The objective of this work was to evaluate the efficiency of purifying and enriching wood tar creosote against wood decay after 48 months in field testing. By distillation of wood tar, the crude wood tar (creosote 1) was recovered at a temperature of 110-255 °C. A fraction of the distilled was washed with a solution of sodium bicarbonate at 9%, resulting in purified wood tar creosote (creosote 2). Creosotes 1 and 2 were enriched with 3% copper naphtenate; 3% zinc naphtenate; 3% of cobalt naphtenate; 2% TBTO; 2% tributil-tin tribromophenate; 2% pentachlorophenol; or 0.4% arsenic trioxide. Stakes of Eucalyptus grandis sapwood were treated by following the full cell process. The efficiency of wood tar creosote solutions was compared with that of coal tar creosote. The essay was established in three locations (Viçosa, Ponte Nova and Leopoldina -Minas Gerais, Brazil). The results showed that creosote 2 + pentaclorofenol was superior to creosotes 1 and 2 + TBTO, to creosotes 1 and 2 + zinc naftenato and to pure creosote 1, being similar to coal tar creosote. Creosote 2 was superior to creosote 1, only in Leopoldina. In general, the average life of untreated wood was between 12 and 24 months. The average life of wood treated with creosote 1 + TBTO was between 24 and 37 months, while that ofwood treated with creosote 1 + zinc naftenato, between 37 and 48 months and that of wood treated with creosote 1 + cobalt naftenato, pure creosote 2, creosote 2 + zinc naftenato or + TBTO was 48 months. At this stage of research it is not possible to estimate the treated wood average life, as compared with the other tested preservative solutions, it since 60% of the stakes did not break.
Wood tar creosote; wood preservatives; field testing
