Potential co-valorization of pyrolysis tars from five wood species form Tunisia as wood preservatives bases: Chemical compositions, antifungal and anti-termite activities

The pyrolysis of five Tunisian wood species (Ceratonia siliqua, Eucalyptus camaldulensis, Eucalyptus maidenii, Pinus pinea, and Quercus canariensis) was carried out in a custom-designed carbonisation reactor developed at the INRGREF's Wood Technology Section (Tunis, Tunisia). This process aimed to produce both char and pyrolysis by-products, particularly pyrolysis oils. The experiments were conducted at temperatures ranging from 450 °C to 550 °C, depending on the wood species, with a controlled heating rate of 1.5 °C/min and a holding time of 8 hours. The global yield of char and pyrolysis liquid was determined for all species combined, followed by a detailed chemical analysis using Gas-Chromatography coupled with Mass Spectrometry (GC-MS) analysis and evaluation of their antifungal and anti-termite properties. The average yield of char and pyrolysis liquid was 27.00 % and 40.00 %, respectively. Chemical characterisation of the pyrolysis tars revealed the presence of methanol, hydroxyacetone, 3-methyl-1,2-cyclopentanedione, acetic and propionic acids, furfural, phenolic compounds, guaiacol derivatives, levoglucosan, and polycyclic aromatic hydrocarbons (PAHs). Chemical composition of tars, mainly the concentration of these previous main compounds, varied according to the wood species. 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. When applied at a 10% concentration, it completely inhibited Coniophora puteana and reduced Trametes versicolor growth by 90% in Petri dish assays. Furthermore, Pinus pinea pyrolysis liquid demonstrated excellent termite resistance, providing full protection and causing complete mortality of exposed termites in screening tests using impregnated filter papers. These findings suggest that pyrolysis tars obtained from the carbonisation of Tunisian wood species could serve as promising natural preservatives for protecting wood against fungal decay and termite attacks.