Weight, porosity and dimensional movement classification of some Nigerian timbers

Abstract

Density, porosity and dimensional characteristics of selected Nigerian guinea savannah wood species were evaluated. Wood samples were collected from wood mills in Ilorin, Kwara State, Nigeria. The wood samples were cut and tested following standard procedures. The values of the densities showed statistical variations within and among wood species. Vitellaria paradoxa heartwood was most dense with value of 1147.60 kg/m³ while the sapwood of Lannea welwitchii was lightest (510.90 kg/m³) in weight. L. welwitchii sapwood was most porous with porosity value of 0.72 while V. paradoxa heartwood was least porous (0.26). Generally, the longitudinal shrinkage and swelling of the wood species were negligible and were not significantly different as observed for radial and volumetric movements. However, heartwood and sapwood of Syzygium guineense had the largest shrinkage and swelling values while V. paradoxa heartwood and sapwood had the least dimensional movements. The wood species were classified into weight, permeability, shrinkage and swelling classes. Based on weight, V. paradoxa was classified into very heavy weight class, Albizia zygia and Anogeisus leiocarpa were grouped as 'heavy', L. welwitchii and Irvingia gabonensis were placed into moderately light class while the other six timbers were moderately heavy. Based on permeability, V. paradoxa is refractory in nature, L. welwitchii and I. gabonensis are permeable while other seven species ranged from resistant to moderately permeable. Based on dimensional movements, V. paradoxa, A. africana, A. zygia and A. leiocarpa were characterised with small dimensional movements while the other six species had medium movements.

Keywords: Weight class; Dimensional anisotropy; permeability; Refractory; Tropical hardwood