The biocidal properties of an industrially used copper-based preservative were evaluated at different planing depths on exposure of pine wood to mold fungi in direct and indirect contamination methods, with simultaneous verification of white rot fungi virulence on wood. The preservative was an aqueous solution of copper carbonate, 2-aminoethanol, and quaternary ammonium compounds. Full cell preservative impregnation efficiency against visual mold fungi growth was tested on sapwood surfaces planed to different depths before impregnation. The virulence of two white rot fungal strains of Trametes versicolor (441 and JPEI) against the dried non-impregnated and impregnated wood samples was also tested. The unplaned surface of impregnated timber was occupied by air-borne contaminants, such as Paecilomyces variottiand Aspergillus niger up to 30%, and, even after impregnation it was necessary to process the surface to avoid micro-fungi settlement. The virulence of the tested rot fungi strains was confirmed by the aggressive degradation of non-impregnated wood with a mass loss of over 40%. Both Trametes sp. strains degraded the preservative-impregnated wood with a mass loss of 3.1% to 4.8%, but degradation by the JPEI strain was more intensive and more dependent on planing depth than the other strain (441).

During industrial wood drying, extractives migrate towards the wood surfaces and make the material more susceptible to photo/biodegradation. The present work provides information about the distribution, quantity and nature of lipophilic substances beneath the surface in air- and kiln-dried Scots pine (Pinus sylvestris L.) sapwood boards. Samples were taken from knot-free sapwood surfaces and the composition of lipophilic extractives, phenols and low-molecular fatty/resin acids layers at different nominal depths below the surface was studied gravimetrically, by UV-spectrometry and by gas chromatography-mass spectrometry (GC-MS). The concentration of total extractives was significantly higher in kiln-dried than in air-dried samples and was higher close to the surface than in the layers beneath. The scatter in the values for the lipophilic extractives was high in both drying types, being highest for linoleic acid and slightly lower for palmitic, oleic and stearic acids. The amount of fatty acids was low in kiln-dried boards, probably due to a stronger degradation due to the high temperature employed. The most abundant resin acid was dehydroabietic acid followed by pimaric, isopimaric, and abietic acids in both drying types. It is concluded that during kiln-drying a migration front is created at a depth of 0.25 mm with a thickness of about 0.5 mm.

Influence of extractives on mould growth on Scots pine sapwood dried in air or in kiln was studied. Boards were sprayed with water mixtures of spores of the fungal species Penicillium sp., Aspergillus sp., Mucor sp., Paecilomyces sp., Trichoderma sp., treated at a temperature of 22ºC at 90% RH, classified into a percentage of covered area. Acetone and water extracts were isolated and analyzed for sugars, nitrogen, ash, resin/fatty acids, glycerol, and phenols. A multivariate Orthogonal Partial Least Squares (OPLS) regression model was developed to study relations between the extent of mould coverage of boards and chemical content. The model describes 51% variability in X and 69% in Y with prediction power of 55%. The results indicated that total acetone soluble extractives and sugars like glucose contributed to increased mould growth whereas fatty acids prevent mould growth.

The thermal modification process essentially involves a controlled degradation of the wood, primarily resulting in the degradation of hemicelluloses. In this study, thermal modification at temperatures of 160, 180 and 210 °C was used in superheated steam. Examined wood samples were iroko (Milicia excelsa (Welw.) C.C. Berg) and padauk (Pterocarpus soyauxii Taub.). Testing of bending properties was done according to the Standard ČSN 49 0116 (ASTM 04.10 WoodD143-09). The samples were loaded by three-point bending. Chemical analysis of total extractives and phenols content, pH and Ec changes and ash content.

The results show that with the increasing temperature of the thermal modification process, the modulus of rupture and density decreases. The force and deflection at the limit of proportionality increased. The thermal modification process affected the chemical characteristics of both species. The distribution of total extractives and phenols varied strongly for iroko, but for padauk decrease with increased treatment temperature and time was observed. Having a more detailed assessment of wood chemical changes and degradation products from structural and non-structural wood components and their resistance to biological attack is necessary for the future development of sustainable technologies for the thermal treatment of iroko and padouk.

This study assesses the potential of an open process for treatment of European Scots pine (Pinus sylvestris) with chemicals that could potentially make the surfaces stronger, more dimensionally stable, or more durable, depending on the treatment solution. The method provides an intermediate solution between full volume impregnation by pressure treatment and superficial surface treatment by dipping. Figuratively speaking, the process creates the equivalent of a layer of coating applied below the wood surfaces rather than above. Two different techniques were compared, namely, heating-and-cooling (H&C) and compression-and-expansion (C&E). Taking into account that commercial suppliers recommend 0.15 to 0.25 L/m² of coating in sawn wood and 0.1 to 0.15 L/m² in planed wood surfaces, then this study demonstrates that the H&C method can impregnate an equivalent amount of solution under the surfaces in less than 15 min using treatment temperatures below 150 °C.

Thermally modified timber (TMT)from Scots pine sapwood similar to Thermo-D quality was impregnated with methacrylate resin by the hot-and-cold method and subsequently cured at elevated temperatures. The results showedthat methacrylate resin could be used to reduce colouring of painted TMT wood during accelerated weathering probably by hindering the migration of extractives. The resin itself did not reduce greying of the unpainted wood. Hardness was only slightly improved by treatment with the resin probably due to a higher density of the material. Formation of blisters occurred but wasreduced by treatment with the resin. Resistance to mould growth by a mixture of Aureobasidium pullulans, Cladosporium cladosporioides, Aspergillus versicolor, Penicillium purpurogenumwas performed by applying EN-15457:2014. Treatment with methacrylic resin hindered the colonisation of the three last mouldfungi.

The discoloration of uncoated wood surfaces in both outdoor and indoor use in non-heated spaces has become an increasing problem in European timber constructions due to the use of less toxic substances for protection and also changes in outdoor climate conditions, necessitating the use of protective coatings. To investigate the effect of methyl methacrylic (MMA) resin for the protection of wood from discoloration and mould growth, resin-treated wood surfaces were studied in a laboratory-scale mould test, as well as in an outdoor weathering test. Non-modified Scots pine and Norway spruce were used, and some of the test materials were also thermally modified. The resin suppressed mould growth for the laboratory-scale experiments. The protective effect was considerably reduced for outdoor tests. The MA resin did not effectively prevent the wood from greying from ultraviolet (UV) radiation exposure; there was some protective effect detected on the pine. The Fourier transform infrared (FTIR) spectra of weathered specimens showed a reduction of lignin-associated absorption bands for all treatments, which corresponded to the UV degradation and greying of the wood surface. It is suggested that MMA resin may provide adequate protection against mould growth on wood without direct exposure to rain and sunshine (e.g., attics, basements, etc).

Research Highlights: In this study, the Generally Recognised as Safe (GRAS) compounds were applied in order to study mould-fungi growth on dried Scots pine sapwood. Background and Objectives: The transition to the use of more sustainable wood-material may be possible by applying GRAS compounds that can control and prevent contamination by primary colonising mould fungi. Materials and Methods: Kiln-dried sawn timber was treated with three different GRAS compounds, and different fungal inoculation methods applied in order to investigate differences in the development of fungal communities. Results: Substances based on potassium silicate significantly reduced fungal growth and mould contamination on the studied wood surfaces. By combining wood-surface treatments with GRAS compounds, fungal-area size as predictors and mould grade as response, a partial least squares (PLS) model that makes it possible to predict mould grade on wood surfaces was developed. The PLS model is a key component in the development of a smart grading-systems equipped by e.g. high-speed digital cameras for the early detection of fungal attack on wood surfaces in different applications. However, the measurements based on chemical characterisation should be the next step to take in order significantly to enhance the model and increase the range of robust applications. In the current study, a multivariate model describing the influence of each fungal-covering area on mould grade was presented for the first time.

The increased concern regarding mould on wood-based building materials has raised a demand for sustainable biocidal treatments to protect early contamination during the construction stage of timber buildings. By providing surface protection for all type of wood-based construction elements already at the construction site will reduce the mould-associated risk for not only the construction elements but also for the indoor climate and dwellers at the use-stage of the building. The purpose was to test the protective effect of commercial water-based treatments containing different biocides on single mould fungi growth in pure culture.

Small specimens of Scots pine sapwood and heartwood, and Norway spruce were treated with four treatments, and a fungal test performed in 90 mm Petri plates. Two samples (treated and untreated control) placed on the plate with a distance between each other, and between, a fungal inoculum placed. Five pure cultures of fungi species used in the study: Aureobasidium sp., Trichoderma sp., Aspergillus sp., Cladosporium sp., Penicillium sp. The specimens exposed at the temperature of 24°C and relative humidity of 90%.

The treatments contained biocides, i.e.: treatment 1: tetramethylol acetylenediurea and iodopropynyl butyl carbamate (IPBC), treatment 2: mixture of several biocides (IPBC, benzisothiazolinone (BIT), methylisothiazolinone (MIT) and 5-chloro-2-methyl-1,2-thiazol-3-one (CMIT)/MIT mixture), treatment 3: IPBC; and treatment 4: mixture of propiconazole and IPBC.

The fungal growth observed in the untreated samples after four days of incubation, the specimens with treatment 4 attacked after eight days, when treatment 1 and 3 had free from fungal mycelia inhibition zone after 22 days of incubation. The moisture content after the test was similar for treated samples in plates with Aureobasidium sp., Aspergillus sp., Cladosporium sp., Penicillium sp., but was significantly higher for Trichoderma sp. The type of wood did not influence fungal growth in comparison to the type of treatment.

Naturally seasoned, kiln-dried, and thermally modified wood has been studied by hyperspectral near-infrared imaging between 980 and 2500 nm in order to obtain spatial chemical information. Evince software was used to explore, preprocess, and analyse spectral data from image pixels and link these data to chemical information via spectral wavelength assignment. A PCA model showed that regions with high absorbance were related to extractives with phenolic groups and aliphatic hydrocarbons. The sharp wavelength band at 2135 nm was found by multivariate analysis to be useful for multivariate calibration. This peak represents the largest variation that characterizes the knot area and can be related to areas in wood rich in hydrocarbons and phenol, and it can perhaps be used for future calibration of other wood surfaces. The discriminant analysis of thermally treated wood showed the strongest differentiation between the planed and rip-cut wood surfaces and a fairly clear discrimination between the two thermal processes. The wavelength band at 2100 nm showed the greatest difference and may correspond to stretching of C=O-O of polymeric acetyl groups, but this requires confirmation by chemical analysis.

The traditional assessment of mould growth is sometimes subjective and can differ from person to person. By applying spectroscopic tools, it is possible to create an individual fingerprint of a wooden material and create databases for obtaining more objective information related to the chemical and biological composition. Side-boards (the flat-sawn sapwood part of the log) of Scots pine were single stacked on stickers and naturally dried indoors at 20°C to an average moisture content (MC) of 4.6%. Another ten side-boards were dried in a small-scale laboratory air-circulation kiln to an average MC of 14%. Another group of side-boards were double-stacked with the bark-side surfaces of each pair turned outwards in order to get a high extractive concentration on these surfaces, and less concentration on opposite surfaces. The different flat-side surfaces were planed according to a planing-depth scheme : 0 mm (unplanned), 0.25, 0.75, and 1.75 mm depth from the surface, and the residual wood particles were collected for further analysis. The planned surfaces were exposed to a mould test, performed by spraying a spore suspension of five mould fungi on the wood surfaces followed by incubation at the temperature of 24°C and 95±3%RH for 35 days. Thereafter, the surfaces were graded according to mould growth. A portable microNIR sensor (wave-length range 900-1670 nm, step 6 nm) was used for NIRspectra detection on the surfaces after mould test, and a data matrix was created. Multivariate analysis of obtained spectra was performed. The results show that the principal component analysis (PCA) can describe and predict 99.7% of the spectroscopic data obtained. No influence of the drying method or planned depth was discovered during classification. Two mould-classes could, however, be clearly separated; no mould, and with mould growth respectively, and the separation could be detected on a 93.4% level.

The study demonstrates that mould growth on the wooden surface could be evaluated by portable MicroNIR spectrometer, which is sensitive enough to detect chemical differences caused by fungal contamination.

Weathering of wood is a complex natural phenomenon that is influenced by factors both in macro and micro-scale. The degradation by weathering constitutes of complex physical-chemical changes influenced by environmental factors such as moisture, sunlight, temperature, chemical compounds, wind, and biological organisms and their related agents. The aim of our study was the evaluation of MIR and NIR spectroscopic technique for characterisation of wood treated by commercial coatings contained different biocidal treatments after weathering in subarctic conditions. Tangential and radial surfaces of the Scots pine and Norway spruce were treated with coatings containing various biocides. Treatment was in the form of fairly transparent wood oil (T), while the two others were coatings that had more of a non-transparent character (H and P). Treatedspecimens and control were placed in various directions on racks outdoor for natural weathering. The measurement of the NIR spectra of specimens that were not exposed, after weathering and dried after weathering, was done by the point-based microNIR portable sensor. Multivariate statistical analysis (MSA) showed that data from types of exposure contributed to less compared to surface treatments in the 3D principal component analysis model (PCA). Grouping pattern around treatments H and P could be obtained as the two individual groups more or less fully separated. From the treatment T and non-treated specimens, no individual grouping behaviour could be observed, however, more intense exposed seemed to be clustered in a different way than mildly exposed ones. A more extensive weather exposure gave also a more degraded surface for T-treated specimens. The NIR portable spectrometer may be used for assessment of the extent of weathering, but the treatment P followed by treatment H had minimal changes. Coefficients Plot in the PLSDA model for different types of exposure for those treatments showed the influence of the NIRwavelengths in classes related to exposure type. The changes caused by weathering phenomenon was evaluated by using multivariate methods in which resulting multivariate model parameters for prediction of the changes were determined. Analysis of the chemical structure of coatings after weathering analysed by mid-infrared spectroscopy gave support to the lower stability of T-treatmentduring weathering.