Mode of action of brown rot decay resistance in modified wood: a review

Abstract

Chemically or physically modified wood materials have enhanced resistance to wood decay fungi. In contrast to treatments with traditional wood preservatives, where the resistance is caused mainly by the toxicity of the chemicals added, little is known about the mode of action of nontoxic wood modification methods. This study reviews established theories related to resistance in acetylated, furfurylated, dimethylol dihydroxyethyleneurea-treated, and thermally modified wood. The main conclusion is that only one theory provides a consistent explanation for the initial inhibition of brown rot degradation in modified wood, that is, moisture exclusion via the reduction of cell wall voids. Other proposed mechanisms, such as enzyme nonrecognition, micropore blocking, and reducing the number of free hydroxyl groups, may reduce the degradation rate when cell wall water uptake is no longer impeded.

Critical moisture conditions for fungal decay of modified wood by basidiomycetes as detected by pile tests

“…For all materials, EMC reduction corresponds to higher WPG or ML TMT . The reduced water sorption is explained by the reduced number of hydroxyl groups in the cell wall that is accessible or available for water (Hill 2007;Esteves et al 2011;Thybring 2013;Ringman et al 2014). …”

“…The protective mechanism of modified timber is based on its hydrophobic character and improved moisture performance (Hill 2007;Ringman et al 2014). Different physiological studies on wood destroying fungi (Viitanen and Ritschkoff 1991;Huckfeldt and Schmidt 2006) showed considerable impact of moisture content (MC) on fungal decay.…”

“…Information is scarce in terms of the changed water uptake behavior and the critical MC for onset of fungal growth (Meyer et al 2012). Furthermore, it is still controversially discussed to which extent decay is influenced by the presence of liquid water in cell lumens (Thygesen et al 2010;Ringman et al 2014). …”

Preserving ancient artifacts for the next millennia

“…Corrosion products diffuse back into the wood where they can cause degradation of cellulose (9). Similar mechanisms have been identified as a key step in brown rot decay (10,11). The fungus first secretes ferric ions, which then diffuse into the wood where they are reduced, eventually forming a hydroxyl radical that damages the cellulose.…”

Topochemical analyses of furfuryl alcohol-modified radiata pine (Pinus radiata) by UMSP, light microscopy and SEM

“…Different approaches are known in this regard, for instance, modifications with melamine formaldehyde (Stamm 1964), with acetic anhydride (Rowell et al 1994), or thermal modification (Militz 2002), the effects of which are based on chemical, biological and physical interactions, resulting in increased durability and dimensional stability (Hill 2006;Ringman et al 2014). Another promising approach is the furfurylation process.…”