Some Physical and Mechanical characterization of Tunisian planted Eucalytusloxophleba and Eucalyptus salmonophloia woods

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Abstract
After the independence in 1957 and with the support of the FAO117, Eucalyptus species were planted in Tunisia in different arboreta throughout the country for close observation and adaptation to climate and soil. The objective of this study is to evaluate the physical and mechanical properties of two species planted in marginal area in Sousse (arboretum El Hanya) in the east of Tunisia (Eucalytus loxophleba and Eucalyptus salmonophloia). The moisture content, specific gravity and volumetric shrinkage were measured. The Mechanical tests were performed to evaluate the hardness, the static bending and the resistance to compression parallel to fiber direction. Preliminary results showed that Eucalytusloxophleba and Eucalyptus salmonophloia have a low dimensional stability. During the drying period, woods showed signs of collapses. On the other hand, both species were highly resistant to compression strength while they were lower on the static bending. Eucalytus loxophleba and Eucalyptus salmonophloia characteristics established within this study were similar to other Eucalyptus species from Tunisia, Morocco, Australia and Brazil. This wood may be used in furniture, structural material and/or biomass energy. Some Physical … Elaieb et al. 538
JCBPS; Section B; February 2017 April 2017, Vol. 7, No. 2; 537-549. E- ISSN: 2249 1929
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537
J. Chem. Bio. Phy. Sci. Sec. B, February 2017 April 2017, Vol. 7, No. 2; 537-549.
Some Physical and Mechanical characterization of
Tunisian planted Eucalytusloxophleba and Eucalyptus
salmonophloia woods
Mohamed Tahar Elaieb1*, Sarra Ben Rhouma1, Ali Khouaja3, Ali Khorchani1,
IssamTouhami1, M.L.Khouja1, Kévin Candelier2*
1 LGVRF, INRGREF, B.P. 10, 2080 Ariana, Tunisia.
2 CIRAD - Unité de Recherches BioWooEB, TA B 114/16, Montpellier, France
3INAT: 43 Avenue Charle Nicole Tunis Belvédère 1002 Tunisia
Received: 24 February 2017; Revised: 11 March 2017; Accepted: 18 March 2017
Abstract: After the independence in 1957 and with the support of the FAO117,
Eucalyptus species were planted in Tunisia in different arboreta throughout the country
for close observation and adaptation to climate and soil. The objective of this study is to
evaluate the physical and mechanical properties of two species planted in marginal area
in Sousse (arboretum El Hanya) in the east of Tunisia (Eucalytus loxophleba and
Eucalyptus salmonophloia). The moisture content, specific gravity and volumetric
shrinkage were measured. The Mechanical tests were performed to evaluate the
hardness, the static bending and the resistance to compression parallel to fiber direction.
Preliminary results showed that Eucalytusloxophleba and Eucalyptus salmonophloia
have a low dimensional stability. During the drying period, woods showed signs of
collapses. On the other hand, both species were highly resistant to compression strength
while they were lower on the static bending. Eucalytus loxophleba and Eucalyptus
salmonophloia characteristics established within this study were similar to other
Eucalyptus species from Tunisia, Morocco, Australia and Brazil. This wood may be used
in furniture, structural material and/or biomass energy.
Keywords: Specific gravity, Eucalytus loxophleba, Eucalyptus salmonophloia,
Mechanical properties, Shrinkage.
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J. Chem. Bio. Phy. Sci. Sec. B, February 2017 April 2017, Vol. 7, No. 2; 537-549.
1. INTRODUCTION
During the colonial period, the Tunisian forest area significantly decreased by human and climatic
aggressions. Indeed, the Tunisian forest area decreased from 1.096 million ha to 844.000 ha between1912
and 1952 illustrating 23% loss during 40 years1.
In a reforestation program with the help of the Food and Agriculture Organization (FAO) after the
independence, quite few Eucalyptus species were planted in different areas of Tunisia. In order to test
their compatibility to climate and soil, many arboreta were settled 2. The objective of this project at the
beginning was for pulp production but the wood produced was then reoriented for industrial use such
particle board MDF and energy. These species were very well adapted to the Tunisian conditions 3,4. In
recent decades, Eucalyptus trees are increasingly used for their essential oils 5 and for honey production.
Nevertheless, in Tunisia, the valorization of Eucalyptus wood remains under estimated and very little
research has been done 6. However the Eucalyptus wood becomes a subject of interest as raw material
for composite panels in many tropical and subtropical countries including Thailand, Chile, Brazil
and Malaysia 7.
According to the FAO, the reforestations based on Eucalyptus covers a surface of 28535 ha in pure
stands and 39000 ha mixed with other species, with an estimated annual Eucalyptus wood production of
120.000 m32. These great efforts of reforestation were undergone in all Tunisia in order to overcome the
land degradation and improve the forest production.
In order to fill the lacks of information concerning Eucalyptus wood properties, the aim of this study is to
characterize the physical (specific gravity, dimensional changes, Fibers Saturation Point) and mechanical
properties (hardness, compression and bending strengths) of two Eucalyptus wood species: Eucalyptus
loxophleba and Eucalyptus salmonophloia, from the arboretum of El Hanyalocated near Sousse in the
east and the semi-arid climate (400 mm rainfall). The results may be useful in reforestation objectives
and forest management strategies.
2. MATERIALS AND METHODS
2.1. Trees selection and sampling:
Eucalyptus loxophleba and Eucalyptus salmonophloia wood species of 50 and 53 years old respectively
were chosen, in this study, to estimate the physical and mechanical properties of Tunisian reforestation
Eucalyptus wood species. 3 trees of each wood species were collected in the “El Hanya” arboretum in the
Sousse region (35°49′ N, 10°38′ E). According to Oger and Lecerq8, the sampling for the determination
of physical and mechanical properties is optimal when the number of sampled trees is comprised between
1 and 5, and should be healthy, free from defects and alteration and have an almost perfectly straight.
The studied site is characterized by a semi-arid bio climate, an annual rainfall of 327 mm/year and
average annual temperatures varying from 14.9 °C to 18.5 °C. The average of maximum temperature of
the warmest month can reach more than 35 °C and the average maximum of the coldest month is around
4 °C. The soil is poorly developed in coastal dunes and leached brown forest in the mountains 9.
2.2. Physical properties
2.2.1. Moisture content, specific gravity and shrinkage: To perform physical and mechanical tests, a
disk 50 mm thick was cut at breast height from each selected tree (Figure 1).The samples were free of
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J. Chem. Bio. Phy. Sci. Sec. B, February 2017 April 2017, Vol. 7, No. 2; 537-549.
defects such tension wood knots, etc10.From each disk, 12 samples of 30 mm width from bark to bark
were cut.
Figure 1: Overview of wood sample selection for the physical and mechanical analyses.
These samples were then cut into strip 20 mm thick. Basic density (Db), Air-dry density (Dm12) [after
conditioning in a climatic room at 20 ±2 °C and 65 ±5% RH] and oven-dry [after drying in an oven at
103°C] density (Dm0) 11, shrinkage (β) [tangential (βt), radial (βr), longitudinal (βl) and volumetric (βv)]12
of the wood samples were determined using wood specimens of 20 × 20 × 10 mm (along the grain). The
Transverse Anisotropy Ratio for Shrinkage (TARS) (β t/ β r) was the ratio between tangential and radial
shrinkage. The densities were determined by the gravimetric method 13.

  
  

Where:
m0= oven-dried weight of the sample (g);
m12= air-dried weight of the sample (g);
Db= basic density of wood (g.cm-3);
Dm0 =oven-dried density of wood (g.cm-3);
Dm12=tair-dried density of wood (g.cm-3);
Vh= green volume of the specimen (cm3);
V0= oven-dried volume of the sample (cm3);
V12 = air-dried volume of wood sample (cm3).
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J. Chem. Bio. Phy. Sci. Sec. B, February 2017 April 2017, Vol. 7, No. 2; 537-549.
Volumetric shrinkage was measured by the following equation (4).
  

Similar operations were used to determine tangential (βt), radial (βr) and longitudinal (βl) shrinkages,
using dimensional variation of the respective orientation.
Figure 2 shows the wood samples repartition for moisture content (a), densities and shrinkages (b)
determination tests.
Moisture content (MC) was calculated by the following equation (5):
  

Where mh is the humid mass of the initial wood sample and m0 is the oven-dried mass of the wood
sample.
Figure 2: Wood sample repartition for moisture content (a), densities and shrinkages (b)
determination tests.
2.2.2. Fibers saturation point (FSP): The Fibers Saturation Point (FSP) of wood is defined as the point
in the drying process at which only water bound in the cell walls remains. An accurate knowledge of the
FSP is important, because at this point the physical characteristics of wood, such as strength, elasticity
and conductivity change markedly. In particular, during drying process of timber, little shrinkage occurs
until the MC is below the FSP.
Forty 50 x 20 x 100 mm (R x T x L) specimens of each wood species were used in this experimental part
to generate shrinkage curves. All specimens were continuously dried at 65°C. During this drying step,
wood samples were taken 2 by 2 (for each wood species), every 15 minutes, to determine the wood
dimensional variations according to the relative humidity evolution. These measurements were
performed until wood samples were dried until their respective mass was stabilized.
(a)
(b)
North
North
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J. Chem. Bio. Phy. Sci. Sec. B, February 2017 April 2017, Vol. 7, No. 2; 537-549.
2.3. Mechanical properties
To perform mechanical resistance tests, three point bending (MOR) and compression tests were carried
out for each wood samples from the selected trees, and results were compared. An INSTRON 4467
Universal Mechanical Test Machine was used for these measurements. Samples were conditioned in a
climate-controlled room with 65±5% RH and at 20±2°C for the time required to stabilize the samples
weights.
2.3.1. Bending test: Three point static bending tests were carried out according to the EN 408 standard14.
The sample size was 300 x 20 mm x 20 mm3 (L x R x T). The moving head speed and span length were
0.09 mm.s-1 and 260 mm, respectively. The load deformation data obtained were analyzed to determine
the modulus of rupture (MOR). The tests were replicated on 20 samples from each selected Eucalyptus
tree.
2.3.2. Compression strength parallel to grain: Compression tests were carried out according to the EN
408 14. Deviating from the standard, a reduced specimen size of 30 x 20 x 20 mm3 (L x R x T) was used.
The moving head speed was 0.09 mm.s-1 to ensure wood sample rupture within 1.5 to 2 minutes. The
load deformation data obtained was analyzed to determine the modulus of rupture (MOR). 20 specimens
per selected tree were tested.
2.3.3. Brinell Hardness (HB): Brinell hardness tests were performed in accordance with EN 408 14. The
force was applied in three steps by a sphere with a diameter of 10 mm. Force was slowly increased by 0.2
kN.s-1 over 15 s. Then, a force of 3 kN was maintained for 25 s before being. Brinell hardness tests were
repeated ten times (five tests for each wood board). Each test was separated by at least 30 mm from the
edge of the wood boards and 25mm from any other test. Ball penetration depth was measured to ± 0.01
mm and applied force was measured to ± 0.005 kN.
3. RESULTS AND DISCUSSION
3.1 Moisture content (MC): Table 1 gives the minimal, maximal and average values of initial moisture
contents of Eucalytusloxophleba and Eucalyptus salmonophloia woods. The initial average Moisture
Contents were 37.1 % for Eucalytusloxophleba wood and 37.8 % for Eucalyptus salmonophloia wood,
with respective minimal values of 21.2 % and 32.3 % and maximal values of 60.8 % and 52.8 %
respectively. In comparison with others Eucalyptus species, the studied samples can be considered as
characterized by low initial moisture content wood when being slaughtered.
Table 1: Average, minimum and maximum wet moisture contents values of EucalytusLoxophleba and
Eucalyptus Salmonophloia woods.
Wood species
Min (%)
Max (%)
Average (%)
SDa (%)
CVb (%)
Eucalytus
loxophleba
21.2
60.8
37.1
6
16.3
Eucalyptus
salmonophloia
32.2
52.8
37.8
3.3
8.8
a Standard Deviation;b Coefficient of Variation.
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