Treatability of refractory wood species after fungal pre-treatment

Abstract

The permeability of many wood species including Douglas fir, Norway spruce, Sitka spruce and fir can be reduced to 1-5% of that of green timber when dried, resulting in a radial penetration of chemical solutions of only a few millimetres . Exploitation of these wood species is not therefore possible for applications where full sapwood impregnation is needed. Additionally 6 mm lateral penetration into exposed heartwood is required for sawn wood in ground contact. Pit closure upon drying is considered to be the reason for loss of penetrability / permeability. The main technologies currently in use to overcome the problem of pit closure are oscillating pressure methods and incising. A novel patented biotechnological method to make refractory wood species treatable, based on the pre-treatment of wood with fungi selected from a wide array of strains, has been developed by LIGNOCELL Wood-Biotechnology GmbH (Austria) and the University of Abertay (Dundee, Scotland). Scaling–up of the pre-treatment method for round wood led to a very simple and successful process, based on spraying the wood with a suspension of fungal spores in a nutrient solution onto non-decontaminated wood. It is also shown in this paper that the method can be extended to heartwood when certain strains of Basidiomycetes are used for pre-treatment which will broaden the field of application of this technology . One very promising result is the pre-treatment effect achieved after acetylation of spruce heartwood. It shows that the pre-treatment method is not only restricted to wood preservatives but can also be used in combination with modern methods to improve the properties of wood. The key to success when using the pre-treatment method is the use of selected fungal strains together with a cheap nutrient solution. The advantage of using fungi compared to enzymes to improve penetrability is that these organisms can be sprayed as relatively cheap spore suspension onto the wood and will act as production and transport system of a broad mixture of enzymes into the wood leading to prevention of pit closure.