A novel enzymatic treatment as a new approach for wood protection
C Fernández-Costas, S Palanti, M Ángeles Sanromán, D Moldes
Wood durability is a worldwide concern and most treatments tend to fail with regard to their efficacy along the time. Weather conditions lead to a loss of the treatment substances into the surrounding environment and, in consequence, generate also a public health concern.
Recently, the employment of oxidative enzymes, such as laccases, has been proposed as a tool for lignocellulosics modification in order to change wood surface by anchoring compounds that confer new properties to wood. Among the advantages of this strategy, it can be highlighted the fact of the formation of covalent bonds between the wood and the compounds of interest. Consequently, future leaching of the linked substances is expected to be avoided and treatments could be long-lasting and safer for the environment. Therefore, enzymatic grafting appears to be a promising methodology for the modification of chemical wood composition and properties.
In this work, a grafting strategy is proposed for providing resistance against wood decay fungi to wood. For this purpose, experimental conditions of the grafting were studied regarding time of reaction, enzyme dose, substrate dose, temperature and operational mode. Kraft lignin was used as a phenolic substrate to model the grafting due to its biocidal properties and to the fact that grafting degree could be determined indirectly by means of colorimetric measurements. In addition, it represents a residue of the paper industry, so, this strategy allows also the exploitation of a waste.
Time of reaction has appeared to be the main factor when the grafting is carried out in aqueous solution. However, in this study it has been proved that the best results of the grafting are achieved when the reaction occurs out of the aqueous medium. Washing with hot water of the treated wood veneers was also performed, to remove substrates not attached, and has revealed a good linkage of the lignin onto wood.
Finally, preliminary durability assays with Coniophora puteana were carried out and have shown good prospective applications for this type of wood treatments.