Enhancing the durability of pine species: studying the efficacy of copper- and silicone-based liquids as a function of chemical loadings and wood species

Fungal decay significantly affects the performance of wood used for outdoor applications. Both biocidal and non-biocidal treatments have been explored to enhance the resistance of wooden materials against decay fungi. This study evaluated the effects of different concentrations of copper-based and silicone-based products on the durability of different pine species (Pinus sp.) against brown-rot fungi. Treated specimens of Pinus radiata, Pinus sylvestris and Pinus palustris were exposed to monocultures of Coniophora puteana, Rhodonia placenta and Antrodia vaillantii after an accelerated ageing procedure. Durability was assessed based on mass loss and durability classes assigned to untreated as well as treated specimens. Both treatments significantly increased the decay resistance, whereas no significant differences could be measured between the wood species or decay fungi. Silicone oil showed a clear concentration–durability relationship: treatments at ≥ 5% provided the maximum protection level and were classified as “very durable” (DC 1) in most cases. For treatments with copper-based preservatives, the highest concentration generally resulted in the highest durability class, although some samples were only moderately durable. This indicated that starting from a concentration of 3%, copper-based treatments contributed to reduce the mass loss. Principal component analysis was applied to verify the relationship between the variables. The results confirmed these patterns and highlighted the potential of intermediate concentrations to optimize the biological durability. Overall, the findings demonstrated that both copper-based and silicone-based treatments effectively enhanced the resistance of sapwood sections of various pine species to different brown-rot fungi, primarily by maintaining low moisture content (MC) and minimizing fungal activity and decay measured on the basis of mass losses (ML) even after fungal exposure.