Assessment of the ease of preservative treatment in the less-valuable Nigerian-grown Ceiba pentandra wood
L Awoyemi, A J Pitman
The hardwood Ceiba pentandra locally known as “araba“ in Nigeria is rarely used for structural and construction works due to its high dimensional instability, low strength and durability values. Samples (25 x 50 x 600mm) were removed from four green boards (25 x 200 x 3000mm) of this species originating from a natural forest stand in Nigeria. The sapwood and heartwood were differentiated by means of colour. Samples were dried at 60oC in a kiln for five days to a final moisture content of 12%. Specimens were then machined and planed to final dimensions of 20 x 20 x 305mm and 20 x 20 x 50mm. Five faces in each specimen were sealed using an epoxy resin (West Systems, UK) to allow treatment in the axial, radial and tangential directions to be assessed. After sealing, the samples were conditioned at a temperature of 20oC and 65% relative humidity and weighed to the nearest milligram. Preservative treatment was carried out by the pressure treatment method using 5% copper sulphate solution. After preservative impregnation, the specimens were conditioned at a temperature of 20°C and 65% relative humidity and were thereafter sprayed with chromazurol.
The dark blue colour shown by all the specimens after the chromazurol spraying indicates the presence of copper and hence confirming that impregnation took place in all the specimens. The photographs of the sections cut through the specimens showed that the preservative had penetrated along the lengths of the sapwood and heartwood stakes with penetration exceeding 300mm. Radial and tangential penetrations were also complete for both the heartwood and sapwood. The results of the T-test analysis of differences in mean preservative uptake show that there are no significant differences in the rate of uptake between heartwood and sapwood in all the three directions. Using the degree of preservative penetration, both the heartwood and sapwood were found to be in 2+ treatability classes according to prCEN/TR 14734, the ease of preservative treatment in this species indicates the possibility of improving its durability rating and thus invariably increases in market value expected.