Antifungal and anti-termite activities relating to chemical composition of pyrolysis liquid from carbonization of five Tunisian wood species

Purpose: The pyrolysis of the 5 most promising Tunisian wood species (Ceratonia siliqua, Eucalyptus camaldulensis, Eucalyptus maidenii, Pinus pinea, and Quercus canariensis) for charcoal production was carried out in a custom-designed carbonization reactor developed at the INRGREF's Wood Technology Section (Tunis, Tunisia). This process aimed to produce both char and pyrolysis by-products, particularly tars. This research is focused on the better understanding of the chemical composition of tars and their mechanisms of anti-fungal and anti-termite activities. Methods: The experiments were conducted at temperatures ranging from 450 to 550 °C, depending on the wood species, with a controlled heating rate of 1.5 °C/min and a holding time of 12 h. The global yield of char and pyrolysis by-products (tars, liquid and gas) were determined for all wood species, separately. Then, the chemical compositions of tars, obtained by pyrolysis liquids decantation process, were analyzed by Gas-Chromatography coupled with Mass Spectrometry (GC–MS) analysis and their antifungal and anti-termite properties were evaluated. Results: The average yield of char and tar was 27.00% and 40.00%, respectively. The level of antifungal and anti-termite properties of the Tunisian wood tars depends on the nature of the initial biomass, which plays a crucial role in the chemical composition of the obtained tars. The effectiveness, in term of biological activity, of the pyrolysis tar is believed to result from the synergetic action of its various chemicals, notably organic acids, phenolics, terpenes, aldehydes and ketones and PAHs compounds. Notably, the chemical profile of the pyrolysis tars was closely linked to their effectiveness in inhibiting fungal growth and repelling termites. Among the tested samples, the tar derived from Pinus pinea exhibited the strongest bioactivity against white and brown fungal strains as well against subterranean termites. Conclusion: These findings suggest that pyrolysis tars obtained from the carbonization of Tunisian wood species could serve as promising natural preservatives for protecting wood against fungal decay and termite attacks. However, further work on formulations should be carried out to ensure extended efficacy over time while minimizing impacts on human health and the environment. Moreover, since all tar solutions contain non-negligible PAHs content, it will be essential to assess the eco-toxicity of these solutions.