 10 h, respectively. Korkut and Guller (2008) found reductions in
air-dry density of 3.87, 4.46 and 8.65%; and in oven-dry density of 3.01, 3.94 and
5.74% for red-bud maple treated at 180�C for 2, 6 and 10 h, respectively. The
results of this study here showed an average reduction in air-dry density of 8.65%
across treatments. This effect can be attributed to the partial loss of bound water
during the treatment; however, other factors are possibly involved in this
phenomenon, i.e., losses of hemicelluloses (pentoses and hexoses) and extractives
compounds (Kamdem et al. 2002; Seborg et al. 1953). No significant difference in
air-dry density was observed between treatments (groups) or for the treatment*con-
dition (untreated and heat-treated) interaction, as presented in Table 3.
For Wloss, a significant difference was observed between treatments and within
treatments under different conditions (Table 3). Indeed, the treatment at 230�C for 2
and 4 h presented a Wloss of 20.5 and 26.5%, respectively, which were statistically
different from the other treatment conditions (Fig. 3). A significant mass loss was also
observed by Esteves et al. (2007). These authors found mass loss (based on the oven-
dry weight) varying between 3.7 and 14.5% for Eucalyptus globulus Labill. wood
submitted to steam heat treatment with temperatures of 190, 200 and 210�C for 2, 6 and
12 h. Also, Brito et al. (2006) found mass loss of 5.19 and 9.68% for Eucalyptusgrandis wood treated at 180 and 200�C. Esteves et al. (2007) stated that eucalypt wood
has a higher mass loss compared with pine wood due to higher hemicelluloses fraction,
which is the first structural compound affected by heat and also the most susceptible
one to thermal degradation. The major cause of mass loss is the moisture loss;
however, several authors have previously shown that it may also be partly attributed to
the degradation of the hemicelluloses, which has been shown to correlate well with the
loss of strength and stiffness in wood (Borrega and Karenlampi 2008, Esteves et al.
2007). No interaction was found between treatment and condition for Wloss (Table 3).
In general, wood thermal degradation induces reductions in mechanical
properties due to the embrittlement of fibers. In this study, there was a significant
reduction in MOEd by 13% for the most severe treatment (230�C for 4 h), but not
for the other treatments (Tables 2 and 4). According to the literature, heat treatment
may have different effects on MOE depending on the species and time–temperature
schedule. Several authors reported an increase or no change in MOE following heat
treatment (Brunetti et al. 2007; Garcia et al. 2006; Santos 2000). For example,
46 Wood Sci Technol (2012) 46:41–52
123
Tab
le2
Des
crip
tive
stat
isti
cs(m
ean
s,st
andar
dd
evia
tio
ns
and
coef
fici
ent
of
var
iati
on
)fo
rai
r-d
ryd
ensi
ty,
wei
ght
loss
,d
yn
amic
mo
du
lus
of
elas
tici
tyan
deq
uil
ibri
um
mois
ture
conte
nt
of
euca
lypt
wood
under
untr
eate
dan
dhea
t-tr
eate
dco
ndit
ions
Tre
atm
ent
Air
-dry
den
sity
(gcm
-3)
Air
-dry
den
sity
Heat
(gcm
-3)
Wlo
ss(%
)M
OE
d(M
Pa)
MO
Ed
Heat
(MP
a)E
MC
(%)
EM
CH
eat
(%)
DE
MC
18
0�C
(15
min
)0
.63
6(0
.07
6)[
11
.95
]0
.60
3(0
.07
8)[
12
.94
]1
0.1
(4.0
)[3
9.6
0]
12
73
5(1
33
7)[
10
.50
]1
26
24
(12
44
)[9
.85
]1
5.1
(2.7
)[1
7.8
8]
7.2
(1.3
)[1
8.0
6]
7.9
(2.2
)[2
7.8
5]
18
0�C
(2h
)0
.63
4(0
.05
1)[
8.0
4]
0.5
99
(0.0
48
)[8
.01
]1
1.1
(2.2
)[1
9.8
2]
11
46
9(2
00
6)[
17
.49
]1
23
29
(20
52
)[1
6.6
4]
15
.1(3
.2)[
21
.19
]7
.0(0
.9)[
12
.86
]8
.1(3
.1)[
38
.27
]
18
0�C
(4h
)0
.61
3(0
.07
5)[
12
.23
]0
.55
4(0
.06
7)[
12
.09
]1
2.1
(3.6
)[2
9.7
5]
11
71
6(2
65
0)[
22
.62
]1
23
41
(27
62
)[2
2.3
8]
13
.9(2
.3)[
16
.55
]5
.5(1
.7)[
30
.91
]8
.5(2
.3)[
27
.06
]
20
0�C
(15
min
)0
.61
7(0
.05
4)[
8.7
5]
0.5
74
(0.0
59
)[1
0.2
8]
8.9
(1.4
)[1
5.7
3]
11
79
6(1
78
9)[
15
.17
]9
79
9(4
02
4)[
41
.07
]1
3.5
(3.2
)[2
3.7
0]
7.7
(1.3
)[1
6.8
8]
6.0
(4.1
)[6
8.3
3]
20
0�C
(2h
)0
.61
5(0
.02
7)[
4.3
9]
0.5
66
(0.0
30
)[5
.30
]1
1.4
(3.4
)[2
9.8
2]
12
05
5(1
77
4)[
14
.72
]1
22
02
(19
62
)[1
6.0
8]
13
.4(3
.7)[
27
.61
]5
.6(0
.6)[
10
.71
]7
.7(3
.8)[
49
.35
]
20
0�C
(4h
)0
.60
4(0
.07
1)[
11
.75
]0
.54
7(0
.06
4)[
11
.70
]1
5.2
(2.8
)[1
8.4
2]
12
34
4(1
64
9)[
13
.36
]1
25
52
(16
28
)[1
2.9
7]
14
.4(4
.8)[
33
.33
]4
.6(0
.6)[
13
.04
]9
.7(4
.6)[
47
.42
]
21
5�C
(15
min
)0
.60
3(0
.07
6)[
12
.60
]0
.50
7(0
.08
0)[
15
.78
]1
0.3
(1.4
)[1
3.5
9]
11
70
6(2
35
0)[
20
.08
]1
23
16
(36
38
)[2
9.5
4]
14
.0(2
.1)[
15
.00
]6
.8(1
.6)[
23
.53
]7
.2(1
.5)[
20
.83
]
21
5�C
(2h
)0
.59
0(0
.06
9)[
11
.69
]0
.54
0(0
.05
1)[
9.4
4]
14
.8(3
.5)[
23
.65
]1
17
18
(20
63
)[1
7.6
1]
12
14
9(1
42
8)[
11
.75
]1
5.0
(2.6
)[1
7.3
3]
4.5
(0.9
)[2
0.0
0]
10
.4(2
.6)[
25
.00
]
21
5�C
(4h
)0
.60
1(0
.05
4)[
8.9
9]
0.5
46
(0.0
48
)[8
.79
]1
4.6
(4.4
)[3
0.1
4]
11
83
6(1
28
4)[
10
.85
]1
13
99
(78
3)[
6.8
7]
14
.1(3
.3)[
23
.40
]3
.9(0
.4)[
10
.26
]1
0.3
(2.9
)[2
8.1
6]
23
0�C
(15
min
)0
.64
2(0
.05
4)[
8.4
1]
0.5
97
(0.0
64
)[1
0.7
2]
10
.7(3
.3)[
30
.84
]1
33
53
(14
88
)[1
1.1
4]
13
30
5(1
61
2)[
12
.12
]1
5.0
(3.3
)[2
2.0
0]
7.2
(1.3
)[1
8.0
6]
7.8
(3.1
)[3
9.7
4]
23
0�C
(2h
)0
.58
4(0
.09
7)[
16
.61
]0
.54
2(0
.07
0)[
12
.92
]2
0.5
(4.0
)[1
9.5
1]
11
16
6(2
69
6)[
24
.14
]1
04
04
(51
18
)[4
9.1
9]
12
.9(3
.8)[
29
.46
]4
.5(0
.8)[
17
.78
]8
.4(3
.0)[
35
.71
]
23
0�C
(4h
)0
.60
5(0
.04
8)[
7.9
3]
0.5
36
(0.0
46
)[8
.58
]2
6.5
(1.5
)[5
.66
]1
26
74
(19
14
)[1
5.1
0]
11
02
2(1
59
4)[
14
.46
]1
4.7
(3.6
)[2
4.4
9]
3.8
(0.8
)[2
1.0
5]
10
.9(3
.0)[
27
.52
]
Dep
end
ant
var
iab
les:
Wlo
ss,
wei
gh
tlo
ss(i
np
erce
nta
ge
of
init
ial
wei
gh
t)fo
llo
win
gh
eat
trea
tmen
t;M
OE
dan
dM
OE
dH
eat,
dy
nam
icm
od
ulu
so
fel
asti
city
bef
ore
and
afte
rh
eat
trea
tmen
t,re
spec
tiv
ely
;E
MC
and
EM
CH
eat,
equ
ilib
riu
mm
ois
ture
con
ten
tb
efo
rean
daf
ter
hea
ttr
eatm
ent,
resp
ecti
vel
y;D
EM
C,
equ
ilib
riu
mm
ois
ture
con
ten
tv
aria
tio
n.
Sta
nd
ard
dev
iati
on
isg
iven
inro
un
db
rack
ets.
Co
effi
cien
to
fv
aria
tio
nis
giv
enin
squ
are
bra
cket
s
Wood Sci Technol (2012) 46:41–52 47
123
Brunetti et al. (2007) reported an increase in MOE of 21.4 and 4.7% for European
cherry and walnut, respectively, both treated at four temperature steps (70�C for 4 h;
100�C for 6 h; 210�C for 25 h; and 50�C for 10 h). On the other hand, other studies
reported a decrease in MOE of heat-treated wood of some species (Borrega and
Karenlampi 2008; Esteves et al. 2007; Korkut and Hiziroglu 2008; Mburu et al.
2008; Shi et al. 2007; Yildiz et al. 2002). Shi et al. (2007) reported a decrease
between 4 and 28% in MOE for heat-treated spruce and pine, while MOE increased
between 15 and 30% for fir, aspen and birch wood when heat-treated within
temperature sets of 200 and 212�C for 3 h. Esteves et al. (2007) observed decreases
of 5 and 15% in MOE of eucalypt wood treated in the temperature ranges from 170
to 200�C. These contradictory results can be explained by the intrinsic character-
istics of the wood of each species and the stability of its chemical compounds
Table 3 Results (F-values) of repeated measurements analysis of variance (ANOVA) for heat-treated
eucalypt wood properties
Source of variation Air-dry density Wloss MOEd EMC
Treatment 0.76NS 2.15* 0.53NS 1.05NS
Condition (untreated and heat-treated) 136.41** 36.04** 0.35NS 572.49**
Treatment Versus Conditiona 0.76NS 0.33NS 1.96* 1.39NS
Dependant variables: Wloss, weight loss (in percentage of initial weight) following heat treatment; MOEd,
dynamic modulus of elasticity; EMC, equilibrium moisture content. a represents the interaction between
treatment and condition (i.e., untreated by heat-treated). NS not significant. * Significant at the 0.05
probability level. ** Significant at the 0.01 probability level
Table 4 Results (F-values) obtained for contrasts between two conditions (untreated vs. heat-treated) for
each treatment of eucalypt wood
Treatment Linear effects of contrast between untreated and heat-treated conditions
Air-dry density Wloss MOEd EMC
180�C (15 min) 5.56* 1.40NS 0.00NS 40.88**
180�C (2 h) 5.69* 2.17NS 2.16NS 41.57**
180�C (4 h) 16.17** 2.86NS 1.56NS 50.70**
200�C (15 min) 4.41* 1.49NS 3.24NS 23.35**
200�C (2 h) 10.66** 2.60NS 0.31NS 41.22**
200�C (4 h) 13.25** 3.30NS 0.22NS 58.86**
215�C (15 min) 24.57** 1.40NS 0.68NS 31.65**
215�C (2 h) 11.44** 3.90NS 0.69NS 70.77**
215�C (4 h) 13.42** 3.40NS 0.25NS 63.49**
230�C (15 min) 9.94** 1.78NS 0.03NS 39.68**
230�C (2 h) 8.22** 5.21* 2.17NS 45.47**
230�C (4 h) 22.93** 10.16** 10.40** 80.12**
Dependent variables: Wloss, weight loss (in percentage of initial weight) following heat treatment; MOEd,
dynamic modulus of elasticity; and EMC: equilibrium moisture content. NS not significant. * Significant
at the 0.05 probability level. ** Significant at the 0.01 probability level
48 Wood Sci Technol (2012) 46:41–52
123
(cellulose, hemicelluloses and lignin) under heat, as well as different process
conditions in some cases.
EMC was reduced significantly after heat treatment within all treatments
(Table 4 and Fig. 4). Depending on the temperature and time conditions, the EMC
was reduced within the range of 40–74% (Fig. 5). Although no significant effect
was observed between treatments, the equilibrium moisture content of heat-treated
wood (EMCHeat) suggests a larger reduction with increasing temperature and time
After Heat Treatment Before Heat TreatmentA
ir-d
ry d
ensi
ty (
g c
m-3
)
0.100
0.200
0.300
0.400
0.500
0.600
0.700
0.800
0 180oC 15 min
180oC 2 h
180oC 4 h
200oC 15 min
200oC 2 h
200oC 4 h
215oC 15 min
215oC 2 h
215oC 4 h
230oC 15 min
230oC 2 h
230oC 4 h
Fig. 2 Mean air-dry density of eucalypt wood before and after heat treatment
Fig. 3 Mean weight loss of heat-treated eucalypt wood as a function of temperature and time
Wood Sci Technol (2012) 46:41–52 49
123
(Fig. 5). The results of this study are similar to those reported by Akyildiz and Ates
(2008) for oak (Quercus petraea Lieb.), chestnut (Castanea sativa Mill.), calabrian
pine (Pinus brutia Ten.) and black pine (Pinus nigra Arnold.) woods treated at 130,
0
5
10
15
20
Before Heat Treatment After Heat Treatment
Eq
uili
bri
um
mo
istu
re c
on
ten
t, E
MC
(%
)
180oC 15 min
180oC 2 h
180o o oC 4 h
200 C 15 min
200 C 2 h
200oC 4 h
215oC 15 min
215oC 2 h
215oC 4 h
230oC 15 min
230oC 2 h
230oC 4 h
Fig. 4 Mean equilibrium moisture content of eucalypt wood before and after heat treatment
Fig. 5 Mean equilibrium moisture content reduction in heat-treated eucalypt wood as a function oftemperature and time
50 Wood Sci Technol (2012) 46:41–52
123
180 and 230�C for 2 and 8 h. Their results showed a decrease from 3 to 50% in
EMC with increasing temperature and time for all species studied. The EMC
reduction indicates an improvement in dimensional stability of eucalypt wood
following heat treatment. However, it is important to mention that the heat-treated
wood samples showed some damage such as parallel-to-grain cracks and end
checks, which could have been caused by the heat treatment itself or by the rapid
increase in treatment temperature.
Although chemical analysis was not the purpose of this study, it is important to
mention a few points since these could give some explanation for the results in EMC.
For example, several authors attributed the EMC reduction to degradation of
hemicelluloses, which are the most hygroscopic polymer of wood. Kamdem et al.
(2002) evaluated EMC and lignin content of heat-treated beech, spruce and pine and
reported significant reductions in EMC and lignin content suggesting the hemicellu-
loses degradation. Also, Rowell et al. (2002) stated that hemicelluloses degrades to
produce volatile products and furan-type compounds, which polymerize under heat
to produce water-insoluble polymers, thereby decreasing the hygroscopic nature of
wood.
Conclusion
The major results and conclusions regarding heat treatment of Eucalyptus grandiswood are given below:
1. Heat treatment reduces air-dry density independent of temperature and time.
2. There were significant differences in weight loss for between and within
treatments. The treatment at 230�C for 2 and 4 h produced weight losses of 20.5
and 26.5%, respectively, which were statistically different from the other
treatment conditions.
3. There was a significant reduction (13%) in the dynamic modulus of elasticity in
the most severe treatment (at 230�C for 4 h), but not in the other treatments.
4. The equilibrium moisture content was significantly reduced after heat treatment
in all treatments. Depending on temperature and time conditions, the
equilibrium moisture content was reduced within the range of 40–74%.
5. These results suggest that heat treatment may improve the dimensional stability
of Eucalyptus grandis wood without significantly affecting the dynamic
modulus of elasticity, except for wood treated at 230�C for 4 h.
6. More research is necessary to evaluate the defects produced in the Eucalyptusgrandis wood submitted to heat and the chemical modifications occurring
during the process.
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