Characterization of Acrocarpus fraxinifolius wood submitted to heat treatment

Abstract

Aiming to provide greater visibility for the wood species Acrocarpus fraxinifolius, the present study sought to analyze the influence of heat treatment on an industrial scale applied to wood species, also popularly known as Indian cedar. The heat treatment was carried out in an autoclave, with temperature and pressure control, and with saturated steam injection, for temperatures 155 ºC, 165 ºC, 175 ºC, and 185 ºC. Physical, chemical, and mechanical tests were carried out for the analyzed wood. The content of holocellulose and total lignin decreased, while the content of extractives showed a substantial increase. The density increased after the heat treatment, however the treated wood showed cracks, and these cracks influenced the significant loss of the values of the mechanical properties of compression, tension, and flexion. The shear showed strength gain for the temperature of 155 ºC, and the wood treated at 165 ºC was equivalent to untreated wood. The woods submitted to temperatures of 175 ºC and 185 ºC presented strength losses. The heat treatment in question contributes to increase the visibility, use and market value of wood.

Full text

ISSN impresa 0717-3644
ISSN online 0718-221X
Maderas. Ciencia y tecnología 2022 (24): 54, 1-12
DOI: 10.4067/s0718-221x2022000100454
1
CHARACTERIZATION OF Acrocarpus fraxinifolius WOOD
SUBMITTED TO HEAT TREATMENT
Carolina A. Barros Oliveira1
https://orcid.org/0000-0002-2253-7322
Karina A. de Oliveira1,♠
https://orcid.org/0000-0001-7307-7912
Vinicius Borges de Moura Aquino2
http://orcid.org/0000-0003-3483-7506
André Luis Christoforo3
https://orcid.org/0000-0002-4066-080X
Julio C. Molina1
https://orcid.org/0000-0002-6204-0206
ABSTRACT
Aiming to provide greater visibility for the wood species Acrocarpus fraxinifolius, the present study
sought to analyze the inuence of heat treatment on an industrial scale applied to wood species, also popularly
known as Indian cedar. The heat treatment was carried out in an autoclave, with temperature and pressure
control, and with saturated steam injection, for temperatures 155 ºC, 165 ºC, 175 ºC, and 185 ºC. Physical,
chemical, and mechanical tests were carried out for the analyzed wood. The content of holocellulose and total
lignin decreased, while the content of extractives showed a substantial increase. The density increased after the
heat treatment, however the treated wood showed cracks, and these cracks inuenced the signicant loss of the
values of the mechanical properties of compression, tension, and exion. The shear showed strength gain
for the temperature of 155 ºC, and the wood treated at 165 ºC was equivalent to untreated wood. The woods
submitted to temperatures of 175 ºC and 185 ºC presented strength losses. The heat treatment in question con-
tributes to increase the visibility, use and market value of wood.
Keywords: Acrocarpus fraxinifolius, chemical analyses, Indian cedar, mechanical properties, thermal
modication, thermal treatment.
INTRODUCTION
With the exploitation of native species prohibited by law in Brazil, one of the alternatives capable of
meeting industrial demand is the management of planted forests with fast-growing species. Currently, 93 % of
the forests planted in Brazil correspond to dierent species of the pine and eucalyptus (IBÁ 2019). However,
to increase the diversity of wood, planting of other species has been introduced in the country.
1São Paulo State University. Department of Mechanical Engineering. Guaratinguetá SP, Brazil.
2Federal University of Southern and Southeastern Pará. Araguaia Engineering Institute. Santana do Araguaia PA, Brazil.
3Federal University of São Carlos. Departamento of Civil Engineering. São Carlos SP, Brazil.
♠Corresponding author: kari.oliveira@outlook.com
Received: 11.11.2020 Accepted: 04.08.2022

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One species that started to be indicated and has been gaining space in reforestation plantations in the North
of Paraná, Southeast and Midwest regions of the country is Acrocarpus fraxinifolius. It is a species native to
Asia, India, Burma and Bangladesh, which was introduced in Brazil in the 1990s, which shows good perfor-
mance and superior growth when compared to plantations in other regions of the world (Carvalho 1998, Higa
and Prado 1998, Prado et al. 2003). This species is known in Asia for mundani and lath tree, and in South
America for pink cedar. In Brazil, the specie became popularly known as Indian cedar (Lorenzi et al. 2003,
Firmino et al. 2015).
Indian cedar produces light and resistant wood, with a density of 438 kg/m³, short bers (1,2 mm), the
productivity of 30 m³/ha year to 45 m³/ha year, reaching 20 meters to 40 meters in height. Its wood is widely
used in civil construction and for the manufacture of furniture and cons (Prado et al. 2003, Lorenzi et al.
2003). However, in Brazil, the specie is still practically unknown, and national studies using the species are
focused on silviculture (Nisgoski et al. 2012, Venturin et al. 2014) and physical and chemical characterization
(Prado et al. 2003). Few studies have been carried out to expand the range of uses of this species, such as the
potential use in OSB panels (Iwakiri et al. 2014), agglomerated wood panels (Trianoski et al. 2013), wood
cement (Oliveira et al. 2020) and other construction applications.
Thus, the present work aimed to characterize the chemical and mechanical properties of Indian cedar
wood, submitted to heat treatment on an industrial scale, carried out in an autoclave, with an application of
heat and pressure, in comparison to untreated wood, seeking to bring more visibility, for the species, in addition
to knowledge and application alternatives for the timber industries, as well as its market value. One way to
increase the use and economic value of Indian cedar wood is to undergo it to heat treatment, which consists of
a procedure used in wood species, which, in their majority, have lighter colors and lower market values.
To perform the heat treatment, the wood is exposed to high temperatures (180 ºC to 280 ºC), usually in
an inert atmosphere, with air deciency or in the presence of water vapor (Homan and Jorissen 2004). Under
these conditions, there are changes in the chemical components of wood, cellulose, hemicellulose, lignin and
extracts (Sundqvist 2004).
Chemical modications benet the wood, by increasing its dimensional stability, hygroscopicity, as well
as increasing biological durability and color change throughout the thickness of the piece, the latter two being
the most coveted benets after heat treatment (Moura et al. 2012, Conte et al. 2014).
The darker color acquired after the heat treatment resembles the tones of tropical woods, replacing the use
of native woods for certain purposes of greater value such as doors, windows, oors, musical instruments, in-
ternal and external furniture, boats, among others, making heat treatment an excellent method for adding value
(Gunduz et al. 2009, Moura and Brito 2011).
Several studies sought to quantify the intensity of color modication in dierent species of wood subjected
to heat treatment, such as for Pinus radiata, Eucalyptus pellita, Tectona grandis, Luehea divaricata, Acacia
auriculiformis, among others. It is observed in these studies that, regardless of the use of dierent heat-treated
species by dierent techniques, uniform browning occurs throughout the thickness of the wood, however with
dierent colorimetric behaviors (Pincelli et al. 2012, Schneid et al. 2014, Zanuncio et al. 2015, Shukla 2019,
Lengowski et al. 2021).
When exposed to sunlight, wood undergoes photooxidation or chemical degradation due to the absorption
of solar radiation and ultraviolet (UV) rays, making it, depending on its chemical composition, more yellowish,
reddish, darkened, pale or greyish, thus compromising its aesthetic appearance (Chang et al. 1982, Ayadi et
al. 2003). Studies have shown that heat treatments can provide greater color stability to wood when exposed
to UV radiation (Ayadi et al. 2003, Garcia et al. 2014), however, the same treatment may not be ecient to
prevent discoloration of dierent woods (Gouveia 2008).
As for the modication of wood color, heat treatment is also considered a preservation method with low
environmental impact due to the non-use of chemical products. After heat treatment, wood becomes more
resistant to fungal decomposition when exposed to the dry rot fungus Serpula lacrymans, white rot fungus
Trametes versicolor, and the brown rot fungi Gloeophyllum trabeum, Coniophora puteana and Postia placenta
(Sivrikaya et al. 2015, Yalcin and Sahin 2015, Salman et al. 2017, Shukla 2019, Kamperidou and Barboutis
2021).

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Increased resistance to termite attack was observed in some, but not all, studied species found in the
literature (Salman et al. 2017, Sivrikaya et al. 2015), as well as the weathering of biotic and abiotic factors
in an external environment (Kamperidou and Barboutis 2021). In order to overcome these disadvantages, the
combination of heat treatment and additional chemical treatment is indicated (Salman et al. 2017).
On the other hand, with the changes in the chemical components of the cell wall of the wood, there is also
a loss of mass and, consequently, a change in the value of mechanical properties, making it impossible to use
heat-treated wood for some structural purposes (Sundqvist 2004, Moura et al. 2012).
The intensity of the changes is the result of a set of variables related to the method used, like as time, tem-
perature, heating cycle and the surrounding atmospheres, and the raw material, like as species, density, initial
moisture content, and extractives content (Sun et al. 2013), being extremely important to characterize dierent
wood species heat-treated by dierent methods.
MATERIALS AND METHODS
Wood
The species used in the present study was the Indian cedar (Acrocarpus fraxinifolius Wight ex Arn.),
With nine years of age, from a plantation in the municipality of Ribeirao Branco, in the interior of the state of
Sao Paulo, southeastern Brazil. The pieces were obtained with dimensions of 6 cm x 16 cm x 3000 cm, and
previously dried at room temperature, until they reached the moisture content of 12 % ± 2 %, for subsequent
performance of the heat treatment.
Heat treatment
The heat treatment was carried out on an industrial scale, in an autoclave, with temperature and pressure
control, and saturated steam injection. Initially, the empty equipment was heated until it reached a temperature
of 100 ºC. Once this temperature was reached, the passage of steam was prevented, and the wooden pieces
were inserted into it.
The thermal treatment was carried out for the following temperatures: 155 ºC, 165 ºC, 175 ºC and 185 ºC.
The maximum pressure used was 735,5 kPa and the heating rate was 1,66 ºC/min. The desired temperature for
the heat treatment was maintained for two hours. Finally, the equipment and the wood cooled simultaneously
to room temperature.
Characterization
The production of the specimens, the mechanical tests, and the density analysis were performed according
to the Brazilian standard ANNEX B of ABNT NBR 7190 (1997). For the mechanical tests, the universal testing
machine EMIC with a capacity of 300 kN, and the software TESC Emic (Instron, Brazil) were used for data
acquisition.
Mechanical tests of compressive strength and stiness (fc0 and Ec0), tensile strength and stiness (ft0 and
Et0), strength and stiness on static bending (fM0 and EM0), and shear strength (fv0) parallel to the bers were
performed.
The apparent density (ρap, 12 %), conventional specic mass, is dened by the ratio between the mass of
the specimen and its volume with the moisture content at 12 %, according to Equation 1, where m12 % is the
mass of the wood at 12 % humidity (g) and V12 % the volume of the wood at 12 % humidity (m³).
(1)
The samples for chemical analysis were obtained according to TAPPI T257-CM-85 (1985). The wood
passed through the grinding process until it passed through particles in a 40 mesh (0,420 mm) sieve using a
chopper and knife mill, both from the MARCONI brand.

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The extractives content was carried out using the TAPPI T264-CM-97 (1997). The removal of the extracts
was carried out in a Soxhlet extractor coupled to a at-bottomed extraction ask, heated by a heating blanket,
carried out in three stages: a) ethanol/toluene extraction for 6 hours; b) 95 % pure ethanol for 5 hours, c) boiling
deionized water for 30 minutes.
After the three steps of removing the extractives, the samples were washed with deionized water, ltered,
and dried in an oven at 103 ºC ± 2 ºC for 24 hours. The extractives content was calculated by Equation 2, where
mi is the initial mass of the absolutely dry sample (g) and mf is the nal mass of the absolutely dry sample (g).
% Extractives 100
mi mf x
mi
−
=
(2)
The determination of the lignin content was carried out by the Klason method, modied by Gomide and
Demuner (1986), called the mini-sample method. The method consisted of treating the sample, free of ex-
tracts, with 72 % sulfuric acid in a water bath at 30 ºC ± 2 ºC for 30 minutes and later, the sample diluted in
84 mL of deionized water is heated in an autoclave at 118 ºC ± 2 ºC, for an hour. The ltered mixture in a
number 2 porosity crucible results in two dierent samples, a solid sample being retained in the crucible and
subsequently oven-dried at 105 ºC ± 3 ºC, for analysis of insoluble lignin, and a ltered liquid sample, for
analysis of soluble lignin.
The insoluble lignin content was calculated by Equation 3, where Pi is the initial weight of the absolutely
dry sample (g) and Pf is the weight of the dry residue (g).
% Insoluble lignin 100
Pf x
Pi
=
(3)
For the determination of soluble lignin, the liquid sample was analyzed by a spectrometer in the ultraviolet
region (UV-VIS) at absorbances of 215 nm and 280 nm, and calculated using Equation 4, where A215 is the
absorbance value at 215 nm, A280 is the absorbance value at 280 nm and ms is the mass of the absolutely dry
sample (g).
4,53 215 280
% Soluble lignin 100
300
xA A x
x ms
−
=
(4)
Holocellulose was calculated by dierence by Equation 5, where Ext is total extractive (%), Lins is
insoluble lignin (%) and Lsol is soluble lignin (%).
( )
%Holocelulose 100 Ext Lins Lsol=−++
(5)
For each heat treatment temperature, as well as for the untreated wood, twelve repetitions were performed
for mechanical tests and density analysis and six for chemical properties analysis.
Statistical analysis
Variation in the density, mechanical and chemical properties of submitted to heat treatment and untreated
wood were compared and analyzed by one-way analysis of variance (ANOVA) at the 5 % level of signicance
using with Minitab statistical software (Minitab Inc., USA).

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RESULTS AND DISCUSSION
The color of the wood is a very important property for the nal consumer, with aesthetics, in some cases,
the determining factor for the selection of a species of wood (Esteves and Pereira 2009). The heat treatment
process used in the present study was able to change and standardize the color of the wood in all its thickness.
Figure 1 shows the eects of the four heat treatment temperatures used (Figure 1b, Figure 1c, Figure 1d
and Figure 1e) in the samples of Indian Cedar, in comparison to untreated wood (Figure 1a).
Figure 1: Color variation of the samples: (a) Untreated and heat-treated at (b) 155ºC, (c) 165 ºC, (d) 175ºC,
and (e) 185 ºC.
The heat-treated samples showed a considerable color change, from light coloration, with yellowish
coloration (untreated wood) to a brownish coloration (heat-treated wood) that gradually darkened with the
increase of the treatment temperature, being the darkest sample obtained with 185 ºC.
Similar changes in the color of the wood were also evident in the studies developed by Cademartori et al.
(2013) for Eucalyptus grandis wood heat-treated in a climate chamber at 180 ºC, 200 ºC, 220 ºC, and 240 ºC
for 4 hours and 8 hours, and by Griebeler et al. (2018) for the same species heat-treated in an autoclave with
steam at 140 ºC, 160 ºC, and 180 ºC.
According to results found in the literature, the darkening of thermally treated wood is caused by the
changes suered by the chemical components of the wood, more specically, by the degradation of holocellu-
lose and extracts, water elimination, formation of carbonaceous coal, and the formation of oxidation products
(Sundqvist 2004, Hill 2006, Esteves et al. 2008, Moura and Brito 2011 and Zanuncio et al. 2015).
The results of the chemical analysis of untreated and heat-treated wood are shown in Table 1.
Table 1: Changes in chemical properties of heat-treated Indian cedar wood at dierent temperatures.
Averages followed by the same letter mean that they do not dier statistically at 5 % probability by Tukey’s test.
Values in parentheses refer to the coecient of variation.
According to the results presented in Table 1, the holocellulose content reduced signicantly for
heat-treated wood in relation to untreated wood. The reduction in the holocellulose content increased from 23,9
% for wood treated at 155 ºC, up to 32,8 % for treatment at 185 ºC. The reduction of holocellulose was also
observed in species of Eucalyptus saligna (Cademartori et al. 2015), Eucalyptus grandis (Cademartori et al.
2015, Batista et al. 2018) and Tectona grandis (Lopes et al. 2022).
According to Santos et al. (2001), holocellulose is the combination of cellulose and other polysaccharides,

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called hemicellulose. Hemicelluloses are dierentiated from cellulose in that they have dierent sugar units in
ve or six carbon atoms.
Therefore, the reduction presented by holocellulose, in the present study, results from the degradation
of the fraction of hemicellulose, since, according to Fengel and Wegener (2003) and Sundqvist (2004), the
heat treatment temperatures used are not high enough to degrade cellulose, which presents a high order in
its crystalline structure and microbrils, and acts as protection against acid attack during hydrolysis. While
hemicelluloses have an amorphous structure and low molecular weight, they are therefore more susceptible to
thermal degradation.
As for the total lignin content, there was no signicant dierence between the means of the untreated wood
and wood heat-treated at 155 °C to 165 °C. Sundqvist (2004) and Soratto (2012) report that lignin is the struc-
tural component of wood that is more resistant to the action of heat, mainly due to the size and complexity of
its structural arrangement, which is able to mitigate the eects produced by high temperatures. For the highest
temperatures, 175 °C and 185 ºC, the total lignin content showed a signicant reduction of 17,5 % and 22,1
%, respectively.
The extractives content gradually increased with the increase in the treatment temperature, from 2,1 %,
of untreated wood, to up to 30,9 %. Increased content of heat-treated wood extractives has been reported in
the literature by Esteves et al. (2011), Batista et al. (2018), Esteves et al. (2022), Lengowski et al. (2021) and
Lopes et al. (2022). It was also observed in the heat treatment of wood particles (Crespo et al. 2014), as well
as in heat treated wood by dierent methods, as in the heat treatment with silicone oil studied by Okon and
Udoakpan (2019).
According to Esteves et al. (2008) and Esteves et al. (2022), the original extracts of the wood are almost
or totally degraded during the heat treatment, with the increase in the content of extracts observed related to
the changes caused in the lignin content and mainly in the degradation of hemicellulose, which results in the
formation of new chemical compounds, which are extracted during extractives analysis.
Table 2 shows the values obtained for the apparent density, and the mechanical properties of stiness and
compressive strength (Ec0 and fc0), stiness and tensile strength (Et0 and ft0), stiness and strength on static
bending (EM0 and fM0), and shear strength (fv0) parallel to the bers, for untreated and heat-treated wood.
Table 2: Changes in mechanical properties of heat-treated Indian cedar wood at dierent temperatures.
Averages followed by the same letter mean that they do not dier statistically at 5 % probability by Tukey’s test. Values in parentheses
refer to the coecient of variation.
A signicant increase was observed in the apparent density of heat-treated Indian cedar wood in relation
to untreated wood. The increase in wood density after heat treatment was also observed for Eucalyptus grandis
heat treated species in an oven at 140 ºC, 160 ºC and 180 ºC by Brito et al. (2006) and at 200 °C and 230 °C
by Batista et al. (2011).
With the degradation of the chemical components of the cell wall of the wood, it was expected that the
density would decrease, as already observed in the literature for the species of Eucalyptus grandis (Calonego
et al. 2014, Batista et al. 2018), Eucalyptus camaldulensis (Unsal and Ayrilmis 2005) and Carpinus betulus L.
(Gunduz et al. 2009). However, Brito et al. (2006) suggested that the increase in heat treatment temperature
was not enough to promote mass loss in the same proportion as the reduction in wood volume.

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It is also observed that the highest density occurred for the heat treatment at 155 °C and later decreased for
the other temperatures, which did not present signicant dierences, we can consider that, probably, the heat
treatment caused the volumetric contraction of the wood and the increase in the temperature used increased the
quantity and/or size of the internal cracks of the pieces, which previously did not exist in the untreated wood,
as can be seen in the regions indicated by the arrows in Figure 2 for the transversal cut of the wood, and in
Figure 3 for the longitudinal cut. These cracks may have contributed to the density reduction and to the loss
of mechanical resistance of the woods submitted to heat treatment.
Figure 2: Cross-section: (a) Untreated wood and (b) Heat-treated wood.
Figure 3: Longitudinal section: (a) Untreated wood and (b) Heat-treated wood.
It should be noted that the monitoring of wood ssures was not the subject of the present study, as well
as the evaluation of mass loss and volumetric contraction of heat-treated wood. Therefore, the explanations
oered are only indicative and, therefore, could only be proven by carrying out more specic studies on the
themes. We emphasize that such analyzes contribute to the scientic qualication of the intensity of the heat
treatment performed.
In general, the mechanical properties were negatively inuenced after heat treatment. The mechanical
properties of compressive strength and stiness (fc0, Ec0), tensile strength (ft0, Et0), and static bending (fM0, EM0)
parallel to the bers, showed signicant reductions, since the property of shear strength parallel to the bers
(fv0), presented strength gain for the rst heat treatment temperature, followed by reductions for the other
studied temperatures.
Reduction in the compressive strength property was also observed by Gunduz et al. (2009) for the wood
of Carpinus betulus, where the greatest loss of strength recorded was 34 % for the treatment at 210 ºC for 12
hours. The same was also observed by Korkut et al. (2008) for Pinus sylvestris wood, the greatest reduction
occurred for treatment at 180 ºC for 10 hours, 25,4 %. Gunduz et al. (2008) reported a maximum reduction
of 27,2 % for the species of Pinus nigra treated, and Unsal and Ayrilmis (2005) reduction of 19,0 % for the
species Eucalyptus camaldulensis, both for treatment at 180 ºC for 10 hours.

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Elaieb et al. (2015), observed similar reduction values of strength and stiness to static bending parallel to
the bers for the species of Pinus halepensis, Pinus radiata, Pinus pinaster and Pinus pinea, heat-treated under
a vacuum atmosphere at 230 ºC, reductions of up to 50 % stiness and up to 70 % strength.
When studying the species of Pinus taeda heat-treated in an electric oven with an inert atmosphere of
nitrogen gas at 180 ºC, Silva et al. (2013) observed a 25 % gain in shear strength for the treatment time of 30
minutes, and for wood treated for 120 minutes, no signicant dierence was found with untreated wood.
On the other hand, Moura et al. (2012) observed a reduction of 23,7 % for Pinus caribea wood heat-treated
at 200 ºC, for the other treatment temperatures studied (140 °C, 160 °C, and 180 ºC) there were no signicant
changes in this property.
The reductions in mechanical properties presented by heat-treated wood are strictly related to the thermal
degradation of the chemical constituents of the cell wall of the wood, especially hemicelluloses (Sundqvist
2004, Moura et al. 2012). In addition, as mentioned above, the cracks in the treated wood also inuenced the
reduction of these properties.
Unfortunately, there are no other studies on Acrocarpus fraxinifolius wood heat-treated in an autoclave,
which makes it dicult to eectively compare the results, however, comparisons with dierent species and
heat treatment processes are important to understand the results obtained.
CONCLUSIONS
The Indian cedar wood (Acrocarpus fraxinifolius) showed uniform browning after the heat treatment in
an autoclave with water vapor and under pressure, allowing the use of the species for aesthetic and decorative
purposes.
After the heat treatment, the wood showed small cracks that may have contributed to the loss of
mechanical strength. The reductions in the mechanical properties of compressive strength, tensile strength, and
static bending parallel to the bers, make it dicult to use for purposes that demand high mechanical strength.
The observed reductions for mechanical properties were up to 53,5 % for strength and 57,4 % for stiness
compression parallel to the bers; 80,2 % for strength and 52,9 % for stiness parallel to the bers; 73,5 % for
strength and 67,0 % for stiness static bending parallel to the bers.
The strength to shear parallel to the bers showed a gain of 64,3 % for heat treatment at 155 ºC, for other
temperatures there was a reduction of up to 55,9 %.
As for the chemical properties, the holocellulose content decreased signicantly with the heat treatment, a
reduction of up to 32,8 %. The total lignin content did not show signicant changes for the heat-treated woods
at 155 °C, 165 °C, and 175 ºC, the maximum reduction was 22,1 %. There was a signicant increase in the
content of extractives, from 9,5 times to 14,5 times more than untreated wood.
It is recommended to carry out tests of color stability and biological resistance, for a better understanding
of the inuence and intensity of the heat treatment.
ACKNOWLEDGMENTS
This work was carried out with the support of the Coordination for the Improvement of Higher Education
Personnel - Brazil (CAPES) - Financing Code 001.

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