Eur. J. Wood Prod. (2014) 72:547–549 DOI 10.1007/s00107-014-0796-6
BRIEF ORIGINAL
Effect of accelerated aging on selected physical and mechanical properties of Bambusa rigida bamboo Xing Yan Huang • Jiu Long Xie • Jin Qiu Qi Jian Feng Hao • Ni Zhou
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Received: 29 November 2013 / Published online: 18 April 2014 Ó Springer-Verlag Berlin Heidelberg 2014
Abstract Bambusa rigida bamboos were subjected to accelerated aging test, and the main physical and mechanical properties before and after aging were comparatively investigated. The results revealed that the aged bamboos lost parts of their original physical and strength properties. Furthermore, mechanical strength properties and basic density of both control and aged specimens increased significantly with the height of the culms, while that for the volumetric shrinkage was reverse. The effect of accelerated aging on the properties of base portion specimens was much more significant than that of the middle and top portions.
1 Introduction Recently, bamboo has become one of the most important non-timber forest products. This is mainly because of its rapid growth rate, renewable nature, high productivity, short maturity period, and multiple uses. Information on physical and mechanical properties of bamboo is important in assessing its suitability for various end-products. For example, the physical properties such as basic density and volumetric shrinkage are considered to be important factors in determining the suitability of bamboo for bamboo floor application and chemical treatment process. X. Y. Huang J. L. Xie J. Q. Qi (&) J. F. Hao N. Zhou College of Forestry, Sichuan Agricultural University, Ya’an 625014, Sichuan, China e-mail:
[email protected] X. Y. Huang e-mail:
[email protected] J. L. Xie e-mail:
[email protected]
Accordingly, the physical and mechanical properties of woody materials can be changed after aging, and methods including long-term (outdoor exposure test) and short-term tests (accelerated aging test) have been used in evaluating the changes in wood properties of woody materials. The accelerated aging test, compared to the outdoor exposure test, is a much more readily method due to the fact that it could be finished within a short time and conducted in an interior place where temperature and humidity are controllable. According to literature (Kojima and Suzuki 2011), the bending properties of wood-based panels with accelerated aging treatment are the same as those with 5 years’ outdoor exposure. Although pilotscale evaluation of wood and bamboo as structural materials has been previously studied using accelerated aging treatment (Kojima and Suzuki 2011; Tomak et al. 2012), there are still limited studies on the evaluation of bamboo properties with respect to aging. Thus, in this study, the physical and mechanical properties of Bambusa rigida bamboo, both before and after accelerated aging treatment were comparatively investigated. The object of this study was to provide a primary understanding of the effect of accelerated aging on bamboo properties.
2 Materials and methods Four-year-old Bambusa rigida bamboos were collected from a bamboo plantation near Yibin, Sichuan, China. Branches and top parts of the culms were removed, followed by subdividing the main culm into three portions (base, middle and top). Thereafter, the culms were transported to the laboratory and stored for air drying until the moisture content of the culms was 14 %. Samples with dimensions of 200 mm 9 35 mm 9 culms wall thickness for the determination of physical and mechanical properties were exposed to accelerated aging
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Eur. J. Wood Prod. (2014) 72:547–549
Table 1 Effect of accelerated aging on selected physical and mechanical properties of Bambusa rigida bamboo Height portion Control
Aged
D (g cm-3)
S (%)
SS (MPa)
CS (MPa)
MOR (MPa)
MOE (GPa) 15.5
Base
0.60
15.8
11.5
69.1
170.3
SD
0.04
0.6
0.2
3.0
12.6
1.9
Middle
0.69
14.3
12.3
82.3
204.6
17.7
SD
0.02
0.5
0.7
2.7
7.7
1.3
Top
0.79
12.5
13.1
87.9
214.3
19.6
SD
0.07
0.5
0.3
2.2
6.3
0.8
Mean
0.69
14.2
12.3
79.8
196.4
17.6
Base
0.59
14.0
8.7
58.2
131.2
12.5
SD
0.03
0.6
0.6
3.7
12.4
0.8
Middle
0.67
13.9
9.7
72.7
189.1
16.9
SD Top
0.06 0.75
0.5 11.3
0.5 11.9
4.4 85.3
11.3 205.6
0.9 18.4
SD
0.05
0.6
0.7
2.1
6.6
0.9
Mean
0.67
13.1
10.1
72.1
175.3
15.9
D represents basic density, S volumetric shrinkage, SS shear strength, CS compressive strength, MOR is modulus of rupture and MOE modulus of elasticity
test. The accelerated aging test was carried out in accordance with the standard method ASTM D 1037-99 (ASTM (1999). The procedure consists of 6 cycles of the following sequence: soaking in water for 1 h at 50 °C, steaming at 95 °C for 3 h, and freezing at -12 °C for 20 h, drying at 100 °C for 3 h, steaming at 95 °C for 3 h, and drying at 100 °C for 18 h. In total 12 days were required. After accelerated aging procedure, the specimens were conditioned at 22 °C and 65 % relative humidity for 6 weeks prior to testing. The studies on physical and mechanical properties were carried out according to methods outlined by Tran (2010) and Zhang et al. (2013). Physical properties include basic density (D, g cm-3) and volumetric shrinkage (S, %). Mechanical properties, including shear strength (SS, MPa), compressive strength (CS, MPa), modulus of rupture (MOR, MPa) and modulus of elasticity (MOE, GPa) were determined using universal Testing Machine RGM-4100. A three point bending test in culm wall direction was conducted. Thirty replicates were carried out for each portion samples. Statistical analysis was carried out using SAS (version 9.1, SAS Institute, Cary, NC). Analysis of variance (ANOVA) was performed to determine significant differences (a = 0.05) among the different samples.
3 Results and discussion The basic density of both control and aged specimens significantly increased from the base to top, while the volumetric shrinkage significantly decreased, which was
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consistent with the findings by Xie et al. (2012). The higher density observed in the middle and top portions may be attributed to the denser vascular bundles of these portions. As shown in Table 1, the basic density and volumetric shrinkage of the aged specimens was lower than that of the controls. The largest decrease in basic density was observed for the specimens from the top portion, and significant reduction in the volumetric shrinkage was observed at the base portion (decreasing rate, 11.0 %). The reason for the reduction in basic density and volumetric shrinkage may be because of the decomposition of hemicelluloses, which could be caused by thermal treatment (Tuong and Li 2011). Furthermore, steam pretreatment can also cause partial hydrolysis of hemicelluloses in both hardwoods and softwoods (Hsu et al. 1988). Meanwhile, the low molecular weight substances, such as tannins, gums and starches extracted by hot water during water and steam cycles may also contribute to the density reduction. As can be seen from Table 1, mechanical properties including SS, CS, MOR, MOE of both control and aged specimens significantly increased with culm height. The results of the variation in mechanical properties along the culm height were similar to the findings by Xie et al. (2012). Compared to the control specimens, the mechanical properties of the aged specimens were lower. The difference in mechanical properties between the control and aged specimens from the base and top portions were not significant, while the accelerated aging treatment significantly affected the mechanical properties of the specimens from the base portion. The mean values of reduction for SS, CS, MOR and MOE after aging were 18.0, 10.1, 11.5 and 10.0 %, respectively.
Eur. J. Wood Prod. (2014) 72:547–549
Accordingly, the reduction in SS, CS, MOR, and MOE of wood specimens with thermal treatment was related to the chemical changes, such as degradation or depolymerization of hemicelluloses and cellulose (Zou et al. 1994; Zhang et al. 2013). Since high temperature or steam was also involved in the accelerated aging cycles, it could be concluded that the reduction in mechanical properties with accelerated aging test is somewhat related to the variation in chemical components before and after the treatment. However, to further clarify the effect of accelerated aging treatment on the mechanical properties it is necessary to investigate the chemical components. Such experimentation is under consideration.
4 Conclusion The basic density and mechanical properties of both control and aged specimens significantly increased from the base to the top. The volumetric shrinkage decreased significantly with height portion. Accelerated aging significantly affected the mechanical properties of the specimens from the base portion, and the mean values of reduction for the S, SS, CS, MOR and MOE after aging were 11.0, 18.0, 10.1, 11.5 and 10.0 %, respectively. Moreover, the basic density of the aged specimens was about 2.0–5.3 % lower than that of the controls. In addition, maximum reductions for volumetric shrinkage and mechanical properties were found in the base portion.
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