Indonesian Journal of Forestry Research Vol. 12 No. 1, April 2025, 135-149

ISSN 2355-7079/E-ISSN 2406-8195

THE SURFACE CHARACTERISTICS AND PHYSICAL PROPERTIES
OF SENGON WOOD AT HIGH-TEMPERATURE HEATING
TREATMENTS
Tushliha A. Fariha1, Sari D. Marbun2, Sudarmanto3, Narto3, Adik Bahanawan3,
Prabu S. Sejati3, Teguh Darmawan3, Dimas Triwibowo3, Danang S. Adi4,
Yusup Amin3, Sarah Augustina3, Wahyu Dwianto3, Rita K. Sari5, Irsan Alipraja5,
Imam Wahyudi5, and EM. Latif R. Kusuma6
Master Student, Faculty of Forestry and Environment, IPB University, Bogor 16680, Indonesia
Faculty of Forestry, Tanjungpura University. Jl. Prof. Dr. H. Hadari Nawawi, Pontianak 78124, Indonesia
3
Research Center for Biomass and Bioproducts, National Research and Innovation Agency,
Jl. Raya Bogor Km 46, Cibinong 16911, Indonesia
4
Research Center for Applied Botany, National Research and Innovation Agency,
Jl. Raya Bogor Km46, Cibinong 16911, Indonesia
5
Faculty of Forestry and Environment, IPB University, Bogor 16680, Indonesia
6
CV. Rubby Jaya Karya, Jl. Poros Desa Bukit Kemuning, Kec. Tapung Hulu,
Kab. Kampar, Riau, Indonesia
1

2

Received: 03 November 2023 , Revised: 29 January 2025, Accepted: 6 March 2025
THE SURFACE CHARACTERISTICS AND PHYSICAL PROPERTIES OF SENGON WOOD AT
HIGH-TEMPERATURE HEATING TREATMENTS. Sengon (Falcataria moluccana Miq.) is a fast-growing
timber species widely distributed in Indonesia. However, its dimensional instability and low surface quality
have limited its widespread use. Wood modification is essential for enhancing these properties, and one
effective approach is heat treatment. This study investigated the effects of different heat treatment methods
and durations on color change, surface roughness, weight loss (WL), decreased density, and dimensional
stability of sengon wood. The heat modification process was conducted using two methods: oven-heating
and hot press-heating, with temperatures set at 200°C for durations ranging from 1 to 5 hours. The results
indicated that oven-heated samples exhibited higher surface roughness, weight loss, density reduction,
and dimensional stability while showing less color change than hot press-heated samples. Additionally,
the hot press-heated samples displayed more significant color changes (darkening) and smoother surface
roughness. WL and decreased density were also more pronounced with longer heating durations, except
for the 4- and 5-hour hot press-heating treatments. Notably, oven-heated samples demonstrated higher
dimensional stability than hot press-heated samples as the duration of heating increased. Based on the
results, the optimal treatment varies depending on the desired product characteristics. For improved surface
qualities with consideration of WL, the optimum treatment is a 2-hour hot press-heating treatment. Higher
dimensional stability can be achieved through a 3-hour oven-heating treatment.
Keywords: Surface characteristic, heat treatments, sengon, physical properties
KARAKTERISTIK PERMUKAAN DAN SIFAT FISIS KAYU SENGON PADA PERLAKUAN PANAS
DENGAN SUHU TINGGI. Sengon (Falcataria moluccana Miq.) merupakan salah satu jenis tanaman cepat tumbuh
yang tersebar luas di Indonesia. Namun, stabilitas dimensi dan kualitas permukaan yang rendah mengakibatkan kayu sengon
tidak dapat diaplikasikan secara luas. Modifikasi kayu diperlukan untuk memperbaiki sifat-sifat tersebut, salah satunya
dengan perlakuan panas. Penelitian ini menganalisa pengaruh metode dan durasi pada penerapan perlakuan panas yang
berbeda terhadap perubahan warna, kekasaran permukaan, penurunan berat (WL), penurunan kerapatan, dan stabilitas
dimensi kayu sengon. Proses modifikasi panas dilakukan menggunakan dua metode, yaitu oven dan hot-press. Pemanasan
dilakukan pada suhu 200°C selama 1 hingga 5 jam. Hasil penelitian menunjukkan bahwa sampel yang dipanaskan dengan
oven memiliki kekasaran permukaan, kehilangan berat, penurunan kerapatan, dan stabilitas dimensi yang lebih tinggi,
*

Corresponding author: sara012@brin.go.id rita_kbu@yahoo.com

©2025 IJFR. Open access under CC BY-NC-SA license. doi:10.59465/ijfr.2025.12.1.135-149

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Indonesian Journal of Forestry Research Vol. 12 No. 1, April 2025, 135-149

ISSN 2355-7079/E-ISSN 2406-8195

namun menghasilkan perubahan warna yang lebih rendah dibandingkan dengan sampel yang dipanaskan dengan hot-press.
Sementara itu, sampel yang dipanaskan dengan hot-press menunjukkan perubahan warna yang lebih signifikan (lebih gelap)
dan permukaan yang lebih halus. WL dan penurunan densitas meningkat seiring bertambahnya durasi pemanasan, kecuali
untuk perlakuan hot-press selama 4 dan 5 jam. Seiring bertambahnya durasi pemanasan, sampel kayu yang dipanaskan
dengan oven menunjukkan stabilitas dimensi yang lebih tinggi dibandingkan dengan sampel yang dipanaskan dengan hotpress. Berdasarkan hasil penelitian, perlakuan yang optimal tergantung pada tujuan produk akhir. Untuk meningkatkan
karakteristik permukaan dengan pertimbangan WL, perlakuan yang optimal adalah pemanasan dengan hot press selama 2
jam. Sementara itu, peningkatan stabilitas dimensi terbaik dapat dihasilkan dari perlakuan pemanasan oven selama 3 jam.
Kata kunci: karakteristik permukaan, perlakuan panas, sengon, sifat fisis

I. INTRODUCTION
Fast-growing species have emerged as viable
plantation forest commodities, serving as
alternative raw materials sources for the woodbased industry in Indonesia. These species are
characterized by their rapid growth rates, shortcutting cycles, and high productivity, as well as
their ability to act as pioneer species for openland rehabilitation and reforestation (Alamsyah
et al., 2007; Augustina et al., 2023; Nuraini et
al., 2023). Sengon (Falcataria moluccana Miq.)
is a fast-growing species recognized for its
lightweight wood, with a specific gravity range
of 0.24 to 0.49 and a strength class of IV-V
(Martawijaya et al., 1989). However, the latter
species is susceptible to wood-destroying
agents due to its low durability (durability class
IV-V). The wood contains more juvenile than
mature wood, contributing to its dimensional
instability (Rahayu et al., 2021). Currently,
the utilization of sengon wood is limited to
lightweight construction, pulpwood, furniture,
and plywood. Therefore, a technological
approach is necessary to enhance its properties
and broaden its applications.
Heat treatment is the oldest wood
modification technique. It offers several novel
properties, including higher dimensional
stability, increased resistance to wood-destroying
agents (such as fungi and microorganisms), an
aesthetically pleasing dark color, lower moisture
content, improved water resistance, and
improved thermal insulation properties (Yildiz
et al., 2006; Sivrikaya et al., 2015). This process
is typically carried out at temperatures ranging

136

from 150 to 240°C for 15 minutes to 24 hours
(Chu et al., 2016; Hill et al., 2021). According
to Hill et al. (2021), thermal conditions applied
below 150°C are defined as thermal aging; those
between 150 and 240°C are classified as thermal
modification; and temperatures above 240°C are
categorized as thermal degradation. In the early
stages of heat treatment, the temperature of
wood increases rapidly. Free water evaporates at
a temperature around 100°C. Meanwhile, some
water vapor will move deeper into the wood,
distancing itself from the heating surface. This
moisture transport generates three distinct
zones: a dry zone near the surface closest to
the heat source, a dehydrating zone, and a wet
zone (Bartlett et al., 2019; Zhang et al., 2017).
Generally, the wood surface (dry zone) has a
slightly higher temperature increase than the
inside (dehydrating zone and wet zone). The
wood surface is unable to attain the ambient
temperature because of thermal resistance
during the heat convection process (Zhang
et al., 2017). The heat treatment alters the
wood’s chemical composition, resulting in
the degradation of hemicellulose, lignin, and
certain extractives (Salca & Hiziroglu, 2014).
Over the last decade, numerous researchers
have explored various heat treatment methods.
These applications include complex processes
such as the ThermoWood, Plato, Rectification,
and Le Bois Perdure/Perdure processes, which
generally utilize vacuum and/or steam under
air (oxygen) or inert gas (nitrogen) conditions.
Other methods include oil heat treatment, which
employs oil as a heat transfer medium without

The Surface Characteristics and Physical Properties of Sengon Wood .........................(Tushliha A. Fariha et al.)

oxygen (Esteves & Pereira, 2009; Korkut &
Budaksci, 2010; Sanberg et al., 2012; Rajković
& Miklečić, 2019), microwave heat treatment
(Mascarenhas et al., 2021), oven treatment
(Yildiz et al., 2006; Kučerová et al., 2016),
and hot pressing in an open system (Qiaofang
et al., 2019; Ding et al., 2022). Although the
more complex methods are preferable for
producing commercially viable products, they
require sophisticated equipment and intricate
procedures. Consequently, simpler methods are
more suitable to apply by small and medium
enterprises (SMEs).
During heat treatment, several surface
characteristics and physical properties of
wood can be altered due to the severity of
heat exposure, which varies with temperature
and duration. Yildiz et al. (2006) studied heattreated spruce (Picea orientalis) wood in an oven
at temperatures of 130, 150, 180, and 200°C
for 2, 6, and 10 hours, respectively. Their results
indicated that the equilibrium moisture content
(EMC) decreases with elevated temperature
and prolonged heat exposure. Consequently,
the treated wood exhibited reduced shrinkage
and swelling behavior, enhancing dimensional
stability. Kučerová et al. (2016) investigated
oven heating European silver fir (Abies alba
L.) wood for 1 hour at various temperatures
(100, 150, 200, 220, 240, 260, and 280°C).
Their findings showed that color changes in the
wood became more noticeable at temperatures
between 200 and 220°C. Moreover, significant
mass loss was noted above 200°C attributable
to hemicellulose degradation, removal of
volatile compounds, and loss of certain
extractives. Ding et al. (2022) examined heattreated Douglas fir (Pseudotsuga menziesii) using a
hot press at 200°C for 380 and 480 minutes and
reported that the treated wood became darker
and hydrophobic in the surface layer, ultimately
improving its dimensional stability. Qiaofang et
al. (2019) treated rubberwood (Hevea brasiliensis)
using a hot press for 1.5 and 3 hours at several
temperatures (170, 185, and 200°C), observing
that the treated wood exhibited higher oven-

dried density, lower EMC, and more excellent
dimensional stability.
It is interesting to observe the straight
forward technologies, such as the oven and hotpress system, and comparing their effectiveness
when applied to fast-growing wood species,
particularly sengon wood (Falcataria moluccana
Miq.). Therefore, this study aimed to evaluate
two heating methods, utilizing an oven and a
hot press system at 200°C, with heat exposure
durations ranging from 1 to 5 hours. The
investigation focused on assessing the impact
of these treatments on various surface quality
characteristics, including color changes and
surface roughness, as well as physical properties
such as weight loss, decreased density, and
dimensional stability. This procedure may
provide an alternate method to improving
these properties, potentially increasing the
value of sengon wood and allowing its use as
a substitute material with quality comparable to
other commercially available wood species.
II. MATERIAL AND METHOD
A. Materials
This study used sengon wood (Falcataria
moluccana (Miq.) Barneby & Grimes) with a
30-35 cm diameter (5-6 years) sourced from
Bogor, West Java, Indonesia. The lower section
of the sengon wood was processed into boards
comprising heartwood and sapwood sections,
measuring 300 cm (length) x 12 cm (width) x
6 cm (thickness). The boards were acclimatized
to ambient temperature (moisture content
12-15%). Subsequently, the boards were cut
into the dimensions of 30 cm (length) x 5 cm
(width) x 2 cm (thickness) and were then sanded
with a 400-grit belt sander to standardize the
surface roughness. The samples were analyzed
for various properties, including color changes,
surface roughness, weight loss (WL), and
density reduction. After treatment, the samples
were cut into the dimension of 2 cm (length) x
2 cm (width) x 2 cm (thickness) and subjected
to dimensional stability testing. The sample
preparation process is presented in Figure 1.

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Indonesian Journal of Forestry Research Vol. 12 No. 1, April 2025, 135-149

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Figure 1. Samples preparation process

B. Methods
Each air-dried sample had its initial weight
and dimensions measured. Subsequently, the
samples were subjected to high-temperature
treatment using two different heating
techniques: oven and hot press (Denes & Lang,
2013; Kučerová et al., 2016; Qiaofang et al.,
2019; Ding et al., 2022). The heating process
was conducted at 200°C for 1, 2, 3, 4, and 5
hours. After treatment, the samples were airdried until they achieved a constant weight.
Each sample was re-weighed and re-measured.
The treated samples were evaluated for
color change, surface roughness, weight loss,
decreased density, and dimensional stability,
with three repetitions for each test parameter.

and after heat treatment, with three repetitions
for each sample. The analysis of color changes
was carried out using the CIE Lab and CIE Lch
methodologies, which included measurements
of L* (brightness), a* (red-green), b* (yellowblue), c* (chroma), and h* (hue) values. In
order to determine the differences in ∆L*, ∆a*,
∆b*, ∆c*, and ∆h*, the measurements of the
untreated wood sample (control) and the treated
wood sample were compared using Equations
(1)–(5). The total color differences (∆E_Lab*
and ∆E_Lch*) were computed using Equations
(6) and (7), as described by Bessala et al. (2023).
The classification of color change is presented
in Table 1, as reported by bNguyen et al. (2018).
...........................(1)
...........................(2)
...........................(3)
...........................(4)
...........................(5)
........(6)
........(7)

a. Color changes
The discoloration of the wood samples
was measured using a Konica Minolta CR 10
colorimeter, equipped with a D65 light source,
photodiode array sensor, and 10° observer
standard. Measurements were performed before
Table 1. Classification of color changes
The value of color changes
<0.2
0.2<

<2

2<

<3

3<

<6

6<

<12
≥12

138

Classification of color changes
No noticeable difference
Minor difference
Color differences were noticeable on a high-quality screen
Color differences were noticeable on a medium-quality screen
Significant difference
Distinct colors

The Surface Characteristics and Physical Properties of Sengon Wood .........................(Tushliha A. Fariha et al.)

b. Surface roughness
The surface roughness was measured before
and after treatment samples utilizing a surface
roughness tester (Mitutoyo SJ-210). The
measurements were executed according to the
International Organization for Standardization
(2021), with a cut-off length of 0.8 mm, a path
length of 6 mm, and a speed of 0.5 mm/s.
Measurements were taken at 10 points with
three repetitions. The parameters for analysis of
surface roughness included average roughness
(Ra), mean peak-to-valley height (Rz), and root
mean square deviation of the profile (Rq). Data
points from each wood sample were collected
and averaged to obtain the final measurements.
c. Weight loss
The wood samples were weighed before
and after treatment, with three repetitions for
each measurement. The calculation of weight
loss (WL) involved determining the difference
in weight between the untreated wood sample
(W0) and the treated wood sample (W1), as
shown in Equation (8) (Bessala et al., 2023).
Each test for weight loss was performed with
three repetitions.
...........................(8)

d. Density reduction
Density ( ) was determined by dividing the
weight of the sample (w) by its volume (V). The
density measurements were taken before and
after treatment, with three repetitions for each
measurement. The objective was to quantify
the decrease in density following the heating
process. The initial density was calculated
using Equation (9). In contrast, the decrease in
density ( ) was determined by subtracting the
final density after heating ( ) from the initial
density ( ), as indicated in Equation (10)
(Bessala et al., 2023).
..........................................(9)
.............................(10)

e. Dimensional stability
After the heat treatments, wood samples
(treated and untreated) with dimensions of 2
cm x 2 cm x 2 cm analyzed for dimensional
stability. They were placed in an oven at 103
± 2°C for 24 hours. The samples were then
weighed and measured to obtain its mass and
volume. The samples were then completely
immersed in water at room temperature for
24 hours. The weight and dimensions of the
wood samples were reassessed after immersion
and drying in an oven at 103 ± 2°C for another
24 hours (Rowell & Ellis, 1978; Sargent,
2019). The difference between the volumetric
swelling coefficient of untreated wood samples
(S0) and treated wood samples (S1), as shown
in Equation (11), was used to calculate antiswelling efficiency (ASE). Meanwhile, water
absorption (WA) was calculated by comparing
the weight of the wood samples before
immersion ( ) and after immersion ( ), as
shown in Equation (12).
................................(11)
................................(12)

C. Analysis
The experimental design was entirely
randomized. Data were presented as mean values
with standard deviations. Analysis of variance
(ANOVA) was used to assess the treatmentaffected color changes, surface roughness,
weight loss, density reduction, and dimensional
stability in both untreated and treated wood. A
subsequent Duncan’s test (significance level P
< 0.05) was conducted if the ANOVA results
indicated a significant impact of the treatment
on each response. The SPSS software was used
to examine the data.
III. RESULT AND DISCUSSION
A. Color changes
Generally, untreated wood samples have a
light color (Nemoto, 2002). Unfortunately, this
light color is less attractive to some consumers,

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Indonesian Journal of Forestry Research Vol. 12 No. 1, April 2025, 135-149

encouraging many modifications, such as heat
treatment, to change the color (Ciritcioğlu et al.,
2017; Hidayat et al., 2017). Throughout the heat
treatment process, the wood samples eventually
change to a darker color as the temperature
and length of treatment increase. According
to Hill (2006), the intensity of color change
is influenced by various factors, including the
heating technique, temperature, and duration
of exposure. This phenomenon also varies
between oven and hot press-heating treatments.
The color change in heated wood samples after
hot press-heating was only observed on the
upper surface, whereas oven-heating resulted
in homogeneous color changes throughout the
entire wood sample, as shown in Figure 2 (a).
This difference may be due to the distinct heat
exposure mechanisms during these treatments.
In hot-press-heating, the principal mechanism
is conduction, which involves the transfer of
heat energy from the hot-press iron plate to the
wood surface. This process is limited to the top
area of the wood samples. According to Cengel
(2002), conduction occurs when heat energy is
transferred, resulting in mutual interaction that
facilitates higher thermal transfer and more
pronounced heat-induced discoloration. In
contrast, the mechanism during oven-heating
is convection, which involves the transfer of
heat between the circulating gas and the solid
wood constituents (Cengel, 2002). As a result,

ISSN 2355-7079/E-ISSN 2406-8195

all parts of the wood samples are heated.
The values of color changes in the wood
samples subjected to both heating treatments
are presented in Table 2. It can be seen that
the parameter values of L*, a*, b*, c*, and h*
of the oven-heated wood samples exhibited
higher values than those of the hot pressheated wood samples. These values were
inversely proportional to the ∆E*(Lab) and
∆E*(Lch) values, with the hot press-heating
treatment yielding higher values than the ovenheating treatment. The lightness value (L*) was
observed to decrease due to discoloration at
200 °C, leading to an overall color change (∆E*)
and resulting in a darker appearance (Denes
& Lang, 2013). The color change ranges, as
measured by ∆E*(Lab) and ∆E*(Lch), were
10.5–25.2 and 10.8–25.4 for the oven-heating
treatment, and 27.3–38.7 and 27.7–39.2 for
the hot press-heating treatment, respectively.
According to the color classification provided
in Table 1 (bNguyen et al., 2018), it can be
observed that most samples exhibited a color
difference classification of ∆E*≥12, except
for the oven-heating treatment for 1 hour,
which fell within the range of 6<∆E*<12. The
findings suggest that applying heat treatment
through hot press-heating resulted in a more
pronounced color change than oven-heating,
as visualized in Figure 2 (b). These results are
contrary to the research by Denes and Lang

(a)

(b)
Figure 2. The changes in color on (a) cross-section and (b) surface of oven-heated and hot press-heated
wood samples

140

The Surface Characteristics and Physical Properties of Sengon Wood .........................(Tushliha A. Fariha et al.)

(2013), which observed that the oven-heated
yellow poplar (Liriodendron tulipifera L.) veneer
was darker than the hot-pressed red oak (Quercus
rubra L.) veneer treated for the same durations
(10, 20, and 30 minutes). This difference in
results is likely due to the significant variation in
treatment duration. Direct exposure to heat (hot
press) for a longer time allows for more color
darkening due to hemicellulose degradation
(Denes & Lang, 2013).
According to Table 2, the color changes (∆E*)
were influenced by longer treatment durations.
Extended treatment duration correlates with a
more significant color change observed. Similar
color changes due to heat treatment methods
and durations have been reported for lime
wood. Lime (Tilia cordata Mill.) wood was ovenheated treatment at 200°C for 1, 2, 3, and 4
hours, resulting in ∆E*(Lab) values of 37.13,
45.14, 50.17, and 53.09, respectively (Olarescu

et al., 2014). A longer duration of treatment
is associated with a corresponding darkening
of the wood samples during the process
(Piernik et al., 2002; aNguyen et al., 2018). The
observed color change indicates the occurrence
of chemical decomposition within the wood
constituents, including hemicellulose, lignin,
and extractives (Williams, 2005). According to
previous studies, temperatures exceeding 190°C
have a detrimental effect on hemicellulose
content (Denes & Lang, 2013; Kacˇikova et
al., 2013). Furthermore, volatile compounds
evaporate when temperatures reach 200°C or
higher, and chemical compounds decompose
(Bekhta & Niemz, 2003; Sivrikaya et al., 2019).
The decrease in hemicellulose, particularly
pentosan, results in the reduction of measurable
color coordinates. This phenomenon ultimately
leads to discernible color changes (Bourgois et
al., 1991).

Table 2. Parameters of color changes in untreated and heated wood samples at different methods and
duration of treatments
Heating
Methods
Untreated
Oven

Time
(h)
1
2
3
4
5

Hot-press

1
2
3
4
5

L*
72.3a ±
1.52
62.8b±
2.8
57.9c ±
2.8
55.5d ±
1.2
50.6e ±
1.1
51.1e ±
1.1
46.8f ±
3.7
39.8g ±
1.9
37.2h ±
2.3
33.1i ±
0.9
35.9h ±
1.1

a*
7.7c ±
1.13
8.2c ±
0.4
9.2b ±
0.3
10.5a ±
0.4
10.9a ±
0.2
10.9a ±
0.1
9.7b ±
0.5
7.6cd ±
1.0
6.9d ±
1.0
3.6f ±
0.6
4.8e ±
0.6

Parameters of Colors Changes
b*
c*
h*
17.4c ± 19.0e ± 66.2b ±
1.51
1.82
1.42
b
cd
20.6 ± 22.2 ± 68.4a ±
0.7
0.7
1.0
21.0ab ± 22.9bc ± 66.4b ±
0.5
0.5
0.9
22.4a ± 24.7a ± 64.9c ±
0.6
0.7
0.5
21.6ab ± 24.2ab ± 63.1d ±
0.6
0.6
0.4
21.7ab ± 24.3ab ± 63.4de ±
0.4
0.3
0.5
c
d
18.4 ± 20.8 ± 62.3ef ±
1.8
1.7
1.6
13.1d ± 15.1f ± 60.1hi ±
1.8
2.0
0.2
11.6e ± 13.5g ± 59.3i ±
2.0
2.2
0.6
6.4g ±
7.3i ±
61.0gh ±
0.9
1.1
1.2
f
h
8.9 ±
10.1 ± 61.3fg ±
1.1
1.2
0.5

∆E*(Lab)
-

∆E*(Lch)
-

10.5f ±
1.4
15.7e ±
1.2
22.3d ±
4.0
23.8d ±
0.8
25.2cd ±
0.6
27.3c ±
3.3
37.8b ±
4.2
38.1b ±
2.9
43.1a ±
2.7
38.7b ±
1.4

10.8f ±
1.5
15.7e ±
1.2
23.1d ±
5.2
24.0d ±
0.9
25.4cd ±
0.7
27.7c ±
3.5
39.1b ±
4.6
39.0b ±
3.0
43.9a ±
3.3
39.2b ±
1.4

Notes: The superscript letters signify the degree of statistical significance (P < 0.05). The various superscript letters denote
significant differences in means between treatments and vice versa.

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Indonesian Journal of Forestry Research Vol. 12 No. 1, April 2025, 135-149

B. Surface roughness
Table 3 shows the observed surface
roughness parameters, which were Rq, Rz, and
Ra. The oven-heated wood samples generally
exhibited higher Rq, Rz, and Ra values than the
hot press-heated wood samples. In contrast, the
decrease in Ra, Rz, and Rq values for the ovenheated samples (5.67–17.09%) was lower than
that for the hot press-heated samples (4.86–
50.84%). This phenomenon was also observed
in the heat treatment process of rubber (Hevea
brasiliensis) wood, where the surface roughness
of samples heated in the oven decreased less
than that of the hot press samples. The Ra
value for a rubber wood oven-heated at 180°C
for 2 hours decreased by 38.4% (Ratnasingam
& Ioras, 2012). This decrease in Ra was lower
than that of hot-pressed rubber wood, which
decreased by 42.59% and 48.74% at 185°C for
1.5 and 3 hours, respectively (Zhu et al., 2021).
These results could be attributed to difference
mechanism in heat treatment method applied.
The oven method utilizes convection to transfer
heat, exposing the sample’s wood surface to the
hot air within the oven. In the hot press method,
heat is transferred through conduction, with
the hot plate in direct contact with the sample’s
surface, allowing a direct heat reaction and

ISSN 2355-7079/E-ISSN 2406-8195

decreasing the wood surface's roughness. Heat
treatment softens the wood fibers in the surface
layer, causing the cell walls to plasticize. This
leads to an enhancement in surface smoothness
(Ayrilmis et al., 2019; Zhu et al., 2021).
Furthermore, surface roughness decreased
with the extension of the heat treatment
duration, as presented in Table 3. Wood
samples that underwent heat treatment for
1 hour exhibited an average decrease in the
Rq, Rz, and Ra values of 6.14–7.32%, 8.77–
9.37%, and 4.86–5.67%, respectively. The
reduction in surface roughness continued with
the treatment duration, reaching a maximum
after 5 hours. Heat treatment for 5 hours
resulted in average decreases in Rq, Rz, and
Ra values of 17.66–52.96%, 19.28–59.18%,
and 17.66–50.84%, respectively. A similar
decrease in surface roughness due to duration
was seen in oriental beech wood treated to
heat treatment at 200°C for 2, 4, and 8 hours,
with reductions of Rq (10.13%, 16.85%, and
37.40%), Rz (8.29%, 17.15%, and 42.01%),
and Ra (12.60%, 17.56%, and 35.53%) (Basyal
et al., 2014). A decrease in Ra of around 10%
was also noted in short rotation teak heated at
200°C for 2 hours (Martha et al., 2021). This
reduction is attributed to alterations in the

Table 3. Parameters of surface roughness in untreated and heated wood samples at different methods and
duration of treatments
Heating
Methods
Untreated
Oven

Hot-press

Time t (h)
1
2
3
4
5
1
2
3
4
5

Parameters of Surface Roughness
Ra (µm)
Rq (µm)
Rz (µm)
10.40a ± 0.21
13.48a ± 0.48
74.61a ± 4.05
9.81b ± 0.23
12.49b ± 0.21
67.62b ± 2.97
b
bc
9.73 ± 0.65
12.42 ± 0.72
66.11b ± 3.40
bc
b
9.57 ± 0.41
12.50 ± 0.65
68.79b ± 2.52
9.04cd ± 0.09
11.67cd ± 0.14
64.28bc ± 1.04
d
de
8.62 ± 0.20
11.10 ± 0.14
60.23cd ± 1.44
9.90b ± 0.12
12.65b ± 0.24
68.07b ± 2.66
e
ef
7.73 ± 0.07
10.36 ± 0.16
57.65d ± 1.14
e
f
7.52 ± 0.11
9.70 ± 0.12
53.01e ± 0.09
6.34f ± 0.53
8.14g ± 0.46
44.74f ± 3.01
g
h
5.11 ± 0.24
6.34 ± 0.30
30.45g ± 0.73

Notes: The superscript letters signify the degree of statistical significance (P < 0.05). The various superscript letters
denote significant differences in means between treatments and vice versa.

142

The Surface Characteristics and Physical Properties of Sengon Wood .........................(Tushliha A. Fariha et al.)

biochemical constituents of the cell wall, which
become more pronounced with increasing
heating duration (Bakar et al., 2013; Basyal et
al., 2014). Additionally, surface roughness can
be influenced by multiple factors, such as wood
species, cutting direction (radial, longitudinal,
or tangential), annual ring width, juvenile and
mature wood, cellular composition, machining
conditions, and cutting characteristics (Sogutlu,
2005; Karagoz et al., 2011; Dundar et al., 2008).
The significant decrease in the Ra value
indicates a progressive increase in the
smoothness of the wood surface. This
phenomenon arises from heat treatment, which
induces plasticization of the wood surface by
modifying the glass transition (Tg) temperature
of the lignin (Korkut et al., 2009) and facilitating
the migration of waxy and fatty substances
from axial parenchyma cells to the outer surface
(Nuopponen et al., 2003). A smoother wood
surface can enhance adhesion between surfaces
and improve the contact angle for wettability
(Krystofiak et al., 2022). Additionally, it can
improve the quality of wood surfaces and
reduce the cost losses associated with sanding
and planning operations (Dundar et al., 2008;
Korkut et al., 2009).
C. Weight loss and density reduction
The analysis of weight loss and density
reduction is important because it indicates the
quality of the treatment (Candelier et al., 2016).
The weight loss showed a positive correlation
with the treatment time, as illustrated by the
data in Figure 3(a). During the 1–5 hours heat
treatment period, weight loss ranged from
12.16% to 15.76% for the oven-heated wood
samples and 8.82% to 12.61% for the hot pressheated wood samples. Olarescu et al. (2014)
indicated that weight loss in lime wood escalated
with heat treatment duration at 200°C for 1 to
4 hours, approximately 4.3% to 9.3%. Notably,
air-dried sengon wood exhibited significantly
higher weight loss than oven-dried lime wood,
as the air-dried sengon wood samples had a
higher initial water content, resulting in greater
evaporation during heating. The initial weight

loss during the heating process can be ascribed
to the evaporation of water molecules and
the breakdown of heat-sensitive substances,
particularly hemicellulose (Aydin & Colakoglu,
2005; Esteves et al., 2008). Furthermore, it
was found that the oven-heating treatment
resulted in greater weight loss than the hot
press-heating treatment. This is reasonable, as
the oven treatment affected the entire wood
surface, while the hot-press treatment primarily
influenced only the top-most surface layer.
Moreover, heat treatment has been observed
to decrease wood density. The untreated wood
sample’s air-dry density is 0.29 g/cm³. Following
a heating period of 1 to 5 hours, the density
decreased. After oven-heating, the wood
density varied from 0.19 to 0.22 g/cm³. The
density positively correlates with the reduction
of density, which varied from 9.42% to 12.89%.
When the wood hot press-heated, its density
decreased by around 3.46% to 8.81%, varying
from 0.21 to 0.28 g/cm³. Similar decreases in
density were observed in heat-treated wood
at 200°C for 2 hours; for example, scots
pine (Pinus sylvestris L.) experienced a density
decreased by 18.41% (Kamperidou et al., 2014),
while poplar (Populus beijingensis W. Y. Hsu) had a
density decreased by 11.17% (Chu et al., 2016).
Additionally, heat-treated beech wood (Fagus
orientalis Lipsky) at 200°C for a duration of 1, 2,
and 3 hours exhibited density losses of 11.17%,
13.68%, and 15.04%, respectively (Percin, 2016).
Extending heat treatment duration enhances
the degradation of various wood chemical
components of wood, including hemicellulose,
lignin, and particularly in the amorphous regions
of cellulose, leads to the formation of microcracks that eventually reduce wood density
(Nabil et al., 2018). Other factors contributing
to density reduction include the evaporation
of extractive substances, overall weight loss,
and a decrease in equilibrium moisture content
(EMC) (Korkut & Kocaefe, 2009; Pelit et al.,
2018).
The decrease in density of oven-heated
samples was more significant than that of the
hot press-heated samples, as illustrated by the

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Indonesian Journal of Forestry Research Vol. 12 No. 1, April 2025, 135-149

(a)

(

ISSN 2355-7079/E-ISSN 2406-8195

(b)

Figure 3. Weight loss (a) and density reduction (b) of the oven-heated ( ;
) and hot press-heated
;
) wood samples. Columns lacking identical superscript letters exhibit significantt differences (p <
0.05).

Figure 4. Relationship between density reduction and weight loss of oven-heated ( ● ) and
hot press-heated ( ● ) wood samples

data in Figure 3 (b). A notable reduction in
density occurred during the heating process for
1 to 2 hours in both treatments. Following this
period, the density values for the oven-heated
samples showed a slight increase during the 3
to 5-hour treatment. In contrast, a continued
decrease in the density occurred of the hot
press-heated wood samples during the 4 and
5-hour treatments. This phenomenon can be
attributed to the reduction in wood dimensions,
particularly on the surfaces of the samples
subjected to hot press-heating. The surfaces of
these samples were charred and degraded, as
shown in Figure 3 (b), leading to a decrease in
the overall volume and consequently affecting
its density.
This finding is supported by a positive
correlation between the decrease in density and
144

weight loss, as shown in Figure 4. A positive
connection is shown between the percentage
decrease in density and weight loss for the
oven-heating treatment (y = 0.7997x - 0.092; R²
= 0.9981) and the hot press-heating treatment
(y = 0.5518x + 0.7016; R² = 0.5758). Notably,
the oven-heating treatment demonstrates a
higher correlation (R² value) compared to the
hot press-heating treatment. This difference
may be attributed to the effect of oven-heating
on the entire wood surface, which enhances
the evaporation of water molecules and the
breakdown of heat-sensitive components.
In contrast, the hot press-heating treatment
primarily affects only the top-most layer of the
wood's surface.

The Surface Characteristics and Physical Properties of Sengon Wood .........................(Tushliha A. Fariha et al.)

D. Dimensional stability
Dimensional stability is a crucial factor to
consider when addressing the shrinkage caused
by the hygroscopic nature of wood. The
dimensional stability was assessed by measuring
the water absorption (WA) and anti-swelling
efficiency (ASE) values. Heat treatment
application reduced WA values and increased
ASE values for the wood samples, as shown in
Figure 5. Compared to hot press-heated wood
samples, oven-heated wood samples had lower
WA values, ranging from 76.93% to 83.34%.
The ASE values for wood samples subjected
to hot press-heating ranged from 24.92% to
32.63%, while those from oven-heating ranged
from 32.71% to 51.46%. This indicates that
oven-heated samples exhibit lower WA values
and higher ASE than hot-pressed samples. This
difference occurs because all wood samples’s
surfaces are exposed to heat during oven-heat
treatment, whereas hot press-heating typically
only affects one side/surface of wood samples.
The findings indicated that the WA value
negatively correlates with heating duration,
while the ASE value shows a positive correlation,
as illustrated in Figure 5. As the length of heat
treatment extended, the WA value diminished.
After 1 hour of heat treatment, the WA values
ranged from 79.36% to 80.65%, decreasing
further to 56.63% and 77.30% after 5 hours. A
similar negative correlation between WA and
heating duration was observed in ash wood

(a)

(Fraxinus angustifolia Vahl.), where the WA
values decreased with longer treatment times.
Specifically, wood heated at 190°C for 3, 6,
and 9 hours exhibited WA values of 42.33%,
41.21%, and 39.54%, respectively (Sahin &
Guler, 2018). Prolonged heating duration
causes hemicellulose degradation and hydroxyl
groups in cellulose amorphous areas to break
down, which reduces hygroscopicity (Weiland
& Guyonnet, 2003).
The decrease in water absorption (WA)
values positively correlates with dimensional
stability, as measured by anti-swelling efficiency
(ASE). The ASE value also shows a positive
correlation with heat treatment duration. Wood
samples heated for 1 hour exhibited ASE
values ranging from 24.92% to 32.71%, which
increased to 32.63% to 51.46% after 5 hours
of heating. The highest ASE value, recorded at
51.46%, was observed in wood samples heated
in an oven for 5 hours. Similar results were
reported in the research by Sahin and Guler
(2018), where the ASE value of ash wood
heated at 190°C for 9 hours was 49.44%. These
findings can be explained by the decreased
hygroscopicity of wood and the modification
of its chemical components during the heating
process (Martha et al., 2021), particularly in
hemicellulose. Hemicellulose degradation
releases organic acids, which reduce hydroxyl
(OH) cross-links within the wood structure.
This reduction in hydroxyl cross-links increases

(b)

Figure 5. Water absorption (a) and anti-swelling efficiency (b) of oven-heated ( ;
) and
hot press-heated ( ;
) wood samples. Columns lacking identical superscript letters exhibit significant
diffrences (p < 0.05)

145

Indonesian Journal of Forestry Research Vol. 12 No. 1, April 2025, 135-149

the hydrophobicity of the wood, thereby
enhancing its dimensional stability (Bekhta &
Niemz, 2003; Bakar et al., 2013). Furthermore,
the migration of extractive substances to the
wood surface has been shown to impede water
penetration (Hill, 2006).
IV. CONCLUSION
Heat treatment of sengon wood resulted
in a darker color, improved surface roughness,
increased weight loss, decreased density, and
enhanced dimensional stability. However, the
differences in heat treatment techniques—
oven versus hot press—led to varying changes
in the characteristics of sengon wood. Ovenheating treatment relies on convection, allowing
heating across the entire wood surface. In
contrast, hot press-heating treatment utilizes
conduction, influencing solely the sample area
in direct contact with the heated iron plate.
Consequently, hot press-heated wood samples
exhibited a darker color, smoother surface
roughness, lower weight loss, reduced density,
and decreased dimensional stability compared
to oven-heated wood. Additionally, longer
heat treatment durations generally result in
more distinct color darkening, lower surface
roughness, greater weight loss, decreased
density, and enhanced dimensional stability.
Based on these findings, treatment selection
depends on the desired outcome. If the goal
is to enhance surface characteristics while
considering weight loss, the optimal treatment
is hot press-heating for 2 hours. Conversely,
if the aim is to improve dimensional stability,
oven-heating for 3 hours is recommended.
Overall, the resistance of heat-treated samples
to organism attack presents an area for potential
future research.
ACKNOWLEDGMENTS
We express our profound gratitude to the
Research Center for Biomass and Bioproducts,
National Research and Innovation Agency
(BRIN), Indonesia, for providing research
facilities and to Talent Management BRIN for

146

ISSN 2355-7079/E-ISSN 2406-8195

conducting the Research Assistance Program.
We also acknowledge The Research Organization
for Nanotechnology and Materials-National
Research and Innovation Agency (BRIN) for
funding support through the 2024 research
grant. We also greatly appreciate CV Ruby Jaya
Karya for the collaboration in developing this
research method.
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