Degradation of thermo-hygro-mechanically (THM)-densified wood by soft-rot fungi

Abstract

Thermo-hygro-mechanical (THM)-densified wood is more resistant to colonisation and degradation by brown-rot fungi than untreated wood. Colonisation and degradation by soft-rot fungi was investigated in treated Norway spruce (Picea abies) and treated beech (Fagus sylvatica) to assess their suitability for utility class 4. Three different treatments were applied: thermal-hygro (TH) treatment, mechanical densification and THM-treatment including densification and post-treatment under saturated steam conditions at different temperatures. For comparison, additional wood specimens were treated with two concentrations of a chromium-copper (CC) wood preservative. After 32 weeks incubation, weight losses induced by soft-rot fungi were lowest in wood treated with CC. Highest weight losses were recorded from TH-treated wood, in which soft-rot erosion attack (type 2) was exclusively observed in spruce. In comparison to controls, significantly lower weight losses by soft-rot fungi were recorded in THM-treated spruce wood, but no such differences were found in beech wood. Microscopical examination showed that in THM-treated wood of spruce, soft-rot type 1 commenced from the outer wood surfaces and cavity formation was not found in deeper regions of the wood samples. THM-treated beech wood was more susceptible to degradation than that of spruce which can be partly explained by the higher syringyl lignin content in beech wood, which is more susceptible to all kinds of degradation. Hyphal colonisation and soft-rot was facilitated within deeper regions of beech wood mainly in the non-occluded lumina of parenchyma cells in multiseriate xylem rays. It can be concluded that THtreated spruce wood and THM-treated beech wood is susceptible to soft-rot and therefore inappropriate for utility class 4.

Resistance of thermo-hygro-mechanically (THM) densified wood to degradation by white rot fungi

“…In a previous study on the soft rot resistance of THMdensified wood, Skyba et al (2008) recorded a pronounced effect of THM treatment in the outer wood surface that suppressed colonisation and degradation of inner regions of the wood samples during incubation. The same phenomenon was observed in the present study in which hyphae were not detected in deeper regions of the wood and cell wall degradation was restricted to the outer surfaces of THM-densified wood.…”

“…However, studies of the resistance of THM-densified beech and Norway spruce wood to soft rot fungi revealed that both types of wood are highly susceptible and therefore inappropriate for use in utility class 4, i.e., in contact with ground or fresh water (Skyba et al 2008).…”

The Influence of a Thermal Treatment on the Decay Resistance of Wood via FTIR Analysis

“…Because of these superior characteristics, wood is popular and widely used in many areas. However, under suitable climatic conditions, wood is easily biodegradable and vulnerable to various organisms like fungi and insects [1,2]. Wood contains cellulose, hemicellulose, lignin, and small amounts of sugars.…”

Lignins as agents for bio-protection of wood

“…Temperature treatments at 160-2008C decrease the hydrophility of wood and improves its bio-durability. Thermohygromechanically treated wood has similarly improved properties (Skyba et al 2008(Skyba et al , 2009. Disadvantages are the loss of mechanical strengths (Biziks et al 2010) and the considerable energy input.…”