Differential retention and leaching of CCA (C) in sapwood and heartwood of Kenyan-grown blue gum (Eucalyptus saligna) and black wattle (Acacia mearnsii)

IRG/WP 05-30371

R Venkatasamy

Retention and leaching of CCA(C) in small samples of sapwood and heartwood of Kenyan-grown blue gum (Eucalyptus saligna) and black wattle (Acacia mearnsii) were tested under laboratory conditions. Clear samples (100mm x 30mm x 40mm) were removed from the sapwood and heartwood of sampled defect-free and sound plantation trees of the two species. These were separately air-dried to 15% MC, end-sealed and pressure-treated with 3% CCA-C (oxide) at a commercial treatment plant. They were then conditioned at ambient temperature, air-dried to 15% MC and retentions calculated on a weight-gain basis (E. saligna: sapwood - 33.3 Kg/M3, heartwood - 6.4 Kg/M3; A. mearnsii: sapwood - 28.7 Kg/M3, heartwood - 5.6 Kg/M3). Batches of samples of sapwood and heartwood of each species were then separately leached in running tap water for 3, 6, 9, 12, 15, 18 and 21 days. After each leaching period, batches of samples were removed, oven-dried to 15% MC, and the amount of preservative leached calculated on a weight-loss basis. After 21 days of leaching, substantial amounts of the preservative were removed from sapwood samples (E. saligna - 44.1%; A. mearnsii - 47.7%), whereas losses of the preservative from heartwood samples were significantly lower, 18.7% and 16.1% for E. saligna and A. mearnsii respectively. The results indicate that although retentions may be higher in sapwood than in heartwood of these two species, fixation of CCA appears to be poorer in sapwood, resulting in higher losses of the preservative through leaching. Mechanisms responsible for differential retention, fixation, and leaching of CCA in sapwood and heartwood on these two species need to be further studied and documented.

Keywords: Sapwood, heartwood, E. saligna, A. mearnsii, CCA(C), retention, fixation, leaching

Conference: 05-04-24/28 Bangalore, India

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