Investigation of the Properties and Suitable Uses for Four Secondary, Lesser-used Wood Species Growing in The Blue Nile State, Sudan

Abstract

This investigation dealt with determination of some properties and suitable uses for four lesser used wood species grown in the Blue Nile State. Four of the secondary wood species which are available in reasonable quantities in Blue Nile State, but are not in common use were selected for this investigation. The selected species comprised: Sterculia setigra (tartar), Acacia polyacantha subsp. campylacantha, (kakamut), Acacia seyal var. seyal (talh) and Diospyros mespiliformis (goghan). Most of our forests are located in poor rural areas. Most of them are degraded natural forests which have been creamed. The remaining stock is composed of some secondary species which are not used even for firewood or charcoal. They are left for conservation. The demand for wood is rising. The aim of the present study is to increase the number of wood species in use and make it more economical to harvest and exploit natural forests sustainably. It is well known that wood processing and utilization are directly affected by wood basic properties. This is why there was a growing concern in combining studies on wood basic properties and wood quality attributes for the different uses. The basic properties determined included some anatomical fiber characteristics, namely: the proportions of the different cell types and their components, fiber diameter (FD), lumen diameter (LD), double cell wall thickness (DCWT), rankle ratio (RR), coefficient of fiber rigidity (CR) and fiber flexibility (FF), as well as fiber length (FL). Most of these properties were determined from macerated fibers, where wood chips from the different species were boiled in concentrated nitric acids in a water bath for ten minutes; the liberated fibers were washed in alcohol and water before staining them with safranin for five minutes and mounting them on temporary glass slides using Canada balsam. Using these slides FL was determined using stereological techniques, while the cross-sectional measurements were determined by a digital reflecting microscope in Giad Material Research Laboratory. Cell proportions, on the other hand, were determined from cross sections prepared by standard procedure and measured using stereological techniques. Physical properties - density, permeability, tangential shrinkage, radial shrinkage and moisture content - in addition to glue bond strength were determined according to standard procedures and so was compression parallel to the grain. Texture and surface quality, however, were determined according to visual grading whereby samples from the different species were given arbitrary numbers from ten to one according to the surface quality and texture – ten being given to the finest texture and grain uniformity and one for the poorest surface. Analysis of variance and Duncan’s Multiple Range test were carried out, looking for the level of significance of the variations in all properties between the species studied. Correlation analysis was also carried out to find relationships between wood basic properties (anatomical and density) and wood quality attributes for the different uses like wood strength, dimensional stability, permeability, gluability and appearance. Anatomical properties showed significant differences between the four species. FL was highest in Tartar (1.75mm) and lowest in kakamut (1.35mm). FD, however, ranged between kakamut (20.85 µm) and talh (12.94µm). LD was highest in kakamut (14.02µm) and lowest in talh (4.97µm). DCWT Ranged between talh (7.94µm) and tartar (6.60µm). Whereas the ratios (RR, CR) were highest in talh (1.75µm), (0.31µm) respectively and lowest in kakamut (0.52µm), (0.17µm), the opposite was the case with FF. Proportions of cell type and their component also showed significant difference between the four species. Physical properties also showed significant differences between the species studies. Talh had the highest density (0.82g/cm³) while tartar had the lowest density (0.38g/cm³). Tangential and radial shrinkage were highest in goghan (10.19), (5.41), respectively and lowest in talh (6.02), (3.06) respectively. Liquid absorption (AB) ranged between Tartar (207.94%) and talh (57.85%). Most of the absorption in tartar was along the grain and very little across the grain. Depth of penetration (PD) was deepest in goghan (1.94cm) and smallest in Tartar (0.21cm). The analysis of variance also showed significant differences in compression parallel to the grain where talh had the highest value, while tartar was the weakest. Glue bond strength (BS) ranged between goghan (27.141Mpa) and Tartar (0.751Mpa), indicating that only goghan and kakamut gave adequate bond strength. With regards to texture goghan had the finest texture and grain uniformity, followed by kakamut and talh while tartar had a moderately course texture. Both kakamut and talh were also figured. According to their quality attributes different wood species were assigned to different uses. Goghan was found suitable for structural uses, high quality furniture internal decorations, carving, handcraft, veneer and high quality plywood. kakamut on the other hand, had similar quality attributes to goghan and can be used for the same uses with preference to goghan. Talh was assigned for structural uses, fixed furniture for student seating and at camping sites. It can also be used for fiberboard and pulp and paper production. Tarar, however, was found suitable for non –load bearing partitions and as an insolating material in sandwich construction as well as for fiberboard and pulp and paper manufacturing. Its low density also makes it suitable for the manufacture of particleboard.