Oil heat-treatment of Eucalyptus nitens (H.Deane & Maiden) Maiden timber
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Keywords
Checking, colour, decay, durability, mass loss, shining gum, strength, thermal modification, nitens, oil
Abstract
Background: Thermal modification of nondurable Eucalyptus nitens timber was reported to result in excessive checking and only marginally improved durability when heat treating in steam or atmospheric environments. This study investigated if oil heat-treatment of E. nitens above 210°C was able to overcome previously reported difficulties.
Methods: Eucalyptus nitens clears were oil heat-treated to 210°C, 220°C and 230°C and assessed for density, stiffness, strength, colour and decay resistance.
Results: Oil heat-treated E. nitens samples showed mass loss matching the highest durability class when tested against the brown-rot Rhodonia placenta (Fr.) Niemelä, K.H.Larss. & Schigel and the white-rot Trametes versicolor (L.) Lloyd, matching Durability Class-2 rated Eucalyptus muelleriana A.W.Howitt heartwood. Oil heat-treated E. nitens samples outperformed Pinus radiata treated with chromated copper arsenate (CCA) to Hazard Class (H3) grade when tested for the brown-rot R. placenta. While oil heat-treatment reduced mean stiffness (MoE) and strength (MoR), the resulting material exceeded characteristic SG8 grade values. No checking was observed in the oil heat-treated E. nitens boards. Letting samples cool outside the oil bath limited uptake of oil to less than 4 mm in depth. The planed product became darker the higher the oil heat-treatment temperature.
Conclusions: Oil heat-treatment above 210°C has the potential to refine E. nitens timber, avoiding excessive degrade and providing decay resistance.
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