1. Crack size in coating and moisture problems comparing thermally modified and native spruce window frame profiles using hygrothermal simulationGregor Vidmar, Rožle Repič, Boštjan Lesar, Miha Humar, 2024, original scientific article Abstract: Fungal growth and degradation of wood may be caused by damage in the surface coating. The larger the cracks, the greater in principle the possibility of moisture-induced problems. Measuring basic unknown material parameters and employing hygrothermal simulations, the suitability and the maximum acceptable vertical crack size in the surface coating for a given bottom window profile made of thermally modified (TM) spruce(wood) with that made of native spruce were compared for location Ljubljana. Validation with the field test data was the second objective of the respective research. The average calculated maximum moisture content in TM spruce is about 4% (kg/kg) lower than that of native spruce. The 3 mm wide crack in the surface coating of a window frame made of native spruce is of the highest concern, whereas a 9 mm wide crack in the coating of a TM spruce profile is still acceptable. As far as moisture content is concerned in our study the TM spruce window frames were proved to be significantly more suitable for installation than the corresponding frames made of native Norway spruce. It was shown that isopleth, VTT and biohygrothermal models for mould growth do not properly capture the comparison between both materials, mainly because they classify both in the same material class/substrate category and they do not consider the material moisture content.
Keywords: hygrothermal simulations, mould growth modelling, cracks in surface coating, thermally modified wood, wooden window frame
Published in DiRROS: 16.10.2024; Views: 286; Downloads: 399
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2. Quality control of thermally modified timber using dynamic vapor sorption (DVS) analysisMiha Humar, Rožle Repič, Davor Kržišnik, Boštjan Lesar, Romana Cerc Korošec, Christian Brischke, Lukas Emmerich, Gregor Rep, 2020, original scientific article Abstract: The importance of thermal modification is increasing worldwide. Increased use of thermally modified timber (TMT) has resulted in a need for reliable quality control, comprising control of variation of the production within defined limits, allowing third-party control in the case of certification and the regulation of customer complaints and claims. Techniques are thus needed to characterise the modification of quality in terms of improved target properties of TMT during industrial production, and of TMT products that have been in service for an arbitrary time. In this study, we aimed to utilise dynamic vapor sorption (DVS) for this purpose. Norway spruce (Picea abies) and European beech (Fagus sylvatica) samples were thermally modified at different temperatures according to different heat treatment techniques: (1) the Silvapro process based on an initial vacuum; (2) an air heat treatment, whereby samples were wrapped in aluminium foil; (3) thermal modification of wood samples in the ambient atmosphere in a laboratory oven. Wood samples from closed processes were analysed for validation. TMT was characterised with respect to mass loss, colour and density. Mass loss of wood due to modification (MLTM) was correlated with factors derived from DVS analysis. The present DVS measurements suggest that the equilibrium wood moisture content (EMC95% RH), the time to reach 10% wood moisture content (t10% MC), and the elongation factor, c, derived from a logarithmic function, can serve as alternative parameters to characterise the quality of several thermal modification processes. Further studies are recommended using other wood species, different modification processes and further parameters gained from DVS measurements to understand the robustness and the predictive power of the applied technique
Keywords: thermal modification, quality control, dynamic vapour sorption, wood, moisture content
Published in DiRROS: 31.08.2023; Views: 783; Downloads: 394
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3. Environmentally friendly protection of European beech against fire and fungal decay using a combination of thermal modification and mineralisationRožle Repič, Andreja Pondelak, Davor Kržišnik, Miha Humar, Nataša Knez, Friderik Knez, Andrijana Sever Škapin, 2024, original scientific article Abstract: The demand for construction timber is continuously increasing, due to its favourable characteristics. However, the adequate protection of wood is key to its successful use, as it is flammable and susceptible to biodegradation. Given that thermal modification enhances the durability of wood, and mineralisation with CaCO3 considerably improves its fire properties, it is worth considering the combined effects of the two methods. European beech (Fagus sylvatica) was selected to determine the effects of a) thermal modification, b) mineralisation through the in-situ formation of CaCO3, and c) a combination of the two procedures, on resistance to decay fungi, reaction to fire and the mechanical properties of the wood. Microscopic analysis and comparisons of the samples before and after exposure to fungi were also conducted. Mineralised wood generally had a slightly alkaline pH value and higher equilibrium moisture content, while thermal modification lowered the equilibrium moisture content. The present study demonstrated the combined effect of thermal modification and mineralisation: the best response to fire as well as resistance to fungi was achieved when the two treatments were combined. Results from the Brinell hardness and three-point bending tests indicate that both modification procedures can slightly impair the mechanical properties of the wood.
Keywords: wood, protection, durability, mechanical properties
Published in DiRROS: 12.07.2023; Views: 810; Downloads: 575
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4. Combining mineralisation and thermal modification to improve the fungal durability of selected wood speciesRožle Repič, Andreja Pondelak, Davor Kržišnik, Miha Humar, Andrijana Sever Škapin, 2022, original scientific article Abstract: The development of non-biocidal and environmentally friendly systems to protect wood against biological decay has become a high priority in recent years. In the present study the impact of an innovative modification procedure, combining two environmentally friendly modification methods: thermal modification and mineralisation, using an aqueous solution of calcium acetoacetate as a precursor, on the fungal durability of wood was evaluated. European beechwood (Fagus sylvatica) and Norway sprucewood (Picea abies) were selected as model wood species. Wood samples were treated using either a single or combination of both methods and exposed to four different fungi: Gloeophyllum trabeum, Rhodonia placenta, Trametes versicolor and Pleurotus ostreatus. The effect of the different modifications on moisture content, dynamic vapour sorption, contact angle and pH value was also evaluated. Overall, the highest durability against Rhodonia placenta, Trametes versicolor and Pleurotus ostreatus was achieved through thermal modification in both wood species, while the combination of mineralisation and thermal modification has a synergistic effect against degradation by Gloeophyllum trabeum. In the case of beechwood the mass loss decreased from 41% for native to 6% for combined modified samples. We proved that the effectiveness of different treatment against fungal decay of wood were in strong dependence of their moisture content, dynamic vapour sorption, contact angle and pH values. The role of fungi on the morphology of the wood and on crystal structure of formed carbonate was investigated using SEM-EDS analysis.
Keywords: thermal modification, wood mineralization, fungal durability, environmentally friendly modification methods
Published in DiRROS: 20.06.2023; Views: 838; Downloads: 760
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