Durability Response of Perishable Wood Species after Pressure Impregnation of Extractives-Based Solutions from Naturally Durable Species of Mozambique

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Abstract

Poor natural durability is a key feature hindering the acceptance of most lesser-used wood species, such as Brachstegia spiciformis, Julbernadia globiflora, and Sterculia appendiculata. Generally, the durability of the aforementioned wood species is improved by impregnating its timber with toxic chemicals contained in standard wood preservatives. In this study, eco-friendly wood preservatives based on extractives sourced from sawdust of naturally durable species such as chanfuta (Afzelia quanzensis) and mecrusse (Androstachys jonhsonnii) were used to treat the group of aforementioned perishable wood species. After pressure treatment, the study assessed the durability responses using standardized in vitro durability test methods against brown rot fungus Postia placenta and white rot fungus Trametes versicolor (EN 113-1:2018) and changes of compression strength parallel to the grain (ISO 3787). The samples of perishable timber species were impregnated with separated extractives-based preservatives of chanfuta and mecrusse in five concentrations (0.5 mg/mL, 1.0 mg/mL, 1.5 mg/mL, 2.0 mg/mL, and 2.5 mg/mL). A subset of treated samples was leached (SS-EN 84:2020-E) to infer preservative fixation and also exposed to the same wood-destroying fungi. The results showed that both extractive formulations (chanfuta and mecrusse) changed the durability ratings of perishable species. Firstly, the subset of treated and unleached samples of Brachystegia spiciformis improved from non-durable to moderately durable, Sterculia appendiculata to durable class and Julbernadia globiflora samples improved to very durable class; secondly, after leaching, the durability remained unchanged (non-durable class) for Brachstegia spiciformis but improved from non-durable to a moderately durable class for both Julbernadia globiflora and Sterculia appendiculata timber species against Trametes versicolor. The compression strength of perishable timber species treated with mecrusse increased and decreased in samples treated with chanfuta. The dosage of both wood extractive formulations did not affect compression strength

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