New perspectives for wood protection: enzyme-based treatments
C Fernández-Costas, S Palanti, M Á Sanromán, D Moldes
Wood protection research is continuously looking for more benign and effective treatments. One of the main concerns deals with the toxicity of the active compounds employed in the formulations of the preservatives, since they could become a health and environmental issue. Secondly, long-lasting treatments are preferred in order to increase the service life of the treated wood. Weathering conditions are responsible of constant leaching of the formulations and most treatments tend to fail with regard to their efficacy along the time due to this phenomenon. In this paper, enzymatic treatment of the wood is proposed as an alternative to the conventional treatments. The main advantage of this novel approach is the covalent fixation of the active compounds to the wood surface. On the contrary, traditionally wood treatments are based on a simple impregnation of wood and they do not ensure a suitable retention of the formulations along the time. It is also a versatile tool which could be applied with a huge range of actives compounds. In the present work, enzymatic grafting is shown with two different active compounds: Kraft lignin and wood extracts. As enzyme, a laccase from Myceliophtora thermophila was chosen due to its ability to oxidize phenolic substrates. Then, stable anchoring of this grafting was assessed and mini-blocks of wood were treated following this procedure to test its efficacy against wood-degrading fungi. Enzymatic grafting was demonstrated to improve resistance to leaching according to the European Standard EN 84. In this way, compounds that have low biocidal activity (when compared with available commercial formulations) become highly effective because of the low lixiviation. Finally, durability assays were accomplished in order to test the real effectiveness of the enzymatic treatments against fungi. From the different treatments studies, enzymatic treatments with the extractives from Pinus spp. have appeared to have a great potential to increase wood durability, reducing the mass losses until only a 4% of the initial mass.