Síntese verde de óxidos de cobre e zinco para preservação da madeira de Pinus elliottii

Abstract

The search for a more environmentally friendly industry is incessant, as a result, researchers from the most diverse fields have been studying processes that use less toxic chemicals and lower energy expenditure. From this concept emerged the green synthesis of nanoparticles, which uses biomolecules from plant extracts and/or microorganisms as reducing and stabilizing agents. The aqueous extract of leaves of the species Eucalyptus dunnii Maiden was used in the synthesis of oxides of copper, zinc and a composite formed by the two, and the calcination temperature of 300 ºC was the lowest at which pure and crystalline oxides were obtained. Copper and zinc oxides have been applied in wood treatment, aiming to improve properties such as hygroscopicity, flammability, resistance to aging, decay and insect attack, but these are generally obtained by other synthesis routes. The wood of Pinus elliottii Engelm has low durability, that is, it is extremely susceptible to the action of biotic (fungi and termites) and abiotic (rain and radiation) deterioration agents. In this context, the oxides synthesized via green chemistry were used in the treatment of P. elliottii wood, evaluating physical, mechanical, thermal and colorimetric properties, as well as resistance to decay and termite attack. The oxides, when applied alone, did not significantly alter the physical and mechanical properties of the wood, only the hardness was negatively affected by copper, but the composite resulted in a decrease in mechanical strength. All treatments caused darkening and decreased thermal stability of wood. Exposure to accelerated aging did not change the mechanical strength, but caused the leaching of particles from the surface of all treated woods, even so they maintained resistance to termite attack, inhibiting mass loss. As for decay resistance, copper oxide was the most efficient treatment against the white-rot fungus Trametes versicolor and the composite against the brown-rot fungus Gloeophyllum trabeum, while zinc oxide had little or no efficacy. The brown-rot has been shown to be resistant to several treatments with nanoparticles, the efficiency of the composite may be linked to the synergy effect between the oxides that compose it. Therefore, the oxides synthesized via green chemistry, which uses aqueous extract of leaves, low temperatures of synthesis and calcination, are also efficient in the treatment of wood, aiming at resistance to biotic deterioration agents.