Ảnh hưởng của tuổi đến sự biến đổi các tính chất vật lý và cơ học của gỗ keo tai tượng (Acacia mangium) trồng tại Thái Nguyên

round and air-dried in two 
months. From each log, small specimens (20 20 320 mm, Radial Tangential 
Longitudinal) were cut at three distances from pith (10, 50, and 90 % of the radial length from 
pith) on four sides (north, south, east, west) for measuring air-dry density (AD), modulus of 
rupture (MOR), and modulus of elasticity (MOE) as described in Figure 1. For 7-year-old trees, 
in each radial direction, small specimens were only cut at two positions: near the pith and near 
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 TNU Journal of Science and Technology 226(01): 50 - 56 
the bark corresponding to 10 and 90% radial positions because of small diameter. The specimens 
were conditioned in a room at a constant temperature (20°C) and relative humidity (60%) to 
constant weight. 
 Table 1. Diameter and height of sample trees 
 Trees D1.3 (cm) Hvn (m) 
 Age 7 
 1 14.0 14.0 
 2 15.6 16.0 
 3 16.6 15.0 
 4 17.2 17.5 
 5 15.9 17.0 
 Age 10 
 6 23.1 17.5 
 7 24.6 16.8 
 8 25.3 16.2 
 9 23.9 18.6 
 10 22.7 19.8 
 Age 14 
 11 18.8 16.2 
 12 24.2 16.5 
 13 27.4 17.0 
 14 24.5 21.0 
 15 23.6 20.4 
 Note: D 1.3 - diameter at breast height (at 1.3 m above the ground), H vn - tree height 
 Figure 1. Method of cutting specimens for experiment from each tree 
2.2. Measuring wood properties 
 AD, MOR, and MOE were assessed in accordance with Vietnamese Industrial Standards 
(TCVN) as described by Duong et al. [6]. AD was determined in according TCVN 8048-2:2009 
(ISO 3131:1975), while MOR and MOE were measured in according to TCVN 8048-3:2009 
(3133:1975) and TCVN 8048-4:2009 (ISO 3349:1975), respectively. Twenty samples were 
randomly chosento test moisture content (MC) after measuring mechanical properties. The 
average MC of the test specimens was 12 ± 0.18%. 
2.2. Data analysis 
 The data in this study was analysed by using the R software (R Core Team) version 4.0.2 [7]. 
Tukey-Kramer HSD test was used for comparing wood properties among the age groups. 
3. Results and Discussions 
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 TNU Journal of Science and Technology 226(01): 50 - 56 
3.1. Variation in AD from the pith to bark 
 Table 2 presents the mean values of AD at 10, 50, and 90 % radial length from the pith to bark 
in trees of Acacia mangium 7-, 10-, and 14-year-old planted in Thai Nguyen. Results of ANOVA 
analysis are also presented in Table 2 to exam that there are significant differences in AD among 
radial positions or not. 
 The mean AD for 7-, 10-, and 14-y-old trees varied from 0.45 to 0.51 g/cm3, 0.47 to 0.54 
g/cm3, and 0.48 to 0.56 g/cm3, respectively (at MC 12%). The findings of the present study are in 
agreement to those in literature. Phi [1] reported an AD of 0.43 – 0.56 g/cm3 of A. mangium 
grown in Binh Duong, Vietnam. In addition, Chowhury et al. [5] reported the mean AD of 10-
year-old A. mangium planted in Bangladesh was 0.52 g/cm3 that is similar with AD observed for 
trees of age 10 in this study. 
 Table 2. Mean of air-dry density (g/cm3) and results of statistical analysis among radial positions in 
 different ages 
 Radial position (%) 
 Age p-value 
 10 50 90 
 7 0.45b ± 0.04 0.51a ± 0.02 *** 
 10 0.47b ± 0.05 0.53a ± 0.03 0.54a ± 0.03 *** 
 14 0.48b ± 0.05 0.55a ± 0.03 0.56a ± 0.03 *** 
Note: a,b,c Mean with different superscript within a row significant difference; ***: p < 0.001 
 The result of ANOVA analysis showed that AD for 7-y-old A. mangium wood was the lowest 
near the pith and the highest near the bark. In 10- and 14-y-old trees, the radial variation pattern 
for AD was similar. AD increased rapidly from the pith to position of 50% radial length before 
becoming constant towards the bark (Table 2). The radial pattern of variation from pith to 
periphery of AD has been reported for A. mangium wood. Makino et al. [4] reported the radial 
variation for basic density of 5- and 7-y-old A. mangium trees planted in Indonesia. Basic density 
gradually increased to about 6 cm from the pith before stabilizing. Kim et al. [8] reported a 
similar pattern of AD for Acacia hybris planted in northern Vietnam. On other hand, Wahyudi et 
al. [9] reported a nearly constant basic density of Azadirachta excelsa from pith to bark. Based on 
the present results and previous reports, radial variation of AD depends on species. 
3.2. Radial variations in mechanical properties 
 Table 3 presents the mean mechanical properties at 10, 50, and 90% radial length from the 
pith of 7-, 10-, and 14-year-old A. mangium trees planted in Thai Nguyen. The mean MOR for 7-
year-old trees at 10 and 90% radial length was 56.73 and 73.05 MPa. The mean MOR for 10- and 
14-year-old trees varied from 61.94 to 76.16 MPa and from 65.13 to 77.99 MPa, respectively. 
Obtained results in the present study were similar to those in previous studies. Shari et al. [10] 
investigated the static bending strength of 6-y-old A. mangium trees planted in different sites. 
This study reported that the overall MORs of A. mangium planted in Indonesia, Malaysia, and 
Thailand were 75.02, 68.15, and 80.54 MPa, respectively. 
 The mean MOE for 7-, 10-, and 14-year-old varied from 6.56 to 8.17 GPa, 7.45 to 9.55 GPa, 
and 7.75 to 10.14 GPa, respectively. Shari et al. [10] also reported that the mean MOE of 6-y-old 
A. mangium trees planted in Indonesia, Malaysia, and Thailand were 6.73, 6.29, and 6.17 GPa, 
respectively. 
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 TNU Journal of Science and Technology 226(01): 50 - 56 
 Table 3. Mean of mechanical properties and results of statistical analysis among radial positions in 
 different ages 
 Radial position from pith (%) 
 Mechanical properties Age p-value 
 10 50 90 
 7 56.73b ± 11.14 73.05a ± 6.47 *** 
 MOR (MPa) 10 61.94b ± 14.67 76.39a ± 11.96 76.16a ± 10.00 ** 
 14 65.13b ± 15.62 77.75a ± 13.30 77.99a ± 9.98 ** 
 7 6.56b ± 0.71 8.17a ± 0.94 *** 
 MOE 
 10 7.45b ± 1.26 9.29a ± 1.07 9.55a ± 0.65 *** 
 (GPa) 
 14 7.75b ± 1.10 9.55a ± 1.07 10.14a ± 0.88 *** 
Note: Note: a,b,c Mean with different superscript within a row significant difference; 
**: p < 0.01; ***: p < 0.001 
 The radial variation patterns for MOR and MOE were similar to those for AD (Table 3). In 
age of 7, the result of statistical analysis showed that there was a significant difference in MOR 
between two positions (near the pith and near the bark). In 10- and 14-y-old trees, MOR and 
MOE increased considerably to the middle position before remaining constant value forward to 
outside (Table 3). Fujimoto et al. [11] reported that the compression strength increased from the 
pith to 5 cm, after which it was almost constant in 30-y-old A. mangium. This pattern is also seen 
in other hardwood species. Machado et al. [12] investigated the radial variation in MOR and 
MOE of Acacia melanoxylon wood. Authors showed that MOR and MOE increased rapidly from 
pith to 50% radial position before stabilizing. This trend may be contributable to the thicker walls 
of fibers in the mature wood than those in the juvenile wood. 
3.3. Effect of age on variation in AD, MOR, and MOE 
 The mean AD for 7-, 10-, and 14-y-old A. mangium trees was 0.48, 0.51, and 0.53 g/cm3, 
respectively (Table 4). The AD increased with increasing tree age. The average AD of 14-year-
old trees increased about 4% compared to that of 10-year-old trees and about 10% compared 7-
year-old trees. However, the analysis of variance indicated that, there is only significant 
difference between AD of age 7 and AD of age 10 and 14, while no significant difference was 
found between AD of age 10 and AD of age 14. 
 Table 4. Physical and mechanical properties in different ages, ANOVA, and Tukey test results 
 Wood Age 
 p-value 
 properties 7 10 14 
 AD (g/cm3) 0.48b ± 0.04 0.51a ± 0.05 0.53a ± 0.05 *** 
 MOR (MPa) 64.38b ± 10.55 71.59a ± 13.92 73.46a ± 14.44 ** 
 MOE (GPa) 7.31b ± 1.15 8.77a ± 1.38 9.10a ± 1.43 *** 
Note: a,b,cMean with different superscript within a row significant difference; 
**: p < 0.01; ***: p < 0.001 
 The mean MOR for 7-, 10-, and 14-y-old A. mangium trees was 64.38, 71.59, and 73.46 MPa, 
respectively. The mean MOE for 7-, 10-, and 14-y-old A. mangium trees was 7.31, 8.77, and 9.10 
GPa, respectively (Table 4). The analysis of variance also indicated that there was no significant 
difference in MOR and MOE between age 10 and age 14, while tree age did have a significant 
effect to MOR and MOE from 7 to 10 years. The results in this study will be an important 
reference for forest growers whether to extent planting time of A. mangium after 10 years or not. 
3.4. The relationship between AD and mechanical properties 
 Coefficients of correlations (r) for relationship between AD and mechanical properties of A. 
mangium planted in Thai Nguyen are summarized in Table 5. AD had significant (p < 0.001) 
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 TNU Journal of Science and Technology 226(01): 50 - 56 
positive linear correlations with MOR in all age levels. Correlation coefficient between AD and 
MOR is 0.72 when combined ages (Figure 2). AD had also significant positive linear 
relationships at the 0.001 confidence level with MOE in all age levels (Table 5). For combined 
ages, the value of correlation coefficient between AD and MOE is 0.78 (Figure 3). The above 
results suggest that AD can be considered to be a powerful indicator for predicting the static 
bending strength of A. mangium planted in Thai Nguyen. Prediction models of mechanical 
properties (MOR, MOE) for A. mangium clear wood in different ages and combined ages are 
presented in Table 5. 
 Table 5. Prediction models of static properties (MOR, MOE) for Acacia mangium wood 
 Modelling Age Equation r p-value 
 7 MOR = 210.89 × AD – 36.05 0.79 *** 
 MOR (MPa) 10 MOR = 243.99 × AD – 53.74 0.82 *** 
 (~AD) 14 MOR = 156.61 × AD – 9.54 0.65 *** 
 Combined ages MOR = 193.44 × AD – 28.28 0.72 *** 
 7 MOE = 21.20 × AD – 2.78 0.73 *** 
 MOE (GPa) 10 MOE = 21.95 × AD – 2.50 0.75 *** 
 (~AD) 14 MOE = 20.13 × AD – 1.57 0.72 *** 
 Combined ages MOE = 23.05 × AD – 3.22 0.78 *** 
Note: ***: p < 0.001 
Figure 2. Relationship between air-dry density (AD) Figure 3. Relationship between air-dry density (AD) 
 and modulus of rupture (MOR) for combined ages and modulus of elasticity (MOE) for combined ages 
 Wood density is an important indicator of the static bending strength properties of wood. The 
present results are comparable with those reported by Makino et al. [4] who found the positive 
correlation of basic density with mechanical properties of A. mangium planted in Indonesia. In 
other hardwood species, Duong and Matsumura [13] found strong positive correlations of AD 
with MOR (r = 0.84) and MOE (r = 0.72) at MC about 12% in Melia azedarach planted in Son 
La, Vietnam. Positive linear relationships between AD and mechanical properties were also 
reports by Machado et al. [12] for Acacia melanoxylon wood. 
4. Conclusions 
 a. Tree age had significantly affected on physical and mechanical properties investigated in this 
study. AD, MOR, and MOE increased rapidly from age 7 to age 10 before stabilizing to age 14. 
 b. In radial direction, AD, MOR, and MOE were lower near the pith and higher near the bark 
in all age levels. In 10- and 14-year-old, wood properties determined in this study increased 
considerably from pith to the middle position before remaining constant value forward to outside. 
 c. AD had a significant positive linear relationship with mechanical properties (MOR, MOE). 
Therefore, AD can be considered to be a powerful indicator for predicting the static bending 
strength of A. mangium planted in Thai Nguyen. 
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