Wood and Cellular Properties of Four New Hevea Species M. A. Norul Izani and S. Mohd. Hamami Universiti Putra Malaysia, Sarawak, Malaysia Abstract Increasing demand for timber and the depletion of natural forests have encouraged the utilization of many less popular species. An understanding of wood properties and behaviour is important to evaluate the potential of these species to produce high quality end products. This study determined the anatomical and physical properties of Hevea species viz H. pauciflora, H. guianensis, H. spruceana, H. benthamiana and H. brasiliensis. Each sample tree was cut into three different height portions (bottom (B), middle (M) and upper (T) parts) and two radial samples (outer (O) and inner (I)). The H. brasiliensis clone, RRIM 912, exhibited the longest fibre length of 1214 m, followed by H. benthamiana (HB, 1200 m), H. pauciflora (HP, 1189 m), H. spruceana (HS, 1158 m) and H. guianensis (HG, 1145 m). Fibre length has a positive correlation with specific gravity. The largest fibre diameter (24.9 m) and lumen diameter (12.5 m) were recorded in H. guianensis. The highest moisture content was obtained from H. spruceana (64.34%) compared to the lowest in the H. brasiliensis clone RRIM 912 (60.01%). A higher moisture content is normally associated with lower strength. Overall, the properties of clone RRIM 912 were found to be comparatively better because of its higher strength due to longer fibre length, thicker cell walls and higher specific gravity than the other Hevea species. Therefore, this species could be used as a general utility timber. Keywords: wood anatomy, forest products, rubber trees, Hevea species, moisture content Proceedings of the FORTROP II: Tropical Forestry Change in a Changing World, 17-20 November 2008, Kasetsart University, Bangkok, Thailand 2 FORTROP II: Tropical Forestry Change in a Changing World Introduction Rubberwood is a valuable timber species for furniture manufacture on a commercial scale due to its beautiful, light and even-coloured texture, comparable strength and easy machining and processing properties (Lew and Sim, 1983; Chew, 1993). In general, the rubber tree species is easy to recognize because it is woody, medium to large sized and presents a typical leaf shedding and renovation pattern (Wycherley, 1992). In 2000, 80% of wooden furniture in Malaysia was made of rubberwood. The rubberwood furniture industry has seen tremendous achievements (Mohammad Nazuri et al., 2000). For decades, Malaysia has been acknowledged as the world’s leading supplier of natural rubber. Thus, rubberwood (Hevea brasiliensis) has been well documented since the 1970’s, and it now is desirable to document the properties of other Hevea species in order to compensate for the shortage of H. brasiliensis in the downstream wood processing industries. They are capable of turning out a wide range of high quality products. Significant research has been carried out to identify new clones or species that will increase timber yield. Other than H. brasiliensis, H. nitida has been found to have potential to produce nine times more timber than the RRIM 600 clone (Najib et al., 1997). Since these various rubberwood species are in the same genus as H. brasiliensis, it is expected that other Hevea species may also have almost the same or even better properties than H. brasiliensis. An understanding of the anatomical properties and wood structure is important because it can encompass the density, mechanical and strength properties and determine the characteristics of potential products. The most common anatomical properties studied are: the proportion of early and latewood, fibre length, cell wall thickness, lumen diameter and the parenchyma proportion (Desch and Dinwoodie, 1983). Fibre length, an important aspect of fibre morphology, is related to the mechanical strength and longitudinal shrinkage and is known to affect the strength properties of paper (Dinwoodie, 1981). Fibre cross-sectional dimensions such as fibre diameter, lumen diameter and wall thickness affect some properties such as strength, shrinkage and swelling, permeability, gluing and machining characteristics (van Buijtenen, 1969). Volume 11: Wood Products and Bio-Based Materials 3 Introduction Among the physical factors that influence strength, the most important ones are specific gravity, moisture content, shrinkage and swelling (Lavers, 1969). The specific gravity of wood is the single most important physical characteristic, to which most mechanical properties of wood are closely correlated. If the specific gravity increases, the strength of wood as well as the stiffness also increases. In the utilization of rubberwood, the study of its structure is important as it establishes the variation in the properties of the wood (Lim and Ani, 1994). This study was conducted to determine the differences in rubberwood properties from five different Hevea sp. i.e. clone RRIM 912 from Hevea brasiliensis, H. pauciflora, H. guainensis, H. spruceana and H. benthamiana. Materials and Methods Sample Collection The five rubberwood species used in this study were H. pauciflora (HP), H. guainensis (HG), H. spruceana (HS), H. benthamiana (HB) and H. brasiliensis clone RRIM 912. Trees aged 15 years were felled from a plantation of the Rubber Research Institute Malaysia (RRIM) at Bandar Penawar, Johor. After felling, the bole of each tree was cut into three lengths of 2 m. In each length, a disc was taken and labeled as either from the top, middle or bottom part. Discs were wrapped in plastic to avoid any changes in moisture content. Anatomical Properties This phase covered the study of fibre morphology and cellular structure along the stem of the rubberwood. Discs from each height were cut into strips with a width of 6 cm across the centre. They were then cut into cubes of 2 cm x 6 cm containing both sapwood and heartwood areas. Each cube was further cut into a 1 cm x 2 cm x 2 cm specimen for slide preparation to determine the cellular structure in the three different planes of a cross, tangential and radial section. Samples of thin sectional slides and macerated wood elements were prepared for anatomical assessment in accordance with the Botanical Microtechnique (Berlyn and Miksche, 1976). 4 FORTROP II: Tropical Forestry Change in a Changing World The microscopic structure of each species was examined using an optical microscope, projection microscope and a scanning electron microscope (Image Analyser) for the measurement of vessel diameter and frequency, fibre diameter and length, lumen diameter, cell wall thickness and the proportion of fibres and rays. Physical Properties Samples for the physical test were cut from the discs of the trees. The samples for physical tests were cut in accordance with ISO 3129-1975 (E) – Wood Sampling Methods and General Requirements for Physical and Mechanical Tests (ISO, 1937). For each small block, the following experiments were carried out: 1) moisture content based on green condition; 2) specific gravity based on dry weight; 3) shrinkage under air dry and oven dry conditions in three different directions (radial, tangential and longitudinal). All the samples were analyzed using analysis of variance (ANOVA) and significant differences between mean values using a least significant difference test (LSD) at p=0.05. Results and Discussions Anatomical Properties Figure 1 shows that the fibre length between the upper and middle parts was not significantly different. Roslan (1998) noted that the mean fibre length of rubberwood fibres was 1.10 mm. The length of fibres usually varies according to tree height, with the middle part possessing the longest fibres, followed by the upper and bottom parts, respectively. The results showed that the fibre length of the rubberwood species in the current study increased from the bottom to the top of the tree. Dinwoodie (1981) noted that fibre length could be considered as the most important aspect in determining the quality of wood because it related to mechanical strength and shrinkage, while also influencing the paper strength properties. Volume 11: Wood Products and Bio-Based Materials 5 Outer Inner 1300 1274 1256 1256 1250 1223 1222 1211 1223 1197 1183 1200 1183 Physical Properties 1150 1129 1097 1100 1090 1097 Fibre length (m) Fibre length Fibre length (m) Fibre length 1050 1000 950 HP HG HB HS RRIM HP HG HB HS RRIM Growth types FFigureigure 1 Mean fibre length for different species of rubberwood in two radial positions. H. guianensis had the highest value for fibre diameter with 24.9 m (Table 1). Figure 2 shows that there was a significant difference between species for Results and Discussions different radial positions. According to Sekhar (1989) and Peel and Peh (1960), the mean fibre diameter of rubberwood was about 22.0 m. Ashaari Anatomical Properties (1980) noted that rubberwood fibre diameter decreased in the outer pith and increased in the inner pith. A higher value for fibre diameter will increase the strength properties of the wood (Mohd Izham, 2001). TTableable 1 Mean values on the anatomical properties of rubberwood. PPropertyroperty SpeciesSpecies PortionPortion RadialRadial positionposition Fibre length 1214a (RRIM 912) 1257a (T) 1220a (O) 1200a (HB) 1234a (M) 1144b (I) 1189a (HP) 1056b (B) 1158b (HS) 1145b (HG) Fibre diameter 24.9a (HG) 24.5a (T) 24.3a (O) 24.3a (HP) 24.3a (M) 23.7b (I) 23.7b (HS) 23.3b (B) 6 FORTROP II: Tropical Forestry Change in a Changing World Table 1 (Cont.) Property Species Portion Radial position Fibre diameter 23.6b (HB) 23.5b (RRIM