Basic properties and processing of palmyrah and nibong palm stems

A study of palmyrah (Borassus flabellifer Linn.) and nibong (Oncosperma tigillaria Ridl.) stem was carried out to investigate anatomical structure, chemical, physical, and mechanical properties as well as drying and sawing recovery rates. Five stems of palmyrah palm were cross-cut into sample discs of 100 mm-thick at every two meters along the height and 2 m-bolts between the discs. Each disc was machined into specimen of hard, medium and soft portions for determining the variation of fibrovascular bundles, initial moisture content, density and shrinkage across the diameter and along the height; chemical compositions were evaluated only from the disc at breast height. The bolts were machined into specimens of 20 mm x20 mm sections for static bending, compression and shear parallel-to-grain tests. Another ten palmyrah stems were converted into boards of 25 mm x 2.0 to 3.5 m for seasoning study. Moreover, 20 stems of palmyrah were cross-cut into 80 bolts of 2.5 m to 3.5 m in length for determining the recovery rate in sawing. On the other hand, 50 stems of nibong palm were employed in basic properties evaluation (5 stems) and processing study (45 stems). The experimental procedures are similar to those for the palmyrah stems. The results indicated that, in transverse section, the structure of these palm stems consists of two distinct zones: peripheral zone (hard, dark, congested fibrovascular bundles) and core zone (soft, light, mainly parenchyma tissues). The number of fibrovascular bundles decreases exponentially from bark to pith in both species. The variation ranges from 130 bundles/cm² (palmyrah) and 81 bundles/cm² (nibong) to bundles/cm² (palmyrah) and 13 bundles/cm² (nibong). The shape of the fibrovascular bundles is oblong in palmyrah and pentagonal in nibong. In both species, the pores (in vascular tissues) are not surrounded by the fibrous bundles. The nibong stem contains more holocellulose (78%) and ash (0.63-2.76%) but less lignin (25-28%) than the palmyrah stem (71-75% holocellulose, 0.53-1.20% ash, 25-33% lignin). The initial moisture content varies from 37% (peripheral zone at 2 m-height) to 273% (core zone at ground level) for palmyrah stems. The density of the peripheral zone at air-dried condition is highest at 2 m-height (1.04 g/cm³) and also to the tip (0.48 g/cm³). For core zone the density is relatively constant (about 0.40 g/cm³) except at the butt (0.26g/cm³) and the tip (0.33 g/cm³). The peripheral zone of palmyrah stems has shrinkage ranges (green to oven dry) of 4.20-15.61, 3.55-10.23, and 0.27-0.91 percent (butt to tip) in tangential, radial and longitudinal directions, respectively. Mechanical tests of palmyrah stems revealed that the peripheral zone of the lower half of the stem is good for construction, especially the air-dried compressive strength (parallel to grain) which is exceptionally high (75 MPa) are also close to high-quality commercial timber, but the shear strength is rather low (10 MPa). Air seasoning of palmyrah lumber (peropheral zone) took only six weeks to reduce moisture content from green to 15 percent which suggested that kiln drying of palmyrah lumber might not be necessary. Finally, the average recovery rate in conversion (by circular saw) of palmyrah stems into lumber is 45 percent.