Abstract
The anatomical, physical, and mechanical properties of 13 Malaysian bamboos and the trend of these properties along the bamboo culms’ height were examined. The results showed that these properties varied between the 13 species and they were also affected by the culm height. From the results obtained, the fibre morphology, as well as radial, longitudinal, and tangential shrinkage from green to oven-dry decreased from the basal to the top of the bamboo culm. In contrast, the opposite trend was observed for the density, modulus of rupture, modulus of elasticity, and percentage of the vascular bundle. The potential usage of 13 bamboo species is also considered.
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Anatomical, Physical, and Mechanical Properties of Thirteen Malaysian Bamboo species
Nordahlia Abdullah Siam,* Mohd Khairun Anwar Uyup, Hamdan Husain, Abd Latif Mohmod, and Mohd Fahmi Awalludin
The anatomical, physical, and mechanical properties of 13 Malaysian bamboos and the trend of these properties along the bamboo culms’ height were examined. The results showed that these properties varied between the 13 species and they were also affected by the culm height. From the results obtained, the fibre morphology, as well as radial, longitudinal, and tangential shrinkage from green to oven-dry decreased from the basal to the top of the bamboo culm. In contrast, the opposite trend was observed for the density, modulus of rupture, modulus of elasticity, and percentage of the vascular bundle. The potential usage of 13 bamboo species is also considered.
Keywords: Anatomical properties; Physical properties; Strength properties; Malaysian bamboo
Contact information: Forest Research Institute Malaysia, 52109 Kepong, Selangor, Malaysia;
* Corresponding author: nordahlia@frim.gov.my
INTRODUCTION
Bamboo is considered a fast-growing plant that is widely used for the manufacture of handicrafts, baskets, furniture, and general merchandise. The use of bamboo has evolved from traditional to more value-added products. According to Xing et al. (2015), bamboo can be regarded as the best alternative for replacing timber because bamboo has high strength and is fast-growing. As stated by Krause and Ghavami (2009), bamboo in its round form demonstrates excellent mechanical properties that make it useful for the construction industry and can reduce the need for steel. Bamboo is a cylindrical, usually hollow, light-weight, and functionally-graded material that demonstrates optimal characteristics for building truss elements that are frequently used in civil construction. In addition, Xing et al. (2015) reported that bamboo is an important raw material for housing and bridge construction in China. Bamboo has also been used in a wide range of engineering and civil construction applications including scaffolding, fiber-reinforced composites, and bridges (Tan et al. 2011). Because the uses of bamboo have become more diversified, it is important to understand the basic anatomical, physical, and mechanical properties of the particular bamboo to assess its suitability for the intended purposes. According to Abd. Latif et al. (1990), Razak et al. (2002, 2005, and 2010), and Wang et al. (2016), the anatomical properties of bamboo are important due to their effect on mechanical properties, preservative absorption, and properties of the end products, especially pulp and paper. Anatomical properties can also influence the bamboo’s durability, toughness, workability, and strength (Liese 1985; Espiloy 1987; Razak et al. 2010). These findings were further supported with a study by Xin et al. (2015), where it was concluded that the anatomical structure of bamboo is basic knowledge for understanding the physical and mechanical properties as well as the utilizations of the bamboo.
Density and shrinkage are considered important factors for determining the suitability of bamboo for various applications, with density being associated with the mechanical properties (Anwar et al. 2005a; Abdullah et al. 2017). Determination of the mechanical properties of bamboo is important to fully understand its behaviour and performance in structural design and industrial use (Shahril and Mansur 2009; Correal and Arbelaez 2010; Gutu 2013).
There are at least 63 species of bamboo in Peninsular Malaysia. Of them, 25 are indigenous, while the rest are known only in cultivation (Abd. Razak and Abd. Latif 1995). From this total number of species, only 13 species are known to be commercially utilized, including Bambusa blumeana (buluh duri), B. vulgaris (buluh aur/minyak), B. heterostachya (buluh galah), Gigantochloa scortechinii (buluh semantan), G. thoii (buluh beting), G. ligulata (buluh tumpat), G. wrayi (buluh beti), and Schizostachyum brachycladum (buluh lemang) (Abd. Razak and Abd. Latif 1995). From these 13 species, B. vulgaris and G. scortechinii were reported as suitable for making particleboard, laminated bamboo boards, ply bamboo, and bamwood (Razak et al. 1997; Jamaluddin et al. 1999; Zaidon et al. 2004; Anwar et al. 2004, 2005b; Hanim et al. 2010; Anwar et al. 2011, 2012). An intensive study on bamboo properties should be conducted for all 13 bamboo species to assess each species’ suitability for end products. Therefore, the objective of this study is to determine the anatomical, physical, and mechanical properties of the 13 species. The trends of these properties along the bamboo culm height were also examined. Based on the derived properties it will be used to determine the bamboo species for suitable end products.
EXPERIMENTAL
Materials
Field sampling
Thirteen species of Malaysian bamboo, Gigantochloa thoii, G. scortechinii, G. ligulata, G. wrayi, G. brang, Schizostachyum brachycladum, S. grande, S. zollingeri, Bambusa vulgaris, B. blumeana, B. heterostachya, B. vulgaris cv Vittata, and Dendrocalamus asper, were obtained from the bamboo plantation research plot, Forest Research Institute Malaysia (FRIM) campus (Kepong, Selangor, Malaysia). Five culms from each species were selected and harvested. Four-year-old bamboos were chosen in this study due to their level of maturity. Sattar et al.(1992) illustrated that bamboo culms start maturing at the age of three years. This age was determined by observing a tag that was placed on the culm during the shoot’s sprouting stage. The bamboo culms were cut at approximately 20 cm above the ground level. Each culm was cut to a length of 12 m and was later subdivided into three equal lengths corresponding to the basal, middle, and top portions. The bamboo culms were split into eight sections using a splitting machine. For assessment on the anatomical, physical, and mechanical properties, split samples were tested at 12% moisture content. A split is a bamboo sample with the periphery and inner skin remaining intact.
Methods
Determination of the anatomical properties of bamboo
The anatomical studies on the types of vascular bundles and their distributions were conducted according to the method outlined by Abd. Latif and Mohd. Tamizi (1992). Bamboo sample blocks were cut into sections of 10 mm × 10 mm × culm wall thickness. The blocks were boiled in distilled water until the bamboo samples softened. Then, 25-µm thick sections were cut using a sledge microtome (Reichert, Vienna, Austria). Each section was stained with aqueous safranin-O (Sigma, New Delhi, India). These sections were washed with 50% ethanol and dehydrated using a series of ethanol solutions with concentrations of 70%, 80%, 90%, and 95% (Merck, Selangor, Malaysia). Then, one drop of Canada Balsam (Merck, Darmsladt, Germany) was placed on top of the section and covered with a cover slip. The slides were oven-dried at 60 °C for a few days.
The maceration technique was used to determine the fibre morphology. Bamboo splits (20 mm × 10 mm × culm wall thickness) were chipped into the size of a matchstick. Then, they were macerated using a mixture of 30% hydrogen peroxide:glacial acetic acid (1:1 ratio) at 45 °C (Wheeler et al. 1989; Abasolo et al. 2005) for 2 to 3 h until all of the lignin had dissolved and the cellulose fibres appeared whitish. The macerating solution was then carefully washed in distilled water until all traces of the acid disappeared. Then, the cellulose fibres were kept in the vials. The vials were then gently agitated to ensure sufficient separation of cellulose fibres. The vials were then half-filled with distilled water and securely capped. The macerated fibres were spread out on a glass slide, drops of safranin-O were added, and a cover slip was applied.
Quantitative measurements of the fibre length, diameter, wall thickness, and lumen diameter were made from the slides using an optical microscope (Olympus Corporation, Tokyo, Japan). The distributions of vascular bundles were determined by counting the number of vascular bundles per mm2 on a cross-section. The fibre wall thickness was obtained by subtracting the value of fibre lumen diameter from fibre diameter and dividing by two. The aspect ratio (fibre length / fibre diameter) and Runkel ratio (2 × wall thickness / lumen diameter) (Singh and Mohanty 2007; Gülsoy et al. 2017) were also calculated.
Determination of some physical and mechanical properties
Physical properties of bamboo splits were tested using methods from the Indian Standards Institution (Anonymous 1976). Samples (20 mm × 20 mm × culm wall thickness) were obtained from the basal, middle, and top portions for analysis of density and shrinkage from green to oven-dry. A total of 1,560 specimens were used in the study.
The radial, longitudinal, and tangential sections of each sample were marked and measured with digital vernier calipers to the nearest 0.01 mm. All samples were placed in an oven dried and maintained at 103 ± 2 °C for 48 h and the shrinkage test was conducted during progress from green to oven-dry conditions. Shrinkage (So) was calculated according to Eq. 1,
(1)
where So is the shrinkage (%) from green to oven-dry conditions, Di is the initial dimension length (mm), and Do is the oven-dry dimension length (mm).
For the modulus of rupture (MOR) and modulus of elasticity (MOE), the split samples of 300 mm × 20 mm were obtained from the basal, middle, and top portions were air-dried in the shade for about one month and then conditioned for two weeks in a conditioning room at 65% relative humidity and 20 °C. A total of 60 specimens were prepared for this study. A 100 KN Shimadzu testing machine (Kyoto, Japan) was used and testing was performed with central loading and a cross-head speed of 0.65 mm/s with two supports over a span of 140 mm. The samples were tested in accordance to the procedure described by Gnanaharan et al. (1994).
Statistical analysis
Statistical analysis was performed using Statistical Analysis System (SAS) version 9.1.3 software (SAS Institute, Cary, NC). A one-way analysis of variance (ANOVA) was conducted to determine whether the differences in means were significant. If the differences were significant, the least significant difference (LSD) test was used to determine which of the means were significantly different from one another.
RESULTS AND DISCUSSION
Physical Characteristics
The identification of a bamboo species at the field usually begins by looking at its physical characteristics. Information gathered on the physical characteristics is important, as it quickens the identification of bamboo specimens that have an absolute characteristic distinction between species such as its culm height, internode length, and culm wall thickness. Based on the physical characteristics of bamboo species such as culm wall thickness, internode, and culm length, it can also be used to determine the suitable end products.
The physical characteristics of the 13 respective bamboo species in this study are presented in Table 1. The highest culm height at 32 m was recorded from S. grande, followed by B. vulgaris cv vittata (30 m), and S. zollingeri (22 m). The S. grande species had the longest internode length at 65 cm, followed by S. zollingeri (55 cm), and S. brachycladum (53 cm). The shortest internode length was measured from the B. blumeana species at 32 cm. The highest value of culm wall thickness was obtained from D. asper (16 mm), followed by G. brang (14 mm). The lowest culm wall thickness value was recorded from the S. zollingeri species at 4 mm.
From the result obtained, Dendrocalamus asper, Gigantochloa, and Bambusa have the thickest culm wall compared to Schizostachyum. On the other hand, Schizostachyum can be characterised by its longest internode and thinnest culm wall. Most Bambusa have shorter internode (except for B. heterostachya) as compared to other bamboo species. Based on the physical properties, species from the genus Schizostachyum is suitable for crafts, satay sticks, basketry, toothpick, water container and other general utility. This species is also use as vessels for cooking glutinous rice, called lemang. While, D. asper, Bambusa and Gigantochloa having the thickest culm wall makes it suitable for parquet, furniture and building structures.
Anatomical Properties
Liese (1998) described the four basic types of vascular bundles, which are vascular bundle types I, II, III, and IV. Type I vascular bundles are usually present in monopodial species of bamboos, whilst vascular bundles of type II, III, and IV are present in sympodial species of bamboos. Figure 1 shows anatomical structures of the 13 species studied. The vascular bundle type of Malaysian bamboo are classified as the following:
Type II: S. brachycladum and S. zollingeri with enlarged fibre sheath at the phloem side.
Type III: G. thoii, G. scortechinii, G. ligulata, G. wrayii, G. brang, S. grande, B. heterostachya, and B. vulgaris cv. vittata with one isolated fibre bundle.
Type IV: B. vulgaris, B. blumeana, and D. asper with a central vascular strand that has small sclerenchyma sheaths, and two isolated fibre strands located at the phloem and protoxylem sides.
The result obtained in this present study is similar with observation made by Grosser and Liese (1971). They also concluded that type IV vascular bundle is related to the thick walled internodes of large size bamboos as found in this study in B. vulgaris, B. blumeana, and D. asper.