Effects of water glass, silane and DMDHEU treatment on the colonisation of wood by sapstaining fungi

The objective of this study was the investigation of the resistance of modifiedwood against sapstaining fungi and the investigation of the influences of fungalgrowth. Specimens of Scots pine sapwood (Pinus sylvestris L.) and Beech wood(Fagus sylvatica L.) were investigated after being treated with an amino-alkylfunctionaloligomeric siloxane, a sodium water glass solution and 1,3-dimethylol-4,5-dihydroxyethylene urea (DMDHEU).The following is a structured outline of this study:Laboratory tests for the resistance against the blue stain fungusAureobasidium pullulansThe objective was to develop a laboratory test method against blue stain formodified wood as well as the determination of the resistance against blue stain.After definition of a suitable test method, the laboratory tests displayed animproved resistance against blue stain for all tested modified wood specimens.Regardless of the wood species, the fungal infestation was reduced but notinhibited. Among the treated specimens, the water glass treated specimensshowed the lowest, the siloxane treated specimens the highest infestationrespectively.Field tests for the determination of the resistance against sapstaining fungiThe fungal infestation was investigated during outside exposure of thespecimens. The infestation of the modified specimens was decelerated. Thespecimens were infested mainly by ascomycetes and deuteromycetes which areubiquitary. The fungal composition displayed only marginal differencescompared to untreated wood. The most dominant fungi which were detected wereTrichoderma sp. and Epicoccum sp. irrespective of wood species andmodification type.Investigation of the influence factors of fungal developmentWood moisture content: The results displayed a reduced equilibrium moisturecontent (EMC) for DMDHEU treated wood compared to the untreated controls.The water glass treatment caused an increase of EMC, which was in the range ofthe untreated controls after a leaching procedure. The siloxane treatment did notcause significant changes in EMC compared to untreated controls.Available simple sugars: A reduction of fungal growth caused by a reducedamount of available simple sugars and their composition was detected for waterglass treated specimens only.Lignin degradation: The lignin degradation during outside exposure,investigated by FTIR-spectroscopy, did not show a reduction in modified woodspecimens, regardless of wood species and modification type.Penetration of fungal hyphae: Macroscopic and microscopic investigationsrevealed a reduced radial penetration of fungal hyphae in DMDHEU treatedwood. A siloxane and water glass treatment inhibited the radial penetration intothe wood tissue. In this case, fungal growth was visible on the specimen surfaceonly.Summarising, the results revealed that the influences of fungal growth weredependent on the type of modification and independent of the wood species. Thereduction of fungal infestation on water glass treated specimens was mainlyinfluenced by the pronounced alkaline pH-value and a reduced content of freeavailable simple sugars. The fungal growth on DMDHEU and siloxane treatedwood was largely influenced by changes in wood moisture content.