Modified wood shows resistance against wood deteriorating fungi, but the mechanisms are still not fully understood. The aim of this paper was to summarise the molecular studies performed on modified wood with regard to brown rot decay fungi. The DNA data showed that fungi are present inside the laboratory wood test samples already after two weeks of inoculation. Generally the fungal DNA content reflects mass loss and wood moisture content. The oxidative gene expression seems to be higher in modified wood than in untreated wood and it tend to increase during incubation. Based on the gene expression data we suggest that the hypothesis of lack of substrate recognition by the fungus should be rejected. In the reviewed studies, total wood moisture content in the samples was generally not low enough to inhibit fungal colonisation. Hence, moisture distribution within the wood should be studied more closely.

Cellulose, one of the most abundant renewable resources, is insoluble in most common solvents but dissolves in aqueous alkali under a narrow range of conditions. To elucidate the solubilization mechanism, we performed electrophoretic NMR on cellobiose, a subunit of cellulose, showing that cellobiose acts as an acid with two dissociation steps at pH 12 and 13.5. Chemical shift differences between cellobiose in NaOH and NaCl were estimated using 2D NMR and compared to DFT shift differences upon deprotonation. The dissociation steps are the deprotonation of the hemiacetal OH group and the deprotonation of one of four OH groups on the nonreducing anhydroglucose unit. MD simulations reveal that aggregation is suppressed upon charging cellulose chains in solution. Our findings strongly suggest that cellulose is to a large extent charged in concentrated aqueous alkali, a seemingly crucial factor for solubilization. This insight, overlooked in the current literature, is important for understanding cellulose dissolution and for synthesis of new sustainable materials.

COST Action FP 1303 “Performance of bio-based building materials” successfully started in October 2013 and an ambitious program was set up for the four year programme. COST Actions provide an excellent opportunity for collaborative research, e.g. in the frame of Round Robin tests.

The idea of this respective test was to distribute a fairly simple test set up to as many places in Europe as possible in order to collect performance data reflecting the range of climatic exposure conditions. Furthermore we wanted to consider performance in its manifold meaning, i.e. optical, aesthetical, moisture and functional performance and durability. In contrast to traditional Round Robin tests aiming on comparative evaluation and validation of results from different test laboratories, this initiative aims on collecting performance data under climatically different exposure conditions. Therefore it was required to provide weather data from the respective test sites to allow establishing relationships between climate conditions and the following measured, which shall be evaluated regularly: decay, discolouration, development of mould and other staining fungi, corrosion, formation of cracks and moisture performance (if data logging device is included). Further details about the test and the first outcomes are presented in this paper.

The surface energy of unmodified and thermally modified spruce wood components was researched at dry and moist conditions using inverse gas chromatography. The results indicate a more pronounced heterogeneous nature of the thermally modified wood surfaces in terms of the dispersive (nonpolar) component of the surface energy, compared with that of the unmodified wood surfaces. The dispersive component of the surface energy of the thermally modified wood ranged between 44 and 38 mJ/m2 corresponding to an increase in surface coverage from a low level and up to about 10%. Suggested explanations for the more distinct heterogeneity of the thermally modified wood sample arerelated to chemical changes of the wood substance which seem to result in certain micromorphological features observed by scanning electron microscopy as alternated fracture surfaces created in the grinding process; and also possible changes or redistribution of the wood extractives. An increase of the MC, representing a change from a dry condition of approximately 0% RH to ca 75% RH, of both the unmodified and thermally modified samples seemed to have a marginal influence on the dispersive component of the surface energy. Possible implications of the results in this study can be found in the tailoring of new compatible and durable material combinations, for example, when using thermally modified wood residuals as a component in new types of biocomposites.

Scots pine (Pinus sylvestris L.) wood was surface densified in its radial direction in an open press with one heated plate to obtain a higher density on the wood surface whilst retaining the overall thickness of the sample. This study investigated the effect of temperature (100, 150 and 200 °C) and press closing speed (5, 10 and 30 mm/min, giving closing times of 60, 30 and 10 s, respectively) on the micromorphology of the cell-wall, as well as changes occurring during set-recovery of the densified wood. The micromorphology was analysed using scanning electron microscopy (SEM) combined with a sample preparation technique based on ultraviolet-excimer laser ablation. Furthermore, the density profiles of the samples were measured. Low press temperature (100 °C) and short closing time (10 s) resulted in more deformation through the whole thickness, whilst increasing the temperature (150 and 200 °C) and prolonging the closing time (30 and 60 s) enabled more targeted deformation closer to the heated plate. The deformation occurred in the earlywood regions as curling and twisting of the radial cell-walls, however, no apparent cell-wall disruption or internal fracture was observed, even at low temperatures and fast press closing speed, nor after soaking and drying of the samples. In the SEM-analysis after soaking and drying, it was noticed that the cells did not completely recover their original form. Thus, part of the deformation was considered permanent perhaps due to viscoelastic flow and plastic deformation of the cell-wall components.

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.

The mode of action of nontoxic wood modifications and the fungal response to modified wood are not fully elucidated. The aim of this study was to investigate the reaction of Postia placenta in terms of gene expression of selected genes upon the encounter of acetylated, DMDHEU-treated and thermally modified wood. Quantitative PCR (qPCR) showed that the investigated P.placentagenes involved in oxidative degradation were expressed at higher levels in modified wood than in untreated wood, while expression levels in modified wood for the investigated genes involved in enzymatic degradation were slightly lower than those in untreated wood. The results indicate that the response of P.placenta upon the encounter of modified wood is to up-regulate the expressionof the oxidative degradation machinery. In addition, our results support the theory that the decay resistance of the herein studied modified woods is due to inhibition of fungal molecules, needed for oxidative degradation of wood polymers, to penetrate the wood cell wall.

Fungal cellulases have been shown to be less efficient in modified wood than in untreated wood (Lekounogou et al. 2008; Vena°s 2008). However, Verma and Mai (2010) showed that cellulase efficacy is partly restored in 1,3-dimethylol-4,5-dihydroxyethyleneurea (DMDHEU) treated wood by pre-treatment with Fenton's reagent, simulating the oxidative degradation phase in initial brown rot decay. In this study, we examined whether Fenton derived hydroxyl radicals (OH) and cellulases are able to cleave polysaccharides in furfurylated and acetylated wood and to what extent enzyme efficacy is increased by oxidative pre-treatment of these materials. The results show that fungal cellulases were able to degrade acetylated wood and that the cellulase efficacy was increased by oxidative pre-treatment by 20%, which is half of the increase in untreated wood. Furthermore, the results indicate that poly(furfuryl alcohol) is degraded by Fenton derived OH. This indicates a possible route for the eventual degradation of modified wood.

The impact of cold temperatures on the shear strength of Scots pine (Pinus sylvestris) joints glued with seven commercially available adhesives was studied in this work. The cold temperatures investigated were: 20, -20, -30, -40, and -50 °C. Generally, within the temperature test range, the shear strength of Scots pine solid wood and wood joints were more resistant to the effect of temperature than those of Norway spruce. As the temperature decreased, only some of the joints' shear strength significantly decreased. In most cases, PUR adhesive yielded the strongest shear strength and MUF adhesive yielded the weakest shear strength. MF adhesive responded to temperature changes in a similar manner to that of PUR and PVAc adhesives. The shear strengths of wood joints with PRF and EPI adhesives were more sensitive to temperature change. For dynamic tests of shear strength, the values for 12-h and 6-day tests under temperature cycles (-20 and 0 °C) were compared. The values for 6-day tests were lower than those for 12-h tests. Therefore, the duration of the samples subjected to the same temperature had a significant impact on shear strength. Our results indicate that PUR adhesive is the most stable whereas the stability of MUF and PRF adhesives decreased significantly.

As wood construction increasingly uses engineered wood products worldwide, concerns arise about the integrity of the wood and adhesives used. Bondline strength is a crucial issue for engineered wood applications, especially in cold climates. In this study, Norway spruce (Picea abies) joints (150 mm × 20 mm × 10 mm) were bonded with seven commercially available adhesives: polyurethane (PUR), polyvinyl acetate (PVAc), emulsion-polymer-isocyanate (EPI), melamine-formaldehyde (MF), phenol-resorcinol-formaldehyde (PRF), melamine-urea-formaldehyde1 (MUF1), and melamine-urea-formaldehyde2 (MUF2). Each adhesive was tested at six temperatures: 20, −20, −30, −40, −50 and −60 °C. Generally, within the temperature test range, temperature changes significantly affected the shear strength of solid wood and wood joints. As the temperature decreased, the shear strength decreased. PUR adhesive in most cases resulted in the strongest shear strength and MUF adhesive resulted in the weakest. MF and PRF adhesives responded to temperature changes in a similar manner to that of the PUR adhesive. The shear strengths of wood joints with PVAc and EPI adhesives were more sensitive to temperature change. At low temperatures, the variability of shear strengths increased with all adhesives. Percent wood failures of joints bonded with different adhesives in most cases were not sensitive to temperature changes.