1. Dynamic mechanical analysis of fpu bonded beech wood at various temperaturesMartin Capuder, Boris Azinović, Andreja Pondelak, Paweł Rutkowski, Magdalena Szumera, Matthew Schwarzkopf, Arkadiusz Kwiecień, Klaudia Śliwa-Wieczorek, Jaka Gašper Pečnik, 2025, published scientific conference contribution Abstract: This study investigates the dynamic mechanical properties of flexible polyurethane (FPU) adhesives bonded to European beech wood (Fagus sylvatica L.) using Dynamic Mechanical Analysis (DMA) over a range of temperatures and frequencies. Samples included clear beech wood and three-layered composite (beech:FPU:beech). DMA tests were performed using a three-point bending setup at 1 Hz and 10 Hz in the temperature range from -120°C to 140°C. The results demonstrated high thermal stability and strong bonding performance of FPU adhesives on beech wood. Frequency-dependent responses varied among FPU types but resembled the behavior of solid wood at lower temperatures. This confirms the suitability of DMA for evaluating adhesive-wood composite behavior under dynamic conditions. The combination of FPU adhesives and beech wood showed potential for thermally stable and energy-dissipating bonded assemblies.
Keywords: dynamic mechanical analysis, FPU, beech wood
Published in DiRROS: 27.08.2025; Views: 460; Downloads: 219
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2. Preliminary assessment of alkali-resistant flax based meshes for reinforcing cementitious compositesJaka Gašper Pečnik, Laetitia Sarah Jennifer Marrot, Marica Mikuljan, Tania Langella, Matthew Schwarzkopf, 2025, original scientific article Abstract: The production of textile-reinforced concrete (TRC) requires less materials and energy in comparison with conventional concrete reinforced with steel rebars, which draws some solutions towards the production of net zero concrete that the Cement and Concrete Industry sector should reach by 2050. To go one step further, this study investigates the development of flax based meshes as basic components for a reinforcement grid in cementitious materials. Flax strands and hybrid strands (combination of flax strands and glass or basalt rovings) were impregnated with an epoxy resin to form meshes. The physical and mechanical properties of the flax based meshes were assessed and the alkaline resistance of these reinforcing materials was evaluated to determine their durability in a cementitious matrix. At isoweight of reinforcement, the flax-based meshes demonstrated the best performance in terms of specific modulus and specific strength compared to the hybrid meshes. The hybrid meshes from the control batch displayed specific properties in the same range, whether they were constituted of AR-glass or basalt. However, the use of alkali-resistant glass rovings strongly mitigated the degradation of the mechanical properties of the hybrids meshes by making them less affected by the alkaline environment, among all the reinforcement meshes. In contrast, hybrid meshes with basalt experienced an extensive reduction in tensile strength and strain after exposure to alkaline environment, due to the corrosion of the basalt fibres. Pull-out tests revealed maximum bond strengths for the flax based meshes embedded in a high-performance concrete matrix.
Keywords: alkali, cement, flax, reinforcement
Published in DiRROS: 27.08.2025; Views: 549; Downloads: 280
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3. Exploratory study on the bending performance of thermo-hydro-mechanically densified Scots pine (Pinus sylvestris L.) at elevated temperaturesLei Han, Matthew Schwarzkopf, Jaka Gašper Pečnik, Wilson Ulises Rojas Alva, Andrea Lucherini, Andreja Kutnar, Dick Sandberg, 2024, other scientific articles Abstract: Thermo-hydro-mechanical (THM) densification is a well-known wood modification procedure for improving the mechanical properties of low-density wood species, but its performance at elevated temperatures is not well understood. The objective of this study was to determine the bending behaviour of densified Scots pine at elevated temperatures. A total of 48 specimens (200 mm (longitudinonal) × 20 mm (radial) × 20 mm (tangential)) were tested to investigate the bending performance under constant temperatures at 25, 50, 125 and 175°C, respectively. It was found that the modulus of rupture (MOR) and modulus of elasticity (MOE) of both un-densified and densified pine decreased with increasing temperature. However, the densified wood exhibited more brittle shear failure but retained higher MOR and MOE than the untreated specimens treated at the same temperature level. In general, the results demonstrate that densification can be a potentially effective method to retain the mechanical properties of wood at elevated temperatures, thereby having a potential maintain the load-bearing capacity during and after fire.
Keywords: densification, wood, fire safety
Published in DiRROS: 28.11.2024; Views: 757; Downloads: 678
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4. Sustainable biocarbon/tung oil coatings with hydrophobic and UV-shielding properties for outdoor wood substratesLaetitia Sarah Jennifer Marrot, Mariem Zouari, Matthew Schwarzkopf, David Brian DeVallance, 2023, original scientific article Abstract: With wood regaining substantial interest as a construction material due to sustainability concerns and aesthetics trends, efficient and safe protection methods are needed to prevent the discouloration and the loss of mechanical properties of this renewable and UV-sensitive material. In this study, sustainable coatings comprising 0 to 20 wt % biocarbon (BC) dispersed in tung oil were developed for wood protection. BC particles were added as ultraviolet (UV) absorbers and were produced by various carbonization routes. The BC powders were characterized in terms of particle size and surface functional groups by Fourier-Transform infrared, and the UV and visible absorbance of dispersed BC powders in water solutions were related to these characteristics.
Two wooden substrates (beech and oak) were coated with the developed coatings and the samples underwent six months of onsite weathering. While the total colour change of uncoated samples and tung oil-coated substrates without BC kept increasing over time and resulted in a clear alteration of the wood surface aesthetics, an increased BC content in the coatings led to enhanced colour stability, with alteration of the colour close to 2 for both wood species after six months of weathering for 10 and 20 wt% BC.
Coating with tung oil made the wooden substrates, initially hydrophilic, become hydrophobic, and the further introduction of biocarbon increased hydrophobicity. However, the increase in BC content was not correlated with an increase in water repellence, the highest water contact angle being observed for 5 % BC, and no further improvement in hydrophobicity was observed with higher BC content. The weathering negatively affected the water repellence of all the samples (i.e., reference samples and coated samples with various BC content). However, the introduction of 20 % BC best protected the decrease in water repellence induced by the onsite weathering.
Keywords: biocarbon, biochar, coating, wood protection, hydrophobic coating, wettability
Published in DiRROS: 30.05.2023; Views: 1731; Downloads: 1316
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