Physical-mechanical properties and natural durability of lesser used wood species from Mozambique
Sammanfattning: The aim of this study is to assess properties of lesser used/known timbers from Mozambique. The studied species were ncurri (Icuria dunensis Wieringa), ntholo (Pseudolachnostylis maprounaefolia Pax), metil (Sterculia appendiculata K. Schum), namuno (Acacia nigrescens Oliv.) and muanga (Pericopsis angolensis Meeuwen). A comprehensive literature review found the Mozambique timber sector to be dominated by very few hardwood species while the rest of 118 lesser used wood species are almost unexplored. The above mentioned lesser used timbers were selected and subjected to descriptive and comparative analyses aiming at describing the physical-mechanical properties and natural durability with regard to prospective end uses. Standard test methods determined density, moisture content, dimensional stability characteristics, colour, natural durability and a number of mechanical properties of the selected lesser used timbers. The study revealed that ntholo and ncurri are heavy timbers with a density in the range of 850-1100 kg/m3 and very low dimensional changes. Metil is a medium light wood with an average density of 550 kg/m3 at 12% moisture content and a coefficient of anisotropy of 1.8 from green to oven-dry state. End use assessments suggest that the timbers of ntholo, muanga and namuno can be used in similar applications as the well known timbers, e.g. internal joineries, tool handles and furniture. Metil timber seems suitable for packaging boxes, plywood and construction purposes. In terms of natural durability, the results showed that heartwood of namuno, muanga and ntholo can be classified as very durable to deterioration and degradation caused by fungi and termites. These timbers showed good performance when untreated samples were exposed in- and above ground field tests providing a good indication of the expected service life and outdoor use features. Wood of metil was classified as non durable to any of the considered hazards and is not recommended for exterior uses unless treated with appropriate wood preservatives. The study determined ntholo timber mechanical properties and examined interrelationships with density and anatomical features of ntholo through regression and correlation analyses. The study found ntholo to be a very dense timber with high mechanical strength in comparison to well known timbers. The regression analyses show that both ntholo sapwood and heartwood densities are poor predictors for the tested mechanical properties, although may provide some indication of tested properties. All tested properties of ntholo sapwood were influenced mainly by ground tissue proportions, while heartwood properties were described by more leveled anatomical predictors. Fiber length was the only anatomical feature significantly correlated to density and all tested mechanical properties of ntholo. The number of vessels/mm2 and % vessels were not significantly correlated to any of the measured properties but appeared to be key anatomical features for predictions under regression analysis. The integrated analysis of results from this study is expected to form a reliable background for a successful utilization of the relatively lesser explored timbers from Mozambique.
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